Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA; Dana Farber Cancer Institute, Boston, MA, USA.
Bruker BioSpin GmbH, Silberstreifen 4, 76287 Rheinstetten, Germany.
J Magn Reson. 2021 Apr;325:106928. doi: 10.1016/j.jmr.2021.106928. Epub 2021 Feb 4.
In NMR spectroscopy, many specialized shaped pulses are available for broadband excitation, beyond the bandwidth of conventional high-powered hard pulses. These shaped pulses typically have long duration. However, long-duration pulses are unsuitable for spectra containing significant homonuclear couplings, such as polyfluorinated compounds in F NMR. J-coupling evolution during the excitation pulse leads to spectral artifacts and incorrect peak integrals. Here, we report an approach to optimal control pulse design which significantly reduces the pulse length required to excite large bandwidths of chemical shift frequencies. The target state phase is not chosen beforehand but is instead only constrained to be linearly dependent on offset frequency. The first-order phase of the target state is then treated as a free-variable, to be optimized at the same time as the RF waveform itself. The resulting spectra are easily phased using standard NMR processing software. We observe that the required pulse length is significantly shorter than for currently available in-phase excitation schemes. Spectral artifacts from homonuclear couplings are avoided. We also demonstrate that pure in-phase excitation can be obtained over the same bandwidth by appending two inversion pulses, at the expense of increased overall duration.
在核磁共振波谱学中，有许多专门设计的形状脉冲可用于宽带激发，超出了传统高功率硬脉冲的带宽。这些形状脉冲通常具有较长的持续时间。然而，长持续时间的脉冲不适合含有显著同核耦合的光谱，例如 F NMR 中的多氟化合物。在激发脉冲期间，J 耦合演化会导致光谱伪影和不正确的峰积分。在这里，我们报告了一种优化控制脉冲设计的方法，该方法可显著减少激发大带宽化学位移频率所需的脉冲长度。目标状态相位不是事先选择的，而是仅约束为与偏移频率线性相关。然后，将目标状态的一阶相位视为自由变量，与 RF 波形本身同时进行优化。得到的光谱可以使用标准的 NMR 处理软件轻松进行相位调整。我们观察到，所需的脉冲长度明显短于目前可用的同相激发方案。避免了同核耦合引起的光谱伪影。我们还证明，通过附加两个反转脉冲，可以在相同的带宽内获得纯同相激发，但会增加总持续时间。
