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Oxidative Repair of Pyrimidine Cyclobutane Dimers by Nitrate Radicals (NO3): A Kinetic and Computational Study

School of Chemistry, Bio21 Institute, The University of Melbourne, 30 Flemington Road, Parkville, Victoria 3010, Australia
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Chemistry 2020, 2(2), 453-469; https://doi.org/10.3390/chemistry2020027
Received: 14 April 2020 / Revised: 6 May 2020 / Accepted: 6 May 2020 / Published: 9 May 2020
Pyrimidine cyclobutane dimers are hazardous DNA lesions formed upon exposure of DNA to UV light, which can be repaired through oxidative electron transfer (ET). Laser flash photolysis and computational studies were performed to explore the role of configuration and constitution at the cyclobutane ring on the oxidative repair process, using the nitrate radical (NO3) as oxidant. The rate coefficients of 8–280 × 107 M−1 s−1 in acetonitrile revealed a very high reactivity of the cyclobutane dimers of N,N’-dimethylated uracil (DMU), thymine (DMT), and 6-methyluracil (DMU6-Me) towards NO3, which likely proceeds via ET at N(1) as a major pathway. The overall rate of NO3 consumption was determined by (i) the redox potential, which was lower for the syn- than for the anti-configured dimers, and (ii) the accessibility of the reaction site for NO3. In the trans dimers, both N(1) atoms could be approached from above and below the molecular plane, whereas in the cis dimers, only the convex side was readily accessible for NO3. The higher reactivity of the DMT dimers compared with isomeric DMU dimers was due to the electron-donating methyl groups on the cyclobutane ring, which increased their susceptibility to oxidation. On the other hand, the approach of NO3 to the dimers of DMU6-Me was hindered by the methyl substituents adjacent to N(1), making these dimers the least reactive in this series. View Full-Text
Keywords: pyrimidine cyclobutane dimers; nitrate radicals; kinetic studies; DFT calculations; oxidation pyrimidine cyclobutane dimers; nitrate radicals; kinetic studies; DFT calculations; oxidation
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MDPI and ACS Style

Haddad, T.; Nathanael, J.G.; White, J.M.; Wille, U. Oxidative Repair of Pyrimidine Cyclobutane Dimers by Nitrate Radicals (NO3): A Kinetic and Computational Study. Chemistry 2020, 2, 453-469. https://doi.org/10.3390/chemistry2020027

AMA Style

Haddad T, Nathanael JG, White JM, Wille U. Oxidative Repair of Pyrimidine Cyclobutane Dimers by Nitrate Radicals (NO3): A Kinetic and Computational Study. Chemistry. 2020; 2(2):453-469. https://doi.org/10.3390/chemistry2020027

Chicago/Turabian Style

Haddad, Tomas, Joses G. Nathanael, Jonathan M. White, and Uta Wille. 2020. "Oxidative Repair of Pyrimidine Cyclobutane Dimers by Nitrate Radicals (NO3): A Kinetic and Computational Study" Chemistry 2, no. 2: 453-469. https://doi.org/10.3390/chemistry2020027

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