CHEMCATCHEM
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DOI: 10.1002/cctc.201400077
Whole-Cell Biocatalysis in Deep-Eutectic-Solvents/Aqueous
Mixtures
[a]
[a, b]
Zaira Maugeri and Pablo Domꢀnguez de Marꢀa*
Whole-cell biocatalysis with the use of baker’s yeast is demon-
strated in different mixtures of water with deep eutectic sol-
vents (DESs; choline chloride/glycerol, 1:2 mol/mol). Enantiose-
lective ketone reduction is observed for long reaction times
tures, and adequate biodegradability that are largely available
at acceptable costs; consequently, a broad number of promis-
[4]
ing applications have already appeared in the open literature.
In a broad sense, DESs are formed if solid quaternary ammoni-
um halide salts (e.g., choline chloride) are combined and
gently heated with hydrogen-bond-donor molecules such as
(
>200 h), which suggests that the whole cells remain stable in
these neoteric solvents. By changing the proportion of the DES
added, a complete inversion of enantioselectivity is observed,
from approximately 95% enantiomeric excess (ee) (S) in pure
water to approximately 95%ee (R) in the pure DES. Presuma-
bly, some (S)-oxidoreductases present in baker’s yeast are
inhibited by DESs.
[4,5]
alcohols, amides, amines, and carboxylic acids. On this basis,
a broad number of biomass-derived compounds may be used
to straightforwardly form novel tailored solvents. In compari-
son to more “classic” ionic liquids, DESs are composed of bio-
degradable and inexpensive materials.
Considering these aspects, some DESs have started to be as-
sessed as tools for biocatalysis as well, either as solvents or as
separative agents to overcome challenging workup proce-
Biocatalysis has emerged in the last decades as a powerful
option to conduct catalytic reactions typically under environ-
[3,6,7]
dures.
teases, and epoxide hydrolases) as robust and versatile enzymes
Examples comprise mainly hydrolases (lipases, pro-
[1]
mentally friendly conditions and with high selectivities. Apart
from the enzymatic (and whole-cell) performance in aqueous
media, the setup of biocatalytic processes under non-aqueous
conditions—the so-called non-conventional media—provides
a practical framework to enhance the solubility of the sub-
strate and product, whilst at the same time providing an
enzyme-friendly working conditions. This has been known for
decades for free enzymes, especially hydrolases, and in recent
years whole cells have also started to be assessed under (bulk)
[1]
already used for many applications. For instance, the use of
different biomass-derived DESs has found application for pro-
teases in peptide synthesis, whereby the (frequent) need to
dissolve substrates with different polarities makes the use of
[6a]
neoteric solvents attractive to reach high substrate loadings.
Apart from using free, isolated enzymes, the setup of whole-
cell-catalyzed reactions enables simple processes with access
[8]
to sophisticated chemistries. Specifically, if cofactor-depen-
dent enzymes (e.g., oxidoreductases) are considered, the possi-
bility of in situ regenerating the cofactor upon establishing
whole-cell biocatalysis represents an asset for its practical im-
plementation. Typically, processes are set in aqueous solutions
[
2]
water-free conditions, such as neat substrates or ionic liq-
[
3]
uids among other non-aqueous media.
In this area, ionic liquids have attracted some interest as
[3]
novel (tailored) solvents for a broad number of applications.
[8]
Although the setup of solvent-free processes (if feasible) clearly
appears as a superior alternative, in some cases the need to
dissolve challenging substrates—or those with different polari-
ties—make the choice of ionic solvents attractive. Yet, prob-
lems associated with the toxicological effects of many ionic liq-
uids, as well as their (still) high price represent important hur-
(emulsions) or in biphasic systems. So far, just a few examples
[3]
of whole-cell redox biocatalysis in virtually water-free or
[9]
micro-aqueous systems have been reported. Another work
showed the integrity of lyophilized E. coli whole cells in
[10]
DESs, but to our knowledge, no reports on whole-cell bioca-
talysis in DESs have been published so far and only examples
of whole cells with ionic liquids mixtures have been
[
3]
dles for their further practical implementation. To overcome
these aspects, over the past decade the so-called deep eutectic
solvents (DESs) have emerged as a new generation of ionic sol-
vents with tailored properties, diminished toxicological fea-
[3,11]
reported.
Herein, the first studies in that line are presented.
As prototypical DESs, choline chloride/glycerol mixtures
(1:2 mol/mol) were built. As whole cells, commercially available
nonhazardous baker’s yeast was used, for which many enantio-
selective reductions of ketones have been reported, catalyzed
[
a] Z. Maugeri, Dr. P. Domꢀnguez de Marꢀa
Institut fꢁr Technische und Makromolekulare Chemie (ITMC)
RWTH Aachen University
by one or more of the multiple redox enzymes present in its
[8,12]
genome.
As a bench reaction, the enantioselective reduc-
Worringerweg 1, 52074 Aachen (Germany)
E-mail: dominguez@itmc.rwth-aachen.de
tion of ethyl acetoacetate was selected (Scheme 1).
Considering that both whole cells and enzymes need a cer-
tain amount of water for their activity, in a first set of experi-
ments different mixtures of the DES and water were assessed
as reaction media for the desired process. A reaction conduct-
ed in pure water was included for comparison. The results are
depicted in Figure 1.
[b] Dr. P. Domꢀnguez de Marꢀa
Present address:
Sustainable Momentum
Ap. Correos 3517. 35004, Las Palmas de Gran Canaria
Canary Islands (Spain)
Homepage: www.sustainable-momentum.net
ꢁ
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 0000, 00, 1 – 3
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