A new homoleptic coordination compound of ruthenium and norfloxacin and its interaction with human serum albumin

• The homoleptic complex [Ru(nor)3] (nor = norfloxacinate) has been obtained.
• The coordination of norfloxacin enhances its water solubility.
• The candidate to metalo-drug was characterized by mass spectrometry and UV–visible and IR spectroscopies.
• [Ru(nor)3] interacts with HSA by static or dynamic mechanism, depending on temperature.
• Hydrogen bonds and van der Waal are the main interactions between complex and HSA.

This work presents a new coordination compound of ruthenium and the norfloxacin antibiotics, as well as its interaction with human serum albumin (HSA). The ESI HRMS spectrum of [Ru(nor)3] (nor = norfloxacinate, C16H17FN3O3−) displayed the protonated molecular ion at m/z 1057.3, while the HRMS/MS spectra displayed peaks at m/z 958.4 and 639.3 assigned to the gaseous phase norfloxacin adducts (Hnor)3·H+ and (Hnor)2·H+. Coordination to Ru(III) remarkably enhances the water solubility of norfloxacin. The complex absorption spectrum in aqueous medium is dominated by the norfloxacin transitions in the UV region but also displays a broad shoulder around 370 nm, which possibly overlaps with ligand-field transitions. Stern–Volmer analysis of human serum albumin (HSA) fluorescence quenching by [Ru(nor)3] showed that both dynamic and static mechanisms contribute to the quenching. Lifetime measurements demonstrated that the predominance of one pathway over the other depends on temperature variations. Finally, the analysis of thermodynamic parameters leads to the conclusions that the interaction of the novel complex with HSA is spontaneous and that this interaction occurs through the formation of hydrogen bonds and van der Waals forces (ΔH = − 259.2 kJ/mol and ΔS = − 779.9 kJ/mol·K).

The homoleptic complex [Ru(nor)3] has been synthesized, and the coordination to ruthenium remarkably influences the solubility of norfloxacin, being the [Ru(nor)3] complex fully water soluble. The compound can be properly stored/transported in the body by human serum albumin, since coordinated norfloxacin interacts with HSA through hydrogen bonds and van der Waal interactions.Figure optionsDownload as PowerPoint slide