Residual intermolecular dipolar interactions may result in undesired spectral features on highly concentrated samples in liquid NMR. Although homonuclear decoupling can be employed to suppress the interactions, it may cause a strong irradiation peak, which obscures the nearby peaks. In order to overcome this shortcoming, a modified CRAZED sequence with three radio-frequency pulses was proposed. The analytical expression derived from the dipolar field treatment was employed to select proper flip angles and phase cycling. Theoretical predictions, experimental observations, and computer simulations demonstrated that the new method effectively suppresses the undesired peaks due to residual dipolar effects.

A novel MRI method based on the intermolecular double-quantum coherence (DQC) for soft tissues is described. DQC images of human brain were obtained for the first time on a whole-body 1.5 T scanner. The combination of quantum and classical formalisms was used to characterize multiple-quantum coherences, and to aid in the design of a DQC imaging sequence. The theoretical analysis suggests that signals from the intermolecular DQCs have higher sensitivity than those from the zeroquantum coherence (ZQC) for human brain, and the sensitivity increases with increased field strength. The DQC signal may provide a new form of contrast for MRI.

A product operator matrix is proposed to describe scalar couplings in liquid NMR. Combination of the product operator matrix and non-linear Bloch equations is employed to describe effects of chemical shift, translational diffusion, dipolar field, radiation damping, and relaxation in multiple spin systems with both scalar and dipolar couplings. A new simulation algorithm based on this approach is used to simulate NMR signals from dipolar field effects in the presence of scalar couplings. Several typical coupled spin systems with both intra-molecular scalar couplings and inter-molecular dipolar couplings are simulated. Monte Carlo methods are incorporated into simulations as well to analyze diffusion process in these complicated spin systems. The simulated results of diffusion and relaxation parameters and 2D NMR spectra are coincident with the experimental measurements, and agree with theoretical predictions as well. The simulation algorithm presented herein therefore provides a convenient means for designing pulse sequences and quantifying experimental results in complex coupled spin systems.

[M6F]5+ clusters were chosen to calculate the F NMR chemical shielding for solid state alkali-metal fluorides MF MsLi, Na, K, Rb.using gauge-independent atomic orbitals (GIAO) at Hartree–Fock (HF) and density functional theory DFT.levels, respectively. The results agree with those measured experimentally, in particular when the relative deviations within the same series are considered. Our results reveal that the variation of chemical shielding from LiF to RbF correlates well with a combined effect from the lattice factor Ry2 and the valency factor Q+Q-

Although the theories and potential applications of intermolecular multiple-quantum coherences iMQCs have been under active investigations for over a decade, discussion of iMQC NMR signal formation was mainly confined in the time domain. In this paper, a full line-shape theory was developed to describe iMQC signals in the frequency domain. Relevant features of the line shape, such as peak height, linewidth, and phase, were investigated in detail. Predictions based on the theory agree well with experimental and simulated results. Since radiation-damping effects always couple with iMQCs in highly polarized liquid-state NMR systems, and strongly radiation-damped signals have many spectral characteristics similar to those of iMQCs, a detailed comparison was also made between them from different spectral aspects. With detailed comparison of peak height, linewidth, and phase, this work demonstrates that the iMQC and radiation-damping phenomena result from two completely different physical mechanisms despite that both present similar signal features and coexist in highly polarized liquid-state NMR systems.