Interaction of thiacloprid with bovine hemoglobin using spectroscopic and molecular modeling methods

The interaction of thiacloprid (TL) to bovine hemoglobin (BHb) under physiological conditions was investigated by using fluorescence spectroscopy, circular dichroism spectroscopy (CD) and molecular modeling. The fluorescence intensity of BHb decreased regularly with the gradual increasing concentration of TL. It is observed that there was a prominent interaction between TL and BHb. The binding constants K-A at 288, 298 and 308 K obtained are 8.04, 5.26 and 3.08 x 10(4) l . mol(-1), respectively. The standard enthalpy change (Delta H-0) and the standard entropy change (Delta S-0) are calculated to be -34.54 KJ . mol(-1) and -25.77 J . mol(-1) . K-1, which indicated that hydrogen bonding forces play major role in the interaction between TL and BHb. The alternations of protein secondary structure in the presence of TL were determined by CD spectroscopy. The results revealed that the content of a-helix was decreased from 51.85% in free BHb to 48.14% in TL-BHb complex. Molecular modeling study and our experimental results both showed that the binding mode of TL-BHb complex could be attributed to hydrogen bonding and hydrophobic interaction.