Synthetic and analytical studies in chemical evolution

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1970

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Studies have been carried out in two different areas of chemical evolution. A comparative analytical study of organogenic compounds in terrestrial and extra-terrestrial (lunar and meteoritic) samples constituted the first part of this work, while an investigation of the polymerization of deoxyribomononucleotides by ultraviolet light constituted the second. Lunar fines from Apollo 11 and Apollo 12 revealed the presence of hydrogen, helium, water, nitrogen, carbon monoxide, and carbon dioxide. A study of energies of volatilization of these species leads to an understanding of their sources. It is concluded that water, carbon dioxide and hydrocarbons lower than C[subscript 6] may be absorbed from the atmosphere. A solar origin is considered to be a certainty for hydrogen and helium, and is expected to contribute greatly to the observed carbon. Several indigenous mineralogical sources are also discussed which might account for the type of carbon and organogenic compounds observed in these experiments. The Pueblito de Allende meteorite showed high levels of pyrolyzable aromatic compounds as well as a distribution of hydrocarbons from C[subscript 1] to C[subscript 6]. Components attributable to the solar wind, as found in the lunar samples, were lacking in this sample. A terrestrial basalt of volcanic origin showed levels of pyrolyzable organic compounds approximating those of the lunar samples. In view of this result the possibility of a high level of terrestrial contamination is considered for the Pueblito de Allende. A sample of the Gunflint Chert evolved copious quantities of carbon dioxide and saturated and aromatic hydrocarbons in agreement with its geological history and its established content of organic material of biological origin. The ultraviolet irradiation of dilute, basic aqueous solutions of deoxymononucleotides is shown to be a plausible prebiological system. These experiments result in the incorporation of the heterocyclic base as well as the phosphate moiety into a product which has a chromatographic behavior similar to an oligonucleotide. This material may be degraded with phosphodiesterases to liberate a product chromatographically indistinguishable from the starting material. An attempt is made to relate these observations and others suggesting the existence of a photosensitized activation of biologically significant phosphate esters to arrive at some reasonable mechanisms for ultraviolet photochemical synthesis of phosphodiester bonds.

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