(204m) Investigation of Electronic Properties of Imidazolium-Based Ionic Liquids in the Presence of Iron Porphyrins for Understanding Their Biodegradability

Imidazolium-based ionic liquids have been shown to be highly effective in a wide variety of chemical engineering applications. These include extractive distillation, catalysis and electrochemistry among many others. This is promoted by multiple factors including their design flexibility, low vapor pressure and favorable solvability. Although being extremely useful in nature, they have been shown to be partially soluble in water and often leave a footprint on the ecosystem. This might percolate through the elements and be detrimental to the quality of essential natural resources. Hence, it becomes imperative to think about a rational design of these liquids that may prove to be environmentally friendly. Though there have been significant investigations into the biodegradability of this class of ionic liquids in the experimental direction, computational attempts have rather lesser in number. A lack of understanding of the degradation phenomena of the above said ionic liquids at the molecular level is the motivation behind this research.

With respect to degradation, oxidation has been proposed to be one of the prime mechanisms through which degradation may occur in nature. Former studies illustrate that cytochrome P-450 and its variants are instrumental in catalyzing oxidation in a variety of different aerobic and anaerobic environments. Fe- porphyrin (FeP) represents the core of this enzyme and an important part of its active site. In the present work, the electronic properties of imidazolium cations were studied in the presence of FeP in complex. Ab initio calculations were performed on these systems varying the alkyl chain length of imidazolium cations.

A quantum mechanical treatment of the overall system was adopted considering these cations as potential substrates to the FeP receptor. To reflect the suggestions of previous quantitative structure biodegradability relationships (QSBR), variations in frontier orbital energies i.e. Highest Occupied and Lowest Unoccupied energy levels (HOMO and LUMO) were investigated in detail. To account for the effect of geometry on the energetics, three different conformations, namely, tail up, tail down and interplanar conformations were considered. Different aspects concerning the HOMO-LUMO energies across different alkyl chain lengths and conformations will be discussed to elucidate the effect of receptor on the dynamics of the local electronic environment of the cations. Variations in key thermodynamic entities of the system, such as Gibbs free energy and entropy give us important information regarding imidazolium cation-FeP interactions, which would also be included in the results.