Hydrophobic property

Octanol-water log P values and the substituent constant n values derived from them have been covered in detail in the previous chapter by A1 Leo. It is of course undeniable that these descriptors have been hugely successful, but they are not the only partition coefficients that can be useful in describing molecular properties. The difference between octanol-water and cyclohexane-water partition coefficients (Alog P) has been shown to be useful in describing brain penetration, and it was proposed that a set of partition coefficients from four different partitioning systems would provide useful, complementary information in order to describe the properties of real membranes. The four partition systems involved water with the following second phases  

In addition to actual partition coefficient measurements, there are a number of other descriptors in which the main property involved is a measure of hydrophobicity. Examples of these are various chromatographic measurements, such as thin layer, paper and reverse phase high performance liquid chromatography. Another interesting treatment is the decomposition of partition coefficients into enthalpic and entropic components, in an attempt to provide more mechanism-based parameters for hydrophobicity. 

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Quantitative Structure—Activity Relationships. Many quantitative stmcture—activity relationship (QSAR) studies of progestins have appeared in the Hterature and an extensive review of this work is available (174). QSAR studies attempt to correlate electronic, steric, and/or hydrophobic properties to progestational activity or receptor binding affinity. A review focusing on the problems associated with QSAR of steroids has been pubUshed (175). 

Another microbial polysaccharide-based emulsifier is Hposan, produced by the yeast Candida lipolytica when grown on hydrocarbons (223). Liposan is apparentiy induced by certain water-immiscible hydrocarbons. It is composed of approximately 83% polysaccharide and 17% protein (224). The polysaccharide portion consists of D-glucose, D-galactose, 2-amino-2-deoxy-D-galactose, and D-galacturonic acid. The presence of fatty acyl groups has not been demonstrated the protein portion may confer some hydrophobic properties on the complex. 

Lecithin (qv), a natural phosphoHpid possessing both hydrophilic and hydrophobic properties, is the most common emulsifier in the chocolate industry (5). The hydrophilic groups of the lecithin molecules attach themselves to the water, sugar, and cocoa soflds present in chocolate. The hydrophobic groups attach themselves to the cocoa butter and other fats such as milk fat. This reduces both the surface tension, between cocoa butter and the other materials present, and the viscosity. Less cocoa butter is then needed to adjust the final viscosity of the chocolate. 

In this study we examined the influence of concentration conditions, acidity of solutions, and electrolytes inclusions on the liophilic properties of the surfactant-rich phases of polyethoxylated alkylphenols OP-7 and OP-10 at the cloud point temperature. The liophilic properties of micellar phases formed under different conditions were determined by the estimation of effective hydration values and solvatation free energy of methylene and carboxyl groups at cloud-point extraction of aliphatic acids. It was demonstrated that micellar phases formed from the low concentrated aqueous solutions of the surfactant have more hydrophobic properties than the phases resulting from highly concentrated solutions. The influence of media acidity on the liophilic properties of the surfactant phases was also exposed. 

Hydrophilic/hydrophobic properties. In water-based systems, the filler should be compatible with water because filler dispersion occurs in an aqueous medium before a polymer emulsion is added. In general, most fillers are hydropho-... 

Like other GFC matrices, including TSK-GEL SW and TSK-GEL PW packings, and dextran and agarose gels, Toyopearl HW resins exhibit some ionic and hydrophobic interaction with samples. The hydrophobic properties of Toyopearl HW resins, however, can be utilized more effectively for improved protein purifications because, unlike numerous other GFC packing materials, Toyopearl HW resins can be used with high levels of organic solvent (38). 

Nylon 12 is produced in a similar way to nylon 6 by the ring opening polymerization of laurolactam. The polymer has a lower water capacity than nylon 6 due to its higher hydrophobic properties. The polymeriza-... 

Deschamps, J. R., Miller, C. E., and Ward, K. B. (1995). Rapid purification of recombinant green fluorescent protein using the hydrophobic properties of an HPLC size-exclusion column. Protein Expression and Purification 6 555-558. 

Possessing both hydrophilic and hydrophobic properties. Bile Acids... 

The FTE SAMs have a good hydrophobic property. Ohio et al. [36] have compared the variation of contact angles with immersing time in a neat FTE and a 100 mM FTE solution. The contact angles of water and hexadecane increased to about 110° and 73° from the initial value 76° and 36°, respectively, after 24 h immersion. Their works also indicate that the adsorption rate in 100 mM FTE solution is slightly faster than that in neat FTE. 

Jarvis and Pethica [51] also investigated adhesion as a function of surface wettability but used a diamond tip for its known hydrophobic properties. They also used magnetic force-controlled AFM and applied forces to magnetic material behind the tip to bring the... 

This separation technique produces very good results for acidic or anionic dye molecules containing carboxylic, sulfonic, and hydroxy groups that can be separated within short run times in an aLkaline medium in a single analysis step. - Natural colorants usually do not contain these functional groups they are usually more voluminous and strongly hydrophobic, properties that complicate their determination by CE. The sample pretreatment is more difQcult when CE (compared to HPLC) is used. 

We recently prepared various types of differently fiuorinated alkyl sulfate ILs and discovered that the hydrophobicity was dependent on the content ratio of the fluorine on the alkyl sulfate anion and 2,2,3,3,4,4,5,5-octafiuoropentyl sulfate salts showed hydrophobic properties. Melting point and viscosity were also dependent on the fluorine contents of the anionic part, while conductivity was determined by the cationic part and not influenced by the fluorine contents. Efficient lipase-catalyzed transesterificafion was demonstrated using hydrophobic 1-butyl-3-methylimidazolium 2,2,3,3,4,4,5,5-octafiuoropentyl sulfate ([bmim][C5E8]) as solvent (Eig. 6). ... 

Taylor, P.. Hydrophobic properties of drugs. In Quantitative Drug Design, Ramsden, C. A. (ed.), Pergamon Press, Oxford, 1990 Vol. 4, pp. 241-294. 

A practical method of modification of polysaccharides by clean oxidation using H2O2 as oxidant and cheap iron phthalocyanine as catalyst has been developed. Since no acids, bases or buffers and no chlorinated compounds were used, a pure product can be recovered without additional treatment. Importantly, this flexible method provides materials with a wide range of DScho and DScooh just by an appropriate choice of the reaction conditions. Oxidized polysaccharides thus obtained possess various, tailormade hydrophihc/hydrophobic properties which have been tested successfully in cosmetic and other apphcations. 

Hanson, M., Unger, K. K., Mant, C. T., and Hodges, R. S., Polymer-coated reversed-phase packings with controlled hydrophobic properties. I. Effect on the selectivity of protein separations, /. Chromatogr., 599, 65, 1992. 

Floyd, T. R., Yu, L. W., and Hartwick, R. A., Use of diluted anion-exchange and hydrophobic properties in separating single-stranded oligodeoxyribonu-cleotides on mixed-ligand stationary phases, Chromatographia, 21, 402, 1986. 

Chmelfk, J. Hudecek, J. Putyera, K. Makovicka, J. Kalous, V. Chmelikova, J., Characterization of the hydrophobic properties of amino acids on the basis of their partition and distribution coefficients in the 1-octanol-water system, Collect. Czech. Chem. Commum. 56, 2030-2040 (1991). 

An important aspect of dye-sensitized solar cells is water-induced desorption of the sensitizer from the surface. Extensive efforts have been made to overcome this problem by introducing hydrophobic properties in the ligands. Complexes that contain hydrophobic ligands ((48)-(53)) have several advantages compared to r/,v-dithiocyanato- u(2,2,-bipyndyl-4,4,-dicarboxylatc)ruthcnium(II) (22) ... 

Experiments have shown the following results. The depth of penetration of the organic compound without catalysts is about 10-14 cm. However, the polymerization time is very long (about 2-3 days) and consumption of the compound is substantial (about 1-2 L/m2). The use of catalysts reduces the duration of the polymerization process to 1-3 hours. In this case the depth of penetration of chemicals into constructive materials is about 5-6 mm and consequently the consumption of organic compounds decreases. The treated materials have hydrophobic properties. The relation R does not depend on humidity of the surface of materials. 

The most important and universal characteristic of the cell is its ability to manipulate the location of ions and molecules. It achieves this by exploiting their hydrophilic and hydrophobic properties so as to compartmentalise them for different functions within a variety of cell membranes. 

These points, however, do not address the central question of how organisms deal with a contaminated environment with which they have to interact in order to obtain energy and metabolites. Crucial to these processes are the cellular processes which can modify the ionisation of molecules, their hydrophilic/ hydrophobic properties, and the matrix within which they exist. Many of these changes occur in the alimentary tract but they also occur at the cellular... 

Like other peptides, the ability of SP to stimulate histamine release is closely related to its ability to mobilize Ca from a cellular pool and to the basic and the hydrophobic properties of its N-terminal and C-terminal amino acids, respectively. In this regard, intact SP (SP, n) is more active than the N-terminal tetrapeptide (SP8 n) with SP,, giving a half-maximal response at 8 x 10 6M and 1 x 10 5 M producing some 40% release [99], The C-terminal heptapeptide, SP, 6 was inactive [99],... 

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