PORPHYRINS IN METEORITES - METAL COMPLEXES IN ORGUEIL, MURRAY, COLD BOKKEVELD, AND MOKOIA CARBONACEOUS CHONDRITES

Porphyrin metal complexes were found to be present in samples of the Orgueil, Murray, Cold Bokkeveld, and Mokoia carbonaceous chondrites. No evidence for similar pigments was found for samples of Vigarano, Indarch, Peace River, and Bruderheim meteorites. Results obtained by absorption spectrophotometry in earlier studies were extended by excitation spectrofluorometry based on analytical demetallation of the porphyrin complexes using methanesulfonic acid. In several instances, the liberated free-base porphyrins were sufficiently abundant to be recovered and transferred to neutral solution for spectral characterization. Soret peak positions ranging from 390 to 413 nm were observed; non-soret peaks occurred in the range from 490 to 615 nm. Fluorescence emission was observed at about 625 and 685 nm, with the peaks at the longer wavelength predominating, in contrast to the reverse pattern for common terrestrial geochemical porphyrins. Extensive evaluations were made of the possibilities of contamination for the origin of the meteorite pigments involving terrestrial soils, dusts, and microorganisms. Porphyrins from fungi and bacteria seemed the most serious potential contaminants, but no evidence of such contamination was found. Since the specific biogenic attributes previously assigned to extraterrestrial porphyrins can no longer be accepted, the meteorite porphyrins may be interpreted as representing either prebiotic chemical evolution, or forms of life or diagenesis appreciably different from those responsible for terrestrial porphyrins. © 1969.