Valine Radiolysis by H+, He+, N+, and S15+ MeV Ions

Abstract

Radiolysis of biomolecules by fast ions has interest in medical applications and astrobiology. The radiolysis of solid D-valine (0.2–2 μm thick) was performed at room temperature by 1.5 MeV H+, He+, N+, and 230 MeV S15+ ion beams. The samples were prepared by spraying/dropping valine-water-ethanol solution on ZnSe substrate. Radiolysis was monitored by infrared spectroscopy (FTIR) through the evolution of the intensity of the valine infrared 2900, 1329, 1271, 948, and 716 cm−1 bands as a function of projectile fluence. At the end of sample irradiation, residues (tholins) presenting a brownish color are observed. The dependence of the apparent (sputtering + radiolysis) destruction cross section, σd, on the beam stopping power in valine is found to follow the power law σd = aSen, with n close to 1. Thus, σd is approximately proportional to the absorbed dose. Destruction rates due to the main galactic cosmic ray species are calculated, yielding a million year half-life for solid valine in space. Data obtained in this work aim a better understanding on the radioresistance of complex organic molecules and formation of radioproducts.

Radiolysis of pyridine in solid water

“…The destruction cross sections scale with a power n of Se, d ~ Se n , with a stronger than linear dependence. This behavior is universal and has been observed for many simple and more complex molecules [8,16,17,27].…”

“…As can be seen from Tables 2 and 3, the intensity of some bands decreases more rapidly with projectile fluence than that of others, thus yielding slightly different values of the associated destruction cross section. In published studies on ion irradiation of COMs (nucleobases and amino acids), individual peaks and/or an average value (mean value of all analyzed peaks) were used to determine the radiation sensitivity [17,[22][23][24][25][26][27]. If such data are to be applied e.g.…”

“…The survival times of COMs in outer space depends on their radio-resistance to the impact of energetic particles to which they are continuously exposed. Taking into account the measured scaling of destruction cross sections (Figure 4) and the flux distribution of ionizing particles, the half life time of COMs in space environments can be estimated [8,17,[25][26][27]]. To give an example, deep inside a dense molecular cloud, where only secondary UV photons induced by cosmic rays are present and primary UV radiation from surrounding stars cannot penetrate, the survival time of solid adenine exposed to cosmic rays was estimated to be of the order of 10…”

Radiation Damage in Biomolecules and Cells

“…Finally, in the framework of radiation protection studies, the protective role of melatonin and Vitamin D [27], as well as hypothermia [28], was reviewed, and valine radiolysis by fast ions was investigated [29]. Furthermore, the changes in radio-sensitivity and responses to ionizing radiation of embryos during the early developmental stages of the preimplantation were analyzed [30], and epigenetic modifications induced by ionizing radiation were critically reviewed [31].…”

Mev Ion and Kev Electron Irradiation Effects on Prebiotic Materials: Radiolysis and Sputtering

“…It is worthwhile mentioning that this model does not have free parameters beyond the default options given by the CASINO code. The parameter D 0 , not used in the code, was measured from the valine radiolysis by MeV ions [61], and it is taken as being the same for degradation by electron beams.…”