HdeA, a molecular chaperone localized in the bacterial periplasm, plays a vital role in maintaining protein homeostasis. Previous studies of HdeA were mainly carried out in in vitro conditions, limiting our understanding of the mechanism of HdeA in its native environment. Outer membrane vesicles of bacteria are extracellular vesicles released by cells into the extracellular milieu in a controlled manner, with contents almost identical to the periplasmic environment. Thus, by enriching HdeA into the bacterial outer membrane vesicles (OMVs), we investigated the conformational changes of HdeA within OMVs via nuclear magnetic resonance (NMR) spectroscopy. The results reveal that HdeA exhibits an acid-dependent conformational change in its native environment. The high-resolution spectrum of HdeA in OMVs indicates that under low pH conditions the function of HdeA is activated through residues S15, W16, T17, S27, T32, E36, G54, T57, C66, Q71, F74 and D83. Moreover, the NMR measurement of HdeA within OMVs provides a promising way for in situ investigation of mechanisms of other periplasmic molecular chaperones via NMR spectroscopy.

This paper investigated the impact of different b-value acquisition ranges (from 0 to 2 500 s/mm²) on the quantitative parameter calculation of six body diffusion models, including mono-exponential (Mono), diffusion kurtosis imaging (DKI), intravoxel incoherent motion (IVIM), stretch exponential model (SEM), fractional-order calculus model (FROC), and continuous time random walk model (CTRW). The influence of different b-value acquisition ranges on parameter calculation was evaluated through correlation between diffusion model parameters, t-test, and the ability to differentiate benign and malignant prostate lesions. The results showed that compared with that of the reference sampling scheme (0~2 500 s/mm²), the difference of the mean value of region of interest (ROI) with the same diffusion parameters gradually increases as the maximum b-value decreases, but the correlation decreases only slightly, and the ability to differentiate between benign and malignant prostate lesions remains at a similar level. Based on the experimental results, a b-value range of 0~1 500 s/mm² is recommended for clinical practice, because this scheme takes collection efficiency into account, the correlation of more than half of its parameters with those of the reference sampling scheme is not less than 0.98, and the difference in the values of area under the curve (AUC) between benign and malignant differentiation is less than 0.01. In addition, the sensitivity of different diffusion models to the b-value scheme varies, with the parameters of SEM and CTRW models being relatively less affected by the b-value range.

This study aims to classify and differentiate mucinous and serous cystic neoplasms of the pancreas using a multi-source feature classification model based on deep learning for preoperative auxiliary diagnosis. Deep learning features and radiomics features were extracted from segmented images using deep learning and radiomics technology, respectively. Clinical features were also evaluated and quantified. LASSO (least absolute shrinkage and selection operator) and cross-validation methods were applied to screen the features, and two multi-source feature models were constructed: the radiomics combined with deep learning (RAD_DL) model and the clinical feature combined with RAD_DL (Clinical_RAD_DL) model. Traditional radiomics (RAD) and deep learning (DL) models were used as controls. SVM (support vector machine), ADAboost (adaptive boosting), Random Forest, and Logistic were selected for classification. The Clinical_RAD_DL feature model shows the best classification performance, with the accuracy of 0.923 1, recall rate of 0.882 4, precision of 0.882 0, F1-score of 0.882 2, and AUC value of 0.912 6. The experimental results indicate that the multi-source feature classification model based on deep learning has good performance in classifying pancreatic serous cystic neoplasms and pancreatic mucinous cystic neoplasms, and can assist clinical accurate diagnosis and treatment.

In this paper, we presented a quantitative refocused INEPT (Refocused Insensitive Nuclei Enhanced by Polarization Transfer) method based on simulated annealing optimization, which utilizes the optimized polarization transfer and refocus delay set to yield nearly uniform enhancement for CH, CH₂ and CH₃ groups. The 180° composite pulses are applied in ¹³C channel to overcome the inhomogeneity of B₁ field and the offset effect to improve the measurement reliability. Simulated annealing optimization is further applied to achieve quantitative spectral editing of refocused INEPT. The above methods were validated using model compounds such as artemisinin and simvastatin, and the relative standard deviations of the quantitative integrals with Case I delay set were 1.6% and 3.3%, respectively. As an application of the proposed method, major fatty acid compositions in soybean oils were determined using quantitative refocused INEPT, and the results were consistent with those determined by conventional quantitative ¹³C NMR, while the measurement time was significantly reduced. The quantitative refocused INEPT method is particularly attractive for rapid, accurate detection of complex systems such as petroleum and polymers.

The structure of hybutimibe was analyzed by ultraviolet absorption spectroscopy, infrared absorption spectroscopy, mass spectrometry, nuclear magnetic resonance (¹H NMR, ¹³C NMR, DEPT, ¹H-¹H COSY, ¹H-¹H NOESY, ¹H-¹³C HSQC and ¹H-¹³C HMBC) spectroscopy and single crystal diffraction. The ¹H and ¹³C NMR signals of hybutimibe were assigned. The crystal structure of hybutimibe was studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and powder X-ray diffraction (PXRD).

Darolutamide is an important drug for the treatment of prostate cancer. When studying its synthesis process, three impurities A, B, and C were discovered and purified in the first step of Suzuki coupling and the second step of hydrolysis deprotection reactions. Impurities A and B came from the first-step reaction, and impurity C came from the second-step reaction. The structures of impurities A and B were further determined through high-resolution mass spectrometry (HRMS), ¹H nuclear magnetic resonance (NMR), and ¹³C NMR methods. It was discovered that impurities A and B were the deborated pinacol ester product of compound 2 and the double coupling product of compound 1, respectively. The accurate structures of compound 3 and impurity C were determined using HRMS, ¹H NMR, ¹³C NMR, ¹H-¹H COSY (correlation spectroscopy), ¹H-¹³C HSQC (heteronuclear singular quantum correlation), ¹H-¹³C HMBC (heteronuclear multiple bond correlation) and ¹H-¹H NOESY (nuclear overhauser effect spectroscopy). The formation mechanisms and avoidance methods of these impurities were also discussed.

Nuclear spin singlet is a special quantum state that lasts longer than T₁ and can be used to study slow diffusion and motion between molecules. The preparation of singlet states is the key to their successful application. Currently, various methods for preparing singlet states have been reported in the literature, which are mainly applicable to isolated two-spin systems. When the nuclear spin involved in the singlet state is coupled to other spins, the preparation efficiency of the singlet state often decreases. In this paper, taking a three-spin system as an example, we studied the effect of non-singlet spin coupling on the preparation efficiency of singlet states under different coupling configurations. The simulation results show that as the singlet spin changes from weak coupling to strong coupling, the preparation efficiency of the singlet state will maintain a certain stability when the coupling between the singlet spin and the non-singlet spin is symmetrical. This characteristic can provide a reference for selecting appropriate spins to prepare singlet states in complex systems. We experimentally verified this conclusion using a three-spin system in the N-acetyl-L-aspartic acid (NAA) molecule. By adjusting the pH of the NAA molecule, the three-spin system can transfer from weak coupling to strong coupling. The experimental results show that the preparation efficiency of the singlet state is significantly higher when the three spins are in strong coupling than that when the spins are in weak coupling.

In recent years, several research units have introduced solid-state nuclear magnetic resonance (NMR) spectrometers. So far, solid-state NMR spectrometers have not been domestically manufactured and the equipment is completely dependent on imports. Therefore, both the instruments and sample preparation systems are expensive. The sample loading rotor is the crucial consumable in the magic angle spinning (MAS) NMR experiment. However, the extremely tough requirement on dimensional precision poses a great challenge in the machining of rotors. By analyzing the characteristics and practical applications of the imported 3.2 mm rotor and its sample preparation tools, we optimized the connection between the rotor parts, improved the sealing of rotor, and developed the MAS rotor and its sample preparation tools independently. The test results show that the self-made MAS rotor can run normally at 12 kHz, which meets the requirements of conventional solid-state NMR experiments. The sample preparation toolbox has advantages of simplicity and safety.

Conventional high-field nuclear magnetic resonance (NMR) spectrometer necessitates advanced superconducting technology, which usually involves a magnet of large volume and high maintenance cost. Moreover, strong magnet often has severe magnetic field inhomogeneity, leading to NMR line broadening. Zero- to ultralow-field (ZULF) NMR emerged as a complementary approach to traditional high-field NMR techniques. In this paper, a portable zero-field NMR spectrometer based on a compact atomic magnetometer was developed, which adopted an integrated control system based on a multi-function data acquisition card (National Instruments PCIe-6353). The spectrometer is of a main magnetic field strength less than 1 nT and enables achieving high-resolution J-spectrum under zero-field environment. Specifically, a series of single pulse excitation experiments for the initial adiabatic state was carried out to calibrate the triaxial magnetic field coils. Then a modified composite pulse sequence was developed to further validate the performance of zero-field NMR spectrometer by single-spin control experiments for the ¹³C-¹H spin system.

The accurate encoding of the spatial position of imaging voxels is crucial for the spatial localization of magnetic resonance imaging (MRI). To guarantee spatial encoding accuracy, it is essential to obtain high-performance gradient magnetic fields. Gradient waveform generators are the core part of generating gradient magnetic fields. This paper briefly introduces the working principle and components of gradient waveform generator, summarizes the research progress of gradient waveform generator based on different design schemes in the past 20 years, and discusses the realization methods in detail of gradient waveform pre-emphasis. Besides, the future research and development direction of gradient waveform generators is prospected.