Ionic L iquid-Coated E nzyme for
Biocatalysis in Organic Solvent
J ae Kwan Lee and Mahn-J oo Kim*
Department of Chemistry, Division of Molecular and
Life Sciences, Pohang University of Science and Technology,
San 31 Hyojadong, Pohang, Kyungbuk 790-784, Korea
Received J une 28, 2002
Abstract: Ionic liquid-coated enzyme (ILCE) is described
as a useful catalyst for biocatalysis in organic solvent. An
ionic liquid, [PPMIM]-[PF6] (1, [PPMIM] ) 1-(3′-phenylpro-
pyl)-3-methylimidazolium), which is solid at room temper-
ature and becomes liquid above 53 °C, was synthesized in
two steps from N-methylimidazole. The coating of enzyme
was done by simply mixing commercially available enzyme
with 1 in the liquid phase above 53 °C and then allowing
the mixture to cool. A representative ILCE, prepared with
a lipase from Pseudomonas cepacia, showed markedly
enhanced enantioselectivity without losing any significant
Nonaqueous biocatalysis provide a useful component
of methodology in organic synthesis.1For example, lipase
catalysis in organic solvents is of great use for the
synthesis of optically active compounds such as chiral
alcohols, acids, and their esters.2However, biocatalysis
in nonaqueous media often suffers from reduced activity,
selectivity, or stability of enzyme.3To overcome these
limitations, many approaches have focused on the de-
velopment of more efficient enzymes by enzyme modifica-
tion, molecular imprinting, additiveaddition, or substrate
matching.4Some recent examples include cross-linked
enzyme crystals4a,band aggregates,4cligand4d-gor inor-
ganic salt4hco-lyophilized enzymes, and enzyme-coated
microcrystals.4iAlthough thesemodified enzymes exhibit
better activity, selectivity, or stability, the procedures for
their preparations in most cases are rather complicated.
Weherein wish toreport for thefirst timean ionic liquid-
coated enzyme (ILCE) that is readily prepared and
exhibits markedly enhanced enantioselectivity and reli-
Recently, a few groups including us5havereported that
ionic liquids6,7havegreat potential as alternativereaction
media for biocatalysis and biotransformation. It was
observed that their use enhanced the selectivity of the
enzyme.5c,dIt was alsodemonstrated that they are useful
as media for the enzymatic reaction of polar substrates,
which are difficult to dissolve in conventional organic
solvents.5fOne of the interesting properties of ionic
liquids, we think, is their insolubility in water or organic
solvents, which led us to envisage that they might be
suitable as the coating materials for immobilizing bio-
catalysts. Particularly, we thought that room-tempera-
ture solid-phase ionic liquids, which become liquid at
elevated temperature, would be of great use for such a
purpose. To test our idea, a novel ionic liquid [PPMIM]-
[PF6] (1, [PPMIM] ) 1-(3′-phenylpropyl)-3-methylimida-
zolium) was synthesized in good yields via twosteps from
N-methylimidazole (Scheme 1). It was observed that the
ionic liquid was solid at room temperature and became
liquid over 53 °C.
As a representative enzyme for the preparation of
ILCE, Pseudomonas cepacia lipase (PCL)8was chosen
since it had been frequently used for biotransformations
in organic solvents. In a typical procedure for the
preparation of ILCE, solid 1 was converted to its liquid
phase by heating above 53 °C. Tothis liquid were added
enzyme powders (0.1 mass equiv) and the resulting
mixture was stirred with a glass rod to get a uniform
heterogeneous solution. The solution was then allowed
tocool toroom temperatureuntil theenzyme-ionic liquid
mixture solidified. The solid phase was broken down to
a small size of particles with a spatula. The small ILCE
particles were then used without any further treatment
in the next experiments for testing their activity and
The enantioselectivity of ILCE was examined with the
transesterification reactions of secondary alcohols 2a-e
(1) (a) Wong, C.-H.; Whitesides, G. M. Enzymes in Synthetic Organic
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(8) This enzyme is available from some commercial suppliers such
as Fluka, Roche, and Amano. We used the one provided by Amano.
SCHE ME 1. Synthesis of Ionic L iquid
10.1021/jo026116q CCC: $22.00 © 2002 American Chemical Society
Published on Web 08/20/2002
J . Org. Chem. 2002, 67, 6845-6847 6845