Coordination of a bishistidine oligopeptide with Ga3+ ion in aqueous solution,

The development of radioisotopes of inorganic elements (as 68Ga(III) and 188Re(I)) has gained much interest in recent years for diagnostic and therapeutic application in nuclear medicine1. Small peptides are employed for complexing the radiometal in a biologically stable environment. They have some advantages: easy of synthesis and modification, tumorpenetrating ability and good biocompatibility2. Aim of the present work has been the interaction between Ga3+ ion with a bishistidine oligopeptide, PHIS (Fig.1) in aqueous solutions, by the following methods: Potentiometry, Spectrofluorimetry, FT−IR and 1HNMR Spectroscopy as also by Circular Dichroism. All the measurements have been investigated at 25 °C in 0.1 M NaClO4 media. Information on coordination sites are obtained with model molecule such as histidine (His). By processing the experimental data, it has been possible to obtain the complexation constants. Spectroscopy data are in agreement with the potentiometric measurement. 1H-NMR measurements conducted in H2O as solvent at different metal/ligand ratio indicate that imidazolic rings are involved in coordination with metal ions investigated .