Novel half-integer quadrupolar solid-state NMR correlation experiments for probing atomic proximities and connectivities in disordered materials

用于探测无序材料中原子邻近性和连通性的新型半整数四极固态核磁共振相关实验

• 批准号: EP/D080576/1
• 负责人: Sharon Ashbrook
• 金额: $ 6.43万
• 依托单位: University of St Andrews
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FD080576%2F1
• 关键词: Novel; half; integer; quadrupolar; solid

When scientists investigate problems, like all good detectives they need clues as to what is happening. For a whole range of key problems, techniques that can reveal the local environment around an atom are crucial to provide insight into the structure at this level, which often governs how a material or molecule behaves. Nuclear Magnetic Resonance (NMR) spectroscopy has increased in importance throughout the sciences as it is an element-specific probe that can distinguish very small changes in the surroundings of different sites (e.g. whether a boron atom is bonded to three or four oxygen atoms and hence adopts a trigonal or a tetrahedral arrangement). NMR exploits the inherent magnetism of atomic nuclei which are at the centre of all atoms: like the alignment of a compass needle in the Earth's magnetic field, nuclear magnets have a preferred direction when placed in a strong magnetic field. This preference, however, is weak and a nuclear magnet can be made to change its direction from, e.g., being aligned with to being aligned against the direction of the magnetic field, by applying a resonant radio wave, i.e., one whose frequency and hence energy matches precisely the energy required to flip the nuclear magnet. The electrons surrounding the atomic nucleus are also inherently magnetic and are affected by the presence of a magnetic field. Importantly, the resonant frequency of a particular nucleus depends very sensitively on this additional response of the electrons, such that the atomic nuclei act as spies of the local electron environment and hence the specific chemical bonding, allowing it to be used to probe environments as described above. The resonant frequency of different nuclear isotopes are well separated such that an NMR spectrum is specific to a particular chosen isotope. (An element can exist as different isotopes whereby there is the same number of protons but a different number of neutrons in the nucleus.) This project considers so-called quadrupolar nuclei which have a quadrupole electronic moment (i.e., there is a non-uniform distribution of electric charge in the nucleus). Over two-thirds of all isotopes are such quadrupolar nuclei, and many important elements, e.g., lithium, boron, oxygen, sodium, aluminium only have NMR-active isotopes that are quadrupolar. Quadrupolar nuclei are often difficult because the strong interaction of the quadrupole moment with the environment generated by the electrons leads to broad lines in NMR spectra. One of the key advantages for NMR is that nuclei experience interactions that convey information about their surroundings. As an example, the dipole interaction arises as the nuclear magnets are not isolated, but rather they interact in an analogous way to how two bar magnets either attract or repel when brought close together. A related interaction is the J coupling where the electrons between the nuclei enable one nucleus to sense another nucleus to which it is chemically bonded. This project will develop new NMR experiments applicable to solid samples that use dipolar interactions and related J couplings to identify through-space proximities or through-bond connectivities between quadrupolar nuclei. A test of a good technique is that it is applicable to a wide range of problems. In this project, the new NMR experiments will be used to determine the atomic-scale structure of glasses that have applications in batteries, dental cement, ovenware, telescope mirrors, and radioactive waste immobilisation. There is always a link between the bulk structure of a material and its hidden atomic-scale structure, hence a better understanding of the latter will enable better materials to be developed. It is through the partnership between problem-based and technique-based scientists that real progress is made.

当科学家调查问题时，就像所有优秀的侦探一样，他们需要关于正在发生的事情的线索。对于一系列关键问题，能够揭示原子周围局部环境的技术对于在这一层面上提供对结构的洞察至关重要，这往往支配着材料或分子的行为。核磁共振(核磁共振)谱在整个科学中的重要性日益增加，因为它是一种特定于元素的探测器，可以区分不同位置环境中非常微小的变化(例如，一个硼原子是与三个氧原子还是四个氧原子键合，从而采用三角或四面体排列)。核磁共振利用了处于所有原子中心的原子核的固有磁性：就像指南针在地球磁场中的对准一样，当放置在强磁场中时，核磁体有一个优先的方向。然而，这种偏好是微弱的，通过施加共振无线电波，即其频率和能量与翻转核磁体所需的能量精确匹配的无线电波，可以使核磁体改变其方向，例如，从与磁场方向对准改为与磁场方向相反。原子核周围的电子本身也是有磁性的，并受到磁场的影响。重要的是，特定原子核的共振频率非常敏感地依赖于电子的这种额外反应，因此原子核充当局部电子环境的间谍，因此特定的化学键，使其能够用于上述探测环境。不同核同位素的共振频率被很好地分开，从而使核磁共振谱特定于所选的特定同位素。(一种元素可以以不同的同位素存在，因此原子核中有相同数量的质子，但有不同数量的中子。)这个项目考虑了所谓的具有四极电子矩的四极核(即，原子核中的电荷分布不均匀)。超过三分之二的同位素是这种四极核，许多重要元素，如锂、硼、氧、钠、铝只具有核磁共振活性的四极同位素。四极核通常是困难的，因为四极矩与电子产生的环境的强烈相互作用导致了核磁共振谱中的宽线。核磁共振的关键优势之一是原子核经历了相互作用，传递了关于其周围环境的信息。例如，偶极相互作用的产生是因为核磁铁不是孤立的，而是以一种类似于两个条形磁铁在靠近时如何吸引或排斥的方式相互作用。一种相关的相互作用是J耦合，在这种耦合中，原子核之间的电子使一个原子核能够感知到它与之化学结合的另一个原子核。该项目将开发适用于固体样品的新的核磁共振实验，这些样品使用偶极相互作用和相关的J耦合来识别四极核之间的通过空间接近或通过键连接。对一项好技术的检验是它适用于广泛的问题。在这个项目中，新的核磁共振实验将被用来确定玻璃的原子级结构，这些玻璃在电池、牙科水泥、烤箱、望远镜镜子和放射性废物固定化方面有应用。材料的整体结构和其隐藏的原子尺度结构之间总是有联系的，因此对后者的更好的理解将有助于开发更好的材料。正是通过基于问题的科学家和基于技术的科学家之间的伙伴关系，才取得了真正的进展。

项目成果

11B solid-state MAS spin-echo NMR experiments: effect of11B abundance and MAS frequency on dephasing

11B 固态 MAS 自旋回波 NMR 实验：11B 丰度和 MAS 频率对移相的影响

• 发表时间: 2010
• 期刊: effect of11B abundance and MAS frequency on dephasing
• 作者: N/a Barrow

Developing B-11 solid state MAS NMR methods to characterise medium range structure in borates

开发 B-11 固态 MAS NMR 方法来表征硼酸盐的中程结构

• 期刊: Physics and Chemistry of Glasses-European Journal of Glass Science and Technology Part B
• 影响因子: 0.6
• 作者: Nathan S Barrow (Co-Author)