Tailoring properties of natural deep eutectic solvents with water to facilitate their applications

Abstract

Previously it was demonstrated that natural deep eutectic solvents (NADES) are promising green solvents for the extraction of natural products. However, despite their potential, an obvious disadvantage of NADES is the high viscosity. Here we explored the dilution effect on the structures and physicochemical properties of NADES and their improvements of applications using quercetin and carthamin. The results of FT-IR and (1)H NMR experiments demonstrated that there are intensive H-bonding interactions between the two components of NADES and dilution with water caused the interactions weaken gradually and even disappeared completely at around 50% (v/v) water addition. A small amount of water could reduce the viscosity of NADES to the range of water and increase the conductivity by up to 100 times for some NADES. This study provides the basis for modulating NADES in a controllable way for their applications in food processing, enzyme reactions, pharmaceuticals and cosmetics.

The Effect of Water upon Deep Eutectic Solvent Nanostructure: An Unusual Transition from Ionic Mixture to Aqueous Solution

“…Therefore, above this point, it is inappropriate to describe the system as a DES, and it should instead be considered as a solution of DES components in water. Importantly, this nanostructure transition point correlates with trends in the physical properties of cholinium DES/water mixtures 8, 12, 23…”

“…All DES interactions are weakened upon addition of 1 molar equivalent of water, except for the strengthened choline–urea hydrogen‐bonding interaction (OH⋅⋅⋅NH 2 ), which is reflected in the coordination numbers shown in the Supporting Information. This unexpected increase in intermolecular interaction strength explains why DES‐1 w systems do not undergo the anticipated viscosity reduction 8, 12. Whilst 80 % (on average) of the original nanostructure is retained at 1 w , even low‐level DES/water mixtures clearly differ from pure DES, with water contributing to the nanostructure and hence altering the physicochemical properties.…”

“…Latent absorbed water is unavoidable, and impacts upon the physicochemical properties of DESs, such as the melting point, with inadequate characterization leading to poor reproducibility 7. A relatively new approach leverages the favorable physicochemical properties of DES/water mixtures, such as lowered viscosity 8. Trends in these properties suggest that there is an upper limit to this hydration above which DESs are more like aqueous solutions 9, 10, 11.…”

Development of a Method Based on Natural Deep Eutectic Solvents for Extraction of Flavonoids from Food Samples

“…These solvents have the following environmental and economic advantages: they are non-volatile, have a low toxicity, are biodegradable, sustainable, and inexpensive, and are made using simple preparation methods. They also show very good physicochemical properties: liquid state below 0°C, adjustable viscosity, a broad range of polarities, and ability to dissolve a wide range of compounds (Paiva et al 2014;Faggian et al 2006;Dai et al 2015). NADES therefore have good potential for the extraction of valuable secondary metabolites for use in the food and pharmaceutical industries.…”

Ultrasound-Assisted Extraction of Polyphenolic Antioxidants from Olive (Olea europaea) Leaves Using a Novel Glycerol/Sodium-Potassium Tartrate Low-Transition Temperature Mixture (LTTM)

“…On the other hand, water content as high as 63.8% (v/v) has been used in glycerol-based LTTMs for the extraction of polyphenolic antioxidants [15]. However, water proportion exceeding 50% may involve danger of LTTM disintegration and loss of their peculiar properties [16].…”