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

• Published in: International journal of molecular sciences 2020-03, Vol.21 (5), p.1893
• Main Authors: Costa, Cíntia A. P. da, Muniz, Gabriel S. Vignoli, Boduch, Philippe, Rothard, Hermann, Silveira, Enio F. da
• Format: Article
• Language: English
• Subjects: amino acid; Amino acids; Astrobiology; Biomolecules; Carbon; Chemical Sciences; Cosmic radiation; Destruction; destruction cross section; Ethanol; Fluence; Galactic cosmic rays; infrared absorption spectroscopy; Infrared spectroscopy; Ion beams; Laboratories; Meteors & meteorites; mev ion irradiation; Organic chemistry; Peptides; Projectiles; Radiochemistry; Radiolysis; Radioresistance; Room temperature; Spectrum analysis; Spraying; Stopping power; stopping power dependence; Valine
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms21051893

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.