Phosphate determination, kinetic

In this paper we discuss the chemistry of aqueous calcium phosphate systems from the point of view of both equilibriiam and kinetic considerations. It will be shown that the chemical composition of the calcium phosphate precipitated under any given set of conditions, may be determined kinetically rather than simply on the basis of thermodynamic driving forces. 

Raney Ni particles become entrapped in the electrodeposited Ni under the influence of a cathodic current and stirring. The electrocatalytic behavior of this material was characterized by the Tafel parameters for H2 evolution for various quantities (mg cm" ) of the Raney particles deposited. Particle size and aging effects were also determined. Kinetic parameters for the HER on various coatings were determined and compared (181). A related process for binding and cementing electrocatalytic Ni powders used a three-dimensional aluminium phosphate polymer (182). The Ni active material developed in the form of spiky filaments. 

M32. Moss, D. W., Kinetics of phosphatase action on naphthyl phosphates determined by a highly sensitive spectrofluorimetric technique. Biochem. J. 76, 32P (1960). 

In a theoretical approach to optimizing the levels of XR and XDH and also XK, the enzyme phosphorylating xylulose to xylulose 5-phosphate, a kinetic model including the three enzymes was constructed [143]. Based on reported kinetic data for the three enzymes, the optimal XR XDH XK ratio was determined to be 1 10 4 for minimal xylitol formation. Experiments confirmed that a decreasing XR XDH ratio decreased xylitol and acetate formation, whereas the formation of ethanol increased. Overproduction of XK enhanced the specific xylose consumption [143]. 

A final requirement for a chemical kinetic method of analysis is that it must be possible to monitor the reaction s progress by following the change in concentration for one of the reactants or products as a function of time. Which species is used is not important thus, in a quantitative analysis the rate can be measured by monitoring the analyte, a reagent reacting with the analyte, or a product. For example, the concentration of phosphate can be determined by monitoring its reaction with Mo(VI) to form 12-molybdophosphoric acid (12-MPA). 

The detritiation of [3H]-2,4,6-trimethoxybenzene by aqueous perchloric acid was also studied, the second-order rate coefficients (107/c2) being determined as 5.44, 62.0, and 190 at 0, 24.6, and 36.8 °C, respectively, whilst with phosphate buffers, values were 3.75, 13.8, and 42.1 at 24.6, 39.9, and 55.4 °C, respectively. The summarised kinetic parameters for these studies are given in Table 134, and notable among the values are the more negative entropies of activation obtained in catalysis by the more negative acids. This has been rationalised in terms of proton transfer... 

The rate of the reaction in various buffer solutions, covering the pH range 4-8, was determined, and in hydrogen phosphate-dihydrogen phosphate buffers the rate at constant pH decreased as the concentration of dihydrogen phosphate increased. Similarly, with acetic acid-acetate and phosphoric acid-dihydrogen phosphate buffers the rate was inversely dependent upon the concentration of the molecular acid in addition, with the latter buffer, the kinetic plots showed an unexplained departure from linearity after 50 % reaction. 

The contractile apparatus may be thought of as the sum of those intracellular components which constitute the machinery of chemomechanical transduction. It is the set of proteins which convert the chemical energy of the terminal phosphate ester bond of ATP into mechanical work. The structure of the contractile apparatus is determined by the connections between the various protein molecules via specific binding sites or, in a minority of cases, via labile covalent linkages. The kinetics of the contractile machinery are determined by the regulation of changes in these connections. 

These two methods produce different release profiles in vitro. Figure 5 demonstrates the release kinetics of BCNU from wafers loaded with 2.5% BCNU pressed from materials produced using these two methods. The wafers containing tritiated BCNU were placed into beakers containing 200-ml aliquots of 0.1 M phosphate buffer, pH 7.4, which were placed in a shaking water bath maintained at 37 C. The shaking rate was 20 cycles/min to avoid mechanical disruption of the wafers. The supernatant fluid was sampled periodically, and the BCNU released was determined by liquid scintillation spectrometry. The BCNU was completely released from the wafers prepared by the trituration method within the first 72 hr, whereas it took just about twice as long for the BCNU to be released from wafers... 

Phosphate ester crystal structures have been determined of zinc 1,5,9-triazacyclononane including an interesting structure containing an oligophosphate bridged zinc unit.450 The zinc complex of 1,5,9-triazacyclododecane was studied as a hydrolysis catalyst for substituted phenyl acetates.451 Kinetic analysis suggested that hydrolysis occurs by a mechanism involving hydroxide attack of a metal-bound carbonyl. 

Because the preceding chromogenic assay rely on choline quantitation, the hydrolysis of substrates with headgroups other than choline cannot be followed. To circumvent this problem, another useful protocol was devised whereby the phosphorylated headgroup produced by the PLCBc hydrolysis is treated with APase, and the inorganic phosphate (Pi) that is thus generated is quantitated by the formation of a blue complex with ammonium molybdate/ascorbic acid 5 nmol of phosphate may be easily detected. This assay, which may also be performed in a 96-well format, has been utilized to determine the kinetic parameters for the hydrolysis of a number of substrates by PLCBc [37,38]. 

The hemoglobin-catalyzed oxidation of o-phenylenediamine to 2,3-diaminophenazine (100), in phosphate-citric acid buffer at pH 5.0, shown in equation 30, is the basis for a kinetic method for determination of H2O2, in a FIA system, measuring at 425 mn by the stopped-flow method. The LOD is 9.2 nM, with RSD 2.08% at 0.5 p,M and linearity in the 50 to 3500 nM range . This colorimetric method was proposed for development as a standard procedure in the Republic of China for determination of H2O2 in foodstuffs . ... 

---