One nanosecond photon correlation spectroscopy on smectic liquid crystal films

We have extended photon correlation spectroscopy down to a one-nanosecond time scale, and applied it to a study of layer undulations in freestanding smectic-A films of two cyanobiphenyl liquid crystals. Temporal correlations in the intensity of scattered light reveal an interesting combination of under- and overdamped modes. The underdamped mode is accurately described by a recently calculated correlation function of the smectic layer displacement, although its frequency and damping rate exhibit stronger dispersion at large optical wave vectors than expected from current dynamical models for smectic films.     

Temperature driven morphological changes of hydrothermally prepared copper oxide nanoparticles

The size and shape of nanocrystals have a strong effect on the optical, electrical and catalytic properties. Therefore, controlling the size, shape and structure of nanocrystals is technically important. The controlled synthesis of CuO nanostructures was achieved using a hydrothermal process by simply controlling the precipitation reaction temperature between copper nitrate trihydrate and sodium hydroxide. The Scanning Electron Microscopy (SEM), EDS, XRD, and FTIR analysis revealed that the synthesized product at 200 °C is of pure copper oxide particles. From Scherrer formula, the prepared CuO particles varied approximately 3–7 nm in size simply by varying the reaction temperature. The synthesized particles exhibited a regular flake like morphology and had a uniform size distribution. The morphology and size depend on the reaction conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermal,physicochemical and spectroscopic studies on some novel organic complexes obtained by green synthesis

Journal of Thermal Analysis and Calorimetry - The solid–liquid equilibrium phase diagram and thermochemical studies on two binary organic systems involving N-methylurea (MU) with...     

X-ray emission from clusters of galaxies and cosmological parameters

Clusters of galaxies are excellent probes of cosmic structure and evolution. X-ray studies of clusters provide some of their key parameters, viz., temperature of the hot intra-cluster gas, its metallicity, X-ray luminosity and surface brightness giving mass distribution and mass-flow rate in the case of cooling flows. X-ray measurements for a large sample of clusters have lead to estimates of the total gravitating mass in them, which can be compared to the virial masses derived from dynamical considerations and gravitational lensing in some of them. X-ray derived total masses are consistent with masses obtained from the other methods after the effects due to the presence of cooling flows are taken into account in the analyses. Estimated virial masses, lack of evolution in X-ray properties, and detection of several very hot clusters at high redshifts indicate a Universe with a low value (≤ 0.3) for the Ω parameter.     

The influence of amine/amide versus bisamide coordination in nickel superoxide dismutase

Nickel superoxide dismutase (NiSOD) is a mononuclear nickel-containing metalloenzyme that catalyzes the disproportionation of superoxide by cycling between NiII and NiIII oxidation states. In the reduced NiII oxidation state, the metal center is ligated by two cysteinate sulfurs, one amide nitrogen, and one amine nitrogen (from the N-terminus), while in the oxidized NiIII state, an imidazole nitrogen coordinates to the metal center. Herein, we expand on a previous report in which we described a functional metallopeptide-based NiSOD model compound [NiII(SODM1)] (SODM1 = H2N-HCDLPCGVYDPA-COOH) by exploring how acylation of the N-terminus (producing [NiII(SODM1-Ac)]) influences the properties of the metallopeptide. Titration results, GPC data, and mass-spectrometry data demonstrate that NiII coordinates to SODM1-Ac in a 1:1 ratio, while variable pH studies show that NiII coordination is strong at a pH of 7.5 and above but not observed below a pH of 6.2. This is higher than [NiII(SODM1)] by approximately 1.0 pH unit consistent with bisamide ligation. Ni K-edge XAS demonstrates that the NiII center is coordinated in a square-planar NiN2S2 coordination environment with Ni-N distances of 1.846(4) A and Ni-S distances of 2.174(3) A. Comparison of the electronic absorption and CD spectrum of [NiII(SODM1)] versus [NiII(SODM1-Ac)] in conjunction with time-dependent DFT calculations suggests a decrease in Ni covalency in the acylated versus unacylated metallopeptide. This decrease in covalency was also supported by DFT calculations and Ni L-edge XAS. [NiII(SODM1-Ac)] has a quasireversible NiII/NiIII redox couple of 0.49(1) V vs Ag/AgCl, which represents a -0.2 V shift compared with [NiII(SODM1)], while the peak separation suggests a change in the coordination environment upon oxidation (i.e., axial imidazole ligation). Using the xanthine/xanthine oxidase assay, we determine that [NiII(SODM1-Ac)] is less active than [NiII(SODM1)] by over 2 orders of magnitude (IC50 = 3(1) x 10-5 vs 2(1) x 10-7 M). Possible reasons for the decrease in activity are discussed.     

Highly sensitive turn-on detection of Ag+ in aqueous solution and live cells with a symmetric fluorescent peptide

This communication presents a symmetric fluorescent peptide (K(d) = 17.4 nM) for hypersensitively detecting Ag(+) in 100% aqueous solution by turn-on response. The peptide penetrated live HeLa cells and detected intracellular Ag(+) by turn-on response.     

Solution structure of a designed cyclic peptide ligand for nickel and copper ions

Nuclear magnetic resonance (NMR) spectroscopy was used to study a cyclic peptide derived from the amino-terminal copper-and-nickel-binding (ATCUN) motif. The three-dimensional structure of the unliganded peptide in aqueous solution was solved by simulated annealing using distance constraints derived from Nuclear Overhauser Effects. A structural model for the Ni(II)-bound complex was also produced based on NMR evidence and prior spectroscopic data, which are consistent with crystal structures of linear ATCUN complexes. Structural interpolation, or ‘morphing’, was used to understand the transition of this highly structured cyclic peptide from its unliganded structure to its metal-ion-bound structure.     

Accelerating universes from compactification on a warped conifold

We find a cosmological solution corresponding to the compactification of 10D supergravity on a warped conifold that easily circumvents the "no-go" theorem given for a warped or flux compactification, providing new perspectives for the study of supergravity or superstring theory in cosmological backgrounds. With fixed volume moduli of the internal space, the model can explain a physical Universe undergoing an accelerated expansion in the 4D Einstein frame, for a sufficiently long time. The solution found in the limit that the warp factor dependent on the radial coordinate y is extremized (giving a constant warping) is smooth and it supports a flat four-dimensional Friedmann-Robertson-Walker cosmology undergoing a period of accelerated expansion with slowly rolling or stabilized volume moduli.     

Fluorinated Boron Nitride Quantum Dots: A New 0D Material for Energy Conversion and Detection of Cellular Metabolism

Quantum dots encompass a broad spectrum of optical, catalytic, and electrochemical properties bringing in novel applications in catalysis, imaging, displays, and optoelectronics. Herein, the unanticipated broad‐spectrum light absorption and high fluorescence quantum yield in fluorinated boron nitride (FBN) quantum dots are discussed. A heterostructure of FBN quantum dots with a wide‐bandgap semiconductor, titania nanotube arrays, exhibits high photocatalytic activity as evidenced by high external quantum efficiency extending from ultraviolet to green region of the solar spectrum (≈24% at 400 nm). The high activity is confirmed using photoelectrochemical hydrogen evolution experiments. Further, it is demonstrated that high fluorescence quantum yield could be tapped for the detection of glycolytic activity in cancer cells compared to normal cells. This finding could shift the paradigm of molecular detection using quantum dots. The 0D structure and the gap states introduced through fluorination are believed to be responsible for these unprecedented characteristics of boron nitride.