Immobilization of hemoglobin on stable mesoporous multilamellar silica vesicles and their activity and stability
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A stable mesoporous multilamellar silica vesicle (MSV) was developed with a gallery pore size of about 14.0 nm. A simulative enzyme, hemoglobin (Hb), was immobilized on this newly developed MSV and a conventional mesoporous silica material SBA-15. The structures and the immobilization of Hb on the mesoporous supports were characterized with x-ray diffraction, transmission electron microscopy, N2 adsorption-desorption isotherms, Fourier transform infrared, ultraviolet-visible spectroscopy, and so forth. MSV is a promising support for immobilizing Hb due to its large pore size and high Hb immobilization capacity (up to 522 mg/g) compared to SBA-15 (236 mg/g). Less than 5% Hb was leached from Hb/MSV at pH 6.0. The activity study indicated that the immobilized Hb retained most peroxidase activity compared to free Hb. Thermal stability of the immobilized Hb was improved by the proctetive environment of MSV and SBA-15. Such an Hb-mesoporous support with high Hb immobilization capacity, high activity, and enhanced thermal stability will be attractive for practical applications.
I. INTRODUCTION
Enzymes are excellent biological catalysts with high selectivity and efficiency, but their use in chemical transformations is severely limited by their poor stability and chemical sensitivity.1 To overcome these limitations, a strategy of immobilization of enzymes on insoluble supports has been extensively investigated and widely used in practical applications for several decades.2–12 The immobilization of enzymes on inorganic matrixes, such as glass, silica gel, metal and metal oxide, is important for applications, due to its good mechanical property, thermal stability, and resistance against microbial attack and organic solvent.13–15 However, in contrast to organic polymers, suitable inorganic matrixes for the immobilization of enzymes are relatively less. This is presumably due to the synthesis difficulties of desirable structures and the absence of relative functional groups in inorganic matrixes compared to that of organic polymers. Among inorganic matrixes, mesoporous silica materials have attracted much attention as promising host materials for the immobilization of enzymes because of their larger surface areas, ordered mesoporous structure,
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0360 2682
J. Mater. Res., Vol. 20, No. 10, Oct 2005
tunable pore sizes and volumes, and well-defined surface properties for modification. After Diaz and Balkus11 first reported the immobilization of cytochrome C, papain, and trypsin in MCM-41, there have been a number of reports describing the use of mesoporous silica materials for immobilizing enzymes. Wright et al.16–18 have described the immobilization of trypsin in MCM-41, MCM-48, and SBA-15 through both physical adsorption and covalent attachment. The amount of enzyme immobilized on the support is related to the pore size of the mesoporous supports, and the pore size and the structure of the support could also affect the activity of
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