952 resultados para MOLECULAR-WEIGHT RATIO
Resumo:
Polyaniline functionalized with imidazole as strategically designed receptor group in its backbone was synthesized for copper binding. The synthesized polymer has been characterized using FTIR, NMR, and UV-Vis spectroscopic techniques. The addition of copper (II) to the polymer distinctly changes the properties such as crystallinity, molecular weight, aggregation, and electronic properties. XRD, DLS, SEM, and four-point probe techniques have been used for study of these changes. It is observed that the secondary ion generated as a result of copper coordination results in the doping of the polyaniline backbone, which enhances the conductivity by one order of magnitude. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 526-534, 2012
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We have demonstrated the synthesis of light-sensitive polyelectrolyte capsules (PECs) by utilizing a novel polyol reduction method and investigated its applicability as photosensitive drug delivery vehicle. The nanostructured capsules were prepared via layer by layer (LbL) assembly of poly(allylamine hydrochloride) (PAN) and dextran sulfate (DS) on silica particles followed by in-situ synthesis of silver nanoparticles (NPs). Capsules without silver NPs were permeable to low molecular weight (A(w), 479 g/mol) rhodamine but impermeable to higher molecular weight fluorescence labeled dextran (FITC-dextran). However, capsules synthesized with silver NPs showed porous morphology and were permeable to higher molecular weight (M(w) 70 kDa) FITC-dextran also. These capsules were loaded with FITC-dextran using thermal encapsulation method by exploiting temperature induced shrinking of the capsules. During heat treatment the porous morphology of the capsules transformed into smooth pore free structure which prevents the movement of dextran into bulk during the loading process. When these loaded capsules are exposed to laser pulses, the capsule wall ruptured, resulting in the release of the loaded drug/dye. The rupture of the capsules was dependent on particle size, laser pulse energy and exposure time. The release was linear with time when pulse energy of 400 mu J was used and burst release was observed when pulse energy increased to 600 mu J.
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The rapidly depleting petroleum feed stocks and increasing green house gas emissions around the world has necessitated a search for alternative renewable energy sources. Hydrogen with molecular weight of 2.016 g/mol and high chemical energy per mass equal to 142 MJ/kg has clearly emerged as an alternative to hydrocarbon fuels. Means for safe and cost effective storage are needed for widespread usage of hydrogen as a fuel.Chemical storage is the one of the safer ways to store hydrogen compared to compressed and liquefied hydrogen. It involves storing hydrogen in chemical bonds in molecules and materials where an on-board reaction is used to release hydrogen. Ammonia–borane, (AB,H3N·BH3) with a potential capacity of 19.6 wt% is considered a very promising solid state hydrogen storage material. It is thermally stable at ambient temperatures. There are two major routes for the generation of H2 from AB: catalytic hydrolysis/alcoholysis and catalytic thermal decomposition. There has been a flurry of research activity on the generation of H2 from AB recently. The present review deals with an overview of our efforts in developing cost-effective nanocatalysts for hydrogen generation from ammonia borane in protic solvents.
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Ultrasonic degradation of commercially important polymers, styrene-butadiene (SBR) rubber, acrylonitrile-butadiene (NBR) rubber, styrene-acrylonitrile (SAN), polybutadiene rubber and polystyrene were investigated. The molecular weight distributions were measured using gel permeation chromatography (GPC). A model based on continuous distribution kinetics approach was used to study the time evolution of molecular weight distribution for these polymers during degradation. The effect of solvent properties and ultrasound intensity on the degradation of SBR rubber was investigated using different pure solvents and mixed solvents of varying volatility and different ultrasonic intensities. (C) 2011 Elsevier B.V. All rights reserved.
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This study presents 100% degradation of H-acid under optimized conditions using Alcaligenes latus, isolated from textile industrial effluent. Gene/s responsible for H-acid degradation was/were found to be present on plasmid DNA. Addition of bipyridyl to incubated medium resulted in accumulation of terminal aromatic compound, suggesting that catechol may be terminal aromatic compound in degradation pathway of H-acid by A. latus. SDS-PAGE of cell free extracts showed two prominent bands close to molecular weight of catechol 1,2-dioxygenase.
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Ultrahigh-molecular-weight polyethylene (UHMWPE) is used as an articulating surface in total hip and knee joint replacement. In order to enhance long-term durability/wear resistance properties, UHMWPE-based polymer-ceramic hybrid composites are being developed. Surface properties such as wettability and protein adsorption alter with reinforcement or with change in surface chemistry. From this perspective, the wettability and protein adsorption behavior of compression-molded UHMWPE-hydroxyapatite (HA)-aluminum oxide (Al2O3)-carbon nanotube (CNT) composites were analyzed in conjunction with surface roughness. The combined effect of Al2O3 and CNT shows enhancement of the contact angle by similar to 37A degrees compared with the surface of the UHMWPE matrix reinforced with HA. In reference to unreinforced UHMWPE, protein adsorption density also increased by similar to 230% for 2 wt.%HA-5 wt.%Al2O3-2 wt.%CNT addition to UHMWPE. An important conclusion is that the polar and dispersion components of the surface free energy play a significant role in wetting and protein adsorption than do the total free energy or chemistry of the surface. The results of this study have major implications for the biocompatibility of these newly developed biocomposites.
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An easy access to a library of simple organic salts derived from tert-butoxycarbonyl (Boc)-protected L-amino acids and two secondary amines (dicyclohexyl- and dibenzyl amine) are synthesized following a supramolecular synthon rationale to generate a new series of low molecular weight gelators (LMWGs). Out of the 12 salts that we prepared, the nitrobenzene gel of dicyclohexylammonium Boc-glycinate (GLY.1) displayed remarkable load-bearing, moldable and self-healing properties. These remarkable properties displayed by GLY.1 and the inability to display such properties by its dibenzylammonium counterpart (GLY.2) were explained using microscopic and rheological data. Single crystal structures of eight salts displayed the presence of a 1D hydrogen-bonded network (HBN) that is believed to be important in gelation. Powder X-ray diffraction in combination with the single crystal X-ray structure of GLY.1 clearly established the presence of a 1D hydrogen-bonded network in the xerogel of the nitrobenzene gel of GLY.1. The fact that such remarkable properties arising from an easily accessible (salt formation) small molecule are due to supramolecular (non-covalent) interactions is quite intriguing and such easily synthesizable materials may be useful in stress-bearing and other applications.
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Reversible addition-fragmentation chain transfer polymerization at 70 A degrees C in N,N-dimethylformamide was used to prepare poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) copolymers in various compositions to afford well-defined polymers with pre-determined molecular weight, narrow molecular weight distribution, and precise chain end structure. The copolymer compositions were determined by H-1 NMR spectroscopy. The reactivity ratios of N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMA) were calculated as r (NIPAM) = 0.838 and r (DMA) = 1.105, respectively, by the extended Kelen-Tudos method at high conversions. The lower critical solution temperature of PNIPAM can be altered by changing the DMA content in the copolymer chain. Differential scanning calorimetry and thermogravimetric analysis at different heating rates were carried out on these copolymers to understand the nature of thermal degradation and to determine its kinetics. Different kinetic models were applied to estimate various parameters like the activation energy, the order, and the frequency factor. These studies are important to understand the solid state polymer degradation of N-alkyl substituted polymers, which show great potential in the preparation of miscible polymer blends due to their ability to interact through hydrogen bonding.
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Phenoloxidases are oxidative enzymes, which play an important role in both cell mediated and humoral immunity. Purification and biochemical characterization of prophenoloxidase from cotton bollworm, Helicoverpa armigera (Hubner) were carried out to study its biochemical properties. Prophenoloxidase consists of a single polypeptide chain with a relative molecular weight of 85 kDa as determined by SDSPAGE, MALDITOF MS and LCESI MS. After the final step, the enzyme showed 71.7 fold of purification with a recovery of 49.2%. Purified prophenoloxidase showed high specific activity and homology with phenoloxidase subunit-1 of Bombyx mori and the conserved regions of copper binding (B) site of phenoloxidase. Purified prophenoloxidase has pH optima of 6.8 and has high catalytic efficiency towards the dopamine as a substrate in comparison to catechol and L-Dopa. The PO activity was strongly inhibited by phenylthiourea, thiourea, dithiothreitol and kojic acid.
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Poly{(N,N-(dimethylamino)ethyl methacrylate]-co-(methyl methacrylate)} copolymers of various compositions were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization at 70 degrees C in N,N-dimethylformamide. The polymer molecular weights and molecular weight distributions were obtained from size exclusion chromatography, and they indicated the controlled nature of the RAFT polymerizations; the polydispersity indices are in the range 1.11.3. The reactivity ratios of N,N-(dimethylamino)ethyl methacrylate (DMAEMA) and methyl methacrylate (MMA) (rDMAEMA = 0.925 and rMMA = 0.854) were computed by the extended KelenTudos method at high conversions, using compositions obtained from 1H NMR. The pH- and temperature-sensitive behaviour were studied in aqueous solution to confirm dual responsiveness of these copolymers. The thermal properties of the copolymers with various compositions were investigated by differential scanning calorimetry and thermogravimetric analysis. The kinetics of thermal degradation were determined by Friedmann and Chang techniques to evaluate various parameters such as the activation energy, the order and the frequency factor. (c) 2012 Society of Chemical Industry
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Riboflavin tetraacetate-catalyzed aerobic photooxidation of 1-(4-methoxyphenyl)ethanol was investigated as a model reaction under blue visible light in different soft gel materials, aiming to establish their potential as reaction vessels for photochemical transformations. Three strategies involving different degrees of organization of the catalyst within the gel network were explored, and the results compared to those obtained in homogeneous and micellar solutions. In general, physical entrapment of both the catalyst and the substrate under optimized concentrations into several hydrogel matrices (including low-molecular-weight and biopolymer-based gels) allowed the photooxidation with conversions between 55 and 100% within 120 min (TOF similar to 0.045-0.08 min(-1); k(obs) similar to 0.011-0.028 min(-1)), albeit with first-order rates ca. 1-3-fold lower than in solution under comparable non-stirred conditions. Remarkably, the organogel made of a cyclohexane-based bisamide gelator in CH3CN not only prevented the photodegradation of the catalyst but also afforded full conversion in less than 60 min (TOF similar to 0.167 min(-1); k(obs) similar to 0.073 min(-1)) without the need of additional proton transfer mediators (e. g., thiourea) as it occurs in CH3CN solutions. In general, the gelators could be recycled without detriment to their gelation ability and reaction rates. Moreover, kinetics could be fine-tuned according to the characteristics of the gel media. For instance, entangled fibrillar networks with relatively high mechanical strength were usually associated with lower reaction rates, whereas wrinkled laminated morphologies seemed to favor the reaction. In addition, the kinetics results showed in most cases a good correlation with the aeration efficiency of the gel media.
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The increasing industrial utilization of polyacrylamide to assist water clarification, sludge conditioning, papermaking, and secondary oil recovery leads to environmental pollution. In this work, an acrylamide degrading bacterium was isolated from paper mill effluent at Charan mahadevi, Tamilnadu, India. The minimal medium containing acrylamide (40 mM) served as a sole source of carbon and nitrogen for acrylamide degrading bacteria. The bacterial strain has grown well in 40 mM acrylamide at pH (6-7) at 30 degrees C. Within 24-48 h acrylamide was converted into acrylic acid and other metabolites. Based on biochemical characteristics and 16S rRNA gene sequence, the bacterial strain was identified as Gram negative, diplobacilli Moraxella osloensis MSU11. The acrylamide hydrolyzing bacterial enzyme acrylamidase was purified by HPLC. The enzyme molecular weight was determined to be approximately 38 kDa by SDS-PAGE using reference enzyme Pectinase. These results show that M. osloensis MSU11 has a potential to degrade the acrylamide present in the environment. (C) 2013 Elsevier Ltd. All rights reserved.
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The last enzyme in the arginine-biosynthesis pathway, argininosuccinate lyase, from Mycobacterium tuberculosis has been cloned, expressed, purified and crystallized, and preliminary X-ray studies have been carried out on the crystals. The His-tagged tetrameric enzyme with a subunit molecular weight of 50.9 kDa crystallized with two tetramers in the asymmetric unit of the orthorhombic unit cell, space group P2(1)2(1)2(1). Molecular-replacement calculations and self-rotation calculations confirmed the space group and the tetrameric nature of the molecule.
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The selective flotation of sphalerite from a sphalerite-galena mineral mixture has been achieved using cells and extracellular secretions of Bacillus megaterium after adaptation to the chosen minerals. The extracellular secretions obtained after thermolysis of bacterial cells adapted to sphalerite yield the highest flotation recovery of sphalerite with a selectivity index value of 24.5, in comparison to the other cellular and extra-cellular bio-reagents studied. The protein profile for the unadapted and mineral-adapted cells has been found to differ distinctly, attesting to variation in the yield and nature of extra-cellular polymeric substances (EPS). The changes induced in the bacterial cell wall components after adaptation to sphalerite or galena with respect to the contents of phosphate, uronic acid and acetylated sugars of B. megaterium have been quantified. The role of the dissolved metal ions from the minerals as well as that of the constituents of extracellular secretions in modulating the surface charge of the bacterial cells as well as the minerals under study has been confirmed using various enzymatic treatments of the bacterial cells. It has been demonstrated that the induction of additional molecular weight protein fractions as well as the higher amount of extracellular proteins and phosphate secreted after adaptation to sphalerite vis-A-vis galena are contributory factors for the selective separation of sphalerite from galena. (C) 2013 Elsevier B.V. All rights reserved.
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An alternating copolymer containing dithienylcyclopentadienone, thiophene and benzothiadiazole was synthesized by palladium (0) catalyzed Stille coupling reaction. Structural characterization of the synthesized alternating copolymer was carried out by NMR and FTIR spectroscopy. This solution processable copolymer shows an excellent thermal stability and has a broad absorption range from 300-800 nm. High LUMO energy level and low band gap of the synthesized copolymers suggest that, this copolymer will be a better donor material for application in organic photovoltaics. Particle size analysis and molecular weight determination of the synthesized copolymer through dynamic light scattering experiment indicates that, high molecular weight copolymer was obtained by this polymerization route. Photovoltaic devices were fabricated from the blend of copolymer and phenyl-C61- butyric acid methyl ester as the active material. Fabricated photovoltaic device results show that this alternating copolymer is a promising candidate for use in organic photovoltaics.