Direct Damage of Deoxyadenosine Monophosphate by Low-Energy Electrons Probed by X-ray Photoelectron Spectroscopy.

Low-energy (3-25 eV) electron interactions with multilayers of 2'-deoxyadenosine 5'-monophosphate (dAMP) were probed using X-ray photoelectron spectroscopy (XPS). Understanding how electrons damage the nucleotide dAMP, which is a building block of DNA, can give insight into how the DNA undergoes radiation damage. Chemical modifications to the constituent units of the nucleotide were revealed in situ through monitoring of the O 1s, C 1s, and N 1s elemental transitions. It is shown that direct electron irradiation causes decomposition of both the base and sugar subunits, as well as cleavage of glycosidic and phosphoester bonds. Incident electrons undergo inelastic energy losses, including creation of core-excited resonances above 3-4 eV. In the condensed phase, these resonances decay via autoionization, producing electronically excited targets and <3 eV electrons. The excited states dissociate and the slow (<3 eV) electrons are captured by neighboring molecules, forming molecular shape resonances that can lead to bond rupture. Since the observed chemical changes were similar at all incident electron energies studied, they can be primarily attributed to formation and decay of transient negative ions. Damage enhancements in the energy ranges typical of all scattering resonances are expected, with the damage probability dominated by the low-energy shape resonances.

A Possible Path to Prebiotic Peptides Involving Silica and Hydroxy Acid-Mediated Amide Bond Formation.

The formation of alanine and glycine oligomers in films produced by drying aqueous mixtures of lactic acid and silica nanoparticles has been studied as a model prebiotic reaction. The addition of silica results in alanine or glycine enrichment in the polymers. Oligomerization proceeds through ester-mediated peptide bond formation in an acidic and evaporative environment at temperatures as low as 85 °C. For both amino acids, the dominant species produced in the presence of silica and lactic acid are rich in amide bonds and deficient in ester linkages. At higher temperatures, glycine and alanine oligomers contain only a single hydroxy acid residue conjugated to the peptide N terminus. Similar product distributions occur with silica particles prereacted with lactic acid, which suggests the catalytic role of a functionalized surface. This work highlights the role minerals might have served in transitioning from oligomers with both ester and amide linkages (depsipeptides) to peptides in a prebiotic context.

The evolution of the surface of the mineral schreibersite in prebiotic chemistry.

We present a study of the reactions of the meteoritic mineral schreibersite (Fe,Ni)3P, focusing primarily on surface chemistry and prebiotic phosphorylation. In this work, a synthetic analogue of the mineral was synthesized by mixing stoichiometric proportions of elemental iron, nickel and phosphorus and heating in a tube furnace at 820 °C for approximately 235 hours under argon or under vacuum, a modification of the method of Skála and Drábek (2002). Once synthesized, the schreibersite was characterized to confirm the identity of the product as well as to elucidate the oxidation processes affecting the surface. In addition to characterization of the solid product, this schreibersite was reacted with water or with organic solutes in a choline chloride-urea deep eutectic mixture, to constrain potential prebiotic products. Major inorganic solutes produced by reaction of water include orthophosphate, phosphite, pyrophosphate and hypophosphate consistent with prior work on Fe3P corrosion. Additionally, schreibersite corrodes in water and dries down to form a deep eutectic solution, generating phosphorylated products, in this case phosphocholine, using this synthesized schreibersite.