Jose J. Flores

Asymmetric Adsorption of Alanine by Quartz

Radioactive D- and L-alanine hydrochloride in 10-5 molar dimethylformamide solution was adsorbed by d- and 1-quartz to the extent of 20 to 30 percent, as shown by radioactivity loss. d-Quartz preferentially adsorbs D-alanine and 1-quartz adsorbs L-alanine. The extent of asymmetric preferential adsorption is about 1.0 to 1.8 percent, at the 99.9 percent confidence level.

Organic synthesis in a simulated Jovian atmosphere—II☆

Abstract Reactions which may occur in the Jovian atmosphere were simulated by passing an electrical discharge through a mixture of methane and ammonia. Analysis of the volatile fraction revealed the presence of several precursors of biologically important compounds. The nonvolatile fraction consisted of an orange-red polymer. This result may provide an explanation for the appearance of the red spot on the planet Jupiter.

Asymmetric adsorption by quartz - A model for the prebiotic origin of optical activity

One mechanism previously proposed for the abiotic accumulation of molecules of one chirality in nature is asymmetric adsorption on the chiral surfaces of optically active quartz crystals. Earlier literature in this field is reviewed, with the conclusion that previous investigations of this phenomenon, using optical rotation criteria, have afforded ambiguous results. We now have studied the adsorption of radioactive D-and L-alanine on powderedd-andl-quartz, using change in radio-activity level as a criterion for both gross and differential adsorption.d-Quartz preferentially adsorbed D-alanine from anhydrous dimethyl-formamide solution, andl-quartz L-alanine. The differential adsorption varied between 1.0 and 1.8%. The implications of these observations are discussed from the viewpoint of early chemical evolution and the origin of optically active organic compounds in nature.

On the asymmetric polymerization of aspartic acid enantiomers by kaolin

SummaryTwo recent reports in the literature claim thatl-aspartic acid polymerizes significantly faster thand-aspartic acid in the presence of kaolin in aqueous solution at 90°. The novelty of these observations and their potential significance for molecular evolution and the origin of optical activity in nature has prompted us to attempt a duplication of the experiments involved—using, however, analytical criteria which we felt would be more reliable than those previously employed. In our experimentsl- andd,l-aspartic acid in 0.01M solution were incubated with kaolin at 90° for 8 days. Careful examination of the aqueous residues from such experiments, however, failed to demonstrate any preferential polymerization ofl- overd-aspartic acid under the influence of kaolin, or indeed any significant gross polymerization of aspartic acid at all.

Colloidally separated samples from Allende residues: Noble gases, carbon and an ESCA-study

Abstract A non-colloidal fraction separated by physical means from an HF HCl -resistant residue of the Allende carbonaceous meteorite exhibits a ratio of isotopically “normal” ( Q -type) xenon to “anomalous” xenon ( X -type) that is ~4 times larger than usually observed. Coincidentally this fraction contains carbon that is isotopically heavier by ~10%. than bulk Allende residue samples. ESCA analyses of companion colloidal separates show that the major portion of the S contained in our HF HCl -residues is elemental rather than a sulfide. They also confirm earlier observations that no elementally distinct surface coating is present, in accord with the absence of a surface-sited sulfur-bearing gas carrier, and that the oxygen content is increased after etching with nitric acid. For these separates noble gas data coupled with the ESCA data for nitrogen and the isotopic data for carbon point to the existence of heterogeneities among the noble gas-, carbon- and nitrogen-bearing phases and, thus, preservation of discrete components from the variety of source regions (or production mechanisms, or both) sampled by the Allende parent body. In sharp contrast to the success of physical and chemical methods in yielding samples in which one of the major noble gas components predominates to an extraordinary degree over the other, carbon isotopic compositions that have been inferred for the respective carrier phases in these same samples are strongly contradictory. Mass and isotope balance considerations lead us to conclude that a major fraction of the carbonaceous matter in Allende is noble-gas-poor, a result that could be confirmed by direct isolation of a sample, the carbon in which is dominated by this variety; and for that reason no simple relationship is discernable yet between observed isotopic compositions and either major noble gas component. Similar ambiguities may exist for nitrogen. The possible relationship between carbon-rich phases in ureilites and carbonaceous chondrites is considered.

Polymerization of amino acids under primitive earth conditions.

SummaryChemical evolution on the primitive earth must have involved the condensation ofα-amino acids to peptides under a variety of conditions. Subjecting a mixture of methane, ammonia, and water to an electric discharge in the presence of free amino acids yields small peptides. The dehydration-condensation may have taken place via ammonium cyanide, the hydrogen cyanide tetramer, or aminonitriles. The experiments may be considered genuinely prebiotic and significant in the context of chemical evolution.

The origin of petroleum porphyrins: Preliminary evidence for protein fragments associated with porphyrins

Abstract A number of amino acids including glycine, alanine, serine, glutamic acid, aspartic acid, leucine and isoleucine were found in hydrolysates of porphyrin and chlorin fractions isolated from petroleum and from ancient and modern sediments. If these are interpreted on the basis of the present preliminary data as residues of proteins originally bonded to biogenic chlorin pigments, molecular weights of about 100–2000 are indicated for the fragments.

Possible role of aminoacetonitrile in chemical evolution

Abstract Aminoacetonitrile can condense with an amino acid such as alanine, in a basic aqueous solution, to give low yields of products that appear to be dipeptides, on the basis of elution times and enzymatic hydrolysis. The predominant reactions, however, are hydrolysis and condensation to give amino and imino acids.

Isotopic characteristics of simulated meteoritic organic matter: 1 — Kerogen-like material

Carbonaceous residues from a variety of laboratory syntheses yield release patterns for C and H isotopes during stepwise combustion that fail to mimic the striking patterns characteristic of meteoritic kerogen-like residues that otherwise superficially resemble them. It seems likely that the meteoritic material comprises a comple mixture of substances having different origins and/or synthesis conditions.