Encapsulation in Sol-Gel Matrices

Several enzymes have been immobilized in sol-gel matrices effectively and employed in diverse applications. Urease, catalase, and adenylic acid deaminase were first encapsulated in sol-gel matrices [72], The encapsulated urease and catalase retained partial activity but adenylic acid deaminase completely lost its activity. After three decades considerable attention has been paid again towards the bioencapsulation using sol-gel glasses. Braun et al. [73] successfully encapsulated alkaline phosphatase in silica gel, which retained its activity up to 2 months (30% of initial) with improved thermal stability. Further Shtelzer et al. [58] sequestered trypsin within a binary sol-gel-derived composite using TEOS and PEG. Ellerby et al. [74] entrapped other proteins such as cytochrome c and Mb in TEOS sol-gel. Later several proteins such as Mb [8], hemoglobin (Hb) [56], cyt c [55, 75], bacteriorhodopsin (bR) [76], lactate oxidase [77], alkaline phosphatase (AP) [78], GOD [51], HRP [79], urease [80], superoxide dismutase [8], tyrosinase [81], acetylcholinesterase [82], etc. have been immobilized into different sol-gel matrices. Hitherto some reports have described the various aspects of sol-gel entrapped biomolecules such as conformation [50, 60], dynamics [12, 83], accessibility [46], reaction kinetics [50, 54], activity [7, 84], and stability [1, 80],... 

Encapsulation of Lipase from Candida rugosa in Sol-Gel Matrices... 

Several bioactive proteins retained their activity and conformation in sol-gel matrices. The sol-gel entrapped heme proteins such as cytochrome c and Mb showed good stability against pH and thermal perturbations compared to protein in solution [29, 55]. The sol-gel caged cytochrome c (cyt c) showed high thermal stability due to the exact fitting of the protein inside the cage, which was controlled by the protein size [56]. Sol-gel encapsulated acid phosphatase [57] and bovine carbonic anhydrase II (BCA II)... 

Antibodies bound by sol-gel encapsulation are used in medicine, immunochro-matography, immunosensors, etc. Immimoglobulins that are trapped retain their ability to bind external antigens from solutions. Antibodie 14D9 catalyze hydrolysis of cyclic acetals, ketals, epoxides, etc. when incorporated in sol-gel matrices. The ability of a sol-gel matrix containing 10% PEG and antiatrazine antibodies to bind atrazine was studied. This matrix recogni2es and binds atrazine and widely distributed herbicides. In this case, neither leaching of antibodies nor nonspecific physical sorption of atrazine on the ceramic matrix occurs. The activity did not decrease... 

Nishikiori H., Tanaka N., Fujii T. Influence of water on molecular forms of rhodamine B in dip-coated thin films. Res. Chem. Intermed. 2000 26 469-482 Pouxviel J.C., Dunn B., Zink J.I. Fluorescence study of aluminosilicate sols and gels doped with hydroxy trisulfonated p3rene. J. Phys. Chem. 1989 93 2134-2139 Pouxviel J.C., Parvaneh S., Knobbe E.T., Dunn B. Interactions between organic dyes and sol-gel matrices. Sohd State Ionics 1989 32/33 646-654 Premkumar J.R., Sagi E., Rozen R., Belkin S., Modestov A.D., Lev O. Fluorescent bacteria encapsulated in sol-gel derived silicate films. Chem. Mater. 2002 14 2676-2686 and references therein... 

In a similar vein, Gelman et al. [25] demonstrated encapsulation by the use of two SiC>2 sol-gel matrices [26,27] to immobilize two catalysts Wilkinson s catalyst and an amine that acts as a base catalyst. The reaction is illustrated in Scheme 5.10. 

Encapsulation of proteins in bulk and thin film sol-gel matrices. Journal of Sol-Gel Science and Technology, 8, 629-634. 

Initially, the sol gel compositions were optimized using Congo red dye as the dopant because of its optical properties. This facilitates monitoring of the release process by optical spectroscopy. Next, the gels were evaluated for their stabilization and release of subtilisin. These sol gel matrices bring about controlled release of the encapsulated enzyme molecules as a response to a change in the water content of the medium (Figure 2.20).15... 

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