Environment Sensitive Gels

The fluorescence lifetime is sensitive to the environment of the fluorophore, and in membranes this usually means the surrounding fatty acyl chains or the membrane protein interfacial region (see summary in Table 5.3). Generally, the lifetime of membrane-bound fluorophores is rather less sensitive to the types of subtle alterations which are encountered in membranes as compared to the fluorescence anisotropy parameters. The gel-to-liquid crystalline phase transition is a notable exception where most fluorophores show an alteration in lifetime properties. Although, again, the anisotropy (see below) is the most sensitive parameter in this regard, the fluorescence lifetime has been used with considerable success in the study of phase transitions and lateral phase separations. Fluorophores used to yield information on the... 

Another example of the sensitivity of 13C MAS NMR to zeolite structure is the work of Jarman and Melchior (331) who could distinguish between TMA+ cations trapped in the ol and / (sodalite) cages in zeolite A structure in the course of crystallization from a precursor gel. If, therefore, the zeolite which is to be analyzed by 13C NMR, so as to evaluate the extent of intergrowth or variable cage environments is synthesized using TMA + cations as templates, then this method, as we show below, seems viable. 

Any sol-gel phase reversible system described above can be used as an erodible matrix system. All the components of the system in the sol state are essentially in the dissolved state, and thus they can be released to the environment in the absence of protecting membranes. During the process of gel to sol transition by the addition of glucose, the incorporated insulin can be released as a function of glucose concentration. There are of course other polymeric systems which can be used in glucose-sensitive erodible insulin delivery. 

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