Exploiting heterogeneous time scale of dynamics to enhance 2D HETCOR solid-state NMR sensitivity

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Science
• Structural Chemistry

Background:

• Multidimensional solid-state NMR, particularly heteronuclear chemical shift correlation (HETCOR) experiments, provides atomic-level insights into molecular systems.
• Conventional HETCOR methods using cross-polarization (CP) or insensitive nuclei enhanced by polarization transfer (INEPT) face limitations with heterogeneous systems exhibiting components with differing mobilities.
• CP is inefficient for mobile components, while INEPT is ineffective for immobile components, leading to challenges in obtaining comprehensive structural and connectivity information.

Purpose of the Study:

• To develop and present two novel 2D pulse sequences for sequential acquisition of 13C/1H HETCOR NMR spectra.
• To enable independent and separate analysis of rigid and mobile components within heterogeneous systems in a single experiment.
• To leverage abundant proton magnetization for enhanced spectral editing and resonance assignments in complex molecular systems.

Main Methods:

• Development of two distinct 2D pulse sequences for 13C/1H HETCOR NMR.
• Application of a 13C-detected HETCOR experiment under slow magic-angle-spinning (MAS) conditions, utilizing multiple-pulse sequences for enhanced 1H resolution.
• Implementation of a 1H-detected HETCOR experiment under ultrafast MAS, combining CP and heteronuclear nuclear Overhauser effect (NOE) polarization transfer for improved 13C signal intensity.

Main Results:

• Successful experimental demonstration of the proposed pulse sequences on two model systems.
• Obtained 2D 13C/1H chemical shift correlation spectra that distinctly resolve rigid and mobile components.
• Validated the capability of the sequences for dynamics-based spectral editing and resonance assignments in heterogeneous materials.

Conclusions:

• The proposed 2D HETCOR NMR pulse sequences effectively address the limitations of conventional methods for analyzing heterogeneous systems.
• These sequences facilitate detailed structural studies by enabling independent characterization of molecular components with varying dynamics.
• The developed techniques offer significant benefits for understanding the interplay between structure and properties in complex molecular systems.