(Ba3MTiMO9)-Ti-III-O-V (M-III = Fe, Ga, Y, Lu, M-V = Nb, Ta, Sb) perovskite oxides Synthesis, structure and dielectric properties

We describe the synthesis structures and dielectric properties of new perovskite oxides of the formula (Ba3MTiMO9)-Ti-III-O-V for M-III = Fe Ga Y Lu and M-V = Nb Ta Sb While M-V = Nb and Ta oxides adopt disordered/partially ordered 3C perovskite structures where M-III/Ti/M-V metal-oxygen octahedra are corner connected the M-V = Sb oxides show a distinct preference for the 6H structure where Sb-V/Ti-IV metal-oxygen octahedra share a common face forming (Sb Ti)O-9 dimers that are corner-connected to the (MO6)-O-III octahedra The preference of antimony oxides (Sb-V 4d(10)) for the 6H structure which arises from a special Sb-V-O chemical bonding that tends to avoid linear Sb-O-Sb linkages unlike Nb-V/Ta-V d(0) atoms which prefer similar to 180 degrees Nb/Ta-O-Nb/Ta linkages - is consistent with the crystal chemistry of M-V-O oxides in general The dielectric properties reveal a significant difference among Mill members All the oxides with the 3C structure excepting those with Mill = Fe show a normal low loss dielectric behaviour with epsilon = 20-60 in the temperature range 50-400 degrees C the M-III = Fe members with this structure (M-V = Nb Ta) display a relaxor-like ferroelectric behaviour with large E values at frequencies <= 1 MHz (50-500 degrees C) (C) 2010 Elsevier Masson SAS All rights reserved

Synthesis, structure and ionic conductivity in scheelite type Li(0.5)Ce(0.5-x)Ln(x)MoO(4) (x=0 and 0.25, Ln = Pr, Sm)

Scheelite type solid electrolytes, Li(0.5)Ce(0.5-x)Ln(x)MoO(4) (x = 0 and 0.25, Ln = Pr, Sm) have been synthesized using a solid state method. Their structure and ionic conductivity (a) were obtained by single crystal X-ray diffraction and ac-impedance spectroscopy, respectively. X-ray diffraction studies reveal a space group of I4(1)/a for Li(0.5)Ce(0.5-x)Ln(x)MoO(4) (x = 0 and 0.25, Ln = Pr, Sm) scheelite compounds. The unsubstituted Li0.5Ce0.5MoO4 showed lithium ion conductivity similar to 10(-5)-10(-3) Omega(-1)cm(-1) in the temperature range of 300-700 degrees C (sigma = 2.5 x 10(-3) Omega(-1) cm(-1) at 700 degrees C). The substituted compounds show lower conductivity compared to the unsubstituted compound, with the magnitude of ionic conductivity being two (in the high temperature regime) to one order (in the low temperature regime) lower than the unsubstituted compound. Since these scheelite type structures show significant conductivity, the series of compounds could serve in high temperature lithium battery operations.

Dynamic structure of charge carrier in polyaniline by near-infrared excited resonance Raman spectroscopy

New vibrational Raman features characteristic to the conductive form of polyaniline have been observed with the near-infrared excitation at 1047 nm. Based on an analogy with the resonance Raman spectrum of Michler's ketone in the lowest excited triplet (T-1) state, we consider these features as due to a dynamic structure of a diimino-1,4-phenylene unit in the polyaniline chain exchanging a positive charge very rapidly. This consideration directly leads to a conducting mechanism in which a positive charge migrates from one nitrogen to the other through the conjugated chain of polyaniline.

First total synthesis of (±)-myltayl-4(12)-ene and single-crystal X-ray structure of exo-12-normyltaylan-4-yl 4-nitrobenzoate

The total synthesis of the unusual sesquiterpene (+/-)-myltayl-4(12)-ene 3 starting from the readily available cyclogeraniol 5 and the single-crystal X-ray structure of the 4-nitrobenzoate 12 of the noralcohol 11 are described.

Molecular Dynamics Investigation of Structure and Transport in the K2O-2SiO2 System Using a Partial Charge Based Model Potential

Potassium disilicate glass and melt have been investigated by using a new partial charge based potential model in which nonbridging oxygens are differentiated from bridging oxygens by their charges. The model reproduces the structural data pertaining to the coordination polyhedra around potassium and the various bond angle distributions excellently. The dynamics of the glass has been studied by using space and time correlation functions. It is found that K ions migrate by a diffusive mechanism in the melt and by hops below the glass transition temperature. They are also found to migrate largely through nonbridging oxygenrich sites in the silicate matrix, thus providing support to the predictions of the modified random network model.

Effect of mutations on the p53 IRES RNA structure Implications for de-regulation of the synthesis of p53 isoforms

Earlier we have demonstrated the presence of internal ribosome entry site (IRES) within tumor suppressor p53 mRNA. Here we have mapped the putative secondary structure of p53-IRES RNA using information from chemical probing and nuclease mapping experiments. Additionally, the secondary structure of the IRES element of the wild-type RNA was compared with cancer-derived silent mutant p53 RNAs. These mutations might result in the conformational alterations of p53-IRES RNAs. The results also indicate decreased IRES activities of the mutants as compared to wild-type RNA. Further, it was observed that some of the cytoplasmic trans-acting factors, critical for enhancing IRES function, were unable to bind mutant RNAs as efficiently as to wild-type. Our results suggest that hnRNP C1/C2 binds to p53-IRES and siRNA mediated partial silencing of hnRNP C1/C2 showed appreciable decrease in IRES function and consequent decrease in the level of the corresponding p53 isoform. Interestingly mutant p53 IRES showed lesser binding with hnRNP C1/C2 protein. Finally, upon doxorubicin treatment, the mutant RNAs were unable to show enhanced p53 synthesis to similar extent compared to wild type. Taken together, these observations suggest that mutations occurring in the p53 IRES might have profound implications for de-regulation of its expression and activity.

Molecular dynamics Investigation of structure and transport in the K2O-2SiO2 system using a partial charge based model potential

Potassium disilicate glass and melt have been investigated by using anew partial charge based potential model in which nonbridging oxygens are differentiated from bridging oxygens by their charges. The model reproduces the structural data pertaining to the coordination polyhedra around potassium and the various bond angle distributions excellently. The dynamics of the glass has been studied by using space and time correlation functions. It is found that K ions migrate by a diffusive mechanism in the melt and by hops below the glass transition temperature. They are also found to migrate largely through nonbridging oxygen-rich sites in the silicate matrix, thus providing support to the predictions of the modified random network model.

Photobehavior of crystalline 4-styrylcoumarin dimorphs: structure-reactivity correlations

4-Styrylcoumarin crystallizes from chloroform and hexane mixture in two morphologically different modifications. The monoclinic form (needles, P2(1)/c) undergoes stereospecific photodimerization producing anti head-to-tail dimer across pyrone double bond, whereas the triclinic modification (prisms, P ($) over bar 1) dimerizes yielding photodimer of the same configuration, but across styrenic double bond. Single crystal X-ray analyses of the dimorphs reveal the packing differences permitting rationalization of the regio- and stereochemistry of the photoproducts. The significantly low dimer yield from the prismatic crystals is rationalized.

Substrate-dependent structure, microstructure, composition and properties of nanostructured TiN films

Titanium nitride films of a thickness of similar to 1.5 mu m were deposited on amorphous and crystalline substrates by DC reactive magnetron sputtering at ambient temperature with 100% nitrogen in the sputter gas. The growth of nanostructured, i.e. crystalline nano-grain sized, films at ambient temperature is demonstrated. The microstructure of the films grown on crystalline substrates reveals a larger grain size/crystallite size than that of the films deposited on amorphous substrates. Specular reflectance measurements on films deposited on different substrates indicate that the position of the Ti-N 2s band at 2.33 eV is substrate-dependent, indicating substrate-mediated stoichiometry. This clearly demonstrates that not only structure and microstructure, but also chemical composition of the films is substrate-influenced. The films deposited on amorphous substrates display lower hardness and modulus values than the films deposited on crystalline substrates, with the highest value of hardness being 19 GPa on a lanthanum aluminate substrate. (C) 2011 Elsevier Ltd. All rights reserved.

Structure-Activity Relationship of Photocytotoxic Iron(III) Complexes of Modified Dipyridophenazine Ligands

Iron(III) complexes FeL(B)] (1-5) of a tetradentate trianionic phenolate-based ligand (L) and modified dipyridophenazine bases (B), namely, dipyrido-6,7,8,9-tetrahydrophenazine (dpqC in 1), dipyrido3,2-a:2',3'-c]phenazine-2-carboxylic acid (dppzc in 2), dipyrido3,2-a:2',3'-c]phenazine-11-sulfonic acid (dppzs in 3), 7-aminodipyrido3,2-a:2',3'-c]phenazine (dppza in 4) and benzoi]dipyridro3,2-a:2',3'-c]phenazine (dppn in 5), have been synthesized, and their photocytotoxic properties studied along with their dipyridophenazine analogue (6). The complexes have a five. electron paramagnetic iron(III) center, and the Fe(III)/Fe(II) redox couple appears at about 0.69 V versus SCE in DMF-0.1 M TBAP. The physicochemical data also suggest that the complexes possess similar structural features as that of its parent complex FeL(dppz)] with FeO3N3 coordination in a distorted octahedral geometry. The DNA-complex and protein-complex interaction studies have revealed that the complexes interact favorably with the biomolecules, the degree of which depends on the nature of the substituents present on the dipyridophenazine ring. Photocleavage Of pUC19 DNA by the complexes has been studied using visible light of 476, 530, and 647 nm wavelengths. Mechanistic investigations with inhibitors show formation of HO center dot radicals via a photoredox pathway. Photocytotoxicity study of the complexes in HeLa cells has shown that the dppn complex (5) is highly active in causing cell death in visible light with sub micromolar IC50 value. The effect of substitutions and the planarity of the phenazine moiety on the cellular uptake are quantified by determining the total Cellular iron content using the inductively coupled plasma-optical emission spectrometry (ICP-OES) technique. The cellular uptake increases marginally with an increase in the hydrophobicity of the dipyridophenazine ligands whereas complex 3 with dppzs shows very high uptake. Insights into the cell death mechanism by the dppn complex 5, obtained through DAFT nuclear staining in HeLa cells, reveal a rapid programmed cell death mechanism following photoactivation of complex 5 with visible light. The effect of substituent on the DNA photocleavage activity of the complexes has been rationalized from the theoretical studies.

Soft-chemical routes to synthesis of solid oxide materials

We describe three different families of metal oxides, viz., (i) protonated layered perovskites, (ii) framework phosphates of NASICON and KTiOPO4 (KTP) structures and (iii) layered and three-dimensional oxides in the H-V-W-O system, synthesized by 'soft-chemical' routes involving respectively ion-exchange, redox deinteracalation and acid-leaching from appropriate parent oxides. Oxides of the first family, HyA2B3O10(A = La/Ca; B = Ti/Nb), exhibit variable Bronsted acidity and intercalation behaviour that depend on the interlayer structure. V2(PO4)3 prepared by oxidative deintercalation from Na3V2(PO4)3 is a new host material exhibiting reductive insertion of lithium/hydrogen, while K0.5Nb0.5 M0.5OPO4(M = Ti, V) are novel KTP-like materials exhibiting second harmonic generation of 1064 nm radiation. HxVxW1-xO3 for x = 0.125 and 0.33 possessing alpha-MoO3 and hexagonal WO3 structures, prepared by acid-leaching of LiVWO6, represent functionalized oxide materials exhibiting redox and acid-base intercalation reactivity.

Soft chemical synthesis of new layered and three-dimensional oxide hydrates, hxVxW1-xO3×yH2O, related to WO3×2 H2O and WO3. times.1/3 H2O

Two new vanadium-tungsten oxide hydrates of the formulas, H0.125V0.125W0.875O3.1.5H2O (I) and Ho.33V0.33W0.67O3.1/3H2O (II), have been synthesized by acid-leaching of LiVWO6 with aqueous HNO3/HCl. While phase I obtained by treatment of LiVWO6 with dilute HNO3/HCl possesses an orthorhombic structure (a = 7.77(3), b = 13.87(6), c = 7.44(3) angstrom) related to WO3.2H2O, phase II, prepared by refluxing LiVWO6 with concentrated HNO3, is isostructural with WO3.1/3H2O. Dehydration of II around 330-degrees-C yields a hexagonal phase (III, a = 7.25(4), c = 7.74(3) angstrom) isotypic with hexagonal WO3. Both land III exhibit redox and acid-base intercalation reactivity characteristic of layered and tunnel structures.

Structure and stability of human telomeric sequence

Telomeric DNA of a variety of vertebrates including humans contains the tandem repeat d(TTAGGG)(n). We have investigated the structural properties of the human telomeric repeat oligonucleotide models d(T(2)AG(3))(4), d(G(3)T(2)A)(3)G(3), and d(G(3)T(2)AG(3)) using CD, gel electrophoresis, and chemical probing techniques. The sequences d(G(3)T(2)A)(3)G(3) and d(T(2)AG(3))(4) assume an antiparallel G quartet structure by intramolecular folding, while the sequence d(G(3)T(2)AG(3)) also adopts an antiparallel G quartet structure but by dimerization of hairpins. In all the above cases, adenines are in the loop. The TTA loops are oriented at the same end of the G tetrad stem in the case of hairpin dimer. Further, the oligonucleotide D(G(3)T(2)AG(3)) forms a higher order structure by the association of two hairpin dimers via stacking of G tetrad planes. Here we show that N-7 of adenine in the hairpin dimer is Hoogsteen hydrogen-bonded. The partial reactivity of loop adenines with DEPC in d(T(2)AG(3))(4) suggests that the intramolecular G quartet structure is highly polymorphic and structures with different loop orientations and topologies are formed in solution. Intra- and interloop hydrogen bonding schemes for the TTA loops are proposed to account for the observed diethyl pyrocarbonate reactivities of adenines. Sodium-induced G quartet structures differ from their potassium-induced counterparts not only in stability but also in loop conformation and interactions. Thus, the overall structure and stability of telomeric sequences are modulated by the cation present, loop sequence, and the number of G tracts, which might be important for the telomere function.

Synthesis, Crystal Structure, and Magnetic Properties of a Ferromagnetically Coupled Angular Trinuclear Copper(11) Complex [Cu3(02CMe)4(bpy)s(HzO)](PF)62

The synthesis, X-ray crystal structure, and magnetic properties of an angular trinuclear copper(II) complex [Cu3(O2CMC)4(bpy)3(H2O)](PF6)2 (1), obtained from a reaction of Cu2(O2CMe)4(H2O)2 With 2,2'-bipyridine (bpy) and NH4PF6 in ethanol, are reported. Complex 1 crystallizes in triclinic space group P1BAR with a = 11.529(1) angstrom, b = 12.121(2) angstrom, c = 17.153(2) angstrom, alpha = 82.01(1)-degrees, beta = 79.42(1)-degrees, gamma = 89.62(1)-degrees, and Z = 2. A total of 6928 data with I > 2.5sigma(I) were refined to R = 0.0441 and R(w) = 0.0557. The structure consists of a trinuclear core bridged by four acetate ligands showing different bonding modes. The coordination geometry at each copper is distorted square-pyramidal with a CuN2O2...O chromophore. The Cu...Cu distances are 3.198(1) angstrom, 4.568(1) angstrom, and 6.277(1) angstrom. There are two monoatomic acetate bridges showing Cu-O-Cu angles of 93.1(1) and 97.5(1)-degrees. Magnetic studies in the temperature range 39-297 K show the presence of a strong ferromagnetically coupled dicopper(II) unit (2J = +158 cm-1) and an essentially isolated copper(II) center (2J' = -0.4 cm-1) in 1. The EPR spectra display an axial spectrum giving g(parallel-to) = 2.28 (A(parallel-to) = 160 X 10(-4) cm-1) and g(perpendicular-to) = 2.06 (A(perpendicular-to) = 12 X 10(-4) cm-1) for the normal copper and two intense isotropic signals with g values 2.70 and 1.74 for the strongly coupled copper pair. The structural features of 1 compare well with the first generation models for ascorbate oxidase.