Probing the coordination properties of glutathione with transition metal ions (Cr2+,Mn2+,Fe2+,Co2+, Ni2+,Cu2+,Zn2+,Cd2+,Hg2+) by density functional theory

Complexes formed by reduced glutathione (GSH) with metal cations (Cr(2+), Mn(2+),Fe(2+),Co(2+),Ni(2+),Cu(2+),Zn(2+),Cd(2+),Hg(2+)) were systematically investigated by the density functional theory (DFT). The results showed that the interactions of the metal cations with GSH resulted in nine different stable complexes and many factors had an effect on the binding energy. Generally, for the same period of metal ions, the binding energies ranked in the order of Cu(2+)>Ni(2+)>Co(2+)>Fe(2+)>Cr(2+)>Zn(2+)>Mn(2+); and for the same group of metal ions, the general trend of binding energies was Zn(2+)>Hg(2+)>Cd(2+). Moreover, the amounts of charge transferred from S or N to transition metal cations are greater than that of O atoms. For Fe(2+),Co(2+),Ni(2+),Cu(2+),Zn(2+),Cd(2+) and Hg(2+) complexes, the values of the Wiberg bond indices (WBIs) of M-S (M denotes metal cations) were larger than that of M-N and M-O; for Cr(2+) complexes, most of the WBIs of M-O in complexes were higher than that of M-S and M-N. Furthermore, the changes in the electron configuration of the metal cations before and after chelate reaction revealed that Cu(2+), Ni(2+),Co(2+) and Hg(2+) had obvious tendencies to be reduced to Cu(+),Ni(+),Co(+) and Hg(+) during the coordination process.