Die Trennung der Bernsteins?ure von Weinstein- und Milchs?ure

Ohne Zusammenfassung     

Interpretation of scoring functions using 3D molecular fields. Mapping the diacyl-hydrazine-binding pocket of an insect ecdysone receptor

A method is presented for the interpretation of receptor docking score values (rough measures of binding affinities) of ligands in terms of 3D molecular field interaction contributions. The FlexX and FlexX-Pharm methods were used to dock the structures of designed sets of ligands into the ligand-binding pocket of a selected receptor. In the next step the relationship was investigated between the FlexX and CScore scores and 3D molecular fields obtained for the docked conformations of the ligands, using the CoMFA (Comparative Molecular Field Analysis) and CoMSIA (Comparative Molecular Similarity Indices Analysis) methods. The approach yielded highly significant CoMFA and CoMSIA models demonstrating that a high portion of the variance in the docking score values of the ligands can be explained by steric, electrostatic, hydrophobic, and hydrogen bond donor and acceptor molecular field interaction contributions. The approach was exemplified by using the crystal structure of the ligand-binding domain of the ecdysone receptor (EcR) of the moth Heliotis virescens as well as virtual molecule libraries of analogues of known diacyl-hydrazine (DAH) type ecdysteroid agonists. By docking appropriately designed virtual compound libraries into the DAH binding pocket of EcR followed by CoMFA and CoMSIA of the docked conformations, hitherto unexplored regions of the receptor cavity could be mapped. By mapping the significant molecular field interaction contributions onto the model of the receptor-ligand complex, important receptor-ligand interactions could be highlighted that may help the design of novel highly scored receptor ligands. An advantage of the method is that no experimental biological activity data are required to exhaustively map the receptor-binding site.     

Combined electrospray ionization source with a velocity map imaging spectrometer for studying large gas phase molecular ions

We present a new compact and versatile experimental set-up that has been designed to perform electron and ion imaging experiments on large multiply charged gas phase molecular and cluster species. It combines an electrospray ionization source, a quadrupole mass filter guiding ion optics and a velocity map imaging spectrometer. Characterization of the spectrometer has been performed on atomic ions. Results obtained on molecular species (stilbene 420 dianions) demonstrate the possibility offered by this experimental set-up.     

Decay of C(60) by delayed ionization and C(2) emission: Experiment and statistical modeling of kinetic energy release

C(60) molecules highly excited in the nanosecond regime decay following ionization and dissociation by emitting a series of carbon dimers, as well as other small fragments if excitation is strong enough. The fragmentation mass spectrum and kinetic energy release of all charged fragments obtained in these experiments are interpreted within the framework of the Weisskopf theory, using a realistic Monte Carlo procedure in which the rates of all relevant decay channels are modeled using Arrhenius expressions. Comparison between the measurements and the simulated spectra allows the distribution of deposited energy to be accurately estimated. The dependence of the fragment kinetic energies on the laser fluence, found in the simulation but not observed in the experimental results, indicates that the small fragments are not necessarily emitted from small fullerenes resulting from C(60) by sequential decay. Rather, direct multifragmentation of C(60) is invoked to interpret the observed patterns. The possible role of post-ionization of neutral emitted fragments is discussed.     

Synchrotron radiation X-ray scattering and diffraction: Applications to structural research in biology

The synchrotron radiation emitted in the X-ray region by high energy particle accelerators constitutes a unique source for research on the structural dynamics of biological systems. The reasons why are described.A summary of how the radiation is extracted, used and detected is given.Examples from recent applications provide an illustration of the range of applicability of these techniques.     

Capacité calorifique molaire du composé Bi.4 Te.6 dans les états solide et liquide

The heat capacities of Bi.4Te. 6 in the solid and liquid states are calculated from the results of the experimental drop calorimetric method, and the heat of fusion of the compound is deduced.

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Zusammenfassung Die Wärmekapazitäten von Bi.4Te. 6 in fester und flüssiger Phase werden aus experimentellen Daten berechnet, die mit der tropfenkalorimetrischen Methode erhalten wurden. Die Schmelzwärme der Verbindung wird abgeleitet.

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« » Bi₄Te₆ , .

     

Influence of the ion-pseudopotential on the electronic shell structure and the dipole strength distribution in metal clusters

Using the pseudo-Hamiltonian technique we investigate, through complete self-consistent ground-state calculations, nonlocal ion-pseudopotential effects on the dipole strength distribution and the electronic shell structure of alkali clusters. The results obtained for sodium clusters are compared to the predictions of the standard jellium model (JM) and to experiments. Some wrong JM-predictions — shift of some low magic sizes, insufficient redshift of the surface plasmon frequency relative to the Mie frequency — are corrected, but a noticeable discrepancy remains with regard to the supershell structure. In the second part of this paper we restore the reliability of the pseudo-Hamiltonian approximation, on which some doubts have been recently cast, because of incorrect predictions concerning the bulk properties of lithium. From a careful analysis of the nonlocal effects in a smoothed ionic background, we show that a specific pseudo-Hamiltonian parametrization has to be systematically selected for ensuring maximum accuracy. We successfully test the suitability of this parametrization in the case of lithium clusters, through a comparison with recently published results obtained using accurate norm-conserving nonlocal pseudopotentials.     

Zur Bestimmung der Glyzerinphosphors?ure in der Milch

Ohne Zusammenfassung     

Optical absorption of LinH clusters

Photoabsorption spectra of free Li_nH clusters have been recorded for n=2 to 9. Clusters are produced by coexpansion of 10–100 mbars of lithium vapor and 2–4 bars of a 98 % / 2 % mixture of argon with hydrogen. Two photon ionization was used to study the X ← B system of Li₂H while beam depletion spectroscopy was used to measure the absorption cross sections of larger clusters. Most observations may be interpreted by the localization of one electron on the hydrogen bonding in agreement with ionization potential measurements.