High-Resolution Two-dimensional NMR Spectroscopy In Inhomogeneous Magnetic Fields

With the features of non-invasive and non-destructive,nuclear magnetic resonance(NMR)has become an indispensable analytical tool widely used in many disciplines,from physics and chemistry to biology and medicine.High-resolution two-dimensional(2D)NMR can alleviate the jam or even overlapping of resonances in conventional one-dimensional(1D)spectra,and release correlation information.In turn,2D NMR has become a routine analytical tool for the elucidation of small organic molecules and study of macromolecular structures.However,the acquisition of high-resolution spectroscopy relies on the highly homogeneous external magnetic fields,which are inaccessible in many cases,such as poorly shimmed fields or intrinsic heterogeneity of magnetic susceptibility in samples.In addition,the long experiment time hinders further applications of 2D NMR.In this dissertation,based on intermolecular multiple-quantum coherences(iMQC),associated spatiotemporal encoding technique,novel methods are developed to retrieve high-resolution 2D spectra in inhomogeneous fields.The related contents can be summarized as follows:1.The efficiency of selective pulses used in homonuclear iMQC methods,is investigated in inhomogeneous fields.Selective pulses may induce more than one distant dipolar field(DDF),and split the resonances into several groups,leading to difficulties in spectral assignment.In order to circumvent this influence,a new method based heteronuclear intermolecular zero-quantum coherence(iZQC)is proposed.Associated with spatiotemporal encoding and coherence transfer technique,the new method can obtain high-resolution 2D J-resolved spectra in inhomogeneous fields via the DDF originated from 2H spins of deuterium agent.With 2H spins excited in advance,the new method can encode 2H spins sufficiently and achieve high-resolution 2D J-resolved spectra in severe inhomogeneous fields.2.High-resolution three-dimensional(3D)J-resolved correlation spectra are achieved in inhomogeneous fields via intermolecular zero-quantum coherence(iZQC)and J modulation detection method.The dephasing induced by field inhomogeneity can be removed by iZQC,thus the spectrum is free of the influence of line broadening in all three dimensions.Associated with spatiotemporal encoding technique,the acquisition of 3D spectrum can be accomplished within the time for a conventional 2D NMR experiment.A COSY spectrum and J-resolved spectrum can be simultaneous obtained after 2D projection.Furthermore,as TOCSY can be attained by changing the coherence transfer module,the coupling networks of compounds are accessible in inhomogeneous fields.3.The spin-lattice relaxation time(T1)plays a critical role in the study of spin dynamics,signal optimization and data quantification.However,the measurement of chemical shifts specific T1 constants is hampered by the magnetic field inhomogeneity due to poorly shimmed external magnetic field or intrinsic magnetic susceptibility heterogeneity in biological tissues.A new protocol is designed to determine chemical shift specific T1 constants in inhomogeneous fields.Based on intermolecular double-quantum coherences,the new method can resolve overlapped peaks in inhomogeneous fields.The measurement results are in consistent with the measurements in homogeneous fields using conventional method.Since spatial encoding technique is involved,the experimental time for the new method is same to the conventional method.With the aid of T1 knowledge,some concealed information can be exploited by Ti weighting experiment.