Search results for "cyclobutane"
showing 10 items of 35 documents
Experimental and Theoretical Study on the Cycloreversion of a Nucleobase-Derived Azetidine by Photoinduced Electron Transfer.
2018
[EN] Azetidines are interesting compounds in medicine and chemistry as bioactive scaffolds and synthetic intermediates. However, photochemical processes involved in the generation and fate of azetidine-derived radical ions have scarcely been reported. In this context, the photoreduction of this four-membered heterocycle might be relevant in connection with the DNA (6-4) photoproduct obtained from photolyase. Herein, a stable azabipyrimidinic azetidine (AZT(m)), obtained from cycloaddition between thymine and 6-azauracil units, is considered to be an interesting model of the proposed azetidine-like intermediate. Hence, its photoreduction and photo-oxidation are thoroughly investigated throug…
Theoretical insight into the intrinsic ultrafast formation of cyclobutane pyrimidine dimers in UV-irradiated DNA: thymine versus cytosine.
2008
The higher formation yields measured in the ultrafast photoinduced formation of cyclobutane thymine dimers (T T) with respect to those of cytosine (C C) are explained, on the basis of ab initio CASPT2 results, by the existence in thymine of more reactive orientations and a less efficient photoreversibility, whereas in cytosine the funnel toward the photolesion becomes competitive with that mediating the internal conversion of the excited-cytosine monomer.
On the Intrinsically Low Quantum Yields of Pyrimidine DNA Photodamages: Evaluating the Reactivity of the Corresponding Minimum Energy Crossing Points
2020
The low quantum yield of photoformation of cyclobutane pyrimidine dimers and pyrimidine-pyrimidone (6-4) adducts in DNA bases is usually associated with the presence of more favorable nonreactive decay paths and with the unlikeliness of exciting the system in a favorable conformation. Here, we prove that the ability of the reactive conical intersection to bring the system either back to the absorbing conformation or to the photoproduct must be considered as a fundamental factor in the low quantum yields of the mentioned photodamage. In support of the proposed model, the one order of magnitude difference in the quantum yield of formation of the cyclobutane thymine dimer with respect to the t…
Molecular Basis of DNA Photodimerization: Intrinsic Production of Cyclobutane Cytosine Dimers
2008
Based on CASPT2 results, the present contribution establishes for the first time that cytosine photodimer formation (CC) is mediated along the triplet and singlet manifold by a singlet-triplet crossing, (T1/S0)X, and by a conical intersection, (S1/S0)CI, respectively. The former can be accessed in a barrierless way from a great variety of photochemical avenues and exhibits a covalent single bond between the ethene C6-C6' carbon atoms of each monomer. The efficiency of the stepwise triplet mechanism, however, would be modulated by the effectiveness of the intersystem crossing mechanism. The results provide the grounds for the understanding of the potential photogenotoxicity of endogenous and…
Squaraine Dyes for Photodynamic Therapy: Study of Their Cytotoxicity and Genotoxicity in Bacteria and Mammalian Cells¶‡
2007
Halogenated squaraine dyes are characterized by long wavelength absorption (>600 nm) and high triplet yields and therefore represent new types of photosensitizers that could be useful for photodynamic therapy. We have analyzed the cytotoxicity and genotoxicity of the bromo derivative 1, the iodo derivative 2 and the corresponding nonhalogenated dye 3 in the absence and presence of visible light. At concentrations of 1-2 microM, 1 and 2 reduced the cloning efficiency of AS52 Chinese hamster ovary cells to less than 1% under conditions that were well tolerated in the dark. Similarly, the proliferation of L5178Y mouse lymphoma cells was inhibited by photoexcited 1 and 2 with high selectivity. …
CCDC 2058519: Experimental Crystal Structure Determination
2021
Related Article: Esa Kukkonen, Elmeri Lahtinen, Pasi Myllyperkiö, Matti Haukka, Jari Konu|2021|New J.Chem.|45|6640|doi:10.1039/D1NJ00456E
CCDC 2058518: Experimental Crystal Structure Determination
2021
Related Article: Esa Kukkonen, Elmeri Lahtinen, Pasi Myllyperkiö, Matti Haukka, Jari Konu|2021|New J.Chem.|45|6640|doi:10.1039/D1NJ00456E
CCDC 893839: Experimental Crystal Structure Determination
2013
Related Article: Emilio Escrivá, Lucía Soto, Juan Server-Carrió, Carlos J. Gómez-García, Guillermo Mínguez Espallargas, Nailette Ruiz, Amparo Sancho, Julia García-Lozano, Carmen Ramírez de Arellano|2013|Polyhedron|56|90|doi:10.1016/j.poly.2013.03.016
CCDC 712097: Experimental Crystal Structure Determination
2011
Related Article: J.Carranza, J.Sletten, F.Lloret, M.Julve|2011|Inorg.Chim.Acta|371|13|doi:10.1016/j.ica.2011.02.087
CCDC 712096: Experimental Crystal Structure Determination
2011
Related Article: J.Carranza, J.Sletten, F.Lloret, M.Julve|2011|Inorg.Chim.Acta|371|13|doi:10.1016/j.ica.2011.02.087