Materials Literature
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A general kinetic model to describe the interaction of two dissimilar olefins with cobalt(II) tetrakis(anisyl)porphyrin complexes in the presence of organic radicals has been developed. The kinetic scheme presumes the formation of organometallic products both by radical addition to Co(II) and by reaction of hydridocob…
We present a theoretical approach to study the dielectric properties of porous ceramics and composite materials and explain the experimentally observed notable influence of the coupling between the components of a saturated porous ceramic on the final behavior of the sample. This model is based on the assumption of a…
The results of susceptibility and neutron inelastic scattering measurements on the pyrochlore compound are presented. The crystal-field ground state of the ion has zero spontaneous magnetization, and a virtually dispersionless crystal-field excitation is observed. It is concluded that the crystal-field interaction dom…
The effect of crystallization temperature on the electrical properties of sol-gel derived Pb(Zr,Ti,Nb)O3 or PNZT capacitors with La0.5Sr0.5CoO3 (LSCO) electrodes has been investigated. It is demonstrated that LSCO//PNZT(4/30/70)//LSCO capacitors can be fabricated at temperatures as low as 550 °C without significant de…
The configurational properties of a heteropolymer with prescribed sequences of known concentrations of dipolar segments are investigated. The theoretical analysis of a model chain capable of aggregation into domains shows that entropic frustrations lead to localized structures. In these structures, polymer size is det…
To investigate the observed huge variations in magnetoresistance between different samples of manganite perovskites we have performed the first high-pressure measurement of magnetoresistance in single crystal ${\mathrm{Nd}}_{0.5}{\mathrm{Sr}}_{0.36}{\mathrm{Pb}}_{0.14}{\mathrm{MnO}}_{3\ensuremath{-}\ensuremath{\delta}…
Helical strands from P2 and P10 units (see structure below), recently predicted by ab initio calculations to be thermodynamically stable, and shortly thereafter discovered as a structural element in (CuI)3P12, might be the major component of amorphous red phosphorus. Radial distribution functions calculated on the bas…
Epoxidations of olefins and oxidations of alcohols can be carried out in the presence of peroxides at relatively low temperatures with Cu2+ histidine complexes that have been immobilized in zeolite cavities (structure from molecular modeling shown on the right). Combined diffuse reflectance and ESR spectroscopic studi…
The dragline silk spun by spiders exhibits unusual tensile strength and the energy required to break it can be higher than that of Kevlar. In his Perspective, Tirrell comments on a research report in the same issue by Simmons et al . ( p. 84 ) that elucidates some of the structural properties that give spider silk its…
The redox behavior is markedly different for the second generation dendrimer 1 (depicted on the right) from that of the first generation dendrimer without the densely packed dendritic structure. The unusually positive FeIII/FeII redox potential of 1 in water (+0.19 V vs. SCE) is attributable to the strong shielding of…
At least four types of silanol groups are present in MCM-41, a novel silicate with uniform mesopores, according to IR spectroscopy. Isolated silanol groups (type 1 in the picture on the right) and those involved in hydrogen bonds were distinguished by partial silylation with chlorotrimethylsilane (CTMS) and chlorotrip…
A complete and accurate set of experimental crystallographic phases to a resolution of 1.8 angstroms was obtained for a 230-residue dimeric fragment of rat mannose-binding protein A with the use of multiwavelength anomalous dispersion (MAD) phasing. An accurate image of the crystal structure could thus be obtained wit…
The first report of the formal potentials of a series of solid metal hexacyanometalates (M + ) n M′[M″ (CN) 6 ] is given (M + = Li + , K + , Na + , Rb + , Cs + ; M′ = Ag, Al, Cd, Co, Cr, Cu, Fe, Ga, In, Mn, Ni, Pb; M″ = Cr, Fe, Mn). A linear correlation exists between the ionic potential Φ = z /r eff of the nitrogen‐b…
The computation of the electron-electron Coulomb interaction is one of the limiting factors in ab initio electronic structure calculations. The computational requirements for calculating the Coulomb term with commonly used analytic integration techniques between Gaussian functions prohibit electronic structure calcula…
Molecular-based ferrimagnetic thin films with high critical temperatures ( T c ) composed of mixed-valence chromium cyanides were synthesized by means of a simple electrochemical route. The highest T c was 270 K, obtained for Cr 2.12 (CN) 6 . The T c values were easily controlled by changing the preparation conditions…
The molecular origin of the exceptional mechanical properties of spider silk is unclear. This paper presents solid-state 2H nuclear magnetic resonance data from unoriented, oriented, and supercontracted fibers, indicating that the crystalline fraction of dragline silk consists of two types of alanine-rich regions, one…
First-principles calculations of the relative stability, structure, and physical properties of carbon nitride polymorphs predict a cubic form of C 3 N 4 with a zero-pressure bulk modulus exceeding that of diamond. Like diamond, this new phase could potentially be synthesized at high pressure and quenched to ambient pr…
Many mineralizing organisms selectively form either calcite or aragonite, two polymorphs of calcium carbonate with very similar crystalline structures. Understanding how these organisms achieve this control has represented a major challenge in the field of biomineralization. Macromolecules extracted from the aragoniti…
The effect of the rate and time of mixing in a batch mixer on the phase structure of polypropylene/polystyrene (PP/PS) blends with various rheological properties of the components was studied. Regions with substantially different average sizes of the dispersed particles were found in the studied blends. Differences be…
Starting from aromatic diamines, a series of bismaleimides (BMIs) and maleimide-terminated structural resins were prepared in solution and characterized. Maleimide-terminated resins were prepared through Michael addition reaction with 3/2 molar ratio of bismaleimide and aromatic diamine as reactants. The structural an…