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High Polarity (high + polarity)
Selected AbstractsEfficient Photosensitized Splitting of Thymine Dimer by a Covalently Linked Tryptophan in Solvents of High PolarityEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2005Qin-Hua Song Abstract Tryptophan-thymine dimer model compounds used to mimic the repair reaction of DNA photolyase have been synthesized. The photosensitized cleavage of the dimer by the covalently linked tryptophan is strongly solvent-dependent with the reaction rates increasing in increasingly polar solvents, for example, the quantum yield , = 0.004 in THF/hexane (5:95) and 0.093 in water. The fluorescence of the tryptophan residue is quenched by the dimer moiety by electron transfer from the excited tryptophan to the dimer. Fluorescence-quenching studies indicated that the electron transfer was efficient in polar solvents. The splitting efficiency of the dimer radical anion within the tryptophan·+,dimer·, species is also remarkably solvent-dependent and increases with the polarity of the solvents. The back-electron-transfer reaction in the charge-separated species, which competes with cleavage, was suppressed in polar solvents. These results are in contrast to those of earlier solvent-dependent studies of indole-dimer systems, but they can be rationalized in terms of the differences in the distances between the chromophore unit and the attached dimer. The pH-dependent measurements of the splitting reaction and the deuterium isotope effect showed that the tryptophan radical cation within the charge-separated species does not deprotonate prior to the cleavage of the dimer radical anion. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Molecular Design of Superabsorbent Polymers for Organic Solvents by Crosslinked Lipophilic Polyelectrolytes,ADVANCED FUNCTIONAL MATERIALS, Issue 24 2008Toshikazu Ono Abstract Molecular design of lipophilic polyelectrolyte gels as superabsorbent polymers that exhibit a high degree of swelling in less-polar and nonpolar organic solvents is demonstrated. A small amount of tetraalkylammonium tetraphenylborate with long alkyl chains as a lipopholic ion pair is incorporated into crosslinked polyacrylates with variable alkyl chain lengths to provide novel lipophilic polyelectrolyte gels. Their swelling degree becomes more than 100 times as much as their dried weights in various organic solvents. The high effectiveness of the swellable solvents shifts to the polar ones by decreasing the length of the alkyl chain. Swelling or collapsing of the lipophilic polyelectrolyte gels originates from both incompatibility of the polymer chains in the media and dissociation of ionic groups. Thus, a unique superabsorbency is observed when the polymer chains have good compatibility with the solvents and the solvents have relatively high polarities enough to dissociate the ionic groups. By varying the polarity of the neutral monomer in these polyelectrolyte gels, the design of gels that can absorb solvents of nearly any polarity is demonstrated. [source] Synthesis and Optoelectronic Properties of Nonpolar Polyrotaxane Insulated Molecular Wires with High Solubility in Organic Solvents,ADVANCED FUNCTIONAL MATERIALS, Issue 21 2008Michael J. Frampton Abstract Hydrophilic polyanionic conjugated polyrotaxanes are readily synthesized in water by Suzuki coupling, but their high polarity and ionic nature limit the potential applications of these materials. Here, we demonstrate three methods for transforming these polar polyelectrolytes into nonpolar lipophilic insulated molecular wires. A water-soluble polyfluorene- alt -biphenylene ,-cyclodextrin (CD) polyrotaxane was converted into nonpolar derivatives by methylation of the carboxylic acid groups with diazomethane and conversion of the hydroxyl groups of the CDs to benzyl ethers, trihexylsilyl ethers, benzoyl esters, and butanoate esters to yield polyrotaxanes that are soluble in organic solvents such as chloroform and cyclohexane. Elemental analysis, NMR spectroscopy, and gel permeation chromatography (GPC) data support the proposed structures of the organic-soluble polyrotaxanes. The extents of reaction of the polyrotaxane CD hydroxyl groups were 55% for trihexylsilyl chloride/imidazole; 81% for benzyl chloride/sodium hydride; 72% for benzoyl chloride/pyridine/4-dimethylaminopyridine; and 98% butanoic anhydride/pyridine/4-dimethylaminopyridine. Alkylation, silylation, and esterification increase the bulk of the encapsulating sheath, preventing interstrand aggregation, increasing the photoluminescence efficiency in the solid state and simplifying the time-resolved fluorescence decay. The organic-soluble polyrotaxanes were processed into polymer light-emitting diodes (PLEDs) from solution in nonpolar organic solvents, thereby excluding ionic impurities from the active layer. [source] Metabolism of chlorpyrifos and chlorpyrifos oxon by human hepatocytes,JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 6 2006Kyoungju Choi Abstract The metabolism of chlorpyrifos (CPS) and chlorpyrifos oxon (CPO) by human hepatocytes and human liver S9 fractions was investigated using LC-MS/MS. Cytochrome P450 (CYP)-dependent and phase II-related products were determined following incubation with CPS and CPO. CYP-related products, 3,5,6-trichloro-2-pyridinol (TCP), diethyl thiophosphate, and dealkylated CPS, were found following CPS treatment and dealkylated CPO following CPO treatment. Diethyl phosphate was not identified because of its high polarity and lack of retention with the chromatographic conditions employed. Phase II-related conjugates, including O- and S-glucuronides as well as 11 GSH-derived metabolites, were identified in CPS-treated human hepatocytes, although the O -sulfate of TCP conjugate was found only when human liver S9 fractions were used as the enzyme source. O -Glucuronide of TCP was also identified in CPO-treated hepatocytes. CPS and CPO were identified using HPLC,UV after CPS metabolism by the human liver S9 fraction. However, CPO was not found following treatment of human hepatocytes with either CPS or CPO. These results suggest that human liver plays an important role in detoxification, rather than activation, of CPS. © 2006 Wiley Periodicals, Inc. J Biochem Mol Toxicol 20:279,291, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20145 [source] Preparation of polymer-supported polyethylene glycol and phase-transfer catalytic activity in benzoate synthesisAICHE JOURNAL, Issue 3 2010Baojiao Gao Abstract The crosslinked polymeric microspheres (GMA/MMA) of glycyl methacrylate (GMA) and methyl methacrylate (MMA) were prepared by suspension polymerization. Polyethylene glycol (PEG) was grafted on GMA/MMA microsphers via the ring-opening reaction of the epoxy groups on the surfaces of GMA/MMA microspheres, forming a polymer-supported triphase catalyst, PEG-GMA/MMA. The Phase-transfer catalytic activity of PEG-GMA/MMA microspheres was evaluated using the esterification reaction of n -chlorobutane in organic phase and benzoic acid in water phase as a model system. The effects of various factors on the phase transfer catalysis reaction of liquid,solid,liquid were investigated. The experimental results show that the PEG-GMA/MMA microspheres are an effective and stable triphase catalyst for the esterification reaction carried out between oil phase and water phase. The polarity of the organic solvent, the ratio of oil phase volume to water phase volume and the density of the grafted PEG on PEG-GMA/MMA microspheres affect the reaction rate greatly. For this investigated system, the solvent with high polarity is appropriate, an adequate volume ratio of oil phase to water phase is 2:1, and the optimal PEG density on the polymeric microspheres is 15 g/100 g. Triphase catalysts offer many advantages associated with heterogeneous catalysts such as easy separation from the reaction mixture and reusability. The activity of PEG-GMA/MMA microspheres is not nearly decreased after reusing of 10 recycles. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Preferential extractability of ,-oryzanol from dried soapstock using different solventsJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 2 2009Raj R Kumar Abstract BACKGROUND: ,-Oryzanol from rice bran has lately gained potential importance because of its proven health benefits. Thus the extractability of ,-oryzanol from the soapstock of crude rice bran oil is important from the perspective of future large-scale production, which would give value addition to this by-product obtained from the rice bran oil industry. The aim of the present study was to investigate the extraction of ,-oryzanol from the drum-dried soapstock of rice bran oil using various solvents. RESULTS: It was found that ,-oryzanol could be extracted most effectively using ethyl acetate, followed by dichloromethane and ethyl methyl ketone. All components of ,-oryzanol have an alcohol group in the ferulate portion giving rise to relatively high polarity, thereby increasing the extraction in more polar solvents efficiently. Ethyl acetate showed maximum extractability of ,-oryzanol by the Soxhlet method. To quantify ,-oryzanol, reverse phase high-performance liquid chromatography (RP-HPLC) was used for fingerprinting the ,-oryzanol analogues with respect to standard ,-oryzanol. CONCLUSION: A new RP-HPLC method for determining the individual components of ,-oryzanol has been reported that can be used for performing an online characterisation of ,-oryzanol analogues by liquid chromatography/mass spectrometry. Copyright © 2008 Society of Chemical Industry [source] Bonding and Bending in Zirconium(IV) and Hafnium(IV) HydrazidesCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2008Heike Herrmann Dr. Abstract Reaction of the dichloro complexes [M(N2TBSNpy)Cl2] (M=Zr: 1, Hf: 2; TBS: tBuMe2Si; py: pyridine) with one molar equivalent of LiNHNPh2 gave mixtures of the two diastereomeric chlorohydrazido(1,) complexes [M(N2TBSNpy)(NHNPh2)Cl] (M=Zr: 3,a,b, Hf: 4,a,b) in which the diphenylhydrazido(1,) ligand adopts a bent ,1 coordination. This mixture of isomers could be cleanly converted into the deep green diphenylhydrazido(2,) complexes [Zr(N2TBSNpy)(NNPh2)(py)] (5) and [Hf(N2TBSNpy)(NNPh2)(py)] (6), respectively, by dehydrohalogenation with lithium hexamethyldisilazide (LiHMDS) in the presence of one molar equivalent of pyridine. Both complexes contain a linearly coordinated hydrazinediide for which a DFT-based frontier orbital analysis established bonding through one , and two , orbitals. A high polarity of the MN bond was found, in accordance with the description of hydrazinediide(2,) acting as a six-electron donor ligand. The pyridine ligand in [M(N2TBSNpy)(NNPh2)(py)] (M=Zr: 5, Hf: 6) is substitutionally labile as established by line-shape analysis of the dynamic spectra (,G,=19,kcal,mol,1). A change in denticity of the hydrazido unit from ,1 to ,2 was studied by DFT methods. Both forms are calculated to be very close in energy and are only separated by shallow activation barriers, which supports the notion of a rapid ,1 to ,2 interconversion. This process is believed to happen early on in the NN scission in the presence of coupling reagents. Frontier orbital and natural population analyses suggest that a primarily charge-controlled nucleophilic attack at N, is unlikely whereas interaction with an electrophile could play an important role. This hypothesis was tested by the reaction of 5 and 6 with one molar equivalent of B(C6F5)3 to give [Zr(N2TBSNpy)(NNPh2){B(C6F5)3}] (7) and [Hf(N2TBSNpy)(NNPh2){B(C6F5)3}] (8). In these products, B(C6F5)3 becomes attached to the N, atom of the side-on bound hydrazinediide and there is an additional interaction of an ortho -F atom of a C6F5 ring with the metal centre. [source] | ||||||||||