Polyaniline doped with α, ω‐alkanedisulfonic acids: preparation and characterization

The use of α, ω‐alkanedisulfonic acid, HO₃S(CH₂)_nSO₃H (n = 1, 4, 6 and 12), as a dopant for polyaniline (PANi) was investigated. This series of disulfonic acids with varying chain lengths were synthesized and used in the doping of PANi. The doped polymers showed conductivity in the range 10^?2 to 10^?1 S cm^?1. Thermal studies showed that the doped polymers, depending on the chain length of α,ω‐alkanedisulfonic acid, were stable up to ca 300 °C and the thermal stability decreased with increasing dopant chain length. The thermal stability of α,ω‐alkanedisulfonic acid‐doped PANi was higher than that of alkanesulfonic acid‐doped PANi which typically degrades around 250 °C, suggesting a moderately broader processing window for α,ω‐alkanedisulfonic acid‐doped PANi for blending with other thermoplastics. Copyright © 2012 Society of Chemical Industry     

Triplet State Interrogation in Supersonic Beams by Surface Electron Ejection

Recently, we have developed an experimental method for the detection of triplet states generated by laser excitation in supersonic beams. It is based on electron ejection from low work-function surfaces by metastable triplet states. We have detected both directly laser-excited triplets and triplets generated via intersystem crossing from laser-excited singlet states. Here, we review the applications of this method and discuss its mechanism. By comparing the laser-induced fluorescence (LIF) spectrum and Surface Electron Ejection by Laser-Excited Metastables (SEELEM), we have measured relative triplet formation quantum yields for several aromatic compounds. By utilizing a detector mounted on a translational stage, we could vary the distance between the pulsed laser excitation and the detector and measure the decay rates of triplets in molecular beams. The major advantage of the method is in extending the measurement of triplet lifetimes to the ∼ 1-ms range. The combination of LIF, SEELEM, and fluorescence quantum yields enabled us to discriminate between intersystem crossing and internal conversion in isoquinoline. SEELEM is now being utilized in studying the spectroscopy and the dynamics of directly laser-excited triplet states. Although the oscillator strength of the lowest triplet state of pyrazine is about 10⁻⁸, we have measured the spectrum and the decay rates of its various vibronic levels. Our results support the notion that surface Penning ionization is the mechanism of SEELEM. The detector is insensitive to vibrational energy (thus enabling the distinction between intersystem crossing and internal conversion). The detection sensitivity of triplets rises with the excess electronic energy and with the lowering of the surface work-function.     

Recent developments in cold plasma-based enzyme activity (browning,cell wall degradation,and antioxidant) in fruits and vegetables

According to the Food and Agriculture Organization of United Nations reports, approximately half of the total harvested fruits and vegetables vanish before they reach the end consumer due to their perishable nature. Enzymatic browning is one of the most common problems faced by fruit and vegetable processing. The perishability of fruits and vegetables is contributed by the various browning enzymes (polyphenol oxidase, peroxidase, and phenylalanine ammonia-lyase) and ripening or cell wall degrading enzyme (pectin methyl-esterase). In contrast, antioxidant enzymes (superoxide dismutase and catalase) assist in reversing the damage caused by reactive oxygen species or free radicals. The cold plasma technique has emerged as a novel, economic, and environmentally friendly approach that reduces the expression of ripening and browning enzymes while increasing the activity of antioxidant enzymes; microorganisms are significantly inhibited, therefore improving the shelf life of fruits and vegetables. This review narrates the mechanism and principle involved in the use of cold plasma technique as a nonthermal agent and its application in impeding the activity of browning and ripening enzymes and increasing the expression of antioxidant enzymes for improving the shelf life and quality of fresh fruits and vegetables and preventing spoilage and pathogenic germs from growing. An overview of hurdles and sustainability advantages of cold plasma technology is presented.     

Glycaemic response of pseudocereal-based gluten-free food products: a review

Rapid digestion and absorption of carbohydrates have become a health issue (high glycaemic index, GI), which can be a matter of greater concern when consumed in large quantities. Depending upon the influence of carbohydrates on the blood sugar levels, GI classifies carbohydrates (on a scale of 100) as low (<55), medium (55–70) and high (>70) GI foods. Among the pseudocereals, chia seed possesses relatively lower GI (28.53), as compared to buckwheat (52.35), amaranth (47.65) and quinoa (61.50). Consumers now prefer foods with a high GI over the ones with low GI to prevent various metabolic alterations. Celiac disease is a lifelong disorder prevalent worldwide and can only be controlled by following a strict lifelong gluten-free diet. Therefore, pseudocereals could be a potential alternate for low GI food and developing gluten-free food products, including bread, cookies, noodles and pasta. This review synthesises the recently published literatures on pseudocereals as a lowering GI and healthy food option. This review also gives insights into developing pseudocereals as a potential and novel ingredient for gluten-free food applications and the latest research conducted worldwide.     

Chemoenzymatic Buta-1,3-diene Synthesis from Syngas Using Biological Decarboxylative Claisen Condensation and Zeolite-Based Dehydration

A method for producing buta-1,3-diene (1,3-BD) by an amalgamation of chemical and biological approaches with syngas as the carbon source is proposed. Syngas is converted to the central intermediate, acetyl-CoA, by microorganisms through a tetrahydrofolate metabolism pathway. Acetyl-CoA is subsequently converted to malonyl-CoA using a carbonyl donor in the presence of a carboxylase enzyme. A decarboxylative Claisen condensation of malonyl-CoA and acetaldehyde ensues in the presence of acyltransferases to form 3-hydroxybutyryl-CoA, which is subsequently reduced by aldehyde reductase to give butane-1,3-diol (1,3-BDO). An ensuing dehydration step converts 1,3-BDO to 1,3-BD in the presence of a chemical dehydrating reagent.     

High-speed wavelength tunable liquid crystal filter

We describe the first high-speed, continuously tunable liquid crystal optical filter suitable for wavelength division multiaccess (WDMA) optical networks. The filter utilizes chiral smectic A* electroclinic liquid crystal as the active cavity material in a Fabry-Perot etalon to obtain microsecond switching speed. Using the commercially available BDH764E liquid crystal material, we demonstrate a tunable optical filter with a switching speed of less than 10 μs and a tuning range of approximately 30 nm, when the filter passband is centered at 1.55 μm     

Effect of metal halides on thermal,mechanical, and electrical properties of polypyromellitimide films

This paper describes the effect of metal halides (Co²⁺, Sn²⁺, and Hg²⁺) on the properties of polyimides. Low temperature, solution polycondensation reaction of pyromellitic dianhydride and 4,4′-diaminodiphenyl ether was used for preparation of a poly(amide-acid) solution in dimethylformamide ([η] = 2.0 dL/g). Films containing 1% (w/w) of cobalt (II) chloride, tin (II) chloride, and mercury (II) chloride were prepared by solution casting of poly(amide-acid) from the DMF solution. Cyclodehydration to polyimide was done by heating the films in nitrogen atmosphere for one hour each at 100°, 200°, and 250°C. The color of the films depended on the dopant and was yellow (HgCl₂ or SnCl₂) or green (CoCl₂) Higher percentage weight loss was observed in doped films in nitrogen atmosphere in the temperature range of 250–400°C. No significant difference in thermal behavior of doped and undoped films was observed above 500°C. Doping reduced the tensile strength of polyimide films, maximum reduction was observed in CoCl₂-doped film. The electrical conductivity of polyimide films as a function of temperature and field was studied. Undoped polyimide showed ohmic behavior up to 150°C. In doped films at lower voltages Poole-Frenkel mechanism was operative, while at high voltages Richardson-Schottky's mechanism was operative. Dielectric relaxation in polyimide films was also studied.     

Correction to: Efficient room temperature methanol sensors based on polyaniline/graphene micro/nanocomposites

Iranian Polymer Journal - The article listed above was initially published with typo error in Eq.&nbsp;(4).     

State of Florida hurricane loss projection model: Atmospheric science component

The State of Florida has developed an open, public model for the purpose of probabilistic assessment of risk to insured residential property associated with wind damage from hurricanes. The model comprises atmospheric science, engineering, and financial/actuarial components and is planned for submission to the Florida Commission on Hurricane Loss Projection Methodology. The atmospheric component includes modeling the track and intensity life cycle of each simulated hurricane within the Florida threat area. When a model storm approaches within a damage threshold distance of a Florida zip code location, the wind field is computed by a slab model of the hurricane boundary layer coupled with a surface layer model based on the results of recent GPS sonde research. A time series of open terrain surface winds is then computed for each zip code in the threatened area. Depending on wind direction, an effective roughness length is assigned to each zip code based on the upstream fetch roughness as determined from remotely sensed land cover/land use products. Based on historical hurricane statistics, thousands of storms are simulated allowing determination of the wind risk for all residential zip code locations in Florida. The wind risk information is then provided to the engineering and loss models to assess damage and average annual loss, respectively.