Water confined (H2O) n=1-10 amino acid-based ionic liquids - A DFT study on the bonding, energetics and IR spectra

Effect of water confinement on the structural properties, energetics, and spectral signatures of amino acid-based ionic liquids (AAILs) is a subject of scientific importance. We have confined AAILs using the water molecules in the form of clusters with size varying from n = 1 to 10. Hydrogen bonds characterize the orientation of water clusters on AAILs. Water molecules predominantly interact via strong electrostatic O-H center dot center dot center dot X (N, O) interactions with anions and form comparatively weaker C-H center dot center dot center dot O bonds with cations. A minimum of n = 3 water molecules is needed to initiate the dilution of AAIL, irrespective of the anion species. The increase in the water molecules beyond n = 3 occupies the interstitial space between anion and cation, weakening the anion-cation interactions. The sequential addition of water molecules in the system shows the cooperative interaction between cationanion, anion-water, cation-water, and water-water units. However, until n = 3, anion-water interaction is predominant, beyond which water-water interaction gains strength progressively. Aliphatic AAILs exhibit stronger hydrogen bonding interaction than aromatic ILs. (C) 2020 Elsevier B.V. All rights reserved.