Biolubricants Based on Epoxidized Vegetable Oils: A Review on Chemical Modifications, Tribological Properties, and Sustainability

Analysis of fatty acid epoxidation by high performance liquid chromatography coupled with evaporative light scattering detection and mass spectrometry

A new approach for epoxidation of fatty acids by a paired electrosynthesis

Recently discovered fungal unspecific peroxygenases from Marasmius rotula and Chaetomium globosum catalyze the epoxidation of unsaturated fatty acids (FA) and FA methyl esters (FAME), unlike the well‐known peroxygenases from Agrocybe aegerita and Coprinopsis cinerea. Reactions of a series of unsaturated FA and FAME with cis‐configuration revealed high (up to 100 %) substrate conversion and selectivity towards epoxidation, although some significant differences were observed between enzymes and substrates with the best results being obtained with the C. globosum enzyme. This and the M. rotula peroxygenase appear as promising biocatalysts for the environmentally‐friendly production of reactive FA epoxides given their self‐sufficient monooxygenase activity and the high conversion rate and epoxidation selectivity.

Hydrolase-catalysed synthesis of peroxycarboxylic acids: Biocatalytic promiscuity for practical applications

Detergent-solubilized and partially purified soybean peroxygenase was shown to actively catalyze, in the presence of alkylhydroperoxides as co-substrates, the epoxidation of mono- and polyunsaturated fatty acids such as oleic and linoleic acids. Octadecenoic acids were found to be better substrates than shorter mono-unsaturated fatty acids (C16:1 or C14:1), but the position of their double bond (at positions 6, 9, or 11) had little effect on the rates of epoxidation. The peroxygenase exhibits a strong stereospecificity since octadecenoic acids with double bonds in trans-configuration were not epoxidized at detectable rates. Oxidation of linoleic acid yielded the two positional monoepoxide isomers and, as the minor product, the diepoxide. An important regioselectivity was, however, observed in this case; i.e. the unsaturation at position 9,10 was epoxidized preferentially to that at 12, 13. Oxidation of oleic acid in the presence of 18O-labeled hydroperoxy-linoleic acid revealed an incorporation of about 80% of the label into the epoxide ring. Products similar to those formed by the peroxygenase by epoxidation of unsaturated free fatty acids such as linoleic acid have been described as important metabolites (leukotoxins) in the defense of plants, e.g. in fungal agressions. This aspect underlines the physiological relevance of this new and potent catalytic activity of the peroxygenase.

Hydroxylated fatty acids were synthesized by epoxidation of unsaturated fatty acids of waste food oil followed by hydrolysis by acylglycerol grouping and oxirane rings. The fatty acid aminoamides of the oils were synthesized by epoxidation of used fooding oil, followed by opening of the oxirane cycle and transamidation of acylglycerols with diethanolamine. The use of lithium soaps of hydroxyacids from waste food oil as an emulsifier-stabilizer, which acts as a lubricant thickener, and the introduction of fatty acid aminoamides of oils as an antioxidant additive into the composition of lubricants made it possible to obtain a plastic (lithium) lubricant. The physicochemical properties of lubricant were investigated and their quality indicators were compared with lubricant based on 12-hydroxystearic acid. The developed lithium lubricant is characterized by improved protective and tribological characteristics, increased stability to oxidation and mechanical stress, does not cause corrosion of non-ferrous metals, and is not inferior to lithium lubricant based on an industrial analog of 12-hydroxystearic acid. The lubricant is intended for friction units of machines and mechanisms. The properties of the resulting lubricant make it possible to predict its long service life in components and mechanisms and the prospects for using the components used in lubricant formulations. On the one hand, these studies make it possible to replace imported components for the production of lubricant thickeners, and on the other hand, to solve the problem of utilization of by-products of oil and fat production.

The immobilized enzyme lipase acts as an efficient, selective and durable catalyst in the direct transformation of unsaturated carboxylic acids to epoxides, which are used as chemical intermediates and bio-lubricants. Experimental data obtained from the epoxidation of a model molecule, oleic acid in a laboratory-scale isothermal batch reactor were critically evaluated and mathematically modelled in the most precise way. Several rival surface reaction mechanisms were proposed and rate equations based on these mechanisms were derived. The rate equations were implemented in a multiphase model for the laboratory-scale batch reactor and the kinetic and adsorption parameters included in the rate equations were estimated with non-linear regression analysis. Based on the parameter estimation statistics and chemical knowledge, the most plausible kinetic models for the chemo-enzymatic epoxidation of oleic acid on the immobilized lipase catalyst were selected. The best kinetic models gave a good reproduction of the experimental data. The models can be used to predict the performance of enzymatic epoxidation of unsaturated fatty acids.

Epoxidation of unsaturated fatty acids by a soluble cytochrome P-450-dependent system from Bacillus megaterium.

Vegetable oils have different unique properties owing to their unique chemical structure. Vegetable oils have a greater ability to lubricate and have higher viscosity indices. Therefore, they are being more closely examined as base oil for biolubricants and functional fluids. In spite of their many advantages, vegetable oils suffer from two major drawbacks of inadequate oxidative stability and poor low-temperature properties, which hinder their utilization as biolubricant base oils. Transforming alkene groups in fatty acids to other stable functional groups could improve the oxidative stability, whereas reducing structural uniformity of the oil by attaching alkyl side chains could improve the low-temperature performance. In that light, the epoxidation of unsaturated fatty acids is very interesting as it can provide diverse side chains arising from the mono- or di-epoxidation of the unsaturated fatty acid. Oxirane ring opening by an acid-catalyzed reaction with a suitable reagent provides interesting polyfunctional compounds.

Epoxidized vegetable oils present a viable substitute for polymers derived from petroleum. This research focuses on the impact of a process parameter on the epoxidation of palm stearin when zeolite ZSM-5 is used as a catalyst. This study synthesized peracetic acid as the oxidizing agent by combining hydrogen peroxide and acetic acid, adjusting molar ratios relative to palm stearin. The optimal relative conversion oxirane (RCO) percentage reached 43.06% at 70 °C, 200 rpm stirring speed, and 0.8 g of catalyst. The acetic acid to palm stearin molar ratio was 1:1, and the hydrogen peroxide to palm stearin ratio was 0.5:1. Both palm stearin and its epoxide derivative have been studied using Fourier-transform infrared spectroscopy, showing the appearance of an oxirane ring at a wavenumber of 1240 cm⁻¹. Kinetic modelling demonstrates that the simulation and experiment show a reasonable discrepancy, considering several assumptions that have been made. After 100 iterations, the reaction rate constant obtained as follows: =0.01 mol⋅L−1⋅min−1, = 1.85 mol⋅L−1⋅min−1, = 29.90 mol⋅L− 1⋅min− 1, and = 0.04 mol⋅L−1⋅min−1.

A unique cytochrome P-450-dependent fatty acid monooxygenase from Bacillus megaterium ATCC 14581 is strongly induced by phenobarbital (Narhi, L. O., and Fulco, A. J. (1982) J. Biol. Chem. 257, 2147-2150) and many other barbiturates (Kim, B.-H., and Fulco, A. J. (1983) Biochem. Biophys. Res. Commun. 116, 843-850). This monooxygenase has now been purified to homogeneity from pentobarbital-induced bacteria as a single polypeptide with a molecular weight of 119,000 +/- 5,000 daltons. In the presence of NADPH and O2, it can catalyze the oxygenation of long chain fatty acids without the aid of any other protein. The enzyme has a catalytic center activity of 4,600 nmol of fatty acid oxygenated per nmol of P-450 (the highest activity yet reported for a P-450-dependent monooxygenase) and also functions as a highly active cytochrome c reductase in the presence of NADPH. The purified holoenzyme is a soluble protein containing 40 mol % hydrophobic amino acid residues and 1 mol each of FAD and FMN/mol of heme. It is isolated and purified in the low spin form but is converted to the high spin form in the presence of long chain fatty acids. The enzyme, which catalyzes the omega-2 hydroxylation of saturated fatty acids and the hydroxylation and epoxidation of unsaturated fatty acids has its highest affinity (Km = 2 +/- 1 microM) for the C15 and C16 chain lengths.

While oat (Avena sativa) has long been known to produce epoxy fatty acids in seeds, synthesized by a peroxygenase pathway, the gene encoding the peroxygenase remains to be determined. Here we report identification of a peroxygenase cDNA AsPXG1 from developing seeds of oat. AsPXG1 is a small protein with 249 amino acids in length and contains conserved heme-binding residues and a calcium-binding motif. When expressed in Pichia pastoris and Escherichia coli, AsPXG1 catalyzes the strictly hydroperoxide-dependent epoxidation of unsaturated fatty acids. It prefers hydroperoxy-trienoic acids over hydroperoxy-dienoic acids as oxygen donors to oxidize a wide range of unsaturated fatty acids with cis double bonds. Oleic acid is the most preferred substrate. The acyl carrier substrate specificity assay showed phospholipid and acyl-CoA were not effective substrate forms for AsPXG1 and it could only use free fatty acid or fatty acid methyl esters as substrates. A second gene, AsLOX2, cloned from oat codes for a 9-lipoxygenase catalyzing the synthesis of 9-hydroperoxy-dienoic and 9-hydroperoxy-trienoic acids, respectively, when linoleic (18:2-9c,12c) and linolenic (18:3-9c,12c,15c) acids were used as substrates. The peroxygenase pathway was reconstituted in vitro using a mixture of AsPXG1 and AsLOX2 extracts from E. coli. Incubation of methyl oleate and linoleic acid or linolenic acid with the enzyme mixture produced methyl 9,10-epoxy stearate. Incubation of linoleic acid alone with a mixture of AsPXG1 and AsLOX2 produced two major epoxy fatty acids, 9,10-epoxy-12-cis-octadecenoic acid and 12,13-epoxy-9-cis-octadecenoic acid, and a minor epoxy fatty acid, probably 12,13-epoxy-9-hydroxy-10-transoctadecenoic acid. AsPXG1 predominately catalyzes intermolecular peroxygenation.

A study was made of the epoxidation of octadecenoic acids with peroxybenzoic acid in benzene. Activation energies, frequency factors, enthalpies of activation, entropies of activation, and free energies of activation were obtained for the following fatty acids: cis‐9‐octadecenoic acid (oleic), trans‐9‐octadecenoic acid (elaidic), 12‐hydroxy‐cis‐9‐octadecenoic acid (ricinoleic), 12‐hydroxy‐trans‐9‐octadecenoic acid (ricinelaidic), cis‐11‐octadecenoic acid (vaccenic), and cis‐6‐octadecenoic acid (petroselinic). It was observed that the reaction rate was adversely affected by the proximity of the carboxyl group, that is, the closer the carboxyl to the reaction site the lower the rate. A shift from a trans to a cis configuration results in an approximate 50% increase in reaction rate with a corresponding decrease in free energy of activation of 260 cal/mol. The effects of isomerism and the replacement of substituent groups on the reaction rate were generally additive. A mechanism for the peroxydation of octadecenoic acids is proposed.

In plants, epoxygenated fatty acids (EFAs) are constituents of oil seeds as well as defence molecules and components of biopolymers (cutin, suberin). While the pleiotropic biological activities of mammalian EFAs have been well documented, there is a paucity of information on the physiological relevance of plant EFAs and their biosynthesis. Potential candidates for EFA formation are caleosin-type peroxygenases which catalyze the epoxidation of unsaturated fatty acids in the presence of hydroperoxides as co-oxidants. However, the caleosins characterized so far, which are mostly localized in seeds, are poor epoxidases. In sharp contrast, quantitative RT-PCR analysis revealed that PXG4, a class II caleosin gene, is expressed in roots, stems, leaves and flowers of Arabidopsis. Expressed in yeast, PXG4 encodes a calcium-dependent membrane-associated hemoprotein able to catalyze typical peroxygenase reactions. Moreover, we show here that purified recombinant PXG4 is an efficient fatty acid epoxygenase, catalyzing the oxidation of cis double bonds of unsaturated fatty acids. Physiological linoleic and linolenic acids proved to be the preferred substrates for PXG4; they are oxidized into the different positional isomers of the monoepoxides and into diepoxides. An important regioselectivity was observed; the C-12,13 double bond of these unsaturated fatty acids being the least favored unsaturation epoxidized by PXG4, linolenic acid preferentially yielded the 9,10-15,16-diepoxide. Remarkably, PXG4 catalyzes exclusively the formation of (R),(S)-epoxide enantiomers, which is the absolute stereochemistry of the epoxides found in planta. These findings pave the way for the study of the functional role of EFAs and caleosins in plants.

Molybdenum complex-catalysed epoxidation of unsaturated fatty acids by organic hydroperoxides