Enantiospecific synthesis of isomers of AES, a new environmentally friendly chelating agent

Three four-step enantiospecific syntheses of different diastereomers of AES, a new biodegradable chelating agent, are described. The stereocenters in each of the isomers are accessible from l- and d-malic and aspartic acids.     

Effect of method of solution on observed molecular weight distribution of barley starch and starch derivatives in size exclusion chromatography

Summary Samples of native barley starch and six starch derivatives were suspended (0.1% sample concentration) in four different solvents: the eluent (pH 11 buffer), dimethylsulfoxide, 0.1 M NaOH or 0.5 M NaOH and kept in a boilling water bath for 5 to 60 minutes or shaken for 60 minutes. The average molecular weight values , and the polydispersity value were determined with a TSK PW-type column using narrow standard calibration. Only a small part of the samples dissolved in the eluent. The dissolution of sample in dimethylsulfoxide was dependent on sample type. Of the NaOH solutions, 0.5 M NaOH was the only one that dissolved all the samples. Therefore, 0.5 M NaOH appears to be the solvent of choice for starch molecules.     

Degradative analysis of aquatic fulvic acid: CuO oxidation versus pyrolysis after tetramethylammonium hydroxide treatments in air and helium atmospheres

The structural composition of Nordic aquatic reference fulvic acid was investigated using chemical and thermal degradation methods: alkaline CuO oxidation and analytical pyrolysis after tetramethylammonium hydroxide (TMAH) pretreatment. Off-line procedures of the TMAH treatments were carried out under both air and helium atmospheres, with the aim of clarifying the effect of oxygen. Irrespective of the fact that the chemical and thermal degradation methods gave qualitatively quite similar basic products (mainly phenols and phenolic acids together with aromatic and aliphatic carboxylic acids), they also revealed their unique selectivity and efficiency for releasing different kinds of structural constituents. The results verify the formation of additional carboxyl functionality in the CuO oxidation. However, some similar oxidative reactions also appeared to take place during the pretreatment procedures of strongly basic TMAH, especially under an air atmosphere. The use of inert and protective atmosphere during the TMAH pretreatment is therefore recommended for producing more relevant structural information about the complex composition of humic substances.     

Determination of biogenic amines in wine by multidimensional liquid chromatography with online derivatisation

An online multidimensional liquid chromatographic system was developed for online clean-up, derivatisation and separation of biogenic amines in wines. The system consists of a cation-exchange precolumn, a derivatisation coil and an analytical column, and a column-switching valve. The entire system can be easily automated. The method proved to be quantitative and sensitive. Limits of detection were below 0.05 mg l(-1) for all amines and linearity was preserved over the tested range (0.05-15 mg l(-1)). The method was applied to the analysis of red wines of different origin.     

The effect of water or salt solution on thin hydrophobic films

Hydrophobic films of polystyrene synthesized in bulk (PS) and by emulsion polymerization in the presence of the cationic surfactant cetyltrimethylammonium bromide (PS-CTAB) or the anionic surfactant sodium dodecyl sulfate (PS-SDS) were characterized by means of ellipsometry, contact angle measurements, and atomic force microscopy. Thin (approximately 65 nm) and thick (approximately 300 nm) films were spin-coated on hydrophilic silicon wafers. PS films presented scarcely tiny holes, while PS-CTAB and PS-SDS films presented holes and protuberances. The former were attributed to dewetting effects and the latter to surfactant clusters. The films were exposed to water or to a 0.1 mol/L NaCl solution for 24 h. Ex situ measurements evidenced strong topographic alterations after the exposure to the fluid. A model based on the diffusion of water (or electrolyte) molecules to the polymer/silcon dioxide interface through holes or defects on the film edges was proposed to explain the appearance of wrinkles and protuberances. In situ ellipsometric measurements were performed and compared with simulations, which considered either a water layer between a polymer and a silcon dioxide layer or an air layer between a polymer and water (medium). In the case of thin PS films, the ellipsometric angles evidenced a very thin (0.5-1.0 nm) air layer between water and the PS films. Upon increasing the PS film thickness, no air layer could be observed by ellipsometry. Regardless of the thickness, the ellipsometric data obtained for PS-CTAB and PS-SDS films did not indicate the presence of an air layer between them and the aqueous media. The dramatic changes in the topography of PS, PS-CTAB, and PS-SDS after immersion in salt solution were explained with proposed models. From a practical point of view, this study is particularly relevant because many hydrophobic polymers are used as substrates for biomedical purposes, where the physiological ionic strength is 0.15 mol/L NaCl.     

Trace analysis of heavy metals in high purity materials by helium-3 activation analysis

A method is described to determine traces of V, Fe, Ni, Zn, Nb and Mo in high purity matrices of niobium, tantalum and tungsten by non-destructive 14 MeV³He activation analysis. The influence of nuclear and γ-ray interferences in the determination of these elements is discussed.     

Micellar electrokinetic capillary chromatography method for direct determination of glucuronides of entacapone and its (Z)-isomer in human urine

This paper describes the validation of a micellar electrokinetic capillary chromatography method for the direct determination of the 3-O-glucuronides of entacapone and its (Z)-isomer, the main urinary metabolites of entacapone in humans. Entacapone is a novel drug which, as a potent inhibitor of catechol-O-methyltransferase (COMT), is used as an adjunct in the standard therapy of Parkinson's disease. The 3-O-glucuronide of another COMT inhibitor, nitecapone, was used as internal standard (I.S.). The validation experiments were performed by using spiked urine samples that were extracted with Sep-Pak C18 cartridges before analysis. Determinations were carried out in a buffer of pH 7.0 containing 25 mM of phosphate, 50 mM of borate and 20 mM of sodium dodecyl sulfate, and by applying 15 kV over a 67 cm (60 cm to the detector) x 75 microns fused-silica capillary. UV detection was at 335 nm. The validity of the method was assessed by investigating the identity of the analytes, selectivity, limit of quantitation, linearity, within-day precision, extraction recovery, between-day precision and accuracy, electroosmotic flow stability and analyte stability. The method proved to be reproducible, sufficiently selective and accurate. Extraction recoveries of the analytes were > 94%. The limit of quantitation (LOQ) was 2 micrograms/ml and the assay was linear in the range 2-150 micrograms/ml with correlation coefficients better than 0.999 for both glucuronides. The repeatability of the method, expressed as the ratio of corrected peak area of the analytes to that of I.S., gave RSD values of < 5% even at the LOQ. Between-day precision (RSD) was < 7.5% for both glucuronides at 7.5 micrograms/ml. Determination of the glucuronide concentrations in urine samples of 34 patients treated with entacapone either orally (200 mg) or intravenously (25 mg) showed the method to be suitable for monitoring the concentrations of the glucuronide of entacapone after both oral and intravenous administration and those of the glucuronide of its (Z)-isomer after oral administration. The limited long term stability of the system requires, however, frequent recalibration in applications involving long sample series.     

Über Struktur und Aktivität der den H2O2-Zerfall katalysierenden Cu2+-Komplexe. V. Vergleich der katalytischen Aktivität der Cu2+-Komplexe isomerer β-Hydroxythiophen-Derivate. Mettallionen und H2O2, 9. Mitteilung

The catalytic properties in H₂O₂ decomposition of the Cu²⁺-chelates of 2- Acetyl-3-hydroxy-thiophene (I) and 3-Acetyl-4-hydroxy-thiophene (II) have been investigated. Evidence is given that the catalytic activity of the chelates is a function of the respective bond orders of the α, β (I) and β, β′ (II) thiophene bonds of the chelate ring.     

Extent of exchange of bromine-82 with bromamine-T in strong acid medium

The extent of exchange of bromine-82 with bromamine-T in strong acid medium is low due to the formation of at lower acid concentrations and bromine at higher acidities. formation occurs over a narrow acid concentration range and is less stable than .     

Reactions of quaternized imidazo-quinazoline and-pyridopyrimidine with active methylene compounds

Summary Syntheses of 1-methylimidazo[1,2-c]quinazolinium iodide (3) and 1-methylimidazo[2,1-f]pyrido[3,2-d]pyrimidinium iodide (4) are described. These tricyclic compounds react with nucleophiles derived from active methylene compounds to give the corresponding open-chain enamines.

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Reaktionen von quaternisierten Imidazo-Chinazolinen und -Pyridopyrimidinen mit Verbindungen mit reaktiven Methylengruppen

Zusammenfassung Synthesen von 1-Methylimidazo[1,2-c]chinazoliniumjodid (3) und 1-Methylimidazo[2,1-f]pyrido[3,2-d]pyrimidiniumjodid (4) werden beschrieben. Diese tricyclischen Verbindungen reagieren mit einigen Carbanionen aus Verbindungen mit reaktiven Methylengruppen, wobei die offenkettigen Enamine entstehen.