Halogenation hydrophobic effects

At first sight these may appear to be reasonably diverse in terms of their chemistry even though there are three halogens in the set. The it values are nicely spread out from hydrophilic (-1.23) to hydrophobic (1.44) but, unfortunately, so are the o values. In general there is no correlation between the hydrophobic substituent constant it and the electronic substituent constant o, but for this set the squared correlation coefficient between these two physicochemical properties is 0.95. In much the same way as the methyl-futile set is uninformative, so would this set be in terms of distinguishing electronic effects from hydrophobic effects in any QSAR model derived from it. 

Halogen Bonding, p. 628 Hydrogen Bonding, p, 658 Hydrophobic Effects, p. 673... 

Here the first term corresponds to A (the coefficient is In(lO) times that in Eqs. (1.27)-(1.29) and is zero for liquid solutes) and the other three terms correspond io B + F, whereas -D + 0- OH) = 0 for such solutes that are devoid of specific interactions. The molar volumes for solid solutes were estimated from group contributions rather than from the densities of the solids. The full solubility expression was applied to 150 solutes, including in addition to those above also polycyclic aromatic hydrocarbons, halogenated hydrocarbons and various pollutants, drugs, and related compounds, with an overall standard deviation in In ssat of 0.45 (RueUe and Kesselring 1998). The hydrophobic contribution remains dominant even when hydrophilic groups are present in the solute molecule, which reduce somewhat the counter-active hydrophobic effect on the solubility. 

The optimum glucocorticoid structure shows a la, 2P-half-chair conformation for ring A, with ring D as a 13-envelope (C-13 is bent up) or a half-chair. Halogenation is most effective in positions 6, 7, 9, and 12. The compounds bind on their p face by hydrophobic binding forces. 

While the properties of polyurethane as an extractant are useful, several problems make it less than ideal. Polyurethanes are far more specific than activated charcoal in removing contaminants. Charcoal separates particles by size, and while it has some specificity, it is well suited for mixtures of diverse chemistries (PAHs vs. halogenated hydrocarbons). Polyurethanes, however, operate on the principle that like dissolves like. They consist of hydrophobic isocyanates and hydrophobic polyalcohols. Thus, the molecules are hydrophobic. The polyalcohol backbone has some polarity, but it is hindered and therefore has a low net polarity. Inasmuch as the extraction effect is based, at least in part, on polarity, polyurethanes are most effective for nonpolar pollutants... 

PVP is a nonionic water-soluble polymer that interacts with water-soluble dyes to form water-soluble complexes with less fabric substantivity than the free dye. Additionally, PVP inhibits soil redeposition and is particularly effective with synthetic fibers and synthetic cotton blends. The polymer comprises hydrophilic, dipolar imido groups in conjunction with hydrophobic, apolar methylene and methine groups. The combination of dipolar and amphiphilic character make PVP soluble in water and organic solvents such as alcohols and partially halogenated alkanes, and will complex a variety of polarizable and acidic compounds. PVP is particularly effective with blue dyes and not as effective with acid red dyes. 

Contact of polysaccharides with halogens may produce sorption complexes. The action of chlorine on cereals has been used to improve baking properties,2253 but the observed effect could be due to the oxidative effect of chlorine on flour polysaccharides (consult Section VII) and other reactions of nonsaccharide flour components. Chlorination of flours increases their viscosity2254,2255 and hydrophobicity.2256 Chlorinated flours have also been reported as adhesives2257 and as oil collectors.2258,2259 Their stability can be increased by neutralization with ammonia.2260... 

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