Developments And Applications Of Fast/High-resolution Multi-dimensional NMR Spectroscopy

Advantages of NMR multi-dimensional(mD)over one-dimensional spectroscopy lies in that:1.resonances are spreaded into an expanded spatial region,and thus higher spectral resolution can be achieved;2.more spectral information about the structure of molecules can be obtained.However,the significantly increased acquisition time keeps a major factor that hinders applications of mD NMR.In addition,the continually extended and deepened applications of NMR spectroscopy also place higher requirements on the robustness and spectral performance of NMR methods.Research topics introduced in this thesis are mainly focused on two aspects:1.developments of pulse sequences for fast mD NMR spectroscopy;2.developments of high-resolution mD spectroscopy for specific NMR applications.This thesis can be segmented into four parts as below:1.Echo train acquisition(ETA)enables acquisition of 2D J-resolved spectroscopy within a single scan,while the acquired data will suffer from serious truncation effects in the chemical shift dimension.Here,the linear prediction is introduced for post-processing of the truncated ETA data.With effective removal of truncation effects,spectral resolutions and signal-to-noise ratio(SNR)are greatly improved.Therefore,the acquisition time for a 2D NMR J-resolved spectrum with good spectral quanlity can be shortened from few minutes to less than 1 second.2.The ZS-based selective-coherence-transfer(SECOT)technique enables ultrafast acquisition of 2D NMR correlated spectra within a single scan.However,cross peaks,that contain crucial information about scalar coupling networks,in homonuclear 2D correlated spectra may easily get contaminated by the nearby strong diagonal peaks and their tails.Here,the same ZS-based diagonal-peak suppression module is introduced for removal of diagonal peaks from the ultrafast 2D SECOT correlated spectra.Therefore,identification and analyses of retained cross peaks can be significantly improved.3.JHH values contain crucial information about molecule structure.However,when dealing with complex molecules,extraction of JHH values can usually be hindered by the limited 1H frequency distribution and the complex J coupling multiplets.Here,a pulse sequence is designed with combination of constant time evolution and selective J refocusing in the indirect dimension for acquisition of 2D selective J-resolved spectroscopy.Only those resonances that are coupled with the selective one will show doublets in the indirect dimension,therefore,corresponding J values can be separately extracted.In comparison with existing J-editing methods,the proposed method possesses higher sensitivity and is much handier.4.Field inhomogeneity introduces spectral line broadening and thus losses of valuable spectral information.Spin-echo correlation spectroscopy(SECSY)obtains high-resolution information about chemical-shift differences between J-coupled nuclei,while echo train acquisition achieves high-resolution J-coupling splittings under inhomogeneous fields.Here,the two modules are combined for fast acquisition of high-resolution 2D J-resolved-like spectroscopy under inhomogeneous magnetic fields.Besides,with utilization of composited pulses,the proposed pulse sequence may be applied to situations with appearance of both B0 and B1 field inhomogeneity,such as NMR remote detections.