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Abstract: Greigite (Fe3S4), a widely occurring iron thiospinel, was investigated using soft X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). XAS and XMCD spectra were recorded at the Fe L-2,L-3 edges for pure synthetic and natural greigite samples. At the Fe L-3 edge, the XAS spectra reveal two main absorption peaks at 707.2 and 708.6 eV, which are interpreted to originate from greigite and an oxidized surface layer on greigite crystals. The XMCD spectra, which are dominated by a greigite signal, contain three peaks at 705.3, 706.2, and 707.7 eV, all with the same sign. The expectation is that the spectrum would have two negative peaks representing Fe2+ and Fe3+ in octahedral coordination, and a positive peak representing Fe3+ in tetrahedral coordination, as found in stoichiometric magnetite (Fe3O4). A reasonable fit of the XMCD data can be achieved without the tetrahedral Fe component, which contradicts magnetic structural information provided by neutron diffraction analysis, and uses unreasonable parameters. The conundrum between theory and experimental data may be caused by the strong covalent effect in sulfides, which causes broadening of the hybridized XMCD peaks and also indicates that multiplet calculations cannot fully predict the properties of greigite. Our results indicate covalent 3d states in greigite, which can destroy the half-metallicity that is present in magnetite. Our measurements represent the best available XAS and XMCD spectra for greigite, but further experimental and modeling information are needed to explain the observed XMCD spectra and to understand what it represents in terms of electronic and magnetic structure. This is important because greigite widely contributes to the magnetic properties of sedimentary rocks.

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Abstract: Porphyrin moieties were rigidly attached to DNA to generate an accurate molecular ruler. Molecular ruler analysis was conducted using steady-state fluorescence, circular dichroism and small angle X-ray scattering spectroscopic techniques, in an attempt to analyse the FRET, exciton coupling and scattering intensity between different porphyrin-porphyrin labelled DNA combinations. A 21-mer test sequence was labelled with a porphyrin in one position on one strand, and seven different positions on seven complementary strands, to overall give seven porphyrin-porphyrin inter-strand combinations. Steady-state fluorescence and circular dichroism spectroscopic analysis of the Soret band revealed individual Watson-Crick bases pair molecular ruler sensitivity. Small angle X-ray scattering attempts between metallated-porphyrin entities did not reveal sufficient scattering at low concentrations, in contrast, an iodinated analogue of the porphyrin system did displayed scattering correlating to different iodine iodine distances. After calibration of the porphyrin system, the moieties were applied to study protein-DNA interactions between Tus, a 36 KDa DNA binding protein, and Ter, a specific 21-mer DNA sequence. Molecular ruler nalysis of the complex required an extended version of the Ter DNA sequence to which modifications were attached. Established FRET pairs FAM and TAMRA were applied to investigate protein-DNA complexation. Native PAGE analysis revealed Tus binds to the extended DNA via a sliding mechanism. Fluorescence analysis of the established FRET pairs identified changes in fluorescence not correlating to changes in FRET, and instead was attributed to emission quenching upon protein binding. Applying the zinc and free base porphyrin version displayed subtle changes in the Soret band circular dichrosim upon complexation, indicating small DNA helical change upon complexation. A 45-mer DNA sequence was designed to form multiple hairpin-duplex conformations with the addition of an appropriate complementary strand. Attaching FRET pairs to the extremes of the DNA sequence enabled multiple DNA conformations, and hence FRET distances to be obtained from one doubly modified DNA sequence. The combinations were characterised by UV-Vis, fluorescence and circular dichroism spectroscopy. Finally, terpyridine labelled DNA sequences selectively formed DNA nanotubes through orthogonal hydrogen bonding and metal complexation interactions. Short DNA strands were designed to self-assemble into long duplexes through a sticky-end approach. Addition of weakly binding metals such as zinc induced the formation of tubular arrays consisting of DNA bundles 50-200 nm wide and 2-50 nm high. TEM displayed additional long distance ordering of the terpyridine-DNA complexes into fibers.

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Abstract: The structures of fourteen new lanthanide frameworks (La, Ce, Eu, Tb, Y and Lu) containing the 2,2- or 2,3-dimethylsuccinate ligands are reported. While the majority of the known 2,2-dimethylsuccinate frameworks feature two dimensionally bonded layers, capped by hydrophobic methyl groups, several of these new frameworks adopt quite different architectures. These include one dimensional inorganically connected chains (La and Ce) with only non-covalent interactions in the other two dimensions, and three dimensional covalently bonded frameworks (Eu and Lu) with spaces in their structure to accommodate the bulky methyl groups. The new 2,3-dimethylsuccinate frameworks (La and Y) adopt three-dimensional covalently bonded frameworks, with the pores in the La phase large enough to accommodate both the methyl groups whilst retaining a small accessible void volume. The factors affecting the formation of structures with different dimensionalities are examined and compared to previously reported transition metal frameworks. In addition, the sequence of phases formed with changing lanthanide size, concentrations and temperatures are rationalised. The luminescent properties of several 1- and 2-D frameworks doped with Eu and Tb are reported, with the Y host exhibiting the most intense emission.

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Abstract: Transition metal–alkane complexes—termed σ-complexes because the alkane donates electron density to the metal from a σ-symmetry carbon–hydrogen (C–H) orbital—are key intermediates in catalytic C–H activation processes, yet these complexes remain tantalizingly elusive to characterization in the solid state by single-crystal x-ray diffraction techniques. Here, we report an approach to the synthesis and characterization of transition metal–alkane complexes in the solid state by a simple gas-solid reaction to produce an alkane σ-complex directly. This strategy enables the structural determination, by x-ray diffraction, of an alkane (norbornane) σ-bound to a d8–rhodium(I) metal center, in which the chelating alkane ligand is coordinated to the pseudosquare planar metal center through two σ-C–H bonds.

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Abstract: Brolly good MOFs: A new series of hydrophobic isoreticular porous Zr oxide dicarboxylate MOFs have been prepared (see picture, Zr blue polyhedra, O red, C black). They have a one-dimensional pore system, a rare combination of Lewis acidity and hydrophobic character, and a higher hydrothermal and mechanical stability than their UiO MOF polymorph counterparts.