Identification and classification of olive oils by high-resolution13C nuclear magnetic resonance

Unsaponifiable matter from 19 olive and olive pomace oils were studied by high-resolution¹³C nuclear magnetic resonance spectroscopy. Their spectra showed characteristic peaks that corresponded to molecular substructures rather than the individual constituents present in the unsaponifiable matter. The presence of squalene and other hydrocarbons, sterols and triterpenic alcohols, in addition to other groups of minor compounds, were observed. Based on the analysis of these spectra, it was possible to distinguish among different grades of olive oils by using stepwise discriminant analysis. This direct method of analysis is suggested to be used in artificial neural networks to define oil identity and quality.     

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.     

13C nuclear magnetic resonance characterization of the reaction products of lamb pregastric lipase-catalyzed hydrolysis of tributyrylglycerol

Lamb pregastric lipase (LPGL), extracted from the tongue root and epiglottis of suckling lamb, has been used to catalyze the hydrolysis of emulsified tributyrylglycerol. Reactions were generally carried out at 35°C and initial pH 7.0. The speciation of the products of the reaction has been examined by ¹³C nuclear magnetic resonance spectroscopy. Varying rates of reaction were produced by increasing the amount of enzyme added relative to the amount of lipid. A system rate parameter, ΔpH/Δt, which is the change in pH (ΔpH) from time zero to the time when the sample was removed (Δt), has been developed. 1,2(2,3)-Dibutyrylglycerol and 2-monobutyrylglycerol have been identified as products of LPGL-catalyzed hydrolysis, while 1,3-dibutyrylglycerol and 1(3)-monobutyrylglycerol are products of uncatalyzed acyl transfer reactions.     

Positional distribution of ω3 Fatty acids in marine lipid triacylglycerols by high-resolution13C nuclear magnetic resonance spectroscopy

The positional distribution [α(1,3)-acyl and ß(2)-acyl] of ω3 fatty acids [18:4(n-3), 20:4(n-3), 20:5(n-3), 22:5(n-3) and 22:6(n-3)] in depot fat of Atlantic salmon (Salmo salar), harp seal oil and cod liver oil triacylglycerols has been examined by¹³C nuclear magnetic resonance (NMR) spectroscopy. The positional distribution data can be defined from the spectrum of the carbonyl (C1 carbon) and the methylene (C2 and glyceryl carbon) regions. In depot fat of Atlantic salmon and cod liver oil, docosahexaenoic acid (DHA) was concentrated in the ß-position of the triacylglycerides with 72.6 and 74.4%, respectively. Only 3.2% of DHA and 4.6% of eicosapentaenoic acid (EPA) were esterified to the ß-position of the triacylglycerides in harp seal oil. EPA is nearly randomly distributed in cod liver oil and muscle lipids of Atlantic salmon, with 37.8 and 39.7%, respectively, in the ß-position. In general, the¹³C NMR-derived data were in accordance with corresponding data reported in the literature obtained by conventional techniques.     

Structure determination of long-chain polyunsaturated triacylgyycerols by high-resolution13C nuclear magnetic resonance

The application of¹³C nuclear magnetic resonance to determine the positional distribution of fatty acids on the glycerol backbone has been investigated. A systematic approach and synthetic triacylglycerols were used to measure the effect on the carbonyl chemical shifts of triacylglycerols by the positional distribution on the glycerol backbone and the number and position of the double bonds within the fatty acids. The correlation of¹³C carbonyl chemical shift to the molecular structure of triacylglycerol was delineated. The assignments for the chemical shifts of the carbonyl nuclei of monoacyltriacylglycerol standards were compiled. The resonance from the carbonyl carbons at the 1,3 positions is resolved from that at the 2 position. The¹³C carbonyl chemical shift was more dependent on the position of the double bonds than the degree of unsaturation of the fatty acids. In particular, little effect was observed in the chemical shifts for fatty acids containing more than two double bonds. However, the chemical shifts were influenced significantly by the position of the first double bond. The difference in the chemical shift of the unsaturated species from that of the saturated species was plotted against the position of the first double bond. A natural logarithmic relationship was found between carbon numbers 5 and 11. Inflection points were found outside of this region at carbon numbers 4 and 13. In addition, the resonances from the saturated species, independent of their chainlength, were degenerate in oil systems, even though small differences were observed in the standards. The applicability of this method was demonstrated in the determination of the composition and positional distribution of the fatty acids in borage and evening primrose oils.     

The composition of hydrogenated fats by high-resolution13C nuclear magnetic resonance spectroscopy

The high-resolution¹³C nuclear magnetic resonance spectra of twelve hydrogenated fats have been examined. Each spectrum contains 50–100 signals and reveals much about the nature of the acyl chains of both double-bond position and configuration. The signals for the ω1, ω2 and ω3 carbon atoms give information on thecis andtrans isomers of the Δ15, Δ14, Δ13 and Δ12 18:1 esters, respectively. Allylic signals distinguish betweencis andtrans esters, and the proportion of totalcis to totaltrans isomers can be obtained from these. Olefinic signals are the most informative, and most of these have been assigned. This leads to a semi-quantitative estimate of the various 18:1 isomers present. Assignments are based mainly on information already in the literature, but some were confirmed after urea fractionation of the acids from a hydrogenated oil in whichcis andtrans monoene acids were separately concentrated.     

Structural characterization of coal-hydrogenation products by proton and carbon-13 nuclear magnetic resonance

Heavy oil derived from coal hydrogenation was separated into saturated fractions, neutral aromatic oil, and asphaltene, and these materials were subsequently fractionated according to the magnitude of their respective molecular sizes by gel-permeation chromatography. These GPC subfractions were analysed by proton and carbon-13 n.m.r. spectroscopy and by an additional procedure using gas chromatography for the paraffinic GPC subfractions. ¹³C-n.m.r. spectra for the GPC subfraction of saturated material showed typical long straight-chain paraffin spectral patterns accompanied by iso-and cycloparaffinic carbon signals. The results from gas-chromatographic measurement for the paraffinic GPC subfractions agree fairly well with the trends of average carbon numbers and contents of straight-chain paraffins obtained by varying the fraction numbers, estimated from ¹³C-n.m.r. analyses. The ratios of aromatic carbon to total carbon (f_a) for aromatic oil and asphaltene GPC subfractions obtained directly from ¹³C-n.m.r. spectra are slightly lower than the results from the ¹H-n.m.r. method assuming x = y = 2 in the Brown—Ladner equation. Peak intensities of the respective carbon species in ¹³C-n.m.r. spectra were compared with the peak intensities of correspondingly bonded species obtained from ¹H-n.m.r. measurement. Some inadequacy was recognized in both measurements. It is assumed that there are two reasons for the discrepancy, one of which is the inaccuracy of ¹³C-n.m.r. results owing to the long relaxation times and the effect of Nuclear Overhauser Enhancement, and another is the application of unsuitable values of x and y for calculations from the Brown—Ladner equation. New analytical treatments for ¹³C-n.m.r. results in combination with ¹H-n.m.r. analyses are suggested in this study to avoid these uncertainties in structural analyses. From this procedure, it is believed that the actual contents of aromatic and aliphatic carbon and appropriate values of x and y can be derived.     

Structural characterization by 13C nuclear magnetic resonance of hydrolysed carboxymethylcellulose

Summary In order to characterize heavyweight carboxymethylcellulose (C.M.C) by ¹³C NMR it is necessary to hydrolysis them. This paper proposes and compares three different ways of degradation: acidic hydrolysis, sonication and enzymatic degradation. Acidic hydrolysis leads to poor results due to a strong alteration of the sample. Sonication gives quite good results but the enzymatic degradation is the most efficient method for degrading C.M.C under good conditions.After hydrolysis, the sample was analysed by ¹³C NMR and HPLC to obtain structural information such as substitution degree, preferential substitution sites and regularity of the substitution along the polymeric chain.     

Information on the composition of fats from their high-resolution13C nuclear magnetic resonance spectra

Based on the interpretation of the high-resolution¹³C nuclear magnetic resonance spectra of 15 spreading fats, baking fats, vegetable creams and an infant formula, it is possible to decide whether the sample contains butterfat, lauric oils, partially hydrogenated fat, linoleic acid or linolenic acid. The data have been interpreted in a semiquantitative manner, and this provides an insight into the nature of the material present in each sample.     

Hypothetical average structures of two coal liquid asphaltenes from solid state 13 C nuclear magnetic resonance and 1 H nuclear magnetic resonance data

The hypothetical average structures of two coal liquid asphaltenes were determined using solid state 13 C NMR and 1 H NMR data. From the 1 H NMR data average molecular structural parameters were obtained using the Brown-Ladner method to get a general average structure. From the solid state 13 C NMR data, estimations of percentages of tertiary and quaternary aromatic carbons and secondary/tertiary and primary/quaternary aliphatic carbons were made. The hypothetical average molecules obtained agreed closely with experimental results.     

1H and 13C nuclear magnetic resonance studies of the synthesis of linear segmented polyurethane elastomers

Linear segmented polyurethane elastomers have been prepared by reaction of polyethyleneoxide with 4,4′-diphenylmethanediisocyanate and the product was subsequently cured with diamines. Chemical analysis of the prepolymer formed using stoichiometric ratios of polyol and diisocyanate indicated that the product was deficient in ‘free’ isocyanate. A number of side reactions can lead to a reduction in the amount of isocyanate available for the chain extension reaction. Infrared, ¹H- and ¹³C-n.m.r. spectroscopy were used to follow the initial end-capping and subsequent chain extension reactions. In order that an unambiguous assignment of the weak peaks observed in the prepolymer and final elastomer spectra could be made, a number of model compounds associated with the side reactions were synthesized and their spectra characterized. It was concluded that the loss of ‘free’ isocyanate in the formation of the prepolymer can be predominantly attributed to the effects of traces of water in the initial reaction mixture.     

Chemical characterization of solid coals through magic-angle 13C nuclear magnetic resonance

Recently developed ¹³C n.m.r. techniques for high resolution in solids are applied to native coals. The quantity and distribution of hydroxyl groups in the samples are determined by combining chemical modification through acetylation with the n.m.r. measurements. Spectral subtraction isolates the reaction product resonances. Spectroscopic separation of protonated and non-protonated carbons through pulse programming techniques is also demonstrated. Finally, the susceptibility of the aliphatic carbons in coals to low-temperature oxidation is shown clearly by subtraction of spectra of the oxidized and unoxidized materials.     

Use of high-resolution 13C nuclear magnetic resonance spectroscopy for the screening of virgin olive oils

¹³C Nuclear magnetic resonance (NMR) spectra of 104 oil samples were obtained and analyzed in order to study the use of this technique for routine screening of virgin olive oils. The oils studied included the following: virgin olive oils from different cultivars and regions of Europe and north Africa, and refined olive, “lampante” olive, refined olive pomace, high-oleic sunflower, hazelnut, sunflower, corn, soybean, rapeseed, grapeseed, and peanut oils, as well as mixtures of virgin olive oils from different geographical origins and mixtures of 5–50% hazelnut oil in virgin olive oil. The analysis of the spectra allowed us to distinguish among virgin olive oils, oils with a high content of oleic acid, and oils with a high content of linoleic acid, by using stepwise discriminant analysis. This parametric method gave 97.1% correct validated classifications for the oils. In addition, it classified correctly all the hazelnut oil samples and the mixtures of hazelnut oil in virgin olive oil assayed. All of these results suggested that ¹³C NMR may be used satisfactorily for discriminating some specific groups of oils, but to obtain 100% correct classifications for the different oils and mixtures, more information than that obtained from the direct spectra of the oils is needed.     

Study of the artificial oxidation of a humic coal by 13C CP/MAS nuclear magnetic resonance

The cross-polarization/magic-angle spinning technique has been applied to obtain ¹³C n.m.r. spectra of samples produced by artificial oxidation of a type III humic coal of southern Utah. The oxygen is mainly incorporated in carboxylic acid and phenol functional groups. Results are confirmed by infra-red spectroscopy.     

Study of the characterization and curing of benzoxazines using 13C solid-state nuclear magnetic resonance

Benzoxazines derived from bisphenol-A, formaldehyde, and primary amines were characterized using ¹³C solid-state NMR spectroscopy. The two 1,3-benzoxazines studied in this work are 2,2′-(3-methyl-4-dihydro-1,3,2-benzoxazine)propane, ( B-m ) and 2,2′-(3-phenyl-4-dihydro-1,3,2-benzoxazine)propane ( B-a ). Solid-state ¹³C-NMR spectra were obtained for B-m and B-a and the observed peak positions were noted. These resonances agreed well with chemical shifts calculated based on the chemical structure. Samples of B-m and B-a were cured at two different temperatures: 150 and 200°C. The polymerizations induced spectral changes including new resonances, intensity changes, and line-width broadenings. Kinetic analysis of the curing data gave different kinetic parameters for the two cure temperatures, which is expected since the first cure temperature is below the material's glass transition temperature (T_g) while the second cure temperature is above the T_g. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1413–1425, 1998     

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.     

Physicochemical characterization of psychosine by 1H nuclear magnetic resonance and electron microscopy

Krabbe's disease is an autosomal recessive disease that affects the lysosomal enzyme galactosylceramidase. The storage of one of its substrates, psychosine (β-galactosylsphingosine), is thought to be responsible for the induction of pathological changes. Psychosine has a free amine group which is necessary for the mediation of its toxic effects. In the present study, the physicochemical properties of psychosine were investigated. Nuclear magnetic resonance (NMR) detected pH titration was used to determine that the amine group had a pKa of 7.18±0.05. Pulsed-field gradient NMR spectroscopy was used to determine that the diffusion coefficient of 2.8 mM psychosine in D₂O at pD 4.46 or 7.04 is 1.16±0.02×10⁻¹⁰ m²/s or 0.77±0.02×10⁻¹⁰ m²/s, respectively. Negative staining electron microscopy (EM) studies of acidic and neutral solutions of psychosine also were performed. At pH 4.5, spherical structures were formed, which were relatively stable between 3, 120, and 216 h following preparation; the diameter ranged from ∼14 nm at the earliest time point to ∼18 nm at the last time point. The critical micelle concentration (CMC) was 1.26 mM at pH 4.0. At pH 7.1, the structures changed from spherical structures with a diameter of 15–23 nm, at the earliest time point, to a heterogeneous population of structures ranging from spherical structures, with a diameter of only a few nm, to irregularly shaped oblong structures that had one or more dimensions exceeding 100 nm. The NMR and EM data indicate that the deprotonation of the amine group causes psychosine to form aggregates that are unstable, which prevents a determination of the CMC at a neutral pH. These data indicate that molecular interactions of psychosine at the acidic pH of the lysosome, where it is normally digested, are more orderly than those at the pH of the cytoplasm or extracellular space where psychosine goes during disease.     

Solid state 13C nuclear magnetic resonance of heavy oil/bitumen-derived solids

Solid state ¹³C n.m.r. analysis of the insoluble organic matter associated with the clay mineral, silica, and heavy metal minerals of heavy oils/bitumen is reported. The conditions under which these measurements can be made are related to the concentration of organic matter found, the nature and amount of paramagnetic constituents, and contact times. The data are related to changes in hydrophilic/hydrophobic surface properties of the solids. The relationship with bitumen losses in recovery processes is also discussed.     

Application of quantitative 13C nuclear magnetic resonance spectroscopy to coal-derived materials

The difficulties associated with obtaining quantitative results from ¹³C nuclear magnetic resonance spectroscopy are discussed. By careful choice of the experimental conditions quantitative results have been obtained for a mixture of model compounds, containing most of the types of carbon linkages present in coal-derived materials, and for an aromatic fraction of a coal extract.