title: Theoretical study of nucleophilic substitution at the disulfide bridge of cyclo-l-cystine.
abstract: The reaction of cyclo-l-cystine with thiolate is examined at the B3LYP/6-31+G level. The two isomers of cyclo-l-cystine differ in their dihedral angle about the disulfide bond; the M isomer (with dihedral angle of -90.1 degrees) is found to be slightly lower in energy. The nucleophilic substitution reaction at sulfur follows the addition-elimination mechanism, exemplified by the hypercoordinate sulfur intermediate on the reaction surface. The reaction is exergonic (DeltaG = -6.16 kcal mol(-1)), and both the entrance and exit transition state lie below the reactant energies.
authors.affiliation: Department of Chemistry, Trinity University, 715 Stadium Drive, San Antonio, TX 78212, USA. sbachrach@trinity.edu
authors.forename: Steven M
authors.initials: SM
authors.lastname: Bachrach
authors.forename: Adam C
authors.initials: AC
authors.lastname: Chamberlin
mesh_terms: D003500:Cyclization; D003553:Cystine / Q000737:chemistry*; D008962:Models, Theoretical; D008968:Molecular Conformation; D015394:Molecular Structure; D013237:Stereoisomerism; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*
chemical_list: D013438:Sulfhydryl Compounds; D013440:Sulfides; D003553:Cystine