Hydrophobic index system

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. 

Fig. 12.19) that seemed to have the widest range of coefficients for the molecular descriptors in the solvation equation. Table 12.10 shows the solvation equations obtained and their normalised coefficients. The equations were obtained from the chromatographic hydrophobicity index data (CHI) of the compounds listed in Table 12.7 by using a 2.5 min linear gradient of the oi anic solvent from 0 to 1009F with 2 ml/min flow rate. The columns used were 4.6 x 50 mm short columns. The application of this fast gradient method makes it possible to obtain CHI values in a given HPLC system in 5 min. 

The hydrophobicity index HI), introduced by Weitkamp and coworkers, is most useful in this context [24]. According to the HI, benzene is expected to compete more favorably with water than with acetonitrile, acetone, or methanol for adsorption in TS-1 micropores, thus maximizing under triphase catalysis the probability of interaction with active sites. This interpretation is supported by competitive adsorption experiments which revealed that the amount of adsorbed benzene in the system TS-l-benzene-H20 was almost ten times greater than for TS-l-benzene-CH3CN [22]. 

CHI is the chromaxo-graphic hydrophobicity index, obtained experimentally via the calibrated HPLC system, here called CHIN for neutrals ... 

All fibers, even bleached ones, seem to have some resinous, hydrophobic material on their surfaces. This material is usually referred to as pitch. We have investigated a bleached sulphite pulp. To remove some of the pitch the pulp can be extracted with ethanol. If, on the other hand, the pulp is heat treated (105 °C 3 h) the pitch is believed to spread over the surface. We made partition experiments for fines fractions from these pulps. A bleached sulphite pulp is of course hydrophilic and all samples partition towards the dextran phase in the basal system. On addition of 0.2 ml 5% P-PEG the hydrophobicity index is 0 for the untreated fiber, for the ethanol extracted fines it is -9 and for the heat treated +5. These results are thus entirely in accordance with our expectations. 

Strkcttire inflkence. The specificity of interphase transfer in the micellar-extraction systems is the independent and cooperative influence of the substrate molecular structure - the first-order molecular connectivity indexes) and hydrophobicity (log P - the distribution coefficient value in the water-octanole system) on its distribution between the water and the surfactant-rich phases. The possibility of substrates distribution and their D-values prediction in the cloud point extraction systems using regressions, which consider the log P and values was shown. Here the specificity of the micellar extraction is determined by the appearance of the host-guest phenomenon at molecular level and the high level of stmctural organization of the micellar phase itself. 

On the basis of data obtained the possibility of substrates distribution and their D-values prediction using the regressions which consider the hydrophobicity and stmcture of amines was investigated. The hydrophobicity of amines was estimated by the distribution coefficient value in the water-octanole system (Ig P). The molecular structure of aromatic amines was characterized by the first-order molecular connectivity indexes ( x)- H was shown the independent and cooperative influence of the Ig P and parameters of amines on their distribution. Evidently, this fact demonstrates the host-guest phenomenon which is inherent to the organized media. The obtained in the research data were used for optimization of the conditions of micellar-extraction preconcentrating of metal ions with amines into the NS-rich phase with the following determination by atomic-absorption method. 

CONTENTS Preface, C. Allen Bush. Thermodynamic Solvent Isotope Effects and Molecular Hydrophobicity, Terrence G. Oas and Eric J. Toone. Membrane Interactions of Hemolytic and Antibacterial Peptides, Karl Lohner and Richard M. Epand. Spin-Labeled Metabolite Analogs as Probes of Enzyme Structure, Chakravarthy Narasimhan and Henry M. Miziorko. Current Perspectives on the Mechanism of Catalysis by the Enzyme Enolase, John M. Brewer and Lukasz Leb-ioda. Protein-DNA Interactions The Papillomavirus E2 Proteins as a Model System, Rashmi S. Hedge. NMR-Based Structure Determination for Unlabeled RNA and DNA, Philip N. Borer, Lucia Pappalardo, Deborah J. Kenwood, and Istvan Pelczer. Evolution of Mononuclear to Binuclear CuA An EPR Study, William E. Antholine. Index. 

Recent studies have made it possible to classify water-organic solvent systems in CCC for separation of organic substances on the basis of the liquid-phase density difference, the solvent polarity, and other parameters from the point of view of stationary-phase retention in a CCC column [1,3-9]. Ito [1] classified some liquid systems as hydrophobic (such as heptane-water or chloroform-water), intermediate (chloroform-acetic acid-water and n-butanol-water) and hydrophilic (such as n-butanol-acetic acid-water) according to the hydrophobicity of the nonaqueous phase. Thirteen two-phase solvent systems were evaluated for relative polarity by using Reichardt s dye to measure solvachromatic shifts and using the solubility of index compounds [6]. 

According to the modern conceptions the Es value is a measure of the lyophilic or lyophobic character of the solute, i.e., an index of the intensity of the solute-solvent interactions. Hydrophobicity and hydrophilicity of a solute are the particular case of the lyophobic and lyophilic character of the solute. The hydrophilicity and hydrophobicity are the measures of the intensity of molecular interactions of a solute or the surface of a solid phase with water in dispersed systems, the dispersing medium in which is water7). 

Referring once more to the effect of the aqueous medium composition upon the relative hydrophobicity of biological solutes, the correlation relationship establish-ecj io3,u6) between the effects of the medium ionic composition on the relative hydrophobicity of serum albumins of various origin and on that of erythrocytes from the same species should be noted. The ionic strength value of the medium in the aqueous ficoll-dextran biphasic system has been used as a quantitative index of the ionic composition of the system, and the ionic composition was varied from 0.11 M phosphate buffer to 0.15 M NaCl in 0.01 M buffer at pH 7.4 116). Partition coefficients of cells in an aqueous polymeric biphasic system are determined as the ratio of a number of the cells in the phase to that of the cells present at the interphase 90). Specific features of the partition behavior of cells in aqueous biphasic systems are discussed in detail elsewhere (see, e.g., Ref. 90 91). It has been established 116) that erythrocytes of different species are distributed in the aqueous ficoll-dextran biphasic system according to the following equation ... 

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