Insoluble matrices

Truly porous, synthetic ion exchangers are also available. These materials retain their porosity even after removal of the solvent and have measurable surface areas and pore size. The term macroreticular is commonly used for resins prepared from a phase separation technique, where the polymer matrix is prepared with the addition of a hq-uid that is a good solvent for the monomers, but in which the polymer is insoluble. Matrices prepared in this way usually have the appearance of a conglomerate of gel-type microspheres held together to... 

The concept of using reagents finked to insoluble matrices to facilitate removal of excess or spent reagent is not new (Scheme 1). The first example was reported as early as 1946, although it is in the seventies that the first important results were obtained, thanks to the pioneering work by Frechet [52], Cainelli [53], Leznoff [54] and Sherrington [55], among others. 

DCC is a waxy solid that is often difficult to remove from a bottle. Its vapors are extremely hazardous to inhalation and to the eyes. It should always be handled in a fume hood. The isourea by-product of a DCC-initiated reaction, dicyclohexyl urea (DCU) (Figure 3.5), is also water-insoluble and must be removed by organic solvent washing. For synthesis of peptides or affinity supports on insoluble matrices this is not a problem, because washing of the support material can be done without disturbing the conjugate coupled to the support. For solution phase chemistry, however, reaction products must be removed by solvent washings, precipitations, or recrystallizations. 

Forming a metal complex may serve to activate NO toward either nucleophilic or electrophilic attack depending on the nature of the metal complex and its oxidation state. Of particular interest biologically are the reactions with nucleophiles since this may well be a mechanism for thionitrosyl formation (e.g. Eq. (55)) as well as for reductively labiliz-ing metals in insoluble matrices like ferritin. 

Cellulose disintegrants have been studied as insoluble matrices for sustained release tablets. Anionically charged carboxymethyl cellulose (sodium salt) was found to be inferior to methyl cellulose and poly(vinyl pyrollidone) as a binding agent for oxyphenbutazone tablets [291], However sodium carboxymethyl cellulose has found application as a dispersing agent for ibuprofen microspheres... 

For synthesis of peptides or affinity supports on insoluble matrices, this is not a problem because washing of the support material can be done without disturbing the conjugate coupled to the support. For solution phase chemistry, however, reaction products must be removed by solvent washings, precipitations, or recrystallizations. 

However, methods that lead to high-yield immobilization in water-insoluble matrices, that is, a small loss in enzyme activity, have been developed, Fig. 17.10. 

Cyanogen bromide (CNBr)-activated insoluble matrices, such as microcrystalline cellulose particles, or paper disks, can be chemically... 

Peppas attribute the difference in disintegration rate between soluble and insoluble matrices to two proposed phenomena—an interface-controlled mechanism and a diffusion-controlled mechanism—as represented in the following equation ... 

Like the experience with tablets, the effect of disintegrants in already rapidly soluble capsule matrices is lower than that in water insoluble matrices. Perhaps doubling the concentration normally required for tablets is needed to effect efficient disintegration and significantly affect dissolution. This need for higher... 

Water-soluble polymers can be crosslinked electrostatically or covalently to give hydrogels. Crosslinked hydrogels absorb water but do not dissolve. The differences in release of drugs from water-insoluble matrices and from swelling hydrogels should be appreciated. 

T. S. Reger, K. D. Janda, Polymer-supported (salcn)Mn catalysts for asymmetric epoxidation A comparison between soluble and insoluble matrices, /. Am. Chem. Soc. 122 (2000) 6929. 

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