Morcombe Corey R, Zilm Kurt W
Department of Chemistry, Yale University, P.O. Box 208107, New Haven, CT 06520-8107, USA.
J Magn Reson. 2003 Jun;162(2):479-86. doi: 10.1016/s1090-7807(03)00082-x.
Solid state 13C magic angle spinning (MAS) NMR spectra are typically referenced externally using a probe which does not incorporate a field frequency lock. Solution NMR shifts on the other hand are more often determined with respect to an internal reference and using a deuterium based field frequency lock. Further differences arise in solution NMR of proteins and nucleic acids where both 13C and 1H shifts are referenced by recording the frequency of the 1H resonance of DSS (sodium salt of 2,2-dimethyl-2-silapentane-5-sulphonic acid) instead of TMS (tetramethylsilane). In this note we investigate the difficulties in relating shifts measured relative to TMS and DSS by these various approaches in solution and solids NMR, and calibrate adamantane as an external 13C standard for solids NMR. We find that external chemical shift referencing of magic angle spinning spectra is typically quite reproducible and accurate, with better than +/-0.03 ppm accuracy being straight forward to achieve. Solid state and liquid phase NMR shifts obtained by magic angle spinning with external referencing agree with those measured using typical solution NMR hardware with the sample tube aligned with the applied field as long as magnetic susceptibility corrections and solvent shifts are taken into account. The DSS and TMS reference scales for 13C and 1H are related accurately using MAS NMR. Large solvent shifts for the 13C resonance in TMS in either deuterochloroform or methanol are observed, being +0.71 ppm and -0.74 ppm from external TMS, respectively. The ratio of the 13C resonance frequencies for the two carbons in solid adamantane to the 1H resonance of TMS is reported.
固态13C魔角旋转（MAS）核磁共振谱通常使用不包含场频锁定的探头进行外部参照。另一方面，溶液核磁共振位移更多是相对于内部参照并使用基于氘的场频锁定来确定。在蛋白质和核酸的溶液核磁共振中还会出现进一步的差异，其中13C和1H位移都是通过记录DSS（2,2 - 二甲基 - 2 - 硅戊烷 - 5 - 磺酸钠）的1H共振频率而非TMS（四甲基硅烷）来进行参照的。在本笔记中，我们研究了在溶液和固体核磁共振中通过这些不同方法测量相对于TMS和DSS的位移时所存在的困难，并校准金刚烷作为固体核磁共振的外部13C标准。我们发现魔角旋转谱的外部化学位移参照通常具有相当高的可重复性和准确性，实现优于±0.03 ppm的精度很容易。只要考虑到磁化率校正和溶剂位移，通过外部参照的魔角旋转获得的固态和液相核磁共振位移与使用典型溶液核磁共振硬件且样品管与外加磁场对齐时测量的位移一致。使用MAS NMR可以准确关联13C和1H的DSS和TMS参照标度。在氘代氯仿或甲醇中，观察到TMS中13C共振有较大的溶剂位移，相对于外部TMS分别为 +0.71 ppm和 -0.74 ppm。报告了固体金刚烷中两个碳的13C共振频率与TMS的1H共振频率之比。
