- Characterization of Aroma-Active Compounds in Italian Tomatoes with Emphasis on New Odorants
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An aroma distillate was prepared by solvent extraction and subsequent SAFE distillation from Italian vine-ripe tomatoes eliciting an intense overall aroma. Application of gc/olfactometry and the aroma extract dilution analysis revealed 44 odor-active compounds, 42 of which could be identified. The highest odor activity value of 2048 was established for the green, grassy (Z)-3-hexenal, the metallic smelling trans-4,5-epoxy-(E)-2-decenal, the potato-like 3-(methylthio)propanal, and the caramel-like 4-hydroxy-2,5-dimethyl-3(2H)-furanone. Of the further odorants, 13 compounds have previously not been reported as tomato odorants. Although most of these showed lower FD-factors, in particular, the coconut/dill-like smelling wine lactone ((3S,3aS,7aR)-3a,4,5,7a-tetrahydro-3,6-dimethylbenzofuran-2(3H)-one) appeared with a quite high FD factor. In addition, a fruity, almond-like odorant (6) with an FD factor of 1024 was detected. By application of high resolution mass spectrometry and polarity considerations, the structure of a methyl-2-ethoxytetrahydropyran isomer was suggested for 6. Four of the five possible isomers, the 3-methyl-, 4-methyl-, 5-methyl-, and 6-methyl-2-ethoxytetrahydropyran were synthesized and showed similar mass spectrometric patterns. However, these were excluded by their different retention indices. Although the synthesis of the remaining 2-methyl-2-ethoxytetrahydropyran resulted in only small yields, which were not sufficient for NMR measurements, this structure is very likely for 6. This compound was never reported as a food constituent before. Finally, quantitation of 23 odorants by stable isotope dilution assays allowed for the preparation of an aroma recombinate resembling the overall aroma of the tomatoes.
- Kreissl, Johanna,Schieberle, Peter
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- Photoinduced proton transfer in a pyridine based polymer gel
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We describe an experimental and theoretical consideration of photoexcited proton transfer in a poly(4-vinyl pyridine)/pyridine gel. Evidence was found for two states of a multiple state process analyzed by DFT modeling. According to the latter, following irradiation at 385 nm, the proton donor is the CH group of the polymer main chain and the proton acceptor is the nitrogen of the polymaric pyridine side chain. Proton transfer is made possible through the assistance of a mobile pyridine solvent molecule acting as a transfer vehicle. Proton transfer promotes both a geometrical rearrangement of the vinyl side chain as well as electronic density redistribution. The photoproduct intermediate - the hydrogen-bonded complex between the protonated solvent pyridine molecule and the deprotonated polymeric pyridine side chain - is identified by its Curie law magnetic susceptibility, ESR spectrum, and fluorescence lifetime measurements. The proton transfer from the nitrogen of the solvent pyridine molecule to the pyridine side chain nitrogen, producing pyridinium, is a thermodynamically favorable relaxation process and occurs without an energy barrier. The protonation of nitrogen on the polymeric side chain was detected by solid state NMR spectroscopy performed on a 15N-polymer enriched gel. The calculations and experimental data suggest a central role for the gel solvent molecule as a catalytic agent and proton transfer vehicle. The process suggested by DFT modeling may have relevance for photosensitive devices in part due to the fact that we have been able to show that long-lived paramagnetism may be included among the inducible properties of soft polymer gels. ? 2010 American Chemical Society.
- Vaganova, Evgenia,Wachtel, Ellen,Leitus, Gregory,Danovich, David,Lesnichin, Stepan,Shenderovich, Ilja G.,Limbach, Hans-Henrich,Yitzchaik, Shlomo
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- Kinetic effects in water and ethylene glycol. Application to high pressure organic synthesis
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The kinetic effect of various Diels-Alder and Michael reactions is studied in water and ethylene glycol vs. organic solvents. The rate enhancement is considerable in water, much less in ethylene glycol. It is proposed that strong solvophobic interactions operate in water whereas the kinetic results in glycol are best explained by hydrogen bonding and polarity effects. From a synthetic point of view, use of the properties of water (hydrophobic interactions) or ethylene glycol (ionogenic medium) associated with the kinetic effect of high pressure may constitute an interesting multiactivation method to increase chemical reactivity. Examples of triactivation (high pressure catalytic Diels-Alder reactions in ethylene glycol) are given.
- Jenner, Gerard,Salem, Ridha Ben
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- Oxidative rearrangement of 2-alkoxy-3,4-dihydro-2H-pyrans: stereocontrolled synthesis of 4,5-cis-disubstituted tetrahydrofuranones including whisky and cognac lactones and crobarbatic acid
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Oxidation of 2-alkoxy-3,4-dihydro-2H-pyrans 3 with dimethyldioxirane or MTO/urea-H2O2 followed by Jones oxidation leads to rearrangement and stereocontrolled formation of 4,5-cis-disubstituted tetrahydrofuranones. The method is applied to the synthesis of the whisky lactone 9, cognac lactone 10 and crobarbatic acid 17.
- Armstrong, Alan,Ashraff, Cassim,Chung, Hunsuk,Murtagh, Lorraine
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experimental part
p. 4490 - 4504
(2009/10/09)
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- Lanthanide catalysts for the hetero Diels-Alder reaction: Effect of ligand structure and acidity
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A series of yttrium, ytterbium, and lanthanum hexa- or heptacoordinate complexes were prepared and their catalytic activities tested in the hetero Diels-Alder reaction between crotonaldehyde and ethyl vinyl ether. It was found that a pKa below
- Spine,Clouston,Berg
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p. 1047 - 1054
(2007/10/03)
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- Novel, air-stable, lanthanide catalysts for the hetero Diels-Alder reaction
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Novel, air-stable, yttrium and ytterbium complexes were found effective in the catalysis of the typical hetero Diels-Alder reaction of crotonaldehyde and ethylvinyl ether. They represent an attractive solution to the problem of ligand lability in the realm of lanthanide catalysts.
- Spino, Claude,Clouston, Laurel,Berg, David
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p. 1762 - 1764
(2007/10/03)
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- LANTHANIDE CATALYSIS OF CYCLOADDITIONS OF HETERODIENES WITH ENOL ETHERS
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The cycloadditions of enol ethers with α,β-unsaturated aldehydes is catalysed by Yb(fod)3.
- Danishefsky, Samuel,Bednarski, Mark
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p. 721 - 724
(2007/10/02)
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- Reaction of Enol Ethers with Formaldehyde and Organoaluminum Compounds
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Reaction of formaldehyde and trimethylaluminum with an enol ether derived from an aldehyde gives the adduct resulting from addition of hydroxymethyl and methyl groups to the enol ether double bond.The threo isomer is formed selectively (90-95percent) from
- Snider, Barry B.,Phillips, Gary B.
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p. 2789 - 2792
(2007/10/02)
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