silicon and pyridine

Metal complexes of chiral oxazoline derivatives immobilized on soluble as well as insoluble supports serve as versatile asymmetric catalysts in a variety of applications. In a few cases recovery and reuse of the chiral ligands have been achieved.

Topics: Catalysis; Combinatorial Chemistry Techniques; Ligands; Oxazoles; Polymers; Pyridines; Silicon; Stereoisomerism; Structure-Activity Relationship

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS), a parallel technique to matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), utilizes inorganic particles or porous surfaces to aid in the desorption/ionization of low-molecular-weight (MW) analytes. As a matrix-free and "soft" LDI approach, SALDI offers the benefit of reduced background noise in the low MW range, allowing for easier detection of biologically significant small MW species. Despite the inherent advantages of SALDI-MS, it has not reached comparable sensitivity levels to MALDI-MS. In relation to mass spectrometry imaging (MSI), intense efforts have been made in order to improve sensitivity and versatility of SALDI-MSI. We describe herein a detailed protocol that utilizes a hybrid LDI method, matrix-enhanced SALDI-MS (ME-SALDI MS), to detect and image low MW species in an imaging mode.

Topics: Analytic Sample Preparation Methods; Aniline Compounds; Molecular Imaging; Molecular Weight; Pyridines; Silicon; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization

The aim of this work was to generate a tunable surface isoelectric point (sIEP), where the surface is modified with two molecules: a weak base (pyridine), carrying a pH dependent positive charge, and a derivative of a strong acid (sulfate), carrying a permanent negative charge in a physiologically relevant pH range. To this end, silicon surfaces were modified with 3-aminopropyltriethoxysilane. These amine-modified surfaces were subsequently derivatized into pyridine- or sulfate-modified surfaces. Then, the surface pKa of pyridine-modified surfaces was determined by a fluorescent nanoparticle adhesion assay (FNAA). Next, these values were used to calculate in which ratio the chemicals must be present in the reaction mixture to generate a mixed pyridine/sulfate-modified surface with a target sIEP. After preparing surfaces with a target sIEP, an FNAA with positively and negatively charged nanoparticles was used to verify the sIEP of the generated surfaces. The FNAA revealed that pyridine-modified surfaces had a pKa of 6.69 ± 0.18. When an sIEP was generated, negative nanoparticles bound to surfaces at pH values below the sIEP and positive nanoparticles bound at pH values above the sIEP. Furthermore, we found sIEP values of 5.97 ± 0.88 when we aimed for an sIEP of 6.2, and 7.12 ± 0.21 when we aimed for an sIEP of 7.1. Finally, the pH dependent binding and release of a negatively and positively charged (bio)polymer was investigated for a target sIEP of 7. A negatively charged polymer (poly(I:C)) was bound at a pH < sIEP and released at a pH > sIEP with a release efficiency of 85 ± 9% and a positively charged polymer (trimethyl chitosan) bound at a pH > sIEP and released at a pH < sIEP with a release efficiency of 72 ± 9%. In conclusion, we established a method for preparing modified silicon surfaces with a tunable sIEP, which can be used for pH-dependent binding and release of biomacromolecules.

Topics: Isoelectric Point; Molecular Structure; Pyridines; Silicon; Surface Properties

Heteroleptic copper(II)-polypyridyl complexes with extended π-conjugated, aromatic terminal units were immobilized on glass/Si substrates to intercalate DNA and cleave it upon photoexposure. Photonuclease activity is shown to be high, well reproducible and non-destructible towards the assembled complexes.

Topics: Coordination Complexes; Copper; Deoxyribonucleases; DNA; Glass; Intercalating Agents; Pyridines; Silicon; Singlet Oxygen; Surface Properties; Ultraviolet Rays

Mechanical abrasion is an extremely simple, rapid, and low-cost method for deposition of carbon-based materials onto a substrate. However, the method is limited in throughput, precision, and surface compatibility for drawing conductive pathways. Selective patterning of surfaces using laser-etching can facilitate substantial improvements to address these current limitations for the abrasive deposition of carbon-based materials. This study demonstrates the successful on-demand fabrication of fully-drawn chemical sensors on a wide variety of substrates (e.g., weighing paper, polymethyl methacrylate, silicon, and adhesive tape) using single-walled carbon nanotubes (SWCNTs) as sensing materials and graphite as electrodes. Mechanical mixing of SWCNTs with solid or liquid selectors yields sensors that can detect and discriminate parts-per-million (ppm) quantities of various nitrogen-containing vapors (pyridine, aniline, triethylamine).

Topics: Aluminum Oxide; Aniline Compounds; Carbon; Electrodes; Ethylamines; Glass; Paper; Polymethyl Methacrylate; Pyridines; Silicon; Surface Properties

Si-H activation in triethyl- and triarylsilanes by a square-planar pyridine-diimine iridium complex with a terminal nitrido unit leads to the corresponding silyl amido complexes, which were unambiguously characterized by X-ray crystallography. Based on detailed combined kinetic and theoretical studies (DFT), direct addition of the Si-H bond to the iridium nitrido unit is proposed. The electronic propensities of the transition states for the Si-H activation were probed with a Hammett series of para-substituted triarylsilanes HSi(C6H5)2(4-C6H4-X). Based on the combination of experimental and theoretical studies, two independent pathways for this process are proposed, which point toward an ambiphilic propensity of the nitrido unit. Alternative pathways and the charge transfer in the transition states were also investigated. Furthermore, the barriers for the related H-H and C-H activation processes in dihydrogen and methane were analyzed.

Topics: Crystallography, X-Ray; Hydrogen; Imines; Iridium; Models, Molecular; Molecular Structure; Organometallic Compounds; Pyridines; Quantum Theory; Silanes; Silicon

Bonding interactions between an electron-deficient region (a sigma-hole) on M and electron donors in MF4-Base complexes, where M = C, Si, Ge, Sn, and Pb, are examined and rationalized. These interactions are seen to transition from weak primarily noncovalent interactions for all bases when M = C to stronger primarily covalent bonds in adducts as the valence shell expands for the heavier M atoms. For M = Ge, Sn, and Pb, the complexes are particularly stable. The consistent axial preference in these systems is anticipated by previous studies and is readily explained from the vantage point of sigma-hole interactions. A series of bound complexes of common bases such as pyridine, tetrahydrofuran, and water are identified, some of which are even more stable than the SiF4·NH3 and SiF4·N(CH3)3 complexes that have already been identified experimentally. Sigma-hole bonding to di- and poly-substituted central atoms, perhaps on par with halogen bonding, is expected to become increasingly important as an ordering interaction in materials science and engineering. Group 14 compounds have distinct advantages in this respect.

Topics: Carbon; Electrons; Fluorides; Furans; Germanium; Lead; Pyridines; Silicon; Static Electricity; Thermodynamics; Tin; Water

The facile synthesis of silicon nanotubes using a surface sol-gel reaction on pyridine nanowire templates is reported and their performance for energy storage is investigated. Organic-inorganic hybrid pyridine/silica core-shell nanowires prepared using surface sol-gel reaction were converted to silica nanotubes by pyrolysis in air; this was followed by the reduction to silicon nanotubes via magnesiothermic reaction. The electrochemical activity of the obtained silicon nanotubes showed excellent cycle stability, suggesting that the hollow one-dimensional structure would be a good candidate for a high-capacity anode for a lithium ion battery.

Topics: Acrylic Resins; Electric Power Supplies; Electrochemical Techniques; Electrodes; Gels; Ions; Lithium; Magnesium; Nanotubes; Nanowires; Oxidation-Reduction; Pyridines; Silicon

Using pyridine as an example, a thermodynamic analysis of the low temperatures adsorption of aromatic organic molecules with a N atom on the Si(100) surface is presented. This study is restricted to the case of an equilibrium with the gas phase. Dative attachment which is the only way to preserve aromaticity is the more stable form of adsorbed pyridine in dilute solutions at low temperatures. Two factors limit the domain of stability of dative attachment: repulsive interactions between dative bonds prevent them from being present in concentrated solutions while aromaticity contributes to a decrease in the entropy, which explains the vanishing of dative bonds at high temperatures even in dilute solutions.

Topics: Adsorption; Benzene Derivatives; Pyridines; Quantum Theory; Silicon; Surface Properties; Thermodynamics

A new form of hybrid carbon-based thin film was prepared via a pyridine chemical vapour deposition method. The as-obtained films consist of agglomerated flowerlike graphene nanowhiskers embedded in a uniform matrix of amorphous carbon. Schottky solar cells made from the hybrid films and n-type silicon show conversion efficiencies of approximately 1% under AM 1.5 illumination.

Topics: Carbon; Membranes, Artificial; Nanostructures; Particle Size; Pyridines; Silicon; Surface Properties

A new general and easily installable silicon-tethered pyridyl-containing directing group (PyDipSi) that allows for highly efficient and regioselective Pd-catalyzed ortho C-H acyloxylation of arenes has been developed. It has also been demonstrated that this directing group can efficiently be removed as well as converted into a variety of other valuable functional groups. In addition, the installation of the PyDipSi directing group along with pivaloxylation and quantitative conversion of the PyDipSi group into a halogen functionality represents a formal three-step ortho oxygenation of haloarenes.

Topics: Carbon; Hydrocarbons, Aromatic; Hydrogen; Pyridines; Silanes; Silicon

The adsorption of a range of molecular species (water, pyridine, and ammonia) is found to reversibly modulate the conductivity of hydrogen-terminated silicon-on-insulator (H-SOI) substrates. Simultaneous sheet-resistance and Hall-effect measurements on moderately doped (10(15) cm(-3)) n- and p-type H-SOI samples mounted in a vacuum system are used to monitor the effect of gas exposure in the Torr range on the electrical-transport properties of these substrates. Reversible physisorption of "hole-trapping" species, such as pyridine (C(5)H(5)N) and ammonia (NH(3)) produces highly conductive minority-carrier channels (inversion) on p-type substrates, mimicking the action of a metallic gate in a field-effect transistor. The adsorption of these same molecules on n-type SOI induces strong electron-accumulation layers. Minority/majority channels are also formed upon controlled exposure to water vapor. These observations can be explained by a classical band-bending model, which considers the adsorbates as the source of a uniform surface charge ranging from +10(11) to +10(12)q cm(-2). These results demonstrate the utility of DC transport measurements of SOI platforms for studies of molecular adsorption and charge-transfer effects at semiconductor surfaces.

Topics: Adsorption; Electric Conductivity; Pyridines; Semiconductors; Silicon; Surface Properties; Water

A close-packed monolayer of zinc 5,10,15,20-tetrakis(3-carboxyphenyl)porphyrin has been prepared and deposited on the thin native oxide covering the surface of an SOI-MOSFET (silicon-on-insulator metal-oxide-semiconductor field effect transistor) using Langmuir-Blodgett techniques. When the device is exposed to amine vapors in a nitrogen atmosphere, the amine coordinates to the zinc atom. The resulting change in electron distribution within the porphyrin leads to a large change in the drain current of the transistor, biased via a back gate. This change is sensitive to both the amount of amine present and the base strength of the amine. Only very small changes in drain current were observed with a monolayer of free base porphyrin or palmitic acid. After exposure to high pyridine concentrations, the device response saturates, but partially recovers after overnight exposure to flowing nitrogen gas. Interestingly, the device response is instantaneously reset by exposure to visible light, suggesting that photode-ligation occurs. An electrical model for the hybrid device that describes its response to ligand binding in terms of a change in the work function of the porphyrin monolayer has been developed. A transistor response to a few hundred attomoles of bound pyridine can be readily detected. This extreme sensitivity, coupled with the ability to reset the device using light, suggests that such systems might be useful as sensors.

Topics: Amines; Electrochemistry; Hydrogen-Ion Concentration; Kinetics; Light; Metalloporphyrins; Models, Molecular; Oxides; Piperidines; Pyridines; Semiconductors; Silicon; Volatilization; Zinc

The adsorption structures of benzene and pyridine on Si(5 5 12)-2 x 1 were studied at 80 K by using a low-temperature scanning tunneling microscope and density functional theory calculations. These structures are different from those observed on low-index Si surfaces: benzene molecules exclusively bind to two adatoms, that is, with di-sigma bonds between carbon atoms and silicon adatoms, leading to the loss of benzene aromaticity; in contrast, pyridine molecules interact with adatom(s) through either Si-N dative bonding or di-sigma bonds. Dative bonding configurations with pyridine aromaticity are the dominant adsorption features and are more stable than di-sigma bonding configurations. Thus the dative bonding of nitrogen-containing heteroaromatic molecules provides a strategy for the controlled attachment of aromatic molecules to high-index surfaces.

Topics: Adsorption; Benzene; Microscopy, Scanning Tunneling; Models, Chemical; Molecular Structure; Pyridines; Sensitivity and Specificity; Silicon; Surface Properties; Temperature