Quantitative 13C Nuclear Magnetic Resonance Research Articles

Distribution of Phospholipids and Triglycerides in Multivesicular Lipid Particles

The distribution of phospholipid and triglyceride molecules in themembranes forming the nonconcentric vesicular network within a multivesicular lipid particle (MLP) and its precursors was investigated. MLP formulations afford controlled release of encapsulated pharmaceuticals over a time period ranging from a few days to a few weeks. The formation of MLP requires the use of a double emulsification process and a neutral lipid such as a triglyceride. MLP formulations with the antineoplastic agent cytarabine encapsulated in the aqueous compartments were prepared that further contained [13C]carbonyl-enriched triolein, and quantitative 13C nuclear magnetic resonance (NMR) experiments were performed to quantitate membrane-soluble and bulk triglyceride. In the NMR spectra of MLP, components attributable to triolein residing in a location similar to that of bilayer phospholipid were not observed. Spectral components attributable to triolein in a liquid-like phase were observed, and the intensity of these components accounted for the triolein present in the sample. Laser scanning confocal microscopy with two phospholipid fluorescent probes, RhodamineDHPE and NBD-PG, and a triglyceride fluorescent probe, BodipyTriglyceride, was used to visualize the distribution of the lipid components in the emulsion precursors of MLP and in MLP themselves with cytarabine, amikacin, morphine, or sucrose encapsulated within the aqueous phases. The confocal micrographs revealed a uniform distribution of the two phospholipid probes in the plane of the membrane, whereas the triglyceride probe accumulated at discrete locations. The NMR and microscopy results are consistent with a structural model for MLP in which triolein acts as a hydrophobic space filler at bilayer intersection points and stabilizes these junctions, and is also present as oil droplets dispersed in the encapsulated aqueous compartments. The experimental approach presented here could provide a rational approach to the development of MLP formulations with variable rates of sustained release, modulated by changes in the distribution of various phospholipids and triglycerides.

Monitoring Biomacromolecular degradation of Calluna Vulgaris in a 23 year field experiment using solid state 13C-NMR and pyrolysis-GC/MS

The qualitative and quantitative changes in lignin, polysaccharide, aliphatic, cutin and protein biomacromolecules in Calluna vulgaris shoots collected at three intervals (initial 0.5 y, 7 y and 23 y) in a field decomposition experiment have been investigated using quantitative solid state 13C nuclear magnetic resonance (NMR) spectroscopy and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Protein showed rapid decomposition with virtually none remaining after 7 y. The absolute weight losses of the other macromolecules after 23 y in the field show the sequence: polysaccharides>aliphatics/cutin>lignin. However, relative decomposition rates varied significantly during each interval, with polysaccharides and aliphatic/cutin being the highest in the first and second intervals, respectively, and polysaccharides being the lowest in the final interval. Py-GC/MS provided evidence that part of the remaining polysaccharides in the 23 y decomposed litter can be attributed to microbial production. Degradation of lignin is shown as progressive oxidation of alcoholic functions into the corresponding ketones or aldehydes and preferential degradation of syringyl over guaiacyl moieties. An unusual preferential removal of p-coumaric acid units over syringyl and guaiacyl units was observed, probably due to selective hydrolysis of its ester bond with lignin moieties either enzymatically by specific microorganisms or chemically. The specific soil environment with its low temperature, high rainfall and high acidity appears to limit microbial activities and leads to accumulation of carbon below ground.

Comonomer sequence assignment of the 13C n.m.r. spectra of some poly(epichlorohydrin) derivaties obtained by nucleophilic substitution

Poly(epichlorohydrin) [poly(oxy-1-chloro-methylethylene)] (PECH) has been modified chemically by basic nucleophiles, such as phenolate, producing dehydrochlorination as side reaction. The comonomer composition of the resulting poly(oxy-1-chloromethylethylene- co-oxy-1-phenoxymethyl-ethylene- co-oxy-1-methyleneethylene) can be determined by quantitative 13C nuclear magnetic resonance (n.m.r.) spectroscopy. Some polymeric models were synthesized in order to make accurate assignments, since most of the signals were not completely resolved. The various 13C n.m.r. signals were assigned to comonomer sequences in the main chain, which were fitted to a Bernouillian statistical model.

Improvement in the determination of triad distributions in ethylene-propylene copolymers by 13C nuclear magnetic resonance

A quantitative 13C nuclear magnetic resonance analysis of an ethylene—propylene copolymer produced on a modern high-field instrument produces a spectrum with eight discrete groups of peaks. Assignment of these peaks provides eight simultaneous equations to describe the six triad distribution numbers. We have demonstrated the advantages of solving directly this over-determined set of equations. We have observed that the relative uncertainty in the different triad numbers is approximately constant, and have used this observation to discuss the uncertainties in individual triad numbers as a function of their concentration.

Quantitative high-resolution 13C nuclear magnetic resonance of anserine and lactate in white muscle of Atlantic salmon (Salmo salar)

Quantitative 13C nuclear magnetic resonance (NMR) spectra of minced white muscle of Atlantic salmon (Salmo salar) were obtained without chemical pretreatment of the sample. The carbon in the metabolites anserine and lactate gave rise to sufficiently resolved signals in the 13C spectrum to permit estimation of the total concentration of these muscle constituents. The NMR data are in good agreement with corresponding data reported in the literature obtained by conventional methods, indicating that all of these metabolites are NMR visible. Information about the muscle pH was obtained from the pH-dependent 13C chemical shift of C14 and C16 in the histidine ring of anserine. Well-resolved 13C NMR spectra obtained from intact muscle of Atlantic salmon demonstrate that NMR will be a useful method to study postmortem changes occurring during storage of fish.

Characterization of hydrogenated derivatives of methyl- and dimethyldicyclopentadiene isomers by gas chromatography–mass spectrometry and carbon-13 nuclear magnetic resonance spectroscopy

The identification of the di- and tetrahydrogenated derivatives of methyl- and dimethyldicyclopentadiene isomers has been performed directly in the hydrogenated mixtures, by comparing the results from the gas chromatography–mass spectrometric mass balance with those from quantitative 13C nuclear magnetic resonance spectra. The assignment of the carbons of these isomers has been realized by analysing data from J-modulated spin-echo sequences and by applying semi-empirical rules for the influence of the methyl groups on the carbon chemical shifts in cyclopentane and norbornane ring systems.

Quantitative determination of castor oil in edible and heat‐abused oils by13C nuclear magnetic resonance spectroscopy

AbstractApplication of13C nuclear magnetic resonance (NMR) spectroscopy for detection of castor oil (CO) in various edible oils, such as coconut oil, palm oil, groundnut oil and mustard oil, is described. Characteristic signals observed at δ 132.4, δ 125.6, δ 71.3, δ 36.8 and δ 35.4 ppm, due to C10, C9, C12, C13 and C11 carbons of ricinoleic acid (RA) in CO, were selected for distinguishing it from edible oils. Quantitative13C NMR spectra of oils were recorded in CDCl3 with a gated decoupling technique. The minimum detection limits for qualitative and quantitative analyses were 2.0 and 3.0%, respectively. The proposed method is simple, nondestructive and requires no sample pretreatment. Its application to heat‐abused oils has also been demonstrated successfully without any of the interferences observed in most other methods.

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

AbstractHigh‐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.

Detection of [U‐13C]eicosapentaenoic acid in rat liver lipids using13C nuclear magnetic resonance spectroscopy

Fatty acid carbons are well-resolved in 13C nuclear magnetic resonance (NMR) spectra of lipid extracts, but application of this methodology to the metabolism of 13C-labelled fatty acids has not yet been reported. In the present study, 13C NMR was used to monitor the presence of 98% [U-13C]eicosapentaenoic acid (EPA) in liver and carcass lipids 24 h after it had been injected into the stomach of a rat. Natural abundance 13C NMR spectra of liver total fatty acid extracts were obtained from four control rats for comparison. At 24 h post-injection, quantitative high resolution 13C NMR showed 13C enrichment in liver fatty acid extracts was present mainly at olefinic and at the n-1 to n-4 carbons, but 13C signal intensities for C-1 to C-4 of [U-13C]EPA were markedly reduced or absent. Small 13C resonances, possibly indicative of some 13C incorporation into docosahexaenoic acid and saturated or monounsaturated fatty acids, were present in spectra of liver fatty acids. Liver and carcass fatty acid composition was similar in both the controls and the EPA-injected rat, suggesting little accumulation of the injected [U-13C]EPA after 24 h. We conclude that the carbon-specific data provided by 13C NMR of lipid extracts may be useful in monitoring the fate of individual carbons during tracer studies using 13C-labelled fatty acids.

Determination of C-7 Isomer Distribution in Commercial Feedstocks by GC-Matrix Isolation-FT-IR-MS

Two mixtures of isomeric C-7 alcohols are analyzed by exploiting the combined spectral information provided by a gas chromatography-matrix isolation-Fourier transform-infrared spectroscopy-mass spectroscopy (GC-MI-FT-IR-MS) instrument and 13C nuclear magnetic resonance (NMR). These complex mixtures are compared with each other and their components identified by examination of their flame ionization detection (FID) traces, reconstructed mass and infrared chromatograms, mass spectra, infrared spectra, and quantitative 13C NMR spectra. The two mixtures are shown to collectively contain a total of eight major isomers, with each individual sample containing seven major isomeric C-7 alcohols. The identities of the eight major components are determined and their matrix isolated-FT-IR and mass spectra are shown.

Analysis of gas chromatography-mass spectrometry library search results with edited and quantitative 13C nuclear magnetic resonance spectra

Des spectres RMN du carbone 13 permettent d'ameliorer la fiabilite des resultats de recherche spectrale en librairie, pour 3 melanges de 4 a 7 composes

Quantitative 13C n.m.r. spectroscopy of a coal-derived oil and the assignment of chemical shifts

The conditions necessary for the recording of quantitative 13C nuclear magnetic resonance spectra of the hexane-soluble oil separated from a coal hydrogenation product have been investigated. Measured values of T 1 for different signals in the spectrum were less than 1 s, and altering the pulse-repetition time beyond 2–4 s had little effect on carbon aromaticities. The nuclear Overhauser effect was suppressed by gating the proton decoupling. Assignments of chemical shifts for various signals in the spectrum of the oil were made by reference to literature spectra of polyaromatic substances and their derivatives. Determinations of different structural carbon types were internally consistent.

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.