The interaction of half-sandwich (η5-Cp)Rh(III) cation with histidine containing peptides and their ternary species with (N,N) bidentate ligands

Our goal was to explore the possible interactions of the potential metallodrug (η5-Cp*)Rh(III) complexes with histidine containing biomolecules (peptides/proteins) in order to understand the most important thermodynamic factors influencing the biospeciation and biotransformation of (η5-Cp*)Rh(III) complexes. To this end, here we report systematic solution thermodynamic and solution structural study on the interaction of (η5-Cp*)Rh(III) cation with histidine containing peptides and their constituents ((N-methyl)imidazole, GGA-OH, GGH-OH, histidine-amide, HGG-OH, GHG-NH2), based on extensive 1H NMR, ESI-MS and potentiometric investigations. The comparative evaluation of our data indicated that (η5-Cp*)Rh(III) cation is able to induce the deprotonation of amide nitrogen well below pH 7. Consequently, at physiological pH the peptides are coordinated to Rh(III) by tridentate manner, with the participation of amide nitrogen. At pH 7.4 the (η5-Cp*)Rh(III) binding affinity of peptides follow the order GGA-OH