Hydrogenation reaction of propyne on Pd-Cu bimetallic catalysts was studied using the heterogeneous parahydrogen-induced polarization (PHIP) nuclear magnetic resonance (NMR) technique. Incipient-wetness impregnation and sequential impregnation were used to prepare Pd-Cu/SiO₂ bimetallic catalysts with different composition and morphology. With the ALTADENA (Adiabatic Longitudinal Transport After Dissociation Engenders Net Alignment) method, it was observed that both the composition and morphology of the bimetallic catalysts had significant influence on the efficiency of PHIP. The catalysts with lower Pd/Cu atom ratio had lower activity but higher polarization efficiency. Compared to isometric impregnation method, the palladium atoms in the Pd-Cu/SiO₂ catalyst synthesized with the sequential impregnation method mostly stayed on the surface of bimetallic nanoparticles, generating larger Pd ensembles and leading to higher catalytic activity and lower polarization efficiency.

Diffusion ordered NMR spectroscopy (DOSY) can be used to determine the apparent molecular weight of proteins (M_protein) by measuring self-diffusion coefficient (D_t-protein). However, D_t-protein is also affected by the property of buffer solution, making the measurements complicated. In this work, 3-(trimethylsilyl) propane sodium sulfonate (DSS) was used as the internal reference molecule and the diffusion coefficient ratio between the target protein and DSS (D_r) was used to characterize the protein in solution. This method reduced the effects of buffer system on M_protein determination, yielding more accurate M_protein measurement. The D_r values of reference proteins with different molecular weight were determined. A correlation curve between D_r and M_protein was established (lgM_protein=-2.6488 lgD_r-0.7863, R²=0.997). Finally, D_r of the C-terminal domain of SARS-CoV main protease (M^pro-C) was determined and to yield its molecular weight. Accuracy and practicability of the fitting curve were demonstrated.

Diffusion ordered spectroscopy (DOSY) is widely used to measure molecular self-diffusion coefficient. In DOSY spectra, the digital resolution of the diffusional coefficient dimension could have notable effects on the measurement accuracy under certain circumstances. In this study, we first assessed the deviation range of the DOSY experiment itself systematically. The magnitudes and sources of deviation induced by digital resolution were then investigated by applying a variety of digital resolutions into the processing of DOSY spectra. It was proposed that relative digital resolution could be compared to relative molecular diffusion coefficient changes, demonstrating directly the effects of digital resolution on diffusion coefficient measurement.

Neodymium-iron-boron (NdFeB) permanent magnets always used to generate a static magnetic field in low field NMR spectrometers has poor temperature stability. Temperature fluctuations will affect the reliability of NMR experiments. In order to improve the stability of low-field magnetic resonance spectrometer, a precise temperature control scheme of permanent magnet based on dual-loop control algorithm was proposed and verified on 0.06 T NMR spectrometer. The results show that the 24 h temperature control accuracy is better than ±0.005℃. And the drift in ¹H resonance frequency decreases from 255 Hz to 15 Hz within 0.5 h, and from 4 950 Hz to 145 Hz within 24 h, compared to that without temperature control. That improves the stability of low-field NMR spectrometer with permanent magnet effectively.

Clinical magnetic resonance imaging (MRI) scanning requires fast image reconstruction. At present, most image reconstruction algorithms are implemented with central processing unit (CPU)-based processing. However, with massive amount of raw data and increasing complexity of the algorithm, CPU-based processing can be inefficient due to lack of computation parallelism and slow computation speed. For this reason, some advanced algorithms are difficult to implement in clinical practice. In this paper, a new image reconstruction algorithm was designed and implemented, which combined multiple cores CPU with multi-graphic processing unit (GPU) to reconstruct magnetic resonance images by distributed parallel computing on the Gadgetron software platform. Taking the Stack of Star (SOS) reconstruction as an example, it was demonstrated that the proposed method improved the reconstruction speed significantly without the requirement of expensive hardware.

Radiofrequency (RF) pulse transmitter is an important part of a nuclear magnetic resonance (NMR) spectrometer. In this paper, a simple NMR RF pulse transmitter was designed based on field programmable gate array (FPGA) and direct digital synthesis (DDS) chip AD9910. Digital modulation of various parameters was achieved. The control accuracy of frequency, phase and amplitude reached 32 bits, 16 bits and 14 bits, respectively. The time accuracy of pulse modulation was 0.01 μs, capable of generating soft/hard pulses with duration longer than 0.1 μs and frequency less than 400 MHz. A "pulse + delay" model was established, and a generic list-type sequence controller was presented, as such the requirements for higher-level control units were reduced. The enveloping waveform of soft pulses was optimized using Hanning window, instead of rectangular window. Simulation and experimental results demonstrated that the use of Hanning window could effectively reduce frequency sidebands of the soft pulses.

Gut microbiota is important for human health. The complex relationship between intestinal flora and bile acid profile has been studied previously. However, few previous studies have determined the profile and functions of bile acids in different intestinal segments, and whether they are related to the distribution of intestinal flora. In this paper, we measured the distribution of bile acids in different intestinal segments of male and female C57BL/6 mice with ultra-high performance liquid chromatography coupled with triple quadrupole mass spectrometry (UPLC-QqQ-MS) based targeted metabonomics analysis and nuclear magnetic resonance (NMR) based untargeted metabonomics analysis. Gender difference in distributions of bile acids were observed, which was more evident in the lower parts of intestine than in the upper part of intestine, especially in the cecum segment. This might be related to the abundance of gut microflora in different intestine segments. This study provided metabolic phenotypes of bile acids in mice of different genders, and demonstrated their interactions with gut microbiota.

Fatty acids are important substrates for the synthesis of membrane phospholipids and other bioactive compounds, and thus play vital roles in mammalian energy metabolism. Fatty acids often bind to proteins in the blood. Albumin is a major carrier and depot of free fatty acids. In this paper, the interactions between human serum albumin (HSA) and fatty acids were studied using nuclear magnetic resonance (NMR)-based histidine selective detection technology T₂W-RD-WaterLOGSY. The spectra of HSA before and after fatty acids binding were compared. It was found that signals of the characterized His in HSA changed significantly with the addition of fatty acids. Two high-affinity binding sites between the HSA and fatty acids were identified from the titration curve. It was also demonstrated that binding to fatty acids could induce conformation changes for HSA.

Long-lived nuclear singlet states are widely used in NMR because they have longer lifetime (T_S) than conventional longitudinal relaxation time (T₁). In this paper, we present a new method to calculate the parameters for preparing long-lived nuclear singlet states, which is applicable to weakly-coupled three-spin systems. It was found that in the same three-spin system, there existed a variety of combination of singlet states with different proportional coefficients. Herein, we prepared two singlet states in an acrylic acid sample. The lifetime of the two states was measured experimentally, which showed significant difference. In addition, the effects of temperature on the singlet state lifetimes of acrylic acid were investigated.

Neuron is the basic unit of nervous system. Studying the fine morphology of neurons is crucial for understanding the structure of neural network and the manner of neural information processing. At present, effective methods to visualize fine morphology of neurons with specific cell types and specific projection are still lacking. In this paper, a recombination vesicular stomatitis virus (VSV) was designed, with nucleoprotein gene mutated and glycoprotein gene deleted. The virus, VSV-△G-NR7A-EGFP, was capable of highlighted morphology of the labelled neurons in a short time. With specific transgenic animals and a helper virus rAAV-EF1α-Dio-Bfp-Tva, it was demonstrated that, a further constructed virus VSV-△G-EnvA-NR7A-EGFP could sparsely and specifically label D2R neurons with nucleus accumbens-lateral hypothalamus (NAc-LH) projection and dopamine neurons with ventral tegmental area (VTA)-NAc projection.

A pentaerythritol stearate sample with unknown composition was analyzed by nuclear magnetic resonance (NMR) spectroscopy (i.e., ¹H NMR, quantitative ¹³C NMR, DEPT135, ¹H-¹H COSY, ¹H-¹H NOESY, ¹H-¹³C HSQC and ¹H-¹³C HMBC). The results indicated that the sample contained mainly monopentaerythritol tetrastearate, but also had small amounts of monopentaerythritol tristearate, monopentaerythritol distearate, dipentaerythritol stearate and tripentaerythritol stearate, as well as a trace amount of multipentaerythritol stearate.

The ultraviolet spectra (UV), infrared spectra (IR), mass spectra (MS) and nuclear magnetic resonance (NMR) spectra (i.e., ¹H NMR, ¹³C NMR, DEPT, HSQC, HMBC, COSY and NOESY) of besifloxacin hydrochloride were acquired and interpreted. All ¹H and ¹³C NMR signals were assigned, and the structure of the compound was determined.

Infrared spectra, ultraviolet spectra, nuclear magnetic resonance (NMR) spectra (i.e., ¹H NMR, ¹³C NMR, DEPT135, ¹H-¹H COSY, ¹H-¹³C HMQC and ¹H-¹³C HMBC) and mass spectra of luliconazole were collected and used to characterize the compound. Differential scanning calorimetry, X-ray power diffraction and elementary analysis were also performed. All ¹H and ¹³C NMR signals of the compound were assigned. The structure of the compound was determined.

Low-field NMR often uses permanent magnet. The signals obtained contain high level of white Gaussian noises, and have low signal-to-noise ratio (SNR). In recent years, many denoising methods have been proposed for low-field NMR measurements. Most of these methods can remove noises without losing useful information contained in the original signals. Wavelet transform is the most popular denoising method among them. In this paper, we first introduced the theory of wavelet transform analysis, followed by review of three wavelet transform denoising methods for low-field NMR, namely the wavelet threshold method, the wavelet transform modulus maximum method and the correlation of wavelet coefficient method. Finally, we showed that four parameters could be calculated to evaluate the denoising performance.