Browsing by Author "Gückel, Friedemann"

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    Excited electronic states of flavin-containing coenzyme models
    (1988) Gückel, Friedemann; Schweitzer, Dieter; Becker, Katja; Schirmer, Rolf Heiner; Zipplies, Matthias F.; Staab, Heinz A.
    In order to gain further insight into the physical basis of flavin-catalyzed reactions, the interactions of a flavin with a second flavin and with other aromatic ring systems were studied. For this purpose compounds through 1 were synthesized These compounds contain the interacting units in defined geometric orientation. A monomeric flavin and glutathione reductase a flavoenzyme of known active-site chemistry, were included as reference molecules. The present report deals with excited triplet states of the flavin compounds as studied by optical spectroscopy and optically detected magnetic resonances (ODMR) at 1.3K.
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    ODMR of triplet states of cofacial dimeric zinc porphyrins
    (1984) Gückel, Friedemann; Schweitzer, Dieter; Collman, James; Bencosme, Sergio; Evitt, Eric R.; Sessler, Jonathan L.
    The triplet-state zero-field splitting parameters and the triplet sublevel decay rates for several monomeric zinc porphyrins and cofacial bis-zinc porphyrin dimers are reported. In the dimers, weak π-electron interactions between the porphyrin subunits are found to exist. Therefore the commonly used exciton model can be applied to obtain structural information about the excited triplet state of the dimers. In the β-linked dimers 1 and 2, the two porphyrin subunits are rotated with respect to one another about the common out-of-plane axis. These results suggest that these compounds were prepared and studied as the anti-, rather than syn-diastereoisomers. A meso-linked porphyrin dimer 3 was also studied.
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    Spectroscopic investigations of the lowest triplet state of s-tetrazines
    (1992) Gückel, Friedemann; Maki, August H.; Neugebauer, Franz A.; Schweitzer, Dieter; Vogler, Helmut
    We report on the electronic and triplet state ODMR spectroscopy of s-tetrazine, 3,6-dimethyl-, 3,6-dimethoxy- and 3,6-bis(methylthio)-s-tetrazines. Zero field splitting parameters were obtained by ODMR monitoring both the delayed fluorescence and the phosphorescence in neat single crystals. The S1 and T1 exciton electronic origins are reported. The zero field splitting tensor is nearly axially symmetric with |D| approximately 0.4 cm-1. This value is found to be in good agreement with calculations based on magnetic dipole-dipole coupling in a 3B3u (nπ*) state. The calculations predict a positive value for D with the major axis passing through the C atoms at the 3 and 6 positions.
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    Structures of 3,6-dimethoxy-1,2,4,5-tetrazine(V) and 3,6-Bis(1-aziridinyl)-1,2,4,5-tetrazine(VI)
    (1987) Krieger, Claus; Fischer, Hans; Neugebauer, Franz A.; Gückel, Friedemann; Schweitzer, Dieter
    (V): C4H6N4O2, Mr=142·12, orthorhombic, Pbca, a=6·865(3), b =13·192(5), c=7·013(3)A, V =635·1(7)A3, Z=4, Dx=1·486gcm-3, λ(MoKα)=0·71069A, μ=1·139cm-1, F(000)=296, T=295K, R=0·043 for 589 unique observed reflections [I ≥ 1·96σ(I)]. (VI): C6H8N6, Mr=164·18, monoclinic, C2/m, a=9·660(2), b=9·077(1), c=4·294(1)A, β=91·07(I)°, V=376·5(2)A3, Z=2, Dx=1·448gcm-3, λ(MoKα)=0·71069 A, μ=0·952 cm-1, F(000)=172, T=295K, R=0·037 for 405 unique observed reflections [I≥1·96σ(I)]. (V) and (VI) are centrosymmetric, with planar 1,2,4,5-tetrazine rings slightly compressed in the C···C direction (N-C-N≅126°). The remarkably short exocyclic C-O [1·328(2)A] and C-N[1·385(1)A] bond distances indicate that the methoxy and aziridinyl substituents act as π donors to the electron-deficient 1,2,4,5-tetrazine system.