The low intrinsic sensitivity of 2D heteronuclear NOE (HOESY) experiment has hampered its applications in structural analysis. The sensitivity of the HOESY experiment can be improved by ¹H detection (inversed detection). Here we present a 2D ¹³C-¹H HOESY experiment with presaturation to further improve its sensitivity by NOE enhancement. In the proposed experiment, t₁ noises in the ¹H detected HOESY spectra are suppressed by pulse field gradient (PFG) coherence selection and phase cycles. It was demonstrated that ¹³C-¹H NOE correlation spectra with improved sensitivity could be obtained with the proposed experiment.

The interaction between chitosan (CS) and 1-hydroxybenzotriazole (HOBt) was characterized by ¹H NMR spectroscopy, NMR diffusion measurement, and solid-state high-resolution ¹³C NMR spectroscopy. It was found that CS and HOBt can form organic complex in aqueous solution, with hydrogenbond interaction as the main binding force. The association constant of CS/HOBt complex was calculated from the self-diffusion coefficient of HOBt. The interaction between CS and HOBt can potentially be utilized for efficient chemical modification of CS.

NOE-enhanced ¹³C NMR spectroscopy was used to study palladium-catalyzed C_sp-C_sp3 bond formation reaction in real-time. The NOE factors for different peaks of the same substance were found to be almost the same throughout the course of reaction. The changes of the concentrations of the reactants and products were measured quantitatively during the reaction. The results of the NMR experiments provided direct evidence for the reaction mechanism proposed by Lei et al (J Am Chem Soc, 2006, 128: 15 048-15 049).

Diffusion tensor imaging (DIT) is a new magnetic resonance imaging (MRI) technology developed from diffusion-weighted imaging, and can be used for tracking white matter tracts and diagnosis of white matter disorders. To date, most of the DTI studies are carried out on high field MRI scanners. In this study, a line-scan DTI method was implemented on a 0.35 T permanentmagnet open MRI scanner, and used to measure the apparent diffusion coefficient (ADC) and the fractional anisotropy (FA) values in normal adult brain. The ADC and FA values measured in this study were found to be comparable with those obtained on high field strength scanners. It was concluded that it is feasible to perform DTI on low field strength MRI scanners under clinical settings for diagnostic purposes.

Temporal lobe structures are involved in various neurodegenerative diseases. In this study, metabolic profiles in the temporal lobes (TL), hippocampus (HPC) and entorhinal cortex (EC) of SD rats were measured by highresolution magic-angle-spinning (HR-MAS) ¹H NMR spectroscopy. Principal components analysis (PCA) was used to classify the HR-MAS ¹H NMR spectra obtained from different brain regions. It was found that TL has relatively low concentrations of myo-inositol and total creatine and relatively high concentrations of N-acetylaspartate and taurine, while HPC has relatively high levels of glycine and choline compounds, and EC has a high level of glutamine. HR-MAS ¹H NMR spectroscopy may provide a valuable tool for monitoring metabolic changes in the temporal lobe structures related to neurodegenerative diseases and pharmacological challenges.

¹³C NMR spectra of Scutellariae baicalensis extracts were obtained. The ¹³C NMR chemical shifts were assigned. The results suggest that the ¹³C NMR spectra of Scutellariae baicalensis extracts show good repeatability, and the spectral characteristics of the extracts obtained from different Scutellariae baicalensis sample were, in general, similar to those effective flavonoid components baicalein, oroxylin A, wogonin and baicalin. Therefore, the ¹³C NMR fingerprints of Scutellariae baicalensis extract may be used as a criterion to check the authenticity of Scutellariae baicalensis and Scutellariae baicalensis products.

Maintenance of acidbase homeostasis is vital for living organism. Changes of H+ concentration (pH) in blood serum may result in adverse physiological consequences. In this study, the effects of pH changes on human blood serum were studied by T₂-weighted and diffusion-weighted ¹H NMR spectroscopy and saturation transferred difference (STD) experiments. The chemical shifts and concentrations of the metabolites in the serum were measured in serum samples with pH varied between 7.0 and 7.8. It was demonstrated that, from pH 7.0 to pH 7.8, the chemical shifts of many low molecular-weight metabolites drifted upfield and the intensities of phenylalanine, tyrosine, histidine, and lactate in the T₂-weighted NMR spectra changed significantly. No significant changes in the protein signals were observed, except that the signal from albumin lysyl shifted towards upfield.

1H NMR spectroscopy and principal component analysis (PCA) were used to characterize the urinary metabolic profiles of rats treated with aconitine (AC). Compared to the control animals, the rats treated with AC showed increased levels of citrate, 2-oxoglutarate and cis-aconitate, and decreased levels of hippurate and phenylacetylglycine in the urine. Such metabolic changes may have reflected, respectively, the changes in body energy metabolism and in the metabolism of intestinal flora in response to AC treatment. Increase of the 2-oxoglutarate level may have also indicated the neurotoxic effects of AC. The results also showed that the changes in urinary metabolic profiles induced by AC were time- and dosage-dependent, being the most prominent between 0~8 hrs post-treatment, returning gradually towards the control level between 8~16 hrs post-treatment in the low-dose group, but not in the high-dose group. The results obtained in this study may be useful for understanding the toxicological effects of AC.

Polyene macrolide antibiotics are cyclic compounds composed of 25 to 37 carbons, with conjugated polyene fragment and substituted by hydroxyl and glycosidation of aminosaccharide. They have the characteristics of light instability, wide antifungal spectrum, high toxicity by intravenous injection and low toxicity by oral administration. In this study, lucensomycin, an antifungal active substance produced from actinomycetes-1356, was characterized by UV, IR, MS, and NMR spectroscopy. It was found that the ¹³C NMR chemical shifts of some of the olefinic carbons of this compound were mistakenly assigned in the literature. The regularity for NMR data of polyene macrolide was also summarized in the paper.

Clindamycin phosphate, an antibiotic drug, was used extensively in clinic. In this study, the ¹H, ¹³C and ³¹P chemical shifts of the compound were assigned using 2D NMR techniques, including DEPT, ¹H-¹H COSY, ¹³C-¹H HSQC and ¹³C-¹H HMBC. The relative stereochemistry was established by the results obtained from quantum chemical calculation and NOESY spectroscopy. The fragmentation pathway of clindamycin phosphate was also analyzed by TOF-MS/MS.

2β, 16β-dipieridino-5α-androstan-3α, 17β-diol is an important intermediate in the synthesis of vecuronium bromide. In this study, the molecular structure of the compound was elucidated by MS, IR, 1D NMR and 2D NMR techniques (i.e., ¹H NMR, ¹³C NMR, DEPT, ¹H-¹H COSY, HSQC and HMBC). The stereochemistry conformation of the compound was confirmed by ROESY experiments. The ¹³C NMR chemical shifts of five other androstan intermediates were also assigned.

A furanosesquiterpenoid, 2-methoxy-5-acetoxy-furanogermacr-1(10)E-en-6- one was isolated from the CHCl₃ extrct of myrrh. Its structure was established by its 1D and 2D NMR (i.e, ¹H-¹H COSY, HSQC and HMBC) spectra. The ¹H and ¹³C chemical shifts of the compound were assigned. The relative stereochemistry of the 1, 10-double bond and that of the methoxyl, methyl, and acetoxy groups were determined by NOESY experiments and analyses of the coupling constants.

Caged intramolecular ketals of β-C-glycosidic ketones were prepared from β-C-glycosidic ketones. The structures of these C-glycosidic derivatives were evaluated with 1D and 2D NMR spectroscopy (i.e., ¹H NMR, ¹³C NMR, DEPT-135, ¹H-¹H COSY, HSQC and HMBC) and high resolution mass spectra. ¹H and ¹³C NMR chemical shifts of these compounds were assigned.

Silk fibers are widely used because of their strong mechanical performance and good biocompatibility. People have tried to understand the natural spinning mechanism of silkworm, the relationship between the structure and the function of silk fibroin, and the factors affecting the secondary structure transition of silk fibroin. Among the methods being used to study silk fibroin, the most effective one is magnetic resonance spectroscopy, including both nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). We have used NMR techniques to study the conformation of silk fibroin and how it is affected by environmental factors such as pH and metal ions (K⁺, Na⁺, Ca²⁺, Cu²⁺ and Zn²⁺) etc. We have also applied EPR spectroscopy to investigate the interaction between Cu(Ⅱ) and silk fibroin in order to discover the intrinsic relationship between conformational transition of silk fibroin and its interaction with Cu(Ⅱ). Besides, a generalized two-dimensional NMR correlation spectroscopy method has been developed for efficiently reducing the traditional 2D NMR experimental time. In this paper, the related work in our group during the past few years is reviewed.