NO-GROUP TRANSFER (TRANSNITROSATION) BETWEEN S-NITROSOTHIOLS AND THIOLS .2.

The kinetics of NO-group transfer have been measured for the reaction between a nitrosothiol (HOCH2CH2SNO) and nine thiols, mostly based on the cysteine structure. The reaction is second-order and there is evid ence for a steric effect for thiols containing 1,1-dimethyl substituen ts (penicillamine derivatives). Reaction occurs via the thiolate anion as shown by the pH-rate constant profile, and a full kinetic analysis for the reactions of two thiols (N-acetylcysteine and glutathione) is quantitatively in agreement with this mechanism. Variation of the nit rosothiol structure for reaction with N-acetylcysteine shows that elec tron-withdrawing substituents in the nitrosothiol promote reaction; th ere is a similarity with the corresponding reactions of alkyl nitrites .