Materials Literature
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Tetraheptylammonium salts of various transition-metal-substituted heteropolyanions with alpha-Keggin ([XW(11)O(39)M](n)()(-)), alpha-Wells-Dawson ([P(2)W(17)O(61)M](m)(-)), and Weakley and Finke structures ([P(2)W(18)O(68)Co(4)](10)(-)) were investigated with respect to their reactivity with CO(2) in nonpolar solvents…
The precipitation polymerization of commercial divinylbenzene in acetonitrile containing up to 40 vol. % toluene or other cosolvents is shown to produce novel porous monodisperse poly(divinylbenzene) microspheres. These microspheres have diameters between 4 and 7 μm, total pore volumes of up to 0.52 cm3/g, and surface…
We advance the novel hypothesis that water in the presence of finite localized strain within fault gouges may lead to the phase transformation of stable minerals into metastable polymorphs of higher free energy density. Under increasing strain, the transformed minerals eventually become unstable, as shown from an appl…
If the amylose fraction of starch is degraded by glucosyltransferases, one or several turns of the amylose helix are hydrolyzed off and their ends are joined together, thereby producing cyclic oligosaccharides called cyclodextrins (CDs) or cycloamyloses (CAs).
Conditions are described under which the nonphysiological substrate mercuric bromide (HgBr2) is rapidly turned over, both by the wild type (CCCC) and by an active site double mutant (CCAA) of mercuric reductase in which the C-terminal cysteines 557' and 558' are replaced by alanine and only the redox-active pair Cys13…
A disordered loop (loop 52-72, residues 52-72) in crystal structures of fructose-1,6-bisphosphatase (FBPase) has been implicated in regulatory and catalytic phenomena by studies in directed mutation. A crystal structure of FBPase in a complex with three zinc cations and the products fructose 6-phosphate (F6P) and phos…
Ultraviolet irradiation of formamide in solid argon forms hydrogen-bonded, carbon- and oxygen-attached complexes NH 3 −CO and NH 3 −OC. Computationally, the carbon-attached complex is 1.2 kJ mol -1 more stable than the oxygen-attached complex. However, a thermal equilibrium of the two structures is found experimentall…
UDP-galactose 4-epimerase catalyzes the interconversion of UDP-galactose and UDP-glucose during normal galactose metabolism. Within recent years the enzyme from Escherichia coli has been studied extensively by both biochemical and X-ray crystallographic techniques. One of several key features in the catalytic mechanis…
In a previous contribution ( J. Phys. Chem. 1994, 98, 4125) we reported EXAFS data collected at ADONE on a high quality Ti−silicalite (TS-1) sample (Ti = 1.47 wt %) dehydrated in a carefully controlled atmosphere at 400 K. The importance of that paper was to definitively clarify that Titanium atoms occupy silicon subs…
The seeded and unseeded precipitation of calcium carbonate from supersaturated aqueous solutions was investigated in a closed system under conditions of constant supersaturation (supersaturation 1.88−3.39) at 25 °C and at pH 9.0 and 10.0. The analysis of our results based on expressions for the supersaturation depende…
Solubilities of four heavy n -alkanes (tricosane, pentacosane, hexacosane, and octacosane) in a solvent containing seven atoms of carbon (heptane, methylcyclohexane, and toluene) are determined by simple thermal analysis. It is shown that the nature of the solvent has no major influence on the solubility and that, in…
2-Oxo-hept-4-ene-1,7-dioate hydratase from Escherichia coli C converts 2-oxo-hept-4-ene-1,7-dioate to 2-oxo-4-hydroxy-hepta-1,7-dioate by the addition of water using magnesium as a cofactor. The enzyme is one of a set of inducible enzymes, known collectively as the homoprotocatechuate meta-fission pathway. The entire…
Mesoporous silica fibers with accessible, highly ordered large periodic pores are directly drawn from a highly viscous surfactant/silicate solution. Poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymers are used as the structure-directing agents under acidic conditions during the synt…
Ultrathin films have been prepared by self-assembling trioctylphosphine oxide, TOPO, capped n-type 20−40 Å diameter CdSe nanoparticles and 1,6-hexadecanethiol, HDT, onto p-doped semiconducting polymers, chemically deposited poly(3-methylthiophene), PMeT (for Device A ), and electrochemically deposited poly(pyrrole), P…
Dynamical stability of the crack front line that propagates between two plates is studied numerically using the simple two-dimensional mass-spring model. It is demonstrated that the straight front line is unstable for low speed while it becomes stable for high speed. For the uniform model, the roughness exponent in th…
Low temperature absorption spectra of doped , and single crystals, grown by the flux method, are reported. A simulation of the energy level scheme is carried out. The effective Hamiltonian includes elementary interactions such as coulombic, spin-orbit, two- and three-body interactions. The crystal field effect is intr…
We investigate the temperature-dependent optical conductivity of ${\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{-}{\mathrm{NaV}}_{2}{\mathrm{O}}_{5}$ in the energy range 4 meV--4 eV. The intensities and the polarization dependence of the detected electronic excitations give a direct indication for a broken-parity…
During the STS-83 Spacelab mission, a sample of Pd78Cu6Si16 was processed in the electromagnetic levitation facility TEMPUS. Surface oscillations of the levitated liquid droplet were excited, and frequency and damping of the oscillations were observed. Under microgravity conditions, the damping constant is simply rela…
Time-resolved photoluminescence (PL) spectra are reported for gas-suspended 1–10 nm diameter SiOx particles formed by laser ablation of Si into 1–10 Torr He and Ar. Three spectral bands (1.8, 2.5 and 3.2 eV) similar to PL from oxidized porous silicon were measured, but with a pronounced vibronic structure. Particle si…
We report on the synthesis of size-classified PbS nanocrystals by differential mobility analysis of a polydisperse aerosol formed by nucleation and aggregation processes in a furnace reactor. The sublimation temperature employed is below the stoichiometric evaporation temperature, thus enabling direct and simple synth…