Autoxidation In Air Research Articles

Alkane Solvent-Derived Acylation Reaction Driven by Electric Fields.

Electric field acceleration of alkyl hydroperoxide activation to acylate amines in the scanning tunneling microscope-based break-junction is reported. Alkyl hydroperoxide mixtures, generated from hydrocarbon autoxidation in air, were found to be competent reagents for the functionalization of gold surfaces. Intermolecular coupling on the surface in the presence of amines was observed, yielding normal alkylamides. This novel mode of alkyl hydroperoxide activation to generate acylium equivalents was found to be responsive to the magnitude of the bias in the break junction, indicating an electric field influence on this novel reactivity.

Mechanistic Insights into Phenol Oxidation by a Copper(II) Complex of a Pyridine‐ and Amide‐Containing Copolymer in an Aqueous Medium

A CuII complex of a pyridine- and amide-containing copolymer (Cu-P1) exhibits effective activity toward phenol hydroxylation in 50 % aqueous methanol solution at apparent pH 8.0 and 25 °C. The complex shows significant first-order rate accelerations of 4.2 × 105 and 1.4 × 105 relative to phenol autoxidation in air and in the presence of 20 mM H2O2, respectively. The reaction mechanisms with H2O2 and air are different on the basis of (a) the different activity profiles for Cu binding, (b) the different deuterium kinetic isotope effects (2.8 in 20 mM H2O2 and 1.2 aerobically), and (c) the formation of a dinuclear substrate–(Cu-P1) complex with H2O2 but a mononuclear one aerobically. The mechanism in the presence of H2O2 is consistent with that of the type-3 dicopper tyrosinase. Although oxidized di-CuII tyrosinase can only use H2O2 for phenol hydroxylation, CuII-P1 can use either air or H2O2 for this process. The studies herein introduce a versatile chemical system for the further exploration of Cu–oxygen chemistry and other types of metal-centered chemistry and for the aerobic degradation of aromatic compounds in environmental and green chemistry.

Synthesis of 2-hydroxy-3-indolinones and 3-hydroxy-2-indolinones by anionic cyclization, in situ oxidation and rearrangement

Lithiation with butyllithium of 2-(benzylamino)benzamides (N-benzyl anthranilamides) occurs at the benzylic position to give an alpha-amino-organolithium that cyclizes to the 3-indolinone (indoxyl) ring (similar to a Parham cyclization). Autoxidation in air gives 2-hydroxy-3-indolinones. In the absence of a proton source, rearrangement of the aryl group from C-2 to C-3 occurs to give the 3-hydroxy-2-indolinone (oxindole) ring. (C) 2010 Elsevier Ltd. All rights reserved.

Copper(I) transfer into metallothionein mediated by glutathione

Rabbit liver metallothionein depleted of Cd(II) and Zn(II) was fully reconstituted using a Cu(I)-GSH complex under strictly anaerobic conditions. Anaerobic fluorescence titration, using an emission band at 625 nm which is diagnostic of the correct insertion of Cu(I) into the thiolate clusters of metallothionein, showed that the fluorescence maximum was obtained on addition of as many Cu(I) equivalents as the available Cu(I)-binding sites in the protein (i.e. 12). Binding was nearly complete within 1 min, and Cu(I)-GSH was much more efficient than Cu(I)-thiourea or Cu(I)-acetonitrile in metallothionein reconstitution. In air, full reconstitution was obtained with stoichiometric copper only when an excess of GSH was present in the reaction mixture. Cu(I)-GSH was also able to displace Zn(II) and Cd(II) from natural metallized thionein. It is concluded that: (a) Cu(I)-GSH is a potential physiological Cu(I) carrier, not only for Cu2+/Zn2+ superoxide dismutase [Ciriolo, Desideri, Paci and Rotilio (1990) J. Biol. Chem. 265, 11030-11034] but also for metallothionein; (b) in the case of metallothionein, physiological concentrations of GSH protect the protein from autoxidation in air and facilitate Cu(I)-thiolate exchange; (c) the natural metal composition of metallothionein may be related to metal bioavailability rather than to evolutionary changes in protein structure.

Zur Kenntnis des Faktors F430 aus methanogenen Bakterien: Über die Natur der Isolierungsartefakte von F430, ein Beitrag zur Chemie von F430 und zur konformationellen Stereochemie der Ligandperipherie von hydroporphinoiden Nickel(II)‐Komplexen

Factor F430 from Methanogenic Bacteria: On the Nature of the Isolation Artefacts of F430, a Contribution to the Chemistry of F430 and the Conformational Stereochemistry of the Ligand Periphery of Hydroporphinoid Nickel(II) ComplexesFactor F430 (1), a coenzyme from methanogenic bacteria, when heated in aqueous solution isomerizes to 12,13‐di‐epi‐F430 (5) via 13‐epi‐F430 (3). The equilibrium mixture of the three F430 isomers in aqueous phosphate buffer solution (pH 7, 100°) contains 88 % of 5, 8 % of 3, and 4 % of 1 (Scheme 1). The structural assignment for the F430 isomers rests on FAB‐MS‐, UV/VIS‐, 1H‐ and 13C‐NMR spectra of their pentamethyl esters. Chemical proof for the double epimerization at the two chiral centers of F430's ring C was provided by ozonolytic degradation of the di‐epimer to give a ring‐C‐derived succinimide derivative that was shown to be the enantiomer of the one previously obtained by ozonolysis of F430M (see Scheme 2). The two F430 ring‐C epimers 3 and 5 are the isolation artefacts described in the earlier F430 literature. F430 is susceptible to autoxidation in air and the product, that absorbs at 560 nm, was shown to be the 12,13‐didehydro derivative 8 of F430 by spectroscopic characterization of its pentamethyl ester 9. The dehydrogenation product 8 can be diastereoselectively reduced with Zn in AcOH to give natural F430 as the main product rather than the thermodynamically more stable F430‐di‐epimer (Scheme 3). In the double epimerization of F430, the two ring‐C side chains change from a trans‐quasi‐diaxial arrangement to the (locally) enantiomorphic position in which the same side chains are again in a trans‐quasi‐diaxial arrangement. This equilibrium paradox as well as the kinetic diastereoselectivity of the reduction of 12,13‐didehydro‐F430 (8) are rationalized to be consequences of the general phenomenon documented earlier (see the preceding paper) according to which hydroporphinoid Ni(II) complexes all show a characteristic conformational ruffling of their ligand system due to the tendency of the (small) Ni(II) ion to contract the size of the ligand's central coordination hole (see Fig. 5 and 6).

Calcium translocation by fatty acid derivatives in a two-phase partition model. Structure-activity relationships

The relationship between structures of fatty acid derivatives, long-chain fatty alcohols, phospholipids and their calcium-transporting activity was investigated using the two-phase model system in which 45Ca is transported from an aqueous to an immiscible organic phase. Calcium translocation by all saturated and unsaturated fatty acids was significant only at 10 mM concentrations, but minimal or negligible below 1 mM; the corresponding methyl esters and alcohols were inactive at 10 mM. Polyunsaturated fatty acid derivatives, prepared by incubation with lipoxygenase (linoleate: oxygen oxidoreductase; EC 1.13.11.12) or by autoxidation in air, showed a markedly increased potency over the parent compounds. The oxidation products of linoleic and arachidonic acids were most potent. For example, the equieffective concentrations were 10 mM for linoleic acid, 0.4 mM for its lipoxygenase metabolites and 0.094 mM for its autoxidation products. Similarly, for arachidonic acid and its derivatives, equieffective concentrations were 10, 0.104 and 0.112 mM, respectively. The potency of the autoxidized fatty acid derivatives varied with both duration of autoxidation and the specific structure. Methyloleate and oleyl alcohol remained inactive even after a prolonged oxidation, whereas methyllinoleate and linoleyl alcohol were very potent only after 4 weeks but not after 1 week autoxidation. The potency of esters and alcohols with three or more double bonds increased significantly even after a short-term autoxidation, reflecting the differences in both the rate of formation and the contribution to calcium-transporting properties of the primary and secondary oxidation products. All phospholipids tested, with the exception of phosphatidylcholine and lysophosphatidylcholine, showed considerable calcium-transporting activities at 0.01 mM or greater concentrations; some members were of similar or greater potencies than the classical calcium ionophores, X537A and A23187.

Electrocyclic reactions. Part VII. Irradiation of 3,5-dibromo-2,6-di-methylhepta-2,5-dien-4-one (αα′-dibromophorone)

Irradiation of 3,5-dibromo-2,6-dimethylhepta-2,5-dien-4-one in hexane under nitrogen at ca. 300 nm yields, as the major product, 2-bromo-5-isopropylidene-3-methylcyclopent-2-enone. The minor product is a symmetrical photodimer, (C9H10O)2, of tricyclo[5.3.0.02,6]decane type, produced by a [π2s+π2s] process; it is susceptible to autoxidation in air.

The autoxidation of ?10-dodecahydroacridine

The autoxidation of Δ10-dodecahydroacridine in heptane in an atmosphere of oxygen has given 12-hydroperoxy-Δ10-dodecahydroacridine, which has been reduced to 12-hydroxy-Δ10-dodecahydroacridine and has been converted into 5-azabicyclo[8,4, 0]tetradecane-6,11-dione. The two latter compounds were also isolated when Δ10-dodecahydro-acridine underwent autoxidation in air in the absence of a solvent.

Oxidation of unsaturated fatty acids by ozone and nitrogen dioxide. A common mechanism of action.

Trace quantities of ozone and nitrogen dioxide, 1.5 ppm, catalyzed the rapid oxidation of unsaturated fatty acids. Nitrogen dioxide-catalyzed oxidations were dependent upon the NO2 concentration in the atmosphere. Both thin films and aqueous emulsions of fatty acids are oxidized by NO2 through a mechanism akin to the spontaneous autoxidation in air. Phenolic antioxidants, including vitamin E, retarded the oxidation. Ozone catalyzed a more rapid and complete oxidation than NO2 by a direct attack upon the double bonds of the fatty acid. Phenolic antioxidants are protective only in aqueous emulsions where the oxidation proceeds by peroxidation as well. Oxidation of essential tissue polyunsaturated fatty acids by O3 and NO2 is a likely common mechanism of toxicity.

The effect of autoxidation on the wettability of a linoleic acid monolayer

The effect of autoxidation of a linoleic acid monolayer on the contact angle with water depended upon the conditions of oxidation and the type of surface upon which the monolayer was formed. For monolayers on a glass surface with which the carboxyl group did not react, autoxidation in air of 0.02% R.H. increased the contact angle with water from zero to 56°. However, on copper where reaction between the surface and the carboxyl group occurred, autoxidation under the same conditions decreased the contact angle from 86° to 76°. Autoxidation in air of 50% R.H. caused no change in the initial contact angle of zero with water when the monolayer was on glass. On copper, aging under these conditions caused the angle to increase from an initial value of 86° to 92°. Contact angles between methylene iodide and the monolayers were not greatly affected by autoxidation under any of the afore-mentioned conditions. Ultraviolet spectra and reductive polarography indicated that secondary oxidation of the initially formed 9- or 13-hydroperoxide of the conjugated octadecadienoic acid occurred to a much greater extent in the drier air. The hypothesis presented explains the wettability results in terms of the ability of the oxidation products to produce a solid, coherent monolayer structure, taking into account the location in the hydrocarbon chain of oxygen-containing functional groups introduced by autoxidation.

Isolation and autoxidation characteristics of ferrolegoglobin

Ferrolegoglobin can be reproducibly isolated from legume root nodules by extraction in 3 M ammonium sulfate solution at pH 9 in a nonoxidizing atmosphere. Hydrogen gas stabilizes ferrolegoglobin allowing more than 1 year's storage at temperatures below −10 °C. without conversion to ferrilegoglobin. The rate of autoxidation of ferrolegoglobin decreases with decreasing oxygen partial pressure, decreasing ionic strength, and decreasing temperature. It increases with decreasing pH. On the basis of ferrolegoglobin autoxidation and electrophoretic data, the heme group of native ferrolegoglobin is not located in an exposed position on the surface of the globin. The molecule undergoes irreversible rearrangement during autoxidation in air, subsequently resulting in exposure of the heme group.

Control of the Enzymic Action of Lipase

A SUBSTANCE has been isolated from the castor oil seed, which controls the reversible action of lipase. The reduced form of this substance, which seems to be the predominating one in seeds, acts as an activator of the hydrolysis of fat by the Ricinus lipase and as an inhibitor of the synthesis of fat from glycerol and oleic acid. The oxidised form, which is easily obtainable from the reduced form by autoxidation in air, acts as an activator for the synthesis and as an inhibitor for the hydrolysis. The intermediary form is indifferent for both synthetic and hydrolytic processes.