Accumulation of ions

Following the discussion in connection with the expansion III. 127, we note that, for a molecular or a solid-state system, the wave function III. 129 will lead to a correct asymptotic behavior of the energy for separated atoms, provided that the factor g has been conveniently chosen so that it increases indefinitely when any one of the electrons is taken away from the others. A more detailed study of g may sometimes be necessary in order to ensure that no excessive accumulation of ions will occur when the system is separated into its constituents. 

Figure 18 shows the dependence of the activation barrier for film nucleation on the electrode potential. The activation barrier, which at the equilibrium film-formation potential E, depends only on the surface tension and electric field, is seen to decrease with increasing anodic potential, and an overpotential of a few tenths of a volt is required for the activation energy to decrease to the order of kBT. However, for some metals such as iron,30,31 in the passivation process metal dissolution takes place simultaneously with film formation, and kinetic factors such as the rate of metal dissolution and the accumulation of ions in the diffusion layer of the electrolyte on the metal surface have to be taken into account, requiring a more refined treatment. 

The charges present on the insulator surface in contact with the solution give rise to an accumulation of ions of opposite sign in the solution layer next to the surface, and thus formation of an electric double layer. Since straightforward electrochemical measurements are not possible at insulator surfaces, the only way in which this EDL can be characterized quantitatively is by measuring the values of the zeta potential in electrokinetic experiments (see Section 31.2). 

Equation (1.42) is fundamental in electrochemistry and lies at the basis of all classical electrochemical techniques. As stated, it is not easy to use, since both flux and concentration will be time dependent in general and we need an explicit relationship between c and t. If we return to Figure 1.9, however, it can be seen that the rate of accumulation of ions in the thin layer between x and x + Sx must be given by ... 

In the ion trap technology, ions are captured in three-dimensional electric fields. The continuous beam of ions fills the trap up to the limit of their space charge. When additional electric fields are applied, ions are ejected sequentially and detected. Accumulation of ions in the trap results in high sensitivity for these instruments. The trap can be operated in MS and MS/MS modes. In the latter, the ions of interest are maintained in the trap, whereas the other ions are excluded. Sequential fragmentation steps can be performed to generate MSn spectra, highly valuable for structural characterization studies. 

The accumulation of ions in the SR is facilitated by binding with a protein, calsequestrin, the major protein in the lumen of the terminal cistemae bnt absent from the rest of the SR. It associates with the membrane close to the Ca -ATPase pnmp in order to bind Ca ions as they enter the SR and facilitate their uptake. 

The total process of photoionization can be divided into two sequential stages accumulation of charges and their recombination/separation. The latter stage is represented by two first terms on the RHS of Eq. (3.290). Setting WR = D = 0, one stops the recombination and conserves the ions at the very same place where they were produced, by forward electron transfer. In such a special case only the last term remains on the RHS of Eq. (3.290) and its integral represents merely the accumulation of ions over time at any given distance ... 

The main difficulty consists in the determination of AWi, which should include (but is not limited to) image forces. It was recently suggested by Ninham and co-workers [14] that the different van der Waals interactions of anions and cations (due to their different polarizabilities) might explain the accumulation of ions near the interface (and not only the depletion provided by the image force alone). However, as emphasized in Ref. [5], the calculations based on ion-dispersion forces predicted that the cations should accumulate and the anions should... 

According to the electroneutrality condition accumulation of ion A becomes practicable owing to diffusion of a large number of coins Y from the solution into the bead (Fig. 3, C, curve II) under the effect of the electric held. 

Mann H. et al. (1992) Microbial accumulation of ion and manganese in different aquatic environments, an elecgtron optical smdy. In Biomineralization of Iron and Manganese, Modem and Ancient Environments (eds. H. C. W. Skinner and R. W. Fitzpatrick). Catena-Verlag, Cremlingen-Destadt, Germany, suppl. 21, pp. 115-132. 

The selected accumulation of ions of noncovalent complexes [74] based on quadrapolar excitation of the ions in the trap. 

In the CHIM method of prospecting a direct current is introduced into the ground by means of a current electrode and an element collection electrode. This facilitates the extraction and accumulation of ions of the metals in zones near electrodes. The subsequent analysis of the extracted metals yields information about their distribution in the rocks in the zone of investigation. 

Senko, M.W. Hendrickson, C.L. Emmett, M.R. Shi, S.D.-H. Marshall, A.G. External Accumulation of Ions for Enhanced Electrospray Ionization Eourier Transform Ion Cyclotron Resonance Mass Spectrometry, J. Am. Soc. Mass Spectrom. 8, 970-976 (1997). 

The potential difference across the electrode/solution interface is dropped by the accumulation of ions of opposite charge in the solution immediately adjacent to the electrode surface in the electrochemical double layer. The spatial distribution of ions gives a potential profile across the double layer into the solution over a distance that is dependent upon the electrolyte concentration. Given this position-dependent potential profile, it is possible that species undergoing electrochemical reaction, which are assumed to reside in the outer Helmholtz plane of the electrical double layer adjacent to the substrate electrode (otherwise known as the plane of closest approach of nonspecifically adsorbed ions), may not actually be at ([is and hence would not experience the full electrical field corresponding to the electrode/solution potential difference. The result of this is that only a part of the measurable applied r] affects the Gibbs energy of activation of the process. The potential at the OHP with respect to solution, (t)s, is denoted t /i and is known as the potential of the (inner limit... 

Uptake of sucrose, Na, Ca ", and other substances into plant vacuoles is carried out by proton antiporters in the vacuolar membrane. Ion channels and proton pumps in the membrane are critical in generating a large enough proton concentration gradient to power accumulation of ions and metabolites in vacuoles by these proton antiporters (see Figure 7-23). 

---