scholarly journals Heavy Atom Tunneling in Organic Reactions at Coupled Cluster Potential Accuracy with a Parallel Implementation of Anharmonic Constant Calculations and Semiclassical Transition State Theory

2022 ◽  
Author(s):  
Giacomo Mandelli ◽  
Chiara Aieta ◽  
Michele Ceotto
Keyword(s):  
Transition State ◽  
Transition State Theory ◽  
Parallel Implementation ◽  
Heavy Atom ◽  
State Theory ◽  
Organic Reactions ◽  
Coupled Cluster ◽  
Potential Accuracy ◽  
Anharmonic Constant

scholarly journals VRAI-Selectivity: Calculation of Selectivity Beyond Transition State Theory

2021 ◽  
Author(s):  
Sanha Lee ◽  
Jonathan Goodman
Keyword(s):  
Transition State ◽  
Transition State Theory ◽  
Reaction Dynamics ◽  
State Theory ◽  
Organic Reactions

In recent years, a growing number of organic reactions in literature have shown selectivity controlled by reaction dynamics rather than by transition state theory. Such reactions are difficult to analyse...

scholarly journals Dynamic barriers and tunneling. New views of hydrogen transfer in enzyme reactions

2003 ◽  
Vol 75 (5) ◽  
pp. 601-608 ◽  
Author(s):  
J. P. Klinman
Keyword(s):  
Transition State ◽  
Transition State Theory ◽  
Hydrogen Transfer ◽  
Isotope Effects ◽  
Heavy Atom ◽  
Chem Phys ◽  
State Theory ◽  
Tunnel Effect ◽  
Tunneling Model ◽  
Wide Range

Hydrogen-transfer processes are expected to show appreciable quantum mechanical behavior. Intensive investigations of enzymes under their physiological conditions show this to be true in practically every example investigated. Initially, tunneling was treated either as a tunneling correction [cf. Bell, The Tunnel Effect in Chemistry, Chapman & Hall, New York, (l980)], or as corner-cutting [Truhlar et al., J. Chem. Phys. 100, 12771 (l996)]. This worked well as long as the observed properties could be explained by “corrections” to transition-state theory. However, over the past several years, enzymatic behaviors have been observed that are so deviant as to lie outside of transition-state theory. This phenomenon is discussed in the context of the enzyme, soybean lipoxygenase. An environmentally coupled hydrogen-tunneling model is presented that derives from the treatments of Kuznetsov and Ullstrup [Can. J. Chem. 77, 689 (l999)], and includes heavy-atom reorganization (temperature-dependent and largely isotope-independent), together with heavy-atom gating (temperature- and isotope-dependent). This treatment can explain a wide range of behaviors and leads to a new view of the origin of kinetic isotope effects in hydrogen-transfer reactions. These properties link enzyme fluctuations to the hydrogen-transfer reaction coordinate, making a quantum view of H-transfer necessarily a dynamic view of catalysis.

Parallel Implementation of Semiclassical Transition State Theory

2019 ◽  
Vol 15 (4) ◽  
pp. 2142-2153 ◽  
Author(s):  
Chiara Aieta ◽  
Fabio Gabas ◽  
Michele Ceotto
Keyword(s):  
Transition State ◽  
Transition State Theory ◽  
Parallel Implementation ◽  
State Theory

The CH(X2Π) + H2O Reaction: Two Transition State Kinetics

2021 ◽  
Author(s):  
Than Lam Nguyen ◽  
Jozef Peeters
Keyword(s):  
Water Vapor ◽  
Transition State ◽  
Ground State ◽  
Transition State Theory ◽  
State Theory ◽  
Coupled Cluster ◽  
Two Dimensional ◽  
Classical Transition ◽  
High Level

The reaction of ground state methylidyne (CH) with water vapor (H2O) is theoretically re-investigated using high-level coupled cluster computations in combination with semi-classical transition state theory (SCTST) and two-dimensional master...

Microscopic Interpretation of Arrhenius Parameters

2018 ◽  
Author(s):  
Niels Engholm Henriksen ◽  
Flemming Yssing Hansen
Keyword(s):  
Activation Energy ◽  
Transition State ◽  
Transition State Theory ◽  
Average Energy ◽  
Zero Point ◽  
State Theory ◽  
Exponential Factor ◽  
Quantum Tunnelling ◽  
Microscopic Interpretation ◽  
The Difference

This chapter reviews the microscopic interpretation of the pre-exponential factor and the activation energy in rate constant expressions of the Arrhenius form. The pre-exponential factor of apparent unimolecular reactions is, roughly, expected to be of the order of a vibrational frequency, whereas the pre-exponential factor of bimolecular reactions, roughly, is related to the number of collisions per unit time and per unit volume. The activation energy of an elementary reaction can be interpreted as the average energy of the molecules that react minus the average energy of the reactants. Specializing to conventional transition-state theory, the activation energy is related to the classical barrier height of the potential energy surface plus the difference in zero-point energies and average internal energies between the activated complex and the reactants. When quantum tunnelling is included in transition-state theory, the activation energy is reduced, compared to the interpretation given in conventional transition-state theory.

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