Ultrafast Chemistry of Water Radical Cation, H2O•+, in Aqueous Solutions

Abstract

Oxidation reactions by radicals constitute a very important class of chemical reactions in solution. Radiation Chemistry methods allow producing, in a controlled way, very reactive oxidizing radicals, such as OH•, CO3•–, NO3•, SO4•–, and N3•. Although the radical cation of water, H2O•+, with a very short lifetime (shorter than 1 ps) is the precursor of these radicals in aqueous solutions, its chemistry is usually known to be limited to the reaction of proton transfer by forming OH• radical. Herein, we stress situations where H2O•+ undergoes electron transfer reaction in competition with proton transfer.

Formation of protonated water–hydrogen clusters in an ion trap mass spectrometer at room temperature

“…H 2 observed during radiolysis of water is usually attributed to the association of two hydrogen radicals: H + H -H 2 . 3,6,9 H in our experiments could possibly be generated upon the dissociation of water radical cations, e.g. 25,26 For water dimers, nonadiabatic ab initio dynamic simulations have supported the theory that the predominant process following the ejection of the electron from the 1b 2 (acceptor) state is not proton transfer but rather dissociation of the free O-H bond in the acceptor molecule, resulting in the formation of OH, H , and 6 The mechanism of H and H 2 generation through the dissociation of the O-H bond of water radical cations in our experiments is indirectly supported by the observation of…”

“…Due to their great importance in both fundamental and applied sciences, the water molecule, its clusters and its various ionic forms have been the subject of numerous experimental and theoretical studies. [1][2][3][4][5][6] The protonated water clusters, H + (H 2 O) n , are the most thoroughly explored water cluster ions in the gas phase. [7][8][9][10] The studies of protonated water clusters have provided rich information on the structures and dynamics of water networks.…”

Importance of radiolytic reactions during high-LET irradiation modalities: LET effect, role of O2 and radiosensitization by nanoparticles

“…H 2 is considered chemically inert and it is often neglected. H 2 O •+ is surely the most reactive oxidant species in water radiolysis but it recombines immediately in the ionization tracks (El Omar et al 2012;Ma et al 2018) and, as a strong Brønsted acid, it also deprotonates to form •OH and hydronium ion (H 3 O + ) within 10 −13 s. With a longer lifetime, hydroxyl radical, •OH, is the most Fig. 1 Sketch of reactions of transient species produced by irradiation in pure water (Baldacchino and Katsumura 2010).…”

Electron Attachment to Cytosine: The Role of Water

“…A significant part of the high energy radiation (UV, X-ray, gamma radiation, ion-beam) is absorbed by liquid water surrounding the biomolecules, and it generates transiently excited water molecules (H2O*), water cation (H2O •+ ), and secondary electrons (SE) [2][3][4][5] . The excited H2O* then autoionizes to form H2O •+ on a femtosecond timescale 6 , and subsequently gets deprotonated to generate OH • and H3O + .…”