Carbynes in meteorites: detection, low-temperature origin, and implications for interstellar molecules.

Carbon from the Allende meteorite is not graphite but carbyne (triply bonded elemental carbon), inasmuch as on heating to 250 degrees to 330 degrees C it releases mainly triply bonded fragments: -(C identical withC)(n),- with n = 1 to 5, and -(C identical withC)(n)-CN, with n = 1 to 3. Although carbynes have been known to form only by condensation of carbon vapor above 2600 K or by explosive shock of > 600 kilobars, it is found that they also form metastably by the reaction 2CO --> CO(2) + C (solid) at 300 degrees to 400 degrees C in the presence of a chromite catalyst. Such low-temperature formation by surface catalysis may be the dominant source of carbynes on the earth and in meteorites, and a major source of interstellar carbynes and cyanopolyacetylenes.

Phenolic ethers in the organic polymer of the murchison meteorite.

Seven phenolic acids and many nonphenolic organic acids, including large amounts of meta-hydroxy (3-hydroxy) benzoic acid and 3-hydroxy-1,5-benzene-dicarboxylic acid, were obtained from the organic polymer of the Murchison C2 chondrite upon oxidation with alkaline cupric oxide. The phenolic acids apparently were derived from phenolic ethers in the polymer, which in turn probably were formed from carbon monoxide and hydrogen by catalytic Fischer-Tropsch type reactions in the solar nebula. In contrast, terrestrial polymers such as lignin, humic acid, and coal yield mainly para-hydroxy (4-hydroxy) benzene derivatives by the same oxidation procedure.

Covalently linked chlorophyll a dimer: A biomimetic model of special pair chlorophyll.

The synthesis of a covalent dimer of chlorophyll a which possesses properties strikingly similar to those exhibited by P700 special pair chlorophyll in vivo is described. The covalent dimer is characterized by several spectroscopic techniques. Hydrogen bonding nucleophiles, such as water, primary alcohols, and primary thiols, are effective in generating a species from solutions of 10 muM covalent dimer in hydrophobic solvents which absorbs light near 700 nm. Formation of this in vitro special pair is a rapid, spontaneous process at room temperature. The range of nucleophiles which promote this process suggests that amino acid residues may function in a similar fashion to form P700 in chlorophyll-protein complexes. The photochemical properties of this in vitro special pair mimic those of in vivo P700 species. The 697 nm absorption of the in vitro special pair undergoes photo-bleaching rapidly in the presence of iodine that results in the production of a cation radical which exhibits an electron spin resonance signal similar to that of oxidized P700 observed in Chlorella vulgaris.

Biosynthesis of deuterated riboflavin: structure determination by NMR and mass spectrometry.

The riboflavin-producing fungus Eremothecium ashbyii was cultured in various growth media containing high concentrations of deuteriuj, and the product was isolated. The structures of highly deuterated riboflavin, in which at least 13 of 15 nonexchangeable hydrogens were replaced by deuterium, and fully deuterated riboflavin, in which all 15 nonexchangeable sites contained deuterium, were established by NMR and mass spectrometry. The aromatic protons (C-5 and C-8) wer partially substituted in the highly deuterated molecule. Information regarding three areas of the biosynthetic pathway within the microorganism was obtained as a result of the formation of these compounds. Extensive solvent interaction, possibly due to passage of sugar through the transaldolase-transketolase pathway, occurs during formation of the ribityl chain. Limited solvent participation takes place during formation of 6,7-dimethyl-8-ribityllumazine, the immediate precursor of riboflavin. Deuteration of the riboflavin C-6 and C-7 methyl groups indicates significant solvent exchange during the final step of the biosynthetic process.

Organic Compounds in Meteorites: They may have formed in the solar nebula, by catalytic reactions of carbon monoxide, hydrogen, and ammonia.

Organic compounds in meteorites seem to have formed by catalytic reactions of CO, H2, and NH3 in the solar nebula, at 360 degrees to 400 degrees K and (4 to 10) x 10-6 atm. The onset of these reactions was triggered by the formation of suitable catalysts (magnetite, hydrated silicates) at these temperatures. These reactions may be a source of prebiotic carbon compounds on the inner planets, and interstellar molecules.

Thiobases in Escherchia coli Transfer RNA: 2-Thiocytosine and 5-Methylaminomethyl-2-thiouracil.

Two new sulfur-containing pyrimidine nucleotides have been isolated from hydrolyzates of Escherichia coli transfer RNA. The structures, 2-thiocytosine and 5-methylaminomethyl-2-thiouracil, have been assigned to the bases as a result of study of ultraviolet and mass spectra. An acid-degradation product, S-methylamino-methyluracil, has been synthesized and is identical to that derived from the natural product.