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  • 1
    ISSN: 1432-2021
    Keywords: Key words Stannite ; Kesterite ; EPR and SQUID measurements ; Spectra simulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract An EPR and SQUID magnetometry study of Cu2FeSnS4 (stannite) and Cu2ZnSnS4 (kesterite) has been performed in order to gain a deeper insight into the crystal chemistry of these minerals, in which the mixed character of bonds lends uncertainty to the determination of the metal valence states. EPR investigations were performed down to almost liquid nitrogen temperature on both natural and synthetic samples of stannite and kesterite. The interpretation of their parameters (g- and T-tensors) was refined by computer simulation. The main feature of all the spectra is the unstructured signal centered at about 0.310 T due to the presence of Cu(II). The absence of structure in the signal is due to spin-spin exchange interaction between Cu(II) and Fe(II), pointing to a diluted distribution of Cu(II). The temperature dependence of the Cu(II) signal can be related to a topological variation of the first-neighbors coordination. The SQUID measurements, while allowing a more precise interpretation of the EPR data, led to a full characterization of magnetic behavior of stannite and kesterite down to liquid helium temperature, evidencing antiferromagnetic interactions between the Fe(II) ions in all samples but in synthetic kesterite. From the EPR and SQUID experimental data no evidence was provided for the existence of two different structures for stannite and kesterite.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 2 (1990), S. 79-84 
    ISSN: 0899-0042
    Keywords: eudismic analysis ; muscarinic ligands ; muscarinic receptors sub-groups ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Eudismic analysis was performed on a set of 14 muscarinic ligands carrying a 1,3-oxathiolane nucleus, in order to obtain information about both the existence of receptor subgroups and of agonist and competitive antagonist interaction sites. The results obtained were compared with those from a study of the enantioselectivity of the pairs of enantiomers. The two approaches do not appear to be completely equivalent and would seem to complement each other usefully.
    Additional Material: 4 Ill.
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  • 3
    ISSN: 0899-0042
    Keywords: analgesic ; cognition enhancer ; ACh releaser ; enantioselectivity ; stereospecific synthesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomers of two α-tropanyl esters, SM21 (1) and PG9 (2), derived from (+)-R-hyoscyamine, that act by increasing the central cholinergic tone, were obtained by esterification after resolution of the corresponding racemic acids [(-)-S-1, (-)-R-2 and (+)-S-2] and by stereospecific synthesis [(+)-R-1]. Their analgesic and cognition-enhancing activities were tested in mice and their ACh-releasing properties determined on rat parietal cortex. These compounds show enantioselectivity in analgesic and cognition-enhancing tests on mice, the eutomers being the isomers which possess the same spatial arrangement of the groups on the chiral atom as (+)-R hyoscyamine [(+)-R-SM21, (+)-S-PG9]. The ACh-releasing effect of the enantiomers of SM21 in rats is in agreement with the results in mice, while PG9 enantiomers do not show any appreciable enantioselectivity in this test. On the basis of the different effects of the 5-HT4 antagonist SDZ 205557 on analgesia induced by the enantiomers of 1 and 2 and by (+)-R-hyoscyamine and the α-tropanyl ester of 2-phenylpropionic acid 3, a mechanism of action is proposed for this class of compounds. © 1996 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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