Showing papers by "Tewodros Asefa published in 2010"

Mesoporous Silica Microparticles Enhance the Cytotoxicity of Anticancer Platinum Drugs

Abstract: We report on the endocytosis and the time-dependent enhanced cytotoxicity of anticancer platinum drugs when the drugs are combined with (or loaded into) one of the two most common types of mesoporous silica materials, MCM-41 or SBA-15. The anticancer drug cisplatin and its isomer transplatin, when loaded on MCM-41 and SBA-15 microparticles, were less cytotoxic to leukemia cells than the drugs alone after 12 h exposure. However, the drug-loaded microparticles exhibited unprecedented enhanced cytotoxicity to the cancerous cells after 24 h of exposure. This cytotoxicity of the drug-loaded microparticles was even higher than of the pure drugs in solutions, suggesting that mesoporous silica microparticles loaded with cisplatin or transplatin enabled a localized intracellular release of the platinum compounds and possibly also facilitated the drug's hydrolysis, enhancing the desired cytotoxic effect.

Poly(allylamine)-stabilized colloidal copper nanoparticles: synthesis, morphology, and their surface-enhanced Raman scattering properties.

Abstract: Poly(allylamine)-stabilized spherical- and rod-shaped copper nanoparticles are synthesized by a simple chemical reaction. The synthesis is performed by the reduction of copper(II) salt with hydrazine in aqueous solution under atmospheric air in the presence of poly(allylamine) (PAAm) capping agent. Noteworthy of the advantages of the synthetic method includes its production of water dispersible copper nanoparticles at room temperature under no inert atmosphere, making the synthesis more environmentally friendly. The resulting copper nanoparticles are investigated by UV−vis spectroscopy and transmission electron microscopy (TEM). The results demonstrate that the amount of NaOH used is important for the formation of the copper nanoparticles while the reaction time and concentration of PAAm play key roles in controlling the size and shape of the nanoparticles, respectively. The resulting colloidal copper nanoparticles exhibit large surface-enhanced Raman scattering (SERS) signals.

Controlled synthesis of water-dispersible faceted crystalline copper nanoparticles and their catalytic properties

Abstract: We report a solution-phase synthetic route to copper nanoparticles with controllable size and shape. The synthesis of the nanoparticles is achieved by the reduction of copper(II) salt in aqueous solution with hydrazine under air atmosphere in the presence of poly(acrylic acid) (PAA) as capping agent. The results suggest that the pH plays a key role for the formation of pure copper nanoparticles, whereas the concentration of PAA is important for controlling the size and geometric shape of the nanoparticles. The average size of the copper nanoparticles can be varied from 30 to 80 nm, depending on the concentration of PAA. With a moderate amount of PAA, faceted crystalline copper nanoparticles are obtained. The as-synthesized copper nanoparticles appear red in color and are stable for weeks, as confirmed by UV/Vis and X-ray photoemission (XPS) spectroscopy. The faceted crystalline copper nanoparticles serve as an effective catalyst for N-arylation of heterocycles, such as the C--N coupling reaction between p-nitrobenzyl chloride and morpholine producing 4-(4-nitrophenyl)morpholine in an excellent yield under mild reaction conditions. Furthermore, the nanoparticles are proven to be versatile as they also effectively catalyze the three-component, one-pot Mannich reaction between p-substituted benzaldehyde, aniline, and acetophenone affording a 100% conversion of the limiting reactant (aniline).

Silica nanosphere-supported shaped Pd nanoparticles encapsulated with nanoporous silica shell: Efficient and recyclable nanocatalysts

Abstract: A synthetic method to a highly efficient heterogeneous nanocatalyst, consisting of silica nanosphere (SiO2) decorated with palladium nanoparticles (Pd–NP) that are further encapsulated within a nanoporous silica shell (Porous-SiO2), is reported. First, monodisperse, 5 nm and 20 nm Pd nanoparticles are synthesized and anchored onto silica nanospheres of ∼250 nm in diameter. These core-shell nanospheres are then coated with a secondary silica shell by the sol–gel process. This is followed by controlled etching of the outer silica shell to yield nanoporous silica shell around the Pd–NP. The thickness of the nanoporous silica shell and its pore structures are controlled by changing the synthetic conditions. The resulting nanoporous silica shell is proved to permit reactants to reach the Pd–NP while at the same time protect them from aggregation. These new nanomaterials, dubbed SiO2/Pd Nanoparticles/Nanoporous SiO2 (or SiO2/Pd–NP/Porous-SiO2) core-shell-shell nanospheres behave as heterogeneous nanocatalyst exhibiting high catalytic activity and turn-over-numbers (TONs) in hydrogenation reaction of various substrates at room temperature and 20 bar hydrogen pressure. The core-shell-shell nanospheres are proven to be versatile catalysts as they are also able to catalyze C–C coupling reactions effectively. Moreover, these heterogeneous nanocatalysts are stable showing negligible Pd leaching and aggregation, and can be recycled multiple times without loss of catalytic activity.

Biocompatibility of calcined mesoporous silica particles with cellular bioenergetics in murine tissues.

Abstract: A novel in vitro system was developed to investigate the effects of two forms of calcined mesoporous silica particles (MCM41-cal and SBA15-cal) on cellular respiration of mouse tissues. O(2) consumption by lung, liver, kidney, spleen, and pancreatic tissues was unaffected by exposure to 200 μg/mL MCM41-cal or SBA15-cal for several hours. Normal tissue histology was confirmed by light microscopy. Intracellular accumulation of the particles in the studied tissues was evident by electron microscopy. The results show reasonable in vitro biocompatibility of the mesoporous silicas with murine tissue bioenergetics.

Isomer-dependent adsorption and release of cis- and trans-platin anticancer drugs by mesoporous silica nanoparticles.

Abstract: We report on adsorption and release of the anticancer drugs cisplatin and transplatin from mesoporous silica nanomaterials, emphasizing the differences between cisplatin and its much less toxic isomer. Two types of particles, MCM-41 and SBA-15, were used, either as just synthesized or after calcination to remove the templates. The particles were characterized by TEM, nitrogen physisorption, and elemental analysis. The UV−vis spectra of cisplatin and transplatin were obtained and the intensities of several bands (205−210 nm, 210−220 nm, 220−235 nm, and 300−330 nm) were found proportional to drug concentrations, allowing their use for measuring drug concentration. To evaluate drug adsorption by nanoparticles, nanoparticles were incubated in drug solutions and removed by centrifugation, after which the supernatants were scanned by spectrometer to determine drug remaining. It was found that calcined MCM adsorbed less cisplatin or transplatin per particle than as-synthesized MCM. SBA nanoparticles adsorbed sli...

Recyclable Dirhodium Catalysts Embedded in Nanoporous Surface‐Functionalized Organosilica Hosts for Carbenoid‐Mediated Cyclopropanation Reactions

Abstract: Recyclable and efficient heterogeneous catalysts have been prepared by embedding dirhodium(II,II) core carboxylate complexes into the amine-functionalized nanosized channels of a mesoporous silica host, amine-SBA-15. Two alternative synthetic procedures for the preparation of the catalysts have been developed and adapted for the immobilization of dirhodium complexes of variable Lewis acidity. The catalytic activity of the resulting solid materials has been evaluated in model cyclopropanation reactions of styrene at variable reaction conditions (reaction substrate, temperature, time, and solvent). Importantly, the designed catalysts, which can be readily recovered and reused, display the reactivity and selectivity profiles exceeding or comparable to their homogeneous dirhodium(II) counterparts.

Substituent‐ and Catalyst‐Dependent Selectivity to Aldol or Nitrostyrene Products in a Heterogeneous Base‐Catalyzed Henry Reaction

Abstract: The aldol and Henry reactions between substituted benzaldehydes and nitroalkanes are among the most important C C bond forming reactions in organic synthesis. These reactions, which are known to be catalyzed by various types of base and organometallic catalysts, enable the synthesis of a number of organic compounds and intermediates useful for the development of many kinds of pharmaceuticals and natural products. 2] However, when catalyzed by many conventional catalysts, both reactions can often result in mixtures of two or three common types of products, such as p-substituted nitrostyrenes and nitroalcohols, as well as Michael products or polymers. For instance, several types of base catalysts are known to produce mixtures of the nitrostyrene, the nitroalcohol, the Michael product, and poly(nitrostyrene) from the Henry reaction between aromatic aldehydes and nitroalkanes. Although the two most common products of the Henry reaction, that is, nitroalcohol and nitrostyrene, have their own significance from the points of view of both synthesis and application, they require challenging laborand time-intensive separation techniques to isolate them from the mixture. Therefore, the design and synthesis of selective catalysts that are capable of producing one of these products in its pure form remains a challenging and important task. Some catalytic synthetic strategies that lead to nitroaldol or nitrostyrene products in somewhat pure forms from the Henry reaction have recently been reported. 5] These include the use of new types of systematically designed organoaminefunctionalized silica gel and mesoporous silica solid catalysts. By immobilizing primary, secondary, or tertiary amine groups, either individually or together, on silica gel, 6] mesoporous silica (MCM-41), or silica–alumina surfaces have been synthesized as solid-base and cooperative catalysts for the Henry reaction and for other base-catalyzed reactions. Unfortunately, many of these catalysts give mixtures of the Henry reaction products. By a multistep imprinting synthetic method, Bass et al. recently succeeded in making amine-functionalized inorganic–organic hybrid silica gel heterogeneous catalysts with and without silanol groups, which are capable of producing either b-nitrostyrene or nitroalcohol product, respectively. The materials’ catalytic activity to selectively produce b-nitrostyrene or nitroalcohol depended on the type of functional groups on the materials, which included polar/acidic, polar/ nonacidic, and nonpolar/nonacidic groups along with primary amines. The material with higher outer dielectric atmosphere (or polar/acidic groups) facilitated an ion-pair mechanism and charge separation in the transition state of the Henry reaction that favored the nitroaldol product. However, the material with lower dielectric atmosphere (nonpolar/nonacidic groups) favored the imine mechanism and the formation of b-nitrostyrene. Although these findings are indeed interesting, the authors only tested the reaction for one substrate, that is, p-nitrobenzaldehyde, and the scope of the catalyst selectivity with respect to the reactant substituents, which we found to be crucial for the reaction selectivity, was not explored. Furthermore, we recently reported that by changing the type of amine groups grafted onto the mesoporous silica materials from primary amine groups to secondary or tertiary amine groups, it is possible to selectively produce either b-nitrostyrene or nitroalcohol as the major product, with typical yields of greater than 90 % in about 10 min. However, this work also demonstrated selectivity only for p-nitrobenzaldehyde reactant. Suzuki et al. reported the synthesis of a mesoporous aminosilica catalyst which exclusively gave b-nitrostyrene without any selectivity towards the aldol product. Motokura et al. demonstrated cooperative catalytic activity to the Henry reaction by supported primary and tertiary amines on a silica–alumina framework. However, although the latter report demonstrated cooperative catalytic activity by the grafted primary and tertiary amines resulting in increased catalytic activity in the Henry reaction, the reaction led to only b-nitrostyrene or its successive Michael product as the major products. Furthermore, the possibility that the primary and tertiary amine groups in the catalyst acted individually to catalyze the Henry reaction to give b-nitrostyrene or nitroalcohol, respectively, as in Ref. [5] , was not discussed. Herein, we report intrinsic substrate-dependent selective catalytic reaction to form nitroaldol or b-nitrostyrene products with secondary and tertiary amine-grafted mesoporous catalysts (Scheme 1). Whereas secondary and tertiary amine-grafted materials are known to catalyze the Henry reaction, they have never before effected substituent-dependent selectivity to the nitroaldol or b-nitrostyrene product. We studied aromatic aldehyde substrates incorporating different types of substituents at their para-, ortho-, and metapositions. Depending on the sub[a] Dr. A. V. Biradar, Prof. T. Asefa Department of Chemistry and Chemical Biology Rutgers, The State University of New Jersey 610 Taylor Road, Piscataway, New Jersey 08854 (USA) Fax: (+ 1) 732-445-2581 E-mail : tasefa@rci.rutgers.edu Homepage: http ://rutchem.rutgers.edu/?q = node/565 [b] Dr. A. V. Biradar, Prof. T. Asefa Department of Chemical and Biochemical Engineering Rutgers, The State University of New Jersey 98 Brett Road, Piscataway, New Jersey 08854 (USA) Fax: (+ 1) 732-445-2581 E-mail : tasefa@rci.rutgers.edu [c] K. K. Sharma Department of Chemistry, Syracuse University Syracuse, New York 13244 (USA) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.200900259.

Continuous Henry reaction to a specific product over nanoporous silica-supported amine catalysts on fixed bed reactor

Abstract: We report a method for continuously producing the nitroaldol, the nitrostyrene, or the Michael product by performing the Henry reaction over a fixed bed reactor that is packed with primary or secondary amine-functionalized nanoporous materials. The % conversion of the reactants as well as the % selectivity to the particular product were found to be strongly dependent on the residence time of the reactants in the reactor (weight hourly spatial velocity or WHSV) as well as the type of reactant, catalyst and reaction temperature used. When a 0.08 M p-hydroxybenzaldehyde solution in nitromethane was passed over the fixed bed reactor containing primary amine-functionalized mesoporous silica catalyst by postgrafting in toluene (AP-T) at 90 °C with WHSV of 0.20, the reactor continuously and selectively generated for hours the p-hydroxy-β-nitrostyrene product with 100% selectivity at 31% reactant conversion (or with 90% selectivity at 88% reactant conversion for WHSV of 0.10). The remaining 12% product in the latter case was the Michael product. The corresponding primary amine-functionalized sample prepared by postgrafting of 3-aminopropyltrimethoxysilane (APTS) in isopropanol (AP-I) also gave similar results with slightly higher efficiency and selectivity to p-hydroxy-β-nitrostyrene. When the same reactant solution was passed over the bed-reactor packed with secondary amine grafted mesoporous silica catalyst by postgrafting in toluene (MAP-T) with WHSV of 0.25 at 90 °C, the reactor also continuously produced selectively the p-hydroxy-β-nitrostyrene product but less efficiently; i.e. with 91% selectivity at 21 reactant conversion for WHSV of 0.20 (or with 85% selectivity at 34% reactant conversion for WHSV of 0.10). Here also, the remaining product was the Michael addition product. Increasing the reaction temperature of the reactor containing the primary amine catalyst to 150 °C at WHSV of 0.10 for p-hydroxybenzaldehyde reactant led to the reversal of the product type from being 90% p-hydroxy-β-nitrostyrene to >85% Michael product with ∼100% reactant conversion. Raising the reaction temperature of the reactor containing a secondary amine catalyst for p-hydroxybenzaldehyde reactant also increasingly favored the formation of the Michael product. When changing the reactant to 0.08 M p-nitrobenzaldehyde, the reactor packed with secondary amine catalyst resulted in the nitroalcohol product with 90% selectivity at 40% reactant conversion for WHSV of 0.15. These results indicate that higher WHSV lead to greater selectivity to a particular product; however, lower WHSV and higher temperatures favor greater reactant conversion reaching as high as ∼100% in all the cases although they can be accompanied by less % selectivity. By simply adjusting the WSHV's or the temperatures to optimum values, one of the products can be exclusively generated in a continuous manner. The continuous reactor and the catalysts were proven to catalyze the reactions and give the respective product(s) continuously for several days. This method can be used as a route for the mass production of industrially and pharmaceutically important p-substituted nitroalcohol, nitrostyrene, or Michael addition product with high selectivity, by simply packing mesoporous catalysts within a fixed bed reactor.

Trimming Nanostructured Walls While Fluorinating their Surfaces: A Route to Making and Widening Pores of Nanoporous Materials and Efficient Catalysts

Abstract: We report on the synthesis and characterization of highly ordered mesoporous fluorosilicas (OMFs) and nanoporous and corrugated fluorosilica nanospheres which contain 2.4−7.0 wt % F, corresponding to a loading of 1.3−3.7 mmol/g. Synthesis of these materials is carried out from parent mesoporous silicas (MCM-41 and SBA-15) and silica nanospheres under ambient conditions using dilute nonaqueous solutions of triethyloxonium tetrafluoroborate (Et3OBF4). As evidenced by nitrogen physisorption measurements, small angle powder X-ray diffraction (XRD), and transmission electron microscopy (TEM), fluorination of the mesostructures is accomplished with only minor alteration of the materials’ overall order. Detailed compositional analyses before and after fluorination are carried out with the aid of FTIR spectroscopy and X-ray photoelectron spectroscopy (XPS) as well as elemental analysis proving the existence of silicon oxyfluoride species. FTIR studies show the appearance of new absorptions (730−750 cm−1) upon flu...

Entrapping Flavin-Containing Monooxygenase on Corrugated Silica Nanospheres and their Recyclable Biocatalytic Activities

Abstract: Synthetic methods and biocatalytic activities of new classes of heterogeneous biocatalysts by immobilizing flavin-containing monooxygenase on corrugated and nanoporous silica nano- spheres are reported. The nanoporous and corrugated silica nanospheres are synthesized by etching silica nanospheres with aqueous KOH solution. The etched nanospheres are proven to have increased surface area, corrugated, cage-like external surfaces, and, most importantly, more accessible and well-suited surfaces to immobilize bigger molecules, such as enzymes. Furthermore, the etched silica nanospheres contain hydrophilic and silanol groups that are conducive for anchor- ing enzymes. By utilizing the structures of the etched silica nanospheres, effective immobilization of flavin-containing monooxygenase 1 (FMO1) is demonstrated. The FMO1 immo- bilized etched silica nanospheres have shown efficient and re- cyclable biocatalytic activity for nicotine oxidation.

Selective and efficient bifunctional and trifunctional nanoporous catalysts and methods of synthesis thereof

Abstract: Selective and efficient multifunctional nanoporous catalysts containing spatially distributed organoamine and silanol groups, and methods of preparation thereof. The catalysts have been observed to be very highly efficient in catalysis of the Henry reaction.

Mesoporous and Nanoporous Materials, and Methods of Synthesizing the Same

Abstract: A method for synthesizing a phosphonic acid functionalized mesoporous metal oxide material (e.g., silica, titania, alumina, preferably silica material) is provided. Further, a method of using the phosphonic acid functionalized mesoporous silica material as a solid acid catalyst in a pinicole-pinacolone rearrangement reaction, and a method of using a phosphonic acid functionalized mesoporous silica material as a solid acid catalyst in a transesterification reaction is provided. A method for preparing a mesoporous titania film for use in a dye sensitized solar cell is also provided.

Spherical and Anisotropic Nonmagnetic Core-Shell Nanomaterials: Synthesis and Characterization

Abstract: The sections in this article are Introduction: Core-Shell Nanomaterials and Their Biological/Medical Applications Nonmagnetic Core-Shell Nanomaterials Synthesis of Cores in Core-Shell Nanostructures Metal Cores Metal Oxide Cores Polymeric Cores Semiconductor Cores Deposition of Shells over the Core Nanomaterials Types of Core-Shell Nanomaterial Metal–Insulator Core-Shell Nanomaterials Metal-Dense Metal Oxide Core-Shell Nanomaterials Metal-Functionalized Metal Oxide Core-Shell Nanoparticles Metal–Porous Metal Oxide Core-Shell Metal–Polymer Core-Shell Nanoparticles Hollow Metal–Metal Oxide Shells by Controlled Core-Dissolution Metal Core–Dendrimer Core-Shell Nanoparticles Metal Core–Semiconducting Metal Oxide Shell Nanoparticles Insulator–Metal Core-Shell Nanomaterials Metal Oxide–Metal Core-Shell Nanostructures Polymer–Metal Core-Shell Nanostructures Insulator–Insulator Core-Shell Nanoparticles Polymer–Metal Oxide Core-Shell Nanomaterials Polymer–Polymer Core-Shell Nanomaterials Biomolecule (Protein) Core–Polymer Shell Core-Shell Nanoparticles Metal Oxide–Metal Oxide Core-Shell Nanomaterials Metal Oxide–Dye-Doped Silica and Dye-Doped Silica–Metal Oxide Core-Shell Nanostructures Metal Oxide–Polymer Core-Shell Nanoparticles Other Inorganic Materials Cores: Metal Oxide Shells Semiconductor–Insulator Core-Shell Nanomaterials Semiconductor–Semiconductor Core-Shell Nanomaterials Semiconductor–Semiconductor–Dendrimer Core-Shell-Shell Nanoparticles Insulator–Semiconductor Core-Shell Nanomaterials Metal–Metal Core-Shell Insulator–Metal Core-Shell Nanoparticles Carbon-Containing Core-Shell Nanomaterials Metal Oxide–Carbon Core-Shell Nanoparticles Other Carbon-Containing Core-Shell Nanomaterials Synthetic Methods to Create Core-Shell Nanomaterials, and their Characterizations Applications Applications in Biology and Medicine Bioimaging and Immunoassay Drug or Biomolecular Delivery Vehicles Core-Shell Nanomaterials for Catalysis Conclusions and Future Prospects Acknowledgments Keywords: core-shell nanoparticles; nonmagnetic nanoparticles; bioimaging; nanomedicine; drug delivery; catalysis; metal oxide nanomaterials