Improvement of ammonia sensing properties of polypyrrole by nanocomposite with graphitic materials

The more sensitive and rapid ammonia gas sensors were prepared with nanocomposites of polypyrrole (PPy) and graphitic materials such as graphite, graphite oxide (GO), and reduced graphene oxide (RGO). Pyrrole was polymerized uniformly on the surface of graphitic materials by in situ polymerization method. The structures of nanocomposites were studied by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy indicating the well-exfoliated GO and RGO in PPy matrix with favorable interfacial interaction. PPy/RGO nanocomposite showed the highly improved response in detecting ammonia gas mainly due to the effective electron charge transfer between PPy and ammonia and the efficient transfer of electrical resistance variation by the uniformly dispersed conductive RGO in PPy. PPy/RGO nanocomposite gas sensor also showed the excellent reproducibility in ammonia sensing behavior during the recovery process at lower temperature of 373 K.     

An investigation of calibration materials for the measurement of metals in ambient particulate matter on filters by LA-ICP-MS

Three different types of simple and low-cost calibration material for the measurement of the metals content of ambient particulate matter (PM) on filters using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) have been compared: cellulose ester filters spiked with multi-element calibration solutions, pellets of compressed ambient particulate matter certified reference material (CRM), and powdered ambient particulate matter CRM adhered to a surface. Elements determined were As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn, each at approximate levels of 1000?ng per filter. Blank filters spiked with multi-elemental standards were found to be significantly more reproducible and repeatable than materials based on powdered reference materials. However, a comparison of these spiked filters with real samples of ambient PM showed that the analytical sensitivities obtained per mass of analyte were significantly different. It is concluded that the spiked filters could act as very effective quality control standards correcting, to within 1%, drifts in LA-ICP-MS measurements of up to 10%, or as indirect calibration materials supported by additional measurements using traditional wet chemical techniques.     

Mixed-ligand oxovanadium complexes incorporating Schiff base ligands: synthesis, DNA interactions, and cytotoxicities

Three oxovanadium complexes, namely [VO(NOSAA)(bpy)] (1) (NOSAA = 2-hydroxy-5-nitrosalicylidene anthranilic acid, bpy = 2,2′-bipyridyl), [VO(NOSAA)(4,4′-dimebpy)] (2) (4,4′-dimebpy = 4,4′-dimethyl-2,2′- bipyridyl), and [VO(NOSAA)(phen)] (3) (phen = 1,10-phenanthroline), have been prepared and characterized. The binding modes and strengths of these complexes with calf thymus DNA (CT-DNA) were studied using various techniques. The chemical nuclease activities and photocleavage reactions of the complexes were also tested. All three complexes interact with CT-DNA through intercalative modes, and complex 3 possesses the largest binding affinity. All three complexes can efficiently cleave pBR322 DNA upon irradiation or under physiological conditions in the presence of H₂O₂, and complex 3 has the best cleaving ability. In vitro experimental results showed that the three complexes are cytotoxic against myeloma (Ag8.653) and gliomas (U251) cell lines and complex 3 again showed the highest efficacy.     

Substrate interaction effects on order to disorder transition behavior in block copolymer films

We present an overview of the recent progress on the phase transition in the block copolymer (BCP) films in terms of the interfacial interactions effects of the substrates and the χ (Flory-Huggins segmental interaction parameter) effects between the two blocks. For the BCP films thinner than a critical thickness (L_c) above which the transition is independent of film thickness, the order-to-disorder transition (ODT) increased or decreased with decreasing film thickness depending on the interfacial interaction types. The rapid and slow changes in the ODT were attributed to the relative magnitude of enthalpic contribution to χ between two blocks. Interestingly, a periodic amplification in the block composition for the BCP films suppressed the compositional fluctuation in the film geometry, resulting in the ODT shifts from the bulk ODTs above L_c. This effect of the BCP films was more illustrated by the ODT shift effects depending on the strength of the preferential interactions on the substrates. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Synthesis of (4R,5S)-(−)- and (4S,5S)-(+)-L-Factors and Muricatacin from D-Glucose

Abstract

In connection with our projects on the synthesis of biologically active 5-hydroxyalkan-4-olides which have a chiral 2.3-diol unit,¹ we have carried out the synthesis of (4R,5S)-(?)- and (4R,5S)-(+)-L-factors (1).² the proposed autoregulators from Streptomyees griseus, and muricatacin (2),³ a biologically active constituent from the seeds of Annona muricata L. via 2.3-dihydroxy aldehydes derived from D-glucose. Hex-3-enofuranose4 was prepared by the elimination of thetriflate derived from D-glucose.     

Electrochemical properties of PEO/PMMA blend-based polymer electrolytes using imidazolium salt-supported silica as a filler

In this study, the composite polymer electrolytes (CPEs) were prepared by solution casting technique. The CPEs consisted of PEO/PMMA blend as a host matrix doped with LiClO₄. Propylene carbonate (PC) was used as plasticizer and a small amount of imidazolium salt-supported amorphous silica (IS-AS) as a filler was prepared by the sol–gel method. At room temperature, the highest conductivity was obtained for the composition having PEO–PMMA–LiClO₄–PC–4wt. % IS-AS with a value of 1.15 × 10^?4 S/cm. In particular, the CPE using the IS-AS filler showed a higher conductivity than any other sample (fumed silica, amorphous silica). Studies of differential scanning calorimetry and scanning electron microscopy indicated that the ionic conductivity increase was due to an expansion in the amorphous phase which enhances the flexibility of polymeric chains and the homogeneous structure of CPEs. It was found that the ionic conductivity and interfacial resistance stability of CPEs was significantly improved by the addition of IS-AS. In other words, the resistance stability and maximum ambient ionic conductivity of CPEs containing IS-AS filler were better than CPEs containing any other filler.     

Improved performance of dye sensitized ZnO nanorod solar cells prepared using TiO2 seed layer

Zinc oxide (ZnO) nanorods of different structures have been grown on indium-doped tin oxide substrates by using TiO₂ as seed layer. The ZnO nanorods have been prepared using TiO₂ seed layers annealed at different temperatures via a simple sol–gel method. The X-ray diffraction result indicates that the prepared samples are of wurtzite structure. Dye sensitized solar cells have been fabricated using the prepared ZnO nanorods. The open circuit voltage, short circuit current density, fill factor, and power conversion efficiency of the ZnO nanorod based dye sensitized solar cells prepared using TiO₂ seed layers annealed at different temperatures have been determined. The improvement in power conversion efficiency may be due to the flower like structured ZnO nanorods with smaller diameter and large specific surface area which paves way for the efficient electron transfer in hybrid solar cells.     

A p‐Quinodimethane‐Bridged Porphyrin Dimer

A p‐quinodimethane (p‐QDM)‐bridged porphyrin dimer 1 has been prepared for the first time. An unexpected Michael addition reaction took place when we attempted to synthesize compound 1 by reaction of the cross‐conjugated keto‐linked porphyrin dimers 8 a and 8 b with alkynyl/aryl Grignard reagents. Alternatively, compound 1 could be successfully prepared by intramolecular Friedel–Crafts alkylation of the diol‐linked porphyrin dimer 14 with concomitant oxidation in air. Compound 1 shows intense one‐photon absorption (OPA, λ_max=955 nm, ε=45400 M ^?1 cm^?1) and a large two‐photon absorption (TPA) cross‐section (σ⁽²⁾_max=2080 GM at 1800 nm) in the near‐infrared (NIR) region due to its extended π‐conjugation and quinoidal character. It also exhibits a short singlet excited‐state lifetime of 25 ps. The cyclic voltammogram of 1 displays multiple redox waves with a small electrochemical energy gap of 0.86 eV. The ground‐state geometry, electronic structure, and optical properties of 1 have been further studied by density functional theory (DFT) calculations and compared with those of the keto‐linked dimer 8 b . This research has revealed that incorporation of a p‐QDM unit into the porphyrin framework had a significant impact on its optical and electronic properties, leading to a novel NIR OPA and TPA chromophore.