Magnetic frustration and dielectric relaxation in insulating Nd2NiMnO6 double perovskites

We have investigated structural, dielectric, and magnetic properties of polycrystalline double perovskite Nd2NiMnO6 compound. The compound crystallizes in monoclinic P2(1)/n symmetry and is partially B-site disordered depending on the synthesis conditions. It undergoes second-order ferromagnetic transition at 192K and shows glassy behaviour at low temperature. The glassy phase is due to anti-site disorder within the homogeneous sample. Temperature and frequency dependent dielectric measurements reveal colossal values of dielectric constant and is best interpreted using Maxwell-Wagner interfacial polarization model. Impedance spectroscopy has been used to analyse the intrinsic dielectric response. This enabled us to differentiate the conduction process at the grain and grain boundaries. Arrhenius behaviour is favoured at the grain boundary, while variable range hopping mechanism is considered most suitable within the grain region. dc conductivity measurements corroborate variable range hopping conduction. (C) 2015 AIP Publishing LLC.

Remarkable visible light-triggered cytotoxicity of mitochondria targeting mixed-ligand cobalt(III) complexes of curcumin and phenanthroline bases binding to human serum albumin

Six new mixed-ligand cobalt(III) complexes of formulation Co(N-N)(2)(O-O)](ClO4)(2) (1-6), where N-N is a N,N-donor phenanthroline base, namely, 1,10-phenanthroline (phen in 1, 2), dipyrido3,2-d:2',3'-f] quinoxaline (dpq in 3, 4), and dipyrido3,2-a:2',3'-c]phenazine (dppz in 5, 6), O-O is acetylacetonate (acac in 1, 3, 5) or curcumin (bis(4-hydroxy-3-methoxyphenyl)-1,6-diene-3,5-dione, cur in 2, 4, 6), have been synthesized and characterized. The X-ray crystal structures of complex 1 (as PF6- salt, 1a) and 3 show distorted octahedral geometries formed by the CoN4O2 core. The complexes 1, 3 and 5 having the simple acac ligand are prepared as control species to understand the role of curcumin. The optimized geometries and the frontier orbitals of the curcumin complexes 2, 4, and 6 are obtained from the DFT calculations. The complexes 2, 4, and 6 having the photoactive curcumin moiety display an absorption band in the visible region near 420 nm and show remarkable photocytotoxicity in HeLa cancer cells with respective IC50 values of 7.4 mu M, 5.1 mu M and 1.6 mu M while being much less toxic in dark. MTT assay using complex 6 shows that it is not significantly photocytotoxic to MCF-10A normal cells. The control complexes having the acac ligand are non-toxic both in the presence and absence of light. The cell death is apoptotic in nature and triggered by the photogeneration of reactive oxygen species. Fluorescence imaging experiments on HeLa cells reveals that complex 6 accumulated primarily inside the mitochondria. Human serum albumin (HSA) binding experiments show that the complexes bind HSA with good affinity, but 6 binds with the highest affinity, with a K-b value of 9.8 x 10(5) M-1. Thus, complex 6 with its negligible toxicity in the dark and in normal cells but remarkable toxicity in visible light holds significant photochemotherapeutic potential.

Remarkable enhancement in photocytotoxicity and hydrolytic stability of curcumin on binding to an oxovanadium(IV) moiety

Oxovanadium(IV) complexes of polypyridyl and curcumin-based ligands, viz. VO(cur)(L)Cl] (1, 2) and VO(scur)(L)Cl] (3, 4), where L is 1,10-phenanthroline (phen in 1 and 3), dipyrido3,2-a:2',3'-c]phenazine (dppz in 2 and 4), Hcur is curcumin and Hscur is diglucosylcurcumin, were synthesized and characterized and their cellular uptake, photocytotoxicity, intracellular localization, DNA binding, and DNA photo-cleavage activity studied. Complex VO(cur)(phen)Cl] (1) has (VN2O3Cl)-N-IV distorted octahedral geometry as evidenced from its crystal structure. The sugar appended complexes show significantly higher uptake into the cancer cells compared to their normal analogues. The complexes are remarkably photocytotoxic in visible light (400-700 nm) giving an IC50 value of <5 mu M in HeLa, HaCaT and MCF-7 cells with no significant dark toxicity. The green emission of the complexes was used for cellular imaging. Predominant cytosolic localization of the complexes 1-4 to a lesser extent into the nucleus was evidenced from confocal imaging. The complexes as strong binders of calf thymus DNA displayed photocleavage of supercoiled pUC19 DNA in red light by generating (OH)-O-center dot radicals as the ROS. The cell death is via an apoptotic pathway involving the ROS. Binding to the VO2+ moiety has resulted in stability against any hydrolytic degradation of curcumin along with an enhancement of its photocytotoxicity.

A transmission electron microscopy and X-ray photoelectron spectroscopy study of annealing induced gamma-phase nucleation, clustering, and interfacial dynamics in reactively sputtered amorphous alumina thin films

Pure alpha-Al2O3 exhibits a very high degree of thermodynamical stability among all metal oxides and forms an inert oxide scale in a range of structural alloys at high temperatures. We report that amorphous Al2O3 thin films sputter deposited over crystalline Si instead show a surprisingly active interface. On annealing, crystallization begins with nuclei of a phase closely resembling gamma-Alumina forming almost randomly in an amorphous matrix, and with increasing frequency near the substrate/film interface. This nucleation is marked by the signature appearance of sharp (400) and (440) reflections and the formation of a diffuse diffraction halo with an outer maximal radius of approximate to 0.23 nm enveloping the direct beam. The microstructure then evolves by a cluster-coalescence growth mechanism suggestive of swift nucleation and sluggish diffusional kinetics, while locally the Al ions redistribute slowly from chemisorbed and tetrahedral sites to higher anion coordinated sites. Chemical state plots constructed from XPS data and simple calculations of the diffraction patterns from hypothetically distorted lattices suggest that the true origins of the diffuse diffraction halo are probably related to a complex change in the electronic structure spurred by the a-gamma transformation rather than pure structural disorder. Concurrent to crystallization within the film, a substantially thick interfacial reaction zone also builds up at the film/substrate interface with the excess Al acting as a cationic source. (C) 2015 AIP Publishing LLC.

Evidence for phase transitions and pseudospin phonon coupling in K-0.9(NH4)(0.1)H2AsO4

This work reports a detailed temperature dependent Raman study on the mixed crystals of K-0.9(NH4)(0.1)H2AsO4 (KADA) from 5K to 300K in the spectral range of 60-1200cm(-1), covering tetragonal to orthorhombic structural phase transition accompanied by paraelectric to ferroelectric transition at T-c* similar to 60K. Multiple phase transitions below transition temperature (Tc* similar to 60K) are marked by the appearance of new modes, splitting of existing ones as well as anomalies in the self-energy parameters (i.e. mode frequencies and damping coefficient) of the phonon modes. Temperature independent behaviour of damping coefficient and abrupt jump in the mode frequency of some of the internal vibrations of AsO4 tetrahedra as well as external vibrations clearly signal long range ferroelectric ordering and proton ordering below T-c*. In addition, we observed that temperature dependence of many prominent phonon modes diverges significantly from their normal anharmonic behaviour below T-c* suggesting potential coupling between pseudospins and phonons. (C) 2015 Author(s).

Significant photocytotoxic effect of an iron(III) complex of a Schiff base ligand derived from vitamin B-6 and thiosemicarbazide in visible light

Iron(III)-Schiff base complexes, namely, Fe(tsc-py)(2)](NO3) (1), Fe(tsc-acpy)(2)](NO3) (2) and Fe(tsc-VB6)(2)](NO3) (3), where tsc-py, tsc-acpy and tsc-VB6 are the respective Schiff bases derived from thiosemicarbazide (tsc) and pyridine-2-aldehyde (tsc-py), 2-acetyl pyridine (tsc-acpy) and vitamin B-6 (pyridoxal, tsc-VB6), have been prepared, structurally characterized and their photocytotoxicity studied in cancer HeLa cells. The single crystal X-ray structures of the complexes 1 and 2 show a distorted octahedral geometry formed by the FeN4S2 core. The low-spin and 1 : 1 electrolytic complexes display a broad absorption band in the visible region. Complexes 1 and 2, without any VB6 moiety are not cytotoxic under light or dark conditions. Complex 3 is significantly photocytotoxic under visible light of 400-700 nm giving an IC50 value of 22.5 mu M in HeLa cells with no dark toxicity (IC50 > 100 mu M). The photo-induced cell death is attributable to apoptotic pathways involving photo-assisted generation of intracellular ROS. The observed photocytotoxicity of complex 3 could be the result of its better photosensitizing property combined with its enhanced uptake into cancer cells via a VB6 transporting membrane carrier (VTC) mediated diffusion pathway due to the presence of the VB6 moiety compared to the two non-vitamin B-6 analogues, complexes 1 and 2.

New single-source precursor for bismuth sulfide and its use as low-cost counter electrode material for dye-sensitized solar cells

One new homoleptic Bi(dtc)(3)] (1) (dtc = 4-hydroxypiperdine dithiocarbamate) has been synthesized and characterized by microanalysis, IR, UV-Vis, H-1 and C-13 spectroscopy and X-ray crystallography. The photoluminescence spectrum for the compound in DMSO solution was recorded. The crystal structure of 1 displayed distorted octahedral geometry around the Bi(III) center bonded through sulfur atoms of the dithiocarbamate ligands. TGA indicates that the compound decomposes to a Bi and Bi-S phase system. The Bi and Bi-S obtained from decomposition of the compound have been characterized by pXRD, EDAX and SEM. Solvothermal decomposition of 1 in the absence and presence of two different capping agents yielded three morphologically different Bi2S3 systems which were deployed as counter-electrode in dye-sensitized solar cells (DSSCs). (C) 2015 Elsevier B.V. All rights reserved.

Iron(III) Complexes of a Pyridoxal Schiff Base for Enhanced Cellular Uptake with Selectivity and Remarkable Photocytotoxicity

Iron(III) complexes of pyridoxal (vitamin B6, VB6) or salicylaldehyde Schiff bases and modified dipicolylamines, namely, Fe(B)(L)](NO3) (15), where B is phenyl-N,N-bis((pyridin-2-yl)methyl)methanamine (phbpa in 1), (anthracen-9-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine (anbpa in 2, 4) and (pyren-1-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine (pybpa in 3, 5) (H2L1 is 3-hydroxy-5-(hydroxymethyl)-4-(((2-hydroxyphenyl)imino)methyl)-2-methylp yridine (13) and H2L2 is 2-(2-hydroxyphenyl-imino)methyl]phenol), were prepared and their uptake in cancer cells and photocytotoxicity were studied. Complexes 4 and 5, having a non-pyridoxal Schiff base, were prepared to probe the role of the pyridoxal group in tumor targeting and cellular uptake. The PF6 salt (1a) of complex 1 is structurally characterized. The complexes have a distorted six-coordinate FeN4O2 core where the metal is in the +3 oxidation state with five unpaired electrons. The complexes display a ligand to metal charge transfer band near 520 and 420 nm from phenolate to the iron(III) center. The photophysical properties of the complexes are explained from the time dependent density functional theory calculations. The redox active complexes show a quasi-reversible Fe(III)/Fe(II) response near -0.3 V vs saturated calomel electrode. Complexes 2 and 3 exhibit remarkable photocytotoxicity in various cancer cells with IC50 values ranging from 0.4 to 5 mu M with 10-fold lower dark toxicity. The cell death proceeded by the apoptotic pathway due to generation of reactive oxygen species upon light exposure. The nonvitamin complexes 4 and 5 display 3-fold lower photocytotoxicity compared to their VB6 analogues, possibly due to preferential and faster uptake of the vitamin complexes in the cancer cells. Complexes 2 and 3 show significant uptake in the endoplasmic reticulum, while complexes 4 and 5 are distributed throughout the cells without any specific localization pattern.

Spin-reorientation and weak ferromagnetism in antiferromagnetic TbMn0.5Fe0.5O3

Orthorhombic single crystals of TbMn0.5Fe0.5O3 are found to exhibit spin-reorientation, magnetization reversal, and weak ferromagnetism. Strong anisotropy effects are evident in the temperature dependent magnetization measurements along the three crystallographic axes a, b, and c. A broad magnetic transition is visible at T-N(Fe/Mn) = 286K due to paramagnetic to A(x)G(y)C(z) ordering. A sharp transition is observed at T-SR(Fe/Mn) = 28 K, which is pronounced along c axis in the form of a sharp jump in magnetization where the spins reorient to G(x)A(y)F(z) configuration. The negative magnetization observed below T-SR(Fe/Mn) along c axis is explained in terms of domain wall pinning. A component of weak ferromagnetism is observed in field-scans along c-axis but below 28 K. Field-induced steps-like transitions are observed in hysteresis measurement along b axis below 28 K. It is noted that no sign of Tb-order is discernible down to 2K. TbMn0.5Fe0.5O3 could be highlighted as a potential candidate to evaluate its magneto-dielectric effects across the magnetic transitions. (C) 2015 AIP Publishing LLC.

Investigations on growth, structure, optical properties and laser damage threshold of organic nonlinear optical crystals of Guanidinium L-Ascorbate

Single crystals of Guanidinium L-Ascorbate (GuLA) were grown and crystal structure was determined by direct methods. GuLA crystallizes in orthorhombic, non-centrosymmetric space group P2(1)2(1)2(1). The UV-cutoff was determined as 325 nm. The morphology was generated and the interplanar angles estimated and compared with experimental values. Second harmonic generation conversion efficiency was measured and compared with other salts of L-Ascorbic acid. Surface laser damage threshold was calculated as 11.3GW/cm(2) for a single shot of laser of 1064 nm wavelength.

Effect of Fe doping on the magnetic ordering temperature of ErMnO3

We studied the effect of Fe doping on structural, magnetic, and dielectric properties of hexagonal ErMnO3 system. For 50% doping of Fe on Mn site in ErMnO3 modulated its crystallographic structure from hexagonal to orthorhombic phase. Accompanied with the structural phase transition in ErMnO3, the magnetic properties are effectively modified. The Fe doped samples exhibit enhancement in antiferromagnetic ordering Neel temperature (T-N) from 77K (ErMnO3) to 280K (ErFe0.5Mn0.5O3). The anomalies observed in the dielectric constant around T-N in doped ErMnO3 samples indicate the coupling between electric and magnetic order parameters. (C) 2015 AIP Publishing LLC.

Optical and dielectric study of strontium modified barium zirconium titanate ceramic prepared by high energy ball milling

Strontium modified barium zirconium titanate with general formula Ba1-xSrxZr0.05Ti0.95O3 ceramics have been prepared by solid state and high energy ball milling technique. The X-ray diffraction and Rietveld refinement studies show that all the compositions have single phase symmetry. The composition BaZr0.05Ti0.95O3 shows orthorhombic symmetric with space group Amm2. The structure changes from orthorhombic to tetragonal with strontium doping up to x = 0.3 and with further addition, changes to cubic. The scanning electron micrographs show that the grain size decreases with increase in strontium content. The temperature dependent dielectric behavior shows three phase transition in the parent material which merges with an increase in Sr content The transition temperature and dielectric constant decreases with an increase in Sr concentration. The phase transition becomes more diffused with increment in doping concentration. The ferroelectric behavior of the ceramics is studied by the hysteresis loop. The optical behavior is studied by the UV-visible spectroscopy and found that the optical band gap increases with Sr concentration. (C) 2015 Elsevier B.V. All rights reserved.

One pot auto-ignition based synthesis of novel Sr2CeO4: Ho3+ nanophosphor for photoluminescent applications

Ho3+ (0.25-7 mol%) doped Sr2CeO4 nanophosphors were synthesized by solution combustion method using urea as fuel. The structural properties of the nanophosphors were investigated by powder X-ray diffraction studies (PXRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. UV-Visible and photoluminescence (PL) spectroscopic techniques were used for analysing the optical properties of the nanoparticles. PXRD and TEM results revealed the formation of Sr2CeO4: Ho3+ nanocrystalline particles with orthorhombic crystal structure. From the UV-Vis studies the optical band gap energy found to decrease from 5.9 to 5.74 eV with increase in dopant concentration. The PL spectra exhibit the broad excitation band from 200 to 400 nm which concurs well with the commercial near UV LED. The PL spectra vary with the dopant content due to energy transfer from the host to the activator. In this present work we demonstrate that color tuning of phosphor can be achieved by merely varying the Ho3+ ions concentration. The CIE and CCT chromaticity coordinates suggests Sr2CeO4: Ho3+ nanophosphors may be potentially applicable as promising single - phased phosphors for lighting applications. (C) 2015 Elsevier B.V. All rights reserved.

New symmetrical dinucleating ligand based assembly of bridged dicopper(II) and dizinc(II) centers: Synthesis, structure, spectroscopy, magnetic properties and glycoside hydrolysis

Two dinuclear copper(II) complexes Li(H2O)(3)(CH3OH)](4)Cu2Br4]Cu-2(cpdp)(mu-O2CCH3)](4)(OH)(2) (1), Cu (H2O)(4)]Cu-2(cpdp)(mu-O2CC6H5)](2)Cl-2 center dot 5H(2)O (2), and a dinuclear zinc(II) complex Zn-2(cpdp)(mu-O2CCH3)] (3) have been synthesized using pyridine and benzoate functionality based new symmetrical dinucleating ligand, N, N'-Bis2-carboxybenzomethyl]-N, N'-Bis2-pyridylmethyl]-1,3-diaminopropan-2-ol (H(3)cpdp). Complexes 1, 2 and 3 have been synthesized by carrying out reaction of the ligand H3cpdp with stoichiometric amounts of Cu-2(O2CCH3)(4)(H2O)(2)], CuCl2 center dot 2H(2)O/C6H5COONa, and Zn(CH3COO)(2)center dot 2H(2)O, respectively, in methanol in the presence of NaOH at ambient temperature. Characterizations of the complexes have been done using various analytical techniques including single crystal X-ray structure determination. The X-ray crystal structure analyses reveal that the copper(II) ions in complexes 1 and 2 are in a distorted square pyramidal geometry with Cu-Cu separation of 3.455(8) angstrom and 3.492(1)angstrom, respectively. The DFT optimized structure of complex 3 indicates that two zinc(II) ions are in a distorted square pyramidal geometry with Zn-Zn separation of 3.492(8)angstrom. UV-Vis and mass spectrometric analyses of the complexes confirm their dimeric nature in solution. Furthermore, H-1 and C-13 NMR spectroscopic investigations authenticate the integrity of complex 3 in solution. Variable-temperature (2-300 K) magnetic susceptibility measurements show the presence of antiferromagnetic interactions between the copper centers, with J = -26.0 cm(-1) and -23.9 cm(-1) ((H) over cap = -2JS(1)S(2)) in complexes 1 and 2, respectively. In addition, glycosidase-like activity of the complexes has been investigated in aqueous solution at pH similar to 10.5 by UV-Vis spectrophotometric technique using p-nitrophenyl-alpha-D-glucopyranoside (4) and p-nitrophenyl-beta-D-glucopyranoside (5) as model substrates. (C) 2015 Elsevier B.V. All rights reserved.

Comparative high pressure Raman studies on perfluorohexane and perfluoroheptane

High pressure Raman spectroscopic studies on perfluorohexane and perfluoroheptane have performed up to 12 GPa. Perfluorohexane under goes two pressure induced transitions: (1) liquid-solid transition at 1.6 GPa and (2) solid-solid transition at 8.2 GPa. On the contrary, perfluoroheptane under goes three phase transitions, they are as follows: (1) liquid-solid transition at 1.3 GPa, (2) intermediate solid I transition at 3 GPa, (3) solid II transition at 7 GPa. The change in slope (d omega/dP) shows that the solid I transition at 3.0 GPa could be the conversion of mid-gauche defect into trans conformers for perfluoroheptane. The pressure induced Raman spectra and the behavior of individual band with pressure shows that the solid phase comprises more than one conformer beyond crystallization. The intensity ratio for both the compounds shows that the high pressure phase beyond 8.2 and 7.0 GPa tends to have close packing with distorted all-trans conformers. (C) 2015 Elsevier B.V. All rights reserved.