Gel entrapped multistep

It is the purpose of this paper to review the existing state of knowledge on gel entrapped multistep enzyme systems with particular reference to their kinetic behavior, and to add some recent results from this laboratory. 

The quantitative data and observations discussed above appear to be consistent with the qualitative concepts put forward by Mosbach and others to explain the behavior of multistep enzyme systems. Mathematical modelling of gel entrapped, multistep, immobilized enzyme systems, using the collocation technique, is quite straightforward and provides the opportunity not only to compare experiment with theory but also to explore the effect of parameters of the system which are experimentally inaccessible. 

Multistep, one-pot sequential reactions are considered to be an ideal synthetic methodology because they do not require isolation and purification procedures for intermediates between reaction steps. They also reduce the necessary time and reagents. Multiple active components are necessary to promote several reactions however, active components are often opposing and mutually destructive when contacting with other components such as Hquid add and base reagents. Such difficulties could be setded by the concept of site isolation [127]. Sol-gel entrapment [128] and polymeric reagents [129-131] have been utilized to achieve the site... 

In all of the multistep immobilized enzyme work done to date, theoretical or experimental, for modelling purposes or for applications, there exists one common factor the chemical reactions are affected by the diffusive processes so that the macroscopically observed kinetics are strongly perturbed by the incorporation of the enzymes into a gel. This perturbation is caused by the development of localized concentrations and concentration gradients within the gel which are quite different from that found in free solution. Only one instance appears to have been reported where exact modelling of real experimental data has been attempted. All other work has been either purely theoretical or qualitative interpretations of limited experimental data. There is still much to be learned of the role played by the gel matrix in affecting the overall kinetic performance of gel entrapped multienzyme systems before they can be well designed for applications or used with any confidence in a quantitative way as models for living systems. 

One of the major drawbacks of liposomes is related to their preparation methods [3,4]. Liposomes for topical delivery are prepared by the same classic methods widely described in the literature for preparation of these vesicles. The majority of the liposome preparation methods are complicated multistep processes. These methods include hydration of a dry lipid film, emulsification, reverse phase evaporation, freeze thaw processes, and solvent injection. Liposome preparation is followed by homogenization and separation of unentrapped drug by centrifugation, gel filtration, or dialysis. These techniques suffer from one or more drawbacks such as the use of solvents (sometimes pharmaceutically unacceptable), an additional sizing process to control the size distribution of final products (sonication, extrusion), multiple-step entrapment procedure for preparing drug-containing liposomes, and the need for special equipment. 

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