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Ring Protons (ring + proton)
Selected AbstractsDesigning 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] Synthesis of rhodium(III) complexes with tris/tetrakis-benzimidazoles and benzothiazoles,quick identification of cyclometallation by nuclear magnetic resonance spectroscopyMAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2009N. Chandrashekhar Abstract Reactions of rhodium(III) halides with multidentate N,S -heterocycles, (LH3) 1,3,5-tris(benzimidazolyl)benzene (L1H3; 1), 1,3,5-tris(N -methylbenzimidazolyl) benzene (L2H3; 2) and 1,3,5-tris(benzothiazolyl)benzene (L3H3; 3), in the molar ratio 1:1 in methanol,chloroform produced mononuclear cyclometallated products of the composition [RhX2(LH2)(H2O)] (X = Cl, Br, I; LH2 = L1H2, L2H2, L3H2). When the metal to ligand (1,3 or 1,2,4,5-tetrakis(benzothiazolyl)benzene [L4H2; 4]) molar ratio was 2:1, the reactions yielded binuclear complexes of the compositions [Rh2Cl5(LH2)(H2O)3] (LH2 = L1H2, L2H2, L3H2) and [Rh2X4(L4)(H2O)2] (X = Cl, Br, I). Elemental analysis, IR and 1H nuclear magnetic resonance (NMR) chemical shifts supported the binuclear nature of the complexes. Cyclometallation was detected by conventional 13C NMR spectra that showed a doublet around ,190 ppm. Cyclometallation was also detected by gradient-enhanced heteronuclear multiple bond correlation (g-HMBC) experiment that showed cross-peaks between the cyclometallated carbon and the central benzene ring protons of 1,3. Cyclometallation was substantiated by two-dimensional 1H1H correlated experiments (gradiant-correlation spectroscopy and rotating frame Overhauser effect spectroscopy) and 1H13C single bond correlated two-dimensional NMR experiments (gradient-enhanced heteronuclear single quantum coherence). The 1H15N g-HMBC experiment suggested the coordination of the heterocycles to the metal ion via tertiary nitrogen. Copyright © 2009 John Wiley & Sons, Ltd. [source] Preparation, characterization, and thermal properties of hydrophilic copolymers: p -chlorophenylmaleimides with hydroxylethyl methacrylate and ,-methyl itaconatePOLYMER INTERNATIONAL, Issue 9 2007Guadalupe del C Pizarro Abstract This work describes the synthesis, characterization, and thermal behavior of copolymers of p -chlorophenylmaleimide (Cl-PhMI) with ,-methyl itaconate (,-MHI) and 2-hydroxyethyl methacrylate (HEMA). Copolymerization was carried out with a radical initiator by varying the feed mole fraction of Cl-PhMI from 0.25 to 0.75. The copolymer composition was determined from the N/C ratio based on elemental analysis data and with 1H NMR spectroscopy for poly(Cl-PhMI- co -HEMA) using a proton signal attributed to the CH3 of HEMA (, = 0.7,1.4 ppm) and the area of aromatic ring protons (, = 7.2,7.8 ppm), where the proton/area relationship confirmed the copolymer compositions calculated by elemental analysis. The monomer reactivity ratios r1 and r2 were determined using the Kelen,Tüdös method. These values demonstrated that copolymerization produced random copolymers with an alternation tendency. The molecular weight and polydispersity were also determined. The thermal behavior can be correlated with the copolymer composition. An increase of the thermal decomposition temperature occurred when the content of Cl-PhMI increased. The glass transition temperature and thermal stability of poly(,-MHI) or poly(HEMA) increased with an increasing amount of Cl-PhMI in the polymer backbone. Copyright © 2007 Society of Chemical Industry [source] New insights into intracellular lipid binding proteins: The role of buried waterPROTEIN SCIENCE, Issue 10 2002Christian Lücke Abstract The crystal structures of most intracellular lipid binding proteins (LBPs) show between 5 and 20 internally bound water molecules, depending on the presence or the absence of ligand inside the protein cavity. The structural and functional significance of these waters has been discussed for several LBPs based on studies that used various biophysical techniques. The present work focuses on two very different LBPs, heart-type fatty acid binding protein (H-FABP) and ileal lipid binding protein (ILBP). Using high-resolution nuclear magnetic resonance spectroscopy, certain resonances belonging to side-chain protons that are located inside the water-filled lipid binding cavity were observed. In the case of H-FABP, the pH- and temperature-dependent behavior of selected side-chain resonances (Ser82 OgH and the imidazole ring protons of His93) indicated an unusually slow exchange with the solvent, implying that the intricate hydrogen-bonding network of amino-acid side-chains and water molecules in the protein interior is very rigid. In addition, holo H-FABP appeared to display a reversible self-aggregation at physiological pH. For ILBP, on the other hand, a more solvent-accessible protein cavity was deduced based on the pH titration behavior of its histidine residues. Comparison with data from other LBPs implies that the evolutionary specialization of LBPs for certain ligand types was not only because of mutations of residues directly involved in ligand binding but also to a refinement of the internal water scaffold. [source] | ||||||||||