Impacts of hydrophobicity and ionicity of phendione-based cobalt(II)/(III) complexes on binding with bovine serum albumin.

For efficient designing of metallodrugs, it is imperative to analyse the binding affinity of those drugs with drug-carrying serum albumins to comprehend their structure-activity correlation for biomedical applications. Here, cobalt(II) and cobalt(III) complexes comprising three phendione ligands, [Co(phendione)(3)]Cl-2 (1) and [Co(phendione)(3)]Cl-3 (2), where, phendione = 1,10-phenanthroline-5,6-dione, has been chosen to contrast the impact of their hydrophobicity and ionicity on binding with bovine serum albumin (BSA) through spectrophotometric titrations. The attained hydrophobicity values using octanol/water partition coefficient method manifested that complex 1 is more hydrophobic than complex 2, which could be attributed to lesser charge on its coordination sphere. The interaction of complexes 1 and 2 with BSA using steady state fluorescence studies revealed that these complexes quench the intrinsic fluorescence of BSA through static mechanism, and the extent of quenching and binding parameters are higher for complex 2. Further thermodynamics of BSA-binding studies revealed that complexes 1 and 2 interact with BSA through hydrophobic and hydrogen bonding/van der Waals interactions, respectively. Further, UV-visible absorption, circular dichroism and synchronous fluorescence studies confirmed the occurrence of conformational and microenvironmental changes in BSA upon binding with complexes 1 and 2. Molecular docking studies have also shown that complex 2 has a higher binding affinity towards BSA as compared to complex 1. This sort of modification of ionicity and hydrophobicity of metal complexes for getting desirable binding mode/strength with drug transporting serum albumins will be a promising pathway for designing active and new kind of metallodrugs for various biomedical applications. Communicated by Ramaswamy H. Sarma