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Groups Leads (groups + lead)
Selected AbstractsChemInform Abstract: Practical Access to Amines by Platinum-Catalyzed Reduction of Carboxamides with Hydrosilanes: Synergy of Dual Si,H Groups Leads to High Efficiency and Selectivity.CHEMINFORM, Issue 8 2010Shiori Hanada Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Cell Adhesion and Cellular Patterning on a Self-Assembled Monolayer of Zeolite L CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Nermin Seda Kehr Abstract Chemically functionalized self-assembled monolayers made by disk-shaped zeolite L nanocrystals are used as models for biocompatible surfaces to study cell-adhesion behavior. Different chemical groups lead to different cellular behavior and fluorescent-molecule-loaded zeolites allow the position of the cells to be determined. Furthermore, a patterned monolayer of asymmetrically functionalized zeolite L obtained by microcontact chemistry is used to grow cells. A spatial recognition of the cells, which proliferate only on the bioactive-molecule-functionalized stripes, is possible. [source] Low-Temperature Restructuring Processes in PolyhydrosilanesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 13 2006Liviu Sacarescu Abstract Summary: This paper presents the structural influence of the SiH functionality on the physicochemical properties of polysilanes. New low-temperature restructuring processes were discovered using thermal analysis (TGA, DSC). Photoluminescent (FL) and X-ray photoelectron spectroscopy (XPS) measurements revealed the optoelectronic properties-chemical structure relationship of the synthesized polymers. Highly reactive SiH groups lead to restructuring of the main polysilane chain. [source] 4,4,-Methylenediphenol,4,4,-bipyridine (2/3): decarboxylation of 5,5,-methylenedisalicylic acid under hydrothermal conditionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2009Zhi-Hui Zhang Reaction of 5,5,-methylenedisalicylic acid (5,5,-H4mdsa) with 4,4,-bipyridine (4,4,-bipy) and manganese(II) acetate under hydrothermal conditions led to the unexpected 2:3 binary cocrystal 4,4,-methylenediphenol,4,4,-bipyridine (2/3), C13H12O2·1.5C10H8N2 or (4,4,-H2dhdp)(4,4,-bipy)1.5, which is formed with a concomitant decarboxylation. The asymmetric unit contains one and a half 4,4,-bipy molecules, one of which straddles a centre of inversion, and one 4,4,-H2dhdp molecule. O,H...N interactions between the hydroxy and pyridyl groups lead to a discrete ribbon motif with an unusual 2:3 stoichiometric ratio of strong hydrogen-bonding donors and acceptors. One of the pyridyl N-atom donors is not involved in hydrogen-bond formation. Additional weak C,H...O interactions between 4,4,-bipy and 4,4,-H2dhdp molecules complete a two-dimensional bilayer supramolecular structure. [source] Self-assembly and morphology of polydimethylsiloxane supramolecular thermoplastic elastomersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2008Nicole E. Botterhuis Abstract Functionalization of polydimethylsiloxanes (PDMS) polymers with hydrogen-bonding ureidopyrimidinone (UPy) groups leads to supramolecular thermoplastic elastomers. In previous studies, no lateral stacking of UPy dimers was observed in UPy-functionalized polymers, unless additional urethane or urea groups were built into the hard block. However, we have shown that when PDMS is used as the soft block, this lateral aggregation of UPy dimers does take place, since long fibers could be observed in the atomic force microscopy (AFM) phase image. Also in bulk, the presence of these interactions was proven by oscillatory shear experiments. We attribute this aggregation to the incompatibility of soft block and hard block, leading to phase separation. Moreover, we have shown that additional urethane or urea groups in the hard block do lead to materials with more fibers and higher melting points. For the UPy-urea functionalized PDMS even single fibers are observed with AFM when dropcasted from a very diluted solution. When the length of the soft block is increased, the morphology changes from fibrous to spherical. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3877,3885, 2008 [source] Separation of structural, geometrical and optical isomers of epoxycarotenoids using triacontyl-bonded stationary phasesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 11 2009Antonio J. Meléndez-Martínez Abstract The efficiency of C30 stationary phases in the separation of carotenes and diverse hydroxycarotenoids has been the subject of several studies. However, little is known concerning their ability to resolve epoxycarotenoids isomers, whose study is of great importance due to the functions they serve and the information they can reveal concerning the processing of foods. We have concluded that C30 columns provide an excellent separation of structural, geometrical and optical isomers of epoxycarotenoids and that the presence of 5,8-epoxide groups leads to a better shape recognition, to the extent that over 10 geometrical,optical isomers of 5,8-epoxycarotenoids have been separated. Additionally, it was observed that these carotenoids elute later than their 5,6-epoxide counterparts, albeit the latter have a longer chromophore. [source] Rh blood group and liver transplantationLIVER TRANSPLANTATION, Issue 10 2007James D. Perkins M.D. Special Section Editor Background Cold ischemia time and the presence of postoperative hepatic arterial thrombosis have been associated with biliary complications (BC) after liver transplantation. An ABO-incompatible blood group has also been suggested as a factor for predisposal towards BC. However, the influence of Rh nonidentity has not been studied previously. Materials Three hundred fifty six liver transplants were performed from 1995 to 2000 at our hospital. BC incidence and risk factors were studied in 345 patients. Results Seventy patients (20%) presented BC after liver transplantation. Bile leakage (24/45%) and stenotic anastomosis (21/30%) were the most frequent complications. Presence of BC in Rh-nonidentical graft-host cases (23/76, 30%) was higher than in Rh-identical grafts (47/269, 17%) (P = 0.01). BC was also more frequent in grafts with arterial thrombosis (9/25, 36% vs 60/319, 19%; P = 0.03) and grafts with cold ischemia time longer than 430 min (26/174, 15% vs 44/171, 26%; P = 0.01). Multivariate logistic regression confirmed that Rh graft-host nonidentical blood groups [RR = 2(1.1-3.6); P = 0.02], arterial thrombosis [RR = 2.6(1.1-6.4); P = 0.02] and cold ischemia time longer than 430 min [RR = 1.8(1-3.2); P = 0.02] were risk factors for presenting BC. Conclusion Liver transplantation using Rh graft-host nonidentical blood groups leads to a greater incidence of BC. [source] Degradation of high barrier ethylene,vinyl alcohol copolymer under mild thermal-oxidative conditions studied by thermal analysis and infrared spectroscopyPOLYMER INTERNATIONAL, Issue 6 2001José M Lagaron Abstract A study of the thermal-oxidative degradation of a high barrier ethylene,vinyl alcohol copolymer with 32,mol% of ethylene (EVOH) has been carried out by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR) under mild temperature conditions above melting. It was found that time exposures of up to 11,h at temperatures between 9 and 33,°C above the EVOH melting point resulted in polymer weight losses of up to 3.6% with colour formation. The weight loss was faster at short times and slowed down with increasing exposure time. DSC showed a small decrease in crystallinity and melting point, melting-peak broadening and a slight increase in the glass transition temperature of the samples subjected to the more severe thermal-oxidative treatment. The FTIR experiments showed transformation of the vinyl alcohol hydroxyl groups into carbonyl groups and creation of double bonds. Changes in degradation kinetics and perhaps in mechanisms are thought to occur with increasing exposure time. Moreover, FTIR measurements suggest that transformation of the hydroxyl groups leads to a weakening of the overall hydrogen bonding strength in the degraded samples, and therefore a reduction in intermolecular cohesion can be anticipated. © 2001 Society of Chemical Industry [source] Macrocyclic Hexaureas: Synthesis, Conformation, and Anion BindingCHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2009Denys Meshcheryakov Dr. Abstract Varied flexibility: Cyclic oligoureas are formed by using anions as templates. Linking of six xanthene and/or diphenyl ether fragments by urea groups leads to the formation of five macrocyclic compounds with a 48-membered ring with variable flexibility (see picture). Their interaction with anions shows a strong influence of acetate and chloride ions on the cyclization from four precursor molecules. Five macrocylic compounds XXXXXX, XXDXXD, XDXDXD, XDDXDD, and DDDDDD with 48-membered rings, in which six xanthene and/or diphenyl ether fragments are linked through six urea (-NH-C(O)-NH-) groups, have been synthesized. In the cyclization step, a linear diamine was allowed to react with the appropriate diisocyanate by using a [5+1] (i.e., "XDXDX+D" for XDXDXD), [4+2] (DDDDDD), or [3+3] (XDDXDD) procedure. Compounds XXXXXX and XXDXXD were prepared from two molecules of the dimeric amine XX and two molecules of the respective monomeric diisocyanate (X or D) in a [2+1+2+1] (or 2×[2+1]) reaction. The (nonoptimized) yields in the cyclization step ranged from 45 to 80,%. The linear precursor diamines or diisocyanates were obtained by analogous condensation reactions by using partial protection with a tert -butoxycarbonyl group. All the macrocyclic compounds and synthetic intermediates were characterized by 1H,NMR and mass spectra. Three different crystal structures were obtained for XDDXDD, which show the molecule in a more or less strongly folded conformation determined by intramolecular hydrogen bonding. The interaction of the hexaureas with selected anions was studied by 1H,NMR spectroscopy and UV absorption spectrophotometry. [source] | |||||||||||||