| Abstract |
Combined pH-metric and spectrophotometric investigations on the complex formation equilibria of Cu-II with guanylurea (H-2 (1)supercript stopNC(=O) 2supercript stopNH.C(=(NH)-N-3) (NH2)-N-4), hereafter, GuH, in the absence and in the presence of glycine (GlyH), in aqueous solution indicates variety of binary and mixed-ligand complexes: Cu(Gu)(+), Cu(Gu)(OH); Cu(Gu)(2), Cu(Gu-H)(Gu)(-), Cu(Gu-H)(2)(2-), Cu(Gu-H)(Gu-2H)(3-) ; Cu(Gly)(+) , Cu(Gly)(OH); Cu(Gly)(Gu); Cu(Gly)(Gu-H)(-), Cu(Gly)(Gu-2H)(2-); (Gly)Cu(Gu)Cu(Gly)(+) , (Gly)Cu(Gu-H)Cu(Gly) and (Gly)Cu(Gu-2H)Cu(Gly)(-) . At pH < 6, guanylurea anion (Gu(-)) acts as a [(C=O), N-3(-)] or [=(NH)-N-1,N-3(-)] bidentate ligand and above pH 7 it is transformed through a coordination equilibrium into a (=N-1(-), =N-3(-)) bidentate ligand, similar to biguanide dianion. Occurrence of dinuclear complex species, (Gly) Cu(Gu)Cu(Gly)(+) , in the complexation equilibria, indicates bridging double bidentate [((NH2)-N-1, N-3(-)), (C=O, (NH2)-N-4)] and/or [((NH2)-N-1, (NH2)-N-4), (C=O, N-3(-))] chelation by Gu(-) ion in an isomeric equilibrium. Above pH 6.5, the dinuclear complex decomposes mostly to the mononuclear species, Cu(Gly)(OH) and Cu(Gu)(OH) and only partly deprotonates to (Gly)Cu(Gu-H)Cu(Gly) and (Gly)Cu(Gu-2H)Cu(Gly)(-). Electronic spectral shifts, with change of pH have been correlated with the possible modes of coordination of guanylurea species. |
