Zhang Rongchun, Nishiyama Yusuke, Ramamoorthy Ayyalusamy
Biophysics and Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109-1055, USA.
JEOL RESONANCE Inc., Musashino, Akishima, Tokyo 196-8558, Japan.
J Chem Phys. 2015 Oct 28;143(16):164201. doi: 10.1063/1.4933373.
A proton-detected 3D (1)H/(13)C/(1)H chemical shift correlation experiment is proposed for the assignment of chemical shift resonances, identification of (13)C-(1)H connectivities, and proximities of (13)C-(1)H and (1)H-(1)H nuclei under ultrafast magic-angle-spinning (ultrafast-MAS) conditions. Ultrafast-MAS is used to suppress all anisotropic interactions including (1)H-(1)H dipolar couplings, while the finite-pulse radio frequency driven dipolar recoupling (fp-RFDR) pulse sequence is used to recouple dipolar couplings among protons and the insensitive nuclei enhanced by polarization transfer technique is used to transfer magnetization between heteronuclear spins. The 3D experiment eliminates signals from non-carbon-bonded protons and non-proton-bonded carbons to enhance spectral resolution. The 2D (F1/F3) (1)H/(1)H and 2D (13)C/(1)H (F2/F3) chemical shift correlation spectra extracted from the 3D spectrum enable the identification of (1)H-(1)H proximity and (13)C-(1)H connectivity. In addition, the 2D (F1/F2) (1)H/(13)C chemical shift correlation spectrum, incorporated with proton magnetization exchange via the fp-RFDR recoupling of (1)H-(1)H dipolar couplings, enables the measurement of proximities between (13)C and even the remote non-carbon-bonded protons. The 3D experiment also gives three-spin proximities of (1)H-(1)H-(13)C chains. Experimental results obtained from powder samples of L-alanine and L-histidine ⋅ H2O ⋅ HCl demonstrate the efficiency of the 3D experiment.
提出了一种质子检测的三维（1）H/（13）C/（1）H化学位移相关实验，用于在超快魔角旋转（ultrafast-MAS）条件下进行化学位移共振的归属、（13）C-（1）H连接性的识别以及（13）C-（1）H和（1）H-（1）H核的邻近性分析。超快-MAS用于抑制包括（1）H-（1）H偶极耦合在内的所有各向异性相互作用，而有限脉冲射频驱动偶极重耦合（fp-RFDR）脉冲序列用于使质子间的偶极耦合重新耦合，并且利用极化转移技术增强的非灵敏核用于在异核自旋之间转移磁化。该三维实验消除了非碳键合质子和非质子键合碳的信号，以提高光谱分辨率。从三维谱中提取的二维（F1/F3）（1）H/（1）H和二维（13）C/（1）H（F2/F3）化学位移相关谱能够识别（1）H-（1）H邻近性和（13）C-（1）H连接性。此外，结合通过（1）H-（1）H偶极耦合的fp-RFDR重耦合实现的质子磁化交换的二维（F1/F2）（1）H/（13）C化学位移相关谱，能够测量（13）C与甚至远程非碳键合质子之间的邻近性。该三维实验还给出了（1）H-（1）H-（13）C链的三自旋邻近性。从L-丙氨酸和L-组氨酸·H2O·HCl粉末样品获得的实验结果证明了该三维实验的有效性。
