Protein binding and antioxidant studies of diimine based emissive surfactant–ruthenium(II) complexes

Abstract

Biophysical interaction of amphiphilic fluorescent surfactant–ruthenium(II) complexes and its precursor ruthenium(II) complexes with drug carrying proteins such as bovine and human serum albumins (BSA and HSA) have been studied through the UV-visible absorption, fluorescence and circular dichroism spectroscopic techniques to correlate the impact of head and tail groups of the metallosurfactants towards the designing of metallodrugs for the biomedical applications. The obtained results showed that both precursor– and surfactant–ruthenium(II) complexes interact with BSA/HSA via ground state protein–complex formation and their quenching follows the static mechanism. The extent of protein quenching and binding parameters resulted that the surfactant–ruthenium(II) complexes effectively interact with protein compared to their precursor–ruthenium(II) complexes, and also those interaction have greatly influenced by the change in the head group size compared to change in the tail group length. Interestingly on increasing the temperature, the protein–complex binding strength was decreased for the precursor–ruthenium(II) complexes, those increased for the surfactant–ruthenium(II) complexes, probably due to the respective involvement of electrostatic and hydrophobic interactions as supported by the thermodynamics of protein–complex interaction. Moreover, the results from UV–visible, synchronous and circular dichroism studies confirmed the occurrence of conformational and micro environmental changes in BSA/HSA upon binding with these complexes. It is also noted that HSA has more binding affinity with surfactant–ruthenium(II) complexes compared to BSA. The free radical scavenging ability against DPPH, ABTS, NO and superoxide free radical assays suggested that surfactant–ruthenium(II) complexes have better free radical scavenging ability compared to precursor–ruthenium(II) complexes. Communicated by Ramaswamy H. Sarma.