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.

γ-alumina transforms to θ-alumina and finally to a-alumina in the sequence of thermal dehydration of　boehmite. We report a detailed theoretical investigation of the γ-to θ-alumina transformation based on firstprinciples　density-functional calculations. Although the unit cells of cubic γ-alumina and monoclinic θ-alumina look quite different, we have identified cells for both the polytypes (with the composition Al16O24) that look very similar and can be continuously transformed one to another. The transformation may be described by a set of aluminum atom migrations between different interstitials while the oxygen atoms remain fixed. Total-energy calculations along the paths of the atomic migrations have been used to map out possible transformation pathways. The calculated conversion rate accurately predicts the experimentally measured transformation temperature. The deduced orientation relationships between the γ-and θ-alumina forms also agree with experimental observations. The formation of several different interfaces observed in domain boundaries of θ-alumina may correspond to different migration paths of the aluminum atoms in neighboring domains during the γ- to θ-alumina phase transition.

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.

To simulate the types of coordination and solution structures of the active site of haloperoxidases, the interaction systems between diperoxovanadate complexes [OV(O2)2L]n-(n=1 or 3, L=oxalate or H2O) and a series of histidine-like ligands in solution have been studied by using 1D multinuclear (1H, 13C, and 51V) NMR, 2D diffusion ordered spectroscopy, and variable-temperature NMR in 0.15 mol/L NaCl ionic medium, representing the physiological conditions of human blood. Some direct NMR data are given for the first time. The reactivity among the histidinelike ligands is imidazole >2-methylimidazole > carnosine ≈ 4-methylimidazole > histidine. Competitive coordination interactions result in a series of new peroxovanadate species [OV(O2)2L']- (L=histidine-like ligands). When the ligands are 4-methylimidazole, histidine, and carnosine, a pair of isomers have been observed, which are attributed to different types of coordination between vanadium atom and ligands. The results of density functional theory calculations provided a reasonable explanation on the relative reactivity of the histidine-like ligands and the molar ratios of isomers. Theoretical results signify the importance of the solvation effect for the reactivity and stability of the interaction systems.

The 19F NMR chemical shieldings of MF2 (M=Zn, Cd, Pb), MF3 (M=Al, Ga, In), and SnF4 were studied by the GIAO-B3LYP method. The aug-cc-pVTZ basis set was used for the inspected fluorine atom, and LanL2DZ for the remaining fluorine atoms. The 3-21G(2d) basis set was utilized for the Al atom, and CRENBL and/or DZVP for the other metal atoms. When appropriate cluster models were employed, the theoretical shieldings agree well with experimental ones. The relativistic and electron correlation effects have greater influence on the calculated results of fluorides containing heavy or transition metal atoms.