Monitoring enzymic peroxidation of NAD by capillary electrophoresis

NAD⁺ is degraded by horse liver alcohol dehydrogenase in a reaction with p-methylbenzyl hydroperoxide, which acts as a pseudo-substrate. An unstable intermediate product (called compound I) is formed, and this is converted into the final product NADX. The reaction can be monitored by capillary electrophoresis. NADX migrates as two well resolved peaks (NADX₁ and NADX₂), which belong probably to the tautomers of the same substance. The intermediate product, compound I, has the same effective mobility as the conformer NADX₂ and it was impossible to separate compound I from NADX₂. The spectra taken during the separation show clearly that the “9-min” peak contains different compounds during the course of the reaction and the NADX₂ is not identical with compound I.     

Separation of enantiomers of butorphanol and cycloamine by capillary zone electrophoresis

Butorphanol tartrate is a synthetic opioid agonist-antagonist used as analgesic, possessing three chiral centres in the basic part of the molecule. Its chiral purity is routinely controlled only by optical rotation. A new capillary zone electrophoresis method, capable to separate the enantiomers of butorphanol and intermediate of its synthesis, cycloamine, was developed. Different electrolyte composition (type and concentration of carrier ion, pH, and organic solvent addition), and type and concentration of several chiral selectors (natural and modified cyclodextrins) were tested. Using the optimized conditions (acidic electrolyte with the addition of highly sulphated gamma-cyclodextrin) as low as 0.05% of undesirable enantiomers can be detected. Selected method characteristics, i.e., linearity (0-50 mg/l), precision (2.5% at 20 mg/l), and accuracy (101 +/- 2% at 20 mg/l) were evaluated. The optimized method was applied for the analysis of real batches of butorphanol and cycloamine. It was found that butorphanol tartrate manufactured by IVAX Pharmaceuticals contains less than 0.05% of undesirable enantiomer.     

Retention indices as identification tool in pyrolysis-capillary gas chromatography

Pyrolysis-capillary gas chromatography (Py-cGC) represents important method to identify the analytes in the mixture after thermal degradation. This combines high effective analyte separation on-line coupled with thermal degradation process that depends on analyte structure. System of retention indices has been used for identification of the analytes after on-line pyrolysis and chromatographic separation. The pyrolysate composition has been studied during thermal degradation of polymethylmethacrylate (PMMA) at different pyrolysis temperatures and chromatographic column conditions. Homologues series of n-alkanes have been used for calculation of pyrolysate Kováts retention indices (I) and compared with mass spectrometric (MS) data of pyrolysate model mixture. To identify PMMA thermal degradation products the high density polyethylene (HDPE) as additive standard producing triplets of the olefin homologous series during co-pyrolysis has been used. These homologous series enable to calculate programmed temperature retention indices (ITPGC) to identify the analytes present in the pyrolysate. Calculated I values were compared with published I values databases to identify analytes yielded at different pyrolysis temperatures.     

Voltammetry of biologically active species and surfactants on new miniaturized and contractible (compressible) mercury electrodes

The adsorption of the polyether-antibiotic monensin from an aqueous solution on mercury was used to investigate the effect of the decreasing size of a stationary mercury drop electrode on the shape of the voltammetric desorption peak of the surfactant. The change of the i-E curve indicated an acceleration of the transport of the surfactant to the electrode as well as of time-dependent changes in the adsorption layer. A decrease of the radius of the hanging mercury drop electrode from 220 μm to 80 μm at a constant accumulation time of t_ac = 70 s resulted in an about 4-fold increase of the evaluated signal (i-E pre-wave) of monensin. A 7-fold increase of the voltammetric desorption peak of monensin at conc. 5 · 10^–7 mol/L was observed as result of a compressive accumulation of the surfactant due to a contraction of the mercury drop electrode. A scheme of an apparatus for voltammetric/polarographic measurements by means of the contractible (compressible) mercury drop electrode is described. The controlled contraction of the electrode surface is presented together with preliminary results covering a new way of accumulation of surfactants, new accumulation effects, effective in adsorptive voltammetry, and other electroanalytical techniques.     

REVIEW: metal complexes as urease inhibitors

Urease plays a significant role in the pathogenesis of several diseases and also has practical implications in other fields, such as agriculture or chemical analysis. Among the multitude of chemical species known to inhibit urease, metal complexes stand out as a special category due to their specific mechanism of action, distinct from purely organic substances. Their inhibitory activity seems to depend on the type of metal and its oxidation state as well as on the coordination environment of the central atom. Furthermore, the study of the interaction between metal ions and their complexes with urease renders valuable insights into detailed catalytic mechanisms of this enzyme. This brief survey attempts to provide an overview of the published research on urease inhibition by metal complexes.     

Electrochemical processes during plating Fe powder particles by Ni and Ni/Cu coating in the fluidized bed

Ni electrodeposition on Fe powder was studied with respect to an inhibiting adsorbed hydroxycomplex layer. Its elimination was done in three possible ways: by increasing the rotation speed of the circular stirring of the suspension, by chemical dissolution of the adsorbed layer during interrupted electrolysis, and by addition of a complexing agent – sodium citrate into the electrolyte. The simultaneous deposition of a Cu/Ni coating was enabled by proper electrolyte composition as to the ratio of both metallic compounds and by the addition of a suitable complexing agent. The Cu/Ni ratio was influenced, beside electrochemical parameters, also by the particle size of the Fe powder and by the suspension density. Increasing the suspension density supports the deposition of Ni, and increasing the particle size supportsthe deposition of Cu. Electronic Publication     

Estrogen-induced cholestasis results in a dramatic increase of b-series gangliosides in the rat liver

Hepatic ganglioside composition was investigated in normal and cholestatic Wistar rats. Cholestasis was induced by 17alpha-ethinylestradiol (EE; 5 mg/kg body weight s.c. for 18 days). As compared with controls, the EE administration resulted in severe cholestasis, as indicated by biochemical as well as morphological signs. Gangliosides isolated from the liver tissue were separated by TLC, with resorcinol-HCl detection and densitometric evaluation. As compared with controls, the total hepatic lipid sialic acid content in cholestatic rats was increased almost 2-fold (44.3 +/- 15.2 vs 79.1 +/- 9.0 nmol/g wet weight of liver tissue, p < 0.01). This increase was primarily due to the increase of ganglioside GD1a (3.6 +/- 1.0 vs 11.8 +/- 3.0 nmol/g wet weight of liver tissue, p = 0.001), as well as to the enormous up-regulation of b-series gangliosides GD3 (0.08 +/- 0.03 vs 2.0 +/- 1.2 nmol/g wet weight of liver tissue, p = 0.002), GD1b (0.1 +/- 0.06 vs 5.4 +/- 1.6 nmol/g wet weight of liver tissue, p = 0.002) and GT1b (0.06 +/- 0.03 vs 6.4 +/- 2.6 nmol/g wet weight of liver tissue, p = 0.002). As the majority of gangliosides are concentrated in cell membranes, our findings suggest that dramatic increase of b-series gangliosides might contribute to the protection of hepatocytes against the deleterious effects of cholestasis.     

Structure and properties of titanium-zinc borophosphate glasses

The structure of 50ZnO-10B₂O₃-40P₂O₅+xTiO₂ glasses prepared by slow cooling (for x=0-24 mol% TiO₂) or by quenching (for x=28-64 mol% TiO₂) was studied by Raman, ³¹P and ¹¹B MAS NMR spectroscopy. TiO₂ incorporates into the glass structure, which results in a decrease in the molar volume and an increase in the glass transition temperature. According to Raman spectra Ti atoms form distorted TiO₆ octahedra and their incorporation into the structural network results in the depolymerization of phosphate chains. ¹¹B NMR spectra of the glasses with increasing TiO₂ content show gradual changes from one symmetrical signal of B(OP)₄ units to a broad complex signal which was separated into five signals ascribed to four different types of BO₄ units and one BO₃ unit. With increasing TiO₂ content a part of boron atoms changes from tetrahedral BO₄ to trigonal BO₃ units, which is ascribed to the formation of TiO₆ units in the glass structure.     

Investigation of the reactivity of powder surfaces by abrasive voltammetry

The ability of abrasive voltammetry to reflect the reactivity of iron powder immobilized on paraffin-impregnated graphite electrodes was investigated. Normal pulse voltammetry was used as the preferred method. The peak shape and position on the potential/time axis reflected both the reactivity of iron powder particles as well as their size fraction. “Relative peak height” defined as peak height to area ratio, i.e., current to charge ratio, correlated well with the rate of the electrochemical dissolution process. It showed not only a decreasing dissolution rate with an increase in particle size, but also the differencies in the dissolution rate of iron powder of various reactive surfaces as a consequence of various pretreatment methods. It was found that chemical pretreatment of the powder always resulted in a faster dissolution process in comparison with other non-chemical pretreatment methods. Received: 30 June 1998 / Accepted: 30 September 1998