Synthesis and characterization of SPE membrane based on sulfonated FEP‐g‐acrylic acid by radiation induced graft copolymerization for PEM fuel cell

A Novel solid polymer electrolyte (SPE) membrane containing both ? COOH and ? SO₃H group has been prepared by simultaneous method of radiation grafting of acrylic acid onto FEP followed by sulfonation. The presence of weakly acidic acrylic acid controls the swelling in water while ? SO₃H group provides conductivity due to its strongly ionic characteristic. FEP‐g‐acrylic acid and its sulfonated derivatives were characterized by their properties. While the mechanical properties decreased, other properties such as ion exchange capacity (IEC), water uptake and ionic conductivity increased with increase in graft content. These properties further changed on sulfonation. Acrylic acid being weakly acidic in nature, conductivity values of the grafted membrane were quite low. However, introduction of strong ? SO₃H group resulted in conductivity closer to Nafion 117. Few sulfonated membranes have been tested with respect to H₂/O₂ fuel cell performance. Short‐term fuel cell test for 100 hr gave a stable performance. These membranes are less expensive compared to Nafion. Copyright © 2004 John Wiley & Sons, Ltd.     

Free Radicals as a Double-Edged Sword: The Cancer Preventive and Therapeutic Roles of Curcumin

Free radicals, generally composed of reactive oxygen species (ROS) and reactive nitrogen species (RNS), are generated in the body by various endogenous and exogenous systems. The overproduction of free radicals is known to cause several chronic diseases including cancer. However, increased production of free radicals by chemotherapeutic drugs is also associated with apoptosis in cancer cells, indicating the dual nature of free radicals. Among various natural compounds, curcumin manifests as an antioxidant in normal cells that helps in the prevention of carcinogenesis. It also acts as a prooxidant in cancer cells and is associated with inducing apoptosis. Curcumin quenches free radicals, induces antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase), and upregulates antioxidative protein markers–Nrf2 and HO-1 that lead to the suppression of cellular oxidative stress. In cancer cells, curcumin aggressively increases ROS that results in DNA damage and subsequently cancer cell death. It also sensitizes drug-resistant cancer cells and increases the anticancer effects of chemotherapeutic drugs. Thus, curcumin shows beneficial effects in prevention, treatment and chemosensitization of cancer cells. In this review, we will discuss the dual role of free radicals as well as the chemopreventive and chemotherapeutic effects of curcumin and its analogues against cancer.     

Asymmetric synthesis of Goniothalesdiol A from (R)-2,3-O-cyclohexylidine glyceraldehyde

Goniothalesdiol A 1 has been synthesized from (R)-2,3-O-cyclohexylidine glyceraldehyde with high stereoselectivity and 22% overall yield in 11 simple steps. The key features of the synthetic strategy include the stereocontrolled allylation of (R)-2,3-O-cyclohexylidine glyceraldehydes; the cross-metathesis with a Grubbs’s second generation catalyst, and the intramolecular base-catalyzed oxy-Michael addition for the formation of the tetrahydropyran ring.     

Magnetic circular dichroism in the luminescence ofF andF A centres in alkali halides

Summary The magnetic circular dichroism has been in the past an excellent tool to clarify the optical cycle of theF centres in alkali halides and the nature of the relaxed excited state. We have used such technique to study the weak doubleF emission found recently in NaI and the luminescence ofF andF _A centres (of both type I and II) in KCl. We have found that the long-wavelengthF emission in NaI and theF _A (I) emission in KCl∶Na⁺ behave like the well-known emission of theF centres, confirming the attribution of the above luminescence in NaI to the normal relaxed excited state. A completely different behaviour is displayed by the short-wavelengthF emission in NaI and by theF _A (II) emission in KCl∶Li⁺. The experimental data have been compared with the Ham and Grevsmuhl vibronic theory of the relaxed excited state.

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Riassunto Gli effetti di dicroismo magnetico circolare hanno costituito in passato un ottimo mezzo per chiarire il ciclo ottico dei centriF in alogenuri alcalini e la natura dello stato eccitato rilassato. Abbiamo usato tale tecnica per studiare la debole doppia emissioneF trovata recentemente in NaI e la luminescenza dei centriF edF _A (di tipo I e II) in KCl. Si è trovato che l'emissioneF a minore energia in NaI e l'emissioneF _A (I) in KCl∶Na⁺ si comportano come la ben nota emissione dei centriF, il che conferma l'attribuzione di tale luminescenza in NaI allo stato eccitato rilassato normale. L'emissioneF a energia maggiore in NaI e l'emissioneF _A (II) in KCl∶Li⁺ mostrano un comportamento completamente diverso. I dati sperimentali sono stati confrontati con la teoria vibronica di Ham e Grevsmuhl dello stato eccitato rilassato.

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Резюме Магнитный круговой дихроизм ранее применялся как инструмент для выяснения оптического циклаF центров в щелочных галогенидах и природы релаксирующего возбужденного состояния. В этой работе мы используем эту технику для исследования слабого двойного F излучения, обнаруженного недавно в NaI и при люминесценцииF иF _A центров (типа I и типа II) в KCl. Мы обнаружили, что длинноволновоеF излучения в NaI иF _A (I) излучение в KCl∶Na⁺ ведет себя как хорошо известное излучениеF центров, что подтверждает приписывание вышеуказанной люминесценции в NaI нормальному релаксирующему возбужденному состоянию. Полностью отличное поведение обнаруживает коротковолновоеF излучение в NaI иF _A (II) излучение в KCl∶Li⁺. Полученные экспериментальные данные сравниваются с вибрационной теорией Гама и Гревсмула для релаксирующего возбужденного состояния.

     

Large Femtosecond Two-Photon Absorption Cross-Sections of Fullerosome Vesicle Nanostructures Derived from Highly Photoresponsive Amphiphilic C(60)-Light-Harvesting Fluorene Dyad

We demonstrated ultrafast femtosecond nonlinear optical (NLO) absorption characteristics of bilayered fullerosome vesicle nanostructures derived from molecular self-assembly of amphiphilic oligo(ethylene glycolated) C(60)-(light-harvesting diphenylaminofluorene antenna). Fullerene conjugates were designed to enhance photoresponse in a femtosecond time scale by applying an isomerizable periconjugation linker between the C(60) cage and diphenylaminofluorene antenna subunit in an intramolecular contact distance of only < 3.0 ?. Morphology of C(60)(>DPAF-EG(12)C(1))-based fullerosome nanovesicles in H(2)O was characterized to consist of a bilayered shell with a sphere diameter of 20-70 nm and a chromophore shell-width of 9.0-10 nm, fitting well with a head-to-head packing configuration of the molecular length. At the estimated effective nanovesicle concentration as low as 5.5 × 10(-8) MV (molecular molar concentration of 5.0 × 10(-4) M) in H(2)O, two-photon absorption (2PA) phenomena were found to be the dominating photophysical events showing a large molar concentration-insensitive 2PA cross-section value equivalent to 8500 GM in a form of nanovesicles, on average. The observed NLO characteristics led to a sharp trend of efficient light-transmittance intensity reduction at the input laser intensity above 100 GW/cm(2).     

Reusable Nano-Zirconia-Catalyzed Synthesis of Benzimidazoles and Their Antibacterial and Antifungal Activities

In this article, a zirconia-based nano-catalyst (Nano-ZrO₂), with intermolecular C-N bond formation for the synthesis of various benzimidazole-fused heterocycles in a concise method is reported. The robustness of this reaction is demonstrated by the synthesis of a series of benzimidazole drugs in a one-pot method. All synthesized materials were characterized using ¹HNMR, ¹³CNMR, and LC-MS spectroscopy as well as microanalysis data. Furthermore, the synthesis of nano-ZrO₂ was processed using a standard hydrothermal technique in pure form. The crystal structure of nano-ZrO₂ and phase purity were studied, and the crystallite size was calculated from XRD analysis using the Debye–Scherrer equation. Furthermore, the antimicrobial activity of the synthesized benzimidazole drugs was evaluated in terms of Gram-positive, Gram-negative, and antifungal activity, and the results were satisfactory.     

A facile one step synthesis of 1,6 ‐dihydro‐7H‐pyrazolo[4,3‐d]‐pyrimidin‐7‐ones

A general synthetic approach to pyrazolo[4,3‐d]pyrimidines is reported. Aldehydes, arylideneanilines, carboxylic acids and orthoesters are used as one‐carbon units for bridging the two amino functions of 4‐amino‐1‐alkyl‐3‐propylpyrazole‐5‐carboxamides.     

Kinetics and mechanism of oxidation of aryl β-styryl ketones by osmium tetroxide in sulphuric acid-acetic acid medium. A structure-reactivity correlation study

Summary Oxidation of aryl -styryl ketones by osmium tetroxide has been studied in H₂SO₄-HOAc medium. The order with respect to osmium is unity in all the cases and the [substrate] order is unity for aryl -styryl ketone and fractional for substituted aryl -styryl ketone. Varying the concentration of [H⁺] at constant ionic strength had practically no effect on the rate; the salt effect is also negligible. Polymerisation did not occur when H₂C- CHCONH₂ was added to the reaction mixture. Increasing the percentage of AcOH decreased the rate. Direct attack at the 58-01 by Os^III in the slow step to give the oxidation product of aryl -styryl ketone, viz. 1-benzoyl-2-arylethane-1,2-diol is suggested and a possible mechanism for the reaction.     

Kinetics and Trapping Parameters of Thermoluminecence of Sr1−xEuxF2+x Mixed Crystrals

The kinetics and trapping parameters of thermoluminescence of Sr_1−xEu_xF_2+x mixed crystals have been calculated by using different methods. The trap depths, frequency factors, and order of kinetics of glow curve pattern in several compositions of the system revealed variations with composition.