Free-radical pathways in the decomposition of ketones over polycrystalline TiO(2): the role of organoperoxy radicals.

The oxidative decomposition of various ketones (including acetone, 2-butanone, 4-heptanone, cyclopentanone and cyclohexanone) over dehydrated TiO(2) (P25) powder is investigated by electron paramagnetic resonance (EPR) spectroscopy. For the first time, a series of thermally unstable radical intermediates are observed both on the activated and reduced TiO(2) surface, depending on the adopted experimental conditions. These radical intermediates are identified as organoperoxy-based species of general formula ROO(.-) and RCO(3) (.-). They are formed by reaction of photogenerated charge carriers (either trapped electrons or trapped holes) with the adsorbed ketones in the presence of molecular oxygen. The organoperoxy intermediates are thermally unstable and decompose at temperatures in the region of 180-250 K. This work demonstrates that free-radical pathways involving both organoperoxy and superoxide radicals can be responsible for the thermal- and photodecomposition of ketones over polycrystalline TiO(2) (P25).     

EPR studies on the thiophenodithiazolyl radical, C4H2S3N

Selective chlorination of thiophene-2,3-dithiol with SO(2)Cl(2) generates the corresponding sulfenyl chloride, 2,3-C(4)H(2)S(SCl)(2). Subsequent condensation with Me(3)SiN(3) yields the thiophenodithiazolylium salt [C(4)H(2)S(3)N]Cl, [TDTA]Cl. The structure of the cation, TDTA+, was established by X-ray diffraction as both its AsF(6)(-) and HSO(4)(-) salts. Reduction of [TDTA]Cl with Ag powder yields the radical TDTA* which was characterised by X- and Q-band (9 and 34 GHz) EPR and ENDOR studies. The spin density distributions estimated from the EPR/ENDOR measurements were found to be in very good agreement with those determined by DFT (B3LYP/6-31G*) indicating that ca 10% of the spin density is delocalised onto the thiophene ring. Comparison of the spin density distributions in TDTA* and the isoelectronic trithiatriazapentalenyl radical C(2)S(3)N(3), TTTA*, indicates that replacement of N by C-H leads to a localisation of the spin density on the dithiazolyl ring.     

Discovery of new mutually orthogonal bioorthogonal cycloaddition pairs through computational screening

Density functional theory (DFT) calculations and experiments in tandem led to discoveries of new reactivities and selectivities involving bioorthogonal sydnone cycloadditions. Dibenzocyclooctyne derivatives (DIBAC and BARAC) were identified to be especially reactive dipolarophiles, which undergo the (3 + 2) cycloadditions with N-phenyl sydnone with the rate constant of up to 1.46 M^–1 s^–1. Most significantly, the sydnone-dibenzocyclooctyne and norbornene-tetrazine cycloadditions were predicted to be mutually orthogonal. This was validated experimentally and used for highly selective fluorescence labeling of two proteins simultaneously.     

无机酸洗脱对胜利褐煤微晶结构及其自燃倾向性的影响

利用XRD、Raman、XPS和FT-IR表征技术,研究无机酸洗脱(HCl、H2SO4、HCl-HF)处理的胜利褐煤微晶结构的变化,采用自行设计的表面吸附仪-GC联用装置,对样品进行不同温度的低温脉冲氧化实验,考察了煤样在不同温度下氧吸附量的变化规律,通过低温脉冲氧吸附规律与TG/DTG和固定床燃烧实验关联,考察了煤样的自燃倾向。结果表明,无机酸洗脱对矿物质的脱除使得煤结构的有序度增加,石墨化程度提高,无机酸洗脱煤样与原煤相比吸氧量明显下降。随着吸附温度的升高,各煤样吸氧量明显增加,且随着脱除矿物质程度的增加,吸氧量呈减小的趋势,导致自燃倾向降低。     

Synthetic,Chemically Defined Polymer‐Coated Microcarriers for the Expansion of Human Mesenchymal Stem Cells

Mesenchymal stem cells (MSC), also called marrow stromal cells, are adult cells that have attracted interest for their potential uses in therapeutic applications. There is a pressing need for scalable culture systems due to the large number of cells needed for clinical treatments. Here, a tailorable thin polymer coating—poly(poly(ethylene glycol) methyl ether methacrylate‐ran‐vinyl dimethyl azlactone‐ran‐glycidyl methacrylate) [P(PEGMEMA‐r‐VDM‐r‐GMA); PVG]—to the surface of commercially available polystyrene and glass microcarriers to create chemically defined surfaces for large‐scale cell expansion is applied. These chemically defined microcarriers create a reproducible surface that does not rely on the adsorption of xenogenic serum proteins to mediate cell adhesion. Specifically, this coating method anchors PVG copolymer through ring opening nucleophilic attack by amine residues on poly‐l ‐lysine that is pre‐adsorbed to the surface of microcarriers. Importantly, this anchoring reaction preserves the monomer VDM reactivity for subsequent functionalization with an integrin‐specific Arg‐Gly‐Asp peptide to enable cell adhesion and expansion via a one‐step reaction in aqueous media. MSCs cultured on PVG‐coated microcarriers achieve sixfold expansion—similar to the expansion achieved on PS microcarriers—and retain their ability to differentiate after harvesting.     

Kit for instant 99mTc labeling of the antimicrobial peptide ubiquicidin 29-41

Summary The ubiquicidin 29-41 fragment (UBI) is a cationic antimicrobial peptide. The aim of this study was to develop an instant kit formulation for the preparation of ^99mTc-UBI 29-41 in high radiochemical yield and to evaluate its use as an infection imaging agent in humans. The components were selected to produce a direct ^99mTc labeling, presumably to the amine groups of Lys and Arg7. ^99mTc-UBI 29-41 obtained from the lyophilized kit showed radiochemical purity of >97% with an average target/non-target ratio of 2.3±0.6 in positive infection sites at 2 hours. Kits were stable at 4 °C for over 6 months.     

Determination of malachite green and leucomalachite green in a variety of aquacultured products by liquid chromatography with tandem mass spectrometry detection

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for determining the residues of malachite green (MG) and leucomalachite green (LMG) in a number of aquatic species. MG and its metabolite were extracted from homogenized tissues with a perchloric acid-acetonitrile solution; the extract was centrifuged; and an aliquot was taken, concentrated, and passed through a chemically bonded octadecyl C18 solid-phase extraction column. The compounds of interest were eluted with acetonitrile, and the eluate was evaporated to dryness. The residue was dissolved in acetonitrile and diluted with water in preparation for analysis by LC/MS/MS. MG and its metabolite were determined by reversed-phase LC using a Luna C18 column with an ammonium hydroxide-formic acid buffer in acetonitrile gradient and MS/MS detection using multiple reaction monitoring. Calibration curves were linear for all analyses between 5 and 500 pg injected for both analytes, with recoveries ranging from 81% for LMG to 98% for MG in salmon spiked at the 1 ng/g level. Detection limits of 0.1 ng/g for both MG and LMG were easily obtainable using the recommended method. The operational errors, interferences, and recoveries for spiked samples compared favorably with those obtained by established methodology. The recommended method is simple, rapid, and specific for monitoring residues of MG and LMG in a number of aquatic species.     

Direct conversion of N-methoxy-N-methylamides (Weinreb amides) to ketones via a nonclassical Wittig reaction

[reaction: see text] N-Methoxy-N-methylamides (Weinreb amides) are converted efficiently into ketones by reaction with alkylidenetriphenylphosphoranes and in situ hydrolysis of the product.     

Anisotropic metal nanoparticles: Synthesis, assembly, and optical applications

This feature article highlights work from the authors' laboratories on the synthesis, assembly, reactivity, and optical applications of metallic nanoparticles of nonspherical shape, especially nanorods. The synthesis is a seed-mediated growth procedure, in which metal salts are reduced initially with a strong reducing agent, in water, to produce approximately 4 nm seed particles. Subsequent reduction of more metal salt with a weak reducing agent, in the presence of structure-directing additives, leads to the controlled formation of nanorods of specified aspect ratio and can also yield other shapes of nanoparticles (stars, tetrapods, blocks, cubes, etc.). Variations in reaction conditions and crystallographic analysis of gold nanorods have led to insight into the growth mechanism of these materials. Assembly of nanorods can be driven by simple evaporation from solution or by rational design with molecular-scale connectors. Short nanorods appear to be more chemically reactive than long nanorods. Finally, optical applications in sensing and imaging, which take advantage of the visible light absorption and scattering properties of the nanorods, are discussed.     

Atomic force microscopy study of beta-substituted-T7 oligothiophene films on mica: mechanical properties and humidity-dependent phases

The structural and mechanical properties of Langmuir-Blodgett monolayer and multilayer films of 3",4"-didecyl-5,2'; 5',2"; 5",2'; 5',2"; 5",2''; 5'',2"-heptathiophene-4'-acetic acid on mica have been studied by atomic force microscopy (AFM) as a function of humidity, temperature, and applied force. The molecules orient with the carboxylic acid group pointing toward the mica surface and expose the alkyl side chains to the air interface. As the load applied by the AFM tip increases, the film is compressed easily from an initial height of 2 to 1.2 nm. After compression the films can support much higher loads without loss of height. The state of aggregation of the molecules was found to be sensitive to the environmental humidity, which induced reversible changes. Annealing the samples with monolayer or multilayer films resulted in irreversible changes when the temperature exceeded approximately 100 degrees C.