RESUMO
Upstream of the efficiency of proton or carbon ion beams in cancer therapy, and to optimize hadrontherapy results, we analysed the chemistry of Fricke solutions in track-end of 64-MeV protons and 1.14-GeV carbon ions. An original optical setup is designed to determine the primary track-segment yields along the last millimetres of the ion track with a sub-millimetre resolution. The Fe3+-yield falls in the Bragg peak to (4.9 ± 0.4) × 10-7 mol/J and 1.9 × 10-7 mol/J, under protons and carbon ions respectively. Beyond the Bragg peak, a yield recovery is observed over 1 mm for proton beams. It is attributed to the intermediate-LET of protons in this region where their energy decreases and energy distribution becomes broader, in relation with the longitudinal straggling of the beam. Consequently to this LET decrease in the distal part of the Bragg peak, Fe3+-yield increases. For the first time, this signature is highlighted at the chemical level under proton irradiation. Nevertheless, this phenomenon is not identified for carbon ion beams since their straggling is lower. It would need a greater spatial resolution to be observed.
Assuntos
COVID-19 , Toxidermias , Líquen Plano , Vacinas , Anticorpos Antivirais , COVID-19/prevenção & controle , Toxidermias/etiologia , Humanos , RNA Mensageiro , SARS-CoV-2RESUMO
This communication reports the first observation of the formation of HOË produced under two different High energy ion beams, (18)O(8+) and (36)Ar(18+) having Linear Energy Transfers (LET) of 65 and 350 eV nm(-1) respectively, at temperatures up to 411 K. Both scavenging with various concentrations of SCN(-) and heavy-ion pulse radiolysis methods are used with an original temperature and pressure regulated optical cell. Deconvolution of kinetics is used to analyze the evolution of HOË track segment yields as a function of time and temperature. It takes care of involving the ionic strength effect and Arrhenius expression in the rate constants correction. The results show a fast decay of HOË yields in the 10(-10)-10(-8) s range which denotes an efficient reactivity of this species in the track structure of the ion beam. This effect is enhanced with the lowest LET of O(8+). Increasing the temperature also accelerates the decays for both ions. These observations are discussed in terms of temperature activation of reactions and the track structure exhibiting the formation of HOË in a "low LET" penumbra around the ionization tracks. HOË track segment yields at 100 ns, of 0.4 × 10(-7) and 0.6 × 10(-7) mol J(-1), respectively for 350 and 65 eV nm(-1), are not affected by temperature.
RESUMO
Resazurin (RNO) reduction by hydrated electrons produces a fluorescent molecule: resorufin (RN). To take advantage of RN fluorescence, a novel setup is designed by implementing fluorescence detection induced by laser in a pulse radiolysis experiment. Time resolved fluorescence spectra were recorded with a fast gated intensified CCD camera during the reduction of RNO from µs to ms. Two 532 nm laser types have been used to describe the short µs range by a 5 ns Q-switch laser and the µs-ms range by a CW DPSS laser. By fitting the simulated model to the experimental data a second order rate constant of 10(9) M(-1) s(-1) was re-evaluated. This method should be considered in the near future in many in situ and real time measurements for evaluating radical production.
Assuntos
Lasers , Oxazinas/análise , Radiólise de Impulso/métodos , Espectrometria de Fluorescência/métodos , Xantenos/análise , Elétrons , Radicais Livres/química , Oxazinas/química , Oxirredução , Radiólise de Impulso/instrumentação , Espectrometria de Fluorescência/instrumentação , Xantenos/químicaRESUMO
A new method for the detection of low concentrations of hydroxyl and superoxide radicals, formed by water radiolysis, is described in this article. The method used is the time resolved chemiluminescence. It has been performed with an electron beam delivered by a Febetron 707 accelerator. This method allows to measure hydroxyl and superoxide radical concentrations in a large range of concentrations, between 10(-5) and 10(-8) M.
Assuntos
Radical Hidroxila/análise , Superóxidos/análise , Água/química , Elétrons , Radicais Livres/análise , Radical Hidroxila/efeitos da radiação , Medições Luminescentes , Radiólise de Impulso , Superóxidos/efeitos da radiaçãoRESUMO
The radiolysis of water with heavy ions of high linear energy transfer (LET) (-dE/dx) is characterized, in deaerated medium, by the production of superoxide anions, the radiolytic yields of which increase with the LET. Radiobiological interest in such radical species comes from the oxidative stress which may be generated by their dismutation in O2 and H2O2 in anoxic medium (radiotherapy with heavy ions). A brief review of the measurements of superoxide free radicals in aqueous solution by indirect or direct methods is presented. Moreover, some experimental results obtained by pulse radiolysis with Ar18+ ions (TEL = 290 keV x microm(-1)), are described. The interpretation of the kinetics takes into account the superoxide absorbance and that of hydrogen peroxide, which is present at the millisecond time scale.
Assuntos
Radiólise de Impulso/métodos , Superóxidos/química , Superóxidos/efeitos da radiação , Água/química , Algoritmos , Argônio , Transferência de Energia , Peróxido de Hidrogênio/química , Peróxido de Hidrogênio/efeitos da radiação , RadioisótoposRESUMO
The formation and decay of HO2/O2- radical from the radiolysis of water by heavy 36S16+ ions (2.7 GeV) have been observed by time-resolved absorption spectroscopy at 260 nm. The experiment was performed at the Grand Accélérateur National d'Ions Lourds (Caen, France). In deaerated water, for a linear energy transfer (LET) of 250 eV/nm, the yield of HO2/O2- is (6 +/- 2) x 10(-9) mol J-1. In aerated solution, an additional formation of O2- is observed due to the reaction of hydrogen atom and e(aq)- with oxygen. The experimental G values are compared to those obtained with light ions for the same LET. The importance of the initial velocity is discussed briefly.