Ion beam processing of DNA origami nanostructures.

DNA origami nanostructures are emerging as a bottom-up nanopatterning approach. Direct combination of this approach with top-down nanotechnology, such as ion beams, has not been considered because of the soft nature of the DNA material. Here we demonstrate that the shape of 2D DNA origami nanostructures deposited on Si substrates is well preserved upon irradiation by ion beams, modeling ion implantation, lithography, and sputtering conditions. Structural changes in 2D DNA origami nanostructures deposited on Si are analyzed using AFM imaging. The observed effects on DNA origami include structure height decrease or increase upon fast heavy ion irradiation in vacuum and in air, respectively. Slow- and medium-energy heavy ion irradiation results in the cutting of the nanostructures or crater formation with ion-induced damage in the 10 nm range around the primary ion track. In all these cases, the designed shape of the 2D origami nanostructure remains unperturbed. Present stability and nature of damages on DNA origami nanostructures enable fusion of DNA origami advantages such as shape and positioning control into novel ion beam nanofabrication approaches.

Infrared Spectroscopic Study on Swift-Ion Irradiation of Solid N2O-H2O Samples: Synthesis of N-O Bearing Species in Astrophysical Ices.

As of early 2022, only six species bearing an N-O bond have been detected toward cold molecular clouds and regions of star formation. It is not clear yet if the small number of N-O bond species found in the interstellar medium so far stems from physical and technological limitations of astronomical detection techniques, or whether in fact molecules that bear an N-O bond are for some reason rare in these objects of the interstellar medium. Astronomical N-O bearing molecules are important because they are part of astrochemical models which propose that they are precursors of hydroxylamine (NH2OH), a species linked to the formation of prebiotic amino acids in space. The aim of this study is the better understanding of the open question of the interstellar synthesis of N-O bearing species. We have analyzed by infrared spectroscopy an astrophysically relevant polar ice mixture of N2O:H2O processed by 90 MeV 136Xe23+ ions, which can mimic the physicochemical processes triggered by cosmic rays in water-covered interstellar ice grains. The results show the formation of N2O3 and of H2O2, but no HN-O species of any kind were detected. Such findings are discussed in light of recent studies from our group and from the literature.

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

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.

Radioresistance of Adenine to Cosmic Rays.

The presence of nucleobases in carbonaceous meteorites on Earth is an indication of the existence of this class of molecules in outer space. However, space is permeated by ionizing radiation, which can have damaging effects on these molecules. Adenine is a purine nucleobase that amalgamates important biomolecules such as DNA, RNA, and ATP. Adenine has a unique importance in biochemistry and therefore life. The aim of this work was to study the effects of cosmic ray analogues on solid adenine and estimate its survival when exposed to corpuscular radiation. Adenine films were irradiated at GANIL (Caen, France) and GSI (Darmstadt, Germany) by 820 MeV Kr33+, 190 MeV Ca10+, 92 MeV Xe23+, and 12 MeV C4+ ion beams at low temperature. The evolution of adenine molecules under heavy ion irradiation was studied by IR absorption spectroscopy as a function of projectile fluence. It was found that the adenine destruction cross section (σd) follows an electronic stopping power (Se) power law under the form: CSen; C is a constant, and the exponential n is a dimensionless quantity. Using the equation above to fit our results, we determined σd = 4 × 10-17 Se1.17, with Se in kiloelectronvolts per micrometer (keV µm-1). New IR absorption bands arise under irradiation of adenine and can be attributed to HCN, CN-, C2H4N4, CH3CN, and (CH3)3CNC. These findings may help to understand the stability and chemistry related to complex organic molecules in space. The half-life of solid adenine exposed to the simulated interstellar medium cosmic ray flux was estimated as (10 ± 8) × 106 years. Key Words: Heavy ions-Infrared spectroscopy-Astrochemistry-Cosmic rays-Nucleobases-Adenine. Astrobiology 17, 298-308.

Radiolysis of astrophysical ice analogs by energetic ions: the effect of projectile mass and ice temperature.

An experimental study of the interaction of highly charged, energetic ions (52 MeV (58)Ni(13+) and 15.7 MeV (16)O(5+)) with mixed H(2)O : C(18)O(2) astrophysical ice analogs at two different temperatures is presented. This analysis aims to simulate the chemical and the physicochemical interactions induced by cosmic rays inside dense, cold astrophysical environments, such as molecular clouds or protostellar clouds as well at the surface of outer solar system bodies. The measurements were performed at the heavy ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds) in Caen, France. The gas samples were deposited onto a CsI substrate at 13 K and 80 K. In situ analysis was performed by a Fourier transform infrared (FTIR) spectrometer at different fluences. Radiolysis yields of the produced species were quantified. The dissociation cross section at 13 K of both H(2)O and CO(2) is about 3-4 times smaller when O ions are employed. The ice temperature seems to affect differently each species when the same projectile was employed. The formation cross section at 13 K of molecules such as C(18)O, CO (with oxygen from water), and H(2)O(2) increases when Ni ions are employed. The formation of organic compounds seems to be enhanced by the oxygen projectiles and at lower temperatures. In addition, because the organic production at 13 K is at least 4 times higher than the value at 80 K, we also expect that interstellar ices are more organic-rich than the surfaces of outer solar system bodies.