31P nuclear magnetic resonance phospholipid analysis of anionic-enriched lecithins

Phosphorus-31 nuclear magnetic resonance provides well-dispersed, quantifiable phospholipid profiles of commercial and laboratory anionic lecithin preparations. Seventeen phospholipids were determined in commercial soybean lecithins. Lecithin refinement to produce anionic-enriched lecithins may be monitored precisely.     

Improved resolution of31P nuclear magnetic resonance spectra of phospholipids from brain

A method is described wherein the resolution of³¹P nuclear magnetic resonance spectra of the lipophilic fraction from a Bligh-Dyer extract of rat brain can be enhanced. The lipids are dispersed as micelles in aqueous solution with sodium deoxycholate, and spectral resolution is further optimized by adjusting the pH and by removing ions from the solution. The application of the method to the study of aging in rat brain serves as an example.     

Meningioma phospholipid profiles measured by31P nuclear magnetic resonance spectroscopy

Fourteen cases of intracranial meningioma were characterized after chloroform/methanol extraction by³¹P nuclear magnetic resonance (NMR) spectroscopy at 202.4 MHz. Each phospholipid class detected in the extracts was identified and quantitated in terms of its molar percentage relative to the total phospholipids measured. The following phospholipids were assayed by³¹P NMR: phosphatidylglycerol, phosphatidic acid, diphosphatidylglycerol, ethanolamine plasmalogen, phosphatidylethanolamine (PE), lysophosphatidylinositol, phosphatidylserine, sphingomyelin, lysophosphatidylcholine (LPC), phosphatidylinositol (PI), sphingosylphosphorylcholine and phosphatidylcholine. In addition, two unidentified phospholipids were detected with resonances at 0.13 and −0.78 ppm, respectively. Three distinct types of spectra were obtained on the extracts and grouped accordingly for comparison purposes. Type 1 tumors showed unusual³¹P NMR profiles with low levels of PE and PI and elevated levels of LPC; type 2 tumors were characterized by low levels of the ethanolamine phospholipids and near equivalent levels of PI and LPC. The spectra of type 1 and type 2 tumors were characteristic of degenerative cells that lacked membrane permeability associated with loss of ethanolamine plasmalogen in the presence of significant phospholipid turnover. Meningiomas belonging to the third spectral type showed characteristics similar to those of normal tissues with normal levels of PE and ethanolamine plasmalogen, as well as very low levels of LPC relative to PI. Type 3 tumors lacked the characteristic signs of degeneration noted in type 1 and type 2 tumors. The data corroborate and augmentin vivo spectroscopic findings reported earlier and demonstrate the value of³¹P NMR spectroscopic phospholipid analysis on lipid extracts for the characterization of meningiomas.     

31P nuclear magnetic resonance studies on alkyl phosphate emulsifiers in cosmetic oil-in-water emulsions

Cosmetic oil-in-water emulsions with a stearyl phosphate emulsifier are examined by means of static and dynamic ³¹P nuclear magnetic resonance (NMR) techniques to characterize the molecular properties of the emulsifier in situ. The interfacially bound emulsifier can be deteced by high-resolution NMR spectroscopy, whereas the excess emulsifier exists as a solid lipid phase not detectable by this technique. The emulsions and the emulsifier raw material, consisting of monostearyl phosphate as well as distearly phosphate, are examined by solid state cross polarization magic angle spinning NMR spectroscopy to prove the existence of solid emulsifier phases in the emulsions. By applying dynamic ³¹P NMR methods to the interfacially bound emulsifier, information about the molecular dynamics at the interface is obtained. The results of the T ₁ and T ₂ relaxation time measurements indicate a restricted motion of the molecules that is dependent on the oil droplet size in the emulsions. This is verified by ³¹P NMR pulsed gradient spin echo self-diffusion measurements on emulsions with different droplet sizes. Only about 5 wt% of the total emulsifier used is bound at the interface; the excess forms solid lipid phases. The coverage of the interface seems to be independent of the emulsifier concentration. Only the monoester of the emulsifier raw material shows interfacial activity. Its mobility indicates the two-dimensional environment of the molecules on the surface of the oil droplets.     

Quantitative31P nuclear magnetic resonance analysis of the phospholipids of erythrocyte membranes using detergent

³¹P Nuclear magnetic resonance (NMR) spectra of human erythrocyte lysates dissolved in sodium cholate were acquired. The narrow resonances of phospholipids were mostly well resolved, allowing identification and accurate quantitative analysis of phospholipid classes of the erythrocyte membranes. The ether-linked phosphatidylethanolamine components of the erythrocyte membranes were identified, based on the removal of plasmalogens by acidolysis and of diacyl phospholipid species by degradation using phospholipase A₁. It was also shown that the introduction of double bonds on the acyl chains of phosphatidylcholine shifted the³¹P NMR resonances to lower frequencies. Quantitative analyses of phospholipids from the spectra were based on their apparent molar concentrations. The recoveries of phospholipids from erythrocytes were significantly higher than those using conventional extraction procedures.     

Alterations in heart and kidney membrane phospholipids in hypertension as observed by 31P nuclear magnetic resonance

Abnormalities of phospholipids in hypertension have previously been described in human erythrocyte, platelet, and plasma lipoproteins. Since the heart and kidney are adversely affected by hypertension, we investigated possible alterations in their membrane phospholipids, which could play a role in the derangement of intracellular ion balance widely observed in hypertension. The phospholipid compositions of heart and kidney from spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were determined by using ³¹P nuclear magnetic resonance (NMR) spectroscopy. Absolute contents of all phospholipids in hypertensive hearts and kidneys were significantly higher than in normotensive hearts and kidneys. Expressed as a fraction of total phospholipid, cardiolipin (CL) and phosphatidylethanolamine plasmalogen (PEp) were significantly increased in SHR hearts compared to WKY hearts (CL and PEp were 7.95±0.22% and 13.16±0.35% in SHR vs. 7.01±0.20% and 11.19±0.42% in WKY rats, P<-0.05), but phosphatidylethanolamine (PE) and phosphatidylcholine (PC) were significantly decreased in SHR (PE and PC were 22.46±0.37% and 44.81±0.43% in SHR vs. 24.02±0.44% and 46.01±0.50% in WKY rats, p≤0.05). In the phospholipids extracted from rat kidneys, the percentage of PE was significantly higher for SHR than for WKY rats (20.37±0.60% vs. 18.43±0.37%, P≤0.05), while PEp and phosphatidylserine (PS) were significantly lower for SHR (PEp and PS were 10.22±0.36% and 8.42 ±0.28% in SHRs vs. 11.29±0.36% and 9.71±0.40% in WKY rats, P≤0.05). The above alterations in phospholipid composition might contribute to the higher oxygen consumption in the hypertensive heart and abnormal intracellular ion concentrations and ion transport in the heart and the kidney in hypertension.     

Phospholipid profiling of sediments using phosphorus-31 nuclear magnetic resonance

A phosphorus-31 nuclear magnetic resonance method has been developed for the determination of aquatic sediment phospholipid profiles that may be generally applied to all soils and deposits containing viable cellular material. A method of scrubbing chloroform/methanol extracts with potassium acid phosphate overcomes adverse signal broadening from the mineral component, permitting eleven sediment phospholipids to be determined at the quantitative level.     

A nuclear magnetic resonance spectroscopic investigation of the headgroup motions of lysophospholipids in bilayers

Fully hydrated lysophospholipids in both the gel and the liquid crystalline states have been shown to exhibit negative phosphorus chemical shift anisotropies (Δσ) by³¹P nuclear magnetic resonance (NMR). The magnitude of Δσ for monoacyl lysophospholipids is found to be smaller than that of the corresponding diacyl phosphospholipids in bilayers by about a factor of two. We present evidence to suggest that the reduction in Δσ can be attributed primarily to an additional motional averaging of the lysophospholipid headgroup, and the additional motion can best be explained by rapid rotational motions of the headgroup about the C(1)-C(2) glycerol bond.     

Solid-state nuclear magnetic resonance investigation of cation siting in LiNaLSX zeolites

The location of Li⁺ and Na⁺ cations in a series of dehydrated low-silica LiNaX zeolites (LiNaLSX, framework Si/Al ratio=1.0) were characterized by ⁷Li and ²³Na magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Depending on the Li⁺ content, up to three lines were observed in the ⁷Li MAS NMR spectra attributed to Li⁺ cations on SI′, SII and SIII sites. The ²³Na MAS NMR spectra of the pure sodium form NaLSX and of LiNaLSX samples with low Li⁺ contents contain up to five lines belong to Na⁺ cations located on SI, SI′, SII, and two different SIII′ sites. LiNaLSX zeolites containing more than 40% of Li⁺ show only a single narrow line in the ²³Na MAS NMR spectra attributed to mobile sodium cations. The populations of the different cation sites were determined from the relative line intensities of the MAS NMR spectra. Below about 70% Li⁺ exchange, lithium cations are located only on sites SI′ and SII. Between 70% and 100% Li⁺ content these sites are fully occupied by Li⁺, and the population of site SIII by Li⁺ increases. It was found that the nitrogen-adsorption capacity correlates well with the occupation of Li⁺ at site SIII.     

A broad-line nuclear magnetic resonance investigation of polyacrylonitrile phase structure and chain conformation

The investigation of polyacrylonitrile (PAN) phase structure has been carried out in connection with its chain conformation by means of analysing the shape, width and the second moment of ¹H BL-n.m.r. lines. A complex structure of the n.m.r. lines within the range of temperatures between −180°C and 115°C is interpreted as resulting from the presence of a specific conformation in the iso- and heterotactic sequences of PAN. A complex shape of the lines in temperatures above 115°C may be explained by heterogeneity of phase structure or by the polymer's microstructure. The line width was found to narrow in the vicinity of 95°C and within the range of 120°C and 160°C, which was attributed to certain changes in the nature of molecular motion. Theoretical and experimental values of the second moment of ¹H BL-n.m.r. line for rigid lattice of PAN were compared. The n.m.r. spectra of two polyacrylonitrile samples heat-treated at 200°C and deuterated respectively, were studied to confirm the presence of specific chain conformation.     

Study by proton nuclear magnetic resonance of the thermal oxidation of oils rich in oleic acyl groups

The oxidation process of olive, hazelnut, and peanut oils at 70°C with circulating air has been studied by means of ¹H NMR. The evolution of the process, including the rate of degradation of the acyl groups and of formation and degradation of primary oxidation products, as well as the rate of formation of secondary oxidation products such as aldehydes, is commented on and compared with the oxidation of oils rich in polyunsaturated acyl groups. Differences that are due not only to the rate of the processes but also to the nature and concentration of the generated aldehydes are observed. Oils rich in monounsaturated acyl groups generate smaller amounts of the geno-and cytotoxic oxygenated aldehydes than oils rich in polyunsaturated acyl groups.     

1H nuclear magnetic resonance as a fast tool for determining the composition of acyl chains in acylglycerol mixtures

Several samples containing different proportions of standard compounds such as tristearin, triolein, trilinolein, and trilinolenin, covering a broad range of compositions, some similar to those of edible oils, were prepared by weight. The ¹H nuclear magnetic resonance (NMR) spectra of these samples were recorded and their signals were assigned. It was shown that concentrations of linolenic acyl groups close to 0.4% or higher can be detected by this technique. The area of 5 discrete proton signals of the spectrum was determined. Considering the ratio between this area and the concentration of the corresponding types of hydrogen atoms in the sample, equations calculating the proportions of the acyl groups were deduced. The high level of agreement between data coming from ¹H NMR spectra and data obtained by weight shows the usefulness of this methodology. In addition, it has the advantage that it is very fast and simple in comparison with the classical methods, and does not require a chemical modification of the sample. For this reason, the described method constitutes a valuable alternative for the determination of the proportions of different acyl groups in acylglycerol mixtures, such as, for example, oils and fats.     

Use of pulsed nuclear magnetic resonance to predict emulsion stability

Pulsed nuclear magnetic resonance (NMR) was used to measure extent of oil solidification during cooling of oil-in-water emulsions. “Percent interaction,” derived from these measurements, was found to correlate well with actual resistance of the emulsion to creaming and phase separation during storage. Average oil droplet size gave a fair correlation with stability, but the correlation of required Hydrophile-Lipophile Balance (HLB) with stability was poor. Pulsed NMR cooling curve measurements on emulsions offer an improved method for prediction of emulsion stability. Presented at the AOCS Meeting in Chicago, September 1976.     

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.     

Molecular mobility in wool fibers as determined from nuclear magnetic resonance studies

The mobility of protons in wool samples of Lincoln, Chokla, and Merino, equilibrated to various moisture contents in the range of 0–98% relative humidity (RH), have been studied by pulsed nuclear magnetic resonance (NMR) technique. Peak height and peak width were determined from absorption and derivative curves and the relaxation times T₁ and T₂ were determined from relaxation curves. The mobility increases with increase in moisture content. Among the three wools, the mobility was high in Merino as compared to the other two wools. The differences in the measured mobilities were related to structural and morphological differences in the three wools. The present analysis suggests that water in wool has at least three different associations, each with a different binding energy.     

Binding properties of coal-tar pitches in relation to nuclear magnetic resonance spectra

The yield of quinoline-insoluble portion from pitches correlates well with the aromatic hydrogen content of the carbon disulphide-soluble fraction scaled up by proportion to the whole pitch, which therefore by implication is an indication of the binding properties. The chemical shifts are explained with reasonable accuracy on the basis of the ring-current, model of Pople applied to fluorene and acenaphthene, which form the chief components of the pitches normally encountered.     

1H nuclear magnetic resonance determination of the yield of the transesterification of rapeseed oil with methanol

The formation of fatty acid methyl esters by transesterification with methanol can be monitored by¹H nuclear magnetic resonance spectroscopy; this accurate determination is simpler than chromatographic methods.     

A solid-state and suspended-state magic angle spinning nuclear magnetic resonance spectroscopic investigation of a 9-ethyladenine molecularly imprinted polymer

Suspended-state high resolution/magic angle spinning nuclear magnetic resonance spectroscopy and solid-state cross-polarization/magic angle spinning nuclear magnetic resonance spectroscopy were employed to study the interactions between 9-ethyladenine and a 9-ethyladenine molecularly imprinted polymer, and a non-imprinted polymer, respectively, both are copolymers of methacrylic acid and ethyleneglycol dimethacrylate. Template-related structural differences between the materials were revealed by contact time measurements and solid-state nuclear magnetic resonance. Rebinding of the template to the imprinted polymer resulted in shorter contact times for nuclei believed to be involved in the binding site interactions whereas the non-imprinted polymer did not exhibit such effects. This indicates that binding site reoccupation has a stiffening effect lowering the mobility of nearby nuclei. More detailed information was obtained from suspended-state saturation transfer difference high resolution/magic angle spinning nuclear magnetic resonance experiments. These revealed molecular level details concerning the interactions of the adenine guests with the polymer binding sites. Thus, a relatively larger transfer of magnetization was observed in the solute when bound to the molecularly imprinted polymer at a position where multiple hydrogen bonds between the analyte and the template can be expected to take place in the molecularly imprinted polymer only.     

A study of molecular motion in polycarbonate by broad line nuclear magnetic resonance

The nuclear magnetic resonance (n.m.r.) second moment has been measured for polycarbonate of bisphenol A over the temperature range 8 to 414K. An extensive study of the saturation behaviour has shown that the maximum previously reported for the second moment at low temperatures is incorrect and arises from selective saturation of the resonance. We have shown that at low radio-frequency power levels the second moment and line shape remain sensibly unchanged over the temperature range 8 to 80K. The rigid solid second moment has been considered theoretically from the intramonomer and interchain interactions with reference to the structures proposed by Prietzschk and by Bonart. We find that the structure of Bonart agrees best with a chain arrangement satisfying Van der Waals contact distances and that the rigid lattice second moment deduced correlates well with that measured for the rigid solid amorphous polymer. The temperature variation of the second moment shows two regions of relaxation processes, the low temperature one corresponding to the onset of methyl group rotations, followed by a region between 160K and the glass transition temperature in which the part of the monomer containing the phenyl and methyl groups acquires considerable mobility. These findings are in agreement with, and complementary to, previous suggestions that the toughness of amorphous polycarbonate of bisphenol A arises from extensive motion of the chains below the glass transition temperature.     

Competition between Li+ and Mg2+ for red blood cell membrane phospholipids: A 31P, 7Li, and 6Li nuclear magnetic resonance study

The mode of action of the lithium ion (Li⁺) in the treatment of manic depression or bipolar illness is still under investigation, although this inorganic drug has been in clinical use for 50 yr. Several research reports have provided evidence for Li⁺/Mg²⁺ competition in biomolecules. We carried out this study to characterize the interactions of Li⁺ and Mg²⁺ with red blood cell (RBC) membrane components to see whether Li⁺/Mg²⁺ competition occurs. ³¹P nuclear magnetic resonance chemical shift measurements of the phospholipids extracted from the RBC membranes indicated that the anionic phospholipids, phosphatidylserine and phosphatidylinositol, bind Li⁺ and Mg²⁺ most strongly. From ⁶Li relaxation measurements, the Li⁺ binding constant to the phospholipid extract was found to be 45±5M⁻¹. Thus, these studies showed that the phospholipids play a major role in metal ion binding. ⁷Li spin-lattice relaxation measurements conducted on unsealed and cytoskeleton-depleted RBC membrane in the presence of magnesium indicated that the removal of the cytoskeleton increases lithium binding to the more exposed anionic phospholipids (357±24 M⁻¹) when compared to lithium binding in the unsealed RBC membrane (221±21 M⁻¹). Therefore, it can be seen that the cytoskeleton does not play a major role in Li⁺ binding or in Li⁺/Mg²⁺ competition.