(428e) Understanding the Geometrical and Electronic Properties of Imidazolium-Based Ionic Liquids in the Presence of Amino Acid Substituted Metal Porphyrins

Ionic liquids have proven themselves to be potential candidates for driving industrial processes in a sustainable fashion due to their environmentally benign properties. These liquids have extremely low vapor pressures that translates to the fact that they have negligible role in air emissions as compared to conventional volatile organic solvents. They are also highly design flexible and their physical, chemical and biological properties may be tuned easily by adapting a suitable combination from a wide array of cations and anions. Out of the myriad of a wide range of possibilities, imidazolium-based ionic liquids have been successfully utilized in diverse applications including catalysis, extractive distillation, liquid-liquid extraction among many others. Although being unique and highly effective in driving complex processes, experimental work on these ionic liquids have raised questions on their toxicity and environmental degradability. Some of them have been shown to be water soluble and may leave a large ecological footprint that may lead to detrimental changes in the ecosystem. Thus, it becomes imperative to include biodegradability in the rational design of ionic liquids. Limited experimental work focused on biodegradation of ionic liquids has suggested that long alkyl chain imidazolium-based ionic liquid cations can undergo hydroxylation in the presence of microbial community while the smaller cation resist any biotransformation. The molecular level details for such transformations have not yet been elucidated.

Cytochrome P-450's have been identified and widely studied for their role in the oxidation of a wide variety of molecules in aerobic and anaerobic environments and can act as a possible enzyme implicated in the hydroxylation of ionic liquids. In order to determine the effect of cytochrome P-450 on the 1-n-alkyl-3-methylimidazolium [C_nmim]⁺ class of ionic liquids, protein environment was modeled with cysteine ligated iron porphyrin (FePCys). Imidazolium cations [C_nmim]⁺ (n=2,4,6,8, and 10) were considered as potential substrates that interact with different variants of FePCys. These variants may be oxygenated (FePOCys) or non-oxygenated referring to the enzymatic cycle of the P-450 enzyme in focus. All the systems considered ([C_nmim]⁺FePCys or [C_nmim]⁺FePOCys) were treated quantum mechanically for understanding the effect of the porphyrin receptor on the electronic environment of imidazolium cations considering their properties in the gas phase as the datum for the same. To include the regioselective and stereoselective aspects of the system, geometrical analyzes were also conducted to identify key cationic orientations. Electronic properties such as frontier orbital energies i.e. Highest Occupied and Lowest Unoccupied energy levels (HOMO and LUMO) were obtained to determine the reactivity of these molecules. Additionally, the results of HOMO and LUMO locations, hybridization of molecular orbitals of FePCys and the cations, and FePOCys and the cations will be presented along with the thermodynamic properties such as binding energy and free energy change upon binding to aid in inferring molecular mechanism of ionic liquid biodegradation.