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  1. Article ; Online: Orientational analysis of atomic pair correlations in nanocrystalline indium oxide thin films

    Justin M. Hoffman / Niklas B. Thompson / Olaf Borkiewicz / Xiang He / Samuel Amsterdam / Zhu-lin Xie / Aaron Taggart / Karen L. Mulfort / Alex B. F. Martinson / Lin X. Chen / Uta Ruett / David M. Tiede

    IUCrJ, Vol 11, Iss 1, Pp 120-

    2024  Volume 128

    Abstract: The application of grazing-incidence total X-ray scattering (GITXS) for pair distribution function (PDF) analysis using >50 keV X-rays from synchrotron light sources has created new opportunities for structural characterization of supported thin films ... ...

    Abstract The application of grazing-incidence total X-ray scattering (GITXS) for pair distribution function (PDF) analysis using >50 keV X-rays from synchrotron light sources has created new opportunities for structural characterization of supported thin films with high resolution. Compared with grazing-incidence wide-angle X-ray scattering, which is only useful for highly ordered materials, GITXS/PDFs expand such analysis to largely disordered or nanostructured materials by examining the atomic pair correlations dependent on the direction relative to the surface of the supporting substrate. A characterization of nanocrystalline In2O3-derived thin films is presented here with in-plane-isotropic and out-of-plane-anisotropic orientational ordering of the atomic structure, each synthesized using different techniques. The atomic orientations of such films are known to vary based on the synthetic conditions. Here, an azimuthal orientational analysis of these films using GITXS with a single incident angle is shown to resolve the markedly different orientations of the atomic structures with respect to the planar support and the different degrees of long-range order, and hence, the terminal surface chemistries. It is anticipated that orientational analysis of GITXS/PDF data will offer opportunities to extend structural analyses of thin films by providing a means to qualitatively determine the major atomic orientation within nanocrystalline and, eventually, non-crystalline films.
    Keywords orientations ; conductive thin films ; atomic layer deposition ; grazing-incidence diffraction ; pair distribution functions ; materials science ; total x-ray scattering ; inorganic chemistry ; film anisotropy ; amorphous materials ; Crystallography ; QD901-999
    Subject code 530
    Language English
    Publishing date 2024-01-01T00:00:00Z
    Publisher International Union of Crystallography
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Article: Electron Paramagnetic Resonance Characterization of the Triheme Cytochrome from Geobacter sulfurreducens

    Ponomarenko, Nina / David M. Tiede / Jens Niklas / Oleg Poluektov / P. Raj Pokkuluri

    Biochemistry. 2018 Jan. 03, v. 57, no. 11

    2018  

    Abstract: Periplasmic cytochrome A (PpcA) is a representative of a broad class of multiheme cytochromes functioning as protein “nanowires” for storage and extracellular transfer of multiple electrons in the δ-proteobacterium Geobacter sulfurreducens. PpcA contains ...

    Abstract Periplasmic cytochrome A (PpcA) is a representative of a broad class of multiheme cytochromes functioning as protein “nanowires” for storage and extracellular transfer of multiple electrons in the δ-proteobacterium Geobacter sulfurreducens. PpcA contains three bis-His coordinated hemes held in a spatial arrangement that is highly conserved among the multiheme cytochromes c3 and c7 families, carries low potential hemes, and is notable for having one of the lowest number of amino acids utilized to maintain a characteristic protein fold and site-specific heme function. Low temperature X-band electron paramagnetic resonance (EPR) spectroscopy has been used to characterize the electronic configuration of the Fe(III) and the ligation mode for each heme. The three sets of EPR signals are assigned to individual hemes in the three-dimensional crystal structure. The relative energy levels of the Fe(III) 3d orbitals for individual hemes were estimated from the principal g-values. The observed g-tensor anisotropy was used as a probe of electronic structure of each heme, and differences were determined by specifics of axial ligation. To ensure unambiguous assignment of highly anisotropic low-spin (HALS) signal to individual hemes, EPR analyses of iron atom electronic configurations have been supplemented with investigation of porphyrin macrocycles by one-dimensional 1H NMR chemical shift patterns for the methyl substituents. Within optimized geometry of hemes in PpcA, the magnetic interactions between hemes were found to be minimal, similar to the c3 family of tetraheme cytochromes.
    Keywords amino acids ; anisotropy ; crystal structure ; cytochromes ; electron paramagnetic resonance spectroscopy ; electrons ; energy ; Geobacter sulfurreducens ; heme ; iron ; magnetism ; nuclear magnetic resonance spectroscopy ; temperature
    Language English
    Dates of publication 2018-0103
    Size p. 1722-1732.
    Publishing place American Chemical Society
    Document type Article
    ZDB-ID 1108-3
    ISSN 1520-4995 ; 0006-2960
    ISSN (online) 1520-4995
    ISSN 0006-2960
    DOI 10.1021/acs.biochem.7b00917
    Database NAL-Catalogue (AGRICOLA)

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  3. Article ; Online: Mimicking Natural Photosynthesis

    Daniel R. Marzolf / Aidan M. McKenzie / Matthew C. O’Malley / Nina S. Ponomarenko / Coleman M. Swaim / Tyler J. Brittain / Natalie L. Simmons / Phani Raj Pokkuluri / Karen L. Mulfort / David M. Tiede / Oleksandr Kokhan

    Nanomaterials, Vol 10, Iss 2143, p

    Designing Ultrafast Photosensitized Electron Transfer into Multiheme Cytochrome Protein Nanowires

    2020  Volume 2143

    Abstract: Efficient nanomaterials for artificial photosynthesis require fast and robust unidirectional electron transfer (ET) from photosensitizers through charge-separation and accumulation units to redox-active catalytic sites. We explored the ultrafast time- ... ...

    Abstract Efficient nanomaterials for artificial photosynthesis require fast and robust unidirectional electron transfer (ET) from photosensitizers through charge-separation and accumulation units to redox-active catalytic sites. We explored the ultrafast time-scale limits of photo-induced charge transfer between a Ru(II)tris(bipyridine) derivative photosensitizer and PpcA, a 3-heme c-type cytochrome serving as a nanoscale biological wire. Four covalent attachment sites (K28C, K29C, K52C, and G53C) were engineered in PpcA enabling site-specific covalent labeling with expected donor-acceptor (DA) distances of 4–8 Å. X-ray scattering results demonstrated that mutations and chemical labeling did not disrupt the structure of the proteins. Time-resolved spectroscopy revealed three orders of magnitude difference in charge transfer rates for the systems with otherwise similar DA distances and the same number of covalent bonds separating donors and acceptors. All-atom molecular dynamics simulations provided additional insight into the structure-function requirements for ultrafast charge transfer and the requirement of van der Waals contact between aromatic atoms of photosensitizers and hemes in order to observe sub-nanosecond ET. This work demonstrates opportunities to utilize multi-heme c-cytochromes as frameworks for designing ultrafast light-driven ET into charge-accumulating biohybrid model systems, and ultimately for mimicking the photosynthetic paradigm of efficiently coupling ultrafast, light-driven electron transfer chemistry to multi-step catalysis within small, experimentally versatile photosynthetic biohybrid assemblies.
    Keywords biohybrids ; biomimetic photosynthesis ; photo-induced electron transfer (PET) ; Ultrafast electron transfer (ET) ; PpcA ; cytochrome c 7 ; Chemistry ; QD1-999
    Subject code 540
    Language English
    Publishing date 2020-10-01T00:00:00Z
    Publisher MDPI AG
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  4. Article: Resolution of Electronic and Structural Factors Underlying Oxygen-Evolving Performance in Amorphous Cobalt Oxide Catalysts

    Kwon, Gihan / Hoyoung Jang / Jun-Sik Lee / Anil Mane / David J. Mandia / Sarah R. Soltau / Lisa M. Utschig / Alex B. F. Martinson / David M. Tiede / Hacksung Kim / Jungho Kim

    Journal of the American Chemical Society. 2018 July 20, v. 140, no. 34

    2018  

    Abstract: Non-noble-metal, thin-film oxides are widely investigated as promising catalysts for oxygen evolution reactions (OER). Amorphous cobalt oxide films electrochemically formed in the presence of borate (CoBi) and phosphate (CoPi) share a common cobaltate ... ...

    Abstract Non-noble-metal, thin-film oxides are widely investigated as promising catalysts for oxygen evolution reactions (OER). Amorphous cobalt oxide films electrochemically formed in the presence of borate (CoBi) and phosphate (CoPi) share a common cobaltate domain building block, but differ significantly in OER performance that derives from different electron–proton charge transport properties. Here, we use a combination of L edge synchrotron X-ray absorption (XAS), resonant X-ray emission (RXES), resonant inelastic X-ray scattering (RIXS), resonant Raman (RR) scattering, and high-energy X-ray pair distribution function (PDF) analyses that identify electronic and structural factors correlated to the charge transport differences for CoPi and CoBi. The analyses show that CoBi is composed primarily of cobalt in octahedral coordination, whereas CoPi contains approximately 17% tetrahedral Co(II), with the remainder in octahedral coordination. Oxygen-mediated 4p–3d hybridization through Co–O–Co bonding was detected by RXES and the intersite dd excitation was observed by RIXS in CoBi, but not in CoPi. RR shows that CoBi resembles a disordered layered LiCoO₂-like structure, whereas CoPi is amorphous. Distinct domain models in the nanometer range for CoBi and CoPi have been proposed on the basis of the PDF analysis coupled to XAS data. The observed differences provide information on electronic and structural factors that enhance oxygen evolving catalysis performance.
    Keywords X-radiation ; X-ray absorption spectroscopy ; X-ray scattering ; borates ; catalysts ; catalytic activity ; chemical bonding ; cobalt ; cobalt oxide ; electrochemistry ; models ; oxygen ; oxygen production ; phosphates
    Language English
    Dates of publication 2018-0720
    Size p. 10710-10720.
    Publishing place American Chemical Society
    Document type Article
    ZDB-ID 3155-0
    ISSN 1520-5126 ; 0002-7863
    ISSN (online) 1520-5126
    ISSN 0002-7863
    DOI 10.1021/jacs.8b02719
    Database NAL-Catalogue (AGRICOLA)

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    In stock of ZB MED Bonn / Germany

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