- Spectroscopic and biocatalytic properties of a chlorophyll-containing extract in silica gel
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UV-Vis absorption and fluorescence spectra of chlorophyll a (in the form of spinach extract) in acetone solution and in silica gel showed a predominance of pigment dimers in its overall concentration and an evident transformation of chlorophyll a to pheophytin with time. The dimerization constant of chlorophyll a in acetone was log Kdim = 2.14, whereas the constants for chlorophyll a and pheophytin a in alcogel were log Kdim = 4.70 and log Kdim = 5.22, respectively. Biocatalytic experiments indicated the possibility of using the pigment embedded in silica gel, i.e. mainly its dimeric form, for biotransformation of α-pinene to pinocarveyl hydroperoxide, trans-pinocarveol, pinocarvone and myrtenal. The advantage of a heterogeneous biocatalytic system (composed of a solvent and silica gel) over a homogeneous system (single phase of chloroform) is the possibility of reusing the biocatalyst with about 10% preservation of its activity.
- Lipke, Agnieszka,Trytek, Mariusz,Fiedurek, Jan,Majdan, Marek,Janik, Ewa
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p. 158 - 164
(2013/10/08)
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- Homo- and heterogeneous α-pinene photooxidation using a protoporphyrin-derived amide
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6,7-Bis[3-(NIμ-tert-butyloxycarbonyllysine methyl ester)]-1,3,5,8-tetramethyl-2,4-divinylporphyrin (3) was synthesized and successfully immobilized in a silica matrix by a sol-gel method. Protoporphyrin (PP)-derived amide 3 showed much higher photostability than its parent PP-IX. Its UV/Vis absorption, excitation, and fluorescence spectra as well as its ability to generate 1O2 were measured both in solution and in the matrix. Subsequently, free and immobilized porphyrins 3 were used as sensitizers in the photooxidation of α-pinene, and their photocatalytic properties were compared. Newly synthesized protoporphyrin (PP)-derived amide 3 is more photostable than PP-IX. Because it is able to generate 1O2, it could be used as a biomimetic catalyst for the oxidation of α-pinene under visible light. After successful immobilization in a silica matrix, a transparent organic-inorganic hybrid was obtained that shows intensive luminescence. Copyright
- Trytek, Mariusz,Lipke, Agnieszka,Majdan, Marek,Pisarek, Sabina,Gryko, Dorota
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p. 1653 - 1658
(2013/04/23)
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- Mechanism of the aerobic oxidation of α-Pinene
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A combined experimental and theoretical approach is used to study the thermal autoxidation of α-pinene. Four different types of peroxyl radicals are generated; the verbenyl peroxyl radical being the most abundant one. The peroxyl radicals propagate a long
- Neuenschwander, Ulrich,Guignard, Florian,Hermans, Ive
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experimental part
p. 75 - 84
(2011/02/21)
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- A family of new 1,2,4-trioxanes by photooxygenation of allylic alcohols in sensitizer-doped polymers and secondary reactions
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Type II photooxygenation (singlet oxygen) is described as a synthetically useful way for the preparation of allylic hydroperoxides and endoperoxides using sensitizer-adsorbed or covalently sensitizer-doped polymeric (macro- or nanosized) containers. Facil
- Bartoschek, Anna,El-Idreesy, Tamer T.,Griesbeck, Axel G.,Hoeinck, Lars-Oliver,Lex, Johann,Miara, Claus,Neudoerfl, Joerg M.
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p. 2433 - 2444
(2007/10/03)
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- Photooxygenation in polystyrene beads with covalently and non-covalently bound tetraarylporphyrin sensitizers
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Two reaction protocols are described which involve the use of polymer supports as reaction media for photooxygenation processes: 1) The use of polystyrene beads (PS) loaded with tetraphenyl- (TPP) or tetratolylporphyrin (TTP), swollen with the substrate in an appropriate organic solvent and subsequent irradiation under air. Products were isolated simply by dissolution in alcoholic solvents and filtration. 2) Covalently linked tetrastyrylporphyrin in polystyrene-divinylbenzene beads were synthesized by emulsifier-free emulsion polymerization and directly used for the photooxygenation protocol described above. The latter alternative allows also the use of less polar solvents for the extraction of the oxygenation products from the polymer beads. From the sensitizer loading degree, an optimal substrate/sensitizer molar ratio of 1,000-2,000 was determined and recyclization is possible for at least five times resulting in a minimum turnover number (with respect to the sensitizer TTP) of 5 × 104 (after five cycles). Both approaches were applied to the ene reaction of singlet oxygen with citronellol (1), the regioisomeric pinenes 3 and 5, and the allylic alcohols 9a - c, respectively, as well as to the [4 + 2]-cycloadditions of singlet oxygen to sorbinol (7) and the chiral diene 11.
- Griesbeck, Axel G.,El-Idreesy, Tamer T.,Bartoschek, Anna
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p. 245 - 251
(2007/10/03)
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- Sustainable photochemistry: Solvent-free singlet oxygen-photooxygenation of organic substrates embedded in porphyrin-loaded polystyrene beads
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A solvent-free photooxygenation process that uses organic substrates embedded in porphyrin-loaded polystyrene beads as solid support is described and applied for ene- and [4+2]-cycloaddition reactions involving singlet oxygen (1Δg).
- Griesbeck, Axel G.,Bartoschek, Anna
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p. 1594 - 1595
(2007/10/03)
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- Azidohydroperoxidation of pinenes: Stereoselectivity pattern and the first X-ray structure of a 2-azidohydroperoxide
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The photoinduced electron transfer of azide anions in the presence of an excited organic dyestuff, oxygen, and α- or β-pinene, respectively, gave 2-azidohydroperoxides in excellent regio- and good diastereoselectivity.
- Griesbeck,Lex,Saygin,Steinwascher
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p. 2205 - 2206
(2007/10/03)
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- INTERVENTION D'UN MECANISME IONIQUE DANS LA PHOTOOXYGENATION SENSIBILISEE DE L'α-PINENE EN MILIEU PROTIQUE
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In protic media, the (singlet oxygen)-(α-pinene) ene reaction is partially deviated towards the formation of bifunctional products (5, 7a, 7b) which provides evidence for zwitterionic intermediates.
- Capdevielle, Patrice,Maumy, Michel
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p. 2417 - 2420
(2007/10/02)
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