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Aqueous choline acetate as reaction medium for the oxidation of kraft lignin with hydrogen peroxide
No full textRecently, choline-based ionic liquids (ILs), a class of biocompatible ILs, have been successfully employed in the pretreatment of lignocellulosic biomass. Nevertheless, their potential as solvents alternative to the more popular yet unfriendly imidazolium ILs in the oxidative depolymerization of lignin appears only marginally explored. In this study, aqueous cholinium acetate, [Ch][AcO], a readily available IL, was used as the reaction solvent for the oxidative depolymerization of Kraft lignin (KL) with H2O2/MoO3. Experimental optimization design was helpful to estimate optimal reaction parameters. Under reasonably mild conditions (H2O2 to KL weight ratio 0.33, 9.2% MoO3, 8% NaOH, 77 °C, 5 h), KL could be converted to 37% of depolymerization oil (KL_Oil), containing nearly 2.5% of aromatic monomers (ArMo), of which vanillin is the most abundant (up to 67%, yield 1.64%), and to 55% of oxidized lignin (OKL) solid fraction. When increasing H2O2/KL up to 1, ArMo yield decreased in favor of aliphatic acids (mainly, malonic acid), originating from ArMo over-oxidation, while OKL fraction enriched with carbonyl functional groups. Interestingly, in the absence of [Ch][AcO], lower ArMo yields (ArMo 1.68%) were observed, with vanillin selectivity dropping to 36% (yield 0.60%), hinting a possible stabilizing effect of the IL on reactive depolymerization intermediates and products. [Ch][AcO] could be regenerated, with <3% mass loss and unaltered chemical structure, and recycled without significant changes in product yields
Continued Progress Towards Efficient Functionalization of Natural and Non Natural Targets Under Mild Conditions. Oxygenation via C-H Bond Activation with Dioxiranes
No full textThe successful isolation and characterization of a dioxirane species in the 1988 opened up a one of the most attractive methods for the efficient oxidation of simple and/or structurally complex molecules. Dioxiranes today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. These are quickly and remarkably recognized as efficient oxygen transfer agents, especially for epoxidations and for a wide range of O-insertion into C-H bonds. Dioxiranes also appear as highly selective (chemo-, regio- and stereo-) oxidants, despite their reactivity under mild and strictly neutral conditions controlled by a combination of steric and electronic factors and possess catalytic activity. In this review, we discuss some of the most recent and significant developments in the selective homogeneous and heterogeneous oxyfunctionalization of non-activated C-H bonds in hydrocarbons of natural and non-natural targets using isolated dioxiranes or more generally, using the ketones (i.e., the dioxirane precursors) as organocatalysts
“Selective Oxidation of Natural Target Molecules using Methyl(trifluoromethyl)dioxirane”
No full text“Amides and dioxiranes: intriguing reactive partners. Experimental and theoretical investigations”.
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Identification of unique cardiolipin and monolysocardiolipin species in Acinetobacter baumannii
Full text linkAcidic glycerophospholipids play an important role in determining the resistance of Gram-negative bacteria to stress conditions and antibiotics. Acinetobacter baumannii, an opportunistic human pathogen which is responsible for an increasing number of nosocomial infections, exhibits broad antibiotic resistances. Here lipids of A. baumannii have been analyzed by combined MALDI-TOF/MS and TLC analyses; in addition GC-MS analyses of fatty acid methyl esters released by methanolysis of membrane phospholipids have been performed. The main glycerophospholipids are phosphatidylethanolamine, phosphatidylglycerol, acyl-phosphatidylglycerol and cardiolipin together with monolysocardiolipin, a lysophospholipid only rarely detected in bacterial membranes. The major acyl chains in the phospholipids are C16:0 and C18:1, plus minor amounts of short chain fatty acids. The structures of the cardiolipin and monolysocardiolipin have been elucidated by post source decay mass spectrometry analysis. A large variety of cardiolipin and monolysocardiolipin species were found in A. baumannii. Similar lysocardiolipin levels were found in the two clinical strains A. baumannii ATCC19606(T) and AYE whereas in the nonpathogenic strain Acinetobacter baylyi ADP1 lysocardiolipin levels were highly reduced
Does hydrogen bonding contribute to lipoperoxidation-dependent membrane fluidity variation? An EPR-spin labeling study
No full textThis study is aimed at making clear the relationship between oxidative stress of the phospholipid bilayer and membrane fluidity. Di-(hydroperoxylinoleoyl)-phosphatidylcholine (diHpLPC) was used as a highly hydroperoxidized and unsaturated phospholipid species in order to investigate the issue. Hydrophylic Interaction Liquid Chromatography-ElectroSpray Ionization-Mass Spectrometry (HILIC-ESI-MS) and NMR spectroscopy were employed to define the structure of the peroxidized phospholipid as 1-(9-hydroperoxy-10c,12t)octadecadienoyl-2-(9t,11c-13-hydroperoxy)octadecadienoyl-sn-glycero-3-phosphorylcholine. This phospholipid's ability to form vesicular structures was confirmed by Sepharose 4B gel filtration and Dynamic Light Scattering (DLS) of its aqueous suspensions. Fatty acid misalignment and fluidity gradient were studied in the bilayer of both supported planar bilayers (SPB) and multilamellar vesicles (MLV) made of different DLPC/diHpLPC mixtures by means of spin labelling-EPR spectroscopy of either n-DSPC or 3-doxylcholestane spin labels embedded in the membranes. It was found that diHpLPC increases both fatty acid misalignment and rigidification with increasing molar ratio in spite of increasing unsaturation of the fatty acid core. Basing on our observations, the observed ability of pure diHpLPC to form rigid and disordered SPB and MLV bilayers is proposed to be dependent on the cross bridging of oxidized linoleoyl chains by mutual hydrogen bonding of hydroperoxyl groups. However, the contribution to the observed overall rigidification of the model membranes by trans double bonds in the peroxidized chains should not be neglected, as a second membrane fluidity effector also arising from lipid peroxidation
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