Solvation Shell Structures of Ammonia in Reline and Ethaline Deep Eutectic Solvents.

Because of increasing atmospheric anthropogenic ammonia (NH 3 ) emission, researchers are devising new techniques to capture NH 3 . Deep eutectic solvents (DESs) are found as potential media for NH 3 mitigation. In the present study, we have carried out ab initio molecular dynamics (AIMD) simulations to decipher the solvation shell structures of an ammonia solute in reline (1:2 mixture of choline chloride and urea) and ethaline (1:2 mixture of choline chloride and ethylene glycol) DESs. We aim to resolve the fundamental interactions which help stabilize NH 3 in these DESs, focusing on the structural arrangement of the DES species in the nearest solvation shell around NH 3 solute. In reline, the hydrogen atoms of NH 3 are preferentially solvated by chloride anions and the carbonyl oxygen atoms of urea. The nitrogen atom of NH 3 renders hydrogen bonding with hydroxyl hydrogen of the choline cation. The positively charged head groups of the choline cations prefer to stay away from NH 3 solute. In ethaline, strong hydrogen bonding interaction exists between the nitrogen atom of NH 3 and hydroxyl hydrogen atoms of ethylene glycol. The hydrogen atoms of NH 3 are found to be solvated by hydroxyl oxygen atoms of ethylene glycol and choline cation. While ethylene glycol molecules play a crucial role in solvating NH 3 , the chloride anions remain passive in deciding the first solvation shell. In both the DESs, choline cations approach NH 3 from their hydroxyl group side. We observe slightly stronger solute-solvent charge transfer and hydrogen bonding interaction in ethaline than those in reline.