Hydrophilic components

Yin et al. [73,74] prepared new microgel star amphiphiles and stndied the compression behavior at the air-water interface. Particles were prepared in a two-step process. First, the gel core was synthesized by copolymerization of styrene and divinylbenzene in diox-ane using benzoylperoxide as initiator. Microgel particles 20 run in diameter were obtained. Second, the gel core was grafted with acrylic or methacryUc acid by free radical polymerization, resulting in amphiphilic polymer particles. These particles were spread from a dimethylformamide/chloroform (1 4) solution at the air-water interface. tt-A cnrves indicated low compressibility above lOmNm and collapse pressnres larger than 40 mNm With increase of the hydrophilic component, the molecnlar area of the polymer and the collapse pressure increased. 

To keep their various ingredients mixed together uniformly, shampoos also contain emulsifiers whose structures include hydrophobic and hydrophilic components. Our inset shows the structure of panthenol, one such... 

In emulsion polymerization, a solution of monomer in one solvent forms droplets, suspended in a second, immiscible solvent. We often employ surfactants to stabilize the droplets through the formation of micelles containing pure monomer or a monomer in solution. Micelles assemble when amphiphilic surfactant molecules (containing both a hydrophobic and hydrophilic end) organize at a phase boundary so that their hydrophilic portion interacts with the hydrophilic component of the emulsion, while their hydrophobic part interacts with the hydrophobic portion of the emulsion. Figure 2.14 illustrates a micellized emulsion structure. To start the polymerization reaction, a phase-specific initiator or catalyst diffuses into the core of the droplets, starting the polymerization. 

Nucleotides, peptides, and amino acids also differ subtly in their polarities Some are more hydro-phobic than others. Thus, separation via reverse phase HPLC is possible. A reverse phase column, such as C18 or C8, has a low- to medium-polarity stationary phase. The more hydrophobic sample components interact to a greater degree with the stationary phase, and therefore elute more slowly than the more hydrophilic components. The sample elution order is from most hydrophilic to most hydrophobic. 

Other aspects of solvation have included the use of surfactants (SDS, CTAB, Triton X-100), sometimes in pyridine-containing solution, to solubilize and de-aggregate hemes, i.e., to dissolve them in water (see porphyrin complexes, Section 5.4.3.7.2). An example is provided by the solubilization of an iron-copper diporphyrin to permit a study of its reactions with dioxygen and with carbon monoxide in an aqueous environment. Iron complexes have provided the lipophilic and hydrophilic components in the bifunctional phase transfer catalysts [Fe(diimine)2Cl2]Cl and [EtsBzNJpeCU], respectively. 

The phase behavior of systems containing pH-sensitive surfactants is another example of non-linearity of the mixing rule. If an oil phase containing an amphiphilic molecule, such as an organic acid, as in the case of naphtenic acids in crude oils, is put into contact with an alkaline water phase, the neutralization takes place at interface and results in a mixture of unneutralized acid (the lipophilic component) and its dissociated alkaline salt (the hydrophilic component). Hence, the interface contains a mixture of two surfactants whose relative proportion depends on the ionization (in the water and at interface), and thus of the pH [75]. 

These observations suggest that the trans-azo ammonium can stabilize the supramolecular channel structure, which is formed by assembling relatively hydrophilic oligoether units based on the molecular recognition in the membrane phase. Compared to the extended molecular form of the trans-azo compound, which is appropriate for covering the hydrophilic component from the outside, the cis compound with a bulky structure cannot stabilize the structure and hence prohibits the assembly formation because it requites a large void structure in the membrane. Therefore, only leaky currents are observable (Figure 26). 

The hydrophilic component of the molecule consists of a tertiary amine in all cases except for prilocaine which contains a secondary amine group (Figure 5.4). This confers water-soluble properties on the molecule. 

Riess demonstrated recently that poly(styrene-b-oxirane) copolymers could act as non-ionic surfactants and lead to water/ toluene microemulsions (29, 30). Using isopropanol as cosurfactant, both 0/W and W/0 microemulsions are obtained (3l). This is a very important conclusion, since PO based diblock copolymers give rise only to 0/W microemulsions under the same experimental conditions (8, 31,). In this respect the "branched structure" of the PO hydrophilic component could favor a decrease in the packing density of the inverse micelle forming molecular and explain the different behavior of the linear and star-shaped PS/PO block copolymers in the W/0 microemulsification process. 

A stable emulsion requires balancing of hydrophobic and hydrophilic components into a uniform suspension. The suspension may be a multicomponent system of emulsifiers, surfactants, stabilizers, and thickeners that are included only to make an aesthetically pleasing product — not for their clinical significance. 

Hydrophobic and Hydrophilic Components of Membrane Lipids A common structural feature of membrane lipids is their amphipathic nature. For example, in phosphatidylcholine, the two fatty acid chains are hydrophobic and the phosphocholine head group is hydrophilic. For each of the following membrane lipids, name the components that serve as the hydrophobic and hydrophilic units (a) phos-phatidylethanolamine (b) sphingomyelin (c) galactosyl-cerebroside (d) ganglioside (e) cholesterol. 

The above photopolymerizable adhesives can be broadly included within the glass of hydrogels even if the hydrophilic components are a material such as polyethylene glycol substituted for water. 

Extracts of the kava root contain both lipophilic and hydrophilic components. The active constituents of kava are referred to as kavalactones or kavapyrones. The active enolides and dienolides are thought to be kawain (kavain), methysticin, and yangonin. 

There are major differences in the chemical compositions of DOM isolated by XAD resins and ultrafiltration (Table I). In rivers and in the ocean, humic substances (XAD isolation) are depleted in N relative to UDOM. The C/N ratios of UDOM are more representative of bulk DOM than those of humic substances. Most of the functional groups identified by NMR are found in more than one class of compounds, so in most cases specific functional groups are not assigned to a particular group of biochemicals. However, in some circumstances it is possible to estimate the fraction of carbon associated with a biochemical class, such as carbohydrates. Carbohydrates are the most abundant polyalcohols in nature, and the ratio (4-5 1) of areas associated with NMR peaks at specific chemical shifts [e.g., 72 ppm (C—O) -102 ppm (O—C—O)] indicates that carbohydrates are their primary source (see Table I for references). In general, humic substances are depleted in carbohydrates (C—O and O—C—O) and enriched in aromatic and unsaturated C (C=C) relative to UDOM (Table I). As mentioned earlier, humic substances are relatively hydrophobic components of DOM, and it is consistent that they are depleted in N and carbohydrates and enriched in aromatic components. The UDOM fraction includes more hydrophilic components that are relatively enriched in N and carbohydrates. Humic substances from the ocean are enriched in aliphatic C (C—C) relative to UDOM, and this could reflect the more hydrophobic nature of the humic substances. 

The XAD-8 resin separation of hydrophobic and hydrophilic components of WSOM was also employed by Sannigrahi et al. (2006). The 13C-NMR results indicated that WSOM in urban atmospheric particles is mostly aliphatic in nature (-95% C mass) with major contributions from alkyl and oxygenated alkyls (-80%), carboxylic acid (-10%), and aromatic functional groups (-4%). The authors also found that urban aerosol WSOC are only qualitatively similar to aqueous humic material in terms of functional group distribution. 

To obtain optimum results in a FAB analysis samples should be relatively pure, though simple mixtures can be tolerated. We routinely perform mixture analysis with FAB, especially in our peptide mapping studies. However, certain shortcomings may arise. Complex mixtures are often plagued by a signal suppression effect where certain mixture components are preferentially ionized at the expense of others. When peptide digests are analyzed the hydrophobic components are ionized with much greater efficiency and the more hydrophilic components are suppressed. Surfactant type... 

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