Dynamic Anionic Speciation and Proton Transfer in Choline/Geranic Acid Mixtures Revealed by Machine-Learned Molecular Dynamics
6 affiliations
- 1Euskal Herriko Unibertsitatea (UPV/EHU
- 2Donostia International Physics Center (DIPC, Manuel Lardizabal Ibilbidea, 4, Euskadi, Spain, 20018
- 3Departamento de Física de Partículas
- 4Universidade de Santiago de Compostela
- 5Europa Plaza, 1, Euskadi, Spain, 20018
- 6Euskal Herriko Unibertsitatea (UPV/EHU, Unibertsitateko Ibilbidea, 7, Vitoria-Gasteiz, Euskadi, Spain, 01006
Abstract
In carboxylate/carboxylic acid-containing ionic liquid systems, oligomeric complex anions have been shown to substantially alter transport properties; yet whether such persistent pairing survives in the presence of water remains an open question. The 1:2 choline/geranic acid mixture (CAGE12) provides an ideal case study: a promising therapeutic solvent unavoidably hydrated in biomedical use. Although hydrogen-bonded geranic acid (AGE)–geranate (GE) oligomeric motifs have been proposed and recently characterized spectroscopically, their prevalence and dynamical relevance in the liquid remain unclear, particularly in application conditions. Here, we employ DFT-trained NeuralIL machine-learned molecular dynamics to investigate hydrated CAGE12 containing 8 wt% water. The simulations reveal a highly dynamic hydrogen-bond network centered on GE, in which AGE, water, and choline continuously compete for coordinating the GE. AGE–GE associations are frequently observed but exhibit sub-picosecond lifetimes, indicating that they are transient structural motifs rather than persistent complex anions. Proton-transferred configurations are found to depend strongly on the local hydrogen-bond environment. Rare AGE-rich coordination environments are associated with proton-transferred configurations that remain stable, whereas the more abundant water-coordinated AGE–GE pairs are associated with reversible proton-transfer events and proton rattling. Overall, hydrated CAGE12 is best described as a dynamically evolving hydrogen-bond network in which transient local coordination, rather than persistent oligomeric anions, governs proton transfer and anionic speciation. These results highlight the critical role of water in disrupting complex anion formation in nonstoichiometric ionic liquids, with direct consequences for their transport and physicochemical properties.
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BibTeX
@misc{loizate2026dynamic,
title = {{Dynamic Anionic Speciation and Proton Transfer in Choline/Geranic Acid Mixtures Revealed by Machine-Learned Molecular Dynamics}},
author = {Mikel Loizate and Hadrián Montes-Campos and Jon Zubeltzu and Elena Formoso and Luis M. Varela and Elixabete Rezabal},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010772/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010772/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Dynamic Anionic Speciation and Proton Transfer in Choline/Geranic Acid Mixtures Revealed by Machine-Learned Molecular Dynamics
AU - Mikel Loizate
AU - Hadrián Montes-Campos
AU - Jon Zubeltzu
AU - Elena Formoso
AU - Luis M. Varela
AU - Elixabete Rezabal
PY - 2026
DA - 2026/10/21
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010772/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010772/v1
AB - In carboxylate/carboxylic acid-containing ionic liquid systems, oligomeric complex anions have been shown to substantially alter transport properties; yet whether such persistent pairing survives in the presence of water remains an open question. The 1:2 choline/geranic acid mixture (CAGE12) provides an ideal case study: a promising therapeutic solvent unavoidably hydrated in biomedical use. Although hydrogen-bonded geranic acid (AGE)–geranate (GE) oligomeric motifs have been proposed and recently characterized spectroscopically, their prevalence and dynamical relevance in the liquid remain unclear, particularly in application conditions. Here, we employ DFT-trained NeuralIL machine-learned molecular dynamics to investigate hydrated CAGE12 containing 8 wt% water. The simulations reveal a highly dynamic hydrogen-bond network centered on GE, in which AGE, water, and choline continuously compete for coordinating the GE. AGE–GE associations are frequently observed but exhibit sub-picosecond lifetimes, indicating that they are transient structural motifs rather than persistent complex anions. Proton-transferred configurations are found to depend strongly on the local hydrogen-bond environment. Rare AGE-rich coordination environments are associated with proton-transferred configurations that remain stable, whereas the more abundant water-coordinated AGE–GE pairs are associated with reversible proton-transfer events and proton rattling. Overall, hydrated CAGE12 is best described as a dynamically evolving hydrogen-bond network in which transient local coordination, rather than persistent oligomeric anions, governs proton transfer and anionic speciation. These results highlight the critical role of water in disrupting complex anion formation in nonstoichiometric ionic liquids, with direct consequences for their transport and physicochemical properties.
ER -