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Substituent effects on OH bond strength and hyperfine properties of phenol, as model for modified tyrosyl radicals in proteins
Author(s) -
Himo Fahmi,
Eriksson Leif A.,
Blomberg Margareta R. A.,
Siegbahn Per E. M.
Publication year - 2000
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(2000)76:6<714::aid-qua4>3.0.co;2-f
Subject(s) - chemistry , substituent , intramolecular force , radical , hydrogen bond , imidazole , anisole , hyperfine structure , bond dissociation energy , photochemistry , galactose oxidase , radical ion , computational chemistry , stereochemistry , medicinal chemistry , dissociation (chemistry) , organic chemistry , ion , molecule , enzyme , physics , quantum mechanics , catalysis
Density functional theory is used to investigate the effects of a variety of substituents (CH 3 , OH, OCH 3 , SH, SCH 3 , NH 2 , NMe 2 , NO 2 , F, Cl, CN, and imidazole) on the phenol OH bond dissociation energy (BDE) and phenoxyl radical hyperfine properties. Substitutions are made at the ortho position to model modified tyrosine residues found in enzymes. The calculations show that besides the electronic effects of the substituents, intramolecular hydrogen bonds between OH and the substituents will contribute considerably to stabilize the parent species. Substituent effects on anisole OMe bond strengths can thus not correctly describe the effects on ortho‐substituted phenol OH bond strengths, as previously proposed. This fact is supported by a series of calculations on o ‐substituted anisoles. The odd‐alternant spin pattern of the phenoxyl radical is conserved for most of the substitutions. In particular, it is predicted that the cysteine crosslink to tyrosine, present in the radical enzyme galactose oxidase, and the histidine crosslink, present in cytochrome‐ c oxidase, will only have minor effects on the BDE and the radical hyperfine coupling constants and spin distribution of the tyrosyl radical. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 76: 714–723, 2000