Asymmetric epoxidation of stilbene by manganese(III) chiral salen complex immobilized in Al-MCM-41
Manganese-exchanged MCM-41 modified with a chiral salen is an effective enantioselective heterogeneous epoxidation catalyst for cis-stilbene.
Materials Literature
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Macromolecular tetrathiafulvalene chemistry
Recent developments in the functionalisation of tetrathiafulvalene (TTF) have enabled TTF units to be covalently linked into macromolecular systems. Convergent syntheses of dendrimers containing TTF units are presented, including a (TTF)13 system in which TTF units are emplaced at all layers of the structural hierarch…
Photochemical Phase Transition Behavior of Polymer Azobenzene Liquid Crystals with Electron-Donating and -Accepting Substituents at the 4,4‘-Positions
Photochemical phase transition behavior of polymer liquid crystals (LCs) with donor−acceptor azobenzene moieties which contain both electron-donating and -accepting substituents at the 4,4‘-positions has been explored. Polymer azobenzene LCs were prepared which show nematic (N) LC behavior in the trans form but no LC…
Ceramic microstructures : control at the atomic level
Introduction and Overviews: Structure and Composition of Interfaces in Ceramics and Ceramic Composites M. Ruhle, et al. Microstructures and Interfaces: Near Atomic Scale Nanochemistry and Structure: Ceramic Grain Boundaries and Interfaces R.W. Carpenter, W. Braue. Sintering and Grain Growth: Microdesigned Interfaces:…
Short-termin vivo evaluation of small-diameter vascular prosthesis composed of segmented poly(etherurethane)/2-methacryloyloxyethyl phosphorylcholine polymer blend
A small-diameter vascular prosthesis with potential for clinical use was prepared from a Dacron prosthesis coated with nonthrombogenic polymeric materials. As a coating material, segmented poly(etherurethane) (SPU; Tecoflex 60) was blended with a phospholipid polymer, 2-methacryloyloxyethyl phosphorylcholine (MPC) pol…
Controlled cleavage of R8Si8O12 frameworks: a revolutionary new method for manufacturing precursors to hybrid inorganic–organic materials
Cube-octameric polyhedral silsesquioxanes (R8Si8O12) react with strong acids (HX) to produce R8Si8O11X2 frameworks resulting from selective cleavage of one Si–O–Si linkage; subsequent hydrolysis affords R8Si8O11(OH)2 frameworks derived from the net hydrolysis of one Si–O–Si linkage in R8Si8O12; these results demonstra…
Taking advantage of the pH and pO2 sensitivity of a luminescent macrocyclic terbium phenanthridyl complex
Strong metal-based emission with [TbL1] in aqueous media occurs in the absence of protons and oxygen; dissolved molecular oxygen quenches the phenanthridyl triplet (1/KSV = 58 Torr O2) but back-energy transfer to the organic triplet occurs efficiently only with the excited protonated complex (pKa″ = 5.7).
Structure and dynamics of all of the stereoisomers of europium complexes of tetra(carboxyethyl) derivatives of dota: ring inversion is decoupled from cooperative arm rotation in the RRRR and RRRS isomers
The absolute configuration of the four stereoisomeric α-substituted derivatives of dota has been defined; in their Eu complexes, 2D-NMR methods have revealed that in solution ring inversion is independent of pendant arm rotation and the (RRRR)-[EuL1a] complex which in the solid state crystallises as a square antiprism…
Critical point in ferroelectric Langmuir-Blodgett polymer films
The ferroelectric critical point has been found in a ferroelectric polymer by exploring the influence of the electric field on the paraelectric-ferroelectric phase transition. Dielectric and pyroelectric measurements on 30-monolayer-thick films of the crystalline copolymer poly(vinylidene fluoride-trifluoroethylene) g…
Fracture : a topical encyclopedia of current knowledge
Part 1 The Surface Energy of Solids: The Phenomenon of Rupture and Flow in Solids, A.A. Griffith Analysis of Stresses and Strains Near the End of a Crack Traversing a Plate, G.R. Irwin Crack Propagation in Continuous Media, G.P. Cherepanov The Next 50 Years of Jet Propulsion, B.L. Koff. Part 2 The Mathematical Theory…
A finite element model of ferroelectric polycrystals
A finite element model of polarization switching in polycrystalline ferroelectric ceramics is developed. A polarization switch in a ferroelectric is the reorientation of the unit cell dipole to a new crystallographic direction. It is assumed that a crystallite switches if the reduction in potential energy of the polyc…
Dislocation motion, constriction and cross-slip in fcc metals
A Finnis/Sinclair-type interatomic potential for copper is used to examine the properties of dissociated screw dislocations in the face-centred cubic lattice.The critical stress for dislocation motion is found to be a sensitive function of the partial dislocation separation, with a lower limit at least 85% smaller tha…
Raman spectroscopic evidence for the existence of 6-molybdoaluminate entities on an Mo/Al2O3 oxidic precursor
A study by Raman spectroscopy of the oxomolybdate surface phase present on an Mo/Al2O3 oxidic precursor reveals the presence of well dispersed 6-molybdoaluminate entities (AlMo6O24H63-) on a 15 wt.% MoO3 oxidic precursor. It is also shown that precipitation of an ammonium 6-molybdoaluminate salt occurs at higher Mo lo…
Reversible anion binding in aqueous solution at a cationic heptacoordinate lanthanide centre: selective bicarbonate sensing by time-delayed luminescence
Reversible displacement of up to two metal bound water molecules at a coordinately unsaturated, cationic lanthanide centre is signalled by increases in the luminescence intensity or lifetime of the emissive lanthanide: selective chelation of hydrogencarbonate is consistent with emission spectroscopic, ESMS and CPL mea…
The fixation and reduction of dinitrogen using lanthanides: praseodymium and neodymium meso-octaethylporphyrinogen–dinitrogen complexes
The meso-octaethylporphyrinogen–sodium–lanthanide complexes, [{(η5 : η1 : η5 : η1-Et8N4)M}Na(thf)2], in the presence of Na metal and under a nitrogen atmosphere, fix and reduce dinitrogen to the [N2]2– anion, as shown by the isolation of the dinuclear complexes containing the [M(µ-η2 : η2-N2)M] moiety [M = Pr, Nd].
Understanding water treeing mechanisms in the development of diagnostic test methods
Recently, several diagnostic methods for measurement of permittivity and dielectric loss have been developed for non-destructive testing of water-tree degraded XLPE cables. Critical degradation is found to be associated with a more than proportional increase of the dielectric properties when increasing the applied tes…
Control of the Structural Stability of the Tubulin Dimer by One High Affinity Bound Magnesium Ion at Nucleotide N-site
Tubulin liganded with GTP at the N-site in the alpha-subunit and with GDP at the E-site in the beta-subunit (GDP-tubulin) reversibly binds one high affinity Mg2+ cation (Kb = 1.1 x 10(7) M-1), whereas tubulin liganded with GTP at both subunits (GTP-tubulin) binds one more high affinity Mg2+. The two cation binding loc…
Remarkable matrix effect in polymer-supported Jacobsen’s alkene epoxidation catalysts
Adaptation of the polymer matrix has allowed high enantioselectivity to be achieved for the first time with a polymer-supported chiral MnIII(salen) alkene epoxidation catalyst.
An intramolecular H3O2 bridge as the resting form of an active metal-bound hydroxide in a dinuclear zinc(II) complex
An intramolecular Zn–O2H3–Zn bridge as a complexed form of metal-bound hydroxide exhibits enhanced reactivity compared to the related Zn–OH–Zn unit, illustrated by the reaction with CO2.
Aluminosilicate mesoporous molecular sieves with enhanced stability obtained by reacting MCM-41 with aluminium chlorohydrate
Aluminosilicate MCM-41 materials prepared by post-synthesis alumination using aqueous aluminium chlorohydrate exhibit remarkably high mechanical and hydrothermal stability and in addition the materials, after steaming at high temperatures, possess stronger Brønsted acid sites compared to the parent material.