The selective cleanup of complex matrices and simultaneous separation of benzo[a]pyrene by solid-phase extraction with MgO microspheres as sorbents

A new method for the selective cleanup of complex matrices and simultaneous separation of benzo[a]pyrene (BaP) was developed in this study. This method was based on solid-phase extraction (SPE) using magnesium oxide microspheres as sorbents, and it eliminated interferences from various impurities, such as lipids, sulphur, pigments, halobenzenes, polychlorodibenzo-p-dioxins and polychlorodibenzofurans. Several parameters, including the volume of rinsing and eluting solvents, the type of loading solvents and SPE sorbents, were optimized systematically. The capability for impurity removal was verified by gel permeation chromatography, gas chromatography, and liquid chromatography. Compared to commercial sorbents (silica gel, florisil and alumina), MgO microspheres exhibited excellent performance in the selective isolation of BaP and removal of impurities. The proposed method was applied to detect BaP in complex samples (sediments, soils, fish, and porcine liver). The limit of quantification (LOQ) was 1.04 ngL(-1), and the resulting regression coefficient (r(2)) was greater than 0.999 over a broad concentration range (9.5-7600 ngL(-1)). In contrast to traditional methods, the proposed method can give rise to higher recovery (85.1-100.8%) and better selectivity with simpler operation and less consumption of organic solvents (20-40 mL).     

Synthesis and surface photochemistry of graphitized carbon quantum dots

Graphitized carbon quantum dots (CQDs) were synthesized by a simple hydrothermal process with cetyltrimethylammonium bromide (CTAB) as the starting material and nitric acid as surface oxidant. The photoluminescent quantum yield (QY) of CQDs could be greatly enhanced through surface esterification with glycol. Based on the structure characterization, we proposed that the CQDs consisted of the stack of graphene sheets sized several nanometers and their excitation-dependent photoluminescence (PL) should be attributed to the n→π* transition of CO bond of surface carboxylic groups. And the PL of CQDs was obviously enhanced by the esterification of carboxylic groups, possibly due to the increase of the molecular coplanarity or the rigidity.     

In situ loading of palladium nanoparticles on mica and their catalytic applications

Mica supported Pd nanocatalysts were prepared by a two-step approach, in which SnCl(2) was first grafted onto mica via its reaction with hydroxyl groups on mica, followed by the in situ reduction of Pd(2+) by Sn(2+) on the surface of mica. The as-prepared Pd-Sn/mica catalysts were characterized by different techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and ICP analysis. The loaded Pd particles existed in the form of Pd(0) confirmed by XPS analysis, and distributed uniformly on mica with average size about 2.6 nm, as confirmed by TEM examination. The activities of the resultant catalysts for Heck reactions of iodobenzene and its derivatives with olefins and selective hydrogenation of citral were investigated. It was demonstrated that the as-prepared catalysts exhibited very high efficiency for these reactions.     

Preparation of electrospun luminescent polyimide/europium nanofibers by simultaneous in situ sol-gel and imidization processes

Comicellization of a star block copolymer poly(ε-caprolactone)-block-poly(diethylamino)ethyl methacrylate (S(PCL-b-PDEAEMA)) and a linear block copolymer methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) (mPEG-b-PCL) was developed to enhance the stability and lower the cytotoxicity of the micelles. The two copolymers self-assembled into the mixed micelles with a common PCL core surrounded by a mixed PDEAEMA/mPEG shell in aqueous solution. This core-shell structure was transformed to the core-shell-corona structure at high pH due to the collapse of the PDEAEMA segment. The properties of the polymeric micelles were greatly dependent on the weight ratio of the two copolymers and the external pH. As increasing the mPEG-b-PCL content, the size and the zeta potential of the mixed micelles were lowered while the pH-dependent stability and the biocompatibility were improved. Moreover, an increase in pH accelerated the release of indomethacin (IND) from the mixed micelles in vitro. These results augured that the mixed micelles could be applied as a stable pH-sensitive release system.     

Effect of Al-doping on the structure and optical properties of electrospun zinc oxide nanofiber films

Electrospun ZnO precursor nanofibers of average diameters 122±64 nm, 117±44 nm and 110±39 nm were fabricated by controlling the Al concentration of a polymeric solution. The resulting nanofibers were characterized by the XRD, SEM, EDS, TEM, XPS and PL. The electrospun Al-doped ZnO nanofiber films were polycrystalline and composed of densely packed grains, with crystallite size ranging from 28.7 nm, 25.7 nm, 25.4 nm to 20.4 nm corresponding to the atomic concentration of aluminum from 0, 1.6, 2.5 to 5.8 at.%. The incorporation of aluminum resulted in a decrease trend in the grain size and lattice parameter of the ZnO nanofiber films. The room temperature PL spectra of all samples show three different emissions, including UV (ultraviolet) emission with an obvious blue shift, Vis (visible) emission and NIR (near infrared) emission, the intensity of which decreases monotonically as the doping concentration is increased except for the highest doping level. The impurity content correlates with changes in the PL spectra, and the appropriate Al doping can improve the optical properties of ZnO nanofibers. The small size effect and Al-doping or the impurity incorporation should be responsible for the blue shift observation in Al-doped ZnO nanofiber films.     

Synthesis, characterization, interaction with DNA, and cytotoxic effect in vitro of new mono- and dinuclear Pd(II) and Pt(II) complexes with benzo[d]thiazol-2-amine as the primary ligand

A series of novel Pd(II) and Pt(II) complexes, [PdL(2)Cl(2)]·DMF (1), [Pd(2)(L-H)(2)(bpy)Cl(2)]·(H(2)O)(2)·DMF (2), [Pd(2)(L-H)(2)(phen)Cl(2)]·2H(2)O (3), [PtL(2)Cl(2)]·H(2)O (4), [Pt(2)(L-H)(2)(bpy)Cl(2)]·2H(2)O (5), and [Pt(2)(L-H)(2)(phen)Cl(2)]·H(2)O (6), where bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and L = 1,3-benzothiazol-2-amine, have been synthesized and characterized. The competitive binding of the complexes to DNA has been investigated by fluorescence spectroscopy. The values of the apparent DNA binding constant, calculated from fluorescence spectral studies, were 3.8 × 10(6) (K(app)(4)), 2.9 × 10(6) (K(app)(1)), 2.4 × 10(6) (K(app)(6)), 2.0 × 10(6) (K(app)(5)), 1.2 × 10(6) (K(app)(3)), and 6.9 × 10(5) (K(app)(2)). The binding parameters for the fluorescence Scatchard plot were also determined. On the basis of the data obtained, it indicates that the six complexes bind to DNA with different binding affinities in the relative order 4 > 1 > 6 > 5 > 3 > 2. Viscosity studies carried out on the interaction of complexes with Fish Sperm DNA (FS-DNA) suggested that all complexes bind by intercalation. Gel electrophoresis assay demonstrates that all the complexes can cleave the pBR 322 plasmid DNA and bind to DNA in a similar mode. The cytotoxic activity of the complexes has been also tested against four different cancer cell lines. The results show that all complexes have activity against KB, AGZY-83a, Hep-G2, and HeLa cells. In general, the Pt(II) complexes were found to be more effective than the isostructural Pd(II) complexes. The mononuclear complexes exhibited excellent activity in comparison with the dinuclear complexes in these four cell lines. Moreover, on the KB cell line (the human oral epithelial carcinoma), the observed result seems quite encouraging for the six complexes with IC(50) values ranging from 1.5 to 8.6 μM. Furthermore, apoptosis assay with hematoxylin-eosin staining shows treatment with the six complexes results in morphological changes of KB cells. The results induce apoptosis in KB cells.     

Protein's electronic polarization contributes significantly to its catalytic function

Ab initio quantum mechanical/molecular mechanical method is combined with the polarized protein-specific charge to study the chemical reactions catalyzed by protein enzymes. Significant improvement in the accuracy and efficiency of free-energy simulation is demonstrated by calculating the free-energy profile of the primary proton transfer reaction in triosephosphate isomerase. Quantitative agreement with experimental results is achieved. Our simulation results indicate that electronic polarization makes important contribution to enzyme catalysis by lowering the energy barrier by as much as 3 kcal/mol.     

Orbital alignment in photodissociation probed using strong field ionization

The photodissociation of molecules often produces atomic fragments with polarized electronic angular momentum, and the atomic alignment, for example, can provide valuable information on the dynamical pathways of chemical reactions unavailable by other means. In this work, we demonstrate for the first time that orbital polarization in chemical reactions can be measured with great sensitivity using strong field ionization by exploiting its extreme nonlinearity.     

Prospect for characterizing interacting soft colloidal structures using spin-echo small angle neutron scattering

Spin-echo small angle neutron scattering (SESANS) provides a new experimental tool for structural investigation. Due to the action of spin-echo encoding, SESANS measures a spatial correlation function in real space, as opposed to the structure factor S(Q), I(Q), in momentum (Q) space measured by conventional small angle neutron scattering. To establish the usefulness of SESANS in structural characterization, particularly for interacting colloidal suspensions, we have previously conducted a theoretical study of the SESANS correlation functions for model systems consisting of particles with uniform density profiles [X. Li, C.-Y. Shew, Y. Liu, R. Pynn, E. Liu, K. W. Herwig, G. S. Smith, J. L. Robertson, and W.-R. Chen J. Chem. Phys. 132, 174509 (2010)]. Within the same framework, we explore in the present paper the prospect of using SESANS to investigate the structural characteristics of colloidal systems consisting of particles with nonuniform intraparticle mass distribution. As an example, a Gaussian model of interacting soft colloids is used to investigate the manifestation of structural softness in a SESANS measurement. The exploration shows a characteristically different SESANS correlation function for interacting soft colloids, in comparison to that of a uniform hard sphere system. The difference arises from the Abel transform imbedded in the mathematical formalism bridging the SESANS spectra and the spatial autocorrelation function.     

Selectivity control in alkylidene carbene-mediated C-H insertion and allene formation

Regioselectivity of alkylidene carbene-mediated C-H insertion was explored utilizing electronic, conformational, steric, and stereoelectronic effects. Relying on these factors, highly regio- and chemoselective carbene insertion reaction of C-H bonds in different environments could be obtained. The observed selectivity clearly indicates that an electronic effect plays a more important role than steric effect. In general, C-H bonds in conformationally rigid cyclic environments are less reactive than those in acyclic systems toward carbene insertion, and in this situation, a competing intermolecular reaction between alkylidene carbene and trimethylsilyldiazomethane led to the formation of allenylsilanes. The formation of allenylsilane becomes more favorable as the concentration of reaction becomes higher, as well as the C-H bonds undergoing insertion becomes electronically and conformationally deactivated.