Cation release

Calcium can be determined as the oxalate by precipitation from homogeneous solution by cation release from the EDTA complex in the presence of oxalate ion.28... 

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. 

Minerals formed in the soil can weather further with increasing quantities of F12C03 and H2O, or other sources of (Pedro, 1982). The cations released into solution (in this case K ) can be moved out of the soil into groundwater, rivers,... 

The metal cations released from the anode migrate through the solution to the cathode. Because Cu is easier to... 

The cations released become bound by electrostatic forces to the polyanionic chain. These counterions can be either mobile (atmospheric) or site-bound at specific centres. 

The polyelectrolyte cements are modern materials that have adhesive properties and are formed by the cement-forming reaction between a poly(alkenoic acid), typically poly(acrylic acid), PAA, in concentrated aqueous solution, and a cation-releasing base. The base may be a metal oxide, in particular zinc oxide, a silicate mineral or an aluminosilicate glass. The presence of a polyacid in these cements gives them the valuable property of adhesion. The structures of some poly(alkenoic acid)s are shown in Figure 5.1. 

As reaction proceeds, the polymer chain (which is in random coil form) unwinds as the charge on it grows as a result of neutralization and ionization. This contributes to thickening of the cement paste. Cations released become bound to the polymer chain. Countercations can either be bound to a polyanionic chain by general electrostatic forces or be site-bound at specific centres. More than one type of site binding is possible. Complex formation and, if the ligand is bidentate, chelate formation enhance the effect. 

From greatest to least these reactions could also be written, instead of with H+ ions as reactants, with water and dissolved C02. In either scheme, the net result of the reaction is the same - cations (Ca2+, Mg2+, Na+, K+ are released, and alkalinity is produced via OH" or HCO 3 production or H+ consumption. In all reactions, the equivalents of cations released are exactly balanced by the equilvalents of add consumed which corresponds to the alkalinity produced. 

Svendrup, H. A. (1990), The Kinetics of Base Cation Release due to Chemical Weathering, Lund University Press, Lund, Sweden. 

As was mentioned before, charge compensation during oxidation in redox polyelectrolyte systems can be achieved by anion uptake or cation release. For example, for a PAH-Os/PVS-modified eledrode, we can write ... 

Figure 2.18 Probe-beam deflection oxidation transients for (a) positively capped (PAH-Os)i5(PSS)i4 and (b) negatively capped (PAH-Os)i5(PSS)i5 in 0.01 M HCI. Anion uptake/cation release appears as a positive/negative PBD signal. Taken from Ref. [150].

D. Sales, D. Sae-Lee, S. Matsuya, I.D. Ana, Short-term fluoride and cations release from polyacid-modified composites in distilled water and an acidic lactate buffer. Biomaterials 21 (2003) 1687-1696. 

A (not-closed) heated solution of ammonia gradually loses ammonia. If a cation is complexed with ammonia, the free-cation concentration will gradually increase as ammonia is lost (a rare example of slow cation release rather than anion release). It will also increase with an increase in temperature, due to the decrease in stability of complexes with increasing temperature. As one example using this principle, thin films of mixed ZnO/Zn(OH)2, which converted to ZnO on heating over 200°C, were deposited from a heated aqueous Zn-ion/ammonia bath. 

There are a number of examples of homogeneous precipitation of hydroxides based on slow cation release, such as destruction of the Fe-EDTA complex with H2O2 (see Ref. 33). In CD, the only well-defined example of this is heating an ammonia complex (e.g. of Cd ). The loss of ammonia by volatilization will gradually increase the concentration of free Cd ions. 

The release of cations is interpreted to have resulted chiefly from two processes an initial release caused by rapid exchange of surface cations for hydrogen followed by a slow release due to structural attack and disintegration of the aluminosilicate lattice. Other processes which could complicate the form of the dissolution curves are adsorption of cations released by structural breakdown, ion exchange on interlayer sites of cations released by structural breakdown and surface exchange (shale only), precipitation of amorphous or crystalline material, and dissolution rate differences among the various crystalline phases. 

Other mechanisms with the involvement of an incipient methyl cation were also proposed.418,460,462 An attack of methyl cation released from extensively polarized methoxy groups on the carbon-hydrogen bond forms pentacoordinated carbocation intermediates that, in turn, yields ethyl methyl ether after the loss of a proton ... 

A point of this reaction is the release of H+ ions—the Bronsted-Lowry approach considers this the appearance of a proton from the acid. A Bronsted-Lowry acid is a proton donor. Note that the hydrogen ion is a proton, hydrogen s nucleus without the electron found in the atom. Then, a Bronsted-Lowry acid must contain a hydrogen. Of course, if the solvent were not to be water, this statement may not work because the cation released could be other than the hydrogen ion, but there might be other ions performing the same service (liquid ammonia autoionizes, Problem 17.3). 

Notice that in step 2, the weathering of an aluminosilicate mineral by the aggressive attack of "H2S04" waters may result in the release of dissolved silica, as well as cations. The ratio of silica to cations released depends on the composition of the primary mineral weathered and its alteration product. The weathering of a carbonate mineral gives cations and bicarbonate. 

Concentration of anions and cations released by roots of mature plants of L. sativa exposed to two different time periods (12 h and 24 h) at different concentrations (0 0.1 and 1 mM) of 2-Benzoxazolinone (BOA). Ions were collected at two washing times (0-4 h and 4-8 h). Root exposure time (h) Root washing time (h) 4-Arrows indicate significant differences at 0,05. (From Reigosa, M. J. et al. 2001. Allelopathy J. 8, 211-220. With permission). 

The superscript (Oxv) is an abbreviation for oxygen vacancy. Because the newly forming layer i is oxygen-rich relative to the decomposing layer — 1, an additional number of oxygen anions are required in order to utilize all of the cations released in the solid-state decomposition of layer i — 1 at xt = 0 and in the presently considered case, these are provided by a new component of the anion vacancy current generated in layer i by this phase boundary reaction. Since layer i must carry, in addition, the anion vacancy currents generated by the phase boundary reactions at Xi = 0, x2 = 0,. . . , j = 0, we have the identity... 

The alkali cations in pfa normally occur almost entirely in the glass, and when the latter reacts may be presumed to enter the alkali-rich silicate that appears to be the initial product. When this phase is decomposed by reaction with Ca, they will be distributed, like alkali cations from any other source, between the solution and the solid hydration products, on which they are probably adsorbed (Section 7.3.2). The C-S-H tends to take them up more strongly as its Ca/Si ratio decreases (BI58,G63) consequently, the alkali cations released from the pfa are less effective in raising the OH concentration of the pore solution than are those released from the cement. The method outlined in Section 7.5.2 for calculating the OH concentration in the pore solution of Portland cement mix was extended to cover Portland-pfa cement mixes taking this into account (T37). 

Another dental cement is zinc silicophosphate, a mixture of zinc phosphate and silicophosphate described above [30]. Cation-releasing powder is formed by mixing... 

Other silicophosphate cements that use cation-releasing silicates are based on wolla-stonite [33], and serpentinite [34,35]. Naturally occurring phosphate cements have also been known [36]. In these cements, silicates are sparsely soluble and release cations (Ca, and Mg ), which react with the phosphate anions to form hydrophosphates and eventually convert to phosphates. This process is similar to that involving zinc phosphate cements, in which hydrophosphates form first, then convert to phosphates during aging. 

The tert-bwXyX cation released in the hydrolysis of the corresponding ester represents a powerful electrophile, prone to react, for example, with the Tyr, or Trp0 -2 ]... 

Octahedral cations released to solution-surface area Increased... 

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