STX13 regulates cargo delivery from recycling endosomes during melanosome biogenesis

Melanosomes are a class of lysosome-related organelles produced by melanocytes. Biogenesis of melanosomes requires the transport of melanin-synthesizing enzymes from tubular recycling endosomes to maturing melanosomes. The SNARE proteins involved in these transport or fusion steps have been poorly studied. We found that depletion of syntaxin 13 (STX13, also known as STX12), a recycling endosomal Qa-SNARE, inhibits pigment granule maturation in melanocytes by rerouting the melanosomal proteins such as TYR and TYRP1 to lysosomes. Furthermore, live-cell imaging and electron microscopy studies showed that STX13 co-distributed with melanosomal cargo in the tubular-vesicular endosomes that are closely associated with the maturing melanosomes. STX family proteins contain an N-terminal regulatory domain, and deletion of this domain in STX13 increases both the SNARE activity in vivo and melanosome cargo transport and pigmentation, suggesting that STX13 acts as a fusion SNARE in melanosomal trafficking pathways. In addition, STX13-dependent cargo transport requires the melanosomal R-SNARE VAMP7, and its silencing blocks the melanosome maturation, reflecting a defect in endosome-melanosome fusion. Moreover, we show mutual dependency between STX13 and VAMP7 in regulating their localization for efficient cargo delivery to melanosomes.

Structural, optical and electrical properties of sulfur-incorporated amorphous carbon films

Amorphous carbon-sulfur (a-C:S) composite films were prepared by vapor phase pyrolysis technique. The structural changes in the a-C:S films were investigated by electron microscopy. A powder X-ray diffraction (XRD) study depicts the two-phase nature of a sulfur-incorporated a-C system. The optical bandgap energy shows a decreasing trend with an increase in the sulfur content and preparation temperature. This infers a sulfur incorporation and pyrolysis temperature induced reduction in structural disorder or increase in sp (2) or pi-sites. The presence of sulfur (S 2p) in the a-C:S sample is analyzed by the X-ray photoelectron spectroscopy (XPS). The sp (3)/sp (2) hybridization ratio is determined by using the XPS C 1s peak fitting, and the results confirm an increase in sp (2) hybrids with sulfur addition to a-C. The electrical resistivity variation in the films depends on both the sulfur concentration and the pyrolysis temperature.

Deformation mechanisms during large strain deformation of nanocrystalline nickel

In this letter, a conclusive evidence of the operation of planar slip along with grain boundary mediated mechanisms has been reported during large strain deformation of nanocrystalline nickel. Dislocation annihilation mechanism such as mechanical recovery has been found to play an important role during the course of deformation. The evidences rely on x-ray based techniques, such as dislocation density determination and crystallographic texture measurement as well as microstructural observation by electron microscopy. The characteristic texture evolution in this case is an indication of normal slip mediated plasticity in nanocrystalline nickel.

Electrical Percolation studies of Polystyrene-multi wall carbon nanotubes Composites

Composites of Polystyrene-multi wall carbon nanotubes (PS-MWNTs) were prepared with loading up to 7 wt% of MWNTs by simple solvent mixing and drying technique. MWNTs with high aspect ratio similar to 4000 were used to make the polymer composites. A very high degree of dispersion of MWNTs was achieved by ultrasonication technique. As a result of high dispersion and high aspect ratio of the MWNTs electrical percolation was observed at rather low weight fraction similar to 0.0021. Characterization of the as prepared PS-MWNTs composites was done by Electron microscopy (EM), X-ray diffraction technique (XRD) and Thermogravimetery analysis (TGA).

Structure and assembly of Sesbania mosaic virus

Sesbania mosaic virus (SeMV) is a ss-RNA (4149 nt) plant sobemovirus isolated from farmer's field around Tirupathi, Andhra Pradesh. The viral capsid (30 nm diameter) consists of 180 copies of protein subunits (MW 29 kDa) organized with icosahedral symmetry. In order to understand the mechanism of assembly of SeMV, a large number of deletion and substitution mutants of the coat protein (CP) were constructed. Recombinant SeMV CP (rCP) as well as the N-terminal rCP deletion mutant Delta N22 were found to assemble in E. coli into virus-like particles (VLPs). Delta N36 and Delta N65 mostly formed smaller particles consisting of 60 protein subunits. Although particlem assembly was not affected due to the substitution of aspartates (D14 and D149) that coordinate calcium ions by asparagines, the stability of the resulting capsids was drastically reduced. Deletion of residues forming a characteristic beta-annulus at the icosahedral 3-folds did not affect the assembly of VLPs. Mutation of a single tryptophan, which occurs near the icosahedral fivefold axis to glutamate or lysine, resulted in the disruption of the capsid leading to soluble dimers that resembled the quasi-dimer structure of the native virus. Replacement of positively charged residues in the amino terminal segment of CP resulted in the formation of empty shells. Based on these observations, a plausible mechanism of assembly is proposed.

Mechanical and Thermal Properties of Eva Blended with Biodegradable Ethyl Cellulose

In this study, biodegradable blend of Poly (Ethylene-co-Vinyl Acetate) (EVA) and Ethyl Cellulose (EC) were prepared. Ethylene vinyl alcohol (EVOH) copolymer was used as an interfacial compatibilizer to enhance adhesion between EVA and EC. The melt blended compatibilized biocomposites were examined for mechanical and thermal properties as per the ASTM standards. It has been found that the EC has a reinforcing effect on EVA leading to enhanced tensile strength and also impart biodegradability. Thus, a high loading of 50% EC could be added without compromising Much on the mechanical properties. Analysis of the tensile data using predictive theories showed an enhanced interaction of the dispersed phase (EC) and the matrix (EVA). The compatibilizing effects of EVOH on these blends were confirmed by the significant improvement in the mechanical properties comparable with neat EVA as also observed by SEM microscopy. The TGA thermograms exhibits two-stage degradation and as EC content increases, the onset temperature for thermal degradation reduces. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1044-1056, 2010

Protoporphyrinogen IX oxidase from Plasmodium falciparum is anaerobic and is localized to the mitochondrion

Earlier studies in this laboratory had shown that the malarial parasite can synthesize heme de novo and inhibition of the pathway leads to death of the parasite. It has been proposed that the pathway for the biosynthesis of heme in Plasmodium falciparum is unique involving three different cellular compartments, namely mitochondrion, apicoplast and cytosol. Experimental evidences are now available for the functionality and localization of all the enzymes of this pathway, except protoporphyrinogen IX oxidase (PfPPO), the penultimate enzyme. In the present study. PfPPO has been cloned, expressed and shown to be localized to the mitochondrion by immunofluorescence microscopy. Interestingly, the enzyme has been found to be active only under anaerobic conditions and is dependent on electron transport chain (ETC) acceptors for its activity. The native enzyme present in the parasite is inhibited by the ETC inhibitors, atovaquone and antimycin. Atovaquone, a well known inhibitor of parasite dihydroorotate dehydrogenase, dependent on the ETC, inhibits synthesis of heme as well in P. falciparum culture. A model is proposed to explain the ETC dependence of both the pyrimidine and heme-biosynthetic pathways in P. falciparum. (C) 2010 Elsevier B.V. All rights reserved.

Inorganic Analogues of Graphene

The discovery of graphene has aroused great interest in the properties and phenomena exhibited by two-dimensional inorganic materials, especially when they comprise only a single, two or a few layers. Graphene-like MoS2 and WS2 have been prepared by chemical methods, and the materials have been characterized by electron microscopy, atomic force microscopy (AFM) and other methods. Boron nitride analogues of graphene have been obtained by a simple chemical procedure starting with boric acid and urea and have been characterized by various techniques that include surface area measurements. A new layered material with the composition BCN possessing a few layers and a large surface area discovered recently exhibits a large uptake of CO2.

Electroless nickel hydroxide: synthesis and characterization

An electroless method of nickel hydroxide synthesis through the complexation-precipitation route which yields a fine particle material having a specific surface area of 178 m2 g–1 has been described. The morphology of this material as revealed by electron microscopy is distinctly different from the turbostratic nature of electrosynthesized nickel hydroxide. While the long range structure as shown by the X-ray diffraction pattern is similar to that of beta-Ni(OH)2, the short range structure as revealed by infrared spectroscopy incorporates characteristics similar to that of agr-Ni(OH)2. Cyclic voltammetry studies show that the electroless nickel hydroxide has a higher coulombic efficiency (>90%), a more anodic reversible potential and a higher degree of reversibility compared to the electrosynthesized nickel hydroxide and conventionally prepared nickel hydroxide.

Growth and extraction of flux free YBCO crystals

An improved flux draining technique for the extraction of grown YBCO crystals from its solvent is reported. This simple and efficient technique facilitates in-situ flux separation in the isothermal region of the furnace. Consequently, the crystals are spared from thermal shock and subsequent damage. Flux-free surfaces of these crystals were studied by optical microscopy. Transmission X-ray topographs of the crystals reveal the dislocations present in them as well as the stresses developed as a result of ferroelastic phase transition occurring during cooling.

Preparation and Characterization of MWCNT/ZnO nanoparticles Hybrid

ZnO nanoparticles (ZnO NPs) were grown on the surface of multiwall carbon nanotubes (MWCNTs) by a wet chemical synthesis route. The anchoring of ZnO NPs on acid-treated MWCNTs was achieved under remarkably mild reaction conditions (low temperature, atmospheric pressure, without any capping agents and no need for subsequent thermal annealing). MWCNT/ZnO NPs hybrid samples with varying loading of ZnO NPs are prepared. A very high degree of dispersion of ZnO NPs over the surface of MWCNT was achieved by suitably controlling the ratio of ZnO NPs and MWCNTs in the solution. The hybrid sample was characterized by electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Transmission electron microscope images of the as-prepared MWCNT/ZnO NPs hybrid reveal that mono-dispersed ZnO NPs are anchored stably on functionalized MWCNTs. The interaction of ZnO NPs with MWCNT surface was interpreted through XPS analysis.

Phase relations and gibbs energies in the system Mn-Rh-O

Phase relations in the system Mn-Rh-O are established at 1273 K by equilibrating different compositions either in evacuated quartz ampules or in pure oxygen at a pressure of 1.01 x 10(5) Pa. The quenched samples are examined by optical microscopy, X-ray diffraction, and energy-dispersive X-ray analysis (EDAX). The alloys and intermetallics in the binary Mn-Rh system are found to be in equilibrium with MnO. There is only one ternary compound, MnRh2O4, with normal spinel structure in the system. The compound Mn3O4 has a tetragonal structure at 1273 K. A solid solution is formed between MnRh2O4 and Mn3O4. The solid solution has the cubic structure over a large range of composition and coexists with metallic rhodium. The partial pressure of oxygen corresponding to this two-phase equilibrium is measured as a function of the composition of the spinel solid solution and temperature. A new solid-state cell, with three separate electrode compartments, is designed to measure accurately the chemical potential of oxygen in the two-phase mixture, Rh + Mn3-2xRh2xO4, which has 1 degree of freedom at constant temperature. From the electromotive force (emf), thermodynamic mixing properties of the Mn3O4-MnRh2O4 solid solution and Gibbs energy of formation of MnRh2O4 are deduced. The activities exhibit negative deviations from Raoult's law for most of the composition range, except near Mn3O4, where a two-phase region exists. In the cubic phase, the entropy of mixing of the two Rh3+ and Mn3+ ions on the octahedral site of the spinel is ideal, and the enthalpy of mixing is positive and symmetric with respect to composition. For the formation of the spinel (sp) from component oxides with rock salt (rs) and orthorhombic (orth) structures according to the reaction, MnO (rs) + Rh2O3 (orth) --> MnRh2O4 (sp), DELTAG-degrees = -49,680 + 1.56T (+/-500) J mol-1. The oxygen potentials corresponding to MnO + Mn3O4 and Rh + Rh2O3 equilibria are also obtained from potentiometric measurements on galvanic cells incorporating yttria-stabilized zirconia as the solid electrolyte. From these results, an oxygen potential diagram for the ternary system is developed.

On the decomposition of ? phase in some rapidly quenched titanium-eutectoid alloys

The decomposition of the beta phase in rapidly quenched Ti-2.8 at. pet Co, Ti-5.4 at. pet Ni, Ti-4.5 at. pet, and 5.5 at. pet Cu alloys has been investigated by electron microscopy. During rapid quenching, two competitive phase transformations, namely martensitic and eutectoid transformation, have occurred, and the region of eutectoid transformation is extended due to the high cooling rates involved. The beta phase decomposed into nonlamellar eutectoid product (bainite) having a globular morphology in Ti-2.8 pet Co and Ti-4.5 pet Cu (hypoeutectoid) alloys. In the near-eutectoid Ti-5.5 pet Cu alloy, the decomposition occurred by a lamellar (pearlite) type, whereas in Ti-5.4 pct Ni (hypereutectoid), both morphologies were observed. The interfaces between the proeutectoid alpha and the intermetallic compound in the nonlamellar type as well as between the proeutectoid alpha and the pearlite were often found to be partially coherent. These findings are in agreement with the Lee and Aaronson model proposed recently for the evolution of bainite and pearlite structures during the solid-state transformations of some titanium-eutectoid alloys. The evolution of the Ti2Cu phase during rapid quenching involved the formation of a metastable phase closely related to an ''omega-type'' phase before the equilibrium phase formed. Further, the lamellar intermetallic compound Ti2Cu was found to evolve by a sympathetic nucleation process. Evidence is established for the sympathetic nucleation of the proeutectoid alpha crystals formed during rapid quenching.

Preparation and characterization of multiwall carbon nanotube/polypyrrole coaxial fibrils

Multiwall carbon nanotube (MWNT)/polypyrrole (PPy) fibrils were fabricated by template-free in situ electrochemical deposition of PPy over MWNTs, and characterized by electron microscopy and electrical measurements. Scanning and transmission electron microscopy studies reveal that PPy coating on the surface of nanotube is quite uniform throughout the length, with the possibility of forming unique Y-junctions. Current (I)-voltage (V) characteristics at various temperatures show nonlinearity due to tunneling and hopping contributions to transport across the barriers. AC conductivity measurements (300-4.2 K) show that the onset frequency scales with temperature, and the nanoscale connectivity in MWNT/PPy fibrils decreases with the lowering of temperature. (C) 2011 Elsevier B.V. All rights reserved.

Synthesis, Thermotropic Behavior, and Permeability Properties of Vesicular Membranes Composed of Cationic Mixed-Chain Surfactants

In order to elucidate the role of the linkage region that connects polar headgroups with hydrophobic segments in a lipid monomer, cationic mixed-chain amphiphiles containing acyl and alkyl hydrophobic segments connected at the level of Me(2)N(+) headgroups 2a-d were synthesized. Related dialkyldimethyl-ammonium ion surfactants 1a-e and diacyl systems 3a-c were also synthesized. Despite mismatch in the connector region, amphiphiles 2a-d form bilayer vesicles like their dialkyl and diacyl counterparts, as revealed by electron microscopy. Introduction of an ester connector function between the polar and hydrophobic parts raises the phase transition temperature (T-m), transition enthalpies, and resistance to ion permeation. Consideration of energy minimized conformations points toward the importance of differences in the depth of chain penetration into the putative bilayer.