Screening of metal complex–amino acid side chain interactions by potentiometric titration

Reversible coordination of amino acid side chains to metal complexes is widely used in protein purification (IMAC technique), but available data on affinity and selectivity of such binding processes are limited. We use potentiometric titration of a series of metal complexes with vacant coordination sites in the presence of molecules resembling amino acid side chain functionalities to screen for new affinities. The investigation confirms documented affinities of imidazole to nickel(II) and copper(II) IDA and NTA complexes, and discovers a hitherto unknown binding of zinc(II)- and cadmium(II) cyclen complexes to imidazole.

Graphical abstractThe interaction of amino acid side chain functional groups with IDA, NTA and cyclen metal complexes was investigated by potentiometric titrations. In addition to already know interactions of M(II)–IDA/M(II)–NTA with imidazole, binding of imidazole to M(II)–cyclen was discovered.Figure optionsDownload full-size imageDownload as PowerPoint slide