Article

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.

Download Full-text

Benzophenone-photosensitized autoxidation of linoleate in solution and sodium dodecyl sulfate micelles

Canadian Journal of Chemistry ◽

10.1139/v87-422 ◽

1987 ◽

Vol 65 (11) ◽

pp. 2529-2540 ◽

Cited By ~ 66

Author(s):

Lawrence Ross Coates Barclay ◽

Kimberly Ann Baskin ◽

Steven Jeffrey Locke ◽

Tanya Diane Schaefer

Keyword(s):

Linoleic Acid ◽

Rate Constants ◽

Sodium Dodecyl ◽

Kinetic Studies ◽

Water Soluble ◽

Peroxyl Radicals ◽

Phenolic Antioxidants ◽

Radical Chain ◽

Geometrical Isomers ◽

Chain Reactions

Diffusion studies show that benzophenone (BP), linoleic acid, and methyl linoleate partition completely into the micelles of phosphate buffer/0.10 M SDS. Water-soluble compounds 4-sulphomethylbenzophenone, sodium salt (BP−), azobis(2-amidinopropane•HCl) (ABAP) and 2,5,7,8-tetramethyl-6-hydroxychroman-2-carboxylate (Trolox) show partial partitioning into the micelles. BP- and BP−-photosensitized oxidation of linoleic acid in 0.50 M SDS exhibited characteristics of free radical chain reactions including: (1) inhibition by phenolic antioxidants, (2) no retardation by singlet oxygen quenchers, and (3) the formation of conjugated hydroperoxides with cis,trans to trans,trans ratios of geometrical isomers typical of autoxidation. Quantitative kinetic studies of the order in substrate, RH, and the rate of chain initiation, Ri, show that the classical rate law, −d[O2]/dt = kp/2kt1/2[RH]Ri1/2 applies to BP-photoinitiated autoxidation of linoleic acid in SDS and the oxidizability (kp/2kt1/2 = 4.42 × 10−2 M−1/2 s−1/2) is the same as that found with a thermal initiator. The rotating sector method gave absolute rate constants for linoleic acid autoxidation in 0.50 M SDS for propagation (kp = 36.2 M−1 s−1) and termination (2kt = 3.52 × 105 M−1 s−1), significantly lower than values in polar organic solvents; attributed to solvation of polar peroxyls in aqueous SDS. Depressed inhibition rate constants (kinh) for α-tocopherol, Trolox, and pentamefhylhydroxychroman (PMHC) in 0.50 M SDS compared to kinh in tert-butyl alcohol are attributed to hydrogen bonding effects on the peroxyl radicals and on the inhibitors.

Download Full-text

Photooxidation of 2-(tert-Butyl)-3-Methyl-2,3,5,6,7,8-Hexahydroquinazolin-4(1H)-one, an Example of Singlet Oxygen ene Reaction

Molecules ◽

10.3390/molecules25215008 ◽

2020 ◽

Vol 25 (21) ◽

pp. 5008

Author(s):

Adrian Méndez ◽

Jonathan Román Valdez-Camacho ◽

Jaime Escalante

Keyword(s):

Singlet Oxygen ◽

Theoretical Study ◽

Solvent Mixture ◽

Ambient Conditions ◽

Ene Reactions ◽

Ene Reaction ◽

Photo Oxidation ◽

Tert Butyl ◽

Nmr Study ◽

Step Mechanism

Singlet oxygen ene reactions produce 2-(tert-butyl)-4a-hydroperoxy-3-methyl-2,4a, 5,6,7,8-hexahydroquinazolin-4(3H)-one quantitatively during diffusion crystallization of 2-(tert-butyl)-3-methyl-2,3,5,6,7,8-hexahydroquinazolin-4(1H)-one in n-hexane/CH2Cl2 solvent mixture. To confirm this photo-oxidation, a 1H-NMR study in CDCl3 was performed with exposure to ambient conditions (light and oxygen), with neither additional reactants nor catalysts. A theoretical study at the B3LyP/6311++G** level using the QST2 method of locating transition states suggests a two-step mechanism where the intermediate, which unexpectedly did not come from the peroxide intermediate, has a low activation energy.

Download Full-text

Kinetic studies of excited singlet oxygen atom O( 1 D) reactions with ethanol

International Journal of Chemical Kinetics ◽

10.1002/kin.21474 ◽

2021 ◽

Author(s):

Hongtao Zhong ◽

Chao Yan ◽

Chu C. Teng ◽

Timothy Y. Chen ◽

Gerard Wysocki ◽

...

Keyword(s):

Oxygen Atom ◽

Singlet Oxygen ◽

Kinetic Studies ◽

Excited Singlet

Download Full-text

ChemInform Abstract: KINETIC STUDIES OF THE REACTION BETWEEN SODIUM DODECYL SULFATE AND PINACYAMOL CHLORIDE

Chemischer Informationsdienst ◽

10.1002/chin.197419207 ◽

1974 ◽

Vol 5 (19) ◽

Author(s):

NOBUHIDE TATSUMOTO ◽

KUNIO TAKEDA ◽

SHUNJI ISSHIKI ◽

TATSUYA YASUNAGA

Keyword(s):

Sodium Dodecyl Sulfate ◽

Sodium Dodecyl ◽

Kinetic Studies ◽

Dodecyl Sulfate

Download Full-text

The photo-oxidation of an enolate anion: evidence for singlet oxygen as the intermediate

Chemical Communications (London) ◽

10.1039/c19670000827 ◽

1967 ◽

pp. 827 ◽

Cited By ~ 3

Author(s):

Robert H. Young ◽

Harold Hart

Keyword(s):

Singlet Oxygen ◽

Photo Oxidation ◽

Enolate Anion

Download Full-text

Thermodynamic and kinetic studies of the interaction of merocyanine 540 with hydrophobic aggregates. 1. Binding of merocyanine 540 to sodium dodecyl sulfate micelles

The Journal of Physical Chemistry ◽

10.1021/j100289a029 ◽

1987 ◽

Vol 91 (5) ◽

pp. 1166-1172 ◽

Cited By ~ 17

Author(s):

G. Dodin ◽

J. Aubard ◽

D. Falque

Keyword(s):

Sodium Dodecyl Sulfate ◽

Sodium Dodecyl ◽

Kinetic Studies ◽

Merocyanine 540 ◽

Dodecyl Sulfate

Download Full-text

Inhibition of the thrombin–fibrinogen reaction by a macromolecular factor from rat liver

Biochemical Journal ◽

10.1042/bj1290083 ◽

1972 ◽

Vol 129 (1) ◽

pp. 83-89 ◽

Cited By ~ 5

Author(s):

Ragnar Flengsrud ◽

Bjarne Østerud ◽

Hans Prydz

Keyword(s):

Molecular Weight ◽

Rat Liver ◽

Gel Electrophoresis ◽

Competitive Inhibition ◽

Polyacrylamide Gel Electrophoresis ◽

Sodium Dodecyl ◽

Liver Homogenate ◽

Kinetic Studies ◽

Disc Electrophoresis ◽

Nitrobenzoic Acid

1. The supernatant obtained by centrifugation of a rat liver homogenate at 100000g for 1h contained a heat-labile macromolecular inhibitor of the thrombin–fibrinogen reaction. 2. The inhibitor was purified to electrophoretic homogeneity by repeated preparative polyacrylamide disc electrophoresis. Inhibition was observed with purified inhibitor equivalent to about 1μg of protein/ml. 3. The inhibitor had a pI of 3.50–3.75, a molecular weight (from sodium dodecyl sulphate–polyacrylamide-gel electrophoresis) of 72000±3000 and was inactivated by p-hydroxymercuribenzoate or 5,5′-dithiobis-(2-nitrobenzoic acid). 4. Kinetic studies revealed a non-competitive inhibition, with the inhibitor probably acting on the thrombin–fibrinogen complex.

Download Full-text

Article

Canadian Journal of Chemistry ◽

10.1139/v97-221 ◽

1998 ◽

Vol 76 (2) ◽

pp. 171-182 ◽

Cited By ~ 1

Author(s):

Fengde Xi ◽

L Ross Barclay

Keyword(s):

Methyl Linoleate ◽

Antioxidant Activities ◽

Lignin Content ◽

Synergistic Effects ◽

Sodium Dodecyl ◽

Ascorbyl Palmitate ◽

Semiquinone Radical ◽

Semiquinone Radicals ◽

Sds Micelles

The antioxidant activities, kinh, of catechol, 1, 4-tert-butylcatechol, 2, and 3,5-di-tert-butylcatechol (DTBC), 3, determined by the inhibited oxygen-uptake method during peroxidation of styrene initiated by AIBN are 55.0 x 104, 88.4 x 104, and 149 x 104 M-1s-1, respectively, and the stoichiometric factors (n) were 2.1-2.3. A decrease by 50-fold in kinh for 3 and a drop of 1.1-1.4 in n observed during inhibited peroxidation of methyl linoleate in aqueous sodium dodecyl sulfate (SDS) initiated by di-tert-butylhyponitrile (DBHN) is attributed to hydrogen bonding by water on the antioxidant and on the intermediate di-tert-butylsemiquinone radical, 5, formed in the inhibition step. Combinations of ascorbyl palmitate with 3 exhibited cooperative (not synergistic) antioxidant effects during inhibited peroxidation of styrene in solution. Combinations of ascorbic acid with 3 exhibited synergistic effects during inhibited peroxidation of methyl linoleate initiated by DBHN in SDS micelles. A profile of the effect of concentration of ascorbate on this synergism indicates a mole of 3 is regenerated per mole of ascorbate. The thiols, homocysteine, and polyethylene glycol thiol (polythiol) also exhibited synergistic effects with DTBC in this inhibition. Either ascorbate or polythiol rapidly reduces di-tert-butyl-ortho-quinone (DTBQ), 4, to 3 in methanol or in SDS micelles, and the combination of 3 + ascorbate acted as an efficient inhibitor in this medium. The esr studies indicate the semiquinone radical, 5, produced photochemically from 3 or spontaneously from 3 + 4 in solution, to be very persistent at room temperature. A pathway, mediated by 5, is proposed to account for the cooperative and synergistic effects observed and for the additional combination effect discovered when the three inhibitors: 3, ascorbate, and a thiol are used in the SDS medium. Combinations of such antioxidants are expected to be useful for inhibition of yellowing of pulps and paper with high lignin content, and to be significant in the in vivo reductions of ortho-quinones and semiquinone radicals formed during oxidations of various biomolecules.Key words: catechols, ascorbate, thiols, radicals, antioxidants.

Download Full-text