title: EPR, ENDOR, and HYSCORE study of the structure and the stability of vanadyl-porphyrin complexes encapsulated in silica: potential paramagnetic biomarkers for the origin of life.
abstract: The possibility of using vanadyl ions as paramagnetic biomarkers for the identification of traces of primitive life fossilized in silica rocks is studied by cw-EPR, ENDOR, HYSCORE, and DFT calculations. It is well-known that porphyrins, which are common to all living organisms, form vanadyl-porphyrin complexes in sediments deposited in oceans. However, the stability of these complexes over a very long time (more than 3 billion years) is not known. By encapsulating vanadyl-porphyrin complexes in silica synthesized by a sol-gel method to mimic SiO(2) sediments, we studied the structure and stability of these complexes upon step heating treatments by monitoring the evolution of the g factor and of the hyperfine interactions with (51)V, (1)H, (14)N, (13)C, and (29)Si nuclei. It is found that vanadyl-porphyrin complexes are progressively transformed into oxygenated vanadyl complexes by transfer of the VO(2+) ion from the porphyrin ring to the mineral matrix. The organic component is transformed into carbonaceous matter which contains paramagnetic centers (IOM(*) centers). To test the validity of this approach, we studied by EPR a 3490 million years old chert (polycrystalline SiO(2) rock) containing some of the oldest putative traces of life. This rock contains oxygenated vanadyl complexes and IOM(*) centers very similar to those found in the synthetic analogues.
authors.affiliation: Laboratoire de Chimie de la Matière Condensée de Paris, Ecole Nationale Supérieure de Chimie de Paris (Chimie ParisTech) and Université Pierre et Marie Curie, UMR-CNRS 7574, 11 rue Pierre et Marie Curie, 75231 Paris cedex 05, France. didier-gourier@chimie-paristech.fr
authors.forename: Didier
authors.initials: D
authors.lastname: Gourier
authors.forename: Olivier
authors.initials: O
authors.lastname: Delpoux
authors.forename: Audrey
authors.initials: A
authors.lastname: Bonduelle
authors.forename: Laurent
authors.initials: L
authors.lastname: Binet
authors.forename: Ilaria
authors.initials: I
authors.lastname: Ciofini
authors.forename: Hervé
authors.initials: H
authors.lastname: Vezin
mesh_terms: D015415:Biomarkers / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D008280:Magnetics; D008665:Metalloporphyrins / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D014638:Vanadates / Q000737:chemistry*
chemical_list: D015415:Biomarkers; D008665:Metalloporphyrins; D014638:Vanadates; D012822:Silicon Dioxide