Frequency and Temperature-Independent Electrical Transport Properties of 2BaO-0.5Na(2)O-2.5Nb(2)O(5)-4.5B(2)O(3) Glass-Ceramics

The temperature (300-973K) and frequency (100Hz-10MHz) response of the dielectric and impedance characteristics of 2BaO-0.5Na(2)O-2.5Nb(2)O(5)-4.5B(2)O(3) glasses and glass nanocrystal composites were studied. The dielectric constant of the glass was found to be almost independent of frequency (100Hz-10MHz) and temperature (300-600K). The temperature coefficient of dielectric constant was 8 +/- 3ppm/K in the 300-600K temperature range. The relaxation and conduction phenomena were rationalized using modulus formalism and universal AC conductivity exponential power law, respectively. The observed relaxation behavior was found to be thermally activated. The complex impedance data were fitted using the least square method. Dispersion of Barium Sodium Niobate (BNN) phase at nanoscale in a glass matrix resulted in the formation of space charge around crystal-glass interface, leading to a high value of effective dielectric constant especially for the samples heat-treated at higher temperatures. The fabricated glass nanocrystal composites exhibited P versus E hysteresis loops at room temperature and the remnant polarization (P-r) increased with the increase in crystallite size.

The key role of polymer grafted nanoparticles in the phase miscibility of an LCST mixture

Blends of bromo-terminated polystyrene (PS-Br) and poly(vinyl methylether) (PVME) exhibit lower critical solution temperatures. In this study, PS-Br was designed by atom transfer radical polymerization and was converted to thiol-capped polystyrene (PS-SH) by reacting with thiourea. The silver nanoparticles (nAg) were then decorated with covalently bound PS-SH macromolecules to improve the phase miscibility in the PS-Br-PVME blends. Thermally induced demixing in this model blend was followed in the presence of polystyrene immobilized silver nanoparticles (PS-g-nAg). The graft density of the PS macromolecules was estimated to be ca. 0.78 chains per nm(2). Although the matrix and the grafted molecular weights were similar, PS-g-nAg particles were expelled from the PS phase and were localized in the PVME phase of the blends. This was addressed with respect to intermediate graft density and favourable PS-PVME contacts from microscopic interactions point of view. Interestingly, blends with 0.5 wt% PS-g-nAg delayed the spinodal decomposition temperature in the blends by ca. 18 degrees C with respect to the control blends. The scale of cooperativity, as determined by differential scanning calorimetry, increased only marginally in the case of PS-g-nAg; however, it increased significantly in the presence of bare nAg particles.

Synthesis of Eu3+-activated BiOF and BiOBr phosphors: photoluminescence, Judd-Ofelt analysis and photocatalytic properties

A series of Bi1-xEuxOX (X = F and Br; x = 0, 0.01, 0.03 and 0.05) phosphors were synthesized at relatively low temperature and short duration (500 degrees C, 1 h). Rietveld refinement results verified that all the compounds were crystallized in the tetragonal structure with space group P4/nmm (no. 129). Photoluminescence spectra exhibit characteristic luminescence D-5(0) -> F-7(J) (J = 0-4) intra-4f shell Eu3+ ion transitions. The magnetic dipole (D-5(0) -> F-7(1)) transition dominates the emission of BiOF:Eu3+, while the electric dipole (D-5(0) -> F-7(2)) peak was stronger in BiOBr:Eu3+ phosphors. The evaluated CIE color coordinates for Bi0.95Eu0.05OBr (0.632, 0.358) are close to the commercial Y2O3:Eu3+ (0.645, 0.347) and Y2O2S:Eu3+ (0.647, 0.343) red phosphors. Intensity parameters (Omega(2), Omega(4)) and various radiative properties such as transition rates (A), branching ratios (beta), stimulated emission cross-section (sigma(e)), gain bandwidth (sigma(e) x Delta lambda(eff)) and optical gain (sigma(e) x tau) were calculated using the Judd-Ofelt theory. It was observed that BiOBr:Eu3+ phosphors have a long lifetime (tau) and better optical gain (sigma(e) x tau) as compared to reported Eu3+ doped materials. Furthermore, these compounds exhibit excellent photocatalytic activity for the degradation of rhodamine B dye under visible light irradiation. The determined radiative properties and photocatalytic results revealed that BiOBr:Eu3+ phosphors have potential applications in energy and environmental remedies, such as to develop red phosphors for white light-emitting diodes, red lasers and to remove toxic organic industrial effluents.

Synthesis, X-ray structure and in vitro cytotoxicity studies of Cu(I/II) complexes of thiosemicarbazone: special emphasis on their interactions with DNA

4-(p-X-phenyl)thiosemicarbazone of napthaldehyde {where X = Cl (HL1) and X = Br (HL2)}, thiosemicarbazone of quinoline-2-carbaldehyde (HL3) and 4-(p-fluorophenyl) thiosemicarbazone of salicylaldehyde (H2L4) and their copper(I) {Cu(HL1)(PPh3)(2)Br]center dot CH3CN (1) and Cu(HL2)(PPh3)(2)Cl]center dot DMSO (2)} and copper(II) {((Cu2L2Cl)-Cl-3)(2)(mu-Cl)(2)]center dot 2H(2)O (3) and Cu(L-4)(Py)] (4)} complexes are reported herein. The synthesized ligands and their copper complexes were successfully characterized by elemental analysis, cyclic voltammetry, NMR, ESI-MS, IR and UV-Vis spectroscopy. Molecular structures of all the Cu(I) and Cu(II) complexes have been determined by X-ray crystallography. All the complexes (1-4) were tested for their ability to exhibit DNA-binding and - cleavage activity. The complexes effectively interact with CT-DNA possibly by groove binding mode, with binding constants ranging from 10(4) to 10(5) M-1. Among the complexes, 3 shows the highest chemical (60%) as well as photo-induced (80%) DNA cleavage activity against pUC19 DNA. Finally, the in vitro antiproliferative activity of all the complexes was assayed against the HeLa cell line. Some of the complexes have proved to be as active as the clinical referred drugs, and the greater potency of 3 may be correlated with its aqueous solubility and the presence of the quinonoidal group in the thiosemicarbazone ligand coordinated to the metal.

First hyperpolarizability of Ru-half-sandwich complexes: The effect of halogen atom substitution on the ancillary ligand

The first hyperpolarizability (beta) of a series of half-sandwich Ru complexes with a mercaptobenzothiazole ligand bearing a halogen atom substitution in the para-position has been investigated by hyper-Rayleigh scattering and quantum chemical calculations. The heterocyclic ligand with a bromine atom in the para position makes it a very good donor and charge flows to the Ru center enhancing the beta value of the complex by a factor of 2 compared to the complex with the ligand without the halogen substitution. The resonance (+R) and the inductive (-I) effects exerted by the halogen atom in the para position push electrons in opposing directions in the complex. For the Br and Cl atoms the resonance effect dominates which enables the ligand to donate electrons to the metal center thereby increasing the hyperpolarizability whereas for the fluorine atom, the inductive effect is dominant which reduces the charge flow to the metal and the hyperpolarizability drops even below that of the unsubstituted ligand. This unprecedented halogen atom effect on beta of metal complexes is reported. (C) 2015 Elsevier By. All rights reserved.

Dynamics of the chemical bond: inter- and intra-molecular hydrogen bond

In this discussion, we show that a static definition of a `bond' is not viable by looking at a few examples for both inter-and intra-molecular hydrogen bonding. This follows from our earlier work (Goswami and Arunan, Phys. Chem. Chem. Phys. 2009, 11, 8974) which showed a practical way to differentiate `hydrogen bonding' from `van der Waals interaction'. We report results from ab initio and atoms in molecules theoretical calculations for a series of Rg center dot center dot center dot HX complexes (Rg = He/Ne/Ar and X = F/Cl/Br) and ethane-1,2-diol. Results for the Rg center dot center dot center dot HX/DX complexes show that Rg center dot center dot center dot DX could have a `deuterium bond' even when Rg center dot center dot center dot HX is not `hydrogen bonded', according to the practical criterion given by Goswami and Arunan. Results for ethane-1,2-diol show that an `intra-molecular hydrogen bond' can appear during a normal mode vibration which is dominated by the O center dot center dot center dot O stretching, though a `bond' is not found in the equilibrium structure. This dynamical `bond' formation may nevertheless be important in ensuring the continuity of electron density across a molecule. In the former case, a vibration `breaks' an existing bond and in the later case, a vibration leads to `bond' formation. In both cases, the molecule/complex stays bound irrespective of what happens to this `hydrogen bond'. Both these cases push the borders on the recent IUPAC recommendation on hydrogen bonding (Arunan et al. Pure. Appl. Chem. 2011, 83 1637) and justify the inclusive nature of the definition.

Solid state structure of p-bromo phenyl 4,5,7-tri-O-benzyl-beta-D-glycero-D-talo-septanoside and an analysis of non-covalent interactions

The solid state structure of a new seven-membered sugar oxepane derivative, namely, p-bromo phenyl 4,5,7-tri-O-benzyl-beta-D-glycero-D-talo-septanoside is discussed, as determined through single crystal X-ray structural determination and in relation to their conformational features. The molecule adopts twist-chair as the preferred conformation, with conformational descriptor (TC2,3)-T-0,1. The solid state packing of molecules is governed by a rich network of non-covalent bonding originating from O-H center dot center dot center dot O, C-H center dot center dot center dot pi, C-H center dot center dot center dot Br and aromatic pi center dot center dot center dot pi interactions that stabilize the packing of molecules in the crystal. (C) 2015 Elsevier Ltd. All rights reserved.

Halogen bonds in some dihalogenated phenols: applications to crystal engineering

3,4-Dichlorophenol (1) crystallizes in the tetragonal space group I4(1)/a with a short axis of 3.7926 (9) angstrom. The structure is unique in that both type I and type II Cl.....Cl interactions are present, these contact types being distinguished by the angle ranges of the respective C-Cl....Cl angles. The present study shows that these two types of contacts are utterly different. The crystal structures of 4-bromo-3-chlorophenol (2) and 3-bromo-4-chlorophenol (3) have been determined. The crystal structure of (2) is isomorphous to that of (1) with the Br atom in the 4-position participating in a type II interaction. However, the monoclinic P2(1)/c packing of compound (3) is different; while the structure still has O-H....O hydrogen bonds, the tetramer O-H.....O synthon seen in (1) and (2) is not seen. Rather than a type I Br....Br interaction which would have been mandated if (3) were isomorphous to (1) and (2), Br forms a Br....O contact wherein its electrophilic character is clearly evident. Crystal structures of the related compounds 4-chloro-3-iodophenol (4) and 3,5-dibromophenol (5) were also determined. A computational survey of the structural landscape was undertaken for (1), (2) and (3), using a crystal structure prediction protocol in space groups P2(1)/c and I4(1)/a with the COMPASS26 force field. While both tetragonal and monoclinic structures are energetically reasonable for all compounds, the fact that (3) takes the latter structure indicates that Br prefers type II over type I contacts. In order to differentiate further between type I and type II halogen contacts, which being chemically distinct are expected to have different distance fall-off properties, a variable-temperature crystallography study was performed on compounds (1), (2) and (4). Length variations with temperature are greater for type II contacts compared with type I. The type II Br....Br interaction in (2) is stronger than the corresponding type II Cl....Cl interaction in (1), leading to elastic bending of the former upon application of mechanical stress, which contrasts with the plastic deformation of (1). The observation of elastic deformation in (2) is noteworthy; in that it finds an explanation based on the strengths of the respective halogen bonds, it could also be taken as a good starting model for future property design. Cl/Br isostructurality is studied with the Cambridge Structural Database and it is indicated that this isostructurality is based on shape and size similarity of Cl and Br, rather than arising from any chemical resemblance.

Role of spacer length in interaction between novel gemini imidazolium surfactants and Rhizopus oryzae lipase

An insight into the effects of new ionic liquid-type gemini imidazolium cationic surfactants on the structure and function of the lipases is of prime importance for their potential application. Changes in the activity, stability and structure of Rhizopus ouzae lipase in the presence of novel gemini surfactants, C-16-3-C(16)im]Br-2 and C-16-12-C(16)im]Br-2 were probed in the present study. Surfactant with shorter spacer length, C-16-3-C(i6)im]Br-2 was found to be better in improving the hydrolytic activity and thermal stability of the lipase. For both the surfactants, activation was concentration dependent. CD spectroscopy results showed a decrease in a-helix and an increase in beta-sheet content in the presence of these surfactants. A higher structural change observed in presence of C-16-12-C(16)im]Br-2 correlated with lower enzyme activity. Isothermal titration calorimetric studies showed the binding to be spontaneous in nature based on sequential two site binding model. The forces involved in binding were found to differ for the two surfactants proving that the spacer length is an important factor which governs the interaction. These surfactants could be used as promising components both in enzyme modification and media engineering for attaining the desired goals in biocatalytic reactions. (C) 2015 Elsevier B.V. All rights reserved.

Influence of the upwelling events on the delta C-13 and delta O-18 of the benthic bivalve shells of the South Western Continental Margin of India

In this study, the influence of the spatial and temporal variability of upwelling intensity and the associated biological productivity observed during different phases of summer monsoon along the southwestern continental margin of India (SWCMI) on the delta C-13 and delta O-18 of the inorganic biogenic carbonate shells was investigated. Multispecies benthic bivalve shells (1-5 mm) separated from ten surface sediment samples of SWCMI (off 12 degrees N, 10 degrees N and 9 degrees N) collected during the onset (OSM) and peak (PSM) phase of the summer monsoon of 2009 were analysed for delta C-13 and delta O-18. Sea surface temperature along the study region indicates prominent upwelling in PSM than in OSM. A comparison of analytical and predicted values for delta O-18 in the bivalve shells confirmed their in situ origin during both the sampling periods. During PSM, the delta C-13 values in the benthic bivalve shells were more depleted in C-13 than during OSM which recorded lower values of delta C-13 in dissolved inorganic carbon of bottom waters expected in the study region in PSM due to the upwelled waters, high surface productivity and the associated high degradation of the organic matter in the subsurface and bottom waters. However, this depletion of delta C-13 was not observed in benthic bivalve shells obtained from 10 degrees N, since it is influenced by high export fluxes of carbon from the Cochin estuary since early monsoon months.

Dual Drug Conjugate Loaded Nanoparticles for the Treatment of Cancer

Two antineoplastic agents, Imatinib (IM) and 5-Fluorouracil (FU) were conjugated by hydrolysable linkers through an amide bond and entrapped in polymeric Human Serum Albumin (HSA) nanoparticles. The presence of dual drugs in a common carrier has the advantage of reaching the site of action simultaneously and acting at different phases of the cell cycle to arrest the growth of cancer cells before they develop chemoresistance. The study has demonstrated an enhanced anticancer activity of the conjugate, and conjugate loaded stealth HSA nanoparticles (NPs) in comparison to the free drug in A-549 human lung carcinoma cell line and Zebra fish embryos (Danio rerio). Hydrolysability of the conjugate has also been demonstrated with complete hydrolysis being observed after 12 h. In vivo pharmacodynamics study in terms of tumor volume and pharmacokinetics in mice for conjugate (IM-SC-FU) and conjugate loaded nanoparticles showed significant anti-cancer activity. The other parameters evaluated were particle size (86nm), Poly Dispersive Index (PDI) (0.209), zeta potential (-49mV), drug entrapment efficiency (96.73%) and drug loading efficiency (89%). Being in stealth mode gives the potential for the NPs to evade Reticulo-Endothelial system (RES), achieve passive targeting by Enhanced Permeation Retention (EPR) effect with controlled release of the therapeutic agent. As the conjugate cleaves into individual drugs in the tumor environment, this promises better suppression of cancer chemoresistance by delivering dual drugs with different modes of action at the same site, thereby synergistically inhibiting the growth of cancerous tissue.