Water soluble chromone Schiff base derivatives as fluorescence receptor for aluminium(III)

A novel water-soluble chromone Schiff base derivatives bearing polyhydroxylated moiety were prepared and applied for specific recognition of metal ions in aqueous medium. Their selective fluorescence response to Al(III) over a variety of other biologically important metal ions were demonstrated. Electronic parameters of the sensors were also studied by quantum chemical computations.     

Binding energies of five molecular pincers calculated by explicit and implicit solvent models

Molecular pincers or tweezers are designed to hold and release the target molecule. Potential applications involve drug distribution in medicine, environment technologies, or microindustrial techniques. Typically, the binding is dominated by van der Waals forces. Modeling of such complexes can significantly enhance their design; yet obtaining accurate complexation energies by theory is difficult. In this study, density functional theory (DFT) computations combined with dielectric continuum solvent model are compared with the potential of mean force approach using umbrella sampling and the weighted histogram analysis method (WHAM) with molecular dynamics (MD) simulations. For DFT, functional and basis set effects are discussed. The computed results are compared to experimental data based on NMR spectroscopic measurements of five synthesized tweezers based on the Tröger's basis. Whereas the DFT computations correctly provided the observed trends in complex stability, they failed to produce realistic magnitudes of complexation energies. Typically, the binding was overestimated by DFT if compared to experiment. The simpler semiempirical PM6‐DH2X scheme proposed lately yielded better magnitudes of the binding energies than DFT but not the right order. The MD‐WHAM simulations provided the most realistic Gibbs binding energies, although the approximate MD force fields were not able to reproduce completely the ordering of relative stabilities of model complexes found by NMR. Yet the modeling provides interesting insight into the complex geometry and flexibility and appears as a useful tool in the tweezers' design. © 2012 Wiley Periodicals, Inc.     

Functionalized surface arrays for spatial targeting of immune cell signaling

The effect of surface topography and chemistry on cellular response is of fundamental importance, especially where living systems encounter device surfaces as in medical implants, tissue engineering, and cell-based sensors. To understand these biological processes on surfaces, there is a widespread interest in tailored surface-active materials produced by a combination of surface chemistry coupled to advanced patterning processes. We utilize self-assembled monolayers (SAMs) as molecular templates with submicrometer-scale spatial resolution to engage and cluster IgE receptors on rat basophilic leukemia (RBL) mast cells. Bioactive templates consisted of gold arrays on silicon with patterns from 1 mum down to 45 nm. These gold arrays served as molecular tethering sites, enabling covalent binding of functionalized self-assembled monolayers of alkanethiols. The free ends of the monolayers were functionalized with 2,4-dinitrophenyl(DNP)-caproate-based ligands which interact specifically with anti-DNP IgE bound to its high affinity cell surface receptor, FcepsilonRI on RBL mast cells. Present results on structures 1 mum down to 600 nm in size indicate that these ligand-immobilized patterned arrays can function as a powerful tool for visualization and systematic characterization of cell membrane involvement in IgE receptor-mediated immune cell signaling.     

Laser-assisted synthesis of superparamagnetic Fe@Au core-shell nanoparticles

A novel method combining wet chemistry for synthesis of an Fe core, 532 nm laser irradiation of Fe nanoparticles and Au powder in liquid medium for deposition of an Au shell, and sequential magnetic extraction/acid washing for purification has been developed to fabricate oxidation-resistant Fe@Au magnetic core-shell nanoparticles. The nanoparticles have been extensively characterized at various stages during and up to several months after completion of the synthesis by a suite of electron microscopy techniques (HRTEM, HAADF STEM, EDX), X-ray diffraction (XRD), UV-vis spectroscopy, inductively coupled plasma atomic emission spectroscopy, and magnetometry. The surface plasmon resonance of the Fe@Au nanoparticles is red shifted and much broadened as compared with that of pure colloidal nano-gold, which is explained to be predominantly a shell-thickness effect. The Au shell consists of partially fused approximately 3-nm-diameter fcc Au nanoparticles (lattice interplanar distance, d = 2.36 A). The 18-nm-diameter magnetic core is bcc Fe single domain (d = 2.03 A). The nanoparticles are superparamagnetic at room temperature (300 K) with a blocking temperature, T(b), of approximately 170 K. After 4 months of shelf storage in normal laboratory conditions, their mass magnetization per Fe content was measured to be 210 emu/g, approximately 96% of the Fe bulk value.     

From imaging to dosimetry: GEANT4-based study on the application of Medipix to neutron dosimetry

An application of Medipix2 using a newly developed segmented multiple thickness polyethylene (PE) converter for fast neutron detection is presented. The system has the ability to provide an energy independent response for the dose equivalent for fast neutrons. The application of weighting factors to each defined thickness of PE allows for a flattening of the response of the detector system for dosimetry applications. Six PE converter segments were applied, and their thicknesses and weighting factors were optimised to obtain the required energy independent detector response. The study performed by means of GEANT4. Its suitability for neutron dosimetry was studied with respect to a previously published work.     

Benzoisothiazole-1,1-dioxide-based synthetic receptor for zinc ion recognition in aqueous medium and its interaction with nucleic acids

Benzoisothiazole-1,1-dioxide-based synthetic receptor was prepared by two step synthesis in 92 % overall yield. Its applicability for the determination of Zn(II) and interction with nucleic acids was studied by absorption spectroscopy. Obtained data, specifically low limit of detection, 0.15 µM (R² = 0.9933), showed the high potential of the tested structure motif for the recognition and determination of Zn(II) ions in aqueous media (water:DMSO; 99:1 (ν/ν)). Alone receptor displayed orderly strongly RNA affinity. Value of LogK was 6.1 and 4.9 for its complex (1:1) with RNA and DNA, respectively. Nevertheless, in presence of complexed Zn(II) ions, its DNA affinity (represent by K, LogK = 5.7) strongly grow to near value obtained for its interaction with RNA. On the other hand, its RNA affinity (LogK = 5.9) displayed not significantly change in the presence of complexed one.     

Characterization challenges for a cellulose nanocrystal reference material: dispersion and particle size distributions

Cellulose nanocrystals (CNCs) have high aspect ratios, polydisperse size distributions, and a strong propensity for aggregation, all of which make them a challenging material for detailed size and morphology characterization. A CNC reference material produced by sulfuric acid hydrolysis of softwood pulp was characterized using a combination of dynamic light scattering (DLS), atomic force microscopy (AFM), transmission electron microscopy, and X-ray diffraction. As a starting point, a dispersion protocol using ultrasonication was developed to provide CNC suspensions with reproducible size distributions as assessed by DLS. Tests of various methods for AFM sample preparation demonstrated that spin coating on a positively charged substrate maximizes the number of individual particles for size analysis, while minimizing the presence of agglomerates. The effects of sample-to-sample variability, analyst bias, and sonication on size distributions were assessed by AFM. The latter experiment indicated that dispersion of agglomerates by sonication did not significantly change the size distribution of individual CNCs in suspension. Comparison with TEM data demonstrated that the two microscopy methods provide similar results for CNC length (mean ~?80 nm); however, the particle width as measured by TEM is approximately twice that of the CNC height (mean 3.5 nm) measured by AFM. The individual crystallite size measured by X-ray diffraction is intermediate between the two values, although closer to the AFM height, possibly indicating that laterally agglomerated CNCs contribute to the TEM width. Overall, this study provides detailed information that can be used to assess the factors that must be considered in measuring CNC size distributions, information that will be useful for benchmarking the performance of different industrially sourced materials.     

Core-Penetrating Rydberg Series of BaF: Single-State and Two-State Fits of New Electronic States in the 4.4 </= n* </= 14.3 Region

We report results of optical-optical double-resonance studies of the Rydberg states of the BaF molecule in the energy region of E = 33 100-38 200 cm(-1) (4.4 相似文献   

Supported lipid bilayers on biocompatible polysaccharide multilayers

Formation of supported lipid bilayers on soft polymer cushions is a useful approach to decouple the membrane from the substrate for applications involving membrane proteins. We prepared biocompatible polymer cushions by the layer-by-layer assembly of two polysaccharide polyelectrolytes, chitosan (CHI) and hyaluronic acid, on glass and silicon substrates. (CHI/HA)(5) films were characterized by atomic force microscopy, giving an average thickness of 57 nm and roughness of 25 nm in aqueous solution at pH 6.5. Formation of zwitterionic lipid bilayers by the vesicle fusion method was attempted using DOPC vesicles at pH 4 and 6.5 on (CHI/HA)(5) films. At higher pH adsorbed lipids had low mobility and large immobile lipid fractions; a combination of fluorescence and AFM indicated that this was attributable to formation of poor quality membranes with defects and pinned lipids rather than to a layer of surface-adsorbed vesicles. By contrast, more uniform bilayers with mobile lipids were produced at pH 4. Fluorescence recovery after photobleaching gave diffusion coefficients that were similar to those for bilayers on PEG cushions and considerably higher than those measured on other polyelectrolyte films. The results suggest that the polymer surface charge is more important than the surface roughness in controlling formation of mobile supported bilayers. These results demonstrate that polysaccharides provide a useful alternative to other polymer cushions, particularly for applications where biocompatibility is important.