Competition between cations

Gompetitive adsorption between different cations is most important when the concentrations of all cations are low and there is competition for the limited number 

Between pH 4.S-6.3, Pb strongly reduced adsorption of Cu on hematite, whereas the effect of Cu on Pb uptake was less pronounced when the concentrations of both cations were the same (Christl and Kretsdimar, 1999). Palmquist et al. (1999) noted that uptake of Cu and Zn from equimolar solutions was additive. 

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The binding capacity of biomass may be significantly decreased by low pFI (below 3.5) and by other complex factors including competition between cation species, metal sequestration with organic molecules in solution, and the physical form of the biosorbent matrix. 

If CL, CM and pH are kept the same for a series of different cations, the position of equilibrium in equation (6a) would depend on the value of the formation constant, (3 , for the metal complex in question and the extent of precipitation on its solubility product, K. The more stable the complex and the lower its solubility in water, the greater the extent of precipitation. Essentially there is a competition between cations M"+, and protons, H+, for the free ligand anion Ox. ... 

The formation of complex ions is the result of cation-anion attractive forces winning out in the competition between cations and H+ for the various ligands, including water. An example is the formation of the monofluoroaluminium complex ion... 

The interaction of natural organics with cations result in various species, but due to the unknown equilibrium constants and the different interactions by various organics involving several mechanisms, the available data is limited. Matlack (1992) modelled the interactions of natural organics with cations in order to determine speciation. He found a general underestimation of the interactions by speciation software due to the assumption of competition between cations. 

The LundegSrdh hypothesis required that 4 monovalent anions and not more than 4 be absorbed per uptake of one O2 molecule in anion respiration and that all anions stimulate respiration to the same extent per anion charge absorbed. Experiment showed that neither condition was fulfilled. It also became clear that one of the ions whose uptake most enhanced respiration was the cation NH4 and that respiration was enhanced when ion uptake is restricted to cation uptake as occurs when a root is surrounded by a moist anion exchange resin. This hypothesis also preeludes an active uptake of ions occurring under anaerobic conditions following upon a period of active aerobic respiration it is a mechanism which would not provide for any storage of the ability to promote aetive ion uptake. In this it is contrary to a number of experimental observations. Further, only one carrier is postulated for all anions and it therefore fails to explain how there is no competition in uptake, for instance, between halide ions and sulphate ions, nor between sulphate and nitrate. It equally leaves unexplained competition between cations. 

If the cation has been unchanged, its ability to act as a hydrogen-bond donor has been unchanged, so why is an effect seen at all I propose that there is competition between the anion and the Reichardt s dye solute for the proton. Thus, the values of the ionic liquids are controlled by the ability of the liquid to act as a hydrogen bond donor (cation effect) moderated by its hydrogen bond acceptor ability (anion effect). This may be described in terms of two competing equilibria. The cation can hydrogen bond to the anion [Equation (3.5-2)] ... 

The simplest primary alkyl cations, CHJ and C2H, are formed from methane and ethane, respectively, by SbPs—PHSO3 (Olah and Schlosberg, 1968 Olah et al., 1969) and by SbPs (Lukas and Kramer, 1971). In these cases, intermolecular electrophilic substitution of these ions at the precursor alkanes leads to oligocondensation products, e.g. tertiary butyl and hexyl ions. In the presence of carbon monoxide it has been found possible to intercept the intermediate CHJ and C2H quantitatively as oxocarbonium ions (Hogeveen et al., 1969 Hogeveen and Roobeek, 1972). The competition between the reactions of the ethyl cation with ethane and carbon monoxide, respectively, is illustrated by the following equations ... 

Then, contrary to what was reported previously, the olefin dissociates from the zirconium metal complex. This conclusion was further supported by other experimental observations. However, it cannot be completely excluded that competition between dissociative and direct rearrangement pathways could occur with the different isomerization processes studied up to now. Note that with cationic zirconocene complexes [Cp2Zr-alkyl], DFT studies suggest that Zr-alkyl isomerizations occur by the classical reaction route, i.e. 3-H transfer, olefin rotation, and reinsertion into the Zr-H bond the olefin ligand appears to remain coordinated to the Zr metal center [89]. 

Scheme 2 Competition between electron transfer (7 8) and water trapping (7 9+10) of sugar radical cation 7...

At variance with the evaporated samples, Am and did not change much for the sol-gel ones, in spite of the difference between AE cation radii size (Fig. lb, c). It can be suggested that the sol-gel method succeeded in better introduction of Nd into a solid solution (supported by the TPD results) which also depended to a lower extent on the cation radii size match. The increase of the lattice anisotropy AO (Fig. Id) and the trend of the local strain values to decrease or remain about constant (Fig. lc) indicated that there was competition between disorder sources of different nature dispersed lattice defects and Nd3+ agglomerates. 

It is noteworthy that both thermal and photoinduced electron-transfer activation of the [ArH, IC1] complex leads to the ion-radical triad. Consequently, iodination versus chlorination represents the competition between ion-pair and radical-pair collapse. This is confirmed by reactivity studies of dimethoxybenzene cation radical with chloride and iodine (atom), respectively,225 i.e.,... 

Such competition between ion-pair collapse of MT+, C(N02)f and the radical-pair collapse of MT+, NO is also readily modulated by the addition of inert salt.14 The description of the solvent and salt effects in equations (82) and (83) is further confirmed by direct kinetics analysis of the decay of the cation radical MT+ on the nanosecond/microsecond timescale. 

When the kinetics indicate that there is competition between bridged and open cations, neither the solvent-dependent stereoselectivity, nor the... 

On the other hand, the involvement of vinyl cationic species in the reaction cannot be ruled out in some cases, as shown in Scheme 4. In this context, it was found that the reaction of 3-butyn-2-one with mesitylene can occur without Pd(OAc)2, clearly indicating the involvement of vinyl cations generated from alkynes and H+ in this reaction.47 1 The yield difference in the presence and in the absence of Pd(OAc)2 may be explained by the competition between [Pd(n)02CF3]+ and vinyl cationic species in the electrophilic substitution of aromatic G-H bonds. Recent kinetic isotope experiments suggest a mechanism involving alkyne coordination to Pd(n) followed by electrophilic aromatic substitution.476... 

AN+- (Reitstoen and Parker, 1991). In other words, the triad of reactive fragments produced in (63) in the charge-transfer excitation of the EDA complex with A-nitropyridinium ion is susceptible to mutual (pairwise) annihilations leading to the Wheland intermediate W and the nucleophilic adduct N (Scheme 12), so that the observed second-order rate constant ku for the spectral decay of ArH+- in Table 3 actually represents a composite of k2 and k2. A similar competition between the homolytic and nucleophilic reactivity of aromatic cation radicals is observed in the reaction triad (55)... 

A special case of coagulation is the "quasi crystal" formation by unit layers of mont-morillonite bearing exchangeable Ca2+ cations (cf. Fig. 3.10). As Sposito (1989) points out, "one can imagine that the competition between the repulsive electrostatic forces and the attractive van der Waals force will, along with random thermal motions, largely determine the behavior of two siloxane surfaces approaching each other to a distance of separation >10 nm. However, at a separation distance of... 

Intensive effort has been devoted to the optimization of CCP structures for improved fluorescence output of CCP-based FRET assays. The inherent optoelectronic properties of CCPs make PET one of the most detrimental processes for FRET. Before considering the parameters in the Forster equation, it is of primary concern to reduce the probability of PET. As the competition between FRET and PET is mainly determined by the energy level alignment between donor and acceptor, it can be minimized by careful choice of CCP and C. A series of cationic poly(fluorene-co-phenylene) (PFP) derivatives (IBr, 9, 10 and 11, chemical structures in Scheme 8) was synthesized to fine-tune the donor/acceptor energy levels for improved FRET [70]. FI or Tex Red (TR) labeled ssDNAg (5 -ATC TTG ACT ATG TGG GTG CT-3 ) were chosen as the energy acceptor. The emission spectra of IBr, 9, 10 and 11 are similar in shape with emission maxima at 415, 410, 414 and 410 nm, respectively. The overlap between the emission of these polymers and the absorption of FI or TR is thus similar. Their electrochemical properties were determined by cyclic voltammetry experiments. The calculated HOMO and LUMO... 

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