Investigation of the association behaviors between bovine serum albumin and 2-(4-methylphenyl)-3-(N-acetyl)-5-(2,4-dichlorophenoxymethyl)-1,3,4-oxodiazoline.

The study was designed to examine the interaction between 2-(4-methylphenyl)-3-(N-acetyl)-5-(2,4-dichlorophenoxymethyl)-1,3,4-oxodiazoline (MPNDO) and bovine serum albumin (BSA) under physiological conditions by using fluorescence spectroscopy, ultraviolet absorption spectroscopy, FT-IR spectroscopy and circular dichroism spectroscopy and atomic force microscope. Spectroscopic analysis of the fluorescence emission quenching and ultraviolet absorption revealed that the quenching mechanism of bovine serum albumin by MPNDO was static quenching procedure. The binding constant and binding sites number at different temperatures were measured. The average binding distances between donor (BSA) and acceptor (MPNDO) was estimated to be 1.46 nm (301 K), based on the Föster non-radioactive energy transfer theory. An average size of 3.1 nm had a high proportion and these dots might be ascribed to BSA, some other dots with an average size of 6.6 nm might result from BSA-MPNDO bioconjugates while the average diameter of MPNDO was 1.6 nm, which was reasonable to conclude that one BSA-MPNDO bioconjugates consisted of one BSA and one MPNDO. The thermodynamic parameters, enthalpy change (ΔH), entropy change (ΔS) and free energy change (ΔG) were calculated, which indicated that the action force was mainly van der Waals forces. The data collected through synchronous fluorescence, FT-IR spectroscopy and circular dichroism spectroscopy demonstrated that the conformation of BSA was not affected obviously in the presence of MPNDO.