Effect of pH on complexation

In the same study (24), the effect of pH on complex formation was studied. Spinach puree adjusted to a pH value of 8.5 had 38% more zinc complex formed than puree with an unadjusted pH value of 6.8. Formation of copper complexes was unaffected by hydrogen ion concentration between pH values of 3.8 and 8.5. 

The effect of pH and complexation on the relative stabilities of the oxidation states of Pu is discussed. A set of ionic radii are presented for Pu in different oxidation states and different coordination numbers. A model for Pu hydration is presented and the relation between hydrolysis and oxidation state evaluated, including the problem of hydrous polymerization. 

Gardner and Yates [26] developed a method for the determination of total dissolved cadmium and lead in estuarine waters. Factors leading to the choice of a method employing extraction by chelating resin, and analysis by carbon furnace atomic absorption spectrometry, are described. To ensure complete extraction of trace metals, inert complexes with humic-like material are decomposed by ozone [27]. The effect of pH on extraction by and elution from chelating resin is discussed, and details of the method were presented. These workers found that at pH 7 only 1-2 minutes treatment with ozone was needed to completely destroy complexing agents such as EDTA and humic acid in the samples. 

The example of uranyl reduction shows the utility of this approach. The concentrations of the two surface complexes vary strongly with pH, and this variation explains the observed effect of pH on reaction rate, using a single value for the rate constant k+. If we had chosen to let the catalytic rate vary with surface area, according to 17.12, we could not reproduce the pH effect, even using H+ and OH-as promoting and inhibiting species (since the concentration of a surface species depends not only on fluid composition, but the number of surface sites available). We would in this case need to set a separate value for the rate constant at each pH considered, which would be inconvenient. 

This finding is the consequence of the distribution of various ruthenium(II) hydrides in aqueous solutions as a function of pH [RuHCl(mtppms)3] is stable in acidic solutions, while under basic conditions the dominant species is [RuH2(mtppms)4] [10, 11]. A similar distribution of the Ru(II) hydrido-species as a function of the pH was observed with complexes of the related p-monosulfo-nated triphenylphosphine, ptpprns, too [116]. Nevertheless, the picture is even more complicated, since the unsaturated alcohol saturated aldehyde ratio depends also on the hydrogen pressure, and selective formation of the allylic alcohol product can be observed in acidic solutions (e.g., at pH 3) at elevated pressures of H2 (10-40 bar [117, 120]). (The effects of pH on the reaction rate of C = 0 hydrogenation were also studied in detail with the [IrCp (H20)3]2+ and [RuCpH(pta)2] catalyst precursors [118, 128].)... 

In comparison to the approach of Ginski et al. [48], the Miyazaki s method appears to be more elaborate and complex and is thus coming closer to the in vivo situation. The device can simulate various effects of pH on dissolution and is, as an open system, closer to in vivo conditions compared to a closed one. However, it exhibits the drawback of not freely adjustable pH values acting on the drug. Low flow rate in the dissolution vessel may limit applications of complete dosage forms and allows predominantly only the use of granules, pellets, or grinded tablets. Furthermore, the application of compendial dissolution devices appears to be a more robust approach. 

It is appropriate now to return to the effect of pH on the [Co(phen)3] oxidation of PCu(I). If protonation at the remote site influences the reaction of PCu(II), then a similar effect might be expected for the reaction of PCu(I) with positively charged complexes. In the case of PCu(I) the kinetics are dominated by the inactivation resulting from the active site protonation. Whereas the pK for the [Fe(CN)g] oxidation is in good agreement with the HNMR independently measured value, the apparent pK obtained with [Co(phen)3] " is significantly higher, an effect which is clear from an inspection of Fig. 10. A two pK fit is possible in the case of [Co(phen)3], as has been illustrated [1,100],... 

The effect of pH on the periodate oxidation of seven anilines has been investigated. " The kinetics of periodate oxidation of aromatic amines have been studied. " - " Periodate oxidation of oxalic acid is catalysed by Mn(II). " The reaction of ethane-1,2-diol with periodate has been investigated under a variety of conditions and the results compared with those of earlier work and analogous studies on pinacol. " The 104 ion is the primary reactant, with H5IO6 as a secondary reactant the reverse is true for pinacol. The complex observed in previous work is shown not to be an intermediate, but rather to deactivate the reactants. 

Th effect of pH on the rate of hydrogenation of water-soluble unsaturated carboxylic acids and alcohols catalyzed by rhodium complexes with PNS [24], PTA [29], or MePTA r [32] phosphine ligands can be similarly explained by the formation of monohydride complexes, [RhHPJ, facilitated with increasing basicity ofthe solvent. 

Fig. 15. Effects of pH on apo- and heme-hemopexin. The Soret region absorbance (filled squares) of rabbit heme-hemopexin was monitored in two separate titrations, from pH 7.4 to 11.8 in one and from pH 7.4 to 3.8 in the other. Similarly, theellipticity at 231 nm of apo-hemopexin (open circles) and of heme-hemopexin (filled circles) was assessed from pH 7.4 to 11.8 and from pH 7.4 to 1.7 111). The heme complex and the tertiary structure are unaffected by pH in the region from pH 6 to 9, and other values are normalized to these.

Fig. 8.14 Effect of pH on dissolution from Al-mica-organo matter complexes. (Hargove 1986)...

Various aspects of in vitro methods, from its first use in 1880 to the 1980s have been discussed by the author (Faithfull, 1984). In particular, the effect of pH on tannin complexes, phosphates and sulphides have been studied. 

Early work with these complexes made use of viscometry in order to investigate the effect of pH on the complexation formation. In working with solutions of PAA and PEG, Bailey et al. [112] found that the complex formed into a precipitate from water solution at around pH 3.8. The pH of the solution affects the ratio of add to acrylate (neutralization) on the PAA chain thus affecting the number of complexes that may be formed. Because of this, these... 

The effect of pH on the formation of dioxygen adducts of 6 (25c), as well as the establishment of volume profiles for the reaction (25b) have been reported. In aqueous solution, dioxygen adducts of 6 form at pH >7, with the kinetics of the reaction remaining approximately constant with those measured at pH < 7. However, at high pH values, the rate drops off by a factor of about five, corresponding to the point at which complex 6 is deprotonated (pK = 11.68). When the rate... 

Additional information <6> (<6> effect of pH on hydrolysis of phospho-en-zyme I complex [9]) [9]... 

Understanding the behavior of acids and bases is essential to every branch of science having anything to do with chemistry. In analytical chemistry, we almost always need to account for the effect of pH on analytical reactions involving complex formation or oxidation-reduction. pH can affect molecular charge and shape—factors that help determine which molecules can be separated from others in chromatography and electrophoresis and which molecules will be detected in some types of mass spectrometry. 

Expressions VII and VIII are identical in form they differ only in the meaning of the constants they contain. In both cases an increase in the borate ion concentration would result in an increase in the diol-boric acid complex. Therefore, an examination of the effect of pH on the equilibrium concentrations of various components of the system cannot be used to determine which of the two boroxy species actually reacts with the diol. 

The amino-acids that make up the primary structure of proteins will change their charge when the pH of the solution is altered due to their acid-base properties (Section 5.3 and Appendix 5.1). The effects of pH on enzyme-catalysed reactions can be complex since both Km and may be affected. Here, only the effects on Kmax are considered, as this usually reflects a single constant rather than several that may be associated within the constant Km (see Section 5.4.4.). It is assumed that pH does not change the limiting step in a multi-step process and that the substrate is saturating at all times. 

Figure 16 The effect of pH on the selectivity of a strong-base resin (AlOIDU) for metal cyanide complexes (after Fleming and Cromberge, ref. 358)...

Dissolution of Al(OH)3 in excess base is just a special case of the effect of complex-ion formation on solubility Al(OH)3 dissolves because excess OH - ions convert it to the soluble complex ion Al(OH)4- (aluminate ion). The effect of pH on the solubility of Al(OH)3 is shown in Figure 16.16. 

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