Hydrophobicity index

In reversed-phase liquid chromatography, the lipophilicity of compounds governs their retention. The properly transformed retention data should reveal the lipophilicity of the compounds. Valko et al. 

In studies on 25 drugs (Berger et al., 1997),IR)cjata were generated by the shakask, Sirius potentiometric, and computational (ACD) methods. Md i palues fell well within the 0.5 pKs unit range. 

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Amino acid Three- letter code One- letter code Mass of residue in. b proteins Accessible surface area, 2 nm Hydrophobicity index ionizable side chain Occurrence in n/ proteins, /o Relative mutabihty... 

The effective carbon number neff is helpful in characterizing surfactants with an inner functional group. Surfactants with isomeric structures can be compared by means of the hydrophobicity index / [69], which indicates the influence of the effective length of the alkane chain on cM ... 

The hydrophobicity index is also suitable for correlating the cM values of various substituted sodium alkane 1-sulfonates [68]. The perfluoroalkyl substituent, e.g., 8 17 has a pronounced hydrophobic effect (/ = 1.66 at 75°C, sodium salt), whereas the hydrophilic disulfonates have values distinctly below 1 (for a-disulfonates, / = 0.75 was derived [70]). Further, it was somewhat surprisingly shown that substituents like 1-hydroxymethyl, 3-hydroxyethoxy, or even the hydroxyethoxyethoxy groups have hydrophobic effects. 

Valko, K., Bevan, C., Reynolds, D. Chromatographic hydrophobicity index by fast-gradient RP-HPLC a high-throughput alternative to log P/log D. Anal. Chem. 1997, 69, 2022-2029. 

As in isocratic mode, the estimate of log P is indirect and based on the construction of a linear retention model between a retention property characteristic of the solute (logkw) and a training set with known logP ci values. To assess the most performing procedures, the three hydrophobicity indexes (( )o, CHI and logkw) were compared on the basis of the solvation equation [41]. These parameters were significantly inter-related with each other, but not identical. Each parameter was related to log P with values between 0.76 and 0.88 for the 55 tested compounds fitting quality associated with the compound nature. 

Valko, K., Siegel, P. New chromatographic hydrophobicity index ( /o) based on the slope and the intercept of the logk versus organic phase concentration plot. J. Chromatogr. 1993, 637,49-61. 

Camurri, G., Zaramella, A. High-throughput liquid chromatography/mass spectrometry method for the determination of the chromatographic hydrophobicity index. Anal. Chem. 2001,... 

Valko et al. [37] developed a fast-gradient RP-HPLC method for the determination of a chromatographic hydrophobicity index (CHI). An octadecylsilane (ODS) column and 50 mM aqueous ammonium acetate (pH 7.4) mobile phase with acetonitrile as an organic modifier (0-100%) were used. The system calibration and quality control were performed periodically by measuring retention for 10 standards unionized at pH 7.4. The CHI could then be used as an independent measure of hydrophobicity. In addition, its correlation with linear free-energy parameters explained some molecular descriptors, including H-bond basicity/ acidity and dipolarity/polarizability. It is noted [27] that there are significant differences between CHI values and octanol-water log D values. 

Column Packing Hydrophobicity Index(a) Silanophilic Index(b) ... 

Kantola, A., Villar, H.O. and Loew, G.H. (1991) Atom based parametrization for a conformationally dependent hydrophobic index. Journal of Computational Chemistry, 12, 681-689. 

Plot net RFI versus protein concentration (%), and then find the slope (S0, a hydrophobic index) of the line by linear regression analysis (or the initial slope at the origin of quadratic fitting for a more precise measurement as seen in Figure B5.2.1, curve 1). 

Many scales, either empirical or measured, have been proposed for the hydrophobicity of amino acid residues in proteins (Nakai and Li-Chan, 1988). The most extensive study on tlje hydrophobicity index of amino acids was published by Wilce et al. (1995). The authors derived four new scales of coefficients from the reversed-phase high-performance liquid chromatographic retention data of 1738 peptides and compared them with 12 previously published scales. 

The PEST search can be conducted at http //www.icnet.uk/LRITu/projects/pest/ runpest.html. Paste the query sequence, enter options, and click Submit button. Candidate PEST sequences with hydrophobicity index and PEST score are returned. 

The effect of zeolite porosity on the reaction rate was also well demonstrated in liquid-phase oxidation over titanium-containing molecular sieves. Indeed, the remarkable activity in many oxidations with aqueous H2O2 of titanium silicalite (TS-1) discovered by Enichem is claimed to be due to isolation of Ti(IV) active sites in the hydrophobic micropores of silicalite.[42,47,68 69] The hydrophobicity of this molecular sieve allows for the simultaneous adsorption within the micropores of both the hydrophobic substrate and the hydrophilic oxidant. The positive role of hydrophobicity in these oxidations, first demonstrated with titanium microporous glasses,[70] has been confirmed later with a series of titanium silicalites differing by their titanium content or their synthesis procedure.[71] The hydrophobicity index determined by the competitive adsorption of water and n-octane was shown to decrease linearly with the titanium content of the molecular sieve, hence with the content in polar Si-O-Ti bridges in the framework for Si/Al > 40.[71] This index can be correlated with the activity of the TS-1 samples in phenol hydroxylation with aqueous H2C>2.[71] The specific activity of Ti sites of Ti/Al-MOR[72] and BEA[73] molecular sieves in arene hydroxylation and olefin epoxidation, respectively, was also found to increase significantly with the Si/Al ratio and hence with the hydrophobicity of the framework. 

Valko et al. have developed chromatographic methods which are based on established reversed phase methods with acetonitrile water gradients. The lipophilicity is characterized as a so-called chromatographic hydrophobicity index (CHI), which approximates the percentage of acetonitrile necessary for equal distribution between mobile and stationary... 

Valko K, Bevan C, Reynolds D (1997) Chromatographic Hydrophobicity Index by Fast-Gradient RP-HPLC A High-Throughput Alternative to log P/log D. Anal Chem 69 2022... 

Table 2 Hydrophobicity Index for zeolite Beta with various Si Al ratios.

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