Search results for "Reactivity"

Molecular dynamics simulation in aqueous solution of N -methylazetidinone as a model of β -lactam antibiotics

1999

In this article, we analyze the results of a molecular dynamics simulation in aqueous solution of the N-methylazetidinone molecule, often used to model β-lactam antibiotics. The radial distribution functions (RDFs) corresponding to the most interesting atoms, in terms of reactivity, are presented. We focus our study on the effect of a polar environment on the molecule. The solvent structure around the system is compared to the structure of β-lactam-water complexes, as obtained in a previous study of reaction mechanisms for the neutral and alkaline hydrolyses of N-methylazetidinone. Two types of complexes have been considered which are related to different hydrolysis mechanisms having simila…

Computational simulations on the binding and reactivity of a nitrile inhibitor of the SARS-CoV-2 main protease.

2021

We present a detailed computational analysis of the binding mode and reactivity of the novel oral inhibitor PF-07321332 developed against the SARS-CoV-2 3CL protease. Alchemical free energy calculations suggest that positions P3 and P4 could be susceptible to improvement in order to get a larger binding strength. QM/MM simulations unveil the reaction mechanism for covalent inhibition, showing that the nitrile warhead facilitates the recruitment of a water molecule for the proton transfer step.

The Mechanism of Diene Polymerisation by Organolanthanide Catalysts Deduced from Microwave Experiments

2005

Isoprene polymerisation performed under microwave irradiation with [Nd(BH 4 ) 3 (THF) 3 ]/Mg(Bu) 2 and [Nd-(BH 4 ) 3 (THE) 3 ]/Al(Et) 3 showed an enhancement in reactivity, with selectivity being only slightly modified. An explanation of the observed effect is proposed based on our current knowledge of the catalytic mechanism and by considering the alkylated complex as an ion pair. An analogy is proposed with the pseudoanionic polymerisation of oxygenated monomers. Finally, depolymerisation is observed under microwave irradiation at high temperature.

Residual Stresses and Reactivity of Solids. Determination and Part Plaid in the Reaction Mechanisms

1996

An ab initio study on the mechanism of the F+O3→FO+O2 reaction: comparative reactivity study along the isoelectronic NH2, OH and F radicals series

2004

Abstract The title reaction has been theoretically studied by using MP2, QCISD, QCISD(T), CCSD(T), CASSCF, and CASPT2 methods with various basis sets. At single-reference MP2 and QCISD levels of theory, the potential energy hypersurface (HPES) shows a two-step reaction mechanism through two transition states (TS1 and TS2) and an intermediate (Int). However, the multiconfigurational CASSCF HPES shows a one-step reaction mechanism, as was previously found for the NH2 + O3 and OH + O3 reactions. The results show that the reactivity of the isoelectronic series of NH2, OH, and F radicals increases from the amino radical to the fluorine atom.

Role of the functional group in n-octydimethylsilanes in the synthesis of C8 reversed-phase silica packings for high-performance liquid chromatography

1986

Abstract C8 reversed-phase packings have been sysnthesised by reaction of a 25-nm pore-size high-performance liquid chromatographic silica (10 μm, as(BET) = 297 m2 g-1) with 2,4-lutidine as base and dichloromethane and N,N-dimethylflormamide as solvents, or without solvents and with the following silanes: n-octyldimenthylchlorosilane (C8-Cl), n-octyldimethylhydroxysilane (C8-OH), n-octyldimethylmethoxysilane (C8-OCH3), n-octyldimethylethoxysilane (C8-OC2H5), n-octyldimethyl(dimethylamino) silane [C8-N(CH3)2], n-octyldimethyl(trifluoroacetoxy)silane (C8- OCOCF3), and bis-(n-octyldimethylsiloxane) (C8-O-C8). C8-Cl, C8-OH and C8-OCH3 each form a reactive intermediate with 2,4-lutidine, favouri…

A study of the mechanism of the oxidative cyclization of benzaldehyde semicarbazones induced by cupric perchlorate in acetonitrile

1995

Treatment of benzaldehyde semicarbazones 1a-i with cupric perchlorate in acetonitrile at 40 provided selectively the corresponding 1,2,4-triazolin-5-ones 2a-i. The relative rate constants for 2a-i formation were determined by the competitive method. The results obtained showed that electron-donating substituents (methyl and methoxy) increase the reaction rate, while the reverse was found for electron-withdrawing substituents (chloro and nitro group). The reactivity data are discussed on the grounds of two possible mechanisms.

Kinetik der Bromierung von Phenolen und phenolischen Mehrkernverbindungen, 1. Mechanismus und meßmethode

1975

Die Bromierung von 2-(2-Hydroxy-5-methylbenzyl)-4,6-dimethylphenol (1) und 2-[2-Hydroxy-3-(2-hydroxy-5-methylbenzyl)-5-methylbenzyl]-4,6-dimethylphenol (2a) wurde in Eisessig bei 22°C untersucht. Die Reaktion last sich fur [Br2]0 = 1,4·10−3 bis 6,0·10−3 mol dm + und Konzentrationen der phenolischen Verbindungen [P]0 zwischen 1,1·10−3 und 5,5·10−3mol dm−3 durch das folgende Geschwindigkeitsgesetz beschreiben: Wahrend die gebildete Bromverbindung keinen Einflus auf die Reaktionsgeschwindigkeit hat, verlangsamt der entstehende Bromwasserstoff die Reaktion. Die Bromierung ist trotzdem zur Bestimmung der Reaktionsfahigkeit von Phenolen und phenolischen Mehrkernverbindungen gut geeignet, da die R…

A Quantitative Model for Alkane Nucleophilicity Based on C−H Bond Structural/Topological Descriptors

2020

A first quantitative model for calculating the nucleophilicity of alkanes is described. A statistical treatment was applied to the analysis of the reactivity of 29 different alkane C−H bonds towards in situ generated metal carbene electrophiles. The correlation of the recently reported experimental reactivity with two different sets of descriptors comprising a total of 86 parameters was studied, resulting in the quantitative descriptor‐based alkane nucleophilicity (QDEAN) model. This model consists of an equation with only six structural/topological descriptors, and reproduces the relative reactivity of the alkane C−H bonds. This reactivity can be calculated from parameters emerging from th…

Preferential CO oxidation over catalysts with well-defined inverse opal structure in microchannels

2008

Catalyst supports of CeO 2 /SiO 2 and Al 2 O 3 with three-dimensionally ordered macroporous structure were fabricated in microchannels by application of PMMA opals as templates. Pt-Rh supported on CeO 2 /SiO 2 showed high efficiency for CO removal in preferential CO oxidation in the presence of excess hydrogen. Pt-Rh supported on Al 2 O 3 with an inverse opal structure showed higher reactivity than that supported on wash-coated Al 2 O 3 layers in microchannel reactor.