Hydrophobic edges

The most stable and diversified porphyrin assemblies were received from protoporphyrin IX derivatives. It is characteristic that no crystal structure of an amphiphilic porphyrin is known. Crystal structures of esters have frequently been solved (see section 7.5), but protoporphyrin IX or similar porphyrins with a hydrophilic and a hydrophobic edge withstood all attempts at crystallization. This may be because they prefer to occur in curved fibrous assemblies. 

The hydrophobic effect on the base pairs. Between the hydrated phos-phate-deoxyribose diesters lie the hydrophobic edges of the base pairs. 

Heating Kemp s acid with appropriate aromatic diamines yields bis-imides with two convergently oriented carboxylic acid groups on the edges of a hydrophobic pocket. Dozens of interesting molecular complexes have been obtained from such compounds and can be traced in the Journal of the American Chemical Society under the authorship of J. Rebek, Jr., (1985 and later e.g. T. Tjivikua, 1990 B). 

Residues 3, 5, 6, and 8 in the N-terminal arm lie in the minor groove and form contacts with either the edge of the bases or with the DNA backbone. Almost all homeodomains contain four conserved residues, Asn 51, Arg 53, Trp 48 and Phe 49, in the middle of the long recognition helix. The first two conserved polar residues interact with DNA. The second two are part of the hydrophobic core of the homeodomain, and are important for the accurate positioning of the recognition helix and the N-terminal arm with respect to... 

Figure 9.11 Amino acid sequences of homeodomains from four differenf franscription factors Anfp is from fhe Antennapedia gene in the fruitfly Drosophila, a2 is from the yeast Mat o2 gene, eng is from fhe engrailed gene in Drosophila and POU is from fhe POU homeodomain in the mammalian gene Oct-1. Residues colored green form the hydrophobic core of the homeodomain, blue form nonspecific interactions with the DNA backbone and red form contacts with the edges of the DNA bases.

In an effort to restrict the location of semiconductor nanoparticles in LB films and inhibit aggregation, the formation of CdS in LB films of calixarenes was investigated [195]. Limiting areas of 3.0 nm and 1.8 nm were obtained on 0.5 mM CdCli, compatible with the cross-sectional areas of the calixarenes. Y-type LB fdms were prepared at 25 mN m on glass, quartz, and silicon. The substrates had been made hydrophobic by treatment with a silane vapor. After H2S treatment overnight in sealed jars, UV absorbance spectra and XPS data were obtained. The absorption edge for the CdS particles formed in the calixarene LB films transferred at pH 5.5 was 3.3 eV as compared with 2.7 eV for films formed in cad-... 

On Pt(lll) the HREELS features due to water are unchanged by the presence of CO. These observations indicate that water and CO adsorb onto separate patches on the surface, in a form of hydrophobic coadsorption. Water condenses into hydrogen-bonded islands, as indicated by the low 0-H stretching frequency. CO spreads to cover the rest of surface, giving a phase similar to that for CO alone, but with a coverage normalized to the water-free, not total, surface area. COCO repulsions, which have been well documented on Pt(lll) (10), produce a surface pressure within the CO patches which bears upon the edges of the water islands. It is this lateral pressure which causes water to desorb from Pt(lll) at lower temperatures in the presence of coadsorbed CO. 

From these observations, a photooxidative scheme has been developed in which a hydrophobic resist becomes hydrophilic upon oxidation induced by deep UV (248 and 193 nm) radiation. Subsequent treatment with TiCLi followed by oxygen reactive ion etching then affords high-resolution, negative-tone patterns. Studies are currently underway to minimize the line edge roughness and background residue present in such patterns. 

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