Harper James K, Strohmeier Mark, Grant David M
Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, UT 84112, USA.
J Magn Reson. 2007 Nov;189(1):20-31. doi: 10.1016/j.jmr.2007.06.017. Epub 2007 Aug 14.
The (1)H-(13)C solid-state NMR heteronuclear correlation (HETCOR) experiment is demonstrated to provide shift assignments in certain powders that have two or more structurally independent molecules in the unit cell (i.e. multiple molecules per asymmetric unit). Although this class of solids is often difficult to characterize using other methods, HETCOR provides both the conventional assignment of shifts to molecular positions and associates many resonances with specific molecules in the asymmetric unit. Such assignments facilitate conformational characterization of the individual molecules of the asymmetric unit and the first such characterization solely from solid-state NMR data is described. HETCOR offers advantages in sensitivity over prior methods that assign resonances in the asymmetric unit by (13)C-(13)C correlations and therefore allows shorter average analysis times in natural abundance materials. The (1)H-(13)C analysis is demonstrated first on materials with known shift assignments from INADEQUATE data (santonin and Ca(OAc)(2) phase I) to verify the technique and subsequently is extended to a pair of unknown solids: (+)-catechin and Ca(OAc)(2) phase II. Sufficient sensitivity and resolution is achieved in the spectra to provide assignments to one of the specific molecules of the asymmetric unit at over 54% of the sites.
（1）H - （13）C 固态核磁共振异核相关（HETCOR）实验表明，它能够为某些晶胞中含有两个或更多结构独立分子（即每个不对称单元中有多个分子）的粉末提供化学位移归属。尽管这类固体通常很难用其他方法进行表征，但HETCOR既能提供分子位置的常规化学位移归属，又能将许多共振峰与不对称单元中的特定分子关联起来。这样的归属有助于对不对称单元中各个分子的构象进行表征，并且本文描述了首个仅基于固态核磁共振数据的此类表征。与之前通过（13）C - （13）C 相关性在不对称单元中进行共振峰归属的方法相比，HETCOR在灵敏度方面具有优势，因此在天然丰度材料中可缩短平均分析时间。首先在从INADEQUATE数据（山道年和醋酸钙（Ca（OAc）₂）I 相）获得了已知化学位移归属的材料上进行（1）H - （13）C 分析，以验证该技术，随后将其扩展到一对未知固体：（+） - 儿茶素和醋酸钙（Ca（OAc）₂）II 相。在光谱中实现了足够的灵敏度和分辨率，能够为不对称单元中超过54%的特定分子位点提供归属。
