Gustavo García

The electronic states of pyrimidine studied by VUV photoabsorption and electron energy-loss spectroscopy

The electronic state spectroscopy of pyrimidine C(4)H(4)N(2) has been investigated using both high resolution VUV photoabsorption in the energy range 3.7 to 10.8 eV (335 to 115 nm) and lower resolution electron energy loss in the range 2 to 15 eV. The low energy absorption band, assigned to the (pi*) <-- 7b(2)(n(N)) (1(1)B(1)<-- 1(1)A(1)) transition, at 3.85(4) eV and the vibrational progressions superimposed upon it have been observed for the first time, due to the availability of a high-resolution photon beam (0.075 nm), corresponding to 3 meV at the midpoint of the energy range studied. Vibronic coupling has been shown to play an important role dictating the nature of the observed excited states, especially for the lowest (1)B(1) state. The 2(1)B(1) state is proposed to have its origin at 7.026 eV according to the vibrational excitation reported in this energy region (7.8-8.4 eV). New experimental evidence of 4(1)A(1) state with a maximum cross section at 8.800 eV is supported by previous ab initio quantum chemical calculations. Rydberg series have been assigned converging to the three lowest ionisation energy limits, 9.32 eV ((2)B(2)), 10.41 eV ((2)B(1)) and 11.1 eV ((2)A(1) + (2)A(2)) with new members reported for the first time and classified according to the magnitude of the quantum defects (delta). Additionally, the absolute differential cross section for inelastic electron scattering has been measured for the most intense band from 6.9 to 7.8 eV assigned to (1)pipi* (3(1)A(1) + 2(1)B(2)).

Negative ion formation in potassium–nitromethane collisions

Ion-pair formation in gaseous nitromethane (CH(3)NO(2)) induced by electron transfer has been studied by investigating the products of collisions between fast potassium atoms and nitromethane molecules using a crossed molecular-beam technique. The negative ions formed in such collisions were analysed using time-of-flight mass spectroscopy. The six most dominant product anions are NO(2)(-), O(-), CH(3)NO(2)(-), OH(-), CH(2)NO(2)(-) and CNO(-). By using nitromethane-d(3) (CD(3)NO(2)), we found that previous mass 17 amu assignment to O(-) delayed fragment, is in the present experiment may be unambiguously assigned to OH(-). The formation of CH(2)NO(2)(-) may be explained in terms of dissociative electron attachment to highly vibrationally excited molecules.

Electron transfer-induced fragmentation of thymine and uracil in atom-molecule collisions

Ion-pair formation has been studied in hyperthermal (30-100 eV) neutral potassium collisions with gas phase thymine (C(5)H(6)N(2)O(2)) and uracil (C(4)H(4)N(2)O(2)). Negative ions formed by electron transfer from the alkali atom to the target molecule were analysed by time-of-flight (TOF) mass spectrometry. The most abundant product anions are assigned to CNO(-) and (U-H)(-)/(T-H)(-) and the associated electron transfer mechanisms are discussed. Special emphasis is given to the enhancement of ring breaking pathways in the present experiments, notably CNO(-) formation, compared with free electron attachment measurements.

N-site de-methylation in pyrimidine bases as studied by low energy electrons and ab initio calculations

Electron transfer and dissociative electron attachment to 3-methyluracil (3meU) and 1-methylthymine (1meT) yielding anion formation have been investigated in atom-molecule collision and electron attachment experiments, respectively. The former has been studied in the collision energy range 14-100 eV whereas the latter in the 0-15 eV incident electron energy range. In the present studies, emphasis is given to the reaction channel resulting in the loss of the methyl group from the N-sites with the extra charge located on the pyrimidine ring. This particular reaction channel has neither been approached in the context of dissociative electron attachment nor in atom-molecule collisions yet. Quantum chemical calculations have been performed in order to provide some insight into the dissociation mechanism involved along the N-CH3 bond reaction coordinate. The calculations provide support to the threshold value derived from the electron transfer measurements, allowing for a better understanding of the role of the potassium cation as a stabilising agent in the collision complex. The present comparative study gives insight into the dynamics of the decaying transient anion and more precisely into the competition between dissociation and auto-detachment.

Electron transfer processes in potassium collisions with 5-fluorouracil and 5-chlorouracil

Electron transfer to uracil (U), 5-chlorouracil (5-ClU) and 5-fluorouracil (5-FU) yielding anion formation has been investigated in 30-100 eV potassium-molecule collisions. The rich fragmentation patterns of all three molecules suggest that electron transfer in collisions with electronegative neutrals may cause efficient damage to RNA. The main ring fragment anion in all the mass spectra was NCO(-) while the production of X(-) (X = F, Cl) was a strong decomposition of the halouracil temporary negative ions. Cl(-) was the most intense fragment anion in the 5-chlorouracil measurements, whereas NCO(-) production dominated in the U and 5-FU data. Arguments based on energetics and vibrational dynamics have been proposed to explain these differences. Electronic coupling between dipole- and valence-bound states may play a particularly important role in the fragmentation pathways of the 5-ClU parent anion. The stabilizing influence of the potassium cation following electron transfer (ionic scattering) on the observed fragmentation patterns is discussed, notably in the context of comparisons with free electron attachment processes.

Modelling low energy electron interactions for biomedical uses of radiation

Current radiation based medical applications in the field of radiotherapy, radio-diagnostic and radiation protection require modelling single particle interactions at the molecular level. Due to their relevance in radiation damage to biological systems, special attention should be paid to include the effect of low energy secondary electrons. In this study we present a single track simulation procedure for photons and electrons which is based on reliable experimental and theoretical cross section data and the energy loss distribution functions derived from our experiments. The effect of including secondary electron interactions in this model will be discussed.

Decomposition of nitroimidazoles by electron transfer

Resumen del trabajo presentado a la 62nd Annual Conference on Magnetism and Magnetic Materials (MMM), celebrada en Pittsburgh (USA) del 6 al 10 de noviembre de 2017.Financial support 224 from Fundacao para a Ciencia e a Tecnologia (Lisboa, Portugal) grants 225 (PTDC/CVT/2006/66114 and UID/CVT/00276/2013)Tese de doutoramento em Ciencias da Saude, apresentada a Faculdade de Medicina da Universidade de CoimbraTrabajo presentado en el 8o Congreso de la Asociacion Iberica de Endocrinologia Comparada (AIEC), celebrado en Madrid del 5 al 7 de septiembre de 2011.Trabajo presentado en la International Conference and Exposition Aquaculture Europe 2017, celebrada en Dubrovnik del 17 al 20 de octubre de 2017.O presente estudo centra-se na analise das paisagens de poder que materializam as dinâmicas sociais e territoriais ocorridas nos finais da Idade do Ferro e inicios de epoca Romana no Noroeste Peninsular. Enquadra-se numa necessidade de se desenvolverem novas e inovadoras metodologias de trabalho, aliadas a uma robustez teorica e a um rigor empirico, cujas interpretacoes permitam a criacao de um novo conhecimento e que tenha aplicabilidade a outros contextos. Esta investigacao foi desenvolvida numa optica da Arqueologia da Paisagem. Assim, adoptou-se uma perspectiva diacronica e uma metodologia interdisciplinar, procurando-se ampliar as metodologias tradicionalmente utilizadas neste tipo de estudos, sobretudo com o recurso as tecnologias geoespaciais, na tentativa de se caracterizar a estruturacao do povoamento e territorio neste periodo e area geografica. O objectivo principal deste estudo reside na tentativa de caracterizacao sociopolitica das comunidades do Noroeste Peninsular, particularmente na sua area Meridional, nos finais da Idade do Ferro e inicios de epoca Romana. Tomaremos como caso de estudo a regiao do Alto Tâmega e Cavado. Trata-se de uma zona de fronteira e de hibridizacao cultural pelo menos desde a Idade do Ferro, localizando-se justamente na transicao entre a area dos oppida ocidentais e a dos pequenos castros orientais. Nesta zona registam-se processos de intensificacao economica, embora mais centrados na exploracao de recursos minerais, ao inves da exploracao e intensificacao agricola, dando lugar a uma estruturacao territorial bastante especifica e a formas particulares de expressao da desigualdade. Procuraremos analisar as dinâmicas territoriais e os processos de continuidade e de mudanca social, bem como as diferentes economias politicas e estrategias de poder, numa epoca onde tem lugar complexas politicas de interaccao cultural, particularmente com o mundo mediterrânico, bem como uma crescente negociacao social e identitaria. Procuraremos definir e clarificar os diferentes modelos de povoamento e as diferentes formas de estruturacao territorial em epoca pre-Romana e Romana. A base fundamental deste trabalho sera a objectivacao dos criterios locacionais e territoriais de cada povoado, com vista a se discriminarem as decisoes sociais que motivaram a eleicao de um determinado sitio, ja que distintos modelos locacionais e territoriais poderao associar-se a diferentes contextos culturais e a distintas formas de organizacao territorial e sociopolitica. Todavia, sera de ressaltar que este trabalho tera sempre um sentido comparativo, procurando-se analisar a variabilidade, mais do que uma reconstrucao positiva das condicoes que possam ter influenciado a localizacao dos sitios. Alem disso, partimos da diversidade regional e da heterogeneidade cultural, ja que mais que um todo homogeneo com uma evolucao unilinear, devemos antes, segundo uma perspectiva pos-colonial, contemplar uma multiplicidade de experiencias historicas particulares a diferentes escalas antes e depois da chegada de Roma. Apos os primeiros contactos com os Romanos, documenta-se uma estruturacao complexa do povoamento do Noroeste, que se manifesta no pleno desenvolvimento de grandes povoados tipo oppidum, que actuariam como verdadeiros lugares centrais do ponto de vista politico. Este fenomeno, que se desenvolve anteriormente a criacao generalizada de novos assentamentos romanos, e arqueologicamente mais visivel na parte Meridional da Galiza e no Norte de Portugal, onde os processos de ?oppidizacao? sao mais massivos e prematuros. Contudo, este processo de sinecismo e de hierarquizacao do povoamento podera ser consequencia de dinâmicas anteriores, uma vez que nao podemos negligenciar os complexos particularismos historicos das comunidades indigenas, tal como parece suceder em outros territorios europeus. Evidentemente que o contacto e a pressao Romana pode ter acelerado e precipitado todo este processo, embora talvez nao se tenha tratado de um processo unidireccional e monocausal. E necessario percepcionar os oppida em relacao estrutural a toda uma serie de fenomenos sociais, politicos e culturais que ocorrem no sul da Callaecia entre os seculos II a.C. e I d.C..This research has been developed on the behalf of a Doctoral (M3.1.2/F/025/2007) and a Post-Doctoral (M3.1.7/F/005/2011) Research Project, both supported by the Regional Fund for Science (FRC) of the Azorean Regional Government. This work was partially funded by Portuguese National Funds through FCT – Fundacao para a Ciencia e Tecnologia (Foundation for Science and Technology), under the project “PTDC/AAC-AMB/098786/2008”.Tese de Doutoramento em Ciencias da Saude, Universidade do Minho Escola de Ciencias da Saude.Trabajo presentado en la European Geosciences Union General Assembly, celebrada en Viena (Austria), del 8 al 13 de abril de 2018Este trabajo ha sido parcialmente financiado por la Fundacao para a Ciencia e Tecnologia, Ministerio da Educacao e Ciencia, Republica Portiguesa (SFRH/BD/44089/2008) y los proyectos: “Origins and Spread of Agriculture in the western Mediterranean region (ERC-2008-AdG 230561)” y “Stable isotopes in Mediterranean natural and agricultural ecosystems: from a mechanistic understanding of isotope fractionation processes in plants to the application in paleoenvironmental research (DGI CGL2009- 13079-C02-01)”.Trabajo presentado en el 18th International Symposium on Pollutant Responses in Marine Organisms (PRIMO 18), celebrado en Trondheim (Noruega) del 24 al 27 de mayo de 2015.VI Simposio Internacional de Ciencias del Mar - VI International Symposium of Marine Sciences (ISMS 2018), 20- 22 June 2018, Vigo.-- 1 pageResumen del poster presentado a la XXXV Reunion Bienal de la Real Sociedad Espanola de Fisica y al 25o Encuentro Iberico de Ensenanza de la Fisica, celebrados en Gijon (Espana) del 13 al 17 de julio de 2015.-- et al.Trabajo presentado en el I Congresso Luso-Extremadurense de Ciencias e Tecnologia, celebrado en Evora (Portugal), del 20 al 21 de octubre de 2017The 2nd International Symposium on Submarine Canyons (INCISE2014), 29th September-1st October 2014, Edinburgh.-- 1 page, 1 figureTrabajo presentado en la 10th International Hydrogenase Conference celebrada en Szeged (Hungria) del 8 al 12 de julio de 2013.An overview of 13C nuclear magnetic resonance (NMR) spectroscopy methods and their applications in the study of the metabolism of brain cells in vitro and in the in vivo brain is presented as well as their implications for modern molecular imaging techniques. Various topics will be discussed, such as general properties of the 13C NMR spectrum, 13C NMR spectroscopy acquisition protocols, determination of fractional 13C enrichment, 13C(2H) NMR methodologies, and the use of 13C hyperpolarized substrates for NMR spectroscopy and imaging. Some illustrative applications are described, both in vitro and in vivo.This study was financially supported by Fundacao Para a Ciencia e a Tecnologia (SFRH7 BPD/5560/2001) and HP BIODIBERIA program at the Real Jardin Botanico (Madrid).Conferencia invitada. -- 7th Conference on Elementary Processes in Atomic Systems,Průhonice, Prague, September 3-6, 2017.-- https://www.jh-inst.cas.cz/tchem/cepas2017/about-cepas-2017/The current international socioeconomic context has been emphasising the need of a new set of individual competencies in order to succeed in the professional world. A new concept of employability has also emerged, with a person-centred approach, which reflects the need to deal effectively with career-related changes (Fugate, Kinicki, & Ashforth, 2004). In a psychosocial perspective, it is assumed an individual ability to adapt to social expectations and to behave according to the changing conditions (Savickas & Porfeli, 2012). On the other hand, the last decade represented a period of profound transformations in the European space of higher education, driven by Bologna guidelines. Higher education institutions are expected to adapt new ways of work organization, promoting new core competencies in future professionals. In this context, the paper will describe a research project which aims to identify and analyse the impact factors on the employability of Portuguese graduates, namely, individual characteristics, curricular experiences during graduation courses and also employer’s characteristics. This project represents an attempt to a closer and necessary articulation between higher education practices and labour market requirements.Trabajo presentado en el MedCLIVAR Conference: Bridging the Mediterranean Climates, celebrado en Belgrado (Serbia) del 17 al 21 de septiembre de 2018Trabajo presentado por Mariana Reis Sobreiro para optar al grado de Doctor por la Universidad de Salamanca y realizado en el Instituto de Biologia Molecular y Celular del Cancer.13 paginas, 7 tablas, 1 figuras, 1 apendice. Special thanks go to Ana Mouro, Joao Luis Mouro, Miguel Porto, Nuno Pires and Sara Dias for assisting in the fieldwork, and Nuno Gomes and associated workers for the EDM loan and field aid.Trabajo presentado en en 16th International Symposium on Fish Nutrition and Feeding (ISFNF 2014), celebrado en Cairns (Australia) del 25 al 30 de mayo de 2014.Tese desenvolvida no quadro do Programa Doutoral em Ciencias e Engenharia do Ambiente, com o financiamento de uma bolsa de doutoramento (SFRH/BD/42168/2007) da Fundacao para a Ciencia e a Tecnologia (FCT) e o apoio dos projectos EROSFIRE II (PTDC/AGR-CFL/70968/2006), e ”FIREREG”(PTDC/AGR-CFL/099420/2008), ambos financiados pela Fundacao para a Ciencia e a Tecnologia (FCT) e o FSE no âmbito do III Quadro Comunitario de Apoio.Editors: A. Campar Almeida, Ana M. S. Bettencourt, D. Moura, Sergio Monteiro-Rodrigues and Maria Isabel Caetano Alves. 29 pp.Trabajo presentado en el 10o Congreso de la Asociacion Iberica de Endocrinologia Comparada (AIEC), celebrado en Castellon (Espana), del 23 al 25 de septiembre de 2015Trabajo presentado en Aquaculture Europe 2019, celebrado en Berlin (Alemania), del 7 al 10 de octubre de 2019Tese de Candidatura ao grau de Doutor em Ciencias Biomedicas submetida ao Instituto de Ciencias Biomedicas de Abel Salazar da Universidade do Porto por Ana Maria Bastos Barros Neto e realizado em el Centro Andaluz de Biologia del Desarrollo, centro mixto CSIC-UPO.Trabajo presentado en el EMS Annual Meeting: European Conference for Applied Meteorology and Climatology, celebrado en Dublin (Irlanda), de 4 al 8 de septiembre de 2017

Demethylation enhancement of 3-methyl-uracil and 1-methyl-thymine in atom-molecule collisions

We report the formation of demethylation in 3-methyl-uracil (3meU) and 1-methyl-thymine (1meT), i.e. (3meU-CH3)− and (1meT-CH3)−, through potassium-molecule collisions at different potassium kinetic energies. Study of the threshold of formation of this fragment can provide a value of threshold energy that can be compared with DEA studies.

Site- and bond-selective H- formation in methylated pyrimidine bases driven by potassium-molecule collisions

In this study we present for the first time site (N1-H / N3-H) and bond (N-H / C-H) selectivity of H− formation in 1-methylthymine, 3-methyluracil and deuterated thymine (C positions) triggered by potassium molecule collisions. By comparing the H loss of these molecules with H loss in thymine and uracil and setting the energy one can predict site and bond selectivity in these set of molecules.

Electron and positron scattering from pyrimidine

In this presentation we report the first low-energy measurements of elastic differential cross sections (DCS) for scattering of electrons (3-50 eV) by pyrimidine, along with cross sections calculated using the Schwinger multichannel variational technique (SMC), and a screening-corrected form of the independent-atom method, or the additivity rule, (SCAR). We also present total scattering, positronium formation, and differential cross sections recently measured at the positron beamline facility at the Australian National University, for positron (1-200 eV) scattering from pyrimidine.