(502b) Enzyme Structure, Function, and Utility in Room Temperature Ionic Liquids

Room temperature ionic liquids (RTILs) are intriguing solvents, which are recognized as ?green' alternatives to volatile organics. Although they offer such advantages as nonvolatility and ability to dissolve various organic and inorganic molecules, there are some challenges in their use including high viscosity leading to mass transfer limitations, and the lack of fundamental information of enzyme structure and function. In particular, the effect of ionic liquids on the transition state of enzymatic reactions remains largely unknown. We have probed the transition state of soybean peroxidase via Hammett analysis for the oxidation of phenols as a function of the physicochemical properties of the RTIL and the degree of solvent hydration. In the course of this work, we also discovered that enzymes exhibited enhanced activity and stability when attached to nanoscale materials, including carbon nanotubes, presumably as a result of overcoming mass transfer limitations in RTILs. Specifically, using proteinase K physically adsorbed onto single-walled carbon nanotubes (SWNTs), we found that the enzyme retained the majority of its native activity and was substantially more stable at elevated temperatures. The high surface area and the nanoscopic dimensions of SWNTs offered high enzyme loading and low mass transfer resistance. These enzyme-SWNT conjugates may provide a unique combination of high activity and stability, and low diffusional limitations in RTILs, thereby overcoming key operational limitations in use of this type of solvent system.