Asynchronising five-fold symmetry sequence for better homonuclear polarisation transfer in magic-angle-spinning...

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy
• Spin physics and quantum information science
• Materials characterization

Background:

• Magic-angle-spinning (MAS) solid-state NMR utilizes spin interaction symmetry for recoupling experiments.
• Rotor-synchronized sequences, like the five-fold symmetry C5₂¹ and its supercycled version SPC5₂¹, are standard for double-quantum (DQ) dipole-dipole recoupling.

Purpose of the Study:

• To investigate an asynchronous implementation of the SPC5₂¹ sequence for enhanced DQ homonuclear polarization transfer.
• To compare the efficiency of asynchronous versus synchronous SPC5₂¹ sequences in MAS solid-state NMR.

Main Methods:

• Designed and implemented an asynchronous version of the SPC5₂¹ sequence by breaking rotor synchronization.
• Introduced two methods to break synchronization: pulse-width variation (PWV) and MAS frequency variation (MASV).
• Applied the asynchronous sequence to U-¹³C-alanine, 1,4-¹³C-labelled ammonium phthalate, and adenosine 5'-triphosphate disodium salt trihydrate (ATP⋅3H₂O).

Main Results:

• The asynchronous SPC5₂¹ sequence demonstrated higher DQ homonuclear polarization transfer efficiency compared to the synchronous version.
• The asynchronous method showed superior performance for spin pairs with small dipole-dipole couplings and large chemical-shift anisotropies, such as ¹³C_o-¹³C_o spin systems.
• Experimental results were corroborated by simulations, validating the enhanced performance of the asynchronous sequence.

Conclusions:

• Asynchronous implementation of symmetry-based recoupling sequences offers a significant advantage in DQ homonuclear polarization transfer efficiency in MAS solid-state NMR.
• The developed asynchronous approach provides a more effective method for studying spin systems with specific coupling and anisotropy characteristics.
• This advancement expands the toolkit for advanced solid-state NMR experiments, enabling more sensitive and detailed molecular structure and dynamics investigations.