Compound radiofrequency-driven recoupling pulse sequences for efficient magnetization transfer by homonuclear dipolar
1Department of Chemistry and Biotechnology, Faculty of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama, 240-8501, Japan.
Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|June 30, 2000
Summary
A new Compound Radiofrequency-Driven Recoupling (CRFDR) pulse sequence enhances magnetization transfer in rotating solids. This method improves efficiency by reducing orientation dependence, showing a 15% increase in experiments.
Area of Science:
- Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy
- Quantum spin dynamics
- Materials science
Background:
- Radiofrequency-Driven Recoupling (RFDR) is used to recouple homonuclear dipolar interactions in rotating solids.
- Orientation dependence of the effective recoupled homonuclear dipolar interaction limits magnetization transfer efficiency.
Purpose of the Study:
- To enhance the maximum transferred magnetization in rotating powdered solids.
- To reduce the orientation dependence of the effective recoupled homonuclear dipolar interaction using a modified RFDR pulse sequence.
Main Methods:
- Development and optimization of the Compound RFDR (CRFDR) pulse sequence, incorporating variable delays (tau(i)) within RFDR pulse units.
- Numerical simulations of a two-spin system to evaluate transfer efficiency.
- Experimental validation using fully (13)C-labeled alanine.
Main Results:
- CRFDR reduces orientation dependence, enhancing effective recoupled homonuclear dipolar interactions.
- Numerical simulations show CRFDR achieves ~70% average transfer efficiency, a 30% improvement over RFDR.
- Experiments demonstrate a ~15% greater maximum magnetization transfer with CRFDR compared to RFDR in alanine.
Conclusions:
- The CRFDR pulse sequence effectively enhances magnetization transfer in rotating solids.
- CRFDR offers a significant improvement in transfer efficiency over standard RFDR, despite requiring longer mixing times.
- Further optimization may be needed to mitigate the effects of chemical shift anisotropy, other dipolar interactions, and relaxation.
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