Interaction of the nitrosyl ruthenium complex [Ru^II (NH.NHq‐R)(tpy)NO]³⁺ with human serum albumin: a spectroscopic and computational investigation

Abstract The interaction between two nitrosyl ruthenium complexes [Ru (NH.NHq–COOH)(tpy)NO](PF 6 ) 3 (RuBDQ) and [Ru (NH.NHq–H)(tpy)NO](PF 6 ) 3 (RuBD) and human serum albumin (HSA) was investigated using spectroscopic and computational methods. From fluorescence experiments, a dynamic quenching mechanism and binding constants at a single site demonstrated the higher stability of the RuBDQ–HSA system at 308 K compared with RuBD–HSA. Thermodynamic parameters indicated that binding of RuBDQ and RuBD to HSA was mainly driven by hydrophobic interaction and hydrogen bonding, respectively. Synchronous fluorescence and FT‐IR results suggested that interactions between both nitrosyl ruthenium complexes and HSA affected protein conformation. Competition experiments revealed that RuBDQ and RuBD bound to Sudlow sites I and II, respectively. Molecular docking results showed that RuBDQ interacted with Ser‐192 and Ala‐291 residues via hydrogen bonding and polar contact, respectively, whereas RuBD associated with Asn‐391 via a polar interaction. Noncovalent interaction results suggested that van der Waals interactions were the main binding forces for both systems, i.e. RuBDQ associated with Trp‐214 via van der Waals interaction and with Ty‐150 via dipole–dipole bonding, whereas RuBD associated with Tyr‐452 via van der Waals forces. The Asp‐391 residue interacted with the nitrosyl ligand via polar contact and the terpyridine ligand via van der Waals interaction.