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Computational and experimental research on mechanism of cis/trans isomerization of oleic acid.

ABSTRACT: The harm of trans-fatty acids to health has aroused public concern. It is believed that the main source of trans-fatty acids in diets is the isomerization of unsaturated fatty acids in edible oils during cooking. However, the information on the isomerization mechanism is very limited. In this paper, we used oleic acid, an unsaturated fatty acid, as a simplified model for edible oil and investigated the mechanism of cis/trans isomerization by computation and experiments. The computational results show that R_c-O-O-H is a very important intermediate, and the cleavage of O-O bond in R_c-O-O-H is the rate-controlling step during the cis/trans isomerization. Using the ATR-FTIR measurements, the contents of elaidic acid were measured quantitatively in sites. The experimental results indicate that the cis/trans isomerization of oleic acid can occur obviously only under oxidizing condition when the temperature is higher than 120 °C.

SUBMITTER: Cheng N

PROVIDER: S-EPMC6129684 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature

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Computational and experimental research on mechanism of cis/trans isomerization of oleic acid.

Cheng Ningning N Zhang Jingjing J Yin Jingmei J Li Shenmin S

Heliyon 20180906 9

The harm of trans-fatty acids to health has aroused public concern. It is believed that the main source of trans-fatty acids in diets is the isomerization of unsaturated fatty acids in edible oils during cooking. However, the information on the isomerization mechanism is very limited. In this paper, we used oleic acid, an unsaturated fatty acid, as a simplified model for edible oil and investigated the mechanism of cis/trans isomerization by computation and experiments. The computational results ...[more]

PMID: 30211332

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Project description:Synthesis and X-ray diffraction structures of cis and trans isomers of ruthenium and osmium metal complexes of general formulas (nBu4N)[cis-MCl4(NO)(Hind)], where M = Ru (1) and Os (3), and (nBu4N)[trans-MCl4(NO)(Hind)], where M = Ru (2) and Os (4) and Hind = 1H-indazole are reported. Interconversion between cis and trans isomers at high temperatures (80-130 °C) has been observed and studied by NMR spectroscopy. Kinetic data indicate that isomerizations correspond to reversible first order reactions. The rates of isomerization reactions even at 110 °C are very low with rate constants of 10(-5) s(-1) and 10(-6) s(-1) for ruthenium and osmium complexes, respectively, and the estimated rate constants of isomerization at room temperature are of ca. 10(-10) s(-1). The activation parameters, which have been obtained from fitting the reaction rates at different temperatures to the Eyring equation for ruthenium [?H(cis-trans)‡ = 122.8 ± 1.3; ?H(trans-cis)‡ = 138.8 ± 1.0 kJ/mol; ?S(cis-trans)‡ = -18.7 ± 3.6; ?S(trans-cis)‡ = 31.8 ± 2.7 J/(mol·K)] and osmium [?H(cis-trans)‡ = 200.7 ± 0.7; ?H(trans-cis)‡ = 168.2 ± 0.6 kJ/mol; ?S(cis-trans)‡ = 142.7 ± 8.9; ?S(trans-cis)‡ = 85.9 ± 3.9 J/(mol·K)] reflect the inertness of these systems. The entropy of activation for the osmium complexes is highly positive and suggests the dissociative mechanism of isomerization. In the case of ruthenium, the activation entropy for the cis to trans isomerization is negative [-18.6 J/(mol·K)], while being positive [31.0 J/(mol·K)] for the trans to cis conversion. The thermodynamic parameters for cis to trans isomerization of [RuCl4(NO)(Hind)]-, viz. ?H° = 13.5 ± 1.5 kJ/mol and ?S° = -5.2 ± 3.4 J/(mol·K) indicate the low difference between the energies of cis and trans isomers. The theoretical calculation has been carried out on isomerization of ruthenium complexes with DFT methods. The dissociative, associative, and intramolecular twist isomerization mechanisms have been considered. The value for the activation energy found for the dissociative mechanism is in good agreement with experimental activation enthalpy. Electrochemical investigation provides further evidence for higher reactivity of ruthenium complexes compared to that of osmium counterparts and shows that intramolecular electron transfer reactions do not affect the isomerization process. A dissociative mechanism of cis?trans isomerization has been proposed for both ruthenium and osmium complexes.

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Computational and experimental research on mechanism of cis/trans isomerization of oleic acid.

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Computational and experimental research on mechanism of cis/trans isomerization of oleic acid.

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