Insertion of a stable dialkylsilylene into silicon-chlorine bonds

The reactions of a stable dialkylsilylene with chlorosilanes such as tetrachlorosilane, dimethyldichlorosilane, and dichlorosilane occurred smoothly at room temperature in hydrocarbon solvents to give the corresponding Si-Cl bond insertion products. In the reaction of the silylene with dichlorosilane, only the Si-Cl bond insertion product was obtained, while a similar reaction with dimethylchlorosilane gave only the Si-H insertion product, emphasizing the remarkable difference in the steric requirements between these two insertion reactions. No reaction took place during the treatment of the silylene with trimethylchlorosilane. The Si-Cl insertion reactions are expected to be applied in the synthesis of new organosilicon frameworks that cannot be obtained by conventional methods.     

A screening method for estrogens using an array-type DNA glass slide.

A new screening assay was described for the determination of endocrine disrupting chemicals (EDCs), such as synthetic estrogens, with an array-type DNA glass slide having characteristics of 1) a high sample throughput, 2) a compact size allowing a small sample volume, and 3) a sensitive determination based on the estrogen-dependent binding of the human estrogen receptor a (hERalpha) with its estrogen responsive element (ERE; Vit. A2 gene promoter). We devised a glass slide on which a thin agarose gel was mounted. Avidin was then covalently immobilized on each well of the glass slide after the gel was activated by a NaIO4 solution. Also, the biotinylated ERE as a DNA probe was immobilized on the gel layer through avidin-biotin binding. After the estrogen-dependent binding of a yellow fluorescent protein-fused hERalpha (YFP-hERalpha) to ERE on the gel layer, the fluorescence intensity of YFP-hERalpha quantitatively extracted into the gel was directly determined with a fluorescence microplate reader. Pre-incubation of YFP-hERalpha with estrogen at 37 degrees C for 30 min enhanced the estrogen-dependent hERalpha-ERE binding. The determined hormonal activities of estrogens on the interaction of YFP-hERalpha with ERE were as follows in their decreasing order: diethylstilbestrol (DES) > 17beta-estradiol (E2) <==> ethynylestradiol (EE2) > 4-hydroxy tamoxifen (OHT) > clomiphene (Clo). The present method provides a sensitive estrogen-dependent dose-response curve down to approximately 10(-13) M in the case of DES. This method will become a competitive alternative to the conventional in vitro assays, such as a DNA-binding assay using radioisotopes.     

A polynomial-time-delay and polynomial-space algorithm for enumeration problems in multi-criteria optimization

We propose a polynomial-time-delay polynomial-space algorithm to enumerate all efficient extreme solutions of a multi-criteria minimum-cost spanning tree problem, while only the bi-criteria case was studied in the literature. The algorithm is based on the reverse search framework due to Avis and Fukuda. We also show that the same technique can be applied to the multi-criteria version of the minimum-cost basis problem in a (possibly degenerated) submodular system. As an ultimate generalization, we propose an algorithm to enumerate all efficient extreme solutions of a multi-criteria linear program. When the given linear program has no degeneracy, the algorithm runs in polynomial-time delay and polynomial space. To best of our knowledge, they are the first polynomial-time delay and polynomial-space algorithms for the problems.     

Algorithmic Folding Complexity

How do we most quickly fold a paper strip (modeled as a line) to obtain a desired mountain-valley pattern of equidistant creases (viewed as a binary string)? Define the folding complexity of a mountain-valley string as the minimum number of simple folds required to construct it. We first show that the folding complexity of a length-n uniform string (all mountains or all valleys), and hence of a length-n pleat (alternating mountain/valley), is O(lg² n). We also show that a lower bound of the complexity of the problems is ??(lg² n/lg lg n). Next we show that almost all mountain-valley patterns require ??(n/lg n) folds, which means that the uniform and pleat foldings are relatively easy problems. We also give a general algorithm for folding an arbitrary sequence of length n in O(n/lg n) folds, meeting the lower bound up to a constant factor.     

A Six-Coordinate Silicon Dihydride Embedded in a Porphyrin: Enhanced Hydride-Donor Properties and the Catalyst-Free Hydrosilylation of CO2

The catalyst-free hydrosilylation of CO₂ under mild conditions remains limited. Herein, we report the synthesis, characterization, and reactivity of 5,10,15,20-tetraphenylporphyrinato(dihydrido)silicon(IV) ( 1 ) as a six-coordinate silicon dihydride. The Si-H moiety of 1 reacts with polar double bonds and CO₂ in the absence of a catalyst to afford hydrosilylated products. Combining the hydrosilylation with subsequent transformation furnishes formic acid from CO₂. Computational studies indicate that the hydride-donor properties of 1 are exceptionally high for a neutral silicon hydride, and that the direct hydride transfer from silicon to carbon is a pivotal step in the hydrosilylation of CO₂ with 1 .     

Patterning cellular motility using an electrochemical technique and a geometrically confined environment

We describe herein a method for controlling the pattern of permissible cell migration and proliferation on a substrate in time and space. Using this method, a confluent monolayer of cells that is confined within a defined region is released into a neighboring region. Incorporated into the method is an electrochemical technique that uses a scanning microelectrode to draw regions on the surface of the system that thereafter can support cell migration and growth. The supporting glass substrate is patterned with regions of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer that are not affected by the electrochemical treatment and also robustly resist cellular overgrowth as well as regions that can be individually switched when electrochemically treated from cell repellent to cell adhering. It is therefore possible to strictly define the areas into which cells can migrate. We found that HeLa cells migrate more rapidly as the width of cell-adhering lanes increases until a width of ca. 50 microm is reached, at which point the migration rate is roughly constant. We also designed a drug assay using our cell migration technique. The technique allows for cell migration only into defined region(s) and therefore may become an important tool for evaluating the biological activity of potential drugs because drug activity and cell motility often directly correlate.     

Structure elucidation of the intermediate in triethylborane-mediated radical addition of oxime ethers with 2D- and 3D-DOSY NMR

The structures of the components in the triethylborane-mediated radical addition reaction of oxime ether were investigated by 1H- and 3D-DOSY NMR methods. It has been impossible to physically separate the unstable intermediates; therefore, the structures were thus far unidentified. It has been possible to elucidate the structures of these unstable intermediates using Diffusion-Ordered Spectroscopy (DOSY) methods for the reaction in an NMR tube. The DOSY methods resolved the spectra of each starting compound, intermediate and product having different diffusion coefficients. The structure of the intermediate was shown to be due to the bonding of diethylborane to the nitrogen atom of the alkoxyamino group.     

Colloidal aggregation in a nematic liquid crystal: topological arrest of particles by a single-stroke disclination line

We numerically study many-body interactions among colloidal particles suspended in a nematic liquid crystal, using a fluid particle dynamics method, which properly incorporates dynamical coupling among particles, nematic orientation, and flow field. Based on simulation results, we propose a new type of interparticle interaction in addition to well-known quadrupolar interaction for particles accompanying Saturn-ring defects. This interaction is mediated by the defect of the nematic phase: upon nematic ordering, a closed disclination loop binds more than two particles to form a sheetlike dynamically arrested structure. The interaction depends upon the topology of a disclination loop binding particles, which is determined by aggregation history.     

A Tetrasilicon Analogue of Bicyclo[1.1.0]but‐1(3)‐ene Containing a Si=Si Double Bond with an Inverted Geometry

Bicyclo[1.1.0]tetrasil‐1(3)‐ene 1 , a tetrasilicon analogue of bicyclo[1.1.0]but‐1(3)‐ene that contains a formal double bond between bridgehead silicon atoms in an inverted geometry, was synthesized and isolated in the form of thermally stable orange crystals. The distance between the bridgehead Si atoms in 1 is much longer than those in typical Si=Si bonds, but still shorter than that of a previously reported pentasila[1.1.1]propellane. DFT calculations suggest that the bridgehead bond in 1 comprises a σ bond with an inverted geometry and a π bond. This notion is supported by the UV/Vis spectrum of 1 , which exhibits several absorption bands in the UV/Vis region. While 1 is stable toward typical trapping agents for Si=Si double bonds, 1 reacts with carbon tetrachloride to furnish a hexachlorotetrasilane.