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Register a new userRadiolysis of Amino Acids by Heavy and Energetic Cosmic Ray Analogs in Simulated Space Environments: $alpha$-Glycine Zwitterion Form
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Williamary Portugal
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In this work, we studied the stability of the glycine molecule in the crystalline zwitterion form, known as {alpha}-glycine ($^{+}$NH$_{3}$CH$_{2}$COO$^{-}$) under action of heavy cosmic ray analogs. The experiments were conducted in a high vacuum chamber at heavy ions accelerator GANIL, in Caen, France. The samples were bombarded at two temperatures (14 K and 300 K) by $^{58}$Ni$^{11+}$ ions of 46 MeV until the final fluence of $10^{13}$ ions cm$^{-2}$. The chemical evolution of the sample was evaluated in-situ using Fourrier Transformed Infrared (FTIR) spectrometer. The bombardment at 14 K produced several daughter species such as OCN$^-$, CO, CO$_2$, and CN$^-$. The results also suggest the appearing of peptide bonds during irradiation but this must be confirmed by further experiments. The halflives of glycine in Interstellar Medium were estimated to be 7.8 $times 10^3$ years (300 K) and 2.8 $times 10^3$ years (14 K). In the Solar System the values were 8.4 $times 10^2$ years (300 K) and 3.6 $times 10^3$ years (14 K). It is believed that glycine could be present in space environments that suffered aqueous changes such as the interior of comets, meteorites and planetesimals. This molecule is present in proteins of all alive beings. So, studying its stability in these environments provides further understanding about the role of this specie in the prebiotic chemistry on Earth.
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Deeply inside dense molecular clouds and protostellar disks, the interstellar ices are protected from stellar energetic UV photons. However, X-rays and energetic cosmic rays can penetrate inside these regions triggering chemical reactions, molecular dissociation and evaporation processes. We present experimental studies on the interaction of heavy, highly charged and energetic ions (46 MeV Ni^13+) with ammonia-containing ices in an attempt to simulate the physical chemistry induced by heavy ion cosmic rays inside dense astrophysical environments. The measurements were performed inside a high vacuum chamber coupled to the heavy ion accelerator GANIL (Grand Accelerateur National dIons Lourds) in Caen, France.textit{In-situ} analysis is performed by a Fourier transform infrared spectrometer (FTIR) at different fluences. The averaged values for the dissociation cross section of water, ammonia and carbon monoxide due to heavy cosmic ray ion analogs are ~2x10^{-13}, 1.4x10^{-13} and 1.9x10^{-13} cm$^2$, respectively. In the presence of a typical heavy cosmic ray field, the estimated half life for the studied species is 2-3x10^6 years. The ice compaction (micropore collapse) due to heavy cosmic rays seems to be at least 3 orders of magnitude higher than the one promoted by (0.8 MeV) protons . In the case of the irradiated H2O:NH3:CO ice, the infrared spectrum at room temperature reveals five bands that were tentatively assigned to vibration modes of the zwitterionic glycine (+NH3CH2COO-).
Formic acid (HCOOH) has been extensively detected in space environments, including interstellar medium (gas and grains), comets and meteorites. Such environments are often subjected to the action of ionizing agents, which may cause changes in the molecular structure, thus leading to formation of new species. Formic acid is a possible precursor of pre-biotic species, such as Glycine (NH2CH2COOH). This work investigates experimentally the physicochemical effects resulting from interaction of heavy and energetic cosmic ray analogues (46MeV 58Ni11+) in H2O:HCOOH (1:1) ice, at 15 K, in ultrahigh vacuum regime, using Fourier transform infrared spectrometry in the mid-infrared region (4000-600 cm-1 or 2.5-12.5 microns). After the bombardment, the sample was slowly heated to room temperature. The results show the dissociation cross-section for the formic acid of 2.4x10^-13 cm2, and half-life due to galactic cosmic rays of 8x10^7 yr. The IR spectra show intense formation of CO and CO2, and small production of more complex species at high fluences.
The discovery of amino acids in meteorites has presented two clues to the origin of their processing subsequent to their formation: a slight preference for left-handedness in some of them, and isotopic anomalies in some of their constituent atoms. In this article we present theoretical results from the Supernova Neutrino Amino Acid Processing (SNAAP) model, which uses electron anti-neutrinos and the magnetic fields from source objects such as supernovae or colliding neutron stars to selectively destroy one amino acid chirality and to create isotopic abundance shifts. For plausible magnetic fields and electron anti-neutrino fluxes, non-zero, positive enantiomeric excesses, $ee$s, defined to be the relative left/right asymmetry in an amino acid population, are reviewed for two amino acids, and conditions are suggested that would produce $ee>0$ for all of the $alpha$-amino acids. The relatively high energy anti-neutrinos that produce the $ee$s would inevitably also produce isotopic anomalies. A nuclear reaction network was developed to describe the reactions resulting from them and the nuclides in the meteorites. At similar anti-neutrino fluxes, assumed recombination of the detritus from the anti-neutrino interactions is shown to produce appreciable isotopic anomalies in qualitative agreement with those observed for D/$^1$H and $^{15}$N/$^{14}$N. The isotopic anomalies for $^{13}$C/$^{12}$C are predicted to be small, as are also observed. Autocatalysis may be necessary for any model to produce the largest $ee$s observed in meteorites. This allows the constraints of the original SNAAP model to be relaxed, increasing the probability of meteoroid survival in sites where amino acid processing is possible. These results have obvious implications for the origin of life on Earth.
The correlations of primary and secondary structures were analyzed using proteins with known structure from Protein Data Bank. The correlation values of amino acid type and the eight secondary structure types at distant position were calculated for distances between -25 and 25. Shapes of the diagrams indicate that amino acids polarity and capability for hydrogen bonding have influence on the secondary structure at some distances. Clear preference of most of the amino acids towards certain secondary structure type classifies amino acids into four groups: alpha-helix admirers, strand admirers, turn and bend admirers and the others. Group four consists of His and Cis, the amino acids that do not show clear preference for any secondary structure. Amino acids from a group have similar physicochemical properties, and the same structural characteristics. The results suggest that amino acid preference for secondary structure type is based on the structural characteristics at Cb and Cg atoms of amino acid. alpha-helix admirers do not have polar heteroatoms on Cb and Cg atoms, nor branching or aromatic group on Cb atom. Amino acids that have aromatic groups or branching on Cb atom are strand admirers. Turn and bend admirers have polar heteroatom on Cb or Cg atoms or do not have Cb atom at all. Our results indicate that polarity and capability for hydrogen bonding have influence on the secondary structure at some distance, and that amino acid preference for secondary structure is caused by structural properties at Cb or Cg atoms.
A two amino acid (hydrophobic and polar) scheme is used to perform the design on target conformations corresponding to the native states of twenty single chain proteins. Strikingly, the percentage of successful identification of the nature of the residues benchmarked against naturally occurring proteins and their homologues is around 75 % independent of the complexity of the design procedure. Typically, the lowest success rate occurs for residues such as alanine that have a high secondary structure functionality. Using a simple lattice model, we argue that one possible shortcoming of the model studied may involve the coarse-graining of the twenty kinds of amino acids into just two effective types.
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