Stability constants poly

N 036 Helix-Coil Stability Constants for the Naturally Occurring Amino Acids in Water. III. Glycine Parameters from Random Poly(hydroxybutylglutamine-co-glycine)"... 

BPEI (6) respectively, have been studied to examine the chelating ability of poly(ethyleneimine)s having different microstructures. From the overall stability constant for Co2+, Ni2 +, Cu2+, Zn2 +, Cd2+, and UO + ions, the chelating ability of LPEI was estimated to be ca 10 times less than that of BPEI for all but U02 +. The branched structure gives a more favorable complexation than the linear structures 22). 

Thickness of the barrier layer, optimized at 220 nm [133], played a crucial role with respect to the chemosensor sensitivity, selectivity and LOD. So, eventually, the chemosensor architecture comprised a gold-film electrode, sputtered onto a 10-MHz resonator, coated with the poly(bithiophene) barrier layer, which was then overlaid with the MIP film. This architecture enabled selective determination of the amine at the nanomole concentration level. LOD for histamine was 5 nM and the determined stability constant of the MIP-histamine complex, XMn> = 57.0 M 1 [131], compared well with the values obtained with other methods [53, 136, 137]. Moreover, due to the adopted architecture, the dopamine chemosensor could determine this amine with the stability constant for the MIP-dopamine complex, XMip = (44.6 4.0) x 106 M-1 and LOD of 5 nM [133], which is as low as that reached by electroanalytical techniques [138]. The MIP-QCM chemosensor for adenine [132] also featured low, namely 5 nM, LOD and the stability constant determined for the MIP-adenine complex, XMIP = (18 2.4) x 104 M, was as high as that of the MIP-adenine complex prepared by thermo-induced co-polymer-ization [139]. The linear concentration range for determination of these amines extended to at least 100 mM. 

Poly(acrylhydroxamic acid)-Cu(II) complex has a high catalytic activity in the decomposition reaction of hydrogen peroxide. From the comparison of complex formation constants (stabilization constants) both in the polymer and the low molecular weight molecule, it was considered that the high activity is owed to a partly dissociated or a solvent coordinated moiety (104,105). Poly(methacryloylacetone)-Cu(II) complex is also investigated (108). 

The stability constants of the Cu2+ complexes with poly(4-vinylpyridine), and with partially quatemized poly(4-vinylpyridine) have been determined by potentiometric... 

In the case of Ag+, only two imidazolyl groups participate in complex formation, and the overall stability constant is log p2 = 8.00, about one order of magnitude larger than the overall formation constant of the Ag/imidazole complex (log p2 = 6.84). Complexes of Cu2 + with poly 4(5)-vinyl-imidazole, poly(N-vinyl-imidazole), and... 

Table 8. Spectrophotometric data and stability constants of copper(II) complexes with poly(amido-amines) (Pm, Pn, P) and their non macromolecular models (Mn, MnP) at 25 °C in 0.1 M NaCl...

Table 65 Redox and Stability Constant Data for Some Con/Coul Poly-carboxylate Complexes ...

As a typical example of Method 1, Nishide el al. cross-linked poly(4-vinyl-pyridine) (PVP) with 1,4-dibromobutane (DB) in the presence of metal ions as templates [2-4], The adsorption behaviour of Cu(II), Co(II), Zn(II), Ni(II), Hg(II) and Cd(II) on the obtained resins was studied. The resins preferentially adsorbed the metal ion which had been used as template. PVP was cross-linked by alkylation of pyridine groups in PVP with DB to yield insoluble PVP resins, of which free pyridines were utilised to coordinate metal ions (Scheme 9.2). The stability constant of the Cu(II) complex of the resin was largest for the resin prepared with Cu(II) as template, being due to its large entropy change for the complexation. 

The first example for Method 2 was reported by Nishide and co-workers, who polymerised a metal complex of 1-vinylimidazole with l-vinyl-2-pyrollidone and divinylbenzene [8]. The metal-vinylimidazole complex was copolymerised, cross-linked with l-vinyl-2-pyrollidone by y-ray irradiation and the template metal ion was removed by treating the polymer complex with an acid. These poly(vinyl-imidazole) (PVI) resins adsorbed metal ions more effectively than the PVI resin prepared without the template. The number of adsorption sites and the stability constant of the Ni(II) complex were larger for the PVI resin prepared with the Ni(II) template, as seen by the smaller dissociation rate constant of Ni(II) from the resin. 

Fig. 6. Correlation of the stability constant for the poly (vinyl acetate) radical with the delocalization stabilization in various solvents...

Similarly, the variation of kp with solvent in methacrylate polymerization can be explained on the assumption that the complexed radical is either inactive or less reactive. Since methyl methacrylate has no aromatic ring in itself, it seems to be possible to estimate the stability constants for the complex formation of the poly (methyl methacrylate) radical end with aromatic solvents. However, since the variation of kp in methyl methacrylate polymerization with solvent is too small, the determination of Ks with significant figures is impossible. Accordingly, it is difficult to estimate the unpurturbed kpo value for methyl methacrylate and thus difficult to estimate the stability constant of the complex in aromatic solvents. 

Sueki, M., Lee, S., Powers, S. R, Denton, J. B., Konishi, Y , Scheraga, H. A. (1984). Helix-coil stability constants for the naturally occurring amino acids in water. 22. Histidine parameters from rsmdom poly[(hydroxybutyl)glutamine-co-L-histidine],... 

The rate constant for spontaneous decomposition was reported to be 40 x i0 s at 65 °C in cyclohexane [101, 103]. The rate of decomposition of PSLi in cyclohexane at 150 °C is 0.205 min corresponding to a 3.5-min half-life [104]. In the presence of 2 equivalents of n,sec-dibutylmagnesium at 100 °C, the rate of decomposition of PSLi is 1.9 X 10 min while it is 6.4 x 10 " in the absence of additive, corresponding to half-lives of 102 and 3 h, respectively [105]. Similar decomposition reactions have been observed for poly(styryl)sodium [102]. The thermal stability of poly(a-methylstyryl)lithium is much lower than that of poly(styryl)lithium. The observed half-lives for spontaneous termination are 5 h and a few minutes at 25 and 60 °C, respectively [106]. The relative thermal stability of styryl carbanionic chain ends follows the order K Na > Li for the alkali metal counterions. 

Comparison of theory with experiment. It will be shown in Section 13.3.2.1 that the flat plate potentials can be used to calculate the osmotic disjoining pressures in concentrated monodisperse sterically stabilized dispersions. Evans and Napper (1977) have compared the theoretical predictions using the above equations with those measured by Homola and Robertson (1976) for polystyrene latex particles stabilized by poly(oxyethylene) of molecular weight ca 2 000 in aqueous dispersion media. The elastic repulsion in the interpenetrational-plus-compressional domain was estimated from the following expression for the constant segment density model... 

Fig. 12.5. The disjoining pressure as a function of the interparticle distance of separation for spheres sterically stabilized by poly(oxyethylene) curve 1, the experimental results of Homola and Robertson (1976) curve 2, constant segment density model. The crosses (x) show the theoretical results for a softened elastic potential (after Evans and Napper, 1977).

The temperature dependence of the steric interaction between sterically stabilized particles mirrors the temperature dependence of [t x(7)]-Croucher and Hair (1978) have calculated the temperature dependence of the steric repulsion between two sterically stabilized particles of poly(acrylonitrile) stabilized by poly(a-methylstyrene) in n-butyl chloride. The particle radius was taken as 100 nm and each steric layer, assumed to be of constant segment density, was taken to be 12 nm thick. The parabolic nature of the repulsion as a function of temperature for two different distances of particle separation is obvious from Fig. 12.10. 

To compare the predictions of cell model calculations with the results of the experiments of Cairns et al. (1976) on poly(methyl methacrylate) latices stabilized by poly(12-hydroxystearic add) in n-dodecane, Cairns et al. (1981) adopted a simple model for the pair potential Uij. This was the constant segment density model of Fischer (1958), as elaterated by Ottewill and Walker (1968). They also considered the modification of that model by Doroszkowski and Lamboume (1971 1973). The latter approach, which allows in a completely arbitrary way for a supposed redistribution of stabilizer segments on close approach of the opposing surface, yields the potential... 

---