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A Brief Background
Published in Nathan Keighley, Miraculous Medicines and the Chemistry of Drug Design, 2020
Understanding electrons is essential to chemistry. In a reaction, chemical bonds must be broken: this may be a heterolytic cleavage, where two electrons in the bond move to one species to form ions, or a homolytic cleavage, where the pair of electrons are shared to produce free radicals. In organic chemistry, the movement of electrons is shown with curly arrows to produce organic reaction mechanisms, which will feature later in the text. Since reactivity is the movement of electrons to break weak bonds and make new, stronger bonds, it is possible to predict how an organic reaction mechanism will proceed. For two reacting molecules, identify where the electrons are coming from. This molecule is termed the nucleophile—a negatively charged ion, or neutral molecule with a lone pair of electrons which are donated to form a covalent bond. The electrons are received by the electron-deficient molecule called an electrophile. Whether a given molecule will react as a nucleophile or an electrophile depends on the functional groups that are present.
Physics of Radiation Biology
Published in Kedar N. Prasad, Handbook of RADIOBIOLOGY, 2020
Electrons lose or gain energy only when they jump from one orbit to another. No change in energy occurs so long as the electrons remain in a specified orbit. Vacancies, or “holes,” exist in electron shells from which electrons have been removed. The vacancies are filled promptly by electrons cascading from energy levels farther from the nucleus. As the vacancies are filled, energy is released — usually in the form of electromagnetic radiation. During the transition of a particular electron, the energy released equals the difference in binding energy between the original and the final energy level for the electron. In most cases, the energy is released as a “photon,” or packet of electromagnetic radiation. Occasionally, the energy may be used to eject a second electron, usually from the same shell as the cascading electrons. The ejected electron is termed an Auger electron. Electromagnetic radiation released during electron transition is termed characteristic radiation, because the photon energies are characteristic of differences in the binding energy of electrons in a specific atom.
Oxidative stress and pre-eclampsia
Published in Pankaj Desai, Pre-eclampsia, 2020
To understand free radicals easily, we will visit the atomic model that was taught to us in schools. Each atom is made of extremely tiny particles called “protons”, “neutrons” and “electrons”. Protons and neutrons are in the centre of the atom, making up the nucleus. Electrons surround the nucleus (Figure 4.1). Protons have a positive charge. Electrons have a negative charge. The charge on the proton and electron are the same size but opposite. Neutrons have no charge. Because opposite charges attract, protons and electrons attract each other. Many new subatomic particles have since been added. The neutrinos and the bosons are some of them. However, for our understanding, the role of free radicals in health and diseases, the simplest model of electrons, protons and neutrons will suffice.
An approach to assessing the contribution of the high LET effect in strategies for Auger endoradiotherapy
Published in International Journal of Radiation Biology, 2023
Pavel Lobachevsky, Colin Skene, Laura Munforte, Andrea Smith, Jonathan White, Roger F. Martin
A quite different highly damaging component of Auger decay is described as molecular fragmentation. Multiple electrons originate from the decaying atom, resulting in a build-up of a positive charge on the daughter atom. The build-up and dissipation of the charge is a dynamic event, and in the case of decay of 125I, the maximum transient charge is about +6 (Kummerle and Pomplun 2012). This is the setting for what has been called a ‘Coulombic explosion’ – repulsion of like charges according to Coulomb’s Law, resulting in molecular fragmentation (Pomplun and Sutmann 2004). The relative contribution of molecular fragmentation versus electron irradiation has been the subject of discussion for decades (Hofer et al. 1978), and they seem to be similar (Lobachevsky and Martin 2000). Although chemical details are uncertain, DNA strand breaks are induced in the vicinity of the decaying atom, and there is a consensus that for DNA labeled by incorporation of 125I-iododeoxyuridine, there is an approximately 1:1 relationship between 125I decays in DNA and decay-induced DNA double-strand breaks (DSBs) (Martin and Feinendegen 2016).
Exploiting active nuclear import for efficient delivery of Auger electron emitters into the cell nucleus
Published in International Journal of Radiation Biology, 2023
Andrey A. Rosenkranz, Tatiana A. Slastnikova, Mikhail O. Durymanov, Georgii P. Georgiev, Alexander S. Sobolev
The value of relative biological efficiency of AEs in cell cultures, estimated using D0 ratio, can reach values of 4.5–4.8 for 125I delivered to the DNA due to both high LET of low energy electrons and multiplicity of their emission from a point source (Yasui et al. 2001). This value obviously depends on both the emitter and its intracellular and intranuclear localization (Dahmen et al. 2016; Freudenberg et al. 2014; Kassis et al. 1987; Kriehuber et al. 2004; McMillan et al. 2015; Pirovano et al. 2020). Electrons of this low energy are relatively densely ionizing radiation and have a high, or rather moderately high, LET. It is generally supposed that the higher the LET, the more complex is the DNA damage (Nikjoo et al. 2002). The longer the foci of DNA damage remains in the cell nucleus, the greater is the probability of reproductive death of cells (Antonelli et al. 2015). LET of low-energy electrons is quite high and can reach approximately 26 keV/µm; however, the range of these electrons lies within the nanometer scale. This is less than the LET of α-particles but enough to cause clustered damage to biomolecules including DNA (Nikjoo et al. 2016; Bordage et al. 2016; Dong et al. 2019).
A comprehensive proteomics analysis of the response of Pseudomonas aeruginosa to nanoceria cytotoxicity
Published in Nanotoxicology, 2023
Lidija Izrael Živković, Nico Hüttmann, Vanessa Susevski, Ana Medić, Vladimir Beškoski, Maxim V. Berezovski, Zoran Minić, Ljiljana Živković, Ivanka Karadžić
Emphasized TCA and β-oxidation are sources of increased amounts of NADH that needs to be oxidized by the electron transport chain. However, upregulation of proteins in the electron transport chain was not found. The electron transport chain proteins are located in the outer cellular membrane, where they pump protons across the membrane and generate ATP using ATP synthase (White 2000). The major driving force that moves protons out of the cell are exergonic redox reactions in the cell membrane in respiring microorganisms. Lower oxygen consumption in NC-amended culture than in the control was observed, but at the same time, the upregulated enzymes of TCA cycle, β-oxidation, and ATP synthase could also be attributed to the alkaliphilic nature of P. aeruginosa san ai (White 2000) and the need for an increased ATP supply. Particularly, enhanced ATP demand in NC-exposed cells could be related to upregulated proteins that need an increased amount of ATP, such as cell shape-determining protein MreB, uniquely found in cells treated with nanomaterial and required to preserve cellular morphology, and overexpressed chaperonin GroEL essential for protein folding. Interestingly, in spite of substantial changes to the cell envelope, ATP synthase was preserved as being of vital importance.