Theoretical studies of thiols and disulfides. Conformations,barriers and proton affinities

Results from an ab-initio MO LCAO SCF study of RSSR, RSH and RS^? (R = H, CH₃) in a minimal and a double zeta basis and cysteine COO^?CH(NH⁺₃)CH₂SH] and cysteine anion in a minimal basis are reported. The barriers and conformational preference of the disulfides are discussed and it is suggested that their origin is more confined to the disulfide region than previously believed. The proton affinities of the different RS^? ions are calculated, whereas the protonation of the disulfide bond is studied by use of the molecular electrostatic potential. The good agreement of the results in the minimal and the double zeta basis is discussed.