Comparative study of an osazone based ligand and its palladium(II) complex with human serum albumin: A spectroscopic, thermodynamic and molecular docking approach

Abstract An osazone based ligand, hexane-3,4-dione-bis(2′-phenylhydrazone) ( LH 2 ), was synthesized by 1:2 M Schiff base condensation of 3,4-hexanedione and phenylhydrazine in dehydrated methanol. Its palladium(II) complex ( 1 ) has also been synthesized. LH 2 and 1 have thoroughly been characterized by several spectroscopic and analytical means. DFT optimized structure of 1 shows that it is a monomeric Pd(II) complex having ‘N 2 Cl 2 ’ coordination chromophore. Our BVS analysis also satisfactorily reproduces the oxidation number of the palladium center. 1 shows irreversible Pd(II)/Pd(I) reduction in its CV in methanol. 1 is three-fold more emissive than LH 2 . This enhanced emission has also been supported by time correlated single photon counting (TCSPC) measurements at room temperature. Human serum albumin (HSA) binding aspects of both LH 2 and 1 have been investigated through various biophysical techniques. The binding constants as determined from Benesi-Hilderbrand plot using the absorbance spectral analyses were found respectively to be 1.18 × 10 5 and 4.38 × 10 4  M − 1 for LH 2 and 1 . The experimental findings confirm that both are good HSA binders. The thermodynamic parameters ( ∆ G °, ∆ H ° and ∆ S °) have also been evaluated by isothermal titration calorimetric (ITC) experiments. These parameters indicate that the binding processes are spontaneous both for LH 2 and 1 . Molecular docking analyses reveal that both LH 2 and 1 reside in domain-I of HSA.