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

International audienceRadiolysis 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 S 15+ 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, σ d , on the beam stopping power in valine is found to follow the power law σ d = aS e n , with n close to 1. Thus, σ d 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 cytosine at cryogenic temperatures by swift heavy ion bombardments

We investigated the radiolysis effects on the cytosine in the solid phase irradiated by swift heavy ions as galactic cosmic ray analogues (GCRs). Infrared (IR) absorption spectroscopy was employed to monitor the physical and chemical radiolytic modifications. The targets were prepared on ZnSe in two different ways: (1) by dropping a nucleobase-water-ethanol solution on the substrate and evaporating the solvent and (2) by sublimation of nucleobase powders in an oven and condensation on the windows. Both types of samples present similar IR absorption spectra. From the exponential decrease of the areas of IR absorption bands as a function of projectile fluence, apparent destruction cross sections (σd) were determined and were found to be very similar for samples prepared using both techniques. The destruction cross section of solid cytosine at cryogenic temperatures follows an electronic stopping (Se) power law: σd = C Sen, where C is a constant and the exponential n is a dimensionless quantity. We determined σd = (3 ± 1) × 10-17 Se (1.25 ±0.06). New absorption features emerge from cytosine degradation, which can be attributed to OCN-, H2CO, and HNCO. By using the observed power law, the half-life of cytosine exposed to galactic cosmic rays was estimated in the order of Mega years. The findings reported here may help a better understanding of complex organic molecule radiostability

Swift heavy ion irradiation of thymine at cryogenic temperature

Thymine (C5H6N2O2) is a basic N-heterocyclic nucleobase in all known organisms, and this molecule is also found in meteoritic materials. This study aims to investigate thymine's physical and chemical modifications under ion irradiation in cryogenic conditions. Space radiation was simulated by exposing thymine at 27 K to 230 MeV 48Ca10+ ions. Fourier transform infrared spectroscopy (FTIR) was employed to monitor the degradation of a 2.8 μm thick sample film under irradiation. From the intensity decrease of the infrared absorptions as a function of ion fluence, the destruction cross-section (σ), required to dissociate or eject a thymine molecule, is deduced by an exponential function. The physical and chemical modifications induced by energetic projectiles can be related to the electronic stopping power Se as σ=Se/D0, where D0=9.6±0.4 eV/molecule is the effective mean dose needed to destroy the thymine molecule at 27 K. Also, new molecular species formed under irradiation are observed and, based on infrared spectra, identified as CN−, OCN−, HCNO, and CO

Norfloxacin and N-Donor Mixed-Ligand Copper(II) Complexes: Synthesis, Albumin Interaction, and Anti-Trypanosoma cruzi Activity

Copper(II) complexes with the first-generation quinolone antibacterial agent norfloxacin containing a nitrogen donor heterocyclic ligand 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen) were prepared and characterized by IR, EPR spectra, molar conductivity, and elemental analyses. The experimental data suggest that norfloxacin was coordinated to copper(II) through the carboxylato and ketone oxygen atoms. The interaction of the copper(II) complexes with bovine serum albumin (BSA) and human serum albumin (HSA) was investigated using fluorescence quenching of the tryptophan residues and copper(II) EPR spectroscopy. The results of fluorescence titration revealed that copper(II) complexes have a moderate ability to quench the intrinsic fluorescence of the albumins through a static quenching mechanism. EPR experiments showed that BSA and HSA Cu(II) sites compete with NOR for Cu(II)-bipy and Cu(II)-phen to form protein mixed-ligand complexes. Copper(II) complexes, together with the corresponding ligands, were evaluated for their trypanocidal activity in vitro against Trypanosoma cruzi, the causative agent of Chagas disease. The tests performed using bloodstream trypomastigotes showed that the Cu(II)-N-donor precursors and the metal complexes were more active than the free fluoroquinolone

Irradiation of nitrogen-rich ices by swift heavy ions: clues for the formation of ultracarbonaceous micrometeorites

Context. Extraterrestrial materials, such as meteorites and interplanetary dust particles, provide constraints on the formation and evolution of organic matter in the young solar system. Micrometeorites represent the dominant source of extraterrestrial matter at the Earth’s surface, some of them originating from large heliocentric distances. Recent analyses of ultracarbonaceous micrometeorites recovered from Antarctica (UCAMMs) reveal an unusually nitrogen-rich organic matter. Such nitrogen-rich carbonaceous material could be formed in a N2-rich environment, at very low temperature, triggered by energetic processes. Aims. Several formation scenarios have been proposed for the formation of the N-rich organic matter observed in UCAMMs. We experimentally evaluate the scenario involving high energy irradiation of icy bodies subsurface orbiting at large heliocentric distances. Methods. The effect of Galactic cosmic ray (GCR) irradiation of ices containing N2 and CH4 was studied in the laboratory. The N2-CH4 (90:10 and 98:2) ice mixtures were irradiated at 14 K by 44 MeV Ni11+ and 160 MeV Ar15+ swift heavy ion beams. The evolution of the samples was monitored using in-situ Fourier transform infrared spectroscopy. The evolution of the initial ice molecules and new species formed were followed as a function of projectile fluence. After irradiation, the target was annealed to room temperature. The solid residue of the whole process left after ice sublimation was characterized in-situ by infrared spectroscopy, and the elemental composition was measured ex-situ. Results. The infrared bands that appear during irradiation allow us to identify molecules and radicals (HCN, CN−, NH3, ...). The infrared spectra of the solid residues measured at room temperature show similarities with that of UCAMMs. The results point towards the efficient production of a poly-HCN-like residue from the irradiation of N2-CH4 rich surfaces of icy bodies. The room temperature residue provides a viable precursor for the N-rich organic matter found in UCAMMs