Mickaël Laguerre, Alexis Lavaud – Naturex, France SUSTAINABILITY
The rise of deep eutectics from nature to cosmetics
Deep eutectic solvents probably evolved very early in the history of living organisms and may reflect a fundamental component of the chemistry of life. Scientists are now rediscovering all kinds of molecule combinations engineered by nature into these unique mixtures. Harnessing these bio-inspired solvents for eco-extraction purposes is one of the most exciting ways to recover phytoactive molecules using the same strategy adopted by plants for their survival. The depletion of fossil resources,
combined with changes in the regulatory, environmental and toxicological frameworks for solvents, puts heavy selective pressure on the development of alternatives to petro-based organic solvents. Finding sustainable and eco-friendly extraction technologies capable of producing extracts with novel phytochemical profiles and enhanced efficacy has become increasingly important.
Andrew Abbott’s discovery of a new type of solvents During the past decade, a new generation of bio-inspired multi-molecular solvents has emerged with a great potential for many industrial applications, especially for the cosmetics sector. In 2003, Andrew Abbott and his collaborators from the University of Leicester1
first coined them as deep
eutectic solvents from the Greek term ‘eutektos’ meaning ‘easily melted’.
a Mp Mp b Mp Mp (A) Mp (B) Mp (A) ∆Tf Ep Mp (B) ∆Tf Ep Mp 100% (A) 50% Ec Mole fraction 100% (B) 100% (A) 50% Ec Mole fraction
Figure 1: Schematic representation of the difference between ‘eutectic solvents’ a) and ‘deep eutectic solvents’ b) on a two-component phase diagram. [Mp: Melting point; Tf: magnitude of the depression of the melting point; Ep: eutectic point; Ec: eutectic composition].
The solvents can be defined as a combination of compounds endowed with a melting point, or a glass transition temperature, much lower than those of their individual components taken separately. In other words, these solvents refer to liquids close to the eutectic composition of the mixture (the so-called eutectic point) that is the molar ratio of the components which gives the lowest melting point (Fig. 1). Put simply, one can imagine solid
powders, or compounds with a melting point at room temperature, which, when mixed in the right proportions, produce a liquid solvent through the formation of a eutectic mixture (eutectigenesis). If deep eutectic solvents result from the standard
Ordered system: solid (crystalline phase)
A A A A
A A A A
A A A A
A
A A A A
A A A
+
B B B B
B B B B
B B B B
B
B B B B
B B B
Eutectigenesis A Figure 2: A simplified view of the eutectigenesis phenomenon at the supramolecular level. February 2016 PERSONAL CARE 45
formation of a eutectic between two components, they differ, however, from most eutectic mixtures, in their very large decrease in melting point (∆Tf), which can be as high as 100-200˚C2
(Fig. 1).
Therefore, Abbott et al. added the term ‘deep’ to the already known concept of eutectic solvents to highlight this difference and to give rise to the so-called ‘deep eutectic solvents’ or ‘DES’. Among many of their idiosyncrasies is
the fact that they do not exhibit vapour pressure, meaning that they do not evaporate at room temperature. Furthermore, their unusual physical chemical properties make them particularly effective in solubilising compounds that are usually poorly soluble in water or lipid
Disordered system: liquid B A
B B
B B A B A B Cavity B 100% (B)
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