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Low Polarity (low + polarity)
Selected AbstractsSelf-Aggregation Tendency of Zirconocenium Ion Pairs Which Model Polymer-Chain-Carrying Species in Aromatic and Aliphatic Solvents with Low PolarityCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2008Luca Rocchigiani From pairs to double pairs: Zirconocene ion pairs bearing an aliphatic chain of variable length were synthesized and investigated by means of NOE and diffusion NMR spectroscopy experiments. The presence of long aliphatic chains allowed an unprecedented investigation of their self-aggregation tendency in cyclohexane (see figure), which has a dielectric constant similar to that of isoparaffins used in industrial plants. [source] A Theoretical Study on the Reactivity of a Rhenium Hydroxo-Carbonyl Complex Towards ,-LactamsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2008Violeta Yeguas Abstract The mechanism of the reaction between the complex [Re(OH)(CO)3(N2C2H4)] and azetidin-2-one or 3-formylamino- N -sulfonatoazetidin-2-one was investigated by using the B3LYP density functional theory methodology in conjunction with the PCM-UAHF model to take into account solvent effects. According to our calculations, the rate-determining energy barrier for the azetidin-2-one case of 38.8 kcal,mol,1, becomes 25.7 kcal,mol,1 in the case of the 3-formylamino- N -sulfonatoazetidin-2-one species. The presence of the sulfonato group is crucial for the cleavage of the ,-lactam N1,C2 bond by the Re complex thanks to the interaction of the sulfonato group with the hydroxy and bidentate ligands of the complex. This could be of interest for the synthesis of ,-amino acids and their derivatives from ,-lactams under mild conditions and in solvents of low polarity promoted by organometallic complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Designing Ionic Liquids: 1-Butyl-3-Methylimidazolium Cations with Substituted Tetraphenylborate CounterionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2003Joep van den Broeke Abstract The hydrophobic, low melting, 1-butyl-3-methylimidazolium (BMIm) salts [BMIm][BPh4] (1), [BMIm][B(C6H4Me-4)4] (2), [BMIm][B{C6H4(CF3)-4}4] (3), [BMIm][B{C6H3(CF3)2 -3,5}4] (4), [BMIm][B{C6H4(C6F13)-4}4] (5), [BMIm][B{C6H4(SiMe3)-4}4] (6), [BMIm][B(C6H4{SiMe2(CH2CH2CF3)}-4)4] (7), [BMIm][B{C6H4(SiMe2C8H17}-4}4] (8) and [BMIm][B(C6H4{SiMe2(CH2CH2C6F13)}-4)4] (9) have been prepared. Systematic variation of the substituents on the tetraphenylborate anion allowed an assessment of their influence on the physical properties of the imidazolium salts. Structural investigations using NMR and IR spectroscopy, combined with single crystal X-ray structure determinations for 2, 3, 5 and 6, revealed hydrogen-bonding interactions between the imidazolium ring protons and the borate anion, both in the solid state and in solution. These interactions are weakened upon the introduction of electron-withdrawing substituents in the anion and follow the order 3,5-(CF3)2 < ,C6F13 < ,CF3 < ,SiMe2CH2CH2C6F13 < ,SiMe2CH2CH2CF3 < ,H < ,Me < ,SiMe3. The melting points of the salts depend primarily on the bulk of the lipophilic substituents, and decrease with increasing size. Bulky lipophilic substituents dramatically enhance the solubility of the imidazolium borates 8 and 9 in hexane and reduce their relative polarity. These unique properties make imidazolium borates 8 and 9 interesting as amphiphilic ionic liquids with low polarity. Attempts to crystallise 7 resulted in decomposition. A single-crystal X-ray structure determination of the product, isolated in 6% yield, showed that a carbene,tris[4-{dimethyl(3,3,3-trifluoropropyl)silyl}phenyl]borane adduct was formed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Reaction of Phenanthrene-9,10-dione with Phenanthrene-9,10-diol: Synthesis and Characterization of the First ortho -Quinhydrone DerivativeHELVETICA CHIMICA ACTA, Issue 4 2004Fausto Calderazzo Treatment of phenanthrene-9,10-dione (PQ) with phenanthrene-9,10-diol (PQH2), as prepared by catalytic hydrogenation of PQ, in toluene solution or in the solid state afforded crystalline ,9,10-phenanthrenequinhydrone' (PQH), the first example of an ortho -quinhydrone. PQH was characterized by analytical and spectroscopic methods, including X-ray and CP/MAS 13C-NMR analyses. The crystal structure of PQH showed pairs of planar molecules linked by H-bonds and organized in columns parallel to the crystallographic axis a. The solid-state structure of PQH was compared with those of the parent compounds, PQ and PQH2, the latter being reported for the first time. PQH was found to be stable in the solid state only, the components PQ and PQH2 being formed upon dissolution in media of even low polarity such as toluene. [source] Noncovalent dimerization of paclitaxel in solution: Evidence from electrospray ionization mass spectrometryJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2002Sarah A. Lorenz Abstract Paclitaxel, a unique antimitotic chemotherapy agent that inhibits cell division by binding to microtubules and prevents them from "depolymerizing," has received widespread interest because of its efficacy in fighting certain types of cancer, including breast and ovarian cancer. Paclitaxel undergoes aggregation at millimolar concentrations in both aqueous media and solvents of low polarity (mimicking hydrophobic environments). Its aggregation may have impact on its aqueous stability and its ability to stabilize microtubules. Here, we investigated the dimerization phenomenon of paclitaxel by electrospray ionization mass spectrometry (ESI-MS). Paclitaxel dimers were stable in solutions of acetonitrile/aqueous ammonium acetate (80/20) and aqueous sodium acetate/acetonitrile (92/8 or 95/5) at various pH values. Additional experiments using solution-phase hydrogen/deuterium exchange were employed to ascertain whether or not the observed dimers were formed in solution or as an artifact of the ESI process by ion,molecule reaction. The evidence supports formation of the dimer in solution, and the approach used can be extended to investigation of other types of drug,drug interactions. © 2002 Wiley-Liss Inc. and the American Pharmaceutical Association J Pharm Sci 91:2057,2066, 2002 [source] Sorption of HOC in soils with carbonaceous contamination: Influence of organic-matter compositionJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2005Kerstin Abelmann Abstract Detailed information about structure and composition of organic sorbents is required to understand their impact on sorption capacity and sorption kinetic of organic pollutants. Therefore, the chemical composition of organic material from 18 geosorbents was investigated by solid-state 13C nuclear-magnetic-resonance (NMR) spectroscopy. Structural parameters such as aromaticity, polarity, and alkyl-C content were related to the Freundlich sorption exponent (1/n) and the sorption coefficient . The geosorbents included three natural and four combusted coals (carbonaceous material), three Histosols, five mineral soils from Germany containing inputs of technogenic carbonaceous material, derived from industrial activities, and four non-contaminated mineral soils from Germany. Equilibrium sorption was measured for five hydrophobic organic compounds and analyzed with the solubility-normalized Freundlich sorption isotherm. With increasing maturation degree, the proportion of polar constituents decreases from the natural soils to the coals. In contrast to the non-polluted mineral soils, the soils with technogenic input are characterized by high aromaticity and low polarity. A positive correlation between sorption coefficient and aromaticity was found. The Freundlich exponent (1/n) is negatively correlated with the aromaticity, denoting an increase of adsorption processes with increasing aromaticity. Likewise, the contribution of partitioning decreases. This sorption mechanism predominates only if the organic matter in the samples contains a high proportion of polar compounds. Sorption von HOC in Böden mit kohleartiger Kontamination: Einfluss der Zusammensetzung des organischen Materials Um den Einfluss von organischen Sorbenten auf die Sorptionskapazität und die Kinetik organischer Schadstoffe zu verstehen, müssen detaillierte Informationen über deren Struktur und Zusammensetzung vorliegen. Aus diesem Grund wurde das organische Material von 18 Geosorbenten mittels der Festkörper- 13C-NMR-Spektroskopie untersucht. Strukturelle Parameter wie zum Beispiel die Aromatizität, die Polarität und der Alkyl-C-Gehalt wurden mit dem Freundlich-Exponenten 1/n und dem Sorptionskoeffizienten korreliert. Die Geosorbenten bestehen aus drei natürlichen und vier thermisch behandelten Kohlen, drei Histosolen und fünf deutschen Mineralböden, die technogenes kohlehaltiges Material aus industriellen Aktivitäten enthalten, sowie vier nicht kontaminierten deutschen Böden. Die Gleichgewichtssorption wurde für fünf hydrophobe, organische Verbindungen gemessen und mit Hilfe der löslichkeitsnormalisierten Freundlich-Isotherme analysiert. Der Anteil der polaren Komponenten nimmt von den natürlichen Böden zu den Kohlen mit zunehmendem Inkohlungsstadium ab. Im Gegensatz zu den nicht kontaminierten Mineralböden weisen die Böden mit technogenen Bestandteilen eine hohe Aromatizität und eine geringe Polarität auf. Zwischen dem und der Aromatizität ergab sich ein positiver Zusammenhang. Der Freundlich Exponent (1/n) korreliert negativ mit der Aromatizität. Dies weist auf eine Zunahme der Adsorptionsprozesse mit Erhöhung der Aromatizität hin. Der Beitrag der Partitionierung sinkt ebenfalls. Dieser Sorptionsmechanismus dominiert nur in den Proben, in denen das organische Material einen hohen Anteil polarer Bestandteile besitzt. [source] Detection of carbonyl groups in triterpenoids by hydroxylamine hydrochloride derivatization using electrospray ionization mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2008Xin Liu A rapid, simple electrospray ionization mass spectrometry (ESI-MS) sensitivity enhancement method for detecting carbonyl groups in triterpenoids has been developed by using hydroxylamine hydrochloride (NH2OH,·,HCl) as a derivatization reagent. We use the oxime formed during the derivatization reactions and its Beckmann rearrangement intermediates as a means of detecting the carbonyl groups originally present in these triterpenoids. In comparison with other derivatization methods reported in the literature, this method is simple, specific and can be used to detect carbonyl groups in triterpenoids which have low polarity and are poorly or non-ionizable. Moreover, it can also be used to detect hydroxyl groups by using the Dess-Martin periodinane (DMP) to convert primary and secondary hydroxyls into carbonyl groups. Copyright © 2008 John Wiley & Sons, Ltd. [source] The isoflavonoid aglycone-rich fractions of Chungkookjang, fermented unsalted soybeans, enhance insulin signaling and peroxisome proliferator-activated receptor-, activity in vitroBIOFACTORS, Issue 4 2006Dae Young Kwon Abstract We investigated anti-diabetic candidates and their mechanisms from the fractions of Chungkookjang (CKJ), a traditional fermented unsalted soybean, by investigating insulin signaling, peroxisome proliferator-activated receptor (PPAR)-, activity and glucose-stimulated insulin secretion, in vitro. Cooked soybeans (CSB) and CKJ, fermented predominantly with Bacillus subtilis, were extracted by 70% EtOH followed by an XAD-4 column chromatography with a serial mixture of solvents comprised of MeOH and water. During fermentation, the contents of isoflavonoid aglycones were elevated, and the fractions enriched with aglycones enhanced insulin-stimulated glucose uptake in 3T3-L1 adipocytes. This increase in glucose uptake resulted from stimulating a translocation of the glucose transporter (GLUT)-4 into the plasma membrane through the phosphorylation of insulin receptor substrate (IRS)-1 and Akt. Especially, daidzein enriched fractions elevated insulin-stimulated glucose uptake by acting as PPAR-, agonist up to levels exhibited when 10 nM insulin is administered. Fractions containing small peptides with low polarity in CKJ slightly increased glucose-stimulated insulin secretion. The data suggest that an increase in isoflavonoid aglycones in CKJ, in comparison to CSB, enhances glucose utilization via activating insulin signaling and stimulates PPAR-, activity in adipocytes. In addition, CKJ contains small peptides improving glucose-stimulated insulin secretion in insulinoma cells. Overall, CKJ is superior to CSB in anti-diabetic action. [source] | ||||||||||