Thermal behaviour of copolymers of methyl methacrylate and 2-ethylhexyl methacrylate

Five copolymer samples containing different mole fractions of methyl methacrylate (MMA) and 2-ethylhexyl methacrylate (EHMA) were prepared by bulk polymerisation at 70°C using 0.2% benzoyl peroxide as an initiator. The copolymer composition was determined by¹H NMR spectroscopy. Molecular weight of copolymers was determined by gel permeation chromatography and viscosity measurements. Thermogravimetric experiments were conducted to evaluate activation energy for the degradation of copolymers. Two to four reaction stages for the weight loss were observed in the copolymers. A decrease in thermal stability was observed by an increase in EHMA content.     

Feasibility and uniqueness of stationary states of nonideal recombinant fermentations?

Summary In recombinant fermentations the plasmid loss probability per generation depends on the specific growth rate, which is related linearly to the dilution rate. A model with this feature and incomplete mixing has been studied analytically for stationary state behavior. While the kinetic parameters place upper limits on the dilution rate for a feasible stationary state in a well-mixed bioreactor, the feasible and nonfeasible regions for an incompletely mixed reactor are separated by either a straight line or a plane, whose position is determined by the mixing conditions.</o:p>     

Donor-acceptor complexes in copolymerization. L. Preparation and microstructure of chlorine-containing alternating conjugated diene–acceptor monomer copolymers

Neighboring monomer units cause significant shifts in the infrared absorption peaks attributed to cis- and trans-1,4 units in conjugated diene-acceptor monomer copolymers. Conjugated diene-maleic anhydride alternating copolymers apparently have a predominantly cis-1,4-structure, while alternating diene-SO₂ copolymers have a predominantly trans-1,4 structure. Alternating copolymers of butadiene, isoprene, and pentadiene-1,3 with α-chloroacrylonitrile and methyl α-chloroacrylate, prepared in the presence of Et_1.5AlCl_1.5(EASC), have trans-1,4 unsaturation. Alternating copolymers of chloroprene with acrylonitrile, methyl acrylate, methyl methacrylate, α-chloroacrylonitrile, and methyl α-chloroacrylate prepared in the presence of EASC-VOCl₃ have trans-1,4 configuration. The reaction between chloroprene and acrylonitrile in the presence of AlCl₃ yields the cyclic Diel-Alder adduct in the dark and the alternating copolymer under ultraviolet irradiation. The equimolar, presumably alternating, copolymers of chloroprene with methyl acrylate and methyl methacrylate undergo cyclization at 205°C to a far lesser extent than theoretically calculated, to yield five and seven-membered lactones. The polymerization of chloroprene in the presence of EASC and acetonitrile yields a radical homopolymer with trans-1,4 unsaturation.     

Structure and dynamics in solvent-polarity-induced aggregates from a c60 fullerene-based dyad

A novel methanofullerene dyad based on a hydrophobic (acceptor C60 moiety)-hydrophilic (bridge with benzene and ester functionalities)-hydrophobic (donor didodecyloxybenzene) network is designed and synthesized. Electronic absorption spectral features revealed the molecule to exhibit a strong tendency to self-aggregate in binary solvent mixtures at room temperature, where the dielectric constant exceeds a critical value, approximately 30. The dynamic structure factors of these spherical aggregates revealed stretched exponential decay with sizes varying between 110 and 250 nm with an increasing concentration, estimated from the dynamic light scattering experiments. However, a loss of shape selectivity of these aggregates was noted at lower water volume fractions in the binary solvent mixtures. The water-extracted spherical clusters were identified to be fractals with a dimension of 1.85, leading to diffusion-limited cluster aggregation as the mechanistic route for clusterization.     

C60 aggregate structure and geometry in nonpolar o-xylene

Consequent to our recent papers on C(60) colloidal aggregates in CS(2) solution (Bokare, A. D.; Patnaik, A. J. Phys. Chem. 2003, 107, 6079-6086) and their probable electron density distribution (Bokare, A. D.; Patnaik, A. J. Chem. Phys. 2003, 119, 4529-4538), the solution-phase structure of C(60) in nonpolar o-xylene is reported using a positronium (Ps) atom as a fundamental probe, mapping changes in the local electron density of the microenvironment. Spontaneous formation of stable aggregates in the colloidal range (approximately 90-150 nm) was observed in a concentration range of 0.14-0.36 g/dm(3), beyond which they broke. An onset concentration for aggregate formation at 0.14 g/dm(3), as against 0.06 g/dm(3) for the polar CS(2) solvent, was noted and was substantiated by complete quenching of pyrene fluorescence at and beyond this onset due to photoinduced electron transfer from the pyrene excited state to the C(60) aggregate. An order-disorder phase transition led to a notable geometry change of the colloidal particles; a sphere-to-nonuniform cylinder transition following an increase in the C(60) concentration from 0.14 to 0.36 g/dm(3) revealed the aggregate curvature/internal modes to have been influenced by energetic/entropic and/or hydrodynamic interactions in the solvent medium. Transmission electron microscopy images of the aggregated clusters, in corroboration with Ps annihilation characteristics and pyrene fluorescence, revealed the clusters to be hexagonally close packed microcrystals.     

Nano-sized polycrystalline bismuth silicon oxide powder by sol–gel technique

Bismuth silicon oxide (Bi₁₂SiO₂₀, BSO) nano crystalline powder was prepared by sol–gel technique using bismuth nitrate and tetraethyl orthosilicate as starting materials. The prepared samples were sintered at various temperatures (750 °C maximum) and characteristic sillenite single cubic phase with crystallite size ~38 nm (calculated from room temperature powder XRD measurements) was realized at 750 °C sintering temperature. SEM analysis showed that the powder contains the nano-sized particles with almost spherical morphology. The observed frequencies in room temperature FTIR spectrum could be assigned to Bi–O, Si–O and Bi–O–Si bonds. The FWHM (full width at half maximum) of the diffraction peaks decreased while the intensity of FTIR absorption lines increased with the increase in the sintering temperature indicating better bond formation and crystallization. The thermograph of the samples recorded in the temperature range 50–1,000 °C showed almost no weight loss after ~575 °C further confirmed the conclusion arrived at from XRD and FTIR analysis. The samples sintered at 750 °C showed about 50% absorbance in 400–600 nm region which was consistent with the pale yellow color of the sample. Broad blue emission centered ~478 nm was observed when excited by 350 nm radiation from a Xe-lamp. The intensity of this broad emission band increased while its FWHM decreased with the increase in sintering temperature. Self-trapped excitons could be responsible for this emission.     

J-aggregates in matrix stabilized two-dimensional azobenzene derivatives

A two-component film technique at the air-water interface has been used for fabricating matrix stabilized azobenzene J-aggregates. Langmuir monolayers of (E)-1-(3-chloro-4-(alkyloxy)phenyl)-2-phenyldiazene (CnCD, n=8,10,12) have been prepared with stearic acid (STA) as the two-dimensional matrix. Miscibility studies at a molecular level, explored from the monolayer pressure-area isotherms revealed a phase separation of the CnCD from the stearic acid matrix at a compression pressure of 10 mN/m. A 43-nm strong red shift in the 350 nm pi-pi * absorption feature implied formation of highly ordered J-aggregates of CnCDs in conformity with atomic force microscopy and micro-Raman spectral characteristics. While a one-component CnCD failed to form a 2D monolayer, the STA supported CnCD binary system crossed a mixed monolayer phase followed by compression, leading to the formation of matrix stabilized CnCD J-aggregates.     

Donor-Acceptor Complexes in Copolymerization. XVI. NMR Analyses of Alternating and Random Copolymers of Styrene and α-Methylstyrene with Acrylonitrile and Methacrylonitrile

An NMR investigation was carried out on random and alternating copolymers of acrylonitrile (AN) with a-methylstyrene (MS) and methacrylonitrile (MAN) with α-methylstyrene and styrene (S). The alternating MS-AN copolymer, prepared by complexation with AlEti_1-5Cl_1-5, was found to have a predominantly coisotactic configuration which was attributed to the interaction between the CH₃ and CN groups. The cotacticity of the alternating copolymer was found to be independent of the temperature of polymerization and the amount of AlEt_1-5Cl_1-5 used for complexation. The NMR spectra of random MS-AN copolymers of varying compositions indicated a high value (0.85) for the coisotacticity probability parameter (σ). The equimolar random MS-AN copolymer was also found to have essentially alternating sequences which was attributed to their low reactivity ratios. The equimolar alternating MS-MAN copolymer was found to have a random stereochemical configuration in which the coisotactic placement was slightly preferrred over the cosyndiotactic placement. The NMR spectrum of the equimolar free radical initiated MS-MAN copolymer lacked the fine structure observed in the spectrum of the alternating copolymer which was attributed to the presence of other sequences. The equimolar alternating S-MAN copolymer was found to have a high coisotactic configuration similar to that observed in the MS-AN copolymer. The equimolar free radical initiated S-MAN copolymer had a random sequence distribution.     

Proteomic Analysis of Sarcoplasmic Peptides of Two Related Fish Species for Food Authentication

Detection of species-specific sarcoplasmic peptides can be used as proteomic markers for fish food authentication and identification of species of origin in processed products. In the present study, proteomics technology was employed for differential characterization of sarcoplasmic peptides of two closely related fish species, Sperata seenghala and Sperata aor. Species-specific peptides were searched in white muscle extracts of the two species for identification of unique peptides that might aid in differentiation of the species, under two-dimensional gel electrophoresis platform. A total of 19 proteins were identified by combined matrix-assisted laser desorption ionization time-of-flight mass spectrometry and liquid chromatography-tandem mass spectrometry, of which nine and two proteins were found to be unique to S. seenghala and S. aor, respectively. One of the proteins, triosephosphate isomerase (TPI) was found to have three isoforms, out of which two were specific to S. aor, and one was specific to S. seenghala. All the three isoforms of TPI were present in the mixed samples of raw protein extracts of S. seenghala and S. aor, an observation that can be exploited to differentiate between the species and detection of deceptive practices of fraudulent substitution of commercially valuable fish species with inferior ones and differential characterization between closely related fish species.