Search results for "Mechanism"
showing 10 items of 1835 documents
First Evidence of Proline Acting as a Bifunctional Catalyst in the Baylis–Hillman Reaction Between Alkyl Vinyl Ketones and Aryl Aldehydes
2008
Proline in the presence of sodium hydrogen carbonate has been found to be an effective catalyst for the Baylis–Hillman reaction between methyl or ethyl vinyl ketone and aryl aldehydes. Screening of several amine catalysts showed that an ionizable carboxylic function directly linked to the secondary amine catalyst plays an important role in the synthesis of the desired product in good yield. The data obtained has allowed us to suggest, for the first time, that proline, sarcosine, pipecolinic acid and homoproline may act as bifunctional catalysts via a bicyclic enaminolactone species as intermediate. Quantum-mechanical calculations (PM3/COSMO and ab initio 3-21G/COSMO) support this mechanism …
Are Heme-Dependent Enzymes Always Using a Redox Mechanism? A Theoretical Study of the Kemp Elimination Catalyzed by a Promiscuous Aldoxime Dehydratase
2020
The design of biocatalysts is a goal to improve the rate, selectivity and environmental friendship of chemical processes in biotechnology. In this regard, the use of computational techniques has provided valuable assistance in the design of enzymes with remarkable catalytic activity. In this paper, hybrid QM/MM simulations have allowed getting an insight into the mechanism of a promiscuous aldoxime dehydratase (OxdA) for the Kemp elimination. We first demonstrate that, based on the use of linear response approximation (LRA) methods, the lowest energy electronic state of the benzisoxazole placed in the active sit of OxdA corresponds to a singlet state, being the triplet and the quintet state…
Insights into the Dynamics of Grotthuss Mechanism in a Proton-Conducting Chiral bioMOF
2016
Proton conduction in solids attracts great interest, not only because of possible applications in fuel cell technologies, but also because of the main role of this process in many biological mechanisms. Metal–organic frameworks (MOFs) can exhibit exceptional proton-conduction performances, because of the large number of hydrogen-bonded water molecules embedded in their pores. However, further work remains to be done to elucidate the real conducting mechanism. Among the different MOF subfamilies, bioMOFs, which have been constructed using biomolecule derivatives as building blocks and often affording water-stable materials, emerge as valuable systems to study the transport mechanisms involve…
Copper-O2 reactivity of tyrosinase models towards external monophenolic substrates: molecular mechanism and comparison with the enzyme.
2011
The critical review describes the known dicopper systems mediating the aromatic hydroxylation of monophenolic substrates. Such systems are of interest as structural and functional models of the type 3 copper enzyme tyrosinase, which catalyzes the ortho-hydroxylation of tyrosine to DOPA and the subsequent two-electron oxidation to dopaquinone. Small-molecule systems involving μ-η²:η² peroxo, bis-μ-oxo and trans-μ-1,2 peroxo dicopper cores are considered separately. These tyrosinase models are contrasted to copper–dioxygen systems inducing radical reactions, and the different mechanistic pathways are discussed. In addition to considering the stoichiometric conversion of phenolic substrates, t…
Molecular recognition and binding mechanism of N-alkyl-benzyltetrahydroisoquinolines to the D1 dopamine receptor. A computational approach
2003
Fil: Suvire, Fernando Daniel. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina. Universidad Nacional de San Luis. Facultad de Quimica, Bioquimica y Farmacia; Argentina
A DFT study of the molecular mechanisms of the nucleophilic addition of ester-derived lithium enolates and silyl ketene acetals to nitrones: Effects …
2006
9 pages, 6 schemes, 3 figures, 2 tables.
Reactions Occurring during the Melt Mixing of Nylon 6 and Oxazoline−Cyclophosphazene Units
2009
Specific reactions of amino and carboxyl end groups of Nylon 6 with the reactive oxazoline groups belonging to a cyclophosphazene compound (referred as CP20XA) were carried out at 240 °C for different times, under inert atmosphere. Ny6 polymers terminated with one specific reactive chain end (-COOH or NH2) were reacted with different amounts of CP20XA to study the kinetic order of the reactions. All Ny6-CP20XA reacted products soluble in trifluoroethanol (TFE) were well characterized by MALDI-TOF MS, FT-IR and ( 1H and 13C) NMR techniques. The MALDI-TOF results show that the oxazoline rings react with the carboxyl chain ends of Ny6 following second-order kinetics. The reactions with amino c…
Voltammetric behaviour of monomeric fac-trioxomolybdenum(VI) complexes with aminocarboxylic ligands in aqueous media
1992
Abstract Cyclic voltammetry, polarography and controlled-potential coulometry experiments have been used to characterize the electrochemical reduction of fac-MoO3L2− complexes (L = aspartic acid or iminodiacetic acid) in aqueous media. These complexes are reduced in two irreversible proton-assisted steps to give an oxo-bridged molybdenum(V) species and then to a molybdenum(III) dimer species. At pH 4.5, the former reduction step for the iminodiacetic acid ligand occurs at Ep = −0.75 V, while the second one appears at −1.12 V vs SCE. The overall electrochemical process can be described in terms of a homogeneous chemical reaction, coupled between two electron transfers (ECE mechanism), that i…
On the Nature of the Enzyme–Substrate Complex and the Reaction Mechanism in Human Arginase I. A Combined Molecular Dynamics and QM/MM Study
2020
We present here a detailed theoretical analysis of L-arginine hydrolysis catalyzed by Human Arginase I (HARGI). Our study combines classical molecular dynamic simulations of different model for the...
Electrosynthesis as a powerful method for the generation of catalytic intermediates: efficient isolation of a palladium aryl halide oxidative additio…
2011
International audience; Polyphosphane ligands of controlled conformation promote highly efficient palladium-catalyzed cross-coupling reactions. Electrosynthesis has been used as a new straightforward method to obtain important intermediates in the search for a better mechanistic understanding. As a proof of concept, the facile synthesis of a phenyl iodopalladium(II) complex (2) was conducted at the electrolysis scale from a readily electrogenerated unstable Pd0 precursor.