A Novel Consideration of Species Distribution of Copper(II)/Histidine System at Physiological pH

Abstract The copper(II)–L‐histidine system plays a pivotal role in copper transport across cell membranes. The coordination mode of copper(II)–L‐histidine species at physiological pH has been elusive in aqueous solution for the last four decades, despite exhaustive characterization studies. Recently, the isolation and the X‐ray crystal structure of the physiological Cu(His)2 complex have been reported. The X‐ray structure is different from all the structures suspected for this complex in solution. We carried out a polarographic analysis to identify copper(II)–L‐histidine species at physiological pH. In our experimental conditions, three copper(II)–L‐histidine species coexist around the physiological pH. These novel considerations can explain the controversy encountered in the investigation of the coordination mode in aqueous solution.