- Oxidative deoximation with H2O2 and MCM-41
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A simple and mild method of oxidative deoximation with 30%H 2O2 and MCM-41 is described. This method is effective for deprotection of ketones and aldehydes.
- Vijayakumari,Reddy, Balakrishna,Nagarapu, Lingaiah
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- A chemical model of catechol-O-methyltransferase. Methylation of 3,4- dihydroxybenzaldehyde in methanol solution
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The reaction of 3,4-dihydroxybenzaldehyde (LH2) and dimethyl sulfate (DMS) in forming m- and p-O-methylated products (vanillin and isovanillin, respectively) in a methanol buffer solution was studied kinetically as a chemical model of catechol-O-methyltransferase (COMT). The O-methylations, especially m-O-methylations, were catalyzed by divalent metal ions such as Cu(II), Mg(II) and Zn(II). A clear Mg(II) catalysis was observed for the first time in this medium. As Mg(II) is an important metal in the COMT catalyzed reaction in vivo, this observation is very interesting. Kinetic analyses of the present data and recalculation of a part of the previous data offered the following evidence. In Cu(II) catalysis, a 1:2 complex(CuL2) was more active than the 1:1 complex (CuL). On the other hand, in Mg(II) catalysis and Zn(II) catalysis, ML was more active than ML2. These facts show that ML2 is not always more active than ML, contrary to previous reports. Methanolysis of DMS, a significant side reaction of this model reaction, and dissociation of LH2 were studied thoroughly as bases for these kinetic analyses.
- Sugata
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- Oxidation of model lignin compounds with peracetic acid under homogeneous catalysis with polyoxometalates
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Oxidation of lignin model compounds with peracetic acid using polyoxometalate manganesecontaining sodium vanadomolybdophosphate Na11[PMo6V5O39Mn(OH)] as a catalyst has been studied. The effect of pH, concentration and nature of the oxidized compound, concentration of the catalyst and peracetic acid, and temperature on kinetics of oxidation and the products composition has been investigated.
- Popova,Beloglazova,Bogolitsyn,Tortseva,Verkholomova,Pokryshkin
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- Continuous flow study of isoeugenol to vanillin: A bio-based iron oxide catalyst
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The use of a biorefinery co-product, such as humins, in combination with an iron precursor in a solvent-free method yields a catalytic material with potential use in selective oxidative cleavage reactions. In particular, this catalyst was found active in the hydrogen-peroxide assisted oxidation of a naturally extracted molecule, isoeugenol, to high added-value flavouring agent, vanillin. By carrying out the reaction in continuous flow, not only a better understanding of the reaction mechanism and of the catalyst deactivation can be achieved, but also important insights for optimised conditions can be developed. The findings of this paper could pave the way to a more sustainable process for the production of a valuable food and perfume additive, vanillin.
- Filiciotto, Layla,Márquez-Medina, María Dolores,Pineda, Antonio,Balu, Alina M.,Romero, Antonio A.,Angelici, Carlo,de Jong, Ed,van der Waal, Jan C.,Luque, Rafael
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- Unprecedented oxidative properties of mesoporous silica materials: Towards microwave-assisted oxidation of lignin model compounds
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The unusual oxidative ability of mesoporous silicas towards oxidation of an important lignin model molecule, 1,2-(4-hydroxy-3methoxy-phenoxy) ethanol, apocynol under microwave irradiation is presented in this work. Mesoporous MCM-41, HMS, SBA-15 and amorphous silica were employed as catalysts in the present study. Different reactivities were obtained for the various silica materials. It was assumed that the substrate conversion and product selectivity were highly influenced by the nature of mesoporous silica materials. Based on the nature of the catalysts and reaction product profile, a plausible mechanism has been proposed.
- Badamali, Sushanta K.,Luque, Rafael,Clark, James H.,Breeden, Simon W.
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- Immobilization of Pd(OAc)2 in ionic liquid on silica: Application to sustainable Mizoroki-Heck reaction
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(Equation Presented) Palladium acetate was supported on amorphous silica with the aid of an ionic liquid, [bmim]PF6. The immobilized catalyst was highly efficient in promoting the Mizoroki-Heck reaction without a ligand in n-dodecane for at least six reuses, in 89-98% yields. The TON and TOF reached 68 400 and 8000, respectively.
- Hagiwara, Hisahiro,Sugawara, Yoshitaka,Isobe, Kohei,Hoshi, Takashi,Suzuki, Toshio
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- Salen complexes with bulky substituents as useful tools for biomimetic phenol oxidation research
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The catalytic properties of bulky water-soluble Co-, Cu-, Fe- and Mn-salen complexes in the oxidation of phenolic lignin model compounds have been studied in aqueous water-dioxane solutions (pH 3-10). Mn catalysts were found to oxidize coniferyl alcohol in a same reaction time as horseradish peroxidase (HRP) enzyme and Mn and Co catalysts showed different regioselectivity suggesting a different substrate to catalyst interaction in the oxidative coupling. When the oxidation of material more relevant to plant polyphenolics was studied, the results indicated that the complexes catalyze one- and two-electron oxidations depending on the bulk of the substrate. Copyright
- Haikarainen, Anssi,Sipil?, Jussi,Pietik?inen, Pekka,Pajunen, Aarne,Mutikainen, Ilpo
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- A three-enzyme-system to degrade curcumin to natural vanillin
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The symmetrical structure of curcumin includes two 4-hydroxy-3-methoxyphenyl substructures. Laccase catalyzed formation of a phenol radical, radical migration and oxygen insertion at the benzylic positions can result in the formation of vanillin. As vanillin itself is a preferred phenolic substrate of laccases, the formation of vanillin oligomers and polymers is inevitable, once vanillin becomes liberated. To decelerate the oligomerization, one of the phenolic hydroxyl groups was protected via acetylation. Monoacetyl curcumin with an approximate molar yield of 49% was the major acetylation product, when a lipase from Candida antarctica (CAL) was used. In the second step, monoacetyl curcumin was incubated with purified laccases of various basidiomycete fungi in a biphasic system (diethyl ether/aqueous buffer). A laccase from Funalia trogii (LccFtr) resulted in a high conversion (46% molar yield of curcumin monoacetate) to vanillin acetate. The non-protected vanillin moiety reacted to a mixture of higher molecular products. In the third step, the protecting group was removed from vanillin acetate using a feruloyl esterase from Pleurotus eryngii (PeFaeA) (68% molar yield). Alignment of the amino acid sequences indicated that high potential laccases performed better in this mediator and cofactor-free reaction.
- Esparan, Vida,Krings, Ulrich,Struch, Marlene,Berger, Ralf G.
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- An efficient environmentally friendly CuFe2O4/SiO2catalyst for vanillyl mandelic acid oxidation in water under atmospheric pressure and a mechanism study
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With the aim of the green production of vanillin, a highly efficient environmentally friendly oxidation system was introduced to oxidize vanillyl mandelic acid (VMA) with a porous CuFe2O4/SiO2 component nano-catalyst in aqueous solution under atmospheric pressure. The N2 adsorption-desorption pattern indicated that CuFe2O4/SiO2 possessed a much higher specific surface area (49.98 m2 g-1) than that of CuFe2O4 (5.02 m2 g-1), which further indicated that the SiO2 substrate restrained the aggregation of CuFe2O4 nanoparticles. The conversion for VMA and selectivity for vanillin reached 98% and 96%, respectively, under atmospheric pressure. The excellent catalytic performance was attributed to the synergistic effect of the catalytic capacity of CuFe2O4 and the adsorption capacity for the reactant of SiO2. Simultaneously, the effect of different reaction conditions for catalyst activity and selectivity were investigated. Furthermore, the probable mechanism of VMA oxidation was investigated by in situ ATR-FTIR, H2-TPR, XPS and 1H NMR. More importantly, the decarboxylation was verified to proceed in basic conditions rather than in conventional acidic conditions. This journal is
- Mao, Haifang,Wang, Hongzhao,Meng, Tao,Wang, Chaoyang,Hu, Xiaojun,Xiao, Zuobing,Liu, Jibo
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- An immobilised Co(ii) and Ni(ii) Schiff base magnetic nanocatalyst via a click reaction: A greener approach for alcohol oxidation
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A Schiff base immobilised nanocatalyst was synthesized via copper catalysed alkyne azide cycloaddition (CuAAC) on a magnetic support. The nanocatalyst exhibited high accessible active sites with a surface area of 76 m2 g-1 for a cobalt complex and 57 m2 g-1 for a nickel complex. A strong interaction between the magnetic support and the Schiff base was achieved by avoiding leaching during the course of reaction. The nanocatalyst efficiently oxidised both primary and secondary alcohols to carbonyl with improved yield in a solventless system rendering a greener approach.
- Bhat, Pooja B.,Bhat, Badekai Ramachandra
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- Enantioselective allylation of tert-butyldimethylsilyl-protected vanillin and synthesis of a lignan derivative isolated from machilus wangchiana
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Various enantioselective allylations and crotylations of tert-butyldimethylsilyl-protected vanillin were undertaken to assess the best methodology to provide the corresponding homoallylic alcohols in high yields with high enantiopurity. In general, most of the tested allylations proceeded with high enantioselectivities (>92 % ee) and in the case of crotylation also with excellent diastereoselectivity (96 % ee, >98 % de). The product obtained from the crotylation reaction was used in the enantioselective synthesis of the unnatural diastereoisomer of a recently isolated lignan derivative.
- Cadart, Timothée,Koukal, Petr,Kotora, Martin
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- Catalytic nitrobenzene oxidation of lignins
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Alkaline nitrobenzene oxidation of hardwood and softwood lignins in the presence of redox and phase-transfer catalysts was studied. The selectivity of oxidation of lignins increased by 1.7 to 1.9 times. A possible mechanism of catalysis is discussed.
- Gogotov,Rybal'chenko,Makovskaya,Babkin
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- Biocatalytic oxidation of 4-vinylphenol by Nocardia
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Nocardia species NRRL 5646 stereospecifically hydrates 4-vinylphenol (15) to S-1-(4′-hydroxyphenyl)ethanol (17), and further oxidizes 17 to 4′-hydroxyacetophenone (18). Labeled metabolites 17 and 18 obtained from incubations in D2O and H218O support initial enzymatic tautomerization of 15 to a reactive quinone methide (16), which adds water in the first reaction. Commitment to catalysis is high in the hydration reaction, while the alcohol dehydrogenation reaction appears to be reversible. The stereochemical features of water addition, alcohol oxidations, and ketone reductions with growing culture biocatalysis were established by chiral HPLC. Alcohol oxidations or ketone reductions in 12 000 × g supernatants preferentially require NADP+-NADPH,H+ as co-factors. The alcohol dehydrogenase has broad substrate specificity, favoring the oxidation of primary alkanols and 4-hydroxybenzyl alcohols.
- Lee, Kyung-Seon,Rosazza, John P.N.
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- Process of lignin oxidation in an ionic liquid coupled with separation
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A novel approach has been developed in order to use lignin as a renewable resource for the production of a high added-value aromatic aldehyde. The concept is based on the use of an ionic liquid as a reversible medium coupled with the separation process, which prevents the aromatic aldehyde products from oxidizing and increases their yields. The conversion of lignin reached 100%, and the total yield of the aromatic aldehydes (vanillin, syringaldehyde and p-hydroxybenzaldehyde) was 29.7% in the coupled process. In addition, the mixture of product and IL phase was easily separated, and the IL phase demonstrated good reusability. Hence, a clean and environmentally friendly strategy for overall utilization of lignin and preparation of an aromatic aldehyde is developed.
- Liu, Shiwei,Shi, Zhongliang,Li, Lu,Yu, Shitao,Xie, Congxia,Song, Zhanqian
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- New synthesis of vanillin by degradation of lignin in presence of functional basic ionic liquid
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The degradation of lignin catalyzed by functional basic ionic liquid was investigated. Higher conversion of lignin and simpler degradation product composition were obtained in the presence of basic ionic liquid, comparing with that under traditional NaOH
- Yi, Fengping,Jiang, Xiaoyan,Niu, Jihua,Zhang, Lirong,Wang, Zhen
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- Continuous-Flow Synthesis of Supported Magnetic Iron Oxide Nanoparticles for Efficient Isoeugenol Conversion into Vanillin
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This work presents the synthesis of iron oxide nanocatalysts supported on mesoporous Al-SBA-15 by using a continuous-flow setup. The magnetic nanomaterials were tested as catalysts in the oxidative disruption of isoeugenol by using hydrogen peroxide as a green oxidant, featuring high activities (63–88 % conversion) and good selectivities to vanillin (44–68 %). The catalytic systems exhibited good magnetic properties when synthesized under continuous-flow conditions at temperatures not exceeding 190 °C. The use of microwave irradiation significantly reduced times of reaction drastically but exerted negative effects on catalyst reusability.
- Marquez-Medina, M. Dolores,Prinsen, Pepijn,Li, Hangkong,Shih, Kaimin,Romero, Antonio A.,Luque, Rafael
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- An efficient and chemoselective deprotection of aryl- and styrenyldithioketals (acetals)
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In this Letter, an efficient and chemoselective deprotection of aryl- and styrenyldithioketals (acetals) is described. After being carefully examined, 10% Pd/C and Amberlite 120 in refluxing methanol was found to be an excellent condition for the chemoselective deprotection of aryl- and styrenyldithioketals (acetals) in good yields. Under this condition, no deprotection and no reduction of alkyldithioketals (acetals) was observed.
- Wang, Eng-Chi,Wu, Chien-Huang,Chien, Shih-Chang,Chiang, Wen-Chang,Kuo, Yueh-Hsiung
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- Platinum-containing catalyst supported on a metal-organic framework structure in the selective oxidation of benzyl alcohol derivatives into aldehydes
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The platinum catalyst supported on the metal-organic framework structure MOF-5 is usable in the selective oxidation of vanillyl and piperonyl alcohols into the corresponding aldehydes.
- Tarasov,Kustov,Isaeva,Kalenchuk,Mishin,Kapustin,Bogdan
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- Multigram Scale Enzymatic Synthesis of (R)-1-(4′-Hydroxyphenyl)ethanol Using Vanillyl Alcohol Oxidase
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The enantioselective oxyfunctionalisation of C?H bonds is a highly interesting reaction, as it provides access to chiral alcohols that are important pharmaceutical building blocks. However, it is hard to achieve using traditional methods. One way in which it can be achieved is through the action of oxidative enzymes. Although many reports of the oxyfunctionalisation capabilities of enzymes at an analytical scale have been published, reports on the use of enzymes to achieve oxyfunctionalisation on a synthetically relevant scale are fewer. Here, we describe the scale-up of the conversion of 4-ethylphenol to (R)-1-(4′-hydroxyphenyl)ethanol using the flavin-dependent enzyme vanillyl alcohol oxidase. The process was optimised by testing different reaction media and substrate and enzyme concentrations and by performing it under an oxygen atmosphere. Under optimised reaction conditions, 4.10 g (R)-1-(4′-hydroxyphenyl)ethanol at 97% ee was obtained from 10 g 4-ethylphenol (isolated yield 36%). These results highlight some of the challenges that can be encountered during scale-up of an enzymatic oxyfunctionalisation process to a synthetically relevant scale and will be of use for the development of enzymatic processes for the synthesis of industrially relevant compounds. (Figure presented.).
- Ewing, Tom A.,Kühn, Jasmin,Segarra, Silvia,Tortajada, Marta,Zuhse, Ralf,van Berkel, Willem J. H.
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- Microbial conversion of vanillin from ferulic acid extracted from raw coir pith
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Coir pith, an agro-industrial residue, is resistant to natural degradation, and its accumulation causes environmental pollution. Ferulic acid, a precursor of vanillin, was extracted from the raw coir pith by chemical pre-treatment such as alkaline hydrolysis, acidification, and liquid–liquid extraction method. The obtained ferulic acid (1.2 g/50 g) was analysed using high-performance liquid chromatography (HPLC) and used as a substrate for biotransformation by Aspergillus niger to vanillic acid, which, in turn, was fermented by using Phanerochaete chrysosporium to vanillin. The quantity of vanillic acid detected by HPLC on the third day of incubation was 0.773 g/L, while the optimal yield of vanillin on the subsequent third day of incubation was 0.628 g/L. Thus, the chemical extraction of ferulic acid from coir pith ensued bioconversion into vanillin. These products are highly valuable and economical to be used in industries such as pharmaceuticals, health, cosmetics, and neutraceuticals.
- Radhakrishnan, Sivaramapillai,Rejani, Chalikkaran Thilakan
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- Fe3O4 Nanoparticles Anchored on Carbon Serve the Dual Role of Catalyst and Magnetically Recoverable Entity in the Aerobic Oxidation of Alcohols
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A composite of Fe3O4 nanoparticles anchored on a carbon support (Fe3O4/C), possessing both superparamagnetism and molecular oxygen activating properties, was prepared by an ammonia-assisted precipitation method. Fe3O4/C could catalyze the selective oxidation of various benzyl alcohols with air as the oxidant source, and could be easily separated and recycled with an external magnet. The small particle size and the interaction between the Fe3O4 nanoparticles and carbon support endow the Fe3O4/C catalyst with relatively high reducibility. Its oxidation state is easy to change. This intrinsic property of the Fe3O4 nanoparticles could be responsible for the high activity of Fe3O4/C in the aerobic oxidation of alcohols.
- Geng, Longlong,Zheng, Bin,Wang, Xiang,Zhang, Wenxiang,Wu, Shujie,Jia, Mingjun,Yan, Wenfu,Liu, Gang
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- Expression and characterization of a 9-cis-epoxycarotenoid dioxygenase from Serratia sp. ATCC 39006 capable of biotransforming isoeugenol and 4-vinylguaiacol to vanillin
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A 9-cis-epoxycarotenoid dioxygenase gene from Serratia sp. ATCC 39,006 (SeNCED) was overexpressed in soluble form in E.coli. SeNCED showed the maximum activity at 30 °C and pH 8.0, and it was stable relatively at range of pH 5–10 and temperature of 20 °C to 30 °C. SeNCED effectively catalyzes the side chain double bond cleavage of isoeugenol and 4-vinylguaiacol to vanillin. The kinetic constant Km values toward isoeugenol and 4-vinylguaiacol were 18.92 mM and 6.31 mM and Vmax values were 50.73 IU/g and 4.77 IU/g, respectively. Moreover, the SeNCED exhibited an excellent organic solvent tolerance and the enzyme activity was substantially improved at presence of 10% of trichloromethane. The produced vanillin was achieved at an around 0.53 g/L (3.47 mM) and 0.33 g/L (2.17 mM) after 8 h reaction at 4 mM of isoeugenol and 4-vinylguaiacol, respectively, using transformed Escherichia coli cells harboring SeNCED in the presence of trichloromethane.
- Tang, Jiao,Shi, Lei,Li, Lulu,Long, Liangkun,Ding, Shaojun
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- Nucleophilic fluorination facilitated by a CsF-CaF2 packed bed reactor in continuous flow
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A simple to prepare, dry and handle packed bed reactor carrying CsF on CaF2, towards nucleophilic fluorinations in continuous flow, is reported. The reactor also proved adaptable for silyl-ether deprotection and trifluoromethylations with Ruppert's reagent. The study includes reactor stability and scale-up investigations.
- Johansen,Lindhardt
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- Benign-by-design preparation of humin-based iron oxide catalytic nanocomposites
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The current acid-catalyzed conversion of biomass feedstocks yields substantial quantities of undesired by-products called humins, for which applications are yet to be found. This work aims to provide a starting point for valorisation of humins via preparation of humin-based iron oxide catalytic nanocomposites from humins and thermally treated humins (foams) via solvent-free methodologies including ball milling and thermal degradation. The prepared materials were found to be active in the microwave-assisted selective oxidation of isoeugenol (conversions >87%) to vanillin, proving the feasibility to use humin by-products as template/composite materials.
- Filiciotto, Layla,Balu, Alina M.,Romero, Antonio A.,Rodríguez-Castellón, Enrique,Van Der Waal, Jan C.,Luque, Rafael
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- A xylenol orange-based screening assay for the substrate specificity of flavin-dependent para-phenol oxidases
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Vanillyl alcohol oxidase (VAO) and eugenol oxidase (EUGO) are flavin-dependent enzymes that catalyse the oxidation of para-substituted phenols. This makes them potentially interesting biocatalysts for the conversion of lignin-derived aromatic monomers to value-added compounds. To facilitate their biocatalytic exploitation, it is important to develop methods by which variants of the enzymes can be rapidly screened for increased activity towards substrates of interest. Here, we present the development of a screening assay for the substrate specificity of para-phenol oxidases based on the detection of hydrogen peroxide using the ferric-xylenol orange complex method. The assay was used to screen the activity of VAO and EUGO towards a set of twenty-four potential substrates. This led to the identification of 4-cyclopentylphenol as a new substrate of VAO and EUGO and 4-cyclohexylphenol as a new substrate of VAO. Screening of a small library of VAO and EUGO active-site variants for alterations in their substrate specificity led to the identification of a VAO variant (T457Q) with increased activity towards vanillyl alcohol (4-hydroxy-3-methoxybenzyl alcohol) and a EUGO variant (V436I) with increased activity towards chavicol (4-allylphenol) and 4-cyclopentylphenol. This assay provides a quick and efficient method to screen the substrate specificity of para-phenol oxidases, facilitating the enzyme engineering of known para-phenol oxidases and the evaluation of the substrate specificity of novel para-phenol oxidases.
- Ewing, Tom A.,Van Noord, Aster,Paul, Caroline E.,Van Berkel, Willem J. H.
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- Oxidative cleavage of isoeugenol to vanillin under molecular oxygen catalysed by cobalt porphyrin intercalated into lithium taeniolite clay
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Three types of Co-porphyrin complexes differing in their porphyrin-ring substituents and nonionic or cationic structure were intercalated into lithium taeniolite (LiTN) using a simple cation exchange method. All the intercalated catalysts displayed expanded clearance spaces (in the range of 0.30-0.51 nm) compared with that of the parent LiTN (0.24 nm). The catalysts were applied for the oxidative cleavage of isoeugenol to vanillin with molecular oxygen as the sole oxidant, and the reaction proceeded effectively under mild reaction conditions. The highest vanillin selectivity of 72% was obtained with CoTPyP/TN, which had the widest clearance space among the three Co-porphyrin catalysts. These intercalated catalysts showed high stability during oxidation, enabling their recycling for at least three runs.
- Adilina, Indri Badria,Hara, Takayoshi,Ichikuni, Nobuyuki,Shimazu, Shogo
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- CuZrO3 nanoparticles catalyst in aerobic oxidation of vanillyl alcohol
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A highly crystalline, mesoporous and perovskite type CuZrO3 nanoparticles catalyst was prepared via a simple and facile one pot solvent evaporation method. The crystal planes (112) and (211) of CuZrO3 were evidenced in HRTEM and SAED imagery by their lattice parameters, 2.83 and 3.15 ?. Also, the crystallite size of synthesized catalyst was measured in a range of 7-10 nm. The catalyst was superior as it possessed many physiochemical properties to perform a liquid phase aerobic oxidation of vanillyl alcohol to selectively produce vanillin under base free conditions. Catalytic activity of the synthesized perovskite type CuZrO3 catalyst was substantially improved by the presence of surface oxygen vacancies speculated in O 1s spectra. Furthermore, a O2-TPD technique was applied to understand the role of surface oxygen vacancy in enhancing catalytic activity. Moreover, numerous partial and full lattice dislocated grain boundaries were observed as a form of structural defects between different planes in HRTEM imagery. The redox capability of this superior catalyst was significantly enriched by the high content of Zr loading and confirmed by low temperature reduction in H2-TPR analysis. Excellent catalytic behavior of CuZrO3 (Cu:2Zr) catalyst (91% conversion and 76% selectivity to vanillin) in liquid phase aerobic oxidation was well correlated with the structural and chemical properties of the catalyst. Moreover, the catalyst was stable for four consecutive oxidation reactions without appreciable loss of catalytic activity.
- Saha, Subrata,Abd Hamid, Sharifah Bee
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- Revisiting alkaline aerobic lignin oxidation
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Lignin conversion to renewable chemicals is a promising means to improve the economic viability of lignocellulosic biorefineries. Alkaline aerobic oxidation of lignin has long been employed for production of aromatic compounds such as vanillin and syringaldehyde, but this approach primarily focuses on condensed substrates such as Kraft lignin and lignosulfonates. Conversely, emerging lignocellulosic biorefinery schemes enable the production of more native-like, reactive lignin. Here, we revisit alkaline aerobic oxidation of highly reactive lignin substrates to understand the impact of reaction conditions and catalyst choice on product yield and distribution. The oxidation of native poplar lignin was studied as a function of temperature, NaOH loading, reaction time, and oxygen partial pressure. Besides vanillin and syringaldehyde, other oxidation products include acetosyringone and vanillic, syringic, and p-hydroxybenzoic acids. Reactions with vanillin and syringaldehyde indicated that these compounds are further oxidized to non-aromatic carboxylic acids during alkaline aerobic oxidation, with syringaldehyde being substantially more reactive than vanillin. The production of phenolic compounds from lignin is favored by high NaOH loadings and temperatures, but short reaction times, as the products degrade rapidly, which is further exacerbated by the presence of oxygen. Under optimal conditions, a phenolic monomer yield of 30 wt% was obtained from poplar lignin. Testing a range of catalysts showed that Cu-containing catalysts, such as CuSO4 and LaMn0.8Cu0.2O3, accelerate product formation; specifically, the catalyst does not increase the maximum yield, but expands the operating window in which high product yields are obtainable. We also demonstrate that other native and isolated lignin substrates that are significantly chemically modified are effectively converted to phenolic compounds. Finally, alkaline aerobic oxidation of native lignins was compared to nitrobenzene oxidation and reductive catalytic fractionation, as these methods constitute suitable benchmarks for lignin depolymerization. While nitrobenzene oxidation achieved a somewhat higher yield, similar monomer yields were obtained through RCF and alkaline aerobic oxidation, especially for lignins with a high guaiacyl- and/or p-hydroxyphenyl-content, as syringyl units are more unstable during oxidation. Overall, this study highlights the potential for aerobic lignin oxidation revisited on native-like lignin substrates.
- Schutyser, Wouter,Kruger, Jacob S.,Robinson, Allison M.,Katahira, Rui,Brandner, David G.,Cleveland, Nicholas S.,Mittal, Ashutosh,Peterson, Darren J.,Meilan, Richard,Román-Leshkov, Yuriy,Beckham, Gregg T.
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- Oxidative depolymerization of lignin in ionic liquids
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Beech lignin was oxidatively cleaved in ionic liquids to give phenols, unsaturated propylaromatics, and aromatic aldehydes. A multiparallel batch reactor system was used to screen different ionic liquids and metal catalysts. Mn(NO3)2 in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [EMIM][CF3SO3] proved to be the most effective reaction system. A larger scale batch reaction with this system in a 300mL autoclave (11g lignin starting material) resulted in a maximum conversion of 66.3% (24h at 100 °C, 84 × 105 Pa air). By adjusting the reaction conditions and catalyst loading, the selectivity of the process could be shifted from syringaldehyde as the predominant product to 2,6-dimethoxy-1,4-benzoquinone (DMBQ). Surprisingly, the latter could be isolated as a pure substance in 11.5 wt% overall yield by a simple extraction/crystallization process.
- St?rk, Kerstin,Taccardi, Nicola,B?smann, Andreas,Wasserscheid, Peter
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- Synthesis of selected aromatic aldehydes under UV-LED irradiation over a hybrid photocatalyst of carbon nanofibers and zinc oxide
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Zinc oxide (ZnO) prepared by chemical vapor deposition was combined with different amounts of carbon nanofibers (CNF) to obtain hybrid materials, which were thoroughly characterized using several techniques. The photocatalytic performance was evaluated towards the photocatalytic synthesis of vanillin (VAD) starting from vanillyl alcohol (VA). The incorporation of the carbon phase in ZnO (from 5% to 20% wt.) was found to increase the surface area and the photocatalytic performance of the materials. The latter was attributed to the efficient separation of charge carriers generated on the optical semiconductor. With the best performing material, the one containing 10% of CNF, the selectivity of the synthesis towards vanillin generation was increased by a factor of 2.5 compared to previous studies, with the additional advantage of carrying the reaction in aqueous medium. The same photocatalyst was successfully applied to the selective synthesis of other aromatic aldehydes, namely anisaldehyde, piperonal, and benzaldehyde. A relationship between the efficiency of the photocatalytic oxidation of the alcohols and the activating nature of their aromatic ring substituents was proposed.
- Fernandes, Raquel A.,Sampaio, Maria J.,Da Silva, Eliana S.,Serp, Philippe,Faria, Joaquim L.,Silva, Cláudia G.
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- Effect of gamma-radiation on major aroma compounds and vanillin glucoside of cured vanilla beans (Vanilla planifolia)
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Cured vanilla beans were irradiated (5, 10, 15, 20 and 30 kGy) for a possible enhancement of vanillin content by radiolysis of vanillin glucoside. The vanillin content of control and irradiated (30 kGy) samples were 26.6 ± 0.85 and 26.9 ± 0.70 mg/g (dw), respectively, while vanillin glucoside were 7.74 ± 0.2 and 7.35 ± 0.35 mg/g (dw). Radiation caused no significant changes (p ≤ 0.05) in aroma constituents. In a pulse radiolysis experiment, vanillin glucoside on reacting with {radical dot}OH radical gave transients with absorption peaks at 360 nm and 410 nm. The species absorbing at 410 nm has been interpreted to be a hydroxyl radical adduct. It decayed at the same rate in the presence of oxygen, while the absorption at 360 nm did not. Results obtained revealed that the more stable one absorbing at 360 nm is aldehydic radical. Hence the highly stable oxygen-carbon linkage between vanillin and glucose limits the possible enhancement of aroma quality of irradiated beans.
- Kishor Kumar,Arul AnanthaKumar,Ahmad,Adhikari,Variyar,Sharma
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- Solid-supported acids for debenzylation of aryl benzyl ethers
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Solid-supported acids have been investigated for aromatic debenzylation reactions. Stoichiometric amounts of solid-supported acids in refluxing toluene with or without 4 equiv of methanol effectively provided the desired aromatic debenzylation products of various systems in moderate to excellent yields (up to 98%).
- Petchmanee, Thaninee,Ploypradith, Poonsakdi,Ruchirawat, Somsak
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- Visible light-driven oxidation of vanillyl alcohol in air with Au-Pd bimetallic nanoparticles on phosphorylated hydrotalcite
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The selective photocatalytic oxidation of vanilla alcohol with air was studied preliminarily using supported Au-Pd bimetallic nanocatalysts. The support, phosphate-modified Mg-Al hydrotalcite (HT-PO43?), was produced first with a sol-gel and ion-exchange method, and then Au-Pd alloy nanocatalysts supported on activated carbon (C) and HT-PO43? were prepared, respectively, by an impregnated-reduction approach. Subsequently, the morphology and property of these two catalysts were characterized by XPS, SEM-EDX, ICP-OES, XRD, HR-TEM and DR-UV-vis. In terms of the photocatalytic reaction, Au-Pd@C and Au-Pd@HT-PO43? exhibited photocatalytic activity and the latter displayed higher selectivity. Under optimized experimental conditions, the conversion rate and selectivity using Au-Pd@HT-PO43? as catalyst were 52.8% and 49.6% respectively, due to the synergistically double dehydrogenative oxidation derived from alloy nanoparticles and basic support. Moreover, the catalysts had good recyclability without significant loss of activity after several recycles. Therefore, this catalyst could recurrently realize production of vanillin from vanilla alcohol under mild reaction conditions, including in the atmosphere, at ambient temperature and with no addition of alkali, which is very important for a potential “green” strategy towards clean and cost-efficient production of vanillin.
- Wu, Miao,Pang, Jin-Hui,Song, Ping-Ping,Peng, Jian-Jun,Xu, Feng,Li, Qiang,Zhang, Xue-Ming
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- Methoxyphenols from burning of Scandinavian forest plant materials
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Semivolatile compounds in smoke from gram-scale incomplete burning of plant materials were assessed by gas chromatography and mass spectrometry. Gas syringe sampling was shown to be adequate by comparison with adsorbent sampling. Methoxyphenols as well as 1,6-anhydroglucose were released in amounts as large as 10 mg kg-1 of dry biomass at 90% combustion efficiency. Wood, twigs, bark and needles from the conifers Norway spruce and Scots pine emitted 12 reported 2-methoxyphenols in similar proportions. Grass, heather and birchwood released the same 2-methoxyphenols but also the corresponding 2,6-dimethoxyphenols which are characteristic of angiosperms. The methoxyphenols are formed from lignin and differ in structure by the group in para position relative to the phenolic OH group. Prominent phenols were those with trans-l-propenyl and ethenyl groups in that position. Vanillin, 4- hydroxy-3-methoxybenzaldehyde, was a prominent carbonyl compound from the conifer materials. (C) 2000 Elsevier Science Ltd.
- Kjaellstrand, Jennica,Ramnaes, Olle,Petersson, Goeran
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- Statistical design of experiments for production and purification of vanillin and aminophenols from commercial lignin
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Lignin is a complex polyphenolic substance that collectively represents the largest renewable source of aromatic carbon on Earth. Despite low yield and purity from depolymerized lignin, bio-derived vanillin (4-hydroxy-3-methoxybenzaldehyde) is a desirable molecule in the food/beverage and fragrance industries. To maximize vanillin yield from commercially-available softwood lignin, a series of oxidation reactions were conducted using a Box-Behnken statistical design. By varying time, temperature and O2 pressure, optimal conditions were selected using the Response Surface Method, and a maximum vanillin yield of 5.3 wtpercent was achieved. Flash chromatography of depolymerized lignin was investigated by comparing anion exchange and reversed-phase resins and fractions were characterized by GC-MS, GPC-HPLC, FT-IR and NMR. Anion exchange separations using 1M NaCl as the sole mobile phase reached a vanillin purity of 55 wt percent. Lastly, the vanillin mixture was reacted via reductive amination, and facile acid-base work up led to the formation of 4-((diethylamino)methyl)-2-methoxyphenol at 94.3 wt percent purity. The aminophenol is an intermediate in the synthesis of pharmaceutical agents, ionic liquids and benzalkonium salts.
- Blauch, David N.,Das, Lalitendu,Dou, Chang,Gladden, John,Liu, Shihong,Socha, Aaron M.,Sun, Ning,Veronee, Charlie
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- Wet aerobic oxidation of lignin into aromatic aldehydes catalysed by a perovskite-type oxide: LaFe1-xCuxO3 (x=0, 0.1, 0.2)
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The perovskite-type oxide catalyst LaFe1-xCuxO 3 (x=0, 0.1, 0.2) was prepared by the solgel method, and tested as a catalyst in the wet aerobic oxidation (WAO) of lignin into aromatic aldehydes. The lignin conversion and t
- Zhang, Junhua,Deng, Haibo,Lin, Lu
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- Liquid-phase oxidation of 2-methoxy-p-cresol to vanillin with oxygen catalyzed by a combination of CoCl2 and N-hydroxyphthalimide
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Liquid-phase oxidation of 2-methoxy-p-cresol to vanillin (4-hydroxy-3-methoxybenzaldehyde), in methanol, with molecular oxygen at atmospheric pressure as oxidant and a combination of cobaltous chloride and N-hydroxyphthalimide (NHPI) as catalyst, has been investigated. The effect of reaction conditions on conversion and selectivity for vanillin was studied systematically. Selectivity for vanillin could be enhanced by optimizing the molar ratio of 2-methoxy-p-cresol to NHPI, the amount of sodium hydroxide, reaction time, reaction temperature, and the volume of methanol, which determined the concentration of the reactants. Under the optimized conditions the yield of vanillin was 90.1 %. Springer Science+Business Media Dordrecht 2013.
- Zhang, Yuecheng,Li, Xiujuan,Cao, Xiaohui,Zhao, Jiquan
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- P450 BM3 Monooxygenase as an Efficient NAD(P)H-Oxidase for Regeneration of Nicotinamide Cofactors in ADH-Catalysed Preparative Scale Biotransformations
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Enzymatic oxidations of primary and secondary alcohols catalysed by nicotinamide dependent alcohol dehydrogenases on the preparative scale require cofactor regeneration systems. Of critical value from an economic and ecological perspective is the application of NAD(P)H-oxidases, which utilise molecular oxygen as a cost-effective, atom-efficient and environmentally benign oxidant to regenerate the cofactor NAD(P)+. Herein, the P450 BM3 monooxygenase from Bacillus megaterium is presented as an NAD(P)H-oxidase for the successful regeneration of both NADP+and NAD+on the preparative scale. This enzyme was exemplarily applied for ADH-catalysed oxidative kinetic resolutions of racemic secondary alcohols and the desymmetrisation of a meso-diol leading to enantiomerically enriched secondary alcohols in both cases. Furthermore, the ADH-catalysed oxidation of a primary alcohol targeting the corresponding aldehyde was performed. The obtained results significantly broaden the scope of feasible oxidative biotransformations, thereby increasing the number of synthetic reactions complying with key challenges of a modern and sustainable chemistry such as mild reaction conditions, environmentally benign solvents, and biodegradable non-toxic catalysts.
- Holec, Claudia,Neufeld, Katharina,Pietruszka, J?rg
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- Mixed Co-Mn oxide-catalysed selective aerobic oxidation of vanillyl alcohol to vanillin in base-free conditions
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Manganese-doped cobalt mixed oxide (MnCo-MO) catalyst was prepared by a solvothermal method. The as-prepared catalyst was characterised by X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, O2 temperature-programmed oxidation and XRD. This catalyst gave 62 % conversion with 83 % selectivity to vanillin in 2 hours for the liquid-phase air oxidation of vanillyl alcohol without using base. Three different types of metal oxides were observed in the prepared catalyst, which could be identified as Co3O4, Mn3O4 and CoMn 2O4. Among these, the tetragonal phase of CoMn 2O4 was found to be more active and selective for vanillyl alcohol oxidation than Co3O4 and Mn3O 4. High-resolution TEM characterisation revealed the morphology of MnCo-MO nanorods with a particle size of 10 nm. Successful recycling of the catalyst was also established in this oxidation reaction. It takes two: Mn in the MnCo mixed oxide (MO) forms a metal hydroperoxo complex simultaneously giving the phenolate ion of vanillyl alcohol under base-free conditions, which undergoes smooth air oxidation to give vanillin with >83 % selectivity (see scheme). The high catalytic activity of the MnCo-MO results from a synergic effect of the MO phases, which is absent in single Mn or Co oxides. Copyright
- Jha, Ajay,Patil, Kashinath R.,Rode, Chandrashekhar V.
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- Pseudohalide assisted aerobic oxidation of alcohols in the presence of visible-light
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Pseudohalides are well known to do similar chemistry like halides. Thiocyanate, a pseudohalide acts like halides in many ways. Thiocyanate radicals ([rad]SCN) are generated from readily available thiocyanate salts using Rose Bengal through single electron transfer (SET) in the presence of visible light. Thiocyanate radicals abstract hydrogen like other halide radicals, so this aspect of chemistry was used for the oxidation of alcohols to their corresponding aldehydes using oxygen as the terminal oxidant. This method shows a broad scope and well tolerance towards various functional groups.
- Sheriff Shah, Sk,Pradeep Singh
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- Nickel hydroxide/cobalt-ferrite magnetic nanocatalyst for alcohol oxidation
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A magnetically separable, active nickel hydroxide (Bronsted base) coated nanocobalt ferrite catalyst has been developed for oxidation of alcohols. High surface area was achieved by tuning the particle size with surfactant. The surface area of 120.94 m2 g-1 has been achieved for the coated nanocobalt ferrite. Improved catalytic activity and selectivity were obtained by synergistic effect of transition metal hydroxide (basic hydroxide) on nanocobalt ferrite. The nanocatalyst oxidizes primary and secondary alcohols efficiently (87%) to corresponding carbonyls in good yields.
- Bhat, Pooja B.,Inam, Fawad,Bhat, Badekai Ramachandra
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- Molybdate Stabilized Magnesium‐Iron Hydrotalcite Materials: Potential Catalysts for Isoeugenol to Vanillin and Olefin Epoxidation
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A series of molybdate-intercalated and stabilized magnesium‐iron hydrotalcite (HMFeMo) materials with different molybdate loadings were successfully prepared by an in-situ hydrothermal method. The prepared HMFeMo materials were systematically characterized using Fourier-transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), Ultraviolet-visible spectroscopy, scanning electron microscopy, thermo-gravimetric analysis, nitrogen adsorption-desorption and X-ray photoelectron spectroscopy (XPS) experiments. The XRD results demonstrated the successful intercalation of molybdate ions in the interlayer space of magnesium-iron hydrotalcite and the stabilization of the layered structure. In addition, the XPS spectra of the HMFeMo materials revealed the presence of molybdenum in a higher-valent oxidation state. The calcination of HMFeMo materials led to the formation of solid solution of mixed metal oxides. Both the as-prepared and calcined HMFeMo catalysts showed promising activity for the epoxidation of cyclooctene, as a model reaction. Furthermore, the performance of the as-prepared and calcined HMFeMo catalysts for the oxidation of a biomass model compound, namely isoeugenol to vanillin, was evaluated. The isoeugenol conversion over the as-prepared HMFeMo catalysts under solvent-free conditions and using tertiary-butyl hydroperoxide in decane as the oxidant was good. Moreover, the isoeugenol conversion and selectivity toward vanillin of HMFeMo0.1, with a molybdate loading of 0.1 mol %, were the highest (86.2% and 83.1%, respectively) of all HMFeMo catalysts in this study at 80 °C for 5 hr. HMFeMo0.1 presented the best catalytic activity for both the epoxidation of cyclooctene and oxidation of isoeugenol to vanillin, and its activity remained unchanged after several runs.
- Neethu, P. P.,Sakthivel, A.,Sreenavya, A.
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- Selective Aerobic Oxidation of Alcohols over Gold-Palladium Alloy Catalysts Using Air at Atmospheric Pressure in Water
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A series of bimetallic Au?Pd alloy nanoparticles (NPs) with varied Au/Pd molar ratios was supported on Gamma-alumina (γ-Al2O3) surface through the co-impregnation-reduction method using HAuCl4 and PdCl2 as metal precursors. Characterization results suggested the high dispersion of Au?Pd alloy NPs, as well as the interplay between the two compositions. Benefitting from the synergistic effects of Au?Pd alloying, the bimetallic Au-Pdx@γ-Al2O3 catalysts were highly efficient for selective aerobic oxidation of various alcohols either aromatic or aliphatic in water using air at atmospheric pressure as a sole oxidant without the need for any cocatalyst. Quantitative yields of corresponding aldehydes or ketones were achieved over Au-Pd1.2@γ-Al2O3 within 2 h, whereas pure Au@γ-Al2O3 or Pd@γ-Al2O3 was far less efficient. More importantly, the “alloying effect” appeared to stabilize the bimetallic NPs against aggregation and poisoning, which made the Au-Pdx@γ-Al2O3 more stable and reusable in the aerobic oxidation of alcohols.
- Zhang, Wei,Xiao, Ziqiang,Wang, Jiajun,Fu, Wenqin,Tan, Rong,Yin, Donghong
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- Rational design of carbon support to prepare ultrafine iron oxide catalysts for air oxidation of alcohols
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A kind of mesoporous carbon support with abundant surface functional groups and a tunable pore size was prepared using a modified hardlate route. This carbon support was demonstrated to be efficient for fabricating ultrafine iron oxide catalysts, and the resultant catalysts exhibit an obviously higher activity in air oxidation of several benzyl alcohols compared with the catalysts with other synthetic carbon as supports. The concrete role of carbon support in the catalyst design was investigated in detail. The negatively charged surface oxygen functional groups serve as strongly active sites for anchoring positively charged Fe3+ ions and lead to high dispersion of iron oxide species. These oxygen functional groups also provide a suitable coordinate environment to increase the electron density of iron centres and form efficient active sites for the oxidation of benzyl alcohols with molecular oxygen.
- Geng, Longlong,Zhang, Min,Zhang, Wenxiang,Jia, Mingjun,Yan, Wenfu,Liu, Gang
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- Enhancement of pancreatic lipase inhibitory activity of curcumin by radiolytic transformation
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The naturally occurring yellow dietary diarylheptanoid curcumin (1) was converted by γ-ray to two new γ-lactones, curculactones A (2) and B (3), as well as four known transformates, erythro-1-(3-methoxy-4-hydroxy-phenyl) -propan-1,2-diol (4), threo-1-(3-methoxy-4-hydroxy-phenyl)-propan-1,2-diol (5), vanillic acid (6), and vanillin (7). The structures of the two new γ-lactone derivatives were elucidated on the basis of spectroscopic methods. The steroisomeric phenylpropanoids 4 and 5 exhibited significantly enhanced inhibitory activity against pancreatic lipase when compared to parent curcumin.
- Kim, Tae Hoon,Kim, Jae Kyung,Ito, Hideyuki,Jo, Cheorun
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- Aerobic oxidation of p-cresols to 4-hydroxy benzaldehydes catalyzed by cobaltous chloride/NHPI/salen-Cu(II) catalytic system
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Oxidation of 2-methoxy-p-cresol, p-cresol, 2-bromo-p-cresol to their corresponding 4-hydroxybenzaldehydes with atmospheric molecular oxygen as oxidant and a combination of cobaltous chloride and N-hydroxyphthalimide (NHPI) as catalyst in methanol has been investigated for the first time. The results indicated that the reaction progress was related to the substituents in the structures of the substrates: the electron-donating group methoxy favors the aerobic reaction but the electron-withdrawing group Br is detrimental to the reaction. The introduction of salen-Cu(II) complexes as the third component into the cobaltous chloride/NHPI catalytic system can considerably improve the aerobic oxidation of p-cresol and 2-brom-p-cresol to the corresponding 4-hydroxybenzaldes.
- Ma, Wenchan,Zhang, Yuecheng,Li, Xiujuan,Zhao, Jiquan
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- Oxidative cleavage of C-C double bond in cinnamic acids with hydrogen peroxide catalysed by vanadium(v) oxide
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We have developed a cheap, green, mild and environmentally friendly method for the selective cleavage of carbon-carbon double bonds with a 30% aqueous solution of hydrogen peroxide as the oxidant and vanadium(v) oxide as the catalyst. The selectivity of the oxidative cleavage of cinnamic acid derivatives 1 depends on the substituents and the solvent used (DME - MeOCH2CH2OMe, TFE - 2,2,2-trifluoroethanol or MeCN). In DME, p-hydroxy derivatives were selectively converted to benzaldehyde derivatives 2, in TFE, oxidative cleavage led to the formation of benzoquinone derivatives 4, while in MeCN, cinnamic acid derivatives were selectively converted to benzoic acid derivatives 3. Ferulic acid 1a was quantitatively and selectively converted to vanillin 2a in a 91% isolated yield on a gram scale. Dimeric difurandione 1a′ was isolated as an intermediate, which was confirmed by in situ ATR-IR spectroscopy, while the formation of diols or epoxides was not observed. The analogous styrene derivative, 4-vinylguaiacol 1e was also selectively converted to either vanillin 2a or 2-methoxyquinone 4a in a high yield. The green metric for the conversion of ferulic acid to vanillin by different methods was calculated and compared to our method, and showed that our method has better environmental parameters.
- Horvat, Monika,Iskra, Jernej
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p. 2073 - 2081
(2022/04/07)
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- PhIO-Mediated oxidative dethioacetalization/dethioketalization under water-free conditions
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Treatment of thioacetals and thioketals with iodosobenzene in anhydrous DCM conveniently afforded the corresponding carbonyl compounds in high yields under water-free conditions. The mechanistic studies indicate that this dethioacetalization/dethioketalization process does not need water and the oxygen of the carbonyl products comes from the hypervalent iodine reagent.
- Du, Yunfei,Ouyang, Yaxin,Wang, Xi,Wang, Xiaofan,Yu, Zhenyang,Zhao, Bingyue,Zhao, Kang
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- Scope and limitations of biocatalytic carbonyl reduction with white-rot fungi
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The reductive activity of various basidiomycetous fungi towards carbonyl compounds was screened on an analytical level. Some strains displayed high reductive activities toward aromatic carbonyls and aliphatic ketones. Utilizing growing whole-cell cultures of Dichomitus albidofuscus, the reactions were up-scaled to a preparative level in an aqueous system. The reactions showed excellent selectivities and gave the respective alcohols in high yields. Carboxylic acids were also reduced to aldehydes and alcohols under the same conditions. In particular, benzoic, vanillic, ferulic, and p-coumaric acid were reduced to benzyl alcohol, vanillin, dihydroconiferyl alcohol and 1-hydroxy-3-(4-hydroxyphenyl)propan, respectively.
- Zhuk, Tatyana S.,Skorobohatko, Oleksandra S.,Albuquerque, Wendell,Zorn, Holger
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supporting information
(2021/02/02)
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- Rapid biosynthesis of phenolic glycosides and their derivatives from biomass-derived hydroxycinnamates
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Biomass-derived hydroxycinnamates (mainly includingp-coumaric acid and ferulic acid), which are natural sources of aromatic compounds, are highly underutilized resources. There is a need to upgrade them to make them economically feasible. Value-added phenolic glycosides and their derivatives, both belonging to a class of plant aromatic natural products, are widely used in the nutraceutical, pharmaceutical, and cosmetic industries. However, their complex aromatic structures make their efficient biosynthesis a challenging process. To overcome this issue, we created three novel synthetic cascades for the biosynthesis of phenolic glycosides (gastrodin, arbutin, and salidroside) and their derivatives (hydroquinone, tyrosol, hydroxytyrosol, and homovanillyl alcohol) fromp-coumaric acid and ferulic acid. Moreover, because the biomass-derived hydroxycinnamates directly provided aromatic units, the cascades enabled efficient biosynthesis. We achieved substantially high production rates (up to or above 100-fold enhancement) relative to the glucose-based biosynthesis. Given the ubiquity of the aromatic structure in natural products, the use of biomass-derived aromatics should facilitate the rapid biosynthesis of numerous aromatic natural products.
- Zhao, Mingtao,Hong, Xulin,Abdullah,Yao, Ruilian,Xiao, Yi
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supporting information
p. 838 - 847
(2021/02/09)
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- Discovery, Biocatalytic Exploration and Structural Analysis of a 4-Ethylphenol Oxidase from Gulosibacter chungangensis
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The vanillyl-alcohol oxidase (VAO) family is a rich source of biocatalysts for the oxidative bioconversion of phenolic compounds. Through genome mining and sequence comparisons, we found that several family members lack a generally conserved catalytic aspartate. This finding led us to study a VAO-homolog featuring a glutamate residue in place of the common aspartate. This 4-ethylphenol oxidase from Gulosibacter chungangensis (Gc4EO) shares 42 % sequence identity with VAO from Penicillium simplicissimum, contains the same 8α-N3-histidyl-bound FAD and uses oxygen as electron acceptor. However, Gc4EO features a distinct substrate scope and product specificity as it is primarily effective in the dehydrogenation of para-substituted phenols with little generation of hydroxylated products. The three-dimensional structure shows that the characteristic glutamate side chain creates a closely packed environment that may limit water accessibility and thereby protect from hydroxylation. With its high thermal stability, well defined structural properties and high expression yields, Gc4EO may become a catalyst of choice for the specific dehydrogenation of phenolic compounds bearing small substituents.
- Alvigini, Laura,Fraaije, Marco W.,Gran-Scheuch, Alejandro,Guo, Yiming,Mattevi, Andrea,Saifuddin, Mohammad,Trajkovic, Milos
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p. 3225 - 3233
(2021/10/04)
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- Selective Aerobic Oxidation of Benzyl Alcohols with Palladium(0) Nanoparticles Suspension in Water
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Abstract: This study concerns one of the rare applications of a suspension of palladium nanoparticles in water for oxidation reactions. The aqueous suspension containing well dispersed nanoparticles of 3.85?nm was obtained following a straightforward procedure involving the reduction of Na2PdCl4 with NaBH4 in the presence of PVP as stabilizing agent. In the way of oxidative catalytic valorisation of lignin, the aqueous suspension was directly applied as catalytic medium for the selective oxidation of vanillic alcohol into vanillin (80?°C, O2, 1?h) with more than 90% yield. Reusability of the catalytic medium has been demonstrated, acting as “quasi-homogeneous catalyst”. More sophisticated lignin-derived substrates like veratryl alcohol and hydrobenzoin gave yields of 50–80% to the respective aldehyde and ketone. In parallel, this as-synthesized suspension was directly used to prepare a Pd/TiO2 catalyst, the latter showing less efficiency for the catalytic transformations. Graphic Abstract: [Figure not available: see fulltext.]
- Bourbiaux, Dolorès,Mangematin, Stéphane,Djakovitch, Laurent,Rataboul, Franck
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p. 3239 - 3249
(2021/03/16)
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- A Synergistic Magnetically Retrievable Inorganic-Organic Hybrid Metal Oxide Catalyst for Scalable Selective Oxidation of Alcohols to Aldehydes and Ketones
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Herein, we report a synergistic silica coated magnetic Fe3O4 catalyst functionalized with nitrogen rich organic moieties and immobilized with cobalt metal ion (FNP-5) for selective oxidation of alcohols to aldehydes and ketones using tert-butyl hydroperoxide (TBHP) as oxidant. The catalyst was rigorously characterized via several techniques which delineate its core-shell structure, magnetic behavior, phase and crystal structure. The Co(III) acts as the active catalytic center for selective oxidation reaction. The control reactions revealed radical mechanistic pathway assisted by the synergism induced by the inorganic-organic hybrid nature of FNP-5. The other features of current protocol involve neat reaction conditions, high TOF values, scalability of product and low E-factor value (1.92). Moreover, FNP-5 could be effortlessly separated via an external magnet, displays recyclability over eight catalytic cycles and exhibits structural integrity even after rigorous use. Overall, these results manifest the understanding of synergistic architectures as sustainable surrogates for selective oxidation reactions.
- Mittal, Rupali,Awasthi, Satish Kumar
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p. 4799 - 4813
(2021/09/30)
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- Chemoselective and ligand-free aerobic oxidation of benzylic alcohols to carbonyl compounds using alumina-supported mesoporous nickel nanoparticle as an efficient recyclable heterogeneous catalyst
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An economically efficient and operationally simple ligand-free protocol for the chemoselective oxidation of benzylic alcohols to carbonyl compounds has been developed using alumina-supported nickel nanoparticles as a stable recyclable heterogeneous catalyst along with potassium tert-butoxide in the presence of aerial oxygen as an eco-friendly oxidant. The aliphatic alcohols remained unaffected under the present condition. Excellent chemoselectivity has also been demonstrated through intermolecular and intramolecular competition experiments. This protocol accommodates a diverse range of substituents with the tolerance of various sensitive moieties during the reaction. The catalyst could be recovered by filtration and reused consecutively without any significant loss in the catalytic activity. Moreover, the heterogeneity of the catalyst has also been established by the “hot filtration method (Sheldon's test)”.
- Das, Asit Kumar,Nandy, Sneha,Bhar, Sanjay
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- An aerobic oxidation of alcohols into carbonyl synthons using bipyridyl-cinchona based palladium catalyst
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We have reported an aerobic oxidation of primary and secondary alcohols to respective aldehydes and ketones using a bipyridyl-cinchona alkaloid based palladium catalytic system (PdAc-5) using oxygen at moderate pressure. ThePdAc-5catalyst was analysed using SEM, EDAX, and XPS analysis. The above catalytic system is used in experiments for different oxidation systems which include different solvents, additives, and bases which are cheap, robust, non-toxic, and commercially available on the industrial bench. The obtained products are quite appreciable in both yield and selectivity (70-85%). In addition, numerous important studies, such as comparisons with various commercial catalysts, solvent systems, mixture of solvents, and catalyst mole%, were conducted usingPdAc-5. The synthetic strategy of oxidation of alcohol into carbonyl compounds was well established and all the products were analysed using1H NMR,13CNMR and GC-mass analyses.
- Cheedarala, Ravi Kumar,Chidambaram, Ramasamy R.,Siva, Ayyanar,Song, Jung Il
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p. 32942 - 32954
(2021/12/02)
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- Sustainable synthesis of vanillin through base-free selective oxidation using synergistic AgPd nanoparticles loaded on ZrO2
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The synergistic effect between bimetallic nanoparticles, as well as the support effect, is particularly important for supported catalysts in heterogeneous catalysis. In this work, an AgPd/ZrO2 bimetallic catalyst was reported for the base-free aerobic oxidation of vanillyl alcohol to vanillin, a challenging transformation of an aromatic bio-alcohol into a valuable fine chemical. The crystalline structure and textural properties of ZrO2 were modulated by using different zirconium precursors and precipitants during the precipitation process. The ZrO2 obtained from zirconium nitrate and trimethylamine was found to be the most suitable support. It displayed abundant reactive oxygen species and the largest specific surface area. Then, an Ag promoter was added to the Pd/ZrO2 catalyst and the synergy between Ag and Pd was tuned by varying their ratios. The Ag0.5Pd1/ZrO2 catalyst showed an enhanced performance, i.e., 100% conversion of vanillyl alcohol and 95% selectivity to vanillin at 120 °C and 3 bar O2 within 4 h, in comparison with the Pd/ZrO2 catalyst (69% and 87%, respectively). Moreover, the vanillin productivity reached 133.0 mol mol-1 h-1, the best result reported in the literature to date. Various characterization methods demonstrated that the addition of Ag can reduce the mean size of Pd nanoparticles (4.9 nm vs. 3.8 nm), and Ag+ species were beneficial to stabilizing Pd0 species in a high fraction due to electron transfer. The reactive Pd0 sites closely interacting with the Ag promoter allowed lowering of the apparent activation energy of the reaction (27.3 vs. 37.5 kJ mol-1). In addition, the Ag0.5Pd1/ZrO2 catalyst exhibited superior stability during consecutive recycling uses owing to the strong metal-support interactions.
- Cao, Qiue,Fang, Wenhao,Jing, Fangli,Lin, Peng,Sun, Weixiao,Tang, Qinghu
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p. 7268 - 7277
(2021/11/27)
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- Efficient Biosynthesis of Vanillin from Isoeugenol by Recombinant Isoeugenol Monooxygenase from Pseudomonas nitroreducens Jin1
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Currently, the biotechnological preparation of fragrances using natural materials attracted growing attention. Enzymatic synthesis of vanillin from isoeugenol by recombinant isoeugenol monooxygenase from Pseudomonas nitroreducens Jin1 was systematically investigated herein. With series of work on the construction of recombinant E. coli over-expressing isoeugenol monooxygenase, optimization of the culture conditions for enzyme production and reaction process for converting isoeugenol into vanillin, an increase of 22-fold in the enzyme activity (2050 U/L) was obtained, and the conversion was significantly increased at high substrate concentration with the aid of magnetic chitosan membrane for product isolation in situ. Under optimal conditions, the product concentration and space-time yield reached 252 mM and 115 g/L/d, respectively, and vanillin was obtained in 82.3% yield and > 99% purity in the gram preparative scale. The developed bioprocess showed application potential for efficient preparation of vanillin from inexpensive natural resources.
- Wang, Qian,Wu, Xiaomei,Lu, Xinyi,He, Yucai,Ma, Baodi,Xu, Yi
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p. 1116 - 1128
(2021/01/11)
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- Catalytic wet hydrogen peroxide oxidation of isoeugenol to vanillin using microwave-assisted synthesized metal loaded catalysts
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Supported metal nanoparticles (Cu, W, Mo among others) have been stabilized on a silica matrix following an efficient and sustainable one-pot microwave-assisted protocol. The materials synthesized were characterized, mainly, by nitrogen adsorption desorption measurements, X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDS). The materials exhibited large surface area and pore size in the mesopore range. The incorporation of metal particles in the silica matrix was also confirmed with particle size in a wide range between 2 and 52 nm. The catalytic activity of the resulting materials was evaluated in the catalytic wet oxidation of isoeugenol into vanillin using hydrogen peroxide as oxidant. The catalysts shown moderate conversions, up to 50–60 % for Cu-MINT with acceptable selectivity towards vanillin production (22–45 %), obtaining dimers as main side products. The stability of the catalysts was investigated as well, obtaining an imperceptible decrease after the fourth use.
- García-Albar, Paloma,Lázaro, Noelia,ALOthman, Zeid A.,Romero, Antonio A.,Luque, Rafael,Pineda, Antonio
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- Metal doping of porous materialsviaa post-synthetic mechano-chemical approach: a general route to design low-loaded versatile catalytic systems
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Mesoporous silica materials (Al-SBA-15 and Al-MCM-41) were successfully doped with two different transition metals (Zr and Fe) by following a mechano-chemical approach. Different metal precursors (metal saltsversusMOF particles) were studied in order to explore their impact on the ultimate catalytic performance of the doped materials. Importantly, doping levels as low as 1 wt% led to significant catalytic improvements for selective mild oxidation reactions under microwave irradiation in a very short reaction time (3 min). Fe-doped materials (0.175 mol% catalyst) resulted in the highest yields, achieving a maximum conversion of 46% and 100% selectivity in the oxidation of benzyl alcohol to benzaldehyde, and 61% conversion and 44% selectivity in the production of vanillin from isoeugenol. Results clearly indicated that the incorporation of Zr or Fe into the structure increased the total acidity of the support, which is then translated into an improved catalytic performance toward the studied oxidation reactions. The recyclability (up to 5 reuses without any treatment; although more reuses are possible after regeneration) of the doped catalysts pointed out their true potential applicability in a sustainable manner. Overall, this work demonstrates that the proposed post-synthetic mechano-chemical approach is an effective good alternative for the preparation of metal-doped porous materials, and is remarkably applicable to different doping metals, allowing thus the straightforward preparation of a library of catalysts with specific catalytic properties depending on the metal incorporated.
- Marquez-Medina, M. Dolores,Luque, Rafael,Balu, Alina M.,Ivars-Barceló, Francisco,Carrillo-Carrión, Carolina
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p. 2103 - 2109
(2021/04/12)
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- Room temperature depolymerization of lignin using a protic and metal based ionic liquid system: an efficient method of catalytic conversion and value addition
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Lignin is one of the most abundant biopolymer which can be utilized to synthesize various chemicalsviaits depolymerization. However, depolymerization of lignin generally occurs under very harsh conditions. Herein, we report the efficient depolymerization of ligninviadissolution in a mixed ionic liquid system: ethyl ammonium nitrate (EAN) + prolinium tetrachloromanganate(ii) [Pro]2[MnCl4] at 35 °C and under atmospheric pressure conditions. The high dissolution of lignin in ethyl ammonium nitrate provided a large number of H-bonding sites leading to the cracking of lignin and subsequent oxidative conversion by [Pro]2[MnCl4]viathe formation of metal-oxo bonding between Mn and lignin molecules. The extracted yield of vanillin was found to be 18-20% on lignin weight basisviaGC-MS analysis. The depolymerization of lignin was confirmed by SEM, FT-IR and PXRD analysis. Since lignin contains UV-absorbing functional groups, the regenerated biomass after the recovery of the depolymerized products was further utilized to synthesize a UV-shielding material. The constructed films from such a material exhibited a high SPF value of 22 and were found to be very effective by limiting the UV degradation of rhodamine B thus making the lignin valorization process economically viable and environmentally sustainable.
- Mehta, Mohit J.,Kulshrestha, Akshay,Sharma, Shweta,Kumar, Arvind
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p. 1240 - 1247
(2021/02/26)
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- Thiols Act as Methyl Traps in the Biocatalytic Demethylation of Guaiacol Derivatives
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Demethylating methyl phenyl ethers is challenging, especially when the products are catechol derivatives prone to follow-up reactions. For biocatalytic demethylation, monooxygenases have previously been described requiring molecular oxygen which may cause oxidative side reactions. Here we show that such compounds can be demethylated anaerobically by using cobalamin-dependent methyltransferases exploiting thiols like ethyl 3-mercaptopropionate as a methyl trap. Using just two equivalents of this reagent, a broad spectrum of substituted guaiacol derivatives were demethylated, with conversions mostly above 90 %. This strategy was used to prepare the highly valuable antioxidant hydroxytyrosol on a one-gram scale in 97 % isolated yield.
- Grimm, Christopher,Kroutil, Wolfgang,Pompei, Simona,Schiller, Christine,Schober, Lukas
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supporting information
p. 16906 - 16910
(2021/07/02)
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- Preparation method of 3-methoxy-4-hydroxybenzaldehyde
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The invention discloses a preparation method of 3-methoxy-4-hydroxybenzaldehyde, which belongs to the technical field of biochemical technology materials. The method comprises the following specific steps of adding o-chlorophenol, anhydrous aluminum chloride and toluene into a three-neck flask, stirring for dissolving, heating for reflux, then adding diethylamine, continuously refluxing, adding formic anhydride lithium salt, adjusting the PH value, carrying out suction filtration, carrying out reduced pressure distillation, and collecting fractions to obtain 3-chloro-4-hydroxybenzaldehyde, and adding the obtained 3-chloro-4-hydroxybenzaldehyde, anhydrous magnesium chloride and benzene into a three-neck flask, mixing, dissolving, heating, refluxing, dropwise adding a 10% sodium hydroxide solution, uniformly adding sodium methoxide in three batches, cooling to room temperature, adjusting the PH value, carrying out suction filtration, and carrying out reduced pressure distillation to finally obtain the 3-methoxy-4-hydroxybenzaldehyde product. Compared with a traditional method, the synthetic route is not long, the reaction condition is mild, and the yield is high.
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Paragraph 0031-0032; 0036-0037; 0041-0042; 0046-0047
(2021/08/06)
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- Exploiting the photocatalytic activity of TiO2towards the depolymerization of Kraft lignin
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Lignin is a promising renewable source of aromatic chemicals. Described herein is a new photocatalytic methodology for depolymerization of oxidized Kraft lignin to industrially relevant aromatic platform chemicals. The photooxidation route begins with oxidation of alcohol moieties using a gold nanoparticle/hydrotalcite composite. Next, the oxidized lignin is subjected to UVA irradiation in the presence of TiO2, leading to a 3-fold decrease of its molecular weight and to the formation of various monolignols. The products obtained in both steps were characterized using FTIR, SEC, GC-MS, and 2D NMR spectroscopy, which confirm the depolymerization of lignin to smaller molecular weight products. This method offers both energetic and chemical advantages over thermochemical processing for lignin valorisation.
- Baker, R. Tom,Crites, Charles-Oneil L.,Gomes de Mendon?a, Fernanda,Hallett-Tapley, Geniece L.,Netto-Ferreira, José Carlos,Tremblay, Luc
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supporting information
p. 15371 - 15377
(2021/09/07)
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- Surfactant-Assisted Ozonolysis of Alkenes in Water: Mitigation of Frothing Using Coolade as a Low-Foaming Surfactant
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Aqueous-phase ozonolysis in the atmosphere is an important process during cloud and fog formation. Water in the atmosphere acts as both a reaction medium and a reductant during the ozonolysis. Inspired by the atmospheric aqueous-phase ozonolysis, we herein report the ozonolysis of alkenes in water assisted by surfactants. Several types of surfactants, including anionic, cationic, and nonionic surfactants, were investigated. Although most surfactants enhanced the solubility of alkenes in water, they also generated excessive foaming during the ozone bubbling, which led to the loss of products. Mitigation of the frothing was accomplished by using Coolade as a nonionic and low-foaming surfactant. Coolade-assisted ozonolysis of alkenes in water provided the desired carbonyl products in good yields and comparable to those achieved in organic solvents. During the ozonolysis reaction, water molecules trapped within the polyethylene glycol region of Coolade were proposed to intercept the Criegee intermediate to provide a hydroxy hydroperoxide intermediate. Decomposition of the hydroxy hydroperoxide led to formation of the carbonyl product without the need for a reductant typically required for the conventional ozonolysis using organic solvents. This study presents Coolade as an effective surfactant to improve the solubility of alkenes while mitigating frothing during the ozonolysis in water.
- Buntasana, Supanat,Hayashi, Jun,Klumphu, Piyatida,Padungros, Panuwat,Saetung, Prakorn,Vilaivan, Tirayut
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supporting information
(2022/02/23)
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- Transaminase-Mediated Amine Borrowing via Shuttle Biocatalysis
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Shuttle catalysis has emerged as a useful methodology for the reversible transfer of small functional groups, such as CO and HCN, and goes far beyond transfer hydrogenation chemistry. While a biocatalytic hydrogen-borrowing methodology is well established, the biocatalytic borrowing of alternative functional groups has not yet been realized. Herein, we present a new concept of amine borrowing via biocatalytic shuttle catalysis, which has no counterpart in chemo-shuttle catalysis and allows efficient intermolecular amine shuttling to generate reactive intermediates in situ. By coupling this dynamic exchange with an irreversible downstream step to displace the reaction equilibrium in the forward direction, high conversion to target products can be achieved. We showcase the potential of this amine-borrowing methodology using a biocatalytic equivalent of both the Knorr-pyrrole synthesis and Pictet-Spengler reaction.
- O'Reilly, Elaine,O'Sullivan, Rachel,Ryan, James,Taday, Freya
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supporting information
(2022/01/04)
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- Oxygen-Free Regioselective Biocatalytic Demethylation of Methyl-phenyl Ethers via Methyltransfer Employing Veratrol- O-demethylase
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The cleavage of aryl methyl ethers is a common reaction in chemistry requiring rather harsh conditions; consequently, it is prone to undesired reactions and lacks regioselectivity. Nevertheless, O-demethylation of aryl methyl ethers is a tool to valorize natural and pharmaceutical compounds by deprotecting reactive hydroxyl moieties. Various oxidative enzymes are known to catalyze this reaction at the expense of molecular oxygen, which may lead in the case of phenols/catechols to undesired side reactions (e.g., oxidation, polymerization). Here an oxygen-independent demethylation via methyl transfer is presented employing a cobalamin-dependent veratrol-O-demethylase (vdmB). The biocatalytic demethylation transforms a variety of aryl methyl ethers with two functional methoxy moieties either in 1,2-position or in 1,3-position. Biocatalytic reactions enabled, for instance, the regioselective monodemethylation of substituted 3,4-dimethoxy phenol as well as the monodemethylation of 1,3,5-trimethoxybenzene. The methyltransferase vdmB was also successfully applied for the regioselective demethylation of natural compounds such as papaverine and rac-yatein. The approach presented here represents an alternative to chemical and enzymatic demethylation concepts and allows performing regioselective demethylation in the absence of oxygen under mild conditions, representing a valuable extension of the synthetic repertoire to modify pharmaceuticals and diversify natural products.
- Grimm, Christopher,Lazzarotto, Mattia,Pompei, Simona,Schichler, Johanna,Richter, Nina,Farnberger, Judith E.,Fuchs, Michael,Kroutil, Wolfgang
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p. 10375 - 10380
(2020/10/02)
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- Selective Oxidation of Alcohols to Carbonyl Compounds over Small Size Colloidal Ru Nanoparticles
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The selective oxidation of alcohols to corresponding aldehydes is one of the most challenging problems in modern chemistry due to over-oxidation of these products further into corresponding acids and esters. Herein, we report an efficient and eco-friendly method for selective oxidation of aliphatic, unsaturated and aromatic alcohols to aldehydes (>90 %) using small size (2 nm) non-supported colloidal Ru nanoparticles. The selectivity rapidly decreases with increase of the size of nanoparticles (from 2 to 10 nm) or after their deposition over support. X-ray photoelectron spectroscopy suggests that this catalytic performance can be attributed to high content Ru?O species on the surface of small size Ru nanoparticles, which undergo reduction with formation of water and aldehyde and easy oxidation cycles during the reaction according to the Mars-van Krevelen mechanism. The presence of surface oxide layer over small size Ru nanoparticles suppresses over-oxidation of aldehydes to acids.
- Zhao, JingPeng,Hernández, Willinton Y.,Zhou, WenJuan,Yang, Yong,Vovk, Evgeny I.,Capron, Mickael,Ordomsky, Vitaly
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p. 238 - 247
(2019/11/14)
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- A metal-free heterogeneous photocatalyst for the selective oxidative cleavage of CC bonds in aryl olefins: via harvesting direct solar energy
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Selective cleavage of CC bonds is highly important for the synthesis of carbonyl containing fine chemicals and pharmaceuticals. Novel methodologies such as ozonolysis reactions, Lemieux-Johnson oxidation reaction etc. already exist. Parallel to these, catalytic methods using homogeneous catalysts also have been discovered. Considering the various advantages of heterogeneous catalysts such as recyclability and stability, couple of transition metal-based heterogeneous catalysts have been applied for this reaction. However, the pharmaceutical industries prefer to use metal-free catalysts (especially transition metal-free) to avoid further leaching in the final products. This is for sure a big challenge to an organic chemist and to the pharmaceutical industries. To make this feasible, a mild and efficient protocol has been developed using polymeric carbon nitrides (PCN) as metal-free heterogeneous photocatalysts to convert various olefins into the corresponding carbonyls. Later, this catalyst has been applied in the gram scale synthesis of pharmaceutical drugs using direct solar energy. Detailed mechanistic studies revealed the actual role of oxygen, the catalyst, and the light source.
- Das, Shoubhik,Hatami, Nareh,Jooss, Christian,Lange, Niklas Simon,Ronge, Emanuel,Schilling, Waldemar,Zhang, Yu
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supporting information
p. 4516 - 4522
(2020/08/10)
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- Method for synthesizing vanillin from eugenol through ozone oxidation
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The invention relates to the technical field of organic chemical synthesis, in particular to a method for synthesizing vanillin from eugenol through ozone oxidation. The method comprises the followingsteps: adding dichlorotris(triphenylphosphine)ruthenium serving as a catalyst into eugenol to perform isomerization reaction to obtain isoeugenol, performing esterification reaction to obtain isoeugenol acetate, performing ozonation, and performing reducing; and carrying out alcoholysis and refining on the acetyl vanillin to obtain a pure product. The method solves the problems of low productionyield, use of a metal oxidant and difficult treatment of wastewater in the eugenol method in the prior art, eugenol isomerization adopts dichlorotris(triphenylphosphine)ruthenium as a catalyst, no wastewater is generated in the process, isoeugenol acetate is oxidized by ozone, the use of a heavy metal oxidant is avoided, and the method conforms to the green development trend. The method has the advantages of environmental protection and high yield.
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- Improved Pd/Ru metal supported graphene oxide nano-catalysts for hydrodeoxygenation (HDO) of vanillyl alcohol, vanillin and lignin
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Pd and Ru nanoparticles supported on graphene oxide (GO) [Pd?GO and Ru?GO] and bimetallic [Pd/Ru?GO] were prepared and well characterized by XRD, FT-IR, EDS, TEM, XPS and ICP-AES analyses. The prepared nano-catalysts were tested for hydrodeoxygenation (HDO) of lignin monomer molecules-vanillyl alcohol and vanillin. In comparison with previously reported methods, Ru?GO and bimetallic Pd/Ru?GO catalysts showed high activity and selectivity, under milder conditions, at room temperature and 145 psi H2 pressure, for the formation of p-creosol, a value added product, as a potential future biofuel with antibacterial and anti-insecticidal properties. The multifold advantages of both these catalysts are in terms of reduced catalyst loading with a lower metal content and ambient temperture conditions resulting in higher conversion of the starting material. Furthermore, the efficacy of the developed methodology using Ru?GO and bimetallic Pd/Ru?GO catalysts under the optimized conditions was tested on the phenolic components of commercial lignin obtained by photo-catalytic fragmentation using TiO2, to obtain a mixture after HDO which contained vanillyl alcohol and p-creosol among others, as indicated by HPLC-MS analysis.
- Arora, Shalini,Gupta, Neeraj,Singh, Vasundhara
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supporting information
p. 2018 - 2027
(2020/04/07)
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- Directly Microwave-Accelerated Cleavage of C?C and C?O Bonds of Lignin by Copper Oxide and H2O2
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Model erythro, phenolic, and nonphenolic lignin β-O-4 dimer compounds are treated with copper oxide and H2O2 at the electronic field maximum position of a single-mode 2.45 GHz microwave system equipped with a cavity resonator. The products obtained through microwave heating and oil-bath heating with the same reaction vessel and temperature profile are quantitatively compared. Dimer degradation is found to proceed through consecutive elementary reactions. The phenolic dimer is dehydroxylated and this is followed by the spontaneous cleavage of Cα?Cβ and C?O?C bonds to produce guaiacol, vanillin, and vanillic acid. The reaction of the nonphenolic dimer produces veratric acid, veratraldehyde, and guaiacol. Microwave irradiation accelerates cleavage of the side chain and the oxidation of vanillin to vanillic acid. However, no acceleration of veratraldehyde oxidation to veratric acid or aromatic ring cleavage to produce dicarboxylic acids is observed. The selective acceleration of elementary reactions during the degradation of model lignin compounds indicates that microwaves interact with reaction intermediates that are sensitive to electromagnetic waves.
- Qu, Chen,Ito, Keigo,Katsuyama, Isamu,Mitani, Tomohiko,Kashimura, Keiichiro,Watanabe, Takashi
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p. 4510 - 4518
(2020/05/18)
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- Selective production of bio-based aromatics by aerobic oxidation of native soft wood lignin in tetrabutylammonium hydroxide
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Aerobic oxidation of native soft wood lignin in an aqueous solution of Bu4NOH facilitates efficient production of vanillin (4-hydroxy-3-methoxybenzaldehyde), which is one of the platform chemicals in industry. Oxidation of Japanese cedar (Cryptomeria japonica) wood flour at 120 °C for 4 h under O2in Bu4NOH-based aqueous solutions produced vanillin in 23.2 wt% yield based on the Klason lignin content of the starting material. This yield was comparable to that in alkaline nitrobenzene oxidation of the same material (27.2%), which indicated that our aerobic oxidation exploited the full potential of the wood flour for vanillin production. Further mechanical investigation with lignin model compounds suggested that the vanillin formation occurred mainly through following successive reactions: alkaline-catalyzed degradation of ?-ether linkages in middle units of lignin polymer to form a glycerol end group, oxidation of the glycerol end group by O2to a HCa?O moiety, and release of vanillin from the HCa?O end. One of the reasons for the high performance of Bu4NOH for the vanillin production was explained by the general understanding in organic chemistry that Bu4OH is a stronger base than simple alkali,e.g.NaOH. The other more fundamental mechanical aspect was that Bu4N+suppressed disproportionation of the vanillin precursor (the CaHO end group) probably due to strong interaction between the cation and the HCa?O end group.
- Hosoya, Takashi,Miyafuji, Hisashi,Yamada, Tatsuhiko,Yamamoto, Kohei
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p. 19199 - 19210
(2020/06/04)
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- Effective Control of Particle Size and Electron Density of Pd/C and Sn-Pd/C Nanocatalysts for Vanillin Production via Base-Free Oxidation
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The effective control of particle size and electron density of metal active sites is challenging yet important for supported nanoparticles, as size effects and promoter effects play vital roles in heterogeneous catalysis on the nanoscale. In this work, we report Pd/C and Sn-Pd/C nanocatalysts for the base-free aerobic oxidation of vanillyl alcohol to vanillin, a challenging reaction not only in the fundamental research of selective oxidation of alcohols but also for the practical transformation of bio-based alcohols to value-added chemicals. We effectively tuned the mean size of Pd nanoparticles from 1.8 to 6.7 nm by varying the temperature used for catalyst preparation and further modified the electron density of the Pd/C catalyst by adding a SnO2 promoter with different loadings. TEM, HAADF-STEM, XPS, CO chemisorption, and in situ DRIFT-IR of CO adsorption characterizations allowed us to get insight into the unique catalytic properties of Pd nanocatalysts. It was conjectured that the base-free aerobic oxidation of vanillyl alcohol to vanillin over the Pd/C catalyst can be a structure-sensitive reaction and the Pd particle size was decisive for the dispersion of Pd, the proportion of catalytically active Pd0 sites, and the intrinsic turnover frequency (iTOF). The 1 wt % Pd/C (1.8 nm) catalyst showed an iTOF value of 268 h-1 and 100% yield to vanillin at 120 °C, 5 bar of O2, and 20 mg of the catalyst within 9 h. We further demonstrated that Sn4+ ions in SnO2 as an electronic promoter can promote Pd/C activity by the formation of highly active, electron-sufficient Pd0 sites which significantly lowered the apparent activation energy of reaction. The 0.1Sn-Pd/C catalyst showed a higher iTOF value of 458 h-1 and a yield of 100% to vanillin at 120 °C, 3 bar of O2 and 15 mg of the catalyst within 6 h. Moreover, we verified a satisfying reusability and an adequate substrate scope over the 0.1Sn-Pd/C catalyst.
- Cao, Qiue,Fang, Wenhao,Lu, Yaowei,Sun, Weixiao,Wang, Yongxing,Wu, Shipeng
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p. 7699 - 7709
(2020/08/21)
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- Mpsc6 binuclear complexes immobilized on graphene oxide for oxidation of lignin model compounds and lignin
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An efficient process for the oxidative degradation of lignin using M-GO (MPSC6 binuclear complexes immobilized on graphene oxide) biomimetic catalysts in acetonitrile was developed in this work. Different M-GO catalysts (M=Co, Cu, Zn and Ni) were used to catalyze the depolymerization of lignin model compounds and organosolv lignin. The results showed that the immobilization of MPSC6 complexes on GO was favorable for regulating the valuable depolymerization of the model compounds and lignin. The optimal solid catalyst Co-GO exhibited high catalytic activity, which showed a 83.04% conversion of phenolic β-O-4 lignin model compound, a 91.26% conversion of veratryl alcohol and a 96.24% conversion of vanillyl alcohol with a catalyst/model compound ratio of 50 mg:10 mmol and a dosage of 15 mmol H2O2 at 80 °C for 3 h. The stuctural changes of organosolv lignin occurred in catalytic oxidation were analyzed in terms of O/C ratio, molecular weight and OH content of lignin samples, and a plausible mechanism involving the formation of aromatic products and muconolactone from lignin depolymerization over M-GO was also proposed.
- Yang, Xiao-Jun,Zhou, Xue-Fei,Zou, Zheng-Rong
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p. 973 - 982
(2021/06/26)
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- Facile synthesis of digestible , rigid-and-flexible, bio-based building block for high-performance degradable thermosetting plastics
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Plastics are indispensable in modern society, but are non-sustainable resources, releasing hazardous chemicals during their service life, and post-disposal issues make traditional plastics a risk. Herein, we report a digestible , rigid-and-flexible, bio-sourced building block for high-performance degradable plastics. This building block was synthesized from the bioresources vanillin (lignin derivative) and glycerol through solvent-free acetalization with a high conversion rate and high selectivity. It could be extremely rapidly degraded into non-toxic vanillin and glycerol under mild acidic conditions even at a similar pH and temperature to gastric juice in the human stomach ( digested ), resulting in the outstanding chemical degradability of its corresponding epoxy thermosets, which is beneficial for their recycling. By virtue of the benzene ring, heterocycle, and methoxyl group-related hydrogen bond, the degradable thermosetting plastic showed much higher mechanical properties (stronger and tougher) and comparable thermal properties relative to a commercial high-performance counterpart based on bisphenol A (BPA). This favorable performance combination has never been reported for plastics. Thus, this bio-derived building block exhibits great potential as a sustainable and upgraded alternative to petroleum-sourced aromatic chemicals such as BPA for high-performance plastics.
- Wang, Binbo,Ma, Songqi,Li, Qiong,Zhang, Hua,Liu, Junjie,Wang, Rong,Chen, Zhiquan,Xu, Xiwei,Wang, Sheng,Lu, Na,Liu, Yanlin,Yan, Shifeng,Zhu, Jin
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supporting information
p. 1275 - 1290
(2020/03/11)
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- A chemoselective photolabile protecting group for aldehydes
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A new and high-efficiency photolabile protecting group (PLPG) for aldehydes is described. The PLPG was introduced to aldehydes by using a Lewis acid. Results showed that the PLPG can be released rapidly and smoothly under ultraviolet (UV) irradiation with high efficiency and low cost. This PLPG can easily synthesized and also be selectively protect aldehydes in the presence of ketones.
- Peng, Tao,Wang, Gang,Wang, Lin,Wen, Xiaoxue,Xu, Jing,Xu, Kaijun,Yang, Hongpeng,Zhang, Shouguo
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supporting information
(2020/02/29)
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- Direct Photorelease of Alcohols from Boron-Alkylated BODIPY Photocages
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BODIPY photocages allow the release of substrates using visible light irradiation. They have the drawback of requiring reasonably good leaving groups for photorelease. Photorelease of alcohols is often accomplished by attachment with carbonate linkages, which upon photorelease liberate CO2 and generate the alcohol. Here, we show that boron-alkylated BODIPY photocages are capable of directly photoreleasing both aliphatic alcohols and phenols upon irradiation via photocleavage of ether linkages. Direct photorelease of a hydroxycoumarin dye was demonstrated in living HeLa cells.
- Fischer, Logan J.,Gehrmann, Elizabeth J.,Peterson, Julie A.,Shrestha, Pradeep,Smith, Emily A.,Wijesooriya, Chamari S.,Winter, Arthur H.,Yuan, Ding
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supporting information
p. 5712 - 5717
(2020/05/19)
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- Engineering Orthogonal Methyltransferases to Create Alternative Bioalkylation Pathways
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S-adenosyl-l-methionine (SAM)-dependent methyltransferases (MTs) catalyse the methylation of a vast array of small metabolites and biomacromolecules. Recently, rare carboxymethylation pathways have been discovered, including carboxymethyltransferase enzymes that utilise a carboxy-SAM (cxSAM) cofactor generated from SAM by a cxSAM synthase (CmoA). We show how MT enzymes can utilise cxSAM to catalyse carboxymethylation of tetrahydroisoquinoline (THIQ) and catechol substrates. Site-directed mutagenesis was used to create orthogonal MTs possessing improved catalytic activity and selectivity for cxSAM, with subsequent coupling to CmoA resulting in more efficient and selective carboxymethylation. An enzymatic approach was also developed to generate a previously undescribed co-factor, carboxy-S-adenosyl-l-ethionine (cxSAE), thereby enabling the stereoselective transfer of a chiral 1-carboxyethyl group to the substrate.
- Bennett, Matthew R.,Cronin, Victoria A.,Herbert, Abigail J.,Micklefield, Jason,Shepherd, Sarah A.,Sung, Rehana
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supporting information
p. 14950 - 14956
(2020/07/04)
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- Regioselectivity of Cobalamin-Dependent Methyltransferase Can Be Tuned by Reaction Conditions and Substrate
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Regioselective reactions represent a significant challenge for organic chemistry. Here the regioselective methylation of a single hydroxy group of 4-substituted catechols was investigated employing the cobalamin-dependent methyltransferase from Desulfitobacterium hafniense. Catechols substituted in position four were methylated either in meta- or para-position to the substituent depending whether the substituent was polar or apolar. While the biocatalytic cobalamin dependent methylation was meta-selective with 4-substituted catechols bearing hydrophilic groups, it was para-selective for hydrophobic substituents. Furthermore, the presence of water miscible co-solvents had a clear improving influence, whereby THF turned out to enable the formation of a single regioisomer in selected cases. Finally, it was found that also the pH led to an enhancement of regioselectivity for the cases investigated.
- Pompei, Simona,Grimm, Christopher,Farnberger, Judith E.,Schober, Lukas,Kroutil, Wolfgang
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p. 5977 - 5983
(2020/10/06)
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- Specific Residues Expand the Substrate Scope and Enhance the Regioselectivity of a Plant O-Methyltransferase
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An isoeugenol 4-O-methyltransferase (IeOMT), isolated from the plant Clarkia breweri, can be engineered to a caffeic acid 3-O-methyltransferase (CaOMT) by replacing three consecutive residues. Here we further investigated functions of these residues by constructing the triple mutant T133M/A134N/T135Q as well as single mutants of each residue. Phenolics with different chain lengths and different functional groups were investigated. The variant T133M improves the enzymatic activities against all tested substrates by providing beneficial interactions to residues which directly interact with the substrate. Mutant A134N significantly enhanced the regioselectivity. It is meta-selective or even specific against most of the tested substrates but para-specific towards 3,4-dihydroxybenzoic acid. The triple mutant T133M/A134N/T135Q benefits from these two mutations, which not only expand the substrate scope but also enhance the regioselectivity of IeOMT. On the basis of our work, regiospecific methylated phenolics can be produced in high purity by different IeOMT variants.
- Tang, Qingyun,Bornscheuer, Uwe T.,Pavlidis, Ioannis V.
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p. 3227 - 3233
(2019/07/04)
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- Mechanochemical synthesis of CuO/MgAl2O4 and MgFe2O4 spinels for vanillin production from isoeugenol and vanillyl alcohol
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CuO/MgAl2O4 and CuO/MgFe2O4 catalysts were successfully synthesized with the use of spinel supports by a very simple and low-cost mechanochemical method. High-speed ball-milling was used to synthesize these catalyst supports for the first time. Materials were subsequently characterized by using XRD, FESEM, TEM, EDS-Dot mapping, XPS, BET-BJH, and Magnetic Susceptibility to investigate the physical-chemical characteristics of the catalysts. Acidity evaluation results indicated that the catalyst with the Mg-Al spinel support had more acid sites. XRD results showed a successful synthesis of the catalysts with large crystal sizes. Both catalysts were used in isoeugenol oxidation and vanillyl alcohol to vanillin reactions, with the CuO/MgAl2O4 showing optimum results. This catalyst provided 67% conversion (74% selectivity) after 2 h and this value improved to 81% (selectivity 100%) with the second reaction after 8 h. The CuO/MgFe2O4 catalyst in the first reaction after five hours revealed 53% conversion (47% selectivity) and after eight hours with the second reaction, the conversion value improved to 64% (100% selectivity). In terms of reusability, CuO/MgAl2O4 showed better results than the CuO/MgFe2O4 catalyst, for both reactions.
- Rahmanivahid, Behgam,de Dios, Maria Pinilla,Haghighi, Mohammad,Luque, Rafael
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- Selective Aerobic Oxidation of Benzylic Alcohols Catalyzed by a Dicyclopropenylidene-Ag(I) Complex
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The unprecedented synthesis, single-crystal X-ray structure, and first catalytic application of a dicarbene-Ag(I) complex [Ag(BAC)2][CO2CF3] (BAC = bis(diisopropyl)aminocyclopropenylidene) is reported. This novel complex provides a versatile catalytic platform for selective aerobic oxidation of benzylic alcohols to aldehyde or ketone products in high yields. Ease of experimental execution coupled with the use of abundant atmospheric molecular oxygen as an oxidant and low catalyst loading are inherit strengths of these oxidations.
- Mir, Roya,Rowshanpour, Rozhin,Dempsey, Katie,Pilkington, Melanie,Dudding, Travis
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p. 5726 - 5731
(2019/05/10)
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- METHOD OF SELECTIVELY OXIDIZING LIGNIN
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A method of selectively reacting lignin or a lignin-derived reactant to yield an aromatic product. The method includes the step of reacting lignin or a lignin-derived reactant with a molybdenum-containing catalyst, in a solvent, and optionally in the presence of an oxidant, for a time and a temperature wherein at least a portion of the lignin or lignin-derived reactant is selectively converted into an aromatic product, preferably coniferaldehyde and/or sinapaldehyde.
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Paragraph 0022
(2019/06/20)
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- Efficient acceptorless photo-dehydrogenation of alcohols and: N -heterocycles with binuclear platinum(ii) diphosphite complexes
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Although photoredox catalysis employing Ru(ii) and Ir(iii) complexes as photocatalysts has emerged as a versatile tool for oxidative C-H functionalization under mild conditions, the need for additional reagents acting as electron donor/scavenger for completing the catalytic cycle undermines the practicability of this approach. Herein we demonstrate that photo-induced oxidative C-H functionalization can be catalysed with high product yields under oxygen-free and acceptorless conditions via inner-sphere atom abstraction by binuclear platinum(ii) diphosphite complexes. Both alcohols (51 examples), particularly the aliphatic ones, and saturated N-heterocycles (24 examples) can be efficiently dehydrogenated under light irradiation at room temperature. Regeneration of the photocatalyst by means of reductive elimination of dihydrogen from the in situ formed platinum(iii)-hydride species represents an alternative paradigm to the current approach in photoredox catalysis.
- Zhong, Jian-Ji,To, Wai-Pong,Liu, Yungen,Lu, Wei,Che, Chi-Ming
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p. 4883 - 4889
(2019/05/16)
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- Aerobic alcohol oxidation catalyzed by CuO-rectorite/TEMPO in water
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An environmentally benign CuO-rectorite was prepared by calcining the co-precipitation product of Cu2+ with an acid-activated rectorite at pH 6. It could be well dispersed in water and used as a co-catalyst with TEMPO to selectively aerobically oxidize alcohols to aldehydes. The conversion of most primary benzylic alcohols was very high under optimized conditions. Interestingly, the oxidation protocol also allowed highly selective transformation of benzylic alcohols containing a phenolic hydroxyl group into the corresponding aldehydes. Additionally, very little copper was leached from the catalyst during the catalytic reaction. CuO-rectorite could be reused by centrifugation and washed with acetonitrile and water. At the same time, its catalytic activity remained high.
- Liu, Wanghui,Yang, Jianhong,Cai, Jun
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p. 549 - 561
(2018/10/15)
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- An Engineered Alcohol Oxidase for the Oxidation of Primary Alcohols
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Structure-guided directed evolution of choline oxidase has been carried out by using the oxidation of hexan-1-ol to hexanal as the target reaction. A six-amino-acid variant was identified with a 20-fold increased kcat compared to that of the wild-type enzyme. This variant enabled the oxidation of 10 mm hexanol to hexanal in less than 24 h with 100 % conversion. Furthermore, this variant showed a marked increase in thermostability with a corresponding increase in Tm of 20 °C. Improved solvent tolerance was demonstrated with organic solvents including ethyl acetate, heptane and cyclohexane, thereby enabling improved conversions to the aldehyde by up to 30 % above conversion for the solvent-free system. Despite the evolution of choline oxidase towards hexan-1-ol, this new variant also showed increased specific activities (by up to 100-fold) for around 50 primary aliphatic, unsaturated, branched, cyclic, benzylic and halogenated alcohols.
- Heath, Rachel S.,Birmingham, William R.,Thompson, Matthew P.,Taglieber, Andreas,Daviet, Laurent,Turner, Nicholas J.
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p. 276 - 281
(2019/01/04)
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- Biotransformation of eugenol to vanillin by a novel strain Bacillus safensis SMS1003
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Due to the extensive applications of vanillin as flavored compound and increasing consumers concern for its natural and environment friendly mode of production, present work was focused on the selection of bacterial isolate capable of producing vanillin using eugenol biotransformation. Bacterial strain SMS1003 is evidenced as the potential strain for vanillin production and identified as Bacillus safensis (GeneBank accession no. MG561863) using biochemical tests and molecular phylogenic analysis of its 16S rDNA gene sequence. Molar yield of vanillin reached up to 10.7% (0.055 g/L) at 96 h of biotransformation using growing culture of B. safensis SMS1003 in following culture conditions: eugenol concentration 500 mg/L; temperature 37 °C; initial pH 7.0; inoculum volume 4%; volume of culture media 10%; and shaking speed 180 rpm. Vanillin was detected as the single metabolite with a molar yield of 26% (0.12 g/L) at 96 h using resting cells of B. safensis SMS1003. Product confirmation was based on spectral scan using photodiode array detector, Fourier-transform infrared spectroscopy, high-performance liquid chromatography, and mass spectroscopy.
- Singh, Archana,Mukhopadhyay, Kunal,Ghosh Sachan, Shashwati
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p. 291 - 303
(2019/01/04)
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