Formation Of Small Pores Research Articles

Titanium carbide derived nanoporous carbon for energy-related applications

High surface area nanoporous carbon has been prepared by thermo-chemical etching of titanium carbide TiC in chlorine in the temperature range 200–1200 °C. Structural analysis showed that this carbide-derived carbon (CDC) was highly disordered at all synthesis temperatures. Higher temperature resulted in increasing ordering and formation of bent graphene sheets or thin graphitic ribbons. Soft X-ray absorption near-edge structure spectroscopy demonstrated that CDC consisted mostly of sp 2 bonded carbon. Small-angle X-ray scattering and argon sorption measurements showed that the uniform carbon-carbon distance in cubic TiC resulted in the formation of small pores with a narrow size distribution at low synthesis temperatures; synthesis temperatures above 800 °C resulted in larger pores. CDC produced at 600–800 °C show great potential for energy-related applications. Hydrogen sorption experiments at −195.8 °C and atmospheric pressure showed a maximum gravimetric capacity of ∼330 cm 3/g (3.0 wt.%). Methane sorption at 25 °C demonstrated a maximum capacity above 46 cm 3/g (45 vol/vol or 3.1 wt.%) at atmospheric pressure. When tested as electrodes for supercapacitors with an organic electrolyte, the hydrogen-treated CDC showed specific capacitance up to 130 F/g with no degradation after 10 000 cycles.

On the solidification of nodular cast iron and its relation to the expansion and contraction

Directional solidification and quench-out thermal analysis experiments have been performed in Mg-treated cast iron alloys. The volume fraction of liquid, austenite and graphite was evaluated. It was observed that the volume fraction of austenite is much larger than expected from the equilibrium phase diagram at the beginning of the solidification process. It was also been observed that the last melt solidifies far below the equilibrium eutectic temperature. The solidification process was analyzed by non-equilibrium thermodynamic models. The theoretical treatment was supported by the observation that the latent heat decreases during the solidification process. The formation of small pores was observed at the very end of the solidification. An explanation for the formation of the small pores is given in terms of a vacancies creep model. The formation of macropores was related to the large fraction of austenite formed during the first part of the solidification process.

Synthesis of Micelle-Templated Silicas from Cetyltrimethylammonium Bromide/1,3,5-Trimethylbenzene Micelles

Micelle-templated silicas (MTS) were synthesized by self-assembly of inorganic silica and micelles of cetyltrimethylammonium bromide (CTAB) containing different amounts of 1,3,5-trimethylbenzene (TMB) at 343 K. Nitrogen sorption isotherms and transmission electron microscopy (TEM) showed that MTS pore size increased with the increase of TMB amount. However, at TMB/CTAB = 5 the material was characterized by double porosity, due to destabilization of the surfactant emulsion (demixed emulsion), whereas at TMB/CTAB = 13 a stable emulsion originated a solid at uniform pore size. The kinetics of formation of these MTS was followed by inserting a radical-surfactant probe in the surfactant mixture and monitoring, by computer-aided EPR analysis, the structural variations of the surfactant aggregates and of the solid over time. In the absence of TMB, the probes monitored the formation of a polar solid at the surface of the micelles. Only at t > 150 min a slow component started contributing to the EPR signal, indicating the formation of the final solid structure. As observed by EPR, at TMB/CTAB = 13, a fast organization of the micelles and a fast condensation of silica accelerated the synthesis process, and in the solid, two probe environments at different polarities were already formed and almost stabilized in the first hour of synthesis. The low polar environment, in which the nitroxide group experienced a relatively high mobility, was attributed to the localization of a portion of TMB in the vicinity of the headgroups of the surfactant aggregates. The proximity of TMB to the silica surface favored and accelerated the formation of siloxane groups. The formation of hydrophobic sites at the surface was also confirmed by 1H NMR, which indicated a lower proton coordination of the surfactants in the presence of TMB, and was further proved on calcined MTS by the decrease in the CBET parameter, which is an indicator of surface polarity. At TMB/CTAB = 5, the kinetics, in the first 100 min of the synthesis monitored by EPR, was equivalent to that found for TMB/CTAB = 13, corresponding to the fast formation of the large porosities. Then, at longer synthesis times, the same slow component as for TMB/CTAB = 0 progressively appeared and contributed to the EPR spectra, corresponding to the final formation of small pores. Therefore, in agreement with the nitrogen sorption isotherms and TEM, the solid formed at TMB/CTAB = 5 is originated by the demixing of the surfactant emulsion into two fractions: the first is TMB-rich and provides a kinetics similar to that of TMB/CTAB = 13; the second is deprived of TMB, providing a kinetics similar to that of TMB/CTAB = 0. Definitely, when TMB is used in the MTS synthesis, the synthesis rate increases and the polarity of MTS surface decreases.

Methods for pore size engineering in ZSM-5 zeolite

Pore size of ZSM-5 zeolite can be engineered by two different methods: (a) the desilication–stabilization (DS) method allows the enlargement of the size of the ZSM-5 zeolite micropores from the average value of 0.53 nm to that of 0.59 nm. (b) The desilication–reinsertion–stabilization (DRS) method results in the narrowing of the size of the zeolite micropores down to 0.46 nm. The DRS method has recently been improved by using the ammonium form of the desilicated zeolite in the reinsertion step. This is probably due to an easier reaction between the zeolite silanol groups and the orthosilicate species, which occurs during the thermal treatment. Such a reaction leads to the zeolite structure stabilization and the formation of smaller pores. Selective adsorption tests with BTX aromatics and catalytic runs performed with methanol at various reaction temperatures, confirm the pore enlargement due to the DS treatment, and the pore narrowing as the result of the DRS treatment.

Modification of the cytoplasmic domain of influenza virus hemagglutinin affects enlargement of the fusion pore.

The fusion activity of chimeras of influenza virus hemagglutinin (HA) (from A/fpv/Rostock/34; subtype H7) with the transmembrane domain (TM) and/or cytoplasmic tail (CT) either from the nonviral, nonfusogenic T-cell surface protein CD4 or from the fusogenic Sendai virus F-protein was studied. Wild-type or chimeric HA was expressed in CV-1 cells by the transient T7-RNA-polymerase vaccinia virus expression system. Subsequently, the fusion activity of the expression products was monitored with red blood cells or ghosts as target cells. To assess the different steps of fusion, target cells were labeled with the fluorescent membrane label octadecyl rhodamine B-chloride (R18) (membrane fusion) and with the cytoplasmic fluorophores calcein (molecular weight [MW], 623; formation of small aqueous fusion pore) and tetramethylrhodamine-dextran (MW, 10,000; enlargement of fusion pore). All chimeric HA/F-proteins, as well as the chimera with the TM of CD4 and the CT of HA, were able to mediate the different steps of fusion very similarly to wild-type HA. Quite differently, chimeric proteins with the CT of CD4 were strongly impaired in mediating pore enlargement. However, membrane fusion and formation of small pores were similar to those of wild-type HA, indicating that the conformational change of the ectodomain and earlier fusion steps were not inhibited. Various properties of the CT which may affect pore enlargement are considered. We surmise that the hydrophobicity of the sequence adjacent to the transmembrane domain is important for pore dilation.

Local thrombus formation in the site of intravenous injection of chlorpromazine: possible colloid-osmotic lysis of the local endothelial cells.

Since amphiphilic drugs are known to interact with biomembranes, we investigated local vessel damage and thrombosis which might be brought about by intravenous dosing using chlorpromazine (CPZ) as a representative compound. CPZ-induced hemolysis was suppressed by an increase in sucrose concentration in the medium, characterizing this hemolysis to be colloid-osmotic lysis, which includes the enhancement of membrane phospholipid fluidity and consequent small pore formation in the membranes. This was supported by the observation that hemolysis by filipin, not featuring the stage of small pore formation, was not affected by sucrose. [14C]Glucose-entrapping liposomes were degraded by CPZ, and this degradation was enhanced by an increase in the intravesicle glucose concentration. These results indicated that the compound could induce colloid-osmotic lysis in erythrocytes and artificial membrane vesicles. CPZ also injured cultured porcine aortic endothelial cells (PAEC), as evidenced by lactate dehydrogenase (LDH) leakage. This injury was also suppressed by increase in sucrose concentration in the medium, suggesting that colloid-osmotic lysis again occurred. When rats were intravenously injected with CPZ, local endothelial cell (EC) injury and associated thrombus formation were observed, suggesting that CPZ's action was also evident in vivo. To our knowledge, this is the first finding which suggests that an intravenously dosed amphiphilic drug can injure local ECs based on a colloid-osmotic lysis mechanism leading to thrombosis.

Hemifusion between Cells Expressing Hemagglutinin of Influenza Virus and Planar Membranes Can Precede the Formation of Fusion Pores that Subsequently Fully Enlarge

The chronological relation between the establishment of lipid continuity and fusion pore formation has been investigated for fusion of cells expressing hemagglutinin (HA) of influenza virus to planar bilayer membranes. Self-quenching concentrations of lipid dye were placed in the planar membrane to monitor lipid mixing, and time-resolved admittance measurements were used to measure fusion pores. For rhodamine-PE, fusion pores always occurred before a detectable amount of dye moved into an HA-expressing cell. However, with DiI in the planar membrane, the relationship was reversed: the spread of dye preceded formation of small pores. In other words, by using DiI as probe, hemifusion was clearly observed to occur before pore formation. For hemifused cells, a small pore could form and subsequently fully enlarge. In contrast, for cells that express a glycosylphosphatidylinositol-anchored ectodomain of HA, hemifusion occurred, but no fully enlarged pores were observed. Therefore, the transmembrane domain of HA is required for the formation of fully enlarging pores. Thus, with the planar bilayer membranes as target, hemifusion can precede pore formation, and the occurrence of lipid dye spread does not preclude formation of pores that can enlarge fully.

A Freeze-Fracture Study Designed to Clarify the Mechanisms of Freezing Injury Due to the Freezing-Induced Close Apposition of Membranes in Cortical Parenchyma Cells of Mulberry

Freezing injury in cortical parenchyma cells of mulberry (Morus bombycis Koidz. cv. Goroji) collected in autumn and spring was closely associated with the occurence of ultrastructural changes in the plasma membrane, namely, formation of aparticulate domains (APD) with accompanying "fracture-jump lesions" and fine irregularities, that were produced by the close apposition of membranes caused by freezing. In order to identify the cause of freezing injury due to the formation of these ultrastructural changes, frozen samples were warmed to near subzero temperatures and structural changes in plasma membranes were examined by freeze-fracture electron microscopy. The results showed that, upon warming to -5°C, stuctures in the APD in the plasma membranes were changed in a variety of ways, which include formation of small pores, shallow slits, deep slits, and wide slits with visible contents, in addition to the absence of fracture jumps. Furthermore, fusion between plasma membranes and closely apposed endomembranes was produced at the APD upon warming to -5°C. It is suggested that structures in the APD seen upon warming to -5°C might represent the variety of structures that form during the process of membrane fusion by interlamellar attachment. Further warming to -3°C resulted in more distinct structural changes in the APD, perhaps as a result of membrane fusion, and led to further structural changes in entire plasma membranes. It is suggested that the occurrence of nonphysiological fusion of membranes at the APD including fracture-jump lesions and fine irregularities might result in freezing injury.

Poly(ethylene glycol)-induced fusion and rupture of dipalmitoylphosphatidylcholine large, unilamellar extruded vesicles

High concentrations (> or = 20 wt %) of poly(ethylene glycol) (PEG) induce large, unilamellar, dipalmitoylphosphatidylcholine model membrane vesicles to fuse when the bilayers contain small amounts of amphipathic peturbant molecules. In addition to fusion, similar concentrations of PEG induce these vesicles to leak their contents. In this paper, we have asked if fusion could occur independently of leakage or if fusion might be described as local bilayer rupture followed by resealing. By following the release of MW 10,000 fluoresceinated dextran trapped inside vesicles, it was determined that PEG-induced leakage was the result of major membrane disruption and not small-pore formation. Fusion of vesicles containing 0.5 mol % palmitic acid was clearly observed at 20 wt % PEG, while 25 wt % was needed to cause rupture. On the other hand, vesicles containing 0.5 mol % lysophosphatidylcholine ruptured at roughly the same concentration needed to induce rupture. Two methods were developed for removing PEG so that fusion products could be characterized. Quasi-elastic light scattering demonstrated that fusing vesicles grew in size and that nonfusing vesicles did not. Moreover, PEG concentrations that induced rupture led to the appearance of species with mean diameters much larger than those of fused vesicles. High-resolution nuclear magnetic resonance showed that the population of large vesicles that correlated with rupture was composed of multilamellar vesicles while the population resulting from fusion alone remained unilamellar. We conclude that, upon incubation with and subsequent removal of PEG, vesicles were either unaffected, or fused to form larger, unilamellar vesicles, or ruptured to form larger, nonunilamellar species.

Effect of Preparation Conditions on Properties of Green and Sintered Body in Alumina

The effect of preparation conditions of alumina ceramics to the properties of green and sintered bodies was investigated. In this experiment, both ball milling and attrition milling techniques were applied to prepare the suspensions, and the effects of the content of an organic binder, the temperature of spray drying, and the pressure of uniaxial mold pressing and CIPing were studied to the properties of green and sintered samples. Results indicated that the density and the pore size distribution of the green compact depended upon the content of a binder, showing the densities of compacts before dewaxing were higher in the case of more amount of an added binder probably due to the effects of improved plasticity and lubricity of granules. After dewaxing, however, the addition of lower amount of a binder contributed to the increase of green densities with the formation of small pores in the matrix. Decrease of an added binder was also effective to obtain the increased density and the improved bending strength after sintering.

Hemolytic mechanism of cytolysin produced from [formula omitted

The characteristics of hemolytic action of cytolysin produced from V. vulnificus were investigated in mouse erythrocytes. The cytolysin bound erythrocyte membranes in temperature-independent manner and then lysed cells temperature-dependently. Hemoglobin release by the cytolysin was completely inhibited by the presence of raffinose or melezitose, but K + release was not affected. The cytolysin-induced hemolysis was always accompanied with the conversion of membrane-bound cytolysin into an oligomer of 210 kDa, corresponding to a tetramer of native cytolysins. Nonesterified cholesterol inactivated the cytolysin by converting active monomeric cytolysin into inactive oligomer. The results suggest that the cytolysin lyses erythrocytes due to the formation of small pores on erythrocyte membrane by cholesterol-mediated oligomerization of the cytolysin.

Magnesium oxide as a catalyst support: The influence of chlorine

The properties of MgO when used as a support material for Ru-Au catalysts have been investigated by thermal analysis, chemical analysis, surface area measurements and X-ray diffraction. During impregnation the support undergoes a bulk hydration but heating to 673 K restores the oxide. In a sample impregnated by water only, the dehydration occurs at 651 K and the surface area increases from 15 to > 300 m 2 g −1, due to the formation of small pores. Great changes in the DTA peak temperature and in the surface area after dehydration are found in the catalysts and in MgO impregnated with HCl solutions. It is shown that these changes are accurately correlated to the amount of chlorine which remains in the solid (deriving from the metal precursor compounds or HCl). The formation of basic magnesium chlorides, shown by X-ray diffraction, seems to favour an easier release of water (i.e., lower DTA peak temperatures and lower apparent activation energies) and to reduce the formation of small pores.