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Geometry optimizations were carried out for the cis and trans forms of Nb 2 W 4 O 19 4 - . The energy difference between the two conformations was found to be 2.3 kcal mol - 1, the structure in which the two Nb atoms are in the cis formation being the most stable. Several isomers of the Nb 2 W 4 O 19 H 3 - anion were…
To obtain insights into the factors that influence the electronic spectra of conjugated porphyrin systems, a series of porphyrins with fused phenanthrene subunits have been synthesized. 9-Nitrophenanthrene reacted with esters of isocyanoacetic acid in the presence of DBU in THF to give a series of phenanthro[9,10- c ]…
ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTTight Knots in PolymersMarc L. MansfieldView Author Information Michigan Molecular Institute, 1910 W. St. Andrews Road, Midland, Michigan 48640 Cite this: Macromolecules 1998, 31, 12, 4030–4032Publication Date (Web):May 20, 1998Publication History Received6 January 1998Publishe…
In this study, we select a catalyst with the highest activity to reduce NO with CO as a reducing reactant from four series of perovskites La 1 - x Sr x BO 3 where B = Mn, Fe, Co, or Ni. The cause for different activities is also closely examined by characterizing the perovskites by XRD, XPS, NO-TPD, and CO-TPR. Activi…
Experiments using a blunted conical indentor show that the low-density amorphous solid form of pressure-amorphized ice deforms under load and behaves like a viscous liquid near 143 K, much before its rapid crystallization to cubic ice. Since a mechanical stress biases the molecular diffusion of a fluid undergoing a Ne…
Bacterial Delta 5-3-ketosteroid isomerase (KSI) from Pseudomonas testosteroni has been intensively studied as a prototype for understanding an enzyme-catalyzed allylic rearrangement involving intramolecular proton transfer. Asp38 serves as a general base to abstract the proton from the steroid C4-H, which is a much st…
The crystalline carbon nanotubes having mesopores that are open at one end, with pore width of 4 ± 0.8 nm, were characterized by XRD, XPS, and HRTEM. The N 2 adsorption isotherm of multiwall carbon nanotubes was measured at 77 K. A hump was observed near P / P 0 = 0.4 in the adsorption isotherm. The adsorption isother…
We report the results of extensive Dynamic Monte Carlo simulations of systems of self-assembled Equilibrium Polymers without rings in good solvent. Confirming recent theoretical predictions, the mean-chain length is found to scale as $\Lav = \Lstar (ϕ/\phistar)^α\propto ϕ^α\exp(δE)$ with exponents $α_d=δ_d=1/(1+γ) \ap…
We consider the growth of a polymer layer on a flat surface in a good solvent by in-situ polymerization. This is viewed as a modified form of diffusion-limited aggregation without branching. We predict theoretically the formation of a pseudo-brush with density rhog(z) \propto z^{-2/3} and characteristic height \propto…
Unconcatenated, unknotted polymer rings in the melt are subject to strong interactions with neighboring chains due to the presence of topological constraints. We study this by computer simulation using the bond-fluctuation algorithm for chains with up to N=512 statistical segments at a volume fraction Φ=0.5 and show t…
We report results of extensive Dynamical Monte Carlo investigations on self-assembled Equilibrium Polymers (EP) without loops in good solvent. (This is thought to provide a good model of giant surfactant micelles.) Using a novel algorithm we are able to describe efficiently both static and dynamic properties of system…
Si anodic dissolution in acidic fluoride medium has been investigated in different regimes (porous silicon formation, electropolishing under stationary and oscillating current) by probe beam deflection (PBD) or the “mirage” technique. Evolution of deflection signal allows monitoring of dissolution processes both under…
A simple model is proposed to calculate the charge distribution in the two-electron-reduced isopolytungstate [W10O32].6- It is shown that the experimentally observed asymmetric excess electron distribution is due to competition of the electronic delocalization between equatorial metal sites and Coulomb repulsion.
Polyethylene glycol (PEG)-linked manganese halogenated porphyrins (Chart 1) catalyzed oxidation of azo dyes (Chart 2) by H 2 O 2 under mild conditions such as pH 8.0 at 25 °C especially when imidazole was present, causing the decoloration of azo dyes. The decoloration of azo dyes by synthetic manganese porphyrins unde…
Dielectric measurements were carried out on undiluted cis -polyisoprene (PI) over a wide frequency range from 10 -4 to 10 5 Hz around the glass transition temperature T g (=200 K). The data indicate that the dielectric loss curves including both the normal and segmental mode processes are superposable in the range abo…
(3 S )-3-[(Benzyloxycarbonyl)methyl]morpholine-2,5-dione (BMD) has been successfully copolymerized with ε-caprolactone for a wide range of mole fractions in the feed. The sequence analysis of the copolymers has also been carried out on the basis of the clear interpretation of the 13 C NMR spectra of the copolymers. DC…
The local structure of glasses in the system Na 2 O−B 2 O 3 −Al 2 O 3 is studied by multinuclear magic-angle spinning (MAS) solid-state NMR spectroscopy at 7.0 and 11.7 T. The 23 Na isotropic chemical shifts vary linearly with Na 2 O concentration, indicating that the sodium ions are homogeneously distributed over the…
Development of an ellipsometry to the case of a coherent far infrared irradiation, low temperatures and small samples is described, including a decision of the direct and inverse problems of the convergent beam ellipsometry for an arbitrary wavelength, measurement technique and a compensating orientation of cryostat w…
We have performed total-energy density-functional calculations using first-principles pseudopotentials to determine the atomic and electronic structure of neutral surface and subsurface vacancies at the GaP(110) surface. The cation as well as the anion surface vacancy show a pronounced inward relaxation of the three n…
A novel synthetic procedure for the preparation of hyperbranched polymers with narrow molecular weight distribution and enhanced degree of branching (DB) has been studied, using computer simulation to model the kinetics of the process. Slow addition of AB m monomers to B f core molecules in solution (“core-dilution/sl…