Organic solvents, absence

It must be emphasised that the above Tables must be used with caution. The presence of a specific group cannot always be established with certainty from the presence of the absorption band, particularly in the deformation vibration region on the other hand, the absence of the appropriate absorption band indicates that the grouping is not present. The physical state in which the substance is examined may have an appreciable influence the Tables apply generally to dilute solutions in organic solvents (see Table I). 

THE STATE OF NITRIC ACID IN INERT ORGANIC SOLVENTS The absence of ions in mixtures of acetic acid and nitric acid is shown by their poor electrical conductivity and the Raman spectra of solutions in acetic acid, nitromethane, and chloroform show only the absorptions of the solvent and molecular nitric acid the bands corresponding to the nitronium and nitrate ions cannot be detected. -... 

The immobilization of reagents onto sorbents often results in increase of their sensitivity and, in some cases, selectivity, allows to simplify the analysis and to avoid necessity of use of toxic organic solvents. At the same time silicas are characterized by absence of swelling, thenual and chemical stability, rapid achievement of heterogeneous equilibrium. 

Phase-transfer catalysis describes the action of special catalysts that assist the transfer of reactive molecules from a polar ( aqueous ) solvent to a nonpolar ( organic ) solvent. In the absence of the phase-transfer catalyst, one of the reagents is confined to one solvent, and the other reagent is confined to the other solvent, so no reaction occurs. Addition of a small amount of catalyst, however, enables one of the reagents to pass into the other solvent thereby initiating a reaction. 

Chemiluminescence. Cypridina luciferin emits light in various organic solvents in the presence or absence of a base. The most efficient... 

In 1988 Masoud and Ishak demonstrated that ( -arenediazo methyl ethers do not react with 2-naphthol in dry organic solvents such as dioxan, ethanol, 2-propanol, but only in the presence of water. The reactions are catalyzed by hydrochloric acid (even in the absence of water). Under such conditions almost quantitative yields of azo compounds were obtained. A careful and extensive kinetic investigation of the HCl-catalyzed dediazoniation of substituted benzenediazo methyl ethers, varying the HC1 concentration and the diazo ether/2-naphthol ratio (the latter either absent or in large excess), and comparing the observed rate constants with Hammett s acidity functions for dioxane and ethanol (see Rochester, 1970) indicated the mechanism shown in Schemes 12-8 to 12-10 (DE = diazo methyl ether, D+ = diazonium ion). 

Enzyme Form Proteins are practically insoluble in most organic solvents therefore, in the absence of any special treatment, they are usually present as a solid suspension. This simplifies catalyst-product separation and enzyme reutilization. 

The simplest way to prepare a biocatalyst for use in organic solvents and, at the same time, to adjust key parameters, such as pH, is its lyophilization or precipitation from aqueous solutions. These preparations, however, can undergo substrate diffusion limitations or prevent enzyme-substrate interaction because of protein-protein stacking. Enzyme lyophilization in the presence of lyoprotectants (polyethylene glycol, various sugars), ligands, and salts have often yielded preparations that are markedly more active than those obtained in the absence of additives [19]. Besides that, the addition of these ligands can also affect enzyme selectivity as follows. 

Several reports have indicated that enzymes are more thermostable in organic solvents than in water. The high thermal stability of enzymes in organic solvents, especially in hydrophobic ones and at low water content, was attributed to increased conformational rigidity and to the absence of nearly all the covalent reactions causing irreversible thermoinactivation in water [23]. 

Reproducibility of the production process in terms of, e.g., size distribution, encapsulation efficiency, and release pattern Absence of unwanted side products (e.g., residues of organic solvents in the bilayer)... 

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