Selective Excitation With Asymmetric Adiabatic Pulses And Research On Novel NMR Methods

Nuclear Magnetic Resonance (NMR) is an important technique to analysis molecular structures, which plays an essential role in chemistry, biology, medicine, and quantum computing, etc. As the rapid development of science and technology, numerous new materials, systems and applications have been proposed, which demand better NMR solutions. In this article, we have proposed some novel NMR methods to solve some important and challenging problems. Based on comprehensive literature research, creative design and rigorous experiments, we have successfully made breakthrough in following areas:(1). A novel selective excitation method based on asymmetric adiabatic pulses is proposed. Existing selective pulses are mainly constructed in the forms of classical shaped pulses, such as the Gaussian pluses, or generated from numerical optimization methods. But all these pulses are very sensitive to radiofrequency (RF) intensity variation, which means their performances are highly dependent on accuracy and stability of the RF intensity. Even a slight deviation of the RF intensity may cause severe degradation in excitation profile. To solve this problem, we propose a method which can realize narrow selective excitation by sequentially applying a pair of phase-opposite asymmetric adiabatic pulses, all within two scans. Retaining the adiabatic character, the new method is very robust to RF intensity variation. Moreover, it has flexible excitation bandwidth ranging from line-selective to narrow band-selective pulses. The method has been testified successfully both in numerical simulations and solution-state NMR experiments.(2). A quantitative method to analyze labeled S spin systems is proposed. Different from non-labeled systems, the reciprocity relation is broken down in labeled systems by residual S spins dipole-dipole interactions and indirect interactions. But under fast MAS, these interactions are reduced considerably and demand a longer time to communicate between different parts of the Hamiltonian. Therefore within a short contact time (<0.5 ms), the same quantitative method can be used for both non-labeled and labeled systems. The method is independent of local structures and can be applied to samples of more than one substance.(3). A method to maximize cross polarization efficiency with multiple RAMP-CP is proposed. Cross polarization (CP) is an essential technique in solid-state NMR spectroscopy. To improve polarization transfer efficiency, numerous modified CP methods have been proposed. But the highest polarization efficiency is still less than 80% so far. In our work, nearly 100% transfer efficiency from proton and methylene (CH2) 13C spins is realized with a natural abundant glycine powder, which is the highest level in this field.(4). An embedded virtual NMR system is proposed. Reliable numerical simulations are an important tool in modern NMR spectroscopy. A series of excellent simulation software have been introduced, such as SIMPSON, Spin-Evolution, etc. Such software always demand a series of instructions and regulation to use the software, which are complex and challenging for NMR experiment operators. To solve the problem, we present VNMRS, which can be embedded in the interface of a commercial NMR operating system, such as VnmrJ. All simulation process from parameter setting to spectrum processing can be operated in the VnmrJ platform.