Topical Problems in the Biosynthesis of Red Blood Pigment

Uroporphyrinogen III plays a key role in the biosynthesis of heme, the red pigment of blood. In vivo studies with specifically ¹⁴C- and ³H-labeled precursors have revealed that the formation uroporphyrinogen III in the organism follows several primary and subsidiary pathways. Model experiments on the pattern of biosynthesis have led to simple and effective methods of synthesizing uroporphyrin analogs and have shown that their production is strongly favored thermodynamically. The biologically porphyrins important thus available permit a mechanistic explanation of the light-induced dermatoses in porphyria diseases and suggest promising medical applications in diagnosis and therapy.     

Amperometric detection of amino acids with a passivated copper electrode

The amperometric behaviour of a copper electrode towards amino acids is studied by means of a rotating disc electrode. A theoretical model describing the anodic background current in a buffer solution and the increase of the current caused by amino acids is checked experimentally. The influences of the amino acid concentration, the rotation speed of the electrode and the composition of the buffer solution are studied. It is proved that chemical dissolution of a passivating film on the electrode surface, which is enhanced by the complexation reaction between the amino acid and copper(II) ions, is the principle of the phenomena observed. The applicability to flow systems is demonstrated.     

Kinetik der Alterung von anodischen Deckschichten auf Aluminium durch Farbstoffaufnahmen

Zusammenfassung Durch Messungen der Alterung (Verminderung der prozentualen Farbstoffaufnahme) der zwei aufeinander liegenden Oxyde auf anodisch oxydiertem Aluminium wurde folgendes festgestellt: Das genannteγ ₂-Al₂O₃ weist keine wesentliche Alterung in der Luft und unter Wasser auf, da es kompakt und geordnet ist. Dasγ ₁-Al₂O₃ altert in der Luft und unter Wasser proportional der Zeit. Seine Alterungsgeschwindigkeit ist proportional der Herstellungsstromdichte. Nach 12 A/dm² nimmt die Alterung nicht mehr zu, da dieses Oxyd die maximale Fehlordnung besitzt. Die Alterung in der Luft ist kleiner als unter Wasser, da dieses mit seinem L?sungsverm?gen für die Rekristallisation günstig ist. Mit zunehmender Temperatur nimmt die Alterungsgeschwindigkeit bis 90°C zu und f?llt darüber hinaus bis zu Null (120°C). Bei h?heren Temperaturen findet eine Verjüngung des Oxyds statt. Dieses Ph?nomen mit Temperaturmaximum ist zum ersten Mal bei heterogenen Reaktionen unter ?nderung eines festen Stoffes festgestellt worden und bedeutet eine Rückreaktion entweder unter Bildung von neuen Fehlordnungen (die Werte der Aktivierungsenergien der Hin- und Rückreaktion sind dafür plausibel) oder eine Freilegung von anwesenden aktiven Zentren, wegen Desorption von Wasser.     

Animal models for treatment of unresectable liver tumours: a histopathologic and ultra-structural study of cellular toxic changes after electrochemical treatment in rat and dog liver

INTRODUCTION: Electrochemical treatment (EChT) has been taken under serious consideration as being one of several techniques for local treatment of malignancies. The advantage of EChT is the minimal invasive approach and the absence of serious side effects. Macroscopic, histopathological and ultra-structural findings in liver following a four-electrode configuration (dog) and a two-electrode EChT design (dog and rat) were studied. MATERIALS AND METHODS: 30 female Sprague-Dawley rats and four female beagle dogs were studied with EChT using Platinum:Iridium electrodes and the delivered dose was 5, 10 or 90 C (As). After EChT, the animals were euthanized. RESULTS: The distribution of the lesions was predictable, irrespective of dose and electrode configuration. Destruction volumes were found to fit into a logarithmic curve (dose-response). Histopathological examination confirmed a spherical (rat) and cylindrical/ellipsoidal (dog) lesion. The type of necrosis differed due to electrode polarity. Ultra-structural analysis showed distinct features of cell damage depending on the distance from the electrode. Histopathological and ultra-structural examination demonstrated that the liver tissue close to the border of the lesion displayed a normal morphology. CONCLUSIONS: The in vivo dose-planning model is reliable, even in species with larger tissue mass such as dogs. A multi-electrode EChT-design could obtain predictable lesions. The cellular toxicity following EChT is clearly identified and varies with the distance from the electrode and polarity. The distinct border between the lesion and normal tissue suggests that EChT in a clinical setting for the treatment of liver tumours can give a reliable destruction margin.     

Improved straightforward chemical synthesis of dihydroxyacetone phosphate through enzymatic desymmetrization of 2,2-dimethoxypropane-1,3-diol

Dihydroxyacetone phosphate (DHAP) was synthesized in high purity and yield in four steps starting from dihydroxyacetone dimer (DHA) (47% overall yield). DHA was converted into 2,2-dimethoxypropane-1,3-diol, which was desymmetrized by acetylation with lipase AK. The alcohol function was phosphorylated to give dibenzyl phosphate ester 4. From 4, two routes were investigated for large-scale synthesis of DHAP. First, acetate hydrolysis was performed prior to hydrogenolysis of the phosphate protective groups. The acetal hydrolysis was finally catalyzed by the phosphate group itself. Second, acetate and acetal hydrolysis were performed in one single step after hydrogenolysis.     

Contactless conductivity detection of synthetic polymers in non-aqueous size-exclusion electrokinetic chromatography

A capacitively coupled contactless conductivity detection (CCD) system has been applied for the detection of neutral synthetic polymers in capillary size-exclusion electrokinetic chromatography (SEEC). Polystyrene standards, that were used as a model compounds, were separated on a capillary column packed with porous 10 microm silica particles with an electrokinetically driven mobile phase, and detected by CCD and UV detection simultaneously. Mass-calibration curves for polystyrene were constructed. Satisfactory results were obtained for the linearity, the run-to-run repeatability (<0.2% for the relative retention and <4% for the peak area) and the robustness of the detector. One of the major issues in this preliminary study was to investigate the origin of the peaks observed for the polystyrene standards. The effect of the molar mass of the polystyrenes on the sensitivity was small. Therefore, the signals obtained could not be explained as the result of an increased viscosity and a decreased solution conductivity of the solute zone. An alternative hypothesis is suggested, and recommendations for further research are given.     

Determination of anionic trace impurities in glycerol by capillary isotachophoresis with enlarged sample load

Glycerol of different quality classifications served as a model for a neutral excess component in the isotachophoretic determination of low-molecular-mass anionic trace impurities. Potential anionic contaminants such as nitrate, sulphate, chlorate, nitrite, oxalate, fluoride formate and phosphate were analysed up to an analyte-to-excess ratio of 1:4·10⁷, thus providing the possibility of checking the sample for the mentioned analytes in the order of 2.5·10⁻⁶–9.5·10⁻⁶%. Because we used a column-coupling isotachophoretic instrument the electrolyte system consisted of two different leading electrolytes, one for the pre-separation (10 mmol/l HCl, β-alanine, pH 3.2) in the first capillary and one for the final separation (5 mmol/l HCl, 1,3-bis[tris(hydroxymethyl)methylamino]propane, β-alanine, pH 3.6) in the second capillary. The terminating electrolyte was citric acid. Due to an increased injection volume of 300 μl, limits of detection (LODs) in the nanomolar range were realised by conductivity detection. The developed method allows simultaneous analysis without sample preparation and/or preconcentration within 25 min and is for that reason suitable for in-place process control.     

Use of non-segmented flow,post-columns reaction detection with miniaturized HPLC systems

Summary The use of non-segmented flow, post-column reaction detection is evaluated for use with miniaturized HPLC. Non-segmented open-tubular reactors with internal diameters 0.1 mm to 0.25 mm and packed-bed reactors with internal diameters of 1 mm, filled with 5 and 10 m particles are evaluated theoretically and experimentally with respect to band broadening and pressure drop characteristics. An integrated system consisting of miniaturized HPLC (1 mm i. d.) columns and compatible hardware is described. An example of the separation of catecholamines is given.     

TG-DTA and FTIR analyses of plasters from byzantine monuments in Balkan region

Historic plasters from wall paintings of Byzantine and post-Byzantine churches situated in the Balkan region were studied. All wall paintings were made with fresco technique and are dated from IX - XVI century. Plaster samples were followed from room temperature to 1000°C by Thermogravimetric (TG) and Differential Thermal Analysis (DTA), and one or two significant temperature regions, corresponding to thermal decomposition mechanisms were observed. The analysis of the plaster samples and the composition characterization was carried out using also, Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Although the main components are calcite and quartz (from sand) in different proportions, there are differences between them such as the presence of gypsum being either as a constituent element or due to environmental pollution. The results are examined comparatively taking into account the creation time and place of the paintings.     

Flow-through radioactivity detection of 3H- and 14C-labelled compounds in reversed-phase liquid chromatography by a liquid scintillation counting technique based on post-column extraction

A method for flow-through liquid scintillation counting in reversed-phase liquid chromatography (RP-LC) based on the continuous extraction of aqueous column eluates with a water-immiscible liquid scintillator is evaluated in terms of sensitivity, reproducibility and extra-column band broadening. ³H- and ¹⁴C-labelled phenylthiohydantoinamino acid derivatives of widely different polarity serve as model compounds. For extractable derivatives, counting efficiencies of over 30 and 80% can be obtained for ³H and ¹⁴C, respectively. The reproducibility and extra-column band broadening depend on the mixing ratio of scintillator and LC eluent; relative standard deviations (peak areas) of less than 3% can be obtained. The sensitivity of flow-through counting can be increased at least 150-fold by storing the segmented scintillator/eluate stream in a capillary storage loop. After the separation is complete, the stream is re-introduced into the radioactivity detector at reduced flow-rates to increase the mean residence time, i.e., the counting time, in the detector.