Metal complexation equilibria

In addition to the two examples above, I have developed TKISolver models for the ideal gas, for two-component mixture concentrations, for acid base chemistry (including the generation of titration curves), for transition metal complex equilibria, for genei gaseous and solution equilibria, and for linear regression (121. 

B. Metal Complexation Equilibria of Carboxy-meihyldextrans and Their Gel Analogs... 

For the precise examination of the complexation equilibria in linear carboxylate polyion systems, the Kj values of the Ag -CmDx and the Ca -CmDx binding equilibria have been examined at various a values [42,43]. In this case, the Kj, values resolved in the presence of trace-level concentrations of metal ion have been substituted for the intrinsic constant, Km values. Concurrent measurements of p[H] and p[M], at equilibrium, of the M /(Na, H )CmDx/Na (excess) system enabled the simultaneous analyses of the acid-dissociation and the metal complexation equilibria. The log K(P, and the log K g values determined on the metal association studies are plotted versus a in Fig. 29. The increase in the log KjS value with a is more pronounced with the higher valent metal ion. It should be pointed out as well that log K, , is greatly influenced by the added salt concentration in the Ca ion-binding system. 

One interesting aspect of the median results in Figure 6 is that phenolic groups account for only 23%, 30%, and 22% of the total acidities of FAs, HAs, and NOM, respectively. In models V and VI (Tipping and Hurley, 1992 Tipping, 1998), which are widely used to describe the pH dependence of metal complexation equilibria in natural waters, 33% of total acidity is attributed to phenolic groups. It is likely that these models overestimate the contribution of phenolic groups to acid-base and metal complexation chemistry of DOM. 

As shown in Example 24-5, deviations from Beer s law appear when the absorbing species undergoes association, dissociation, or reaction with the solvent to give products that absorb differently from the analyte. The extent of such departures can be predicted from the molar absorptivities of the absorbing species and the equilibrium constants for the equilibria involved. Unfortunately, since we are usually unaware that such processes are affecting the analyte, there is often no opportunity to correct the measurement. Typical equilibria that give rise to this effect include monomer-dimer equilibria, metal complexation equilibria when more than one complex is present, acid-base equilibria, and solvent-analyte association equilibria. 

Due to practical significance and theoretical interest, much effort has been made to clarify the unique characteristics of metal ion/polyelectrolyte mixture solutions in various disciplines of chemistry. Since a proper equilibrium expression for metal ion binding to polymer molecules is indispensable for the quantification of the physicochemical properties, apparent or macroscopic equilibrium constants have been determined. Unfortunately, however, these overall constants are usually defined arbitrarily, being dependent on the research groups, the experimental techniques, and the systems to be investigated hence they are not comparable with each other nor re-latable to the intrinsic equilibrium constants defined at respective reaction sites. Compared with the situation for the equilibrium analyses of metal complexation with monomer ligands, to which the law of mass action can directly be applied, complete analytical treatment of the metal ion/ polyelectrolyte complexation equilibria has not yet been established even at the present time. There are essential difficulties inherent in the analyses of metal complexation equilibria in polyelectrolyte solutions. 

As has been discussed in Sec. II.B, hydrophobicity of supporting cations is expected to enhance the apparent complexation of weak acidic polyelectrolytes, and it is of interest to study how the metal complexation equilibria are affected by the addition of hydrophobic supporting cations, such as tetra-alkyl ammonium ions. Representative plots obtained by a potentiometric titration study on Ca2+/PAA in the presence of excess TMA+C1 salt [43] are shown in Figure 15. By comparison of the log(Arca)app vs. a plots of the systems of Ca2+/PAA/Na+ with Ca2+/PAA/TMA+, it is apparent that Ca2+ complexation is highly enhanced by the addition of TMA+ at any salt con-... 

Prototropic and metal complexation equilibria of nalidixic acid in the physiological pH region, Int f. Pharm., 9, 191-198 (1981). 

With metal complex equilibria, where formation rather than dissociation constants are employed (Chapter 5), the expression looks a little different because log p and not pp is the customary notation. For the formation of FeY" from Fe and EDTA anion, Y" , for example,... 

The Lewis acidity level is denoted by pM, the negative logarithm of the concentration of a metal ion M, just as the pH is used as a measure of the Bronsted acidity level. Further, it is necessary to consider stepwise formation constants in metal complex equilibria just as is done with calculations involving polybasic Bronsted acid dissociations. Just as those calculations are systematized and simplified by the use of aC to describe the concentrations of all species, so too is the definition of a set of a values that represent the fractions of the total concentration present as each metal complex species in these cases. 

Metal-complex equilibria calculations are accomplished in the same manner as those for polybasic acid equilibria. For this piupose, we have defined a set of fractions to ajyjL to represent the ratios of the concentrations of the metal containing species to the analytical concentration of the metal, Cj. Thus, incorporating the equilibrium constant expression in Equations 5-1 and 5-2 and rearranging, we obtain in (5-3) expressions for the a values that are functions of the equilibrium constants and the free (i.e., not bound to M) ligand concentration. 

METAL COMPLEX EQUILIBRIA INVOLVING SEVERAL COMPLEXING AGENTS... 

Abstract - The experimental and computational methods of the determination of the effect of solvents on the protonation and metal complexation equilibria of macromolecular bioligands is discussed. The effect of the solvent dependence of the secondary structure (e.g. conformation) of bioligands on these processes is especially emphasized. 

Such complex investigations in non-aqueous solvents and especially in water - organic solvent mixtures could lead to the determination of the solvent effect. Such investigations are currently made in our laboratory. In most of the cases the solvent dependence of metal complexation equilibria is in strong correlation with that of the protonation reactions. 

Despite the obvious beauty of this approach and the enormous research work dedicated to its technical realization there is no example of a covalently surface bonded hydroformylation catalyst in industry so far. The main difficulty that has been encountered is unacceptably high metal leaching from the support, mainly due to unfavorable ligand-metal complexation equilibria. Therefore, the best results have been reported for bidentate, covalently anchored ligands, with Rh leaching in the range 100-1000 ppb. Other drawbacks of the approach in... 

To utilize poly(acrylic acid) (represented as HL) as a chelating polymer in polymer-assisted ultrafiltration based removal of a divalent heavy metal (M", n = 2) present in wastewater, it is useful to consider the following polymer ligand-metal complexation equilibria ... 

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