Molecular conformations of aminophenylimidazoles exhibiting antiulcer activities

To experimentally clarify a possible stereostructure-activity relationship proposed for H2-receptor antagonists, three 5-aminophenylimidazoles (1, 2 and 3), in which respective amino groups are located on the ortho, meta and para positions of the benzene ring, were synthesized and examined for their conformational characteristics using X-ray diffraction and proton nuclear magnetic resonance (1H-NMR) methods, and for antiulcer activities on rats and H2-receptor antagonist activities in guinea pig. The ortho isomer 1, which preferentially formed an intramolecular N-H (amino)...N (imidazole) hydrogen bond, showed the highest antiulcer activity with half the efficacy of cimetidine. On the other hand, none of 1, 2 and 3 showed significant H2-receptor antagonist activity. Based on these results, the conformational characteristic for the exhibition of antiulcer activity has been discussed.     

Spectroscopic study on interaction of nucleic acid base with tryptophan-containing tripeptides: acetyl-Trp-X-Trp-NHCH3 (X = Gly, Asn, Asp, Gln and Glu).

As part of a series of peptides designed to have binding ability selective for each of the nucleic acid bases, five tripeptides consisting of N-acetyl-Trp-X-Trp-NHCH3 (X = Gly, Asn, Asp, Gln and Glu) were synthesized, and their abilities to form complexes with four different nucleotides were examined by the fluorescence and phase distribution methods. The association constants obtained indicated that, depending on the sort of X residue, the peptides showed a variation in their interaction with guanosine monophosphate (GMP), while no noticeable selectivity was observed for other nucleotides adenosine monophosphate (AMP), uridine monophosphate (UMP) and cytidine monophosphate (CMP). The binding mode of N-acetyl-Trp-Asp-Trp-NHCH3 for the guanine base was further investigated using the proton nuclear magnetic resonance (1H-NMR) method. The mode was suggested to involve intimate cooperation of (1) the hydrogen bond formation between the carboxyl group of the Asp side chain and the guanine C2-amino group, and (2) the stacking interaction of the base with two terminal Trp residues of the peptide. Such interaction was strengthened by the protonation of the guanine base. A tentative binding mode is proposed based on these results.     

Core-level reflectance spectroscopy of germanium by means of synchrotron radiation

Reflectance spectra due to 3d core-levels of Ge have been measured in the photon-energy region from 29 to 38 eV by means of synchrotron radiation. Second-energy-derivative spectra have newly shown pairs of doublet structures with energy separation of the Ge $\text{3d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{?}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ core-level splitting. The observed doublet structures are assigned to the transitions from the $\text{3d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ and $\text{3d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ core-levels to the flat regions of the conduction band around the particular symmetry points of Δ₆^c and L(₃^c(L₆^c, L_4,5^c).     

Raman scattering in hydrogenated amorphous silicon under high pressure

The first studies on the pressure dependences of the first-order Raman spectra in plasma-deposited a-Si:H films are reported. With increasing pressure up to 25 kbar the TO optical phonon band shows a shift in peak to higher frequencies with a sharpening of width while the TA acoustic phonon band shows a shift in peak to lower frequencies with a broadening of width. The LO optical phonon band shows a shift in peak to higher frequencies whereas the LA acoustic phonon band remains unchanged. These pressure effects are discussed with changes in force constant and structural disorder. The alloying effect of H atoms on the Raman spectra is also discussed while comparing the pressure effects.     

Diffusion im Nylon 12/Wasser-System

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Asymmetrische Synthese, katalysiert durch Poly-L-alanin

Ohne Zusammenfassung