Rafique Ul Islam

Conjugated polymer stabilized palladium nanoparticles as a versatile catalyst for Suzuki cross-coupling reactions for both aryl and heteroaryl bromide systems

A simple and efficient procedure for Suzuki coupling of aryl bromides with phenylboronic acid, catalyzed by an in situ-generated palladium(0)–polymer composite in the absence of any phosphine ligand, has been reported. The catalyst is remarkably active having a high TOF value for both aryl and heteroaryl systems, and is recyclable up to three runs with minimum loss of efficiency.

Efficient nucleic acid transduction with lipoplexes containing novel piperazine- and polyamine-conjugated cholesterol derivatives

To advance the use of cationic lipids for non-viral nucleic acid vector formulation, a panel of novel nitrogen heterocycle cholesteryl derivatives containing a biodegradable carbamate linker was synthesised. Optimally acting piperazine and cyclen compounds had nucleic acid-binding and lipoplex nanoparticle formation properties that were suitable for their use as non-viral vectors. It was found that the lipoplexes formed were capable of efficient non-toxic nucleic acid delivery to cells in culture. The chemical structure of individual cationic lipids, which is likely to influence lipoplex formation, affected efficiency of DNA or RNA transfection. The results indicated that the cyclen containing compound possessing two cholesteryl moieties resulted in efficient siRNA-mediated target gene silencing but was a poor reagent for DNA transfection.

Inhibition of hepatitis B virus replication in vivo using lipoplexes containing altritol-modified antiviral siRNAs

Chronic infection with the hepatitis B virus (HBV) occurs in approximately 6% of the worlds population and carriers of the virus are at risk for complicating hepatocellular carcinoma. Current treatment options have limited efficacy and chronic HBV infection is likely to remain a significant global medical problem for many years to come. Silencing HBV gene expression by harnessing RNA interference (RNAi) presents an attractive option for development of novel and effective anti HBV agents. However, despite significant and rapid progress, further refinement of existing technologies is necessary before clinical application of RNAi-based HBV therapies is realised. Limiting off target effects, improvement of delivery efficiency, dose regulation, and preventing reactivation of viral replication are some of the hurdles that need to be overcome. To address this we assessed the usefulness of the recently described class of altritol-containing synthetic siRNAs (ANA siRNAs), which were administered as lipoplexes and tested in vivo in a stringent HBV transgenic mouse model. Our observations show that ANA siRNAs are capable of silencing of HBV replication in vivo. Importantly, non specific immunostimulation was observed with unmodified siRNAs, and this undesirable effect was significantly attenuated by ANA modification. Inhibition of HBV replication of approximately 50% was achieved without evidence for induction of toxicity. These results augur well for future application of ANA siRNA therapeutic lipoplexes.

Catalytic Activity of Metal Nanoparticles Supported on Nitrogen-Doped Carbon Spheres

A support plays a crucial role in the activity and selectivity of catalysts. Heterogeneous catalysts are typically supported on inorganic oxides to enhance the surface area of the active sites. When compared to homogeneous catalysts, the supports also provide a method of separating the catalyst from the reactant/product at the end of the reaction. Carbon has been used as a support in many reactions because of its physicochemical properties that includes high surface area, thermal and mechanical stability, electronic behavior, low density, inertness, and, most importantly, its tailored structure. Carbon supports have thus been used extensively over many decades. Those used in the past, have typically been based on activated carbon. However, the recent interest in shaped carbon materials (tubes, horns, coils, onions, etc.), has led to much interest in the synthesis and properties of new carbon morphologies. For example, metals supported in particular on carbon nanotubes are being actively studied. Another form of carbon that has been used extensively in industry is the carbon sphere, but few reports on its use as a carbon support in catalysis have been described to date. Nitrogen-doped carbon spheres (N–CSs), less than 1 mm in diameter, have been synthesized and used as a support in a few studies. For example, Jang et al. reported the use of Pd supported on nitrogen doped magnetic carbon nanoparticles (Pd on a high surface area materials containing Fe) as a catalyst for C C bond forming reactions. Herein, we report on the utilization of N–CSs as supports for Ru, Pd, and V catalysts in chemoselective hydrogenation, C C bond formation (Heck, Suzuki), and oxidation reactions respectively. The doped carbon spheres were easily prepared, low-surface-area materials and formed strong bonds to the metals, leading to high activities and selectivities. In every case, the key feature related to the size of the metal nanoparticles stabilized on the spheres. We have previously reported a synthetic procedure for the fabrication of carbon spheres (CSs) by chemical vapor deposition (CVD). In brief, CSs were prepared using acetylene as the carbon source at a carbonization temperature of 900 8C for 2 h. To prepare the nitrogen-doped CSs, the process was modified to allow the acetylene gas to bubble through an ammonium hydroxide or acetonitrile solution (preferably ammonium hydroxide; see the Supporting Information for details of the synthesis). Elemental analysis of the as-synthesized material indicated the presence of 1–1.5 wt% nitrogen. The material obtained after CVD was subjected to an acid treatment with 1:3 concentrated HNO3/H2SO4 (30 mL per 0.5 g of CSs at 70 8C for 3 h). Acid-treated CSs were then washed with water until the filtrate was pH 7 and dried at 80 8C. Metal loading (3 wt%) was then carried out by a wet impregnation method. The N–CSs and metal-loaded N–CSs were structurally characterized by transmission electron microscopy (TEM; Figure 1A– C), high-resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray (EDX) spectroscopy (Figure 1D–F). The N–CSs had diameters ranging from 400 to 750 nm (see the Supporting Information for SEM image) and were accreted (Figure 1C, inset). The morphology of the spheres remained unaffected after acid treatment and metal loading. The average diameter of the metal particles loaded on the carbon was determined from TEM analysis. EDX analysis revealed almost 2.7wt% loading for all metals (Figure 1). TEM images for Ru/N–CSs and Pd/N–CSs showed average particle sizes of 3–5 and 2–4 nm, respectively, whereas for V/N–CSs vanadium oxide formed a film over the N–CSs. Further details of the catalyst characterization will be reported elsewhere. The new catalysts were investigated for chemoselective hydrogenation of diketones (Table 1), Heck and Suzuki carbon– carbon coupling reactions (Tables 2 and 3), and oxidation of styrene (Table 4). The catalysts showed impressive activity and recyclability in all reactions. In addition, all of the reactions were performed under mild reaction conditions. Catalytic methods, utilizing molecular hydrogen to reduce olefins, ketones, and imines, is in widespread industrial practice and is relatively straightforward. However, hydrogenation of diketones to ketols (monohydroxyketones) is a more challenging task. Ketols are of immense importance for the synthesis of fine chemicals, as they provide two different functionalities for chemical manipulation within the same molecule. Several attempts have been made to hydrogenate diketones using supported cinchonidine , 2,2’-bis(diphenylphosphino)-1,1’binaphthyl (binap), and 1,5-cyclooctadiene (cod) metal complexes. Recently, a gold catalyst supported on titanium oxide was reported to effect chemoselective transfer hydrogenation of a diketone to a ketol with conversion and selectivity [a] Dr. A. A. Deshmukh, Dr. R. Ul Islam, Prof. W. A. L. van Otterlo, Prof. N. J. Coville Molecular Science Institute, and School of Chemistry University of Witwatersrand, Private Bag No. 3 Johannesburg 2050 (South Africa) Fax: (+27)11-7176749 E-mail : neil.coville@wits.ac.za [b] Dr. A. A. Deshmukh, Prof. M. J. Witcomb, Prof. N. J. Coville DST/NRF Centre of Excellence in Strong Materials University of Witwatersrand, Private Bag No. 3 Johannesburg 2050 (South Africa) [c] Prof. M. J. Witcomb Microscopy and Microanalysis Unit, University of Witwatersrand Private Bag No. 3, Johannesburg 2050 (South Africa) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.200900224.

Polymer immobilized Cu(I) formation and azide-alkyne cycloaddition: A one pot reaction.

During the polymerization of aniline using copper sulphate, act as an oxidizing agent, the in-situ synthesized Cu(I) ion catalyzed the cyclo-addition between azides and alkynes. This work represents the merging of two steps, synthesis of the catalyst and application of the catalyst, in a one pot reaction. The elimination of the separate catalyst synthesis step is economic in terms of cost and time. As aniline was used as one of the reactant components so there is no requirement to use additional base for this reaction that further eliminates the cost of the process. Again, the catalyst can be readily recovered by filtration and efficiently used for the several sets of reactions without any significant loss of catalytic activity.

Metal–Polymer Hybrid Material as a Catalyst for the Heck Coupling Reaction Under Phosphine-Free Conditions

Abstract A method is described for making a poly-aminophenol-based hybrid material by in situ polymerization of aminophenol using palladium acetate as the oxidant. The oxidative polymerization of aminophenol leads to the formation of poly-aminophenol, while the reduction of palladium acetate results in the formation of palladium nanoparticles. The palladium nanoparticles were found to be highly dispersed and stabilized throughout the polymer matrix. The hybrid nanocomposite material showed excellent catalytic efficiency with respect to a Heck coupling reaction at a relatively low temperature and under flexible conditions.

Formation of metal nanoparticles in a polymer nanofiber: a hybrid material for gas-phase catalytic reactions

This paper describes the synthesis and characterization of a metal–polymer hybrid material formed by the combination of palladium nanoparticles and poly-o-phenylenediamine (poly-PDA). The preparation technique is based on an in situ, one-pot chemical synthesis route using palladium acetate and o-phenylenediamine as precursors. The composite material was characterized by optical, thermal and micro-analytical techniques. The characterization techniques show the successful synthesis of the hybrid material. This composite material was used as a catalyst for a model gas-phase hydrogenation reaction. The activation and deactivation of the catalyst is discussed in relation to the effect of temperature and the phase transition of the polymer.

Light effect on Click reaction: Role of photonic quantum dot catalyst

Due to the light excitation, the valence band electron of the copper (I) sulfide quantum dot transfer to the conduction band and act as a scavenger of the terminal proton of the alkyne in the presence of organic azide with the formation of 1,4-disubstituted 1,2,3-triazoles, where the copper(I) species of Cu2S act as a catalyst for the reaction. The above cycloaddition reaction between alkyne and azide is commonly known as the Click reaction. In this study, experiments were carried out under the exposure of ultra-violate and daylight and also dark environment. According to the original recommendation for the Click reaction, the role of the base was also considered for this experiment. We found that the effect of conduction band electron is more efficient than the recommended conventional base mediated reaction procedure.

Enhancement of transfection activity in HEK293 cells by lipoplexes containing cholesteryl nitrogen-pivoted aza-crown ethers

Two nitrogen-pivoted aza-crown ethers (aza-CEs) linked to the cholesteryl-fused ring system N-(cholesteryloxycarbonyl)aza-15-crown-5 and N-(cholesteryloxycarbonyl)aza-18-crown-6 have been incorporated into cationic liposomes containing the cytofectin 3β[N-(N′,N′-dimethylaminopropane) carbamoyl] cholesterol (Chol-T) and the neutral co-lipid dioleoylphosphatidylethanolamine. These novel liposomes form stable complexes with plasmid DNA and afford it good protection from serum nuclease digestion. Ethidium displacement studies suggest that the DNA is more loosely packed in aza-CE containing lipoplexes, a finding which is supported by band shift assays that reveal N/P end point ratios of 2:1, 3:1 and 3.5:1 for Chol-T control liposomes, aza-15-crown-5 and aza-18-crown-6 containing liposomes, respectively. The transfection activities of crown ether-containing lipoplex formulations in the human embryonic kidney cell line HEK293 are twofold greater than those achieved by Chol-T lipoplexes not containing the aza-CEs. This observation may be attributable to the more loosely packed DNA, which facilitates disassembly, and to endosomal perturbations caused by macrocycle entrapped cations.