Hydrophobicity, determining

Transport of amino acids across a chloroform liquid membrane with these carriers also revealed a high specificity (Scheme 2). For efficient transport, an aromatic side chain must be present and the distance between the aryl and ammonium functions is optimal in the P-aryl systems. Neither oe-phenyl-glycine 42 nor y-phenyl-butyrine 43 are transported to significant extents 25a>. These results are shown in Table 2. The selectivity with 13 contrasts sharply for that observed with typical detergents wherein side chain hydrophobicity determines the relative transport rates. 

BETA derivatives of C9-C22 saturated fatty acids, as well as the Cig unsaturated acids, oleic and elaidic, were prepared and evaluated in the previous publication (11). Hydrophobicity determination, via contact angle measurements, proved to be nondiscriminatory and, therefore, a more meaningful test, the sand penetration test was devised. 

Kato, A. and Nakai, S. 1980. Hydrophobicity determined by a fluorescence probe method and its correlation with surface properties of proteins. Biochim. Biophys. Acta 624, 13-20. 

Kaliszan, R. High performance liquid chromatographic methods and procedures of hydrophobicity determination. Quant. Struct.-Act. Relatsh. 1990, 9, 83-87. 

The intensity of fluorescence and the wavelength of maximum intensity depend on the polarity of the environment. Thus a Try residue located in a nonpolar region emits fluorescence at 330-332 nm, and in complete exposure to water at 350-353 nm. Furthermore, electron withdrawing groups, like carboxyl, azo, and nitro groups, as well as different salt ions, have a quenching effect on fluorescence. However, measurements of intrinsic fluorescence and of fluorescence quenching have not found wide application in hydrophobicity determinations, because they are restricted to the effect of aromatic a.a. residues. 

Figure 6.1 The amino acids classified according to their solubility in water. The R-group, which is either hydrophilic or hydrophobic, determines their solubility.

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