The energetics of nucleophilic opening and closing of protonated disulphide bridges formula presented has been studied for the case of two sulphur-containing (H2S and CH3SH) nucleophiles. The energetics of this reaction was compared to that of the nucleophilic opening and closing of disulphide bridges with thiolate ions: formula presented In the former case a not so good nucleophile is combined with an excellent leaving group, and in the latter case a superior nucleophile is combined with a relatively poor leaving group. The barrier heights for these SN2-type reactions were found to be comparable as calculated by ab initio MO methods. In addition, two oxygen-containing nucleophiles (H2O, HCONH-CH[CH2OH]-CONH2) have also been studied in the following reaction: formula presented The water molecule is not nucleophilic enough to open the disulphide bridge. However, in a serine residue, in which the oxygen of the side-chain OH group is activated through backbone/side-chain hydrogen bonding, the hydroxy group is sufficiently nucleophilic to open the disulphide bridge, just like the sulphur-containing nucleophiles mentioned above.
- Nucleophilic substitution
- S-S linkage
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry