Solvent signal suppression is essential for biological NMR spectroscopy. For applications using reversed-phase HPLC-NMR or studies of natural product extracts with mixed solvents, simultaneous suppression of the signals from multiple solvents is often required in order to get high quality NMR spectrum. There are a number of approaches developed for solvent signal suppression. Although most of these approaches can be used for multiple solvent signals suppression, simple methods with high suppression efficiency are still needed. In this article, double WATERGATE approach was extended for such purpose. Two simple extensions, DSSW5 (Double Solvent Suppression WATERGATE) and GASP-W5 (GASP-based WATERGATE), were established and used to acquire one- and two-dimensional (1D & 2D) NMR spectra in HPLC-NMR and from natural product extracts, respectively. The results demonstrated that the new methods are easy to implement and applicable for routine NMR spectroscopy.

A series of amides of piperidin were synthesized and used for studies on the partial doublebond feature of the amide bonds. ¹H and ¹³C NMR spectra of 2-(3, 5-dinitrophenyl)-1-(piperidin-1-yl) ethanone (compound 1) were acquired at various temperatures. The results showed that the C-N bond of the piperidin amides exhibited partially double-bond character at 20 ℃ (293 K) , suggesting that the chemical shifts of a and b, c and d in compound 1 were very- different due to the two rotameric states. With increasing temperature, the two peaks of non-equivalent -CH₂- groups collapsed into one peak due to the fast rotation of the C-N bond. The rate constant for the dynamic process detected for compound 1 was 380 s^-1, and the free energy of activation for compound 1 at coalescence temperature (343 K) was 67 kJ · mol^-1.

The time domain analysis method provided by the jMRUI software was applied to quantify in vivo ¹H magnetic resonance spectra obtained from the brain with simulated priori knowledge base set. The residual water signals were filtered through HankelLanczos singular value decomposition (HLSVD) algorithm. The QUEST arithmetic was used for metabolite quantification, with simulated short echo spectra (TE=28 ms) of the metabolites as prior knowledge. The results showed that that the concentrations of brain metabolites could be estimated effectively from the ¹H spectra using the QUEST method. It was demonstrated that, by introducing priori knowledge base sets, the difficulties in metabolite quantification concerning the complexity of the spectra and peak overlapping could be overcame.

The polymerization reaction between coniferin and soluble lignin in the effluents from paper mill, catalyzed by lignin oxidase, was investigated. Gel permeation chromatography (GPC) was used to analyze the molecular weights of the polymerization products. It was shown that the molecular weight Mn increased from 326 to 1 068. FT-IR, isotopic tracer method and NMR spectroscopy were employed to determine the chemical structure of the polymer obtained. It was demonstrated by 13C tracer method and 13C NMR that the polymer yielded contains interconnected β-O-4, β-β, β-5 and β-structures. The content of coniferyl alcohol was relatively high in the product. The polymerization products of lignin became increasingly insoluble and easier to precipitate as their molecular grew higher. The polymerization reaction, therefore, can be used to reduce the concentration of water-soluble lignin in the effluents from paper mill.

In this paper the reaction product of α-tocopherol and DPPH^·radical in DMSO was analyzed by NMR spectroscopy, and found to have a tetraalkylbenzoquinonoid group. The reactive ratio of α-tocopherol to DPPH^· was confirmed to be 1∶2 with ESR spectroscopy. Based on these two results, it is proposed that the reaction pathway of α-tocopherol and DPPH^·has two steps.

Cyclovirobuxinum D was isolated from traditional Chinese medicine Buxus icrophylla Sieb. et Zucc, for treating coronary heart disease and arrhythmias. High performance liquid preparation chromatography was used for separation and purification. ¹³C and ¹H chemical shifts of the compound were assigned using 1D and 2D NMR techniques including ¹H NMR, ¹³C NMR, COSY, DEPT, HMQC and HMBC. The structure of the compound was determined from the NMR data.

Rhapontin, 3-hydroxy-5-(2-(3-hydroxyl-4-methoxyphenyl) ethenyl) phenyl-β-D- glucopyranoside, was a natural product isolated from the plant. Its structure was elucidated by combined use of 1D NOE and 2D NMR techniques including ¹H-¹H COSY, HMQC and HMBC. The ¹H and ¹³C chemical shifts of the compound were completely assigned. Corrections were made for the incorrect previous assignment.

The structure and configuration of N, N′-didodecylacetamidinium bicarbonate were determined by ¹H-, ¹³C-, and various two dimensional nuclear magnetic resonance spectroscopy, including gCOSY (homonuclear correlation spectroscopy), gHSQC (¹H-detected heteronuclear single quantum coherence) and gHMBC (¹H-detected heteronuclear multiple-bond coherence). The ¹H and ¹³C chemical shifts were assigned. Effects of temperature and solvents of different polarity (CDCl₃ and DMSO-d₆) on the ratio of different configuration were also investigated. The compound was shown to have two configurations in CDCl₃, A[E, Z] and B[E, E], and the portion of B[E, E] isomer increased with the temperature. Only the A[E, Z] isomer existed in the DMSO-d₆ solution.

AM-MAA copolymer was prepared by treating the aqueous solution of monomers with UV irradiation. The percent conversion was up to 100% with a 45 min irradiation. ¹H NMR、¹³C NMR、DEPT、gHMQC、gHMBC and proton relaxation measurements were used to analyze segmental motion, sequence structure and the linking mode of the monomers in the copolymer. The results of relaxation time measurements revealed that the longer the reaction time was, the quicker the movement of the molecules in the main chain. However, the motion of the polymer segments was not influenced significantly by the increase of irradiation time．

A new NQR(Nuclear Quadrupole Resonance)-based method for explosive detection is introduced. The underlying principles and the conditions for explosive detection are analyzed. A test system for explosive detection based on NQR was developed, which was shown to be able to detect NQR signals from RDX, TNT, HMX, PETN, and TETRYL explosive samples at room temperature. These results demonstrated that it is feasible to use the method for explosive detection.

Inductive effect is one of the most important effects in organic chemistry. We propose a new inductive effect parameter for neutral groups (I_G), which describes the “inner-shielding” and “outer-shielding” effects in NMR. It was shown that the ¹³C NMR chemical shifts (CS) of alcohols can be predicted from I_G, polarization effect index (PEI) and α, β, γ structural parameters as follow:

CS=-2.3+[20.696 7(ΣΔI)+18.386 5(ΣΔPEI)-0.011 1(ΣΔI/ΣΔPEI)

+1.239 7(ΣΔPEI/ΣΔI)-5.800 9N^α_C+4.260 4N^β_C-1.758 3

-3.346 0N^γ_C+32.376 3]. 
Experimental results showed that the above model had good stability and predictive ability. The correlation coefficient R of the equation was found to be 0.994 7, and the cross-validation correlation coefficient R_CV by the LOO method was 0.992 7.

An equation: δ_cal=δ_0n+Δα+Δβ+Δγ+c, for the calculation of ¹⁵N chemical shifts of substituted imines was provided. The five substituent parameters were obtained by linear least square regression analysis on the data from four different kinds of imines (PhCH=N-X, RHC=NC₆H₅, RHC=NCH₃ and RHC=N-i-C₃H₇). The accuracy of the results calculated with the model was checked using 34 ¹⁵N NMR chemical shifts in 34 substituted imines as a test set. The confidence limit was found to be 99.5%, and the calculating errors for about 95% of the compounds were less than 3.0 (with relative errors of 0.3%). The effects of p-substituent on the chemical shifts of the ¹⁵N atoms of aromatic imines were also analyzed.

An active Q-switching circuit using a transformer is described for reducing the recovery time of NQR probes. A MOSFET was used to control the coupling and decoupling states of the Q-switching circuit to the probe so that it did not operate during the reception of NQR signals. The performance of the circuits was demonstrated by experimental results. It was shown that the circuit did not create new ringing, and caused no loss in sensitivity.

The configuration of multiple radiofrequency receivers is becoming more and more popular on magnetic resonance imaging (MRI) systems nowadays. One problem associated with multiplereceiver MRI is that the noise levels may differ among different receiver channels, affecting the homogeneousness of the reconstructed images. In the paper, a noise homogenization method for multiplereceiver MRI is proposed. In the method, the scaling factor for each receiver channel is adjusted according to the noise level in the channel measured by a modified Y factor method. The performance of the proposed method was evaluated experimentally.

A spiro compound with polyfluoroalkyl group was synthesized. Its structure was elucidated by ¹H NMR, ¹³C NMR, IR, MS, 2D NMR and X-diffraction. The spectral features and the space structure of the compound were also discussed.

2-Chloro-4-(4-chlorophenoxy) acetophenone and 4-chloro-2-(4-chlorophenoxy) acetophenone are isomeric compounds. It is difficult to distinguish these two compounds by 1D NMR. In this paper, ¹H NMR and ¹³C NMR chemical shifts of the two compounds were assigned, and 2D NMR techniques were used to elucidate their structures.

Recent NMR studies on aggregation and modulation of PEO-PPO-PEO block copolymer in aqueous solution are reviewed. Because of the unique advantages of the NMR techniques, ¹H, ¹³C and ²H NMR, as well as NMRbased relaxation and diffusion measurements, have been widely used for studying the aggregation and interaction of PEO-PPO-PEO block copolymer in complex systems. The results of many research groups, including our own, have indicated that modulation of the properties of PEO-PPO-PEO block copolymer in solution plays the most important role in the applications of this compound.

Protein isotope labeling is crucial for NMR studies of the three-dimensional structure and dynamics of proteins in solution. Protein expression systems and isotope labeling have been widely used, both of which have been proven useful. However, as the field progresses, the studies on protein with NMR are becoming increasingly difficult with these conventional techniques. Recently, some new isotope protein labeling strategies and new protein expression systems have emerged as tools for studying large proteins by solution NMR. In this paper, these novel protein isotope labeling methods and alternative protein expression systems are reviewed.