The dynamics of charged, neutral and flexible molecules dissolved in binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate and water
Dabney, Michael J., II
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As a result of the current drive toward more environmentally benign (aka "green") chemistries, ionic liquids ("IL") have become a focus of significant investigation and research. In fact, ILs have already found use as solvent systems in industrial cleaning, polymerizations, separations, and synthesis. Additionally, ILs are increasingly being used to replace molecular solvents in biocatalytic systems. Some of the potential advantages afforded by using ILs in biocatalysis include increased catalytic activity and stability, improved product enantioselectivity, and catalytic reusability. However, much of this research is conducted with limited knowledge concerning the biocatalyst behavior when dissolved in IL systems. This dissertation addresses this issue by investigating the solvation properties of the water-miscible ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF 4 ]). Toward this end, the steady-state and time-resolved fluorescence of three charged and one neutral fluorescent probes; rhodamine 6G chloride (R6G), 4-(dicyanomethylene)-2-methyl-6-( p -dimethylaminostyryl)- 4H -pyran (DCM), BODIPY 492/515 disulfonate (BPY), and Lucifer Yellow Carbohydrazide (LYCH) were explored as a function of water concentration when dissolved in [bmim][BF 4 ]. Additionally, the steady-state behavior (e.g., emission and anisotropy) of a well-known protein, glucose oxidase (GOx), were monitored as a function of temperature when dissolved in mixtures of 90% [bmim][BF 4 ] and 10% (v/v) phosphate buffer. To further elucidate the GOx behavior, we also investigated the behavior and folding kinetics of the key GOx co-factor, flavin adenine dinucleotide (FAD), as a function of water concentration when dissolved in [bmim][BF 4 ]. The results of this research demonstrate that there is little to no interaction between bulk [bmim][BF 4 ] and charged species dissolved in this IL. Additionally, the presence of water significantly alters the fluorescence from the solvatochromic probes dissolved in [bmim][BF 4 ]. It was also found that [bmim][BF 4 ] alters the melting point of GOx, increasing the melting point by ∼8oC in comparison to the melting point in phosphate buffer. Finally, the FAD folding kinetics are greatly perturbed when dissolved in mixtures of [bmim][BF 4 ]/H 2 O as compared to pure H 2 O.