Meteorite polymer

The insoluble fraction is composed primarily of a poorly characterized, structurally heterogeneous, macromolecular material, which has been variously named, but commonly referred to as either a meteorite polymer or kerogenlike material Hayatsu et al. [45,46] concluded that the material is comprised of condensed aromatic, heteroaromatic, and hydroaromatic ring systems in up to four-ring clusters, cross linked by short methyl chains, ethers, sulfides and biphenyl groups. 

Polyamides are converted to polypeptides (as just shown), and nucleotides, because of the dehydrating properties of polyamides, to polynucleotides. This hypothetical model can accept the delivery of HCN polymers from space (e.g., via meteorites) as well as photochemical reactions in a reducing atmosphere. In spite of some convincing experimental evidence, the HCN world favoured by Matthews still awaits further convincing experimental evidence (this is also true for other hypothetical worlds ). 

Another recent interesting finding is that previously unknown organic polymers or "amorphous carbon," which are noble gas carriers in meteorites, are actually carbynes. Five different carbynes have been identified in the Murchison and Allende carbonaceous... 

An alternative to the terrestrial synthesis of the nucleobases is to invoke interstellar chemistry. Martins has shown, using an analysis of the isotopic abundance of 13C, that a sample of the 4.6 billion year old Murchison meteorite which fell in Australia in 1969 contains traces of uracil and a pyrimidine derivative, xanthine. Samples of soil that surrounded the meteor when it was retrieved were also analyzed. They gave completely different results for uracil, consistent with its expected terrestrial origin, and xanthine was undetectable [48], The isotopic distributions of carbon clearly ruled out terrestrial contamination as a source of the organic compounds present in the meteorite. At 0°C and neutral pH cytosine slowly decomposes to uracil and guanine decomposes to xanthine so both compounds could be the decomposition products of DNA or RNA nucleobases. They must have either travelled with the meteorite from its extraterrestrial origin or been formed from components present in the meteorite and others encountered on its journey to Earth. Either way, delivery of nucleobases to a prebiotic Earth could plausibly have been undertaken by meteors. The conditions that formed the bases need not have been those of an early Earth at all but of a far more hostile environment elsewhere in the Solar System. That environment may have been conducive to the production of individual bases but they may never have been able to form stable DNA or RNA polymers this development may have required the less extreme conditions prevalent on Earth. 

Alternative amino acids are easily conceived, both in theory and from experiment. Many alternative amino acids are known in meteorites (Figure 4.5). Several classes, including alpha-methylamino acids, form secondary structures more easily than do standard terran amino acids. Little is known, however, about the ability of polymers built from them to support catalysis. 

This interpretation has been questioned by Chang and Mack (1978), who found that water-soluble organics, especially amino acid extracts from the Murchison meteorite, were almost as heavy as carbonate C [8C (PDB) = -1-23 to -l-44%o vs. +44.4%o], in contrast to the much lighter insoluble polymer (—15.3 to —16.8%o) or benzene-methanol extracts ( + 5.0%o)- They suggested that these various forms of carbon represent several stages of carbon condensation in the solar nebula, in different environments separated in space and possibly in time . 

Of course, if the isotopic variations in N and O are due in part to heterogeneities of the nebula, then one must admit this possibility for C as well. But the isotopically distinct carbon phases — carbonate, polymer, and amino acids — all coexist in the same meteorite, which makes origins in different regions rather less probable. Still, this possibility must be kept in mind. 

It appears that FTT reactions can account reasonably well for most features of organic matter in meteorites. The only alternative process, the Miller-Urey synthesis, fails to account for the aliphatic and aromatic hydrocarbons, nitrogen heterocyclics, many oxygen compounds, the polymer, and carbon isotope fractionations, though it remains an alternative and perhaps superior source of amino acids and may, in an extended sense, be responsible for the deuterium enrichments. 

Bandurski E. E. and Nagy B. (1976) The polymer-like material in the Orgueil meteorite. Geochim. Cosmochim. Acta 40, 1397-1406. 

Before carbonaceous chondrites arrive on the Eartli, tire carbon-bearing materials in tliem may imdergo shock events in at least tire following tliree stages die fonnation of parent bodies by accretion of interstellar medimn particles, the break-up of the parent bodies by their mutual collisions, and die fall of meteorites on the Earth traversing the atmosphere. Through these shock events, primitive carbonaceous materials diat had been present in the interstellar medium would become more complex compounds and they would be detected in meteorites. Shock reacdons may have promoted the secondaiy production of heavier and more complicated PAHs such as the insoluble polymers of muldple benzene rings detected in meteorites. 

It is reported that 1,4-dibromonaphthalene can be formed selectively and in 90% yield by irradiation of naphthalene and 1-bromonaphthalene with stoichiometric amounts of bromine and with the minimum amount of CH2CI2 as solvent at —30 to — SO C. In contrast, l,2,3,4,5-pentabromo-l,2,3,4-tetrahyd-ronaphthalenes result from irradiation of 1-bromonaphthalene in CCI4 at — 30°C, whereas at 77°C only 1,5-dibromonaphthalene is formed and in 80% yield. Two of the more unusual examples of the photoinduced introduction of groups into aromatic rings which have been described within the year are the formation of 1-cyanopyrene in a yield of up to 73% from irradiation at the interface of a solution of pyrene and 1,4-dicyanobenzene in propylene carbonate and an aqueous solution of NaCN in a polymer microchannel chip, and the addition of a variety of groups e.g. NH2, OMe, CN, and CO2H) to coronene by irradiation of arene-ice mixtures at low temperature and pressure." The latter work provides the first experimental evidence that such functionalized arenes, which are detected in primitive meteorites and interplanetary dust particles, may have arisen, at least in part, from photochemistry in ice. 

NEXAFS spectroscopy and microscopy provide a new approach to study carbon-based materials. During the last couple of years, nexafs microscopy has been successfully applied to materials characterization in a variety of fields ranging from polymer science andbiology to meteoritics (1,83,99). Here, the discussion is focused... 

Analytical pyrolysis has been used successfiilly in many disciplines such as polymer chemistry, organic geochemistry, soil chemistry, forensic sciences, food science, environmental studies, microbiology, and extraterrestrial studies involving meteorites and lunar samples. A large number of organic substances found in nature are unsuitable for direct analysis by modern techniques such as column chromatography and mass spectrometry. This may be due to their complex structure and polar and nonvolatile character. 

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