Krishna K. Sharma

Cytotoxicity of mesoporous silica nanomaterials.

We here measure the toxicity of MCM-41, a mesoporous silica nanomaterial, two of its functionalized analogs, AP-T, which has grafted aminopropyl groups and MP-T, which has grafted mercaptopropyl groups, and spherical silica nanoparticles (SiO(2)), toward human neuroblastoma (SK-N-SH) cells. Since the particles studied are not soluble in aqueous media, the metric used to report the cytotoxicity of these materials is a new quantity, Q(50), which is the number of particles required to inhibit normal cell growth by 50%. Determining the number of particles per gram of material applied to the cells required both the calculated and experimentally determined surface areas of these nanomaterials. This study shows that Q(50) increases in the order, MCM-41<MP-T<AP-T approximately SiO(2), showing that on a per particle basis, MCM-41 is the most cytotoxic material studied. For the three mesoporous silica materials in this study, cytotoxicity appears related to the adsorptive surface area of the particle, although the nature of the functional group cannot be ruled out. Silica nanospheres have the lowest surface area of the particles studied but since they exhibit a Q(50) value similar to that of AP-T, shape may also be important in the cytotoxicity of these materials.

Recent advances in nanostructured chemosensors and biosensors.

Over the past few decades the fabrication of nanoscale materials for use in chemical sensing, biomedical and biological analyses has proven a promising avenue. Nanomaterials show promise in such chemical and biological analysis mainly due to their highly tunable size- and shape-dependent chemical and physical properties. Furthermore, they exhibit unique surface chemistry, thermal stability, high surface area and large pore volume per unit mass that can be exploited for sensor fabrication. This review will discuss the chemical and physical properties of nanomaterials necessary for use as chemosensors and biosensors. It will also highlight some noteworthy recent avenues using nanoscale materials as scaffolds for chemosensing and biosensing. Nanomaterials that have proven to be useful for the fabrication of sensors, as reviewed herein, have compositions including metals, metal oxides, chalcogenides and polymers. Their structures range from nanoparticles, nanorods, and nanowires to nanoporous and core-shells. Examples of the different types of structures and compositions as well as sensors and biosensors fabricated from them will be described. Some nanomaterials are functionalized with various kinds of ligands and bioactive groups to produce sensitive and selective sensors for specific analytes. The combination of two or more types of nanostructures with core-shell type nanoassemblies and other composite structures, in addition to advantageous features enhancing sensitivity and response time of related sensors, are also discussed.

Mesoporous Silica Nanoparticles Inhibit Cellular Respiration

We studied the effect of two types of mesoporous silica nanoparticles, MCM-41 and SBA-15, on mitochondrial O 2 consumption (respiration) in HL-60 (myeloid) cells, Jurkat (lymphoid) cells, and isolated mitochondria. SBA-15 inhibited cellular respiration at 25-500 microg/mL; the inhibition was concentration-dependent and time-dependent. The cellular ATP profile paralleled that of respiration. MCM-41 had no noticeable effect on respiration rate. In cells depleted of metabolic fuels, 50 microg/mL SBA-15 delayed the onset of glucose-supported respiration by 12 min and 200 microg/mL SBA-15 by 34 min; MCM-41 also delayed the onset of glucose-supported respiration. Neither SBA-15 nor MCM-41 affected cellular glutathione. Both nanoparticles inhibited respiration of isolated mitochondria and submitochondrial particles.

Controlled Synthesis of Water-Dispersible Faceted Crystalline Copper Nanoparticles and Their Catalytic Properties

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).

Isolation and X-ray structure of [(µ-H)Ru3(CO)9(µ3-PhNCPh)], the catalytically active cluster in Ru3(CO)12-catalysed transfer hydrogenation of benzylideneaniline

(µ-H)Ru3(CO)9(µ3-PhNCPh)(1) has been isolated from an Ru3(CO)12-based catalytic system for the transfer hydrogenation of benzylideneaniline and found to be catalytically active; the X-ray structure of (1) is reported.

Cluster catalysed selective transfer hydrogenation of α,β-unsaturated aldehydes

H4Ru4(CO)8L4(L = PBu3n) catalyses selective transfer hydrogenation of α,β-unsaturated aldehydes to α,β-unsaturated alcohols; kinetic and deuterium labelling studies indicate involvement of cluster intermediates and no participation by the cluster hydrides.

Platinum-silver clusters: synthesis and crystal structure of [Pt3Ag(μ-CO)3(PPh3)5]ClO4 · 2H2O

Abstract Reaction of [NBu4]2[Pt12(CO)24] with [Ag(PPh3)4]ClO4 and PPh3 leads to two isolable platinum-silver clusters; the title complex was characterised by single crystal X-ray diffraction. the Pt3Ag core is tetrahedral; one Pt atom is seven-coordinated, the other two are six-coordinate.

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

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.

Carbonyl cluster derived polystyrene supported platinum for asymmetric hydrogenation of α-ketoesters

Ion-pairing of anionic carbonyl clusters with cinchona alkaloid groups on cross-linked polystyrene is a viable method for the synthesis of asymmetric catalysts for the hydrogenation of methyl pyruvate.

Solution and crystal structures of the hydridoruthenium raft clusters H2Ru6(CO)15(L)(C6H4O) (L = CO, P(OMe)3)

Abstract The structures of H 2 Ru 6 (CO) 14 (L)(C 6 H 4 O) (L = CO, (P(OMe 3 ) in solution (as indicated by 1 H NMR studies) and in the solid state (as indicated by X-ray studies) are discussed. The two-dimensional COSEY spectrum of the unsubstituted cluster shows the presence of two isomers in solution, whereas in the solid state only one form is present. There is no evidence for more than one isomer for the phosphite-substituted cluster in solution or in the solid state. Long-range 31 P- 1 H couplding differentiates between the 1 H NMR signals of the doubly- and triply-bridging hydrides. Reactions of Ru 3 (CO) 12 with para -substituted phenols XC 6 H 4 OH (X = NO 2 , NH 2 ) are also reported.