From: Mary Ann Liebert Inc.
Posted: Tuesday, October 30, 2007
Astrobiology October 2007, 7(5): 733-744
We used Time Domain 1H Nuclear Magnetic Resonance (NMR) to characterize changes in proton exchange between water and sugar enantiomers at different concentrations of H217O ( 15–450 mM) and found that dissociation of the (_)-enantiomers of glucose and ribose occurs at significantly higher rates at higher concentrations of H217O. The mechanism behind this enantioselective effect is unclear. The hypothesis we propose is that the large magnetic field (Bo 0.6T) applied during NMR measurements induces electric moments opposite in sign for the D and L-isomers. Because 17O has a nuclear electric quadrupole moment ≠ 0, asymmetrically hydrated complexes may form between the Bo-polarized enantiomers and H217O. Either H217O is more often hydrating the (+) than the (_)-enantiomers—and consequently pK differences between H216O and H217O lead to differences in proton exchange between enantiomers and water—or the orientation of H217O relative to the Bo-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.
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