Search results for "Pyrimidine Dimers"
showing 4 items of 14 documents
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…
Protective effect of trehalose-loaded liposomes against UVB-induced photodamage in human keratinocytes
2014
Trehalose, a naturally occurring non-reducing disaccharide, is known to act as a major protein stabilizer that can reduce ultraviolet B (UVB)-induced corneal damage when topically applied to the eye. However, due to the low skin permeability of trehalose, which makes the development of topical formulations difficult, its use as a skin photoprotective agent has been limited. Previous findings demonstrated that liposomes may significantly improve the intracellular delivery of trehalose. Therefore, the present study aimed to assess the protective effects of trehalose-loaded liposomes against UVB-induced photodamage using the immortalized human keratinocyte cell line, HaCaT. The effects were al…
UV-B exposure causes DNA damage and changes in protein expression in northern pike (Esox lucius) posthatched embryos.
2012
The ongoing anthropogenically caused ozone depletion and climate change has increased the amount of biologically harmful UV-B radiation, which is detrimental to fish in embryonal stages. The effects of UV-B radiation on the levels and locations of DNA damage manifested as cyclobutane pyrimidine dimers (CPDs), heat shock protein 70 (HSP70) and p53 protein in newly hatched embryos of pike were examined. Pike larvae were exposed in the laboratory to current and enhanced doses of UV-B radiation. UV-B exposure caused the formation of CPDs in a fluence rate-dependent manner, and the CPDs were found deeper in the tissues with increasing fluence rates. UV-B radiation induced HSP70 in epidermis, and…