Mechanistic and Conformational Studies on the Interaction of a Platinum(II) Complex Containing an Antiepileptic Drug, Levetiracetam, With Bovine Serum Albumin by Optical Spectroscopic Techniques in Aqueous Solution

Fluorescence spectroscopy in combination with circular dichroism (CD) and ultraviolet-visible (UV–vis) absorption spectroscopy were employed to investigate the binding of a new platinum(II) complex containing an antiepileptic drug “Levetiracetam” to bovine serum albumin (BSA) under the physiological conditions. In the mechanism discussion, it was proved that the fluorescence quenching of BSA by Pt(II) complex is a result of the formation of Pt(II) complex–BSA complex. The thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures (283, 298, and 310 K) were calculated, and the negative value for ΔH and ΔS indicate that the hydrogen bonds and van der Waals interactions play major roles in Pt(II) complex–BSA association. Binding studies concerning the number of binding sites (n~1) and apparent binding constant Kb were performed by fluorescence quenching method. The site marker competitive experiments indicated that the binding of Pt(II) complex to BSA primarily took place in site II. Based on the Förster’s theory, the average binding distance between Pt(II) complex and BSA was obtained (r = 5.29 nm). Furthermore, UV–vis, CD, and synchronous fluorescence spectrum were used to investigate the structural change of BSA molecules with addition of Pt(II) complex. These results indicate that the binding of Pt(II) complex to BSA causes apparent change in the secondary structure of BSA and do affect the microenvironment around the tryptophan residue.