Polar carboxyl groups

Stearate ion contains two very different str-uctural units—a long nonpolar- hydrocarbon chain and a polar- carboxylate group. The electrostatic potential map of sodium stearate in Figure 19.5 illustrates how different most of the molecule is from its polar- carboxyl-ate end. 

Structure of PEAD is similar to that of PTMS except that the number of nonpolar ethylene units between polar carboxylate groups is smaller. The thermal degradation behavior of PVC/PEAD blends was observed to be similar to that of PVC/PTMS blends and can be explained on a similar basis described earlier. 

Furthermore from the computed area of the cross-section of the interface occupied by one soap molecule it is clear that the molecules of the soap are relatively close together and orientated in a plane at right angles to the interface. As has already been noted in the case of the air-water interface the fatty acids are orientated with their polar carboxyl groups in the water phase we would consequently anticipate that in the oil-water interface the same orientation would occur, the hydrocarbon chain being immersed in the paraffin phase and the polar —OOONa or —COOK group in the aqueous phase. Such orientation is an important factor in the... 

Thus, the ordered phases of BS and C21 are quite analogous, except that C21 lacks a polar carboxyl group along its stiffer molecular backbone. 

Wetting by water of AA/BMA films indicated that in freshly contacted films, the wettability increased due to the exposure of the polar carboxyl groups, as the hydrogen-bonding capability of the solvent increased. Longer exposure time to water leveled the availability of hydrophilic groups at the film/air interface. 

Figure 36.2 represents two prodrugs of ampicillin pivampicillin and bacampicillin. They both result from the esterification of the polar carboxylic group with a lipophilic, enzymatically labile ester. The main properties of these prodrugs can be summarized as follows ... 

As the molecular weight of the acids increase the proportion of non-polar hydrocarbon to polar carboxyl group increases. As a result, the solubility in the polar solvent, water, decreases. 

Sodium stearate has a polar carboxylate group at one end of a long hydrocarbon chain. The carboxylate group is hydrophilic ( water-loving ) and tends to confer water solubility on the molecule. The hydrocarbon chain is lipophUic ( fat-loving ) and tends to associate with other hydrocarbon chains. The compromise achieved by sodium stearate when it is placed in water is to form a colloidal dispersion of spherical aggregates called micelles. Each micelle is composed of 50-100 individual molecules. Micelles form spontaneously when the carboxylate concentration exceeds a certain minimum value called the critical micelle concentration. A representation of a micelle is shown in Figure 19.5. 

Polar carboxylate groups dot the surface of the micelle. There they bind to water molecules and to sodium ions. The nonpolar hydrocarbon chains are directed toward the interior of the micelle, where individually weak but cumulatively significant induced-dipole/induced-dipole forces bind them together. Micelles are approximately spherical because a sphere encloses the maximum volume of material for a given surface area and... 

Marchessault and R5,nby formulated an induction-stabilization theory, in which it was supposed that the glycosidic bond is stabilized by the inductive effect of the polar carboxyl group (see also. Refs. 117-119). According to this theoiy, the presence of an electronegative group, such as a... 

When soap is dissolved in water, the carboxylate end actually dissolves. The hydrocarbon part is repelled by the water molecules so that a thin film of soap is formed on the surface of the water with the hydrocarbon chains protruding outward. When soap solution comes in contact with oil or grease, the hydrocarbon part dissolves in the oil or grease, but the polar carboxylate group remains dissolved in water. When particles of oil or grease are surrounded by soap molecules, the resulting "units" formed are called micelles. A simplified view of this phenomenon is shown in Figure 15.4. 

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