85 research outputs found
Photoionization of methanol: a molecular source for the prebiotic chemistry
No full textMethanol is one of the most abundant and ubiquitous molecules in the space. Its chemistry is fundamental to
understand the molecular growing from prebiotic molecules, ions and radicals. In this work the reaction of
labelled methanol CD3OH•+ radical cation, produced with different internal energies by monochromatic synchrotron
radiation, with neutral CD3OH was studied. The dynamics of the main reaction channels were investigated
by theoretical calculations. The results show how these processes can be considered suitable pathways for
the formation of fundamental species as CH3O(H)H+, CH3O•, •CH2OH, CH2O which are potential precursors to
prebiotic molecules
A Synchrotron Radiation Study of Nitroimidazoles and their Derivatives
No full textNitroimidazole derived molecules are used in radiotherapy thanks to their capability to sensitize hypoxic tumor cells to radiation by ‘mimicking’ the effects of the presence of oxygen as a damaging agent. Inthis work we present the results of a bottom-up approach, which goes from the model molecule to the real drugs used in therapy. Mass spectrometry and several spectroscopic techniques (XPS, PES, NEXAFS, PEPICO) basedon the use of synchrotron radiation have been combined with computational methods to link the electronic and geometric structure of the molecule to their functions.The investigation of the fragmentation patterns of the nitroimidazole isomers [1,2] has allowed to understand their capacity to produce reactive molecular species like nitric oxide, carbon monoxide or hydrogencyanide and their potential impact on the biological system. Guided by these results, the fragmentation mechanisms of metronidazole and misonidazole, the two radiosensitisers built on the 5-nitroimidazole and 2-nitroimidazole compounds used in therapy, as well as the 1-Methyl-5-nitroimidazole have been investigated. The results on these more complex systems suggest that different mechanisms are active. The release of nitric oxideis hampered by the efficient formation of nitrous acid or nitrogen dioxide and the long and branched tails attached to the imidazole ring increase the ring stability, providing an efficient channel for excess energy dissipation
"Insights into 2-Chloropyrimidine fragmentation through a thermochemical analysis of the ionic fragments"
No full textIn the present work we have studied the photoinduced ion chemistry of the 2Cl-pyrimidine
molecule in the energy region 9−14 eV. The theoretical gas phase enthalpies of formation of the main
fragments calculated using the G3B3 and G2 ab initio methods are compared to the experimental values,
derived by the measured appearance energy of the fragments. This approach provides new insights into
both the geometric structure of the ionic fragments and the basic mechanisms governing the molecular
fragmentation
Ionic route to atmospheric relevant HO2 and protonated formaldehyde from methanol cation and O2
No full textGas-phase ion chemistry influences atmospheric processes, particularly in the formation of cloud condensation nuclei by producing ionic and neutral species in the upper troposphere–stratosphere region impacted by cosmic rays. This work investigates an exothermic ionic route to the formation of hydroperoxyl radical (HO2) and protonated formaldehyde from methanol radical cation and molecular oxygen. Methanol, a key atmospheric component, contributes to global emissions and participates in various chemical reactions affecting atmospheric composition. The two reactant species are of fundamental interest due to their role in atmospheric photochemical reactions, and HO2 is also notable for its production during lightning events. Our experimental investigations using synchrotron radiation reveal a fast hydrogen transfer from the methyl group of methanol to oxygen, leading to the formation of CH2OH+ and HO2. Computational analysis corroborates the experimental findings, elucidating the reaction dynamics and hydrogen transfer pathway. The rate coefficients are obtained from experimental data and shows that this reaction is fast and governed by capture theory. Our study contributes to a deeper understanding of atmospheric processes and highlights the role of ion-driven reactions in atmospheric chemistry
Ion Chemistry of Carbon Dioxide in Nonthermal Reaction with Molecular Hydrogen
No full text[Image: see text] The exothermic hydrogen transfer from H(2) to CO(2)(·)(+) leading to H and HCO(2)(+) is investigated in a combined experimental and theoretical work. The experimental mass/charge ratios of the ionic product (HCO(2)(+)) and the ionic reactant (CO(2)(·)(+)) are recorded as a function of the photoionization energy of the synchrotron radiation. Theoretical density functional calculations and variational transition state theory are employed and adapted to analyze the energetic and the kinetics of the reaction, which turns out to be barrierless and with nonthermal rate coefficients controlled by nonstatistical processes. This study aims to understand the mechanisms and energetics that drive the reactivity of the elementary reaction of CO(2)(·)(+) with H(2) in different processes
Gas Phase Oxidation of Carbon Monoxide by Sulfur Dioxide Radical Cation: Reaction Dynamics and Kinetic Trend With the Temperature
No full textGas phase ion chemistry has fundamental and applicative purposes since it allows the study of the chemical processes in a solvent free environment and represents models for reactions occurring in the space at low and high temperatures. In this work the ion-molecule reaction of sulfur dioxide ion SO2.+ with carbon monoxide CO is investigated in a joint experimental and theoretical study. The reaction is a fast and exothermic chemical oxidation of CO into more stable CO2 by a metal free species, as SO2.+, excited into ro-vibrational levels of the electronic ground state by synchrotron radiation. The results show that the reaction is hampered by the enhancement of internal energy of sulfur dioxide ion and the only ionic product is SO.+. The theoretical approach of variational transition state theory (VTST) based on density functional electronic structure calculations, shows an interesting and peculiar reaction dynamics of the interacting system along the reaction path. Two energy minima corresponding to [SO2–CO].+ and [OS–OCO].+ complexes are identified. These minima are separated by an intersystem crossing barrier which couples the bent 3B2 state of CO2 with C2v symmetry and the 1A1 state with linear D∞h symmetry. The spin and charge reorganization along the minimum energy path (MEP) are analyzed and eventually the charge and spin remain allocated to the SO.+ moiety and the stable CO2 molecule is easily produced. There is no bottleneck that slows down the reaction and the values of the rate coefficient k at different temperatures are calculated with capture theory. A value of 2.95 × 10−10 cm3s−1molecule−1 is obtained at 300 K in agreement with the literature experimental measurement of 3.00 × 10−10 ± 20% cm3s−1molecule−1, and a negative trend with temperature is predicted consistently with the experimental observations
VUV Photofragmentation of Chloroiodomethane: The Iso-CH2ICl and Iso-CH2ClI Radical Cation Formation
No full textDihalomethanes XCH2Y (X and Y= F, Cl, Br and I) are a class of compounds involved in several processes leading to the release of halogen atoms, ozone consumption and aerosol particle formation. Neutral dihalomethanes have been largely studied, but chemical physics properties and processes involving their radical ions, like the pathways of their decomposition, have not been completely investigated. In this work the photodissociation dynamics of the ClCH2I molecule has been explored in the photon energy range 9-21 eV using both VUV rare gas discharge lamps and synchrotron radiation. The experiments show that among the different fragment ions, CH2I+ and CH2Cl+, which correspond to the Cl- and I-losses, respectively, play a dominant role. The experimental ionization energy of ClCH2I and the appearance energies of the CH2I+ and CH2Cl+ ions are in agreement with the theoretical results obtained at the MP2/CCSD(T) level of theory. Computational investigations have been also performed to study the isomerization of geminal [ClCH2I].+ into the iso-chloroiodomethane isomers: [CH2I-Cl].+ and [CH2Cl-I].+
Ionization of 2‐ and 4(5)‐Nitroimidazoles Radiosensitizers: A “Kinetic Competition” Between NO(2) and NO Losses
No full textNitroimidazoles are a class of chemicals with a remarkable broad spectrum of applications from the production of explosives to the use as radiosensitizers in radiotherapy. The understanding of thedynamics of their fragmentation induced by ionizing sources is of fundamental interest. The goal of this work is to theoretically investigate the kinetic competition between the two most important decomposition channels of 2, 4 and 5‐Nitroimidazole cations: the NO and NO(2) losses. The calculated rate constants of the two processes are in very good agreement with the experimental Photoelectron‐Photoion Coincidence (PEPICO) branching ratio. This study solves the intriguing and theoretically unexplained experimental observation that 2‐Nitroimidazole, at variance with the other two regio‐isomers is a source for only NO at low energies (<12.76 eV). This is a key point for biomedical application of the nitroimidazoles, because NO is the vasodilator that favors the reoxigenation of hypoxic tumor tissues
Generazione di impulsi nell’ultravioletto estremo per lo studio di dinamiche ultraveloci in molecole di interesse biologico
No full textLAUREA MAGISTRAL
Halogen Migration in the Photofragmentation of Halothane
No full textThe photofragmentation of halothane (CF3CHBrCl) was studied with synchrotron radiation by photoionization efficiency (PIE) measurements and photoelectron–photoion coincidence (PEPICO) experiments, as well as by a theoretical exploration of potential energy surfaces. Among the other fragments, the formation of the CHClF+ and CHBrF+ ions, which involves the transfer of a F atom between the two moieties of the parent molecule, was observed. To understand the mechanisms leading to the halogen migration, a detailed theoretical study of the production of CHClF+, m/z 67+, based on DFT calculations and natural bond orbital (NBO) analysis was conducted. The results contribute to the understanding of the photochemistry of halothane, its polluting behavior in the high atmosphere, and the formation of highly reactive species
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