Details

Autor(en) / Beteiligte

• Zhang, Rongchun
• Nishiyama, Yusuke
• Sun, Pingchuan
• Ramamoorthy, Ayyalusamy

Titel

Phase cycling schemes for finite-pulse-RFDR MAS solid state NMR experiments

Ist Teil von

• Journal of magnetic resonance (1997), 2015-03, Vol.252, p.55-66

Ort / Verlag

United States: Elsevier Inc

Erscheinungsjahr

2015

Quelle

MEDLINE

Beschreibungen/Notizen

• [Display omitted] •Efficiencies of XY-based phase cycles for fp-RFDR experiments are investigated.•Effects of higher-order terms and cross terms in fp-RFDR Hamiltonian are analyzed.•XY414 is recommended based on its best performance under all conditions.•RFDR efficiency depends on the duty factor and homonuclear dipolar couplings.•Higher-order dipolar coupling terms enhance magnetization transfer efficiency. The finite-pulse radio frequency driven dipolar recoupling (fp-RFDR) pulse sequence is used in 2D homonuclear chemical shift correlation experiments under magic angle spinning (MAS). A recent study demonstrated the advantages of using a short phase cycle, XY4, and its super-cycle, XY414, for the fp-RFDR pulse sequence employed in 2D 1H/1H single-quantum/single-quantum correlation experiments under ultrafast MAS conditions. In this study, we report a comprehensive analysis on the dipolar recoupling efficiencies of XY4, XY412, XY413, XY414, and XY814 phase cycles under different spinning speeds ranging from 10 to 100kHz. The theoretical calculations reveal the presence of second-order terms (T10T2,±2, T1,±1T2,±1, etc.) in the recoupled homonuclear dipolar coupling Hamiltonian only when the basic XY4 phase cycle is utilized, making it advantageous for proton–proton magnetization transfer under ultrafast MAS conditions. It is also found that the recoupling efficiency of fp-RFDR is quite dependent on the duty factor (τ180/τR) as well as on the strength of homonuclear dipolar couplings. The rate of longitudinal magnetization transfer increases linearly with the duty factor of fp-RFDR for all the XY-based phase cycles investigated in this study. Examination of the performances of different phase cycles against chemical shift offset and RF field inhomogeneity effects revealed that XY414 is the most tolerant phase cycle, while the shortest phase cycle XY4 suppressed the RF field inhomogeneity effects most efficiently under slow spinning speeds. Our results suggest that the difference in the fp-RFDR recoupling efficiencies decreases with the increasing MAS speed, while ultrafast (>60kHz) spinning speed is advantageous as it recouples a large amount of homonuclear dipolar couplings and therefore enable fast magnetization exchange. The effects of higher-order terms and cross terms between various interactions in the effective Hamiltonian of fp-RFDR are also analyzed using numerical simulations for various phase cycles. Results obtained via numerical simulations are in excellent agreement with ultrafast MAS experimental results from the powder samples of glycine and l-alanine.