(544ar) Investigation of Molecular Properties of Imidazolium-Based Ionic Liquids in the Presence of Cysteine Ligated Iron Porphyrins for Understanding Their Biodegradability

Imidazolium-based ionic liquids are one of the most widely studied ionic liquids. Tremendous flexibility in the design and low vapor pressures are the main drivers for their potential applications. Although regarded as environmentally friendly solvents, experimental studies have concluded some ionic liquids are partially soluble in water and toxic to aquatic organisms. Thus, it is highly desirable to biodegrade ionic liquids before they are released into environment. Experimental investigations into ionic liquid biodegradation have primarily focused on the potential for biodegradation by various organisms and identification of degradation products; however, no molecular level understanding is currently available for the biodegradation pathway.

Previous studies have proposed the cytochrome P-450 and its variants as candidate enzymes for ionic liquid biodegradation. Cysteine-ligated iron-porphyrin (FePCys) represents the core of this enzyme and the central part of its active site. In the present work, the electronic and geometrical properties of imidazolium cations were studied in the presence of FePCys in complex at quantum mechanical level using the density functional theory calculations. The effect of increasing alkyl chain length in the 1-n-alkyl-3-methylimidazolium homologous series (n = 2, 4, 6, 8, and 10) on the binding energy of the cation with FePCys was investigated by employing dispersion corrections. Additionally, the binding energy was decomposed into its polarization, dispersion, repulsion, and exchange contributions to understand the dominant interactions responsible for the binding. The variation in the binding energy due to conformations presented to the FePCys was also assessed.