Studying the interaction between trinuclear ruthenium complexes and human serum albumin by means of fluorescence quenching

This work reports for the first time a systematic investigation of the interaction between HSA and trinuclear ruthenium complexes, by using fluorescence spectroscopy and the Stern-Volmer model. The compounds investigated have general formula [Ru3O(CH3COO)6(3-pic)2(L)]PF6, where L=NO or H2O and 3-pic=3-methylpyridine. For both complexes it was observed that the increase of Ksv values (in the order of 104 M−1) with increasing temperature, signaling a dynamic quenching of HSA fluorescence. However, analysis of the quenching rate constants and Kb values shows that the contribution of the static quenching is significant. Particularly in the case of the nitrosyl complex, the relatively high value of Kb observed (178.44×103 M−1, 308 K) suggests that this compound can be efficiently stored and transported in the body by HSA. The interaction of the complexes with HSA is spontaneous (ΔG<0). Complex [Ru3O(CH3COO)6(3-pic)2(NO)]PF6 displays interaction with HSA by hydrophobic forces (∆H=215 kJ mol−1 and ∆S=796 J mol−1 K−1), likely because of the nitrosyl lipophilicity, while complex [Ru3O(CH3COO)6(3-pic)2(H2O)]PF6 is involved in the formation of hydrogen bonds with HSA (∆H=−75.5 kJ mol−1 and ∆S=−231 J mol−1 K−1), through its aquo ligand.