Ultrafast fragmentation of highly-excited doubly-ionized deoxyribose: role of the liquid water environment.

Ab initio molecular dynamics simulations are used to investigate the fragmentation dynamics following the double ionization of 2-deoxy-D-ribose (DR), a major component in the DNA chain. Different ionization scenarios are considered to provide a complete picture. First focusing on isolated DR2+, fragmentation patterns are determined for the ground electronic state, adding randomly distributed excitation energy to the nuclei. These patterns differ for the two isomers studied. To compare thermal and electronic excitation effects, Ehrenfest dynamics are also performed, allowing to remove the two electrons from selected molecular orbitals. Two intermediate-energy orbitals, localized on the carbon chain, were selected. The dissociation pattern corresponds to the most frequent pattern obtained when adding thermal excitation. On the contrary, targeting the four deepest orbitals, localized on the oxygen atoms, leads to selective ultrafast C-O and/or O-H bond dissociation. To probe the role of environment, a system consisting of a DR molecule embedded in liquid water is then studied. The two electrons are removed from either the DR or the water molecules directly linked to the sugar through hydrogen bonds. Although the dynamics onset is similar to that of isolated DR when removing the same deep orbitals localized on the sugar oxygen atoms, the subsequent fragmentation patterns differ. Sugar damage also occurs following the Coulomb explosion of neighboring H2O2+ molecules due to interaction with the emitted O or H atoms.

Radiation-Responsive Benzothiazolines as Potential Cleavable Fluorogenic Linkers for Drug Delivery.

Radiosensitive compounds can be useful for the detection of radiations and also as prodrugs that can be activated during a radiotherapy. Herein we describe the use of benzothiazolines, which upon treatment with 137 Cs produced γ-irradiation in water give rise to fluorescent benzothiazoles and concomitant release of amines or carboxylic acids. In a proof of concept study, we showed that benzothiazolines may be used as new cleavable linkers that can be triggered upon irradiation.

Superoxide Production under Soft X-ray Irradiation of Liquid Water.

Soft X-rays behave like particles with high linear energy transfer, as they deposit a large amount of their energy in the nanometric range, triggered by inner-shell ionization. In water, this can lead to the formation of a doubly ionized water molecule (H2O2+) and the emission of two secondary electrons (photoelectron and Auger electron). Our focus lies on detecting and quantifying the superoxide (HO2°) production via the direct pathway, i.e., from the reaction between the dissociation product of H2O2+, i.e., the oxygen atom (∼4 fs), and the °OH radicals present in the secondary electron tracks. The HO2° yield for 1620 eV photons, via this reaction pathway, was found to be 0.005 (±0.0007) µmol/J (formed within the ∼ps range). Experiments were also performed to determine the yield of HO2° production via another (indirect) pathway, involving solvated electrons. The indirect HO2° yield, measured experimentally as a function of photon energy (from 1700 to 350 eV), resulted in a steep decrease at around 1280 eV and a minimum close to zero at 800 eV. This behavior in contradiction with the theoretical prediction reveals the complexity hidden in the intratrack reactions.