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1

Spectrally edited 2D 13C13C NMR spectra without diagonal ridge for characterizing 13C-enriched low-temperature carbon materials  

NASA Astrophysics Data System (ADS)

Two robust combinations of spectral editing techniques with 2D 13C13C NMR have been developed for characterizing the aromatic components of 13C-enriched low-temperature carbon materials. One method (exchange with protonated and nonprotonated spectral editing, EXPANSE) selects cross peaks of protonated and nearby nonprotonated carbons, while the other technique, dipolar-dephased double-quantum/single-quantum (DQ/SQ) NMR, selects signals of bonded nonprotonated carbons. Both spectra are free of a diagonal ridge, which has many advantages: Cross peaks on the diagonal or of small intensity can be detected, and residual spinning sidebands or truncation artifacts associated with the diagonal ridge are avoided. In the DQ/SQ experiment, dipolar dephasing of the double-quantum coherence removes protonated-carbon signals; this approach also eliminates the need for high-power proton decoupling. The initial magnetization is generated with minimal fluctuation by combining direct polarization, cross polarization, and equilibration by 13C spin diffusion. The dipolar dephased DQ/SQ spectrum shows signals from all linkages between aromatic rings, including a distinctive peak from polycondensed aromatics. In EXPANSE NMR, signals of protonated carbons are selected in the first spectral dimension by short cross polarization combined with dipolar dephasing difference. This removes ambiguities of peak assignment to overlapping signals of nonprotonated and protonated aromatic carbons, e.g. near 125 ppm. Spin diffusion is enhanced by dipolar-assisted rotational resonance. Before detection, CH dipolar dephasing by gated decoupling is applied, which selects signals of nonprotonated carbons. Thus, only cross peaks due to magnetization originating from protonated C and ending on nearby nonprotonated C are retained. Combined with the chemical shifts deduced from the cross-peak position, this double spectral editing defines the bonding environment of aromatic, COO, and CO carbons, which is particularly useful for identifying furan and arene rings. The CO carbons, whose chemical shifts vary strongly (between 212 and 165 ppm) and systematically depend on their two bonding partners, show particularly informative cross peaks, given that one bonding partner is defined by the other frequency coordinate of the cross peak. The new techniques and the information content of the resulting spectra are validated on sulfuric-acid treated low-temperature carbon materials and on products of the Maillard reaction. The crucial need for spectral editing for correct peak assignment is demonstrated in an example.

Johnson, Robert L.; Anderson, Jason M.; Shanks, Brent H.; Fang, Xiaowen; Hong, Mei; Schmidt-Rohr, Klaus

2013-09-01

2

1H and 13C NMR spectral assignments of chalcones bearing pyrazoline-carbothioamide groups.  

PubMed

Chalcones are known to act on various physiological targets. As a result, structural modifications of chalcones have been studied extensively. Benzochalcones, in which the A-ring of chalcone is substituted with a naphthalene unit, inhibits breast cancer resistance protein. Chalcones in which the ?,?-unsaturated carbonyl group is switched with a pyrazoline moiety are potent cytotoxic agents against various cancer cell lines, and chalcones with a pyrazoline-1-carbothioamide group instead of an ?,?-unsaturated carbonyl group exhibit antimicrobial activities. The present report describes hybrid molecules designed from benzochalcone and pyrazoline-carbothioamide. Methoxylation of plant-derived polyphenols alters their hydrophobicity, resulting in changes in biological function and intracellular compartmentation. In the current study, 22 novel methoxylated 3-(naphthalen-2-yl)-N,5-diphenyl-pyrazoline-1-carbothioamide derivatives were prepared. This report provides complete assignments of their (1)H and (13)C NMR data, which can be used to subsequently identify chalcones bearing pyrazoline-carbothioamide groups. PMID:23784987

Yoon, Hyuk; Ahn, Seunghyun; Park, Mijoo; Kim, Dong-Wook; Kim, Sang Ho; Koh, Dongsoo; Lim, Yoongho

2013-06-19

3

1H NMR, 13C NMR and mass spectral studies of some Schiff bases derived from 3-amino-1,2,4-triazole  

NASA Astrophysics Data System (ADS)

Heterocyclic Schiff bases derived from 3-amino-1,2,4-triazole and different substituted aromatic aldehydes are prepared and subjected to 1H NMR, 13C NMR and mass spectral analyses. 1H NMR spectra in DMSO exhibit a sharp singlet within the 9.35-8.90 ppm region which corresponds to the azomethine proton. The position of this signal is largely dependent on the nature of the substituents on the benzal moiety. It is observed that the shape, position and the integration value of the signal of the aromatic proton of the triazole ring ( 5C) are clearly affected by the rate of exchange, relaxation time, concentration of solution as well as the solvent used. 13C NMR is taken as substantial support for the results reached from 1H NMR studies. The mass spectral results are taken as a tool to confirm the structure of the investigated compounds. The base peak (100%), mostly the M-1 peak, indicates the facile loss of hydrogen radical. The fragmentation pattern of the unsubstituted Schiff base is taken as the general scheme. Differences in the other schemes result from the effect of the electronegativity of the substituents attached to the aromatic ring.

Issa, Y. M.; Hassib, H. B.; Abdelaal, H. E.

2009-11-01

4

Sesquiterpenoids in subtribe Centaureinae (Cass.) Dumort (tribe Cardueae, Asteraceae): Distribution, (13)C NMR spectral data and biological properties.  

PubMed

Asteraceae Bercht. & J. Presl is one of the biggest and most economically important plant families. The taxonomy and phylogeny of Asteraceae is rather complex and according to the latest and most reliable taxonomic classification of Panero & Funk, based on the analysis of nine chloroplast regions, the family is divided into 12 subfamilies and 35 tribes. One of the largest tribes of Asteraceae is Cardueae Cass. with four subtribes (Carlininae, Echinopinae, Carduinae and Centaureinae) and more than 2500 species. Susanna & Garcia-Jacas have organized the genera of Centaureinae (about 800 species) into seven informal groups, which recent molecular studies have confirmed: 1. Basal genera; 2. Volutaria group; 3. Rhaponticum group; 4. Serratula group; 5. Carthamus group; 6. Crocodylium group; 7. Centaurea group. This review summarizes reports on sesquiterpenoids from the Centaureinae subtribe of the Asteraceae family, as well as the (13)C NMR spectral data described in the literature. It further reviews studies concerning the biological activities of these metabolites. For this work, literature data on sesquiterpenes from the Centaureinae subtribe were retrieved with the help of the SciFinder database and other similar data banks. All entries from 1958 until the end of 2011 were considered. This review is addressed to scientists working in the metabolomics field such as chemists, botanists, etc., the spectroscopic data reported make this work a good tool for structural elucidation, the biological section gives useful information to those who wish to study the structure activity relationships. PMID:23948259

Bruno, Maurizio; Bancheva, Svetlana; Rosselli, Sergio; Maggio, Antonella

2013-08-12

5

Brominated Compounds from Marine Sponges of the Genus Aplysina and a Compilation of Their 13C NMR Spectral Data  

PubMed Central

Aplysina is the best representative genus of the family Aplysinidae. Halogenated substances are its main class of metabolites. These substances contribute greatly to the chemotaxonomy and characterization of the sponges belonging to this genus. Due to their pharmacological activities, these alkaloids are of special interest. The chemistry of halogenated substances and of the alkaloids has long been extensively studied in terrestrial organisms, while the number of marine organisms studied has just started to increase in the last decades. This review describes 101 halogenated substances from 14 species of Aplysina from different parts of the world. These substances can be divided into the following classes: bromotyramines (A), cavernicolins (B), hydroverongiaquinols (C), bromotyrosineketals (D), bromotyrosine lactone derivatives (E), oxazolidones (F), spiroisoxazolines (G), verongiabenzenoids (H), verongiaquinols (I), and dibromocyclohexadienes (J). A compilation of their 13C NMR data is also part of the review. For this purpose 138 references were consulted.

Lira, Narlize Silva; Montes, Ricardo Carneiro; Tavares, Josean Fechine; da Silva, Marcelo Sobral; da Cunha, Emidio V. L.; de Athayde-Filho, Petronio Filgueiras; Rodrigues, Luis Cezar; da Silva Dias, Celidarque; Barbosa-Filho, Jose Maria

2011-01-01

6

Fullerene C70 characterization by 13C NMR and the importance of the solvent and dynamics in spectral simulations.  

PubMed

The nuclear magnetic resonance (NMR) spectroscopy combined with theoretical calculations is an important tool for fullerene identification. However, the accuracy of available theoretical methods is often not adequate. Therefore, in this work, different computational aspects needed to simulate realistically chemical shifts in the C70 molecule are investigated by density functional theory (DFT) calculations. The importance of the functional choice, basis set, solvent, and molecular motions was assessed. The solvent was simulated using the implicit conductor-like polarized continuum model. The molecular motions were included via anharmonic corrections and averaging of snapshots obtained from classical and first-principles molecular dynamics (MD) simulations. Comparison to experiment revealed that density functional calculations typically overestimate the (13)C NMR chemical shifts. Hybrid functionals, such as BHandH and BHandHLYP, and long-range corrected functionals, such as wB97xd and CAM-B3LYP, give the best results. While the solvent has a minor effect (chemical shift changes by ~1 ppm), the vibrational and dynamical effects are surprisingly large, causing changes up to 9 ppm. Consideration of the latter was also necessary to explain the observed temperature dependence. While the dynamical corrections for MD performed in vacuum were overestimated, inclusion of the solvent in simulations provided more realistic results. The study thus points out the importance of an appropriate solvent model and a complex approach to the modelling, balancing the static, dynamic and environmental factors. PMID:23653057

Kaminský, Jakub; Bud?šínský, Miloš; Taubert, Stefan; Bou?, Petr; Straka, Michal

2013-05-08

7

Peptide internal motions on nanosecond time scale derived from direct fitting of (13)C and (15)N NMR spectral density functions.  

PubMed

NMR relaxation-derived spectral densities provide information on molecular and internal motions occurring on the picosecond to nanosecond time scales. Using (13)C and (15)N NMR relaxation parameters [T(1), T(2), and NOE] acquired at four Larmor frequencies (for (13)C: 62.5, 125, 150, and 200 MHz), spectral densities J(0), J(omega(C)), J(omega(H)), J(omega(H) + omega(C)), J(omega(H) - omega(C)), J(omega(N)), J(omega(H) + omega(N)), and J(omega(H) - omega(N)) were derived as a function of frequency for (15)NH, (13)C(alpha)H, and (13)C(beta)H(3) groups of an alanine residue in an alpha-helix-forming peptide. This extensive relaxation data set has allowed derivation of highly defined (13)C and (15)N spectral density maps. Using Monte Carlo minimization, these maps were fit to a spectral density function of three Lorentzian terms having six motional parameters: tau(0), tau(1), tau(2), c(0), c(1), and c(2), where tau(0), tau(1) and tau(2) are correlation times for overall tumbling and for slower and faster internal motions, and c(0), c(1), and c(2) are their weighting coefficients. Analysis of the high-frequency portion of these maps was particularly informative, especially when deriving motional parameters of the side-chain methyl group for which the order parameter is very small and overall tumbling motions do not dominate the spectral density function. Overall correlation times, tau(0), are found to be in nanosecond range, consistent with values determined using the Lipari-Szabo model-free approach. Internal motional correlation times range from picoseconds for methyl group rotation to nanoseconds for backbone N-H, C(alpha)-H, and C(alpha)-C(beta) bond motions. General application of this approach will allow greater insight into the internal motions in peptides and proteins. PMID:10968972

Mayo, K H; Daragan, V A; Idiyatullin, D; Nesmelova, I

2000-09-01

8

/Sup 13/C-NMR Assignment, Structure, and Dynamics of Deoxyoligonucleotides.  

National Technical Information Service (NTIS)

The unique spectral properties of /sup 13/C-NMR for studying nucleic acids and some of the important features of /sup 13/C-NMR in oligonucleotide studies are demostrated. The main difficulty in studying oligonucleotides by /sup 13/C-NMR and recent improve...

N. Zanatta P. N. Borer G. C. Levy

1986-01-01

9

Synthesis and NMR Spectral Analysis of Amine Heterocycles: The Effect of Asymmetry on the [superscript 1]H and [superscript 13]C NMR Spectra of N,O-Acetals  

ERIC Educational Resources Information Center

|The stereochemical investigation is conducted to give students the combined experience of chemical synthesis of amines and N-heterocycles and structural stereochemical analysis using NMR spectroscopy. Students are introduced to the concept of topicity-stereochemical relationships between ligands within a molecule by synthesizing N,O-acetals.|

Saba, Shahrokh; Ciaccio, James A.; Espinal, Jennifer; Aman, Courtney E.

2007-01-01

10

Functional groups identified by solid state 13C NMR spectroscopy  

Technology Transfer Automated Retrieval System (TEKTRAN)

Animal manure is generally high in organic matter intensity so it is well suitable for 13C nuclear magnetic resonance (NMR) analysis. Solid-state 13C NMR techniques used in characterizing organic matter and its components include, but are not limited to, cross-polarization /magic angle spinning (CP...

11

Localized in vivo13C NMR spectroscopy of the brain  

PubMed Central

Localized 13C NMR spectroscopy provides a new investigative tool for studying cerebral metabolism. The application of 13C NMR spectroscopy to living intact humans and animals presents the investigator with a number of unique challenges. This review provides in the first part a tutorial insight into the ingredients required for achieving a successful implementation of localized 13C NMR spectroscopy. The difficulties in establishing 13C NMR are the need for decoupling of the one-bond 13C–1H heteronuclear J coupling, the large chemical shift range, the low sensitivity and the need for localization of the signals. The methodological consequences of these technical problems are discussed, particularly with respect to (a) RF front-end considerations, (b) localization methods, (c) the low sensitivity, and (d) quantification methods. Lastly, some achievements of in vivo localized 13C NMR spectroscopy of the brain are reviewed, such as: (a) the measurement of brain glutamine synthesis and the feasibility of quantifying glutamatergic action in the brain; (b) the demonstration of significant anaplerotic fluxes in the brain; (c) the demonstration of a highly regulated malate-aspartate shuttle in brain energy metabolism and isotope flux; (d) quantification of neuronal and glial energy metabolism; and (e) brain glycogen metabolism in hypoglycemia in rats and humans. We conclude that the unique and novel insights provided by 13C NMR spectroscopy have opened many new research areas that are likely to improve the understanding of brain carbohydrate metabolism in health and disease.

Gruetter, Rolf; Adriany, Gregor; Choi, In-Young; Henry, Pierre-Gilles; Lei, Hongxia; Oz, Gulin

2006-01-01

12

Development of LC-13C NMR.  

National Technical Information Service (NTIS)

This study involves the development of C-13 nuclear resonance as an on-line detector for liquid chromatography (LC-C-13 NMR) for the chemical characterization of aviation fuels. The initial focus of this study was the development of a high sensitivity flo...

H. C. Dorn J. S. Wang T. E. Glass

1986-01-01

13

[1H and 13C NMR investigation of nifedipine].  

PubMed

1H-13C shift-shift correlation based assignment of the 13C and 1H NMR spectra of nifedipin are presented along with some results of MM+ and PM3 conformation analysis. Both computation methods yield asymmetric low energy conformers. MM+ molecular dynamics simulations give similar results. A lower limit to the interconversion rate of the asymmetric low energy conformers is determined using magnetic shielding differences obtained by TNDO/2 calculations. PMID:8714360

Kövesdi, I; Kapillerné, D R

1996-01-01

14

13C-NMR data of daphnane diterpenoids.  

PubMed

Daphnane diterpenoids are mainly distributed in Thymelaeaceae and Euphorbiaceae and have various bioactivities. About 100 daphnane diterpenoids have been isolated from natural plants. In this review, we systematically summarize the (13)C-NMR data of daphnane diterpenoids isolated from natural plants over the past several decades and briefly discussed their biological activities and basic structural-activity relationship. PMID:23813597

Wang, Hong-Bing; Liu, Li-Ping; Wang, Xiao-Yang

2013-06-27

15

Study of molecular interactions with 13C DNP-NMR.  

PubMed

NMR spectroscopy is an established, versatile technique for the detection of molecular interactions, even when these interactions are weak. Signal enhancement by several orders of magnitude through dynamic nuclear polarization alleviates several practical limitations of NMR-based interaction studies. This enhanced non-equilibrium polarization contributes sensitivity for the detection of molecular interactions in a single NMR transient. We show that direct (13)C NMR ligand binding studies at natural isotopic abundance of (13)C gets feasible in this way. Resultant screens are easy to interpret and can be performed at (13)C concentrations below muM. In addition to such ligand-detected studies of molecular interaction, ligand binding can be assessed and quantified with enzymatic assays that employ hyperpolarized substrates at varying enzyme inhibitor concentrations. The physical labeling of nuclear spins by hyperpolarization thus provides the opportunity to devise fast novel in vitro experiments with low material requirement and without the need for synthetic modifications of target or ligands. PMID:20022775

Lerche, Mathilde H; Meier, Sebastian; Jensen, Pernille R; Baumann, Herbert; Petersen, Bent O; Karlsson, Magnus; Duus, Jens Ø; Ardenkjaer-Larsen, Jan H

2009-12-03

16

Spectral editing for in vivo 13C magnetic resonance spectroscopy  

PubMed Central

In vivo detection of carboxylic/amide carbons is a promising technique for studying cerebral metabolism and neurotransmission due to the very low RF power required for proton decoupling. In the carboxylic/amide region, however, there is severe spectral overlap between acetate C1 and glutamate C5, complicating studies that use acetate as an astroglia-specific substrate. There are no known in vivo MRS techniques that can spectrally resolve acetate C1 and glutamate C5 singlets. In this study, we propose to spectrally separate acetate C1 and glutamate C5 by a two-step J-editing technique after introducing homonuclear 13C-13C scalar coupling between carboxylic/amide carbons and aliphatic carbons. By infusing [1,2-13C2]acetate instead of [1-13C]acetate the acetate doublet can be spectrally edited because of the large separation between acetate C2 and glutamate C4 in the aliphatic region. This technique can be applied to studying acetate transport and metabolism in brain in the carboxylic/amide region without spectral interference.

Xiang, Yun; Shen, Jun

2012-01-01

17

An in Vivo 13C NMR Analysis of the Anaerobic Yeast Metabolism of 1-13C-Glucose  

Microsoft Academic Search

A biochemistry laboratory experiment that studies the dynamics of the anaerobic yeast metabolism of 1-13C-D-glucose via NMR is described. Fleischmann's Active Dry yeast, under anaerobic conditions, produces primarily 2-13C-ethanol and some 1-13C-glycerol as end products. An experiment is described in which the yeast is subjected to osmotic shock from an increasing sodium chloride concentration. Under these conditions, the yeast increases

Brent J. Giles; Zenziwe Matsche; Ryan D. Egeland; Ryan A. Reed; Scott S. Morioka; Richard L. Taber

1999-01-01

18

QUANTITATIVE SOLID-STATE 13C NMR SPECTROSCOPY OF ORGANIC MATTER FRACTIONS IN LOWLAND RICE SOILS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Spin counting on solid-state **13C cross-polarization (CP) nuclear magnetic resonance (NMR) spectra of two humic fractions isolated from tropical lowland soils showed that only 32-81% of potential **13C NMR signal was detected. The observability of **13C NMR signal (Cobs) was higher in the mobile h...

19

A solid state 13C-NMR study of kerogen degradation during black shale weathering  

Microsoft Academic Search

Solid state 13C nuclear magnetic resonance (NMR) spectroscopy is used to examine kerogen composition in weathering profiles of the Monterey, Green River, Woodford, and New Albany formations. Techniques include cross polarization (CP) and Bloch decay (BD) spectral acquisition, dipolar dephasing (DD), spin counting, experiments to provide estimates of relaxation times (T1?H and T1H), and proton spin relaxation editing (PSRE). It

S. T Petsch; R. J Smernik; T. I Eglinton; J. M Oades

2001-01-01

20

A 13C NMR spectrometric method for the determination of intramolecular ?13C values in fructose from plant sucrose samples.  

PubMed

Recent developments in (13) C NMR spectrometry have allowed the determination of intramolecular (13) C/(12) C ratios with high precision. However, the analysis of carbohydrates requires their derivatization to constrain the anomeric carbon. Fructose has proved to be particularly problematic because of a byproduct occurring during derivatization and the complexity of the NMR spectrum of the derivative. Here, we describe a method to determine the intramolecular (13) C/(12) C ratios in fructose by (13) C NMR analysis of the acetyl-isopropylidene derivative. We have applied this method to measure the intramolecular (13) C/(12) C distribution in the fructosyl moiety of sucrose and have compared this with that in the glucosyl moiety. Three prominent features stand out. First, in sucrose from both C(3) and C(4) plants, the C-1 and C-2 positions of the glucosyl and fructosyl moieties are markedly different. Second, these positions in C(3) and C(4) plants show a similar profile. Third, the glucosyl and fructosyl moieties of sucrose from Crassulacean acid metabolism (CAM) metabolism have a different profile. These contrasting values can be interpreted as a result of the isotopic selectivity of enzymes that break or make covalent bonds in glucose metabolism, whereas the distinctive (13) C pattern in CAM sucrose probably indicates a substantial contribution of gluconeogenesis to glucose synthesis. PMID:21388380

Gilbert, Alexis; Silvestre, Virginie; Robins, Richard J; Tcherkez, Guillaume; Remaud, Gérald S

2011-03-09

21

An in Vivo 13C NMR Analysis of the Anaerobic Yeast Metabolism of 1-13C-Glucose  

NASA Astrophysics Data System (ADS)

A biochemistry laboratory experiment that studies the dynamics of the anaerobic yeast metabolism of 1-13C-D-glucose via NMR is described. Fleischmann's Active Dry yeast, under anaerobic conditions, produces primarily 2-13C-ethanol and some 1-13C-glycerol as end products. An experiment is described in which the yeast is subjected to osmotic shock from an increasing sodium chloride concentration. Under these conditions, the yeast increases the ratio of glycerol to ethanol. The experiment can be accomplished in a single laboratory period.

Giles, Brent J.; Matsche, Zenziwe; Egeland, Ryan D.; Reed, Ryan A.; Morioka, Scott S.; Taber, Richard L.

1999-11-01

22

(13) C NMR spectroscopy of copoly(arylenephthalide) derivatives with diphenyloxide and terphenyl fragments in the main chain.  

PubMed

(1) H and (13) ? NMR spectral assignments have been provided for low-molecular reference monomers, poly(diphenyleneoxidephthalide) and periodic copoly(arylenephthalide) derivatives such as AB, ABB, and ABBB (where A?=?terphenylenephthalide and B?=?diphenyleneoxidephthalide) using (1) H-(1) H COSY, (1) H-(13) C HSQC and HMBC NMR techniques. Distinctive (13) C NMR chemical shifts of a main chain have been observed containing fragments of similar structures and lateral phthalate groups being part of various diads. Copyright © 2013 John Wiley & Sons, Ltd. PMID:23921970

Kraikin, Vladimir A; Fatykhov, Akhnef A; Sakhipova, Il'nara I; Sedova, Elvira A; Egorov, Aleksandr E; Salazkin, Sergey N

2013-08-07

23

NMR crystallography: the effect of deuteration on high resolution 13C solid state NMR spectra of a 7-TM protein.  

PubMed

The effect of deuteration on the 13C linewidths of U-13C, 15N 2D crystalline bacteriorhodopsin (bR) from Halobacterium salinarium, a 248-amino acid protein with seven-transmembrane (7TM) spanning regions, has been studied in purple membranes as a prelude to potential structural studies. Spectral doubling of resonances was observed for receptor expressed in 2H medium (for both 50:50% 1H:2H, and a more highly deuterated form) with the resonances being of similar intensities and separated by <0.3 ppm in the methyl spectral regions in which they were readily distinguished. Line-widths of the methyl side chains were not significantly altered when the protein was expressed in highly deuterated medium compared to growth in fully protonated medium (spectral line widths were about 0.5 ppm on average for receptor expressed both in the fully protonated and highly deuterated media from the C delta, C gamma 1, and C gamma 2 Ile 13C signals observed in the direct, 21-39 ppm, and indirect, 9-17 ppm, dimensions). The measured 13C NMR line-widths observed for both protonated and deuterated form of the receptor are sufficiently narrow, indicating that this crystalline protein morphology is suitable for structural studies. 1) decoupling comparison of the protonated and deuterated bR imply that deuteration may be advantageous for samples in which low power 1H decoupling is required. PMID:18001693

Varga, K; Aslimovska, L; Parrot, I; Dauvergne, M-T; Haertlein, M; Forsyth, V T; Watts, A

2007-10-04

24

Labeling strategies for 13C-detected aligned-sample solid-state NMR of proteins.  

PubMed

(13)C-detected solid-state NMR experiments have substantially higher sensitivity than the corresponding (15)N-detected experiments on stationary, aligned samples of isotopically labeled proteins. Several methods for tailoring the isotopic labeling are described that result in spatially isolated (13)C sites so that dipole-dipole couplings among the (13)C are minimized, thus eliminating the need for homonuclear (13)C-(13)C decoupling in either indirect or direct dimensions of one- or multi-dimensional NMR experiments that employ (13)C detection. The optimal percentage for random fractional (13)C labeling is between 25% and 35%. Specifically labeled glycerol and glucose can be used at the carbon sources to tailor the isotopic labeling, and the choice depends on the resonances of interest for a particular study. For investigations of the protein backbone, growth of the bacteria on [2-(13)C]-glucose-containing media was found to be most effective. PMID:19781966

Filipp, Fabian V; Sinha, Neeraj; Jairam, Lena; Bradley, Joel; Opella, Stanley J

2009-09-02

25

1H and 13C NMR chemical shift assignments of spiro-cycloalkylidenehomo- and methanofullerenes by the DFT-GIAO method.  

PubMed

The (1)H and (13)C NMR chemical shifts of spiro-cycloalkylidene[60]fullerenes were assigned using experimental NMR data and the Density Functional Theory (DFT)-Gauge Independence Of Atomic Orbitals method (GAIO) calculation method in the Perdew Burke Ernzerhof (PBE)/3z approach. The calculated values of the (13)C NMR chemical shifts adequately reproduce the experimental values at this quantum chemistry approach. Similar assignments will be helpful for (13)C NMR spectral analysis of homo- and methano[60]fullerene derivatives for structure elucidation and to determine the influence of fullerene frames on substituents and the influence of substituents on fullerene cores. PMID:21452349

Khalilov, L M; Tulyabaev, A R; Yanybin, V M; Tuktarov, A R

2011-03-31

26

NMR at cryogenic temperatures: A {sup 13}C NMR study of ferrocene  

SciTech Connect

A new cryogenic apparatus is described that can be used to obtain NMR spectra at temperatures down to 8--10 K. The static solid {sup 13}C NMR spectrum of ferrocene is recorded at that temperature. Spectra recorded at higher temperatures show that ferrocene is still freely rotating about its 5-fold symmetry axis on the {sup 13}C NMR time scale at 45--50 K. A comparison of the principal values of the {sup 13}C chemical-shift tensor obtained from the room- and low-temperature spectra of ferrocene indicates that the lowest frequency chemical shift principal component, {delta}{sub 33}, is tilted off this symmetry axis by approximately 12{degree}. Quantum chemical calculations of the chemical-shift tensor, completed on structures of ferrocene from the literature as well as on optimized structures with the cyclopentadienyl rings locked in both the staggered and eclipsed arrangements, predict the angle between the {delta}{sub 33} direction and the rotation axis to be between 11 and 15{degree}, depending upon the geometry used in the calculation. The calculations also predict the sign of the angular perturbation, information not obtained from the experiment. An explanation of this angular change in the {delta}{sub 33} direction is provided by the composition of the molecular orbitals.

Orendt, A.M.; Facelli, J.C.; Jiang, Y.J.; Grant, D.M. [Univ. of Utah, Salt Lake City, UT (United States)

1998-09-24

27

In vivo 13C-NMR studies on the metabolism of the lugworm Arenicola marina.  

PubMed

13C-NMR natural-abundance spectra of specimens of Arenicola marina obtained, showed seasonal changes in the concentration of some metabolites, with the osmolite alanine as well as triacylglyceride storage compounds present at high concentrations. Glycogen was sometimes only barely detectable due to the low natural abundance level of 13C. Glycogenic metabolism of the lugworm A. marina was studied in vivo by 13C-NMR spectroscopy using 13C-labelled glucose. During recovery from a hypoxic period [1-13C]glucose was incorporated into glycogen. [1-13C]Glucose was injected 5 h after the end of hypoxia to guarantee sufficient and reliable 13C labelling of glycogen. An earlier injection of [1-13C]glucose led to considerably diminished incorporation of 13C-labelled glucosyl units into glycogen, probably due to the consumption of the available glucose as fuel for ATP production. No scrambling of 13C into the C6 position of glycogen was observed, indicating a lack of gluconeogenic activity. 13C was also incorporated into the C3 positions of alanine and alanopine. To assign correctly this last 13C-NMR resonance, the compound was synthesized biochemically. No labelling of glycogen was observed when [3-13C]alanine was injected into the coelomic cavity with similar incubation conditions being used. The 13C of [1-13C]glucose, incorporated into glycogen, showed a very low turnover rate in normoxic lugworms as shown by two 13C(1H)-NMR spectra, one obtained 48 h after the other. On the other hand, in hypoxia lugworms the signal due to 13C-labelled glycogen decreased very rapidly proving a high turnover rate. The disappearance of 13C from glycogen during the first 24 h of hypoxia indicates that the last glycosyl units to be synthesized are the first to be utilized. Lugworms were quite sensitive to the 1H-decoupling field used for obtaining the 13C(1H)-NMR spectra, especially at 11.7 T. Using bi-level composite-pulse decoupling and long relaxation delays, no tissue damage or stress-dependent phosphagen mobilization, as judged by 31P-NMR spectroscopy, was observed. PMID:2226445

Juretschke, H P; Kamp, G

1990-10-01

28

Isolation and purification of deoxyribonucleosides from 90% 13C-enriched DNA of algal cells and their characterization by 1H and 13C NMR.  

PubMed

13C-enriched deoxyribonucleosides have been isolated from the DNA of Algal cells grown in an atmosphere of 90% 13C-labelled carbon dioxide. The 13C enriched DNA was quantitatively hydrolysed with DNase I, snake venom phosphodiesterase I and alkaline phosphatase of intestinal mucosa. The resulting deoxyribonucleosides were separated by preparative reversed-phase high pressure liquid chromatography in 60 minutes with detection by ultraviolet absorption at 254 nm. The final products were obtained in milligram quantities in high purity and in high yield. The 1H resonances of the base and sugar protons of these deoxyribonucleosides appear as well resolved multiplets in the 600 MHz NMR spectrum, due to the extensive 1H-13C couplings. Similarly, the 13C resonances of these deoxyribonucleosides appear as multiplets in the 75.5 MHz 13C NMR spectrum, due to 13C-13C couplings. The 1H-13C and 13C-13C coupling constants were also measured and tabulated. The isotopic enrichment of 13C these deoxyribonucleosides was obtained by integration of the 1H and/or 13C NMR spectra. It was found that the enrichment varied from carbon to carbon and species to species in the range of 70-89%, suggesting differential uptake and assimilation of 90% 13CO2 during metabolism pathways. This protocol provides experimentally useful quantities of 13C-enriched deoxyribonucleosides, which may be incorporated into site-specifically labeled oligonucleotides by chemical synthesis. PMID:4000954

Chandrasegaran, S; Kan, L S; Sillerud, L O; Skoglund, C; Bothner-By, A A

1985-03-25

29

Isolation and purification of deoxyribonucleosides from 90% 13C-enriched DNA of algal cells and their characterization by 1H and 13C NMR.  

PubMed Central

13C-enriched deoxyribonucleosides have been isolated from the DNA of Algal cells grown in an atmosphere of 90% 13C-labelled carbon dioxide. The 13C enriched DNA was quantitatively hydrolysed with DNase I, snake venom phosphodiesterase I and alkaline phosphatase of intestinal mucosa. The resulting deoxyribonucleosides were separated by preparative reversed-phase high pressure liquid chromatography in 60 minutes with detection by ultraviolet absorption at 254 nm. The final products were obtained in milligram quantities in high purity and in high yield. The 1H resonances of the base and sugar protons of these deoxyribonucleosides appear as well resolved multiplets in the 600 MHz NMR spectrum, due to the extensive 1H-13C couplings. Similarly, the 13C resonances of these deoxyribonucleosides appear as multiplets in the 75.5 MHz 13C NMR spectrum, due to 13C-13C couplings. The 1H-13C and 13C-13C coupling constants were also measured and tabulated. The isotopic enrichment of 13C these deoxyribonucleosides was obtained by integration of the 1H and/or 13C NMR spectra. It was found that the enrichment varied from carbon to carbon and species to species in the range of 70-89%, suggesting differential uptake and assimilation of 90% 13CO2 during metabolism pathways. This protocol provides experimentally useful quantities of 13C-enriched deoxyribonucleosides, which may be incorporated into site-specifically labeled oligonucleotides by chemical synthesis.

Chandrasegaran, S; Kan, L S; Sillerud, L O; Skoglund, C; Bothner-By, A A

1985-01-01

30

13C nuclear magnetic resonance data of lanosterol derivatives—Profiling the steric topology of the steroid skeleton via substituent effects on its 13C NMR  

NASA Astrophysics Data System (ADS)

The 13C NMR spectra of over 24 tetracyclic triterpenoid derivatives have been structurally analyzed. The 13C NMR chemical shifts allow one to probe the steric topology of the rigid steroid skeleton and inductive effects of its substituents. Use of deuterium labeling in chemical shift assignment and B-ring aromatic terpenoids are also featured.

Dias, Jerry Ray; Gao, Hongwu

2009-12-01

31

n Butane conversion on sulfated zirconia: in situ 13 C MAS NMR monitoring of the kinetics of the 13 C-label scrambling and isomerization  

Microsoft Academic Search

The kinetics of the conversion of 13C-labeled n-butane adsorbed on sulfated zirconia (SZ) were monitored by in situ13C MAS NMR spectroscopy. Rate constants of n- to isobutane isomerization and of the 13C-isotope scrambling from the primary to the secondary carbon atoms in n-butane were determined. The monomolecular scrambling of the 13C-label in adsorbed n-butane has an activation energy of 17 ± 3 kcal

A. G. Stepanov; M. V. Luzgin; S. S. Arzumanov; W. Wang; M. Hunger; D. Freude

2005-01-01

32

The dynamics of GATG glycodendrimers by NMR diffusion and quantitative (13)C relaxation.  

PubMed

The dynamics of GATG glycodendrimers have been investigated by NMR translational diffusion and quantitative (13)C relaxation studies (Lipari-Szabo model-free), allowing the determination of the correlation times describing the dendrimer segmental orientational mobility. PMID:20445946

Novoa-Carballal, Ramon; Säwén, Elin; Fernandez-Megia, Eduardo; Correa, Juan; Riguera, Ricardo; Widmalm, Göran

2010-05-06

33

In vivo 13C NMR spectroscopy and metabolic modeling in the brain: a practical perspective  

Microsoft Academic Search

In vivo 13C NMR spectroscopy has the unique capability to measure metabolic fluxes noninvasively in the brain. Quantitative measurements of metabolic fluxes require analysis of the 13C labeling time courses obtained experimentally with a metabolic model. The present work reviews the ingredients necessary for a dynamic metabolic modeling study, with particular emphasis on practical issues.

Pierre-Gilles Henry; Gregor Adriany; Dinesh Deelchand; Rolf Gruetter; Malgorzata Marjanska; Gqlin Oz; Elizabeth R. Seaquist; Alexander Shestov; Kamil Ugùurbil

2006-01-01

34

NATURAL ABUNDANCE 13C NMR SPECTROSCOPY OF DOUBLE-STRANDED DNA  

EPA Science Inventory

Although 13C NMR spectroscopy has already proved extremely useful in studies of biopolymers, including t-RNA's, and single-stranded polynucleotides, no successful study of native double-stranded DNA has been reported. This failure is mainly due to extremely unfavorable 13C spin r...

35

Analysis of positional distribution of fatty acids in palm oil by 13 C NMR spectroscopy  

Microsoft Academic Search

The13C NMR spectrum of the carbonyl carbons of the acyl groups of triacylglycerols of palm oil has been shown to give the composition\\u000a of saturated, oleic and linoleic acyl groups at the 1,3-positions and at the 2-position of the glycerol moiety. Except for\\u000a the lack of differentiation of the saturated fatty acids, the13C NMR technique provides the same information as

Soon Ng

1985-01-01

36

Characterization by 13C n.m.r. spectroscopy of base oils produced by different processes  

Microsoft Academic Search

The hydrocarbon composition of base oils produced by different processes—hydrotreatments (hydrocracking and wax isomerization), solvent refining plus hydrofinishing, and severe hydrofinishing—were determined by 13C n.m.r. spectroscopy. Structural parameters such as normal and iso-paraffin contents, average chain length and number of branching sites were estimated by new equations derived after complete assignment of signals in the 5–21 ppm 13C n.m.r. region.

Amarjeet S. Sarpal; Gurpreet S. Kapur; Suman Mukherjee; Surendra K. Jain

1997-01-01

37

13 C NMR spectroscopy of amino acid mixtures  

Microsoft Academic Search

In this work the composition of certain low-molecular-weight components, including free amino acids, in hydrolysates of pig liver tissue at different stages of enzymatic hydrolysis, was determined by the method of ~3C NMR spectroscopy. EXPERIMENTAL Products of enzymatic hydrolysis of a homogenate of pig liver tissue in phosphate buffer [i0], samples of the preparation hepahydryl and artificial mixtures of various

S. V. Tarabakin; V. P. Panov; I. G. Sarkisova; E. V. Bykova

1982-01-01

38

/sup 13/C NMR chemical shift assignments for gammacerane (tetrahymane)  

SciTech Connect

The carbon-13 NMR chemical shift values were obtained and assigned for each carbon atom of the pentacyclic triterpane gammacerane. Thirteen resonances of nearly unit intensity and one resonances of approximately two intensity units were observed which supports the proposed C/sub 2/ symmetry. The assignments were made by comparison with similar molecules and off-resonance decoupling. Relative to podocarpane C-7 and C-9 resonances of gammacerane were found to be shifted upfield instead of the expected downfield shift. These shifts are attributed to subtle conformational effects and an accentuated ..gamma..-effect due to the rigidity of the carbon skeleton.

Netzel, D.A.; Linn, D.E.

1980-07-01

39

A CP\\/MAS 13C-NMR study of cellulose structure on the surface of refined kraft pulp fibers  

Microsoft Academic Search

The average lateral fibril and fibril aggregate dimensions and the crystallinity of the cellulose in a spruce kraft pulp were investigated by CP\\/MAS 13C-NMR spectroscopy in combination with spectral fitting. Cellulose isolated by chlorite-delignification and acid hydrolysis from fines fractions enriched in surface material and long fiber fractions enriched in bulk material exhibited no major differences in either lateral dimensions

Eva-Lena Hult; Tiina Liitiä; Sirkka Liisa Maunu; Bo Hortling; Tommy Iversen

2002-01-01

40

Insights into the metabolic response to traumatic brain injury as revealed by 13C NMR spectroscopy  

PubMed Central

The present review highlights critical issues related to cerebral metabolism following traumatic brain injury (TBI) and the use of 13C labeled substrates and nuclear magnetic resonance (NMR) spectroscopy to study these changes. First we address some pathophysiologic factors contributing to metabolic dysfunction following TBI. We then examine how 13C NMR spectroscopy strategies have been used to investigate energy metabolism, neurotransmission, the intracellular redox state, and neuroglial compartmentation following injury. 13C NMR spectroscopy studies of brain extracts from animal models of TBI have revealed enhanced glycolytic production of lactate, evidence of pentose phosphate pathway (PPP) activation, and alterations in neuronal and astrocyte oxidative metabolism that are dependent on injury severity. Differential incorporation of label into glutamate and glutamine from 13C labeled glucose or acetate also suggest TBI-induced adaptations to the glutamate-glutamine cycle.

Bartnik-Olson, Brenda L.; Harris, Neil G.; Shijo, Katsunori; Sutton, Richard L.

2013-01-01

41

Structural characteristics of marine sedimentary humic acids by CP\\/MAS 13C NMR spectroscopy  

Microsoft Academic Search

Humic acids from sediments of different depositional environments have been studied by solid-state 13C NMR and the results compared with the traditional wet chemical analysis. Results obtained are well in agreement with the previous literature reports that the carboxyl content measured by NMR correlated better with the total acidity, as well as with the carboxyl content obtained by wet chemical

Sugandha Sardessai; Solimabi Wahidullah

1998-01-01

42

Comprehensive signal assignment of (13)c-labeled lignocellulose using multidimensional solution NMR and (13)c chemical shift comparison with solid-state NMR.  

PubMed

A multidimensional solution NMR method has been developed using various pulse programs including HCCH-COSY and (13)C-HSQC-NOESY for the structural characterization of commercially available (13)C labeled lignocellulose from potatoes (Solanum tuberosum L.), chicory (Cichorium intybus), and corn (Zea mays). This new method allowed for 119 of the signals in the (13)C-HSQC spectrum of lignocelluloses to be assigned and was successfully used to characterize the structures of lignocellulose samples from three plants in terms of their xylan and xyloglucan structures, which are the major hemicelluloses in angiosperm. Furthermore, this new method provided greater insight into fine structures of lignin by providing a high resolution to the aromatic signals of the ?-aryl ether and resinol moieties, as well as the diastereomeric signals of the ?-aryl ether. Finally, the (13)C chemical shifts assigned in this study were compared with those from solid-state NMR and indicated the presence of heterogeneous dynamics in the polysaccharides where rigid cellulose and mobile hemicelluloses moieties existed together. PMID:24010724

Komatsu, Takanori; Kikuchi, Jun

2013-09-06

43

Fast Spatially Encoded 3D NMR Strategies for (13)C-Based Metabolic Flux Analysis.  

PubMed

The measurement of site-specific (13)C enrichments in complex mixtures of (13)C-labeled metabolites is a powerful tool for metabolic flux analysis. One of the main methods to measure such enrichments is homonuclear (1)H 2D NMR. However, the major limitation of this technique is the acquisition time, which can amount to a few hours. This drawback was recently overcome by the design of fast COSY experiments for measuring specific (13)C-enrichments, based on single-scan 2D NMR. However, these experiments are still limited by overlaps because of(1)H-(13)C splittings, thus limiting the metabolic information accessible for complex biological mixtures. To circumvent this limitation, we propose to tilt the (1)H-(13)C coupling into a third dimension via fast-hybrid 3D NMR methods combining the speed of ultrafast 2D NMR with the high resolution of conventional methods. Two strategies are described that allow the acquisition of a complete 3D J-resolved-COSY spectrum in 12 min (for concentrations as low as 10 mM). The analytical potentialities of both methods are evaluated on a series of (13)C-enriched glucose samples and on a biomass hydrolyzate obtained from Escherichia coli cells. Once optimized, the two complementary experiments lead to a trueness and a precision of a few percent and an excellent linearity. The advantages and drawbacks of these approaches are discussed and their potentialities are highlighted. PMID:24006900

Boisseau, Renaud; Charrier, Benoît; Massou, Stéphane; Portais, Jean-Charles; Akoka, Serge; Giraudeau, Patrick

2013-09-24

44

1H-NMR and 13C-NMR lipid profiles of human renal tissues.  

PubMed

Lipids from human renal tissues are studied by means of (1)H- and (13)C-NMR spectroscopy. The total lipid fractions obtained from healthy kidneys, malignant renal cell carcinomas, and benign oncocytomas are characterized and analyzed to elucidate the main differences between the functional and neoplastic tissues. In all cases the lipid components are well identified. The healthy kidney is characterized by high amounts of triglycerides and the presence of cholesterol in its free form. On the contrary, renal cell carcinomas contain high amounts of cholesterol that are almost completely esterified as oleate, suggesting an intracellular localization of the cholesteryl esters synthesis. Cholesteryl esters are considered markers of renal cell carcinomas, thus supporting recent theories that these compounds play a leading role in cell proliferation. Oncocytomas are particularly rich in phosphatidylcholine and, analogous to the healthy kidney, are completely lacking in cholesteryl esters. Healthy kidneys and oncocytomas appear to have other similarities if compared with renal cell carcinomas: a very high fatty acyl/cholesterol ratio, the presence of dolichols, and a higher grade of unsaturation. The (13)C data suggest a new method for the direct evaluation of the saturated/unsaturated fatty acyl ratio. PMID:12583011

Tugnoli, V; Bottura, G; Fini, G; Reggiani, A; Tinti, A; Trinchero, A; Tosi, M R

2003-01-01

45

sup 13 C NMR for the assessment of human brain glucose metabolism in vivo  

SciTech Connect

Proton-decoupled {sup 13}C NMR spectra of the human head were obtained during hyperglycemic glucose clamping using intravenous infusions of (1-{sup 13}C)glucose in normal volunteers. In addition to {sup 13}C signals of mobile lipids, a variety of new metabolite resonances could be resolved for the first time in the human brain. At an enrichment level of 20% (1-{sup 13}C)glucose, the signals of {alpha}- and {beta}-glucose at 92.7 and 96.6 ppm, respectively, could be detected in the human brain after only an infusion period of 15 minutes. The spatial localization of the different regions of interest was confirmed by {sup 13}C NMR spectroscopic imaging with a time resolution of 9 minutes. Increasing the enrichment level to 99% (1-{sup 13}C)glucose not only improved the time resolution but allowed the detection of metabolic breakdown products of (1-{sup 13}C)glucose. The time course of {sup 13}C label incorporation into the C{sub 2}, C{sub 3}, and C{sub 4} resonances of glutamate/glutamine and into lactate could be recorded in the human brain. These results suggest the possibility of obtaining time-resolved, spatially selective, and chemically specific information on the human body.

Beckman, N.; Seelig, J. (Univ. of Basel (Switzerland)); Turkalj, I.; Keller, U. (Univ. Hospital, Basel (Switzerland))

1991-07-02

46

Matrix-free dynamic nuclear polarization enables solid-state NMR (13)C-(13)C correlation spectroscopy of proteins at natural isotopic abundance.  

PubMed

We introduce a general approach for dynamic nuclear polarization (DNP) enhanced solid-state NMR that overcomes the current problems in DNP experiments caused by the use of frozen solutions. Notably, we report for the first time a 2D (13)C-(13)C correlation spectrum of a protein without the use of isotopic labeling. PMID:24013616

Takahashi, Hiroki; Hediger, Sabine; De Paëpe, Gaël

2013-10-21

47

Characterization of uniformly and atom-specifically (13)C-labeled heparin and heparan sulfate polysaccharide precursors using (13)C NMR spectroscopy and ESI mass spectrometry.  

PubMed

The biological actions of heparin and heparan sulfate, two structurally related glycosaminoglycans, depend on the organization of the complex heparanome. Due to the structural complexity of the heparanome, the sequence of variably sulfonated uronic acid and glucosamine residues is usually characterized by the analysis of smaller oligosaccharide and disaccharide fragments. Even characterization of smaller heparin and heparan sulfate oligosaccharide or disaccharide fragments using simple 1D (1)H NMR spectroscopy is often complicated by the extensive signal overlap. (13)C NMR signals, on the other hand, overlap less and therefore, (13)C NMR spectroscopy can greatly facilitate the structural elucidation of the complex heparanome and provide finer insights into the structural basis for biological functions. This is the first report of the preparation of anomeric carbon-specific (13)C-labeled heparin and heparan sulfate precursors from the Escherichia coli K5 strain. Uniformly (13)C- and (15)N-labeled precursors were also produced and characterized by (13)C NMR spectroscopy. Mass spectrometric analysis of enzymatically fragmented disaccharides revealed that anomeric carbon-specific labeling efforts resulted in a minor loss/scrambling of (13)C in the precursor backbone, whereas uniform labeling efforts resulted in greater than 95% (13)C isotope enrichment in the precursor backbone. These labeled precursors provided high-resolution NMR signals with great sensitivity and set the stage for studying the heparanome-proteome interactions. PMID:20832774

Nguyen, Thao K N; Tran, Vy M; Victor, Xylophone V; Skalicky, Jack J; Kuberan, Balagurunathan

2010-08-21

48

Characterization of uniformly and atom-specifically 13C-labeled heparin and heparan sulfate polysaccharide precursors using 13C NMR spectroscopy and ESI mass spectrometry  

PubMed Central

The biological actions of heparin and heparan sulfate, two structurally related glycosaminoglycans, depend on the organization of the complex heparanome. Due to the structural complexity of the heparanome, the sequence of variably sulfonated uronic acid and glucosamine residues is usually characterized by the analysis of smaller oligosaccharide and disaccharide fragments. Even characterization of smaller heparin/heparan sulfate oligosaccharide or disaccharide fragments using simple 1D 1H NMR spectroscopy is often complicated by the extensive signal overlap. 13C NMR signals, on the other hand, overlap less and therefore, 13C NMR spectroscopy can greatly facilitate the structural elucidation of the complex heparanome and provide finer insights into the structural basis for biological functions. This is the first report of the preparation of anomeric carbon-specific 13C-labeled heparin/heparan sulfate precursors from the Escherichia coli K5 strain. Uniformly 13C- and 15N-labeled precursors were also produced and characterized by 13C NMR spectroscopy. Mass spectrometric analysis of enzymatically fragmented disaccharides revealed that anomeric carbon-specific labeling efforts resulted in a minor loss/scrambling of 13C in the precursor backbone, whereas uniform labeling efforts resulted in greater than 95% 13C isotope enrichment in the precursor backbone. These labeled precursors provided high-resolution NMR signals with great sensitivity and set the stage for studying the heparanome–proteome interactions.

Nguyen, Thao K. N.; Tran, Vy M.; Victor, Xylophone V.; Skalicky, Jack J.; Kuberan, Balagurunathan

2010-01-01

49

Intramolecular 1H-13C Distance Measurement in Uniformly 13C, 15N Labeled Peptides by Solid-State NMR  

PubMed Central

A 1H-13C frequency-selective REDOR (FS-REDOR) experiment is developed for measuring intramolecular 1H-13C distances in uniformly 13C, 15N-labeled molecules. Theory and simulations show that the experiment removes the interfering homonuclear 1H-1H, 13C-13C and heteronuclear 1H-15N, 13C-15N dipolar interactions while retaining the desired heteronuclear 1H-13C dipolar interaction. Our results indicate that this technique, combined with the numerical fitting, can be used to measure a 1H-13C distance up to 5 Å. We also demonstrate that the measured intramolecular 1H-13C distances are useful to determine dihedral angles in proteins.

Li, Shenhui; Su, Yongchao; Hong, Mei

2012-01-01

50

A two-dimensional 1H detected 13C NMR investigation of pyruvate metabolism in Halobacterium salinarium.  

PubMed

Two-dimensional 1H detected 13C NMR spectroscopy has been used to study the intracellular metabolism of [3-(13)C]pyruvate in Halobacterium salinarium. The method, resulting in considerable improvement in spectral resolution and signal-to-noise ratio, is well suited for studying transient metabolic intermediates. Pyruvate utilization by the bacterium is a double exponential function with rate constants of 49.13 and 4.67x10(-3) per min. The relative 13C enrichment is the fastest for C-3 glutamate. Glutamate C-4 labeling decreases initially and increases later on during incubation, while glutamine C-3 is high to begin with and exhibits a declining trend. The glutamate labeling indicates a high initial flux through pyruvate carboxylase and extensive randomizing of the label in the tricarboxylic acid cycle. PMID:9504417

Majumdar, A; Sonawat, H M

1998-01-01

51

Acetone hydration in supercritical water: 13C-NMR spectroscopy and Monte Carlo simulation  

Microsoft Academic Search

The 13C-NMR chemical shift of acetone delta(13C=O) was measured in aqueous solution at high temperatures up to 400 °C and water densities of 0.10-0.60 g\\/cm3 for the study of hydration structure in the supercritical conditions. The average number NHB of hydrogen bonds (HBs) between an acetone and solvent waters and the energy change DeltaE upon the HB formation were evaluated

Yoshihiro Takebayashi; Satoshi Yoda; Tsutomu Sugeta; Katsuto Otake; Takeshi Sako; Masaru Nakahara

2004-01-01

52

Detection of human muscle glycogen by natural abundance /sup 13/C NMR  

SciTech Connect

Natural abundance /sup 13/C nuclear magnetic resonance spectroscopy was used to detect signals from glycogen in the human gastrocnemius muscle. The reproducibility of the measurement was demonstrated, and the ability to detect dynamic changes was confirmed by measuring a decrease in muscle glycogen levels after exercise and its subsequent repletion. Single frequency gated /sup 1/H decoupling was used to obtain decoupled natural abundance /sup 13/C NMR spectra of the C-1 position of muscle glycogen.

Avison, M.J.; Rothman, D.L.; Nadel, E.; Shulman, R.G.

1988-03-01

53

A 13C-NMR study of exopolysaccharide synthesis in Rhizobium meliloti Su47 strain  

NASA Astrophysics Data System (ADS)

Metabolic pathways implied in the synthesis of succinoglycan produced by the Su47 strain of R. meliloti were evaluated by 13C-NMR spectroscopy after incubation with [1{-}13C] or [2{-}13C] glucose. The biosynthesis of this polymer by R. meliloti from glucose occurred by a direct polymerisation of the introduced glucose and by the pentose phosphate pathway. Les voies métaboliques impliquées dans la synthèse du succinoglycane produit par la souche Su47 de R. meliloti ont été évaluées par la spectroscopie de RMN du carbone 13 après incubation des cellules avec du [1{-}13C] ou [2{-}13C] glucose. La biosynthèse de ce polymère à partir du glucose se produit par polymérisation directe du glucose et par la voie des pentoses phosphate.

Tavernier, P.; Portais, J.-C.; Besson, I.; Courtois, J.; Courtois, B.; Barbotin, J.-N.

1998-02-01

54

Dynamic nuclear polarization-enhanced 13C NMR spectroscopy of static biological solids  

NASA Astrophysics Data System (ADS)

We explore the possibility of using dynamic nuclear polarization (DNP) to enhance signals in structural studies of biological solids by solid state NMR without sample spinning. Specifically, we use 2D 13C13C exchange spectroscopy to probe the peptide backbone torsion angles (?, ?) in a series of selectively 13C-labeled 40-residue ?-amyloid (A?1–40) samples, in both fibrillar and non-fibrillar states. Experiments are carried out at 9.39 T and 8 K, using a static double-resonance NMR probe and low-power microwave irradiation at 264 GHz. In frozen solutions of A?1–40 fibrils doped with DOTOPA-TEMPO, we observe DNP signal enhancement factors of 16–21. We show that the orientation- and frequency-dependent spin polarization exchange between sequential backbone carbonyl 13C labels can be simulated accurately using a simple expression for the exchange rate, after experimentally determined homogeneous 13C lineshapes are incorporated in the simulations. The experimental 2D 13C13C exchange spectra place constraints on the ? and ? angles between the two carbonyl labels. Although the data are not sufficient to determine ? and ? uniquely, the data do provide non-trivial constraints that could be included in structure calculations. With DNP at low temperatures, 2D 13C13C exchange spectra can be obtained from a 3.5 mg sample of A?1–40 fibrils in 4 h or less, despite the broad 13C chemical shift anisotropy line shapes that are observed in static samples.

Potapov, Alexey; Yau, Wai-Ming; Tycko, Robert

2013-06-01

55

Ketogenesis in the living rat followed by 13C-NMR spectroscopy. Infusion of [1,3-13C]octanoate.  

PubMed

13C-NMR spectroscopy was used as a noninvasive approach to study the metabolism of [1,3-13C]octanoate in rat liver. Using a properly adjusted surface coil a liver selection of better than 90% was achieved in the intact animal without abdominal surgery. After infusion of [1,3-13C]octanoate via the jugular vein different patterns of metabolites were observed depending on the physiological state of the rat. In the fasted animal, the major metabolites were those of the Krebs cycle while in the diabetic animal ketogenic end products were predominant. As a fatty acid of medium chain length octanoate is imported into the inner mitochondrial space without control by the carnitine acyl transferase system. Hence, the metabolic differences observed between diabetic and fasted rats result from an intramitochondrial control mechanism. The in vivo 13C-NMR results therefore support previous biochemical in vitro studies which concluded that a major control of ketone body production occurs in the inner mitochondrial space, presumably via the redox potential of the liver. As an unexpected result, 13C-NMR provides evidence for the transitory esterification of the infused 13C-labeled octanoic acid. The corresponding 13C-NMR chemical shifts are typical for glycerides. PMID:3593540

Pahl-Wostl, C; Seelig, J

1987-03-01

56

Evaluation of nonpolar metabolites in plant extracts by 13C NMR spectroscopy.  

PubMed

(13)C nuclear magnetic resonance (NMR) spectroscopy was explored as a simple and efficient technique for the quantitative analysis of nonpolar metabolites in plants. The method was first optimized with a mixture of known metabolites and then applied to the nonpolar leaf extracts of plants harvested in the Valencian community (eastern Spain) belonging to three different genera: Euphorbia (Euphorbiaceae), Araujia (Apocynaceae), and Morus (Moraceae). Furthermore, an exhaustive analysis of Euphorbia characias leaf and stem extracts from different geographic locations allowed that quantitative (13)C NMR spectroscopy is a suitable tool for metabolic profiling purpose. PMID:21955286

Palomino-Schätzlein, Martina; Escrig, Pablo V; Boira, Herminio; Primo, Jaime; Pineda-Lucena, Antonio; Cabedo, Nuria

2011-10-07

57

/sup 13/C NMR spectra of tertiary alcohols of the fluorene and azafluorene series  

SciTech Connect

The /sup 13/C NMR spectra of tertiary alcohols of the fluorene and 2- and 4-azafluorene series with phenyl and benzyl radicals at the C/sup 9/ position were analyzed. Substituents at C/sup 9/ mainly affect the chemical shifts of the signals for the ring carbon atoms at positions 4a, 4b, 8a, and 9a. The /sup 13/C NMR spectra of saturated solutions of the alcohols in deuterochloroform and DMSO-d/sub 6/ were obtained on a Bruker WP-80 spectrometer with accumulation by the pulse technique and with Fourier transformation.

Zakharov, V.F.; Pleshakov, V.G.; Gaivoronskaya, L.A.; Sarkar, S.K.; Prostakov, N.S.

1987-09-20

58

High resolution 13C-detected solid-state NMR spectroscopy of a deuterated protein  

PubMed Central

High resolution 13C-detected solid-state NMR spectra of the deuterated beta-1 immunoglobulin binding domain of the protein G (GB1) have been collected to show that all 15N, 13C?, 13C? and 13C? sites are resolved in 13C13C and 15N–13C spectra, with significant improvement in T2 relaxation times and resolution at high magnetic field (750 MHz). The comparison of echo T2 values between deuterated and protonated GB1 at various spinning rates and under different decoupling schemes indicates that 13C? T2? times increase by almost a factor of two upon deuteration at all spinning rates and under moderate decoupling strength, and thus the deuteration enables application of scalar-based correlation experiments that are challenging from the standpoint of transverse relaxation, with moderate proton decoupling. Additionally, deuteration in large proteins is a useful strategy to selectively detect polar residues that are often important for protein function and protein–protein interactions.

Tang, Ming; Comellas, Gemma; Mueller, Leonard J.

2011-01-01

59

In Vivo Neurochemical Profiling of Rat Brain by 1H-[13C] NMR Spectroscopy. Cerebral Energetics and Glutamatergic/GABAergic Neurotransmission  

PubMed Central

The simultaneous quantification of excitatory and inhibitory neurotransmission and the associated energy metabolism is crucial for a proper understanding of brain function. While the detection of glutamatergic neurotransmission in vivo by 13C NMR spectroscopy is now relatively routine, the detection of GABAergic neurotransmission in vivo has remained elusive due to the low GABA concentration and spectral overlap. Using 1H-[13C] NMR spectroscopy at high magnetic field in combination with robust spectral modeling and the use of different substrates, [U-13C6]-glucose and [2-13C]-acetate, it is shown that GABAergic, as well as glutamatergic neurotransmitter fluxes can be detected non-invasively in rat brain in vivo.

van Eijsden, Pieter; Behar, Kevin L.; Mason, Graeme F.; Braun, Kees P.J.; de Graaf, Robin A.

2010-01-01

60

Development of a 13C-optimized 1.5-mm high temperature superconducting NMR probe  

NASA Astrophysics Data System (ADS)

We report a 1.5-mm NMR probe based on high temperature superconductors operating at 14.1 T optimized for 13C detection. The probe has a total sample volume of about 35 microliters (?L) with an active volume of 20 ?L and provides exceptional mass sensitivity for 13C detection. The probe also has excellent 1H sensitivity and employs a 2H lock; 15N irradiation capability can be added in the future. The coils are cooled to about 20 K using a standard Agilent cryogenic refrigeration system, and the sample temperature is regulated near room temperature. The coil design considerations are discussed in detail. This probe is ideal for directly detected 13C NMR experiments for natural products chemistry and metabolomics applications, for which 35 ?L is an optimal sample volume. The outstanding 13C sensitivity of this probe allowed us to directly determine the 13C connectivity on 1.1 mg of natural abundance histidine using an INADEQUATE experiment. We demonstrated the utility of this probe for 13C-based metabolomics using a synthetic mixture of common natural abundance metabolites whose concentrations ranged from 1 to 5 mM (40-200 nmol).

Ramaswamy, Vijaykumar; Hooker, Jerris W.; Withers, Richard S.; Nast, Robert E.; Brey, William W.; Edison, Arthur S.

2013-10-01

61

Development of a (13)C-optimized 1.5-mm high temperature superconducting NMR probe.  

PubMed

We report a 1.5-mm NMR probe based on high temperature superconductors operating at 14.1T optimized for (13)C detection. The probe has a total sample volume of about 35microliters (?L) with an active volume of 20?L and provides exceptional mass sensitivity for (13)C detection. The probe also has excellent (1)H sensitivity and employs a (2)H lock; (15)N irradiation capability can be added in the future. The coils are cooled to about 20K using a standard Agilent cryogenic refrigeration system, and the sample temperature is regulated near room temperature. The coil design considerations are discussed in detail. This probe is ideal for directly detected (13)C NMR experiments for natural products chemistry and metabolomics applications, for which 35?L is an optimal sample volume. The outstanding (13)C sensitivity of this probe allowed us to directly determine the (13)C connectivity on 1.1mg of natural abundance histidine using an INADEQUATE experiment. We demonstrated the utility of this probe for (13)C-based metabolomics using a synthetic mixture of common natural abundance metabolites whose concentrations ranged from 1 to 5mM (40-200nmol). PMID:23969086

Ramaswamy, Vijaykumar; Hooker, Jerris W; Withers, Richard S; Nast, Robert E; Brey, William W; Edison, Arthur S

2013-07-29

62

31P NMR saturation-transfer and 13C NMR kinetic studies of glycolytic regulation during anaerobic and aerobic glycolysis.  

PubMed

31P NMR saturation-transfer techniques have been employed in glucose-grown derepressed yeast to determine unidirectional fluxes in the upper part of the Embden-Meyerhof-Parnas pathway. The experiments were performed during anaerobic and aerobic glycolysis by saturating the ATP gamma resonances and monitoring changes in the phosphomonoester signals from glucose 6-phosphate and fructose 1,6-bis-phosphate. These experiments were supplemented with 13C NMR measurements of glucose utilization rates and 13C NMR label distribution studies. Combined with data obtained previously from radioisotope measurements, these 31P and 13C NMR kinetic studies allowed estimation of the net glycolytic flow in addition to relative flows through phosphofructokinase (PFK) and Fru-1,6-P2ase during anaerobic and aerobic glycolysis. The 31P NMR saturation-transfer results are consistent with previous results obtained from measurements of metabolite levels, radioisotope data, and 13C NMR studies [den Hollander, J.A., Ugurbil, K., Brown, T.R., Bednar, M., Redfield, C., & Shulman, R.G. (1986a) Biochemistry 25, 203-211], providing additional support for in vivo measurement of the flows during glycolysis. PMID:2962638

Campbell-Burk, S L; den Hollander, J A; Alger, J R; Shulman, R G

1987-11-17

63

Complete assignment of 1H and 13C NMR spectra of standard neo-?-carrabiose oligosaccharides  

Microsoft Academic Search

Standard Eucheuma denticulatum ?-carrageenan was degraded with the Alteromonas fortis ?-carrageenase. The most abundant products, the neo-?-carratetraose and neo-?-carrahexaose were purified by permeation gel chromatography, and their corresponding 1H and 13C NMR spectra were fully assigned.

Diane Jouanneau; Patrick Boulenguer; Jacques Mazoyer; William Helbert

2010-01-01

64

Characterizing biomass fast pyrolysis oils by 13C-NMR and chemometric analysis  

Technology Transfer Automated Retrieval System (TEKTRAN)

Several biomass fast pyrolysis oils were characterized by 13C and DEPT NMR analysis to determine chemical functional group compositions as related to their energy content. Pyrolysis oils were produced from a variety of feedstocks including energy crops, woods, animal wastes and oil seed presscakes,...

65

Modification of the Varian XL100 NMR spectrometer for submilligram natural abundance 13C analyses  

Microsoft Academic Search

Quadrature detection modifications and a microcell arrangement are described for the Varian XL-100 NMR spectrometer which routinely improve sensitivity in 13C Fourier transform sample-limited studies by a factor of 4–5. The power requirement of the rf pulse amplifier is relaxed by a factor of 4. Previously attainable resolution is not affected.

D. M. Wilson; R. W. Olsen; A. L. Burlingame

1974-01-01

66

13C NMR analysis of polyphenol biosynthesis in grape cells: Impact of various inducing factors  

Microsoft Academic Search

13C NMR spectroscopy was used as a complement to high performance liquid chromatography (HPLC) or spectrophotometry to analyse stilbene and anthocyanin metabolism in grape cell cultures. Stilbene and anthocyanin biosynthesis are closely related. Anthocyanins are major components of grape quality whereas stilbenes play a crucial role in defence mechanisms and are strongly correlated to natural grapevine resistance. Stimulation of stilbene

Cassandrine Saigne-Soulard; Tristan Richard; Jean-Michel Mérillon; Jean-Pierre Monti

2006-01-01

67

Enantiomeric differentiation of bornyl acetate by 13C-NMR using a chiral lanthanide shift reagent.  

PubMed

The enantiomeric differentiation of bornyl acetate was carried out by 13C-NMR spectroscopy using a chiral lanthanide shift reagent. The technique was successfully applied to the determination of the enantiomer of bornyl acetate present in the essential oil of Inula graveolens. PMID:12892421

Baldovini, Nicolas; Tomi, Félix; Casanova, Joseph

68

A solid state 13C-NMR study of kerogen degradation during black shale weathering  

NASA Astrophysics Data System (ADS)

Solid state 13C nuclear magnetic resonance (NMR) spectroscopy is used to examine kerogen composition in weathering profiles of the Monterey, Green River, Woodford, and New Albany formations. Techniques include cross polarization (CP) and Bloch decay (BD) spectral acquisition, dipolar dephasing (DD), spin counting, experiments to provide estimates of relaxation times (T 1?H and T 1H), and proton spin relaxation editing (PSRE). It is demonstrated that CP/MAS (cross polarization/magic angle spinning) spectra obtained on isolated kerogens provide reliable characterization of kerogen composition (compared with BD spectra and whole-rock samples). Highly aliphatic (polymethylenic) kerogens are not appreciably altered during weathering. Aromatic and/or branched aliphatic kerogens accumulate oxidation products and preferentially lose aliphatic relative to aromatic carbon during weathering. No relation is observed between T 1?H times and either kerogen composition or degree of weathering; T 1H times correlate with aromaticity. Two distinct components within kerogens are discerned by PSRE: one highly aliphatic (largely polymethylenic) component and one mixed aliphatic/aromatic component. During weathering, the highly aliphatic component remains largely unaltered, while the mixed component loses aliphatic carbon and accumulates carbonyl oxidation products. Thus it appears that kerogen weathering is dominated by two separate processes: Linear alkyl fragments are cleaved without oxidation, and aromatic/branched alkyl fragments are oxidized while attached to the kerogen macromolecule and then cleaved.

Petsch, S. T.; Smernik, R. J.; Eglinton, T. I.; Oades, J. M.

2001-06-01

69

1H and 13C NMR assignments of new methoxylated furanoflavonoids from Lonchocarpus araripensis.  

PubMed

Two new polymethoxylated flavonoids, 2',5',6'-trimethoxy-[2'',3'' : 3',4']furano dihydrochalcone and 2,4',4,5-tetramethoxy-[2'',3'' : 6,7]-furanodihydroaurone, were isolated from the root barks of Lonchocarpus araripensis, along with the known compounds 3,4,5,6-tetramethoxy-[2'',3'' : 7,8]-furanoflavan, 3,6-dimethoxy-1'',1''-dimethylcromene-[2'',3'' : 7,8]-flavone, 3',4'-methylenodioxy-5,6-dimethoxy-[2'',3'' : 7,8]-furanoflavone, 3,5,6-trimethoxy-[2'',3'' : 7,8]-furanoflavanone, 3,5,6-trimethoxy-[2'',3'' : 7,8]-furanoflavone, and 6alpha-hydroxy-medicarpin. The complete (1)H and (13)C NMR assignments of the new furan flavonoids were performed using 1D and 2D pulse sequences, including COSY, HSQC, and HMBC experiments, and comparison with spectral data for analog compounds from the literature, particularly for the new furanodihydroaurone because of several inconsistencies on the carbonyl chemical shifts from the literature. PMID:18932264

Lima, Almi F; Mileo, Paulo Graziane M; Andrade-Neto, Manoel; Braz-Filho, Raimundo; Silveira, Edilberto R; Pessoa, Otília Deusdênia L

2009-02-01

70

13 C- 2 H correlation NMR spectroscopy studies of the in vivo transformations of natural products from Artemisia annua  

Microsoft Academic Search

13C-2H correlation NMR spectroscopy (13C-2H COSY) permits the identification of 13C and 2H nuclei which are connected to one another by a single chemical bond via the sizeable 1JCD coupling constant. The practical development of this technique is described using a 13C-2H COSY pulse sequence which is derived from the classical 13C-1H correlation experiment. An example is given of the

G. D. Brown

2003-01-01

71

Interactions of myristic acid with bovine serum albumin: a 13C NMR study.  

PubMed Central

Interactions of myristic acid with bovine serum albumin were studied by 13C NMR spectroscopy at 50.3 MHz using 90% isotopically substituted [1-13C]-, [3-13C]-, and [14-13C]myristic acids, either individually or in a combination of all three with albumin. At pH 7.4, two or more resonances of different intensities were observed for each 13C-enriched myristic acid. Carboxyl and methylene C-3 resonances corresponding to the major myristic acid environment(s) exhibited pH-dependent chemical shift changes indicative of protonation below pH 6.7; in contrast, carboxyl groups in minor environments were resistant to protonation. 13C NMR spectra obtained as a function of the molar ratio of [3-13C]- and [14-13C]myristic acid to bovine serum albumin (from 0.7 to 5.6) revealed at least two narrow resonances for each carbon at all molar ratios. Thus, bovine serum albumin binding sites for myristic acid are heterogeneous with respect to titration behavior and with respect to the local magnetic environment at both the polar and the nonpolar ends of the fatty acid. The narrow resonances observed for the methylene and methyl carbons are inconsistent with complete immobilization of the protein-bound acid molecules. Together with spin- lattice relaxation times and nuclear Overhauser enhancements, the linewidth results indicate that bound myristic acid has internal motions that are rapid compared with overall protein tumbling and that the C-3 methylene carbon is more restricted than the terminal methyl carbon.

Hamilton, J A; Cistola, D P; Morrisett, J D; Sparrow, J T; Small, D M

1984-01-01

72

Chemical shift changes and line narrowing in 13C NMR spectra of hydrocarbon clathrate hydrates.  

PubMed

The solid-state (13)C NMR spectra of various guest hydrocarbons (methane, ethane, propane, adamantane) in clathrate hydrates were measured to elucidate the local structural environments around hydrocarbon molecules isolated in guest-host frameworks of clathrate hydrates. The results show that, depending on the cage environment, the trends in the (13)C chemical shift and line width change as a function of temperature. Shielding around the carbons of the guest normal alkanes in looser cage environments tends to decrease with increasing temperature, whereas shielding in tighter cage environments tends to increase continuously with increasing temperature. Furthermore, the (13)C NMR line widths suggest, because of the reorientation of the guest alkanes, that the local structures in structure II are more averaged than those in structure I. The differences between structures I and II tend to be very large in the lower temperature range examined in this study. The (13)C NMR spectra of adamantane guest molecules in structure H hydrate show that the local structures around adamantane guests trapped in structure H hydrate cages are averaged at the same level as in the ? phase of solid adamantane. PMID:23607335

Kida, Masato; Sakagami, Hirotoshi; Takahashi, Nobuo; Nagao, Jiro

2013-05-09

73

Glucose and lactate metabolism in the awake and stimulated rat: a 13C-NMR study  

PubMed Central

Glucose is the major energetic substrate for the brain but evidence has accumulated during the last 20 years that lactate produced by astrocytes could be an additional substrate for neurons. However, little information exists about this lactate shuttle in vivo in activated and awake animals. We designed an experiment in which the cortical barrel field (S1BF) was unilaterally activated during infusion of both glucose and lactate (alternatively labeled with 13C) in rats. At the end of stimulation (1 h) both S1BF areas were removed and analyzed by HR-MAS NMR spectroscopy to compare glucose and lactate metabolism in the activated area vs. the non-activated one. In combination with microwave irradiation HR-MAS spectroscopy is a powerful technical approach to study brain lactate metabolism in vivo. Using in vivo 14C-2-deoxyglucose and autoradiography we confirmed that whisker stimulation was effective since we observed a 40% increase in glucose uptake in the activated S1BF area compared to the ipsilateral one. We first determined that lactate observed on spectra of biopsies did not arise from post-mortem metabolism. 1H-NMR data indicated that during brain activation there was an average 2.4-fold increase in lactate content in the activated area. When [1-13C]glucose + lactate were infused 13C-NMR data showed an increase in 13C-labeled lactate during brain activation as well as an increase in lactate C3-specific enrichment. This result demonstrates that the increase in lactate observed on 1H-NMR spectra originates from newly synthesized lactate from the labeled precursor ([1-13C]glucose). It also shows that this additional lactate does not arise from an increase in blood lactate uptake since it would otherwise be unlabeled. These results are in favor of intracerebral lactate production during brain activation in vivo which could be a supplementary fuel for neurons.

Sampol, Denys; Ostrofet, Eugene; Jobin, Marie-Lise; Raffard, Gerard; Sanchez, Stephane; Bouchaud, Veronique; Franconi, Jean-Michel; Bonvento, Gilles; Bouzier-Sore, Anne-Karine

2013-01-01

74

13C NMR of polyolefins with a new high temperature 10 mm cryoprobe.  

PubMed

Recently, a high temperature 10 mm cryoprobe was developed. This probe provides a significant sensitivity enhancement for (13)C NMR of polyolefins at a sample temperature of 120-135 degrees C, as compared to conventional probes. This greatly increases the speed of NMR studies of comonomer content, sequence distribution, stereo- and regioerrors, saturated chain end, unsaturation, and diffusion of polymers. In this contribution, we first compare the (13)C NMR sensitivity of this probe with conventional probes. Then, we demonstrate one of the advantages of this probe in its ability to perform 2D Incredible Natural Abundance Double Quantum Transfer Experiment (2D INADEQUATE) in a relatively short period of time. The 2D INADEQUATE has been rarely used for polymer studies because of its inherently very low sensitivity. It becomes even more challenging for studying infrequent polyolefin microstructures, as low probability microstructures represent a small fraction of carbons in the sample. Here, the 2D INADEQUATE experiment was used to assign the (13)C NMR peaks of 2,1-insertion regioerrors in a poly(propylene-co-1-octene) copolymer. PMID:19665405

Zhou, Zhe; Kümmerle, Rainer; Stevens, James C; Redwine, David; He, Yiyong; Qiu, Xiaohua; Cong, Rongjuan; Klosin, Jerzy; Montañez, Nikki; Roof, Gordon

2009-07-18

75

1H to 13C Energy Transfer in Solid State NMR Spectroscopy of Natural Organic Systems  

NASA Astrophysics Data System (ADS)

Cross polarization (CP) magic angle spinning (MAS) 13C-NMR spectroscopy is a solid state NMR technique widely used to study chemical composition of organic materials with low or no solubility in the common deuterated solvents used to run liquid state NMR experiments. Based on the magnetization transfer from abundant nuclei (with spin of 1 -2) having a high gyromagnetic ratio (?), such as protons, to the less abundant 13C nuclei with low ? values, 13C-CPMAS NMR spectroscopy is often applied in environmental chemistry to obtain quantitative information on the chemical composition of natural organic matter (NOM) (Conte et al., 2004), although its quantitative assessment is still matter of heavy debates. Many authors (Baldock et al., 1997; Conte et al., 1997, 2002; Dria et al., 2002; Kiem et al., 2000; Kögel-Knabner, 2000; Preston, 2001), reported that the application of appropriate instrument setup as well as the use of special pulse sequences and correct spectra elaboration may provide signal intensities that are directly proportional to the amount of nuclei creating a NMR signal. However, many other papers dealt with the quantitative unsuitability of 13C-CPMAS NMR spectroscopy. Among those, Mao et al. (2000), Smernik and Oades (2000 a,b), and Preston (2001) reported that cross-polarized NMR techniques may fail in a complete excitation of the 13C nuclei. In fact, the amount of observable carbons via 13C-CPMAS NMR spectroscopy appeared, in many cases, lower than that measured by a direct observation of the 13C nuclei. As a consequence, cross-polarized NMR techniques may provide spectra where signal distribution may not be representative of the quantitative distribution of the different natural organic matter components. Cross-polarization is obtained after application of an initial 90° x pulse on protons and a further spin lock pulse (along the y axis) having a fixed length (contact time) for both nuclei (1H and 13C) once the Hartmann-Hahn condition is matched. The Hartmann-Hahn condition can be expressed as ?HB1H = ?CB1C, where ?H and ?C are the gyromagnetic ratios of protons and carbons, whereas B1H and B1C are the 1H and 13C radio-frequency (r.f.) fields applied to the nuclei. The Hartmann-Hahn condition is affected by the H-C dipolar interaction strength (Stejskal & Memory, 1994). All the factors affecting dipolar interactions may mismatch the Hartmann-Hahn condition and prevent a quantitative representation of the NOM chemical composition (Conte et al., 2004). It has been reported that under low speed MAS conditions, broad matching profiles are centered around the Hartmann-Hahn condition....... With increasing spinning speed the Hartmann-Hahn matching profiles break down in a series of narrow matching bands separated by the rotor frequency (Stejskal & Memory, 1994). In order to account for the instability of the Hartmann-Hahn condition at higher rotor spin rates (>10 kHz), variable amplitude cross-polarization techniques (RAMP-CP) have been developed (Metz et al., 1996). So far, to our knowledge, the prevailing way used to obtain quantitative 13C-CPMAS NMR results was to optimize the 1H and 13C spin lock r.f. fields on simple standard systems such as glycine and to use those r.f. field values to run experiments on unknown organic samples. The aim of the present study was to experimentally evidence that the stability of the Hartmann-Hahn condition was different for different samples with a known structure. Moreover, Hartmann-Hahn profiles of four different humic acids (HAs) were also provided in order to show that the 1H/13C r.f. spin lock field strength must also be tested on the HAs prior to a quantitative evaluation of their 13C-CPMAS NMR spectra. Baldock, J.A., Oades, J.M., Nelson, P.N., Skene, T.M., Golchin, A. & Clarke, P., 1997. Assessing the extent of decomposition of natural organic materials using solid-state C-13 NMR spectroscopy. Australian Journal of Soil Research, 35, 1061-1083. Conte, P., Piccolo, A., van Lagen, B., Buurman, P. & de Jager, P.A., 1997. Quantitative Aspects of So

Berns, Anne E.; Conte, Pellegrino

2010-05-01

76

Molecular dynamics in supercooled glycerol: Results from 13C NMR spectroscopy  

NASA Astrophysics Data System (ADS)

13C NMR spectra of glycerol are collected over the entire temperature range of supercooling: Tg(185 K)<=T<=Tm(293 K). The temperature dependent evolution of the 13C NMR line shape indicates dynamical averaging of the chemical shift anisotropy at the carbon sites with increasing temperature, resulting from isotropic tumbling of the constituent molecules. This isotropic reorientation dynamics involves random molecular jumps over all possible angles, and its time scale is in excellent agreement with the ?-relaxation time scale of the supercooled liquid. The increasing activation energy of such molecular jumps with decreasing temperature and hence the fragility of supercooled glycerol are likely to be related to the corresponding temperature dependence of the average number of hydrogen bonds per molecule. The absence of any ? peak in the dielectric relaxation spectra of supercooled glycerol is possibly related to a strong coupling between intramolecular dynamics and the tumbling of the entire molecule as a whole.

Jain, P.; Levchenko, A.; Yu, P.; Sen, S.

2009-05-01

77

13C solid-state NMR of gramicidin A in a lipid membrane.  

PubMed Central

The natural-abundance 13C NMR spectrum of gramicidin A in a lipid membrane was acquired under magic-angle spinning conditions. With fast sample spinning (15 kHz) at approximately 65 degrees C the peaks from several of the aliphatic, beta-, alpha-, aromatic, and carbonyl carbons in the peptide could be resolved. The resolution in the 13C spectrum was superior that observed with 1H NMR under similar conditions. The 13C linewidths were in the range 30-100 Hz, except for the alpha- and beta-carbons, the widths of which were approximately 350 Hz. The beta-sheet-like local structure of gramicidin A was observed as an upfield shift of the gramicidin alpha and carbonyl resonances. Under slow sample spinning (500 Hz), the intensity of the spinning sidebands from 13C in the backbone carbonyls was used to determine the residual chemical shift tensor. As expected, the elements of the residual chemical shift tensor were consistent with the single-stranded, right-handed beta6.3 helix structure proposed for gramicidin A in lipid membranes.

Quist, P O

1998-01-01

78

Molecular dynamics of C60.2S8: A 13C NMR study  

NASA Astrophysics Data System (ADS)

13C NMR studies of polycrystalline C60.2S8 are reported. At room temperature, the static 13C NMR spectra are similar to the 13C spectrum of polycrystalline C60, which suggests that C60 molecules undergo fast reorientational motion within the solvate lattice as within pure crystalline C60. This observation seems to contradict previous x-ray results that were interpreted in terms of motionless C60 molecules within the solvate lattice; however, it agrees with thermodynamic measurements according to which the enthalpy for the departure of sulfur from the solvate is nearly equal to that of pure sulfur sublimation. The evolution of the shielding tensor as a function of temperature is also reported: it exhibits a steep change near 150 K that corresponds to a slowing down of the C60 rotational motion. Finally, according to the variation of the 13C spin-lattice relaxation time T1 vs temperature, the dynamics of C60 molecules, which consists in jumps between symmetry-equivalent orientations, can be considered as ruled by two activation energies, 15.3 and 24.8 kJ mol-1.

Grell, A.-S.; Masin, F.; Céolin, R.; Gardette, M. F.; Szwarc, H.

2000-08-01

79

(1) H and (13) C NMR characterization of new cycloartane triterpenes from Mangifera indica.  

PubMed

From the stem bark of Mangifera indica, seven cycloartane-type secondary metabolites were isolated. Compound 1 has been isolated for the first time from M. indica, whereas compounds 2 (2a and 2b, as an epimeric mixture), 3, and 4 are new triterpenoid-type cycloartanes. Unambiguous (13) C and (1) H NMR assignments for these compounds and the known compounds mangiferonic acid (compound 5), isomangiferolic acid (compound 6), ambolic acid (compound 7), and friedelin (compound 8) are reported; the latter because full NMR data for these compounds are not available in the literature. PMID:22271257

Escobedo-Martínez, Carolina; Concepción Lozada, M; Hernández-Ortega, Simón; Villarreal, María Luisa; Gnecco, Dino; Enríquez, Raúl G; Reynolds, William

2012-01-23

80

Solid state 13C-NMR spectroscopy and XRD studies of commercial and pyrolytic carbon blacks  

Microsoft Academic Search

The bulk chemistry of commercial carbon blacks and carbon blacks obtained by vacuum pyrolysis (CBP) of used tires was investigated by 13C-NMR spectroscopy with and without magic angle spinning of the sample. Two different kinds of carbon atoms can be distinguished: Graphite like carbon atoms in poly-condensed aromatic rings and carbon atoms in a less ordered environment. Commercial carbon blacks

Hans Darmstadt; Christian Roy; Serge Kaliaguine; Guoying Xu; Michèle Auger; Alain Tuel; Veda Ramaswamy

2000-01-01

81

NMR 13 C spectra and effects of conjugation in alkoxy- and alkylthioethylenes  

Microsoft Academic Search

1.The NMR-13C spectra of a number of vinyl alkyl sulfides was studied. An analysis of the chemical shifts of the carbons of the multiple bond gives unambiguous evidence that weak p-p conjugation of the heteroatom with the multiple bond, the intensity of which is three times lower than in vinyl alkyl ethers, operates in these compounds.2.The chemical shifts of13Cß in

G. A. Kalabin; B. A. Trofimov; V. M. Bzhezovskii; D. F. Kushnarev; S. V. Amosova; N. K. Gusarova; M. L. Al'pert

1975-01-01

82

Calculation of the 13 C NMR shieldings of the C0 2 complexes of aluminosilicates  

NASA Astrophysics Data System (ADS)

13 C NMR shieldings have been calculated using the random-phase-approximation, localized-orbital local-origins version of ab initio coupled Hartree-Fuck perturbation theory for CO 2 and and for several complexes formed by the reaction of CO 2 with molecular models for aluminosilicate glasses, H 3 TOT'H3 3 -n , T,T' = Si,Al. Two isomeric forms of the CO 2 -aluminosilicate complexes have been considered: (1) "CO 2 -like" complexes, in which the CO 2 group is bound through carbon to a bridging oxygen and (2) "CO 3 -like" complexes, in which two oxygens of a central CO 3 group form bridging bonds to the two TH 3 groups. The CO 2 -like isomer of CO 2 -H 3 SiOSiH 3 is quite weakly bonded and its 13 C isotropic NMR shielding is almost identical to that in free CO 2 . As Si is progressively replaced by Al in the --H terminated aluminosilicate model, the CO 2 -like isomers show increasing distortion from the free CO 2 geometry and their 13 C NMR shieldings decrease uniformly. The calculated 13 C shielding value for H 3 AlO(CO 2 )AlH 3 -2 is only about 6 ppm larger than that calculated for point charge stabilized CO 3 -2 . However, for a geometry of H 3 SiO(CO 2 ) AlH 3 -1 , in which the bridging oxygen to C bond length has been artificially increased to that found in the --OH terminated cluster (OH) 3 SiO(CO 2 )Al(OH) 3 -1 , the calculated 13 C shielding is almost identical to that for free CO 2 . The CO 3 -like isomers of the CO 2 -aluminosili-cate complexes show carbonate like geometries and 13 C NMR shieldings about 4-9 ppm larger than those of carbonate for all T,T' pairs. For the Si,Si tetrahedral atom pair the CO 2 -like isomer is more stable energetically, while for the Si,Al and Al,Al cases the CO 3 -like isomer is more stable. Addition of Na + ions to the CO 3 -2 or H 3 AlO(CO 2 )AlH 3 -2 complexes reduces the 13 C NMR shieldings by about 10 ppm. Complexation with either Na + or CO 2 also reduces the 29 Si NMR shieldings of the aluminosilicate models, while the changes in 27 Al shielding with Na + or CO 2 complexation are much smaller. Complexation with CO 2 greatly increases the electric field gradient at the bridging oxygen of H 3 AlOAlH 3 -2 , raising it to a value similar to that found for Si---O---Si linkages. Comparison of these results with the experimental 13 C NMR spectra support the formation of CO 2 -like complexes at SiOSi bridges in albite glasses and CO 3 -like complexes at SiOAl and AlOAl bridges in albite and nepheline glasses. Changes in the calculated shieldings as Na + ions are added to the complexes suggest that some of the observed complexes may be similar in their CO 2 -aluminosilicate interactions, but different with respect to the positions of the charge-compensating Na + ions.

Tossell, J. A.

1995-04-01

83

Effects of chemical treatments on the quality and quantitative reliability of solid-state 13 C NMR spectroscopy of mineral soils  

Microsoft Academic Search

Three mineral soils were treated by chemical methods traditionally used to increase cross polarization magic angle spinning technique (CP-MAS) 13C nuclear magnetic resonance (NMR) spectral quality. Treatment with 2% HF\\/BF3 produced the highest quality spectra followed by 4% sodium dithionite and 0.05M tin(II) chloride, respectively. The improvement in spectral quality was due to both reduction in the paramagnetic character of

Michael Schilling; William T. Cooper

2004-01-01

84

J-deconvolution using maximum entropy reconstruction applied to 13C-13C solid-state cross-polarization magic-angle-spinning NMR of proteins.  

PubMed

Scalar couplings between 13C spins can impair both resolution and sensitivity in 13C-labeled preparations. It is demonstrated that deconvolution of magic-angle-spinning NMR data with maximum entropy (MaxEnt) reconstruction allows the removal of splittings due to J-couplings without expenses in sensitivity. A combination of MaxEnt reconstruction in t2 with selective pulses in t1 produces fully J-resolved data in both dimensions. The possibility to obtain J-resolved 13C-13C data without compromising the sensitivity is particularly important for solid-state NMR of "difficult" biological samples, like membrane proteins, where sacrifices in signal-to-noise are fatal. The method is demonstrated using preparations of alpha-spectrin SH3 domain (62 residues) as small test system and of outermembrane protein G as example of a membrane protein with higher molecular weight (281 residues). Both preparations were obtained using [2-13C]-glycerol as the carbon source during the bacterial growth. PMID:17488078

Scholz, Ingo; Jehle, Stefan; Schmieder, Peter; Hiller, Matthias; Eisenmenger, Frank; Oschkinat, Hartmut; van Rossum, Barth-Jan

2007-05-09

85

Dipolar Cross-Relaxation Modulates Signal Amplitudes in the 1H NMR Spectrum of Hyperpolarized [13C]Formate  

PubMed Central

The asymmetry in the doublet of a spin coupled to hyperpolarized 13C has been used previously to measure the initial polarization of 13C. We tested the hypothesis that a single observation of the 1H NMR spectrum of hyperpolarized 13C formate monitors 13C polarization. Depending on the microwave frequency during the polarization process, in-phase or out-of-phase doublets were observed in the 1H NMR spectrum. Even in this simple two-spin system, 13C polarization was not reflected in the area of the JCH doublet due to strong heteronuclear cross-relaxation. The Solomon equations were used to model the proton signal as a function of time after polarization and to estimate 13C polarization from the 1H NMR spectra.

Harrison, Crystal; Mander, William; Malloy, Craig R.; Sherry, A. Dean

2007-01-01

86

Metabolic pathways for ketone body production. 13C NMR spectroscopy of rat liver in vivo using 13C-multilabeled fatty acids.  

PubMed

The hormonal regulation of ketogenesis in the liver of living rat has been studied noninvasively with 13C nuclear magnetic resonance. The protocol involved the use of a surface coil that was placed on the skin of the rat, directly over the normal location of the liver. Signals from superficial tissue were suppressed with a 180 degrees pulse at the center of the coil. A resolution of 0.6 ppm was obtained in the 13C NMR spectra at 20.1 MHz, which was equal to or better than that observed in experiments where the liver was surgically exposed and surrounded with radiofrequency coil. The spatial selection for the liver was better than 90%, with extrahepatic adipose tissue contributing only a very small amount of signal. The metabolic activities of the liver were investigated by infusion of 13C-labeled butyrate in the jugular vein of the anesthetized rat. The rate of butyrate infusion was chosen to be close to the maximum oxidative capacity of the rat liver, and the 13C signal intensities were enhanced by using doubly labeled [1,3-13C]butyrate as a substrate. Different 13C NMR spectra and hence different metabolites were observed depending on the hormonal state of the animal. In the fasted rat, the most intense 13C signal came from the end product of the Krebs cycle, namely, HCO3, with additional resonances from glutamine and glutamate. Weak resonances of the ketone bodies 3-hydroxybutyrate and acetoacetate could also be detected and allowed an evaluation of the "redox state" of the in vivo liver.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:3801392

Pahl-Wostl, C; Seelig, J

1986-11-01

87

DNA Duplex Dynamics: NMR Relaxation Studies of a Decamer with Uniformly ^13C-Labeled Purine Nucleotides  

NASA Astrophysics Data System (ADS)

Dynamics in a DNA decamer duplex, d(CATTTGCATC) . d(GATGCAAATG), were investigated via a detailed ^13C NMR relaxation study. Every 2'-deoxyadenosine and 2'-deoxyguanidine was chemically enriched with 15% ^13C and 98% ^15N isotopes. Six nuclear relaxation parameters [R(^13C_z), R(^1H_z), R(2^1H_z^13C_z), R(^13C_x), R(2^1H_z^13C_x) and steady-state ^13C{^1H} NOE] were measured at 600 MHz and three were measured at 500 MHz (^1H frequency) for the CH spin systems of sugar 1', 3', and 4' as well as base 8 and 2 positions. A dependence of relaxation parameter values on chemical position was clearly observed; however, no sequence-specific variation was readily evident within our experimental error of ~5-10%, except for 3' and 5' termini. It was demonstrated that the random 15% ^13C enrichment effectively suppressed both scalar and dipolar contributions of the neighboring carbons and protons on the relaxation parameters. To analyze dynamics via all observed relaxation parameters, full spectral density mapping (1992, J. W. Peng and G. Wagner, J. Magn. Reson. 98, 308) and the ``model-free'' approach (1982, Lipari and Szabo, J. Am. Chem. Soc. 104, 4546) were applied complementarily. A linear correlation between three spectral density values, J(omega_C), J(omega_H - omega_C), and J(omega_H + omega_C) was observed in plots containing all measured values, but not for the other spectral density terms including J(0). These linear correlations reflect the effect of overall motion and similar internal motions for each CH vector in the decamer. The correlations yielded two correlation times, 3-4 ns and 10-200 ps. One value, 3-4 ns, corresponds to the value of 3.3 ns obtained for the overall isotropic tumbling correlation time determined from analysis of ^13C T1solarT2 ratios. The possibility of overall anisotropic tumbling was examined, but statistical analysis showed no advantage over the assumption of simple isotropic tumbling. Lack of correlations entailing J(0) implies that a relatively slow chemical exchange contributes to yielding of effective J_eff(0) values. Based on spectral density mapping and the T1solarT2 ratio analysis, three basic assumptions were initially employed (and subsequently justified) for the model-free calculation: isotropic overall tumbling, one internal motion, and the presence of chemical exchange terms. Except for terminal residues, the order parameter S^2 and the corresponding fast internal motion correlation time were determined to be about 0.8 +/- 0.1 and 20 +/- 20 ps, respectively, for the various CH vectors. Only a few differences were observed between or within sugars and bases. The internal motion is very fast (ps-ns time scale) and its amplitude restricted; e.g., assuming a simple wobble-in-a-cone model, the internal motion is restricted to an angular amplitude of +/-22.5 deg for each of the 1', 3', 4', 2, and 8 positions in the purine nucleotides in the entire duplex.

Kojima, Chojiro; Ono, Akira; Kainosho, Masatsune; James, Thomas L.

1998-12-01

88

Analysis of Hydroperoxides in Solid Polyethylene by MAS (13)C NMR and EPR  

SciTech Connect

{sup 13}C-enriched polyethylene was subjected to {gamma}-irradiation in the presence of air at 25 and 80 C for total doses ranging from 71 to 355 kGy. Significant quantities of hydroperoxides were detected in the 25 C irradiated sample by {sup 13}C magic angle spinning NMR spectroscopy. This method of detection was performed on the solid polymer and required no chemical derivatization or addition of solvent. The chemical stability and subsequent products of the hydroperoxide species were studied by annealing the irradiated samples in air at temperatures ranging from 22 to 110 C. A time-temperature superposition analysis provided an activation energy of 108 kJ/mol for the hydroperoxide decomposition process. The primary products of hydroperoxide decomposition were ketones and secondary alcohols with lesser amounts of acids and esters. EPR measurements suggest that the reactive hydroperoxide species reside in the amorphous phase of polyethylene, consistent with degradation occurring in the amorphous phase.

ASSINK,ROGER A.; CELINA,MATHIAS C.; DUNBAR,TIMOTHY D.; ALAM,TODD M.; CLOUGH,ROGER LEE; GILLEN,KENNETH T.

1999-11-19

89

Direct measurement of brain glucose concentrations in humans by sup 13 C NMR spectroscopy  

SciTech Connect

Glucose is the main fuel for energy metabolism in the normal human brain. It is generally assumed that glucose transport into the brain is not rate-limiting for metabolism. Since brain glucose concentrations cannot be determined directly by radiotracer techniques, the authors used {sup 13}C NMR spectroscopy after infusing enriched D-(1-{sup 13}C)glucose to measure brain glucose concentrations at euglycemia and at hyperglycemia in six healthy children. Brain glucose concentrations averaged 1.0 {plus minus} 0.1 {mu}mol/ml at euglycemia and 1.8-2.7 {mu}mol/ml at hyperglycemia. Michaelis-Menten parameters of transport were calculated from the relationship between plasma and brain glucose concentrations. The brain glucose concentrations and transport constants are consistent with transport not being rate-limiting for resting brain metabolism at plasma levels >3 mM.

Gruetter, R.; Novotny, E.J.; Boulware, S.D.; Rothman, D.L.; Mason, G.F.; Shulman, G.I.; Shulan, R.G.; Tamborlane, W.V. (Yale Univ., New Haven, CT (United States))

1992-02-01

90

Direct observation of glycogen synthesis in human muscle with sup 13 C NMR  

SciTech Connect

On the basis of previous indirect measurements, skeletal muscle has been implicated as the major site of glucose uptake and it has been suggested that muscle glycogen formation is the dominant pathway. However, direct measurements of the rates of glycogen synthesis have not been possible by previous techniques. The authors have developed {sup 13}C NMR methods to measure directly the rate of human muscle glycogen formation from infused, isotopically labeled (1-{sup 13}C)glucose. They show that under conditions of imposed hyperglycemia and hyperinsulinemia, a majority of the infused glucose was converted to muscle glycogen in a normal man. This directly shows that muscle is the major site of glucose disposal under these conditions, and provides quantitation of the glucose flux to muscle glycogen.

Jue, T.; Rothman, D.L.; Shulman, G.I.; Tavitian, B.A.; DeFronzo, R.A.; Shulman, R.G. (Yale Univ., New Haven, CT (USA))

1989-06-01

91

Intracellular flux analysis in hybridomas using mass balances and in vitro (13)C nmr.  

PubMed

Intracellular fluxes are important in defining cellular physiology and its changes in response to environmental variations. Stoichiometric balances combined with extra cellular metabolite measurements were applied to the estimation of intracellular fluxes and the study of energy metabolism in the hybridoma cell line ATCC CRL 1606. Redundant measurements allowed the evaluation of the consistency of the stoichiometry, measurements, and pseudo-steady-state assumption leading to refinement of the assumed biochemistry and identification of measurement errors. To validate the flux estimates, two batch experiments were performed with glucose labeled in the 1 position with (13)C. The distribution of (13)C in secreted lactate was measured via nuclear magnetic resonance spectroscopy (NMR) and compared to that predicted from the estimated intracellular fluxes. There was good agreement between the measured and estimated isotope distributions, demonstrating the validity of the flux estimates obtained from stoichiometric balances. (c) 1995 John Wiley & Sons, Inc. PMID:18623182

Zupke, C; Stephanopoulos, G

1995-02-20

92

NMR analyses of the cold cataract. III. /sup 13/C acrylamide studies  

SciTech Connect

/sup 13/C-enriched acrylamide was employed to further delineate the action of this compound in preventing the cold cataract phenomenon when it is incorporated (in vitro) into young human and rabbit lenses. The extent of acrylamide incorporation, in the dark and with concurrent UV exposure, was monitored by /sup 13/C NMR spectroscopy. These studies provide further evidence that UV exposure causes permanent acrylamide photobinding within the lens. In such lenses, the gamma crystallin fraction of the soluble lens proteins is affected to the greatest extent. It appears to become aggregated and/or combined with the alpha and beta fractions resulting in an apparent loss of most of the gamma monomers. There is also an age-related effect with respect to the amount of acrylamide that can be incorporated into the lens. The decrease in acrylamide incorporation with age directly parallels the age-related decline in gamma crystallin levels.

Lerman, S.; Megaw, J.M.; Moran, M.N.

1985-10-01

93

Determination of the DNA sugar pucker using sup 13 C NMR spectroscopy  

SciTech Connect

Solid-state {sup 13}C NMR spectroscopy of a series of crystalline nucleosides and nucleotides allows direct measurement of the effect of the deoxyribose ring conformation on the carbon chemical shift. It is found that 3{prime}-endo conformers have 3{prime} and 5{prime} chemical shifts significantly (5-10 ppm) upfield of comparable 3{prime}-exo and 2{prime}-endo conformers. The latter two conformers may be distinguished by smaller but still significant differences in the carbon chemical shifts at the C-2{prime} and C-4{prime} positions. High-resolution solid-state NMR of three modifications of fibrous calf thymus DNA shows that these trends are maintained in high-molecular-weight DNA and confirms that the major ring pucker in A-DNA is 3{prime}-endo, while both B-DNA and C-DNA are largely 2{prime}-endo. The data show that {sup 13}C NMR spectroscopy is a straightforward and useful probe of DNA ring pucker in both solution and the solid state.

Santos, R.A.; Tang, P.; Harbison, G.S. (State Univ. of New York, Stony Brook (USA))

1989-11-28

94

High-resolution solid state sup 13 C NMR of bacteriorhodopsin: Characterization of (4- sup 13 C)asp resonances  

SciTech Connect

Solid state {sup 13}C nuclear magnetic resonance measurements of bacteriorhodopsin labeled with (4-{sup 13}C)Asp show that resonances of single amino acids can be resolved. In order to assign and characterize the resonances of specific Asp residues, three different approaches were used. (1) Determination of the chemical shift anisotropy from side-band intensities provides information about the protonation state of Asp residues; (2) relaxation studies and T{sub 1} filtering allow one to discriminate between resonances with different mobility; (3) a comparison of the spectra of light- and dark-adapted bacteriorhodopsin provides evidence for resonances from aspartic acid residues in close neighborhood of the chromophore. In agreement with other investigations, four resonances are assigned to internal residues. Two of them are protonated in the ground state up to pH 10 (Asp{sub 96} and Asp{sub 115}). All other detected resonance, including Asp{sub 85} and Asp{sub 212}, are due to deprotonated aspartic acid. Two lines due to the two internal deprotonated groups change upon dark and light adaptation, whereas the protonated Asp residues are unaffected.

Metz, G.; Siebert, F. (Inst. fuer Biophysik und Strahlenbiologie der Universitaet, Freiburg (West Germany) Max-Planck-Inst. fuer Biophysik, Frankfurt (West Germany)); Engelhard, M. (Max-Planck-Inst. fuer Ernaehrungsphysiologie, Dortmund (West Germany))

1992-01-21

95

Determination of Spin-Lattice Relaxation of Time Using (Super 13)C NMR: An Undergraduate Physical Chemistry Laboratory Experiment  

ERIC Educational Resources Information Center

An experiment designed for the physical chemistry laboratory where (super 13)C NMR is applied to determine the spin-lattice relaxation time for carbon atoms in n-hexanol is proposed. It is concluded that students learn the principles and concepts of NMR spectroscopy as well as dynamic NMR experiments.

Gasyna, Zbigniew L.; Jurkiewicz, Antoni

2004-01-01

96

Combined use of filtered and edited 1 H NMR spectroscopy to detect 13 C-enriched compounds in complex mixtures.  

PubMed

In conventional metabolism and pharmacokinetic studies, radioactive isotopes are used to identify and quantify the breakdown products of xenobiotics. However, the stable isotope (13) C provides a cheaper and less hazardous alternative. Metabolites of (13) C-enriched xenobiotics can be detected, quantified and identified by (13) C-filtered NMR spectroscopy. However, one obstacle to using (13) C is its 1.1% natural abundance that produces a background signal in (13) C-filtered NMR spectra of crude biological extracts. The signal makes it difficult to distinguish between (13) C-enriched xenobiotics resonances from endogenous metabolites unrelated to the xenobiotic. This study proposes that the (13) C background signal can be distinguished from resonances of (13) C-enriched xenobiotics by the absence of a (12) C component in the xenobiotic. This is detected by combined analysis of (13) C-filtered and -edited NMR spectra. The theory underlying the approach is described and the method is demonstrated by the detection of sub-microgram amounts of (13) C-enriched phenacetin in crude extracts of hepatocyte microsomes. PMID:22407896

Howe, P W A; Ament, Z; Knowles, K; Griffin, J L; Wright, J

2012-03-08

97

Determination of [{sup 13}C]pyrene sequestration in sediment microcosms using flash pyrolysis--GC--MS and {sup 13}C NMR  

SciTech Connect

In this study, the use of a {sup 13}C-labeled pollutant probe, [{sup 13}C]pyrene, and the application of flash pyrolysis--GC--MS and CPMAS {sup 13}C NMR provided analytical capabilities to study pyrene interactions with soluble and insoluble compartments of sedimentary organic matter (S{sub D}OM) during whole sediments incubations in aerated microcosms. Surface sediments were collected from a site of previous hydrocarbon contamination in New Orleans, LA. Over a period of 60 days, humic acid and humin fractions of S{sub D}OM accumulated increasing amounts of pyrene that were resistant to exhaustive extraction with organic solvents. The sequestered pyrene was evident in CPMAS {sup 13}C NMR spectra of humin fractions. The amount of sequestered pyrene in humic materials was quantified by flash pyrolysis--GC--MS, a technique that destroys the three-dimensional structure of macromolecular S{sub D}OM. Noncovalent binding of pyrene to humic materials in S{sub D}OM was greater in sediments incubated with biological activity than biocide-treated sediments. The combined analytical approaches demonstrate that the sequestered pyrene, or bound residue, is noncovalently associated with S{sub D}OM and has not undergone structural alteration. Implications of these data are discussed in reference to S{sub D}OM diagenesis and long-term availability of bound pollutant residues in sediments.

Guthrie, E.A.; Bortiatynski, J.M.; Hardy, K.S.; Kovach, E.M. [Pennsylvania State Univ., University Park, PA (United States). Center for Environmental Chemistry and Geochemistry; Van Heemst, J.D.H.; Hatcher, P.G. [Ohio State Univ., Columbus, OH (United States); Richman, J.E. [Univ. of Minnesota, St. Paul, MN (United States)

1999-01-01

98

Solid-State NMR Determination of Sugar Ring Pucker in 13C-Labeled 2?-Deoxynucleosides  

Microsoft Academic Search

The H3?–C3?–C4?–H4? torsional angles of two microcrystalline 2?-deoxynucleosides, thymidine and 2?-deoxycytidine·HCl, doubly 13C-labeled at the C3? and C4? positions of the sugar ring, have been measured by solid-state magic-angle-spinning nuclear magnetic resonance (NMR). A double-quantum heteronuclear local field experiment with frequency-switched Lee–Goldberg homonuclear decoupling was used. The H3?–C3?–C4?–H4? torsional angles were obtained by comparing the experimental curves with numerical simulations,

Lorens van Dam; Niels Ouwerkerk; Andreas Brinkmann; Jan Raap; Malcolm H. Levitt

2002-01-01

99

Hydrogen-bonding effects and 13C-NMR of the DNA double helix.  

PubMed Central

13C-nmr chemical shifts of the nucleotides in DNA are sensitive to hydrogen bonding, especially for three of the carbons immediately bonded to exocyclic oxygen or nitrogen atoms acting as H-bond acceptors or donors. GuoC2, GuoC6 and ThdC4 are strongly deshielded (about 1 ppm) upon Watson-Crick pairing in oligodeoxynucleotide duplexes, regardless of the base sequence. Deshielding at these sites may be useful to distinguish bases involved in Watson-Crick pairs from unpaired bases.

Borer, P N; LaPlante, S R; Zanatta, N; Levy, G C

1988-01-01

100

/sup 13/C NMR spectra and structure of azo derivatives of phenol and resorcinol  

SciTech Connect

The /sup 13/C NMR spectra of arylazo derivatives of phenol and resorcinol in organic and aqueous media were studied. It was shown that in all solvents, including an alkaline medium, the derivatives of phenol retain the azo form. The resorcinol derivatives are present in the azo form in organic and acid media only. During ionization of the OH proton occurring in alkaline media, resorcinol derivatives are transformed into the other tautomeric form, the quinoid form, which is stabilized by an intramolecular hydrogen bond.

Fedorov, L.A.; Sokolovskii, S.A.; Ermakov, A.N.

1987-09-01

101

13 C-NMR Regioisomeric Analysis of EPA and DHA in Fish Oil Derived Triacylglycerol Concentrates  

Microsoft Academic Search

The regio-isomeric distribution of the omega-3 polyunsaturated fatty acids (PUFA) cis-5,8,11,14,17-eicosapentaenoic acid (EPA) and cis-4,7,10,13,16,19-docosahexaenoic acid (DHA) in the triacylglycerols (TAG) of anchovy\\/sardine fish oil was determined by 13C nuclear magnetic resonance (NMR) analysis under quantitative conditions. From the measurements of sn-1,3 and sn-2 carbonyl peak areas it was established that EPA was mainly located in the sn-1,3 positions, whereas

Erick Reyes Suárez; Paul F. Mugford; Alfred J. Rolle; Ian W. Burton; John A. Walter; Jaroslav A. Kralovec

2010-01-01

102

CP\\/MAS 13C NMR analysis of cellulase treated bleached softwood kraft pulp  

Microsoft Academic Search

Fully bleached softwood kraft pulps were hydrolyzed with cellulase (1,4-(1,3:1,4)-?-d-glucan 4-glucano-hydrolase, EC 3.2.1.4) from Trichoderma reesei. Supra-molecular structural features of cellulose during enzymatic hydrolysis were examined by using CP\\/MAS 13C NMR spectra in combination with line-fitting analysis. Different types of cellulose allomorphs (cellulose I?, cellulose I?, para-crystalline) and amorphous regions were hydrolyzed to a different extent by the enzyme used.

Yunqiao Pu; Cherie Ziemer; Arthur J. Ragauskas

2006-01-01

103

1H and 13C NMR study on some substituted azolidine derivatives  

NASA Astrophysics Data System (ADS)

The 1H and 13C NMR spectra carried out on R overlineN·CH 2·CH 2·X·C ?O (where for R = H, X = NH, NMe, NEt, CH 2, S, O; for R = Me, X = NMe, CH 2; for R = Et, X = NEt) are reported. The comparison of these results with those obtained for the thionic and selonic isologues shows that sulphur and selenium have a greater deshielding effect on the ring than oxygen. The resonance of the carbons not involved in the ? system have been correlated with the ? charges calculated by the DEL RE method.

Cerioni, Giovanni; Cristiani, Franco; Devillanova, Francesco A.; Diaz, Angelo; Verani, Gaetano

104

Enantiomeric differentiation of acyclic terpenes by 13C NMR spectroscopy using a chiral lanthanide shift reagent.  

PubMed

The 13C NMR behaviour of ten acyclic terpene alcohols was examined in the presence of a chiral lanthanide shift reagent (CLSR). For each alcohol, we measured the lanthanide-induced shift (LIS) on the signals of the carbons and the splitting of some signals, which allowed the enantiomeric differentiation. As expected, the LIS decreased with the number of bonds between the binding function and the considered carbon. The enantiomeric splitting is observed for several signals in the spectrum of each compound. The influence of the hindrance of the binding function (primary, secondary or tertiary alcohol) and that of the stereochemistry of the double bonds is discussed. PMID:15593244

Blanc, Marie-Cécile; Bradesi, Pascale; Casanova, Joseph

2005-02-01

105

Identifying inter-residue resonances in crowded 2D (13)C- (13)C chemical shift correlation spectra of membrane proteins by solid-state MAS NMR difference spectroscopy.  

PubMed

The feasibility of using difference spectroscopy, i.e. subtraction of two correlation spectra at different mixing times, for substantially enhanced resolution in crowded two-dimensional (13)C-(13)C chemical shift correlation spectra is presented. With the analyses of (13)C-(13)C spin diffusion in simple spin systems, difference spectroscopy is proposed to partially separate the spin diffusion resonances of relatively short intra-residue distances from the longer inter-residue distances, leading to a better identification of the inter-residue resonances. Here solid-state magic-angle-spinning NMR spectra of the full length M2 protein embedded in synthetic lipid bilayers have been used to illustrate the resolution enhancement in the difference spectra. The integral membrane M2 protein of Influenza A virus assembles as a tetrameric bundle to form a proton-conducting channel that is activated by low pH and is essential for the viral lifecycle. Based on known amino acid resonance assignments from amino acid specific labeled samples of truncated M2 sequences or from time-consuming 3D experiments of uniformly labeled samples, some inter-residue resonances of the full length M2 protein can be identified in the difference spectra of uniformly (13)C labeled protein that are consistent with the high resolution structure of the M2 (22-62) protein (Sharma et al., Science 330(6003):509-512, 2010). PMID:23708936

Miao, Yimin; Cross, Timothy A; Fu, Riqiang

2013-05-25

106

13 C NMR analysis of production and accumulation of osmoregulatory metabolites in the salt-tolerant yeast Debaryomyces hansenii  

Microsoft Academic Search

High resolution 13C NMR combined with chemical analysis were used to study the formation of metabolites from [1-13C]-labelled glucose by the salt-tolerant yeast Debaryomyces hansenii after transfer to media containing 8% NaCl. Time course spectroscopy of an aerobic cell suspension showed [1,3-13C]glycerol as the predominant end product. Perchloric acid extracts revealed additional less prominent incorporation of label into arabinitol, trehalose,

Per-Ake Jovall; Inga Tunblad-Johansson; Lennart Adler

1990-01-01

107

A new decoupling method for accurate quantification of polyethylene copolymer composition and triad sequence distribution with 13C NMR.  

PubMed

(13)C NMR is a powerful analytical tool for characterizing polyethylene copolymer composition and sequence distribution. Accurate characterization of the composition and sequence distribution is critical for researchers in industry and academia. Some common composite pulse decoupling (CPD) sequences used in polyethylene copolymer (13)C NMR can lead to artifacts such as modulations of the decoupled (13)C NMR signals (decoupling sidebands) resulting in systematic errors in quantitative analysis. A new CPD method was developed, which suppresses decoupling sidebands below the limit of detection (less than 1:40,000 compared to the intensity of the decoupled signal). This new CPD sequence consists of an improved Waltz-16 CPD, implemented as a bilevel method. Compared with other conventional CPD programs this new decoupling method produced the cleanest (13)C NMR spectra for polyethylene copolymer composition and triad sequence distribution analyses. PMID:17524686

Zhou, Zhe; Kümmerle, Rainer; Qiu, Xiaohua; Redwine, David; Cong, Rongjuan; Taha, Angela; Baugh, Dan; Winniford, Bill

2007-05-23

108

Temperature dependence of protein backbone motion from carbonyl 13C and amide 15N NMR relaxation  

NASA Astrophysics Data System (ADS)

The NMR spin lattice relaxation rate (R1) and the rotating-frame spin lattice relaxation rate (R1?) of amide 15N and carbonyl 13C (13C?) of the uniformly 13C- and 15N-labeled ubiquitin were measured at different temperatures and field strengths to investigate the temperature dependence of overall rotational diffusion and local backbone motion. Correlation between the order parameter of the N H vector, SNH2, and that of the carbonyl carbon, SC2, was investigated. The effective SC2 was estimated from the direct fit of the experimental relaxation rates and from the slope of 2R2 - R1 vs. B2 using Lipari Szabo formalism. The average SNH2 decreased by 5.9%, while the average SC2 decreased by 4.6% from 15 to 47 °C. At the extreme low and high temperatures the difference in the temperature dependence of the order parameters vanishes. At the intermediate temperatures they do not change by the same amount but they follow the same trend. On the same peptide plane along the protein sequence, SC2 and SNH2 are highly correlated. The results suggest that fast local motion experienced at the site of the N H vector and carbonyl nucleus is more complicated than previously thought and it cannot be easily described by one single type of motion in a broad range of temperature.

Chang, Shou-Lin; Tjandra, Nico

2005-05-01

109

Increasing 13C CP-MAS NMR resolution using single crystals: application to model octaethyl porphyrins.  

PubMed

Octaethyl porphyrin (OEP) and its Ni and Zn derivatives are considered as model compounds in biochemical, photophysical, and fossil fuel chemistry. They have thus been investigated by high-resolution solid-state (13)C NMR using powders, but peak assignment has been difficult because of large line widths. Arguing that a significant cause of broadening might be the anisotropic bulk magnetic susceptibility, we utilized single crystals in our (13)C cross-polarization magic angle spinning (CP-MAS) measurements and observed a nearly 2-fold line narrowing. This enhanced resolution enabled us to assign chemical shifts to each carbon for all the three compounds. The new assignments are now in agreement with X-ray structural data and allowed us to probe the motional dynamics of the methyl and methylene carbons of the OEP side chains. It is apparent that the use of single crystals in (13)C CP-MAS measurements has a significantly wider impact than previously thought. PMID:22679901

Dugar, Sneha; Fu, Riqiang; Dalal, Naresh S

2012-07-24

110

Discrimination of Cod Liver Oil According to Wild\\/Farmed and Geographical Origins by GC and 13 C NMR  

Microsoft Academic Search

The objective of this study was to test the possibility of using lipid profiles obtained by gas chromatography (GC) and 13C nuclear magnetic resonance (NMR) in authentication of cod liver oils according to wild\\/farmed and geographical origin. GC\\u000a and 13C-NMR data of cod liver oil from wild and farmed fish from different locations in Norway and Scotland were obtained, and

Inger B. Standal; Angelika Praël; Lesley McEvoy; David E. Axelson; Marit Aursand

2008-01-01

111

Magnetization and 13C NMR spin-lattice relaxation of nanodiamond powder  

SciTech Connect

The bulk magnetization at temperatures of 1.8-400 K and in magnetic fields up to 70 kOe, the ambient temperature {sup 13}C NMR spin-lattice relaxation, T{sub 1,c}, and the elemental composition of three nanodiamond powder samples have been studied. The total magnetization of nanodiamond can be explained in terms of contributions from (1) the diamagnetic effect of carbon, (2) the paramagnetic effect of unpaired electrons present in nanodiamond grains, and (3) ferromagnetic-like and (4) superparamagnetic contributions from Fe-containing particles detected in spatially resolved energy-dispersive spectroscopy. Contributions (1) and (2) are intrinsic to nanodiamond, while contributions (3) and (4) arise from impurities naturally present in detonation nanodiamond samples. {sup 13}C NMR T{sub 1,c} relaxation would be unaffected by the presence of the ferromagnetic particles with the bulk magnetization of {approx} 0.01 emu/g at 300 K. Thus, a reduction of T{sub 1,c} by 3 orders of magnitude compared to natural and synthetic microdiamonds confirms the presence of unpaired electrons in the nanodiamond grains. The spin concentration in nanodiamond powder corresponds to {approx}30 unpaired electrons per {approx}4.6 nm diameter nanodiamond grain.

Levin, E.M.; Fang, X.W.; Bud'ko, S.L.; Straszheim, W.E.; McCallum, R.W.; Schmidt-Rohr, K.

2008-02-15

112

Electronic properties and 13C NMR structural study of Y3N@C88.  

PubMed

In this paper, we report the synthesis, purification, (13)C NMR, and other characterization studies of Y(3)N@C(88). The (13)C NMR, UV-vis, and chromatographic data suggest an Y(3)N@C(88) having an IPR-allowed cage with D(2)(35)-C(88) symmetry. In earlier density functional theory (DFT) computational and X-ray crystallographic studies, it was reported that lanthanide (A(3)N)(6+) clusters are stabilized in D(2)(35)-C(88) symmetry cages and have reduced HOMO-LUMO gaps relative to other trimetallic nitride endohedral metallofullerene cage systems, for example, A(3)N@C(80). In this paper, we report that the nonlanthanide (Y(3)N)(6+) cluster in the D(2)(35)-C(88) cage exhibits a HOMO-LUMO gap consistent with other lanthanide A(3)N@C(88) molecules based on electrochemical measurements and DFT computational studies. These results suggest that the reduced HOMO-LUMO gap of A(3)N@C(88) systems is a property dominated by the D(2)(35)-C(88) carbon cage and not f-orbital lanthanide electronic metal cluster (A(3)N)(6+) orbital participation. PMID:21506556

Fu, Wujun; Zhang, Jianyuan; Champion, Hunter; Fuhrer, Tim; Azuremendi, Hugo; Zuo, Tianming; Zhang, Jianfei; Harich, Kim; Dorn, Harry C

2011-04-20

113

13C and 31P NMR for the diagnosis of muscular phosphorylase-kinase deficiency  

NASA Astrophysics Data System (ADS)

To further develop and specify the range of medical applications of in vivo NMR spectroscopy for the study of myopathies, it is ncessary to study the largest number of well characterized cases. We here report on the 31P and 13C NMR study of a purely muscular form of phosphorylase-kinase (PK) deficiency. Abnormalities were observed that agree with and increase our pathophysiological knowledge, in particular on the activation of phosphorylase and PK. Also, the abnormalities are different from those found in other clinically similar metabolic myopathies and could be used for the differential diagnosis. Afin de continuer à développer et préciser les applications médicales de la spectroscopie RMN in vivo, il faut étudier le plus grand nombre possible de cas bien caractérisés. Nous avons étudié ici une forme purement musculaire de déficit en phosphorylase-kinase (PK) par RMN du phosphore 31 et du carbone 13. Les altérations observées sont en accord avec et augmentent nos connaissances physiopathologiques, par exemple concernant l'activation de la phosphorylase et PK. Par ailleurs, la combinaison d'altérations observées en 31P et 13C est différente de celle retrouvée dans d'autres myopathies métaboliques cliniquement semblables et pourrait être utilisée pour le diagnostic différentiel.

Jehenson, P.; Duboc, D.; Laforet, P.; Eymard, B.; Lombès, A.; Fardeau, M.; Brunet, P.; Syrota, A.

1998-02-01

114

Location of a cation-binding site in the loop between helices F and G of bacteriorhodopsin as studied by 13C NMR.  

PubMed Central

The high-affinity cation-binding sites of bacteriorhodopsin (bR) were examined by solid-state 13C NMR of samples labeled with [3-13C]Ala and [1-13C]Val. We found that the 13C NMR spectra of two kinds of blue membranes, deionized (pH 4) and acid blue at pH 1.2, were very similar and different from that of the native purple membrane. This suggested that when the surface pH is lowered, either by removal of cations or by lowering the bulk pH, substantial change is induced in the secondary structure of the protein. Partial replacement of the bound cations with Na+, Ca2+, or Mn2+ produced additional spectral changes in the 13C NMR spectra. The following conclusions were made. First, there are high-affinity cation-binding sites in both the extracellular and the cytoplasmic regions, presumably near the surface, and one of the preferred cation-binding sites is located at the loop between the helix F and G (F-G loop) near Ala196, consistent with the 3D structure of bR from x-ray diffraction and cryoelectron microscopy. Second, the bound cations undergo rather rapid exchange (with a lifetime shorter than 3 ms) among various types of cation-binding sites. As expected from the location of one of the binding sites, cation binding induced conformational alteration of the F-G interhelical loop.

Tuzi, S; Yamaguchi, S; Tanio, M; Konishi, H; Inoue, S; Naito, A; Needleman, R; Lanyi, J K; Saito, H

1999-01-01

115

A variable-director 13C NMR analysis of lyotropic aramide solutions  

NASA Astrophysics Data System (ADS)

The order and dynamics of two aromatic polyamides in their lyotropic phases were investigated with the aid of variable-director nuclear magnetic resonance (NMR). In these experiments polymers were dissolved in concentrated sulfuric acid and allowed to equilibrate inside the main NMR magnetic field B0 to yield macroscopically-aligned liquid crystalline solutions. These ordered fluids were then rotated away from equilibrium for brief periods of time, and their natural abundance 13C NMR spectra collected as a function of different angles between the liquid crystalline director and B0. The resulting spectra showed peaks shifting as well as broadening as a function of the director's orientation, variations that were also found to be concentration- and temperature-dependent. All such changes could be successfully accounted for on the basis of an exchange model involving molecular reorientations of the polymer chains that are occurring in the intermediate NMR time scale. Based on this assumption, the experimental line shapes could be used to extract a detailed description of the macromolecular order and dynamics in these fluids. The former appeared substantially high, and not very different from the one characterizing order in commercial extruded aramide fibers. The latter enabled an estimation of the hydrodynamic radii adopted by the macromolecules in their mesophases, which ended up in close agreement with dimensions recently reported on the basis of small-angle neutron scattering analyses.

Grinshtein, Julia; McElheny, Dan; Frydman, Veronica; Frydman, Lucio

2001-03-01

116

Purity analysis of hydrogen cyanide, cyanogen chloride and phosgene by quantitative (13)C NMR spectroscopy.  

PubMed

Hydrogen cyanide, cyanogen chloride and phosgene are produced in tremendously large quantities today by the chemical industry. The compounds are also particularly attractive to foreign states and terrorists seeking an inexpensive mass-destruction capability. Along with contemporary warfare agents, therefore, the US Army evaluates protective equipment used by warfighters and domestic emergency responders against the compounds, and requires their certification at > or = 95 carbon atom % before use. We have investigated the (13)C spin-lattice relaxation behavior of the compounds to develop a quantitative NMR method for characterizing chemical lots supplied to the Army. Behavior was assessed at 75 and 126 MHz for temperatures between 5 and 15 degrees C to hold the compounds in their liquid states, dramatically improving detection sensitivity. T(1) values for cyanogen chloride and phosgene were somewhat comparable, ranging between 20 and 31 s. Hydrogen cyanide values were significantly shorter at 10-18 s, most likely because of a (1)H--(13)C dipolar contribution to relaxation not possible for the other compounds. The T(1) measurements were used to derive relaxation delays for collecting the quantitative (13)C data sets. At 126 MHz, only a single data acquisition with a cryogenic probehead gave a signal-to-noise ratio exceeding that necessary for certifying the compounds at > or = 95 carbon atom % and 99% confidence. Data acquired at 75 MHz with a conventional probehead, however, required > or = 5 acquisitions to reach this certifying signal-to-noise ratio for phosgene, and >/= 12 acquisitions were required for the other compounds under these same conditions. In terms of accuracy and execution time, the NMR method rivals typical chromatographic methods. PMID:17924355

Henderson, Terry J; Cullinan, David B

2007-11-01

117

13C NMR studies of hydrocarbon guests in synthetic structure H gas hydrates: experiment and computation.  

PubMed

(13)C NMR chemical shifts were measured for pure (neat) liquids and synthetic binary hydrate samples (with methane help gas) for 2-methylbutane, 2,2-dimethylbutane, 2,3-dimethylbutane, 2-methylpentane, 3-methylpentane, methylcyclopentane, and methylcyclohexane and ternary structure H (sH) clathrate hydrates of n-pentane and n-hexane with methane and 2,2-dimethylbutane, all of which form sH hydrates. The (13)C chemical shifts of the guest atoms in the hydrate are different from those in the free form, with some carbon atoms shifting specifically upfield. Such changes can be attributed to conformational changes upon fitting the large guest molecules in hydrate cages and/or interactions between the guests and the water molecules of the hydrate cages. In addition, powder X-ray diffraction measurements revealed that for the hexagonal unit cell, the lattice parameter along the a-axis changes with guest hydrate former molecule size and shape (in the range of 0.1 Å) but a much smaller change in the c-axis (in the range of 0.01 Å) is observed. The (13)C NMR chemical shifts for the pure hydrocarbons and all conformers were calculated using the gauge invariant atomic orbital method at the MP2/6-311+G(2d,p) level of theory to quantify the variation of the chemical shifts with the dihedral angles of the guest molecules. Calculated and measured chemical shifts are compared to determine the relative contribution of changes in the conformation and guest-water interactions to the change in chemical shift of the guest upon clathrate hydrate formation. Understanding factors that affect experimental chemical shifts for the enclathrated hydrocarbons will help in assigning spectra for complex hydrates recovered from natural sites. PMID:21329330

Lee, Jong-Won; Lu, Hailong; Moudrakovski, Igor L; Ratcliffe, Christopher I; Ohmura, Ryo; Alavi, Saman; Ripmeester, John A

2011-02-17

118

NMR-Based Structural Modeling of Graphite Oxide Using Multidimensional 13C Solid-State NMR and ab Initio Chemical Shift Calculations  

PubMed Central

Chemically modified graphenes and other graphite-based materials have attracted growing interest for their unique potential as lightweight electronic and structural nanomaterials. It is an important challenge to construct structural models of noncrystalline graphite-based materials on the basis of NMR or other spectroscopic data. To address this challenge, a solid-state NMR (SSNMR)-based structural modeling approach is presented on graphite oxide (GO), which is a prominent precursor and interesting benchmark system of modified graphene. An experimental 2D 13C double-quantum/single-quantum correlation SSNMR spectrum of 13C-labeled GO was compared with spectra simulated for different structural models using ab initio geometry optimization and chemical shift calculations. The results show that the spectral features of the GO sample are best reproduced by a geometry-optimized structural model that is based on the Lerf?Klinowski model (Lerf, A. et al. Phys. Chem. B1998, 102, 4477); this model is composed of interconnected sp2, 1,2-epoxide, and COH carbons. This study also convincingly excludes the possibility of other previously proposed models, including the highly oxidized structures involving 1,3-epoxide carbons (Szabo, I. et al. Chem. Mater.2006, 18, 2740). 13C chemical shift anisotropy (CSA) patterns measured by a 2D 13C CSA/isotropic shift correlation SSNMR were well reproduced by the chemical shift tensor obtained by the ab initio calculation for the former model. The approach presented here is likely to be applicable to other chemically modified graphenes and graphite-based systems.

2010-01-01

119

Carbonyl 13C NMR spectrum of basic pancreatic trypsin inhibitor: resonance assignments by selective amide hydrogen isotope labeling and detection of isotope effects on 13C nuclear shielding.  

PubMed

The carbonyl region of the natural abundance 13C nuclear magnetic resonance (NMR) spectrum of basic pancreatic trypsin inhibitor is examined, and 65 of the 66 expected signals are characterized at varying pH and temperature. Assignments are reported for over two-thirds of the signals, including those of all buried backbone amide groups with slow proton exchange and all side-chain carbonyl groups. This is the first extensively assigned carbonyl spectrum for any protein. A method for carbonyl resonance assignments utilizing amide proton exchange and isotope effects on nuclear shielding is described in detail. The assignments are made by establishing kinetic correlation between effects of amide proton exchange observed in the carbonyl 13C region with development of isotope effects and in the amide proton region with disappearance of preassigned resonances. Several aspects of protein structure and dynamics in solution may be investigated by carbonyl 13C NMR spectroscopy. Some effects of side-chain primary amide group hydrolysis are described. The main interest is on information about intramolecular hydrogen-bond energies and changes in the protein due to amino acid replacements by chemical modification or genetic engineering. PMID:2464371

Tüchsen, E; Hansen, P E

1988-11-15

120

Ab initio study of {sup 13}C NMR chemical shifts for the chromophores of rhodopsin and bacteriorhodopsin. 2. Comprehensive analysis of the {sup 13}C chemical shifts of protonated all-trans-retinylidene Schiff base  

SciTech Connect

Theoretical analysis was performed for the {sup 13}C chemical shifts of the retinal chromophore in bacteriorhodopsin (bR) by means of ab initio NMR shielding calculation, based on the localized orbital/ local origin method. In order to comprehensively investigate the correlation between the {sup 13}C chemical shieldings of the unsaturated carbons and physicochemical perturbations relating to the spectral tuning of bacteriorhodopsin, the following three factors are taken into account in the present calculation: (1) change in strength of the hydrogen bonding between protonated retinylidene Schiff base and its counterion, (2) conformational changes about single bonds of the conjugated chain, and (3) electrostatic interactions between the Schiff base and electric dipoles. On the basis of these calculations, we successfully find a molecular model for which the shielding calculation almost completely reproduces the observed chemical shift data for the chromophore of bR. 47 refs., 13 figs.

Sakurai, Minoru; Wada, Mitsuhito; Inoue, Yoshio [Tokyo Inst. of Technology, Yokohama (Japan); Tamura, Yusuke; Watanabe, Yoichi [Cray Research Japan Ltd., Tokyo (Japan)

1996-02-01

121

Determination of glucan phosphorylation using heteronuclear (1) H,(13) C double and (1) H,(13) C,(31) P triple-resonance NMR spectra.  

PubMed

Phosphorylation and dephosphorylation of starch and glycogen are important for their physicochemical properties and also their physiological functions. It is therefore desirable to reliably determine the phosphorylation sites. Heteronuclear multidimensional NMR-spectroscopy is in principle a straightforward analytical approach even for complex carbohydrate molecules. With heterogeneous samples from natural sources, however, the task becomes more difficult because a full assignment of the resonances of the carbohydrates is impossible to obtain. Here, we show that the combination of heteronuclear (1) H,(13) C and (1) H,(13) C,(31) P techniques and information derived from spectra of a set of reference compounds can lead to an unambiguous determination of the phosphorylation sites even in heterogeneous samples. Copyright © 2013 John Wiley & Sons, Ltd. PMID:23913630

Schmieder, Peter; Nitschke, Felix; Steup, Martin; Mallow, Keven; Specker, Edgar

2013-08-04

122

Probing RNA dynamics via longitudinal exchange and CPMG relaxation dispersion NMR spectroscopy using a sensitive 13C-methyl label  

PubMed Central

The refolding kinetics of bistable RNA sequences were studied in unperturbed equilibrium via 13C exchange NMR spectroscopy. For this purpose a straightforward labeling technique was elaborated using a 2?-13C-methoxy uridine modification, which was prepared by a two-step synthesis and introduced into RNA using standard protocols. Using 13C longitudinal exchange NMR spectroscopy the refolding kinetics of a 20?nt bistable RNA were characterized at temperatures between 298 and 310?K, yielding the enthalpy and entropy differences between the conformers at equilibrium and the activation energy of the refolding process. The kinetics of a more stable 32?nt bistable RNA could be analyzed by the same approach at elevated temperatures, i.e. at 314 and 316?K. Finally, the dynamics of a multi-stable RNA able to fold into two hairpin- and a pseudo-knotted conformation was studied by 13C relaxation dispersion NMR spectroscopy.

Kloiber, Karin; Spitzer, Romana; Tollinger, Martin; Konrat, Robert; Kreutz, Christoph

2011-01-01

123

Probing RNA dynamics via longitudinal exchange and CPMG relaxation dispersion NMR spectroscopy using a sensitive 13C-methyl label.  

PubMed

The refolding kinetics of bistable RNA sequences were studied in unperturbed equilibrium via (13)C exchange NMR spectroscopy. For this purpose a straightforward labeling technique was elaborated using a 2'-(13)C-methoxy uridine modification, which was prepared by a two-step synthesis and introduced into RNA using standard protocols. Using (13)C longitudinal exchange NMR spectroscopy the refolding kinetics of a 20 nt bistable RNA were characterized at temperatures between 298 and 310K, yielding the enthalpy and entropy differences between the conformers at equilibrium and the activation energy of the refolding process. The kinetics of a more stable 32 nt bistable RNA could be analyzed by the same approach at elevated temperatures, i.e. at 314 and 316 K. Finally, the dynamics of a multi-stable RNA able to fold into two hairpin- and a pseudo-knotted conformation was studied by (13)C relaxation dispersion NMR spectroscopy. PMID:21252295

Kloiber, Karin; Spitzer, Romana; Tollinger, Martin; Konrat, Robert; Kreutz, Christoph

2011-01-19

124

13C, 15N CPMAS NMR and GIAO DFT calculations of stereoisomeric oxindole alkaloids from Cat's Claw ( Uncaria tomentosa)  

Microsoft Academic Search

Oxindole alkaloids, isolated from the bark of Uncaria tomentosa [Willd. ex Schult.] Rubiaceae, are considered to be responsible for the biological activity of this herb. Five pentacyclic and two tetracyclic alkaloids were studied by solid-state NMR and theoretical GIAO DFT methods. The 13C and 15N CPMAS NMR spectra were recorded for mitraphylline, isomitraphylline, pteropodine (uncarine C), isopteropodine (uncarine E), speciophylline

Katarzyna Paradowska; Micha? Wolniak; Maciej Pisklak; Jan A. Gli?ski; Matthew H. Davey; Iwona Wawer

2008-01-01

125

Phase transitions of monoglyceride emulsifier systems and pearlescent effects in cosmetic creams studied by 13C NMR spectroscopy and DSC  

Microsoft Academic Search

The present work investigates the phase transitions of monoglyceride emulsifier systems and pearlescent effects in cosmetic creams using 13C-NMR spectroscopy and DSC. The four phases of monoglyceride emulsifier systems – the coagel, gel phase, liquid-crystalline lamellar phase, and cubic phase – can be characterized in creams at appropriate temperatures by NMR spectroscopy. The phase transition temperatures were determined by DSC.

Cécile Alberola; Bernhard Blümich; Detlef Emeis; Klaus-Peter Wittern

2006-01-01

126

Imazalil–cyclomaltoheptaose (?-cyclodextrin) inclusion complex: preparation by supercritical carbon dioxide and 13C CPMAS and 1H NMR characterization  

Microsoft Academic Search

An inclusion complex between imazalil (IMZ), a selected fungicide, and cyclomaltoheptaose (?-cyclodextrin, ?CD) was obtained using supercritical fluid carbon dioxide. The best preparation conditions were determined, and the inclusion complex was investigated by means of 1H NMR spectroscopy in aqueous solution and 13C CPMAS NMR spectroscopy in the solid state. Information on the geometry of the ?CD\\/IMZ complex was obtained

Simona Lai; Emanuela Locci; Alessandra Piras; Silvia Porcedda; Adolfo Lai; Bruno Marongiu

2003-01-01

127

13C solid-state NMR analysis of heterogeneous structure of beeswax in native state  

NASA Astrophysics Data System (ADS)

I investigated the molecular structure of natural wax from Japanese bees (Apis cerana japonica) in its native state (neither purified nor recrystallized) by 13C and 1H solid-state NMR. Two strong 13C peaks at 32.9 and 34.0 ppm were attributed to signals from internal-chain methylene carbons [int-(CH2)] in two types of crystal form. The peak at 32.9 ppm was assigned to an orthorhombic crystal form, and that at 34.0 ppm was assigned to a triclinic or monoclinic form. In both crystalline regions, bi-exponential decay of 13C spin-lattice relaxation [T1(C)] for the crystalline peaks due to chain diffusion was observed. 1H spin-lattice relaxation [T1(H)] values for protons of the CH3 group and for int-(CH2) in the crystalline and amorphous regions were identical; this was interpreted as being due to averaging of the T1(H) relaxation rates via spin diffusion. In contrast, although the T_{{1}_{\\rho}}(H) decay curves for protons of the CH3 group and for int-(CH2) in the amorphous and orthorhombic forms were almost identical, those of the triclinic or monoclinic forms were different. This unhomogeneous character of T_{{1}_{\\rho}}(H) was interpreted as resulting from differences in the molecular composition of each crystal form. Moreover, two components with long and short 1H spin-spin relaxation [T2(H)] values, arising from the mobile and rigid phases, respectively, were observed at above about -30 °C.

Kameda, Tsunenori

2005-12-01

128

13C-NMR relation study of heparin-disaccharide interactions with tripeptides GRG and GKG.  

PubMed Central

Heparin is a polydisperse sulphated copolymer consisting mostly of 1-->4 linked glucosamine and uronic acid residues, i.e. 2-deoxy-2-sulphamido-D-glucopyranose 6-sulphate and L-idopyranosyluronic acid 2-sulphate. 13C NMR has been used to study the interactions of heparinase-derived and purified heparin disaccharide with N- and C-terminally-blocked tripeptides GRG and GKG. Titration of the disaccharide with peptide indicates that GRG binds the disaccharide more strongly than does GKG, with interactions in either case being stronger at uronate ring positions. In the presence of GRG, a carboxylate pKa depression suggests electrostatic interactions between the arginine guanidinium group and the uronate carboxylate group. 13C relaxation data have been acquired for all disaccharide and peptide carbons in the presence and absence of GRG and GKG. 13C relaxation rates for the disaccharide are significantly faster in the presence of peptide, especially with GRG. Analysis of these relaxation data has been done in terms of molecular diffusion constants, D [symbol: see text] and D parallel, and an angle alpha between D parallel and a molecular frame defined by the moment of inertia tensor calculated for an internally rigid disaccharide. Disaccharide conformational space in these calculations has been sampled for both uronate half-chair forms (2H1 and 1H2) and over a range of glycosidic bond angles defined by motional order parameters and inter-residue nuclear Overhauser effects (+/- 30 degree from the average). In the absence of peptide, the ratio D [symbol: see text] /D parallel falls between 0.4 and 0.7; therefore molecular diffusion occurs preferentially about D parallel, which runs through both disaccharide rings. In the presence of peptide, D [symbol: see text] /D parallel is decreased, indicating that GRG is oriented along D parallel and proximal to the uronic acid ring. A model for this is shown.

Mikhailov, D; Mayo, K H; Pervin, A; Linhardt, R J

1996-01-01

129

WAXS and 13C NMR study of Gluconoacetobacter xylinus cellulose in composites with tamarind xyloglucan.  

PubMed

- Model composites, produced using cellulose from stationary cultures of the bacterium Gluconoacetobacter xylinus and tamarind xyloglucan, were examined by wide-angle X-ray scattering (WAXS) and CP/MAS solid-state (13)C NMR spectroscopy. The dominant crystallite allomorph of cellulose produced in culture media with or without xyloglucan was cellulose I(alpha) (triclinic). The presence of xyloglucan in the culture medium reduced the cross-section dimensions of the cellulose crystallites, but did not affect the crystallite allomorph. However, when the composites were refluxed in buffer, the proportion of cellulose I(beta) allomorph increased relative to that of cellulose I(alpha). In contrast, cellulose I(alpha) remained the dominant form when cellulose, produced in the absence of xyloglucan, was then heated in the buffer. Hence the presence of xyloglucan has a profound effect on the formation of the cellulose crystallites by G. xylinus. PMID:18048015

Bootten, Tracey J; Harris, Philip J; Melton, Laurence D; Newman, Roger H

2007-11-17

130

The structure of freshwater humic substances as revealed by 13C-NMR spectroscopy  

NASA Astrophysics Data System (ADS)

Freshwater humic substances from Lake Celyn, Gwynedd, N. Wales have been investigated by 13C-NMR spectroscopy. Carboxyl, aromatic, o-alkyl and alkyl resonances can be recognised. Varying pulse delay from 0.43 s to 2.5 sec has little effect on the magnitude of the signal ascribed to aromatic carbon, but there is a small nuclear Overhauser effect (1.45 at a pulse delay of 0.8 sec). The results show-that 24% of the Lake Celyn humic acid carbon is carboxyl and 40% is aromatic. The high proportion of aromatic carbon suggests the Lake Celyn humic acid is largely formed from terrestrial humic substances from the surrounding peaty watershed.

Wilson, M. A.; Barron, P. F.; Gillam, A. H.

1981-10-01

131

Structure of humic acids in zonal soils from 13C NMR data  

NASA Astrophysics Data System (ADS)

The structure of humic acids (HAs) in zonal soil types—soddy-podzolic soils (two samples), gray forest soil (one sample), and chernozems (two samples)—was quantitatively studied by 13C NMR spectros-copy. In the series considered, the content of unsubstituted carbon in the aromatic fragments of HAs increased, and the fraction of unsubstituted aliphatic structures decreased. HAs of soddy-podzolic soils were found to be enriched with carbohydrate fragments compared to HAs of chernozems and gray forest soil. The carbon skeleton of HAs from typical rich chernozem contained significantly more aliphatic and carbohydrate fragments compared to typical chernozem, which probably reflected the lower degree of HA transformation in rich chernozem.

Kholodov, V. A.; Konstantinov, A. I.; Kudryavtsev, A. V.; Perminova, I. V.

2011-09-01

132

Direct measurement of brain glucose concentrations in humans by 13C NMR spectroscopy.  

PubMed Central

Glucose is the main fuel for energy metabolism in the normal human brain. It is generally assumed that glucose transport into the brain is not rate-limiting for metabolism. Since brain glucose concentrations cannot be determined directly by radiotracer techniques, we used 13C NMR spectroscopy after infusing enriched D-[1-13C]glucose to measure brain glucose concentrations at euglycemia and at hyperglycemia (range, 4.5-12.1 mM) in six healthy children (13-16 years old). Brain glucose concentrations averaged 1.0 +/- 0.1 mumol/ml at euglycemia (4.7 +/- 0.3 mM plasma) and 1.8-2.7 mumol/ml at hyperglycemia (7.3-12.1 mM plasma). Michaelis-Menten parameters of transport were calculated to be Kt = 6.2 +/- 1.7 mM and Tmax = 1.2 +/- 0.1 mumol/g.min from the relationship between plasma and brain glucose concentrations. The brain glucose concentrations and transport constants are consistent with transport not being rate-limiting for resting brain metabolism at plasma levels greater than 3 mM.

Gruetter, R; Novotny, E J; Boulware, S D; Rothman, D L; Mason, G F; Shulman, G I; Shulman, R G; Tamborlane, W V

1992-01-01

133

Solid-state sup 13 C NMR study of tyrosine protonation in dark-adapted bacteriorhodopsin  

SciTech Connect

Solid-state 13C MAS NMR spectra were obtained for dark-adapted bacteriorhodopsin (bR) labeled with (4'-13C)Tyr. Difference spectra (labeled minus natural abundance) taken at pH values between 2 and 12, and temperatures between 20 and -90 degrees C, exhibit a single signal centered at 156 ppm, indicating that the 11 tyrosines are protonated over a wide pH range. However, at pH 13, a second line appears in the spectrum with an isotropic shift of 165 ppm. Comparisons with solution and solid-state spectra of model compounds suggest that this second line is due to the formation of tyrosinate. Integrated intensities indicate that about half of the tyrosines are deprotonated at pH 13. This result demonstrates that deprotonated tyrosines in a membrane protein are detectable with solid-state NMR and that neither the bR568 nor the bR555 form of bR present in the dark-adapted state contains a tyrosinate at pH values between 2 and 12. Deprotonation of a single tyrosine in bR568 would account for 3.6% of the total tyrosine signal, which would be detectable with the current signal-to-noise ratio. We observe a slight heterogeneity and subtle line-width changes in the tyrosine signal between pH 7 and pH 12, which we interpret to be due to protein environmental effects (such as changes in hydrogen bonding) rather than complete deprotonation of tyrosine residue(s).

Herzfeld, J.; Das Gupta, S.K.; Farrar, M.R.; Harbison, G.S.; McDermott, A.E.; Pelletier, S.L.; Raleigh, D.P.; Smith, S.O.; Winkel, C.; Lugtenburg, J. (Massachusetts Institute of Technology, Cambridge (USA))

1990-06-12

134

Uniform sup 13 C isotope labeling of proteins with sodium acetate for NMR studies: Application to human carbonic anhydrase II  

SciTech Connect

Uniform double labeling of proteins for NMR studies can be prohibitively expensive, even with an efficient expression and purification scheme, due largely to the high cost of ({sup 13}C{sub 6}, 99%)glucose. The authors demonstrate here that uniformly (>95%) {sup 13}C and {sup 15}N double-labeled proteins can be prepared for NMR structure/function studies by growing cells in defined media containing sodium (1,2-{sup 13}C{sub 2},99%)acetate as the sole carbon source and ({sup 15}N, 99%)ammonium chloride as the sole nitrogen source. In addition, the authors demonstrate that this labeling scheme can be extended to include uniform carbon isotope labeling to any desired level (below 50%) by utilizing media containing equal amounts of sodium (1-{sup 13}C, 99%)acetate and sodium (2-{sup 13}C, 99%)acetate in conjunction with unlabeled sodium acetate. This technique is less labor intensive and more straightforward than labeling using isotope-enriched algal hydrolysates. These labeling schemes have been used to successfully prepare NMR quantities of isotopically enriched human carbonic anhydrase II. The activity and the {sup 1}H NMR spectra of the protein labeled by this technique are the same as those obtained from the protein produced from media containing labeled glucose; however, the cost of the sodium (1,2-{sup 13}C{sub 2}, 99%)acetate growth media is considerably less than the cost of the ({sup 13}C{sub 6}, 99%)glucose growth media. They report here the first published {sup 13}C and {sup 15}N NMR spectra of human carbonic anhydrase II as an important step leading to the assignment of this 29-kDa zinc metalloenzyme.

Venters, R.S.; Calderone, T.L.; Spicer, L.D.; Fierke, C.A. (Duke Univ., Durham, NC (USA))

1991-05-07

135

Coupling XRD, EXAFS, and (13)C NMR to Study the Effect of the Carbon Stoichiometry on the Local Structure of UC1±x.  

PubMed

A series of uranium carbide samples, prepared by arc melting with a C/U ratio ranging from 0.96 to 1.04, has been studied by X-ray diffraction (XRD), (13)C nuclear magnetic resonance (NMR), and extended X-ray absorption fine structure (EXAFS). XRD determines phase uniqueness and the increase of the lattice parameter versus the carbon content. In contrast, (13)C NMR detects the different carbon environments in the lattice and in this study, clearly identifies the presence of discrete peaks for carbon in the octahedral lattice site in UC and an additional peak associated with excess carbon in hyperstoichiometric samples. Two peaks associated with different levels of carbon deficiency are detected for all hypostoichiometric compositions. More than one carbon environment is always detected by (13)C NMR. This exemplifies the difficulty in obtaining a perfect stoichiometric uranium monocarbide UC1.00. The (13)C MAS spectra of uranium carbides exhibit the effects resulting from the carbon content on both the broadening of the peaks and on the Knight shift. An abrupt spectral change occurs between hypo- and hyperstoichiometric samples. The results obtained by EXAFS highlight subtle differences between the different stoichiometries, and in the hyperstoichiometric samples, the EXAFS results are consistent with the excess carbon atoms being in the tetrahedral interstitial position. PMID:24063301

Carvajal Nuñez, U; Martel, L; Prieur, D; Lopez Honorato, E; Eloirdi, R; Farnan, I; Vitova, T; Somers, J

2013-09-24

136

Dynamic nuclear polarization-enhanced 1H-13C double resonance NMR in static samples below 20 K  

NASA Astrophysics Data System (ADS)

We demonstrate the feasibility of one-dimensional and two-dimensional 1H-13C double resonance NMR experiments with dynamic nuclear polarization (DNP) at 9.4 T and temperatures below 20 K, including both 1H-13C cross-polarization and 1H decoupling, and discuss the effects of polarizing agent type, polarizing agent concentration, temperature, and solvent deuteration. We describe a two-channel low-temperature DNP/NMR probe, capable of carrying the radio-frequency power load required for 1H-13C cross-polarization and high-power proton decoupling. Experiments at 8 K and 16 K reveal a significant T2 relaxation of 13C, induced by electron spin flips. Carr-Purcell experiments and numerical simulations of Carr-Purcell dephasing curves allow us to determine the effective correlation time of electron flips under our experimental conditions. The dependence of the DNP signal enhancement on electron spin concentration shows a maximum near 80 mM. Although no significant difference in the absolute DNP enhancements for triradical (DOTOPA-TEMPO) and biradical (TOTAPOL) dopants was found, the triradical produced greater DNP build-up rates, which are advantageous for DNP experiments. Additionally the feasibility of structural measurements on 13C-labeled biomolecules was demonstrated with a two-dimensional 13C-13C exchange spectrum of selectively 13C-labeled ?-amyloid fibrils.

Potapov, Alexey; Thurber, Kent R.; Yau, Wai-Ming; Tycko, Robert

2012-08-01

137

Identification and quantitative determination of lignans in Cedrus atlantica resins using 13C NMR spectroscopy.  

PubMed

Identification and quantitative determination of individual components of resin collected on the trunk of 28 Cedrus atlantica trees, grown in Corsica, has been carried out using 13C NMR spectroscopy. Eight resin acids bearing either the pimarane or abietane skeleton, two monoterpene hydrocarbons and four oxygenated neutral diterpenes have been identified, as well as three lignans, scarcely found in resins. Three groups could be distinguished within the 28 resin samples. The nine samples of Group I had their composition dominated by diterpene acids (33.7-45.8%), with abietic acid (6.2-18.7%) and isopimaric acid (5.1-12.6%) being the major components. The four samples of Group II contained resin acids (main components) and lignans in moderate amounts (up to 10.3%). Conversely, lignans (38.8-63.8%) were by far the major components of the 15 samples of Group III. Depending on the sample, the major component was pinoresinol (18.1-38.9%), lariciresinol (17.2-33.7%) or lariciresinol 9'-acetate (16.9-29.1%). Finally, due to the high biological interest in lignans, a rapid procedure, based on 1H NMR spectroscopy, was developed for quantification of lignans in resins of C. atlantica. PMID:21485279

Nam, Anne-Marie; Paoli, Mathieu; Castola, Vincent; Casanova, Joseph; Bighelli, Ange

2011-03-01

138

Quantitation of crystalline and amorphous forms of anhydrous neotame using 13C CPMAS NMR spectroscopy.  

PubMed

Although most drugs are formulated in the crystalline state, amorphous or other crystalline forms are often generated during the formulation process. The presence of other forms can dramatically affect the physical and chemical stability of the drug. The identification and quantitation of different forms of a drug is a significant analytical challenge, especially in a formulated product. The ability of solid-state 13C NMR spectroscopy with cross polarization (CP) and magic-angle spinning (MAS) to quantify the amounts of three of the multiple crystalline and amorphous forms of the artificial sweetener neotame is described. It was possible to quantify, in a mixture of two anhydrous polymorphic forms of neotame, the amount of each polymorph within 1-2%. In mixtures of amorphous and crystalline forms of neotame, the amorphous content could be determined within 5%. It was found that the crystalline standards that were used to prepare the mixtures were not pure crystalline forms, but rather a mixture of crystalline and amorphous forms. The effect of amorphous content in the crystalline standards on the overall quantitation of the two crystalline polymorphic forms is discussed. The importance of differences in relaxation parameters and CP efficiencies on quantifying mixtures of different forms using solid-state NMR spectroscopy is also addressed. PMID:16258988

Offerdahl, Thomas J; Salsbury, Jonathon S; Dong, Zedong; Grant, David J W; Schroeder, Stephen A; Prakash, Indra; Gorman, Eric M; Barich, Dewey H; Munson, Eric J

2005-12-01

139

13C-NMR study of the interaction of bacterial alginate with bivalent cations.  

PubMed

The effect of bivalent cations on solutions of extracellular polymeric substances (EPS) isolated from Pseudomonas aeruginosa was monitored by means of solid-state nuclear magnetic resonance. In particular, the binding of Ca2+ and Mg2+ to the alginate in aqueous solution was studied by determining the spin-lattice relaxation rates, line widths and line shapes of 13C nuclei under variation of the ion concentration. Both cations differ strongly in their affinity towards bacterial alginate. Spectral data indicate that the strong binding capacity of calcium is connected to the formation of a chelate complex, in which binding occurs particularly with the monomer units in alternating mannuronate-guluronate blocks. In contrast to this, binding of magnesium ions was found to be much weaker and non-specific. PMID:14599588

Lattner, Daniel; Flemming, Hans-Curt; Mayer, Christian

2003-11-01

140

Structural Characterization of Humic Materials Using ^13C NMR Techniques: A Comparison of Solution- and Solid-State Methods  

NASA Astrophysics Data System (ADS)

The analysis of the carbon type distribution and chemical structure of natural organic matter (NOM) by ^13C NMR spectroscopy is an important technique for understanding its origins and reactivity. While prior work has used solution-state NMR techniques, solid-state NMR has the potential to provide this information using less instrument time and sample manipulation, while providing an array of advanced filtering techniques. Analyses of four isolated humic materials with ^13C solid-state magic angle spinning (MAS) NMR techniques are described, including three commercially available samples and one fulvic acid sample isolated from the Rio Grande in New Mexico. This study demonstrates the utility of solid-state ^13C NMR for aquatic NOM structural characterization, comparing these results to the existing solution-state determinations. The solid-state ^13C MAS NMR results are used to determine % carbon distribution, estimates of elemental composition (%C, %H, %(O+N)), aromatic fraction (fa), nonprotonated aromatic fraction (faN), an estimate of aromatic cluster size, and ratio of sp^2 to sp^3 carbons. A Gaussian deconvolution method is introduced that allows for a detailed analysis of carbon type.

Clewett, Catherine; Alam, Todd; Osantowski, Eric; Pullin, Michael

2011-10-01

141

Elucidation of anaplerotic pathways in Corynebacterium glutamicum via 13 C-NMR spectroscopy and GC-MS  

Microsoft Academic Search

We have obtained direct evidence indicating the presence of pyruvate-carboxylating activity in Corynebacterium glutamicum, a lysine-overproducing bacterium. This evidence was obtained through the use of 13C nuclear magnetic resonance (NMR) spectroscopy and gas chromatography\\/mass spectrometry (GC-MS) of secreted metabolites in\\u000a a lysine fermentation. The distribution of 13C label after multiple turns in the tricarboxylic acid cycle was accounted for properly

S. M. Park; C. Shaw-Reid; A. J. Sinskey; G. Stephanopoulos

1997-01-01

142

Complete 1H and 13C NMR assignment of digeneaside, a low-molecular-mass carbohydrate produced by red seaweeds.  

PubMed

Digeneaside (alpha-D-mannopyranosyl-(1-->2)-D-glycerate) was extracted from the red algae, Bostrychia binderii, and purified by adsorption and gel-filtration chromatography. HPLC and ESI-MS techniques were used to follow purification steps and characterize digeneaside. NMR spectroscopy experiments (1D 1H, 13C, DEPT and 2D HMQC, COSY and TOCSY) were used to fully assign the 1H and 13C spectra. PMID:16442514

Ascêncio, Sérgio D; Orsato, Alexandre; França, Robson A; Duarte, M Eugênia R; Noseda, Miguel D

2006-01-26

143

Reactions of the mustard simulant 2-chloroethyl phenyl sulfide with self-decontaminating sorbents. A 13C MAS NMR study  

Microsoft Academic Search

Decomposition reactions for the mustard simulant 2-chloroethyl phenyl sulfide (13C-labelled, CEPS?) sorbed on ?-alumina, polydivinylbenzene (impregnated with NaOH, polyethylene glycol and polyethylenimine) (DVBNaOH), and Ambergard® XE-555, were characterized in situ using 13C MAS NMR. CEPS? hydrolyzes on ?-alumina to form 2-hydroxyethyl phenyl sulfide. On DVBNaOH, CEPS? eliminates HCl to yield vinyl phenyl sulfide. No products were observed on XE-555, where

George W. Wagner; Philip W. Bartram

1996-01-01

144

Complete (1)H and (13)C NMR chemical shift assignments of mono- to tetrasaccharides as basis for NMR chemical shift predictions of oligosaccharides using the computer program CASPER.  

PubMed

(1)H and (13)C NMR chemical shift data are used by the computer program CASPER to predict chemical shifts of oligo- and polysaccharides. Three types of data are used, namely, those from monosaccharides, disaccharides, and trisaccharides. To improve the accuracy of these predictions we have assigned the (1)H and (13)C NMR chemical shifts of eleven monosaccharides, eleven disaccharides, twenty trisaccharides, and one tetrasaccharide; in total 43 compounds. Five of the oligosaccharides gave two distinct sets of NMR resonances due to the ?- and ?-anomeric forms resulting in 48 (1)H and (13)C NMR chemical shift data sets. In addition, the pyranose ring forms of Neu5Ac were assigned at two temperatures, due to chemical shift displacements as a function of temperature. The (1)H NMR chemical shifts were refined using total line-shape analysis with the PERCH NMR software. (1)H and (13)C NMR chemical shift predictions were subsequently carried out by the CASPER program (http://www.casper.organ.su.se/casper/) for three branched oligosaccharides having different functional groups at their reducing ends, namely, a mannose-containing pentasaccharide, and two fucose-containing heptasaccharides having N-acetyllactosamine residues in the backbone of their structures. Good to excellent agreement was observed between predicted and experimental (1)H and (13)C NMR chemical shifts showing the utility of the method for structural determination or confirmation of synthesized oligosaccharides. PMID:24036391

Rönnols, Jerk; Pendrill, Robert; Fontana, Carolina; Hamark, Christoffer; d'Ortoli, Thibault Angles; Engström, Olof; Ståhle, Jonas; Zaccheus, Mona V; Säwén, Elin; Hahn, Liljan E; Iqbal, Shahzad; Widmalm, Göran

2013-07-10

145

Solid-state 13C NMR analysis of size and density fractions of marine sediments: Insight into organic carbon sources and preservation mechanisms  

NASA Astrophysics Data System (ADS)

Burial of organic carbon (OC) in ocean sediments acts as the ultimate long-term sink for both terrestrial and marine carbon, however, the mechanisms controlling the preservation of this carbon are poorly understood. To better understand these mechanisms, we applied solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, along with elemental, stable carbon isotopic (?13C) and lignin phenol analyses, to size and density fractions of sediments influenced by either mixed terrestrial and marine OC inputs (Washington Coast slope) or dominantly marine inputs (Mexican Margin). Elemental, isotopic and lignin analyses all reveal that within the Washington Coast sediment, the OC mixes linearly between nitrogen-poor and 13C-depleted, lignin-rich OC in the large and light fractions and nitrogen-rich and 13C-enriched, lignin-poor OC in the small and dense fractions, suggesting that this sediment contains a two-component mixture of terrestrial vascular plant- and marine-derived OC. The integral areas of each of seven NMR spectral regions in the different samples trend linearly when plotted versus ?13C signature, with most R2 values of 0.78 or greater, demonstrating that the NMR spectra of the two sources of carbon also mix linearly between the two endmembers. The terrestrial endmember in this sediment appears to be dominated by lignin and black carbon whereas the source of the marine endmember is less clear from the NMR spectra. In contrast, all of the analyses indicate that OC in the Mexican Margin sediment fractions is homogenous and derives almost exclusively from marine sources. It appears that selective preservation of (bio)chemically recalcitrant lignin and black carbon is the primary mechanism of preservation of terrestrial OC, whereas mineral-protection is the dominant mechanism preserving marine OC in the Washington coast sediment. There is little evidence showing that either preservation mechanism functions in the Mexican Margin sediments.

Dickens, Angela F.; Baldock, Jeffrey A.; Smernik, Ronald J.; Wakeham, Stuart G.; Arnarson, Thórarinn S.; Gélinas, Yves; Hedges, John I.

2006-02-01

146

Comparison of rotational barriers of related diphenylmethyl anions and cations studied by 13C NMR spectroscopy: Mechanistic and structural considerations*  

PubMed Central

The rotational barriers of diphenylmethyl anions and cations were measured through their temperature-dependent 13C NMR spectra. The ground state structures were found to possess a symmetrical propeller nature. The mechanism for phenyl rotation involves a nonsynchronous process, in which in the transition state one ring is coplanar with, and the other is perpendicular to, the plane formed by the central carbon and its bonds. The barriers of rotation in the carbanions vary with the strength of chelation of the potassium gegenion, whereas the 13C NMR shifts remain unaffected. Changing substituents in the para position of the aromatic rings allowed both the elucidation of structure and mechanism and the observation of effects of changes in electron distribution on the height of the barrier and the 13C NMR shifts.

Olah, George A.; Watkins, Michael I.

1980-01-01

147

DFT calculations of 1H and 13C NMR chemical shifts in transition metal hydrides.  

PubMed

Transition metal hydrides are of great interest in chemistry because of their reactivity and their potential use as catalysts for hydrogenation. Among other available techniques, structural properties in transition metal (TM) complexes are often probed by NMR spectroscopy. In this paper we will show that it is possible to establish a viable methodological strategy in the context of density functional theory, that allows the determination of 1H NMR chemical shifts of hydride ligands attached to transition metal atoms in mononuclear systems and clusters with good accuracy with respect to experiment. 13C chemical shifts have also been considered in some cases. We have studied mononuclear ruthenium complexes such as Ru(L)(H)(dppm)2 with L = H or Cl, cationic complex [Ru(H)(H2O)(dppm)2]+ and Ru(H)2(dppm)(PPh3)2, in which hydride ligands are characterized by a negative 1H NMR chemical shift. For these complexes all calculations are in relatively good agreement compared to experimental data with errors not exceeding 20% except for the hydrogen atom in Ru(H)2(dppm)(PPh3)2. For this last complex, the relative error increases to 30%, probably owing to the necessity to take into account dynamical effects of phenyl groups. Carbonyl ligands are often encountered in coordination chemistry. Specific issues arise when calculating 1H or 13C NMR chemical shifts in TM carbonyl complexes. Indeed, while errors of 10 to 20% with respect to experiment are often considered good in the framework of density functional theory, this difference in the case of mononuclear carbonyl complexes culminates to 80%: results obtained with all-electron calculations are overall in very satisfactory agreement with experiment, the error in this case does not exceed 11% contrary to effective core potentials (ECPs) calculations which yield errors always larger than 20%. We conclude that for carbonyl groups the use of ECPs is not recommended, although their use could save time for very large systems, for instance in cluster chemistry. The reliance of NMR chemical shielding on dynamical effects, such as intramolecular rearrangements or trigonal twists, is also examined for H2Fe(CO)4, K+[HFe(CO)](-), HMn(CO)5 and HRe(CO)5. The accuracy of the theory is also examined for complexes with two dihydrogen ligands (Tp*RuH(H2)2 and [FeH(H2)(DMPE)2]+) and a ruthenium cluster, [H3Ru4(C6H6)4(CO)]+. It is shown that for all complexes studied in this work, the effect of the ligands on the chemical shielding of hydrogen coordinated to metal is suitably calculated, thus yielding a very good correlation between experimental chemical shifts and theoretical chemical shielding. PMID:18648699

del Rosal, I; Maron, L; Poteau, R; Jolibois, F

2008-05-07

148

Acetone hydration in supercritical water: 13C-NMR spectroscopy and Monte Carlo simulation  

NASA Astrophysics Data System (ADS)

The 13C-NMR chemical shift of acetone ?(13C=O) was measured in aqueous solution at high temperatures up to 400 °C and water densities of 0.10-0.60 g/cm3 for the study of hydration structure in the supercritical conditions. The average number NHB of hydrogen bonds (HBs) between an acetone and solvent waters and the energy change ?E upon the HB formation were evaluated from the ? and its temperature dependence, respectively. At 400 °C, NHB is an increasing function of the water density, the increase being slower at higher water densities. The acetone-water HB formation is exothermic in supercritical water with larger negative ?E at lower water densities (-3.3 kcal/mol at 0.10 g/cm3 and -0.3 kcal/mol at 0.60 g/cm3), in contrast to the positive ?E in ambient water (+0.078 kcal/mol at 4 °C). The corresponding Monte Carlo simulations were performed to calculate the radial and orientational distribution functions of waters around the acetone molecule. The density dependence of NHB calculated at 400 °C is in a qualitative agreement with the experimental results. In the supercritical conditions, the HB angle in a neighboring acetone-water pair is weakly influenced by the water density, because of the absence of collective HB structure. This is in sharp contrast to the hydration structure in ambient water, where the acetone-water HB formation is orientationally disturbed by the tetrahedral HB network formation among the surrounding waters.

Takebayashi, Yoshihiro; Yoda, Satoshi; Sugeta, Tsutomu; Otake, Katsuto; Sako, Takeshi; Nakahara, Masaru

2004-04-01

149

Hyperpolarized 13C Spectroscopy and an NMR-Compatible Bioreactor System for the Investigation of Real-Time Cellular Metabolism  

PubMed Central

The purpose of this study was to combine a three-dimensional NMR-compatible bioreactor with hyperpolarized 13C NMR spectroscopy in order to probe cellular metabolism in real time. JM1 (immortalized rat hepatoma) cells were cultured in a three-dimensional NMR-compatible fluidized bioreactor. 31P spectra were acquired before and after each injection of hyperpolarized [1-13C] pyruvate and subsequent 13C spectroscopy at 11.7 T. 1H and two-dimensional 1H-1H-total correlation spectroscopy spectra were acquired from extracts of cells grown in uniformly labeled 13C-glucose, on a 16.4 T, to determine 13C fractional enrichment and distribution of 13C label. JM1 cells were found to have a high rate of aerobic glycolysis in both two-dimensional culture and in the bioreactor, with 85% of the 13C label from uniformly labeled 13C-glucose being present as either lactate or alanine after 23 h. Flux measurements of pyruvate through lactate dehydrogenase and alanine aminotransferase in the bioreactor system were 12.18 ± 0.49 nmols/sec/108 cells and 2.39 ± 0.30 nmols/sec/108 cells, respectively, were reproducible in the same bioreactor, and were not significantly different over the course of 2 days. Although this preliminary study involved immortalized cells, this combination of technologies can be extended to the real-time metabolic exploration of primary benign and cancerous cells and tissues prior to and after therapy.

Keshari, Kayvan R.; Kurhanewicz, John; Jeffries, Rex E.; Wilson, David M.; Dewar, Brian J.; Van Criekinge, Mark; Zierhut, Matthew; Vigneron, Daniel B.; Macdonald, Jeffrey M.

2010-01-01

150

13C NMR isotopomer analysis reveals a connection between pyruvate cycling and glucose-stimulated insulin secretion (GSIS).  

PubMed

Cellular metabolism of glucose is required for stimulation of insulin secretion from pancreatic beta cells, but the precise metabolic coupling factors involved in this process are not known. In an effort to better understand mechanisms of fuel-mediated insulin secretion, we have adapted 13C NMR and isotopomer methods to measure influx of metabolic fuels into the tricarboxylic acid (TCA) cycle in insulinoma cells. Mitochondrial metabolism of [U-13C3]pyruvate, derived from [U-13C6]glucose, was compared in four clonal rat insulinoma cell 1-derived cell lines with varying degrees of glucose responsiveness. A 13C isotopomer analysis of glutamate isolated from these cells showed that the fraction of acetyl-CoA derived from [U-13C6]glucose was the same in all four cell lines (44 +/- 5%, 70 +/- 3%, and 84 +/- 4% with 3, 6, or 12 mM glucose, respectively). The 13C NMR spectra also demonstrated the existence of two compartmental pools of pyruvate, one that exchanges with TCA cycle intermediates and a second pool derived from [U-13C6]glucose that feeds acetyl-CoA into the TCA cycle. The 13C NMR spectra were consistent with a metabolic model where the two pyruvate pools do not randomly mix. Flux between the mitochondrial intermediates and the first pool of pyruvate (pyruvate cycling) varied in proportion to glucose responsiveness in the four cell lines. Furthermore, stimulation of pyruvate cycling with dimethylmalate or its inhibition with phenylacetic acid led to proportional changes in insulin secretion. These findings indicate that exchange of pyruvate with TCA cycle intermediates, rather than oxidation of pyruvate via acetyl-CoA, correlates with glucose-stimulated insulin secretion. PMID:11880625

Lu, Danhong; Mulder, Hindrik; Zhao, Piyu; Burgess, Shawn C; Jensen, Mette V; Kamzolova, Svetlana; Newgard, Christopher B; Sherry, A Dean

2002-03-01

151

Density Functional Studies of the 13C NMR Chemical Shifts in Single-Walled Carbon Nanotubes  

NASA Astrophysics Data System (ADS)

Density functional theory has been used to compute the electronic structure and 13C NMR chemical shifts of finite (9,0) single-walled carbon nanotubes (SWNTs) capped with fullerene hemispheres and with hydrogen atoms. The chemical shifts and HOMO-LUMO gaps were found to be dependent upon the mode of capping. The shifts of semiconducting and metallic tubes were estimated as being around 130 ppm and 141 ppm, respectively. Periodic boundary calculations on infinite zigzag (n,0) SWNTs with 7<=n<=17 were performed. These entities can be characterized by a family index, ? = mod(n,3), and the chemical shifts can be fitted well by a function inversely proportional to the diameter of the tube and proportional to a constant which depends on the nanotube family. Direct comparison of the molecular and periodic approaches can be made if benzene is used as the internal reference. Such a comparison indicates that capping may have a strong effect on the computed properties. Calculations on infinite zigzag (7<=n<=10) amine functionalized SWNTs have been performed. The functional group may react with a C-C bond which is parallel or diagonal to the tube axis and both sites have been considered. The shifts of the carbons directly attached to the group are sensitive to the bond which has been functionalized and may therefore be used to discriminate between the two products. Functionalization induces a significant line broadening of the NMR signals but it does not dramatically change the average shift of the unfunctionalized SWNT carbons.

Zurek, Eva; Autschbach, Jochen

2007-12-01

152

Preparation of partially 2H/13C-labelled RNA for NMR studies. Stereo-specific deuteration of the H5" in nucleotides.  

PubMed

An effective in vitro enzymatic synthesis is described for the production of nucleoside triphosphates (NTPs) which are stereo-specifically deuterated on the H5" position with high selectivity (>98%), and which can have a variety of different labels (13C, 15N, 2H) in other positions. The NTPs can subsequently be employed in the enzymatic synthesis of RNAs using T7 polymerase from a DNA template. The stereo-specific deuteration of the H5" immediately provides the stereo-specific assignment of H5' resonances in NMR spectra, giving access to important structural parameters. Stereo-chemical H-exchange was used to convert commercially available 1,2,3,4,5,6,6-2H-1,2,3,4,5,6-13C-D-glucose (d7-13C6-D-glucose) into [1,2,3,4,5,6(R)-2H-1,2,3,4,5,6-13C]-D-glucose (d6-13C6-D-glucose). [1',3',4',5"-2H-1',2',3',4',5'-13C]GTP (d4-13C5-GTP) was then produced from d6-13C6-D-glucose and guanine base via in vitro enzymatic synthesis employing enzymes from the pentose-phosphate, nucleotide biosynthesis and salvage pathways. The overall yield was approximately 60 mg NTP per 1 g glucose, comparable with the yield of NTPs isolated from Escherichia coli grown on enriched media. The d4-13C5-GTP, together with in vitro synthesised d5-UTP, d5-CTP and non-labelled ATP, were used in the synthesis of a 31 nt RNA derived from the primer binding site of hepatitis B virus genomic RNA. (13C,1H) hetero-nuclear multiple-quantum spectra of the specifically deuterated sample and of a non-deuterated uniformly 13C/15N-labelled sample demonstrates the reduced spectral crowding and line width narrowing compared with 13C-labelled non-deuterated RNA. PMID:11917025

Cromsigt, Jenny; Schleucher, Jürgen; Gustafsson, Tomas; Kihlberg, Jan; Wijmenga, Sybren

2002-04-01

153

Preparation of partially 2H/13C-labelled RNA for NMR studies. Stereo-specific deuteration of the H5?? in nucleotides  

PubMed Central

An effective in vitro enzymatic synthesis is described for the production of nucleoside triphosphates (NTPs) which are stereo-specifically deuterated on the H5?? position with high selectivity (>98%), and which can have a variety of different labels (13C, 15N, 2H) in other positions. The NTPs can subsequently be employed in the enzymatic synthesis of RNAs using T7 polymerase from a DNA template. The stereo-specific deuteration of the H5?? immediately provides the stereo-specific assignment of H5? resonances in NMR spectra, giving access to important structural parameters. Stereo-chemical H-exchange was used to convert commercially available 1,2,3,4,5,6,6-2H-1,2,3,4,5,6-13C-d-glucose (d7-13C6-d-glucose) into [1,2,3,4,5,6(R)-2H-1,2,3,4,5,6-13C]-d-glucose (d6-13C6-d-glucose). [1?,3?,4?,5??-2H-1?,2?,3?,4?,5?-13C]GTP (d4-13C5-GTP) was then produced from d6-13C6-d-glucose and guanine base via in vitro enzymatic synthesis employing enzymes from the pentose-phosphate, nucleotide biosynthesis and salvage pathways. The overall yield was ?60 mg NTP per 1 g glucose, comparable with the yield of NTPs isolated from Escherichia coli grown on enriched media. The d4-13C5-GTP, together with in vitro synthesised d5-UTP, d5-CTP and non-labelled ATP, were used in the synthesis of a 31 nt RNA derived from the primer binding site of hepatitis B virus genomic RNA. (13C,1H) hetero-nuclear multiple-quantum spectra of the specifically deuterated sample and of a non-deuterated uniformly 13C/15N-labelled sample demonstrates the reduced spectral crowding and line width narrowing compared with 13C-labelled non-deuterated RNA.

Cromsigt, Jenny; Schleucher, Jurgen; Gustafsson, Tomas; Kihlberg, Jan; Wijmenga, Sybren

2002-01-01

154

Solvent and free-radical effects on the /sup 13/C NMR spectra of hydrocarbons  

SciTech Connect

The proton-decoupled /sup 13/C NMR spectra of benzene, naphthalene, azulene, acenaphthylene, fluoranthene, phenanthrene, and 6,6-pentamethylenefulvene have been obtained in dilute solutions in cyclohexane, triethylamine, di-n-butyl ether, diisopropyl ether, diethyl carbon, tetrahydrofuran, butyronitrile, ..gamma..-butyrolactone, propylene carbonate, dimethyl sulfoxide, benzene, toluene, fluorobenzene, anisole, acetophenone, benzonitrile, and nitrobenzene. It has been found that (1) the chemical shifts (relative to an external reference) of both alternant and nonalternant hydrocarbons are sensitive to solvent dipolarity-polarizability effects. (2) In the case of select solvents (aliphatic, monofunctional compound with one single dominant bond moment) there is a generally good correlation between the solvent-induced chemical shifts (SICS) and the ..pi..* scale of solent dipolarity-polarizability. (3) Aromatic solvent induced shifts (ASIS) and specific interactions are significant in aromatic solvents, although dipolarity-polarizability contributions are still very important. (4) With very few exceptions, SICS (relative to cyclohexane solvent) are downfield, and the results are not in favor of the simple reaction field model. (5) For aromatic hydrocarbons, there is a clear proportionality between the SICS and the paramagnetic shifts induced by the stable free-radical 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO). (6) There is no simple relationship between the SICS and the calculated electronic charge distribution of the solute molecules.

Abboud, J.M.; Auhmani, A.; Bitar, H.; El Mouhtadi, M.; Martin, J.; Rico, M.

1987-03-04

155

{sup 13}C NMR studies of ethylene adsorbed on Ru-Y zeolite  

SciTech Connect

The adsorption of ethylene on reduced co-cation-exchanged Ru-Y zeolites has been studied with {sup 13}C solid-state NMR. Self-hydrogenation of ethylene to ethane and butane is observed at room temperature. 2-Butenes are intermediates in the reaction. Coadsorption of hydrogen and ethylene leads to an increase in the rate of hydrogenation, with the initial rate being roughly first order in hydrogen overpressure. The rate follows a co-cation dependence in the order Ru-H-Y > Ru-Ca-Y > Ru-Na-Y. At intermediate temperatures some butane isomerizes to isobutane in all zeolites studied, presumably through a carbocation intermediate formed at the acid sites either inherent in Ru-H-Y or created upon reduction of the metal in Ru-Ca-Y and Ru-Na-Y. At temperatures above 623 K, carbon-carbon bond cleavage is complete yielding only methane. Following evacuation of samples, signals from residual carbon are observed in the alkyl region, but are not well resolved. 27 refs., 12 figs., 1 tab.

Kye, Y.S.; Wu, S.X.; Apple, T.M. [Rensselaer Polytechnic Inst., Troy, NY (United States)

1992-03-19

156

13C NMR study of commensurate antiferromagnetism in (TMTTF)2Br  

NASA Astrophysics Data System (ADS)

Quasi-one-dimensional organic conductors (TMTCF)2X have various electric and magnetic properties. Although theoretical and experimental studies have suggested that (TMTTF)2Br has the properties of commensurate antiferromagnetism, details of the magnetic structure of this compound are unclear. Two types of antiferromagnetism are expected, one due to a localized electron and the other to the nesting of the Fermi surface. We therefore assessed the antiferromagnetic structure of (TMTTF)2Br using 13C NMR. Site assignment of the observed antiferromagnetic spectrum confirmed that there were two magnetic molecular sites, with staggered moments and amplitude of 0.11?B/molecule, as well as nonmagnetic molecular sites. A commensurate structure with antiferromagnetic ordering of (????) along a one-dimensional chain would be expected as the freezing of antiferromagnetic fluctuations in the charge-ordered phase of the (TMTTF)2AsF6 salt. The presence of a nodal site is strongly suggestive of the nesting type antiferromagnetism. The fine structure of the antiferromagnetic spectrum suggests superlattice along the interchain direction. We could not observe line broadening due to the charge order above the antiferromagnetic transition.

Hirose, Shinji; Liu, Yang; Kawamoto, Atsushi

2013-09-01

157

13C n.m.r. studies of the thermal behaviour of aqueous solutions of cellulose ethers  

Microsoft Academic Search

Solution state n.m.r, techniques have been used to study 10% w\\/v aqueous solutions of methylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose. 13 C n.m.r, spectra taken at temperatures from ambient to 70°C show loss of peak intensities of both backbone and substituent signals due to liquid\\/solid phase separation processes at high temperatures. The substituents on methylcellulose become immobile and those on hydroxypropylcellulose retain

Roger N. Ibbett; Kevin Philp; Duncan M. Price

1992-01-01

158

Determination of petroselinic acid in Umbelliflorae seed oils by combined GC and 13 C NMR spectroscopy analysis  

Microsoft Academic Search

Synthetic triolein and tripetroselinin mixtures were examined by13C NMR spectroscopy, showing marked chemical shift differences of the olefinic carbon atoms. Peak height ratios were compared\\u000a to weight values for quantitative determination of oleic and petroselinic acids in seed oils, since these two fatty acids\\u000a are quantitated together by GC analysis. Values observed for NMR peak height ratios were fairly close

J. F. Mallet; E. M. Gaydou; A. Archavlis

1990-01-01

159

Mobility of lipid in complexes of amylose–fatty acids by deuterium and 13C solid state NMR  

Microsoft Academic Search

Palmitic and lauric acid complexes with amylose were studied by solid state methods: 13C CP\\/MAS NMR, deuterium NMR, X-ray powder diffraction and differential scanning calorimetry (DSC). The crystalline amylose complexes were found to be in a V-type sixfold single chain helix. The melting points of the complexes were over 100°C, at least 40–50°C higher than the melting points of the

P Lebail; A Buleon; D Shiftan; R. H Marchessault

2000-01-01

160

Assignment of non-crystalline forms in cellulose I by CP\\/MAS 13C NMR spectroscopy  

Microsoft Academic Search

Non-crystalline forms of cellulose in birch pulp, cotton linters and Cladophora sp were studied by CP\\/MAS 13C NMR spectroscopy. New assignments were made for the NMR-signals in the lower shift part of the C-4 region (80–86ppm). These signals were assigned to cellulose at accessible fibril surfaces, cellulose at inaccessible fibril surfaces and hemicellulose. Also, further evidence was found for para-crystalline

Kristina Wickholm; Per Tomas Larsson; Tommy Iversen

1998-01-01

161

Discovering [superscript 13]C NMR, [superscript 1]H NMR, and IR Spectroscopy in the General Chemistry Laboratory through a Sequence of Guided-Inquiry Exercises  

ERIC Educational Resources Information Center

|This sequence of three guided-inquiry labs is designed for a second-semester general chemistry course and challenges students to discover basic theoretical principles associated with [superscript 13]C NMR, [superscript 1]H NMR, and IR spectroscopy. Students learn to identify and explain basic concepts of magnetic resonance and vibrational…

Iler, H. Darrell; Justice, David; Brauer, Shari; Landis, Amanda

2012-01-01

162

FTIR and Solid State 13C NMR Spectroscopy of Proteins of Wet Cooked and Popped Sorghum and Maize  

Microsoft Academic Search

Fourier transform infrared (FTIR) and solid state13C NMR spectroscopic methods were used to investigate changes in maize and sorghum proteins on wet cooking and popping. FTIR spectra indicated that wet cooking led to proteins in two normal sorghums, namely NK 283 (a red hybrid) and KAT 369 (a white variety), two sorghum mutants (P850029 and P851171) and a maize hybrid

K. G. Duodu; H. Tang; A. Grant; N. Wellner; P. S. Belton; J. R. N. Taylor

2001-01-01

163

Acetylation of raw cotton for oil spill cleanup application: an FTIR and 13C MAS NMR spectroscopic investigation  

Microsoft Academic Search

Fourier transform infrared (FTIR) and 13C MAS NMR spectroscopy have been used to investigate the acetylation of raw cotton samples with acetic anhydride without solvents in the presence of different amounts of 4-dimethylaminopyridine (DMAP) catalyst. This is a continuation of our previous investigation of acetylation of commercial cotton in an effort to develop hydrophobic, biodegradable, cellulosic sorbent materials for cleaning

Moses O Adebajo; Ray L Frost

2004-01-01

164

Complete assignment of (1)H and (13)C NMR spectra of standard neo-iota-carrabiose oligosaccharides.  

PubMed

Standard Eucheuma denticulatum iota-carrageenan was degraded with the Alteromonas fortis iota-carrageenase. The most abundant products, the neo-iota-carratetraose and neo-iota-carrahexaose were purified by permeation gel chromatography, and their corresponding (1)H and (13)C NMR spectra were fully assigned. PMID:20038459

Jouanneau, Diane; Boulenguer, Patrick; Mazoyer, Jacques; Helbert, William

2009-12-26

165

Class selection of amino acid metabolites in body fluids using chemical derivatization and their enhanced 13C NMR  

PubMed Central

We report a chemical derivatization method that selects a class of metabolites from a complex mixture and enhances their detection by 13C NMR. Acetylation of amines directly in aqueous medium with 1,1?-13C2 acetic anhydride is a simple method that creates a high sensitivity and quantitative label in complex biofluids with minimal sample pretreatment. Detection using either 1D or 2D 13C NMR experiments produces highly resolved spectra with improved sensitivity. Experiments to identify and compare amino acids and related metabolites in normal human urine and serum samples as well as in urine from patients with the inborn errors of metabolism tyrosinemia type II, argininosuccinic aciduria, homocystinuria, and phenylketonuria demonstrate the method. The use of metabolite derivatization and 13C NMR spectroscopy produces data suitable for metabolite profiling analysis of biofluids on a time scale that allows routine use. Extension of this approach to enhance the NMR detection of other classes of metabolites has also been accomplished. The improved detection of low-concentration metabolites shown here creates opportunities to improve the understanding of the biological processes and develop improved disease detection methodologies.

Shanaiah, Narasimhamurthy; Desilva, M. Aruni; Nagana Gowda, G. A.; Raftery, Michael A.; Hainline, Bryan E.; Raftery, Daniel

2007-01-01

166

13C solid-state NMR chromatography by magic angle spinning 1H T1 relaxation ordered spectroscopy  

NASA Astrophysics Data System (ADS)

An efficient method to separate the 13C NMR spectra of solid mixtures is introduced. The 1H longitudinal (T1) relaxation time is used to separate the overlapping 13C chemical shift spectra of solid mixtures via an inverse Laplace transform (ILT) of the relaxation dimension. The resulting 2D spectrum of the mixture contains separate 13C spectra for each component of the mixture that are identical to 13C spectra of the isolated materials. The separation is based on the equalization of 1H T1 values in a single domain by rapid 1H spin diffusion and on the 1H T1 value differences between different domains. The introduction of a general ILT scheme enables efficient and reduced data acquisition time. The method is demonstrated on a mixture of two disaccharides and on a commercial drug containing several compounds.

Nishiyama, Yusuke; Frey, Michael H.; Mukasa, Sseziwa; Utsumi, Hiroaki

2010-02-01

167

(13)C Solid-state NMR chromatography by magic angle spinning (1)H T(1) relaxation ordered spectroscopy.  

PubMed

An efficient method to separate the (13)C NMR spectra of solid mixtures is introduced. The (1)H longitudinal (T(1)) relaxation time is used to separate the overlapping (13)C chemical shift spectra of solid mixtures via an inverse Laplace transform (ILT) of the relaxation dimension. The resulting 2D spectrum of the mixture contains separate (13)C spectra for each component of the mixture that are identical to (13)C spectra of the isolated materials. The separation is based on the equalization of (1)H T(1) values in a single domain by rapid (1)H spin diffusion and on the (1)H T(1) value differences between different domains. The introduction of a general ILT scheme enables efficient and reduced data acquisition time. The method is demonstrated on a mixture of two disaccharides and on a commercial drug containing several compounds. PMID:19900827

Nishiyama, Yusuke; Frey, Michael H; Mukasa, Sseziwa; Utsumi, Hiroaki

2009-10-25

168

Study of phospholipid structure by 1H, 13C, and 31P dipolar couplings from two-dimensional NMR.  

PubMed Central

Various motionally averaged 31P-1H, 13C-1H, 1H-1H, and 31P-13C dipolar couplings were measured for natural-abundance and unoriented phosphocholine in the L alpha phase. The couplings were obtained and assigned by a variety of advanced and partly novel two-dimensional solid-state NMR experiments. Whereas 31P-1H and 31P-13C dipolar couplings provide long-range structural constraints, geminal 1H-1H couplings and the signs of 13C-1H couplings are important new elements in a segmental order-tensor analysis of the lipid headgroup and glycerol backbone. The implications of these measured dipolar couplings for the conformational exchange of the lipid headgroup and the bending of the headgroup from the glycerol backbone are discussed. These dipolar couplings are also analyzed semiquantitatively in terms of the segmental order tensor. Images FIGURE 2

Hong, M; Schmidt-Rohr, K; Nanz, D

1995-01-01

169

Modified Spectral Editing Methods for 13C CP/MAS Experiments in Solids  

NASA Astrophysics Data System (ADS)

The spectral editing approach of Zilm and coworkers utilizes polarization, polarization inversion, and spin depolarization methods for enhancing or suppressing NMR spectral lines in solids. The proposed pulse sequences allow nonprotonated C, CH, CH2, and CH3 types of carbon resonances to be separated from one another and identified accordingly. The former method tentatively separates the nonprotonated C and CH3 peaks with a cutoff shift of 35 ppm. This shift is a reasonable demarcation shift for a preponderance of organic molecules, but exceptions do exist that could constitute a serious drawback in a few instances. The new approach separates the nonprotonated C and CH3 carbon peaks unequivocally using modified pulse sequences similar to those of Zilm. Further, both the CH only and CH2 only spectra, respectively, can be acquired directly from combining so called (+) and (-) sequences using different spectral delay periods and pulse parameters. The (+) and the (-) pulse sequences produce signals for the nonprotonated and methyl carbons that have essentially the same amplitude but opposite phases. These spectra, combined with the previously reported CH3 and nonprontonated C only spectra, offer a complete spectral editing technique for solid samples. Examples of these spectral editing methods are provided for 3-methylglutaric acid, fumaric acid monoethyl ester, and two complex natural products: methyl o-methylpodocarpate and 10-deacetylbaccatin III.

Hu, Jian Zhi; Harper, James K.; Taylor, Craig; Pugmire, Ronald J.; Grant, David M.

2000-02-01

170

Compartmentation of cerebral glutamate in situ as detected by 1H/13C n.m.r.  

PubMed Central

Incorporation of 13C label from either [1-13C]glucose to glutamate C-4 and lactate C-3 or from [2-13C]acetate to glutamate C-4 was monitored in situ in a superfused brain slice preparation by using 1H-detected/13C-edited (1H/13C) n.m.r. spectroscopy. The fractional enrichments of both metabolites were determined by this means in both brain slices and acid extracts of the preparations in order to assess their 1H-n.m.r. detectabilities. The 1H/13C satellite resonances from glutamate C-4 and lactate C-3 in brain tissue were followed from 4 min onwards in the presence of 5 mM [1-13C]glucose. Fractional enrichment of glutamate C-4 in the slice preparations was higher than in their acid extracts throughout the incubation of 100 min; at 30 min the enrichment was 15.9 +/- 0.6% in the slice preparations and 10.6 +/- 0.9% in extracts and at 100 min 24.5 +/- 1.7% compared with 19.7 +/- 0.4%, respectively. In contrast, lactate C-3 reached a steady-state fractional enrichment of approx. 43% by 15 min and there was no difference between the values determined in the slice preparations and the acid extracts. There was a significant difference between the glutamate C-4 fractional enrichments in the brain slices (7.4 +/- 0.6%) and extracts (5.1 +/- 0.3%) after 60 min of incubation with [2-13C]acetate. Thus 13C label from both glucose and exogenous acetate enters a pool of glutamate that is more amenable to 1H n.m.r. detection than total acid-extracted brain biochemical glutamate, whereas lactate is labelled with full 1H n.m.r. visibility. The results are discussed in the light of the biochemical factors that affect glutamate 1H-n.m.r. susceptibility and thus its n.m.r. visibility.

Kauppinen, R A; Pirttila, T R; Auriola, S O; Williams, S R

1994-01-01

171

Method for determining molar concentrations of metabolites in complex solutions from two-dimensional 1H-13C NMR spectra.  

PubMed

One-dimensional (1D) (1)H nuclear magnetic resonance (NMR) spectroscopy is used extensively for high-throughput analysis of metabolites in biological fluids and tissue extracts. Typically, such spectra are treated as multivariate statistical objects rather than as collections of quantifiable metabolites. We report here a two-dimensional (2D) (1)H-(13)C NMR strategy (fast metabolite quantification, FMQ, by NMR) for identifying and quantifying the approximately 40 most abundant metabolites in biological samples. To validate this technique, we prepared mixtures of synthetic compounds and extracts from Arabidopsis thaliana, Saccharomyces cerevisiae, and Medicago sativa. We show that accurate (technical error 2.7%) molar concentrations can be determined in 12 min using our quantitative 2D (1)H-(13)C NMR strategy. In contrast, traditional 1D (1)H NMR analysis resulted in 16.2% technical error under nearly ideal conditions. We propose FMQ by NMR as a practical alternative to 1D (1)H NMR for metabolomics studies in which 50-mg (extract dry weight) samples can be obtained. PMID:17985927

Lewis, Ian A; Schommer, Seth C; Hodis, Brendan; Robb, Kate A; Tonelli, Marco; Westler, William M; Sussman, Michael R; Markley, John L

2007-11-07

172

Analysis of Hydroperoxides in Solid Polyethylene by MAS (13)C NMR and EPR;Macromolecules.  

National Technical Information Service (NTIS)

13C-enriched polyethylene was subjected to y-irradiation in the presence of air at 25 and 80degC for total doses ranging from 71 to 355 kGy. Significant quantities of hydroperoxides were detected in the 25degC irradiated sample by 13C magic angle spinning...

Assink Celina Dunbar Alam Clough

1999-01-01

173

/sup 31/P NMR saturation-transfer and /sup 13/C NMR kinetic studies of glycolytic regulation during anaerobic and aerobic glycolysis  

SciTech Connect

/sup 31/P NMR saturation-transfer techniques have been employed in glucose-gown derepressed yeast to determine unidirectional fluxes in the upper part of the Embden-Meyerhof-Parnas pathway. The experiments were performed during anaerobic and aerobic glycolysis by saturating the ATP/sub ..gamma../ resonances and monitoring changes in the phosphomonoester signals from glucose 6-phosphate and fructose 1,6-bisphosphate. These experiments were supplemented with /sup 13/C NMR measurements of glucose utilization rates and /sup 13/C NMR label distribution studies. Combined with data obtained previously from radioisotope measurement, these /sup 31/P and /sup 13/C NMR kinetic studies allowed estimation of the net glycolytic flow in addition to relative flows through phosphofructokinase (PFK) and Fru-1,6-P/sub 2/ase during anaerobic and aerobic glycolysis. The /sup 31/P NMR saturation-transfer results are consistent with previous results obtained from measurements of metabolite levels, radioisotope data, and /sup 13/C NMR studies, providing additional support for in vivo measurement of the flows during glycolysis.

Campbell-Burk, S.L.; den Hollander, J.A.; Alger, J.R.; Shulman, R.G.

1987-11-17

174

Complete analysis of the 1 H- and 13 C-NMR spectra of four blood-group A active oligosaccharides  

Microsoft Academic Search

The fully assigned1H and13C-NMR spectra of four group A oligosaccharides by use of multiple-relayed, coherence-transfer chemical-shift-correlated spectroscopy (multiple-RELAY-COSY) and1H-\\/13C-correlation spectroscopy are reported. These analyses were performed on the following compounds:\\u000a$$\\\\begin{array}{*{20}c} {III - A;GalNAc\\\\alpha 1 - 3[Fuc\\\\alpha 1 - 2]Gal:} \\\\\\\\ {VI - A;GalNAc\\\\alpha 1 - 3[Fuc\\\\alpha 1 - 2]Gal\\\\beta 1 - 3[Fuc\\\\alpha 1 - 4]GlcNAc\\\\beta 1 - 3Gal:} \\\\\\\\

Gérard Strecker; Jean-Michel Wieruszeski; Jean-Claude Michalski; Jean Montreuil

1989-01-01

175

Low-temperature solid-state /sup 13/C NMR studies of the retinal chromophore in rhodopsin  

SciTech Connect

Magic angle sample spinning (MASS) /sup 13/C NMR spectra have been obtained of bovine rhodopsin regenerated with retinal prosthetic groups isotopically enriched with /sup 13/C at C-5 and C-14. In order to observe the /sup 13/C retinal chromophore resonances, it was necessary to employ low temperatures (-15 ..-->.. -35/sup 0/C) to restrict rotational diffusion of the protein. The isotropic chemical shift and principal values of the chemical shift tensor of the /sup 13/C-5 label indicate that the retinal chromophore is in the twisted 6-s-cis conformation in rhodopsin, in contrast to the planar 6-s-trans confirmation found in bacteriorhodopsin. The /sup 13/C-14 isotropic shift and shift tensor principal values show that the Schiff base C=N bond is anti. Furthermore, the /sup 13/C-14 chemical shift (121.2 ppm) is within the range of values (120-123 ppm) exhibited by protonated (C=N anti) Schiff base model compounds, indicating that the C=N linkage is protonated. The results are discussed with regard to the mechanism of wavelength regulation in rhodopsin.

Smith, S.O.; Palings, I.; Copie, V.; Raleigh, D.P.; Courtin, J.; Pardoen, J.A.; Lugtenburg, J.; Mathies, R.A.; Griffin, R.G.

1987-03-24

176

Regio-selective detection of dynamic structure of transmembrane alpha-helices as revealed from (13)C NMR spectra of [3-13C]Ala-labeled bacteriorhodopsin in the presence of Mn2+ ion.  

PubMed Central

13C Nuclear magnetic resonance (NMR) spectra of [3-(13)C]Ala-labeled bacteriorhodopsin (bR) were edited to give rise to regio-selective signals from hydrophobic transmembrane alpha-helices by using NMR relaxation reagent, Mn(2+) ion. As a result of selective suppression of (13)C NMR signals from the surfaces in the presence of Mn(2+) ions, several (13)C NMR signals of Ala residues in the transmembrane alpha-helices were identified on the basis of site-directed mutagenesis without overlaps from (13)C NMR signals of residues located near the bilayer surfaces. The upper bound of the interatomic distances between (13)C nucleus in bR and Mn(2+) ions bound to the hydrophilic surface to cause suppressed peaks by the presence of Mn(2+) ion was estimated as 8.7 A to result in the signal broadening to 100 Hz and consistent with the data based on experimental finding. The Ala C(beta) (13)C NMR peaks corresponding to Ala-51, Ala-53, Ala-81, Ala-84, and Ala-215 located around the extracellular half of the proton channel and Ala-184 located at the kink in the helix F were successfully identified on the basis of (13)C NMR spectra of bR in the presence of Mn(2+) ion and site-directed replacement of Ala by Gly or Val. Utilizing these peaks as probes to observe local structure in the transmembrane alpha-helices, dynamic conformation of the extracellular half of bR at ambient temperature was examined, and the local structures of Ala-215 and 184 were compared with those elucidated at low temperature. Conformational changes in the transmembrane alpha-helices induced in D85N and E204Q and its long-range transmission from the proton release site to the site around the Schiff base in E204Q were also examined.

Tuzi, S; Hasegawa, J; Kawaminami, R; Naito, A; Saito, H

2001-01-01

177

Homonuclear decoupled 13C chemical shift anisotropy in 13C doubly labeled peptides by selective-pulse solid-state NMR  

NASA Astrophysics Data System (ADS)

We describe a new experiment for measuring homonuclear-decoupled anisotropic chemical shift patterns in doubly 13C-labeled compounds under magic-angle spinning. The experiment combines a pair of selective and non-selective 180° pulses to suppress the 13C-13C scalar and dipolar interactions. This is combined with the recently developed SUPER technique to recouple the chemical shift anisotropy. Demonstrations on 13C? and 13CO-labeled amino acids and peptides show that accurate chemical shift powder patterns can be obtained. This permits the use of chemical shift anisotropy for conformational studies of suitably extensively 13C-labeled peptides and proteins.

Hong, Mei; Yao, Xiaolan

2003-02-01

178

FT-IR, UV–vis, 1H and 13C NMR spectra and the equilibrium structure of organic dye molecule disperse red 1 acrylate: A combined experimental and theoretical analysis  

Microsoft Academic Search

This study reports the characterization of disperse red 1 acrylate compound by spectral techniques and quantum chemical calculations. The spectroscopic properties were analyzed by FT-IR, UV–vis, 1H NMR and 13C NMR techniques. FT-IR spectrum in solid state was recorded in the region 4000–400cm?1. The UV–vis absorption spectrum of the compound that dissolved in methanol was recorded in the range of

Mehmet Cinar; Ali Coruh; Mehmet Karabacak

2011-01-01

179

(1)H, (13)C, and (15)N NMR assignments of a Drosophila Hedgehog autoprocessing domain.  

PubMed

The Hedgehog (Hh) signaling pathway plays important roles in embryonic growth and patterning in different organisms. Abnormal activity of the Hh signaling pathway has been associated to cancers, holoprosencephaly and autism spectrum disorders. The backbone and side chain resonance assignments of a Drosophila Hh autoprocessing domain have been determined based on triple-resonance experiments with the [(13)C, (15)N]-labeled and [(2)H, (13)C, (15)N])-labeled proteins. PMID:23765287

Xie, Jian; Du, Zhenming; Callahan, Brian; Belfort, Marlene; Wang, Chunyu

2013-06-14

180

Thermal maturity of type II kerogen from the New Albany Shale assessed by13C CP/MAS NMR  

USGS Publications Warehouse

Thermal maturity of oil and gas source rocks is typically quantified in terms of vitrinite reflectance, which is based on optical properties of terrestrial woody remains. This study evaluates 13C CP/MAS NMR parameters in kerogen (i.e., the insoluble fraction of organic matter in sediments and sedimentary rocks) as proxies for thermal maturity in marine-derived source rocks where terrestrially derived vitrinite is often absent or sparse. In a suite of samples from the New Albany Shale (Middle Devonian to the Early Mississippian, Illinois Basin) the abundance of aromatic carbon in kerogen determined by 13C CP/MAS NMR correlates linearly well with vitrinite reflectance. ?? 2004 Elsevier Inc. All rights reserved.

Werner-Zwanziger, U.; Lis, G.; Mastalerz, M.; Schimmelmann, A.

2005-01-01

181

Solid-state 13C NMR spectroscopy studies of xylans in the cell wall of Palmaria palmata (L. Kuntze, Rhodophyta).  

PubMed

The chemical structure and interactions of the cell wall polysaccharides from the red edible seaweed Palmaria palmata were studied by liquid-like magic-angle-spinning (MAS) and cross-polarization MAS (CPMAS) solid-state 13C NMR spectroscopy. The liquid-like MAS and CPMAS 13C NMR spectra of the rehydrated algal powder revealed the presence of beta-(1-->4)/beta-(1-->3)-linked D-xylan with chemical shifts close to those observed in the solution 13C NMR spectrum of the polysaccharide. Observation of mix-linked xylan in the liquid-like MAS 13C NMR spectrum indicated that part of this cell wall polysaccharide is loosely held in the alga. The CPMAS NMR spectrum of the dry algal powder alcohol insoluble residue (AIR) showed broad peaks most of which corresponded to the mix-linked xylan. Hydration of AIR induced a marked increase in the signal resolution also in the CPMAS NMR spectra together with a shift of the C-3 and C-4 signals of the (1-->3)- and (1-->4)-linked xylose, respectively. Such modifications were present in the spectrum of hydrated (1-->3)-linked xylan from the green seaweed Caulerpa taxifolia and absent in that of (1-->4)-linked xylan from P. palmata. This result emphasizes the important role of (1-->3) linkages on the mix-linked xylan hydration-induced conformational rearrangement. The mix-linked xylan signals were observed in the CPMAS NMR spectrum of hydrated residues obtained after extensive extractions by NaOH or strong chaotropic solutions indicating strong hydrogen bonds or covalent linkages. T(1 rho) relaxations were measured close or above 10 ms for the mix-linked xylan in the dry and hydrated state in AIR and indicated that the overall xylan chains likely remain rigid. Rehydration of the mix-linked xylan lead to a decrease in the motion of protons bounded to the C-1 and C-4 carbons of the (1-->4)-linked xylose supporting the re-organization of the xylan chains under hydration involving junction-zones held by hydrogen bonds between adjacent (1-->4)-linked xylose blocks. The CPMAS NMR spectrum of both dry and rehydrated residues obtained after NaOH and HCl extractions demonstrated the presence of cellulose and (1-->4)-linked xylans. The structures of the different polysaccharides are discussed in relation to their interactions and putative functions on the cell wall mechanical properties in P. palmata. PMID:12860427

Lahaye, Marc; Rondeau-Mouro, Corinne; Deniaud, Estelle; Buléon, Alain

2003-07-22

182

Triterpenes in the hexane extract of leaves of Olea europaea L.: analysis using 13C-NMR spectroscopy.  

PubMed

Two neutral triterpenes and a triterpene acid were identified and quantified directly, in the absence of any purification steps, in a precipitate obtained during the industrial extraction of the leaves of Olea europaea L. using 13C-NMR spectroscopy (spectrometer operating at 4.7 T equipped with a 10 mm probe). The method was optimised in order to reduce the duration of analysis with a routine NMR spectrometer. Together with long-chain linear compounds, erythrodiol, uvaol and oleanolic acid accounted for 27.3, 18.3 and 12.5% of the precipitate, respectively. PMID:17623370

Duquesnoy, Emilie; Castola, Vincent; Casanova, Joseph

183

Secondary structure of peptides 16 th . Characterization of proteins by means of 13 C NMR CP\\/MAS spectroscopy  

Microsoft Academic Search

50.3 or 75.4 MHz13C NMR cross-polarization\\/magic angle spinning spectra of human hair, horse hair, horse hoof, parrot feather, sperm whale myoglobin, and horse heart cytochrome C were measured. The spectra of human hair and horse hair indicate nearly equal mole fractions of?-sheets anda-helices and a low percentage of amorphous regions, whereas horse hoof contains a higher fraction of amorphous proteins.

H. R. Kricheldorf; D. Miiller

1984-01-01

184

Indirect photometry and multinuclear 13C and 183W NMR study of tungstate complexes of sugar acids  

Microsoft Academic Search

The tungstate complexes of the sugar acids, meso-tartaric and l-gulonic acids, have been studied in aqueous solutions. Indirect photometry has been used to determine the stability constants and the stoichiometry of these colourless complexes. Multinuclear 13C and 183W NMR spectroscopies have been used to specify the structures of the complexes and the sites of chelation of the ligand. For meso-tartaric

Miloudi Hlaïbi; Mustapha Hor; Amina Riad; Fatiha Toumri; Jean-François Verchère; Stella Chapelle

2008-01-01

185

Identification and quantitative determination of furanodiene, a heat-sensitive compound, in essential oil by 13C-NMR.  

PubMed

A method based on 13C-NMR has been used as a tool for the identification and quantitative determination of two furanic sesquiterpenes: a heat-sensitive compound, furanodiene, and its rearrangement product, furanoelemene. Following a preliminary study using artificial mixtures which permitted the construction and verification of calibration curves for each compound, the method was used for the qualitative and quantitative analysis of furanodiene and furanoelemene in the essential oil of Smyrnium olusatrum. PMID:11704963

Baldovini, N; Tomi, F; Casanova, J

186

Structural characterization of olive mill waster-water after aerobic digestion using elemental analysis, FTIR and 13C NMR  

Microsoft Academic Search

Aerobic digestion of olive mill waster-water (OMW) has been conducted under various medium conditions to determine the best treatment involving good stabilisation and maturity of these residues. Analysis by various chemical methods of elemental analysis, FTIR and 13C NMR spectroscopies show the high content of raw olive mill waster-water of the less condensed structures of phenols, organic acids, alcohol, fatty

Mohamed Hafidi; Soumia Amir; Jean-Claude Revel

2005-01-01

187

New Synthetic Glucosyl-Curcuminoids, and their 1 H and 13 C NMR Characterization, from Curcuma longa L  

Microsoft Academic Search

Turmeric extracts, among which curcumin and bis-demethoxycurcumin, are by far known for their therapeutic activities. In this\\u000a study we propose easy and low cost synthetic pathways in order to obtain glucosyl-curcuminoids, safe and water soluble potential\\u000a drugs and dyes, which may be implied in different fields ranging from pharmacology to food chemistry. The complete 1H and 13C NMR characterization of

Monica Saladini; Sandra Lazzari; Francesca Pignedoli; Roberto Rosa; Ferdinando Spagnolo; Erika Ferrari

2009-01-01

188

NaLSX zeolite with chemisorbed methyl groups studied by powder neutron diffraction and 13C MAS NMR  

NASA Astrophysics Data System (ADS)

Powder samples of NaLSX faujasite (Si/Al =1) in dehydrated state and with adsorbed methyl iodide were investigated by neutron diffraction and 13C MAS NMR. The distribution of Na+ cations and chemisorbed methylium ions in the frame of NaLSX was estimated by Rietveld refinement. Surface methoxy group were located mostly at O1 and O4 lattice oxygen. The changes in populations of cationic sites after chemisorption were detected.

Vratislav, Stanislav; Dlouhá, Maja; Bosá?ek, Vladimír

2004-07-01

189

13C/15N-19F Intermolecular REDOR NMR Study of the Interaction of TAR RNA with Tat Peptides  

PubMed Central

The complex of the HIV TAR RNA with the viral regulatory protein Tat is of considerable interest, but the plasticity of this interaction has made it impossible so far to establish the structure of that complex. In order to explore a new approach to obtain structural information on protein-RNA complexes, we performed 13C/15N-19F REDOR NMR experiments in the solid state on TAR bound to a peptide comprising the RNA-binding section of Tat. A critical arginine in the peptide was uniformly 13C and 15N labeled and 5-fluorouridine was incorporated at the U23 position of TAR. REDOR irradiation resulted in dephasing of the 13C and 15N resonances, indicating proximity of the U23(5F)-C and U23(5F)-N spin pairs. Best fits to the REDOR data shows the U23(5F)-C distances and the U23(5F)-N distances are in good agreement with the distances obtained from solution NMR structures of partial complexes of Tat with TAR. These results demonstrate that it is possible to study protein-RNA complexes using solid-state REDOR NMR measurements, adding to a growing list of solid state techniques for studying protein-nucleic acid complexes.

Huang, Wei; Varani, Gabriele; Drobny, Gary P.

2010-01-01

190

A complete 1H and 13C NMR data assignment for 3-phenylmethylene-1H,3H-naphtho-[1,8-c,d]-pyran-1-one.  

PubMed

Complete assignments of the 1H and 13C NMR chemical shifts for 3-phenylmethylene-1H,3H-naphtho-[1,8-c,d]-pyran-1-one were done by means of one- and two-dimensional NMR techniques, including 1H-(1)H COSY, HMQC and HMBC spectra. Ab initio quantum chemistry calculations and a shift prediction by an incremental method provided values close to the proposed assignments. All mid-IR spectral bands are given as reference data. The DRIFT FTIR, ATR FTIR and Raman spectra are given as a Supplementary data in JCAMP-DX format, version 4.24. In addition, a method of compound's synthesis, that has the product yield higher as compared to already known data in the literature, is given. PMID:21169052

Penchev, Plamen N; Stoyanov, Neyko M; Marinov, Marin N

2010-12-02

191

Solid-state 13C NMR analysis of Lower Cretaceous Baganuur (Mongolia) lignite  

NASA Astrophysics Data System (ADS)

The transformation of plant matter into peat and coal has two steps, called the biochemical and geochemical stages of coalification. Biochemical coalification begins with the accumulation of dead vegetable matter and ends at the rank of subbituminous coal. The rank of Baganuur lignite ranges from lignite to subbituminous coal. It is transition between biochemical and physico-chemical coalification stages. The changes of chemical structure of coal during the transition between above mentioned two stages were studied by solid state CP/MAS 13C NMR. The most predominant alteration is the disappearance of the resonances from oxygenated aliphatic carbons (63 ppm), protonated aromatic carbons (114 ppm), oxygen-substituted aromatic carbons (144 ppm) and carbonyl carbons (195 ppm). In addition, the intensity of resonances from methoxyl carbons (56 ppm) and oxygenated aliphatic carbons (72 ppm) decreased. While the intensities of resonance from aliphatic (30 ppm), protonated aromatic (125 ppm) and carboxyl carbon (174 ppm) increased or remained almost constant. The relative percent of O-substituted aromatic carbons decreased by ~25% mainly due to the intensity loss of the peak at 144 ppm, indicating removal of O-containing functional groups substituted to aromatic carbons. It is consistent with the decreased relative percent (~75%) of the peak at 114 ppm from protonated aromatic carbons nearby oxygen-substituted aromatic carbons. In addition, the resonance from 125 ppm was shifted to 128 ppm and its relative area increased by ~20%, indicating replacement of O-substituent of aromatic rings by hydrogen or carbon. Protonated aromatic carbons at least two bond away from an oxygen-substituted aromatic carbons give a resonance at 125 ppm and carbon-substituted aromatic carbons give a resonance at 130-132 ppm. With the increase relative percent of C-substituted aromatic carbons, their resonance were overlapped with protonated aromatic carbons and shifted to higher ppm. A decreasing area of oxygenated aliphatic carbons (~15 %) could be explained by ?-O-4 ether cleavage and loss of hydroxyl groups from side-chains as well as complete removal of cellulosic material. In addition, those deoxygenating reactions are more likely responsible for the increased relative intensity of aliphatic carbons. In detail, the relative percent of methyl groups at 14 ppm remained almost constant (decreased only by ~4%), while that of methylene increased by 20%. During the ?-O-4 ether cleavage and loss of hydroxyl groups from side-chains, relative amount of CH2 should increase in respect to O-containing original structures. Finally, the relative percentage of carboxyl/carboxyl carbons were decreased by ~25%, mainly due to diminished intensity of carbonyl carbons at 195 ppm. The intensity loss of carbonyl carbons increased from biochemical stage (~10%) to the beginning of physico-chemical stage (~70%).

Erdenetsogt, B.; Lee, I.; Lee, S.; Ko, Y.

2009-12-01

192

13C NMR isotopomeric analysis and its application in the study of endocrine cell metabolism and function.  

PubMed

Defining mechanisms and enzymatic paths critical to cellular function (e.g., secretion) of endocrine cells is a key research goal that can lead toward novel avenues of therapeutic intervention for a variety of disorders. 13C NMR spectroscopy and isotopomer analysis of cell extracts are excellent tools to quantitatively assess metabolism through intermediate labeling and estimate carbon entry to the TCA cycle. Discussed are: cell lines and in vitro culturing; extraction of intracellular material; NMR spectroscopy of the extract; isotopomeric analysis and modeling to obtain relative metabolic fluxes to the TCA cycle. This paper describes issues related to the application of NMR spectroscopic techniques on cell line extracts. Included are results of two studies that illustrate considerations that must be taken when performing analogous studies on neuroendocrine tissue: one involving the effect of media composition on cell behavior and isotopomer labeling; the second looking at effects of applying different metabolic models to 13C data and inferences that may be drawn. NMR isotopomeric analysis is a powerful technique that may be applied to better understand endocrine cell function. PMID:17465328

Simpson, Nicholas E; Constantinidis, Ioannis

2007-01-01

193

13C NMR Guides Rational Design of Nanocatalysts via Chemisorption Evaluation in Liquid Phase  

Microsoft Academic Search

The search for more efficient heterogeneous catalysts remains critical to the chemical industry. The Sabatier principle of maximizing catalytic activity by optimizing the adsorption energy of the substrate molecule could offer pivotal guidance to otherwise random screenings. Here we show that the chemical shift value of an adsorbate (formic acid) on metal colloid catalysts measured by 13C nuclear magnetic resonance

Karaked Tedsree; Chun Wong Aaron Chan; Simon Jones; Qian Cuan; Wei-Kun Li; Xue-Qing Gong; Shik Chi Edman Tsang

2011-01-01

194

Solution behavior and complete sup 1 H and sup 13 C NMR assignments of the coenzyme B sub 12 derivative (5 prime -deoxyadenosyl)cobinamide using modern 2D NMR experiments, including 600-MHz sup 1 H NMR data  

SciTech Connect

Two-dimensional (2D) NMR methods have been used to assign completely the {sup 1}H and {sup 13}C NMR spectra of the (5{prime}-deoxyadenosyl)cobinamide cation (AdoCbi{sup +}) in D{sub 2}O. Most of the {sup 1}H spectral assignments were made by using 2D homonuclear shift correlation spectroscopy (COSY), homonuclear Hartmann-Hahn spectroscopy (HOHAHA), absorption-mode (phase sensitive) 2D nuclear Overhauser effect (NOE) spectroscopy, and spin-locked NOE spectroscopy (also called ROESY, for rotating-frame Overhauser enhancement spectroscopy). Most of the protonated carbon resonances were assigned by using {sup 1}H-detected heteronuclear multiple-quantum coherence (HMQC) spectroscopy. The nonprotonated carbon resonances, as well as the remaining unassigned {sup 1}H and {sup 13}C NMR signals, were assigned from long-range {sup 1}H-{sup 13}C connectivities determined from {sup 1}H-detected multiple-bond heteronuclear multiple-quantum coherence spectroscopy (HMBC). Comparison of the {sup 13}C chemical shifts and {sup 1}H NOEs of AdoCbi{sup +} with those of coenzyme B{sup 12} ((5{prime}-deoxyadenosyl)cobalamin) and its benzimidazole-protonated, base-off form indicates that the electronic properties and structure of AdoCbi{sup +} are similar to that of coenzyme B{sup 12} in the protonated, base-off form. The {sup 13}C chemical shifts of most of the carbons of AdoCbi{sup +} do not vary significantly from those of base-off, benzimidazole-protonated coenzyme B{sup 12}, indicating that the electronic environment of the corrin ring is also similar in both compounds. However, significant differences in the chemical shifts of some of the corresponding carbons of the b, d, e, and f corrin side chains in AdoCbi{sup +} and in base-off, benzimidazole-protonated coenzyme B{sub 12} indicate that the positions of these side chains may be different in AdoCbi{sup +} compared to base-off coenzyme B{sup 12}.

Pagano, T.G.; Yohannes, P.G.; Marzilli, L.G. (Emory Univ., Atlanta, GA (USA)); Hay, B.P.; Scott, J.R.; Finke, R.G. (Univ. of Oregon, Eugene (USA))

1989-02-15

195

13C-13C dipolar recoupling under very fast magic angle spinning in solid-state nuclear magnetic resonance: Applications to distance measurements, spectral assignments, and high-throughput secondary-structure determination  

NASA Astrophysics Data System (ADS)

A technique is presented to recouple homonuclear dipolar couplings between dilute spin pairs such as 13C-13C systems under very fast magic angle spinning (MAS) in solid-state nuclear magnetic resonance (NMR) spectroscopy. The presented technique, finite pulse rf driven recoupling (fpRFDR), restores homonuclear dipolar interactions based on constructive usage of finite pulse-width effects in a phase- and symmetry-cycled ?-pulse train in which a rotor-synchronous ? pulse is applied every rotation period. The restored effective dipolar interaction has the form of a zero-quantum dipolar Hamiltonian for static solids, whose symmetry in spin space is different from that obtained by conventional rf driven recoupling (RFDR) techniques. It is demonstrated that the efficiency of recoupling by fpRFDR is not strongly dependent on chemical shift differences or resonance offsets in contrast to previous recoupling methods under very fast MAS. To realize distance measurements without effects of spin relaxation, a constant-time version of fpRFDR (CT-fpRFDR) is introduced, in which the effective evolution period is varied by refocusing dipolar evolution with a rotor-synchronized solid echo while the total recoupling period is kept constant. From CT-fpRFDR experiments at a spinning speed of 30.3 kHz in a field of 17.6 T, the 13C-13C distance of [1-13C]Ala-[1-13C]Gly-Gly was determined to be 3.27 Å, which agrees well with the value of 3.20 Å obtained by x-ray diffraction. Also, two-dimensional (2D) 13C/13C chemical-shift correlation NMR spectrum in a field of 9.4 T was obtained with fpRFDR for fibrils of the segmentally 13C- and 15N-labeled Alzheimer's ?-Amyloid fragments, A?16-22 (residues 16-22 taken from the 40-residue A? peptide) in which Leu-17 through Ala-21 are uniformly 13C- and 15N-labeled. Most 13C resonances for the main chain as well as for the side chains are assigned based on 2D 13C/13C chemical-shift correlation patterns specific to amino-acid types. Examination of the obtained 13C chemical shifts revealed the formation of ?-strand across the entire molecule of A?16-22. Possibility of high throughput determination of global main-chain structures based on 13C shifts obtained from 2D 13C/13C chemical-shift correlation under very fast MAS is also discussed for uniformly/segmentally 13C-labeled protein/peptide samples.

Ishii, Yoshitaka

2001-05-01

196

[13C]NMR studies of the effect of the somatostatin analogue octreotide on hepatic glycogenesis and glycogenolysis.  

PubMed

NMR spectroscopy is a useful tool for monitoring multiple intermediate metabolic pathways in different organs in intact animals and humans. We report the effect of the somatostatin analogue octreotide on the fate of 13C-labeled glucose administered to fasted and well-fed rats as determined by NMR spectroscopy. The production of 13C-labeled glycogen and its subsequent breakdown after the end of infusion was identified with a time resolution of 7 min. Hepatic glycogen synthesis was not different between control and octreotide-treated animals but persisted for 15 min after the end of the infusion only in control animals. Glycogenolysis, however, was initiated immediately after the end of infusion in octreotide-treated animals where the half-life of glycogen was 40 min compared with 68 min in control animals. However, once initiated, the rate of glycogenolysis was not significantly altered by octreotide. Although octreotide had no effect on glucose signal intensities in fasted animals, 13C glucose signals were more intense in octreotide compared with control well-fed animals. In conclusion, octreotide alters rat hepatic metabolism by accelerating the onset of glycogenolysis and stimulating glucose accumulation without significantly interfering with glycogen synthesis. PMID:7854973

Ezzat, S; Pahl-Wostl, C; Rudin, M; Harris, A G

1994-01-01

197

Uranyl nitrate inhibits lactate gluconeogenesis in isolated human and mouse renal proximal tubules: A {sup 13}C-NMR study  

SciTech Connect

As part of a study on uranium nephrotoxicity, we investigated the effect of uranyl nitrate in isolated human and mouse kidney cortex tubules metabolizing the physiological substrate lactate. In the millimolar range, uranyl nitrate reduced lactate removal and gluconeogenesis and the cellular ATP level in a dose-dependent fashion. After incubation in phosphate-free Krebs-Henseleit medium with 5 mM L-[1-{sup 13}C]-, or L-[2-{sup 13}C]-, or L-[3-{sup 13}C]lactate, substrate utilization and product formation were measured by enzymatic and NMR spectroscopic methods. In the presence of 3 mM uranyl nitrate, glucose production and the intracellular ATP content were significantly reduced in both human and mouse tubules. Combination of enzymatic and NMR measurements with a mathematical model of lactate metabolism revealed an inhibition of fluxes through lactate dehydrogenase and the gluconeogenic enzymes in the presence of 3 mM uranyl nitrate; in human and mouse tubules, fluxes were lowered by 20% and 14% (lactate dehydrogenase), 27% and 32% (pyruvate carboxylase), 35% and 36% (phosphoenolpyruvate carboxykinase), and 39% and 45% (glucose-6-phosphatase), respectively. These results indicate that natural uranium is an inhibitor of renal lactate gluconeogenesis in both humans and mice.

Renault, Sophie; Faiz, Hassan; Gadet, Rudy; Ferrier, Bernard; Martin, Guy; Baverel, Gabriel [Metabolomique et Maladies Metaboliques, Institut National de la Sante et de la recherche Medicale, Unit 820, Faculte de Medecine R.T.H. Laennec, Universite de Lyon, 7-11 rue G. Paradin, 69372 Lyon Cedex 08 (France); Conjard-Duplany, Agnes, E-mail: agnes.duplany@recherche.univ-lyon1.f [Metabolomique et Maladies Metaboliques, Institut National de la Sante et de la recherche Medicale, Unit 820, Faculte de Medecine R.T.H. Laennec, Universite de Lyon, 7-11 rue G. Paradin, 69372 Lyon Cedex 08 (France)

2010-01-01

198

Metabolic engineering applications of in vivo sup 31 P and sup 13 C NMR studies of Saccharomyces cerevisiae  

SciTech Connect

With intent to quantify NMR measurements as much as possible, analysis techniques of the in vivo {sup 31}P NMR spectrum are developed. A systematic procedure is formulated for estimating the relative intracellular concentrations of the sugar phosphates in S. cerevisiae from the {sup 31}P NMR spectrum. In addition, in vivo correlation of inorganic phosphate chemical shift with the chemical shifts of 3-phosphoglycerate, {beta}-fructose 1,6-diphosphate, fructose 6-phosphate, and glucose 6-phosphate are determined. Also, a method was developed for elucidation of the cytoplasmic and vacuolar components of inorganic phosphate in the {sup 31}P NMR spectrum of S. cerevisiae. An in vivo correlation relating the inorganic phosphate chemical shift of the vacuole with the chemical shift of the resonance for pyrophosphate and the terminal phosphate of polyphosphate (PP{sub 1}) is established. Transient measurements provided by {sup 31}P NMR are applied to reg1 mutant and standard strains. {sup 31}P and {sup 13}C NMR measurements are used to analyze the performance of recombinant strains in which the glucose phosphorylation step had been altered.

Shanks, J.V.

1989-01-01

199

A suite of amino acid residue type classification pulse sequences for 13C-detected NMR of proteins  

NASA Astrophysics Data System (ADS)

A suite of 13C-detected NMR pulse sequences to edit the correlation peaks of the CACO and CON spectra according to the amino acid residue type is presented. The pulse sequences exploit the topology of the C? carbon and led to the sorting of the CACO or CON signals into several classes depending on the nature of the generating residue. A set of four or eight correlation spectra is recorded where the sign of the cross peaks changes from one spectrum to another according to the amino acid type of the corresponding residue in the protein sequence. Linear combination of these spectra produces subspectra showing signals from residues having similar C? topology. The presence of weak breakthrough peaks does not prevent the proper classification, since this is obtained from the subspectrum in which the correlation peak is more intense. The experiments were tested on a globular protonated protein (13C, 15N labeled Ubiquitin), on a globular deuterated protein (2H, 13C, 15N labeled Ubiquitin), and on an intrinsically disordered protein (13C, 15N labeled Nupr1).

Pantoja-Uceda, David; Santoro, Jorge

2013-09-01

200

The identification of vicinally substituted cyclohexane isomers in their mixtures by 1H and 13C NMR spectroscopy  

NASA Astrophysics Data System (ADS)

The radical addition reactions of organobromine compounds, XBr (X=CH 2COOMe, PhCH 2, CHBr 2 and CCl 3) with cyclohexene afforded mixtures of cis/ trans isomer pairs of 1-X-2-Br-cyclohexanes. In addition to benzyl benzoyloxy derivatives are formed also, when benzoyl peroxide is used as an initiator. Owing to the great difficulties in separating these cis/ trans isomer pairs, they are identified directly in their mixtures by NMR spectroscopy. In addition to one-dimensional (1D) 1H, proton decoupled 13C and DEPT-135, also two-dimensional (2D) 13C- 13C INADEQUATE as well as 1H- 13C HMQC experiments have been used in assigning the signals of each compound in their mixtures. The identification of each isomer was based on comparison of experimental 3JH,H coupling constants with theoretical ones based on the well-known Karplus type relationship. The more stable conformation for each isomer was estimated using the semiempirical AM1 molecular orbital method. The calculations support the isomer pair elucidations.

Laihia, Katri; Kolehmainen, Erkki; Nevalainen, Tapio; Kauppinen, Reijo; Vasilieva, Tamara T.; Terentiev, Alexander B.

2000-02-01

201

Solid-State Selective 13C Excitation and Spin Diffusion NMR to Resolve Spatial Dimensions in Plant Cell Walls  

SciTech Connect

The average spatial dimensions between major biopolymers within the plant cell wall can be resolved using a solid-state NMR technique referred to as a {sup 13}C cross-polarization (CP) SELDOM (selectively by destruction of magnetization) with a mixing time delay for spin diffusion. Selective excitation of specific aromatic lignin carbons indicates that lignin is in close proximity to hemicellulose followed by amorphous and finally crystalline cellulose. {sup 13}C spin diffusion time constants (T{sub SD}) were extracted using a two-site spin diffusion theory developed for {sup 13}C nuclei under magic angle spinning (MAS) conditions. These time constants were then used to calculate an average lower-limit spin diffusion length between chemical groups within the plant cell wall. The results on untreated {sup 13}C enriched corn stover stem reveal that the lignin carbons are, on average, located at distances {approx}0.7-2.0 nm from the carbons in hemicellulose and cellulose, whereas the pretreated material had larger separations.

Foston, M.; Katahira, R.; Gjersing, E.; Davis, M. F.; Ragauskas, A. J.

2012-02-15

202

Amino-acid selective experiments on uniformly 13C and 15N labeled proteins by MAS NMR: Filtering of lysines and arginines  

NASA Astrophysics Data System (ADS)

Amino-acid selective magic-angle spinning (MAS) NMR experiments can aid the assignment of ambiguous cross-peaks in crowded spectra of solid proteins. In particular for larger proteins, data analysis can be hindered by severe resonance overlap. In such cases, filtering techniques may provide a good alternative to site-specific spin-labeling to obtain unambiguous assignments that can serve as starting points in the assignment procedure. In this paper we present a simple pulse sequence that allows selective excitation of arginine and lysine residues. To achieve this, we make use of a combination of specific cross-polarization for selective excitation [M. Baldus, A.T. Petkova, J. Herzfeld, R.G. Griffin, Cross polarization in the tilted frame: assignment and spectral simplification in heteronuclear spin systems, Mol. Phys. 95 (1998) 1197 1207.] and spin diffusion for transfer along the amino-acid side-chain. The selectivity of the filter is demonstrated with the excitation of lysine and arginine side-chain resonances in a uniformly 13C and 15N labeled protein preparation of the ?-spectrin SH3 domain. It is shown that the filter can be applied as a building block in a 13C 13C lysine-only correlation experiment.

Jehle, Stefan; Rehbein, Kristina; Diehl, Anne; van Rossum, Barth-Jan

2006-12-01

203

Amino-acid selective experiments on uniformly 13C and 15N labeled proteins by MAS NMR: Filtering of lysines and arginines.  

PubMed

Amino-acid selective magic-angle spinning (MAS) NMR experiments can aid the assignment of ambiguous cross-peaks in crowded spectra of solid proteins. In particular for larger proteins, data analysis can be hindered by severe resonance overlap. In such cases, filtering techniques may provide a good alternative to site-specific spin-labeling to obtain unambiguous assignments that can serve as starting points in the assignment procedure. In this paper we present a simple pulse sequence that allows selective excitation of arginine and lysine residues. To achieve this, we make use of a combination of specific cross-polarization for selective excitation [M. Baldus, A.T. Petkova, J. Herzfeld, R.G. Griffin, Cross polarization in the tilted frame: assignment and spectral simplification in heteronuclear spin systems, Mol. Phys. 95 (1998) 1197-1207.] and spin diffusion for transfer along the amino-acid side-chain. The selectivity of the filter is demonstrated with the excitation of lysine and arginine side-chain resonances in a uniformly 13C and 15N labeled protein preparation of the alpha-spectrin SH3 domain. It is shown that the filter can be applied as a building block in a 13C-13C lysine-only correlation experiment. PMID:16990042

Jehle, Stefan; Rehbein, Kristina; Diehl, Anne; van Rossum, Barth-Jan

2006-09-20

204

Analysis of hydrocarbon chain conformation using double quantum coherence /sup 13/C NMR  

SciTech Connect

The recent development of a double quantum coherence method for the observation of /sup 13/C-/sup 13/C scalar coupling constants without the need for isotopic labeling provides an alternative approach to the hydrocarbon chain conformation problem. The method is particularly suitable for this application since one-, two-, and three-bond carbon-carbon coupling constant values in hydrocarbons are typically of significantly different magnitudes, and observation of coupling constants of selected magnitude may be enhanced by the appropriate choice of pulse intervals. Consequently, J/sub CC/ values, which are dependent on the subtended dihedral angle, can be selectively observed. In order to evaluate the potential of this approach, studies on a 90% octanol-10% benzene-d/sub 6/ solution, with the latter serving for the deuterium lock were carried out. A representative /sup 13/C double quantum coherence spectrum of the region containing the octanol C-7 resonances with pulse intervals chosen to optimize couplings with magnitude close to 4.0 Hz is illustrated.

Phillippi, M.A. (Clorox Technical Center, Pleasanton, CA); Wiersema, R.J.; Brainard, J.R.; London, R.E.

1982-12-15

205

Application of the {sup 13}C NMR magic angle turning experiment to coal studies  

SciTech Connect

One of the important contributions of high resolution {sup 13}C CP/MAS to coal science is the measurement of the structural parameters of coal. It has been demonstrated that the structural parameters directly derived from {sup 13}C CP/MAS experiments can be utilized to predict the details of coal devolatilization and char formation processes. One of the advantages of spinning a solid sample at the magic angle is the reduction of the line broadening contributions due to the chemical shift anisotropy (CSA). The chemical shift anisotropy is proportional to the strength of the external magnetic field and the CSA of aromatic carbons (200-240 ppm) is greater than that of the aliphatic carbons (20-100 ppm). When the sample is spun at the magic angle the CSA induced powder patterns break up into spinning sidebands and, in order to obtain a {sup 13}C CP/MAS spectrum in which the aromatic carbon sidebands do not overlap the aliphatic carbon signals, it is necessary to spin the sample at approximately 4 KHz at a magnetic field of 2.35 Tesla. At a higher magnetic field strength a greater spinning rate is required. High speed magic angle spinning not only reduces the contributions of the spinning side bands but it also destroys very useful information on the local electronic environment that is embedded in the principal values of the CSA tensors.

Pugmire, R.J.; Wang, W.; Solum, M.S.; Grant, D.M.; Hu, J.Z. [Univ. of Utah, Salt Lake City, UT (United States)]|[Chinese Academy of Science, Wuhan (China)

1995-12-31

206

A variable-director 13C NMR analysis of lyotropic aramide solutions  

Microsoft Academic Search

The order and dynamics of two aromatic polyamides in their lyotropic phases were investigated with the aid of variable-director nuclear magnetic resonance (NMR). In these experiments polymers were dissolved in concentrated sulfuric acid and allowed to equilibrate inside the main NMR magnetic field B0 to yield macroscopically-aligned liquid crystalline solutions. These ordered fluids were then rotated away from equilibrium for

Julia Grinshtein; Dan McElheny; Veronica Frydman; Lucio Frydman

2001-01-01

207

Hydrocarbon type analysis of jet fuels by /sup 1/H and /sup 13/C NMR  

SciTech Connect

This report describes the application of NMR spectroscopy to the chemical characterization without prior chromatographic separation of jet fuels and various fuel blends containing varying amounts of paraffinic and aromatic constituents. Equations are derived by which the total percent paraffins and aromatics as well as percent monoaromatics and diaromatics can be calculated. Computer programs for the various calculations are included. The results obtained by NMR are compared to those obtained by MS.

Netzel, D.A.; Hunter, P.M.

1981-05-01

208

Ring-substituted benzohydroxamic acids: 1H, 13C and 15N NMR spectra and NH-OH proton exchange.  

PubMed

NMR spectra (1H, 13C, 15N) of para- and meta-substituted benzohydroxamic acids were studied in dry dimethyl sulfoxide solutions. The 13C chemical shifts were very close to those found by cross-polarization magic angle spinning in solids, the hydroxamic (not hydroximic) structure of which is unambiguous. The hydroxamic structure of these acids in DMSO solutions was proved independently by their 15N chemical shifts. The 15N and 1H chemical shifts of the NH-OH fragment showed excellent mutual dependences and dependences on the nature of the ring substituent. According to these dependences and ab initio energy calculations, all the acids assume the same Z conformation. Proton exchange between hydroxamic OH and NH groups in DMSO proceeded by both intra- and intermolecular exchange and the rates did not exhibit any simple relationship to the substituent constants. PMID:15861383

Schraml, Jan; Tkadlecová, Marcela; Pataridis, Statis; Soukupová, Ludmila; Blechta, Vratislav; Roithová, Jana; Exner, Otto

2005-07-01

209

Interactions of D-cellobiose with p-toluenesulfonic acid in aqueous solution: a (13)C NMR study.  

PubMed

The effects of adding D(2)SO(4), and p-toluenesulfonic acid-d to D-cellobiose dissolved in D(2)O were investigated at 23°C by plotting (13)C NMR chemical shift changes (??) against the acid to D-cellobiose molar ratio. (13)C Chemical shifts of all 18 carbon signals from ? and ? anomers of D-cellobiose showed gradual decreases due to increasing acidity in aqueous D(2)SO(4) medium. The C-1 of the ? anomer showed a slightly higher response to increasing D(+) concentration in the surrounding. In the aqueous p-toluenesulfonic acid-d medium, C-6' and C-4' carbons of both ?, and ? anomeric forms of D-cellobiose are significantly affected by increasing the sulfonic acid concentrations, and this may be due to a 1:1 interaction of p-toluenesulfonic acid-d with the C-6', C-4' region of the cellobiose molecule. PMID:22036122

Amarasekara, Ananda S; Owereh, Onome S; Ezeh, Brian

2011-10-05

210

Properties of sesame oil by detailed 1H and 13C NMR assignments before and after ozonation and their correlation with iodine value, peroxide value, and viscosity measurements  

Microsoft Academic Search

Gaseous ozone chemically reacts with unsaturated triglyceride substrates leading to ozonated derivatives with a wide potential applications, ranging from the petrochemical to the pharmaceutical industry. To date, an ultimate understanding of the ozone reactivity during sesame oil ozonation process as well as detailed 1H and 13C NMR assignments are lacking. A practical advantage of NMR is that a single NMR

Alessandro Sega; Iacopo Zanardi; Luisa Chiasserini; Alessandro Gabbrielli; Velio Bocci; Valter Travagli

2010-01-01

211

Humic acids as proxies for assessing different Mediterranean forest soils signatures using solid-state CPMAS 13C NMR spectroscopy.  

PubMed

Humic acids (HAs) of four representative forest soils profiles from Central Spain (two with different vegetation - pine and oak - but same parent material - granitie, and two with same vegetation - holm oak - but different parent material - granite and limestone) were investigated by solid-state cross polarization with magic angle spinning (13)C nuclear magnetic resonance (NMR) spectroscopy. The objectives included the investigation of the impact of different forest properties on HA composition, assessing how the structural characteristics of the HA vary with soil depth, and evaluating the role of HA as surrogates for mapping the different forest soils signatures using structural data derived from (13)C NMR spectroscopy. On average, alkyl C is the dominant C constituent (38-48% of the total NMR peak area) in all HA samples, followed by aromatic (12-22%) and O-alkyl C (12-19%), and finally carboxyl C (7.0-10%). The NMR data also indicated that HA composition is likely to be differently affected by the soil physico-chemical properties and type of forest vegetation. The structural characteristics of the HA from soil under oak did not differ broadly downward in the profile, whereas soil HA under pine forest exhibits a somewhat higher recalcitrant nature as a consequence of a higher degree of decomposition. The soil HA from holm oak forests differed from the other two forest soils, exhibiting a progressive decomposition of the alkyl C structures with increasing depth, while the carbohydrate-like indicator (O-alkyl C) is apparently being protected from mineralization in the horizons below the ground level. Overall, these differences in soil HA NMR signatures are an important diagnostic tool for understanding the role of different soil environmental factors on the structural composition of HA from Mediterranean forest soils. PMID:23332874

Duarte, Regina M B O; Fernández-Getino, Ana P; Duarte, Armando C

2013-01-18

212

Phase behavior and 13C NMR spectroscopic analysis of the mixed methane + ethane + propane hydrates in mesoporous silica gels.  

PubMed

In this study, the phase behavior and quantitative determination of hydrate composition and cage occupancy for the mixed CH(4) + C(2)H(6) + C(3)H(8) hydrates were closely investigated through the experimental measurement of three-phase hydrate (H)-water-rich liquid (L(W))-vapor (V) equilibria and (13)C NMR spectra. To examine the effect of pore size and salinity, we measured hydrate phase equilibria for the quaternary CH(4) (90%) + C(2)H(6) (7%) + C(3)H(8) (3%) + water mixtures in silica gel pores of nominal diameters of 6.0, 15.0, and 30.0 nm and for the quinary CH(4) (90%) + C(2)H(6) (7%) + C(3)H(8) (3%) + NaCl + water mixtures of two different NaCl concentrations (3 and 10 wt %) in silica gel pores of a nominal 30.0 nm diameter. The value of hydrate-water interfacial tension for the CH(4) (90%) + C(2)H(6) (7%) + C(3)H(8) (3%) hydrate was found to be 47 ± 4 mJ/m(2) from the relation of the dissociation temperature depression with the pore size of silica gels at a given pressure. At a specified temperature, three-phase H-L(W)-V equilibrium curves of pore hydrates were shifted to higher pressure regions depending on pore sizes and NaCl concentrations. From the cage-dependent (13)C NMR chemical shifts of enclathrated guest molecules, the mixed CH(4) (90%) + C(2)H(6) (7%) + C(3)H(8) (3%) gas hydrate was confirmed to be structure II. The cage occupancies of each guest molecule and the hydration number of the mixed gas hydrates were also estimated from the (13)C NMR spectra. PMID:20964277

Lee, Seungmin; Cha, Inuk; Seo, Yongwon

2010-10-21

213

Cytosine ribose flexibility in DNA: a combined NMR 13C spin relaxation and molecular dynamics simulation study  

PubMed Central

Using 13C spin relaxation NMR in combination with molecular dynamic (MD) simulations, we characterized internal motions within double-stranded DNA on the pico- to nano-second time scale. We found that the C–H vectors in all cytosine ribose moieties within the Dickerson–Drew dodecamer (5?-CGCGAATTCGCG-3?) are subject to high amplitude motions, while the other nucleotides are essentially rigid. MD simulations showed that repuckering is a likely motional model for the cytosine ribose moiety. Repuckering occurs with a time constant of around 100 ps. Knowledge of DNA dynamics will contribute to our understanding of the recognition specificity of DNA-binding proteins such as cytosine methyltransferase.

Duchardt, Elke; Nilsson, Lennart

2008-01-01

214

Magnetic field dependence of 13 C photo-CIDNP MAS NMR in plant photosystems I and II  

Microsoft Academic Search

Photochemically induced dynamic nuclear polarization is observed in the two photosynthetic reaction centers of plants, photosystem\\u000a I (PSI) and photosystem II (PSII) by13C magic-angle spinning nuclear magnetic resonance (NMR) at three different magnetic fields 17.6, 9.4, and 4.7 T. There is\\u000a a significant difference in field dependence detected in the light-induced signal pattern of the two photosystems. For PSII\\u000a the

E. Roy; A. Diller; Alia; P. Gast; H. J. van Gorkom; H. J. M. de Groot; G. Jeschke; J. Matysik

2007-01-01

215

Biosynthesis of pyrroloquinoline quinone. 1. Identification of biosynthetic precursors using /sup 13/C labeling and NMR spectroscopy  

SciTech Connect

The biosynthesis of pyrroloquinoline quinone (PQQ) in the methylotropic bacterium methylobacterium AM1 has been investigated using /sup 13/C-labelling of the products and NMR spectroscopy. The data indicated that the quinoline portion of PQQ is formed by a novel condensation of N-1, C-2, -3, and -4 of glutamate with a symmetrical six-carbon ring derived from the shikimate pathway. It is postulated that tyrosine is the shikimate-derived percursor, since pyrrole could be formed by the internal cyclization of the amino acid backbone. 18 references, 2 figures, 2 tables.

Houck, D.R.; Hanners, J.L.; Unkefer, C.J.

1988-09-28

216

Identification and quantitative determination of carbohydrates in ethanolic extracts of two conifers using 13C NMR spectroscopy.  

PubMed

We developed a method for the direct identification and quantification of carbohydrates in raw vegetable extracts using (13)C NMR spectroscopy without any preliminary step of precipitation or reduction of the components. This method has been validated (accuracy, precision and response linearity) using pure compounds and artificial mixtures before being applied to authentic ethanolic extracts of pine needles, pine wood and pine cones and fir twigs. We determined that carbohydrates represented from 15% to 35% of the crude extracts in which pinitol was the principal constituent accompanied by arabinitol, mannitol, glucose and fructose. PMID:18299126

Duquesnoy, Emilie; Castola, Vincent; Casanova, Joseph

2008-01-12

217

Kinetic analysis of glycogen turnover: relevance to human brain (13)C-NMR spectroscopy.  

PubMed

A biophysical model of the glycogen molecule is developed, which takes into account the points of attack of synthase and phosphorylase at the level of the individual glucose chain. Under the sole assumption of steric effects governing enzyme accessibility to glucosyl residues, the model reproduces the known equilibrium structure of cellular glycogen at steady state. In particular, experimental data are reproduced assuming that synthase (1) operates preferentially on inner chains of the molecule and (2) exhibits a faster mobility than phosphorylase in translocating from an attacked chain to another. The model is then used to examine the turnover of outer versus inner tiers during the labeling process of isotopic enrichment (IE) experiments. Simulated data are fitted to in vivo (13)C nuclear magnetic resonance spectroscopy measurements obtained in the human brain under resting conditions. Within this experimental set-up, analysis of simulated label incorporation and retention shows that 7% to 35% of labeled glucose is lost from the rapidly turning-over surface of the glycogen molecule when stimulation onset is delayed by 7 to 11.5?hours after the end of [1-(13)C]glucose infusion as done in actual procedures. The substantial label washout before stimulation suggests that much of the subsequent activation-induced glycogenolysis could remain undetected. Overall, these results show that the molecular structure significantly affects the patterns of synthesis and degradation of glycogen, which is relevant for appropriate design of labeling experiments aiming at investigating the functional roles of this glucose reserve. PMID:23756693

Dinuzzo, Mauro

2013-06-12

218

sup 13C solid-state NMR study of ethylene oxidation over supported silver catalysts.  

National Technical Information Service (NTIS)

Solid-state NMR has been used to study the interaction of ethylene with oxygen in the absence of promoters and moderators over silica-supported silver catalysts. Experiments using nitrous oxide and oxygen as the oxidants have been carried out over Ag/SiO(...

S. Hosseini

1992-01-01

219

Glutamic Acid Residues of Bacteriorhodopsin at the Extracellular Surface as Determinants for Conformation and Dynamics as Revealed by Site-Directed Solid-State 13C NMR  

PubMed Central

We recorded 13C NMR spectra of [3-13C]Ala- and [1-13C]Val-labeled bacteriorhodopsin (bR) and a variety of its mutants, E9Q, E74Q, E194Q/E204Q (2Glu), E9Q/E194Q/E204Q (3Glu), and E9Q/E74Q/E194Q/E204Q (4Glu), to clarify contributions of the extracellular (EC) Glu residues to the conformation and dynamics of bR. Replacement of Glu-9 or Glu-74 and Glu-194/204 at the EC surface by glutamine(s) induced significant conformational changes in the cytoplasmic (CP) surface structure. These changes occurred in the C-terminal ?-helix and loops, and also those of the EC surface, as viewed from 13C NMR spectra of [3-13C]Ala- and [1-13C]Val-labeled proteins. Additional conformational changes in the transmembrane ?-helices were induced as modified retinal-protein interactions for multiple mutants involving the E194Q/E204Q pair. Significant dynamic changes were induced for the triple or quadruple mutants, as shown by broadened 13C NMR peaks of [1-13C]Val-labeled proteins. These changes were due to acquired global fluctuation motions of the order of 10?4–10?5 s as a result of disorganized trimeric form. In such mutants 13C NMR signals from Val residues of [1-13C]Val-labeled triple and quadruple mutants near the CP and EC surfaces (including 8.7-Å depth from the surface) were substantially suppressed, as shown by comparative 13C NMR studies with and without 40 ?M Mn2+ ion. We conclude that these Glu residues at the EC surface play an important role in maintaining the native secondary structure of bR in the purple membrane.

Saito, Hazime; Yamaguchi, Satoru; Ogawa, Keiji; Tuzi, Satoru; Marquez, Mercedes; Sanz, Carolina; Padros, Esteve

2004-01-01

220

1H and 13C NMR data to aid the identification and quantification of residual solvents by NMR spectroscopy.  

PubMed

We present reference data and a javascript web page which allow the rapid identification and quantification of residual solvents by NMR. The data encompass all of the ICH-prescribed solvents and were obtained for a number of NMR solvents. We also present an example of its application. PMID:15809983

Jones, Ian C; Sharman, Gary J; Pidgeon, Julia

2005-06-01

221

13C NMR studies of the fluxes in the central metabolism of Corynebacterium glutamicum during growth and overproduction of amino acids in batch cultures  

Microsoft Academic Search

The carbon flux distribution in the central metabolism of Corynebacterium glutamicum was studied in batch cultures using [1-13C]- and [6-13C]glucose as substrate during exponential growth as well as during overproduction of l-lysine and l-glutamate. Using the 13C NMR data in conjunction with stoichiometric metabolite balances, molar fluxes were quantified and normalised to the glucose uptake rate, which was set to

K. Sonntag; J. Schwinde; A. A. Graaf; A. Marx; B. J. Eikmanns; W. Wiechert; H. Sahm

1995-01-01

222

Land use Effects on Storage, Stability and Structure of Organic Carbon in Soil Density Fractions Revealed by 13C Natural Abundance and CPMAS 13C NMR  

NASA Astrophysics Data System (ADS)

The type of land use and soil cultivation are important factors controlling organic carbon storage (SOC) in soils and they can also influence the relative importance, the structure, and the stability of different SOC pools. The objectives of our study were: i) to quantify the SOC stocks in different density fractions (mineral-associated soil organic matter > 2 g cm-3 (Mineral-SOM), free particulate organic matter < 1.6 g cm-3 (free POM), light occluded particulate organic matter < 1.6 g cm-3 (occluded POM<1.6) and dense occluded particulate organic matter 1.6 to 2.0 g cm-3 (occluded POM1.6-2.0)) of silty soils under different land use (spruce forest, grassland, maize, wheat), ii) to determine the structure of these SOC fractions by CPMAS 13C NMR spectroscopy, and iii) to analyse the stability of these SOC fractions in the maize soil on the basis of the stable isotope composition of SOC. The SOC concentration in the A horizon increased in the order wheat (12.7 g kg-1) < maize (13.0 g kg-1) < grassland (24.5 g kg-1) < spruce (40.5 g kg-1). The major part (86-91%) of the SOC was associated with the heavy mineral fraction at the grassland, maize and wheat site. In the A horizon of the spruce soil, the particulate organic matter accounted for 52% of the total SOC content. The chemical structure of the soil organic matter (SOM) was influenced by litter quality, the intensity of litter decomposition and the related production and storage of microbially-derived substances. SOM of the acid forest soil was characterized by large amounts of POM with a high content of spruce litter-derived alkyl C. In the biologically more active grassland and maize soil, litter-derived POM was decomposed more rapidly and SOC stocks were dominated by mineral-associated SOM which contained greater proportions of aryl and carbonyl C. The cultivation of the grassland soil induced enhanced mineralization of POM and in particular of mineral-associated SOM. The faster SOC turnover was associated with a relative accumulation of aromatic and carbonyl C structures in the mineral-bound SOM. In all soils, the free particulate organic matter had a smaller proportion of alkyl C and a larger proportion of O-alkyl C than the particulate organic matter occluded in aggregates. The mean age of the SOM in the density fractions of the maize soil increased with increasing aromaticity in the order free POM (22 yr) < occluded POM1.6-2.0 (49 yr) < mineral-associated SOM (63 yr). The results showed that the type of land use influenced the distribution pattern of litter carbon to functionally different SOM pools which represented different stages of SOM decomposition and humification. Additionally, the type of land use influenced the chemical structure of SOM in soil density fractions. Thus, the effect of land use on SOM storage should not only be assessed in terms of total C stocks but also with respect to changes of SOC structure, stability and function.

Flessa, H.; Helfrich, M.; John, B.; Yamashita, T.; Ludwig, B.

2004-12-01

223

Solid-state {sup 13}C MAS NMR study of methanol-to-hydrocarbon chemistry over H-SAPO-34  

SciTech Connect

{sup 13}C solid-state MAS NMR was used to probe the chemistry of a number of species involved in the methanol-to-hydrocarbon process over H-SAPO-34 molecular sieve at both high (573 K) and low (473-563 K) temperature ranges and at very low conversion (<0.1%). Isobutane was the only hydrocarbon product observed at 473 and 573 K. Evidence for the operation of a stepwise methylation reaction via surface-bound species derives from, first, the treatment of several samples with different loadings of methanol at 523-563 K and, second, when either [{sup 13}C]methanol is coadsorbed with [{sup 12}C]ethene over the catalyst or [{sup 12}C]ethene is reacted with pre-[{sup 13}C]methylated SAPO-34. The hydrocarbon products in these experiments were mainly isobutane and isopentane as well as methane, ethene, and propane. Based on these experimental findings, a number of mechanistic approaches concerning the very first stages of the reaction are discussed. 56 refs., 13 figs., 3 tabs.

Salehirad, F.; Anderson, M.A. [UMIST, Manchester (United Kingdom)

1996-12-01

224

15N and 13C NMR Determination of Methionine Metabolism in Developing Soybean Cotyledons 1  

PubMed Central

The metabolism of d- and l-methionine by immature cotyledons of soybean (Glycine max, L. cv Elf) grown in culture has been investigated using solid-state 13C and 15N nuclear magnetic resonance. d-Methionine is taken up by the cotyledons and converted to an amide, most likely by N-malonylation. About 16% of the l-methionine taken up is incorporated intact into protein, and 25% remains as soluble methionine. Almost two-thirds of the l-methionine that enters the cotyledons is degraded. The largest percentage of this is used in transmethylation of the carboxyl groups of pectin. Methionine is not extensively converted to polyamines. We attribute the stimulation of growth of the cotyledons by exogenous methionine to the bypassing of a rate-limiting methyl-transfer step in the synthesis of methionine itself, and subsequently of pectins and proteins.

Coker, George T.; Garbow, Joel R.; Schaefer, Jacob

1987-01-01

225

Acetylcholinesterase-catalyzed acetate - water oxygen exchange studied by /sup 13/C-NMR  

SciTech Connect

The kinetics of the oxygen exchange reaction between (l-/sup 13/C,/sup 18/O/sub 2/)acetate and H/sub 2//sup 16/O catalyzed by homogeneous acetyl-cholinesterase from the electric eel, Electrophorus electricus, was studied using the /sup 18/O-isotope-induced shift on /sup 13/C-nuclear magnetic resonance spectra. Pseudo-first-order rate constants for the exchange reactions were determined at pH values from 4.5 to 8. The exchange reaction exhibits a maximum at pH 5.8. The apparent catalytic rate constant for the exchange reaction is 10/sup 2/ to 10/sup 4/ times smaller than that for the deacylation of the acetyl-enzyme intermediate over the pH range tested. Oxygen exchange occurs by a random sequential pathway rather than by multiple (coupled) exchange. The inhibition of acetylcholinesterase by sodium acetate showed a sigmoidal dependence on pH, with K/sub i/ increasing 2.5 orders of magnitude over the pH range. Protonation of an active site residue having an apparent pKa of 6.8 is associated with an increase in acetate binding. Deacylation also exhibits a sigmoidal dependence on (H/sup +/). The experimental data fits titration curves with inflection points at 5.0 +/- 0.3 and 6.7 +/-0.1. Results support the role of histidine in acetylation of the active site serine, but the conjugate base of another active site residue with a pKa of 5.0 appears necessary for maximal catalytic activity in both the deacylation and exchange reactions.

Van Etten, R.L.; Dayton, B.; Cortes, S.

1986-05-01

226

Preservation of proteinaceous material during the degradation of the green alga Botryococcus braunii: A solid-state 2D 15N 13C NMR spectroscopy study  

Microsoft Academic Search

Using solid-state cross-polarization-magic-angle-spinning (CPMAS) 13C and 15N nuclear magnetic resonance (NMR) and 2-D double cross polarization (DCP) MAS 15N 13C NMR techniques, microbially degraded Botryococcus braunii was analyzed to study the chemical nature of organic nitrogen in the algal residue. The amide linkage, as found in protein, was observed as the major nitrogen component in 201-day-old degraded algae. No significant

Xu Zang; Reno T. Nguyen; H. Rodger Harvey; Heike Knicker; Patrick G. Hatcher

2001-01-01

227

Extensive backbone dynamics in the GCAA RNA tetraloop analyzed using 13C NMR spin relaxation and specific isotope labeling.  

PubMed

Conformational dynamics play a key role in the properties and functions of proteins and nucleic acids. Heteronuclear NMR spin relaxation is a uniquely powerful site-specific probe of dynamics in proteins and has found increasing applications to nucleotide base side chains and anomeric sites in RNA. Applications to the nucleic acid ribose backbone, however, have been hampered by strong magnetic coupling among ring carbons in uniformly 13C-labeled samples. In this work, we apply a recently developed, metabolically directed isotope labeling scheme that places 13C with high efficiency and specificity at the nucleotide ribose C2' and C4' sites. We take advantage of this scheme to explore backbone dynamics in the well-studied GCAA RNA tetraloop. Using a combination of CPMG (Carr-Purcell-Meiboom-Gill) and R(1rho) relaxation dispersion spectroscopy to explore exchange processes on the microsecond to millisecond time scale, we find an extensive pattern of dynamic transitions connecting a set of relatively well-defined conformations. In many cases, the observed transitions appear to be linked to C3'-endo/C2'-endo sugar pucker transitions of the corresponding nucleotides, and may also be correlated across multiple nucleotides within the tetraloop. These results demonstrate the power of NMR spin relaxation based on alternate-site isotope labeling to open a new window into the dynamic properties of ribose backbone groups in RNA. PMID:19049467

Johnson, James E; Hoogstraten, Charles G

2008-12-10

228

1H, 13C NMR and DFT Study of Hydrogen Bonding in Imidazolium-based Ionic Liquids.  

PubMed

The ionic liquid 1-decyl-3-methyl-imidazolium bromide [C10mim][Br], the neat material, and also dissolved (~0.01 mole fraction) in various dielectric media (acetonitrile, benzene, chloroform, dichloromethane, methanol, 2-butanol and H2O) was studied using 1H and 13C NMR spectroscopy. The most important interaction in this compound is considered to be the Br-...H-C2+ hydrogen bond, which is formed between the anions and cations. The obtained results show that dielectric medium influence mostly the behavior of the Br-...H-C2+ bridge proton. The changes observed in 1H and 13C NMR spectra of [C10mim][Br] with increasing solvents polarity and temperature can be explained applying the model of the lengthening of the H2...Br- bond with the accompanying thickening of the solvation shell of bromine anion and C2-H bond contraction. The short-range order effects related to the configuration of neighboring dipoles of solvent molecules are more important for the solvation ability of small anions than the bulk solvent field effect. However, the solvents, molecules of which tend to associate via hydrogen bonding, can significantly affect the dynamics of anions. PMID:24062104

Balevi?ius, Vytautas; Gdaniec, Zofia; Džiaugys, Lukas; Kuliešius, Feliksas; Maršalka, Ar?nas

2011-09-01

229

Acid-base equilibrium in aqueous solutions of 1,3-dimethylbarbituric acid as studied by 13C NMR spectroscopy  

NASA Astrophysics Data System (ADS)

13C NMR spectra of 1,3-dimethylbarbituric acid in aqueous solutions of various acidities and for various solute concentrations have been recorded and interpreted. The spectra recorded at pH = 2 and below contain the signals of the neutral solute molecule exclusively, while the ones recorded at pH = 7 and above only the signals of the appropriate anion, which has been confirmed by theoretical GIAO-DFT calculations. The signals in the spectra recorded for solutions of pH < 7 show dynamic broadenings. The lineshape analysis of these signals has provided information on the kinetics of the processes running in the dynamic acid-base equilibrium. The kinetic data determined this way have been used to clarify the mechanisms of these processes. The numerical analysis has shown that under the investigated conditions deprotonation of the neutral solute molecules undergoes not only via a simple transfer of the C-H proton to water molecules but also through a process with participation of the barbiturate anions. Moreover, the importance of tautomerism, or association, or both these phenomena for the kinetics of the acid-base transformations in the investigated system has been shown. Qualitatively similar changes of 13C NMR spectra with the solution pH variation have been observed for the parent barbituric acid.

Gryff-Keller, A.; Kraska-Dziadecka, A.

2011-12-01

230

Experimental and theoretical study of substituent effect on 13C NMR chemical shifts of 5-arylidene-2,4-thiazolidinediones  

NASA Astrophysics Data System (ADS)

The electronic structure of 5-arylidene-2,4-thiazolidinediones has been studied by using experimental and theoretical methodology. The theoretical calculations of the investigated 5-arylidene-2,4-thiazolidinediones have been performed by the use of quantum chemical methods. The calculated 13C NMR chemical shifts and NBO atomic charges provide an insight into the influence of such a structure on the transmission of electronic substituent effects. Linear free energy relationships (LFERs) have been further applied to their 13C NMR chemical shifts. The correlation analyses for the substituent-induced chemical shifts (SCS) have been performed with ? using SSP (single substituent parameter), field (?F) and resonance (?R) parameters using DSP (dual substituent parameter), as well as the Yukawa-Tsuno model. The presented correlations account satisfactorily for the polar and resonance substituent effects operative at C?, and C7 carbons, while reverse substituent effect was found for C?. The comparison of correlation results for the investigated molecules with those obtained for seven structurally related styrene series has indicated that specific cross-interaction of phenyl substituent and groups attached at C? carbon causes increased sensitivity of SCS C? to the resonance effect with increasing of electron-accepting capabilities of the group present at C?.

Ran?i?, Milica P.; Trišovi?, Nemanja P.; Mil?i?, Miloš K.; Ajaj, Ismail A.; Marinkovi?, Aleksandar D.

2013-10-01

231

Determination of the DNA sugar pucker using sup 13 C NMR spectroscopy  

Microsoft Academic Search

Solid-state ¹³C NMR spectroscopy of a series of crystalline nucleosides and nucleotides allows direct measurement of the effect of the deoxyribose ring conformation on the carbon chemical shift. It is found that 3â²-endo conformers have 3â² and 5â² chemical shifts significantly (5-10 ppm) upfield of comparable 3â²-exo and 2â²-endo conformers. The latter two conformers may be distinguished by smaller but

R. A. Santos; P. Tang; G. S. Harbison

1989-01-01

232

13 C NMR Study of Halogen Bonding of Haloarenes:  Measurements of Solvent Effects and Theoretical Analysis ‡  

Microsoft Academic Search

Solvent effects on the NMR spectra of symmetrical (X ) F( 1), X ) Cl (2), X ) Br (3), X ) I( 4), X ) NO2 (5), X ) CN (6)) and unsymmetrical (X ) I, Y ) MeO (7), Y ) PhO (8)) para-disubstituted acetophenone azines X-C6H4-CMedN-NdCMe-C6H4-Y and of models X-C6H4-CMedN- Z( X) I, Z ) H( 9),

Rainer Glaser; Naijun Chen; Hong Wu; Nathan Knotts; Martin Kaupp

2004-01-01

233

[sup 13]C solid-state NMR study of ethylene oxidation over supported silver catalysts  

SciTech Connect

Solid-state NMR has been used to study the interaction of ethylene with oxygen in the absence of promoters and moderators over silica-supported silver catalysts. Experiments using nitrous oxide and oxygen as the oxidants have been carried out over Ag/SiO[sub 2] catalyst at temperature ranging from 298 to 613 K. Standard cross-polarization with magic angle spinning (CP/MAS), CP/MAS with dipolar dephasing, and single-pulse experiments have been applied to identify carbon-containing species that are formed on the surface of catalyst at various temperatures. Ethylene, acetic acid, carbon dioxide, ethane and an alkoxy species have been identified. Under the above experimental conditions, no ethylene oxide is detected by NMR. In pursuit of a better understanding of the chemistry taking place on the catalyst, silica-supported silver catalysts as well as pure silica were dosed with labeled ethylene, carbon dioxide and ethylene oxide. It was found that under conditions employed in this study, ethylene oxide reacts with both metal and silica support and thus cannot be observed as the reaction product. Ethylene oxide, however, has been observed after the saturation of silica surface with unlabeled ethylene oxide prior to ethylene oxidation. In conjunction with this project, the author has designed and constructed a multiport high vacuum glass apparatus which was used for sample preparation prior to the NMR experiments as well as chemisorption measurements and a single-coil double resonance probe.

Hosseini, S.

1992-01-01

234

15N and 13C{14N} NMR investigation of the major nitrogen-containing segment in an aquatic fulvic acid: evidence for a hydantoin derivative.  

PubMed

A nitrogen-rich segment in a fulvic acid (FA) from Pony Lake, a coastal pond in Antarctica, was investigated by (15)N and (13)C{(14)N} solid-state NMR techniques. As reported previously, the (13)C{(14)N} spectrum of C bonded to N exhibits a peak at 157 ppm that is assigned to an sp(2)-hybridized carbon bonded to at least two nitrogen atoms. This segment contains 48% of all N in the sample. (15)N NMR shows distinct signals, 20 ppm upfield and downfield from the typical peptide resonance; dipolar dephasing confirmed that they are due to protonated N. The well-resolved downfield peak, which accounts for 1/4 of the spectral area, cannot be assigned to aromatic heterocycles, such as purines, because the fraction of aromatic C bonded to N in this sample is very small. Analysis of (15)N chemical-shift trends and (15)N NMR of model compounds, such as arginine and its derivatives, excludes assignment to a guanidinium ion or to substituted guanidino groups. Similarly, ureido groups, -NH-CO-NH-, that are not bonded to a second C = O do not match the observed (15)N peaks in the FA, since both N resonate upfield from the peptide resonance. On the other hand, all chemical shifts are matched within the observed range by the -C(alkyl)-NH-CO-NH-CO-C structure found in two nonaromatic heterocycles, hydantoin and dihydrouracil. The five-membered hydantoin ring, which is found in the purine metabolite allantoin, provides a better match than the six-membered dihydrouracil ring. Regular uracil or thymine fails to produce adequate agreement with observed chemical shifts. PMID:22170241

Fang, Xiaowen; Mao, Jingdong; Cory, Rose M; McKnight, Diane M; Schmidt-Rohr, Klaus

2011-12-01

235

Restraints on backbone conformations in solid state NMR studies of uniformly labeled proteins from quantitative amide 15N-15N and carbonyl 13C-13C dipolar recoupling data  

PubMed Central

Recent structural studies of uniformly 15N, 13C-labeled proteins by solid state nuclear magnetic resonance (NMR) rely principally on two sources of structural restraints: (i) restraints on backbone conformation from isotropic 15N and 13C chemical shifts, based on empirical correlations between chemical shifts and backbone torsion angles; (ii) restraints on inter-residue proximities from qualitative measurements of internuclear dipole–dipole couplings, detected as the presence or absence of inter-residue crosspeaks in multidimensional spectra. We show that site-specific dipole–dipole couplings among 15N-labeled backbone amide sites and among 13C-labeled backbone carbonyl sites can be measured quantitatively in uniformly-labeled proteins, using dipolar recoupling techniques that we call 15N-BARE and 13C-BARE (BAckbone REcoupling), and that the resulting data represent a new source of restraints on backbone conformation. 15N-BARE and 13C-BARE data can be incorporated into structural modeling calculations as potential energy surfaces, which are derived from comparisons between experimental 15N and 13C signal decay curves, extracted from crosspeak intensities in series of two-dimensional spectra, with numerical simulations of the 15N-BARE and 13C-BARE measurements. We demonstrate this approach through experiments on microcrystalline, uniformly 15N, 13C-labeled protein GB1. Results for GB1 show that 15N-BARE and 13C-BARE restraints are complementary to restraints from chemical shifts and inter-residue crosspeaks, improving both the precision and the accuracy of calculated structures.

Hu, Kan-Nian; Qiang, Wei; Bermejo, Guillermo A.; Schwieters, Charles D.; Tycko, Robert

2013-01-01

236

sup 13 C solid-state NMR study of ethylene oxidation over supported silver catalysts  

SciTech Connect

Solid-state NMR has been used to study the interaction of ethylene with oxygen in the absence of promoters and moderators over silica-supported silver catalysts. Experiments using nitrous oxide and oxygen as the oxidants have been carried out over Ag/SiO{sub 2} catalysts at temperature ranging from 298 to 613 K. Standard cross-polarization with magic angle spinning (CP/MAS), CP/MAS with dipolar dephasing, and single-pulse experiments have been applied to identify carbon containing species that are formed on the surface of catalyst at various temperatures. Ethylene, acetic acid, carbon dioxide, ethane and an alkoxy species have been identified. Under the above experimental conditions, no ethylene oxide is detected by NMR. In pursuit of a better understanding of the chemistry taking place on the catalyst, silica-supported silver catalysts as well as pure silica were dosed with labeled ethylene, carbon dioxide and ethylene oxide. It was found that under conditions employed in this study, ethylene oxide reacts with both metal and silica support and thus can not be observed as the reaction product. Ethylene oxide, however, has been observed after saturation of silica surface with unlabeled ethylene oxide prior to ethylene oxidation. A multiport high vacuum glass apparatus was developed along with a single-coil double resonance probe.

Hosseini, S.

1992-07-21

237

{sup 13}C solid-state NMR study of ethylene oxidation over supported silver catalysts  

SciTech Connect

Solid-state NMR has been used to study the interaction of ethylene with oxygen in the absence of promoters and moderators over silica-supported silver catalysts. Experiments using nitrous oxide and oxygen as the oxidants have been carried out over Ag/SiO{sub 2} catalysts at temperature ranging from 298 to 613 K. Standard cross-polarization with magic angle spinning (CP/MAS), CP/MAS with dipolar dephasing, and single-pulse experiments have been applied to identify carbon containing species that are formed on the surface of catalyst at various temperatures. Ethylene, acetic acid, carbon dioxide, ethane and an alkoxy species have been identified. Under the above experimental conditions, no ethylene oxide is detected by NMR. In pursuit of a better understanding of the chemistry taking place on the catalyst, silica-supported silver catalysts as well as pure silica were dosed with labeled ethylene, carbon dioxide and ethylene oxide. It was found that under conditions employed in this study, ethylene oxide reacts with both metal and silica support and thus can not be observed as the reaction product. Ethylene oxide, however, has been observed after saturation of silica surface with unlabeled ethylene oxide prior to ethylene oxidation. A multiport high vacuum glass apparatus was developed along with a single-coil double resonance probe.

Hosseini, S.

1992-07-21

238

Recent applications of /sup 13/C NMR spectroscopy to biological systems  

SciTech Connect

Carbon-13 nuclear magnetic resonance (NMR) spectroscopy, in conjunction with carbon-13 labelling, is a powerful new analytical technique for the study of metabolic pathways and structural components in intact organelles, cells, and tissues. The technique can provide, rapidly and non-destructively, unique information about: the architecture and dynamics of structural components; the nature of the intracellular environment; and metabolic pathways and relative fluxes of individual carbon atoms. With the aid of results recently obtained by us and those reported by a number of other laboratories, the problems and potentialities of the technique will be reviewed with emphasis on: the viscosities of intracellular fluids; the structure and dynamics of the components of membranes; and the primary and secondary metabolic pathways of carbon in microorganisms, plants, and mammalian cells in culture.

Matwiyoff, N.A.

1981-01-01

239

Complexation of rhodium(II) tetracarboxylates with aliphatic diamines in solution: (1) H and (13) C NMR and DFT investigations.  

PubMed

The complexation of rhodium(II) tetraacetate, tetrakistrifluoroaceate and tetrakisoctanoate with a set of diamines (ethane-1,diamine, propane-1,3-diamine and nonane-1,9-diamine) and their N,N'-dimethyl and N,N,N',N'-tetramethyl derivatives in chloroform solution has been investigated by (1) H and (13) C NMR spectroscopy and density functional theory (DFT) modelling. A combination of two bifunctional reagents, diamines and rhodium(II) tetracarboxylates, yielded insoluble coordination polymers as main products of complexation and various adducts in the solution, being in equilibrium with insoluble material. All diamines initially formed the 2?:?1 (blue), (1?:?1)n oligomeric (red) and 1?:?2 (red) axial adducts in solution, depending on the reagents' molar ratio. Adducts of primary and secondary diamines decomposed in the presence of ligand excess, the former via unstable equatorial complexes. The complexation of secondary diamines slowed down the inversion at nitrogen atoms in NH(CH3 ) functional groups and resulted in the formation of nitrogenous stereogenic centres, detectable by NMR. Axial adducts of tertiary diamines appeared to be relatively stable. The presence of long aliphatic chains in molecules (adducts of nonane-1,9-diamines or rhodium(II) tetrakisoctanoate) increased adduct solubility. Hypothetical structures of the equatorial adduct of rhodium(II) tetraacetate with ethane-1,2-diamine and their NMR parameters were explored by means of DFT calculations. Copyright © 2013 John Wiley & Sons, Ltd. PMID:23943201

Ja?wi?ski, Jaros?aw; Sadlej, Agnieszka

2013-08-13

240

Halogen effect on structure and (13) C NMR chemical shift of 3,6-disubstituted-N-alkyl carbazoles.  

PubMed

Structures of selected 3,6-dihalogeno-N-alkyl carbazole derivatives were calculated at the B3LYP/6-311++G(3df,2pd) level of theory, and their (13) C nuclear magnetic resonance (NMR) isotropic shieldings were predicted using density functional theory (DFT). The model compounds contained 9H, N-methyl and N-ethyl derivatives. The relativistic effect of Br and I atoms on nuclear shieldings was modeled using the spin-orbit zeroth-order regular approximation (ZORA) method. Significant heavy atom shielding effects for the carbon atom directly bonded with Br and I were observed (~-10 and ~-30?ppm while the other carbon shifts were practically unaffected). The decreasing electronegativity of the halogen substituent (F, Cl, Br, and I) was reflected in both nonrelativistic and relativistic NMR results as decreased values of chemical shifts of carbon atoms attached to halogen (C3 and C6) leading to a strong sensitivity to halogen atom type at 3 and 6 positions of the carbazole ring. The predicted NMR data correctly reproduce the available experimental data for unsubstituted N-alkylcarbazoles. Copyright © 2013 John Wiley & Sons, Ltd. PMID:23922027

Radula-Janik, Klaudia; Kupka, Teobald; Ejsmont, Krzysztof; Daszkiewicz, Zdzislaw; Sauer, Stephan P A

2013-08-06

241

Interaction of chicken liver basic fatty acid-binding protein with fatty acids: a 13C NMR and fluorescence study.  

PubMed

Two different groups of liver fatty acid-binding proteins (L-FABPs) are known: the mammalian type and the basic type. Very few members of this second group of L-FABPs have been characterized and studied, whereas most of the past studies were concerned with the mammalian type. The interactions of chicken liver basic fatty acid-binding protein (Lb-FABP) with 1-(13)C-enriched palmitic acid (PA) and oleic acid (OA) were investigated by (13)C NMR spectroscopy. Samples containing fatty acids (FA) and Lb-FABP at different molar ratios exhibited only a single carboxylate resonance corresponding to bound FA, and showed a binding stoichiometry of 1:1 both for PA and for OA. Fluorescence spectroscopy measurements yielded the same binding stoichiometry for the interaction with cis-parinaric acid [K(d) = 0.38(4) microM]. Competition studies between cis-parinaric acid and the natural ligands indicated a decreasing affinity of chicken Lb-FABP for PA, OA, and retinoic acid (RA). (13)C NMR proved that pH and ionic strength affect complex stability. The carboxyl signal intensity reversibly decreased upon lowering the pH up to 5. The pH dependence of the bound carboxyl chemical shift yielded an apparent pK(a) of 4.8. A decrease of the integrated intensity of the bound carboxylic signal in the NMR spectra was observed while increasing the chloride ion concentration up to 200 mM. This body of evidence indicates that the bound FA is completely ionized at pH 7.4, that its polar head is positioned in a solvent-accessible region, that a FA-protein strong ionic bond is not present, and that high ionic strength causes the release of the bound FA. The reported results show that, insofar as the number of bound ligands and its relative affinity for different FAs are concerned, chicken Lb-FABP is remarkably different from the mammalian liver FABPs, and, within its subfamily, that it is more similar to catfish Lb-FABP while it behaves quite differently from shark or axolotl Lb-FABPs. PMID:11601984

Beringhelli, T; Goldoni, L; Capaldi, S; Bossi, A; Perduca, M; Monaco, H L

2001-10-23

242

1H and 13C NMR spectra of 3,8-dimethoxyfuro[3,2-g]coumarin and maculine from Esenbeckia grandiflora Martius (Rutaceae).  

PubMed

One- and two-dimensional NMR experiments were used for the unambiguous assignment of the (1)H and (13)C NMR chemical shifts of the furoquinoline alkaloid maculine (1) and the new furanocoumarin 3,8-dimethoxyfuro[3,2-g]coumarin (2). PMID:16025550

Nunes, F M; Barros-Filho, B A; de Oliveira, M C F; Andrade-Neto, M; de Mattos, M C; Mafezoli, J; Pirani, J R

2005-10-01

243

Ab initio/GIAO-CCSD(T) calculated 13C-11B NMR chemical shift relationships in isoelectronic hypercoordinate carbonium and boronium as well as carbenium and borenium ions.  

PubMed

Good linear correlations between GIAO-CCSD(T) calculated (11)B NMR chemical shifts of hypercoordinate boronium 1-6b and borenium 7-9b ions and (13)C NMR chemical shifts of the corresponding isoelectronic carbonium 1-6a and carbenium 7-9a ions, respectively, were found. PMID:23656357

Rasul, Golam; Prakash, G K Surya; Olah, George A

2013-05-22

244

Complete 1H, 13C, 19F and 31P NMR data assignment of CWC-related chemicals N,N-dialkyl-P-alkyl phosphonamidic fluorides.  

PubMed

The complete multinuclear (1)H, (13)C, (31)P and (19)F NMR data of symmetrically substituted amines containing N,N-dialkyl-P-alkyl phosphonamidic fluorides are presented. Assignment was achieved, using various one-and two-dimensional NMR experiments. PMID:20225190

Sharma, Mamta; Goud, D Raghavender; Gupta, A K; Suryanarayana, M V S

2010-05-01

245

Cytosine ribose flexibility in DNA: a combined NMR 13C spin relaxation and molecular dynamics simulation study.  

PubMed

Using (13)C spin relaxation NMR in combination with molecular dynamic (MD) simulations, we characterized internal motions within double-stranded DNA on the pico- to nano-second time scale. We found that the C-H vectors in all cytosine ribose moieties within the Dickerson-Drew dodecamer (5'-CGCGAATTCGCG-3') are subject to high amplitude motions, while the other nucleotides are essentially rigid. MD simulations showed that repuckering is a likely motional model for the cytosine ribose moiety. Repuckering occurs with a time constant of around 100 ps. Knowledge of DNA dynamics will contribute to our understanding of the recognition specificity of DNA-binding proteins such as cytosine methyltransferase. PMID:18579564

Duchardt, Elke; Nilsson, Lennart; Schleucher, Jürgen

2008-06-25

246

Conformational evaluation and detailed 1H and 13C NMR assignments of flavoxate, a urinary tract antispasmodic agent.  

PubMed

1H and 13C NMR chemical shift assignments for the urinary tract antispasmodic flavoxate (1) and flavoxate hydrochloride (2) were obtained from one- and two-dimensional measurements. A Monte Carlo random search using molecular mechanics, followed by geometry optimization of each minimum energy structure employing DFT calculations at the B3LYP/6-31G* level, and a Boltzmann analysis of the total energies, provided accurate molecular models which describe the conformational behavior of flavoxate (1). The electron density surfaces for the global minimum and the second minimum conformers 1a and 1b of this L-type Ca2+ channel inhibitor were calculated. The presence of both conformers in solution was demonstrated in full agreement with 2D NOESY data and NOE difference spectroscopy. PMID:16426792

Pérez-Hernández, Nury; Morales-Ríos, Martha S; Cerda-García-Rojas, Carlos M; Joseph-Nathan, Pedro

2006-01-19

247

Exclusively heteronuclear (13) C-detected amino-acid-selective NMR experiments for the study of intrinsically disordered proteins (IDPs).  

PubMed

Carbon-13 direct-detection NMR methods have proved to be very useful for the characterization of intrinsically disordered proteins (IDPs). Here we present a suite of experiments in which amino-acid-selective editing blocks are encoded in CACON- and CANCO-type sequences to give (13) C-detected spectra containing correlations arising from a particular type or group of amino acid(s). These two general types of experiments provide the complementary intra- and inter-residue correlations necessary for sequence-specific assignment of backbone resonance frequencies. We demonstrate the capabilities of these experiments on two IDPs: fully reduced Cox17 and WIP(C) . The proposed approach constitutes an independent strategy to simplify crowded spectra as well as to perform sequence-specific assignment, thereby demonstrating its potential to study IDPs. PMID:23060071

Bermel, Wolfgang; Bertini, Ivano; Chill, Jordan; Felli, Isabella C; Haba, Noam; Kumar M V, Vasantha; Pierattelli, Roberta

2012-10-11

248

The influence of thermochemical treatments on the lignocellulosic structure of wheat straw as studied by natural abundance (13)C NMR.  

PubMed

The effects of thermochemical treatments (aquathermolysis, pyrolysis, and combinations thereof) on the lignocellulosic structure and composition of wheat straw were studied with (13)C and (1)H solid state NMR spectroscopy and proton T1? relaxation measurements. Results show that aquathermolysis removes hemicellulose, acetyl groups, and ash minerals. As a result, the susceptibility of lignocellulose to pyrolysis is reduced most likely due to the removal of catalytically active salts, although recondensation of lignin during aquathermolysis treatment can also play a role. In contrast to pyrolysis of wheat straw, pyrolysis of aquathermolysed wheat straw leaves traces of cellulose in the char as well as more intense lignin methoxy peaks. Finally, it was found that both pyrolysis chars contain aliphatic chains, which were attributed to the presence of cutin or cutin-like materials, a macromolecule that covers the aerial surface of plants, not soluble in water and seemingly stable under the pyrolysis conditions applied. PMID:23973979

Habets, S; de Wild, P J; Huijgen, W J J; van Eck, E R H

2013-07-29

249

Communication: Competition between ?...? interaction and halogen bond in solution: A combined 13C NMR and density functional theory study  

NASA Astrophysics Data System (ADS)

Competition between ?...? interaction and halogen bond in solution has been investigated by using carbon nuclear magnetic resonance spectroscopy (13C NMR) combined with density functional theory calculation. Both experimental and theoretical results clearly show that there are no C-Cl...? or C-Br...? halogen bonds and only the ?...? interactions exist in the binary liquid mixtures of C6D6 with C6F5Cl and C6F5Br, respectively. The case is totally different for the binary liquid mixtures of C6D6 with C6F5I in which the C-I...? halogen bonds not the ?...? interactions are present. The important role of entropy in the competition between ?...? interaction and halogen bond in solution was also discussed.

Zhang, Yu; Ji, Baoming; Tian, Anmin; Wang, Weizhou

2012-04-01

250

Enantiomeric differentiation of oxygenated p-menthane derivatives by 13C NMR using Yb(hfc)3.  

PubMed

The (13)C NMR behaviour of 21 p-menthanic terpene bearing an oxygenated function (alcohol, ketone, acetate) was examined in the presence of a chiral lanthanide shift reagent (Yb(hfc)(3)). For each monocyclic compound, we measured the lanthanide-induced shift (LIS) on the signals of the carbons and the splitting of signals allowing the enantiomeric differentiation. Some general features were found about their LIS behaviour: experimental data establishing distinct patterns for carvomenthone-like compounds and menthone-like compounds. The enantiomeric splitting was observed for the majority of signals in the spectrum of each compound. In the case of alcohols and acetates, the influence of the relative stereochemistry (cis vs trans) of isopropyl(ene) and the binding function was discussed. PMID:18828150

Lanfranchi, Don Antoine; Blanc, Marie-Cécile; Vellutini, Muriel; Bradesi, Pascale; Casanova, Joseph; Tomi, Félix

2008-12-01

251

The Discovery-Oriented Approach to Organic Chemistry. 1. Nitration of Unknown Organic Compounds. An Exercise in 1H NMR and 13C NMR Spectrosopy for Sophomore Organic Laboratories  

NASA Astrophysics Data System (ADS)

Nitration is one of the most fundamental reactions in organic chemistry. However, the majority of the nitration experiments found in the standard lab textbooks are of the "cookbook" variety and convey none of the excitement associated with discovery in experimental chemistry. We have developed two simple nitration experiments that present the student with a puzzle and are a good exercise in 1H NMR and 13C NMR spectroscopy. 13 C NMR spectroscopy is a powerful structure elucidation tool and yet not many examples of the use of 13C NMR spectroscopy in organic lab experiments can be found. The experiment involves nitration of unknown organic compounds and product analysis by 1H NMR and 13C NMR spectroscopy, which enables the student to determine the identity of the unknown. In spite of the simplicity of the experiment, the element of discovery ensures that student interest and enthusiasm are retained.

McElveen, Sonia R.; Gavardinas, Kostas; Stamberger, Jean A.; Mohan, Ram S.

1999-04-01

252

31P and 13C NMR spectroscopic study of wild type and multidrug resistant Ehrlich ascites tumor cells.  

PubMed

Steady-state 31P NMR spectra of wild type EHR2 Ehrlich ascites tumor cells and multidrug resistant EHR2/DNR+ cells, immobilized in agarose threads, and continuously perfused with medium, showed temperature-dependent differences in the levels of intracellular phosphate metabolites. At 37 degrees C, the EHR2/DNR+ cells contained four times more phosphocreatine (PCr) than the EHR2 cells. At 20 degrees C, the EHR2 cells contained 80% more of phosphodiesters (PDE), the levels of PCr being equal. The quantitative metabolite level data are based on T1 relaxation times data and are normalized for the protein content of the cells. Perfusion of the cells with azide, an inhibitor of mitochondrial respiration, had no effect on the ATP level, and caused no changes in glucose consumption and lactate production. Azide perfusion, combined with glucose depletion, caused rapid drop in the ATP content, which was reestablished after renewed perfusion with glucose. Similarly, perfusion with 2,4-dinitrophenol, an uncoupler of the respiration chain, had no effect on the phosphate metabolites. These results demonstrate that aerobic glycolysis is the main route by which glucose is metabolised under the conditions used (glucose concentration in medium 2 g/L). Rates of uptake and phosphorylation of 2-deoxy-D-glucose were measured by following the formation of intracellular [6-13C]2-deoxy-D-glucose-6-phosphate by 13C NMR; at 37 degrees C the observed rates for EHR2 and EHR2/DNR+ cells were equal, about 10 nmol/(min x mg protein), whereas at 20 degrees C the wild type cells produced the 6-phosphate at an approximately twice the rate found for the resistant cells [about 4 and 2 nmol/(min x mg protein), respectively].(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8260748

Rasmussen, J; Hansen, L L; Friche, E; Jaroszewski, J W

1993-01-01

253

Chemical Changes During 6 Years of Decomposition of 11 Litters in Some Canadian Forest Sites. Part 2. 13 C Abundance, Solid-State 13 C NMR Spectroscopy and the Meaning of “Lignin”  

Microsoft Academic Search

There is still a poor understanding of how changes in the organic composition of litter contribute to slowing or even cessation\\u000a of decomposition. Using 13C nuclear magnetic resonance (NMR) spectroscopy of samples from the Canadian Intersite Decomposition Experiment (CIDET), we\\u000a asked whether increasing lignin per se could account for the well-known increase in acid-unhydrolyzable residue (AUR), and secondly, using three

Caroline M. Preston; Jason R. Nault; J. A. Trofymow

2009-01-01

254

The guest ordering and dynamics in urea inclusion compounds studied by solid-state 1H and 13C MAS NMR spectroscopy  

NASA Astrophysics Data System (ADS)

Urea inclusion compounds with different guest species were studied by 13C CP MAS and 1H MAS NMR spectroscopy. It is possible to arrange the asymmetric guest species in three different ways: head-head, head-tail and tail-tail. 13C CP MAS NMR studies indicate that the preference arrangement is determined by the interaction strength of the end functional groups. 13C relaxation experiments are used to study the dynamic properties of urea inclusion compounds. 13C relaxation studies on urea inclusion compounds with n-alkane or decanoic acid show that the 13C T1 and 13C T1? values exhibit the position dependence towards the center of the chain, indicating internal chain mobility. The analysis of variable-temperature 13C T1? experiments on urea inclusion compounds with hexadecane and pentadecane, for the first time, suggests that chain fluctuations and lateral motion of n-alkane guests may contribute to the 13C T1? relaxation.

Yang, Xiaorong; Müller, Klaus

2011-12-01

255

Measurement of three-bond, 13C'-13C beta J couplings in human ubiquitin by a triple resonance, E. COSY-type NMR technique.  

PubMed

A [CO]HN(CA)CB-E.COSY pulse scheme is described for measurement of three-bond couplings, 3JC'C beta, between carbonyl and aliphatic C beta carbons in ubiquitin, uniformly enriched with 13C and 15N. A Karplus relation, 3JC'C beta = 1.28 cos2(phi - 120 degrees) -1.02 cos(phi - 120 degrees) + 0.30 Hz, is obtained by correlating the 3JC'C beta values measured for human ubiquitin with backbone phi angles from its crystal structure. As predicted, the new Karplus parametrization yields 3JC'C beta values slightly larger than previously obtained by quantitative J correlation [Hu, J.-S. and Bax, A. (1997) J. Am. Chem. Soc., 119, 6360-6368], but considerably smaller than what has been reported on the basis of other E.COSY-type measurements carried out on flavodoxin. PMID:9679294

Hu, J S; Bax, A

1998-02-01

256

In situ measurement of magnesium carbonate formation from CO2 using static high-pressure and -temperature 13C NMR.  

PubMed

We explore a new in situ NMR spectroscopy method that possesses the ability to monitor the chemical evolution of supercritical CO(2) in relevant conditions for geological CO(2) sequestration. As a model, we use the fast reaction of the mineral brucite, Mg(OH)(2), with supercritical CO(2) (88 bar) in aqueous conditions at 80 °C. The in situ conversion of CO(2) into metastable and stable carbonates is observed throughout the reaction. After more than 58 h of reaction, the sample was depressurized and analyzed using in situ Raman spectroscopy, where the laser was focused on the undisturbed products through the glass reaction tube. Postreaction, ex situ analysis was performed on the extracted and dried products using Raman spectroscopy, powder X-ray diffraction, and magic-angle spinning (1)H-decoupled (13)C NMR. These separate methods of analysis confirmed a spatial dependence of products, possibly caused by a gradient of reactant availability, pH, and/or a reaction mechanism that involves first forming hydroxy-hydrated (basic, hydrated) carbonates that convert to the end-product, anhydrous magnesite. This carbonation reaction illustrates the importance of static (unmixed) reaction systems at sequestration-like conditions. PMID:22676479

Surface, J Andrew; Skemer, Philip; Hayes, Sophia E; Conradi, Mark S

2012-06-11

257

Acetylation of raw cotton for oil spill cleanup application: an FTIR and 13C MAS NMR spectroscopic investigation  

NASA Astrophysics Data System (ADS)

Fourier transform infrared (FTIR) and 13C MAS NMR spectroscopy have been used to investigate the acetylation of raw cotton samples with acetic anhydride without solvents in the presence of different amounts of 4-dimethylaminopyridine (DMAP) catalyst. This is a continuation of our previous investigation of acetylation of commercial cotton in an effort to develop hydrophobic, biodegradable, cellulosic sorbent materials for cleaning up oil spills. The FTIR data have again provided a clear evidence for successful acetylation. The NMR results further confirm the successful acetylation. The extent of acetylation was quantitatively determined using the weight percent gain (WPG) due to acetylation and by calculating the ratio R between the intensity of the acetyl C?O stretching band at 1740-1745 cm -1 and the intensity of C?O stretching vibration of the cellulose backbone at about 1020-1040 cm -1. The FTIR technique was found to be highly sensitive and reliable for the determination of the extent of acetylation. The level of acetylation of the raw cotton samples was found to be much higher than that of cotton fabrics and the previously studied commercial cotton. The variation of the R and WPG with reaction time, amount of DMAP catalyst and different samples of raw cotton is discussed.

Adebajo, Moses O.; Frost, Ray L.

2004-08-01

258

Molecular composition of recycled organic wastes, as determined by solid-state (13)C NMR and elemental analyses.  

PubMed

Using solid state (13)C NMR data and elemental composition in a molecular mixing model, we estimated the molecular components of the organic matter in 16 recycled organic (RO) wastes representative of the major materials generated in the Sydney basin area. Close correspondence was found between the measured NMR signal intensities and those predicted by the model for all RO wastes except for poultry manure char. Molecular nature of the organic matter differed widely between the RO wastes. As a proportion of organic C, carbohydrate C ranged from 0.07 to 0.63, protein C from <0.01 to 0.66, lignin C from <0.01 to 0.31, aliphatic C from 0.09 to 0.73, carbonyl C from 0.02 to 0.23, and char C from 0 to 0.45. This method is considered preferable to techniques involving imprecise extraction methods for RO wastes. Molecular composition data has great potential as a predictor of RO waste soil carbon and nutrient outcomes. PMID:23896223

Eldridge, S M; Chen, C R; Xu, Z H; Nelson, P N; Boyd, S E; Meszaros, I; Chan, K Y

2013-07-27

259

Soil organic matter dynamics as characterized with 1H and 13C solid-state NMR techniques  

NASA Astrophysics Data System (ADS)

Soil organic matter (SOM) is a complex and heterogeneous matter. Characterization by solid-state NMR methods on 1H and 13C nuclei is therefore demanding. Our goal is to obtain information on the dynamic behaviour of soil samples and to study the influence of external parameters on both structure and dynamics. We regard water molecules to be the pivotal agent of soil dynamics by generating a network between organic matter via intermolecular hydrogen bonding, which leads to cross linking of organic matter and increases its rigidity. Although 1H solid-state NMR on non-rotating samples are not so commonly used for soil characterization, they enable the differentiation of proton mobilities via their linewidths which are resulting from differences in the dipole-dipole coupling strengths. Therefore, even weak molecular interactions such as hydrogen bonding can be differentiated and changes due to heat treatments and the short and long term behaviour followed. Though in principle a simple technique, static 1H measurements are complicated by several means, one of them is the high abundance in almost all matter including probe head material that has to be excluded for analysis. Finally, we selected 1H DEPTH [1] and Hahn-echo sequences to distinguish different mobilities in soil, mainly free moving water and water fixed in the soil matrix. After decomposition using Gaussian and Lorentzian lineshapes, the relative amounts of mobile and rigid water molecules can be obtained. By heating the samples above 100°C in sealed glass tubes, the proposed water network is destroyed and able to rebuild after cooling. This long term behaviour is studied on the course of months. Furthermore, the instant changes before and after heating are shown for a series of soil samples to characterize soils based on this water network model. To combine the information obtained on the 1H mobility with focus on water dynamics, 13C 2D WISE (wideline separation) measurements were done. This method yields 1H mobilities of carbon containing molecules, in our case the soil organic matter. On the one hand, this can be correlated with the results from the static 1H measurements and on the other hand, mobility changes before, during and after a heating event can be studied. Combining the various information from NMR together with data from DSC (differential scanning calorimetry), a better understanding and perhaps a contribution to a modern model of soil dynamics can be reached.

Jäger, Alex; Schwarz, Jette; Bertmer, Marko; Schaumann, Gabriele E.

2010-05-01

260

Determination of Oxidative Glucose Metabolism In Vivo in the Young Rat Brain Using Localized Direct-Detected 13 C NMR Spectroscopy  

Microsoft Academic Search

Determination of oxidative metabolism in the brain using in vivo 13C NMR spectroscopy (13C MRS) typically requires repeated blood sampling throughout the study to measure blood glucose concentration and fractional\\u000a enrichment (input function). However, drawing blood from small animals, such as young rats, placed deep inside the magnet\\u000a is technically difficult due to their small total blood volume. In the

Kathleen Ennis; Dinesh Kumar Deelchand; Ivan Tkac; Pierre-Gilles Henry; Raghavendra Rao

261

Insight into the Binding of Antifreeze Proteins to Ice Surfaces via 13C Spin Lattice Relaxation Solid-State NMR  

PubMed Central

The primary sequences of type I antifreeze proteins (AFPs) are Ala rich and contain three 11-residue repeat units beginning with threonine residues. Their secondary structures consist of ?-helices. Previous activity study of side-chain mutated AFPs suggests that the ice-binding side of type I AFPs comprises the Thr side chains and the conserved i + 4 and i + 8 Ala residues, where i indicates the positions of the Thrs. To find structural evidence for the AFP's ice-binding side, a variable-temperature dependent 13C spin lattice relaxation solid-state NMR experiment was carried out for two Ala side chain 13C labeled HPLC6 isoforms of the type I AFPs each frozen in H2O and D2O, respectively. The first one was labeled on the equivalent 17th and 21st Ala side chains (i + 4, 8), and the second one on the equivalent 8th, 19th, and 30th Ala side chains (i + 6). The two kinds of labels are on the opposite sides of the ?-helical AFP. A model of Ala methyl group rotation/three-site rotational jump combined with water molecular reorientation was tested to probe the interactions of the methyl groups with the proximate water molecules. Analysis of the T1 data shows that there could be 10 water molecules closely capping an i + 4 or an i + 8 methyl group within the range of van der Waals interaction, whereas the surrounding water molecules to the i + 6 methyl groups could be looser. This study suggests that the side of the ?-helical AFP comprising the i + 4 and i + 8 Ala methyl groups could interact with the ice surface in the ice/water interface.

Mao, Yougang; Ba, Yong

2006-01-01

262

13 C-detected NMR experiments for measuring chemical shifts and coupling constants in nucleic acid bases  

Microsoft Academic Search

The paper presents a set of two-dimensional experiments that utilize direct 13C detection to provide proton–carbon, carbon–carbon and carbon–nitrogen correlations in the bases of nucleic acids. The set\\u000a includes a 13C-detected proton–carbon correlation experiment for the measurement of 13C13C couplings, the CaCb experiment for correlating two quaternary carbons, the HCaCb experiment for the 13C13C correlations in cases where one of

Radovan Fiala; Vladimír Sklená?

2007-01-01

263

Specific 12C?D212C?D2S13C?HD2 Isotopomer Labeling of Methionine To Characterize Protein Dynamics by 1H and 13C NMR Relaxation Dispersion  

PubMed Central

Protein dynamics on the micro- to millisecond time scale is increasingly found to be critical for biological function, as demonstrated by numerous NMR relaxation dispersion studies. Methyl groups are excellent probes of protein interactions and dynamics because of their favorable NMR relaxation properties, which lead to sharp signals in the 1H and 13C NMR spectra. Out of the six different methyl-bearing amino acid residue types in proteins, methionine plays a special role because of its extensive side-chain flexibility and the high polarizability of the sulfur atom. Methionine is over-represented in many protein–protein recognition sites, making the methyl group of this residue type an important probe of the relationships among dynamics, interactions, and biological function. Here we present a straightforward method to label methionine residues with specific 13CHD2 methyl isotopomers against a deuterated background. The resulting protein samples yield NMR spectra with improved sensitivity due to the essentially 100% population of the desired 13CHD2 methyl isotopomer, which is ideal for 1H and 13C spin relaxation experiments to investigate protein dynamics in general and conformational exchange in particular. We demonstrate the approach by measuring 1H and 13C CPMG relaxation dispersion for the nine methionines in calcium-free calmodulin (apo-CaM). The results show that the C-terminal domain, but not the N-terminal domain, of apo-CaM undergoes fast exchange between the ground state and a high-energy state. Since target proteins are known to bind specifically to the C-terminal domain of apo-CaM, we speculate that the high-energy state might be involved in target binding through conformational selection.

2012-01-01

264

The role of solid state 13C NMR spectroscopy in studies of the nature of native celluloses.  

PubMed

Published spectroscopic observations pertaining to the crystal structure of native celluloses are reviewed for the purpose of defining our current level of understanding about crystalline polymorphism in these materials. Emphasis is placed on observations from solid state 13C nuclear magnetic resonance (NMR), which first led to the postulate that most native, semicrystalline celluloses are composites of two crystalline allomorphs, labeled Ialpha and Ibeta. Historical background is presented, highlighting the structural controversies which mainly arose because different native celluloses were used, each one representing a different mixture of allomorphs. Input from Raman, infrared (IR) and electron diffraction data is included in the discussion of our current understanding of polymorphism in native celluloses. Also noted is the input from more recently studied celluloses (e.g., Halocynthia) as well as from newer processes that convert the Ialpha to the Ibeta form. On the basis of Raman and IR observations, it is argued that the Ialpha and Ibeta allomorphs differ in hydrogen bonding patterns only and that backbone conformations are nearly identical. Also, the point is made that the absence of correlation field splittings in the Raman spectra calls into question (although it does not disprove) whether the normal two-chain-per-unit-cell, monoclinic Ibeta allomorph really possesses two equivalent chains. Considerable discussion is devoted to the allomorphic composition of cellulose crystallites in higher plants. Published methods of NMR lineshape analysis for the higher plant celluloses are reviewed and critiqued, both from the point of view of lineshape theory and from the point of view of self-consistency of inferences that are based on lineshape analyses for different carbons (particularly C1 and C4). It is concluded that higher plant celluloses most likely possess a minor amount of the Ialpha allomorph where the Ialpha/Ibeta ratio is probably less than 0.25. PMID:10903080

Atalla, R H; Vanderhart, D L

1999-10-01

265

Interactions between a humic acid and a paramagnetic cation as assessed by CPMAS 13C NMR spectroscopy  

NASA Astrophysics Data System (ADS)

Humic substances (HSs) are natural organic materials playing a very important role in environment due to their ability in interacting with organic and inorganic compounds. From the one side, HSs can reduce the toxic effects of organic and inorganic contaminants, while, from the other side, they can enhance availability of nutrients, such as cations, to living organisms including plants. For this reason it is very crucial to understand the mechanisms of the interactions between humic substances and the environmentally relevant chemical components. In the present work, we have investigated the mechanisms of interaction between a HS and iron (III) by using cross polarization magic angle spinning (CPMAS) 13C NMR spectroscopy. For that, complexes between HS and different amounts of Fe(III) were prepared. All the HS-Fe(III) complexes were analysed by variable contact time (VCT) NMR experiments in order to obtain estimations of the values of the cross-polarization time (TCH) and the proton longitudinal relaxation time in the rotating frame (T1rho(H)). Results confirmed literature findings by which carboxyl groups are the most important humic fraction endowing with the ability to chelate Fe(III). However, our results also demonstrated that direct bondages between HS and Fe(III) involve the remaining polar systems such as carbohydrates and peptides. Conversely, alkyls and aromatics appeared not to be directly bound to the paramagnetic iron (III). We also evaluated the distances between Fe(III) and the different functional groups in the HS through the analysis of the proton spin diffusion into the HS-Fe(III) complexes.

Conte, P.; van Lagen, B.

2009-04-01

266

Kinetics and {sup 13}C NMR study of oxygen incorporation into PVC- and pitch-derived materials  

SciTech Connect

The kinetics of oxygen incorporation into a PVC-derived material with pitch-like characteristics was studied by isothermal thermogravimetric analysis at temperatures ranging from 200 to 270{sup o}C. Activation energy, E{sub a}, pre-exponential factor, A, and rate constants, kT, were obtained from the weight-gain curves recorded during reactions of the material with molecular oxygen, which were analyzed following a kinetic first-order model. The numerical values obtained were E{sub a} = 100.5 kJ/mol and A = 1.6 x 1010 h{sup -1}. The extent of the oxidation at a fixed temperature was monitored by elemental analysis, and the chemical changes in the materials were followed by solid-state {sup 13}C NMR. The study was next extended to the chars obtained from three coal tar pitches with different softening points (55, 85, and 110{sup o}C). Comparisons were then established between the determined kinetic parameters and the chemical/structural aspects and compositions of each analyzed material. 23 refs., 7 figs., 3 tabs,

Gisele F. Altoe; Jair C.C. Freitas; Alfredo G. Cunha; Francisco G. Emmerich; Mark E. Smith [Universidade Federal do Esprito Santo, Vitria (Brazil). Departamento de Fsica

2009-03-15

267

Unilateral NMR, 13C CPMAS NMR spectroscopy and micro-analytical techniques for studying the materials and state of conservation of an ancient Egyptian wooden sarcophagus.  

PubMed

A multi-technique approach was employed to study a decorated Egyptian wooden sarcophagus (XXV-XXVI dynasty, Third Intermediate Period), belonging to the Museo del Vicino Oriente of the Sapienza University of Rome. Portable non-invasive unilateral NMR was applied to evaluate the conservation state of the sarcophagus. Moreover, using unilateral NMR, a non-invasive analytical protocol was established to detect the presence of organic substances on the surface and/or embedded in the wooden matrix. This protocol allowed for an educated sampling campaign aimed at further investigating the state of degradation of the wood and the presence of organic substances by (13)C cross polarization magic angle spinning (CPMAS) NMR spectroscopy. The composition of the painted layer was analysed by optical microscopy (OM), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Raman and surface enhanced (resonance) Raman spectroscopy (SERS/SERRS), infrared and GC-MS techniques, evidencing original components such as clay minerals, Egyptian green, indigo, natural gums, and also highlighting restoration pigments and alteration compounds. The identification of the wood, of great value for the reconstruction of the history of the artwork, was achieved by means of optical microscopy. PMID:20931176

Proietti, Noemi; Presciutti, Federica; Di Tullio, Valeria; Doherty, Brenda; Marinelli, Anna Maria; Provinciali, Barbara; Macchioni, Nicola; Capitani, Donatella; Miliani, Costanza

2010-10-08

268

Complete 1 H, 13 C and 15 N NMR assignments and secondary structure of the 269-residue serine protease PB92 from Bacillus alcalophilus  

Microsoft Academic Search

The 1H, 13C and 15N NMR resonances of serine protease PB92 have been assigned using 3D tripleresonance NMR techniques. With a molecular weight of 27 kDa (269 residues) this protein is one of the largest monomeric proteins assigned so far. The side-chain assignments were based mainly on 3D H(C)CH and 3D (H)CCH COSY and TOCSY experiments. The set of assignments

Rasmus H. Fogh; Dick Schipper; Rolf Boelens; Robert Kaptein

1995-01-01

269

13 C NMR analysis and gas uptake measurements of pure and mixed gas hydrates: Development of natural gas transport and storage method using gas hydrate  

Microsoft Academic Search

13C NMR spectra were obtained for pure CH4, mixed CH4+THF, and mixed CH4+Neohexane hydrates in order to identify hydrate structure and cage occupancy of guest molecules. In contrast to the pure\\u000a CH4 hydrates, the NMR spectra of the mixed CH4+THF hydrate verified that methane molecules could occupy only the small portion of 512 cages because the addition of THF, water-soluble

Yu-Taek Seo; Huen Lee

2003-01-01

270

The studies of tautomerism in 6-mercaptopurine derivatives by 1H 13C, 1H 15N NMR and 13C, 15N CPMAS-experimental and quantum chemical approach  

NASA Astrophysics Data System (ADS)

Tautomerism in 6-mercaptopurine (6mpH), 2,6-dimercaptopurine (2,6dmp) and 6-mercaptopurine-9-riboside (6mp-9rb) was studied in the solution with 2D NMR methods-1H 13C HMBC and 1H 15N HMQC. The 15N NMR signals were assigned and the distribution of mobile protons proposed on the basis of ?13C, ?15N chemical shifts and JHC, JHN coupling constants, determined with HECADE. These heterocycles appear in DMSO-d6 as the thionic species with predominance of the following tautomers: N(1)H, N(7)H for 6mpH; N(1)H, N(3)H, N(7)H for 2,6dmp; N(1)H for 6mp-9rb. Quantum-chemical NMR calculations by GIAO method(RHF/6-31G**//B3LYP/6-31G**) allowed to evaluate the ratios of N(7)H, N(9): N(7), N(9)H tautomeric forms as ca. 3:1 for 6mpH and nearly 10:0 for 2,6dmp. The 13C and 15N CPMAS spectra were measured for solid 6mpH·H2O, anhydrous 6mpH, 2,6dmp and 6-mercaptopurinium chloride (6mpH2Cl), confirming the thionic character of all compounds. The 15N chemical shifts in the solid phase were calculated (B3LYP/6 31G**) for 6mpH·H2O and 6mpH2Cl, basing on the re-determined single crystal X-ray data (optimised with RHF/3-21G**).

Pazderski, Leszek; ?akomska, Iwona; Wojtczak, Andrzej; Sz?yk, Edward; Sitkowski, Jerzy; Kozerski, Lech; Kamie?ski, Bohdan; Ko?mi?ski, Wiktor; Tousek, Jaromír; Marek, Radek

2006-03-01

271

13C-NMR determination of simultaneous xylose and glucose fermentation by a newly isolated strain (G11) of Klebsiella planticola  

Microsoft Academic Search

In vivo NMR techniques and substrates selectively enriched with 13C were used to follow the step-by-step metabolism of glucose and xylose, on their own or as mixed substrates in the ratio as they occur in hydrolysates from hemicellulose. The organism used was a newly isolated strain of Klebsiella planticola isolated from soil where maize has been cultivated for 30 years.

C. Rossi; N. Marchettini; A. Donati; D. Medaglini; M. Valassina; S. Bastianoni; E. Cresta

1995-01-01

272

Condensation degree of burnt peat and plant residues and the reliability of solid-state VACP MAS 13C NMR spectra obtained from pyrogenic humic material  

Microsoft Academic Search

Charred organic matter is assumed to contain heavily condensed polycyclic aromatic domains with a considerable proportion of core carbons. To examine their possible underestimation using variable amplitude (VA) cross polarization (CP) magic angle spinning (MAS) 13C nuclear magnetic resonance (NMR), the condensation degree of a peat subjected to thermal oxidation at 350°C for up to 180s was examined by means

Heike Knicker; Kai Uwe Totsche; Gonzalo Almendros; Francisco J. González-Vila

2005-01-01

273

A 13C CP\\/MAS NMR evaluation of the structural changes in wheat straw subjected to different chemical and biological pulping conditions  

Microsoft Academic Search

Wheat straw pulps prepared by chemical (soda) and biological (enzymatic or fungal) treatments were analyzed by 13C CP\\/MAS NMR spectrometry under quantitative acquisition conditions. The most significant changes reflected in the spectra as a result of soda cooking correspond to: (i) decrease of methoxyl content of the residual lignin (56, 153, 147 and 135 ppm), and (ii) deacetylation of hemicellulose

M. E. Guadalix; G. Almendros; A. T. Martínez; F. J. González-Vila; U. Lankes

1997-01-01

274

A Discovery-Based Hydrochlorination of Carvone Utilizing a Guided-Inquiry Approach to Determine the Product Structure from [superscript 13]C NMR Spectra  

ERIC Educational Resources Information Center

This experiment describes a discovery-based method for the regio- and stereoselective hydrochlorination of carvone, appropriate for a 3-h second-semester organic chemistry laboratory. The product is identified through interpretation of the [superscript 13]C NMR and DEPT spectra are obtained on an Anasazi EFT-60 at 15 MHz as neat samples. A…

Pelter, Michael W.; Walker, Natalie M.

2012-01-01

275

1 H, 13 C and 15 N NMR backbone assignments of the 269-residue serine protease PB92 from Bacillus alcalophilus  

Microsoft Academic Search

The 1H, 13C and 15N NMR resonances of the backbone of serine protease PB92 have been assigned. This 269-residue protein is one of the largest monomeric proteins assigned so far. The amount and quality of information available suggest that even larger proteins could be assigned with present methods. Measured chemical shifts show excellent agreement with the secondary structure.

Rasmus H. Fogh; Dick Schipper; Rolf Boelens; Robert Kaptein

1994-01-01

276

A Discovery-Based Hydrochlorination of Carvone Utilizing a Guided-Inquiry Approach to Determine the Product Structure from [superscript 13]C NMR Spectra  

ERIC Educational Resources Information Center

|This experiment describes a discovery-based method for the regio- and stereoselective hydrochlorination of carvone, appropriate for a 3-h second-semester organic chemistry laboratory. The product is identified through interpretation of the [superscript 13]C NMR and DEPT spectra are obtained on an Anasazi EFT-60 at 15 MHz as neat samples. A…

Pelter, Michael W.; Walker, Natalie M.

2012-01-01

277

High-resolution solid-state {sup 13}C and {sup 15}N NMR spectroscopy of pyrazole and 3,5-dimethylpyrazole adsorbed on alumina and silica  

SciTech Connect

Using pyrazole and 3,5-dimethylpyrazole mixtures with alumina and silica, high-resolution solid state {sup 13}C and {sup 15}N CPMAS NMR was performed to compare the spectra. The NH-N proton tautomers resulting depend strongly on the environment. 70 refs., 8 figs., 4 tabs.

Aguilar-Parrilla, F.; Limbach, H.H. [Ciudad Universitaria, Madrid (Spain); Claramunt, R.M. [Instituto de Quimica Medica, Madrid (Spain)] [and others

1994-09-01

278

Organic matter transformations in lignocellulosic waste products composted or vermicomposted ( eisenia fetida andrei): Chemical analysis and 13C CPMAS NMR spectroscopy  

Microsoft Academic Search

Lignocellulosic wastes (of maple) were composted and vermicomposted for 10 months under controlled conditions. Chemical and 13C CPMAS NMR spectroscopic analyses were made to characterize the transformations of the organic matter. At first, the total organic matter and carbon mass underwent a relatively rapid decrease. There was a concomitant decomposition of polysaccharides including cellulose. The degradation of aromatic structures and

M. Vinceslas-Akpa; M. Loquet

1997-01-01

279

FT-RAMAN AND 13C CP-MAS NMR SPECTROSCOPIC ASSESSMENT OF CONFORMATIONAL CHANGES IN PROTEIN AND STARCH UNDER VARIOUS PARABOILING CONDITIONS FOR RICE  

Technology Transfer Automated Retrieval System (TEKTRAN)

FT-Raman and solid-state 13C CP-MAS NMR spectroscopies were employed to assess the conformational changes to protein and starch in rice under variable conditions of parboiling. TOX 3108 rice from Ghana, was parboiled by the soaking-steaming-drying method under conditions that mimicked various local...

280

Structural Description of Humic Substances from Subtropical Coastal Environments using Elemental Analysis, FT-IR and 13C-Solid State NMR Data  

Microsoft Academic Search

SIERRA, M.M.D.; GIOVANELA, M.; PARLANTI, E.; ESTEVES, V.I.; DUARTE, A.C.; FRANSOZO, A., and SORIANO-SIERRA, E.J., 2004. Structural description of humic substances from subtropical coastal environments using elemental analysis, FT-IR and 13 C-solid state NMR

M. M. D. Sierra; M. Giovanela; E. Parlanti; V. I. Esteves; A. C. Duarte; A. Fransozo; E. J. Soriano-Sierra

2004-01-01

281

The nature of fullerene solution collisional dynamics. A 13C DNP and NMR study of the C 60/C 6D 6/TEMPO system  

NASA Astrophysics Data System (ADS)

The solution dynamical behavior of the novel fullerene, C 60 and free radical nitroxide, TEMPO in deuterated benzene (C 6D 6) was examined utilizing a flow liquid—liquid intermolecular transfer (L 2IT) 13C dynamic nuclear polarization (DNP) technique. The 13C DNP ultimate enhancement, 13C NMR paramagnetic contact shift, and corresponding spin—lattice nuclear relaxation rates are consistent with a model for the C 6o/TEMPO nuclear—electron interaction which is dominated by a rotationally driven dipolar relaxation mechanism. A dipolar dominated enhancement was also observed for a solid—liquid intermolecular transfer (SLIT) 13C DNP experiment employing the C 60/C 6D 6 system with polarization transfer from a silica phase immobilized nitroxide (SPIN) sample.

Dorn, H. C.; Gu, J.; Bethune, D. S.; Johnson, R. D.; Yannoni, C. S.

1993-03-01

282

Soil organic degradation: bridging the gap between Rock-Eval pyrolysis and chemical characterization (CPMAS 13C NMR)  

NASA Astrophysics Data System (ADS)

Being a source of mineral nutrients, organic matter contributes to soil chemical fertility and acts on soil physical fertility through its role in soil structure. Soil organic matter (SOM) is a key component of soils. Despite the paramount importance of SOM, information on its chemistry and behaviour in soils is incomplete. Numerous methods are used to characterize and monitor OM dynamics in soils using different approaches (Kogel-Knabner, 2000). Two of the main approaches are evaluated and compared in this study. Rock-Eval pyrolysis (RE pyrolysis) provides a description of a SOM's general evolution using its thermal resistance. The second tool (13C CPMAS NMR) aims to give precise and accurate chemical information on OM characterization. The RE pyrolysis technique was designed for petroleum exploration (Lafargue et al., 1998) and because of its simplicity, it has been applied to a variety of other materials such as soils or Recent sediments (Disnar et al., 2000; Sebag, 2006). Recently, RE pyrolysis became a conventional tool to study OM dynamics in soils. In RE pyrolysis, a peak deconvolution is applied to the pyrolysis signal in order to get four main components related to major classes of organic constituents. These components differ in origin and resistance to pyrolysis: labile biological constituents (F1), resistant biological constituents (F2), immature non-biotic constituents (F3) and a mature refractory fraction (F4) (Sebag, 2006; Coppard, 2006). Main advantages of the technique are its repeatability, and rapidity to provide an overview of OM properties and stocks. However, do the four major classes used in the literature reflect a pertinent chemical counterpart? To answer this question, we used 13C Nuclear Magnetic Resonance Spectroscopy in the solid state (13C CPMAS NMR) to collect direct information on structural and conformational characteristics of OM. NMR resonances were assigned to chemical structures according to five dominant forms: alkyl C, O-alkyl C, aromatic C and phenolic C and carbonyl-carboxyl C. Moreover, in order to avoid the influence of pedogenesis, we decided to use "less complex OM", i.e. compost samples. The choice to use compost samples has been dictated by the fact that i) composting processes are well described and referenced in the literature, and ii) these samples have already been studied previously (Albrecht, 2009). Significantly high correlations are observed between classes, or indices, from RE pyrolysis and main classes of organic matter detected by NMR e.g. F1 and labile / easily degradable components (alkyl C et O-alkyl C); F3/F4 and humified OM (aromatic C and phenolic C); R index (contributions of bio-macromolecules) and phenolic and aromatic C; I index (related to immature OM) and labile / easily degradable components (alkyl C et O-alkyl C). This work confirms the interest of RE pyrolysis in soil science (notably by using the R/I index ratio). Compost was an ideal model with a clear chronological evolution of organic matter. The next step consists of using more complex samples such as bulk soil samples. REFERENCES Albrecht, R., Joffre, R., Le Petit, J., Terrom, G., Périssol, C. 2009. Calibration of Chemical and Biological Changes in Cocomposting of Biowastes Using Near-Infrared Spectroscopy. Environmental Science & Technology, 43(3), 804-811. Copard, Y., Di-Govanni, C., Martaud, T., Alberic, P., Olivier, J.E. 2006. Using Rock-Eval 6 pyrolysis for tracking fossil organic carbon in modern environments: implications for the roles of erosion and weathering. Earth Surface Processes and Landforms, 31(2), 135-153. Disnar, J.R., Guillet, B., Keravis, D., Di-Giovanni, C., Sebag, D. 2003. Soil organic matter (SOM) characterization by Rock-Eval pyrolysis: scope and limitations. Organic Geochemistry, 34(3), 327-343. Kogel-Knabner, I. 2000. Analytical approaches for characterizing soil organic matter. Organic Geochemistry, 31(7-8), 609-625. Lafargue, E., Marquis, F., Pillot, D. 1998. Rock-Eval 6 applications in hydrocarbon exploration, production, and soil contamination studi

Albrecht, Remy; Sebag, David; Verrecchia, Eric

2013-04-01

283

Pronounced stereospecificity of (1)H, (13)C, (15)N and (77)Se shielding constants in the selenophenyl oximes as shown by NMR spectroscopy and GIAO calculations.  

PubMed

In the (1)H and (13)C NMR spectra of 1-(2-selenophenyl)-1-alkanone oximes, the (1)H, the (13)C-3 and (13)C-5 signals of the selenophene ring are shifted by 0.1-0.4, 2.5-3.0 and 5.5-6.0 ppm, respectively, to higher frequencies, whereas those of the (13)C-1, (13)C-2 and (13)C-4 carbons are shifted by 4-5, approximately 11 and approximately 1.7 ppm to lower frequencies on going from the E to Z isomer. The (15)N chemical shift of the oximic nitrogen is larger by 13-16 ppm in the E isomer relative to the Z isomer. An extraordinarily large difference (above 90 ppm) between the (77)Se resonance positions is revealed in the studied oxime isomers, the (77)Se peak being shifted to higher frequencies in the Z isomer. The trends in the changes of the measured chemical shifts are well reproduced by the GIAO calculations of the (1)H, (13)C, (15)N and (77)Se shielding constants in the energy-favorable conformation with the syn orientation of the-C=N-O-H group relative to the selenophene ring. PMID:19582802

Afonin, Andrei V; Pavlov, Dmitry V; Ushakov, Igor A; Schmidt, Elena Yu; Mikhaleva, Al'bina I

2009-10-01

284

Tracing bacterial metabolism using multi-nuclear (1H, 2H, and 13C) Solid State NMR: Realizing an Idea Initiated by James Scott  

NASA Astrophysics Data System (ADS)

Approximately 6 years ago, while at the Geophysical Laboratory, James Scott became interested in the application of Solid State Nuclear Magnetic Resonance Spectroscopy to study bacterial metabolism. As often happens, other experiments intervened and the NMR experiments were not pursued. We have revisited Jame's question and find that using a multi-nuclear approach (1H, 2H, and 13C Solid State NMR) on laboratory cell culture has some distinct advantages. Our experiments involved batch cultures of E. coli (MG1655) harvested at stationary phase. In all experiments the growth medium consisted of MOPS medium for enterobacteria, where the substrate is glucose. In one set of experiments, 10 % of the water was D2O; in another 10 % of the glucose was per-deuterated. The control experiment used both water and glucose at natural isotopic abundance. A kill control of dead E. coli immersed in pure D2O for an extended period exhibited no deuterium incorporation. In both deuterium enriched experiments, considerable incorporation of deuterium into E. coli's biomolecular constituents was detected via 2H Solid State NMR. In the case of the D2O enriched experiment, 58 % of the incorporated deuterium is observed in a sharp peak at a frequency of 0.31 ppm, consistent with D incorporation in the cell membrane lipids, the remainder is observed in a broad peak at a higher frequency (centered at 5.4 ppm, but spanning out to beyond 10 ppm) that is consistent with D incorporation into predominantly DNA and RNA. In the case of the D-glucose experiments, 61 % of the deuterium is observed in a sharp resonance peak at 0.34 ppm, also consistent with D incorporation into membrane lipids, the remainder of the D is observed at a broad resonance peak centered at 4.3 ppm, consistent with D enrichment in glycogen. Deuterium abundance in the E. coli cells grown in 10 % D2O is nearly 2X greater than that grown with 10 % D-glucose. Very subtle differences are observed in both the 1H and 13C solid-state NMR experiments, most notably in the spectral region corresponding to glycogen H and C, respectively. Interestingly, whereas in both experiments the predominant site of incorporation was in the membrane lipids, the line width of the aliphatic-D resonance in the D2O enriched experiment is 67 % wider than that observed in the D-glucose enriched experiment. This difference could be due to greater residual 1H-2H dipolar coupling in membrane lipids synthesized with 10 % D2O due to D being incorporated during NADP(D) reduction of the fatty acid precursor during synthesis and the H-glucose being the source of carbon and hydrogen starting with acetyl-CoA. In the case of the D-glucose experiment, the narrower absorption line may be consistent with individual FA's being more homogeneously deuterated. Analysis of the membrane lipids is currently being performed via GCMS in order to gain potentially more insight to guide interpretation of the 2H solid state NMR spectra.

Cody, G.; Fogel, M. L.; Jin, K.; Griffen, P.; Steele, A.; Wang, Y.

2011-12-01

285

Interaction between a recombinant prion protein and organo-mineral complexes as evidenced by CPMAS 13C-NMR  

NASA Astrophysics Data System (ADS)

Prion proteins (PrP) are the main responsible for Transmissible Spongiform Encephalopathies (TSE). The TSE etiological agent is a misfolded form of the normal cellular prion protein. The amyloidal aggregates accumulated in the brain of infected animals and mainly composed of PrPSc exhibit resistance to protease attack and many conventional inactivating procedures. The prion protein diseases cause an environmental issue because the environment and in particular the soil compartment can be contaminated and then become a potential reservoir and diffuser of TSEs infectivity as a consequence of (i) accidental dispersion from storage plants of meat and bone meal, (ii) incorporation of contaminated material in fertilizers, (iii) possible natural contamination of pasture soils by grazing herds, and (v) burial of carcasses. The environmental problem can be even more relevant because very low amounts of PrPSc are able to propagate the disease. Several studies evidenced that infectious prion protein remains active in soils for years. Contaminated soils result, thus, a possible critical route of TSE transmission in wild animals. Soil can also protect prion protein toward degradation processes due to the presence of humic substances and inorganic components such as clays. Mineral and organic colloids and the more common association between clay minerals and humic substances can contribute to the adsorption/entrapment of molecules and macromolecules. The polymerization of organic monomeric humic precursors occurring in soil in the presence of oxidative enzymes or manganese and iron oxides, is considered one of the most important processes contributing to the formation of humic substances. The process is very fast and produces a population of polymeric products of different molecular structures, sizes, shapes and complexity. Other molecules and possibly biomacromolecules such as proteins may be involved. The aim of the present work was to study by CPMAS 13C-NMR the interactions between a non pathogenic ovine recombinant prion protein and a model soil system represented by a manganese oxide in the form of birnessite (?-MnO2), coated with a polymerized catechol. To better understand the effect of the polymerization process, PrP was added to the birnessite-cathecol system either before or after the polymerization processes. The NMR spectra of the prion protein interacting directly with birnessite revealed disappearance of the signals due to the paramagnetic nature of manganese oxide or abiotic degradation. Conversely, the signal pattern of the protein re-appeared as it is mixed to the soil-like system either during or after the catechol polymerization process. Results suggested that the possible interactions of the prion protein on soil systems can be mediated by natural organic matter. However, deeper studies on more complex real soil systems are needed to definitely confirm such hypothesis.

Russo, F.; Scotti, R.; Gianfreda, L.; Conte, P.; Rao, M. A.

2009-04-01

286

Alkaline Hydrolysis/Polymerization of 2,4,6-Trinitrotoluene: Characterization of Products by 13C and 15N NMR  

USGS Publications Warehouse

Alkaline hydrolysis has been investigated as a nonbiological procedure for the destruction of 2,4,6-trinitrotoluene (TNT) in explosives contaminated soils and munitions scrap. Nucleophilic substitutions of the nitro and methyl groups of TNT by hydroxide ion are the initial steps in the alkaline degradation of TNT. Potential applications of the technique include both in situ surface liming and ex situ alkaline treatment of contaminated soils. A number of laboratory studies have reported the formation of an uncharacterized polymeric material upon prolonged treatment of TNT in base. As part of an overall assessment of alkaline hydrolysis as a remediation technique, and to gain a better understanding of the chemical reactions underlying the hydrolysis/polymerization process, the soluble and precipitate fractions of polymeric material produced from the calcium hydroxide hydrolysis of unlabeled and 15N-labeled TNT were analyzed by elemental analysis and 13C and 15N nuclear magnetic resonance spectroscopy. Spectra indicated that reactions leading to polymerization included nucleophilic displacement of nitro groups by hydroxide ion, formation of ketone, carboxyl, alcohol, ether, and other aliphatic carbons, conversion of methyl groups to diphenyl methylene carbons, and recondensation of aromatic amines and reduced forms of nitrite, including ammonia and possibly hydroxylamine, into the polymer. Compared to the distribution of carbons in TNT as 14% sp 3- and 86% sp2-hybridized, the precipitate fraction from hydrolysis of unlabeled TNT contained 33% sp3- and 67% sp 2-hybridized carbons. The concentration of nitrogen in the precipitate was 64% of that in TNT. The 15N NMR spectra showed that, in addition to residual nitro groups, forms of nitrogen present in the filtrate and precipitate fractions include aminohydroquinone, primary amide, indole, imine, and azoxy, among others. Unreacted nitrite was recovered in the filtrate fraction. The toxicities and susceptibilities to microbial or chemical degradation of the polymeric materials remain unknown.

Thorn, K. A.; Thorne, P. G.; Cox, L. G.

2004-01-01

287

13C NMR longitudinal relaxation time studies of a molecular tweezers derived from a calixarene-porphyrin conjugate.  

PubMed

Zn(II)porphyrin-substituted calix[4]arene 1 serves as molecular tweezers for 1,4-diazabicyclo[2.2.2] octane (DABCO) selectively, which led to the formation of Ensemble I. The molecular segments composing the calixarene cavity change upon inclusion of DABCO as Ensemble I were evaluated through (13)C NMR longitudinal relaxation times (T(1)) for the first time. As for Ensemble I, the 1:1 complex should be formed. The T(1) values for Ensemble I are generally smaller than those for 1: in CDCl(2)CDCl(2), DT1 = 5.03 s for C-1, 5.31 s for C-2, 0.13 s for C-3, 0.7 s for C-4, and 0.16 s for C-5. This substantiates that the rings of Ensemble I are firmly freezed because of the two-point coordination by DABCO. In 1, the T1 values for C-3 are always greater than those for C-4, and the difference between C-3 and C-4 is slight. As for Ensemble I, on the other hand, the difference between C-3 and C-4 is large. We can suggest two different motions for phenol units in 1 and Ensemble I: a rotational motion around a C-1 to C-4 axis (A) and a seesaw motion around a C-2 to C-2' axis (B). The data indicate that in Ensemble I motion (A) is predominant over motion (B). This indicates that motion (B) is specifically suppressed because of the two-point coordination interactions in Ensemble I. PMID:17898477

Arimura, Takashi; Nishioka, Takuya; Suga, Yasuhiro; Kumamoto, Satoshi; Tsuchiya, Youichi; Yamaguchi, Tomohiko; Tachiya, Masanori

2007-01-01

288

Dynamics and orientation of transmembrane peptide from bacteriorhodopsin incorporated into lipid bilayer as revealed by solid state (31)P and (13)C NMR spectroscopy.  

PubMed

13C and (31)P NMR spectra of a transmembrane peptide, [1-(13)C]Ala(14)-labeled A(6-34), of bacteriorhodopsin incorporated into dimyristoylphosphatidylcholine (DMPC) bilayer were recorded to clarify its dynamics and orientation in the lipid bilayer. This peptide is shown to take an alpha-helical form both in liquid crystalline and gel phases, as viewed from the conformation dependent (13)C chemical shifts. In addition, this peptide undergoes rapid rigid-body rotation about the helical axis at ambient temperature as viewed from the axially symmetric (13)C chemical shift anisotropy, whereas this symmetric anisotropy is changed to an asymmetric pattern at temperatures below 10 degrees C. We further incorporated the peptide into the spontaneously aligned DMPC bilayer to applied magnetic field, induced by dynorphin (dynorphin:DMPC =1:10), a heptadeca-opioid peptide with very high affinity to opioid receptor, in order to gain insight into its orientation in the bilayer. This magnetically aligned system turned out to be persistent even at 0 degrees C as viewed from (31)P NMR spectra of the lipid bilayer, after this peptide was incorporated into this system [A(6-34): dynorphin: DMPC = 4:10:100]. It was found from the (13)C NMR spectra of [1-(13)C]Ala(14) A(6-34) that the helical axis of A(6-34) is oriented parallel to the bilayer normal irrespective of the presence or absence of reorientation motion about the helical axis at a temperature above the lowered gel to liquid crystalline phase transition. PMID:11787000

Kimura, Shigeki; Naito, Akira; Tuzi, Satoru; Saitô, Hazime

2002-02-01

289

Field-cycling NMR investigations of (13)C-(1)H cross-relaxation and cross-polarisation: the nuclear solid effect and dynamic nuclear polarisation.  

PubMed

A field-cycling NMR investigation of (1)H-(13)C polarisation transfer using cross-relaxation and the nuclear solid effect (NSE) is described. Dynamic nuclear polarisation (DNP) of the (13)C spins is observed when forbidden transitions are driven by r.f. irradiation at the sum and difference Larmor frequencies of the two nuclei. When the (1)H spins are pre-polarised, a significant transfer of polarisation to the (13)C nuclei is achieved in a time short compared with the spin-lattice relaxation time of (13)C. The cross-polarisation arising from the NSE is studied as a function of B-field and time. These results are compared with the solutions of the differential equations that govern the coupled system of (1)H-(13)C spins. The effects of cross-relaxation are incorporated into the model for the first time and good agreement between theory and experiment is obtained. The experiments have been conducted at 20K on a (13)C-enriched sample of benzoic acid. PMID:18539011

Noble, D L; Frantsuzov, I; Horsewill, A J

2008-05-03

290

A 13C solid-state NMR investigation of the alkynyl carbon chemical shift tensors for 2-butyne-1,4-diol.  

PubMed

The alkynyl carbon chemical shift (CS) tensors for 2-butyne-1,4-diol are reported, based on analyses of the carbon-13 NMR spectra of stationary-powder and slow magic-angle spinning (MAS) samples for which the alkynyl carbon nuclei are enriched in 13C. NMR spectra of slow MAS samples exhibit spinning-frequency-dependent fine structure typical of crystallographically equivalent but magnetically distinct nuclei. Simulated spectra of slow MAS samples of this two-spin system are particularly sensitive to the relative orientations of the CS tensors. In addition, the value of 1J(13C, 13C), +175 +/- 10 Hz, is determined by examination of the total NMR lineshape of slow MAS samples. The CS tensors are almost axially symmetric, delta11 = 158.9 +/- 1.0 ppm and delta22 = 155.7 +/- 1.0 ppm; the direction of greatest shielding is approximately along the alkynyl C-C bond, delta33 = -57.8 +/- 2.0 ppm. Both the magnitudes of the principal components of the CS tensors and their orientations are in agreement with those predicted from first-principles calculations at the HF and MP2 levels of theory. This study demonstrates the importance of examining the NMR spectra of homonuclear two-spin systems with and without MAS under a variety of conditions (e.g., two or more applied magnetic fields and slow MAS). PMID:11949820

Bernard, Guy M; Wasylishen, Roderick E

291

Towards hyperpolarized 13C-succinate imaging of brain cancer  

NASA Astrophysics Data System (ADS)

We describe a novel 13C enriched precursor molecule, sodium 1-13C acetylenedicarboxylate, which after hydrogenation by PASADENA (Parahydrogen and Synthesis Allows Dramatically Enhanced Nuclear Alignment) under controlled experimental conditions, becomes hyperpolarized 13C sodium succinate. Fast in vivo 3D FIESTA MR imaging demonstrated that, following carotid arterial injection, the hyperpolarized 13C-succinate appeared in the head and cerebral circulation of normal and tumor-bearing rats. At this time, no in vivo hyperpolarized signal has been localized to normal brain or brain tumor. On the other hand, ex vivo samples of brain harvested from rats bearing a 9L brain tumor, 1 h or more following in vivo carotid injection of hyperpolarized 13C sodium succinate, contained significant concentrations of the injected substrate, 13C sodium succinate, together with 13C maleate and succinate metabolites 1-13C-glutamate, 5-13C-glutamate, 1-13C-glutamine and 5-13C-glutamine. The 13C substrates and products were below the limits of NMR detection in ex vivo samples of normal brain consistent with an intact blood brain barrier. These ex vivo results indicate that hyperpolarized 13C sodium succinate may become a useful tool for rapid in vivo identification of brain tumors, providing novel biomarkers in 13C MR spectral-spatial images.

Bhattacharya, Pratip; Chekmenev, Eduard Y.; Perman, William H.; Harris, Kent C.; Lin, Alexander P.; Norton, Valerie A.; Tan, Chou T.; Ross, Brian D.; Weitekamp, Daniel P.

2007-05-01

292

Improved ^13C Natural-abundance Correction Methods in REDOR NMR Distance Measurements used for Restrained Molecular Dynamics of Shikimate-3-Phosphate and Glyphosate  

NASA Astrophysics Data System (ADS)

The 1.1translation of rotational-echo double-resonance (REDOR) NMR data into dipolar couplings when ^31P or ^19F is observed. An equation for calculating dipolar couplings to specific ^13C labels in the presence of substantial natural-abundance ^13C background dephasing was derived. The equation results were compared to a calculation of REDOR dephasing that assumed a model lattice containing a central ^31P and 64 possible carbon sites. A single lattice was used to fit all data for four differently labeled protein complexes. Thus, ^31P-^13C dipolar couplings were obtained and translated into internuclear distances for complexes of 5-enolpyruvyl-shikimate-3- phosphate synthase (EPSPS), shikimate-3-phosphate (S3P), and glyphosate (Glp). Restrained molecular dynamics simulations of S3P and Glp compared to unrestrained simulations of the EPSPS tetrahedral intermediate and its phosphonate analog show that Glp is unlikely to act as an intermediate or transition state analog.

McDowell, L. M.; Klug, C. A.; Beusen, D. D.; Schaefer, J.

1996-03-01

293

13C-NMR study of glucose and pyruvate catabolism in four acetogenic species isolated from the human colon  

Microsoft Academic Search

Glucose fermentation by four acetogenic species (two Clostridium strains, one Streptococcus strain and Ruminococcus hydrogenotrophicus) isolated from the human colon was of a mixed-acid type, whereas pyruvate metabolism was characterised by homoacetogenesis. Acetate formation from [1-13C] and [2-13C]glucose was consistent with the formation of acetyl-SCoA from pyruvate generated by the Embden-Meyerhof-Parnas pathway. Labelling of lactate and ethanol demonstrated that these

Marion Leclerc; Annick Bernalier; Marielle Lelait; Jean-Philippe Grivet

1997-01-01

294

Metabolism of [U-13C5] glutamine in cultured astrocytes studied by NMR spectroscopy: first evidence of astrocytic pyruvate recycling.  

PubMed

Metabolism of [U-13C5]glutamine was studied in primary cultures of cerebral cortical astrocytes in the presence or absence of extracellular glutamate. Perchloric acid extracts of the cells as well as redissolved lyophilized media were subjected to nuclear magnetic resonance and mass spectrometry to identify 13C-labeled metabolites. Label from glutamine was found in glutamate and to a lesser extent in lactate and alanine. In the presence of unlabeled glutamate, label was also observed in aspartate. It could be clearly demonstrated that some [U-13C5]glutamine is metabolized through the tricarboxylic acid cycle, although to a much smaller extent than previously shown for [U-13C5]glutamate. Lactate formation from tricarboxylic acid cycle intermediates has previously been demonstrated. It has, however, not been demonstrated that pyruvate, formed from glutamate or glutamine, may reenter the tricarboxylic acid cycle after conversion to acetyl-CoA. The present work demonstrates that this pathway is active, because [4,5-13C2]glutamate was observed in astrocytes incubated with [U-13C5]-glutamine in the additional presence of unlabeled glutamate. Furthermore, using mass spectrometry, mono-labeled alanine, glutamate, and glutamine were detected. This isotopomer could be derived via the action of pyruvate carboxylase using 13CO2 produced within the mitochondria or from labeled intermediates that had stayed in the tricarboxylic acid cycle for more than one turn. PMID:8931491

Sonnewald, U; Westergaard, N; Jones, P; Taylor, A; Bachelard, H S; Schousboe, A

1996-12-01

295

Solid-state [sup 13]C NMR studies of ionic surfactants adsorbed on C-18 and C-8 silicas: Implications for micellar liquid chromatography  

SciTech Connect

Solid-state [sup 13]C NMR spectroscopy techniques, including cross polarization (CP), magic angle spinning (MAS), and high-power proton decoupling, have been used to study the interactions of two ionic surfactants with octadecylsilica (C-18) and octylsilica (C-8) HPLC stationary phases. The two surfactants, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), are commonly used in micellar reversed-phase liquid chromatography (RPLC). Variable contact time CP/MAS [sup 13] C NMR data suggest that differences in selectivity between SDS and CTAB micellar RPLC are due to the differing nature of the SDS and CTAB-bonded phase association. For CTAB the association leads to a more hydrophobic bulk stationary phase, whereas SDS adsorption results in the formation of an anionic, hydrophilic surface layer. These results suggest that proper matching of surfactant monomer and bonded stationary phase is critical to ensure selective separations in micellar RPLC.

Lavine, B.K.; Hendayana, S.; Han, J.H.; Tetreault, J. (Clarkson Univ., Potsdam, NY (United States). Dept. of Chemistry); Cooper, W.T. III; He, Y. (Florida State Univ., Tallahassee, FL (United States). Dept. of Chemistry)

1994-07-01

296

Mechanism of formation of humus coatings on mineral surfaces 3. Composition of adsorbed organic acids from compost leachate on alumina by solid-state 13C NMR  

USGS Publications Warehouse

The adsorption of compost leachate DOC on alumina is used as a model for elucidation of the mechanism of formation of natural organic coatings on hydrous metal oxide surfaces in soils and sediments. Compost leachate DOC is composed mainly of organic acid molecules. The solid-state 13C NMR spectra of these organic acids indicate that they are very similar in composition to aquatic humic substances. Changes in the solid-state 13C NMR spectra of compost leachate DOC fractions adsorbed on alumina indicate that the DOC molecules are most likely adsorbed on metal oxide surfaces through a combination of polar and hydrophobic interaction mechanisms. This combination of polar and hydrophobic mechanism leads to the formation of bilayer coatings of the leachate molecules on the oxide surfaces.

Wershaw, R. L.; Llaguno, E. C.; Leenheer, J. A.

1996-01-01

297

Synthesis, NMR spectroscopic characterization and structure of a divinyldisilazane-(triphenylphosphine)platinum(0) complex: observation of isotope-induced chemical shifts (1)?(12/13)C((195)Pt).  

PubMed

Tetramethyldivinyldisilazane-(triphenylphosphine)platinum(0) was prepared, characterized in solid state by X-ray crystallography and in solution by multinuclear magnetic resonance spectroscopy ((1)H, (13)C, (15)N, (29)Si, (31)P and (195)Pt NMR). Numerous signs of spin-spin coupling constants were determined by two-dimensional heteronuclear shift correlations (HETCOR) and two-dimensional (1)H/(1)H COSY experiments. Isotope-induced chemical shifts (1)?(12/13)C((195)Pt) were measured from (195)Pt NMR spectra of the title compound as well as of other Pt(0), Pt(II) and Pt(IV) compounds for comparison. In contrast to other heavy nuclei such as (199)Hg or (207)Pb, the "normal" shifts of the heavy isotopomers to low frequencies are found, covering a range of >500 ppb. PMID:23483657

Wrackmeyer, Bernd; Klimkina, Elena V; Schmalz, Thomas; Milius, Wolfgang

2013-03-11

298

Combined analysis by GC (RI), GC-MS and 13C NMR of the supercritical fluid extract of Abies alba twigs.  

PubMed

Two samples (leaves and twigs) of Abies alba Miller from Corsica were extracted using supercritical CO2 and their chemical compositions were compared with those of the essential oils obtained from the same batch of plant material. In total 45 components were identified using combined analysis by GC (RI), GC-MS and 13C NMR. It was observed that the contents of monoterpenes (mainly represented by limonene, alpha-pinene and camphene) were significantly lower in the supercritical fluid extract (SFE) than in the essential oil (EO). Conversely, the proportions of sesquiterpenes were much higher in CO2 extracts than in essential oils (around 30% vs 4%). Cis-abienol, a diterpene alcohol, was identified only in SFE, and the proportions of this constituent (7.5% and 17.3%) were determined using quantitative 13C NMR since it was under estimated using the standard conditions of GC. PMID:21299139

Duquesnoy, Emilie; Marongiu, Bruno; Castola, Vincent; Piras, Alessandra; Porcedda, Silvia; Casanova, Joseph

2010-12-01

299

High resolution 13C-solid state NMR of bacteriorhodopsin: assignment of specific aspartic acids and structural implications of single site mutations.  

PubMed

Three mutant strains of Halobacterium sp. GRB with the site of mutation in the bacterioopsin gene (PM 326: Asp96----Asn; PM 374: Asp96----Gly; PM 384: Asp85----Glu) were grown in a synthetic medium containing (4-13C)-Asp. The mutant bacteriorhodopsins labeled with (4-13C)-Asp (37%-45%), and owing to the metabolism of Halobacteria also with (11-13C)-Trp (50%-100%), were isolated as purple membranes and 13C Solid State Magic Angle Sample Spinning (MASS) Nuclear Magnetic Resonance (NMR) spectra of the samples were taken. The Asp96 mutants lacked the signal at 171.3 ppm which was previously assigned to a protonated internal Asp (Engelhard et al. 1989a). This observation supports the conclusion that Asp96 is protonated in the ground state. PM 384 (Asp85----Glu) has an absorption maximum at 610 nm. It can be converted into a purple form (lambda max = 540 nm) by treatment with a detergent (CHAPSO). The NMR-spectra of these two species differ from each other and from the wild type. The intensity of the resonance at 173 ppm in the wild type spectrum is reduced in both forms of the mutant protein. It is probable that this signal is caused by Asp85. The amino acid changes result not only in a perturbation of their direct environment but also effects on Trp residues and the chromophore protein interaction can be observed. PMID:1968385

Engelhard, M; Hess, B; Metz, G; Kreutz, W; Siebert, F; Soppa, J; Oesterhelt, D

1990-01-01

300

Theoretical predictions of the two-dimensional solid-state NMR spectra: A case study of the 13C–1H correlations in metergoline  

NASA Astrophysics Data System (ADS)

A new method for the treatment of data from multidimensional solid-state NMR investigations is described. It approximates the theoretical NMR chemical shifts from the chemical shielding values obtained by first-principles calculations and subsequently treats these results to quantify the similarity between predicted and experimental chemical shift correlations. The test case of this approach is performed for the measured and several sets of computed 13C–1H heteronuclear correlations in the polymorphic form I of metergoline, which is relatively large, pharmaceutically active system. The proposed protocol is general, however, and it can be immediately applied to study other compounds and nuclei.

Czernek, Ji?í; Brus, J.

2013-10-01

301

1H and 13C NMR Assignments of Cytotoxic 3S-1,2,3,4-Tetrahydro-?-carboline-3-carboxylic Acid from the Leaves of Cichorium endivia  

PubMed Central

An amino acid, 3S-1,2,3,4-tetrahydro-?-carboline-3-carboxylic acid, was isolated for the first time from the leaves of Cichorium endivia. The complete assignment of its 1H and 13C NMR spectroscopic data was carried out also for the first time based on extensive 1D and 2D NMR experiments. Cytotoxicity of this isolated compound against HCT-8 and HepG2 human cancer cell lines was evaluated for the first time, with moderate activities being found.

Wang, Fu-Xin; Deng, An-Jun; Wei, Jin-Feng; Qin, Hai-Lin; Wang, Ai-Ping

2012-01-01

302

Multinuclear 183W and 13C NMR and indirect photometry study for the identification and the characterization of new complexes of sugar acids  

Microsoft Academic Search

Colourless tungstate complexes of the sugar acids, l-manonnic, d-glucaric and galactaric acids have been studied in aqueous solutions. Multinuclear 13C and 183W NMR have been used to identify the structures of the complexes and the sites of chelation of each ligand. Indirect photometry has been used to determine the stoichiometry and the stability constants of the complexes.For mannonic acid, two

Miloudi Hlaïbi; Mustapha Hor; Mohamed Riri; Abdelkhalek Benjjar; Jean-François Verchère

2009-01-01

303

A 13C and 183W NMR study of d-glycero- d-gulo- heptonic acid as a multisite ligand in tungstate complexes  

Microsoft Academic Search

The formation of complexes (x, y, z) between x tungstate ions, y d-glycero-d-gulo-heptonate ions, and z protons was studied in aqueous solution by 13C and 183W NMR spectroscopy. The overall equilibrium constant for the complex-forming reaction was obtained by a competition method, showing that a (2,2,2) species prevails at pH 4–5. Depending on the pH, various species are formed that

Miloudi Hlaïbi; Mohammed Benaïssa; Catherine Busatto; Jean-François Verchère; Stella Chapelle

1995-01-01

304

13C-NMR analysis of decomposing litter and fine roots in the semi-arid Mulga Lands of southern Queensland  

Microsoft Academic Search

Plant litter and fine roots are important carbon (C) inputs to soil and a direct source of CO2 to the atmosphere. Solid-state carbon-13 nuclear magnetic resonance (13C-NMR) spectroscopy was used to investigate the nature of C changes during decomposition of plant litter and fine roots of mulga (Acacia aneura F. Muell. Ex. Benth.), wheat (Triticum aestivum L.), lucerne (Medicago sativa)

Nicole J. Mathers; Rajesh K. Jalota; Ram C. Dalal; Sue E. Boyd

2007-01-01

305

Conformational Changes of the BS2 Operator DNA upon Complex Formation with the Antennapedia Homeodomain Studied by NMR with 13C\\/ 15N-labeled DNA  

Microsoft Academic Search

The NMR structures have been determined for a13C\\/15N doubly labeled 14 base-pair DNA duplex comprising the BS2 operator sequence both free in solution and in the complex with theAntennapedia homeodomain. The impact of the DNA labeling is assessed from comparison with a previous structure of the same complex that was determined using isotope labeling only for the protein. Differences between

César Fernández; Thomas Szyperski; Martin Billeter; Akira Ono; Hideo Iwai; Masatsune Kainosho; Kurt Wüthrich

1999-01-01

306

(1)H, (13)C and (15)N NMR backbone assignments of the 269-residue serine protease PB92 from Bacillus alcalophilus.  

PubMed

The (1)H, (13)C and (15)N NMR resonances of the backbone of serine protease PB92 have been assigned. This 269-residue protein is one of the largest monomeric proteins assigned so far. The amount and quality of information available suggest that even larger proteins could be assigned with present methods. Measured chemical shifts show excellent agreement with the secondary structure. PMID:22911160

Fogh, R H; Schipper, D; Boelens, R; Kaptein, R

1994-01-01

307

The distribution of ?5 polyene acids in some pine seed oils between the ?- and ?-chains by 13C-NMR spectroscopy  

Microsoft Academic Search

Seven Pinus seed oils, previously examined by gas chromatography (Ref. [3]), have been re-examined by 13C-NMR spectroscopy. The spectra clearly indicate the presence of ?5 acids (mainly a C18 ?5, 9, 12 isomer) and almost all the signals have been assigned on the basis of relevant data already in the literature for ?5 esters. Using the intensities of appropriate signals

Frank D Gunstone; Shirley Seth; Robert L Wolff

1995-01-01

308

1 H and 13 C NMR spectra of 2-substituted 5-nitrofurans and conformation of chemotherapeutic preparations of the 5-nitrofuran series  

Microsoft Academic Search

The1H and13NMR spectra of t-nitrofuran and 17 2-substituted 5-nitrofurans were investigated. The ?1H and ?13C substituent increments [? = ?(2-X-5-nitrofuran) ?(5-nitrofuran)] in the spectra of these compounds were analyzed by comparison\\u000a with the analogous 5-methylfuran and furan derivatives, and the change in the sensitivity of the chemical shifts of the ring\\u000a protons and the carbon atoms to the effects of

Yu. Yu. Popelis; É. É. Liepin'sh

1980-01-01

309

1 H and 13 C NMR spectra of 2-substituted 5-nitrofurans and conformation of chemotherapeutic preparations of the 5-nitrofuran series  

Microsoft Academic Search

The1H and13NMR spectra of t-nitrofuran and 17 2-substituted 5-nitrofurans were investigated. The ?1H and ?13C substituent increments [? = d(2-X-5-nitrofuran) d(5-nitrofuran)] in the spectra of these compounds were analyzed by comparison with the analogous 5-methylfuran and furan derivatives, and the change in the sensitivity of the chemical shifts of the ring protons and the carbon atoms to the effects of

Yu. Yu. Popelis; É. É. Liepin'sh

1980-01-01

310

Multidimensional 1H 13C HETCOR and FSLG-HETCOR NMR study of sphingomyelin bilayers containing cholesterol in the gel and liquid crystalline states  

Microsoft Academic Search

13C cross polarization magic angle spinning (CP-MAS) and 1H MAS NMR spectra were collected on egg sphingomyelin (SM) bilayers containing cholesterol above and below the liquid crystalline phase transition temperature (Tm). Two-dimensional (2D) dipolar heteronuclear correlation (HETCOR) spectra were obtained on SM bilayers in the liquid crystalline (Lalpha) state for the first time and display improved resolution and chemical shift

Gregory P. Holland; Todd M. Alam

2006-01-01

311

Multidimensional 1H– 13C HETCOR and FSLG-HETCOR NMR study of sphingomyelin bilayers containing cholesterol in the gel and liquid crystalline states  

Microsoft Academic Search

13C cross polarization magic angle spinning (CP-MAS) and 1H MAS NMR spectra were collected on egg sphingomyelin (SM) bilayers containing cholesterol above and below the liquid crystalline phase transition temperature (Tm). Two-dimensional (2D) dipolar heteronuclear correlation (HETCOR) spectra were obtained on SM bilayers in the liquid crystalline (L?) state for the first time and display improved resolution and chemical shift

Gregory P. Holland; Todd M. Alam

2006-01-01

312

Solid-state NMR characterization of cross-linking in EPDM\\/PP blends from 1H– 13C polarization transfer dynamics  

Microsoft Academic Search

A novel approach for solid-state NMR characterization of cross-linking in polymer blends from the analysis of 1H–13C polarization transfer dynamics is introduced. It extends the model of residual dipolar couplings under permanent cross-linking, typically used to describe 1H transverse relaxation techniques, by considering a more realistic distribution of the order parameter along a polymer chain in rubbers. Based on a

Mihaela Aluas; Claudiu Filip

2005-01-01

313

Bacterial siderophores: structure elucidation, and 1 H, 13 C and 15 N two-dimensional NMR assignments of azoverdin and related siderophores synthesized by Azomonas macrocytogenes ATCC 12334  

Microsoft Academic Search

Two major azoverdins were isolated from the cultures of Azomonas macrocytogenes ATCC 12334 grown in irondeficient medium. Their structures have been established using fast atom bombardment-mass spectroscopy, homonuclear and heteronuclear two-dimensional 15N, 13C and 1H NMR, and circular dichroism techniques. These siderophores are chromopeptides possessing at the N-terminal end of their peptide chain the chromophore derived from 2,3-diamino-6,7-dihydroxyquinoline common to

Jean-Jacques Bernardini; Caroline Linget-Morice; François Hoh; S. Karen Collinson; Pavel Kyslík; William J. Page; Anne Dell; Mohamed A. Abdallah

1996-01-01

314

Molecular ordering of cellulose after extraction of polysaccharides from primary cell walls of Arabidopsis thaliana: a solid-state CP\\/MAS 13C NMR study  

Microsoft Academic Search

Solid-state CP\\/MAS 13C NMR spectroscopy was used to determine the effects of three different sequential extraction procedures, used to remove non-cellulosic polysaccharides, on the molecular ordering of cellulose in a cell-wall preparation containing mostly primary cell walls obtained from the leaves of the model dicotyledon, Arabidopsis thaliana. The extractions were 50 mM trans-1,2-diaminocyclohexane N,N,N?,N?-tetraacetic acid (CDTA) and 50 mM sodium

Lynette M. Davies; Philip J. Harris; Roger H. Newman

2002-01-01

315

2H NMR and 13C-IRMS analyses of acetic acid from vinegar, 18O-IRMS analysis of water in vinegar: International collaborative study report  

Microsoft Academic Search

An international collaborative study of isotopic methods applied to control the authenticity of vinegar was organized in order to support the recognition of these procedures as official methods. The determination of the 2H\\/1H ratio of the methyl site of acetic acid by SNIF–NMR (site-specific natural isotopic fractionation–nuclear magnetic resonance) and the determination of the 13C\\/12C ratio, by IRMS (isotope ratio

Freddy Thomas; Eric Jamin

2009-01-01

316

Direct identification and quantitative determination of costunolide and dehydrocostuslactone in the fixed oil of Laurus novocanariensis by 13C-NMR spectroscopy.  

PubMed

The fixed oil of Laurus novocanariensis (previously L. azorica) contains mostly glycerides together with minor non-saponifiable compounds. The direct identification and quantitative determination of costunolide and dehydrocostuslactone, two sesquiterpene lactones components of the oil that exhibit biological activities, is described. The analysis was carried out using 13C-NMR spectroscopy (signal acquisition with inverse gated decoupling of protons; diglyme as internal standard) without separation, derivatisation or any sample preparation. PMID:15881118

Ferrari, Bernard; Castilho, Paula; Tomi, Félix; Rodrigues, Ana Isabel; do Ceu Costa, Maria; Casanova, Joseph

317

Identification and quantitative determination of eudesmane-type acids from the essential oil of Dittrichia viscosa sp. viscosa using 13C-NMR spectroscopy.  

PubMed

A procedure that allows the identification and quantitative determination of eudesmane-type acids in the acidic part of the essential oil of Dittrichia viscosa sp. viscosa is described. The method involves the computer-aided analysis of the 13C-NMR spectrum of the mixture without the requirement of previous separation or derivatisation. The quantitative procedure was verified with costic acid standard and applied to three other acids which possess the same eudesmane framework. PMID:15997846

Blanc, Marie-Cécile; Bradesi, Pascale; Casanova, Joseph

318

13C CP/MAS NMR Studies of Hemoprotein Models with and without an Axial Hindered Base: (13)C Shielding Tensors and Comparison with Hemoproteins and X-ray Structural Data.  

PubMed

13C cross-polarization magic-angle-spinning (CP/MAS) NMR spectra of several carbonmonoxide (93-99% (13)C enriched) hemoprotein models with 1,2-dimethylimidazole (1,2-diMeIm) and 1-methylimidazole (1-MeIm) as axial ligands are reported. This enables the (13)CO spinning sideband manifold to be measured and hence the principal components of the (13)CO chemical shift tensor to be obtained. Negative polar interactions in the binding pocket of the cap porphyrin model and inhibition of Fe-->CO back-donation result in a reduction in shielding anisotropy; on the contrary, positive distal polar interactions result in an increase in the shielding anisotropy and asymmetry parameter in some models. It appears that the axial hindered base 1,2-dimethylimidazole has little direct effect on the local geometry at the CO site, despite higher rates of CO desorption being observed for such complexes. This suggests that the mechanism by which steric interactions are released for the 1,2-diMeIm complexes compared to 1-MeIm complexes does not involve a significant increase in bending of the Fe-C-O unit. The asymmetry of the shielding tensor of all the heme model compounds studied is smaller than that found for horse myoglobin and rabbit hemoglobin. PMID:11666486

Gerothanassis, I. P.; Momenteau, M.; Barrie, P. J.; Kalodimos, C. G.; Hawkes, G. E.

1996-04-24

319

Probing polymorphism and reactivity in the organic solid state using 13C NMR spectroscopy: Studies of p-Formyl-trans-cinnamic acid  

NASA Astrophysics Data System (ADS)

p-Formyl-trans-cinnamic acid (p-FCA) is known to exist in two different crystal phases (denoted ? and ?). When crystals of the ? phase of p-FCA are exposed to UV radiation, a solid state dimerization reaction occurs to produce 4,4'-diformyl-?-truxinic acid. In contrast, crystals of the ? phase of p-FCA are photostable. It is shown in this paper that high resolution solid state 13C NMR spectroscopy is a sensitive technique for distinguishing the ? and ? phases of p-FCA, and can be used to investigate, in detail, the chemical transformation that occurs upon UV irradiation of the ? phase. Specifically, the 13C NMR spectra presented here were recorded using the TOSS (total suppression of sidebands) pulse sequence; this is based upon the standard 13C CPMAS (cross polarization/magic angle sample spinning/high power 1H decoupling) method, but has the additional feature that all orders of spinning sidebands are eliminated from the spectrum. The photoproduct obtained from UV irradiation of ?-p-FCA contains a significant noncrystalline component (assessed via powder X-ray diffraction), and our NMR studies suggest that this noncrystalline component of the photoproduct contains some amount of the ? phase of the monomer p-FCA. A mechanism is proposed to explain the fact that UV irradiation of ?-p-FCA can generate, in addition to the expected photodimer, an impurity amount of the ? phase of p-FCA.

Harris, Kenneth D. M.; Thomas, John M.

1991-09-01

320

Linear free energy relationships applied to the reactivity and the 13C NMR chemical shifts in 4-[[(substituted phenyl)imino]methyl]benzoic acids  

NASA Astrophysics Data System (ADS)

Linear free energy relationships (LFER) were applied to the kinetic data and 13C NMR chemical shifts in 4-[[(substituted phenyl)imino]methyl]benzoic acids. The correlation analysis for the kinetic data and substituent-induced chemical shifts (SCS) with ? using single substituent parameter (SSP), as well as inductive (?I) and various resonance (?R) parameters using dual-substituent parameter (DSP), were carried out. The presented calculations account satisfactorily for the polar and resonance substituent effects having similar contributions at all carbons studied. Negative ? values were found for several correlations (reverse substituent effect). Exceptionally good Hammett correlation of 13C NMR chemical shifts of azomethine carbon with electrophilic substituent constants ?+ indicates a significant resonance interaction in the aniline part of molecules. The conformations of investigated compounds have been studied by the use of DFT method, and together with 13C NMR chemical shifts and kinetic data, give a better insight into the influence of such a structure on the transmission of electronic substituent effects. New ? constants for substituted phenyliminomethyl group have been calculated.

Marinkovi?, Aleksandar D.; Jovanovi?, Bratislav Ž.; Assaleh, Fathi H.; Vajs, Vlatka V.; Jurani?, Milan I.

2012-03-01

321

Real-time detection of 13C NMR labeling kinetics in perfused EMT6 mouse mammary tumor cells and betaHC9 mouse insulinomas.  

PubMed

A method was developed for obtaining high signal-to-noise 13C NMR spectra of intracellular compounds in metabolically active cultured cells. The method allows TCA cycle labeling kinetics to be determined in real time without significant oxygen transport limitations. Cells were immobilized on the surface of nonporous microcarriers that were either uncoated or coated with polypeptides and used in a 12-cm3 packed bed. The methods were tested with two EMT6 mouse mammary tumor cell lines, one strongly adherent and the other moderately adherent, and a weakly adherent mouse insulinoma line (betaHC9). For both EMT6 lines, NTP and oxygen consumption measurements indicated that the number of cells in the spectrometer ranged from 6 x 10(8) to 1 x 10(9). During infusion of [1-13C]glucose, labeling in C-4 glutamate (indicative of flux into the first half of the TCA cycle) could be detected with 15-min resolution. However, labeling for C-3 and C-2 glutamate (indicative of complete TCA cycle activity) was fivefold lower and difficult to quantify. To increase TCA cycle labeling, cells were infused with medium containing [1,6-13C2]glucose. A 2.5-fold increase was observed in C-4 glutamate labeling and C-3 and C-2 glutamate labeling could be monitored with 30-min resolution. Citrate synthase activity was indirectly detected in real time, as [3,4-13C2]glutamate was formed from [2-13C]oxaloacetate and [2-13C]acetate (of acetyl-CoA). Cell mass levels observed with betaHC9 cells were somewhat lower. However, the 13C S/N was sufficient to allow real-time monitoring of the response of intracellular metabolite labeling to a step change in glucose and a combined glutamine/serum pulse. PMID:15334410

Mancuso, A; Beardsley, N J; Wehrli, S; Pickup, S; Matschinsky, F M; Glickson, J D

2004-09-30

322

13C-NMR study of glucose and pyruvate catabolism in four acetogenic species isolated from the human colon.  

PubMed

Glucose fermentation by four acetogenic species (two Clostridium strains, one Streptococcus strain and Ruminococcus hydrogenotrophicus) isolated from the human colon was of a mixed-acid type, whereas pyruvate metabolism was characterised by homoacetogenesis. Acetate formation from [1-13C] and [2-13C]glucose was consistent with the formation of acetyl-SCoA from pyruvate generated by the Embden-Meyerhof-Parnas pathway. Labelling of lactate and ethanol demonstrated that these metabolites were formed by reduction of pyruvate and acetyl-SCoA, respectively. In contrast, the reductive pathway of acetate formation was the preferential means of re-oxidising cofactors formed during [1-13C]pyruvate catabolism. PMID:9011041

Leclerc, M; Bernalier, A; Lelait, M; Grivet, J P

1997-01-15

323

A new Schiff base compound N,N'-(2,2-dimetylpropane)-bis(dihydroxylacetophenone): synthesis, experimental and theoretical studies on its crystal structure, FTIR, UV-visible, 1H NMR and 13C NMR spectra.  

PubMed

The Schiff base compound, N,N'-(2,2-dimetylpropane)-bis(dihydroxylacetophenone) (NDHA) is synthesized through the condensation of 2-hydroxylacetophenone and 2,2-dimethyl 1,3-amino propane in methanol at ambient temperature. The yellow crystalline precipitate is used for X-ray single-crystal determination and measuring Fourier transform infrared (FTIR), UV-visible, (1)H NMR and (13)C NMR spectra. Electronic structure calculations at the B3LYP, PBEPBE and PW91PW91 levels of theory are performed to optimize the molecular geometry and to calculate the FTIR, (1)H NMR and (13)C NMR spectra of the compound. Time-dependent density functional theory (TDDFT) method is used to calculate the UV-visible spectrum of NDHA. Vibrational frequencies are determined experimentally and compared with those obtained theoretically. Vibrational assignments and analysis of the fundamental modes of the compound are also performed. All theoretical methods can well reproduce the structure of the compound. The (1)H NMR and (13)C NMR chemical shifts calculated by all DFT methods are consistent with the experimental data. However, the NMR shielding tensors computed at the B3LYP/6-31+G(d,p) level of theory are in better agreement with experimental (1)H NMR and (13)C NMR spectra. The electronic absorption spectrum calculated at the B3LYP/6-31+G(d,p) level by using TD-DFT method is in accordance with the observed UV-visible spectrum of NDHA. In addition, some quantum descriptors of the molecule are calculated and conformational analysis is performed and the results were compared with the crystallographic data. PMID:21763188

Saheb, Vahid; Sheikhshoaie, Iran

2011-06-12

324

1H and 13C Fourier Transform NMR Characterization of Jet Fuels Derived from Alternate Energy Sources.  

National Technical Information Service (NTIS)

This report discusses LC-superscript 1H NMR studies from semi-preparative to analytical column size in order to establish ultimate chromatographic resolution conditions. It explores quantitative approaches for LC-superscript 1H NMR including a dual efflue...

H. C. Dorn

1980-01-01

325

Fluorescence, CD, attenuated total reflectance (ATR) FTIR, and sup 13 C NMR characterization of the structure and dynamics of synthetic melittin and melittin analogues in lipid environments  

SciTech Connect

The structure and dynamics of synthetic melittin (MLT) and MLT analogues bound to monomyristoylphosphatidylcholine micelles, dimyristoylphosphatidylcholine vesicles, and diacylphosphatidylcholine films have been investigated by fluorescence, CD, attenuated total reflectance (ATR) FTIR, and {sup 13}C NMR spectroscopy. All of these methods provide information about peptide secondary structure and/or about the environment of the single tryptophan side chain in these lipid environments. ATR-FTIR data provide additional information about the orientation of helical peptide segments with respect to the bilayer plane. Steady-state fluorescence anisotropy, fluorescence lifetime, and {sup 13}C NMR relaxation data are used in concert to provide quantitative information about the dynamics of a single {sup 13}C{alpha}-labeled glycine incorporated into each of the MLT peptides at position 12. The cumulative structural and dynamic data are consistent with a model wherein the N-terminal {alpha}-helical segment of these peptides is oriented perpendicular to the bilayer plane. Correlation times for the lysolipid-peptide complexes provide evidence for binding of a single peptide monomer per micelle. A model for the membranolytic action of MLT and MLT-like peptides is proposed.

Weaver, A.J.; Prendergast, F.G. (Mayo Foundation, Rochester, MN (United States)); Kemple, M.D. (Indiana Univ.-Purdue Univ., Indianapolis (United States)); Brauner, J.W.; Mendelsohn, R. (Rutgers, The State Univ. of New Jersey, Newark (United States))

1992-02-11

326

Sensitivity Enhancement in 13C Solid-State NMR of Protein Microcrystals by Use of Paramagnetic Metal Ions for Optimizing 1H T1 Relaxation  

PubMed Central

We discuss a simple approach to enhance sensitivity for 13C high-resolution solid-state NMR for proteins in microcrystals by reducing 1H T1 relaxation times with paramagnetic relaxation reagents. It was shown that 1H T1 values can be reduced from 0.4-0.8 s to 60-70 ms for ubiquitin and lysozyme in D2O in the presence of 10 mM Cu(II)Na2EDTA without substantial degradation of the resolution in 13C CPMAS spectra. Faster signal accumulation using the shorter 1H T1 attained by paramagnetic doping provided sensitivity enhancements of 1.4-2.9 for these proteins, reducing the experimental time for a given signal-to-noise ratio by a factor of 2.0-8.4. This approach presented here is likely to be applicable to various other proteins in order to enhance sensitivity in 13C high-resolution solid-state NMR spectroscopy.

Wickramasinghe, Nalinda P.; Kotecha, Mrignayani; Samoson, Ago; Past, Jaan; Ishii, Yoshitaka

2007-01-01

327

Recoupling of chemical shift anisotropies in solid-state NMR under high-speed magic-angle spinning and in uniformly 13C-labeled systems  

NASA Astrophysics Data System (ADS)

We demonstrate the possibility of recoupling chemical shift anisotropy (CSA) interactions in solid-state nuclear magnetic resonance (NMR) under high-speed magic-angle spinning (MAS) while retaining a static CSA powder pattern line shape and simultaneously attenuating homonuclear dipole-dipole interactions. CSA recoupling is accomplished by a rotation-synchronized radio-frequency pulse sequence with symmetry properties that permit static CSA line shapes to be obtained. We suggest a specific recoupling sequence, which we call ROCSA, for which the scaling factors for CSA and homonuclear dipole-dipole interactions are 0.272 and approximately 0.05, respectively. This sequence is suitable for high-speed 13C MAS NMR experiments on uniformly 13C-labeled organic compounds, including biopolymers. We demonstrate the ROCSA sequence experimentally by measuring the 13C CSA patterns of the uniformly labeled, polycrystalline compounds L-alanine and N-acetyl-D,L-valine at MAS frequencies of 11 and 20 kHz. We also present experimental data for amyloid fibrils formed by a 15-residue fragment of the ?-amyloid peptide associated with Alzheimer's disease, in which four amino acid residues are uniformly labeled, demonstrating the applicability to biochemical systems of high molecular weight and significant complexity. Analysis of the CSA patterns in the amyloid fibril sample demonstrates the utility of ROCSA measurements as probes of peptide and protein conformation in noncrystalline solids.

Chan, Jerry C. C.; Tycko, Robert

2003-05-01

328

Backbone and Ile-?1, Leu, Val Methyl 1H, 13C and 15N NMR chemical shift assignments for human interferon-stimulated gene 15 protein  

PubMed Central

Human interferon-stimulated gene 15 protein (ISG15), also called ubiquitin cross-reactive protein (UCRP), is the first identified ubiquitin-like protein containing two ubiquitin-like domains fused in tandem. The active form of ISG15 is conjugated to target proteins via the C-terminal glycine residue through an isopeptide bond in a manner similar to ubiquitin. The biological role of ISG15 is strongly associated with the modulation of cell immune function, and there is mounting evidence suggesting that many viral pathogens evade the host innate immune response by interfering with ISG15 conjugation to both host and viral proteins in a variety of ways. Here we report nearly complete backbone 1HN, 15N, 13C?, and 13C?, as well as side chain 13C?, methyl (Ile-?1, Leu, Val), amide (Asn, Gln), and indole N–H (Trp) NMR resonance assignments for the 157-residue human ISG15 protein. These resonance assignments provide the basis for future structural and functional solution NMR studies of the biologically important human ISG15 protein.

Yin, Cuifeng; Ma, Li-Chung; Cort, John R.; Swapna, G. V. T.; Krug, Robert M.

2011-01-01

329

High-resolution sup 13 C NMR study of the topography and dynamics of methionine residues in detergent-solubilized bacteriorhodopsin  

SciTech Connect

The proton transport membrane protein bacteriorhodopsin has been biosynthetically labeled with (methyl-{sup 13}C)methionine and studied by high-resolution {sup 13}C NMR after solubilization in the detergent Triton X-100. The nine methionine residues of bacteriorhodopsin give rise to four well-resolved {sup 13}C resonances, two of which are shifted upfield or downfield due to nearby aromatic residues. Methionine residues located on the hydrophilic surfaces, on the hydrophobic surface, and in the interior of the protein could be discriminated by studying the effects of papain proteolysis, glycerol-induced viscosity increase, and paramagnetic broadening by spin-labels on NMR spectra. Such data were used to evaluate current models of the bacteriorhodopsin transmembrane folding and tertiary structure. T{sub 2} and NOE measurements were performed to study the local dynamics of methionine residues in bacteriorhodopsin. For the detergent-solubilized protein, hydrophilic and hydrophobic external residues undergo a relatively large extent of side chain wobbling motion while most internal residues are less mobile. In the native purple membrane and in reconstituted bacteriorhodopsin liposomes, almost all methionine residues have their wobbling motion severely restricted, indicating a large effect of the membrane environment on the protein internal dynamics.

Seigneuret, M.; Neumann, J.M.; Levy, D.; Rigaud, J.L. (URA-CNRS, Gif-sur-Yvette (France))

1991-04-23

330

Conformational exchange on the microsecond time scale in alpha-helix and beta-hairpin peptides measured by 13C NMR transverse relaxation.  

PubMed

13C-NMR relaxation experiments (T(1), T(2), T(1)(rho), and NOE) were performed on selectively enriched residues in two peptides, one hydrophobic staple alpha-helix-forming peptide GFSKAELAKARAAKRGGY and one beta-hairpin-forming peptide RGITVNGKTYGR, in water and in water/trifluoroethanol (TFE). Exchange contributions, R(ex), to spin-spin relaxation rates for (13)C(alpha) and (13)C(beta) groups were derived and were ascribed to be mainly due to peptide folding-unfolding. To evaluate the exchange time, tau(ex), from R(ex), the chemical shift difference between folded and unfolded states, Deltadelta, and the populations of these states, p(i), were determined from the temperature dependence of (13)C chemical shifts. For both peptides, values for tau(ex) fell in the 1 micros to 10 micros range. Under conditions where the peptides are most folded (water/TFE, 5 degrees C), tau(ex) values for all residues in each respective peptide were essentially the same, supporting the presence of a global folding-unfolding exchange process. Rounded-up average tau(ex) values were 4 micros for the helix peptide and 9 micros for the hairpin peptide. This 2-3-fold difference in exchange times between helix and hairpin peptides is consistent with that observed for folding-unfolding of other small peptides. PMID:11258895

Nesmelova, I; Krushelnitsky, A; Idiyatullin, D; Blanco, F; Ramirez-Alvarado, M; Daragan, V A; Serrano, L; Mayo, K H

2001-03-01

331

An NMR study of alterations in [1- 13 C ]glucose metabolism in C6 glioma cells by gliotoxic amino acids  

Microsoft Academic Search

A series of glutamate analogues, known as gliotoxins, are toxic to astrocytes in culture, and are inhibitors or substrates of high affinity sodium-dependent glutamate transporters. The mechanisms by which these gliotoxins cause toxicity are not fully understood. The effects of a series of gliotoxic amino acids (l-?-aminoadipate, l-serine-O-sulphate, d-aspartate and l-cysteate) on metabolism of [1-13C]glucose were examined in C6 glioma

Lorraine Brennan; Chandralal Hewage; J. Paul G. Malthouse; Gethin J. McBean

2003-01-01

332

Effects of added paramagnetic ions on the 13 C CP\\/MAS NMR spectrum of a de-ashed soil  

Microsoft Academic Search

A de-ashed soil was reacted with a series of paramagnetic (Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Pr3+, Eu3+) and non-paramagnetic (Na+, Ca2+, Zn2+) ions. Amendment with non-paramagnetic ions did not effect the NMR properties of the soil organic matter (SOM), whereas a number of NMR properties including signal intensity, broadness and relaxation rate constants (T1?H, T1H, T1C) were effected by the

Ronald J Smernik; J. Malcolm Oades

1999-01-01

333

/sup 13/C NMR analysis of the effects of electron radiation on graphite/polyetherimide composites. Final report  

SciTech Connect

Initial investigations have been made into the use of high resolution nuclear magnetic resonance (NMR) for the characterization of radiation effects in graphite and Kevlar fibers, polymers, and the fiber/matrix interface in graphite/polyetherimide composites. Sample preparation techniques were refined. Essential equipment has been procured. A new NMR probe was constructed to increase the proton signal-to-noise ratio. Problem areas have been identified and plans developed to resolve them.

Ferguson, M.W.

1989-03-01

334

Carbon-proton scalar couplings in RNA. 3D heteronuclear and 2D isotope-edited NMR of a [sup 13]C-labeled extra-stable hairpin  

SciTech Connect

Long range carbon-proton scalar couplings were measured for an RNA hairpin of 12 nucleotides using 3D and [sup 13]C-edited 2D NMR. The large one-bond carbon-proton scalar couplings ([sup 1]J[sub CH]) and small n-bond couplings ([sup 1]J[sub CH]) produce ECOSY type cross-peaks, thus facilitating the determination of the sign and magnitude of the smaller [sup 2]J[sub CH] or [sup 3]J[sub CH]. The UUCGRNA hairpin (5[prime]-rGGACUUCGGUCC-3[prime]), whose structure has been determined by our laboratory, was uniformly [sup 13]C-labeled at 30% isotopic enrichment. The observed [sup 1]J[sub CH] couplings were then correlated to the known structure. The signs of [sup 2]J[sub C4[prime]H5[prime

Hines, J.V.; Landry, S.M.; Varani, G.; Tinoco, I. Jr. (Univ. of California, Berkeley, CA (United States) Lawrence Berkeley Lab., CA (United States))

1994-06-29

335

Quantum-chemical analysis of paramagnetic 13C NMR shifts of iron-bound cyanide ions in heme-protein environments  

NASA Astrophysics Data System (ADS)

Paramagnetic 13C NMR chemical shifts of iron-bound cyanide ions located in biological environments such as heme-proteins are significantly sensitive to the environments. These chemical shifts are due to negative spin density at 13C induced by the open-shell iron center. In order to examine the environments effects on the electronic states around heme parts, ab initio calculations were performed for model systems of heme-proteins. The proximal residues in proteinparts of cytochrome c, hemoglobin, myoglobin and horseradish peroxidase were included in the model systems with the common active site (cyanide imidazole porphyrinato iron(III)) to take account of the environments effects. The calculated paramagnetic shifts of model systems reproduce the experimental trend of corresponding heme-proteins. It is found that the effects of proximal residues on the electronic states of the heme-parts are significant for these hemeproteins. In this abstract we focused on the calculations and analysis of cytochrome c.

Yamaki, Daisuke; Hada, Masahiko

2012-12-01

336

The spectroscopic (FT-IR, FT-Raman and 1H, 13C NMR) and theoretical studies of cinnamic acid and alkali metal cinnamates  

NASA Astrophysics Data System (ADS)

The effect of alkali metals (Li ? Na ? K ? Rb ? Cs) on the electronic structure of cinnamic acid (phenylacrylic acid) was studied. In this research many miscellaneous analytical methods, which complement one another, were used: infrared (FT-IR), Raman (FT-Raman), nuclear magnetic resonance (1H, 13C NMR) and quantum mechanical calculations. The spectroscopic studies lead to conclusions concerning the distribution of the electronic charge in molecule, the delocalization energy of ?-electrons and the reactivity of metal complexes. The change of metal along with the series: Li ? Na ? K ? Rb ? Cs caused: (1) the change of electronic charge distribution in cinnamate anion what is seen via the occurrence of the systematic shifts of several bands in the experimental and theoretical IR and Raman spectra of cinnamates, (2) systematic chemical shifts for protons 1H and 13C nuclei.

Kalinowska, Monika; ?wis?ocka, Renata; Lewandowski, W?odzimierz

2007-05-01

337

Backbone dynamics of a model membrane protein: assignment of the carbonyl carbon /sup 13/C NMR resonances in detergent-solubilized M13 coat protein  

SciTech Connect

The major coat protein of the filamentous bacteriophage M13 is a 50-residue amphiphilic polypeptide which is inserted, as an integral membrane-spanning protein, in the inner membrane of the Escherichia coli host during infection. /sup 13/C was incorporated biosynthetically into a total of 23 of the peptide carbonyls using labeled amino acids (alanine, glycine, lysine, phenylalanine, and proline). The structure and dynamics of carbonyl-labeled M13 coat protein were monitored by /sup 13/C nuclear magnetic resonance (NMR) spectroscopy. Assignment of many resonances was achieved by using protease digestion, pH titration, or labeling of the peptide bond with both /sup 13/C and /sup 15/N. The carbonyl region of the natural-abundance /sup 13/C NMR spectrum of M13 coat protein in sodium dodecyl sulfate solution shows approximately eight backbone carbonyl resonances with line widths much narrower than the rest. Three of these more mobile residues correspond to assigned peaks (glycine-3, lysine-48, and alanine-49) in the individual amino acid spectra, and another almost certainly arises from glutamic acid-2. A ninth residue, alanine-1, also gives rise to a very narrow carbonyl resonance if the pH is well above or below the pK/sub a/ of the terminal amino group. These data suggest that only about four residues at either end of the protein experience large-amplitude spatial fluctuations; the rest of the molecule is essentially rigid on the time scale of the overall rotational tumbling of the protein-detergent complex. The relative exposure of different regions of detergent-bound protein was monitored by limited digestion with proteinase K. Comparable spectra and digestion patterns were obtained when the protein was solubilized in sodium deoxycholate, suggesting that the coat protein binds both amphiphiles in a similar fashion.

Henry, G.D.; Weiner, J.H.; Sykes, B.D.

1987-06-16

338

Roles of Arginine and Lysine Residues in the Translocation of a Cell-Penetrating Peptide from 13C, 31P and 19F Solid-State NMR  

PubMed Central

Cell-penetrating peptides (CPPs) are small cationic peptides that cross the cell membrane while carrying macromolecular cargoes. We use solid-state NMR to investigate the structure and lipid interaction of two cationic residues, Arg10 and Lys13, in the CPP penetratin. 13C chemical shifts indicate that Arg10 adopts a rigid ?-strand conformation in the liquid-crystalline state of anionic lipid membranes. This behavior contrasts with all other residues observed so far in this peptide, which adopt a dynamic ?-turn conformation with coil-like chemical shifts at physiological temperature. Low-temperature 13C-31P distances between the peptide and the lipid phosphates indicate that both the Arg10 guanidinium C? and the Lys13 C? lie in close proximity to the lipid 31P (4.0 - 4.2 Å), proving the existence of charge-charge interaction for both Arg10 and Lys13 in the gel-phase membrane. However, since lysine substitution in CPPs are known to reduce their translocation ability, we propose that low temperature stabilizes both lysine and arginine interactions with the phosphates, whereas at high temperature the lysine-phosphate interaction is much weaker than the arginine-phosphate interaction. This is supported by the unusually high rigidity of the Arg10 sidechain and its ?-strand conformation at high temperature. The latter is proposed to be important for ion pair formation by allowing close approach of the lipid headgroups to guanidinium sidechains. 19F and 13C spin diffusion experiments indicate that penetratin is oligomerized into ?-sheets in gel-phase membranes. These solid-state NMR data indicate that guanidinium-phosphate interactions exist in penetratin, and guanidinium groups play a stronger structural role than ammonium groups in the lipid-assisted translocation of CPPs across liquid-crystalline cell membranes.

Su, Yongchao; Doherty, Tim; Waring, Alan J.; Ruchala, Piotr; Hong, Mei

2009-01-01

339

31P and 13C NMR studies of oxygen transfer during catalysis by 3-deoxy-D-manno-octulosonate cytidylyltransferase from Escherichia coli.  

PubMed

[18O]3-Deoxy-D-manno-octulosonate (KDO), labeled at the anomeric oxygen, was prepared by exchange with [18O]H2O and used to follow the route of oxygen transfer during cytidine 5'-monophosphate-3-deoxy-D-manno-octulosonate (CMP-KDO) formation catalyzed by 3-deoxy-D-manno-octulosonate cytidylyl-transferase (CMP-KDO synthetase). The 31P-NMR signal of the phosphoryl group of CMP-KDO (-5.85 ppm), which appeared as a single resonance when CMP-KDO formation took place with unenriched KDO, appeared as two peaks when CMP-KDO formation took place in the presence of a mixture of [16O]-and [18O]KDO. These results demonstrate the retention of 18O during CMP-KDO formation. Confirmation that the labeled oxygen in CMP-KDO was retained in the "bridge" position between CMP and KDO came from 13C-NMR studies of CMP-KDO formed in the presence of 90% [2-13C, 18O] KDO. The prominent C-2 KDO resonance in CMP-KDO, which is normally a doublet at 101.4 ppm (Kohlbrenner, W.E., and Fesik, S.W. (1985) J. Biol. Chem. 260, 14695-14700), appeared as four peaks when a mixture of [2-13C,16O]- and [2-13C, 18O]KDO was used, confirming the direct bonding of 18O to the C-2 of KDO in CMP-KDO. These results are consistent with a nucleophilic displacement mechanism for CMP-KDO formation. PMID:3031027

Kohlbrenner, W E; Nuss, M M; Fesik, S W

1987-04-01

340

Selective 13C labeling of nucleotides for large RNA NMR spectroscopy using an E. coli strain disabled in the TCA cycle  

PubMed Central

Escherichia coli (E. coli) is an ideal organism to tailor-make labeled nucleotides for biophysical studies of RNA. Recently, we showed that adding labeled formate enhanced the isotopic enrichment at protonated carbon sites in nucleotides. In this paper, we show that growth of a mutant E. coli strain DL323 (lacking succinate and malate dehydrogenases) on 13C-2-glycerol and 13C-1,3-glycerol enables selective labeling at many useful sites for RNA NMR spectroscopy. For DL323 E. coli grown in 13C-2-glycerol without labeled formate, all the ribose carbon atoms are labeled except the C3? and C5? carbon positions. Consequently the C1?, C2? and C4? positions remain singlet. In addition, only the pyrimidine base C6 atoms are substantially labeled to ~96% whereas the C2 and C8 atoms of purine are labeled to ~5%. Supplementing the growth media with 13C-formate increases the labeling at C8 to ~88%, but not C2. Not unexpectedly, addition of exogenous formate is unnecessary for attaining the high enrichment levels of ~88% for the C2 and C8 purine positions in a 13C-1,3-glycerol based growth. Furthermore, the ribose ring is labeled in all but the C4? carbon position, such that the C2? and C3? positions suffer from multiplet splitting but the C5? position remains singlet and the C1? position shows a small amount of residual C1?–C2? coupling. As expected, all the protonated base atoms, except C6, are labeled to ~90%. In addition, labeling with 13C-1,3-glycerol affords an isolated methylene ribose with high enrichment at the C5? position (~90%) that makes it particularly attractive for NMR applications involving CH2-TROSY modules without the need for decoupling the C4? carbon. To simulate the tumbling of large RNA molecules, perdeuterated glycerol was added to a mixture of the four nucleotides, and the methylene TROSY experiment recorded at various temperatures. Even under conditions of slow tumbling, all the expected carbon correlations were observed, which indicates this approach of using nucleotides obtained from DL323 E. coli will be applicable to high molecular weight RNA systems.

Thakur, Chandar S.; Sama, Jacob N.; Jackson, Melantha E.; Chen, Bin

2010-01-01

341

Lipid metabolism in T47D human breast cancer cells: 31P and 13C-NMR studies of choline and ethanolamine uptake.  

PubMed

31P and 13C-NMR were used to determine the kinetics of choline and ethanolamine incorporation in T47D clone 11 human breast cancer cells grown as small (150 microns) spheroids. Spheroids were perfused inside the spectrometer with 1,2-13C-labeled choline or 1,2-13C-labeled ethanolamine (0.028 mM) and the buildup of labeled phosphoryl-choline (PC) or phosphorylethanolamine (PE) was monitored. Alternatively the PC and GPC pools were prelabeled with 13C and the reduction of label was monitored. 31P spectra were recorded from which the overall energetic status as well as total pool sizes could be determined. The ATP content was 8 +/- 1 fmol/cell, and the total PC and PE pool sizes were 16 and 14 fmol/cell, respectively. PC either increased by 50% over 24 h or remained constant, while PE remained constant in medium without added ethanolamine but increased 2-fold within 30 h in medium containing ethanolamine, indicating a dependence on precursor concentration in the medium. The 31P and 13C data yielded similar kinetic results: the rate of the enzymes phosphocholine kinase and phosphoethanolamine kinase were both on the order of 1.0 fmol/cell per h, and the rate constants for CTP:phosphocholine cytidyltransferase and CTP:phosphoethanolamine kinase were 0.06 h-1 for both enzymes. The kinetics of choline incorporation did not alter in the presence of 0.028 mM ethanolamine indicating that they have non-competing pathways. PMID:1657190

Ronen, S M; Rushkin, E; Degani, H

1991-10-16

342

NMR experiments for resonance assignments of 13 C, 15 N doubly-labeled flexible polypeptides: Application to the human prion protein hPrP(23–230)  

Microsoft Academic Search

A combination of three heteronuclear three-dimensional NMR experiments tailored for sequential resonance assignments in uniformly 15N, 13C-labeled flexible polypeptide chains is described. The 3D (H)N(CO-TOCSY)NH, 3D (H)CA(CO-TOCSY)NH and 3D (H)CBCA(CO-TOCSY)NH schemes make use of the favorable 15N chemical shift dispersion in unfolded polypeptides, exploit the slow transverse 15N relaxation rates of unfolded polypeptides in high resolution constant-time [1H, 15N]-correlation experiments,

Aizhuo Liu; Roland Riek; Gerhard Wider; Christine von Schroetter; Ralph Zahn; Kurt Wüthrich

2000-01-01

343

NMR experiments for resonance assignments of 13C, 15N doubly-labeled flexible polypeptides: Application to the human prion protein hPrP(23-230)  

Microsoft Academic Search

A combination of three heteronuclear three-dimensional NMR experiments tailored for sequential resonance as- signments in uniformly 15N, 13C-labeled flexible polypeptide chains is described. The 3D (H)N(CO-TOCSY)NH, 3D (H)CA(CO-TOCSY)NH and 3D (H)CBCA(CO-TOCSY)NH schemes make use of the favorable 15N chemical shift dispersion in unfolded polypeptides, exploit the slow transverse 15N relaxation rates of unfolded polypep- tides in high resolution constant-time (

Aizhuo Liu; Roland Riek; Gerhard Wider; Christine von Schroetter; Ralph Zahn; Kurt Wüthrich

2000-01-01

344

Combined analysis of  Cymbopogon giganteus Chiov. leaf oil from Ivory Coast by GC\\/RI, GC\\/MS and  13C-NMR  

Microsoft Academic Search

The composition of the essential oil isolated by hydrodistillation from the leaves of Cymbopogon giganteus Chiov. growing wild in Ivory Coast, was determined by GC\\/RI, GC\\/SM and 13C-NMR after fractionation on silica gel. The oil was characterized by high contents of trans- and cis-p-mentha-2,8-dien-1-ols (18.4% and 8.7%, respectively), cis- and trans-p-mentha-1(7),8-dien-2-ols (16.0% and 15.7% respectively), and limonene (12.5%). Forty-six components

Jean Brice Boti; Alain Muselli; Félix Tomi; Gérard Koukoua; Thomas Yao N’Guessan; Jean Costa; Joseph Casanova

2006-01-01

345

Composition and chemical variability of the leaf oil from Corsican Juniperus thurifera. Integrated analysis by GC(RI), GC-MS and 13C NMR.  

PubMed

The composition of 16 samples of leaf oil from Corsican Juniperus thurifera was investigated by integrated techniques, GC, GC-MS and 13C NMR. K-means partitioning and PCA analysis of the data allowed the definition of a main group (14 samples) dominated by limonene (mean = 52.2%, SD = 6.4) and alpha-pinene (mean = 7.2%, SD = 3.8). Limonene and beta-elemol (up to 19.7%) were identified as the major components of two atypic samples. PMID:21299138

Ottavioli, Josephine; Casanova, Joseph; Bighelli, Ange

2010-12-01

346

1 H, 13 C and 15 N random coil NMR chemical shifts of the common amino acids. I. Investigations of nearest-neighbor effects  

Microsoft Academic Search

Summary  In this study we report on the 1H, 13C and 15N NMR chemical shifts for the random coil state and nearest-neighbor sequence effects measured from the protected linear hexapeptide\\u000a Gly-Gly-X-Y-Gly-Gly (where X and Y are any of the 20 common amino acids). We present data for a set of 40 peptides (of the\\u000a possible 400) including Gly-Gly-X-Ala-Gly-Gly and Gly-Gly-X-Pro-Gly-Gly, measured

David S. Wishart; Colin G. Bigam; Arne Holm; Robert S. Hodges; Brian D. Sykes

1995-01-01

347

/sup 13/C NMR spectra of cyclic nitrones. 2. 1- and 4-substituted 2,2,5,5-tetramethyl-3-imidazoline 3-oxides  

SciTech Connect

The chemical shift of the carbon atom of the nitrone group in the /sup 13/C NMR spectra of 3-imidazoline 3-oxides lies in the region of 117-152 ppm and depends on the electronic effect of the substituents at positions 1, 4, and 5 of the heterocycle. Increase in the electron-withdrawing character of the substituent at these positions leads to an upfield shift of the signal for the nitrone carbon atom, and this corresponds to the increase in electron density on it.

Grigor'ev, I.A.; Shchukin, G.I.; Martin, V.V.; Mamatyuk, V.I.

1985-08-01

348

/sup 13/C NMR spectra of cyclic nitrones. 1. 2-substituted 4-methyl- and 4-phenyl-1-hydroxy-5,5-dimethyl-3-imidazoline 3-oxides  

SciTech Connect

The introduction of an N-oxide oxygen atom into azomethines leads to an upfield shift of the signals for the carbon atom of the C=N group in the /sup 13/C NMR spectra by 30-33 ppm. This is consistent with the increase in the electron density on this atom. The signal of the nitrone carbon atom is observed in the region of 140-147 ppm, depending on the nature of the substituent at the C/sub (2)/ atom of the 3-imidazoline 3-oxide ring.

Grigor'ev, I.A.; Martin, V.V.; Shchukin, G.I.; Mamatyuk, V.I.; Volodarskii, L.B.

1985-08-01

349

Gliotoxins disrupt alanine metabolism and glutathione production in C6 glioma cells: a 13C NMR spectroscopic study  

Microsoft Academic Search

Gliotoxins are a group of amino acids that are toxic to astrocytes, and are substrates of high-affinity sodium-dependent glutamate transporters. In the present study, C6 glioma cells were preincubated for 20h in the presence of 400?M l-?-aminoadipate, l-serine-O-sulphate, d-aspartate or l-cysteate, as well as in the presence of the poorly transported l-glutamate uptake inhibitor, l-anti-endo-methanopyrrolidine dicarboxylate. In experiments following [3-13C]alanine

Lorraine Brennan; Chandralal Hewage; J. Paul G. Malthouse; Gethin J. McBean

2004-01-01

350

Observation of cytoplasmic and vacuolar malate in maize root tips by sup 13 C-NMR spectroscopy. [Zea mays L  

SciTech Connect

The accumulation of malate by maize (Zea mays L.) root tips perfused with KH{sup 13}CO{sub 3} was followed by {sup 13}C nuclear magnetic resonance spectroscopy. In vivo nuclear magnetic resonance spectra contained distinct signals from two pools of malate in maize root tips, one at a pH {approximately}5.3 (assigned to the vacuole) and one at a pH > 6.5 (assigned to the cytoplasm). The ratio of cytoplasmic to vacuolar malate was lower in 12 millimeter long root tips than in 2 millimeter root tips. The relatively broad width of the signals from C1- and C4-labeled vacuolar malate indicated heterogeneity in vacuolar pH. During the 3 hour KH{sup 13}CO{sub 3} treatment, {sup 13}C-malate accumulated first primarily in the cytoplasm, increasing to a fairly constant level of {approximately}6 millimolar by 1 hour. After a lag, vacuolar malate increased throughout the experiment.

Chang, K.; Roberts, J.K.M. (Univ. of California, Riverside (USA))

1989-01-01

351

Cold Denaturation of Barstar: 1H, 15N and 13C NMR Assignment and Characterisation of Residual Structure  

Microsoft Academic Search

Detection of residual structure in denatured proteins is of interest because fleetingly structured regions may be initiation points of the folding pathway. Residual structure in this context is not the definition of one stable conformation but a population phenomenon. Acid, thermal and solvent-denatured states have recently been examined by NMR spectroscopy, but cold-denatured states have not been characterised to date.

Kam-Bo Wong; Stefan M. V. Freund; Alan R. Fersht

1996-01-01

352

(1)H, (13)C, (15)N backbone and side chain NMR resonance assignments of BPSL1050 from Burkholderia pseudomallei.  

PubMed

BPSL1050 is a 13.9 kDa protein produced by the Gram-negative bacterium Burkholderia pseudomallei, the etiological agent of melioidosis. Immunodetection assays against sera patients using protein microarray suggest BPSL1050 involvement in melioidosis. Herein we report its backbone and side chains NMR assignment. PMID:23616103

Gaudesi, Davide; Quilici, Giacomo; Musco, Giovanna

2013-04-25

353

Identification of a high concentration of scyllo-inositol in the brain of a healthy human subject using 1H- and 13C-NMR.  

PubMed

The peak at 3.35 ppm in the 1H-NMR spectrum characteristic for scyllo-inositol may be a marker for cerebral pathology, although it has a well-known constant concentration relative to myo-inositol. Such a peak was observed with an intensity at least 300% above normal in the brain of a healthy volunteer. The scyllo-inositol signal was assigned based on the detection of a corresponding peak at 74.5 ppm in the 13C-NMR spectrum and on the demonstration of singlet characteristics of the proton signal. The presence of substantial brain concentrations of scyllo-inositol suggests that scyllo-inositol metabolism may be regulated independently from myo-inositol and that such concentrations are compatible with normal health. PMID:9469716

Seaquist, E R; Gruetter, R

1998-02-01

354

Complete 1H, 13C and 15N NMR assignments and secondary structure of the 269-residue serine protease PB92 from Bacillus alcalophilus.  

PubMed

The 1H, 13C and 15N NMR resonances of serine protease PB92 have been assigned using 3D triple-resonance NMR techniques. With a molecular weight of 27 kDa (269 residues) this protein is one of the largest monomeric proteins assigned so far. The side-chain assignments were based mainly on 3D H(C)CH and 3D (H)CCH COSY and TOCSY experiments. The set of assignments encompasses all backbone carbonyl and CHn carbons, all amide (NH and NH2) nitrogens and 99.2% of the amide and CHn protons. The secondary structure and general topology appear to be identical to those found in the crystal structure of serine protease PB92 [Van der Laan et al. (1992) Protein Eng., 5, 405-411], as judged by chemical shift deviations from random coil values, NH exchange data and analysis of NOEs between backbone NH groups. PMID:7787423

Fogh, R H; Schipper, D; Boelens, R; Kaptein, R

1995-04-01

355

(1)H and (13)C NMR assignments of eight nitrogen containing compounds from Nocardia alba sp.nov (YIM 30243(T)).  

PubMed

An unprecedented new natural product named nocarsin A (1), 5H-4a,6,7a-triazacyclopenta[cd]indene-5,7(6H)-dione (1), together with seven known compounds lumichrome (2), cyclo (L-Leu-L-Tyr) (3), cyclo (L-Ala-L-Ile) (4), cyclo (L-Ala-L-Leu) (5), cyclo (L-Val-L-Ala) (6), 5-methyluracil (7) and uracil (8), was isolated from Nocardia alba sp.nov (YIM 30243(T)), which was isolated from a soil sample collected from Yunnan Province, P. R. China. NMR techniques including COSY, HSQC, ROESY, and HMBC were used to elucidate the structures of these compounds. We report the unambiguous assignments of the (1)H and (13)C NMR spectra of the new compound nocarsin A (1). PMID:19165845

Ding, Zhang-Gui; Zhao, Jiang-Yuan; Yang, Pei-Wen; Li, Ming-Gang; Huang, Rong; Cui, Xiao-Long; Wen, Meng-Liang

2009-04-01

356

13C NMR and fluorescence analysis of tryptophan dynamics in wild-type and two single-Trp variants of Escherichia coli thioredoxin.  

PubMed Central

The rotational motion of tryptophan side chains in oxidized and reduced wild-type (WT) Escherichia coli thioredoxin and in two single-tryptophan variants of E. coli thioredoxin was studied in solution in the temperature range 20-50 degrees C from 13C-NMR relaxation rate measurements at 75.4 and 125.7 MHz and at 20 degrees C from steady-state and time-resolved trp fluorescence anisotropy measurements. Tryptophan enriched with 13C at the delta 1 and epsilon 3 sites of the indole ring was incorporated into WT thioredoxin and into two single-trp mutants, W31F and W28F, in which trp-28 or trp-31 of WT thioredoxin was replaced, respectively, with phenylalanine. The NMR relaxation data were interpreted using the Lipari and Szabo "model-free" approach (G. Lipari and A. Szabo. 1982. J. Amer. Chem. Soc. 104:4546-4559) with trp steady-state anisotropy data included for the variants at 20 degrees C. Values for the correlation time for the overall rotational motion (tau m) from NMR of oxidized and reduced WT thioredoxin at 35 degrees C agree well with those given by Stone et al. (Stone, M. J., K. Chandrasekhar, A. Holmgren, P. E. Wright, and H. J. Dyson. 1993. Biochemistry. 32:426-435) from 15N NMR relaxation rates, and the dependence of tau m on viscosity and temperature was in accord with the Stokes-Einstein relationship. Order parameters (S2) near 1 were obtained for the trp side chains in the WT proteins even at 50 degrees C. A slight increase in the amplitude of motion (decrease in S2) of trp-31, which is near the protein surface, but not of trp-28, which is partially buried in the protein matrix, was observed in reduced relative to oxidized WT thioredoxin. For trp-28 in W31F, order parameters near 1 (S2 > or = 0.8) at 20 degrees C were found, whereas trp-31 in W28F yielded the smallest order parameters (S2 approximately 0.6) of any of the cases. Analysis of time-resolved anisotropy decays in W28F and W31F yielded S2 values in good agreement with NMR, but gave tau m values about 60% smaller. Generally, values of tau e, the effective correlation time for the internal motion, were < or = 60 ps from NMR, whereas somewhat longer times were obtained from fluorescence. The ability of NMR and fluorescence techniques to detect subnanosecond motions in proteins reliably is examined.

Kemple, M D; Yuan, P; Nollet, K E; Fuchs, J A; Silva, N; Prendergast, F G

1994-01-01

357

Changes in dynamics of SRE-RNA on binding to the VTS1p-SAM domain studied by 13C NMR relaxation.  

PubMed

RNA recognition by proteins is often accompanied by significant changes in RNA dynamics in addition to conformational changes. However, there are very few studies which characterize the changes in molecular motions in RNA on protein binding. We present a quantitative (13)C NMR relaxation study of the changes in RNA dynamics in the pico-nanosecond time scale and micro-millisecond time scale resulting from interaction of the stem-loop SRE-RNA with the VTS1p-SAM domain. (13)C relaxation rates of the protonated carbons of the nucleotide base and anomeric carbons have been analyzed by employing the model-free formalism, for a fully (13)C/(15)N-labeled sample of the SRE-RNA in the free and protein-bound forms. In the free RNA, the nature of molecular motions are found to be distinctly different in the stem and the loop region. On binding to the protein, the nature of motions becomes more homogeneous throughout the RNA, with many residues showing increased flexibility at the aromatic carbon sites, while the anomeric carbon sites become more rigid. Surprisingly, we also observe indications of a slow collective motion of the RNA in the binding pocket of the protein. The observation of increased motions on binding is interesting in the context of growing evidence that binding does not always lead to motional restrictions and the resulting entropy gain could favor the free energy of association. PMID:18698768

Oberstrass, Florian C; Allain, Frédéric H-T; Ravindranathan, Sapna

2008-08-13

358

Light-induced chromophore activity and signal transduction in phytochromes observed by 13C and 15N magic-angle spinning NMR  

PubMed Central

Both thermally stable states of phytochrome, Pr and Pfr, have been studied by 13C and 15N cross-polarization (CP) magic-angle spinning (MAS) NMR using cyanobacterial (Cph1) and plant (phyA) phytochrome sensory modules containing uniformly 13C- and 15N-labeled bilin chromophores. Two-dimensional homo- and heteronuclear experiments allowed most of the 13C chemical shifts to be assigned in both states. Chemical shift differences reflect changes of the electronic structure of the cofactor at the atomic level as well as its interactions with the chromophore-binding pocket. The chromophore in cyanobacterial and plant phytochromes shows very similar features in the respective Pr and Pfr states. The data are interpreted in terms of a strengthened hydrogen bond at the ring D carbonyl. The red shift in the Pfr state is explained by the increasing length of the conjugation network beyond ring C including the entire ring D. Enhanced conjugation within the ?-system stabilizes the more tensed chromophore in the Pfr state. Concomitant changes at the ring C propionate carboxylate and the ring D carbonyl are explained by a loss of hydrogen bonding to Cph1-His-290 and transmittance of conformational changes to the ring C propionate via a water network. These and other conformational changes may lead to modified surface interactions, e.g., along the tongue region contacting the bilin chromophore.

Rohmer, Thierry; Lang, Christina; Hughes, Jon; Essen, Lars-Oliver; Gartner, Wolfgang; Matysik, Jorg

2008-01-01

359

A comparison of dissolved humic substances from seawater with Amazon River counterparts by sup 13 C-NMR spectrometry  

SciTech Connect

Although dissolved organic matter (DOM) in seawater constitutes one of the major reservoirs of reduced carbon on earth, the biochemical and geographic origins of this material and its hydrophobic humic component remain unclear. Rivers have been suggested as a potentially important source of marine DOM, but this implication has not yet been systematically tested by direct comparisons of the bulk structural characteristics of DOM isolated from representative ocean reservoirs and their major river sources. The authors report here such a comparison and find that dissolved humic substances isolated from surface and deep seawater in the East Equatorial and north Central Pacific are enriched in nitrogen and {sup 13}C and depleted in unsaturated carbon with respect to counterparts from the Amazon River system. Based on these observations, riverine dissolved humic substances appear to comprise a small fraction of seawater humic substances and therefore must be efficiently and rapidly removed from the ocean.

Hedges, J.I. (Univ. of Washington, Seattle (United States)); Hatcher, P.G. (Pennsylvania State Univ., University Park (United States)); Ertel, J.R. (Univ. of Georgia, Athens (United States)); Meyers-Schulte, K.J. (Naval Ocean Research Group, San Diego, CA (United States))

1992-04-01

360

Solid-state 13C NMR studies of a large fossil gymnosperm from the Yallourn Open Cut, Latrobe Valley, Australia  

USGS Publications Warehouse

A series of samples taken from the cross section of a 3-m-diameter fossilized gymnospermous log (Araucariaceae) in the Yallourn Seam of the Australian brown coals was examined by solid state 13C nuclear magnetic resonance to delineate chemical changes related to the combined processes of peatification and coalification. The results show that cellulosic materials were degraded and lost on the periphery of the log, however, the degree of such degradation in the central core is substantially less. The lignin is uniformly altered by coalification reactions to a macromolecular substance displaying decreased aryl ether linkages but significantly greater amounts of carbon linkages compared to modern lignin. Changes in the methoxyl carbon contents of lignin in cross section reveal demethylation reactions, but these do not appear to be related to degree of carbon linking. Both the degredation of cellulosic materials and demethylation of lignin appear to be early diagenetic processes occurring during peatification independently of the coalification reactions. ?? 1989.

Bates, A. L.; Hatcher, P. G.

1989-01-01

361

13C NMR, micro-FTIR and fluorescence spectra, and pyrolysis-gas chromatograms of coalified foliage of late Carboniferous medullosan seed ferns, Nova Scotia, Canada: Implications for coalification and chemotaxonomy  

Microsoft Academic Search

The cuticles and cuticle-free compressions of three Carboniferous medullosan seed-fern leaf species (Macroneuropteris scheuchzeri, Neuropteris ovata var. simonii and Alethopteris lesquereuxii) were analyzed by elemental, 13C nuclear magnetic resonance (NMR), micro-FTIR (Fourier transform infrared) and coal petrographic techniques. The 13C NMR spectra of the cuticle-free compressions and the associated whole coal (high volatile A\\/B bituminous coal rank) are generally similar

Paul C Lyons; William H Orem; Maria Mastalerz; Erwin L Zodrow; Angelika Vieth-Redemann; R. Marc Bustin

1995-01-01

362

Experimental and simulated 1H and 13C NMR spectra (GIAO/DFT approach) and molecular and crystal structures of dimethyl-dinitro-azo- and dimethyl-dinitro-hydrazo-pyridines  

NASA Astrophysics Data System (ADS)

The 1H and 13C NMR spectra of the 4,4?(or 6,6?)-dimethyl-3,3?-dinitro-2,2?-azo- and hydrazo-pyridine have been measured in the solid state and solution. The spectral data have been analyzed on the basis of DFT quantum chemical calculations using the B3LYP/6-311G, 6-311++G and 6-311G?? approaches. The structures of all molecules have been optimized starting from trans and cis molecular geometry and additionally from diimino form for hydrazoderivatives and compared to the XRD data. The optimization process always led to the trans - isomers. The influence of the azo-bond on the electronic properties of the whole system was analyzed. The role of the hydrogen bond in the structure stabilization of the hydrazo-derivatives has been discussed.

Wandas, M.; Kucharska, E.; Michalski, J.; Talik, Z.; Lorenc, J.; Hanuza, J.

2011-10-01

363

In situ kinetic study on hydrothermal transformation of D-glucose into 5-hydroxymethylfurfural through D-fructose with 13C NMR.  

PubMed

Kinetics of hydrothermal reaction of D-glucose was investigated at 0.02 M over a temperature range of 120-160 °C by applying in situ (13)C NMR spectroscopy. D-Glucose was found to be reversibly transformed first into D-fructose (intermediate) and successively into 5-hydroxymethylfurfural (5-HMF) through dehydration. The carbon mass balance has been kept within the detection limit, and no other reaction pathways are present. The hydrothermal reaction of d-glucose is thus understood as that of D-fructose in the sense that the D-glucose reaction proceeds only through D-fructose. All the isomers of D-glucose and D-fructose were detected by the in situ (13)C NMR in D(2)O: they are the open chains and the pyranoses and furanoses of ?- and ?-types. The ?-forms are the most stable due to the hydration. For both D-glucose and D-fructose, the isomers are in a rapid equilibrium for each monosaccharide, and they are treated collectively in the kinetic analysis of the slower hydrothermal reactions. The reactions are of the first order with respect to the concentrations of D-glucose and D-fructose, and D-glucose converts to 5-HMF on the order of hours. The kinetic parameters were determined by the in situ method. PMID:22070574

Kimura, Hiroshi; Nakahara, Masaru; Matubayasi, Nobuyuki

2011-11-09

364

Residue specific hydration of primary cell wall potato pectin identified by solid-state 13C single-pulse MAS and CP/MAS NMR spectroscopy.  

PubMed

Hydration of rhamnogalacturonan-I (RG-I) derived from potato cell wall was analyzed by (13)C single-pulse (SP) magic-angle-spinning (MAS) and (13)C cross-polarization (CP) MAS nuclear magnetic resonance (NMR) and supported by (2)H SP/MAS NMR experiments. The study shows that the arabinan side chains hydrate more readily than the galactan side chains and suggests that the overall hydration properties can be controlled by modifying the ratio of these side chains. Enzymatic modification of native (NA) RG-I provided samples with reduced content of arabinan (sample DA), galactan (sample DG), or both side chains (sample DB). Results of these samples suggested that hydration properties were determined by the length and character of the side chains. NA and DA exhibited similar hydration characteristics, whereas DG and DB were difficult to hydrate because of the less hydrophilic properties of the rhamnose-galacturonic acid (Rha-GalA) backbone in RG-I. Potential food ingredient uses of RG-I by tailoring of its structure are discussed. PMID:21462966

Larsen, Flemming H; Byg, Inge; Damager, Iben; Diaz, Jerome; Engelsen, Søren B; Ulvskov, Peter

2011-04-14

365

/sup 13/C and /sup 1/H NMR spectra and structure of the products from the condensation of 1,3-dicarbonyl compounds with aldehydes  

SciTech Connect

The structure of the diadducts formed in the reaction of 1,3-dicarbonyl compounds with aldehydes in a ratio of 2:1 under the conditions of the Knoevenagel condensation was studied by /sup 13/C and /sup 1/H NMR spectroscopy. It was shown that acyclic tetracarbonyl compounds are formed in the absence of a catalyst while substituted cyclohexanones are formed in the presence of piperidine. The acyclic tetracarbonyl compounds exist mainly in the tetraketo form in solution, and the presence of the monoenol form was established for dimethyl 2,4-diacetylpentanedioate in CD/sub 2/Cl/sub 2/. The most characteristic signals which distinguish between the cyclic diadducts and the acyclic products are the signals of the C/sup 5/ (delta 72 ppm) and C/sup 6/ (delta 52 ppm) atoms. The presence of a keto-enol equilibrium in 2,4-diacetyl-5-hydroxy-3-(p-methoxyphenyl)-5-methylcyclohexanone was demonstrated by /sup 13/C NMR.

Emelina, E.E.; Gindin, V.A.; Ershov, B.A.

1988-05-20

366

A computational NICS and 13C NMR characterization of the substitution patterns of C70-2x(BN)x fullerenes (x=1-25)  

NASA Astrophysics Data System (ADS)

A density functional study has been performed to investigate the electronic and magnetic properties of BN substituted fullerenes C70-2x(BN)x (x=1, 2, 3, 6, 9, 12, 15, 17, 19, 21, 23 and 25) based on the NMR parameters and NICS index. The calculated 13C chemical shielding (CS) tensors are found to be perturbed at the first and second neighbors of the doped atoms while the other distant carbon atoms not to be influenced significantly. 13C Chemical shifts (?iso) of the second neighbors of nitrogen and boron are significantly shifted to upfield and downfield (the second neighboring effects), respectively. Besides, chemical shifts are also affected by the curvature of the corresponding sites; for example, the perturbed sites at the caps yield smaller absolute values of chemical shifts than those located at the equator. Nucleus independent chemical shifts (NICS) at the cage centers of heterofullerenes (from -25.29 to -8.80) demonstrate that all the substituted species are aromatic, but less than C70 (-27.29). The predicted NICS values may be useful for identification of the heterofullerenes through their endohedral 3He NMR chemical shifts.

Ghafouri, Reza; Anafcheh, Maryam

2012-11-01

367

sup 13 C and sup 15 N NMR studies on the interaction between 6,7-dimethyl-8-ribityllumazine and lumazine protein  

SciTech Connect

The interaction between the prosthetic group 6,7-dimethyl-8-(1{prime}-D-ribityl)lumazine and the lumazine apoproteins from two marine bioluminescent bacteria, one from a relatively thermophilic species, Photobacterium leiognathi, and the other from a psychrophilic species, Photobacterium phosphoreum, was studied by {sup 13}C and {sup 15}N NMR using various selectively enriched derivatives. It is shown that the electron distribution in the protein-bound 6,7-dimethyl-8-ribityllumazine differs from that of free 6,7-dimethyl-8-ribityllumazine in buffer. The {sup 13}C and {sup 15}N chemical shifts indicate that the protein-bound 6,7-dimethyl-8-ribityllumazine is embedded in a polar environment and that the ring system is strongly polarized. It is concluded that the two carbonyl groups play an important role in the polarization of the molecule. The N(3)-H group is not accessible to bulk solvent. The N(8) atom is sp{sup 2} hybridized and has {delta}+ character. Nuclear Overhauser effect studies indicate that the 6,7-dimethyl-8-ribityllumazine ring is rigidly bound with no internal mobility. The NMR results indicate that the interaction between the ring system and the two apoproteins is almost the same.

Vervoort, J.; Mueller, F. (Agricultural Univ., Wageningen (Netherlands)); O'Kane, D.J.; Lee, J. (Univ. of Georgia, Athens (USA)); Bacher, A.; Strobl, G. (Technical Univ. of Munich (West Germany))

1990-02-20

368

1H- and 13C-NMR investigation of redox-state-dependent and temperature-dependent conformation changes in horse cytochrome c.  

PubMed

The redox-state dependent changes in chemical shift, which have been measured for almost 100 CHn groups in the 13C-NMR spectra of horse cytochrome c [Santos, H., and Turner, D. L. (1992) Eur. J. Biochem. 206, 721-728], have been used to investigate the nature of the redox-related change in conformation. Apart from the haem and its axial ligands, the shifts are found to be dominated by the electron-nuclear dipolar coupling in the oxidised form, as was the case in 1H-NMR studies. These pseudocontact shifts are well described by using an empirically determined magnetic susceptibility tensor in conjunction with atomic coordinates for the horse cytochrome c. The groups which fit least well are located in the vicinity of Trp59. Comparison between 1H and 13C shifts and their temperature dependence shows that the differences from expectation based on a single structure for both oxidation states are caused largely by changes in the diamagnetic contribution to the chemical shifts. Since these are different for 1H and 13C resonances they indicate, independently from crystal structure data, some redox-related movement of the protein under the haem. The significance of these results for understanding electron transfer pathways is discussed. Finally, the temperature dependence of the pseudocontact shifts in the range 30-50 degrees C is shown to be anomalous. Approximately half of the anomalous effect may be attributed to Zeeman mixing of the electronic wavefunctions with a spin-orbit coupling constant lambda = 241 cm-1, while the other half is attributed to thermal expansion of the protein. PMID:8382154

Turner, D L; Williams, R J

1993-02-01

369

Cycling of dissolved and particulate organic matter at station Aloha: Insights from 13C NMR spectroscopy coupled with elemental, isotopic and molecular analyses  

NASA Astrophysics Data System (ADS)

Compositions of ultrafiltered dissolved organic matter (UDOM) and ultrafiltered particulate organic matter (UPOM) were characterized in samples collected from a depth profile (20-4000 m) in the North Pacific at Station Aloha. 13C Nuclear Magnetic Resonance (NMR) analyses together with ?13C values, carbon/nitrogen (C/N) ratios and molecular characterizations of UDOM and UPOM indicate different bulk chemical compositions and sources for these two size fractions. Carbohydrates and amino acids are the major biomolecules present in UDOM and UPOM. At all depths, UPOM had higher amino acid and lower carbohydrate contents compared to UDOM. UDOM and UPOM samples showed a decrease in the relative contribution of carbohydrates to the total organic carbon with increasing depth, whereas the contributions of lipids increased. Amino acids did not show any clear depth trends for UDOM, but decreased in UPOM. The compositional trends with depth indicate that selective degradation processes, which preferentially remineralize reactive biomolecules such as carbohydrates, affect UDOM and UPOM compositions in the water column. Molecular analyses of carbohydrates and amino acids characterized ˜9% of the C in UDOM and ˜28% of the C in UPOM. Although a relatively small proportion of the total C was characterizable with molecular analyses, the depth trends and the ratio of amino acids to carbohydrates in UPOM and UDOM were similar to those determined by 13C NMR. This suggests that the organic matter fraction characterized by molecular analyses is representative of the molecularly uncharacterized fraction of organic matter. It is postulated that the molecularly uncharacterized fraction is encapsulated or shielded by a hydrolysis-resistant matrix or the individual amino acid and sugar units have been altered to form a chemical entity unrecognizable by the molecular analyses.

Sannigrahi, Poulomi; Ingall, Ellery D.; Benner, Ronald

2005-08-01

370

FT-IR, UV-vis, 1H and 13C NMR spectra and the equilibrium structure of organic dye molecule disperse red 1 acrylate: a combined experimental and theoretical analysis.  

PubMed

This study reports the characterization of disperse red 1 acrylate compound by spectral techniques and quantum chemical calculations. The spectroscopic properties were analyzed by FT-IR, UV-vis, (1)H NMR and (13)C NMR techniques. FT-IR spectrum in solid state was recorded in the region 4000-400 cm(-1). The UV-vis absorption spectrum of the compound that dissolved in methanol was recorded in the range of 200-800 nm. The (1)H and (13)C NMR spectra were recorded in CDCl(3) solution. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational wavenumbers were calculated and scaled values were compared with experimental FT-IR spectrum. A satisfactory consistency between the experimental and theoretical spectra was obtained and it shows that the hybrid DFT method is very useful in predicting accurate vibrational structure, especially for high-frequency region. The complete assignments were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts were calculated using the gauge-invariant atomic orbital (GIAO) method. A study on the electronic properties were performed by timedependent DFT (TD-DFT) and CIS(D) approach. To investigate non linear optical properties, the electric dipole moment ?, polarizability ?, anisotropy of polarizability ?? and molecular first hyperpolarizability ? were computed. The linear polarizabilities and first hyperpolarizabilities of the studied molecule indicate that the compound can be a good candidate of nonlinear optical materials. PMID:21958518

Cinar, Mehmet; Coruh, Ali; Karabacak, Mehmet

2011-09-09

371

89Y and 13C NMR cluster and carbon cage studies of an yttrium metallofullerene family, Y3N@C(2n) (n = 40-43).  

PubMed

The members of a new family of yttrium trimetallic nitride-templated (TNT) endohedral metallofullerenes (EMFs), Y(3)N@C(2n) (n = 40-43), have been synthesized and purified. On the basis of experimental and computational (13)C NMR studies, we propose cage structures for Y(3)N@I(h)-C(80) (IPR allowed), Y(3)N@D(5h)-C(80) (IPR allowed), Y(3)N@C(s)-C(82) (non-IPR), Y(3)N@C(s)-C(84) (non-IPR), and Y(3)N@D(3)-C(86) (IPR allowed). A significant result is the limited number of isomers found for each carbon cage. For example, there are 24 isolated pentagon rule (IPR) and 51 568 non-IPR structures possible for the C(84) cage, but only one major isomer of Y(3)N@C(s)-C(84) was found. The current study confirms the unique role of the trimetallic nitride (M(3)N)(6+) cluster template in the Kratschmer-Huffman electric-arc process for fullerene cage size and high symmetry isomer selectivity. This study reports the first (89)Y NMR results for Y(3)N@I(h)-C(80,) Y(3)N@C(s)(51365)-C(84), and Y(3)N@D(3)(19)-C(86), which reveal a progression from isotropic to restricted (Y(3)N)(6+) cluster motional processes. Even more surprising is the sensitivity of the (89)Y NMR chemical shift parameter to subtle changes in the electronic environment at each yttrium nuclide in the (Y(3)N)(6+) cluster (more than 200 ppm for these EMFs). This (89)Y NMR study suggests that (89)Y NMR will evolve as a powerful tool for cluster motional studies of EMFs. PMID:19639998

Fu, Wujun; Xu, Liaosa; Azurmendi, Hugo; Ge, Jiechao; Fuhrer, Tim; Zuo, Tianming; Reid, Jonathan; Shu, Chunying; Harich, Kim; Dorn, Harry C

2009-08-26

372

Solid state 13C NMR analysis of shales and coals from Laramide Basins. Final report, March 1, 1995--March 31, 1996  

SciTech Connect

This Western Research Institute (WRI) jointly sponsored research (JSR) project augmented and complemented research conducted by the University of Wyoming Institute For Energy Research for the Gas Research Institute. The project, {open_quotes}A New Innovative Exploitation Strategy for Gas Accumulations Within Pressure Compartments,{close_quotes} was a continuation of a project funded by the GRI Pressure Compartmentalization Program that began in 1990. That project, {open_quotes}Analysis of Pressure Chambers and Seals in the Powder River Basin, Wyoming and Montana,{close_quotes} characterized a new class of hydrocarbon traps, the discovery of which can provide an impetus to revitalize the domestic petroleum industry. In support of the UW Institute For Energy Research`s program on pressure compartmentalization, solid-state {sup 13}C NMR measurements were made on sets of shales and coals from different Laramide basins in North America. NMR measurements were made on samples taken from different formations and depths of burial in the Alberta, Bighorn, Denver, San Juan, Washakie, and Wind River basins. The carbon aromaticity determined by NMR was shown to increase with depth of burial and increased maturation. In general, the NMR data were in agreement with other maturational indicators, such as vitrinite reflectance, illite/smectite ratio, and production indices. NMR measurements were also obtained on residues from hydrous pyrolysis experiments on Almond and Lance Formation coals from the Washakie Basin. These data were used in conjunction with mass and elemental balance data to obtain information about the extent of carbon aromatization that occurs during artificial maturation. The data indicated that 41 and 50% of the original aliphatic carbon in the Almond and Lance coals, respectively, aromatized during hydrous pyrolysis.

Miknis, F.P.; Jiao, Z.S.; Zhao, Hanqing; Surdam, R.C.

1998-12-31

373

Expression and purification of 15N- and 13C-isotope labeled 40-residue human Alzheimer's ?-amyloid peptide for NMR-based structural analysis  

PubMed Central

Amyloid fibrils of Alzheimer’s ?-amyloid peptide (A?) are a primary component of amyloid plaques, a hallmark of Alzheimer’s disease (AD). Enormous attention has been given to the structural features and functions of A? in amyloid fibrils and other type of aggregates in associated with development of AD. This report describes an efficient protocol to express and purify high-quality 40-residue A?(1–40), the most abundant A? in brains, for structural studies by NMR spectroscopy. Over-expression of A?(1–40) with glutathione S-transferase (GST) tag connected by a Factor Xa recognition site (IEGR?) in E. Coli resulted in the formation of insoluble inclusion bodies even with the soluble GST tag. This problem was resolved by efficient recovery of the GST-A? fusion protein from the inclusion bodies using 0.5% (w/v) sodium lauroyl sarcosinate as solubilizing agent and subsequent purification by affinity chromatography using a glutathione agarose column. The removal of the GST tag by Factor Xa enzymatic cleavage and purification by HPLC yielded as much as ~7 mg and ~1.5 mg of unlabeled A?(1–40) and uniformly 15N- and/or 13C-protein A?(1–40) from 1 L of the cell culture, respectively. Mass spectroscopy of unlabeled and labeled A? and 1H/15N HSQC solution NMR spectrum of the obtained 15N-labeled A? in the monomeric form confirmed the expression of native A?(1–40). It was also confirmed by electron micrography and solid-state NMR analysis that the purified A?(1–40) self-assembles into ?-sheet rich amyloid fibrils. To the best of our knowledge, our protocol offers the highest yields among published protocols for production of recombinant A?(1–40) samples that are amendable for an NMR-based structural analysis. The protocol may be applied to efficient preparation of other amyloid-forming proteins and peptides that are 13C- and 15N-labeled for NMR experiments.

Long, Fei; Cho, Wonhwa; Ishii, Yoshitaka

2011-01-01

374

Sulfite action in glycolytic inhibition: in vivo real-time observation by hyperpolarized (13)C NMR spectroscopy.  

PubMed

Detecting the molecular targets of xenobiotic substances in vivo poses a considerable analytical challenge. Here, we describe the use of an NMR-based tracer methodology for the instantaneous in vivo observation of sulfur(IV) action on cellular metabolism. Specifically, we find that glycolytic flux is directed towards sulfite adducts of dihydroxyacetone phosphate and pyruvate as off-pathway intermediates that obstruct glycolytic flux. In particular, the pyruvate-sulfite association hinders the formation of downstream metabolites. The apparent in vivo association constant of pyruvate and sulfite agrees with the apparent inhibition constant of CO(2) formation, thus supporting the importance of pyruvate interception in disturbing central metabolism and inhibiting NAD regeneration. PMID:22961998

Meier, Sebastian; Solodovnikova, Natalia; Jensen, Pernille R; Wendland, Jürgen

2012-09-07

375

Solid-state and solution /sup 13/C NMR in the conformational analysis of methadone-hydrochloride and related narcotic analgesics  

SciTech Connect

Solid state and solution /sup 13/C NMR have been used to study the conformations of the racemic mixtures and single enantiomers of methadone hydrochloride, alpha and beta methadol hydrochloride, and alpha and beta acetylmethadol hydrochloride. The NMR spectra acquired for the compounds as solids, and in polar and nonpolar solvents are compared, in order to determine the conformation of the molecules in solution. To determine the reliability of assigning solution conformations by comparing solution and solid state chemical shift data, three bond coupling constants measured in solution are compared with those calculated from X-ray data. The conformations of the racemic mixture and plus enantiomer of methadone hydrochloride have been shown to be very similar in the solid state, where minor differences in conformation can be seen by comparing NMR spectra obtained for the solids. Also shown is that the molecules of methadone hydrochloride have conformations in polar and in nonpolar solvents which are very similar to the conformation of the molecules in the solid state.

Sumner, S.C.J.

1986-01-01

376

Use of solid waste for chemical stabilization: Adsorption isotherms and {sup 13}C solid-state NMR study of hazardous organic compounds sorbed on coal fly ash  

SciTech Connect

Adsorption of hazardous organic compounds on the Dave Johnston plant fly ash is described. Fly ash from Dave Johnston and Laramie River power plants were characterized using elemental, x-ray, and {sup 29}Si NMR; the Dave Johnston (DJ) fly ash had higher quartz contents, while the Laramie River fly ash had more monomeric silicate anions. Adsorption data for hydroaromatics and chlorobenzenes indicate that the adsorption capacity of DJ coal fly ash is much less than that of activated carbon by a factor of >3000; but it is needed to confirm that solid-gas and solid-liquid equilibrium isotherms can indeed be compared. However, for pyridine, pentachlorophenol, naphthalene, and 1,1,2,2-tetrachloroethane, the DJ fly ash appears to adsorb these compounds nearly as well as activated carbon. {sup 13}C NMR was used to study the adsorption of hazardous org. cpds on coal fly ash; the nuclear spin relaxation times often were very long, resulting in long experimental times to obtain a spectrum. Using a jumbo probe, low concentrations of some hazardous org. cpds could be detected; for pentachlorophenol adsorbed onto fly ash, the chemical shift of the phenolic carbon was changed. Use of NMR to study the adsorption needs further study.

Netzel, D.A.; Lane, D.C.; Rovani, J.F.; Cox, J.D.; Clark, J.A.; Miknis, F.P.

1993-09-01

377

Hydrolysis of Functional Monomers in a Single-bottle Self-etching Primer--Correlation of 13C NMR and TEM Findings  

PubMed Central

Self-etching primers/adhesives that combine acidic methacrylate monomers with water in a single bottle are hydrolytically unstable and require refrigeration to extend their shelf-lives. This study tested the null hypothesis that one year of intermittent refrigeration of a 4-MET-containing simplified self-etching primer does not result in hydrolytic changes that are identifiable by transmission electron microscopy and 13C NMR spectroscopy. Human dentin was bonded with UniFil Bond immediately after being unpacked, or after one year of intermittent refrigeration at 4°C. Fresh and aged primers were analyzed by NMR for chemical changes. Ultrastructural observations indicated that there was an augmentation in etching capacity of the aged adhesive that was not accompanied by resin infiltration or effective polymerization. New NMR peaks detected from the aged ethanol-based primer confirmed that degradation occurred initially via esterification with ethanol, followed by hydrolysis of both ester groups in the 4-MET. Hydrolysis of functional methacrylate monomers occurs despite intermittent refrigeration.

Nishiyama, N.; Tay, F. R.; Fujita, K.; Pashley, D. H.; Ikemura, K.; Hiraishi, N.; King, N. M.

2008-01-01

378

Multimodal inclusion complexes between barbiturates and 2-hydroxypropyl-beta-cyclodextrin in aqueous solution: isothermal titration microcalorimetry, (13)C NMR spectrometry, and molecular dynamics simulation.  

PubMed

Multiple types (structures) of inclusion complexes between barbiturates and 2-hydroxypropyl-beta-cyclodextrin (HPCD) were evaluated by isothermal titration microcalorimetry and (13)C NMR spectroscopy. The geometries of the inclusion complexes were suggested by molecular dynamics simulation. Barbituric acid (BA), barbital (B), amobarbital (AB), pentobarbital (PB), secobarbital (SB), cyclobarbital (CB), and phenobarbital (PHB) were used as barbiturates with different substituents on the barbituric acid ring and compared for inclusion types in aqueous solution. The association constants (K), stoichiometries, and thermodynamic parameters change in free energy (DeltaG) change in enthalpy (DeltaH), and change in entropy [DeltaS] for each type of complex were determined from the calorimetric data. The inclusion complexation was largely entropy driven because of hydrophobic interactions. The values of K increased in the order BA13)C Nuclear Magnetic Resonance (NMR) chemical shifts for the substituent R2 of barbiturates. These types were very stable in aqueous solution at various pHs. The second type of complex, with low affinity (K(2)), was characterized by large negative values of DeltaH(2) and small positive DeltaS(2), reflecting van der Waals' interactions in the un-ionized forms of barbiturates at pH values less than pK(a). The values of K(2) were markedly decreased to <10(3) M(-1) as the barbiturates were ionized over pH 8. Thus, in the second type, the barbituric acid ring contributed to forming the complexes. The geometries were stabilized by hydrogen bond formation between the hetero atoms in the barbituric acid ring and the secondary hydroxyl groups on the rim of the cyclodextrin. The (13)C NMR chemical shifts of C4 and C6 carbons in the barbituric acid ring were moved upfield significantly by the inclusion complexation. On the other hand, B and BA could form only one type of complex, the lid-type supramolecular complex with small association constants. PMID:11536223

Aki, H; Niiya, T; Iwase, Y; Yamamoto, M

2001-08-01

379

Application of Spectroscopic Techniques (FT-IR, 13C NMR) to the analysis of humic substances in volcanic soils along an environmental gradient (Tenerife, Canary Islands, Spain)  

NASA Astrophysics Data System (ADS)

Andosols and andic soils are considered as efficient C-sinks in terms of C sequestration. These soils are usually developed from volcanic materials, and are characterized by a predominance of short-range ordered minerals like allophanes, imogolite and other Fe and Al oxyhydroxides. Such materials occur commonly associated with organic compounds, thus generating highly stable organo-mineral complexes and leading to the accumulation of a high amount of organic carbon. Spectroscopic methods like FT-IR and 13C NMR are suitable for the analysis of the chemical structure of soil humic substances, and allow identifying distinct functional groups and protein, lipids, lignin, carbohydrate-derived fragments. In this work we study the structural features of four soils developed on Pleistocene basaltic lavae in Tenerife (Canary Island, Spain), distributed along an altitudinal climatic gradient. The soil sequence comprises soils with different degree of geochemical evolution and andic character, including a mineral ‘Hypersalic Solonchak' (Tabaibal de Rasca), a slightly vitric ‘Luvic Phaeozem' (Los Frailes), a degraded and shallow ‘Endoleptic, fulvic, silandic Andosol' (Siete Lomas), and a well-developed and deep ‘Fulvic, silandic, Andosol' (Ravelo). Samples of the raw soil and humic and fulvic acids isolated from the surface horizons were analyzed. The results show a low content of organic carbon in the mineral soil, the inherited humin predominating, and a very high content of humic and fulvic acids in Andosols. The FT-IR and 13C NMR spectra of the raw soil samples show a low resolution, related to interferences from mineral complexes signals, particularly in soils with lower organic carbon content. 13C NMR shows a predominance of O-alkyl carbon (derived of carbohydrates) in andic soils, whereas O-alkyl and aromatic fractions are most evident in the mineral soil. The humic acids spectra are characterized by a dominance of alkyl and aromatic fractions with a high degree of maturity, and a minor presence of O-alkyl and carbonyl carbon. The humic acids of the mineral soil are rich in lignin fragments, whereas those of the andic soils are more aromatic and have a higher degree of oxidation. O-alkyl carbon dominates in fulvic acids, exhibiting an enrichment in aromatic compounds and a lower oxidation degree in the mineral soil. These results point to a poorly-transformed organic matter resulting from direct humification processes, in the non-andic soil. On the other hand, the humic substances in the andic soils show a high degree of maturity, with a low presence of lignin fragments and a higher oxidation degree.

Rodriguez Rodriguez, Antonio; María Armas Herrera, Cecilia; González Pérez, José Antonio; González-Vila, Francisco Javier; Arbelo Rodríguez, Carmen Dolores; Mora Hernández, Juan Luis; Polvillo Polo, Oliva

2010-05-01

380

Elucidating Metabolic Pathways for Amino Acid Incorporation Into Dragline Spider Silk using 13C Enrichment and Solid State NMR  

PubMed Central

Spider silk has been evolutionarily optimized for contextual mechanical performance over the last 400 million years. Despite precisely balanced mechanical properties, which have yet to be reproduced, the underlying molecular architecture of major ampullate spider silk can be simplified being viewed as a versatile block copolymer. Four primary amino acid motifs: polyalanine, (GA)n, GPGXX, and GGX (X = G,A,S,Q,L,Y) will be considered in this study. Although synthetic mimetics of many of these amino acid motifs have been produced in several biological systems, the source of spider silk’s mechanical integrity remains elusive. Mechanical robustness may be a product not only of the amino acid structure but also of the tertiary structure of the silk. Historically, solid state Nuclear Magnetic Resonance (ssNMR) has been used to reveal the crystalline structure of the polyalanine motif; however, limitations in amino acid labeling techniques have obscured the structures of the GGX and GPGXX motifs thought to be responsible for the structural mobility of spider silk. We describe the use of metabolic pathways to label tyrosine for the first time as well as to improve the labeling efficiency of proline. These improved labeling techniques will allow the previously unknown tertiary structures of major ampullate silk to be probed.

Creager, Melinda S.; Izdebski, Thomas; Brooks, Amanda E.; Lewis, Randolph V.

2013-01-01

381

Elucidating metabolic pathways for amino acid incorporation into dragline spider silk using 13C enrichment and solid state NMR.  

PubMed

Spider silk has been evolutionarily optimized for contextual mechanical performance over the last 400 Ma. Despite precisely balanced mechanical properties, which have yet to be reproduced, the underlying molecular architecture of major ampullate spider silk can be simplified being viewed as a versatile block copolymer. Four primary amino acid motifs: polyalanine, (GA)(n), GPGXX, and GGX (X = G,A,S,Q,L,Y) will be considered in this study. Although synthetic mimetics of many of these amino acid motifs have been produced in several biological systems, the source of spider silk's mechanical integrity remains elusive. Mechanical robustness may be a product not only of the amino acid structure but also of the tertiary structure of the silk. Historically, solid state nuclear magnetic resonance (ssNMR) has been used to reveal the crystalline structure of the polyalanine motif; however, limitations in amino acid labeling techniques have obscured the structures of the GGX and GPGXX motifs thought to be responsible for the structural mobility of spider silk. We describe the use of metabolic pathways to label tyrosine for the first time as well as to improve the labeling efficiency of proline. These improved labeling techniques will allow the previously unknown tertiary structures of major ampullate silk to be probed. PMID:21334448

Creager, Melinda S; Izdebski, Thomas; Brooks, Amanda E; Lewis, Randolph V

2011-02-17

382

Characterization and comparison of two ligno-cellulosic substrates by (13)C CP/MAS NMR, XPS, conventional pyrolysis and thermochemolysis.  

PubMed

Ligno-cellulosic substrates (LCSs) isolated from wheat straw and bran exhibit high complexing capacities and may have important applications for metal removal from industrial effluents. These two LCSs were examined in the present work by spectroscopic and pyrolytic methods (solid state cross polarization magic angle spinning (CP/MAS) (13)C NMR, XPS, conventional Curie pyrolysis (Cupy)/GC/MS, and TMAH thermochemolysis/GC/MS). This combined study highlighted the limitation of some of the above methods when applied to ligno-cellulosic materials and the resulting biases and the usefulness of TMAH thermochemolysis. A large difference in composition was observed between bran- and straw-LCS due to a much higher contribution of alkyl moieties in the former. These moieties correspond to fatty acids esterified to the ligno-cellulosic macromolecular structure and such carboxylic functions should play an important role for metal complexation. PMID:12194046

Gauthier, A; Derenne, S; Dupont, L; Guillon, E; Largeau, C; Dumonceau, J; Aplincourt, M

2002-06-25

383

Detailed analysis of the essential oil from Cistus albidus L. by combination of GC/RI, GC/MS and 13C-NMR spectroscopy.  

PubMed

The composition of the essential oil of Cistus albidus (L.) obtained from plants growing wild in Provence (France) has been investigated using GC-RI (RI = retention indices), GC/MS and (13)C-NMR. Eighty-eight components were reported accounting for 81.8% of the essential oil. This essential oil was characterized by a high content of sesquiterpenes with alpha-zingiberene (12.8%), alpha-curcumene (7.7%), (E)-beta-caryophyllene (5.9%), alpha-cadinol (5.4%), alpha-bisabolol (4.1%), caryophyllene oxide (3.8%), allo-aromadendrene (3.4%), delta-cadinene (3.4%), and germacrene D (3.1%) being the main components. PMID:18932091

Paolini, Julien; Tomi, Pierre; Bernardini, Antoine-François; Bradesi, Pascale; Casanova, Joseph; Kaloustian, Jacques

2008-01-01

384

Non-fermi liquid behavior of the organic superconductor ?-(BEDT-TTF)4Hg2.89Br8 probed by 13C-NMR  

NASA Astrophysics Data System (ADS)

We assessed 13C-NMR measurements in an organic salt, ?-(BEDT-TTF)4Hg2.89Br8, which exhibits superconductivity at 4.3 K under ambient pressure. We observed that (T1T)-1 of H // and ? layer at ambient pressure increased as the temperature was decreased to 7 K, but decreased further at lower temperatures, suggesting that the decrease of (T1T)-1 was not due to the superconductive fluctuations, but due to the magnetism of the conduction electrons. Application of pressure suppresses (T1T)-1, with (T1T)-1 becoming constant above 2 GPa. These results suggest that applying pressure alters the electron system from a non-Fermi liquid (NFL) to a Fermi liquid (FL) state and that antiferromagnetic fluctuations contribute to the origin of NFL behavior. Whereas most organic conductors show Fermi liquid behavior, this salt is an organic superconductor that shows NFL behavior due to the antiferromagnetic fluctuations.

Eto, Yoshihiro; Itaya, Megumi; Kawamoto, Atsushi

2010-06-01

385

13C-NMR studies of polyunsaturated triacylglycerols of type AAA and mixed triacylglycerols containing saturated, acetylenic and ethylenic acyl groups  

Microsoft Academic Search

The 13C-NMR spectroscopic properties of eight triacylglycerols of type AAA containing polyunsaturated fatty acids, viz. 18:2(9Z,12Z) 18:2(9Z,12E), 18:2(9E,12Z) 18:2(9E,12E), 18:2(8E,12Z) 18:3(9Z,12Z,15Z) 20:3(5Z,11Z,14Z) and 20:4(5Z,11Z,14Z,17Z), have been studied. From the carbon shift values of the various carbon atoms, it is possible to confirm the position and geometry of the unsaturated centers in the acyl chains. Many of the similarly positioned carbon

Marcel S. F Lie Ken Jie; C. C Lam

1995-01-01

386

FT-IR, 1H, 13C NMR, ESI-MS and semiempirical investigation of the structures of Monensin phenyl urethane complexes with the sodium cation  

NASA Astrophysics Data System (ADS)

In this paper three forms of phenyl urethane of Monensin i.e. its acid form (H-MU) and its 1:1 complex with NaClO4 (H-MU-Na) and its sodium salt (Na-MU) were obtained and their structures were studied by FT-IR, 1H and 13C NMR, ESI MS and PM5 methods. The FT-IR data of Na-MU complexes demonstrate that the Cdbnd O urethane group is not engaged in the complexation of the sodium cation. However spectroscopic studies of H-MU-Na complex show that the structure in which this Cdbnd O urethane groups participate in the complexation is also present, but it is in the minority. The PM5 semiempirical calculations allow visualisation of all structures and determination of the hydrogen bond parameters.

Huczy?ski, Adam

2013-06-01

387

Primidone - An antiepileptic drug - characterisation by quantum chemical and spectroscopic (FTIR, FT-Raman, 1H, 13C NMR and UV-Visible) investigations  

NASA Astrophysics Data System (ADS)

The solid phase FTIR and FT-Raman spectra of primidone were recorded in the regions 4000-400 cm-1 and 4000-100 cm-1, respectively. The vibrational spectra were analysed and the observed fundamentals were assigned and analysed. The experimental wavenumbers were compared with the theoretical scaled vibrational wavenumbers determined by DFT methods. The Raman intensities were also determined with B3LYP/6-31G(d,p) method. The total electron density and molecular electrostatic potential surface of the molecule were constructed by using B3LYP/6-311++G(d,p) method to display electrostatic potential (electron + nuclei) distribution. The HOMO and LUMO energies were measured. Natural bond orbital analysis of primidone has been performed to indicate the presence of intramolecular charge transfer. The 1H and 13C NMR spectra were recorded and the chemical shifts of the molecule were calculated.

Arjunan, V.; Santhanam, R.; Subramanian, S.; Mohan, S.

2013-05-01

388

5Trifluoromethyl1,2-dimethyl-1H-pyrazolium chlorides: synthesis and 1 H , 13 C , 19 F and 35 Cl NMR chemical shifts  

Microsoft Academic Search

The one-pot synthesis of nine novel 5-trifluoromethyl-1,2-dimethyl-1H-pyrazolium chlorides 2 from the cyclocondensation of 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones 1 [CF3C(O)CH=C(R1)OR, where R1=H, Me, n-Pr, n-Hex, Ph, 4-Me-C6H4, 4-F-C6H4, 4-Cl-C6H4, 4-NO2-C6H4, and R=Me, Et] with 1-2-dimethyl hydrazine, in quantitative yields, is reported. The 1H, 13C, 19F and 35Cl NMR chemical shifts of compounds 2 also are described.

Marcos A. P Martins; Rogério F Blanco; Claudio M. P Pereira; Paulo Beck; Sergio Brondani; Wilson Cunico; Nilo E. K Zimmermann; Helio G Bonacorso; Nilo Zanatta

2002-01-01

389

Composition of the leaf, stem bark and root bark oils of Isolona cooperi investigated by GC (retention index), GC-MS and 13C-NMR spectroscopy.  

PubMed

The leaf, stem bark and root bark oils of Isolona cooperi Hutchinson & Dalziel from the Ivory Coast have been analysed by GC (retention index), GC-MS and 13C-NMR spectroscopy. Two types of essential oil were produced by the plant. The leaf and stem bark oils were monoterpene-rich, containing principally (Z)-beta-ocimene and gamma-terpinene and three lactones, 5-[(E and Z)-hexylidene]-5H-furan-2-ones and massoia lactone, were present in appreciable amounts. Conversely, the root bark oil was dominated by 5-isopentenylindole and (E)-beta-caryophyllene. The strategy for the analysis of each oil was adapted according to the nature of the components. PMID:16223093

Boti, Jean Brice; Koukoua, Gérard; N'Guessan, Thomas Yao; Muselli, Alain; Bernardini, Antoine-François; Casanova, Joseph

390

Solid-state NMR characterization of cross-linking in EPDM/PP blends from 1H-13C polarization transfer dynamics.  

PubMed

A novel approach for solid-state NMR characterization of cross-linking in polymer blends from the analysis of (1)H-(13)C polarization transfer dynamics is introduced. It extends the model of residual dipolar couplings under permanent cross-linking, typically used to describe (1)H transverse relaxation techniques, by considering a more realistic distribution of the order parameter along a polymer chain in rubbers. Based on a systematic numerical analysis, the extended model was shown to accurately reproduce all the characteristic features of the cross-polarization curves measured on such materials. This is particularly important for investigating blends of great technological potential, like thermoplastic elastomers, where (13)C high-resolution techniques, such as CP-MAS, are indispensable to selectively investigate structural and dynamical properties of the desired component. The validity of the new approach was demonstrated using the example of the CP build-up curves measured on a well resolved EPDM resonance line in a series of EPDM/PP blends. PMID:15681133

Aluas, Mihaela; Filip, Claudiu

2005-05-01

391

Changes in the compound classes of dissolved organic matter along an estuarine transect: A study using FTIR and 13C NMR  

NASA Astrophysics Data System (ADS)

In this work, we use Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy ( 13C NMR) data to quantify the changes of major chemical compound classes (carboxylic acid, amide, ester, aliphatic, aromatic and carbohydrate) in high molecular weight (HMW, >1 kDa) dissolved organic matter (DOM) isolated along a transect through the Elizabeth River/Chesapeake Bay system to the coastal Atlantic Ocean off Virginia, USA. Results show that carboxylic acids and aromatic compounds are lost along the transect, while HMW DOC becomes enriched in carbohydrate moieties that could have a mid-transect source, perhaps the intensive red tide bloom ( Choclodinium polykrikoides) which occurred during our sampling period. Taking the second derivative of the FTIR spectra resolved three pools of de-protonated carboxylic acids at our Dismal Swamp site (used to represent terrestrial organic matter in this area): one carboxylic acid pool, complexed with iron, seems to be lost between the Dismal Swamp and river sites; the second appears biogeochemically active throughout the riverine transect, disappearing in the coastal ocean sample; the third seems refractory, with the potential to be transported to and to accumulate within the open ocean. Five-member ring esters (?-lactones) were the major ester form in the Dismal Swamp; aliphatic and acetate esters were the dominant esters in the estuary/marine DOM. No amide groups were detectable in Dismal Swamp DOM; secondary amides were present at the estuarine/marine sites. Coupling FTIR with 13C NMR provides new insights into the biogeochemical roles of carboxylic acid, amide and ester compounds in aquatic ecosystems.

Abdulla, Hussain A. N.; Minor, Elizabeth C.; Dias, Robert F.; Hatcher, Patrick G.

2010-07-01

392

Ionization of isocitrate bound to pig hear NADP/sup +/-dependent isocitrate dehydrogenase: /sup 13/C NMR study of substrate binding  

SciTech Connect

Isocitrate and ..cap alpha..-ketoglutarate have been synthesized with carbon-13 enrichment at specific positions. The /sup 13/C NMR spectra of these derivatives were measured as a function of pH. The magnitudes of the changes in chemical shifts with pH for free isocitrate and the magnesium-isocitrate complex suggest that the primary site of ionization at the ..beta..-carboxyl. In the presence of the enzyme NADP/sup +/-dependent isocitrate dehydrogenase and the activating metal magnesium, the carbon-13 resonances of all three carboxyls remain constant from pH 5.5 to pH 7.5. Thus, the carboxyls remain in the ionized form in the enzyme-isocitrate complex. The ..cap alpha..-hydroxyl carbon resonance could not be located in the enzyme-isocitrate complex, suggesting immobilization of this group. Magnesium produces a 2 ppm downfield shift of the ..beta..-carboxyl but does not change the resonances of the ..cap alpha..- and ..gamma..-carboxyls. This result is consistent with metal activation of both the dehydrogenation and decarboxylation reactions. The /sup 13/C NMR spectrum of ..cap alpha..-ketoglutarate remains unchanged in the presence of isocitrate dehydrogenase, implying the absence of alterations in geometry in the enzyme-bound form. Formation of the quaternary complex with Mg/sup 2 +/ and NADPH leads to loss of the ..cap alpha..-ketoglutarate resonances and the appearance of new resonances characteristic of ..cap alpha..-hydroxyglutarate. In addition, a broad peak ascribed to the enol form of ..cap alpha..-ketoglutarate is observed. The substantial change in the shift of the ..beta..-carboxyl of isocitrate and the lack of significant shifts in the other carboxyls of isocitrate or ..cap alpha..-ketoglutarate suggest that interaction of the ..beta..-carboxyl with the enzyme contributes to the tighter binding of isocitrate and may be significant for the oxidative decarboxylation function of isocitrate dehydrogenase.

Ehrlich, R.S.; Colman, R.F.

1987-06-16

393

NMR studies of (U- sup 13 C)cyclosporin A bound to cyclophilin: Bound conformation and protions of cyclosporin involved in binding  

SciTech Connect

Cyclosporin A (CsA), a potent immunosuppressant, is known to bind with high specificity to cyclophilin (CyP), a 17.7 kDa protein with peptidyl-prolyl isomerase activity. In order to investigate the three-dimensional structure of the CsA/CyP complex, the authors have applied a variety of multidimensional NMR methods in the study of uniformly {sup 13}C-labeled CsA bound to cyclophilin. The {sup 1}H and {sup 13}C NMR signals of cyclosporin A in the bound state have been assigned, and, from a quantitative interpretation of the 3D NOE data, the bound conformation of CsA has been determined. Three-dimensional structures of CsA calculated from the NOE data by using a distance geometry/simulated annealing protocol were found to be very different form previously determined crystalline and solution conformations of uncomplexed CsA. In addition, from CsA/CyP NOEs, the portions of CsA that interact with cyclophilin were identified. For the most part, those CsA residues with NOEs to cyclophilin were the same residues important for cyclophilin binding and immunosuppressive activity as determined from sturcture/activity relationships. The structural information derived in this study together with the known structure/activity relationships for CsA analogues may prove useful in the design of improved immunosuppressants. Moreover, the approach that is described for obtaining the structural information is widely applicable to the study of small molecule/large molecule interactions.

Fesik, S.W.; Gampe, R.T. Jr.; Eaton, H.L.; Gemmecker, G.; Olejniczak, E.T.; Neri, P.; Holzman, T.F.; Egan, D.A.; Edalji, R.; Simmer, R.; Helfrich, R.; Hochlowski, J.; Jackson, M. (Abbott Labs., Abbott Park, IL (United States))

1991-07-02