Hydrophilic carboxyl group

After drying, the aluminum resinates are immobile below 100°C and are oriented with the hydrophilic carboxyl groups combined with aluminum on the fiber surface, and the hydrophobic bulk of the rosin molecule oriented outwardly. 

Bde salts, cholesterol, phosphoHpids, and other minor components are secreted by the Hver. Bile salts serve three significant physiological functions. The hydrophilic carboxylate group, which is attached via an alkyl chain to the hydrophobic steroid skeleton, allows the bile salts to form water-soluble micelles with cholesterol and phosphoHpids in the bile. These micelles assist in the solvation of cholesterol. By solvating cholesterol, bile salts contribute to the homeostatic regulation of the amount of cholesterol in the whole body. Bile salts are also necessary for the intestinal absorption of dietary fats and fat-soluble vitamins (24—26). 

Figure 18 UV photopatterning method. The molecular structure of a photocleavable SAM formed on glass surfaces. UV irradiation through masks placed on top of SAM-modified microchannels leads to the production of hydrophilic carboxylate groups in the irradiated regions (Zhao et al, 2001).

Fig. 26 Conjecture of chain conformation is illustrated for PXcMA polymer monolayers at AIW (a) in the dilute regime and (b) in the semi-dilute regime. Gray balls represent hydrophilic carboxyl groups and black lines represent hydrocarbon chains...

Emulsification of grease. In a soapy solution, grease is emulsified by forming micelles coated by the hydrophilic carboxylate groups of the soap. 

Amphiphilic compounds — Compounds that possess both a hydrophilic and a hydrophobic part. Examples are carbonic acids, having a hydrophobic alkyl chain and a hydrophilic carboxyl group, lecithins, lipids, and many other organic compounds. See also -> hydrophilicity, and -> hydrophobic effect. 

The octanol log F values begin at —0.54 for formic, rise to —0.17 for acetic, and 0.33 for propionic. That is, it takes between two and three lipophilic methylene groups to balance the hydrophilic carboxyl group and allow octanol to share the solute equally with water. In oleyl alcohol/ water it takes one additional methylene before a carboxylic acid is lipophilic enough to be equally shared—i.e., log F(0ieyiaic.) = 0 between propionic and butyric acids. In nitrobenzene/water it takes two additional methylenes, in benzene/water it takes three, and in carbon tetrachloride it takes about 4.5 additional methylenes before log F = 0. 

Cholesterol is composed almost entirely of CHj groups and is therefore water-insoluble. Estradiol is likewise relatively water-insoluble. Flowever, cholic acid contains a hydrophilic carboxyl group, and three hydroxyl groups. As shown by the dashed lines, the three hydroxyl groups all lie on one side of the molecule, thus creating a hydrophilic surface. 

Table 3 Hsts hydrodynamic parameters of 2M5VP-MAA copolymers of different composition [38]. At a 90 mol% content of 2M5VP imits atpH=1.2 the optical anisotropy of the polyampholyte is negative in sign and approaches the po-ly(2-methyl-5-vinylpyridine) anisotropy value. A change of the anisotropy sign from negative to positive is observed in the alkaline region. This indicates the formation of compact particles at pH=13,stabilizedby the hydrophobic interactions of methyvinylpyridine groups composing the nuclei of the particles. In this case the polyampholyte macromolecule is protected from the precipitation due to hydrophilic carboxylic groups associated with water molecules.

When sodium stearate is placed in water, the hydrophilic carboxylate group encourages the formation of a solution the lipophilic alkyl chain discourages it. The compromise achieved is to form a colloidal dispersion of aggregates called micelles (Figure 18.5). Micelles form spontaneously when the carboxylate concentration exceeds a certain minimum value called the critical micelle concentration. Each micelle is composed of 50-100 individual molecules, with the polar carboxylate groups directed toward its outside where they experience attractive forces with water and sodium ions. The nonpolar hydrocarbon chains are directed toward the interior of the micelle, where individually... 

Micelle formation accounts for the fact that soaps dissolve in water. The nonpolar (and thus hydrophobic) alkyl chains of the soap remain in a nonpolar environment—in the interior of the micelle. The polar (and therefore hydrophilic) carboxylate groups are exposed to a polar environment—that of the aqueous phase. Because the surfaces of the micelles are negatively charged, individual micelles repel each other and remain dispersed throughout the aqueous phase. 

A carboxylic acid consists of two regions of different polarity a polar, hydrophilic carboxyl group, which... 

The first four aliphatic carboxylic acids are infinitely soluble in water because the hydrophilic carboxyl group more than counterbalances the hydrophobic hydrocarbon chain. As the size of the carbon chain increases, the hydrophobic group becomes dominant, and solubility in water decreases. 

Soap micelles. Nonpolar (hydrophobic) hydrocarbon chains are clustered in the interior of the micelle, and polar (hydrophilic) carboxylate groups are on the surface of the micelle. Soap micelles repel each other because of their negative surface charges. 

Recall from Section 19.2B that the formation of soap micelles is driven by these same noncovalent forces. The polar (hydrophilic) carboxylate groups of soap molecules lie on the surface of the micelle and associate with water molecules, and the nonpolar (hydrophobic) hydrocarbon chains cluster within the micelle and thus are removed from contact with water. 

The low-molecular-weight carbmylic acids are infinitely soluble in water because the hydrophilic carboxyl group more than counterbalances the hydrophobic hydrocarbon chain. 

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