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PubMed2006

Water exclusion at the nanometer scale provides long-term passivation of silicon (111) grafted with alkyl monolayers.

This work is a quantitative study of the conditions required for a long-term passivation of the interface silicon-alkyl monolayers prepared by thermal hydrosilyation of neat 1-alkenes on well-defined H-Si(111) surfaces. We present electrochemical capacitance measurements (C-U) in combination with ex situ atomic force microscopy (AFM) observations and X-ray photoelectron spectroscopy (XPS) measurements. Capacitance measurements as a function of the reaction time and XPS data reveal close correlations between the chemical composition at the interface and its electronic properties. A very low density of states is found if suboxide formation is carefully prevented. The monitoring of C-U plots and AFM imaging upon exposure of the sample in diverse conditions indicate that the initial electronic properties and structure of the interface are long-lasting only when the monolayer surface coverage is theta > 0.42. A model demonstrates that this threshold value corresponds to a monolayer with intermolecular channels narrower than approximately 2.82 A, which is equal to the diameter of a water molecule. Water exclusion from the monolayer promotes long-term passivation of the silicon surface against oxidation in air and water as well as perfect corrosion inhibition in 20% NH(4)F. We provide two criteria to assess when a sample is optimized: The first one is an effective dielectric constant <2.5, and the second one is a very characteristic energy diagram at open circuit potential.

Alkenes↗

PubMed2005

Formation of disilanes in the reaction of stable silylenes with halocarbons.

Reactions of stable silylenes 1 and 2 with a variety of halogenated organic compounds have been studied. Depending on the nature of the halocarbon, the products can be disilanes, LSiX-LSiR, or monosilanes, LSiXR, or a mixture of both types of products. Hexachloroethane reacts with the silylenes to give mainly the dichlorodisilane, LSiX-LSiX. The experimental results are rationalized in terms of several related free-radical chain mechanisms.

Crystallography, X-Ray↗

PubMed1981

Correction of a lower eyelid deformity caused by multiple extrusions of alloplastic orbital floor implants.

The case of a young woman is presented in whom a silicone orbital floor implant became extruded into the maxillary sinus 8 years after its insertion for an orbital floor fracture. Two subsequent attempts at correction using silicone only compounded the problem. Ultimate correction, in two stages, required (1) an iliac bone graft to the infraorbital rim and orbital floor defects, along with a temporal muscle flap and nasal antrostomy; and (2) an upper lateral cartilage chondromucosal graft and a full-thickness postauricular skin graft. A warning is sounded against the use of alloplastic materials for major orbital floor defects, particularly when there have been problems with these materials.

Adult↗

PubMed1980

Architecture of normal pancreas as revealed by retrograde injection.

The architecture of the pancreas was revealed by retrograde injection of the pancreatic ductal system of normal rats with a silicone rubber compound, and subsequent study of the preparation by light microscopy and scanning electron microscopy. The injected material became associated with both ducts and "acinar" areas. Examination of these specimens suggests that the arrangement of the exocrine pancreas is that of a complexly curving and branching system of tubules which anastomose and end blindly. This architecture, which is not that of a true acinar gland, provides a rational basis for the understanding of the simple dedifferentiative changes that accompany pancreatic carcinogenesis, and which have been generally interpreted as representing ductular proliferation.

Animals↗

PubMed2001

Monolithic capillary electrophoresis device with integrated fluorescence detector.

A monolithic capillary electrophoresis system with integrated on-chip fluorescence detector has been microfabricated on a silicon substrate. Photodiodes in the silicon substrate measure fluorescence emitted from eluting molecules. The device incorporates an on-chip thin-film interference filter that prevents excitation light from inhibiting the fluorescence detection. A transparent AZO conducting ground plane is also used to prevent the high electric fields used for the separation from interfering with the photodiode response. Separations of DNA restriction fragments have been performed in these devices with femtogram detection limits using SYBR Green I intercalating dye.

Bacteriophage phi X 174↗

PubMed2006

Removal of some organic pollutants in water employing ceramic membranes impregnated with cross-linked silylated dendritic and cyclodextrin polymers.

Triethoxysilylated derivatives of poly(propylene imine) dendrimer, polyethylene imine and polyglycerol hyperbranched polymers and beta-cyclodextrin have been synthesized and characterized. These compounds impregnated ceramic membranes made from Al(2)O(3), SiC and TiO(2) and subsequently sol-gel reaction led to their polymerization and chemical bond formation with the ceramic substrates. The resulting organic-inorganic filters were tested for the removal of a variety of organic pollutants from water. They were found to remove of polycyclic aromatic hydrocarbons (up to 99%), of monocyclic aromatic hydrocarbons (up to 93%), trihalogen methanes (up to 81%), pesticides (up to 43%) and methyl-tert-butyl ether (up to 46%).

Ceramics↗

PubMed2002

Preparation of microspheres by an emulsification-complexation method.

Microspheres were prepared by complexation of a cationic polymer, polyquaternium-24, and an anionic surfactant, sodium lauryl sulfate (SLS). The cationic polymer solution was emulsified in dimethylsiloxane to give water in silicone emulsion (W/Si), and it was used as a template for the formation of microspheres. The emulsion was dispersed into the SLS solution. In this process, two kinds of droplets, silicone dropletes and microspheres composed of the cationic polymer and SLS, were formed, evidenced by X-ray energy dispersive spectra. The mean diameter of the microspheres was reduced from 105.7 to 64.8 mum as the stirring rate for W/Si preparation increased from 300 to 1000 rpm. It is believed that water droplets in W/Si emulsion, when exposed to SLS solution, could be solidified by the complexation of the cationic polymer and the anionic surfactant.

Dimethylpolysiloxanes↗

PubMed2004

Total synthesis of (+)-brasilenyne. Application of an intramolecular silicon-assisted cross-coupling reaction.

The first enantioselective total synthesis of (+)-brasilenyne (1) has been achieved in 19 linear steps, with 5.1% overall yield from l-(S)-malic acid. The construction of the oxonin core containing a 1,3-cis,cis diene unit was accomplished with a tandem ring-closing metathesis/silicon-assisted intramolecular cross-coupling reaction. In addition, a key propargylic stereogenic center was created through a novel, highly diastereoselective ring opening of a 1,3-dioxolanone promoted by TiCl(4). This reaction proceeded through an oxocarbenium ion intermediate and the asymmetric induction was fully controlled by l-malic acid residue. The C(8) stereogenic center was set by a reagent-controlled asymmetric allylboration.

Alkynes↗

PubMed2005

Comparison of carbon-silicon hyperconjugation at the 2- and 4-positions of the N-methylpyridinium cation.

[structure: see text] N-Methyl-2-trialkylsilylmethylpyridinium cations 6a-c and 4-trialkylsilylmethylpyridinium cations 5a-c were prepared and investigated using (29)Si and (13)C NMR and single-crystal X-ray crystallography. Systematic differences in the (29)Si chemical shifts and (29)Si-(13)C one-bond coupling constants for these cations suggested that the Si-CH(2) bond interacts more strongly at the 2-position of the electron-deficient pyridinium ring than at the 4-position. This result is supported by the X-ray structures of the pyridinium cations 5b and 6b.

Carbon↗

PubMedDate not supplied

Two-liquid-phase slurry bioreactors to enhance the degradation of high-molecular-weight polycyclic aromatic hydrocarbons in soil.

High-molecular-weight (HMW) polycyclic aromatic hydrocarbons (PAHs) are pollutants that persist in the environment due to their low solubility in water and their sequestration by soil and sediments. The addition of a water-immiscible, nonbiodegradable, and biocompatible liquid, silicone oil, to a soil slurry was studied to promote the desorption of PAHs from soil and to increase their bioavailability. First, the transfer into silicone oil of phenanthrene, pyrene, chrysene, and benzo[a]pyrene added to a sterilized soil (sandy soil with 0.65% total volatile solids) was measured for 4 days in three two-liquid-phase (TLP) slurry systems each containing 30% (w/v) soil but different volumes of silicone oil (2.5%, 7.5%, and 15% [v/v]). Except for chrysene, a high percentage of these PAHs was transferred from soil to silicone oil in the TLP slurry system containing 15% silicone oil. Rapid PAH transfer occurred during the first 8 h, probably resulting from the extraction of nonsolubilized and of poorly sorbed PAHs. This was followed by a period in which a slower but constant transfer occurred, suggesting extraction of more tightly bound PAHs. Second, a HMW PAH-degrading consortium was enriched in a TLP slurry system with a microbial population isolated from a creosote-contaminated soil. This consortium was then added to three other TLP slurry systems each containing 30% (w/v) sterilized soil that had been artificially contaminated with pyrene, chrysene, and benzo[a]pyrene, but different volumes of silicone oil (10%, 20%, and 30% [v/v]). The resulting TLP slurry bioreactors were much more efficient than the control slurry bioreactor containing the same contaminated soil but no oil phase. In the TLP slurry bioreactor containing 30% silicone oil, the rate of pyrene degradation was 19 mg L(-)(1) day(-)(1) and no pyrene was detected after 4 days. The degradation rates of chrysene and benzo[a]pyrene in the 30% TLP slurry bioreactor were, respectively, 3.5 and 0.94 mg L(-)(1) day(-)(1). Low degradation of pyrene and no significant degradation of chrysene and benzo[a]pyrene occurred in the slurry bioreactor. This is the first report in which a TLP system was combined with a slurry system to improve the biodegradation of PAHs in soil.

Biodegradation, Environmental↗

PubMed2005

Single-crystal CdSe nanowires prepared via vapor-phase growth assisted with silicon.

Hexagonal cadmium selenide (CdSe) nanowires, with diameter around 20 nm, were synthesized using a simple vapor-phase growth. Silicon (Si) powder acts as a source material assisting the synthesis, which is very important to the formation of the CdSe nanowires. We also suggest that self-catalysis at the Cd-terminated (0001) surface, together with the assistance action of Si, leads to the formation of wire-like structures to be formed. Meanwhile, the assistance of Si is responsible for the fineness and uniformity of the CdSe nanowires. The possible growth mechanism of the CdSe nanowires is proposed, and the optical property of the as-grown CdSe nanowires is characterized.

Cadmium Compounds↗

PubMed1990

The microvascular pattern of the supraspinatus tendon.

The vascular pattern of the supraspinatus tendon was studied in 18 human anatomic specimens. The ages of the specimens ranged from 26 to 84 years. Selective vascular injection with a silicon-rubber compound allowed visualization of the vascular bed of the rotator cuff and humeral head. The presence of a hypovascular or critical zone close to the insertion of the supraspinatus tendon into the humeral head was confirmed. However, only a uniformly sparse vascular distribution was found at the articular side, as opposed to the well-vascularized bursal side. This was also confirmed with histologic sections of the tendon. The poor vascularity of the tendon in this area could be a significant factor in the pathogenesis of degenerative rotator cuff tears.

Adult↗

PubMed1978

Trace elements in kidney stones from three areas in the United States.

A large number of trace elements has been found in calcium stones (whewellite, weddellite, and apatite) and in struvite. Significantly fewer elements, with lower abundances, are found in uric acid and cystine. With the exception of four trace elements (lead, silicon, strontium, and zine), the trace element assemblages are identical in the oxalates (whewellite and weddellite); struvite is also similar but with notable exceptions. In general, apatite contains approximately twice the level of trace element abundances as do the oxalates. This study is based on the distribution of 20 elements in 186 mimeralogically identified urinary calculi from three generalized areas of the United States (northeast, southeast, and midwest). In general, there is no statistical difference in the trace element assemblages of mineralogically identical stones from the three areas.

Aluminum↗

PubMed2004

Identification of endogenous surrogate ligands for human P2Y receptors through an in silico search.

G protein-coupled receptors (GPCRs) are distributed widely throughout the human body, and nearly 50% of current medicines act on a GPCR. GPCRs are considered to consist of seven transmembrane alpha-helices that form an alpha-helical bundle in which agonists and antagonists bind. A 3D structure of the target GPCR is indispensable for designing novel medicines acting on a GPCR. We have previously constructed the 3D structure of human P2Y(1) (hP2Y(1)) receptor, a GPCR, by homology modeling with the 3D structure of bovine rhodopsin as a template. In the present study, we have employed an in silico screening for compounds that could bind to the hP2Y(1)-receptor model using AutoDock 3.0. We selected 21 of the 30 top-ranked compounds, and by measuring intracellular Ca(2+) concentration, we identified 12 compounds that activated or blocked the hP2Y(1) receptor stably expressed in recombinant CHO cells. 5-Phosphoribosyl-1-pyrophosphate (PRPP) was found to activate the hP2Y(1) receptor with a low ED(50) value of 15 nM. The Ca(2+) assays showed it had no significant effect on P2Y(2), P2Y(6), or P2X(2) receptors, but acted as a weak agonist on the P2Y(12) receptor. This is the first study to rationally identify surrogate ligands for the P2Y-receptor family.

Animals↗

PubMed1997

Distribution of organosilicon polymers in augmentation mammaplasties at autopsy.

Silicone-containing breast implants have been used since 1963 for cosmetic augmentation and breast reconstruction. Currently, there is intense debate regarding the extent and mechanism of migration of silicone from the area of implant. The current study compares tissue distribution of organosilicon polymers between women with and without silicone breast implants to determine the extent of silicone migration from breast implants. Samples were collected at autopsy from 15 individuals with bilateral breast implants with no known history of chest trauma and from 14 age- and sex-matched controls. Capsule, breast, axillary lymph nodes, abdominal fat, liver, lung, and spleen were collected for analysis of organosilicon polymers by atomic absorption spectrometry and for examination by light microscopy. Blood was collected for analysis of rheumatoid factor and antinuclear antibodies. Silicone was observed microscopically in at least one capsule section from all implant cases and in at least one lymph node in 8 of 15 implant cases. Silicone was not observed in lymph nodes from control cases. Organosilicon polymers were extracted from tissue using heptane, and the silicon content of the extract was quantitated by atomic absorption spectrometry. Silicon was detected in all capsules; statistically significant increases of organosilicon polymers were measured in axillary lymph nodes, breast, and abdominal fat from individuals with silicone breast implants when compared with the nonimplant group. Measurable amounts of organosilicon polymers were found in tissues from the nonimplant group. Suitable blood specimens were analyzed for the presence of rheumatoid factor and antinuclear antibodies. All nine implant cases tested were negative for the presence of antinuclear antibodies. Three implant cases which were tested for rheumatoid factor also were negative. We conclude that organosilicon polymers routinely migrate from the site of breast implantation to regional tissues near the implant site. Tissues from nonimplant cases often contained measurable amounts of organosilicon polymers, and tissue distribution was variable within any single individual: this is consistent with the wide-spread use and form of organosilicon polymers.

Adult↗

PubMed1991

Charge calculations in molecular mechanics. Part 8. Partial atomic charges from classical calculations.

The CHARGE2 programme, which involves the classical calculation of both the inductive and resonance contributions to the partial atomic charges in molecules is described, and the charges and electrostatic potentials obtained presented for some illustrative examples. In substituted methanes (CH3X, CF3X, CCl3X) the effects of varying the electronegativity of the substituents and the alpha- and beta-substituent contributions are clearly illustrated for a variety of substituent groups X. The problems involved in the inclusion of silicon into this scheme are detailed, together with the methods of overcoming them. The partial atomic charges (sigma and pi contributions) and electrostatic potentials for some silicon oxygen compounds are presented and discussed. The partial atomic charges from CHARGE2 for all the natural amino acids as their N-acetyl, N'-methylamides are given and compared with those obtained from the AMBER and ECEPP/2 force fields. Considerable differences in these figures are observed, with the AMBER charges consistently much larger than those from the other two methods. The CHARGE2 partial atomic charges and electrostatic potentials for the four common nucleic acids, adenine, cytosine, guanine and thymine, are given and compared with those derived from other calculations. Again there is general similarity but also there are considerable differences, with those from the AMBER force field somewhat larger than the other methods.

Amino Acids↗

PubMed2005

Infrared intensities of some SiH-containing compounds in the gas-phase.

Infrared intensities measured in the gas-phase are reported for CH3SiH3, CH3SiD3, (CH3)2SiH2, (CH3)2SiD2, (SiH3)2CH2, (SiD3)2CH2, Si2H6, SiH2Cl2 and (SiH3)2O. These are compared with theoretical estimates from HF, MP2 and B3LYP calculations with the 6-311G** basis set. Literature values of nuCH intensities per bond from 18 compounds correlate linearly with the values calculated at MP2 and B3LYP levels: the corresponding HF plot is slightly curved. The new HC(Si) data fit these correlations adequately. In similar plots for SiH stretching intensity, the point for SiH2Cl2 is displaced, especially at the HF level. The lack of relation of nuCH or nuSiH intensity to Mulliken atomic charge points to the effect of varying atomic charge flux in the parameter thetamu/thetar. Anomalies associated with nuSiH intensities influenced by chlorine or OR substitution and previously explained by d(pi)-p(pi) bonding are attributed instead to charge flux variation. For silyl groups, deformation band intensities are roughly additive according to the number of such groups. However, this is not the case for the methyl symmetric deformation bands in methyl and dimethyl silanes.

Models, Molecular↗

PubMed2004

Electron spin resonance study of phosphorus-nitroxides from 1,3-additions of silicon-phosphorus reagents to nitrones.

This article explores a new, convenient route to beta-phosphorus nitroxides. Specifically, the reaction sequence involves the novel 1,3-addition of trimethylsilyl phosphites (e.g. diethyl) or trimethylsilyl phosphines (e.g. diphenyl) to aldo-nitrones [e.g. alpha-phenyl-N-tert-butylnitrone (PBN) or 5,5-dimethyl-l-pyrroline-N-oxide (DMPO)] or keto-nitrones [e.g. 2-ethyl-5,5-dimethyl-1 pyrroline-N-oxide (2-Et-DMPO) or 2-phenyl-5,5-dimethyl-l-pyrroline-N-oxide (2-Ph-DMPO)] to form alpha-phosphityl- or alpha-phosphinyl-O-silylhydroxylamines. Acidic hydrolysis provides the corresponding hydroxylamines that are easily oxidized to the title beta-phosphorus-nitroxides. ESR spectroscopic analysis revealed some very large beta-phosphorus hyperfine splittings (i.e. in excess of 5 mT). For this reason and their remarkable stability (persistence) some of these nitroxides show promise as integral components in new, improved weak-field dynamic nuclear polarization (DNP) magnetometers.

Cyclic N-Oxides↗