Evaluation Of Dissociation Constants Research Articles

Quantum chemical evaluation of dissociation constants. Test calculations

Quantum chemical evaluation of dissociation constants. Test calculations

Evaluation of dissociation constants from competition binding experiments based on the relative binding ratio

Methods probing protein-DNA associations include direct binding titrations and competition binding experiments. For the latter, we present here a simple procedure allowing the quantitative evaluation of dissociation constants. We show that the ratio between the fraction of a DNA probe bound to protein in the absence of competitor and that in the presence of competitor is, at large competitor concentrations, a linear function of the competitor concentration, and we derive equations allowing the dissociation constant for the protein-competitor complex to be evaluated from the slope. We show further that a self-competition experiment, where the DNA probe and competitor are chemically the same species, can be used as a complement to a direct titration to determine the fraction of protein that is correctly folded for specific DNA binding. Thus, such a combination of direct and self-competition titration can be used as a check of the conformational purity of DNA binding proteins.

Application of Davis method to estimation of ions activity coefficients at the evaluation of dissociation constants of aromatic dicarboxylic acids in organic solvents

Validity of the Davis method for the estimation of activity coefficients of the ions forming in an acid-base system at the evaluation of thermodynamic dissociation constants of aromatic acids in dimethylformamide medium is evidenced.

Protein S and C4b-binding protein levels in patients with stroke: implications for protein S regulation.

Protein S circulates either free or bound to C4b-binding protein (C4b-BP). Only free protein S possesses cofactor activity for protein C, a physiologic anticoagulant. Deficiencies of either protein C or protein S are associated with increased thrombotic risk. Over a 23-month period, 40 patients with low free protein S were identified. Eight of these patients were found to have suffered a stroke. This study examined the relationship between total S, free S, and C4b-BP in 15 healthy adult volunteers, in 20 patients with normal protein S levels, in 40 patients with decreased free protein S levels, and in 8 patients with combined low free S levels and stroke. Total and free protein S and C4b-BP levels were determined using the method of Laurell. In healthy adults, free protein S increased with increasing total protein S (r = 0.60). In patients with normal free S, the total S level increased as C4b-BP increased (r = 0.74), and the free S level remained constant. In patients with low free S, total S did not increase with increasing C4b-BP. In stroke patients, the correlation between free S and total S was actually negative (r = -0.449). Evaluation of dissociation constants for the protein S-C4b-BP complex revealed enhanced binding in patients with low levels of free protein S. A non-C4b-BP protein S binding protein, a previously undescribed regulatory factor which modulates S binding to C4b-BP, or shifts in the amount of non-protein S binding C4b-BP are possible explanations of these results.

Evaluation of dissociation constants of ammonium ion in aqueous lithium perchlorate and lithium chloride-sodium chloride mixed solutions

The Pitzer approach has been applied to the evaluation of dissociation constants of ammonium ion in lithium perchlorate and lithium chloride-sodium chloride mixed solutions at 25°C. The calculated values showed good agreement with the observed values, provided all the higher-order interaction terms (θ's and Ψ's) concerned were introduced. The unknown Ψ(NH4LiClO4) value was determined from the isopiestic measurements of NH4ClO4−LiClO4 mixed solutions. Parameters in the Pitzer formalism for ammonia-ion interactions involved in LiCl and NaCl media were determined by use of the activity coefficients of ammonia measured in LiCl−NaCl mixed solutions by a transpiration method.

Optical and voltammetric studies on tetraphenylethylene salts

Optical spectra of tetraphenylethylene salts with lithium, potassium, rubidium, and tetrabutylammonium as counter ions, were recorded in tetrahydrofuran. Also the optical spectrum of sodium salt of tetraphenylethylene was recorded at very high dilution. On computer resolution of the optical spectra it was found that the observed bands were composed of three peaks, located around 385, 490, and 585 nm. Depending upon the counter ions and the environments these occur in different height ratios. These findings pointed to ion pairs formation and helped in elucidating their structure. The cyclic voltammetric studies on tetraphenylethylene helped in the evaluation of dissociation constant of T2-, M+ and the disproportination constant 2T.- ⇄ T2- + T. The former was found to be 1.2 . 10-5 mol 1-1, the latter 0.42 in dimethylformamide.

Multiple binding sites of carboxypeptidase B: the evaluation of dissociation constants by quantitative affinity chromatography.

Multiple binding sites of carboxypeptidase B: the evaluation of dissociation constants by quantitative affinity chromatography.

Evaluation of dissociation constants of weak electrolytes from conductance data by multiparametric curve-fitting

Evaluation of dissociation constants of weak electrolytes from conductance data by multiparametric curve-fitting

Evaluation of dissociation constants of weak electrolytes from conductance data by multiparametric curve-fitting

Summary A procedure is described for evaluating the thermodynamic dissociation constant of a weak electrolyte from conventional data on the concentration dependence of its equivalent conductance but without prior knowledge of its equivalent conductance at infinite dilution or of the concentration dependence of the equivalent conductance of any related strong electrolyte under the same conditions. The classical data of MacInnes and Shedlovsky for aqueous solutions of acetic acid are used to illustrate the procedure and to emphasize the constraints that should be imposed. It is concluded that statistical criteria for goodness of fit may usefully be supplemented by a demand for the most stable fit, and that the agreement between the conductometric and potentiometric values for the dissociation constant of acetic acid is very much better than has been believed.

Evaluation of dissociation constants and activity coefficients from solubility measurements

Evaluation of dissociation constants and activity coefficients from solubility measurements