Vibrational studies of the disulfide group in proteins : Part II. Ab initio force fields and normal mode frequencies of dimethyl, methylethyl, and diethyl disulfides

Abstract

The geometric parameters and quadratic force constants of dimethyl disulfide, methylethyl disulfide, and diethyl disulfide in all their stable conformations and transition state conformations have been obtained from ab initio Hartree--Fock calculations with a 3-21G* basis set. Thirteen scale factors applied to the ab initio force field allow the reproduction of 62 observed frequencies with an average error of 0.5%. Relationships between the SS and CS stretch frequencies and the conformer internal rotation geometry are obtained. The results reported here provide a good basis for further investigation of the vibrational spectra of proteins containing cystine residues.