A new method based on low background instrumental neutron activation analysis for major,trace and ultra-trace element determination in atmospheric mineral dust from polar ice cores

Dust found in polar ice core samples present extremely low concentrations, in addition the availability of such samples is usually strictly limited. For these reasons the chemical and physical analysis of polar ice cores is an analytical challenge. In this work a new method based on low background instrumental neutron activation analysis (LB-INAA) for the multi-elemental characterization of the insoluble fraction of dust from polar ice cores is presented. Thanks to an accurate selection of the most proper materials and procedures it was possible to reach unprecedented analytical performances, suitable for ice core analyses. The method was applied to Antarctic ice core samples. Five samples of atmospheric dust (μg size) from ice sections of the Antarctic Talos Dome ice core were prepared and analyzed. A set of 37 elements was quantified, spanning from all the major elements (Na, Mg, Al, Si, K, Ca, Ti, Mn and Fe) to trace ones, including 10 (La, Ce, Nd, Sm, Eu, Tb, Ho, Tm, Yb and Lu) of the 14 natural occurring lanthanides. The detection limits are in the range of 10⁻¹³–10⁻⁶ g, improving previous results of 1–3 orders of magnitude depending on the element; uncertainties lies between 4% and 60%.     

Donor–acceptor rod–coil block copolymers comprising poly[2,7‐(9,9‐dihexylfluorene)‐alt‐bithiophene] and fullerene as compatibilizers for organic photovoltaic devices

The successful synthesis is described for a donor–acceptor rod–coil block copolymer comprising blocks of poly[2,7‐(9,9‐dihexylfluorene)‐alt‐bithiophene] (F6T2) and polystyrene functionalized with fullerene (PS(C₆₀)) (F6T2‐b‐PS(C₆₀)). This new material was obtained by combining Suzuki polycondensation with radical addition fragmentation chain transfer. The block copolymer was characterized by nuclear magnetic resonance, gel permeation chromatography, and optical spectroscopy methods. Photophysical data for (F6T2‐b‐PS(C₆₀)) and a related block copolymer (F6T2‐b‐PS(PCBM)) (PCBM, phenyl‐C61‐butyric acid methyl ester) are reported and their performance as compatibilizers in bulk heterojunction organic solar cells is assessed. It is demonstrated that the addition of the rod–coil block copolymers to the active layer extends the operational stability of organic photovoltaic devices. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 888–903     

An Arm‐First Approach to Cleavable Mikto‐Arm Star Polymers by RAFT Polymerization

Redox‐cleavable mikto‐arm star polymers are prepared by an “arm‐first” approach involving copolymerization of a dimethacrylate mediated by a mixture of macroRAFT agents. Thus, RAFT copolymerization of the monomers BMA, DMAEMA, and OEGMA, with the disulfide dimethacrylate cross‐linker (DSDMA), bis(2‐methacryloyl)oxyethyl disulfide, mediated by a 1:1:1 mixture of three macroRAFT agents with markedly different properties [hydrophilic, poly[oligo(ethylene glycol) methacrylate]—P(OEGMA)_8–9; cationizable, poly[2‐(dimethylamino)ethyl methacrylate]—P(DMAEMA); hydrophobic, poly(n‐butyl methacrylate)—P(BMA)] provides low dispersity mikto‐arm star polymers. Good control (Đ < 1.3) is observed for the target P(DMAEMA)/P(OEGMA)/P(BMA) (3:3:1) mikto‐arm star, a double hydrophilic P(DMAEMA)/P(OEGMA) (3:3) mikto‐arm star and a hydrophobic P(BMA) homo‐arm star. However, Đ for the target mikto‐arm stars increases with an increase in either the ratio [DSDMA]:[total macroRAFT] or the fraction of hydrophobic P(BMA) macroRAFT agent. The quaternized mikto‐arm star in dilute aqueous solution shows a monomodal particle size distribution and an average size of ≈145 nm.

     

A Leslie-Gower Holling-type II ecoepidemic model

The modified Leslie-Gower and Holling-type II predator-prey model is generalized in the context of ecoepidemiology, with disease spreading only among the prey species. A new feature is introduced, the intraspecific competition of infected prey. All the equilibria are characterized and the existence of a Hopf bifurcation at the coexistence equilibrium is shown.     

Purification and stability of glutaryl-7-ACA acylase from pseudomonas sp.

The enzyme glutaryl-7-ACA acylase fromPseudomonas sp. NCIMB 40474, produced by a recombinantEscherichia coli host, was purified to homogeneity. The enzyme is a tetramer composed of two couples of asymmetric dimers, each of them constituted of two subunits of mol wt 18 and 52 kDa, respectively. It was found that glutaric acid, one of the products of the substrate hydrolysis, is an effective acylase inhibitor. Between pH 6.0 and pH 10.0, the enzymatic activity is almost constant, but below pH 6.0 it progressively declines. The acylase activity decreased sharply as a function of guanidine HC1 concentration. The loss is significant even at concentrations of denaturant lower than those causing unfolding, as suggested by UV spectroscopy and fluorescence emission studies. In these conditions (low denaturant concentration and low pH) the inactivation of the enzyme is caused by the tetramer dissociation into dimers. The lability of the quaternary structure of the enzyme is a key feature that must be taken into account for the improvement of the catalyst stability.     

On the numerical evaluation of Cauchy transforms

In this paper we consider simple methods for the reconstruction of the Cauchy transform over a curve when an explicit parametrization of the latter is not provided. The methods consist of replacing the parametrization of the curve by piecewise polynomial interpolation followed by the use of Newton-Cotes type formulae for the integration. The order of convergence of the resulting quadrature is higher than would be expected on the basis of considerations involving just interpolation theory, provided that the Cauchy transform is evaluated at known nodes on the curve. These results allow the calculation of the Cauchy transform at other points with the same accuracy if this scheme is followed by an interpolatory formula of sufficiently high accuracy.     

Poly(ethylene oxide)/poly(ethyl methacrylate) blends: Crystallization,melting behavior,and miscibility

Results of an investigation of isothermal crystallization and thermal behavior of poly(ethylene oxide)/poly(ethyl methacrylate) (PEO/PEMA) blends are reported. The blend composition and the crystallization temperature strongly influence the crystallization process from the melt and the melting temperature of PEO. The addition of PEMA to PEO causes a depression in the spherulite growth rate, in the overall kinetic crystallization constant, and in the melting temperature. Experimental data on the radial growth rate G and overall kinetic rate constant K_n are analyzed by means of the latest kinetic theory. From this analysis it emerges that the crystallization of pure PEO and PEO in the blend conforms to the regime I process of surface secondary nucleation. The depression of the melting temperature cannot be explained only in terms of a diluent effect due to the compatibility of the two components in the melt. Annealing and morphological effects, dependent on composition and time, must also be taken into account.     

Substituent effects on the chain‐transfer behavior of 7‐methylene‐2‐methyl‐1,5‐dithiacyclooctane in the presence of disulfides and thiols

The chain‐transfer behavior of 7‐methylene‐2‐methyl‐1,5‐dithiacyclooctane was investigated in the presence of four chain‐transfer agents: thiophenol (PhSH), thiobenzoic acid (BzSH), diphenyl disulfide (PhSSPh), and dibenzoyl disulfide (BzSSBz). The chain‐transfer constants for these compounds at 60 °C were 0.38 (PhSH), 0.76 (BzSH), 0.24 (PhSSPh), and 0.05 (BzSSBz). The variations in the thiol chain‐transfer constants could be explained in terms of the stability of the resulting radicals. The chain transfer to the disulfides, however, appeared to be determined by the electronic character of the disulfide bond, and this suggests that the transfer took place via an addition–fragmentation mechanism. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4421–4425, 2002     

The reaction of acyl peroxides with 2,2,6,6-tetramethylpiperidinyl-1-oxy

Benzoyl ana lauroyl peroxides undergo induced decomposition by 2,2,6,6-tetramethylpiperidinyl-1-oxy to form acyloxy radicals and carboxylic acid in equimolar amounts. Formation of the carboxylic acid does not involve free acyloxy radicals.