1,721,228 research outputs found
A novel and efficient synthesis of tocopheryl quinones by homogeneous and heterogeneous methyltrioxorhenium/hydrogen peroxide catalytic systems
No full textA convenient and efficient application of heterogeneous poly(4-vinylpyridine), poly(4-vinyl-pyridine N-oxide), and polystyrene/ methylrhenium trioxide systems for the selective oxidation of tocopherols and tocopherol derivatives to the corresponding ortho- and para-tocopherylquinones is described. Environment friendly, easily available, and low-cost hydrogen peroxide (H2O2) was used as the oxygen atom donor. The antiviral activity of the newly synthesized tocopherylquinones and their parent tocopherols against influenza A virus is also reported. On the basis of the biological assay, the activity of tocopherols against influenza virus is higher than that showed by the corresponding tocopherylquinones, thus suggesting, for the first time, a drawback effect of the oxidative metabolism on the antiviral activity of these compounds. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA
Role of clays in the prebiotic synthesis of sugar derivatives from formamide
No full textWe describe here the role of montmorillonite KSF in the prebiotic synthesis of amino sugar derivatives starting from a mixture of formamide and formaldehyde as simple chemical precursors. Since amino sugars are key intermediates in the synthesis of complex nucleic acid derivatives, this procedure opens a novel pathway for the formation of nucleosides under plausible primordial conditions. © 2010 Taylor & Francis
Ultrasound-assisted functionalization of polyphenols #32
No full textNatural polyphenols are a class of compounds that are available in quantities from renewable resources. Natural polyphenols, among them especially lignins and tannins, thus represent important precursors for a variety of valorizations, ranging from the production of biofuel via the use as source for bulk aromatic chemicals to applications in material science areas. Ultrasonication has been used both for isolating and for subsequently valorizing natural polyphenols. This chapter introduces important structural characteristics of lignins and tannins in order to set the background for a series of applications of ultrasound in connection with polyphenols; these applications comprise isolation methods as well as valorization approaches
Dye Degradation by Layer-by-Layer Immobilised Peroxidase/Redox Mediator Systems
No full textHorseradish peroxidase (HRP) was immobilised on Eupergit C250L resin coated with poly-electrolytes, or by entrapment inside pre-formed layer-by-layer (LbL) micro-capsules of poly-electrolytes. In these systems, namely HRP/E-LbL, HRPm/LbL and HRPm/LbLp, the native enzyme retained its catalytic activity. Immobilised HRP showed a significant activity in the oxidation of selected azo, quinoline and fluorone dyes with H2O2 as the primary oxidant under mild experimental conditions, and HRPm/LbL was the best catalyst. A comparison between the catalytic efficiency of different redox mediators for HRP activity was made by using 1-hydroxybenzotriazole (HOBt), violuric acid (VLA) and veratrylic alcohol (VA). As a general trend, azo dyes were degraded in higher yields, and HOBt was the best mediator for the oxidation. The degradation yield increased on increasing the reaction time and reached the highest value after 12h, which is comparable with that observed for native HRP. Notably, HRPm/LbL retained its catalytic activity for more runs. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Coordination Complexes and One-Step Assembly of Lignin for Versatile Nanocapsule Engineering
No full textNanoencapsulation of active substances with controlled release in harmless matrices has been the subject of numerous scientific efforts mainly due to the significant biomedical potential of such endeavors. Lignin, the environmentally sustainable byproduct of the pulp and paper industry, contains a multitude of phenolic hydroxyl groups, some of which, are known to readily and strongly chelate with iron ions. In this effort we demonstrated that the concerted use of chelation chemistry, oil in water emulsion principles, and low energy sonication, offers a facile, one-pot strategy to assemble lignin nanocapsules (LNCs) of a controlled architecture. Under these conditions capsules are shown to rapidly assemble utilizing two driving forces, the π-stacking propensity of lignin and its metal chelating ability at alkaline pH. Detailed size exclusion chromatographic evidence validates that the formation of capsules is driven mainly by the enumerated physical interactions with no significant chemical modification of the lignin. The developed process was systematically optimized so as to create the foundations for the morphology and the yield of the capsules being modulated as a function of sonication time, power, and surface contact area. Both pure LNCs and Fe-LNCs were synthesized in high yields with size distributions varying from 0.3 to 6 μm and their release efficiencies were evaluated in detail. As anticipated, the complexation effects of the phenolic OH groups offered to the Fe-LNCs, increased stability, reduced shell thickness (allowing for greater loading efficiencies), and lower release kinetics, compared to LNCs
Origin of informational polymers: The concurrent roles of formamide and phosphates
No full textFormamide chemistry provides a unitary system by gathering all of the precursors needed to synthesise pregenetic informational polymers in a single milieu. This is not observed with HCN chemistry. With common catalysts, formamide affords all of the precursor nucleobases, photochemically condenses into acyclonucleosides, favours transphosphorylation and enhances micellar aggregation of surfactants. Also, formamide provides a set of physicochemical conditions that thermodynamically favour the polymeric state of nucleotides over the monomers. In the origin-of-informational-polymers scenario, formamide acts in every step, the least characterised being the set of its reactions with phosphates. On this matter, we report two complementary sets of results: 1) the synthesis of prebiotic precursors from formamide, which are catalysed by soluble and mineral phosphates - we observed the formation of rich mixtures that include uracil, 9H-purine, cytosine, dihydrouracil, hypoxanthine, adenosine, urea, parabanic acid, the amino acid H-formylglycine and the peptide-condensing agent carbodiimide; and 2) the protection of ribo-and deoxyribophosphoester bonds by phosphates. The relevance of these effects with respect to the origin of informational polymers is discussed. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA
A novel and efficient catalytic epoxidation of olefins with adducts derived from methyltrioxorhenium and chiral aliphatic amines
No full textNitrogen-based adducts derived from methyltrioxorhenium(VII) and chiral aliphatic amines have been synthesized and applied to the efficient catalytic epoxidation of olefins with urea hydrogen peroxide complex as the primary oxidant. These complexes retain their catalytic activity when microencapsulated in polystyrene. A moderate steroinduction was obtained in the epoxidation of prochiral olefins with complexes between methyltrioxorhenium and chiral trans-1,2-cyclohexyldiamine. The values of steroinduction were found to increase after the microencapsulation process. © 2008 Elsevier Inc. All rights reserved
A novel and efficient synthesis of highly oxidized lignans by a methyltrioxorhenium/hydrogen peroxide catalytic system. Studies on their apoptogenic and antioxidant activity
No full textHighly oxidized lignans produced during the cytochrome P-450 metabolism in the cells show biological activities significantly different from those of their parent natural compounds. Lignans precursors of mammalian enterolignans were treated with a methyltrioxorhenium/hydrogen peroxide catalytic system to afford new compounds oxidized at benzylic as well as in arylic positions. The evaluation of the antioxidant and apoptogenic activity by in vivo protocols of these compounds showed some interesting structure-activity relationships related to the oxidation degree of the molecules. © 2009 Elsevier Ltd. All rights reserved
Advances in the prebiotic synthesis of nucleic acids bases: Implications for the origin of life
No full textPrebiotic chemistry plays a central role in the investigation of the possible scenarios of the early chemical environments. Its goal is to shed light on the events involved in the synthesis of initial biomolecules and on the self-organization processes that led the last common ancestor. Even though a well defined scenario for the physico-chemical conditions on the primitive Earth is not available, one can assume that a synthetic pathway, in order to be considered prebiotic, should use the simplest chemicals and the most common conditions present at that time. Low molecular weight molecules such as hydrogen cyanide and formaldehyde, easily formed from the primitive atmosphere by ultraviolet light, heat or electric discharge as energy sources, have been considered as prebiotic precursors. Here we focus on the attempts to identify the prebiotic events originating purine and pirimidine nucleic acids bases, the necessary components for the assembling of nucleosides, nucleotides and oligonucleotides. © 2004 Bentham Science Publishers Ltd
Identification and quantification of radical species by31P NMR-based spin trapping - A case study: NH4OH/H2O2-based hair bleaching
No full textThe31P NMR-spectroscopy-based spin trap technique involving 5-diisopropoxy-phosphoryl-5-methyl-1-pyrroline-N-oxide (DIPPMPO) was used to achieve quantitative analyses of the radical species that are generated in different bleaching solutions. These solutions comprised a mixture of an ammonium salt and hydrogen peroxide. This spin trap-based approach was also applied, with modifications, to the study of bleaching systems of human hair. The obtained results clearly revealed the subtle differences in both the nature and the amounts of the radical species generated in different bleaching solutions, and when allowed to react on hair samples. Generally, the main species involved in the oxidation processes were superoxide and amino radicals. Their amounts, however, showed a significant variation upon the kind of bleaching system and nature of the hair, i.e., virgin or dyed hair
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