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Digitale Medien

Three-dimensional structure of a glycosphingolipid having a novel carbohydrate linkage, Gal beta 1-4(Fuc alpha 1-3)Glc beta 1-3Gal beta, determined by theoretical calculations (1998)

Kawakami, Jun ; Kawakami, Yasushi ; Nakamura, Kazuo ; [weitere]

Springer

Glycoconjugate journal 15 (1998), S. 107-113

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ISSN: 1573-4986

Schlagwort(e): conformation ; glycosphingolipid ; theoretical calculation ; Cer, ceramide ; Fuc, fucose ; Gal, galactose ; Glc, glucose ; Hex, hexose ; NMR, nuclear magnetic resonance ; ROESY, rotating frame Overhauser effect spectroscopy ; SEGLx, Gal beta 1-4(Fuc alpha 1-3)Glc beta 1-3Gal beta 1-Cer (a glycosphingolipid from S erinacei)

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie

Notizen: Abstract The novel glycosphingolipid, SEGLx (Gal beta 1-4(Fuc alpha 1-3)Glc beta 1-3Gal beta Cer), which was identified by us (Kawakami Y, et al. (1993) J Biochem 114: 677-83), shows a characteristic spectrum on 1H-NMR analysis, in which the anomeric proton resonances of a reducing end galactose and a glucose are split. To elucidate the structural characteristics of SEGLx, we determined its three-dimensional (3D) structure by means of computer simulation, involving such techniques as molecular mechanics (MM2), the semiempirical molecular orbital method (AM1), molecular dynamics (Amber), and computer 3D modelling. With the hypothesis that all OH group(s) of a ceramide participate in intramolecular hydrogen bonds, two kinds of stable conformers, horizontal and right-angled ones, were formed, depending on the ceramide species. The present findings suggest that the chemical species of both the long chain base and fatty acid moieties, mainly the occurrence of OH group(s), affect the chemical shifts of the anomeric proton resonances not only of the reducing terminal galactose but also the penultimate glucose through the formation of intramolecular hydrogen bonds. Computer simulation through theoretical calculation and 3D modelling was shown to be the best means of confirming the results obtained by experimental analysis.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1006908020370

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Digitale Medien

Intramolecular fluorescence quenching and exciplex formation in ω-(1-pyrenyl)alkyl para-substituted benzoates (1994)

Kawakami, Jun ; Iwamura, Michiko

Chichester : Wiley-Blackwell

Journal of Physical Organic Chemistry 7 (1994), S. 31-42

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ISSN: 0894-3230

Schlagwort(e): Organic Chemistry ; Physical Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Physik

Notizen: Measurements of absorption and emission spectra, fluorescence quantum yields (Φf) and lifetimes (τf) of ω-(1-pyrenyl)alkyl para-substituted benzoates PnX (X = H, Cl, CF3, CN, NO2, with n = 1-4) were carried out in solvents of various polarity. Intramolecular interaction in the ground state is not observed in any of these compounds. PnCN (n = 2-4) shows an intramolecular exciplex emission in solvents of low to high polarity. The broad, structureless emission at longer wavelength observed in ethyl acetate solution of P1CN is ascribed to an ‘exciplex-type’ emission which does not require actual overlapping of the two chromophores. P2CF3 also shows an exciplex emission in solvents of medium to high polarity. The solvent dependence of both Φf and τf increases as the electron-withdrawing ability of the para-sustituents increases. The relationship between fluorescence quenching by electron transfer and para-substituent of PnX is discussed by means of the free energy for electron transfer, ΔGET, obtained from the oxidation and reduction potentials of pyrene and methyl para-substituted benzoates in acetonitrile, respectively. PnH, with positive ΔGET, does not show a solvent dependence of Φf, except for P1H, in which ca 40% of the fluorescence is quenched in acetonitrile. PnCl, with slightly negative ΔGET, shows more efficient quenching, but does not show exciplex emission. PnCN, PnCF3 and PnNO2 have ΔGET values between -0·36 and -0·65 eV, and their fluorescence is fairly efficiently quenched. The fluorescence of PnCN is concluded to be strongly quenched by intersystem crossing from the singlet exciplex to the locally excited pyrene, and by electron transfer from the pyrene part to the benzoate part. That the formation of a singlet exciplex is necessary for intersystem crossing in bichromophoric compounds containing pyrene is thus clearly illustrated.

Zusätzliches Material: 5 Ill.