Theoretical study of nucleophilic substitution at the disulfide bridge of cyclo-l-cystine.
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.
Bachrach
Steven M
SM
Department of Chemistry, Trinity University, 715 Stadium Drive, San Antonio, TX 78212, USA. sbachrach@trinity.edu
Chamberlin
Adam C
AC
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*
D013438:Sulfhydryl Compounds; D013440:Sulfides; D003553:Cystine