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Es wird eine neue pH-Indikatormethode zur Harnstoffbestimmung beschrieben. Die Methode zeichnet sich durch gute Präzision und Richtigkeit aus. Der aus 150 Wertepaaren ermittelte Korrelationskoeffizient beträgt mit der DAM-Methode r = 0,9970 und mit der GLDH-Methode r = 0,9971. Die Richtigkeitsversuche charakterisieren die Methode als praxisgerecht. Wegen der schnellen Durchführung ist die Methode auch für Notfall-Laboratorien zu empfehlen.
By means of differential thermoanalysis, the miscibility of the main polar tetraether lipid of Thermoplasma acidophilum with two ester lipids, dipalmitoyl phosphatidylcholine and dipalmitoyl phosphatidylglycerol, resp., in the presence of excess water was studied. It is shown that with increasing fraction of tetraether lipid in the mixture, the transition range of dipalmitoyl phosphatidylcholine is broadened and the temperature of the maximum heat flow (Tm) is shifted to lower temperatures; furthermore, the enthaply change (ΔH) of the transition declines. Similar results were obtained with mixtures of tetraether lipid with dipalmitoyl phosphatidylglycerol. It is therefore concluded that the main polar tetraether lipid of Thermoplasma acidophilum , which essentially forms monomolecular layers, is able to form stable common phases with bilayer-forming ester lipids. Miscibility of the tetraether lipid with dipalmitoyl phosphatidylglycerol, which are both monovalent anions at neutral pH, is also observed in the presence of high proton or calcium ion concentrations.
The bipolar main tetraether lipid (MPL) of Thermoplasma acidophilum has been shown to form typical liquid expanded films at the air-water interface. The limiting molecular area at the collaps pressure is approximately Ac=73 Å2 per molecule. Monopolar aiphytanyl diether lipids were found to occupy the same area at high surface pressure as MPL. Thus, it was concluded that in the monofilm only one of the two polar headgroups of the MPL molecules is hydrated, i.e. that the single MPL molecules arc oriented upright. The packing properties of MPT. in the monofilm are determined by the properties of the branched alkyl chains only; the polar head groups do not contribute to the space requirement in the film. The collaps pressure of the MPL film is approximately 39 mN m-1 at 8°C. At a surface pressure of π = 30 mN m-1 and 20 °C the film is stable for many hours.
The recently developed stereospecific sodium salt glycosylation procedure has been successfully applied to the synthesis of the β-ᴅ-2′-deoxyribofuranosides of benzimidazole, 5,6-dihalogeno benzimidazoles, and some 2-substituted analogues in high yield. The 5,6-dibromo analogue was obtained by bromination of the parent nucleoside. These have all been characterized by spectroscopic methods, including 1H NMR, which permitted analyses of their solution conformations and comparison with those of the corresponding ribofuranosides. Some biological aspects, including preliminary results on cytotoxicity and antiviral activity, are briefly considered.
The marine diatoms Bellerochea yucatanensis and Thalassiosira rotula were grown at different salinities (20/25, 35, and 40/45‰ salinity (S), respectively) under normal air (0.035 vol.% CO2). No significant variations in the percentage of gross photosynthetic products (e.g. total amino acids, sugar phosphates) were found as a function of salinity during growth. The bulk of the soluble 14C-radioactivity was detected in amino acids. 14C-labelling of glutamine increased markedly with salinity. Low salt - grown algae are characterized by enhanced amino acid pools, mainly of aspartic acid, asparagine and glutamine. It was found that the tested amino acids are not involved in osmoregulation.
The cyanobacterium Anabaena flos-aquae (strain 1444) grown at different intensities of white light (900, 3500 and 30000 lux) showed changes in the content and composition of the pigments. Phycocyanin was more affected by high light conditions during growth than chlorophyll a. In comparison to in low white light grown cyanobacteria number of phycobilisomes and thylakoids decreased under strong light. A diminution of 14CO2 fixation, total amino acid content, glutamic acid and glutamine pools was found in strong white light grown cells. Under these conditions the majority of 14C-labelling was measured in sugar phosphates. After pressure treatment a marked increase of 14C-incorporation into amino acids could be obtained. Results were discussed with reference to regulation of buoyancy in Anabaena flos-aquae.
The reduction potentials of 40 aromatic nitro compounds Rπ(NO2)n with Rπ = benzene, naphthalene, anthracene, fluorene and carbazole and n = 1 to 4 nitro groups are determined by cyclic voltammetry in DMF under aprotic conditions. The perturbation by the strongly electron accepting substituents can be rationalized via correlation with HMO eigenvalues. Based on reversibility criteria, the electrochemical behaviour is discussed and the compounds are classified with respect to reversible or irreversible one-electron transfer as well as up to 4 (quasi)-reversible reduction steps. The CV data measured can be used to predict redox reactions of aromatic nitro compounds in inert solvents.
The synthesis of [Ph4As+]2[Cl4Re(NS)(NSCl)2-] · CH2Cl2 (4) from the reaction of S4N4, Cl4ReN, and Ph4AsCl is reported. CH2Cl2 is used as solvent. The reaction of S4N4 with Re2Cl10 similarly leads to the salt [Ph4As+][Cl2ReNS-] (5) in a smaller yield. 4 crystallizes in the triclinic space group P1̅ with Z = 2, a - 10.434(2), b = 12.1454(6), c = 21.125(2) Å, a = 81.210(6), β = 86.70(1), γ = 76.624(8)°.
The 1:2 molecular complexes formed from 1,4-phenylenebis(dimethylphosphane) and boranes, trialkyl-aluminum and -gallium have been reduced by potassium in THF in the presence of a K+- complexing crown ether. The bis(borane) complex anion radicals proved to be quite persistent, whereas corresponding aluminum radical complexes could only be observed below 240 K. The bis(trimethylgallium) complex gave gallium metal on reduction with potassium. An ESR spectroscopic comparison with the anion radicals of the free ligand, of corresponding chalcogenides, imines and phosphonium salts demonstrates negligible effects of P-complexation on the π spin distribution but high sensitivity of the 31P coupling constant towards coordination of electrophiles at the basic P(III) centers