Competing cations

Because this diketene acetal is so susceptible to cationic polymerization, acids cannot be used to catalyze its condensation with diols because the competing cationic polymerization of the diketene acetal double bonds leads to a crosslinked product. Linear polymers can, however, be prepared by using iodine in pyridine (11). Polymer structure was verified by 13c nmR spectroscopy as shown in Fig. 

Lombnres P, Chang AC, Singh BR. Organic ligand, competing cation, and pH effects on dissolution of zinc in soils. Pedosphere 2008 18 92-101. 

It was pointed out that the ratios between the protonated, sodiated, and potassiated forms of the molecular ions, the clusters and the doubly charged ions exhibited relatively high day-to-day variations. Obviously, changing contents of competing cations derived from the sample as well as from impurities in the solvents interfered with the formation of a desired species. 

In a similar study (Comans et al., 1990), the reversibility of Cs+ sorption on illite was studied by examining the hysteresis between adsorption and desorption isotherms and the isotopic exchangeability of sorbed Cs+. Apparent reversibility was found to be influenced by slow sorption kinetics and by the nature of the competing cation. Cs+ migrates slowly to energetically favorable interlayer sites from which it is not easily released. 

There may also be effects via the concentrations of competing cations at the root surface. In studies of short-term uptake of Zn by rice from nutrient solutions containing realistic Zn " " concentrations, Giordano and Mortvedt (1974) found uptake was inhibited by various metabolic inhibitors and by Fe +, Mn +, Ca and Mg + as Cl salts at typical concentrations in flooded soil solutions. Translo-... 

The lonsiv ion exchange resins are extraction technologies used to separate radionuclides from alkaline wastewater in the presence of competing cations. These resins include lonsiv IE-910 and lonsiv IE-911, which are manufactured using a new class of crystalline silicotitanates (CSTs) invented by researchers from Sandia National Laboratory (SNL) and Texas A M University. CSTs demonstrate high distribution coefficients in acidic, neutral, and alkaline solutions with high concentrations of competitive ions such as sodium and potassium. The affinity of CSTs for strontium in neutral or alkaline wastes is also high. 

Offers the only technology that can remove cesium and strontium from alkaline solutions in the presence of competing cations without additional treatment steps. 

In the complexation reaction cryptand must compete with solvent molecules for the cations in solution. Thus solvents such as methanol with low dielectric constant and solvating power offer a preferrable reaction environment but we have achieved quantitative yields in water. The main problem encountered in syntheses of cryptates has been the presence of other cations such as Na and KT competing for the cryptand. Care is taken to minimize the concentration of competing cations of size similar to the cation intended for complexation by using lithium salts for buffering solutions.-... 

Wahlberg, J. S., and Dewar, R. S., "Ion Exchange on Minerals Comparison of Distribution Coefficients for Strontium Exchange from Solutions Containing One and Two Competing Cations," U. S. Geol. Surv. Bull., (1964), 1140-D. 

At high pH, the sensitivity of the distribution coefficient to the concentration of the competing cation is somewhat less than... 

The effects of these factors can be illustrated by considering the formation of a 1 1 complex in a hypothetical soil solution at constant ionic strength in the presence of equimolar concentrations of the reactants, in the absence of competing cations and anions, and at pH = pKl = 4 for the dissociation of the monoprotic acid from which the complexing anion is derived (Fig. 9.1). Equilibrium modelling (using TITRATOR Cabaniss, 1987) indicates that >50% of the total cation concentration will not be complexed with the anion unless the pK for the formation of the species is approximately >7.7. The pK value is more than halved,... 

Once concentrations are determined, Eqs. (18.1) and (18.2) can be used to determine the individual components of the ion atmosphere. The effectiveness of one cation species out competing another cation was summarized in Fig. 18.1 by monitoring the number of competing cations (CC) and background cations (BC) associated with the DNA in accordance with Eq. (18.3). In Eq. (18.3) the competition constant was determined as the midpoint ([M] 2) of the BC association assuming a two state model ... 

OCp]3 can be calculated directly if the concentrations of all ligands and of all competing cations are known (21). Where this information is not available, ISE s can in principle enable conventional single-ion activites to be measured directly. The limited sensitivity of present-day ISE s precludes their use in natural waters,/ although they Ccin be. used in experimental systems involving elevated concentrations of trace metals. Provided that the salinity remains constant, a cell without liquid junction, composed of perfectly selective chloride and lead ISE s could be used. The difference between the emfs measured in the sample (E ) and in a standard solution with the same tanperature and major ion composition (Eg) would be given by... 

Experimental studies. Sorption of radionuclides by colloids is affected by the same solution composition parameters discussed in the previous section on sorption processes. The important parameters include pH, redox conditions, the concentrations of competing cations such as Mg " " and K, and the concentrations of organic ligands and carbonate. The high surface area of colloids leads to relatively high uptake of radionuclides compared to the rock matrix. This means that a substantial fraction of mobile radionuclides could be associated with carrier colloids in some systems. The association of radionuclides with naturally occurring colloids and studies of radionuclide uptake by colloids in laboratory systems give some indication of the potential importance of colloid-facilitated radionuclide transport in the environment as discussed below. 

The effect of different physico-chemical parameters, namely pH, ionic strength, presence of a competing cation and cation concentration, has been studied in order to understand complexation mechanisms. 

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