Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy

High-resolution nuclear magnetic resonance (NMR) spectroscopy provides useful data for analyzing fatty acid compositions of edible vegetable oils. Quantitation of each fatty acid was carried out by evaluation of particular peaks. According to the ¹H NMR method, terminal methyl protons, divinyl protons, and allyl protons are useful to calculate linolenic acid, linoleic acid, and oleic acid, respectively. The ω-2 carbon, divinyl carbon, and allylic carbons were used for calculation of these acids by the ¹³C NMR method. Compositional results obtained by NMR coincided well with those of the conventional gas chromatography (GC) method. Results from ¹³C NMR were in better agreement with those from GC than were the results obtained by the ¹H NMR method.     

Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy

High-resolution nuclear magnetic resonance (NMR) spectroscopy provides useful data for analyzing fatty acid compositions of edible vegetable oils. Quantitation of each fatty acid was carried out by evaluation of particular peaks. According to the ¹H NMR method, terminal methyl protons, divinyl protons, and allyl protons are useful to calculate linolenic acid, linoleic acid, and oleic acid, respectively. The ω-2 carbon, divinyl carbon, and allylic carbons were used for calculation of these acids by the ¹³C NMR method. Compositional results obtained by NMR coincided well with those of the conventional gas chromatography (GC) method. Results from ¹³C NMR were in better agreement with those from GC than were the results obtained by the ¹H NMR method.     

Synthesis and spectroscopic properties of long-chain aza,aziridine and azetidine fatty esters

Reaction of 1-mesyloxynonane with methyl 8-aminooctanoate gives methyl 9-azastearate (I, 20%); treatment of methyl 9(10),10(9)-azidohydroxyoctadecanoate and methyl 10-azido-12-hydroxyoctadecanoate with triphenylphosphine furnishes the corresponding aziridine derivative (II, 75%) and two geometric azetidine isomers (IIIa and IIIb, 37%), respectively. The aza function in compound I, the aziridine nucleus in compound II and the azetidine system in compounds IIIa, IIIb were characterized by¹H nuclear magnetic resonance (NMR) and¹³C NMR spectral analysis. The infrared spectral analyses of compounds (I), (II) and (IIIa,IIIb) showed characteristic absorption bands at 3200–3300 cm⁻¹ for the N-H stretching vibration.     

The effect of fatty acid composition on the acrylation kinetics of epoxidized triacylglycerols

Epoxidized oils, epoxidized triacylglycerols, and epoxidized fatty acid methyl esters were made by reaction with performic acid formed in situ. The extent of epoxidation was ca. 95% for all of the epoxidized samples, as determined by ¹H nuclear magnetic resonance. The epoxidized samples were reacted with an excess of acrylic acid for different reaction times. The acrylation reaction was found to have a first-order dependence on the epoxide concentration for all oils, pure triacylglycerols, and fatty acid methyl esters. However, the rate constant of acrylation was found to depend on the composition of the epoxidized material. The acrylation rate constant for 9,10-epoxystearic acid was 96 L²/(mol²·min). The rate constant of acrylation for the epoxides on 9,10,12,13-diepoxystearic acid was 60 L²/(mol²·min). The acrylation rate constant for the epoxides on 9,10,12,13,15,16-triepoxystearic acid was 50 L²/(mol²·min). Thus, the rate constant of acrylation increased as the number of epoxides per fotty acid decreased. Multiple epoxides per fatty acid decrease the reactivity of the epoxides because of steric hindrance effects, and the oxonium ion, formed as an intermediate during the epoxyacrylic acid reaction, is stabilized by local epoxide groups. These results were used to derive an acrylation kinetic model that predicts rate constants from fatty acid distributions in the oil. The predictions of the model closely match the experimentally determined rate constants.     

Synthesis of dimer and oligomers from (R)-methyl hydnocarpate

We report synthesis and characterization of dimer and oligomer acids from chaulmoogra oil. (R)-Methyl hydnocarpate (methyl ester of the major fatty acid component of chaulmoogra oil) was brominated to give threo-2,3-dibromocyclopentane-1-methyl undecanoate. Formation of two diastereoisomers, viz., threo-2(R),3(R)-dibromocyclopentane-1(R)-methyl undecanoate and threo-2(S),3(S)-dibromocyclopentane-(R)-1-methyl undecanoate, was observed. Dehydrobromination of bromo derivatives using alcoholic KOH gave a cyclopentadiene derivative as intermediate, which underwent Diels-Alder reaction to give dimer and oligomer fatty acids. The products were characterized by ultraviolet, direct exposure probe-mass spectroscopy, ¹H nuclear magnetic resonance (NMR), and ¹³C NMR spectroscopic techniques.     

C NMR study on structure, composition and curing behavior of phenol-urea-formaldehyde resole resins

Phenol-urea-formaldehyde (PUF) resole resins were synthesized and analyzed by both liquid and solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy. The liquid ¹³C NMR analysis indicated that the co-condensation reactions between the phenolic ring and the urea unit occurred during the synthesis of the resins. The addition of the urea component effectively reduced the free formaldehyde content in the resin systems. Methylene ether bridges in the resins were found to be mainly associated with the urea units. pH had significant influences on the structure and composition of the resins. Solid-state ¹³C NMR measurements of the cured resins suggested that the pH probably affected the curing mechanism. A longer time and a higher temperature can generally accelerate the curing process and increase the rigidity of the cured network.     

Identification of cyclopentenyl fatty acids by 1H and 13C nuclear magnetic resonance

Gorlic, chaulmoogric and hydnocarpic fatty acids, specific to the seed oil of the genus Hydnocarpus sp. (Flacourtiaceae), are determined only with difficulty by gas chromatography. These fatty acids were isolated in their methyl ester form by a combination of different chromatographic techniques (thin-layer chromatography/Ag⁺ and high-pressure liquid chromatography). The proton and carbon nuclear magnetic resonance analysis of these fatty acid methyl esters showed some characteristic signals of the cyclopentenyl ring. The presence of these signals in the proton and/or carbon nuclear magnetic resonance spectrum of an oil thus will allow us to confirm the presence of these cyclopentenyl fatty acids in lipids.     

Quantitative analysis of partial acylglycerols and free fatty acids in palm oil by 13C nuclear magnetic resonance spectroscopy

The chemical shifts, spin-lattice relaxation times (T ₁), and one-bond C−H coupling constants of the glycerol carbons of mono-, di-, and triacylglycerols in CDCI₃ solution are presented and discussed. The glycerol carbons have low T ₁ values (<1.0 s) and full nuclear Overhauser effect and also exhibit broader linewidths than the aliphatic carbons, suggesting that the glycerol carbons are at or near the T ₁ minimum for the dipole-dipole relaxation mechanism. Therefore, for quantitative measurement of the composition of partial acylglycerols (relative to the triacylglycerols) in palm oil, the nuclear magnetic resonance (NMR) spectrum of the β-carbons, which lie exclusively in the region δ68.3–72.1 ppm, should preferably be acquired at medium or low magnetic fields and at an elevated temperature in order to ensure that the condition for extremely narrow spectral lines is satisfied. The chemical shifts and spinlattice relaxation times of the aliphatic C-2 and C-3 carbons and of the carbonyl carbons (C-1) of acyl groups present in palm oil are also presented and discussed. The presence of free fatty acid in the palm oil is easily detected and quantified in the spectrum of the aliphatic carbons. The presence of partial acylglycerols in palm oil can also be detected and/or quantified in the NMR spectra of the C-2 and the carbonyl carbons. The quantitative analysis of the glycerol carbons of a known mixture of acylglycerols obtained by using this method is presented.     

Synthesis of triglyceride estolides from lesquerella and castor oils

Triglyceride (TG) estolides were synthesized from the hydroxy moieties of lesquerella and castor oils with oleic acid. Complete esterification of the hydroxy oils was possible when a slight excess of oleic acid was employed (1 to 1.5 mole equivalents). The estolides could be formed in the absence of catalyst at 175 to 250°C under vacuum or a nitrogen atmosphere. The optimal reaction conditions were found to be under vacuum at 200°C for 12 h for lesquerella and 24 h for castor oil. The lesquerella esterification reaction was completed in half the time of the for castor and with lower equivalents of oleic acid due to the difunctional hydroxy nature of lesquerella TG compared to the trifunctional nature of castor TG. Interesterification or dehydration of the resulting estolides to conjugated FA was not a significant side reaction, with only a slight amount of dehydration occurring at the highest temperature studied, 250°C. Use of a mineral-or Lewis-acid catalyst increased the rate of TG-estolide formation at 75°C but resulted in the formation of a dark oil, and the reaction did not go to completion in 24 h. Estolide numbers (i.e., degree of estolide formation) for the reaction and characterization of the products were made by ¹H NMR and ¹³C NMR. The decrease in the hydroxy methine signal at 3.55 ppm was used to quantify the degree of esterification by comparing this integral to the integral of the alpha methylene protons on the glycerine at 4.28 and 4.13 ppm.     

Synthesis of cis-12, 13-epoxy-cis-9-octadecenol and 12(13)-hydroxy-cis-9-octadecenol from vernonia oil using lithium aluminum hydride

Reduction of vernonia oil methyl esters (VOME) into epoxy fatty alcohol and diols was achieved with lithium aluminum hydride (LAH), under reflux and room temperature conditions, by using hexane and tetrahydrofuran (THF) as solvents. The reactions of VOME with LAH in hexane produced cis-12,13-epoxy-cis-9-octadecenol as a major product with an isolated yield of 73.6%, whereas the reaction with LAH in THF gave isomers of 12(13)-hydroxy-cis-9-octadecenol as the major products with an isolated yield of 95.1%. LAH was similarly reacted with vernonia oil (VO) to give the same products in lower yields. ¹H nuclear magnetic resonance (NMR), ¹³C NMR, gas chromatography-mass spectrometry, and infrared were used to characterize these products. This study demonstrates the ability to control the reactivity of the epoxy functionality in VO or VOME with the choice of polar or nonpolar solvents, and extends the range of oleochemicals that can be derived from vernonia oil.     

Occurrence of conjugated fatty acids in the seed oil ofcouepia longipendula (chrysobalanaceae)

The seeds ofCouepia longipendula contain 74.2% oil. Gas chromatography (GC) and gas chromatography/ mass spectrometry (GC/MS) of the methyl esters and oxazoline derivatives of the fatty acids and ultraviolet (UV), infrared (IR),¹H-nuclear magnetic resonance (NMR) and¹³C-NMR spectra of the oil showed the presence of palmitic (25.2%), palmitoleic (0.9%), stearic (6.2%), oleic (26.5%), vaccenic (0.4%), linoleic (7.4%), arachidic (0.3%), α-eleostearic (11.3%) and α-licanic (21.8%) acids. Licanic acid methyl ester was isolated by thin-layer chromatography (TLC) and the¹³C-NMR and¹H-NMR data are presented.     

Off-line coupling of high-performance liquid chromatography and 1H nuclear magnetic resonance for the identification of filbertone in hazelnut oil

A new procedure is presented for off-line coupling of high-performance liquid chromatography and proton nuclear magnetic resonance spectroscopy (¹H NMR) in hazelnut oil analysis. The optimization of some parameters affecting both the liquid chromatography preseparation step and the effective multiple-solvent suppression required for the NMR study enabled us to determine the presence in a hazelnut oil of (E)-5-methyl-hept-2-en-4-one (filbertone), a marker previously proposed to detect the adulteration of olive oil with hazelnut oil. The described procedure requires the filtration of the oil prior to its introduction into the chromatographic system and combines the advantages of providing sufficient sensitivity and selectivity with simple methodology and reduced sample handling.     

Determination of cyclopropenoid fatty acids inSterculia seed oils from senegal

Seed oils ofSterculia tomentosa andS. tragacantha (Sterculiaceae) were found to contain malvalic (5.8 and 5.1%), sterculic (11.3 and 30.2%) and dihydrosterculic (0.9 and 0.5%) acids. The total amount of these two cyclopropenoid fatty acids was established by¹H nuclear magnetic resonance and their cooccurrence by gas chromatography. Besides these unusual compounds, the main common fatty acids were palmitic (20 and 24%), oleic (21 and 15%) and linoleic (30 and 16%) acids.     

The triglyceride composition,structure, and presence of estolides in the oils ofLesquerella and related species

Members of the genusLesquerella, native to North America, have oils containing large amounts of hydroxy fatty acids and are under investigation as potential new crops. The triglyceride structure of oils from twenty-fiveLesquerella species in the seed collection at our research center has been examined after being hydrolysis-catalyzed by reverse micellar-encapsulated lipase and alcoholysis-catalyzed by immobilized lipase. These reactions, when coupled with supercritical-fluid chromatographic analysis, provide a powerful, labor-saving method for oil triglyceride analysis. A comprehensive analysis of overall fatty acid composition of these oils has been conducted as well.Lesquerella oils (along with oils from two other Brassicaceae:Physaria floribunda andHeliophilia amplexicaulis) have been grouped into five categories: densipolic acid-rich (Class I); auricolic acid-rich (Class II); lesquerolic acid-rich (Class III); an oil containing a mixture of hydroxy acids (Class IV); and lesquerolic and erucic acid-rich (Class V). The majority of Class I and II triglycerides contain one or two monoestolides at the 1- and 3-glycerol positions and a C₁₈ polyunsaturated acyl group at the 2-position. Most Class III and IV oil triglycerides contain one or two hydroxy acids at the 1- and 3-positions and C₁₈ unsaturated acid at the 2-position. A few of the Class III oils have trace amounts of estolides. The Class V oil triglycerides are mostly pentaacyl triglycerides and contain monestolide and small amounts of diestolide. Our triglyceride structure assignments were supported by¹H nuclear magnetic resonance data and mass balances.     

Quantitative high-resolution13C and1H nuclear magnetic resonance of ω3 fatty acids from white muscle of atlantic salmon (Salmo salar)

High-resolution¹³C nuclear magnetic resonance (NMR) spectra have been obtained and used to define the ω3 (n-3) fatty acid distribution in lipid extract and white muscle from Atlantic salmon (Salmo salar). The¹³C spectrum of lipid extracted from muscle gives quantitative information about the individual n-3 fatty acids, 18:2n-6, 20:1/22:1 and groups of fatty acids. The quantitative data compare favorably with those obtained by gas-liquid chromatography. The¹H NMR spectrum of the lipid extract gives information about the amount of 22:6n-3 and the total content of n-3 fatty acids. The¹³C NMR technique also revealed the positional distribution (1,3- and 2-acyl) of the important 20:5n-3 and 22:6n-3 acids in the triacylglycerol molecules. In the quantitative¹³C NMR spectrum of white muscle, the methyl region of the acyl chains of triacylglycerols gave rise to sufficiently resolved signals to permit estimation of the total concentration of lipids and the n-3 fatty acid content. The NMR data are in good agreement with corresponding data obtained by traditional methods.     

Rapid determination of iodine value by 1H nuclear magnetic resonance spectroscopy

High-resolution ¹H nuclear magnetic resonance (¹H NMR) has been found to be an effective tool for the direct, rapid, and automated determination of the iodine value (IV) of vegetable oils, including hydrogenated oils (IV=45.9–140.2). The total time required to obtain the ¹H NMR data is about 3 min per sample. The IV is calculated from the number of double-bonded protons and the average molecular weight derived directly from the spectrum. The average of olefinic protons and allylic plus divinyl protons area was used to calculate the absolute number of double-bonded protons. The ¹H NMR results were compared with those obtained by the traditional Wijs-cyclohexane methods. The correlation coefficient between traditional IV and the novel ¹H NMR method was r ²=0.9994 for the regression equation Y=0.9885X + 2.8084, where X was the result given by the traditional method. With the proposed regression equation, IV calculated by the ¹H NMR method was within an error of ± 1 unit of the result obtained by the traditional method. The proposed method is practically viable if one can afford to have the NMR system.     

Carbonization mechanisms resulting from intumescence association with the ammonium polyphosphate-pentaerythritol fire retardant system

In this work we study the thermal behavior of an ammonium polyphosphate-pentaerythritol mixture, fire-retardant additive for polyolefins and most particularly the carbonization process resulting from an intumescent phenomenon. The study has been carried out using Micro-Raman and ¹³C, ¹H, ³¹P NMR of the solid state spectroscopies. It is shown that the structure consists in phoscarbonaceous and polyaromatic species. These latter form an anisotropic structure above 280°C. This structure grows when the temperature increases. Finally, a reactional scheme of the carbonization of the intumescent system is proposed.     

Correlations between SARA fractions and physicochemical properties with H NMR spectra of vacuum residues from Colombian crude oils

Areas of resonance signals present in 12 frequency bins of the ¹H NMR spectra of the vacuum residues of five Colombian crudes and a blend were correlated with their SARA components and some physicochemical properties. The residues studied were obtained from light paraffinic to heavy aromatic Colombian crudes. Correlations between the NMR spectra and properties were obtained with partial least square PLS and multiple linear regression MLR. Prediction models for SARA obtained by PLS had R² > 0.97 while CV − q² was between 0.92 and 0.99. Models obtained with MLR for SARA showed a high for the first three components and a lower one for asphaltene. The R² of the prediction models for density, API Gravity, S, N, Ni ppm and wax %m content plus nC5- and -C7 insolubles were >0.988 while CV − q² was between 0.87 and 0.99. The proposed correlation methods are fast and less costly than the conventional ones.     

Use of 13C nuclear magnetic resonance distortionless enhancement by polarization transfer pulse sequence and multivariate analysis to discriminate olive oil cultivars

Distortionless enhancement by polarization transfer (DEPT) pulse sequence was used to set up a quantitative high-resolution ¹³C nuclear magnetic resonance (NMR) method to discriminate olive oils by cultivars and geographical origin. DEPT pulse sequence enhances the intensity of NMR signals from nuclei of low magnetogyric ratio. The nuclear spin polarization is transferred from spins with large Boltzmann population differences (usually protons) to nuclear species characterized by low Boltzmann factors, e.g., ¹³C. The signal enhancement of ¹³C spectra ensures the accuracy of resonance integration, which is a major task when the resonance intensities of different spectra must be compared. The resonances of triglyceride acyl chains C _n:0, C_18:1, C_18:2, and C_18:3, were also assigned. Multivariate analysis was carried out on the 35 carbon signals obtained. By using variable reduction techniques, coupled with standard statistical methods—partial least squares and principal components analysis—it was largely possible to separate the samples according to their variety and region of origin. With one problem variety removed, 100% prediction of the three remaining varieties was achieved. Similarly, by using the three regions with greatest representation in the data, all but one of a test set of 34 samples were correctly predicted. Thus, the composition of olive oils from different cultivars and of different geographical origin were compared and successfully studied by multivariate analysis. These considerations in conjunction with the structural elucidations of triglyceride molecules demonstrated that ¹³C NMR is among the most powerful techniques yet described for analysis of olive oils.     

Sequence analysis of poly(ethylene/1,4-cyclohexanedimethylene terephthalate) copolymer using H and C NMR

The triad-level sequence analysis of poly(ethylene/1,4-cyclohexanedimethylene terephthalate) copolymer was reported in a solvent system of o-chlorophenol/deuterated chloroform mixture (50/50 v/v) at 80 °C using 600 MHz ¹H NMR. The well-resolved alcoholic CH₂ proton peak of the glycol units was observed, which made the detailed sequence analysis possible. The peaks of the cis- and trans-forms of the 1,4-cyclohexanedimethylene glycol units were split into the triad sequence in the chain and could be assigned by a comparison of the spectra with those of homopolymers and by an additional two-dimensional heteronuclear multiple bond correlation observation. The triad sequence distributions centered on 1,4-cyclohexanedimethylene glycol units were determined, which was independent of the cis- and trans-forms of the units and controlled according to Bernoullian statistics.