Theoretical Studies of Species Related to Acrolein Hydrogenation

Abstract  

Unsaturated alcohols, usually produced from selective hydrogenation of unsaturated aldehydes, are important fine chemical intermediates used to synthesize pharmaceuticals and flavoring materials. Acrolein, the smallest member in α, β-unsaturated aldehydes, is the model system for studying selective hydrogenation of α, β-unsaturated aldehydes. So far most theoretical work is about adsorption and reactions of acrolein and its related species on surfaces. In the present paper we systematically studied the geometries, electronic structures, stability and transformation of various species derived from stepwise hydrogenation of acrolein in the gas phases. We identified the most stable intermediates for each system and determined the energy barrier for intermolecular conversion between isomers for various species with different content of hydrogen. All these results are valuable and informative for understanding the surface chemistry of hydrogenation of α, β-unsaturated aldehydes.     

Reaction of thiobarbituric acid with saturated aldehydes

The reaction of thiobarbituric acid (TBA) with saturated aldehydes, i.e., 1-butanal, 1-hexanal and 1-heptanal, produced a 455-nm yellow and a 532-nm red pigment. Formation of the pigments depended on the reaction conditions. The yellow pigment was unstable in the presence of excess amounts of the saturated aldehydes. The red pigment was formed only when the reaction was performed at a TBA/aldehyde ratio of 1∶1 in aqueous acetic acid. Formation of the yellow and red pigments required molecular oxygen. The colorless adducts, intermediates for the yellow and the red pigments, were isolated from the reaction mixtures. Aldol condensation and dehydration of 2 mol of the saturated aldehydes initially gave the α,β-unsaturated aldehydes, which in turn reacted with TBA to form the colorless adducts, pyranopyrimidine derivatives. The adducts were then converted into the yellow and red pigments under aerobic conditions.     

Application of new methods and analytical approaches to research on polyunsaturated fatty acid homeostasis

New methods and analytical approaches are important to challenge and/or validate established beliefs in any field including the metabolism of polyunsaturated fatty acids (PUFA; polyunsaturates). Four methods that have recently been applied toward obtaining a better understanding of the homeostasis of PUFA include the following: whole-body fatty acid balance analysis, magnetic resonance imaging (MRI), ¹³C nuclear magnetic resonance (NMR) spectroscopy, and gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Whole-boby balance studies permit the measurement of both the percentage of oxidation of linoleate and α-linolenate and their conversion to long-chain PUFA. This method has shown that β-oxidation to CO₂ is normally the predominant metabolic fate of linoleate and α-linolenate. Furthermore, models of experimental undernutrition in both humans and animals show that β-oxidation of linoleate and α-linolenate markedly exceeds their intake, despite theoretically sufficient intake of linoleate or α-linolenate. Preliminary results suggest that by using MRI to measure body fat content, indirect whole-body linoleate balance can be done in living humans, ¹³C NMR spectroscopy provided unexpected evidence that linoleate and α-linolenate were metabolized into lipids synthesized de novo, an observation later quantified by tracer mass balance done using GC-C-IRMS. This latter method showed that within 48 h of dosing with ¹³C-α-linolenate, >80% underwent β-oxidation to CO₂ by suckling rats, whereas 8–9% was converted to newly synthesized lipids and <1% to docosahexaenoate. Further application of these recently developed methods in different models should clarify the emerging importance of β-oxidation and carbon recycling in PUFA homeostasis in mammals including humans.     

The effect of intermittent and continuous heating of soybean oil at frying temperature on the formation of 4-hydroxy-2-trans-nonenal and other α-, β-unsaturated hydroxyaldehydes

4-Hydroxy-2-trans-nonenal (HNE) is a cytotoxic secondary lipid peroxidation product of linoleic acid. Previous investigations in this laboratory showed that HNE is formed in thermally oxidized soybean oil, which is high in linoleic acid. Continuous exposure of the oil to frying temperature (185°C) for up to 6 h graduallyincreased the formation of HNE and other polar lipophilic aldehydes. Additional investigations in this laboratory showed that HNE is absorbed into food fried in thermally oxidized oil in the same concentration as was found in the oil. In the present experiment, the effect of intermittent heating on the formation of HNE in soybean oil was compared with continuous heating. Soybean oil samples were heated either for 1 h each day for five sequential days or for 5 h continuously at 185±5°C. The thermally oxidized soybean oil samples were analyzed by HPLC for the presence of HNE and three other polar lipophilic α-,β-unsaturated hydroxyaldehydes: 4-hydroxy-2-trans-hexanal, 4-hydroxy-2-trans-octenal, and 4-hydroxy-2-trans-decenal. Under intermittent and continuous heating over a total of 5 h, the concentration of these compounds increased similarly. These results indicate that the formation of HNE and other hydroxyaldehydes at frying temperature is a cumulative result of oxidation of PUFA over time.     

Effects of quenching mechanisms of carotenoids on the photosensitized oxidation of soybean oil

The effects of 0, 1.0 × 10”⁻⁵, 2.5 × 10⁻⁵, and 5.0 × 10⁻⁵ M β-apo-8'-carotenal, β-carotene, and canthaxanthin on the photooxidation of soybean oil in methylene chloride containing 3.3 × 10⁻⁹ M chlorophyll b were studied by measuring peroxide values and conjugated diene content. β-Apo-8'-carotenal, β-carotene, and canthaxanthin contain 10,11, and 13 conjugated double bonds, respectively. The peroxide values and conjugated diene contents of oils containing the carotenoids were significantly lower (P<0.05) than those of control oil containing no carotenoid. As the number of conjugated double bonds of the carotenoids increased, the peroxide values of soybean oils decreased significantly (P<0.05). The quenching mechanisms and kinetics of the carotenoids in the photosensitized oxidation of soybean oil were studied by measuring peroxide values. The steady-state kinetics study showed that carotenoids quenched singlet oxygen to reduce chlorophyll-sensitized photooxidation of soybean oil. The singlet-oxygen quenching rate constants ofβ- apo-8'-carotenal, β-carotene, and canthaxanthin were 3.06 × 10⁹, 4.60 × 10⁹, and 1.12 × 10¹⁰ M⁻¹sec⁻¹, respectively.     

Reliability of <Superscript>1</Superscript>H NMR Analysis for Assessment of Lipid Oxidation at Frying Temperatures

The reliability of a method using ¹H NMR analysis for assessment of oil oxidation at frying temperatures was examined. During heating and frying at 180 °C, changes of soybean oil signals in the ¹H NMR spectrum including olefinic (5.16–5.30 ppm), bisallylic (2.70–2.88 ppm), and allylic (1.94–2.15 ppm) proton signals relative to glyceride backbone CH₂ (5.30–5.46 ppm) and aliphatic CH₂ (1.05–1.71 ppm) signals showed strong correlations with conventional analytical methods including total polar compounds, polymerized triacylglycerols, and changes of linoleic acid and linolenic acid peaks in gas chromatography. For oils rich in oleic acid, mid‐oleic sunflower oil (NuSun) and high oleic soybean oil, only the olefinic and allylic proton signals are recommended for analysis due to the relatively low intensity of the bisallylic proton signal. Under these heating and frying conditions, signals indicating intermediate oxidation products, hydroperoxides, were not detected while very small signals corresponding to a variety of aldehydes including alkanal, branched alkenal, 2‐alkenal, and aldehydes of conjugated dienes and epoxides were observed. In this study, it was found that the ¹H NMR method is a fast, convenient, and reliable analytical method to determine the oxidation state of frying oil.     

Biphasic Hydrogenation of α,β-unsaturated Aldehydes with Hydrosoluble Rhodium and Ruthenium Complexes

Abstract  

The hydrosoluble complexes [Rh(CO)(Pz)(L)]_2, and [RuH(CO)(CH₃CN)(L)₃][BF₄] [L = TPPMS (triphenylphosphinemonosulfonated) and TPPTS (triphenylphosphine-trisulfonated)] were evaluated in the selective hydrogenation of α,β-unsaturated aldhydes in biphasic media The Rh complexes produced the saturated aldehydes while the Ru complexes generated the alcohols with high chemoselectivity. The catalytic phase can be recycled up to five times.     

The sterols ofCucurbita moschata (“calabacita”) seed oil

From the sterol fraction of seed oil from commercialCucurbita moschata Dutch (“calabacita”) Δ⁵ and Δ⁷ sterols having saturated and unsaturated side chain were isolated by chromatographic procedures and characterized by spectroscopic (¹H and¹³C-nuclear magnetic resonance, mass spectrometry) methods. The main components were identified as 24S-ethyl 5α-cholesta-7,22E-dien-3β-ol (α-spinasterol); 24S-ethyl 5α-cholesta-7,22E, 25-trien-3β-ol (25-dehydrochondrillasterol); 24S-ethyl 5α-cholesta-7, 25-dien-3β-ol; 24R-ethylcholesta-7-en-3β-ol (Δ⁷-stigmastenol) and 24-ethyl-cholesta-7, 24(28)-dien-3β-ol (Δ^7,24(28)-stigmastadienol).Lipids 31, 1205–1208 (1996).     

Sterols ofKalanchoe pinnata: First report of the isolation of both C-24 epimers of 24-alkyl-Δ25-sterols from a higher plant

Eighteen sterols were isolated from the aerial parts ofKalanchoe pinnata (Crassulaceae) including four novel sterols,viz. (24R)-stigmasta-5,25-dien-3β-ol (24-epiclerosterol), (24R)-5α-stigmasta-7,25-dien-3β-ol, 5α-stigmast-24-en-3β-ol, and 25-methyl-5α-ergost-24(28)-en-3β-ol. 24-Epiclerosterol and its Δ⁷-analog occur together with their 24S/β-epimers in the same plant making this the first report of the isolation of both C-24 epimers of Δ²⁵-unsaturated 24-alkylsterols from a non-marine organism. Iodine-catalyzed isomerization of stigmasta-5,24-dien-3β-ol (24-ethyldesmosterol), the main sterol ofK. pinnata, yielded 24-epiclerosterol among other products.     

Long-term behavior of oil-based varnishes and paints I. Spectroscopic analysis of curing drying oils

The curing of drying oils at 60°C has been investigated by Fourier transform infrared spectroscopy and Fourier transform Raman analysis of linseed oil and poppyseed oil. In the first step, hydroperoxides are formed (broad vibration band centered around 3425 cm⁻¹) with concomitant conjugation and cis-trans isomerization of the double bonds (disappearance of cis bands at 3011 and 716 cm⁻¹, appearance of trans conjugated and trans nonconjugated bands at 987 and 970 cm⁻¹). The subsequent decomposition of hydroperoxides in the presence of oxygen leads to the formation of alcohols (nitrite band at 779 cm⁻¹ after nitrogen monoxide treatment), aldehydes (bands at 2810 and 2717 cm⁻¹ in gas phase), ketones (saturated and unsaturated at 1720 and 1698 cm⁻¹, respectively), carboxylic acids (saturated and unsaturated acid fluorides identified at 1843 and 1810 cm⁻¹ after SF₄ treatment), and peresters or γ-lactones (near 1770 cm⁻¹). A rapid decrease in the double-bond concentration is recorded when curing continues, and the formation of epoxides, characterized by a vibration band at 885 cm⁻¹, is observed. Thermolysis experiments have suggested the proposal of a reaction of addition of peroxyl radicals on the conjugated double bonds as a probable mechanism. This mechanism explains both the rapid disappearance of conjugated double bonds and the formation of epoxides as intermediate products observed in the initial step of curing.     

13C nuclear magnetic resonance spectroscopic analysis of the triacylglycerol composition ofBiota orientalis and carrot seed oil

¹³C nuclear magnetic resonance (NMR) spectroscopic analysis of the whole oil (triacylglycerols) ofBiota orientalis seeds confirms the presence of oleate [18:1(9Z)], linoleate [18:2(9Z, 12Z)], linolenate [18:3((9Z, 12Z, 15Z)], 20:3 (5Z, 11Z, 14Z), 20:4(5Z, 11Z, 14Z, 17Z), and saturated fatty acids in the acyl groups by comparing the observed carbon shifts with previously established shift data for model triacylglycerols. This technique shows that the saturated, 20:3 and 20:4 fatty acids are distributed mainly in the α-acyl positions, whereas oleate, linoleate, and linolenate are randomly acylated to the α- and β-positions of the glycerol “backbone”. Stereospecific hydrolysis of theBiota oil with pancreatic lipase, followed by chromatographic analysis of fatty esters, reveals the presence of trace amounts of 16:0(0.7%), 18:0(0.5%), 20:3 (0.4%), and 20:4 (1.3%) in the β-position of the glycerol “backbone”, which are undetectable by¹³C NMR technique on the whole oil. Semiquantitative assessment of the¹³C NMR signal intensities gives the relative percentages of the fatty acid distribution as: saturated 16:0, 18:0 (12.0% α-acyl), oleate (7.7% α-acyl 8.7% β-acyl), total linoleate and linolenate (31.7% α-acyl; 24.2% βacyl), total 20:3 and 20:4 (15.7% α-acyl). The¹³C NMR spectroscopic analysis of carrot seed oil identifies the presence of saturated (18:0), 18:1(6Z), 18:1(9Z), and 18:2(9Z, 12Z). The saturated fatty acid is found in the α-acyl positions. Semi-quantitative assessment of the signal intensities gives the relative percentages of the fatty acids as: 18:0 (4.5% α-acyl), 18:1(6Z) (49.6% α-acyl; 19.7% β-acyl), oleate (6.5% α-acyl; 8.6% β-acyl) and linoleate (5.2% α-acyl; 6.9% β-acyl).     

Physicochemical and Stability Characteristics of Flaxseed Oils During Pan-heating

Flaxseed oils are used in stir-frying in parts of China. In this study, flaxseed oils were heated at approximately 150 °C as a thin film in a frying pan for 3 and 6 min, respectively. Pan-heating caused loss of tocopherols, plastochromanol-8, phenolic acids and chlorophyll pigments. There was a significant decrease in the linolenic acid resulting in a concomitant relative increase in palmitic, stearic, oleic and linoleic acids in the oils after pan heating. Positive CIELAB “b*” color value, which indicates yellowness and levels of β-carotene and lutein in these oils showed a 42–56% and 8–53% decrease, respectively. Peroxide values, p-anisidine values, percentage of conjugated dienoic acid, specific extinction at 232 and 270 nm and food oil sensor readings of these oils showed significant increases to levels exceeding good oil quality indices. Acid values only showed one to twofold increase from fresh oil values of 0.65–2.23 mg KOH/g of sample. These results indicate that significant levels of oxidation products would be present in flaxseed oils after pan heating. The flaxseed oil with a lower amount of PUFA appeared to be more degraded suggesting that the major factor affecting the oxidative stability of the flaxseed oils during pan-heating was not the degree of unsaturation but was dependent on the complex interaction between the fatty acids and minor constituents in the oils. Presented at the American Oil Chemists’ Society 97th Annual Meeting & Expo, St. Louis, MO, 30 April–3 May, 2006.     

The reaction of picric acid with epoxides. II. The detection of epoxides in heated oils

A colorimetric method, based upon the reaction of the oxirane group with picric acid, was used to determine the epoxide content of heated vegetable oils. The picration method is particularly suitable for measuring small quantities of epoxide because it is much more sensitive than the common titrimetric methods, and it is not subject to interference from cyclopropene, conjugated dieneols, or α, β-unsaturated carbonyls. Thin-layer chromatography was used to separate mixtures of picrated, epoxidized methyl esters. Separation ofcis- andtrans-methyl epoxystearate, methyl epoxyoleate, and methyl diepoxystearate in a mixture of these four esters was achieved in this manner. The presence of saturatedcis- andtrans-epoxystearates and unsaturated epoxides was demonstrated in heated vegetable oils. Presented, in part, at the AOCS Meeting in Cincinnati, October 1965.     

Sterols and fatty acids of a whisk fernPsilotum nudum

The sterols and fatty acids ofPsilotum nudum were investigated. The 4,4-dimethyl- and 4α-methylsterol fractions contained 24β-methyl-Δ²⁵-unsaturated sterols,viz., cyclolaudenol and 24β-methyl-25-dehydrolophenol, respectively, as dominant sterols among the other components common in vascular plants. 24-Methylcholesterol (mixture of C-24 epimers) and sitosterol constituted the dominant sterols in the 4-demethylsterol fraction. This is the first identification of 24-methylene-5α-lanost-8-en-3β-ol, 24β-methyl-25-dehydrolophenol, codisterol, isofucosterol, 24-methylene-25-methylcholesterol and avenasterol in a fern. The major fatty acids were 16:0, 18:1, 18:2, 18:3 and 20:3. In addition, several C₂₀ fatty acids with various unsaturation were found to be present in low concentrations.     

Effect of α- and γ-tocopherols on thermal polymerization of purified high-oleic sunflower triacylglycerols

The antipolymerization effects of α- and γ-tocopherols were compared in model systems composed of purified high-oleic sunflower triacylglycerols at 180°C. γ-Tocopherol was much more effective as an antipolymerization inhibitor than α-tocopherol, partly due to lower oxidizability/disappearance. Purified triacylglycerols of sunflower, rapeseed, and high-oleic sunflower oils were less stable than their nonpurified forms containing tocopherols. Results confirmed that tocopherols per se can act as antipolymerization agents in high-oleic oils at frying temperatures. No synergism was observed when α- and γ-tocopherols were present together although larger amounts of residuals were left for both tocols. Results suggested that high-oleic/high-γ-tocopherol oils (such as high-oleic canola and high-oleic soybean oils) may provide better frying oils than high-oleic/high-α-tocopherol oils (such as high-oleic sunflower oil).     

Studies on phytosterol oxides. II: Content in some vegetable oils and in French fries prepared in these oils

Hydrogenated rapeseed oil/palm oil blend, sunflower oil and high-oleic sunflower oil, and French fries fried in these oils were assessed for contents of sterol oxidation products. Different oxidation products of phytosterols (7α- and 7β-hydroxy-sito-and campesterol, 7-ketosito- and 7-ketocampesterol, 5α,6α-epoxy-sito- and campesterol, 5β,6β-epoxy-sito-and campesterol, dihydroxysitosterol and dihydroxycampesterol) were identified and quantiated by gas chromatography (GC) and GC-mass spectroscopy. Rapeseed oil/palm oil blend contained 41 ppm total sterol oxides before frying operations. After two days of frying, this level was increased to 60 ppm. Sunflower oil and high-oleic sunflower oil had 40 and 46 ppm sterol oxides, respectively, before frying operations. After two days of frying operations, these levels increased to 57 and 56 ppm, respectively. In addition to campesterol and sitosterol oxidation products, small amounts of 7α- and 7β-hydroxystigmasterol were detected in the oil samples. Total sterol oxides in the lipids of French fries fried at 200°C in rapeseed oil/palm oil blend, sunflower oil, and high-oleic sunflower oil were 32, 37, and 54 ppm, respectively. The levels of total oxidized sterols, calculated per g sample, ranged from 2.4 to 4.0 ppm. In addition to the content of phytosterol oxides, full scan mass spectra of several oxidation products of stigmasterol are reported for the first time. Part of these results were presented at the 86th Annual Meeting of the AOCS, May 7–11, 1995, San Antonio, TX.     

Varietal and crop year effects on lipid composition of walnut (Juglans regia) genotypes

The FA, unsaponifiable, and volatile constituents of oil from three walnut varieties from two consecutive crop years were studied. The walnut oils (WO) were rich in PUFA and low in saturated FA. The tocopherol fraction consisted mainly of γ-tocopherol. High contents of β-sitosterol were found, together with campesterol and Δ⁵-avenasterol in similar amounts. Methylsterols present in WO were identified as cycloartenol, cyclolaudenol, cycloeucalenol, and 24-methylenecycloartanol. The hydrocarbon fraction was characterized by the predominance of C₁₄–C₂₀ n-alkanes. The major volatiles were aldehydes produced through the linoleic acid oxidative pathway. FA, methylsterols, and some hydrocarbons presented statistically significant differences among varieties. Most of this variation was due to the genotype. The Franquette variety was noteworthy by its higher oil and oleic acid contents. In contrast, tocopherols and volatile compounds showed minor differences among varieties; they were strongly influenced by the crop year. Chemical data were subjected to principal component analysis. The parameters that gave the greatest discrimination between the walnut varieties were oleic and linolenic acids, tetradecane, eicosane, tetracosane, cycloartenol, and 24-methylenecycloartanol. These components presented the major varietal influences and could be useful to determine the identity of walnut genotypes.     

Studies on the hypohalogenation of long chain α,β-unsaturated acids

As a result of hypohalogenation, a series oferythro 2(3)-halo-3(2)-hydroxy derivatives of C₁₆, C₁₈ and C₂₂ α, β-unsaturated acids have been prepared. The structures of the individual isomers were established by chemical and spectral methods. The major products were shown to be 2-halo-3-hydroxy alkanoic acids. Unlike internal halohydrins, the isomeric mixture of these derivatives of long chain α, β-unsaturated acids was successfully resolved by column chromatography.     

A multivariate study of the correlation between tocopherol content and fatty acid composition in vegetable oils

The main biochemical function of the tocopherols is believed to be the protection of polyunsaturated fatty acids (PUFA) against peroxidation. A critical question that must be asked in reference to this is whether there is a biochemical link between the tocopherol levels and the degree of unsaturation in vegetable oils, the main source of dietary PUFA and vitamin E. We used a mathematical approach in an effort to highlight some facts that might help address this question. Literature data on the relative composition of fatty acids (16:0, 16:1, 18:0, 18:1, 18:2, and 18:3) and the contents of tocopherols (α-, β-, δ-, and γ-tocopherol) in 101 oil samples, including 14 different botanical species, were analyzed by principal-component analysis and linear regression. There was a negative correlation between α- and γ-tocopherols (r=0.633, P<0.05). Results also showed a positive correlation between linoleic acid (18:2) and α-tocopherol (r=0.549, P<0.05) and suggested a positive correlation between linolenic acid (18:3) and γ-tocopherol.     

Membrane docosahexaenoic acid vs. eicosapentaenoic acid and the beating function of the cardiomyocyte and its regulation through the adrenergic receptors

The β-adrenergic system in cardiac muscle cells is influenced by the n-3 polyunsaturated fatty acid (PUFA) content in cell membranes. This study deals with the specific effect of docosahexaenoic acid (DHA) as compared to other n-3 PUFA, without modification of the arachidonic acid content. Increasing the DHA content in the phospholipids of isolated cardiomyoxytes did not provoke electrical or contraction modifications, except for a slightly lower plateau phase (−2 mV). Conversely, the β-adrenergic function was affected at several levels: (i) the receptor affinity for dihydroalprenolol tended to decrease (Kd) without alteration of the number of β-binding sites (β_max); (ii) the isoproterenol-induced (10⁻⁷ M and 10⁻⁶M) cAMP production was significantly decreased (−20%); and (iii) the positive chronotropic response to β-adrenergic stimulation (isoproterenol, 10⁻⁷ M) was significantly enhanced (+80%). In order to further investigate the relationship between the decreased cAMP and the increased chronotropic response, the cells were treated with dibutyryl-cAMP, a perment analogue of cAMP, which elicited a significantly higher chronotropic response in DHA-enriched cells than in EPA-enriched cells (+50%). The increase in DHA content in cardiac cell membranes phospholipids may thus affect the β-adrenergic system through an increase of cAMP efficiency. Although the membrane phosphatidylinositols were largely involved in the PUFA alterations, none of the parameters related to α-adrenergic system (chronotropic response, receptor density, affinity for prasozin, and inositide phosphate production) were influenced by the membrane DHA content.