Temperature organic solvents and

The presence of a covalent acyl-enzyme intermediate in the catalytic reaction of the serine proteases made this class of enzymes an attractive candidate for the initial attempt at using subzero temperatures to study an enzymatic mechanism. Elastase was chosen because it is easy to crystallize, diffracts to high resolution, has an active site which is accessible to small molecules diffusing through the crystal lattice, and is stable in high concentrations of cryoprotective solvents. The strategy used in the elastase experiment was to first determine in solution the exact conditions of temperature, organic solvent, and proton activity needed to stabilize an acyl-enzyme intermediate for sufficient time for X-ray data collection, and then to prepare the complex in the preformed, cooled crystal. Solution studies were carried out in the laboratory of Professor A. L. Fink, and were summarized in Section II,A,3. Briefly, it was shown that the chromophoric substrate -carbobenzoxy-L-alanyl-/>-nitrophenyl ester would react with elastase in both solution and in crystals in 70 30 methanol-water at pH 5.2 to form a productive covalent complex. These... 

Yield of Glycosidase-Catalyzed Synthesis of Oligosaccharides. The yield of glycosidase-catalyzed synthesis depends on a number of parameters such as reaction time, temperature, organic solvent, and substrate concentration. 

What distinguishes water from ordinary organic solvents and justifies the term hydrophobic interaction is the molecular origin of the effect, being entropy driven in pure water at room temperature and resulting primarily from the strong water-water interactions. 

Naphthenic acids are viscous hquids, with phenohc and sulfur impurities present that are largely responsible for their characteristic odor. Their colors range from pale yeUow to dark amber. An odor develops upon storage of the refined acids. Naphthenic acids have wide boiling point ranges at high temperatures (250—350°C). They are completely soluble in organic solvents and oils but are insoluble (<50 mg/L) in water. Commercial naphthenic acids are available in... 

Several process improvements using aqueous solution at elevated temperatures (350 °C) and pressure (16) or using an organic solvent and an acid at milder temperatures (<80 C) have been described for o-l L) (17). 

Caprolactam, mol wt 113.16, is a white, hygroscopic, crystalline soHd at ambient temperature, with a characteristic odor. It is very soluble in water and in most common organic solvents and is sparingly soluble in high molecular weight aUphatic hydrocarbons. Molten caprolactam is a powerful solvent for polar and nonpolar organic chemicals. Selected physical properties and solubiUties of caprolactam are Hsted in Tables 1 and 2, respectively. 

Cobalt(Il) dicobalt(Ill) tetroxide [1308-06-17, Co O, is a black cubic crystalline material containing about 72% cobalt. It is prepared by oxidation of cobalt metal at temperatures below 900°C or by pyrolysis in air of cobalt salts, usually the nitrate or chloride. The mixed valence oxide is insoluble in water and organic solvents and only partially soluble in mineral acids. Complete solubiUty can be effected by dissolution in acids under reducing conditions. It is used in enamels, semiconductors, and grinding wheels. Both oxides adsorb molecular oxygen at room temperatures. 

The aqueous micellai solutions of some surfactants exhibit the cloud point, or turbidity, phenomenon when the solution is heated or cooled above or below a certain temperature. Then the phase sepai ation into two isotropic liquid phases occurs a concentrated phase containing most of the surfactant and an aqueous phase containing a surfactant concentration close to the critical micellar concentration. The anionic surfactant solutions show this phenomenon in acid media without any temperature modifications. The aim of the present work is to explore the analytical possibilities of acid-induced cloud point extraction in the extraction and preconcentration of polycyclic ai omatic hydrocai bons (PAHs) from water solutions. The combination of extraction, preconcentration and luminescence detection of PAHs in one step under their trace determination in objects mentioned allows to exclude the use of lai ge volumes of expensive, high-purity and toxic organic solvents and replace the known time and solvent consuming procedures by more simple and convenient methods. 

The usual range of film coefficient values is 40-50 for organic solvents and light petroleum fractions such as hexanes 25 for heavier materials such as aniline, straw oil, etc. and 0.5-3 for low temperature (10-40°F) subcooling of heavier organics and inorganics such as chlorine. 

Gozdz et al. (of Bellcore) [25] recognized that poly (vinylidene difluoride) hexafluoropropylene (PVDF HFP) copolymers could form gels with organic solvents and developed an entire battery based on this concept. Typically, the gel separator is 50 pm thick and comprises 60wt. % polymer. In the Bellcore process the separator is laminated to the electrodes under pressure at elevated temperature. The use of the PVDF HFP gelling agent increases the resistivity of the electrolyte by about five times which limits the rate capability of such batteries. 

Nylons tend to show very good resistance to organic solvents, and also to fuels and oils. They are, however, readily attacked by concentrated mineral acids at room temperature and by alkalis at elevated temperatures. 

Experiments were undertaken in various organic solvents and over a wide range of temperatures. 

Diamantane-based polymers are synthesized to take advantage of their stiffness, chemical and thermal stability, high glass transition temperature, improved solubility in organic solvents, and retention of their physical properties at high temperatures. All these special properties result from their diamantane-based molecular structure [90]. Polyamides are high-temperature polymers with a broad range of applications in different scientific and industrial fields. However, their process is very difficult because of poor solubility and lack of adequate thermal stability retention [90]. Incorporation of 1,6- or... 

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