Natural Abundance 13C Spectra Research Articles

Surface-Sensitive NMR Detection of the Solid Electrolyte Interphase Layer on Reduced Graphene Oxide

Forming a stable solid electrolyte interphase (SEI) is critical for rechargeable batteries' performance and lifetime. Understanding its formation requires analytical techniques that provide molecular-level insight. Here, dynamic nuclear polarization (DNP) is utilized for the first time to enhance the sensitivity of solid-state NMR (ssNMR) spectroscopy to the SEI. The approach is demonstrated on reduced graphene oxide (rGO) cycled in Li-ion cells in natural abundance and 13C-enriched electrolyte solvents. Our results indicate that DNP enhances the signal of outer SEI layers, enabling detection of natural abundance 13C spectra from this component of the SEI on reasonable time frames. Furthermore, 13C-enriched electrolyte measurements at 100 K provide ample sensitivity without DNP due to the vast amount of SEI filling the rGO pores, thereby allowing differentiation of the inner and outer SEI layer composition. Developing this approach further will benefit the study of many electrode materials, equipping ssNMR with the necessary sensitivity to probe the SEI efficiently.

Magnetic resonance spectroscopy investigations of brown adipose tissue and isolated brown adipocytes.

Brown adipose tissue and collagenase-isolated brown adipocytes were investigated in rats by means of 1H and 13C nuclear magnetic resonance spectroscopy. After chloroform-methanol extraction of brown adipose tissue, proton and natural abundance 13C spectra of the chloroform fraction showed resonances attributable to triglycerides, and were qualitatively similar to those of the corresponding fraction of white adipose tissue. By means of quantitative analysis of 1H spectra, fatty acid unsaturation and polyunsaturation in triglycerides were found to be lower in brown than white adipose tissue; moreover, unsaturation parameters decreased in triglyceride fatty acids of brown adipose tissue upon norepinephrine administration or cold acclimatization of rats, and were affected by the age of donors. The molar percentage of mono- and polyunsaturated C18 fatty acids in triglycerides was determined from 13C spectra and found to change in the early post-natal period. Isolated, agarose-embedded brown adipocytes from 4-day-old rats showed a number of peaks in the carbohydrate region of 1H spectra that were not present in spectra of white adipocytes and almost disappeared in brown fat cells of older animals. These peaks could be restored by insulin exposure. Natural abundance 13C spectra of isolated brown adipocytes were resolved enough to allow unambiguous assignment of resonances to carbons of fatty acids, glycerol, glucose, ethanolamine, and choline. Calculation of the mono- to polyunsaturated fatty acids ratio in the cells was also performed. Nuclear magnetic resonance spectroscopy is a useful tool for the investigation of brown adipose tissue and adipocytes therefrom.

Whole-Core Analysis by 13C NMR

SummaryA whole-core nuclear magnetic resonance (NMR) system was used to obtain natural abundance 13C spectra. The system enables rapid, nondestructive measurements of bulk volume of movable oil, aliphatic/aromatic ratio, oil viscosity, and organic vs. car bonate carbon. 13C NMR can be used in cores where the ‘HNMR spectrum is too broad to resolve oil and water resonances separately.A 51/4-in. 13C/1H NMR coil was installed on a General Electric (GE) CSI-2T NMR imager/spectrometer. With a 4-in.-OD whole core, good 13C signal/noise ratio (SNR) is obtained within minutes, while 1H spectra are obtained in seconds. NMR measurements have been made of the 13C and 1H density of crude oils with a wide range of API gravities. For light- and medium-gravity oils, the 13C and 1H signal per unit volume is constant within about 3.5%. For heavy crudes, the 13C and 1H density measured by NMR is reduced by the shortening of spin-spin relaxation times. 13 C and 1H NMR spin-lattice relaxation times were measured on a suite of Cannon viscosity standards, crude oils (4 to 60°API), and alkanes (C5 through C16) with viscosities at 77°F ranging from 0.5 cp to 2.5 × 107 cp. The 13C and 1H relaxation times show a similar correlation with viscosity from which oil viscosity can be estimated accurately for viscosities up to 100 cp. The 13 C surface relaxation rate for oils on water-wet rocks is very low.Nonproton decoupled 13C NMR is shown to be insensitive to kerogen; thus, 13 C NMR measures only the movable hydrocarbon content of the cores. In carbonates, the 13C spectrum also contains a carbonate powder pattern useful in quantifying inorganic carbon and distinguishing organic from carbonate carbon.

Analysis of glycogen storage disease by in vivo13C NMR comparison of normal volunteers with a patient

Broadband proton-decoupled natural abundance 13C spectra of the human calf, liver, and head were obtained from normal volunteers and a patient with glycogen type IIIA storage disease. Two concentric and coplanar surface coils of diameters 8.0 cm and 13.0 cm were used for 13C (at 16.0 MHz) and 1H (at 63.6 MHz), respectively. A WALTZ-8 sequence lead to homogeneous decoupling over a large volume. In addition to lipid resonances a variety of other metabolite resonances could be resolved. The glycogen concentration in the muscle and the liver of normal volunteers varied considerably depending on dietary preparation and physical exercise. The glycogen level in the liver and the calf of a patient with glycogen type IIIA storage disease was increased by a factor of 2-3 compared to normal, well-trained volunteers. Proton-decoupled 13C spectra of human head are reported for the first time. The spectra are dominated by lipid resonances but an additional resonance at 54.0 ppm is clearly visible. The proton-decoupled 13C head spectrum of a patient with glycogen type IIIA storage disease revealed additional resonances between 71.0 and 85.0 ppm.

Proton‐decoupled, overhauser‐enhanced, spatially localized carbon‐13 spectroscopy in humans

Spatially localized, natural abundance, carbon (13C) NMR spectroscopy has been combined with proton (1H) decoupling and nuclear Overhauser enhancement to improve 13C sensitivity up to five-fold in the human leg, liver, and heart. Broadhand-decoupled 13C spectra were acquired in 1 s to 17 min with a conventional 1.5-T imaging/spectroscopy system, an auxiliary 1H decoupler, an air-cooled dual-coil coplanar surface probe, and both depth-resolved surface coil spectroscopy (DRESS) and one-dimensional phase-encoding gradient NMR pulse sequences. The surface coil probe comprised circular and figure-eight-shaped coils to eliminate problems with mutual coupling of coils at high decoupling power levels applied during 13C reception. Peak decoupler RF power deposition in tissue was computed numerically from electromagnetic theory assuming a semi-infinite plane of uniform biological conductor. Peak values at the surface were calculated at 4 to 6 W/kg in any gram of tissue for each watt of decoupler power input excluding all coil and cable losses, warning of potential local RF heating problems in these and related experiments. The average power deposition was about 9 mW/kg per watt input, which should present no systemic hazard. At 3 W input, human 13C spectra were decoupled to a depth of about 5 cm while some Overhauser enhancement was sustained up to about 3 cm depth, without ill effect. The observation of glycogen in localized natural abundance 13C spectra of heart and muscle suggests that metabolites in the citric acid cycle should be observable noninvasively using 13C-labeled substrates.

Spectroscopy and imaging with a 4 tesla whole-body MR system.

Magnetic resonance (MR) spectroscopy and imaging experiments on humans were performed with a whole-body MR system at a static field of 4 tesla. Spectroscopic studies focussed on 1H, 13C, and 31P. Imaging of humans turned out to be possible, although below the optimum at this field. This holds especially for body imaging, since RF penetration effects and dielectric resonances influence the RF field homogeneity. Excellent volume selective proton spectra of the human cerebrum and cerebellum were obtained using the stimulated echo method. Natural abundance carbon spectra of the human calf were acquired both undecoupled and with narrowband decoupling, resolving the various triglyceride resonances. Broadband decoupling, however, would have violated SAR guidelines. Liver glycogen was detected on natural abundance 13C spectra.

13C-NMR studies of horse ferrocytochrome c: Assignment and temperature dependence of methyl resonances

The 13C and proton chemical shifts of 53 of the 55 methyl resonances of horse ferrocytochrome c have been determined by editing natural abundance 13C spectra according to the number of attached protons, observing the temperature dependence of the chemical shifts, and correlating 13C and proton chemical shifts in two-dimensional spectra. Previous assignements of proton shifts allow 16 of the 13C resonances to be assigned firmly.

Natural-abundance 13C NMR measurement of hepatic glycogen in the living rabbit

r3C NMR is currently being exploited for the study of biochemical events in living systems. We have followed metabolic reactions of ‘3C-labeled substrates in suspensions of intact cells (Z-4), in perfused organs (57), as well as in the living rat (8) and guinea pig (9). Because 13C is only 1.1% abundant, 13C NMR observations in the absence of labeling require either longer signal accumulation times, or more concentrated metabolites. Natural-abundance 13C spectra have been obtained from lowconcentration metabolites in various organisms and tissues (10) and excised muscle (II, 12), but many hours of accumulation were required. We have shown that it is possible to obtain strong natural-abundance 13C signals in a few minutes’ accumulation from the high concentration of depot fat in the human arm and in different parts of the rat (8). Hepatic glycogen, which is concentrated in the liver of the fed animal, has been observed with natural-abundance i3C NMR at 8.5 T with good signal-to-noise in excised liver (13) and in perfused liver ( 7). It has also been observed in phosphorylase kinase-deficient living rats at 4.7 T using a surface coil in conjunction with a surgical procedure (14). Sillerud and Shulman (7) have shown that 100% of the “C in hepatic glycogen is observable despite the high molecular weight of this polymer. These results suggest that hepatic glycogen might be easily observed in the normal living animal using a surface coil without surgical intervention; however, a previous study of the living rat done at 1.9 T (13) showed only weak signals from hepatic glycogen. In the present 1.9 T study of the living rabbit we have observed strong signals from liver glycogen under conditions which mimic those under which man might be studied. NMR spectra were recorded with an Oxford Research Systems TMR spectrometer operating at 20.2 MHz for 13C in the pulse-Fourier transform mode. The 13C signals were observed with a two-turn surface coil constructed from 3 mm diameter copper wire. The coil diameter was 4.2 cm. The 90” pulse width for a small sample placed at the center of the coil was 17 psec. The coil was positioned 2.0 cm from the center of the magnet volume of homogeneous field where the liver was positioned. Proton decoupling was obtained by using a one-turn 8 cm diameter surface coil which was coaxial with the i3C coil. In a phantom experiment adequate decoupling was obtained

Oxygen-18 isotope shifts on the 13C nuclear magnetic resonance of metal carbonyl derivatives

The oxygen-18 isotope shifts on the natural abundance 13C spectra of oxygen-18 enriched samples of W(CO) 8 and W(CO) 5PPh 3 have been observed to be 0.040 ppm (0.61 Hz at 15.03 MHz) upfield from that of a 13C nucleus bearing an oxygen-16 atom.

13C magnetic resonance evidence for anisotropic molecular motion in collagen fibrils

Relaxation times and integrated intensities have been obtained from dipolar decoupled 13C magnetic resonance spectra of reconstituted fibrils of chick calvaria collagen enriched at the glycine C a and C′ positions. The data obtained are consistent with a model in which collagen molecules reorient about the long axis of the helix with a rotational diffusion constant ( R 1) of ~10 7 s −1, a value similar to that expected for the helix in solution. Data obtained from natural abundance 13C spectra of native (crosslinked) calf achilles tendon and rat tail tendon provide evidence of rapid anisotropic reorientation for at least 75% of the carbons in these tissues. Hence, our preliminary data indicate that, in these materials, the intermolecular interactions in the fibrilar collagen lattice can accommodate rapid reorientation at a majority of carbon sites.

Long range 13C 1H spin-spin coupling constants in amino acids. Conformational applications

Two-bond and three-bond 13Cz.sbnd; 1H spin coupling constants have been measured in a series of amino acids from their natural abundance 13C spectra. It is shown that by considering the 13CCCH coupling constants between the α-CO 2 − and the β-protons it is possible to obtain side-chain conformational information concerning the rotamer populations which is not available from studies of HH coupling constants alone. The potential usefulness of other 13C 1H coupling constants in conformational studies of amino acids and peptides is discussed.

13C 1H coupling in natural-abundance 13C spectra: applications to branched sugars, disaccharides, and alcohol groups

13C 1H coupling in natural-abundance 13C spectra: applications to branched sugars, disaccharides, and alcohol groups

A Carbon-13 Nuclear Magnetic Resonance Study of Cation Solvation in Alcohols

Natural abundance 13C spectra of solvent coordinated to the cation have been observed in solutions of Mg(II) and Al(III) salts in alcohols. Carbon shielding changes induced by cations resemble those induced by electronegative substituents; a sign reversal between the β and γ positions is found in both instances. Solvent exchange rates correspond to those found by 1H n.m.r.; this confirms that whole molecule exchange is dominant. Selective relaxation of the solvation shell signals at low temperatures reflects differences in conformational mobility within the solvation complex.

CARBON-13 NMR: A TOOL FOR STUDYING DEUTERIUM EXCHANGE KINETICS IN COBALT(III) AMINOCARBOXYLATES

Abstract Carbon-13 nmr spectral assignments of some Cobalt(III) Aminocarboxylates are presented. Natural abundance 13C spectra were obtained with a Varian Associates XL-100/15 FT nmr spectrometer equipped with an integration subroutine and a broad band proton decoupler. The kinetics of deuterium substitution on glycinate rings of Co(III)EDTA, Co(III)CyDTA, and Co(III)PDTA were studied. Rate constants obtained here are in good agreement with those obtained in previous pmr studies. Rate constants for some glycinate proton exchanges that were previously unattainable by pmr are also presented. The advantages of using 13C nmr over pmr in these studies are discussed. This study was done at 95°C and pD = 1.5. The rate of isotopic exchange was monitored by the decrease in the proton decoupled integral of the 13C resonances.

13C nuclear magnetic resonance spectra of some ergosta-dienes and -trienes

The natural abundance 13C spectra of several ergosta-dienes and -trienes, measured at 25·2 MHz, have been completely assigned by using off-resonance decoupling, acetylation shifts, and lanthanide-induced shifts. The effect of functional groups on the chemical shifts is highly sensitive to the environments of the functional group and the carbon atom under consideration, and analogies from simpler systems (e.g. cyclohexanes) are not always reliable.

The nuclear magnetic resonance spectra of fluoroaromatics. Part V. The 13C spectra of some fluorobenzenes and fluorobenzofurans

The natural abundance 13C spectra of some 1-substituted 2,3-difluorobenzenes and of some 6-substituted 3-ethoxycarbonyl-4,5,7-trifluoro-2-methylbenzofurans have been obtained. The spectra have been assigned by use of 1H and 19F decoupling techniques, together with a consideration of the 13C substituent chemical shifts, and of 13C–19F coupling constants. Comparison of 13C substituent chemical shifts in substituted benzenes and benzofurans suggests that these parameters can be safely transferred from one aromatic system to another. Substituent effects on 13C–19F coupling constants have been evaluated, and the effects of ortho-substituents on 1J couplings shown to occur via a π-bond mechanism.

Natural abundance 13C spectra of proteins: Carboxy-myoglobin and hemoglobin

In the past few years the high resolution NMR technique has been successfully applied in studies of biologically important molecules. However, due to the large number of the protons present, the proton NMR spectra of the proteins studied [l-3] are so poorly resolved that a detailed complete interpretation has never been possible. Despite this complexity, the assignments of some resonances to particular groups was possible, when their relative changes furnished some indications of the conformational variations occurring. This is so of the proton resonances of the amino acid residues near to the heme group in hemoglobin and myoglobin (i.e. histidine residues) which are differently affected in the oxy and deoxy forms by the ring current, contact, and pseudocontact shifts [3]. However, no detailed and complete analysis of the spectra has been achieved. The relative simplicity of the 13C natural abundance spectra resulting from large chemical shifts, absence of any spin-spin coupling, relatively narrow lines not seriously broadened by dipolar interactions, suggests that better resolution and more detailed information oan be obtained from 13C NMR spectra. The chief obstacle to date has been the low sensitivity resulting from the character of the ’ 3C nucleus itself and from its low natural abundance (1 per cent) [4,8]. This limitation has been overcome by the use of the Fourier transform NMR technique [9, lo], In this paper we report the results obtained with this technique for myoglobin and hemoglobin.