Microenvironment Effects on the Excited State Properties of Psoralens: a Clue to Their Photobiological Activity

Sousa, Cristina; Melo, Teresa Sá e

doi:10.1111/j.1751-1097.1996.tb03011.x

Cited by 10 publications

(5 citation statements)

References 20 publications

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“…In reversed micelles, the polarity trend with is similar to w 0 the one observed in dioxaneÈwater mixtures, conÐrming the ability of these mixtures to simulate interfaces. 19,21,23,53 The acidity of the medium is similar to the one observed in bulk water for in accordance with earlier results in w 0 [ 20, proton-transfer reactions.54h56 The trend of a is very similar to the trend observed by Politi and Chaimovich56 for the water activity measured using as probe b-naphthol-6-sulfonate (bN6S). The normalized values of a are superimposed with the water activity measured with bN6S (see Fig.…”

Section: Aot Reversed Micellessupporting

confidence: 85%

Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules

Laia¹,

Costa²

1999

Phys. Chem. Chem. Phys.

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The solvatochromism of both absorption and emission spectra of two centro-symmetrical squaraine dyes was studied in pure solvents, dioxaneÈwater mixtures and AOT (Aerosol OT, bis(2-ethylhexyl)sodium sulfosuccinate) reversed micelles. The shifts observed in pure solvents are relatively large and are associated with non-negligible soluteÈsolvent polar interactions. Good empirical correlations with the n* polarity scale (a measure of the solvent dipolar character) and with the solvent proticity a scale (a measure of the solvent acidity character) were obtained. Preferential solvation by water was not observed in the dioxaneÈwater mixtures enabling the calculation of n*, a and polarity scale values, the latter in a good agreement with E T 30 literature values. Similar trends of these parameters in AOT reversed micelles were found, but some deviations are observed at low water contents due to probe distribution at two di †erent interfacial sites.

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Section: Aot Reversed Micellessupporting

confidence: 85%

Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules

Laia¹,

Costa²

1999

Phys. Chem. Chem. Phys.

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“…For CTAB and Triton X-100 micelles, the fluorescence maxima are closer to those in water, indicating a slightly more polar environment than that for SDS. Note that similar data are available in the literature for these and related substrates in some of the same solvents, including micellar solutions; − the data in Table provide a consistent set of data measured under the same conditions for correlation with the transient studies reported herein.…”

Section: Resultssupporting

confidence: 61%

Electron-Transfer Reactions in Micelles: Dynamics of Psoralen and Coumarin Radical Cations

et al. 2001

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Radical cations of several psoralens and coumarins have been generated by photoionization in aqueous micellar solution for a comparison of their dynamic behavior with results observed previously in aqueous solution. The photoionization efficiencies are significantly higher in anionic sodium dodecyl sulfate (SDS) micelles than in aqueous solution as a result of favorable electrostatic effects that lead to rapid ejection of the electron into the aqueous phase. By contrast, much lower quantum yields are measured in neutral and cationic micelles. Experiments with anionic quenchers that are soluble only in the aqueous phase demonstrate that exit of the radical cations from anionic SDS micelles is too slow to measure (<105 s-1) under our conditions. Exit rate constants from neutral Triton X-100 micelles are approximately an order of magnitude faster. Comparison of equilibrium constants for both triplet and radical cations of 4,5‘,8-trimethylpsoralen demonstrates that electrostatic effects lead to an order of magnitude enhancement of the affinity of the radical cation for the anionic vs neutral micelles, as compared to the triplet of the same substrate. The slow exit of the radical cation from the micelle facilitates the measurement of rate constants for reaction of the micelle-incorporated radical cations with both water soluble quenchers and species for which exchange between micelle and aqueous phases is rapid on the time scale of the radical cation lifetime. This work provides some of the first kinetic data for dynamics of exit of reactive radical cations from micelles and indicates that these species may provide useful probes for studying electron-transfer dynamics in micellar media.

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“…Understanding the basis for either the phototherapeutic or harmful effects of PUVA therapy will require a detailed examination of the overall reactivity of the psoralen excited state and the reactive species formed from it as well as knowledge of the localization of the substrate. In this context it should be noted that the photophysical properties of psoralens and coumarins are strongly medium dependent (21,22). Further it has been shown that approximately 80% of bound 8-MOP detected after UVA irradiation of mouse skin is localized in protein and lipid fractions (23).…”

Section: Introductionmentioning

confidence: 98%

Reactions of Psoralen Radical Cations with Biological Substrates†¶

Wood¹,

Mnyusiwalla²,

Chen³

et al. 2007

Photochemistry and Photobiology

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The reactions of several psoralen and coumarin radical cations with biological substrates such as nucleotides, amino acids and alkenes that serve as models for unsaturated fatty acids have been examined. The radical cations were generated by laser photoionization of the parent psoralen or coumarin in aqueous buffer in most cases. Easily oxidized substrates such as tyrosine, tryptophan and guanosine monophosphate react with the 8-methoxypsoralen and several methoxy-substituted coumarin radical cations with rate constants in excess of 2 ؋ 10 9 M Ϫ1 s Ϫ1 . In each case reaction occurs via electron transfer, as demonstrated by the observation of quencher-derived radical cations or radicals by transient absorption spectroscopy. For other substrates such as histidine, methionine and adenosine monophosphate the measured rate constants are significantly slower and vary with the oxidation potential of both the parent psoralen or coumarin and the quencher, again indicative of electron transfer reactivity. Most of the alkenes studied also react with the psoralen or coumarin radical cations via electron transfer, although there is some evidence for addition for linoleic acid. Product studies carried out using both lamp and laser irradiation in the presence of deoxyguanosine as a radical cation trap lead to the formation of characteristic base-derived Type-I (electron transfer) products. This lends support to our previous hypothesis that photoionization occurs via a monophotonic process and is thus relevant to conditions used in clinical phototherapeutic applications of psoralens. The results demonstrate the relevance of electron transfer chemistry to the use of psoralens and related compounds as photoactivated drugs.

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Microenvironment Effects on the Excited State Properties of Psoralens: a Clue to Their Photobiological Activity

Cited by 10 publications

References 20 publications

Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules

Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules

Electron-Transfer Reactions in Micelles: Dynamics of Psoralen and Coumarin Radical Cations

Reactions of Psoralen Radical Cations with Biological Substrates†¶

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