Stability constants evaluation

A practical application of the spectral intensity of hypersensitive transitions in lanthanide ions is the determination of stability constants. Bukietynska et al. (1977, 1981a,b) have evaluated the stability constants of lanthanide complexes from the changes of the oscillator strength of hypersensitive transitions as a function of the ligand concentration. The method was applied to acetate, propionate, glycolate, lactate and a-hydroxyisobutyrate complexes of Nd ", Ho and Er +. Bukiet5mska et al. claim that this spectrophotometric method is superior to the potentiometric method, since the best results for the latter method can be obtained only for the first complexation steps. The stability constants evaluated at several temperatures have been used also to calculate the thermodynamic quantities AG, AH and AS. 

MA( , ) + A. MA n-[MA( , )][A] Ky, Kfy being called the step-wise stability constants. Overall stability constants, designated may be evaluated by multiplication of the individual stability constants, e.g. 

Thus, a can be calculated (it is sometimes negligible), and the rate constants are evaluated graphically or by least-squares analysis the estimates of k and k must be consistent with the known stability constant. 

Some suggested calculation procedures and the variation in results obtained from different calculation methods for evaluation of concentration stability constants of metal ion complexes in aqueous solution. A. M. Bond, Coord. Chem. Rev., 1971,6, 377-405 (43),... 

Despite the problems of direct experimental evaluation of plutonium stability constants, they are needed in modeling of the behavior of plutonium in reprocessing systems in waste repositories and in geological and environmental media. Actinide analogs such as Am+3, Th+, NpOj and UOj2 can be used with caution for plutonium in the corresponding oxidation states and values for stability constants of these analogues are to be found also in reference 20. 

Combined dipole moment and Kerr effect studies are regularly used by Russian workers for the conformational analysis of phosphorus heterocyc1es.135 230 In a study of the interaction of phenol with phosphoryl groups the Kerr effect was used to evaluate not only the extent of hydrogen bonding but also the influence of changes in polarity and polarisation upon stability constants.231 In a similar study the orientation of the aryl groups of 1,3,5-triazaphosphorines (82) were shown to be less coplanar than biphenyl in the gas phase. 2 3 2... 

A number of novel dioxo variants of the tetraazamacrocycles have been synthesized and stability constants were measured with Cu2+.114 A few of these were further evaluated as chelating agents with 64Cu.115 Structural differences included ring size (from 12 to 14) and placement of the oxo groups. Of the six variations synthesized, only one, l,4,8,ll-tetraazacyclotetradecane-3-9-dione(14N402-3,9), readily formed a complex (Figure 9). 

In order to determine the stability constants for a series of complexes in solution, we must determine the concentrations of several species. Moreover, we must then solve a rather complex set of equations to evaluate the stability constants. There are several experimental techniques that are frequently employed for determining the concentrations of the complexes. For example, spectrophotometry, polarography, solubility measurements, or potentiometry may be used, but the choice of experimental method is based on the nature of the complexes being studied. Basically, however, we proceed as follows. A parameter is defined as the average number of bound ligands per metal ion, N, which is expressed as... 

A computer program has been used to calculate the magnitude of systematic errors incurred in the evaluation of equivalence points in hydrochloric acid titrations of total alkalinity and carbonate in seawater by means of Gran plots. Hansson [13] devised a modification of the Gran procedure that gives improved accuracy and precision. The procedure requires approximate knowledge of all stability constants in the titration. 

The most controversial issue is the number and exact stoichiometries of the iron(III)-sulfito complexes formed under different experimental conditions. Earlier, van Eldik and co-workers reported the formation of a series of [Fe(SO ) ]3-2" (n = to 3) complexes and the [Fe(S03)(0H)] complex (89,91,92). The stability constants of these species were determined by evaluating time resolved rapid-scan spectra obtained from the sub-second to several minutes time domain. The cis-trans isomerization of the complexes was also considered, under feasible circumstances. In contrast, Betterton interpreted his results assuming the formation and linkage isomerization of a single complex, [Fe(SC>3)]+ (93). In agreement with the latter results, Conklin and Hoffmann also found evidence only for the formation of a mono-complex (94). However, their results were criticized on the basis that the experiments were made in 1.0 M formic acid/formate buffer where iron(III) existed mainly as formato complex(es). Although these reactions could interfere with the formation of the sulfito complex, they were not considered in the evaluation of the results (95). Finally, van Eldik and co-workers re-examined the complex-formation reactions and presented additional data in support of... 

Stability constants of metal complexes with inorganic ligands are generally well known [30], Inorganic speciation of metals can therefore easily be evaluated by thermodynamic calculations if the composition of the solution is known [29,31],... 

Figure 41. Evaluating the stability of the simple example pathway shown in Fig. 40 Metabolic states and the corresponding saturation parameters are sampled randomly and their stability is evaluated. For each sampled model, the largest positive part within the spectrum of eigenvalues is recorded. Shown is the probability of unstable models, as a function of (A) The size of the system. Here the number of regulatory interactions increases proportional to the length of pathway (number of metabolites). Other parameters are maximal reversibility ymax 1 and p 0.5. (B) An increasing number of regulatory interactions. The number of metabolites m 100 is constant. Maximal reversibility ymax 1 and p 0.5. (C) Maximal reversibility v /v . and p 0.5. Other...

Recently262, the apparent stability constants of the complexes between aromatic fluoro derivatives and amines (shown in equilibrium 31, Kc in moL1 dm3) in toluene- were evaluated by 19F chemical shift measurements. 

Li and Wang described a convenient linear plotting protocol that permits one to evaluate stability constants for the formation of reversible metal hgand complexes. Added accuracy is achieved over classical approaches, because their generalized equations quantitatively account for side-reactions of metal ion and/or ligand as well as the difference between the total and free ligand concentration. 

The electrochemical properties of Cd(II) complexes with inorganic ligand presented in early papers were discussed by Hampson and Latham [72]. Later, electrochemical investigations of cadmium complexes were oriented on the mechanism of complex formation, determination of stoichiometry and stability constants, mechanisms of reduction on the electrodes, and evaluation of kinetic parameters of these processes. The influence of ligands and solvents on stability and kinetic parameters of electroreduction was also studied. 

The polarographic experimental and calculated curves of complex formation with the following ligands N, Ai -bis(2-pyridyl methyl)- ,2-diaminoethane [118], picolinic acid [119], Ai-(2-hydroxyethyl)ethylenedi-amine [120], 1-hydroxyethylenediphospho-nic acid [121], and Ai-(2-hydroxyethyl)imi-nodiacetic acid [122] was used for modeling the Cd(II)-Kgand systems. The stoichiometry and stability constants of formed complexes were evaluated. The same method was used for determinations of stability constants of Cd(II) complexes with monoaza-12-crown-4 ether in aqueous solution in the presence of an excess of sodium ions [123]. 

Owing to the inadequacy of the mathematical model available for analysis of the amine extraction system (7), accurate values of the stability constants could not be evaluated for the Hs Pbn1-" system in the presence of NaCl. However, using the values of stability constants obtained by Bertazzi for the system (C2H5)3PbCln1 n in LiCl at 8.0 m (10), viz. 0 = 3.5, 02 = 1.0, 0s = 0.1, the neutral species Hs PbCl0 (n = 1) is seen to be dominant. Therefore a simple solvent extraction would be expected to remove a certain amount of triethyl lead from solution. As shown in Table II, this is seen to be so. However,... 

Most of the work on the boric acid-diol reaction during the last twenty years has been done to determine the coordination number of the diol (number of diol molecules) in the complex and to evaluate the equilibrium constant (often called a stability constant) for a number of diol-boric acid reactions. Several techniques have been used to study these questions, including polarimetry (7), optical rotatory dispersion (8), polarography (9), conductivity (3), vapor pressure osmometry (10), and electrochemistry (II, 12, 13). The most frequently studied system has been the electrochemical (pH) titration of boric acid or borax solutions with various diols. 

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 constant is evaluated from the linearized plot according to... 

Tripathi GNR (1998) Electron-transfer component in hydroxyl radical reactions observed by time resolved resonance Raman spectroscopy. J Am Chem Soc 120 4161-4166 TsaiT, Strauss R, Rosen GM (1999) Evaluation of various spin traps for the in vivo in situ detection of hydroxyl radical. J Chem Soc Perkin Trans 2 1759-1763 Tsay L-Y, Lee K-T, Liu T-Z (1998) Evidence for accelerated generation of OH radicals in experimental obstructive jaundice of rats. Free Rad Biol Med 24 732-737 Ulanski P, von Sonntag C (2000) Stability constants and decay of aqua-copper(lll) - a study by pulse radiolysis with conductometric detection. Eur J Inorg Chem 1211-1217 Veltwisch D, Janata E, Asmus K-D (1980) Primary processes in the reactions of OH radicals with sul-phoxides. J Chem Soc Perkin Trans 2 146-153... 

Anderegg, G. Amaud-Neu, F. Delgado, R. Felcman, J. Popov, K. Critical evaluation of stability constants of metal complexes of complexones for biomedical and environmental applications. PureAppl. Chem. 2005, 77 (8), 1445-1495. 

Portanova, R. Lajunen, L.H.J. Tolazzi, M. Piispanen, J. Critical evaluation of stability constants for alpha-hydroxycarboxylic acid complexes with protons and metal ions and the accompanying enthalpy changes. Part II. Aliphatic 2-hydroxycarboxylic acids. Pure Appl. Chem. 2003, 75 (4), 495-540. 

Misono, M. Saito, Y. Evaluation of softness from the stability constants of metal-ion complexes. Bull. Chem. Soc. Jpn, 1970, 43 (12), 3680-3684. 

Schnitzer, M., and E. H. Hansen. 1970. Organo-metallic interactions in soils. 8. An evaluation of methods for the determination of stability constants of metal-fulvic acid complexes. Soil Science 109 333-340. 

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