Applications of the CSA-amplified PASS experiment

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Chemical Physics

Background:

• Measuring small chemical shift anisotropies (CSAs) often requires slow magic-angle spinning (MAS), which can be unstable.
• The CSA-amplified PASS experiment offers a potential solution by correlating spinning sidebands at different frequencies.

Purpose of the Study:

• To experimentally evaluate the reliability of the CSA-amplified PASS experiment for measuring small CSAs.
• To investigate the impact of large scaling factors and pulse imperfections on spectral accuracy.
• To explore the application of this technique for sites with homonuclear dipolar coupling.

Main Methods:

• Experimental validation of the CSA-amplified PASS experiment.
• Utilizing large scaling factors (N=27) in the CSA-amplified PASS experiment.
• Numerical simulations and experimental demonstration on uniformly 13C enriched l-histidine monohydrochloride monohydrate to study homonuclear dipolar coupling effects.

Main Results:

• Accurate chemical shift sideband intensities were obtained at the effective spinning frequency using the F(1) projection, even with large scaling factors.
• The experiment demonstrated robustness against significant pulse imperfections.
• Numerical simulations and experimental data confirmed the effects of homonuclear dipolar coupling on CSA-amplified PASS spectra.

Conclusions:

• The CSA-amplified PASS experiment is a reliable method for measuring small CSAs, accommodating unstable spinning frequencies and pulse imperfections.
• The technique is also applicable for characterizing chemical shift anisotropies in the presence of homonuclear dipolar coupling, relevant for biological molecules and abundant nuclei.