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Query: UNIPROT:Q86TM3 (cage)
 29,987 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

During the tip approach to hydrophobic surfaces like the water/air interface, the measured interaction force reveals a strong attraction with a range of approximately 250 nm at some points along the interface. The range of this force is approximately 100 times larger than the measured for gold (approximately 3 nm) and 10 times larger than the one for hydrophobic silicon surfaces (approximately 25 nm). At other points the interface exerts a medium range repulsive force growing stepwise as the tip approaches the interface plane, consequently the hydrophobic force is a strong function of position. To explain these results we propose a model where the force on the tip is associated with the exchange of a small volume of the interface with a dielectric permittivity epsilon(int) by the tip with a dielectric permittivity epsilon(tip). By assuming a oscillatory spatial dependence for the dielectric permittivity it is possible to fit the measured force profiles. This dielectric spatial variation was associated with the orientation of the water molecules arrangement in the interfacial region. Small nanosized hydrogen-bond connected cages of water molecules present in bulk water at the interface are oriented by the interfacial electric field generated by the water molecules broken bonds, one broken hydrogen bond out of every four. This interfacial field orients small clusters formed by approximately 100 water molecules into larger clusters (approximately 100 nm). In the limit of small (less than 5 nm thick) water molecule cages we have modeled the static dielectric permittivity (epsilon) as the average response of those cages. In these regions the dielectric permittivity for water/air interfaces decreases monotonically from the bulk value epsilon approximately 80 to approximately 2 at the interface. For regions filled with medium size cages, the tip senses the structure of each cage and the static dielectric permittivity is matched to the geometrical features of these cages sized approximately 25 to 40 nm. Interfacial electric energy density values were calculated using the electric field intensity and the dielectric permittivity obtained by the fitting of the experimental points. The integration of the electric energy density along the interfacial region gives a value of 0.072 J m(-2) for interfacial energy density for points where the hydrophobic force has a range of approximately 250 nm. Regions formed by various clusters result in lower values of the interfacial energy density.
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PMID:Water molecule clusters measured at water/air interfaces using atomic force microscopy. 1635 37

By ab initio supercomputer simulation highly symmetrical cage-structures of silicon with nanometer-sizes were predicted without any experimental parameters. These novel structures, which now are called silicon fullerenes have been produced experimentally following our theoretical predictions. Since silicon is manufactured with ultra-high purity and cheep in cost, and is safe for health, all of these facts make it possible to be used in medical applications. Some of these nanostructured materials have appropriate optical properties emitting strong visible light suitable for cancer detections with additional peptide which has antigen-antibody reaction. Presently we select CdSe nanoparticles for actual in vivo experiments which already commercialized, and successful results to detect the exact position of cancer for mouse from outside of the body have been obtained.
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PMID:[Discovery of silicon fullerene and its application to nanomedicine]. 1645 73

Silicon fullerene like nanostructures with six carbon atoms on the surface of Si60 cages by substitution, as well as inside the cage at various symmetry orientations have been studied within the generalized gradient approximation to density functional theory. Full geometry optimizations have been performed without any symmetry constraints using the Gaussian 03 suite of programs and the LANL2DZ basis set. Thus, for the silicon atom, the Hay-Wadt pseudopotential with the associated basis set are used for the core electrons and the valence electrons, respectively. For the carbon atom, the Dunning/Huzinaga double zeta basis set is employed. Electronic and geometric properties of the nanostructures are presented and discussed in detail. It was found that optimized silicon-carbon fullerene like nanostructures have increased stability compared to bare Si60 cage and the stability depends on the orientation of carbon atoms, as well as on the nature of bonding between silicon and carbon atoms and also on the carbon-carbon bonding.
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PMID:Novel silicon-carbon fullerene-like nanostructures: an Ab initio study on the stability of Si54C6 and Si60C6 clusters. 1657 68

In pentane solution, 2 equiv of the icosahedral CB(11)Me(12)(*) radical cleaves the Si-Si bond of hexaalkyldisilanes by boron to silicon methyl transfer with formation of 2 equiv of methyltrialkylsilanes. The loss of a methyl radical converts the CB(11)Me(12)(*) radical into an internally charge-compensated "boronium ylide" CB(11)Me(11) with a naked vertex, which can be formally viewed as a deprotonated hypercloso carborane. It has been isolated as an air-sensitive solid, stable only below approximately -60 degrees C. The naked vertex appears to be in position 12 since the material reacts instantaneously with alcohols and ethers to form the 12-alkoxy anions 12-CB(11)Me(11)OR. It reacts with many other nucleophiles to yield more complex mixtures containing similar products. DFT calculations for the four CB(11)Me(11) isomers give closed-shell ground-state electronic structures. For the isomer with naked vertex 12, a DFT computational search failed to reveal any skeletal dimers, apparently due to excessive methyl-methyl repulsions, and only a cyclic dimer bound through weak interactions of one of the 7-methyl hydrogen atoms on each cage with the empty exocyclic orbitals on B12 of the other cage was found. Natural hybrid orbital populations suggest that the three possible isomers of monomeric boronium ylides are close to true singlet ylides, with triplet states approximately 50 kcal/mol higher. The calculated electronic structure of the carbonium ylide is close to a singlet carbene, with a triplet state approximately 16 kcal/mol higher. An attempted preparation of Me(3)C(+)CB(11)Me(12)(-) yielded neopentane and products consistent with a sequential loss of methyl groups from the carborane cage with a transient formation of similar boronium ylides. Probable mechanisms of these methyl transfer reactions are considered, and the possibly quite general role of "ylide" structures in Lewis acid induced substitution reactions on the boron vertices of carboranes and boranes is noted.
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PMID:CB11Me11 boronium ylides: carba-closo-dodecaboranes with a naked boron vertex. 1666 78

We have performed unconstrained search for low-lying structures of medium-sized silicon clusters Si(31)-Si(40) and Si(45), by means of the minimum-hopping global optimization method coupled with a density-functional based tight-binding model of silicon. Subsequent geometric optimization by using density-functional theory with the PBE, BLYP, and B3LYP functionals was carried out to determine the relative stability of various candidate low-lying silicon clusters obtained from the unconstrained search. The low-lying characteristics of these clusters can be affirmed by comparing the binding energies per atom of these clusters with previously determined lowest-energy clusters(Si(n)) in the size range of 21</=n</=30. In view of the fact that there exist numerous low-lying "endohedral fullerenelike" isomers for each size in the range 30</=n</=40, we used the homologue carbon-fullerene cage to classify different families of isomers. This structural classification allows us to focus on generic features of various isomers and to group many apparently different isomers into a single family. In addition, we report a new family of low-lying clusters which have "Y-shaped three-arm" structures. Isomers in this "handmade" family can be energetically competitive as the endohedral fullerene isomers when the total energies are calculated with the BLYP or B3LYP functional.
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PMID:Structures and relative stability of medium-sized silicon clusters. V. Low-lying endohedral fullerenelike clusters Si31-Si40 and Si45. 1667 39

Iron substituted cubic cage type mesoporous molecular sieves (FeSBA-1) were synthesized for the first time in a highly acidic media using cetyltriethylammonium bromide as a template. The amount of Fe incorporation in SBA-1 can easily be controlled by the simple adjustment of the molar hydrochloric acid-to-silicon ratio. All the materials were unambiguously characterized by AAS, XRD, N2 adsorption, UV-Vis DRS, XPS, and ESR spectroscopy. The results from AAS, XRD, and N2 adsorption reveal that the iron atom can be incorporated in the framework of SBA-1 matrix without altering the structural order and the textural parameters. The nature and the coordination of iron atoms were extensively studied by XPS spectroscopy, and the results revealed that most of the iron atoms in FeSBA-1 are in +3 coordination state. UV-Vis DRS and ESR studies confirmed that the majority of the Fe atoms in FeSBA-1 exist in a tetrahedral coordination environment (most probably occupying framework positions). tert-Butylation of phenol employing tert-butanol as the alkylation agent was carried out over FeSBA-1 catalysts with different iron content and the results are compared with one-dimensional mesoporous catalysts. The influence of various reaction parameters such as reaction temperature, reactant feed ratio, weight hourly space velocity, and time-on-stream affecting the activity and selectivity of FeSBA-1 were also studied. Under the optimized reaction conditions, the FeSBA-1(36) catalyst showed superior catalytic performance for the tert-butylation of phenol as compared to the uni-dimensional mesoporous catalysts.
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PMID:Characterization and catalytic performances of three-dimensional mesoporous FeSBA-1 catalysts. 1680 Apr 96

The challenges associated with synthesizing expanded semiconductor frameworks with cage-like crystal structures continue to be of interest. Filled low-density germanium and silicon framework structures have distinct properties that address important issues in thermoelectric phonon glass-electron crystals, superconductivity and the possibility of Kondo insulators. Interest in empty framework structures of silicon and germanium is motivated by their predicted wide optical bandgaps of the same magnitude as quantum dots and porous silicon, making them and their alloys promising materials for silicon-based optoelectronic devices. Although almost-empty Na(1-x)Si136 has already been reported, the synthesis of guest-free germanium clathrate has so far been unsuccessful. Here we report the high-yield synthesis and characteristics of germanium with the empty clathrate-II structure through the oxidation of Zintl anions in ionic liquids under ambient conditions. The approach demonstrates the potential of ionic liquids as media for the reactions of polar intermetallic phases.
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PMID:A guest-free germanium clathrate. 1698 8

Mouthpieces and masks change breathing, and distract the subject. Accepted non-invasive methods avoid this problem, inductive plethysmographs and respiratory magnetometers, but are expensive and unusable in magnetic resonance imaging (MRI) scanners. Because changes in ventilation affect arterial gases, and thus cerebral blood flow, measurement of breathing is desirable during many functional MRI studies. Using an old principle, we constructed an inexpensive, non-invasive device unaffected by magnetic fields. We adapted a simple calibration method to reduce error and make the method accessible to more users. 'Pneumobelts' consist of flexible corrugated silicon tubes worn around the rib cage (RC) and the abdomen (AB). Changes in RC and AB are determined from pressure changes within the 'pneumobelts'. Estimates of tidal volume are generated from the sum of the RC and AB changes. We empirically determined the appropriate RC weighting as 1.3:1 (RC:AB). Volume estimation was tested (n = 9) in different body positions and during different breathing maneuvers. The weighted sum of the two signals gave an accurate estimate of tidal volume with tidal volumes less than 1200 ml (mean error = 6-7%). Breaths over 1900 ml produced larger errors (mean error = 11-16%). Our results are generalizable to any linear circumference measuring device.
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PMID:An inexpensive, MRI compatible device to measure tidal volume from chest-wall circumference. 1723 87

The purpose of this study was to develop an instrument (the Purdue instrument) and the corresponding methodologies to measure the electrostatic charge development (chargeability) of dry powders when they are in dynamic contact with stainless steel surfaces. The system used an inductive noncontact sensor located inside an aluminum Faraday cage and was optimized to measure the charging capabilities of a fixed volume of powder (0.5 cc). The chargeability of 5,5-diphenyl-hydantoin, calcium sulfate dihydrate, cimetidine, 3 grades of colloidal silicon dioxide, magnesium stearate, 4 grades of microcrystalline cellulose, salicylic acid, sodium carbonate, sodium salicylate, spray-dried lactose, and sulfinpyrazone were tested at 4 linear velocities, and the particle size distribution effect was assessed for 3 different grades of colloidal silicon dioxide and 4 different grades of microcrystalline cellulose. The chargeability values exhibited a linear relationship for the range of velocities studied, with colloidal silicon dioxide exhibiting the maximum negative chargeability and with spray-dried lactose being the only compound to exhibit positive chargeability. The instrument sensitivity was improved by a factor of 2 over the first generation version, and the electrostatic charge measurements were reproducible with relative standard deviations ranging from nondetectable to 33.7% (minimum of 3 replicates). These results demonstrate the feasibility of using the Purdue instrument to measure the electrostatic charge control capabilities of pharmaceutical dry powders with a reasonable level of precision.
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PMID:Chargeability measurements of selected pharmaceutical dry powders to assess their electrostatic charge control capabilities. 1728 49

We present a multistate complete active space second-order perturbation theory computational study aimed to predict the low-lying electronic excitations of four compounds that can be viewed as two disilane units connected through alkane bridges in a bicyclic cage. The analysis has focused on 1,4-disilyl-1,4-disilabicyclo[2.2.1]heptane (1a), 1,4-bis(trimethylsilyl)-1,4-disilabicyclo[2.2.1]heptane (1b), 1,4-disilyl-1,4-disilabicyclo[2.1.1]hexane (2a), and 1,4-bis(trimethylsilyl)-1,4-disilabicyclo[2.1.1]hexane (2b). The aim has been to find out the nature of the lowest excitations with significant oscillator strengths and to investigate how the cage size affects the excitation energies and the strengths of the transitions. Two different substituents on the terminal silicon atoms (H and CH3) were used in order to investigate the end group effects. The calculations show that the lowest allowed excitations are of the same character as that found in disilanes but now red-shifted. As the cage size is reduced from a 1,4-disilabicyclo[2.2.1]heptane to a 1,4-disilabicyclo[2.1.1]hexane, the Si...Si through-space distance decreases from approximately 2.70 to 2.50 A and the lowest allowed transitions are red-shifted by up to 0.9 eV, indicating increased interaction between the two Si-Si bonds. The first ionization potential, which corresponds to ionization from the Si-Si sigma orbitals, is lower in 1b and 2b than in Si2Me6 by approximately 0.9 and 1.2 eV, respectively. Moreover, 1b and 2b, which have methyl substituents at the terminal Si atoms, have slightly lower excitation energies than the analogous species 1a and 2a.
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PMID:Electronic excitations of 1,4-disilyl-substituted 1,4-disilabicycloalkanes: a MS-CASPT2 study of the influence of cage size. 1738 76


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