Deciphering radical transport in the large subunit of class I ribonucleotide reductase

Incorporation of 2,3,6-trifluorotyrosine (F(3)Y) and a rhenium bipyridine ([Re]) photooxidant into a peptide corresponding to the C-terminus of the β protein (βC19) of Escherichia coli ribonucleotide reductase (RNR) allows for the temporal monitoring of radical transport into the α2 subunit of RNR. Injection of the photogenerated F(3)Y radical from the [Re]-F(3)Y-βC19 peptide into the surface accessible Y731 of the α2 subunit is only possible when the second Y730 is present. With the Y-Y established, radical transport occurs with a rate constant of 3 × 10(5) s(-1). Point mutations that disrupt the Y-Y dyad shut down radical transport. The ability to obviate radical transport by disrupting the hydrogen bonding network of the amino acids composing the colinear proton-coupled electron transfer pathway in α2 suggests a finely tuned evolutionary adaptation of RNR to control the transport of radicals in this enzyme.     

Screening structure-property correlations and device performance of Ir(III) complexes in multi-layer PhOLEDs

The structure-property correlations of a set of heteroleptic red- and green-emitting Ir(III) complexes with different temperature sensitivities and charge trapping capabilities are described, revealing superb performance in multi-layer phosphorescent organic light-emitting diodes (PhOLEDs) expressed by very high maximum luminous efficiencies up to 36.8 cd A(-1). Using 2-phenylpyridine and with 2-(naphthalen-1-yl)pyridine as the C^N ligand, the resulting red emitting complex featured a maximum luminous efficiency of 10.8 cd A(-1); one of the most excellent device performances within this class of red Ir(III) emitters.     

Dramatic thermal stability of virus-polymer conjugates in hydrophobic solvents

We have developed a method for integrating the self-assembling tobacco mosaic virus capsid into hydrophobic solvents and hydrophobic polymers. The capsid was modified at tyrosine residues to display an array of linear poly(ethylene glycol) chains, allowing it to be transferred into chloroform. In a subsequent step, the capsids could be transferred to a variety of hydrophobic solvents, including benzyl alcohol, o-dichlorobenzene, and diglyme. The thermal stability of the material against denaturation increased from 70 °C in water to at least 160 °C in hydrophobic solvents. With a view toward material fabrication, the polymer-coated TMV rods were also incorporated into solid polystyrene and thermally cast at 110 °C. Overall, this process significantly expands the range of processing conditions for TMV-based materials, with the goal of incorporating these templated nanoscale systems into conductive polymer matrices.     

Ground-Based Gamma Ray Astronomy

This paper is the write-up of a rapporteur talk given by the author at the 33rd International Cosmic Ray Conference in Rio de Janeiro, Brazil, in 2013. It attempts to summarize results and developments in ground-based gamma-ray observations and instrumentation from among the ～300 submissions to the gamma-ray sessions of the meeting. Satellite observations and theoretical developments were covered by a companion rapporteur (Stawarz, L., 33rd ICRC, Rio de Janeiro, Brazil, Rapporteur talk: Space-based Gamma-Ray Astronomy, 2013). Any review of this nature is unavoidably subjective and incomplete. Nevertheless, the article should provide a useful status report for those seeking an overview of this exciting and fast-moving field.     

Influence of clay concentration on the gas barrier of clay-polymer nanobrick wall thin film assemblies

The influence of the clay deposition suspension concentration on gas barrier thin films of sodium montmorillonite (MMT) clay and branched polyethylenimine (PEI), created via layer-by-layer assembly, was investigated. Films grown with MMT suspension concentrations ranging from 0.05 to 2.0 wt % were analyzed for their growth as a function of deposited polymer-clay bilayers (BL) and their thickness, clay concentration, transparency, nanostructure, and oxygen barrier as a function of the suspension concentration. The film thickness doubles and the visible light transmission decreases less than 5% as a function of MMT concentration for 20-BL films. Atomic force and transmission electron microscope images reveal a highly aligned nanobrick wall structure, with quartz crystal microbalance measurements revealing a slight increase in the film clay concentration as the MMT suspension concentration increases. The oxygen transmission rate (OTR) through these 20-BL composites, deposited on a 179 μm poly(ethylene terephthalate) film, decreases exponentially as a function of the MMT clay concentration. A 24-BL film created with 2.0 wt % MMT has an OTR below the detection limit of commercial instrumentation (<0.005 cc/m(2)·day·atm). This study demonstrates an optimal clay suspension concentration to use when creating LbL barrier films, which minimizes deposition steps and the overall processing time.     

Obliquely propagating ion-acoustic shock waves in a degenerate quantum plasma

A theoretical investigation has been carried out on the propagation of non-linear ion-acoustic shock waves (IASHWs) in a magnetized degenerate quantum plasma system composed of inertial non-relativistic positively charged light and heavy ions, inertialess non-relativistically or ultra-relativistically degenerate electrons and positrons. The reductive perturbation method has been employed to derive the Burgers' equation. It has been observed that under consideration, our plasma model supports only positive potential shock structure. It is also found that the amplitude and steepness of the IASHWs have been significantly modified by the variation of ion kinematic viscosity, oblique angle, number density, and charge state of the plasma species. The results of our present investigation will be helpful for understanding the propagation of IASHWs in white dwarfs and neutron stars.     

Commensurability oscillations in NdBa2Cu3Oy single crystals

Commensurability between inter-vortex distance and crystal lattice constant is investigated by angular dependent magnetization in very pure twinned and twin-free NdBa₂ Cu₃ O_y single crystals. With increasing temperature the incommensurate states split up and become finally commensurate with half the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within the unit cell and discussed with respect to temperature, field, anisotropy, and twin structure.     

Random fluorene copolymers with on‐chain quinoxaline acceptor units

Two series of novel random polyfluorene copolymers containing quinoxaline units were prepared by stressing the coupling according to Yamamoto. The first series contains 2,3‐bis‐(4′‐tert‐butyl‐biphenyl‐4‐yl)benzo[g]quinoxaline and the second series 2,3‐bis‐(4′‐tert‐butyl‐biphenyl‐4‐yl)quinoxaline as energy accepting unit. The copolymers were identified by gel permeation chromatography, infrared spectroscopy, and nuclear magnetic resonance spectroscopy. Thermal properties were analyzed by thermal gravimetric analysis and differential scanning calorimetry revealing amorphous copolymers that are stable up to 430 °C. The morphology was investigated using atomic force microscopy. The optical properties in solutions and thin films were analyzed. Furthermore, the thin film electro‐optical properties were determined in monolayer polymer light‐emitting devices. Single layer devices were built with efficiencies ranging from 0.15 to 2.0 cd/A. For the random copolymers with 5 mol % benzo[g]quinoxazoline in the polyfluorene backbone some threefold efficiency enhancement from 1.1 to 3.0 cd/A was achieved by utilizing an ultra thin interlayer of poly(9,9‐di‐n‐octylfluorene‐2,7‐diyl)‐alt‐[1,4‐phenylene‐(4‐sec‐butylphenylimino)‐1,4‐phenylene] between PEDOT:PSS and the emissive random copolymer layer. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4773–4785, 2007     

Determining a 'safe' high-mass limit in matrix-assisted laser desorption/ionisation time-of-flight mass spectra of coal derived materials with reference to instrument noise

Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd.