Damage Induced to DNA and Its Constituents by 0–3 eV UV Photoelectrons^†

Abstract

The complex physical and chemical interactions between DNA and 0–3 eV electrons released by UV photoionization can lead to the formation of various lesions such as base modifications and cleavage, crosslinks and single strand breaks. Furthermore, in the presence of platinum chemotherapeutic agents, these electrons can cause clustered lesions, including double strand breaks. We explain the mechanisms responsible for these damages via the production 0–3 eV electrons by UVC radiation, and by UV photons of any wavelengths, when they are produced by photoemission from nanoparticles lying within about 10 nm from DNA. We review experimental evidence showing that a single 0–3 eV electron can produce these damages. The foreseen benefits UV‐irradiation of nanoparticles targeted to the cell nucleus are mentioned in the context of cancer therapy, as well as the potential hazards to human health when they are present in cells.

Low-Energy Electron Damage to Plasmid DNA in Thin Films: Dependence on Substrates, Surface Density, Charging, Environment, and Uniformity

“…Moreover, amino acids constitute the DNA-binding protein tail of the histones in the nucleus; when bound to plasmids, the resulting complexes could result in highly significant targets to understand the mechanisms of LEE-induced damage to the genome. Considering the established role of LEEs in the processes of radiosensitization − ,− and photosensitization, ,− combining chemotherapeutic drugs, radiosensitizers, photosensitizers, or nanoparticles with amino-acid-DNA complexes in lyophilized films could pave the way to significant advances in the development of efficient cancer treatments.…”

“…During the last two decades, our knowledge of the interaction of low-energy (0–20 eV) electrons (LEEs) with DNA has been derived from experiments performed with various types of targets ranging from fundamental units (i.e., the bases, sugar, and phosphate groups), − oligonucleotides , to plasmid DNA, − which is composed of thousands of base pairs. The results were obtained from different types of LEE-impact experiments on gaseous molecules, such as the bases, − deoxyribose-ring analogs, , phosphate model compounds, nucleosides, monophosphate nucleosides, and such molecules embedded in water clusters − or as binary H 2 O-biomolecule targets. , Experiments in water were performed with electrons generated by laser beams , and pulse radiolysis. − Many LEE-impact experiments were performed in vacuum on thin films of oligonucleotides attached to an origami template. − Because LEEs account for the major portion of the secondary electron (SE) distribution produced by ionizing radiation, research in this field has contributed in many ways to our present comprehension of the mechanisms of radiobiological damage and their applications, − including the sensitization of radiotherapy − and phototherapy. ,− During about the same length of time, comprehensive theoretical descriptions of the interactions between DNA and LEEs have emerged in the literature. ,− …”

Physical Differences between Man-Made and Cosmic Microwave Electromagnetic Radiation and Their Exposure Limits, and Radiofrequencies as Generators of Biotoxic Free Radicals

“…For example, the binding energy of the C-C bond is 3.6 eV, and the two carbon molecules can be separated from each other (by covalent bond homolytic split) upon irradiation with one photon at 345 nm [55]. Molecular bond breaking by photons is the reason why UV radiation is biologically harmful [56,57]. At shorter photon wavelengths or higher photon energies, the excess photon energy is compensated as kinetic energy of photofragments, causing localised mechanical damages.…”

The valence electron affinity of uracil determined by anion cluster photoelectron spectroscopy

“…Low-energy electrons can induce strand breaks in DNA, even at electron energies below the ionization energy of individual components and below the dissociation energies of covalent bonds in the biopolymer. [1][2][3] The initial step is believed to involve the electron attachment to valence states of components of DNA, forming temporary negative ions that can then lead to bond-rupture through a long-range dissociative electron attachment process. [4][5][6] The nucleobases in particular have received much attention as the site for initial electron attachment via their low-lying valence states that are of p* character.…”