Lidija B. Pfendt

Study of heterogeneous equilibria in saturated aqueous solutions of some 7-chloro-1,4-benzodiazepines

Acid-base equilibria in heterogeneous and homogeneous systems of some sparingly soluble benzodiazepines (diazepam, prazepam, chlordiazepoxide and medazepam) were investigated in aqueous solution and the corresponding equilibrium constants were determined by the application of pH-metric, spectrophotometric and solubility methods. The sites of protonation were predicted on the basis of the analysis of the corresponding carbon-13 nuclear magnetic resonance spectra. In addition, buffer characteristics of saturated aqueous solutions of these drugs in the presence of the solid phase were investigated and it was established that they possess a very high buffer capacity over a specific pH range.

Study on protolytic equilibria of lorazepam and oxazepam by UV and NMR spectroscopy

Protolytic equilibria in homogeneous and heterogeneous systems of lorazepam and oxazepam, which are sparingly soluble ampholytes from the class of 1,4-benzodiazepines, were studied at 25 degrees C and ionic strength of 0.1 M. Acidity constants and equilibrium constants in a heterogeneous system were determined. On the basis of the analysis of the corresponding 13C- and 1H-NMR spectra, deprotonation site in the molecules of the investigated compounds was predicted. Finally, the correlation between chemical shifts in the 1H-NMR spectra and the acidity of the amide proton of 1,4-benzodiazepines was established.

Study of protolytic equilibria of flurazepam

Protolytic equilibria of flurazepam, a diprotic base which is sparingly soluble in water, were investigated. The investigations were carried out in the pH range 0–12, at constant ionic strength (0.1 M NaCl) and 25 ± 0.1 °C, by the application of spectrophotometric, pH-metric and solubility methods. The acidity, hydrolysis and equilibrium constants in the heterogeneous system were determined. In addition, a method, based on the application of a formation function to the hydrolytic process, is proposed. Finally, buffer characteristics of flurazepam in the homogeneous and heterogeneous systems were studied.

Spectrophotometric determination of tungsten(VI) with rutin

Abstract A new spectrophotometric method for the determination of microamounts of tungsten(VI) with rutin has been developed. The effect of a large number of foreign ions was investigated, and the separation and determination of tungsten in the presence of the interfering ions examined are presented.

Derivative spectrophotometric method for determination of acidity constants of single step acid-base equilibria.

A general derivative spectrophotometric method for determination of acidity constants is developed. The method appears suitable in cases when classical spectrophotometry cannot be employed due to little differences in the absorption spectra of conjugated acid-base pairs. Based on theoretical considerations, seven variants of the method have been established and their validity was checked, determining acidity constants of lorazepam and flurazepam as model compounds.

Study of protolytic, hydrolytic and solubility equilibria of midazolam

Protolytic equilibria of midazolam in the pH range 0–12 were investigated. Acidity, hydrolysis, equilibrium constants in the heterogeneous system and the solubility of midazolam were determined [I= 0.1 mol l–1(NaCl), 25 °C]. A spectrophotometric method was developed for the investigation of the mechanism of hydrolysis and the determination of the corresponding equilibrium constants. In addition, buffer characteristics of the two-phase and single-phase midazolam buffers were investigated.

Study of heterogeneous equilibria in solutions of EDTA complexes of copper(II), zinc(II) and cadmium(II)

Abstract It has been established that from the solutions of copper(II)-, zinc(II) and cadmium(II)-EDTA complexes, respectively, in the presence of potassium nitrate and at pH-values lower than 3.5, compounds of the general formula KH 3 (MeY) 2 are precipitated. The corresponding heterogeneous equilibria have been studied at I = 1M and t = 25°C, by application of three independent methods, using the formation function, by means of the solubility of the complex and by determination of the protons bound to the complex in the solution. The results obtained were in agreement. Using the equilibrium constants determined in the heterogeneous systems, the protonation constants of the corresponding metal(II)-EDTA complexes in the homogeneous systems have been calculated. The calculated values were in accordance with those obtained earlier by us in homogeneous systems[1].

Study of equilibria in solutions of some protonated metal(II)-edta complexes☆

Abstract Equilibria in acidic solutions of EDTA complexes of nickel(II), cobalt(II), lead(II), mercury(II), copper(II), zinc(II) and cadmium(II) respectively, were investigated by pH-metric method (1M KNO3; 25°C). It has been established that in addition to monoprotonated complexes some polyprotonated complexes are formed. The protonation constants of these complexes have been determined.

Two-phase buffer systems containing a sparingly soluble diprotic acid as the solid phase

Two-phase buffer systems consisting of a sparingly soluble diprotic acid and its saturated aqueous solution (buffered phase) are investigated. The equations for the dependence of buffer capacity onpH and for evaluation of dilution effects in two-phase buffers of this type are derived. Theoretical considerations are experimentally verified on four buffer systems containing 1,2-, 1,3-, 1,4-benzenedicarboxylic and octanedioic acid. The main characteristic of the buffers of this type is a very high buffer capacity within a narrowpH range.ZusammenfassungZweiphasen-Puffersysteme, bestehend aus einer schwerlöslichen diprotischen Säure und ihrer gesättigten wäßrigen Lösung (gepufferte Phase), wurden untersucht. Die Gleichungen für die Abhängigkeit der Pufferkapazität vompH und für die Berechnung der Verdünnungseffekte in derartigen Zweiphasen-Puffersystemen wurden aufgestellt. Dabei wurden die theoretischen Betrachtungen an vier Puffersystemen, die Benzol-1,2-, -1,3- und-1,4-dikarbonsäuren bzw. Oktandisäure enthielten, experimentell geprüft. Die wichtigste Eigenschaft solcher Puffer ist ihre sehr hohe Pufferkapazität innerhalb eines engenpH-Bereiches.

Spectrophotometric determination of microquantities of molybdenum

SummaryA new spectrophotometric method for the determination of microquantities of molybdenum (VI) and rutin, respectively, has been described. In order to take all the advantages of this very sensitive method, the effect of some foreign ions on these determinations has been studied and a combined chromatographic-spectrophotometric procedure for the separation and the determination of microamounts of molybdenum (VI) in the presence of a large number of interfering ions has been developed.ZusammenfassungEine neue spektralphotometrische Methode zur Bestimmung von Mikromengen von Molybdän(VI) bzw. von Rutin wurde beschrieben und der Einfluß einiger Fremdionen auf diese Bestimmung untersucht. Um die Anwendungsmöglichkeiten dieser Methode zu erweitern, wurde ein kombiniertes chromatographisch-spektrophotometrisches Verfahren zur Abtrennung und Bestimmung von Mikromengen Molybdän(VI) in Gegenwart einer größeren Zahl störender Ionen ausgearbeitet.