Materials Literature
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We report the first investigation of the photo-response of the conductivity of a new class of organic semiconductors based on functionalized pentacene. These materials form high quality single crystals that exhibit a thermally activated resistivity. Unlike pure pentacene, the functionalized derivatives are readily sol…
The anchoring of nematic liquid crystals on surfaces with grafted liquid crystalline chain molecules is studied by computer simulations and within a mean field approach. The computer simulations show that a swollen layer of collectively tilted chains may induce untilted homeotropic (perpendicular) alignment in the nem…
The meander instability of a vicinal surface growing under step flow conditions is studied within a solid-on-solid model. In the absence of edge diffusion the selected meander wavelength agrees quantitatively with the continuum linear stability analysis of Bales and Zangwill [Phys. Rev. B {\bf 41}, 4400 (1990)]. In th…
Silver Schottky contacts were fabricated on (112̄0) n-ZnO epilayers, which were grown on R-plane sapphire substrates by metalorganic chemical-vapor deposition. The flatband barrier height was determined to be 0.89 and 0.92 eV by current–voltage and capacitance–voltage measurements, respectively. The ideality factor wa…
Rietveld neutron powder profile analysis of the compound Na(0.5)Bi(0.5)TiO(3) (NBT) is reported over the temperature range 5-873 K. The sequence of phase transitions from the high-temperature prototypic cubic structure (above 813 K), to one of tetragonal (673-773 K) and then rhombohedral structures (5-528 K) has been…
There has been much recent interest in a so-called “giant-dielectric phenomenon” displayed by an unusual cubic perovskite-type material, CaCu3Ti4O12; however, the origin of the high permittivity has been unclear [M. A. Subramanian, L. Dong, N. Duan, B. A. Reisner, and A. W. Sleight, J. Solid State Chem. 151, 323 (2000…
The architecture of an engineered tissue substitute plays an important role in modulating tissue growth. A novel poly(D,L-lactide-co-glycolide) (PLGA) structure with a unique architecture produced by an electrospinning process has been developed for tissue-engineering applications. Electrospinning is a process whereby…
AlC n, AlC n +, and AlC n - ( n = 1−7) clusters have been studied by means of the B3LYP density functional method. Results of their equilibrium geometries, electronic energies, dipole moments, and vibrational frequencies are reported. The energy calculations show that the open-chain linear or quasi-linear isomers with…
Three families of phosphorus-containing dendrimers having chiral ferrocenic subunits precisely placed at one individual shell within their skeleton are synthesized. The influence of the progressive “burying” of the chiral ferrocene derivatives upon their electrochemical and chiroptical properties is reported. It is sh…
Base-catalyzed cross condensation of dipropylmaleonitrile 1 with bis(dimethylamino)maleonitrile 2 in an equimolar ratio afforded the porphyrazines 3a, 4a, 5a, 6a and 7a. Subsequent demetalation of 5a with TFA followed by remetalation with Zn(OAc)(2) gave ligand 5c in good yield. Compound 5c was, in turn, selectively o…
The electropolymerization and optical properties of poly(3,4-ethylenedioxythiophene) (PEDOT) was investigated in detail by a combined electrochemistry and surface plasmon spectroscopy setup. The simultaneous electrochemical−surface plasmon spectroscopy (EC-SPS) technique allowed for characterization of the changing di…
The influence of macromolecular architecture on the physical properties of polymeric materials has been studied by comparing poly(benzyl ether) dendrons with their exact linear analogues. The results clearly confirm the anticipation that dendrimers are unique when compared to other architectures. Physical properties,…
NMR studies on a series of poly(lactic acid)−poly(ethylene oxide) (PLA−PEG) diblock copolymers have been carried out in d 6 -acetone and in D 2 O. Nanoparticles of the PLA−PEG copolymers were obtained using a modified interfacial polymer deposition−solvent evaporation technique (Fessi, H.; Devissaguet, J. P.; Puisieux…
Epimerases and racemases are enzymes that catalyze the inversion of stereochemistry in biological molecules. In this article, three distinct examples are used to illustrate the wide range of chemical strategies employed during catalysis, and the diverse set of ancestors from which these enzymes have evolved. Glutamate…
The complexes Fe2(OCHPh2)6 and L2FeOR (R = Et or CHPh2, L = N,N'-bis(trimethylsilyl)benzamidinate) were structurally characterized, and comparative studies of the behavior of those compounds comprising the same alkoxide (Ph2HCO-) in polymerizations of -caprolactone (CL) and D,L-lactide (LA) were performed. Both Fe2(OC…
Electron-donating π-conjugated polymers with dithiafulvene moiety ( 4 ) or with diselenafulvene moiety ( 5 ) were prepared by cycloaddition polymerization of chalcogenoketenes derived from aromatic diynes ( 3 ). The solubilities of the polymers strongly depended on the structures. The diselenafulvene polymers ( 5 ) sh…
As part of a high-throughput, structural proteomic project we have used NMR spectroscopy to determine the solution structure and ascertain the function of a previously unknown, conserved protein (MtH895) from the thermophilic archeon Methanobacterium thermoautotrophicum. Our findings indicate that MtH895 contains a ce…
The crystal structure of rimkorolgite, ideally Ba[Mg 5 (H 2 O) 7 (PO 4 ) 4 ](H 2 O), (monoclinic, P 2 1 / c, a = 8.3354(9), b = 12.8304(13), c = 18.313(2) A, β = 90.025(2)°, V = 1958.5(4) A 3 , Z = 4) has been solved by direct methods and refined to R 1 = 0.052 using X-ray diffraction data collected from a crystal twi…
Self-assembled monolayers of 1-(10-mercaptodecyl)imidazole on Au electrodes were used to bind cobalt “picket fence” porphyrin (cobalt 5,10,15,20-tetrakis(α,α,α,α-2-pivalamidophenyl)porphyrin) to the electrode surface. The binding involved coordination of the cobalt center of the porphyrin to the pendant imidazole grou…
The dynamics of propylene glycol (PG) and its 7-mer have been investigated by quasielastic neutron scattering (QENS). In the case of PG we used two techniques; ordinary QENS and neutron spin-echo (NSE). The QENS and NSE experiments were carried out at the temperature ranges 300–420 K and 260–340 K, respectively. The Q…