Studies On The Structure-activity Relationship Of Ionic Liquids-enzyme Activity

This dissertation systematically studied the toxicity of ionic liquids towards five enzymes including catalase,trypsin,lumbrokinase,lactic dehydrogenase and lipase.The IL-enzyme interaction mechanism was investigated.The main contents and results are as follows:(1)The toxic effects of nine ionic liquids(ILs)on the catalase activity were investigated using fluorescence,ultraviolet absorption and circular dichroism(CD)spectroscopy.The interactions of ILs and the catalase on the molecular level were studied.The experimental results indicated that ILs could inhibit the catalase activity and their inhibitory ability depended on the hydrophobicity and hydrogen bonding.The CD spectroscopy suggested that catalase molecules retained their native secondary structures in the presence of low concertation of ILs.(2)The toxicity of ionic liquids(ILs)was evaluated by using trypsin as biomarker.Experimental results indicated that the trypsin activity was inhibited by ILs and the degree of inhibition highly depended on the chemical structures of ILs.Primary analysis illustrated that hydrophobicity of ILs was one of the driven forces ruling the interactions of ILs and trypsin.Both negative ?H and ?S suggested hydrogen bonding was the major driven forces underlying the interaction of IL-trypsin.To assess the toxicity of ILs,it should be considered the combination of the hydrogen bonding ability and hydrophobicity of ILs.A regression based model was established to correlate the relationship of the inhibitory ability,hydrophobicity and hydrogen bonding ability of ILs.(3)In this section,the hydrolysis of casein by lumbrokinase in the presence of ionic liquids(ILs)was studied.The experimental results indicated that at low IL concentration,the addition of ILs could remarkably increase the lumbrokinase activity due to enhancing the hydrophilicity of casein by forming the IL-casein complex.However,at higher IL concentration,significant decrease in lumbrokinase activity was observed because of the destruction of hydrogen bond network of lumbrokinase by ILs.Fluorescence analysis indicated that hydrogen bonding was the main driven force ruling the interaction of ILs and lumbrokinase.The formation of ionic liquids micelles also resulted in the loss of enzyme activity.(4)This section aimed to evaluate the toxicity of six imidazolium-based ILs with lactic dehydrogenase(LDH)as biomarker.It was found that the more hydrophobic ILs had a major effect on the inhibition of LDH activity.Moreover,the interactions of ILs and the LDH on the molecular level were investigated using fluorescence spectroscopy.By analyzing the fluorescence behavior of LDH with the addition of ILs,it is confirmed that hydrophobicity was the major driven force in the interaction process as expected.(5)The effects of ionic liquids(ILs)on the lipase activity were studied by UV-Vis spectroscopy and the IL-lipase interaction mechanism was investigated by fluorescence technique.Experimental results indicated that the lipase activity was inhibited by ILs.The inhibitory ability of the Cl--and Br--based ILs increased with increasing the alkyl chain length in the IL cation.Thermodynamic parameters suggested hydrophobicity was the major driven force for the Cl--and Br--based ILs.For the ILs,[C4mim]BF4,[C4mim]TfMs,[C4mim]ClO4 and [C4mim]N(CN)2,hydrogen bonding was the main driven force ruling the interaction of these ILs and lipase.A regression-based equation was developed to describe the relationship of the inhibitory ability of ILs and their hydrophobicity and hydrogen bonding ability.