Comparative multi spectroscopic approach to study the interactions between nitrosyl ruthenium complexes and HSA

Prodrugs are based on metal complexes, which are synthesized in order to develop nitric oxide donor agents1. Nitrosyl ruthenium complexes, like [Ru(L)(tpy)NO]3+ – L1=3,4-diiminebenzoic acid or L2=phenylenediimine –, demonstrated promising results as hypotensive2. In this work, we will demonstrate the multi spectroscopic experimental results about the interactions between RuL1/RuL2 and HSA. Fluorescence suppression results indicate that quenching of HSA is initiated by RuL1 and RuL2 by a dynamic mechanism. The binding constants (Kb) found were 11.00x104 and 3.45x104 L mol-1, respectively, demonstrating the high affinity between complexes and HSA. Thermodynamic parameters obtained suggested that hydrophobic and hydrogen interactions stabilize the HSA–RuL1 and HSA–RuL2 systems, respectively. The average distances between complexes and solo Trp-214, estimated based on Förster's energy theory were 3.01 and 3.38 nm, respectively. Synchronous fluorescence results demonstrated that the RuL1 complex affects the microenvironment conformation near the Trp residue, while RuL2 affects near the Tyr residue.