Electron Transfer between Genetically Modified Hansenula polymorpha Yeast Cells and Electrode Surfaces via Os‐complex modified Redox Polymers

Graphite electrodes modified with redox‐polymer‐entrapped yeast cells were investigated with respect to possible electron‐transfer pathways between cytosolic redox enzymes and the electrode surface. Either wild‐type or genetically modified Hansenula polymorpha yeast cells over‐expressing flavocytochrome b2 (FC b₂) were integrated into Os‐complex modified electrodeposition polymers. Upon increasing the L ‐lactate concentration, an increase in the current was only detected in the case of the genetically modified cells. The overexpression of FC b₂ and the related amplification of the FC b₂/L ‐lactate reaction cycle was found to be necessary to provide sufficient charge to the electron‐exchange network in order to facilitate sufficient electrochemical coupling between the cells, via the redox polymer, to the electrode. The close contact of the Os‐complex modified polymer to the cell wall appeared to be a prerequisite for electrically wiring the cytosolic FC b₂/L ‐lactate redox activity and suggests the critical involvement of a plasma membrane redox system. Insights in the functioning of whole‐cell‐based bioelectrochemical systems have to be considered for the successful design of whole‐cell biosensors or microbial biofuel cells.     

Structural studies of five layer Aurivillius oxides: A2Bi4Ti5O18 (A=Ca, Sr, Ba and Pb)

The room temperature structures of the five layer Aurivillius phases A₂Bi₄Ti₅O₁₈ (A=Ca, Sr, Ba and Pb) have been refined from powder neutron diffraction data using the Rietveld method. The structures consist of [Bi₂O₂]²⁺ layers interleaved with perovskite-like [A₂Bi₂Ti₅O₁₆]²⁻ blocks. The structures were refined in the orthorhombic space group B2eb (SG. No. 41), Z=4, and the unit cell parameters of the oxides are a=5.4251(2), b=5.4034(1), c=48.486(1); a=5.4650(2), b=5.4625(3), c=48.852(1); a=5.4988(3), b=5.4980(4), c=50.352(1); a=5.4701(2), b=5.4577(2), c=49.643(1) for A=Ca, Sr, Ba and Pb, respectively. The structural features of the compounds were found similar to n=2-4 layers bismuth oxides. The strain caused by mismatch of cell parameter requirements for the [Bi₂O₂]²⁺ layers and perovskite-like [A₂Bi₂Ti₅O₁₆]²⁻ blocks were relieved by tilting of the TiO₆ octahedra. Variable temperature synchrotron X-ray studies for Ca and Pb compounds showed that the orthorhombic structure persisted up to 675 and 475 K, respectively. Raman spectra of the compounds are also presented.     

The metastable Ni7±xS6, and mixed Ni6±x(S1−ySey)5, phases

The closely related, narrowly non-stoichiometric, metastable as well as thermodynamically stable “phases” in the metal-rich part of the Ni–S phase diagram near the nominal composition Ni_7±xS₆ have been carefully re-investigated via electron diffraction and transmission electron microscope imaging. Two quite distinct polymorphs have been identified, a minority incommensurate interface-modulated polymorph and a (heavily twinned) majority I1a1, a=2a_p, b=2b_p, c=−a_p+c_p superstructure (of an underlying Bmmb, a_p3.3, b_p16.4, c_p11.3 Å parent structure) polymorph. The incommensurate polymorph is shown to be very closely related to the only known polymorph of Ni_6±xSe₅ and is rapidly stabilized to room temperature upon doping of the sulfide compounds with selenium.     

The Phase Relations in the System In2O3–TiO2–MgO at 1100 and 1350°C

The phase relations in the system In₂O₃–TiO₂–MgO at 1100 and 1350°C are determined by a classical quenching method. In this system, there are four pseudobinary compounds, In₂TiO₅, MgTi₂O₅ (pseudobrookite type), MgTiO₃ (ilmenite type), and Mg₂TiO₄ (spinel type) at 1100°C. At 1350°C, in addition to these compounds there exist a spinel-type solid solution Mg_2−xIn_2xTi_1−xO₄ (0≤x≤1) and a compound In₆Ti₆MgO₂₂ with lattice constants a=5.9236(7) Å, b=3.3862(4) Å, c=6.3609(7) Å, β=108.15(1)°, and q=0.369, which is isostructural with the monoclinic In₃Ti₂FeO₁₀ in the system In₂O₃–TiO₂–MgO. The relation between the lattice constants of the spinel phase and the composition nearly satisfies Vegard's law. In₆Ti₆MgO₂₂ extends a solid solution range to In₂₀Ti₁₇Mg₃O₆₇ with lattice constants of a=5.9230(5) Å, b=3.3823(3) Å, c=6.3698(6) Å, β=108.10(5)°, and q=0.360. The distributions of constituent cations in the solid solutions are discussed in terms of their ionic radius and site preference effect.     

Reagentless lactate electrodes based on electrocatalytic oxidation of flavocytochrome b2

Flavocytochrome b₂ (L-lactate :cytochrome c reductase, E.C. 1.1.2.3) from Hansenula anomala was entrapped on the surface of electrodes modified with various kinds of carbon black. The electrocatalytic oxidation of a reduced enzyme by the electroactive surface groups of carbon black enables this enzyme electrode to be used for the determination of lactate. The electrodes operate at ?0.2 to ?0.1 V vs. SCE (pH 7.0), which is low enough to avoid interference from ascorbic acid. Linear calibration graphs up to 0.5 mM lactate were obtained. Electrochemical measurements of lactate in human blood plasma and cell culture fluids showed good agreement with the results of spectrophotometric measurements.     

High-pressure preparation, crystal structure, and properties of the new rare-earth oxoborate β-Dy2B4O9

In this work we report about a new rare-earth oxoborate β-Dy₂B₄O₉ synthesized under high-pressure/high-temperature conditions from Dy₂O₃ and boron oxide B₂O₃ in a B₂O₃/Na₂O₂ flux with a walker-type multianvil apparatus at 8 GPa and 1000°C. Single crystal X-ray structure determination of β-Dy₂B₄O₉ revealed: , a=616.2(1) pm, b=642.8(1) pm, c=748.5(1) pm, α=102.54(1)°, β=97.08(1)°, γ=102.45(1)°, Z=2, R1=0.0151, wR₂=0.0475 (all data). The compound exhibits a new structure type which is built up from bands of linked BO₃- (Δ) and tetrahedral BO₄-groups (□). The Dy³⁺-cations are positioned in the voids between the bands. According to the conception of fundamental building blocks β-Dy₂B₄O₉ can be classified with the notation 2Δ6□:Δ3□=4□=3□Δ. Furthermore we report about temperature-resolved in situ powder diffraction measurements and IR-spectroscopic investigations on β-Dy₂B₄O₉.     

Structure Study of Bi2.5Na0.5Ta2O9 and Bi2.5Nam−1.5NbmO3m+3 (m=2-4) by Neutron Powder Diffraction and Electron Microscopy

The crystal structures of Bi_2.5Na_0.5Ta₂O₉ and Bi_2.5Na_m-1.5Nb_mO_3m+3 (m=3,4) have been investigated by the Rietveld analysis of their neutron powder diffraction patterns (λ=1.470 Å). These compounds belong to the Aurivillius phase family and are built up by (Bi₂O₂)²⁺ fluorite layers and (A_m-1B_mO_3m+1)^2- (m=2-4) pseudo-perovskite slabs. Bi_2.5Na_0.5Ta₂O₉ (m=2) and Bi_2.5Na_2.5Nb₄O₁₅ (m=4) crystallize in the orthorhombic space group A2₁am, Z=4, with lattice constants of a=5.4763(4), b=5.4478(4), c=24.9710 (15) and a=5.5095(5), b=5.4783(5), c=40.553(3) Å, respectively. Bi_2.5Na_1.5Nb₃O₁₂ (m=3) has been refined in the orthorhombic space group B2cb, Z=4, with the unit-cell parameters a=5.5024(7), b=5.4622(7), and c=32.735(4) Å. In comparison with its isostructural Nb analogue, the structure of Bi_2.5Na_0.5Ta₂O₉ is less distorted and bond valence sum calculations indicate that the Ta-O bonds are somewhat stronger than the Nb-O bonds. The cell parameters a and b increase with increasing m for the compounds Bi_2.5Na_m-1.5Nb_mO_3m+3 (m=2-4), causing a greater strain in the structure. Electron microscopy studies verify that the intergrowth of mixed perovskite layers, caused by stacking faults, also increases with increasing m.     

A novel Mo(V) diphosphate with an intersecting tunnel structure: Sr(MoO)2(P2O7)2

A novel Mo(V) diphosphate Sr(MoO)₂P₂O₇ has been synthesized. It crystallizes in the space group P2₁/n with a=7.925(1) Å, b=7.739(1) Å, c=9.485(1) Å and β=91.05(1)°. Its original framework consists of MoP₂O₁₁ units built up of one P₂O₇ group sharing two apices with one MoO₆ octahedron. The MoP₂O₁₁ units share corners, forming [MoP₂O₁₀]_∞ chains running along [101]. The assemblage of these chains forms the [Mo₂P₄O₁₆]_∞ intersecting tunnel framework. The Sr²⁺ cations are located at the tunnel intersection, showing a distorted cubic coordination. This structure is compared to those of Ba(MoO)₂P₂O₇ and LiMoOP₂O₇, which are also built up of MoP₂O₁₁ units forming [MoP₂O₁₀]_∞ chains, but with different configurations.     

On the microstructure and symmetry of apparently hexagonal BaAl2O4

The P6₃ (a=2a_p, b=2b_p, c=c_p) crystal structure reported for BaAl₂O₄ at room temperature has been carefully re-investigated by a combined transmission electron microscopy and neutron powder diffraction study. It is shown that the poor fit of this P6₃ (a=2a_p, b=2b_p, c=c_p) structure model for BaAl₂O₄ to neutron powder diffraction data is primarily due to the failure to take into account coherent scattering between different domains related by enantiomorphic twinning of the P6₃22 parent sub-structure. Fast Fourier transformation of [0 0 1] lattice images from small localized real space regions (∼10 nm in diameter) are used to show that the P6₃ (a=2a_p, b=2b_p, c=c_p) crystal structure reported for BaAl₂O₄ is not correct on the local scale. The correct local symmetry of the very small nano-domains is most likely orthorhombic or monoclinic.     

Subsolidus phase relations and crystal structure of compounds in the PrOx-CaO-CuO system

The subsolidus phase relations of the PrO_x-CaO-CuO pseudo-ternary system sintered at 950-1000°C have been investigated by X-ray powder diffraction. In this system, there exist one compound Ca₁₀Pr₄Cu₂₄O₄₁, one Ca₂Pr₂Cu₅O₁₀-based solid solution, seven three-phase regions and two two-phase regions. The crystal structures of Ca₁₀Pr₄Cu₂₄O₄₁ and Ca₂Pr₂Cu₅O₁₀-based solid solution have been determined. Compound Ca₁₀Pr₄Cu₂₄O₄₁ crystallizes in an orthorhombic cell with space group D_2h²⁰−Cccm, Z=4. Its lattice parameters are a=11.278(2) Å, b=12.448(3) Å and c=27.486(8) Å. The crystal structure of Ca₂Pr₂Cu₅O₁₀-based solid solution is an incommensurate phase based on the orthorhombic NaCuO₂ type subcell. The lattice parameters of the subcell of the Ca_2.4Pr_1.6Cu₅O₁₀ are a₀=2.8246(7) Å, b₀=6.3693(5) Å, c₀=10.679(1) Å, and those of the orthorhombic superstructure are with a=5a₀, b=b₀, c=5c₀. The Ca_2.4Pr_1.6Cu₅O₁₀ structure can also be determined by using a monoclinic supercell with space group C_2h⁵−P2₁/c, Z=4, a=5a₀, b=b₀, and β=104.79(1)° or 136.60(1)°, V=5a₀b₀c₀.     

The dual role of cytochrome c2 in the facultative phototrophic bacteriumRhodopseudomonas capsulata

Succinate oxidation is stimulated by addition of cytochrome c₂ in cytochrome c₂-deficient spheroplasts from the M6-mutant and from the wild type strain ofRhodopseudomonas capsulata. Inhibition of the alternative oxidase in the wild type by CO facilitates this observation. The finding confirms a dual role of cytochrome c₂, in photosynthetic and in respiratory electron transport.

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Die doppelte Rolle von Cytochrome c₂ in Rhodopseudomonas capsulata

Zusammenfassung Die Oxidation von Succinat wird durch Zugabe von Cytochrom c₂ zu Cytochrom c₂-defizienten Sphäroplasten der Mutante M6 und des Wildtyps vonRhodopseudomonas capsulata stimuliert. Die Hemmung der alternativen Oxidase durch CO im Wildtyp erleichtert diese Beobachtung. Der Befund bestätigt die Doppelrolle von Cytochrom c₂ im photosynthetischen und respiratorischen Elektronentransport.

     

Syntheses and characterization of two oxoborates, (Pb3O)2(BO3)2MO4 (M=Cr, Mo)

Two oxoborates, (Pb₃O)₂(BO₃)₂MO₄ (M=Cr, Mo), have been prepared by solid-state reactions below 700 °C. Single-crystal XRD analyses showed that the Cr compound crystallizes in the orthorhombic group Pnma with a=6.4160(13) Å, b=11.635(2) Å, c=18.164(4) Å, Z=4 and the Mo analog in the group Cmcm with a=18.446(4) Å, b=6.3557(13) Å, c=11.657(2) Å, Z=4. Both compounds are characterized by one-dimensional chains formed by corner-sharing OPb₄ tetrahedra. BO₃ and CrO₄ (MoO₄) groups are located around the chains to hold them together via Pb–O bonds. The IR spectra further confirmed the presence of BO₃ groups in both structures and UV–vis diffuse reflectance spectra showed band gaps of about 1.8 and 2.9 eV for the Cr and Mo compounds, respectively. Band structure calculations indicated that (Pb₃O)₂(BO₃)₂MoO₄ is a direct semiconductor with the calculated energy gap of about 2.4 eV.     

Die Kristallstruktur von Ca2As2O7

The structure of Ca₂As₂O₇ (a ₀=7.05,b ₀=9.30,c ₀=4.89 Å; =101.3°; space groupC2/m-C _2h ³ ;Z=2) has been solved from 465 independent X-ray intensities collected on aWeissenberg-type diffractometer up to anR-factor of 2.4% for all intensities. The structure of Ca₂As₂O₇ represents a further Thortveitite structure type.

     

Crystal structure refinement of basic tellurium nitrate: A reformulation as (Te2O4H)+(NO3)−

Basic tellurium nitrate crystallizes in the space group Pnma witha=14.607 (1),b=8.801 (1), andc=4.4633 (4) Å. Full-matrix least-squares refinement of automatic diffractometer data converged to a residualR=0.036 (R _w =0.046) for 899 independent reflections. A detailed analysis of the structural data leads us to reformulate this compound as (Te₂O₄H)⁺(NO₃)^– with a basic structural element consisting of a charged two-dimensional puckered Te₂O₄H⁺ network with discrete NO₃ ^– anions, an example of apositively-charged network structure.

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Verfeinerung der Kristallstruktur von basischem Telluriumnitrat. Eine Umformulierung in (Te₂O₄H)⁺(NO₃)^–

Zusammenfassung Basisches Telluriumnitrat kristallisiert in der Raumgruppe Pnma mita=14,607 (1),b=8,801 (1) undc=4,4633 (4) Å. Die verfeinernde Auswertung der Diffraktometerdaten konvergierte zuR=0,036 (R _w =0.046) für 899 unabhängige Reflexe. Eine detaillierte Analyse der Strukturdaten führte zu einer Umformulierung dieser Verbindung als (Te₂O₄H)⁺(NO₃)^–, wobei die Basisstruktur aus einem geladenen, zweidimensionalen, gefalteten Te₂O₄H⁺ Netzwerk mit getrennten NO₃ ^– Anionen besteht. Es stellt dies ein Beispiel einerpositiv geladenen Netzstruktur dar.

     

X-ray diffraction and Mössbauer spectroscopy studies of LiFe0.5Ti1.5O4 – A new primitive cubic ordered spinel

LiFe_0.5Ti_1.5O₄ was synthesized by solid-state reaction carried out at 900 °C in flowing argon atmosphere, followed by rapid quenching of the reaction product to room temperature. The compound has been characterized by X-ray powder diffraction (XRD) and ⁵⁷Fe Mössbauer effect spectroscopy (MES). It crystallizes in the space group P4₃32, a = 8.4048(1) Å. Results from Rietveld structural refinement indicated 1:3 cation ordering on the octahedral sites: Li occupies the octahedral (4b) sites, Ti occupies the octahedral (12d) sites, while the tetrahedral (8c) sites have mixed (Fe/Li) occupancy. A small, about 5%, inversion of Fe on the (4b) sites has been detected. The MES data is consistent with cation distribution and oxidation state of Fe, determined from the structural data.The title compound is thermally unstable in air atmosphere. At 800 °C it transforms to a mixture of two Fe³⁺ containing phases – a face centred cubic spinel Li_(1+y)/2Fe_(5−3y)/2Ti_yO₄ and a Li_(z−1)/2Fe_(7−3z)/2Ti_zO₅ – pseudobrookite. The major product of thermal treatment at 1000 °C is a ramsdellite type lithium titanium iron(III) oxide, accompanied by traces of rutile and pseudobrookite.     

尖晶石型LiMn2O4晶体结构及锂离子筛H+/Li+交换性质研究

采用密度泛函理论平面波超软赝势和广义梯度近似法对尖晶石型LiMn2O4及其锂离子筛HMn2O4的晶体结构和性质进行了从头计算。PW91泛函最为有效,Li+被H+取代后HMn2O4晶胞收缩,点阵常数从LiMn2O4的0.823 nm减小至0.799 nm,其XRD峰也相应向高角度方向明显位移。经同种格点原子的XRD分析表明,Mn、O两元素对XRD方式和强度起着决定作用。其中Li呈+1价完全离子化,可被H+彻底交换,H与周围O在等电子密度图中呈现电子云相互连接,只带有0.42个正电荷。价轨道分态密度表明,Mn-O之间强的共价键合主要归因于Mn-d和O-p在费米能级下-7.3~-1.6 eV间的轨道重叠,形成了有利于H+/Li+交换的骨架空穴隧道。阵点和空穴多面体的体积遵守如下顺序:V8a>V48f>V8b、V16c>V16d、V16c>V48f。Li+最易迁移至邻近的16c位置,碱金属离子的交换受到离子半径和作用能大小的限制。     

Ab initio structure determination of new compound Li4CaB2O6

A new compound, Li₄CaB₂O₆, has been synthesized by solid-state reaction and its structure has been determined from powder X-ray diffraction data by direct methods. The refinement was carried out using the Rietveld methods and the final refinement converged with R_p=10.4%, R_wp=14.2%, R_exp=4.97%. This compound belongs to the orthorhombic space group Pnnm, with lattice parameters a=9.24036(9) Å, b=8.09482(7) Å, and c=3.48162(4) Å. Fundamental building units are isolated [BO₃]³⁻ anionic groups, which are all parallel to the a-b plane stacked along the c-axis. The Ca atoms are six-coordinated by the O atoms to form octahedral coordination polyhedra, which are joined together through edges along the c-axis, forming infinitely long three-dimensional chains. The Li atoms have a four-fold and a five-fold coordination with O atoms that lead to complex Li-O-Li chains that also extend along the c-axis. The infrared spectrum of Li₄CaB₂O₆ was also studied, which is consistent with the crystallographic study.     

Synthesis, Crystal Structure, and Magnetic Properties of a Novel Layered Manganese Oxide Sr2MnGaO5+δ

New Sr₂MnGaO_4.97 complex oxide was synthesized by solid state reaction in sealed silica tubes at 950–1000°C. The Sr₂MnGaO_4.97 crystal structure was refined from X-ray powder diffraction data. Sr₂MnGaO_4.97 is based on the Ima2 brownmillerite-type structure with apically elongated MnO₆ octahedra due to a Jahn–Teller effect. Electron diffraction and high-resolution electron microscopy showed that local ordering of the left-and right-hand chains of GaO₄ tetrahedra in Sr₂MnGaO_4.97 leads to a superstructure with a doubling of the b parameter of the orthorhombic unit cell. The formal oxidation state of Mn (V_Mn) can be varied by thermal treatments at elevated oxygen pressure (450°C, 20 bar of O₂). The oxygen insertion induces a structure transformation in oxidized Sr₂MnGaO_5.47 material with the formation of a tetragonal perovskite-like structure (aa_p, c2c_p) with oxygen vacancies located in the Ga layers. The oxidation is accompanied by a significant compression of the Mn–O apical distances and a suppression of the Jahn–Teller deformation. Both Sr₂MnGaO_4.97 and Sr₂MnGaO_5.47 can probably be treated as canted antiferromagnets with T_N=150 and 80 K, respectively.     

The reactions and composition of the surface intermediate species in the selective catalytic reduction of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> with ethylene over Co-ZSM-5

A pretreatment-transient reaction product analysis method was applied to study the reactions and average composition of the possible surface intermediate species in selective catalytic reduction with ethylene of NO _x over Co-ZSM-5. The reactions of the surface species, formed by the pretreatment of Co-ZSM-5 in a NO/C₂H₄/O₂ mixture at 275°C, with the NO/O₂ flow produced much more N₂ than that with the individual NO or O₂ flow. The similarity of N₂/CO _x /H₂O product distribution generated from the above surface species-NO/O₂ reactions and that from the normal NO/C₂H₄/O₂ flow reactions implies that the surface species NC _a O _b H _c formed in the three-component pretreatment process is very likely the primary intermediate surface species generated during the real flow reactions. The in situ FT-IR (DRIFT) spectroscopy measurements of the surface species support the above conclusion.     

A new approach to the preparation of microcrystalline ZnNb2O6 photocatalysts via a water-soluble niobium-citrate-peroxo compound

A water-soluble niobium-citrate-peroxo compound was synthesized by using Nb₂O₅ as a precursor. This niobium compound solution was successfully applied to the preparation of microcrystalline ZnNb₂O₆ photocatalysts via a water-based sol-gel method. The results indicated that pure ZnNb₂O₆ could be obtained in a temperature range from 750 to 950 °C. The absorption edge of ZnNb₂O₆ located at about 305 nm, corresponding to a band gap of ca. 4.06 eV. The photocatalytic activities of the as-prepared samples for the methyl orange degradation were evaluated under UV light (λ = 254 nm). It was found that the sample obtained at 850 °C showed the highest photocatalytic activity due to its suitable surface area and crystallinity.