Transition state

About: Transition state is a research topic. Over the lifetime, 4978 publications have been published within this topic receiving 117965 citations. The topic is also known as: transition state of elementary reaction.

Locating all transition states and studying the reaction pathways of potential energy surfaces

Abstract: We propose a new method for calculating all stationary states, including saddle points of all orders, of a potential energy surface based on the αBB deterministic branch and bound global optimization algorithm. This method is based on rigorous optimization methods and offers a theoretical guarantee of enclosing all solutions to the equation ∇V=0. We apply this method to Murrel–Sorbie analytic potential energy surfaces of HCN, HSiN, HBO, and CS2, and to the Empirical Conformational Energy Program for Peptides (ECEPP/3) potential energy surfaces of alanine, alanine dipeptide, and tetra-alanine. For alanine, alanine dipeptide, and tetra-alanine, we proceed to analyze the topography of the potential energy surface by calculating reaction pathways, transition rate matrices, time-evolution of occupation probabilities, and rate disconnectivity graphs.

Deuterium and tritium exchange in enzyme kinetics.

Abstract: The theory of the isotopic exchange of deuterium and tritium between an enzyme-substrate complex and the solvent is derived for 16 different types of experiment involving measurements of initial velocities and of the isotopic content of the reactants and products as a function of the extent of reaction. It is shown how the data from these experiments can be analyzed to obtain the rate constants for the individual steps and thereby the Gibbs free energies of the intermediates and transition states in the reaction. The effects of isotopic substitution on each intermidiate and transition state are also found and this allows conclusions to be drawn as to the extent to which a proton is in flight in a particular transition state. Neither substrate handling (that is, on-off steps), nor the isotopic exchange with the solvent, is assumed to be rapid.

Decomposition of beta -hydroxypropoxy radicals in the oh-initiated oxidation of propene. a theoretical and experimental study

Abstract: Environmental chamber studies of the OH-initiated oxidation of propene have been carried out in the presence of nitrogen oxides under conditions relevant to the atmosphere. The major products observed at all temperatures studied (220−300 K) are CH2O and CH3CHO, indicating that the β-hydroxypropoxy radicals formed in the oxidation process (from reaction of the corresponding β-hydroxypropylperoxy radicals with NO) predominantly undergo unimolecular decomposition. A full theoretical study of the chemistry of the dominant β-hydroxypropylperoxy, β-hydroxypropylperoxynitrite, and β-hydroxypropoxy species has been carried out. On the basis of B3LYP-DFT/6-31G** quantum chemical characterizations, the most stable conformations of the oxy radicals are found to contain intramolecular hydrogen bonds, which provide stabilizations of about 2 kcal/mol. The internal hydrogen bond in the lowest-energy oxy species is found to persist in the transition states for C−C bond rupture, which keeps the barrier to their decomposit...