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1

(13)C NMR spectral assignment of 1,4-diarylpiperazinones.  

PubMed

The piperazinone derivatives have potential application in the pharmaceutical, polymer and textile fields. The present work describes the preparation of a series of new 1,4-diarylsubstituted-2-piperazinones by condensation of substituted N,N'-bis-(2-hydroxyphenyl)-ethylenediamines with glyoxal and the complete (13)C NMR spectral assignment accomplished using APT, HMQC and HMBC techniques. Substituent chemical-shift effects (SCS) were calculated, which showed different values for the lactam- and amine-substituted aromatic rings. The results show that predictions based on SCS effects are not simple for these molecules due to electronic and steric effects. Moreover, in the case of the ortho-substituted derivative 2 g, the NMR spectra reveal a dynamic behavior related to restricted rotation of the phenyl groups (atropisomerism). PMID:16259039

Abreu, Arturo; Ochoa, Ma Eugenia; Farfán, Norberto; Santillan, Rosa

2006-01-01

2

Evaluation of a 1H-13C NMR Spectral Library  

Microsoft Academic Search

A simple database of 13C\\/1H-13C spectral lists for 11 673 natural products was created in standard commercial database format. Over 50% of the spectra were predicted using HOSE code descriptors derived from the 50% of spectra having experimental values. Prediction errors obtained by prediction of and comparison to the experimental spectra revealed an exponentially decaying dependence between the average absolute

S. K. Smith; Jamieson M. Cobleigh; V. Svetnik

2001-01-01

3

1H and 13C NMR spectral data of new saponins from Cordia piauhiensis.  

PubMed

Two new bidesmoside triterpenoid saponins were isolated from stems of Cordia piauhiensis. Their structures, characterized as 3-O-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl pomolic acid 28-O-beta-D-glucopyranosyl ester (1) and 3-O-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl oleanolic acid 28-O-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl ester (2), were unequivocally established after extensive NMR (1H, 13C, DEPT 135 degrees, COSY, HSQC, HMBC, TOCSY, and NOESY) studies. PMID:17559167

Santos, Renata P; Silveira, Edilberto R; Uchôa, Daniel Esdras de A; Pessoa, Otília Deusdênia L; Viana, Francisco Arnaldo; Braz-Filho, Raimundo

2007-08-01

4

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

2013-08-01

5

Optimized Spectral Editing of 13C MAS NMR Spectra of Rigid Solids Using Cross-Polarization Methods  

NASA Astrophysics Data System (ADS)

Combinations of 13C magic-angle spinning (MAS) NMR experiments employing cross polarization (CP), cross polarization-depolarization (CPD), and cross polarization-depolarization-repolarization are analyzed quantitatively to derive simple and general procedures for optimized spectral editing of 13C CP/MAS NMR spectra of rigid solids by separation of the 13C resonances into CH n subspectra ( n = 0, 1, 2, and 3). Special attention is devoted to a differentiation by CPD/MAS of CH and CH 2 resonances since these groups behave quite similarly during spin lock under Hartmann-Hahn match and are therefore generally difficult to distinguish unambiguously. A general procedure for the design of subexperiments and linear combinations of their spectra to provide optimized signal-to-noise ratios for the edited subspectra is described. The technique is illustrated by a series of edited 13C CP/MAS spectra for a number of rigid solids ranging from simple organic compounds (sucrose and l-menthol) to complex pharmaceutical products (calcipotriol monohydrate and vitamin D 3) and polymers (polypropylene, polyvinyl alcohol, polyvinyl chloride, and polystyrene).

Sangill, R.; Rastrupandersen, N.; Bildsoe, H.; Jakobsen, H. J.; Nielsen, N. C.

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

2013-06-21

7

Synthesis of 4-methyl-8-oxo-4e-nonenal by the oxidative cleavage of e-geranylacetone. A /sup 13/C NMR spectral study of the intermediates  

SciTech Connect

The oxidative cleavage of E-geranylacetone for the preparation of 4-methyl-8-oxo-4E-nonenal was improved. A /sup 13/C NMR spectral study of the intermediates, 9-bromo-6,10-dimethyl-10-hydroxy-5E-undecen-2-one, 6,10-dimethyl-9,10-epoxy-5E-undecen-2-one, and 6,10-dimethyl-9,10-dihydroxy-5E-undecen-2-one and a side-product, 2,2,5,5-tetramethyl-4-(3-methyl-7-oxo-3E-octenyl)-1,3-dioxolane showed the predominant conformations of these compounds in the solvents studied

Mizyuk, V.L.; Struchkov, M.I.; Kharchevnikov, A.P.

1987-11-10

8

A computer-based approach to describe the 13C NMR chemical shifts of alkanes by the generalized spectral moments of iterated line graphs  

PubMed

A recently introduced strategy to quantitative structure-property relationship studies is used to model the sum of 13C NMR chemical shifts of alkanes. This graph theoretical approach is based on the spectral moments of the iterated line graph sequence (ILGS). The statistical quality of the model developed by using the present approach is compared to those obtained by using spectral moments of the bond matrix or the embedding frequencies of alkanes as independent variables. The embedding frequencies were computed on the basis of the spectral moments of the ILGS. The emphasis of this work is on the structural interpretation of the results. Consequently, the contributions of the different structural fragments of alkanes to the 13C NMR chemical shift sum are computed by the three theoretical approaches. The advantages and disadvantages of the use of these approaches are analyzed on the basis of computational expenditure, i.e. computer time and memory, and the statistical quality, complexity, and structural interpretation of the models developed. PMID:10719638

Estrada

2000-03-01

9

Graphite lamellar compounds 13C NMR studies  

NASA Astrophysics Data System (ADS)

13C NMR (natural abundance, room temperature) in a range of graphite lamellar compounds with donors or acceptors is interpreted in terms of charge transfer. The observed shifts and structure are related to anisotropic chemical shifts, or to Knight shifts, or a combination of both effects. Donors shifts - towards high field - agree with an important indirect Knight shift superimposed to a chemical shift. Using Fermi level density of states N( EF) deduced from Mizutani and co-workers measurements, large charge transfer are deduced: 0.3< f<1. Acceptors compounds show narrow lines with a 150 ppm axial anisotropy, the H0 ? ( a, b) component being undisplaced as compared to the graphite one: f appears small or negligible. Donors results are consistent with the occurring of a narrow energy band just above the graphite Fermi level resulting in high N( EF). In acceptors, they seem to be characteristic of 2-D compounds without covalent bonding, the main effect of acceptor molecules being to separate the graphitic planes.

Conard, J.; Estrade, H.; Lauginie, P.; Fuzellier, H.; Furdin, G.; Vasse, R.

1980-01-01

10

13 C CP\\/MAS NMR study of a wood\\/phenol–formaldehyde resin bondline  

Microsoft Academic Search

The dynamics and interactions of a wood powder\\/phenol–formaldehyde (PF) resin composite are evaluated by solid-state 13C NMR. A 13C labeled and perdeuterated PF resin, with low molecular weight distribution, is synthesized and cured in the neat state and also in combination with yellow-poplar wood powder. The 13C NMR spectral features and cross-polarization dynamics of the PF hydroxymethyl and methylene nuclei

Marie-Pierre G. Laborie; Charles E. Frazier

2006-01-01

11

Quantification of high-resolution (1)h-[(13)c] NMR spectra from rat brain extracts.  

PubMed

NMR spectroscopy in combination with (13)C-labeled substrate infusion is a unique technique to obtain information about dynamic metabolic fluxes noninvasively in vivo. In many cases, the in vivo information content obtained during dynamic (13)C studies in rodents can be enhanced by high-resolution (1)H-[(13)C] NMR spectroscopy on brain extracts. Previously, it has been shown that (1)H NMR spectra from rat brain extracts can be accurately quantified with a spectral fitting routine utilizing simulated basis sets using complete prior knowledge of chemical shifts and scalar couplings. The introduction of (13)C label into the various metabolites presents complications that demand modifications of the spectral fitting routine. As different multiplets within a given molecule accumulate various amounts of (13)C label, the fixed amplitude relationship between multiplets typical for (1)H NMR spectra must be abandoned. In addition, (13)C isotope effects lead to spectral multiplet patterns that become dependent on the amount of (13)C label accumulation, thereby preventing the use of a common basis set. Here a modified spectral fitting routine is presented that accommodates variable (13)C label accumulation and (13)C isotope effects. Spectral fitting results are quantitatively compared to manual integration on column-separated samples in which spectral overlap is minimized. PMID:24773047

de Graaf, Robin A; Chowdhury, Golam M I; Behar, Kevin L

2014-05-20

12

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

13

Molecular structure, vibrational spectra and (13)C and (1)H NMR spectral analysis of 1-methylnaphthalene by ab initio HF and DFT methods.  

PubMed

The Fourier transform infrared (FT-IR) and FT-Raman of 1-methylnaphthalene (1MN) have been recorded and analyzed. The equilibrium geometry, bond lengths, bond angles and harmonic vibrational frequencies have been investigated with the help of density functional theory (DFT) method. Vibrational spectroscopic assignments of 1-methylnaphthalene (1MN) are carried out with the help of quantum chemical calculation. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule are calculated by the Gauge including atomic orbital (GIAO) method. The molecular stability and bond strength have been investigated by using natural bond orbital analysis (NBO). The assignments of vibrational spectra have been carried out with the help of normal co-ordinate analysis (NCA) following the scaled quantum mechanical force field (SQMFF) methodology. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shift of the molecular is depend only on the structure of the molecule. The calculated HOMO and LUMO energy shows that charge transfer interactions take place within the molecule. Finally, the calculation results are applied to simulate infrared and Raman spectra of the title compound which show good agreement with observed spectra. PMID:24996214

Shailajha, S; Rajesh Kannan, U; Sheik Abdul Kadhar, S P; Isac Paulraj, E

2014-12-10

14

Development of LC-13C NMR  

NASA Technical Reports Server (NTRS)

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 flow C-13 NMR probe. Since C-13 NMR sensitivity is of paramount concern, considerable effort during the first year was directed at new NMR probe designs. In particular, various toroid coil designs were examined. In addition, corresponding shim coils for correcting the main magnetic field (B sub 0) homogeneity were examined. Based on these initial probe design studies, an LC-C-13 NMR probe was built and flow C-13 NMR data was obtained for a limited number of samples.

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

1986-01-01

15

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

16

Exp 13 C-NMR Tracer to Probe Coalification.  

National Technical Information Service (NTIS)

Solid-state NMR tracer experiments of synthetically prepared ( exp 13 C)lignins coalified under simulated geological conditions have illuminated a general chemical scheme for coalification. The labeling studies provide the first direct evidence for the co...

R. E. Botto R. Hayatsu R. G. Scott R. L. McBeth R. E. Winans

1985-01-01

17

13 C NMR and mass spectrometry of soil organic matter  

Microsoft Academic Search

Liquid state, high resolution 13C NMR spectroscopy and mass spectrometry were used to study the composition and structure of soil organic matter (SOM) using\\u000a soil extracts from two long-term experiments at the Rothamsted Experimental Station. Both one- and two-dimensional NMR techniques\\u000a were applied. 13C NMR sub-spectra of the CH\\u000a n\\u000a (n=0...3) groups, obtained by the Distortionless Enhancement by Polarisation Transfer

Galya I. Ivanova; Edward W. Randall

2003-01-01

18

Study of molecular interactions with 13C DNP-NMR  

NASA Astrophysics Data System (ADS)

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 13C NMR ligand binding studies at natural isotopic abundance of 13C gets feasible in this way. Resultant screens are easy to interpret and can be performed at 13C concentrations below ?M. 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.

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

2010-03-01

19

State-of-the-Art Direct 13C and Indirect 1H-[13C] NMR Spectroscopy In Vivo  

PubMed Central

Carbon-13 NMR spectroscopy in combination with 13C-labeled substrate infusion is a powerful technique to measure a large number of metabolic fluxes non-invasively in vivo. It has been used to quantify glycogen synthesis rates, establish quantitative relationships between energy metabolism and neurotransmission and evaluate the importance of different substrates. All measurements can, in principle, be performed through direct 13C NMR detection or via indirect 1H-[13C] NMR detection of the protons attached to 13C nuclei. The choice for detection scheme and pulse sequence depends on the magnetic field strength, whereas substrate selection depends on the metabolic pathways that are studied. 13C NMR spectroscopy remains a challenging technique that requires several non-standard hardware modifications, infusion of 13C-labeled substrates and sophisticated processing and metabolic modeling. Here the various aspects of direct 13C and indirect 1H-[13C] NMR are reviewed with the aim of providing a practical guide.

de Graaf, Robin A.; Rothman, Douglas L.; Behar, Kevin L.

2013-01-01

20

13C-NMR study of cresyl benzoates  

NASA Astrophysics Data System (ADS)

The proton-decoupled 13C FT—NMR spectra of para-, meta- and ortho-cresyl benzoates have been recorded and the observed signals have been assigned following the substituent additivity rule. The important features of diagnostic value of these spectra are discussed.

Srivastava, S. P.; Bhatnagar, A. K.; Joshi, G. C.

21

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

2013-09-01

22

Spectral assignments and anisotropy data of cellulose I(alpha): 13C-NMR chemical shift data of cellulose I(alpha) determined by INADEQUATE and RAI techniques applied to uniformly 13C-labeled bacterial celluloses of different Gluconacetobacter xylinus strains.  

PubMed

Solid-state (13)C-NMR spectroscopy was used to characterize native cellulose pellicles from two strains of Gluconacetobacter xylinus (ATCC 53582, ATCC 23769), which had been statically cultivated in Hestrin-Schramm (HS) medium containing fully (13)C-labeled beta-D-glucose-U-(13)C(6) as the sole source of carbon. For both samples, the (13)C-NMR chemical shifts were completely assigned for each (13)C-labeled site of cellulose I(alpha) with the aid of 2D refocused INADEQUATE NMR. To determine the principal chemical shift tensor components, a pulse sequence based on the recoupling of anisotropy information (RAI) was applied at 10 kHz MAS. The detailed (13)C tensors of cellulose I(alpha) from different bacterial celluloses are thus available now for the first time, and these results have been compared with previously published data of nonenriched material and with theoretical predictions. PMID:18781703

Hesse-Ertelt, Stephanie; Witter, Raiker; Ulrich, Anne S; Kondo, Tetsuo; Heinze, Thomas

2008-11-01

23

Exp 13 C NMR Studies of Bacterial Dihydrofolate Reductase Containing (Methyl- exp 13 C)Methionine and (Guanido- exp 13 C)Arginine.  

National Technical Information Service (NTIS)

(Methyl- exp 13 C)methionine and (guanido- exp 13 C)arginine have been incorporated with high efficiency by Streptococcus faecium var. Durans strain A into dihydrofolate reductase isoenzyme 2 and exp 13 C NMR spectra have been obtained for the labeled enz...

N. A. Matwiyoff R. E. London T. E. Walker R. L. Blakley L. Cocco

1978-01-01

24

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

2010-03-01

25

Structural and spectral assignment of a new diterpenoid isolated from Ballota undulata and a complete (1)H and (13)C NMR data assignment for three other structurally related compounds.  

PubMed

The structure of 3beta-hydroxyballotinone, a new labdane diterpenoid isolated from Ballota undulata, has been established by NMR spectroscopic studies. In addition, complete and unambiguous assignments of the (1)H and (13)C NMR spectra of three other already known labdanes (ballotinone, ballonigrin and ballonigrinone) isolated from the same source have been achieved. The assignments are based on 2D shift-correlated (1)H--(1)H COSY, (1)H--(13)C gHSQC [(1)J(C,H)] and (1)H--(13)C gHMBC [(n)J(C,H) (n = 2 and 3)], and NOE experiments. PMID:17661434

Hussein, Ahmed A; Jimeno, María L; Rodríguez, Benjamín

2007-10-01

26

1H and 13C{1H} NMR spectral parameters of sulfur mustards, nitrogen mustards, and lewisites: computing and predicting of reference spectra for chemical identification.  

PubMed

The (1)H and (13)C{(1)H} chemical shifts and (1)H spin-spin couplings of sulfur mustards, nitrogen mustards, and lewisites scheduled in the Chemical Weapons Convention, and those of bis(2-chloromethyl)disulfide, were determined in CDCl(3), CD(2)Cl(2), and (CD(3))(2)CO. Accurate parameters of this kind of series can be used for evaluating the current molecular modeling programs and the chemical shift and coupling constant prediction possibilities of the programs. Several prediction tests were made with commercial programs, and the results are reported here. PMID:22374852

Haapaniemi, Esa; Mesilaakso, Markku

2012-03-01

27

13C NMR studies on vinasses effluent treated with iron  

Microsoft Academic Search

Controlling the concentration and toxicity of propionic acid in upflow anaerobic sludge blanket (UASB) reactors is a challenging problem in biological wastewater treatment. Addition of FeSO4·7H2O and FeCl3·6H2O to vinasses effluent yields a precipitate and considerably reduction of propionic acid in solution. This is due to the coordination of volatile fatty acids (VFAs) to metal ions, according to 13C NMR

T. Pandiyan; C. Durán de Bazúa; K. Ilangovan; A. Noyola

1999-01-01

28

13C 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. PMID:23921970

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

2013-10-01

29

Isotopic multiplets in the /sup 13/C NMR spectra of partially deuterated ammonium derivatives. Spectral effects of isotopic asymmetry at a nitrogen atom  

SciTech Connect

Multiplets due to upfield deuterium isotope effects on the /sup 13/C chemical shifts can be observed when hydrogen exchange is slow relative to the magnitude of the isotope effect. Deuterium isotope effects have been reported for amine, amide, and amino acid systems. The chemical shift values and the magnitudes of the isotope effect for spermidine, as well as for the other substances are in the range 0.055-0.097 ppm/deuteron for the two bond isotope effect. Values at the lower end of this range are observed with higher substitution on the nitrogen or carbon atoms. The three-bond isotope effect is in the range 0.025-0.051 ppm/deuteron. For amino acids and their derivatives, partial deuteration of the ..cap alpha.. ammonium group gives rise to isotopic multiplets in the carboxyl as well as in the identification of terminal residues of peptides.

Reuben, J.

1985-03-06

30

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

31

Structural properties of carbon nanotubes derived from 13C NMR  

NASA Astrophysics Data System (ADS)

We present a detailed experimental and theoretical study on how structural properties of carbon nanotubes can be derived from 13C NMR investigations. Magic angle spinning solid state NMR experiments have been performed on single- and multiwalled carbon nanotubes with diameters in the range from 0.7 to 100 nm and with number of walls from 1 to 90. We provide models on how diameter and the number of nanotube walls influence NMR linewidth and line position. Both models are supported by theoretical calculations. Increasing the diameter D, from the smallest investigated nanotube, which in our study corresponds to the inner nanotube of a double-walled tube to the largest studied diameter, corresponding to large multiwalled nanotubes, leads to a 23.5 ppm diamagnetic shift of the isotropic NMR line position ?. We show that the isotropic line follows the relation ? = 18.3/D + 102.5 ppm, where D is the diameter of the tube and NMR line position ? is relative to tetramethylsilane. The relation asymptotically tends to approach the line position expected in graphene. A characteristic broadening of the line shape is observed with the increasing number of walls. This feature can be rationalized by an isotropic shift distribution originating from different diamagnetic shielding of the encapsulated nanotubes together with a heterogeneity of the samples. Based on our results, NMR is shown to be a nondestructive spectroscopic method that can be used as a complementary method to, for example, transmission electron microscopy to obtain structural information for carbon nanotubes, especially bulk samples.

Abou-Hamad, E.; Babaa, M.-R.; Bouhrara, M.; Kim, Y.; Saih, Y.; Dennler, S.; Mauri, F.; Basset, J.-M.; Goze-Bac, C.; Wågberg, T.

2011-10-01

32

Dipolar-coupling-mediated total correlation spectroscopy in solid-state 13C NMR: selection of individual 13C-13C dipolar interactions.  

PubMed

Herein is described a useful approach in solid-state NMR, for selecting homonuclear (13)C-(13)C spin pairs in a multiple-(13)C homonuclear dipolar coupled spin system. This method builds upon the zero-quantum (ZQ) dipolar recoupling method introduced by Levitt and coworkers (Marin-Montesinos et al., 2006) by extending the originally introduced one-dimensional (1D) experiment into a two-dimensional (2D) method with selective irradiation scheme, while moving the (13)C-(13)C mixing scheme from the transverse to the longitudinal mode, together with a dramatic improvement in the proton decoupling efficiency. Selective spin-pair recoupling experiments incorporating Gaussian and cosine-modulated Gaussian pulses for inverting specific spins were performed, demonstrating the ability to detect informative, simplified/individualized, long-range (13)C-(13)C homonuclear dipolar coupling interactions more accurately by removing less informative, stronger, short-range (13)C-(13)C interactions from 2D correlation spectra. The capability of this new approach was demonstrated experimentally on uniformly (13)C-labeled Glutamine and a tripeptide sample, GAL. PMID:20392659

Spano, Justin; Wi, Sungsool

2010-06-01

33

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

34

Silver(I) Cation Complexation with 3?,3'?-Bis(pyridine-n-carboxy) Lithocholic Acid 1,2-Ethanediol Diesters (n = 2–4): 1H, 13C and 15N NMR Spectral Studies and Molecular Orbital Calculations  

Microsoft Academic Search

Three isomeric molecular clefts: 3a,3'a-bis(pyridine-n-carboxy) lithocholic acid 1,2-ethanediol diesters (n = 2–4) 1–3 have been synthesized and their structures ascertained by 1H, 13C NMR and MALDI TOF MS. Their complex formation with Ag+-cation (added as AgO3 SCF3) have been investigated by means of NMR and molecular orbital calculations. The coordination behaviour of the silver(I) cation is dependent on the isomerism

Erkki Kolehmainen; Jari Tamminen; Reijo Kauppinen; Juha Linnanto

1999-01-01

35

Stable isotope-enhanced two- and three-dimensional diffusion ordered 13C NMR spectroscopy (SIE-DOSY 13C NMR)  

NASA Astrophysics Data System (ADS)

The feasibility of obtaining high quality homonuclear or heteronuclear diffusion-ordered 13C NMR data is shown to be greatly improved by using 13C isotopically-enriched samples. Stable isotope-enhanced diffusion ordered (SIE-DOSY) 13C NMR has been applied to 13C-enriched carbohydrates, and has been used to determine diffusion coefficients for pentose and hexose monosaccharides, and a disaccharide and trisaccharide. These 2D spectra were obtained with as little as 8 min of acquisition time. Fully resolved 3D DOSY-HMQC NMR spectra of [U- 13C]xylose, [U- 13C]glucose, and [1- 13C gal]lactose were obtained in 5 h. Sample derivatization with [ carbonyl- 13C]acetate (peracetylation) extends the usefulness of the technique to included non-labeled sugars; the 13C-carbonyl - carbohydrate ring proton 1H- 13C correlations also provide additional structural information, as shown for the 3-D DOSY-HMQC analysis of a mixture of maltotriose and lactose per-[ carbonyl- 13C]acetates.

Vermillion, Karl; Price, Neil P. J.

2009-06-01

36

1H, 13C NMR spectral and single crystal structural studies of toxaphene congeners. Quantum chemical calculations for preferred conformers of 2,5- endo,6- exo,8,9,9,10,10-octachloro-2-bornene and their DFT/GIAO 13C chemical shifts  

NASA Astrophysics Data System (ADS)

The 1H and 13C NMR chemical shifts for six toxaphene congeners: 2- exo,3- endo,6- exo,8,9,10-hexachloro- ( 1), 2- exo,3- endo,5- exo,9,9,10,10-heptachloro- ( 2), 2- exo,3- endo,6- exo,8,9,10,10-heptachloro- ( 3), 2- exo,3- endo,5- exo,6- endo,8,9,10-heptachloro- ( 4), 2- exo,3- endo,5- exo,6- endo,8,9,9,10-octachlorobornane ( 5) and 2,5- endo,6- exo,8,9,9,10,10-octachloro-2-bornene ( 6) are reported. Their chemical shift assignments have been obtained by means of Pulsed Field Gradient (PFG) Double Quantum Filtered (DQF) 1H, 1H correlation spectroscopy (COSY), PFG 1H, 13C Heteronuclear Multiple Quantum Coherence (HMQC) and PFG 1H, 13C Heteronuclear Multiple Bond Correlation (HMBC) experiments. A single crystal X-ray structural analysis was made for compounds 1, 3, 4 and 6. The prevalences of two octachlorobornene rotamers ( 6 a, 6 b) were elucidated by ab initio MO method and single point DFT/GIAO calculations for 13C chemical shifts. Theoretical calculations proved that the single crystal structure of 6 corresponds its most stable conformer in solution.

Laihia, K.; Valkonen, A.; Kolehmainen, E.; Suontamo, R.; Nissinen, M.; Nikiforov, V.; Selivanov, S.

2005-11-01

37

Quantitative solid-state 13C NMR with signal enhancement by multiple cross polarization.  

PubMed

A simple new method is presented that yields quantitative solid-state magic-angle spinning (MAS) (13)C NMR spectra of organic materials with good signal-to-noise ratios. It achieves long (>10ms) cross polarization (CP) from (1)H without significant magnetization losses due to relaxation and with a moderate duty cycle of the radio-frequency irradiation, by multiple 1-ms CP periods alternating with (1)H spin-lattice relaxation periods that repolarize the protons. The new method incorporates previous techniques that yield less distorted CP/MAS spectra, such as a linear variation ("ramp") of the radio-frequency field strength, and it overcomes their main limitation, which is T1? relaxation of the spin-locked (1)H magnetization. The ramp of the radio-frequency field strength and the asymptotic limit of cross polarization makes the spectral intensity quite insensitive to the exact field strengths used. The new multiCP pulse sequence is a "drop-in" replacement for previous CP methods and produces no additional data-processing burden. Compared to the only reliable quantitative (13)C NMR method for unlabeled solids previously available, namely direct-polarization NMR, the measuring time is reduced by more than a factor of 50, enabling higher-throughput quantitative NMR studies. The new multiCP technique is validated with 14-kHz MAS on amino-acid derivatives, plant matter, a highly aromatic humic acid, and carbon materials made by low-temperature pyrolysis. PMID:24374751

Johnson, Robert L; Schmidt-Rohr, Klaus

2014-02-01

38

13C solid state NMR investigation of structural relaxation of the polymer backbone in poly (ethylmethacrylate).  

PubMed

Geometry and time scale of structural relaxation of poly(n-alkylmethacrylates) above the glass transition is studied by temperature dependent one- and two-dimensional 13C-NMR spectroscopy. The geometry of the isotropization of the polymer backbone as deduced from detailed analysis of spectral line shapes is identified as random angular jumps. Analysis of echo decays confirms that at a given temperature this isotropization can adequately be described with a single correlation time. The results are discussed in terms of conformational memory and local structure recently identified in these polymeric glasses. PMID:15589734

Wind, Michael; Brombacher, Lothar; Heuer, Andreas; Graf, Robert; Spiess, Hans Wolfgang

2005-01-01

39

NMR structure analysis of uniformly (13)C-labeled carbohydrates.  

PubMed

In this study, a set of nuclear magnetic resonance experiments, some of them commonly used in the study of (13)C-labeled proteins and/or nucleic acids, is applied for the structure determination of uniformly (13)C-enriched carbohydrates. Two model substances were employed: one compound of low molecular weight [(UL-(13)C)-sucrose, 342 Da] and one compound of medium molecular weight ((13)C-enriched O-antigenic polysaccharide isolated from Escherichia coli O142, ~10 kDa). The first step in this approach involves the assignment of the carbon resonances in each monosaccharide spin system using the anomeric carbon signal as the starting point. The (13)C resonances are traced using (13)C-(13)C correlations from homonuclear experiments, such as (H)CC-CT-COSY, (H)CC-NOESY, CC-CT-TOCSY and/or virtually decoupled (H)CC-TOCSY. Based on the assignment of the (13)C resonances, the (1)H chemical shifts are derived in a straightforward manner using one-bond (1)H-(13)C correlations from heteronuclear experiments (HC-CT-HSQC). In order to avoid the (1) J CC splitting of the (13)C resonances and to improve the resolution, either constant-time (CT) in the indirect dimension or virtual decoupling in the direct dimension were used. The monosaccharide sequence and linkage positions in oligosaccharides were determined using either (13)C or (1)H detected experiments, namely CC-CT-COSY, band-selective (H)CC-TOCSY, HC-CT-HSQC-NOESY or long-range HC-CT-HSQC. However, due to the short T2 relaxation time associated with larger polysaccharides, the sequential information in the O-antigen polysaccharide from E. coli O142 could only be elucidated using the (1)H-detected experiments. Exchanging protons of hydroxyl groups and N-acetyl amides in the (13)C-enriched polysaccharide were assigned by using HC-H2BC spectra. The assignment of the N-acetyl groups with (15)N at natural abundance was completed by using HN-SOFAST-HMQC, HNCA, HNCO and (13)C-detected (H)CACO spectra. PMID:24771296

Fontana, Carolina; Kovacs, Helena; Widmalm, Göran

2014-06-01

40

In vivo 13C NMR metabolite profiling: potential for understanding and assessing conifer seed quality  

Microsoft Academic Search

High-resolution 13C MAS NMR spectroscopy was used to profile a range of primary and secondary metabo- lites in vivo in intact whole seeds of eight different conifer species native to North America, including six of the Pinaceae family and two of the Cupressaceae family. In vivo 13C NMR provided information on the total seed oil content and fatty acid composition

Victor V. Terskikh; J. Allan Feurtado; Shane Borchardt; Michael Giblin; Suzanne R. Abrams; Allison R. Kermode

2009-01-01

41

PENDANT 13C NMR Spectroscopy Applied to CHn Groups  

NASA Astrophysics Data System (ADS)

Polarization enhancement nurtured during attached nucleus testing (PENDANT) NMR spectroscopy gives signals of quaternary carbon atoms in addition to signals indicative of CH, CH2 and CH3 groups. In this study, using product operator theory, analytical description of PENDANT NMR spectroscopy for CHn (ISn, I = 1/2, S = 1/2, n = 0, 1, 2, 3) spin systems are presented. Simulation and experimental results of PENDANT NMR spectroscopy are also presented. Theoretical results are found to be in exact agreement with the simulation results and in good agreement with the experimental ones.

Gençten, Azmi; Šaka, Irfan; Gümüš, Sedat

2006-05-01

42

13C NMR as a general tool for the assignment of absolute configuration.  

PubMed

(13)C NMR, alone or in combination with (1)H NMR, allows the assignment of the absolute configuration of chiral alcohols, amines, carboxylic acids, thiols, cyanohydrins, sec,sec-diols and sec,sec-aminoalcohols, derivatized with appropriate chiral auxiliaries. This extends the assignment possibilities of NMR to fully deuterated and to nonproton containing compounds. PMID:20886140

Louzao, Iria; Seco, José Manuel; Quiñoá, Emilio; Riguera, Ricardo

2010-11-14

43

Direct (13)C NMR detection in HPLC hyphenation mode: analysis of Ganoderma lucidum terpenoids.  

PubMed

Solid phase extraction (SPE) was introduced as a crucial step in the HPLC-SPE-NMR technique to enable online analyte enrichment from which proton-detected NMR experiments on submicrogram amounts from complex mixtures were possible. However, the significance of direct-detected (13)C NMR experiments is indubitable in simplifying structural elucidations. In the current study, we demonstrated direct (13)C NMR detection of triterpenoids from a Ganoderma lucidum extract in hyphenation mode. The combined advantage of a cryogenically cooled probe, miniaturization, and multiple trapping enabled the first reported application of HPLC-SPE-NMR analysis using direct-detected (13)C NMR spectra. HPLC column loading, accumulative SPE trappings, and the effect of different elution solvents were evaluated and optimized. A column loading of approximately 600 ?g of a prefractionated triterpenoid mixture, six trappings, and an acquisition time of 13 h resulted in spectra with adequate signal-to-noise ratios to detect all C-13 signals. PMID:22515483

Wubshet, Sileshi G; Johansen, Kenneth T; Nyberg, Nils T; Jaroszewski, Jerzy W

2012-05-25

44

Rapid 1H[13C]-resolved diffusion and spin-relaxation measurements by NMR spectroscopy.  

PubMed

Hadamard-encoded heteronuclear-resolved NMR diffusion and relaxation measurements allow overlapping signal decays to be resolved with substantially shorter measuring times than are generally associated with 2D heteronuclear cross-correlation experiments. Overall measuring time requirements can be reduced by approximately an order of magnitude, compared to typical 2D heteronuclear single-quantum correlation-resolved diffusion or relaxation measurements. Specifically, in cases where chemical shift correlation information provides enhanced spectral resolution, the use of Hadamard encoding can be used to overcome uniqueness challenges that are associated with the analysis of concurrent dynamic processes and the extraction of time constants from overlapping exponential signal decays. This leads to substantially improved resolution of similar time constants than can be achieved solely through the use of post-acquisition processing techniques. In the ideal case of complete spectral separation of the signal decays, the usual constraint that time constants must be sufficiently different to resolve by exponential analysis can be circumvented entirely. Hadamard-based pulse sequences have been used to determine 1H[13C]-resolved diffusion coefficients and spin-relaxation time constants for the chemically similar components of an aqueous solution of ethanol, glycerol, and poly(ethylene glycol), and a dye-containing block-copolymer solution, which exhibit significant spectral overlap in their 1H NMR spectra. PMID:16104738

Steinbeck, Christian A; Chmelka, Bradley F

2005-08-24

45

Interactions of acyl carnitines with model membranes: a 13C-NMR study  

Microsoft Academic Search

Esterification of fatty acids with the small polar molecule carnitine is a required step for the regulated flow of fatty acids into mitochondrial inner matrix. We have studied the interactions of acyl carnitines (ACs) with model membranes (egg yolk phosphatidylcholine (PC) vesicles) by 13 C-nuclear magnetic resonance (NMR) spectroscopy. Us- ing AC with 13 C-enrichment of the carbonyl carbon of

Jet K. Ho; Richard I. Duclos; James A. Hamilton

2002-01-01

46

Exp 13 C NMR Characterization of the Halthane Pre-Polymer System.  

National Technical Information Service (NTIS)

A cursory exp 13 C NMR analysis of Halthane pre-polymer components was initiated for the purpose of establishing a data file for potential use as a product qualification base. A exp 13 C analysis of the hydrolysis of 4,4'-diphenylmethane diisocyanate (MDI...

G. L. Clink

1978-01-01

47

13C and 1H MAS NMR studies of graphite oxide and its chemically modified derivatives  

Microsoft Academic Search

Graphite oxide (GO) and several of its derivatives have been studied using 13C and 1H NMR. The 13C NMR lines at 60, 70 and 130 ppm have been re-assigned. The > C?C < double bonds are relatively stable in comparison with the C?O?C and C?O?H groups. There are at least two magnetically inequivalent C?O?H sites, and the structure does not

Anton Lerf; Heyong He; Thomas Riedl; Michael Forster; Jacek Klinowski

1997-01-01

48

Structural determination of epsilon-lactams by 1H and 13C NMR.  

PubMed

The thermodynamic products (epsilon-lactams) of the degradation of ten different spirocyclic oxaziridines were analyzed by 1H and 13C NMR spectroscopy. The preferred conformations were determined by examining the homonuclear spin-spin coupling constant and the chemical shift effects of the N-substituent and the alkyl group of the aliphatic ring on 1H and 13C NMR spectra. PMID:19722187

Montalvo-González, Rubén; Ariza-Castolo, Armando

2009-12-01

49

Magnesium chloride: an efficient 13C NMR relaxation agent for amino acids and some carboxylic acids  

NASA Astrophysics Data System (ADS)

A series of amino acids and carboxylic acids were determined by 13C NMR spectroscopy. The results showed that addition of 3 M MgCl 2, led to shortening of relaxation time and 13C NMR integral area of samples was well proportional to the number of carbon atoms with reliability more than 95%. So MgCl 2 is proposed as an efficient relaxation agent for analysis of amino acids and some carboxylic acids.

Tian, Jinping; Yin, Yingwu; Sun, Hongbing; Luo, Xiaofeng

2002-12-01

50

Elucidating proline dynamics in spider dragline silk fibre using 2H-13C HETCOR MAS NMR.  

PubMed

(2)H-(13)C HETCOR MAS NMR is performed on (2)H/(13)C/(15)N-Pro enriched A. aurantia dragline silk. Proline dynamics are extracted from (2)H NMR line shapes and T1 in a site-specific manner to elucidate the backbone and side chain molecular dynamics for the MaSp2 GPGXX ?-turn regions for spider dragline silk in the dry and wet, supercontracted states. PMID:24686512

Shi, Xiangyan; Yarger, Jeffery L; Holland, Gregory P

2014-05-14

51

/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

52

(13)C NMR relaxation and reorientation dynamics in imidazolium-based ionic liquids: revising interpretation.  

PubMed

The temperature dependencies of (13)C NMR relaxation rates in [bmim]PF6 ionic liquid have been measured and the characteristic times (?c) for the cation reorientation have been recalculated. We found the origin of the incorrect ?c temperature dependencies that were earlier reported for ring carbons in a number of imidazolium-based ILs. After a correction of the approach (13)C T1, the relaxation data allowed us to obtain the characteristic times for an orientation mobility of each carbon, and a complicated experiment, such as NOE, was not required. Thus the applicability of (13)C NMR relaxation rate measurements to the calculation of the characteristic times for reorientation of all the carbons of the [bmim](+) cation was confirmed and our findings have shown that a (13)C NMR relaxation technique allowed its application to ionic liquids to be equally successful as for other liquid systems. PMID:24733492

Matveev, Vladimir V; Markelov, Denis A; Brui, Ekaterina A; Chizhik, Vladimir I; Ingman, Petri; Lähderanta, Erkki

2014-05-14

53

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

54

Silver(I) complexes of selenourea ( 13 C and 15 N labeled); characterization by 13 C, 15 N and 107 Ag NMR  

Microsoft Academic Search

Silver(I) complexes of selenourea (Seu), Ag(Seu)NO3 and Ag(Seu)2NO3 have been prepared and characterized by elemental analysis, IR and NMR (1H,13C,15N and 107Ag) spectroscopy. An upfield shift in 13C NMR and downfield shifts in 1H and 15N NMR for selenourea resonances are consistent with the selenium coordination to Ag(I). In 107Ag NMR, the AgNO3 signal is deshielded by more than 600

Saeed Ahmad; Anvarhusein A. Isab

2002-01-01

55

2H-DNP-enhanced 2H-13C solid-state NMR correlation spectroscopy.  

PubMed

Perdeuteration of biological macromolecules for magic angle spinning solid-state NMR spectroscopy can yield high-resolution (2)H-(13)C correlation spectra and the method is therefore of great interest for the structural biology community. Here we demonstrate that the combination of sample deuteration and dynamic nuclear polarization yields resolved (2)H-(13)C correlation spectra with a signal enhancement of epsilon > or = 700 compared to a spectrum recorded with microwaves off and otherwise identical conditions. To our knowledge, this is the first time that (2)H-DNP has been employed to enhance MAS-NMR spectra of a biologically relevant system. The DNP process is studied using several polarizing agents and the technique is applied to obtain (2)H-(13)C correlation spectra of U-[(2)H, (13)C] proline. PMID:20458422

Maly, Thorsten; Andreas, Loren B; Smith, Albert A; Griffin, Robert G

2010-06-14

56

1 H, 13 C and 15 N chemical shift referencing in biomolecular NMR  

Microsoft Academic Search

A considerable degree of variability exists in the way that 1H, 13C and 15N chemical shifts are reported and referenced for biomolecules. In this article we explore some of the reasons for this situation and propose guidelines for future chemical shift referencing and for conversion from many common 1H, 13C and 15N chemical shift standards, now used in biomolecular NMR,

David S. Wishart; Colin G. Bigam; Jian Yao; Frits Abildgaard; H. Jane Dyson; Eric Oldfield; John L. Markley; Brian D. Sykes

1995-01-01

57

Semiquantitative analysis of thiophenic compounds in light cycle oil (LCO) using 13C NMR spectroscopy  

Microsoft Academic Search

S-methyltetrafluoroborate salts of the thiophenic compounds (CH3-S+:BF4?) present in LCO petroleum fractions were obtained and analyzed by 1H and 13C NMR spectroscopy. The methylation of the samples was carried out using 99.5% 13C enriched methyl iodine, to improve the sensitivity of the technique. The amount of the methylated derivatives was determined by the internal standard method; using dioxane as a

J. C Poveda Jaramillo; D. R Molina Velazco; C Baldrich

2004-01-01

58

13C-Formylation for Improved NMR Profiling of Amino Metabolites in Biofluids  

PubMed Central

The increased interest in metabolite profiling is driving the need for improved analytical techniques with greater performance for a variety of important applications. Despite their limited sensitivity NMR methods are attractive because of their simplicity, reproducibility, quantitative nature, and wide applicability. The use of chemoselective isotopic tags has the potential to advance the application of NMR for analyzing metabolites in complex biofluids by allowing detection of metabolites down to the low ?M level with high resolution and specificity. Here, we report a new 13C-tagging method using 13C-formic acid that delivers high sensitivity, good quantitation and excellent resolution for 1H-13C 2D NMR profiling of amino metabolites. High reproducibility (CV = 2%) was observed for metabolites in urine with concentrations down to 10 ?M. As amino compounds comprise an important class of metabolites and small molecules of biological roles, this new method therefore should be amenable to a variety of applications.

Ye, Tao; Zhang, Shucha; Mo, Huaping; Tayyari, Fariba; Gowda, G. A. Nagana; Raftery, Daniel

2010-01-01

59

Solid state structures of phenylpyruvates as studied by high resolution 13C NMR spectroscopy  

NASA Astrophysics Data System (ADS)

High resolution solid state 13C NMR measurements were made on phenylpyruvic acid and its sodium, lithium and calcium salts, using the total suppression of spinning side bands and the dipolar diphasing technique. The spectra of their 2- 13C enriched analogs were also recorded. The NMR data were discussed by reference to the solution spectra, and the following definitive evidence was obtained: the acid, the hydrated sodium and lithium salts and the dehydrated sodium salt take the enol, the diol and the keto form, respectively, but the hydrated calcium salt exists in the keto form. The 13C NMR signal of the gem-diol carbon was found to appear at 98 ppm. The calcium salt has two doublets at 166 and 134 ppm which originate from the carbons C(1) and C(4); this splitting suggests that the carboxylate group and/or the phenyl ring in the phenylpyruvate anion are oriented in two different ways.

Kuwae, Akio; Hanai, Kazuhiko; Oyama, Kaoru; Uchino, Masazumi; Lee, Ho-Hi

1993-01-01

60

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

61

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 13C-13C 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 13C-13C 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 13C-13C 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

62

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

PubMed Central

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 13C-13C 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 13C-13C 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 13C-13C exchange spectra can be obtained from a 3.5 mg sample of A?1–40 fibrils in 4 hr or less, despite the broad 13C chemical shift anisotropy line shapes that are observed in static samples.

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

2013-01-01

63

Fullerene anions of different sizes and shapes: a 13C NMR and density-functional study.  

PubMed

A combined experimental and theoretical study was conducted on numerous higher fullerene anions with different sizes and shapes, C76-D2, C78-C2v, C78-D3, C84-D2, and C84-D2d. The corresponding fullerenes were reduced by lithium metal to diamagnetic multiply charged anions. The centers of gravity of the 13C NMR spectra of all the multiply charged anions were deshielded, relative to those of the neutral fullerenes. The results of density functional (DFT) computations of the 13C NMR spectra and the molecular orbitals (MOs) of possible polyanion reduction products suggest that hexaanions were the species formed. PMID:12790590

Sternfeld, Tamar; Thilgen, Carlo; Chen, Zhongfang; Siefken, Siefke; Schleyer, Paul von Ragué; Thiel, Walter; Diederich, François; Rabinovitz, Mordecai

2003-06-13

64

13C-NMR spectra and contact time experiment for Skjervatjern fulvic and humic acids  

USGS Publications Warehouse

The T(CP) and T(1p) time constants for Skjervatjern fulvic and humic acids were determined to be short with T(CP) values ranging from 0.14 ms to 0.53 ms and T(1p) values ranging from 3.3 ms to 5.9 ms. T(CP) or T(1p) time constants at a contact time of 1 ms are favorable for quantification of 13C-NMR spectra. Because of the short T(CP) values, correction factors for signal intensity for various regions of the 13C-NMR spectra would be necessary at contact times greater than 1.1 ms or less than 0.9 ms. T(CP) and T(1p) values have a limited non-homogeneity within Skjervatjern fulvic and humic acids. A pulse delay or repeat time of 700 ms is more than adequate for quantification of these 13C-NMR spectra. Paramagnetic effects in these humic substances are precluded due to low inorganic ash contents, low contents of Fe, Mn, and Co, and low organic free-radical contents. The observed T(CP) values suggest that all the carbon types in Skjervatjern fulvic and humic acids are fully cross-polarized before significant proton relaxation occurs. The 13C-NMR spectra for Skjervatjern fulvic acid is similar to most aquatic fulvic acids as it is predominantly aliphatic, low in aromaticity (fa1 = 24), low in phenolic content, high in carboxyl content, and has no resolution of a methoxyl peak. The 13C-NMR spectra for Skjervatjern humic acid is also similar to most other aquatic humic acids in that it is also predominantly aliphatic, high in aromaticity (fa1 = 38), moderate in phenolic content, moderate in carboxyl content, and has a clear resolution of a methoxyl carbon region. After the consideration of the necessary 13C-NMR experimental conditions, these spectra are considered to be quantitative. With careful consideration of the previously determined 13C-NMR experimental conditions, quantitative spectra can be obtained for humic substances in the future from the HUMEX site. Possible changes in humic substances due to acidification should be determined from 13C-NMR data.

Malcolm, R. L.

1992-01-01

65

Quantification of amounts and (13)C content of metabolites in brain tissue using high- resolution magic angle spinning (13)C NMR spectroscopy.  

PubMed

Metabolic pathway mapping using (13)C NMR spectroscopy has been used extensively to study interactions between neurons and glia in the brain. Established extraction procedures of brain tissue are time consuming and may result in degradation of labile substances. We examined the potential of mapping (13)C-enriched compounds in intact brain tissue using high-resolution magic angle spinning (HR-MAS) NMR spectroscopy. Sprague-Dawley rats received an intraperitoneal injection of [1,6-(13)C]glucose, and 15 min later the animals were subjected to microwave fixation of the brain. Quantification of concentration and (13)C labelling of metabolites in intact rat thalamus were carried out based on exogenous ethylene glycol concentrations measured from (1)H NMR spectra using an ERETIC (Electronic REference To access In vivo Concentrations) signal. The results from intact tissue were compared with those from perchloric acid-extracted brain tissue. Amounts of (13)C labelling at different positions (C2, C3 and C4) in glutamate, glutamine, gamma-aminobutyric acid and aspartate measured in either intact tissue or perchloric acid extracts were not significantly different. Proton NMR spectra were used for quantification of six different amino acids plus lactate, inositol, N-acetylaspartate, creatine and phosphocreatine. Again, results were very similar when comparing the methods. To our knowledge, this is the first time quantitative (13)C NMR spectroscopy measurements have been carried out on intact brain tissue ex vivo using the HR-MAS technique. The results show that HR-MAS (13)C NMR spectroscopy in combination with (1)H NMR spectroscopy and the ERETIC method is useful for metabolic studies of intact brain tissue ex vivo. PMID:19012315

Risa, Oystein; Melø, Torun Margareta; Sonnewald, Ursula

2009-04-01

66

Aging effects on vulcanized natural rubber studied by high resolution solid state 13C-NMR  

Microsoft Academic Search

The vulcanization chemistry, network formation and thermal oxidative aging effects of unfilled and carbon-black filled natural rubber vulcanized with organic peroxide, efficient vulcanization (EV) system and conventional sulfur system are studied by solid state 13C-NMR spectroscopy. Cis–trans isomerization and different sulfide structures are detected and identified through the chemical shift values of the extra NMR lines, which are observed in

J. Y Buzaré; G Silly; J Emery; G Boccaccio; E Rouault

2001-01-01

67

Absolute configuration and complete assignment of 13C NMR data for new sesquiterpenes from Maytenus chiapensis.  

PubMed

Five new dihydro-beta-agarofuran sesquiterpenes (1-5) were isolated from the leaves of Maytenus chiapensis. The structures of 1-5 were determined by means of 1D and 2D NMR techniques. A semiselective HMBC technique was applied in order to obtain complete (13)C NMR assignments. Absolute configurations were determined by CD studies and chemical correlations and on biogenetic grounds. Compound 4 showed weak activity against a multidrug-resistant Leishmania tropica line. PMID:12713421

Núñez, Marvin J; Cortés-Selva, Fernando; Bazzocchi, Isabel L; Jiménez, Ignacio A; González, Antonio G; Ravelo, Angel G; Gavin, José A

2003-04-01

68

13 C-NMR-spectroscopic investigations on precipitated polyanion-polycation-complexes  

Microsoft Academic Search

High resolution solid state 13C-NMR spectra are reported for polyanion-polycation-eomplexes of poly(dimethyldiallyl)-ammonium chloride with some copolymers of acrylic acid and acrylamide, as well as for some component polyelectrolytes. The Coulombic interaction between the macro-ions definitely leads to changes in position and shape of the NMR signals, and an influence of anionic charge density on signal shape is observed. A stepwise

Joachim Kötz; Jürgen Kunze; Karl-Joachim Linow; Burkart Philipp

1986-01-01

69

13C CP MAS NMR and DFT study of vascular-selective drugs felodipine and amlodipine  

NASA Astrophysics Data System (ADS)

Amlodipine besylate (AM) and felodipine (FL) have been studied in solid by 13C CP MAS NMR and DFT. The spectra have been successfully reproduced from the theoretical calculations of the nuclear magnetic shielding tensors, using the GIAO method, after the SCF partial geometry optimisation. A very good correlation between the 13C chemical shifts and quadrupole coupling constants for chlorobenzene, AM and FL was obtained. 13C NMR as well as 35Cl NQR do not differentiate between S and R enantiomers of AM and FL due to the symmetry of the 4-aryl ring comprising one (AM) or two (FL) chlorine atoms oriented in a perpendicular fashion over the 1,4-DHP ring.

Latosi?ska, J. N.

2008-09-01

70

Hyaluronan Forms Specific Stable Tertiary Structures in Aqueous Solution: A 13C NMR Study  

Microsoft Academic Search

13C NMR spectra of aqueous solutions of hyaluronan (HA) of high molecular mass, before and after digestion with testicular hyaluronidase, and of hyaluronan methyl ester were obtained at 125.8 MHz. Carbonyl peaks were assigned by using selective decoupling techniques. Spectra of digested and undigested HA showed sharp signals, except for that assigned to the acetamido carbonyl carbon in the high

John E. Scott; Frank Heatley

1999-01-01

71

13C CPMAS NMR investigations of cellulose polymorphs in different pulps  

Microsoft Academic Search

In order to obtain information about the crystallinity and polymorphs of cellulose, and the occurrence of hemicelluloses in pulp fibers, wood cellulose, bacterial cellulose, cotton linters, viscose, and celluloses in different pulps were investigated by solid state 13C CPMAS NMR spectroscopy. A mixed softwood kraft pulp and a dissolving-grade pulp were treated under strongly alkaline and acidic conditions and the

Sirkka Maunu; Tiina Liitiä; Seppo Kauliomäki; BO HORTLING; JORMA SUNDQUIST

2000-01-01

72

cis- and trans-Neocnidilide; 1H- and 13C-NMR Data of Some Phthalides.  

PubMed

The (1)H- and (13)C-NMR spectra of several naturally occurring phthalides are reported; among others, the new natural compound 3,3alpha- CIS-neocnidilide isolated from APIUM GRAVEOLENS L. (and also found to be present in ANETHUM GRAVEOLENS L.). For some compounds, data are compared with previously published data. PMID:17268969

Fischer, F C; Gijbels, M J

1987-02-01

73

13C NMR spectroscopy studies of forest soil microbial activity: glucose uptake and fatty acid biosynthesis  

Microsoft Academic Search

The intimate association of soil microorganisms with the soil matrix complicates analysis of their metabolism, since thorough separation of intact cells from the matrix is very difficult using standard protocols. Thus, in the study reported here, in situ glucose decomposition and metabolism in humus from a coniferous forest soil was monitored and evaluated using ‘solution state’ 13C NMR, which can

Peter Lundberg; Alf Ekblad; Mats Nilsson

2001-01-01

74

Analysis of Epoxy Resin Formulations by exp 13 C NMR Spectroscopy.  

National Technical Information Service (NTIS)

The chloroform soluble components of several epoxy resin formulations were analyzed by exp 13 C NMR spectroscopy. The technique permits the components of an epoxy resin formulation to be identified on a routine basis with a high degree of confidence. Narm...

R. A. Assink F. T. Gurule

1981-01-01

75

Suppressing one-bond homonuclear 13C,13C scalar couplings in the J-HMBC NMR experiment: application to 13C site-specifically labeled oligosaccharides.  

PubMed

Site-specific (13)C isotope labeling is a useful approach that allows for the measurement of homonuclear (13)C,(13)C coupling constants. For three site-specifically labeled oligosaccharides, it is demonstrated that using the J-HMBC experiment for measuring heteronuclear long-range coupling constants is problematical for the carbons adjacent to the spin label. By incorporating either a selective inversion pulse or a constant-time element in the pulse sequence, the interference from one-bond (13)C,(13)C scalar couplings is suppressed, allowing the coupling constants of interest to be measured without complications. Experimental spectra are compared with spectra of a nonlabeled compound as well as with simulated spectra. The work extends the use of the J-HMBC experiments to site-specifically labeled molecules, thereby increasing the number of coupling constants that can be obtained from a single preparation of a molecule. PMID:24395678

Pendrill, Robert; Sørensen, Ole W; Widmalm, Göran

2014-03-01

76

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

77

Cryogenic probe 13C NMR spectroscopy of urine for metabonomic studies.  

PubMed

Cryogenic probe technology can significantly compensate for the inherently low sensitivity of natural abundance 13C NMR spectroscopy. This now permits its routine use in NMR spectroscopy of biofluids, such as urine or plasma, with acquisition times that enable a high throughput of samples. Metabonomic studies often generate numerous samples in order to characterize fully the time-dependent biochemical response to stimuli, but until now, they have been largely conducted using 1H NMR spectroscopy because of its high sensitivity and hence efficient data acquisition. Here, we demonstrate that information-rich 13C NMR spectra of rat urine can be obtained using appropriately short acquisition times suitable for biochemical samples when using a cryogenic probe. Furthermore, these data were amenable to automated pattern recognition analysis, which produced a profile of the metabolic response to the model hepatotoxin hydrazine that was consistent with earlier studies. Thus, a new source of detailed and complementary information is available to metabonomics using cryogenic probe 13C NMR spectroscopy. PMID:12236374

Keun, Hector C; Beckonert, Olaf; Griffin, Julian L; Richter, Christian; Moskau, Detlef; Lindon, John C; Nicholson, Jeremy K

2002-09-01

78

Solid-state 13C NMR study of na-cellulose complexes.  

PubMed

The interaction of microcrystalline cellulose from cotton and aqueous sodium hydroxide was investigated by 13C NMR solid-state spectroscopy as a function of temperature and sodium hydroxide concentration. When the concentration of NaOH was increased, the initial cellulose spectrum was replaced successively by that of Na-cellulose I followed by that of Na-cellulose II. In Na-cellulose I, each carbon atom occurred as a singlet, thus implying that one glucosyl moiety was the independent magnetic residue in the structure of this allomorph. In addition, the occurrence of the C6 near 62 ppm is an indication of a gt conformation for the hydroxymethyl group of Na-cellulose I. In Na-cellulose II, the analysis of the resonances of C1 and C6 points toward a structure based on a cellotriosyl moiety as the independent magnetic residue, in agreement with the established X-ray analysis that has shown that for this allomorph, the fiber repeat was also that of a cellotriosyl residue. For Na-cellulose II, the occurrence of the C6 in the 60 ppm region indicates an overall gg conformation for the hydroxymethyl groups. A comparison of the spectra recorded at 268 K and at room temperature confirms the stronger interaction of NaOH with cellulose when the temperature is lowered. In the Q region, corresponding to NaOH concentrations of around 9% and temperatures below 277 K, most of the sample was dissolved and no specific solid-state 13C NMR spectrum could be recorded, except for that of a small fraction of undissolved cellulose I. The same experiment run on a wood pulp sample leads to a new spectrum, with spectral characteristics different from those of Na-cellulose I and Na-cellulose II. This new spectrum is assigned to the Q phase, which appears to result from topological constraints that are present in whole wood pulp fibers but not in microcrystalline cellulose. A spectrum recorded for samples in the Na-cellulose III conditions resembled that of Na-cellulose II but of lower resolution. Similarly, a spectrum of a sample of Na-cellulose IV was identical to that of hydrated cellulose II. These observations have allowed us to propose a simplified phase diagram of the cellulose/NaOH system in terms of temperature and NaOH concentration. This diagram, which is simpler than the one deduced from X-ray analysis, consists of only four different regions partially overlapping. PMID:17661517

Porro, Fabrizio; Bédué, Olivier; Chanzy, Henri; Heux, Laurent

2007-08-01

79

Dynamics and order of nonionic surfactants in neat liquid and micellar solution from multifield /sup 13/C NMR relaxation and /sup 13/C NMR chemical shifts  

SciTech Connect

The /sup 13/C NMR chemical shifts and spin-lattice relaxation times have been determined for nonionic oligo(oxyethylene)dodecyl ether surfactants (C/sub 12/E/sub x/) in water (C/sub 12/E/sub 5/) and as neat liquids (C/sub 12/E/sub 3/, C/sub 12/E/sub 4/, C/sub 12/E/sub 6/). For the ethylene oxide chains the chemical shifts suggest that a trans conformer around the C-C bonds becomes more stable when the temperature is increased or if the environment is made more apolar. This agrees with the predictions of a recent theoretical model for the conformation of ethylene oxide chains. The ordinary upfield shift corresponding to an increased population of gauche conformers was observed for the alkyl chains at increased temperature. The spin-lattice relaxation for micellar and neat nonionic surfactants was found to be magnetic field dependent. Using the so-called two-step relaxation model of Wennerstroem they have obtained order parameter and fast correlation time profiles in addition to a slow correlation time. These parameters provide novel information on the nonionic surfactant aggregates in water and on the structure of neat nonionic surfactant liquids. /sup 13/C NMR spectra of C/sub 12/E/sub 5/ in anisotropic phases show unusually narrow lines, an observation providing information on chain order.

Ahlnaes, T.; Karlstroem, G.; Lindman, B.

1987-07-16

80

Structural Monitoring of Oligosaccharides through 13C Enrichment and NMR Observation of Acetyl Groups  

PubMed Central

Structural characterization of biomolecules by NMR methods frequently requires the enrichment of magnetically active isotopes at particular molecular sites. Introduction is usually achieved biosynthetically through the use of bacterial cultures grown on isotopically enriched media, but for certain types of molecules—cell-surface carbohydrates of mammalian origin, for example—this is not practical. Here we explore a means of introducing 13C-enriched sites, postisolation in natural carbohydrate products, and illustrate an ability to acquire sufficient information to select appropriate conformational models from among energetically allowed sets. The application presented involves replacement of native N-acetyl groups with 13C-labeled acetyl groups in a simple disaccharide derivative, (GlcNAc)2-OBu, or O-butyl-chitobiose. The assignment of the two acetyl groups introduced is based on a novel combination of NMR and mass spectrometry data. Structural information is obtained from chemical shift anisotropy offsets of 13C carbonyl resonances and 13C-13C dipolar couplings between the labeled methyl and carbonyl carbons of the acetyl groups. Although the application is to a relatively simple system, it lays the groundwork for application to biologically important complex carbohydrate systems.

Yu, Fei; Prestegard, J. H.

2006-01-01

81

Determination of fructose metabolic pathways in normal and fructose-intolerant children: A sup 13 C NMR study using (U- sup 13 C)fructose  

SciTech Connect

An inborn deficiency in the ability of aldolase B to split fructose 1-phosphate is found in humans with hereditary fructose intolerance (HFI). A stable isotope procedure to elucidate the mechanism of conversion of fructose to glucose in normal children and in HFI children has been developed. A constant infusion of D-(U-{sup 13}C)fructose was given nasogastrically to control and to HFI children. Hepatic fructose conversion to glucose was estimated by examination of {sup 13}C NMR spectra of plasma glucose. Significantly lower values ({approx}3-fold) for fructose conversion to glucose were obtained for the HFI patients as compared to the controls. A quantitative determination of the metabolic pathways of fructose conversion to glucose was derived from {sup 13}C NMR measurement of plasma ({sup 13}C)glucose isotopomer populations. The finding of isotopomer populations of three adjacent {sup 13}C atoms at glucose C-4 ({sup 13}C{sub 3}-{sup 13}C{sub 4}-{sup 13}C{sub 5}) suggests that there is a direct pathway from fructose, by-passing fructose-1-phosphate aldolase, to fructose 1,6-bisphosphate. The metabolism of fructose by fructose-1-phosphate aldolase activity accounts for only {approx}50% of the total amount of hepatic fructose conversion to glucose. In view of the marked decline by 67% in synthesis of glucose from fructose in HFI subjects found in this study, the extent of ({sup 13}C)glucose formation from a trace amount of (U-{sup 13}C)fructose infused into the patient can be used as a safe and noninvasive diagnostic test for inherent faulty fructose metabolism.

Gopher, A.; Lapidot, A. (Weizmann Institute of Science, Rehovot (Israel)); Vaisman, N. (Kaplan Hospital, Rehovot (Israel)); Mandel, H. (Rambam Hospital, Haifa (Israel))

1990-07-01

82

Methylation patterns of aquatic humic substances determined by 13C NMR spectroscopy  

USGS Publications Warehouse

13C NMR spectroscopy is used to examine the hydroxyl group functionality of a series of humic and fulvic acids from different aquatic environments. Samples first are methylated with 13C-labeled diazomethane. The NMR spectra of the diazomethylated samples allow one to distinguish between methyl esters of carboxylic acids, methyl ethers of phenolic hydroxyls, and methyl ethers of phenolic hydroxyls adjacent to two substituents. Samples are then permethylated with 13C-labeled methyl iodide/NaH. 13C NMR spectra of permethylated samples show that a significant fraction of the hydroxyl groups is not methylated with diazomethane alone. In these spectra methyl ethers of carbohydrate and aliphatic hydroxyls overlap with methyl ethers of phenolic hydroxyls. Side reactions of the methyltion procedure including carbon methylation in the CH3I/NaH procedure, are also examined. Humic and fulvic acids from bog, swamp, groundwater, and lake waters showssome differences in their distribution of hydroxyl groups, mainly in the concentrations of phenolic hydroxyls, which may be attributed to their different biogeochemical origins. ?? 1987.

Thorn, K. A.; Steelink, C.; Wershaw, R. L.

1987-01-01

83

Quantitative 13C NMR analysis of sequence distributions in poly(ethylene-co-1-hexene).  

PubMed

Different 13C NMR methods of determining triad distributions in two poly(ethylene-co-1-hexene) copolymers are examined using high signal-to-noise ratio 13C NMR spectra of the copolymers dissolved in deuterated 1,2,4-trichlorobenzene at 398 K. This examination includes a comparison of three integration techniques. The experimental impact of decoupler sidebands and significantly nonequal 13C NOE values are examined. A least-squares regression analysis technique for solving for triad mole fractions is tested and appears to be more reliable than two published algebraic expressions (and other expressions examined in the work reported here). The resultant triad mole fractions are compared to sequence distribution parameters expected by Bernoullian and first-order Markovian statistical models. On the basis of 13C NMR-determined average reactivity ratios, the copolymer designated sample B (5.3 mol % 1-hexene) appears to be a Bernoullian copolymer resulting from a single-site catalytic system. The copolymer designated sample S (3.6 mol % 1-hexene overall) is better described as a mixture of polyethylene and a Bernoullian copolymer with 6.4 mol % 1-hexene content, and thus appears to result from a multisite catalytic system. PMID:15456293

Seger, Mark R; Maciel, Gary E

2004-10-01

84

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

2013-05-23

85

Identification of natural metabolites in mixture: a pattern recognition strategy based on (13)C NMR.  

PubMed

Because of their highly complex metabolite profile, the chemical characterization of bioactive natural extracts usually requires time-consuming multistep purification procedures to achieve the structural elucidation of pure individual metabolites. The aim of the present work was to develop a dereplication strategy for the identification of natural metabolites directly within mixtures. Exploiting the polarity range of metabolites, the principle was to rapidly fractionate a multigram quantity of a crude extract by centrifugal partition extraction (CPE). The obtained fractions of simplified chemical composition were subsequently analyzed by (13)C NMR. After automatic collection and alignment of (13)C signals across spectra, hierarchical clustering analysis (HCA) was performed for pattern recognition. As a result, strong correlations between (13)C signals of a single structure within the mixtures of the fraction series were visualized as chemical shift clusters. Each cluster was finally assigned to a molecular structure with the help of a locally built (13)C NMR chemical shift database. The proof of principle of this strategy was achieved on a simple model mixture of commercially available plant secondary metabolites and then applied to a bark extract of the African tree Anogeissus leiocarpus Guill. & Perr. (Combretaceae). Starting from 5 g of this genuine extract, the fraction series was generated by CPE in only 95 min. (13)C NMR analyses of all fractions followed by pattern recognition of (13)C chemical shifts resulted in the unambiguous identification of seven major compounds, namely, sericoside, trachelosperogenin E, ellagic acid, an epimer mixture of (+)-gallocatechin and (-)-epigallocatechin, 3,3'-di-O-methylellagic acid 4'-O-xylopyranoside, and 3,4,3'-tri-O-methylflavellagic acid 4'-O-glucopyranoside. PMID:24555703

Hubert, Jane; Nuzillard, Jean-Marc; Purson, Sylvain; Hamzaoui, Mahmoud; Borie, Nicolas; Reynaud, Romain; Renault, Jean-Hugues

2014-03-18

86

15N and13C NMR investigation of hydroxylamine-derivatized humic substances  

USGS Publications Warehouse

Five fulvic and humic acid samples of diverse origins were derivatized with 15N-labeled hydroxylamine and analyzed by liquid-phase 15N NMR spectrometry. The 15N NMR spectra indicated that hydroxylamine reacted similarly with all samples and could discriminate among carbonyl functional groups. Oximes were the major derivatives; resonances attributable to hydroxamic acids, the reaction products of hydroxylamine with esters, and resonances attributable to the tautomeric equilibrium position between the nitrosophenol and monoxime derivatives of quinones, the first direct spectroscopic evidence for quinones, also were evident. The 15N NMR spectra also suggested the presence of nitriles, oxazoles, oxazolines, isocyanides, amides, and lactams, which may all be explained in terms of Beckmann reactions of the initial oxime derivatives. INEPT and ACOUSTIC 15N NMR spectra provided complementary information on the derivatized samples. 13C NMR spectra of derivatized samples indicated that the ketone/quinone functionality is incompletely derivatized with hydroxylamine. ?? 1991 American Chemical Society.

Thorn, K. A.; Arterburn, J. B.; Mikita, M. A.

1992-01-01

87

Double cross polarization /sup 13/C-NMR experiment in solid fossil fuel structure analysis  

SciTech Connect

The Double Cross Polarization /sup 13/C-MAS/NMR experiment has been used to derive a new operational classification of solid fossil fuels based on chemical reactivity. The method requires labeling reactive sites in the organic matrix with a magnetically active isotope not present in the precursor material, and using the local, isolated dipole-dipole interaction between this nucleus and nearby /sup 13/C nuclei to detect via cross polarization the carbon centers in the vicinity of the label. The technique is a marriage of chemistry and spectroscopy and the information content of the DCP spectra is defined by both partners. /sup 1/H-/sup 13/C-/sup 31/P DCP/MAS /sup 13/C-NMR spectroscopy has been used to statistically describe phenolic ortho-substitution patterns of coals via their aryl phosphinate or phosphate derivatives. In these applications of DCP NMR the new, detailed structure and/or reactivity information is realized by detection of carbon resonances one or more bonds removed from the reaction center, but in a volume element of intramolecular dimensions. To the extent that intermolecular contributions to the spectrum are detected, and not recognized as such, the structure/reactivity correlation is weakened. Direct substitution of phosphorus on the aromatic rings in the organic matrix of the coal is not readily accomplished. This environment potentially can be labeled with fluorine in a selective fashion using newly developed reagents. The possibility of determining the changes in average ring substitution patterns as a function of chemical treatment or coal diagenesis emerges. Recent developments in the field of DCP /sup 13/C NMR are presented.

Hagaman, E.W.; Woody, M.C.

1988-01-01

88

Differentiation and quantification of synthetic phosphatidylethanol (PEth) homologues by (1)H- and (13)C-NMR in polar organic solvents.  

PubMed

Various phosphatidylethanol (PEth) derivatives, the corresponding reversed positional isomers (RPI-PEths), lyso-PEth-16:0, and penta-deuterium-labeled PEth analogs (d5-PEths), were synthesized by enzyme-independent synthetic routes. A general solvent system consisting of a mixture of acetone-d6 and methanol-d4 (97:3; v/v) was found to provide a good solubilizing capacity and excellent hydrogen-1 NMR ((1)H-NMR) peak resolution of various PEth homologues. Analytical differentiation of PEth from the corresponding RPI-PEth by carbon-13 NMR ((13)C-NMR) was demonstrated by comparison of the (13)C-NMR signals of the carbonyl groups, the allylic positions, and of the ?-carbons. An exemplary stable long-term room temperature, DMSO-d6-based, and proton-sensitive quantitative nuclear magnetic resonance ((1)H-qNMR) independently quantified calibrator comprising PEth-16:0/18:1 for liquid chromatography (tandem) mass spectrometry (LC-MS/MS) analytical applications were prepared by employment of sodium dodecyl sulfate (SDS) as a solubilizing additive. In summary, novel hypothetically occurring PEth derivatives, e.g., RPI-PEths, have been independently synthesized with regio- and stereochemical control. Use of polar organic solvents, e.g., mixtures of acetone-d6 and methanol-d4 or DMSO-d6, improves spectral line shapes as compared to traditional hydrophobic solvents and allow for analytical differentiation between closely related PEth derivatives, as well as LC-MS/MS-independent concentration determination of dissolved single species by employment of (1)H-qNMR. PMID:24866709

Wensbo Posaric, David; Andersson, Anders; Bergquist, Karl-Erik; Isaksson, Anders

2014-07-01

89

Molecular structure of crude beeswax studied by solid-state 13C NMR  

PubMed Central

13C Solid-state NMR experiments were performed to investigate the structure of beeswax in the native state (crude beeswax) for the first time. From quantitative direct polarization 13C MAS NMR spectrum, it was found that the fraction of internal-chain methylene (int-(CH2)) component compared to other components of crude beeswax was over 95%. The line shape of the int-(CH2) carbon resonance region was comprehensively analyzed in terms of NMR chemical shift. The 13C broad peak component covering from 31 to 35ppm corresponds to int-(CH2) carbons with trans conformation in crystalline domains, whereas the sharp signal at 30.3 ppm corresponds to gauche conformation in the non-crystalline domain. From peak deconvolution of the aliphatic region, it was found that over 85% of the int-(CH2) has a crystal structure and several kinds of molecular packing for int-(CH2), at least three, exist in the crystalline domain. Abbreviation: NMR nuclear magnetic resonance int-(CH2) internal-chain methylene CP cross-polarization MAS magic angle spinning

Kameda, Tsunenori

2004-01-01

90

Optimizing the 13C- 14N REAPDOR NMR Experiment: A Theoretical and Experimental Study  

NASA Astrophysics Data System (ADS)

The optimum 14N pulse lengths in the 13C- 14N rotational-echo adiabatic-passage double-resonance (REAPDOR) NMR experiment are determined from calculations and from experiments on samples of glycine and L-alanine. The REAPDOR experiment utilizes the adiabatic passages that 14N spins make between the 14N Zeeman energy levels during the application of a single, short 14N radiofrequency pulse. Use of a short 14N irradiation time of less than one-quarter of a rotor period ensures that the number of 14N spins that undergo more than one passage is minimized. This simplifies calculations describing 13C dipolar dephasing and provides better agreement between calculations and experiments. Recovery of the 13C- 14N dipolar couplings and 14N quadrupolar coupling constants and asymmetry parameters is described.

Ba, Yong; Kao, Hsien-Ming; Grey, Clare P.; Chopin, Lamy; Gullion, Terry

1998-07-01

91

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

92

Host-guest interactions in fluorinated polymer electrolytes: A 7Li-13C NMR study  

NASA Astrophysics Data System (ADS)

Gel-type electrolytes based on fluorinated polymers are of interest for electrochemical devices. We present a 7Li-13C solid-state NMR and modulated differential scanning calorimetry (MDSC) study of gel electrolytes based on a copolymer poly(vinylidene fluoride) (PVdF)-hexafluoropropylene (HFP) activated with a nonaqueous solution ethylene carbonate (EC)-propylene carbonate (PC)-LiN(CF3SO2)2. We show that the narrowing of the Li lineshape is decoupled from the glass transition. The behavior of the longitudinal relaxation times, T1, confirms that the host polymer matrix simply behaves like a quasiinert cage for the solution. These results are confirmed by 13C NMR at the magic angle (MAS) data, which show that the presence of the polymer does not significantly affect the chemical shift changes induced in the EC/PC carbons by the imide salt.

Mustarelli, P.; Quartarone, E.; Capiglia, C.; Tomasi, C.; Ferloni, P.; Magistris, A.

1999-08-01

93

Solid state 13C NMR characterisation study on fourth generation Ziegler-Natta catalysts.  

PubMed

In this study, solid state (13)C NMR spectroscopy was utilised to characterize and identify the metal-ester coordination in active fourth generation (phthalate) Ziegler-Natta catalysts. It is known that different donors affect the active species in ZN catalysts. However, there is still limited data available of detailed molecular information how the donors and the active species are interplaying. One of the main goals of this work was to get better insight into the interactions of donor and active species. Based on the anisotropy tensor values (?(11), ?(22), ?(33)) from low magic-angle spinning (MAS) (13)C NMR spectra in combination with chemical shift anisotropy (CSA) calculations (?(aniso) and ?), both the coordinative metal (Mg/Ti) and the symmetry of this interaction between metal and the internal donor in the active catalyst (MgCl(2)/TiCl(4)/electron donor) system could be identified. PMID:22425229

Heikkinen, Harri; Liitiä, Tiina; Virkkunen, Ville; Leinonen, Timo; Helaja, Tuulamari; Denifl, Peter

2012-01-01

94

13C NMR spectroscopy for the quantitative determination of compound ratios and polymer end groups.  

PubMed

(13)C NMR spectroscopic integration employing short relaxation delays was evaluated as a quantitative tool to obtain ratios of diastereomers, regioisomers, constitutional isomers, mixtures of unrelated compounds, peptoids, and sugars. The results were compared to established quantitative methods such as (1)H NMR spectroscopic integration, gas chromatography, and high-performance liquid chromatography and were found to be within <3.4% of (1)H NMR spectroscopic values (most examples give results within <2%). Acquisition of the spectra took 2-30 min on as little as 10 mg of sample, proving the general utility of the technique. The simple protocol was extended to include end group analysis of low molecular weight polymers, which afforded results in accordance with (1)H NMR spectroscopy and matrix-assisted laser desorption-ionization time-of-flight spectrometry. PMID:24601654

Otte, Douglas A L; Borchmann, Dorothee E; Lin, Chin; Weck, Marcus; Woerpel, K A

2014-03-21

95

13C NMR studies of the molecular dynamics of chlorpromazine in solution  

NASA Astrophysics Data System (ADS)

The optimum structure, which is expected to lead to biological activity, of chlorpromazine hydrochloride salt (compound ( I)) in solution was determined on the basis of NMR data and molecular orbital calculations; compound ( I) favours a bent structure in which the side-chain tilts toward the chlorinated benzene ring. The molecular mobility of compound ( I) in CDCl 3 and D 2O was also examined on the basis of 13C NMR spin-lattice relaxation time ( T1). T1 depends on the magnetic field strength and the solvent. The dependence indicates that the molecular mobility of compound ( I) is larger in D 2O than in CDCl 3

Sakamoto, Yohko; Ishii, Tomoko; Kurokawa, Noriko; Aoki, Toshikazu; Ohshima, Shigeru

1996-02-01

96

Radiation oxidation of polypropylene: A solid-state 13C NMR study using selective isotopic labeling  

Microsoft Academic Search

Polypropylene samples, in which the three different carbon atoms along the chain were selectively labeled with carbon-13, were subjected to radiation under inert and air atmospheres, and to post-irradiation exposure in air at various temperatures. By using solid-state 13C NMR measurements at room temperature, we have been able to identify and quantify the oxidation products. The isotopic labeling provides insight

Daniel M. Mowery; Roger A. Assink; Dora K. Derzon; Sara B. Klamo; Robert Bernstein; Roger L. Clough

2007-01-01

97

Using Neural Networks for 13C NMR Chemical Shift Prediction-Comparison with Traditional Methods  

NASA Astrophysics Data System (ADS)

Interpretation of 13C chemical shifts is essential for structure elucidation of organic molecules by NMR. In this article, we present an improved neural network approach and compare its performance to that of commonly used approaches. Specifically, our recently proposed neural network ( J. Chem. Inf. Comput. Sci. 2000, 40, 1169-1176) is improved by introducing an extended hybrid numerical description of the carbon atom environment, resulting in a standard deviation (std. dev.) of 2.4 ppm for an independent test data set of ˜42,500 carbons. Thus, this neural network allows fast and accurate 13C NMR chemical shift prediction without the necessity of access to molecule or fragment databases. For an unbiased test dataset containing 100 organic structures the accuracy of the improved neural network was compared to that of a prediction method based on the HOSE code ( hierarchically ordered spherical description of environment) using S PECI NFO. The results show the neural network predictions to be of quality (std. dev.=2.7 ppm) comparable to that of the HOSE code prediction (std. dev.=2.6 ppm). Further we compare the neural network predictions to those of a wide variety of other 13C chemical shift prediction tools including incremental methods (C HEMD RAW, S PECT OOL), quantum chemical calculation (G AUSSIAN, C OSMOS), and HOSE code fragment-based prediction (S PECI NFO, ACD/CNMR, P REDICTI T NMR) for the 47 13C-NMR shifts of Taxol, a natural product including many structural features of organic substances. The smallest standard deviations were achieved here with the neural network (1.3 ppm) and S PECI NFO (1.0 ppm).

Meiler, Jens; Maier, Walter; Will, Martin; Meusinger, Reinhard

2002-08-01

98

Quantifying the chemical composition of soil organic carbon with solid-state 13C NMR  

NASA Astrophysics Data System (ADS)

The vulnerability of soil organic carbon (SOC) to biological decomposition and mineralisation to CO2 is defined at least partially by its chemical composition. Highly aromatic charcoal-like SOC components are more stable to biological decomposition than other forms of carbon including cellulose. Solid-state 13C NMR has gained wide acceptance as a method capable of defining SOC chemical composition and mathematical fitting processes have been developed to estimate biochemical composition. Obtaining accurate estimates depends on an ability to quantitatively detect all carbon present in a sample. Often little attention has been paid to defining the proportion of organic carbon present in a soil that is observable in solid-state 13C NMR analyses of soil samples. However, if such data is to be used to inform carbon cycling studies, it is critical that quantitative assessments of SOC observability be undertaken. For example, it is now well established that a significant discrimination exists against the detection of the low proton content polyaromatic structures typical of charcoal using cross polarisation 13C NMR analyses. Such discrimination does not exist where direct polarisation analyses are completed. In this study, the chemical composition of SOC as defined by cross polarisation and direct polarisation13C NMR analyses will be compared for Australian soils collected from under a diverse range of agricultural managements and climatic conditions. Results indicate that where significant charcoal C contents exist, it is highly under-represented in the acquired CP spectra. For some soils, a discrimination against alkyl carbon was also evident. The ability to derive correction factors to compensate for such discriminations will be assessed and presented.

Baldock, J. A.; Sanderman, J.

2011-12-01

99

Insulator-metal transition in Rb 4C 60 under pressure from 13C-NMR  

Microsoft Academic Search

We present an NMR study of Rb4C60 performed under pressure up to 12 kbar. The temperature dependence of the 13C spin-lattice relaxation rate is activated at ambient pressure and becomes Korringa-like under pressure. The behaviour of the relaxation is interpreted in terms of one channel due to excited intramolecular triplet states above the Jahn-Teller ground state plus another one related

R. Kerkoud; P. Auban-Senzier; D. Jérome; S. Brazovskii; I. Luk'Yanchuk; N. Kirova; F. Rachdi; C. Goze

1996-01-01

100

13C NMR studies of acetate metabolism during sporulation of Saccharomyces cerevisiae.  

PubMed Central

The sporulation of Saccharomyces cerevisiae in the presence of [2-13C]acetate was studied by 13C NMR spectroscopy. The fate of 13C label was analyzed in vivo and in cell extracts. During the first 4 hr of sporulation the major metabolite produced from [2-13C]acetate utilization was glutamate. From the labeling pattern observed it is concluded that both the tricarboxylic acid cycle and the glyoxylate cycle are operating. After about 4 hr trehalose is made. Comparison of the doublet/singlet ratios for C-1,1(1) and C-6,6(1) of trehalose shows a steady drop in the ratio of C-1, C-2-coupled species over trehalose labeled only at C-1 in the C-1, 2 segment of the molecule. The negative correlation of this ratio with that for the C-5, 6 segment indicates a cycling of glucose through the hexose monophosphate shunt. Subsequently fatty acid biosynthesis commences. Large amounts of saturated fatty acid were made. There were conspicuous differences observed in the metabolism of [2-13C]acetate between sporulating and vegetatively growing cells.

Dickinson, J R; Dawes, I W; Boyd, A S; Baxter, R L

1983-01-01

101

13C CP/MAS NMR and DFT studies of thiazides  

NASA Astrophysics Data System (ADS)

The 13C MAS solid state NMR spectra of four sulphonamide derivatives of 1,2,4-benzothiadiazine-1,1-dioxides, commonly known as thiazides, were recorded and the chemical shifts and chemical shift anisotropy (CSA) were measured. Analysis of the experimental 13C shielding parameters was supported by DFT theoretical calculations carried out within the gauge-including atomic orbital (GIAO), semiempirical Typed Neglect of Differential Overlap (TNDO/2) approach and by the spectra estimations performed by ChemNMR Pro 6.0, ACD-I/LAB, SpecInfo and gNMR. It was found that the chemical shifts obtained with ChemNMR Pro 6.0, ACD-I/LAB, SpecInfo and gNMR were insensitive to the substitution effects, whereas the semiempirical TNDO/2 and density functional theory (DFT) B3LYP/6-311+G(2d,p) methods allowed estimation of the influence of substituents on the chemical shielding and consequently, the chemical shift. The influence of the substituents at C3 position of the ring on the chemical shifts was analysed on the basis of the experimental data and results of the DFT calculations. The values of the chemical shifts and the low values of the anisotropy parameter for the C3 atom in HCTZ, TCTZ and ATZ, strongly indicated that three thiazides HCTZ, TCTZ and ATZ occurred in the form of HCTZ type with the C3 carbon atom participating in a single bond. The following ordering of the substituents according to the increasing electron accepting properties was found: -H<-CH 2SCH 2CH?CH 2<-CHCl 2. A detailed analysis of the inductive and coupling effects was made on the basis of 13C chemical shifts and chemical shielding tensor asymmetry parameters on the C3 and C6 carbon atoms.

Latosi?ska, J. N.

2003-02-01

102

Metabolites of [3-13C]1,2-dibromo-3-chloropropane in male rats studied by 13C and 1H-13C correlated two-dimensional NMR spectroscopy.  

PubMed

Metabolism of 1,2-dibromo-3-chloropropane (DBCP) was examined by direct 13C and 1H-13C correlated two-dimensional NMR spectroscopy of bile and urine of male albino rats treated intraperitoneally with [3-13C]DBCP at 81 mg/kg. The 3-13C label was introduced at 99% enrichment by coupling [13C]paraformaldehyde with vinyllithium to give [1-13C]allyl alcohol which was converted to allyl chloride with carbon tetrachloride/triphenylphosphine and then brominated. Fifteen 13C NMR signals were observed for biliary metabolites and twelve for urinary metabolites. Nine of the biliary metabolite 13C NMR signals were very similar or identical to those for nine urinary metabolites. The DBCP-derived moieties of five metabolites were identified by comparison of their 13C NMR chemical shifts, 13C multiplicities [obtained via the distortionless enhancement by polarization transfer (DEPT) pulse sequence], and chemical shifts of the directly-attached protons (obtained via two-dimensional NMR) with those of authentic standards. They were E- and Z-RSCH2CH = 13CHCl, RSCH2CHOH13CH2Cl, RSCH2CHOH13CH2OH and RS13CH2CHOHCH2OH, where R is probably glutathionyl in bile and N-acetylcysteinyl in urine. The mechanism proposed for formation of both the E- and Z-isomers of RSCH2CH = 13CHCl involves radical-initiated dehydrobromination followed by reaction of the intermediate allylic bromides with glutathione (GSH). The RSCH2CHOHCH2Cl conjugate may arise from direct GSH conjugation and hydrolysis of the secondary bromine via a thiiranium ion intermediate. The proposed origin of the RSCH2CHOHCH2OH conjugate labeled at either carbon-1 or carbon-3 is oxidation of DBCP at the bromomethyl or chloromethyl substituent, respectively, followed by two spontaneous dehydrohalogenations to give the highly reactive 2-bromopropenal, and addition of GSH followed by reduction of the aldehyde functionality. An alternative mechanism for the formation of the RSCH2CHOHCH2Cl and RSCH2CHOHCH2OH derivatives involves carbon-2 oxidation to give 1-bromo-3-chloroacetone followed by reaction with GSH and reduction of the ketone functionality with or without hydrolysis of the chloro substituent. 2-Bromopropenal, 1-bromo-3-chloroacetone, or GSH conjugates derived from these intermediates may be involved in the male reproductive toxicity, nephrotoxicity and genotoxicity of DBCP. PMID:3421999

Dohn, D R; Graziano, M J; Casida, J E

1988-09-15

103

In Situ 13C MAS NMR Study of n-Hexane Conversion on Pt and Pd Supported on Basic Materials  

Microsoft Academic Search

n-Hexane conversion was studiedin situon Pt and Pd supported on aluminum-stabilized magnesium oxide and Pt on Zeoite KL catalysts (Pt\\/Mg(Al)O, Pd\\/Mg(Al)O and Pt\\/KL) by means of13C MAS NMR spectroscopy.n-Hexane 1-13C was used as a labelled reactant. Forty NMR lines corresponding to 14 different products were resolved and identified. The NMR line assignments were confirmed by adsorption of model compounds. The

Irina I. Ivanova; Anne Pasau-Claerbout; Michaèl Seirvert; Niels Blom; Eric G. Derouane

1996-01-01

104

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

105

Complete 1H and 13C NMR assignments and anti fungal activity of two 8-hydroxy flavonoids in mixture.  

PubMed

A mixture of the two new flavonols 8-hydroxy-3, 4', 5, 6, 7-pentamethoxyflavone (1) and 8-hydroxy-3, 3', 4', 5, 6, 7-hexamethoxyflavone (2) was isolated from a commercial sample of Citrus aurantifolia. An array of one- (1HNMR, {1H}-13C NMR, and APT-13C NMR) and two-dimensional NMR techniques (COSY, NOESY, HMQC and HMBC) was used to achieve the structural elucidation and the complete 1H and 13C chemical shift assignments of these natural compounds. In addition, the antifungal activity of these compounds against phytopathogenic and human pathogenic fungi was investigated. PMID:17625676

Johann, Susana; Smânia-Jr, Artur; Pizzolatti, Moacir G; Schripsema, Jan; Braz-Filho, Raimundo; Branco, Alexsandro

2007-06-01

106

13C NMR spectroscopy of the insoluble carbon of carbonaceous chondrites  

NASA Technical Reports Server (NTRS)

13C NMR spectra have been obtained of the insoluble carbon residues resulting from HF-digestion of three carbonaceous chondrites, Orgueil (C1), Murchison (CM2), and Allende (CV3). Spectra obtained using the cross polarization magic-angle spinning technique show two major features attributable respectively to carbon in aliphatic/olefinic structures. The spectrum obtained from the Allende sample was weak, presumably as a consequence of its low hydrogen content. Single pulse excitation spectra, which do not depend on 1H-13C polarization transfer for signal enhancement were also obtained. These spectra, which may be more representative of the total carbon in the meteorite samples, indicate a greater content of carbon in aromatic/olefinic structures. These results suggest that extensive polycyclic aromatic sheets are important structural features of the insoluble carbon of all three meteorites. The Orgueil and Murchison materials contain additional hydrogenated aromatic/olefinic and aliphatic groups.

Cronin, J. R.; Pizzarello, S.; Frye, J. S.

1987-01-01

107

13C NMR spectroscopy of the insoluble carbon of carbonaceous chondrites.  

PubMed

13C NMR spectra have been obtained of the insoluble carbon residues resulting from HF-digestion of three carbonaceous chondrites, Orgueil (C1), Murchison (CM2), and Allende (CV3). Spectra obtained using the cross polarization magic-angle spinning technique show two major features attributable respectively to carbon in aliphatic/olefinic structures. The spectrum obtained from the Allende sample was weak, presumably as a consequence of its low hydrogen content. Single pulse excitation spectra, which do not depend on 1H-13C polarization transfer for signal enhancement were also obtained. These spectra, which may be more representative of the total carbon in the meteorite samples, indicate a greater content of carbon in aromatic/olefinic structures. These results suggest that extensive polycyclic aromatic sheets are important structural features of the insoluble carbon of all three meteorites. The Orgueil and Murchison materials contain additional hydrogenated aromatic/olefinic and aliphatic groups. PMID:11542083

Cronin, J R; Pizzarello, S; Frye, J S

1987-01-01

108

13C-NMR determination of the molecular dynamics of cholesterol in dimyristoylphosphatidylcholine vesicles.  

PubMed

Using 13C-NMR measurements of T1, T2 and the nuclear Overhauser enhancement factor at 50.32, 90.56 and 150.87 MHz, we have measured the dynamics of cholesterol in dimyristoylphosphatidylcholine (DMPC) vesicles from 28 to 50 degrees C. Using the model-free approach of Lipari and Szabo, we have found that at 37 degrees C the motion of the rigid steroid ring can be described by an equal contribution from two effective motions with correlation times of 63 and 0.85 ns. The C26 and C27 carbon atoms of cholesterol were found to have an effective correlation time of 8 +/- 2 ps and a value for the square of the generalised order parameter of 0.03 +/- 0.01. The corresponding values for the C25 carbon atom were 17 +/- 4 ps and 0.09 +/- 0.02, showing slower motion and greater order for this carbon atom, which is nearer to the rigid steroid ring. Apart from the effect of vesicle size on T2, no concentration dependence of the dynamics of cholesterol was detected over the cholesterol concentration range 2-30 mol%. The order parameters and correlation times from the present 13C-NMR experiments are shown to be compatible with those from 2H-NMR experiments. This establishes the validity of the present approach, which we are currently extending to low concentrations of cholesteryl oleate in DMPC vesicles. PMID:8118912

Higinbotham, J; Beswick, P H; Malcolmson, R J; Reed, D; Parkinson, J A; Sadler, I H

1993-11-01

109

Molecular composition of humic substances in tundra soils (13C-NMR spectroscopic study)  

NASA Astrophysics Data System (ADS)

Functional groups and molecular fragments of humic substances (HSs) from cryohydromorphic peat gley tundra and surface-gley tundra soils have been identified by 13C-NMR spectroscopy. The analysis of HS preparations has shown that the molecules of humic acids (HAs) are enriched with aromatic fragments compared to fulvic acids (FAs). Aliphatic chains, carbohydrate- and amino acid-type structures prevail in the carbon skeleton of the FAs. An integrated parameter of the HS hydrophobicity has been proposed. The parameter represents the total portion of unoxidized carbon atoms and allows indirectly assessing the amphiphilic properties of HSs.

Lodygin, E. D.; Beznosikov, V. A.; Vasilevich, R. S.

2014-05-01

110

The truncated driven NOE and 13C NMR sensitivity enhancement in magnetically-aligned bicelles  

Microsoft Academic Search

The truncated driven nuclear Overhauser effect (NOE) sequence is examined as a means of sensitivity enhancement in 13C NMR spectroscopy of magnetically-aligned bicelles consisting of 4.5:1 mixtures of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) plus DHPC (1,2-dihexanoyl-sn-glycero-3-phosphocholine), with 1mole% DMPE-PEG 2000 (1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-methoxy(polyethylene glycol)-2000). Steady-state NOE enhancements were observed at all carbon segments except the lipid carbonyls, but full NOE enhancements were obtained only for

Peter M. Macdonald; Ronald Soong

2007-01-01

111

Chemistry, 13C-NMR Study and Pharmacology of Two Saponins from Colubrina asiatica.  

PubMed

From the leaves of COLUBRINA ASIATICA B RONGEN (Rhamnaceae) two saponins have been isolated and structurally elucidated, mainly by (13)C-NMR-spectroscopic methods, as jujubogenin-3-O-[2-O-acetyl-3-O-(3-O-beta-D-xylopyranosyl-4-O-acetyl-beta-D-glucopyranosyl)-alpha-L-arabinoside] (colubrinoside) and jujubogenin-3-O- [2-O-acetyl -3-O- (2-O- beta -D- xylopyranosyl-beta-D-glucopyranosyl)-alpha-L-arabinoside] (colubrin) respectively. Both saponins inhibit the spontaneous motility of mice, even at low doses (1 mg/ kg), they show an antagonistic effect on amphetamine and exert a synergistic activity on chlordiazepoxide. PMID:17404972

Wagner, H; Ott, S; Jurcic, K; Morton, J; Neszmelyi, A

1983-07-01

112

Analysis of epoxy resin formulations by /sup 13/C NMR spectroscopy  

SciTech Connect

The chloroform soluble components of several epoxy resin formulations were analyzed by /sup 13/C NMR spectroscopy. The technique permits the components of an epoxy resin formulation to be identified on a routine basis with a high degree of confidence. Narmco's 5208 contained MY-720 and EpiRez SU-7 or SU-8. Two versions of Ferro's CE-9000 contained ERL-0510 and EpiRez SU-7 or SU-8. Although the method is semiquantitative, it was able to distinguish between the two versions of Ferro's CE-9000 in which the concentration of ERL-0510 differs by approximately a factor of two.

Assink, R.A.; Gurule, F.T.

1981-02-01

113

Identifying Inter-Residue Resonances in Crowded 2D 13C-13C Chemical Shift Correlation Spectra of Membrane Proteins by Solid-State MAS NMR Difference Spectroscopy  

PubMed Central

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 13C-13C chemical shift correlation spectra is presented. With the analyses of 13C-13C 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 (MAS) 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 protonconducting 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 13C labeled protein that are consistent with the high resolution structure of the M2 (22–62) protein (Sharma et al. 2010).

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

2013-01-01

114

Experimental and calculated 1H, 13C, 15N NMR spectra of famotidine  

NASA Astrophysics Data System (ADS)

Famotidine, 3-[[[2-[(aminoiminomethyl)amino]-4-thiazolyl]methyl]thio]- N-(aminosulfonyl), is a histamine H 2-receptor blocker that has been used mainly for the treatment of peptic ulcers and the Zollinger-Ellison syndrome. Its NMR spectra in different solvents were reported earlier; however, detailed interpretation has not been done thus far. In this work, experimental 1H, 13C and 15N NMR spectra of famotidine dissolved in DMSO-d 6 are shown. The assignment of observed chemical shifts is based on quantum chemical calculation at the Hartree-Fock/6-31G ? level. The geometry optimization of the famotidine molecule with two internal hydrogen bonds, i.e. [N(3)-H(23)⋯N(9) and N(3)⋯H(34)-N(20)], is done by using the B3LYP method with the 6-31G ? basis set.

Bara?ska, M.; Czarniecki, K.; Proniewicz, L. M.

2001-05-01

115

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

Microsoft Academic Search

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 ?-(1?4)\\/?-(1?3)-linked d-xylan with chemical shifts close to those observed in the solution

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

2003-01-01

116

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

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

2011-03-10

118

13C NMR investigation of nonenzymatic glucosylation of protein. Model studies using RNase A.  

PubMed

Nonenzymatic glucosylation of protein is initiated by the reversible condensation of glucose in its open chain form with the amino groups on the protein. The initial product is an aldimine (Schiff base) which cyclizes to the glycosylamine derivative. The aldimine can undergo a slow Amadori rearrangement to yield the relatively stable ketoamine adduct which is structurally analogous to fructose. 13C NMR has been used to characterize these early products of nonenzymatic glucosylation, using RNase A as a model protein. C-1 of the beta-pyranose anomer of the glycosylamine was identified at 88.8 ppm in the spectrum of RNase glucosylated approximately 1:1 with D-[1-13C]glucose. C-1 of the Amadori product was also apparent in this spectrum, resonating as a pair of intense peaks at 52.7 and 53.1 ppm. The anomeric (C-2) resonances of the Amadori adduct were seen in the spectrum of RNase glucosylated approximately 1:1 with [U-13C]glucose. This spectrum was interpreted by comparison to the spectra of reference compounds: D-fructose, fructose-glycine, N alpha-formyl-N epsilon-fructose-lysine, and glucosylated poly-L-lysine. In the protein spectrum, the most intense of the C-2 resonances was that of the beta-fructopyranose anomer at 95.8 ppm. The alpha- and beta-fructofuranose anomers were also observed at 101.7 and 99.2 ppm, respectively. One unidentified signal in the anomeric region was observed in the spectra of poly-L-lysine and RNase, both glucosylated with [U-13C]glucose; no comparable resonances were observed in the spectra of the model compounds. PMID:6643480

Neglia, C I; Cohen, H J; Garber, A R; Ellis, P D; Thorpe, S R; Baynes, J W

1983-12-10

119

(13)C NMR-based metabolomics for the classification of green coffee beans according to variety and origin.  

PubMed

(13)C NMR-based metabolomics was demonstrated as a useful tool for distinguishing the species and origins of green coffee bean samples of arabica and robusta from six different geographic regions. By the application of information on (13)C signal assignment, significantly different levels of 14 metabolites of green coffee beans were identified in the classifications, including sucrose, caffeine, chlorogenic acids, choline, amino acids, organic acids, and trigonelline, as captured by multivariate analytical models. These studies demonstrate that the species and geographical origin can be quickly discriminated by evaluating the major metabolites of green coffee beans quantitatively using (13)C NMR-based metabolite profiling. PMID:22989016

Wei, Feifei; Furihata, Kazuo; Koda, Masanori; Hu, Fangyu; Kato, Rieko; Miyakawa, Takuya; Tanokura, Masaru

2012-10-10

120

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

121

Orientational order of two fluoro- and isothiocyanate-substituted nematogens by combination of 13C NMR spectroscopy and DFT calculations.  

PubMed

Orientational order properties of two nematogens containing a fluoro- and isothiocyanate-substituted biphenyl moiety have been investigated by means of (13)C NMR spectroscopy. (13)C NMR spectra acquired on static samples under high-power (1)H-decoupling allowed both (13)C chemical shift anisotropies and (13)C-(19)F couplings to be measured. These data were used to determine the local principal order parameter and biaxiality for the different rigid fragments of the molecules. To this aim, advanced DFT methods for the calculation of geometrical parameters and chemical shift tensors were used. The orientational order parameters obtained by NMR have been critically compared with those obtained by dielectric spectroscopy. Trends of order parameters with temperature have been analyzed in terms of both mean field theory and the empirical Haller equation. PMID:24605890

Calucci, Lucia; Carignani, Elisa; Geppi, Marco; Macchi, Sara; Mennucci, Benedetta; Urban, Stanislaw

2014-03-27

122

1H-Detected 13C photo-CIDNP as a sensitivity enhancement tool in solution NMR.  

PubMed

NMR is a powerful yet intrinsically insensitive technique. The applicability of NMR to chemical and biological systems would be substantially extended by new approaches going beyond current signal-to-noise capabilities. Here, we exploit the large enhancements arising from (13)C photochemically induced dynamic nuclear polarization ((13)C photo-CIDNP) in solution to improve biomolecular NMR sensitivity in the context of heteronuclear correlation spectroscopy. The (13)C-PRINT pulse sequence presented here involves an initial (13)C nuclear spin polarization via photo-CIDNP followed by conversion to anti-phase coherence and transfer to (1)H for detection. We observe substantial enhancements, up to ?200-fold, relative to the dark (laser off) experiment. Resonances of both side-chain and backbone CH pairs are enhanced for the three aromatic residues Trp, His, and Tyr, the ?(32) peptide, and the drkN SH3 protein. The sensitivity of this experiment, defined as signal-to-noise per square root of unit time (S/N)(t), is unprecedented in the NMR polarization enhancement literature dealing with polypeptides in solution. Up to a 16-fold larger (S/N)(t) than for the (1)H-(13)C SE-HSQC reference sequence is achieved, for the ?(32) peptide. Data collection time is reduced up to 256-fold, highlighting the advantages of (1)H-detected (13)C photo-CIDNP in solution NMR. PMID:21548581

Lee, Jung Ho; Sekhar, Ashok; Cavagnero, Silvia

2011-06-01

123

Simultaneous steady-state and dynamic 13C NMR can differentiate alternative routes of pyruvate metabolism in living cancer cells.  

PubMed

Metabolic reprogramming facilitates cancer cell growth, so quantitative metabolic flux measurements could produce useful biomarkers. However, current methods to analyze flux in vivo provide either a steady-state overview of relative activities (infusion of (13)C and analysis of extracted metabolites) or a dynamic view of a few reactions (hyperpolarized (13)C spectroscopy). Moreover, although hyperpolarization has successfully quantified pyruvate-lactate exchanges, its ability to assess mitochondrial pyruvate metabolism is unproven in cancer. Here, we combined (13)C hyperpolarization and isotopomer analysis to quantify multiple fates of pyruvate simultaneously. Two cancer cell lines with divergent pyruvate metabolism were incubated with thermally polarized [3-(13)C]pyruvate for several hours, then briefly exposed to hyperpolarized [1-(13)C]pyruvate during acquisition of NMR spectra using selective excitation to maximize detection of H[(13)C]O3(-) and [1-(13)C]lactate. Metabolites were then extracted and subjected to isotopomer analysis to determine relative rates of pathways involving [3-(13)C]pyruvate. Quantitation of hyperpolarized H[(13)C]O3(-) provided a single definitive metabolic rate, which was then used to convert relative rates derived from isotopomer analysis into quantitative fluxes. This revealed that H[(13)C]O3(-) appearance reflects activity of pyruvate dehydrogenase rather than pyruvate carboxylation followed by subsequent decarboxylation reactions. Glucose substantially altered [1-(13)C]pyruvate metabolism, enhancing exchanges with [1-(13)C]lactate and suppressing H[(13)C]O3(-) formation. Furthermore, inhibiting Akt, an oncogenic kinase that stimulates glycolysis, reversed these effects, indicating that metabolism of pyruvate by both LDH and pyruvate dehydrogenase is subject to the acute effects of oncogenic signaling on glycolysis. The data suggest that combining (13)C isotopomer analyses and dynamic hyperpolarized (13)C spectroscopy may enable quantitative flux measurements in living tumors. PMID:24415759

Yang, Chendong; Harrison, Crystal; Jin, Eunsook S; Chuang, David T; Sherry, A Dean; Malloy, Craig R; Merritt, Matthew E; DeBerardinis, Ralph J

2014-02-28

124

High-resolution solid-state 13C NMR spectroscopy of the paramagnetic metal-organic frameworks, STAM-1 and HKUST-1.  

PubMed

Solid-state (13)C magic-angle spinning (MAS) NMR spectroscopy is used to investigate the structure of the Cu(II)-based metal-organic frameworks (MOFs), HKUST-1 and STAM-1, and the structural changes occurring within these MOFs upon activation (dehydration). NMR spectroscopy is an attractive technique for the investigation of these materials, owing to its high sensitivity to local structure, without any requirement for longer-range order. However, interactions between nuclei and unpaired electrons in paramagnetic systems (e.g., Cu(II)-based MOFs) pose a considerable challenge, not only for spectral acquisition, but also in the assignment and interpretation of the spectral resonances. Here, we exploit the rapid T(1) relaxation of these materials to obtain (13)C NMR spectra using a spin-echo pulse sequence at natural abundance levels, and employ frequency-stepped acquisition to ensure uniform excitation of resonances over a wide frequency range. We then utilise selective (13)C isotopic labelling of the organic linker molecules to enable an unambiguous assignment of NMR spectra of both MOFs for the first time. We show that the monomethylated linker can be recovered from STAM-1 intact, demonstrating not only the interesting use of this MOF as a protecting group, but also the ability (for both STAM-1 and HKUST-1) to recover isotopically-enriched linkers, thereby reducing significantly the overall cost of the approach. PMID:23202442

Dawson, Daniel M; Jamieson, Lauren E; Mohideen, M Infas H; McKinlay, Alistair C; Smellie, Iain A; Cadou, Romain; Keddie, Neil S; Morris, Russell E; Ashbrook, Sharon E

2013-01-21

125

Topotecan dynamics, tautomerism and reactivity--1H/13C NMR and ESI MS study.  

PubMed

Topotecan (TPT) is in clinical use as an antitumor agent, hycamtin. Because of this, it requires both biologically and chemically useful information to be available. TPT acts by binding to the covalent complex formed by nicked DNA and topoisomerase I. This has a poisonous effect since inserted into the single-strand nick and TPT inhibits its religation. We used NMR to trace TPT dynamics, tautomerism and solvolysis products in various solvents and conditions. Chemical stability was assessed in methanol and DMSO as compared to water, and the regioselectivity of the N- and O-methylation was studied using various alkylating agents. The reaction products of quaternization of the nitrogen atom and methylation of the oxygen atom were characterized by means of ESI MS, (1)H/(13)C-HMBC and -HSQCAD NMR. We have focused on the NMR characterization of TPT with an anticipation that its aggregation, tumbling properties and the intramolecular dipolar interactions will be a common feature for other compounds described in this article. These features can also be useful in tracing the interactions of this class of topoisomerase I (TopoI) poisons with DNA. Moreover, the results explained shed light on the recently disclosed problem of lack of stability of TPT in the heart tissue homogenate samples using the analytical assays developed for this class of compounds carried out in the presence of methanol. PMID:20623719

Hyz, Karolina; Kawecki, Robert; Bednarek, Elzbieta; Bocian, Wojciech; Sitkowski, Jerzy; Kozerski, Lech

2010-08-01

126

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)] [Tokyo Inst. of Technology, Yokohama (Japan); Tamura, Yusuke; Watanabe, Yoichi [Cray Research Japan Ltd., Tokyo (Japan)] [Cray Research Japan Ltd., Tokyo (Japan)

1996-02-01

127

{sup 13}C chemical shift anisotropies for carbonate ions in cement minerals and the use of {sup 13}C, {sup 27}Al and {sup 29}Si MAS NMR in studies of Portland cement including limestone additions  

SciTech Connect

{sup 13}C isotropic chemical shifts and chemical shift anisotropy parameters have been determined for a number of inorganic carbonates relevant in cement chemistry from slow-speed {sup 13}C MAS or {sup 13}C({sup 1}H) CP/MAS NMR spectra (9.4 T or 14.1 T) for {sup 13}C in natural abundance. The variation in the {sup 13}C chemical shift parameters is relatively small, raising some doubts that different carbonate species in Portland cement-based materials may not be sufficiently resolved in {sup 13}C MAS NMR spectra. However, it is shown that by combining {sup 13}C MAS and {sup 13}C({sup 1}H) CP/MAS NMR carbonate anions in anhydrous and hydrated phases can be distinguished, thereby providing valuable information about the reactivity of limestone in cement blends. This is illustrated for three cement pastes prepared from an ordinary Portland cement, including 0, 16, and 25 wt.% limestone, and following the hydration for up to one year. For these blends {sup 29}Si MAS NMR reveals that the limestone filler accelerates the hydration for alite and also results in a smaller fraction of tetrahedrally coordinated Al incorporated in the C-S-H phase. The latter result is more clearly observed in {sup 27}Al MAS NMR spectra of the cement–limestone blends and suggests that dissolved aluminate species in the cement–limestone blends readily react with carbonate ions from the limestone filler, forming calcium monocarboaluminate hydrate. -- Highlights: •{sup 13}C chemical shift anisotropies for inorganic carbonates from {sup 13}C MAS NMR. •Narrow {sup 13}C NMR chemical shift range (163–171 ppm) for inorganic carbonates. •Anhydrous and hydrated carbonate species by {sup 13}C MAS and {sup 13}C({sup 1}H) CP/MAS NMR. •Limestone accelerates the hydration for alite in Portland – limestone cements. •Limestone reduces the amount of aluminium incorporated in the C-S-H phase.

Sevelsted, Tine F. [Instrument Centre for Solid-State NMR Spectroscopy, Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), Aarhus University, DK-8000 Aarhus C (Denmark)] [Instrument Centre for Solid-State NMR Spectroscopy, Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), Aarhus University, DK-8000 Aarhus C (Denmark); Herfort, Duncan [Aalborg Portland A/S,Cementir Holding S.p.A., DK-9100 Aalborg (Denmark)] [Aalborg Portland A/S,Cementir Holding S.p.A., DK-9100 Aalborg (Denmark); Skibsted, Jørgen, E-mail: jskib@chem.au.dk [Instrument Centre for Solid-State NMR Spectroscopy, Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), Aarhus University, DK-8000 Aarhus C (Denmark)] [Instrument Centre for Solid-State NMR Spectroscopy, Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), Aarhus University, DK-8000 Aarhus C (Denmark)

2013-10-15

128

1 H- and 13 C-NMR spectroscopic studies of lipid extracts of the red alga Gracilaria longa  

Microsoft Academic Search

Lipid extracts of the red algaGracilaria longa were studied by1H- and13C-NMR spectroscopy. Peaks in the13C-NMR spectra attributable to sterols, chlorophylls and carotenoids allowed free and acylated cholesterol, chlorophylla and lutein to be identified as the most abundant components of these classes. A content of 0.5 0.1 ?moles of total cholesterol\\/g\\u000a wet alga was estimated from the1H-NMR spectrum, which also allowed

Piero Pollesello; Renato Toffanin; Erminio Murano; Roberto Rizzo; Sergio Paoletti; Bjarne J. Kvaml

1992-01-01

129

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

130

A 13C NMR study on the adsorption characteristics of HEMA to dentinal collagen.  

PubMed

To develop a more effective primer, we must understand how 2-hydroxyethylmethacrylate, the HEMA primer, enhances bonding at the resin-dentin interface. In this study, to obtain an insight into the adhesion mechanisms of adhesive resin to etched dentin through HEMA, we examined the adsorption characteristics of HEMA to dentinal collagen by using the 13C NMR technique. The addition of dentinal collagen to the HEMA solution resulted in a decrease in T(1) values of carbons attributed to the HEMA, thus reflecting an interaction between HEMA and collagen. Specifically, a reduction in the T(1) value in the ester carbonyl carbon attributed to HEMA greater than that in the other carbons suggested the formation of a hydrogen bond between the ester carbonyl group in HEMA and the dentinal collagen. PMID:12161458

Nishiyama, N; Suzuki, K; Komatsu, K; Yasuda, S; Nemoto, K

2002-07-01

131

The effect of sample hydration on 13C CPMAS NMR spectra of fulvic acids  

USGS Publications Warehouse

Three fulvic acids, two of which have been well studied by a number of other groups (Armadale and Suwannee river fulvic acids) have been examined by high resolution solid-state 13C-NMR techniques to delineate the effect of absorbed water. Two main effects of absorbed water were observed: (1) changes in spin lattice relaxation times in the rotating frame and cross polarization times and (2) total loss of signal so that some fulvic acid is effectively in solution. These results suggest that discrepancies in the literature concerning observed relative signal intensities from different structural groups are due to absorbed water and emphasize the necessity for proper precautionary drying before spectroscopic analysis. ?? 1991.

Hatcher, P. G.; Wilson, M. A.

1991-01-01

132

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

PubMed

Fully bleached softwood kraft pulps were hydrolyzed with cellulase (1,4-(1,3:1,4)-beta-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(alpha), cellulose I(beta), para-crystalline) and amorphous regions were hydrolyzed to a different extent by the enzyme used. Also observed was a rapid initial phase for hydrolysis of regions followed by a slow hydrolysis phase. Cellulose I(alpha), para-crystalline, and non-crystalline regions of cellulose are more susceptible to enzymatic hydrolysis than cellulose I(beta) during the initial phase. After the initial phase, all the regions are then similarly susceptible to enzymatic hydrolysis. PMID:16442511

Pu, Yunqiao; Ziemer, Cherie; Ragauskas, Arthur J

2006-04-10

133

A multinuclear 1H, 13C and 11B solid-state MAS NMR study of 16- and 18-electron organometallic ruthenium and osmium carborane complexes.  

PubMed

The first (1)H, (13)C, (31)P and (11)B solid state MAS NMR studies of electron-deficient carborane-containing ruthenium and osmium complexes [Ru/Os(p-cym)(1,2-dicarba-closo-dodecaborane-1,2-dithiolate)] are reported. The MAS NMR data from these 16-electron complexes are compared to those of free carborane-ligand and an 18-electron triphenylphosphine ruthenium adduct, and reveal clear spectral differences between 16- and 18-electron organometallic carborane systems in the solid state. PMID:24554004

Barry, Nicolas P E; Kemp, Thomas F; Sadler, Peter J; Hanna, John V

2014-04-01

134

Coupling XRD, EXAFS, and 13C NMR to study the effect of the carbon stoichiometry on the local structure of UC(1±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 UC(1.00). 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

2013-10-01

135

Assignment of the 1H and 13C NMR of tocotrienols.  

PubMed

Vitamin E is a family of chromanols that vary by the degree of methylation of the chroman ring as well as the nature of the hydrophobic side chain at C2 that serves to anchor these lipids in biological membranes. The tocopherols contain saturated side chains, whereas the tocotrienols contain three sites of unsaturation and are derived from geranylgeranyl diphosphate. A growing interest in the unique biological activities of the tocotrienols has led us to begin syntheses of isotopically substituted forms and other derivatives that will be useful for probing the metabolism and membrane behavior of the tocotrienols. In order to be certain of our ability to selectively modify sites on the parent molecules it was necessary to make as complete an assignment of the 1H and 13C NMR as possible. Herein we report multidimensional NMR data (HSQC, COSY, ADEQUATE(1,1), C--H HMBC, and NOESY) that have allowed us to assign the identity of almost all the resonances for alpha-, beta-, gamma-, and delta-tocotrienol. PMID:18236416

Ohnmacht, Stephan; West, Ryan; Simionescu, Razvan; Atkinson, Jeffrey

2008-03-01

136

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

137

Determination of full 13C isotopomer distributions for metabolic flux analysis using heteronuclear spin echo difference NMR spectroscopy  

Microsoft Academic Search

13C-isotopomer labeling experiments play an increasingly important role in the analysis of intracellular metabolic fluxes for genetic engineering purposes. 13C NMR spectroscopy is a key technique in the experimental determination of isotopomer distributions. However, only subsets of isotopomers can be quantitated using this technique due to redundancies in the scalar coupling patterns and due to invisibility of the 12C isotope

Albert A de Graaf; Matthias Mahle; Michael Möllney; Wolfgang Wiechert; Peter Stahmann; Hermann Sahm

2000-01-01

138

Fractionation and characterization of sludge bacterial extracellular polymers by FT-IR, 13C-NMR, 1H-NMR.  

PubMed

Sludge bacterial extracellular (BEP) polymers exhibit a strong affinity with metals in addition to their role in the bioflocculation of activated sludge. It is of utmost importance in elucidating the chemical characterization of sludge BEP prior to a better understanding of its environmental behavior. Sludge BEP extracted from activated sludge was characterized by FT-IR, 1H-NMR, and 13C-NMR and fractionated into 6 fractions (hydrophilic acid, base, and neutral; and hydrophobic acid, base, and neutral). The results indicated that sludge BEP contained more polysaccharides but fewer amino acids or proteinaceous materials compared to dissolved organic matter (DOM) derived from sludge. No aromatic substance was found in sludge BEP as indicated by NMR. Sludge BEP was dominated by hydrophilic fractions, accounting for 65% of total DOC of sludge BEP and hydrophilic neutral constituted about 58% of the hydrophilic fraction. The chemical fraction and characterization indicated that sludge BEP might exhibit a higher capability in enhancing the transport of the associated contaminants through porous media than that of sludge DOM. PMID:11794684

Zhou, L X; Liang, J R; Zha, X H; Wong, J W

2001-01-01

139

Spectral-Density Mapping of 13C ?- 1H ?Vector Dynamics Using Dipolar Relaxation Rates Measured at Several Magnetic Fields  

NASA Astrophysics Data System (ADS)

The spectral-density mapping of a 13C ?- 1H ?vector of Leu 10in the 22-residue peptide hormone motilin [P. Allard, J. Jarvet, A. Ehrenberg, and A. Gräslund, J. Biomol. NMR5,133-146 (1995)] is extended in this paper to three polarizing fields 9.4, 11.7, and 14.1 T in order to improve the accuracy of the calculated spectral-density function J(?) and to extend the sampling range up to 750 MHz. The problem with a usually large relative error in J(? H) is eliminated since the generally more precise J(? H- ? C) and J(? H+ ? C) determined at other fields appear at nearly the same frequencies. The fitting of dynamic models to the points of spectral density was made with error weighting, and the influence of J(? H) was found to be negligible. Therefore, the high-frequency part of the spectral-density function is determined essentially without influence from the two transverse-type relaxation rates. In the case of a carbon-proton vector, the relaxation is mainly determined by dipolar interaction and is only weakly influenced by other relaxation mechanisms, which makes it particularly suitable for the spectral-density mapping technique. The measured relaxation rates in the time domain are transformed into the frequency domain by spectral-density mapping, and the slopes in different frequency regions are important parameters when comparing experimental data with theoretical models of motion. Using an adjustable internuclear distance reff, combined with the model-free approach, it is possible to obtain a reasonable fit to measured spectral-density points at J(0) and around J(? C). At the same time, however, the high-frequency slope of the spectral-density function defined by J(? H- ? C) and J(? H+ ? C) could not be reproduced.

Jarvet, Jüri; Allard, Peter; Ehrenberg, Anders; Gräslund, Astrid

140

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

2008-08-14

141

13C and 1H NMR (Nuclear Magnetic Resonance) studies of solid polyolefines  

NASA Technical Reports Server (NTRS)

The basis of H-1 and C-13 high-resolution NMR investigations of solid polymers is outlined. The C-13 NMR spectra of solid syndiotactic and isotactic polypropene are discussed and their interpretation in terms of conformation and chain-packing effects are reviewed. The effects of decreasing temperature on the C-13 high-resolution spectrum of an annealed sample of isotactic polypropene is described and interpreted in terms of the crystal structure. The question of the proportion of the sample giving rise to C-13 signals is addressed and some results reported. The main cause for observing only part of the total sample is shown to be the H-1 rotating frame spin-lattice relaxation behavior. The H-1 spin-lattice relaxation and spectral characteristics of a number of polyolefin samples are summarized and the role of spin-diffusion discussed.

Cudby, M. E. A.; Harris, R. K.; Metcalfe, K.; Packer, K. J.; Smith, P. W. R.

1983-01-01

142

Thermal maturity of type II kerogen from the New Albany Shale assessed by 13C CP/MAS NMR.  

PubMed

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. PMID:15589735

Werner-Zwanziger, Ulrike; Lis, Grzegorz; Mastalerz, Maria; Schimmelmann, Arndt

2005-01-01

143

13C and 113Cd NMR studies of the chelation of metal ions by the calcium binding protein parvalbumin.  

PubMed

13C NMR spectra are presented for the calcium binding protein parvalbumin (pI 4.25) from carp muscle in several different metal bound forms: with Ca2+ in both the CD and EF calcium binding sites, with Cd2+ in both sites, with 113Cd2+ in both sites, and with 113Cd2+ in the CD site and Lu3+ in the EF site. The different metals differentially shift the 13C NMR resonances of the protein ligands involved in chelation of the metal ion. In addition, direct 13C-113Cd spin-spin coupling is observed which allows the assignment of protein carbonyl and carboxyl 13C NMR resonances to ligands directly interacting with the metal ions in the CD and EF binding sites. The displacement of 113Cd2+ from the EF site by Lu3+ further allows these resonances to be assigned to the CD or EF site. The occupancy of the two sites in the two cadmium species and in the mixed Cd2+/Lu3+ species is verified by 113Cd NMR. The resolution in these 113Cd NMR spectra is sufficient to demonstrate direct interaction between the two metal binding sites. PMID:3932596

Bjornson, M E; Corson, D C; Sykes, B D

1985-10-01

144

13 C– 1 H dipolar-assisted rotational resonance in magic-angle spinning NMR  

Microsoft Academic Search

A new 13C13C recoupling mechanism which occurs under magic-angle spinning (MAS) is presented. The mechanism can basically be attributed to rotational resonance (R2), but the conventional R2 condition is modified by a recoupled 13C–1H dipolar interaction. The 13C–1H recoupling is attained by 1H rf irradiation fulfilling a rotary-resonance condition. The present method does not have the drawbacks associated with rf

K. Takegoshi; Shinji Nakamura; Takehiko Terao

2001-01-01

145

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

146

Classification of vegetable oils by high-resolution 13 C NMR spectroscopy using chromatographically obtained oil fractions  

Microsoft Academic Search

13C NMR spectra of oil fractions obtained chromatographically from 109 vegetable oils were obtained and analyzed to evaluate\\u000a the potential use of those fractions in the classification of vegetable oils and to compare the results with the NMR analysis\\u000a of complete oils. The oils included the following: virgin olive oils from different cultivars and regions of Europe and north\\u000a Africa;

Rosario Zamora; Gemma Gómez; Francisco J. Hidalgo

2002-01-01

147

The truncated driven NOE and (13)C NMR sensitivity enhancement in magnetically-aligned bicelles.  

PubMed

The truncated driven nuclear Overhauser effect (NOE) sequence is examined as a means of sensitivity enhancement in (13)C NMR spectroscopy of magnetically-aligned bicelles consisting of 4.5:1 mixtures of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) plus DHPC (1,2-dihexanoyl-sn-glycero-3-phosphocholine), with 1 mole% DMPE-PEG 2000 (1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-methoxy(polyethylene glycol)-2000). Steady-state NOE enhancements were observed at all carbon segments except the lipid carbonyls, but full NOE enhancements were obtained only for the most mobile carbon segments, specifically the choline quaternary methyls and terminal acyl chain methyls of both DMPC and DHPC, as well as the ethylene oxide segments of the PEG head group of DMPE-PEG 2000. Other carbon segments exhibited NOE enhancements that scaled with mobility as determined by transient NOE measurements combined with spin-lattice relaxation measurements. We conclude that the truncated driven NOE provides sensitivity enhancement complimentary to that yielded by cross-polarization techniques and for mobile membrane-associated species may be preferred for its robustness and ease of setup. PMID:17596978

Macdonald, Peter M; Soong, Ronald

2007-09-01

148

The truncated driven NOE and 13C NMR sensitivity enhancement in magnetically-aligned bicelles  

NASA Astrophysics Data System (ADS)

The truncated driven nuclear Overhauser effect (NOE) sequence is examined as a means of sensitivity enhancement in 13C NMR spectroscopy of magnetically-aligned bicelles consisting of 4.5:1 mixtures of DMPC (1,2-dimyristoyl- sn-glycero-3-phosphocholine) plus DHPC (1,2-dihexanoyl- sn-glycero-3-phosphocholine), with 1 mole% DMPE-PEG 2000 (1,2-dimyristoyl- sn-glycero-3-phosphoethanolamine- N-methoxy(polyethylene glycol)-2000). Steady-state NOE enhancements were observed at all carbon segments except the lipid carbonyls, but full NOE enhancements were obtained only for the most mobile carbon segments, specifically the choline quaternary methyls and terminal acyl chain methyls of both DMPC and DHPC, as well as the ethylene oxide segments of the PEG head group of DMPE-PEG 2000. Other carbon segments exhibited NOE enhancements that scaled with mobility as determined by transient NOE measurements combined with spin-lattice relaxation measurements. We conclude that the truncated driven NOE provides sensitivity enhancement complimentary to that yielded by cross-polarization techniques and for mobile membrane-associated species may be preferred for its robustness and ease of setup.

Macdonald, Peter M.; Soong, Ronald

2007-09-01

149

An efficient NMR method for the characterisation of 14N sites through indirect 13C detection  

PubMed Central

Nitrogen is one of the most abundant elements and plays a key role in the chemistry of biological systems. Despite its widespread distribution, the study of the naturally occurring isotope of nitrogen, 14N (99.6%), has been relatively limited as it is a spin-1 nucleus that typically exhibits a large quadrupolar interaction. Accordingly, most studies of nitrogen sites in biomolecules have been performed on samples enriched with 15N, limiting the application of NMR to samples which can be isotopically enriched. This precludes the analysis of naturally occurring samples and results in the loss of the wealth of structural and dynamic information that the quadrupolar interaction can provide. Recently, several experimental approaches have been developed to characterize 14N sites through their interaction with neighboring ‘spy’ nuclei. Here we describe a novel version of these experiments whereby coherence between the 14N site and the spy nucleus is mediated by the application of a moderate rf field to the 14N. The resulting 13C/14N spectra show good sensitivity on natural abundance and labeled materials; whilst the 14N lineshapes permit the quantitative analysis of the quadrupolar interaction.

Jarvis, James A.; Haies, Ibraheem M.

2013-01-01

150

sup 13 C magic-angle spinning NMR studies of bathorhodopsin, the primary photoproduct of rhodopsin  

SciTech Connect

Magic-angle spinning NMR spectra have been obtained of the bathorhodopsin photointermediate trapped at low temperature (<130 K) by using isorhodopsin samples regenerated with retinal specifically {sup 13}C-labeled at positions 8, 10, 11, 12, 13, 14, and 15. Comparison of the chemical shifts of the bathorhodpsin resonances with those of an all-trans-retinal protonated Schiff base (PSB) chloride salt show the largest difference (6.2 ppm) at position 13 of the protein-bound retinal. Small differences in chemical shift between bathorhodopsin and the all-trans PSB model compound are also observed at positions 10, 11, and 12. The effects are almost equal in magnitude to those previously observed in rhodopsin and isorhodopsin. Consequently, the energy stored in the primary photoproduct bathorhodopsin does not give rise to any substantial change in the average electron density at the labeled positions. The data indicate that the electron and structural properties of the protein environment are similar to those in rhodopsin and isorhodopsin. In particular, a previously proposed perturbation near position 13 of the retinal appears not to change its position significantly with respect to the chromophore upon isomerization. The data effectively exclude charge separation between the chromophore and a protein residue as the main mechanism for energy storage in the primary photoproduct and argue that the light energy is stored in the form of distortions of the bathorhodopsin chromophore.

Smith, S.O. (Yale Univ., New Haven, CT (United States)); Courtin, J.; de Groot, H.; Gebhard, R.; Lugtenburg, J. (Rijksuniversiteit te Leiden (Netherlands))

1991-07-30

151

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

152

An efficient NMR method for the characterisation of 14N sites through indirect 13C detection.  

PubMed

Nitrogen is one of the most abundant elements and plays a key role in the chemistry of biological systems. Despite its widespread distribution, the study of the naturally occurring isotope of nitrogen, (14)N (99.6%), has been relatively limited as it is a spin-1 nucleus that typically exhibits a large quadrupolar interaction. Accordingly, most studies of nitrogen sites in biomolecules have been performed on samples enriched with (15)N, limiting the application of NMR to samples which can be isotopically enriched. This precludes the analysis of naturally occurring samples and results in the loss of the wealth of structural and dynamic information that the quadrupolar interaction can provide. Recently, several experimental approaches have been developed to characterize (14)N sites through their interaction with neighboring 'spy' nuclei. Here we describe a novel version of these experiments whereby coherence between the (14)N site and the spy nucleus is mediated by the application of a moderate rf field to the (14)N. The resulting (13)C/(14)N spectra show good sensitivity on natural abundance and labeled materials; whilst the (14)N lineshapes permit the quantitative analysis of the quadrupolar interaction. PMID:23589073

Jarvis, James A; Haies, Ibraheem M; Williamson, Philip T F; Carravetta, Marina

2013-05-28

153

Thermal unfolding in a GCN4-like leucine zipper: 13C alpha NMR chemical shifts and local unfolding curves.  

PubMed Central

13C alpha chemical shifts and site-specific unfolding curves are reported for 12 sites on a 33-residue, GCN4-like leucine zipper peptide (GCN4-lzK), ranging over most of the chain and sampling most heptad positions. Data were derived from NMR spectra of nine synthetic, isosequential peptides bearing 99% 13C alpha at sites selected to avoid spectral overlap in each peptide. At each site, separate resonances appear for unfolded and folded forms, and most sites show resonances for two folded forms near room temperature. The observed chemical shifts suggest that 1) urea-unfolded GCN4-lzK chains are randomly coiled; 2) thermally unfolded chains include significant transient structure, except at the ends; 3) the coiled-coli structure in the folded chains is atypical near the C-terminus; 4) only those interior sites surrounded by canonical interchain salt bridges fail to show two folded forms. Local unfolding curves, obtained from integrated resonance intensities, show that 1) sites differ in structure content and in melting temperature, so the equilibrium population must comprise more than two molecular conformations; 2) there is significant end-fraying, even at the lowest temperatures, but thermal unfolding is not a progressive unwinding from the ends; 3) residues 9-16 are in the lowest melting region; 4) heptad position does not dictate stability; 5) significant unfolding occurs below room temperature, so the shallow, linear decline in backbone CD seen there has conformational significance. It seems that only a relatively complex array of conformational states could underlie these findings.

Holtzer, M E; Lovett, E G; d'Avignon, D A; Holtzer, A

1997-01-01

154

Comprehensive determination of protein tyrosine pKa values for photoactive yellow protein using indirect 13C NMR spectroscopy.  

PubMed

Upon blue-light irradiation, the bacterium Halorhodospira halophila is able to modulate the activity of its flagellar motor and thereby evade potentially harmful UV radiation. The 14 kDa soluble cytosolic photoactive yellow protein (PYP) is believed to be the primary mediator of this photophobic response, and yields a UV/Vis absorption spectrum that closely matches the bacterium's motility spectrum. In the electronic ground state, the para-coumaric acid (pCA) chromophore of PYP is negatively charged and forms two short hydrogen bonds to the side chains of Glu-46 and Tyr-42. The resulting acid triad is central to the marked pH dependence of the optical-absorption relaxation kinetics of PYP. Here, we describe an NMR approach to sequence-specifically follow all tyrosine side-chain protonation states in PYP from pH 3.41 to 11.24. The indirect observation of the nonprotonated (13)C(?) resonances in sensitive and well-resolved two-dimensional (13)C-(1)H spectra proved to be pivotal in this effort, as observation of other ring-system resonances was hampered by spectral congestion and line-broadening due to ring flips. We observe three classes of tyrosine residues in PYP that exhibit very different pK(a) values depending on whether the phenolic side chain is solvent-exposed, buried, or hydrogen-bonded. In particular, our data show that Tyr-42 remains fully protonated in the pH range of 3.41-11.24, and that pH-induced changes observed in the photocycle kinetics of PYP cannot be caused by changes in the charge state of Tyr-42. It is therefore very unlikely that the pCA chromophore undergoes changes in its electrostatic interactions in the electronic ground state. PMID:22325281

Oktaviani, Nur Alia; Pool, Trijntje J; Kamikubo, Hironari; Slager, Jelle; Scheek, Ruud M; Kataoka, Mikio; Mulder, Frans A A

2012-02-01

155

Comprehensive Determination of Protein Tyrosine pKa Values for Photoactive Yellow Protein Using Indirect 13C NMR Spectroscopy  

PubMed Central

Upon blue-light irradiation, the bacterium Halorhodospira halophila is able to modulate the activity of its flagellar motor and thereby evade potentially harmful UV radiation. The 14 kDa soluble cytosolic photoactive yellow protein (PYP) is believed to be the primary mediator of this photophobic response, and yields a UV/Vis absorption spectrum that closely matches the bacterium's motility spectrum. In the electronic ground state, the para-coumaric acid (pCA) chromophore of PYP is negatively charged and forms two short hydrogen bonds to the side chains of Glu-46 and Tyr-42. The resulting acid triad is central to the marked pH dependence of the optical-absorption relaxation kinetics of PYP. Here, we describe an NMR approach to sequence-specifically follow all tyrosine side-chain protonation states in PYP from pH 3.41 to 11.24. The indirect observation of the nonprotonated 13C? resonances in sensitive and well-resolved two-dimensional 13C-1H spectra proved to be pivotal in this effort, as observation of other ring-system resonances was hampered by spectral congestion and line-broadening due to ring flips. We observe three classes of tyrosine residues in PYP that exhibit very different pKa values depending on whether the phenolic side chain is solvent-exposed, buried, or hydrogen-bonded. In particular, our data show that Tyr-42 remains fully protonated in the pH range of 3.41–11.24, and that pH-induced changes observed in the photocycle kinetics of PYP cannot be caused by changes in the charge state of Tyr-42. It is therefore very unlikely that the pCA chromophore undergoes changes in its electrostatic interactions in the electronic ground state.

Oktaviani, Nur Alia; Pool, Trijntje J.; Kamikubo, Hironari; Slager, Jelle; Scheek, Ruud M.; Kataoka, Mikio; Mulder, Frans A.A.

2012-01-01

156

Phase characterization and study of molecular order of a three-ring mesogen by 13C NMR in smectic C and nematic phases.  

PubMed

Molecules exhibiting a thermotropic liquid-crystalline property have acquired significant importance due to their sensitivity to external stimuli such as temperature, mechanical forces, and electric and magnetic fields. As a result, several novel mesogens have been synthesized by the introduction of various functional groups in the vicinity of the aromatic core as well as in the side chains and their properties have been studied. In the present study, we report three-ring mesogens with hydroxyl groups at one terminal. These mesogens were synthesized by a multistep route, and structural characterization was accomplished by spectral techniques. The mesophase properties were studied by hot-stage optical polarizing microscopy, differential scanning calorimetry, and small-angle X-ray scattering. An enantiotropic nematic phase was noticed for lower homologues, while an additional smectic C phase was found for higher homologues. Solid-state high-resolution natural abundance (13)C NMR studies of a typical mesogen in the solid phase and in the mesophases have been carried out. The (13)C NMR spectrum of the mesogen in the smectic C and nematic phases indicated spontaneous alignment of the molecule in the magnetic field. By utilizing the two-dimensional separated local field (SLF) NMR experiment known as SAMPI4, (13)C-(1)H dipolar couplings have been obtained, which were utilized to determine the orientational order parameters of the mesogen. PMID:21877696

Kalaivani, S; Narasimhaswamy, T; Das, Bibhuti B; Lobo, Nitin P; Ramanathan, K V

2011-10-13

157

Chemical characteristics of dissolved organic matter during composting of different organic wastes assessed by 13C CPMAS NMR spectroscopy  

Microsoft Academic Search

This research aimed at assessing the chemical changes occurring in DOM extracted from different composting substrates by means of 13C CPMAS NMR spectroscopy. During composting a reduction of carbohydrates and an increase of aromatic, phenolic, carboxylic and carbonylic C were observed. The highest increase in alkyl C and the lowest increase in aromatic C were explained by the presence of

P. Caricasole; M. R. Provenzano; P. G. Hatcher; N. Senesi

2010-01-01

158

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

Microsoft Academic Search

Cellular metabolism of glucose is required for stimulation of insulin secretion from pancreatic 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

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

2002-01-01

159

Using similarity searches over databases of estimated 13C NMR spectra for structure identification of natural product compounds  

Microsoft Academic Search

Structure elucidation for natural product compounds is assisted by making similarity comparisons between the uncharacterized experimental 13C NMR spectrum with relevant databases of estimated spectra. Databases of estimated spectra are deduced from a small set of assigned structures using HOSE codes. Using spectra estimated from structures circumvents problems of inconsistent, incomplete, missing or irrelevant data. It also enables rapid generation

Athanasios Tsipouras; John Ondeyka; Claude Dufresne; Seok Lee; Gino Salituro; Nancy Tsou; Michael Goetz; Sheo Bux Singh; Simon K. Kearsley

1995-01-01

160

1H, 13C NMR studies and GIAO\\/DFT calculations of substituted N-(4-aryl-1-piperazinylbutyl) derivatives, new analogues of buspirone  

Microsoft Academic Search

13C cross-polarisation (CP) magic angle spinning (MAS) NMR data are reported for seven piperazinylbutyl derivatives of 1,4-dichloro-dibenzo[e,h]bicyclo[2,2,3]octane-2,3-dicarboimide, new analogues of buspirone (anxiolytic drug). The assignment of solid state 13C NMR spectra were made with an aid of variable contact time experiments, as well as by comparison with solution data and calculated shielding constants. 13C CPMAS NMR spectra showed a disorder

Maciej Pisklak; Jerzy Kossakowski; Miros?aw Perli?ski; Iwona Wawer

2004-01-01

161

Two-dimensional 13C NMR study of the substance P fragment Arg?Pro?Lys?Pro  

NASA Astrophysics Data System (ADS)

The N-terminal Substance P fragment Arg 1?Pro 2?Lys 3?Pro 4 (SP 1-4) has been studied by means of natural abundance 13C NMR. By the combined application of various two-dimensional {13C}/{1H} correlation techniques, all 13C resonances in both isomeric forms (cis and trans about the Lys 3?Pro 4 peptide bond) including the quaternary carbons could be assigned unambiguously. The experimental details are outlined and the results are discussed in terms of the peptide conformation. From the data it can be concluded that the cis-SP 1-4 is stabilized by a charge interaction between the end group of the Lys 3 side chain and the deprotonated carboxyl group at the C-terminal end of the peptide. A ring-like interaction with the Arg 1 residue can be excluded. Some 13C? 1H long-range coupling constant have also been measured.

Otter, Albin; Kotovych, George

162

Effects of ammonia on the anaplerotic pathway and amino acid metabolism in the brain: an ex vivo 13 C NMR spectroscopic study of rats after administering [ 2- 13 C ] glucose with or without ammonium acetate  

Microsoft Academic Search

The 13C-label incorporation into glutamate, glutamine, aspartate and ?-aminobutyric acid (GABA) from [2-13C] glucose was measured by 13C nuclear magnetic resonance (NMR) spectroscopy to directly examine the effects of ammonia on the activity of pyruvate carboxylase (i.e., the anaplerotic pathway) and the amino acid metabolism in the rat brain in vivo. Rats were sacrificed by exposure to microwaves at 7.5,

Tomoyuki Kanamatsu; Yasuzo Tsukada

1999-01-01

163

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

164

AM1 Parameters for the Prediction of 1H and 13C NMR Chemical Shifts in Proteins  

NASA Astrophysics Data System (ADS)

The semiempirical quantum mechanical description of NMR chemical shifts has been implemented at the AM1 level with NMR-specific parameters to reproduce experimental 1H and 13C NMR chemical shifts. The methodology adopted here is formally the same as that of the previously published finite perturbation theory GIAO-MNDO-NMR approach [ Wang, B. ; et al. J. Chem. Phys. 2004, 120, 24 . ]. The primary impetus for this parametrization was the accurate capture of chemical environments of atoms in biological systems. Protein-specific parameters were developed on a training set that comprised five globular protein systems with varied secondary structure and a range in size from 46-61 amino acid residues. A separate set of parameters was developed using a training set of small organic compounds with an emphasis on functional groups that are relevant to biological studies. Our approach can be employed using semiempirical (AM1) geometries and can be executed at a fraction of the cost of ab initio and DFT methods, thus providing an attractive option for the computational NMR studies of much larger protein systems. Analysis carried out on 3340 1H and 2233 13C chemical shifts for protein systems shows significant improvement over the standard AM1 parameters. Using 1H and 13C specific parameters, the rms errors are from 1.05 and 21.28 ppm to 0.62 and 4.83 ppm for hydrogen and carbon, respectively.

Williams, Duane E.; Peters, Martin B.; Wang, Bing; Roitberg, Adrian E.; Merz, Kenneth M.

2009-10-01

165

/sup 13/C NMR studies of porphobilinogen synthase: observation of intermediates bound to a 280,000-dalton protein  

SciTech Connect

/sup 13/C NMR has been used to observe the equilibrium complex of (4-/sup 13/C)-5-aminolevulinate ((4-/sup 13/C)ALA) bound to porphobilinogen (PBG) synthase (5-aminolevulinate dehydratase), a 280,000-dalton protein. (4-/sup 13/C)ALA (chemical shift = 205.9 ppm) forms (3,5-/sup 13/C)PBG (chemical shifts = 121.0 and 123.0 ppm). PBG prepared from a mixture of (4-/sup 13/C)ALA and (/sup 15/N)ALA was used to assign the 121.0 and 123.0 ppm resonances to C/sub 5/ and C/sub 3/, respectively. For the enzyme-bound equilibrium complex formed from holoenzyme and (4-/sup 13/C)ALA, two peaks of equal area with chemical shifts of 121.5 and 127.2 ppm are observed (line widths approx. 50 Hz), indicating that the predominant species is probably a distorted form of PBG. When excess free PBG is present, it is in slow exchange with bound PBG, indicating an exchange rate of < 10 s/sup -1/, which is consistent with the turnover rate of the enzyme. For the complex formed from (4-/sup 13/C)ALA and methyl methanethiosulfonate (MMTS) modified PBG synthase, which does not catalyze PBG formation, the predominant species is a Schiff base adduct (chemical shift = 166.5 ppm, line width approx. 50 Hz). Free ALA is in slow exchange with the Schiff base. Activation of the MMTS-modified enzyme-Schiff base complex with /sup 113/Cd and 2-mercaptoethanol results in the loss of the Schiff base signal and the appearance of bound PBG with the same chemical shifts as for the bound equilibrium complex with Zn(II) enzyme. Neither splitting nor broadening from /sup 113/Cd-/sup 13/C coupling was observed.

Jaffe, E.K.; Markham, G.D.

1987-07-14

166

A 13C{31P} REDOR NMR Investigation of the Role of Glutamic Acid Residues in Statherin-Hydroxyapatite Recognition  

PubMed Central

The side chain carboxyl groups of acidic proteins found in the extra-cellular matrix (ECM) of mineralized tissues play a key role in promoting or inhibiting the growth of minerals such as hydroxyapatite (HAP), the principal mineral component of bone and teeth. Among the acidic proteins found in the saliva is statherin, a 43-residue tyrosine-rich peptide that is a potent lubricant in the salivary pellicle and an inhibitor of both HAP crystal nucleation and growth. Three acidic amino acids – D1, E4, and E5 – are located in the N-terminal 15 amino acid segment, with a fourth amino acid, E26, located outside the N-terminus. We have utilized 13C{31P} REDOR NMR to analyze the role played by acidic amino acids in the binding mechanism of statherin to the HAP surface by measuring the distance between the ?-carboxyl 13C spins of the three glutamic acid side chains of statherin (residues E4, E5, E26) and 31P spins of the phosphate groups at the HAP surface. 13C{31P} REDOR studies of glutamic-5-13C acid incorporated at positions E4 and E26 indicate a 13C–31P distance of more than 6.5 Å between the side chain carboxyl 13C spin of E4 and the closest 31P in the HAP surface. In contrast, the carboxyl 13C spin at E5 has a much shorter 13C–31P internuclear distance of 4.25±0.09 Å, indicating that the carboxyl group of this side chain interacts directly with the surface. 13C T1? and slow-spinning MAS studies indicate that the motions of the side chains of E4 and E5 are more restricted than that of E26. Together, these results provide further insight into the molecular interactions of statherin with HAP surfaces.

Ndao, Moise; Ash, Jason T.; Breen, Nicholas F.; Goobes, Gil; Stayton, Patrick S.; Drobny, Gary P.

2011-01-01

167

A combined DFT - NMR study of cyclic 1,2-diones and methyl ethers of their enols: The power and limitations of the method based on theoretical predictions of 13C NMR chemical shifts  

NASA Astrophysics Data System (ADS)

A series of cyclic 1,2-diones and methyl ethers of their enols were investigated by a combined 13C NMR/computational DFT method to establish their preferred solution structures. The optimum molecular geometries and magnetic shielding constants of carbon nuclei were calculated with GIAO DFT [PBE1PBE/6-311++G(2d,p) PCM] method for the investigated molecules allowing for enolization and dynamic conformational equilibriums occurring in the solutions. These compounds served simultaneously as model compounds for testing the effectiveness and limitations of the exploited method of investigating molecular structures based on comparison of the theoretically calculated magnetic shielding constants and experimental 13C NMR chemical shifts. Generally, a very good agreement between experimental and theoretical data was obtained for the investigated group of compounds, which proved the applied level of theory and used methodology to be adequate and should ensure a high accuracy of the 13C NMR chemical shift predictions. Some divergences between the experiment and theory could be interpreted as the results of insufficiencies of the molecular modelling and the effects of neglecting vibrational/librational molecular motions. Furthermore, we report herein an observation of an unexpected 1H NMR spectral pattern for 2,3-dimethoxycyclodeca-1,3-diene (diether of cyclodecadione dienol), which was interpreted to be caused by the slow (in NMR time scale) enantiomerization of this molecule which preferentially assumes a chiral conformation.

Kubicki, Dominik; Gryff-Keller, Adam; Szczeci?ski, Przemys?aw

2012-08-01

168

3-Oxo-12alpha-hydroxyfriedelane from Maytenus gonoclada: structure elucidation by (1)H and (13)C chemical shift assignments and 2D-NMR spectroscopy.  

PubMed

The compounds 3-oxofriedelane (1), 3beta-hydroxyfriedelane (2), 3,11-dioxofriedelane (3), 3,16-dioxofrie delane (4) and 3-oxo-12alpha-hydroxyfriedelane (5) were isolated from the hexane extract of Maytenus gonoclada Mart. (Celastraceae) leaves. Structural formula and the stereochemistry of the new pentacyclic triterpene 3-oxo-12alpha-hydroxyfriedelane (5) were established through (1)H and (13)C NMR and DEPT 135 spectral data including 2D experiments (HMBC, HMQC, COSY, and NOESY) and mass spectrometry (GC-MS). PMID:17729233

Oliveira, Mauro Lúcio G; Duarte, Lucienir Pains; Silva, Grácia Divina F; Filho, Sidney Augusto Vieira; Knupp, Vagner Fernandes; Alves, Fernando Gomes P

2007-10-01

169

Multinuclear NMR ( 1H, 13C, 15N and 107Ag) studies of the silver cyanide complexes of thiourea and substituted thioureas  

Microsoft Academic Search

The NMR (1H, 13C, 15N and 107Ag) studies of the silver(I) cyanide (AgCN) complexes of thiourea (Tu), N,N?-dimethylthiourea (Dmtu) and tetramethylthiourea (Tmtu) were carried out in dimethyl sulfoxide. An upfield shift in 13C NMR and downfield shifts in 1H, 15N and 107Ag NMR are consistent with the sulfur coordination to silver(I). The NMR data shows that ?C?S–AgCN complexes are stable

Saeed Ahmad; Anvarhusein A. Isab; Waqar Ashraf

2002-01-01

170

Complexation of oxygen ligands with dimeric rhodium(II) tetrakistrifluoroacetate in chloroform: 1H, 13C NMR and DFT studies  

NASA Astrophysics Data System (ADS)

The complexation of dimeric rhodium(II) tetrakistrifluoroacetylate with 25 ligands containing oxygen atoms: alcohols, ethers, ketones, aldehydes, carboxylic acids and esters in chloroform solution have been investigated by 1H and 13C NMR spectroscopy and Density Functional Theory (DFT) methods. Investigated ligands form 1:1 adducts in our experimental conditions, with stability constants in the order of several hundred mol-1. The exchange of ligands in solution is fast on the NMR spectroscopic timescale. The decrease of longitudinal relaxation times T1 in ligands in the presence of rhodium salt has been tested as the means of determination of the complexation site in ligands. The influence of complexation on chemical shifts in ligands was evaluated by a parameter complexation shift ?? (?? = ?add - ?lig). These parameters were positive (>0 ppm) and did not exceed 1 ppm for 1H NMR; and varied from ca. -5 to +15 ppm in the case of 13C NMR. The calculation by DFT methods using the B3LYP functional (structure optimization, electronic energy) and B3PW91 functional (shielding), and combinations of the (6-31G(2d), 6-311G++(2d,p), and LANL2DZ basis sets, followed by scaling procedures reproduced satisfactorily 1H and 13C chemical shifts and, with some limitations, allowed to estimate ?? parameters.

G?aszczka, Rafa?; Ja?wi?ski, Jaros?aw

2013-03-01

171

Kinetic study of littorine rearrangement in Datura innoxia hairy roots by (13)C NMR spectroscopy.  

PubMed

The kinetics of tropane alkaloid biosynthesis, particularly the isomerization of littorine into hyoscyamine, were studied by analyzing the kinetics of carbon-13 ((13)C) in metabolites of Datura innoxia hairy root cultures fed with labeled tropoyl moiety precursors. Both littorine and hyoscyamine were the major alkaloids accumulated, while scopolamine was never detected. Feeding root cultures with (RS)-phenyl[1,3-(13)C(2)]lactic acid led to (13)C spin-spin coupling detected on C-1' and C-2' of the hyoscyamine skeleton, which validated the intramolecular rearrangement of littorine into hyoscyamine. Label from phenyl[1-(13)C]alanine or (RS)-phenyl[1,3-(13)C(2)]lactic acid was incorporated at higher levels in littorine than in hyoscyamine. Initially, the apparent hyoscyamine biosynthesized rate (v(app)()hyo = 0.9 micromol (13)C.flask(-1).d(-1)) was lower than littorine formation (v(app)()litto = 1.8 micromol (13)C.flask(-1).d(-1)), suggesting that the isomerization reaction could be rate limiting. The results obtained for the kinetics of littorine biosynthesis were in agreement with the role of this compound as a direct precursor of hyoscyamine biosynthesis. PMID:12193016

Lanoue, Arnaud; Boitel-Conti, Michèle; Portais, Jean-Charles; Laberche, Jean-Claude; Barbotin, Jean-Noël; Christen, Philippe; Sangwan-Norreel, Brigitte

2002-08-01

172

Solid-state 13C NMR study of cholesteric liquid crystals.  

PubMed

We investigated the structural behavior of cholesteric liquid crystals of 4-(hexyloxy)-4'-cyanobiphenyl (6OCB) in an 11.7 T magnetic field by solid-state (13)C nuclear magnetic resonance. Five 6OCB cholesteric liquid crystal systems were prepared with 4-methoxyphenyl 3,4-O-isopropylidene-2,6-bis-O-(4-methylbenzoyl)-?-d-galactopyranoside (CR), in which 6OCB was doped with 0.51, 1.00, 2.34, 5.60, and 6.47 mol % CR, giving products with helical twisting powers (HTPs) of 0.28, 0.54, 1.27, 3.05, and 3.52 ?m(-1), respectively. Analyses of the alignment-induced shifts showed that the liquid crystals directors in pure 6OCB and 6OCB doped with 0.51 and 1.00 mol % CR become aligned with the 11.7 T magnetic field direction. However, 6OCB doped with 2.34, 5.60, and 6.47 mol % CR retained their cholesteric structures when the magnetic field was applied. The critical HTP value for resisting realignment by magnetic field was estimated to be approximately 1.27 ?m(-1). A biaxiality of the phase was partially considered during spectral simulations, although the molecular shape of 6OCB can be defined as cylinderical when it is rotating rapidly. Our current understanding is that the order parameters in the cholesteric structures are not uniform; i.e., the molecular directors already aligned almost perpendicular to the magnetic field are significantly perturbed by the external field. PMID:24188010

Yamada, Kazuhiko; Marumo, Kazuhiro; Kang, Sungmin; Deguchi, Kenzo; Nakai, Toshihito; Shimizu, Tadashi; Watanabe, Junji

2013-12-19

173

Hyperfine-Shifted 13C and 15N NMR Signals from Clostridium pasteurianum Rubredoxin: Extensive Assignments and Quantum Chemical Verification  

PubMed Central

Stable isotope-labeling methods, coupled with novel techniques for detecting fast-relaxing NMR signals, now permit detailed investigations of paramagnetic centers of metalloproteins. We have utilized these advances to carry out comprehensive assignments of the hyperfine-shifted 13C and 15N signals of the rubredoxin from Clostridium pasteurianum (CpRd) in both its oxidized and reduced states. We used residue-specific labeling (by chemical synthesis) and residue-type-selective labeling (by biosynthesis) to assign signals detected by one-dimensional 15N NMR spectroscopy, to nitrogen atoms near the iron center. We refined and extended these 15N assignments to the adjacent carbonyl carbons by means of one-dimensional 13C[15N] decoupling difference experiments. We collected paramagnetic-optimized SuperWEFT 13C[13C] constant time COSY (SW-CT-COSY) data to complete the assignment of 13C signals of reduced CpRd. By following these 13C signals as the protein was gradually oxidized, we transferred these assignments to carbons in the oxidized state. We have compared these assignments with hyperfine chemical shifts calculated from available X-ray structures of CpRd in its oxidized and reduced forms. The results allow the evaluation of the X-ray structural models as representative of the solution structure of the protein, and they provide a framework for future investigation of the active site of this protein. The methods developed here should be applicable to other proteins that contain a paramagnetic center with high spin and slow electron exchange.

2009-01-01

174

Synthesis and Solid-State NMR Structural Characterization of 13C-Labeled Graphite Oxide  

Microsoft Academic Search

The detailed chemical structure of graphite oxide (GO), a layered material prepared from graphite almost 150 years ago and a precursor to chemically modified graphenes, has not been previously resolved because of the pseudo-random chemical functionalization of each layer, as well as variations in exact composition. Carbon-13 (13C) solid-state nuclear magnetic resonance (SSNMR) spectra of GO for natural abundance 13C

Weiwei Cai; Richard D. Piner; Frank J. Stadermann; Sungjin Park; Medhat A. Shaibat; Yoshitaka Ishii; Dongxing Yang; Aruna Velamakanni; Sung Jin An; Meryl Stoller; Jinho An; Dongmin Chen; Rodney S. Ruoff

2008-01-01

175

Solubilization and localization of weakly polar lipids in unsonicated egg phosphatidylcholine: A sup 13 C MAS NMR study  

SciTech Connect

The weakly polar lipids cholesteryl ester, triacylglycerol, and diacylglycerol incorporate to a limited extent into the lamellar structure of small unilamellar vesicles. The localization of the carbonyl group(s) at the aqueous interface was detected by ({sup 13}C)carbonyl chemical shift changes relative to the neat unhydrated lipid. This study uses {sup 13}C NMR to investigate the interactions of thes lipids with unsonicated (multilamellar) phosphatidylcholine, a model system for cellular membranes and surfaces of emulsion particles with low curvature. Magic angle spinning reduced the broad lines of the unsonicated dispersions to narrow lines comparable to those from sonicated dispersions. ({sup 13}C)Carbonyl chemical shifts revealed incorporation of the three lipids into the lamellar structure of the unsonicated phospholipids and a partial hydration of the carbonyl groups similar to that observed in small vesicles. Other properties of interfacial weakly polar lipids in multilayers were similar to those in small unilamellar bilayers. There is thus a general tendency of weakly polar lipids to incorparate at least to a small extent into the lamellar structure of phospholipids and take on interfacial properties that are distinct from their bulk-phase properties. This pool of surface-located lipid is likely to be directly involved in enzymatyic transformations and protein-mediated transport. The {sup 13}C magic angle spinning NMR method may be generally useful for determining the orientation of molecules in model membranes.

Hamilton, J.A. (Boston Univ. School of Medicine, MA (United States)); Fujito, D.T.; Hammer, C.F. (Georgetown Univ., Washington, DC (United States))

1991-03-19

176

Milk identification of different species: 13C-NMR spectroscopy of triacylglycerols from cows and buffaloes' milks.  

PubMed

Triacylglycerols from cows and buffaloes' milk fat were investigated by 13C nuclear magnetic resonance (NMR) spectroscopy. By the addition of pure triacylglycerols standards, we identified the resonances of both milk fats, and the peaks were used for qualitative and quantitative analysis of acyl groups. Multivariate analysis treatment of triacylglycerols distribution and composition parameters enabled us to identify milk. This study shows that NMR can safely be used to quantitate milk fatty acid content, providing unique information for milk identification of different animal species. PMID:11104260

Andreotti, G; Trivellone, E; Lamanna, R; Di Luccia, A; Motta, A

2000-11-01

177

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

178

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

179

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 O 1 and O 4 lattice oxygen. The changes in populations of cationic sites after chemisorption were detected.

Vratislav, Stanislav; Dlouhá, Maja; Bosá?ek, Vladim?´r.

180

Characterization of Acacia mangium polyflavonoid tannins by MALDI-TOF mass spectrometry and CP-MAS 13C NMR  

Microsoft Academic Search

The MALDI-TOF mass spectrometry (MS) and solid state CP-MAS 13C Nuclear Magnetic Resonance (NMR) spectroscopic technique were introduced to characterize Acacia mangium tannin (condensed tannins). The MALDI-TOF MS illustrated a series of peaks corresponding to oligomers of condensed tannins of up to 11 flavonoid units (3200Da). A. mangium condensed tannins were found to consist predominantly of prorobinetinidin combined with profisetinidin

Yeoh Beng Hoong; Antonio Pizzi; Harald Pasch

2010-01-01

181

Thermal maturity of type II kerogen from the New Albany Shale assessed by 13C CP\\/MAS NMR  

Microsoft Academic Search

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

Ulrike Werner-Zwanziger; Grzegorz Lis; Maria Mastalerz; Arndt Schimmelmann

2005-01-01

182

Toward dynamic isotopomer analysis in the rat brainin vivo: automatic quantitation of13C NMR spectra using LCModel  

Microsoft Academic Search

The LCModel method was adapted to analyze localized in vivo 13C NMR spectra obtained from the rat brain invivo at 9.4 T. Prior knowledge of chemical-shifts, J-coupling constants and J-evolution was included in the analysis. Up to 50 different isotopomer signals corresponding to 10 metabolites were quantified simultaneously in 400ml volumes in the rat brain in vivo during infusion of

Pierre-Gilles Henry; Gülin Öz; Stephen Provencher; Rolf Gruetter

2003-01-01

183

1 H- and 13 C-NMR Characterization of the Molecular Components of the Lipid Fraction of Pecorino Sardo Cheese  

Microsoft Academic Search

In this work the molecular fatty components of Pecorino Sardo Protected Designation of Origin (PS PDO) cheese were characterized\\u000a through an exhaustive investigation of the 1H- and 13C-NMR spectra of the extracted lipids. Several fatty acids (FA), such as long chain saturated, oleic, linoleic, linolenic,\\u000a butyric, capric, caprylic, caproic, trans vaccenic, conjugated linoleic acid (cis9, trans11–18:2), and caproleic (9–10:1) were

P. Scano; R. Anedda; M. P. Melis; M. A. Dessi’; A. Lai; T. Roggio

184

Aspects of the chemical structure of soil organic materials as revealed by solid-state13C NMR spectroscopy  

Microsoft Academic Search

Solid-state cross-polarisation\\/magic-angle-spinning3C nuclear magnetic resonance (CP\\/MAS13C NMR) spectroscopy was used to characterise semi-quantitatively the organic materials contained in particle size and density fractions isolated from five different mineral soils: two Mollisols, two Oxisols and an Andosol. The acquired spectra were analysed to determine the relative proportion of carboxyl, aromatic, O-alkyl and alkyl carbon contained in each fraction. Although similar types

J. A. Baldock; J. M. Oades; A. G. Waters; X. Peng; A. M. Vassallo; M. A. Wilson

1992-01-01

185

Dynamics of the biosynthesis of methylursubin in plant cells employing in vivo 13C NMR without labelling  

Microsoft Academic Search

In vivo NMR experiments with a digital 600 MHz instrument, exploiting the natural abundance of 13C, allowed us for the first time to follow the biosynthesis of the newly detected glycoside, methylursubin (4-methoxyphenyl-O-?-d-primeveroside), from 4-methoxyphenol through the intermediate methylarbutin in cell suspensions of the Indian medical plant, Rauwolfia serpentina. The metabolic dynamics indicate that, within 48 hr, 4-methoxyphenol is almost

Ralf Lutterbach; Joachim Stöckigt

1995-01-01

186

In vivo 13C NMR Measurements of Cerebral Glutamine Synthesis as Evidence for Glutamate-Glutamine Cycling  

Microsoft Academic Search

The cerebral tricarboxylic acid (TCA) cycle rate and the rate of glutamine synthesis were measured in rats in vivo under normal physiological and hyperammonemic conditions using 13C NMR spectroscopy. In the hyperammonemic animals, blood ammonia levels were raised from control values of ≈ 0.05 mM to ≈ 0.35 mM by an intravenous ammonium acetate infusion. Once a steady-state of cerebral

N. R. Sibson; A. Dhankhar; G. F. Mason; K. L. Behar; D. L. Rothman; R. G. Shulman

1997-01-01

187

13C CP\\/MAS NMR study of the interaction of bile acids with barley ?- d-glucan  

Microsoft Academic Search

Dietary ?-d-glucan is associated with low blood cholesterol levels due to increased excretion of bile acids, but there is little evidence for the mechanism involved in enhanced bile acid clearance. Solid-state 13C NMR spectroscopy has now been used to investigate the possibility of specific binding between a representative bile acid salt, glycocholic acid, and barley ?-glucan. From the similarity in

Richard K. Bowles; Keith R. Morgan; Richard H. Furneaux; Graeme D. Coles

1996-01-01

188

Unraveling the 13C NMR Chemical Shifts in Single-Walled Carbon Nanotubes: Dependence on Diameter and Electronic Structure  

SciTech Connect

The atomic specificity afforded by nuclear magnetic resonance (NMR) spectroscopy could enable detailed mechanistic information about single-walled carbon nanotube (SWCNT) functionalization as well as the noncovalent molecular interactions that dictate ground-state charge transfer and separation by electronic structure and diameter. However, to date, the polydispersity present in as-synthesized SWCNT populations has obscured the dependence of the SWCNT {sup 13}C chemical shift on intrinsic parameters such as diameter and electronic structure, meaning that no information is gleaned for specific SWCNTs with unique chiral indices. In this article, we utilize a combination of {sup 13}C labeling and density gradient ultracentrifugation (DGU) to produce an array of {sup 13}C-labeled SWCNT populations with varying diameter, electronic structure, and chiral angle. We find that the SWCNT isotropic {sup 13}C chemical shift decreases systematically with increasing diameter for semiconducting SWCNTs, in agreement with recent theoretical predictions that have heretofore gone unaddressed. Furthermore, we find that the {sup 13}C chemical shifts for small diameter metallic and semiconducting SWCNTs differ significantly, and that the full-width of the isotropic peak for metallic SWCNTs is much larger than that of semiconducting nanotubes, irrespective of diameter.

Engtrakul, C.; Irurzun, V. M.; Gjersing, E. L.; Holt, J. M.; Larsen, B. A.; Resasco, D. E.; Blackburn, J. L.

2012-03-14

189

Identification of metabolites of [1,2,3-(13)C]Propargyl alcohol in mouse urine by (13)C NMR and mass spectrometry and comparison to rat.  

PubMed

Species differences in the metabolism of acetylenic compounds commonly used in the formulation of pharmaceuticals and pesticides have not been investigated. To better understand the in vivo reactivity of this bond, the metabolism of propargyl alcohol (PA), 2-propyn-1-ol, was examined in rats and mice. An earlier study (Banijamali, A. R.; Xu, Y.; Strunk, R. J.; Gay, M. H.; Ellis, M. C.; Putterman, G. J. J. Agric. Food Chem. 1999, 47, 1717-1729) in rats revealed that PA undergoes extensive metabolism primarily via glutathione conjugation. The current research describes the metabolism of PA in CD-1 mice and compares results for the mice to those obtained for rats. [1,2,3-(13)C;2,3-(14)C]PA was administered orally to the mice. Approximately 60% of the dose was excreted in urine by 96 h. Metabolites were identified, directly, in whole urine by 1- and 2-D (13)C NMR and HPLC/MS and by comparison with the available reference compounds. The proposed metabolic pathway involves glucuronide conjugation of PA to form 2-propyn-1-ol-glucuronide as well as oxidation of PA to the proposed intermediate 2-propynal. The aldehyde undergoes conjugation with glutathione followed by further metabolism to yield as final products 3,3-bis[(2-acetylamino-2-carboxyethyl)thio]-1-propanol, 3-[(2-acetylamino-2-carboxyethyl)thio]-3-[(2-amino-2-carboxyethyl)thi o]-1-propanol, 3,3-bis[(2-amino-2-carboxyethyl)thio]-1-propanol, 3-[(2-amino-2-carboxyethyl)thio]-2-propenoic acid, and 3-[(2-formylamino-2-carboxyethyl)thio]-2-propenoic acid. A small portion of 2-propynal is also oxidized to result in the excretion of 2-propynoic acid. On the basis of urinary metabolite data, qualitative and quantitative differences are noted between rats and mice in the formation of the glucuronide conjugate of PA and in the formation of 2-propynoic acid and metabolites derived from glutathione. These metabolites represent further variation on glutathione metabolism following its addition to the carbon-carbon triple bond compared to those described for the rat. PMID:11052721

Banijamali, A R; Xu, Y; DeMatteo, V; Strunk, R J; Sumner, S J

2000-10-01

190

Experimental 25Mg and 13C NMR and Computational Modeling Studies of Amorphous Mg-Ca Carbonates  

NASA Astrophysics Data System (ADS)

Nuclear magnetic resonance (NMR) spectroscopy of synthetic Mg-Ca amorphous carbonates (AMC-ACC) provides direct, element specific structural information about these complicated phases. The 13C, 25Mg, and 43Ca resonances are typically broad and span the chemical shift ranges of all the crystalline polymorphs in the Ca-Mg-CO3-H2O system. In a fashion similar to our previous analysis of 43Ca NMR results for ACC,1 here we integrate new experimental 13C and 25Mg spectra obtained at 20T for samples with Mg/(Ca+Mg) ratios from x=0 to x=1 with quantum chemical calculations of the NMR parameters of the crystalline phases using CASTEP calculations, simulations of the spectra using the SIMPSON software, and classical molecular dynamics calculations. XRD and 13C NMR results are in general agreement with the one-phase/two-phase model of ACC-AMC derived from thermochemical work by others.2 13C-NMR spectra of amorphous materials having intermediate compositions can not be completely fit by mechanical mixing of ACC and AMC end members—requiring a degree of Ca/Mg solid solution. Amorphous samples in two-phase region crystallize to assemblages of dolomite-like (x~0.5) and hydromagnesite-like (x~1) defective structures, but we also observe aragonite co-nucleation in the presence of excess water, indicative of a more complex evolution. While 43Ca NMR of X-ray amorphous materials shows featureless, symmetric, Gaussian line shapes, the large quadrupole moment of 25Mg gives rise to superposition of several quadrupolar line shapes representing different local structural environments. Singularities of static Mg spectra are best explained by local environments similar to nequehonite, hydromagnesite, and landsfordite. The spectra can not exclude minor contributions from anhydrous phases dolomite, huntite, and magnesite. Additional sites having very large quadrupolar coupling and/or site asymmetry are not explained by any known reference phases. CITATIONS (1) Singer, J. W.; Yazaydin, A. O.; Kirkpatrick, R. J.; Bowers, G. M. Chemistry of Materials 2012, 24, 1828. (2) Radha, A. V.; Fernandez-Martinez, A.; Hu, Y.; Jun, Y.-S.; Waychunas, G. A.; Navrotsky, A. Geochimica et Cosmochimica Acta 2012, 90, 83. Comparison of experimental Mg-NMR of an amorphous precursor to cation-disordered dolomite (above), with first principal simulations of reference phases (below).

Singer, J. W.; Yazaydin, A. O.; Kirkpatrick, R. J.; Saharay, M.; Bowers, G. M.

2012-12-01

191

Local protein structure and dynamics at kinked transmembrane ?-helices of [1- 13C]Pro-labeled bacteriorhodopsin as revealed by site-directed solid-state 13C NMR  

NASA Astrophysics Data System (ADS)

We have recorded 13C NMR spectra of [1- 13C]Pro-labeled bacteriorhodopsin (bR) and P50G, P91G, and P186A mutants under fully hydrated condition, by high-resolution solid-state NMR utilizing cross polarization-magic angle spinning (CP-MAS) and dipolar decoupled-magic angle spinning (DD-MAS) techniques. Seven well-resolved 13C NMR signals including a shoulder peak were distinguished by CP-MAS NMR, although only two signals were resolved by DD-MAS NMR. We assigned these 13C NMR signals among them to Pro50, 91 and 186 residues at the kinks in the inner part of the transmembrane ?-helices, on the basis of compared peak-intensities between wild type bR and the above-mentioned site-directed mutants, together with aid of Mn 2+-induced suppression of peaks from residues located near at the surfaces due to accelerated spin-spin relaxation times. It turned out that these Pro 13C NMR signals of wild type were appreciably broadened at temperature below -40 °C as in [3- 13C]Ala-bR, as a result of superposition of a variety of frozen conformers of the transmembrane ?-helices exhibiting dispersion of chemical shifts. This means that the dynamic behavior of bR as viewed from Pro residue is very similar to that of ordinary amino acid residues such as Ala, Val, Phe, etc. Further, it was found that no appreciable conformational change was noted for wild type bR within a temperature range between -20 and 35 °C at these kinked portions, although such change was noted at 35 °C for Y185F mutant which lacks interchain hydrogen bonding interaction as observed for wild type bR between the side-chains of Asp212 and Tyr185.

Tuzi, Satoru; Naito, Akira; Saitô, Hazime

2003-06-01

192

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

193

Mechanism studies of the conversion of 13C-labeled n-butane on zeolite H-ZSM-5 by using 13C magic angle spinning NMR spectroscopy and GC-MS analysis.  

PubMed

By using 13C MAS NMR spectroscopy (MAS = magic angle spinning), the conversion of selectively 13C-labeled n-butane on zeolite H-ZSM-5 at 430-470 K has been demonstrated to proceed through two pathways: 1) scrambling of the selective 13C-label in the n-butane molecule, and 2) oligomerization-cracking and conjunct polymerization. The latter processes (2) produce isobutane and propane simultaneously with alkyl-substituted cyclopentenyl cations and condensed aromatic compounds. In situ 13C MAS NMR and complementary ex situ GC-MS data provided evidence for a monomolecular mechanism of the 13C-label scrambling, whereas both isobutane and propane are formed through intermolecular pathways. According to 13C MAS NMR kinetic measurements, both pathways proceed with nearly the same activation energies (E(a) = 75 kJ mol(-1) for the scrambling and 71 kJ mol(-1) for isobutane and propane formation). This can be rationalized by considering the intermolecular hydride transfer between a primarily initiated carbenium ion and n-butane as being the rate-determining stage of the n-butane conversion on zeolite H-ZSM-5. PMID:16163765

Luzgin, Mikhail V; Stepanov, Alexander G; Arzumanov, Sergei S; Rogov, Vladimir A; Parmon, Valentin N; Wang, Wei; Hunger, Michael; Freude, Dieter

2005-12-23

194

In Vivo Metabolic Evaluation of Breast Tumor Mouse Xenografts for Predicting Aggressiveness Using the Hyperpolarized 13C-NMR Technique  

PubMed Central

In vivo imaging/spectroscopic biomarkers for solid tumor aggressiveness are needed in the clinic to facilitate cancer diagnosis and treatment strategies. In mouse models of human melanoma and breast cancer we were able to detect the metabolic differences among tumors of different metastatic potential and between normal and cancer tissues by optical imaging of the mitochondrial redox state of snap-frozen tissue samples. Such metabolic differences indicate that tumors of different aggressiveness have different metabolic homeostasis, which supports that kinetic parameters such as rate constant(s) can also serve as bio-markers for cancer aggressiveness and treatment response. Here we present our preliminary study on the mouse xenografts of the aggressive and indolent human breast cancer cell lines using the hyperpolarized 13C-NMR (HP-NMR) technique. By recording the time courses of 13C-pyruvate tracer and its metabolite signals in vivo, particularly the 13C-lactate signal, the apparent rate constants of both the forward and reverse reactions catalyzed by lactate dehydrogenase (LDH) were extracted via the ratiometric modeling of the two-site exchange reaction that we developed. Data from four breast tumors (MCF-7, MDA-MB-468, and MDA-MB-231 medium and large) with different aggressiveness are included. We demonstrate the feasibility to quantify the apparent rate constants of LDH reactions in breast tumor xenografts.

Xu, H.N.; Kadlececk, S.; Pullinger, B.; Profka, H.; Cai, K.; Hariharan, H.; Rizi, R.; Li, L.Z.

2014-01-01

195

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

196

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

197

Design of spectral-spatial outer volume suppression RF pulses for tissue specific metabolic characterization with hyperpolarized 13C pyruvate  

NASA Astrophysics Data System (ADS)

[1- 13C] pyruvate pre-polarized via DNP has been used in animal models to probe changes in metabolic enzyme activities in vivo. To more accurately assess the metabolic state and its change from disease progression or therapy in a specific region or tissue in vivo, it may be desirable to separate the downstream 13C metabolite signals resulting from the metabolic activity within the tissue of interest and those brought into the tissue by perfusion. In this study, a spectral-spatial saturation pulse that selectively saturates the signal from the metabolic products [1- 13C] lactate and [1- 13C] alanine was designed and implemented as outer volume suppression for localized MRSI acquisition. Preliminary in vivo results showed that the suppression pulse did not prevent the pre-polarized pyruvate from being delivered throughout the animal while it saturated the metabolites within the targeted saturation region.

Chen, Albert P.; Leung, Kevin; Lam, Wilfred; Hurd, Ralph E.; Vigneron, Daniel B.; Cunningham, Charles H.

2009-10-01

198

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

199

13C NMR Relaxation Studies of Molecular Motion in Peptide Fragments from Human Transthyretin  

NASA Astrophysics Data System (ADS)

Natural-abundance 13C T1 and NOE measurements have been made for backbone and side-chain sites in peptide fragments of transthyretin (TTR 10-20, TTR 105-115, and TTR 105-115 Met111) at 13C Larmor frequencies of 125 and 75 MHz. These peptides have previously been implicated in the formation of amyloid fibrils, The data were systematically assessed for their consistency with theoretical relaxation parameters derived from models of molecular motion, It was shown that of four models, ranging from simple isotropic motion to one defining internal wobbling of the 13C- 1H vector, the "model-free approach" (Lipari and Szabo, J. Am. Chem. Soc.104, 4546, 1982) was best able to predict the experimental data, These peptides exhibited overall correlation times close to 1 ns. Internal motions with effective correlation times of 0.08 ns were observed for backbone carbon sites, and side-chain carbons exhibited more rapid and less ordered motions, No indication of retarded motion due to the presence of small peptide aggregates was detected, in agreement with reports of the rapid incorporation of these species into amyloid fibrils.

Jarvis, J. A.; Craik, D. J.

200

A (13)C NMR analysis of the effects of electron radiation on graphite/polyetherimide composites  

NASA Technical Reports Server (NTRS)

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, Milton W.

1989-01-01

201

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

202

Hydrolysis of a phospholipid in an inert lipid matrix by phospholipase A sub 2 : A sup 13 C NMR study  

SciTech Connect

A new approach to study phospholipase A{sub 2} mediated hydrolysis of phospholipid vesicles, using {sup 13}C NMR spectroscopy, is described. ({sup 13}C)Carbonyl-enriched dipalmitoylphosphatidylcholine (DPPC) incorporated into nonhydrolyzable ether-linked phospholipid bilayers was hydrolyzed by phospholipase A{sub 2} (Crotalus adamanteus). The {sup 13}C-labeled carboxyl/carbonyl peaks from the products (lyso-1-palmitoyl-phosphatidylcholine (LPPC) and palmitic acid (PA)) were well separated from the substrate carbonyl peaks. The progress of the reaction was monitored from decreases in the DPPC carbonyl peak intensities and increases in the product peak intensities. DPPC peak intensity changes showed that only the sn-2 ester bond of DPPC on the outer monolayer of the vesicle was hydrolyzed. Most, but not all, of the DPPC in the outer monolayer was hydrolyzed after 18-24 h. There was no movement of phospholipid from the inner to the outer monolayer over the long time periods (18-24 h) examined. On the basis of chemical shift measurements of the product carbonyl peaks, it was determined that, at all times during the hydrolysis reaction, the LPPC was present only in the outer monolayer of the bilayer and the PA was bound to the bilayer and was {approximately} 50% ionized at pH {approximately} 7.2. Bovine serum albumin extracted most of the LPPC and PA from the product vesicles, as revealed by chemical shift changes after addition of the protein. The capability of {sup 13}C NMR spectroscopy to elucidate key structural features without the use of either shift reagents or separation procedures which may alter the reaction equilibrium makes it an attractive method to study this enzymatic process.

Bhamidipati, S.P.; Hamilton, J.A. (Boston Univ. School of Medicine, MA (USA))

1989-08-08

203

(1)H and (13)C NMR chemical shifts of methacrylate molecules associated with DMPC and/or DPPC liposomes.  

PubMed

In the light of recent developments, changes in (1)H and (13)C NMR chemical shifts of methacrylate molecule associated with DMPC (L-alpha dimyristoylphosphatidylcholine) or DPPC (L-alpha-dipalmitoylphosphatidylcholine) liposomes as a model for mimic native lipid bilayers were studied at 30, 37, and 52 degrees C. The chemical shifts of 3Ha, 3C, and 4C resonances in methacrylates (see Fig. 2) were greatly shifted higher field, suggesting the methacrylate molecule-lipid bilayer interaction. Comparison of the findings with methyl methacrylate (MMA), ethylene dimethacrylate (EDMA), and triethyleneglycol dimethacrylate (TEGDMA) revealed that the interaction of dimethacrylates (EDMA, TEGDMA) was greater than monomethacrylate, MMA. Their interaction with DMPC liposomes was also judged by a differential scanning calorimetry (DSC), indicating that the interaction was characterized by decreasing the enthalpy, entropy, and transition co-operativity. The evidence of the upfield NMR-shifts for methacrylate molecules was also judged by the descriptors such as the reactivity (HOMO-LUMO energy) and the electrostatic function (partial charges) between methacrylate molecules and DPPC, calculated by a PM 3 semiempirical MO method. The upfield NMR shifts were considerably well interpreted from the descriptors. NMR screening technique in methacrylates to phospholipid targets would be highly valuable in biomaterial developments. Figure 2 Changes in (1)H and (13)C NMR chemical shifts of methacrylate molecule associated with DMPC or DPPC liposomes. DMPC liposomes/MMA (1:1, molar ratio) and DMPC/TEGDMA (1:1) liposomes were measured at 30 degrees C. In DPPC liposome system, the rippled gel phase was measured at 30 degrees C, whereas the liquid crystalline phase for MMA and for both EDMA and TEGDMA were measured at 52 degrees C and 37 degrees C, respectively. PMID:16393908

Fujisawa, Seiichiro; Ishihara, Mariko; Kadoma, Yoshinori

2005-01-01

204

Infrared, 1H and 13C NMR spectra, structural charcterization and DFT calculations of novel adenine-cyclodiphosp(V)azane derivatives.  

PubMed

Adenine tetrachlorocyclodiphospha(V)zane derivatives (III(a-c)) were prepared by the reaction of hexachlorocyclodiphospha(V)zane derivatives (I(a-c)) and adenine (II) as precursors. The synthesized compound's and their structures (III(a-c)) were firmly characterized (based on the presence of an inversion center) using FT-IR (4000-200 cm(-1)), UV-vis. (190-800 nm), (1)H, (13)C NMR and Mass spectral measurements in addition to C, H, N, P elemental analysis. The compounds (III(a-c)) were found to be a 1:2 molar ratio of (I(a-c)) and adenine (II) adducts, respectively. Confident and complete vibrational assignments are proposed for nearly all fundamental vibrations, along with detailed interpretation for all observed signals in both (1)H and (13)C NMR spectra of the investigated phospha(V)zanes (III(a-c)). In addition, unconstrained geometry optimization of III(a-c) were carried out by means of DFT-B3LYP/3-21G(d) calculations to provide new insight into the structural parameters and molecular geometries of compounds III(a-c). The results are reported herein and compared with similar molecules whenever appropriate. PMID:21937263

Mohamed, Tarek A; Zoghaib, Wajdi M; Shaaban, Ibrahim A; Farag, Rabei S; Alajhaz, Abd Elnasser M A

2011-12-01

205

Calculation of the 13C NMR chemical shift of ether linkages in lignin derived geopolymers: . Constraints on the preservation of lignin primary structure with diagenesis  

NASA Astrophysics Data System (ADS)

Methodology for the calculation of 13C NMR shieldings on molecular organic fragments, representative of monomers in a type III kerogen, is presented. Geometry optimization of each molecular fragment was carried out using Density Functional Theory employing the generalized gradient approximation. NMR shieldings were calculated using the Individual Gauge for Localized Orbital Method. Convincing agreement was obtained between calculated and experimentally derived isotropic chemical shielding values over a broad frequency range. Shielding calculations employing the localized orbitals/local origin method resulted in nearly identical results. NMR chemical shift static powder patterns also exhibit excellent agreement with experimental values. These quantum mechanical calculations were applied to determine the extent of lignin primary structure preservation with diagenesis. Specifically, the calculations were used to assess whether inhomogeneous spectral broadening due to both functional group variation and local configurational variability may inhibit the detection of otherwise significant quantities of alkyl-aryl ethers in lignin derived geopolymers. Determination of the chemical-shielding tensor principle axis values reveals a strong correlation between anisotropy and asymmetry with local configuration effects such as dihedral rotation, phenyl group rotation, and bond angle variation. These results indicate that a range of 9 ppm in the isotropic chemical shift can be ascribed to local configuration. Consequently, an upper limit of 5% alkyl-aryl-linkages may go undetected using NMR spectroscopy on lignin-derived geopolymers at the liginite-sub-bituminous transition. It is concluded that the primary structure of lignin does not persist in kerogens even at relatively low thermal maturities.

Cody, G. D.; Sághi-Szabó, G.

1999-01-01

206

Calculation of the {sup 13}C NMR chemical shift of ether linkages in lignin derived geopolymers: Constraints on the preservation of lignin primary structure with diagenesis  

SciTech Connect

Methodology for the calculation of {sup 13}C NMR shielding on molecular organic fragments, representative of monomers in a type 3 kerogen, is presented. Geometry optimization of each molecular fragment was carried out using Density Functional Theory employing the generalized gradient approximation. NMR shieldings were calculated using the Individual Gauge for Localized orbital Method. Convincing agreement was obtained between calculated and experimentally derived isotropic chemical shielding values over a broad frequency range. Shielding calculations employing the localized orbitals/local origin method resulted in nearly identical results. NMR chemical shift static powder patterns also exhibit excellent agreement with experimental values. These quantum mechanical calculations were applied to determine the extent of lignin primary structure preservation with diagenesis. Specifically, the calculations were used to assess whether inhomogeneous spectral broadening due to both functional group variation and local configurational variability may inhibit the detection of otherwise significant quantities of alkyl-aryl ethers in lignin derived geopolymers. Determination of the chemical-shielding tensor principle axis values reveals a strong correlation between anisotropy and asymmetry with local configuration effects such as dihedral rotation, phenyl group rotation, and bond angle variation. These results indicate that a range of 9 ppm in the isotropic chemical shift can be ascribed to local configuration. Consequently, an upper limit of 5% alkyl-aryl-linkages may go undetected using NMR spectroscopy on lignin-derived geopolymers at the liginite-sub-bituminous transition. It is concluded that the primary structure of lignin does not persist in kerogens even at relatively low thermal maturities.

Cody, G.D.; Saghi-Szabo, G. [Carnegie Institution of Washington, Washington, DC (United States). Geophysical Lab.] [Carnegie Institution of Washington, Washington, DC (United States). Geophysical Lab.

1999-01-01

207

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

2010-11-25

208

13 C CP (cross-polarization) MAS (magic angle spinning) NMR and GIAO-CHF calculations of buspirone analogues  

Microsoft Academic Search

13C CP (cross-polarization) MAS (magic angle spinning) solid state NMR spectra of buspirone analogue 3a,4,7,7a-tetrahydro-2-{4-[4-(2-quinolinyl)-1-piperazinyl]butyl}-4,7-ethane-1H-isoindole-1,3(2H)-dione were recorded. In the spectra of hydrochloride and hydrobromide, two sets of signals appeared, in agreement with single crystal X-ray diffraction data indicating that in each of the salts two independent cations were present in the crystal unit. The largest shielding differences of 3.2–4.6 ppm

A. Szelejewska-Wo?niakowska; Z. Chilmonczyk; A. Le?; I. Wawer

1998-01-01

209

Chemical characteristics of dissolved organic matter during composting of different organic wastes assessed by (13)C CPMAS NMR spectroscopy.  

PubMed

This research aimed at assessing the chemical changes occurring in DOM extracted from different composting substrates by means of (13)C CPMAS NMR spectroscopy. During composting a reduction of carbohydrates and an increase of aromatic, phenolic, carboxylic and carbonylic C were observed. The highest increase in alkyl C and the lowest increase in aromatic C were explained by the presence of hardly degradable pine needles in the substrate, whereas the highest reduction in carbohydrates and the highest increase of the alkyl C/O-alkyl C ratio were attributed to the presence of highly degradable materials such as spent yeast from beer production. PMID:20594836

Caricasole, P; Provenzano, M R; Hatcher, P G; Senesi, N

2010-11-01

210

Solid state 13C NMR and FT-IR spectroscopy of the cocoon silk of two common spiders  

NASA Astrophysics Data System (ADS)

The structure of the silk from cocoons of two common spiders, Araneus diadematus (family Araneidae) and Achaearanea tepidariorum (family Theridiidae) was investigated by means of 13C solid state NMR and FT-IR spectroscopies. The combined use of these two techniques allowed us to highlight differences in the two samples. The cocoon silk of Achaearanea tepidariorum is essentially constituted by helical and ?-sheet structures, whereas that of Araneus diadematus shows a more complex structure, containing also ?-strands and ?-turns. Moreover, the former silk is essentially crystalline while the latter contains more mobile domains. The structural differences of the two cocoon silks are ascribed to the different habitat of the two species.

Bramanti, Emilia; Catalano, Donata; Forte, Claudia; Giovanneschi, Mario; Masetti, Massimo; Veracini, Carlo Alberto

2005-11-01

211

Use of solid-state 13C NMR in structural studies of humic acids and humin from Holocene sediments  

USGS Publications Warehouse

13C NMR spectra of solid humic substances in Holocene sediments have been obtained using cross polarization with magic-angle sample spinning techniques. The results demonstrate that this technique holds great promise for structural characterizations of complex macromolecular substances such as humin and humic acids. Quantifiable distinctions can be made between structural features of aquatic and terrestrial humic substances. The aliphatic carbons of the humic substances are dominant components suggestive of input from lipid-like materials. An interesting resemblance is also noted between terrestrial humic acid and humin spectra. ?? 1980.

Hatcher, P. G.; VanderHart, D. L.; Earl, W. L.

1980-01-01

212

Structural determination of 3beta-stearyloxy-urs-12-ene from Maytenus salicifolia by 1D and 2D NMR and quantitative 13C NMR spectroscopy.  

PubMed

Six pentacyclic triterpenoids, 3beta-stearyloxy-urs-12-ene (1), friedelin (2), 3beta-friedelinol (3), alpha-amyrin (4), beta-amyrin (5), and lupeol (6), have been isolated from the hexane extract of Maytenus salicifolia Reissek (Celastraceae) leaves. The molecular and structural formula as well as the stereochemistry of a new pentacyclic triterpene (1) were determined using data obtained from 1H and 13C NMR spectra, DEPT135 and by 2D HSQC, HMBC, COSY and NOESY experiments. The molecular formula C48H84O2 was established using quantitative 13C NMR, and the molecular weight (692 Da) was confirmed by elemental analysis and mass spectrometry (GC-MS). PMID:16358293

Miranda, R R S; Silva, G D F; Duarte, L P; Fortes, I C P; Filho, S A Vieira

2006-02-01

213

Automated amino acid side-chain NMR assignment of proteins using 13 C- and 15 N-resolved 3D [ 1 H, 1 H]-NOESY  

Microsoft Academic Search

ASCAN is a new algorithm for automatic sequence-specific NMR assignment of amino acid side-chains in proteins, which uses\\u000a as input the primary structure of the protein, chemical shift lists of 1HN, 15N, 13C?, 13C? and possibly 1H? from the previous polypeptide backbone assignment, and one or several 3D 13C- or 15N-resolved [1H,1H]-NOESY spectra. ASCAN has also been laid out for

Francesco Fiorito; Torsten Herrmann; Fred F. Damberger; Kurt Wüthrich

2008-01-01

214

Structural characterisation of humic acid-bound PAH residues in soil by 13 C -CPMAS-NMR-spectroscopy: evidence of covalent bonds  

Microsoft Academic Search

The fate of 13C-labelled phenanthrene and fluoranthene in different soil systems during biodegradation was studied. The soil humic acid fraction was isolated followed by structural characterisation using 13C-cross polarisation magic angle spinning nuclear magnetic resonance spectroscopy (13C-CPMAS-NMR). It could be demonstrated that especially the ratio between the concentrations of polycyclic aromatic hydrocarbons (PAHs) and soil humus matrix limits the usefulness

Thomas Käcker; Erhard T. K. Haupt; Christian Garms; Wittko Francke; Hans Steinhart

2002-01-01

215

Synergistic effect of the simultaneous chemometric analysis of (1)H NMR spectroscopic and stable isotope (SNIF-NMR, (18)O, (13)C) data: Application to wine analysis.  

PubMed

It is known that (1)H NMR spectroscopy represents a good tool for predicting the grape variety, the geographical origin, and the year of vintage of wine. In the present study we have shown that classification models can be improved when (1)H NMR profiles are fused with stable isotope (SNIF-NMR, (18)O, (13)C) data. Variable selection based on clustering of latent variables was performed on (1)H NMR data. Afterwards, the combined data of 718 wine samples from Germany were analyzed using linear discriminant analysis (LDA), partial least squares-discriminant analysis (PLS-DA), factorial discriminant analysis (FDA) and independent components analysis (ICA). Moreover, several specialized multiblock methods (common components and specific weights analysis (ComDim), consensus PCA and consensus PLS-DA) were applied to the data. The best improvement in comparison with (1)H NMR data was obtained for prediction of the geographical origin (up to 100% for the fused data, whereas stable isotope data resulted only in 60-70% correct prediction and (1)H NMR data alone in 82-89% respectively). Certain enhancement was obtained also for the year of vintage (from 88 to 97% for (1)H NMR to 99% for the fused data), whereas in case of grape varieties improved models were not obtained. The combination of (1)H NMR data with stable isotope data improves efficiency of classification models for geographical origin and vintage of wine and can be potentially used for other food products as well. PMID:24909771

Monakhova, Yulia B; Godelmann, Rolf; Hermann, Armin; Kuballa, Thomas; Cannet, Claire; Schäfer, Hartmut; Spraul, Manfred; Rutledge, Douglas N

2014-06-23

216

Structural studies on the oligomers from the polysaccharide of Gracilaria textorii (Rhodophyta) using ?-agarase and13C-NMR spectroscopy  

NASA Astrophysics Data System (ADS)

The 60% ethanolic extract from Gracilaria textorii (Rhodophyta) was degraded with ?-agarase, and certain charged (sulfated) and neutral oligosaccharides were separated by using DEAE Sephadex A25 and Bio- gel P6, P2 chromatographic techniques. Some of the charged oligomers were verified to be neoagarotetraose-63-sulfate (DP2), neoagarohexaose-63, 65-disulfate (DP3) and neoagarooctaose-63, 65, 67-trisulfate (DP4) by using13C- and1H-NMR spectroscopy. One neutral oligomer was assumed to be a mixture of methylated neoagarotetraoses (DP2) by1H-NMR spectroscopy. These oligomers assigned by their chemical shifts may be used as the model compounds for the structural investigation of the agar-type sulfated polysaccharides using the ?-agarase degradation method.

Ji, Minghou; Lahaye, M.; Yaphe, W.

1990-06-01

217

Kinetic analysis of glycogen turnover: relevance to human brain 13C-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

2013-10-01

218

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

219

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

220

Synthesis of silver(I) complexes of thiones and their characterization by 13C, 15N and 107Ag NMR spectroscopy  

Microsoft Academic Search

Silver(I) complexes of thiones (L), [LAgNO3] and [AgL2]NO3 have been prepared and characterized by elemental analysis, IR and NMR (1H, 13C, 15N and 107Ag) spectroscopy. An upfield shift in the C?S resonance of thiones in 13C NMR and downfield shifts in N?H resonances in 1H and 15N NMR are consistent with the sulfur coordination to silver(I). In 107Ag NMR, the

Anvarhusein A Isab; Saeed Ahmad; Mohammed Arab

2002-01-01

221

A high-resolution sup 13 C solid-state NMR study of meso-tetraphenylporphyrin and its zinc(II) complex  

SciTech Connect

High-resolution {sup 13}C solid-state NMR spectra of meso-tetraphenylporphyrin (TPP) and its zinc(II) complex (ZnTPP) are assigned by reference to low-temperature solution NMR results and using {sup 1}H- {sup 13}C cross-polarization magic-angle-spinning (CP/MAS). The splittings of the signals from pyrrole carbons in TPP are attributed to kinetic solid-state states involved in the migration of the central hydrogen atom.

Rocha, J.; Kolodziejski, W.; Klinowski, J. (Univ. of Cambridge (United Kingdom)); Cavaleiro, J.A.S. (Univ. of Aveiro (Portugal))

1992-01-01

222

Structural studies of bacterial cellulose through the solid-phase nitration and acetylation by CP\\/MAS 13 C NMR spectroscopy  

Microsoft Academic Search

The solid-phase nitration and acetylation processes of bacterial cellulose have been investigated mainly by CP\\/MAS 13C NMR spectroscopy to clarify the features of these reactions in relation to the characterization of the disordered component included in the microfibrils. CP\\/MAS 13C NMR spectra of bacterial and Valonia cellulose samples are markedly changed as the nitration progresses, in a similar way to

Hiroyuki Yamamoto; Fumitaka Horii; Asako Hirai

2006-01-01

223

Hydrolysis of post-consume poly(ethylene terephthalate) with sulfuric acid and product characterization by WAXD, 13C NMR and DSC  

Microsoft Academic Search

Post-consume PET was hydrolysed with commercial sulfuric acid (96%) with varying reaction times (5–120min). The structure of the material obtained was analysed by 13C NMR, DSC, and WAXD and the results were correlated with reaction time. 13C NMR shows a decrease in chain size with reaction time and an increase in the number of carboxyl groups at the end of

Gizilene M. de Carvalho; Edvani C. Muniz; Adley F. Rubira

2006-01-01

224

The effect of free cholesterol on the solubilization of cholesteryl oleate in phosphatidylcholine bilayers: A 13C-NMR study.  

PubMed

The solubilization of cholesteryl oleate in sonicated phosphatidylcholine vesicles containing between 0 and 50 mol% cholesterol was studied by 13C-NMR using isotopically enriched [carbonyl-13C]cholesteryl oleate. The carbonyl-13C chemical shift from cholesteryl oleate in the phospholipid/cholesterol bilayer was significantly downfield from that for cholesteryl oleate in an oil phase and the peak area, relative to that of the phospholipid carbonyl, was used to determine bilayer solubility of the ester. The solubility (with respect to phospholipid) in the phospholipid bilayer without cholesterol (2.9 mol%) was only moderately reduced (to 2.3 mol%) at cholesterol levels up to 33 mol% but showed a more marked reduction to 1.4 mol% at 40 mol% cholesterol or 1.2 mol% at 50 mol% cholesterol. Since the vesicles containing 50 mol% cholesterol were larger (520 +/- 152 A diameter) than those with no cholesterol (291 +/- 97 A diameter), we measured the solubility of cholesteryl oleate in large vesicles with no cholesterol, prepared by extrusion through polycarbonate membrane filters, and found it similar to that in small, sonicated vesicles with no cholesterol. Therefore, the larger size of vesicles was not the factor responsible for the decreased cholesteryl oleate solubility at high cholesterol contents. A more direct effect of cholesterol is envisioned where the ester becomes displaced to deeper regions of the bilayer. PMID:3741856

Spooner, P J; Hamilton, J A; Gantz, D L; Small, D M

1986-08-21

225

(13)C NMR investigations and the molecular order of 4-(trans-4'-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT).  

PubMed

The static 1D (13)C and 2D Proton Encoded Local Field (PELF) NMR experiments are carried out in the nematic phase of a less viscous liquid crystal 4-(trans-4'-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT) with a view to find orientational order. The PELF spectra provide better resolution which facilitates the assignment of cyclohexyl and phenyl ring carbons relatively easy. For the cyclohexyl unit, four pairs of dipolar splitting are clearly noticed in contrast to earlier reports on structurally similar mesogens where only two pairs of doublets are seen. The linear relationship between anisotropic chemical shifts and orientational order is established and semi-empirical parameters are obtained to aid the study of the order behaviour of 6CHBT over the entire nematic range. The data further fitted to the Haller equation and a reasonably good agreement is observed. The temperature dependence trends of orientational order parameters extracted for various carbons using (13)C-(1)H dipolar couplings with those of (13)C chemical shifts are compared. A gradual decrease in the order parameter is noticed for different molecular segments while traversing from the core to the aliphatic chain via the cyclohexyl ring. The notable decreasing trends of order parameters along the chain are observed similar to those of the corresponding phenyl cyclohexanes reported earlier. PMID:24919592

Lobo, Nitin P; Phani Kumar, B V N; Narasimhaswamy, T; Mandal, Asit Baran

2014-06-25

226

Multinuclear (13C, 17O, 57Fe) NMR studies of carbonmonoxy heme proteins and synthetic model compounds.  

PubMed

13C, 17O and 57Fe NMR spectra of several carbonmonoxy hemoprotein models with varying polar and steric effects of the distal organic superstructure, constraints of the proximal side, and porphyrin ruffling are reported. Both heme models and heme proteins obey a similar excellent linear delta(13C) versus nu(C-O) relationship which is primarily due to modulation of pi-back-bonding from the Fe d(pi) to CO pi* orbital by the distal pocket polar interactions. The lack of correlation between delta(13C) and delta(17O) suggests that the two probes do not reflect a similar type of electronic and structural perturbation. delta(17O) is not primarily influenced by the local distal field interactions and does not correlate with any single structural property of the Fe-C-O unit; however, atropisomerism and deformation of the porphyrin geometry appear to play a significant role. 57Fe shieldings vary by nearly 900 ppm among various hemes and an excellent correlation was found between delta(57Fe) and the absolute crystallographic average displacement of the meso carbon atoms, /Cm/, relative to the porphyrin core mean plane. The excellent correlation between iron-57 shieldings and the average shieldings of the meso carbons of the porphyrin skeleton of TPP derivatives suggests that the two probes reflect a similar type of electronic and structural perturbation which is primarily porphyrin ruffling. PMID:10830891

Kalodimos, C G; Gerothanassis, I P; Pierattelli, R; Troganis, A

2000-04-01

227

Photochemically induced dynamic nuclear polarisation in entire bacterial photosynthetic units observed by 13C magic-angle spinning NMR  

NASA Astrophysics Data System (ADS)

Photochemically induced dynamic nuclear polarisation has been observed from entire photosynthetic units (PSUs) bound to chromatophore membrane (membrane-bound PSU) of the purple bacteria Rhodobacter sphaeroides, which have been selectively 13C-isotope enriched at all BChl and BPheo cofactors. These 1.5 MDa membrane-bound protein complexes comprise reaction centres as well as the antenna systems called light harvesting complexes I and II. Due to light-induced enhancement of nuclear polarisation, the 13C magic-angle spinning (MAS) NMR spectrum shows absorptive lines originating from the cofactors involved into the photochemical machinery and allowing the determination of the electronic ground state structure at atomic resolution. Addition of detergent released intact PSU from the chromatophore membrane (so called detergent solubilised PSU) and caused significant changes in the sign and intensity pattern of the light-induced MAS NMR spectrum. In contrast, detergent solubilised PSU and detergent solubilised bacterial reaction centres with the same isotope label pattern exhibit essentially the same chemical shifts with only minor differences in the intensity pattern. The pronounced differences between intact membrane-bound and detergent solubilised PSU are tentatively explained by the loss of self-orientation of the membrane-bound samples by solubilisation. This interpretation suggests that the theoretically predicted anisotropy of the light-induced nuclear polarisation has been observed for the first time.

Prakash, Shipra; Alia; Gast, Peter; Jeschke, Gunnar; de Groot, Huub J. M.; Matysik, Jörg

2003-12-01

228

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

229

Evolution of organic matter during composting of different organic wastes assessed by CPMAS {sup 13}C NMR spectroscopy  

SciTech Connect

In this paper, the evolution of organic matter (OM) during composting of different mixtures of various organic wastes was assessed by means of chemical analyses and CPMAS {sup 13}C NMR spectroscopy measured during composting. The trends of temperatures and C/N ratios supported the correct evolution of the processes. The CPMAS {sup 13}C NMR spectra of all composting substrates indicated a reduction in carbohydrates and an increase in aromatic, phenolic, carboxylic and carbonylic C which suggested a preference by microorganisms for easily degradable C molecules. The presence of hardly degradable pine needles in one of the substrates accounted for the lowest increase in alkyl C and the lowest reduction in carbohydrates and carboxyl C as opposite to another substrate characterized by the presence of a highly degradable material such as spent yeast from beer production, which showed the highest increase of the alkyl C/O-alkyl C ratio. The highest increase of COOH deriving by the oxidative degradation of cellulose was shown by a substrate composed by about 50% of plant residues. The smallest increases in alkyl C/O-alkyl C ratio and in polysaccharides were associated to the degradation of proteins and lipids which are major components of sewage sludge. Results obtained were related to the different composition of fresh organic substrates and provided evidence of different OM evolution patterns as a function of the initial substrate composition.

Caricasole, P. [Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA 23529 (United States); Provenzano, M.R., E-mail: Provenza@agr.uniba.it [Dipartimento di Biologia e Chimica Agroforestale ed Ambientale, Universita di Bari, Via G. Amendola 165/a, 70126 Bari (Italy); Hatcher, P.G. [Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA 23529 (United States); Senesi, N. [Dipartimento di Biologia e Chimica Agroforestale ed Ambientale, Universita di Bari, Via G. Amendola 165/a, 70126 Bari (Italy)

2011-03-15

230

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

231

1H-13C hetero-nuclear dipole-dipole couplings of methyl groups in stationary and magic angle spinning solid-state NMR experiments of peptides and proteins  

PubMed Central

13C NMR of isotopically labeled methyl groups has the potential to combine spectroscopic simplicity with ease of labeling for protein NMR studies. However, in most high resolution separated local field experiments, such as polarization inversion spin exchange at the magic angle (PISEMA), that are used to measure 1H–13C hetero-nuclear dipolar couplings, the four-spin system of the methyl group presents complications. In this study, the properties of the 1H–13C hetero-nuclear dipolar interactions of 13C-labeled methyl groups are revealed through solid-state NMR experiments on a range of samples, including single crystals, stationary powders, and magic angle spinning of powders, of 13C3 labeled alanine alone and incorporated into a protein. The spectral simplifications resulting from proton detected local field (PDLF) experiments are shown to enhance resolution and simplify the interpretation of results on single crystals, magnetically aligned samples, and powders. The complementarity of stationary sample and magic angle spinning (MAS) measurements of dipolar couplings is demonstrated by applying polarization inversion spin exchange at the magic angle and magic angle spinning (PISEMAMAS) to unoriented samples.

Wu, Chin H.; Das, Bibhuti B.; Opella, Stanley J.

2010-01-01

232

Polymeric adducts of rhodium(II) tetraacetate with aliphatic diamines: natural abundance 13C and 15N CPMAS NMR investigations.  

PubMed

Complexation properties of dimeric rhodium(II) tetracarboxylates have been utilised in chemistry, spectroscopy and organic synthesis. Particularly, the combination of these rhodium salts with multifunctional ligands results in the formation of coordination polymers, and these are of interest because of their gas-occlusion properties. In the present work, the polymeric adducts of rhodium(II) tetraacetate with flexible ligands exhibiting conformational variety, ethane-1,2-diamine, propane-1,3-diamine and their N,N'-dimethyl- and N,N,N',N'-tetramethyl derivatives, have been investigated by means of elemental analysis, (13)C CPMAS NMR, (15)N CPMAS NMR and density functional theory modelling. Elemental analysis and NMR spectra indicated the axial coordination mode and regular structures of (1 : 1)n oligomeric chains in the case of adducts of ethane-1,2-diamine, N,N'-dimethylethane-1,2-diamine N,N,N',N'-tetramethylethane-1,2-diamine and N,N,N',N'-tetramethylpropane-1,3-diamine. Propane-1,3-diamine and N,N'-dimethylpropane-1,3-diamine tended to form heterogeneous materials, composed of oligomeric (1 : 1)n chains and the additive of dirhodium units containing equatorially bonded ligands. Experimental findings have been supported by density functional theory modelling of some hypothetical structures and gauge-invariant atomic orbital calculations of NMR chemical shifts. PMID:24123364

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

2013-12-01

233

/sup 15/N and /sup 13/C NMR determination of methionine metabolism in developing soybean cotyledons  

SciTech Connect

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 /sup 13/C and /sup 15/N 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. The authors 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, G.T. III; Garbow, J.R.; Schaefer, J.

1987-03-01

234

Helix-helix interconversion rates of short 13C-labeled helical peptides as measured by dynamic NMR spectroscopy.  

PubMed

The rates at which a peptide hexamer and a peptide octamer interconvert between left- and right-handed helical forms in CD2Cl2 solution have been characterized by 13C dynamic NMR (DNMR) spectroscopy. The peptide esters studied are Fmoc-(Aib)n-OtBu (n = 6 and 8), where Fmoc is 9-fluorenylmethyoxycarbonyl and Aib is the strongly helix-forming residue alpha-aminoisobutyric acid. Because the Aib residue is itself achiral, homooligomers of this residue form a 50/50 mixture of enantiomeric 3(10)-helices in solution. It has been demonstrated (R.-P. Hummel, C. Toniolo, and G. Jung, Angewandte Chemie International Edition, 1987, Vol. 26, pp. 1150-1152) that oligomers of Aib interconvert on the millisecond timescale. We have performed lineshape analysis of 13C-NMR spectra collected for our peptides enriched with 13C at a single residue. Rate constants for the octamer range from 6 s(-1) at 196 K to about 56,500 s(-1) at 320 K. At all temperatures, the hexamer interconverts about three times faster than the octamer. Eyring plots of the data reveal experimentally indistinguishable DeltaH++ values for the hexamer and octamer of 37.8 +/- 0.6 and 37.6 +/- 0.4 kJ mol(-1) respectively. The difference in the rates of interconversion is dictated by entropic factors. The hexamer and octamer exhibit negative DeltaS++ values of -29.0(-1) +/- 2.5 and -37.3 +/- 1.7 J K(-1) mol(-1), respectively. A mechanism for the helix-helix interconversion is proposed. and calculated DeltaG++ values are compared to the estimate for a decamer undergoing a helix-helix interconversion. PMID:15657893

Kubasik, Matthew; Kotz, James; Szabo, Christopher; Furlong, Theresa; Stace, Justin

2005-06-01

235

1 H and 13 C NMR observation of the reaction of acetic acid with titanium isopropoxide  

Microsoft Academic Search

Hydrogen and carbon NMR spectroscopy have been used to investigate the chemical modification process of titanium isopropoxide by acetic acid. The spectra confirm the belief that the titanium isopropoxide exchanges isopropyl groups with modifying acetate groups to form a molecule with approximate stoichiometry Ti(OiPr)2(OAc)2. This stoichiometry results even when enough acetic acid is present in solution to allow for significantly

Dunbar P Birnie III; Norbert J. Bendzko

1999-01-01

236

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

Microsoft Academic Search

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\\/SiOâ catalysts at temperature ranging from 298 to 613 K. Standard cross-polarization with magic angle spinning (CP\\/MAS), CP\\/MAS with dipolar dephasing, and

Hosseini

1992-01-01

237

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

Microsoft Academic Search

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,

Hosseini

1992-01-01

238

13C-NMR study of the inhibition of delta-chymotrypsin by a tripeptide-glyoxal inhibitor.  

PubMed Central

A new inhibitor, Z-Ala-Pro-Phe-glyoxal (where Z is benzyloxycarbonyl),has been synthesized and shown to be a competitive inhibitor of delta-chymotrypsin, with a K(i) of 25+/-8 nM at pH 7.0 and 25 degrees C. Z-Ala-Pro-[1-(13)C]Phe-glyoxal and Z-Ala-Pro-[2-(13)C]Phe-glyoxal have been synthesized, and (13)C-NMR has been used to determine how they interact with delta-chymotrypsin. Using Z-Ala-Pro-[2-(13)C]Phe-glyoxal we have detected a signal at 100.7 p.p.m. which we assign to the tetrahedral adduct formed between the hydroxy group of Ser-195 and the (13)C-enriched keto-carbon of the inhibitor. This signal is in a pH-dependent slow exchange with a signal at 107.6 p.p.m. which depends on a pK(a) of approximately 4.5, which we assign to oxyanion formation. Thus we are the first to detect an oxyanion pK(a) in a reversible chymotrypsin-inhibitor complex. A smaller titration shift of 100.7 p.p.m. to 103.9 p.p.m. with a pK(a) of approximately 5.3 is also detected due to a rapid exchange process. This pK(a) is also detected with the Z-Ala-Pro-[1-(13)C]Phe-glyoxal inhibitor and gives a larger titration shift of 91.4 p.p.m. to 97.3 p.p.m., which we assign to the ionization of the hydrated aldehyde hydroxy groups of the enzyme-bound inhibitor. Protonation of the oxyanion in the oxyanion hole decreases the binding efficiency of the inhibitor. From this decrease in binding efficiency we estimate that oxyanion binding in the oxyanion hole reduces the oxyanion pK(a) by 1.3 pK(a) units. We calculate that the pK(a)s of the oxyanions of the hemiketal and hydrated aldehyde moieties of the glyoxal inhibitor are both lowered by 6.4-6.9 pK(a) units on binding to chymotrypsin. Therefore we conclude that oxyanion binding in the oxyanion hole has only a minor role in decreasing the oxyanion pK(a). We also investigate how the inhibitor breaks down at alkaline pH, and how it breaks down at neutral pH in the presence of chymotrypsin.

Djurdjevic-Pahl, Aleksandra; Hewage, Chandralal; Malthouse, J Paul G

2002-01-01

239

[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

240

13C-Flux Spectral Analysis of Host-Pathogen Metabolism Reveals a Mixed Diet for Intracellular Mycobacterium tuberculosis  

PubMed Central

Summary Whereas intracellular carbon metabolism has emerged as an attractive drug target, the carbon sources of intracellularly replicating pathogens, such as the tuberculosis bacillus Mycobacterium tuberculosis, which causes long-term infections in one-third of the world’s population, remain mostly unknown. We used a systems-based approach—13C-flux spectral analysis (FSA) complemented with manual analysis—to measure the metabolic interaction between M. tuberculosis and its macrophage host cell. 13C-FSA analysis of experimental data showed that M. tuberculosis obtains a mixture of amino acids, C1 and C2 substrates from its host cell. We experimentally confirmed that the C1 substrate was derived from CO2. 13C labeling experiments performed on a phosphoenolpyruvate carboxykinase mutant revealed that intracellular M. tuberculosis has access to glycolytic C3 substrates. These findings provide constraints for developing novel chemotherapeutics.

Beste, Dany J.V.; Noh, Katharina; Niedenfuhr, Sebastian; Mendum, Tom A.; Hawkins, Nathaniel D.; Ward, Jane L.; Beale, Michael H.; Wiechert, Wolfgang; McFadden, Johnjoe

2013-01-01

241

1H and 13C NMR assignments for two new cordiaquinones from roots of Cordia leucocephala.  

PubMed

From the roots of Cordia leucocephala (Boraginaceae), two new meroterpenoid naphthoquinones, 6-[10-(12,12-dimethyl-13alpha-hydroxy-16-methenyl-cyclohexyl)ethyl]-1,4-naphthalenedione (cordiaquinone L) and 5-methyl-6-[10-(12,12-dimethyl-13beta-hydroxy-16-methenyl-cyclohexyl)methyl-1,4-naphthalenedione (cordiaquinone M) were isolated. Their structures were elucidated after detailed 1D and 2D NMR (COSY, HSQC, HMBC and NOESY) data analyses and comparison with literature data for analogous compounds. PMID:19025970

Diniz, Jaécio Carlos; Viana, Francisco Arnaldo; Oliveira, Odaci Fernandes; Maciel, Maria Aparecida M; Torres, Maria da Conceição de Menezes; Braz-Filho, Raimundo; Silveira, Edilberto R; Pessoa, Otília Deusdênia L

2009-02-01

242

Intramolecular non-bonded interactions and ?- and ?-hydroxy substituent 13C NMR chemical shifts  

NASA Astrophysics Data System (ADS)

A systematic study of ?- and ?-substituent 13C chemical shifts (SCS) in terms of intramolecular non-bonded interactions has been carried out. It is demonstrated that for a variety of molecules substituted with an OH substituent (cf. some conformationally non-rigid multifunctional alcohols ( I-IX in Table 1), 1-hydroxy ( 1a) and 2-hydroxy ( 1b) substituted adamantanes, exo 2-hydroxy ( 2a), endo 2-hydroxy ( 2b), 1-hydroxy ( 2c), and 7-hydroxy ( 2d) substituted norbornanes, and the hydroxy derivative of caged compound ( 3)), ?- and ?-SCS for primary, secondary and tertiary carbon atoms can be compared to the total local van der Waals and electrostatic non-bonded interaction energies in the same correlation. Furthermore, it is shown that the relationship can be extended to molecules bearing two such substituents, e.g. in the dihydroxy derivatives of certain caged compounds ( 4a) to ( 4c) and ( 5). The local electrostatic potentials are mostly responsible for the variations of ?- and ?-SCS in the series I-IX, and ( 1)-( 5) substituted molecules. On the other hand, ?- and ?-SCS in the strained ( 6) and ( 7) molecules are mainly influenced by changes in the local van der Waals interaction energies. This approach presents a more consistent treatment of the influences of geometric distortions and electronic interactions on chemical shifts of sp3 hybridized carbon atoms.

Pachter, Ruth; Wessels, Philippus L.

1988-08-01

243

13C MAS NMR studies of crystalline cholesterol and lipid mixtures modeling atherosclerotic plaques.  

PubMed Central

Cholesterol and cholesteryl esters are the predominant lipids of atherosclerotic plaques. To provide fundamental data for the quantitative study of plaque lipids in situ, crystalline cholesterol (CHOL) and CHOL/cholesteryl ester (CE) mixtures with other lipids were studied by solid-state nuclear magnetic resonance with magic-angle-sample spinning. Highly distinctive spectra for three different crystalline structures of CHOL were obtained. When CHOL crystals were mixed with isotropic CE oil, solubilized CHOL (approximately 13 mol % CHOL) was detected by characteristic resonances such as C5, C6, and C3; the excess crystalline CHOL (either anhydrous or monohydrate) remained in its original crystalline structure, without being affected by the coexisting CE. By use of 13C-enriched CHOL, the solubility of CHOL in the CE liquid-crystalline phase (approximately 8 mol %) was measured. When phosphatidylcholine was hydrated in presence of CHOL and CE, magic-angle-sampling nuclear magnetic resonance revealed liquid-crystalline CHOL/phosphatidylcholine multilayers with approximately an equal molar ratio of CHOL/phosphatidylcholine. Excess CHOL existed in the monohydrate crystalline form, and CE in separate oil or crystalline phases, depending on the temperature. The magic-angle-sampling nuclear magnetic resonance protocol for identifying different lipid phases was applied to intact (ex vivo) atherosclerotic plaques of cholesterol-fed rabbits. Liquid, liquid-crystalline, and solid phases of CE were characterized. Images FIGURE 2

Guo, W; Hamilton, J A

1996-01-01

244

The production of recombinant (15)N, (13)C-labelled somatostatin 14 for NMR spectroscopy.  

PubMed

Structural studies of human peptide hormone somatostatin 14 (SS14) require high amounts of isotopically labelled SS14 to be produced. Here we report a method for effective production of isotopically labelled SS14. SS14 was expressed as a fusion protein with thioredoxin in Escherichia coli. Co-expression of a longer polypeptide product lowered the yield of the target peptide and complicated its purification. The side product contained the N-terminal 6His-tag together with the thioredoxin fusion partner and the specific enzymatic cleavage site-containing linker followed by an unknown peptide starting with the first 7N-terminal amino acid residues of SS14, as revealed by the Edman degradation. The combination of DNA sequence analysis, the Edman degradation, and high-resolution mass spectrometry allowed to identify the amino acid sequence of the unknown peptide. The appearance of the side product was attributed to inefficient termination of mRNA translation. The stop codon and its downstream sequence optimization allowed eliminating the side product synthesis. The optimized expression system, purification protocol, and post-translational modification procedure yielded 1.5mg of SS14 per liter of minimal medium. Nearly 99% incorporation of (13)C and (15)N isotopes was achieved, as demonstrated by high-resolution mass spectrometry. PMID:24698890

Nespovitaya, Nadezhda; Barylyuk, Konstantin; Eichmann, Cédric; Zenobi, Renato; Riek, Roland

2014-07-01

245

13C cell wall enrichment and ionic liquid NMR analysis: progress towards a high-throughput detailed chemical analysis of the whole plant cell wall.  

PubMed

The ability to accurately and rapidly measure plant cell wall composition, relative monolignol content and lignin-hemicellulose inter-unit linkage distributions has become essential to efforts centered on reducing the recalcitrance of biomass by genetic engineering. Growing (13)C enriched transgenic plants is a viable route to achieve the high-throughput, detailed chemical analysis of whole plant cell wall before and after pretreatment and microbial or enzymatic utilization by (13)C nuclear magnetic resonance (NMR) in a perdeuterated ionic liquid solvent system not requiring component isolation. 1D (13)C whole cell wall ionic liquid NMR of natural abundant and (13)C enriched corn stover stem samples suggest that a high level of uniform labeling (>97%) can significantly reduce the total NMR experiment times up to ~220 times. Similarly, significant reduction in total NMR experiment time (~39 times) of the (13)C enriched corn stover stem samples for 2D (13)C-(1)H heteronuclear single quantum coherence NMR was found. PMID:22768393

Foston, Marcus; Samuel, Reichel; Ragauskas, Arthur J

2012-09-01

246

Characterization of alkyl carbon in forest soils by CPMAS 13C NMR spectroscopy and dipolar dephasing  

USGS Publications Warehouse

Samples obtained from forest soils at different stages of decomposition were treated sequentially with chloroform/methanol (extraction of lipids), sulfuric acid (hydrolysis), and sodium chlorite (delignification) to enrich them in refractory alkyl carbon. As revealed by NMR spectroscopy, this treatment yielded residues with high contents of alkyl carbon. In the NMR spectra of residues obtained from litter samples, resonances for carbohydrates are also present, indicating that these carbohydrates are tightly bound to the alkyl carbon structures. During decomposition in the soils this resistant carbohydrate fraction is lost almost completely. In the litter samples the alkyl carbon shows a dipolar dephasing behavior indicative of two structural components, a rigid and a more mobile component. As depth and decomposition increase, only the rigid component is observed. This fact could be due to selective degradation of the mobile component or to changes in molecular mobility during decomposition, e.g., because of an increase in cross linking or contact with the mineral matter of the soil.

Kogel-Knabner, I.; Hatcher, P. G.

1989-01-01

247

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

248

{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

249

3-Methylglutaric acid as a 13C solid-state NMR standard.  

PubMed

The calibration of a solid-state NMR spectrometer requires setting the magic angle, setting the reference and decoupler frequencies, ensuring that the magnetic field is homogeneous across the sample volume, optimizing the signal-to-noise ratio, determining the pi/2 pulse durations, and optimizing the Hartman-Hahn matching condition. Each task has one or more widely accepted standards, such as potassium bromide for setting the magic angle, adamantane for optimizing magnet homogeneity, and hexamethylbenzene or glycine for measuring the signal-to-noise ratio. We show that all of these tasks can be performed using 3-methylglutaric acid (MGA). In the case of high-powered decoupling, the CH(2) and CH carbon peaks of MGA provide an opportunity to evaluate the decoupling in a manner that is superior to any of the commonly used standard compounds. Thus, MGA can be used as a single solid-state NMR standard compound to perform all calibration steps except for magnet shimming. PMID:16887343

Barich, Dewey H; Gorman, Eric M; Zell, Mark T; Munson, Eric J

2006-10-01

250

Combined (1)H-NMR and (1)H-(13)C HSQC-NMR to improve urinary screening in autism spectrum disorders.  

PubMed

Autism spectrum disorders (ASD) are neurodevelopmental diseases with complex genetic and environmental etiological factors. Although genetic causes play a significant part in the etiology of ASD, metabolic disturbances may also play a causal role or modulate the clinical features of ASD. The number of ASD studies involving metabolomics is increasing, and sometime with conflicting findings. We assessed the metabolomics profiling of urine samples to determine a comprehensive biochemical signature of ASD. Furthermore, to date no study has combined metabolic profiles obtained from different analytical techniques to distinguish patient with ASD from healthy individuals. We obtained (1)H-NMR spectra and 2D (1)H-(13)C HSQC NMR spectra from urine samples of patients with ASD or healthy controls. We analyzed these spectra by multivariate statistical data analysis. The OPLS-DA model obtained from (1)H NMR spectra showed a good discrimination between ASD samples and non-ASD samples (R(2)Y(cum) = 0.70 and Q(2) = 0.51). Combining the (1)H NMR spectra and the 2D (1)H-(13)C HSQC NMR spectra increased the overall quality and predictive value of the OPLS-DA model (R(2)Y(cum) = 0.84 and Q(2) = 0.71), leading to a better sensitivity and specificity. Urinary excretion of succinate, glutamate and 3-methyl-histidine differed significantly between ASD and non-ASD samples. Urinary screening of children with neurodevelopmental disorders by combining NMR spectroscopies (1D and 2D) in multivariate analysis is a better sensitive and a straightforward method that could help the diagnosis ASD. PMID:24841505

Nadal-Desbarats, Lydie; Aïdoud, Nacima; Emond, Patrick; Blasco, Hélène; Filipiak, Isabelle; Sarda, Pierre; Bonnet-Brilhault, Frédérique; Mavel, Sylvie; Andres, Christian R

2014-06-01

251

Spectral fitting for signal assignment and structural analysis of uniformly 13C-labeled solid proteins by simulated annealing based on chemical shifts and spin dynamics.  

PubMed

We describe an approach for the signal assignment and structural analysis with a suite of two-dimensional (13)C-(13)C magic-angle-spinning solid-state NMR spectra of uniformly (13)C-labeled peptides and proteins. We directly fit the calculated spectra to experimental ones by simulated annealing in restrained molecular dynamics program CNS as a function of atomic coordinates. The spectra are calculated from the conformation dependent chemical shift obtained with SHIFTX and the cross-peak intensities computed for recoupled dipolar interactions. This method was applied to a membrane-bound 14-residue peptide, mastoparan-X. The obtained C', C(alpha) and C(beta) chemical shifts agreed with those reported previously at the precisions of 0.2, 0.7 and 0.4 ppm, respectively. This spectral fitting program also provides backbone dihedral angles with a precision of about 50 degrees from the spectra even with resonance overlaps. The restraints on the angles were improved by applying protein database program TALOS to the obtained chemical shifts. The peptide structure provided by these restraints was consistent with the reported structure at the backbone RMSD of about 1 A. PMID:17612797

Matsuki, Yoh; Akutsu, Hideo; Fujiwara, Toshimichi

2007-08-01

252

Phytotoxicity, not nitrogen immobilization, explains plant litter inhibitory effects: evidence from solid-state 13C NMR spectroscopy.  

PubMed

Litter decomposition provides nutrients that sustain ecosystem productivity, but litter may also hamper root proliferation. The objectives of this work were to assess the inhibitory effect of litter decomposition on seedling growth and root proliferation; to study the role of nutrient immobilization and phytotoxicity; and to characterize decomposing litter by (13)C NMR spectroscopy. A litter-bag experiment was carried out for 180 d with 16 litter types. Litter inhibitory effects were assessed by two bioassays: seed germination and root proliferation bioassays. Activated carbon (C) and nutrient solutions were used to evaluate the effects of phytotoxic factors and nutrient immobilization. An inhibitory effect was found for all species in the early phase of decomposition, followed by a decrease over time. The addition of activated C to litter removed this inhibition. No evidence of nutrient immobilization was found in the analysis of nitrogen dynamics. NMR revealed consistent chemical changes during decomposition, with a decrease in O-alkyl and an increase in alkyl and methoxyl C. Significant correlations were found among inhibitory effects, the litter decay rate and indices derived from NMR. The results show that it is possible to predict litter inhibitory effects across a range of litter types on the basis of their chemical composition. PMID:21574999

Bonanomi, Giuliano; Incerti, Guido; Barile, Elisa; Capodilupo, Manuela; Antignani, Vincenzo; Mingo, Antonio; Lanzotti, Virginia; Scala, Felice; Mazzoleni, Stefano

2011-09-01

253

Complexation of rhodium(II) tetracarboxylates with aliphatic diamines in solution: 1H and 13C 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. PMID:23943201

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

2013-10-01

254

Unlocking the molecular structure of fungal melanin using 13C biosynthetic labeling and solid-state NMR.  

PubMed

Melanins are enigmatic pigments found in all biological kingdoms that are associated with a variety of functions, including microbial virulence. Despite being ubiquitous in nature, melanin pigments have long resisted atomic-level structural examination because of their insolubility and amorphous organization. Cryptococcus neoformans is a human pathogenic fungus that melanizes only when provided with exogenous substrate, thus offering a unique system for exploring questions related to melanin structure at the molecular level. We have exploited the requirement for exogenous substrate in melanin synthesis as well as the capabilities of high-resolution solid-state nuclear magnetic resonance (NMR) to establish the predominantly aliphatic composition of l-dopa melanin and to introduce (13)C labels that permit the identification of proximal carbons in the developing biopolymer. By swelling solid melanin samples in organic solvents and using two-dimensional heteronuclear NMR in conjunction with magic-angle spinning, we have identified chemical bonding patterns typical of alkane, alkene, alcohol, ketone, ester, and indole functional groups. These findings demonstrate the feasibility of a novel approach to determining the structure of melanin using metabolic labeling and NMR spectroscopy. PMID:12846559

Tian, Shiying; Garcia-Rivera, Javier; Yan, Bin; Casadevall, Arturo; Stark, Ruth E

2003-07-15

255

Solid state 13C and 2H NMR investigations of paramagnetic [Ni(II)(acac)2L2] complexes.  

PubMed

Nine structurally related paramagnetic acetylacetonato nickel(II) complexes: [Ni(acac)2] and trans-[Ni(acac)2(X)2]nH/D2O, X = H2O, D2O, NH3, MeOH, PMePh2, PMe2Ph, or [dppe]1/2, n = 0 or 1, dppe = 1,2-bis(diphenylphosphino)ethane, as well as cis-[Ni(F6-acac)2(D2O)2], F6-acac = hexafluoroacetylonato, have been characterized by solid state (13)C MAS NMR spectroscopy. (2)H MAS NMR was used to probe the local hydrogen bonding network in [Ni(acac)2(D2O)2]D2O and cis-[Ni(F6-acac)2(D2O)2]. The complexes serve to benchmark the paramagnetic shift, which can be associated with the resonances of atoms of the coordinated ligands. The methine (CH) and methyl (CH3) have characteristic combinations of the isotropic shift (?) and anisotropy parameters (d, ?). The size of the anisotropy (d), which is the sum of the chemical shift anisotropy (CSA) and the paramagnetic electron-nuclei dipolar coupling, is much more descriptive than the isotropic shift. Moreover, the CSA is found to constitute up to one-third of the total anisotropy and should be taken into consideration when (13)C anisotropies are used for structure determination of paramagnetic materials. The (13)C MAS NMR spectra of trans-[Ni(acac)2(PMe2Ph)2], trans-[Ni(acac)2(PMePh2)2], and the noncrystallographically characterized trans-[Ni(acac)2(dppe)]n were assigned using these correlations. The complexes with L = H2O, D2O, NH3, and MeOH can be prepared by a series of solid state desorption and sorption reactions. Crystal structures for trans-[Ni(acac)2(NH3)2] and trans-[Ni(acac)2(PMePh2)2] are reported. PMID:24325293

Lennartson, Anders; Christensen, Lene Ulrikke; McKenzie, Christine J; Nielsen, Ulla Gro

2014-01-01

256

Unusual ordering of a dioxyethylene chain in dialkoxy laterally substituted nematogen as evidenced by 13C NMR  

NASA Astrophysics Data System (ADS)

We report the synthesis of a liquid crystalline compound containing four rings in the main core, two lateral hexyloxy chains and a terminal dioxyethylene methyl ether chain. This compound presents a wide nematic range starting from room temperature. The ordering of the chains has been studied by 13C NMR in the liquid crystalline phase. The 13C chemical shifts proved folding back of the lateral chains along the main core, and extended conformation of the dioxyethylene chain. The values of order parameters were derived from the transient oscillations of 13C magnetization observed during variable contact-time cross-polarization experiments. For the dioxyethylene chain, the order parameters decrease monotonically along the chain without exhibiting odd-even oscillation and are noticeably smaller than those found in terminal alkoxy chains. These effects are interpreted by the change in geometrical and conformational characteristics of the dioxyethylene chain. Nous décrivons la synthèse d'un composé mésogène contenant quatre cycles aromatiques dans le cœur central, deux chaînes latérales de type hexyloxy et une chaîne terminale de type mono ester méthylique du dioxyéthylène. Ce composé présente un large domaine nématique à partir de la température ambiante. L'ordre orientationnel des chaînes a été mesuré par RMN 13C dans l'état nématique. L'évolution des déplacements chimiques 13C sur l'échantillon statique indique que les chaînes latérales sont repliées dans la direction du long axe moléculaire, et que la chaîne dioxyéthylène est orientée suivant cette même direction. Les valeurs des paramètres d'ordre ont été obtenues en analysant les oscillations transitoires pendant la montée de l'aimantation en utilisant une séquence classique de polarisation croisée. Pour la chaîne dioxyéthylène, ces valeurs décroissent de manière monotone sans présenter l'alternance habituelle pour les positions paires ou impaires des atomes dans la chaîne. De plus, ces valeurs sont relativement plus faibles que celles trouvées dans les mésogènes classiques. Ces effets donnent une indication sur la modification des caractéristiques géométriques et conformationelles le long de la chaîne dioxyéthylène.

Rayssac, V.; Lesot, P.; Bayle, J.-P.; Miyajima, S.

1998-05-01

257

13(C) NMR and X-ray crystallographic determination of the structures of some isomeric phenylquinoxalines  

NASA Astrophysics Data System (ADS)

The good thermal and hydrolytic stability of polyphenylquinoxalines has prompted many investigations for characterization and property correlations for these polymers. The presence of isomers in polyphenylquinoxalines as a result of the ring forming polymerization reaction has been noted. The existence of isomers contributes to the amorphous form of these polymers and inhibits crystalline polymer formation. Unequivocal structural assignments were made for the two isomeric quinoxalines isolated from the reaction of 3-bromobenzil with 4-iodo-O-phenylenediamine as well as for their respective acetylene terminated derivatives. The higher melting isomers were assigned the structures 3-(3-bromophenyl)-2-phenyl-6-iodoquinoxaline and 3-(3-ethynylphenyl)-2-phenyl-6-ethynylquinox-aline, and the lower melting isomers were assigned the structures 2-(3-bromophenyl)-3-phenyl-6-iodoquinoxaline and 2-(3-ethynylphenyl)-3-phenyl-6-ethynylquinoxaline. Both x-ray crystallographic analysis and C-13 NMR analyses were used and were in complete agreement.

Hedberg, F. L.; Bush, D. L.; Ryan, M. T.; Harvey, R. A.; Fratini, A. V.

1985-05-01

258

Diffusion coefficient of CO(2) molecules as determined by (13)C NMR in various carbonated beverages.  

PubMed

In this paper, the NMR technique was used, for the first time, to accurately determine the diffusion coefficient D of CO(2)-dissolved molecules in various carbonated beverages, including champagne and sparkling wines. This parameter plays an important role concerning the bubble growth during its rise through the liquid (see ref 3). The diffusion coefficient of CO(2)-dissolved molecules D was compared with that deduced from the well-known Stokes-Einstein equation and found to significantly deviate from the general trend expected from Stokes-Einstein theory, i.e, D(SE) proportional, variant 1/eta, where D(SE) is the Stokes-Einstein diffusion coefficient and eta the viscosity of the liquid medium. PMID:14664507

Liger-Belair, Gerard; Prost, Elise; Parmentier, Maryline; Jeandet, Philippe; Nuzillard, Jean-Marc

2003-12-17

259

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

260

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

2012-11-01

261

Solid state (13)C NMR and FT-IR spectroscopy of the cocoon silk of two common spiders.  

PubMed

The structure of the silk from cocoons of two common spiders, Araneus diadematus (family Araneidae) and Achaearanea tepidariorum (family Theridiidae) was investigated by means of (13)C solid state NMR and FT-IR spectroscopies. The combined use of these two techniques allowed us to highlight differences in the two samples. The cocoon silk of Achaearanea tepidariorum is essentially constituted by helical and beta-sheet structures, whereas that of Araneus diadematus shows a more complex structure, containing also beta-strands and beta-turns. Moreover, the former silk is essentially crystalline while the latter contains more mobile domains. The structural differences of the two cocoon silks are ascribed to the different habitat of the two species. PMID:16257700

Bramanti, Emilia; Catalano, Donata; Forte, Claudia; Giovanneschi, Mario; Masetti, Massimo; Veracini, Carlo Alberto

2005-11-01

262

Characterization of coal chars from a flash pyrolysis process by cross polarization/magic angle spinning /sup 13/C NMR  

SciTech Connect

In the last two decades, flash pyrolysis has been used to investigate the sturcture of coal and shale. The development of /sup 13/C cross polarization (CP) and Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) spectroscopy with high-power proton decoupling has allowed investigators to obtain spectra of the organic matter in solid coal. This paper reports the results of this technique applied to the study of chars produced by the flash pyrolysis of coal at progressively higher temperatures. The investigation has given valuable insight into the changes of organic composition of coal during carbonization as well as the optimum temperature for efficient conversion of coal into liquids and gases. (2 tables, 3 figures, 28 refs.)

Chou, M.M. (Illinois State Geological Survey, Champaign); Dickerson, D.R.; Mckay, D.R.; Frye, J.S.

1983-01-01

263

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

2013-10-01

264

A solid-state [sup 13]C NMR study of the molecular motion of ethylene adsorbed on a silver surface  

SciTech Connect

The reorientation of ethylene on a silver catalyst surface has been studied by solid-state [sup 13]C NMR. The static cross-polarization spectra at different temperatures have been measured. Different jump site models are proposed to simulate the experimental results. It was found that the models involving a low number of jump sites are more sensitive to the experimental details. By comparison of the simulated and experimental results, the 6- and 4-site jump models are chosen as the most satisfactory model to fit the experimental spectra. On the basis of this representation, the activation energy derived for the jump process is 4.3 kJ/mol. From the simulated results, it was concluded that the symmetry axis for the motion of the ethylene at low temperatures ([minus]173 to ca. [minus]45[degrees]C) is perpendicular to the plane of the ethylene molecule. At higher temperatures motion about other axes is initiated such that at room temperature a nearly isotropically averaged [sup 13]C shielding tensor is observed. 20 refs., 9 figs.

Jianxin Wang; Ellis, P.D. (Univ. of South Carolina, Columbia (United States))

1993-01-13

265

13C-NMR study of charge order state of the organic conductor ??-(BEDT-TTF)2IBr2  

NASA Astrophysics Data System (ADS)

It is said that the quasi-two dimensional organic conductor (BEDT-TTF)2X forming two columns structure like ? or ? salts, shows charge order (CO) state at low temperature. To confirm the existence of the CO state and the electron magnetism in ?? phase whose symmetry is different from that of ? and ? phases, we investigated 13C-NMR on ??-(BEDT-TTF)2IBr2, in which one-sided central carbon on BEDT-TTF molecules is substituted with 13C. As a result, the change of spectrum was observed at 200 K which corresponds to CO transition and the angular dependence of spectrum at 15 K indicated that the charge ordering pattern was intra-column separating type. The spectrum in paramagnetic state can be examined by not only the difference of the charge density on on-site molecule but also the contribution from off-site molecules. This result suggested that the hyperfine coupling tensor changes after CO transition in which the charge separates extremely.

Hirose, S.; Kawamoto, A.

2010-06-01

266

13C-NMR study of charge order state of the organic conductor ??-(BEDT-TTF)2IBr2  

NASA Astrophysics Data System (ADS)

It is said that the quasi-two dimensional organic conductor (BEDT-TTF)2X forming two columns structure like ? or ? salts, shows charge order (CO) state at low temperature. To confirm the existence of the CO state and the electron magnetism in ?? phase whose symmetry is different from that of ? and ? phases, we investigated 13C-NMR on ??-(BEDT-TTF)2IBr2, in which one-sided central carbon on BEDT-TTF molecules is substituted with 13C. As a result, the change of spectrum was observed at 200 K which corresponds to CO transition and the angular dependence of spectrum at 15 K indicated that the charge ordering pattern was intra-column separating type. The spectrum in paramagnetic state can be examined by not only the difference of the charge density on on-site molecule but also the contribution from off-site molecules. This result suggested that the hyperfine coupling tensor changes after CO transition in which the charge separates extremely.

Hirose, S.; Kawamoto, A.

267

Characterization of glycated proteins by 13C NMR spectroscopy. Identification of specific sites of protein modification by glucose.  

PubMed

13C NMR spectroscopy has been used to characterize Amadori (ketoamine) adducts formed by reaction of [2-13C]glucose with free amino groups of protein. The spectra of glycated proteins were acquired in phosphate buffer at pH 7.4 and were interpreted by reference to the spectra of model compounds, N alpha-formyl-N epsilon-fructose-lysine and glycated poly-L-lysine (GlcPLL). The anomeric carbon region of the spectrum (approximately 90-105 ppm) of glycated cytochrome c was superimposable on that of N alpha-formyl-N epsilon-fructose-lysine, and contained three peaks characteristic of the alpha- and beta-furanose and beta-pyranose anomers of Amadori adducts to peripheral lysine residues on protein (pK alpha approximately 10.5). The spectrum of GlcPLL yielded six anomeric carbon resonances; the second set of three was displaced about 2 ppm to lower shielding of the first and was assigned to the Amadori adduct at the alpha-amino terminus (pK alpha approximately 7.5). The spectrum of glycated RNase was similar to that of GlcPLL, but contained a third set of three signals attributable to modification of active site lysine 41 (pK alpha approximately 8.8). The assignments for RNase were confirmed by analysis of spectra taken at pH 4 and under denaturing conditions. The spectrum of glycated hemoglobin was comparable to that of GlcPLL, and distinct resonances could be assigned to Amadori adducts at amino-terminal valine and intrachain N epsilon-lysine residues. Chemical analyses were performed to measure the relative extent of alpha- and epsilon-amino group modification in the glycated macromolecules, and the results were compared with estimates based on integration of the NMR spectra. PMID:2985592

Neglia, C I; Cohen, H J; Garber, A R; Thorpe, S R; Baynes, J W

1985-05-10

268

Structure and composition analysis of natural gas hydrates: 13C NMR spectroscopic and gas uptake measurements of mixed gas hydrates.  

PubMed

Gas hydrates are becoming an attractive way of storing and transporting large quantities of natural gas, although there has been little effort to understand the preferential occupation of heavy hydrocarbon molecules in hydrate cages. In this work, we present the formation kinetics of mixed hydrate based on a gas uptake measurement during hydrate formation, and how the compositions of the hydrate phase are varied under corresponding formation conditions. We also examine the effect of silica gel pores on the physical properties of mixed hydrate, including thermodynamic equilibrium, formation kinetics, and hydrate compositions. It is expected that the enclathration of ethane and propane is faster than that of methane early stage hydrate formation, and later methane becomes the dominant component to be enclathrated due to depletion of heavy hydrocarbons in the vapor phase. The composition of the hydrate phase seems to be affected by the consumed amount of natural gas, which results in a variation of heating value of retrieved gas from mixed hydrates as a function of formation temperature. 13C NMR experiments were used to measure the distribution of hydrocarbon molecules over the cages of hydrate structure when it forms either from bulk water or water in silica gel pores. We confirm that 70% of large cages of mixed hydrate are occupied by methane molecules when it forms from bulk water; however, only 19% of large cages of mixed hydrate are occupied by methane molecules when it forms from water in silica gel pores. This result indicates that the fractionation of the hydrate phase with heavy hydrocarbon molecules is enhanced in silica gel pores. In addition when heavy hydrocarbon molecules are depleted in the vapor phase during the formation of mixed hydrate, structure I methane hydrate forms instead of structure II mixed hydrate and both structures coexist together, which is also confirmed by 13C NMR spectroscopic analysis. PMID:19658414

Seo, Yutaek; Kang, Seong-Pil; Jang, Wonho

2009-09-01

269

Motional dynamics of residues in a beta-hairpin peptide measured by 13C-NMR relaxation.  

PubMed Central

Structurally characterizing partially folded peptides is problematic given the nature of their transient conformational states. 13C-NMR relaxation data can provide information on the geometry of bond rotations, motional restrictions, and correlated bond rotations of the backbone and side chains and, therefore, is one approach that is useful to assess the presence of folded structure within a conformational ensemble. A peptide 12mer, R1GITVNG7KTYGR12, has been shown to partially fold in a relatively stable beta-hairpin conformation centered at NG. Here, five residues, G2, V5, G7, Y10, G11, were selectively 13C-enriched, and 13C-NMR relaxation experiments were performed to obtain auto- and cross-correlation motional order parameters, correlation times, bond rotation angular variances, and bond rotational correlation coefficients. Our results indicate that, of the three glycines, G7 within the hairpin beta-turn displays the most correlated phi(t),psi(t) rotations with its axis of rotation bisecting the angle defined by the H-C-H bonds. These positively correlated bond rotations give rise to "twisting" type motions of the HCH group. V5 and Y10 phi,psi bond rotations are also positively correlated, with their CbetaCalphaH groups undergoing similar "twisting" type motions. Motions of near-terminal residues G2 and G11 are less restricted and less correlated and are best described as wobbling-in-a-cone. V5 and Y10 side-chain motions, aside from being highly restricted, were found to be correlated with phi,psi bond rotations. At 303 K, where the hairpin is considered "unfolded," the peptide exists in a transient, collapsed state because backbone and side-chain motions of V5, G7, and Y10 remain relatively restricted, unlike their counterparts in GXG-based tripeptides. These results provide unique information toward understanding conformational variability in the unfolded state of proteins, which is necessary to solve the protein folding problem.

Ramirez-Alvarado, M.; Daragan, V. A.; Serrano, L.; Mayo, K. H.

1998-01-01

270

Additional insights from very-high-resolution 13C NMR spectra of long-chain n-alkanes.  

PubMed

New information has been obtained from very-high-resolution (13) C NMR studies of a series of long-chain n-alkanes. These compounds are fundamentally important in the petroleum industry and are essential to the life of some plants, flowers, and insects. At least partial resolution of the ten different (13) C NMR signals of n-C20 H42 is observed at 11.7?T for solutions in C6 D6 or C6 D5 CD3 . A (13) C T1 inversion-recovery experiment provides much more detailed information than in previous studies of long-chain n-alkanes, demonstrates a steady increase in the relaxation times of the ten different carbons proceeding from the middle to the end of the chain because of segmental motion, and thus confirms the assignments for the interior carbons. In contrast, there is significant overlap for the signals for C-7 and the more interior carbons in a solution of n-C16 or longer chain alkanes in CDCl3 . Not only are the chemical shifts sensitive to the solvent used, but also the relative chemical shifts change. Signals for the interior carbons of the odd-number alkanes in CDCl3 are better resolved than in the spectra of their even-number counterparts. Some mixed aromatic solvent systems give increased dispersion of the cluster of C-6 through C-10 signals of n-C20 H42 , n-C21 H44 , and n-C22 H46 . However, none of the solvents used could even partially resolve the C-10 and C-11 signals of n-C21 H44 or n-C22 H46 at 11.7?T, which may result from a different distribution of conformers for n-C21 H44 or n-C22 H46 than for n-C20 H42 and shorter n-alkanes. PMID:23893374

Alemany, Lawrence B

2013-10-01

271

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

272

1H and (13)C NMR and Molecular Dynamics Study of Chiral Recognition of Camphor Enantiomers by alpha-Cyclodextrin.  

PubMed

1H and (13)C NMR spectra of the complexes of camphor enantiomers with alpha-cyclodextrin in D(2)O manifest splittings due to chiral recognition. The complexes were found to be of 1:2 guest-to-host stoichiometry. Free energies of the complex formation obtained from (1)H NMR titration data are equal to -7.95 +/- 0.09 kcal mol(-)(1) for the complex with (1S,4S)- and -7.61 +/- 0.06 kcal mol(-)(1) for that with (1R,4R)-enantiomer. Thus, the free energy difference between the complexes is equal to 0.34 +/- 0.11 kcal mol(-)(1), with the complex involving the (1S,4S)-camphor more stable. A strong positive cooperativity of the guests binding has been found. In agreement with experimental results, molecular dynamics simulations yielded greater stability of the complex with (1S,4S)-camphor. However, they reproduced only qualitatively the experimental trend since the corresponding difference in average energies obtained from molecular dynamic simulations carried out in a water solution is equal to 5 kcal/mol with the CVFF force field. PMID:11674211

Dodziuk, Helena; Ejchart, Andrzej; Lukin, Oleg; Vysotsky, Myroslav O.

1999-03-01

273

Molecular composition of recycled organic wastes, as determined by solid-state 13C 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

2013-11-01

274

Preparation of uniformly (13)C,(15)N-labeled recombinant human amylin for solid-state NMR investigation.  

PubMed

A number of diseases are caused by the formation of amyloid fibrils. Detailed understanding of structural features of amyloid fibers is of great importance for our understanding of disease progression and design of agents for diagnostics or potential prevention of protein aggregation. In lack of 3D crystal ordering, solid-state NMR forms the most suited method to determine the structures of the fibrils with atomic resolution. To exploit this potential, large amounts of isotopic-labeled protein need to be obtained through recombinant protein expression. However, expression and purification of amyloidogenic proteins in large amounts remains challenging due to their aggregation potential, toxicity for cells and difficult purification. In this work, we report a method for the production of large amounts of uniformly labeled (13)C,(15)N-human amylin, being one of the most amyloidogenic peptides known. This method utilizes inclusion bodies-directed expression and cheap chemical cleavage with cyanogen bromide in order to minimize the cost of the procedure compared to the use of less efficient proteolytic enzymes. We demonstrate the formation of amylin fibrils in vitro characterized using biophysical methods and electron microscopy, show toxicity towards human cells, and demonstrate that produced material may form the basis for structure determination using solid-state NMR. PMID:24751876

Kosicka, Iga; Kristensen, Torsten; Bjerring, Morten; Thomsen, Karen; Scavenius, Carsten; Enghild, Jan J; Nielsen, Niels Chr

2014-07-01

275

Study of the metabolism of /sup 13/C labeled substrates by /sup 13/C NMR spectroscopy of intact cells, tissues, and organs  

SciTech Connect

Carbon-13 nuclear magnetic resonance spectroscopy, in conjunction with carbon-13 labeling, has become an important analytical technique for the study of biological systems and biologically important molecules. The growing list of its well established applications to isolated molecules in solution includes the investigation of: metabolic pathways; the microenvironments of ligands bound to proteins; the architecture and dynamics of macromolecules; the structures of coenzymes and other natural products; and the mechanisms of reactions. Recently interest has been reawakened in the use of the technique for the study of metabolic pathways and structural components in intact organelles, cells, and tissues. The promise and problems in the use of /sup 13/C labeling in such investigations can be illustrated by the results on suspensions of the yeast, Candida utilis.

Matwiyoff, N.A.; London, R.E.; Hutson, J.Y.

1982-01-01

276

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

277

Cycling of dissolved and particulate organic matter at station Aloha: Insights from 13C NMR spectroscopy coupled with elemental, isotopic and molecular analyses  

Microsoft Academic Search

Compositions of ultrafiltered dissolved organic matter (UDOM) and ultrafiltered particulate organic matter (UPOM) were characterized in samples collected from a depth profile (20–4000m) 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

Poulomi Sannigrahi; Ellery D. Ingall; Ronald Benner

2005-01-01

278

Transformation of organic matter from maize residues into labile and humic fractions of three European soils as revealed by 13C distribution and CPMAS-NMR spectra  

Microsoft Academic Search

Summary The dynamics of incorporation of fresh organic residues into the various fractions of soil organic matter have yet to be clarified in terms of chemical structures and mechanisms involved. We studied by 13C- dilution analysis and CPMAS-13C-NMR spectroscopy the distribution of organic carbon from mixed or mulched maize residues into specific defined fractions such as carbohydrates and humic fractions

R. S PACCINI; A. P ICCOLO; G. H ABERHAUER; M. H. G ERZABEK

2000-01-01

279

Conformational and dynamical behaviors of cross-linked poly(?-methyl l-glutamate) gel as studied by high-resolution solid-state 13C NMR spectroscopy  

Microsoft Academic Search

Cross-linked poly(?-methyl l-glutamate) (PMLG) was prepared by the ester-amide exchange reaction using diaminododecane as a cross-linker and was swollen by chloroform (CHCl3), trifluoracetic acid (TFA) and a mixture of TFA and CHCl3. The structural and dynamical analyses of the PMLG gel were carried out by means of high-resolution solid-state 13C NMR spectroscopy. From the experimental results on 13C chemical shifts

Chenhua Zhao; Shingo Matsukawa; Masatoshi Kobayashi; Isao Ando

1998-01-01

280

(13)C NMR Analysis of 3,6-Dihydro-2H-pyrans: Assignment of Remote Stereochemistry Using Axial Shielding Effects.  

PubMed

The rational analysis of (13)C NMR axial shielding effects has enabled the assignment of remote relative stereochemistry in 3,6-oxygen-substituted 3,6-dihydro-2H-pyrans. Comparison of the (13)C NMR shifts of equivalent centers in cis- and trans-substituted 3,6-dihydro-2H-pyrans allows the relative configuration at the C3 and C6 positions to be defined in diastereoisomeric mixtures. Density functional calculations were used to validate this method and assess the conformational bias present in the ring system. Ultimately, the coupling of computational chemistry with this (13)C NMR-based method provided a reliable and convenient method for stereochemical assignment of a single diastereomer. This approach provides a facile and complementary alternative to the practices previously employed for determining the relative configuration in 3,6-dihydro-2H-pyrans. PMID:24874030

Bartlett, Mark J; Northcote, Peter T; Lein, Matthias; Harvey, Joanne E

2014-06-20

281

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

282

Insight into the binding of antifreeze proteins to ice surfaces via 13C spin lattice relaxation solid-state NMR.  

PubMed

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 alpha-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 (13)C spin lattice relaxation solid-state NMR experiment was carried out for two Ala side chain (13)C labeled HPLC6 isoforms of the type I AFPs each frozen in H(2)O and D(2)O, 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 alpha-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 T(1) 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 alpha-helical AFP comprising the i + 4 and i + 8 Ala methyl groups could interact with the ice surface in the ice/water interface. PMID:16648161

Mao, Yougang; Ba, Yong

2006-08-01

283

Structural studies on agar fractions extracted sequentially from chinese red sea weeds: Gracilaria sjeostedtii, G. textorii and G. salicornia using 13 C-NMR and IR spectroscopy  

Microsoft Academic Search

The polysaccharides of three species of ChineseGracilaria (Rhodophyta) were extracted by sequential solvent extraction and the chemical structures of the fractions obtained were investigated\\u000a by using13C-NMR and IR spectroscopy.\\u000a \\u000a The13C-NMR spectra showed that the main extract, cold water fraction, fromG. sjeostedtii consisted of repeating disaccharides of agarobiose and (1?3)-?-D-galactopyranosy 1-(1?4)-?-L-galactopyranose 6-sulfate, the\\u000a latter being a precursor to agarobiose and converted

Minghou Ji; M. Lahaye; W. Yaphe

1988-01-01

284

A 13C-NMR study of exudation and storage of carbohydrates and amino acids in the ectomycorrhizal edible mushroom Cantharellus cibarius.  

PubMed

(13)C-NMR analyses of Cantharellus cibarius growth media were performed. We found exudation of trehalose and mannitol, which may explain the phenomenon of reproducing Pseudomonas bacteria observed inside fruit bodies. Exudation varied with strain and environment. NMR analyses of stored (13)C was also performed. Trehalose, mannitol, and arginine were revealed. The mannitol pathway seems to play an important role for trehalose production in this species. This is the first study of the fate of the photosynthetically derived carbon in the highly appreciated edible ectomycorrhizal mushroom Cantharellus cibarius. PMID:21156488

Rangel-Castro, J Ignacio; Danell, Eric; Pfeffer, Philip E

2002-01-01

285

Specific 12C?D(2)12C?D(2)S13C?HD(2) isotopomer labeling of methionine to characterize protein dynamics by 1H and 13C NMR relaxation dispersion.  

PubMed

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 (1)H and (13)C 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 (13)CHD(2) 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 (13)CHD(2) methyl isotopomer, which is ideal for (1)H and (13)C spin relaxation experiments to investigate protein dynamics in general and conformational exchange in particular. We demonstrate the approach by measuring (1)H and (13)C 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. PMID:23106551

Weininger, Ulrich; Liu, Zhihong; McIntyre, Deane D; Vogel, Hans J; Akke, Mikael

2012-11-14

286

Improving the accuracy of computed 13C NMR shift predictions by specific environment error correction: fragment referencing.  

PubMed

The accuracy of both Gauge-including atomic orbital (GIAO) and continuous set of gauge transformations (CSGT) (13)C NMR spectra prediction by Density Functional Theory (DFT) at the B3LYP/6-31G** level is shown to be usefully enhanced by employing a 'fragment referencing' method for predicting chemical shifts without recourse to empirical scaling. Fragment referencing refers to a process of reducing the error in calculating a particular NMR shift by consulting a similar molecule for which the error in the calculation is easily deduced. The absolute accuracy of the chemical shifts predicted when employing fragment referencing relative to conventional techniques (e.g., using TMS or MeOH/benzene dual referencing) is demonstrated to be improved significantly for a range of substrates, which illustrates the superiority of the technique particularly for systems with similar chemical shifts arising from different chemical environments. The technique is particularly suited to molecules of relatively low molecular weight containing 'non-standard' magnetic environments, e.g., ? to halogen atoms, which are poorly predicted by other methods. The simplicity and speed of the technique mean that it can be employed to resolve routine structural assignment problems that require a degree of accuracy not provided by standard incremental or hierarchically ordered spherical description of environment (HOSE) algorithms. The approach is also demonstrated to be applicable when employing the MP2 method at 6-31G**, cc-pVDZ, aug-cc-pVDZ, and cc-pVTZ levels, although none of these offer advantage in terms of accuracy of prediction over the B3LYP/6-31G** DFT method. PMID:24138675

Andrews, Keith G; Spivey, Alan C

2013-11-15

287

Multivariate analysis of CPMAS 13C-NMR spectra of soils and humic matter as a tool to evaluate organic carbon quality in natural systems  

Microsoft Academic Search

Summary A series of humic and fulvic acids isolated from different sources, size-fractions separated from a humic acid, and three soils of different origin were subjected to CPMAS 13C-NMR spectroscopy to obtain the distribution of their carbon contents. The relative areas of chemical shift regions in NMR spectra were used to apply a principal component analysis (PCA) to the three

D. SMEJKALOVA; R. S PACCINI; A. P ICCOLO

288

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

289

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

290

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

291

Radical Pairs with Rotational Fluidity in the Photochemical Reaction of Acetophenone and Cyclohexane in the Zeolite NaY: A 13C CPMAS NMR and Product Analysis Study  

PubMed Central

The photochemical reaction of acetophenone and cyclohexane in the zeolite NaY occurs by combination of the geminate radical pairs to give products that reveal a significant amount of rotational fluidity, which was also documented by intermolecular nuclear dipolar interactions measurements using cross polarization 13C NMR (CPMAS) experiments.

Amboya, Ammee; Nguyen, Tina; Huynh, Hien T.; Brown, Ashley; Ratliff, Gretchen; Yonutas, Heather; Natarajan, Arunkumar

2010-01-01

292

Comparative study of two fractions of riverine dissolved organic matter using various analytical pyrolytic methods and a 13C CP\\/MAS NMR approach  

Microsoft Academic Search

Two fractions of dissolved organic matter (DOM) from a French river, the Gartempe, were obtained using the XAD resin fractionation procedure and were termed hydrophobic acid (HPOA) and transphilic acid (TPIA) according to this method. The composition of these two fractions was investigated with solid state CP\\/MAS 13C NMR, Curie point pyrolysis at 650 °C, with and without tetramethylammonium hydroxide

Joëlle Templier; Sylvie Derenne; Jean-Philippe Croué; Claude Largeau

2005-01-01

293

Estimating the molecular composition of a diverse range of natural organic materials from solid-state 13 C NMR and elemental analyses  

Microsoft Academic Search

Most techniques for determining the chemical nature of natural organic matter in soil, sediment and water require prior extraction or concentration steps that are not quantitative and that create artifacts. 13C nuclear magnetic resonance (NMR) analysis can avoid these problems, but it gives little information at the scale of molecules. Here we show that the molecular composition of a diverse

Paul N. Nelson; Jeffrey A. Baldock

2005-01-01

294

13C chemical shift map of the active cofactors in photosynthetic reaction centers of Rhodobacter sphaeroides revealed by photo-CIDNP MAS NMR.  

PubMed

13C photo-CIDNP MAS NMR studies have been performed on reaction centers (RCs) of Rhodobacter sphaeroides wild type (WT) that have been selectively labeled with an isotope using [5-13C]-delta-aminolevulinic acid.HCl in all the BChl and BPhe cofactors at positions C-4, C-5, C-9, C-10, C-14, C-15, C-16, and C-20. 13C CP/MAS NMR and 13C-13C dipolar correlation photo-CIDNP MAS NMR provide a chemical shift map of the cofactors involved in the electron transfer process in the RC at the atomic scale. The 13C-13C dipolar correlation photo-CIDNP spectra reveal three strong components, originating from two BChl cofactors, called P1 and P2 and assigned to the special pair, as well as one BPhe, PhiA. In addition, there is a weak component observed that arises from a third BChl cofactor, denoted P3, which appears to originate from the accessory BChl BA. An almost complete set of assignments of all the aromatic carbon atoms in the macrocycles of BChl and BPhe is achieved in combination with previous photo-CIDNP studies on site-directed BChl/BPhe-labeled RCs [Schulten, E. A. M., Matysik, J., Alia, Kiihne, S., Raap, J., Lugtenburg, J., Gast, P., Hoff, A. J., and de Groot, H. J. M. (2002) Biochemistry 41, 8708-8717], allowing a comprehensive map of the ground-state electronic structure of the photochemically active cofactors to be constructed for the first time. The reasons for the anomaly of P2 and the origin of the polarization on P3 are discussed. PMID:17630781

Prakash, Shipra; Alia, A; Gast, Peter; de Groot, Huub J M; Jeschke, Gunnar; Matysik, Jörg

2007-08-01

295

Resonance assignment of 13C/15N labeled solid proteins by two- and three-dimensional magic-angle-spinning NMR.  

PubMed

The comprehensive structure determination of isotopically labeled proteins by solid-state NMR requires sequence-specific assignment of 13C and 15N spectra. We describe several 2D and 3D MAS correlation techniques for resonance assignment and apply them, at 7.0 Tesla, to 13C and 15N labeled ubiquitin to examine the extent of resonance assignments in the solid state. Both interresidue and intraresidue assignments of the 13C and 15N resonances are addressed. The interresidue assignment was carried out by an N(CO)CA technique, which yields Ni-C alpha i-1 connectivities in protein backbones via two steps of dipolar-mediated coherence transfer. The intraresidue connectivities were obtained from a new 3D NCACB technique, which utilizes the well resolved C beta chemical shift to distinguish the different amino acids. Additional amino acid type assignment was provided by a 13C spin diffusion experiment, which exhibits 13C spin pairs as off-diagonal intensities in the 2D spectrum. To better resolve carbons with similar chemical shifts, we also performed a dipolar-mediated INADEQUATE experiment. By cross-referencing these spectra and exploiting the selective and extensive 13C labeling approach, we assigned 25% of the amino acids in ubiquitin sequence-specifically and 47% of the residues to the amino acid types. The sensitivity and resolution of these experiments are evaluated, especially in the context of the selective and extensive 13C labeling approach. PMID:10549131

Hong, M

1999-09-01

296

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

297

Identification of isotopomers in natural abundance using two dimensional laser induced fluorescence: S1-S0 spectral shifts for the four 13C isotopomers of fluorobenzene  

NASA Astrophysics Data System (ADS)

The spectral shifts associated with the S1-S0000 transition for the four 13C isotopomers of fluorobenzene have been determined using two dimensional laser induced fluorescence (2D-LIF), demonstrating this to be a powerful tool for separating overlapped spectral features associated with molecular species of the same mass. The 13C isotopomers were assigned with the aid of ab initio calculations of the magnitude of the vibrational frequency changes on 13C substitution. The 2D-LIF technique is expected to be useful for separating overlapped spectra from species such as configurational isomers, where mass-based spectroscopic techniques can have difficulty.

Gascooke, Jason R.; Lawrance, Warren D.

2013-01-01

298

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

299

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

300

Characterization of acetylated 4-O-methylglucuronoxylan isolated from aspen employing 1H and 13C NMR spectroscopy.  

PubMed

Water-soluble hemicelluloses were extracted from milled aspen wood (Populus tremula) employing microwave oven treatment at 180 degrees C for 10 min. The final pH of this extract was 3.5. From this extract oligo- and polysaccharides were isolated and subsequently fractionated by size-exclusion chromatography. The structures of the saccharides in three of the fractions obtained were determined by 1H and 13C NMR spectroscopy, using homonuclear and heteronuclear two-dimensional techniques. The polysaccharides present in the two fractions eluted first were O-acetyl-(4-O-methylglucurono)xylans. The average degree of acetylation of the xylose residues in these compounds was 0.6. The structural element -->4)[4-O-Me-alpha-D-GlcpA-(1-->2)][3-O-Ac]-beta-D-Xylp-(1 --> could also be identified. On the average, these two xylans were composed of the following (1-->4)-linked beta-D-xylopyranosyl structural elements: unsubstituted (50 mol%), 2-O-acetylated (13 mol%), 3-O-acetylated (21 mol%), 2,3-di-O-acetylated (6 mol%) and [MeGlcA alpha-(1-->2)][3-O-acetylated] (10 mol%). Most of the 4-O-methylglucuronyl and acetyl substituents in the isolated polysaccharides survived the microwave oven treatment. The third fraction, eluted last, contained acetylated xylo-oligosaccharides, with minor contamination by an acetylated mannan. In the case of these xylo-oligosaccharides, the average degree of acetylation was 0.3. PMID:11125823

Teleman, A; Lundqvist, J; Tjerneld, F; Stålbrand, H; Dahlman, O

2000-12-01

301

The alternating of substituent effect on the 13C NMR shifts of all bridge carbons in cinnamyl aniline derivatives  

NASA Astrophysics Data System (ADS)

Bridge carbon 13C NMR shifts of a wide set of substituted cinnamyl anilines p-XC6H4CHdbnd CHCHdbnd NC6H4Y-p (Xdbnd NO2, Cl, H, Me, MeO, or NMe2; Ydbnd NO2, CN, CO2Et, Cl, F, H, Me, MeO or NMe2) had been used as a probe to study the change of substituent effect in the conjugated system. The goal of this work was to study the difference among the substituent effect on SCS of all bridge carbons, and find the alternating of substituent effect in this model compounds. In this study, it was found that the change of the inductive effect and the conjugative effect on different bridge carbons is related to the bond number (m) from the substituent to the corresponding carbon, and the adjusted parameters ?F(rel)? and ?R(ver)? can be suitable to scale the difference of the inductive effect and the conjugative effect on bridge carbons. Moreover, because of the difference of substituent effect on bridge carbons, the substituent cross-interaction item ??2??2=? was not suitable simply to scale the interaction between substituents X and Y for all bridge carbons, so the ??2 was recommended to be divided into two parts: ??F(rel)2??F(rel)2=? and ??R(ver)2??R(ver)2=?. With ?F(rel)?, ?R(ver)?, ??F(rel)2, ??R(ver)2, and ?C,parent, the obtained correlation equation can be used to correlate with the 159 sorts of SCS of the different bridge carbon in cinnamyl aniline derivatives. The correlation coefficient is 0.9993, and the standard deviation is only 0.53 ppm. The multi-parameter correlation equation can be recommended to predict well the corresponding bridge carbons SCS of disubstituted cinnamyl anilines.

Chen, Guanfan; Cao, Chenzhong; Zhu, Yun; Wu, Zhenxing; Wu, Xiangsi

2012-12-01

302

Major Groove Width Variations in RNA Structures Determined by NMR and Impact of 13C residual chemical shift anisotropy and 1H-13C residual dipolar coupling on refinement  

PubMed Central

Ribonucleic acid structure determination by NMR spectroscopy relies primarily on local structural restraints provided by 1H-1H NOEs and J-couplings. When employed loosely, these restraints are broadly compatible with A- and B-like helical geometries and give rise to calculated structures that are highly sensitive to the force fields employed during refinement. A survey of recently reported NMR structures reveals significant variations in helical parameters, particularly the major groove width. Although helical parameters observed in high-resolution X-ray crystal structures of isolated A-form RNA helices are sensitive to crystal packing effects, variations among the published X-ray structures are significantly smaller than those observed in NMR structures. Here we show that restraints derived from aromatic 1H-13C residual dipolar couplings (RDCs) and residual chemical shift anisotropies (RCSAs) can overcome NMR restraint and force field deficiencies and afford structures with helical properties similar to those observed in high-resolution X-ray structures.

Tolbert, Blanton S; Miyazaki, Yasuyuki; Barton, Shawn; Kinde, Benyam; Starck, Patrice; Singh, Rashmi; Bax, Ad

2010-01-01

303

sup 31 P and sup 13 C-NMR studies of the phosphorus and carbon metabolites in the halotolerant alga, Dunaliella salina  

SciTech Connect

The intracellular phosphorus and carbon metabolites in the halotolerant alga Dunaliella salina adapted to different salinities were monitored in living cells by {sup 31}P- and {sup 13}C-nuclear magnetic resonance (NMR) spectroscopy. The {sup 13}C-NMR studies showed that the composition of the visible intracellular carbon metabolites other than glycerol is not significantly affected by the salinity of the growth medium. The T{sub 1} relaxation rates of the {sup 13}C-glycerol signals in intact cells were enhanced with increasing salinity of the growth medium, in parallel to the expected increase in the intracellular viscosity due to the increase in intracellular glycerol. The {sup 31}P-NMR studies showed that cells adapted to the various salinities contained inorganic phosphate, phosphomonoesters, high energy phosphate compounds, and long chain polyphosphates. In addition, cells grown in media containing up to 1 molar NaCl contained tripolyphosphates. The tripolyphosphate content was also controlled by the availability of inorganic phosphate during cell growth. Phosphate-depleted D. salina contained no detectable tripolyphosphate signal. Excess phosphate, however, did not result in the appearance of tripolyphosphate in {sup 31}P-NMR spectra of cells adapted to high (>1.5 molar NaCl) salinities.

Bental, M.; Oren-Shamir, M.; Avron, M.; Degani, H. (Weizmann Institute of Science, Rehovot (Israel))

1988-06-01

304

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

305

Structural investigation of Titan tholins by solution-state 1H, 13C, and 15N NMR: one-dimensional and decoupling experiments.  

PubMed

Titan, the largest moon of Saturn, is enveloped in a reddish brown organic haze. Titan haze is presumed to be formed from methane and nitrogen (CH(4) and N(2)) in Titan's upper atmosphere through energetic photochemistry and particle bombardment. Though Titan haze has been directly investigated using methods including the Cassini mission, its formation mechanism and the contributing chemical structures and prebiotic potential are still not well developed. We report here the structural investigation of the (13)C and (15)N labeled, simulated Titan haze aerosol (tholin) by solution-state NMR. The one-dimensional (1)H, (13)C, and (15)N NMR spectra and decoupling experiments indicate that the tholin sample contains amine, nitrile, imine, and N-heteroaromatic compounds of tremendous import in understanding complex organic chemistry in anaerobic, extraterrestrial environments. PMID:22489539

He, Chao; Lin, Guangxin; Upton, Kathleen T; Imanaka, Hiroshi; Smith, Mark A

2012-05-17

306

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

307

Joint Spatial-Spectral Reconstruction and k-t Spirals for Accelerated 2D Spatial/1D Spectral Imaging of 13C Dynamics  

PubMed Central

Purpose To develop a novel imaging technique to reduce the number of excitations and required scan time for hyperpolarized 13C imaging. Methods A least-squares based optimization and reconstruction is developed to simultaneously solve for both spatial and spectral encoding. By jointly solving both domains, spectral imaging can potentially be performed with a spatially oversampled single echo spiral acquisition. Digital simulations, phantom experiments, and initial in vivo hyperpolarized [1-13C]pyruvate experiments were performed to assess the performance of the algorithm as compared to a multi-echo approach. Results Simulations and phantom data indicate that accurate single echo imaging is possible when coupled with oversampling factors greater than six (corresponding to a worst case of pyruvate to metabolite ratio < 9%), even in situations of substantial T2* decay and B0 heterogeneity. With lower oversampling rates, two echoes are required for similar accuracy. These results were confirmed with in vivo data experiments, showing accurate single echo spectral imaging with an oversampling factor of 7 and two echo imaging with an oversampling factor of 4. Conclusion The proposed k-t approach increases data acquisition efficiency by reducing the number of echoes required to generate spectroscopic images, thereby allowing accelerated acquisition speed, preserved polarization, and/or improved temporal or spatial resolution. Magn Reson Med

Gordon, Jeremy W.; Niles, David J.; Fain, Sean B.; Johnson, Kevin M.

2014-01-01

308

13C and 15N NMR study of 1,2,4-triazolo[1,5- a]pyrimidines with one tautomerism-introducing substituent  

NASA Astrophysics Data System (ADS)

The 13C NMR spectra of a large variety of 7-OH (7-SH, 7-NH 2) substituted 1,2,4-triazolo[1,5- a]pyrimidines were studied and assigned by a whole arsenal of 2D NMR methods. The C-7 chemical shifts were not sufficiently characteristic to differentiate the lactim and the three lactam tautomers of the compounds studied. However, the 15N NMR resonances, which were assigned by the various possible N,H coupling constants, proved that the 7-OH- and 7-SH-substituted 1,2,4-triazolo[1,5- a]pyrimidines exist as an equilibrium of the N 4H and the N 3H tautomers, which is fast on the NMR time scale. PM3 quantum-chemical calculations corroborate this result obtained experimentally.

Kleinpeter, E.; Thomas, St.; Fischer, G.

1995-09-01

309

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

310

Measurement of carbonyl chemical shifts of excited protein states by relaxation dispersion NMR spectroscopy: comparison between uniformly and selectively 13 C labeled samples  

Microsoft Academic Search

Carr–Purcell–Meiboom–Gill (CPMG) relaxation dispersion nuclear magnetic resonance (NMR) spectroscopy has emerged as a powerful\\u000a method for quantifying chemical shifts of excited protein states. For many applications of the technique that involve the\\u000a measurement of relaxation rates of carbon magnetization it is necessary to prepare samples with isolated 13C spins so that experiments do not suffer from magnetization transfer between coupled

Patrik Lundström; D. Flemming Hansen; Lewis E. Kay

2008-01-01

311

13 C NMR studies of fatty acid-protein interactions: comparison of homologous fatty acid-binding proteins produced in the intestinal epithelium  

Microsoft Academic Search

A high-resolution, solution-state NMR method for characterizing and comparing the interactions between carboxyl 13C-enriched fatty acids (FA) and individual binding sites on proteins has been developed. The utility of this method results from the high degree of resolution of carboxyl from other carbon resonances and the high sensitivity of FA carboxyl chemical shifts to intermolecular environmental factors such as degree

David P. Cistola; James C. Sacchettini; Jeffrey I. Gordon

1990-01-01

312

Assignment of 13C NMR chemical shift and microstructure of copolymers of 2-chloroethyl vinyl ether-maleic anhydride and n-butyl vinyl ether-maleic anhydride  

Microsoft Academic Search

Summary  \\u000a The chemical shift in the 13C NMR spectra of copolymers of 2-chloroethyl vinyl ether (CEVE) and maleic anhydride (MA), and of n-butyl vinyl ether (BVE)\\u000a and MA is assigned. It is found that both copolymers are made of completely alternating monomer unit sequences and that the\\u000a proportion of cis linkage configuration at the cyclic MA units is 45 %

Nguyen T. H. Ha; Kiyohisa Fujimori; Peter C. Henry; David J. Tucker

1999-01-01

313

Supercritical CO2 extract from needles of Pinus nigra ssp. laricio: combined analysis by GC, GC-MS and 13C NMR.  

PubMed

The chemical composition of the volatile concentrate prepared by supercritical CO(2) extraction of the needles of Pinus nigra Arnold ssp. laricio Poiret from Corsica was investigated using GC (RI), GC-MS and (13)C NMR spectroscopy. The major component was by far manoyl oxide (63%), a compound of potential interest for the perfumery and pharmaceutical industries. Consequently, the supercritical fluid extract of P. nigra ssp. laricio (yield 1.60%) could be considered as a source of this diterpene. PMID:17654290

Duquesnoy, Emilie; Marongiu, Bruno; Castola, Vincent; Piras, Alessandra; Porcedda, Silvia; Casanova, Joseph

2007-07-20

314

Changes in the compound classes of dissolved organic matter along an estuarine transect: A study using FTIR and 13C NMR  

Microsoft Academic Search

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, >1kDa) dissolved organic matter (DOM) isolated along a transect through the Elizabeth River\\/Chesapeake Bay system to the coastal Atlantic Ocean

Hussain A. N. Abdulla; Elizabeth C. Minor; Robert F. Dias; Patrick G. Hatcher

2010-01-01

315

Combined use of 13C- and 19F-NMR to analyse the mode of action and the metabolism of the herbicide isoxaflutole  

Microsoft Academic Search

13C-Nuclear magnetic resonance was used to characterize the effects of the trifluoromethyl herbicide isoxaflutole on plant metabolism. A specific accumulation of tyrosine and phenylalanine in pea leaves was observed after treatment with this herbicide, consistent with an inhibition of 4-hydroxyphenylpyruvate dioxygenase (HPPD), an enzyme involved in plastoquinone and tocopherol synthesis and the known target of isoxaflutole. 19F-NMR permitted the analysis

Serge Aubert; Kenneth E Pallett

2000-01-01

316

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

317

Isolation and 1H/13C-NMR Studies on 19,20-Dihydrocondylocarpine: An Alkaloid from the Leaves of Ervatamia coronaria and Alstonia scholaris.  

PubMed

Studies on the alkaloidal constituents of the leaves of Ervatamia coronaria Stapf and Alstonia scholaris have resulted in the isolation of (20 S)-19,20-dihydrocondylocarpine which has not been previously reported from these plants. The stereochemistry at C-20 was established with the help of n. O. e. difference measurements. (13)C-NMR assignments have been made by polarisation transfer techniques. PMID:17345322

Atta-ur-Rahman; Alvi, K A; Muzaffar, A

1986-08-01

318

monitoring Biomacromolecular degradation of Calluna Vulgaris in a 23 year field experiment using solid state 13C-NMR and pyrolysis-GC\\/MS  

Microsoft Academic Search

The qualitative and quantitative changes in lignin, polysaccharide, aliphatic, cutin and protein biomacromolecules in Calluna vulgaris shoots collected at three intervals (initial 0.5y, 7y and 23y) in a field decomposition experiment have been investigated using quantitative solid state 13C nuclear magnetic resonance (NMR) spectroscopy and pyrolysis-gas chromatography\\/mass spectrometry (Py-GC\\/MS). Protein showed rapid decomposition with virtually none remaining after 7y. The

Y. Huang; B. A. Stankiewicz; G. Eglinton; C. E. Snape; B. Evans; P. M. Latter; P. Ineson

1998-01-01

319

One-azabicyclic compounds. 22. Stereochemistry and /sup 13/C NMR spectra of salts of pyrrolizidine and its homologs with protonic acids  

SciTech Connect

/sup 13/C NMR spectra were obtained for pyrrolizidinium salts and their homologs and their signals were assigned. With the exception of highly strained cis-3,8-H-cis-5,8-H-3,5-dimethylpyrrolizidine (VI), all the bases studied upon their direct mixing with CF/sub 3/CO/sub 2/H form salts only with cis-fused rings in the cation. Mixtures of salts with cis- and trans-fused pyrrolizidinium fragments are formed upon the reaction of cis-3,8-H-methyl- (III) and cis-3,8-H-cis-5,8-H-3,5-dimethylpyrrolizidine (VI) under conditions close to those for kinetically-controlled amine protonation. The /sup 13/C NMR spectra of the isomeric pyrrolizidinium salts obtained as a result of the absorption of base VI by sulfuric acid were used to evaluate the conformational equilibrium in the starting compound VI. The /sup 13/C NMR chemical shifts of unsubstituted trans-fused pyrrolizidinium salts were predicted.

Subbotin, O.A.; Skvortsov, I.M.

1986-06-01

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

Reversal of metabolic deficits by lipoic acid in a triple transgenic mouse model of Alzheimer's disease: a 13C NMR study.  

PubMed

Alzheimer's disease is an age-related neurodegenerative disease characterized by deterioration of cognition and loss of memory. Several clinical studies have shown Alzheimer's disease to be associated with disturbances in glucose metabolism and the subsequent tricarboxylic acid (TCA) cycle-related metabolites like glutamate (Glu), glutamine (Gln), and N-acetylaspartate (NAA). These metabolites have been viewed as biomarkers by (a) assisting early diagnosis of Alzheimer's disease and (b) evaluating the efficacy of a treatment regimen. In this study, 13-month-old triple transgenic mice (a mouse model of Alzheimer's disease (3xTg-AD)) were given intravenous infusion of [1-(13)C]glucose followed by an ex vivo (13)C NMR to determine the concentrations of (13)C-labeled isotopomers of Glu, Gln, aspartate (Asp), GABA, myo-inositol, and NAA. Total ((12)C+(13)C) Glu, Gln, and Asp were quantified by high-performance liquid chromatography to calculate enrichment. Furthermore, we examined the effects of lipoic acid in modulating these metabolites, based on its previously established insulin mimetic effects. Total (13)C labeling and percent enrichment decreased by ?50% in the 3xTg-AD mice. This hypometabolism was partially or completely restored by lipoic acid feeding. The ability of lipoic acid to restore glucose metabolism and subsequent TCA cycle-related metabolites further substantiates its role in overcoming the hypometabolic state inherent in early stages of Alzheimer's disease. PMID:24220168

Sancheti, Harsh; Kanamori, Keiko; Patil, Ishan; Díaz Brinton, Roberta; Ross, Brian D; Cadenas, Enrique

2014-02-01

322

Compounds of L(+)-ascorbic acid with dimethylthallium(III), dimethyltin(IV), and dibutyltin(IV): Synthesis, solid-state spectroscopy (CP\\/MAS 13C NMR and IR), and multi-NMR behavior in aqueous solution  

Microsoft Academic Search

Reaction of L(+)-ascorbic acid (H2Asc) with TlMe2OOCCH3, SnMe2O, and SnBu2Cl2 (in this last case, in the presence of Et3N) afforded [TlMe2(HAsc)]·12C3H8O, [SnMe2(Asc)], and [SnBu2(Asc)], respectively. The new compounds were studied in the solid state by CP\\/MAS 13C NMR and IR spectroscopy, and in aqueous solution by 1H, 13C, 205Tl, and 119Sn NMR spectroscopy. The thallium compound behaves as a salt.

José S. Casas; María V. Castaño; María S. García-Tasende; Teresa Pérez-Alvarez; Agustín Sánchez; José Sordo

1996-01-01

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

2011-10-15

324

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  

NASA Astrophysics Data System (ADS)

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, 1H NMR and 13C 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, 1H NMR and 13C 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 1H NMR and 13C 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 1H NMR and 13C 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.

Saheb, Vahid; Sheikhshoaie, Iran

2011-10-01

325

A new salen base 5-(phenylazo)-N-(2-amino pyridine) salicyliden Schiff base ligand: synthesis, experimental and density functional studies on its crystal structure, FTIR, 1H NMR and 13C NMR spectra.  

PubMed

A novel Schiff base ligand 5-(phenylazo)-N-(2-amino pyridine) salicyliden is prepared through the condensation of 5-(phenylazo) salicylaldehyde and 2-amino pyridine in methanol at room temperature. The orange crystalline precipitate is used for X-ray crystallography and measuring Fourier transform (FTIR), 1H NMR and 13C NMR spectra. Density functional theory (DFT) calculations at the B3LYP, MPWB1K and B3PW91 levels of theory is used to optimize the geometry and calculate the FTIR, 1H NMR and 13C NMR spectra of the compound. The vibrational frequencies determined experimentally are compared with those obtained theoretically and a vibrational assignment and analysis of the fundamental modes of the compound is performed. We found that the MPWB1K method predicts low vibrational frequencies better than the commonly used B3LYP method. Although the B3PW91 method overestimates the 1H NMR chemical shifts, the values computed at the B3LYP level of theory are in accordance with experimental 1H NMR spectrum. However, both B3LYP and B3PW91 methods tend to overestimate 13C NMR chemical shifts. In addition, a few quantum descriptors of the molecule are calculated and conformational analysis is performed and the result was compared with crystallographic data. PMID:20889369

Sheikhshoaie, Iran; Saheb, Vahid

2010-12-01

326

A new salen base 5-(phenylazo)-N-(2-amino pyridine) salicyliden Schiff base ligand: Synthesis, experimental and density functional studies on its crystal structure, FTIR, 1H NMR and 13C NMR spectra  

NASA Astrophysics Data System (ADS)

A novel Schiff base ligand 5-(phenylazo)-N-(2-amino pyridine) salicyliden is prepared through the condensation of 5-(phenylazo) salicylaldehyde and 2-amino pyridine in methanol at room temperature. The orange crystalline precipitate is used for X-ray crystallography and measuring Fourier transform (FTIR), 1H NMR and 13C NMR spectra. Density functional theory (DFT) calculations at the B3LYP, MPWB1K and B3PW91 levels of theory is used to optimize the geometry and calculate the FTIR, 1H NMR and 13C NMR spectra of the compound. The vibrational frequencies determined experimentally are compared with those obtained theoretically and a vibrational assignment and analysis of the fundamental modes of the compound is performed. We found that the MPWB1K method predicts low vibrational frequencies better than the commonly used B3LYP method. Although the B3PW91 method overestimates the 1H NMR chemical shifts, the values computed at the B3LYP level of theory are in accordance with experimental 1H NMR spectrum. However, both B3LYP and B3PW91 methods tend to overestimate 13C NMR chemical shifts. In addition, a few quantum descriptors of the molecule are calculated and conformational analysis is performed and the result was compared with crystallographic data.

Sheikhshoaie, Iran; Saheb, Vahid

2010-12-01

327

Chemical and nanometer-scale structure of kerogen and its change during thermal maturation investigated by advanced solid-state 13C NMR spectroscopy  

NASA Astrophysics Data System (ADS)

We have used advanced and quantitative solid-state nuclear magnetic resonance (NMR) techniques to investigate structural changes in a series of type II kerogen samples from the New Albany Shale across a range of maturity (vitrinite reflectance R0 from 0.29% to 1.27%). Specific functional groups such as CH 3, CH 2, alkyl CH, aromatic CH, aromatic C-O, and other nonprotonated aromatics, as well as "oil prone" and "gas prone" carbons, have been quantified by 13C NMR; atomic H/C and O/C ratios calculated from the NMR data agree with elemental analysis. Relationships between NMR structural parameters and vitrinite reflectance, a proxy for thermal maturity, were evaluated. The aromatic cluster size is probed in terms of the fraction of aromatic carbons that are protonated (˜30%) and the average distance of aromatic C from the nearest protons in long-range H-C dephasing, both of which do not increase much with maturation, in spite of a great increase in aromaticity. The aromatic clusters in the most mature sample consist of ˜30 carbons, and of ˜20 carbons in the least mature samples. Proof of many links between alkyl chains and aromatic rings is provided by short-range and long-range 1H- 13C correlation NMR. The alkyl segments provide most H in the samples; even at a carbon aromaticity of 83%, the fraction of aromatic H is only 38%. While aromaticity increases with thermal maturity, most other NMR structural parameters, including the aromatic C-O fractions, decrease. Aromaticity is confirmed as an excellent NMR structural parameter for assessing thermal maturity. In this series of samples, thermal maturation mostly increases aromaticity by reducing the length of the alkyl chains attached to the aromatic cores, not by pronounced growth of the size of the fused aromatic ring clusters.

Mao, Jingdong; Fang, Xiaowen; Lan, Yeqing; Schimmelmann, Arndt; Mastalerz, Maria; Xu, Ling; Schmidt-Rohr, Klaus

2010-04-01

328

Saturation-recovery metabolic-exchange rate imaging with hyperpolarized [1-13C] pyruvate using spectral-spatial excitation.  

PubMed

Within the last decade hyperpolarized [1-13C] pyruvate chemical-shift imaging has demonstrated impressive potential for metabolic MR imaging for a wide range of applications in oncology, cardiology, and neurology. In this work, a highly efficient pulse sequence is described for time-resolved, multislice chemical shift imaging of the injected substrate and obtained downstream metabolites. Using spectral-spatial excitation in combination with single-shot spiral data acquisition, the overall encoding is evenly distributed between excitation and signal reception, allowing the encoding of one full two-dimensional metabolite image per excitation. The signal-to-noise ratio can be flexibly adjusted and optimized using lower flip angles for the pyruvate substrate and larger ones for the downstream metabolites. Selectively adjusting the excitation of the down-stream metabolites to 90° leads to a so-called "saturation-recovery" scheme with the detected signal content being determined by forward conversion of the available pyruvate. In case of repetitive excitations, the polarization is preserved using smaller flip angles for pyruvate. Metabolic exchange rates are determined spatially resolved from the metabolite images using a simplified two-site exchange model. This novel contrast is an important step toward more quantitative metabolic imaging. Goal of this work was to derive, analyze, and implement this "saturation-recovery metabolic exchange rate imaging" and demonstrate its capabilities in four rats bearing subcutaneous tumors. PMID:22648928

Schulte, Rolf F; Sperl, Jonathan I; Weidl, Eliane; Menzel, Marion I; Janich, Martin A; Khegai, Oleksandr; Durst, Markus; Ardenkjaer-Larsen, Jan Henrik; Glaser, Steffen J; Haase, Axel; Schwaiger, Markus; Wiesinger, Florian

2013-05-01

329

13 C CP\\/MAS and 2 H NMR study of tert-butyl alcohol dehydration on H-ZSM-5 zeolite. Evidence for the formation of tert-butyl cation and tert-butyl silyl ether intermediates  

Microsoft Academic Search

The dehydration reaction of tert-butyl alcohol, selectively labelled with13C in CH3 or C-O groups (t-BuOH[2-13C2] andt-BuOH[1-13C]), as well as selectively deuterated in methyl groups (t-BuOH[2-2H9]), was studied on H-ZSM-5 zeolite simultaneously with13 C CP\\/MAS and2H solid state NMR. When adsorbed and dehydrated on zeolite at 296 K,t-BuOH[2-13C1] andt-BuOH[1-13C] give rise to identical13C CP\\/MAS NMR spectra of oligomeric aliphatic products. This

Alexander G. Stepanov; Kirill I. Zamaraev; John M. Thomas

1992-01-01

330

Noninvasive evaluation of liver metabolism by 2H and 13C NMR isotopomer analysis of human urine  

Microsoft Academic Search

Mammalian liver disposes of acetaminophen and other ingested xenobiotics by forming soluble glucuronides that are subsequently removed via renal filtration. When given in combination with the stable isotopes 2H and 13C, the glucuronide of acetaminophen isolated from urine provides a convenient “chemical biopsy” for evaluating intermediary metabolism in the liver. Here, we describe isolation and purification of urinary acetaminophen glucuronide

Shawn C. Burgess; Brian Weis; John G. Jones; Erin Smith; Matthew E. Merritt; David Margolis; A. Dean Sherry; Craig R. Malloya

2003-01-01

331

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

332

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

333

Backbone and Ile-?1, Leu, Val methyl 1H, 13C and 15N NMR chemical shift assignments for human interferon-stimulated gene 15 protein.  

PubMed

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 (1)H(N), (15)N, (13)C', and (13)C(?), as well as side chain (13)C(?), 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. PMID:21544738

Yin, Cuifeng; Aramini, James M; Ma, Li-Chung; Cort, John R; Swapna, G V T; Krug, Robert M; Montelione, Gaetano T

2011-10-01

334

Tricarboxylic acid cycle inhibition by Li+ in the human neuroblastoma SH-SY5Y cell line: a 13C NMR isotopomer analysis.  

PubMed

Li+ effects on glucose metabolism and on the competitive metabolism of glucose and lactate were investigated in the human neuroblastoma SH-SY5Y cell line using 13C NMR spectroscopy. The metabolic model proposed for glucose and lactate metabolism in these cells, based on tcaCALC best fitting solutions, for both control and Li+ conditions, was consistent with: (i) a single pyruvate pool; (ii) anaplerotic flux from endogenous unlabelled substrates; (iii) no cycling between pyruvate and oxaloacetate. Li+ was shown to induce a 38 and 53% decrease, for 1 and 15 mM Li+, respectively, in the rate of glucose conversion into pyruvate, when [U-13C]glucose was present, while no effects on lactate production were observed. Pyruvate oxidation by the tricarboxylic acid cycle and citrate synthase flux were shown to be significantly reduced by 64 and 84% in the presence of 1 and 15 mM Li+, respectively, suggesting a direct inhibitory effect of Li+ on tricarboxylic acid cycle flux. This work also showed that when both glucose and lactate are present as energetic substrates, SH-SY5Y cells preferentially consumed exogenous lactate over glucose, as 62% of the acetyl-CoA was derived from [3-13C]lactate while only 26% was derived from [U-13C]glucose. Li+ did not significantly affect the relative utilisation of these two substrates by the cells or the residual contribution of unlabelled endogenous sources for the acetyl-CoA pool. PMID:16095758

Fonseca, Carla P; Jones, John G; Carvalho, Rui A; Jeffrey, F Mark H; Montezinho, Liliana P; Geraldes, Carlos F G C; Castro, M M C A

2005-11-01

335

13C CP MAS NMR and GIAO-CHF/DFT calculations of flavonoids: Morin, kaempferol, tricin, genistein, formononetin and 3,7-dihydroxyflavone  

NASA Astrophysics Data System (ADS)

13C CP MAS NMR spectra of the flavonoids: morin, kaempferol, 3,7-dihydroxyflavone, tricin and isoflavones: genistein and formononetin were recorded to characterize solid-state conformations. Intramolecular hydrogen bonds forming five-, six- and seven-membered rings are present in the two morin molecules in the crystals - their 13C resonances have been assigned with the aid of the calculated shielding constants. Linear relationships between the calculated shielding constants ?DFT (ppm) and chemical shifts ( ?CPMAS, ppm) were obtained for all studied compounds. Higher correlation coefficients suggest that the conformation with "clockwise" orientation of both OH groups is more probable in the solid 3,7-dihydroxyflavone, whereas in the solid formononetin the OH and OCH 3 substituents are directed "anticlockwise". The barrier to the rotation of phenyl ring B decreases in the order: morin (2'-OH, 3-OH) > kaempferol (3-OH) > tricin.

Zieli?ska, Agnieszka; Paradowska, Katarzyna; Jakowski, Jacek; Wawer, Iwona

2008-02-01

336

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

337

Stoichiometric relationship between Na(+) ions transported and glucose consumed in human erythrocytes: Bayesian analysis of (23)Na and (13)C NMR time course data.  

PubMed

We examined the response of Na(+),K(+)-ATPase (NKA) to monensin, a Na(+) ionophore, with and without ouabain, an NKA inhibitor, in suspensions of human erythrocytes (red blood cells). A combination of (13)C and (23)Na NMR methods allowed the recording of intra- and extracellular Na(+), and (13)C-labeled glucose time courses. The net influx of Na(+) and the consumption of glucose were measured with and without NKA inhibited by ouabain. A Bayesian analysis was used to determine probability distributions of the parameter values of a minimalist mathematical model of the kinetics involved, and then used to infer the rates of Na(+) transported and glucose consumed. It was estimated that the numerical relationship between the number of Na(+) ions transported by NKA per molecule of glucose consumed by a red blood cell was close to the ratio 6.0:1.0, agreeing with theoretical prediction. PMID:23601315

Puckeridge, Max; Chapman, Bogdan E; Conigrave, Arthur D; Grieve, Stuart M; Figtree, Gemma A; Kuchel, Philip W

2013-04-16

338

False AA'X Spin-Spin Coupling Systems in 13C NMR: Examples Involving Phosphorus and a 20-Year-Old Mystery in Off-Resonance Decoupling  

NASA Astrophysics Data System (ADS)

It is common in both NMR textbooks and journal articles to loosely describe certain ABX spin systems, in which the nuclei in the AB pair are rendered chemically inequivalent by proximity of one to 12C and the other to 13C, as AA'X spin systems. While the chemical shifts normally are indistinguishable and so for all practical purposes such systems can be analyzed as AA'X, there is a danger that when the chemical shifts are not the same, one may fail to recognize that fact due to the assumption that the isotopomer shift is always insignificant. Examples of such false AA'X spectra are described for diphosphorus organic and organometallic compounds, in which DeltavPP' = 2.5 - 4 Hz using a 400 MHz (1H) NMR spectrometer; at lower field strength the ABX splitting might be expected to disappear due to the reduction in DeltavPP'. An example involving 13C off-resonance decoupling in the NMR spectra of maleic anhydride was shown to depend on decoupler power: at low power, the system is ABX, while at the high power normally used it is AA'X. The chemical inequivalence of the "AA'" pair in this 1H213C system is not due to an isotopic shift, but rather to the off-resonance irradiation itself, and the results explain a 20-year-old discrepancy in published spectra.

Hersh, William H.

1997-12-01

339

Linear free energy relationships of the 1H and 13C NMR chemical shifts of 3-methylene-2-substituted-1,4-pentadienes  

NASA Astrophysics Data System (ADS)

Linear free energy relationships (LFER) were applied to the 1H and 13C NMR chemical shifts ( ?N, N= 1H and 13C, respectively) in the unsaturated backbone of cross-conjugated trienes 3-methylene-2-substituted-1,4-pentadienes. The NMR data were correlated using five different LFER models, based on the mono, the dual and the triple substituent parameter (MSP, DSP and TSP, respectively) treatment. The simple and extended Hammett equations, and the three postulated unconventional LFER models obtained by adaptation of the later, were used. The geometry data, which are needed in Karplus-type and McConnell-type analysis, were obtained using semi-empirical MNDO-PM3 calculations. In correlating the data the TSP approach was more successful than the MSP and DSP approaches. The fact that the calculated molecular geometries allow accurate prediction of the NMR data confirms the validity of unconventional LFER models used. These results suggest the s- cis conformation of the cross-conjugated triene as the preferred one. Postulated unconventional DSP and TSP equations enable the assessment of electronic substituent effects in the presence of other interfering influences.

Valenti?, Nataša V.; Vitnik, Željko; Kozhushkov, Sergei I.; de Meijere, Armin; Uš?umli?, Gordana S.; Jurani?, Ivan O.

2005-06-01

340

Multidimensional solid-state NMR studies of the structure and dynamics of pectic polysaccharides in uniformly 13C-labeled Arabidopsis primary cell walls  

SciTech Connect

Plant cell wall (CW) polysaccharides are responsible for the mechanical strength and growth of plant cells; however, the high-resolution structure and dynamics of the CW polysaccharides are still poorly understood because of the insoluble nature of these molecules. Here, we use 2D and 3D magic-angle-spinning (MAS) solid-state NMR (SSNMR) to investigate the structural role of pectins in the plant CW. Intact and partially depectinated primary CWs of Arabidopsis thaliana were uniformly labeled with 13C and their NMR spectra were compared. Recent 13C resonance assignment of the major polysaccharides in Arabidopsis thaliana CWs allowed us to determine the effects of depectination on the intermolecular packing and dynamics of the remaining wall polysaccharides. 2D and 3D correlation spectra show the suppression of pectin signals, confirming partial pectin removal by chelating agents and sodium carbonate. Importantly, higher cross peaks are observed in 2D and 3D 13C spectra of the depectinated CW, suggesting higher rigidity and denser packing of the remaining wall polysaccharides compared with the intact CW. 13C spin–lattice relaxation times and 1H rotating-frame spin–lattice relaxation times indicate that the polysaccharides are more rigid on both the nanosecond and microsecond timescales in the depectinated CW. Taken together, these results indicate that pectic polysaccharides are highly dynamic and endow the polysaccharide network of the primary CW with mobility and flexibility, which may be important for pectin functions. This study demonstrates the capability of multidimensional SSNMR to determine the intermolecular interactions and dynamic structures of complex plant materials under near-native conditions. Copyright © 2012 John Wiley & Sons, Ltd.

Dick-Perez, Marilu; Wang, Tuo; Salazar, Andre; Zabotina, Olga A.; Hong, Mei

2012-07-08

341

Internal motion time scales of a small, highly stable and disulfide-rich protein: a 15N, 13C NMR and molecular dynamics study.  

PubMed

Motions of the backbone C alpha H alpha and threonine C beta H beta bonds of toxin alpha were investigated using natural abundance 13C NMR and molecular dynamics. Measurement of the 13C longitudinal and transverse relaxation rates employed ACCORDION techniques together with coherence selection by pulsed field gradients and sensitivity enhancement through the use of preservation of equivalent pathway, thus allowing a considerable reduction of the required spectrometer time. 13C R1, R2, 1H-->13C NOE were obtained, as well as the variations of R1 rho (90 degrees) as a function of the rf field strength. These data were compared to those recorded by 1H and 15N NMR on a labelled sample of the toxin [Guenneugues et al. (1997) Biochemistry, 36, 16097-16108]. Both sets of data showed that picosecond to nanosecond time scale motions are well correlated to the secondary structure of the protein. This was further reinforced by the analysis of a 1 ns molecular dynamics simulation in water. Several C alpha H alpha and threonine C beta H beta experimentally exhibit fast motions with a correlation time longer than 500 ps, that cannot be sampled along the simulation. In addition, the backbone exhibits motions on the microsecond to millisecond time scale on more than half of its length. Thus, toxin alpha, a highly stable protein (Tm = 75 degrees C at acidic pH) containing 61 amino acids and 4 disulfides, shows important internal motions on time scales ranging from 0.1-0.5 ps, to 10-100 ps, 1 ns, and about 30 microseconds to 10 ms. PMID:10382305

Guenneugues, M; Gilquin, B; Wolff, N; Ménez, A; Zinn-Justin, S

1999-05-01

342

Complete assignments of the (1)H and (13)C chemical shifts and J(H,H) coupling constants in NMR spectra of D-glucopyranose and all D-glucopyranosyl-D-glucopyranosides.  

PubMed

Complete assignment of the (1)H and (13)C NMR spectra of all possible d-glucopyranosyl-d-glucopyranosides was performed and the (1)H chemical shifts and proton-proton coupling constants were refined by computational spectral analyses (using PERCH NMR software) until full agreement between the calculated and experimental spectra was achieved. To support the experimental results, the (1)H and (13)C chemical shifts and the spin-spin coupling constants between the non-hydroxyl protons of alpha- and beta-d-glucopyranose (1a and 1b) were calculated with density functional theory (DFT) methods at the B3LYP/pcJ-2//B3LYP/6-31G(d,p) level of theory. The effects of different glycosidic linkage types and positions on the glucose ring conformations and on the alpha/beta-ratio of the reducing end hydroxyl groups were investigated. Conformational analyses were also performed for anomerically pure forms of methyl d-glucopyranosides (13a and 13b) and fully protected derivatives such as 1,2,3,4,6-penta-O-acetyl-d-glucopyranoses (14a and 14b). PMID:17980865

Roslund, Mattias U; Tähtinen, Petri; Niemitz, Matthias; Sjöholm, Rainer

2008-01-14

343

Distinctive influence of two hexafluoro solvents on the structural stabilization of Bombyx mori silk fibroin protein and its derived peptides: 13C NMR and CD studies.  

PubMed

Employing high-resolution (13)C solution NMR and circular dichroism (CD) spectroscopic techniques, the distinctive influence of two intimately related hexafluoro solvents, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and hexafluoroacetone trihydrate (HFA), on the structural characteristics of Bombyx mori (B. mori) silk fibroin, the chymotrypsin precipitate (C(p)) fraction, and two synthetic peptides, (AGSGAG)(5) and (AG)(15), is described. The observed (13)C solution NMR and CD spectra of these polypeptides in HFIP and HFA revealed a distinctive influence on their conformational characteristics. The (13)C NMR spectra, as analyzed from the unique chemical shifts of C(alpha) and C(beta) resonances of constituent residues revealed that fibroin largely assumes helical conformation(s) in both solvents. However, the peak shifts were greater for the samples in HFIP, indicating that the types of helical structure(s) may be different from the one populated in HFA. Similar structural tendencies of these polypeptides were reflected in CD spectra. The observed CD patterns, i.e., a strong positive band at approximately 190 nm and negative bands at approximately 206 and 222 nm, have been attributed to the preponderance of helical structures. Of the two prevalent helical structures, alpha-helix and 3(10)-helix, the evidence emerged for the fibroin protein in favor of 3(10)-helical structure stabilization in HFIP and its significant disruption in HFA, as deduced from the characteristic R1 (=[theta](190)/[theta](202)) and R2 (=[theta](222)/[theta](206)) ratios, determined from the CD data. Conversely, the native polypeptides and synthetic peptide fragments derived from highly crystalline regions of the silk fibroin protein sustained predominantly an unordered structure in HFA solvent. PMID:16398492

Ha, Sung-Won; Asakura, Tetsuo; Kishore, Raghuvansh

2006-01-01

344

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

345

1H and 13C NMR Chemical Shift Assignments and Conformational Analysis for the Two Diastereomers of the Vitamin K Epoxide Reductase Inhibitor Brodifacoum  

SciTech Connect

Proton and 13C NMR chemical shift assignments and 1H-1H scalar couplings for the two diastereomers of the vitamin K epoxide reductase (VKOR) inhibitor brodifacoum have been determined from acetone solutions containing both diastereomers. Data were obtained from homo- and heteronuclear correlation spectra acquired at 1H frequencies of 750 and 900 MHz over a 268-303 K temperature range. Conformations inferred from scalar coupling and 1-D NOE measurements exhibit large differences between the diastereomers. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Cort, John R.; Cho, Herman M.

2009-10-01

346

Homogeneous Catalysis of the Water Gas Shift Reaction by Bridged Dinuclear Pyrazolate Rhodium Complexes. FT-IR, 1H and 13C NMR In Situ Studies  

Microsoft Academic Search

Homogeneous catalysts for the water gas shift reaction prepared from Rh2(µ-Pz)2(COD)2 (Pz = pyrazolate ion and COD = 1,5-cyclooctadiene) in aqueous organic solvent media (pyridine, 4-picoline or 2-ethoxyethanol) and Rh2(µ-Pz)2(CO)2(TPPMS)2 (TPPMS = meta-sulfonatophenyl-diphenyldiphosphine) in acidic aqueous media under mild conditions are described. In situ FT-IR, 1H and 13C NMR spectroscopic studies of the Rh2(µ-Pz)2(COD)2 catalytic system reveal the presence of

A. J. Pardey; M. Fernández; M. A. Moreno; J. Alvarez; A. B. Rivas; M. C. Ortega; B. Mendez; P. J. Baricelli; C. Longo

2000-01-01

347

Short, synthetic and selectively 13C-labeled RNA sequences for the NMR structure determination of protein-RNA complexes  

PubMed Central

We report an optimized synthesis of all canonical 2?-O-TOM protected ribonucleoside phosphoramidites and solid supports containing [13C5]-labeled ribose moieties, their sequence-specific introduction into very short RNA sequences and their use for the structure determination of two protein–RNA complexes. These specifically labeled sequences facilitate RNA resonance assignments and are essential to assign a high number of sugar–sugar and intermolecular NOEs, which ultimately improve the precision and accuracy of the resulting structures. This labeling strategy is particularly useful for the study of protein–RNA complexes with single-stranded RNA in solution, which is rapidly an increasingly relevant research area in biology.

Wenter, Philipp; Reymond, Luc; Auweter, Sigrid D.; Allain, Frederic H.-T.; Pitsch, Stefan

2006-01-01

348

Solid-state 13C NMR study of banana liquid crystals - 2: Alkyl tail-group packing environments in the hexagonal columnar phase  

NASA Astrophysics Data System (ADS)

Solid-state 13C nuclear magnetic resonance (NMR) measurements were performed in order to obtain the packing structure of alkyl tail in the hexagonal columnar phase of the banana-shaped N(1,7)-S16 molecule. In this phase, NMR chemical shifts assigned to the internal methylene carbons at an amorphous state appear as two peaks, indicating that the two alkyl tails are placed under two different chemical environments. From combined cross-polarization/magic-angle spinning and pulse saturation transfer/magical-angle spinning measurements, two alkyl tails were found to have the different mobility. Such two different environments are not unusual in conventional mesophases, but in the hexagonal columnar phase formed by cylindrical columns composed of enclosed smectic layers; one of the alkyl tails is located inside and the other is located outside the columnar structure.

Kurosu, Hiromichi; Endo, Yumi; Kimura, Saori; Hashimoto, Tomoko; Harada, Motoi; Lee, Eun-Woo; Sone, Masato; Watanabe, Junji; Kang, Sungmin

2013-05-01

349

Solid-state 13C NMR study of banana liquid crystals - 1: Two different alkyl tail-group packing environments in the B7 phase  

NASA Astrophysics Data System (ADS)

Solid-state 13C nuclear magnetic resonance (NMR) measurements were performed for the B7 phase of the banana-shaped molecule P-8-O-PIMB(NO 2). In this phase, NMR chemical shifts assigned to five methylene carbons on the alkyl tail appear as at least seven peaks, indicating that the two alkyl tails within a single molecule have different packing structures. Combined CP/MAS and PST/MAS measurements show that one of the alkyl tails has dense packing with low molecular mobility and the other has loose packing with high molecular mobility. Thus, it can be concluded that both the polar bent and molecular axes are tilted toward the layer in the B7 phase of P-8-O-PIMB(NO 2), exhibiting molecular leaning.

Kurosu, Hiromichi; Nakanishi, Saki; Kimura, Saori; Kang, Sungmin; Li, Xiaodong; Sone, Masato; Watanabe, Junji

2012-01-01

350

The Synthesis, Characterization, and Application of 13C-Methyl Isocyanide as an NMR Probe of Heme Protein Active Sites  

PubMed Central

The cytochromes P450 (CYPs) play a central role in a variety of important biological oxidations, such as steroid synthesis and the metabolism of xenobiotic compounds, including most drugs. Because CYPs are frequently assayed as drug targets or as anti-targets, tools that provide confirmation of active-site binding and information on binding orientation would be of great utility. Of greatest value are assays that are reasonably high throughput. Other heme proteins, too—such as the nitric oxide synthases (NOSs), with their importance in signaling, regulation of blood pressure, and involvement in the immune response—often display critical roles in the complex functions of many higher organisms, and also require improved assay methods. To this end, we have developed an analog of cyanide, with a 13CH3-reporter group attached to make methyl isocyanide. We describe the synthesis and use of 13C-methyl isocyanide as a probe of both bacterial (P450cam) and membrane-bound mammalian (CYP2B4) CYPs. The 13C-methyl isocyanide probe can be used in a relatively high-throughput 1-D experiment to identify binders, but it can also be used to detect structural changes in the active site based on chemical shift changes, and potentially nuclear Overhauser effects between probe and inhibitor.

McCullough, Christopher; Pullela, Phani Kumar; Im, Sang-Choul; Waskell, Lucy; Sem, Daniel

2014-01-01

351

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

2008-09-10

352

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

353

Theoretical and experimental 1H, 13C and 15N NMR studies of N-alkylation of substituted tetrazolo[1,5-a]pyridines.  

PubMed

The (15)N as well as (1)H and (13)C chemical shifts of nine substituted tetrazolopyridines and their corresponding tetrazolopyridinium salts have been determined by using NMR spectroscopy at the natural abundance level of all nuclei in CD(3)CN. In this paper, we report, for the first time, the N-alkylation reaction of electron deficient tetrazolopyridines. The treatment of tetrazolopyridines 5-13 with one equivalent of trialkyloxonium tetrafluoroborate leads to a mixture of two isomers, i.e. N3- and N2-alkyl tetrazolo[1,5-a]pyridinium salts. It has been observed that the N3-isomer is always the major isomer, except in the case of the CF(3) substituent, where the two isomers are obtained in the same amount. The quaternary tetrazolopyridinium nitrogen N3 is shielded by around 100 ppm (parts per million) with respect to the parent tetrazolopyridine. Experimental data are interpreted by means of density functional theory (DFT) calculations, including solvent-induced effects, within the conductor-like polarizable continuum model (CPCM). Good agreements between theoretical and experimental (1)H, (13)C and (15)N NMR were found. The combination of multinuclear magnetic resonance spectroscopy with gauge including atomic orbital (GIAO) DFT calculations is a powerful tool in the structural elucidation for both neutral and cationic heterocycles and in the determination of the orientation of N-alkylation of tetrazolopyridines. PMID:19937909

Berionni, Guillaume; Pégot, Bruce; Goumont, Régis

2010-02-01

354

Crystallinity and Miscibility of Poly(vinyl isobutyl ether)/Poly(?-L-lysine) Blends by Solid State 13C NMR Study  

NASA Astrophysics Data System (ADS)

The relation between crystallinity and miscibility of semicrystalline polymer blends of poly(vinyl isobutyl ether) (PVIBE) and poly(?-L-lysine) (?-PL) is investigated by 13C cross-polarization with magic-angle-spinning (CPMAS) NMR (nuclear magnetic resonance) and DSC measurements. Analysis of the 1H spin-lattice relaxation curves observed from both PVIBE and ?-PL signals, which are indirectly obtained from well-resolved 13C CPMAS NMR spectra, suggested that the domains of ?-PL in the blends are in the range of 50-100 nm scale. Two-spin or three-spin models were used to simulate the 1H relaxation curves taking into account the contribution of a 1H spin-diffusion rate between PVIBE and ?-PL. Furthermore, it was found that blending ?-PL largely influences the crystallinity of PVIBE but that of ?-PL is little affected by blending PVIBE except for 10/1 composition. The observed melting point of ?-PL shifted towards lower temperature accompanied by PVIBE content. This shift was explained by the Gibbs-Thomson effect that the decrease of thickness of crystalline phase causes the depression of the melting point.

Asano, Atsushi; Murata, Yoshifumi; Kurotsu, Takuzo

355

Search for basic relationships between "molecular size" and "chemical structure" of aquatic natural organic matter--answers from 13C and 15N CPMAS NMR spectroscopy.  

PubMed

To investigate the structural composition of natural organic matter (NOM), a 3-step micro- and ultrafiltration procedure was applied to 3 surface waters from southern Germany, and fractions from all filtration steps were collected. The NOM was characterized using solid-state 13C and 15N nuclear magnetic resonance (NMR) techniques. Routine integration of the 13C NMR spectra and extended data analysis procedures were carried out for a quantitative comparison of the structural components as well as for the elucidation of structural fractionation patterns. A common feature of the large molecular size fractions was the predominance of polysaccharide material, with the dissolved high molecular weight organics being mostly enriched in N-acetylated polysaccharides derived from microbial leftovers. Aromatic structures like lignin and tannin derivatives were most abundant in the intermediate size fraction. All membranes were found to be highly permeable for branched aliphatics, i.e. isoprenoids. Fouling layers of the ultrafiltration membrane were significantly enriched in long-chain aliphatics (lipids). Biofouling was not observed on any of the membranes. Overall, a strong interdependence between the chemical structural characteristics of NOM components and their size, shape, or interaction characteristics could be shown. The results provide the basis for a better understanding of water process technologies as treatment effectiveness is strongly dependent on the chemical composition and the "size" distribution of NOM. PMID:17959215

Lankes, Ulrich; Lüdemann, Hans-Dietrich; Frimmel, Fritz H

2008-02-01

356

Characterization of the adsorbed state of isoprene on alumina and copper-alumina catalysts by sup 13 C NMR and in situ diffuse reflectance infrared spectroscopy  

SciTech Connect

In situ {sup 13}C NMR spectroscopy and diffuse reflectance infrared spectroscopy (DRIFTS) have been used to characterize the adsorbed states of isoprene on both {gamma}-Al{sub 2}O{sub 3} and Cu/{gamma}-Al{sub 2}O{sub 3} catalysts. Both techniques have been shown to be quite complementary and provide very fine information. Isoprene molecules are physisorbed only at room temperature on alumina. On reduced copper-alumina, isoprene is mainly physisorbed, but a few chemisorbed species are evidenced. Taking into account the {sup 13}C NMR line-width variations and the IR results, an adsorption model is proposed for Cu/{gamma}-Al{sub 2}O{sub 3}: reduced copper induces a selective orientation for the physisorbed isoprene molecules. The chemisorbed species detected by DRIFTS is attributed to a {pi}-complex of isoprene with Cu{sup +} sites on the reduced copper-alumina spinel surface. The physisorbed species is the precursor of this {pi}-complex, and this view agrees with the selectivity of isoprene hydrogenation on copper catalysts.

Rigole, M.; Depecker, C.; Wrobel, G.; Legrand, P.; Guelton, M.; Bonnelle, J.P. (Universite des Sciences et Techniques de Lille Flandres-Artois, Villeneuve d'Ascq (France))

1990-08-23

357

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

358

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

359

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

360

An alternative NMR method to determine nuclear shielding anisotropies for molecules in liquid-crystalline solutions with (13)C shielding anisotropy of methyl iodide as an example.  

PubMed

An alternative NMR method for determining nuclear shielding anisotropies in molecules is proposed. The method is quite simple, linear and particularly applicable for heteronuclear spin systems. In the technique, molecules of interest are dissolved in a thermotropic liquid crystal (LC) which is confined in a mesoporous material, such as controlled pore glass (CPG) used in this study. CPG materials consist of roughly spherical particles with a randomly oriented and connected pore network inside. LC Merck Phase 4 was confined in the pores of average diameter from 81 to 375 A and LC Merck ZLI 1115 in the pores of average diameter 81 A. In order to demonstrate the functionality of the method, the (13)C shielding anisotropy of (13)C-enriched methyl iodide, (13)CH(3)I, was determined as a function of temperature using one dimensional (13)C NMR spectroscopy. Methane gas, (13)CH(4), was used as an internal chemical shift reference. It appeared that methyl iodide molecules experience on average an isotropic environment in LCs inside the smallest pores within the whole temperature range studied, ranging from bulk solid to isotropic phase. In contrast, in the spaces in between the particles, whose diameter is approximately 150 microm, LCs behave as in the bulk. Consequently, isotropic values of the shielding tensor can be determined from spectra arising from molecules inside the pores at exactly the same temperature as the anisotropic ones from molecules outside the pores. Thus, for the first time in the solution state, shielding anisotropies can easily be determined as a function of temperature. The effects of pore size as well as of different LC media on the shielding anisotropy are examined and discussed. PMID:18338070

Tallavaara, Pekka; Jokisaari, Jukka

2008-03-28

361

Plant cell wall profiling by fast maximum likelihood reconstruction (FMLR) and region-of-interest (ROI) segmentation of solution-state 2D 1H-13C NMR spectra  

PubMed Central

Background Interest in the detailed lignin and polysaccharide composition of plant cell walls has surged within the past decade partly as a result of biotechnology research aimed at converting biomass to biofuels. High-resolution, solution-state 2D 1H–13C HSQC NMR spectroscopy has proven to be an effective tool for rapid and reproducible fingerprinting of the numerous polysaccharides and lignin components in unfractionated plant cell wall materials, and is therefore a powerful tool for cell wall profiling based on our ability to simultaneously identify and comparatively quantify numerous components within spectra generated in a relatively short time. However, assigning peaks in new spectra, integrating them to provide relative component distributions, and producing color-assigned spectra, are all current bottlenecks to the routine use of such NMR profiling methods. Results We have assembled a high-throughput software platform for plant cell wall profiling that uses spectral deconvolution by Fast Maximum Likelihood Reconstruction (FMLR) to construct a mathematical model of the signals present in a set of related NMR spectra. Combined with a simple region of interest (ROI) table that maps spectral regions to NMR chemical shift assignments of chemical entities, the reconstructions can provide rapid and reproducible fingerprinting of numerous polysaccharide and lignin components in unfractionated cell wall material, including derivation of lignin monomer unit (S:G:H) ratios or the so-called SGH profile. Evidence is presented that ROI-based amplitudes derived from FMLR provide a robust feature set for subsequent multivariate analysis. The utility of this approach is demonstrated on a large transgenic study of Arabidopsis requiring concerted analysis of 91 ROIs (including both assigned and unassigned regions) in the lignin and polysaccharide regions of almost 100 related 2D 1H–13C HSQC spectra. Conclusions We show that when a suitable number of replicates are obtained per sample group, the correlated patterns of enriched and depleted cell wall components can be reliably and objectively detected even prior to multivariate analysis. The analysis methodology has been implemented in a publicly-available, cross-platform (Windows/Mac/Linux), web-enabled software application that enables researchers to view and publish detailed annotated spectra in addition to summary reports in simple spreadsheet data formats. The analysis methodology is not limited to studies of plant cell walls but is amenable to any NMR study where ROI segmentation techniques generate meaningful results. Please see Research Article: http://www.biotechnologyforbiofuels.com/content/6/1/46/.

2013-01-01

362

NMR detection of side chain–side chain hydrogen bonding interactions in 13C\\/15N-labeled proteins  

Microsoft Academic Search

We describe the direct observation of side chain–side chain hydrogen bonding interactions in proteins with sensitivity-enhanced NMR spectroscopy. Specifically, the remote correlation between the guanidinium nitrogen 15Ne of arginine 71, which serves as the hydrogen donor, and the acceptor carboxylate carbon 13CO2? of aspartate 100 in a 12 kDa protein, human FKBP12, is detected via the trans-hydrogen bond 3hJNe CO2? coupling

Aizhuo Liu; Weidong Hu; Ananya Majumdar; Michael K. Rosen; Dinshaw J. Patel

2000-01-01

363

Rapid 3D NMR using the filter diagonalization method: application to oligosaccharides derivatized with 13C-labeled acetyl groups  

Microsoft Academic Search

Rapid 3D NMR spectroscopy of oligosaccharides having isotopically labeled acetyl “isotags” was made possible with high resolution in the indirect dimensions using the filter diagonalization method (FDM). A pulse sequence was designed for the optimal correlation of acetyl methyl protons, methyl carbons, and carbonyl carbons. The multi-dimensional nature of the FDM, coupled with the advantages of constant-time evolution periods, resulted

Geoffrey S. Armstrong; Kristin E. Cano; Vladimir A. Mandelshtam; A. J. Shaka; Brad Bendiakb

2004-01-01

364

Trace level detection of compounds related to the chemical weapons convention by 1H-detected 13C NMR spectroscopy executed with a sensitivity-enhanced, cryogenic probehead.  

PubMed

Two-dimensional 1H-13C HSQC (heteronuclear single quantum correlation) and fast-HMQC (heteronuclear multiple quantum correlation) pulse sequences were implemented using a sensitivity-enhanced, cryogenic probehead for detecting compounds relevant to the Chemical Weapons Convention present in complex mixtures. The resulting methods demonstrated exceptional sensitivity for detecting the analytes at trace level concentrations. 1H-13C correlations of target analytes at < or = 25 microg/mL were easily detected in a sample where the 1H solvent signal was approximately 58,000-fold more intense than the analyte 1H signals. The problem of overlapping signals typically observed in conventional 1H spectroscopy was essentially eliminated, while 1H and 13C chemical shift information could be derived quickly and simultaneously from the resulting spectra. The fast-HMQC pulse sequences generated magnitude mode spectra suitable for detailed analysis in approximately 4.5 h and can be used in experiments to efficiently screen a large number of samples. The HSQC pulse sequences, on the other hand, required roughly twice the data acquisition time to produce suitable spectra. These spectra, however, were phase-sensitive, contained considerably more resolution in both dimensions, and proved to be superior for detecting analyte 1H-13C correlations. Furthermore, a HSQC spectrum collected with a multiplicity-edited pulse sequence provided additional structural information valuable for identifying target analytes. The HSQC pulse sequences are ideal for collecting high-quality data sets with overnight acquisitions and logically follow the use of fast-HMQC pulse sequences to rapidly screen samples for potential target analytes. Use of the pulse sequences considerably improves the performance of NMR spectroscopy as a complimentary technique for the screening, identification, and validation of chemical warfare agents and other small-molecule analytes present in complex mixtures and environmental samples. PMID:18345646

Cullinan, David B; Hondrogiannis, George; Henderson, Terry J

2008-04-15

365

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  

NASA Astrophysics Data System (ADS)

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 4000-400 cm -1. The UV-vis absorption spectrum of the compound that dissolved in methanol was recorded in the range of 200-800 nm. The 1H and 13C 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.

Cinar, Mehmet; Coruh, Ali; Karabacak, Mehmet

2011-12-01

366

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

2011-12-01

367

Spectral Atlas of the nu(Sub 12) Fundamental of (13)C(12)CH6 in the 12 Micron Region.  

National Technical Information Service (NTIS)

The recent discovery of the minor isotopomer of ethane, (13)C(12)CH6, in the planetary atmospheres of Jupiter and Neptune, added ethane to the molecules which can be used to determine isotopic (12)C(12)C ratios for the jovian planets. The increased spectr...

M. Weber D. C. Reuter J. M. Sirota W. E. Blass J. J. Hillman

1994-01-01

368

High nematic ordering in a bent-core smectogen showing a biaxial nematic phase: A 13C NMR study  

NASA Astrophysics Data System (ADS)

Carbon-13 NMR spectroscopy has been used to probe the orientational ordering of a bent-core liquid crystal A131. Both the carbon chemical shift tensors in a rotating solid sample and chemical shifts from the aligned mesophases were determined. These results allow us to probe the local order parameters of the five phenyl rings in the liquid crystalline molecule. It is found that the conformation and ordering of the bent-shaped core significantly change between the uniaxial and biaxial nematic phases, with the highest local nematic order not associated to the central ring in this azo substituted bent-core mesogen.

Dong, Ronald Y.; Kumar, Satyendra; Prasad, Veena; Zhang, Jing

2007-11-01

369

Solid-state 13C NMR studies of dissolved organic matter in pore waters from different depositional environments  

USGS Publications Warehouse

Dissolved organic matter (DOM) in pore waters from sediments of a number of different depositional environments was isolated by ultrafiltration using membranes with a nominal molecular weight cutoff of 500. This > 500 molecular weight DOM represents 70-98% of the total DOM in these pore waters. We determined the gross chemical structure of this material using both solid-state 13C nuclear magnetic resonance spectroscopy and elemental analysis. Our results show that the DOM in these pore waters appears to exist as two major types: one type dominated by carbohydrates and paraffinic structures and the second dominated by paraffinic and aromatic structures. We suggest that the dominance of one or the other structural type of DOM in the pore water depends on the relative oxidizing/reducing nature of the sediments as well as the source of the detrital organic matter. Under dominantly anaerobic conditions carbohydrates in the sediments are degraded by bacteria and accumulate in the pore water as DOM. However, little or no degradation of lignin occurs under these conditions. In contrast, sediments thought to be predominantly aerobic in character have DOM with diminished carbohydrate and enhanced aromatic character. The aromatic structures in the DOM from these sediments are thought to arise from the degradation of lignin. The large amounts of paraffinic structures in both types of DOM may be due to the degradation of unidentified paraffinic materials in algal or bacterial remains. ?? 1987.

Orem, W. H.; Hatcher, P. G.

1987-01-01

370

13C NMR, 15N NMR and quantum-chemical study of the tautomerism of 2-substituted 5-Me-7-OH-1,2,4-triazolo[1,5-a]pyrimidines  

NASA Astrophysics Data System (ADS)

The 13C and 15N NMR spectra of a series of differently 2-substituted 5-Me-7-OH-1,2,4-triazolo[1,5-a]pyrimidines were recorded and the chemical shifts assigned by employing the whole arsenal of 1D and 2D NMR spectroscopic methods. Both the 13C chemical shifts of the C-7 carbon atoms and the line shape of the 15N resonances of N-3 and N-4, respectively, were not sufficiently characteristic to differentiate the lactim and the three lactam tautomers of the compounds studied. However, by calculating both the formation energies and the 13C as well as 15N chemical shifts of the various tautomers by quantumchemical ab-initio calculations at the 6-31G? level, the preferred tautomer(s) could be unequivocally assigned. The solvent effect on the present tautomerism, which proved very strong, could be studied quantitatively by including the present NMR solvent in the accompanying calculations employing a self-consistent isodensity polarized continuum model (SCIPCM).

Kleinpeter, E.; Koch, A.; Fischer, G.; Askolin, C.-P.

1997-11-01

371

Time-resolved 1H and 13C NMR spectroscopy for detailed analyses of the Azotobacter vinelandii mannuronan C-5 epimerase reaction.  

PubMed

AlgE2, AlgE4, and AlgE6 are members of a family of mannuronan C-5 epimerases encoded by Azotobacter vinelandii, and are active in the biosynthesis of alginate, where they catalyze the post-polymerization conversion of beta-D-mannuronic acid residues into alpha-L-guluronic acid residues. To study the kinetics and mode of action of these enzymes, homopolymeric mannuronan and other alginate samples with various composition were epimerized by letting the enzymatic reaction take place in an NMR tube. Series of 1H NMR spectra were recorded to obtain a time-resolved picture of the epimerization progress and the formation of specific monomer sequences. Starting from mannuronan, guluronic acid contents of up to 82% were introduced by the enzymes, and the product specificity, substrate selectivity, and reaction rates have been investigated. To obtain direct information of the GulA-block formation, similar experiments were performed using a 13C-1-enriched mannuronan as substrate. The NMR results were found to be in good agreement with data obtained by a radioisotope assay based on 3H-5-labeled substrates. PMID:11985894

Hartmann, Martin; Duun, Anne Sissel; Markussen, Sidsel; Grasdalen, Hans; Valla, Svein; Skjåk-Braek, Gudmund

2002-03-15

372

Dipolar-dephasing 13C NMR studies of decomposed wood and coalified xylem tissue: Evidence for chemical structural changes associated with defunctionalization of lignin structural units during coalification  

USGS Publications Warehouse

A series of decomposed and coalified gymnosperm woods was examined by conventional solid-state 13C nuclear magnetic resonance (NMR) and by dipolar-dephasing NMR techniques. The results of these NMR studies for a histologically related series of samples provide clues as to the nature of codification reactions that lead to the defunctionalization of lignin-derived aromatic structures. These reactions sequentially involve the following: (1) loss of methoxyl carbons from guaiacyl structural units with replacement by hydroxyls and increased condensation; (2) loss of hydroxyls or aryl ethers with replacement by hydrogen as rank increases from lignin to high-volatile bituminous coal; (3) loss of alkyl groups with continued replacement by hydrogen. The dipolar-dephasing data show that the early stages of coalification in samples examined (lignin to lignite) involve a decreasing degree of protonation on aromatic rings and suggest that condensation is significant during coalification at this early stage. An increasing degree of protonation on aromatic rings is observed as the rank of the sample increases from lignite to anthracite.

Hatcher, P. G.

1988-01-01

373

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

374

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

375

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

376

Structural diversity of amyloid fibril formed in human calcitonin as revealed by site-directed 13C solid-state NMR spectroscopy.  

PubMed

Fibril formation in human calcitonin (hCT) from aqueous solution at pH 4.1 was examined and compared with those at pH 3.3 and 7.5 corresponding to three different net charges by means of site-directed (13)C solid-state NMR spectroscopy. Notably, the observed (13)C chemical shifts and lineshapes of the (13)C CP/MAS spectra differed substantially among fibrils prepared at different pHs. It was found that antiparallel beta-sheet structures were formed at pH 7.5 and 4.1 in the central core regions. In the C-terminal region, random coils were formed at both pH 7.5 and 4.1, although the random coil region at pH 4.1 was larger than that at pH 7.5. Fibrillation kinetics analyzed by a two-step autocatalytic reaction mechanism showed that the rate constants k(1) and k(2) for nucleation and maturation reactions of the fibril formation, respectively, were separately determined and the values correlated well with the net positive charges of Lys(18) and His(20) rather than the existence of a negative charge of Asp(15). Further, an attempt was made to assess interatomic distances between amide nitrogen and carbonyl carbon of neighboring chains of (13)C, (15)N-labeled hCT and a model pentapeptide by (13)C REDOR measurements by taking into account its dipolar interaction analyzed by the 3 spin system proposed previously. A unique chain packing of the antiparallel beta-sheets was proposed as a dominant fibril structure, although the possibility of a contribution of chain packing consisting of sliding one or two residues perpendicular to the fibril direction cannot be ruled out. In addition, it appears that the phenyl rings of Phe(16) are aligned on the same side of the beta-sheet and make the beta-sheet stable by forming pi-pi interactions between the beta-strands. PMID:14745805

Naito, Akira; Kamihira, Miya; Inoue, Ryozo; Saitô, Hazime

2004-02-01

377

A joined theoretical-experimental investigation on the 1H and 13C NMR signatures of defects in poly(vinyl chloride).  

PubMed

1H and 13C chemical shifts of PVC chains have been evaluated using quantum chemistry methods in order to evidence and interpret the NMR signatures of chains bearing unsaturated and branched defects. The geometrical structures of the stable conformers have been determined using molecular mechanics and the OPLS force field and then density functional theory with the B3LYP functional and the 6-311G(d) basis set. The nuclear shielding tensor has been calculated at the coupled-perturbed Kohn-Sham level (B3LYP exchange-correlation functional) using the 6-311+G(2d,p) basis set. The computational scheme accounts for the large number of stable conformers of the PVC chains, and average chemical shifts are evaluated using the Maxwell-Boltzmann distribution. Moreover, the chemical shifts are corrected for the inherent and rather systematic errors of the method of calculation by employing linear regression equations, which have been deduced from comparing experimental and theoretical results on small alkane model compounds containing Cl atoms and/or unsaturations. For each type of defect, PVC segments presenting different tacticities have been considered because it is known from linear PVC chains that the racemic (meso) dyads are characterized by larger (smaller) chemical shifts. NMR signatures of unsaturations in PVC chains have been highlighted for the internal -CH=CH- and -CH=CCl- units as well as for terminal unsaturations like the chloroallylic -CH=CH-CH2Cl group. In particular, the 13C chemical shifts of the two sp2 C atoms are very close for the chloroallylic end group. The CH2 and CHCl units surrounding an unsaturation present also specific 13C chemical shifts, which allow distinguishing them from the others. In the case of the proton, the CH2 unit of the -CHCl-CH2-CCl=CH- segment presents a larger chemical shift (2.6-2.7 ppm), while some CHCl units close to the -CH=CH- unsaturations appear at rather small chemical shifts (3.7 ppm). The -CH2Cl and -CHCl-CH2Cl branches also display specific signatures, which result in large part from modifications of the equilibrium conformations and their reduced number owing to the increased steric interactions. These branches lead to the appearance of 13C peaks at lower field associated either to the CH unit linking the -CH2Cl and -CHCl-CH2Cl branches (50 ppm) or to the CHCl unit of the ethyl branches (60 ppm). The corresponding protons resonate also at specific frequencies: 3.5-4.0 ppm for the -CH2Cl branch or 3.8-4.2 ppm for the terminal unit of the -CHCl-CH2Cl branch. Several of these signatures have been detected in the experimental 1H and 13C NMR spectra and are consistent with the reaction mechanisms. PMID:18975894

d'Antuono, Philippe; Botek, Edith; Champagne, Benoît; Wieme, Joris; Reyniers, Marie-Françoise; Marin, Guy B; Adriaensens, Peter J; Gelan, Jan M

2008-11-27

378

NMR studies of nucleic acids. Deuterium isotope effects on sup 13 C chemical shifts in hydrogen-bonded complexes of pyrimidines and purines  

SciTech Connect

{sup 13}C NMR spectra were recorded for chloroform solutions of 2',3'-O-isopropylidene-5'-O-acetyladenosine (1), 2',3',5'-O-tribenzoyluridine (2), 2',3'-O-isopropylidene-5'-O-acetyluridine (2a), 2',3'-O-isopropylidene-5'-O-(tert-butyldimethylsilyl)guanosine (3), and 2',3'-O-isopropylidene-5'-O-(tert-butyldimethylsilyl)cytidine (4) in which the imino hydrogens were partially exchanged with deuterium. Upfield two-bond deuterium isotope effects (DIE) on {sup 13}C chemical shifts were detected under conditions of slow exchange as multiple peaks for the appropriate resonances and ranged in magnitude from 40 ppB for the amino interaction with C2 in guanosine to 217 ppB for the imino interaction with C4 in the uridine self-association dimer. {sup 13}C chemical shifts and DIEs for 2 were measured at 12 different concentrations from 219 to 231 K. The data were used in an iterative procedure to estimate chemical shifts at C2 and C4 for monomeric and dimeric forms of 2, equilibrium constants and enthalpies for self-association, and the distribution of isomeric self-association dimers. Enthalpies for formation of hydrogen bonds to C2 and C4 in 2 were similar, {Delta}H = {minus}1.8 kcal/mol. DIEs at C2 and C4 increased upon formation of a hydrogen bond to the carbonyl oxygens. The maximal increase for each center was estimated to be 90 ppB. Small increases were also observed in DIEs when nucleosides 1-4 were mixed with their complementary bases. 38 refs., 3 figs., 7 tabs.

Gmeiner, W.H.; Poulter, C.D.

1988-11-09

379

The structure and (local) stability constants of borate esters of mono- and di-saccharides as studied by 11B and 13C NMR spectroscopy.  

PubMed

The formation of borate esters of various mono- and di-saccharides in aqueous solution was studied by 11B and 13C NMR spectroscopy. Association constants K(B-L) at a carbohydrate-borate molar ratio of 1:1, pH 7, and 25 degrees C were determined and compared with literature values obtained from potentiometry. The association constants K(B-L) were converted into local association constants Kloc(B-L) by using the distribution of the various anomeric forms in D2O. In this way, values of Kloc(B-L) were obtained, which appear to be characteristic of the configuration concerned. They explain the favourable effect of borate in the alkaline isomerisation of lactose into lactulose. At a low molar ratio (1:3) of carbohydrate-borate, predominantly diborate esters (B-)2L were formed. PMID:8156542

van den Berg, R; Peters, J A; van Bekkum, H

1994-02-01

380

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

381

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

382

Low-temperature cross-polarization/magic angle spinning /sup 13/C NMR of solid methane hydrates: structure, cage occupancy, and hydration number  

SciTech Connect

/sup 13/C NMR spectra of methane trapped in solid type I hydrate and in a mixed methane/propane type II hydrate were studied at -80/sup 0/C under cross-polarization and magic angle spinning conditions. Type I could be distinguished from type II structures due to the chemical shift pattern of methane trapped in the large and small cages. In agreement with the statistical theory of clathrate hydrate formation, methane was found to occupy both large and small cages in each structure to a significant extent. In the case of type I methane hydrate, the distribution of methane over the two sites was obtained, and together with a previous determination of the ..mu.. potential of the empty lattice with respect to ice, a hydration number of 6.05 +/- 0.06 was determined.

Ripmeester, J.A.; Ratcliffe, C.I.

1988-01-28

383

Conformation and molecular packing of n-alkyl side chains protruding from ?-helical poly ( L-glutamates) as studied by 13C CP/MAS NMR spectroscopy  

NASA Astrophysics Data System (ADS)

13C NMR spectra of a series of poly( L-glutamates) with n-alkyl side chains of various lengths ( n = (number of carbon atoms in the alkyl group) = 8, 12, 14, 16 and 18) were recorded by the cross polarization/magic angle spinning method, in order to elucidate conformational features and molecular packing through the observation of 13 13C chemical shifts. From these experimental results, it was found that the main chain of the poly(?- n-alkyl L-glutamates) takes the ?-helical conformation irrespective of side chain length, and the n-alkyl side chains can participate in the crystallization if they are long enough. In these side chain crystallites, all- trans zigzag conformation of alkyl chain was clarified and the type of molecular packing was presumed based on the reference data of n-alkanes. Further, we discuss the conformation of n-alkyl side chains of poly( n-stearyl L-glutamate) in isotropic solution and liquid crystalline solution.

Tsukahara, Makoto; Yamanobe, Takeshi; Komoto, Tadashi; Watanabe, Junji; Ando, Isao; Uematsu, Ichitaro

1987-07-01

384

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

385

Fingerprints of molecular structure and hydrogen bonding effects in the /sup 13/C NMR spectra of monosaccharides with partially deuterated hydroxyls  

SciTech Connect

A new NMR approach to structure elucidation of carbohydrates in solution is presented. Examined in detail are the isotopic multiplets in /sup 13/C NMR spectra that result from partial deuteration of the hydroxyls for a series of monosaccharides and some of their deoxy and methyl glycoside derivatives in Me/sub 2/SO-d/sub 6/ solutions. Chemical shift and isotope effect data are presented for the pyranose and furanose forms of aldopentoses, aldohexoses, and ketohexoses. The results show that the magnitude of the ..gamma.. effect resulting from deuteration of a hydroxyl on a vicinal carbon atoms is sensitive to the relative geometric relationship, cis or trans, of the hydroxyls in vicinal diol arrays. Thus, the multiplet pattern for carbons 3 and 4 of the pyranose ring can serve as a fingerprint of molecular structure at the pentopyranose level. The aldopentoses and ketohexoses are amenable to structural analysis by this simple approach. Ambiguity will arise for pairs of aldohexoses related to each other by epimerization at C5. Intramolecular hydrogen bonding between the hydroxyls at C2 and C4 in ..cap alpha..-D-talopyranose gives rise to some unusual effects. A mechanism involving isotopic perturbation of the equilibrium between the hydrogen-bonded structures O4-H...O2-H and O2-H...O4-H is suggested as the possible source of these effects. Similarly, the extra splitting observed in the /sup 13/C resonance of C3 of ..beta..-D-fucofuranose are rationalized in terms of an equilibrium between the hydrogen-bonded structures C5-O5-H...O3-H and Cl-O1-H...O3-H. The approach of isotopic multiplets appears to be uniquely suited for the study of such structures.

Reuben, J.

1984-10-17