Quenching of singlet oxygen by aliphatic amines

Monroe, Bruce M.

doi:10.1021/j100534a016

Cited by 95 publications

(71 citation statements)

References 9 publications

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“…The effect, however, is rather small since k Q goes from 1.7 · 10 8 M À1 s À1 for 1 (no a-methyl groups) to 8.9 · 10 7 M À1 s À1 for 4 (4 a-methyl groups). A possible explanation is that, as previously proposed by Monroe [7], the a-methyl groups reduce the rate by a steric effect since the formation of the exciplex requires a close approach of 1 O 2 to the N-atom of the amine. The entity of the steric effect is probably much larger than that appearing from the rate data.…”

mentioning

confidence: 80%

Quenching of Singlet Oxygen by Tertiary Aliphatic Amines. Structural Effects on Rates and Products

Baciocchi

Giacco

Lapi

2006

Helvetica Chimica Acta

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In memoriam Professor Hanns FischerA kinetic and product study of the reaction of a series of a-methyl-substituted N-methylpiperidines with thermally generated 1 O 2 in MeCN was carried out. It was found that as the number of a-methyl groups (Me in a-position relative to the N-atom) increases, the rate of 1 O 2 quenching (physical plus chemical) slightly decreases. This finding shows that, with respect to the reaction rate, steric effects are much more important than electronic effects as the latter should have produced the opposite result. The opposite outcome was instead found for the chemical quenching that leads to the N-demethylation products and N-formyl derivatives. The same trend was observed for the ratio between N-demethylation and formation of the N-formyl derivatives (NH/NCHO ratio). All these results are consistent with the mechanism reported in Scheme 1 where an exciplex is first formed that by a H-atom transfer process produces an a-amino-substituted C-radical. The latter forms the product of N-demethylation by one electron oxidation, or affords the N-formyl derivative by radical coupling (Scheme 1). Similar results were obtained with N,N-dimethylcyclohexanamine. However, this acyclic amine exhibited behaviors quite distinct from those of the N-methylpiperidines series, with respect to reaction rate, extent of chemical quenching, and NH/NCHO ratio.

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mentioning

confidence: 80%

Quenching of Singlet Oxygen by Tertiary Aliphatic Amines. Structural Effects on Rates and Products

Baciocchi

Giacco

Lapi

2006

Helvetica Chimica Acta

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“…These include the nature of the triplet excited state, i.e. n-π* or π-π*, and structural factors within the collision complex formed between oxygen and the organic molecule for example as determined for amines (46). Of particular importance is how this can influence the ability of the nascent singlet oxygen to escape from the collision complex and, as in this case, avoid the back reaction of the nascent singlet oxygen being quenched by 5HT.…”

Section: Formation and Quenching Of Singlet Oxygen In Solutions Of 5hmentioning

confidence: 99%

Identification and reactivity of the triplet excited state of 5-hydroxytryptophan

Dad¹,

Bisby²,

Clark³

et al. 2005

Journal of Photochemistry and Photobiology B: Biology

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Both the neurotransmitter serotonin and the unnatural amino acid 5-hydroxytryptophan (5HT), contain the 5-hydroxyindole chromophore. The photochemistry of 5HT is being investigated in relation to the multiphoton excitation of this chromophore to produce a characteristic photoproduct with green fluorescence ('hyperluminescence'). Laser flash photolysis (308 nm) of 5HT in aqueous solution at neutral pH produces both the neutral 5-indoloxyl radical (λ max 400-420 nm) and another transient absorption with λ max 480 nm and lifetime of 2 μs in deaerated solutions. Based on quenching by oxygen and β-carotene, the species at 480 nm is identified as the triplet excited state of 5HT. In acidic solution a new oxygen-insensitive intermediate with λ max 460 is assigned to the radical cation of 5HT. Time-resolved measurements of luminescence at 1270 nm have shown that the triplet state of 5HT is able to react with oxygen to form singlet excited oxygen ( 1 O 2 *) with a quantum yield of ∼0.1. However, 5HT has also been found to be an effective quencher of singlet oxygen with a second order rate constant of 1.3 × 10 8 dm 3 mol -1 s -1 . The results are discussed in the light of recent observations on the multiphoton-excited photochemistry of serotonin.

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“…each having the same initial concentration of rubrene, are each exposed to the same amount of 1 O 2 , the singlet oxygen quenching rate constant (k ox-Q + k q ) can be calculated from the following equation (27,28): It is seen that the singlet oxygen rate constant (k ox-Q + k q ) can be calculated from four experimentally determinable quantities and two rate constants. Both the lifetime of 1 O 2 (1/k d ) and the rate of addition of 1 O 2 to rubrene (k ox ) in a number of solvents can be obtained from previous papers.…”

Section: Antiphoto-oxidative Activity Of Sesamol In Methylenementioning

confidence: 99%

“…Both the lifetime of 1 O 2 (1/k d ) and the rate of addition of 1 O 2 to rubrene (k ox ) in a number of solvents can be obtained from previous papers. We adapted k ox ) 5.3 × 10 7 M -1 s -1 and k d ) 1.7 × 10 4 s -1 from the literature (27,31). Table 1.…”

Section: Antiphoto-oxidative Activity Of Sesamol In Methylenementioning

confidence: 99%

Antiphoto-oxidative Activity of Sesamol in Methylene Blue- and Chlorophyll-Sensitized Photo-oxidation of Oil

Kim

Choi

Jung

2003

J. Agric. Food Chem.

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The effects and mechanism of sesamol on the methylene blue- or chlorophyll-sensitized photo-oxidations of soybean oil have been studied. Sesamol showed strong antiphoto-oxidative activity in both methylene blue-and chlorophyll-sensitized photo-oxidations of soybean oil in a dose-dependent manner. The 1.0 x 10(-3) M sesamol treatments showed 84.7 and 43.4% inhibitions of methylene blue- and chlorophyll-sensitized photo-oxidations of soybean oil in methylene chloride. The antiphoto-oxidative activity of sesamol was comparable to that of delta-tocopherol in both methylene blue- and chlorophyll-sensitized photo-oxidations, at the same molar basis. Sesamol effectively inhibited rubrene oxidation with a chemical source of singlet oxygen in microemulsion, showing its strong singlet oxygen quenching ability. The results suggested that the antiphoto-oxidative activity of sesamol in the photo-oxidation of oil was, at least in part, due to its singlet oxygen scavenging activity. The singlet oxygen quenching rate constant (k(ox-Q) + k(q)) of sesamol was determined to be 1.9 +/- 0.3 x 10(7) M(-1) s(-1). This represents the first report on the antiphoto-oxidative activity of sesamol in the sensitized photo-oxidation of oil, and its bimolecular singlet oxygen quenching ability.

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Quenching of singlet oxygen by aliphatic amines

Cited by 95 publications

References 9 publications

Quenching of Singlet Oxygen by Tertiary Aliphatic Amines. Structural Effects on Rates and Products

Quenching of Singlet Oxygen by Tertiary Aliphatic Amines. Structural Effects on Rates and Products

Identification and reactivity of the triplet excited state of 5-hydroxytryptophan

Antiphoto-oxidative Activity of Sesamol in Methylene Blue- and Chlorophyll-Sensitized Photo-oxidation of Oil

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