Ring complexes of S-nitrosothiols with Cu⁺: A density functional theory study

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 (H₂NCH ₂CH₂SNO) and deaminated (HOOCCH₂CH ₂SNO) 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.