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At least 163 records · Page 9Linked to original sources
PubMed2006

A new type of N-heterocyclic silylene with ambivalent reactivity.

The synthesis of a novel divalent silicon compound by debromination of the corresponding dibromosilyl precursor is reported. The silylene possesses a unique reactivity toward electrophiles of the type R-X (R = H, silyl; X = halogen, triflate) in comparison with the germanium congener. DFT calculations suggest that this is due to a much higher basicity of the silylene versus that of germylene lone-pair electrons. Thus, addition of Me3SiX to the silylene (X = OSO2CF3, triflate) furnishes the corresponding (kinetically favored) 1,4-adduct which subsequently rearranges to the thermodynamically favored 1,1-adduct.

Journal Article↗
PubMed2005

A mesoporous template route to the low-temperature preparation of efficient green light emitting Zn2SiO4:Mn phosphors.

Green light emitting Zn2SiO4:Mn phosphors have been prepared via a low-temperature solid-state reaction using mesoporous silica SBA-15 template. This mesoporous silica template method features low-temperature formation of phosphors and easy doping. The structure and morphology of the phosphors were characterized by XRD, SEM, TEM, and N2 adsorption/desorption techniques, which confirmed the single crystallinity, ordered mesostructure, closed pore channels, and elongated ropelike morphology. The luminescent properties were examined by photoluminescence spectroscopy at room temperature, and the results of fluorescence decay time measurements show non-single-exponential decay behavior and a decrease of the decay time with an increase of the Mn concentration.

Light↗
PubMed2006

Protein-resistant polymer coatings on silicon oxide by surface-initiated atom transfer radical polymerization.

The modification of silicon oxide with poly(ethylene glycol) to effectively eliminate protein adsorption has proven to be technically challenging. In this paper, we demonstrate that surface-initiated atom transfer radical polymerization (SI-ATRP) of oligo(ethylene glycol) methyl methacrylate (OEGMA) successfully produces polymer coatings on silicon oxide that have excellent protein resistance in a biological milieu. The level of serum adsorption on these coatings is below the detection limit of ellipsometry. We also demonstrate a new soft lithography method via which SI-ATRP is integrated with microcontact printing to create micropatterns of poly(OEGMA) on glass that can spatially direct the adsorption of proteins on the bare regions of the substrate. This ensemble of methods will be useful in screening biological interactions where nonspecific binding must be suppressed to discern low probability binding events from a complex mixture and to pattern anchorage-dependent cells on glass and silicon oxide.

Adsorption↗
PubMed2005

Surprising reactions of a 2H-azaphosphirene complex with a silylene.

Reaction of the 2H-azaphosphirene complex with the silylene yielded the bicyclic carbene complex as sole product at ambient temperature; the reaction was less selective at elevated temperatures; additionally, the synthesis and structure of the first 1,2,4,3-azadiphosphasilol-5-ene complex is presented.

Alkenes↗
PubMed2002

Anatomy of the ulnar artery as it relates to the transverse carpal ligament.

The anatomic relationship between the ulnar artery and transverse carpal ligament (TCL) as an aid in planning for minimally invasive carpal tunnel surgery was investigated. The anatomic course of the ulnar artery and its branches toward the TCL and the location of the median nerve were determined in 24 fresh cadaver hands perfused with a silicone compound. The ulnar artery coursed from 7 mm ulnar to 2 mm radial to the hook of hamate. The average distance between the superficial palmar arch and the distal margin of the TCL was 12 mm as measured along the flexor tendon of the ring finger. The location of the median nerve extended an average of 11 mm radial to the hook of hamate. A small arterial branch (average diameter, 0.7 mm) from the ulnar artery ran transversely just over the TCL in 6 of the 24 specimens. This branch was consistently located within 15 mm proximal to the TCL distal margin. These and other microscopic observations indicated that transecting the ligament at approximately 5 mm radial to the radial margin of the hook of hamate may minimize postoperative bleeding and avoid iatrogenic vascular and neural injury.

Adult↗
PubMed1994

Staged replacement of the canine trachea with ringed polyethylene terephthalate grafts.

The reconstruction of extensive defects of the trachea ist best accomplished by the use of the patient's own tissue. Unfortunately, this is not always feasible and several prosthetic devices for replacement of the trachea have been described. In an experimental study staged tracheal replacements were performed in five dogs using a ringed polyethylene terephthalate (PET) tubular prosthesis previously cultured in the major omentum of the subjects. A set of stainless-steel arches embodied in silicone compound was designed to prevent collapse of the prosthesis. One of the subjects died on the 10th post-operative day of an unidentified cause and the remaining four eventually developed signs of respiratory distress. The cause of the respiratory insufficiency was anastomotic stenosis in every case. Infection, erosion, collapse or displacement were not observed. The rings designed to avoid collapse of the prosthesis represent a suitable alternative for use as external reinforcement in the tracheal situation. The PET grafts implanted as tracheal prosthesis according to the guidelines of this protocol consistently developed anastomotic stenosis and failed to support a functional respiratory epithelium. A further conclusion is that the use of absorbable sutures encourages anastomotic dehiscence and thus must be avoided.

Animals↗
PubMed1996

Cavity ringdown laser absorption spectroscopy and time-of-flight mass spectroscopy of jet cooled platinum silicides.

The cavity ringdown technique (CRLAS) has been employed to measure the gas phase absorption spectrum of the platinum silicide molecule in the 350 nm region. All nine of the measured rovibronic bands are assigned to a single 1 sigma-1 sigma electronic transition, with a ground state vibrational frequency of omega "e = 549.0(3) cm-1, and a bond length of r"0 = 2.069(1) angstroms. The results of this study are compared with experimental data for the coinage metal silicides. Additionally, time-of-flight mass spectrometric results indicate that a variety of polyatomic metal silicides are formed in our molecular jet expansion.

Lasers↗
PubMed1996

Chip PCR. I. Surface passivation of microfabricated silicon-glass chips for PCR.

The microreaction volumes of PCR chips (a microfabricated silicon chip bonded to a piece of flat glass to form a PCR reaction chamber) create a relatively high surface to volume ratio that increases the significance of the surface chemistry in the polymerase chain reaction (PCR). We investigated several surface passivations in an attempt to identify 'PCR friendly' surfaces and used those surfaces to obtain amplifications comparable with those obtained in conventional PCR amplification systems using polyethylene tubes. Surface passivations by a silanization procedure followed by a coating of a selected protein or polynucleotide and the deposition of a nitride or oxide layer onto the silicon surface were investigated. Native silicon was found to be an inhibitor of PCR and amplification in an untreated PCR chip (i.e. native slicon) had a high failure rate. A silicon nitride (Si(3)N(4) reaction surface also resulted in consistent inhibition of PCR. Passivating the PCR chip using a silanizing agent followed by a polymer treatment resulted in good amplification. However, amplification yields were inconsistent and were not always comparable with PCR in a conventional tube. An oxidized silicon (SiO(2) surface gave consistent amplifications comparable with reactions performed in a conventional PCR tube.

Base Sequence↗
PubMed2001

Anatomical consideration of reverse-flow island flap transfers from the midpalm for finger reconstruction.

Primary soft-tissue coverage for large palmar defects of the fingers is a difficult problem for cases in which homodigital or heterodigital flaps cannot be used. The aim of this study was to explore the vascular and neural anatomy of the midpalmar area to assess the possibility of reverse island flaps from this area. In 24 cadaver hands perfused with a silicone compound, the arterial pattern of the superficial palmar arch and common palmar digital artery was examined. The cutaneous perforating arteries and nerve branches supplying the midpalmar area were dissected, and the number, location, and arterial diameter of these branches were measured. In six other specimens, the common palmar digital artery was injected to determine the skin territory supplied by the artery. The superficial palmar arch contained the three common palmar digital arteries and its terminal branch coursed along the radial margin of the index metacarpus. This terminal branch had three to six cutaneous perforators (diameter range, 0.1 to 0.5 mm) and supplied the radial aspect of the midpalmar area located over the ulnar half of the adductor pollicis muscles. The midpalmar area was divided into two regions-the proximal and distal-according to the vascular distributions. The proximal region contained dense aponeurosis and thin subcutaneous tissue, and the cutaneous perforators were rather sparse (between three and nine) and had a small diameter (0.1 to 0.3 mm). The distal region, which had loose aponeurosis and abundant subcutaneous tissue, had a rich vascular supply from the common and proper digital artery. Perforating arteries of this region coursed frequently in an oblique fashion and the number of perforators (between eight and 15) and their arterial diameters (diameter range, 0.1 to 0.5 mm) were higher than those of the proximal region. The area of skin perfused by the common palmar digital artery was 5 x 3 cm at the distal midpalmar region. There were three to five cutaneous nerve branches from the palmar digital nerve supplying the midpalmar area. From this study, two different reverse flaps were proposed. First, a 5 x 2 cm flap from the distal midpalmar region was elevated on the basis of the common and proper palmar digital artery. Measurement of the rotation arc revealed that the pivot point of this flap was located at the proximal interphalangeal joint level and could cover the finger pulp of the digits. The second flap candidate was that from the radial aspect of the midpalm, which was supplied by the terminal branch of the superficial palmar arch. In studies with cadaver hands, connection of this artery with the deep arterial system enabled this flap to reach the thumb pulp. These flaps may be a useful reconstruction option for significant palmar soft-tissue loss of the fingers.

Adult↗
PubMed1989

Measurement of human lumbar spine ligaments during loaded and unloaded motion.

Length changes in the ligaments of human lumbar spine motion segments were investigated in order to find conditions under which unusual stress or stress reduction is found in the longitudinal ligaments and facet joint capsules. Flexibility measurements were performed under load. Increasing load and height reduction in the motion segment increases the flexibility. The anterior and posterior longitudinal ligament normally operate in the elastic part of their stress-strain curve. Destruction of the intervertebral disc leads to a dislocation of the centers of rotation in the motion segment. Two types of facet joint capsules were observed. Height reduction in the motion segment leads to abnormal strains in one type sooner than in the other, which can be normalized by slight flexion. Injection of a silicone compound into the disc normalizes many of the changes in the motion segment due to height reduction.

Humans↗
PubMed1984

Health effects of silicon tetrachloride. Report of an urban accident.

A spill of silicon tetrachloride (SiCl4) at a chemical plant caused the evacuation of several thousand people from an industrial park; 28 persons sought medical attention. Most of the affected individuals suffered only transient eye and upper airway irritation. Six of the plant employees were later referred for detailed evaluation of possible lung injury, but no definite evidence of SiCl4-induced pulmonary dysfunction was found. Five of these workers also experienced recurrent headaches, and two complained of pedal dysesthesias after the accident. Although the temporal relationship between the exposure and onset of these symptoms is notable, no definite etiologic relationship could be established.

Accidents, Occupational↗
PubMed2004

Interruption of the bilateral segmental arteries at several levels: influence on vertebral blood flow.

STUDY DESIGN: The effect of ligation of the bilateral segmental arteries at the levels of T11, T12, and T13 on blood flow of the T12 vertebra was studied in a dog model. OBJECTIVES: To determine the reduction of the vertebral blood flow resulting from interruption of bilateral segmental arteries at one to three vertebral levels. SUMMARY OF BACKGROUND DATA: Intraoperative hemorrhage can be sometimes massive in patients with hypervascular spinal tumors, especially in radical resection such as total en bloc spondylectomy. The recent development of new embolization techniques ensures more aggressive, more extensive, and safer preoperative embolization for spinal tumors. METHODS: The blood flow of the T12 vertebra of 12 female dogs was measured after ligation of the bilateral segmental arteries at one to three levels, including the T12. Spinal cord evoked potentials were recorded in this procedure. Spinal angiography using a silicon compound was performed on another 10 dogs after clipping and section of the bilateral segmental arteries. RESULTS: The blood flow of the T12 vertebra decreased to 70.13 +/- 6.37% of the control value after ligation of the bilateral segmental arteries of T12, to 46.48 +/- 8.97% after ligation of the bilateral segmental arteries of T12 and either T11 or T13, to 24.11 +/- 8.31% after ligation of T11, T12, and T13, respectively. The angiogram after ligation and section of T12 and the two levels including T12 showed thick and clear contrast medium in the cut distal ends of the T12 segmental arteries. After interruption at three levels (T11, T12, and T13), however, the cut distal ends of the T12 segmental arteries were seen thin and faint on the angiogram. No significant changes occurred in spinal cord evoked potentials after ligation of the segmental arteries at three levels in all six dogs. CONCLUSION: Interruption of the bilateral segmental arteries at three levels, one target vertebra and the two adjacent vertebrae, reduced the blood flow of the target vertebra to one fourth of the control value in the lower thoracic spine in dogs. This result suggests that preoperative embolization at three levels, the levels of the tumor vertebra and the adjacent vertebrae above and below it, may reduce intraoperative hemorrhage effectively during total en bloc spondylectomy for hypervascular spinal tumors.

Angiography↗
PubMed2003

Genotyping on a thermal gradient DNA chip.

Silicon-based chips with discrete, independently temperature-controlled islands have been developed for use in DNA microarray hybridization studies. Each island, containing a heater made of a diffusion layer and a temperature sensor based on a p-n junction, is created on a silicon dioxide/nitride surface by anisotropic etching. Different reactive groups are subsequently added to the surface of the islands, and allele-specific oligonucleotide probes are attached to discrete spots on the chip. Hybridization is performed with Cy5-tagged single-stranded targets derived by PCR from genomic DNA. Results are assessed by measuring fluorescence of bound dye-tagged targets after hybridization and washing. Temperatures at each island can be set at different values to obtain optimal distinction between perfect matches and mismatches. This approach facilitates definition of optimal temperatures for probe/target annealing and for distinction between perfectly matched versus mismatched solution-phase targets. The thermal gradient DNA chips were then tested for genotyping, and the results for four different loci in two genes are presented. Unambiguous typing was achieved for clinically relevant loci within the factor VII and hemochromatosis genes.

Factor VII↗
PubMed2000

A new relation between bond valence and bond distance.

A new empirical relationship s = s0(R0 - lambda)3/(R - lambda)3 between bond distances and bond valences is proposed, where s is the bond valence for the bond distance R, s0 is the reference bond valence for the reference system with the reference bond distance R0 and lambda is the sum of the cation radii of bonding atoms defined by Pauling. Since lambda is the size of the inner electron region, R - lambda represents the valence electron region between bonding atoms. The new relationship was derived based on the following three hypotheses. (i) The number of electrons (p) in the volumes of (R - lambda)3 in a coordination polyhedron are equal, even if the bond distances are not equal to each other. (ii) The average electron density p/(R - lambda)3 is a measure of covalent bond strength. (iii) The sum of the average electron densities around the central atom is conserved, even if the coordination number changes. The new relationship is applicable not only to polyhedra with one type of ligand atom, but also to polyhedra with two or more types of ligand atoms and explains why the Brown-Shannon formula [Brown & Shannon (1973). Acta Cryst. A29, 266-282] and the Brown-Altermatt formula [Brown & Altermatt (1985). Acta Cryst. B41, 244-247] work well. The new relationship was applied to a penta-coordinated silicon compound, strong hydrogen-bond systems and some organic compounds with carbon-carbon bonds.

Journal Article↗
PubMed1992

Maturation of interdependence between extra-alveolar arteries and lung parenchyma in piglets.

Mechanical interdependence between intrapulmonary structures and parenchyma has not been studied previously in immature postnatal lungs. To study these interactions, lung elastic moduli were measured by pressure-volume and punch indentation studies in lobes excised from 3-day-old (n = 6), 1-month-old (n = 6), and 3-month-old (n = 7) piglets. After extra-alveolar arteries were filled with a radiopaque fluid silicone compound, transpulmonary pressure and arterial pressure were varied independently as the lobar vein was occluded. Arterial diameters and lengths were measured from radiographs. Behavior of 3-month-old lungs was consistent with previous studies of adult lungs, but results were unique in 3-day-old lungs. That is, during stepwise deflation of the immature lungs 1) intravascular pressures fell when arteries were occluded experimentally, 2) arteries increased their diameters when kept at a constant intravascular pressure, and 3) arterial lengths decreased by less than 3%. Behavior of 1-month-old lungs was intermediate. A previous continuum mechanics analysis of pressure-diameter behavior was modified to account for compression by alveolar pressure as vascular diameters increase. It was concluded that 1) radial and axial dimensions of extra-alveolar arteries are virtually independent of parenchymal expansion in newborn piglet lungs and 2) periarterial interstitial pressures increase as these lungs are inflated. Our interpretation of these findings is that a mechanical association of the arteries to the parenchyma occurs gradually with postnatal maturation.

Animals↗
PubMed2001

Synthesis of mesoporous silica monoliths with embedded nanoparticles.

Mesostructured silica-nanoparticle monolithic composites have been synthesized by dispersing prefabricated nanoparticles of gold or zeolite (silicalite) in ethanolic reaction mixtures containing SiCl4 and a Pluronic triblock copolymer template. Whereas silicalite nanoparticles were used directly, surface functionalization of the gold nanoparticles with either primed silicate ions or a discrete 3-5-nm-thick silica shell was required to increase the interfacial compatibility with the hydrophilic poly(ethylene oxide) blocks. Under these conditions, the resulting monoliths consisted of distributed nanoparticles within an ordered mesostructured silica matrix. Removal of the polymer template by calcination produced corresponding mesoporous silica-nanoparticle replicas. The combination of the structure and the porosity of the silica framework with the crystal chemical properties of the embedded nanoparticles suggests that such composites should be useful as multifunctional materials.

Chlorides↗
PubMed2005

Structure and growth mechanism study of Wurtzite CdSe nanorods grown by solvothermal techniques.

Hexagonal cadmium selenide nanorods 32-170 nm in length and 12-28 nm in diameter were grown by a solvothermal technique by reacting cadmium chloride and selenium powders in ethylenediamine at 140 degrees C. Using electron microscopy, the shape, size, and crystal structure of the nanorods were determined. A detailed microscopy analysis revealed that the nanorods grow through the coalescence of very small particles or fiberlike structures of the compound. The size, shape and strain structures in the nanorods are defined by their growth mechanism.

Cadmium↗