Location of Ions

The smaller Na ion is able to reside within the plane of a quartet, whereas ammonium and potassium ions coordinate between two G-quartets. On 

It is clear that, if available, monocations such as potassium and sodium will be incorporated into a quadruplex. The potassium and ammonium ions are too large to be coordinated by a single G-quartet in a coplanar fashion. As a result, coordination of these ions occurs between two G-quartets planes. Each quadruplex involving n quartets will then accommodate n — 1) of these specific ions. For example, quantitative determination of ammonium peak intensity revealed that three NH4 ions are placed between four quartets. In contrast, the smaller Na ion (ionic radius of 1.18 A) allows for in-plane coordination. Multiple Na ions are therefore not restricted to the spacing between G-quartets, and can move further away form each other to reduce electrostatic repulsions. In any case, empty sites between quartets are probably very rare. In fact, although vacant coordination sites are likely to exist (as ions move between sites, see below), their lifetime must be very short as demonstrated, for example, by Federiconi et who determined a site occupancy of 0.97 K ions per tetramer in GMP quadruplexes prepared in 0.5 M KCl. 

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These uncertainties as to the location of ions such as OH- or F" cast doubt on the validity of the quantitative models which are used to treat micellar rate effects. The problem is less serious for reactions of less hydrophilic ions which bind strongly and specifically to micelles, and it should be relatively unimportant for bimolecular reactions of non-ionic reagents. It is probable also that the volume element of reaction decreases as the concentration of ionic reagent is increased, which would speed reaction. 

The most important and universal characteristic of the cell is its ability to manipulate the location of ions and molecules. It achieves this by exploiting their hydrophilic and hydrophobic properties so as to compartmentalise them for different functions within a variety of cell membranes. 

As stated previously, it is difficult to assign ions to a few discrete "mean planes of adsorption" and have these mean planes correspond in every case to the location of ions expected from hypothetical structure and bonding at the hydrous oxide surface. 

The "Agl" model for location of ions in the oxide-water interface is probably the best reasonably simple interpretation. 

FT-ICR detection is accomplished by monitoring the image current induced by the orbiting ion packet as it cycles between the two receiver plates of the ceU. After formation by an ionization event, all trapped ions of a given mIz have the same cyclotron frequency but have random positions in the FT-ICR cell. The net motion of the ions under these conditions does not generate a signal on the receiver plates of the FT-ICR cell because of the random locations of ions. To detect cyclotron motion, an excitation pulse must be applied to the FT-ICR cell so that the ions bunch... 

Microscopic examination of ablated particles showed that only the outer layer of dust particles was consistently being vaporized. Barringer knew that AIRTRACE was collecting the particles from the soil micro-layer the location of ion accumulation in the soil. 

Major locations of ion and water exchange in the nephron, showing sites of action of the diuretic drugs. 

On what basis does the Stem model distinguish the potential location of ions near a surface under the influence of an electrical potential ... 

Although the overall phenomena observed during polymerization seem to be accounted for, several interesting questions about the crystal morphology, primary and secondary nucleation mechanism, directiveness of polymer chain and crystal growth, and location of ion and counter-ion... 

Figure 8.22 Schematic diagram of a nuclear gas cooled reactor showing the location of ion exchange treatments [From Amberlite Ion Exchange Resins in Nuclear Power Technology , Rohm and Haas (European Region)]...

Figure 8.23 Schematic diagram of a pressurized water reactor showing the location of ion exchange treatments...

Location of Ion Binding Sites in the Gramicidin Channel by High-Resolution Lamellar Diffraction... 

The following example, taken from one of the earliest reports of the application of XAFS to zeolites, deals with the coordination and location of ion-exchanged manganese ions in zeolite Y [55]. Figure 5 shows the FTs obtained on an aqueous solution of Mn + (Fig. 5a) as well as those obtained on the ion-exchanged zeolite... 

Another possibility is the location of ion in interstitial position, for example interstitial solid solution of Na in C3A. Still another possibihty is the cationic vacancies formation. It is the substitntion of calcium ions by chrominm(III) in octahedral positions in C3S with cationic vacancy formation (extraction sohd solntion). 

Mass Resolution In TOF-MS, mass resolution is related to the temporal width of the isomass ions packet when that packet arrives at the detector (i.e., R = t/At). In the ion source, ions are accelerated out of the source region with inherent dispersion in time (instant of ion formation), space (location of ion at the time of acceleration), and velocity (owing to differences in the initial kinetic energy of ions). These are the three primary factors that limit the resolution in a TOP instrument [11, 13, 16]. The initial kinetic energy (KE) of ions (i.e., KE before acceleration) is given by KE = where no is the initial velocity, which will be in a random direction after acceleration, KE = gV + mvl. The temporal dispersion creates uncertainty in the ions arrival time at the detector. The contribution of this factor can be minimized by the use of a very short ionization pulse and/or a fast-rise ion-extraction pulse, and also by increasing the flight path. Multiturn and multipass research TOP mass spectrometers are available to... 

Rodopoulosb, T. (2010) Orientation and mutual location of ions at the surface of ionic liquids. Phys. Chem. Chem. 

The location of ion cores near singular surfaces of inert gas crystals and simple ionic crystals such as the alkali halides and simple oxides (eg. MgO) has been the subject of considerable theoretical work over a long period of time. The prime reason for the theoretical interest in these materials is that many of the bulk properties can reasonably well be described using pair potentials. For the alkali halides calculations have been made of the ion positions, electronic dipoles and surface energies for some of the most closely packed surfaces, (111) and (100). A comprehensive and critical review of earlier work in this area has been given by Benson and Yun(l). 

Thermal ellipsoids are indicative not only of the extent of atom or group motion but also of their directionality. These ellipsoids can be overlaid on the average positions of ions and of backbone atoms to promote an understanding of the extent and cooperativity of backbone—counterion motions. Figure 10 shows the motion of counterions around DNA successive locations of ions along the trajectory are connected, the initial ion positions are indicated by means of small spheres, and the average structure df DNA is displayed for... 

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