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Low-energy electron-induced decomposition of 5-trifluoromethanesulfonyl-uracil: A potential radiosensitizer
Publication . Ameixa, J.; Arthur-Baidoo, E.; Meißner, R.; Makurat, S.; Kozak, W.; Butowska, K.; Ferreira Da Silva, F.; Rak, J.; Denifl, S.; CeFITec – Centro de Física e Investigação Tecnológica; DF – Departamento de Física; AIP - American Institute of Physics
5-trifluoromethanesulfonyl-uracil (OTfU), a recently proposed radiosensitizer, is decomposed in the gas-phase by attachment of low-energy electrons. OTfU is a derivative of uracil with a triflate (OTf) group at the C5-position, which substantially increases its ability to undergo effective electron-induced dissociation. We report a rich assortment of fragments formed upon dissociative electron attachment (DEA), mostly by simple bond cleavages (e.g., dehydrogenation or formation of OTf-). The most favorable DEA channel corresponds to the formation of the triflate anion alongside with the reactive uracil-5-yl radical through the cleavage of the O-C5 bond, particularly at about 0 eV. Unlike for halouracils, the parent anion was not detected in our experiments. The experimental findings are accounted by a comprehensive theoretical study carried out at the M06-2X/aug-cc-pVTZ level. The latter comprises the thermodynamic thresholds for the formation of the observed anions calculated under the experimental conditions (383.15 K and 3 × 10-11 atm). The energy-resolved ion yield of the dehydrogenated parent anion, (OTfU-H)-, is discussed in terms of vibrational Feshbach resonances arising from the coupling between the dipole bound state and vibrational levels of the transient negative ion. We also report the mass spectrum of the cations obtained through ionization of OTfU by electrons with a kinetic energy of 70 eV. The current study endorses OTfU as a potential radiosensitizer agent with possible applications in radio-chemotherapy.
In Situ AFM Imaging of Adsorption Kinetics of DPPG Liposomes: A Quantitative Analysis of Surface Roughness
Publication . Duarte, Andreia A.; Marquês, Joaquim T.; Brasil, Francisco; Viana, Ana S.; Tavares, Pedro; Raposo, Maria; CeFITec – Centro de Física e Investigação Tecnológica; DF – Departamento de Física; DQ - Departamento de Química; UCIBIO - Applied Molecular Biosciences Unit; Cambridge University Press
The adsorption of intact liposomes on surfaces is of great importance for the development of sensors and drug delivery systems and, also, strongly dependent on the surface roughness where the liposomes are adsorbed. In this paper, we analyzed, by using atomic force microscopy in liquid, the evolution of the morphology of gold surfaces and of poly(allylamine hydrochloride) (PAH) surfaces with different roughness during the adsorption of liposomes prepared with the synthetic phospholipid 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)]. Our results reveal the following. On smooth surfaces of Au only and Au with PAH, the liposomes open and deploy on the substrate, creating a supported-lipid bilayer, with the opening process being faster on the Au/PAH surface. On rough substrates of Au coated with polyelectrolyte multilayers, the liposomes were adsorbed intact on the surface. This was corroborated by power spectral density analysis that demonstrates the presence of superstructures with an average lateral size of 43 and 87 nm, in accordance with two and four times the mean liposome hydrodynamic diameter of about 21 nm. In addition, this work presents an adequate and effective methodology for analysis of adsorption phenomena of liposomes on rough surfaces.
Desenvolvimento de um Sistema para o Crescimento de Cristais com Propriedades de Óptica não-linear de KDP
Publication . Canhoto, Francisco Jorge Aleluia; Ribeiro, Paulo; Raposo, Maria de Fátima
de potássio (KDP) tem sido objecto de estudo ao longo dos anos. O principal interesse
pelos cristais de KDP advém da grande variedade de aplicações tecnológicas, nomeadamente
nas áreas da fotónica e dos lasers. Entre as aplicações em que são mais utilizados,
os cristais de KDP destacam-se em fotónica no controlo de luz fazendo uso das suas
propriedades electroópticas, sendo por excelência cristais utilizados para comutação e
conversão de frequência. A produção de cristais de KDP com grandes dimensões envolve
a utilização de sistemas com grandes volumes de solução, o que exige o uso de grandes
quantidades de matéria-prima. Nesta perspectiva importa desenvolver metodologias e
instrumentação adequadas que permitam a obtenção de cristais em pequenos reactores
apropriados para funcionar em laboratório. A presente dissertação descreve o desenvolvimento
de um sistema de cristalização que possibilita a produção de cristais de KDP
transparentes e uniformes a partir de uma semente de cristal num cristalizador de vidro
do tipo Holden pelo método de redução de temperatura, a partir de um volume pequeno
de solução saturada. O sistema desenvolvido é constituído por um reactor de vidro onde
é colocada a solução de KDP, uma plataforma rotativa de aço inoxidável que serve como
suporte da semente de cristal colocada dentro da solução e um banho termostatizado que
é usado para o controlo da temperatura cuja taxa de redução é controlada a partir de um
computador, através de uma interface gráfica. Este sistema permitiu a produção de cristais
de KDP perfeitos com dimensões 5x5x15 mm3, o que é corroborado pelo coeficiente
electroóptico medido r63 de (10,7 1,5) pm/V com um desvio de 0,9%.
Side-pumped continuous-wave Nd:YAG solar laser with 5.4% slope efficiency
Publication . Liang, Dawei; Vistas, Cláudia R.; Almeida, Joana; Tibúrcio, Bruno D.; Garcia, Dário; CeFITec – Centro de Física e Investigação Tecnológica; DF – Departamento de Física; North-Holland | Elsevier
The authors report here a significant progress in side-pumped solar laser slope efficiency by pumping a 3.0 mm diameter, 30 mm length Nd:YAG single-crystal laser rod through a heliostat-parabolic mirror solar energy collection and concentration system with 0.9 m2 effective collection area. A large fused silica aspheric lens allowed an efficient focusing of the concentrated solar power from the focal zone of the parabolic mirror into the laser rod mounted within a novel two-dimensional semi-cylindrical pump cavity. 15.3 W continuous-wave 1064 nm solar laser power was measured, resulting in 5.40% slope efficiency and 2.43% solar-to-laser conversion efficency, being 2.08 and 2.30 times, respectively, more than the previous records by side-pumping configuration. The 5.40% slope efficiency is also 1.08 times more than the previous record with Nd:YAG single-crystal rod by end-side-pumping approach. By adopting an asymmetric laser resonator, this novel side-pumping scheme also enabled an efficient production of high-quality solar laser beams in either TEM11 (4.0 W), TEM01 * (doughnut-shaped, 2.9 W), TEM10 (3.2 W) or TEM00 (2.8 W) mode profiles.
Temporal evolution of roughness development on polymer surfaces exposed to non-thermal plasma
Publication . Felix, Taís; Benetoli, Luís O. B.; Sério, Susana; Dotto, Marta E. R.; Debacher, Nito A.; DF – Departamento de Física; CeFITec – Centro de Física e Investigação Tecnológica; Sociedade Brasileira de Quimica / Sociedade Brasileira de Qu�mica, SBQ
Processes such as ablation, erosion and corrosion generally create roughness patterns on solid surfaces. Despite the randomness of this phenomenon, some patterns can be described mathematically by studying statistically the mechanisms behind them. This paper reports an experimental study on the temporal evolution of the roughness development of polymer surfaces exposed to argon non-thermal plasma under reduced pressure of 5 mbar and 65 W of applied power. The substrates studied were polypropylene, high density polyethylene, polyamide-6 and poly(ether ether)ketone. The mean roughness data as well as the saturation roughness values showed differences between polyolefin and polymers containing heteroatoms and notably the dependence of the etching on the packing density of the polymer chains. The plasma-etched surfaces were described statistically as self-affine surfaces using scaling law analysis, exhibiting roughness exponents of α ca.0.73 ± 0.2 and growth exponents of β ca. 1.0 ± 0.1. The roughness increases and decreases successively during treatment although presenting a general linear behavior in a non-monotonous way, as a function of time. The models for the shadowing and redistribution of active species can be complemented with the transient crosslinking model of the observed flattening stages.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
5876
Número da atribuição
UID/FIS/00068/2013