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All total 1912 Articles be found
All total 1912 Articles be foundCatalytic degradation of an organophosphorus agent at Zn-OH sites in a metal-organic framework
Mian, Mohammad Rasel,Islamoglu, Timur,Afrin, Unjila,Goswami, Subhadip,Cao, Ran,Kirlikovali, Kent O.,Hall, Morgan G.,Peterson, Gregory W.,Farha, Omar K.
, p. 6998 - 7004 (2020)
Chemical warfare agents (CWAs), and in particular organophosphorus nerve agents, still pose a significant threat to society due to their continued use despite international bans. While nature has constructed a variety of enzymes that are capable of rapidly hydrolyzing organophosphorus substrates, the poor stability of enzymes outside of buffered solutions has limited their use in practical applications, such as in filters or on protective suits. As a result, we have explored the use of metal-organic frameworks (MOFs) as robust and tunable catalytic materials in which the nodes can be tailored to resemble the active sites found in these enzymes. We identified the Zn-based MOF, MFU-4l, as a promising hydrolysis catalyst due to the presence of Zn(II)-OH groups on the nodes, which are structurally reminiscent of the active sites in carbonic anhydrase (CA), a Zn-based enzyme that has been shown to efficiently catalyze the hydrolysis of phosphate esters. Indeed, MFU-4l can rapidly hydrolyze both the organophosphorus nerve agent, GD, and its simulant, DMNP, with half-lives as low as 1 min, which is competitive with the some of best heterogeneous hydrolysis catalysts reported to date.
Influence of activated carbons on the kinetics and mechanisms of aromatic molecules ozonation
Merle,Pic,Manero,Mathé,Debellefontaine
, p. 166 - 172 (2010)
Companies have been looking for new methods for treating toxic or refractory wastewaters; which can mainly be used prior to or after or in connexion with biological treatment processes. This paper compares conventional ozone oxidation with activated carbon (AC) promoted ozone oxidation, which helps developing a mechanism involving HO{radical dot} radical. For a compound which is quite easy to oxidise, like 2,4-dichlorophenol (2,4-DCP) conventional ozonation is efficient enough to remove the initial molecule. The mechanism involved mainly consists of an electrophilic attack on the aromatic ring, which is activated by the donor effect of the -OH group, then followed by a 1,3 dipolar cycloaddition (Criegee mechanism) that leads to aliphatic species, mainly carboxylic acids. Yet, the addition of AC, through the presence of HO{radical dot} radical, enhances the removal of these species which are more refractory. For a refractory compound like nitrobenzene (NB), with a de-activated aromatic ring because of the attractive effect of -NO2, conventional ozonation is inefficient. On the contrary, this molecule can be quite easily removed with AC promoted oxidation and it is found that the mechanism (electrophilic attack followed by a 1,3 dipolar cycloaddition) is quite similar to the one corresponding to conventional ozonation, but with less selectivity. For both molecules, a mass balance has established that the by-products accounting for more than 75% of the remaining COD can be quantified. A significant part is composed of carboxylic acids (acetic, oxalic, etc.), which could afterwards be easily removed in an industrial wastewater treatment process followed by a final biological treatment step.
Biomimicking, metal-chelating and surface-imprinted polymers for the degradation of pesticides
Erdem, Murat,Say, Ridvan,Ers?z, Arzu,Denizli, Adil,Türk, Hayrettin
, p. 238 - 243 (2010)
Molecularly imprinted polymer beads (PIBs) and non-imprinted (control) polymer beads (NIBs) have been prepared from methacryloylhistidine-Co2+, -Ni2+, and -Zn2+ monomers and applied as catalyst in the hydrolysis of paraoxo
A simple DNase model system comprising a dinuclear Zn(II) complex in methanol accelerates the cleavage of a series of methyl aryl phosphate diesters by 1011-1013
Neverov, Alexei A.,Liu, C. Tony,Bunn, Shannon E.,Edwards, David,White, Christopher J.,Melnychuk, Stephanie A.,Brown, R. Stan
, p. 6639 - 6649 (2008)
The di-Zn(II) complex of 1,3-bis[N1,N′1-(1,5,9- triazacyclododecyl)]propane with an associated methoxide (3:Zn(II) 2:-OCH3) was prepared and its catalysis of the methanolysis of a series of fourteen methyl aryl phosphate diesters (6) was studied at sspH 9.8 in methanol at 25.0 ± 0.1°C. Plots of kobs vs [3:Zn(II)2: -OCH3]free for all members of 6 show saturation behavior from which KM and kcatmax were determined. The second order rate constants for the catalyzed reactions (k catmax/KM) for each substrate are larger than the corresponding methoxide catalyzed reaction (k2-OMe) by 1.4 × 108 to 3 × 109-fold. The values of kcatmax for all members of 6 are between 4 × 10 11 and 3 × 1013 times larger than the solution reaction at sspH 9.8, with the largest accelerations being given for substrates where the departing aryloxy unit contains ortho-NO 2 or C(=O)OCH3 groups. Based on the linear Bronsted plots of kcatmax vs sspK aof the phenol, βIg values of -0.57 and -0.34 are determined respectively for the catalyzed methanolysis of regular substrates that do not contain the ortho-NO2 or C(=O)OCH3 groups, and those substrates that do. The data are consistent with a two step mechanism for the catalyzed reaction with rate limiting formation of a catalyst-coordinated phosphorane intermediate, followed by fast loss of the aryloxy leaving group. A detailed energetics calculation indicates that the catalyst binds the transition state comprising [CH3O -:6]?, giving a hypothetical [3:Zn(II) 2:CH3O-:6]? complex, by -21.4 to -24.5 kcal/mol, with the strongest binding being for those substrates having the ortho-NO2 or C(=O)OCH3 groups.
Guanidine based self-assembled monolayers on Au nanoparticles as artificial phosphodiesterases
Salvio, Riccardo,Cincotti, Antonio
, p. 28678 - 28682 (2014)
Gold nanoparticles passivated with a long chain alkanethiol decorated with a phenoxyguanidine moiety were prepared and investigated as catalysts in the cleavage of the RNA model compound HPNP and diribonucleoside monophosphates. The catalytic efficiency and the high effective molarity value of the Au monolayer protected colloids points to a high level of cooperation between the catalytic groups.
Structural flexibility enhances the reactivity of the bioremediator glycerophosphodiesterase by fine-tuning its mechanism of hydrolysis
Hadler, Kieran S.,Mitic, Natasa,Ely, Fernanda,Hanson, Graeme R.,Gahan, Lawrence R.,Larrabee, James A.,Ollis, David L.,Schenk, Gerhard
, p. 11900 - 11908 (2009)
The glycerophosphodiesterase from Enterobacter aerogenes (GpdQ) belongs to the family of binuclear metallohydrolases and has attracted recent attention due to its potential in bioremediation. Formation of a catalytically competent binuclear center is prom
A unique nickel system having versatile catalytic activity of biological significance
Chattopadhyay, Tanmay,Mukherjee, Madhupama,Mondal, Arindam,Maiti, Pali,Banerjee, Arpita,Banu, Kazi Sabnam,Bhattacharya, Santanu,Roy, Bappaditya,Chattopadhyay,Mondai, Tapan Kumar,Nethaji, Munirathinam,Zangrando, Ennio,Das, Debasis
, p. 3121 - 3129 (2010)
A new dinuclear nickel(ll) complex, [Ni2(LH2)(H 2O)2(OH)(NO3)](NO3)3 (1), of an "end-off" compartmental ligand 2,6-bis(N-ethylpiperazine- iminomethyl)-4-methyl-phenolato, has been synthesized and structurally characterized. The X-ray single crystal structure analysis shows that the piperazine moieties assume the expected chair conformation and are protonated. The complex 1 exhibits versatile catalytic activities of biological significance, viz. catecholase, phosphatase, and DNA cleavage activities, etc. The catecholase activity of the complex observed is very dependent on the nature of the solvent. In acetonitrile medium, the complex is inactive to exhibit catecholase activity. On the other hand, in methanol, it catalyzes not only the oxidation of 3,5-ditert-buty !catechol (3,5-DTBC) but also tetrachlorocatechol (TCC), a catechol which is very difficult to oxidize, under aerobic conditions. UV-vis spectroscopic investigation shows that TCC oxidation proceeds through the formation of an intermediate. The intermediate has been characterized by an electron spray ionizaton-mass spectrometry study, which suggests a bidentate rather than a monodentate mode of TCC coordination in that intermediate, and this proposition have been verified by density functional theory calculation. The complex also exhibits phosphatase (with substrate p-nitrophenylphosphate) and DNA cleavage activities. The DNA cleavage activity exhibited by complex 1 most probably proceeds through a hydroxyl radical pathway. The bioactivity study suggests the possible applications of complex 1 as a site specific recognition of DNA and/or as an anticancer agent.
Designed four-helix bundle catalysts - The engineering of reactive sites for hydrolysis and transesterification reactions of p-nitrophenyl esters
Baltzer, Lars,Broo, Kerstin S.,Nilsson, Helena,Nilsson, Jonas
, p. 83 - 91 (1999)
Four-helix bundle proteins have been designed that catalyze the hydrolysis and transesterification reactions of p-nitrophenyl esters by a cooperative nucleophilic and general acid mechanism. The catalysts consist of two 42-residue peptides that fold into
Mesoporous zeolites as enzyme carriers: Synthesis, characterization, and application in biocatalysis
Mitchell, Sharon,Pérez-Ramírez, Javier
, p. 28 - 37 (2011)
We study the application of hierarchical ZSM-5 zeolites, combining micropores and intracrystalline mesopores, as carriers for lipase enzymes compared with purely microporous ZSM-5 and mesoporous MCM-41. Strategies to improve enzyme immobilization by modif
Isotope effects and medium effects on sulfuryl transfer reactions
Hoff,Larsen,Hengge
, p. 9338 - 9344 (2001)
Kinetic isotope effects and medium effects have been measured for sulfuryl-transfer reactions of the sulfate ester p-nitrophenyl sulfate (pNPS). The results are compared to those from previous studies of phosphoryl transfer, a reaction with mechanistic similarities. The N-15 and the bridge O-18 isotope effects for the reaction of the pNPS anion are very similar to those of the p-nitrophenyl phosphate (pNPP) dianion. This indicates that in the transition states for both reactions the leaving group bears nearly a full negative charge resulting from a large degree of bond cleavage to the leaving group. The nonbridge O-18 isotope effects support the notion that the sulfuryl group resembles SO3 in the transition state. The reaction of the neutral pNPS species in acid solution is mechanistically similar to the reaction of the pNPP monoanion. In both cases proton transfer from a nonbridge oxygen atom to the leaving group is largely complete in the transition state. Despite their mechanistic similarities, the phosphoryl- and sulfuryl-transfer reactions differ markedly in their response to medium effects. Increasing proportions of the aprotic solvent DMSO to aqueous solutions of pNPP cause dramatic rate accelerations of up to 6 orders of magnitude, but only a 50-fold rate increase is observed for pNPS. Similarly, phosphoryl transfer from the pNPP dianion to tert-amyl alcohol is 9000-fold faster than the aqueous reaction, while the sulfuryl transfer from the pNPS anion is some 40-fold slower. The enthalpic and entropic contributions to these differing medium effects have been measured and compared.
Organoruthenium(II) compounds with pyridyl benzoxazole/benzthiazole moiety: studies on DNA/protein binding and enzyme mimetic activities
Gomathi, Asaithambi,Vijayan, Paranthaman,Viswanathamurthi, Periasamy,Suresh, Shanmugam,Nandhakumar, Raju,Hashimoto, Takeshi
, p. 1645 - 1666 (2017)
We report herein synthesis and characterization of four new organoruthenium(II) complexes of the type [RuH(CO)(PPh3)2(L1,2)]Cl (1, 3) and [Ru(CO)(Cl)2(AsPh3)(L1,2)] (2, 4) derived from the reaction of [RuHCl(CO)(EPh3)3] (E?=?P or As) with 2-(pyridine-2yl)benzoxazole (L1) and 2-(pyridine-2yl)benzthiazole (L2). Single-crystal X-ray diffraction data of 2 proved octahedral geometry of the complexes with a 1 : 1 ratio between the metal and the coordinated ligands. The binding affinities of 1–4 toward calf-thymus DNA (CT-DNA) and BSA were thoroughly studied by various spectroscopic techniques. Furthermore, the coordination compounds exhibit catecholase-like activities in the aerial oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone and phosphatase-like activities in the hydrolysis of 4-nitrophenyl phosphate to 4-nitrophenolate ion. The kinetic parameters have been determined using Michaelis–Menten approach. The highest kcat values suggested that coordination compounds exhibit higher rates of catalytic efficacy.
Selective debenzylation of aromatic benzyl ethers by silica-supported sodium hydrogen sulfate
Zhou, Linna,Wang, Wenjing,Zuo, Li,Yao, Shanyan,Wang, Wei,Duan, Wenhu
, p. 4876 - 4878 (2008)
A new debenzylation of aromatic benzyl ethers by silica-supported sodium hydrogen sulfate is described. The process proceeds selectively and efficiently in good to excellent yields without affecting sensitive functional groups such as nitro, COOMe, aldehyde, ketone, and tosyl.
Iron-catalyzed conversion of unactivated aryl halides to phenols in water
Ren, Yunlai,Cheng, Lin,Tian, Xinzhe,Zhao, Shuang,Wang, Jianji,Hou, Chaodong
, p. 43 - 45 (2010)
Although iron is low-cost and environmentally friendly, there is no report about iron-catalyzed conversion of unactivated aryl halides to phenols. In this Letter, a new method for the present conversion was developed with iron compounds as the catalyst and water as the solvent. The suggested method allowed a series of unactivated aryl bromides and aryl iodides to be converted into the corresponding substituted phenols in moderate to high yields.
Molecular Design of Non-Leloir Furanose-Transferring Enzymes from an α-L-Arabinofuranosidase: A Rationale for the Engineering of Evolved Transglycosylases
Bissaro, Bastien,Durand, Julien,Biarns, Xevi,Planas, Antoni,Monsan, Pierre,O'Donohue, Michael J.,Faur, Rgis
, p. 4598 - 4611 (2015)
The vast biodiversity of glycoside hydrolases (GHs) constitutes a reservoir of readily available carbohydrate-acting enzymes that employ simple substrates and hold the potential to perform highly stereopecific and regioselective glycosynthetic reactions. However, most GHs preferentially hydrolyze glycosidic bonds and are thus characterized by a hydrolysis/transglycosylation partition in favor of hydrolysis. Unfortunately, current knowledge is insufficient to rationally modify this partition, specifically mutating key molecular determinants to tip the balance toward transglycosylation. In this study, in the absence of precise knowledge concerning the hydrolysis/transglycosylation partition in a hydrolytic GH51 α-L-arabinofuranosidase, we describe how an iterative protein engineering approach has been used to create the first non-Leloir transarabinofuranosylases. In the first step, random mutagenesis yielded a point mutation (R69H) at a position that is highly conserved in clan GH-A. Characterization of R69H revealed that this enzyme displays high transglycosylation activity but severely reduced (61-fold) activity on pNP-α-L-arabinofuranoside. Upon recombination of R69H with other point mutations selected using semirational or in silico approaches, transfer rates close to 100% and transarabinofuranosylation yields of the main (1→2)-linked oligosaccharide product of 80% (vs 11% for the wild-type) were obtained. Combining data presented here with knowledge drawn from the literature, we suggest that the creation of non-Leloir transglycosylases necessarily involves the destabilization of the highly developed transition states that characterize the predominantly hydrolytic exo-acting GHs; this is an efficient way to prevent ubiquitous water molecules from performing the deglycosylation step. (Figure Presented).
Antibody catalyzed modification of amino acids. Efficient hydrolysis of tyrosine benzoate
Benedetti,Berti,Colombatti,Flego,Gardossi,Linda,Peressini
, p. 715 - 716 (2001)
Esterase antibody 522c2, the first example of a catalytic antibody specifically programmed to control the reactivity of functional groups on the side chain of tyrosine, accelerates the hydrolysis of benzoate esters of L-tyrosine and tyrosine-containing dipeptides by a factor of 104 and is moderately active against other benzoate esters.
Parallel Behavior in Kinetic and NMR Effects: Secondary Deuterium Isotope Effects on the Alkaline Hydrolysis of Esters
Matta, Michael S.,Broadway, Dale E.,Stroot, Michele K.
, p. 4916 - 4918 (1987)
β-Deuterium secondary kinetic isotope effects (β-D KIEs) on the alkaline hydrolysis of the p-nitrophenyl esters of acetic, propanoic, butanoic, and pentanoic acids in pH 10.70, 0.20 M carbonate buffer at 25 deg C tend to increase with increasing chain length of the esters up to the pentanoate.The β-D KIEs are respectively 0.975 +/- 0.004, 0.960 +/- 0.002, 0.940 +/- 0.001, and 0.948 +/- 0.004.The activation energies of the esterolyses of the isotopically light esters follow a similar pattern, as do the 13C NMR nuclear shieldings in CDCl3 of the isotopically light parent carboxylic acids (20.9, 27.4, 35.9, and 33.8 (ppm)) and 13C NMR one-bond isotope shifts produced by disubstitution of deuterium for hydrogen at the α-carbons of the acids (0.45, 0.55, 0.60, and 0.59 (ppm)).Correlation of nuclear shieldings and isotope shifts is known from previous work.The possibility is considered that all of the kinetics-based and NMR relationships are linked through the operation of a common ground-state feature of the ester and acid alkyl chains.
Insights into Catalytic Hydrolysis of Organophosphonates at M-OH Sites of Azolate-Based Metal Organic Frameworks
Cao, Ran,Chen, Haoyuan,Farha, Omar K.,Islamoglu, Timur,Kirlikovali, Kent O.,Mian, Mohammad Rasel,Snurr, Randall Q.
, p. 9893 - 9900 (2021)
Organophosphorus nerve agents, a class of extremely toxic chemical warfare agents (CWAs), have remained a threat to humanity because of their continued use against civilian populations. To date, Zr(IV)-based metal organic framework (MOFs) are the most pre
Low ionic liquid concentration in water: A green and simple approach to improve activity and selectivity of lipases
Filice, Marco,Romero, Oscar,Abian, Olga,De Las Rivas, Blanca,Palomo, Jose M.
, p. 49115 - 49122 (2014)
The activity of several commercial and genetically engineered lipases, already immobilized on octyl-Sepharose, in aqueous solutions containing ionic liquids (ILs) in a molar concentration of 0.01 mol L-1 was investigated. Strong variations in t
Influence of Water Structure on Solvolysis in Water-in-Oil Microemulsions
Garcia-Rio, L.,Leis, J. R.,Iglesias, E.
, p. 12318 - 12326 (1995)
The kinetics of solvolysis of diphenylmethyl chloride, 4-nitrophenyl chloroformate, benzoyl chloride, p-anisoyl chloride, and bis(4-nitrophenyl)carbonate in water/AOT/isooctane microemulsions with various water/surfactant mole ratios W (AOT = sodium bis(2-ethylhexyl)sulfosuccinate) were interpreted by using a pseudophase model in which the substrates are assumed to be distributed between the isooctane and interface phases.The W-dependence of the intrinsic rate constants k for solvolysis at the interface depends on the solvolysis mechanism: for SN1 reactions, k decreased with W, which is attributed to decreasing polarity of the interface; contrariwise, SN2 reactions are accelerated by decreasing W, which is attributed to increasing nucleophilicity of interfacial water.
A Dinuclear Dysprosium Complex as an Air-Stable and Recyclable Catalyst: Applications in the Deacetylation of Carbohydrate, Aliphatic, and Aromatic Molecules
Chiu, Ting-Yu,Chin, Wei,Guo, Jiun-Rung,Liang, Chien-Fu,Lin, Po-Heng
, p. 627 - 633 (2019)
Two dinuclear DyIII complexes, [Dy2(hmb)2(OTf)2(H2O)4]?HOTf?2 THF (A?HOTf?2 THF) and [Dy2(hmi)3(H2O)2]?2 HOTf (B?2 HOTf), have been synthesized by the reaction of Dy(OTf)3 and the Schiff-base ligands H2hmb (N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide) or H2hmi ((2-hydroxy-3-methoxyphenyl)methylene isonicotinohydrazine). Disarmed glycosyl trichloroacetimidates can be activated by complex A in the synthesis of 1,2-trans-glycosides with primary and secondary acceptors. This method offers an efficient route to selectively deacetylated monosaccharides and disaccharides in high yields and a green catalyst that can be easily recycled and reused.
Hydrolysis of nitrophenyl esters catalyzed by modified cyclodextrin in water pools in reversed micelles
Nakamura,Sugama
, p. 4682 - 4685 (1984)
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Parallel synthesis of alkyl methacrylate latexes for use as catalytic media
Miller, Paul D.,Ford, Warren T.
, p. 1151 - 1152 (1998)
Among thirty-two anion exchange latexes prepared by parallel synthesis, those containing 2-ethylhexyl methacrylate units are the most active as catalytic media for alkaline hydrolysis of p-nitrophenyl alkanecarboxylates.
Isolation and characterization of a beta-primeverosidase-like endo-manner beta-glycosidase from Aspergillus fumigatus AP-20.
Yamamoto, Shigeru,Okada, Masamichi,Usui, Taichi,Sakata, Kanzo
, p. 801 - 807 (2002)
A novel beta-glycosidase-producing microorganism was isolated from soil and identified as Aspergillus fumigatus AP-20 based on its taxonomical characteristics. The enzyme was found to be an extracellular protein in the culture of the isolated fungus and w
Kinetic investigation of the phenolysis of phenyl 4-nitrophenyl and phenyl 2,4-dinitrophenyl carbonates
Castro, Enrique A.,Angel, Mauricio,Pavez, Paulina,Santos, Jose G.
, p. 2351 - 2354 (2001)
The reactions of phenyl 4-nitrophenyl carbonate (PDNPC) and phenyl 2,4-dinitrophenyl carbonate (PDNPC) with a homogeneous series of phenoxide anions are subjected to a kinetic investigation in water at 25.0 °C, ionic strength 0.2 mol dm-3 (KCl). Under phenoxide or total phenol excess over the substrate all these reactions obey pseudo first-order kinetics and are first order in phenoxide. The Bronsted-type plots for the nucleophilic rate constants are linear with slopes 0.61 and 0.49 for the phenolysis of PNPC and PDNPC, respectively. The magnitude of these slopes and the absence of curvature in the Brnsted plot at pKa = 7.1 for the PNPC reactions are consistent with concerted mechanisms (one step) for both reaction series. PDNPC is more reactive than PNPC toward phenoxide nucleophiles; this can be explained by the presence of a second nitro group in PDNPC, which (i) leaves its carbonyl carbon more positively charged than that of PNPC, making the former a better electrophile, and (ii) makes 2,4-dinitrophenoxide a better leaving group than 4-nitrophenoxide. The larger nucleophilic rate coefficients found in this work relative to those obtained in the concerted phenolysis of 4-nitrophenyl and 2,4-dinitrophenyl methyl carbonates is explained by a stronger electron withdrawal from PhO compared to MeO. Comparison of the concerted phenolysis of PNPC with the stepwise reactions of quinuclidines with the same substrate indicates that substitution of a quinuclidino group in a zwitterionic tetrahedral intermediate by a phenoxy group greatly destabilises the intermediate.
A strategic approach of enzyme engineering by attribute ranking and enzyme immobilization on zinc oxide nanoparticles to attain thermostability in mesophilic Bacillus subtilis lipase for detergent formulation
Khan, Mohd Faheem,Kundu, Debasree,Hazra, Chinmay,Patra, Sanjukta
, p. 66 - 82 (2019)
The present study envisaged rationalized protein engineering approach to attain thermostability in a mesophilic Bacillus subtilis lipase. Contributing amino acids for thermostability were analyzed from homologous thermophilic-mesophilic protein dataset th
A Mild Strategy for the Preparation of Phenols via the Ligand-Free Copper-Catalyzed O-Arylation of para -Toluenesulfonic Acid
Tan, Bryan Yong-Hao,Teo, Yong-Chua
, p. 1814 - 1819 (2016)
A facile and simple ligand-free copper-catalyzed reaction to synthesize substituted phenols is reported. The reaction presumably proceeds via an O-arylsulfonate intermediate that is hydrolyzed to afford good to excellent yields of up to 88%. This protocol provides an alternative to existing reports which use strong hydroxide salts as the direct hydroxylation partner. Demonstrating a wide substrate scope and functional group tolerance, this protocol can also be applied to inexpensive and commercially available carboxylic acids to yield phenols.
Cellular zwitterionic metabolite analogs simultaneously enhance reaction rate, thermostability, salt tolerance, and substrate specificity of α-glucosidase
Deguchi, Eisuke,Koumoto, Kazuya
, p. 3128 - 3134 (2011)
We investigated the structural effects of metabolite analogs derived from a naturally-occurring zwitterionic metabolite, glycine betaine, on the activity of several hydrolases. The initial velocities of the hydrolases were enhanced by the addition of the
Substrate modulation of the activity of an artificial nanoesterase made of peptide-functionalized gold nanoparticles
Pengo, Paolo,Baltzer, Lars,Pasquato, Lucia,Scrimin, Paolo
, p. 400 - 404 (2007)
Nanozymes with a heart of gold: A functional artificial protein has been prepared by grafting a dodecapeptide onto the surface of gold nanoparticles (see picture). The system catalyzes the hydrolysis of carboxylate esters and features enzyme-like properti
Kinetics and speciation of paraoxon hydrolysis by zinc(II)-azamacrocyclic catalysts
Kennedy, Daniel J.,Mayer, Brian P.,Baker, Sarah E.,Valdez, Carlos A.
, p. 123 - 131 (2015)
Four Zn2+-azamacrocyclic complexes were investigated for their ability to catalyze the hydrolysis of the toxic organophosphate (OP) pesticide diethyl paraoxon. Of the four complexes studied, Zn2+-1,5,9-triazacyclododecane (Zn2+-[12]aneN3) was found to be the most effective catalyst with a pseudo-first order reaction rate of k = 6.08 ± 0.23 × 10-4 min-1. Using 31P nuclear magnetic resonance (NMR) spectroscopy, the two products diethyl phosphate (DEP) and ethyl (4-nitrophenyl) phosphate (E4NPP) were identified for both catalyzed and background hydrolysis of paraoxon. Reaction rate and selectivity for formation of the non-toxic DEP were observed to correlate with catalyst pKa. The rate of formation of toxic E4NPP, however, was independent of both the presence and nature of the catalyst. The potential roles of buffer concentration and product inhibition were also investigated. Background hydrolysis at elevated reaction temperatures (50°C) displayed no preference for DEP over that of E4NPP despite substantial differences between the characteristics (i.e., pKa values) of the two leaving groups (ethoxide vs. 4-nitrophenoxide anions). As with previous observations of these types of metal-catalyzed hydrolyses, we invoke the formation of a trigonal bipyramidal-like transition state involving a Zn-coordinated phosphate bond, with the leaving group at the apical position and the incoming HO- anion approaching from the opposite end. Kinetic rates for catalytic hydrolysis display an overwhelming propensity for DEP formation, and suggest the importance of steric restrictions on transition state structure, namely a concerted arrangement of the azamacrocycle in opposition to the bulky 4-nitrophenoxy group.
Hydrolysis of organophosphate esters: Phosphotriesterase activity of metallo-ss-lactamase and its functional mimics
Tamilselvi,Mugesh, Govindasamy
, p. 8878 - 8886 (2010)
The phosphotriesterase (PTE) activity of a series of binuclear and mononuclear zinc(II) complexes and metallo-β-lactamase (mβl) from Bacillus cereus was studied. The binuclear complex 1, which exhibits good mβl activity, shows poor PTE activity. In contrast, complex 2, a poor mimic of mβl, exhibits much higher activity than 1. The replacement of Cl - ligands by OH- is important for the high PTE activity of complex 2 because this complex does not show any catalytic activi-ty in methanol. The natural enzyme mssl from B. cereus is also found to be an inefficient catalyst in the hydrolysis of phosphotriesters. These observations indicate that the binding of -lactam substrates at the binuclear zinc(II) center is different from that of phosphotriesters. Furthermore, phospho diesters, the products from the hydrolysis of triesters, significantly inhibit the PTE activity of mβl and its functional mimics. Although the mononuclear complexes 3 and 4 exhibited significant mβl activity, these complexes are found to be almost inactive in the hydrolysis of phosphotriesters. These observations indicate that the elimination of phosphodiesters from the reaction site is important for the PTE activity of zinc(II) complexes.
Rationally Designed Double-Shell Dodecahedral Microreactors with Efficient Photoelectron Transfer: N-Doped-C-Encapsulated Ultrafine In2O3 Nanoparticles
Sun, Liming,Li, Rong,Zhan, Wenwen,Wang, Fan,Zhuang, Yuan,Wang, Xiaojun,Han, Xiguang
, p. 3053 - 3060 (2019)
It is desirable but challenging to design efficient micro-/nanoreactors for chemical reactions. In this study, we have fabricated mesoporous double-shelled hollow microreactors composed of N-doped-C-coated ultrafine In2O3 nanoparticles [N-C/In2O3 HD (hollow dodecahedron)] by the thermolysis of a dodecahedral In-based framework in Ar atmosphere. The obtained N-C/In2O3 HD exhibited excellent activity in the photocatalytic oxidative hydroxylation of a series of arylboronic acid substrates. This property can be attributed to its enhanced optical absorption and efficient separation of photo-generated electron–hole pairs, imparted by the unique structure and uniformly coated N-doped C layers. Furthermore, we found O2.? to be the critical active species in the process of photocatalytic oxidative hydroxylation of arylboronic acids, and the formation mechanism of this radical is also proposed. Theoretical calculations further confirmed that the N-doped C layer serves as an electron acceptor and revealed the microscopic charge-carrier migration path through the In2O3/N-doped graphite interfaces. Thus, photo-generated electrons from hybrid states of In2O3, composed of In 5s and 2p orbitals, are transferred into the hybrid states of N-doped graphite, composed of C 2p and N 2p orbitals. The present study may be helpful for understanding and designing carbon-based micro-/nanoreactors for photocatalytic reactions, and may also be useful for investigating related micro-/nanoreactors.
Phenol transformation photosensitised by quinoid compounds
Maurino, Valter,Bedini, Andrea,Borghesi, Daniele,Vione, Davide,Minero, Claudio
, p. 11213 - 11221 (2011)
The phototransformation of phenol in aqueous solution was studied with different quinoid compounds, which are usually detected on atmospheric particulate matter: 2-ethylanthraquinone (EtAQ), benzanthracene-7,12-dione (BAD), 5,12-naphthacenequinone (NQ), 9,10-anthraquinone (AQ), and 2,6-dihydroxyanthraquinone (DAQ). All the studied quinones were able to sensitise the phototransformation of phenol. Under blue-light irradiation the approximated, polychromatic quantum yields for phenol photodegradation were in the order AQ > BAD > EtAQ > NQ > DAQ. Quantum mechanical calculations showed that AQ and DAQ have a very different spin distribution in the triplet state (largely located on the carbonyl oxygen and delocalised over the aromatic ring, respectively) that could account for the difference in reactivity. The spin distribution of EtAQ is similar to that of AQ. Under simulated sunlight, EtAQ induced the highest rate of phenol degradation. Radiation-excited EtAQ would oxidise both ground-state EtAQ and phenol; a kinetic model that excludes the OH radical and singlet oxygen as reactive species is supported by the experimental data. Quinones were also able to oxidise nitrite to nitrogen dioxide, thereby inducing phenol nitration. Such a process is a potential source of nitrogen dioxide and nitrophenols in the atmospheric aerosols. the Owner Societies.
Use of MoO2Cl2(DMF)2 as a precursor for molybdate promoted hydrolysis of phosphoester bonds
Tome, Catia M.,Oliveira, M. Conceicao,Pillinger, Martyn,Goncalves, Isabel S.,Abrantes, Marta
, p. 3901 - 3907 (2013)
Phosphoester bond cleavage of para-nitrophenylphosphate (pNPP), a commonly used model substrate, is accelerated by using the complex MoO2Cl 2(DMF)2 (1) (DMF = dimethylformamide) as a hydrolysis promoting agent, even when c
Lithium pipecolinate as a facile and efficient ligand for copper-catalyzed hydroxylation of aryl halides in water
Jing, Linhai,Wei, Jiangtao,Zhou, Li,Huang, Zhiyong,Li, Zhengkai,Zhou, Xiangge
, p. 4767 - 4769 (2010)
Direct hydroxylation of a wide scope of aryl halides was catalyzed by a combination of CuI and lithium pipecolinate in water with yields up to 92%.
Enzyme shielding in an enzyme-thin and soft organosilica layer
Correro, M. Rita,Moridi, Negar,Schützinger, Hansj?rg,Sykora, Sabine,Ammann, Erik M.,Peters, E. Henrik,Dudal, Yves,Corvini, Philippe F.-X.,Shahgaldian, Patrick
, p. 6285 - 6289 (2016)
The fragile nature of most enzymes is a major hindrance to their use in industrial processes. Herein, we describe a synthetic chemical strategy to produce hybrid organic/inorganic nanobiocatalysts; it exploits the self-assembly of silane building blocks at the surface of enzymes to grow an organosilica layer, of controlled thickness, that fully shields the enzyme. Remarkably, the enzyme triggers a rearrangement of this organosilica layer into a significantly soft structure. We demonstrate that this change in stiffness correlates with the biocatalytic turnover rate, and that the organosilica layer shields the enzyme in a soft environment with a markedly enhanced resistance to denaturing stresses. Important soft skills: Hybrid organic/inorganic nanobiocatalysts were created by the immobilization of enzymes on amino-modified silica nanoparticles and subsequent self-assembly and polycondensation of silane building blocks at the surface of the enzymes. The soft environment of the organosilica layer shielded the enzymes from denaturing stresses; however, the enzymes retained their conformational freedom and thus their catalytic activity (see picture).
Nylon–MOF Composites through Postsynthetic Polymerization
Kalaj, Mark,Denny, Michael S.,Bentz, Kyle C.,Palomba, Joseph M.,Cohen, Seth M.
, p. 2336 - 2340 (2019)
Hybridization of metal–organic frameworks (MOFs) and polymers into composites yields materials that display the exceptional properties of MOFs with the robustness of polymers. However, the realization of MOF–polymer composites requires efficient dispersion and interactions of MOF particles with polymer matrices, which remains a significant challenge. Herein, we report a simple, scalable, bench-top approach to covalently tethered nylon–MOF polymer composite materials through an interfacial polymerization technique. The copolymerization of a modified UiO-66-NH2 MOF with a growing polyamide fiber (PA-66) during an interfacial polymerization gave hybrid materials with up to around 29 weight percent MOF. The covalent hybrid material demonstrated nearly an order of magnitude higher catalytic activity for the breakdown of a chemical warfare simulant (dimethyl-4-nitrophenyl phosphate, DMNP) compared to MOFs that are non-covalently, physically entrapped in nylon, thus highlighting the importance of MOF–polymer hybridization.
Mesoporous Core-Shell Nanostructures Bridging Metal and Biocatalyst for Highly Efficient Cascade Reactions
Gao, Jing,Gao, Shiqi,Jiang, Yanjun,Liu, Yunting,Ma, Li,Wang, Zihan
, p. 1375 - 1380 (2020)
Mesoporous core-shell structured nanocatalysts with a PdPt bimetallic core and enzyme-immobilized polydopamine (PDA) shell were designed, in which the PDA shell worked as a barrier to position the bimetallic core and enzyme in separated locations. The accessible mesoporous structures of both the core and shell significantly facilitate mass transfer and catalyst utilization, improving the synergistic catalytic abilities in cascade reactions. The obtained bifunctional nanocatalysts enabled efficient two-step one-pot cascade reactions of different types: dynamic kinetic resolution of primary amines in organic solvent with high yield and enantioselectivity (up to 99% yield and 98% ee) and degradation of organophosphate nerve agent in aqueous solution with high rate constant and turnover frequency number values (0.8 min-1 and 20 min-1, respectively).
The catalytic serine of meta-cleavage product hydrolases is activated differently for C-O bond cleavage than for C-C bond cleavage
Ruzzini, Antonio C.,Horsman, Geoff P.,Eltis, Lindsay D.
, p. 5831 - 5840 (2012)
meta-Cleavage product (MCP) hydrolases catalyze C-C bond fission in the aerobic catabolism of aromatic compounds by bacteria. These enzymes utilize a Ser-His-Asp triad to catalyze hydrolysis via an acyl-enzyme intermediate. BphD, which catalyzes the hydrolysis of 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) in biphenyl degradation, catalyzed the hydrolysis of an ester analogue, p-nitrophenyl benzoate (pNPB), with a kcat value (6.3 ± 0.5 s-1) similar to that of HOPDA (6.5 ± 0.5 s-1). Consistent with the breakdown of a shared intermediate, product analyses revealed that BphD catalyzed the methanolysis of both HOPDA and pNPB, partitioning the products to benzoic acid and methyl benzoate in similar ratios. Turnover of HOPDA was accelerated up to 4-fold in the presence of short, primary alcohols (methanol > ethanol > n-propanol), suggesting that deacylation is rate-limiting during catalysis. In the steady-state hydrolysis of HOPDA, kcat/Km values were independent of methanol concentration, while both kcat and Km values increased with methanol concentration. This result was consistent with a simple model of nucleophilic catalysis. Although the enzyme could not be saturated with pNPB at methanol concentrations of >250 mM, kobs values from the steady-state turnover of pNPB at low methanol concentrations were also consistent with a nucleophilic mechanism of catalysis. Finally, transient-state kinetic analysis of pNPB hydrolysis by BphD variants established that substitution of the catalytic His reduced the rate of acylation by more than 3 orders of magnitude. This suggests that for pNPB hydrolysis, the serine nucleophile is activated by the His-Asp dyad. In contrast, rapid acylation of the H265Q variant during C-C bond cleavage suggests that the serinate forms via a substrate-assisted mechanism. Overall, the data indicate that ester hydrolysis proceeds via the same acyl-enzyme intermediate as that of the physiological substrate but that the serine nucleophile is activated via a different mechanism.
The mechanism by which 4-hydroxy-2,2,6,6-tetramethylpiperidene-1-oxyl (tempol) diverts peroxynitrite decomposition from nitrating to nitrosating species
Bonini, Marcelo G.,Mason, Ronald P.,Augusto, Ohara
, p. 506 - 511 (2002)
Tempol is a stable nitroxide radical that has been shown to protect laboratory animals from the injury associated with conditions of oxidative and nitrosoactive stress. Tempol's protective mechanisms against reactive oxygen species have been extensively studied, but its interactions with reactive nitrogen species remain little explored. Recently, it has been shown that tempol is a potent inhibitor of peroxynitrite-mediated phenol nitration while it increases phenol nitrosation by a complex mechanism [Carrol et al. (2000) Chem. Res. Toxicol. 13, 294]. To obtain further mechanistic insights, we reexamined the interaction of peroxynitrite with tempol in the absence and presence of carbon dioxide. Stopped-flow kinetic studies confirmed that tempol does not react directly with peroxynitrite but levels off the amount of oxygen (monitored with an oxygen electrode) and nitrite (monitored by chemiluminescence) produced from peroxynitrite in the presence and absence of carbon dioxide to about 30% and 70% of the initial oxidant concentration at pH 5.4, 6.4, and 7.4. Tempol inhibited phenol nitration while increasing the amounts of 4-nitrosophenol, that attained yields close to 30% of the peroxynitrite in the presence of carbon dioxide at pH 7.4. Fast-flow EPR experiments showed detectable changes in the instantaneous tempol concentration (maximum of 15%) only in the presence of carbon dioxide. Under these conditions, the instantaneous concentration of the carbonate radical anion was reduced by tempol in a concentration-dependent manner. The results indicate that tempol is oxidized by peroxynitrite-derived radicals (·OH and CO3·-, in the absence and presence of carbon dioxide, respectively) to the oxoammonium cation which, in turn, is reduced back to tempol while oxidizing peroxynitrite to oxygen and nitric oxide. The latter reacts rapidly with peroxynitrite-derived nitrogen dioxide to produce the nitrosating species, dinitrogen trioxide. Overall, the results support a role for peroxynitrite and its derived radicals in the tissue pathology associated with inflammatory conditions.
Solvent effects on reactions of hydroxide and oximate ions with phosphorus(V) esters
Bunton, Clifford A.,Gillitt, Nicholas D.,Kumar, Anurag
, p. 221 - 228 (1997)
Second-order rate constants of reactions of OH-, 2,3-butanedionemonooximate and 2-hydroxybenzaldoximate ions with aryl phosphate, phosphinate and thioarylphosphinate esters go through minima with decreasing water content of aqueous acetonitrile, tert-butyl alcohol and N-methyl-2-pyrrolidone. For reactions in H2O-MeCN the solvent effects are analyzed in terms of activity coefficients of the anionic nucleophiles and transition states. In the drier solvents partial desolvation of the nucleophiles increases rates. Nucleophilicities of several oximates and inorganic anions are compared in water.
Inhibition of Yersinia protein tyrosine phosphatase by phosphonate derivatives of calixarenes
Vovk, Andriy I.,Kononets, Lyudmyla A.,Tanchuk, Vsevolod Yu.,Cherenok, Sergiy O.,Drapailo, Andriy B.,Kalchenko, Vitaly I.,Kukhar, Valery P.
, p. 483 - 487 (2010)
Inhibition of Yersinia protein tyrosine phosphatase by calix[4]arene mono-, bis-, and tetrakis(methylenebisphosphonic) acids as well as calix[4]arene and thiacalix[4]arene tetrakis(methylphosphonic) acids have been investigated. The kinetic studies reveal
Motif-guided identification of a glycoside hydrolase family 1 α-L-arabinofuranosidase in bifidobacterium adolescentis
Suzuki, Hirokazu,Murakami, Ayano,Yoshida, Ken-Ichi
, p. 1709 - 1714 (2013)
Members of glycoside hydrolase family 1 (GH1) cleave glycosidic linkages with a variety of physiological roles. Here we report a unique GH1 member encoded in the genome of Bifidobacterium adolescentis ATCC 15703. This enzyme, BAD0156, was identified from over 2,000 GH1 sequences accumulated in a database by a genome mining approach based on a motif sequence. A recombinant BAD0156 protein was characterized to confirm that this enzyme alone specifically hydrolyzes p-nitrophenyl-α-L-arabinofuranoside among the 24 pnitrophenyl- glycosides examined. Among natural glycosides, α-1,5-linked arabino-oligosaccharides served as substrates, but arabinan, debranched arabinan, arabinoxylan, and arabinogalactan did not. A time course analysis of arabino-oligosaccharide hydrolysis indicated that BAD0156 is an exo-acting enzyme. These results suggest that BAD0156 is an α-L-arabinofuranosidase. This is the first report of a GH1 enzyme that acts specifically on arabinosides, providing information on GH1 substrate specificity.
Functional characterization of salt-tolerant microbial esterase WDEst17 and its use in the generation of optically pure ethyl (R)-3-hydroxybutyrate
Wang, Yilong,Xu, Yongkai,Zhang, Yun,Sun, Aijun,Hu, Yunfeng
, p. 769 - 776 (2018)
The two enantiomers of ethyl 3-hydroxybutyrate are important intermediates for the synthesis of a great variety of valuable chiral drugs. The preparation of chiral drug intermediates through kinetic resolution reactions catalyzed by esterases/lipases has been demonstrated to be an efficient and environmentally friendly method. We previously functionally characterized microbial esterase PHE21 and used PHE21 as a biocatalyst to generate optically pure ethyl (S)-3-hydroxybutyrate. Herein, we also functionally characterized one novel salt-tolerant microbial esterase WDEst17 from the genome of Dactylosporangium aurantiacum subsp. Hamdenensis NRRL 18085. Esterase WDEst17 was further developed as an efficient biocatalyst to generate (R)-3-hydroxybutyrate, an important chiral drug intermediate, with the enantiomeric excess being 99% and the conversion rate being 65.05%, respectively, after process optimization. Notably, the enantio-selectivity of esterase WDEst17 was opposite than that of esterase PHE21. The identification of esterases WDEst17 and PHE21 through genome mining of microorganisms provides useful biocatalysts for the preparation of valuable chiral drug intermediates.
Guanidine-based polymer brushes grafted onto silica nanoparticles as efficient artificial phosphodiesterases
Savelli, Claudia,Salvio, Riccardo
, p. 5856 - 5863 (2015)
Polymer brushes grafted to the surface of silica nanoparticles were fabricated by atom-transfer radical polymerization (ATRP) and investigated as catalysts in the cleavage of phosphodiesters. The surfaces of silica nanoparticles were functionalized with an ATRP initiator. Surface-initiated ATRP reactions, in varying proportions, of a methacrylate moiety functionalized with a phenylguanidine moiety and an inert hydrophilic methacrylate species afforded hybrid nanoparticles that were characterized with potentiometric titrations, thermogravimetric analysis, and SEM. The activity of the hybrid nanoparticles was tested in the transesterification of the RNA model compound 2-hydroxypropyl para-nitrophenylphosphate (HPNP) and diribonucleoside monophosphates. A high catalytic efficiency and a remarkable effective molarity, thus overcoming the effective molarities previously observed for comparable systems, indicate the existence of an effective cooperation of the guanidine/guanidinium units and a high level of preorganization in the nanostructure. The investigated system also exhibits a marked and unprecedented selectivity for the diribonucleoside sequence CpA. The results presented open up the way for a novel and straightforward strategy for the preparation of supramolecular catalysts.
β-D-GLUCOSIDASE-CATALYSED TRANSFER OF THE GLYCOSYL GROUP FROM ARYL β-D-GLUCO- AND β-D-XYLO-PYRANOSIDES TO PHENOLS
Aerts, Guido M.,Opstal, Omer Van,Bruyne, Clement K. De
, p. 221 - 234 (1982)
The effect of phenols on the hydrolysis of substituted phenyl β-D-gluco- and β-D-xylo-pyranosides by β-D-glucosidase from Stachybotrys atra has been investigated.Depending on the glycon part of the substrate and on the phenol substituent, the hydrolysis is either inhibited or activated.With aryl β-D-glucopyranosides, such transfer does not occur when phenols are used as acceptors, but it does occur with anilines.A two-steps mechanism, in which the first step is partially reversible, is proposed to explain these observations.A qualitative analysis of the various factors determing the overall effect of the phenol is given.
Participation of an Extended p-Oxo Ketene Intermediate in the Dissociative Alkaline Hydrolysis of Aryl 4-Hydroxycinnamates
Cevasco, Giorgio,Thea, Sergio
, p. 6274 - 6278 (1994)
The alkaline hydrolysis of 4-hydroxycinnamate esters of acidic phenols follows an E1cB mechanism and involves the participation of an "extended" p-oxo ketene intermediate.The apparent bimolecular rate constant (kaKa/Kw) for the hydrolysis of the 2,4-dinitrophenyl ester is some 2500-fold larger than that determined from the Hammett relationship for the BAc2 alkaline hydrolysis of substituted 2,4-dinitrophenyl cinnamates.The positive value of entropy of activation for the hydrolysis of 2,4-dinitrophenyl 4'-hydroxycinnamate and trapping experiments with nitrogen nucleophiles are consistent with the dissociative pathway.A change from a E1cB to a BAc2 mechanism is expected for esters with leaving groups having pKa higher than ca. 6.7.The higher E1cB reactivity of 2,4-dinitrophenyl 4'-hydroxycinnamate compared to that of the corresponding 4'-hydroxybenzoate is due to the vinylene group that further favors the dissociative route, probably increasing the stability of the unsaturated intermediate.
Evolution of metal complex-catalysts by dynamic templating with transition state analogs
Matsumoto, Masaomi,Estes, Deven,Nicholas, Kenneth M.
, p. 1847 - 1852 (2010)
The elicitation of hydrolytic catalysts from a dynamic library of imine-zinc(II) complexes (and their precursor aldehydes and amines) via templating with pro-transition state analogs (pro-TSA) is described. pro-TSA (2-pyridyl)phosphonate 2 amplifies a ben
A Simple Method for the Selective Deprotection of p-Methoxybenzyl Ethers by Cerium(III) Chloride Heptahydrate and Sodium Iodide
Cappa, Anna,Marcantoni, Enrico,Torregiani, Elisabetta,Bartoli, Giuseppe,Bellucci, Maria Cristina,Bosco, Marcella,Sambri, Letizia
, p. 5696 - 5699 (1999)
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Isoenzymes of pig-liver esterase reveal striking differences in enantioselectivities
Hummel, Anke,Bruesehaber, Elke,Boettcher, Dominique,Trauthwein, Harald,Doderer, Kai,Bornscheuer, Uwe T.
, p. 8492 - 8494 (2007)
(Graph Presented) An esterase toolbox: A set of isoenzymes of pig liver esterases (PLE) is identified, cloned, and overexpressed in E. coli. They show striking differences in enantioselectivity and enantiopreference in the kinetic resolution of acetates o
Characterization of alkaline phosphatase PhoK from Sphingomonas sp. BSAR-1 for phosphate monoester synthesis and hydrolysis
Lukesch, Michael,Tasnádi, Gábor,Ditrich, Klaus,Hall, Mélanie,Faber, Kurt
, (2020)
The biocatalytic activity of a so far underexploited alkaline phosphatase, PhoK from Sphingomonas sp. BSAR-1, was extensively studied in transphosphorylation and hydrolysis reactions. The use of high-energy phosphate donors and oligophosphates as suitable
A highly photosensitive covalent organic framework with pyrene skeleton as metal-free catalyst for arylboronic acid hydroxylation
Chen, Ying,Huo, Jianqiang,Zhang, Yubao
, (2022/03/16)
Covalent organic frameworks (COFs) have been widely utilized in metal-free photocatalytic synthesis base on their excellent properties such as super conjugation, porosity and stability. In this work, we synthesized a new COF material using 1,3,6,8-Tetrakis (p-formylphenyl)pyrene (TFPPy) and 2,2′-Dimethylbenzidine (DMBZ) as basic units through Schiff base condensation reaction. The new COF (TF-DM COF) was applied as metal-free catalyst for hydroxylation of arylboronic acids. The results indicated that the extended π conjugation of COFs enhanced the absorption of visible light, and the large porosity (BET surface area: 113.782 m2g?1) accelerated the reaction rate. Good recyclability enables it with multiple applications, which result in a great reducing of the cost. This study reports that TF-DM COF has a broad application prospect as a new generation of metal-free photocatalysts for organic conversions.
A Mechanistic Study on the Non-enzymatic Hydrolysis of Kdn Glycosides
Nejatie, Ali,Colombo, Cinzia,Hakak-Zargar, Benyamin,Bennet, Andrew J.
, (2022/01/13)
Sialic acids are biologically important carbohydrates that are prevalent throughout nature. We are interested in their intrinsic reactivity in aqueous solution and how such reactivity affects the design of substrates for investigation of enzymes that process these sugars. To probe the reactivity differences between two sialic acid family members N-acetylneuraminic acid and Kdn we measured the rate constants for hydrolysis of 4-nitrophenyl 3-deoxy-d-glycero-α-d-galacto-non-2-ulosonide in aqueous solution. The kinetic data is consistent with glycosidic C?O bond cleavage occurring via four mechanistic pathways, and these are: (i) hydronium ion-catalyzed hydrolysis of the neutral sugar; (ii) hydronium ion-catalyzed hydrolysis of the glycosidic carboxylate; (iii) water-catalyzed hydrolysis of the anionic glycoside; and (iv) base-promoted reaction of the anionic glycoside. To study the effects of C-5 substitution on the Kdn glycoside we made 4-nitrophenyl 5-O-methyl-α-Kdn glycoside and determined its rate constants for hydrolysis. All hydrolytic rate constants for both Kdn glycosides were larger than those reported for the parent N-acetyl-α-neuraminide. The water-catalyzed reaction (pathway iii) exhibited a βlg value of ?1.3±0.1. We conclude that the larger rate constants associated with C5-oxygen containing sialosides results from less steric congestion at the hydrolytic transition states than for the parent C-5 acetamido glycoside.
A copper nitride catalyst for the efficient hydroxylation of aryl halides under ligand-free conditions
Mitsudome, Takato,Mizugaki, Tomoo,Xu, Hang,Yamaguchi, Sho
supporting information, p. 6593 - 6597 (2021/08/10)
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.
Electrochemical-induced hydroxylation of aryl halides in the presence of Et3N in water
Ke, Fang,Lin, Chen,Lin, Mei,Long, Hua,Wu, Mei,Yang, Li,Zhuang, Qinglong
supporting information, p. 6417 - 6421 (2021/08/03)
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.
Microwave-assisted synthesis of para-nitrophenol using calcium nitrate
Buan, Ivy Joyce Arenas,Duldulao, Dyanne Jane Cid
, p. 243 - 246 (2021/03/29)
Conventional process of nitrating phenolic compounds involves the use of excess corrosive reagents that impose environmental threats. Rapid and environmentally friendly microwave-assisted nitration of phenol has been employed to limit the use of corrosive
