Ring complexes of S-nitrosothiols with Cu+:: a density functional theory studyt

The density functional theory (DFT) method B3P86/6-311+G(2df,p) has been employed to investigate the complexes formed upon interaction of Cu+ with nitrosylated cysteine (CysNO) and its decarboxylated (H2NCH2CH2SNO) and deaminated (HOOCCH2CH2SNO) derivatives. Optimized structures, relative enthalpies and relative free energies have been calculated and compared. In addition, the effects of binding an H2O molecule to the Cu+ centre in the resulting complexes have also been considered. It is found that the most stable complexes are formed when Cu+ coordinates to the S-nitrosothiol via S of the -SNO group. This results in dramatic lengthenings of the S-N bond with concomitant shortening of the N-O bond. In contrast, when Cu+ coordinates via the nitrogen of the -SNO group, a shortening of the S-N bond with lengthening of the N-O bond is observed. These effects are tempered by the electron donating ability of other functional groups also coordinated with the Cu+ centre in the complexes and on the coordination state of the Cu+ ion.