Enantiospecific Response in Cross-Polarization Solid-State Nuclear Magnetic Resonance of Optically Active Metal Organic Frameworks

We report herein on a NMR-based enantiospecific
response for a
family of optically active metal–organic frameworks. Cross-polarization
of the 1H–13C couple was performed, and
the intensities of the 13C nuclei NMR signals were measured
to be different for the two enantiomers. In a direct-pulse experiment,
which prevents cross-polarization, the intensity difference of the 13C NMR signals of the two nanostructured enantiomers vanished.
This result is due to changes of the nuclear spin relaxation times
due to the electron spin spatial asymmetry induced by chemical bond
polarization involving a chiral center. These experiments put forward
on firm ground that the chiral-induced spin selectivity effect, which
induces chemical bond polarization in the J-coupling,
is the mechanism responsible for the enantiospecific response. The
implications of this finding for the theory of this molecular electron
spin polarization effect and the development of quantum biosensing
and quantum storage devices are discussed.