高速魔角旋转下基于组合π脉冲的射频驱动重耦同核双量子固体NMR相关实验研究OA北大核心CSTPCD

This study presents a way to improve the performance of radio frequency-driven recoupling(RFDR)sequences in solid-state nuclear magnetic resonance(NMR)spectroscopy.Traditional RF-DR sequences typically employ single rectangular π pulses,which may prove to be inefficient,espe-cially in experiments under high-speed magic angle spinning(MAS)conditions that have become more popular in recent years.To address this issue,we proposed using composite π pulses to replace the traditional single rectangular π pulses in RFDR sequences.The updated RFDR sequence enables more precise control over nuclei spins and provides better performance in double-quantum(DQ)ex-periments compared to the traditional module based on single rectangular π pulses.Our focus was specifically on the investigation of multiple composite π pulses,which are suitable for use under high-speed MAS conditions.To evaluate the efficacy of DQ excitation of these composite π pulses within the RFDR sequence,we conducted a comprehensive investigation by using numerical simula-tions and experiments.Initially,we analyzed the impact of two critical factors on the performance of RFDR in DQ excitation experiments:resonance offset and radio frequency(RF)field inhomogene-ity.The resonance offset signifies the difference between the nuclei Larmor frequency and the fre-quency of the applied RF field,while the RF field inhomogeneity describes the variations in RF field strength throughout the sample.Through a comparative analysis of outcomes from a single rectangular π pulse and multiple composite π pulses,we identified a promising RFDR sequence based on a com-posite π pulse.Subsequently,this optimized RFDR sequence was integrated into DQ experiments and tested via one-dimensional(1D)and two-dimensional(2D)experiments on 19 F for sodium hexaflu-orosilicate or 1 H for L-histidine.The results confirmed that,under high-speed MAS conditions,the RFDR sequence with appropriate composite π pulses can offer several advantages over the traditional RFDR with single rectangular π pulses.Firstly,it achieves higher efficiency in homonuclear DQ ex-citation,resulting in a significant reduction in experimental time.Secondly,it improves the DQ ex-citation bandwidth,allowing for improved excitation of nuclei across a broader range of chemical shifts.Lastly,it exhibits good tolerance to RF field inhomogeneity,simplifying experimental setup and facilitating extended experimental durations.In summary,this study explored the efficacy of composite π pulses in optimizing RFDR sequences under high-speed MAS.The utilization of compos-ite π pulse in RFDR sequences enhances robustness and efficiency in DQ correlation experiments,which provides crucial technical support for investigating nuclear interactions within strongly coupled spin systems present in diverse solid-state materials.