Heteronuclear polarization transfer by symmetry-based recoupling sequences in solid-state NMR

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy
• Quantum spin dynamics
• Materials characterization

Background:

• Conventional Hartmann-Hahn cross-polarization is challenging for nuclei with low gyromagnetic ratios or strong anisotropic interactions.
• Efficient spin polarization transfer is crucial for various solid-state NMR applications.

Purpose of the Study:

• To develop and demonstrate new methods for transferring spin polarization between different nuclear isotopes in magic-angle-spinning solid-state NMR.
• To enable accurate heteronuclear distance measurements using the polarization transfer trajectory.
• To provide an alternative to conventional cross-polarization for difficult spin systems.

Main Methods:

• Utilizing symmetry-based recoupling sequences on one radiofrequency channel.
• Employing a sequence of one to three strong radiofrequency pulses on a second channel.
• Applying a phase shift to recoupling sequences synchronized with a pi/2 pulse.

Main Results:

• Successful demonstration of spin polarization transfer in 1H-13C, 1H-15N, and 19F-109Ag systems.
• The polarization transfer trajectory provides a means to estimate heteronuclear distances.
• The new method is effective for nuclei with low gyromagnetic ratios and strong anisotropic spin interactions.

Conclusions:

• The developed methods offer a powerful new tool for solid-state NMR spectroscopy.
• This technique expands the applicability of cross-polarization to a wider range of nuclear spin systems.
• The ability to measure heteronuclear distances enhances structural elucidation capabilities in solid materials.