Investigations On The Interactions Between Ionic Liquids And Proteins

Ionic liquids have been rapidly developed in the analysis of biological macromolecules (protein separation and purification, crystallization, determination). Excellent performances of ionic liquids have attracted extensive atttentions for studying the interactions between ionic liquids and biomacromolecules. Information on the interactions is crucial for understanding the protein functions in ionic liquids and providing theoretical basis for molecular design of ionic liquids and further applications. Therefore the understanding of interactions between ionic liquids and biological systems is highly necessary.The first part of the thesis reviews the structures and properties of proteins and ionic liquids. The methods for studying the interactions between proteins and small molecules are briefly overviewed. In addition, progresses on the studies of interactions between ionic liquids and proteins are summarized.In the second part, the interactions between1,3-dimethylimidazole iodine and model proteins, e.g., bovine serum albumin, bovine hemoglobin and lysozyme, are studied by spectroscopy, i.e., UV-vis, fluorescence and circular dichroism and molecular modeling. The results indicated that effective static quenehing process occurred between1,3-dimethylimidazole iodine and model proteins. The binding constants and the number of binding sites of1,3-dimethylimidazole iodine and model proteins are also obtained. Circular dichroism is used for the study of structural changes in the model proteins. The a-helix content of model proteins are decreased. Binding modes are simulated between1,3-dimethylimidazole iodine and BSA, Hb, Lys.In the third part, the investigations on the activity and structure of hemoglobin via interactions with1-dodecyl-3-methylimidazole bromine (C12mimBr) have been done consequently. Conductivity measurements show that the critical micelle concentration of1-dodecyl-3-methylimidazole bromine increases from9.5×10-3to1.1×10-2mol L-1. UV Spectra display that the effect of1-dodecyl-3-methylimidazole bromine on Hb is strongly concentration-dependent and the metHb convert to hemichrome at appropriate concentration of1-dodecyl-3-methylimidazole bromine. Initial fluorescence enhancement with addition of1-dodecyl-3-methylimidazole bromine is due to conversion-enhanced fluorescence, while reduction of fluorescence is observed with further addition of the ionic liquid, which indicated conformational change of the protein. When1-dodecyl-3-methylimidazole bromine forms micelle, peptide chain extention resulting from packaged heme group leads to the deactivation of hemoglobin and causes enhancement of fluorescence intensity. In addition, activity assay and circular dichroism are used to study the activity and structural changes in hemoglobin and simulate optimal binding mode and binding site between1-dodecyl-3-methylimidazole bromine and hemoglobin.