Chiroptical properties of cyclo-L-cystine

Abstract

The chiroptical properties associated with the two lowest-energy disulphide transitions in cyclo-L-cystine are calculated on an independent systems model in which both static coupling and dynamic coupling between the dioxopiperazine and disulphide moieties are considered. The structure of cyclo-L-cystine requires that the dihedral angle within the disulphide group be nearly ±90°, with both P and P chirality permitted. Special emphasis is placed on calculating the vicinal contributions to disulphide optical activity arising from dissymrretric interactions between the dioxopiperazine and disulphide moieties. Available circular dichroism spectra of cyclo-L-cystine in solution are discussed and interpreted in terms or the calculated results.