Counterions mobility

Chemical No interaction with the sample Good solubility High buffer capacity over wide pH range Low pH variation as a function of temperature Availability in different salt forms Low counterion mobility Mobility matching Good salting-in characteristics... 

In biological systems and most industrial applications, the aqueous solution contains in addition to the counterions mobile salt ions. Salt ions of opposite charge are drawn to the charged object and modify the coun-... 

In such a case, no conclusion about the mechanisms can be reached from the form of 4(t) and the observed rate will be determined primarily by the fastest process. By extension of the argument, one easily sees that marked deviation of any of the parallel processes from exponential decay will be reflected in the overall rate with possible change in the functional form. Thus, if the rotation is described by exp(-2D t) as in Debye-Perrin theory, and the ion displacements by a non-exponential V(t), one finds from eq 5 that 4(t) = exp(-2D t)V(t) and the frequency response function c(iw) = L4(t) = (iai + 2D ) where iKiw) = LV(t). This kind of argument can be developed further, but suffices to show the difficulties in unambiguous interpretation of observed relaxation processes. Unfortunately, our present knowledge of counterion mobilities and our ability to assess cooperative aspects of their motion are both too meagre to permit any very definitive conclusions for DNA and polypeptides. 

Radeva Ts, Widmaier J, Petkanchin I. Adsorption of hydrolyzed polyacrylamides on ferric oxide particles counterion mobility in stabilized suspensions. J Colloid Interface Sci 1997 189 23-26. 

The ion activity can be replaced by concentration to a first approximation. The co-ion concentration can be calculated with the Donnan equation based on the capacity of an ion-exchange membrane. It is more difficult to determine the ions mobility ratio. The counterion mobility can be calculated based on isoconductivity point for the appropriate ionic form. The mobility of co-ions can be determined based on a seh-diffusion coefficient measurement. 

The shape of the curves is essentially the same as in solution electrolyte. The currents are smaller, due to the slower scan rates and reduced counterion mobility in the polymer. 

The electrical conductivity of an lEM is essentially due to the concentrations and motilities of fixed charges of the membrane. The electrical conductivity due to the counterion mobility [60] is directly connected with the diffusion coefficient [61]. During the lEM electrical conductivity experiments, the gradient of concentration and pressure are negligible [7], the Nemst-Planck s equation for two counterions (1 and 2) can be written as ... 

However, the gels showed almost no distinct concentration dependence of A, which was somewhat smaller than that of linear polymer solutions when concentrations were higher than 0.25 M. We consider that the presumable polymer chain coiling effect occurs at higher concentrations for polymer solutions and may be canceled by the increasing cross-linking points, which condense counterions and lead to decreases in the counterion mobility and A of gels. 

AMPHIPHILE CHAIN DYNAMICS WATER AND COUNTERIONS MOBILITY... 

When a polymer of (Xe > o-jon, such as polypyrrole in the oxidized state, is subjected to changes of the applied electrode potential, during the transient state electric fields develop in the polymer matrix and then disappear as electronic and ionic charge carriers migrate to new equilibrium positions [19,27,31,184]. The analyses may be based on the concepts derived for redox polymers under the condition that the hopping mobility of the electrons exceeds the counterion mobility. It has been shown [31] that in this case the system behavior is again diffusiona in character. The coated electrode behaves like a porous metal electrode with pores of limited depth. Numerous experimental reports on this behavior of conducting polymers have appeared in the literature the first was probably that of Bull et al. in 1982 [214]. 

Counterion mobility in the particle s double layer should be smaller... 

Surface active electrolytes produce charged micelles whose effective charge can be measured by electrophoretic mobility [117,156]. The net charge is lower than the degree of aggregation, however, since some of the counterions remain associated with the micelle, presumably as part of a Stem layer (see Section V-3) [157]. Combination of self-diffusion with electrophoretic mobility measurements indicates that a typical micelle of a univalent surfactant contains about 1(X) monomer units and carries a net charge of 50-70. Additional colloidal characterization techniques are applicable to micelles such as ultrafiltration [158]. 

The ion transport number is defined as the fraction of current carried through the membrane by counterions. If the concentration of fixed charges in the membrane is high compared to the concentration of the ambient solution, then the mobile ions in the IX membrane are mosdy counterions, co-ions are effectively excluded, and the ion transport number then approaches 1. Commercial membranes have ion transport numbers in dilute solutions of ca 0.85—0.95. The relationship between ion transport number and current efficiency is shown in Figure 3 where is the fraction of current carried by the counterions (anions) through the AX membrane and is the fraction of current carried by the counterions (cations) through the CX membrane. The remainder of the current (1 — in the case of the AX membranes and (1 — in the case of the CX membranes is carried by co-ions and... 

Membranes Ion-exchange membranes are highly swollen gels containing polymers with a fixed ionic charge. In the interstices of the polymer are mobile counterions. A schematic diagram of a cation-exchange membrane is depicted in Fig. 22-57. 

The mechanism by which analytes are transported in a non-discriminate manner (i.e. via bulk flow) in an electrophoresis capillary is termed electroosmosis. Eigure 9.1 depicts the inside of a fused silica capillary and illustrates the source that supports electroosmotic flow. Adjacent to the negatively charged capillary wall are specifically adsorbed counterions, which make up the fairly immobile Stern layer. The excess ions just outside the Stern layer form the diffuse layer, which is mobile under the influence of an electric field. The substantial frictional forces between molecules in solution allow for the movement of the diffuse layer to pull the bulk... 

The ionic or polar substances can be seperated without any reaction on specially treated chromatographic columns and detected refractometrically. This is necessary because alkyl sulfosuccinates show only small absorption in the UV-visible region no sensitive photometric detection can be obtained. Separation problems can arise when common steel columns filled with reverse phase material (or sometimes silica gel) are used. This problem can be solved by adding a suitable counterion (e.g., tetrabutylammonium) to the mobile phase ( ion pair chromatography ). This way it is possible to get good separation performance. For an explanation of separation mechanism see Ref. 65-67. A broad review of the whole method and its possibilities in use is given in an excellent monograph [68]. 

An analysis of the hydration structure of water molecules in the major and minor grooves in B-DNA has shown that there is a filament of water molecules connecting both the inter and the intra phosphate groups of the two strands of B-DNA. However, such a connectivity is absent in the case of Z-DNA confirming earlier MC simulation results. The probability density distributions of the counterions around DNA shows deep penetration of the counterions in Z-DNA compared to B-DNA. Further, these distributions suggest very limited mobility for the counterions and show well defined counter-ion pattern as originally suggested in the MC study. 

When a charged particle is placed in aqueous media, however, the mobility may no longer be proportional to the intrinsic particle charge, since free counterions in solution will associate and move with the particle and thereby alter the net force exerted on the particle by the electric and fluid flow fields. The region of free or mobile counterions surrounding the particle has been termed the electrical double layer or ionic atmosphere. 

Gorin has extended this analysis to include (1) the effects of the finite size of the counterions in the double layer of spherical particles [137], and (2) the effects of geometry, i.e. for cylindrical particles [2]. The former is known as the Debye-Huckel-Henry-Gorin (DHHG) model. Stigter and coworkers [348,369-374] considered the electrophoretic mobility of polyelectrolytes with applications to the determination of the mobility of nucleic acids. 

---