Olefinic Resonances Research Articles

Fat unsaturation measures in tibial, subcutaneous and breast adipose tissue using short and long TE MRS at 3 T

Fat unsaturation and poly-unsaturation measures can be obtained in vivo with magnetic resonance spectroscopy (MRS) through the olefinic (≈5.4 ppm) and diallylic (≈2.8 ppm) resonances, respectively. Long echo time (TE) MRS sequences have been previously optimized for olefinic/methylene (≈1.3 ppm) or olefinic/methyl (≈0.9 ppm) measures. The objectives of this work, using a Point RESolved Spectroscopy (PRESS) sequence, are to: 1) Investigate olefinic, methyl and methylene resonance decay in subcutaneous, tibial, and breast adipose tissue to determine if a direct comparison of unsaturation measures can be made without correction for T2 losses. 2) Assess intra-individual fat unsaturation and poly-unsaturation measures in the three adipose tissues. 3) Estimate correction factors for olefinic to methylene ratios to compensate for J-coupling and T2 relaxation losses that take place when increasing PRESS TE from 40 ms to 200 ms (previously optimized long-TE). 4) Investigate the utility of an inversion recovery for resolving the olefinic resonance from water in adipose tissue.PRESS spectra were acquired from the three adipose regions (breast in female only) in healthy volunteers at 3 T. It was found that olefinic and methyl signal decays faster in breast tissue compared to in tibial bone marrow. Poly-unsaturation measures (diallylic/methylene) differ for tibial bone marrow compared to subcutaneous and breast adipose tissue, with average values of 1.7 ± 0.4, 2.2 ± 0.4, and 2.3 ± 0.8%, respectively. PRESS (TE = 40 ms) with an inversion recovery resolves the olefinic and water resonances in breast tissue with a signal to noise ratio approximately six times greater than that using PRESS with a TE of 200 ms. Stimulated Echo Acquisition Mode (STEAM) with a TE of 20 ms (mixing time of 20 ms) was also combined with IR to resolve the olefinic resonance from that of water is spinal bone marrow.

Effect of triglyceride glycerol CH signal on olefinic resonance quantification with proton magnetic resonance spectroscopy at 3 T

The in-vivo Magnetic Resonance Spectroscopy (MRS) techniques STimulated Echo Acquisition Mode (STEAM) and Point RESolved Spectroscopy (PRESS) are used to assess fat unsaturation levels in human adipose tissue by measuring the olefinic proton resonance at ≈5.4 ppm. At clinical field strengths, the resonance is overlapped by that of the triglyceride glycerol CH proton at ≈5.2 ppm. In the presented work, olefinic resonance contamination by that of the glycerol CH proton for STEAM and PRESS as a function of echo time (TE) is assessed at 3 T. MRS spectra were acquired from the triglyceride tricaprylin (contains glycerol but no olefinic protons), and from free oleic acid (contains olefinic but no glycerol protons) using STEAM (TE of 20 to 300 ms, mixing time of 20 ms) and PRESS (TE of 40 to 300 ms), with TE increments of 10 ms. Estimated olefinic signal contamination by the glycerol CH resonance was evaluated for short-TE (STEAM with TE of 20 ms and PRESS with TE of 40 ms) for human adipose tissue based on a literature composition and using the spectra acquired for tricaprylin and oleic acid. Contaminations of ≈20% for STEAM with a TE = 20 ms and ≈13% for PRESS with a TE = 40 ms were obtained. Glycerol CH contributions to the olefinic resonance was also estimated for eight oils in a similar manner. High-resolution in-vitro 16.5 T Nuclear Magnetic Resonance (NMR) spectra of the oils suggest that in the absence of significant T2 relaxation and J-coupling effects, 9 to 17% (depending on unsaturated fatty acid content) of the olefinic signal is attributable to the glycerol CH proton. The signal yield responses of the glycerol CH and the olefinic protons as a function of TE indicate that a TE of 90 ms for STEAM and a TE of 200 ms for PRESS are suitable for quantification of the olefinic resonance with minimal impact from the glycerol CH resonance. Signal area yields relative to those obtained with short-TE were 30% and 29% for the olefinic resonance and 4% and 5% for the glycerol resonance for STEAM with a TE of 90 ms and PRESS with a TE of 200 ms, respectively. The efficacy of the timings was verified in vivo on tibial bone marrow.

Intra- and interindividual variability of fatty acid unsaturation in six different human adipose tissue compartments assessed by 1 H-MRS in vivo at 3T.

It is generally accepted that the amount and distribution of adipose tissue (AT) in the human body play an important role in the pathogenesis of metabolic diseases. In addition, metabolic effects of released saturated fatty acids (FAs) in blood are known to be more critical than those of unsaturated FAs. However, little is known about the variability in unsaturation of FAs in various AT compartments. The aim of this prospective study was the assessment of mono- and polyunsaturated FAs in various AT compartments by localized 1 H-MRS in order to obtain insight into the intra- and interindividual variability. Associations of FA unsaturation with intrahepatic lipids (IHLs), insulin sensitivity and related AT volumes were analyzed. Fifty healthy Caucasians (36 male, 14 female) participated in this study. Spectroscopic examinations were performed in subcutaneous adipose tissue in the neck (SCATneck ), abdominal deep subcutaneous adipose tissue (DSCAT), abdominal superficial subcutaneous adipose tissue (SSCAT), visceral adipose tissue (VAT), tibial bone marrow (BM) and subcutaneous adipose tissue of the lower leg (SCATcalf ) at 3T. Unsaturated index (UI) was calculated by the ratio of olefinic and methyl resonances, polyunsaturated index (PUI) by the ratio of diallylic and methyl resonances. Volumes of AT compartments (by T1 -weighted MRI) and IHL (single-voxel STEAM) were assessed at 1.5T, insulin sensitivity by an oral glucose tolerance test. UI was highest for SCATcalf (0.622) and lowest for BM (0.527). Highest PUI was observed for SSCAT (0.108), lowest for BM (0.093). Significant intraindividual differences between UIs-but not PUIs-are present for most compartments. There is a non-significant trend for higher UI in males but otherwise no correlation to anthropometric data (age, BMI). A significant negative correlation between UI and AT volume was observed for VAT but for none of the other compartments. Neither UIs nor PUIs show a relation with IHL; insulin sensitivity is significantly correlated to UI in BM (p<0.01). Unsaturation indices in several distinct AT compartments are location dependent. Our cohort showed only moderate gender-related differences, with a trend towards less unsaturated FAs (mainly PUI) in females. In BM, insulin resistant subjects are characterized by a higher UI compared with the insulin sensitive ones. Further studies in larger cohorts are necessary to gain further insight into unsaturation of AT.

Aspects of spinal bone marrow fat to water quantification with magnetic resonance spectroscopy at 3 T

Aspects of spinal bone marrow fat to water ratio (FWR) quantification with magnetic resonance spectroscopy (MRS) at 3 T were examined in this work. A Point RESolved Spectroscopy (PRESS) sequence with TE = 40 ms and TE = 70 ms was employed to obtain spectra from L3 and T7 vertebrae of twenty healthy volunteers within the age range of 21–50 years (8 female, 12 male); measurements from the C4 vertebra were obtained from 19 of the volunteers. The spectra were used to determine FWR and fat and water T2 values. Spectra were fitted to yield areas for the fat peak (≈1.3 ppm), the water peak (≈4.7 ppm) and the olefinic resonance (≈5.3 ppm). Ignoring the olefinic contribution to the water signal results in about 10% lower FWRs using short-TE PRESS and overestimates water T2 by about 8% in the L3 vertebrae. Neglecting to correct for T2 relaxation resulted in an average overestimation of FWR by a factor 3.11 ± 1.30 (when comparing T2 corrected FWR to that obtained with PRESS TE = 40 ms) in L3 vertebrae. Paired t-tests were employed to investigate statistical significance of differences between different pairs of vertebrae in each volunteer. On average, it was found that FWRs in the T7 and C4 vertebrae were approximately 75% and 57%, respectively, of the corresponding value for the L3 vertebra in each volunteer (p-values < 0.01). Fat T2 values were on average, in each volunteer, lower in C4 vertebrae compared to those of L3 and T7 (17% and 23% lower, respectively) and C4 water T2 values were ≈6% lower than the T7 values. To our knowledge, this is the first MRS study to examine the variation of FWR and T2 values across different vertebral sections.

Comparison of optimized long echo time STEAM and PRESS proton MR spectroscopy of lipid olefinic protons at 3 Tesla

To investigate the response of lipid olefinic protons (≈ 5.35 ppm) as a function of STEAM (Stimulated Echo Acquisition Mode) mixing time (TM), and echo time (TE), to find values that resolve the olefinic resonance from water in vivo while retaining sufficient olefinic signal. PRESS (Point RESolved Spectroscopy) and STEAM experiments with varying timing parameters (TE and also TM for STEAM) were conducted on nine oils (almond, canola, cod liver, corn, linseed, peanut, sesame, sunflower, and walnut oil), and on vertebral bone marrow in vivo at 3 Tesla (T). Olefinic and methylene (methyl + methylene in vivo) peak areas were measured. Optimal STEAM parameters were found to be TM = 20 ms and TE = 100 ms. The STEAM olefinic/methylene area ratios (ranging between 0.1 and 0.4) calculated for each oil correlated well with ratios deduced from oil compositions in the literature (R(2) = 0.975). The optimized STEAM sequence resolved the olefinic peak from water in vivo and yielded on average 1.91 times more olefinic signal compared with a previously optimized PRESS (TE = 200 ms) sequence tailored for the same purpose. Olefinic/(methyl + methylene) area ratios obtained with optimized STEAM and PRESS in vivo were linearly correlated (R(2) = 0.972). A STEAM sequence with TE = 100 ms and TM = 20 ms provides an alternative to the previously optimized PRESS (TE = 200 ms) sequence for determining relative amounts of lipid unsaturation at 3T.

Divalent Platinum Complexes of the Carbanion 2-C6F4AsPh2: Monodentate or Bidentate Coordination?

The reaction of [PtI2(1,5-COD)] with 2-LiC6F4AsPh2 affords the planar platinum(II) fluoroaryl complex [PtI(κC-2-C6F4AsPh2)(1,5-COD)] (7), in which the arsenic atom is not coordinated to the metal atom. Attempts to prepare the bis(chelate) complex [Pt(κ2As,C-2-C6F4AsPh2)2] analogous to the known phosphorus compound failed. Removal of iodide ion from 7 with TlPF6 gave [Pt(κ2As,C-2-C6F4AsPh2)(1,5-COD)]PF6 (8), in which 2-C6F4AsPh2 is now coordinated as a bidentate ligand, giving a four-membered chelate ring. Alternatively, protonolysis (with triflic acid) of the methyl complex [PtMe(κC-2-C6F4AsPh2)(1,5-COD)] (15), which is obtained from 7 and dimethylzinc, gives the triflate salt 16 of the same chelate cation. The chelate As,C ring in 8 is readily reopened when the complex is treated with pyridine or with halide ions, forming respectively [Pt(py)(κC-2-C6F4AsPh2)(1,5-COD)]PF6 (9) and [PtX(κC-2-C6F4AsPh2](1,5-COD)] (X = Cl (10), Br (11), I (7)). The appearance of two pairs of olefinic COD resonances in the proton NMR spectra of 7, 10, 11, and 15 may indicate that there is restricted rotation about the Pt−κC-2-C6F4AsPh2 bond; the additional signals are not evident in the spectra of 8 or 16. Complexes 7 and 10 form the 1:1 adducts [PtX(μ-2-C6F4AsPh2)(1,5-COD)AuY] (X = Cl, Y = I (12); X = Y = I (13); X = Y = Cl (14)) by attachment of gold(I) halides to their dangling arsenic atoms. In 12 the halides are scrambled between platinum and gold. The X-ray structures of 7, 8, 9, 12, 15, and 16 are reported, and possible reasons for the poorer chelating ability of 2-C6F4AsPh2 in comparison with that of 2-C6H4PPh2 are discussed.

Long echo time proton magnetic resonance spectroscopy for estimating relative measures of lipid unsaturation at 3 T

To examine the behavior of lipid olefinic and diallylic resonances as a function of PRESS (point resolved spectroscopy) echo time (TE) to determine an optimal long TE value for their measurement at 3 T. Experiments were conducted on nine oils (almond, canola, cod liver, corn, linseed, peanut, sesame, sunflower, and walnut oil) and on vertebral and tibial bone marrow in vivo at 3 T. The methylene (or methyl + methylene), diallylic, and olefinic resonances were measured with PRESS with multiple TEs. J-coupling evolution effects on the olefinic and diallylic peaks appeared to be minimized when TE = 200 msec. The TE = 200 msec olefinic/methylene and diallylic/methylene peak area ratios calculated for each oil correlated well with ratios deduced from oil compositions in the literature (R(2) = 0.92 and 0.98 for the olefinic and diallylic protons, respectively). In addition, the relative amounts of bone marrow unsaturation of vertebral and tibial bone marrow inferred from the TE = 200 msec olefinic/(methyl + methylene) peak area ratio agreed with values estimated from the literature. A PRESS sequence with a long TE value of 200 msec is suitable for determining relative amounts of lipid unsaturation at 3 T.

Sci-Sat AM: Brachy - 12: Resolving the olefinic lipid resonance from water in proton magnetic resonance spectra of vertebral bone marrow at 3 T.

Proton magnetic resonance spectroscopy (MRS) of vertebral lipids has been shown to be relevant in the study of cancer. The olefinic resonance (≈ 5.4 ppm) yields a measure of lipid unsaturation. However, its measurement with standard short echo time (TE) MRS sequences is difficult due to the large overlapping water signal. The purpose of this work is to optimize the TE of a PRESS (Point RESolved Spectroscopy) sequence to measure the olefinic resonance from spinal bone marrow with minimal losses due to J-coupling and minimal contamination from water at 3 T, a field strength becoming more common in the clinic. Experiments were conducted on nine oils and on L4 vertebral bone marrow in vivo at 3 T. The methyléne (or methyl + méthyléne), and olefinic resonances were measured with PRESS using multiple TEs. The effects of J-coupling evolution of the olefinic protons appeared to be minimal when TE = 200 ms. The TE = 200 ms olefinic/methylene peak area ratios calculated for each oil correlated well with ratios deduced from oil compositions in the literature (R2 = 0.92). The TE = 200 ms PRESS spectra obtained from vertebra of four volunteers showed negligible contribution from water to the olefinic resonance, thereby enabling the olefinic peak area to be quantified more accurately. The results of this work demonstrate that a PRESS sequence with TE = 200 ms is suitable for measuring relative levels of lipid unsaturation and for resolving the olefinic resonance from contaminating water signal in spinal bone marrow.

PRESS echo time behavior of triglyceride resonances at 1.5 T: Detecting ω-3 fatty acids in adipose tissue in vivo

Aim This study investigated the impact of fatty acid (FA) composition on the echo time behavior of triglyceride resonances in a clinical setting. The feasibility of 1H NMR spectroscopy to detect these resonances was also evaluated in human adipose tissue in vivo. Method Ten edible oils chosen to cover a wide spectrum of FA compositions were used as phantom material. The detailed FA composition and intrinsic proton spectra of the oils were characterized by gas chromatography and high-resolution 1H NMR spectroscopy (11.7 T), respectively. The detailed echo time behavior of the oils were subsequently measured by 1H NMR spectroscopy in a clinical scanner (1.5 T) using PRESS. The effect of temperature was investigated in five oils. Results The olefinic (5.3 ppm) and diallylic (2.8 ppm) resonances exhibited distinct J-modulation patterns independent of oil FA composition. The methylene resonance (1.3 ppm) displayed an exponential decay, with the apparent T 2 showing a weak positive correlation with oil unsaturation ( R = 0.628, P = 0.052), probably a result of changes in viscosity. For the methyl resonance (0.9 ppm), oils high in ω-3 FA displayed a markedly different J-modulation pattern compared to non-ω-3 oils. The characteristic J-modulation of the ω-3 methyl group could be attributed to the phase behavior of the ω-3 methyl triplet signal (all triplet lines in-phase at TE of 135 ms), a result of the ω-3 methyl end forming a first order spin system. The ω-3 methyl outer triplet line at 1.08 ppm of the TE = 140 ms spectrum was found to be useful for determining the ω-3 content of the oils ( R = 0.999, standard error of estimate (SE) 0.80). The olefinic and diallylic proton resonance (measured at TE = 50 ms) areas correlated with the olefinic ( R = 0.993, SE 0.33) and diallylic ( R = 0.997, SE 0.19) proton contents calculated from the GC data. Information derived from long echo time spectra (TE = 200) demonstrated good correlations to GC data and showed no change with increasing temperature (and T 2). In 1H NMR spectra (1.5 T) of adipose tissue in five healthy subjects, the analytically important olefinic and diallylic resonances were clearly resolved with a coefficient of variation of 1.6% and 8.4%, respectively, for repeated measurements. The characteristic phase behavior of the ω-3 methyl outer triplet line at 1.08 ppm could also be detected at very long echo times (470 and 540 ms). Conclusion Fatty acid composition has an impact on the echo time behavior of triglyceride resonances. Long TE spectra can resolve ω-3 FA in adipose tissue in vivo. These findings will benefit long TE studies of tissue lipids.

Oxidation in fish lipids during thermal stress as studied by 13C nuclear magnetic resonance spectroscopy

Abstract13C Nuclear magnetic resonance spectroscopy has been applied to elucidate the mechanism of lipid oxidation occurring during thermal treatment of fish. Effects of temperature and time of processing have been studied by means of a model system of lipids, extracted from salmon (Salmo salar) muscle, to simulate industrial conditions of canning. Unsaturated fatty acids located at the sn‐2 position of the glycerol moiety were the most prone to oxidative damage. Regarding the mechanism of the reaction, results inferred from olefinic and methylenic resonances indicated a higher susceptibility of the allylic sites closest to the carbonyl group, followed by those placed near the methyl terminal group. Unsaturations located in the middle of the carbon chain did not show much damage. The glyceryl region provided an unusual resonance at 53.4 ppm, which could be assigned to a hydroxylic compound formed during process.

Characterization of mechanically sheared ethylene-propylene copolymers by high resolution NMR

We report high-resolution solution-state NMR experiments on chain ends generated in ethylene–propylene copolymers by mechanical shearing in an extruder. The use of the higher resolution of the 13C-NMR spectrum, in a two-dimensional 1H-13C chemical shift correlation experiment, has allowed the complete resolution and assignment of the olefinic chain-end region of the 1H-NMR spectrum. Simultaneously, the assignments of the 13C olefinic resonances, previously identified [A. C. Kolbert, J. G. Didier, and L. Xu, Macromolecules, 29, 8591 (1996)] are confirmed. An iterative method for calculating the average molecular weight, based on quantitative measurements of the olefinic 1H-NMR peak intensities is introduced and these results are compared with measurements from 13C-NMR and size exclusion chromatography and correlated to reduced viscosities. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1955–1961, 1997

High-resolution 13C-NMR olefinic spectra of DHA and EPA acids, methyl esters and triacylglycerols

The high-resolution 13C-NMR spectra of the olefinic carbons of two major n-3 polyunsaturated fatty acids of fish oils, DHA (22:6, n-3) and EPA (20:5, n-3), were recorded at 100.64 MHz in chloroform- d solutions on standard free acids, methyl esters, Atlantic tuna ( Thunnus alalunga) triacylglycerols and methyl esters. All olefinic resonances were resolved in DHA and EPA acids and methyl esters, the number of olefinic signals corresponding to that of unsaturated carbons. The order of the spin-lattice relaxation times ( T 1) and the chemical shift differences (Δδ) between signal pairs related to the same double bond led to the complete assignment of DHA and EPA olefinic carbons in acids and methyl esters. The DHA and EPA olefinic shifts of Thunnus alalunga triacylglycerols were also studied and compared with those of methyl esters. The possibility of using 13C-NMR olefinic carbons for the analysis of fish lipids and oils is discussed.

Effects of bis homoallylic and homoallylic hydroxyl substitution on the olefinic 13C resonance shifts in fatty acid methyl esters.

Substitution of a hydroxyl group at the bis homoallylic position (OH group located three carbons away from the olefinic carbon) in C18 unsaturated fatty acid esters (FAE) induces a 0.73 +/- 0.05 ppm upfield and a 0.73 +/- 0.06 ppm downfield shift on the delta and epsilon olefinic 13C resonances relative to the unsubstituted FAE, respectively. If the hydroxyl group is located on the carboxyl side of the double bond of the bis homoallylic hydroxy fatty acid esters (BHAHFA), the olefinic resonances are uniformly shifted apart by [formula: see text] where delta delta dbu represents the absolute value of the double bond resonance separation in the unsubstituted FAE and 1.46 ppm is the sum of the absolute values of the delta and epsilon shift parameters. With hydroxyl substitution on the terminal methyl side of the double bond, the olefinic shift separation is equal to [formula: see text] In homoallylic (OH group located two carbons away from the olefinic carbon) substituted FAE the gamma and delta induced hydroxyl shifts for the cis double bond resonances are +3.08 and -4.63 ppm, respectively while the trans double bond parameters are +4.06 and -4.18 ppm, respectively. The double bond resonance separation in homoallylic hydroxy fatty acid esters (HAHFA) can be calculated from the formula [formula: see text] for cis and [formula: see text] for the trans case when the OH substitution is on the carboxyl side of the double bond. Conversely, when the OH resides on the terminal methyl side, the double bond shift separations for cis and trans isomers are [formula: see text] and [formula: see text] respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Localized in vivo 1H spectroscopy of human skeletal muscle: Normal and pathologic findings

To obtain high signal to noise ratio in small volume elements (8 cm 3), in vivo 1H NMR spectroscopy of normal and diseased human skeletal muscle was performed using a double spin-echo localization method on a 1.5-T whole body system. High resolved spectra of normal calf muscle show the well known resonances of lipids (methyl, methylene, olefinic, and other fatty acid resonances), creatine/phosphocreatine, choline/carnitine, taurine, and histidine with good intraindividual reproducibility. Pronounced intraindividual differences in the lipid range were found between different upper thigh muscle groups. On pathologic conditions like myopathia, myositis or irradiation damage the spectral lipid content was increased. Three months after local irradiation of the medial vastus muscle (50 Gy), the localized 1H NMR spectrum showed a complete loss of the choline and creatine signals. In a case of M. Behçet with muscular involvement the relative reduction of the choline signal may provide an insight in the pathobiochemistry. The results of our investigations in nine healthy volunteers and three patients are presented in detail including relaxation times of the metabolites.

Quantitative Analysis of Vulcanized SBR/EPDM Diblends. Magic Angle Spinning 13C-NMR Experiments at 80°C

Abstract A new quantitative expression has been derived in order to estimate the styrene-butadiene ratio from the 13C-NMR olefinic resonances. With the help of this expression, the cis-1,4, trans-1,4, vinyl-1,2, butadiene and styrene ratios could be determined. From the aliphatic region, subsequently, the ethylene and propylene contents could be determined and finally the SBR/EPDM blend ratio. From the 13C-solid-state-NMR spectrum, no evidence could be obtained for homo- or co-vulcanization. The 13C-NMR spectra of the blends are simply a co-addition of the 13C-NMR solution spectra of SBR and EPDM rubbers. No evidence has been found for cis-1,4/trans-1,4 ratio changes for SBR (in comparison to the starting material).

1H and 13C NMR studies of tissue from normal and diseased mice. Analysis of T1 and T2 relaxation profiles of triglycerides in liver.

The study was initiated to gain a better understanding of the manifestation of disease in the lipid dynamics in tissue. We have performed high resolution 13C and 1H NMR relaxation measurements on the observable lipid resonances in liver and adipose tissue, excised from mice which were normal fed, normal fasted, and infected with the malarial parasite Plasmodium berghei. We have observed that, although the parasite does not invade the hepatocytes, the composition of the liver lipids changes along with nutritional status and disease state. Analysis of the liver lipids using gas chromatography showed that in all cases studied (normal or malarial, fed or fasted) the phospholipid content of the liver remains constant. The triglyceride content, however, shows an increase of up to fourfold in both 24-hour fasted controls and highly parasitized mice. The fatty acid compositions of the triglycerides in 24-hour fasted normal and highly parasitized mice are altered, when compared with fed controls or with mice having a low level of infection. The unsaturation index increases twofold. The 13C T1 experiments on the methylene and olefinic resonances of liver give a single exponential decay. The value for a particular carbon is independent of the origin of the tissue, the nutritional status or the disease state of the animal. In contrast, both 1H and 13C T2 relaxation of the methylene and olefinic carbon resonances can generally be best analyzed as the sum of two exponential decays (based on an F-test). The 13C T2 values and the pre-exponential weighting factors are independent of the origin of the tissue examined. The T2 data could also be analyzed in terms of a distribution of relaxation times, a physically more realistic model. Lastly, our results suggest that the 1H and 13C resonances of lipids in the cells of diseased or normal liver tissues do not give rise to "long" T2 values, as have been observed in cancer cells with metastatic potential.

13C nuclear magnetic resonance study of olefinic resonances in polymers containing regularly spaced double bonds. An incremental approach concerning neighbouring effects: application to polynorbornene

Polymers with double bonds spaced regularly along the backbone (for example, 1,4-polybutadiene, polyalkenamers, polynorbornenes, etc.) show olefinic 13C nuclear magnetic resonances, depending both on the carbon atom that is considered and on the configuration— cis or trans—of the neighbouring double bonds. Very different spectral features are observed. A general and simple formalism is proposed with a view to describing and measuring these neighbouring effects; it uses two additive incremental parameters of chemical shift variation. The relative values of these two parameters determine the spectral features of the olefinic resonances for a given polymer of that type. The different cases are discussed and polynorbornene is used here to illustrate the usefulness of this formalism.

Characterization of butadiene‐acrylonitrile‐methacrylic acid terpolymer by 13C and 1H NMR

AbstractThe proton noise‐decoupled 13C NMR spectra were used to characterize the terpolymer of butadiene (BD), acrylonitrile (AN), and methacrylic acid (MMA) prepared by emulsion polymerisation. Assignments for the various triads of butadiene units adjacent to acrylonitrile in the terpolymer were made by comparing the olefinic and aliphatic carbon resonances of a butadiene (B)‐acrylonitrile (A) copolymer. Measurement of intensities of olefinic resonances in the nitrile environment for the terpolymer gives information about the BBB, BBA, ABB and ABA triads distribution, BBA and ABA being predominant. The intensities of methylene carbon resonances of the various triads for BD units connected to AN show a similar trend. The relative populations of various triads calculated from the peak intensities show that the terpolymer has a random structure. The assignments pertaining to BD units were made by comparison with 13C resonances of polybutadiene. The distribution of trans‐1,4‐, cis‐1,4‐ and 1,2‐units in the terpolymer indicates that the terpolymer has a random structure.

Conformational analysis by NMR. 13C nuclear magnetic resonance spectra of saturated and unsaturated carboxylic acids and their corresponding esters and anhydrides

The 13C NMR spectra of a large number of closely related saturated and unsaturated dicarboxylic acids and their anhydrides and derivatives have been analyzed to determine the structural and electronic effects which govern their chemical shifts. In monocarboxylic acids the conversion of an acid to its methyl ester causes an upfield shift of −5.9 ± 0.5 ppm for the carboxyl carbon while in diacids the effect is only −1.6 ± 0.6 ppm. The conversion of an aliphatic monocarboxylic acid (or its methyl ester) to the corresponding anhydride causes an upfield shift of −3.2 ± 0.6 ppm in the carboxyl carbon resonance. The closure of saturated diacids to their corresponding anhydrides has a variety of effects which can, in general, be rationalized in terms of the stereochemistry and structure of the diacids. The closure of an α,β-unsaturated diacid to its corresponding anhydride causes an upfield shift of −2.6 ± 1.1 ppm in the carboxyl carbon resonance and a downfield shift of 6.4 ± 1.2 ppm in the olefinic carbon resonance. These and other additivity effects and regularities in the 13C chemical shifts of these diacids and anhydrides are discussed in terms of electronic and steric effects.

Determination of unsaturation in ethylene-propylene terpolymers and butyl rubber by time-averaged 1H n.m.r. measurements

The time-averaged 1H n.m.r. spectra of ethylene-propylene-dicyclopentadiene, ethylene-propylene-ethylidene norbornene and isobutylene-isoprene copolymers were measured. Assignments of the olefinic resonances were carried out by comparing the spectra with those of each homopolymer and strarting monomers. The concentration of the olefinic unit in copolymer was determined by measuring the intensity ratio between the olefinic proton signal and the signal of trichloroethylene which was added as an internal standard of intensity measurements. The concentrations of unsaturation in copolymers determined by using the iodine-mercuric acetate method were proportional to those determined by the n.m.r. method. The accuracy and precision of the n.m.r. measurements were shown to be better than 10% for a mixture of polyisobutylene and polyisoprene containing 1.24 mol % of unsaturation as a model compound of isobutylene-isoprene copolymer.