Zero and Low-Field Nuclear Magnetic Resonance (NMR)

核磁共振是分析化学、材料科学、化合物筛选和新药开发等领域的一种强有力的工具。磁共振成像(MRI)是核磁共振的一个分支，它利用与研究人体内部结构相同的科学原理，为诊断和认知(神经)生物医学成像提供了至关重要的工具。核磁共振和核磁共振的一个主要缺点是需要大的、固定的和昂贵的超导磁体和相关的基础设施。在化学系化学测量和成像计划的支持下，以及分子和细胞生物科学系分子生物物理计划的共同资助下，加州大学伯克利分校的Alex Pines教授和Dmitry Budker教授及其团队寻求提供新的方法，使磁共振数据能够在不需要巨大磁铁的情况下获得，并且具有简单的基础设施，从而使用紧凑、可移动的设备产生信息和图像，并且成本降低了10-100倍。这项研究对从化学到生物医学的技术创新产生了重大影响，同时有助于培养一支先进的劳动力队伍。传统核磁共振和核磁共振中强磁场Bo的目的有两个：a)作为一种极化核自旋的手段；b)有效地感应检测磁化进动。每个信号与场的大小成正比，因此总的检测信号与场的平方成正比。这解释了高场(及其相应的高频)用于光谱分析和成像的优势。目前商用核磁共振仪器的典型磁场范围为10-25特斯拉。为了省去高场，需要另一种偏振和检测手段。偏振可以通过光抽运和/或对氢诱导的偏振来实现。这两种方法都在零场到超低场(ZULF)产生“超极化”，实际上比高场下的热自旋极化大几个数量级。对于检测，需要一个非感应式量子探测器。以前的研究利用了工作在液氦温度下的超导量子干涉器件(SQUID)的高灵敏度。Pines和Budker教授现在正在使用激光原子磁强计，这种仪器也可以在室温下以高灵敏度探测超低进动。到目前为止，他们已经产生了具有高信噪比和10 MHz数量级线宽的ZULF谱。在这个项目中，他们正在将方法扩展到包括：1)用于自旋去耦合的复杂的ZULF脉冲序列；2)选择激发单一跃迁的方法；3)用于原子自旋相互作用的二维光谱；4)自旋同位素的分离；以及5)量子关联。从这项工作中得到的光谱和信息可能会增强核磁共振波谱在分析化学和化学生物学中的适用性。

Nuclear magnetic resonance (NMR) is a powerful tool for applications in analytical chemistry, materials science, and the screening of compounds in search for new medications. Magnetic resonance imaging (MRI), an offshoot of NMR, capitalizes on the same scientific principles study structures inside the human body, providing a critically important tool for diagnostic and cognitive (neurological) biomedical imaging. A major drawback of both NMR and MRI is the need for large, immobile, and costly superconducting magnets and associated infrastructure. With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, and co-funding from the Molecular Biophysics Program in the Division of Molecular and Cellular Biosciences, Professors Alex Pines and Dmitry Budker and their groups at the University of California - Berkeley, seek to provide new methodology that enables magnetic resonance data to be obtained without the need for the huge magnets and with simple infrastructure, thereby producing information and images with equipment that is compact, mobile and less costly by a factor of 10-100. The research offers significant impact on technical innovation from chemistry to biomedicine, while contributing to the training of an advanced workforce.The purpose of the high magnetic field, Bo, in traditional NMR and MRI is twofold: a) to act as a means of polarizing the nuclear spins and b) for the efficient inductive detection of the magnetization precession. Each is proportional to the magnitude of the field so the total detected signal is proportional to the square of that field. This accounts for the advantage of high fields (and their corresponding high frequencies) for spectroscopy and imaging. Typical magnetic fields for current commercial NMR instrumentation range from 10-25 Tesla. In order to dispense with the high field, alternative means of polarization and detection are required. Polarization can be accomplished by optical pumping and/or parahydrogen-induced polarization. Both methods produce "hyperpolarization" at zero to ultralow fields (ZULF) which is in fact several orders of magnitude greater than the thermal spin polarization at high field. For detection, a non-inductive quantum detector is required. Previous research utilized the high sensitivity of a superconducting quantum interference device (SQUID) that operates at liquid helium temperature. Professors Pines and Budker are now employing a laser atomic magnetometer that can also detect ultralow precession with high sensitivity but at room temperature. To date, they have produced ZULF spectra with high signal/noise and with line widths of the order of 10mHz. In this project, they are expanding the methodology to include: 1) sophisticated ZULF pulse sequences for spin decoupling; 2) approaches to selective excitation of single transitions; 3) two-dimensional spectroscopy for atomic spin interactions; 4) separation of spin isotopomers; and 5) quantum correlations. The spectra and information emanating from this work may enhance the applicability of NMR spectroscopy in analytical chemistry and chemical biology.