NMR over nine orders of magnitude in the magnetic field

核磁共振（NMR）是物理科学中最通用的光谱学形式之一，其应用范围从基础物理学、量子理论、化学、材料科学和生物化学到结构生物学和临床应用（特别是以磁共振成像（MRI）的形式）。在大多数情况下，核磁共振波谱使用尽可能强的磁场，因为这通常产生最强的信号与原子核的不同化学位置的高分辨率。然而，在某些情况下，需要在一定范围的磁场上执行核磁共振，包括超低场状态，其中磁屏蔽用于获得比地球磁场小三个数量级以上的非常小的磁场。在这种超低场状态下的核磁共振在几个方面是非常特殊的。首先，核磁共振谱的信息量不是由化学位移决定的，而是由自旋-自旋耦合决定的。其次，在这种情况下，线宽不像在普通核磁共振中那样受磁场不均匀性的支配，而是受耗散效应（弛豫）的支配。通常可以实现极窄的线宽（毫赫兹）。第三，不同种类的核自旋在超低磁场下紧密耦合，产生了异核长寿命态等特殊现象，而这些现象在大磁场下是不存在的。第四，光学磁强计技术可用于检测核自旋的磁性，而不是传统核磁共振中使用的电磁感应。因此，零至超低场（ZULF）制度提供了一种特殊形式的核磁共振，它与普通核磁共振波谱具有完全不同的性质，其特征和可能性才刚刚开始探索。目前在英国没有设备可以在超低磁场条件下观察核磁共振信号。提出的研究涉及构建一种装置，该装置以快速和高度控制的方式在普通核磁共振磁体的高场区域和磁屏蔽室之间穿梭样品，配备光学磁力计，用于检测ZULF状态下的核磁共振信号。该设备将使我们能够以极高的精度探索ZULF体系中的自旋动力学，并利用ZULF体系作为高场核磁共振程序的一部分。这允许许多多维核磁共振实验，其中两种制度的优势可以结合起来。此外，该设备允许在非常宽的磁场范围内探索核磁共振弛豫的可能性，允许在非常宽的时间尺度范围内探测分子运动。此外，该设备将允许开发用于在ZULF状态下操纵核自旋系统的先进方法，例如开发“ZULF解耦”序列，该序列使系统表现得好像不同同位素类型的原子核之间的自旋-自旋耦合被抑制。这将使ZULF核磁共振信号更窄，信息更丰富，更容易解释。拟议中的设备将是世界上独一无二的，并将作为研究设施提供给英国科学界。在研究项目的最后阶段，将提供一个研讨会和培训课程，以促进这种特殊形式的核磁共振知识向英国科学家的转移。

Nuclear magnetic resonance (NMR) is one of the most versatile forms of spectroscopy in the physical sciences, with applications spanning the full range from fundamental physics, quantum theory, chemistry, materials science and biochemistry to structural biology and clinical applications (especially in the form of magnetic resonance imaging, MRI). In most cases, NMR spectroscopy employs the strongest possible magnetic field, since this usually generates the strongest signals with high resolution of the different chemical sites of the atomic nuclei. Nevertheless, there are circumstances in which it is desirable to perform NMR over a range of magnetic fields, including the ultralow field regime, in which magnetic shielding is used to achieve very small magnetic fields over three orders of magnitude smaller than the earth's magnetic field. NMR in this ultralow field regime is very special in several ways. Firstly, the information content of the NMR spectrum is determined not by chemical shifts but by spin-spin couplings. Secondly, the line width in this regime is not governed by the magnetic field inhomogeneity, as in ordinary NMR, but by dissipation effects (relaxation). Extremely narrow linewidths (millihertz) are often achieved. Thirdly, the different species of nuclear spins are tightly coupled in the ultralow magnetic field regime, giving rise to the special phenomena such as heteronuclear long-lived states, which do not exist in larger magnetic fields. Fourthly, optical magnetometry techniques may be used to detect the magnetism of the nuclear spins, as opposed to electromagnetic induction, which is used in conventional NMR. The zero-to-ultralow field (ZULF) regime therefore offers a special form of NMR which has a quite different nature to ordinary NMR spectroscopy, and whose features and possibilities are only just starting to be explored. There is currently no equipment in the UK which allows observation of NMR signals in the ultralow magnetic field regime. The proposed research involves the construction of a device which shuttles a sample in a rapid and highly controlled way between the high-field region of an ordinary NMR magnet and a magnetically shielded chamber, equipped with optical magnetometers for the detection of the NMR signal in the ZULF regime. This equipment will allow us to explore the spin dynamics in the ZULF regime with great precision and also exploit the ZULF regime as part of a high-field NMR procedure. This allows numerous multidimensional NMR experiments in which the advantages of both regimes may be combined. In addition the equipment allows the possibility to explore NMR relaxation over a very wide range of magnetic fields, allowing the probing of molecular motion over an extremely wide range of timescales. In addition the equipment will permit the development of advanced methodology for manipulating nuclear spin systems in the ZULF regime, such as the development of "ZULF decoupling" sequences which cause the system to behave as if spin-spin couplings between nuclei of different isotopic types are suppressed. This will make the ZULF NMR signals narrower, more informative, and easier to interpret. The proposed equipment will be world-unique and will be made available to the UK scientific community as a research facility. A workshop and training course will be provided during the final stages of the research project in order to facilitate the transfer of knowledge on this special form of NMR to UK scientists.