"Enzymes in Mesoporous Silicates"

Edmond Magner

Materials and Surface Science Institute, Department of Chemical and Environmental Sciences, University of Limerick, Limerick

edmond.magner@ul.ie

Mesoporous silicates (MPS) were first described by Beck et al.1 in 1991. MPS possess large surface areas (up to 1000 m2 g-1), highly ordered pore structures and very tight pore size distributions (PSD); properties which have made these materials attractive candidates for a wide range of applications in catalysis2, sensor3, and separation technologies4. These materials have pore channels of diameter 1.5 to 10 nm which are of a similar size range to many proteins. MPS possess a number of additional attributes, which make them attractive candidates for the immobilisation of proteins. It is possible to chemically modify their surfaces with various functional groups, enabling electrostatic attraction or repulsion between an MPS and the biological molecule of interest to be maximised5. As a result of their silicate inorganic framework, MPS are chemically and mechanically stable and are resistant to microbial attack.

A systematic examination of the interactions between proteins and MPS6-9 showed that the amount and stability of adsorbed protein depended on the MPS pore diameter, isoelectric point (of both the protein and MPS), degree of hydrophilicity /hydrophobicity and on the type of surfactant template used to synthesise the MPS. The adsorption of a range of enzymes on to MPS has been examined: α-chymotrypsin, pepsin, horseradish peroxidase, glucose oxidase, subtilisin, lipases, and xylanase. Surprisingly, the rate of reaction is not diminished when the enzymes are held within the pores, indicating that there are no diffusional limitations. Substantial rate enhancements (1000-fold) have been observed in non-aqueous solvents, while the immobilized proteins are substantially more stable towards thermal denaturation10,11. Biocatalytic reactors based on MPS are robust and stable.

[1] Klibanov, A.M. Nature, 2001, 409, 241.
[2] Johnson, B. F. G. et al. Chem. Commun.
[3] Zhang, Z., Suo, J., Zhang, X., Li, S. Chem. Commun. 1998, 241.
[4] Chakraborty, P. J. Mater. Sci. 1998, 33, 2235.
[5] Han, Y.-J., Stucky, G. D., Butler, A. J. Amer. Chem. Soc. 1999, 121, 9897.
[6] Deere, J, E. Magner, J.G. Wall, B.K. Hodnett, J. Phys. Chem. B, 2002, 106, 7340-7347.
[7] Deere, J, E. Magner, J.G. Wall, B.K. Hodnett, Chem. Comm. 2001, 466-467.
[8] Deere, J., E. Magner, J. G. Wall and B. K. Hodnett, Catalysis Letters, 2003, 85, 19-23.
[9] Deere, J.,et al. Langmuir, 2004, 20, 532-536.
[10] Deere, J., E. Magner, J. G. Wall and B. K. Hodnett. Biotech. Prog., 2003, 19, 1238-1243.
[11] Goradia, D., J. Cooney, B.K. Hodnett, and E. Magner, J. Mol. Cat. B, 2005, in press.