95 ℃水溶液体系中TiCl4溶胶水解法制备纯金红石纳米粉体(英)

Titanium dioxide (TiO2) nanoparticles of rutile phase were synthesized by hydrolysis of TiCl₄ at 95 ℃ in aqueous solution. The samples as prepared and calcined at 500 ℃ were characterized by XRD, TG-DTA and TEM. The sample as prepared was of imperfect rutile structure, and its morphology was rod-like with a diameter of 10～20 nm, a length of 20～80 nm and an aspect ratio of 2～4. The structure of the sample calcined at 500 ℃ was a perfect rutile one, and its morphology was rod-like with a diameter of 15～25 nm, a length of 25～105 nm and an aspect ratio of 2～4. These results indicate that calcination temperature has a positive effect on the structure and the size of rutile nanocrystals, and has no effect on the aspect ratio of rutile nanocrystal. A model for the formation mechnism of rutile nanocrystal in aqueous solution under hydrolysis conditions has been proposed.     

Coating Carbon Nanotubes with Europium Oxide

Carbon nanotubes (CNTS) coating with europium oxide by a simple method is reported in this letter for the first time. The CNTS were refluxed in a solution of nitric acid containing europium nitrate, and the pH value was subsequently ajusted with ammonia solution. At last, the mixture was filtered and annealed. The TEM micrograph showed that the CNTS were covered with a uniform thin layer with thickness of about 15 nm. The XRD results revealed that the CNTS were coated with europium oxide.     

Fabrication of Tubular Structure Agglomerates of Calcium Carbonate by Using Collodion Film

A novel and simple method for preparing tubular structure agglomerates of calcium carbonate (CC-tube) is described. Calcium chloride and sodium carbonate aqueous solutions were used as reactants separated by a collodion film (a nitrocellulose material) in aqueous solution. The effects of the concentrations of calcium chloride and sodium carbonate aqueous solutions on the morphology and phase structure of the as-obtained samples were investigated. The CC-tube growth was prevented with the increase of reactant concentration from 0.5 to 1.0 mol•L－1. Compared with Na2CO3 aqueous solution, it is favourable to grow calcite crystals in CaCl2 aqueous solution. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron- microscopy.     

Thermal oxide synthesis and characterization of Fe_3O_4 nanorods and Fe_2O_3 nanowires

Fe3O4 nanorods and Fe2O3 nanowires have been synthesized through a simple thermal oxide reaction of Fe with C2H2O4 solution at 200-600℃ for 1 h in the air. The morphology and structure of Fe3O4 nanorods and Fe2O3 nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals Fe3O4 nanorods with cubic structure and the av...     

Fluorocarbon- containing hydrophobically modified poly(N-isopropylacrylamide)

A fluorocarbon-modified poly(N-isopropylacrylamide) has been synthesized by copolymerization of N-isopropyl acrylamide with a small amount of acrylate or methacrylate containing a perfluoroalkyl group. It was found that the hydrophilicity of macromolecular backbone is an important factor to the solution properties of the copolymers and that hydrophobic association between fluorocarbon groups is stronger than that between the corresponding hydrocarbon analogies. The viscosity of some of the copolymer solutions was very sensitive to temperature. It was dilatant at higher fluorocarbon comonomer content ( > 0.20-1.0 mol%) and was Newtonian at very low fluorocarbon comonomer content (0.03-0.2 mol% ) . Evidence for hydrophobic association of the fluorocarbon groups was obtained from the effects of adding Nad and surfactants on the solution viscosity. The LC-ST properties of these copolymers were studied by DSC method and this was also found to be consistent with hydrophobic association between the fluorocarbo     

Rheological behaviors of a series of hyperbranched polyethers

Hyperbranched polyethers with different structures and molecular weights(MW) were synthesized using the A2+B3 approach by varying monomer ratio, A2 structure, and reaction time. Effects of backbone structure and MW on melt rheological behaviors were investigated by both small amplitude oscillatory shear and steady shear measurements. Master curves were constructed using the time-temperature superposition principle and compared. In the reduced frequency range covered, lg G″~lg(ω·aT) always show a slope of 1.0, suggesting a terminal zone behavior; in contrast, unexpected step changes or plateaus are observed on lg G′ master curves. Effects of backbone structure and MW on master curves were discussed. The Cox-Merz rule was tested at different temperatures and was found to be applicable when flow instability was absent.     

Influence of pH values in the preparation of CuO-CeO2 on its catalytic performance for the preferential oxidation of CO in excess hydrogen

CuO-CeO2 catalyst prepared with co-precipitation showed high catalytic performance for the preferential oxidation of CO in excess hydrogen (PROX). Influence of pH values in the preparation of CuO-CeO2 on its catalytic performance was investigated in this work. The CuO-CeO2 catalyst prepared at pH = 13.03 had the smallest particle size (5.4 nm), the largest surface areas (138 m2/g) and the highest activity with CO conversion of 99.6% at 130 ℃. The CuO-CeO2 catalyst was characterized using BET, XRD and TPR techniques. The results showed that when the pH value of the mixed solution containing Cu and Ce species was properly adjusted, both the adsorption layers and diffusion layers of the formed colloidal particles in hydroxide precursor of CuO-CeO2 were modified, resulting in the better catalytic performance for PROX on the final CuO-CeO2 catalyst.     

NMR Analysis to Identify Biuret Groups in Common Polyureas

Polyureas(PU) are well known as a class of high impact engineering materials, and widely used also in emerging advanced applications. As a general observation, most of them are only soluble in a very limited number of highly protonic solvents, which makes their chemical structure analysis a great challenge. Besides the presence of abundant hydrogen bonding, the poor solubility of PU in common organic solvents is often ascribed to the formation of biuret crosslinking in their molecular chains. To clarify the presence of biuret groups in PU has been of great interest. To this end, two samples, based on hexamethylene diisocyanate(HDI) and toluene diisocyanate(TDI) respectively, were synthesized by precipitation polymerization of each of these diisocyanates in water-acetone at30 °C. Their chemical structures were analyzed by high resolution magic angle spinning(HR-MAS) NMR, and through comparison of their NMR spectra with those of specially prepared biuret-containing polyurea oligomers, it was concluded that biuret group was absent in all the PU prepared at 30 °C. In addition, this NMR analysis was also applied to a PU obtained by copolymerization of TDI with ethylene diamine(EDA) and water at 65 °C in EDA aqueous solution. It was confirmed that biuret unit was also absent in this PU and that EDA was more active than water towards TDI. The presence of EDA was crucial to the formation of uniform PU microspheres. This study provides therefore a reliable method for the analysis of PU chemical structure.     

STUDIES ON ULTRASONIC GRAFTING OF POLY(VINYL ACETATE) WITH POLY(ETHYLENE OXIDE)

The ultrasonic degradation of poly(ethylene oxide) and poly(vinyl acetate) in benzene solution, and grafting reaction of poly(vinyl acetate) with poly(ethylene oxide) were studied. It is found that the chain-scission reactions follow the course suggested by D. W. Ovenall. The structure of the copolymer was identified by IR, NMR and DTA, showing that the copolymer prepared is a graft copolymer mainly. The copolymer formed by irradiating 1% PEO/PVAc solution (PEO/PVAc:1/1 by weight) for a period of 10 rain at 18.2 kHZ, with 2.0 A input current on reversed main circuit, amounts to 10.5%.     

Microstructure and corrosion behavior of electroless deposited Ni-P/CeO2 coating

Electroless Ni-P/nano-CeO2 composite coating was prepared in acidic condition, and its microstructure and corrosive property were compared with its CeO2-free counterpart. Scanning electronic microscopy （SEM） and X-ray diffraction （XRD） spectrometer were used to examine surface morphology and structure of the as-plated coating. Differential scanning calorimeter （DSC） and transmission electronic microscopy （TEM） were used to study the coating＇s phase change at high temperature. The coating＇s corrosive behavior in 3%NaCl ＋ 5%H2SO4 solution was also investigated. The results showed that Ni-P coating had partial amorphous structure mixed with nano-crystals, while the Ni-P/CeO2 coating had perfect amorphous structure. In high-temperature condition, Ni3P precipitation and Ni crystallization took place in both coatings but at different temperatures, while the Ni-P/CeO2 coating had sintered phase of NiCe2O4 spinels. The anti-corrosion property was better in the CeO2-containing coating, and this was due to its less liability to undergo local-cell corrosion than its CeO2-free counterpart. Ni-P/CeO2 coating＇s pure amorphous structure was the result of Ni＇s hindered crystal-typed deposition and P＇s promoted deposition.     

Solution Structure of Conomarphin, a Novel Conopeptide Containing D-Amino Acid at pH 5

Conomarphin, a novel conopeptide containing D-amino acid, was identified from the venom of Conus marmoreus and classified into M-superfamily of conotoxin. In this article, we reported the 3D structure of conomarphin at pH 5 determined using 2D ¹H NMR method in aqueous solution. Twenty converged structures of this peptide were obtained based on 205 distance constraints, 8 dihedral angle constraints, and 2 hydrogen bond constraints. The root mean square deviation (RMSD) values of the backbone atoms were (0.074±0.029) nm. The refined structure of conomarphin at pH 5 contains a short 3¹⁰-helix at C-terminal of the peptide. It was also characterized by a loose loop centered at Ala6. Comparison of structural and electrostatic potential between conomarphin at pH 3 and pH 5 were presented. Although the solution structure of conomarphin at pH 5 shared part of the same secondary structure element with the structure of conomarphin at pH 3, it adopted a distinctive backbone conformation with the overall molecule resembling a “flexual arm” when viewed from the front. Structural differences implied that this conopeptide was rather pH sensitive and its bioactivity in vivo might be related to the acidity.     

Determination of the major solution conformation of tyrocidine A,using molecular mechanics energy minimization and NMR-derived distance and torsion angle constraints

Molecular mechanics energy calculations coupled with nuclear magnetic resonance-determined distance and torsion angle constraints have been used to determine the three-dimensional structure of tyrocidine A, a cyclic decapeptide which exists largely as a single conformation in solution. Two open-chain polyalanine models were used to represent separate halves of the peptide backbone and a combinatorial method of searching conformation space used to generate candidate structures consistent with experimental distance constraints. These structures were energy-minimized using the AMBER molecular mechanics forcefield and the resulting conformations classified by factor analysis of their Cartesian coordinates. Representative low-energy conformers of the two halves of the backbone were fused together and two candidate conformations of the completed backbone refined by further minimization using both distance and torsional constraints. Side chains were then added as their experimentally preferred rotamers and the whole molecule minimized without constraints to give the final model structure. This shows type II' and III ß turns at residues 4–5 and 9–10, respectively, coupled by twisted antiparallel strands which show hydrogen bonds between all four pairs of opposing peptide groups. The backbone conformation of residues 2–6 closely resembles that found in the crystal structure of gramicidin S.     

Backbone cleavages of [M - H](-) anions derived from caerin 1 peptides and some synthetic modifications. Molecular recognition initiating internal cyclisation of Glu23

The collision induced spectra of [M - H](-) anions from of caerin 1 peptides and some synthetic modifications show the usual alpha, beta and beta' backbone cleavages together with Ser (epsilon,gamma) and Glu (gamma) cleavages which break the peptide backbone in the vicinity of those residues. All of these cleavages require the peptide backbone to be flexible. There is also a backbone cleavage of a type not observed before. This cleavage involves nucleophilic attack of the carboxylate anion of the Glu23 side chain at the backbone CH of Ile 21. We propose that this cleavage requires the caerin peptide to be in an alpha helical conformation (the 3D structure that this peptide adopts in solution) in order that the interacting groups are held in close proximity.     

Backbone-only protein solution structures with a combination of classical and paramagnetism-based constraints: a method that can be scaled to large molecules.

Herein, it is shown that a medium-resolution solution structure of a protein can be obtained with the sole assignment of the protein backbone and backbone-related constriants if a derivative with a firmly bound paramagnetic metal is available. The proof-of-concept is provided on calbindin D9k, a calcium binding protein in which one of the two calcium ions can be selectively substituted by a paramagnetic lanthanide ion. The constraints used are HN (and Ha) nuclear Overhauser effects (NOEs), hydrogen bonds, dihedral angle constriants from chemical shifts, and the following paramagnetism-based constraints: 1) pseudocontact shifts, acquired by substituting one (or more) lanthanide(s) in the C-terminal calcium binding site; 2) N-HN residual dipolar couplings due to self-orientation induced by the paramagnetic lanthanide(s); 3) cross-correlations between the Curie and internuclear dipole-dipole interactions; and 4) paramagnetism-induced relaxation rate enhancements. An upper distance limit for internuclear distances between any two backbone atoms was also given according to the molecular weight of the protein. For this purpose, the paramagnetism-based constraints were collectively implemented in the program CYANA for solution structure determinations, similarly to what was previously done for the program DYANA. The method is intrinsically suitable for large molecular weight proteins.     

Site specificity of the (alpha)C--H bond dissociation energy for a naturally occurring beta-hairpin peptide-An ab initio study

A naturally occurring beta-hairpin peptide (PDB ID 1UAO) was used as a model to study the backbone oxidation of a protein with ab initio calculation at the B3LYB/6-31G(d) without any constraints. The (alpha)C--H bond dissociation energy of three different glycyl radicals located at different sites on the beta-hairpin peptide was calculated to evaluate the site specificity of backbone oxidation. The molecular and electronic structures of these glycyl radicals were analyzed to rationalize this site specificity. The overall molecular structure of the alpha-H abstracted beta-hairpin peptide remained almost unchanged with the exception of the local conformation of the attacked residue. However, the (alpha)C--H bond strength varied dramatically among these different sites.     

Solid-state NMR yields structural constraints on the V3 loop from HIV-1 Gp120 bound to the 447-52D antibody Fv fragment

Solid-state NMR measurements were performed on the complex of an 18-residue peptide derived from the V3 loop sequence of the gp120 envelope glycoprotein of the HIV-1 MN strain with Fv fragments of the human anti-gp120 monoclonal antibody 447-52D in a frozen glycerol/water solution. The peptide was uniformly (15)N- and (13)C-labeled in a 7-residue segment containing the conserved GPGR motif in the epitope. (15)N and (13)C NMR chemical shift assignments for the labeled segment were obtained from two-dimensional (13)C-(13)C and (15)N-(13)C magic-angle spinning NMR spectra. Reductions in (13)C NMR line widths and changes in chemical shifts upon complex formation indicate the adoption of a well-defined, antibody-dependent structure. Intramolecular (13)C-(13)C distances in the complex, which constrain the peptide backbone and side chain conformations in the GPGR motif, were determined from an analysis of rotational resonance (RR) data. Structural constraints from chemical shifts and RR measurements are in good agreement with recent solution NMR and crystallographic studies of this system, although differences regarding structural ordering of certain peptide side chains are noted. These experiments explore and help delineate the utility of solid state NMR techniques as structural probes of peptide/protein complexes in general, potentially including membrane-associated hormone/receptor complexes.     

Synthesis and structural model of an alpha(2,6)-sialyl-t glycosylated MUC1 eicosapeptide under physiological conditions

To study the effect of O-glycosylation on the conformational propensities of a peptide backbone, a 20-residue peptide (GSTAPPAHGVTSAPDTRPAP) representing the full length tandem repeat sequence of the human mucin MUC1 and its analogue glycosylated with the (2,6)-sialyl-T antigen on Thr11, were prepared and investigated by NMR and molecular modeling. The peptides contain both the GVTSAP sequence, which is an effective substrate for GalNAc transferases, and the PDTRP fragment, a known epitope recognized by several anti-MUC1 monoclonal antibodies. It has been shown that glycosylation of threonine in the GVTSAP sequence is a prerequisite for subsequent glycosylation of the serine at GVTSAP. Furthermore, carbohydrates serve as additional epitopes for MUC1 antibodies. Investigation of the solution structure of the sialyl-T glycoeicosapeptide in a H(2)O/D(2)O mixture (9:1) under physiological conditions (25 degrees C and pH 6.5) revealed that the attachment of the saccharide side-chain affects the conformational equilibrium of the peptide backbone near the glycosylated Thr11 residue. For the GVTSA region, an extended, rod-like secondary structure was found by restrained molecular dynamics simulation. The APDTR region formed a turn structure which is more flexibly organized. Taken together, the joined sequence GVTSAPDTR represents the largest structural model of MUC1 derived glycopeptides analyzed so far.     

Structure of a cyclic peptide with a catalytic triad, determined by computer simulation and NMR spectroscopy

Summary We report the design of a cyclic, eight-residue peptide that possesses the catalytic triad residues of the serine proteases. A manually built model has been relaxed by 0.3 ns of molecular dynamics simulation at room temperature, during which no major changes occurred in the peptide. The molecule has been synthesised and purified. Two-dimensional NMR spectroscopy provided 35 distance and 7 torsion angle constraints, which were used to determine the three-dimensional structure. The experimental conformation agrees with the predicted one at the -turn, but deviates in the arrangement of the disulphide bridge that closes the backbone to a ring. A 1.2 ns simulation at 600 K provided extended sampling of conformation space. The disulphide bridge reoriented into the experimental arrangement, producing a minimum backbone rmsd from the experimental conformation of 0.8 . At a later stage in the simulation, a transition at Ser³ produced more pronounced high-temperature behaviour. The peptide hydrolyses p-nitrophenyl acetate about nine times faster than free histidine.     

Eu3+掺杂的LaBO3荧光粉制备及发光性能

采用水热法合成前驱体,后经热处理方式制备不同晶相的LaBO3∶Eu^3+荧光粉。通过X射线衍射(XRD)、电子扫描电镜(SEM)、红外光谱和荧光光谱对样品的结构、形貌和发光性能进行了研究。并研究了硼酸用量、热处理温度及初始溶液pH等对晶相结构和发光性能的影响。XRD研究结果表明:合成样品具有单斜结构、正交结构及单斜和正交两相混合结构。适当的硼酸用量、较高的热处理温度及较高的初始溶液pH值易于获得正交结构的荧光粉。红外光谱显示:pH值和硼酸用量影响前驱体成分,热处理温度影响晶相的转变。SEM结果显示:LaBO3∶Eu^3+荧光粉的晶粒尺寸随着pH值的增加逐渐减小,与XRD计算结果相一致。荧光光谱结果表明:正交结构的LaBO3∶Eu^3+发光粉具有较高的紫外吸收和较为纯正的红色发射强度。