title: Position-Specific Isotope Analysis of Xanthines: A (13)C Nuclear Magnetic Resonance Method to Determine the (13)C Intramolecular Composition at Natural Abundance.
abstract: The natural xanthines caffeine, theobromine, and theophylline are of major commercial importance as flavor constituents in coffee, cocoa, tea, and a number of other beverages. However, their exploitation for authenticity, a requirement in these commodities that have a large origin-based price-range, by the standard method of isotope ratio monitoring by mass spectrometry (irm-MS) is limited. We have now developed a methodology that overcomes this deficit that exploits the power of isotopic quantitative (13)C nuclear magnetic resonance (NMR) spectrometry combined with chemical modification of the xanthines to enable the determination of positional intramolecular (13)C/(12)C ratios (δ(13)Ci) with high precision. However, only caffeine is amenable to analysis: theobromine and theophylline present substantial difficulties due to their poor solubility. However, their N-methylation to caffeine makes spectral acquisition feasible. The method is confirmed as robust, with good repeatability of the δ(13)Ci values in caffeine appropriate for isotope fractionation measurements at natural abundance. It is shown that there is negligible isotope fractionation during the chemical N-methylation procedure. Thus, the method preserves the original positional δ(13)Ci values. The method has been applied to measure the position-specific variation of the (13)C/(12)C distribution in caffeine. Not only is a clear difference between caffeine isolated from different sources observed, but theobromine from cocoa is found to show a (13)C pattern distinct from that of caffeine.
authors.affiliation: †EBSI team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes, CNRS UMR 6230, 2 rue de la Houssinière, BP 92208, F-44322 cedex 3 Nantes, France.
authors.forename: Didier G
authors.initials: DG
authors.lastname: Diomande
authors.affiliation: †EBSI team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes, CNRS UMR 6230, 2 rue de la Houssinière, BP 92208, F-44322 cedex 3 Nantes, France.|‡Spectromaitrise, CAPACITÉS SAS, 26 boulevard Vincent Gâche, 44200 Nantes, France.
authors.forename: Estelle
authors.initials: E
authors.lastname: Martineau
authors.affiliation: §Earth-Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan.
authors.forename: Alexis
authors.initials: A
authors.lastname: Gilbert
authors.affiliation: †EBSI team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes, CNRS UMR 6230, 2 rue de la Houssinière, BP 92208, F-44322 cedex 3 Nantes, France.
authors.forename: Pierrick
authors.initials: P
authors.lastname: Nun
authors.affiliation: ∥Institute of Food Chemistry, Braunschweig University of Technology, Schleinitzstrasse 20, DE-38106 Braunschweig, Germany.
authors.forename: Ariaki
authors.initials: A
authors.lastname: Murata
authors.affiliation: ⊥Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503, Japan.
authors.forename: Keita
authors.initials: K
authors.lastname: Yamada
authors.affiliation: #Graduate School of Engineering, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8561, Japan.
authors.forename: Naoharu
authors.initials: N
authors.lastname: Watanabe
authors.affiliation: †EBSI team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes, CNRS UMR 6230, 2 rue de la Houssinière, BP 92208, F-44322 cedex 3 Nantes, France.
authors.forename: Illa
authors.initials: I
authors.lastname: Tea
authors.affiliation: †EBSI team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes, CNRS UMR 6230, 2 rue de la Houssinière, BP 92208, F-44322 cedex 3 Nantes, France.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Robins
authors.affiliation: §Earth-Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan.|⊥Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503, Japan.
authors.forename: Naohiro
authors.initials: N
authors.lastname: Yoshida
authors.affiliation: †EBSI team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes, CNRS UMR 6230, 2 rue de la Houssinière, BP 92208, F-44322 cedex 3 Nantes, France.
authors.forename: Gérald S
authors.initials: GS
authors.lastname: Remaud
mesh_terms: D066241:Carbon-13 Magnetic Resonance Spectroscopy / Q000379:methods*; D008745:Methylation; D014970:Xanthines / Q000737:chemistry*
chemical_list: D014970:Xanthines