(532e) QM and QM/MM Treatment of Ionic Liquid Binding to Cysteinated Porphyrin

Ionic liquids have the potential for driving industrial processes in a sustainable fashion due to their environmentally benign characteristics such as low vapor pressure, design flexibility and flammability. Although the negligible vapor pressure has potential to eliminate air emissions compared to conventional industrial solvents, the aqueous solubility of ionic liquids presents environmental concerns due to their toxicity. Thus biodegradation of ionic liquids is critical in the overall life-cycle assessment of these solvents. Experimental investigations have suggested that ionic liquids can be biodegraded under a variety of conditions; however, the molecular level explanations are currently lacking. To provide an insight into the biodegradation pathway, we select the ionic liquids 1-n-alkyl-3-methylimidazolium [C_nmim]⁺ (n=2, 4, 6, 8, and 10) and cytochrome P-450 as the enzyme for their role in the oxidation of wide variety of molecules in aerobic and anaerobic environments. The catalytic site of the enzyme is modeled as an iron porphyrin molecule conjugated with the amino acid cysteine (FePCys). The ionic liquid-FePCys interaction is modeled using dispersion-corrected density functional theory to obtain binding energy. Components of the binding energy are obtained using the localized molecular orbital (LMO) energy decomposition analysis approach. As an enhanced description of the enzymes’ active site, residues in the neighborhood of the central core were coupled in a QM/MM framework. Results from both the QM and QM/MM models will be compared to elucidate the effects of the ionic liquid substrates and relative orientations of ionic liquids and FePCys. Implications of these results in terms of ionic liquid biodegradation will be discussed.