A bilogarithmic method for the spectrophotometric evaluation of stability constants of 1:1 weak complexes from mole ratio data

Boccio, Maravillas; Sayago, Ana; Asuero, Agustín G.

doi:10.1016/j.ijpharm.2006.03.026

Cited by 12 publications

(5 citation statements)

References 32 publications

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“…The distinctly different shapes for the Job plot allow for determination of the equilibrium stoichiometry for systems with small equilibrium constants. Indeed, previous methods to determine reaction stoichiometry and/or binding constant are applicable only for rather small equilibrium constants. ,,,, …”

Section: Theoretical Prediction Of Job Plotsmentioning

confidence: 99%

“…Because of its utility and simplicity, Job’s method has been utilized to interrogate a wide variety of systems, including ligand/metal complexes, complexes of inorganic anions and organometallic compounds, , the binding of DNA to fluorescent dyes, and the interaction of organic hosts and guests, , to name just a few. Because of the widespread use of Job’s method, several reports highlighting the technical aspects of the method have been published. − ,− In particular, a number of techniques have been developed to directly determine the formation constant of the complexes that are investigated by fitting of Job plot curves. ,,,, …”

Section: Introductionmentioning

confidence: 99%

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Getting More out of a Job Plot: Determination of Reactant to Product Stoichiometry in Cases of Displacement Reactions and n:n Complex Formation

2011

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The method of continuous variation (often referred to as Job's method) is an easy and common method for the determination of the reactant stoichiometry of chemical equilibria. The traditional interpretation of Job plots has been limited to complex association equilibria of the type nA + mB ⇌ A(n)B(m), while little focus has been placed upon displacement type reactions (e.g., A + B ⇌ C + D), which can give Job plots that look quite similar. We developed a novel method that allows the user to accurately distinguish between 1:1 complex association, 2:2 complex association, and displacement reactions using nothing more than a pocket calculator. This method involves preparing a Job plot of the system under investigation (using regularly spaced mole fractions), normalizing the measured quantities (such as the concentration of A(n)B(m) or C for the above reactions) to their maximum value (i.e., at mole fraction 0.5), and determining the sum of the normalized values. This sum is then compared with theoretically predicted normalized sum values that depend on the nature of the equilibrium. The relationship between, on the one hand, the sum of the normalized values and, on the other hand, the reaction equilibrium constant and the concentration of the stock solutions used for the preparation of the Job plot is also explored. The use of this new technique for the interpretation of Job plots permits users to readily determine information that can be obtained otherwise only with laborious additional experiments, as illustrated by the analysis of four Job plots taken from the literature.

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Section: Theoretical Prediction Of Job Plotsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Getting More out of a Job Plot: Determination of Reactant to Product Stoichiometry in Cases of Displacement Reactions and n:n Complex Formation

2011

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“…The two classical methods as well as the new expressions have been applied to the pK a evaluation of the methylglyoxal bis (4-phenyl-3thiosemicarbazone) (MGBPT). [18][19] Although this reagent has two close pK a corresponding to the equilibria of the type expressed in the following scheme 20 applying the Coleman or Polster methods 1,[21][22][23] it can be shown that in the range of about 10-12pH, the two species corresponding to the first ionization equilibrium are found from a practical point of view.…”

Section: Methodsmentioning

confidence: 99%

Optimization of intersecting straight lines methods for the evaluation of acidity constants of single equilibria from spectrophotometric data

Martín

Asuero

Herrador

et al. 2018

PPIJ

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The acid dissociation constant (Ka) is among the most frequently used physicochemical parameters, and its determination is of interest to many research fields. A number of graphical methods has been proposed for the spectrophotometric evaluation of acidity constants of single equilibrium HR=H+R (charges omitted for the sake of generality), in those cases in which the limit absorbance's of the pure species HR or R, A1 and A0, respectively, are unknowns. The raw values of absorbance's versus pH data are transformed in linear functions, which allow to evaluate the unknown parameter Ka and A0/or A1 by a graphical approach or by the application of the least squares method. Among the various methods proposed the double reciprocal, Agren-Sommer and Nash methods yield to a family of intersecting straight lines when experimental measurements of absorbance and pH are made at different wavelengths. The purpose of this paper is to critically examine these methods on the basis of the requirements of single linear regression.

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“…This paper forms part of an investigation [9] [13] into the uses of bilogarithmic methods and hyperbolic functions in parameter estimation. Methods based on the application of spectrophotometric measurements have been the subject [14]- [16] of recent studies.…”

Section: S Beaumont Et Almentioning

confidence: 99%

A Potentiometric Evaluation of Stability Constants of Two-Step Overlapping Equilibria via a Bilogarithmic Hyperbolic Cosine Method

Beaumont¹,

Martín²,

Asuero³

2016

JASMI

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A bilogarithmic hyperbolic cosine method for the evaluation of overlapping formation constants at varying (or fixed) ionic strength is devised in this paper and applied to data reported in the analytical literature, i.e. succinic acid system, Cu(II)-glycine system and Ag(I)-aminobutan-1-ol system. The method is based on the linearization of the formation function ñ = f(pH) or ñ = f(pL) data. A theoretical slope of unity should be obtained thus proving the correctness of the assumed equilibria. An additional advantage of the bilogarithmic method proposed is that it provides a closed scale representation of Y and X unlike other plots. This paper forms part of an investigation into the uses of bilogarithmic methods and hyperbolic functions in parameter estimation. Methods based on the application of spectrophotometric measurements have been the subject of recent studies.

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A bilogarithmic method for the spectrophotometric evaluation of stability constants of 1:1 weak complexes from mole ratio data

Cited by 12 publications

References 32 publications

Getting More out of a Job Plot: Determination of Reactant to Product Stoichiometry in Cases of Displacement Reactions and n:n Complex Formation

Getting More out of a Job Plot: Determination of Reactant to Product Stoichiometry in Cases of Displacement Reactions and n:n Complex Formation

Optimization of intersecting straight lines methods for the evaluation of acidity constants of single equilibria from spectrophotometric data

A Potentiometric Evaluation of Stability Constants of Two-Step Overlapping Equilibria via a Bilogarithmic Hyperbolic Cosine Method

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