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. 2016 Dec 7;21(12):1683.
doi: 10.3390/molecules21121683.

Stereoselective Fluorescence Quenching in the Electron Transfer Photooxidation of Nucleobase-Related Azetidines by Cyanoaromatics

Ana B Fraga-Timiraos  1 , Gemma M Rodríguez-Muñiz  2 , Vicente Peiro-Penalba  3 , Miguel A Miranda  4 , Virginie Lhiaubet-Vallet  5
Affiliations

Stereoselective Fluorescence Quenching in the Electron Transfer Photooxidation of Nucleobase-Related Azetidines by Cyanoaromatics

Ana B Fraga-Timiraos et al. Molecules. .

Abstract

Electron transfer involving nucleic acids and their derivatives is an important field in bioorganic chemistry, specifically in connection with its role in the photo-driven DNA damage and repair. Four-membered ring heterocyclic oxetanes and azetidines have been claimed to be the intermediates involved in the repair of DNA (6-4) photoproduct by photolyase. In this context, we examine here the redox properties of the two azetidine isomers obtained from photocycloaddition between 6-aza-1,3-dimethyluracil and cyclohexene. Steady-state and time-resolved fluorescence experiments using a series of photoreductants and photooxidants have been run to evaluate the efficiency of the electron transfer process. Analysis of the obtained quenching kinetics shows that the azetidine compounds can act as electron donors. Additionally, it appears that the cis isomer is more easily oxidized than its trans counterpart. This result is in agreement with electrochemical studies performed on both azetidine derivatives.

Keywords: DNA repair; energy and charge transfer; nucleobase analogues; photolyase; redox potential.

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Conflict of interest statement

The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Figures

Scheme 1
Scheme 1
Synthesis of cis isomer 2a and trans isomer 2b from 6-aza-1,3-dimethyluracil (1).
Figure 1
Figure 1
Structure of the used photosensitizers (PS).
Figure 2
Figure 2
Fluorescence emission spectra for (a) CAR (λexc = 310 nm) and (b) DMA (λexc = 310 nm) in the presence of increasing amounts of 2b (0–12.5 mM) as well as (c,d) DCN (λexc = 310 nm), (e,f) DCA (λexc = 375 nm), and (g,h) CNN (λexc = 310 nm) in the presence of increasing amounts of 2a (left panel) or 2b (right panel) (0–12.5 mM). The quencher concentration is 0 (black), 2.5 (red), 5 (green), 7.5 (blue), 10 (light blue) and 12.5 mM (pink).
Figure 3
Figure 3
Fluorescence kinetic traces obtained for DCN (λexc = 310 nm) (a,b), DCA (λexc = 375 nm) (c,d) and CNN (λexc = 310 nm) (e,f) in the presence of increasing amounts of 2a (left panel) or 2b (right panel) from 0 to 12.5 mM. Inset: corresponding Stern Volmer plots. The quencher concentration is 0 (black), 2.5 (red), 5 (green), 7.5 (blue), 10 (light blue) and 12.5 mM (pink).
Figure 4
Figure 4
Cyclic voltammograms of 2a (red line, 1 mM) and 2b (black line, 1 mM) in acetonitrile using 0.1 M Bu4NClO4 as electrolyte. Scan rate: 0.5 V·s−1.
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