Anomalous optical phonons in Cs-0.9(NH4)(0.1)H2AsO4: a temperature-dependent Raman study

We determine the nature of coupled phonons in mixed crystal of Cs-0.9(NH4)(0.1)H2AsO4 using inelastic light scattering studies in the temperature range of 5 K to 300 K covering a spectral range of 60-1100 cm(-1). The phase transition in this system are marked by the splitting of phonon modes, appearance of new modes and anomalies in the frequency as well as linewidth of the phonon modes near transition temperature. In particular, we observed the splitting of symmetric (v(1)) and antisymmetric (v(3)) stretching vibrations associated with AsO4 tetrahedra below transition temperature (T-c(*) similar to 110 K) attributed to the lowering of site symmetry of AsO4 in orthorhombic phase below transition temperature. In addition, the step-up (hardening) and step-down (softening) of the AsO4 bending vibrations (v(4) (S9, S11) and v(2) (S6)) below transition temperature signals the rapid development of long range ferroelectric order and proton ordering. The lowest frequency phonon (S1) mode observed at similar to 92 cm(-1) shows anomalous blue shift (similar to 12 %) from 300 K to 5 K with no sharp transition near T-c(*) unlike other observed phonon modes signaling its potential coupling with the proton tunneling mode. (C) 2013 Author(s).

Plant latex mediated green synthesis of ZnAl2O4:Dy3+ (1-9 mol%) nanophosphor for white light generation

ZnAl2O4:Dy3+ (1-9 mol%) nanophosphors were synthesized by a simple, cost effective and environmental friendly route using Euphorbia tirucalli plant latex. The structural properties and morphological features of the phosphors were well studied by PXRD, FTIR, SEM and TEM measurements. The luminescent properties of ZnAl2O4:Dy3+ (1-9 mol%) nanophosphors were investigated from the excitation and emission spectra. The phosphor performance was evaluated by color co-ordinates. The values were well located in the near white region as a result it was highly useful for the fabrication of green component in WLEDs. The average particle size was found to be similar to 9-18 nm and same was confirmed by TEM and Scherrer's method. The highest photoluminescence (PL) and thermoluminescence (TL) intensity was obtained to be similar to 7 mol% Dy3+ concentration. A single TL glow peak was recorded at 172 degrees C at a warming rate of 2.5 degrees Cs (1). The intensity at 172 degrees C peak increases linearly up to 1 kGy and after that it diminishes. PL intensity was studied with different plant latex concentration (2-8 ml) and highest PL intensity was recorded for similar to 8 ml. The optimized phosphor showed good reusability, low fading and wide range of linearity with gamma-dose hence the phosphor was quite useful in radiation dosimetry. (C) 2013 Elsevier B.V. All rights reserved.

Direct hexagonal transition of amorphous (Ge2Sb2Te5)(0.9)Se-0.1 thin films

Ge2Sb2Te5 (GST) is well known for its phase change properties and applications in memory and data storage. Efforts are being made to improve its thermal stability and transition between amorphous and crystalline phases. Various elements are doped to GST to improve these properties. In this work, Se has been doped to GST to study its effect on phase change properties. Amorphous GST film crystallized in to rock salt (NaCl) type structure at 150 degrees C and then transformed to hexagonal structure at 250 degrees C. Interestingly, Se doped GST ((GST)(0.9)Se-0.1) film crystallized directly into hexagonal phase and the intermediate phase of NaCl is not observed. The crystallization temperature (T-c) of (GST)(0.9)Se-0.1 is around 200 degrees C, which is 50 degrees C higher than the T-c of GST. For (GST)(0.9)Se-0.1, the threshold switching occurs at about 4.5V which is higher than GST (3 V). Band gap (E-opt) values of as deposited films are calculated from Tauc plot which are 0.63 eV for GST and 0.66 eV for (GST)(0.9)Se-0.1. The E-opt decreases for the films annealed at higher temperatures. The increased T-c, E-opt, the contrast in resistance and the direct transition to hexagonal phase may improve the data readability and thermal stability in the Se doped GST film. (C) 2014 AIP Publishing LLC.

1,9-Pyrazoloanthrone as a Colorimetric and ``Turn-On'' Fluorometric Chemosensor: Structural Implications

A colorimetric and ``turn-on'' fluorescent chemosensor based on 1,9-pyrazoloanthrone specifically for cyanide and fluoride ion detection shows a remarkable solid state reaction when crystals of tetrabutylammonium cyanide and fluoride are brought in physical contact with 1,9-pyrazoloanthrone. X-ray crystal structures of 1,9-pyrazoloanthrone and complexes have been determined, and the ion sensing activity (detection limit of 0.2 and 2 ppb) has been inferred based on spectroscopic and structural features.

Alkyl chain substituted 1,9-pyrazoloanthrones exhibit prominent inhibitory effect on c-Jun N-terminal kinase (JNK)

N-Alkyl substituted pyrazoloanthrone derivatives were synthesized, characterized and tested for their in vitro inhibitory activity over c-Jun N-terminal kinase (JNK). Among the tested molecules, a few derivatives showed significant inhibitory activity against JNK with minimal off-target effect on other mitogen-activated protein kinase (MAP kinase) family members such as MEK1/2 and MKK3,6. These results suggested that N-alkyl (propyl and butyl) bearing pyrazoloanthrone scaffolds provide promising therapeutic inhibitors for JNK in regulating inflammation associated disorders.

C-11/C-9 Helices in Crystals of alpha beta Hybrid Peptides and Switching Structures between Helix Types by Variation in the alpha-Residue

Close-packed helices with mixed hydrogen bond directionality are unprecedented in the structural chemistry of alpha-polypeptides. While NMR studies in solution state provide strong evidence for the occurrence of mixed helices in (beta beta)(n) and (alpha beta)(n) sequences, limited information is currently available in crystals. The peptide structures presented show the occurrence of C-11/C-9 helices in (alpha beta)(n) peptides. Transitions between C-11 and C-11/C-9 helices are observed upon varying the alpha-amino acid residue.

N-Alkyl derivative of 1,9-pyrazoloanthrone as a sensor for picric acid

The N-alkyl derivative of 1,9-pyrazoloanthrone has been synthesized, characterized and evaluated as a potent sensor for picric acid.

A Reactive Intermediate, Ni-5(C6H4N3)(6)(CO)(4)], in the Formation of Nonameric Clusters of Nickel, Ni-9(C6H4N3)(12)(CO)(6)] and Ni-9(C6H4N3)(12)(CO)(6)].2(C3H7NO)

Three new molecular compounds, Ni-5(bta)(6)(CO)(4)], I, Ni-9(bta)(12)(CO)(6)], II, Ni-9(bta)(12)(CO)(6)]. 2(C3H7NO), III, (bta = benzotriazole) were prepared employing solvothermal reactions. Of these, I have pentanuclear nickel, whereas II and III have nonanuclear nickel species. The structures are formed by the connectivity between the nickel and benzotriazole giving rise to the 5- and 9-membered nickel clusters. The structures are stabilised by extensive pi aEuro broken vertical bar pi and C-H... pi interactions. Compound II and III are solvotamorphs as they have the same 9-membered nickel clusters and have different solvent molecules. To the best of our knowledge, the compounds I-III represent the first examples of the same transition element existing in two distinct coordination environment in this class of compounds. The studies reveal that compound I is reactive and could be an intermediate in the preparation of II and III. Thermal studies indicate that the compounds are stable upto 350(a similar to)C and at higher temperatures (similar to 800(a similar to)C) the compounds decompose into NiO. Magnetic studies reveal that II is anti-ferromagnetic.

Solvatochromism of 9,10-phenanthrenequinone: An electronic and resonance Raman spectroscopic study

Solvent effects play a vital role in various chemical, physical, and biological processes. To gain a fundamental understanding of the solute-solvent interactions and their implications on the energy level re-ordering and structure, UV-VIS absorption, resonance Raman spectroscopic, and density functional theory calculation studies on 9,10-phenanthrenequinone (PQ) in different solvents of diverse solvent polarity has been carried out. The solvatochromic analysis of the absorption spectra of PQ in protic dipolar solvents suggests that the longest (1n-pi(1)*; S-1 state) and the shorter (1 pi-pi(1)*; S-2 state) wavelength band undergoes a hypsochromic and bathochromic shift due to intermolecular hydrogen bond weakening and strengthening, respectively. It also indicates that hydrogen bonding plays a major role in the differential solvation of the S-2 state relative to the ground state. Raman excitation profiles of PQ (400-1800 cm(-1)) in various solvents followed their corresponding absorption spectra therefore the enhancements on resonant excitation are from single-state rather than mixed states. The hyperchromism of the longer wavelength band is attributed to intensity borrowing from the nearby allowed electronic transition through vibronic coupling. Computational calculation with C-2 nu symmetry constraint on the S-2 state resulted in an imaginary frequency along the low-frequency out-of-plane torsional modes involving the C=O site and therefore, we hypothesize that this mode could be involved in the vibronic coupling. (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).

Direct Observation of Thermal Equilibrium of Excited Triplet States of 9,10-Phenanthrenequinone. A Time-Resolved Resonance Raman Study

The photochemistry of aromatic ketones plays a key role in various physicochemical and biological processes, and solvent polarity can be used to tune their triplet state properties. Therefore, a comprehensive analysis of the conformational structure and the solvent polarity induced energy level reordering of the two lowest triplet states of 9,10-phenanthrenequinone (PQ) was carried out using nanosecond-time-resolved absorption (ns-TRA), time-resolved resonance Raman (TR3) spectroscopy, and time dependent-density functional theory (TD-DFT) studies. The ns-TRA of PQ in acetonitrile displays two bands in the visible range, and these two bands decay with similar lifetime at least at longer time scales (mu s). Interestingly, TR3 spectra of these two bands indicate that the kinetics are different at shorter time scales (ns), while at longer time scales they followed the kinetics of ns-TRA spectra. Therefore, we report a real-time observation of the thermal equilibrium between the two lowest triplet excited states of PQ assigned to n pi* and pi pi* of which the pi pi* triplet state is formed first through intersystem crossing. Despite the fact that these two states are energetically close and have a similar conformational structure supported by TD-DFT studies, the slow internal conversion (similar to 2 ns) between the T-2(1(3)n pi*) and T-1(1(3)pi pi*) triplet states indicates a barrier. Insights from the singlet excited states of PQ in protic solvents J. Chem. Phys. 2015, 142, 24305] suggest that the lowest n pi* and pi pi* triplet states should undergo hydrogen bond weakening and strengthening, respectively, relative to the ground state, and these mechanisms are substantiated by TD-DFT calculations. We also hypothesize that the different hydrogen bonding mechanisms exhibited by the two lowest singlet and triplet excited states of PQ could influence its ISC mechanism.

On the Structural Stability of Melt Spun Ribbons of Fe95-x Zr (x) B4Cu1 (x=7 and 9) Alloys and Correlation with Their Magnetic Properties

Melt spun ribbons of Fe95-x Zr (x) B4Cu1 with x = 7 (Z7B4) and 9 (Z9B4) alloys have been prepared, and their structure and magnetic properties have been evaluated using XRD, DSC, TEM, VSM, and Mossbauer spectroscopy. The glass forming ability (GFA) of both alloys has been calculated theoretically using thermodynamical parameters, and Z9B4 alloy is found to possess higher GFA than that of Z7B4 alloy which is validated by XRD results. On annealing, the amorphous Z7B4 ribbon crystallizes into nanocrystalline alpha-Fe, whereas amorphous Z9B4 ribbon shows two-stage crystallization process, first partially to bcc solid solution which is then transformed to nanocrystalline alpha-Fe and Fe2Zr phases exhibiting bimodal distribution. A detailed phase analysis using Mossbauer spectroscopy through hyperfine field distribution of phases has been carried out to understand the crystallization behavior of Z7B4 and Z9B4 alloy ribbons. In order to understand the phase transformation behavior of Z7B4 and Z9B4 ribbons, molar Gibbs free energies of amorphous, alpha-Fe, and Fe2Zr phases have been evaluated. It is found that in case of Z7B4, alpha-Fe is always a stable phase, whereas Fe2Zr is stable at higher temperature for Z9B4. (C) The Minerals, Metals & Materials Society and ASM International 2015