78
they observed that hen egg white lysozyme fibrillation was considerably faster in
ionic liquids than in water or pH 2 buffer. Various spectroscopic and microscopic
techniques revealed nanofibers of up to 1 μm in length, with a diameter depending
on the ionic liquid used (Silva et al. 2018a). The presence of the acetate anion was
found to favor the formation of β-sheet structures which are more inclined to aggregate and produce fibrils. In another work, acetate and other carboxylic acids were
used in combination with choline chloride to form deep eutectic solvents that were
then used as a medium for the formation of lysozyme nanofibers in acidic solution
(Silva et al. 2018b). The dimensions of the fibers depended on the nature of the
carboxylic acid, the longest fibers being obtained with lactic acid. Again, the formation was rapid, complete within a few hours. The nanofibers so generated were
incorporated into carbohydrate-based films where they increased the tensile
strength.
Qu et al. have investigated the possibility of creating materials for drug delivery
from proteins dissolved in deep eutectic solvents (Qu et al. 2019). They tested the
plasticizing properties of deep eutectic solvents, in particular “Glyceline,” choline
chloride:glycerol 1:2, with two plant-derived globular proteins, zein from maize and
soy protein. Although the solvents modified the properties of the proteins, the resulting materials were not as strong and ductile as those using PEG or fatty acid modifiers. On the other hand, when gelatin, a fibrous protein, was incorporated into
Glyceline mixtures, a material with high ductile strength was obtained. The choline
chloride could be replaced by imipramine hydrochloride, forming a therapeutic
deep eutectic solvent, and patches could be prepared that increased the penetration
of the drug into bovine skin.
Another enzyme whose activity has been improved by incorporation into a deep
eutectic solvent is versatile peroxidase, a heme peroxidase of fungal origin. It has
potential industrial applications for which an alternative to organic solvents would
be desirable. Thus, a deep eutectic solvent composed of choline chloride and glycerol (1:2) was tested (Mamashli et al. 2018). The activity of the enzyme at neutral
pH was higher in the solvent-buffer mixtures than in buffer alone. A number of
techniques, including circular dichroism and fluorescence spectroscopy, showed
changes in protein structure in the deep eutectic solvent, with exposure of hydrophobic regions and rearrangement of the heme group. Furthermore, the thermal
stability of the enzyme was improved in deep eutectic solvent.
Interferon-α2 (IFN-α2) is a cytokine with several therapeutic applications in the
treatment of cancer and liver disease. However, therapeutic proteins are notoriously
difficult to formulate, store, and handle. Lee et al. investigated the formulation of
this protein in several natural deep eutectic solvents with particular focus on its
thermal stability (Lee et al. 2018). An equimolar mixture of choline chloride and
fructose was found to preserve the biological activity of interferon-α2 during a 2-h
incubation at temperatures of 37 °C, 50 °C, and even 70 °C. Circular dichroism and
fluorescence spectroscopy experiments showed that the protein conformation was
preserved when it was heated in the choline chloride:fructose deep eutectic solvents, in contrast to the modifications observed when it was formulated in
C.-H. Nguyen et al.
they observed that hen egg white lysozyme fibrillation was considerably faster in
ionic liquids than in water or pH 2 buffer. Various spectroscopic and microscopic
techniques revealed nanofibers of up to 1 μm in length, with a diameter depending
on the ionic liquid used (Silva et al. 2018a). The presence of the acetate anion was
found to favor the formation of β-sheet structures which are more inclined to aggregate and produce fibrils. In another work, acetate and other carboxylic acids were
used in combination with choline chloride to form deep eutectic solvents that were
then used as a medium for the formation of lysozyme nanofibers in acidic solution
(Silva et al. 2018b). The dimensions of the fibers depended on the nature of the
carboxylic acid, the longest fibers being obtained with lactic acid. Again, the formation was rapid, complete within a few hours. The nanofibers so generated were
incorporated into carbohydrate-based films where they increased the tensile
strength.
Qu et al. have investigated the possibility of creating materials for drug delivery
from proteins dissolved in deep eutectic solvents (Qu et al. 2019). They tested the
plasticizing properties of deep eutectic solvents, in particular “Glyceline,” choline
chloride:glycerol 1:2, with two plant-derived globular proteins, zein from maize and
soy protein. Although the solvents modified the properties of the proteins, the resulting materials were not as strong and ductile as those using PEG or fatty acid modifiers. On the other hand, when gelatin, a fibrous protein, was incorporated into
Glyceline mixtures, a material with high ductile strength was obtained. The choline
chloride could be replaced by imipramine hydrochloride, forming a therapeutic
deep eutectic solvent, and patches could be prepared that increased the penetration
of the drug into bovine skin.
Another enzyme whose activity has been improved by incorporation into a deep
eutectic solvent is versatile peroxidase, a heme peroxidase of fungal origin. It has
potential industrial applications for which an alternative to organic solvents would
be desirable. Thus, a deep eutectic solvent composed of choline chloride and glycerol (1:2) was tested (Mamashli et al. 2018). The activity of the enzyme at neutral
pH was higher in the solvent-buffer mixtures than in buffer alone. A number of
techniques, including circular dichroism and fluorescence spectroscopy, showed
changes in protein structure in the deep eutectic solvent, with exposure of hydrophobic regions and rearrangement of the heme group. Furthermore, the thermal
stability of the enzyme was improved in deep eutectic solvent.
Interferon-α2 (IFN-α2) is a cytokine with several therapeutic applications in the
treatment of cancer and liver disease. However, therapeutic proteins are notoriously
difficult to formulate, store, and handle. Lee et al. investigated the formulation of
this protein in several natural deep eutectic solvents with particular focus on its
thermal stability (Lee et al. 2018). An equimolar mixture of choline chloride and
fructose was found to preserve the biological activity of interferon-α2 during a 2-h
incubation at temperatures of 37 °C, 50 °C, and even 70 °C. Circular dichroism and
fluorescence spectroscopy experiments showed that the protein conformation was
preserved when it was heated in the choline chloride:fructose deep eutectic solvents, in contrast to the modifications observed when it was formulated in
C.-H. Nguyen et al.