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71.
The binary system Li2Se-In2Se3 was investigated in the range of 40 to 100 mol% In2Se3 by thermoanalytical and X-ray methods. The system is characterized by two eutectic points. Beside the two binary components
and the known ternary compound LiInSe2 another ternary compound crystallizes in this binary system at 83.3 mol% In2Se3. This compound was identified as LiIn5Se8. In contrast to (Cu, Ag)IB5
IIIC8
VI compounds such as CuIn5S8 [1] it does not crystallize in the spinel structure. LiIn5Se8 shows a stratified structure. The melting point was determined to be at 810°C. Starting from room temperature up to the melting
point no phase transitions were observed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
72.
Use of molecular dynamics in the design and structure determination of a photoinducible beta-hairpin
Kräutler V Aemissegger A Hünenberger PH Hilvert D Hansson T van Gunsteren WF 《Journal of the American Chemical Society》2005,127(13):4935-4942
The study presented here consists of three parts. In the first, the ability of a set of differently substituted diazobenzene-based linkers to act as photoswitchable beta-turn building blocks was assessed. A 12-residue peptide known to form beta-hairpins was taken as the basis for the modeling process. The central (beta-turn) residue pair was successively replaced by six symmetrically ((o,o), (m,m), or (p,p)) substituted (aminomethyl/carboxymethyl or aminoethyl/carboxyethyl) diazobenzene derivatives leading to a set of peptides with a photoswitchable backbone conformation. The folding behavior of each peptide was then investigated by performing molecular dynamics simulations in water (4 ns) and in methanol (10 ns) at room temperature. The simulations suggest that (o,o)- and (m,m)-substituted linkers with a single methylene spacer are significantly better suited to act as photoswitchable beta-turn building blocks than the other linkers examined in this study. The peptide containing the (m,m)-substituted linker was synthesized and characterized by NMR in its cis configuration. In the second part of this study, the structure of this peptide was refined using explicit-solvent simulations and NOE distance restraints, employing a variety of refinement protocols (instantaneous and time-averaged restraining as well as unrestrained simulations). We show that for this type of systems, even short simulations provide a significant improvement in our understanding of their structure if physically meaningful force fields are employed. In the third part, unrestrained explicit-solvent simulations starting from either the NMR model structure (75 ns) or a fully extended structure (25 ns) are shown to converge to a stable beta-hairpin. The resulting ensemble is in good agreement with experimental data, indicating successful structure prediction of the investigated hairpin by classical explicit-solvent molecular dynamics simulations. 相似文献
73.
Lindén AA Hermanns N Ott S Krüger L Bäckvall JE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,11(1):112-119
Eight different flavin derivatives have been synthesized and the electronic effects of substituents in various positions on the flavin redox chemistry were investigated. The redox potentials of the flavins, determined by cyclic voltammetry, correlated with their efficiency as catalysts in the H2O2 oxidation of methyl p-tolyl sulfide. Introduction of electron-withdrawing groups increased the stability of the reduced catalyst precursor. 相似文献
74.
Alexandra Tsybizova Christopher Brenig Christoph Kieninger Bernhard Kräutler Peter Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(25):7252-7264
Aryl-cobalamins are a new class of organometallic structural mimics of vitamin B12 designed as potential ‘antivitamins B12’. Here, the first cationic aryl-cobinamides are described, which were synthesized using the newly developed diaryl-iodonium method. The aryl-cobinamides were obtained as pairs of organometallic coordination isomers, the stereo-structure of which was unambiguously assigned based on homo- and heteronuclear NMR spectra. The availability of isomers with axial attachment of the aryl group, either at the ‘beta’ or at the ‘alpha’ face of the cobalt-center allowed for an unprecedented comparison of the organometallic reactivity of such pairs. The homolytic gas-phase bond dissociation energies (BDEs) of the coordination-isomeric phenyl- and 4-ethylphenyl-cobinamides were determined by ESI-MS threshold CID experiments, furnishing (Co−C )-BDEs of 38.4 and 40.6 kcal mol−1, respectively, for the two β-isomers, and the larger BDEs of 46.6 and 43.8 kcal mol−1 for the corresponding α-isomers. Surprisingly, the observed (Co−C )-BDEs of the Coβ-aryl-cobinamides were smaller than the (Co−C )-BDE of Coβ-methyl-cobinamide. DFT studies and the magnitudes of the experimental (Co−C )-BDEs revealed relevant contributions of non-bonded interactions in aryl-cobinamides, notably steric strain between the aryl and the cobalt-corrin moieties and non-bonded interactions with and among the peripheral sidechains. 相似文献
75.
B. Henc P.W. Jolly R. Salz S. Stobbe G. Wilke R. Benn R. Mynott K. Seevogel R. Goddard C. Krüger 《Journal of organometallic chemistry》1980,191(2):449-475
A series of 1 : 1 adducts have been prepared by treating the bis-η3-allyl complexes of nickel, palladium and platinum with tertiary phosphines. Investigations of their structure in solution as well as in the crystal have shown that both 18-electron (η3-allyl)2ML complexes as well as 16-electron (η1-allyl)-(η3-allyl)ML complexes may be formed. 相似文献
76.
In situ pulsed force mode scanning force microscopy (PFM-SFM) images of phase separated solid-supported lipid bilayers are discussed with the help of computer simulations. Simultaneous imaging of material properties and topography in a liquid environment by means of PFM-SFM is severely hampered by hydrodynamic damping of the cantilever. Stiffness and adhesion images of solid-supported membranes consisting of cholesterol, sphingomyelin, and 1,2-dioleyl-phosphatidylcholine obtained in aqueous solution exhibit contrast inversion of adhesion and stiff. ness images depending on parameters such as driving frequency, amplitude, and trigger setting. Simulations using a simple harmonic oscillator model explain experimental findings and give a deeper insight into the way PFM-SFM experiments have to be performed in order to obtain interpretable results and hence pave the way for reliable material contrast imaging at high speed. 相似文献
77.
W. Krätschmer 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,19(4):405-408
At the beginning two remarks. One to the nomenclature: Fullerite does not name a specific substance; it names a solid entirely consisting of fullerenes, i.e. closed-cage all-carbon molecules. When our method of synthesis is applied, a solid is obtained in which C60 is the most abundant species. This material may thus be called C60-fullerite. The other remark regarding the production of fullerite: in view of the ease with which this could be achieved, I have the feeling that fullerene molecules must belong to a very frequently overlooked molecular species in carbon chemistry. Since the synthesis is simple and does not require many words to be described, I thought it might be interesting to tell how we came to make fullerite. 相似文献
78.
G. Basar H-D Kronfeldt S. Kröger 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,36(1):35-39
The hyperfine structure of the odd configurations 5d 96p and 5d 86s6p was studied with laser optogalvanic spectroscopy and high resolution interferometry in a platinum hollow cathode. A parametric hyperfine structure analysis for the configurations (5d+6s)96p with 10 excited odd-parity levels was performed for195Pt. We obtained one-electron hfs parameters,a 5d 01 =1160(320) MHz,a 6s 10 =35600(5300) MHz anda 6p 01 =1300(780) MHz for the configuration 5d 86s6p. The corresponding $\left\langle {r^{ - 3} } \right\rangle _{nl}^{k_s k_l } $ values are compared with those known for other 5d-elements. 相似文献
79.
Zusammenfassung Das Verhalten von Polypropylen im elektrischen Wechselfeld wurde im Frequenzbereich von 0,15 kHz bis 300 kHz und im Temperaturbereich von –75 C bis +140 C untersucht. Es konnte sowohl ein Tieftemperaturdispersionsgebiet —-Absorption — als auch ein Hochtemperaturdispersionsgebiet —-Absorption — beobachtet werden. Die Untersuchungsergebnisse wurden, um die Breite des Dispersionsgebietes und die zugehörigen -Stufen zu bestimmen, nach demCole-Cole-Kreisbogengesetz analysiert. Aus dem Anstieg der Geraden: logf
max 1/T
K wurden sowohl für die- als auch fur die-Absorption die experimentellen Aktivierungsenergien berechnet. Eine Deutung der Ergebnisse wurde versucht. 相似文献
80.
Electrochemical studies of famotidine were carried out using voltammetric techniques: cyclic voltammetry, linear sweep and square wave adsorptive stripping voltammetry. The dependence of the current on pH, buffer concentration, nature of the buffer, and scan rate was investigated. The best results for the determination of famotidine were obtained in MOPS buffer solution at pH 6.7. This electroanalytical procedure enabled to determine famotidine in the concentration range 1 × 10−9–4 × 10−8 mol L−1 by linear sweep adsorptive stripping voltammetry (LS AdSV) and 5 × 10−10–6 × 10−8 mol L−1 by square wave adsorptive stripping voltammetry (SW AdSV). Repeatability, precision and accuracy of the developed methods were checked. The detection and quantification limits were found to be 1.8 × 10−10 and 6.2 × 10−10 mol L−1 for LS AdSV and 4.9 × 10−11 and 1.6 × 10−10 mol L−1 for SW AdSV, respectively. The method was applied for the determination of famotidine in urine. 相似文献