James G. Lawless

HCN - A plausible source of purines, pyrimidines and amino acids on the primitive earth

SummaryDilute (0.1M) solutions of HCN condense to oligomers at pH 9.2. Hydrolysis of these oligomers yields 4,5-dihydroxypyrimidine, orotic acid, 5-hydroxyuracil, adenine, 4-aminoimidazole-5-carboxamide and amino acids. These results, together with the earlier data, demonstrate that the three main classes of nitrogen-containing biomolecules, purines, pyrimidines and amino acids may have originated from HCN on the primitive earth. The observation of orotic acid and 4-aminoimidazole-5-carboxamide suggests that the contemporary biosynthetic pathways for nucleotides may have evolved from the compounds released on hydrolysis of HCN oligomers.

Amino acids indigenous to the murray meteorite.

Analysis of the Murray meteorite, a type II carbonaceous chondrite, has led to the identification of 17 amino acids. For seven of the amino acids nearly equal amounts of the D and L isomers are present, and 11 of the amino acids are not found in protein. These results suggest that these amino acids, like the amino acids of the Murchison meteorite, are extraterrestrial in origin.

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.

Amino acids in the Murchison meteorite

Abstract Continued investigation of the Murchison meteorite by gas chromatography combined with mass spectrometry has led to the characterization of at least 17 amino acids in addition to the 18 identified in earlier work. The total population consists of a wide variety of linear and cyclic difunctional and polyfunctional amino acids, of which the linear difunctional amino acids show a general decrease in concentration as the number of carbon atoms in the amino acid molecule increases. These results are consistent with the hypothesis that the amino acids are present as the result of an extraterrestrial, abiotic synthesis.

pH profile of the adsorption of nucleotides onto montmorillonite. I. Selected homoionic clays.

The effect of adsorbed ions and pH on the adsorption of several purine and pyrimidine nucleotides on montmorillonite was studied. The cations used to prepare homoionic montmorillonite were Na+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+. The nucleotides studied were 5′-, 3′-, and 2′-AMP, and 5′-CMP in the pH range 2 through 12. The results show that preferential adsorption amongst nucleotides and similar molecules is dependent upon pH and the nature of the substituted metal cation in the clay. At neutral pH, it was observed that 5′-AMP was more strongly adsorbed than 2′-AMP, 3′-AMP, and 5′-CMP. Cu2+ and Zn2+ clays showed enhanced adsorption of 5′-AMP compared to the other cation clays studied in the pH range 4–8. Below pH 4, the adsorption is attributed to cation and anion exchange adsorption mechanisms; above pH 4, anion exchange may also occur, but the adsorption (when it occurs) likely depends on a complexation mechanism occurring between metal cation in the clay exchange site and the biomolecule. It is thus proposed that homoionic clays may have played a significant role in the concentration mechanism of biomonomers in the prebiotic environment, a prerequisite step necessary for the formation of biopolymers in the remaining steps leading to the origin of life.

The role of metal ions in chemical evolution - Polymerization of alanine and glycine in a cation-exchanged clay environment

SummaryThe effect of the exchangeable cation on the condensation of glycine and alanine was investigated using a series of homoionic bentonites. A cycling procedure of drying, warming and wetting was employed. Peptide bond formation was observed, and the effectiveness of metal ions to catalyze the condensation was Cu2+ > Ni2+ ≈ Zn2+ > Na+. Glycine showed 6% of the monomer incorporated into oligomers with the largest detected being the pentamer. Alanine showed less peptide bond formation (a maximum of 2%) and only the dimer was observed.

Heterocyclic compounds recovered from carbonaceous chondrites

Abstract N-heterocyclic compounds were recovered from the Murchison, C2, Murray, C2, and Orgueil C1 carbonaceous chondrites. Combined gas chromatograpby-low resolution mass spectrometry and gas chromatography-high resolution mass spectrography of trimethylsilyl derivatives provided data permitting identification of some of the extracted material. Three major groups of compounds were observed: 1. (1) the 4-hydroxypyrimidines, 2. (2) N,N,C-alkyl-ketohexahydropyrimidines, and 3. (3) a heterogenous class of (speculative) pyrimidines. All meterorites contained representatives of the first two groups and a unique assortment of the third. No biological N-heterocyclics nor triazines were recovered. The relevance of these findings to chemical evolution is discussed.

pH profile of the adsorption of nucleotides onto montmorillonite. II. Adsorption and desorption of 5'-AMP in iron-calcium montmorillonite systems.

The interaction of 5′-AMP with montmorillonite saturated with various ratios of two metals found ubiquitously on the surface of Earth, that is, iron and calcium, is investigated. Adsorption and desorption of the nucleotide were studied in the pH range of 2–12 at three levels of addition: 0.080, 0.268 and 0.803 mmole 5′-AMP per gram of clay. Two desorption stages were employed — H2O wash and NaOH extraction (pH=12.0). 5′-AMP was preferentially adsorbed on the Fe-containing clays relative to the Ca clay. The nucleotide was fully recovered by the two desorption stages, mostly by the NaOH extraction. The evidence at hand indicates that 5′-AMP reaction with clay is affected by electrostatic interactions involving both attraction and repulsion forces. Some specific adsorption, possibly the result of covalent bonding and complex formation with the adsorbed ion, cannot be ruled out for iron but does not appear to operate for calcium. Changes in pH cause varying degrees of attraction and repulsion of 5′-AMP and may have been operating on the primitive Earth, leading to sequences of adsorption and release of this biomolecule.

Interaction between ATP, metal ions, glycine, and several minerals

SummaryThe adsorption of ATP and ADP on montmorillonite, kaolinite, and A1(OH)3 was studied as a funtion of pH and, for montmorillonite and kaolinite, as a funtion of the ionic composition of the system. The three minerals exhibit different adsorption charcteristics. Mg2+- and Zn2+-montmorillonite adsorb ATP and ADP more than Na+-montmorillonite, presumably because of complex formation. In kaolinite, the effect of these divalent cations is small. Pure ATP decomposes upon heating, and the rate of the decomposition is accelerated by the presence of glycine. Drying and heating glycine to 70°C under vacuum in the presence of ATP results in abiotic peptide formation with yields up to 0.25%. This peptide formation also occurs when kaolinite or montmorillonite is added to the system. The presence of kaolinite, Mg2+-or Zn2+-koalinite, or Mg2+-montmorillonite results in a reduction in the rate of the ATP decomposition in the abiotic peptide synthesizing system. These results suggest that one role for clays and metal ions in chemical evolution may have been the stabilization of nucleotides during prebiotic peptide synthesis.

Carbon, Carbides, and Methane in an Apollo 12 Sample

Total carbon in the Apollo 12 sample 12023 fines was 110 micrograms per gram of sample with a carbon isotopic abundance δ13C (relative to the Pee Dee belemnite standard) of +12 per mil. Hydrolysis of the fines with deuterium chloride yielded undeuterated methane along with deuterated hydrocarbons, thus confirming the presence of 7 to 21 micrograms of carbon per gram of sample as carbide and about 2 micrograms of carbon per gram of sample as indigenous methane. After vacuum pyrolysis of the fines to 1100�C the following gases were detected in the relative abundance: carbon monoxide 〉 carbon dioxide 〉 methane. Variations of the δ13C value with the pyrolysis temperature indicated the presence of carbon with more than one range of isotopic values. The observed δ13C value of +14 per mil for lunar carbide is much higher than that of carbide in meteorites. These results suggest that lunar carbide is either indigenous to the moon or a meteoritic contribution that has been highly fractionated isotopically.