Trans Isomerization Of Double Bonds Research Articles

Antioxidant and anti-isomerization effects of sesamol and resveratrol on high oleic acid peanut oil

In the present study, the protective effects of sesamol and resveratrol on high oleic acid peanut oil were investigated. Different amounts of sesamol, resveratrol, and their combinations were added to the high oleic acid peanut oil to investigate the antioxidant effect and anti-isomerization effect to prevent cis to trans isomerization of double bonds. Rancimat results showed that the oil had the longest oxidation inducing time after adding 0.08% sesamol or 0.06% resveratrol (v/v). Thermogravimetric analysis suggested that when sesamol and resveratrol were added at 0.08% and 0.04% (v/v), the oxidation decomposition temperature was the highest. Schaal oven experiments indicated that the addition of sesamol and resveratrol could significantly reduce the peroxide content of high oleic acid peanut oil. The total fatty acid content in the oil samples increased significantly after high temperature treatment at 180 °C or 240 °C, and three new thermal isomerization trans products were measured (C18:1-9t, C18:2-9c,12t, C18:2-9t,12c). Meanwhile, the addition of sesamol (0.08%, v/v) or resveratrol (0.06%, v/v) significantly reduced the content of unsaturated fatty acid. For high oleic acid peanut oil heated to 180 °C, sesamol and resveratrol showed a better inhibitory effect on the production of trans-oleic acid than when heating at 240 °C.

Photoisomerization of fluorinated 1,3-dimethyl-5-propenyl uracils

The photo-induced cis / trans isomerization of double bonds in fluorinated derivatives of 1,3-dimethyl-5-propenyl uracils was investigated. The more sterically congested isomers were the major products in the observed photostationary states. The results of DFT calculations suggest that photo-induced cis / trans isomerization of this compounds can run through the formation of radical species, which are the transition states produced during photoexcitation. Preference of the formation of more sterically hindered isomers in photostationary state one can rationalize on the basis of the difference in oscillator strength and the role of equilibration between conformers s-cis / s-trans . ► Photo-induced cis / trans isomerization of fluorinated 1,3-dimethyl-5-propenyl uracils. ► DFT calculations suggest the formation of radical species as the transition states. ► The more sterically congested isomers were the major products in the photostationary states. ► Stereoselectivity is a result from the difference in oscillator strength and the role of s- cis / s-trans equilibration. We investigated the photo-induced cis / trans isomerization of double bonds in fluorinated derivatives of 1,3-dimethyl-5-propenyl uracils. When 1,3-dimethyl-5-( E -1,2,3,3,3-pentafluoropropenyl)uracil was irradiated by light λ > 300 nm, we obtained the photostationary state involving equilibration with 1,3-dimethyl-5-( Z -1,2,3,3,3-pentafluoropropenyl)uracil where the more sterically congested isomer Z was the major product ( E : Z = 1:1.5). Irradiation of Z isomer as the starting material also led to the identical photostationary state. In the case of 1,3-dimethyl-5-(1,3,3,3-tetrafluoropropenyl)uracil the more sterically congested isomer E was even more abundant ( Z : E = 1:7.5). The results of DFT calculations suggest that photo-induced cis / trans isomerization of these compounds can run through the formation of allylmethylene biradical species, which are the transition states produced during photoexcitation. Preference of the formation of more sterically hindered isomers in photostationary state one can rationalize on the basis of the difference in oscillator strength and the role of equilibration between conformers s-cis / s-trans .

Cis– trans isomerization of carbon double bonds in monounsaturated triacylglycerols via generation of free radicals

We investigated the heat-induced cis/ trans isomerization of double bonds in monounsaturated lipids. When triolein (9- cis, 18:1) was heated around 180 °C, small amounts of isomerization products were obtained depending on the heating period. The heat-induced isomerization of triolein was considerably suppressed by the addition of different antioxidants or under nitrogen stream, and these additives simultaneously inhibited the thermal oxidation of double bonds in triolein. Therefore, an intermediate of the thermal oxidation reaction might be responsible for the heat-induced isomerization of the double bonds in triolein. The thermodynamics of the heat-induced isomerization of triolein (9- cis, 18:1) and trielaidin (9- trans, 18:1) were investigated using Arrhenius plot. The Arrhenius activation energies of cis double bonds in triolein and trans double bonds in trielaidin were 106 kJ/mol and 137 kJ/mol, respectively. The calculated internal rotational barrier heights of these double bonds were similar to those of the double bond of 2-butene radical and significantly lower than those of non-radicalized double bonds in 2-butene. These results suggest that heat-induced cis/ trans isomerization of triolein and trielaidin occurs mainly through the formation of radical species, which are the intermediates produced during thermal oxidation. The activation energy difference between the two forms suggests that trans trielaidin radicals are more stable than cis triolein radicals. The high thermodynamic stability of the trans double bonds in lipid radicals would influence the population of cis and trans isomers in edible oils and contribute to slight accumulation of trans-18:1 isomers during heating or industrial processing.

Detection of trans-isomers of hydrocarbon residues of lipid molecules by IR absorption

IR spectroscopy is used for a comparative analysis of the trans-isomerization of double bonds in hydrocarbon residuals of lactic and hydrogenated lipids. The maximum of the absorption band of the trans-isomers for all the lipid samples is found to lie at 965 cm −1 . An absorption band at 970 cm −1 is discovered in the spectra of the lactic lipids near the analytic band of the trans-isomers at 965 cm −1 . Based on a gaussian approximation for their absorption spectral bands, the trans-isomer content in the lactic lipid samples is 10-11%. The absorption by lipid molecules at 970 cm −1 has to be taken into account when determining the trans-isomer content of fat and oil products.

The formation of alkyl and alkenyl methanesulfonates and their reduction to hydrocarbons

Methanesulfonates of saturated and unsaturated long-chain alcohols are conveniently obtained in good purity and high yields. They can be converted, quantitatively, to hydrocarbons by reduction with lithium aluminum hydride. The procedure is applicable to the preparation of alkanes and alkenes. cis, trans-Isomerization of double bonds does not occur.