ct6b00007_si_001.xlsx (83.15 kB)
α‑Hydrogen Abstraction by •OH and •SH Radicals from Amino Acids and Their Peptide Derivatives
dataset
posted on 2016-03-07, 14:48 authored by Bun Chan, Amir Karton, Christopher J. Easton, Leo RadomWe have used computational quantum
chemistry to investigate the
thermochemistry of α-hydrogen abstraction from the full set
of amino acids normally found in proteins, as well as their peptide
forms, by •OH and •SH radicals. These reactions, with
their reasonable complexity in the electronic structure (at the α-carbon),
are chosen as a consistent set of models for conducting a fairly robust
assessment of theoretical procedures. Our benchmarking investigation
shows that, in general, the performance for the various classes of
theoretical methods improves in the order nonhybrid DFT → hybrid
DFT → double-hybrid DFT → composite procedures. More
specifically, we find that the DSD-PBE-P86 double-hybrid DFT procedure
yields the best agreement with our high-level W1X-2 vibrationless
barriers and reaction energies for this particular set of systems.
A significant observation is that, when one considers relative instead
of absolute values for the vibrationless barriers and reaction energies,
even nonhybrid DFT procedures perform fairly well. To exploit this
feature in a cost-effective manner, we have examined a number of multilayer
schemes for the calculation of reaction energies and barriers for
the abstraction reactions. We find that accurate values can be obtained
when a “core” of glycine plus the abstracting radical
is treated by DSD-PBE-P86, and the substituent effects are evaluated
with M06-2X. Inspection of the set of calculated thermochemical data
shows that the correlation between the free energy barriers and reaction
free energies is strongest when the reactions are either endergonic
or nearly thermoneutral.