Stability constants ternary complexes

Table XIX contains stability constants for complexes of Ca2+ and of several other M2+ ions with a selection of phosphonate and nucleotide ligands (681,687-695). There is considerably more published information, especially on ATP (and, to a lesser extent, ADP and AMP) complexes at various pHs, ionic strengths, and temperatures (229,696,697), and on phosphonates (688) and bisphosphonates (688,698). The metal-ion binding properties of cytidine have been considered in detail in relation to stability constant determinations for its Ca2+ complex and complexes of seven other M2+ cations (232), and for ternary M21 -cytidine-amino acid and -oxalate complexes (699). Stability constant data for Ca2+ complexes of the nucleosides cytidine and uridine, the nucleoside bases adenine, cytosine, uracil, and thymine, and the 5 -monophosphates of adenosine, cytidine, thymidine, and uridine, have been listed along with values for analogous complexes of a wide range of other metal ions (700). Unfortunately comparisons are sometimes precluded by significant differences in experimental conditions.

Amino-acid Complexes. A small, but reproducible, stereoselective effect has been observed in both the free energy and enthalpy changes associated with formation of [Ni(L,L-methioninate)2]. The meso-complex [Ni(o-Met)(L-Met)] is more stable in AH than the optically active NiL2 by 1.0 (0.1) kJ mol" L The stereoselectivity is attributed to terdentate co-ordination and so supports weak co-ordination of the thioether group. Formation constants of nickel(ii) and copper(ii) with N -benzyl-L-histidine and N N -dibenzyl-L-histidine and of the ternary complexes with d- and L-histidine have been measured. Stabilization of ternary complexes is small but significant stereoselectivity is found with ternary nickel complexes, when the meso configuration is preferred in each case with copper, stereoselectivity is small or absent. The i.r. spectra of tra s-[Ni(Gly)2(H20)2] and its 0-, N-, 1- C-, and 2- C-labelled... 

Complexation in CDs is molecule specific and generally ternary complexes are favoured. However, a-CD includes single phenyl and naphthyl groups (small molecules), y6-CD accepts naphthyl and heavily substituted phenyl groups, and y-CD attracts bulky steroid type molecules. The stability constants of complex formation vary from 10 to 10 with a formation time Ti/2 0.001-1.0 ms. These complex formation properties of CDs have been utilized for chiral resolution of enantiomers, as the two enantiomers form inclusion diastereoisomeric complexes. Other properties of CDs are given in Table 6.1. 

Celecoxib HP-(3-CD HPMC Physical mixing, co-evaporation Water Increase in value of stability constant of complex on addition of HPMC to complexation medium along with brief autoclaving, which was reflected by better dissolution parameters of ternary complex than the drug alone [68]... 

NMR signals of the amino acid ligand that are induced by the ring current of the diamine ligand" ". From the temperature dependence of the stability constants of a number of ternary palladium complexes involving dipeptides and aromatic amines, the arene - arene interaction enthalpies and entropies have been determined" ". It turned out that the interaction is generally enthalpy-driven and counteracted by entropy. Yamauchi et al. hold a charge transfer interaction responsible for this effect. 

KP and v can, in contrast to kp, not be determined via the concentration gradient for binary and ternary mixed micelles, because for the calculation of the Nemstian distribution a constant CMC and an almost constant partial molar volume must be assumed. The calculation of aggregation constants of simple bile salt systems based on Eq. (4) yields similar results (Fig. 8b). Assuming the formation of several concurrent complexes, a brutto stability constant can be calculated. For each application of any tenside, suitable markers have to be found. The completeness of dissolution in the micellar phase is, among other parameters, dependent on the pH value and the ionic strength of the counterions. Therefore, the displacement method should be used, which is not dependent on the chemical solubilization properties of markers. For electrophoretic MACE studies, it is advantageous for the micellar constitution (structure of micelle, type of phase micellar or lamellar) to be known for the relevant range of concentrations (surfactant, lipids). 

The polarographic method has been used to determine the stability constants and kinetic parameters of ternary complexes of Zn(II) with L-lysine, L-omithine, L-serine, L-phenylglycine, L-phenylalanine, L-glutamic acid, and L-aspartic acid as primary ligands and picoline as secondary ligand at pH 8.5 [103] and also of zinc complexation by extracellular polymers extracted from activated sludge [104]. 

Complexants other than alcohols (e.g., amines, nitriles, tert-butyl compounds, surfactants, and multiple fluorophores) can also be detected by the method of Scheme 2 [279-284], Bohne and Yang have replaced alcohols with amino acids [285], although the zwitterionic charge distribution and increased steric requirements of the former lead to smaller stability constants of the ternary complex. Notwithstanding, tryptophan, leucine, and phenylalanine produce measurable changes in the I III ratio of pyrene emission, thereby allowing for their detection at mM levels. 

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. 

Here, the adsorption of valine on different cation-exchanged montmorillonites is described (Nagy and Konya 2004). A discussion of the kinds of interactions that are possible in the ternary system of montmorillonite/valine/metal ions will be presented, and a description how the metal ions can affect these interactions. The interlayer cations (calcium, zinc, copper ions) were chosen on the basis of the stability constants of their complexes with valine. The adsorption of valine on montmorillonite is interpreted using a surface-complexation model. 

Type IV includes chiral phases that usually interact with the enantiomeric analytes through the formation of metal complexes. There are usually used to separate amino acid enantiomers. These types of phases are also called ligand exchange phases. The transient diastereomeric complexes are ternary metal complexes between a transitional metal (usually Cu +), an amino acid enantiomeric analyte, and another compound immobilized on the CSP which is able to undergo complexation with the transitional metal (see also the ligand exchange section. Section 22.5). The two enantiomers are separated based on the difference in the stability constant of the two diastereomeric species. The mobile phases used to separate such enantiomeric analytes are usually aqueous solutions of copper (II) salts such as copper sulfate or copper acetate. To modulate the retention, several parameters—such as the pH of the mobile phase, the concentration of the copper ion, or the addition of an organic modifier such as acetonitrile or methanol in the mobile phase—can be varied. 

Ono, N. Hirayama, F. Arima, H. Uekama, K. Determination of stability constant of P-cyclodextrin complexes using the membrane permeation technique and the permeation behavior of drug-competing agent-P-cyclodextrin ternary systems. Eur. J. Pharm. Sci. 1999, 8 (2), 133-139. 

The metallobiochemistry of staphylococcal nuclease has been extensively investigated. It was shown early that the tripositive lanthanide ions, Ln, are potent competitive inhibitors of the enzyme, binding to it with K s of about 9/uM and acting with inhibitory constants of l-2 iM. The binding of Ln + ions enhances the binding of pdTp. Ln " ions, but not Ca, stabilize the enzyme toward tryptic proteolysis. The paramagnetism of Gd " was exploited in H and P resonance relaxation studies on pdTp bound in the ternary complex to determine that the structure in solution was consistent with the observed x-ray structure. Some differences were observed but these were of uncertain significance. 

Kinetic studies of reversible inhibition by substrate analogs give evidence of the mode of action of the inhibitor and the types of enzyme-inhibitor complex formed, and estimates of their dissociation constants. The complexes may be isolated and sometimes crystallized. Studies of the stabilities, optical properties, and structures of ternary complexes of enzymes, coenzymes, and substrate analog in particular, as stable models of the catalytically active ternary complexes or of the transition state for hydride transfer (61,79,109,115-117), can only be touched upon here there is direct evidence with several enzymes that the binding of coenzymes is firmer in such complexes than in their binary complexes (85,93,118), which supports the indirect, kinetic evidence already mentioned for a similar stabilization in active ternary complexes. 

The equilibria in the nickel(II)-imidazole-chloride ternary system have been investigated by means of pH-metric and spectrophotometric titrations in 3 M Na(C104, Cl) solution. The latter method was used to determine the stability constant of the binary NiCr complex in the nickel(II)-chloride system. The concentration range studied was [NP" ] = 0.096 to 0.300 M and [Cl ] = 1.25 to 3.00 M. The log, yff value obtained (- (0.47 0.10)) is in good agreement with that determined from potentiometric data in... 

Scheme 1-15 Self-replicating system designed by Rebek and co-workers. The template 57 (X = OCgF5) binds to the two substrates 55 and 56, generating a ternary complex 55-57-S6. Then 55 and 56 react to generate another molecule of template 57. Stability constants are shown for the 55-56 and 57-57 complexes.

---