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.
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.
Gourier
Didier
D
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
Delpoux
Olivier
O
Bonduelle
Audrey
A
Binet
Laurent
L
Ciofini
Ilaria
I
Vezin
Hervé
H
D015415:Biomarkers / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D008280:Magnetics; D008665:Metalloporphyrins / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D014638:Vanadates / Q000737:chemistry*
D015415:Biomarkers; D008665:Metalloporphyrins; D014638:Vanadates; D012822:Silicon Dioxide