FULL PAPER
DOI: 10.1002/chem.201203833
Enzyme Entrapped in Polymer-Modified Nanopores: The Effects of
Macromolecular Crowding and Surface Hydrophobicity
Jia Liu, Juan Peng, Shuai Shen, Qianru Jin, Can Li,* and Qihua Yang*[a]
Abstract: Macromolecular crowding is
an ubiquitous phenomenon in living
cells that significantly affects the func-
tion of enzymes in vivo. However, this
effect has not been paid much atten-
tion in the research of the immobiliza-
tion of enzymes onto mesoporous
silica. Herein, we report the combined
effects of macromolecular crowding
and surface hydrophobicity on the per-
formance of an immobilized enzyme by
accommodating lipase molecules into a
series of mesoporous silicas with differ-
ent amounts of inert poly(methacry-
late) (PMA) covalently anchored
inside the nanopores. The incorpora-
tion of the PMA polymer into the
nanopores of mesoporous silica enables
the fabrication of a crowded and hy-
drophobic microenvironment for the
immobilized enzyme and the variation
in polymer content facilitates an adjust-
ment of the degree of crowding and
surface properties of this environment.
Based on this system, the catalytic fea-
tures of immobilized lipase were inves-
tigated as a function of polymer con-
tent in nanopores and the results indi-
cated that the catalytic efficiency, ther-
mostability, and reusability of immobi-
lized lipase could all be improved by
taking advantage of the macromolecu-
lar crowding effect and surface hydro-
phobicity. These findings provide in-
sight into the possible functions of the
macromolecular crowding effect, which
should be considered and integrated
into the fabrication of suitable mesopo-
rous silicas to improve enzyme immo-
bilization.
Keywords: biocatalysis · immobili-
zation · lipase · mesoporous materi-
als · nanopores
Introduction
ed as one of the main reasons for this decreased activity.
Previous studies have shown that the nature of the mesopo-
rous silica, such as its textural properties (pore size, surface
area, and pore volume), surface charge(s), and surface hy-
drophobicity/hydrophilicity play important roles in deter-
mining the catalytic efficiency and stability of the immobi-
lized enzymes.[3,12–14] However, the macromolecular crowd-
ing effect of an enzyme, one of the key characteristics in the
cellular environment and intimately coupled to the enzyme
function in vivo, has not been paid enough attention in
terms of enzyme immobilization.[15–17]
Cells are a crowded environment, in which the macromo-
lecules, such as proteins, nucleic acids, lipids, and other cy-
toskeletons, can occupy up to 40% of the total cellular
volume.[16–18] In such a crowded environment, the enzymes
behave in different ways to their dilute solutions in test
tubes.[19] Experimental and theoretical studies have been
performed to mimic the intracellular environment by adding
crowding agents, such as ficoll, dextran, and PEG, into the
buffer solution of enzymes. The presence of these crowding
agents, which do not participate directly in a particular bio-
logical process, can decrease the amount of free space and
the volume of solvent available to the protein and, thus, can
significantly affect the dynamics and conformation of the
enzymes. It has been demonstrated that macromolecular
crowding could stabilize the folded (native) state of enzyme,
restrain the dissociation of multiple enzyme, increase the ef-
fective concentrations of the enzyme molecules, and modu-
late the affinity between the enzyme and the substrate
whilst inducing alteration in the enzyme structure.[16,20–24]
Enzymes that display high catalytic efficiency and selectivity
under mild conditions are promising catalysts for use in the
chemical and pharmaceutical industries.[1,2] However, the
practical application of native enzyme suffers from severe
limitations owing to its low stability against heat, extreme
pH values, and organic solvents, as well as the difficulty in
its separation and reuse.[3,4] Pleasingly, the immobilization of
the native enzyme onto solid materials could partly solve
these problems and facilitate its use in continuous produc-
tion processes, which are favorable for industrial applica-
tions.[5–8] Mesoporous silicas have emerged as a new class of
promising candidates for enzyme immobilization owing to
their large surface area, ordered porous structure, narrow
pore-size distribution, facile functionalization, and chemical
and mechanical stability.[9–11] However, enzymes that are ac-
commodated inside mesoporous silicas often exhibit lower
activity compared with the native enzymes. The altered mi-
croenvironment around the immobilized enzymes is regard-
[a] J. Liu, J. Peng, S. Shen, Q. Jin, Prof. Dr. C. Li, Prof. Dr. Q. Yang
State Key Laboratory of Catalysis
Dalian Institute of Chemical Physics
Chinese Academy of Sciences
457 Zhongshan Road, Dalian 116023 (China)
Fax : (+86) 411-84694447
Supporting information for this article is available on the WWW
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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