Copper(II) Complexes of Histamine and 3-Methyl Histamine

Abstract

IN previous communications from this laboratory^1–3 evidence has been presented that acid dissociations occur from the 1 : 1 cupric complexes of histidine and histamine. In the presence of equimolar cupric chloride, one equivalent of alkali additional to that needed by either of the ligands alone is required to titrate all the acid produced. When the ligand/ copper(II) ratio is 2 : 1 the amount of alkali required is the same as in the absence of the metal. From these facts it was concluded² that a co-ordinated water molecule and not the hydrogen attached to the uncoordinated imidazole nitrogen was the source of the acid ionization from the 1 : 1 complexes. As a further test of this idea, we have investigated the copper(II) complexes of 3-methyl histamine.