On the synthesis of geometric isomers of 2-methyl (or phenyl)-4-[α-arylethylidene]-5(4H)-oxazolones

Several Z-2-methyl(or phenyl)-4-[α-arylethylidene]-5(4H)-oxazolones 3Z, 4Z were prepared. The results obtained were compared by diazomethane insertion and condensation procedure. In order to synthesize E-2-phenyl-4-[α-arylethylidene]-5(4H)-oxazolones 4E hydrogen bromide isomerization in dry benzene was used.     

Thermogravimetric analysis of polycarbonates and polythiocarbonates from diphenols with methyl groups

The thermal behaviour of polycarbonates and polythiocarbonates derived from biphenols with methyl groups in the aromatic rings was studied by dynamic thermogravimetry. The thermal degradation temperatures (TDT) were determined, showing that polythiocarbonates are more stable than the corresponding polycarbonates. The kinetic parameters of the thermal decomposition were determined by using the Arrhenius relationship, and showed two steps for the degradation of the polycarbonates, the first being a zero-order process and the second having first-order kinetics; the steps were associated with two different reaction mechanisms. Polythiocarbonates degraded according to first-order kinetics.     

Resolution of ternary mixtures of nitrofurantoin, furazolidone and furaltadone by application of Partial Least Squares analysis to the differential pulse polarographic signals

The abilities of the Partial Least Squares (PLS) methods in the resolution of ternary mixtures of organic compounds (furaltadone, furazolidone and nitrofurantoin) by using their differential pulse polarographic (DPP) signals are reported. The applicability of these methods to resolve very overlapped peaks whose E(p) also changes with concentration is demonstrated. The analysis of both synthetic and real samples has been made with satisfactory results. The relative error of prediction (REP) is 8.7% for FD, 7.7% for FZ and 6.7% for NF by application of the PLS-2 method.     

Rapid spectrophotometric determination of chlorate with dimedone bisthiosemicarbazone monohydrochloride

Summary Dimedone bisthiosemicarbazone monohydrochloride has been examined to evaluate its usefulness as a reagent for rapid and sensitive Spectrophotometric determination of chlorate (0.5–5.0 ppm) by oxidation of the reagent in 70% perchloric acid medium and measurement of the yellow product. The molar absorptivity at 417 nm is 1.86×10⁴ l·mole^–1·cm^–1. The relative standard deviation is 1.6% for 2.5 ppm of chlorate.

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Spektropbotometrische Bestimmung von Chlorat mit Dimedonbisthiosemicarbazon-monocblorhydrat (I)

Zusammenfassung Die Verwendbarkeit von I als Reagens für die rasche und empfindliche spektrophotometrische Bestimmung von 0,5–5,0 ppm Chlorat durch Oxydation von I in 70%iger Perchlorsäure und Messung des gelben Reaktionsproduktes wurde untersucht. Die molare Absorptivität bei 417 nm beträgt 1,86×10⁴ l·mol^–1·cm^–1. Die relative Standardabweichung beträgt 1,6% für 2,5 ppm Chlorat.

     

Phototoxic effects of Hypericum extract in cultures of human keratinocytes compared with those of psoralen

Extracts of Hypericum perforatum (St. John's wort) are used in the treatment of depression. They contain the plant pigment hypericin and hypericin derivates. These compounds have light-dependent activities. In order to estimate the potential risk of phototoxic skin damage during antidepressive therapy, we investigated the phototoxic activity of hypericin extract using cultures of human keratinocytes and compared it with the effect of the well-known phototoxic agent psoralen. The absorbance spectrum of our Hypericum extract revealed maxima in the whole UV range and in parts of the visible range. We cultivated human keratinocytes in the presence of different Hypericum concentrations and irradiated the cells with 150 mJ/cm2 UVB, 1 J/cm2 UVA or 3 h with a white light of photon flux density 2.6 mumol m-2 s-1. The determination of the bromodeoxyuridine incorporation rate showed a concentration- and light-dependent decrease in DNA synthesis with high hypericin concentrations (> or = 50 micrograms/mL) combined with UVA or visible light radiation. In the case of UVB irradiation a clear phototoxic cell reaction was not detected. We found phototoxic effects even with 10 ng/mL psoralen using UVA with the same study design as in the case of the Hypericum extract. These results confirm the phototoxic activity of Hypericum extract on human keratinocytes. However, the blood levels that are to be expected during antidepressive therapy are presumably too low to induce phototoxic skin reactions.     

Multiple Keys for a Single Lock: The Unusual Structural Plasticity of the Nucleotidyltransferase (4′)/Kanamycin Complex

The most common mode of bacterial resistance to aminoglycoside antibiotics is the enzyme‐catalysed chemical modification of the drug. Over the last two decades, significant efforts in medicinal chemistry have been focused on the design of non‐ inactivable antibiotics. Unfortunately, this strategy has met with limited success on account of the remarkably wide substrate specificity of aminoglycoside‐modifying enzymes. To understand the mechanisms behind substrate promiscuity, we have performed a comprehensive experimental and theoretical analysis of the molecular‐recognition processes that lead to antibiotic inactivation by Staphylococcus aureus nucleotidyltransferase 4′(ANT(4′)), a clinically relevant protein. According to our results, the ability of this enzyme to inactivate structurally diverse polycationic molecules relies on three specific features of the catalytic region. First, the dominant role of electrostatics in aminoglycoside recognition, in combination with the significant extension of the enzyme anionic regions, confers to the protein/antibiotic complex a highly dynamic character. The motion deduced for the bound antibiotic seem to be essential for the enzyme action and probably provide a mechanism to explore alternative drug inactivation modes. Second, the nucleotide recognition is exclusively mediated by the inorganic fragment. In fact, even inorganic triphosphate can be employed as a substrate. Third, ANT(4′) seems to be equipped with a duplicated basic catalyst that is able to promote drug inactivation through different reactive geometries. This particular combination of features explains the enzyme versatility and renders the design of non‐inactivable derivatives a challenging task.     

Defect clustering in double doped fluorite crystals with Lu and Gd

Abstract

Solid solutions Ca¹ x-^yLu^xGd^y F_2+x+y for 10^?4 ≤ x ≤ 2 × 10^?2 and y=0.0001 have been studied by electron paramagnetic resonance (EPR) and ionic thermal currents (ITC). It has been found that the ITC spectrum from 77 to 420 K is very weak and the main peak is attributed to the relaxation of both Lu³⁺-F^? _x and Gd³⁺F^? _i nn dipoles. No polarizable clusters are present in the temperature range explored here. The EPR spectra show the presence of Gd³⁺ tetragonal and cubic centers due to the local and non local compensation, respectively. The continuous decrease in the molar fraction of Gd³⁺ tetragonal centers together with the low concentration of Lu nn dipoles is an evidence of the existence at these low and intermediate concentrations of large clusters such as the cubo-octahedral hexamer which has been proposed for CaF₂ crystals very highly doped with small trivalent cations.