Non-isothermal gas flow in microchannel with equal wall temperatures

A non-isothermal two-dimensional compressible subsonic slip gas flows is analyzed in this paper. It is pressure-driven steady flow in microchannels with variable cross section (convergent, divergent, and constant height channel). Since the flows correspond to microspaces, the rarefaction effect is taken in account. The obtained gas temperature profiles are non-uniform. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Configuration and conformational equilibrium of (±)-trans-1-oxo-3-thiophen-2-yl-isochroman-4-carboxylic acid methyl ester

The X-ray analysis of 1-oxo-3-thiophen-2-yl-isochroman-4-carboxylic acid methyl ester 1 confirmed its trans-configuration and a conformation with diaxial H-3 and H-4 atoms in solid state. NMR experiments indicated that trans-1 exists in solution in both expected conformers. In CDCl₃ and especially in CD₃OD or DMSO, the conformational equilibrium is shifted towards the conformer with diequatorial H-3 and H-4, which was also determined by 2D NOESY experiments. The shift is due to the greater polarity of that conformer deduced by ab initio calculations.     

Trityl salt—initiated polymerization of α-methylstyrene

The initiation reaction of the polymerization of α-methylstyrene by trityl tetrachloroferate and tritylhexachloroantimonate in 1,2-dichloroethane at 20°C was studied. The rate constants were 14 × 10^?3 and 27 × 10^?3 L mol^?1s^?1, respectively. The dissociation constants of tritylterachloroferate (K_d = 0.88 × 10^?4M^?1) and tritylhexachloroantimonate (K_d = 2.64 × 10^?4M^?1) was determined. The effect of electron acceptors and donors on the dissociation equilibrium and initiation rate was investigated. It was shown that in strongly dissociated ion pairs such as stable carbenium salts the electron donors and acceptors have no appreciable effect on the magnitude of the dissociation. The temperature dependence of the rate constants in the ?20–+20°C range yielded the following thermodynamic parameters for trityltetrachloroferate: E_i = 8.54 kcal/mol; A = 3.2 × 10⁴ mol^?1s^?1; ΔH* = 8 kcal/mol; and S* = ?39.8 eu.     

Polyelectrolyte complex nanoparticles from N‐carboxyethylchitosan and polycationic double hydrophilic diblock copolymers

For the first time, the polyelectrolyte complex (PEC) formation tool was used for preparation of core‐shell nanoparticles form the natural polyampholyte N‐carboxyethylchitosan (CECh) and weak polycationic (protonated) polyoxyethylene‐b‐poly[2‐(dimethyl‐amino)ethyl methacrylate] (POE‐b‐PDMAEMA) diblock copolymers. The performed dynamic light scattering analyses revealed that nanoparticles with a PEC core and a POE shell could be formed at mixing ratio between the oppositely charged groups equal to 1/1 depending on CECh molar mass, polymerization degree of PDMAEMA block and ionic strength. The results were confirmed by the performed AFM and cryo‐TEM analyses. When high molar mass CECh was used, core‐shell nanoparticles were obtained with the diblock copolymer of the shortest PDMAEMA block at ionic strength (I) of 0.01. At ionic strength value close to the physiological one (I = 0.1) secondary aggregation occurred. Spherical nanoparticles at I = 0.1 were obtained upon lowering the CECh molar mass. Depending on the polymer partners and medium parameters the size of the obtained particles varied from 60 to 600 nm. The X‐ray photoelectron spectra evidenced the hydrophilic POE‐block shell—coacervate CECh/PDMAEMA‐block core structure. The nanoparticles are stable in a rather narrow pH range around 7.0, thus revealing the high pH‐sensitivity of the obtained core‐shell particles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2105–2117, 2009     

Non‐Woven Fibrous Materials with Antibacterial Properties Prepared by Tailored Attachment of Quaternized Chitosan to Electrospun Mats from Maleic Anhydride Copolymer

In order to impart antibacterial properties to microfibrous electrospun materials from styrene/maleic anhydride copolymers, quaternized chitosan derivatives (QCh) containing alkyl substituents of different chain lengths are covalently attached to the mats. A complete inhibition of the growth of bacteria, S. aureus (Gram‐positive) and E. coli (Gram‐negative), for a contact time of 30–120 min or a decrease of the bacterial titer by 2–3 log units is observed depending on the quaternization degree, the chain length of the alkyl substituent, and the molar mass of QCh. The modified mats are also effective in suppressing the adhesion of pathogenic S. aureus bacteria.

     

Contact Process in a Wedge

We prove that the supercritical one-dimensional contact process survives in certain wedge-like space-time regions, and that when it survives it couples with the unrestricted contact process started from its upper invariant measure. As an application we show that a type of weak coexistence is possible in the nearest-neighbor “grass-bushes-trees” successional model introduced in Durrett and Swindle (Stoch. Proc. Appl. 37:19–31, 1991).     

Simultaneous HPLC determination of caffeine, theobromine, and theophylline in food, drinks, and herbal products

A rapid and selective high-performance liquid chromatographic (HPLC) method is developed for the separation and determination of caffeine, theobromine, and theophylline. The chromatography is performed on a Zorbax Eclipse XDB-C8 column (4.6 x 150 mm i.d., 5-microm particle size) at 25 degrees C, with a mobile phase of water-THF (0.1% THF in water, pH 8)-acetonitrile (90:10, v/v). The flow rate is 0.8 mL/min, and detection is by UV at 273 nm. This method permits the simultaneous determination of caffeine, theobromine, and theophylline in food, drinks, and herbal products with detection limits of 0.07-0.2 mg/L and recoveries of 100.20-100.42%. Correlation coefficients, for the calibration curves in the linear range of 0.2-100 mg/L, are greater than 0.9999 for all compounds. The within- and between-day precision is determined for both retention times and peak area. The data suggests that the proposed HPLC method can be used for routine quality control of food, drinks, and herbal products.     

The diradical character of polyacenequinododimethides

Abstract  

An electronic structure study of singlet and triplet states of two series of polyacenequinododimethides was performed using the B3LYP method. It was found that the ground state of all examined polyacenequinododimethides is a singlet with significant diradical character. The diradical character of the compounds under investigation was estimated using the unrestricted symmetry-broken and complete active space methods. It was shown that polyacene-2,3-quinododimethides have more pronounced diradical character than polyacene-2,x-quinododimethides. The diradical character of polyacene-2,x-quinododimethides monotonically increases with their increasing molecular size. Within the series of polyacene-2,3-quinododimethides the diradical character is not a monotonic function of the number of hexagons. It was found that pentacene-2,3-quinododimethide has the most pronounced diradical character in this series. It can be predicted on the basis of the singlet–triplet gap values that even higher polyacenequinododimethides will be singlet, but not triplet molecules.     

Electrospun microfibrous poly(styrene-alt-maleic anhydride)/poly(styrene-co-maleic anhydride) mats tailored for enzymatic remediation of waters polluted by endocrine disruptors

Novel bicomponent microfibrous mats containing targeted amount of reactive maleic anhydride groups were prepared by electrospinning of mixed solutions of poly(styrene-alt-maleic anhydride) and poly(styrene-co-maleic anhydride). Then, amino-functionalized P(St-alt-MA)/P(St-co-MA) mats were obtained by reaction with p-phenylenediamine. ATR-FTIR and XPS spectroscopy were used to characterize pristine and modified P(St-alt-MA)/P(St-co-MA) mats. On the next step, laccase from Trametes versicolor was covalently attached onto the modified mats; the average amount of immobilized enzyme was 40 ± 0.7 mg/g mat. The catalytic activity of the immobilized enzyme was studied in respect to bisphenol A (BPA) endocrine disruptor. The optimum activity of the immobilized enzyme was reached at maximum flow rate of 1.3 mL/s. After 90 min the BPA concentration was reduced by 60% and the catalytic activity of microfibrous mats remained stable for about 30 successive reuses. In addition, the relative activity of laccase immobilized on the microfibrous mats was displayed in a broader pH range as compared to that of the free one.     

Electrospun non-woven nanofibrous hybrid mats based on chitosan and PLA for wound-dressing applications

Continuous defect-free nanofibers containing chitosan (Ch) or quaternized chitosan (QCh) were successfully prepared by one-step electrospinning of Ch or QCh solutions mixed with poly[(L-lactide)-co-(D,L-lactide)] in common solvent. XPS revealed the surface chemical composition of the bicomponent electrospun mats. Crosslinked Ch- and QCh-containing nanofibers exhibited higher kill rates against bacteria S. aureus and E. coli than the corresponding solvent-cast films. SEM observations showed that hybrid mats were very effective in suppressing the adhesion of pathogenic bacteria S. aureus. The hybrid nanofibers are promising for wound-healing applications.