Hydrogenation of linolenate. XI. Nuclear magnetic resonance investigation

Nuclear magnetic resonance (NMR) spectra have been obtained during the hydrogenation of methyl linolenate with platinum, nickel and sulfur-poisoned-nickel catalysts and during the reduction of linolenic acid with hydrazine. Structural changes have been studied by “proton counting” techniques and include those for the total unsaturation (olefinic protons), 15,16-double bond (β-olefinic methyl protons), 1,4-pentadienes (di-α-olefinic methylene protons) and allylic methylene (α-olefinic methylene protons). The number of olefinic protons is inversely related to the degree of saturation as determined by iodine value, GLC and hydrogen absorption. Amounts of double bonds in the 15,16-position and in the 1,4-pentadiene structures decrease linearly with increasing saturation, but the slopes of lines differ for specific catalysts. Sulfur-poisoned pickel has the most negative slope, followed by electrolytic nickel, and then platinum and hydrazine. Amounts of α-olefinic structures with increasing saturation are roughly constant for hydrazine and platinum during reduction with the first mole of hydrogen; they fall to zero at complete saturation. For the two nickel catalysts, the α-olefinic structures increase during absorption of the first mole and a half of hydrogen before dropping to zero. The possibility of substituting NMR measurements for iodine value, alkali-isomerization spectrophotometric determination and other structural analyses is discussed. Presented at AOCS Meeting in Minneapolis, 1963. A laboratory of the No. Utiliz. Res. & Dev. Div., ARS, USDA.     

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.     

Nuclear magnetic resonance determination of bacteriostats

A rapid high-resolution NMR method has been developed for the determination of soap and detergent bacteriostats. The method can be used to identify six common commercial bacteriostats (3,4,4′-trichlorocarbanilide; 3-trifluoromethyl-4,4′-dichlorocarbanilide; 4′,5-dibromosalicylanildie; 3,5-dibromosalicylanilide; 3,4′,5-tribromosalicylanilide; and ehxachlorophene) and all two-component mixtures prepared from them. This method can also be used to determine the relative concentrations of these bacteriostats in all two-component mixtures. The precision and accuracy of the method are estimated to be within 3% absolute.     

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.     

Marine phospholipids as dietary carriers of long‐chain polyunsaturated fatty acids

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are polyunsaturated fatty acids (PUFA) of the n‐3 series. Fish oil is a classical source of n‐3 PUFA, where they occur in the form of triacylglycerols (TAG). However, new sources of n‐3 PUFA esterified in phospholipids (PL) are emerging. We prepared liposomes from a natural marine lipid extract and examined their behaviour under conditions mimicking that of the gastrointestinal tract. This physicochemical approach proved that liposomes could be used as an effective oral PUFA delivery system. In vivo studies in rats were performed to examine the metabolic fate of EPA (20:5 n‐3) and DHA (22:6 n‐3) delivered either in PL from liposomes or in TAG from oil. Liposome ingestion increased PUFA bioavailability in lymph compared with fish oil. The proportion of n‐3 PUFA esterified in the sn‐2 position of chylomicron TAG depended on the dietary lipid source. Complex time‐course profiles were observed for plasma lipids with liposome supplementation over a 2‐week period, suggesting time‐dependent regulations. Taken together, the type of PUFA, EPA or DHA, as well as its intramolecular distribution in chylomicron TAG seemed to influence the metabolic fate of the fatty acids and their physiological activities.     

Nuclear magnetic resonance and stereoregularity of PVC

The decoupled α-proton spectrum of PVC was examined using a 220 MHz NMR spectrometer. All of the ten possible pentads were detected and an assignment is given based on Bernoullian statistics. This assignment is in general agreement with conclusions reached by previous workers except for some modifications in the heterotatic resonances. Triad tacticity data were obtained from the pentads and were used to estimate the differential enthalpy and entropy changes for bulk PVC polymerized in the temperature range 70°C to ?50°C.     

Nuclear magnetic resonance spectroscopy spectroscopic investigation of the aging mechanism of polyethylene terephthalate vascular prostheses

This article attempts to develop and prove a technique to determine the degradation of polyethylene terephthalate (PET) for vascular prostheses. The implicit goal is to be able to quantify the amount of degradation to study the effect of in vivo aging. Nuclear magnetic resonance spectroscopy (¹H‐NMR) provides a comprehensive view of chemical macromolecular structures. Examination of a series of PET vascular prostheses showed significant chemical differences between the virgin prostheses and the explants collected after aging, especially for diethylene glycol and cyclic oligomers groups. Aging was investigated in terms of chemical scission of ester and ether linkages caused by hydrolytic reaction during the in vivo stay. Besides, we extended this ¹H‐NMR technique to determine hydroxyl end‐group concentrations and therefore the average number of macromolecular weight. To validate ¹H‐NMR results, complementary techniques, the chemical titration method and the classical viscosimetric method, were used. The results showed an increase of hydroxyl end‐group concentration and a decrease in the macromolecular weight for the explants. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of polyunsaturated phospholipids by lipase-catalyzed transesterification

Transesterifications were investigated to determine a means for preparing polyunsaturated phospholipids simply from soy phospholipid, sardine oil, and two kinds of microbial lipases originating fromCandida cylindracea andRhizopus delemar. The optimum reaction conditions forCandida cylindracea lipase were: 4 g of sardine oil, 10 mL of water, 0.7 g of lipase, 10 mL of hexane, 48 hr of reaction time at 37°C for 3 g of soy phospholipid, for which the transesterification ratio reached approximately 45%. Recovery of phospholipid was low, because hydrolysis also occurred under these reaction conditions. However, hydrolysis could be suppressed by using glycerine instead of water, and the recovery of phospholipid increased to 47%, although the transesterification ratio was reduced to 32%. Rhizopus delemar lipase has 1,3-specificity for triglycerides, and the transesterification ratio was approximately 37% in the 1-position of phospholipid. The resulting phospholipid was rich in polyunsaturated fatty acids and linoleic acid, while the total percentage of polyunsaturated fatty acids incorporated was 18.4%. Therefore, polyunsaturated phospholipids can be prepared easily by transesterification of soy phospholipid with fish oil by means of commercial lipases.     

Nuclear magnetic resonance spectra of two reductively ethylated fuels

A lignite (67.2% C daf) and a coal (89.0% C daf) have been reductively ethylated by Sternberg's procedure⁴ and the spectra, in particular the ¹H and ¹³C n.m.r. spectra, of the products have been obtained. The distribution of hydrogen atoms and, in less detail, of carbon atoms in the reductively ethylated fuels has been determined. It is emphasized that both reductively ethylated fuels contained a variety of structures. The carbon aromaticities of the reductively ethylated lignite and the reductively ethylated coal were 0.41 ± 0.08 and 0.40 ? 0.54 respectively. The aromatic nuclei of the reductively ethylated coal were more highly substituted than those of the reductively ethylated lignite. The ¹H n.m.r. spectra indicate that the reductively ethylated coal and lignite possessed ≈3.5 and ≈2.5 substituents per benzene ring respectively. Resolved absorption in the ¹³C n.m.r. spectra suggests lower figures than these and it was evident that some of the benzene rings in both materials but especially in the reductively ethylated lignite were lightly substituted. The ¹³C n.m.r. spectra show that both materials contained branched and unbranched paraffin chains. Much of the ¹³C n.m.r. spectra however consisted of unresolved absorptions and the ¹³C n.m.r. measurements suggest that the reductively ethylated materials consisted of rigid, relatively immobile molecules of moderate molecular weight. ¹³C n.m.r. absorption by carbon atoms adjacent to aromatic rings was amongst that which was not resolved — though the rings themselves gave resolved absorptions — and this suggests that the aromatic rings were on the periphery of a rigid, perhaps alicyclic, structure.     

Nuclear magnetic resonance study of PEO-chitosan based polymer electrolytes

This work investigates lithium dynamics in a series of polymer electrolytes formed by poly(ethylene oxide) PEO, chitosan (QO), amino propil siloxane (pAPS) and lithium perchlorate by means of nuclear magnetic resonance techniques. Lithium (⁷Li) lineshapes and spin-lattice relaxation times were measured as a function of temperature. The results suggest that the chemical functionality of QO, particularly the amine group, participate in coordinating lithium ion in the composites. The competition between QO and PEO for lithium ions is evident in the binary system. In the ternary electrolyte containing PEO, QO and pAPS, it is observed that the lithium ions can competively interact with the two polymers. The heterogeneity, at a local microscopic scale, is revealed by a temperature-dependent equilibrium of lithium ion concentration between at least two different microphases; one dominated by the interactions with chitosan and the other one with polyether. The data of the ternary electrolyte was analysed by assuming two lithium dynamics, the first one associated to the motion of the lithium ion dissolved in PEO and the second one associated to those complexed by the chitosan.     

Nuclear magnetic resonance for determining oil content of seeds

Twelve seed oils containing a variety of functional groups were examined with a commercial broad-band nuclear magnetic resonance (NMR) spectrometer. Instrument response (integrator readout) was directly related to hydrogen content of the oil (r=0.999), regardless of the structures present. NMR techniques were applied to the determination of oil in intact, partially dried seeds from 18 plant species containing 1.5–53% oil having a variety of structures. The correlation between integrator readout (calculated to a uniform 25-g sample weight) and oil content (determined by extraction with petroleum ether) is excellent (r=0.993). If the readout is further modified by a correction for the variation in hydrogen content of the oils, the correlation becomes 0.996.     

Solid-state 13C nuclear magnetic resonance investigation of poly(oxetanes): Effect of chain conformation

Carbon-13 nuclear magnetic resonance (n.m.r.) in the solid state has been applied to the study of poly(oxetane) and poly(3,3-dimethyloxetane). Two different crystalline modifications, with T₂G₂ and T₃G conformations, have been prepared for each of the polymers. The corresponding ¹³C chemical shifts for each sample, both amorphous and crystalline, have been determined. Single resonances for the methylene carbons α to the oxygens are observed for the crystal forms having T₂G₂ conformation. Two resonances are observed for these carbons in each of the crystals having T₃G conformation. The equivalence of these carbons in the T₂G₂ conformation and their inequivalence, within the same monomer unit, in the T₃G conformation is a property of the isolated chain. It is argued that the observed n.m.r. inequivalence in the T₃G crystalline forms has the same origin.     

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.     

Nuclear magnetic resonance spectral analysis of polymer-supported reagents and catalysts

High resolution and cross-polarisation/magic angle spinning nuclear magnetic resonance spectroscopy of crosslinked polystyrene and of reagents and catalysts supported on crosslinked polystyrene and silica gel are reviewed. The materials studied include ionexchange resins, resins in solid phase peptide synthesis, organic synthetic reagents, phase transfer catalysts, transition metal catalysts, and liquid chromatography column packings. ¹³C and ³¹P n.m.r. spectra have been used to identify structures and to study macromolecule and micromolecule dynamics. New spectra of crosslinked polystyrenes and supported reagents are reported. Procedure to obtain qualitative and quantitative spectra are recommended.     

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.     

Nuclear magnetic resonance chemical shift: comparison of estimated secondary structures in peptides by nuclear magnetic resonance and circular dichroism

Traditionally, CD has been used extensively for peptides insecondary structure analysis. In recent years, NMR chemicalshifts and nuclear Overhauser enhancements have been widelyused in conjunction with CD to assess the secondary structuresof peptides and proteins; however, there are many instanceswhere the estimation of secondary structure contents differssignificantly between the two methods. In order to elucidatethe perceived differences between the two methods, secondarystructure estimations by CD and ¹H NMR chemical shifts werecompared for over 50 peptides. The linear peptides investigatedwere largely unstructured, {small tilde}15–50 residuesin size, and lacked stable tertiary conformation. These peptideswere studied in different solvent systems including water, alcohol—water,micelles and urea. A strong correlation exists for secondarystructure assessment by CD and NMR chemical shifts; however,an interesting trend of higher estimation of helical contentsby NMR was observed for peptide fragments from globular proteinsstudied in water. This may be a result of associative propertiesof these peptides in water. Addition-ally, a new method of quantitatingsecondary structure contents based on ¹H NMR chemical shiftsis reported.     

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.     

Nuclear magnetic resonance approach to the characterization of siloxane-silica network-like structures

This work deals with mesh size properties of network-like structures associated with random siloxane-silica mixtures. The transverse magnetic relaxation function of protons is shown to obey a superposition property controlled by the silica concentration C_Si, in the range 0C_Si0.50 (w/w). Correspondingly, its invariant mathematical structure is governed by the average residual energy of dipole-dipole interactions only. The parameter Δ_e is given the role of a timescale shift factor; it is related to the average mesh size of a given network. Nuclear magnetic resonance measurements show that silica aggregates do not induce any strong deviation from the primary entanglement system established in a pure siloxane melt. Whether infinite siloxane-silica clusters are swollen by polymer chains or whether finite size clusters are diluted in a siloxane melt, the resulting networks are described by similar distribution functions of elementary chains connecting neighbouring entanglements; these functions are shifted towards smaller mesh sizes upon addition of silica. These properties hold for several high molecular weight samples: , 2.4 × 10⁵ and 1.6 × 10⁵, respectively.