Triplet oxidation

As in the case of DIBF, both are CTX and MK are triplet sensitizers. However, CTX appears to undergo triplet oxidation, in that a new band attributed to the... 

Catalytic oxidation of isobutyraldehyde with air at 30—50°C gives isobutyric acid [79-31-2] ia 95% yield (5). Certain enzymes, such as horseradish peroxidase, cataly2e the reaction of isobutyraldehyde with molecular oxygen to form triplet-state acetone and formic acid with simultaneous chemiluminescence (6). 

The salts of some enamines crystallize as hydrates. In such cases it is possible that they are derived from either the tautomeric carbinolamine or the amino ketone forms. Amino ketone salts (93) ( = 5, 11) can serve as examples. The proton resonance spectra of 93 show that these salts exist in the open-chain forms in trifluoroacetic acid solution, rather than in the ring-closed forms (94, n = 5, 11). The spectrum of the 6-methylamino-l-phenylhexanone cation shows a multiplet at about 2.15 ppm for phenyl, a triplet for the N-methyl centered at 7.0 ppm and overlapped by signals for the methylene protons at about 8.2 ppm. The spectrum of 93 ( = 11) was similar. These assignments were confirmed by determination of the spectrum in deuterium oxide. Here the N-methyl group of 93 showed a sharp singlet at about 7.4 ppm since the splitting in —NDjMe was much reduced from that of the undeuterated compound. 

In addition, there are many surface modification processes that use triplet sensitizers to permit oxidation reactions. In a typical process, polyisocyanate is applied on a polyolefin together with a sensitizer such as benzo-phenone and then irradiated with UV light. As shown in Eq. (15) the sensitizer has an oxidizing effect to produce hydroxyl groups over the polymer surface. These hydroxyl groups finally react with isocyanate to provide a functional polymer [56,57]. 

Oxepin has also been converted photochemically to phenol in 74% yield. This reaction occurs under irradiation conditions by which benzene oxide is excited to a triplet state, e.g. by irradiation in acetone as solvent.207 A rare example for a nucleophilic catalysis of the aromatization of an oxepin/benzene oxide to a phenol has been reported for /err-butyl oxepin-4-carboxylate which undergoes a rearrangement reaction in the presence of trimethylamine to give a mixture of /m-butyl 3-hydroxybenzoate (94%) and 4-hydroxybenzoate (6%).243... 

Hurley and Testa (Ref 17) exposed nitrobenzene in isopropyl alcohol, degassed and in air, to a mercury lamp at 3660A Products in the absence of air were acetone and phenyl-hydroxylamine (PHA). In air PHA was oxidized to nitro sob enzene which couples with PHA to form azoxybenzene. They hypothesized that the triplet molecule abstracted H-atoms from the solvent no effect was noted with ben zene as solvent. They also worked with nitrobenzene in isopropyl alcohol-water mixts containing HC1 with a mercury lamp at 3660A (Ref 18), and found that the quantum yields depended on pH and isopropyl alcohol content, but were independent of oxygen with acid present. Their conclusion was that the quantum yield consisted of two parts, H abstraction by the triplet, and protonation of the triplet... 

Interestingly, preliminary calculations (3-21G basis set) estimate the AH of the triplet SO (and ethylene) generation from the parent thiirane oxide (16a) to be about 18kcalmol-1 166. 

Two attractive routes to thiolene oxide and dioxide are the diene-SO104 and diene-S02298 cycloadditions, respectively. These cycloadditions are highly stereoselective at both carbons of the diene systems and at sulfur (see equation 62 for specifics) which, in the case of sulfoxide formation, proceed via attack of triplet SO on the diene. Equation 112 shows an example of such a cycloaddition104. The overall yields are significantly improved by running the cycloadditions in the absence of oxygen and by the use of excess diene. 

Third, students understanding of the triplet relationship for a particular type of reaction may be further consolidated by carrying out additional similar reactions using different reactants (e.g., using several metal oxides to react with different dilute acids will help illustrate the similarities in the chemical reactions although different salts are produced). Once students become aware of the similarities in the chemical reactions, they would be more likely to meaningfully deduce the ionic equations for the chemical reactions instead of the common practice of cancelhng out the spectator ions from the overall balanced chemical equation. 

Consequently, the antioxidant activity of GA in biological systems is still an unresolved issue, and therefore it requires a more direct knowledge of the antioxidant capacity of GA that can be obtained by in vitro experiments against different types of oxidant species. The total antioxidant activity of a compound or substance is associated with several processes that include the scavenging of free radical species (eg. HO, ROO ), ability to quench reactive excited states (triplet excited states and/ or oxygen singlet molecular 1O2), and/or sequester of metal ions (Fe2+, Cu2+) to avoid the formation of HO by Fenton type reactions. In the following sections, we will discuss the in vitro antioxidant capacity of GA for some of these processes. 

Figure lb shows the transient absorption spectra of RF (i.e. the difference between the ground singlet and excited triplet states) obtained by laser-flash photolysis using a Nd Yag pulsed laser operating at 355 nm (10 ns pulse width) as excitation source. At short times after the laser pulse, the transient spectrum shows the characteristic absorption of the lowest vibrational triplet state transitions (0 <— 0) and (1 <— 0) at approximately 715 and 660 nm, respectively. In the absence of GA, the initial triplet state decays with a lifetime around 27 ps in deoxygenated solutions by dismutation reaction to form semi oxidized and semi reduced forms with characteristic absorption bands at 360 nm and 500-600 nm and (Melo et al., 1999). However, in the presence of GA, the SRF is efficiently quenched by the gum with a bimolecular rate constant = 1.6x10 M-is-i calculated... 

Huvaere, K., and Skibsted, L. H. (2009) Light-Induced Oxidation of Tryptophan and Histidine. Reactivity of Aromatic N-Heterocycles toward Triplet-Excited Flavins, Journal of American and Chemical Society, Vol. 131, (May 2009) pp. 8049-8060, ISSN 0002-7863. 

Lu, C. Y. Lui, Y.Y. (2002). Electron transfer oxidation of tryptophan and tyrosine by triplet states and oxidized radicals of flavin sensitizers a laser flash photolysis study. Biochimica et Biophysica Acta (BBA) - General Subjects, Vol. 1571, No.l, (May 2002), pp. 71-76, ISSN 0304-4165... 

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