Counter-ion release

Figure 6.16 Reconformation of adsorbed cationic polyacrylamide (MW 4 x 106) on cellulose fibres as shown by the kinetics of adsorption and adsorption stoichiometry (measured by counter ion release).

Table 11.2. Radiolysis of N2O-and NjO/Oj-saturated solutions of polynucleotides, poly-deoxyribonucleotides and ssDNA. G values of counter-ion release and strand breakage (unit 10 7 mol J ). (Lemaire et al. 1984 Adinarayana et al. 1988) ...

Drving force for self-assembly + entropy gain through counter-ion release... 

Schematic drawings describing the phenomenon of counter-ion condensation near charged 179 rods (1) and sheets (2) and the resulting counter-ion release as the rods and sheets form a complex (3)... 

Thus, the number of counter ions released from the DNA backbone upon binding of another charged molecule may be determined from the plot of logic versus log [M" "], where the slope equals rm/r. The parameter m represents the charge of the binding molecule and r is the fraction of counter... 

Cholanic acid also possesses the ability of transporting cations across a lipophilic membrane but the selectivity is not observed because it contains no recognition sites for specific cations. In the basic region, monensin forms a lipophilic complex with Na+, which is the counter ion of the carboxylate, by taking a pseudo-cyclic structure based on the effective coordination of the polyether moiety. The lipophilic complex taken up in the liquid membrane is transferred to the active region by diffusion. In the acidic region, the sodium cation is released by the neutralization reaction. The cycle is completed by the reverse transport of the free carboxylic ionophore. 

The photolysis of arenediazonium salts has been widely used for intramolecular cyclizations in the synthesis of 1-phenylethylisoquinoline alkaloids by Kametani and Fukumoto (review 1972). An example is the photolysis of the diazonium ion 10.73, which resulted in the formation of O-benzylandrocymbine (10.74) (Kametani et al., 1971). The mechanism of this cyclization is obviously quite complex, since the carbon (as cation or radical ) to which the diazonio group is attached in 10.73 does not react with the aromatic CH group, but with the tertiary carbon (dot in 10.73), forming a quinone-like ring (10.74). In our opinion the methyl cation released is likely to react with the counter-ion X- or the solvent. 

The cyclohexane-containing system (203) was also prepared in an attempt to obtain metal complexes with clam type geometries (Owen, 1983). As for the previous system, it was considered that such complexes might show enhanced shielding of the cation, from both the solvent and the counter ion present, but still allow the bound metal to be readily released on demand. As is evident from our earlier discussion, both these are desirable properties for metal-ion transport systems. 

Retention of proteins in ion exchange chromatography is mainly caused by electrostatic effects. Because both the protein and the surface have an electrical double layer associated to it, there is an increase in entropy when the two surfaces approach each other. This is due to a release of counter ions from the two double layers when they overlap. The model that is discussed here is based on a solution of the linearized Poisson-Boltzmann for two oppositely charged planar surfaces. We also show the result from a model where the protein is considered as a sphere and the... 

Reaction of P ion with the carrier QCl at the external interface releasing the counter-ion Cl... 

One approach to entrapping guest molecules is to use a different ionic environment inside the hydrophilic portion of liposomes. This is used with, for example, doxorubicin, where the drug is precipitated inside the central liposomal core containing sulfate ions. The precipitation reaction between the charged drug molecules and the counter-ion is controlled by pH and enables the drug to be trapped inside the carrier and, subsequently, released slowly when injected into the body. 

As previously mentioned, molecules that are present within the interface may be able to bind or release electrons from the outer electron hull that surrounds the positively charged proton-neutron core—i.e., they can be ionized. In systems with interfacial boundaries containing ions that carry a charge, a spatial distribution of counter ions surrounding the interface will develop. The number of counter ions will decrease as the distance from the interface increases. The counter ion atmosphere is also referred to as the ion cloud. The... 

Separation of mono- and di-ester pyrrolizidine alkaloids has been achieved by ion-pair adsorption t.l.c., using chloride (or iodide) as the counter-ion.48 Chloranil has been used to oxidize pyrrolizidine alkaloids on t.l.c. The pyrrole derivatives that were formed were then detected with Ehrlich s reagent49 or sulphuric acid.50 Mixtures of pyrrolizidine alkaloids have been separated by h.p.l.c. on a reversed-phase styrene-divinylbenzene resin.51 In a sensitive method for the detection of pyrrolizidine alkaloids, the protonated alkaloids were complexed with aqueous methyl orange. The dye was then released from the complex and estimated spectrophotometrically.52... 

In accounting for the yield of carbon dioxide,which is equivalent to about 20% of the yield of hydroxyl radicals, it would be reasonable to suppose that the carboxyl group of the glucuronic-acid subunit is involved. If this is the case, some release of condensed counter ions might be expected following decarboxylation. Such a process would be expected to contribute to the conductivity changes observed in the pulse-radiolysis experiments described later. 

PPy films containing polymeric counter ions can be used to control the transport of metal ions through the film (Davey et al., 2001). A solution, containing Na, K, Ca and Mg cations, is separated from pure water by an electro-polymerised film which in the oxidised state is impermeable to the cations. Applying a square wave potential that switches the films from the oxidised to the reduced state incorporates cations from the solution and releases some of them into the water, so that the film is rendered permeable. Permeation rates scale with cation size. This process is distinct from the permeation of neutral species described in Section 10.3.7(c). 

A rate equation is simply a mathematical function that is found to describe the observed rate of release or uptake of a given counter-ion with respect to the resin or external solution. This is not to be confused with the rate mechanism, or to put it another way, a fit of data to a rate equation does not necessarily prove the mechanism. Many types of mathematical functions have been shown to describe... 

---