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Projeto de investigação
Decomposition of biological molecular targets by electron transfer experiments
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A Simple Electron-Density Based Force Field Model for High-Energy Interactions between Atoms and Molecules
Publication . Romero, J; Limao-Vieira, P; Hermansson, K; Probst, Michael; DF – Departamento de Física; CeFITec – Centro de Física e Investigação Tecnológica; ACS - American Chemical Society
In high-energy molecular dynamics or Monte Carlo simulations, standard force fields optimized for simulations at ambient temperatures are inadequate. This is largely because their repulsive parts have been regarded as not very significant, even well below zero interaction energies. It is, therefore, not obvious which force fields to resort to for simulating hot gases or plasmas. A force field model that uses the electronic densities of noninteracting atoms or molecules within the pair approximation is introduced. We start by deriving a naïve model that neglects any exchange and correlation effects between the electronic clouds and then correct this model by adding a term calibrated from ab initio calculations using the CCSD(T)/cc-pVTZ level of theory. The resulting expression for this term can be regarded as a simple exchange-correlation function. We compare the results for the repulsive part of the potential energy hypersurfaces with the force fields commonly used on some dimers of small molecules.
Electron Scattering from 1-Methyl-5-Nitroimidazole
Publication . Lozano, Ana I.; Álvarez, Lidia; García-Abenza, Adrián; Guerra, Carlos; Kossoski, Fábris; Rosado, Jaime; Blanco, Francisco; Oller, Juan Carlos; Hasan, Mahmudul; Centurion, Martin; Weber, Thorsten; Slaughter, Daniel S.; Mootheril, Deepthy M.; Dorn, Alexander; Kumar, Sarvesh; Limão-Vieira, Paulo; Colmenares, Rafael; García, Gustavo; DF – Departamento de Física; CeFITec – Centro de Física e Investigação Tecnológica; MDPI - Multidisciplinary Digital Publishing Institute
In this study, we present a complete set of electron scattering cross-sections from 1-Methyl-5-Nitroimidazole (1M5NI) molecules for impact energies ranging from 0.1 to 1000 eV. This information is relevant to evaluate the potential role of 1M5NI as a molecular radiosensitizers. The total electron scattering cross-sections (TCS) that we previously measured with a magnetically confined electron transmission apparatus were considered as the reference values for the present analysis. Elastic scattering cross-sections were calculated by means of two different schemes: The Schwinger multichannel (SMC) method for the lower energies (below 15 eV) and the independent atom model-based screening-corrected additivity rule with interferences (IAM-SCARI) for higher energies (above 15 eV). The latter was also applied to calculate the total ionization cross-sections, which were complemented with experimental values of the induced cationic fragmentation by electron impact. Double differential ionization cross-sections were measured with a reaction microscope multi-particle coincidence spectrometer. Using a momentum imaging spectrometer, direct measurements of the anion fragment yields and kinetic energies by the dissociative electron attachment are also presented. Cross-sections for the other inelastic channels were derived with a self-consistent procedure by sampling their values at a given energy to ensure that the sum of the cross-sections of all the scattering processes available at that energy coincides with the corresponding TCS. This cross-section data set is ready to be used for modelling electron-induced radiation damage at the molecular level to biologically relevant media containing 1M5NI as a potential radiosensitizer. Nonetheless, a proper evaluation of its radiosensitizing effects would require further radiobiological experiments.
A complete data set for the simulation of electron transport through gaseous tetrahydrofuran in the energy range 1–100 eV
Publication . García-Abenza, Adrián; Lozano, Ana Isabel; Álvarez, Lidia; Oller, Juan Carlos; Blanco, F.; Stokes, Peter; White, R. D.; Urquijo, Jaime De; Limão-Vieira, Paulo; Jones, D. B.; Brunger, Michael J.; García, G.; CeFITec – Centro de Física e Investigação Tecnológica; DF – Departamento de Física; Springer
Abstract: A self-consistent data set, with all the necessary inputs for Monte Carlo simulations of electron transport through gaseous tetrahydrofuran (THF) in the energy range 1–100 eV, has been critically compiled in this study. Accurate measurements of total electron scattering cross sections (TCSs) from THF have been obtained, and considered as reference values to validate the self-consistency of the proposed data set. Monte Carlo simulations of the magnetically confined electron transport through a gas cell containing THF for different beam energies (3, 10 and 70 eV) and pressures (2.5 and 5.0 mTorr) have also been performed by using a novel code developed in Madrid. In order to probe the accuracy of the proposed data set, the simulated results have been compared with the corresponding experimental data, the latter obtained with the same experimental configuration where the TCSs have been measured. Graphic Abstract: [Figure not available: see fulltext.]
Total Electron Detachment and Induced Cationic Fragmentation Cross Sections for Superoxide Anion (O2−) Collisions with Benzene (C6H6) Molecules
Publication . Guerra, Carlos; Kumar, Sarvesh; Aguilar-Galindo, Fernando; Díaz-Tendero, Sergio; Lozano, Ana I.; Mendes, Mónica; Oller, Juan C.; Limão-Vieira, Paulo; García, Gustavo; DF – Departamento de Física; CeFITec – Centro de Física e Investigação Tecnológica; MDPI - Multidisciplinary Digital Publishing Institute
In this study, novel experimental total electron detachment cross sections for O2− collisions with benzene molecules are reported for the impact energy range (10–1000 eV), as measured with a transmission beam apparatus. By analysing the positively charged species produced during the collision events, relative total ionisation cross sections were derived in the incident energy range of 160–900 eV. Relative partial ionisation cross sections for fragments with m/z ≤ 78 u were also given in this energy range. We also confirmed that heavier compounds (m/z > 78 u) formed for impact energies between 550 and 800 eV. In order to further our knowledge about the collision dynamics governing the fragmentation of such heavier molecular compounds, we performed molecular dynamics calculations within the framework of the Density Functional Theory (DFT). These results demonstrated that the fragmentation of these heavier compounds strongly supports the experimental evidence of m/z = 39–42, 50, 60 (u) cations formation, which contributed to the broad local maximum in the total ionisation observed from 550 to 800 eV. This work reveals the reactivity induced by molecular anions colliding with hydrocarbons at high energies, processes that can take place in the interstellar medium under various local conditions.
Bound Electron Enhanced Radiosensitisation of Nimorazole upon Charge Transfer
Publication . Kumar, Sarvesh; Ben Chouikha, Islem; Kerkeni, Boutheïna; García, Gustavo; Limão-Vieira, Paulo; DF – Departamento de Física; CeFITec – Centro de Física e Investigação Tecnológica; MDPI - Multidisciplinary Digital Publishing Institute
This novel work reports nimorazole (NIMO) radiosensitizer reduction upon electron transfer in collisions with neutral potassium (K) atoms in the lab frame energy range of 10-400 eV. The negative ions formed in this energy range were time-of-flight mass analyzed and branching ratios were obtained. Assignment of different anions showed that more than 80% was due to the formation of the non-dissociated parent anion NIMO#~ at 226 u and nitrogen dioxide anion NC2- at 46 u. The rich fragmentation pattern revealed that significant collision induced the decomposition of the 4-nitroimidazole ring, as well as other complex internal reactions within the temporary negative ion formed after electron transfer to neutral NIMO. Other fragment anions were only responsible for less than 20% of the total ion yield. Additional information on the electronic state spectroscopy of nimorazole was obtained by recording a K+ energy loss spectrum in the forward scattering direction (9 « 0°), allowing us to determine the most accessible electronic states within the temporary negative ion. Quantum chemical calculations on the electronic structure of NIMO in the presence of a potassium atom were performed to help assign the most significant lowest unoccupied molecular orbitals participating in the collision process. Electron transfer was shown to be a relevant process for nimorazole radiosensitisation through efficient and prevalent non-dissociated parent anion formation.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
3599-PPCDT
Número da atribuição
PTDC/FIS-AQM/31281/2017