Luminescent Probing of Enantiopure and Racemic alpha-Amino Acid
Доклады на конференциях
The overwhelming majority of racemates in the crystalline state have different physical properties comparing to pure enantiomers1 what can be easier revealed for true racemic compounds. On the other hand the formation of homo- and heterochiral aggregates (such as dimers, non-covalent oligomeric clusters, nanoparticles, crystals etc.) is not limited to the solid state what sometimes also allows distinguishing racemates from enantiopure species. For the analysis of this fundamental behavior of enantiomeric mixtures here we propose photoluminescent (PL) spectroscopy that is known to be one of the most sensitive physical method. The limitations for applying PL methods caused by forbidden intersystem crossing can be overcome by the “heavy atom effect”. Our approach is based on the well known ability of lanthanide ions to coordinate with different functional groups of organic compounds that are Lewis bases. Applying luminescent probing with ions of 4f (Gd3+, Eu3+, Tb3+, La3+) and 5f (UO22+) elements we revealed drastic differences in PL and PL excitation spectra of racemic and enantiopure α-amino acids – alanine and phenylalanine with simultaneous studies of their electronic states. Depending on the enantiomeric composition of the samples (L, DL and non-racemic L-enriched mixtures) we observed different intensities of the electronic and vibronic transitions.
Until now there are no efficient and routine techniques for determination of enantiomeric excess based on the differences between racemic mixtures and pure enantiomers. Our methodology can lay the foundation of a new approach to chiral analysis without any chiral auxiliaries and not analyzing the polarization of the light (“achiral chiral analysis”).
This work was supported by the Boreskov Institute of Catalysis of the Siberian Branch of the Russian Academy of Sciences and by the Russian Foundation for Basic Research (partially by projects RFBR 16 33 00369 and by CNRS/RFBR 16-53-150004).
1 J. Jacques, A. Collet, S.H. Wilen, Enantiomers, Racemates and Resolutions, Krieger, 1994.