Insolubilizing type

As pointed out by Heller (2), polymer erosion can be controlled by the following three types of mechanisms (1) water-soluble polymers insolubilized by hydrolytically unstable cross-links (2) water-insoluble polymers solubilized by hydrolysis, ionization, or protonation of pendant groups (3) hydrophobic polymers solubilized by backbone cleavage to small water soluble molecules. These mechanisms represent extreme cases the actual erosion may occur by a combination of mechanisms. In addition to poly (lactic acid), poly (glycolic acid), and lactic/glycolic acid copolymers, other commonly used bioerodible/biodegradable polymers include polyorthoesters, polycaprolactone, polyaminoacids, polyanhydrides, and half esters of methyl vinyl ether-maleic anhydride copolymers (3). 

Irreversible insolubilization of proteins may occur mainly through formation of both intermolecular disulfide and hydrophobic bonds. The product can be quite different depending on the relative contribution of these two types of bonds. The hydrophobic bonds are formed among the hydrophobic amino acid side chains contributed by valine, leucine, isoleucine, phenylalanine, etc. 

Alternatively, co-culture of tumor and host cells can be made so that the two cell types are either in the same, or in separate compartments, with or without direct cell contact. Effects on tumor cell growth in the absence of direct cellular contact suggests the presence of soluble, secreted factor(s), whereas when the growth effects require direct cell contact it is a hint that the responsible growth factor(s) are insolubilized either on the cell surface, or in the BM. 

In general terms. Type I erosion encompasses water-soluble polymers that have been insolubilized by hydrolytically unstable crosslinks. Type II erosion includes polymers that are initially water-insoluble and are solubilized by hydrolysis, ionization, or protonation of a pendant group. Type III erosion includes hydrophobic polymers that are converted to small water-soluble molecules by backbone cleavage. 

The most widely used polymer system that bioerodes by Type I erosion or by a combination of Type I and Type III erosion is gelatin that has been insolubilized by heat treatment, aldehyde treatment, or chromic acid treatment. 

The model in Figure 5 includes formation of both soluble and insoluble complexes of sHsp and substrate. The formation of insoluble sHsp/substrate complexes is consistent with the in vivo transition of sHsps to an insoluble, structure-bound form under many stress conditions as discussed above. At present we can provide only speculative explanations for this insolubility in the context of the chaperone model of sHsp function. From in vitro studies, it is clear that the ability of sHsps to keep substrates soluble is dependent on the sHsp-to-substrate ratio, the rate of substrate denaturation, and other factors in vitro conditions can be manipulated to cause precipitation of sHsp and substrate, as well as to maintain substrate solubility. Thus, insolubilization could result from a type of overload of the soluble binding capacity of the sHsps. Since in vivo there is good evidence that the insolubilization is reversible, this leads to the intriguing question of the mechanism of resolubilization, and whether this is also a function of Hsp70 systems, or if additional components are required. Alternatively, sHsp insolubilization in vivo could result from interaction with insoluble components in the cell. 

Water flux through reverse osmosis membranes is considerably dependent on the hydrophilic character of the barrier layer. In the composite membrane approach, highly hydrophilic barrier layer compositions can be used, suitably insolubilized by crosslinking. To a large extent, water flux and salt rejection can be controlled by the type and extent of crosslinking. 

A type of mixed anhydride derivative (2, see p. 322) has been produced by reaction of O-(carboxymethyl) cellulose with ethyl chloro-formate, and is useful in insolubilization of macromolecules because of its nucleophilic susceptibility. ... 

The structure of Blue Dextran 2000, a water-soluble commercial derivative, involves a triazine type of dye covalently linked to dextran, and, in a way analogous to that used for other dyed polysaccharides, has been employed for the assay of dextranase. The ability of Blue Dextran 2000 to bind proteins cannot be attributed to formation of a covalent link, because no chloro groups remain on the triazinyl rings. The binding must involve an ionic bond between the protein and the sulfonic groups of the dye residue, and, in one case, the association could be reversed by using 0-(2-diethylaminoethyl) cellulose to abstract the dyed polysaccharide. Other chlorotriazinyl dyes have been used in the preparation of dyed derivatives of amylopectin, laminaran, dextrans, pectin, pelvetian, zosterine, and cellulose. As already mentioned, triazine-dyed polysaccharides are useful in enzyme insolubilization. 

One type of affinity-chromatography material of particular interest in carbohydrate chemistry is the insolubilized derivative of concanavalin A, a phytohemagglutin that shows specificity towards certain carbohydrates. 

Cold stabilization is also partially effective in preventing other types of colloidal precipitation. It helps to prevent ferric casse by insolubilizing ferric phosphate in white wines and ferric tannate in reds. However, even after aeration to promote the formation of the Fe + ions involved in these mechanisms, only small quantities of iron are eliminated. Fining at the same time as cold stabilization improves treatment effectiveness but is never sufficient to prevent ferric casse completely. 

As part of their formulation, polyacid-modified composite resins also contain a small fraction of basic glass filler of the type used in glass-ionomer cements [1]. Such glasses are typically calcium (or strontium) alumino-fluorosiUcates, and react with acids in the presence of water to release ions. The ions released, particularly calcium (or strontium) and aluminium react with the acid to form salts, which in the case of glass-ionomers, are insoluble because they form ionic crosslinks with the polymeric acid. The ions effectively insolubilize the acid-functional polymer chains by this reaction, as well as stiffening the material due to coil expansion and ion-binding. This type of chemistry is available to polyacid-modified composite resins once moisture is present, and these materials are designed for this reaction to occur in the early part of their existence. 

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