Reactions in Tirapazamine Induced by the Attachment of Low-Energy Electrons: Dissociation Versus Roaming of OH

Vienna (P30332) PD/BD/114447/2016 PTDC/FIS-AQM/31215/2017 PD/00193/2012 UID/Multi/ 04378/2019 UID/FIS/00068/2019Tirapazamine (TPZ) has been tested in clinical trials on radio-chemotherapy due to its potential highly selective toxicity towards hypoxic tumor cells. It was suggested that either the hydroxyl radical or benzotriazinyl radical may form as bioactive radical after the initial reduction of TPZ in solution. In the present work, we studied low-energy electron attachment to TPZ in the gas phase and investigated the decomposition of the formed TPZ− anion by mass spectrometry. We observed the formation of the (TPZ–OH)− anion accompanied by the dissociation of the hydroxyl radical as by far the most abundant reaction pathway upon attachment of a low-energy electron. Quantum chemical calculations suggest that NH2 pyramidalization is the key reaction coordinate for the reaction dynamics upon electron attachment. We propose an OH roaming mechanism for other reaction channels observed, in competition with the OH dissociation.publishersversionpublishe

Ring formation and hydration effects in electron attachment to misonidazole

This research was funded by CZECH SCIENCE FOUNDATION grant number 19-01159S; Czech Ministry of Education Youth and Sports via OP RDE Grant no. CZ.02.2.69/0.0/16_027/0008355; S.D. acknowledges funding from the FWF, Vienna (P30332).We study the reactivity of misonidazole with low-energy electrons in a water environment combining experiment and theoretical modelling. The environment is modelled by sequential hydration of misonidazole clusters in vacuum. The well-defined experimental conditions enable computational modeling of the observed reactions. While the NO- 2 dissociative electron attachment channel is suppressed, as also observed previously for other molecules, the OH- channel remains open. Such behavior is enabled by the high hydration energy of OH- and ring formation in the neutral radical co-fragment. These observations help to understand the mechanism of bio-reductive drug action. Electron-induced formation of covalent bonds is then important not only for biological processes but may find applications also in technology.publishersversionpublishe

Phenanthrene: Establishing Lower and Upper Bounds to the Binding Energy of a Very Weakly Bound Anion

Quite a few molecules do not form stable anions that survive the time needed for their detection; their electron affinities (EA) are either very small or negative. How does one measure the EA if the anion cannot be observed? Or, at least, can one establish lower and upper bounds to their EA? We propose two approaches that provide lower and upper bounds. We choose the phenanthrene (Ph) molecule whose EA is controversial. Through competition between helium evaporation and electron detachment in HenPh- clusters, formed in helium nanodroplets, we estimate the lower bound of the vertical detachment energy (VDE) of Ph- as about – 3 meV. In the second step, Ph is complexed with calcium whose electron affinity is just 24.55 meV. When CaPh- ions are collided with a thermal gas of argon, one observes Ca- product ions but no Ph-, suggesting that the EA of Ph is below that of Ca

Electronic Transitions in Rb2+ Dimers Solvated in Helium

We have measured depletion spectra of the heteronuclear (85Rb87Rb+) dimer cation complexed with up to 10 He atoms. Two absorption bands are observed between 920 and 250 nm. The transition into the repulsive 12Sigmau+ state of HeRb2+ gives rise to a broad feature at 790 nm (12650 cm–1); it exhibits a blueshift of 98 cm–1 per added He atom. The transition into the bound 1 2Piu state of HeRb2+ reveals vibrational structure with a band head at \u3c 15522 cm–1, a harmonic constant of 26 cm–1, and a spin-orbit splitting of \u3c 183 cm–1. The band experiences an average redshift of –38 cm–1 per added He atom. Ab initio calculations rationalize the shape of the spectra and spectral shifts with respect to the number of helium atoms attached. For a higher number of solvating helium atoms, symmetric solvation on both ends of the Rb2+ ion is predicted

Reaktionen in Tirapazamin induziert durch die Anlagerung von niederenergetischen Elektronen: Dissoziation versus Roaming von OH

P30332 PD/BD/114447/2016 PTDC/FIS‐AQM/31215/2017 PD/00193/2012 UID/Multi/ 04378/2019 UID/FIS/00068/2019Tirapazamin (TPZ) wurde aufgrund seiner potenziell hochselektiven Toxizität gegenüber hypoxischen Tumorzellen in klinischen Studien zur Radio‐Chemotherapie getestet. Dabei wurde vorgeschlagen, dass sich entweder das Hydroxyl‐Radikal oder das Benzotriazinyl‐Radikal nach der anfänglichen Reduktion von TPZ als bioaktives Radikal bildet. In dieser Arbeit beschäftigten wir uns mit der niederenergetischen Elektronenanlagerung an TPZ in der Gasphase und untersuchten die Zersetzung des gebildeten TPZ‐Anions mittels Massenspektrometrie. Wir beobachteten die Bildung des (TPZ‐OH)− Anions, begleitet von der Abspaltung des Hydroxyl‐radikals als dem bei weitem häufigsten Reaktionsweg. Quanten‐chemische Berechnungen legen nahe, dass die NH2‐Pyramidalisierung die Schlüsselkoordinate für die Reaktions‐dynamik bei Elektronenanlagerung ist. Für andere beobachtete Reaktionskanäle schlagen wir einen OH‐Roaming‐Mechanismus vor, der in Konkurrenz zur OH‐Dissoziation steht.publishersversionpublishe

SF6+: Stabilizing Transient Ions in Helium Nanodroplets

There are myriads of ions that are deemed too short-lived to be experimentally accessible. One of them is SF6+. It has never been observed, although not for lack of trying. We demonstrate that long-lived SF6+ can be formed by doping charged helium nanodroplets (HNDs) with sulfur hexafluoride; excess helium is then gently stripped from the doped HNDs by collisions with helium gas. The ion is identified by high-resolution mass spectrometry (resolution m/Dm = 15000), the close agreement between the expected and observed yield of ions that contain minor sulfur isotopes, and collision-induced dissociation (CID) in which mass-selected HenSF6+ ions are collided with helium gas. Under optimized conditions, the yield of SF6+ exceeds that of SF5+. The procedure is versatile and suitable to stabilize many other transient molecular ions

Formation of Temporary Negative Ions and Their Subsequent Fragmentation upon Electron Attachment to CoQ0 and CoQ0H2

P30332 153377/2016‐0 304571/2018‐0 PTDC/FIS‐AQM/31215/2017 PD/00193/2012 UID/FIS/00068/2020 PD/BD/142768/2018Ubiquinone molecules have a high biological relevance due to their action as electron carriers in the mitochondrial electron transport chain. Here, we studied the dissociative interaction of free electrons with CoQ0, the smallest ubiquinone derivative with no isoprenyl units, and its fully reduced form, 2,3-dimethoxy-5-methylhydroquinone (CoQ0H2), an ubiquinol derivative. The anionic products produced upon dissociative electron attachment (DEA) were detected by quadrupole mass spectrometry and studied theoretically through quantum chemical and electron scattering calculations. Despite the structural similarity of the two studied molecules, remarkably only a few DEA reactions are present for both compounds, such as abstraction of a neutral hydrogen atom or the release of a negatively charged methyl group. While the loss of a neutral methyl group represents the most abundant reaction observed in DEA to CoQ0, this pathway is not observed for CoQ0H2. Instead, the loss of a neutral OH radical from the CoQ0H2 temporary negative ion is observed as the most abundant reaction channel. Overall, this study gives insights into electron attachment properties of simple derivatives of more complex molecules found in biochemical pathways.publishersversionpublishe

Formation of Temporary Negative Ions and Their Subsequent Fragmentation upon Electron Attachment to CoQ0 and CoQ0 H2

Publisher Copyright: © 2022 Wiley-VCH GmbH.The front cover artwork is provided by Prof. Stephan Denifl's group at the University of Innsbruck, Austria, in collaboration with Prof. Filipe Ferreira da Silva's group at NOVA University Lisbon, Portugal, and Prof. Dr. Márcio Varella's group at University of São Paulo, Brazil, as well as with Prof. Dr. Martin Beyer and Prof. Dr. Milan Ončak also at the University of Innsbruck, Austria. The image shows the main fragmentation pathways of both coenzyme Q0 (CoQ0 ) and CoQ0 H2 upon electron attachment in the gas phase. Read the full text of the Research Article at 10.1002/cphc.202100834.publishersversionpublishe

How changed physical chemistry into nanotechnology and nanotechnology into physical chemistry?

Our subject matter of the work is: How changed physical chemistry into nanotechnology and nanotechnology into physical chemistry