EPR and optical investigations of manganese ions in alkali lead tetraborate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectra of Mn2+ ions in different alkali lead tetraborate glasses 90R2B4O7+9.25PbO+0.75MnSO4 (R=Li, Na and K) and 90Li2B4O7+(10-x)PbO+xMnSO4 (x=0.1, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5 and 2 mol%) have been studied. The EPR spectrum of all the glass samples exhibit three resonance signals at g=2.0, 3.3 and 4.3. The resonance signal at g=2.0 is attributed to the Mn2+ ions in an environment close to an octahedral symmetry. The resonance signals at g=3.3 and 4.3 have been attributed to the rhombic symmetry of the Mn2+ ions. The effect of temperature (123-433 K) and the composition dependence of EPR signals have been studied for Mn2+ ions in lithium lead tetraborate glasses. It is interesting to observe that the variation of paramagnetic susceptibility (chi) with temperature obeys Curie-Weiss law. From the slope of 1/chi versus T graph, the Curie constant (C) has been evaluated. The zero-field splitting (zfs) parameter D has been calculated for different alkali lead tetraborate glasses from the intensities of the allowed hyperfine lines. The optical absorption spectrum exhibits three bands. An intense and broad band at lower energy side has been assigned to the spin-allowed (5Eg-->5T2g) transition of Mn3+ ions in an octahedral symmetry. The intense and sharp band and a broad band at higher energy side have been assigned to charge transfer bands. A red shift is observed with increase of alkali ion size. The optical band gap energy (Eopt) decreases, whereas the Urbach energies (DeltaE) increases with increase of Mn content. The theoretical values of optical basicity (Lambdath) of the glasses have also been evaluated.     

Studies directed towards the synthesis of antascomicin A: stereoselective synthesis of the C22-C34 fragment of the molecule

A stereoselective synthesis of the C22-C34 fragment of the non-immunosuppressive immunophilin-binding natural product, antascomicin A was achieved using d-quinic acid as the starting material and highly stereoselective aldol reactions were employed, as key steps, to build the remaining stereocentres at C23, C26 and C27.     

Structural and spectral studies of an iron(III) complex [Fe(Pranthas)2][FeCl4] derived from 2-acetylpyridine-N(4), N(4)-(butane-1, 4-diyl) thiosemicarbazone (HPranthas)

A novel iron(III) complex of 2-acetylpyridine N(4), N(4)-(butyl-1, 4-diyl) thiosemicarbazone (HPranthas), [Fe(Pranthas)₂]FeCl₄ was synthesized and physico-chemically characterized by means of partial elemental analysis, magnetic measurements (polycrystalline state), UV-Vis and IR spectroscopies. The presence of spin-paired iron(III) cation with ground state is revealed by the EPR and Mössbauer spectral data. Structure of the free ligand HPranthas and the complex [Fe(Pranthas)₂]FeCl₄ were solved by single crystal X-ray diffraction. The framework of iron(III) complex consists of a discrete monomeric cationic entity containing low spin iron(III) in a slightly distorted octahedral environment. The metal ion is bonded to one sulfur and two nitrogens of each thiosemicarbazone molecule. The tetrachloroferrate(III) ion acts as counterion.     

Solution combustion derived nanocrystalline Zn(2)SiO(4):Mn phosphors: a spectroscopic view

Manganese doped nanocrystalline willemite powder phosphors Zn(2-x)Mn(x)SiO(4) (0.1(6)A(1) ground state. The mechanism involved in the generation of a green emission has been explained in detail. The effect of Mn content on luminescence has also been studied.     

Development and validation of a liquid chromatographic method for monitoring of process-related synthetic organic impurities of profenofos in technical products

A simple and rapid reversed-phase high-performance liquid chromatographic method for the monitoring of process-related synthetic organic impurities of profenofos (PFS) is developed. Impurities are separated and determined on a reversed-phase Hypersil C(18) column using gradient elution of 50 mM ammonium formate buffer-acetonitrile as a mobile phase and detection at 230 nm at ambient temperature. The method is validated with respect to accuracy, precision, linearity, and limits of detection and quantitation. The method is found to be suitable not only for monitoring the reactions involved in the process development of PFS, but also quality assurance, as it can detect impurities at the level of 1.5 x 10(-8) g.     

Camphor-derived thioureas: Synthesis and application in asymmetric Kabachnik-Fields reaction

A series of camphor-derived thiourea organocatalysts 3a–f were designed and synthesized from(1R,3S)-camphoric acid 1 and applied to the one-pot three-component Kabachnik–Fields reaction. Catalyst 3c was found to be an efficient organocatalyst for the reaction of 2-cyclopropylpyrimidin-4-carbaldehyde 4,various amines 5, and diphenylphosphite 6 to yield the corresponding enantioselective a-aminophosphonates 7a–e in 74%–82% yields and 14%–35% ee.     

Enhanced dielectric and magnetic properties of Cr / Co and Mn co-doped single phase multiferroic bismuth ferrite nanoparticles

Multiferroic nanoparticles of single-phase bismuth ferrite (BiFeO₃ or BFO) by choosing transition metal ions of chromium (Cr)/cobalt (Co) in A-sites and manganese (Mn) in B-sites were synthesized by using sol-gel autocombustion method. X-ray diffraction (XRD) data reveal the existence of rhombohedrally distorted perovskite structure for all the samples. High resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDAX) studies were carried out to estimate the particle size, morphology along with the chemical purity of the samples. Dielectric studies as a function of frequency and temperature resemble typical space charge polarization with almost negligible dielectric losses in the doped samples. Magnetic measurements using vibrating sample magnetometer reveals the considerable enhancement in the magnetic order in Co/Cr and Mn co-doped samples. The obtained structural, microstructural, dielectric and magnetic results were well recommended that the influence of co-doping in BFO will certainly modify its spin cycloid structure and hence enhanced properties in these doped samples. Thus, these co-doped samples were suggested to be well suitable for the multifunctional based devices such as spintronic, multifunctional memories, and for sensors.     

Typical superparamagnetism with improved electrical properties of nano modified bismuth ferrite multiferroic composites

Multiferroic composites with the chemical formula, (0.5) BiFeO₃ + (0.5) Ni_0.5Zn_0.5Fe₂O₄, in bulk and nano forms were synthesized by preparing bismuth ferrite (BiFeO₃ or BFO) in bulk (B) and nano (N) forms and nickel zinc ferrite (Ni_0.5Zn_0.5Fe₂O₄or NZFO) in nano form. Single phase BFO was synthesized using conventional solid-state reaction as well as sol-gel autocombustion methods and NZFO powders were prepared by using sol-gel autocombustion method, respectively. X-ray diffraction (XRD) studies reveal the existence of rhombohedrally distorted perovskite structure for BFO and cubic spinel phase for NZFO in single phase as well as composite samples. Microstructural studies and energy dispersive spectroscopy (EDS) data reveal the formation of grains, intergranular porosities and chemical purity of the synthesized samples. Dielectric and AC conductivity measurements confirm the existence of space charge polarization along with the small polaron model in these composites. Ferroelectric and magnetic studies show that there was a considerable enhancement in the ferroelectric and magnetic orders for the nano form of the BFO (N) + NZFO composite. The observed remnant polarization values 2.80388 & 7.75901 μC/cm², saturation magnetization values 37.96072 & 40.47491emu/gm for bulk BFO (B) + NZFO and nano BFO (N) + NZFO composites, respectively. Interestingly, both the samples exhibit superparamagnetic behaviour at room temperature with coercivities close to zero. This typical behaviour is attributed to the corresponding anisotropic contributions originated from the individual constituents. The observed variations in BFO (N) + NZFO sample attributed to the corresponding structural modifications brought about by the variations due to its size effect in the present work.     

Meglumine sulfate-catalyzed one-pot green synthesis and antioxidant activity of α-aminophosphonates

A green and efficient synthetic protocol has been developed for the synthesis of a new series of substituted diethyl(((2-methoxy-5-(trifluoromethyl)phenyl)amino)(phenyl)methyl)phosphonates via a one-pot three-component reaction of 2-methoxy-5-trifluoromethyl aniline with various aromatic-substituted aldehydes and diethyl phosphite using meglumine sulfate as an eco-friendly catalyst at room temperature under solvent-free conditions. The merits of this method are high product yield, short reaction time, easy workup, and purification. All the synthesized compounds were evaluated for the antioxidant activity by DPPH, NO, and H₂O₂ methods using ascorbic acid as a standard. The compounds 4a and 4g showed the highest antioxidant activity than that of the standard ascorbic acid.     

Asymptotics of work distributions in a stochastically driven system

We determine the asymptotic forms of work distributions at arbitrary times T, in a class of driven stochastic systems using a theory developed by Nickelsen and Engel (EN theory) [D. Nickelsen and A. Engel, Eur. Phys. J. B 82, 207 (2011)], which is based on the contraction principle of large deviation theory. In this paper, we extend the theory, previously applied in the context of deterministically driven systems, to a model in which the driving is stochastic. The models we study are described by overdamped Langevin equations and the work distributions in path integral form, are characterised by having quadratic augmented actions. We first illustrate EN theory, for a deterministically driven system – the breathing parabola model, and show that within its framework, the Crooks fluctuation theorem manifests itself as a reflection symmetry property of a certain characteristic polynomial, which also determines the exact moment-generating-function at arbitrary times. We then extend our analysis to a stochastically driven system, studied in references [S. Sabhapandit, EPL 89, 60003 (2010); A. Pal, S. Sabhapandit, Phys. Rev. E 87, 022138 (2013); G. Verley, C. Van den Broeck, M. Esposito, New J. Phys. 16, 095001 (2014)], for both equilibrium and non-equilibrium steady state initial distributions. In both cases we obtain new analytic solutions for the asymptotic forms of (dissipated) work distributions at arbitrary T. For dissipated work in the steady state, we compare the large T asymptotic behaviour of our solution to the functional form obtained in reference [New J. Phys. 16, 095001 (2014)]. In all cases, special emphasis is placed on the computation of the pre-exponential factor and the results show excellent agreement with numerical simulations. Our solutions are exact in the low noise (β →?∞) limit.