ChemInform Abstract: STEREOCHEMISTRY AND PRODUCT DISTRIBUTION IN THE SINGLET OXYGEN CYCLOADDITION WITH 7,7-DISUBSTITUTED 1,3,5-CYCLOHEPTATRIENES

1983 ◽  
Vol 14 (37) ◽  
Author(s):  
W. ADAM ◽  
F. ADAMSKY ◽  
F.-G. KLAERNER ◽  
E.-M. PETERS ◽  
K. PETERS ◽  
...  
Keyword(s):  
Singlet Oxygen ◽  
Product Distribution

Article

1998 ◽  
Vol 76 (12) ◽  
pp. 1805-1816
Author(s):  
L Ross C Barclay ◽  
Jennifer K Grandy ◽  
Heather D MacKinnon ◽  
Heather C Nichol ◽  
Melinda R Vinqvist
Keyword(s):  
Oxygen Uptake ◽  
Singlet Oxygen ◽  
Sodium Azide ◽  
Lignin Content ◽  
Sodium Dodecyl ◽  
Kinetic Studies ◽  
Product Distribution ◽  
Geometrical Isomers ◽  
Photo Oxidation ◽  
Tert Butyl

3,5-Di-tert-butyl-ortho-quinone, 6, and 1-(3,4-dimethoxyphenyl-2-(2-methoxyphenoxy)-1-propanone, 7, models for oxidized lignin and for lignin, were used as sensitizers of photo-oxidation. Product studies by HPLC from oxidation of methyl linoleate in solution sensitized by 6 or 7, and in sodium dodecyl sulfate (SDS) sensitized by 6, showed a product distribution of six hydroperoxides, the four conjugated 9- and 13-hydroperoxides of the geometrical isomers: trans-10, cis-12 (2), cis-9, trans-11 (3), trans-10, trans-12 (4), and trans-9, trans-11 (5)-octadecadienoates plus two nonconjugated hydroperoxides. The higher cis/trans to trans/trans (ct/tt) of geometrical isomers (2 + 3//4 + 5) compared to ct/tt from known thermal free-radical peroxidations (Type 1) indicate that singlet oxygen (Type 2) oxidation occurs in reactions sensitized by 6 or 7. Kinetic studies by oxygen uptake are reported on oxidations of hydrocarbons 1-phenyl-2-methylpropene,8, and trans-stilbene,9, sensitized by the quinone, 6, or by a dye, Rose Bengal. Quenching studies imply singlet oxygen reactions. Milled wood lignin undergoes self-initiated photo-oxidation in water, and oxygen uptake was quenched by sodium azide. Cellobiose, a cellulose model, undergoes sensitized photo-oxidation using model quinone, 6, in a mixture of tert-butyl alcohol and water or using the sensitizers benzophenone or the lignin model, 7, delivered on a solid support, silica gel, and these oxidations were quenched with sodium azide. These results implicate singlet oxygen in the photo-yellowing of high lignin content wood pulps.Key words: lignin models, ortho-quinone, photo-oxidation, singlet oxygen, lignin, cellobiose.

Stereochemistry and product distribution in the singlet oxygen cycloaddition with 7,7-disubstituted 1,3,5-cycloheptatrienes

1983 ◽  
Vol 116 (5) ◽  
pp. 1848-1859 ◽  
Author(s):  
Waldemar Adam ◽  
Friedhelm Adamsky ◽  
Frank-Gerrit Klärner ◽  
Eva-Maria Peters ◽  
Karl Peters ◽  
...  
Keyword(s):  
Singlet Oxygen ◽  
Product Distribution

Controlled oxidations of benzo[a]pyrene

1986 ◽  
Vol 64 (7) ◽  
pp. 1247-1253 ◽  
Author(s):  
E. Lee-Ruff ◽  
H. Kazarians-Moghaddam ◽  
M. Katz
Keyword(s):  
Singlet Oxygen ◽  
High Field ◽  
Chemical Shifts ◽  
Product Distribution ◽  
Major Product ◽  
Nuclear Overhauser Enhancement ◽  
Nuclear Overhauser ◽  
Singlet Oxygen Reaction ◽  
Proton Chemical Shifts ◽  
Oxygen Reaction

The four diones derived from benzo[a]pyrene oxidation have been characterized by high-field nuclear magnetic resonance techniques including 2-D COSY and selective nuclear Overhauser enhancement. All the proton chemical shifts for these four quinones have been uneqivocally assigned. The direct photoxidation of benzo[a]pyrene gives a product distribution very similar to the TPP photosensitized oxygenation, suggesting singlet oxygen is involved in the former. A major product, which was characterized as the 6-seco derivative 6 and not previously reported, was detected in the singlet oxygen reaction. The presence of this product suggests a possible mechanism for quinone formation in the singlet oxygen reaction. One-electron oxidations of benzo[a]pyrene were carried out using tris(p-bromophenyl)aminium hexachloroantimonate and quenching of the radical cation with superoxide or water. The product distribution in this case was quite different from that obtained in the direct photooxidation.

DNA-porphyrin hybrids as reaction centers for photosensitized ene reactions with singlet oxygen

2012 ◽  
Vol 16 (05n06) ◽  
pp. 488-498 ◽  
Author(s):  
Rüdiger Haug ◽  
Helmut Griesser ◽  
Thomas Sabirov ◽  
Clemens Richert
Keyword(s):  
Singlet Oxygen ◽  
Solid Phase ◽  
Product Distribution ◽  
Reaction Centers ◽  
Ene Reactions ◽  
Ene Reaction ◽  
Reaction Solution ◽  
Starting Point ◽  
Recent Developments ◽  
Set Up

Recent developments in DNA-mediated nanostructuring have paved the way for the development of novel reaction centers. As part of a project focused on nanostructured reaction centers for reactions catalyzed by porphyrins, we have developed a solid-phase synthesis of tetrakis(p-hydroxyphenyl)porphyrin-oligonucleotide hybrids. In these hybrids, up to four nucleic acid chains are linked to the phenolic substituents of the porphyrin via phosphodiester linkages. A representative hybrid with one oligonucleotide chain of the sequence TTAA was found to survive light irradiation under aerobic conditions for 2 h with less than 35% oxidation of the DNA chain. An assay measuring the diastereo- and enantioselectivity of the photosensitized ene reaction of mesitylol with singlet oxygen was set up that provides diastereomeric ratios via NMR of aliquots of the reaction solution. Enantiomers were separated gas chromatographically on a chiral stationary phase and were assigned based on the product distribution obtained with an enantiomerically enriched starting material. Our results are a starting point for the exploration of nanostructured reaction media based on DNA and porphyrins.

Use of thermomechanical pulp fibers from waste woods for making eco-friendly cushioning material

TAPPI Journal ◽  
2010 ◽  
Vol 9 (7) ◽  
pp. 15-21 ◽  
Author(s):  
JI-YOUNG LEE ◽  
CHUL-HWAN KIM ◽  
JEONG-MIN SEO ◽  
HO-KYUNG CHUNG ◽  
KYUNG-KIL BACK ◽  
...  
Keyword(s):  
Impact Test ◽  
Product Distribution ◽  
Expanded Polystyrene ◽  
Thermomechanical Pulp ◽  
Fiber Structure ◽  
Pulp Fibers ◽  
Cationic Starch ◽  
Thermal Insulating ◽  
Surface Sizing ◽  
The Impact

Eco-friendly cushioning materials were made with thermomechanical pulps (TMPs) from waste woods collected from local mountains in Korea, using a suction-forming method without physical pressing. The TMP cushions had superior shock-absorbing performance, with lower elastic moduli than expanded polystyrene (EPS) or molded pulp. Even though the TMP cushions made using various suction times had many voids in their inner fiber structure, their apparent densities were a little higher than that of EPS and much lower than that of molded pulp. The addition of cationic starch contributed to an increase in the elastic modulus of the TMP cushions without increasing the apparent density, an effect which was different from that of surface sizing with starch. In the impact test, the TMP cushions showed a more ductile pattern than the brittle EPS. The porosity of the TMP cushion was a little less than that of EPS and much greater than that of molded pulp. The porous structure of the TMP cushions contributed to their excellent thermal insulating capacity, which was equivalent to that of EPS. In summary, the TMP packing cushions showed great potential for surviving external impacts during product distribution.

Fluoroquinolone Antimicrobials: Singlet Oxygen, Superoxide and Phototoxicity

1998 ◽  
Vol 67 (4) ◽  
pp. 399 ◽  
Author(s):  
Lydia J. Martínez ◽  
Robert H. Sik ◽  
Colin F. Chignell
Keyword(s):  
Singlet Oxygen
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