Background: Biocatalysis has many attractive features in the context of green chemistry,
due to the high efficiency of chemical transformations and the renewable character of the enzymes
used. Since the beginning of this century, ILs have emerged as exceptionally interesting non-aqueous
reaction media for biotransformations because of their unique solvent properties, headed by their negligible
vapour pressure and their exceptional ability to maintain enzymes in active and stable conformations.
However, the goal of green chemistry is much more than simply replacing hazardous solvents
with environmentally benign ones, and it is necessary to devise new clean methodologies that
will fulfil the sustainable requirements for efficient transformations of substrates, product recovery
and the reuse of all the elements of the reaction system.
Results: The use biocatalyst in IL/scCO2 biphasic systems was the first approach forward to develop integral
green chemical processes in non-aqueous environments. The combination of these sustainable
tools provides synergies in both biocatalyst performance (i.e. improved activity and enantioselectivity,
enhanced stability, etc.), and the genuine separation technologies of nearly pure products. Sponge-Like
Ionic Liquids (SLILs) were recently reported as a new platform for green biocatalytic chemical processes
using straightforward technologies. These SLILs are a new class of hydrophobic ILs based on cations
with long alkyl side-chains (e.g. 1-octadecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide,
([C18mim][NTf2], etc.), which behaves as a sponge-like system by switching from liquid to solid phase as
the temperature changes. Thus, such ILs are able to dissolve (“soak up”) hydrophobic compounds as a
liquid phase, and products can then be “wrung out” by centrifugation of the resulting solid phase after
cooling. Based on this property, clean biocatalytic processes for the production of nearly pure compounds
of high added value (e.g. geranyl acetate, anisyl acetate, biodiesel, monolaurin, etc.) can be easily designed
by the coupling of both biotransformation and separation steps, in a sustainable approach of high
potential for practical applications at industrial level.
Conclusions: The use of biocatalytic approaches in green non-conventional reaction media holds
much promise for the development of a sustainable chemical manufacturing industry. The combination
of enzymes with multiphase neoteric systems (SLILs, ILs and/or scCO2) should be explored in
the near future, as a clear strategy for developing integral new green multi-catalytic synthetic processes
of industrial interest (e.g. pharmaceutical drugs).