Hydrophobic wedge

Surfactants employed for w/o-ME formation, listed in Table 1, are more lipophilic than those employed in aqueous systems, e.g., for micelles or oil-in-water emulsions, having a hydrophilic-lipophilic balance (HLB) value of around 8-11 [4-40]. The most commonly employed surfactant for w/o-ME formation is Aerosol-OT, or AOT [sodium bis(2-ethylhexyl) sulfosuccinate], containing an anionic sulfonate headgroup and two hydrocarbon tails. Common cationic surfactants, such as cetyl trimethyl ammonium bromide (CTAB) and trioctylmethyl ammonium bromide (TOMAC), have also fulfilled this purpose however, cosurfactants (e.g., fatty alcohols, such as 1-butanol or 1-octanol) must be added for a monophasic w/o-ME (Winsor IV) system to occur. Nonionic and mixed ionic-nonionic surfactant systems have received a great deal of attention recently because they are more biocompatible and they promote less inactivation of biomolecules compared to ionic surfactants. Surfactants with two or more hydrophobic tail groups of different lengths frequently form w/o-MEs more readily than one-tailed surfactants without the requirement of cosurfactant, perhaps because of their wedge-shaped molecular structure [17,41]. 

Thus complete intercalation of the aromatic PAH between the bases of DNA, in the manner described above for flat molecule such as proflavine, did not seem to be a likely mechanism for the carcinogenic action of these compounds. Since alkylation and intercalation are not simultaneously possible for steric reasons, and since one molecule is wedge-shaped and the other is flatter, it was considered more likely that the action of these compounds arose from their alkylating ability they could alkylate a base of DNA and then, since the bulky aromatic hydrophobic group would possibly not remain protruding into the hydrophilic environment, it is possible that the aromatic PAH group could then lie in one of the grooves of DNA. 

The van der Waals model of monomeric insulin (1) once again shows the wedge-shaped tertiary structure formed by the two chains together. In the second model (3, bottom), the side chains of polar amino acids are shown in blue, while apolar residues are yellow or pink. This model emphasizes the importance of the hydrophobic effect for protein folding (see p. 74). In insulin as well, most hydrophobic side chains are located on the inside of the molecule, while the hydrophilic residues are located on the surface. Apparently in contradiction to this rule, several apolar side chains (pink) are found on the surface. However, all of these residues are involved in hydrophobic interactions that stabilize the dimeric and hexameric forms of insulin. 

Micellisation permits strong water-water interaction (hydrogen bonding) which would otherwise be prevented if the surfactant was in solution as single molecules wedged between the solvent water molecules. This is a most important factor in micelle formation and also of course, in any adsorption process at an aqueous interface. It is often referred to as the hydrophobic effect49. 

A series of peptide analogs of class A and class L amphipathic helices were synthesized and studied (Tytler et ai, 1993). Two of these peptides, designated 18A and 18L, were modeled as idealized a helices, energy minimized, and displayed in cross section (Tytler etal., 1993). The overall cross-sectional shape of a class A amphipathic helix in the snorkel orientation was found to be that of a wedge with a polar base and a hydrophobic apex, schematically illustrated in Fig. 6A. In contrast, the shape of a class L amphipathic helix in cross section is reciprocal to that of a class A amphipathic helix i.e., an inverted wedge with its apex at the polar face and its base buried in the lipid (Fig. 6B). 

Bilayer vesicles, especially the non-isotonic ( stressed ) kind or those which contain large amounts of dissolved cholesterol, can also be made to leak with the aid of molecular harpoons . These are membrane-disruptive surfactants comprised of a rigid, wedge-shaped hydrophobic unit attached to a hydrophilic chain, e.g. 22. It was discovered that just one harpoon molecule per ten... 

In ERa s LBD [42-44, 52], H2-H11 and the hairpin P-sheet form a wedge-shaped hydrophobic ligand-binding cavity, while HI2, in the agonist bound conformation,... 

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