81
attenuated total reflection demonstrated increased lipid content in treated cells.
Importantly, Escherichia coli cells did not develop resistance after multiple or prolonged exposures to the choline:geranic acid solvent.
Another mechanism of activity of deep eutectic solvents against bacteria was
investigated by Sadaf et al. (Sadaf et al. 2018). In in vitro studies, they looked at the
ability of a formulation that they named “maline,” composed of malonic acid and
choline chloride in a 2:1 molar ratio to inhibit the activity of an extracellular enzyme,
β-lactamase from Bacillus cereus. As in the studies on lysozyme reported above,
circular dichroism and intrinsic fluorescence were used to monitor protein structure.
This showed a transition of α-helix to random coil in the presence of maline,
together with fluorescence quenching that could have been due to loss of the tertiary
structure of the protein.
The antimicrobial activity of a number of natural deep eutectic solvents was
tested toward several bacterial species, as well as a yeast strain and three human cell
lines by Radošević et al. (Radošević et al. 2018). The highest activity toward bacteria was obtained with deep eutectic solvents containing organic acids – oxalic,
malic, and citric. The yeast Candida albicans was quite resistant to these solvents.
They also recorded cytotoxic effects toward human tumor cells lines HeLa and
MCF-7 with a choline chloride:oxalic acid deep eutectic solvent while a normal cell
line, HEK293T, was more resistant. The antioxidant capacity of the deep eutectic
solvents was measured by their capacity to absorb oxygen radicals. Most of the
solvents tested had oxygen scavenging properties. One deep eutectic solvent, composed of betaine, malic acid, and proline, stimulated mammalian cell growth while
having strong antioxidant properties.
Recently, Silva et al. investigated the antimicrobial properties of deep eutectic
solvents formed entirely from fatty acids, combining capric acid with other saturated fatty acids of longer chain length (Silva et al. 2019). They observed activity
against Gram-positive bacteria and Candida albicans, particularly with a capric
acid:lauric acid formulation. A significant result is that these deep eutectic solvents
could promote the detachment of Escherichia coli biofilms (Fig. 2.5).
Therapeutic Deep Eutectic Solvents for Applications in the Oral Cavity
As mentioned above, Lim et al. formed a complex between erythritol and betaine in
an attempt to treat biofilms in the oral cavity (Lim et al. 2017). The extracellular
matrix secreted by the bacteria in these biofilms makes them extremely resistant to
antibiotics. Detachment of Streptococcus mutans biofilms observed in an in vitro
assay was observed after application of the betaine:erythritol (2:1) mixture but not
with the components separately. Measurements by atomic force microscopy showed
a reduction in the adhesive strength of the biofilm after contact with the betaineerythritol mixture. It was observed that the water-insoluble extracellular polysaccharide could be dissolved in this mixture. These results are encouraging for the
treatment of dental plaque because the constituent molecules are nontoxic. In a
related study, the same group observed activity against biofilms of a complex
2 Deep Eutectic Solvents for Innovative Pharmaceutical Formulations
attenuated total reflection demonstrated increased lipid content in treated cells.
Importantly, Escherichia coli cells did not develop resistance after multiple or prolonged exposures to the choline:geranic acid solvent.
Another mechanism of activity of deep eutectic solvents against bacteria was
investigated by Sadaf et al. (Sadaf et al. 2018). In in vitro studies, they looked at the
ability of a formulation that they named “maline,” composed of malonic acid and
choline chloride in a 2:1 molar ratio to inhibit the activity of an extracellular enzyme,
β-lactamase from Bacillus cereus. As in the studies on lysozyme reported above,
circular dichroism and intrinsic fluorescence were used to monitor protein structure.
This showed a transition of α-helix to random coil in the presence of maline,
together with fluorescence quenching that could have been due to loss of the tertiary
structure of the protein.
The antimicrobial activity of a number of natural deep eutectic solvents was
tested toward several bacterial species, as well as a yeast strain and three human cell
lines by Radošević et al. (Radošević et al. 2018). The highest activity toward bacteria was obtained with deep eutectic solvents containing organic acids – oxalic,
malic, and citric. The yeast Candida albicans was quite resistant to these solvents.
They also recorded cytotoxic effects toward human tumor cells lines HeLa and
MCF-7 with a choline chloride:oxalic acid deep eutectic solvent while a normal cell
line, HEK293T, was more resistant. The antioxidant capacity of the deep eutectic
solvents was measured by their capacity to absorb oxygen radicals. Most of the
solvents tested had oxygen scavenging properties. One deep eutectic solvent, composed of betaine, malic acid, and proline, stimulated mammalian cell growth while
having strong antioxidant properties.
Recently, Silva et al. investigated the antimicrobial properties of deep eutectic
solvents formed entirely from fatty acids, combining capric acid with other saturated fatty acids of longer chain length (Silva et al. 2019). They observed activity
against Gram-positive bacteria and Candida albicans, particularly with a capric
acid:lauric acid formulation. A significant result is that these deep eutectic solvents
could promote the detachment of Escherichia coli biofilms (Fig. 2.5).
Therapeutic Deep Eutectic Solvents for Applications in the Oral Cavity
As mentioned above, Lim et al. formed a complex between erythritol and betaine in
an attempt to treat biofilms in the oral cavity (Lim et al. 2017). The extracellular
matrix secreted by the bacteria in these biofilms makes them extremely resistant to
antibiotics. Detachment of Streptococcus mutans biofilms observed in an in vitro
assay was observed after application of the betaine:erythritol (2:1) mixture but not
with the components separately. Measurements by atomic force microscopy showed
a reduction in the adhesive strength of the biofilm after contact with the betaineerythritol mixture. It was observed that the water-insoluble extracellular polysaccharide could be dissolved in this mixture. These results are encouraging for the
treatment of dental plaque because the constituent molecules are nontoxic. In a
related study, the same group observed activity against biofilms of a complex
2 Deep Eutectic Solvents for Innovative Pharmaceutical Formulations