Hydrophobic areas, formation

FIG. 23 Schematic drawing of using microcontact printing for obtaining hydrophobic areas on a gold-coated substrate. After pattern transfer (a and b), incubation with an S-layer protein solution (c) leads to the formation of a protein monolayer on the hydrophobic areas only. 

The direct evidence of the formation of hydrophobic areas (HA) was obtained by scanning electron microscopy" cf. Figs. 6 and 7. 

The balance of favorable minimization of hydrophobic area and unfavorable reduction of conformational states upon folding will determine the stability of the protein. As these forces tend to be large and comparable in magnitude, the free enthalpy of formation of a protein is the sum of two large opposing forces and may thus be negative or positive. In any case, a folded and catalytically active protein is always just a few kilojoules away from instability. 

Incomplete coverage of the surface of such a fifth-generation POPAM dendrimer exposes hydrophobic areas of adamantyl units remaining uncomplexed by cyclodextrins on the dendritic outer shell [38]. Pyrenes were used as neutral fluorescence probes to examine whether this might lead to aggregation in water driven by the hydrophobic effect [39a]. Their inclusion in the dendrimer/cyclo-dextrin aggregate leads to changes in fluorescence intensity and in the vibrational fine structure. Formation of excimers was also observed. 

Fig. 13 Constitutional adaptation to the environment in the hydrophobically-driven component selection on formation of a rigid rod dynamer from amphiphilic monomers. Polycondensation occurs in aqueous solution with preferential incorporation of the monomer presenting the largest hydrophobic area. Selectivity is progressively lost in solutions containing increasing amounts of organic solvent, acetonitrile...

The high yield at the equilibrium position should be attributed to the formation of a hydrophobic area in water as shown in Figure 13.2. 

The ability of CDs to form intermolecular complexes with other molecules was already known in the early twentieth century. Another important property of CDs is that each glucose molecule in this macrocycle contains live chiral carbon atoms, which results in a chiral recognition ability in complex formation. This property of CDs was first evidenced by Cramer [1]. The relative easy availability from regenerable natural sources, the existence in various sizes, the stable structure, the localized hydrophobic area, the solubility in the hydrophilic solvents, the ability of intermolecular complex formation and the chiral recognition ability together with their nontoxicity, ultraviolet (UV) transparency, feasibility of their modification, and so forth contributed greatly to the establishment of CDs as a... 

LM-pectin will gel only in the presence of divalent cations. Increasing the concentration of divalent cations (only calcium ion is used in food applications) increases the gelling temperature and gel strength. Divalent cations are unnecessary for the formation of a HM-pectin gel because of the low number of carboxylate groups that need to be bridged and because of the formation of hydrophobic areas parallel to the helix axes by a columnar stacking of methyl ester groups (15). 

Recently, Slattery and Evard (171) proposed a model for the formation and structure of casein micelles from studies devoted to association products of the purified caseins. They proposed that the micelle is composed of polymer subunits, each 20 nm in diameter. In the micellar subunits the nonpolar portion of each monomer is oriented radially inward, whereas the charged acidic peptides of the Ca2+-sensitive caseins and the hydrophilic carbohydrate-containing portion of K-casein are near the surface. Asymmetric distribution of K-casein in a micelle subunit results in hydrophilic and hydrophobic areas on the subunit surface. In this situation, aggregation through hydrophobic interaction forms a porous micelle (Figure 10). Micelle growth is limited by the eventual concentration, at the micelle surface, of subunits rich in K-casein. 

Discrepancies between retention properties and either summated hydrophobicity or linear hydropathy parameters are expected to become more significant as the molecular size of the solute increases. A number of algorithms are available to predict the secondary structure of peptides and proteins such as the Chou-Fasman [51] method for predicting a-heUx and j8-sheet formation and other procedures [52,53] which determine the probability of heUx formation in a particular solvent environment. These approaches assist in the location of potential hydrophobic areas on the surface of a molecule via characterisation of amphipathic regions. For example, the probability profile shown in Fig. 11 indicates that an amphipathic a-helix can form in the C-terminal region of human )8-endorphin, a peptide which... 

An outstanding approaeh for the development of drug delivery systems has been recently presented by Zhang and Ma [99], In this work, the use of a P-cyclodextrin (P-CD) containing DHBC has been proposed for the inclusion of many hydrophobic substances. In their work, the synthesis of a bloek eopolymer with a PEG block and a polyaspartamide block carrying some P-CD units has been described. The P-CD imits are used as host sites for a plethora of hydrophobic small molecules, like pyrene and comnarine, as well as for hydrophobic polymers. However, the formation of inclusion complexes leads to the creation of located hydrophobic areas within the copolymer domain, which, in turn, has as a result the formation... 

If the agent is adsorbed on the surface and oriented so that hydrophobic areas are produced, these areas on different particles come together to form a micelle. The particles are held together by the powerful surface tension forces around the negative radius of curvature at the zone of contact, the so-called "hydrophobic bond." It is also possible to consider this as the adsorption of two silica particles on opposite sides of a surfactant micelle in solution. However, flocculation can occur when the concentration of cationic surfactant is less than the critical concentration for micelle formation in the absence of silica particles, suggesting that the micelle is stabilized by being at the point of contact between solid particles... 

The subsequent addition of tetralkoxysilane (TEOS) in acidic (or even neutral) conditions leads to the formation of a silica core, due to the fact that, especially before hydrolysis, alkoxysilane are rather apolar species and tend to migrate and accumulate in the central part of the polymeric micelles, the more hydrophobic area where the silicate condensation is promoted. This induces the formation of the silica nanoparticles only inside the micelles, as the condensation proceeds, leading to the entrapment of the surfactants molecules and to the final silica core-PEG shell architecture (Fig. 13). 

Foams are dispersions of gases in liquids. Proteins stabilize by forming flexible, cohesive films around the gas bubbles. During impact, the protein is adsorbed at the interface via hydrophobic areas this is followed by partial unfolding (surface denaturation). The reduction of surface tension caused by protein adsorption facilitates the formation of new interfaces and further gas bubbles. The partially unfolded proteins associate while forming stabilizing films. 

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