title: Thiyl radicals abstract hydrogen atoms from the (alpha)C-H bonds in model peptides: absolute rate constants and effect of amino acid structure.
abstract: Thiyl radicals are important intermediates in biological oxidative stress and enzymatic reactions, for example, the ribonucleotide reductases. On the basis of the homolytic bond dissociation energies (BDEs) only, the (alpha)C-H bonds of peptides and proteins would present suitable targets for hydrogen abstraction by thiyl radicals. However, additional parameters such as polar and conformational effects may control such hydrogen-transfer processes. To evaluate the potential of thiyl radicals for hydrogen abstraction from (alpha)C-H bonds, we provide the first absolute rate constants for these reactions with model peptides. Thiyl radicals react with (alpha)C-H bonds with rate constants between 1.7 x 10(3) M(-1) s(-1) (N-acetylproline amide) and 4 x 10(5) M(-1) s(-1) (sarcosine anhydride). However, the correlation of rate constants with BDEs is poor. Rather, these reactions may be controlled by conformation and dynamic flexibility around the (alpha)C-H bonds.
authors.affiliation: Department of Pharmaceutical Chemistry, University of Kansas, 2095 Constant Avenue, Lawrence, Kansas 66047, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Nauser
authors.forename: Christian
authors.initials: C
authors.lastname: Schöneich
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D003543:Cysteamine / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D007700:Kinetics; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry*; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D000596:Amino Acids; D005609:Free Radicals; D010455:Peptides; D003543:Cysteamine; D006859:Hydrogen