Functional groups, hydrophobic

Besides the electrostatic potential effect on reactivity, functionalized polyelectrolytes have a variety of interesting features worthy of study. If a polyelectrolyte is covalently modified with highly hydrophobic functional groups, it provides an unusual opportunity to study the chemical reactions of normally otherwise water insoluble functional groups in aqueous solution. Furthermore, a structural organization via hydrophobic interactions may occur in aqueous solution [25 — 31], which is of general scientific importance and is worth studying for its own sake. 

PMBQ represents a special class of polyelectrolytes with hydrophobic functional groups, which tends to form aggregates in solution and exhibits a high affinity to hydrophobic surfaces. The presence of hydrophobic parts in PMBQ enhanced its flocculation performance in different dispersions. We have shown that formation of hydrophobic aggregates of PMBQ was responsible for the considerable broadening of the flocculation window that is extremely important and desirable for industrial application. 

The rate constants for such outer-sphere reactions can therefore differ markedly from those corresponding to true weak-overlap pathways, even after correction for electrostatic double-layer effects. This can cause some difficulties with the operational definition of inner-sphere electrocatalysis considered above, whereby outer-sphere reactions are regarded as "non-catalytic processes. In addition, there is evidence that inner- rather than outer-sphere pathways can provide the normally preferred pathways at metal-aqueous interfaces for reactants containing hydrophobic functional groups [116]. 

Foams form where surface-active chemicals or "surfactants" are present. Surfactants also are called amphipathic agents and are characterized by the presence of both hydrophilic and hydrophobic functional groups (7). Surface-active agents that may be present in natural waters include fulvic and humic acids, collectively termed humic substances, (2,3), fatty acids and lipids (4), and proteins (5), and all have been identified as contributing surfactants in the few characterization studies that have been conducted on natural foams in freshwater environments (5-70) and marine surface layers (77-76). 

Solid-phase extraction is a technique in which hydrophobic functional groups are bonded to solid particle surfac s and act as the extracting phase. They reduce the need for large volumes of organic solvents. 

Figure 2.21 Binding of analyte molecules to hydrophobic interaction chromatography (HIC) media. Structured water covers the hydrophobic functional groups on the gel beads and hydrophobic surfaces of analyte molecules. This water is partially displaced when hydrophobic interactions take place between hydrophobic surfaces (see Hydrophobic effect, Chapter 1). Interactions are driven in part by entropy gains due to released water.

Chemical modification of the silanol groups on the capillary walls can be performed to render them very hydrophilic or very hydrophobic. A hydrophilic surface, obtained by treatment with sulphonic acid, maintains a constant, high EOF. Hydrophobic functional groups attached to the surface lead to suppression of the EOF. A problem with chemical modifications is that their long-term stability is often very poor. 

Perfumes are blends of essences, water and ethanol. Most essences are oil soluble and are not soluble in water. Ethanol has the drawbacks of a low boiUng point, high volatility, low durability, being lipophobic, and being hard to emulsify. Thus, a surfactant is frequently added to emulsify essences. By adding a hydrophobic functional group at the oil soluble essence particles, oil in a water type of emulsion is formed. To ensure the stability of the perfume. 

Non-covalent interaction Since the process involves water as anti-solvent, based on hydrophobicity of the compound, dmg-polymer interactions are favored over the drug-water or polymer-water interactions. Therefore, compounds with logP greater than 3 and polymers having hydrophobic functional groups provide the... 

Sing WT, Lee CL, Yeo SL, Lim SP, Sim MM (2001) Arylalfcylidene rhodanine with bulky and hydrophobic functional group as selective HCV NS3 protease inhibitor. Bioorg Med Chem Lett 11 91 94... 

Fig. 6.22 Catalytic formation of trishydrazone hydrogelator 19c from soluble building blocks 19a and 19b leads to supersaturation followed by fiber formation, which eventually crosslink to form a network that traps Ae surrounding solvent, leading to gelation, lighter part = hydrophilic, darker part = hydrophobic functional groups. Reprinted by permission from Macmillan Publishers Ltd Ref. [44], copyright 2013...

HASE thickeners are polyacrylate dispersions that contain a higher amoimt of carboxyUc acids, predominantly acryUc acid or methacryUc acid. Upon neutralisation during the paint manufacturing they sweU and thicken the paint. Due to additional hydrophobic functional groups attached to the polymer backbone, they can interact with the hydrophobic part of surfactants and the hydrophobic entities of other thickener molecules forming a kind of micellar strucmre in the water phase. In addition, they can interact with hydro-phobic domains on the surface of emulsion polymer binders. This extensive hydrophobic interactions improve efficiency of the HASE thickener and helps the coating formulation... 

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