Formation Of Open Channels Research Articles

Resorcinol-formaldehyde-assisted dissolution-regrowth strategy for synthesis of hollow silica nanoparticles with tunable morphology

A surfactant-free, resorcinol-formaldehyde (RF)-assisted dissolution-regrowth strategy has been reported to prepare hollow silica nanoparticles with various morphologies. RF, as a pore-forming agent, is introduced into a typical stöber system (ethanol-water-ammonia) to achieve the purpose of pore-forming and as a nanoplatform. As the reaction progresses, the initially formed RF core gradually dissolves and then slowly deposits on the silica shell formed by the outer layer, resulting in the formation of a hollow structure. The RF deposited in the silica shell is then further removed by calcination in air, and a silica shell layer with a rough surface can be successfully obtained. More importantly, when additional phenolic is added to the reaction system again at the desired time, the hollow nanostructures with open pores can also be prepared. The formation of open channels is mainly attributed to the removal of RF in the SiO2/RF composite shell by calcination. Other experimental parameters such as ethanol-to-water ratio, ammonia concentration, and reaction temperature are also investigated. The internal cavity can be precisely adjusted from 100 to 175 nm, and the thickness of the silica shell can be tuned from 25 to 60 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are employed to characterize the morphology, structure, and evolution process of the resulting hollow silica nanoparticles. A possible mechanism to account for the formation of hollow silica nanoparticles with different morphologies is also proposed. In addition, the adsorption of bovine serum albumin (BSA) by hollow silica nanoparticles with rough surface and mesoporous structure is also performed, and the results show that hollow mesoporous silica nanoparticles are more effective for the immobilization of BSA.

Germanium Nanoparticle-Dispersed Reduced Graphene Oxide Balls Synthesized by Spray Pyrolysis for Li-Ion Battery Anode

Simple fabrication of a powdered Ge-reduced graphene oxide (Ge-rGO) composite via spray pyrolysis and reduction is introduced herein. Successful incorporation of the rGO nanosheets with Ge hindered the aggregation of Ge and conferred enhanced structural stability to the composite by alleviating the mechanical stress associated with drastic volume changes during repeated cycling. The Li-ion storage performance of Ge-rGO was compared with that of powdered Ge metal. The reversible discharge capacity of Ge-rGO at the 200th cycle was 748 mA h g−1 at a current density of 1.0 A g−1 and Ge-rGO showed a capacity of 375 mA h g−1 even at a high current density of 5.0 A g−1. The excellent performance of Ge-rGO is attributed to the structural robustness, enhanced electrical conductivity, and formation of open channels between the rGO nanosheets, which facilitated electrolyte penetration for improved Li-ion diffusion. Key words: Lithium ion batteries, Germanium, Graphene, Carbon composite, Spray pyrolysis

Novel charge transfer supramolecular assemblies with Keggin anions and 2-amino-5-nitropyridine

Several novel compounds with the non-linear optical chromophore 2-amino-5-nitropyridine (2A5NP) and Keggin polyoxoanions (alpha-isomers), having the general formula (2A5NP)(m)H(n)[XM12O40].xH2O, M = Mo, W, were synthesised. Compounds were obtained with X = P, n = 3, m = 3 and 4 and X = Si, n = m = 4 (x = 2-6). Thus, for each of the anions [PMo12O40]3- and [PW12O40]3- two different compounds were obtained, with the same anion and organic counterpart but with a different stoichiometric ratio. These presented different charge transfer properties and thermal stability. All compounds were characterised by spectroscopic and analytical techniques. The single crystal X-ray diffraction structure of (2A5NP)4H3[PMo12O40].2.5H2O.0.5C2H5OH showed that the water solvent molecules and the organic chromophores are assembled via infinite one-dimensional chains of hydrogen bonds with formation of open channels, which accommodate [PMo12O40]3- and ethanol solvent molecules.

Electrochemical study of monolayers of heterocyclic thiols self-assembled on polycrystalline gold electrode: the effect of solution pH on redox kinetics

Monolayer assembly of 2-mercaptobenzothiazole (MBT) and 2-mercaptobenzimidazole (MBI) onto gold surface from its dilute ethanol solutions has been investigated by electrochemistry. Aqueous redox probes, such as Fe(CN) 6 4−/3− and Ru(NH 3) 6 3+/2+ can sufficiently diffuse into the monolayer of MBT and MBI, because significant diffusion-limited current peaks are observed when the reduction/oxidation reactions take place in acidic solution, showing that the monolayer is very loosely packed or dominated by defects. However, the study on the electron transfer (ET) of Fe(CN) 6 4−/3− and Ru(NH 3) 6 3+/2+ in neutral solution confirms that the MBT and MBI monolayer, can passivate the gold electrode surface rather effectively for its low ratio of pinhole defects. These unusual properties of MBT and MBI monolayers are attributed to the protonation of the N atom, at the MBT and MBI molecules in acidic solution. It is proposed that two effects, which exist at the same time, decide the electron transfer kinetics in acidic solution. First, the attractive or repulsive interaction between the positively charged monolayer and negatively or positively charged probes. Second, the repulsion among the positively charged monolayer molecules that results in the structure reorganization or reorientation, and less compactness of the monolayer, even the formation of open channels in monolayer provided that the repulsion among monolayer molecules is strong enough.

Optimisation of Injection Moulding Process for Silicon Nitride Components

The major objective of this study was to develop an optimised process for manufacturing silicon nitride components. The effects of solid content, binder type, debinding solvent, and thermal debinding heat profile were investigated. Injection parameters such as pressure, speed, and temperature were also investigated and were found to have substantial influence on the mechanical properties of products. Solvent debinding before thermal debinding substantially reduced the debinding time through the formation of open channels in the binder. A debinding model is proposed based on experimental observations. The defects were considerably reduced and strength was enhanced by cold isostatic pressing without causing significant dimensional changes in the sintered body. Complex shaped silicon nitride blades with density 97% of theoretical and 880 MN m−2 in bend strength were made successfully. PM/0704

Inhibition of Glycosylation Induces Formation of Open Connexin-43 Cell-to-Cell Channels and Phosphorylation and Triton X-100 Insolubility of Connexin-43

We transfected the cDNA for the cell-to-cell channel protein connexin-43 (Cx43) into Morris hepatoma H5123 cells, which express little Cx43 and lack gap junctional communication (open cell-to-cell channels). We found that cells overexpressing Cx43 nonetheless lacked open cell-to-cell channels, but that inhibition of glycosylation by tunicamycin induced open channels in these cells. Tunicamycin also induced biochemical changes in Cx43 protein; the level increased, and a considerable fraction became phosphorylated and Triton X-100 insoluble, in contrast to untreated cells where Cx43 was non-phosphorylated and Triton X-100 soluble. Although tunicamycin caused the formation of open channels, channels were not found aggregated into gap junctional plaques, as they are when they have been induced by elevation of intracellular cAMP. The results suggest that although Cx43 itself is not glycosylated, other glycosylated proteins influence Cx43 posttranslational modification and the formation of Cx43 cell-to-cell channels.

The effect of hyperglycemia on brain capillary permeability in the lizard, Anolis carolinensis. A freeze-fracture analysis of blood-brain barrier pathology

The anatomical basis of the blood-brain barrier in the American chameleon, Anolis carolinensis, is the system of tight intercellular junctions that occurs between apposed endothelial cells of brain capillaries. Under normal physiological conditions, capillaries in the brain cortex of these animals remain sealed by interendothelial zonulae occludentes and, consequently, escape of exogenous tracer proteins such as horseradish peroxidase (HRP) into the extracellular compartment of the central nervous system is prevented. Systemic injection of 2.7 mg of d-glucose into chameleons results in increased brain capillary permeability, as evidenced by escape of HRP or Trypan blue into the intercellular spaces of central neuropil. Freeze-fracture analysis of brain capillary endothelia of glucose-hyperglycemic lizards revealed no alteration of the ridge and groove construction of endothelial tight junctions, indicating that although the blood-brain interface becomes leaky during severe hyperglycemia, the capillary zonulae occludents are not affected. Evidence obtained in this study strongly supports the notion that the increased capillary permeability is the result of amplified transendothelial transport. The effect is manifest as and facilitated by the formation of chains of pinocytotic vesicles derived from the luminal surface of the endothelial cells, which fuse to create open trans-endothelial conduits. It is likely that formation of open channels that traverse brain capillary endothelial cells, as a response to hyperglycemia, could allow temporarily unrestricted passage of a wide range of molecules, some potentially toxic, into the CNS extracellular milieu. This is the first report to unequivocally document with freeze-cleave techniques, that abnormally elevated levels of blood sugar can affect blood-brain interface permeability. This finding suggests that similar consequences may be expected to result from diabetic hyperglycemia in humans.