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Cluster Assembly (cluster + assembly)
Selected AbstractsContinuous, Atmospheric Process to Create Organic Clusters and Nanostructured, Functional Films,ADVANCED FUNCTIONAL MATERIALS, Issue 5 2006R. Jagannathan Abstract An atmospheric process based on compressed CO2 is used to create stable clusters of small organic molecules. These clusters, 1,10,nm in size, are used as building blocks to assemble thin films on various substrates. Cluster assembly of these films is verified by using low-angle X-ray diffraction. The surface quality of these cluster-assembled films is similar to that of films usually prepared via the vacuum process. Several functional organic light-emitting diode devices have been prepared, in which only the doped emissive layer has been deposited by our process. The radiometric features and efficiencies of these devices match those of vacuum-built devices. Atomic force microscopy of these molecular clusters reveals that they are liquid-like at standard atmospheric conditions. Coatings of these clusters on cloth and stainless steel have been found to be superhydrophobic in nature. [source] Theoretical Study on a Class of Organometallic Complexes Based on All-Metal Aromatic Ga3, Through Sandwiching StabilizationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2008Li-ming Yang Abstract We report the theoretical study on a class of organometallic complexes containing the all-metal aromatic unit Ga3, on the basis of density functional theory calculations on a series of model sandwich-like compounds [DM(Ga3)]q, as well as those of the saturated compounds [DMn(Ga3)] [D = Ga3,, Cp,(C5H5,); M = Li, Na, K, Be, Mg, Ca] and extended compounds (Cp,)m(Li+)n(Ga3,)o (m, n, and o are integers). For the six metals, the all-metal aromatic Ga3, can only be assembled and stabilized in the "heterodecked sandwich" scheme (e.g. [CpM(Ga3)]q,) so as to avoid cluster fusion. Moreover, we designed a novel class of all-metal aromatic "metalloid" compounds. The ground state heterodecked sandwich species (Cp),(M)q+(Ga3), (M = Li, Na, K, q = 1; M = Be, Mg, Ca, q = 2) and the extended sandwich species (Cp,)m(Li+)n(Ga3,)o are mainly ionic bonded, cluster-assembled "polyatomic molecule", grown from the combination of Cp,, M atoms, and Ga3,. As a prototype for ionic bonding involving intact Ga3, subunits, [CpM(Ga3)]q, may be a stepping stone toward forming ionic, cluster-assembled all-metal aromatic Ga3 -based bulk solids or materials. Additionally, our results for the first time showed that the electronic, structural, and aromatic properties of the all-metal aromatic Ga3, could be well retained during cluster assembly, which is indicative of "building block" character. Bearing the significant difference in bonding patterns between our designed metalloid compounds and the known metalloid species, synthesis of these novel species might present an attractive challenge to experimental chemists. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Bacterial IscU is a well folded and functional single domain proteinFEBS JOURNAL, Issue 11 2004Salvatore Adinolfi Iron,sulfur clusters are widely represented in most organisms, but the mechanism of their formation is not fully understood. Of the two main proteins involved in cluster formation, NifS/IscS and NifU/IscU, only the former has been well studied from a structural point of view. Here we report an extensive structural characterization of Escherichia coli IscU. We show by a variety of physico-chemical techniques that E. coli IscU construct can be expressed to high purity as a monomeric protein, characterized by an ,, fold with high ,-helix content. The high melting temperature and the reversibility of the thermal unfolding curve (as measured by CD spectroscopy) hint at a well ordered stable fold. The excellent dispersion of cross peaks in the 1H- 15N correlation spectrum is consistent with these observations. Monomeric E. coli IscU is able to provide a scaffold for Iron,sulfur cluster assembly, but has no direct interaction with either Fe(II) or Fe(III) ions, suggesting the need of further partners to achieve a stable interaction. [source] Role of glutathione in the formation of the active form of the oxygen sensor FNR ([4Fe-4S]·FNR) and in the control of FNR functionFEBS JOURNAL, Issue 15 2000Quang Hon Tran The oxygen sensor regulator FNR (fumarate nitrate reductase regulator) of Escherichia coli is known to be inactivated by O2 as the result of conversion of a [4Fe-4S] cluster of the protein into a [2Fe-2S] cluster. Further incubation with O2 causes loss of the [2Fe-2S] cluster and production of apoFNR. The reactions involved in cluster assembly and reductive activation of apoFNR isolated under anaerobic or aerobic conditions were studied in vivo and in vitro. In a gshA mutant of E. coli that was completely devoid of glutathione, the O2 tension for the regulatory switch for FNR-dependent gene regulation was decreased by a factor of 4,5 compared with the wild-type, suggesting a role for glutathione in FNR function. In isolated apoFNR, glutathione could be used as the reducing agent for HS, formation required for [4Fe-4S] assembly by cysteine desulfurase (NifS), and for the reduction of cysteine ligands of the FeS cluster in FNR. Air-inactivated FNR (apoFNR without FeS) could be reconstituted to [4Fe-4S]·FNR by the same reaction as used for apoFNR isolated under anaerobic conditions. The in vivo effects of glutathione on FNR function and the role of glutathione in the formation of active [4Fe-4S]·FNR in vitro suggest an important role for glutathione in the de novo assembly of FNR and in the reductive activation of air-oxidized FNR under anaerobic conditions. [source] Mesoscopic Structure and Properties of Liquid Crystalline Mesophase Pitch and Its Transformation into Carbon FiberTHE CHEMICAL RECORD, Issue 2 2002Isao Mochida Abstract The history and present state of the art in the chemistry of mesophase pitch, which is an important precursor for carbon fiber and other high-performance industrial carbons, are reviewed relative to their structural properties. The structural concepts in both microscopic and macroscopic views are summarized in terms of the sp2 carbon hexagonal plane as a basic unit common to graphitic materials, its planar stacking in clusters, and cluster assembly into microdomains and domains, the latter of which reflect the isochromatic unit of optical anisotropy. Such a series of structural units is described in a semiquantitative manner corresponding to the same units of graphitic materials, although the size and stacking height of the hexagonal planes (graphitic sheets) are very different. Mesophase pitch is a liquid crystal material whose basic structural concepts are maintained in the temperature range of 250 to 350,°C. The melt flow and thermal properties are related to its micro- and mesoscopic structure. The structure of mesophase-pitch,based carbon fiber of high tensile strength, modulus, and thermal conductivity has been formed through spinning, and has inherited the same structural concepts of mesophase pitch. Stabilization settles the structure in successive heat treatments up to 3000,°C. Carbonization and graphitization enable growth of the hexagonal planes and their stacking into units of graphite. Such growth is governed and controlled by the alignment of micro- and mesoscopic structures in the mesophase pitch, which define the derived carbon materials as nanostructural materials. Their properties are controlled by the nanoscopic units that are expected to behave as nanomaterials when appropriately isolated or handled. © 2002 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 2:81,101, 2002: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.10016 [source] Role of IscS in Fe-S cluster assembly in Trypanosoma bruceiTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 2 2005O. SMÍD Despite the significance of proteins containing iron-sulfur cluster (Fe,S proteins), the processes of Fe,S cluster assembly and maturation of Fe,S proteins are poorly understood. However, several key proteins involved in the assembly have been identified, notably IscS, a cystein desulfurase, which provides sulfur for Fe,S cluster and IscU, a metallochaperone acting as a scaffold for cluster assembly. In this work, we studied the process of Fe,S cluster biosynthesis in Trypanosoma brucei by identifying the homologue of IscS in the T. brucei (TbIscS). To address the function of TbIscS, we inhibited its expression by means of RNA interference (RNAi). After RNAi induction, generation time of the TbIscS knock-down cell line was significantly prolonged. All types of mitochondrial ATP production in the cells were severely affected. Analysis of glucose metabolism end products determined pyruvate as major excreted metabolite of the induced cells, while the uninduced cells produced only small amount of this glycolytic end product. These data demonstrate that mitochondrial metabolism is impaired in cells with TbIscS knocked down. To test whether the observed phenomena were results of Fe,S cluster assembly disruption, we examined the Fe,S cluster-dependent activity of aconitase. This enzyme is localized in its active form in mitochondrion as well as in cytosol of T. brucei. After RNAi induction we observed the reduction of aconitase activity in both compartments (approx. 70% reduction in cytosol, approx. 30% in mitochondria). Western blots together with the EPR analysis showed that the reduction in cytosolic activity was due to impaired Fe,S cluster formation, while decrease in aconitase activity in mitochondria corresponded to the reduced level of the protein. [source] | ||||||||||