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11.
E. Hartung K. Heide R. Naumann K. H. Jost W. Hilmer 《Journal of Thermal Analysis and Calorimetry》1983,26(2):277-284
In spite of numerous investigations the literature data on the thermal decomposition of borax are contradictory. On the basis of thermal, X-ray, gas analytical and optical investigations this fact can be attributed to the complex decomposition mechanism. After the release of about 8 mole water the reaction product is an X-ray amorphous phase, having the thermal behaviour of glass. From this glass sodium diborate (Na2O.2B2O3) crystallizes between 500–600? with further mass loss. Sodium diborate decomposes from about 700? incongruently yielding NaBO2 vapor and B2O3 glass phase. After evaporation of NaBO2 is completed the rate of evaporation of B2O3 increases considerably. 相似文献
12.
Rodella Cristiane B. Franco Roberto W.A. Magon Claudio J. Donoso Jose P. Nunes Luis A.O. Saeki Margarida J. Aegerter Michel A. Sargentelli Vagner Florentino Ariovaldo O. 《Journal of Sol-Gel Science and Technology》2002,25(1):83-88
Raman spectroscopy and Electron Paramagnetic Resonance (EPR) studies were performed on a series of V2O5/TiO2 catalysts prepared by a modified sol-gel method in order to identify the vanadium species. Two species of surface vanadium were identified by Raman measurements, monomeric vanadyls and polymeric vanadates. Monomeric vanadyls are characterized by a narrow Raman band at 1030 cm–1 and polymeric vanadates by two broad bands in the region from 900 to 960 cm–1 and 770 to 850 cm–1. The Raman spectra do not exhibit characteristic peaks of crystalline V2O5. These results are in agreement with those of X-ray Diffractometry (XRD) and Fourier Transform Infrared (FT-IR) previously reported (C.B. Rodella et al., J. Sol-Gel Sci. Techn., submitted). At least three families of V4+ ions were identified by EPR investigations. The analysis of the EPR spectra suggests that isolated V4+ ions are located in sites with octahedral symmetry substituting for Ti4+ ions in the rutile structure. Magnetically interacting V4+ ions are also present as pairs or clusters giving rise to a broad and structureless EPR line. At higher concentration of V2O5, a partial oxidation of V4+ to V5+ is apparent from the EPR results. 相似文献
13.
Roland Prewo Jost H. Bieri Subhendu Narayan Ganguly Max Viscontini 《Helvetica chimica acta》1982,65(3):1094-1099
The Configuration at C(6) of Natural 5,6,7,8-Tetrahydro-L-biopterin and of its Pentaacetate The structure of (6.R)-pentaacetyl-5,6,7,8-tetrahydro-L-biopterin, one of two diastereoisomers obtained by catalytic hydrogenation and subsequent acetylation of L-biopterin, has been determined by X-ray diffraction analysis. The space group is P212121, a=8,053(l), b=14,955(3), c= 21,502 (4) Å. The asymmetric unit contains one molecule of the biopterin derivative and one of ethyl acetate. The R-configuration can be assigned to C(6) by reference to the known configurations of the other asymmetric C-atoms. As hydrolysis of this diastereoisomer yields the natural 5, 6,7,8-tetrahydro-L-biopterin, the latter also possesses the (6 R)-configuration. 相似文献
14.
Conformational analysis of 5,6,7,8-tetrahydropteroic acid and 5,6,7,8-tetrahydro-L -folic acid In the 360-MHz-1H-NMR.-spectrum of (6R, S)-9,9-dideuterio-5, 6, 7, 8-tetrahydropteroic acid (racemic) (XIII) (AMX-System, Fig. 4) and (6R, S)-9,9-dideuterio-5, 6, 7, 8-tetrahydro-L -folic acid (diastereomeric) (XVI) the Ha–C(6) and Ha–C(7) show a vicinal coupling constant of 6,7 Hz and the Ha–C(6) and He–C(7) one of 3,2 Hz. The first coupling constant provides evidence for an approximate trans-diaxal arrangement of Ha–C(6) and Ha–C(7), and the second for a gauche conformation of Ha–C(6) and He–C(7). The tetrahydropyrazine ring in the racemic 5, 6, 7, 8-tetrahydropteroic acid (III) and in the diastereomeric 5, 6, 7, 8-tetrahydro-L -folic acid (XVII) exists therefore in a half-chair conformation with a pseudoequatorial position of the side chain at C(6) (Fig.5). 相似文献
15.
Summary The successful application of the formerly presented concept of diffusion-averaged molecular weight, Md, to vacuum residues of crude oils, or their fractions, is described. The samples for establishing the calibration curve, logDvs. logM, were crude oil fractions with polydispersities smaller than 1.1. In a surprisingly good approximation the calibration curve is independent of the origin of these fractions if 500<M<10000. The validity of our calibration curve was demonstrated with more than 10 crude oil residues and with some of their hydrogenation residues [2]. 相似文献
16.
K. Wagner W. Görner M. Hedrich P. Jost C. Segebade 《Analytical and bioanalytical chemistry》1998,362(4):382-386
The analysis of halogens in various matrices is described. Activation analysis with mainly high energy bremsstrahlung (PAA)
and pile neutrons (NAA) was applied. In the case of chlorine, fast procedures were worked out requiring not more than 100
min for one determination. The particular problems of fluorine analysis are discussed. The described techniques were applied
for the following cases: Determination of total chlorine resp. bromine in oil samples; determination of chlorine in wood,
glasses and TiN powders; determination of iodine in ZnSe single crystals using instrumental photoactivation.The limits of
detection are: (interference-free in μg/g) F: 0.03/–; Cl: 0.1/0.05; Br: 0.04/0.003 and I: 0.1/0.01 using PAA/NAA. Activation
analysis, being independent upon the chemical status of the analyte and usually less affected by blank problems has been found
to be a useful complement to conventional chemical analysis.
Received: 28 February 199 / Revised: 14 April 1998 / Accepted: 18 April 1998 相似文献
17.
Separation of the Diastereomers (6R)- and (6S)-5,6,7,8-Tetrahydro-L -biopterin The mixture of the diastereomers of the tetraacetylderivative IV of (6RS)-5,6,7,8-tetrahydro-L -biopterin could be separated by fractional crystallisation in methanol into the diastereomers IV A and IV B. Hydrolysis with hydrochloric acid gives the pure, diastereomeric, (6R)- and (6S)-5,6,7,8-tetrahydro-L -biopterins. 相似文献
18.
Esam Khalifa Hans-Jürg Furrer Jost H. Bieri Max Viscontini 《Helvetica chimica acta》1978,61(7):2739-2743
Regiospecific deuteriation of folic acid Introduction of a nitroso function at the N (10)-position of folic acid activates the C(9)-hydrogen atoms in such a way, that the exchange of H with D at this position, in NaOD-solution, is extremely facilitated. This fact is utilized in the synthesis of 9,9-dideuterio-folic acid (IV), 7,9,9-trideuterio-folic acid (VII) and 7-deuterio-folic acid (IX). These three products are necessary for the 1H-NMR.-spectroscopical determination of the conformation of 5,6,7,8-tetrahydrofolic acid and its derivatives. 相似文献
19.
20.
Murat Acemoglu Roland Prewo Jost Hans Bieri Conrad Hans Eugster 《Helvetica chimica acta》1984,67(1):175-183
Synthesis and X-Ray Structure of (6′RS,8′RS,2E)- and (6′RS,8′SR,2E)-3-Methyl-3-(2′,2′,6′-trimethyl-7′-oxabicyclo[4.3.0]non-9′-en-8′-yl)-2-propenal ([(5RS,8RS)- and (5RS,8SR)-5,8-Epoxy-5,8-dihydro-ionylidene]acetaldehyde) To check our previous spectroscopic assignments of the structures of trans- and cis-substituted furanoid end groups of carotenoid-5,8-epoxides, we now have synthesized the title compounds. An X-ray structure determination of a single crystal of the trans-isomer (±)- -10A is in agreement with the 1 H-NMR spectroscopic arguments: isomers with Δδ (H? C(7), H? C(8)) = 0.15–0.22 ppm and J > 1.4 for H? C(7) belong to the cis-series; Δδ in trans-compounds is < 0.07 ppm, and H? C(7) appears as a broad singulett. 相似文献