Triplet state studies of β-carbolines

Varela, Ana; Douglas, Peter; Miguel, Maria

doi:10.1016/s1010-6030(01)00551-2

Cited by 36 publications

(43 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…On the basis of the overlap of the scaled absorption and fluorescence spectra, we obtain an S 1 excitation energy for Ho of 306 kJ mol À1 . From phosphorescence spectra, [9] we estimate a T 1 energy of~260 kJ mol À1 . Thus, the S 1 -T 1 energy gap is well below the 94 kJ mol À1 excitation energy of O 2 (a 1 D g ) and, as such, we can exclude channel 1 from further consideration with the present system.…”

Section: à3mentioning

confidence: 99%

Fluorescence Quenching by Oxygen: “Debunking” a Classic Rule

et al. 2010

View full text Add to dashboard Cite

It has long been accepted that oxygen-induced deactivation of an organic molecule's fluorescent state (i.e. the lowest excited singlet state, S 1 ) proceeds exclusively via intersystem crossing (ISC) to produce the triplet excited state, T 1 . [1][2][3][4] Oxygeninduced S 1 !S 0 internal conversion (IC) to produce the singlet ground state, S 0 , is thought not to occur. In a light-filled world where S 1 generation is commonplace and where molecular oxygen can be found at appreciable concentrations, this phenomenon can have significant implications. Among other things, it means that much O 2 -dependent photochemistry derives from the T 1 state and, as such, can yield unique and characteristic products.To our knowledge, only 9,10-diphenylanthracene has been presented as an exception to the rule that O 2 always induces S 1 !T 1 ISC.[5] Even in this case, however, the data are not as convincing as one might otherwise desire. We recently suggested that b-carbolines, bCs, may provide substantive evidence that an O 2 -induced S 1 !S 0 transition can actually occur. [6] We now demonstrate that the O 2 -dependent photophysics of selected bCs indeed provide an "exception to the rule" and that O 2 -induced S 1 !S 0 IC can efficiently compete with O 2 -induced S 1 !T 1 ISC. The present data, point to the possibility that other molecules will respond to O 2 like the bCs, limiting T 1 -derived chemistry or behavior which, in turn, opens new options for the design and application of unique photochemical, photophysical, and photobiological systems.The bCs used, norharmane (nHo, R 1 = R 2 = H), harmane (Ho, R 1 = H, R 2 = CH 3 ) and N-methylharmane (NMeHo, R 1 = R 2 = CH 3 ), Scheme 1, are water soluble compounds of significant biological importance whose behavior depends on pH.[6] Although the S 1 !S 0 phenomenon presented herein is observed in both alkaline and acidic media, it is more pronounced in the latter and, as such, we limit our discussion to data recorded at pH 5. We also limit our discussion to Ho; data for nHo and NMeHo can be found in the Supporting Information.For Ho, the fluorescence quantum yield, F F , decreases as the concentration of dissolved oxygen increases (Figure 1 a). This is expected with the bimolecular quenching of S 1 by O 2 . Indeed, these compounds have an S 1 lifetime (~20-25 ns) [6][7][8] that is long enough for O 2 -induced deactivation to play a prominent role.If O 2 indeed induces S 1 !T 1 ISC, one would then expect to see a corresponding increase in the triplet state yield. This was not the case. Rather, we observed a distinct and pronounced decrease in the T 1 yield as the O 2 concentration was increased (Figure 1 b). The latter data were recorded in time-resolved ab- [a] Dr.

show abstract

Section: à3mentioning

confidence: 99%

Fluorescence Quenching by Oxygen: “Debunking” a Classic Rule

et al. 2010

View full text Add to dashboard Cite

show abstract

“…It is well known that harmine phototoxicity in vivo involves the generation of reactive oxygen species (Larson et al, 1988;Varela et al, 2001), which have a short lifetime in biological systems (<0.04 µs) and consequently a radius of action of <0.02 µm (Peng et al, 1996).…”

Section: Discussionmentioning

confidence: 99%

“…The renewed interest in β-carbolines also uncovered their activity as photosensitizers, mainly due to their high triplet quantum yield (Varela et al, 2001) and their efficient generation of both singlet oxygen and superoxide anions (Chae & Ham, 1986;Calle et al, 1996). In connection with this, a number of studies performed in our laboratory and by other groups have demonstrated that β-carbolines possess a powerful in vivo and in vitro photocytotoxic activity in different experimental systems (Hudson et al, 1986;Hazen & Gutiérrez-Gonzálvez, 1988;Larson et al, 1988).…”

Section: Introductionmentioning

confidence: 99%

Ultrastructural changes induced in HeLa cells after phototoxic treatment with harmine

Pérez-Martı́n

Labrador

Freire

et al. 2004

J of Applied Toxicology

View full text Add to dashboard Cite

In the present work, we have continued our studies on harmine phototoxicity in human tumour cells. The toxicity of harmine in the dark was analysed by a quantitative neutral red uptake assay, and subcellular sensitive targets following harmine photosensitization were de fi ned by electron microscopic analysis of HeLa cells. The results obtained indicated that this compound shows a clear dose-dependent cytotoxic effect in the dark. The combined treatment with suitable doses of harmine and UV radiation was very effective at an early stage, although maximal cell killing appeared 48 h after photodynamic activation. Ultrastructural examination of HeLa cells immediately after the photodynamic treatment revealed lysosomal destabilization and profound cytoplasmic vacuolization that evolved to cytolysis, which is typical of necrotic cell death. It is concluded that harmine could be a valuable photosensitizer whose biological applications merit further evaluation.

show abstract

“…Recently, Varela et al 19 described the phosphorescence spectra, φ p and τ p at 77 K for the neutral and cationic forms of compounds 1, 2 and 3. The values obtained and the conclusions reached are similar to those discussed above.…”

Section: Emission At 77 Kmentioning

confidence: 99%

Electronic spectroscopy of the β-carboline derivatives nitronorharmanes, nitroharmanes, nitroharmines and chloroharmines in homogeneous media and in solid matrix

Tarzi¹,

Ponce²,

Cabrerizo³

et al. 2006

Arkivoc

View full text Add to dashboard Cite

Electronic spectra (absorption, fluorescence and phosphorescence emission spectra) of nitro-β-carboline derivatives (nitronorharmanes, nitroharmanes and nitroharmines) in acetonitrile and in methanol solution at 298 K and in solid matrix at 77 K have been recorded and compared with those of the corresponding β-carbolines and chloroharmine derivatives. The electronic absorption spectra of triplet transients of these β-carbolines, the triplet lifetime, τ T , and the intersystem crossing quantum yield, φ isc , were measured by Laser Flash Photolysis at 298 K. The dynamic properties of the lowest excited singlet and triplet states (τ f , τ p , φ f and φ p ) have been measured in the same experimental conditions. From these data, the radiative and radiationless rate constants (k o f , k isc and k ic ) were derived. The intramolecular spin -orbital coupling effect on the spectroscopic data and photophysical rate constant were also analyzed.

show abstract

Triplet state studies of β-carbolines

Cited by 36 publications

References 41 publications

Fluorescence Quenching by Oxygen: “Debunking” a Classic Rule

Fluorescence Quenching by Oxygen: “Debunking” a Classic Rule

Ultrastructural changes induced in HeLa cells after phototoxic treatment with harmine

Electronic spectroscopy of the β-carboline derivatives nitronorharmanes, nitroharmanes, nitroharmines and chloroharmines in homogeneous media and in solid matrix

Contact Info

Product

Resources

About