Manu V S, Veglia Gianluigi
Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, United States.
Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, United States; Department of Chemistry, University of Minnesota, Minneapolis, MN 55455, United States.
J Magn Reson. 2016 Dec;273:40-46. doi: 10.1016/j.jmr.2016.09.021. Epub 2016 Sep 27.
Identity operation in the form of π pulses is widely used in NMR spectroscopy. For an isolated single spin system, a sequence of even number of π pulses performs an identity operation, leaving the spin state essentially unaltered. For multi-spin systems, trains of π pulses with appropriate phases and time delays modulate the spin Hamiltonian to perform operations such as decoupling and recoupling. However, experimental imperfections often jeopardize the outcome, leading to severe losses in sensitivity. Here, we demonstrate that a newly designed Genetic Algorithm (GA) is able to optimize a train of π pulses, resulting in a robust identity operation. As proof-of-concept, we optimized the recoupling sequence in the transferred-echo double-resonance (TEDOR) pulse sequence, a key experiment in biological magic angle spinning (MAS) solid-state NMR for measuring multiple carbon-nitrogen distances. The GA modified TEDOR (GMO-TEDOR) experiment with improved recoupling efficiency results in a net gain of sensitivity up to 28% as tested on a uniformly C, N labeled microcrystalline ubiquitin sample. The robust identity operation achieved via GA paves the way for the optimization of several other pulse sequences used for both solid- and liquid-state NMR used for decoupling, recoupling, and relaxation experiments.
以π脉冲形式的恒等操作在核磁共振光谱学中被广泛使用。对于一个孤立的单自旋系统，偶数个π脉冲序列执行恒等操作，使自旋状态基本保持不变。对于多自旋系统，具有适当相位和时间延迟的π脉冲序列调制自旋哈密顿量以执行诸如去耦和重新耦合等操作。然而，实验缺陷常常危及结果，导致灵敏度严重损失。在这里，我们证明新设计的遗传算法（GA）能够优化π脉冲序列，从而实现稳健的恒等操作。作为概念验证，我们优化了转移回波双共振（TEDOR）脉冲序列中的重新耦合序列，TEDOR脉冲序列是生物魔角旋转（MAS）固态核磁共振中用于测量多个碳 - 氮距离的关键实验。经改进的重新耦合效率的GA修饰TEDOR（GMO - TEDOR）实验，在均匀C、N标记的微晶泛素样品上测试时，灵敏度净增益高达28%。通过GA实现的稳健恒等操作为用于固态和液态核磁共振的去耦、重新耦合和弛豫实验的其他几个脉冲序列的优化铺平了道路。
