Substituent effects on OH bond strength and hyperfine properties of phenol, as model for modified tyrosyl radicals in proteins

• Density functional theory is used to investigate the effects of a variety of substituents (CH3, OH, OCH3, SH, SCH3, NH2, NMe2, NO2, F, Cl, CN, and imidazole) on the phenol O-H 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 O-Me bond strengths can thus not correctly describe the effects on ortho-substituted phenol O-H 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.

Nyckelord

phenol

substituent effects

radical

density functional theory

bond dissociation energy

cytochrome-c-oxidase

ribonucleotide reductase

galactose-oxidase

electron-transfer

photosystem-ii

density

dissociation

exchange

anisoles

energy

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)