Laser-plasma accelerator based femtosecond high-energy radiation chemistry and biology

International audienceRegarding the different protocols used for external cancer radiotherapy (X or. rays, electron, proton or ions beams) or radioimmunotherapy (Auger electron emitting radionuclides), the initial energy deposited in integrated biological systems (biomolecular and sub-cellular targets) represents a decisive parameter for the primary and more delayed radiation damage. A short-range energy distribution governs mainly (i)) the early survival probability of secondary electrons, (ii)) the spatio-temporal distribution of short-lived reactive radicals inside nascent tracks, (iii)) the primary biomolecular alterations triggered by low energy secondary electrons. The thorough understanding of these fundamental processes requires a real-time investigation of primary radiation events, typically in the temporal range 10(-14) - 10(-11) s. Laser-plasma accelerators based High Energy Radiation Femtochemistry (HERF) represents a newly emerging interdisciplinary field which can be driven in strong synergy with the generation of ultrashort particle beams in the MeV energy domain. The innovating developments of HERF would favour the investigation of prethermal radiation processes in aqueous and biochemically relevant environments. In this way, the quantum character of a very-short lived low-energy electron state (p-like configuration) represents a promising sub-nanometric probe to explore early radiation processes in native tracks. The specific properties of ultra-short electron beams accelerated by TW laser are very useful for future developments of spatio-temporal radiation biophysics in complex biological systems such as living cells

Synergy between low and high energy radical femtochemistry

International audienceThe deleterious effects of ionizing radiation on integrated biological targets being dependent on the spatio-temporal distribution of short-lived radical processes, a thorough knowledge of these early events requires a real-time probing in the range 10(-15) - 10(-10) s. This manuscript review is focused on the synergy that exists between low (1-10 eV) and high (MeV) energy radiation femtochemistry (LERF, HERE respectively). The synergy remains crucial for the investigation of primary radical processes that take place within the prethermal regime of low energy secondary electrons. The quantum character of very-short lived electron in a prehydrated configuration provides a unique sub-nanometric probe to spatially explore some early radiation-induced biomolecular damage. This approach would foreshadow the development of innovative applications for spatio-temporal radiation biology such as, (i)) a highly-selective pro-drug activation using well-defined quantum states of short-lived radicals, (ii)) the real-time nanodosimetry in biologically relevant environments, and (iii)) the ultrashort irradiation of living cell

FEMTOSECOND SPECTROSCOPY OF SOLVATED ELECTRON IN AQUEOUS MEDIA

The elucidation of detailed mechanisms of ultrafast events that occur in molecular charge transfer or reaction dynamics has been made possible by recent advances in spectroscopy techniques that use ultrashort laser pulse generation. Ultrashort laser pulses (100 femtoseconds duration, 1 fs = 10-15 s) allow to initiate selective photochemical processes (single charge transfer for instance) and to obtain unique informations on the dynamics of primary steps of radical reactions involving ultrafast electron or proton transfer : formation of the hydration cage around an electron, encounter pair formation, ion-molecule reaction. Recent investigations on the non-equilibrium states of electron in aqueous media are discussed

Femtosecond reactivity of electron in aqueous solutions

Femtosecond optical techniques allowing the generation of intense optical pulses from the near ultraviolet to the near infrared are used in the monitoring of ultrafast photophysical and photochemical reactions in aqueous solutions. Selected examples for dynamics of electron solvation in water and aqueous solution of ferrocyanide are discussed.Les techniques optiques femtosecondes qui permettent d'engendrer des impulsions intenses du proche UV au proche infrarouge sont utilisées pour étudier des réactions physicochimiques et photochimiques ultra-rapides dans des solutions aqueuses. Des résultats de l'étude dynamique de la solvatation d'un électron dans l'eau et une solution saline concentrée seront discutés

FEMTOSECOND INFRARED AND VISIBLE SPECTROSCOPY OF EXCESS ELECTRON IN NEAT DIMETHYLSULFIDE

Preliminary femtosecond spectroscopic studies of primary events occurring in the neat dimethylsulfide at 294 K following initial energy deposition are presented. A transient induced absorbance in the infrared (1330 nm) appears in 120 fs after the ultraviolet photoionization of dimethylsulfide. Considering scavenging experiments, we assign this signal to the solvated electron [MATH]. In the visible spectral region ([MATH] = 420 nm), a short lived species, formed in less than 300 fs has been observed. A tentative assignment of this transient component is directed toward the existence of a solvated or complexed form of the primary anion resulting from the direct electron attachment to solvent molecule