Stability constants measurement

If the stability constant measurements are coupled with enthalpy determinations, then entropy values (as well as the corresponding free energy values) may be calculated ... 

Stability constants, measured in methanol solution, for alkaline earth complexes of a number of ionophores are given in Table XVI (280,289,571-577).8 The values for the complexes of valinomycin and enniatin B lie between the values for the crown ethers 15C5 and 18C6 (cf. Section II.C.5 above), for the middle four entries the values are slightly higher. Stabilities of enniatin B complexes show a modest maximum for Ca2+, and of valinomycin complexes show stabilities increasing up to Ba2+ (281). LogAi values for the Ca2+ complexes of acetate, benzoate, and salicylate are between 4.5 and 4.7 in methanol (578) - the... 

For a variety of reasons, it is difficult to measure stability constants of metals with Hum, and the use of stability constants measured under a given set of solution conditions (so-called conditional constants ) for a different set of conditions (e.g., at a different pH or different set of metals and Hum concentrations) must be done cautiously. Significant advances were made during the past decade in ways to model metal-Hum binding, and a sufficient variety of conditional binding constants are now available at least to approximate the metal-binding behavior of natural water and soil solutions containing Hum. 

Therefore, the K24 stability constant measures the formation of all complexes C2 such as ... 

In contrast to stability constants, there are very few data for enthalpies and entropies of complex formation for hydroxypyranonate and hydroxypyridinonate complexes. Early studies on zinc-maltolate (190) and first-row transition metal(II) complexes of kojate (191) gave estimates of enthalpies and entropies of formation from temperature variation of stability constants, though as accurate stability constant measurements are only possible over a rather short temperature range the Aff and AS values obtained cannot be of high precision. 

A majority of the host systems mentioned so far have been shown to encapsulate halide guests as a consequence of the symmetrical nature of their binding pockets, which readily adapt to the spherical symmetry of the halide ion. A study of the bis-tren macrobicyclic ligand 19-6H, however, has revealed that, in addition to accommodating halide anions, it is also able to encapsulate azide, N, within its cylindrical cavity. Solution stability constant measurements indicate that the host... 

Organoindium thiocyanate derivatives do not appear to have been reported. The results of stability constant measurements for In3+/NCS have been reviewed the recommended values are similar to those for In3+/Cr systems.9... 

Stability constant measurements have demonstrated the presence of indium(III) nitrite complexes in methanol, and the crystalline compound In(N02)3-Me0H has been isolated.157... 

Indium orthophosphate is essentially insoluble in water, but salts of [In(P04)2]3- and [In2(P04)4]6- have been prepared,163 and a solution phase complex with the H2POj anion has been identified.164 The coordination chemistry of In3+ with the higher phosphates is at present ill defined. Stability constant measurements,9 and preparative and spectroscopic studies7 suggest that In06 is the central core of the compounds in the solid state. The same appears to be true for the complexes reported for L = fluorophosphate,165 methylphosphonate,166 dichlorophosphate,167 dimethylthiophosphate,168 diethylthiophosphinate169,170 and diisopropyl-methylphosphonate.171... 

The [Cr(en)3]2+ and [Cr(pn)3]2+ salts have reflectance spectra (Table 11) resembling those of the hexaammines, and the six N donor atoms are assumed to complete tetragonally distorted octahedra around the metal. Stability constant measurements (Table 39) have shown that the ions [Cr(en)(aq)]2+ (vmax= 18 300 cm-1, e = 25 dm3 mol-1 cm-1) and [Cr(en)2(aq)]2+ (vma = 17 500 cm-1, e = 17 dm3 mol-1 cm-1) exist in aqueous solution, but that, as in the copper(II) system, the third ethylenediamine molecule is only weakly bound, and care is needed to prevent loss of en from tris(amine) complexes in the preparations. Several bis(amine) complexes, e.g. [CrBr2(en)2], have been isolated, and these are assigned trans structures because of IR spectral resemblances to the corresponding oopper(II) complexes. Since the spectrum of [Cr(S04)(en)2] also shows the presence of bidentate sulfate, this is assigned a trans octahedral structure with bridging anions. 

From stability constant measurements (Table 39) the [Cr(trien)]2+ ion (juefl =4.9BM,... 

The redox properties of the copper(II) ion in saturated polyaza macrocyclic complexes CuN4 and CuNj have been shown1020 to vary with the chelate ring size, and the very negative E° values (Figure 62) are consistent with a macrocyclic effect , from stability constant measurements.976... 

Stability constant measurements have shown that imidazoles form some of the most stable complexes of all N-heterocyclic ligands. Some thermodynamic data are given in Table 12. 

Apart from the isolation of the Cu11 complexes728 Cu(2,4itri)2+, Cu(2,4-tri-H)(2,4-tri)3+ and Cu(2,4 tri-H)2+, this ligand has been used mainly in stability constant measurements.729,730 In this series of Cu11 complexes it is proposed that the longer arm of the ligand is the one that is preferentially protonated.729... 

A large number of experimental data including stability constant measurements [11] [12] indicate that, at neutral pH, N(7) of guanine is a better metal-binding site than N(7) of adenine. This observation is also supported by modern quantum-chemical calculations with the inclusion of electron correlation effects which reveal that polarity of the bases and the corresponding basicity of the N(7) site decreases in the order guanine > inosine > adenine > 2-aminoadenine [13]. 

Stability constant measurements have been undertaken to show that in basic solution mixed amino acid ligands with two amino acid moieties present, i.e. NH2—C(R)—C—N—C(R )— COOH), yield complexes with log K values of the order of 6 to 7 384 such compounds appear to bind the amine nitrogen.385... 

It is evident from stability-constant measurements that the monoglyceride of tetradecanoic acid forms the most stable complex. Enthalpies of melting of the complex increase proportionally with the length of the carbon chain of the fatty acid residue. Binding parameters (Table LII)717 show that the complexes are weak and they can be readily decomposed by other competing agents. As shown by Kim and Hill,863 cyclomaltoheptaose forms binary complexes with lysolecithin and ternary complexes with lysolecithin and amylose. The complex of lysolecithin with amylose is disrupted by cyclomaltoheptaose. 

A detailed tabulation of data (231, 379, 381, 382) and some isolated results (43, 76, 394, 580b, 731) for the kinetics of formation and dissociation of complexes of these ligands may be found in the literature. Representative data are presented in Table VII. Where a direct comparison is possible, stability constants measured kinetically agree with the values determined by other means. For a reaction scheme which may be represented by... 

Many stability constant measurements have been made and an indication of how misleading the analysis using them can be is provided by Findlow et al. (46) These authors aimed to calculate the speciation of aluminum in human and bovine milk using two sets of stability constants for AP -citrate. Calculations with one set of constants indicated —80% of the AP+ was bound into neutral complexes, but the second set of constants, considered to be more accurate than the first, showed that less than 10% of the AP was in the form of neutral complexes. 

Complex formation of Np(lV) with NCS ion has been extensively studied using TTA and HDNNS solvent extraction with in different conditions [58]. Table 6 presents values of stability constants measured in 2M NaC104 at 298K. 

The results of stability constants measurements are summarized in Table 10. 

Amine Donors. Complexes with l,3-bis[2(S)-aminomethyl-l-pyrrolidinyl]propane and other optically active tetra-amines containing pyrrolidinyl groups with six-membered chelate rings have been studied, and the stereochemistry of the complex depends on the position of the two pyrrolidinyl groups in the ligand. Studies of ability of similar complexes to hydrolyse esters have been reported. Stability constant measurements for nickel(ii) monoamine complexes have been made in a number of hydroxylic solvents. Magnetic and optical spectral measurements of some nickel(ii) succinimide and mixed amine-succinimide complexes indicate that... 

Ketones of the general structure 265 have complexing features rather similar to those of the esters 264. Stability constant measurements and extraction data indicate that the cyclic tetrameric ketones are better than their ester analogs for the extraction of Li and also for Rb and Cs". The ketone 265c has a broader range of extraction capability than its cyclic tetramer and hexamer counterparts but shows little selectivity among the cations. 

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