Stability constants probability

The low TTA dependence at 35.0°C probably is attributable to dissolution of TTA in the aqueous phase. Observation of fourth-power dependence on acidity argues against any change in the extraction mechanism (e.g., Pu(IV) reduction or NO3 involvement). An aqueous Pu(TTA)3+ complex has been reported (14, 15) and this possibility has been considered in the error analysis of the Pu(IV)-sulfate stability constants. 

Mohamed [63] investigated the complexation behavior of amodiaquine and primaquine with Cu(II) by a polarographic method. The reduction process at dropping mercury electrode in aqueous medium is reversible and diffusion controlled, giving well-defined peaks. The cathodic shift in the peak potential (Ep) with increasing ligand concentrations and the trend of the plot of EVl versus log Cx indicate complex formation, probably more than one complex species. The composition and stability constants of the simple complexes formed were determined. The logarithmic stability constants are log Bi = 3.56 log B2 = 3.38, and log B3 = 3.32 [Cu(II)-primaquine at 25 °C]. 

Many correlations have been made between the stability constants for a series of complexes and other properties. For example, basicity of the ligands, ionic radii, dipole moments, and other properties have been correlated with the stability constants of the complexes. However, before comparisons such as these are made, the stability constants should be corrected statistically to take into account the fact that successive complexes do not have the same probability of forming. 

Rossotti, F. J. C., and Rossotti, H. (1961). Determination of Stability Constants. McGraw-Hill, New York. Probably the most respected treatise on stability constants and experimental methods for their determination. 

Since the stability constants increase from water to methanol, it is probable that the dissociation rates decrease too. They indeed decrease markedly in methanol-chloroform (143 Table 13) with respect to methanol they are very slow in chloroform (127). 

The charge on the R group also has a pronounced effect on the equilibrium constant of homolysis of complexes with metal-carbon -bonds. Comparing the stability constants of homolysis for (hedta)Fein-R for R= CH3 and CO, Table III (46), shows that the complexes for R = C02 are considerably more stable, than those formed with R= CH3 (46). This difference is attributed to the stronger electrostatic interaction between the central cation and the C02 ligand and probably due to some d- interaction (46). 

Stability constant determinations are few 1170 they are summarized in Table 100. Complexa-tion by acidic amino acids is obviously of relevance to the tanning of leather the stability constants for L-glutamic and aspartic acid1171 complexes are much greater than those for glycine or L-alanine.1172,1173,1174 This is probably because the acidic amino acids form tridentate complexes. In contrast, cysteine1173 appears to form glycine-like complexes in moderately acidic solution however, in the solid state L-cysteine is known to be tridentate vide infra). 

If it is true that the structural form of D-glucose which reacts with boric acid is the a-D-pyranose form, then that form probably exists in a boat or twist conformation in the complex. This implies that the study of the stability constants of sugar borate ester might give information about the ability of various carbohydrates to form such boat or twist conformations (10, 21). 

The study of the structure of the sugars in solution can be approached chemically if the chemistry used is as sensitive to sugar structure as sugars are diverse in their structure. The boric acid-sugar reaction could serve this purpose if some of the fundamental aspects of this reaction were understood. Priority should probably be given to (1) the determination of the structure of the borate-sugar complex, (2) the evaluation of the stability constants for these complexes, and (3) the determination of the mechanism of the reaction. 

The stability constants of the FeIU siderophore complexes are some of the largest known, e.g. the ferrichrome and ferrioxamine E complexes have log values of the order 29 and 32 respectively as compared to a value of 25 for Fe(edta). So strong are these complexes that microbes have been observed to leach iron from stainless steel vessels. Not surprisingly the siderophores also find use in treating cases of iron poisoning and for the elimination of iron from cases of thalassaemia.84 Complexation of Fe11 is considerably weaker than that of FeIU and this is probably utilized for the release of the iron within the cells. 

As was observed in the case of the extraction of zirconium and hafnium from nitrate media, it is probable that the different tendencies of the metals towards hydrolysis has some effect on the selectivity observed,298 313 expecially in view of the proved extraction of hydroxo complexes. The extraction of both metals decreases markedly in the presence of sulfate ions in the aqueous phase (a feature that is utilized in the stripping of the loaded hafnium with sulfuric acid), although the selectivity for hafnium over zirconium is simultaneously increased on account of the higher stability constants of the inextractable sulfato complexes of zirconium.298... 

Menger et al. synthesized a Ci4H29-attached copper(II) complex 3 that possessed a remarkable catalytic activity in the hydrolysis of diphenyl 4-nitrophenyl phosphate (DNP) and the nerve gas Soman (see Scheme 2) [21], When 3 was used in great excess (ca. 1.5 mM, which is more than the critical micelle concentration of 0.18 mM), the hydrolysis of DNP (0.04 mM) was more than 200 times faster than with an equivalent concentration of the nonmicellar homo-logue, the Cu2+-tetramethylethylenediamine complex 9, at 25°C and pH 6 (Scheme 4). The DNP half-life is calculated to be 17 sec with excess 1.5 mM 3 at 25°C and pH 6. The possible reasons for the rate acceleration with 3 were the enhanced electrophilicity of the micellized copper(II) ion or the acidity of the Cu2+-bound water and an intramolecular type of reaction due to the micellar formation. On the basis of the pH(6-8.3)-insensitive rates, Cu2+-OH species 3b (generated with pK3 < 6) was postulated to be an active catalytic species. In this study, the stability constants for 3 and 9 and the thermodynamic pvalue of the Cu2+-bound water for 3a —> 3b + H+ were not measured, probably because of complexity and/or instability of the metal compounds. Therefore, the question remains as to whether or not 3b is the only active species in the reaction solution. Despite the lack of a detailed reaction mechanism, 3 seems to be the best detoxifying reagent documented in the literature. 

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