Functionalization of partially reduced graphene oxide by metal complex as electrode material in supercapacitor

Research on Chemical Intermediates - High electrical conductivity and high surface area are two main parameters which influence supercapacitor electrode performance. Graphene has gained prominence...     

An injectable chitosan-based hydrogel reinforced by oxidized nanocrystalline cellulose and mineral trioxide aggregate designed for tooth engineering applications

The complex anatomy of teeth limits the accessibility and efficacy of regenerative treatments. Therefore, the application of well-known inducers as injectable hydrogels for the regeneration of the dentin-pulp complex is considered a promising approach. In this regard, this study aimed to develop an injectable hydrogel containing mineral trioxide aggregate (MTA). The injectable chitosan/oxidized-nanocrystalline cellulose/MTA (CS/OCNC/MTA) hydrogels were prepared, and the physicochemical properties of these hydrogels were evaluated by TGA, FTIR, Rheological analysis, and SEM. Moreover, the effect of MTA on the swelling and degradability of scaffolds was assessed. The proliferative effects of synthesized hydrogels were also determined on human dental pulp stem cells (hDPSCs) by MTT assay. For induction of differentiation and biomineralization in these cells, the alkaline phosphatase activity and Alizarin Red S staining tests were performed in the presence of fabricated scaffolds. The proliferation of hDPSCs was significantly increased in the presence of these hydrogels. Moreover, the addition of MTA to hydrogel structure dramatically improved the differentiation of hDPSCs. These results suggested that this novel injectable hydrogel provides appropriate physiochemical properties and can be considered a promising scaffold for regenerative endodontic procedures.

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Flow injection chemiluminescence determination of hydrazine by oxidation with chlorinated isocyanurates

A rapid and sensitive flow injection chemiluminescence (CL) method is described for the determination of hydrazine based on the CL generated during its reaction with either sodium dichloroisocyanurate (SDCC) or trichloroisocyanuric acid (TCCA) in alkaline medium. The emission intensity is greatly enhanced if dichlorofluorescein (DCF) as sensitizer is present in the reaction medium. The presence of citrate prevents the precipitation of some cations in the reaction medium and also causes an enhancement in emission intensity. The effect of analytical and flow injection variables on these CL systems and determination of hydrazine are discussed. The optimum parameters for the determination of hydrazine were studied and were found to be the following: SDCC and TCCA both 1x10(-3) M; NaOH, 2x10(-1) M; DCF, 5x10(-6) M; citrate, 1x10(-3) M and flow rate, 3.8 ml min(-1). The optimized method yielded 3sigma detection limits of 2x10(-7) and 3x10(-7) M for hydrazine with SDCC and TCCA oxidants, respectively. The method is simple, fast, sensitive, and precise and was applied to the determination of hydrazine in water samples.     

Synthesis and characterization of new optically active poly(amide‐imide)s containing epiclon and L‐methionine moieties in the main chain

Epiclon [3a,4,5,7a‐tetrahydro‐7‐methyl‐5‐(tetrahydro‐2,5‐dioxo‐3‐furanyl)‐1,3‐isobenzofurandione] (1) was reacted with L ‐methionine (2) in acetic acid and the resulting imide‐acid 3 was obtained in high yield. The diacid chloride 4 was prepared from diacid derivative 3 by reaction with thionyl chloride. Thermostable poly(amide‐imide)s containing epiclon structure were synthesized by reacting of diacid chloride 4 with various aromatic diamines. Polymerization reaction was performed by two conventional methods: low temperature solution polycondensation and short period reflux conditions. In order to compare conventional solution polycondensation reaction methods with microwave‐assisted polycondensation, the reactions were also carried out under microwave conditions with a small amount of o‐cresol that acts as a primary microwave absorber. The reaction mixture was irradiated for 6 min with 100% radiation power. Several new optically active poly(amide‐imide)s with inherent viscosity ranging from 0.15 to 0.36 dl/g were obtained with high yield. All of the above polymers were fully characterized by ¹H‐NMR, FT‐IR, elemental analyses and specific rotation techniques. Some structural characterizations and physical properties of these new optically active poly(amide‐imide)s are reported. Copyright © 2005 John Wiley & Sons, Ltd.     

An accurate expression for radial distribution function of the Lennard-Jones fluid

A simple and accurate expression for radial distribution function (RDF) of the Lennard-Jones fluid is presented. The expression explicitly states the RDF as a continuous function of reduced interparticle distance, temperature, and density. It satisfies the limiting conditions of zero density and infinite distance imposed by statistical thermodynamics. The distance dependence of this expression is expressed by an equation which contains 11 adjustable parameters. These parameters are fitted to 353 RDF data, obtained by molecular dynamics calculations, and then expressed as functions of reduced distance, temperature and density. This expression, having a total of 65 constants, reproduces the RDF data with an average root-mean-squared deviation of 0.0152 for the range of state variables of 0.5  T^*  5.1 and 0.35  ρ^*  1.1 (T^*=kT/ε and ρ^* = ρσ³ are reduced temperature and density, respectively). The expression predicts the pressure and the internal energy of the Lennard-Jones fluid with an uncertainty that is comparable to that obtained directly from the molecular dynamics simulations.     

Preparation and characterization of new thermally stable and optically active poly(ester‐imide)s by direct polycondensation with thionyl chloride in pyridine

4,4′‐hexafluoroisopropylidene‐2,2‐bis‐(phthalic acid anhydride) (1) was reacted with L ‐methionine (2) in acetic acid and the resulting N,N′–(4,4′‐hexafluoroisopropylidenediphthaloyl)‐bis‐L ‐methionine (4) was obtained in high yield. The direct polycondensation reaction of this diacid with several aromatic diols such as bisphenol A (5a), phenolphthalein (5b), 1,4‐dihydroxybenzene (5c), 4,4′‐dihydroxydiphenyl sulfide (5d), 4,6‐dihydroxypyrimidine (5e), 4,4′‐dihydroxydiphenyl sulfone (5f) and 2,4′‐dihydroxyacetophenone (5g) was carried out in a system of thionyl chloride and pyridine. Expecting that the reaction with thionyl chloride in pyridine might involve alternative intermediates different from an acyl chloride, the polycondensation at a higher temperature favorable for the reaction of the expected intermediate with nucleophiles was attempted, and a highly thermally stable poly(ester‐imide) was obtained by carrying out the reaction at 80°C. All of the above polymers were fully characterized by ¹H‐NMR, ¹⁹F‐NMR FT‐IR spectroscopy, elemental analysis and specific rotation. Some structural characterization and physical properties of these optically active poly(ester‐ imide)s are reported. Copyright © 2006 John Wiley & Sons, Ltd.     

The effect of block copolymer structure on the internalization of polymeric micelles by human breast cancer cells

The objective of this study was to assess the effect of hydrophilic/hydrophobic block chain lengths on the internalization of poly(ethylene oxide)-block-poly(varepsilon-caprolactone) (PEO-b-PCL) micelles by cancer cells. PEO-b-PCL block copolymers with varied PEO and PCL chain lengths were synthesized, assembled to polymeric micelles and loaded with a hydrophobic fluorescent probe (DiI) through a co-solvent evaporation method of physical encapsulation. The slow release of the fluorescent probe from the micellar structure was evidenced following DiI transfer to lipid vesicles. The extent of micellar uptake by cancer cells was investigated through their incubation with MCF-7 cells followed by measurement of the fluorescent emission intensity of DiI (lambda=550 nm) in separated lysed cells. Cellular internalization of polymeric micelles was confirmed by laser scanning microscopy. The mechanism of micellar uptake was investigated by pretreatment of MCF-7 cells with chlorpromazine and cytochalasin B. Encapsulation of DiI in PEO-b-PCL micelles lowered the extent and rate of hydrophobic probe internalization by cancer cells. For polymeric micelles with 5000 gmol(-1) of PCL and varied PEO molecular weights of 2000, 5000 and 13,000 gmol(-1), maximum uptake was observed at a PEO molecular weight of 5000 gmol(-1). For polymeric micelles with 5000 gmol(-1) of PEO and varied PCL molecular weights of 5000, 13,000 and 24,000 gmol(-1), maximum uptake was observed at 13,000 gmol(-1) of PCL. Chlorpromazine reduced the cellular uptake of PEO-b-PCL micelles independent from the block copolymer structure, pointing to the involvement of clathrin mediated endocytosis mechanisms in the uptake of polymeric micelles by cancer cells. Inhibition of cellular uptake of PEO-b-PCL micelles by cytochalasin B, on the other hand, was found to be dependent on the chemical structure of the core/shell forming blocks.     

Ionic Liquids Modify the Performance of Carbon Based Potentiometric Sensors

A new type of potentiometric sensor based on a recently constructed carbon ionic liquid electrode (CILE) is described. Two kinds of ionic liquids, i.e., N‐octylpyridinium hexafluorophosphate (OPFP) and 1‐butyl‐3‐methylimidazoluim hexafluorophosphate (BMFP) were tested as binder for construction of the carbon composite electrode. The characteristics of these electrodes as potentiometric sensors were evaluated and compared with those of the traditional carbon paste electrode (CPE). The results indicate that potentiometric sensors constructed with ionic liquid show an increase in performance in terms of Nernstian slope, selectivity, response time, and response stability compared to CPE.     

An active and selective heterogeneous catalytic system for Michael addition

Potassium fluoride doped natural zeolite was found to be an efficient and selective solid base catalyst for 1,4-Michael addition. The catalyst is easily prepared and the workup procedure simplified by simple filtration.All products were obtained in high yields as well as short reaction times.