Study of the probable reason why Ni(II) is excluded from metalloenzymes

Abstract

The formation constants of the complexes of the type [NiAL], where A=2,2′-bipyridyl, 1,10-phenanthroline, 2-(2′-pyridyl) benzimidazole, or 2-(2′-pyridyl) imidazoline and L=ethylenediamine, 1,2-diaminopropane, N-methyl-ethylenediamine, glycine, α-alanine, β-alanine, malonate, histidine, or histamine have been determined in dioxan-water (1∶1 v/v) medium and μ=0·2 mol dm⁻³ NaClO₄ at 30°C. The values of ΔlogK _M (logK ^MA_MAL −logK ^M_ML ) in Ni(II) complexes have been compared with corresponding Cu(II) complexes. It is observed that for [NiAL] complexes, where L=L¹ to L⁷, ΔlogK is more negative than for the corresponding [CuAL] complexes whereas in cases where L=L⁸, or L⁹, ΔlogK for Ni(II) complexes is less negative than for the corresponding Cu(II) complexes. The reason has been discussed.