On the Mechanism of Quenching of Singlet Oxygen by Amines‐iii. Evidence for a Charge‐transfer‐like Complex

Abstract

A series of amines were found to quench singlet oxygen in the order tertiary > secondary > primary, with a reasonable correlation between the log of their rate constant of quenching and their ionization potential. In addition, a Hammett rho plot gave a rho value of -1.39 for the quenching of singlet oxygen by a series of substituted N,N-dimethylanilines, in good agreement with the results obtained by a different method. It was found that some of the amines (anilines) quenched the triplet state of the dye-sensitizer (Rose Bengal) used for the production of singlet oxygen. Corrections in the results were made in the calculations of rates of quenching of singlet oxygen to allow for the triplet-state quenching. No extensive quenching of the singlet state of the dye was observed at the concentrations of the amines necessary for singlet-oxygen quenching. In one case (N,N ,N',N'-tetramethylphenylenediamine) there was no observable chemical reaction between singlet oxygen and the amine. It was concluded that singlet oxygen undergoes physical quenching by the amines via partial charge-transfer intermediates. 233 ROBERT

The Quenching of Singlet Oxygen (1Δg) by Transition Metal Chelates

“…The k, values for DABCO, p-carotene, and N-isopropyl-N'-phenyl-p-phenylenediamine in Table 6 Our amine k, values are lower than the published values perhaps because of a solvent polarity effect as suggested by Young et al (23). Our low polarity solvents would not stabilize a '0,-amine charge transfer complex as effectively as the high polarity solvents employed previously (9,26).…”

“…For rubrene, k,, = 6.0 x lo7 M-' S-' can be calculated from the kd/k,, value of 1.4 x M (23) in methanol, where k, = 9 x lo4 s 1 (23). A very similar value of k,, (rubrene) = 7.8 x lo7 M -I s-' can be derlved from p-carotene quenching data (k,,(rubrene) = 3k,,(tetramethylethylene) (24) = 150k,,(2-methyl-2-pentene) (3), k,(Pcarotene)/k,,(2-methyl-2-pentene) = 2 x lo4 (9) and k,([3-carotene) = 1.3 x 1 0 '~ IM-' s-' (18)).…”

Proline modulates the intracellular redox environment and protects mammalian cells against oxidative stress

“…Our cellular studies concur with this finding and suggest that proline exhibits specificity toward H 2 O 2 -induced stress. In addition to reacting with •OH, proline is an efficient quencher of 1 O 2 and has been shown to protect keratinocytes against photodamage [25,54]. 1 O 2 is generated mainly by UV light but is also formed by peroxidases causing tremendous oxidative damage to proteins, lipids, and DNA [55].…”

“…1 O 2 is generated mainly by UV light but is also formed by peroxidases causing tremendous oxidative damage to proteins, lipids, and DNA [55]. The quenching of 1 O 2 by secondary amines is well documented and enables polyamines to protect DNA from oxidative damage [39,54,56,57].…”

A kinetic study on singlet molecular oxygen (O2(1Δg)) generation and quenching by dihydroxynaphthalenes

“…~v e i t s within the [O2(lAg)-DHN] encounter pair would subsequently result either in intersystem crossing to yield ground-state triplet oxygen or photooxidation products. This mechanism has been postulated to account for the bimolecular reactions of OZ(lAg) with indoles, amines, sulfides, phenols, and dihydroxybenzenes, among other families of compounds (4,10,(23)(24)(25)(26). On structural grounds, one can expect a certain similarity in the photooxidative kinetic behaviour of DHN to that of phenols and dihydroxybenzenes.…”