When combined at particular molar fractions, sugars, aminoacids or organic
acids a present a high melting point depression, becoming liquids at room
temperature. These are called Natural Deep Eutectic Solvents – NADES and are
envisaged to play a major role on the chemical engineering processes of the
future. Nonetheless, there is a significant lack of knowledge of its fundamental and
basic properties, which is hindering their industrial applications. For this reason it
is important to extend the knowledge on these systems, boosting their application
development [1].
In this work, we have developed and characterized NADES based on choline
chloride, organic acids, amino acids and sugars. Their density, thermal behavior,
conductivity and polarity were assessed for different compositions. The
conductivity was measured from 0 to 40 °C and the temperature effect was well
described by the Vogel-Fulcher-Tammann equation. The morphological
characterization of the crystallizable materials was done by polarized optical
microscopy that provided also evidence of homogeneity/phase separation.
Additionally, the rheological and thermodynamic properties of the NADES and the
effect of water content were also studied. The results show these systems have
Newtonian behavior and present significant viscosity decrease with temperature
and water content, due to increase on the molecular mobility. The anhydrous
systems present viscosities that range from higher than 1000Pa.s at 20°C to less
than 1Pa.s at 70°C. DSC characterization confirms that for water content as high
as 1:1:1 molar ratio, the mixture retains its single phase behavior. The results obtained demonstrate that the NADES properties can be finely
tunned by careful selection of its constituents. NADES present the necessary
properties for use as extraction solvents. They can be prepared from inexpensive
raw materials and tailored for the selective extraction of target molecules. The
data produced in this work is hereafter importance for the selection of the most
promising candidates avoiding a time consuming and expensive trial and error
phase providing also data for the development of models able to predict their
properties and the mechanisms that allow the formation of the deep eutectic
mixtures.Rita Craveiro and Alexandre Paiva are grateful for financial support from
Fundação para a Ciência e a Tecnologia (FCT) through the grants PTDC/EQUEPR/12191/2010/ENIGMA
and SFRH/BPD/44946/2008. The research leading
to these results has received funding from through the projects ENIGMA -
PTDC/EQU-EPR/121491/2010, PTDC/QUI-QUI/119210/2010, PTDC/EQUEQU/122106/2010,
PEst-C/EQB/LA0006/2013 from the European Union's Seventh
Framework Programme (FP7/2007-2013) under grant agreement n°
REGPOT-CT2012-316331-POLARIS and from Project “Novel smart and biomimetic
materials for innovative regenerative medicine approaches (Ref.: RL1 -
ABMR - NORTE-01-0124-FEDER-000016)” co-financed by North Portugal Regional
Operational Programme (ON.2 – O Novo Norte), under the National Strategic
Reference Framework (NSRF), through the European Regional Development
Fund (ERDF)
