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Strong Hydrogen Bonding (strong + hydrogen_bonding)
Selected AbstractsEnol Forms of 1,3-Indanedione, Their Stabilization by Strong Hydrogen Bonding, and Zwitterion-Assisted InterconversionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2010Mark Sigalov Abstract By analyzing NMR spectroscopic data, and supported by IR, UV/Vis, Raman, dielectrometry, and DFT techniques, a comprehensive study of the 1:2 adducts of picolinaldehyde and 1,3-indanediones is presented. The parent indanedione derivative 5 exists in an equilibrium between all-keto and enol forms, the latter being stabilized by an intramolecularO,H···N hydrogen bond. Only the all-keto form was observed in the 5,6-dimethoxy compound 6, whereas solely the enol tautomer was observed with its 5,6-dichloro analogue 7. Polar solvents and low temperatures shift the equilibrium towards the enol tautomer in 5. The structure of adduct 8, formed with isonicotinaldehyde, prevents the formation of intramolecular O,H···N hydrogen bonds and thus it exists in the all-keto form in low polar solvents. However, in DMSO solutions it adopts a zwitterionic form with a strong anionic O,···H···O hydrogen bond. Thus, the enol form in indanedione adducts was unequivocally characterized in solution and the factors that determine the keto,enol tautomerism, namely electronic effects, solvent, temperature, and intramolecular hydrogen bonds, have been methodically studied by spectroscopic and quantum mechanical methods. [source] Manifestation of a Chiral Smectic C Phase in Diphenylbutadiene-Cored Bolaamphiphilic Sugars,ADVANCED FUNCTIONAL MATERIALS, Issue 11 2008Suresh Das Abstract A series of symmetrical bolaamphiphiles possessing a diphenylbutadiene core and glucopyranoside head groups linked together by oligomethylene spacers, were synthesized and their thermotropic liquid crystalline properties investigated by polarized light optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optic switching. In spite of the presence of chiral centers, amphiphilic sugars in general do not exhibit macroscopic chirality and this phenomenon is attributed to strong hydrogen bonding between sugar head groups resulting in microphase-segregated layer like arrangements. In the present study all the molecules investigated exhibited the smectic C* phase, i.e., tilted lamellar phase with macroscopic chiral ordering of the molecules. The stability of this phase increased with increase in the length of the oligomethylene spacers. Whereas for derivatives with spacers containing ,4 methylene groups, the smectic C* phase was observed only in the cooling phase, for those containing spacers with ,5 methylene groups this phase was observed both in the heating and cooling cycles. The absorption and fluorescence spectra of these materials suggest that the unusual observation of macroscopic chirality in these bolaamphiphiles containing free hydroxyl groups could be attributed to self-aggregating behavior of the diphenylbutadiene core. [source] Aerobic, Chemoselective Oxidation of Alcohols to Carbonyl Compounds Catalyzed by a DABCO-Copper Complex under Mild ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2007Sreedevi Mannam Abstract A DABCO-copper(I) chloride complex (5 mol,%) together with TEMPO (5 mol,%) in nitromethane as solvent has been used as an efficient catalytic system for the selective oxidation of benzylic and allylic alcohols into the corresponding carbonyl compounds at room temperature where molecular oxygen acts as an ultimate, stoichiometric oxidant and water is the only by-product. The solid-state structure determination of the DABCO-copper complex shows that the copper is in the +II oxidation state with trigonal bipyramidal geometry and exists in a linear polymeric structure due to strong hydrogen bonding. [source] pH-sensitive alginate/soy protein microspheres as drug transporterJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2007Hua Zheng Abstract The complex microspheres based on alginate (AL) and soy protein isolate (SPI) were prepared by solution blending and then Ca2+ crosslinking, and their function as drug carrier was explored as well. The effects of composition on the structures of microspheres were studied, and the XRD results proved the miscibility between components. Meanwhile, FTIR results suggested that such miscibility was driven by strong hydrogen bonding. Especially, the complex microsphere with equal content of AL and SPI had the best miscibility by morphological analysis, shown as a smooth and uniform surface of SEM images. The controlled release function of the complex microspheres was verified using theophylline as a drug model, that is, the swelling and drug release were affected by pH conditions and showed obvious differences under given pH of stomach, intestine, and colon. Moreover, the intestine and colon may be optimal site for prompt release of drugs. Except for the attribution of AL component to pH sensitivity, the complex microspheres also inherited the bioactivity of SPI component, which may lower irritants of drug to the tissues in body. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Raman spectroscopic study of the vivianite arsenate mineralsJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2003Ray L. Frost Abstract The molecular structures of the vivianite-type arsenate minerals were studied using a combination of Raman and infrared spectroscopy. The Raman spectra of the hydroxyl-stretching regions are complex with overlapping bands at 3419, 3209, 3185 and 3010 cm,1. This complexity is reflected in the water HOH bending modes with strong infrared bands in the 1660,1685 cm,1 region indicating strong hydrogen bonding to arsenate anions in adjacent layers. The Raman arsenate AsO stretching region shows strong similarity between the vivianite arsenate minerals. In the infrared spectra complexity exists with multiple antisymmetric stretching vibrations observed, indicating a reduction of symmetry. Strong infrared bands around 700 and 560 cm,1 are attributed to librational modes of water. Vibrational spectra enable the structure of the minerals to be determined and, whilst similarities exist in the spectral patterns, sufficient differences exist to determine the identification of the minerals. In particular, Raman spectroscopy assists in the identification of the complex isomorphous substitution in these vivianite arsenate minerals. Copyright © 2003 John Wiley & Sons, Ltd. [source] Properties and Bioapplications of Blended Cellulose and Corn Protein FilmsMACROMOLECULAR BIOSCIENCE, Issue 9 2009Quanling Yang Abstract A series of blend films have been prepared from cellulose and corn protein in a NaOH/urea solution by a simple, low cost, and ,green' pathway. Their structure and properties are characterized by amino acid analysis, X-ray diffraction, scanning electron microscopy, thermogravimetry, and tensile testing. The results reveal that a certain miscibility exists between cellulose and corn protein and their thermal stability and mechanical properties are improved significantly, compared with the protein materials, when the protein content is less than 18 wt.-%. The protein, which contains tyrosine and histidine, could remain in the blend films after being washed for ten days, which indicates the strong hydrogen bonding between the hydroxy groups of cellulose and the hydroxyphenyl of tyrosine and imidazolyl of histidine in the protein. Furthermore, they exhibit good biocompatibility capable of supporting cell adhesion and proliferation. [source] Synthesis and Properties of Poly(vinyl alcohol)/Synthetic F-montmorillonite NanocompositesCHINESE JOURNAL OF CHEMISTRY, Issue 8 2009Junhao ZHANG Abstract F-montmorillonite (F-MMT) was synthesized by a hydrothermal method at 493 K for 72 h, in which a little of hydroxyl radical is replaced by fluoride ion in the silicate structure. Poly(vinyl alcohol) (PVA)/F-MMT nanocomposites were prepared using the synthetic F-MMT by a solution-intercalation method. The F-MMT and PVA/ F-MMT nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that the flake structured F-MMT is homogeneously dispersed in PVA, forming an exfoliated nanocomposite structure. Thermogravimetric analysis, mechanical performance and UV-visible spectroscopy were applied to test the properties of PVA nanocomposites, which indicate that the thermal stability and mechanical performance are enhanced distinctly, without a sacrifice in optical clarity. The improvement of mechanical and thermal properties was attributed to the homogeneous and good dispersion of F-MMT in polymeric matrix and the strong hydrogen bonding between O,,H of PVA and F,, of F-MMT. [source] | |||||||||||||