New Methods For High-Resolution Selective Refocusing J Spectroscopy

Nuclear magnetic resonance is one of the important methods for analyzing the chemical composition and molecular structure,and it can provide pivotal information such as chemical shifts and scalar couplings.Among them,measuring proton-proton scalar coupling constants is an important subject in nuclear magnetic resonance spectroscopy.In 1D spectra,chemical shifts and scalar couplings are often difficult to measure due to crowded peaks and complex coupling splitting patterns.In recent years,in order to accurately measure J coupling constants,a great number of 2D selective refocusing methods have been proposed.However,in most 2D selective refocusing methods,the application of gradient coding technology reduces the spectral sensitivity,and the axial peaks in the spectra affect the accurate measurement of J coupling constants.In this work,two kinds of 2D selective refocusing methods for measuring scalar coupling constants are proposed,including the selective refocusing method using perfect echo to improve the spectral sensitivity and the selective refocusing method for obtaining absorptive mode 2D NMR spectra without axial peaks.The specific work is as follows:First,the basic principles and development of NMR are introduced.Next,the methods for measuring scalar coupling constants are introduced.Finally,the perfect echo module and its related applications are introduced,and two new selective refocusing methods are described in detail in this paper.Combining perfect echo module with Zangger-Sterk(ZS)decoupling technique and selective refocusing technique,a 2D selective refocusing method for measuring J coupling constants with improved signal-to-noise ratio(SNR)is designed.The SNR of this method not only can be higher than the currently known Gradient-encoded homonuclear SElective ReFocusing spectroscopy(G-SERF)method,but also performs better than the Pure Shift Yielded by CHirp Excitation to DELiver Individual Couplings(PSYCHEDELIC)method in some samples.Moreover,this method can also be applied in strongly coupled spin systems.Because of the improvement of the spectral SNR,it facilitates the measurement of the J coupling constants in the NMR spectra,thereby facilitating the analysis of the molecular structure.In the conventional 2D selective refocusing methods for measuring scalar coupling constants,the splitting signals that are used to measure the J coupling constants are often overlapped with strong spectral axial peaks.Therefore,a selective coherent transfer module based on perfect echo combined with PSYCHEDELIC module is proposed to measure the Jcoupling constants without axial peaks.This method not only can suppress the axial peaks,but also obtain the pure absorptive mode spectra.Compared with other selective refocusing methods without axial peaks,this method is suitable for all spin systems.This method can obtain absorptive 2D spectra with removing axial peaks,which will facilitate the measurement of the Jcoupling constants in molecular structure analysis.