TD-~1HNMR Measurements Show Enantioselective Dissociation of Ribose and Glucose in the Presence of H_2~(17)O

摘要

We used Time Domain ~1H Nuclear Magnetic Resonance (NMR) to characterize changes in proton exchange between water and sugar enantiomers at different concentrations of H_2~(17)O (～15-450 mM) and found that dissociation of the (-)-enantiomers of glucose and ribose occurs at significantly higher rates at higher concentrations of H_2~(17)O. The mechanism behind this enantioselective effect is unclear. The hypothesis we propose is that the large magnetic field (B_o ～0.6T) applied during NMR measurements induces electric moments opposite in sign for the d and L-isomers. Because ~(17)O has a nuclear electric quadrupole moment ≠ 0, asymmetrically hydrated complexes may form between the B_o-polarized enantiomers and H_2~(17)O. Either H_2~(17)O is more often hydrating the (+)- than the (-)-enantiomers-and consequently pK differences between H_2~(16)O and H_2~(17)O lead to differences in proton exchange between enantiomers and water-or the orientation of H_2~(17)O relative to the B_o-polarized enantiomers is different, in total or in part, which leads to hydrated complexes with different spatial geometries and different proton exchange properties. This effect is significant for Magneto-Chiral Stereo-Chemistry (MCSC) and astrobiology, and it may help us better understand specific instances of mass independent isotopic fractionation and aid in the development of new technologies for chiral and isotopic separation.