2078-12-8Relevant articles and documents
Identification of an acyl-enzyme intermediate in a meta-cleavage product hydrolase reveals the versatility of the catalytic triad
Ruzzini, Antonio C.,Ghosh, Subhangi,Horsman, Geoff P.,Foster, Leonard J.,Bolin, Jeffrey T.,Eltis, Lindsay D.
, p. 4615 - 4624 (2012)
Meta-cleavage product (MCP) hydrolases are members of the α/β-hydrolase superfamily that utilize a Ser-His-Asp triad to catalyze the hydrolysis of a C-C bond. BphD, the MCP hydrolase from the biphenyl degradation pathway, hydrolyzes 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) to 2-hydroxypenta-2,4-dienoic acid (HPD) and benzoate. A 1.6 A resolution crystal structure of BphD H265Q incubated with HOPDA revealed that the enzyme's catalytic serine was benzoylated. The acyl-enzyme is stabilized by hydrogen bonding from the amide backbone of 'oxyanion hole' residues, consistent with formation of a tetrahedral oxyanion during nucleophilic attack by Ser112. Chemical quench and mass spectrometry studies substantiated the formation and decay of a Ser112-benzoyl species in wild-type BphD on a time scale consistent with turnover and incorporation of a single equivalent of 18O into the benzoate produced during hydrolysis in H218O. Rapid-scanning kinetic studies indicated that the catalytic histidine contributes to the rate of acylation by only an order of magnitude, but affects the rate of deacylation by over 5 orders of magnitude. The orange-colored catalytic intermediate, ESred, previously detected in the wild-type enzyme and proposed herein to be a carbanion, was not observed during hydrolysis by H265Q. In the newly proposed mechanism, the carbanion abstracts a proton from Ser112, thereby completing tautomerization and generating a serinate for nucleophilic attack on the C6-carbonyl. Finally, quantification of an observed pre-steady-state kinetic burst suggests that BphD is a half-site reactive enzyme. While the updated catalytic mechanism shares features with the serine proteases, MCP hydrolase-specific chemistry highlights the versatility of the Ser-His-Asp triad.
H3O2 bridging ligand in a metal-organic framework. Insight into the Aqua-Hydroxo?hydroxyl equilibrium: A combined experimental and theoretical study
D'Vries, Richard F.,De La Pena-O'Shea, Victor A.,Snejko, Natalia,Iglesias, Marta,Gutierrez-Puebla, Enrique,Monge, M. Angeles
, p. 5782 - 5792 (2013)
A metal-organic framework (MOF) bearing the aqua-hydroxo species (O 2H3)- in the framework, as well as the processes that govern the equilibrium aqua-hydroxo (O2H 3)-?hydroxyl (OH) in Sc-MOFs, are studied experimentally and theoretically. Computational studies were employed to determine the relative energies for the two compounds that coexist under certain hydrothermal conditions at pH 3(3,5-DSB)2(μ-O2H3)(μ-OH) 2(H2O)2] (from now on, (O2H 3)Sc-MOF; 3,5-DSB = 3,5-disulfobenzoic acid) was obtained as a pure and stable phase. It was impossible to isolate [Sc3(3,5-DSB) 2(μ-OH)3(H2O)4] as a pure phase, as it turned out to be the precursor of (O2H3)Sc-MOF. Additionally, a third compound that appears at pH between 3.5 and 4, [Sc 3(3,5-DSB)(μ-OH)6(H2O)] and a fourth, [Sc(3,5-DSB)(Phen)(H2O)](H2O), in whose formula neither OH groups nor H3O2- anions appear, are reported for comparative purposes. A study of the (O2H3)Sc-MOF electronic structure, and some heterogeneous catalytic tests in cyanosilylation of aldehydes reactions, are also reported.
Production of acyloxysilane
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Paragraph 0059-0064, (2021/10/30)
[A] a method for producing functional chemicals useful as efficient acyloxysilane. The silanol Si-to-OH bond [a], in the presence of a catalyst, comprising the step of reacting a carboxylic acid anhydride, Si-to-OCO bond (OCO is, oxycarbonyl groups (=O) O-a C shown. ) Having an acyloxysilane manufacturing method, wherein the catalyst, or (2) (1) production of acid catalyst selected from the next acyloxysilane. (1) 3 - 15 Of the periodic table of the first group the first group element selected from the perchlorate salt, trifluoromethanesulfonic acid salt, a bis (trifluoromethanesulfonyl imide) salt, lithium hexafluorophosphate salt, chloride, or bromide; inorganic acids; or an organic acid. (2) Inorganic or organic solid acid compounds[Drawing] no
Trimethylsilyl Esters as Novel Dual-Purpose Protecting Reagents
Chang, Ting-Shuo,Chen, Jyun-Siao,Hsieh, Ya-Chi,Hsu, Hsiao-Lin,Huang, Po-Hsun,Liu, Jen-Wei,Liu, Yu-Hao,Luo, Shun-Yuan,Wu, Hsin-Ru,Wu, Ren-Tsung,Zhang, Kai-Min
supporting information, (2021/12/02)
Trimethylsilyl esters, AcOTMS, BzOTMS, TCAOTMS, etc., are inexpensive and chemically stable reagents that pose a negligible environmental hazard. Such compounds prove to serve as efficient dualpurpose reagents to respectively achieve acylation and trimethylsilylation of alcohols under acidic or basic conditions. Herein, a detailed study on protection of various substrates and new methodological investigations is described.
IMINE-TYPE QUATERNARY AMMONIUM SALT CATALYST, PREPARATION METHOD THEREOF AND USE THEREOF FOR PREPARATION OF POLYISOCYANATE COMPOSITION
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Paragraph 0022; 0077; 0079, (2020/12/13)
Disclosed is an imine-type quaternary ammonium salt catalyst, wherein the catalyst has a general structure formula shown by formula I below; in the formula, R1 and R2, respectively, are independently selected from a C1-C20 linear alkyl or a branched C3-C20 alkyl, and a C1-C20 hydroxylalkyl, a C3-C8 cycloalkyl, and arylated alkyl; R3 is a linear or branched alkyl, cycloalkyl or aryl; and R4 is hydrogen, aryl, a linear C1-C15 alkyl or branched C3-C15 alkyl. Also disclosed are a method for preparing the catalyst and a polyisocyanate composition prepared therefrom. The catalyst, by introducing an imine structure, on the basis of ensuring high catalytic activity thereof, is allowed to have properties of high temperature decomposition and inactivation, and when applied to the synthesis of polyisocyanate, can effectively prevent the risk of explosive polymerization caused by an uncontrolled reaction.
Copper-Catalyzed Enantioselective Radical 1,4-Difunctionalization of 1,3-Enynes
Zeng, Yuehua,Chiou, Mong-Feng,Zhu, Xiaotao,Cao, Jie,Lv, Daqi,Jian, Wujun,Li, Yajun,Zhang, Xinhao,Bao, Hongli
supporting information, p. 18014 - 18021 (2020/11/02)
Chiral allenes are important structural motifs frequently found in natural products, pharmaceuticals, and other organic compounds. Asymmetric 1,4-difunctionalization of 1,3-enynes is a promising strategy to construct axial chirality and produce substituted chiral allenes from achiral substrates. However, the previous state of the art in 1,4-difunctionalization of 1,3-enynes focused on the allenyl anion pathway. Because of this, only electrophiles can be introduced into the allene backbones in the second functionalization step, consequently limiting the reaction and allene product types. The development of asymmetric 1,4-difunctionalization of 1,3-enynes via a radical pathway would complement previous methods and support expansion of the toolbox for the synthesis of asymmetric allenes. Herein, we report the first radical enantioselective allene formation via a group transfer pathway in the context of copper-catalyzed radical 1,4-difunctionalization of 1,3-enynes. This method addresses a longstanding unsolved problem in asymmetric radical chemistry, provides an important strategy for stereocontrol with free allenyl radicals, and offers a novel approach to the valuable, but previously inaccessible, chiral allenes. This work should shed light on asymmetric radical reactions and may lead to other enantioselective group transfer reactions.
A simple and efficient room temperature silylation of diverse functional groups with hexamethyldisilazane using CeO2 nanoparticles as solid catalysts
Anbu, Nagaraj,Vijayan, Chellappa,Dhakshinamoorthy, Amarajothi
, (2019/06/08)
In this study, a mild and efficient method is developed for the silylation of diverse functional groups using CeO2 nanoparticles (n-CeO2) as solid catalysts with hexamethyldisilazane (HMDS) as silylating agent at room temperature. Alcohols, phenols and acids are silylated to their respective silyl derivatives with faster reaction rate while amines and thiols required relatively longer reaction time. Moreover, the solid catalyst is easily be separated from the reaction mixture and recycled more than five times without any obvious decay in its activity. Powder X-ray diffraction (XRD), transmission electron microscope (TEM), UV–vis diffuse reflectance spectra (UV-DRS) and Raman analyses revealed identical structural integrity, particle size, absorption edge and valence state for the reused solid compared to the fresh solid catalyst.
Method for Producing Acyloxysilanes, Acyloxysilanes Obtained Thereby, and Use of Same
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Paragraph 0131, (2018/03/25)
An object of the invention is to provide a method for efficiently producing an acyloxysilane which is useful as a functional chemical, an acyloxysilane obtained thereby, and the use thereof. The present invention provides: a method for producing an acyloxysilane, including a reaction step of reacting an alkoxysilane with a carboxylic anhydride in the presence of a catalyst, wherein the alkoxysilane is a specified alkoxysilane represented by General Formula (I), the carboxylic anhydride is a specified carboxylic acid represented by General Formula (IIA) or (IIB), the catalyst is an acid catalyst, and an acyloxysilane obtained in the reaction step is a specified acyloxysilane represented by General Formula (IIIA) or (IIIB); and the use of the acyloxysilane as a surface treatment agent or the like.
Synthesis of trimethylsilyl carboxylates by HMDS under solvent-free conditions
Jereb, Marjan,Lakner, Janja
, p. 5713 - 5723 (2016/08/23)
A broad set of structurally different carboxylic acids were transformed into their trimethylsilyl esters with HMDS in a practically completely solvent-free process, while a catalytic amount of iodine was required in some cases. The process has several advantages over the known methods: untreated reactants, air atmosphere, mild and neutral conditions, no evolution of hydrogen halide, no need of an additional base, low amount of waste, completely without chromatography, low consumption of energy, and operational simplicity.
Fe(TAML)Li/(diacetoxyiodo)benzene-mediated oxidation of alcohols: Evidence for mild and selective C-O and C-C oxidative cleavage in lignin model transformations
Napoly, Francois,Jean-Gerard, Ludivine,Goux-Henry, Catherine,Draye, Micheline,Andrioletti, Bruno
, p. 781 - 787 (2014/03/21)
A novel combination of Fe(TAML)Li and (diacetoxyiodo)- benzene for the oxidation of primary and secondary alcohols at 25 °C in acetone is reported. In view of the interesting ability of this system to selectively cleave specific types of C-C bonds of elaborated alcohols, the application of this novel combination to the oxidative cleavage of lignin model molecules was investigated. Considering the numerous supported versions of the oxidant as well as the mild conditions employed, the developed methodology appears to be a promising lignin depolymerization strategy.
