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Journal articles on the topic "Silicate tetrahedra"
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Day, Maxwell C., and Frank C. Hawthorne. "A structure hierarchy for silicate minerals: chain, ribbon, and tube silicates." Mineralogical Magazine 84, no. 2 (February 26, 2020): 165–244. http://dx.doi.org/10.1180/mgm.2020.13.
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AbstractA structure hierarchy is developed for chain-, ribbon- and tube-silicate based on the connectedness of one-dimensional polymerisations of (TO4)n− tetrahedra, where T = Si4+ plus P5+, V5+, As5+, Al3+, Fe3+, B3+, Be2+, Zn2+ and Mg2+. Such polymerisations are described by a geometrical repeat unit (with ng tetrahedra) and a topological repeat unit (or graph) (with nt vertices). The connectivity of the tetrahedra (vertices) in the geometrical (topological) repeat units is denoted by the expression cTr (cVr) where c is the connectivity (degree) of the tetrahedron (vertex) and r is the number of tetrahedra (vertices) of connectivity (degree) c in the repeat unit. Thus cTr = 1Tr12Tr23Tr34Tr4 (cVr = 1Vr12Vr23Vr34Vr4) represents all possible connectivities (degrees) of tetrahedra (vertices) in the geometrical (topological) repeat units of such one-dimensional polymerisations. We may generate all possible cTr (cVr) expressions for chains (graphs) with tetrahedron (vertex) connectivities (degrees) c = 1 to 4 where r = 1 to n by sequentially increasing the values of c and r, and by ranking them accordingly. The silicate (sensu lato) units of chain-, ribbon- and tube-silicate minerals are identified and associated with the relevant cTr (cVr) symbols. Following description and association with the relevant cTr (cVr) symbols of the silicate units in all chain-, ribbon- and tube-silicate minerals, the minerals are arranged into decreasing O:T ratio from 3.0 to 2.5, an arrangement that reflects their increasing structural connectivity. Considering only the silicate component, the compositional range of the chain-, ribbon- and tube-silicate minerals strongly overlaps that of the sheet-silicate minerals. Of the chain-, ribbon- and tube-silicates and sheet silicates with the same O:T ratio, some have the same cVr symbols (vertex connectivities) but the tetrahedra link to each other in different ways and are topologically different. The abundance of chain-, ribbon- and tube-silicate minerals decreases as O:T decreases from 3.0 to 2.5 whereas the abundance of sheet-silicate minerals increases from O:T = 3.0 to 2.5 and decreases again to O:T = 2.0. Some of the chain-, ribbon- and tube-silicate minerals have more than one distinct silicate unit: (1) vinogradovite, revdite, lintisite (punkaruaivite) and charoite have mixed chains, ribbons and/or tubes; (2) veblenite, yuksporite, miserite and okenite have clusters or sheets in addition to chains, ribbons and tubes. It is apparent that some chain-ribbon-tube topologies are favoured over others as of the ~450 inosilicate minerals, ~375 correspond to only four topologically unique graphs, the other ~75 minerals correspond to ~46 topologically unique graphs.
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Nagashima, M., and T. Armbruster. "Ardennite, tiragalloite and medaite: structural control of (As5+,V5+,Si4+)O4 tetrahedra in silicates." Mineralogical Magazine 74, no. 1 (February 2010): 55–71. http://dx.doi.org/10.1180/minmag.2010.074.1.55.
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AbstractSeveral silicate-minerals, such as ardennite – Mn2+4MgAl5[Si5(As5+,V5+)O22](OH)6, Z = 2, tiragalloite – Mn2+4[Si3As5+O12(OH)], Z = 4 and medaite – Mn2+6[Si5(V5+,As5+)O18(OH)], Z = 4 possess (V5+,As5+,P5+)O4 tetrahedra. Using electron-microprobe analysis (EMPA) and single-crystal X-ray diffraction methods, the crystal chemistry of ardennite from Salam-Château, Belgium and the Vernetto mine, Italy, tiragalloite from the Gambatesa mine, Italy, and medaite from the Molinello mine, Italy and the Fianel mine, Switzerland, were studied. Structure refinements converged to R1 values of 2.10–5.67%. According to chemical analysis, the Σ(As+V+P) content increases with decreasing Si content. Thus, Si replaces pentavalent cations in tetrahedral coordination. The (As5+,V5+,P5+,Si4+)O4 tetrahedra are categorized by their connections to SiO4 tetrahedra. The (As5+,V5+,P5+,Si4+)O4 tetrahedron of ardennite is isolated, and those of tiragalloite and medaite terminate a tetrahedral chain. The <T–O> of the isolated (As5+,V5+,P5+,Si4+)O4 tetrahedron shows a positive correlation with the mean ionic radius. For (As5+,V5+,P5+,Si4+)O4 tetrahedra with one T–O–T link, <T–O> and mean ionic radius are also correlated. In addition, the longest bridging T–O bond occurs between (As,V,P,Si)O4 and the adjacent SiO4 tetrahedron. The bridging O atom is over-bonded to satisfy the charge requirement of Σ(As+V+Si).
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Klein, Wilhelm, and Martin Jansen. "Crystal Structure of Silver Chromate Silicate, Ag6(CrO4)(SiO4)." Zeitschrift für Naturforschung B 65, no. 1 (January 1, 2010): 8–12. http://dx.doi.org/10.1515/znb-2010-0102.
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The new silver chromate silicate Ag6(CrO4)(SiO4) has been obtained from Ag2O and SiO2 by solid-state reaction at elevated temperature and oxygen pressure in stainless-steel autoclaves. It crystallizes in space group I41/amd (no. 141) with a = 7.256(2), c = 17.584(6) Å, V = 925.9(5) Å3, Z = 4; the structure refinement was based on 314 independent reflections and resulted in R1 = 0.0488, wR2 = 0.0987 (I ≥ 2σ (I)). The crystal structure consists of isolated CrO4 and SiO4 tetrahedra which are linked by Ag cations. The two different types of Ag atoms are in a square-planar fourfold, and linear twofold coordination by oxygen atoms, respectively. The linearly coordinated Ag atoms combined with the SiO4 tetrahedra form a three-dimensional 3∞[Ag4SiO4] framework, accommodating the CrO4 tetrahedra and the remaining Ag atoms in the voids. The CrO4 tetrahedron shows slightly enlarged displacement parameters indicating somewhat enhanced librational motion of the rigid body
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Krüger, Hannes, Volker Kahlenberg, and Karen Friese. "Na2Si3O7: an incommensurate structure with crenel-type modulation functions, refined from a twinned crystal." Acta Crystallographica Section B Structural Science 62, no. 3 (May 15, 2006): 440–46. http://dx.doi.org/10.1107/s010876810600663x.
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The structure of metastable, incommensurately modulated Na2Si3O7 has been determined from single-crystal X-ray diffraction data. In contrast to previous investigations which stated that the compound crystallizes in an orthorhombic space group, this study shows that the compound is monoclinic with a pseudo-orthorhombic cell and is affected by twinning. The structure is described in the (3 + 1)-dimensional superspace. Crenel-type modulation functions are used to account for an aperiodic sequence of right- and left-handed zweier single chains of silicate tetrahedra. The modulation mainly affects one of the two symmetrically independent tetrahedral chains, which are connected to build up [Si3O7]2− layers. Sodium cations are coordinated by five oxygen ligands and provide linkage between adjacent tetrahedral sheets. Distortions of the silicate tetrahedra and crystal chemical relationships of the title compound to sodium and lithium di- and metasilicates are discussed in detail.
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Hawthorne, Frank. "Connectivity and formula-generating functions for sheet-silicate minerals." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C1089. http://dx.doi.org/10.1107/s2053273314089104.
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Silicate sheets may be described by two-dimensional nets in which the vertices of the net are occupied by tetrahedra, and the edges of the net represent linkages between tetrahedra. A plane net must contain 3-connected vertices, but not all vertices need to be 3-connected. Simple silicate structures may thus be generated from simple 3-connected plane nets (e.g. 63, 4.82, 4.6.8, (4.6.8)2(6.82)1, etc.). More complicated silicate nets may be generated by various "building operations": (1) Insertion: insertion of 2- and 4-connected vertices into 3-connected plane nets; (2) Repetition: generation of double (or triple) nets by topological symmetry operations that retain transitivity at the junction between the repeated elements. Diversity is also introduced within the sheets of tetrahedra by [1] adjacent apical tetrahedron vertices pointing in the same or different directions, and [2] by folding of the sheets. For simple structures, net type strongly affects the stoichiometry of the resultant structure as the unit cells of the various nets are of different sizes (and shapes), although the stoichiometry may also be affected by non-tetrahedral components. Building operations strongly affect the stoichiometry of the resultant sheet, and this effect may be quantified. We define a formula-generating function F(k,l,...) that generates the formula of a sheet with specific topological features denoted by the indices k,l,... . A simple 3-connected net results in sheets of the form (T2O5)n where n denotes the number of (T2O5)n in the unit cell of the underlying net (for 63, n = 1; for 4.82, n = 2; for (4.6.8)2(6.82)1, n = 3, etc). Plane nets with k 3-connected vertices and l inserted 2-connected vertices result in sheets of the form [T(k+l) O(2.5k+3l)], where (...) are subscripted. Single- and double-sheet structures may be generated from the function F(k,l) = T(N{k+l}) O(N{3k+2.5l}-n{N-1}) where N = 1 and 2 for single- and double-sheets, respectively, and (...) are subscripted.
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Jestel, Nancy L., Jeremy M. Shaver, and Michael D. Morris. "Hyperspectral Raman Line Imaging of an Aluminosilicate Glass." Applied Spectroscopy 52, no. 1 (January 1998): 64–69. http://dx.doi.org/10.1366/0003702981942339.
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An aluminosilicate glass, which is a model for glass formulations used as dental restorations, was examined by hyperspectral Raman line imaging. The data set consisted of more than 30000 spectra, which were analyzed by using factor analysis. Nine score images were constructed from the nine significant factors identified. Three factors represent convolutions of noise, background, and offset. The other six factors represent Raman spectra of different bonding environments of the silicate tetrahedron. Three of those factors contain narrow Raman features. These are associated with a fully polymerized silica network, with a silicate tetrahedron with one nonbridging oxygen, and with an alumina-related inclusion or a silicate tetrahedron with two nonbridging oxygens. The last three significant factors contain broad Raman bands representing continua of slightly different bonding environments of silicate tetrahedra with 0–4 nonbridging oxygens. The score images reveal that the glass, although not homogeneous, has few regions with discrete heterogeneities. The different bonding networks commingle and could be interconnected.
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Champness, P. E., and R. W. Devenish. "Elemental mass loss in silicate minerals during x-ray analysis." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 4 (August 1990): 804–5. http://dx.doi.org/10.1017/s0424820100177155.
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It has long been recognised that silicates can suffer extensive beam damage in electron-beam instruments. The predominant damage mechanism is radiolysis. For instance, damage in quartz, SiO2, results in loss of structural order without mass loss whereas feldspars (framework silicates containing Ca, Na, K) suffer loss of structural order with accompanying mass loss. In the latter case, the alkali ions, particularly Na, are found to migrate away from the area of the beam. The aim of the present study was to investigate the loss of various elements from the common silicate structures during electron irradiation at 100 kV over a range of current densities of 104 - 109 A m−2. (The current density is defined in terms of 50% of total current in the FWHM probe). The silicates so far ivestigated are:- olivine [(Mg, Fe)SiO4], a structure that has isolated Si-O tetrahedra, garnet [(Mg, Ca, Fe)3Al2Si3AO12 another silicate with isolated tetrahedra, pyroxene [-Ca(Mg, Fe)Si2O6 a single-chain silicate; mica [margarite, -Ca2Al4Si4Al4O2O(OH)4], a sheet silicate, and plagioclase feldspar [-NaCaAl3Si5O16]. Ion- thinned samples of each mineral were examined in a VG Microscopes UHV HB501 field- emission STEM. The beam current used was typically - 0.5 nA and the current density was varied by defocussing the electron probe. Energy-dispersive X-ray spectra were collected every 10 seconds for a total of 200 seconds using a Link Systems windowless detector. The thickness of the samples in the area of analysis was normally 50-150 nm.
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Hawthorne, Frank C., Yulia A. Uvarova, and Elena Sokolova. "A structure hierarchy for silicate minerals: sheet silicates." Mineralogical Magazine 83, no. 1 (November 9, 2018): 3–55. http://dx.doi.org/10.1180/mgm.2018.152.
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AbstractThe structure hierarchy hypothesis states that structures may be ordered hierarchically according to the polymerisation of coordination polyhedra of higher bond-valence. A hierarchical structural classification is developed for sheet-silicate minerals based on the connectedness of the two-dimensional polymerisations of (TO4) tetrahedra, where T = Si4+ plus As5+, Al3+, Fe3+, B3+, Be2+, Zn2+ and Mg2+. Two-dimensional nets and oikodoméic operations are used to generate the silicate (sensu lato) structural units of single-layer, double-layer and higher-layer sheet-silicate minerals, and the interstitial complexes (cation identity, coordination number and ligancy, and the types and amounts of interstitial (H2O) groups) are recorded. Key aspects of the silicate structural unit include: (1) the type of plane net on which the sheet (or parent sheet) is based; (2) the u (up) and d (down) directions of the constituent tetrahedra relative to the plane of the sheet; (3) the planar or folded nature of the sheet; (4) the layer multiplicity of the sheet (single, double or higher); and (5) the details of the oikodoméic operations for multiple-layer sheets. Simple 3-connected plane nets (such as 63, 4.82 and 4.6.12) have the stoichiometry (T2O5)n (Si:O = 1:2.5) and are the basis of most of the common rock-forming sheet-silicate minerals as well as many less-common species. Oikodoméic operations, e.g. insertion of 2- or 4-connected vertices into 3-connected plane nets, formation of double-layer sheet-structures by (topological) reflection or rotation operations, affect the connectedness of the resulting sheets and lead to both positive and negative deviations from Si:O = 1:2.5 stoichiometry. Following description of the structural units in all sheet-silicate minerals, the minerals are arranged into decreasing Si:O ratio from 3.0 to 2.0, an arrangement that reflects their increasing structural connectivity. Considering the silicate component of minerals, the range of composition of the sheet silicates completely overlaps the compositional ranges of framework silicates and most of the chain-ribbon-tube silicates.
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Bunker, B. C., D. M. Haaland, K. J. Ward, T. A. Michalske, W. L. Smith, J. S. Binkley, C. F. Melius, and C. A. Balfe. "Infrared spectra of edge-shared silicate tetrahedra." Surface Science 210, no. 3 (March 1989): 406–28. http://dx.doi.org/10.1016/0039-6028(89)90603-1.
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Bunker, B. C., D. M. Haaland, K. J. Ward, T. A. Michalske, W. L. Smith, J. S. Binkley, C. F. Melius, and C. A. Balfe. "Infrared spectra of edge-shared silicate tetrahedra." Surface Science Letters 210, no. 3 (March 1989): A80—A81. http://dx.doi.org/10.1016/0167-2584(89)90813-x.
Full textDissertations / Theses on the topic "Silicate tetrahedra"
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Downs, Robert T. "Librational displacements of silicate tetrahedra in response to temperature and pressure." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/39442.
Full textBook chapters on the topic "Silicate tetrahedra"
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Liebau, Friedrich. "Influence of Non-Tetrahedral Cation Properties on the Structure of Silicate Anions." In Structural Chemistry of Silicates, 170–265. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/978-3-642-50076-3_10.
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Rocha, João, and Zhi Lin. "6. Microporous Mixed Octahedral-Pentahedral- Tetrahedral Framework Silicates." In Micro- and Mesoporous Mineral Phases, edited by Giovanni Ferraris and Stefano Merlino, 173–202. Berlin, Boston: De Gruyter, 2005. http://dx.doi.org/10.1515/9781501509513-006.
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Bunker, Bruce C., and William H. Casey. "Aqueous Polymerization of Silicates and Aluminosilicates." In The Aqueous Chemistry of Oxides. Oxford University Press, 2016. http://dx.doi.org/10.1093/oso/9780199384259.003.0022.
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Part Five of this book is devoted to silicates for several important reasons. First, silicates represent critical components of our planet and our lives. Silicon is the second most abundant element in Earth’s crust after oxygen, representing about 28% of the atoms present. As such, transformations of silicate minerals dominate much of the aqueous geochemistry of Earth. Every day, each of us encounters materials and objects the primary constituents of which are silicon oxides and related phases such as aluminosilicates. Granite facings on buildings, bricks, glass, pottery, ceramics, engineered materials used in water purification, catalysis, electronics, and even the optical fibers used in our most advanced communication systems are all silica based. Aluminosilicate minerals are even used as food additives. A key attribute of silicates that distinguishes them from most of the oxides highlighted in Parts One through Four of this book is that the Si(IV) cation is almost always present in a tetrahedral rather than in an octahedral coordination geometry. Exceptions include a few high-pressure phases such as stishovite (see Chapter 2) and a limited number of chelated Si(IV) complexes (see Section 14.3). The authors know of no stable compounds where Si(IV) is coordinated to only three oxygen atoms. The pathways for both forming and destroying silicate bonds are substantially different than for octahedral metal ions. Ligand-exchange pathways for silicate ions are via nucleophilic attack, where the coordination number increases in a transition state from four to five or even six (see Section 14.3 and Chapters 4 and 5). These contrast with pathways for octahedral metal ions, such as Al(III), where it is easier to decrease the coordination number from six to five or four in dissociative ligand exchange reactions. Of course, Si(IV) is not the only common element capable of forming tetrahedral oxide species. As outlined in Chapters 2 and 4, any cation with an ionic radius between roughly 0.03 nm and 0.055 nm can fit within the tetrahedral void between four close-packed oxygen anions, as expressed by Linus Pauling’s First Rule of coordination chemistry (see Chapter 2).
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Tossell, John A., and David J. Vaughan. "Applications to Silicate, Carbonate, and Borate Minerals and Related Species." In Theoretical Geochemistry. Oxford University Press, 1992. http://dx.doi.org/10.1093/oso/9780195044034.003.0007.
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The most abundant materials making up the crust of the earth (i.e., the “rock-forming minerals”) can be regarded as dominated by oxyanion units; notably, the units that can be formally represented by SiO44- and AlO45- clusters of the silicate minerals, and the CO32- unit of the carbonates. less common, but geochemically interesting, oxyanion units include, for example, BO33-, BeO46- , and PO43-. in this chapter, applications of quantum-mechanical calculations and experimental techniques to such materials are considered. first, the silicates are discussed, commencing with the large amount of work undertaken on the olivines, before considering such work as has so far been done on the other silicate minerals and related materials. second, the most important of the nonsilicate rock-forming mineral groups, the carbonates, are discussed. finally, although of less petrological importance but interesting geochemically and in terms of contrast with the othergroups, the borates and related species are considered. in each case, geometric aspects of structure and the problems of calculating structural properties are considered before going on to consider electronic structures and the factors controlling stabilities and a wider range of physical properties. in all of these materials, there is considerable interest in the, bonding in the oxyanion unit and how this is affected by, and controls, the interaction with counterions or the polymeric units. the building up of the minerals by such interactions exerts the dominant control over their crystal chemistries and properties and thus forms a central theme of this chapter. the silicate minerals are, of course, characterized by the presence of the tetrahedral siO4 cluster unit and the crystal chemistry and classification of silicates dominated by the structures built up by the linking together (polymerization) of these units. in the “simplest” of the silicates, the island silicates such as the olivine minerals (dominated by the forsterite (Mg2 SiO4)-fayalite (Fe2SiO4) solid solution series), the sio4 units are isolated by counterions such as Mg2+, Fe2+, Ca2+.
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"silica tetrahedron." In Dictionary Geotechnical Engineering/Wörterbuch GeoTechnik, 1231. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-41714-6_193574.
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Kumari, Neeraj, and Chandra Mohan. "Basics of Clay Minerals and Their Characteristic Properties." In Clay and Clay Minerals [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.97672.
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Clay minerals such as kaolinite, smectite, chlorite, micas are main components of raw materials of clay and formed in presence of water. A large number of clays used to form the different structure which completely depends on their mining source. They are known as hydrous phyllosilicate having silica, alumina and water with variable amount of inorganic ions like Mg2+, Na+, Ca2+ which are found either in interlayer space or on the planetary surface. Clay minerals are described by presence of two-dimensional sheets, tetrahedral (SiO4) and octahedral (Al2O3). There are different clay minerals which are categorized based on presence of tetrahedral and octahedral layer in their structure like kaolinite (1:1 of tetrahedral and octahedral layers), smectite group of clay minerals (2:1 of tetrahedral and octahedral layers) and chlorite (2:1:1 of tetrahedral, octahedral and octahedral layers). The particle size of clay minerals is <2microns which can be present in form of plastic in presence of water and solidified when dried. The small size and their distinctive crystal structure make clay minerals very special with their unique properties including high cation exchange capacity, swelling behavior, specific surface area, adsorption capacity, etc. which are described in this chapter. Due to all these unique properties, clay minerals are gaining interest in different fields.
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Taber, Douglass F. "Functional Group Protection: The Kraus Synthesis of Bauhinoxepin J." In Organic Synthesis. Oxford University Press, 2013. http://dx.doi.org/10.1093/oso/9780199965724.003.0013.
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Amos B. Smith III of the University of Pennsylvania found (Synlett 2009, 3131) that the advanced SAMP intermediate 1 could be deprotected to 2 without racemization under mild oxidative conditions. Akihiko Ouchi of the National Institute of Advanced Industrial Science and Technology, Tsukuba, showed (Organic Lett. 2009, 11, 4870) that the C-Te of 3 was easily oxidized to the aldehyde 4. Secondary C-Te bonds were converted to ketones. Asit K. Chakraborti of NIPER prepared (J. Org. Chem. 2009, 74, 5967) esters by warming an acid 5 with an alcohol 6 in the presence of acidic silica gel. Gilles Quéléver of Aix-Marseille Université established (Tetrahedron Lett. 2009, 50, 4346) that a cyanomethyl ester 8, readily prepared from the acid, efficiently exchanged with an alcohol 9 to give the ester 10. Martin J. Lear of the National University of Singapore protected (Tetrahedron Lett. 2009, 50, 5267) an alcohol 11 as the p -methoxybenzyl ether 13 under mild conditions (AgOTf/DTBMP) with the new reagent 12 . Isao Kadota of Okayama University selectively removed (Tetrahedron Lett. 2009, 50, 4552) the primary PMB ether from 14 to give 15. Hiromishi Fujioka of Osaka University, starting (Organic Lett. 2009, 11, 5138) from 16, was able to selectively prepare either the primary protected 18 or the secondary protected 19. In other developments (not pictured), Mattie S. M. Timmer and Brendan A. Burkett of Victoria University of Wellington devised (Tetrahedron Lett. 2009, 50, 7199) a convenient preparation for azulene-containing α-keto esters. The distinctively colored protecting group was conveniently removed in the presence of other esters by treatment with o-phenylenediamine. Scott D. Taylor of the University of Waterloo established (J. Org. Chem. 2009, 74, 9406) a robust protocol for converting alcohols to the corresponding protected sulfates. P. Shanthan Rao of the Indian Institute of Chemical Technology, Hyderabad, showed (Tetrahedron Lett. 2009, 50, 7099) that an amine 20 was formylated by warming with formic acid in the presence of ZnCl2. The easily hydrolyzed formamide 21 is readily converted to the corresponding isonitrile. Shiyue Fang of Michigan Technological University selectively monoacylated (Tetrahedron Lett. 2009, 50, 5741) the symmetrical diamine 22 using phenyl esters.
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Sposito, Garrison. "Soil Particle Surface Charge." In The Chemistry of Soils. Oxford University Press, 2016. http://dx.doi.org/10.1093/oso/9780190630881.003.0011.
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Structural charge arises on the surfaces of soil mineral particles in which either cation vacancies or isomorphic substitutions of cations by cations of lower valence occur. The principal minerals bearing structural charge are therefore the micas (Section 2.2), the 2:1 clay minerals (Section 2.3), or the Mn(IV) oxide, birnessite (Section 2.4). These three classes of mineral are all layer type and the cleavage surface on which their structural charge is manifest is a plane of O ions. The plane of O ions on the cleavage surface of a layer-type aluminosilicate is called a siloxane surface.This plane is characterized by hexagonal symmetry in the configuration of its constituent O ions, as shown at the top of Fig. 2.3 and, more explicitly, on the right side of Fig. 2.4, where a portion of the siloxane surface of the micas is depicted. Reactive molecular units on the surfaces of soil particles are termed surface functional groups. The functional group associated with the siloxane surface is the roughly hexagonal (strictly speaking, ditrigonalbecause the hexagonal symmetry is distorted when the tetrahedral sheet is fused to an octahedral sheet to form a layer) cavity formed by six corner-sharing silica tetrahedra. This cavity has a diameter of about 0.26 nm. The reactivity of the siloxane cavity depends on the nature of the electronic charge distribution in the layer structure. If there are no nearby isomorphic cations substitutions to create a negative charge, the O ions bordering the siloxane cavity function as an electron cloud donor that can bind molecules weakly through the van der Waals interaction. These interactions are akin to those underlying the hydrophobic interaction, discussed in Section 3.5, because the O in the siloxane surface can form only very weak hydrogen bonds with water molecules. Therefore, uncharged patches on siloxane surfaces may be considered hydrophobic regions to a certain degree, with, accordingly, an attraction for hydrophobic organic molecules. However, if isomorphic substitution of Al3+ by either Fe2+ or Mg2+ occurs in the octahedral sheet, the resulting structural charge is manifest on the siloxane cavities, as discussed in Section 2.3.
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Taber, Douglass. "Functional Group Protection." In Organic Synthesis. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199764549.003.0013.
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Alcohols are usually protected as alkyl or silyl ethers. Michael P. Jennings of the University of Alabama found (Tetrahedron Lett. 2008, 49, 5175) that pyridinium tribromide can selectively remove the TBS (or TES) protection from the primary alcohol of a protected primary-secondary alcohol such as 1. Propargyl ethers are useful because they are stable, but can be selectively removed in the presence of other protecting groups. Shino Manabe and Yukishige Ito at RIKEN showed (Tetrahedron Lett. 2008, 49, 5159) that SmI2 could reductively remove a propargyl group in the presence of acetonides (illustrated, 3), MOM, benzyl and TBS ethers. Hisanaka Ito of the Tokyo University of Pharmacy and Life Sciences took advantage (Organic Lett. 2008, 10, 3873) of the reducing power of Cp2Zr to selectively remove the allyl ethers from 5, to give 6. These conditions might also remove propargyl ethers. Esters can also be useful protecting groups. Naoki Asao of Tohoku University developed (Tetrahedron Lett . 2008, 49, 7046) the o-alkynyl ester 7. Au catalyst in EtOH removed the ester, leaving benzoates, acetates, OTBS and OTHP intact. Alternatively, an o-iodobenzoate can be removed by Sonogashira coupling followed by the Au hydrolysis. N-Formylation is usually accomplished using mixed anhydrides. Weige Zhang and Maosheng Chang of Shenyang Pharmaceutical University put forward ( Chem. Commun. 2008 , 5429) an intriguing alternative, heating a secondary amine 9 with KCN in the presence of dimethyl malonate to give 10. Many of the current methods for amination that have been developed deliver the aryl amine. John F. Hartwig of the University of Illinois established (J. Am. Chem. Soc. 2008, 130, 12220) that exposure of the amine 11 to Boc2O followed by CAN led to the protected, dearylated amine 12. Adam McCluskey of The University of Newcastle observed (Tetrahedron Lett. 2008, 49, 6962) that microwave heating removed Boc protecting groups when there was a free carboxylic acid elsewhere in the molecule. Michael Lefenfeld of SiGNa Chemistry and James E. Jackson of Michigan State University used (Organic Lett. 2008, 10, 5441) easilyhandled Na/silica gel to remove primary and secondary sulfonamides (e.g. 15 → 16). Methanesulfonamides were also removed under these conditions.
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Taber, Douglass. "Synthesis of Heteroaromatics." In Organic Synthesis. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199764549.003.0066.
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Yasutaka Ishii of Kansai University has developed (J. Org. Chem. 2007, 72, 8820) a novel route to furans, using a mixed-metal catalyst to effect condensation of an aldehyde or 1,3 diketone such as 1 with an acceptor such as 2 to give the 3-furoate 3. In a complementary approach, Yong-Min Liang of Lanzhou University has found (J. Org. Chem. 2007, 72, 10276) that diazoacetate 5 will condense with an alkynyl ketone to give the 2-furoate 6. David W. Knight of Cardiff University has shown (Tetrahedron Lett. 2007, 48, 7709) that an alkynyl diol such as 7, readily available by dihydroxylation of the corrresponding alkenyl alkyne, cyclized to the furan on exposure to AgNO3 on silica gel. Professor Knight has also (Tetrahedron Lett. 2007, 48, 7906) established a route to poly-substituted pyrroles 10, by iodination of alkynyl sulfonamides such as 9. Similarly, Richard C. Larock of Iowa State University found (J. Org. Chem. 2007, 72, 9643) that I-Cl cyclized methoximes such as 11 to the corresponding iodo isoxazole 12, and Stephen L. Buchwald of MIT uncovered (Organic Lett. 2007, 9, 5521) the cyclization of an enamide such as 13 with I2 to the corresponding oxazole 14. In developing a more efficient route to a new class of materials that he has named “triazolamers”, Paramjit S. Arora of New York University was able (J. Org. Chem. 2007, 72, 7963) to effect diazo transfer to the amine 15 and subsequent condensation with 16 to give 17, without isolation of the intermediate azide. C. V. Asokan and E. R. Anabha of Mahatma Gandhi University have described (Tetrahedron Lett. 2007, 48, 5641) the activation of a ketone 18 followed by condensation with malononitrile 19 to give the pyridine 20. Hans-Ulrich Reissig of the Freie Universität Berlin has established (Organic Lett. 2007, 9, 5541) a complementary three-component coupling of a nitrile 21 with the allenyl anion 22, followed by a carboxylic acid 23 to deliver the pyridine 24. Akio Saito and Yuji Hanzawa of the Showa Pharmaceutical University have reported (Tetrahedron Lett. 2007, 48, 6852) the intramolecular Rh-catalyzed cyclization of a methoxime lactone such as 25 to the pyridine 26.
Conference papers on the topic "Silicate tetrahedra"
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Peto, Marinela, Erick Ramirez-Cedillo, Mohammad J. Uddin, Ciro A. Rodriguez, and Hector R. Siller. "Mechanical Behavior of Lattice Structures Fabricated by Direct Light Processing With Compression Testing and Size Optimization of Unit Cells." In ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-12260.
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Abstract Lattice structures used for medical implants offer advantages related to weight reduction, osseointegration, and minimization of stress shielding. This paper intends to study and to compare the mechanical behavior of three different lattice structures: tetrahedral vertex centroid (TVC), hexagonal prism vertex centroid (HPVC), and cubic diamond (CD), that are designed to be incorporated in a shoulder hemiprosthesis. The unit cell configurations were generated using nTopology Element Pro software with a uniform strut thickness of 0.5 mm. Fifteen cuboid samples of 25mm × 25mm × 15 mm, five for each unit cell configuration, were additively manufactured using Direct Light Printing (DLP) technology with a layer height of 50μm and a XY resolution of 73μm. The mechanical behavior of the 3D printed lattice structures was examined by performing mechanical compression testing. E-silicone (methacrylated silicone) was used for the fabrication of samples, and its mechanical properties were obtained from experimental tensile testing of dog-bone samples. A methodology for size optimization of lattice unit cells is provided, and the optimization is achieved using nTopology Element Pro software. The generated results are analyzed, and the HPVC configuration is selected to be incorporated in the further design of prosthesis for bone cancer patients.