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The ir‐spectra in the NH stretching region of Piv‐Pro‐NHMe and Boc‐Pro‐NHMe have been studied in carbon tetrachloride and chloroform solutions over a wide range of concentrations. Based on the concentration dependence of the NH stretching bands, it has been shown that the characteristic NH stretching band due to the C 7 intramolecular hydrogen bond is around 3335 cm −1 . Intermolecular hydrogen bonding also occurs to a small extent in these peptides, giving rise to a slight concentration dependence of the NH stretching bands. The band around 3335 cm −1 need not necessarily be due to C 7 hydrogen bonds alone as proposed by Tsuboi et al. or to intermolecular hydrogen bonding alone as proposed by Maxfield et al.; this conclusion is supported by studies on Boc‐Leu‐NHMe, which undergoes only intermolecular hydrogen bonding. We have shown that Z‐Aib‐Aib‐OMe and Z‐Aib‐Ala‐OMe form C 7 intramolecular hydrogen bonds in addition to C 5 intramolecular hydrogen bonds. The present studies also show that all the peptides studied exist in more than one conformation in solution.
XPS and LIII X-ray absorption edge studies regarding the valence state of cerium have been carried out on the intermetallic compounds CeCo2, which becomes superconducting at low temperatures. It is observed from XPS that the surface shows both Ce3+ and Ce4+ valence states, while the X-ray absorption edge studies reveal only Ce4+ in the bulk. Thus valence fluctuation and superconductivity do not coexist in the bulk of this compound.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Welchen Einfluß hat die gleichzeitige Anwesenheit der Elemente Nickel und Kupfer in einem Hydrierkatalysator auf die Art der bei Katalysatorreduktion gebildeten Spezies? Röntgen-photo- und Auger-elektronenspektroskopisch wurde versucht, diese Frage zu beantworten. Es wurden Ni0-, Ni2⊕-, Cu0-und Cu⊕-Spezies nachgewiesen, wobei eine Zunahme an Ni0 mit dem Kupfergehalt und eine an Cu0 mit dem Nickelgehalt beobachtet wurde.
Molecular dynamics calculations of Ne and Ar in the cages of β-hydroquinone have been carried out. Radial distribution of the guest atoms, energy distribution functions, mean square displacements and power spectra have been obtained. The guest atoms are found to be completely entrapped in the cages, with Ar performing restricted one-dimensional motion and Ne performing restricted three-dimensional motion.
Gas sensing characteristics of YBa2Cu3O7−δ, La2−x SrxCuO4, and Bi2Y1−xCaxSr2Cu2O8 have been examined. La2−x SrxCuO4 (x = 0.075), and Bi2YSr2Cu2O8 are found to show good sensitivity (≈10 ppm) to ethyl alcohol and such vapours.
