Mercury binding by ferrocenoyl peptides with sulfur-containing side chains: Electrochemical, spectroscopic and structural studies

Ferrocenoyl peptides incorporating amino acids derived from either l-methionine, l-cysteine or dl-homocysteine have been synthesised and investigated as agents for heavy metal binding and detection. Heavy metal–peptide interactions have been characterised using cyclic voltammetry to follow changes in the potential of the Fe(II)/Fe(III) redox couple, revealing that these systems interact with mercury(II) ions more strongly than with other thiophilic heavy metals such as cadmium(II), silver(I) and lead(II). Proton NMR experiments have demonstrated 1:1 peptide:mercury binding and enabled quantitative characterisation of this binding interaction. Crystal structures for two of these ferrocenoyl peptide derivatives have been elucidated, revealing that these compounds adopt a P-1,3′ open solid state conformation in the absence of mercury; this arrangement precludes intramolecular hydrogen bonding between chains, while extensive intermolecular hydrogen bonding is evident. The particular affinity of these systems for mercury(II) opens the possibility of incorporating them in new, biologically inspired sensors for detecting this toxic pollutant.