Singlet Oxygen Generation by Furocoumarin Triplet States—i. Linear Furocoumarins (Psoralens)

Knox, C. N.; Land, Edward J.; Truscott, T. George

doi:10.1111/j.1751-1097.1986.tb05616.x

Cited by 38 publications

(21 citation statements)

References 26 publications

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“…These absorptions are attributed to the respective triplet states; in all cases, the absorption maxima are consistent with those previously determined in a variety of organic solvents. 31,32 Excitation of coumarin and 7-methylcoumarin under the same conditions did not result in any significant absorption in the 350-700 nm region, consistent with literature reports of low triplet yields for related compounds. 33 However, the three methoxysubstituted coumarins yielded transient absorption spectra with λ max values between 470 and 500 nm, as shown in Figure 2b for 67-DMC.…”

Section: Generation Of Radical Cations Via Photosensitized Electron Tsupporting

confidence: 89%

Photoionization and Photosensitized Electron-Transfer Reactions of Psoralens and Coumarins

Wood

Johnston

1998

J. Phys. Chem. A

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Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/eng/view/object/?id=12169fb9-38e7-4837-9393-0a3781639501 http://nparc.cisti-icist.nrc-cnrc.gc.ca/fra/voir/objet/?id=12169fb9-38e7-4837-9393-0a3781639501 13, 1997; In Final Form: March 18, 1998 The radical cations of several psoralens (furocoumarins) and coumarins have been generated via direct excitation (λ ex ) 355 nm) in aqueous solution and/or via photosensitized electron transfer in acetonitrile and characterized using transient absorption spectroscopy. Significant photoionization yields were observed for 8-methoxypsoralen (8-MOP) and three methoxy-substituted coumarins in aqueous buffer and for 4,5′,8-trimethylpsoralen in aqueous acetonitrile. Of those, 6,7-dimethoxycoumarin (67-DMC) was found to have the highest quantum (0.2 ( 0.03) yield for photoionization in aqueous buffer following direct excitation at both 355 and 308 nm. Laser energy dependence plots for the photoionization process are linear and pass through (0,0) for λ ex ) 355, 308, and 266 nm, providing strong evidence for a monophotonic process. The photoionization results are compared with both the one-electron oxidation potentials of the compounds (obtained via cyclic voltammetry) and the fluorescence quantum yields and lifetimes (obtained via single photon counting). The results demonstrate that photoionization is of general importance in psoralen and coumarin photochemistry and varies substantially in efficiency, depending on the structure, photophysical parameters, and environment of the substrate. The observation of photoionization upon low-intensity UVA irradiation is clearly significant with respect to the clinical use of these compounds in psoralen UVA therapy.

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Section: Generation Of Radical Cations Via Photosensitized Electron Tsupporting

confidence: 89%

Photoionization and Photosensitized Electron-Transfer Reactions of Psoralens and Coumarins

Wood

Johnston

1998

J. Phys. Chem. A

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“…(IS). The (DT = 0.21, reported for TMP in benzene (19) is assumed to be a corrected value for a dioxane solution, because both solvents display very close dielectric properties as already described (IS). In the present work a QT = 0.07 was ohserved for TMA in dioxane, which is slightly different from that reported (0.13) in benzene (20).…”

Section: Methodsmentioning

confidence: 99%

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

Sousa

Melo

1996

Photochem & Photobiology

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The singlet and triplet excited state parameters (phi f, tau t and phi T) of psoralen (PSO) and derivatives 4,6,4'-trimethylangelicin (TMA) and 4,5',8-trimethylpsoralen (TMP) show an extreme sensitivity to solvation in dioxane/water mixtures. These effects are attributed to the variation of the S1-->S0 internal conversion rate constant kic, which is the nonradiative deactivation path dominating their photophysical behavior. Depending on the compound, kic is very high, (approximately 1 x 10(10) s-1) in nonpolar solvents and then decreases to a low value (3 x 10(8) s-1), with increasing solvent polarity. This work shows that dioxane/water mixtures display the same solvent-induced changes in the electronic structure of psoralens during solvation as those induced by the biological microenvironment sensed by the drug's localization. This mixture matches the photophysical parameters of psoralens observed in protic and aprotic pure solvents, in micelles, in liposomes and in human serum low-density lipoproteins (LDL). They can be used to probe the solvating ability of the interaction site in macrocyclic hosts. A particular localization site, i.e. the more (TMA and TMP) or less (PSO) lipophilic sites found when in interaction with LDL, determines the amount of the triplet reactive state of psoralens and the molecular mechanism available for photoreaction: oxic (type I and type II) or anoxic (type III) pathways.

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“…However, higher doses than the ones used in the present study of both light and psoralen are usually required in order to demonstrate the photodynamic effect. Furthermore, 3-carbethoxypsoralen (27,28) and also 3-carbethoxy-8-methylpsoralen (results not shown) are > 20 times as efficient as 8-methoxypsoralen in producing singlet oxygen. This relation is not reflected in the results concerning inhibition of RNA synthesis (Fig.…”

Section: Discussionmentioning

confidence: 99%

Syntheses of rRNA, 5.8S, 5S and tRNA are inhibited equally by 8-methoxypsoralen phototreatment ofTetrahymena thermophila

Nielsen¹

1987

Nucl Acids Res

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Treatment of the ciliated protozoan Tetrahymena thermophila with 8-methoxypsoralen combined with long wavelength ultraviolet irradiation (tWA, X 360 nm) resulted in a dose dependent equal inhibition of the synthesis of rRNA, 5.8S, 5S and tRNA. Similar results were obtained with 3-carbethoxy-8-methylpsoralen which predominantly forms DNA mono-adducts. In contrast the synthesis of tRNA in T. thermophila was much less sensitive than that of rRNA, 5.8S and 5S RNA to treatment with short wavelength ultraviolet irradiation (UVB, X -254 nm). These results are interpreted in favor of a mechanism by which psoralen-DNA adducts (crosslinks >> monoadducts) inhibit RNA transcription initiation (in contrast to UVB which causes premature chain termination). Furthermore it is argued that RNA synthesis is regulated in equally sized domains regardless of the gene-size.

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Singlet Oxygen Generation by Furocoumarin Triplet States—i. Linear Furocoumarins (Psoralens)

Cited by 38 publications

References 26 publications

Photoionization and Photosensitized Electron-Transfer Reactions of Psoralens and Coumarins

Photoionization and Photosensitized Electron-Transfer Reactions of Psoralens and Coumarins

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

Syntheses of rRNA, 5.8S, 5S and tRNA are inhibited equally by 8-methoxypsoralen phototreatment ofTetrahymena thermophila

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