National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA.
National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA.
J Magn Reson. 2023 Mar;348:107380. doi: 10.1016/j.jmr.2023.107380. Epub 2023 Jan 20.
Double-cross polarization to the satellite-transitions (STs) of half-integer quadrupolar nuclei is demonstrated using proton-detected heteronuclear correlation (HETCOR) under fast magic-angle spinning (MAS). By placing the rf frequency away from the central-transition (CT) and selective to the STs, average Hamiltonian theory shows a scaled effective rf field with a phase equal to the complex ST spinning sideband being irradiated. Such an effective rf field can excite and spinlock STs but the phase spread usually leads to signal cancellation in one-step excitation or cross polarization experiments. The cancellation does not occur for two-step double cross-polarization (DCP) HETCOR experiments, therefore high efficiencies can be obtained. With careful magic-angle calibration, ST and double-quantum ST (DQST) HETCOR experiments are demonstrated with the Cl nuclei in histidine·HCl·HO. These experiments provide additional information over the commonly observed CT spectra and near isotropic resolution in the case of DQST of spin S = 3/2 quadrupolar nuclei.
利用快速魔角旋转（MAS）下质子探测异核相关（HETCOR）实验，对半整数 quadrupolar 核的卫星跃迁（STs）进行双交叉极化。通过将射频频率放置在中央跃迁（CT）之外并选择性地针对 STs，平均哈密顿理论表明，受到照射的具有与复杂 ST 旋转边带相等相位的标度有效射频场。这种有效射频场可以激发和自旋锁定 STs，但相位展宽通常会导致一步激发或交叉极化实验中的信号消除。对于两步双交叉极化（DCP）HETCOR 实验，这种消除不会发生，因此可以获得高效率。通过仔细的魔角校准，在组氨酸·HCl·HO 中的 Cl 核上进行了 ST 和双量子 ST（DQST）HETCOR 实验。这些实验提供了比通常观察到的 CT 谱更多的信息，并且在自旋 S=3/2 quadrupolar 核的 DQST 情况下具有各向同性分辨率。
