Havlin Robert H, Park Gregory H J, Mazur Tanya, Pines Alexander
Materials Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, USA.
J Am Chem Soc. 2003 Jul 2;125(26):7998-8006. doi: 10.1021/ja0342244.
This contribution describes a method that manipulates the alignment director of a liquid crystalline sample to obtain anisotropic magnetic interaction parameters, such as dipolar coupling, in an oriented liquid crystalline sample. By changing the axis of rotation with respect to the applied magnetic field in a spinning liquid crystalline sample, the dipolar couplings present in a normally complex strong coupling spectrum are scaled to a simple weak coupling spectrum. This simplified weak coupling spectrum is then correlated with the isotropic chemical shift in a switched angle spinning (SAS) two-dimensional (2D) experiment. This dipolar-isotropic 2D correlation was also observed for the case where the couplings are scaled to a degree where the spectrum approaches strong coupling. The SAS 2D correlation of C(6)F(5)Cl in the nematic liquid crystal I52 was obtained by first evolving at an angle close to the magic angle (54.7 degrees ) and then directly detecting at the magic angle. The SAS method provides a 2D correlation where the weak coupling pairs are revealed as cross-peaks in the indirect dimension separated by the isotropic chemical shifts in the direct dimension. Additionally, by using a more complex SAS method which involves three changes of the spinning axis, the solidlike spinning sideband patterns were correlated with the isotropic chemical shifts in a 2D experiment. These techniques are expected to enhance the interpretation and assignment of anisotropic magnetic interactions including dipolar couplings for molecules dissolved in oriented liquid crystalline phases.
本论文描述了一种方法，该方法通过操纵液晶样品的取向 director 来获取取向液晶样品中的各向异性磁相互作用参数，如偶极耦合。在旋转的液晶样品中，通过改变相对于外加磁场的旋转轴，通常复杂的强耦合谱中存在的偶极耦合被缩放到一个简单的弱耦合谱。然后，在切换角度旋转（SAS）二维（2D）实验中，将这个简化的弱耦合谱与各向同性化学位移相关联。对于耦合被缩放到谱接近强耦合程度的情况，也观察到了这种偶极 - 各向同性二维相关性。通过首先在接近魔角（54.7 度）的角度下演化，然后在魔角下直接检测，获得了向列型液晶 I52 中 C(6)F(5)Cl 的 SAS 二维相关性。SAS 方法提供了一种二维相关性，其中弱耦合对在间接维度中表现为交叉峰，在直接维度中由各向同性化学位移分隔。此外，通过使用一种更复杂的 SAS 方法，该方法涉及旋转轴的三次变化，在二维实验中将类固体旋转边带模式与各向同性化学位移相关联。这些技术有望增强对各向异性磁相互作用（包括溶解在取向液晶相中的分子的偶极耦合）的解释和归属。
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