Sol-gel encapsulation

S.3.2 Sol-Gel Encapsulation of Reactive Species Another new and attractive route for tailoring electrode surfaces involves the low-temperature encapsulation of recognition species within sol-gel films (41,42). Such ceramic films are prepared by the hydrolysis of an alkoxide precursor such as, Si(OCH3)4 under acidic or basic condensation, followed by polycondensation of the hydroxylated monomer to form a three-dimensional interconnected porous network. The resulting porous glass-like material can physically retain the desired modifier but permits its interaction with the analyte that diffuses into the matrix. Besides their ability to entrap the modifier, sol-gel processes offer tunability of the physical characteristics... 

Scheme 5.11 Reaction routes for various saturated and unsaturated carboxylic acids and alcohols using a rhodium catalyst and a lipase. s-g indicates sol-gel encapsulation of the catalyst superscript u and s indicate unsaturated and saturated compounds,...

Dave, B.C., Dunn, B., Valentine, J.S. and Zink, J.I. (1994) Sol-gel encapsulation methods for biosensors. Analytical Chemistry, 66, 1120A-1127A. 

Gill, I. and Ballesteros, A. (2000) Bioencapsulation within synthetic polymers (Part 1) Sol-gel encapsulated biologicals. Trends in Biotechnology, 18, 282-296. 

Applications of sol-gel-processed interphase catalysts. Chemical Reviews, 102, 3543-3578. Pierre, A.C. (2004) The sol-gel encapsulation of enzymes. Biocatalysis and Biotransformation, 22, 145-170. Shchipunov, Yu.A. (2003) Sol-gel derived biomaterials of silica and carrageenans. Journal of Colloid and Interface Science, 268, 68-76. Shchipunov Yu.A. and Karpenko T.Yu. (2004) Hybrid polysaccharide-silica nanocomposites prepared by the sol-gel technique. Langmuir, 20, 3882-3887. 

Eggers, D.K. and Valentine, J.S. (2001) Crowding and hydration effects on protein conformation a study with sol-gel encapsulated proteins. Journal of Molecular Biology, 314, 911-922. 

Reliable measurements of L-lactate are of great interest in clinical chemistry, the dairy and vine industry, biotechnology, or sport medicine. In particular, blood lactate levels are indicative of various pathological states, including shock, respiratory insufficiencies, and heart and liver diseases. Silica sol-gel encapsulation of the lactate dehydrogenase and its cofactor was employed as a disposable sensor for L-lactate51. The sensor utilized the changes in absorbance or fluorescence from reduced cofactor nicotinamide adenine dinucleotide (NADH) upon exposure to L-lactate. 

Bailey R.T., Cruickshank F.R., Deans G., Gillanders R.N., Tedford M.C., Characterization of a fluorescent sol-gel encapsulated erythrosine B dissolved oxygen... 

B.C. Dave, B. Dunn, J.S. Valentine, and J.I. Zink, Sol-gel encapsulation methods for biosensors. Anal. Chem. 66, 1120A-1126A (1994). 

J. Yu, S. Liu, and H.X. Ju, Mediator-free phenol sensor based on titania sol-gel encapsulation matrix for immobilization of tyrosinase by a vapor deposition method. Biosens. Bioelectron. 19, 509-514 (2003). 

R.A. Doong and H.C. Tsai, Immobilization and characterization of sol-gel-encapsulated acetylcholinesterase fiber-optic biosensor. Anal. Chim. Acta 434, 239-246 (2001). 

R. Ciriminna and M. Pagliaro, Tailoring the Catalytic Performance of Sol-Gel-Encapsulated Tetra-n-propylammonium Perruthenate (TPAP) in Aerobic Oxidation of Alcohols, Chem. Eur. J., 2003, 9, 5067. 

M. T. Reetz, P. Tielmann, W. Wiesenhofer, W. Konen and A. Zonta, Second Generation Sol-Gel Encapsulated Lipases Robust Heterogeneous Biocatalysts, Adv. Synth. Catal., 2003, 345, 717. 

Premkumar and co-workers demonstrated that sol-gel encapsulation meets all these requirements. In a series of articles they demonstrated successful encapsulation of recombinant E. coli which responded to different stress conditions by expression of fluorescent proteins (such as green and red fluorescent proteins) or bioluminescence in thin sol-gel... 

Molecular sol-gel encapsulation adds value because, once entrapped in a sol-gel matrix, molecules retain their basic physical and chemical properties that define the practical value of those molecules, but encapsulation also expands the properties conferring a whole new set... 

In general, sol-gel encapsulation ensures chemical protection of the valued entrapped dopants. Encapsulation provides... 

Entrapment in polymeric matrices is a variation of noncovalent attachment where the support is instead generated in the presence of the enzyme. A particularly popular entrapment technique is sol-gel encapsulation, where the enzyme is trapped within an Si02 matrix formed by acid- or base-catalysed hydrolysis of tetraalkoxysilanes in the presence of enzyme. ° The technique can be tuned to provide the appropriate microenvironment for each enzyme in much the same way as can be done with other immobihzation methods. ... 

Pierre, A.C., The sol-gel encapsulation of enzymes. Biocatal. Biotrans., 2004,22, 145-170 and references cited therein. 

The use of supported (i.e., heterogenized) homogeneous catalysts offers another possibility for easy catalyst separation. New examples include polymer-anchored Schiff-base complexes of Pd(TT),446 PdCl2(PhCN)2 supported on heterocyclic polyamides,447 various Pd complexes supported on crosslinked polymers 448 sol-gel-encapsulated Rh-quatemary ammonium ion-pair catalysts,449 and zwitterionic Rh(T) catalysts immobilized on silica with hydrogen bonding.450... 

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