Autoxidation Research Articles

A preliminary assessment of singlet oxygen scavenging, cytotoxic and genotoxic properties of Geranium macrorrhizum extracts.

Strong radical-scavenging activity of Geranium macrorrhizum extracts isolated by using various solvent systems has been reported previously. This study aimed at expanding the knowledge on the bioactivities of antioxidatively active G. macrorrhizum butanol fraction, which was isolated from ethanolic extract (EB), and water fraction, which was isolated from water extract (WW) by measuring their singlet oxygen scavenging properties, as well as preliminary assessment of cytotoxicity and genotoxicity toward mammalian cells. The cytotoxicity (necrosis induction) of the extracts in bovine leukemia virus-transformed lamb kidney fibroblasts (line FLK) was partly prevented by antioxidants and stimulated by the prooxidant BCNU (N,N'-bis(2-chloroethyl)-N-nitrosourea). This indicates that the cytotoxicity of G. macrorrhizum extracts is at least partly attributed to their prooxidant action, presumably due to the formation of quinoidal products of their (auto)oxidation. The latter was evidenced by the nature of the peroxidase-catalyzed oxidation products, which supported DT-diaphorase-catalyzed oxidation of NADPH and participated in conjugation reactions with reduced glutathione. The genotoxic properties were studied using chromosome aberration (CA) and sister chromatid exchange (SCE) tests in human lymphocytes in vitro and Drosophila melanogaster somatic mutation and recombination test (SMART) in vivo. In the CA test, only the highest doses of both fractions significantly increased chromosome aberration frequency. In the SCE test, both fractions induced SCEs in a clear dose-dependent manner. G. macrorrhizum extracts were not genotoxic in the SMART test in vivo. Our data indicate that in spite of the possible beneficial (antioxidant) effects of Geranium extracts, the possibilities of their use as ingredients of functional foods and/or food supplements should be further examined due to their cyto- and genotoxic effects resulting mainly from the action of quercetin-derived components abundant in the extracts.

New example of Ramberg-Böcklund reaction initiated by Michael addition

Only isolated cases were reported [1–4] on the synthesis of functionalized olefins from α-haloalkyl vinyl sulfones through Ramberg–Bo..cklund reaction initiated by Michael addition. The limitations of this reaction evidently depend both on the structure of the initial substrate and on the nature of the used reagent. For instance, it was established in [5] that the treatment with potassium tert-butylate, a strong base but a weak nucleophile, of α-haloalkyl vinyl sulfones containing an allyl hydrogen atom promoted the so-called vinylogic Ramberg–Bo..cklund reaction leading to the formation of conjugated dienes. For instance, by this procedure nona-1,3diene was obtained in 72% yield proceeding from 1-(bromomethylsulfonyl)oct-1-ene. We showed in [6] that the treatment with the typical Michael reagents, enolates of CH-acids, of bromomethyl β-styryl sulfone led to the cyclization initiated by Michael addition giving tetrahydrothiophene S,S-dioxide derivative. We report here that at treating 1-(bromomethylsulfonyl)cyclohex-1-ene (I) with sodium dimethyl malonate (20°C, 17 h) from the three mentioned possible reaction routes proceeds the one consisting in the Ramberg–Bocklund reaction initiated by Michael addition: The functionalized derivative of methylenecyclohexane II is obtained. Unsaturated sulfone I was obtained in a two-stage process involving the addition of BrCH2SO2Br to cyclohexene (CH2Cl2, 10°C, 24 h, no special initiation was required) and the dehydrobromination of the adduct in a water-dioxane solution of Na2CO3 at heating (50°C, 30 h). SO2CH2Br

Recent Mechanistic Insights in the Singlet Oxygen Ene Reaction

Singlet oxygen reacts with alkenes, which bear allylic hydrogens,in an ene fashion to afford allylic hydroperoxides. This reaction,apart from its synthetic usefulness, has received extensive mechanisticattention. Numerous experimental studies (e.g., trapping of intermediates,deuterium kinetic isotope effects, regio- or stereoselectivity studiesetc.) and to a lesser extend computational work, support a stepwisemechanism with the formation of a three-membered ring (perepoxide-like)intermediate. This Account mainly highlights our group’searlier and recent experimental efforts to ascertain facts relatingto this concept. 1 Introduction 2 Theoretical Calculations 3 Kinetic Isotope Effects 4 Regioselectivity 4.1 ‘ CIS Effect’ Selectivity 4.2 ANTI ‘ CIS Effect’ Selectivity 4.3 The Large Group Nonbonding Effect 4.4 GEMINAL Selectivity with Respectto Allylic or Vinyl Substituent 4.5 Electron-Withdrawing Group at the α- and β-Position 4.6 Regioselective Self-Sensitized Oxygenation of Fullerene Derivatives 4.7 Solvent and Electronic Effects 4.7.1 Site Selectivity in the ¹ O 2 EneReaction of α,β-Unsaturated Esters and Acids 4.7.2 Site Selectivity in the ¹ O 2 EneReaction of Allylic Alcohols 4.7.3 SYN Selectivity of β,β-Dimethylstyrene 4.7.4 Site Selectivity of Isobutenylarenes 4.7.5 ‘Push-Pull’ Electronic Effect 5 Studies on Diastereoselectivity 5.1 Diastereoselectivity in Self-Sensitized Oxygenation of a FullereneDerivative 5.2 Diastereoselectivity in the ¹ O 2 EneReaction of Chiral Functionalized Alkenes 6 Stereochemistry 7 Hypersensitive Probes in the ¹ O 2 EneReaction 8 The ¹ O 2 Ene Reaction in ConfinedMedia 9 Concluding Remarks

Synthesis of 2,5-Disubstituted Pyrrolidines from N-Alkenyl and Alkynyl N-Benzoyloxysulfonamides Catalyzed by (CuOTf)2

A new synthetic method of 2,5-disubstituted pyrrolidines is developed by the cyclization of unsaturated N-benzoyl-oxysulfonamides by (CuOTf) 2 -C 6 M in refluxing dichloroethane. Various N-4- and N-5-alkenyl and alkynyl N-benzoyloxysulfonamides are cyclized to give pyrrolidines. The cyclization proceeds via addition of sulfonamidoyl radicals to intramolecular unsaturated bonds or allylic hydrogen abstraction with the radical intermediates.

A Change of Detergency of Fatty Soils Adhered to Clothes Owing to Autoxidation

A Change of Detergency of Fatty Soils Adhered to Clothes Owing to Autoxidation

Dinuclear Allylpalladium Complexes ofC2-Symmetric Pyrazolate-Bridged Bis(oxazoline) Ligands (pyrbox's): Structures, Dynamic Behavior, and Application in Asymmetric Allylic Alkylation

A series of new chiral binucleating pyrazolate-based N-donor ligands (3a−d) with oxazoline side arms (coined pyrbox's) have been synthesized. Bimetallic methallylpalladium complexes (4a−d) of these ligands were obtained, and the solid-state structures of complexes 4a,c were characterized by X-ray diffraction. NMR spectroscopy revealed that in solution 4a−d exist as three different isomers that differ in the orientation of the two methallyl ligands. Exchange between the isomers (i.e., allyl rotation) was observed in two-dimensional NOESY NMR experiments as syn/syn and anti/anti interconversion of the allylic hydrogen atoms; kinetic parameters for the fluxional behavior have been determined. The catalytic activity of the complexes was tested in palladium-catalyzed allylic alkylation of rac-(E)-1,3-diphenylallyl acetate. By comparison of the set of complexes 4a−d that feature different ligand scaffolds, both steric and electronic factors were found to be important for enantiocontrol, and a model has been pro...

Asymmetric addition of trimethylsilylcyanide to N-benzylimines catalyzed by recyclable chiral dimeric V(V) salen complex

Chiral dimeric vanadium (V) salen complex (10 mol%) derived from 5,5-Methylene di-[( S,S)-{ N-(3- tert-butyl salicylidine)- N′-(3′,5′-di- tert-butyl salicylidene)]-1,2-cyclohexanediamine] with vanadyl suphate followed by auto oxidation was used as efficient catalyst for enantioselective Strecker reaction of N-benzylimines with TMSCN at −30 °C. Excellent yield (92%) of α-aminonitrile and high chiral induction was achieved (ee up to 94%) in case of 2-methoxy substituted N-benzylimines in 10 h. The catalytic system worked well up to four cycles with retention of enantioselectivity.

The Ti-MWW catalyst - its characteristic and catalytic properties in the epoxidation of allyl alcohol by hydrogen peroxide

The Ti-MWW catalyst - its characteristic and catalytic properties in the epoxidation of allyl alcohol by hydrogen peroxide Ti-MWW, one of the latest titanium-silicalite catalysts, has been prepared by direct hydrothermal synthesis using hexamethyleneimine as a structure-directing agent. The characteristic of the catalyst was performed by means of the following methods: XRD, SEM, IR, UV-vis and X'Ray microanalysis. The catalytic properties of Ti-MWW have been compared with those of the conventional titanium-silicalites TS-1 and TS-2 in the epoxidation of allyl alcohol with hydrogen peroxide. The process has been described by the following main functions: the selectivity of the transformation to glycidol in relation to allyl alcohol consumed, the conversions of the substrates (allyl alcohol and hydrogen peroxide) and the selectivity of the transformation to organic compounds in relation to hydrogen peroxide consumed.

Stability of biodiesel and its blends: A review

Biodiesel consists of long chain fatty acid esters derived from feed stocks such as vegetable oils, animal fats and used frying oil, etc. which may contain more or less unsaturated fatty acids which are prone to oxidation accelerated by exposure to air during storage and at high temperature may yield polymerized compounds. Auto oxidation of biodiesel can cause degradation of fuel quality by affecting the stability parameters. Biodiesel stability includes oxidation, storage and thermal stability. Oxidation instability can led to the formation of oxidation products like aldehydes, alcohols, shorter chain carboxylic acids, insolubles, gum and sediment in the biodiesel. Thermal instability is concerned with the increased rate of oxidation at higher temperature which in turn, increases the weight of oil and fat due to the formation of insolubles. Storage stability is the ability of liquid fuel to resist change in its physical and chemical characteristics brought about by its interaction with its environment and may be affected by interaction with contaminants, light, factors causing sediment formation, changes in color and other changes that reduce the clarity of the fuel. These fuel instabilities give rise to formation of undesirable substances in biodiesel and its blends beyond acceptable quantities as per specifications and when such fuel is used in engine, it impairs the engine performance due to fuel filter plugging, injector fouling, deposit formation in engine combustion chamber and various components of the fuel system. The present review attempts to cover the different types of fuel stabilities, mechanism of occurrence and correlations/equations developed to investigate the impact of various stability parameters on the stability of the fuel. A review of the use of different types of natural and synthetic antioxidants has also been presented which indicates that natural antioxidants, being very sensitive to biodiesel production techniques and the distillation processes have varying impacts on fuel stability and available literature is very much scarce. The work on the use of synthetic antioxidants on the stability of biodiesel (both distilled and undistilled) from various resources has indicated that out of various 8 synthetic antioxidants studied so far only 3 antioxidants have been found to increase the fuel stability significantly. However, effectiveness of these antioxidants is in the order of TBHQ > PY > PG.

Kinetic Study of the Prooxidant Effect of α‐Tocopherol. Hydrogen Abstraction from Lipids by α‐Tocopheroxyl Radical

A kinetic study of the prooxidant effect of alpha-tocopherol was performed. The rates of allylic hydrogen abstraction from various unsaturated fatty acid esters (ethyl stearate 1, ethyl oleate 2, ethyl linoleate 3, ethyl linolenate 4, and ethyl arachidonate 5) by alpha-tocopheroxyl radical in toluene were determined, using a double-mixing stopped-flow spectrophotometer. The second-order rate constants (k (p)) obtained are <1 x 10(-2) M(-1 )s(-1) for 1, 1.90 x 10(-2) M(-1 )s(-1) for 2, 8.33 x 10(-2 )M(-1 )s(-1) for 3, 1.92 x 10(-1) M(-1 )s(-1) for 4, and 2.43 x 10(-1 )M(-1 )s(-1) for 5 at 25.0 degrees C. Fatty acid esters 3, 4, and 5 contain two, four, and six -CH(2)- hydrogen atoms activated by two pi-electron systems (-C=C-CH(2)-C=C-). On the other hand, fatty acid ester 2 has four -CH(2)- hydrogen atoms activated by a single pi-electron system (-CH(2)-C=C-CH(2)-). Thus, the rate constants, k (abstr)/H, given on an available hydrogen basis are k (p)/4 = 4.75 x 10(-3 )M(-1 )s(-1) for 2, k (p)/2 = 4.16 x 10(-2) M(-1 )s(-1) for 3, k (p)/4 = 4.79 x 10(-2 )M(-1 )s(-1) for 4, and k (p)/6 = 4.05 x 10(-2 )M(-1 )s(-1) for 5. The k (abstr)/H values obtained for 3, 4, and 5 are similar to each other, and are by about one order of magnitude higher than that for 2. From these results, it is suggested that the prooxidant effect of alpha-tocopherol in edible oils, fats, and low-density lipoproteins may be induced by the above hydrogen abstraction reaction.

The use of antioxidants in vegetable oils – A review

The shelf life of vegetable oils in food uses and their applicability in industrial situations is greatly dependent on their oxidative stabilities. Methods of improving oxidative stability values currently available include genetic modifications, compositional changes via chemical means, as well as the inhibition of oxidation by means of substances known as antioxidants. This paper reviews the properties of vegetable oils which predispose them to auto oxidation reactions, explores the nature and mechanisms of the operation of antioxidants in brief, and finally summarizes current research efforts geared towards identifying and evaluating the effectiveness and commercial promise of less toxic new antioxidants derived as natural extracts from various plant species.

The use of antioxidants in vegetable oils – A review

The shelf life of vegetable oils in food uses and their applicability in industrial situations is greatly dependent on their oxidative stabilities. Methods of improving oxidative stability values currently available include genetic modifications, compositional changes via chemical means, as well as the inhibition of oxidation by means of substances known as antioxidants. This paper reviews the properties of vegetable oils which predispose them to auto oxidation reactions, explores the nature and mechanisms of the operation of antioxidants in brief, and finally summarizes current research efforts geared towards identifying and evaluating the effectiveness and commercial promise of less toxic new antioxidants derived as natural extracts from various plant species.

Organic base catalyzed carbonyl allylation of methyl trifluoropyruvate with activated alkenes

The carbonyl allylation of methyl trifluoropyruvate (MeTFP) with activated alkenes has been investigated in detail using organic bases as catalysts. Organic bases, such as DMAP, Et 3N, DABCO, NMM, Et 2NH, and quinine, could deprotonate the allylic hydrogen of activated alkenes and furnish nucleophilic species to undergo the addition reaction with methyl trifluoropyruvate and afford versatile homoallylic alcohols with CF 3 group in excellent yields. The 19F NMR monitoring indicated that the isomerization induced by base gave two separable diastereoisomers in an equilibrium ratio of 1:3. The relative configuration of hydroxy and the neighboring alkyl group in the major diastereoisomer was determined as syn-configuration by X-ray diffraction analysis.

Theoretical Insights into Enantioselective Catalysis: The Mechanism of the Kharasch–Sosnovsky Reaction

The mechanism of the Kharasch-Sosnovsky reaction has been investigated using B3 LYP/6-31G* calculations on a chiral reaction model [cyclohexene+tert-butyl perbenzoate-->cyclohex-2-enyl benzoate+tert-butyl alcohol, catalyzed by a chiral bisoxazoline-copper(I) complex]. Although two previous reaction mechanisms have been considered, the results are consistent with a new mechanistic pathway. This path involves ligand exchange between the catalyst-cyclohexene complex with tert-butyl perbenzoate to give a catalyst-perester complex, which undergoes an (either one- or two-step) oxidative addition reaction to yield a copper(III) complex. The limiting step of the Kharasch-Sosnovsky reaction consists of an intramolecular step involving the abstraction of an allylic hydrogen from cyclohexene [which is pi-bound to the copper(III) complex]. The resulting allyl-copper(III) complex (subsequent to the loss of tert-butanol) can undergo a haptotropic rearrangement by means of an eta1-allyl/eta3-allyl equilibrium, leading to scrambling between vinylic and allylic positions when an isotopically labeled substrate is used. The allyl-copper(III) ion undergoes a stereospecific reductive elimination involving the pi-bond migration to yield a reaction product-catalyst complex, which can regenerate the alkene-copper(I) complex by ligand exchange. The proposed reaction mechanism is consistent with all known experimental results (including enantioselectivity data).

Elucidation of the Double-Bond Position of Long-Chain Unsaturated Fatty Acids by Multiple-Stage Linear Ion-Trap Mass Spectrometry with Electrospray Ionization

Linear ion-trap (LIT) MS2 mass spectrometric approach toward locating the position of double bond(s) of unsaturated long-chain fatty acids and toward discerning among isomeric unsaturated fatty acids as dilithiated adduct ([M-H+2Li]+) ions are described in this report. Upon resonance excitation in a LIT instrument, charge-remote fragmentation that involves beta-cleavage with gamma-H shift (McLafferty rearrangement) is the predominant fragmentation pathway seen for the [M-H+2Li]+ ions of monoenoic long-chain fatty acids. The fragmentation process results in a dilithiated product ion of terminally unsaturated fatty acid, which undergoes consecutive McLafferty rearrangement to eliminate a propylene residue, and gives rise to another dilithiated adduct ion of terminally unsaturated fatty acid. In addition to the above-cited fragmentation process, the [M-H+2Li]+ ions of homoconjugated dienoic long-chain fatty acids also undergo alpha-cleavage(s) with shift of the allylic hydrogen situated between the homoconjugated double bonds to the unsaturated site. These fragmentation pathways lead to two types of CC bond cleavages that are allylic (alpha-cleavage) or vinylic, respectively, to the proximal CC double bond, resulting in two distinct sets of ion series, in which each ion series is separated by a CH2CHCH (40 Da) residue. These latter fragmentations are the predominant processes seen for the polyunsaturated long-chain fatty acids. The spectrum feature dependent on the position of unsaturated double bond(s) affords unambiguous assignment of the position of double bond(s) of long-chain unsaturated fatty acids.

EVALUATION OF ANTIOXIDANT ACTIVITY OF SOME SPICES AND THEIR APPLICATION IN CROISSANT AND FILLING CREAM

Natural antioxidants have gained considerable interest in recent years for their role in preventing the auto oxidation of fats, oils and fat containing food products. In this study, six spices containing natural antioxidants were evaluated for their re-tarding fat oxidation compared to butylated hy-droxyl toluene (BHT). The yield obtained from water extract of the tested spices ranged between 20% and 50 %. Carob gave the highest yield fol-lowed by anise and cinnamon, then caraway and fennel, while ginger gave the lowest yield .The free radical scavenging activities measured by 2-diphenyl-1-picryl-hydrazyl (DPPH) were 88.08%, 81.69%, 79.62% , 78.93% , 73.06% , and 71.50 % for cinnamon, anise, carob, caraway ginger, and fennel, respectively at concentration of 2250 μg/ml. Cinnamon showed higher antioxidant ac-tivity on linoleic acid oxidation than BHT fol-lowed by anise, carob and ginger. While, fennel and caraway recorded closely antioxidant activity to that of BHT at low concentration of 100 μg/ml. Total phenolic content of the tested spices varied ranging from 11.19 to 22.95 mg as gallic acid / gm dry extract in carob and caraway, respectively. Depending upon the sensory evaluation of crois-sant containing different levels of tested spices, a concentration of 1.5% of anise, caraway fennel and cinnamon was chosen, while the chosen con-centration of ginger was 2.5% and carob was 1% for testing their effectiveness against oxidation of lipid in croissant. However, a concentration of 2% of anise, fennel, ginger and carob was chosen while, the chosen concentration of caraway and cinnamon was 1% for testing their effectiveness against oxidation of lipid in filling cream. Addi-tion of tested spices gave an excellent antioxidant effect on croissant and filling cream compared with the effect of BHT. The increase in both per-oxide and acid values after 14 and 28 days respec-tively were lower than of control and BHT. Carob, ginger, caraway and cinnamon were more effec-tive in controlling lipid oxidation during storage. In conclusion addition of tested spices as sources of effective natural antioxidants retarded lipid oxi-dation and maintain the quality of croissant and filling cream during storage.

Comments on the paper “Low-bromide containing MC catalyst for the autoxidation of para-xylene” by B. Saha and J.H. Espenson [J. Mol. Catal. A 271 (2007) 1–5

Comments on the paper “Low-bromide containing MC catalyst for the autoxidation of para-xylene” by B. Saha and J.H. Espenson [J. Mol. Catal. A 271 (2007) 1–5

Epoxidation of allyl alcohol with hydrogen peroxide over titanium silicalite TS‐2 catalyst

AbstractThe influence of the technological parameters on the course of the epoxidation of allyl alcohol with 30% H2O2 in the presence of titanium silicalite TS‐2 catalyst and methanol as a solvent was studied. The process was performed in an autoclave at the autogenic pressure. The influence of temperature in the range 20–120 °C, molar ratio of allyl alcohol/H2O2 (1:1–10:1), methanol concentration in the reaction mixture (10–80% w/w), catalyst TS‐2 concentration (0.1–2.0% w/w) and reaction time (1–8 h) were investigated. The functions describing the process were: selectivity of transformation to glycidocidol in relation to allyl alcohol consumed, selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed, conversions of allyl alcohol and hydrogen peroxide. Copyright © 2007 Society of Chemical Industry

Copolymerization ofsec‐butenyl acetate with styrene via emulsion polymerization

AbstractThe incorporation of allylic monomers into highly reactive vinyl polymerizations provides a means to control molecular weight, conversion, and Trommsdorff effect to produce copolymers with desirable performance characteristics. The copolymerization behavior of styrene withsec‐butenyl acetate, whose copolymerization properties have not been reported, is investigated. Copolymers were produced via semicontinuous emulsion polymerization and characterized via NMR, gel permeation chromatography, differential scanning calorimetry, dynamic light scattering, and atomic force microscopy. A high degree of chain termination due to allylic hydrogen abstraction was observed, as expected, with resultant decreases in molecular weight and in monomer conversion. However, high conversions were achieved, and it was possible to incorporate high percentages of the allylic acetate comonomer into the polymer chain. Copolymer thermal properties are reported. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3191–3203, 2007

Towards EPC-syntheses of the structural class of cochleamycins and macquarimicins. Part 3: EPC-syntheses of the β-keto lactone subunits and first attempts towards the syntheses of the pentacyclic antibiotics of this group

Practical EPC-syntheses of δ-substituted-β-keto δ-lactones, subunits of the cochleamycins and macquarimicins, are presented. In consequence Tietze's tandem reaction is employed to combine δ-allyl-β-keto δ-lactone with a hydrindene derivative, the second subunit of these acetogenic antibiotics. Model reactions for the final oxidative radical tandem cyclization reveal that the electrophilic radical cyclizes exclusively in exo- trig fashion. However, with the intended precursor of macquarimicin C allylic hydrogen abstraction thwarted the oxidative radical tandem cyclization.