Bildung siliciumorganischer Verbindungen. 89. Selektive Photobromierung von Si-methylierten Carbosilanen

Formation of Organosilicon Compounds. 89. Selective Photobromination of Si-methylated Carbosilanes A selective photobromination of the C atoms in the skeleton of Si-methylated carbosilanes is reported. (me₃Si? CH₂)₂Sime₂ reacts to me₃Si? CBr₂? Sime₂? CH₂? Sime₃ in good yields (me = CH₃); the second CH₂ group is considerably slower brominated. Photobromination of (me₂Si? CH₂)₃ consecutively yields a and b . Also from (me₂Si? CH₂)₄ the derivative with one CBr₂ group is accessible. Bromination of tertiary CH groups is highly preferred; this is shown by the selective formation of c . The C-bromination of SiBr-substituted carbosilanes is significantly more difficult; nevertheless (Brme₂Si)₂CH₂ selectively forms (Brme₂Si)₂CBr₂. Brme₂Si? CH₂? Sime₂? CH₂? Sime₃ forms Brme₂Si? CH₂? Sime₂? CBr₂? Sime₃, i. e., only the CH₂ group non-adjacent to SiBr is attacked. The formation of CHBr groups could not be detected. Higher temperatures and longer reaction times increase the formation of polymers.     

Inhibition of prostaglandin and leukotriene biosynthesis by gingerols and diarylheptanoids.

The rhizomes of Zingiber officinale (ginger) and Alpinia officinarum contain potent inhibitors against prostaglandin biosynthesizing enzyme (PG synthetase). Gingerols and diarylhepatanoids were identified as active compounds. Their possible mechanism of action which was deduced from the structures of active compounds indicated that the inhibitors would also be active against arachidonate 5-lipoxygenase, an enzyme of leukotriene (LT) biosynthesis. This was verified by testing their inhibitory effects on 5-lipoxygenase prepared from RBL-1 cells. A diarylheptanoid with catechol group was the most active compound against 5-lipoxygenase, while yakuchinone A was the most active against PG synthetase.     

Homodimerization of spiro{bicyclo[2.2.1]Hepta-2,5-Diene-7,1′-cyclopropane}, catalyzed by group VIII transition metal complexes

Conclusions The homodimerization of spiro{bicyclo[2.2.1]hepta-2,5-diene-7,1-cyclopropane} (I) has been investigated in the presence of Ni-, Fe-, Co-, Rh-, and Ir-based metal complex catalysts. Depending on the nature of the metal and its ligand environment cyclodimerization of (I) can take place via [2+2]-, [2+2+2]-, and [4+4]-cycloaddition schemes, to give high yields of hepta-, octa-, and nonacyclic strained hydrocarbons.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2592–2599, November, 1988.     

Bioanalysis of (E)-5-(2-bromovinyl)-2'-deoxyuridine

(E)-5-(2-Bromovinyl)-2'-deoxyuridine is an antiviral drug that is experimentally used for modulation of the antitumour effect of fluoropyrimidines, such as ftorafur and 5-fluorouracil. The isolation of the analyte, in the presence of 5-fluorouracil, from the matrix is performed either by means of a simple protein precipitation (plasma) or by means of a liquid-liquid extraction with ethyl acetate (urine). Following pretreatment, the analyte is analysed by reversed-phase chromatography and quantified by absorbance detection at 307 nm. The minimum detectable concentration in plasma and urine samples is ca. 6 ng/ml. The recovery after deproteination of plasma samples is 75%, while after liquid-liquid extraction of urine the recovery amounts 92%. The degree of protein binding of the analyte, measured by ultrafiltration, is found to be 97%. These data allow the bioanalysis of (E)-5-(2-bromovinyl)-2'-deoxyuridine for pharmacokinetic studies.     

Solvatochromic equilibria of cobalt(II) chloride in binary mixtures of dipolar aprotic solvents with water

The visible absorption spectra of CoCl₂ in binary mixtures of acetone, dmf, dma and dmso with H₂O show the existence of configuration equilibria between tetrahedral (T) and octahedral (O) species. Linear correlations between the values of log K (K = [O]/[T]) and the mole fraction of H₂O, _w, have been observed in all the systems under study; their slopes decrease linearly with an increase of the donor number, DN, of the organic component of the mixture. The formation of octahedral species is enthalpy favoured but entropy disfavoured. It was found that both H and S values change linearly with _w and the slopes of these relationships depend clearly on the DN values.     

Sol-gel-derived micron scale optical fibers for chemical sensing

We report for the first time on the preparation of organically-doped room temperature processed sol-gel-derived micron scale optical fibers as platforms for chemical- and bio-sensors. Micron scale optical fibers are drawn from fluorescent dye-doped tetraethoxysilane (TEOS)-derived sol-gel solution processed under ambient conditions. Such a simple methodology to entrap organic and even bioactive species within the optical fiber offers many advantages over more conventional ways of immobilizing organic probes for the development of optical sensors. Specifically, we report on the photophysical properties of fluorescein (a pH sensitive fluorescent dye) and rhodamine 6G (R6G; laser dye) entrapped within sol-gel-derived optical fibers. We present the preliminary results on the viability of such doped optical fibers for chemical sensing. Our results demonstrate that a fluorescein-doped sol-gel-derived optical fiber responds to ammonia and acid vapors with a response time of 1–2 seconds.     

Micro determination of olefinic unsaturation. Reaction of N-bromosuccinimide with olefins in polar medium

Summary A micro method for the determination of olefinic unsaturation in organic compounds has been developed. 2–10 mg sample dissolved in acetic acid is reacted with a known excess of N-bromosuccinimide at room temperature and the excess reagent is back titrated iodometrically. The maximum deviation in the results is ±2%. The compounds containing electron withdrawing groups close to the C=C site are not reactive and hence could not be determined by this procedure.

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Mikrobestimmung der Ungesättigtheit von Olefinen. Reaktion von N-Bromsuccinimid mit Olefinen in polarem Medium

Zusammenfassung 2–10mg der Probe werden in Essigsäure gelöst, mit überschüssigem Reagens versetzt und der Überschuß jodometrisch zurücktitriert. Der maximale Fehler der Ergebnisse beträgt ±2%. Verbindungen, die benachbart zur C=C-Doppelbindung elektronenentziehende Gruppen enthalten, können nicht analysiert werden.

     

Diffractive proteon fragmentation in 16, 32, and 110 GeV/cK − p interactions and the diffractive production of heavy quarks(s\bar s,c\bar c)

The inclusive proton diffraction dissociation cross sections in 16, 32, and 110 GeV/cK ^? p interactions are determined from the spike nearx=1 in the inclusive negative particle spectra and are compared to those obtained inK?p interactions using other selection methods at various energies. The same procedure is applied to events containing aV ⁰ in order to obtain the cross section for diffractive \(s\bar s\) production. While the total cross section for proton diffraction is found to be approximately constant in the energy range studied here, proton diffraction yielding an \(s\bar s - pair\) is found to increase significantly. In particular it is almost constant at 85 μb forΛ ⁰ and Σ production but for \(NK\bar K\) it rises from zero at 16 GeV.c to about 200 μb at 110 GeV/c. From the result for \(s\bar s\) diffractive production an estimate for the \(c\bar c\) diffractive production cross section of approximately 1–10 μb at 110 GeV/c is obtained.     

Raman spectra of titanium dioxide

First-order Raman spectra have been recorded at room temperature for the anatase and rutile phases of polycrystalline titanium dioxide using an argon ion laser as exciter. The high-temperature rutile phase was found to be stabilized at temperatures below 450°C. Anatase transforms to rutile phase at ～750°C. All the Raman active fundamentals predicted by group theory are observed.     

Determination of lanthanum in large steel samples by the neutron activation method

In view of the inhomogeneous distribution of lanthanum in steel, large samples should be used for the determination of this element. The method elaborated consists in the preparation of an average samople by dissolving 50 g steel and analysing an aliquot of the obtained solution corresponding to 0.5 g of steel. In order to reduce the activity of the sample, iron and some other elements are separated from the steel solution by electrolysis prior to irradiation. The amount of lanthanum contamination introduced during the pre-irradiation treatment of the sample is relatively low (10^?10–10^?9 g) if the treatment is carried out under suitable conditions. The post-irradiation treatment consists in the separation of²⁴Na by shaking the sample solution with Sb₂O₅. The¹⁴⁰La-activity is measured by means of a γ-spectrometer (1.6 MeV photopeak).