Strong association

This chapter presents a general method for estimating nonidealities in a vapor mixture containing any number of components this method is based on the virial equation of state for ordinary substances and on the chemical theory for strongly associating species such as carboxylic acids. The method is limited to moderate pressures, as commonly encountered in typical chemical engineering equipment, and should only be used for conditions remote from the critical of the mixture. 

There are two enthalpy corrections for strongly associating vapors. The dominant term is due to the combined enthalpies of reaction of the stoichiometric species, Ah, to form the true... 

System type refers to whether vapor phase contains strongly associating (dimerizing) components or not. 

Biological Activities and Analogues. Somatostatin exerts some neurotropic actions, eg, as a tranquilizer and as a spontaneous motor activity depressor. It also lengthens barbiturate anesthesia time and induces sedation and hypothermia. These actions are consistent with the strong association between somatostatin and GABA in the primate cerebral cortex, 90—95% of somatostatin-positive ceHs also contain GABA (100). 

Complex Ion Formation. Phosphates form water-soluble complex ions with metallic cations, a phenomenon commonly called sequestration. In contrast to many complexing agents, polyphosphates are nonspecific and form soluble, charged complexes with virtually all metallic cations. Alkali metals are weakly complexed, but alkaline-earth and transition metals form more strongly associated complexes (eg, eq. 16). Quaternary ammonium ions are complexed Htde if at all because of their low charge density. The amount of metal ion that can be sequestered by polyphosphates generally increases... 

H-Bonding, Strongly Associative (HBSA) Water Primary amides Secondary amides Polyacids Dicarboy lic acids Monohydro) acids Polyj)henols Oximes Hydroj laniines Amino alcohols Polyols... 

Tbe term structural foam was originally coined by Union Carbide to describe an injection moulded thermoplastic cellular material with a core of relatively low density and a high-density skin. The term has also been used to describe rigid foams that are load bearing. Today it is commonly taken to imply both of the above requirements, i.e. it should be load bearing and with a core of lower density than the skin. In this section the broader load-bearing definition will be used. Whilst structural foams are frequently made from polymers other than polystyrene, this polymer is strongly associated with such products and it is convenient to deal with the topic here. 

When the relationship between the distribution coefficient of a solute and solvent composition, or the corrected retention volume and solvent composition, was evaluated for aqueous solvent mixtures, it was found that the simple relationship identified by Purnell and Laub and Katz et al. no longer applied. The suspected cause for the failure was the strong association between the solvent and water. As a consequence, the mixture was not binary in nature but, in fact, a ternary system. An aqueous solution of methanol, for example, contained methanol, water and methanol associated with water. It follows that the prediction of the net distribution coefficient or net retention volume for a ternary system would require the use of three distribution coefficients one representing the distribution of the solute between the stationary phase and water, one representing that between the stationary phase and methanol and one between the stationary phase and the methanol/water associate. Unfortunately, as the relative amount of association varies with the initial... 

The selenium analogue [PhCNSeSeN] and cyano-functionalized diselenadiazolyl radicals adopt cofacial dimeric structures, e.g., 11.4 (E = Se), with unequal Se Se interactions of ca. 3.15 and 3.35 A. In the latter case the radical dimers are linked together by electrostatic CN Se contacts.Tellurium analogues of dithiadiazolyl radicals (or the corresponding cations) are unknown, but calculations predict that the radical dimers, e.g., 11.4 (E = Te), will be more strongly associated than the sulfur or selenium analogues. ... 

It should be emphasized here that the four major complexes of the electron transport chain operate quite independently in the inner mitochondrial membrane. Each is a multiprotein aggregate maintained by numerous strong associations between peptides of the complex, but there is no evidence that the complexes associate with one another in the membrane. Measurements of the lateral diffusion rates of the four complexes, of coenzyme Q, and of cytochrome c in the inner mitochondrial membrane show that the rates differ considerably, indicating that these complexes do not move together in the membrane. Kinetic studies with reconstituted systems show that electron transport does not operate by means of connected sets of the four complexes. 

The reason for the efficient epoxidation of explicitly allylic alcohols with this system can be found in the strong associative interactions occurring between the substrate and the catalyst. The [Ti(tartrate)(OR)2]2 dimer 1, which is considered to be the active catalyst in the reaction, will generate structure 2 after the addition of... 

For weakly and moderately associated electrolytes, 10< (A<104, no problem generally occurs in obtaining reliable values for KA and A0 from conductivity measurements. Strong association, however, as known for many salts in the solvent class 6, often entails unrealistic A ... 

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