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，就像所有好侦探一样，他们都需要有关正在发生的事情的线索。对于一系列关键问题，可以揭示原子周围本地环境的技术对于在此级别上洞悉结构至关重要，这通常控制材料或分子的行为。在整个科学中，核磁共振（NMR）光谱的重要性增加了，因为它是一种元素特异性探针，可以区分不同地点周围环境的非常小的变化（例如，硼原子是否粘合到三个或四个氧原子，因此采用三角形或四个方面的布置）。 NMR利用了所有原子中心的原子核的固有磁性：就像在地球磁场中的指南针对齐一样，核磁铁在放置在强磁场中时具有首选方向。然而，这种偏好是弱的，可以通过施加谐振无线电波（即，其频率及其频率匹配的能量与磁场所需的能量相匹配，从而使其方向从相抵触到与磁场的方向对齐的方向。原子核周围的电子也固有地磁性，并受磁场的存在影响。重要的是，特定核的谐振频率非常敏感地取决于电子的额外响应，因此原子核充当局部电子环境的间谍，从而充当特定的化学键合，从而使其可用于探测上述环境。不同核同位素的谐振频率很好地分开，因此NMR光谱特定于特定选择的同位素。 （一个元素可以作为不同的同位素存在，在该同位素中存在相同数量的质子，但核中有不同数量的中子。）该项目认为具有四极杆电子力矩的所谓四核核（即，核中电荷不均匀分布）。超过三分之二的所有同位素是四极核，例如锂，硼，氧，钠，铝，铝，铝，仅具有四型四极性的NMR活性同位素。四极核通常很困难，因为四极力矩与电子产生的环境的强相互作用导致NMR光谱中的宽线。 NMR的关键优势之一是，核经历了传达有关其周围环境的信息的相互作用。例如，偶极相互作用是因为核磁体不是隔离的，而是以类似方式相互作用，以与两个条形磁体靠近时吸引或排斥。相关的相互作用是j耦合，其中核之间的电子使一个核能够感知其化学键合的另一个核。该项目将开发新的NMR实验，适用于使用偶极相互作用和相关J耦合的实心样品，以通过空间接近度或四极核之间的键连接性来识别。一项好技术的测试是它适用于广泛的问题。在该项目中，新的NMR实验将用于确定在电池，牙科水泥，烤箱，望远镜镜子和放射性废物固定化中应用的玻璃的原子尺度结构。材料的批量结构与其隐藏的原子尺度结构之间总是存在联系，因此对后者的更好理解将使更好的材料得以发展。通过基于问题和基于技术的科学家之间的伙伴关系，取得了真正的进步。

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)