ASM 2019

Poster (P51)


Effect of Change in Composition of the Mixture of Bio-compatible Ionic Liquid Cholinium Glycinate and Water on its Structural Organization and Microscopic Dynamics

Aditya Gupta, Supreet Kaur, and Hemant K. Kashyap

Department of Chemistry, Indian Institute of Technology Delhi, Delhi


The mixture of bio-compatible ionic liquid cholinium glycinate and water has been employed in various applications in recent past, but extensive understanding of their structure and dynamics is lacking in literature. We have carried out an all-atom molecular dynamics simulations to explore the effect of water content on structural organization and microscopic dynamics of aqueous cholinium glycinate ([Ch][Gly]), a bio-compatible ionic liquid (IL), using GROMACS-5.1.1 software. Here we have calculated total X-ray scattering structure function, S(q), their partial components, and real-space correlation functions for whole composition range (xw=0.0 to 0.75). A principal peak in the total structure function of the neat [Ch][Gly] IL at around q=1.4 Å-1 is observed in S(q). This peak decreases in intensity and shift towards shorter length scales with increase in the water mole fraction. We also observed that upto xw=0.25 the structure of the mixture is IL-like and further addition of water disrupts the IL structure significantly and at xw=0.75 water starts playing a major role in deciding the structure of the system. Subsequently partial S(q)s shows that the origin of principal peak is due to correlations between counter ions. Hydrogen bond analysis shows that there is competition between water molecules and anions to form hydrogen bond with the cation. Also, strong hydrogen bonding is observed between [Gly]- anion and water, which depreciates with increase in hydration level. Distance-angle distribution function supports the presence of hydrogen bonding in our system by giving maximum probability in the area which is in accordance with the hydrogen bond geometrical criteria (HDA = 30° and r(DA) ≤ 0.35 nm). Hydrogen bond auto-correlation plots reveals that dynamics gets slower with decrease in mole fraction of water. The spatial distribution functions also affirms the observations we got from hydrogen bonding analysis and radial distribution functions. We have also investigated dynamics to see the effect of hydration on transport properties of IL. The mean square displacement of the ions and ionic conductivity are also significantly affected by water, both showing a non-linear increase with increasing water content. The [Gly]- anion is found to show faster dynamics on addition of water as compared to [Ch]+ cation. The cation is found to exhibit longer VACF relaxation time as compared to anion that further tends to get slower by adding water.

References:

1. Das, S.; Karmakar, T.; Balasubramanian, S. Molecular Mechanism behind Solvent Concentration-Dependent Optimal Activity of Thermomyces lanuginosus Lipase in a Biocompatible Ionic Liquid: Interfacial Activation through Arginine Switch. J. Phys. Chem. B 2016, 120, 11720-11732.

 

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