Carbon-13 nuclear magnetic resonance analysis of intact oilseeds

High resolution natural abundance¹³C nuclear magnetic resonance (NMR) spectra of intact oilseeds have been obtained by Fourier transform techniques. The spectra can be interpreted in terms of the relative concentrations of the major fatty acids in the oilseed. The¹³C NMR spectra are well resolved despite the fact that¹H NMR spectra of the same seeds are poorly resolved. The difference in resolution can be attributed to the simplicity of the¹³C NMR spectra in which all spin-spin coupling can be removed, in which the separation of lines is increased by a factor of 30, and in which line broadening due to intermolecular dipolar interactions is not important. The¹³C NMR Fourier transform technique is sufficiently sensitive that a high quality spectrum can be obtained from a single soybean, for example, in about 10 minutes. Similar spectra of single seeds can be obtained in comparable times for corn, castor bean, peanut, sunflower seed, and rapeseed. Because the NMR technique is nondestructive, it can be used to select individual oilseeds for use in breeding programs designed to improve oil quality. By employing some special experimental NMR line narrowing techniques, it also appears feasible to obtain moderately well resolved, natural abundance¹³C NMR spectra of the immobile, rigid protein, and carbohydrate components of an intact oilseed, as well as the more mobile oil components.     

Physical Properties and Biodegradation of Lactide-based Poly(ethy1ene glycol) Polymer Networks for Tissue Engineering

Summary New lactide-based poly(ethy1ene glycol) (PEG) polymer networks (GL-PEG) have been prepared by photopolymerization using two nontoxic niacromers, triacrylated lactic acid oligomer emanating from a glycerol center (GL) and monoacrylated PEG. These materials may use as polymer scaffolds in tissue engineering because they provide biodegradable, cell-adhesion resistant, and ligand-immobilizable characteristics. The thermal and mechanical properties of the resulting GL-PEG networks were evaluated and their biodegradability was investigated in phosphate buffered saline (PBS) at 80°C. The glass transition temperature (Tg) of all networks after degradation relatively decreased and the trend was similar to those before biodegradation, whereas thermal decomposition temperature (Td_1/2) increased in all networks to a certain degree. The tensile strength decreased as PEG was incorporated and as the molecular weight and content of PEG increased due to the soft PEG chains. Degradation rate of GL-PEG networks was controlled by the ratio of GL to PEG, and generally the rate of GL-PEG networks was faster than that of GL homonetworks. Received: 29 November 2002/Revised version: 5 February 2003/Accepted: 11 February 2003 Correspondence to Dong Keun Han     

Carbon-13 nuclear magnetic resonance spectra of model hydroaromatic hydrocarbons and solvent

Carbon-13 chemical shifts are reported for tetralin, hydrophenanthrenes and hydropyrenes and their alkyl substituted derivatives. Mono- and di- plus tri-aromatic fractions of hydrogenated phenanthrene and pyrene were also examined by carbon-13 n.m.r. and, wherever possible, the components in them identified.     

Carbon-13 magnetic resonance of coal-derived liquids

Carbon-13 Nuclear Magnetic Resonance Spectroscopy has been applied to coal-derived liquids in order to obtain additional information regarding molecular structure and composition. The data have demonstrated that, although the chemical structure is extremely complex, a significant amount of material is present in the form of normal paraffinic material both as free paraffins and alkyl substituents on aromatic and hydroaromatic materials. Semiquantitative estimates are made of the alkyl content of the liquids and the atom percentage of this material that must exist in the unprocessed coal.     

Carbon-13 nuclear magnetic resonance study of ethylene-1-octene and ethylene-4-methyl-1-pentene copolymers

Detailed assignments of ¹³C n.m.r. signals of ethylene-1-octene and ethylene-4-methyl-1-pentene copolymers, members of the linear low-density polyethylene (LLDPE) family, are presented. The equations relating signal intensities to the monomer sequences are given. Using these equations, the characterization of these copolymers by the triad monomer sequences is possible. From the analysis by the triad sequence, it is suggested that these 1-olefins have a tendency to be present isolated in the copolymer chain.     

Carbon-13 nuclear magnetic resonance measurement of oil composition in single viable soybeans

High-resolution, natural abundance¹³C NMR spectra of intact, viable soybeans have been obtained by Fourier transform techniques. The spectra are interpreted in terms of the relative concentrations of the major fatty acids present in the soybean triglycerides. This nondestructive analysis is sufficiently fast and accurate to permit the selection of individual soybeans for use in a genetic breeding program designed to reduce the undesirably high linolenic acid content of soybean oil.     

Synthesis of heterobifunctional poly(ethy1ene glycol) containing an acryloyl group at one end and an isocyanate group at the other end

Summary A New heterobifunctional poly(ethylene glycol) (PEG) having a polymerizable acryloyl group at one end and an isocyanate group at the other end was prepared in three efficient steps from commercially available t–Boc–PEG–NH₂. The end groups were characterized by ¹H NMR and MALDI–TOF–MS spectroscopy. Conjugation of the resulting PEG onto dextran via stable urethane linkage gave the PEG graft polymer with an acryloyl group at the free end of the graft chain.     

Study of the amorphous phase in semicrystalline poly(ethy1ene terephthalate) via dynamic mechanical thermal analysis

Summary Characters of amorphous phase in semicrystalline poly(ethy1ene terephthalate) (PET) were investigated systematically via dynamic mechanical thermal analysis (DMTA) in this paper. It was found that the storage modulus (E') and the glass transition temperature (T_g) of semicrystalline PET changed with the degree of crystallinity (X_c). T_g showed good linearity with X_c. However, neither reduction of E' in the T_g region (ΔlgE') nor loss tangent (tanδ) at the T_g presented linearity with X_c, which suggests that the two-phase model was not suitable for semicrystalline PET. It was also confirmed that the physical aging reduced the chain segmental mobility, producing higher T_g. Received: 22 July 2OO2/Revised version: 19 September 2002/ Accepted: 23 September 2002 Correspondence to Qingrong Fan e-mail: qrfan@pplas.icas.ac.cn, Tel.: +86-10-62563065, Fax: +86-10-62559373     

Carbon-13 nuclear magnetic resonance study of a divinylbenzene–p-cresol oligomer mixture

¹³C NMR has been found to be useful in elucidating the structure of a complex condensation product. Study of a divinylbenzene–p-cresol oligomer mixture has shown structural units consisting of approximately 85% 2,6-substituted p-cresol, 5–10% 2,5-substituted p-cresol, and 5–10% 2-substituted p-cresol endgroups.     

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.     

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.     

The structure determination of leucoanthraquinones by proton and carbon-13 nuclear magnetic resonance spectroscopy

Leucoquinizarin reacts with amines to give mono- and diaminoanthraquinones. Since contamination by diaminoanthraquinones greatly influences the quality of monoaminoanthraquinones as dyestuffs (and vice versa), it is important to elucidate the structure of leucoanthraquinones in connection with the reactivity and selectivity of the reaction with amines. The structure of the leuco compound of 1,4-bis(butylamino)anthraquinone was assigned to be 1,4-dibutylamino-2,3-dihydroanthracene-9,10-dione by p.m.r. However, the structure of the leuco compounds of 1,4-dihydroxyanthraquinone(quinizarin) and 1-butylamino-4-hydroxyanthraquinone could not be determined definitely by p.m.r. alone. An examination of ¹³C-n.m.r. spectra of anthraquinones and leucoanthraquinones afforded convincing data. The structures of the leuco compounds of quinizarin and 1-butylamino-4-hydroxyanthraquinone were concluded to be 9,10-dihydroxy-2,3-dihydroanthracene-1,4-dione and 1-butylamino-10-hydroxy-2,3-dihydroanthracene-4,9-dione respectively. The reactive species of leucoquinizarin are discussed on the basis of the results.     

Carbon-13 NMR investigation of spin-lattice relaxation mechanism of poly(4-methyl-1-pentene)

Carbon-13 spin-lattice relaxation rates (1/T₁) and nuclear Overhauser enhancement (NOE) measurements were performed on poly(4-methyl-1-pentene) above the glass transition temperature in order to explain the segmental motion of the molecule by means of high resolution nuclear magnetic resonance spectroscopy. Experiments were carried out for poly(4-methyl-1-pentene) with low, medium, and high molecular weights. The similarity of the T₁ values showed that for polymers with a degree of polymerization (DP) > 100 the relaxation behavior of the carbon atoms no longer depends on molecular weight. The temperature effects were studied at 358, 363, 373, 383, 393, and 403 K, both on 25.18 and 100.61 MHz magnetic fields. Finally, several mathematical T₁ models were applied to study the change of T₁ encountered by the individual carbon atoms. The results reveal that the more factors being considered in the calculation the more consistent will be the results obtained with the T₁ model. A comparison showed that parameters used in the DLM T₁ model gives the best fit. © 1994 John Wiley & Sons, Inc.     

Solid state nuclear magnetic resonance study of highly oriented poly(glycolic acid)

The structure of isotropic and highly drawn poly(glycolic acid) (PGA) fibres is investigated using solid-state ¹H NMR spectroscopy. Relaxation times in the rotating frame (T1ρ) using a spin-lock method at 100 °C indicate that isotropic PGA can be adequately described by two phases, a rigid crystalline phase and an amorphous mobile phase with relaxation times of 16.6 and 0.9 ms, respectively. A crystallinity of 40% is obtained by this method and agrees well with previous calorimetric studies. In contrast, T1ρ measurements indicate that oriented PGA is 50% crystalline and can be adequately described by a three phase model consisting of: rigid crystalline material with long relaxation time, semi-rigid non-crystalline material with intermediate mobility and relaxation time and highly mobile non-crystalline material with the shortest relaxation time. It was found that the crystalline phase has a T1ρ=53 and T1ρ=39 ms when the fibre direction is at 0 and 90° relative to the external magnetic field, respectively. This difference in relaxation time is associated with higher spin interactions at 0°, reducing the effect on the mobility of the chains. The WAXS orientation averages P₂=0.99 and P₄=0.96 obtained from the azimuthal scans of the (020) and (002) reflections indicate a highly oriented crystalline structure. These results are used to contrast the structural information obtained from measurements and theoretical calculations of the rigid-lattice anisotropy of the second moment (M₂), from which the orientation averages P₂=0.96 and P₄=0.94 were obtained on the basis of a published crystal structure. The discrepancies found are associated with small differences between the published crystal structure and that required to explain the spin interactions among adjacent molecules.     

Interpretation of broad line nuclear magnetic resonance in oriented poly(ethylene terephthalate)

Broad line nuclear magnetic resonance measurements on oriented poly(ethylene terephthalate) sheets have been reconsidered, in the light of recent infra-red data on similar materials. It is shown that the n.m.r. anisotropy is consistent with a model for the molecular orientation, in which the fraction of the polymer in the trans conformation is highly oriented, whereas the gauche fraction is sensibly isotropic.     

Broadline nuclear magnetic resonance studies of some poly(N-substituted maleimides)

Broadline nuclear magnetic resonance studies have been carried out on a number of poly(N-substituted maleimides) and compared with existing dielectric relaxation information. In general, the results have confirmed the existence of a ring deformation relaxation mode in these polymers and, in addition, dielectrically inactive motion involving the nonpolar nitrogen substituent has been detected. Apparent activation energies have been calculated for all the transitions and have been modified to include relaxation time distributions where the necessary information exists.     

Rapid determination of iodine value by 1H nuclear magnetic resonance spectroscopy

High-resolution ¹H nuclear magnetic resonance (¹H NMR) has been found to be an effective tool for the direct, rapid, and automated determination of the iodine value (IV) of vegetable oils, including hydrogenated oils (IV=45.9–140.2). The total time required to obtain the ¹H NMR data is about 3 min per sample. The IV is calculated from the number of double-bonded protons and the average molecular weight derived directly from the spectrum. The average of olefinic protons and allylic plus divinyl protons area was used to calculate the absolute number of double-bonded protons. The ¹H NMR results were compared with those obtained by the traditional Wijs-cyclohexane methods. The correlation coefficient between traditional IV and the novel ¹H NMR method was r ²=0.9994 for the regression equation Y=0.9885X + 2.8084, where X was the result given by the traditional method. With the proposed regression equation, IV calculated by the ¹H NMR method was within an error of ± 1 unit of the result obtained by the traditional method. The proposed method is practically viable if one can afford to have the NMR system.