Chemical vapor deposited boron carbide : growth by a vapor-liquid-solid process

Detailed analytical electron microscope (AEM) studies of yellow whiskers produced by chemical vapor deposition (CVD)1 show that two basic types of whiskers are produced at low temperatures (between 1200°C and 1400°C) and low boron to carbon gas ratios. Both whisker types show planar microstructures such as twin planes and stacking faults oriented parallel to, or at a rhombohedral angle to, the growth direction. For both whisker types, the presence of droplet-like terminations containing both Si and Ni indicate that the growth process during CVD is via a vapor-liquid-solid (VLS) mechanism.

Hydrogen spillover mechanism on a pd-doped mg surface as revealed by ab initio density functional calculation

The hydrogenation kinetics of Mg is slow, impeding its application for mobile hydrogen storage. We demonstrate by ab initio density functional theory (DFT) calculations that the reaction path can be greatly modified by adding transition metal catalysts. Contrasting with Ti doping, a Pd dopant will result in a very small activation barrier for both dissociation of molecular hydrogen and diffusion of atomic H on the Mg surface. This new computational finding supports for the first time by ab initio simulationthe proposed hydrogen spillover mechanism for rationalizing experimentally observed fast hydrogenation kinetics for Pd-capped Mg materials.

Study of particulate matter removal mechanism by using non-thermal plasma technology

Numbers of diesel engines in both stationary and mobile applications are increasing nowadays. Diesel engines emit lower Hydrocarbon (HC) and Carbon monoxide (CO) than gasoline engines. However, they can produce more nitrogen oxides (NOx) and have higher particulate matter (PM). On the other hand, emissions standards are getting stringent day by day due to considerable concerns about unregulated pollutants and particularly ultrafine particles deleterious effect on human health. Non-thermal plasma (NTP) treatment of exhaust gas is known as a promising technology for both NOx and PM reduction by introducing plasma inside the exhaust gas. Vehicle exhaust gases undergo chemical changes when exposed to plasma. In this study, the PM removal mechanism using NTP by applying high voltage pulses of up to 20 kVpp with a repetition rate of 10 kHz are investigated. It is found that, voltage increase not necessarily has a positive effect on PM removal in diesel engine emissions.

Histone deacetylase inhibitors target diabetes via chromatin remodeling or as chemical chaperones?

Globally, obesity and diabetes (particularly type 2 diabetes) represents a major challenge to world health. Despite decades of intense research efforts, the genetic basis involved in diabetes pathogenesis & conditions associated with obesity are still poorly understood. Recent advances have led to exciting new developments implicating epigenetics as an important mechanism underpinning diabetes and obesity related disease. One epigenetic mechanism known as the "histone code" describes the idea that specific patterns of post-translational modifications to histones act like a molecular "code" recognised and used by non-histone proteins to regulate specific chromatin functions. One modification which has received significant attention is that of histone acetylation. The enzymes which regulate this modification are described as lysine acetyltransferases or KATs and histone deacetylases or HDACs. Due to their conserved catalytic domain HDACs have been actively targeted as a therapeutic target. Some of the known inhibitors of HDACs (HDACi) have also been shown to act as "chemical chaperones" to alleviate diabetic symptoms. In this review, we discuss the available evidence concerning the roles of HDACs in regulating chaperone function and how this may have implications in the management of diabetes. © 2009 Bentham Science Publishers Ltd.

Tunable “Nano-Shearing” : A physical mechanism to displace nonspecific cell adhesion during rare cell detection

We report a tunable alternating current electrohydrodynamic (ac-EHD) force which drives lateran fluid motion within a few nanometers of an electrode surface. Because the magnitude of this fluid shear force can be tuned externally (e.g., via the application of an ac electric field), it provides a new capability to physically displace weakly (nonspecifically) bound cellular analytes. To demonstrate the utility of the tunable nanoshearing phenomenon, we present data on purpose-built microfluidic devices that employ ac-EHD force to remove nonspecific adsorption of molecular and cellular species. Here, we show that an ac-EHD device containing asymmetric planar and microtip electrode pairs resulted in a 4-fold reduction in nonspecific adsorption of blood cells and also captured breast cancer cells in blood, with high efficiency (approximately 87%) and specificity. We therefore feel that this new capability of externally tuning and manipulating fluid flow could have wide applications as an innovative approach to enhance the specific capture of rare cells such as cancer cells in blood.

Nanoherding : plasma-chemical synthesis and electric-charge-driven self organization of SiO2 nanodots

We report on the chemical synthesis of the arrays of silicon oxide nanodots and their self-organization on the surface via physical processes triggered by surface charges. The method based on chemically active oxygen plasma leads to the rearrangement of nanostructures and eventually to the formation of groups of nanodots. This behavior is explained in terms of the effect of electric field on the kinetics of surface processes. The direct measurements of the electric charges on the surface demonstrate that the charge correlates with the density and arrangement of nanodots within the array. Extensive numerical simulations support the proposed mechanism and prove a critical role of the electric charges in the self-organization. This simple and environment-friendly self-guided process could be used in the chemical synthesis of large arrays of nanodots on semiconducting surfaces for a variety of applications in catalysis, energy conversion and storage, photochemistry, environmental and biosensing, and several others.

The effect of temperature on the mechanism of photoluminescence from plasma-nucleated, nitrogenated carbon nanotips

Nitrogenated carbon nanotips (NCNTPs) have been synthesized using customized plasma-enhanced hot filament chemical vapor deposition. The morphological, structural, and photoluminescent properties of the NCNTPs are investigated using scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. The photoluminescence measurements show that the NCNTPs predominantly emit a green band at room temperature while strong blue emission is generated at 77 K. It is shown that these very different emission behaviors are related to the change of the optical band-gap and the concentration of the paramagnetic defects of the carbon nanotips. The studies shed light on the controversies on the photoluminescence mechanisms of carbon-based amorphous films measured at different temperatures. The relevance of the results to the use of nitrogenated carbon nanotips in light-emitting optoelectronic devices is discussed.

Observations on the formation, growth and chemical composition of aerosols in an urban environment

The charge and chemical composition of ambient particles in an urban environment were determined using a Neutral Particle and Air Ion Spectrometer and an Aerodyne compact Time-Of-Flight Aerosol Mass Spectrometer. Particle formation and growth events were observed on 20 of the 36 days of sampling, with eight of these events classified as strong. During these events, peaks in the concentration of intermediate and large ions were followed by peaks in the concentration of ammonium and sulphate, which were not observed in the organic fraction. Comparison of days with and without particle formation events revealed that ammonium and sulphate were the dominant species on particle formation days while high concentrations of biomass burning OA inhibited particle growth. Analyses of the degree of particle neutralisation lead us to conclude that an excess of ammonium enabled particle formation and growth. In addition, the large ion concentration increased sharply during particle growth, suggesting that during nucleation the neutral gaseous species ammonia and sulphuric acid react to form ammonium and sulphate ions. Overall, we conclude that the mechanism of particle formation and growth involved ammonia and sulphuric acid, with limited input from organics.

Graphitization of nanocrystalline carbon microcoils synthesized by catalytic chemical vapor deposition

Graphitization, a common process involving the transformation of metastable nongraphitic carbon into graphite is one of the major present-day challenges for micro- and nanocarbons due to their unique structural character and highly unusual thermal activation. Here we report on the successful graphitization of nanocrystalline carbon microcoils prepared by catalytic chemical vapor deposition and post-treated in argon atmosphere at temperatures ∼2500 °C for 2 h. The morphology, microstructure, and thermal properties of the carbon microcoils are examined in detail. The graphitization mechanism is discussed by invoking a model of structural transformation of the carbon microcoils. The results reveal that after graphitization the carbon microcoils are prominently purified and feature a clear helical morphology, as well as a more regular and ordered microstructure. The interlayer spacing of the carbon microcoils decreases from 0.36 to 0.34 nm, whereas the mean crystal sizes in the c - and a -directions increase from 1.64 to 2.04 nm and from 3.86 to 7.21 nm, respectively. Thermal treatment also substantially improves the antioxidation properties of the microcoils by lifting the oxidation onset temperature from 550 to 672 °C. This process may be suitable for other nongraphitic micro- and nanomaterials.

Binding mechanism of affinity ligands for purification of plasmid DNA

Plasmid DNA for therapeutic and vaccination purposes must be highly purified. The high selectivity of affinity chromatography makes it ideal for the isolation of pDNA from complex biological feed stocks. Affinity chromatography makes use of the biological function and/or individual chemical structure of the interacting molecules. However, the success of any affinity purification protocol is dependent on the availability of suitable ligands. In this study, surface plasmon resonance (SPR) based Biacore system has been employed for the detection and quantification of the binding between lac operon (lacO) sequence contained in a pDNA and synthetic peptides based on the DNA-binding domain of the lac repressor protein, lad. The equilibrium dissociation constant (K D) and association and dissociation rate constants (ka, kd) for the interaction between plasmid DNA and designed peptides were determined.

Chemical Modification Studies of Gelonin - Involvement of Arginine Residues in Biological-Activity

Gelonin inhibits protein synthesis by inactivating the eukaryotic 60 S ribosomal subunit by an unknown mechanism. The protein was purified in high yield by a new method using Cibacron blue F3GA-Sepharose. Chemical modification studies reveal that arginine residues are essential for biological activity.

Biophysical response of living cells to boron nitride nanoparticles: Uptake mechanism and bio-mechanical characterization

Boron nitride nanomaterials have attracted significant interest due to their superior chemical and physical properties. Despite these novel properties, investigation on the interaction between boron nitride nanoparticle (BN NP) and living systems has been limited. In this study, BN NP (100–250 nm) is assessed as a promising biomaterial for medical applications. The toxicity of BN NP is evaluated by assessing the cells behaviours both biologically (MTT assay, ROS detection etc.) and physically (atomic force microscopy). The uptake mechanism of BN NP is studied by analysing the alternations in cellular morphology based on cell imaging techniques. The results demonstrate in vitro cytocompatibility of BN NP with immense potential for use as an effective nanoparticle for various bio-medical applications.

Mode of Coordination and Chemical Reactivity of Alpha-Imine Hydrasone Ligands

Interaction of nickel(I1) and copper(I1) complexes of 4,9-dimethy1-5,8-diazadodeca-4,8diene-2,1 ldione, Ni(baen) and 4,6,9-trimethyl-5, 8diazadodeca-4,8-diene-2,ll-dione, Ni(bapn), with arene diazonium chlorides in buffered solutions of methanol yielded metal derivatives of glyoxaliminearylhydrazones. This typical electrophilic addition at the 3-carbon of the complex occurs owing to the pseudo aromatic behaviour of the chelate ring. A mechanism which predicts the attack of the diazonium cation through the coordination shell of the metal is well documented from the available experimental evidences. The chemical reactivity of a few complexes with a single residual non-substituted y-carbon is reasonably manifested by their reaction with phenyl isocyanate.

Kinetic mechanism of the interaction of D-cycloserine with serine hydroxymethyltransferase

The kinetic mechanism for the interaction of D-cycloserine with serine hydroxymethyltransferase (EC2.1.2.1) from sheep liver was established by measuring changes in the activity, absorbance, and circular dichoism (CD) of the enzyme. The irreversible inhibition of the enzyme was characterized by three detectable steps: an initial rapid step followed by two successive steps with rate constants of 5.4 X s-l and 1.4 X lo4 s-l. The first step was distinguished by a rapid disappearance of the enzyme absorbance peak at 425 nm, a decrease in the enzyme activity to 25% of the uninhibited velocity, and a lowering of the CD intensity at 432 nm to about 65% of the original value. The second step of the interaction was accompanied by a complete loss of enzyme.