Universität Stuttgart
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Item Open Access On attempts at solvolytic generation of aryl cations(1976) Subramanian, Lakshminarayanapuram R.; Hanack, Michael; Chang, Lawrence W. K.; Imhoff, Michael A.; Schleyer, Paul v. R.; Effenberger, Franz; Kurtz, Walter; Stang, Peter; Dueber, Thomas E.The solvolysis of phenyl triflate (3), phenyl nonaflate (4), o-methylphenyl nonaflate (5), o-cyclopropylphenyl nonaflate (6), o-methoxyphenyl triflate (7), 2,6-dimethoxyphenyl triflate (S), 2,6-diisopropylphenyl triflate (9), 33- dimethoxyphenyl triflate (lo), 3,5-dicyclopropylphenyl triflate (11), 3,5-di(2-methylcyclopropyl)phenyl triflate (12), 2,4,6-tricyclopropylphenyltr iflate (13), and 2,4,6-triisopropylphenytlr iflate (14) were examined in great detail under a wide variety of conditions. In highly polar nonnucleophilic solvents no reaction was observed and the unreacted triflates were recovered quantitatively. In the presence of nucleophiles or nucleophilic solvents the sole products observed were the corresponding phenols. Careful labeling and product studies showed that these phenols arose by nucleophilic attack on sulfur and S-0 bond cleavage. We have not been able to find any evidence for aryl cation intermediates.Item Open Access Properties of amphiphilic terminally substituted conjugated nonaene- and 2-docosylnonaene carboxylic acids in monolayers at the air-water interface(1991) Effenberger, Franz; Meller, Paul; Ringsdorf, Helmut; Schlosser, HubertIn the present communication, we report thesynthesis of conjugated nonaene- and 2-docosylnonaene carboxylic acids with different terminal substituents. These substituents have been chosen so that their spectroscopic properties differ from those of the polyene chain; they also have specific electron donor, electron acceptor or redox properties to allow for specific and selective excitation (energy intake). Because of the amphiphilic character of these compounds, pressure-area isotherms were determined in monolayers at the air-water interface.Item Open Access Photochromic thiophenefulgides : photokinetics of two isopropyl derivatives(1991) Ulrich, Karl; Port, Helmut; Wolf, Hans Christoph; Wonner, Johann; Effenberger, Franz; Ilge, Hans-DieterFor two photochromic isopropyl-thiophenefulgides a complete photokinetic analysis is given. For one compound (5b), the partial quantum yield for the colouring process (ΦEC = 54%) is the highest value found for thiophenefulgides. EZ-isomerisations do not play an important role. The colouring quantum yield is temperature independent down to 20 K, whereas bleaching requires little thermal activation. In case of an adamantylidene substituted isopropyl-thiophenefulgide (5c), the bleaching efficiency (ΦCE = 31%) is very high. Upon heating of the cyclic products, thermal bleaching occurs with an activation energy of 1 eV.Item Open Access A novel synthetic route to L-proline (Amino acids ; 7)(1986) Drauz, Karl-Heinz; Kleemann, Axel; Martens, Jürgen; Scherberich, Paul; Effenberger, FranzReaction of L-5-oxoproline esters L-2 with phosgene at 0° C gives L-5,51-dichloro-1-(chlorocarbonyl)proliene esters L-6 ,which readily lose hydrogen chloride to form L-5-chloro-1-(chloroarbonyl)-4,5-dehydroproline esters L-7. Catalytic hydrogenation (Pd/C, 180 bar) of L-7 yields L-1-(chlorocarbonyl)proline esters L-15 and thence, upon hydrolysis, L-proline ( L17 ). A "one-pot reaction" for the whole sequence is described, starting from easily accessible L-5-oxoproline esters and yielding L-proline in 78% overall yield and 99.7% optical purity.Item Open Access MO-theoretisch konzipierte Kandidaten für ein neuartiges Konzept einer lichtinduzierten Elektronenpumpe(1985) Stohrer, Wolf-Dieter; Paape, Rainer; Effenberger, Franz; Bäuerle, PeterMO-theory suggests 3 as a likely candidate for a newly designed conception to replace a given redox potential by a lower one with the aid of light.Item Open Access Experimental and theoretical aspects of the formation of radical cations from tripyrrolidinobenzenes and their follow-up reactions(1990) Effenberger, Franz; Stohrer, Wolf-Dieter; Mack, Karl Ernst; Reisinger, Friedrich; Seufert, Walter; Kramer, Horst E.A.; Föll, Rudolf; Vogelmann, EkehardtTripyrrolidinobenzene radical cations(1*+), obtained from the corresponding arenes by oxidation with silver nitrate, are specially stabilized and thus allow specific reaction pathways of arene radical cations to be investigated separately and individually. Radical cations 1*+ ,for instance, generated under exclusion of oxygen, undergo dimerization to 2, or they abstract hydrogen from the solvent to form 3. In a pure oxygen atmosphere, the O2 reaction products 6 and 7 are formed, respectively, either exclusively or together with 2 and 3. Kinetic measurements give the following order of reactivity for these individual processes: reaction with O2 > dimerization. > H-abstraction from solvent. The changes in the product spectrum upon modification of the reaction conditions are in accord with the kinetic results. The dimeric u complexes 2 show surprisingly facile dissociation into two radical cations, two (1*+)with a much higher dissociation rate for the alkyl derivatives 2b-d than for 2a. Dissociation is enhanced substantially by light or in the presence of π donors. Individual product formation, rate of reactions of the radical cations 1*+, and photochemical cleavage of the dimeric σ complexes 2 can be rationalized, by qualitative and quantitative MO considerations, in terms of their relative frontier orbital energies.Item Open Access Elektronen-Transfer bei den Reaktionen von Halogen-σ-Komplexen des 1,3,5-Tris(1-pyrro-lidinyl)benzols mit Nucleophilen (Aminobenzole ; 21)(1990) Effenberger, Franz; Bäuerle, Peter; Seufert, Walter; Stohrer, Wolf-DieterIodo, bromo, chloro, and thiocyanato σ-complexes 4, accessible as crystalline compounds from 1,3,5-tris(1-pyrrolidinyl)benzene (1) with halogens and dirhodan, respectively, react with nucleophiles or bases under dehalogenation, deprotonation, dimerization, or H σ-complex formation. The product formation depends on the redox potentials of the σ-complexes (acceptors) and the nucleophiles (donors), on the leaving tendency of the substituents on C-1 of the σ-complexes, and on the reaction time. The unexpected reactions are interpreted by an electron transfer from the nucleophile Y| to the σ-complex A+ to give the radical A*, a subsequent heterolytic dissociation to the 1,3,5-tris(1-pyrrolidinyl)benzene radical cation C.+, and its follow-up reactions (addition of nucleophiles, dimerization, and H abstraction). The H σ-complex 6 results the most stable final product after long reaction times because of its lowest acceptor properties and the poor nucleofugal leaving tendency of a hydride ion.Item Open Access Photoregulation of α-chymotrypsin activity in organic media : effects of bioimprinting(1994) Willner, Itamar; Lion-Dagan, Mazzi; Rubin, Shai; Wonner, Johann; Effenberger, Franz; Bäuerle, Peterα-Chymotrypsin exhibits photoswitchable activities in an organic solvent after covalent modification of the protein backbone with thiophenefulgide active ester (2). The thiophenefulgide-modified α-chymotrypsin exhibits reversible photoisomerizable properties between states (3)-E and (3)-C. The modified α-chymotrypsin, where nine lysine residues are substituted by thiophenefulgide units, retains 60% of the activity of the native enzyme. The activities of thiophenefulgide-modified α-chymotrypsin toward esterification of N-acetyl-L-phenylalanine (4) by ethanol in cyclohexane are controlled by the configuration of the attached photoisomerizable component and by prior bioimprinting of the protein backbone with the reaction substrate (4). The esterification of (4) in cyclohexane using bioimprinted (3)-C is two-fold faster than in the presence of (3)-E. In the presence of a nonbioimprinted enzyme, esterification of (4) by (3)-C is five-fold faster than with (3)-E. The activity of bioimprinted (3)-E toward esterification of (4) is 4.5-fold higher than that of nonbioimprinted (3)-E. Switchable cyclic esterification of (4) is accomplished by sequential photoisomerization of the thiophenefulgide-modified α-chymotrypsin between states (3)-C and (3)-E.Item Open Access Crystallization and preliminary X-ray diffraction studies of mandelonitrile lyase from almonds(1994) Lauble, Hanspeter; Müller, Kirsten; Schindelin, Hermann; Förster, Siegfried; Effenberger, FranzSingle crystals of three different isoenzymes of (R)-(+) mandelonitrile lyase (hydroxynitrile lyase) from almonds (Prunus amygdalus) have been obtained by hanging drop vapor diffusion using polyethylene glycol 4000 and isopropanol as co-precipitants. The crystals belong to the monoclinic space group P2l with unit cell parameters a = 69.9, b = 95.1, c = 95.6 Å, and β = 118.5°. A complete set of diffraction data has been collected to 2.6 Å resolution on native crystals of isoenzyme III.Item Open Access The effect of N-methyl-formimino-methylester on the neural olfactory threshold in albino mice(1984) Schmidt, C.; Schmidt, Uwe; Breipohl, Winrich; Effenberger, FranzThe effects of N-methyl-formimino-methylester were studied in albino mice. Very short exposure (0.5 and 1 s) to the concentrated vapour led to an increase of the neural olfactory threshold to geraniol . There was a slow recovery of the olfactory sensitivity and after about 40 days the threshold values returned to normal.