(382ab) Analysis of Interactions between Ionic Liquid Cations and Enzymatic Core of Cytochrome P-450 in a Quantum Mechanical (QM) Framework

Ionic liquids have the potential for driving industrial processes in a sustainable fashion due to their environmentally benign characteristics like inherent low vapor pressure and flammability. Their extremely low vapor pressures translate to the fact that they have negligible role in air emissions as compared to conventional industrial solvents. Ionic liquids can also be flexibly designed in order to obtain desirable physical properties. This design could be carried out by choosing from thousands of possible combinations of cations and anions. Out of the myriad of a wide range of ionic liquid classes, imidazolium-based and pyridinium-based ionic liquids have been some of the most successfully utilized in diverse applications. Suitable variants of these types of ionic liquids have been applied in catalysis, extractive distillation, liquid-liquid extraction among many others. Though being proved to be highly effective in driving complex industrial processes, experimental investigations have raised questions on their environmental degradability. Thus, it becomes imperative to include rational design into their synthesis. From an experimental point of view, considerable efforts have been put in this direction but molecular level details have not been explored in detail computationally. The present work aims to provide physical insight into the phenomena of ionic liquid biodegradability to aid in the future design of these solvents.

Cytochrome P-450 has been identified and widely studied for their role in oxidation of a wide variety of molecules in aerobic and anaerobic environments. Thus, to develop a computational framework related to biodegradability, it was considered important to capture the effects of the cytochrome on imidazolium-based ([C_nmim]⁺) and pyridinium-based ([C_nPy]⁺) ionic liquid cations. For this, the enzymatic center of the P-450 molecule (heme) was modeled as an iron porphyrin molecule with an Fe-based center (FeP). The cations were included in the model as a potential substrate for the P-450 enzyme in complexation with the heme receptor. This interaction was modeled using DFT calculations by adapting a purely quantum mechanical framework. To include the conformational effects, two different conformations of the ionic liquid cation, namely, tail up and tail down conformations, were considered in this work varying the 1-n-alkyl chain on the cation progressively along the homologous series (n =2,4,6,8,10). Result and discussion would describe the intermolecular interactions between FeP and ionic liquid cation obtained from the population analysis as well as reactivity indices calculated from either model. Also, key analysis of the orbital energetics and thermodynamics of the system would be included that would aid in determining key conclusions regarding the above considered ionic liquid’s mechanism of biodegradation.