Dissociation, complex

The equilibrium constant for a reaction in which a metal—ligand complex dissociates to form uncomplexed metal ion and ligand (Kd). 

Direct. Some radionucHdes are packaged in solution for direct sampling (qv) via a septum and injection into the patient. GalHum-67 is a marker of inflammation, infection, and various tumor types. Its half-life is 78.3 h and it is suppHed as the gallium citrate salt. Indium-111 chloride is suppHed for the labeling of white blood ceUs. The In chloride is mixed with oxine (9-hydroxyquinoline) to form a lipophilic, cationic In oxine complex, which enters the white blood ceU. The complex dissociates within the ceU, and the cationic In " ion is trapped within the ceU, owing to its charge. 

In another fluxional process involving ruthenium instead of rhodium, it has been shown that the rate-controlling step is the complex dissociation and that the ligand exchanges between the two annular nitrogen atoms by an intermolecular process. 

Chain reactions such as those described above, in which atomic species or radicals play a rate-determining part in a series of sequential reactions, are nearly always present in processes for the preparation of thin films by die decomposition of gaseous molecules. This may be achieved by thermal dissociation, by radiation decomposition (photochemical decomposition), or by electron bombardment, either by beams of elecuons or in plasmas. The molecules involved cover a wide range from simple diatomic molecules which dissociate to atoms, to organometallic species with complex dissociation patterns. The... 

KCff, or the dissociation constant of a diug, refers to the rate at which the drug-receptor complex dissociates into separate diug and receptor units. 

The various copolymerization models that appear in the literature (terminal, penultimate, complex dissociation, complex participation, etc.) should not be considered as alternative descriptions. They are approximations made through necessity to reduce complexity. They should, at best, be considered as a subset of some overall scheme for copolymerization. Any unified theory, if such is possible, would have to take into account all of the factors mentioned above. The models used to describe copolymerization reaction mechanisms arc normally chosen to be the simplest possible model capable of explaining a given set of experimental data. They do not necessarily provide, nor are they meant to be, a complete description of the mechanism. Much of the impetus for model development and drive for understanding of the mechanism of copolymerization conies from the need to predict composition and rates. Developments in models have followed the development and application of analytical techniques that demonstrate the inadequacy of an earlier model. 

Coordination compounds containing bidentate ligands are often thermally more stable than those comprised of related monodentate ligands, e.g. ethylenediamine (en) complexes dissociate at a higher temperature than those of ammonia or pyridine. Compounds containing a ring structure, such as coordinated salicylaldehyde (sal) and acetyl-acetonate (acac), are particularly stable, and may often be sublimed... 

The oxidized Fe protein MgADP complex dissociates from the reduced MoFe protein... 

However, some data have been more difficult to incorporate into the mechanism shown in Figs. 8 and 9. As reported 21) in Section II,B the Fe protein can be reduced by two electrons to the [Fe4S4]° redox state. In this state the protein is apparently capable of passing two electrons to the MoFe protein during turnover, although it is not clear whether dissociation was required between electron transfers. More critically, it has been shown that the natural reductant flavodoxin hydroquinone 107) and the artificial reductant photoexcited eosin with NADH 108) are both capable of passing electrons to the complex between the oxidized Fe protein and the reduced MoFe protein, that is, with these reductants there appears to be no necessity for the complex to dissociate. Since complex dissociation is the rate-limiting step in the Lowe-Thorneley scheme, these observations could indicate a major flaw in the scheme. 

The poor stability of anthocyanins with simple stractures can be overcome by intermolecular copigmentation reaction, that is, an association with different compounds, especially polyphenolic ones, stabilized by n-n intermolecular and hydrogen bonds. However, this complex dissociates at high temperatures. ... 

Let us assume that for a particular enzyme-inhibitor pair, association is diffusion limited so that k, is I O9 M s1. Fixing k n at this value, and using Equation (7.26), we can determine the value of koB for different values of Kn as summarized in Table 7.3 (this is taken from the more comprehensive table presented in Chapter 2). We have already seen examples in Chapter 6 of compounds with A) values (or Kf values) in the lOnM to lOpM range for which the half-life for binary complex dissociation is far longer than 2 hours. For example, we saw that inhibition of COX2 by DuP697 resulted in a final E I complex with Kf = 5 nM and the lm for complex... 

Let us now consider the the reverse of the binary complex dissociation reaction that we just described. We now turn our attention to the kinetics of association between an enzyme molecule and a ligand. The association reaction is described as follows ... 

It is known that organoboron halide-imidazole complexes dissociate diming equilibrium 56 however, charges disappear upon dissociation. In such a matrix, mobile ions should not originate from the matrix. Therefore, the polymer electrolytes composed of boron halide-imidazole complexes were considered to be appropriate for selective ion transport. 

Kinetics evaluation software generates the values of ka (rates of complex formation) and kd (rates of complex dissociation) by fitting the data to interaction models. In a sensorgram, if binding occurs as sample passes over a prepared sensor surface, the response increases and is registered upon equilibrium, a constant signal is reached. The signal decreases when the sample is replaced with buffer, since the bound molecules dissociate. 

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