Study on the Interaction Between ${\mathrm{Cu}}{\left( {{\mathrm{phen}}} \right)}^{{2 + }}_{3}$ and Bovine Serum Albumin by Spectroscopic Methods

Abstract

In this work, the interaction between ${\text{Cu}}\left( {{\text{phen}}} \right)_3^{\,\,2 + }$ and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy combined with UV–vis absorption and circular dichroism (CD) spectroscopic techniques under physiological conditions. The fluorescence data proved that the fluorescence quenching of BSA by ${\text{Cu}}\left( {{\text{phen}}} \right)_3^{\,\,2 + }$ was the result of the ${\text{Cu}}\left( {{\text{phen}}} \right)_3^{\,\,2 + } - {\text{BSA}}$ complex formation. The binding constants (K _a) between ${\text{Cu}}\left( {{\text{phen}}} \right)_3^{\,\,2 + }$ and BSA at four different temperatures were calculated according to the modified Stern–Volmer equation. The enthalpy change (ΔH) and entropy change (ΔS) were calculated to be 10.74 kJ mol^-1 and 54.35 J mol^-1 K^-1, respectively, which indicated that electrostatic interactions played a major role in the formation of ${\text{Cu}}\left( {{\text{phen}}} \right)_3^{\,\,2 + } - {\text{BSA}}$ complex. The distance r between the donor (BSA) and acceptor$\left[ {{\text{Cu}}\left( {{\text{phen}}} \right)_3^{\,\,2 + } } \right]$ was obtained to be 3.55 nm based on Förster’s energy transfer theory. The synchronous fluorescence and CD spectroscopy results showed that the polarity of the residues increased and the lost of the α-helix content of BSA (from 59.84 to 53.70%). These indicated that the microenvironment and conformation of BSA were changed in the presence of ${\text{Cu}}\left( {{\text{phen}}} \right)_3^{\,\,2 + }$.