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Resilience of Malic Acid Natural Deep Eutectic Solvent Nanostructure to Solidification and Hydration

Hammond, Oliver S.; Bowron, Daniel T.; Jackson, Andrew J. LU ; Arnold, Thomas; Sanchez-Fernandez, Adrian; Tsapatsaris, Nikolaos LU ; Garcia Sakai, Victoria and Edler, Karen J. LU (2017) In Journal of Physical Chemistry B 121(31). p.7473-7483
Abstract

Little is presently known about the unique nanostructure of deep eutectic solvents (DES). The order of the liquid-solid phase transition is contended and whether DES-water mixtures are merely aqueous solutions, or have properties dominated by the eutectic pair, is unclear. Here, we unambiguously show the structure of choline chloride-malic acid (malicine) as a liquid, and also in solid and hydrated forms, using neutron total scattering on D/H isotope-substituted samples, and quasi-elastic neutron scattering (QENS). Data were refined using empirical potential structure refinement. We show evidence for a stoichiometric complex ion cluster in the disordered liquid, with strong choline-chloride bonding and a hydrogen bond donor (HBD)... (More)

Little is presently known about the unique nanostructure of deep eutectic solvents (DES). The order of the liquid-solid phase transition is contended and whether DES-water mixtures are merely aqueous solutions, or have properties dominated by the eutectic pair, is unclear. Here, we unambiguously show the structure of choline chloride-malic acid (malicine) as a liquid, and also in solid and hydrated forms, using neutron total scattering on D/H isotope-substituted samples, and quasi-elastic neutron scattering (QENS). Data were refined using empirical potential structure refinement. We show evidence for a stoichiometric complex ion cluster in the disordered liquid, with strong choline-chloride bonding and a hydrogen bond donor (HBD) contribution. The 1:1 eutectic stoichiometry makes these ionic domains more well-defined, with less HBD clustering than seen previously for reline. There is minimal structural difference for the solidified material, demonstrating that this DES solidification is a glass transition rather than a first order phase change. QENS data support this by showing a gradual change in solvent dynamics rather than a step change. The DES structure is mostly retained upon hydration, with water acting both as a secondary smaller HBD at closer range to choline than malic acid, and forming transient wormlike aggregates. This new understanding of DES structure will aid understanding of the properties of these novel green solvents on the molecular length scale in chemical processes, as well as giving an insight into the apparent role of natural DESs in plant physiology.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Physical Chemistry B
volume
121
issue
31
pages
11 pages
publisher
The American Chemical Society
external identifiers
  • scopus:85027329050
  • wos:000407655800009
ISSN
1520-6106
DOI
10.1021/acs.jpcb.7b05454
language
English
LU publication?
yes
id
85e3d128-096c-42c8-9243-b3634c536e65
date added to LUP
2017-08-29 13:13:26
date last changed
2018-03-04 05:05:08
@article{85e3d128-096c-42c8-9243-b3634c536e65,
  abstract     = {<p>Little is presently known about the unique nanostructure of deep eutectic solvents (DES). The order of the liquid-solid phase transition is contended and whether DES-water mixtures are merely aqueous solutions, or have properties dominated by the eutectic pair, is unclear. Here, we unambiguously show the structure of choline chloride-malic acid (malicine) as a liquid, and also in solid and hydrated forms, using neutron total scattering on D/H isotope-substituted samples, and quasi-elastic neutron scattering (QENS). Data were refined using empirical potential structure refinement. We show evidence for a stoichiometric complex ion cluster in the disordered liquid, with strong choline-chloride bonding and a hydrogen bond donor (HBD) contribution. The 1:1 eutectic stoichiometry makes these ionic domains more well-defined, with less HBD clustering than seen previously for reline. There is minimal structural difference for the solidified material, demonstrating that this DES solidification is a glass transition rather than a first order phase change. QENS data support this by showing a gradual change in solvent dynamics rather than a step change. The DES structure is mostly retained upon hydration, with water acting both as a secondary smaller HBD at closer range to choline than malic acid, and forming transient wormlike aggregates. This new understanding of DES structure will aid understanding of the properties of these novel green solvents on the molecular length scale in chemical processes, as well as giving an insight into the apparent role of natural DESs in plant physiology.</p>},
  author       = {Hammond, Oliver S. and Bowron, Daniel T. and Jackson, Andrew J. and Arnold, Thomas and Sanchez-Fernandez, Adrian and Tsapatsaris, Nikolaos and Garcia Sakai, Victoria and Edler, Karen J.},
  issn         = {1520-6106},
  language     = {eng},
  month        = {08},
  number       = {31},
  pages        = {7473--7483},
  publisher    = {The American Chemical Society},
  series       = {Journal of Physical Chemistry B},
  title        = {Resilience of Malic Acid Natural Deep Eutectic Solvent Nanostructure to Solidification and Hydration},
  url          = {http://dx.doi.org/10.1021/acs.jpcb.7b05454},
  volume       = {121},
  year         = {2017},
}