Crystallization and time-dependent changes in betaine-urea-water natural deep eutectic solvents

Lamya Al Fuhaid, Maria F. Nava-Ocampo, Szilárd S. Bucs, Robert Verpoorte, Young Hae Choi, Geert Jan Witkamp, Andreia S.F. Farinha*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


The ability to predict eutectic compositions resulting in a liquid (natural) deep eutectic solvent [(NA)DES] at room temperature or below widens their applicability range. This study examines the effect of the components’ molar ratio and water content on the stability and supramolecular network of betaine-urea-water (BUW) NADES. It also explores time-dependent changes in the solvents and possible methods to determine the stability. After being prepared at elevated temperatures (≥70 °C), some BUW crystallized upon cooling or seeding with pre-existing crystals, creating orthorhombic betaine hydrate crystals. BUW ratios yielding liquid NADES were determined by proton nuclear magnetic resonance (1H NMR), identifying a solid–liquid boundary. Moreover, BUW conductivity decreased continually over time, suggesting a dynamic state of the solvents. Our results indicate that betaine crystallization depends on water and urea concentrations, supporting the reported synergistic effect. Additionally, this work demonstrates 1H NMR as a method to predict BUW ratios forming liquid NADES.

Original languageEnglish (US)
Article number122718
JournalJournal of Molecular Liquids
StatePublished - Oct 1 2023

Bibliographical note

Funding Information:
This work was supported by King Abdullah University of Science and Technology (KAUST), Thuwal, SA. The authors thank Dr. Youyou Yuan from the KAUST Imaging and Characterization Core Lab for resolving the crystal structure.

Publisher Copyright:
© 2023


  • Bonding
  • Crystallization
  • DES
  • Metastability
  • Time-dependence

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics
  • Condensed Matter Physics
  • Spectroscopy
  • Physical and Theoretical Chemistry
  • Materials Chemistry


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