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Large Channels (large + channel)
Selected Abstracts[Me4N][Cu2(NCS)3] , A Compound Having a Framework Structure with Large Channels.CHEMINFORM, Issue 51 2005R. Dilshad Abstract For Abstract see ChemInform Abstract in Full Text. [source] Modern and ancient fluvial megafans in the foreland basin system of the central Andes, southern Bolivia: implications for drainage network evolution in fold-thrust beltsBASIN RESEARCH, Issue 1 2001B. K. Horton ABSTRACT Fluvial megafans chronicle the evolution of large mountainous drainage networks, providing a record of erosional denudation in adjacent mountain belts. An actualistic investigation of the development of fluvial megafans is presented here by comparing active fluvial megafans in the proximal foreland basin of the central Andes to Tertiary foreland-basin deposits exposed in the interior of the mountain belt. Modern fluvial megafans of the Chaco Plain of southern Bolivia are large (5800,22 600 km2), fan-shaped masses of dominantly sand and mud deposited by major transverse rivers (Rio Grande, Rio Parapeti, and Rio Pilcomayo) emanating from the central Andes. The rivers exit the mountain belt and debouch onto the low-relief Chaco Plain at fixed points along the mountain front. On each fluvial megafan, the presently active channel is straight in plan view and dominated by deposition of mid-channel and bank-attached sand bars. Overbank areas are characterized by crevasse-splay and paludal deposition with minor soil development. However, overbank areas also contain numerous relicts of recently abandoned divergent channels, suggesting a long-term distributary drainage pattern and frequent channel avulsions. The position of the primary channel on each megafan is highly unstable over short time scales. Fluvial megafans of the Chaco Plain provide a modern analogue for a coarsening-upward, > 2-km-thick succession of Tertiary strata exposed along the Camargo syncline in the Eastern Cordillera of the central Andean fold-thrust belt, about 200 km west of the modern megafans. Lithofacies of the mid-Tertiary Camargo Formation include: (1) large channel and small channel deposits interpreted, respectively, as the main river stem on the proximal megafan and distributary channels on the distal megafan; and (2) crevasse-splay, paludal and palaeosol deposits attributed to sedimentation in overbank areas. A reversal in palaeocurrents in the lowermost Camargo succession and an overall upward coarsening and thickening trend are best explained by progradation of a fluvial megafan during eastward advance of the fold-thrust belt. In addition, the present-day drainage network in this area of the Eastern Cordillera is focused into a single outlet point that coincides with the location of the coarsest and thickest strata of the Camargo succession. Thus, the modern drainage network may be inherited from an ancestral mid-Tertiary drainage network. Persistence and expansion of Andean drainage networks provides the basis for a geometric model of the evolution of drainage networks in advancing fold-thrust belts and the origin and development of fluvial megafans. The model suggests that fluvial megafans may only develop once a drainage network has reached a particular size, roughly 104 km2, a value based on a review of active fluvial megafans that would be affected by the tectonic, climatic and geomorphologic processes operating in a given mountain belt. Furthermore, once a drainage network has achieved this critical size, the river may have sufficient stream power to prove relatively insensitive to possible geometric changes imparted by growing frontal structures in the fold-thrust belt. [source] Pattern and process in the distribution of North American freshwater fishBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010DAVID GRIFFITHS Published species lists were analysed to determine the contributions of dispersal, habitat preference, river channel size, body size, and glacial history to large-scale patterns in freshwater fish species richness in North America, north of central Mexico. Total species richness declines to the north and west but the pattern for endemics differs from that of widespread species. Mississippi Basin regions are more species rich than more isolated, coastal, regions. Richness declines more rapidly with increasing latitude in riverine specialist than in habitat generalist species. Levels of endemism are greatest in species found in small- to medium-sized river channels. The strong Rapoport effect, more marked in migratory than resident species, is correlated with habitat preference, channel size, and glacial history. Body size increases with latitude, largely as a result of a trend from small resident to large migrant species. In unglaciated regions, ancestral species survived in large habitats because these are longer-lived, more extensive, less isolated and more stable than headwaters, permitting larger populations and lower extinction levels. Reduced levels of gene flow in small, peripheral, channels isolated by larger downstream habitats have resulted in the production of many, small range, small-bodied species. The latitudinal richness gradient is a consequence of speciation and extinction events in unglaciated faunas and an increasing domination of faunas by generalist, large bodied, large channel, recolonizing species in more northern regions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 46,61. [source] Multivalent Binding of Small Guest Molecules and Proteins to Molecular Printboards inside MicrochannelsCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2008Manon Abstract ,-Cyclodextrin (,-CD) monolayers have been immobilized in microchannels. The host,guest interactions on the ,-CD monolayers inside the channels were comparable to the interactions on ,-CD monolayers on planar surfaces, and a divalent fluorescent guest attached with a comparable binding strength. Proteins were attached to these monolayers inside microchannels in a selective manner by employing a strategy that uses streptavidin and orthogonal linker molecules. The design of the chip, which involved a large channel that splits into four smaller channels, allowed the channels to be addressed separately and led to the selective immobilization of antibodies. Experiments with labeled antibodies showed the selective immobilization of these antibodies in the separate channels. [source] A Series of One- to Three-Dimensional Copper Coordination Polymers Based on N-Heterocyclic LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2006Xiang He Abstract A family of copper coordination polymers containing different N-heterocyclic ligands, namely [Cu(CN)(dmpyz)]n (1),[Cu2(CN)2(imz)]n (2), [Cu3(CN)(trz)2]n (3), [Cu6(CN)6(dmtrz)3]n(4), [Cu2(CN)(5-metta)]n (5), [Cu2(CN)(5-phtta)]n (6), and {[Cu6(CN)6(dmtrz)]2[Cu2(CN)2(dmtrz)2]}n (7) has been prepared and structurally characterized by X-ray crystallography. The crystal structures of 1 and 2 are 1D chain frameworks. Compound 3 is a twofold interpenetrating 2D supramolecular framework in which the cyanide groups act as bridging ligands to link the copper centers into an unusual bilayer motif with large channels. Compounds 4,6 all possess 3D networks. Compound 4 is constructed by two parts: 2D rectangular-grid layers and {Cu2(CN)2(dmtrz)2} building blocks. Compound 5 is built up by X-shaped chains that connect each other in an ABAB arrangement to generate the3D network. The structure of 6 is a 3D network includingone-dimensional square-grid channels, with a shortest Cu2···Cu2A (A: ,x + 1, ,y + 1, ,z) distance of about 2.347(1) Å. Compound 7 features a peculiar 3D + 1D network in which 1D guest metal-organic polymer chains are filled in an unusual 3D architecture constructed by double helical host tubes. Compounds 1,7 show a systematic variation in dimensionality from 1D to 3D to 3D + 1D. The luminescence properties of these compounds have been also studied. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Poly[diaqua(,-4,4,-bipyridine-,2N:N,)bis(,-cyanido-,2C:N)bis(cyanido-,C)nickel(II)copper(II)]: a metal,organic cyanide-bridged frameworkACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2008Olha Sereda The structure of the title compound, [NiCu(CN)4(C10H8N2)(H2O)2]n or [{Cu(H2O)2}(,-C10H8N2)(,-CN)2{Ni(CN)2}]n, was shown to be a metal,organic cyanide-bridged framework, composed essentially of ,Cu,4,4,-bpy,Cu,4,4,-bpy,Cu, chains (4,4,-bpy is 4,4,-bipyridine) linked by [Ni(CN)4]2, anions. Both metal atoms sit on special positions; the CuII atom occupies an inversion center, while the NiII atom of the cyanometallate sits on a twofold axis. The 4,4,-bpy ligand is also situated about a center of symmetry, located at the center of the bridging C,C bond. The scientific impact of this structure lies in the unique manner in which the framework is built up. The arrangement of the ,Cu,4,4,-bpy,Cu,4,4,-bpy,Cu, chains, which are mutually perpendicular and non-intersecting, creates large channels running parallel to the c axis. Within these channels, the [Ni(CN)4]2, anions coordinate to successive CuII atoms, forming zigzag ,Cu,N[triple-bond]C,Ni,C[triple-bond]N,Cu, chains. In this manner, a three-dimensional framework structure is constructed. To the authors' knowledge, this arrangement has not been observed in any of the many copper(II),4,4,-bipyridine framework complexes synthesized to date. The coordination environment of the CuII atom is completed by two water molecules. The framework is further strengthened by O,H...N hydrogen bonds involving the water molecules and the symmetry-equivalent nonbridging cyanide N atoms. [source] Mesoporous Silica Nanosphere-Supported Chiral Ruthenium Catalysts: Synthesis, Characterization, and Asymmetric Hydrogenation StudiesCHEMCATCHEM, Issue 3 2009David Abstract Chiral RuCl2,diphosphine,diamine complexes with a pendant siloxy group were synthesized and characterized by NMR spectroscopy and mass spectrometry. The Ru complexes were grafted onto three different types of mesoporous silica nanospheres (MSNs) through the siloxane linkage, and the resulting MSN-supported Ru catalysts were highly active for the asymmetric hydrogenation of aromatic ketones, to afford chiral secondary alcohols, and racemic arylaldehydes, to give chiral primary alcohols. Excellent activities and enantioselectivities were observed for these MSN-supported Ru catalysts owing to readily accessible and uniform catalytic sites within the large channels of MSNs (diameters of >2,nm) and short diffusion lengths for the organic compounds as a result of small nanoparticle sizes of less than 1,,m. This catalyst immobilization strategy with MSN supports should be amenable to the design of many highly active and enantioselective heterogeneous asymmetric catalysts. [source] Hydrothermal Syntheses, Crystal Structure and Thermal Behavior of [(CH3)2NH2]2[B5O6(OH)4]2·[HCON(CH3)2] and [NH3CH2CH2NH3]2[B14O20(OH)6]CHINESE JOURNAL OF CHEMISTRY, Issue 11 2009Ping Li Abstract Two novel organic base templated nonmetal borates [(CH3)2NH2]2[B5O6(OH)4]2·[HCON(CH3)2] (?) and [NH3CH2CH2NH3]2[B14O20(OH)6] (II) have been synthesized under hydrothermal conditions, and characterized by elemental analyses, FT-IR spectroscopy, X-ray diffraction, and TG-DTA. Their crystal structures were determined from single crystal X-ray diffraction. The crystal structure of compound I is characterized by forming a 3D supramolecular structure with large channels along axes b and c through OH···O hydrogen-bonding among the [B5O6(OH)4], anions. The crystal structure of compound II is characterized by forming a 3D supramolecular structure with large channels along axis a and direction [111] through OH···O hydrogen-bonding among the [B14O20(OH)6]4, anions. The templating organic amine cations in I and II are both obtained through in situ hydrothermal reactions, and are both located in the channels of the 3D supramolecular structure, respectively. Their thermal behavior has been also investigated. [source] | ||||||||||