The performance of solid-state NMR proton-driven spin-diffusion (PDSD) and second-order Hamiltonian among analogous nuclei plus (SHA+) sequences for probing ¹⁵N-¹⁵N through-space correlations in ¹⁵N-labelled g-C₃N₄ samples were compared at high magnetic fields with moderate magic angle spinning (MAS) frequencies. It was found that, relative to the PDSD sequence, the SHA+ sequence is more efficient in terms of yielding polarization transfer between the ¹⁵N atoms as long as one of the nitrogen atoms bonds to protons. The results are useful in guiding the choice of solid-state nuclear magnetic resonance (SS-NMR) sequences for studying nitrogen-doped carbon-based materials.

Atomic electronegative space distance vector (AESDV) which characterizing the microenvironment of equivalent carbon atoms was constructed based on the three-dimensional structures of aromatic ethers. The AESDV was then employed in combination with atomic hybridation state index (AHSI) to calculate ¹³C NMR chemical shifts of 46 carbon atoms in 9 aromatic ethers, and to explore quantitative structure spectroscopy relationship. With multiple linear regression (MLR), a model with a correlation coefficient (R) of 0.964 and a standard deviation (SD) of 8.763 was obtained. Cross-validation of the model was performed by leave-one-out procedure (LOO), resulting in a correlation coefficient (R_CV) of 0.948 and a standard deviation (SD_CV) of 10.362. Furthermore, the 9 aromatic ethers were randomly assigned into a training set and a test set, respectively, to validate this model, and the correlation coefficients R_test1 and R_test2 were found to be 0.979 and 0.939, and the standard deviations SD_test1 and SD_test2 to be 6.400 and 10.162, respectively. The results showed that the model established can be used to predict ¹³C NMR chemical shifts in aromatic ethers.

The influence of hydrogen bonding on the shielding tensors and quadrupole coupling constant (Q_CC) of oxygen atoms in [¹⁷O-2] thymine, [¹⁷O-4] thymine, [¹⁷O-2] uracil, [¹⁷O-4] uracil, [¹⁷O-2] cytosine, and [¹⁷O-6] guanine monohydrate has been studied by high quality quantum chemical calculations with different cluster models. The results showed that both hydrogen bonding and van der Waals (vdW) interactions are crucial for accurate prediction of isotropic ¹⁷O chemical shifts (d_O). In addition, experimentally measured ¹⁷O chemical shifts in these bases decrease with the increase of intermolecular hydrogen bonding interactions, and such interactions need to be accounted for in the theoretical models in order to obtain satisfactory calculated results. Relative to that of d_O, the calculation of ¹⁷O shielding tensors (d₁₁, d₂₂ and d₃₃) are even more model-dependent. NMR parameters calculated by periodic structure models taking all hydrogen bonding interactions and non-bonding vdW interactions into account were found to be in good agreement with the experimental results. Further analysis revealed that intermolecular hydrogen bonding-induced decrease of d_O is mainly due to the increase of ¹⁷O negative charge density coming from the carboxyl (C=O) carbon. Furthermore, it was found that hydrogen bonding and weak interaction have remarkable effects on calculated ¹⁷O quadrupole coupling constant (Q_CC) as well. In conclusion, it is essential to take intermolecular hydrogen bonding and weak interactions into accounts in theoretical calculations in order to predict NMR parameters of biological samples correctly.

Under the concept of personal-based health care, different health management strategies are needed for different populations. To achieve this goal, the first step is to characterize the health-related differences among different populations. To this end, we recruited a total of 31 athletes and 42 labor workers to exam population-level differences in their urinary metabonome. First morning urine was collected and stored at -80℃ until use. ¹H NMR spectra of the urine samples were collected on a 600 MHz spectrometer. The data collected were then used to build supervised and unsupervised pattern recognition models (PCA model and OPLS-DA model) to differentiate the two populations. Metabolites contributing significantly to the population difference in urinary metabonome were identified by VIP plot, among which false positives were discovered by receiver operating characteristic curve (ROC) and t-test. Predictive PLS-DA model was built, and validated by internal cross-validation, permutation tests and external prediction. The results showed that a PLS-DA model built upon 20 discriminating metabolites had the best predictive accuracy (AUC = 0.998), and the most significant level (p = 3.34×10^-5). In addition, all samples from the external prediction set were classified correctly, suggesting that the PLS-DA model built upon 20 discriminating metabolites had high sensitivity and specificity.

Mequindox is a member of the quinoxaline family, and widely used in Chinese veterinary industry as an antibacterial drug. Toxicity of mequindox and the underlying mechanisms have been studied previously. However, endogenous metabolic alterations in animals caused by mequindox exposure are currently unknown. This study investigated the effects of acute mequindox exposure (10 mg/kg body weight) on urinary metabonome in pigs using an NMR-based metabonomics approach. The results showed that acute mequindox exposure significantly decreased the levels of creatine, hippurate and p-cresol glucuronide in the urine of treated pigs, whereas the levels of p-cresol and benzoate increased significantly. The changes of urinary metabolic profiles were long-lasting, and did not recover at 144 h post-exposure. At the dose given, mequindox mainly caused disturbance of gut microbial ecosystem. This study provided useful information on the effects of mequindox on metabolism in pigs, and might guide the safe application of mequindox in veterinary industry.

Compound acetylsalicylic acid tablet is a clinical drug having antipyretic, analgesic and anti-inflammatory effects. The present methods to analyze the active ingredients in this drug have many disadvantages. In this study, we used polydimethylsiloxane (PDMS)-assisted diffusion ordered NMR spectroscopy (DOSY), DOSY-correlated spectroscopy (COSY), and relative quantitative ¹H NMR techniques to analyze the three main active ingredients in this drug. The content ratios among the 3 components could be obtained. It is argued that PDMS-assisted DOSY provides a convenient and efficient method for pharmaceutical quality control of compound acetylsalicylic acid tablets.

The critical micelle concentration (CMC) of Triton X-100 (TX-100) and cetyltrimethylammonium bromide (CTAB) was measured by nuclear magnetic resonance (NMR) technologies at different temperature. The average residence time of TX-100 and CTAB were determined by one-dimensional line shape analysis. The average residence time of both compounds decreased with increasing temperature, suggesting that the rate of TX-100 and CTAB molecules entering/leaving the micelles increased with temperature. The apparent activation energy of the exchange process was calculated with the Arrhenius equation, and found to be 17.6 kJ/mol for TX-100 and 75.3 kJ/mol for CTAB. The apparent activation energy likely reflected the strength of hydrophobic interaction; while the average residence time depended not only on the hydrophobic interaction but also on the molecular structure.

Two unknown polyether modified organic silicone surfactants were studied by NMR techniques (i.e., ¹H NMR, DEPT135, ¹³C qNMR, ¹H-¹H COSY, ¹H-¹³C HSQC, ¹H-¹³C HMBC, ²⁹Si qNMR and ¹H-²⁹Si HMBC). The NMR signals were assigned. The results indicated that the two silicone surfactants could be distinguished from each other by ¹H-²⁹Si HMBC. The main component of sample A was polyethylene oxide modified polydimethylsiloxane surfactant with a linear ABA structure, and sample B had a comb BAB structure. The average molecular weight of the two compounds was 1 967 and 7 191, respectively.

A quantitative ¹H NMR method was established for analysis of contents of vitamin B1, vitamin B2, nicotinamide and calcium pantothenate in Compound Vitamin B Tablets. The experimental settings were as following: delay time (D₁) 1.0 s, pulse width (P₁) 3.0 μs, number of sampling (NS) 500 times, 1,4-benzenedialdehyde peak at δ 10.12 (2H) as the internal standard, and deuterated DMSO-d₆ as the solvent. The peaks for quantitative analysis were: vitamin B1 at δ 9.60~9.90 (1H), vitamin B2 at δ 11.36 (1H), nicotinamide at δ 9.01 (1H) and calcium pantothenate at δ 0.78 (12H). The slopes of the standard curves obtained for the 4 components were close to theoretically predicted values. Calibration with vitamin B1 and calcium pantothenate reference substances yielded correlation coefficients (r) above 0.999 and recovery ratio near 100%. Finally, the method was applied to 4 real samples, and the results suggested that it is simple to use, accurate and reliable.

A slotted-tube microwave cavity with a volume of 11 mL was designed for miniaturized high-performance rubidium atomic frequency standards (RAFS). The magnetic field orientation factor of the cavity was measured to be 0.83. A miniaturized physics package for RAFS was designed based on the dimensions of the cavity, and a desk prototype of RAFS was built. Short-term frequency stability of the miniaturized RAFS built was measured to be better than 2×10¹²/√τ, suggesting that the microwave cavity can be utilized for construction of RAFS with small size and high performance.

Polarization of hyperpolarized xenon-129 gas prepared by spin exchange optical pumping (SEOP) is affected by many operating parameters. In this study, we measured polarization of hyperpolarized xenon-129 gas on a low field (0.002 T) NMR system, and used the results of such measurements to optimize the operating parameters of SEOP. The optimal operating temperature was first determined. Then the optimal building time for isotopically enriched and naturally abundant xenon-129 gases was determined to be 15 min and 22 min, respectively. The pressure and composition of the gases in the optical pumping process were then optimized to minimize spectral shift, broadening and lineshape change of the rubidium atom absorption lines. Finally, the optimal laser wavelength was determined. In conclusion, measuring polarization of hyperpolarized xenon-129 gas with low-field NMR provides an experimental basis for optimizing operating parameters of SEOP.

Bone mineral density (BMD) measured by dual energy X-ray absorptiometry is often used as an index for diagnosis of osteoporosis. However, ionization radiation is present in X-ray BMD measurement, and the result can be inaccurate in some caese. In this work, we constructed an NMR equipment that used a Q-switch to achieve echo time as low as 80 ms, and thus have the potential to be used for BMD measurement. In the T₂ relaxation time spectra of bone measured by this equipment, the peak area at 300~500 ms was found to change linearly with the BMD measured by X-ray absorptiometry. Based on this observation, we put forward a method to measure in vitro BMD with NMR T₂ relaxation time spectra. This kind of method has advantages such as high measuring speed, no ionization radiation, and high cross-period comparability.

Moisture in wood affects its physical properties. Time-domain nuclear magnetic resonance (TD-NMR) technique can be used to monitor water state changes and migration, providing a powerful tool to study changes of water in wood during drying and product processing. In this study, water states and migration in Beijing poplar were monitored by TD-NMR during high-temperature drying. Free induction decay (FID) and transverse relaxation time (T₂) of water were measured. The results showed that both FID and T₂ signals were linearized with moisture content, hence the moisture content in the whold drying process can be calculated. Free water with long relaxation time in heart wood showed a trend of first decrease and then increase and decrease again at last, this phenomenon did not happen in the sap wood. In the heart wood, the most abundant moisture is the water with magnitude of 10 ms relaxation time. But the moisture content of each water state has small difference in sap wood, and the most abundant moisture is the water with magnitude of 100 ms relaxation time. During high temperature drying process, the moisture percentage decrease faster in sap wood than that in heart wood, and the evaporation rate of free water is significantly faster than the bound water.

Ferrocenyl compounds were widely used and extensively studied due to their excellent thermal, redox, electronic, optic, magnetic and catalytic properties. Electron spin resonance (ESR) is a method that can be used to study paramagnetic behaviors, electronic structure, electron transfer and molecular interactions of ferrocenyl compounds. In addition, ESR possesses advantages such as high sensitivity, easy sample treatment and nondestructive testing. This article reviewed recent progresses in ESR studies on ferrocenyl compounds.

J coupling gives rise to spectral multiplets (i.e. resonance from one spin is split into a group of equally spaced lines placed symmetrically around the chemical shift). Such spectral splitting contains information on molecular structure, and is therefore useful for structural elucidation. However, when the number of spin increases and many spectral multiplets are present, the spectra, especially proton spectra, could become very crowded, making structural elucidation and quantitative analysis difficult. Using the pure shift (i.e., broadband homonuclear decoupling) proton NMR technique, one could collapse spectral multiplets into singlets, and obtain spectra containing only chemical shift information. In this paper, we give brief introductions to three most widely used pure shift proton NMR techniques, namely BIRD, ZS, and PSYCHE, and describe typical applications of such techniques.