EFFECT OF NI(II) BINDING ON THE TAUTOMERISM OF GUANINE - A QUANTUM-CHEMICAL NDDO INVESTIGATION

Using the semiempirical quantum-chemical method NDDO/MC calculations w ere carried out on some aqua and ammine Ni(II) complexes with the guan ine nucleic base. The results obtained suggest that the greatest influ ence of the transition metal is on the keto-enol tautomerism of guanin e. The effect on the tautomerism is shown to be connected with a charg e transfer from guanine to form a coordinative bond with Ni(II). In th e octahedral Ni(II)-guanine complex the charge transfer from the heter ocycle is small and such a complex stabilizes the keto form. Conversel y, the planar complex facilitates greater charge transfer and leads to stabilization of the enol tautomer.