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Electron Capture by the Thiyl Radical and Disulfide Bond: Ligand Effects on the Reduction Potential
Author(s) -
Roos Goedele,
De Proft Frank,
Geerlings Paul
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201203188
Subject(s) - chemistry , ligand (biochemistry) , redox , polar , electron transfer , disulfide bond , ion , electron affinity (data page) , crystallography , stereochemistry , photochemistry , computational chemistry , molecule , inorganic chemistry , receptor , organic chemistry , biochemistry , physics , astronomy
The effect of non‐polar and polar ligands and of monovalent cations on the one‐electron reduction potential of the thiyl radical and the disulfide bond was evaluated. The reduction potentials E ° for the CH 3 S . – n L/CH 3 S − – n L and CH 3 SSCH 3 –L/CH 3 SSCH 3 .− –L redox couples were calculated at the B3LYP, M06‐2X and MP2 levels of theory, with n =1, 2 and L=CH 4 , C 2 H 4 , H 2 O, CH 3 OH, NH 3 , CH 3 COOH, CH 3 CONH 2 , NH 4 + , Na + , K + and Li + . Non‐polar ligands decrease the E ° value of the thiyl radical and disulfide bond, while neutral polar ligands favour electron uptake. Charged polar ligands and cations favour electron capture by the thiyl radical while disfavouring electron uptake by the disulfide bond. Thus, the same type of ligand can have a different effect on E ° depending on the redox couple. Therefore, properties of an isolated ligand cannot uniquely determine E °. The ligand effects on E ° are discussed in terms of the vertical electron affinity and reorganization energy, as well as molecular orbital theory. For a given redox couple, the ligand type influences the nature of the anion formed upon electron capture and the corresponding reorganization process towards the reduced geometry.