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131.
B. Lehmann M. Wahlen R. Zumbrunn H. Oeschger W. Schnell 《Applied Physics A: Materials Science & Processing》1977,13(2):153-158
The feasibility of IR laser spectroscopy as a technique for the measurement of small abundances of stable and radioactive
isotopes has been examined. Theoretical considerations and first experimental results with two laser systems are presented:
1) Coincidences between emission lines of a CO2-laser and absorption lines of13C-substituted ethylene can be used to determine the13C-concentration of C2H4. 2) A tunable PbS-diode laser emitting in the 4.3 μm-spectral region of the rotation-vibration bands of CO2 can be used to determine abundances of12C,13C,16O,17O and18O in small samples of CO2. With optimized performance, sensitivities up to 10−9–10−10 seem possible, and for higher abundances an accuracy of 10−3. This should allow geophysical isotope studies to be performed and it is hoped that the technique will eventually be applicable
to measuring the activity of long-lived radioisotopes. 相似文献
132.
High‐Resolution Rotational Spectroscopy Study of the Smallest Sugar Dimer: Interplay of Hydrogen Bonds in the Glycolaldehyde Dimer
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Sabrina Zinn Dr. Chris Medcraft Dr. Thomas Betz Priv.‐Doz. Dr. Melanie Schnell 《Angewandte Chemie (International ed. in English)》2016,55(20):5975-5980
Molecular recognition of carbohydrates plays an important role in nature. The aggregation of the smallest sugar, glycolaldehyde, was studied in a conformer‐selective manner using high‐resolution rotational spectroscopy. Two different dimer structures were observed. The most stable conformer reveals C2‐symmetry by forming two intermolecular hydrogen bonds, giving up the strong intramolecular hydrogen bonds of the monomers and thus showing high hydrogen bond selectivity. By analyzing the spectra of the 13C and 18O isotopologues of the dimer in natural abundance, we could precisely determine the heavy backbone structure of the dimer. Comparison to the monomer structure and the complex with water provides insight into intermolecular interactions. Despite hydrogen bonding being the dominant interaction, precise predictions from quantum‐chemical calculations highly rely on the consideration of dispersion. 相似文献
133.
Ojars Y A. Neilands Ineta Sudmale Barbara Schnell Krassimira Georgieva Thomas Kappe 《Journal of heterocyclic chemistry》1998,35(1):157-160
The title compounds are obtained by three different methods. The aminothiocarbonylthiolation of barbituric acids 1 and aminouracil ( 5 ) can be accomplished in one step by reaction with thiuram disulfides in the presence of potassium carbonate. On the other hand, compounds 4 can be obtained via the salt of chloro derivative 2 or the corresponding iodonium ylides 3 . The aminouracil derivative 7 was obtained in a similar fashion from 5 directly or via iodonium betaine 6 . 相似文献
134.
Papadopoulos P Floudas G Schnell I Klok HA Aliferis T Iatrou H Hadjichristidis N 《The Journal of chemical physics》2005,122(22):224906
We report on the origin of the liquid-to-glass transition in a series of oligopeptides of gamma-benzyl-L-glutamate up to the polymer (PBLG), and in Poly-Z-L-lysine (PZLL) and Polyglycine (PGly) using dielectric spectroscopy as a function of temperature and pressure. We show that temperature is the dominant control variable of the dynamics associated with the peptidic "glass transition." This is an intrinsic feature of the peptide dynamics, irrespective of the type of amino acid and of the peptide secondary structure. The influence of the type of secondary structure (alpha helix vs beta sheet) on the liquid-to-glass dynamics is discussed. 相似文献
135.
Zusammenfassung Ein Detektor wird beschrieben, der durch elektrische Funkenentladung in Edelgasatmosphäre weniger als 10–8 g flüchtiger Substanzen wie Hexan oder Benzol nachzuweisen gestattet.
A sensitive discharge detector for gaschromatography
Summary The detector described allowes the detection of less than 10–8 g of volatile substances like hexane or benzene by means of electric spark discharge in noble gas atmosphere (Argon).相似文献
136.
Victoria L. Heywood Thomas P. J. Alford Julius J. Roeleveld Siebe J. Lekanne Deprez Abraham Verhoofstad Jarl Ivar van der Vlugt Srgio R. Domingos Melanie Schnell Anthony P. Davis Tiddo J. Mooibroek 《Chemical science》2020,11(20):5289
We report the direct observation of tetrel bonding interactions between sp3-carbons of the supramolecular synthon 3,3-dimethyl-tetracyanocyclopropane (1) and tetrahydrofuran in the gas and crystalline phase. The intermolecular contact is established via σ-holes and is driven mainly by electrostatic forces. The complex manifests distinct binding geometries when captured in the crystalline phase and in the gas phase. We elucidate these binding trends using complementary gas phase quantum chemical calculations and find a total binding energy of −11.2 kcal mol−1 for the adduct. Our observations pave the way for novel strategies to engineer sp3-C centred non-covalent bonding schemes for supramolecular chemistry.sp3-C⋯THF tetrel bonding was observed in the crystalline state and in the gas phase. Density functional calculations revealed interaction energies up to −11.2 kcal mol−1 and showed that these adducts are held together mainly by electrostatics. 相似文献
137.
E. Schnell 《Monatshefte für Chemie / Chemical Monthly》1965,96(4):1302-1307
Zusammenfassung Die Absorption charakteristischer Röntgenstrahlung leichter Elemente wird zum qualitativen Nachweis von Halogen und Schwefel in gaschromatographisch getrennten, flüchtigen Verbindungen herangezogen.
Mit 3 Abbildungen
Frau Professor Dr.Erika Cremer zum Geburtstag gewidmet. 相似文献
The absorption of characteristic X-rays of light elements serves as a qualitative detector for halogens and sulfur in volatile compounds separated by gas chromatography.
Mit 3 Abbildungen
Frau Professor Dr.Erika Cremer zum Geburtstag gewidmet. 相似文献
138.
Schlegel B Laggner C Meier R Langer T Schnell D Seifert R Stark H Höltje HD Sippl W 《Journal of computer-aided molecular design》2007,21(8):437-453
The human histamine H(3) receptor (hH(3)R) is a G-protein coupled receptor (GPCR), which modulates the release of various neurotransmitters in the central and peripheral nervous system and therefore is a potential target in the therapy of numerous diseases. Although ligands addressing this receptor are already known, the discovery of alternative lead structures represents an important goal in drug design. The goal of this work was to study the hH(3)R and its antagonists by means of molecular modelling tools. For this purpose, a strategy was pursued in which a homology model of the hH(3)R based on the crystal structure of bovine rhodopsin was generated and refined by molecular dynamics simulations in a dipalmitoylphosphatidylcholine (DPPC)/water membrane mimic before the resulting binding pocket was used for high-throughput docking using the program GOLD. Alternatively, a pharmacophore-based procedure was carried out where the alleged bioactive conformations of three different potent hH(3)R antagonists were used as templates for the generation of pharmacophore models. A pharmacophore-based screening was then carried out using the program Catalyst. Based upon a database of 418 validated hH(3)R antagonists both strategies could be validated in respect of their performance. Seven hits obtained during this screening procedure were commercially purchased, and experimentally tested in a [(3)H]N(alpha)-methylhistamine binding assay. The compounds tested showed affinities at hH(3)R with K ( i ) values ranging from 0.079 to 6.3 muM. 相似文献
139.
Schnell M Lützow P Veldhoven Jv Bethlem HL Küpper J Friedrich B Schleier-Smith M Haak H Meijer G 《The journal of physical chemistry. A》2007,111(31):7411-7419
A linear AC trap for polar molecules in high-field seeking states has been devised and implemented, and its characteristics have been investigated both experimentally and theoretically. The trap is loaded with slow 15ND3 molecules in their ground state (para-ammonia) from a Stark decelerator. The trap's geometry offers optimal access as well as improved loading. We present measurements of the dependence of the trap's performance on the switching frequency, which exhibit a characteristic structure due to nonlinear resonance effects. The molecules are found to oscillate in the trap under the influence of the trapping forces, which were analyzed using 3D numerical simulations. On the basis of expansion measurements, molecules with a velocity and a position spread of 2.1 m/s and 0.4 mm, respectively, are still accepted by the trap. This corresponds to a temperature of 2.0 mK. From numerical simulations, we find the phase-space volume that can be confined by the trap (the acceptance) to be 50 mm3 (m/s)3. 相似文献
140.
We consider a diffusion model with limit cycle reaction functions. In an unbounded domain, diffusion spreads pattern outwards
from the source. Convection adds instability to the reaction–diffusion system. We see the result of the instability in a readiness
to create pattern. In the case of strong convection, we consider that the first-order approximation may be valid for some
aspects of the solution behaviour. We employ the method of Riemann invariants and rescaling to transform the reduced system
into one invariant under parameter change. We carry out numerical experiments to test our analysis. We find that most aspects
of the solution do not comply with this, but we find one significant characteristic which is approximately first order. We
consider the correspondence of the Partial Differential Equation with the Ordinary Differential Equation along rays from the
initiation point in the transformed system. This yields an understanding of the behaviour. 相似文献