选择性脉冲自旋序转移增加了仲氢诱导的NMR对不灵敏核的放大，并使极化转移更加鲁棒
Selectively pulsed spin order transfer increases parahydrogen-induced NMR amplification of insensitive nuclei and makes polarization transfer more robust
AI总结：
本文提出一种用于仲氢诱导极化的选择性脉冲自旋序转移新方法phSPINEPT+，通过抑制不需要的间接自旋相互作用，实现了对所有弱耦合自旋系统均有效的鲁棒极化转移，在不完全或非氘标记分子中实现了显著的13C超极化。
摘要：
我们描述了一种仲氢诱导极化（PHIP）的脉冲自旋序转移（SOT）新方法，该方法通过频率选择性地仅激发所需的质子，能够在不完全2H标记的分子中实现接近100%的极化。虽然在脉冲SOT开始时对1H使用选择性脉冲（SP）之前已被考虑过，但在SOT期间使用SP可以抑制不需要的间接自旋-自旋相互作用。结果，对于phINEPT+序列的SP变体（我们称之为phSPINEPT+），我们实现了更鲁棒的SOT。因此，我们首次报道了一种对所有弱耦合自旋系统都有效的序列。我们的模拟表明，如果忽略弛豫，该方法在弱耦合三自旋系统和部分或完全2H标记的分子中，将接近100%的仲氢衍生自旋序转化为13C超极化。在实验中，我们证明了1-13C-hydroxyethyl propionate-d3和1-13C-ethyl acetate-d6的高13C超极化分别为15.8%和12.6%，如果仲氢富集度为100%，这分别对应于约47%和约38%。即使在非2H标记的分子中，也实现了显著的13C极化，例如，对于100% pH2模拟值高达20%，而对于1-13C-ethyl pyruvate和50% pH2，实验获得了1.25%，这可以通过更快的氢化进一步提高。因此，可能不再需要全氘标记，例如，当研究新的PHIP试剂时，全氘分子的合成过于复杂，或者当希望避免关于试剂代谢转化速率的动力学同位素效应时。在SOT期间使用SP似乎非常有前景，并可扩展到PHIP及其他背景下的其他序列，使其对实验缺陷或真实分子环境不那么敏感。
英文摘要：
We describe a new method for pulsed spin order transfer (SOT) of parahydrogen induced polarization (PHIP) that enables close to 100 % polarization in incompletely 2H-labeled molecules by exciting only the desired protons in a frequency-selective manner. While a selective pulse (SP) on 1H at the beginning of pulsed SOT had been considered before, using SPs during the SOT suppresses undesired indirect spin-spin interactions. As a result, we achieved a more robust SOT for the SP variants of the phINEPT+ sequence that we refer to as phSPINEPT+. Thereby, for the first time, we report a sequence that is effective for all weakly coupled spin systems. Our simulations show that the method converts close to 100 % of the parahydrogen-derived spin order into 13C hyperpolarization in weakly coupled three-spin systems and partially or fully 2H-labeled molecules if relaxation is neglected. Experimentally we demonstrate high hyperpolarization of 13C with 15.8 % for 1-13C-hydroxyethyl propionate-d3 and 12.6 % for 1-13C-ethyl acetate-d6, which corresponds to ~47 % and ~38 % if the enrichment of parahydrogen had been 100 %. Even in non-2H-labeled molecules, a remarkable 13C polarization is achieved, e.g. up to 20 % were simulated for 100 % pH2, and 1.25 % were obtained experimentally for 1-13C-ethyl pyruvate and 50 % pH2, which can be further improved by faster hydrogenation. As a result, full deuterium labeling may no longer be required e.g., when new PHIP agents are investigated, the synthesis of fully deuterated molecules is too complex, or when a kinetic isotope effect regarding the metabolic conversion rate of an agent is to be avoided. Using SPs during SOT seems very promising and may be extended to other sequences in the context of PHIP and be-yond to make them less prone to experimental imperfections or real molecular environments.
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