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Identification and mode of formation of hopanoid nitriles in archaeological soils.

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Title: Identification and mode of formation of hopanoid nitriles in archaeological soils.
Authors: Adam, Pierre1 padam@unistra.fr, Schaeffer, Philippe1, Schmitt, Gaby1, Bailly, Lucile1, Courel, Blandine1, Fresnais, Margaux1, Fossurier, Carole2,3, Rohmer, Michel4
Source: Organic Geochemistry. Jan2016, Vol. 91, p100-108. 9p.
Subjects: Nitriles, Ring formation (Chemistry), Antiquities, Extraction (Chemistry), Mass spectrometry, Carbon isotopes
Abstract: In the course of investigation of lipid extracts from archaeological soils from two Merovingian tombs (7th Century, Ichtratzheim, France) in an agricultural area, a series of N-containing hopanoids was detected. They were postulated to correspond to C 31 –C 33 hopanoid nitriles on the basis of mass spectrometry. The C 32 homologue was unambiguously identified by comparison with a standard obtained by synthesis. The mode of formation of the compounds was investigated using laboratory simulation experiments involving either N -acetyl-aminobacteriohopanetriol as a model compound representative of bacterial hopanoids with polyfunctionalized side chains, or C 32 hopan-32-al. The experiments led us to propose that the formation of the nitriles from C 35 biohopanoid polyols could result from a two step process involving initially an oxidation step leading to the shortening of the functionalized side chain and a second step during which N is incorporated. In the context of the soils containing archaeological wood remains from tombs and found in an agricultural area, oxidants would certainly be available, notably in the form of O 2 diffusing from the surface or H 2 O 2 produced during wood degradation by wood-rotting fungi. Possible N sources could be residual N from the decomposing body within the tomb or manure and fertilizers used for field amendment. The laboratory experiments also gave a better insight into the diagenetic processes leading to the side chain shortening of the hopanoids. In particular, it could be shown that C 31 hopanoids also derive from tetrafunctionalized hopanoids upon diagenesis and not solely from pentafunctionalized hopanoids as generally suggested in the literature. [ABSTRACT FROM AUTHOR]
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Abstract:In the course of investigation of lipid extracts from archaeological soils from two Merovingian tombs (7th Century, Ichtratzheim, France) in an agricultural area, a series of N-containing hopanoids was detected. They were postulated to correspond to C 31 –C 33 hopanoid nitriles on the basis of mass spectrometry. The C 32 homologue was unambiguously identified by comparison with a standard obtained by synthesis. The mode of formation of the compounds was investigated using laboratory simulation experiments involving either N -acetyl-aminobacteriohopanetriol as a model compound representative of bacterial hopanoids with polyfunctionalized side chains, or C 32 hopan-32-al. The experiments led us to propose that the formation of the nitriles from C 35 biohopanoid polyols could result from a two step process involving initially an oxidation step leading to the shortening of the functionalized side chain and a second step during which N is incorporated. In the context of the soils containing archaeological wood remains from tombs and found in an agricultural area, oxidants would certainly be available, notably in the form of O 2 diffusing from the surface or H 2 O 2 produced during wood degradation by wood-rotting fungi. Possible N sources could be residual N from the decomposing body within the tomb or manure and fertilizers used for field amendment. The laboratory experiments also gave a better insight into the diagenetic processes leading to the side chain shortening of the hopanoids. In particular, it could be shown that C 31 hopanoids also derive from tetrafunctionalized hopanoids upon diagenesis and not solely from pentafunctionalized hopanoids as generally suggested in the literature. [ABSTRACT FROM AUTHOR]
ISSN:01466380
DOI:10.1016/j.orggeochem.2015.10.013