Autoprotolysis in aqueous organic solvent mixtures. Water/dipolar protophilic solvent binary systems

Anion and sugar recognition by 2,6-pyridinedicarboxamide bis-boronic acid derivatives

Two 2,6-pyridinedicarboxamide derivatives containing arylboronic acid fragments were prepared and fully characterized including X-ray crystal diffraction analysis of a pinacol ester. These compounds are potential bifunctional receptors for sugars and anions. Acid dissociation and stability constants for complexation of both receptors with glucose and fructose were determined by potentiometric titrations in aqueous DMSO. Also, binding of alizarin red S indicator was studied spectrophotometrically and a highly sensitive detection of fructose by an indicator displacement assay was proposed. Complexation with anions was studied by 1H NMR titrations in DMSO-d6. Binding of acetate anion occurs only via hydrogen bonding to OH groups of boronic acid fragments and does not affect signals of NH protons but chloride anion induces large shift of the signals of NH protons and small shifts of the signals of OH groups. This behavior makes possible anion discrimination based on preference in the type of binding site rather than simply on anion basicity as is typical for majority of neutral hydrogen bonding anion receptors.

Acid–base and coordination properties of 2-phenyl-3-hydroxy-4-quinolones in aqueous media

2-Phenyl-3-hydroxy-4-quinolones bind metal ions with selective fluorescence response in aqueous media.

Influence of mobile phase acid-base equilibria on the chromatographic behaviour of protolytic compounds

A review about the influence of mobile phase acid-base equilibria on the liquid chromatography retention of protolytic analytes with acid-base properties is presented. The general equations that relate retention to mobile phase pH are derived and the different procedures to measure the pH of the mobile phase are explained. These procedures lead to different pH scales and the relationships between these scales are presented. IUPAC rules for nomenclature of the different pH are also presented. Proposed literature buffers for pH standardization in chromatographic mobile phases are reviewed too. Since relationships between analyte retention and mobile phase pH depends also on the pKa value of the analyte, the solute pKa data in water-organic solvent mixtures more commonly used as chromatographic mobile phase are also reviewed. The solvent properties that produce variation of the pKa values with solvent composition are discussed. Chromatographic examples of the results obtained with the different procedures for pH measurement are presented too. Application to the determination of aqueous pKa values from chromatographic retention data is also critically discussed.

Retention of ionizable compounds on HPLC. 12. The properties of liquid chromatography buffers in acetonitrile-water mobile phases that influence HPLC retention

The addition of acetonitrile to aqueous buffers to prepare RP HPLC mobile phases changes the buffer properties (pH and buffer capacity). This variation is studied for ace tate, phosphate, phthalate, citrate, and ammonia buffers in acetonitrile-water mixtures up to 60% in acetonitrile (v/v). Equations are proposed to relate pH and buffer capacity change of these buffers to the initial aqueous pH value and to the volume fraction of acetonitrile added. It is demonstrated that the pH change of the buffer depends not only on the initial aqueous pH of the buffer and on the percentage of acetonitrile added but also on the particular buffer used. The proposed equations allow an accurate prediction of this ionization for the studied buffers. Since the retention of acid/base compounds shows a strong dependence of their degree of ionization, the equations are used to predict the change in this ionization with addition of acetonitrile when the RP HPLC mobile phase is prepared. This prediction allows estimation of the retention of an acid/base compound in a particular acetonitrile-water buffered mobile phase.