Bioconjugation of Proteins with a Paramagnetic NMR and Fluorescent Tag

Site‐specific labeling of proteins with lanthanide ions offers great opportunities for investigating the structure, function, and dynamics of proteins by virtue of the unique properties of lanthanides. Lanthanide‐tagged proteins can be studied by NMR, X‐ray, fluorescence, and EPR spectroscopy. However, the rigidity of a lanthanide tag in labeling of proteins plays a key role in the determination of protein structures and interactions. Pseudocontact shift (PCS) and paramagnetic relaxation enhancement (PRE) are valuable long‐range structure restraints in structural‐biology NMR spectroscopy. Generation of these paramagnetic restraints generally relies on site‐specific tagging of the target proteins with paramagnetic species. To avoid nonspecific interaction between the target protein and paramagnetic tag and achieve reliable paramagnetic effects, the rigidity, stability, and size of lanthanide tag is highly important in paramagnetic labeling of proteins. Here 4′‐mercapto‐2,2′: 6′,2′′‐terpyridine‐6,6′′‐dicarboxylic acid (4MTDA) is introduced as a a rigid paramagnetic and fluorescent tag which can be site‐specifically attached to a protein by formation of a disulfide bond. 4MTDA can be readily immobilized by coordination of the protein side chain to the lanthanide ion. Large PCSs and RDCs were observed for 4MTDA‐tagged proteins in complexes with paramagnetic lanthanide ions. At an excitation wavelength of 340 nm, the complex formed by protein–4MTDA and Tb³⁺ produces high fluorescence with the main emission at 545 nm. These interesting features of 4MTDA make it a very promising tag that can be exploited in NMR, fluorescence, and EPR spectroscopic studies on protein structure, interaction, and dynamics.     

Mechanism and Cellular Kinetic Studies of the Enhancement of Antioxidant Activity by Using Surface‐Functionalized Gold Nanoparticles

The enhanced antioxidant activity of surface‐functionalized gold nanoparticles (AuNPs) synthesized by self‐assembly has attracted great attention, but little is known about the mechanism behind the enhanced activity. To address this challenge, the antioxidant activity of Au@PEG3SA (i.e., surface‐functionalization of spherical AuNPs with the antioxidant salvianic acid A) was used as an example to illustrate the mechanism of the enhanced activity. Evaluation of the antioxidant activity was performed in a radical‐scavenging reaction between Au@PEG3SA and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical. As expected, the rate constant for the reaction of Au@PEG3SA with DPPH was about nine times greater than that for the salvianic acid A monomer. A comparative analysis of the spectral characteristics of Au@PEG3SA and the salvianic acid A monomer further imply that the enhancement of the antioxidative reaction kinetics may be ascribed to the variation in the transition state for the DPPH‐radical scavenging reaction through π–π stacking interactions between and among adjacent groups on the surface of Au@PEG3SA. On the other hand, the kinetic enhancement of Au@PEG3SA on reactive‐oxygen‐species (ROS) scavenging can be observed in living cells and in vivo, which possibly provides new insight for the bioapplication of self‐assembly of surface‐functionalized AuNPs.     

2-苯基-4-硒唑甲酸的铜(Ⅱ)配合物的合成、晶体结构和生物活性

采用水热法合成了一种新型铜(Ⅱ)配合物[Cu₂(NO₃)₂L(phen)₂(H₂O)] NO₃(HL=2-苯基-4-硒唑甲酸, phen=1,10-邻菲啰啉)。用元素分析、红外光谱等表征手段确定了配合物的组成;用单晶X-射线衍射测定了配合物的晶体结构。配合物C₃₄H₂₄Cu₂N₈O₁₂Se属于三斜晶系, 空间群P1。用溴化乙锭荧光探针法研究了配合物与DNA的相互作用。分别考察了配体和配合物对五种细菌:大肠埃氏杆菌(E.coli), 表皮葡萄球菌(S.epidermidis), 草绿色链球菌(S.viridans), 金黄色葡萄球菌(S. aureus), 鲍曼不动杆菌(A.baumanii)的抗菌活性。同时也考察了配体和配合物对人类胰腺癌PANC-28细胞和人类肝癌HuH7细胞的体外增殖抑制作用。实验结果表明配合物具有良好的生物活性。     

(Ca,Me)La4Si3O13:Eu3+(Me=Sr,Ba)荧光粉的结构和发光特性

采用高温固相法制备了(Ca,Me)La4Si3O13∶Eu3+(Me=Sr,Ba)系列红色荧光体,考察了Eu3+掺杂浓度和Sr2+,Ba2+置换对荧光体结构和发光特性的影响。Eu3+最佳掺杂浓度为nEu3+∶nLa3+=1∶7,5D0-7F2与5D0-7F1跃迁发射强度比为2.55。Eu3+掺杂使晶胞参数a和c呈线性变小,对c的影响大于a,使a/c比增大。Sr2+和Ba2+分别置换基质中的Ca2+可以形成完全固溶体,晶胞参数随Sr2+或Ba2+的置换量增加呈线性增大,使a/c比减小。各发射峰强度在Sr2+置换量为0.4 mol时出现极大值,但随Ba2+置换量的增加而不断增强,全置换后荧光强度最大。荧光体的色坐标为(0.638 5,0.353 0)。     

Approximation properties for solutions to non‐Lipschitz stochastic differential equations with Lévy noise

In this paper, we consider the non‐Lipschitz stochastic differential equations and stochastic functional differential equations with delays driven by Lévy noise, and the approximation theorems for the solutions to these two kinds of equations will be proposed respectively. Non‐Lipschitz condition is much weaker condition than the Lipschitz one. The simplified equations will be defined to make its solutions converge to that of the corresponding original equations both in the sense of mean square and probability, which constitute the approximation theorems. Copyright © 2014 John Wiley & Sons, Ltd.     

Tighter uncertainty principles for periodic signals in terms of frequency

In this study, we propose some new uncertainty principles for periodic signals with sharper lower bounds than those in the existing ones. The improved lower bounds, in particular, are related to the frequency of the signal. Three examples are employed to demonstrate sharpness of the new uncertainty principles. Copyright © 2014 John Wiley & Sons, Ltd.     

New chiral biscarboline N,N′-dioxide derivatives as catalyst in enantioselective reduction of ketoimines with trichlorosilane

New axial N,N′-dioxide secondary amide derived from l-tryptophan was synthesized and firstly employed in catalytic enantioselective reduction of ketoimines with trichlorosilane. It was found that 4f was an effective catalyst with excellent reactivity and good enantioselectivity. Possible mechanism for the catalytic procedure was tentatively proposed.     

Easily Accessible Auxiliary for Palladium‐Catalyzed Intramolecular Amination of C(sp2)?H and C(sp3)?H Bonds at δ‐ and ε‐Positions

An easily synthesized and accessible N,O‐bidentate auxiliary has been developed for selective C H activation under palladium catalysis. The novel auxiliary showed its first powerful application in C H functionalization of remote positions. Both C(sp²) H and C(sp³) H bonds at δ‐ and ε‐positions were effectively activated, thus giving tetrahydroquinolines, benzomorpholines, pyrrolidines, and indolines in moderate to excellent yields by palladium‐catalyzed intramolecular C H amination.     

Determination of four sulfonylurea herbicides in tea by matrix solid‐phase dispersion cleanup followed by dispersive liquid–liquid microextraction

Matrix solid‐phase dispersion combined with dispersive liquid–liquid microextraction has been developed as a new sample pretreatment method for the determination of four sulfonylurea herbicides (chlorsulfuron, bensulfuron‐methyl, chlorimuron‐ethyl, and pyrazosulfuron) in tea by high‐performance liquid chromatography with diode array detection. The extraction and cleanup by matrix solid‐phase dispersion was carried out by using CN‐silica as dispersant and carbon nanotubes as cleanup sorbent eluted with acidified dichloromethane. The eluent of matrix solid‐phase dispersion was evaporated and redissolved in 0.5 mL methanol, and used as the dispersive solvent of the following dispersive liquid–liquid microextraction procedure for further purification and enrichment of the target analytes before high‐performance liquid chromatography analysis. Under the optimum conditions, the method yielded a linear calibration curve in the concentration range from 5.0 to 10 000 ng/g for target analytes with a correlation coefficients (r²) ranging from 0.9959 to 0.9998. The limits of detection for the analytes were in the range of 1.31–2.81 ng/g. Recoveries of the four sulfonylurea herbicides at two fortification levels were between 72.8 and 110.6% with relative standard deviations lower than 6.95%. The method was successfully applied to the analysis of four sulfonylurea herbicides in several tea samples.