The effect of varying carboxylate ligation on the electronic environment of N2O(x) (x = 1-3) nonheme iron: a DFT analysis

Mononuclear nonheme iron oxygenase (MNO) enzymes contain a subclass of metalloproteins capable of catalyzing the O(2)-dependent hydroxylation of unactivated substrates at a ferrous ion center coordinated to a highly conserved His-His-Glu/Asp motif. These enzymes, which utilize additional reducing equivalents obtained from the decarboxylation of a coordinated α-ketoglutarate (αKG) cofactor, do not readily interact with O(2) in the absence of αKG binding. Density functional theory calculations with the B3LYP functional were performed to gain insight into the electrochemical behavior of three sets of Fe(II/III) complexes containing a core N, N, O facial binding motif in which the number of carboxylate ligands was systematically altered, to provide one, two (cis) or three (fac) labile sites. The calculated trend in Fe(II/III) reduction potentials was observed to parallel that observed in cyclic voltammetry experiments, showing a decrease in potential (stabilized oxidized state) with increasing carboxylate ligation. This trend does not appear to be the result of differential charge on the metal complex. Changes in the redox-active molecular orbital (RAMO) energy due to covalent effects dominate across the series of complexes when chloride is modeled as the labile ligand, with the π anti-bonding nature of the RAMO being an important factor. With water molecules as the labile ligands, however, a much steeper redox dependence on the number of carboxylate ligands is observed and this effect seems to be largely electrostatic in origin. Differential relaxation of the occupied molecular orbitals in the ferric complexes appears to contribute to the redox trend as well. Finally, these observations are placed in the context of MNO enzyme mechanisms.     

Laser machined macro and micro structures on glass for enhanced light trapping in solar cells

In order to increase the efficiency of solar cell modules it is necessary to make the optimum use of light incident upon them. Much research has been done on improving light absorption through front surface texturisation and light trapping schemes. Laser light is commonly used in industry for various applications including marking and texturisation. By controlling laser parameters, it is possible to tailor macro and micro structures in most materials. The CO₂ laser used in this investigation emits radiation at 10.6 μm with the ability to pulse in the micro-second range. The laser was used to ablate grooved textures in the fused quartz material, used in this study as the light trapping medium, following which an analysis of the effects of the laser parameters on the texture geometry and surface morphology was performed through a combination of cross sectioning and scanning electron microscopy. Transmission through the textured glass was improved for most samples after acid etching. The light trapping effects of the best performing textures were analysed by investigating the effects on a silicon solar cell’s performance at varying angles of incidence. Results indicated a significant increase in light trapping when light was incident at acute angles. For an angle of incidence of 10^° a relative increase in efficiency of up to 51 % was observed.     

Randomly Pk-decomposable graphs

A graph $G$ is $H$-decomposable if it can be expressed as an edge-disjoint union of subgraphs, each subgraph isomorphic to $H$. If $G$ has the additional property that every $H$-decomposable subgraph of $G$ is part of an $H$-decomposition of $G$, then $G$ is randomly $H$-decomposable. Using computer assistance, we provide in this paper a characterization of randomly path-decomposable graphs for paths of length 11 or less. We also prove the following two results: (1) With one small exception, randomly $P_k$-decomposable graphs with a vertex of odd degree do not contain a $P_{k+1}$-subgraph, (2) When the edges of a $P_k$-subgraph are deleted from a connected randomly $P_k$-decomposable graph, the resulting graph has at most one nontrivial component.     

Radial oscillations of neutron stars in strong magnetic fields

The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to include strong magnetic field. It is found that magnetized neutron stars support higher maximum mass whereas the effect of magnetic field on radial stability for observed neutron star masses is minimal.     

The reactions of [Fe(CO)5-n(CNAr)n] (n = 1 or 2; Ar = aryl) with dicyclopentadiene

Although [Fe(CO)₃(CNAr)₂] complexes fail to react with dicyclopentadiene at 140°C, under the same conditions [Fe(CO)₄(CNAr)] complexes give high yields of [Fe₂(η-C₅H₅(CO)₃(CNAr)] and [Fe₂(η-C₅H₅)₂(CO)₂-(CNAr)₂], with the product ratios depending very much on the aryl group (Ar).     

A Unified Approach to Couple Aromatic Heteronucleophiles to Azines and Pharmaceuticals

Coupling aromatic heteronucleophiles to arenes is a common way to assemble drug‐like molecules. Many methods operate via nucleophiles intercepting organometallic intermediates, via Pd‐, Cu‐, and Ni‐catalysis, that facilitate carbon‐heteroatom bond formation and a variety of protocols. We present an alternative, unified strategy where phosphonium salts can replicate the behavior of organometallic intermediates. Under a narrow set of reaction conditions, a variety of aromatic heteronucleophile classes can be coupled to pyridines and diazines that are often problematic in metal‐catalyzed couplings, such as where (pseudo)halide precursors are unavailable in complex structures with multiple polar functional groups.     

The use of cationic surfactants to control the structure of zinc oxide films prepared by chemical vapour deposition

This paper describes a powerful and versatile new method for controlling the structure of zinc oxide thin films prepared by aerosol assisted chemical vapour deposition, based on the use of a common surfactant. The technique combines the benefits of solution and vapour based methods and leads to high quality morphologically-defined and orientated thin films.     

High-speed counter-current chromatography for the study of defense metabolites in wheat. Characterization of 5,6-O-methyl trans-aconitic acid

High-speed counter-current chromatography (HSCCC) methods were developed for the study of induced defense metabolites in wheat (Triticum aestivum) against powdery mildew (Blumeria graminis f. sp. tritici). A single HSCCC purification step afforded extraction of mg-quantities of an induced compound with antifungal activity. Subsequent LC-MS and NMR analyses have led to the characterization of 5,6-O-methyl trans-aconitic acid, the first such report of this compound in a plant species. The inducible nature of aconitic acid was evidenced by comparing the metabolite profiles of leaf extracts from plants treated or not with soluble silicon and infected or not with powdery mildew. In a second step, dual-mode HSCCC was used to enhance the separation of other forms of aconitic acid in wheat. Based on these results, it was concluded that 5,6-O-methyl trans-aconitic acid plays an important role as a defense molecule in wheat plants and that HSCCC is a powerful separation method for purifying such compounds from complex plant-pathogen interactions.     

Synthesis by extrusion: continuous,large-scale preparation of MOFs using little or no solvent

Grinding solid reagents under solvent-free or low-solvent conditions (mechanochemistry) is emerging as a general synthetic technique which is an alternative to conventional solvent-intensive methods. However, it is essential to find ways to scale-up this type of synthesis if its promise of cleaner manufacturing is to be realised. Here, we demonstrate the use of twin screw and single screw extruders for the continuous synthesis of various metal complexes, including Ni(salen), Ni(NCS)₂(PPh₃)₂ as well as the commercially important metal organic frameworks (MOFs) Cu₃(BTC)₂ (HKUST-1), Zn(2-methylimidazolate)₂ (ZIF-8, MAF-4) and Al(fumarate)(OH). Notably, Al(fumarate)(OH) has not previously been synthesised mechanochemically. Quantitative conversions occur to give products at kg h^–1 rates which, after activation, exhibit surface areas and pore volumes equivalent to those of materials produced by conventional solvent-based methods. Some reactions can be performed either under completely solvent-free conditions whereas others require the addition of small amounts of solvent (typically 3–4 mol equivalents). Continuous neat melt phase synthesis is also successfully demonstrated by both twin screw and single screw extrusion for ZIF-8. The latter technique provided ZIF-8 at 4 kg h^–1. The space time yields (STYs) for these methods of up to 144 × 10³ kg per m³ per day are orders of magnitude greater than STYs for other methods of making MOFs. Extrusion methods clearly enable scaling of mechanochemical and melt phase synthesis under solvent-free or low-solvent conditions, and may also be applied in synthesis more generally.