Position-specific isotope analyses: recent developments and perspectives in biogeochemistry

In 1961 Abelson & Hoering shown that the intramolecular 13C distribution in amino acids was not homogeneous, namely the carboxylic acid positions were 13C-enriched compared with the mean of the remaining C-atoms in the molecule [1]. Nearly 20 years later, Monson & Hayes were able to demonstrate that even and odd positions in acetogenic fatty acids also showed non-statistical 13C isotope distributions, and that the pattern varied depending on the organism [2]. It took a further decade for the intramolecular 13C distribution in the key metabolite, glucose, to be defined [3]. Overall, these data suggest that position-specific isotope analyses (PSIA) give access to unprecendented information on the formation and degradation processes of a given molecule. Although informative, much of this work was incomplete, a number of positions having to be deduced by difference. This limitation arose mainly due to the lack of techniques enabling the separation and quantification of 13C isotopomers of the target molecule. The past decades have witnessed technological developments for PSIA, including quantitative 13C NMR [4] and on-line pyrolysis coupled with isotope ratio spectrometry [5]. This breakthrough has made possible a comprehensive view of the determinants governing intramolecular isotope composition of molecules of biogeochemical interest. In this seminar, I will review the techniques used for PSIA along with their drawbacks and advantages. I will then present their potential in (i) biogeochemistry of natural gas [6](ii) differntiation biological vs. non-biological organic matter [7](iii) source of pollutants and (bio)remediation [8]. [1] Abelson & Hoering 1961 PNAS [2] Monson & Hayes 1980 J. Biol. Chem.; Monson & Hayes 1982 J. Biol. Chem. [3] Rossmann et al. 1991 Plant Physiol. [4] Caytan et al. 2007 Anal. Chem. [5] Corso & Brenna 1997 PNAS [6] Gilbert et al. 2013 Org. Geochem. [7] Gilbert et al. 2013 Org. Geochem. [8] Julien et al. 2015 Env. Sci. Tech. ; Julien et al. 2016 Talanta