Nuclear magnetic resonance (NMR) spectroscopy has found wide applications in fields of chemistry, biology, medicine, materials, etc, benefitting from its features of non-invasion, high resolution and high-throughput information. Recently, a high level of interest has reemerged in the development of pure shift NMR techniques which aim for significantly improving spectral resolution in overlapped regions. According to studies on new techniques and related applications by our group, herein we briefly review how pure shift technique is developed, and what would be next challenges in its development and extensive applications.

Fast magnetic resonance imaging (MRI) has been attracting more and more research interests in recent years. With the emergence of big data and development of advanced deep learning algorithms, neural network has become a common and effective tool for image reconstruction in fast MRI. One main challenge to the deep learning-based methods for fast MRI reconstruction is the trade-off between the network performance and the network capacity. Few previous studies have used the deep learning-based methods in parallel imaging. In this work, a deep recursive cascaded convolutional network (DRCCN) architecture was designed for parallel MRI, with reduced number of network parameters while maintaining a satisfactory performance. The experimental results demonstrated that, compared to the classical methods, image reconstruction with the well-trained DRCCN networks were more accurate and less time consuming.

Magic-angle spinning (MAS) rotor, a device for high-speed spinning of solid samples, is an essential component of the probes used in solid-state nuclear magnetic resonance (NMR) experiments. In this study, a 4 mm MAS rotor was designed and fabricated in-house. Fluid-solid coupling simulation was carried out to compute the stress and strain in the MAS rotor. Modal analysis was performed to determine the various modes and critical speeds of the MAS rotor. Actual spinning speed test and MAS NMR sampling were carried out to test the performance of the rotor. The results showed that the MAS rotor built in-house could operate normally at a spinning speed up to 14 kHz. The ¹H NMR signals of adamantane collected at 4 kHz and 12.5 kHz were collected and compared. These results demonstrated that the 4 mm MAS rotor built in-house could meet the requirements of conventional solid-state NMR experiments.

Scalar coupling is an important parameter in nuclear magnetic resonance (NMR). The proton-proton coupling constant J_H-H provides valuable information on molecular structure. However, determining J_H-H value in complex coupling networks is still challenging. Here, we propose a method called simultaneous multi-slice selective constant-time J-resolved spectroscopy (SMS-SECTJRES) to measure J_H-H values of all coupling networks of a molecule simultaneously in one experiment. In this method, gradient-encoded selective refocusing is used during a fixed evolution time, combined with echo planar spectroscopic imaging (EPSI) detection module to extract different selective J-edited spectra in different spatial positions. This new method is conducive to reveal coupling networks and the analysis of molecular structures.

Gradient coils generate gradient magnetic fields that are essential in the magnetic response imaging. The gradient coils are usually designed by the target field method. In this work, we attempted to design matrix gradient coils with particle swarm optimization and the genetic algorithm. Finite element simulation calculation demonstrated that the average non-uniformity in the x and y directions was 0.851%, and the average non-uniformity in the z direction was 1.013%.

Hyperpolarized ¹²⁹Xe NMR has a detection sensitivity up to 10 000 times higher than that in the conventional ¹H NMR. Hyperpolarized ¹²⁹Xe gas has only one NMR signal, but can produce multiple signals when combined with molecular cages, providing the chances to develop targeted molecular probes. In this paper, water-soluble cucurbit[6]uril nanoparticles were used for loading hyperpolarized ¹²⁹Xe gas to construct targeted molecular probes. It was observed that such molecular probes had double "cage" signals and the potential to be developed into multi-functional probes.

Cytochrome c is an important multifunctional protein, which plays important roles in the respiratory chain and cell apoptosis. Characterization of conformational changes of cytochrome c is essential to elucidate the molecular mechanism underlying its functions. Isotope-labeled proteins are usually needed for nuclear magnetic resonance (NMR)-based protein structure elucidation. However, post-translational modification of cytochrome c makes it difficult to be labelled by isotopes. In this work, ¹H-¹³C HSQC NMR experiment was used to characterize the conformational changes of naturally purified wild-type cytochrome c in the redox process, focusing on the side chain methyl groups. It was observed that this method could detect the signals of most methyl groups within 2 h, and the methyl groups detected with apparent chemical shift change were coincide with its conformation change. The results indicated that it is possible to use the method proposed to study the conformational changes of proteins at natural abundance or post-translational modified proteins.

In operando nuclear magnetic resonance (in operando NMR) was used to investigate the effects of co-catalysts and wavelength of light on the products of photocatalytic methanol reforming, as well as the hydrogen production rate, in a real solid-liquid reaction environment. The results demonstrated that adding co-catalysts (i.e., anatase TiO₂ modified with different isolated noble metal atoms) could affect the yields of reforming products to some extents, but had only little effects on the reaction kinetics. And the wavelength of light also had a large effect on the yields. It was concluded that the co-catalysts might play important roles in providing the redox capacity and the synergistic effects between methanol oxidation and hydrogen production.

Thermo-responsiveness and self-assembly behaviors of poly(sodium-p-styrene sulfonate)-block-poly (N-isopropylacrylamide) (PSSS₅₀-b-PNIPAM₃₀₀) in pure water and binary solvents (i.e., water/methanol and water/acetone) were investigated by ¹H NMR, dynamic light scattering (DLS), and transmission electron microscopy (TEM). It was found that the PNIPAM chains had a lower lowest critical solution temperature (LCST) in the water/methanol and water/acetone binary solvents than in water. Temperature-induced collapse of PNIPAM in water/acetone binary solvent was evidently weaker compared to the collapses in pure water and water/methanol binary solvent. The DLS and TEM results demonstrated that the self-assembly process and morphology of PSSS₅₀-b-PNIPAM₃₀₀ in aqueous solution could be fine-tuned with the addition of small molecule solvent.

Diffusion tensor imaging (DTI) was used to evaluate micro-structural changes and structural connectivity in the TX mice model of Wilson's disease (WD) at 9.4 T. Region of interest (ROI) analysis showed that mean fractional anisotropy (FA) values in the hippocampus, caudate putamen and lateral globus pallidus of the TX mice decreased significantly, relative to those in the control mice. The mean diffusivity (MD) values in these regions showed no significant inter-group differences. The results of fiber tracking demonstrated that structural connectivity of in the brain of TX mice was maintained, indicating that the effects of copper accumulation in these mice were mainly regional.

Tumor is a metabolic disease. The effect of oncogene expression on the metabolism of cancer cells is one of the hotspots in cancer research. In this study, ¹H NMR-based metabonomics analysis was used to explore the metabolic characteristics of glioma cell lines with low expression of SIRT7, and to identify the characteristic metabolites and metabolic pathways related to the expression of SIRT7. The results showed that there were significant differences in metabolic profiles between the SIRT7 low expression group and the control group, and 22 aqueous metabolites were found to vary significantly. Compared with the control group, the concentration of 12 metabolites including lactate, glycine, and glutamate, and so on, increased in SIRT7 low expression glioma cell lines, while the concentration of 10 metabolites such as valine, leucine, lysine, et al. decreased. Pathway enrichment analysis indicated that the metabolic pathways of aminoacyl-tRNA biosynthesis, tyrosine metabolism, and so on, were closely related to the low expression of SIRT7. The results provide a theoretical basis for further mechanism elucidation of SIRT7 regulating glioma cell metabolism.

A C₂-symmetric host (host 1) was synthesized by derivatization of chiral diphenylethylenediamine with phenylisocyanate. High-resolution proton nuclear magnetic resonance (¹H NMR) was used to investigate whether the chiral host could be used for enantiomeric discrimination of its structural analogues:α-phenylethylamine (guest 2), α-(p-methoxyphenyl)ethylamine (guest 9) and their derivatives (guests 3~8 and 10~13), and hydrogen-bonding interactions underlying the enantiomeric discrimination. It was observed that the host was able to recognize the urea and amide derivatives of the two primary amines, except for guests 7 and 12 bearing two NO₂ groups. The host had stronger hydrogen-bonding interactions with the urea derivatives of guests 2 and 9 than with the corresponding amide derivatives, and high enantiomeric discrimination ability for the CHCH₃ groups of the (R)- and (S)-urea derivatives.

Choriocarcinoma (CC) is a malignant trophoblastic tumor that occurs in women of childbearing age. Its cure rate could be over 90% following single drug or multidrug chemotherapy with methotrexate, 5-fluorouracil and etc. Chemoresistance is the main cause of treatment failure in CC, and the mechanisms have yet to be elucidated. Most of the previous works on the chemoresistance of CC focused on the transcript and protein levels, and much less attention was put on the metabolic level. In this study, the metabolomic phenotypes of two lines of CC cell, methotrexate-resistant cell (JEG3R) and methotrexate-sensitive cell (JEG3), as well as the medium extracts, were investigated using an NMR-based metabonomics method. The results showed that the chemoresistance of CC was likely related to disturbed glucose metabolism. Glucitol accumulation was observed only in the JEG3R cell line, suggesting the involvement of aldose reductase in the development of chemoresistance. In addition, methotrexate chemoresistance was also associated with lactate accumulation and stimulated alanine synthesis to fuel the Krebs cycle. The levels of amino acids, nucleotides and phosphocholine in the resistant line showed significant differences from the non-resistant line, and positive correlations with the proliferation rate of CC. This study provided insights into the chemoresistance of CC from the metabolism aspect.

Molecular dynamics of semi-crystalline poly(3-hydroxybutyrate) (PHB) and copolymers poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) containing 5 wt.% (PHBV5) and 12 wt.% (PHBV12) 3-hydroxyvalerate monomer was studied with solid-state NMR spectroscopy. Proton spin-lattice relaxation times in the laboratory frame (T₁) and rotating frame (T_1ρ) were measured over the temperature range of 150~370 K. Kubo-Tomita expression fitting to the changes of relaxation times with temperature was used to obtain the molecular dynamics parameters (i.e., E_a and τ₀) in the crystalline and amorphous regions of PHB, PHBV5 and PHBV12. These results yielded molecular-level insights into the structural modification and enhancement of the PHB.

Interactions between 5-fluorouracil (5-FU) and PAMAM in D₂O solution were studied by NMR spectroscopy. The results of ¹H NMR chemical shift titration experiments demonstrated that 5-FU molecules bonded to the surface of PAMAM, and the results of ¹³C NMR chemical shift titrations experiments disclosed that hydrogen-bond interactions and/or hydrophobic interaction ins existed in the interior pockets of PAMAM and 5-FU. These results were further supported by ¹H and ¹⁹F relaxation time measurements. The NOESY experiment was used to confirm the presence of 5-FU encapsulation in the PAMAM-5-FU complexes. This study provides a methodology for studying the interactions between dendrimers and drug molecules.

Nuclear magnetic resonance (NMR) spectroscopy is an effective way to obtain in situ chemical information in biological tissues, and used in various application fields, including biology, food and medicine. It is often desirable to acquire high-resolution spectra of obtain more information of the sample, such as J-couplings, split structure and etc. However, acquiring high-resolution spectra under inhomogeneous field can be challenging. It has been shown previously that intermolecular double-quantum coherence (iDQC) derived from remote dipole-dipole interactions are insensitive to magnetic field inhomogeneity, and can be utilized to obtain high-resolution spectra under inhomogeneous fields. In this work, the IDEAL-II sequence was used to detect iDQC in butyl methacrylate, tomato and watermelon under inhomogeneous fields to obtain high-resolution spectra of these samples. The results demonstrated that the iDQC technology may provide a valuable tool in food science research.