Transient absorption spectra and quenching of coumarin excited states by nucleic acid bases

Kang, Hyuk; Shin, Eun Ju; Shim, Sang Chul

doi:10.1016/1011-1344(92)80036-u

Cited by 13 publications

(8 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, the three methoxy-substituted coumarins yielded transient absorption spectra with λ max values between 470 and 500 nm, as shown in Figure b for 67-DMC. These transients reacted with oxygen and are assigned to the triplet−triplet absorption spectra in good agreement with literature reports for a variety of coumarins, including 57-DMC, in water and organic solvents. ,− The spectra in Figure b also show weak absorptions at longer wavelength that are not removed by oxygen and are similar to the radical cation spectra obtained by chloranil photosensitization. Similarly, weak absorptions consistent with radical cation formation were also observed for 57-DMC.…”

Section: Resultssupporting

confidence: 89%

“…Considerable research efforts have been directed toward identifying the excited-state intermediates involved in the photocycloaddition chemistry of psoralens that are used in PUVA. Early attention focused on characterization of the triplet states of 8-MOP and other psoralens by transient absorption spectroscopy 8 and the measurement of singlet oxygen yields. − A number of coumarin photosensitizers have also attracted attention since they do not form diadducts and can serve as models for the initial furan monoadduct that is the precursor to DNA cross-links. − More recently, the importance of binding to proteins, cycloaddition reactions with unsaturated fatty acids, , and electron-transfer reactions ,− in psoralen photochemistry has been examined. A detailed understanding of the molecular basis for both the therapeutic and harmful effects of PUVA therapy is obviously required to aid in the further development of potential new therapeutic agents.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Photoionization and Photosensitized Electron-Transfer Reactions of Psoralens and Coumarins

Wood

Johnston

1998

J. Phys. Chem. A

View full text Add to dashboard Cite

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.

show abstract

Section: Resultssupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Photoionization and Photosensitized Electron-Transfer Reactions of Psoralens and Coumarins

Wood

Johnston

1998

J. Phys. Chem. A

View full text Add to dashboard Cite

show abstract

“…Simultaneously, addition of thymine (up to 10 mM) does not change τ S . These observations are in agreement with the results of Kang et al 17 on absence of 8-MOP fluorescence quenching by DNA or nucleotides. Thus a solely triplet-triplet quenching mechanism for the reaction between 8-MOP and nucleobases can be considered.…”

Section: -Mop With Nucleic Acidssupporting

confidence: 93%

Excited singlet state and photoionization of 8-methoxypsoralen. Picosecond transient absorption study

Gurzadyan

2002

Photochem Photobiol Sci

View full text Add to dashboard Cite

Time-resolved pico- and nanosecond transient absorption measurements of 8-methoxypsoralen (8-MOP) were performed in different solvents at room temperature. The excited singlet state has two strong absorption bands with maxima at 430 and 630-690 nm. The lifetime of the first excited singlet state, tau(s), ranges from <10 ps up to 2.7 ns, being shorter in low-polar solvents (toluene, THF) and longer in highly polar water, TFE and HFIP. The rate of the singlet depopulation decreases exponentially with increasing solvent polarity as expressed by the Dimroth-Reichardt (ET(N)) or Gutmann solvent acceptor number (AN). In aqueous ethanol solution (H2O: EtOH 10:1), addition of the synthetic nucleobase 2-aminopurine slightly decreased the lifetime tau(s). The long-time (t > 5 ns) absorption spectrum remaining after the complete decay of the S1 state is due to the hydrated electron e(aq) and the radical cation 8-MOPF.+. Ionization is due to both, one and two-quantum excitation. In the intensity range I = 10(6)-10(9) W cm(-2) the quantum yield of electron ejection (ionization) phi(i) does not depend on the intensity of radiation, therefore the ionization is monophotonic, phi(i) = 0.03. At intensities 1> 5 x 10(9) W cm(-2) phi1 becomes larger due to two-quantum excitation followed by ionization.

show abstract

“…Psoralen triplet states have been shown previously to be quenched by nucleic acid bases (39,47) viu both physical quenching and, with pyrimidines, photocycloaddition. Triplet energy transfer is energetically unfeasible in all cases.…”

Section: Discussionmentioning

confidence: 98%

Generation and Characterization of Psoralen Radical Cations

Wood

Johnston²

1997

Photochem & Photobiology

View full text Add to dashboard Cite

Abstract— Radical cations of psoralen, 8‐methoxypsoralen(8‐MOP) and 5‐methoxypsoralen have been generated by photosensitized electron transfer in acetonitrile and aqueous buffer/acetonitrile (1:1) and have absorption maxima at 600, 650 and 550 nm, respectively. The radical cations have lifetimes of 5 p.s under these conditions, are unreactive toward oxygen and show behavior typical of ar‐ylalkene radical cations in their reactivity toward nucle‐ophiles and the precursor psoralens. Direct 355 nm excitation of 8‐MOP in aqueous buffer at physiological pH results in monophotonic photoionization to give 8‐MOP*+ with a quantum yield of 0.015.The 8‐MOP*+ reacts with both guanosine and adenosine mononucleotides (k= 2.5 times 109 and 3.4 times 107 M‐1 s1, respectively) via electron transfer to give the purine radical cations, but does not react with pyrimidine mononucleotides. These results suggest that reactions of psoralen radical cations generated by electron transfer or photoionization may be involved in psoralen/UVA therapy.

show abstract

Transient absorption spectra and quenching of coumarin excited states by nucleic acid bases

Cited by 13 publications

References 35 publications

Photoionization and Photosensitized Electron-Transfer Reactions of Psoralens and Coumarins

Photoionization and Photosensitized Electron-Transfer Reactions of Psoralens and Coumarins

Excited singlet state and photoionization of 8-methoxypsoralen. Picosecond transient absorption study

Generation and Characterization of Psoralen Radical Cations

Contact Info

Product

Resources

About