Enhanced solubility

These polymers possess enhanced solubility compared to the aromatic polyamides with no deterioration in thermal stability. Their Ts vary from... 

A further factor affecting k- is the air-sea temperature difference. When the sea is colder than the air above it, the enhanced solubility of the gas in the water (relative to the air temperature) tends to increase kj. This will occur in summer in sub-polar waters and over upwelling regions. The opposite is also found, and much of the ocean equatorward of 45"" latitude is colder than the overlying air for much of the year. However, air-sea temperature differences are generally less than 2-3 "C so that this effect results in a less than 10% modulation of k- on average. 

Whereas the butylated resins have enhanced solubility in organic solvents, enhanced solubility in water (which is rather limited in resins of high molecular weight) is required for some purposes and this may be achieved in a number of ways. For example, in acid condensation of urea and formaldehyde in the presence of sodium bisulphite the following reaction takes place ... 

The presence of ether linkages in the polymer molecule imparts chain flexibility, lowers glass transition temperature, and enhances solubility while maintaining the desired high temperature characteristics [192]. Recently, polyether imines were prepared by the reaction of different diamines with 4,4 -[l,4-phenylene bis(oxy)] bisbenzaldehyde [184]. The polymers synthesized by the solution method were yellow to white in color and had inherent viscosities up to 0.59 dl/g in concentrated H2SO4. Some of these polyimines can be considered as... 

Ewald20 23 made a few measurements on these systems at 80°C in order to show that the formation of a hydrogen bond between iodoform and an ether leads to an enhanced solubility in the gas phase as well as in the liquid phase. In the absence of such a bond, the solubility in methyl ether would be expected to be about the same as that in propane. Ewald found solubilities that were up to four times greater. 

Unsymmetrical azo-compounds find application as initiators of polymerization in special circumstances, for example, as initiators of living radical polymerization [e.g. triphenylmethylazobenzene (30) (see 9.3.4)], as hydroxy radical sources [e.g. a-hydroperoxydiazene (31) (see 3.3.3,1)1, for enhanced solubility in organic solvents [e.g. f-butylazocyclohexanecarbonitrile (32)J, or as high temperature initiators [e.g. t-butylazoformamide (33)]. They have also been used as radical precursors in model studies of cross-termination in copolymerization (Section... 

The effect of fluoride was further demonstrated by the increase in plutonium solubility in deionized water from about 11 percent to essentially 100 percent by addition of sufficient NaF to raise the fluoride concentration to that of basalt ground water. It is likely that the enhanced solubility of plutonium in waters containing high fluoride concentrations is the result of stabilization of Pu(IV) in solution by formation of fluoride complexes. Normally Pu(IV) is the least soluble of the four... 

Supercritical fluids (SCFs) are compounds that exist at a temperature and pressure that are above their corresponding critical values [70,71]. They exhibit the properties of both gases and Hquids. With gases, they share the properties of low surface tension, low viscosity, and high diffusivity. Their main Hquid-like feature is the density, which results in enhanced solubility of solutes compared with the solubility of gases. Furthermore, the solubility of solutes can be manipulated by changes in pressure and temperature near the critical point [72]. 

Silver salts demonstrate how complexation enhances solubility. Figure 18-13 shows that silver will precipitate or dissolve in aqueous solution depending on the species that are present. Starting with a solution of silver nitrate, addition of aqueous NaCl causes AgCl to precipitate ... 

A variety of new water-soluble ligands are being developed and the role of additives, particularly for enhancing solubility of sparingly soluble solutes in water, has been assessed even the use of (3-cyclodextrin to increase solubility has been studied. 

The driving force for the transfer process was the enhanced solubility of Br2 in DCE, ca 40 times greater than that in aqueous solution. To probe the transfer processes, Br2 was recollected in the reverse step at the tip UME, by diffusion-limited reduction to Br . The transfer process was found to be controlled exclusively by diffusion in the aqueous phase, but by employing short switching times, tswitch down to 10 ms, it was possible to put a lower limit on the effective interfacial transfer rate constant of 0.5 cm s . Figure 25 shows typical forward and reverse transients from this set of experiments, presented as current (normalized with respect to the steady-state diffusion-limited current, i(oo), for the oxidation of Br ) versus the inverse square-root of time. 

Properly folded native proteins tend to aggregate less than when unfolded. Solution additives that are known to stabilize the native proteins in solution may inhibit aggregation and enhance solubility. A diverse range of chemical additives are known to stabilize proteins in solution. These include salts, polyols, amino acids, and various polymers. Timasheff and colleagues have provided an extensive examination of the effects of solvent additives on protein stability [105]. The unifying mechanism for protein stabilization by these cosolvents is related to their preferential exclusion from the protein surface. With the cosolvent preferentially excluded, the protein surface is... 

As mentioned earlier, siloxanes impart a number of beneficial properties to polymeric systems into which they are incorporated, including enhanced solubility, resistance to degradation in aggressive oxygen environments, impact resistance and modified surface properties. These particular advantages render polysiloxane-modified polyimides attractive for aerospace, microelectronic and other high performance applications (40-43). 

The basic mechanism for surfactants to enhance solubility and dissolution is the ability of surface-active molecules to aggregate and form micelles [35], While the mathematical models used to describe surfactant-enhanced dissolution may differ, they all incorporate micellar transport. The basic assumption underlying micelle-facilitated transport is that no enhanced dissolution takes place below the critical micelle concentration of the surfactant solution. This assumption is debatable, since surfactant molecules below the critical micelle concentration may improve the wetting of solids by reducing the surface energy. 

Nandi I, Bateson M, Bari M, Joshi HN (2003) Synergistic effect of PEG-400 and cyclodextrin to enhance solubility of progesterone. AAPS Pharm Sci Tech 4 E1... 

The incorporation of an ionizable center, such as an amine or similar function, into a template can bring a number of benefits, including water solubility. A key step in the discovery of the protease inhibitor, indinavir was the incorporation of a basic amine (and a pyridine) into the backbone of hydroxyethylene transition state mimic compounds L-685,434 to enhance solubility (and potency) (Fig. 1.2) [17]. 

It may seem curious to make specific mention of this matter, but in a biological context, it is crucial. The nuclei of porphyrins and related systems are hydrophobic it appears to be generally desirable that the photosensitizer has some degree of intermediate polarity (i.e., amphiphilic properties Section 9.22.3) and the incorporation of a metal, such as zinc(II), which can take on an axial ligand (e.g., H20 in aqueous media, or RNH2 in a biological fluid), or magnesium(II), which can take on two, is expected to enhance solubility in hydroxylic solvents, and shift the... 

Unfortunately, the relatively low solubility of /8-cyclodextrin has precluded its widespread use as a solubilizing agent. To enhance the solubility of /8-cyclodextrin, much work has been carried out on possible derivatizations of the /8-cyclodextrin skeleton. 2-Hydroxypropyl-/3-cyclodextrin has been found to exhibit the desired enhanced solubility, while still retaining the optimal binding characteristics of underivatized /8-cyclodextrin. In addition, this derivative is relatively nontoxic and may even be used in parenteral applications [63],... 

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