Metal complexes of histamine [4(5)-(2-aminoethyl)imidazole] and isohistamine [2-(2-aminoethyl)imidazole]

Abstract

A study has been made of the copper(II), nickel(II), and cobalt(II) complexes of histamine [4(5)-(2-aminoethyl)imidazole] and ‘isohistamine’[2-(2-aminoethyl)imidazole] in aqueous solution 0·1 M in nitrate ions at 25·0°. The acid dissociation constants of the protonated ligand species HA⁺ and H₂A²⁺ have been measured (A = histamine or isohistamine). Formation curves have been obtained and accurate formation constants for the metal complexes have been calculated by a least-squares method. It is pointed out that in earlier work so-called 2-(2-aminoethyl)imidazole was in fact 4(5)-aminomethyl-2-methylimidazole.