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NMR Studies of Protein Solution Structures and Dynamics
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HU Yun-fei1 , JIN Chang-wen1，2 *
Chinese Journal of Magnetic Resonance, 2009, 26(2): 151-172.
As one of the major techniques for determining high-resolution protein structures, high-field solution NMR has achieved remarkable developments during the past twenty years. With the advances of advanced spectrometer hardware, NMR pulse techniques and protein labeling strategies, the size of the protein that can be studied by solution NMR now exceeds 25 k, and can reach tens and even hundreds of kilo Dalton. In addition, solution NMR has also been widely used in the studies of protein dynamics, and is the only technology that can be used to probe protein motions at multiple sites simultaneously. In this review, we briefly summarize the methods for studying protein structures and dynamics using solution NMR, accompanied by examples to demonstrate the latest developments in the field.
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Interactions between Diperoxovanadate and 2-Methyl-imidazole Studied by NMR Spectroscopy
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ZHU Xiong-bin1 ； YU Xian-yong2 ； CAI Shu-hui2 ；CHEN Zhong2 *
Chinese Journal of Magnetic Resonance, 2009, 26(2): 206-215.
To understand the effects of organic ligands on reaction equilibrium, the interactions between diperoxovanadate complexes [OV(O2 )2 LL′]n -n =1~3; LL′=oxalate, picolinate, 2,2′-bipyridine, and 1,10-phenanthroline) and 2-methyl-imidazole in 0.15 mol/L NaCl ionic medium, which was used to mimick physiological conditions, were explored using multinuclear (1 H, 1 3C, and 5 1V) NMR spectroscopy and variable temperature experiments. The experimental results indicated the reactivities of the four diperoxovanadate complexes with 2-methyl-imidazole were as follows: bpV(oxalate)>bpV(picolinate)>bpV(2,2′-bipyridine)>bpV(1,10-phenanthroline). Both the coordination capability and the steric effects of the organic ligands affected reaction equilibrium. New sixcoordinated peroxovanadate species [OV(O2 )2 (2-methyl-imidazole)]- were formed due to competitive coordination.
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An ESR Study of Lithium-stored Silicon
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ZHOU Xiao-rong1 *; LIU Xiao-bo1 ; ZHUANG Lin2 ; LU Jun-tao2
Chinese Journal of Magnetic Resonance, 2009, 26(2): 223-229.
In this paper, lithium stored silicon were prepared with the electrochemical reaction method. The electron spin resonance (ESR) signals of silicon and lithium-stored silicon were measured. The ESR intensity of silicon showed a linear change with the reciprocal of the temperature, indicative of the presence of Curie spins, which may come from localized spin centers, such as crystal defects and hanging bonds on the surface. In lithium-stored silicon, however, both Pauli spins and Curie spins were shown to be present. The amplitude of integrated ESR signals owing to Curie spins in lithium-stored silicon was 2~3 times higher than that in silicon. The effects of temperature on the g factor and line width (ΔH pp ) of the ESR signals were also investigated. It could be concluded that when lithium ion reacts with silicon in the electrochemical reaction, compensating electrons from the external circuit mostly took part in forming the covalent bonds between Li and Si, and contributed little to the ESR intensity.
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Theoretical Investigations of 13 C NMR Parameters of the Functionalized Carbon Nanotubes
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WANG Lin*
Chinese Journal of Magnetic Resonance, 2009, 26(2): 230-238.
Surface chemical modification of carbon nanotubes has become a hot research topic nowadays. The dispersion of carbon nanotubes in polar solvents can be greatly improved by attaching hydrophilic groups onto their surfaces, increasing the range of their application. In this study, a C80 H20 model was used to represent the (10, 0) zig-zag carbon nanotube. Based on this model, the structures, dipole moments and the nuclear magnetic resonance parameters were calculated for a series of functionalized nanotubes, including nitrene and carbene modification, as well as 1, 2- and 1, 4-fluorination. The results indicated that the high level density functional theory (DFT) calculations can be used to predict the 13 C chemical shifts of the modified nanotubes. The calculated results also provided the characteristic chemical shifts values of nitrene-, carbene- and 1, 2- and 1,4-fluorinated nanotubes, which would be helpful for experimental spectrogram assignments. Combined with NMR experiments, these predicted characteristic chemical shifts can be further used to monitor the addition mechanism and the extent of surface modifications on nanotubes.
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Structural Elucidation of Three Flavonoids Extracted from the Rhizomes of Ligularia vellerea by NMR Spectroscopy
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WANG Cai-fang1,2 ；LI Jun-ping1,3 ；LI Rao-rao4 ；ZHAO Yu2 ；ZHANG Yan-bing1 ；ZHANG Zhen-zhong1
Chinese Journal of Magnetic Resonance, 2009, 26(2): 264-271.
Two chalcones and one flavonone were isolated from the rhizomes of Ligularia vellerea : 3, 2′, 4′-trihydroxy-4-methoxy-chalcone (1), 4, 2′, 4′-trihydroxy-chalcone (2) and 7, 3′-dihydroxy-4′-methoxy flavonoe (3). The structures of these three compounds were elucidated by 1D and 2D NMR (including 1 H-1 H COSY、HSQC and HMBC). The positions of the methoxyl and the hydroxyl groups in each compound were determined.
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31 P NMR Analysis of Malathion and Primary Organic Phosphorus Impurities in Malathion EC
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YANG Xiao-yun*；FEI Zhi-ping；XU Han-hong
Chinese Journal of Magnetic Resonance, 2009, 26(2): 279-288.
31 P NMR was used to analyze the contents of malathion and primary organic phosphorus impurities in malathion EC. All 31 P NMR spectra were recorded on a Bruker Avance 600 spectrometer at 25 ℃ with 85% H3 PO4 used as an internal standard. The contents of malathion, isomalathion, MeOOSPS trimester, MeOOOPS trimester and malaoxon in malathion EC were found to be 44.92%, 0.55%, 0.05%, 0.22% and 0.11% respectively, and the RSD 0.07%, 2.10%, 2.88%, 0.94% and 1.58% respectively. The results indicated that 31 P NMR method is an effective tool for analyzing malathion EC, and thus useful in practical pesticide analyses.
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The Latest IUPAC Conventions for NMR
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BI Yu-jie; CHEN Zhi-wei*; CHEN Zhong
Chinese Journal of Magnetic Resonance, 2009, 26(2): 289-300.
The International Union of Pure and Applied Chemistry (IUPAC) is an organization "serves to advance the worldwide aspects of the chemical sciences and to contribute to the application of chemistry in the service of Mankind". It has published a number of recommendations regarding the reporting of NMR data, such as chemical shifts, referencing procedures, unified scale, standard state, magic angle spinning (MAS) and referencing in solids. In 2008, IUPAC provided the latest 17 recommendations as a supplement to those that were not discussed in detail in the past conventions. The recommendations included temperature and solvent effects on chemical shift, referencing, magnetic susceptibility correction, comments on Ξ values of frequency ratio, and referencing in solids.
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