Large magnetoresistance in low temperature metallic region of manganite compounds (La0.7−2xEux)(Ca0.3Srx)MnO3 (0.05≤x≤0.15)

Magnetoresistance (MR) and magnetization (dc and ac) measurements have been carried out on the manganites, (La_0.7−2xEu_x)(Ca_0.3Sr_x)MnO₃ (0.05≤x≤0.15), in the temperature range of 5-320 K. At 5 K, an unusually large MR of almost 98% is observed in the x=0.15 sample, nearly up to fields of 4-5 T. This large high-field MR occurs in the metallic region, far below the insulator-metal transition temperature, and does not vary linearly with applied field. The unusual magnetoresistance is explained in the light of various possibilities such as phase segregation, cluster spin-glass behavior, etc.     

Electronic excitation in phosphorus-containing molecules. II. Inner shell electron energy loss spectra of PF5, OPF3 AND OPCl3

Electron energy loss Spectroscopy has been used to obtain the inner shell excitation spectra of PF₅, OPF₃ and OPCl₃ in the P 2p,2s (L-shell) region as well as in the respective ligand K shell (F 1s, O 1s) and L shell (Cl 2p and 2s) regions. The spectra are compared and contrasted with earlier reported spectra obtained on the trivalent phosphorus compounds (PH₃, PCl₃, PF₃ and P(CH₃)₃). The spectra were obtained using an impact energy of 2.5keV and a scattering angle of about 1°. The spectra reported here are typical of molecules with electronegative ligands in that the discrete portions of the spectra show strong transitions to virtual molecular orbitais. In addition, intense features are observed at or just beyond the ionization edge attributable to transitions to trapped inner well states, while broad features further into the continuum can be ascribed to σ^*(P—L) shape-resonances (L = ligand). This resonance assignment was supported by a comparison with the corresponding spectra for PF₃ and PCl₃.     

Metal-free synthesis of calixsalen-type cavitands for the recognition of fluoride ion

Novel calixsalen-type cavitands have been synthesized using metal-free synthesis from simple and inexpensive materials, such as ethylenediamine and 5,5′-methylene-bis-salicylaldehyde derivatives. The cavitand 1 containing salen functionality recognizes fluoride ion. Fluoride ions switch on fluorescence on binding with the cavitand 1. Substitution on bis-salicylaldehyde part of calixsalen-type cavitand shows change in recognition behavior. On the attachment of electron withdrawing substituent, such as nitro group, the cavitand lost its fluorescence properties but proved to be a better colorimetric probe showing marked color change from pale yellow to red on addition of tetrabutyl ammonium salt of fluoride ion to the solution of cavitand. The nitro substituted cavitand is highly sensitive and selective for fluoride anion and hence is a promising candidate for development of colorimetric chemosensor. The binding of the cavitands with fluoride ion is investigated using ¹H NMR-titration experiments.     

Unsmoothing over balls via plane wave decomposition

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5-Amino-dU: a nucleoside analogue in the central strand of DNA triplex for orientation selective binding of A/G/C/T in the third strand

[formula: see text] 5-Amino-dU, a designed nucleoside analogue, when placed in the central strand of DNA triple helix, recognizes all four bases A, G, C, and T in the third strand, with a selectivity based on the orientation (parallel/antiparallel) of the third strand.     

LC-nanospray-MS/MS analysis of hydrophobic proteins from membrane protein complexes isolated by blue-native electrophoresis

The application of two-dimensional electrophoresis for the identification of hydrophobic membrane proteins is principally hampered by precipitation of many of these proteins during first-dimension, isoelectric focusing. Therefore new strategies towards the identification and characterization of membrane proteins are being developed. In this work we present a direct and rapid approach from blue-native gels to mass spectrometry, which allows the analyses of complete complexes and prevents protein aggregation of hydrophobic regions during electrophoresis. We combine blue-native gel electrophoresis and liquid chromatography--nanospray-iontrap tandem mass spectrometry to analyze the composition of oxidative phosphorylation complexes I, III, IV and V from bovine-heart mitochondria as a model system containing a number of highly hydrophobic proteins. Bands from blue-native gels were subjected either to in-gel or to in-solution tryptic digestion. The obtained peptide mixtures were further analyzed by liquid chromatography--tandem mass spectrometry and the corresponding proteins were identified by database search. From a total of 86 proteins, 67 protein subunits could be identified including all highly hydrophobic components, except the ND4L and ND6 subunits of complex I. We demonstrate that liquid chromatography--tandem mass spectrometry combined to blue-native electrophoresis is a straightforward tool for proteomic analysis of multiprotein complexes, and especially for the identification of very hydrophobic membrane protein constituents that are not accessible by common isoelectric focusing/sodium dodecyl sulphate gel electrophoresis.     

Nanosized magnesium oxide as catalyst for the rapid and green synthesis of substituted 2-amino-2-chromenes

A nanosized magnesium oxide catalyzed three-component condensation reaction of aldehyde, malononitrile, and α-naphthol proceeded rapidly in water-PEG to afford corresponding 2-amino-2-chromenes in high yields at room temperature. The greener protocol was found to be fairly general and the catalyst was reused in subsequent reactions with consistent activity.     

Spatially Resolved Kinetic Model of Parahydrogen Induced Polarisation (PHIP) in a Microfluidic Chip

We report a spatially resolved kinetic finite element model of parahydrogen-induced polarisation (PHIP) in a microfluidic chip that was calibrated using on-chip and off-chip NMR data. NMR spectroscopy has great potential as a read-out technique for lab-on-a-chip (LoC) devices, but is often limited by sensitivity. By integrating PHIP with a LoC device, a continuous stream of hyperpolarised material can be produced, and mass sensitivities of have been achieved. However, the yield and polarisation levels have so far been quite low, and can still be optimised. To facilitate this, a kinetic model of the reaction has been developed, and its rate constants have been calibrated using macroscopic kinetic measurements. The kinetic model was then coupled with a finite element model of the microfluidic chip. The model predicts the concentration of species involved in the reaction as a function of flow rate and position in the device. The results are in quantitative agreement with published experimental data.     

Extraction of microamounts of caesium into different organic solvents in the presence of sodium dipicrylaminate

A study has been made of the extraction of microamounts of caesium from the aqueous phase into 28 organic solvents in the presence of sodium dipicrylaminate and nitrate, and the extraction of macroamounts of ceasium and rubidium dipicrylaminates from nitrobenzene and nitromethane into some other organic solvents. The equilibrium constants of the reaction Cs _a ⁺ +Na _O ⁺ =Cs _O ⁺ +Na _a ⁺ were determined and a correlation with the water content of the organic phase has been discussed.