Elementary reaction

About: Elementary reaction is a research topic. Over the lifetime, 2972 publications have been published within this topic receiving 76110 citations.

Adapting the nudged elastic band method for determining minimum-energy paths of chemical reactions in enzymes.

Abstract: Optimization of reaction paths for enzymatic systems is a challenging problem because such systems have a very large number of degrees of freedom and many of these degrees are flexible. To meet this challenge, an efficient, robust and general approach is presented based on the well-known nudged elastic band reaction path optimization method with the following extensions: (1) soft spectator degrees of freedom are excluded from path definitions by using only inter-atomic distances corresponding to forming/breaking bonds in a reaction; (2) a general transformation of the distances is defined to treat multistep reactions without knowing the partitioning of steps in advance; (3) a multistage strategy, in which path optimizations are carried out for reference systems with gradually decreasing rigidity, is developed to maximize the opportunity of obtaining continuously changing environments along the path. We demonstrate the applicability of the approach using the acylation reaction of type A β-lactamase as an example. The reaction mechanism investigated involves four elementary reaction steps, eight forming/breaking bonds. We obtained a continuous minimum energy path without any assumption on reaction coordinates, or on the possible sequence or the concertedness of chemical events. We expect our approach to have general applicability in the modeling of enzymatic reactions with quantum mechanical/molecular mechanical models.

Ab initio evaluation of primary cyclo-hexane oxidation reaction rates

Abstract: Naphthenes are chemical species that are always present in liquid hydrocarbon fuels and their pyrolysis and oxidation can play an important role in real liquid fuel combustion. In spite of its practical relevance, the chemical kinetics of naphthene pyrolysis and oxidation is not yet thoroughly investigated and there is not a general agreement on the role and rate of several elementary reactions involved. In this paper, the kinetics of the pyrolysis and oxidation of a simple naphthene, namely cyclo -hexane, has been investigated through detailed kinetic modeling. Ab initio calculations were performed to estimate the kinetic parameters of some primary reactions following the oxygen attack to the cyclo -hexane radical. In fact, due to the complex behavior induced by the ring structure of cyclo -hexane, such data were difficult to determine through thermo-chemical methods. Density functional theory (B3LYP/6-31g(d, p)) was adopted to determine structure and vibrational frequencies of transition states and reaction intermediates, while energies were evaluated using the G2MP2 approach. The kinetic parameters of the investigated primary reactions were then introduced in a general detailed kinetic model consisting of elementary reactions whose kinetic constants were taken from the literature. The so obtained kinetic model was used to simulate ignition delay times and species concentrations measured in various experiments reported in the literature. The agreement between experimental data and theoretical predictions shows the validity of the chosen approach and supports the correctness of the proposed kinetic model.

Absolute rate constants for the reactions O(3P) atoms with HCl and HBr

Abstract: A flow tube method has been used to determine rate constants for the elementary reactions: Oxygen atoms were produced by adding a small excess of NO to a stream of partially dissociated nitrogen, and their reaction with hydrogen halide was monitored by observing the intensity of the NO + O afterglow Experiments were carried out at temperatures from 293 to 440°K with HCl, and from 267 to 430°K with HBr The role of secondary reactions was minimised and the residual effects were allowed for The rate constants for the primary reactions could be matched by Arrhenius expressions: where the units are cm3/molec·sec and the errors correspond to a standard deviation

Highly effective synthesis of ethanol by CO2-hydrogenation on well balanced multi-functional FT-type composite catalysts

Abstract: Novel composite catalysts for selective synthesis of ethanol by hydrogenation of carbon dioxide have been developed. The three different kinds of elementary reaction functions for ethanol synthesis were undertaken. These catalytic functions were partial-reduction of CO 2 to CO, C–C bond formation, and –OH group formation. Furthermore, in order to stabilize the optimum reductive state of the catalyst during reaction under a high conversion or a high reaction rate condition, both hydrogen spillover and inverse spillover functions were combined with the above-mentioned composite catalysts. Based on the properties of the elemental catalysts to be combined, their adopting ratios and configurations were most appropriately chosen. As a result, ethanol could be synthesized by exceeding the value, which was expected from the Schultz–Flory (SF) probability law for the distribution of alcohols having different carbon numbers. The highest STY of ethanol amounted to 874 or 476 g l −1 h −1 under the conditions of CO 2 conversion of 31.1% or 54.5%, respectively, applying different catalyst combinations and reaction conditions.