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At least 811 records · Page 45Linked to original sources
PubMed2004

Thermogravimetric studies of benzoylthiourea-modified MCM-41 after adsorption of mercury ions from aqueous solutions.

High-resolution thermogravimetry (HR TG) was used to study the adsorption of mercury(II) ions by modified MCM-41 material and regeneration of the loaded adsorbent with mercury ions by using different eluents. The weight change curves were measured for MCM-41 samples modified with 1-benzoyl-3-propylthiourea ligand loaded with mercury ions. The differential thermogravimetric (DTG) curves were analyzed to investigate the adsorption of mercury ions by the aforementioned multifunctional ligand and to monitor the decomposition of the metal-ligand complexes. A series of experiments performed for different Hg(2+):ligand ratios allowed us to correlate the adsorption data for mercury ions measured by means of UV spectrophotometry with those obtained by HR TG analysis. The DTG results provided additional information about mercury-ligand interactions as well as the thermal stability of mercury-ligand complexes. This study shows that HR TG is a very attractive technique for studying the adsorption of mercury ions on modified nanoporous silicas and monitoring their regeneration. Since the samples used are small, this method seems to be promising for studying adsorption systems of environmental significance.

Adsorption↗
PubMed2004

An endothelial and astrocyte co-culture model of the blood-brain barrier utilizing an ultra-thin, nanofabricated silicon nitride membrane.

The endothelial cells comprising brain capillaries have extremely tight intercellular junctions which form an essentially impermeable barrier to passive transport of water soluble molecules between the blood and brain. Several in vitro models of the blood-brain barrier (BBB) have been studied, most utilizing commercially available polymer membranes affixed to plastic inserts. There is mounting evidence that direct contact between endothelial cells and astrocytes, another cell type found to have intimate interaction with the brain side of BBB capillaries, is at least partially responsible for the development of the tight intercellular junctions between BBB endothelial cells. However, the membranes commonly used for BBB in vitro models are lacking certain attributes that would permit a high degree of direct contact between astrocytes and endothelial cells cultured on opposing sides. This work is based on the hypothesis that co-culturing endothelial and astrocyte cells on opposite sides of an ultra-thin, highly porous membrane will allow for increased direct interaction between the two cell types and therefore result in a better model of the BBB. We used standard nanofabrication techniques to make membranes from low-stress silicon nitride that are at least an order of magnitude thinner and at least two times more porous than commercial membrane inserts. An experimental survey of pore sizes for the silicon nitride membranes suggested pores approximately 400 nm in diameter are adequate for restricting astrocyte cell bodies to the seeded side while allowing astrocyte processes to pass through the pores and interact with endothelial cells on the opposite side. The inclusion of a spun-on, cross-linked collagen membrane allowed for astrocyte attachment and culture on the membranes for over two weeks. Astrocytes and endothelial cells displayed markers specific to their cell types when grown on the silicon nitride membranes. The transendothelial electrical resistances, a measure of barrier tightness, of endothelial and astrocyte co-cultures on the silicon nitride membranes were comparable to the commercial membranes, but neither system showed synergy between the two cell types in forming a tighter barrier. This lack of synergy may have been due to the loss of ability of commercially available primary bovine brain microvascular endothelial cells to respond to astrocyte differentiating signals.

Animals↗
PubMed2005

Fabrication and characterization of high-temperature microreactors with thin film heater and sensor patterns in silicon nitride tubes.

In this paper the fabrication and electrical characterization of a silicon microreactor for high-temperature catalytic gas phase reactions, like Rh-catalyzed catalytic partial oxidation of methane into synthesis gas, is presented. The microreactor, realized with micromachining technologies, contains silicon nitride tubes that are suspended in a flow channel. These tubes contain metal thin films that heat the gas mixture in the channel and sense its temperature. The metal patterns are defined by using the channel geometry as a shadow mask. Furthermore, a new method to obtain Pt thin films with good adhesive properties, also at elevated temperatures, without adhesion metal is implemented in the fabrication process. Based on different experiments, it is concluded that the electrical behaviour at high temperatures of Pt thin films without adhesion layer is better than that of Pt/Ta films. Furthermore, it is found that the temperature coefficient of resistance (TCR) and the resistivity of the thin films are stable for up to tens of hours when the temperature-range during operation of the microreactor is below the so-called "burn-in" temperature. Experiments showed that the presented suspended-tube microreactors with heaters and temperature sensors of Pt thin films can be operated safely and in a stable way at temperatures up to 700 degrees C for over 20 h. This type of microreactor solves the electrical breakdown problem that was previously reported by us in flat-membrane microreactors that were operated at temperatures above 600 degrees C.

Biosensing Techniques↗
PubMed2005

The oxidation of water by cerium(IV) catalysed by nanoparticulate RuO2 on mesoporous silica.

Mesoporous silicates are prepared by templating on the hexagonal (H1) mesophase of surfactant bipyridine complexes of ruthenium(II) using a true liquid-crystal templating approach. On calcination, the surfactant template is removed except for the central metal ion that is oxidised, forming nanoparticles of RuO2 that deposit within the pores. RuO2 is a known oxidation catalyst and, despite its anhydrous nature in these silicates, is found to be very active in catalyzing the oxidation of water by acidic CeIV.

2,2'-Dipyridyl↗
PubMed2005

Atomic scale modelling of the cores of dislocations in complex materials part 2: applications.

In an accompanying article, we have described a methodology for the simulation of dislocations in structurally complex materials. We illustrate the applicability of this method through studies of screw dislocations in a structurally simple ionic ceramic (MgO), a molecular ionic mineral (forsterite, Mg2SiO4), a semi-ionic zeolite (siliceous zeolite A) and a covalent molecular crystalline material (the pharmaceutical, orthorhombic paracetamol-II). We focus on the extent of relaxation and the structure of the dislocation cores and comment on similarities and points of disparity between these materials. It is found that the magnitude of the relaxation varies from material to material and does not simply correlate with the magnitude of the principal elastic constants in an easily predictable fashion, or with the size of the cohesive lattice energy or length of the Burgers vector, which emphasises the need to model the non-linear forces and atomic structure of the core.

Acetaminophen↗
PubMed2005

The coordination chemistry of the C1-symmetric bis(silyl)methyl ligand [CH(SiMe3){SiMe(OMe)2}]- revisited: Li/M- (M = Zn, Tl, Ce), Li4- or Ce2-methoxy-bridged alkyls.

The following crystalline oligonuclear metal alkyls have been synthesised under mild conditions and structurally characterised: [(THF)Li(mu-A)(mu-Cl)(mu3-OMe)Zn]2, [Li(mu-A)2Tl]2(4 and 4'), [Li4(mu-A)3(micro3-OMe)]5, [(mu-A)Li2(mu-A)2(mu3-OMe)Ce(A)](6) and [Ce(A)(mu2-OMe){mu2-OS(O)(CF3)O}]2(11)[= CH(SiMe3){SiMe(OMe)2}]. Compounds 2-6 were obtained from [Li(mu-A)]infinity(1) and ZnCl2(3), TlCl (4 and 4' and 5) and CeCl3(6), and 11 was isolated from K(A)(prepared from 1 + KOBu(t)) and cerium(III) triflate Ce(OTf)3. The principal novel features are (i) and (ii) as follows. As for (i), the diversity of ligand-to-metal bonding is noteworthy, the ligand being (a)C,O-bridging in 3{as in the known compounds 1 and in [Li2Mg5(mu3-OMe)6(mu2-OMe)2(mu2-A)4](2)}; (b)C,O,O'-bridging and O,O'-chelating in 4 and 4'; (c)C,O,O'-bridging in 5; (d)C,O,O'-bridging and C,O-chelating in 6; and (e)C,O-chelating in 11. Regarding (ii), it is interesting that the ligand [A]- is surprisingly ready to undergo fragmentation by Si-OMe cleavage and thereby present bridging methoxy ligands (mu2-OMe)2 to a pair of Ce3+ ions in 11, or mu3-OMe acting as a cap for triangular arrays of three hard metal ions (Mg3 in 2, LiZn2 in 3, Li3 in 5, and Li2Ce in 6).

Alkanes↗
PubMed2005

Structure and stability of oxygen adsorption on Si(n) (n = 5-10) clusters.

The structures, binding energies, and electronic properties of one oxygen atom (O) and two oxygen atoms (2O) adsorption on silicon clusters Si(n) with n ranging from 5 to 10 are studied systematically by ab initio calculations. Twelve stable structures are obtained, two of which are in agreement with those reported in previous literature and the others are new structures that have not been proposed before. Further investigations on the fragmentations of Si(n)O and Si(n)O2 (n = 5-10) clusters indicate that the pathways Si(n)O --> Si(n-1) + SiO and Si(n)O2 --> Si(n-2) + Si2O2 are most favorable from thermodynamic viewpoint. Among the studied silicon oxide clusters, Si8O, Si9O, Si5O2 and Si8O2 correspond to large adsorption energies of silicon clusters with respect to O or 2O, while Si8O, with the smallest dissociation energy, has a tendency to separate into Si7 + SiO. Using the recently developed quasi-atomic minimal-basis-orbital method, we have also calculated the unsaturated valences of the neutral Si(n) clusters. Our calculation results show that the Si atoms which have the largest unsaturated valences are more attractive to O atom. Placing O atom right around the Si atoms with the largest unsaturated valences usually leads to stable structures of the silicon oxide clusters.

Adsorption↗
PubMed2005

A missing allene of heavy Group 14 elements: 2-germadisilaallene.

The first stable 2-germadisilaallene was synthesized by the reduction of a 2 ratio 1 mixture of a stable dialkylsilylene and dichlorogermylene-dioxane complex with KC8; the 2-germadisilaallene showed dynamic disorder similar to the corresponding trisilaallene in the solid state.

Alkadienes↗
PubMed2003

Single-molecule near-field optical energy transfer microscopy with dielectric tips.

The fluorescence lifetime and the fluorescence rate of single molecules are recorded as a function of the position of a Si3N4 atomic force microscopy tip with respect to the molecule. We observe a decrease of the excited state lifetime and the fluorescence rate when the tip apex is in close proximity to the molecule. These effects are attributed to the fact that the dielectric tip converts non-propagating near-fields to propagating fields within the dielectric tip effectively quenching the fluorescence. The spatial extension of the quenching area is of subwavelength dimensions. The results are discussed in terms of molecular fluorescence in a system of stratified media. The experiment provides surprising new insights into the interactions between a fluorescent molecule and a dielectric tip. The methodology holds promise for applications in ultra high-resolution near-field optical imaging at the level of single fluorophores.

Carbocyanines↗
PubMed2004

[Biocompatibilty of silicon nitride ceramic in vitro. A comparative fluorescence-microscopic and scanning electron-microscopic study].

BACKGROUND: With regard to its favorable physical properties, silicon nitride ceramic is considered as biomaterial for human medical application. Minor controversy exists about the biocompatibility of the material. METHODS: Cytotoxicity testing, cell viability and morphology assessment was performed applying the L929-mice fibroblast cell culture model in a direct contact assay. Testing materials were silicon nitride ceramics of different surface properties and titanium alloy as a reference. Polyvinylchloride served as a negative control. The cells were stained with bisbenzimide and propidium iodine for double fluorochromasia viability testing, and evaluated by inversion-fluorescence microscopy. Scanning electron microscopy was applied to additionally investigate cell morphology. RESULTS: No cytotoxic effects were observed on the silicon nitride ceramic samples; moreover cell morphology remained the same as on titanium. Avital cells were present exclusively on PVC. The cell growth in the silicon nitride samples showed no significant differences compared to titanium. Cell counts on all polished surfaces showed significantly higher numbers. Scanning electron microscopy revealed typical fibroblast morphology with filiform extensions. CONCLUSION: The current results indicate a favorable biocompatibility of silicon nitride ceramic. Cell growth, viability and morphology are comparable to parameters of titanium. Polished surfaces appear to promote cell growth. Further in vivo studies are mandatory prior to human medical application. Owing to its favorable physiochemical properties, especially its superior resistance to mechanical stress, silicon nitride could serve as a biomaterial for osteosynthesis of bone with mucosal attachment.

Alloys↗
PubMed1991

Facial translocation approach to the cranial base: the anatomic basis.

Surgical exposure of the nasopharyngeal region of the cranial base is difficult because of its proximity to key anatomic structures. Our laboratory study outlines the anatomic basis for a new approach to this complex topography. Dissections were performed on eight cadaver halves and two fresh specimens injected with intravascular silicone rubber compound. By utilizing facial soft tissue translocation combined with craniofacial osteotomies; a wide surgical field can be obtained at the skull base. The accessible surgical field extends from the contralateral custachian tube to the ipsilateral geniculate ganglion, including the nasopharyax; clivus, sphonoid, and cavernous sinuses, the entire infratemporal fossa, and superior orbital fissure. The facial translocation approach offers previously unavailable wide and direct exposure, with a potential for immediate reconstruction, of this complex region of the cranial base.

Journal Article↗
PubMed2005

Ab initio molecular-orbital study of structures and energetics of Si3H3 neutral and anion.

The geometric structures and isomeric stabilities of various stationary points in Si(3)H(3) neutral and its anion are investigated at the coupled-cluster singles, doubles (triples) [CCSD(T)] level of theory. For geometrical surveys, the basis sets used are of the Dunning's correlation consistent basis sets of triple-zeta quality for the neutral. To the anions, the Dunning's correlation consistent basis sets of double-zeta quality with diffuse functions are applied. For the three lower-lying anion isomers, the Dunning's correlation consistent basis sets of triple-zeta quality with diffuse functions (aug-cc-pVTZ) are also used. The final energies for the optimized stationary points are calculated at the CCSD(T) level of theory with the aug-cc-pVTZ basis sets. The basis sets of 6-311++G(3df,2pd) were also used for the lower-lying anion isomers. The Gaussian-2 method was performed only for the lower-lying anion isomers to clarify the relative stabilities. The global minimum neutral 1 (C(1):(2)A) has an unsymmetrical hydrogen-bridged bond; the conformer 2 in C(s) symmetry is a saddle point connecting the two equivalent isomers 1. Two lower-lying isomers (3 and 4) are also predicted within the energy range of 20 kJmol. In the anion, however, the conformer 4 (C(s):(1)A(')) with five formal valence electrons is a global minimum. Two more isomers (2 and 3) lie within 20 kJmol as in the neutral; the conformer 1 converts to the isomer 2. The quartets for the neutrals and diradical triplets for the anions were further studied; lower-lying quartets and triplets, competing with the corresponding doublet and singlet, respectively, were not found in the present systems. The vertical and adiabatic electron affinities of the global minimum neutral 1, producing the second lowest-lying anion isomer 2, amount to 2.18 and 2.35 eV, respectively, at the CCSD(T)/aug-cc-pVTZ level of theory. The electron addition to the third lowest-lying neutral isomer 4 produces the largest vertical electron affinities of 2.48 eV. The D(3h) structure, being the global minimum in the corresponding Si(3)H(3) (+) cation (trisilacyclopropenyl cation), converts to the isomer 8 (C(s)) or 11 (C(2)) due to the Jahn-Teller effect in the Si(3)H(3) neutral.

Anions↗