Circulardichroismus des disulfidchromophors in S-alkylthio-L-cysteinen und L-glutathion

Abstract

The inherently dissymmetric disulfide chromophore imparts two optically active transitions with opposite signs at 250 nm to molecules related to L-cystine and possessing a disulfide grouping C-S-S-C with P- or M-helical arrangement. The transition of this intrinsically optically active chromophore exhibits a strong dependence of its rotational strength on the torsional angle ϕ. The open-chain S-alkylthio-L-cysteines show large temperature coefficients of their two negative Cotton effects at 250 nm and 200 nm in the range of 0°C to 100°C in acidic aqueous medium. For the S-S-chromophore of oxidized L-glutathione a similarly strong temperature dependence is found. On the other hand, the carbonyl part of these molecules shows the normal Kauzmann-Eyring effect. The dissociation equilibria largely influence the magnitude and position of the disulfide Cotton effects. With increasing pH bathochromic shifts of the 250 nm disulfide band are found.