- Cyclic voltammetry and computational chemistry studies on the evaluation of the redox behavior of parabens and other analogues
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Parabens are antimicrobial preservatives widely used in pharmaceutical, cosmetic and food industries. The alkyl chain connected to the ester group defines some important physicochemical characteristics of these compounds, including the partition coefficient and redox properties. The voltammetric and computational analyses were carried out in order to evaluate the redox behavior of these compounds and other phenolic analogues. A strong correlation between chemical substituents inductive effects of parabens with redox potentials was observed. Using cyclic voltammetry and glassy carbon working electrode, only one irreversible anodic peak was observed around 0.8 V for methylparaben (MP), ethylparaben (EP), propylparaben (PP), butylparaben (BP), benzylparaben (BzP) and p-substituted phenolic analogues. The electrodonating inductive effect of alkyl groups was demonstrated by the anodic oxidation potential shift to lower values as the carbon number increases and, therefore the parabens (and other phenolic analogues) oxidation processes to the quinonoidic forms showed great dependence on the substituent pattern.
- Gil, Eric De S.,Andrade, Carolina H.,Barbosa, Nu?sia L.,Braga, Rodolpho,Serrano, Si?lvia H. P.
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- FONTANESIOSIDE AND 5-HYDROXYSECOLOGANOL FROM FONTANESIA PHILLYREODES
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The iridoid content of Fontanesia phillyreoides was investigated by reverse phase chromotography of the ethanolic extract of the aerial parts.Five known iridoid compounds, i.e. loganic acid, secologanoside, secologanic acide, secologanol and swertiamarin, besides verbascoside were isolated.In addition, two novel secoiridoids, named 5-hydroxysecologanol and fontanesioside, were isolated and characterized.Their structures were determined by NMR spectroscopy and by chemical evidence.
- Damtoft, Soeren,Franzyk, Henrik,Jensen, Soeren Rosendal
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- Improved performance of titanate nanostructures for manganese adsorption and posterior pollutants photocatalytic degradation
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In this work, the synthesis of novel manganese-modified titanate nanowires, with enhanced photocatalytic activity for pollutants degradation, is described. Distinct modified titanate nanowires samples were produced by manganese doping (Mn-TNT) and by Mn ion-exchange (TNW/Mn). The characterization of the samples was performed by XRD, DRS, TEM, PL and XPS. The structural characterisation indicates that Mn can be incorporated in the crystalline structure in two distinct positions: replacing some Ti4+ in the TiO6 octahedra and/or replacing Na+ in the interlayers. For the TNW/Mn sample, the Mn was found only in the interlayers. However, for Mn-TNW the metal was present in both possible positions. The produced materials demonstrate to be photo-active in a wider range of radiation then pristine TNW, even starting to absorb in the visible range. The PL and XPS results indicate a decrease on the photogenerated charge carriers recombination for the metal-containing samples. The photocatalytic performance of the modified samples was tested for the hydroxyl radical production. Both Mn modified samples (Mn-TNW and TNW/Mn) demonstrated to be catalytic for this reaction. The photocatalytic degradation of the preservative methyl-paraben, considered an emergent pollutant was also studied. For this process, the results indicate that the mechanism of degradation is dependent on the photocatalyst surface ionic character. The best photocatalytic performance was achieved by the doped Mn-TNW sample, with 62% of removal of a 10 ppm methyl-paraben aqueous solution (0.13 g catalyst/L solution), after 90 min of irradiation.
- Sousa, Sara C.A.,Cardoso,Monteiro
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- Amethystin, the coloring principle of Stentor amethystinus
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Among the ciliates, Stentor amethystinus stands out for its conspicuous red-violet color compared to its blue- and red-colored relatives Stentor coeruleus and Blepharisma japonicum. Rich blooms in German lakes allowed us to collect sufficient organisms to isolate the pigments and elucidate the structure of the main component amethystin (4) by spectroscopic methods as a carboxy derivative of blepharismin. Depending on conditions, the carboxy group appears as an orthoester or as a mixture of the orthoester and small amounts of a hydroxylactone. Derivatives of both isomeric forms were obtained by acetylation and methylation supporting the proposed structures. On reaction of amethystin with base in the presence of oxygen, oxyamethystin and, under vigorous conditions, p-hydroxybenzoic acid were formed. In addition to 4, two homologues, an isomer of amethystin, and stentorin F (1b) were identified in the primary extract. Further, a biosynthetic scheme is proposed linking stentorin, blepharismin, and amethystin type compounds to the hypothetical protostentorin as a common intermediate.
- H?fle, Gerhard,Reinecke, Silke,Laude, Uwe,Spitzner, Dietrich
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- A HYDROXYBUTENOLIDE FROM SPHAGNUM SPECIES
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One of the main products formed by peroxidative degredation of sphagnum acid in vitro is identified as (-)2,5-dihydro-5-hydroxy-4--furan-2-one, abbreviated as hydroxybutenolide.It seems to be the first report of the isolation of this compound.Peroxidase isozymes isolated from Sphagnum magellanicum have specific preferences in degrading sphagnum acid.Hydroxybutenolide is a naturally occurring component in Sphagnum spp.Occurrin g mainly bound to the cell wall.In contrast to sphagnum acid, hydroxybutenolide is not excreted into the surrounding medium by living Sphagnum plantlets. Key Word Index- Sphagnum magellanicum; Sphagnaceae; bryophyta; sphagnum acid; Degradation; peroxidase; isoenzymes; hydroxybutenoide; cell wall.
- Wilschke, Juergen,Sprengel, Birgit,Wolff, Christian,Rudolph, Hansjoerg
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- The catalytic mechanism of the hotdog-fold enzyme superfamily 4-hydroxybenzoyl-coa thioesterase from arthrobacter sp. Strain SU
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The hotdog-fold enzyme 4-hydroxybenzoyl-coenzyme A (4-HB-CoA) thioesterase from Arthrobacter sp. strain AU catalyzes the hydrolysis of 4-HB-CoA to form 4-hydroxybenzoate (4-HB) and coenzyme A (CoA) in the final step of the 4-chlorobenzoate dehalogenation pathway. Guided by the published X-ray structures of the liganded enzyme (Thoden, J. B., Zhuang, Z., Dunaway-Mariano, D., and Holden H. M. (2003) J.Biol. Chem. 278, 43709-43716), a series of site-directed mutants were prepared for testing the roles of active site residues in substrate binding and catalysis. The mutant thioesterases were subjected to X-ray structure determination to confirm retention of the native fold, and in some cases, to reveal changes in the active site configuration. In parallel, the wild-type and mutant thioesterases were subjected to transient and steady-state kinetic analysis, and to 18O-solvent labeling experiments. Evidence is provided that suggests that Glu73 functions in nucleophilic catalysis, that Gly65 and Gln58 contribute to transition-state stabilization via hydrogen bond formation with the thioester moiety and that Thr77 orients the water nucleophile for attack at the 4-hydroxybenzoyl carbon of the enzyme-anhydride intermediate. The replacement of Glu73 with Asp was shown to switch the function of the carboxylate residue from nucleophilic catalysis to base catalysis and thus, the reaction from a two-step process involving a covalent enzyme intermediate to a single-step hydrolysis reaction. The E73D/T77A double mutant regained most of the catalytic efficiency lost in the E73D single mutant. The results from 31P NMR experiments indicate that the substrate nucleotide unit is bound to the enzyme surface. Kinetic analysis of site-directed mutants was carried out to determine the contributions made by Arg102, Arg150, Ser120, and Thr121 in binding the nucleotide unit. Lastly, we show by kinetic and X-ray analyses of Asp31, His64, and Glu78 site-directed mutants that these three active site residues are important for productive binding of the substrate 4-hydroxybenzoyl ring.
- Song, Feng,Zhuang, Zhihao,Latham, John,Dunaway-Mariano, Debra,Thoden, James B.,Holden, Hazel M.,Trujillo, Michael
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- Controlling structure and porosity in catalytic nanoparticle superlattices with DNA
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Herein, we describe a strategy for converting catalytically inactive, highly crystalline nanoparticle superlattices embedded in silica into catalytically active, porous structures through superlattice assembly and calcination. First, a body-centered cubic (bcc) superlattice is synthesized through the assembly of two sets of 5 nm gold nanoparticles chemically modified with DNA bearing complementary sticky end sequences. These superlattices are embedded in silica and calcined at 350 °C to provide access to the catalytic nanoparticle surface sites. The calcined superlattice maintains its bcc ordering and has a surface area of 210 m2/g. The loading of catalytically active nanoparticles within the superlattice was determined by inductively coupled plasma mass spectrometry, which revealed that the calcined superlattice contained approximately 10% Au by weight. We subsequently investigate the ability of supported Au nanoparticle superlattices to catalyze alcohol oxidation. In addition to demonstrating that calcined superlattices are effective catalysts for alcohol oxidation, electron microscopy reveals preservation of the crystalline structure of the bcc superlattice following calcination and catalysis. Unlike many bulk nanoparticle catalysts, which are difficult to characterize and susceptible to aggregation, nanoparticle superlattices synthesized using DNA interactions offer an attractive bottom-up route to structurally defined heterogeneous catalysts, where one has the potential to independently control nanoparticle size, nanoparticle compositions, and interparticle spacings.
- Auyeung, Evelyn,Morris, William,Mondloch, Joseph E.,Hupp, Joseph T.,Farha, Omar K.,Mirkin, Chad A.
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- Transesterification reactions of parabens (alkyl 4-hydroxybenzoates) with polyols in aqueous solution
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Accelerated stability tests of aqueous solutions containing parabens and polyols were performed using concentrations similar to pharmaceutical and cosmetic formulations. Reaction products were detected in these solutions by HPLC and identified by chromatographic and spectroscopic means. Using xylitol and methylparaben as model reactants, three unknown peaks having the relation 1:2:4 were obtained together with the hydrolysis product 4-hydroxybenzoic acid. Diode array detection gave identical UV spectra for each peak with a maximum at 255 nm. The structures of the isomeric 1-, 2-, and 3-xylityl 4- hydroxy-benzoic acid esters were proved by means of LC-MS, GC-MS, and NMR and correlated to the peaks in the HPLC chromatograms. The rate of the transesterification was shown to be highest in strongly alkaline medium (ph 10-11), whereas equilibration of the reaction was optimally balanced at pH 8- 9. An increase of polyol concentration enhanced the formation of the esters. The reactivity of different substituted parabens was higher in the case of parabens with a short alkyl ester function. Similar reaction profiles were observed with C3-C6 polyols, but no transesterification took place when aldoses were used.
- Hensel,Leisenheimer,Muller,Busker,Wolf-Heuss,Engel
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- Efficient catalytic oxidation of alcohol to carbonyl compounds over CoFe hydrotalcites
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A series of CO32--CoxFe-LDHs (x = 2, 3, 4 and 5) compounds with different Co/Fe ratios have been prepared, characterized and introduced into the selective oxidation of alcohols by tert-butylhydroperoxide. The characterization including XRD, SEM, FTIR, TG/DTG, DR UV-vis, N2 adsorption and XPS showed that the hydrotalcite structure was well formed with different Co/Fe ratios, and the ratio has significant influence on the materials' morphologies, physical properties and the composition of Co2+/Co3+/Fe3+. The effects of varied reaction conditions on the catalytic oxidation have been investigated, and the results indicate that the co-existence of Co2+ and Co3+ is beneficial to the catalytic activity. Comparison experiments showed that substitution of Al with Fe could markedly increase the surface area of the material, and a synergistic effect might exist between Co and Fe in the CoFe hydrotalcites for the alcohol oxidation. In addition, the catalyst also exhibited excellent stability and catalytic performance in the oxidation of varied alcohols.
- Zhou,Pan,Wu,Qian,He,Chen
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- Evidence from Activation Volumes for an Eliminative Mechanism in the Hydrolysis of 2,4-Dinitrophenyl 4-Hydroxybenzoate
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A positive volume of activation is found for the hydrolysis of 2,4-dinitrophenyl 4-hydroxybenzoate, differentiating its mechanism from the BAc2 route used by other esters, all of which have been negative values.
- Isaacs, Neil S.,Najem, Tariq
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- Tailoring an alien ferredoxin to support native-like P450 monooxygenase activity
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A ferredoxin associated with biological Fe-S cluster assembly has been remodelled to transfer electrons to a P450 enzyme and support substrate oxidation at 80% of the physiological ferredoxin activity, opening up the possibility of tailoring ferredoxins to reconstitute the activity of P450 enzymes for which the electron transfer partner proteins are not known.
- Bell, Stephen G.,McMillan, James H. C.,Yorke, Jake A.,Kavanagh, Emma,Johnson, Eachan O. D.,Wong, Luet-Lok
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- Inactivation of bacillus subtilis spores using various combinations of ultraviolet treatment with addition of hydrogen peroxide
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This study aims at comparing the inactivation of Bacillus subtilis spores by various combinations of UV treatment and hydrogen peroxide (H 2O2) addition. The combinations included sequential (UV-H2O2, H2O2-UV) and simultaneous (UV/H2O2) processes. Results showed that B. subtilis spores achieved a certain inactivation effect through UV treatment. However, hardly any inactivation effect by H2O2 alone was observed. H2O2 had a significant synergetic effect when combined with UV treatment, while high irradiance and H2O2 concentration both favored the reaction. When treated with 0.60 mm H 2O2 and 113.0 μW/cm2 UV irradiance for 6 min, the simultaneous UV/H2O2 treatment showed significantly improved disinfection effect (4.13 log) compared to that of UV-H2O2 (3.03 log) and H2O2-UV (2.88 log). The relationship between the inactivation effect and the exposure time followed a typical pseudo-first-order kinetics model. The pseudo-first-order rate constants were 0.478, 0.447 and 0.634 min-1, for the UV-H 2O2, H2O2-UV and UV/H 2O2 processes, respectively, further confirming the optimal disinfection effect of the UV/H2O2 process. The disinfection could be ascribed to the OH radicals, as verified by the level of para-chlorobenzoic acid (pCBA). The facility used in the experiments was a collimated beam apparatus containing a low-pressure mercury lamp. Petri dishes (90 mm diameter) with 40 mL samples were exposed to the UV in the collimated beam apparatus and stirred gently by a magnetic stirring apparatus. The inactivation of Bacillus subtilis spores of various combinations of UV treatment and H2O2 addition were compared, including sequential (UV-H2O2, H2O2-UV) and simultaneous (UV/H2O2) processes.
- Zhang, Yongji,Zhang, Yiqing,Zhou, Lingling,Tan, Chaoqun
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- Interaction of Methylparaben Preservative with Selected Sugars and Sugar Alcohols
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The interaction of methylparaben preservative with selected sugars (glucose, fructose, sucrose, lactose, maltose, cellobiose) and sugar alcohols (lactitol, maltitol) were demonstrated in this study. It was observed that the formation of transesterification reaction products between methylparaben and the selected sugars occurred only under mild reaction conditions (e.g., pH 7.4 at 50 deg C ), which were confirmed by HPLC-UV studies and mass spectrometry. On the other hand, under alkaline conditions and high temperature, degradation of the sugars predominated. Because sugars could easily undergo many possible degradation reactions and isomerization including on-column anomerization, the chromatograms of the reaction products were more complicated than those obtained from sugar alcohols. Sucrose, a nonreducing sugar, was much more stable than other selected sugars. The chromatogram of the transesterification reaction products of methylparaben with sucrose clearly showed eight peaks, which were likely to correspond to the same number of hydroxyl groups of sucrose. To compare the rate of the transesterification reaction of methylparaben with sucrose to that with sorbitol, kinetic studies were carried out. Similar rate constants were observed: 5.4 x 10-7 L mol-1 s-1 and 4.9 x 10-7 L mol-1 s-1 for sucrose and sorbitol, respectively.
- Ma, Minhui,Lee, Tony,Kwong, Elizabeth
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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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p. 838 - 847
(2021/02/09)
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- Biocatalytic Cross-Coupling of Aryl Halides with a Genetically Engineered Photosensitizer Artificial Dehalogenase
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Devising artificial photoenzymes for abiological bond-forming reactions is of high synthetic value but also a tremendous challenge. Disclosed herein is the first photobiocatalytic cross-coupling of aryl halides enabled by a designer artificial dehalogenase, which features a genetically encoded benzophenone chromophore and site-specifically modified synthetic NiII(bpy) cofactor with tunable proximity to streamline the dual catalysis. Transient absorption studies suggest the likelihood of energy transfer activation in the elementary organometallic event. This design strategy is viable to significantly expand the catalytic repertoire of artificial photoenzymes for useful organic transformations.
- Fu, Yu,Huang, Jian,Wu, Yuzhou,Liu, Xiaohong,Zhong, Fangrui,Wang, Jiangyun
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supporting information
p. 617 - 622
(2021/02/03)
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- An Anionic, Chelating C(sp3)/NHC ligand from the Combination of an N-heterobicyclic Carbene and Barbituric Heterocycle
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The coordination chemistry of the anionic NHC1-based on an imidazo[1,5-a]pyridin-3-ylidene (IPy) platform substituted at the C5 position by an anionic barbituric heterocycle was studied with d6(Ru(II), Mn(I)) and d8(Pd(II), Rh(I), Ir(I), Au(III)) transition-metal centers. While the anionic barbituric heterocycle is planar in the zwitterionic NHC precursor 1·H, NMR spectroscopic analyses supplemented by X-ray diffraction studies evidenced the chelating behavior of ligand 1-through the carbenic and the malonic carbon atoms in all of the complexes, resulting from a deformation of the lateral barbituric heterocycle. The complexes were obtained by reaction of the free carbene with the appropriate metal precursor, except for the Au(III) complex 10, which was obtained by oxidation of the antecedent gold(I) complex [AuCl(1)]?with PhICl2as an external oxidant. During the course of the process, the kinetic gold(I) intermediate 9 resulting from the oxidation of the malonic carbon of the barbituric moiety was isolated upon crystallization from the reaction mixture. The νCOstretching frequencies recorded for complex [Rh(1)(CO)2] (5) demonstrated the strong donating character of the malonate-C(sp3)/NHC ligand 1-. The ruthenium complex [Ru(1)Cl(p-cymene)] (11) was implemented as a precatalyst in the dehydrogenative synthesis of carboxylic acid derivatives from primary alcohols and exhibited high activities at low catalyst loadings (25-250 ppm) and a large tolerance toward functional groups.
- Benaissa, Idir,Gajda, Katarzyna,Vendier, Laure,Lugan, No?l,Kajetanowicz, Anna,Grela, Karol,Michelet, Véronique,César, Vincent,Bastin, Stéphanie
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p. 3223 - 3234
(2021/09/30)
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- Isotruxene-based porous polymers as efficient and recyclable photocatalysts for visible-light induced metal-free oxidative organic transformations
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Two new isotruxene-based porous polymers were prepared and demonstrated to be highly efficient, metal-free heterogeneous photocatalysts for oxidative transformations using air as the mild oxidant under visible-light irradiation. Both catalysts show excellent recyclability. In addition, the reactions can be performed in water, further indicating the greenness of this method. This journal is
- Zhang, Haowen,Zhang, Xiao,Zheng, Ying,Zhou, Cen
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supporting information
p. 8878 - 8885
(2021/11/27)
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- MOF-Zn-NHC as an efficient N-heterocyclic carbene catalyst for aerobic oxidation of aldehydes to their corresponding carboxylic acids: Via a cooperative geminal anomeric based oxidation
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As an efficient heterogenous N-heterocyclic carbene (NHC) catalyst, MOF-Zn-NHC was used in the aerobic oxidation of aryl aldehydes to their corresponding carbocyclic acids via an anomeric based oxidation. Features such as mild reaction conditions and no need for a co-catalyst or oxidative reagent can be considered as the major advantages of the presented method in this study. This journal is
- Babaee, Saeed,Zarei, Mahmoud,Zolfigol, Mohammad Ali
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p. 36230 - 36236
(2021/12/02)
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- Cleavage of Carboxylic Esters by Aluminum and Iodine
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A one-pot procedure for deprotecting carboxylic esters under nonhydrolytic conditions is described. Typical alkyl carboxylates are readily deblocked to the carboxylic acids by the action of aluminum powder and iodine in anhydrous acetonitrile. Cleavage of lactones affords the corresponding ω-iodoalkylcarboxylic acids. Aryl acetylates undergo deacetylation with the participation of the neighboring group. This method enables the selective cleavage of alkyl carboxylic esters in the presence of aryl esters.
- Sang, Dayong,Yue, Huaxin,Fu, Yang,Tian, Juan
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p. 4254 - 4261
(2021/03/09)
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- Reaction of Diisobutylaluminum Borohydride, a Binary Hydride, with Selected Organic Compounds Containing Representative Functional Groups
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The binary hydride, diisobutylaluminum borohydride [(iBu)2AlBH4], synthesized from diisobutylaluminum hydride (DIBAL) and borane dimethyl sulfide (BMS) has shown great potential in reducing a variety of organic functional groups. This unique binary hydride, (iBu)2AlBH4, is readily synthesized, versatile, and simple to use. Aldehydes, ketones, esters, and epoxides are reduced very fast to the corresponding alcohols in essentially quantitative yields. This binary hydride can reduce tertiary amides rapidly to the corresponding amines at 25 °C in an efficient manner. Furthermore, nitriles are converted into the corresponding amines in essentially quantitative yields. These reactions occur under ambient conditions and are completed in an hour or less. The reduction products are isolated through a simple acid-base extraction and without the use of column chromatography. Further investigation showed that (iBu)2AlBH4 has the potential to be a selective hydride donor as shown through a series of competitive reactions. Similarities and differences between (iBu)2AlBH4, DIBAL, and BMS are discussed.
- Amberchan, Gabriella,Snelling, Rachel A.,Moya, Enrique,Landi, Madison,Lutz, Kyle,Gatihi, Roxanne,Singaram, Bakthan
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supporting information
p. 6207 - 6227
(2021/05/06)
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- A copper nitride catalyst for the efficient hydroxylation of aryl halides under ligand-free conditions
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Copper nitride (Cu3N) was used as a heterogeneous catalyst for the hydroxylation of aryl halides under ligand-free conditions. The cubic Cu3N nanoparticles showed high catalytic activity, comparable to those of conventional Cu catalysts with nitrogen ligands, demonstrating that the nitrogen atoms in Cu3N act as functional ligands that promote hydroxylation.
- Mitsudome, Takato,Mizugaki, Tomoo,Xu, Hang,Yamaguchi, Sho
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supporting information
p. 6593 - 6597
(2021/08/10)
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- Electrochemical-induced hydroxylation of aryl halides in the presence of Et3N in water
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A thorough study of mild and environmentally friendly electrochemical-induced hydroxylation of aryl halides without a catalyst is presented. The best protocol consists of hydroxylation of different aryl iodides and aryl bromides by water solution in the presence of Et3N under air, affording the target phenols in good isolated yields. Moreover, aryl chlorides were successfully employed as substrates. This methodology also provides a direct pathway for the formation of deoxyphomalone, which displayed a significant anti-proliferation effect.
- Ke, Fang,Lin, Chen,Lin, Mei,Long, Hua,Wu, Mei,Yang, Li,Zhuang, Qinglong
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supporting information
p. 6417 - 6421
(2021/08/03)
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- Photocatalytic synthesis of phenols mediated by visible light using KI as catalyst
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A transition-metal-free hydroxylation of iodoarenes to afford substituted phenols is described. The reaction is promoted by KI under white LED light irradiation and uses atmospheric oxygen as oxidant. By the use of triethylamine as base and solvent, the corresponding phenols are obtained in moderate to good yields. Mechanistic studies suggest that KI and catalysis synergistically promote the cleavage of C-I bond to form free aryl radicals.
- Huiqin, Wei,Wu, Mei
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supporting information
(2021/11/30)
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- A Dual-Function Highly Crystalline Covalent Organic Framework for HCl Sensing and Visible-Light Heterogeneous Photocatalysis
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Covalent organic frameworks (COFs) offer great potential for various advanced applications such as photocatalysis, sensing, and so on because of their fully conjugated, porous, and chemically stable unique structural architecture. In this work, we have designed and developed a truxene-based ultrastable COF (Tx-COF-2) by Schiff-base condensation between 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 5,5,10,10,15,15-hexamethyl-10,15-dihydro-5H-diindeno(1,2-a:1′,2′-c)fluorene-2,7,12-tricarbaldehyde (Tx-CHO) for the first time. The resulting COF possesses excellent crystallinity, permanent porosity, and high Brunauer-Emmett-Teller (BET) surface areas (up to 1137 m2 g-1). The COF was found to be a heterogeneous, recyclable photocatalyst for efficient conversion of arylboronic acids to phenols under visible-light irradiation, an environmentally friendly alternative approach to conventional metal-based photocatalysis. Besides, Tx-COF-2 provides an immediate naked-eye color change (1 s) and fluorescence "turn-on"phenomena upon exposure to HCl. The response is highly sensitive, with an ultralow detection limit of up to 4.5 nmol L-1.
- Addicoat, Matthew A.,Nailwal, Yogendra,Pal, Santanu Kumar,Wonanke, A. D. Dinga
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p. 6595 - 6604
(2021/07/20)
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- Coordination Polymers as a Functional Material for the Selective Molecular Recognition of Nitroaromatics and ipso-Hydroxylation of Arylboronic Acids
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We report the synthesis and structural characterization of two coordination polymers (CPs), namely; [{Zn(L)(DMF)4} ? 2BF4]α (1) and [{Cd(L)2(Cl)2} ? 2H2O]α (2) (where L=N2,N6-di(pyridin-4-yl)naphthalene-2,6-dicarboxamide). Crystal packing of 1 reveals the existence of channels running along the b- and c-axis filled by the ligated DMF and lattice anions, respectively. Whereas, crystal packing of 2 reveals that the metallacycles of each 1D chain are intercalating into the groove of adjacent metallacycles resulting in the stacking of 1D loop-chains to form a sheet-like architecture. In addition, both 1 and 2 were exploited as multifunctional materials for the detection of nitroaromatic compounds (NACs) as well as a catalyst in the ipso-hydroxylation of aryl/heteroarylboronic acids. Remarkably, 1 and 2 showed high fluorescence stability in an aqueous medium and displayed a maximum 88% and 97% quenching efficiency for 4-NPH, respectively among all the investigated NACs. The mechanistic investigation of NACs recognition suggested that the fluorescence quenching occurred via electron as well as energy transfer process. Furthermore, the ipso-hydroxylation of aryl/heteroarylboronic acids in presence of 1 and 2 gave up to 99% desired product yield within 15 min in our established protocol. In both cases, 1 and 2 are recyclable upto five cycles without any significant loss in their efficiency.
- Bhasin, K. K.,Husain, Ahmad,Kumar, Girijesh,Rani, Pooja
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- Highly efficient heterogeneous V2O5@TiO2 catalyzed the rapid transformation of boronic acids to phenols
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A V2O5@TiO2 catalyzed green and efficient protocol for the hydroxylation of boronic acid into phenol has been developed utilizing environmentally benign oxidant hydrogen peroxide. A wide range of electron-donating and the electron-withdrawing group-containing (hetero)aryl boronic acids were transformed into their corresponding phenol. The methodology was also applied successfully to transform various natural and bioactive molecules like tocopherol, amino acids, cinchonidine, vasicinone, menthol, and pharmaceuticals such as ciprofloxacin, ibuprofen, and paracetamol. The other feature of the methodology includes gram-scale synthetic applicability, recyclability, and short reaction time.
- Upadhyay, Rahul,Singh, Deepak,Maurya, Sushil K.
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supporting information
p. 3925 - 3931
(2021/08/24)
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- Transforming a Fluorochrome to an Efficient Photocatalyst for Oxidative Hydroxylation: A Supramolecular Dimerization Strategy Based on Host-Enhanced Charge Transfer
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The development of non-covalent synthetic strategy to fabricate efficient photocatalysts is of great importance in theranostic and organic materials. Herein, a fluorochrome N,N′-dimethyl 2,5-bis(4-pyridinium)thiazolo[5,4-d]thiazolediiodide (MPT) was transformed into an efficient photocatalyst through supramolecular dimerization in the cavity of cucurbit[8]uril (CB[8]). The host-enhanced charge transfer interaction within the supramolecular dimer 2MPT-CB[8] dramatically promoted intersystem crossing to produce triplet. In addition, the staggered conformation of 2MPT-CB[8] facilitated the energy transfer and electron transfer of the triplet. As a result, 2MPT-CB[8] could serve as a high-efficiency photocatalyst for the oxidative hydroxylation of arylboronic acids. This supramolecular dimerization strategy enriches the supramolecular engineering of functional π-systems. It is anticipated that this strategy can be extended to fabricate various π-systems with tailor-made functions.
- Tang, Bohan,Xu, Weiquan,Xu, Jiang-Fei,Zhang, Xi
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supporting information
p. 9384 - 9388
(2021/03/22)
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- β-Diketone boron difluoride dye-functionalized conjugated microporous polymers for efficient aerobic oxidative photocatalysis
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Incorporation of organic chromophores into conjugated micro/mesoporous polymers (CMPs) provides a promising avenue for developing recyclable heterogeneous photocatalysts by overcoming tedious separation and low reusability of homogeneous organic dye-based photocatalysts. However, the design principle and the underlying structure-property relationship for fabricating and selecting various organic dye-embedded CMPs for efficient photocatalysis have not been well-constructed so far. In this study, we described the rational fabrication of two new CMPsviathe one-step Sonogashira coupling using β-diketone boron difluoride dye as the key linker and commonly used building blocks (triphenylamine/triphenylbenzene) as the cores. The resulting boron-dye containing CMPs were efficiently employed as the metal-free photocatalysts in two typical aerobic oxidative organic transformations including coupling of benzylamine and oxidation of aryl boronic acids to corresponding aryl phenols, which have never been explored with other boron-dye-embedded CMPs. They exhibited superior photocatalytic performance compared to their boron-free counterparts due to their wide visible-light absorption, narrow optical bandgaps, and extended π-conjugation due to boron-complexation. The present study establishes β-diketone boron difluoride dyes as efficient building blocks for fabricating new CMP-based photocatalysts.
- Dong, Kaixun,Gong, Weitao,Hassan, Mehdi,Liu, Lu,Ning, Guiling
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p. 3905 - 3913
(2021/06/18)
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- Aqueous selective photocatalytic oxidation of salicyl alcohol by TiO2 catalysts: Influence of some physico-chemical features
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Partial photocatalytic oxidation of salicyl alcohol (2-hydroxybenzyl alcohol) to salicylaldehyde in water was investigated under environmental friendly conditions in the presence of home-prepared and commercial TiO2 (Merck and Aeroxide P25) samples under UVA irradiation. The photocatalysts were characterized by using BET, XRD, SEM and/or TEM techniques. The effects of crystallinity degree, pH (3–11) and presence of a hole trap (ethanol) on the photocatalytic activity and product selectivity were investigated. 4-Hydroxybenzyl alcohol was also used to study the influence of the position of the substituent group in the aromatic ring. High alcohols conversion and product selectivity values were obtained at pH = 11 by using well crystallized TiO2 samples. The conversion values significantly decreased by increasing the hole trap concentration, whereas the selectivity values increased slightly. The selectivity towards the corresponding aldehyde after 30% of alcohol conversion was significantly higher for 4-HBA (48%) than for 2-HBA (32%), due to the role of the para position of the substituent group. In order to clarify the different selectivity of the products, various experiments have been also performed starting from the products; these results indicate that the selectivity is also strongly dependent on the stability of the formed products under the experimental conditions used. By concluding, this article reports that the conversion and selectivity values for the studied reaction depend both on the TiO2 type and on the substrate.
- Yurdakal, Sedat,Bellardita, Marianna,Pibiri, Ivana,Palmisano, Leonardo,Loddo, Vittorio
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- Hydrolysis of amides to carboxylic acids catalyzed by Nb2O5
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Hydrolysis of amides to carboxylic acids is an industrially important reaction but is challenging due to the difficulty of cleaving the resonance stabilized amidic C-N bond. Twenty-three heterogeneous and homogenous catalysts were examined in the hydrolysis of acetamide. Results showed that Nb2O5was the most effective heterogeneous catalyst with the greatest yield of acetic acid. A series of Nb2O5catalysts calcined at various temperatures were characterized and tested in the hydrolysis of acetamide to determine the effects of crystal phase and surface properties of Nb2O5on catalytic performance. The high catalytic performance observed was attributed mainly to the facile activation of the carbonyl bond by Lewis acid sites that function even in the presence of basic inhibitors (NH3and H2O). The catalytic studies showed the synthetic advantages of the present method, such as simple operation, catalyst recyclability, additive free, solvent free, and wide substrate scope (>40 examples; up to 95% isolated yield).
- Siddiki,Rashed, Md. Nurnobi,Touchy, Abeda Sultana,Jamil, Md. A. R.,Jing, Yuan,Toyao, Takashi,Maeno, Zen,Shimizu, Ken-Ichi
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p. 1949 - 1960
(2021/03/26)
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- Efficiency of lithium cations in hydrolysis reactions of esters in aqueous tetrahydrofuran
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Lithium cations were observed to accelerate the hydrolysis of esters with hydroxides (KOH, NaOH, LiOH) in a water/tetrahydrofuran (THF) two-phase system. Yields in the hydrolysis of substituted benzoates and aliphatic esters using the various hydroxides were compared, and the effects of the addition of lithium salt were examined. Moreover, it was presumed that a certain amount of LiOH was dissolved in THF by the coordination of THF with lithium cation and hydrolyzed esters even in the THF layer, as in the reaction by a phase-transfer catalyst.
- Hayashi, Kazuhiko,Ichimaru, Yoshimi,Sugiura, Kirara,Maeda, Azusa,Harada, Yumi,Kojima, Yuki,Nakayama, Kanae,Imai, Masanori
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p. 581 - 594
(2021/06/06)
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- Identification of a bacteria-produced benzisoxazole with antibiotic activity against multi-drug resistant Acinetobacter baumannii
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The emergence of multi-drug resistant pathogenic bacteria represents a serious and growing threat to national healthcare systems. Most pressing is an immediate need for the development of novel antibacterial agents to treat Gram-negative multi-drug resistant infections, including the opportunistic, hospital-derived pathogen, Acinetobacter baumannii. Herein we report a naturally occurring 1,2-benzisoxazole with minimum inhibitory concentrations as low as 6.25 μg ml?1 against clinical strains of multi-drug resistant A. baumannii and investigate its possible mechanisms of action. This molecule represents a new chemotype for antibacterial agents against A. baumannii and is easily accessed in two steps via de novo synthesis. In vitro testing of structural analogs suggest that the natural compound may already be optimized for activity against this pathogen. Our results demonstrate that supplementation of 4-hydroxybenzoate in minimal media was able to reverse 1,2-benzisoxazole’s antibacterial effects in A. baumannii. A search of metabolic pathways involving 4-hydroxybenzoate coupled with molecular modeling studies implicates two enzymes, chorismate pyruvate-lyase and 4-hydroxybenzoate octaprenyltransferase, as promising leads for the target of 3,6-dihydroxy-1,2-benzisoxazole.
- Deering, Robert W.,Whalen, Kristen E.,Alvarez, Ivan,Daffinee, Kathryn,Beganovic, Maya,LaPlante, Kerry L.,Kishore, Shreya,Zhao, Sijing,Cezairliyan, Brent,Yu, Shen,Rosario, Margaret,Mincer, Tracy J.,Rowley, David C.
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p. 370 - 380
(2021/02/22)
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- Electrochemical oxidation of diclofenac on CNT and M/CNT modified electrodes
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The electrochemical oxidation of diclofenac (DCF), a non-steroidal anti-inflammatory drug considered as an emerging pollutant (frequently detected in wastewater), was investigated on CNT, Pt/CNT and Ru/CNT modified electrodes based on Carbon Toray in aqueous media. The electroreactivity of DCF on these modified electrodes was studied using cyclic voltammetry and the kinetic parameters were calculated from the scan rate study. Cyclic voltammograms show several oxidation processes, which confirm the interaction between DCF and the catalyst surface necessary for direct oxidation processes. Constant potential electrolysis of DCF was carried out on carbon nanotubes (CNT) and metal supported CNT (M/CNT) modified electrodes, in 0.1 M NaOH and 0.1 M Na2CO3/NaHCO3buffer media. The highest DCF conversion (88% after 8 h of electrolysis) was found in carbonate buffer medium, for Ru/CNT, while the best carbon mineralization efficiency (corresponding to 48% of the oxidized DCF) was obtained on Pt/CNT modified electrode in 0.1 M NaOH medium. The products of the electrolyses were identified and quantified by HPLC-MS, GC-MS, HPLC-UV-RID and IC. The results show the presence of some low molecular weight carboxylic acids, confirming the cleavage of the aromatic rings during the oxidation process.
- Ferreira, M.,Figueiredo, J. L.,Fonseca, A. M.,Güney, S.,Ku?niarska-Biernacka, I.,Neves, I. C.,Parpot, P.,Pereira, M. F. R.,Soares, O. S. G. P.
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p. 12622 - 12633
(2021/07/25)
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- Selective hydroxylation of aryl iodides to produce phenols under mild conditions using a supported copper catalyst
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Owing to the high activity and low-cost, copper-based catalysts are promising candidates for transforming aromatic halides to yield phenols. In this work, we report the selective hydroxylation of aromatic iodides to produce phenols using an atomically dispersed copper catalyst (Cu-ZnO-ZrO2) under mild reaction conditions. The reactions were conducted without the use of additional organic ligands, and the protection of an inert atmosphere environment is not required. The catalyst can be easily prepared, scalable, and is very efficient for a wide range of substrates. The catalytic reactions can be carried out with only 1.24 mol% Cu loading, which shows great potential in mass production.
- Auni, Anika,Ding, Guodong,Hao, Leiduan,Li, Tao,Li, Xiaoyu,Xu, Haiping,Zhang, Qiang
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p. 25348 - 25353
(2021/08/03)
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- Copper (II) immobilized on magnetically separable L-arginine-β-cyclodextrin ligand system as a robust and green catalyst for direct oxidation of primary alcohols and benzyl halides to acids in neat conditions
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Copper (II) immobilized on L-arginine-β-cyclodextrin-functionalized magnetite nanoparticles (nano-Fe3O4@L-arginine-CD-Cu(II)) were successfully synthesized and fully characterized using FT-IR, XRD, SEM, EDX, ICP, TGA and VSM techniques. The catalytic activity of these magnetically retrievable nanoparticles was evaluated in the direct oxidation of primary alcohols and benzyl halides to acids in neat conditions that was observed to proceed well and products were obtained in good yields. In addition to showing good catalytic activity, the magnetic catalyst is easy to synthesize and can be recycled at least five times with little loss in activity.
- Nejad, Masoumeh Jadidi,Salamatmanesh, Arefe,Heydari, Akbar
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- Acceptorless dehydrogenative oxidation of primary alcohols to carboxylic acids and reduction of nitroarenes via hydrogen borrowing catalyzed by a novel nanomagnetic silver catalyst
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A novel silver nano magnetic catalyst was devised for dehydrogenative oxidation of aromatic and aliphatic alcohols to the corresponding acid with water as the sole oxygen source and hydrogen gas as the only by-product. The designed catalytic system advantages from easy recovery of magnetic materials i.e. magnetic decantation, being economically viable and environmentally friendly. Furthermore, the catalytic reaction is able to reduce aryl nitro compounds in the absence of any reducing agent.
- Yazdani, Elahe,Heydari, Akbar
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supporting information
(2020/08/14)
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- Method for synthesizing phenol or derivative thereof in aqueous phase by photocatalytic one-pot method
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The invention discloses a method for synthesizing phenol or a derivative thereof in an aqueous phase by a photocatalytic one-pot method. The method comprises the following steps: by taking a compoundaryl halide shown in formula (I) as a raw material and water as a solvent, adding a catalyst and an auxiliary agent, and carrying out reacting under the conditions of alkali and visible light to obtain the phenol or the derivative (II) thereof. Compared with the prior art, the method is applicable to a large number of functional groups, high in yield, few in byproducts, simple and safe to operate,low in cost and environmentally friendly, wherein R is selected from substituted or non-substituted phenyl, pyridyl, quinolyl or pyrimidinyl; X is selected from halogen; the substituted phenyl is substituted by C1-C4 alkyl, C1-C4 alkoxy, hydroxyl, halogen, cyano, aldehyde group, nitro, amino, acetyl or carboxyl; and the substituted pyridyl, quinolyl or pyrimidinyl is pyridyl, quinolyl or pyrimidinyl substituted by C1-C4 alkyl.
- -
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Paragraph 0032-0033; 0056-0057; 0085-0106
(2020/12/08)
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- Expanding the repertoire of nitrilases with broad substrate specificity and high substrate tolerance for biocatalytic applications
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Enzymatic conversion of nitriles to carboxylic acids by nitrilases has gained significance in the green synthesis of several pharmaceutical precursors and fine chemicals. Although nitrilases from several sources have been characterized, there exists a scope for identifying broad spectrum nitrilases exhibiting higher substrate tolerance and better thermostability to develop industrially relevant biocatalytic processes. Through genome mining, we have identified nine novel nitrilase sequences from bacteria and evaluated their activity on a broad spectrum of 23 industrially relevant nitrile substrates. Nitrilases from Zobellia galactanivorans, Achromobacter insolitus and Cupriavidus necator were highly active on varying classes of nitriles and applied as whole cell biocatalysts in lab scale processes. Z. galactanivorans nitrilase could convert 4-cyanopyridine to achieve yields of 1.79 M isonicotinic acid within 3 h via fed-batch substrate addition. The nitrilase from A. insolitus could hydrolyze 630 mM iminodiacetonitrile at a fast rate, effecting 86 % conversion to iminodiacetic acid within 1 h. The arylaliphatic nitrilase from C. necator catalysed enantioselective hydrolysis of 740 mM mandelonitrile to (R)-mandelic acid in 4 h. Significantly high product yields suggest that these enzymes would be promising additions to the suite of nitrilases for upscale biocatalytic application.
- Rayavarapu, Pratima,Shah, Shikha,Sunder, Avinash Vellore,Wangikar, Pramod P.
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p. 289 - 296
(2020/05/18)
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- Mechanistic study of carboxylic acid and phosphate ester cleavage by oximate metal complexes surpassing the limiting reactivity of highly basic free oximate anions
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Two tridentate and one tetradentate new ligands containing the terminal oxime group separated from secondary amino and pyridine groups as additional binding sites by two or three methylene groups have been prepared. Their acid-base properties, as well as the composition and stability of their complexes with Zn(ii) and Cd(ii) ions, were determined by potentiometric and spectrophotometric titrations. The X-ray structure of a Cd(ii) complex of a related tridentate oxime ligand previously studied in solution was determined. All oximate complexes show high reactivity in the cleavage of aryl acetates, paraoxon, parathion and 4-nitrophenyl diphenyl phosphate, with rate constants significantly surpassing the limiting rate constants observed for highly basic free oximate anions. The second-order rate constants for individual oximate complexes in solution are assigned to each ligand, metal cation and substrate. The results of the cleavage of 4-substituted phenyl acetates were analyzed in terms of Br?nsted correlations with the leaving group pKa, which demonstrated a change in the rate determining step from the nucleophilic attack to the leaving group departure upon an increase in the leaving group basicity. The zero slope of the Br?nsted correlation for the nucleophilic attack indicates transition state stabilization through electrophilic assistance by the metal ion. This interpretation is supported by metal selectivity in the relative efficiency of the cleavage of paraoxon and parathion. The existence of the alpha-effect in ester cleavage by coordinated oximates is confirmed by an analysis of the Br?nsted correlations with the nucleophile basicity for metal bound oximate and alkoxo or hydroxo nucleophiles. The very high reactivity of the oximate complexes of the new ligands is attributed to transition state stabilization and to the removal of the solvational imbalance of oximate anions that impedes the expected increase in the reactivity of highly basic free anions.
- Flores-Alamo, Marcos,Gómez-Tagle, Paola,Lugo-González, José Carlos,Yatsimirsky, Anatoly K.
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supporting information
p. 2452 - 2467
(2020/03/05)
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- Structural insights into the role of the acid-alcohol pair of residues required for dioxygen activation in cytochrome P450 enzymes
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The cytochrome P450 heme monooxygenases commonly use an acid-alcohol pair of residues, within the I-helix, to activate iron-bound dioxygen. This work aims to clarify conflicting reports on the importance of the alcohol functionality in this process. Mutants of the P450, CYP199A4 (CYP199A4D251N and CYP199A4T252A), were prepared, characterised and their crystal structures were solved. The acid residue of CYP199A4 is not part of a salt bridge network, a key feature of paradigmatic model system P450cam. Instead, there is a direct proton delivery network, via a chain of water molecules, extending to the surface. Nevertheless, CYP199A4D251N dramatically reduced the activity of the enzyme consistent with a role in proton delivery. CYP199A4T252A decreased the coupling efficiency of the enzyme with a concomitant increase in the hydrogen peroxide uncoupling pathway. However, the effect of this mutation was much less pronounced than reported with P450cam. Its crystal structures revealed fewer changes at the I-helix, compared to the P450cam system. The structural changes observed within the I-helix of P450cam during oxygen activation do not seem to be required in this P450. These differences are due to the presence of a second threonine residue at position 253, which is absent in P450cam. This threonine forms part of the hydrogen bonding network, resulting in subtle structural changes and is also present across the majority of the P450 superfamily. Overall, the results suggest that while the acid-alcohol pair is important for dioxygen activation this process and the method of proton delivery can differ across P450s. Graphic abstract[Figure not available: see fulltext.].
- Coleman, Tom,Stok, Jeanette E.,Podgorski, Matthew N.,Bruning, John B.,De Voss, James J.,Bell, Stephen G.
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p. 583 - 596
(2020/04/15)
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- Light and oxygen-enabled sodium trifluoromethanesulfinate-mediated selective oxidation of C-H bonds
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Visible light-induced organic reactions are important chemical transformations in organic chemistry, and their efficiency highly depends on suitable photocatalysts. However, the commonly used photocatalysts are precious transition-metal complexes and elaborate organic dyes, which hamper large-scale production due to high cost. Here, for the first time, we report a novel strategy: light and oxygen-enabled sodium trifluoromethanesulfinate-mediated selective oxidation of C-H bonds, allowing high-value-added aromatic ketones and carboxylic acids to be easily prepared in high-to-excellent yields using readily available alkyl arenes, methyl arenes and aldehydes as materials. The mechanistic investigations showed that the treatment of inexpensive and readily available sodium trifluoromethanesulfinate with oxygen under irradiation of light could in situ form a pentacoordinate sulfide intermediate as an efficient photosensitizer. The method represents a highly efficient, economical and environmentally friendly strategy, and the light and oxygen-enabled sodium trifluoromethanesulfinate photocatalytic system represents a breakthrough in photochemistry. This journal is
- Fu, Hua,Liu, Can,Liu, Yong,Yang, Haijun,Zhu, Xianjin
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supporting information
p. 4357 - 4363
(2020/07/14)
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- Copper and L-(?)-quebrachitol catalyzed hydroxylation and amination of aryl halides under air
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L-(?)-Quebrachitol, a natural product obtained from waste water of the rubber industry, was utilized as an efficient ligand for the copper-catalyzed hydroxylation and amination of aryl halides to selectively give phenols and aryl amines in water or 95percent ethanol. In addition, the hydroxylation of 2-chloro-4-hydroxybenzoic acid was validated on a 100-g scale under air.
- Bao, Xuefei,Chen, Guoliang,Dong, Jinhua,Du, Fangyu,Li, Hui,Liang, Xinjie,Wu, Ying,Zhang, Yongsheng
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supporting information
(2020/08/03)
-
- Vinylene-Bridged Two-Dimensional Covalent Organic Frameworks via Knoevenagel Condensation of Tricyanomesitylene
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Vinylene-bridged covalent organic frameworks (COFs) have shown great potential for advanced applications because of their high chemical stability and intriguing semiconducting properties. Exploring new functional monomers available for the reticulation of vinylene-bridged COFs and establishing effective reaction conditions are extremely desired for enlarging the realm of this kind of material. In this work, a series of vinylene-bridged two-dimensional (2D) COFs are synthesized by Knoevenagel condensation of tricyanomesitylene with ditopic or tritopic aromatic aldehydes. With use of appropriate secondary amines as catalysts, high-crystalline vinylene-bridged COFs were achieved, exhibiting long-range ordered structures, well-defined nanochannels, high surface areas (up to 1231 m2 g-1), and excellent photophysical properties. Under a low loading amount and short reaction time, they enable aerobic photocatalytic transformation of arylboronic acids to phenols with high efficiency and excellent recyclability. This work demonstrates a new functional monomer, tricyanomesitylene, feasible for the general synthesis of vinylene-bridged COFs with potential application in photocatalytic organic transformation, which instigates further research on such kind of material.
- Bi, Shuai,Thiruvengadam, Palani,Wei, Shice,Zhang, Wenbei,Zhang, Fan,Gao, Lusha,Xu, Junsong,Wu, Dongqing,Chen, Jie-Sheng,Zhang, Fan
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supporting information
p. 11893 - 11900
(2020/08/06)
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- A scalable and green one-minute synthesis of substituted phenols
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A mild, green and highly efficient protocol was developed for the synthesis of substituted phenols via ipso-hydroxylation of arylboronic acids in ethanol. The method utilizes the combination of aqueous hydrogen peroxide as the oxidant and H2O2/HBr as the reagent under unprecedentedly simple and convenient conditions. A wide range of arylboronic acids were smoothly transformed into substituted phenols in very good to excellent yields without chromatographic purification. The reaction is scalable up to at least 5 grams at room temperature with one-minute reaction time and can be combined in a one-pot sequence with bromination and Pd-catalyzed cross-coupling to generate more diverse, highly substituted phenols.
- Elumalai, Vijayaragavan,Hansen, J?rn H.
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p. 40582 - 40587
(2020/11/18)
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- Aerobic photooxidative hydroxylation of boronic acids catalyzed by anthraquinone-containing polymeric photosensitizer
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We report herein the synthesis of a polymeric photosensitizer and its application in aerobic photooxidative hydroxylation of boronic acids. The polymeric photosensitizer was synthesized by the condensation of anthraquinone-2-carbonyl chloride (AQ-2-COCl) with poly (2-hydroxyethyl methacrylate) (PHEMA). The photo-oxidative hydroxylation of boronic acids using anthraquinone-containing-poly (2-hydroxyethyl methacrylate) (AQ-PHEMA) was then explored and shown to exhibit high efficiency and broad scope. Moreover, AQ-PHEMA could be easily recovered and reused for more than 20 times without significant loss of the catalytic activity.
- Chen, Yang,Ding, Aishun,Hu, Jianhua
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p. 7927 - 7932
(2020/03/11)
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- Helical Carbenium Ion: A Versatile Organic Photoredox Catalyst for Red-Light-Mediated Reactions
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Red light has the advantages of low energy, less health risks, and high penetration depth through various media. Herein, a helical carbenium ion (N,N′-di-n-propyl-1,13-dimethoxyquinacridinium (nPr-DMQA+) tetrafluoroborate) has been used as an organic photoredox catalyst for photoreductions and photooxidations in the presence of red light (λmax = 640 nm). It has catalyzed red-light-mediated dual transition-metal/photo-redox-catalyzed C-H arylation and intermolecular atom-transfer radical addition through oxidative quenching. Moreover, its potential in photooxidation catalysis has also been demonstrated by successful applications in red-light-induced aerobic oxidative hydroxylation of arylboronic acids and benzylic C(sp3)-H oxygenation through reductive quenching. Thus, a versatile organic photoredox catalyst (helical carbenium ion) for red-light-mediated photoredox reactions has been developed.
- Mei, Liangyong,Veleta, José M.,Gianetti, Thomas L.
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supporting information
p. 12056 - 12061
(2020/08/07)
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- Iridium complex-linked porous organic polymers for recyclable, broad-scope photocatalysis of organic transformations
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Two rigid porous organic polymers (Ir-POP-1 and Ir-POP-2) were prepared from the coupling reactions of tetraphenylmethane tetraborate and two [Ir(ppy)2(dtbbpy)]+-based bitopic linkers and applied as heterogeneous visible-light photocatalysts for organic transformations. Ir-POP-2 was found to exhibit high catalytic activity for a wide range of organic reactions, which include Smiles-Truce rearrangement of alkyliodides, desulfurative conjugate addition to Michael acceptors, and aerobic oxidations of sulfides and arylboronic acids. For all the transformations, Ir-POP-2 could achieve heterogeneous photocatalytic efficiency that rivals that of the homogeneous prototype iridium complexes. This remarkably high photocatalytic performance has been attributed to the large pore size of the conjugated backbone. The new heterogeneous photocatalyst was also highly stable to achieve good recyclability for all the studied reactions and could be reused eight to nineteen times.
- Xu, Zi-Yue,Luo, Yi,Zhang, Dan-Wei,Wang, Hui,Sun, Xing-Wen,Li, Zhan-Ting
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supporting information
p. 136 - 143
(2020/01/21)
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- Hydroxylamine promoted Fe(III)/Fe(II) cycle on ilmenite surface to enhance persulfate catalytic activation and aqueous pharmaceutical ibuprofen degradation
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This study demonstrates a new system for the degradation of emerging pharmaceutical contaminants (e.g., ibuprofen) in water by coupling the naturally occurring ilmenite with hydroxylamine (HA) and persulfate (PS). Ilmenite was able to activate persulfate to generate sulfate radicals (SO4?·) and hydroxyl radicals (HO·). The radical generation was greatly improved by adding small amount of hydroxylamine into the solution, due to the efficient Fe(III)/Fe(II) cycle on the ilmenite surface promoted by HA, which was confirmed by X-ray photoelectron spectroscopy and electron paramagnetic resonance (EPR) spectroscopy analysis. SO4?· and HO· contributed comparably to ibuprofen degradation, which was verified by the radical scavenging tests. The degradation was enhanced with increasing ilmenite, PS and HA dosages, but the HA exhibited strong scavenging effect at its high concentrations. The ilmenite/PS/HA process worked well in the real treated wastewater, because the surface-controlled radical generation was less affected by the water matrix. However, the formation of bromate in the bromide-containing water by this process should be concerned. Ibuprofen was partially mineralized, and the degradation products were identified by ESI-tqMS. A radical-induced degradation pathway was proposed based on the product identification. This work provides the mechanistic insights on persulfate activation based on the surface-controlled catalytic processes. It also offers a new strategy to degrade emerging contaminants in water and sheds light on the environmental functions of natural minerals.
- Yin, Ran,Hu, Lingling,Xia, Dehua,Yang, Jingling,He, Chun,Liao, Yuhong,Zhang, Qing,He, Jia
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p. 294 - 302
(2019/05/10)
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- Electrochemical oxidation of amoxicillin on carbon nanotubes and carbon nanotube supported metal modified electrodes
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The electrolysis of amoxicillin (AMX) was carried out on CNT, Pt/CNT and Ru/CNT modified electrodes based on Carbon Toray in 0.1 M NaOH, 0.1 M NaCl and 0.1 M Na2CO3/NaHCO3 buffer (pH 10) media with the aim of studying the significance of two factors, electrode material and pH, on the oxidative degradation and mineralization of AMX. For this purpose, the electrolysis products were identified by HPLC-MS and GC–MS, and quantified by HPLC-UV-RID and IC. The highest carbon mineralization efficiency, corresponding to 30% of the oxidized AMX, was found for Pt/CNT modified electrode in carbonate buffer medium. Regarding to the AMX conversion, the results show that the effect of pH is higher than that of the electrode material. Principal component analysis allowed to determine the experimental parameters vs. product distribution relationship and to elucidate the oxidation pathways for the studied electrodes. The results show that the hydroxylation of the aromatic ring and the nitrogen atom play an important role on the efficient degradation of AMX.
- Ferreira, Marta,Kuzniarska-Biernacka, Iwona,Fonseca, António M.,Neves, Isabel C.,Soares, Olívia S.G.P.,Pereira, Manuel F.R.,Figueiredo, José L.,Parpot, Pier
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p. 322 - 331
(2019/07/10)
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- Nickel-catalyzed removal of alkene protecting group of phenols, alcohols via chain walking process
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An efficient nickel-catalyzed removal of alkene protection group under mild condition with high functional group tolerance through chain walking process has been established. Not only phenolic ethers, but also alcoholic ethers can be tolerated with the retention of stereocenter adjacent to hydroxyl group. The new reaction brings the homoallyl group into a start of new type of protecting group.
- Meng, Chenkai,Niu, Haolin,Ning, Juehan,Wu, Wengang,Yi, Jun
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- A short-chain dehydrogenase plays a key role in cellulosic D-lactic acid fermentability of Pediococcus acidilactici
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Phenolic aldehydes from lignocellulose pretreatment are strong inhibitors of cell growth and metabolism of cellulosic lactic acid bacteria. Their low solubility and recalcitrance highly reduce the removal efficiency of various detoxification methods. This study shows a simultaneous conversion of phenolic aldehydes and fermentation of D-lactic acid by Pediococcus acidilactici using corn stover feedstock. Vanillin was found to be the strongest phenolic aldehyde inhibitor to P. acidilactici. The overexpression of a short-chain dehydrogenase encoded by the gene CGS9114_RS09725 from Corynebacterium glutamicum was identified to play a key role in D-lactic acid fermentability of P. acidilactici. The engineered P. acidilactici with the genome integration of CGS9114_RS09725 showed the accelerated vanillin reduction and improved cellulosic D-lactic acid production. This study reveals that vanillin conversion is crucial for D-lactic acid fermentation, and the direct expression of a specific vanillin reduction gene in lactic acid bacterium efficiently improves cellulosic D-lactic acid production.
- Qiu, Zhongyang,Fang, Chun,Gao, Qiuqiang,Bao, Jie
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- Hydroxyl radical ratio type fluorescent probe as well as preparation method and application thereof
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The invention relates to a novel fluorescence resonance energy transfer (FRET) probe Rho-Bob, which is constructed by connecting rhodamine B (Rho) with an N2O type benzopyrrole boron complex (Bobpy),and is used for OH ratio type fluorescence detection and imaging. Rho-Bob shows the characteristic of being sensitive to the hydrophilicity/hydrophobicity of the environment, and has excellent mitochondrial localization capability. Rho-Bob is successfully applied to intracellular .OH ratio type fluorescence imaging. The .OH can be generated by a Fenton reaction, and can also be generated by activation of intracellular drugs. The Rho-Bob probe has high selectivity and sensitivity to hydroxyl radicals, and the detection limit is as low as a nanomole level (680nM). According to the invention, .OHgenerated by artemisinin molecules in cell mitochondria is observed for the first time by using Rho-Bob, and endogenous hydroxyl radicals are found to exist in zebra fish gastrointestinal tracts (GI)under normal culture conditions for the first time. The invention not only provides the practical probe for .OH detection and imaging, but also provides an important thought for constructing novel ratiometric probes of other ROS.
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Paragraph 0080-0082; 0090-0093
(2020/05/08)
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- Revisiting terephthalic acid and coumarin as probes for photoluminescent determination of hydroxyl radical formation rate in heterogeneous photocatalysis
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We investigated in detail the applicability of two radical scavengers – coumarin (COUM) and terephthalic acid (TA) – as probe compounds in a widely used photoluminescent (PL) determination of OH? radical rate formation of photocatalysts. The study reveals that precautions must be taken when using either of the two compounds as neither allows a direct determination of the absolute OH? radical formation rate. Chromatographic analyses of irradiated COUM and TA solutions revealed that both probe compounds reacted via more than one pathway, out of which, only one pathway in each case yielded the measured photoluminescent 7-hydroxycoumarin (7-OHC) and 2-hydroxyterephthalic acid (TAOH), respectively. Applicability of both probes was also tested on three model TiO2-based catalysts (anatase TiO2 nanorods (TNR), anatase TiO2 nanoparticles (TNP), amorphous TiO2 nanorods (a-TNR)). Regardless of the probe compound used, the order of relative OH? radical formation rates determined for these catalysts was the same (TNR a-TNR) and in good correlation with the order of bisphenol A (BPA) degradation rates. This demonstrates that (i) formation of OH? radicals is the predominating criterion when probing a photocatalyst's activity (but not the only one) and that (ii) TA and COUM potentially enable a relative evaluation of photocatalytic materials, despite the numerous shortcomings of these probes. However, in order to allow for general inter-laboratory comparisons the photoluminescence method should clearly be standardized with precisely defined experimental parameters.
- ?erjav, Gregor,Albreht, Alen,Pintar, Albin,Vovk, Irena
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- Synthesis of Phenols via Metal-Free Hydroxylation of Aryl Boronic Acids with Aqueous TBHP
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An alternate procedure for oxidative hydroxylation of aryl boronic acids with aqueous TBHP to access phenols is described. The protocol tolerated various functional groups substituted with aromatic rings. The reaction was performed in water and free from transition metal oxidants.
- Shaikh, Tanveer MahmadAlli
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- The construction of accelerated catalytic Fenton reaction based on Pd/MIL-101(Cr) and H2
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A novel catalytic Fenton system based on H2 and the solid catalyst Pd/MIL-101(Cr) (MHACF-MIL-101(Cr)) was developed at normal temperature and pressure. In this system, the reduction process of FeIII back to FeII was accelerated significantly. Using only trace levels of FeII at the beginning of the reaction, MHACF-MIL-101(Cr) provided continuous production of hydroxyl radicals and rapid degradation of the model contaminant 4-chlorophenol (10 mg L-1) under the initial conditions of pH 3, 25 μM FeII, 25 mM H2O2, 85 mL min-1 H2 and 2 g L-1 Pd/MIL-101(Cr). The activity of the solid catalyst gradually decreased from 100% to about 70% after 6 consecutive degradation reaction cycles of 18 h. This may mainly be attributed to the structural damage and the surface area reduction of this catalyst.
- Liu, Xin,Gao, Shi-Qian,Fan, Jin-Hong,Li, Xiao-Meng,Qin, He-He,Wang, Jun-Xia,Ma, San-Jian,Liu, Zhong-Xing,Yu, Yang
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p. 8179 - 8188
(2019/06/08)
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- Fe3O4@SiO2@Im[Cl]Mn(III)-complex as a highly efficient magnetically recoverable nanocatalyst for selective oxidation of alcohol to imine and oxime
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An efficient and environmentally friendly oxidation process for the one-pot preparation of oxime, imine and carbonyl compounds through alcohol oxidation in the presence of H2O2 and/or O2 have been developed by a melamine-Mn(III) Schiff base complex supported on Fe3O4@SiO2–Cl nanoparticles, named as Fe3O4@SiO2@Im[Cl]Mn(III)-complex nanocomposite, at room temperature. Direct oxidation of alcohol to carboxylic acid was performed using the catalyst in the presence of molecular O2 at room temperature in a different approach. The oxidation products were obtained with excellent yields and high TOFs. The properties of the catalyst were characterized by Fourier transform infrared spectroscopy (FTIR), elemental analysis (C, H, N), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), dynamic light scattering (DLS), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), inductive coupled plasma (ICP), cyclic voltammetry (CV), nuclear magnetic resonance (1H & 13C NMR), vibration sample magnetometer (VSM), Brunauer– Emmett–Teller (BET) and differential pulse voltammetry (DPV) analyses. The mechanism of the oxidation processes was investigated for the both H2O2 and O2 oxidants. The role of the imidazolium moiety in the catalyst as a secondary functionality was investigated. Chemoselectivity behavior of the catalyst was studied by some combinations. The catalyst could be recycled from the reaction mixture by a simple external magnet and reused for several times without any considerable reactivity loss.
- Kazemnejadi, Milad,Alavi, Seyyedeh Ameneh,Rezazadeh, Zinat,Nasseri, Mohammad Ali,Allahresani, Ali,Esmaeilpour, Mohsen
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p. 230 - 249
(2019/03/28)
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- Highly active bidentate N-heterocyclic carbene/ruthenium complexes performing dehydrogenative coupling of alcohols and hydroxides in open air
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Eight bidentate NHC/Ru complexes, namely [Ru]-1-[Ru]-8, were designed and prepared. In particular, [Ru]-2 displayed extraordinary performance even in open air for the dehydrogenative coupling of alcohols and hydroxides. Notably, an unprecedentedly low catalyst loading of 250 ppm and the highest TON of 32 800 and TOF of 3200 until now were obtained.
- Wang, Zhi-Qin,Tang, Xiao-Sheng,Yang, Zhao-Qi,Yu, Bao-Yi,Wang, Hua-Jing,Sang, Wei,Yuan, Ye,Chen, Cheng,Verpoort, Francis
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supporting information
p. 8591 - 8594
(2019/07/25)
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- Application of quebrachitol in hydrolysis reaction of copper-catalyzed aryl halide
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The invention belongs to the technical field of drug synthesis, and provides application of quebrachitol in a hydrolysis reaction of a copper-catalyzed aryl halide. According to the hydrolysis reaction, copper serves as a catalyst, quebrachitol serves as a ligand, and the hydrolysis reaction is carried out on the aryl halide. The invention further provides a catalytic system of the hydrolysis reaction of the aryl halide. The reaction system comprises the copper catalyst, the quebrachitol, alkali and water, and the system is environmentally friendly and is suitable for industrial application.
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Paragraph 0034-0038
(2019/07/16)
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- A Green Alternative for the Conversion of Arylboronic Acids/Esters into Phenols Promoted by a Reducing Agent, Sodium Sulfite
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Hydroxylation of arylboronic acids and arylboronic esters using sodium sulfite and oxygen as the source of ultimate oxidant proceeds rapidly in water under transition metal-free conditions. This remarkable mild and environmentally benign protocol represents a green alternative to synthesize phenols using inexpensive starting materials in a simple methodology. This new application for sodium sulfite shows a wide tolerance of functional groups, and it is compatible with oxidizable functionalities.
- Castro-Godoy, Willber D.,Schmidt, Luciana C.,Argüello, Juan E.
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p. 3035 - 3039
(2019/05/15)
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- Ultrastable Covalent Organic Frameworks via Self-Polycondensation of an A2B2 Monomer for Heterogeneous Photocatalysis
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Easy preparation, high stability, prominent activity, and excellent recyclability are four key elements for high-performance heterogeneous photocatalysts. Developing covalent organic framework (COF)-based heterogeneous photocatalysts possessing all of these traits is highly challenging. In this study, we successfully synthesized an imine-linked BBO-COF by the "two-in-one" strategy featuring the above four merits. Highly crystalline and porous BBO-COF can be easily prepared in at least 11 different simplex solvents independent of their polarity and boiling points and even under an air atmosphere. Moreover, BBO-COF exhibits extraordinary chemical stability and photostability in strong acid (12 M HCl), corrosive base (12 M NaOH), and visible light for 7 days. Furthermore, BBO-COF exhibited prominent photocatalytic activity toward oxidative hydroxylation reaction of arylboronic acids with excellent substrates tolerance and reusability. This "two-in-one" design strategy open a new avenue for facile constructing novel functional COFs with tailor-made properties.
- Yan, Xiaoli,Liu, Huan,Li, Yusen,Chen, Weiben,Zhang, Ting,Zhao, Ziqiang,Xing, Guolong,Chen, Long
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p. 7977 - 7983
(2019/11/03)
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- Multifunctional Tubular Organic Cage-Supported Ultrafine Palladium Nanoparticles for Sequential Catalysis
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The imine condensation reaction of 5,5′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)diisophthalaldehyde with cyclohexanediamine resulted in a shape-persistent multifunctional tubular organic cage (MTC1). It exhibits selective fluorescence sensing towards divalent Pd ions with a very low detection limit (38 ppb), suggesting effective complexation between these two species. Subsequent reduction of MTC1 and Pd(OAc)2 with NaBH4 afforded a cage-supported catalyst with well-dispersed ultrafine Pd nanoparticles (NPs) in a narrow size distribution (1.9±0.4 nm), denoted as Pd?MTC1-1/5. Such ultrafine Pd NPs in Pd?MTC1-1/5, in cooperation with photocatalytically active MTC1, enable efficient sequential reactions involving visible light-induced aerobic hydroxylation of 4-nitrophenylboronic acid to 4-nitrophenol and the following hydride reduction with NaBH4. This is the first example of a multifunctional organic cage capable of sensing, directing nanoparticle growth, and catalyzing sequential reactions.
- Sun, Nana,Wang, Chiming,Wang, Hailong,Yang, Le,Jin, Peng,Zhang, Wei,Jiang, Jianzhuang
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supporting information
p. 18011 - 18016
(2019/11/14)
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- Remote Para-C-H Acetoxylation of Electron-Deficient Arenes
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One formidable challenge in sp2 C-H activation is how to achieve high para selectivity on electron-deficient arenes because such site selectivity is disfavored by the electronic bias induced by the electron-withdrawing groups. The first highly selective para-C-H acetoxylation of various benzoic acids using a nitrile-based template was realized. Removal of the template leads to para-hydroxylated benzoic acids, which are versatile intermediates for a wide range of synthetically useful transformations.
- Li, Minghong,Shang, Ming,Xu, Hui,Wang, Xing,Dai, Hui-Xiong,Yu, Jin-Quan
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supporting information
p. 540 - 544
(2019/01/14)
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