摘要
基于偶极耦合的同核相关固体核磁共振实验广泛应用于结构表征,RFDR是其中最广泛使用的零量子同核重耦序列之一。此前的研究中证明了RFDR的重耦效率非常依赖于魔角旋转转速、共振偏置、射频场不均匀性、化学位移各项异性及其它多种因素。本文基于对称性序列原理,在中等和高转速下考察了一系列RNN1(N≥4,N为偶数)对称性序列,并结合多种相位循环,以充分研究零量子重耦序列原理并实现均匀的宽带同核重耦。不同RN对称性序列的零量子偶极重耦效率进一步在13C、15N均匀标记的L-组氨酸以及微晶动力蛋白轻链(LC8)样品上得到检验。
The considerable demand of robust solid-state nuclear magnetic resonance(NMR)sequences has been met by the development in solid-state NMR hardware and probe design,particularly for fast magic angle spinning(MAS).Fast MAS enhances spectral resolution,however,it makes many conventional methods unusable because of the need of significantly high radiofrequency(RF)field strength and the intrinsic inefficiencies under such condition.Dipolar-based homonuclear recoupling sequences are widely used for structural analysis,and radio-frequency driven recoupling(RFDR)is one of the most popular zero-quantum(ZQ)homonuclear recoupling sequence.Previous studies demonstrated that RFDR efficiency strongly depends on factors such as MAS frequency,resonance offset,RF field inhomogeneity,and chemical shift anisotropy(CSA).To alleviate these dependencies,different RFDR phase cycles have been proposed.To completely understand the principle of ZQ recoupling sequences and achieve uniform broadband homonuclear recoupling under fast MAS conditions,we herein utilize the theory of symmetry sequences and propose a series of RNN1(N≥4,N is even)sequences with various phase cycles under both moderate and fast MAS conditions.We simulated the influence of MAS rate,resonance offset,RF field strength,RF mismatch,and heteronuclear decoupling on ZQ homonuclear polarization transfer efficiency.We verified the ZQ dipolar recoupling efficiencies of various RN symmetry sequences using U-13C,15N-labeled L-histidine and microcrystalline U-13C,15N-labeled dynein light chain(LC8)protein.The basic R4 sequence showed the worst broadband ZQ polarization transfer performance theoretically and experimentally,while the basic R6 sequence could efficiently achieve ZQ dipolar recoupling within moderate bandwidth.Under low to moderate MAS conditions,high-power 1H decoupling could considerably enhance the polarization transfer efficiency,while homonuclear recoupling sans heteronuclear decoupling is recommended under fast MAS conditions.Super phase cycling enhanced ZQ polarization transfer efficiency and bandwidth and resulted in significantly reduced sensitivity to RF mismatch.RNixy3 and RNixy4 sequences with 6*N and 8*N phase cycling steps,respectively,were preferred.The R4ixy3 sequence with fewer phase cycling steps showed comparable,or even slightly better,performance to the R4ixy4 sequence.As shown in the simulations,by choosing proper RF field strengths,1.5*ωr<ω1<3*ωr,uniform broadband ZQ recoupling with R4ixy3 or R4ixy4 sequences could be achieved under fast MAS conditions,which would be significant for the accurate determination of spatial proximities and internuclear distances.By prolonging the mixing time,the RN ZQ scheme could provide more cross peaks,where medium-to long-range spatial correlations could be included;these correlations are essential for structural determination in complex systems.
作者
纪毅
梁力鑫
Changmiao Guo
包信和
Tatyana Polenova
侯广进
Yi Ji;Lixin Liang;Changmiao Guo;Xinhe Bao;Tatyana Polenova;Guangjin Hou(State Key Laboratory of Catalysis,Dalian Institute of Chemical Physics,Chinese Academy of Sciences,Dalian 116023,Liaoning Province,P.R.China;University of Chinese Academy of Sciences,Beijing 100049,P.R.China;Department of Chemistry and Biochemistry,University of Delaware,Newark,Delaware 19716,United States;Pittsburgh Center for HIV Protein Interactions,University of Pittsburgh School of Medicine,Pittsburgh,PA 15261,United States)
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2020年第4期95-105,共11页
Acta Physico-Chimica Sinica
基金
国家自然科学基金(21773230)
辽宁省“兴辽英才计划”项目(XLYC1807207)
中国科学院大连化学物理研究所科研创新基金(Y7611105T5)
美国NIH基金(P50GM082251,P30GM103519,P30GM110758)资助。
