Facile fabrication of amphiphilic gold nanoparticles with V-shaped brushes from block copolymers with a trithiocarbonate group as the junction

Amphiphilic gold nanoparticles grafted with V-shaped brushes (Au-V-brushes) were prepared by grafting a polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer with a trithiocarbonate group as the junction to the Au surface. The obtained Au-V-brushes were subjected to solubility test and UV-vis, FT-IR, TEM and DLS characterizations. It is found that the Au-V-brushes are soluble in both water and organic solvents. In the common solvent DMF, the size of the Au-V-brushes is about 17 nm, whereas in selective solvents (toluene and water) aggregates of 70-90 nm are formed. Phase transfer of the Au-V-brushes from the water phase into the toluene phase occurs upon addition of Na(2)SO(4) into water and the Au-V-brushes can also transfer from the toluene phase to the interface of toluene and water phases after addition of citric acid in the water phase.     

Construction and deconstruction of multilayer films containing polycarboxybetaine: effect of pH and ionic strength

The influences of pH and NaCl concentration of dipping solutions and the pH and NaCl concentration of disintegration solutions on the disintegration behaviors of poly(4-vinylpyridiniomethanecarboxylate) (PVPMC)/poly(sodium 4-styrenesulfonate) (PSS) (PVPMC/PSS) multilayer films were investigated by ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), quartz crystal microbalance (QCM) and atomic force microscopy (AFM). It was found that the disintegration rates and degrees of PVPMC/PSS multilayer films in neutral water could be well controlled by changing pH of dipping solutions and immersion time during the disintegration process. Furthermore, PVPMC/PSS multilayer films could be disintegrated completely and rapidly in pH 8 alkali solution or physiological condition (i.e., 0.15 M NaCl solution). The controllable disintegration of PVPMC/PSS multilayer films was then utilized to fabricate PEC/PSS free-standing multilayer films, in which PEC was a positively charged polyelectrolyte complex made from excessive poly(diallyldimethylammonium) (PDDA) and PSS. The experimental results indicated that the disintegration rates of PVPMC/PSS sacrificial sublayer strongly affected the integrity of the resultant PEC/PSS free-standing multilayer films. Only free-floating PEC/PSS was released from neutral water by disintegrating PVPMC/PSS multilayer sublayers. However, large size flat and tube-like PEC/PSS free-standing multilayer films with good mechanical properties were obtained facilely from pH 8 alkali solution and 0.15 M NaCl solution, respectively. The preparation of such free-standing films at physiological condition may be useful in the biological or medical application.     

Facile patterning of upconversion NaYF4:Yb,Er nanoparticles

Different kinds of highly ordered patterns of NaYF(4):Yb,Er nanoparticles on gold substrates were fabricated using a simple method combining micro-contact printing and "breath figures" techniques. Ordered arrays of water droplets were first formed in the hydrophilic regions of patterned self-assembled monolayers (SAMs). This was subsequently submerged in a chloroform solution of NaYF(4):Yb,Er nanoparticles. The particles were spontaneously assembled at the interface of chloroform/water droplet surface, leading to different kinds of uniform patterns after solvent evaporation. The structures of NaYF(4):Yb,Er particles patterns depended on the dimension of the substrate, the concentration of the NaYF(4):Yb,Er nanoparticles and the water condensation process.     

Palladium complexes affect the aggregation of human prion protein PrP106-126

Many neurodegenerative disorders are induced by protein conformational change. Prion diseases are characterized by protein conformational conversion from a normal cellular form (PrP(C)) to an abnormal scrapie isoform (PrP(Sc)). PrP106-126 is an accepted model for studying the characteristics of PrP(Sc) because they share many biological and physiochemical properties. To understand how metal complexes affect the property of the prion peptide, the present work investigated interactions between Pd complexes and PrP106-126 based on our previous research using Pt and Au complexes to target the peptide. The selected compounds (Pd(phen)Cl(2), Pd(bipy)Cl(2), and Pd(en)Cl(2)) showed strong binding affinity to PrP106-126 and affected the conformation and aggregation of this active peptide in a different binding mode. Our results indicate that it may be the metal ligand-induced spatial effect rather the binding affinity that contributes to better inhibition on peptide aggregation. This finding would prove valuable in helping design and develop novel metallodrugs against prion diseases.     

Porous ZnCo2O4 nanowires synthesis via sacrificial templates: high-performance anode materials of Li-ion batteries

A simple microemulsion-based method has been developed to synthesize ZnCo(2)(C(2)O(4))(3) nanowires that can be transformed to porous ZnCo(2)O(4) nanowires under annealing conditions. The morphology of porous ZnCo(2)O(4) nanowires can be tuned by the initial ZnCo(2)(C(2)O(4))(3) nanowires and the annealing temperatures. The as-synthesized porous ZnCo(2)O(4) nanowires have been applied as anode materials of Li-ion batteries, which show superior capacity and cycling performance. The porous one-dimensional (1D) nanostructures and large surface area are responsible for the superior performance. Moreover, it is indicated that porous ZnCo(2)O(4) nanowires synthesized at low annealing temperature (500 °C) show larger capacity and better cycling performance than that prepared at high annealing temperature (700 °C), because of their higher porosity and larger surface area.     

Singlet and triplet energy transfers in tetra-(meso-truxene)zinc(II)- and tetra-(meso-tritruxene)zinc(II) porphyrin and porphyrin-free base dendrimers

The synthesis, optical properties, and energy transfer features of four dendrimers composed of meso-tetrasubstituted zinc(II) porphyrin (ZnP) or a free base (P) central core, where the substituents are four truxene (Tru) or four tritruxene dendrons (TriTru), TruP, TriTruP, TruZnP, and TriTruZnP, are reported. Selective excitation of the truxene donors results in a photoinduced singlet energy transfer from the truxenes to the porphyrin acceptor. The rates for singlet energy transfer (k(ET)), evaluated from the change in the fluorescence lifetime of the donors (Tru and TriTru) in the presence and absence of the acceptor (P or ZnP) for TruP, TruZnP, TriTruP, and TriTruZnP, are 5.9, 1.2, 0.87, and 0.74 (ns)(-1) at 298 K and 2.6, 2.6, 2.7, and 1.2 (ns)(-1) at 77 K, respectively. A slow triplet-triplet energy transfer from truxene to porphyrin cores in glassy 2MeTHF at 77 K is also reported with rates of 1.3 × 10(3) and 0.10 × 10(2) s(-1) for TruZnP and TriTruZnP, respectively. If the Dexter mechanism for the triplet energy transfers is considered, these slow rates are easily explained by a poor orbital overlap between the truxene and porphyrin π systems. The fluorescence quantum yields (Φ(F)) are 0.20 and 0.16 for TruP and TriTruP and 0.08 and 0.10 for TruZnP and TriTruZnP, respectively at 298 K. At 298 K, a phosphorescence from TruZnP at 795 nm was also observed and is associated with the ZnP chromophore.     

Lewis acid catalyzed cyclization of glycals/2-deoxy-D-ribose with arylamines: additional findings on product structure and reaction diastereoselectivity

The cyclization reactions of arylamines with 2-deoxy-D-ribose or glycals were reinvestigated in the current report. In the montmorillonite KSF- or InCl(3)-initiated reactions of 2-deoxy-D-ribose with arylamines, a pair of diastereomeric tetrahydro-2H-pyran-fused tetrahydroquinolines was obtained in a nearly 1:1 ratio where the structure of one diastereomer was incorrectly assigned in the literature. Meanwhile, the diastereoselectivity in InBr(3)-catalyzed cyclization of glycals with arylamines was also incorrectly reported previously. It was found that high diastereomeric selectivity was achieved only when a C5-substituted glycal was used; otherwise, a pair of diastereomers was obtained in moderate yield with 1:1 diastereomeric ratio. Furthermore, tetrahydrofuran-fused tetrahydroquinolines 5b and 5b' were also prepared successfully by using TBDPS-protected ribose as the glycal precursor and montmorillonite KSF as the activator.     

Pd-catalyzed asymmetric allylic etherizations with oximes by chiral alkene-phosphine ligands

Palladium-catalyzed asymmetric allylic etherizations with a variety of oximes as nucleophiles utilizing a chiral alkene-phosphine hybrid ligand have been successfully achieved for the first time to afford the optical active oxime ethers in high yields with good to excellent enantioselectivities.     

Organocatalytic asymmetric conjugate addition and cascade acyl transfer reaction of α-nitroketones

Organocatalytic asymmetric conjugate addition of α-nitroketones to β,γ-unsaturated α-keto esters has been developed. A pyrrolidine-based thiourea-tertiary amine was identified as the best catalyst. The reaction was found to proceed via cascade conjugate addition and acyl transfer reaction. A number of α-nitroketones and β,γ-unsaturated α-keto esters were examined in this transformation. 5-Nitro-2-acyloxypent-2-enoates were obtained in good yields (up to 99%) and enantioselectivities (up to 99% ee). The products could be hydrolyzed to provide 5-nitro-2-oxopentanoates, which are not available from the direct addition of nitromethane to β,γ-unsaturated α-keto esters.     

Comparative study of the interaction of O2 and C2H4 with small vanadium clusters from density functional theory

We have studied C(2)H(4) and O(2) molecules separately or simultaneously for adsorption on V(n) (n = 2-8) clusters, and V(n) clusters catalyzed ethylene oxidation to acetaldehyde using spin-polarized density functional theory calculations. Molecular adsorption and clear size-dependent adsorption energy are predicted for C(2)H(4). O(2) is dissociately adsorbed with nearly constant adsorption energy. In the case of coadsorption, O(2) and C(2)H(4) adsorb on the V(n) surface simultaneously. Each keeps the same adsorption form, molecular or dissociative, as in separate adsorption. The noted cooperative effect is noted in C(2)H(4) and O(2) coadsorption, which activates the C-C double bond of C(2)H(4) and favors its oxidization. Furthermore, both the separate and coadsorptions result in magnetic enhancement or reduction of V(n), which is found to be dependent on the cluster size and the adsorbates. In addition, we reveal the reaction mechanism of V(2) (V(6))-catalyzed ethylene oxidation to acetaldehyde and find the overall reaction is exothermic and barrierless.