Acidity plays a crucial role in determining the catalytic activities of solid acid catalysts. Among the available techniques, solid-state NMR spectroscopy is considered one of the most powerful tools for acidity characterization of solid acid catalysts. This review aims at introducing some of the most interesting progresses in recent developments and applications of solid-state NMR techniques for acidity characterization of solid acid catalysts.

Pulse sequences for heteronuclear single-quantum coherence (HSQC) and heteronuclear double-quantum coherence (HDQC) experiments for spin 1/2-spin 1 coupled spin systems were evaluated theoretically and experimentally. The results showed that zero-quantum transition occurs in the HDQC experiment. Therefore, this experiment in fact should be an HMQC experiment. The results also showed that HSQC experiment is more sensitive than HDQC experiment.

The structure of small molecular rings (C₅H₁₁N₂)+ and (C₇H₁₂N₂)²⁺ in tungstate and molybdate complexes {WO₂(C₁₀H₆O₂)₂(C₅H₁₁N₂)₂[H₂N(CH₂)₃NH₂]}₃  (1),  {(C₅H₁₁N₂)₂[H₂N(CH₂)₃NH₂][MoO₂(C₁₀H₆O₂)₂]} (2) and {(C₇H₁₂N₂)₂[MoO₂(C₁₀H₈O₂)₂]} (3) were studied by ¹H and ¹³C NMR. The NMR data of (C₅H₁1N₂)⁺ in complexes 1 and 2 indicated  the existence of two six-membered rings, which are composed of 1,3-diaminopropane and acetonitrile. The NMR spectra of (C7H12N2)²⁺ in complex 3 indicated the existence of a seven-membered ring, which is composed of ethylenediamine and acetylacetone, inferring a formation mechanism of nucleophilic additionelimination reactions. The synthesis of small molecular rings in complexes 1~3 have not been reported in other systems. In our works, these ring structures precipitated with the host-frames as new products in complexes 1~3, as confirmed by crystal structure analysis and NMR data.

An NMR-based metabonomic approach was applied to study the metabolic changes in the kidneys of db/db mice. Mice of this strain have autosomal recessive defects in the leptin receptor gene, which cause type Ⅱ diabetes and diabetic nephropathy. Metabonomic analysis in conjunction with partial least squares (PLS) analysis following orthogonal signal correction (OSC) indicated that the aqueous extract of the kidneys of db/db mice has a different metabolic profiles from that of the wild type mice, with significantly reduced levels of glutamate, acetate, choline and glycine, slight decreased levels of valine, creatinine, nicotinamide, phenylalanine and tyrosine, and significantly increased levels of lactate and sugars. The results of this study provided useful data for further understanding of type Ⅱ diabetic nephropathy.

Intrinsic viscosity (η)  and molecular motion in ternary solution of poly (N-vinyl pyrrolidone) (PVP) in mixed solvents H₂O/C₃H₆O with different volume fractions of C₃H₆O were studied by viscosity and T_2H measurements and ¹H NMR spectroscopy. It was found that: η  increased first and then decreased rapidly with increasing volume fraction of C₃H₆O. T_2H  decreased first and then increased with the increasing volume fraction of C₃H₆O. A maximum value of η appeared at a C₃H₆O volume fraction of 40%  at which point T_2H had a minimum value. Adding C₃H₆O destructed hydrogen bonds among the H₂O molecules, and dissociated free H₂O molecules could be adsorbed by PVP. Some of them might stay in the interior of PVP chain, while others might come to bind -CO of PVP chain. This would lead to increases in coil dimension and η of PVP. On the other hand, hydrogen bonds between PVP and H₂O could cause restriction in molecular motion. With a C₃H₆O fraction volume of 40%, the content of water were not high enough to extend PVP coils. Instead, the existence of water might shrink the PVP coils, making molecules motion faster.

As the non-human primate (NHP) brain is gyroencephalic, structurally and functionally similar to the human brain, NHP stroke models provide an ideal platform for investigating the mechanism of ischemic brain injury and developing therapeutical treatment. In this paper, various NHP ischemic stroke models studied recently are summarized. The imaging protocols available for quantitative MRI measurements of NHP stroke models are introduced.  In addition, data acquisition and physiological motion correction of high-resolution diffusion tensor imaging and continuous arterial-spin-labeling(CASL) based perfusion imaging for NHP are illustrated and discussed. The article provides an overview of NHP stroke models and approach for implementing quantitative multi-parameter MRI evaluation to characterize stroke injury for therapy and drug discovery.

Seven molybdenum and tungsten octahedral complexes, with benzene-1,2-diol as a ligand and ethylenediamine 1, 2-diaminopropane and 1, 3-diaminopropane as counterions, respectively, were synthesized under normal temperature. The interactions between adenosinetriphosphate (ATP) and these compounds: (NH₂CH₂CH₂NH₃)₃[Mo(V)O₂(OC₆H₄O)₂] (1)，(NH₂CH₂CH₂NH₃)₂[W(VI)O₂(OC₆H₄O)₂] (2)，(NH₂CH₂CH₂NH₃)_2.5[Mo(V)_0.5W(VI)_0.5O₂(O₂C₆H₄)]₂] (3)，(NH₃CH₂CHNH₂CH₃)₃[Mo(V)O₂(OC₆H₄O)₂] (4)，(NH₃ CH₂CHNH₂CH₃)₂[W(VI)O₂(OC₆H₄O)₂] (5)，(NH₃CH₂CHNH₂CH₃)_2.5[Mo(V)_0.5W(VI)_0.5O₂(OC₆H₄O)₂] (6)，(NH₃CH₂CH₂CH₃NH₂)_2.5[Mo(V)_0.5W(VI)_0.5O₂ (OC₆H₄ O)₂] (7) were studied by LC-NMR. The results showed that the valence of the center ions were +5 when the complexes were dissolved in D₂O and the reduction of W(VI) to W(V) occurs . W(V)  could be oxidized again when ATP solution was mixed with the original solution and hydrolysis of benzene-1,2-diol ligand took place.

The magnetic field shape is critical to the performance of Nuclear Magnetic Resonance Well Logging tools. In order to understand and reconstruct the investigation characteristics of four international leading NMR tools,  MRILP,  CMR,  MREx,  and MR Scanner,  their field distribution is simulated by Finite Elements Method(FEM). The influence of sensor configurations on field distribution is analyzed,  and then sensor performance and influence factors are investigated. The results indicated that inhomogeneous field configurations are better than homogeneous field ones. Centric sensors have relatively simple geometries and high signal intensity,  however,  their measurements are sensitive to the mud,  while eccentric ones have complicate geometries,  low signal intensity,  but they have various configurations and no restriction for mud type and salinity.

The deleted in liver cancer 2 (DLC2), a tumor suppression gene which is frequently found to be underexpressed in hepatocellular carcinoma, encodes a multi-domain protein comprising a sterile- α-motif domain (DLC2-SAM). Previous NMR structural studies of the SAM domain protein (DLC2-SAM) revealed a unique four helical bundle structure, distinct from any other known SAM domain structures.  In the present study, we have applied ¹⁵N-¹H residual dipolar couplings as additional constraints to refining the solution structures of the DLC2-SAM together with nuclear Overhauser enhancement and TALOS data. The resulting structures show improved quality factors when comparing with the structures derived without RDC constraints and have a lower Q factor. Orientations of the helices, in particular the helix 4, are validated by residual dipolar coupling data. Our RDC-refined human DLC2-SAM structures resemble those of murine DLC2-SAM. The unique structures of the SAM domain from DLC family implicate that the SAM domain may serve novel functions although these have not yet been unveiled.

Chemical shift isotropy and anisotropy of isotactic and syndiotactic polypropylene (denoted as iPP and sPP, respectively) were predicted by quantum chemical calculation. ¹³C chemical shift anisotropy (CSA) powder patterns of iPP were successfully determined with the separation of undistorted powder patterns by effortless recoupling (SUPER) experiments. It was found that the results from quantum chemical calculation are in good accordance with that from solid-state NMR experiments. These results indicate that the combination of quantum chemical calculation and solid-state NMR experiment is a powerful tool in elucidating the microstructure of polymers. The two important solid-state NMR techniques for obtaining ¹³C CSA powder pattern, SUPER and recoupling of anisotropy information (RAI), were compared, with their advantages and disadvantages discussed using methylmalonic acid as a sample compound.

Oxiracetam is often used as a nootropic agent. In this study, the NMR characteristics and conformation of oxiracetam were investigated. It was shown that the protons on the sidechain methylene group are magnetic nonequivalent because of the anisotropy effect of pyrrolidine ring. H₆ and H₃ showed long-range coupling, due to the partial double-bond character of the amide bond on the pyrrolidine ring. Pyrrolidine ring favored envelope conformation. Hindered internal rotation of another amide bond on the side chain was also analyzed.

Many compounds containing imidazo[2,1-b][1,3,4]thiadiazole ring showed pharmacological properties such as anticancer, antitubercular, antibacterial, antifungal, anticonvulsant, analgesic activities. In this paper, a novel compound which may have potential pharmaceutical applications, 2-[(2-benzoxazolinone-3-yl)methyl]-6-phenyl-imidazo[2,1-b][1,3,4] thiadiazole, was synthesized. Its ¹H and ¹³C NMR chemical shifts were assigned using 2D NMR techniques, including gHMQC, gHMBC and ¹H-¹H COSY.

MRI is an effective and non-invasive method which has been applied to engineering field in recent years. In this study, MRI was used to monitor tetrahydrofuran (THF) hydrate formation under ambient pressure and its saturation in bulk solution and in glass beads pack. It was shown that MRI is an effective method for monitoring hydrate formation. To measure saturation of hydrate formed in bulk and glass beads, grayscale images obtained were firstly converted to binary images, which were then analyzed by the threshold segmentation method.

Twenty eyeballs from 10 rats were scanned at 7 T with T₁-eighted imaging and T₂-weighted imaging sequences. The structures of eyeballs on the images were evaluated, and the retinal thickness was measured on T₂-weighted images. Most of the anatomical structures within the eyeballs could be distinguished on the images, including: cornea, lens crystalline, vitreous body, retina, sclera, iris and ciliary body, as well as the optic nerves. The thickness of retina determined with MRI was 209±20 μm, which was consistent with previous reports. There was no significant difference for the retinal thickness between MRI and the microscopic measurements. The findings from this -study- suggest that MRI can provide detailed anatomical imaging of rat eyeballs and optic nerve, and can be employed as a useful tool for investigating models of ophthalmological diseases.

In this study, 7-hydroxycoumarin was nitrified using nitric acid in ethanol solvent to obtain 6-nitro-7-hydroxycoumarin. Phosphorylation of 6nitro-7-hydroxycoumarin, however, could not be realized using the traditional Atheron-Todd reaction. By adding a little potassium carbonate into the reaction vessel, the phosphorylation reaction occurred successfully. Complete assignment of the ¹H and ¹³C NMR chemical shifts of phosphorylated 6-nitro-7-hydroxycoumarin was achieved with 2D NMR techniques, including DEPT, ¹H-¹H COSY, HSQC and HMBC. The structure of the compound was also elucidated by X-ray crystallography.

The molecular structures of diastereomers of difenoconazole were elucidated by 1D NMR and 2D NMR techniques (¹H NMR, ¹³C NMR, DEPT, ¹H-¹H COSY, HSQC and HMBC). The ¹H and ¹³C NMR chemical shifts of the diastereomers were assigned.

1D and 2D NMR, including ¹H NMR, ¹³C NMR, DEPT, HSQC, HMBC) methods were used to elucidate the structures of two semi-synthetic pennogenin compounds: pennogenin-3-O-α-L- rhamnopyranosyl-(1→2)-α-D-glucopyranoside (1) and  pennogenin-3-O-{α-L-rhamnopyranosyl-(1→2)-[α-L-rhamnopyranosyl-(1→4)]}-α-D-glucopyranoside (2). The ¹³C and ¹H NMR chemical shifts of these two compounds were assigned and analyzed. No identical structures were found in the natural products.

Two triterpene saponins were isolated from the roots of Dipsacus asperoides C. Y. Cheng et T. M. Ai. The structure of compound 1 was determined by chemical and physical methods, including spectral analysis techniques such as ESI-MS, ¹H NMR, ¹³C NMR, ¹H-¹H COSY, HMQC and HMBC. The compound was found to be oleanolic acid-3-O-α-L-arabinopyra-28-O-β-D-glucopyranoside-(1→6)-β-D-glucopyranoside ester. Moreover, the ¹H NMR chemical shifts of the compound were assigned.

Structural and spectral characteristics of the cyclic diarylheptanoids were reviewed. The UV, IR and NMR characteristics of cyclic diarylheptanoids were summarized, as well as the methods used to determine the absolute configuration of these compounds. It was shown that natural cyclic diarylheptanoids have different structural characteristics, particularly the H-6 of cyclic diphenyl ether diarylheptanoids. This work will provide a basic reference for studying the structure of the cyclic diarylheptanoids.