10:45 AM - 12:15 PM
[BBG01-P01] A new method for enantiomer-specific carbon and nitrogen isotope analyses of underivatized amino acids
Keywords:Amino acid, Stable isotope analysis, Enantiomer, Chiral separation
Most amino acids in nature have two enantiomers. While lives mainly synthesize and use L-amino acids, D-amino acids also widely exist, especially in microbial cell walls, fossils and extraterrestrial materials. Stable carbon and nitrogen isotope (δ13C, δ15N) analyses of amino acid enantiomers have been used to study the sources and fate of amino acids in a wide range of researches in microbial ecology, archeology and cosmochemistry. However, applications of enantiomer-specific δ13C and δ15N analyses are still limited due to the analytical difficulties. Although a few methods based on GC/C/IRMS have been developed (Silfer et al. 1991, Takano et al. 2010), they require a chemical derivatization of amino acids, which limits the number of analyzable of amino acid enantiomers and potentially causes an error propagation in data calibration, especially for carbon isotope measurements.
In this study, we developed a new method for δ13C and δ15N analyses of underivatized amino acid enantiomers simultaneously, based on chiral HPLC separation and EA/IRMS measurement. To our knowledge, this is the first example of δ13C and δ15N analyses of underivatized amino acid enantiomers. L- and D-enantiomers of each amino acid were isolated using a chiral HPLC column, ReproSil Chiral-AA column (Dr. Maisch, Germany). It has a stationary phase based on cyclic antibiotic teicoplanin aglycone, a novel type of chiral selector. After the post-column purification, δ13C and δ15N values of isolated enantiomers were determined individually by EA/IRMS. We successfully achieved the separation of L- and D-enantiomers of 15 proteinogenous amino acids (Ala, Val, Phe, Leu, Glu, Asp, Ser, Arg, Pro, Tyr, Ile, Thr, Met, Lys, His), with all D-enantiomers eluting before respective L-enantiomers. δ13C and δ15N values of amino acid enantiomers were not changed after HPLC separation, indicating a good reliability of analyses. By coupling this column with a multidimensional HPLC system for isolating individual amino acids (Sun et al. 2020), we analyzed L- and D-amino acids in natural samples, such as peptidoglycan isolated from a gram-positive bacterium Bacillus subtilis. In this presentation, we will show the details of the method, perspectives regarding the δ13C and δ15N heterogeneity of L- and D-amino acids in nature, and future applications of this method to enantiomer-specific radiocarbon measurements (Ishikawa et al. 2018).
In this study, we developed a new method for δ13C and δ15N analyses of underivatized amino acid enantiomers simultaneously, based on chiral HPLC separation and EA/IRMS measurement. To our knowledge, this is the first example of δ13C and δ15N analyses of underivatized amino acid enantiomers. L- and D-enantiomers of each amino acid were isolated using a chiral HPLC column, ReproSil Chiral-AA column (Dr. Maisch, Germany). It has a stationary phase based on cyclic antibiotic teicoplanin aglycone, a novel type of chiral selector. After the post-column purification, δ13C and δ15N values of isolated enantiomers were determined individually by EA/IRMS. We successfully achieved the separation of L- and D-enantiomers of 15 proteinogenous amino acids (Ala, Val, Phe, Leu, Glu, Asp, Ser, Arg, Pro, Tyr, Ile, Thr, Met, Lys, His), with all D-enantiomers eluting before respective L-enantiomers. δ13C and δ15N values of amino acid enantiomers were not changed after HPLC separation, indicating a good reliability of analyses. By coupling this column with a multidimensional HPLC system for isolating individual amino acids (Sun et al. 2020), we analyzed L- and D-amino acids in natural samples, such as peptidoglycan isolated from a gram-positive bacterium Bacillus subtilis. In this presentation, we will show the details of the method, perspectives regarding the δ13C and δ15N heterogeneity of L- and D-amino acids in nature, and future applications of this method to enantiomer-specific radiocarbon measurements (Ishikawa et al. 2018).