Hydrophobic indicators

TABLE 21 Hydrophobicity Indices / for Positionally Isomeric Surfactants RZ ... 

HPLC log P techniques, first described by Mirrlees et al. [374] and Unger et al., [375], are probably the most frequently used methods for determining log/1. The directly measured retention parameters are hydrophobicity indices, and need to be converted to a log P scale through the use of standards. The newest variants, breadths of scope, and limitations have been described in the literature [292-298]. A commercial automated HPLC system based on an extension of the approach described by Slater et al. [150] has just introduced by Sirius (www. sirius-analytical. com). 

Woodbum, K.B., Delfino, J.J., and Rao, P.S.C. Retention of hydrophobic solutes on reversed-phase liquid chromatography supports Correlation with solute topology and hydrophobicity indices, Chemosphere, 24(8) 1037-1046, 1992. 

Hydrophobicity indices are fromKyte, J. Doolittle, R. F. A,J.Mol. Biol., 157,105-132(1982). dNI) means that the values are not determined, because the mutant enzymes from denatured structure. CNA means that the mutant enzymes were not analyzed, because they were not secreted in the culture medium. 

Protein content, particularly in urine or cerebrospinal fluid, may also be estimated by methods based on precipitation using sulfosalicylic acid (an anionic protein precipitant) or heat. The turbidity, which is a measure of protein concentration, can be quantitated by spectropho-tometric absorbance methods or light scattering analysis. Absorbance of a hydrophobic indicator dye that binds to protein and changes color is also used. 

Valko, K., Plass, M., Bevan, C., Reynolds, D. and Abraham, M.H. (1998) Relationships between the chromatographic hydrophobicity indices and solute descriptors obtained by using several reversed-phase, diol, nitrile, cyclodextrin and immobilised artificial membrane bonded high-performance liquid chromatography columns. 

The dependence of deposition on degree of hydrophobicity indicates that van der Waals forces play an important role in deposition of quaternary ammonium conditioners [35], This conclusion is consistent with the entropy-driven deposition demonstrated by Ohbu et al. [37] for a monoalkyl quat and by Stapleton [38] for a protonated long-chain amine. 

Heat-treating (> 800 °C) fully deprived cristobal-ite of surface radicals and induced hydrophobicity, indicating that hydrophobicity is at least one of the surface properties determining the cytotoxic potential of a dust as tested on proUferating cells of the mouse monocyte macrophage cell line J774 (Fubini et al. 1999). 

An alternative approach is to use hydrophobic indicators, which remain in the chloroform layer throughout the titration and give a very sharp colour change. Eppert and Liebscher [15] used dimethyl yellow (cationic) in titrations with carbethoxypentadecyltrimethylammonium bromide (Septonex). The colour change in the chloroform layer is from pink to yellow and is very sharp. Tsubouchi and Matsuoka [16] used the potassium salt of the ethyl ester of tetrabromophenolphthalein (anionic) for titration with tetradecyldimethylbenzylammonium chloride (Zephir-an) in a solution buffered at pH 6. The chloroform layer starts off yellow, becomes green near the end-point and turns sky blue when one drop of excess titrant is added. 

The hydrophobic indices, i., the ratios of hydrophobic to hydrophilic surface areas, of seven monosaccharides have been determined. They were found to correlate well with the partition coefficients of the polystyrene-water system for monosaccharides. The concept of hydrophobic indices is important in the consideration of the hydrophobic interactions of flat molecules in aqueous solution. In an effort to establish quantitative structure-activity relationships for carbohydrates, an experimental data-matrix containing the values of sixteen monosaccharides in thirteen solvent systems was subjected to principal component analysis (PCA). Four PC s (t -t ) were found... 

To simplify the 3D treatment of lipophilicity, Loew et al. proposed an alternative method that decomposes partition coefficients into parameters associated with atoms using hydrophobic indices p. A set of adjustable parameters depending only on atomic numbers (N) were determined by linear regression with experimental log values using four different models (Eqs. [28— [31]). 

T. Nusser, T. Balogh, and G. Naray-Szabo, /. Mol. Struct., 297, 127 (1993). The Average Molecular Electrostatic Field as a QSAR Descriptor. 5. Hydrophobicity Indices for Small Molecules. 

Taking account of its presence in starch and cellulose, glucose is the world s most plentiful biomolecule. It is also among the most hydrophilic of carbohydrates. See Miyajima, K., Machida, K., Taga, T., Homaksu, H. and Nakagaki, M. (1988) Correlation Between the Hydrophobic Nature of Monosaccharides and Cholates, and their Hydrophobic Indices, Journal of the Chemical Society Faraday Transactions 1 84,2537-2544. 

The dynamics of micelle formation and disintegration as well as micellar solubilization and exit of an especially neutral solubilizate of moderate polar-ity/hydrophobicity indicate that assumptions 3 to 5 may easily break down for fast reactions and, under such conditions, the rate of a micellar-mediated reaction cannot be expected to follow a simple first- or second-order rate law. The rate law of such a reaction will constimte a transcendental kinetic equation because of the consecutive nature of the reaction. However, such an expected kinetic complexity has not been reported in any study on the effects of micelles on reaction rates. 

Procedure Determination of Cationic Surfactants by Two-Phase Titration with a Hydrophobic Indicator (90)... 

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