A Pd-8 Tetrafacial Molecular Barrel as Carrier for Water Insoluble Fluorophore

A new carbazole-based tetraimidazole ligand 1,3,6,8-tetra(1H-imidazol-1-yl)-9-methyl-9H-carbazole (L) has been synthesized. The unsymmetrical nature of L as well as the rotational freedom of imidazole donor moieties around C-N bond make it a special building unit, which upon treatment with cis-(tmeda)Pd(NO3)(2) produced an unprecedented single linkage-isomeric Pd-8 tetrafacial molecular nanobarrel (PSMBR-1) tmeda N,N,N',N'-tetramethylethane-1,2-diamine]. Unlike closed architectures, open barrel architecture of water-soluble PSMBR-1 makes it an ideal host for some water insoluble polyaromatic hydrocarbons in aqueous medium; one such inclusion complex coroneneCPSMBR-1 was characterized by X-ray diffraction study. Moreover, the potential application of PSMER-1 as carrier in aqueous medium for the transportation of water insoluble fluorophore (perylene) for live cell imaging is explored.

Cell-Membrane-Mimicking Lipid-Coated Nanoparticles Confer Raman Enhancement to Membrane Proteins and Reveal Membrane-Attached Amyloid-beta Conformation

Identifying the structures of membrane bound proteins is critical to understanding their function in healthy and diseased states. We introduce a surface enhanced Raman spectroscopy technique which can determine the conformation of membrane-bound proteins, at low micromolar concentrations, and also in the presence of a substantial membrane-free fraction. Unlike conventional surface enhanced Raman spectroscopy, our approach does not require immobilization of molecules, as it uses spontaneous binding of proteins to lipid bilayer-encapsulated Ag nanoparticles. We apply this technique to probe membrane-attached oligomers of Amyloid-beta(40) (A beta(40)), whose conformation is keenly sought in the context of Alzheimer's disease. Isotope-shifts in the Raman spectra help us obtain secondary structure information at the level of individual residues. Our results show the presence of a beta-turn, flanked by two beta-sheet regions. We use solid-state NMR data to confirm the presence of the beta-sheets in these regions. In the membrane-attached oligomer, we find a strongly contrasting and near-orthogonal orientation of the backbone H-bonds compared to what is found in the mature, less-toxic A beta fibrils. Significantly, this allows a ``porin'' like beta-barrel structure, providing a structural basis for proposed mechanisms of A beta oligomer toxicity.

Tungsten-based nanomaterials (WO3 & Bi2WO6): Modifications related to charge carrier transfer mechanisms and photocatalytic applications

Heterogeneous photocatalysis is an ideal green energy technology for the purification of wastewater. Although titania dominates as the reference photocatalyst, its wide band gap is a bottleneck for extended utility. Thus, search for non-TiO2 based nanomaterials has become an active area of research in recent years. In this regard, visible light absorbing polycrystalline WO3 (2.4-2.8 eV) and Bi2WO6 (2.8 eV) with versatile structure-electronic properties has gained considerable interest to promote the photocatalytic reactions. These materials are also explored in selective functional group transformation in organic reactions, because of low reduction and oxidation potential of WO3 CB and Bi2WO6 VB, respectively. In this focused review, various strategies such as foreign ion doping, noble metal deposition and heterostructuring with other semiconductors designed for efficient photocatalysis is discussed. These modifications not only extend the optical response to longer wavelengths, but also prolong the life-time of the charge carriers and strengthen the photocatalyst stability. The changes in the surface-bulk properties and the charge carrier transfer dynamics associated with each modification correlating to the high activity are emphasized. The presence of oxidizing agents, surface modification with Cu2+ ions and synthesis of exposed facets to promote the degradation rate is highlighted. In depth study on these nanomaterials is likely to sustain interest in wastewater remediation and envisaged to signify in various green energy applications. (C) 2015 Elsevier B.V. All rights reserved.

Estimation of background carrier concentration in fully depleted GaN films

Buffer leakage is an important parasitic loss mechanism in AlGaN/GaN high electron mobility transistors (HEMTs) and hence various methods are employed to grow semi-insulating buffer layers. Quantification of carrier concentration in such buffers using conventional capacitance based profiling techniques is challenging due to their fully depleted nature even at zero bias voltages. We provide a simple and effective model to extract carrier concentrations in fully depleted GaN films using capacitance-voltage (C-V) measurements. Extensive mercury probe C-V profiling has been performed on GaN films of differing thicknesses and doping levels in order to validate this model. Carrier concentrations as extracted from both the conventional C-V technique for partially depleted films having the same doping concentration, and Hall measurements show excellent agreement with those predicted by the proposed model thus establishing the utility of this technique. This model can be readily extended to estimate background carrier concentrations from the depletion region capacitances of HEMT structures and fully depleted films of any class of semiconductor materials.

Rapid NMR Assignments of Proteins by Using Optimized Combinatorial Selective Unlabeling

A new approach for rapid resonance assignments in proteins based on amino acid selective unlabeling is presented. The method involves choosing a set of multiple amino acid types for selective unlabeling and identifying specific tripeptides surrounding the labeled residues from specific 2D NMR spectra in a combinatorial manner. The methodology directly yields sequence specific assignments, without requiring a contiguously stretch of amino acid residues to be linked, and is applicable to deuterated proteins. We show that a 2D N-15,H-1]HSQC spectrum with two 2D spectra can result in approximate to 50% assignments. The methodology was applied to two proteins: an intrinsically disordered protein (12kDa) and the 29kDa (268 residue) -subunit of Escherichia coli tryptophan synthase, which presents a challenging case with spectral overlaps and missing peaks. The method can augment existing approaches and will be useful for applications such as identifying active-site residues involved in ligand binding, phosphorylation, or protein-protein interactions, even prior to complete resonance assignments.

Localized Charge Carrier Transport Properties of Zn1-x Ni (x) O/NiO Two-Phase Composites

We report the localized charge carrier transport of two-phase composite Zn1-x Ni (x) O/NiO (0 a parts per thousand currency sign x a parts per thousand currency sign 1) using the temperature dependence of ac-resistivity rho (ac)(T) across the N,el temperature T (N) (= 523 K) of nickel oxide. Our results provide strong evidence to the variable range hopping of charge carriers between the localized states through a mechanism involving spin-dependent activation energies. The temperature variation of carrier hopping energy epsilon (h)(T) and nearest-neighbor exchange-coupling parameter J (ij)(T) evaluated from the small poleron model exhibits a well-defined anomaly across T (N). For all the composite systems, the average exchange-coupling parameter (J (ij))(AVG) nearly equals to 70 meV which is slightly greater than the 60-meV exciton binding energy of pure zinc oxide. The magnitudes of epsilon (h) (similar to 0.17 eV) and J (ij) (similar to 11 meV) of pure NiO synthesized under oxygen-rich conditions are consistent with the previously reported theoretical estimation based on Green's function analysis. A systematic correlation between the oxygen stoichiometry and, epsilon (h)(T) and J (ij)(T) is discussed.

Electron transfer amongst flavo- and hemo-proteins: diffusible species effect the relay processes, not protein-protein binding

Hitherto, electron transfer (ET) between redox proteins has been deemed to occur via donor-acceptor binding, and diffusible reactive species are considered as deleterious side-products in such systems. Herein, ET from cytochrome P450 reductase (CPR, an animal membrane flavoprotein) and horseradish peroxidase (HRP, a plant hemoprotein) to cytochrome c (Cyt c, a soluble animal hemoprotein) was probed under diverse conditions, using standard assays. ET in the CPR-Cyt c system was critically inhibited by cyanide and sub-equivalent levels of polar one-electron cyclers like copper ions, vitamin C/Trolox and superoxide dismutase. In the presence of lipids, inhibition was also afforded by amphipathic molecules vitamin E, palmitoyl-vitamin C and the membrane hemoprotein, cytochrome b(5). Such nonspecific inhibition (by diverse agents in both aqueous and lipid phases) indicated that electron transfer/relay was effected by small diffusible agents, whose lifetimes are shortened by the diverse radical scavengers. When CPR was retained in a dialysis membrane and Cyt c presented outside in free solution, ET was still observed. Further, HRP (taken at nM levels) catalyzed oxidation of a phenolic substrate was significantly inhibited upon the incorporation of sub-nM levels of Cyt c. The findings imply that CPR-Cyt c or HRP-Cyt c binding is not crucial for ET. Further, fundamental quantitative arguments (based on diffusion/collision) challenge the erstwhile protein-protein binding-assisted ET hypothesis. It is proven beyond reasonable doubt that mobile and diffusible electron carriers (ions and radicals) serve as ``redox-relay agents'' in the biological ET models/setup studied.