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11.
A correction method is proposed for the quantitative determination of stoichiometric ratios in porous materials by electron microprobe analysis. Analysis of this kind of material is complicated by an imperfect surface that can only be improved to some extent. The correction is based on a linear dependence (different for each element) of the analyses on a sum of weight concentrations of oxides. With this correction it is possible to use analyses affected by the imperfection of the surface with much better confidence compared to common normalisation. An example is presented for a series of ceramic superconductors Bi2.1(SrCa)2.9Cu2O8+. 相似文献
12.
Giovanna Marini-Bettòlo Soumya P. Sahoo Gerald A. Poulton Thomas Y.R. Tsai Karel Wiesner 《Tetrahedron》1980,36(6):719-721
Some years ago an empirical rule, which allows the prediction of product stereochemistry in cis-photocycloaddition reactions of α,β-unsaturated ketones and olefins was tentatively proposed. Several additional examples, both selected from the literature and synthesized in our laboratory, seem to strengthen the validity of the rule. 相似文献
13.
Quanwei?Yu Jens?Fr?mmel Thomas?WolffEmail author Karel?Procházka 《Colloid and polymer science》2004,282(9):1039-1043
Solid stoichiometric complexes of [3,12]-ionene and dodecyl sulfate form upon reaction of the bromide of the ionene and the silver salt of dodecyl sulfate in methanol. IR, DSC, and TG investigations indicated that the solid complexes are stable between 30 and 120 °C. TG and DSC also showed that the complexes easily take up water at ambient conditions. These samples are optically isotropic. When exposed to an increased humidity they exhibit optical anisotropy, i.e., birefringence, which is caused by the formation of a hexagonal mesogenic phase. Mesogenicity is necessarily accompanied by a further uptake of water (4–5 H2O molecules per ionic unit), which is dependent on the relative humidity. The phase behavior as a function of temperature and controlled relative humidity was studied using birefringence measurements and polarizing microscopy. 相似文献
14.
Klika KD Imrich J Danihel I Böhm S Kristian P Hamul'aková S Pihlaja K Koch A Kleinpeter E 《Magnetic resonance in chemistry : MRC》2005,43(5):380-388
The configuration and dynamic behavior of O-allyl-S-methyl-N-(acridin-9-yl)iminothiocarbonate (1) and its S-allyl-O-methyl regioisomer (2) were studied using quantum chemical calculations and by applying a novel graphical method to scatter maps obtained from MD simulations for evaluation of an NOE-weighted internuclear distance (r(NOE)). Energy calculations indicated that the Z configuration was predominant for each compound and, further, this was supported both by the calculated chemical shifts and the r(NOE). Both N-inversion- and rotation-type transition-state structures were also calculated for the E/Z isomerization process, the results indicating that the preferred interconversion mechanism for 1 is N-inversion, but contrastingly, interconversion via rotation is equally as probable as N-inversion for 2. This supports the notion that one or the other or both pathways can be active and each system needs to be assessed on a case-by-case basis. 相似文献
15.
Herein, we report the first use of chiral alkaloid brucine to synthesize novel porphyrin-brucine conjugate capable of acting as a gelator of methanol and acetonitrile at extremely low level of concentration. The synthesis, characterization and spectral properties of gelator based on a novel structural motif, quaternized alkaloid conjugates, are described. Different spectroscopic methods (1H NMR spectroscopy, Raman and infrared spectroscopy, and spectroscopy of electronic and vibrational circular dichroism) were used for characterization of the prepared organogel. The aggregation of the gelator studied by UV-vis spectroscopy and electronic circular dichroism showed the formation of chiral J-aggregates in water and water-methanol (1:1) mixture. A new methodology for the determination of functional groups involved in gel formation based on vibrational circular dichroism is presented. 相似文献
16.
17.
Meersman F Dirix C Shipovskov S Klyachko NL Heremans K 《Langmuir : the ACS journal of surfaces and colloids》2005,21(8):3599-3604
In a cellular environment, the presence of macromolecular cosolutes and membrane interfaces can influence the folding-unfolding behavior of proteins. Here we report on the pressure stability of alpha-chymotrypsin in the ternary system bis(2-ethylhexyl)sodium sulfosuccinate-octane-water using FTIR spectroscopy. The ternary system forms anionic reverse micelles which mimic cellular conditions. We find that inclusion of a single protein molecule in a reverse micelle does not alter its conformation. When pressurized in bulk water, alpha-chymotrypsin unfolds at 750 MPa into a partially unfolded structure. In contrast, in the ternary system, the same pressure increase induces a random coil-like unfolded state, which collapses into an amorphous aggregate during the decompression phase. It is suggested that the unfolding pathway is different in a cell-mimicking environment due to the combined effect of multiple factors, including confinement. A phase transition of the reverse micellar to the lamellar phase is thought to be essential to provide the conditions required for unfolding and aggregation, though the unfolding is not a direct result of the phase transition. Our observations therefore suggest that membranes may cause the formation of alternative conformations that are more susceptible to aggregation. 相似文献
18.
Wu L Lemr K Aggerholm T Cooks RG 《Journal of the American Society for Mass Spectrometry》2003,14(2):152-160
The kinetic method is applied to differentiate and quantify mixtures of isomeric tripeptides based on the competitive dissociations of divalent metal ion-bound clusters in an ion trap mass spectrometer. This methodology is extended further to determine compositions of ternary mixtures of the isomers Gly-Gly-Ala (GGA), Ala-Gly-Gly (AGG), and Gly-Ala-Gly (GAG). This procedure also allows to perform chiral quantification of a ternary mixture of optical isomers. The divalent metal ion Ca(II) is particularly appropriate for isomeric distinction and quantification of the isobaric tripeptides Gly-Gly-Leu/Gly-Gly-Ile (GGL/GGI). Among the first-row transition metal ions, Cu(II) yields remarkably effective isomeric differentiation for both the isobaric tripeptides, GGI/GGL using GAG as the reference ligand, and the positional isomers GAG/GGA using GGI as the reference ligand. This is probably due to agostic bonding: alpha-agostic bonding occurs between Cu(II) and GAG and beta-agostic bonding between Cu(II) and GGI, each produces large but different steric effects on the stability of the Cu(II)-bound dimeric clusters. These data form the basis for possible future quantitative analyses of mixtures of larger peptides such as are generated, for example, in combinatorial synthesis of peptides and peptide mimics. 相似文献
19.
Karel Obruba 《Mikrochimica acta》1961,49(5):801-805
Zusammenfassung Es wurde eine Mikromethode für die Bestimmung von Oxyäthylengruppen ausgearbeitet. Das Prinzip der Methode beruht darauf, daß Äthylenoxydverbindungen beim Sieden mit Jodwasserstoffsäure neben anderen Produkten eine äquivalente Menge Jod liefern, die durch Titration mit Natriumthiosulfat bestimmt wird.Es wurde eine einfache Apparatur erprobt, die selbst geringe Jodverluste verhindert.
Herrn Dipl.-Ing.J. Simandl danken wir für die anregende Diskussion und die Überlassung von oxyäthylierten Aminen. Herrn Dipl.-Ing.J. Kami danken wir für die Überlassung von Proben reiner Polyglykoläther. Die Wasserbestimmung nachK. Fischer führte HerrZ. Netuil aus. 相似文献
Summary A micromethod has been worked out for the determination of oxyethylene groups. Its principle is based on the fact that on boiling with hydriodic acid, the ethylene oxide compounds yield, along with other products, an equivalent quantity of iodine, which can be measured by titration with sodium thiosulfate.A simple apparatus has been tested, which prevents the loss of even slight amounts of iodine.
Résumé On a mis au point une microméthode pour doser les groupes oxéthyles. Le principe de la méthode repose sur le fait que les composés de l'oxyde d'éthylène, portés à l'ébullition avec de l'acide iodhydrique, libèrent, à côté d'autres produits, une quantité équivalente d'iode que l'on titre par le thiosulfate de sodium.On a expérimenté un appareil simple qui empêche les pertes en iode, même faibles.
Herrn Dipl.-Ing.J. Simandl danken wir für die anregende Diskussion und die Überlassung von oxyäthylierten Aminen. Herrn Dipl.-Ing.J. Kami danken wir für die Überlassung von Proben reiner Polyglykoläther. Die Wasserbestimmung nachK. Fischer führte HerrZ. Netuil aus. 相似文献
20.
Marian Čerňanský Přemysl Vaněk Karel Král Radmila Krupková 《Monatshefte für Chemie / Chemical Monthly》2002,133(6):799-806
Summary. In this investigation the crystallization of PbTiO3 upon annealing of pure nanopowders and PbTiO3–SiO2 (1:1 v/v) nanocomposite powders prepared by the sol-gel technique was studied. Using X-ray diffraction phase analysis, the
start of PbTiO3 crystallization in pure PbTiO3 powders was detected at 400°C. Distinct crystallization of PbTiO3 in PbTiO3–SiO2 nanocomposites starts at 700°C, whereas SiO2 remains amorphous. There are indications that an interface interaction between the PbTiO3 and the SiO2 phase plays an important role in hindering the crystallization of PbTiO3. The particle size (size of coherently scattering regions) was estimated from the broadening of the X-ray diffraction line
profiles. The average size of PbTiO3 nanocrystallites increases with temperature and time of annealing, the influence of temperature being more significant than
that of the annealing time. Differential scanning calorimetry confirmed the results of the X-ray diffraction with respect
to the start of the crystallization. Laser beam scattering and scanning electron microscopy provided the statistical distribution
of the grain size and the morphology of the powder grains, showing that each grain of the powders contains several nanocrystallites
(coherently scattering regions).
Received October 4, 2001. Accepted (revised) December 14, 2001 相似文献