Dissociation constant, determination

Directions are provided in this experiment for determining the dissociation constant for a weak acid. Potentiometric titration data are analyzed by a modified Gran plot. The experiment is carried out at a variety of ionic strengths and the thermodynamic dissociation constant determined by extrapolating to zero ionic strength. 

By correlating the observed spectral changes with the concentrations of added cycloamylose, dissociation constants of the cycloamylose-substrate adducts may be calculated (Rossotti and Rossotti, 1961). Values of the dissociation constants determined in this manner for a variety of complexes are presented in Table II. In most cases, stoichiometries of the complexes have been shown to be 1 1 from the presence of distinct isosbestic points in the spectrophotometric titrations. In a few cases, additional spectral perturbations are observed as the cycloamylose concentration is increased, indicating more complex modes of association. Methyl orange, for example,... 

Summary of Dissociation Constants Determined FOR Complexes between Benzhydroxamio Acid (2) AND Resting State Horseradish Peroxidase"... 

The product was extracted with ethyl ether and after evaporation of the solvent the dry residue was recrystallized from CCl AtCHjCOOH was identified by ion-exchange chromatography. Its dissociation constant determined by the measurement of its distribution between... 

A measurement of the ability of a buffer system to limit the change in pH of a solution upon the addition of an increment of strong base. ft is the reciprocal of the slope of the pH-neutralization curve. Consider the simple equilibrium, HA H+ -h A where K = [H+][A ]/ [HA] in which K is a practical dissociation constant determined under conditions of constant ionic strength. In such systems the practical pK is equal to the pH of solution when there are equal concentrations of the two buffer species. Since the total concentration of the two... 

III. In this way we obtain, with the ion-pair dissociation constant determined from conductance data, a value of 5.3 x 10-5 for the average stability constant of the triple ions (K3 from eqn. 13), This should be compared with 1.24 x lCT M as derived from conductance indicates an important fraction of simple ions over the largest part of the concentration range studied. 

More recently (55) triethyloxonium hexachloroantimonate has also been used as an initiator of the polymerisation of this monomer, and its dissociation constant determined as 5.3 x 10 5 M at 20° C in methylene chloride. Penczek (54) has also studied the dissociation of l,3dioxolan-2-ylium hexafluoroarsenate and hexa-fluoroantimonate,... 

Dissociation Constants, Determination of, for Two-Substrate Enzyme Systems... 

The dissociation constant determined most recently by Schumacher et al. [129] by NMR spectroscopy in 0.5 M Na2S04 is pK = 13.10 at 25 °C. The kinetic analysis performed by these authors shows that under conditions where the overall reaction is kinetically controlled by the surface reaction, the deposition rate R is directly proportional to the concentration of the methylene glycolate anion MG ... 

In a more recent study Sigwalt et al. [41] investigated the use of carbazyl sodium to initiate PS polymerization in tetrahydrofuran (THF). This initiator produced only one living end per chain. Excellent agreement with the results obtained on amphianionic polymer was obtained. At levels of living ends below 10 molel the rate coefficient found for ion pairs was 3 x 10" 1 mole sec and for free ions 4 1 mole sec . The dissociation constant (determined kinetically) was 6.4 x 10 mole 1 . ... 

In the case where both Ajn and Aout are fast, the ratio of the apparent forward and backward rate constants is identical with the dissociation constant determined by equilibrium methods. A different situation prevails in the range where the ratio Ain/A4 is very small. Under such a regime, the brief protonation-dissociation cycle will not propagate into the core, and the dynamics will be controlled only by the rate of the surface reactions. For such specific cases there will be a marked difference between the pKs, derived from the kinetic experiment, and pKobs obtained by equilibrium measurements. Consequently, it is only the accurate kinetic analysis that can furnish the precise description of the system and yields the information about the events that follow the protonation. 

This is the Cheng-Prusoflf equation, where [L] is the concentration of radioactive ligand used in the experiment and Kd its dissociation constant determined from the Scatchard plot. Finally, if the displacement is of the noncompetitive type, then, = IC50. 

The relative contribution of each interaction was calculated from the ratio of the ligand dissociation constant determined with the mutant enzyme to that determined with wild-type yeast ODCase... 

Measures of biological performance used in the assays presented in this chapter include K, the reversible inhibition constant determined under equilibrium conditions K, the reversible dissociation constant determined under equilibrium conditions IC50, the concentration required for 50% inhibition EC , the concentration required to produce % of a maximal effect (relative to a reference) ED , the in vivo dose required to produce n% of a maximal effect (relative to a reference) K, the Michaelis constant K, the apparent dissociation constant for a competitive antagonist as obtained in a functional assay and CIC95 (cell culture minimum inhibitory concentration), the concentration that inhibits more than 95% of the spread of infection. The reader should refer to original literature reports for complete descriptions of the assays. 

Dissociation constants determined by deconvolution of transient emission spectra Dissociation constants determined by UV-titrations with camphor Value represents an upper-limit estimate of the dissociation constant... 

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