High-resolution 13C Nuclear Magnetic Resonance Research Articles

High-resolution solid state 13C nuclear magnetic resonance spectra of 3,4-methylenedioxyamphetamine hydrochloride and related compounds and their mixtures with lactose

Differences between solution and solid state 13C nuclear magnetic resonance spectra of some amphetamines namely, 3,4-methylenedioxyamphetamine·HCl, ( R, S)-MDA·HCl, the methyl derivative 3,4-methylenedioxy- N-methylamphetamine·HCl, ( R, S)-MDMA·HCl, the ethyl derivative, ( R, S)-MDEA·HCl, and the analogues ( R, S)-methamphetamine·HCl, (−)-ephedrine·HCl (the 3 R,2 S enantiomer as numbered here), and (+)-pseudo-ephedrine·HCl (the 3 S,2 S enantiomer as numbered here) have been studied and related to their crystal structure. For ( R, S)-MDMA·HCl, an interesting new finding is that the observed solid state chemical shifts changed when lactose monohydrate was added as a dry powder and thoroughly mixed at room temperature. This experiment mimicked the illicit production of “Ecstasy” tablets. The mixing phenomena with lactose observed for ( R, S)-MDMA·HCl was not seen for the other compounds studied. The results are discussed in terms of hydrogen bonding and possible polymorphs. It appears that lactose affects crystal packing by reducing conformational rigidity so that the molecule more closely resembles that in solution.

Spin density distribution of the conduction electrons in diperylene hexafluorophosphate analysed by high-resolution NMR

High-resolution 13C nuclear magnetic resonance with 1H cross polarization and 1H decoupling under magic angle spinning is measured for the quasi-one dimensional organic conductor diperylene hexafluorophosphate (including tetrahydrofurane solvent molecules) at temperatures between 160 K and 270 K. Ab initio molecular orbital calculations are used for chemical shift analysis and for assignment of Knight shifted lines and individual carbon positions. The coexistence of neutral perylene molecules and perylene radicals in the same radical cation salt is revealed. From Knight and chemical shifts we were able to distinguish two inequivalent perylene radicals within the conducting stack. The spin density distribution of the molecular electronic wave function is determined quantitatively for these radicals.

Biodegradable blends of high molecular weight poly(ethylene oxide) with poly(3-hydroxypropionic acid) and poly(3-hydroxybutyric acid): a miscibility study by DSC, DMTA and NMR spectroscopy

The miscibility of high molecular weight poly(ethylene oxide) blends with poly(3-hydroxypropionic acid) and poly(3-hydroxybutyric acid) (P(3HB)) has been investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and high-resolution solid state 13C nuclear magnetic resonance (NMR). The DSC thermal behaviour of the blends revealed that the binary blends of poly(ethylene oxide)/poly(3-hydroxypropionic acid) (OP blends) were miscible over the whole composition range while the miscibility of poly(ethylene oxide)/poly(3-hydroxybutyric acid) blends (OB blends) was dependent on the blend composition. OB blends were found to be partly miscible at the middle P(3HB) contents (25 %, 50 %) and miscible at other P(3HB) contents (10 %, 75 % and 90 %). Single-phase behaviour for OP blends and phase separation behaviour for OB blends were observed from DMTA. The results from NMR spectroscopy revealed that the two components in the OP50 blend were intimately mixed on a scale of about 35 nm, while the domain sizes in the OB blend with a P(3HB) content of 50 % were larger than about 32 nm. © 2000 Society of Chemical Industry

Miscibility of poly(epichlorohydrin)/poly(vinyl acetate) blends investigated with high-resolution solid-state 13C NMR

The miscibility of poly(epichlorohydrin) (PECH)/poly(vinyl acetate) (PVAc) blends were investigated by differential scanning calorimeter and 13C cross polarization (CP) combined with magic angle spinning (MAS) spectroscopy. All the blends displayed single but increasing glass transition temperature with increased PVAc concentration. This indicates that the blend system is miscible on the scale of 10–30 nm for the entire composition. To examine the miscibility of the system on the scale below 10 nm, high-resolution solid-state 13C nuclear magnetic resonance experiment was carried out. The measurement of cross polarization rate between proton and 13C carbon nuclei ( T CH) showed that intermolecular cross polarization was slightly enhanced with increase of PECH composition. Single effective 1H spin–lattice relaxation ( T 1) time was found for PECH/PVAc. This observation suggests that interdomain spin–spin communications among all the protons in PECH/PVAc blends were possible on the scale of 10–30 nm, which is in good agreement with the DSC results. In the 1H rotating-frame spin–lattice relaxation ( T 1ρ) experiment, however, the blends displayed two-component exponential relaxation behavior, implying that interdomain spin–spin communications among all the protons were not possible within the time of 1H T 1ρ. Therefore, the domain size is estimated to be 3–30 nm in diameter.

Acyl positional distribution of glycerol tri-esters in vegetable oils: a 13C NMR study

It has recently been shown that high-resolution 13C nuclear magnetic resonance (NMR) spectroscopy is a technique which can provide valuable information about the acyl distribution and acyl positional distribution (1,3-acyl and 2-acyl) of glycerol tri-esters of different vegetable oils. It has also been observed that many of the carbon atoms of α- and β- acyl chains in tri-acyl-glycerol show different 13C NMR chemical shifts. However, previous assignments of 13C NMR spectra are either tentative or incomplete. Thus, through a series of INADEQUATE experiments, we made a full assignment of all 13C resonances of glycerol tri-esters. We also noticed a strong concentration dependence of the shifts of all resonances. Thus, in vegetable oils, the full assignment of 13C resonances must be made by progressive addition of known glycerol tri-esters. Following this method, we report a full assignment of the 13C spectra of seed and olive oils obtaining an accurate analysis of the acyl positional distribution (1,3-acyl and 2-acyl) of glycerol tri-esters. From the knowledge of the acyl positional distribution (1,3-acyl and 2-acyl) of glycerol tri-esters interesting biochemical information can be achieved.

Production of poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid) and poly(4-hydroxybutyric acid) without subsequent degradation by Hydrogenophaga pseudoflava.

A Hydrogenophaga pseudoflava strain was able to synthesize poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid) [P(3HB-co-4HB)] having a high level of 4-hydroxybutyric acid monomer unit (4HB) from gamma-butyrolactone. In a two-step process in which the first step involved production of cells containing a minimum amount of poly(3-hydroxybutyric acid) [P(3HB)] and the second step involved polyester accumulation from the lactone, approximately 5 to 10 mol% of the 3-hydroxybutyric acid (3HB) derived from the first-step culture was unavoidably reincorporated into the polymer in the second cultivation step. Reincorporation of the 3HB units produced from degradation of the first-step residual P(3HB) was confirmed by high-resolution 13C nuclear magnetic resonance spectroscopy. In order to synthesize 3HB-free poly(4-hydroxybutyric acid) [P(4HB)] homopolymer, a three-stage cultivation technique was developed by adding a nitrogen addition step, which completely removed the residual P(3HB). The resulting polymer was free of 3HB. However, when the strain was grown on gamma-butyrolactone as the sole carbon source in a synthesis medium, a copolyester of P(3HB-co-4HB) containing 45 mol% 3HB was produced. One-step cultivation on gamma-butyrolactone required a rather long induction time (3 to 4 days). On the basis of the results of an enzymatic study performed with crude extracts, we suggest that the inability of cells to produce 3HB in the multistep culture was due to a low level of 4-hydroxybutyric acid (4HBA) dehydrogenase activity, which resulted in a low level of acetyl coenzyme A. Thus, 3HB formation from gamma-butyrolactone is driven by a high level of 4HBA dehydrogenase activity induced by long exposure to gamma-butyrolactone, as is the case for a one-step culture. In addition, intracellular degradation kinetics studies showed that P(3HB) in cells was completely degraded within 30 h of cultivation after being transferred to a carbon-free mineral medium containing additional ammonium sulfate, while P(3HB-co-4HB) containing 5 mol% 3HB and 95 mol% 4HB was totally inert in interactions with the intracellular depolymerases. Intracellular inertness could be a useful factor for efficient synthesis of the P(4HB) homopolymer and of 4HB-rich P(3HB-co-4HB) by the strain used in this study.

Examination of miscibility at molecular level of poly(hydroxyether of bisphenol A)/poly(N-vinyl pyrrolidone) blends by cross-polarization/magic angle spinning13C nuclear magnetic resonance spectroscopy

The miscibility of poly(hydroxyether of bisphenol A) (phenoxy) and poly(N-vinyl pyrrolidone) (PVP) was investigated by differential scanning calorimetry (DSC) and high-resolution solid-state nuclear magnetic resonance (NMR) techniques. The DSC studies showed that the phenoxy/PVP blends have a single, composition-dependent glass transition temperature (Tg). The S-shaped Tg-composition curve of the phenoxy/PVP blends was reported, which is indicative of the strong intermolecular hydrogen-bonding interactions. To examine the miscibility of the system at molecular level, high-resolution solid-state 13C nuclear magnetic resonance (NMR) technique was employed. Upon adding phenoxy to system, the chemical shift of carbonyl carbon resonance of PVP was observed to shift downfield by 1.6 ppm in the 13C cross-polarization (CP)/magic angle spinning (MAS) together with the high-power dipolar decoupling (DD) spectra when the concentration of phenoxy is 90 wt %. The observation was responsible for the formation of intermolecular hydrogen bonding. The proton spin-lattice relaxation time T1(H) and the proton spin-lattice relaxation time in the rotating frame T1ρ(H) were measured as a function of the blend composition. The T1(H) result was in good agreement with the thermal analysis, i.e., the blends are completely homogeneous on the scale of 20 ∼ 30 nm. The six results of T1ρ(H) further indicated that the blends were homogeneous on the scale of 40 ∼ 50Å. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2291–2300, 1998

Fructose-1,6-bisphosphate preserves adenosine triphosphate but not intracellular pH during hypoxia in respiring neonatal rat brain slices.

Fructose-1,6-bisphosphate (FBP) sometimes provides substantial cerebral protection during hypoxia or ischemia. 31P/1H nuclear magnetic resonance spectroscopy of cerebrocortical slices was used to study the effects of FBP on hypoxia-induced metabolic changes. In addition, 13C-labeled glucose was administered and 13C nuclear magnetic resonance spectroscopy was used to search for FBP-induced modulations in glycolysis and the pentose-phosphate pathway. In each experiment, 80 slices (350 microm) obtained from ten 7-day-old Sprague-Dawley rat litter mates were placed together in a 20-mm nuclear magnetic resonance tube, perfused, and subjected to 30 min of hypoxia (PO2 < 3 mmHg). Nine experiments were performed, with n = 3 in each of three groups: (1) no treatment with FBP; (2) 60 min of prehypoxia treatment with FBP (2 mM); and (3) 60 min of posthypoxia treatment with FBP (2 mM). 31P/1H Interleaved nuclear magnetic resonance spectra at 4.7 T provided average adenosine triphosphate, intracellular pH, and lactate. Cresyl violet stains of random slices taken at predetermined time points were studied histologically. Some experiments had [2-13C]glucose in the perfusate. Slices from these studies were frozen for perchloric acid extraction of intracellular metabolites and studied with high-resolution 13C nuclear magnetic resonance spectroscopy at 11.75 T. With no pretreatment with FBP, hypoxia caused an approximately 50% loss of adenosine triphosphate, an approximately 700% increase in lactate, and a decrease in intracellular pH to approximately 6.4. Pretreatment with FBP resulted in no detectable loss of adenosine triphosphate, no increase in lactate, and minimal morphologic changes but did not alter decreases in intracellular pH. 13C Nuclear magnetic resonance spectra of extracted metabolites showed that pretreatment caused accumulation of [1-13C]fructose-6-phosphate, an early pentose-phosphate pathway metabolite. Posthypoxic treatment with FBP had no effects compared with no treatment. During severe hypoxia, pretreatment with FBP completely preserves adenosine triphosphate and almost completely preserves cell morphology but does not alter hypoxia-induced decreases in intracellular pH. Pretreatment also substantially augments the flux of glucose into the pentose-phosphate pathway.

Dynamic mechanical and 13C n.m.r. analyses of the effects of antiplasticization on the β secondary relaxation of aryl-aliphatic epoxy resins

The antiplasticization of epoxy networks based on diglycidylether of bisphenol A (DGEBA) and hexamethylene diamine was investigated by both dynamic mechanical analysis and high-resolution solid-state 13C nuclear magnetic resonance (n.m.r.) spectroscopy. Particular attention was paid to the influence of the antiplasticizer on the β secondary transition. In the case of densely crosslinked networks, the relevant loss peak of the antiplasticized material is dramatically reduced compared with that of the pure resin. The cooperative modes responsible for the high-temperature part of the β relaxation in the pure networks do not show up in the antiplasticized systems. N.m.r. measurements clearly demonstrate that the loss peak reduction is accompanied by a strong decrease in the mobility of the CH 2 groups that are close to the nitrogen crosslinks. In agreement with these observations, the efficiency of the antiplasticizer is weaker in the loosely crosslinked networks where the cooperative modes of the β transition are reduced. In the quasi-linear systems, where the β motions tend to be restricted to isolated motions, the efficiency of the antiplasticizer almost vanishes. This molecular description of the antiplasticization mechanism, in terms of hindrance of the short-scale cooperative motions in the glassy state, can be viewed as a dynamic coupling between the polymer and antiplasticizer molecule.

Miscibility of Polyoxymethylene Blends as Revealed by High-resolution Solid-state13C-NMR Spectroscopy

The miscibility of polyvinylphenol (PVPh) or terpenephenol (TPh) with polyoxymethylene (POM) was examined by high-resolution solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. It was found that the driving force for the mixing of POM and PVPh is the hydrogen-bonding interaction between the phenolic OH group of PVPh and the ether oxygen of POM, and that the mixing is preferentially induced in the noncrystalline phase. 1H relaxation time experiments indicated that POM/PVPh blends were homogeneous on a scale of 20–30 nm but heterogeneous on a scale of 2–3 nm. On the other hand, Fourier transform infrared and cross-polarization/magic-angle-spinning 13C-NMR (nuclear magnetic resonance) spectra revealed that POM and TPh are also mixed in the noncrystalline phase through the intermolecular hydrogen-bonding interaction, while some fraction of POM is still crystallizable. Moreover, the domain size of the micro-phase separation was estimated to be about 1 nm by the direct 1H spin-diffusion measurements, suggesting almost homogeneous mixing on a molecular level in the noncrystalline phase. © 1997 John Wiley & Sons, Ltd.

Perturbations of glucose metabolism associated with HIV infection in human intestinal epithelial cells: a multinuclear magnetic resonance spectroscopy study.

To analyse the effect of HIV-1 infection on the glucose metabolism of human intestinal epithelial cells. HT-29 cells were infected with HIV-1NDK and studied 3 weeks (acutely infected cells) or 9 months (chronically infected cells) post-infection. Perchloric acid extracts were analysed by high-resolution 1H, 31P and 13C nuclear magnetic resonance spectroscopy. Metabolite concentrations and specific 13C enrichments were quantified for chronically infected, acutely infected and control cells grown in Dulbecco's modified Eagle's medium containing natural-abundance or 1-13C-enriched glucose to determine significant differences between infected and non-infected cells. Chronically HIV-infected cells showed alterations in glycerol-3-phosphate (+40%), fructose-1,6-diphosphate (-66%), uridine diphosphate glucuronic acid (-33%), lactate (+75%) and [1-13C]glucose (+181%) levels, and in specific lactate 3-13C enrichment (+19%) when compared with controls. Acutely infected cells exhibited decreased fructose-1,6-diphosphate (-58%) and increased nicotinamide adenine dinucleotide (+33%) levels relative to controls. HIV-1 infection results in a disturbance of glycolytic and oxidative activities in human intestinal epithelial cells. This finding supports the concept that HIV-1 may directly impair some metabolic functions of the intestinal epithelium, and that it can be considered a potential aetiological agent for HIV-associated enteropathy.

High resolution 13C NMR investigation of A6C 60 ( A=K, Rb, Cs) and Ba 3C 60

We report the result of 13C nuclear magnetic resonance (NMR) measurements on A 6C 60 ( A=K, Rb, Cs) and Ba 3C 60. By using high-resolution magic angle spinning, we were able to identify an isotropic line around 156 ppm for all investigated compounds. NMR spectra of the saturated alkali compounds are quite similar. The corresponding isotropic lines show three narrow components consistent with orientationally ordered C 60 molecules leading to three non-equivalent carbon sites in these compounds as reported by x-ray studies. No line splitting was observed for the Ba 3C 60 isotropic line.

13C and1H amorphous linewidths in semicrystalline poly(4-hydroxybutyrate) and poly(3-co-4-hydroxybutyrate) aboveTg by high resolution and solid-state NMR experiments

The high-resolution 13C and 1H nuclear magnetic resonance (NMR) linewidths of semi-crystalline poly(4-hydroxybutyrate), P4HB, and poly(3-hydroxybutyrate-co-4-hydroxybutyrate), (P3/4HB-18, 18% 4HB units) in the amorphous phase and in the melt are studied as a function of temperature and magnetic field strength. Measurements of the 13C spin-spin relaxation times under the same experimental conditions show that the natural line-width is a minor contributor to the line-broadening observed in the 13C spectra of the solid polymers. A variety of coherent averaging solid-state NMR methods are used to examine possible contributions from various line-broadening mechanisms. It is shown that magnetic susceptibility and chemical shift dispersion are the major factors for the broadening of the proton and carbon resonances of P4HB in the amorphous phase and the melt, respectively. Incomplete motional narrowing due to a slow motional mode restricted in amplitude by the presence of crystallites and/or chain constraints was found to be the major line-broadening factor for P3/4HB-18 in the amorphous phase. Correlations between crystalline morphology, physical and mechanical properties, and polymer chain dynamics are discussed, along with the way these factors affect the NMR linewidth data presented. © 1996 John Wiley & Sons, Inc.

Influence of 60Co γ-Ray irradiation on the morphology of crystalline polyethylene studied by high-resolution solid-state 13C NMR

The relationship and influence of varying 60Co γ-ray irradiation doses, in the range 0.77–5.2 MGy, on the morphology of polyethylene have been investigated using high-resolution solid-state 13C nuclear magnetic resonance analyses through variation of different phase components, T1c, T2c relaxation parameters, and line width. The cross-linking in the irradiated polyethylene takes place mainly in the non-crystalline regions. However, distortion and damage to the folded chain of the crystal lattice are observed in the crystalline regions. For the interfacial phase, both cross-linking and distortion could occur. As a result, part of the crystalline component transformed into a non-crystalline one. It was also found that the orthorhombic crystalline lattice transformed into a monoclinic one within the crystalline phase in polyethylene under higher doses of irradiation.

Synthesis of polyesters as binders for deinkable inks. I. Structural analysis of the polyesterification betweeno-phthalic anhydride and neopentyl glycol in bulk at 200°C by high resolution13C nuclear magnetic resonance (13C-NMR)

Analysis of the polyesterification in bulk without any external catalyst at 200°C of o-phthalic anhydride with neopentyl glycol (2,2-dimethyl-1,3-propanediol) with a mole ratio ([(SINGLE BOND) COOH]/[ (SINGLE BOND) OH]) = 0.7 has been carried out by high resolution 13C nuclear magnetic resonance (13C-NMR). Polyesters can be analyzed by 13C-NMR spectra because of the fact that both o-phthalic acid (o-phthalic anhydride) and neopentyl glycol carbons are sensitive to sequence effects. Spin-lattice relaxation times T1, of quaternary, tertiary and secondary carbons in different structures are in the 0.1–6.5 s range depending on the neighboring residue effects in the polymer chain. © 1996 John Wiley & Sons, Inc.

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.

Determination of extent of reaction in dimethacrylate-based dental composites using solid-state 13C m.a.s. n.m.r. spectroscopy and comparison with FTi.r. spectroscopy

The instrumental conditions required for the determination of the extent of reaction in dimethacrylate-based dental composites using high-resolution solid-state 13C nuclear magnetic resonance (n.m.r.) techniques have been investigated. In the absence of paramagnetic fillers, clearly resolved carbonyl resonances for reacted and unreacted methacrylate groups were observed. The two peaks showed considerably different relaxation times using cross-polarization excitation, and accurate relative intensities could be only be obtained using direct excitation of the 13C nuclei with a pulse interval of at least 30s. Chemical shielding anisotropy spinning sidebands were observed for the reacted peak, but not for the unreacted. A spin-rate-dependent centreband intensity correction factor to account for this difference was evaluated using model triethyleneglycol dimethacrylate materials. The proportion of unreacted methacrylate groups determined using n.m.r. was essentially unaffected by spin rate, dipolar decoupling field strength and temperature, but was only about one-half that determined using infra-red spectroscopy. The origin of the discrepancy is as yet unclear.

High-resolution solid-state 13C nuclear magnetic resonance investigation of local motions in model epoxy resins

The local dynamics of some ‘model’ epoxy networks based on various diepoxides and diamines was investigated in the bulk state using high-resolution solid-state 13C nuclear magnetic resonance. The strength of the 13C-1H dipolar coupling was determined from the rises of 13C magnetization in cross-polarization experiments using very short contact times. A restricted motional averaging of the 13C-1H dipolar coupling was observed below the glass transition temperature for the hydroxypropyl ether groups and methylene carbons adjacent to the crosslinks, indicating the existence of local motions of these units in the tens of kilohertz range. The extent and temperature dependence of the motional averaging depend on the chemical structure of the epoxy network considered. Comparison with results derived from dynamic mechanical experiments leads to the conclusion that the motions of the hydroxypropyl ether groups are likely to participate in the phenomena responsible for the β secondary relaxation. Moreover, the relatively high mobility of the central methylene units in the aliphatic sequences of the diglycidyl ether of the butanediol-based network, and of the hexamethylenediamine-based network, can be associated with the γ relaxation of epoxy networks.

Study of natural diamonds by dynamic nuclear polarization-enhanced 13C nuclear magnetic resonance spectroscopy

The results of a study of two types of natural-diamond crystals by dynamic nuclear polarization (DNP)-enhanced high-resolution solid-state 13C nuclear magnetic resonance (NMR) are reported. The home-built DNP magic-angle spinning (MAS) 13C NMR spectrometer operates at 54 GHz for electrons and 20.2 MHz for carbons. The power of the microwave source was about 30 W and the highest DNP enhancement factor came near to 10 3. It was shown that in the MAS spectra the 13C NMR linewidths of the I b-type diamond were broader than those of I aB3-type diamond. From the hyperfine structure of the DNP enhancement as a function of frequency, four kinds of nitrogen-centred and one kind of carbon-centred free radicals could be identified in the I b-type diamond. The hyperfine structures of the DNP enhancement curve that originated from the anisotropic hyperfine interaction between electron and nuclei could be partially averaged out by MAS. The 13C polarization time of DNP was rather long, i.e. 1500 s, and the spin—lattice relaxation time (without microwave irradiation) was about 300 s, which was somewhat shorter than anticipated. Discussions on these experimental results have been made in this report.

High-resolution 13C nuclear magnetic resonance in alkali intercalated fullerene C60

We present the results of 13C nuclear magnetic resonance (NMR) measurements on potassium and rubidium doped Buckminster fullerene C60 at room temperature. By using high-resolution magic angle spinning NMR spectroscopy we were able to identify and characterize the different, thermodynamically stable phases. Based on an analysis of the different NMR spectra, we discuss the effects of the intercalation on the molecular dynamics as well as on the electronic properties in these compounds.