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ABSTRACT: The size-dependent phase-transfer property of metal nanoparticles is used to develop a simple experimental procedure that can effectively refine the particle size from colloidal solutions prepared by wet-chemistry. The protocol calls for firstly the mixing of the metal hydrosol with an ethanol solution of dodecylamine, and then the extraction of the dodecylamine-stabilized metal nanoparticles into toluene. This method offers an effective approach to prepare metal nanoparticles with narrow size distribution from an arbitrary particle size distribution.
Journal of Nanoscience and Nanotechnology 02/2013; 13(2):1278-81. · 1.56 Impact Factor
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ABSTRACT: Mastery of the structure of nanomaterials enables control of their properties to enhance their performance for a given application. Herein we demonstrate the synthesis of metal nanomaterials with hollow interiors or cage-bell structures based on the inside-out diffusion of Ag in core-shell structured nanoparticles. It begins with the synthesis of core-shell Ag-M or core-shell-shell M(A)-Ag-M(B) nanoparticles in an organic solvent. Ag is then extracted from the core or the inner shell by bis(p-sulfonatophenyl)phenylphosphane, which binds strongly with Ag(I)/Ag(0) to allow the complete removal of Ag in 24-48 h, leaving behind an organosol of hollow or cage-bell structured metal nanomaterials. Because of their relatively lower densities, which usually translate to a higher surface area than their solid counterparts, the hollow and cage-bell structured metal nanomaterials are especially relevant to catalysis. For example, cage-bell structured Pt-Ru nanoparticles were found to display outstanding methanol tolerance for the cathode reaction of direct methanol fuel cells (DMFCs) as a result of the differential diffusion of methanol and oxygen in the cage-bell structure.
Journal of the American Chemical Society 06/2012; 134(28):11602-10. · 9.91 Impact Factor
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ABSTRACT: A novel method for the organocatalytic syn diacetoxylation of alkenes has been developed using aryl iodides as efficient catalysts. A broad range of substrates, including electron-rich as well as electron-deficient alkenes, are smoothly transformed by the new procedure, furnishing the desired products in good to excellent yields with high diastereoselectivity (up to >19:1 dr).
Organic Letters 06/2012; 14(13):3336-9. · 5.86 Impact Factor
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ABSTRACT: Hydrogels with the advantages of prolonging drug release and administration convenience are necessary for intravaginal drug delivery to prevent sexual transmission of human immunodeficiency virus and other vaginal infections. In this study, the thermosensitive hydrogel of methylcellulose modified by stearic acid (MCS) were evaluated in the presence of NaCl and phosphates, which exhibited sol-to-gel transition performance at body temperature or even lower. The in vitro cytotoxicity and in vivo mucosal irritation were investigated and the results showed that MCS hydrogel possessed good biocompatibility similar with hydroxyethyl cellulose (HEC) gel. Significantly, the release studies revealed that MCS hydrogel could control tenofovir sustained release for 10 h without burst release, longer than that from HEC gel or poloxamer 407 hydrogel. Therefore, MCS thermosensitive hydrogel would be a promising carrier for intravaginal delivery of antiviral drugs for long time controlled release.
Journal of Materials Science Materials in Medicine 05/2012; 23(8):1913-9. · 2.32 Impact Factor
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ABSTRACT: Heterogeneous Au-Pt nanostructures have been synthesized using a sacrificial template-based approach. Typically, monodispersed Au nanoparticles are prepared first, followed by Ag coating to form core-shell Au-Ag nanoparticles. Next, the galvanic replacement reaction between Ag shells and an aqueous H(2)PtCl(6) solution, whose chemical reaction can be described as 4Ag + PtCl(6)(2-)→ Pt + 4AgCl + 2Cl(-), is carried out at room temperature. Pure Ag shell is transformed into a shell made of Ag/Pt alloy by galvanic replacement. The AgCl formed simultaneously roughens the surface of alloy Ag-Pt shells, which can be manipulated to create a porous Pt surface for oxygen reduction reaction. Finally, Ag and AgCl are removed from core-shell Au-Ag/Pt nanoparticles using bis(p-sulfonatophenyl)phenylphosphane dihydrate dipotassium salt to produce heterogeneous Au-Pt nanostructures. The heterogeneous Au-Pt nanostructures have displayed superior catalytic activity towards oxygen reduction in direct methanol fuel cells because of the electronic coupling effect between the inner-placed Au core and the Pt shell.
Dalton Transactions 03/2012; 41(10):2898-903. · 3.84 Impact Factor
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ABSTRACT: DNA damaging agents typically induce an apoptotic cascade in which p53 plays a central role. However, absence of a p53-mediated response does not necessarily abrogate programmed cell death, due to the existence of p53-independent apoptotic pathways, such as those mediated by the pro-apoptotic molecule ceramide. We compared ceramide levels before and after DNA damage in human osteosarcoma (U2OS) and colon cancer (HCT116) cells that were either expressing or deficient in p53. When treated with mitomycin C, p53-deficient cells, but not p53-expressing cells, showed a marked increase in ceramide levels. Microarray analysis of genes involved in ceramide metabolism identified acid ceramidase (ASAH1, up-regulated), ceramide glucosyltransferase (UGCG, down-regulated), and galactosylceramidase (GALC, up-regulated) as the three genes most affected. Experiments employing pharmacological and siRNA agents revealed that inhibition of UGCG is sufficient to increase ceramide levels and induce cell death. When inhibition of UGCG and treatment with mitomycin C were combined, p53-deficient, but not p53-expressing cells, showed a significant increase in cell death, suggesting that the regulation of sphingolipid metabolism could be used to sensitize cells to chemotherapeutic drugs.
Biochimica et Biophysica Acta 02/2012; 1821(7):943-53. · 4.66 Impact Factor
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ABSTRACT: Novel well-defined hydrophilic cationic polymers with different length of polycation chain for gene delivery, poly(vinyl pyrrolidone)-graft-poly(2-dimethylaminoethyl methacrylate)s (PPDs), were synthesized by atom transfer radical polymerization (ATRP). The chemical structures and compositions of these polymers were characterized by FT-IR, (1)H-NMR and GPC. The experimental results of dynamic light scattering (DLS), ζ-potential and transmission electron microscopy (TEM) indicated that PPD could condense plasmid DNA (pDNA) to form nanocomplexes. Agarose gel retardation assays demonstrated that PPD could encapsulate plasmid DNA completely when the N/P ratio is equal to or above 3. MTT assay and in vitro gene transfection results indicated that PPD/pDNA complexes exhibited high transfection efficiency concomitant with obvious cytotoxicity. Furthermore, bovine serum albumin (BSA) was utilized to assembly with the binary complexes of PPD/pDNA to screen the residual surface positive charges of complexes in order to decrease cytotoxicity of the binary complexes. Physicochemical properties were characterized and the results indicated that the coating of BSA was able to decrease the zeta potential of the nano-sized PPD/pDNA complexes nearly to electroneutrality without interfering with DNA condensation ability. The ternary complexes of BSA/PPD/pDNA demonstrated no cytotoxicity and also maintained high gene transfection efficiency in HepG2 cells in 10% serum compared with that in serum-free condition.
Journal of Biomaterials Science Polymer Edition 01/2012; · 1.69 Impact Factor
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ABSTRACT: Ceramide has been suggested to participate in the neuronal cell death that leads to Alzheimer's disease (AD), but its role is not yet well-understood. We compared the levels of six ceramide subspecies, which differ in the length of their fatty acid moieties, in brains from patients who suffered from AD, other neuropathological disorders, or both. We found elevated levels of Cer16, Cer18, Cer20, and Cer24 in brains from patients with any of the tested neural defects. Moreover, ceramide levels were highest in patients with more than one neuropathologic abnormality. Interestingly, the range of values was higher among brains with neural defects than in controls, suggesting that the regulation of ceramide synthesis is normally under tight control, and that this tight control may be lost during neurodegeneration. These changes, however, did not alter the ratio between the tested ceramide species. To explore the mechanisms underlying this dysregulation, we evaluated the expression of four genes connected to ceramide metabolism: ASMase, NSMase 2, GALC, and UGCG. The patterns of gene expression were complex, but overall, ASMase, NSMase 2, and GALC were upregulated in specimens from patients with neuropathologic abnormalities in comparison with age-matched controls. Such findings suggest these genes as attractive candidates both for diagnostic purposes and for intervening in neurodegenerative processes.
Journal of Alzheimer's disease: JAD 01/2012; 29(3):537-47. · 3.74 Impact Factor
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ABSTRACT: In this study, well-defined amphiphilic cationic triblock copolymers with different lengths of polycationic chain, methoxy poly(ethylene glycol)-b-poly(D,L-lactide)-b-poly(2-dimethylaminoethyl methacrylate) (mPEG-b-PDLLA-b-PDMA), were synthesized and evaluated as carriers for gene delivery. The prepared copolymers can self-assemble into spherical core–shell nanoparticles (NPs). The NPs have a very low critical micelle concentration (CMC) value with only 0.025 mg mL À1 . Both copolymers can completely condense the pDNA into spherical complexes when the N/P ratio is equal to or above 3. Bovine serum albumin challenging and DNase I protection assay results demonstrate the mPEG-b-PDLLA-b-PDMA NPs can effectively protect the DNA against protein and nucleases. MTT assay results indicate that mPEG-b-PDLLA-b-PDMA NP/pDNA complexes exhibit obviously lower cytotoxicity compared with commercial gene transfection reagent Lipofectamine 2000/pDNA complexes. Subsequently, in vitro gene transfection studies in HeLa cells without serum show that mPEG 113 -b-PDLLA 10 -b-PDMA 120 NP/pDNA complexes exhibit higher transfection efficiency than Lipofectamine 2000. Although the transfection efficiency is lower than that in the absence of serum, mPEG 113 -b-PDLLA 10 -b-PDMA 120 NPs still display equivalent gene transfection efficiency compared to Lipofectamine 2000 when N/P ratio is above 15 in DMEM with 10% serum.
Soft Matter 11/2011; 8(7):2252-2260. · 4.39 Impact Factor
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ABSTRACT: Selective syn and anti diacetoxylations of alkenes have been achieved using a PhI(OAc)(2)/BF(3)·OEt(2) system in the presence and absence of water, respectively. A broad range of substrates including electron-deficient alkenes (such as α,β-unsaturated esters) could be elaborated efficiently at room temperature with this methodology, furnishing the desired products in good to excellent yields and diastereoselectivity. In particular, a multigram-scale diastereoselective diacetoxylation of methyl cinnamate (5.00 g) was also accomplished in a few hours, maintaining the same efficiency as small-scale reaction. This novel methodology provides an alternative approach for the preparation of various 1,2-diols.
The Journal of Organic Chemistry 11/2011; 76(24):9997-10004. · 4.45 Impact Factor
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ABSTRACT: Controlling the morphology of transition-metal nanoparticles (TMNPs) can be an effective way to produce nanomaterials with favourable properties (activity and selectivity, etc.). Here we reported the shape control syntheses of TMNPs including Ru, Rh, Pd, Os, Ir, Pt, alloy PtRu, PtOs, and PtRuOs by co-reducing their metal precursors and Ag(I) ions in an organic medium. In this approach, Ag(I) ions were reduced first for their higher reduction potential, leading to the formation of spherical Ag nanoparticles. Then the subsequently reduced atoms of other transition-metals grew on the pre-existing Ag nanoparticles, resulting in the TMNPs with spherical or quasi-spherical shapes. In the absence of Ag precursors, the TMNPs obtained under same experimental conditions were dominated by irregular shapes, for example, rods, multi-pods, worm-like, or star-like, etc. The dependence of the property on the shape of the particles was also demonstrated using the catalytic oxidation of methanol as an example.Graphical abstractAn Ag facilitated approach for the shape control of transition-metal nanoparticles was developed, which is actually built on the formation of core–shell Ag-metal structures although the syntheses were carried out in a one-pot way.Highlights► We developed a Ag-facilitated approach to control the shape of transition-metal nanoparticles (TMNPs). ► Quasi-spherically shaped TMNPs were prepared by co-reducing the metal precursors and Ag(I) ions in an organic medium. ► The shape control of TMNPs was actually based on the formation of core-shell Ag-metal structures. ► The Ag facilitated alloy TMNPs showed superior catalytic activities towards methanol oxidation.
Colloids and Surfaces A Physicochemical and Engineering Aspects 385:85-90. · 2.24 Impact Factor
