Research

Overview: Isotopes, isotopologues and isotopomers

My research consists in exploring the isotopic structure of organic molecules.

Organic molecules are mainly made of elements CHONS. Each element can be substituted by its heavy isotope in the structure of the molecule. Any substitution leads to a new molecule called "isotopologue".

For instance, for ethanol C2H6O, there are 276 possible isotopic substitutions (276 isotopologues; See figure opposite).

When isotopologues have the same isotopic substitution but at different positions, they are called isotopomers. The relative concentration of isotopomers is called position-specific isotope analysis.

1. Method development for position-specific isotope analysis of organic compounds

We develop methods that enable the separation of isotopomer and their quantification with sufficient precision. We use 2 types of techniques:

Nuclear Magnetic Resonance (NMR): nucleus (13C, 2H) with different chemical environments resonate at different frequencies. This approach was developed in the University of Nantes by Martin and Martin in the 80's for ethanol deuterium isotope composition. In the last decade, it was implemented for the measurement of 13C isotopomers.

On-line pyrolysis coupled with IRMS: We developed a system based on pyrolysis of organic molecules and subsequent analysis of the fragments formed ("on-line" pyrolsysis system originally developed by Corso and Brenna (link)). The system allows PSIA of organic molecules (ethanol, acetic acid, hydrocarbons, ...) with a high precision and a sample amount on the order of the micromole or lower.

On-line pyrolysis system developed at Tokyo Tech for position-specific isotope analysis

2. Isotope fractionation associated with biological processes

We try to understand how isotopes are distributed in living organisms (plants, bacteria, yeast...).

The determination of position-specific isotope patterns in biomolecules allows better insights into the conditions and pathways by which they are formed and allows predictions to be made as to pathway intermediates and enzyme mechanisms

3. Hydrocarbons biogeochemistry

We try to understand the mechanisms and condition of synthesis of hydrocarbons.

In addition, we are interested in abiotic (i.e. non-biological) synthesis of hydrocarbons and their relationship to early life and microbial communities.

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