Genetic instability of deoxyribonucleic acid (DNA) repeating sequences has been found to associate with hereditary neurodegenerative diseases.  It has been suggested that self-expansion of CTG and CCTG repeats would occur through the formation of unusual structures during DNA replication, leading to myotonic dystrophy type 1 (DM1) and myotonic dystrophy type 2 (DM2), respectively.  Although x-ray crystallography is a powerful technique in solving DNA structures, there has not been any successful structure determination of CTG or CCTG repeats probably due to the fact that the growth of diffraction-quality crystals has been hampered by the intrinsic flexibility of these repeating sequences.  Therefore, nuclear magnetic resonance (NMR) spectroscopy remains to be the only technique that allows studying DNA structures at individual residue level.  Recently, we have successfully overcome the challenges in NMR structural studies of CTG and CCTG repeats, including the severe signal overlap due to the repetitive nature of repeating sequences and the increase in spectral complexity owing  to the presence of multiple conformers and conformational exchange.  With appropriate sample design, sample handling technique, sequence modification and/or single-site substitution experiments, we have determined the structural features of CTG and CCTG repeats using ¹H and ³¹P NMR spectroscopy.  This review provides an account of the strategies that have been applied in these studies.

Time-domain analysis (TDA) is one of the most important NMR methods used in fluid identification and porosity calculation. It shows great advantages in reservoir evaluation, but there are also certain limitations. In order to investigate the adaptability of TDA in hydrocarbon identification under different reservoir conditions, numerical simulation was used in this study to analyze the factors influencing the outcomes of TDA, including longitudinal relaxation time T₁, polarization time T_W, porosity, hydrocarbon saturation, hydrogen index HI and polarization function. It is concluded that when acquisition mode D9TW is chosen, the viscosity of oil that can be measured by TDA is less than 9 mPa.s. After changing the short waiting time up to 2 s while keeping the long waiting time constant, the minimal viscosity reduces to less than 4 mPa.s. We also found the intensity of differential signals correlated positively with all the influencing factors mentioned above. With real low SNR NMR data, TDA can effectively identify hydrocarbon and calculate porosity only under the conditions that the differential porosities of hydrocarbon are greater than 1.5 p.u.

A new wavelet transform-based method for measuring the oil content of fiber with low-field NMR was introduced. Firstly, free induction decays (FID) of the standard fibers were collected and used to calculate the calibration curve through linear fitting. Secondly, the signals of the testing fiber were collected with different numbers of averages, and wavelet soft threshold was used to filter each of the collected signals. Finally, the oil content of the fiber was calculated by comparing the filtered NMR signals with the calibration curve. Practical applications were used to validate the  effectiveness of the new method.

In NMR logging, the noise amplitude of ringing is often high, impacting echo signals detection. The phase-alternate pulse sequence (PAPS) technique is a conventional method to reduce NMR ringing. However, the amplitude of ringing is frequency-dependent, and the PAPS technique is effective at certain frequency, leading to a lower vertical resolution. Taking advantage of the feature that the echo signals change with the variation of RF pulse wherase the ringing noise keeps constant, we proposed a novel method, combining PAPS and stackingbetweenechoes, to reduce NMR ringing under downhole condition. The results showed that this method has improved efficiency. The echo train measured by the new method had the characters of high SNR and high vertical resolution compared to that measured by the PAPS technique, and the stacking between the echo trains was not limited to one frequency.

The distribution of water and oil is a very important property of porous media such as rock cores. The study on water flooding is an essential part in the research of enhanced oil recovery (EOR). Nuclear magnetic resonance (NMR) diffusion-relaxation two-dimensional (2D) distribution function (spectrum) provides a large variety of information of fluids in porous media. Compared with NMR 1D relaxation spectrum, the 2D spectrum greatly improves the ability to separate water from oil. In this article, two sets of core flooding experiments were conducted. The relaxation spectra of water were extracted from the 2D spectra acquired with different oil saturations,and used to calculate wettability and distribution of water and oil in different pores under the condition of higher oil viscosity. It was shown that the difficulty of oil and water separation by traditional 1D NMR relaxation spectrum can be overcome by using the 2D method.

LD130 is the fusion protein of baculoviruse Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV). The N terminal conserved region of subunit F₁ in LD130 is the fusion peptide, which actively induces membrane fusion processes. NMR methods were used to identify the solution structure of the fusion peptide under membrane simulated enviornment at low pH. The fusion peptide appeared to be an amphiphilic structure composed of a flexible coil in the N-terminus, and a regular α-helix from L3 to V16. The structure of the LD130 fusion peptide allows us to further investigate the structure-functional relationship of the fusion peptide.

The paper introduces the design of the software system in an integrated NMR spectrometer console. The software system is composed of two parts: the console software composed of embedded Linux operation system and real-time control software and the GUI control software in PC. The communication between the console and PC is achieved by network and programmed based on SOCKET such that the console can be controlled and updated in remote. The software system was tested by NMR experiments. This paper elaborates the design concepts and methods of the software system.

A completelly functional 500 MHz NMR spectrometer, developed by ourselves, was evaluated for its performance. System debugging was performed to demonstrate the basic functions of each unit. Performance tests were performed to evaluate the specifications, including power linearity, signal stability and field-frequency lock system. The solvent suppression experiement was performed to verified the functionality of the spectrometer. Satisfactory results (Line shape 0.43/5.46/10.73 Hz; signal-to-noise ratio 728∶1) were obtained with a normal indirect detection probe manufactured by JS Research Inc. The ourcomes of the experiments demonstrates that the self-developed NMR spectrometer can fulfill the demands of routine NMR experiments.

Slotted tube cavity has been used in rubidium atomic frequency standards, but the microwave field distribution inside the cavity is unknown. Recently we calculated the microwave field distribution inside the cavity using high frequency structure simulation software (HFSS), and measured the field distribution experimentally with the optical-microwave double resonance method. The theoretical and experimental results were found consistent with each other. The results showed that magnetic lines of the microwave field lay along the cavity axis, impling that the cavity is suitable for applications in atomic frequency standards. The results also showed that the field distribution is spatially inhomogeneous, suggesting that the cavity needs to be improved further, since field inhomogeneity could affect the signal intensity of atomic clock transition.

The mode matching method was used to analyze the resonant characteristics of TE₀₁₁ and TE₁₁₁ modes of a cylindrical resonant cavity loaded with ceramics material. The cavity is of smaller volume than those commonly used, and can be utilized in miniaturized rubidium atomic clocks. By calculating the resonant frequency of the cavity and comparing the result with that calculated with the commercial software, the correctness of the method was verified. In addition, the effects of the dimension of ceramics material on the resonant frequency were analyzed.

Two glucosylated steroidal saponins of Tb were elucidated as pennogenin-3-O-α-D-glucopyranosyl-(1→3)-[α-L-rhamnopyranosyl-(1→2)]-β-D-glucopyranoside (1), and pennogenin-3-O-α-D-glucopyranosyl-(1→4)-α-D-glucopyranosyl-(1→3)-[α-L-rhamnopyranosyl-(1→2)]-β-D-glucopyrannoside (2) by MS, ¹H NMR, ¹³C NMR, COSY, HSQC and HMBC analysis. 1 and 2 are new compounds. The ¹³C and ¹H NMR chemical shifts of these two new compounds were assigned.

One known ent pimarane type diterpenoid, 3α, 19-dihydroxyl ent pimara-  9(11), 15-diene, has been isolated from the roots of Euphorbia yinshanica for the first time. Its structure has been  confirmed by 2D spectral methods (¹H-¹H COSY, HMBC, HMQC, ROESY), and its NMR signals have been  first completely assigned.

The structures of pure and mixed enantiomer of moxifloxacin hydrochloride were elucidated by NMR. The chemical shift of the spectral peaks were assigned using ¹H and ¹³C NMR, COSY, HSQC, HMBC and 2D NOESY techniques, as well as ¹⁹F-¹³C coupled splitting. It was found that ¹⁹F-¹³C coupling exists not only in the sixmembered ring, but also in the fivemembered heterocyclic ring, and that ⁴J_FC in the five-membered heterocyclic ring is larger than ³J_FC and ⁴J_FC in the sixmembered ring. The spectral characteristics of the pure and mixed enantiomer of moxifloxacin hydrochloride were summarized. A method was proposed to differentiate the pure and mixed enantiomer of moxifloxacin hydrochloride.

As widely used medicines in the world, phytomedicines played important roles in human health. The analysis of herbal medicines is important for the development of new drugs and functional food. Such analysis includes traditional methods, including metabolite extraction, component isolation and structure elucidation, and the hyphenated techniques with the combination of chromatographic and spectroscopic techniques. Here, we review the general procedures of traditional methods and hyphenated techniques for phytomedicine analysis with emphasis on the hyphenated HPLC-DAD-SPE-NMR-MS techniques.