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 K-SV, values (in the order of 10(4) M-1) with increasing temperature, signaling a dynamic quenching of HSA fluorescence. However, analysis of the quenching rate constants and K-b values shows that the contribution of the static quenching is significant. Particularly in the case of the nitrosyl complex, the relatively high value of K-b observed (178.44 x 10(3) 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 (Delta G < 0). Complex [Ru3O(CH3COO)(6)(3-pic)(2)(L)]PF6 displays interaction with HSA by hydrophobic forces (Delta H=215 kJ mol(-1) and Delta S=796 J mol(-1) K-1), likely because of the nitrosyl lipophilicity, while complex Ru3O(CH3COO)(6)(3-pic)(2)(L)]PF6 is involved in the formation of hydrogen bonds with HSA (Delta H= -75.5 kJ mol(-1) and AS = -231 J mol(-1) K-1), through its aquo ligand. (C) 2015 Elsevier B.V. All rights reserved.