Composite alignment media for the measurement of independent sets of NMR residual dipolar couplings

The measurement of independent sets of NMR residual dipolar couplings (RDCs) in multiple alignment media can provide a detailed view of biomolecular structure and dynamics, yet remains experimentally challenging. It is demonstrated here that independent sets of RDCs can be measured for ubiquitin using just a single alignment medium composed of aligned bacteriophage Pf1 particles embedded in a strained polyacrylamide gel matrix. Using this composite medium, molecular alignment can be modulated by varying the angle between the directors of ordering for the Pf1 and strained gel matrix, or by varying the ionic strength or concentration of the Pf1 particles. This approach offers significant advantages in that greater experimental control can be exercised over the acquisition of multi-alignment RDC data while a homogeneous chemical environment is maintained across all of the measured RDC data.     

盐酸2-芳基-3,5,5-三甲基-2-吗啉醇的合成

盐酸2-芳基-3; 5; 5-三甲基-2-吗啉醇的合成;盐酸芳基三甲基吗啉醇; 胺化; 合成     

Facile Iron‐Mediated Dispersant‐Free Suspension Polymerization of Methyl Methacrylate via Reverse ATRP in Water

An iron‐mediated reverse ATRP of methyl methacrylate (MMA) is successfully carried out in water in the absence of any dispersants, using a water‐soluble 2,2′‐azobis(2‐methylpropionamidine) dihydrochloride (V‐50) as the initiator and the stabilizer, and using an oil‐soluble N,N‐butyldithiocarbamate ferrum (Fe(S₂CN(C₄H₉)₂)₃) as the catalyst without adding any additional ligands. Micron‐sized PMMA particles with UV light‐sensitive ‐S₂CN(C₄H₉)₂ end group are obtained, and monomer droplet nucleation and suspension polymerization mechanism are proposed. Polymerization results demonstrated typical “living”/controlled characteristics of ATRP: first‐order polymerization kinetics, linear increase of molecular weights with monomer conversion and narrow molecular weight distributions for the resultant PMMA particles. NMR spectroscopy and chain‐extension experiments under UV light irradiation confirm the attachment and livingness of UV light‐sensitive ‐S₂CN(C₄H₉)₂ group in the chain end.

     

Development of Dispersive Liquid‐Liquid Microextraction Based on Solidification of Floating Organic Drop for the Determination of Trace Cobalt in Water Samples

A liquid‐phase microextraction technique was developed using dispersive liquid‐liquid microextraction based on solidification of floating organic drop combined with flame atomic absorption spectrometry, for the extraction and determination of trace amounts of cobalt in water samples. Microextraction efficiency factors, such as the type and volume of extraction and dispersive solvents, pH, extraction time, the chelating agent amount, and ionic strength were investigated and optimized. Under optimum conditions, an enrichment factor of 160 was obtained from 10.0 mL of water sample. The calibration graph was linearin the range of 1.15‐110 μg L^?1 with a detection limit of 0.35 μg L^?1. The relative standard deviation for ten replicate measurements of 10 and 100 μg L^?1 of cobalt were 3.26% and 2.57%, respectively. The proposed method was assessed through the analysis of certified reference water or recovery experiments.     

The structure and catalytic activity of anatase and rutile titania supported manganese oxide catalysts for selective catalytic reduction of NO by NH3

The structure and catalytic properties of anatase and rutile supported manganese oxide catalysts prepared by impregnation method have been studied by using X-ray diffraction (XRD), laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), H(2) temperature-programmed reduction (H(2)-TPR) and BET surface area measurements combined with activity testing of selective catalytic reduction (SCR) of NO by NH(3). It has been shown that the manganese oxide loadings on the two TiO(2) supports exert great influences on the SCR activity. For the rutile supported manganese oxide catalysts, increasing manganese oxide loading leads to the increase of reducibility of dispersed manganese oxide species and the rate constant k, which reaches a maximum around 9.6 × 10(-6) mol g(Mn)(-1) s(-1) at 0.5 mmol Mn per 100 m(2) TiO(2). When the manganese oxide loading is beyond this value, the existence of amorphous MnO(x) multiple layers will certainly reduce the ratio of manganese oxide species exposed on the surface and the reducibility of dispersed manganese oxide species, resulting in the rapid decrease of rate constant k. The LRS and XPS results have revealed that for the anatase supported manganese oxide catalysts manganese oxide species exist in Mn(+4) as a major species with Mn(+3) species and partially undecomposed Mn-nitrate as the minor species. Under the SCR reaction conditions, Mn(+3) species on anatase are oxidized to Mn(+4) species, inserting in the surface of anatase and promoting the anatase-to-rutile transformation in the surface layers of the anatase support. Since these Mn(4+) cations are actually dispersed on the support with a rutile shell-anatase core structure and its concentration is very near to that of MnO(x)/TiO(2) (R) catalyst, the relation between the rate constant k and the MnO(x) loading on the anatase support is similar to that on the rutile support, and that the rate constant k values for anatase and rutile supported manganese oxide catalysts are very close at the same MnO(x) loading.     

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.     

Understanding the electronic energy transfer pathways in the trimeric and hexameric aggregation state of cyanobacteria phycocyanin within the framework of Förster theory

In the present study, the electronic energy transfer pathways in trimeric and hexameric aggregation state of cyanobacteria C‐phycocyanin (C‐PC) were investigated in term of the Förster theory. The corresponding excited states and transition dipole moments of phycocyanobilins (PCBs) located into C‐PC were examined by model chemistry in gas phase at time‐dependent density functional theory (TDDFT), configuration interaction‐singles (CIS), and Zerner's intermediate neglect of differential overlap (ZINDO) levels, respectively. Then, the long‐range pigment‐protein interactions were approximately taken into account by using polarizable continuum model (PCM) at TDDFT level to estimate the influence of protein environment on the preceding calculated physical quantities. The influence of the short‐range interaction caused by aspartate residue nearby PCBs was examined as well. Only when the protonation of PCBs and its long‐ and short‐range interactions were properly taken into account, the calculated energy transfer rates (1/K) in the framework of Förster model at TDDFT/B3LYP/6‐31+G* level were in good agreement with the experimental results of C‐PC monomer and trimer. Furthermore, the present calculated results suggested that the energy transfer pathway in C‐PC monomer is predominant from β‐155 to β‐84 (1/K = 13.4 ps), however, from α‐84 of one monomer to β‐84 (1/K = 0.3–0.4 ps) in a neighbor monomer in C‐PC trimer. In C‐PC hexamer, an additional energy flow was predicted to be from β‐155 (or α‐84) in top trimer to adjacent β‐155 (or α‐84) (1/K = 0.5–2.7 ps) in bottom trimer. © 2013 Wiley Periodicals, Inc.     

A Facile Synthesis of Pyrimidone Derivatives and Single-Crystal Characterization of Pymetrozine

A facile and efficient synthetic methodology for the preparation of aza-pyrimidone and beno-pyrimidone derivatives is described, in which the triazinone ring and dihydroquinazolin-2(1H)-one was convenient constructed. The structures of all the newly synthesized compounds were characterized by mass, ¹H NMR, and infrared spectroscopy. In additional, the crystal of pymetrozine was obtained to find useful information such as configuration and molecular action mechanisms.     

N,N-二(2-苯并咪唑亚甲基)甲胺高氯酸盐的晶体和电子结构

合成了三齿配体N,N-二(2-苯并咪唑亚甲基)甲胺(MN3)的高氯酸盐.对该化合物进行了元素分析、紫外和红外表征;采用X射线衍射方法测定了该化合物的晶体结构,依据晶体结构数据使用G98程序对配体(MN3)进行了量子化学计算.     

Reactivity of bis(pyrazol-1-yl)methanes functionalized by 2-hydroxyphenyl and 2-methoxyphenyl on the methine carbon atom with W(CO)5THF

Reactions of 2-hydroxyphenyl and 2-methoxyphenylbis(pyrazol-1-yl)methanes as well as 2-hydroxyphenyl and 2-methoxyphenylbis(3,5-dimethylpyrazol-1-yl)methanes with W(CO)₅THF have been carried out. Heating 2-hydroxyphenylbis(pyrazol-1-yl)methane (L¹) with W(CO)₅THF in THF at reflux yielded complex (L¹)W(CO)₄.L¹, while similar reaction of 2-hydroxyphenylbis(3,5-dimethylpyrazol-1-yl)methane (L²) with W(CO)₅THF resulted in the cleavage of a C_sp3-N bond to generate 1,2-bis(2-hydroxyphenyl)-1,2-bis(3,5-dimethylpyrazol-1-yl)ethane (L) and pyrazole derivative W(CO)₅(3,5-Me₂PzH) (Pz = pyrazol-1-yl). These two fragments were connected together through strong O…H-N and O-H…N hydrogen bonds to form complex L.[W(CO)₅(3,5-Me₂PzH)]₂. The analogous results were observed in the treatment of 2-methoxyphenylbis(pyrazol-1-yl)methane (L³) with W(CO)₅THF, which gave product L′.[W(CO)₅(PzH)]₂ (L′ = 1,2-bis(2-methoxyphenyl)-1,2-bis(pyrazol-1-yl)ethane) as well as certain amount of complex (L³)W(CO)₄. In addition, during the reaction of 2-methoxyphenylbis(3,5-dimethylpyrazol-1-yl)methane (L⁴) with W(CO)₅THF, partial decomposition reactions took place to yield complexes (L⁴)W(CO)₄ and W(CO)₅(3,5-Me₂PzH), but no hydrogen bond was found between these two moieties.