Hydrophobic quality

Surfactants are organic compounds that possess surface-active properties. This unique property of the surfactant is due to the presence of hydrophilic and hydrophobic qualities in the same molecule. The hydrophilic part of the molecule has affinity toward the aqueous phase and the hydrophobic part of the molecule interacts with the oil phase. This unique property of the surfactant molecules helps in its movement toward the interface and reduces the surface tension between the two immiscible phases. This dual behavior of surfactant molecules is responsible for their wide range of application in products such as cleansers, creams, lotions, shampoos, agricultural products, and medicines. 

Fig. 6.15 Water immersion test for hydrophobic quality a GSA-SDS, b GSA-SDS/FMWNT specimen...

It should be mentioned that, in principle, it should be possible to make a combined modification of the surface in order to reduce (or increase) the dispersion interaction and the electrical component of the adhesive forces simultaneously. Thus, methylation gives a hydrophobic quality to the surface and promotes a reduction in the adhesion of particles. At the same time methylation intensifies the acceptor properties of the surface and may reduce the electrical component of adhesion, if on adhesion the surface reveals itself as a donor. 

Hydrophobe-modified copolymers of acrylate esters with acryflc or methacryflc acid are finding increasing use as high quality thickeners for both trade sales and industrial paints (186). Formulations thickened with these unique water-soluble polymers show excellent flow and leveling characteristics. 

Table 3 shows some physicochemical properties used as international GA quality parameters, for example moisture, total ash content, volatile matter and internal energy, with reference to gums taken from Acacia Senegal species in Sudan (FAO, 1990, Larson Bromley, 1991). The physicochemical properties of GA may vary depending on the origin and age of trees, the exudation time, the storage type, and climate. The moisture content facilitates the solubility of GA carbohydrate hydrophilic and hydrophobic proteins. The total ash content is used to determine the critical levels of foreign matter, insoluble matter in... 

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 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. 

A new quality in the analysis of hydrophobically post-translational modified proteins could be achieved by the construdion of lipidated proteins in a combination of bioorganic synthesis of activated lipopeptides and bacterial expression of the protein backbone as described before. The physicochemical properties of such artificial lipoproteins differ substantially from those of the corresponding lipopeptides. The pronounced dominance of the hydrophilic protein moiety (e.g. for the Ras protein 181 amino acids) over a short lipopeptide with one or two hydrophobic modifications keeps the construct soluble up to 1CT4 M, while the biotinylated or fluorescence labeled lipopeptides exhibit low solubility in aqueous solutions and can be applied in the biophysical experiments only in vesicle integrated form or dissolved in organic solvent. 

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