Hydrophobic group

The generally low chemical, mechanical and thennal stability of LB films hinders their use in a wide range of applications. Two approaches have been studied to solve this problem. One is to spread a polymerizable monomer on the subphase and to polymerize it either before or following transfer to the substrate. The second is to employ prefonned polymers containing hydrophilic and hydrophobic groups. 

The nature of soliite-solnte and solute-solvent in teraction s is dependent on the solvent environment. Solvent influences the hydrogen-bon ding pattern, solute surface area, and hydrophilic and hydrophobic group exposures. 

A flow chart showing the various phases leading to the final compound is reproduced ii Figure 12.35. The first step was a 3D database search of a subset of the Cambridge Structura Database. The pharmacophore for this search comprised two hydrophobic groups and i... 

Model verification provides a common-sense check of results. One quick check is to compare the minimized energy to that of similar proteins. It is also important to examine the structure to ensure that hydrophobic groups point inward and hydrophilic groups point outward. 

Protein tertiary structure is also influenced by the environment In water a globu lar protein usually adopts a shape that places its hydrophobic groups toward the interior with Its polar groups on the surface where they are solvated by water molecules About 65% of the mass of most cells is water and the proteins present m cells are said to be m their native state—the tertiary structure m which they express their biological activ ity When the tertiary structure of a protein is disrupted by adding substances that cause the protein chain to unfold the protein becomes denatured and loses most if not all of Its activity Evidence that supports the view that the tertiary structure is dictated by the primary structure includes experiments m which proteins are denatured and allowed to stand whereupon they are observed to spontaneously readopt their native state confer matron with full recovery of biological activity... 

Polymers in Solution. Polyacrylamide is soluble in water at all concentrations, temperatures, and pH values. An extrapolated theta temperature in water is approximately —40° C (17). Insoluble gel fractions are sometimes obtained owing to cross-link formation between chains or to the formation of imide groups along the polymer chains (18). In very dilute solution, polyacrylamide exists as unassociated coils which can have an eUipsoidal or beanlike stmcture (19). Large aggregates of polymer chains have been observed in hydrolyzed polyacrylamides (20) and in copolymers containing a small amount of hydrophobic groups (21). 

Eig. 1. Schematic bioactive polyphosphazenes. (a) General stmcture, where X = hydrophilic /hydrophobic group that hydrolyzes with concurrent polymer breakdown, Y = difunctional group for attaching bioactive agent to polymer, and T = bioactive agent, (b) Actual example where X = —OC H, Y = and... 

Fig. 4. Multilayer films where ( ) represent a hydrophobic group and (B) a hydrophilic one (a) Y-type, (b) X-type, and (c) Z-type.

Lecithin (qv), a natural phosphoHpid possessing both hydrophilic and hydrophobic properties, is the most common emulsifier in the chocolate industry (5). The hydrophilic groups of the lecithin molecules attach themselves to the water, sugar, and cocoa soflds present in chocolate. The hydrophobic groups attach themselves to the cocoa butter and other fats such as milk fat. This reduces both the surface tension, between cocoa butter and the other materials present, and the viscosity. Less cocoa butter is then needed to adjust the final viscosity of the chocolate. 

Hydrophobic Interaction. This is the tendency of hydrophobic groups, especially alkyl chains such as those present in synthetic fibers, and disperse dyes to associate together and escape from the aqueous environment. Hydrophobic bonding is considered (7) to be a combination of van der Waals forces and hydrogen bonding taking place simultaneously rather than being a completely new type of bond or intermolecular force. 

The subunits of an oligomeric protein typically fold into apparently independent globular conformations and then interact with other subunits. The particular surfaces at which protein subunits interact are similar in nature to the interiors of the individual subunits. These interfaces are closely packed and involve both polar and hydrophobic interactions. Interacting surfaces must therefore possess complementary arrangements of polar and hydrophobic groups. 

We modified polyanionic polymers by use of a grafting reaction of hydrophobic groups onto the polymers. After an extensive evaluation for the affinity of the hy-drophobically modified (hydrophobized) polymers to cell membrane, the immuno-stimulating activity of polymers was investigated by in vitro or ex vivo experiments. Consequently, the increased biological activity was found in the hydrophobized polymer, indicating that... 

There was no distinct difference between polymers having different molecular weights. From the data in Figures 2, 4, 5, and 6, it seems to be established that the affinity of polyanionic polymers for cell membrane is adjustable by a simple grafting of hydrophobic groups. 

Based on these observations in Figs. 8 and 9, it is suggested that the hydrophobic group modification (hy-drophobization) is an effective method for improving the immuno-stimulating activity of polyanionic polymers. 

One of the most important characteristics of the emulsifier is its CMC, which is defined as the critical concentration value below which no micelle formation occurs. The critical micelle concentration of an emulsifier is determined by the structure and the number of hydrophilic and hydrophobic groups included in the emulsifier molecule. The hydrophile-lipophile balance (HLB) number is a good criterion for the selection of proper emulsifier. The HLB scale was developed by W. C. Griffin [46,47]. Based on his approach, the HLB number of an emulsifier can be calculated by dividing... 

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