Depending on the annealing temperature, PEO/LiAsF₆ complex can form two different crystalline structures. The ¹³C NMR spectra of both structures show high spectral resolution. In this study, 2D exchange ¹³C experiment and ¹³C fp-RFDR (finite-pulse radio-frequency-driven recoupling) DQ-SQ (double quantum-single quantum) experiment were used to assign the resonances of crystalline PEO/LiAsF₆ complexes. The results are useful for better understanding of the molecular motions in different crystalline structures.

Polyoxometalates (POMs) are metal cluster compounds formed by transition metal atoms with d⁰ or d¹ electron configuration via edge or corner polycondensation. Because of their unique molecular structures and physical/chemical properties, POMs have been widely used in functional materials, catalytic chemistry and medicinal chemistry etc. Vanadium-substituted POMs often have high catalytic activities for hydrocarbon oxidation, and such activities are mainly related to the number of vanadium atom and the electron environment these atoms are in. Solid-state NMR, as one of the most important methods to characterize solid acid materials, has been widely applied to study POMs. In this paper, butanyl cations and vanadium atoms in Lindqvist and Keggin oxopolytungstates were characterized by ¹³C and ⁵¹V solid state NMR spectroscopy to obtain information on the local environment these cations and vanadium centers are in. Such information is important for understanding the oxidation catalytic mechanism. It is concluded that ⁵¹V solid state NMR spectroscopy can be a quick, convenient and nondestructive tool to study the local environment for vanadium atoms and the bulk morphologies of POMs.

In MRI, rigid-body motion with limited amplitude can be tracked effectively by using navigator echo, and then corrected with the information provided by the navigator echo. However, tracking and correction of large and/or non-rigid motion artifact by means of navigator echo could be problematic. Images with a sparse representation in a given domain can be accurately reconstructed from undersampled datasets by using nonlinear reconstruction algorithms, such as compressed sensing. In this study, we developed an imaging technique using pseudo-random k-space trajectory for acquisition combined with motion tracking by navigator echo. After discarding the motion corrupted lines in k-space, the randomly undersampled dataset was reconstructed using compressed sensing. Experimental results demonstrated that good image quality can be obtained with this technique even in the presence of large non-rigid motions.

Magnetic resonance imaging (MRI) was used to visualize the diffusion of CO₂ in decane, while the pressure was monitored via a double-chamber pressure decay method (PVT). The signal intensities on the MRI images were analyzed to reveal the distribution of dimensionless CO₂ content. Based on Fick's law, we computed the diffusion coefficient related to diffusion time and diffusion distance using the finite volume method. The overall average diffusion coefficient can be obtained at any diffusion time. Comparing the overall average diffusion coefficient obtained by the MRI method during diffusion equilibrium time with that obtained by the PVT method showed a 2.7% error. The diffusion coefficient decreased along the diffusing direction, and declined exponentially with time. The overall average diffusion coefficient decreased with the extension of diffusion time. The results obtained in this study were comparable to previous results obtained under similar experimental conditions.

Type 1 diabetes mellitus (T1DM) is a chronic metabolic disease characterized by insulin deficiency. Chronic T1DM causes damages to multiple organs. Numerous cross-sectional studies have shown that T1DM patients had significant cerebral atrophy, compared to normal subjects. However, few previous studies investigated progressive changes of cerebral atrophy over time in T1DM. In this study, a rat model of T1DM was established by a single dose of intraperitoneal injection of streptozotocin (STZ). Magnetic resonance imaging (MRI) was employed to measure the volumetric changes of the brain at 12 weeks and 20 weeks after STZ induction to follow the progressive brain atrophy assessment between these two time points. Histochemical staining was used assess neuropathologic changes in the brain regions showing progressive atrophy. The MRI results demonstrated that the STZ-treated rats had significantly reduced volume of grey matter (GM), white matter (WM) and whole brain, as compared to control. Voxel-wise analysis revealed significant effect of group×time interaction in multiple GM and WM regions. Results of Nissl staining and hematein-eosin staining (HE) indicate significant neuronal abnormality in the brain regions showing progressive atrophy, including somatosensory cortex, motor cortex and hippocampal CA3 region.

Venous blood oxygen saturation, cerebral microbleeds, iron deposition and tissue calcification can be measured by quantitative susceptibility mapping (QSM) via deconvolving the magnetic resonance (MR) phase signal. However, accurate estimation of phase signal and magnitude image in QSM may be affected by flow-induced errors in the presence of field gradient, which would ultimately lead to errors in the quantitative susceptibility map reconstructed. The aim of this study is to develop a method for correcting the flow-induced errors in phase signal and magnitude image in QSM. Flow-compensated data acquisition was achieved using a three-dimensional full flow compensated multi-echo gradient echo sequence. Phantom and in vivo experiments were carried out to validate the method proposed. The results of these experiments demonstrated that flow compensation can reduce errors in the phase signal and magnitude images. Improved quantitative susceptibility map of the superior sagittal sinus vein in human brain could be obtained with the proposed method.

In the design of optimized radiofrequency excitation pulse with limited amplitude, the variance of the pulse excitation efficiency is taken into account to improve the excitation efficiency. It was shown that this method can significantly reduce the inhomogeneity of broadband excitation. The effects of different weights and pulse amplitude restrictions are also discussed in terms of how to achieve better excitation results.

Parahydrogen-induced polarization (PHIP) can enhance NMR signals significantly, and thus has shown great prospects in chemistry, biology, medical science and so on. In practice, the amplitude of NMR signal enhancement by PHIP, however, is often limited by experiment setup. In this work, it was demonstrated the signal enhancement in PHIP experiments can be optimized by choosing appropriate experimental conditions, including temperature, pressure and the way to introduce parahydrogen into the PHIP experiment. The reaction system of 1-hexyne and [Rh(COD)(dppb)]BF₄ was chosen as the example to illustrate how to optimize experimental conditions in PHIP experiments.

Oil-based drilling fluids show advantages such as high shale inhibition and good lubrication, and are beneficial for borehole stability and protecting the oil layers in unconventional horizontal and deep wells. However, oil-based drilling fluids often have strong fluorescent signals and high total hydrocarbon ratio, such that it is difficult to wash the rock debris clean when these fluids are used, resulting in contamination of oil in the layer and making identification and evaluation of oil layers problematic. In this work, high-resolution low-field NMR while drilling was used to monitor the oil content in drilling fluids. The results showed that oil-based drilling fluids had different NMR characteristics from mixed drilling fluids. The latter is an oil-in-water system, such that the new peaks would arise in the T₂ spectrum when drilling into oil layer. The former is a water-in-oil system, and no new peaks would arise in the T₂ spectrum when drilling into the oil layer. Under such circumstance, however, heavy oil could be identified via oil characterization, and middle and light oil could be determined by analyzing oil content in the oil layer. This method proposed was applied in Well S903H with complex geology and the use of oil-based drilling fluid. It was proved that drilling fluid NMR technique an effective method for identifying oil layers.

Movable oil saturation is an important parameter to consider when evaluating movable reserves. Adapted for the method to measure movable fluid saturation, a new low-field NMR method to measure movable oil saturation was developed, and demonstrated through oil-driving-water and water-driving-oil centrifuge experiments. Experiments were conducted on 24 samples from Maling oilfield. The results indicated that the reasonable centrifugal forces for low-permeability sandstone in oil-driving-water and water-driving-oil experiments were 2.28 and 0.22 MPa, respectively. The movable oil saturation was measured between 17.06% and 60.49%, and the average was 41.95%. The movable oil saturation was primarily determined by throat with a size of 0.5 μm, and the volume of movable oil increased with the throat radius. The correlation coefficient between movable oil saturation and permeability was found to be 0.845, higher than the correlation coefficient between movable oil saturation and porosity. The results of these agreed well with the actuality of the formation. It is concluded that the new method for measuring movable oil saturation is valid and practical, and represents significant improvement over the conventional approach.

Echo signals obtained on low-field NMR spectrometer are often weak, and have low signal-to-noise ratio, such that the signals are easily to be buried in background noise. Aiming at solving this problem, an improved non-local means (NLM) algorithm for filtering CPMG echo signals was proposed. First, based on analysis of parameter selection methods, an adaptive damping parameter selection method with Stein unbiased risk estimation was selected for the NLM algorithm. According to the characteristics of the echo signal, an improved method using different signal point data variance was employed to find the width of the neighborhood window for the NLM algorithm. Lastly, the NLM algorithm was implemented with optimized parameters. The results on simulated and experimental data sets were reported. Compared with the existing NLM algorithm, the improved NLM algorithm was shown to be able to produce better results concerning both the filtered signals and inversed spectra.

Polydimethylsiloxane (PDMS) has been used as the virtual “stationary phase” (VSP) for chromatographic NMR. Its separation capability towards halogenated compounds was investigated. Diffusion coefficients of n-pentane, 1-bromopentane and 1,5-dibromopentane contained in a mixture were measured with high-resolution liquid-state diffusion-ordered NMR spectroscopy (DOSY). In the absence of PDMS, these diffusion coefficients were close, and as a result, the three components could not be separated. In contrast, the diffusion coefficients were markedly different from each other in the presence of PDMS, leading to excellent separation. In addition, the effects of sample temperature and solution viscosity on separation performance were also investigated. It was observed that separation performance improved as sample temperature rose; and reduced as solution viscosity increased.

The structure of the title compound (MB07133) was determined by one-dimensional (i.e., ¹H and ¹³C NMR) and two-dimensional (i.e., ¹H-¹H COSY, gHSQC and gHMBC) NMR techniques. The ¹H and ¹³C NMR chemical shifts were assigned. The crystal structure of the compound was determined using X-ray single crystal diffraction. The spectral feature and crystal structure of the compound, as well as the structure-function relationship with respective to its use as a prodrug, were discussed.

Gefitinib (Iressa) is a new targeted anticancer agent for refractory non-small cell lung cancer (NSCLC). This paper presents theoretical calculation of infrared spectrum (IR), ultraviolet visible spectrum (UV-Vis), ¹H and ¹³C NMR spectra of Gefitinib using density functional theory (DFT). All results were calculated by five methods, B3LYP, BHandHLYP, M06-2X, CAM-B3LYP and LC-wPBE with 6-311++G** basis set. The IR data obtained from the CAM-B3LYP and M06-2X methods are in good agreement with experimental reports. The calculated ¹H NMR chemical shifts were found to be reproduced the corresponding experimental values at the B3LYP//GIAO level. The B3LYP//CSGT method showed the best performance in terms of ¹³C NMR chemical shifts.

Ultraviolet spectrum, infrared spectrum, mass spectra and nuclear magnetic resonance spectra (i.e., ¹H NMR, ¹³C NMR, ³¹P NMR, DEPT-135, COSY, HSQC and HMBC) of tenofovir disoproxil fumarate were collected and interpreted. All NMR signals were assigned. Based on the mass spectral data, the possible fragmentation pathways were discussed. The infrared spectrum was used to analyze the types of vibration of the functional groups in the compound. The structure of the compound was determined.