Disassociation

At room temperature phenol is a white, crystalline mass. Phenol gradually turns pink if it contains impurities or is exposed to heat or light. It has a distinctive sweet, tarry odor, and burning taste. Phenol has limited solubiUty in water between 0 and 65°C. Above 65.3°C phenol and water are miscible in all proportions. It is very soluble in alcohol, ben2ene, chloroform, ether, and partially disassociated organics in general. It is less soluble in paraffinic hydrocarbons. The important physical properties of phenol are Hsted in Table 1. 

For combustion with air at standard temperature and pressure. These flame temperatures are calculated for 100 percent theoretical air, disassociation considered. Data from Gas Engineers Handbook, Industrial Press, New York, 1965. 

Effect of tamperature on the N2O4-NO2 system at equilibrium. At 0°C (tube at right. N2O4, which is colorless, predominates. At 50°C Itube at left), some of the N204 has disassociated to give the deep brown color of NO2. 

One function of HK is to present the substrates of factor Xlla in a conformation that facilitates their activation [25, 26]. More difficult to explain is the effect of HK on the rate of factor XII activation in plasma since HK does not interact with factor XII, nor does it augment the activity of kaiiikrein. This effect seems to be largely indirect. First, HK is required for efficient formation of kaiiikrein in surface-activated plasma [26, 27]. Second, since kaiiikrein can disassociate from surface-bound... 

Arrhenius proposed the idea that when an acid dissolves in water, it dissociates, or breaks, into its ions. This process is called ionization or disassociation. For example, the compound hydrogen chloride dissociates into a positive hydrogen ion and a negative chlorine ion when dissolved in water. This disassociation forms hydrochloric acid. 

Arrhenius thought something similar to disassociation happened to bases, too. But he believed that instead of releasing a positive hydrogen ion like acids do, bases contributed a hydroxide ion to the solution. A hydroxide ion is a negative ion, and it is written OH-. For example, if the base sodium hydroxide is dissolved in water, it will break up into sodium ions and hydroxide ions, as follows ... 

When placed in water, some acids and bases completely ionize, or dissociate into their ions—but others do not. Acids and bases that completely ionize are called strong acids and strong bases. Strong acids are defined as acids that have a pH of 0-4. Strong bases have pH values of 10-14. On the other hand, weak acids and weak bases do not disassociate completely in water. This leads to a pH value that is closer to neutral, because some of the hydrogen ions are still attached to other atoms, decreasing the hydrogen ion concentration. 

Standardized procedures were adopted with regard to sample preparation, recovery of toxicant, and chemical assay. In order to determine the nature and magnitude of penetrated residues, it was necessary to disassociate all extra-surface residues. The techniques originally developed to effect this separation and which were used in most of the DDT penetration studies have been described by Gunther 11). Certain modifications which have been developed subsequently in connection with the parathion studies are described in detail below since this phase of penetration studies assumes singular importance (see also 14). 

This simplified representation of the morphology shows spheres of polystyrene embedded in a continuous soft elastomeric polybutadiene phase. Here the polystyrene domains act as pseudo crosslinks and the polybutadiene conveys elasticity to the material. When heated above the Tg of polystyrene, the domains soften, disassociate, and the material can be made to flow. When cooled, the polystyrene domains reform and elastomeric behaviour returns. 

The thicker lines represent the sequences of hard urethane segments, and the clusters of these effectively act as crosslinks, making the material act as a conventional elastomer. When the temperature is raised high enough, the clusters disassociate and the material can be made to flow when subsequently cooled, the clusters can reform and the material again exhibits elastomeric properties. Thus these materials show elastomeric behaviour at room temperature, but can be processed as thermoplastics. Hence the name of the material class - thermoplastic elastomers. 

Phosphoric acid is a relatively strong acid and can cause extensive damage to polysaccharides. Ammonium phosphate salts are good fire retardants (1,7,13,18,22), are inexpensive, and should not cause acid-catalyzed hydrolysis or dehydration. However, if ammonium phosphate-treated wood is exposed to heat, ammonia will be given off and phosphoric acid will be left (7,39-43). The critical temperature at which monoammonium phosDhate thermally disassociates has been reported to be 166° (39), 170° (47), or 190°C (40). 

However, the relatively low reported Ea of 8.14 kcal/mol (43) suggests that even moderately warm temperatures over several years, such as roof structures experience during the summer months, may be sufficient to form phosphoric acid. Ammonium sulfate, which can also thermally disassociate to form an acid (7,40), may cause even more degradation to lumber than ammonium phosphates (40,44). This thermal disassociation of ammonium salts may be the cause of the premature degradation recently observed in some fire retardant treated plywood roofing material. 

The a chain binds IL-2 with low affinity, with binding being characterized by high subsequent association-disassociation rates. The y subunit does not interact directly with IL-2. It is sometimes known as yc (common), as it also appears to be a constituent of the IL-4, -7, -9, -13 and -15 receptors. 

Darnay, B. and Aggarwal, B. 1997. Early events in TNF signalling - a story of associations and disassociations. Journal of Leukocyte Biology 61(5), 559-566. 

Addition of zinc in order to promote Zn-insulin crystal growth (which take longer to disassociate and, hence, longer to leak into the bloodstream from the injection depot site). 

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