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Vibrational spectroscopy and molecular dynamics simulation of choline oxyanions salts
Journal article   Open access   Peer reviewed

Vibrational spectroscopy and molecular dynamics simulation of choline oxyanions salts

Icaro F. T. de Souza, Vitor H. Paschoal, Kalil Bernardino, Thamires A. Lima, Luke L. Daemen, Z. Y. and Mauro C. C. Ribeiro
Journal of molecular liquids, v 340, p117100
15 Oct 2021
DOI: https://doi.org/10.1016/j.molliq.2021.117100
url
https://www.sciencedirect.com/science/article/am/pii/S0167732221018249View
SubmittedOpen Access (Publisher-Specific),  Open

Abstract

Chemistry Chemistry, Physical Physics, Atomic, Molecular & Chemical Science & Technology Physical Sciences Physics
The structure of choline salts containing the anions acetate, [Chol][Ac], and dihydrogen phosphate, [Chol] [DHP], were investigated by infrared, Raman, and inelastic neutron scattering (INS). The chosen systems allow for the comparison of structural effects related to the bond acceptor characteristic of [Ac] and the simultaneous acceptor and donor characteristics of [DHP] in forming hydrogen bonds (H-bond) in salts of [Chol], which is itself prone to forming H-bonds. Different computational tools were used for the analysis of different spectral ranges. The calculation of the low-frequency range of Raman and INS spectra of the crystalline phases at low-temperatures by solid state DFPT (density functional perturbation theory) unveils the coupling between vibrations of the H-bonds and intramolecular modes. Changes observed in the spectral pattern of lattice and [DHP] modes upon heating crystalline [Chol][DHP] are analogous to the ferroelectric-paraelectric phase transition known in the potassium salt of [DHP]. The fingerprint region of the vibrational spectra provides information concerning the [Chol] conformation in the solid phase (gauche in [Chol][Ac] and anti in [Chol][DHP]) and in aqueous solution. DFT calculations of ionic pairs and ionic clusters unveil the interplay between [Chol] conformation and the [DHP] ability to form H-bonded dimers of anions. The high-frequency spectral range and the structures driven by H-bonds are discussed using classical molecular dynamics (MD) simulations. The MD simulations of aqueous solutions highlight the strong anion-cation H-bond in [Chol][Ac], in contrast to the strong anion-anion H-bond in [Chol][DHP] due to occurrence of dimers and larger clusters of [DHP]. (c) 2021 Elsevier B.V. All rights reserved.

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Chemistry, Physical
Physics, Atomic, Molecular & Chemical
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