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Journal Article 
Immobilization of cholesterol esterase in mesoporous silica materials and its hydrolytic activity toward diethyl phthalate 
Orita, T; Tomita, M; Saito, T; Nishida, N; Kato, K 
Materials Science and Engineering C: Materials for Biological Applications
ISSN: 0928-4931
EISSN: 1873-0191 
Cholesterol esterase (CE, cholesteryl ester hydrolase, EC from porcine pancreas (molecular weight 400-500 kDa) exhibits hydrolytic activity
toward various toxic organic phthalate esters. CE was confined in the nanospace (diameter 3-30
nm) of five types of mesoporous silica (MPS) that differ in structural properties such as pore
diameter, pore volume, and particle morphology. These structural properties were characterized by
transmission electron microscopy, small-angle X-ray diffraction, N-2 adsorption-desorption
experiments, solid-state C-13 nuclear magnetic resonance (NMR), and solid-state Si-29 NMR.
Catalytic activities of immobilized and free CE were evaluated by the hydrolysis of diethyl
phthalate in phosphate buffer solutions containing an organic cosolvent. Optimal activity
recovery was achieved when CE was immobilized in n-decane-functionalized MPS, which had a large
pore size (22.5 nm). The immobilization also protected against effects of temperature within the
range 30 degrees C-60 degrees C; CE immobilized in n-decyl-functionalized MPS exhibited better
thermal stability than in non-functionalized MPS or free CE Moreover, it retained approximately
60% of its catalytic activity even after six catalytic cycles. (c) 2012 Elsevier B.V. All rights
Cholesterol esterase; Enzyme; Mesoporous silica; Phthalate esters; Thermal stability 
• Diethyl phthalate (DEP)
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