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Reductive Conditions (reductive + condition)
Selected AbstractsReduction-Sensitive Self-Aggregates as a Novel Delivery SystemMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 8 2010Ju Eun Kim Abstract Methoxy PEG amine with molecular weight of 5k and , -caprolactone with molecular weight of 1,960 were conjugated to a peptide comprising three cysteine residues. The shift of peak molecular weight and narrow molecular weight distribution in GPC trace without any noticeable shoulder as well as 1H NMR analysis confirmed the successful synthesis of the copolymer. A modified O/W dialysis system was employed to prepare self-aggregates having the size around 210,nm. During the dialysis, stabilized aggregates were obtained by intermolecular disulfide bonds via oxidation. Critical aggregate concentration (CAC) of the copolymer was determined as 0.07,mg,·,mL,1 and disulfide-stabilized self-aggregates remained stable regardless of the concentration without displaying CAC. Doxorubicin-loading amount and efficiency was 8.7 and 26.0%, respectively. Release profile of doxorubicin below CAC at 37,°C showed a sustained release and the addition of D,L -dithiothreitol (DTT) after 24,h triggered a burst release of doxorubicin. Intermolecular disulfide bonds via oxidation stabilized the polymeric aggregates even in the diluted condition similar to that in the bloodstream and addition of DTT destabilized the aggregates to burst encapsulated doxorubicin in the reductive condition. [source] Speciation of Arsenic under Dynamic ConditionsENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 6 2008J. Ackermann Abstract In periodically flooded soils, reductive conditions can occur, which favor the dissolution of Fe (hydr)oxides. Fe (hydr)oxides such as goethite are important sorbents for arsenate (AsV), which is the dominant As species in soils under aerobic conditions. Hence, the dissolution of Fe (hydr)oxides under reductive conditions can result in the mobilization and reduction of AsV and, thus, in an increase in the bioavailability of arsenic. The temporal dynamics of these processes and possible re-sorption or precipitation of arsenite (AsIII) formed are poorly understood. Under controlled laboratory conditions, the temporal change in the redox potential and arsenic speciation with time after a simulated flooding event in a quartz-goethite organic matter substrate, spiked with AsV, was examined. During a period of 6,weeks, substrate solutions were sampled weekly using micro-suction cups and analyzed for pH, AsIII and AsV, Fe, Mn and P concentrations. Redox potentials and matric potentials were determined in situ in the substrate-bearing cylinders. The redox potential and the ratio between AsIII and AsV concentrations remained unchanged during the experiment without organic matter application. With organic matter applied, the redox potential decreased and the AsIII concentrations in the substrate solution increased while the total As concentrations in the substrate solution strongly decreased. An addition of goethite (1,g/kg) per se led to a decrease of the total As in the substrate solution (almost 50,%). In respect to the potential As availability for plants, and consequently, the transfer into the food chain, the results are difficult to evaluate. The lower the total As concentrations in the substrate solution, determined with decreasing redox potential, the least plant As uptake will occur. This effect may however be compensated by a shift of the molar P/AsV ratio in the solution in favor of AsV which is expected to increase the As uptake. [source] Hydrogen Atom Transfer Experiments Provide Chemical Evidence for the Conformational Differences between C - and O -DisaccharidesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2010Elisa I. León Abstract The glycopyran-6- O -yl radical promoted hydrogen atom transfer reaction (HAT) between the two pyranose units of ,- D -Manp -(1,4)-,- D -Glcp and ,- D -Manp -(1,4a)-4a-carba-,- D -Glcp disaccharides provides supporting chemical evidence for the conformational differences between O - and C -glycosyl compounds. In the O -disaccharide the 6-alkoxyl radical, generated under oxidative or reductive conditions, abstracts exclusively the hydrogen at C-5, via a completely regioselective 1,8-HAT reaction. This may be attributable to the conformational restriction of the glycosidic and aglyconic bonds due principally to steric and stereoelectronic effects. On the contrary, very little regioselectivity is observed in the homologous C -disaccharide and a mixture of compounds generated by 1,5-, 1,6-, and 1,8-HAT processes where the abstraction occurs at hydrogen atoms positioned at C-4a, C-1,, and C-5,, respectively, has been obtained. This study has been extended to simpler O - and C -glycosides, where the aglycon was a straight n -alkyl alcohol tether of five atoms; in general, all of the results obtained are shown to be consistent with a major conformational flexibility of the C -glycosidic bond. [source] Synthesis of 3-(Tosylalkyl)indazoles and their Desulfonylation Reactions , A New Entry to 3-Substituted Indazoles by an Unprecedented Friedel,Crafts ProcessEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2009Silvia Campetella Abstract Reaction of indazoles with aldehydes in the presence of p -toluenesulfinic acid affords the corresponding sulfonyl indazoles in satisfactory yields. The reported Friedel,Crafts process is rather unusual on indazoles because of the reduced electronic density of the heterocycle. The obtained sulfonyl indazoles can be desulfonylated under reductive conditions, finally leading to 3-alkylated indazoles.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Carbodiazenylation of Olefins by Radical Iodine Transfer and Addition to Arenediazonium SaltsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2006Olga Blank Abstract Carbodiazenylation of olefins can be achieved with arenediazonium salts under reductive conditions. The method can be extended to aliphatic substituents when iodine compounds are present in the reaction mixture. Incorporation is achieved through a radical iodine transfer. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] An aminoisoflavone , salicyloylindole ring transformationJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 3 2004Werner Löwe A series of 2,-nitroisoflavones 8,10, 15, 22, 27 and 28 was prepared via the (2-nitro-phenyl)-acetic acids 1, 13, 19 and 25. In order to obtain the corresponding 2,-aminoisoflavones the reduction of 8,10, 15, 22, 27 and 28 was undertaken. Surprisingly, new 3-salicyloylindoles instead of the expected 2,-aminoisoflavones were the main reduction products. In the following paper the preparation of the 2,-nitroisoflavones 8,10, 15, 22, 27 and 28 as well as the reduction experiments obtaining the 2,-aminoisoflavones 33 and 35 and the 3-salicyloylindoles 29,32, 34 and 36 will be described. Furthermore, a possible mechanism responsible for the formation of the 3-salicyloylindoles from 2,-nitroisoflavones under reductive conditions will be discussed. [source] Design, synthesis, characterization and in-vivo activity of a novel salmon calcitonin conjugate containing a novel PEG-lipid moietyJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 3 2010Weiqiang Cheng Abstract Objectives The aim of the study was to explore (1) the synthesis of a novel poly(ethylene glycol) modified lipid (PEG-lipid, PL) containing a chemically active tri-block linker, ,-maleimido lysine (Mal), and its conjugation with salmon calcitonin (sCT), and (2) the biophysical properties and activity of the resulting conjugate, Mal-PL-sCT, relative to the control, 2PEG-Mal-sCT, which comprises sCT conjugated with ,-palmitoyl- N -,-maleimido- l -lysine at cysteine 1 and cysteine 7, and PEG moieties at lysine 11 and lysine 18 via a conventional stepwise method. Methods The PEG-lipid was obtained by condensing palmitic acid derivative of ,-maleimido lysine with methoxy poly(ethylene glycol) amine. Under reductive conditions, the PEG-lipid readily reacted with sCT to yield the resultant compound, Mal-PL-sCT. Key findings Dynamic light scattering analyses suggested that Mal-PL-sCT and 2PEG-Mal-sCT exhibited robust helical structures with a high tendency to aggregate in water. Both compounds were more stable against intestinal degradation than sCT, although Mal-PL-sCT was less stable than 2PEG-Mal-sCT. However, 2PEG-Mal-sCT did not possess hypocalcaemic activity while Mal-PL-sCT retained the hypocalcaemic activity of sCT when it was subcutaneously injected in the rat model. Multiple functional groups may be conjugated to a peptide via a tri-block linker without the risk of obliterating the intrinsic bioactivity of the peptide. Conclusions The resultant novel PEG-lipid has a potential role to optimize protein and peptide delivery. [source] Optical Spectra of Copper-Doped Zn-Phosphate GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Adrian Goldstein Copper-containing, binary, Zn-phosphate glasses were melted under reductive conditions. The profile of their optical spectra and their color change drastically when the ZnO content of the host is modified. An increase in the host's ZnO concentration tilts the copper oxidation state's equilibria toward the reduced species Cu+ and Cu0. In hosts containing more than 52 mol% ZnO, the Cu0 aggregates precipitate upon melt cooling to form ruby glasses. The ruby color also appears in glasses including 50 mol% ZnO, after thermal treatments. The effect of ZnO increase, in the composition of binary Zn-phosphate glasses, on the redox equilibria of a copper dopant, is inverse to that caused by increase of Na2O content in the case of Na-phosphate hosts. [source] Improving Gene Delivery Efficiency of Bioreducible Poly(amidoamine)s via Grafting with Dendritic Poly(amidoamine)sMACROMOLECULAR BIOSCIENCE, Issue 4 2010Ya-Nan Xue Abstract Dendritic poly(amidoamine)s (PAMAM)s were introduced into the side chains of disulfide-containing poly(amidoamine)s via repetitive Michael addition and amidation. The bioreducible poly(amidoamine)s grafted with dendritic polyamidoamines showed high buffer capacity, low cytotoxicity and strong DNA binding ability at low N/P ratio. They were able to condense DNA into small sized polycation/DNA complexes, which degraded and released the incorporated DNA under reductive conditions. In comparison to the original disulfide-containing poly(amidoamine) with aminoethyl side chain, the grafting of the bioreducible poly(amidoamine) with dendrimer greatly improved the transfection efficiencies of 293T and HeLa cells with foreign DNA at various N/P ratios. The structure,gene delivery property relations of dendrimer-grafted polycations will provide valuable insight into the design of highly efficient and less toxic polycationic gene carriers. [source] Expression, purification, crystallization and preliminary crystallographic analysis of the PAB0955 gene productACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 2 2005Stéphanie Gras PAB0955 from Pyrococcus abyssi is a prototype of a new Walker-type ATPase/GTPase conserved in archaea and eukaryota but not found in bacteria. PAB0955 has been expressed, purified and crystallized, and it has been shown that this thermostable protein is dimeric in reductive conditions. Crystals have been obtained either without nucleotide or in the presence of GDP or GTP,S. Preliminary X-ray crystallographic data up to 2.08,Å resolution have been collected from these crystals. [source] Asymmetric Allylation of Methyl Ketones by Using Chiral Phenyl CarbinolsCHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2009Abstract To methyl or to alkyl? High induced facial selectivities and excellent yields are obtained in the allylation of aliphatic methyl ketones by using a structurally simple phenylbenzyl auxiliary to give the corresponding homoallylic ethers (see scheme). The transferred auxiliary has a very good protecting quality and can easily be removed. Novel chiral auxiliaries for the stereoselective allylation of aliphatic methyl ketones with allyltrimethylsilane and their use in the synthesis of homoallylic ethers are described. In a multicomponent domino process catalyzed by trifluoromethanesulfonic acid, the allyl moiety and the auxiliary are transferred onto the substrate to yield tertiary homoallylic ethers. The most useful auxiliary for a general application turned out to be the trimethylsilyl ether of phenyl benzyl carbinol with an induced diastereoselectivity of 90:10 using ethyl methyl ketone and 94:6 using isopropyl methyl ketone as substrates. The transferred substituted benzyl moiety has good protecting properties in subsequent transformations and can easily be removed under reductive conditions to provide the corresponding homoallylic alcohol. The origin of the high selectivity could be elucidated by identifying the relevant transition states using quantum-chemical calculations. An excellent agreement between calculated and experimentally observed selectivities was obtained assuming an oxocarbenium ion as intermediate. [source] | |||||||||||||