High-affinity binding and direct electron transfer to solid metals by the Shewanella oneidensis MR-1 outer membrane c-type cytochrome OmcA

The purified outer membrane bacterial protein OmcA binds densely to the surface of hematite (Fe2O3), permitting direct electron transfer to this solid mineral to reduce Fe (III) with an electron flux of about 1013 electrons /cm2/s. In the presence of hematite, there is a substantial increase in the amplitude of internal protein motions that correlate with metal reduction. Binding is highly favorable, with a partition coefficient of approximately 2 x 105 (DeltaGo' = -28 kJ/mol), where approximately 1014 OmcA proteins bind per cm2 to the solid metal surface, indicating the utility of using purified OmcA in the construction of a biofuel cell.     

Crystal structure, physical properties and HRTEM investigation of the new oxonitridosilicate EuSi2O2N2

The new layered oxonitridosilicate EuSi₂O₂N₂ has been synthesized in a radio‐frequency furnace at temperatures of about 1400 °C starting from europium(III ) oxide (Eu₂O₃) and silicon diimide (Si(NH)₂). The structure of the yellow material has been determined by single‐crystal X‐ray diffraction analysis (space group P1 (no. 1), a=709.5(1), b=724.6(1), c=725.6(1) pm, α=88.69(2), β=84.77(2), γ=75.84(2)°,V=360.19(9)×10⁶ pm³, Z=4, R1=0.0631, 4551 independent reflections, 175 parameters). Its anionic Si₂O₂N₂^2? layers consist of corner‐sharing SiON₃ tetrahedra with threefold connecting nitrogen and terminal oxygen atoms. High‐resolution transmission electron micrographs indicate both ordered and disordered crystallites as well as twinning. Magnetic susceptibility measurements of EuSi₂O₂N₂ exhibit Curie–Weiss behavior above 20 K with an effective magnetic moment of 7.80(5) μ_B Eu^?1, indicating divalent europium. Antiferromagnetic ordering is detected at 4.5(2) K. EuSi₂O₂N₂ shows a field‐induced transition with a critical field of 0.50(5) T. The four crystallographically different europium sites cannot be distinguished by ¹⁵¹Eu Mössbauer spectroscopy. The room‐temperature spectrum is fitted by one signal at an isomer shift of δ=?12.3(1) mm s^?1 subject to quadrupole splitting of ΔE_Q=?2.3(1) mm s^?1 and an asymmetry parameter of 0.46(3). Luminescence measurements show a narrow emission band with regard to the four crystallographic europium sites with an emission maximum at λ=575 nm.     

High resolution 1H detected 1H,13C correlation spectra in MAS solid-state NMR using deuterated proteins with selective 1H,2H isotopic labeling of methyl groups

MAS solid-state NMR experiments applied to biological solids are still hampered by low sensitivity and resolution. In this work, we employ a deuteration scheme in which individual methyl groups are selectively protonated. This labeling scheme allows the acquisition of proton carbon correlation spectra with a resolution comparable to that in solution-state NMR experiments. We observe an increase in resolution by a factor of 10-15 compared to standard heteronuclear correlation experiments using PMLG for 1H,1H dipolar decoupling in the indirect dimension. At the same time, the full sensitivity of the proton-based experiment is retained. In comparison to the heteronuclear detected version of the experiment, a gain in sensitivity of a factor of approximately 4.7 is achieved.     

Electron binding energies of hydrated H3O+ and OH-: photoelectron spectroscopy of aqueous acid and base solutions combined with electronic structure calculations

The electronic structure of hydrated H3O+ and OH- is probed in a water jet by photoelectron spectroscopy employing 100 eV photons. The first ionization potential for OH- at 9.2 eV and the second ionization potential for H3O+ at 20 eV are resolved, corresponding to the removal of an electron from the 2ppi highest occupied molecular orbital and from the 1e orbital, respectively. These assignments are supported by present computational results based on a combination of molecular dynamics and ab initio calculations.     

alpha- and beta-FOX-7, polymorphs of a high energy density material, studied by X-ray single crystal and powder investigations in the temperature range from 200 to 423 K

The alpha-beta phase transition in the novel energetic material 1,1-diamino-2,2-dinitroethylene, C2H4N4O4 (FOX-7), has been studied by single-crystal X-ray investigations at five different temperatures over the 200-393 K range. In these investigations, the positions of the hydrogen atoms were experimentally determined without any geometric constraints. In addition, X-ray powder investigations using the Guinier technique have been performed to characterize the beta-phase up to 423 K. The alpha-beta phase transition at 389 K is first order, shows a discontinuous increase of the molar volume and entropy (DeltaV = 1.75 cm3/mol, X-ray investigation; DeltaS = 1.5 cal/K mol, DSC analysis), and can be classified as displacive. The hitherto unknown structure of beta-FOX-7 was solved at 393 K and showed simple structural relations to the alpha-polymorph. The characteristic bonding in wave-shaped layers is now found for beta-FOX-7 (P2(1)2(1)2(1), z = 4, a= 6.9738(7) A, b = 6.635(1) A, c = 11.648(2) A, 393 K), as well as for alpha-FOX-7 (P2(1)/n, z = 4, a = 6.9467(7) A, b = 6.6887(9) A, c = 11.350(1) A, beta = 90.143(13) degrees , 373 K). Interestingly, whereas the intramolecular C-C, C-N, N-O, and N-H bond distances remain nearly unchanged for both polymorphs over the whole temperature range from 200 to 393 K, the two nitro groups deviate strongly from the molecular plane formed by the two carbon and two amino nitrogen atoms. In alpha-FOX-7 at 373 K, the nitro groups are twisted -47 and +6 degrees with respect to the carbon-carbon bond, but in beta-FOX-7 at 393 K, these twist angles are changed to -36 and +20 degrees . Within the layers, the FOX-7 molecules show strong pi-conjugation and extensive intra- and intermolecular hydrogen bonding. In this investigation, we have been able to show that alpha- and beta-FOX-7 build up different nets of intermolecular hydrogen bonds. In alpha-FOX-7, each oxygen atom of the nitro groups is involved in two hydrogen bonds resulting in two intramolecular and six intermolecular hydrogen bonds. But in beta-FOX-7 this coordination changes, and half of the oxygen atoms build up two and the other half build up three hydrogen bonds leading to two intramolecular and eight intermolecular hydrogen bonds. The average intermolecular hydrogen bond distance increases slightly from 2.31 A in alpha-FOX-7 to 2.52 A in beta-FOX-7. The C-NO2 bonds are of particular interest because they are referred to as the detonation trigger. It has been suggested that these bonds could be strengthened by the extensive intermolecular hydrogen bonding within the layers in both polymorphs. Such bond strengthening via cooperative effects was proposed in earlier DFT calculations on FOX-7 and may be one key to understanding its low sensitivity and high activation energy to impact.     

The rule parameters in liquid adsorption chromatography of polymer homologous series and their determination

The separation of polymer homologous series is governed by two rule parameters: the interaction parameter c of the repeat unit and the sorbent surface S (relation of pore volume to pore diameter). The interaction parameter is independent on column dimensions and pore diameter. In a plot of elution volumes Vn versus the difference DeltaV =Vn -Vn-1 in elution volumes of consecutive oligomers, straight lines are obtained, the intercept of which yields the accessible volume. Using the accessible volume as the hold-up volume in the calculation of the retention factor k, a strictly linear dependence of ln k versus the number of the repeat units n is observed (Martin's plot). The interaction parameter c can be determined experimentally by three different approaches: from the slope in a plot of V versus DeltaV, from the slope in Martin's plot (ln k versus n), and from the intercept in a plot of ln(DeltaV) versus n. The pore surface is obtained from the intercept in Martin's plot (ln k versus n) or the intercept in a plot of ln(DeltaV) versus n. The results obtained by the different approaches agree very well. The theoretical predictions are verified by comparison with the experimental data obtained on columns with different pore diameter and pore volume and thus, different pore surface at conditions corresponding to the same interaction parameter.     

Preparative separation of a multicomponent peptide mixture by mass spectrometry

We report on the first multiplex preparative separation by mass spectrometry of bio-organic molecules in the 200-350 Da mass range that is typical for synthetic drugs. A five-component mixture consisting of two di- and three tripeptides has been separated by mass using a specially designed mass spectrometer. The instrument for preparative separations consists of an electrospray ionization (ESI) source, ion transfer optics, an electrostatic sector, and an inhomogeneous-field magnetic mass analyzer that achieves linear mass dispersion of ion beams. Protonated peptides produced by electrospray were separated, nondestructively landed on a 16-channel array of dry collector plates, and reconstituted in solution. The preparation procedures and the instrumental conditions have been optimized to maximize the ion currents. The significant features of the special mass spectrometer are high ion currents and simultaneous separation and collection of mixture components.