Polyion transfer

Non-equilibrium processes at the sample/membrane interface and across the bulk membrane bias the selectivity and detection limits of the electrodes. Elimination of these nonequilibrium effects by operating the electrodes under complete equilibrium conditions will be of both practical and fundamental significance. While non-equilibrium responses are useful for potentiometric polyion-selective electrodes, it is not obvious whether potentiometry based on mixed ion-transfer potentials is a better transduction mechanism than amperome-try/voltammetry based on selective polyion transfer (65, 66). Ion-transfer electrochemistry at polarized liquid/liquid interfaces is introduced in Chapter 17 of this handbook. 

Since the electrostatic potential sharply decreases with increasing distance from the polyelectrolyte cylinder, the degree of reactivity modification by functional groups fixed to the polyion is strongly dependent on the distance from the cylinder surface. Considerable electrostatic potential effects on the photoinduced forward and thermal back electron transfer reactions, which will be discussed in the following chapters, can be attributed to the functional chromophore groups directly attached to the polyelectrolyte back-bone through covalent bonds. 

Cells of the type in Scheme 11 represent the simplest case of cells with a bi-ionic potential [3]. Hence, in the case of a larger number of ions transferred through the organic phase a multi- or polyionic potential should be considered. Liquid ion-selective electrodes operate on the basis of cells of the type in Scheme 10 their selectivity can be examined with the use of Scheme 11 and polyionic cells. 

Ion exchange is actually a far more complicated process than the simple exchange of one cation for another or one anion for another, particularly for complex polyions such as proteins and oligonucleotides. Each ion of the stationary or mobile phase is surrounded by a cluster of counterions and water. When an ion in the mobile phase is transferred to the stationary phase, the cluster of counterions and water surrounding it is partially or completely displaced. A similar event occurs at the binding site of the stationary phase. Ions displaced from the stationary phase undergo the converse process. The... 

Tb clarify the effect of addition of a cationic HC surfactant on phase separation behavior in the mixed monolayers of anionic HC and FC surfactants polyion complexed with cationic polymers, the mixed monolayers containing three amphiphilic components complexed with PVA were transferred on various substrate plates and studied by AFM, FFM, SSPM, and SIMS. As a cationic surfactant, ODTMAC was examined. 

LB films prepared from poly-thiophene-3-acetic acid stearylamine or sulfonated polyaniline stearylamine polyion complexes, transferred to substrates, and doped by SbCls Absorption and infrared spectra, X-ray diffraction, and conductivity measurements Lateral d.c. conductivities of doped films were moisture dependent and were as high as 2 S cm"molecular organization consisted of randomly oriented polymers lying as extended chains parallel between the substrates and sandwiched between layers of stearylamine molecules whose chains were interdigitated 772... 

Reactions of polyion interchange involve the transfer of the polyion chain, incorporated in the polymer complex, to another polyion present in the solution (Kabanov et al., 1985). These processes are... 

Immobilization of nanoparticles and enzymes onto electrode surfaces using various entrapment chemistries, that is, sol-gels, layered polyions, and hydrogels, has allowed for greater functionality and improved stability. Crumbliss and coworkers demonstrated the direct electron transfer between the redox center of HRP by evaporation... 

The aim of this contribution is to represent the widespread occurrence of r-type radical ions in a variety of electron-transfer processes it should help to illustrate the state of the art in terms of the identification and characterizations of aromatic compounds in a variety of redox stages predominately by spectroscopic techniques. Aromatic (radical) polyions were upon the first species inspected by such techniques. Their structures were generally interpreted by the simplistic Huckel model and, in many cases, an astonishing agreement between the experimental results and models were found. 

Har ada-Shiba M, Yamauchi K, Harada A, Takamisawa I, Shimo-kado K, Kataoka K (2002) Polyion complex micelles as vectors in gene therapy hannacokinetics and in vivo gene transfer. Gene Ther 9 407 14. 

In recent years reversible one-electron transfer could be achieved with P450s assembled in or at biomembrane-like films, inorganic and organic polyion layers and surfactant modifiers. 

Recently diblock copolymers of PEG and ionic segments were prepared by atom-transfer radical polymerization of methacrylic aminoester using a monofunctionalized PEG macroinitiator and then subsequent quaternization. Like others [60] these polymers form so called polyion complex micelles by electrostatic interaction with oppositely charged molecules (e.g. drugs, oligonucleotides), where the PEG block acts as a steric stabilizer [67]. 

In this section, we discuss the interaction of a counterion and a rodlike segment of a polyion as a function of separation distance r between the two [59], We consider as well the coion-polyion [59] and polyion-polyion pair potentials [57,58]. In the latter case, the two polyions may be identically charged or oppositely charged. For each type of pair, there is a polyion selfenergy of the form of Eq. 1 (for the polyion-polyion pairs the factor P is replaced by 2P). The essential difference from Eq. 1 is that the number of condensed counterions 9 is now a function of the pair separation distance, 9 = 9(r). Similarly, in the transfer free energy Eq. 2, both 9 and the condensed layer partition function Q depend on r. In addition to the self-assem-... 

Similar expressions apply to the other types of pairs, and all of them contain the zeroth-order modified Bessel function of the second kind K0(xr), or, simply, the Bessel K0 function. In Figure 1 we show a graph of the smoothly decreasing nonoscillatory Bessel K0 function, which can subsequently be contrasted with the pair potentials w(r) that emerge only after the three free energy terms (polyion self-energy, counterion transfer, and direct pair interaction) are added and minimized, a procedure that involves determination of the functions 0(r) and Q(r). 

The electric transport number of an ionic species is defined as the fraction of the total charge transferred, which is transported by the ionic species. Thus the polyion electric transport number fp is... 

FIG. 1 Schematic illustration of the transference cell. M, ion-exchange membrane V, volume of measuring compartment C, polyelectrolyte concentration E, electric field Up, velocity of polyion. 

S Yabuki, F. Mizutani, Y. Hirata, Current response to D-fructose based on electron transfer from fructose dehydrogenase incorporated in a polyion complex membrane, Bunseki Kagaku, 1998, 47, 1103-1105. 

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