Hydrophobic bases

Iwase, K., Komatsu, K., Hirono, S., Nakagawa, S., Moriguchi, I. (1985) Estimation of hydrophobicity based on the solvent-accessible surface area of molecules. Chem. Pharm. Bull. 33, 2114-2121. 

For ETFE- -PSSA membranes with the same lEC, water uptake is higher than MeOH uptake of the membrane, but for Nation and S-SEBS membranes, MeOH uptake of membrane is always higher than water uptake. Chemical structure and morphology of membranes affect the solvent absorption. Nafion is considered to consist of ionic clusters that are separated from the polymer phase. For grafted polymers, heterogeneity exists to some extent due to the hydrophobic base polymer however, a regular clustered structure, as in the case of Nafion, has not been proposed for these materials. 

We encountered the properties of hydrophilic and hydrophobic molecules in our thoughts about driving forces for formation of three-dimensional protein structures. Specifically, proteins fold in a way that puts most of the hydrophobic amino acid side chains into the molecular interior, where they can enjoy each other s company and avoid the dreaded aqueous environment. At the same time, they fold to get the hydrophilic amino acid side chains onto the molecular surface, where they happily interact with that enviromnent. The same ideas are important for the double-stranded helical structure of DNA. The hydrophobic bases are localized within the double hehx, where they interact with each other, and the strongly hydrophilic sugar and phosphate groups are exposed on the exterior of the double helix to the water environment. Now, we need to understand something more about structural features that control these properties. 

The regular system of hydrogen bonds in DNA is destroyed in DNA/NaOH solution and the DNA molecule is partly transformed from a double spiral to a chaotic ball [118]. This transformation may promote the interaction of DNA molecules with CNTs. The ssDNA adsorption on CNTs was greater than for dsDNA molecules [117,118], suggesting that the adsorption of DNA on CNT is presumably via hydrophobic interactions between the nanotubes and the hydrophobic bases on DNA. 

The double helix structure of DNA has the hydrophobic bases pointing to the centre of the helix in an almost planar arrangement. These base-pairs are closely stacked perpendicular to the long axis of the chain, and are attracted to each other by Van der Waals forces. The hydrophilic phosphates are negatively charged at the pH of the cell and point to the outside. 

Reverse phase chromatography (RPC) hydrophobicity-based separation... 

Hydrophobic bases Weak hydrophobic acids Hydrophobic neutrals... 

Hydrophobic Base Fraction. The hydrophobic base fraction was adjusted to pH 10. A 50-/uL aliquot of the aqueous solution was subjected to HPLC analysis to test for the presence of 5-chlorouracil. The remaining aqueous solution was solvent extracted with methylene chloride. The extract was first concentrated in a Kudema-Danish apparatus, then under a stream of N2, and analyzed by GC-FID and GC-MS. 

Preliminary experiments resulted in the formation of a precipitate due to the presence of inorganic salts when the pH of the test solution was raised to 10 for the first passage through the XAD-8 column to isolate the hydrophobic base fraction. Initially, desalting the solution with a cation-exchange resin (i.e., AG-50-X8, Na+ form) was tried before... 

Note OA = hydrophobic acid (XAD-8) OB = hydrophobic base (XAD-8) ON = hydrophobic neutral (XAD-8) IB = hydrophilic base (AG MP-50) EF = final effluent (solvent extraction) NQ = found but not quantitated. 

In consideration of the results presented in Tables II and III, it was decided to integrate the resins and carbon columns in a single scheme as shown in Figure 1. The test solution was adjusted to pH 7 immediately following the AG MP-50 column and processed through the Carbopack B column. The results from one experiment conducted under these conditions practically confirmed the overall process performance anticipated from the individual experiments (see Table IV). Trimesic acid, stearic acid, and humic acids were found in the hydrophobic acid fraction quinoline was primarily quantitated in the hydrophobic base fraction, whereas a small amount of it was also detected in the hydrophobic neutral fraction. Isophorone, biphenyl, 1-chlorododecane, 2,6-di-ter -butyl-4-methylphenol, 2,4 -dichlorobiphenyl, 2,2 5,5 -tetrachlorobiphenyl, anthraquinone, and phenanthrene were re-... 

The hydrophobic oils evaluated in phase behavior studies were diesel, dodecane, and hexadecane. A commercial Diesel was selected based on its occurrence as a subsurface contaminant and its hydrophobicity. Based on... 

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