Acid-base Equilibria In Solutions Research Articles

Using Mechanistic Modeling for Understanding Antibiotics Purification with Ion Exchange Chromatography

ABSTRACT In this work, we studied the purification with ion exchange chromatography of an aminoglycoside antibiotic industrially produced by Fareva. To do so, we performed a set of well targeted experiments and developed a physical model properly describing the ion exchange mechanism and acid-base equilibria in solution using the simulation software Ypso-Ionic. Our approach allowed us to rationalize few intriguing observations like the unexpectedly low capacity of the resin for the antibiotic or the strong influence of the counterion on the separation of two isomers of the antibiotic. Our findings illustrate the strength of using rigorous ion exchange models – as opposed to the often used classical adsorption models – to describe ion exchange chromatography.

THE USE OF TRISTIMULUS COLORIMETRY METHOD APPROACHES IN ACID-BASE EQUILIBRIUM STUDY IN DYES SOLUTIONS (REVIEW)

The present review is concerned with application possibility of tristimulus colorimetry method and argumentation of theoretical basis, and experimental approach of tristimulus colorimetry functions values use as analytical response in studies of acid-base equilibria in solutions of multifunctional organic compounds. A conceptual model is proposed, it is based on the change in tristimulus colorimetry function values in the ionization of functional groups of multifunctional compounds. The definitions of the corresponding terms are described. It has been established that use tristimulus colorimetry functions value as analytical response allows differentiating similar in acid-base characteristics functional groups, to determine the corresponding values of the ionization constants and to build a holistic picture about existing acid-base equilibria in a wide range of acidity of the medium. The values of tristimulus colorimetry functions of the specific and total color difference, the yellowness index, as well as the principles of their calculation within different color spaces by the example of polyfunctional compounds (about 50), namely different classes of dyes (azo-, triphenylmethane, xanthene, anthraquinone and pyrilium derivatives). It is established that all specified functions are suitable for the determination of p Kа , and the use of functions of full color difference makes it possible to simplify the mathematical apparatus for processing experimental data. The advantages of tristimulus colorimetry method before classical instrumental methods (spectrophotometry, potentiometry, conductometry) of studying acid-base equilibria in solutions of polyfunctional compounds are shown.

Generalization of Acid-Base Diagrams Based on the Unified pH-Scale.

So far, pH‐lgc i diagrams have been exclusively used for the theoretical description of acid‐base equilibria in aqueous solutions. Here, this approach is extended to include acid‐base equilibria in nonaqueous non‐hydrogen‐bond‐donor (non‐HBD) solvents following the acid‐base theory of Brønsted and Lowry, and using a unified pH scale (pHabs scale). This way, it is possible to estimate the approximate concentrations of all the species involved in acid‐base equilibria in a solution at any solution acidity pH(HS) , and vice versa. The diagrams are excellent to illustrate the differences in behavior of species involved in the solution equilibria in different solvents, for example, an aqueous solution of acetic acid is an acidic solution; however, the same concentration of acetic acid in DMSO has a pHabsH2O value of about 10.6, that is, it is a basic solution with reference to the aqueous pH scale.

Acid-base equilibria in solutions of polyacid bases (Model and experiment): II. Thermodynamic dissociation constants of tribasic acids

A model is developed for estimating thermodynamic dissociation constants of tribasic acids in organic solvents, with an example of ethanol solution of citric acid in which the functional groups are neutralized jointly.

Acid-base equilibria in solutions of polyacid bases (model and experiment): I. Thermodynamic dissociation constants of protonated mono- and diacid bases

A procedure was developed for determining the dissociation constants of protonated mono-and diacid bases. The procedure is based on a new approach to estimating and taking into account the concentrations of all the equilibrium species forming in the course of titration with a strong acid, with the aim to calculate the ionic strength of the solution and the activity coefficients.

Acid-base equilibria in solutions of cephotaxime and cephtriaxone

The concentration constants of acid-base equilibria in aqueous solutions of cephotaxime and cephtriaxone were determined pH-metrically at 20°C against the background of 0.1, 0.4, 0.7, and 1.0 M solutions of KCl and KNO3. The thermodynamic constants of these equilibria were calculated by the extrapolation of the concentration constants to zero ionic strength according to the Huckel equation. Cephotaxime and cephtriaxone ionic form sizes were calculated by the semiempirical PM3 method for energetically favorable conformations.

Thermodynamic Constants of Acid-Base Equilibria in Solutions of Penicillins

The constants of acid-base equilibria in solutions of benzylpenicillin, carbenicillin, and ampicillin at 20°C were determined by pH-metric titration (supporting electrolytes 0.1, 0.4, 0.7, and 1.0 M KCl and KNO3). The sizes of the ionic species of the penicillins in their energetically favorable conformation were determined by the PM3 semiempirical method. The thermodynamic equilibrium constants were estimated by extrapolation of the concentration constants to zero ionic strength by the Huckel equation, taking into account the calculated sizes of the ions.

Electrochemical polymerization of N-methyl-10,10-dimethylphenazasiline

N-methyl-10,10-dimethylphenazasiline (SIN) was polymerized by electrochemical oxidation at +1.3 V in methylene chloride. Acid-base equilibria in solution between the heterocyclic nitrogen and the protons produced by the coupling reaction were detected. The oxidized polymer deposits on platinum or ITO electrodes to give strongly adherent and electrochromic coatings.

On theSCF theory of continuum solvent effects representation II. Quantum chemical calculation of thermodynamic properties of some acid-base equilibria in solution

Further developments in the local reaction field (LRF) model of solvent effects are presented. The improved formalism, including dielectric saturation effects, permits a better description of the solvent polarization vector. As a result, the calculation of entropies of solvation is significantly improved with respect to the standard reaction field models, allowing a complete thermodynamic picture of ion solvation to be obtained. The calculated thermodynamic functions of solvation are combined with gas-phase proton affinities to yield theoretical estimates of solution equilibrium properties in some acid-base processes. Some preliminary results concerning the basicity of primary alkylamines in water are used to illustrate the reliability of the present approach.

Micro-ionization acidity constants for tetracyclines from fluorescence measurements

The pH vs. fluorescence intensity profiles for a number of tetracyclines are investigated. Fluorescence is obtained in alkaline solutions and is associated with the ionized form of the phenolic-β-diketone site of these molecules. The shape of the pH vs. fluorescence intensity profiles is best explained by representing the acid-base equilibria in solution by a micro-ionization scheme. In combination with measurements made on model compounds in which the dimethylammonium site was either blocked or removed, it proved possible to estimate values for the micro-ionization constants in aqueous solution; p k 13 values of 7.82, 7.85 and 7.04 were obtained for tetracycline, oxytetracycline and demethylchlortetracyline, respectively.

Practical acid dissociation constants, temperature coefficients, and buffer capacities for some biological buffers in solutions containing dimethyl sulfoxide between 25 and −12 °C

Acid dissociation constants ( K a ), usually expressed as p K a (- log K a ) can be considered as indices of acid-base equilibria in solution and their evaluation under the solution conditions that exist during the exposure of biological systems to low temperatures are as important as the measurement of pH per se. The assignment of pH∗ standards to define pH∗ scales in the binary mixed solvent, dimethyl sulfoxide-water (27), has provided the basis for measuring the p K a ∗ values of some biological buffers in mixtures of Me 2SO and H 2O which have particular relevance to studies which demonstrate the “pH-dependent” recovery of smooth muscle after low-temperature storage (9, 31). “Practical” ionization conslants in water (p K′ a ) and in 20% ( w w ) and 30% ( w w ) dimethylsulfoxide-water (p K a ∗) have been measured by potentiometric titration of a range of zwitterionic buffer compounds at 25, 0, −5.5, and −12 °C together with the respective buffer capacities and temperature coefficients. Measurements have been made with reference to the relevant standard states for each solvent system, thereby endowing the values with as much thermodynamic significance as possible.