Xia Youlin, Moran Sean, Nikonowicz Edward P, Gao Xiaolian
Department of Biology and Biochemistry, University of Houston, Houston, TX 77004-5001, USA.
Magn Reson Chem. 2008 May;46(5):432-5. doi: 10.1002/mrc.2195.
A pulse sequence of z-restored spin echo, -pi-beta-tau-pi-tau-, employing a pi pulse in the middle of the delay (2tau) to form a spin echo and the two pi pulses together to restore the residual longitudinal magnetization back to + z direction, is described. (13)C spectra of organic compounds provide a wealth of structural information; however, (13)C 1D spectra acquired using reverse geometry probes can have significant baseline humps or rolls because of pulse ring-down within the coil. The baseline distortions are especially apparent in spectra acquired using cryogenically enhanced probes. The baseline problem may be alleviated by extending the delay between the last pulse and the starting point of acquisition. However, uses of long delay times introduce large negative first-order phase corrections which themselves produce baseline roll. The prescribed experiment can be used to completely remove the hump, roll or dip in the baseline of the (13)C spectrum and at the same time obtain sensitivity similar to the experiment of a single beta pulse. We believe that this experiment will be of general applications in acquiring high-quality (13)C NMR data with reverse geometry probes and spectral interpretation.
描述了一种z恢复自旋回波脉冲序列，即“-π-β-τ-π-τ-”，在延迟（2τ）的中间使用一个π脉冲形成自旋回波，两个π脉冲共同作用将剩余纵向磁化恢复到+z方向。有机化合物的(13)C谱提供了丰富的结构信息；然而，使用反向几何探头采集的(13)C一维谱可能会由于线圈内的脉冲衰减而出现明显的基线隆起或起伏。基线畸变在使用低温增强探头采集的谱中尤为明显。通过延长最后一个脉冲与采集起点之间的延迟，可以缓解基线问题。然而，使用长延迟时间会引入较大的负一阶相位校正，这本身会产生基线起伏。规定的实验可用于完全消除(13)C谱基线中的隆起、起伏或凹陷，同时获得与单个β脉冲实验相似的灵敏度。我们相信，该实验在使用反向几何探头采集高质量(13)C NMR数据及光谱解释方面将具有广泛的应用。
