Autoxidation Research Articles

Fragrance Compound Geraniol Forms Contact Allergens on Air Exposure. Identification and Quantification of Oxidation Products and Effect on Skin Sensitization

Fragrances are common causes of contact allergy. Geraniol (trans-3,7-dimethyl-2,6-octadiene-1-ol) is an important fragrance terpene. It is considered a weak contact allergen and is used for fragrance allergy screening among consecutive dermatitis patients. Analogous to other monoterpenes studied, such as limonene and linalool, geraniol has the potential to autoxidize on air exposure and form highly allergenic compounds. The aim of the present study was to investigate and propose a mechanism for the autoxidation of geraniol at room temperature. To investigate whether allergenic compounds are formed, the sensitizing potency of geraniol itself, air-exposed geraniol, and its oxidation products was determined using the local lymph node assay in mice. The results obtained show that the allylic alcohol geraniol follows an oxidation pattern different from those of linalool and limonene, which autoxidize forming hydroperoxides as the only primary oxidation products. The autoxidation of geraniol follows two paths, originating from allylic hydrogen abstraction near the two double bonds. From geraniol, hydrogen peroxide is primarily formed together with aldehydes geranial and neral from a hydroxyhydroperoxide. In addition, small amounts of a hydroperoxide are formed, analogous to the formation of the major linalool hydroperoxide. The autoxidation of geraniol greatly influenced the sensitizing effect of geraniol. The oxidized samples had moderate sensitizing capacity, quite different from that of pure geraniol. The hydroperoxide formed is believed to be the major contributor to allergenic activity, together with the aldehydes geranial and neral. On the basis of the present study and previous experience, we recommend that the possibility of autoxidation and the subsequent formation of contact allergenic oxidation products are considered in risk assessments performed on fragrance terpenes.

Epoxidation of allyl chloride and hydrogen peroxide over titanium silicalite‐1 film on SiO2 pellet support

AbstractTitanium silicalite‐1 (TS‐1) films were prepared on SiO2 pellet supports via an in situ hydrothermal synthesis method and were characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), scanning electron microscopy (SEM) and 29Si magic angle spinning nuclear magnetic resonance (Si MAS NMR). The growth time of TS‐1 film had a strong effect on its morphology and the thickness and size of the crystals. The uniformity and thickness of TS‐1 films increased with increase of growth times. The epoxidation of allyl chloride (ACH) with dilute hydrogen peroxide to form epichlorohydrin (ECH) over the TS‐1 films was carried out in a fixed bed reactor. The conversion of ACH and the selectivity to ECH over the TS‐1 films of the second growth were higher than that of the first growth, the third and the fourth growth. And the conversion and selectivity as a function of time‐on‐stream gave a good stable performance in an extended test up to at least 19 h. The final steady‐state conversion and selectivity were approximately 86% and 55%, respectively. Copyright © 2007 Society of Chemical Industry

Controlling Photoreactions with Restricted Spaces and Weak Intermolecular Forces: Exquisite Selectivity during Oxidation of Olefins by Singlet Oxygen

Highly regioselective photooxidation of methyl cycloalkenes has been performed in an aqueous medium by selectively blocking two of the three allylic hydrogens through supramolecular steric effect. Hydrophobic, steric, and weak intermolecular C−H−π interactions are suggested to be responsible for the specific orientation of the olefin within a water-soluble, deep-cavity cavitand with eight carboxylic acid groups.

Paramagnetic (Alkene)Rh and (Alkene)Ir Complexes: Metal or Ligand Radicals?

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Low‐Basicity Oxygen Atoms: A Key in the Search for Propylene Epoxidation Catalysts

Gotta have copper: DFT studies indicate that the performance of heterogeneous epoxidation catalysts depends on the first step in the reaction between oxygen atoms and propylene molecules coadsorbed on the metal surface (see picture; C yellow, H light blue, O red). The high basicity of oxygen atoms on silver favors allylic hydrogen stripping, whereas the low basicity of oxygen atoms on copper favors metallacycle formation and subsequent epoxidation.

Electrospray Ionization Multiple Stage Quadrupole Ion-Trap and Tandem Quadrupole Mass Spectrometric Studies on Phosphatidylglycerol from Arabidopsis Leaves

Phosphatidylglycerol (PG) is the major phospholipid of plant chloroplasts. PG from Arabidopsis thaliana has an unusual fatty acyl chain, 3-trans-hexadecenoyl (Delta(3)16:1) in the sn-2 position of the major 18:3/Delta(3)16:1-PG species, as well as in 18:2/Delta(3)16:1-PG and 16:0/Delta(3)16:1-PG. Upon low-energy collisionally activated dissociation (CAD) in a tandem quadrupole or in an ion-trap mass spectrometer, the [M - H]- ions of the PG molecules containing Delta(3)16:1 give product-ion spectra that are readily distinguishable from those arising from PGs without the Delta(3)16:1 species. The Delta(3)16:1-fatty acyl-containing PGs are characterized by MS(2) product-ion mass spectra that contain predominant [M - H - 236]- ions arising from loss of the Delta(3)16:1-fatty acyl substituent as a ketene. This is attributable to the fact that the alpha-hydrogen of the Delta(3)16:1-fatty acid substituent involved in the ketene loss is an allylic hydrogen, which is very labile. This leads to preferential neutral loss of 236 and drastic decline in the neutral loss of 254 (i.e., loss as a fatty acid), the unique features that signify the presence of Delta(3)16:1-fatty acyl containing PGs. The neutral loss scan of 236, thus, provides a sensitive tandem quadrupole mass spectrometric means to identify Delta(3)16:1-containing PG species in lipid mixtures. This low-energy tandem mass spectrometric approach also permits the structures of the Arabidopsis PGs that consist of two isomeric structures to be unveiled.

Variable Markovnikov Orientation and “cis Effect” in Ene Reactions of Nitrosocarbonyl Intermediates

Nitrosocarbonyl intermediates, generated at room temperature by the mild oxidation of nitrile oxides, undergo clean ene reactions with trisubstituted olefins. Allylic hydrogens on the more congested side of the alkene are exclusively abstracted (the "cis effect"), thus resembling singlet oxygen behavior. Nitrosocarbonyl benzene follows a Markovnikov orientation and abstracts preferentially the twix hydrogens over the lone ones. With the more sterically demanding nitrosocarbonyl mesitylene, the Markovnikov directing effect is relieved, and comparable twix and lone abstraction are observed.

Allylic hydrogen abstraction II. H-abstraction from 1,4 type polyalkenes as a model for free radical trapping by polyunsaturated fatty acids (PUFAs)

Unsaturated radicals, containing different number of delocalized electrons, are formed via H-atom abstractions with CH(3), iso-C(3)H(7), OOH and OH radicals from (Z,Z) and (E,E)-hepta-2,5-dienes. These reactions and the relative stability of the different allyl-type radicals formed, were studied within the BH&HLYP method, using a 6-311+G(3df,2p) basis set, as well as within the G3MP2 level of theory on BH&HLYP/6-31G(d) geometries. The biallyl type radicals (involving 5 electrons delocalized on 5 carbon atoms) are more stable, by about 47.6 +/- 0.4 kJ mol(-1), than monoallyl type radicals (which involve 3 electrons delocalized on 3 carbon atoms). Three types of the H-atom abstractions were distinguished: direct H-abstraction with CH(3), indirect abstraction with a higher barrier height with iso-C(3)H(7), OOH and a non-direct quasi-barrierless H-abstraction with OH radicals. These observations were also confirmed by the activation entropy versus activation enthalpy as well as the Evans-Polányi's plots. The OOH-hepta-2,5-diene complexes are found to be extremely stable (from -19.6 to 22.3 kJ mol(-1)). The room temperature rate constants were calculated with transition state theory. Formations of monoallyl and biallyl radicals through H-abstraction with OH are fast; the calculated rate constants range from 5.84 x 10(-11) to 1.92 x 10(-9) cm(3) molecule(-1) s(-1) at room temperature. These reactions may play a key role in the "very low temperature combustion" like biological oxidations.

Paramagnetic (Alkene)Rh and (Alkene)Ir Complexes: Metal or Ligand Radicals?

AbstractIn this review a detailed overview is given of the (electronic) structure and reactivity of open‐shell (paramagnetic) alkene rhodium and iridium complexes Mx(alkene) (M = Rh, Ir; x = 0, +II). In most cases these species are highly reactive, but some notable exceptions of stable species for which not much reactivity has been described are also included (section 2). Understanding the electronic structure of the reactive nitrogen‐ligand‐based [MII(por)(alkene)] and [MII(alkene)(N‐ligand)]2+ species (section 3) is complicated by a substantial spin distribution over the metal and the alkene ligand. This dual‐mode metallo‐radical and ligand radical behavior is reflected by their high and diverse reactivity. Metallo‐radical character is demonstrated by a variety of metal‐to‐radical coupling reactions with a series of other radicals, as well as metal‐based allylic hydrogen atom abstractions from MII(α‐alkene) species. On the other hand, (donor induced) ligand radical character is crucial in a variety of M–C and C–C radical coupling reactions, C–O bond formation by oxygenation of MII(alkene) species and alkene “insertions” into (por)M–H bonds. The review concludes with some speculations about possible roles of paramagnetic M(olefin) (M = Rh, Ir) species in catalytic olefin oxygenation and carbene transfer reactions.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Effect of network heterogeneities on the physical properties of nitrile rubbers cured with dicumyl peroxide

AbstractThe scope of this study is to continue our earlier studies on the peroxide curing of diene elastomers. The effect of peroxide content and temperature on the curing and mechanical properties of NBR and H‐NBR rubbers with different acrilonitrile content was evaluated. Experimental evidence indicates that saturated rubbers behave as expected whereas in unsaturated nitrile rubbers abstraction of allylic hydrogen and addition to the double bonds can act as mechanism of crosslinking, the weight of each mechanism is dependent of DCP content and curing temperature. The addition mechanism produces densely crosslinked zones or clusters, generating a heterogeneous network with effect on the vulcanizate properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3377–3382, 2007

Comparative Analysis of the Volatile Components in the Fresh Roots and Rhizomes of Curcuma wenyujin by Static Headspace Gas Chromatography Mass Spectrometry

AbstractStatic headspace GC‐MS method coupled with H/D exchange was firstly developed to determine and identify the volatile components in the fresh root and rhizome of Curcuma wenyujin. The TIC chromatograms of 3 batches of fresh roots harvested at different time showed significant difference in the volatile components:the constitution was the same but the content of them was different. More than 60 volatile components in fresh roots (Root of C. wenyujin) and rhizomes (Rhizome of C. wenyujin) of C. wenyujin were detected, of which 51 and 48 volatile components were identified respectively. The fresh roots and rhizomes of C. wenyujin were found to have the similar volatile components. The contents of these components were calibrated by the response of β‐elemene. In addition, the principal active component, β‐elemene, was further confirmed and relatively quantified by its standard. γ‐terpinene showed obvious allylic hydrogen/deuterium exchange using deuterium oxide which gave a new method to identify some compounds containing allylic hydrogen. At the same time, the active hydrogen compounds were also further confirmed. The results show that HS‐GC‐MS method is a fast, simple and efficient way for the analysis of volatile components from medical plants.

Optimization of the reaction parameters of epoxidation of allyl alcohol with hydrogen peroxide over TS-2 catalyst

The influence of technological parameters on the epoxidation of allyl alcohol to glycidol with 30 wt.% hydrogen peroxide was presented. The reaction was performed in a autoclave at autogenic pressure and in methanol medium (protic solvent). The influence of the following parameters was investigated: temperature (15–90 °C), the molar ratio AA/H 2O 2 (0.5–5), methanol concentration in reaction mixture (5–90 wt.%), TS-2 concentration in reaction mixture (0.1–2.0 wt.%) and the reaction time (15–120 min). The optimum conditions were established by the mathematical method of design of experiments (rotatable-uniform design). The received results were described by the following mathematical functions: selectivity of transformation to glycidol in relation to consumed allyl alcohol and hydrogen peroxide and conversion of allyl alcohol and H 2O 2. The courses of functions for appropriate parameters were plotted in the system of two variable parameters. The optimum parameters of the epoxidation process were established based on the analyses of the layer drawings.

Mechanism of the Diphenyldisulfone-Catalyzed Isomerization of Alkenes. Origin of the Chemoselectivity: Experimental and Quantum Chemistry Studies

Polysulfone- and diphenyldisulfone-catalyzed alkene isomerizations are much faster for 2-alkyl-1-alkenes than for linear, terminal alkenes. The mechanism of these reactions has been investigated experimentally for the isomerization of methylidenecyclopentane into 1-methylcyclopentene, and theoretically [CCSD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p) calculations] for the reactions of propene and 2-methylpropene with a methanesulfonyl radical, MeSO2*. On heating, polysulfones and (PhSO2)2 equilibrate with sulfonyl radicals, RSO2*. The latter abstract allylic hydrogen atoms in one-step processes giving allylic radical/RSO2H pairs that recombine within the solvent cage producing the corresponding isomerized alkene and RSO2*. The sulfinic acid, RSO2H, can diffuse out from the solvent cage (H/D exchange with MeOD,D2O) and reduce an allyl radical. Calculations did not support other possible mechanisms such as hydrogen exchange between alkenes, electron transfer, or addition/elimination process. Kinetic deuterium isotopic effects measured for the (PhSO2)2-catalyzed isomerization of methylidenecyclopentane and deuterated analogues and calculated for the H abstraction from 2-methylpropene and deuterated analogues by CH3SO2* are consistent also with the one-step hydrogen transfer mechanism. The high chemoselectivity for this reaction is not governed by an exothermicity difference but by a difference in ionization energies of the alkenes. Calculations for CH3SO2* + propene and CH3SO2* + 2-methylpropene show a charge transfer of 0.34 and 0.38 electron, respectively, from the alkenes to the sulfonyl radical in the transition states of these hydrogen abstractions.

Thermal Chemistry of 1-Methyl-1-Cyclopentene and Methylene Cyclopentane on Pt(111) Surfaces: Evidence for Double-Bond Isomerization

The thermal chemistry of 1-methyl-1-cyclopentene (1MCp(=)) and methylene cyclopentane (MeCp) was investigated on clean and hydrogen- and deuterium-predosed Pt(111) single-crystal surfaces by temperature-programmed desorption and reflection-absorption infrared spectroscopy. It was found that MeCp isomerizes easily to 1MCp(=) but that the reverse reaction does not occur, at least under our experimental conditions. The MeCp to 1MCp(=) isomerization is aided by the presence of coadsorbed hydrogen, and occurs through the formation of a common 1-methyl-1-cyclopentyl (1MCp-Pt) surface intermediate; that intermediate then undergoes beta-hydride elimination selectively at the ring position to form the 1MCp(=) product. In addition to this isomerization, both 1MCp(=) and MeCp also dehydrogenate on the Pt(111) surface to form a methylcyclopentadiene species, at 325 and 350 K, respectively. A small amount of benzene desorption is detected above 500 K with both reactants, indicative of a ring enlargement reaction. No evidence for the activation of any of the allylic hydrogens was obtained in either molecule.

홍삼에 함유된 갈변물질 및 산성다당체에 대한 연구현황

In the browning reaction of Korean ginseng, it appears that enzymatic and non-enzymatic browning reaction occurred In initial stage of steaming fresh ginseng at low temperature, and then non-enzymatic browning reaction followed in the drying period after steaming. Browning reaction of red ginseng occurred between min of steaming at , and browning pigments of red ginseng were mostly water soluble substances. The structural characteristics of water soluble browning reaction products(WS-BRPs) isolated from Korean red ginseng were showed the presence of hydroxyl, amide carbonyl and aliphatic methane groups. From sugar analysis it was identified that L and S-1, melanoidins isolated from red ginseng, contained two kinds of sugars, glucose and xylose, and the other melanoidin S-2 contained the previous and fructose. In order to find out pertinent methods for the acceleration of browning during ginseng processing, various treatment were made on fresh ginseng with sugars, amino acids and inorganic nitrogenous compounds and the extent of browning was measured. Among sugar tested, maltose resulted in the greatest acceleration of browning followed in decreasing order by glucose and lactose, whereas pentoses, fructose, sucrose and raffinose had negligible effect. A marked browning occurred in ginseng treated with basic amino acids, while the extent of browning was not greatly increased when ginseng was treated with aliphatic amino acids, hydroxyl amino acids, or acidic amino acids. The brown color intensity gradually increased with an increase of glucose concentration far up to 0.5M. L, S-1, and S-2 were found to have an ability to donate hydrogen to DPPH, and also they had anti-oxidative activity in the experiments of hydrogen peroxide scavenging, inhibitory activity in the formation of MDA from linoleic acid, auto oxidation of ok-brain homogenates, lipid peroxidation by the enzymatic and non-enzymatic system in liver microsome fraction, and mitochondrial fraction etc. The amounts of acidic polysaccharide(AP) in red ginseng were higher than those of wild and cultured Panax quinquefolius, Panax notoginseng as well as white ginseng (Panax ginseng). In white ginseng, the AP amount is no difference in root ages or sizes, also, the AP amount of ginseng body was similar to that of rhizome, but was higher than that of leaf and epidermis. Addition of red ginseng acidic polysaccharide(RGAP) increased production of nitric oxide(NO) and tumor necrosis factor (TNF)- in the rodent macrophage cultures, and treatment of RGAP in vivo stimulated tumoricidal activities of natural killer (NK) cells.

5-Trideuteromethyl-α-tocotrienol and 5-14CH3-α-tocotrienol as biological tracers of tocotrienols

The tocotrienols have attracted increased attention recently as evidence has accrued that their biological activities are significantly different from tocopherols. The biokinetics and metabolic fate of tocopherols have long been studied using deuteromethylated forms of α-tocopherol prepared by a stannous chloride catalysed paraformaldehyde methylation of γ- and δ-tocopherols. We show here that his methodology is not an efficient route to deuterated α-tocotrienol because of low yields and extensive exchange of allylic hydrogens under the prolonged acidic conditions of the deuteromethylation. Instead, we have prepared deuteromethylated and 14C-radiolabelled α-tocotrienol by aminomethylation at C-5 of γ-tocotrienol (available from palm oil), followed by reduction with NaCNBD3 in refluxing iso-butanol. The deuteromethylation procedure is amenable to multi-gram scale reactions. Copyright © 2006 John Wiley & Sons, Ltd.

Free radical oxidation (autoxidation) of alkenones and other microalgal lipids in seawater

The free radical oxidation (autoxidation) of long chain alkenones derived from haptophyte microalgae was studied in the laboratory in the presence of a radical initiator (di- tert-butyl nitroxide) and a radical enhancer ( tert-butyl hydroperoxide). Alkenones were autoxidized faster than analogues of other common marine lipids such as phytyl acetate, methyl oleate and cholesteryl acetate. Alkenone autoxidation rates increased in an approximately linear fashion with the number of double bonds present in the molecule and so autoxidation has the potential to affect values of U 37 K ′ . The process seems to involve allylic hydrogen abstraction and subsequent oxidation of the allylic radical to form products that can be analysed as alkene polyols after NaBH 4 reduction. Evidence for the autoxidation of lipids in seawater was obtained from analysis of organic matter in sediment traps deployed at the DYFAMED site in the northwestern Mediterranean Sea. High contents of specific autoxidation products of monounsaturated fatty acids and the chlorophyll phytyl side chain were recognized in samples collected during post-bloom conditions, but not during a phytoplankton bloom event. Biomarkers for autoxidation include the presence of 8- and 11-hydroxyoctadec- cis-9-enoic acids and various phytol diols and triols. These same samples also showed anomalously high U 37 K ′ values (equivalent to an inferred temperature change of at least 2 °C), consistent with the results of the autoxidation experiments, but opposite to that expected for any effect due to nutrient limitation on haptophyte cells. Our work demonstrates that autoxidation of lipids may occur in seawater and that this has the potential to affect alkenone distributions, especially where residence times of particles are long. In such circumstances this might lead to a warm bias in estimates of palaeotemperature derived from alkenone ratios in sediments.

Heterogeneous Alkene Epoxidation: Past, Present and Future

AbstractFor Abstract see ChemInform Abstract in Full Text.

Reactivity of Ru [dbnd]O species in RuO 2/CeO 2 catalysts prepared by a wet reduction method

The paper deals with the reactivity of RuO 2/CeO 2 prepared by a wet reduction method: ruthenium was supported on Ce(OH) 3, which was precipitated by alkali-hydrolysis of Ce(NO 3) 3, under a reduction condition with formaldehyde at pH 11 and transformed into RuO 2/CeO 2 catalysts by calcination in air at 773 K. The catalysts were investigated with an ESR technique and were tested for oxidation of propylene. They had no ESR signals by themselves at room temperature, but gave two sets of anisotropic signals upon contact with propylene. These signals were derived from the reaction products between Ru O and propylene. The intensities of the signals were kept unchanged at room temperature for more than 1 h in the absence of excess propylene. The signals decayed in the presence of excess propylene and the upfield signal decayed more rapidly. A prior heating of the catalyst in air at 473 K or above caused the increase in the intensity of the upfield signal. The time course of the signal changes discriminated between ethylene and olefins with allylic hydrogen toward Ru O species.

Enzymatic carotenoid degradation and aroma formation in nectarines ( Prunus persica)

C-13 norisoprenoids such as β-ionone, 3 hydroxy-β-ionone, and 3 hydroxy-5,6-epoxy-β-ionone are important carotenoid related aroma compounds in fruits. Apart from chemical degradation (photo-oxygenation, (auto)oxidation, thermal degradation), enzymatic cleavage is an important flavor formation pathway [ Enzell, C. (1985). Biodegradation of carotenoids – an important route to aroma compounds. Pure and Applied Chemistry, 57(5), 693–700; Winterhalter, P., & Rouseff, R. (Eds.). (2001). Carotenoid-derived aroma compounds. ACS symposium series 802, Washington, DC: American Chemical Society (ISBN 0-8412-3729-8)]. In nectarines, the content of carotenoid degradation products depends on the degree of maturity. In fully ripened fruit up to 40% of the aglycons are C-13 norisoprenoids [Aubert, C., Günata, Z., Ambid, C., & Baumes, R. (2003). Changes in physicochemical characteristics and volatile constituents of yellow- and white-fleshed nectarines during maturation and artificial ripening. Journal of Agriculture and Food Chemistry, 51(10), 3083–3091]. Regiospecific carotenoid cleavage enzymes have been shown to be involved in aroma formation in different plants and fruits [Bouvier, F., Suire, C., Mutterer, J., & Camara, B. (2003). Oxidative remodeling of chromoplast carotenoids: identification of the carotenoid dioxygenase CsCCD and CsZCD genes involved in crocus secondary metabolite biogenesis. Plant Cell, 15(1), 47–62; Fleischmann, P., Studer, K., & Winterhalter, P., (2002). Partial purification and kinetic characterization of a carotenoid cleavage enzyme from quince fruit ( Cydonia oblonga). Journal of Agriculture and Food Chemistry, 50(6), 1677–1680; Fleischmann, P., Watanabe, N., & Winterhalter, P., (2003). Enzymatic carotenoid cleavage in star fruit ( Averrhoa carambola). Phytochemistry, 63(2), 131–137; Schwartz, Qin & Zeevaart, 2001]. This paper describes the isolation and partial characterization of carotenoid cleavage enzymes in nectarines, isolated from ripe skin of commercially available fruit. The enzyme is characterized by its kinetic parameters ( v max, K m, time constant, temperature dependence, activation energy).