Effective Hamiltonians by optimal control: solid-state NMR double-quantum planar and isotropic dipolar recoupling

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Solid-State NMR
• Quantum Control

Background:

• Dipolar recoupling is crucial for structural analysis in solid-state NMR.
• Existing pulse sequences have limitations in handling experimental complexities and efficiency.
• Tailoring effective Hamiltonians is key to overcoming these limitations.

Purpose of the Study:

• To design novel radio-frequency (rf) pulse sequences using optimal control algorithms for solid-state NMR.
• To achieve efficient dipolar recoupling, including isotropic mixing, in powder samples.
• To improve signal-to-noise ratios in 2D NMR experiments.

Main Methods:

• Application of optimal control algorithms to design rf pulse sequences.
• Numerical construction of pulse sequences to accommodate experimental conditions (inhomogeneous rf fields, chemical shift spread, sample orientation, spinning).
• Design of sequences for planar double-quantum and homonuclear isotropic mixing dipolar coupling Hamiltonians.

Main Results:

• Development of improved dipolar recoupling sequences for planar double-quantum and zero-quantum effective Hamiltonians.
• First demonstration of homonuclear isotropic mixing sequences enabling simultaneous, efficient transfer of I(x), I(y), and I(z) polarizations.
• Numerical and experimental validation on (13)C(alpha),(13)C(beta)-L-alanine, showing substantial sensitivity gains over conventional methods.

Conclusions:

• Optimal control algorithms provide a powerful tool for designing sophisticated NMR pulse sequences.
• The novel isotropic mixing sequences offer a significant advantage in signal-to-noise ratio for solid-state NMR.
• These advancements facilitate more efficient structural determination of powdered materials using NMR.