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

Cíntia A. P. da Costa,Hermann Rothard,Enio F. da Silveira,Philippe Boduch,Gabriel S. Vignoli Muniz

doi:10.3390/ijms21051893

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.

Highlights

Amino acids are building-blocks of proteins, essential in the dynamics of all living organisms
Where E is the galactic cosmic ray (GCR) energy per nucleon, E0 is a parameter considered here as equal to 400 MeV, and where E is the kinetic energy of species j, Φj(E) is its flux density and σd,j(E) its apparent destruction cross section given by Equation (1); for the current calculations, we have considered a = 1.0 × 10−20 cm3/keV
Thin films of D-valine were irradiated by four MeV ion beams

Summary

Introduction

Amino acids are building-blocks of proteins, essential in the dynamics of all living organisms. They play an important role in cell signalization, and in the innate immune system. These stable organic molecules are constituted by carbon, hydrogen, oxygen, and nitrogen. The first one is related to the dipole moment of the amino acid, which is different in solid and gas phases. In solid phase, the mentioned structure is preserved ( at high temperatures). For both polar and apolar side chains, the molecule has a significant dipole moment and is called zwitterion. Endoergic reactions may occur several times with nearby amino acids producing larger peptides [1]

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Conclusion