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1

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

PubMed

Two robust combinations of spectral editing techniques with 2D (13)C-(13)C NMR have been developed for characterizing the aromatic components of (13)C-enriched low-temperature carbon materials. One method (exchange with protonated and nonprotonated spectral editing, EXPANSE) selects cross peaks of protonated and nearby nonprotonated carbons, while the other technique, dipolar-dephased double-quantum/single-quantum (DQ/SQ) NMR, selects signals of bonded nonprotonated carbons. Both spectra are free of a diagonal ridge, which has many advantages: Cross peaks on the diagonal or of small intensity can be detected, and residual spinning sidebands or truncation artifacts associated with the diagonal ridge are avoided. In the DQ/SQ experiment, dipolar dephasing of the double-quantum coherence removes protonated-carbon signals; this approach also eliminates the need for high-power proton decoupling. The initial magnetization is generated with minimal fluctuation by combining direct polarization, cross polarization, and equilibration by (13)C spin diffusion. The dipolar dephased DQ/SQ spectrum shows signals from all linkages between aromatic rings, including a distinctive peak from polycondensed aromatics. In EXPANSE NMR, signals of protonated carbons are selected in the first spectral dimension by short cross polarization combined with dipolar dephasing difference. This removes ambiguities of peak assignment to overlapping signals of nonprotonated and protonated aromatic carbons, e.g. near 125 ppm. Spin diffusion is enhanced by dipolar-assisted rotational resonance. Before detection, C-H dipolar dephasing by gated decoupling is applied, which selects signals of nonprotonated carbons. Thus, only cross peaks due to magnetization originating from protonated C and ending on nearby nonprotonated C are retained. Combined with the chemical shifts deduced from the cross-peak position, this double spectral editing defines the bonding environment of aromatic, COO, and C=O carbons, which is particularly useful for identifying furan and arene rings. The C=O carbons, whose chemical shifts vary strongly (between 212 and 165 ppm) and systematically depend on their two bonding partners, show particularly informative cross peaks, given that one bonding partner is defined by the other frequency coordinate of the cross peak. The new techniques and the information content of the resulting spectra are validated on sulfuric-acid treated low-temperature carbon materials and on products of the Maillard reaction. The crucial need for spectral editing for correct peak assignment is demonstrated in an example. PMID:23871898

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

2013-09-01

2

13C NMR spectral characterization of epimeric rotenone and some related tetrahydrobenzopyranofurobenzopyranones  

USGS Publications Warehouse

The 13C nuclear magnetic resonance (nmr) spectra of epimers of rotenone and four 12a-hydroxy-analogues were examined to determine the stereochemical effect of the B/C ring fusion involving the 6a- and 12a-carbon centers. Chemical shift differences between the epimeric carbon resonances of cis- and trans-6a,12a-compounds were notably larger than those of diastereoisomers derived from the same B/C ring junction stereochemistry. Results of the spectral analysis have been useful for the quantification of mixtures of epimers and for the measurement of rates of epimerization and oxygenation.

Abidi, S.L.; Abidi, M.S.

1983-01-01

3

13C-nmr spectral assignment and evaluation of the cytotoxic potential of rotenone.  

PubMed

Unambiguous 13C-nmr assignments for the widely used pesticide rotenone have been made through the judicious use of APT, CSCM 1D, and selective INEPT spectroscopy. Also, in order to more fully characterize the biologic potential of rotenone, studies were performed with cultured cells. Intense, but nonspecific, activity was observed in the P-388 lymphocytic leukemia, KB carcinoma of the nasopharynx, and a number of human cancer cell types: e.g., HT-1080 human fibrosarcoma, LU-1 lung cancer, COL-2 colon cancer, MEL-2 melanoma, and BC-1 breast cancer cell lines in vitro. PMID:2614425

Blaskó, G; Shieh, H L; Pezzuto, J M; Cordell, G A

1989-01-01

4

Spectrally edited 2D 13 C NMR spectra without diagonal ridge  

E-print Network

structure Melanoidin structure Furan rings Ketones Double-quantum NMR a b s t r a c t Two robust is particularly useful for identifying furan and arene rings. The C@O carbons, whose chemical shifts vary strongly

Hong, Mei

5

Solid state 13C NMR of unlabeled phosphatidylcholine bilayers: spectral assignments and measurement of carbon-phosphorus dipolar couplings and 13C chemical shift anisotropies.  

PubMed

The direct measurement of 13C chemical shift anisotropies (CSA) and 31P-13C dipolar splitting in random dispersions of unlabeled L alpha-phase phosphatidylcholine (PC) has traditionally been difficult because of extreme spectral boradening due to anisotropy. In this study, mixtures of dimyristoyl phosphatidylcholine (DMPC) with three different detergents known to promote the magnetic orientation of DMPC were employed to eliminate the powder-pattern nature of signals without totally averaging out spectral anisotropy. The detergents utilized were CHAPSO, Triton X-100, and dihexanoylphosphatidylcholine (DHPC). Using such mixtures, many of the individual 13C resonances from DMPC were resolved and a number of 13C-31P dipolar couplings were evident. In addition, differing line widths were observed for the components of some dipolar doublets, suggestive of dipolar/chemical shift anisotropy (CSA) relaxation interference effects. Oriented sample resonance assignments were made by varying the CHAPSO or DHPC to DMPC ratio to systematically scale overall bilayer order towards the isotropic limit. In this manner, peaks could be identified based upon extrapolation to their isotropic positions, for which assignments have previously been made (Lee, C.W.B., and R.G. Griffin. 1989. Biophys. J. 55:355-358; Forbes, J., J. Bowers, X. Shan, L. Moran, E. Oldfield, and M.A. Moscarello. 1988. J. Chem. Soc., Faraday, Trans. 1 84:3821-3849). It was observed that the plots of CSA or dipolar coupling versus overall bilayer order obtained from DHPC and CHAPSO titrations were linear. Estimates of the intrinsic dipolar couplings and chemical shift anisotropies for pure DMPC bilayers were made by extrapolating shifts and couplings from the detergent titrations to zero detergent. Both detergent titrations led to similar "intrinsic" CSAs and dipolar couplings. Results extracted from an oriented Triton-DMPC mixture also led to similar estimates for the detergent-free DMPC shifts and couplings. The results from these experiments were found to compare favorably with limited measurements made from pure L alpha PC. This detergent-based method for assigning spectra and for determining dipolar couplings and CSA in detergent-free systems should be extendable to other lipid systems. The resulting data set from this study may prove useful in future modeling of the structure and dynamics of DMPC bilayers. In addition, the fact that experiments utilizing each of the three detergents led to similar estimates for the spectral parameters of pure DMPC, and the fact that spectral parameter versus bilayer order plots were linear, indicate that the averaged conformation and dynamics of DMPC in the presence of the three detergents are very similar to those of pure L alpha DMPC. PMID:8431541

Sanders, C R

1993-01-01

6

Isolation of Spinasterol and its Glucoside from Cell Suspension Cultures of Saponaria officinalis: 13C-NMR Spectral Data and Batch Culture Production.  

PubMed

Spinasterol and spinasteryl glucoside have been isolated as the exclusive sterols from cell suspension cultures of SAPONARIA OFFICINALIS and identified by MS, (1)H-NMR and (13)C-NMR spectral data. This result confirms the taxonomical vicinity of this plant to Chenopodiaceae and Amaranthaceae where Delta (7)-sterols were also described to be present. With more than 44% of total sterol content, the spinasteryl glucoside content is higher than in most of the common plants. This shows a particularly active glycosylation process probably in relation with the biosynthesis of saponosides. PMID:17340524

Henry, M; Chantalat-Dublanche, I

1985-08-01

7

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

PubMed Central

Aplysina is the best representative genus of the family Aplysinidae. Halogenated substances are its main class of metabolites. These substances contribute greatly to the chemotaxonomy and characterization of the sponges belonging to this genus. Due to their pharmacological activities, these alkaloids are of special interest. The chemistry of halogenated substances and of the alkaloids has long been extensively studied in terrestrial organisms, while the number of marine organisms studied has just started to increase in the last decades. This review describes 101 halogenated substances from 14 species of Aplysina from different parts of the world. These substances can be divided into the following classes: bromotyramines (A), cavernicolins (B), hydroverongiaquinols (C), bromotyrosineketals (D), bromotyrosine lactone derivatives (E), oxazolidones (F), spiroisoxazolines (G), verongiabenzenoids (H), verongiaquinols (I), and dibromocyclohexadienes (J). A compilation of their 13C NMR data is also part of the review. For this purpose 138 references were consulted. PMID:22163189

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

2011-01-01

8

1H and 13C NMR spectral studies of some 4H-3,1-benzoxazin-4-ones and their 2-acylaminobenzoic acid precursors.  

PubMed

The 1H and 13C NMR spectra of twelve 4H-3,1-benzoxazine-4-ones and of their acylaminobenzoic acid precursors are presented. Differentiation between these two series of compounds is best achieved through the characteristic J(CH) coupling interactions in the high frequency carbonyl region. Some 4H-pyrido[2,3-d][1,3]oxazin-4-ones have also been studied and some earlier literature assignments revised. PMID:10845537

Osborne, A G; Goolamali, Z

2000-05-01

9

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

ERIC Educational Resources Information Center

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

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

2007-01-01

10

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

NASA Astrophysics Data System (ADS)

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 1H and 13C 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 1H and 13C 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.

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

2014-12-01

11

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

12

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

13

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. PMID:14679498

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

2006-01-01

14

Medium and Long-Distance 1H– 13C Heteronuclear Correlation NMR in Solids  

Microsoft Academic Search

A simple method for obtaining 1H–13C HETCOR solid-state NMR spectra reflecting only medium- and long-range 1H–13C correlation peaks is presented. By dephasing the magnetization of protons directly bonded to a 13C nucleus, the short-range correlation peaks, which contain limited structural information, can be cleanly suppressed without reducing the long-range cross peaks significantly. The resulting reduction of resonance overlap simplifies spectral

X. L. Yao; K. Schmidt-Rohr; M. Hong

2001-01-01

15

1H and 13C NMR assignments for the cyanine dyes SYBR Safe and thiazole orange.  

PubMed

Analysis of (1)H and (13)C NMR and mass spectral data for the fluorescent nucleic acid stain SYBR Safe indicates that it contains a cyanine-based cationic core structure identical to thiazole orange. The difference between these two compounds is the type of N-substitution on the quinolinium ring system (SYBR Safe, n-Pr; thiazole orange, Me). The (1)H and (13)C NMR resonances for both compounds were assigned on the basis of one- and two-dimensional (COSY, ROESY, HSQC, and HMBC) experiments. The preferred conformation of these compounds was computed by ab initio methods and found to be consistent with the NMR data. PMID:23137048

Evenson, William E; Boden, Lauren M; Muzikar, Katy A; O'Leary, Daniel J

2012-12-01

16

Theoretical studies on structures, 13 C NMR chemical shifts, aromaticity,  

E-print Network

of capping hydrogen atoms at the open ends of a SWCNT changes the chemical activity of the SWCNTTheoretical studies on structures, 13 C NMR chemical shifts, aromaticity, and chemical reactivity The geometries, chemical shifts, aromaticity, and reactivity of finite-length open-ended armchair single- walled

Wang, Yan Alexander

17

13C NMR assessment of decomposition patterns during composting of forest and shrub biomass  

Microsoft Academic Search

A laboratory experiment was designed to investigate the degradation patterns of leaves from 12 forest and shrub species typical of Mediterranean ecosystems by solid-state 13C NMR. The spectral data have been compared with those for the major organic fractions, and elementary composition in three transformation stages (zero time, intermediated and advanced (168 d)). The plant material in general showed a

G Almendros; J Dorado; F. J González-Vila; M. J Blanco; U Lankes

2000-01-01

18

Natural-abundance sup 13 C NMR study of glycogen repletion in human liver and muscle  

SciTech Connect

Optimizing the surface-coil design and spectral-acquisition parameters has led to the observation of the {sup 13}C NMR natural abundance glycogen signal in man at 2.1 T. Both the human muscle and hepatic glycogen signals can be detected definitively with a time resolution of {approx}13 min. A {sup 1}H/{sup 13}C concentric surface coil was used. The {sup 1}H outer coil was 11 cm in diameter; the {sup 13}C inner coil was 8 cm in diameter. The coils were tuned to 89.3 MHz and 22.4 MHz, respectively. The {sup 1}H coil was used for optimizing field homogeneity (shimming) the magnet and for single-frequency decoupling of the C{sub 1} glycogen signal. Total power deposition from both the transmitter pulse and the continuous wave decoupling did not exceed the Food and Drug Administration guideline of 8 W/kg of tissue. Experiments were done for which healthy subjects returned to the magnets at different times for {sup 13}C NMR measurement. The spectral difference between experiments was within the noise in the C{sub 1} glycogen region. Because of the spectral reproducibility and the signal sensitivity, hepatic glycogen repletion can be followed. Four hours postprandial, hepatic glycogen increases by 3.8 times from the basal fasted state. The hepatic glycogen data correspond directly to previous biopsy results and support the use of {sup 13}C NMR as a noninvasive probe of human metabolism.

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

1989-03-01

19

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

20

Spectral editing in 13C solid-state NMR at high magnetic field using fast MAS and spin-echo dephasing.  

PubMed

A simple method is proposed for separating NMR resonances from protonated and non-protonated aromatic carbons in solids under fast magic angle spinning (MAS). The approach uses a MAS-synchronized spin-echo to exploit the differences in rotational recoupling of the dipolar interactions while fully refocusing the isotropic chemical shifts. This strategy extends the relevant time scale of spin evolution to milliseconds and circumvents the limitation of the traditional dipolar dephasing method, which in fast rotating solids is disrupted by rotational refocusing. The proposed approach can be used for quantitative measurement of carbon aromaticities in complex solids with poorly resolved spectra, as demonstrated for model compounds. PMID:22951436

Mao, Kanmi; Kennedy, Gordon J; Althaus, Stacey M; Pruski, Marek

2012-01-01

21

Complete 1H and 13C NMR spectra of pregnenolone.  

PubMed

Assignments for signals from 1H and 13C in the NMR spectra of pregnenolone (1), 16-dehydropregnenolone (2), and the 3-acetate of 1 (3) were validated by two-dimensional correlated spectroscopy (2D COSY) and heteronuclear single quantum coherence (HSQC). The narrow band of overlapping signals from H-7, H-2, and H-4 was resolved by exploiting three-bond coupling in the 2D COSY spectra and heteronuclear correlation. Assignments were based on high intensity cross peaks from long-range coupling by H-18 with H-17 and H-12 (axial). Similar cross peaks were observed for H-17 with H-21. Low intensity cross peaks were seen for H-4 coupled with H-6 and H-7, and also H-16 (quasi-axial) with H-14 of 1 and 3. Assignments based on 2D COSY spectra were confirmed by correlation peaks from HSQC. This now corrects the earlier conflicts among assignments reported for 13C signals of 1 and 3. Accurate assignments were similarly derived for signals from C-2, C-7, C-8, and C-21 of 1 and 3, and C-15 and C-16 of 1, 2, and 3. The complete sets of 1H and 13C NMR data for pregnenolone, pregnenolone 3-acetate, and 16-dehydropregnenolone serve as reference standards. PMID:7676476

Szendi, Z; Forgó, P; Sweet, F

1995-06-01

22

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. PMID:22172286

Xiang, Yun; Shen, Jun

2012-01-01

23

Accurate measurements of 13C-13C distances in uniformly 13C-labeled proteins using multi-dimensional four-oscillating field solid-state NMR spectroscopy  

NASA Astrophysics Data System (ADS)

Application of sets of 13C-13C internuclear distance restraints constitutes a typical key element in determining the structure of peptides and proteins by magic-angle-spinning solid-state NMR spectroscopy. Accurate measurements of the structurally highly important 13C-13C distances in uniformly 13C-labeled peptides and proteins, however, pose a big challenge due to the problem of dipolar truncation. Here, we present novel two-dimensional (2D) solid-state NMR experiments capable of extracting distances between carbonyl (13C') and aliphatic (13Caliphatic) spins with high accuracy. The method is based on an improved version of the four-oscillating field (FOLD) technique [L. A. Straasø, M. Bjerring, N. Khaneja, and N. C. Nielsen, J. Chem. Phys. 130, 225103 (2009)] which circumvents the problem of dipolar truncation, thereby offering a base for accurate extraction of internuclear distances in many-spin systems. The ability to extract reliable accurate distances is demonstrated using one- and two-dimensional variants of the FOLD experiment on uniformly 13C,15N-labeled-L-isoleucine. In a more challenging biological application, FOLD 2D experiments are used to determine a large number of 13C'-13Caliphatic distances in amyloid fibrils formed by the SNNFGAILSS fibrillating core of the human islet amyloid polypeptide with uniform 13C,15N-labeling on the FGAIL fragment.

Straasø, Lasse Arnt; Nielsen, Jakob Toudahl; Bjerring, Morten; Khaneja, Navin; Nielsen, Niels Chr.

2014-09-01

24

Two-Dimensional Dynamic-Director 13 C NMR of Liquid Crystals  

E-print Network

director, in synchrony with the acquisition of a 2D chemical shift correlation spectrum. By monitoringTwo-Dimensional Dynamic-Director 13 C NMR of Liquid Crystals Dan McElheny, Min Zhou, and Lucio resonance (NMR) experiment for facilitating the resolution and assignment of liquid crystalline 13 C NMR

Frydman, Lucio

25

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

NASA Astrophysics Data System (ADS)

A simple new method is presented that yields quantitative solid-state magic-angle spinning (MAS) 13C NMR spectra of organic materials with good signal-to-noise ratios. It achieves long (>10 ms) cross polarization (CP) from 1H 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 1H 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 1H 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 13C 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.

Johnson, Robert L.; Schmidt-Rohr, Klaus

2014-02-01

26

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

PubMed Central

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

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

1985-01-01

27

Magic-angle-spinning 13C NMR with atomic resolution of a photosynthetic reaction center enriched in [4?-13C]tyrosine  

NASA Astrophysics Data System (ADS)

Low-temperature magic-angle-spinning (MAS) 13C NMR was used to investigate reaction centers of Rhodobacters sphaeroides R26 specifically enriched in [4'- 13C]tyrosine, allowing the investigation of variations in chemical environment, in particular at the phenolic oxygen. The level of incorporation was determined with mass spectrometry and is ?98%. Magic-angle-spinning 13C difference NMR spectra with atomic resolution were obtained. In the signal of the 28 tyrosines only five MAS patterns with different isotropic shifts and intensities are observed. Most of the spectral intensity is spread over two components (?60% and ?30%). This suggests that the protein provides mainly two different chemical environments, which is ascribed to the polar and non-polar protein regions. Two small MAS patterns contain ?4% of the total integrated intensity, corresponding with the signal intensities of individual tyrosines, and have an unusually low isotropic shift. This may reflect interactions with the cofactors, for instance ring-currents in the macroaromatic cycles. The data provide compelling evidence that all tyrosines in the dark-adapted R26 photosynthetic reaction centers are normally protonated.

de Groot, H. J. M.; Raap, J.; Winkel, C.; Hoff, A. J.; Lugtenburg, J.

1990-06-01

28

13 C NMR spectroscopic characterization of trimethylol propane ester lubricants  

Microsoft Academic Search

The ability to identify the different acyl groups present in lubricants composed of mixed acid esters of trimethylol propane\\u000a by13C nuclear magnetic resonance spectroscopy is demonstrated. The technique discriminates between esters with acyl groups containing\\u000a between 5 and 10 carbon atoms and can be used similarly to identify acyl groups in pentaerythritol or neopentyl glycol ester\\u000a lubricants.

P. W. R. Smith

1992-01-01

29

1H, 15N and 13C NMR Assignments of Mouse Methionine Sulfoxide Reductase B2  

PubMed Central

A recombinant mouse methionine-r-sulfoxide reductase 2 (MsrB2?S) isotopically labeled with 15N and 15N/13C was generated. We report here the 1H, 15N and 13C NMR assignments of the reduced form of this protein. PMID:19636904

Breivik, Ashild S.; Aachmann, Finn L.; Sal, Lena S.; Kim, Hwa-Young; Del Conte, Rebecca; Gladyshev, Vadim N.; Dikiy, Alexander

2011-01-01

30

NATURAL ABUNDANCE 13C NMR SPECTROSCOPY OF DOUBLE-STRANDED DNA  

EPA Science Inventory

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

31

A comparative CP\\/MAS 13C-NMR study of cellulose structure in spruce wood and kraft pulp  

Microsoft Academic Search

CP\\/MAS 13C-NMR spectroscopy in combination with spectral fitting was used to study the supermolecular structure of the cellulose fibril in spruce wood and spruce kraft pulp. During pulping, structures contributing to inaccessible surfaces in the wood cellulose are converted to the cellulose Iß allomorph, that is, the degree of order is increased. This increase is also accompanied by a conversion

Eva-Lena Hult; Per Tomas Larsson; Tommy Iversen

2000-01-01

32

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. PMID:24109452

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

2013-01-01

33

{sup 13}C and {sup 31}P NMR study of paramagnetic lanthanide(III) texaphyrins  

SciTech Connect

{sup 13}C NMR was used to study the rare earth complexes, LnTx(NO{sub 3}){sub 2} (Ln = La, Ce, Pr, Nd, Eu, Y; Tx = texaphyrins). The authors present {sup 31}P NMR spectra for rare earth diphenyl phosphonates.

Lisowski, J.; Sessler, J.L.; Mody, T.D. [Univ. of Texas, Austin, TX (United States)

1995-08-16

34

/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

35

Metabolite Characterization in Peritoneal Dialysis Effluent Using High-resolution 1H and 1H-13C NMR Spectroscopy  

E-print Network

Metabolite analysis of peritoneal dialysis (PD) effluent may provide information regarding onset and progression of complications associated with prolonged PD therapy. In this context, the NMR detectable small metabolites of PD effluent samples were characterized using high resolution 1H and 1H-13C NMR spectroscopy. The various spectra were recorded (at 800 MHz proton frequency) on PD effluent samples obtained after 4 hour (intraperitoneal) dwell time from patients with end stage renal failure (ESRF) and continuing normally on PD therapy. Inspite of devastating spectral feature of PD effluent due to the presence of intense resonances from glucose and lactate, we were able to identify about 53 small endogenous metabolites (including many complex coupled spin systems) and more than 90 % of the total CH cross peaks of 1H-13C HSQC spectrum were identified specific to various metabolites of PD effluent. We foresee that the characteristic fingerprints of various metabolites of control PD effluent samples will be us...

Guleria, Anupam; Rawat, Atul; Khetrapal, C L; Prasad, Narayan; Kumar, Dinesh

2014-01-01

36

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

SciTech Connect

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

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

1988-03-01

37

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

38

Diastereotopic splitting in the 13C NMR spectra of sulfur homofullerenes and methanofullerenes with chiral fragments.  

PubMed

Using gauge-invariant atomic orbital PBE/3? quantum chemistry approach, (13)C NMR chemical shifts and diastereotopic splittings of sp(2) fullerenyl carbons of a number of sulfur homofullerenes and methanofullerenes have been predicted and discussed. An anisochrony of fullerene carbons is caused by a chiral center of attached moieties. Clearly distinguishable diastereotopic pairs (from 8 to 11) of fullerenyl carbons of homofullerenes were observed. Unambiguous assignments of (13)C NMR chemical shifts were performed, and diastereotopic splittings of methanofullerenes were observed for ?, ? and ? to a functionalization site. PMID:24347398

Tulyabaev, Arthur R; Tuktarov, Airat R; Khalilov, Leonard M

2014-01-01

39

Probing 27Al-13C proximities in metal-organic frameworks using dynamic nuclear polarization enhanced NMR spectroscopy.  

PubMed

We show how (27)Al-(13)C proximities in the microporous metal-organic framework MIL-100(Al) can be probed using advanced (27)Al-(13)C NMR methods boosted by Dynamic Nuclear Polarization. PMID:24301188

Pourpoint, Frédérique; Thankamony, Aany Sofia Lilly; Volkringer, Christophe; Loiseau, Thierry; Trébosc, Julien; Aussenac, Fabien; Carnevale, Diego; Bodenhausen, Geoffrey; Vezin, Hervé; Lafon, Olivier; Amoureux, Jean-Paul

2014-01-28

40

Solid-State 13C NMR of Liquid Crystalline Polyesters: Variations in Morphology, Alignment, and Dynamics within a Homologous Series  

E-print Network

D and 2D NMR experiments also illustrated substantial differences in the degree of motional dynamicsSolid-State 13C NMR of Liquid Crystalline Polyesters: Variations in Morphology, Alignment liquid crystals. 13C NMR experiments showed that the nematic ordering achieved by these synthetic

Frydman, Lucio

41

Isotopic 13C NMR spectrometry to assess counterfeiting of active pharmaceutical ingredients: site-specific 13C content of aspirin and paracetamol.  

PubMed

Isotope profiling is a well-established technique to obtain information about the chemical history of a given compound. However, the current methodology using IRMS can only determine the global (13)C content, leading to the loss of much valuable data. The development of quantitative isotopic (13)C NMR spectrometry at natural abundance enables the measurement of the (13)C content of each carbon within a molecule, thus giving simultaneous access to a number of isotopic parameters. When it is applied to active pharmaceutical ingredients, each manufactured batch can be characterized better than by IRMS. Here, quantitative isotopic (13)C NMR is shown to be a very promising and effective tool for assessing the counterfeiting of medicines, as exemplified by an analysis of aspirin (acetylsalicylic acid) and paracetamol (acetaminophen) samples collected from pharmacies in different countries. It is proposed as an essential complement to (2)H NMR and IRMS. PMID:19481896

Silvestre, Virginie; Mboula, Vanessa Maroga; Jouitteau, Catherine; Akoka, Serge; Robins, Richard J; Remaud, Gérald S

2009-10-15

42

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

PubMed Central

The simultaneous quantification of excitatory and inhibitory neurotransmission and the associated energy metabolism is crucial for a proper understanding of brain function. While the detection of glutamatergic neurotransmission in vivo by 13C NMR spectroscopy is now relatively routine, the detection of GABAergic neurotransmission in vivo has remained elusive due to the low GABA concentration and spectral overlap. Using 1H-[13C] NMR spectroscopy at high magnetic field in combination with robust spectral modeling and the use of different substrates, [U-13C6]-glucose and [2-13C]-acetate, it is shown that GABAergic, as well as glutamatergic neurotransmitter fluxes can be detected non-invasively in rat brain in vivo. PMID:19818103

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

2010-01-01

43

13C NMR spectra for IPR isomers of fullerene C 86  

Microsoft Academic Search

Structures of all the 19 isolated-pentagon-rule abiding isomers of fullerene C86 have been optimized using density functional theory at the B3LYP\\/6-31G level of theory. Isomers 16 and 17 have low total energies and large HOMO–LUMO gaps. 13C NMR chemical shieldings are obtained employing the gauge-independent atomic orbital method. The good agreement between the predicted and the measured NMR spectra allows

Guangyu Sun; Miklos Kertesz

2002-01-01

44

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

45

Development of a 13C-Optimized 1.5-mm High Temperature Superconducting NMR Probe  

PubMed Central

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

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

2013-01-01

46

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

47

Adiabatic 1H decoupling scheme for very accurate intensity measurements in 13C NMR  

NASA Astrophysics Data System (ADS)

Adiabatic proton decoupling has been optimized in order to obtain accurate quantitative measurements of intensities on 13C NMR spectra. For each offset, the minimum adiabaticity factor (Km) reached during the pulse was computed. This Km profile was used to optimize the peak value and the swept frequency range of the adiabatic pulses. With a cosinus amplitude modulation, offset-independent-adiabaticity, and the M4P5-M4P9-M4P5'-M4P9' phase cycle, an accuracy of 2‰ for the 13C NMR measurements was reached. An approach using bi-labeled 13C acetic acid and ethanol at 99% allowed a fine experimental determination of the uniformity of the decoupling profile. The comparison with WALTZ-16 highlights the improvements in the uniformity of the proton decoupling.

Tenailleau, Eve; Akoka, Serge

2007-03-01

48

High-resolution proton NMR studies of intracellular metabolites in yeast using 13C decoupling  

NASA Astrophysics Data System (ADS)

The resolution and specificity of 1H NMR in studies of yeast cellular metabolism were increased by feeding a 13C-labeled substrate and observing 1H difference spectra in the presence and absence of 13C decoupling fields. [2- 13C]Acetate was utilized as a respiratory substrate in an aerobic suspension of Saccharomyces cerevisiae. The broad cellular background proton resonances are removed by the technique, leaving only signals from the protons of the substrate, or its metabolites, that are coupled to 13C. Spectra of the yeast suspension after acetate feeding show the disappearance of label from the acetate pool and the subsequent appearance of 13C in glutamate C 3 and C 4 and in aspartate C 3. These results are in accord with the known fluxes of metabolites. Selective single-frequency 13C decoupling was used to provide assignments for the difference signals. The limitations on single-frequency decoupling coming from finite decoupling fields are investigated. The technique shows a potential for application in a wide variety of systems where the resolution of the 13C spectrum may be combined with the sensitivity for proton detection to observe metabolites that have been previously unobservable.

Sillerud, Laurel O.; Alger, Jeffry R.; Shulman, Robert G.

49

Conformational studies by 1H and 13C NMR of lisinopril  

NASA Astrophysics Data System (ADS)

Lisinopril, N-N-[( s-1-carboxy-3-phenylpropyl]- L-lysyl- L-proline) (MK-521), is an inhibitor of angiotensin-converting enzyme and a new drug for the treatment of hypertension. 1H and 13C NMR studies have shown that the s-cis equilibrium about the amide bond is strongly dependent on the configuration of the chiral centres. Vicinal coupling constants of stereochemical significance were obtained in deuterated solvent using NMR techniques. Comparison with values calculated for lisinopril using potential energy calculations and NMR show that lisinopril exists in preferred optimum conformation in solution.

Sakamoto, Yohko; Ishi, Tomoko

1993-10-01

50

Characterization of covalent protein conjugates using solid-state sup 13 C NMR spectroscopy  

SciTech Connect

Cross-polarization magic-angle spinning (CPMAS) {sup 13}C NMR spectroscopy has been used to characterize covalent conjugates of alachlor, an {alpha}-chloroacetamide hapten, with glutathione (GSH) and bovine serum albumin (BSA). The solid-state NMR method demonstrates definitively the covalent nature of these conjugates and can also be used to characterize the sites of hapten attachment to proteins. Three different sites of alachlor binding are observed in the BSA system. Accurate quantitation of the amount of hapten covalently bound to GSH and BSA is reported. The solid-state {sup 13}C NMR technique can easily be generalized to study other small molecule/protein conjugates and can be used to assist the development and refinement of synthetic methods needed for the successful formation of such protein alkylation products.

Garbow, J.R.; Fujiwara, Hideji; Sharp, C.R.; Logusch, E.W. (Monsanto Co., St. Louis, MO (United States))

1991-07-23

51

An in vivo 13C NMR study on the effect of dietary sugar on pyruvate cycling during glucogenesis from (2- 13C)pyruvate in Manduca sexta L  

Microsoft Academic Search

Pyruvate cycling from (2-13C)pyruvate was detected in vivo in intact 5th instar Manduca sexta larvae by application of NMR spectroscopy. Cycling was evident from the enrichment of C3 in alanine following transamination of recycled pyruvate in larvae maintained on casein-based diets with or without sucrose. This metabolism is assumed to principally occur in the fat body. Analysis of 13C enriched

S. N. Thompson; D. B. Borchard

1996-01-01

52

High Resolution 1H Detected 1H,13C Correlation Spectra in MAS Solid-State NMR using Deuterated Proteins with Selective 1  

E-print Network

-state nuclear magnetic resonance (ssNMR) has developed rapidly over the past few years. This development led pattern indicating the isotopic distribution. We show in this communication that, out of all expected decoupling yields a major improvement in the spectral quality (Figure 1B). Typical 13C line widths

Skrynnikov, Nikolai

53

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

54

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

55

Solid state 13C NMR in conducting polymers F. Devreux (*), G. Bidan (**), A. A. Syed(**,+) and C. Tsintavis (**)  

E-print Network

1595 Solid state 13C NMR in conducting polymers F. Devreux (*), G. Bidan (**), A. A. Syed al. [1], the so-called solid-state high-resolution 13C NMR (CMR) could be a promis- ing way material for battery appli- cations. 2. Experimental High resolution CMR is achieved in solids by averag

Paris-Sud XI, Université de

56

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

57

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

58

Conformational analysis of 9,10-dihydroanthracenes. Molecular mechanics calculations and /sup 13/C NMR  

SciTech Connect

The conformational analyses of 9, 10-dihydroanthracene and several of its methylated and ethylated derivatives are studied by empirical force field calculations (MM2 and MMPI). The computational results are considered in light of previous and current carbon NMR data. Model compounds are examined which involve fixed, planar, and boat-shaped conformations about the central ring, and these /sup 13/C NMR data are then compared with flexible systems. It is concluded that carbon chemical shifts and carbon-hydrogen coupling constants are consistent with the results of molecular mechanics calculations which indicate a greater tendency for planarity around the central ring than previously considered.

Rabideau, P.W.; Mooney, J.L.; Lipkowitz, K.B.

1986-12-24

59

1H, 13C NMR studies of new 3-aminophenol isomers linked to pyridinium salts.  

PubMed

(1)H and (13)C NMR spectroscopic data of 20 new non-symmetrical compounds were assigned by a combination of 1D and 2D NMR experiments (DEPT, HSQC, and HMBC). These compounds contain a 4-(N,N-dimethylamino)- or 4-(pyrrolidin-1-yl)pyridinium moiety and a 3-nitro-, 3-amino-, or 3-hydroxyphenyl ring, linked by p-xylene, 4,4'-dimethylbiphenyl, 1,2-bis(p-tolyl)ethane, or 1,4-bis(p-tolyl)butane. PMID:24170481

Schiaffino-Ortega, Santiago; Espinosa, Antonio; Gallo, Miguel A; López-Cara, L Carlota; Entrena, Antonio

2014-01-01

60

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

61

High-resolution 13C NMR studies of cellulose and cellulose oligomers in ionic liquid solutions.  

PubMed

High-resolution 13C NMR studies of cellulose and cellulose oligomers dissolved in the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) show that the beta-(1-->4)-linked glucose oligomers are disordered in this medium and have a conformational behavior which parallels the one observed in water, and thus, reveal that the polymer is disordered in IL solution as well. PMID:15770258

Moulthrop, Jason S; Swatloski, Richard P; Moyna, Guillermo; Rogers, Robin D

2005-03-28

62

Mechanism of Aniline Methylation on Zeolite Catalysts Investigated by In Situ 13 C NMR Spectroscopy  

Microsoft Academic Search

The alkylation reaction of aniline with methanol on zeolites HY and CsOH\\/CsNaY was studied by in situ13C NMR spectroscopy under flow and batch conditions. Attention was focused on the identification of intermediates and on the determination of the formation mechanisms of N-methylaniline, N,N-dimethylaniline, and toluidines. To refine the main steps of the reaction, the transformations of the following individual compounds

I. I. Ivanova; E. B. Pomakhina; A. I. Rebrov; W. Wang; M. Hunger; J. Weitkamp

2003-01-01

63

2H and 13C NMR investigation of deuterofullerites C60Dx  

NASA Astrophysics Data System (ADS)

Deuterofullerites C60Dx have been studied by 2H and 13C NMR. These fullerites have two types of carbon-deuterium bonds: C-D terminal bonds, characterized by the quadrupole coupling constant (QCC) of 171 kHz, and -C ... D ... C- bridging bonds with a QCC of 56 kHz. The latter is responsible for the rigid lattice found in these fullerites, which is untypical of fullerenes.

Tarasov, V. P.; Muravlev, Y. B.; Fokin, V. N.; Shulga, Y. M.

64

On accuracy of the 13C NMR chemical shift GIAO calculations of fullerene C 60 derivatives at PBE\\/3? approach  

Microsoft Academic Search

The correlation analysis of the calculated by means of GIAO PBE\\/3? method and experimental (2D NMR INADEQUATE) 13C NMR chemical shifts of C60 derivatives was performed. It was shown that the computational method with sufficient accuracy (r.m.s.?5ppm) reproduces the experimental 13C NMR chemical shifts of the sp2-fullerene carbon atoms uncoupled with the sp3-fullerene carbons. By quality description the GIAO method

Arthur R. Tulyabaev; Leonard M. Khalilov

2011-01-01

65

Molecular motion of micellar solutes: a /sup 13/C NMR relaxation study  

SciTech Connect

A series of simple NMR relaxation experiments have been performed on nitrobenzene and aniline dissolved in the ionic detergents sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (CTAB). Using /sup 13/C relaxation rates at various molecular sites, and comparing data obtained in organic media with those for micellar solutions, the viscosity at the solubilization site was estimated and a detailed picture of motional restrictions imposed by the micellar enviroment was derived. Viscosities of 8 to 17 cp indicate a rather fluid environment for solubilized nitrobenzene; both additives exhibit altered motional preferences in CTAB solutions only. As an aid in interpretation of the NMR data, quasi-elastic light scattering and other physical techniques have been used to evaluate the influence of organic solutes on micellar size and shape. The NMR methods are examined critically in terms of their general usefulness for studies of solubilization in detergent mice

Stark, R.E.; Kasakevich, M.L.; Granger, J.W.

1982-02-04

66

UV/vis, 1H, and 13C NMR spectroscopic studies to determine mangiferin p Ka values  

NASA Astrophysics Data System (ADS)

The acid constants of mangiferin (a natural xanthonoid) in aqueous solution were determined through an UV/vis spectroscopic study employing the SQUAD program as a computational tool. A NMR study complements the p Ka values assignment and evidences a H-bridge presence on 1-C. The chemical model used was consistent with the experimental data obtained. The p Ka values determined with this procedure were as follows: H 4(MGF) = H 3(MGF) - + H +, pK(6-H) = 6.52 ± 0.06; H 3(MGF) - = H 2(MGF) 2- + H +, pK(3-H) = 7.97 ± 0.06; H 2(MGF) 2- = H(MGF) 3- + H +, pK(7-H) = 9.44 ± 0.04; H(MGF) 3- = (MGF) 4- + H +, pK(1-H) = 12.10 ± 0.01; where it has been considered mangiferin C 19H 18O 11 as H 4(MGF). Mangiferin UV/vis spectral behavior, stability study in aqueous solution as well as NMR spectroscopy studies: one-dimensional 1H, 13C, 2D correlated 1H/ 13C performed by (g)-HSQC and (g)-HMBC methods; are also presented. p Ka values determination of H 4(MGF) in aqueous solution is a necessary contribution to subsequent pharmacokinetic study, and a step towards the understanding of its biological effects.

Gómez-Zaleta, Berenice; Ramírez-Silva, María Teresa; Gutiérrez, Atilano; González-Vergara, Enrique; Güizado-Rodríguez, Marisol; Rojas-Hernández, Alberto

2006-07-01

67

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

68

sup 13 C and sup 31 P NMR studies of myocardial metabolism  

SciTech Connect

The fluxes through two enzyme systems have been measured in perfused or in in vivo heart using NMR: phosphocreatine kinase, and glycogen synthase and phosphorylase. The rates of synthesis and degradation of glycogen were monitored in vivo in fed, fasted, and diabetic rat heart during infusions of {sup 13}C-1-glucose and insulin using proton-decoupled {sup 13}C-NMR at 1.9 and 4.7 tesla. The enzyme activities of glycogen synthase and glycogen phosphorylase were also measured in this tissue which had been freeze clamped at the end of the experiment, for comparison with the synthetic rates. For normal fed, fasted, and diabetic animals, synthesis rates were 0.28, 0.16, and 0.15 {mu}mol/min.gww respectively. Glycogen synthase i activity was 0.23, 0.14, and 0.14 {mu}mol/min.gww in these hearts at the end of the experiment, when measured at appropriate substrate and activator concentrations, and follow activation time courses that are consistent with being the main rate determinant for net synthesis in all cases. Turnover of glycogen was studied by observing the preformed {sup 13}C-1-glycogen signal during infusion of {sup 12}C-glucose and insulin, and was found to be close to zero. Extracted phosphorylase a activity was approximately ten times that of synthase i under these circumstances. In order to fully interpret the turnover studies, glycogenolysis of preformed {sup 13}C-glycogen was observed after a bolus of glucagon. The glycogen had either been synthesized from {sup 13}C-1-glucose for a single hour, or during an hour of {sup 13}C-glucose and a subsequent hour of {sup 12}C-glucose infusion. The author observed that breakdown follows an exponential time course related to the phosphorylase a activation state and that the last synthesized glycogen breaks down at the rate of 2.5 {mu}mol/min.gww, five times faster than that synthesized an hour earlier.

Laughlin, M.R.

1988-01-01

69

High-resolution solid-state 13C CP MAS NMR spectra of some ?-cyclodextrin inclusion complexes with nitriles  

NASA Astrophysics Data System (ADS)

?-cyclodextrin inclusion complexes of 3-aminobenzonitrile, 4-aminobenzonitrile, and adamantane-1-carbonitrile were studied by means of high-resolution solid-state CP MAS 13C NMR spectroscopy. The interactions between the host and guest molecules are discussed.

Okazaki, M.; McDowell, C. A.

1983-11-01

70

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

NASA Astrophysics Data System (ADS)

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

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

2007-08-01

71

Multinuclear NMR ( 1H, 13C and 19F) spectroscopic re-examination of the solvolytic behaviour of flurazepam dihydrochloride  

Microsoft Academic Search

The dissolution of reference and archival samples of flurazepam dihydrochloride (2) was studied in DMSO-d6 and in D2O by 1H-, 13C- and 19F-NMR spectroscopy to identify and distinguish solvated species of the parent drug (2), the “benzophenone” (4) and glycine (5) hydrochloride degradation products. In DMSO-d6, for most samples, only the ring intact form (2) could be detected by 13C-NMR

B. A. Dawson; D. B. Black; G. A. Neville

1995-01-01

72

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

73

/sup 13/C NMR studies of the molecular flexibility of antidepressants  

SciTech Connect

The solution dynamics of a series of clinically potent antidepressants have been investigated by measuring /sup 13/C NMR relaxation parameters. Correlation times and internal motional rates were calculated from spin-lattice relaxation times and nuclear Overhauser effects for the protonated carbons in mianserin, imipramine-like antidepressants, and amitriptyline-like antidepressants. These data were interpreted in terms of overall molecular tumbling, internal rotations, and inherent flexibility of these structures. Of particular interest was the conformational variability of the tricyclic nucleus of the tricyclic antidepressants, where the data indicated a fivefold difference in mobility of the dimethylene bridge of imipramine-like antidepressants relative to amitriptyline-like compounds. The implications of such a difference in internal motions is discussed in relation to previous NMR studies and to the reported differences in pharmacological activity of these antidepressants.

Munro, S.L.; Andrews, P.R.; Craik, D.J.; Gale, D.J.

1986-02-01

74

Solid-state /sup 13/C NMR and X-ray diffraction of dermatan sulfate  

SciTech Connect

Dermatan sulfate in the solid state has been studied by /sup 13/C CP/MAS nmr and X-ray diffraction in order to establish the ring conformation of the L-iduronate moiety. The solid state nmr spectrum is similar to the solution spectrum obtained previously, indicating that a ring conformation at least approximating to /sup 1/C/sub 4/ predominates in the solid state. X-ray powder diffraction data from the same sample indicate the presence of the 8-fold helix form previously observed by fiber diffraction, and interpreted in terms of a /sup 4/C/sub 1/ ring form. A likely explanation of the results is that a distorted /sup 1/C/sub 4/ L-iduronate ring conformation, not considered in the initial X-ray analysis, may emerge to provide a satisfactory interpretation of all available physical-chemical data.

Winter, W.T.; Taylor, M.G.; Stevens, E.S.; Morris, E.R.; Rees, D.A.

1986-05-29

75

Investigations on ferroelectric liquid crystal by high resolution TEM and solid state 13C NMR.  

PubMed

In order to investigate the structural and dynamical properties of ferroelectric liquid crystal (FLC) in different phases a model compound [4-(3)-(S)-methyl-2-(S)-chloropentanoyloxy)]-4'-nonyloxy-biphenyl (3M2CPNOB) is synthesized. High resolution transmission electron microscopy (HR-TEM) is applied to observe the morphology of 3M2CPNOB and temperature-dependent solid state (13)C NMR to record (13)C chemical shifts at different phases. A liquid nitrogen quenching method is used to maintain the conformation of the mesophases for HR-TEM experiments. TEM images show that all the smectic A (SmA), smectic C* (SmC*) and crystalline phases have lamellar morphology. The interplanar distances in the crystalline phase are smaller than those in SmA and SmC* phases because of denser arrangement of the molecules. Both (13)C chemical shifts and line shape vary with different phases. The experimental results suggest that SmC* phase as an intermediate occurs in the anisotropy transition process from SmA to crystalline phase, the helical structure of the SmC* phase unwinds in the magnetic field and the conformations of the SmA and isotropic phase are very similar. PMID:21967597

Zhao, Yongxia; Yang, Yanqin; Xu, Jingwei; Yang, Wei; Zhou, Yunchun; Jiang, Zijiang; Ge, Xin

2011-11-17

76

Kinetic analyses of liver phosphatidylcholine and phosphatidylethanolamine biosynthesis using (13)C NMR spectroscopy.  

PubMed

Choline and ethanolamine are substrates for de novo synthesis of phosphatidylcholine (PtdC) and phosphatidylethanolamine (PtdE) through the CDP-choline and CDP-ethanolamine pathways. In liver, PtdE can also be converted to PtdC by PtdE N-methyltransferase (PEMT). We investigated these kinetics in rat liver during a 60 min infusion with (13)C-labeled choline and ethanolamine. NMR analyses of liver extracts provided concentrations and (13)C enrichments of phosphocholine (Pcho), phosphoethanolamine (Peth), PtdC, and PtdE. Kinetic models showed that the de novo and PEMT pathways are 'channeled' processes. The intermediary metabolites directly derived from exogenous choline and ethanolamine do not completely mix with the intracellular pools, but are preferentially used for phospholipid synthesis. Of the newly synthesized PtdC, about 70% was derived de novo and 30% was by PEMT. PtdC and PtdE de novo syntheses displayed different kinetics. A simple model assuming constant fluxes yielded a modest fit to the data; allowing upregulated fluxes significantly improved the fit. The ethanolamine-to-Peth flux exceeded choline-to-Pcho, and the rate of PtdE synthesis (1.04 micromol/h/g liver) was 2-3 times greater than that of PtdC de novo synthesis. The metabolic pathway information provided by these studies makes the NMR method superior to earlier radioisotope studies. PMID:11880242

Reo, Nicholas V; Adinehzadeh, Mehdi; Foy, Brent D

2002-02-28

77

1H and 13C resonance designation of antimycin A1 by two-dimensional NMR spectroscopy  

USGS Publications Warehouse

Complete 1H and 13C resonance assignments of antimycin A1 were accomplished by two-dimensional NMR techniques, viz. 1H homonuclear COSY correlation, heteronuclear 13C-1H chemical shift correlation and long-range heteronuclear 13C-1H COLOC correlation. Antimycin A1 was found to consist of two isomeric components in a 2:1 ratio based on NMR spectroscopic evidence. The structure of the major component was newly assigned as the 8-isopentanoic acid ester. The spectra of the minor component were consistent with the known structure of antimycin A1.

Abidi, S. L.; Adams, B. R.

1987-01-01

78

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. PMID:21252295

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

2011-01-01

79

Characterization of trimethyllysine 115 in calmodulin by 14N and 13C NMR spectroscopy.  

PubMed

In this paper, we describe three approaches to study the single trimethyllysine 115 in calmodulin. First, 14N NMR spectroscopy has been used as a novel spectroscopic tool. Because of the unique symmetrical tetrahedral substitution of its side chain, the trimethyllysine residue gives rise to a sharp 14N NMR resonance; hence, this has allowed the detection and quantitation of the level of trimethylation. Trimethyllysine side chains of bovine testis calmodulin and yeast cytochrome c were shown to have a high mobility in aqueous solution as determined by 14N NMR relaxation measurements. Second, we have purified mammalian calmodulin from an overproducing Escherichia coli strain. By comparison of the 1H-13C heteronuclear multiple quantum coherence spectra of 13C-dimethylated calmodulin samples from bovine testis and E. coli, the resonance for Lys-115 in bacterially expressed calmodulin could be identified. pH titration experiments showed that epsilon-NH2 group of Lys-115 has a normal pKa value both in the apo and Ca2+ forms of the protein and in a complex of calmodulin with a 22-residue calmodulin-binding peptide derived from myosin light chain kinase. Third, we have shown that mutation of Lys-115 to the uncharged Gln residue does not alter the ability of the protein to stimulate the enzymes cyclic nucleotide phosphodiesterase and myosin light chain kinase. These results show that the trimethylation of Lys-115 is not caused by an unusual pKa and reactivity of its epsilon-NH2 group and that its side chain remains flexible. Moreover, our data suggest that the introduction of a permanent positive charge on Lys-115 by trimethylation is also not the major reason for this specific post-translational modification. PMID:8106489

Zhang, M; Huque, E; Vogel, H J

1994-02-18

80

sup 13 C and sup 31 P NMR (Nuclear Magnetic Resonance) studies of prostate tumor metabolism  

SciTech Connect

The current research on prostate cancer by NMR spectroscopy and microscopy will most significantly contribute to tumor diagnosis and characterization only if sound biochemical models of tumor metabolism are established and tested. Prior searches focused on universal markers of malignancy, have to date, revealed no universal markers by any method. It is unlikely that NMRS will succeed where other methods have failed, however, NMR spectroscopy does provide a non-invasive means to analyze multiple compounds simultaneously in vivo. In order to fully evaluate the ability of NMRS to differentiate non-malignant from malignant tissues it is necessary to determine sufficient multiple parameters from specific, well-diagnosed, histological tumor types that, in comparison to normal tissue and non-neoplastic, non-normal pathologies from which the given neoplasm must be differentiated, one has enough degrees of freedom to make a mathematically and statistically significant determination. Confounding factors may consist of tumor heterogeneity arising from regional variations in differentiation, ischemia, necrosis, hemorrhage, inflammation and the presence of intermingled normal tissue. One related aspect of our work is the development of {l brace}{sup 13}C{r brace}-{sup 1}H metabolic imaging of {sup 13}C for metabolic characterization, with enhanced spatial localization (46). This should markedly extend the range of potential clinical NMR uses because the spatial variation in prostate metabolism may prove to be just as important in tumor diagnoses as bulk (volume-averaged) properties themselves. It is our hope that NMRS and spectroscopic imaging will reveal a sound correlation between prostate metabolism and tumor properties that will be clinically straightforward and useful for diagnosis.

Sillerud, L.O.; Halliday, K.R.; Freyer, J.P; Griffey, R.H.; Fenoglio-Preiser, C.

1989-01-01

81

{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

82

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

83

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

84

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

PubMed Central

We demonstrate the feasibility of one-dimensional and two-dimensional 1H–13C double resonance NMR experiments with dynamic nuclear polarization (DNP) at 9.4 T and temperatures below 20 K, including both 1H–13C cross-polarization and 1H decoupling, and discuss the effects of polarizing agent type, polarizing agent concentration, temperature, and solvent deuteration. We describe a two-channel low-temperature DNP/NMR probe, capable of carrying the radio-frequency power load required for 1H–13C cross-polarization and high-power proton decoupling. Experiments at 8 K and 16 K reveal a significant T2 relaxation of 13C, induced by electron spin flips. Carr–Purcell experiments and numerical simulations of Carr–Purcell dephasing curves allow us to determine the effective correlation time of electron flips under our experimental conditions. The dependence of the DNP signal enhancement on electron spin concentration shows a maximum near 80 mM. Although no significant difference in the absolute DNP enhancements for triradical (DOTOPA-TEMPO) and biradical (TOTAPOL) dopants was found, the triradical produced greater DNP build-up rates, which are advantageous for DNP experiments. Additionally the feasibility of structural measurements on 13C-labeled biomolecules was demonstrated with a two-dimensional 13C–13C exchange spectrum of selectively 13C-labeled ?-amyloid fibrils. PMID:22743540

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

2012-01-01

85

^13C Solid NMR Study of Devulcanization and Revulcanization of SBR Ne  

NASA Astrophysics Data System (ADS)

As part of a larger effort in support of recycling of rubber-based composites, we have used ^13C CP-MAS NMR spectroscopy and relaxation to study molecular and segmental mobilities in styrene-butadiene random copolymers before and after sulfur crosslinking, after subsequent devulcanization using a thermal ultrasound technique, and following revulcanization. Tracking the cis-trans ratio indicates that overall network crosslink density increases during each of these steps, including devulcanization, which produces mesoscale network aggregates and substantial amounts of sol. This observation is confirmed by the transverse (T_2) relaxation times, which show that molecular/segmental mobilities monotonically decrease in the same sequence. Analysis of these effects requires the invocation of alterations in sulfur crosslinking, i.e. density, distribution, and functionality, including extensive cyclization. Measurements of the glass transition temperatures in melt, network, sol , and revulcanizate are in accord with this picture.

Massey, J.; Levin, V.; Isayev, A.; von Meerwall, E.

1996-03-01

86

Identification of archaeological triterpenic resins by the non-separative techniques FTIR and 13C NMR: the case of Pistacia resin (mastic) in comparison with frankincense.  

PubMed

The use of spectroscopic techniques such as Fourier-transform infrared (FTIR) spectroscopy and carbon 13 nuclear magnetic resonance ((13)C NMR) using the J-mod experiment is proposed as an effective alternative to gas chromatography-mass spectrometry (GC-MS) for the analysis and identification of natural resin samples found in archaeological environments. The spectral features of the most common diterpenic and triterpenic resins and also two gum-resins are reported and discussed for both techniques. The analytical procedure based on the combined use of FTIR and (13)C NMR is then applied to two archaeological samples from the Milano of the Roman age allowing their identification as Pistacia resin, or mastic, as confirmed by the traditional GC-MS method, and also elucidating some effects of aging on such material. PMID:24291439

Bruni, Silvia; Guglielmi, Vittoria

2014-01-01

87

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

NASA Astrophysics Data System (ADS)

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

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

2006-02-01

88

Localized in vivo 13C-NMR of Glutamate Metabolism in the Human Brain: Initial Results at 4 Tesla  

Microsoft Academic Search

Using optimized administration of 13C-labeled glucose, the time course of the specific activity of glucose was measured directly by in vivo 13C-NMR in the human brain at 4 Tesla. Subsequent label incorporation was measured at the C2, C3 and C4 positions of both glutamate and the well-resolved C2, C3 and C4 resonances of glutamine and at the C2 and C3

Rolf Gruetter; Elizabeth R. Seaquist; Suckwon Kim

1998-01-01

89

/sup 1/H and /sup 13/C NMR studies on carbon dioxide hydrate  

SciTech Connect

/sup 13/C NMR line shapes are reported for /sup 13/CO/sub 2/. 7/sup 2///sub 3/H/sub 2/O in the temperature range 77-250 K. At high temperatures (T greater than or equal to 200 K) the axially symmetric powder pattern leads to a model in which the guest molecule rotates about the hydrate cage symmetry axis while the guest molecule's long axis is constrained to lie in a plane which makes a maximum angle of 31/sup 0/ with the equatorial plane of the cage. At lower temperatures, the motion is more restricted and is characterized by a distribution of motional modes. Several such distributed motional modes were considered in interpreting the line shape at 77 K. /sup 1/H NMR spin-lattice relaxation time measurements show that water molecules reorientate with a correlation time of 14.9 ..mu..s at 233 K and a characteristic activation energy of 31.6 kJ/mol. 21 references, 6 figures.

Ratcliffe, C.I.; Ripmeester, J.A.

1986-03-27

90

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

PubMed

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

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

2005-12-01

91

13C NMR signal detection of iron-bound cyanide ions in ferric cyanide complexes of heme proteins.  

PubMed

13CN ion appears to have the greatest potential to probe the heme environment of the ferric heme proteins; however, a resonance of the iron-bound (13)CN ion in ferric heme proteins has not yet been located. We show here the first detection of (13)C NMR signals of the iron-bound (13)CN for heme proteins and their model complexes in an unexpectedly large upfield region. This study demonstrates that the (13)C NMR signal of the iron-bound (13)CN is a sensitive probe to study the nature of the proximal ligand in ferric heme protein. PMID:12022815

Fujii, Hiroshi

2002-05-29

92

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

93

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

PubMed Central

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

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

2002-01-01

94

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

95

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

96

Combined effects of an oxidative enzyme and dissolved humic substances on 13 C-labelled 2,4-D herbicide as revealed by high-resolution 13 C NMR spectroscopy  

Microsoft Academic Search

  Phenoxyalkanoic acids are a widely used class of herbicides. This work employed high-resolution 13C NMR to study the structural changes induced by humic substances and horseradish perodixase on 2,4-dichorophenoxyacetic acid\\u000a (2,4-D) 13C-labelled in the side chain. NMR spectra showed that humic substances chemically catalyze abiotic splitting of [13C]2,4-D into 2,4-dichlorophenol and [13C]acetic acid at pH 7 but not at pH

A Piccolo; P Conte; A Cozzolino; M Paci

2001-01-01

97

Metabolic characterization of Lactococcus lactis deficient in lactate dehydrogenase using in vivo 13C-NMR.  

PubMed

The metabolism of glucose by nongrowing cells of Lactococcus lactis strain FI7851, constructed from the wild-type L. lactis strain MG1363 by disruption of the lactate dehydrogenase (ldh) gene [Gasson, M.J., Benson, K., Swindel, S. & Griffin, H. (1996) Lait 76, 33-40] was studied in a noninvasive manner by 13C-NMR. The kinetics of the build-up and consumption of the pools of intracellular intermediates mannitol 1-phosphate, fructose 1,6-bisphosphate, 3-phosphoglycerate, and phosphoenolpyruvate as well as the utilization of [1-13C]glucose and formation of products (lactate, acetate, mannitol, ethanol, acetoin, 2,3-butanediol) were monitored in vivo with a time resolution of 30 s. The metabolism of glucose by the parental wild-type strain was also examined for comparison. A clear shift from typical homolactic fermentation (parental strain) to a mixed acid fermentation (lactate dehdydrogenase deficient; LDHd strain) was observed. Furthermore, high levels of mannitol were transiently produced and metabolized once glucose was depleted. Mannitol 1-phosphate accumulated intracellularly up to 76 mM concentration. Mannitol was formed from fructose 6-phosphate by the combined action of mannitol-1-phosphate dehydrogenase and phosphatase. The results show that the formation of mannitol 1-phosphate by the LDHd strain during glucose catabolism is a consequence of impairment in NADH oxidation caused by a highly reduced LDH activity, the transient production of mannitol 1-phosphate serving as a regeneration pathway for NAD+ regeneration. Oxygen availability caused a drastic change in the pattern of intermediates and end-products, reinforcing the key-role of the fulfilment of the redox balance. The flux control coefficients for the step catalysed by mannitol-1-phosphate dehydrogenase were calculated and the implications in the design of metabolic engineering strategies are discussed. PMID:10849005

Neves, A R; Ramos, A; Shearman, C; Gasson, M J; Almeida, J S; Santos, H

2000-06-01

98

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

NASA Astrophysics Data System (ADS)

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 into chemical reaction mechanisms, since oxidation products can be traced back to their positions of origin on the macromolecule. The major products include peroxides and alcohols, both formed at tertiary carbon sites along the chain. Other products include methyl ketones, acids, esters, peresters, and hemiketals formed from reaction at the tertiary carbon, together with in-chain ketones and esters from reaction at the secondary chain carbon. No evidence is found of products arising from reactions at the methyl side chain. Significant temperature-dependent differences are apparent; for example much higher yields of chain-end methyl ketones, which are the indicator product of chain scission, are generated for both elevated temperature irradiation and for post-irradiation treatment at elevated temperatures. Time-dependent plots of yields of the various oxidation products have been obtained under a wide range of conditions, including the post-irradiation oxidation of a sample at room temperature in air that has been monitored for 2 years. Radiation-oxidation products of polypropylene are contrasted to products measured for 13C-labeled polyethylene in an earlier investigation: the peroxides formed in irradiated polypropylene are remarkably longer lived, the non-peroxidic products are significantly different, and the overall ratios of oxidation products in polypropylene change relatively little as a function of the extent of oxidation.

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

2007-05-01

99

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. PMID:9251820

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

1997-01-01

100

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. PMID:23589073

Jarvis, James A.; Haies, Ibraheem M.

2013-01-01

101

Characterization of Stratum Corneum Molecular Dynamics by Natural-Abundance 13C Solid-State NMR  

PubMed Central

Despite the enormous potential for pharmaceutical applications, there is still a lack of understanding of the molecular details that can contribute to increased permeability of the stratum corneum (SC). To investigate the influence of hydration and heating on the SC, we record the natural-abundance 13C signal of SC using polarization transfer solid-state NMR methods. Resonance lines from all major SC components are assigned. Comparison of the signal intensities obtained with the INEPT and CP pulse sequences gives information on the molecular dynamics of SC components. The majority of the lipids are rigid at 32°C, and those lipids co-exist with a small pool of mobile lipids. The ratio between mobile and rigid lipids increases with hydration. An abrupt change of keratin filament dynamics occurs at RH?=?80–85%, from completely rigid to a structure with rigid backbone and mobile protruding terminals. Heating has a strong effect on the lipid mobility, but only a weak influence on the keratin filaments. The results provide novel molecular insight into how the SC constituents are affected by hydration and heating, and improve the understanding of enhanced SC permeability, which is associated with elevated temperatures and SC hydration. PMID:23626744

Bouwstra, Joke A.; Sparr, Emma; Topgaard, Daniel

2013-01-01

102

Characterization of cerebral glutamine uptake from blood in the mouse brain: implications for metabolic modeling of (13)C NMR data.  

PubMed

(13)C Nuclear Magnetic Resonance (NMR) studies of rodent and human brain using [1-(13)C]/[1,6-(13)C2]glucose as labeled substrate have consistently found a lower enrichment (?25% to 30%) of glutamine-C4 compared with glutamate-C4 at isotopic steady state. The source of this isotope dilution has not been established experimentally but may potentially arise either from blood/brain exchange of glutamine or from metabolism of unlabeled substrates in astrocytes, where glutamine synthesis occurs. In this study, the contribution of the former was evaluated ex vivo using (1)H-[(13)C]-NMR spectroscopy together with intravenous infusion of [U-(13)C5]glutamine for 3, 15, 30, and 60?minutes in mice. (13)C labeling of brain glutamine was found to be saturated at plasma glutamine levels >1.0?mmol/L. Fitting a blood-astrocyte-neuron metabolic model to the (13)C enrichment time courses of glutamate and glutamine yielded the value of glutamine influx, VGln(in), 0.036±0.002??mol/g per minute for plasma glutamine of 1.8?mmol/L. For physiologic plasma glutamine level (?0.6?mmol/L), VGln(in) would be ?0.010??mol/g per minute, which corresponds to ?6% of the glutamine synthesis rate and rises to ?11% for saturating blood glutamine concentrations. Thus, glutamine influx from blood contributes at most ?20% to the dilution of astroglial glutamine-C4 consistently seen in metabolic studies using [1-(13)C]glucose. PMID:25074745

Bagga, Puneet; Behar, Kevin L; Mason, Graeme F; De Feyter, Henk M; Rothman, Douglas L; Patel, Anant B

2014-10-01

103

Determination of C-23 configuration in (20R)-23-hydroxycholestane side chain of steroid compounds by 1H and 13C NMR spectroscopy.  

PubMed

Epimeric (20R,23R)- and (20R,23S)-23-hydroxycholestane steroids were synthesized. Their structures were elucidated by extensive 1H and 13C NMR spectroscopy and application of the Mosher's method. All proton and carbon signals of the side chains were assigned. Based on these assignments spectral data allow the determination of the C-23 stereochemistry of (20R)-23-hydroxycholestane side chains of the new natural steroids by comparison with spectra of the obtained model compounds. As a result, the C-23 configuration of two steroid compounds from the starfishes Lethasterias nanimensis chelifera and Lethasterias fusca was established. PMID:24273850

Kicha, Alla A; Kalinovsky, Anatoly I; Antonov, Alexander S; Radchenko, Oleg S; Ivanchina, Natalia V; Malyarenko, Timofey V; Savchenko, Alexander M; Stonik, Valentin A

2013-09-01

104

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. PMID:19678690

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

2011-01-01

105

Prediction of protein 13C ? NMR chemical shifts using a combination scheme of statistical modeling and quantum-mechanical analysis  

NASA Astrophysics Data System (ADS)

Quantitative structure-property relationships (QSPRs) on the basis of constitutional, topological, geometrical, and electrostatic descriptors are developed for 2454 13C ? NMR chemical shifts of 21 structure-known, high-quality monomeric proteins. In this procedure, heuristic approach is employed to perform variable-selection for obtaining few independent and significant descriptors. Coupled with various machine learning methods, including MLR, PLS, LSSVM, RF, and GP, these selected variables are then used to create both linear and nonlinear statistical models with the experimentally determined 13C ? NMR chemical shifts of proteins. In addition, the secondary structural effect and environmental influence on protein chemical shifts are also investigated in detail through structural survey and quantum-mechanical calculations. We demonstrate that (i) relationship between 13C ? NMR chemical shifts and local structural features is, to some extent, nonlinear, and (ii) the 13C ? chemical shift values are not only determined by corresponding side-chain conformations, but also affected from the arrangement and configuration of spatially vicinal residues.

Liu, Xiuhong; Ren, Yanrong; Zhou, Peng; Shang, Zhicai

2011-05-01

106

A study of the experimental and theoretical infrared, Raman, 1H and 13C NMR spectra of the biochemicals valeric and valproic acids  

NASA Astrophysics Data System (ADS)

The structural stability, vibrational, 1H and 13C NMR spectra of valeric and valproic acids were investigated by the B3LYP calculations with the 6-311G** basis set. Valeric acid is predicted to exist predominantly in the planar cis form (80% abundance). Valproic acid is predicted to have an equilibrium mixture of 68% gauche-1 and 32% gauche-2 structures at 298.15 K. The spectral feature of the Osbnd H stretching mode in the infrared spectra of both acids suggests the presence of strong H-bonding in the condensed phase of valeric acid and weak H-bonding in the case of valproic acid. The harmonic and anharmonic vibrational wavenumbers were computed at the B3LYP level of theory and tentative vibrational assignments were provided on the basis of combined theoretical and experimental infrared and Raman data of the molecules. Not all of the calculated anharmonic wavenumbers showed a consistent trend with the observed wavenumbers. The 1H and 13C NMR spectra of both acids were interpreted by experimental and DFT calculated chemical shifts of the two acids. The RMSD between experimental and theoretical 1H and 13C chemical shifts for valeric acid is 1.8 and 3.8 ppm, whereas for valproic acid, it is 1.4 and 4.5 ppm, respectively.

Badawi, Hassan M.; Förner, Wolfgang; Ali, Shaikh A.

2014-10-01

107

Solid-state high-resolution 13C-NMR study of crosslinks in heavily gamma-irradiated polyethylene  

NASA Astrophysics Data System (ADS)

Chemical species produced by heavy ?-irradiation to high-density polyethylene were identified by solid-state high-resolution 13C-NMR, that is, by the CP-MAS method. The majority of chemical species responsible for crosslinks are tertiary carbons, even after such a heavy dosage as 995 Mrad of ?-irradiation. The MAS method, without CP, was used to detect selectively the NMR signal from 13C in amorphous regions. By using a Torchia pulse sequence, spectra from either crystalline or amorphous regions are observed selectively. The results indicate that short branches are produced preferentially in amorphous regions. More crosslinks are produced (by nearly 3.6 times) in amorphous regions than in crystalline regions.

Sohma, J.; Qun, Chen; Yuanshen, Wang; Xue-Wen, Qu; Shiotani, M.

108

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

USGS Publications Warehouse

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

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

2005-01-01

109

Conformational distribution of baclofen analogues by 1H and 13C NMR analysis and ab initio HF MO STO-3G or STO-3G* calculations  

NASA Astrophysics Data System (ADS)

The conformations of 3-(substituted furan-2-yl) and 3-(substituted thien-2-yl)-?-aminobutyric acid 1-9 in solution (D 2O) are estimated from high-resolution (300 MHz) 1H NMR coupling data. Conformations and populations of conformers are calculated by means of a modified Karplus-like relationship for the vicinal coupling constants. The results are compared with X-ray crystallographic investigations (torsion angles) and ab initio HF MO ST-3G or STO-3G* calculations. 1H NMR spectral analysis shows how 1-9 in solution retain the preferred g- conformation around the C3?C4 bond, as found in the solid state, while a partial rotation is set up around the C2?C3 bond: the conformations about C2?C3 are all highly populated in solution. The 13C spin-lattice relaxation times are also discussed.

Vaccher, Claude; Berthelot, Pascal; Debaert, Michel; Vermeersch, Gaston; Guyon, René; Pirard, Bernard; Vercauteren, Daniel P.; Dory, Magdalena; Evrard, Guy; Durant, François

1993-12-01

110

Determination of the average degree of quaternization of N, N, N-trimethylchitosan by solid state 13C NMR  

Microsoft Academic Search

A novel method in which the quaternary salt of chitosan, N,N,N-trimethylchitosan (TMC) was synthesized using dimethylsulfate as the methylant agent is described. Although the synthesis of chitosan quaternary salts has been reported extensively, there remains some uncertainty in determining the resultant average degree of quaternization, DQ¯, in the final products. Here we used CP-MAS 13C NMR spectroscopy, that was able

Douglas de Britto; Lucimara Aparecida Forato; Odílio B. G. Assis

2008-01-01

111

The complete assignment of the 13C NMR spectra of lasalocid and the sodium salt-complex of the antibiotic.  

PubMed

All thirty-four signals observed in the 13C nmr of both the free acid form (Ia) and sodium salt (Ib) of the polyether antibiotic lasalocid have been assigned. This was achieved using model compounds such as 3-methylsalicylic acid, the retroaldol ketones from both lasalocid and lysocellin and a gamma-lactone from a third polyether, salinomycin. The last assignments to be made were accomplished using biosynthetically enriched samples of the antibiotic. PMID:659326

Seto, H; Westley, J W; Pitcher, R G

1978-04-01

112

Cross-polarization/magic-angle sample-spinning 13C NMR spectroscopic study of chlorophyll a in the solid state  

PubMed Central

Solid-state cross-polarization/magic-angle sample-spinning 13C NMR spectra have been recorded on chlorophyll a-water aggregates, methyl pyrochlorophyllide a, and methyl pyropheophorbide a (derivatives that lack a phytyl chain). Spectra have also been collected under a decoupling regime in which resonances of certain hydrogen-bearing carbon atoms are suppressed. These observations are used to assign the solid-state spectra. PMID:16593410

Brown, Charles Eric; Spencer, Robert B.; Burger, Vern T.; Katz, Joseph J.

1984-01-01

113

13C NMR study of molecular ordering in a discotic columnar mesophase V. Rutar, R. Blinc, M. Vilfan  

E-print Network

'hexapentyloxy-triphénylène a été déterminée en utilisant la spectroscopie de résonance magnétique nucléaire de haute résolution du in the columnar liquid crystalline phase of hexapentoxy-triphenylene has been determined using high resolution proton enhanced 13C NMR spectroscopy. The chains have been found to be preferentially in the extended

Paris-Sud XI, Université de

114

Practical aspects of high-sensitivity multidimensional 13C MAS NMR spectroscopy of perdeuterated proteins  

NASA Astrophysics Data System (ADS)

The double nucleus enhanced recoupling (DONER) experiment employs simultaneous irradiation of protons and deuterons to promote spin diffusion processes in a perdeuterated protein. This results in 4-5 times higher sensitivity in 2D 13C-13C correlation experiments as compared to PDSD [1]. Here, a quantitative comparison of PDSD, 1H-DARR, 2H-DARR, and 1H + 2H DONER has been performed to analyze the influence of spin diffusion on polarization transfer processes. Cross peak buildup curves were analyzed to obtain guidelines for choosing the best experimental parameters. The largest cross peak intensities were observed for the DONER experiments. The fastest build-up rate was observed in the 2H-DARR experiment within a buildup range of ˜18-45 ms, whereas values between 24 and 69 ms are observed for the DONER experiment. Furthermore, the effects of direct excitation and cross polarization (CP) are compared. A comparison between DONER and RFDR experiments reveal ˜50% more intense cross peaks in the C?-CO and C?-Calip regions of the 2D 13C-13C DONER spectrum applying proton CP (1H-13C). As a parameter determining the S/N in 13C-13C correlation experiments, proton CP efficiency is investigated using deuterated samples with proton/deuterium ratios at 20%, 40%, and 100% H2O. Sufficiently strong 13C CPMAS signal intensity is observed for such proteins even with very low proton concentration. The effect of proton and/or deuterium decoupling is analyzed at various MAS spinning frequencies. Deuterium decoupling was found most crucial for obtaining high resolution. Long range correlations are readily observed representing distances up to ˜6 Å by using DONER approach.

Akbey, Ümit; van Rossum, Barth-Jan; Oschkinat, Hartmut

2012-04-01

115

Use of {sup 13}C NMR to assess the biodegradation of 1-{sup 13}C-labeled acenaphthene in the presence of creosote polynuclear hydrocarbons (PAHs) and naphthalene by mixed bacterial cultures  

SciTech Connect

1-{sup 13}C-acenaphthene mixed with creosote PAH`s or naphthalene was incubated with bacterial strains known to degrade naphthalene, phenanthrene and acenaphthene. After incubation, the reaction mixtures were extracted with organic solvent, and the biodegradation products were identified by {sup 13}C NMR. An accumulation of intermediate degradation products was identified and attributed to the non-specific action of naphthalene catabolic pathways of the mixed bacterial cultures. An acenaphthene degrading strain, Pseudomonas sp. strain A2279 was added to the nixed bacterial cultures to minimize the formation of the observed dead-end products. The {sup 13}C NMR spectra obtained from the experiments in which strain A2279 was present clearly showed the complete biodegradation of 1-{sup 13}C-acenaphthene without the accumulation of {sup 13}C-labeled products. This set of experiments clearly demonstrates the utility of {sup 13}C NMR as an effective tool for the assessment of the biodegradation of PAH`s such as 1-{sup 13}C-acenaphthene by various microbial strains.

Selifonov, S.A. [Univ. of Minnesota, St. Paul, MN (United States); Bortiatynski, J.M.; Nanny, M.A.; Hatcher, P.G. [Pennsylvania State Univ., University Park, PA (United States)

1996-10-01

116

13C NMR reveals no evidence of n-?* interactions in proteins.  

PubMed

An n = ?* interaction between neighboring carbonyl groups has been postulated to stabilize protein structures. Such an interaction would affect the (13)C chemical shielding of the carbonyl groups, whose paramagnetic component is dominated by n = ?* and ? = ?* excitations. Model compound calculations indicate that both the interaction energetics and the chemical shielding of the carbonyl group are instead dominated by a classical dipole-dipole interaction. A set of high-resolution protein structures with associated carbonyl (13)C chemical shift assignments verifies this correlation and provides no evidence for an inter-carbonyl n = ?* interaction. PMID:22876300

Worley, Bradley; Richard, Georgia; Harbison, Gerard S; Powers, Robert

2012-01-01

117

Conformational changes at mesophase transitions in a ferroelectric liquid crystal by comparative DFT computational and (13)C NMR study.  

PubMed

In this work, we report a detailed investigation on both the conformational and the orientational ordering properties of a ferroelectric liquid crystal mesogen, namely, M10/**, through the combination of high resolution solid state (13)C NMR and density functional theory (DFT) computational methods. The trends of the observed (13)C chemical shift in the blue, cholesteric, and ferroelectric SmC* phases of M10/** were analyzed in terms of conformational changes occurring in the flexible parts of the molecule. In particular, we focused on the aliphatic alpha methylenoxy carbons because of their high sensitivity to mesophase environment, as evidenced by experimental (13)C chemical shift anisotropy (CSA). DFT computation of the chemical shift tensors as a function of geometrical parameters, such as dihedral angles, put in evidence significant changes in the average conformation at the mesophase transitions. The conformations predicted by DFT have been validated by comparing the calculated (13)C chemical shifts with those experimentally observed for the alkoxylic carbons, whose relative orientation plays a key role in establishing the overall conformation of the molecule in each liquid crystalline phase. Furthermore, the orientational order parameters of the relevant flexible fragments were calculated and found to be in good agreement with those characterizing similar systems, thus validating our approach. PMID:20701374

Marini, Alberto; Domenici, Valentina

2010-08-19

118

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

119

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

SciTech Connect

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

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

2012-02-15

120

13C NMR and electrospray ionization mass spectrometric study of sucrose aqueous solutions at high pH: NMR measurement of sucrose dissociation constant  

Microsoft Academic Search

The 13C NMR technique is used for the measurement of the first dissociation constant of sucrose (HL) in highly alkaline solutions. In 1.0M NaCl\\/NaOH medium and for 25°C, the concentration dissociation constant (pK1) was 13.1±0.3; and, for 60 °C, pK1=12.30±0.05. The ?-d-fructofuranosyl ring was found to be responsible for dissociation. The NMR data reveal no clear evidence of the second

K. I. Popov; N. Sultanova; H. Rönkkömäki; M. Hannu-Kuure; J. Jalonen; L. H. J. Lajunen; I. F. Bugaenko; V. I. Tuzhilkin

2006-01-01

121

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

122

Paramagnetic 13C and 15N NMR analyses of cyanide- (13C15N-) ligated ferric peroxidases: the push effect, not pull effect, modulates the compound I formation rate.  

PubMed

Paramagnetic (13)C and (15)N NMR spectroscopy of heme-bound cyanide ((13)C(15)N) was utilized to quantitatively distinguish the electron donor effect (the push effect) from the proximal histidine and hydrogen-bonding effect (the pull effect) from the distal amino acid residues in cytochrome c peroxidase (CcP), ascorbate peroxidase (APX), lignin peroxidase (LiP), and manganese peroxidase (MnP). Paramagnetic (13)C NMR signals of heme-bound (13)C(15)N of these peroxidases were observed in a wide range, -3501 ppm (CcP), -3563 ppm (APX), -3823 ppm (MnP), and -3826 ppm (LiP), while paramagnetic (15)N NMR signals of those were detected in a narrow range, 574 ppm (ARP), 605 ppm (CcP), 626 ppm (LiP), and 654 ppm (MnP). Detailed analysis, combined with the previous results for horseradish peroxidase and Arthromyces ramosus peroxidase, indicated that the push effect is quite different among these peroxidases while the pull effect is similar. More importantly, a strong correlation between the (13)C NMR shift (the push effect) and the compound I formation rate was observed, indicating that the push effect causes a variation in the compound I formation rate. Comparison of the (13)C and (15)N NMR results of these peroxidases with their crystal structures suggests that the orientation of the proximal imidazole plane to the heme N-Fe-N axis controls the push effect and the compound I formation rate of peroxidase. PMID:19187033

Nonaka, Daisuke; Wariishi, Hiroyuki; Fujii, Hiroshi

2009-02-10

123

The structural properties of the transmembrane segment of the integral membrane protein phospholamban utilizing 13C CPMAS, 2H, and REDOR solid-state NMR spectroscopy  

Microsoft Academic Search

Solid-state NMR spectroscopic techniques were used to investigate the secondary structure of the transmembrane peptide phospholamban (TM-PLB), a sarcoplasmic Ca2+ regulator. 13C cross-polarization magic angle spinning spectra of 13C carbonyl-labeled Leu39 of TM-PLB exhibited two peaks in a pure 1-palmitoyl-2-oleoyl-phosphocholine (POPC) bilayer, each due to a different structural conformation of phospholamban as characterized by the corresponding 13C chemical shift. The

Ethan S. Karp; Elvis K. Tiburu; Shadi Abu-Baker; Gary A. Lorigan

2006-01-01

124

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

125

1H and 13C NMR signal assignment of benzylisoquinoline alkaloids from Fumaria officinalis L. (Papaveraceae).  

PubMed

The NMR signal assignments of a series of structurally divergent benzylisoquinolines isolated from Fumaria officinalis L. (Fumariaceae, Papaverales), namely adlumine, corlumine, corydamine, cryptopine, fumarophycine, O-methylfumarophycine, hydrastine, parfumine, protopine and sinactine, are presented. PMID:15366062

Seger, Christoph; Sturm, Sonja; Strasser, Eva-Maria; Ellmerer, Ernst; Stuppner, Hermann

2004-10-01

126

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

127

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

128

A 13C CP\\/MAS NMR spectroscopy and AFM study of the structure of Glucagel™, a gelling ?-glucan from barley  

Microsoft Academic Search

The structure of Glucagel™, a mixed-linked (1?3), (1?4)-?-d-glucan extracted from barley, was examined using 13C CP\\/MAS NMR spectroscopy and atomic force microscopy (AFM). Results from 13C CP\\/MAS NMR spectroscopy showed that Glucagel™ contained regions with two distinct conformations. In some of the regions the ?-glucan chains associated to form a unique conformation, the A-conformation, while in the other regions the

Keith R. Morgan; Clive J. Roberts; Saul J. B. Tendler; Martyn C. Davies; Phil M. Williams

1999-01-01

129

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

130

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

Microsoft Academic Search

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

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

2001-01-01

131

Cationic closo-carboranes 2. Do computed 11B and 13C NMR chemical shifts support their experimental availability?  

PubMed

(11)B and (13)C NMR spectra of so-far experimentally unknown carbon-rich cationic closo-carboranes C(3)B(n-3)H(n)(+) (n = 5, 6, 7, 10, 12) have been calculated at the GIAO-MP2 level and subsequently analyzed to reveal the nature of bonding in these potentially weakly coordinating cations. All previous rules derived for understanding (11)B NMR spectra of borane derivatives can be applied to realistically account for the corresponding shieldings. The correlated wavefunction for n = 5 and, to a lesser extent, for n = 10 seems to be decisive when trying to compute realistic shielding tensors, which is in agreement with the corresponding known dicarbaboranes. For other cluster dimensions noncorrelated wavefunctions also work well, in particular in relation to the corresponding dicarbaboranes. All these observations strongly support the fact that experimental availability of these unique clusters is possible. PMID:23175322

Hnyk, Drahomír; Jayasree, Elambalassery G

2013-03-30

132

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

133

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

PubMed Central

Conformational dynamics play a key role in the properties and functions of proteins and nucleic acids. Heteronuclear NMR spin relaxation is a uniquely powerful site-specific probe of dynamics in proteins and has found increasing applications to nucleotide base side chains and anomeric sites in RNA. Applications to the nucleic acid ribose backbone, however, have been hampered by strong magnetic coupling among ring carbons in uniformly 13C-labeled samples. In this work, we apply a recently-developed, metabolically-directed isotope labeling scheme that places 13C with high efficiency and specificity at the nucleotide ribose C2’ and C4’ sites. We take advantage of this scheme to explore backbone dynamics in the well-studied GCAA RNA tetraloop. Using a combination of CPMG (Carr-Purcell-Meiboom-Gill) and R1? relaxation dispersion spectroscopy to explore exchange processes on the microsecond to millisecond timescale, we find an extensive pattern of dynamic transitions connecting a set of relatively well-defined conformations. In many cases, the observed transitions appear to be linked to C3’-endo/C2’-endo sugar pucker transitions of the corresponding nucleotides, and may also be correlated across multiple nucleotides within the tetraloop. These results demonstrate the power of NMR spin relaxation based on alternate-site isotope labeling to open a new window into the dynamic properties of ribose backbone groups in RNA. PMID:19049467

Johnson, James E.; Hoogstraten, Charles G.

2009-01-01

134

The retrogradation properties of glutinous rice and buckwheat starches as observed with FT-IR, 13C NMR and DSC.  

PubMed

The experiment was conducted to study the retrogradation properties of glutinous rice and buckwheat starch with wavelengths of maximum absorbance, FT-IR, (13)C NMR, and DSC. The results show that the starches in retrograded glutinous rice starch and glutinous rice amylopectin could not form double helix. The IR results show that protein inhabits in glutinous rice and maize starches in a different way and appearance of C-H symmetric stretching vibration at 2852 cm(-1) in starch might be appearance of protein. Retrogradation untied the protein in glutinous amylopectin. Enthalpies of sweet potato and maize granules are higher than those of their retrograded starches. The (13)C NMR results show that retrogradation of those two starches leads to presence of ?-anomers and retrogradation might decompose lipids in glutinous rice amylopectin into small molecules. Glutinous rice starch was more inclined to retrogradation than buckwheat starch. The DSC results show that the second peak temperatures for retrograded glutinous rice and buckwheat starches should be assigned to protein. The SEM results show that an obvious layer structure exists in retrograded glutinous rice amylopectin. PMID:24360894

Lian, Xijun; Wang, Changjun; Zhang, Kunsheng; Li, Lin

2014-03-01

135

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

136

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

137

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

PubMed Central

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 13C 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 [1-13C]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

2013-01-01

138

Identification and Quantitative Determination of Dipropylene Glycol in Terpene Mixtures Using 13C NMR Spectroscopy  

Microsoft Academic Search

A method that allows direct identification and quantitative determination of dipropylene glycol (DPG) using C NMR spectroscopy was developed. The quantitative procedure was checked and validated with commercially available DPG, controlled with two DPG-added essential oils, and then applied to commercial “Extraits de parfum” (perfume extracts).

Josephine Ottavioli; Joseph Casanova; Ange Bighelli

2011-01-01

139

Cadmium chloride inhibits lactate gluconeogenesis in isolated human renal proximal tubules: a cellular metabolomic approach with 13C-NMR.  

PubMed

As part of a study on cadmium nephrotoxicity, we studied the effect of cadmium chloride (CdCl2) in isolated human renal proximal tubules metabolizing the physiological substrate lactate. Dose-effect experiments showed that 10-500 ?M CdCl2 reduced lactate removal, glucose production and the cellular levels of ATP, coenzyme A, acetyl-coenzyme A and of reduced glutathione in a dose-dependent manner. After incubation with 5 mM L: -[1-(13)C]-, or L: -[2-(13)C]-, or L: -[3-(13)C] lactate or 5 mM L: -lactate plus 25 mM NaH(13)CO3 as substrates, substrate utilization and product formation were measured by both enzymatic and carbon 13 NMR methods. Combination of enzymatic and NMR measurements with a mathematical model of lactate metabolism previously validated showed that 100 ?M CdCl2 caused an inhibition of flux through lactate dehydrogenase and alanine aminotransferase and through the entire gluconeogenic pathway; fluxes were diminished by 19% (lactate dehydrogenase), 28% (alanine aminotransferase), 28% (pyruvate carboxylase), 42% (phosphoenolpyruvate carboxykinase), and 52% (glucose-6-phosphatase). Such effects occurred without altering the oxidation of the lactate carbons or fluxes through enzymes of the tricarboxylic acid cycle despite a large fall of the cellular ATP level, a marker of the energy status and of the viability of the renal cells. These results that were observed at clinically relevant tissue concentrations of cadmium provide a biochemical basis for a better understanding of the cellular mechanism of cadmium-induced renal proximal tubulopathy in humans chronically exposed to cadmium. PMID:21153630

Faiz, Hassan; Conjard-Duplany, Agnès; Boghossian, Michelle; Martin, Guy; Baverel, Gabriel; Ferrier, Bernard

2011-09-01

140

1H and 13C NMR signal assignment of cucurbitacin derivatives from Citrullus colocynthis (L.) Schrader and Ecballium elaterium L. (Cucurbitaceae).  

PubMed

2D NMR-derived 1H and 13C NMR signal assignments of six structurally closely related cucurbitacin derivatives are presented. The investigated 2-O-beta-D-glucopyranosylcucurbitacins I, J, K, and L were obtained from Citrullus colocynthis (L.) Schrader whereas the aglyca cucurbitacin E and I were isolated from Ecballium elaterium L. PMID:15772995

Seger, Christoph; Sturm, Sonja; Mair, Maria-Elisabeth; Ellmerer, Ernst P; Stuppner, Hermann

2005-06-01

141

Effect of Oxygen Concentration on Viability and Metabolism in a Fluidized-Bed Bioartificial Liver Using 31P and 13C NMR Spectroscopy  

PubMed Central

Many oxygen mass-transfer modeling studies have been performed for various bioartificial liver (BAL) encapsulation types; yet, to our knowledge, there is no experimental study that directly and noninvasively measures viability and metabolism as a function of time and oxygen concentration. We report the effect of oxygen concentration on viability and metabolism in a fluidized-bed NMR-compatible BAL using in vivo 31P and 13C NMR spectroscopy, respectively, by monitoring nucleotide triphosphate (NTP) and 13C-labeled nutrient metabolites, respectively. Fluidized-bed bioreactors eliminate the potential channeling that occurs with packed-bed bioreactors and serve as an ideal experimental model for homogeneous oxygen distribution. Hepatocytes were electrostatically encapsulated in alginate (avg. diameter, 500??m; 3.5×107 cells/mL) and perfused at 3?mL/min in a 9-cm (inner diameter) cylindrical glass NMR tube. Four oxygen treatments were tested and validated by an in-line oxygen electrode: (1) 95:5 oxygen:carbon dioxide (carbogen), (2) 75:20:5 nitrogen:oxygen:carbon dioxide, (3) 60:35:5 nitrogen:oxygen:carbon dioxide, and (4) 45:50:5 nitrogen:oxygen:carbon dioxide. With 20% oxygen, ?-NTP steadily decreased until it was no longer detected at 11?h. The 35%, 50%, and 95% oxygen treatments resulted in steady ?-NTP levels throughout the 28-h experimental period. For the 50% and 95% oxygen treatment, a 13C NMR time course (?5?h) revealed 2-13C-glycine and 2-13C-glucose to be incorporated into [2-13C-glycyl]glutathione (GSH) and 2-13C-lactate, respectively, with 95% having a lower rate of lactate formation. 31P and 13C NMR spectroscopy is a noninvasive method for determining viability and metabolic rates. Modifying tissue-engineered devices to be NMR compatible is a relatively easy and inexpensive process depending on the bioreactor shape. PMID:22835003

Jeffries, Rex E.; Gamcsik, Michael P.; Keshari, Kayvan R.; Pediaditakis, Peter; Tikunov, Andrey P.; Young, Gregory B.; Lee, Haakil; Watkins, Paul B.

2013-01-01

142

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

PubMed

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

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

2001-10-23

143

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

144

13C and 1H chemical shift assignments and conformation confirmation of trimedlure-Y via 2-D NMR  

NASA Astrophysics Data System (ADS)

The conformation of 1,1-dimethylethyl 5-chloro- cis-2-methylcyclohexane-1-carboxylate (trimedlure-Y) was confirmed as 1,2,5 equatorial, axial, equatorial via 13C, 1H, APT, CSCM and COSY NMR analyses. The carbon and proton nuclei in trimedlure-Y and the previously unassigned eight cyclohexyl protons (1.50-2.60 ppm) in 1,1-dimethylethyl 5-chloro- trans-2-methylcyclohexane-1-carboxylate (trimedlure-B 1; 1,2,5 equatorial, equatorial, equatorial) were also characterized by these methods. The effects of the 2-CH 3 in the axial or equatorial conformation upon the chemical shifts of the other nuclei in the molecule are discussed.

Warthen, J. D.; Waters, R. M.; McGovern, T. P.

145

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

PubMed

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

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

2008-12-01

146

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

PubMed Central

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

Duchardt, Elke; Nilsson, Lennart

2008-01-01

147

Probing Interactions between ?-Glucan and Bile Salts at Atomic Detail by (1)H-(13)C NMR Assays.  

PubMed

Polysaccharides are prospective hosts for the delivery and sequestration of bioactive guest molecules. Polysaccharides of dietary fiber, specifically cereal (1 ? 3)(1 ? 4)-?-glucans, play a role in lowering the blood plasma cholesterol level in humans. Direct host-guest interactions between ?-glucans and conjugated bile salts are among the possible molecular mechanisms explaining the hypocholesterolemic effects of ?-glucans. The present study shows that (1)H-(13)C NMR assays on a time scale of minutes detect minute signal changes in both bile salts and ?-glucans, thus indicating dynamic interactions between bile salts and ?-glucans. Experiments are consistent with stronger interactions at pH 5.3 than at pH 6.5 in this in vitro assay. The changes in bile salt and ?-glucan signals suggest a stabilization of bile salt micelles and concomitant conformational changes in ?-glucans. PMID:25375023

Mikkelsen, Mette Skau; Cornali, Sofia Bolvig; Jensen, Morten G; Nilsson, Mathias; Beeren, Sophie R; Meier, Sebastian

2014-11-26

148

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

149

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

SciTech Connect

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

Matwiyoff, N.A.

1981-01-01

150

Cerebral glucose metabolism and the glutamine cycle as detected by in vivo and in vitro 13C NMR spectroscopy.  

PubMed

We review briefly 13C NMR studies of cerebral glucose metabolism with an emphasis on the roles of glial energetics and the glutamine cycle. Mathematical modeling analysis of in vivo 13C turnover experiments from the C4 carbons of glutamate and glutamine are consistent with: (i) the glutamine cycle being the major cerebral metabolic route supporting glutamatergic neurotransmission, (ii) glial glutamine synthesis being stoichiometrically coupled to glycolytic ATP production, (iii) glutamine serving as the main precursor of neurotransmitter glutamate and (iv) glutamatergic neurotransmission being supported by lactate oxidation in the neurons in a process accounting for 60-80% of the energy derived from glucose catabolism. However, more recent experimental approaches using inhibitors of the glial tricarboxylic acid (TCA) cycle (trifluoroacetic acid, TFA) or of glutamine synthase (methionine sulfoximine, MSO) reveal that a considerable portion of the energy required to support glutamine synthesis is derived from the oxidative metabolism of glucose in the astroglia and that a significant amount of the neurotransmitter glutamate is produced from neuronal glucose or lactate rather than from glial glutamine. Moreover, a redox switch has been proposed that allows the neurons to use either glucose or lactate as substrates for oxidation, depending on the relative availability of these fuels under resting or activation conditions, respectively. Together, these results suggest that the coupling mechanisms between neuronal and glial metabolism are more complex than initially envisioned. PMID:15145545

García-Espinosa, María A; Rodrigues, Tiago B; Sierra, Alejandra; Benito, Marina; Fonseca, Carla; Gray, Heather L; Bartnik, Brenda L; García-Martín, María L; Ballesteros, Paloma; Cerdán, Sebastián

2004-01-01

151

13C NMR Characterization of an Exchange Reaction between CO and CO2 Catalyzed by Carbon Monoxide Dehydrogenase†  

PubMed Central

Carbon monoxide dehydrogenase (CODH) catalyzes the reversible oxidation of CO to CO2 at a nickel?iron?sulfur cluster (the C-cluster). CO oxidation follows a ping-pong mechanism involving two-electron reduction of the C-cluster followed by electron transfer through an internal electron transfer chain to external electron acceptors. We describe 13C NMR studies demonstrating a CODH-catalyzed steady-state exchange reaction between CO and CO2 in the absence of external electron acceptors. This reaction is characterized by a CODH-dependent broadening of the 13CO NMR resonance; however, the chemical shift of the 13CO resonance is unchanged, indicating that the broadening is in the slow exchange limit of the NMR experiment. The 13CO line broadening occurs with a rate constant (1080 s?1 at 20 °C) that is approximately equal to that of CO oxidation. It is concluded that the observed exchange reaction is between 13CO and CODH-bound 13CO2 because 13CO line broadening is pH-independent (unlike steady-state CO oxidation), because it requires a functional C-cluster (but not a functional B-cluster) and because the 13CO2 line width does not broaden. Furthermore, a steady-state isotopic exchange reaction between 12CO and 13CO2 in solution was shown to occur at the same rate as that of CO2 reduction, which is approximately 750-fold slower than the rate of 13CO exchange broadening. The interaction between CODH and the inhibitor cyanide (CN?) was also probed by 13C NMR. A functional C-cluster is not required for 13CN? broadening (unlike for 13CO), and its exchange rate constant is 30-fold faster than that for 13CO. The combined results indicate that the 13CO exchange includes migration of CO to the C-cluster, and CO oxidation to CO2, but not release of CO2 or protons into the solvent. They also provide strong evidence of a CO2 binding site and of an internal proton transfer network in CODH. 13CN? exchange appears to monitor only movement of CN? between solution and its binding to and release from CODH. PMID:18589895

2008-01-01

152

13C NMR study of the metal-insulator transition in (DMe-DCNQI)2Cu systems with partial deuteration  

NASA Astrophysics Data System (ADS)

The electronic states of a series of (DMe-DCNQI)2Cu systems with nondeuterated and partially deuterated methyl groups in a DMe-DCNQI molecule have been investigated by 13C NMR measurements at the cyano carbon sites. The Knight shift of the nondeuterated specimen, which is metallic in the whole temperature range, is not scaled to the total spin susceptibility, demonstrating that the metallic state has several electronic bands with different local spin susceptibility due to the ?-d hybridization. In the insulating phases of the partially deuterated specimens, 13C NMR spectra are split into two lines, one of which has a nearly zero shift and the other has a large positive shift with the Curie-Weiss temperature dependence. The former line comes from the cyano group coordinated to the nonmagnetic Cu+ ion, while the latter comes from the cyano group coordinated to the magnetic Cu2+ ion. The sign of the shift and intensity analysis provide an evidence that, in the insulating phase, spin is localized exclusively at one-third of the Cu sites without any population on the DCNQI molecule. This is considered as a manifestation of strong electron correlation in the Cu sites. The low-temperature reentrant metallic state in the partially deuterated system is found to be just the same as the stable metallic state in the nondeuterated system through the shift and relaxation rate behaviors. No fluctuations are observed in the vicinity of the metal-insulator and insulator-metal reentrant transitions, showing that the transitions are of the first order.

Kawamoto, A.; Miyagawa, K.; Kanoda, K.

1998-07-01

153

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

154

13 C and 1 H NMR spectra and stereoconfiguration of 1,4-adducts of the Diels-Alder reaction of furan with methyl acrylate and maleic anhydride  

Microsoft Academic Search

13C and1H NMR spectra were taken for the 1,4-adducts of furan with methyl acrylate and maleic anhydride. The13C chemical shifts are characteristic: these values for C1, C3, and C6 (adducts (I) and (II)) and C1, C4 C2, C3, C5, and C6 (adducts (III) and (IV)) depend on the orientation of the substituent at C2 in the case of methyl acrylate

Vo So Bogdanov; M. V. Kel'tseva; V. M. Zhulin

1990-01-01

155

Comparative sup 13 C and sup 31 P NMR assessment of altered metabolism during graded reductions in coronary flow in intact rat hearts  

SciTech Connect

{sup 13}C NMR spectroscopy may offer a unique ability to characterize the metabolic response to graded reductions in coronary flow since it allows repeated, nondestructive identification of products of intermediary metabolism in the same heart. The sensitivity of {sup 13}C parameters of glucose metabolism was compared with changes in levels of phosphocreatine, ATP, and pH as determined by {sup 31}P NMR in the intact, beating rat heart model during graded reductions in coronary flow. Experiments were performed during 60 min of perfusion with (1-{sup 13}C)glucose at normal flow and at the reduced flow rates of 5 and 2 ml/min. During flow at 5 ml/min, isovolumic developed pressure fell to 51 {plus minus} 4% of control. Although phosphocreatine, ATP, and pH were not changed, (3-{sup 13}C)lactate was increased. In addition, the time to 50% maximum enrichment of (2-{sup 13}C)glutamate was prolonged indicating that glucose-supported flux through the tricarboxylic acid (TCA) cycle was decreased. The relative anaplerotic contribution to citrate synthase-supported TCA flux was increased from 6% to 35%. These {sup 13}C metabolic changes could not be reproduced by reduced (1-{sup 13}C)glucose delivery in the absence of ischemia, although similar reduced TCA flux indices were reproduced in additional hearts when workload was reduced by low calcium perfusion. Therefore, the information provided by {sup 13}C NMR spectroscopy can be a more sensitive indicator of flow-induced alterations in cardiac metabolism than that provided by the much more commonly used {sup 31}P NMR technique.

Weiss, R.G.; Chacko, V.P.; Glickson, J.D.; Gerstenblith, G. (Johns Hokpins Hospital, Baltimore, MD (USA) Johns Hopkins Univ. School of Medicine, Baltimore, MD (USA))

1989-08-01

156

The influence of heme ruffling on spin densities in ferricytochromes c probed by heme core 13C NMR  

PubMed Central

The heme in cytochromes c undergoes a conserved out-of-plane distortion known as ruffling. For cytochromes c from the bacteria Hydrogenobacter thermophilus and Pseudomonas aeruginosa, NMR and EPR spectra have been shown to be sensitive to the extent of heme ruffling and to provide insights into the effect of ruffling on electronic structure. Using mutants of each of these cytochromes that differ in the amount of heme ruffling, NMR characterization of the low-spin (S=1/2) ferric proteins has confirmed and refined the developing understanding of how ruffling influences spin distribution on heme. The chemical shifts of the core heme carbons were obtained through site-specific labeling of the heme via biosynthetic incorporation of 13C-labeled 5-aminolevulinic acid derivatives. Analysis of the contact shifts of these core heme carbons allowed Fermi contact spin densities to be estimated, and changes upon ruffling to be evaluated. The results allow a deconvolution of contributions to heme hyperfine shifts and a test of the influence of heme ruffling on electronic structure and hyperfine shifts. The data indicate that as heme ruffling increases, the spin densities on the ?-pyrrole carbons decrease, while the spin densities on the ?-pyrrole carbons and meso carbons increase. Furthermore, increased ruffling is associated with stronger bonding to the heme axial His ligand. PMID:24187968

Kleingardner, Jesse G.; Bowman, Sarah E. J.

2013-01-01

157

Development and application of aromatic [(13)C, (1)H] SOFAST-HMQC NMR experiment for nucleic acids.  

PubMed

Higher sensitivity of NMR spectrometers and novel isotopic labeling schemes have ushered the development of rapid data acquisition methodologies, improving the time resolution with which NMR data can be acquired. For nucleic acids, longitudinal relaxation optimization in conjunction with Ernst angle excitation (SOFAST-HMQC) for imino protons, in addition to rendering rapid pulsing, has been demonstrated to yield significant improvements in sensitivity per unit time. Extending such methodology to other spins offers a viable prospect to measure additional chemical shifts, thereby broadening their utilization for various applications. Here, we introduce the 2D [(13)C, (1)H] aromatic SOFAST-HMQC that results in overall sensitivity gain of 1.4- to 1.7-fold relative to the conventional HMQC and can also be extended to yield long-range heteronuclear chemical shifts such as the adenine imino nitrogens N1, N3, N7 and N9. The applications of these experiments range from monitoring real-time biochemical processes, drug/ligand screening, and to collecting data at very low sample concentration and/or in cases where isotopic enrichment cannot be achieved. PMID:25186910

Sathyamoorthy, Bharathwaj; Lee, Janghyun; Kimsey, Isaac; Ganser, Laura R; Al-Hashimi, Hashim

2014-11-01

158

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

PubMed

Fourier transform infrared (FTIR) and 13C MAS NMR spectroscopy have been used to investigate the acetylation of raw cotton samples with acetic anhydride without solvents in the presence of different amounts of 4-dimethylaminopyridine (DMAP) catalyst. This is a continuation of our previous investigation of acetylation of commercial cotton in an effort to develop hydrophobic, biodegradable, cellulosic sorbent materials for cleaning up oil spills. The FTIR data have again provided a clear evidence for successful acetylation. The NMR results further confirm the successful acetylation. The extent of acetylation was quantitatively determined using the weight percent gain (WPG) due to acetylation and by calculating the ratio R between the intensity of the acetyl C=O stretching band at 1740-1745 cm(-1) and the intensity of C-O stretching vibration of the cellulose backbone at about 1020-1040 cm(-1). The FTIR technique was found to be highly sensitive and reliable for the determination of the extent of acetylation. The level of acetylation of the raw cotton samples was found to be much higher than that of cotton fabrics and the previously studied commercial cotton. The variation of the R and WPG with reaction time, amount of DMAP catalyst and different samples of raw cotton is discussed. PMID:15249021

Adebajo, Moses O; Frost, Ray L

2004-08-01

159

Supramolecular assembly of dendritic polymers elucidated by 1H and 13C solid-state MAS NMR spectroscopy.  

PubMed

Advanced solid-state NMR methods under fast magic-angle spinning (MAS) are used to study the structure and dynamics of large supramolecular systems, which consist of a polymer backbone with dendritic side groups and self-assemble into a columnar structure. The NMR experiments are performed on as-synthesized samples, i.e., no isotopic enrichment is required. The analysis of (1)H NMR chemical-shift effects as well as dipolar (1)H-(1)H or (1)H-(13)C couplings provide site-specific insight into the local structure and the segmental dynamics, in particular, of phenyl rings and -CH(2)O- linking units within the dendrons. Relative changes of (1)H chemical shifts (of up to -3 ppm) serve as distance constraints and allow protons to be positioned relative to aromatic rings. Together with dipolar spinning sideband patterns, pi-pi packing phenomena and local order parameters (showing variations between 30% and 100%) are selectively and precisely determined, enabling the identification of the dendron cores as the structure-directing moieties within the supramolecular architecture. The study is carried out over a representative selection of systems which reflect characteristic differences, such as different polymer backbones, sizes of dendritic side groups, or length and flexibility of linking units. While the polymer backbone is found to have virtually no effect on the overall structure and properties, the systems are sensitively affected by changing the generation or the linkage of the dendrons. The results help to understand the self-assembly process of dendritic moieties and aid the chemical design of self-organizing molecular structures. PMID:14570506

Rapp, Almut; Schnell, Ingo; Sebastiani, Daniel; Brown, Steven P; Percec, Virgil; Spiess, Hans Wolfgang

2003-10-29

160

Assignment of 13C Resonances in the Phencyclone-Norbornadiene Adduct Via 2D NMR. 13C Evidence for Hindered Rotation of Unsubstituted Bridgehead Phenyl Rings  

Microsoft Academic Search

C NMR chemical shift assignments were obtained for the Diels-Alder adduct of phencyclone with norbornadiene in CD2Cl2 and in CDCl3 solution. The C spectrum at 50.3 MHz, as well as the H spectrum at 200.1 MHz, show evidence for hindered rotation of the two unsubstituted bridgehead phenyl rings of the adduct at ambient temperatures. In CD2Cl2 solution, all 19 of

Yangdong Xu; Laurine A. LaPlanche; Robert Rothchild

1993-01-01

161

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

PubMed

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

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

2011-03-01

162

Determination of the structural changes by Raman and 13C CP/MAS NMR spectroscopy on native corn starch with plasticizers  

NASA Astrophysics Data System (ADS)

The plasticizing - antiplasticizing effect of water and glycerol contents on native corn starch samples is investigated by FT-Raman and 13C CP/MAS NMR spectroscopy. The presence of both amorphous and crystalline structural phases was evidenced in pure native corn starch and also in the samples containing plasticizers. Among the crystalline starch structures, the A- and V- types were suggested by CP/MAS NMR spectra.

Cozar, O.; Filip, C.; Cioica, N.; Coţa, C.; Tripon, C.; Nagy, E. M.

2013-11-01

163

13C- and 15N-NMR spectroscopic examination of the transformation of organic nitrogen in plant biomass during thermal treatment  

Microsoft Academic Search

Structural changes in lignocellulosic biomass heated under conditions comparable to those encountered in several types of natural or planned burnings have been studied by solid-state 13C- and 15N-CPMAS NMR spectroscopy of 15N-enriched ryegrass (Lolium rigidum) after being subjected to progressive thermal treatment. The solid-state 15N-NMR spectra of biomass subjected to severe heating revealed amide-N in forms which are resistant to

H. Knicker; G. Almendros; F. J. González-Vila; F. Martin; H.-D. Lüdemann

1996-01-01

164

Molecular structure, vibrational and 13C NMR spectra of two ent-kaurenes spirolactone type diterpenoids rabdosinate and rabdosin B: a combined experimental and density functional methods.  

PubMed

The title compounds, rabdosinate and rabdosin B, were isolated from the leaves of Isodon japonica, and characterized by IR-NMR spectroscopy. The molecular geometry, vibrational frequencies and gauge including atomic orbital (GIAO-13C) chemical shift values of the title compounds have been calculated by using DFT/B3LYP method with 6-311++G(d,p) basis set. In addition, obtained results were related to the linear regression of experimental 13C NMR chemical shifts values. The integral equation formalism polarized continuum model (IEFPCM) was used in treating chloroform solvation effects on optimized structural parameters and 13C chemical shifts. Besides, molecular electrostatic potential (MEP), HOMO-LUMO analysis were performed by the B3LYP method. PMID:25123947

Wang, Tao; Wang, Xueliang

2015-01-25

165

Use of ionic liquids in the study of fruit ripening by high-resolution 13C NMR spectroscopy: 'green' solvents meet green bananas.  

PubMed

Banana pulps at any ripening stage can be completely dissolved in solvent systems based on the ionic liquid (IL) 1-n-butyl-3-methylimidazolium chloride ([C4mim]Cl), and variations in the carbohydrate composition of the fruit analyzed directly on the resulting solutions using high-resolution 13C NMR spectroscopy. PMID:16465316

Fort, Diego A; Swatloski, Richard P; Moyna, Patrick; Rogers, Robin D; Moyna, Guillermo

2006-02-21

166

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

Microsoft Academic Search

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

M. Vinceslas-Akpa; M. Loquet

1997-01-01

167

In situ {sup 13}C MAS NMR study of n-hexane conversion on Pt and Pd supported on basic materials  

SciTech Connect

n-Hexane conversion was studied in situ on Pt and Pd supported on aluminum-stabilized magnesium oxide and Pt on Zeolite KL catalysts (Pt/Mg(Al)O, Pd/Mg(Al)O and Pt/KL) by means of {sup 13}C MAS NMR spectroscopy. n-Hexane 1-{sup 13}C 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 NMR results were further quantified and compared with continuous flow microreactor tests. Four parallel reaction pathways were identified under flow conditions: isomerization, cracking, dehydrocyclization, and dehydrogenation. Aromatization occurs via two reaction routes: (1) n-hexane dehydrogenation towards hexadienes and hexatrienes, followed by dehydrogenation of a cyclic intermediate. The former reaction pathway is prevented under NMR batch conditions. High pressures induced in the NMR cells at high reaction temperatures (573, 653 K) shift the reaction equilibrium towards hydrogenation. NMR experiments showed that on Pt catalysts aromatization occurs via a cyclohexane intermediate, whereas on Pd it takes place via methylcyclopentane ring enlargement. 54 refs., 15 figs., 3 tabs.

Ivanova, I.I.; Pasau-Claerbout, A.; Seivert, M.; Derouane, E.G. [Facultes Universitaires N.D. de la Paix, Namur (Belgium)] [and others] [Facultes Universitaires N.D. de la Paix, Namur (Belgium); and others

1996-02-01

168

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

169

1H and 13C NMR studies of glycine in anisotropic media: Double-quantum transitions and the effects of chiral interactions  

NASA Astrophysics Data System (ADS)

The 1H NMR spectrum of glycine in stretched gelatin gel and in cromolyn liquid crystal displays a well-resolved doublet due to 1H- 1H dipolar interaction. Multiple spectra were obtained within a wide range of offset frequencies of partially saturating radio-frequency (RF) radiation to generate steady-state irradiation envelopes or z-spectra of glycine. Maximal suppression of the doublet occurred when the irradiation was applied exactly at the centre frequency, between the two glycine peaks. This phenomenon is due to double-quantum transitions and is similar to our previous work on quadrupolar nuclei 2H (HDO) and 23Na +. When the 13C isotopomer glycine-2- 13C was used, the same effect was found in twice, split by 1JCH + 2 DCH. Additional signals in 1H and 13C NMR due to prochiral-chiral interactions were found when glycine-2- 13C was dissolved in chiral anisotropic gelatin and ?-carrageenan gels. The NMR spectra were successfully simulated assuming a 2JHH coupling constant of -16.5 Hz and two distinct dipolar coupling constants for the - 13CH 2- group ( DC,HA, and DC,HB).

Naumann, Christoph; Kuchel, Philip W.

2011-07-01

170

Solid state {sup 1}H and {sup 13}C NMR structural investigation of a poly(ethylene oxide) hydrogel  

SciTech Connect

A cross-linked poly (ethylene oxide)/polyurethane hydrogel cross-linked with 1,2,6 hexane-triol and designated PEG4050/1HT [measured M{sup n} of 4050 for poly (ethylene oxide) glycol (PEG) and a mole ratio of 1:1 for the PEG to the 1,2,6 hexane-triol] has been characterized by high resolution {sup 1}H and {sup 13}C NMR. {sup 1}H thermal (T{sub 1}) and rotating frame (T{sub 1{rho}}) and {sup 13}CT{sub 1} relaxation times were determined for the powdered dry and swollen hydrogel with the standard variants of the cross-polarization pulse sequence which was used in conjunction with magic-angle spinning (MAS). The rotating frame relaxation measurements confirmed that crystalline and amorphous regions were present in the dry hydrogel but showed unabiguously that the crystalline regions are confined to the poly (ethylene oxide) chains, Upon hydration, there is a decrease in the cross polarization efficiency from the enhanced mobility by the poly (ethylene oxide) chains are affected to a much greater extent that the urethane and hexane segments, the characteristic time constant, T{sub CH} increasing by more than order of magnitude compared to no more than a factor of two for the latter. Clearly, the hydration involves hydrogen bonding between the water and principally the oxygens in the poly (ethylene oxide) chains. The {sup 1}H MAS spectra of the dry and hydrated samples confirmed that considerable averaging of the dipolar interactions occurs on hydration to give a well-resolved spectrum.

Badiger, M.V.; Graham, N.B.; Law, R.V.; Snape, C.E. [Univ. of Strathclyde, Glasgow (United Kingdom)

1993-12-31

171

Separation of aromatic-carbon 13C NMR signals from di-oxygenated alkyl bands by a chemical-shift-anisotropy filter  

Microsoft Academic Search

Selection of alkyl-carbon and suppression of aromatic-carbon 13C nuclear magnetic resonance (NMR) signals has been achieved by exploiting the symmetry-based, systematic difference in their 13C chemical-shift anisotropies (CSAs). Simple three- or five-pulse CSA-recoupling sequences with “gamma-integral” cleanly suppress the signals of all sp2- and sp-hybridized carbons. The chemical-shift-anisotropy-based dephasing is particularly useful for distinguishing the signals of di-oxygenated alkyl (O–C–O)

J.-D. Mao; K. Schmidt-Rohr

2004-01-01

172

Solid-state 19F and 13C NMR of room temperature fluorinated graphite and samples thermally treated under fluorine: Low-field and high-resolution studies  

NASA Astrophysics Data System (ADS)

Room temperature graphite fluorides consisting of raw material and samples post-treated in pure fluorine atmosphere in the temperature range 100-500 °C have been studied by solid-state NMR. Several NMR approaches have been used, both high and low-field 19F, 19F MAS and 13C MAS with 19F to 13C cross polarization. The modifications, in the graphitic lattice, of the catalytic iodine fluorides products have been examined. A transformation of the C-F bond character from semi-ionic to covalent has been found to occur at a post-treatment temperature close to 400 °C. It is shown that covalency increases with temperature.

Giraudet, J.; Dubois, M.; Guérin, K.; Pinheiro, J. P.; Hamwi, A.; Stone, W. E. E.; Pirotte, P.; Masin, F.

2005-04-01

173

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

174

Synthesis and multinuclear NMR study ( 1H, 11B, 13C, 14N, 15N, 31P, 77Se) of N-azolyl-phosphorus compounds  

NASA Astrophysics Data System (ADS)

The synthesis of N-azolyl (pyrrole, pyrazole, 1,2,4-triazole) phosphorus compounds containing P III or P V is described. The title compounds were studied by multinuclear NMR ( 1H, 11B, 13C, 14N, 15N, 31P, 77Se) with particular emphasis on [ 15N]NMR parameters. Experimental details are given for the natural abundance [ 15N]NMR spectra and the advantage of the various techniques is discussed. The comparison between values 1J( 31P 15N azole) and 1J( 31P 15N alkyl) shows that the nature of the lone electron pair of the trigonal nitrogen atoms is of minor importance as far as the changes in the magnitude of the coupling constants are concerned. Sterical interactions and inductive effects are reflected by the [ 15N]NMR parameters. Both P III and P V appear to be very weak ?-acceptors as is evident from ? 15N and ? 13C values. P?N( dp)? interactions are hardly reflected by [ 15N]NMR parameters.

Wrackmeyer, Bernd

175

Molecular Characterization of Compost at Increasing Stages of Maturity. 2. Thermochemolysis?GC-MS and 13 C-CPMAS-NMR Spectroscopy  

Microsoft Academic Search

Off-line pyrolysis TMAH-GC-MS (thermochemolysis) and solid-state 13C NMR spectroscopy were applied for the direct molecular characterization of composted organic biomasses after 60, 90, and 150 days of maturity. Off-line thermochemolysis of both fresh and mature composts released various lignin-derived molecules, the quantitative measurement of which was used to calculate structural indices related to compost maturity. These indicated that most of

Riccardo Spaccini; Alessandro Piccolo

2007-01-01

176

A practical synthesis of the 13C/15N-labelled tripeptide N-formyl-Met-Leu-Phe, useful as a reference in solid-state NMR spectroscopy  

PubMed Central

Summary A mild synthetic method for N-formyl-Met-Leu-Phe-OH (1) is described. After Fmoc solid phase peptide synthesis, on-bead formylation and HPLC purification, more than 30 mg of the fully 13C/15N-labelled tripeptide 1 could be isolated in a typical batch. This peptide can be easily crystallised and is therefore well suited as a standard sample for setting up solid-state NMR experiments. PMID:18982075

Lopez, Jakob J; Durner, Gerd; Glaubitz, Clemens

2008-01-01

177

NMR and molecular modeling in environmental chemistry: prediction of 13C chemical shifts in selected C 10-chloroterpenes employing DFT\\/GIAO theory  

Microsoft Academic Search

Accurate predictions of 13C NMR chemical shifts (standarderror?1.7 ppm) are achieved for a subset of chlorinated bornanes by empirical scaling of shifts from GIAO calculations with geometries obtained from HF\\/6-31G* calculations. The optimized molecular geometries were compared with X-ray structures for three of the toxaphene components most frequently detected in environmental samples (Parlar nos. 26, 50 and 62), and the

Kari Tuppurainen; Juhani Ruuskanen

2003-01-01

178

Hydrolysis of Functional Monomers in a Single-bottle Self-etching Primer—Correlation of 13C NMR and TEM Findings  

Microsoft Academic Search

Self-etching primers\\/adhesives that combine acidic methacrylate monomers with water in a single bottle are hydrolytically unstable and require refrigeration to extend their shelf-lives. This study tested the null hypothesis that one year of intermittent refrigeration of a 4-MET-containing simplified self-etching primer does not result in hydrolytic changes that are identifiable by transmission electron microscopy and 13C NMR spectroscopy. Human dentin

N. Nishiyama; F. R. Tay; K. Fujita; D. H. Pashley; K. Ikemura; N. Hiraishi; N. M. King

2006-01-01

179

Alterations in the natural abundance /sup 13/C NMR spectra of skeletal muscle membranes depending on the extraction medium of muscle  

SciTech Connect

Minced rat muscles were extracted with NaCl solution with additions: 1) 10 mM EDTA, or 2) 2 mM MgCl/sub 2/, or 3) None (final ionic strength equivalent to 150 mM NaCl, pH 7.0). The total muscle membranes were pelleted between 1500 and 252,000 x g. All membranes were washed several times by homogenization with 0.05 M NaCl, pH 6.1, and centrifugation at 252,000 x g. The final pellets were suspended in /sup 2/H/sub 2/O to contain 150 mg membrane protein/ml in 30% /sup 2/H/sub 2/O. /sup 13/C NMR spectra were recorded at 50.3 MHz, under fully relaxed conditions. The spectral pattern varied according to the extraction medium of muscle: Relative to None addition, EDTA caused a decrease in the intensity of the polyunsaturated carbon resonance (128.6 ppm), whereas with MgCl/sub 2/ the opposite effect was found. Metal analysis, after combustion of the membranes, showed 1.1-1.6 mol Ca/sup 2 +/ per 10/sup 5/ g protein in None and Mgcl/sub 2/ membranes, and 1000-times less Ca/sup 2 +/ in EDTA membranes. The Mg/sup 2 +/ content of the membranes was not affected by EDTA, however, it was increased 5-fold when MgCl/sub 2/ was present in the extraction medium. Thus, the results indicate that membrane-bound Ca/sup 2 +/ and Mg/sup 2 +/ alter the conformation of membrane-phospholipis.

Barany, M.; Arus, C.; Anderson, J.A.; Marotta, S.F.

1986-03-01

180

A novel tridentate Schiff base dioxo-molybdenum(VI) complex: Synthesis, experimental and theoretical studies on its crystal structure, FTIR, UV-visible, 1H NMR and 13C NMR spectra  

NASA Astrophysics Data System (ADS)

A new dioxo-molybdenum(VI) complex [MoO2(L)(H2O)] has been synthesized, using 5-methoxy 2-[(2-hydroxypropylimino)methyl]phenol as tridentate ONO donor Schiff base ligand (H2L) and MoO2(acac)2. The yellow crystals of the compound are used for single-crystal X-ray analysis and measuring Fourier Transform Infrared (FTIR), UV-visible, 1H NMR and 13C NMR spectra. Electronic structure calculations at the B3LYP and PW91PW91 levels of theory are performed to optimize the molecular geometry and to calculate the UV-visible, FTIR, 1H NMR and 13C NMR spectra of the compound. Vibrational assignments and analysis of the fundamental modes of the compound are performed. Time-dependent density functional theory (TDDFT) method is used to calculate the electronic transitions of the complex. All theoretical methods can well reproduce the structure of the compound. The 1H NMR shielding tensors computed at the B3LYP/DGDZVP level of theory is in agreement with experimental 1H NMR spectra. However, the 13C NMR shielding tensors computed at the B3LYP level, employing a combined basis set of DGDZVP for Mo and 6 - 31 + G(2df,p) for other atoms, are in better agreement with experimental 13C NMR spectra. The electronic transitions calculated at the B3LYP/DGDZVP level by using TD-DFT method is in accordance with the observed UV-visible spectrum of the compound.

Saheb, Vahid; Sheikhshoaie, Iran; Stoeckli-Evans, Helen

2012-09-01

181

Multidimensional spatial-spectral holographic interpretation of NMR photography  

Microsoft Academic Search

A spectral holographic interpretation arises naturally in nuclear magnetic resonance (NMR) photography from either the intrinsic chemical shift anisotropy of the spin system or the field inhomogeneity due to the applied spatial encoding gradients. We can thus think of NMR photography as arising from a “diffraction” off a spatial-spectral holographic grating. The spatial holographic component arises from a high dielectric

Andrew J. M. Kiruluta

2006-01-01

182

Multidimensional spatial-spectral holographic interpretation of NMR photography  

Microsoft Academic Search

A spectral holographic interpretation arises naturally in nuclear magnetic resonance (NMR) photography from either the intrinsic chemical shift anisotropy of the spin system or the field inhomogeneity due to the applied spatial encoding gradients. We can thus think of NMR photography as arising from a ``diffraction'' off a spatial-spectral holographic grating. The spatial holographic component arises from a high dielectric

Andrew J. M. Kiruluta

2006-01-01

183

Evaluation of a semipolar solvent system as a step toward heteronuclear multidimensional NMR-based metabolomics for 13C-labeled bacteria, plants, and animals.  

PubMed

Nuclear magnetic resonance (NMR) has become a key technology in metabolomics, with the use of stable isotope labeling and advanced heteronuclear multidimensional NMR techniques. In this paper, we focus on the evaluation of extraction solvents to improve NMR-based methodologies for metabolomics. Line broadening is a serious barrier to detecting signals and the annotation of metabolites using multidimensional NMR. We evaluated a series of NMR solvents for easy and versatile single-step extraction using the (13)C-labeled photosynthetic bacterium Rhodobacter sphaeroides, which shows pronounced broadening of NMR signals. The performance of each extraction solvent was judged using 2D (1)H-(13)C heteronuclear single quantum coherence (HSQC) spectra, considering three metrics: (1) distribution of the line width at half height, (2) number of observed signals, and (3) the total observed signal intensity. Considering the total rank values for the three metrics, we chose methanol-d(4) (MeOD) as a semipolar extraction solvent that can sufficiently sharpen the line width and affords better-quality NMR spectra. We also evaluated the series of extraction solvents by means of inductively coupled plasma optical emission spectroscopy (ICP-OES) based ionomics approach. It was also indicated that MeOD is useful for excluding paramagnetic ions as well as macromolecules in an easy single-step extraction. MeOD extraction also appeared to be effective for other bacterial and animal samples. An additional advantage of this semipolar solvent is that it supplements the aqueous (polar) buffer system reported by many groups. The flexible, appropriate application of polar and semipolar extraction should contribute to the large-scale analysis of metabolites. PMID:21208007

Sekiyama, Yasuyo; Chikayama, Eisuke; Kikuchi, Jun

2011-02-01

184

Recoupling of chemical shift anisotropies in solid-state NMR under high-speed magic-angle spinning and in uniformly 13C-labeled systems  

NASA Astrophysics Data System (ADS)

We demonstrate the possibility of recoupling chemical shift anisotropy (CSA) interactions in solid-state nuclear magnetic resonance (NMR) under high-speed magic-angle spinning (MAS) while retaining a static CSA powder pattern line shape and simultaneously attenuating homonuclear dipole-dipole interactions. CSA recoupling is accomplished by a rotation-synchronized radio-frequency pulse sequence with symmetry properties that permit static CSA line shapes to be obtained. We suggest a specific recoupling sequence, which we call ROCSA, for which the scaling factors for CSA and homonuclear dipole-dipole interactions are 0.272 and approximately 0.05, respectively. This sequence is suitable for high-speed 13C MAS NMR experiments on uniformly 13C-labeled organic compounds, including biopolymers. We demonstrate the ROCSA sequence experimentally by measuring the 13C CSA patterns of the uniformly labeled, polycrystalline compounds L-alanine and N-acetyl-D,L-valine at MAS frequencies of 11 and 20 kHz. We also present experimental data for amyloid fibrils formed by a 15-residue fragment of the ?-amyloid peptide associated with Alzheimer's disease, in which four amino acid residues are uniformly labeled, demonstrating the applicability to biochemical systems of high molecular weight and significant complexity. Analysis of the CSA patterns in the amyloid fibril sample demonstrates the utility of ROCSA measurements as probes of peptide and protein conformation in noncrystalline solids.

Chan, Jerry C. C.; Tycko, Robert

2003-05-01

185

Comparison of ovine, bovine and porcine mucosal heparins and low molecular weight heparins by disaccharide analyses and 13C NMR  

Microsoft Academic Search

Ovine, porcine and bovine heparin were compared by NMR, disaccharide composition, optical rotation, elemental analyses, HPSEC and USP analyses. There were some differences found in the NMR and disaccharide composition of the heparins. Ovine heparin contained less monosulphated and disulphated disaccharides than porcine or bovine mucosal heparins. The heparins were approximately equivalent in USP activity.Low molecular weight ovine, porcine and

D. K. Watt; S. C. Yorke; G. C. Slim

1997-01-01

186

Quantum-chemical analysis of paramagnetic 13C NMR shifts of iron-bound cyanide ions in heme-protein environments  

NASA Astrophysics Data System (ADS)

Paramagnetic 13C NMR chemical shifts of iron-bound cyanide ions located in biological environments such as heme-proteins are significantly sensitive to the environments. These chemical shifts are due to negative spin density at 13C induced by the open-shell iron center. In order to examine the environments effects on the electronic states around heme parts, ab initio calculations were performed for model systems of heme-proteins. The proximal residues in proteinparts of cytochrome c, hemoglobin, myoglobin and horseradish peroxidase were included in the model systems with the common active site (cyanide imidazole porphyrinato iron(III)) to take account of the environments effects. The calculated paramagnetic shifts of model systems reproduce the experimental trend of corresponding heme-proteins. It is found that the effects of proximal residues on the electronic states of the heme-parts are significant for these hemeproteins. In this abstract we focused on the calculations and analysis of cytochrome c.

Yamaki, Daisuke; Hada, Masahiko

2012-12-01

187

Stoichiometric Relationship between Na+ Ions Transported and Glucose Consumed in Human Erythrocytes: Bayesian Analysis of 23Na and 13C NMR Time Course Data  

PubMed Central

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 13C and 23Na NMR methods allowed the recording of intra- and extracellular Na+, and 13C-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.

2013-01-01

188

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

189

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

190

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

191

Single crystal structure, spectroscopic (FT-IR, FT-Raman, 1H NMR, 13C NMR) studies, physico-chemical properties and theoretical calculations of 1-(4-chlorophenyl)-3-(4-nitrophenyl)triazene.  

PubMed

In this paper, we will report a combined experimental and theoretical investigation of the molecular structure and spectroscopic parameteres (FT-IR, FT-Raman, (1)H NMR, (13)C NMR) of 1-(4-chlorophenyl)-3-(4-nitrophenyl)triazene, CNT. The optimized geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities were obtained at the B3LYP/6-311++G(d,p) level of theory and thermodynamic functions were calculated at the same level. A detailed interpretation of the Infrared, Raman and NMR spectra of the compound was reported as well. Analysis of experimental NMR chemical shifts was supported by quantum chemical calculations and HOSE code fragment based prediction tool (ACD/NMR). The theoretical results showed an excellent agreement with the experimental values. The physico-chemical properties (such as logP, hydrophobicity, …) were also calculated using three commercially available programs. PMID:22343079

Fereyduni, E; Rofouei, M K; Kamaee, M; Ramalingam, S; Sharifkhani, S M

2012-05-01

192

Single crystal structure, spectroscopic (FT-IR, FT-Raman, 1H NMR, 13C NMR) studies, physico-chemical properties and theoretical calculations of 1-(4-chlorophenyl)-3-(4-nitrophenyl)triazene  

NASA Astrophysics Data System (ADS)

In this paper, we will report a combined experimental and theoretical investigation of the molecular structure and spectroscopic parameteres (FT-IR, FT-Raman, 1H NMR, 13C NMR) of 1-(4-chlorophenyl)-3-(4-nitrophenyl)triazene, CNT. The optimized geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities were obtained at the B3LYP/6-311++G(d,p) level of theory and thermodynamic functions were calculated at the same level. A detailed interpretation of the Infrared, Raman and NMR spectra of the compound was reported as well. Analysis of experimental NMR chemical shifts was supported by quantum chemical calculations and HOSE code fragment based prediction tool (ACD/NMR). The theoretical results showed an excellent agreement with the experimental values. The physico-chemical properties (such as log P, hydrophobicity, …) were also calculated using three commercially available programs.

Fereyduni, E.; Rofouei, M. K.; Kamaee, M.; Ramalingam, S.; Sharifkhani, S. M.

2012-05-01

193

Secondary structure and side-chain 1H and 13C resonance assignments of calmodulin in solution by heteronuclear multidimensional NMR spectroscopy.  

PubMed

Heteronuclear 2D and 3D NMR experiments were carried out on recombinant Drosophila calmodulin (CaM), a protein of 148 residues and with molecular mass of 16.7 kDa, that is uniformly labeled with 15N and 13C to a level of greater than 95%. Nearly complete 1H and 13C side-chain assignments for all amino acid residues are obtained by using the 3D HCCH-COSY and HCCH-TOCSY experiments that rely on large heteronuclear one-bond scalar couplings to transfer magnetization and establish through-bond connectivities. The secondary structure of this protein in solution has been elucidated by a qualitative interpretation of nuclear Overhauser effects, hydrogen exchange data, and 3JHNH alpha coupling constants. A clear correlation between the 13C alpha chemical shift and secondary structure is found. The secondary structure in the two globular domains of Drosophila CaM in solution is essentially identical with that of the X-ray crystal structure of mammalian CaM [Babu, Y., Bugg, C. E., & Cook, W.J. (1988) J. Mol. Biol. 204, 191-204], which consists of two pairs of a "helix-loop-helix" motif in each globular domain. The existence of a short antiparallel beta-sheet between the two loops in each domain has been confirmed. The eight alpha-helix segments identified from the NMR data are located at Glu-6 to Phe-19, Thr-29 to Ser-38, Glu-45 to Glu-54, Phe-65 to Lys-77, Glu-82 to Asp-93, Ala-102 to Asn-111, Asp-118 to Glu-127, and Tyr-138 to Thr-146. Although the crystal structure has a long "central helix" from Phe-65 to Phe-92 that connects the two globular domains, NMR data indicate that residues Asp-78 to Ser-81 of this central helix adopt a nonhelical conformation with considerable flexibility. PMID:1909892

Ikura, M; Spera, S; Barbato, G; Kay, L E; Krinks, M; Bax, A

1991-09-24

194

Experimental (FT-IR, FT-Raman, UV-Vis, 1H and 13C NMR) and computational (density functional theory) studies on 3-bromophenylboronic acid  

NASA Astrophysics Data System (ADS)

Structurally, boronic acids are trivalent boron-containing organic compounds that possess one alkyl substituent (i.e., C-Br bond) and two hydroxyl groups to fill the remaining valences on the boron atom. We studied 3-bromophenylboronic acid (3BrPBA); a derivative of boronic acid. This study includes the experimental (FT-IR, FT-Raman, 1H and 13C NMR, UV-Vis) techniques and theoretical (DFT-density functional theory) calculations. The experimental data are recorded, FT-IR (4000-400 cm-1) and FT-Raman spectra (3500-10 cm-1) in the solid phase. 1H and 13C NMR spectra are recorded in DMSO solution. UV-Vis spectrum is recorded in the range of 200-400 nm for each solution (in ethanol and water). The theoretical calculations are computed DFT/B3LYP/6-311++G(d,p) basis set. The optimum geometry is also obtained from inside for possible four conformers using according to position of hydrogen atoms after the scan coordinate of these structures. The fundamental vibrations are assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and parallel quantum solutions (PQS) program. 1H and 13C NMR chemical shifts are racked on by using the gauge-invariant atomic orbital (GIAO) method. The time-dependent density functional theory (TD-DFT) is used to find HOMO and LUMO energies, excitation energies, oscillator strengths. The density of state of the studied molecule is investigated as total and partial density of state (TDOS and PDOS) and overlap population density of state (OPDOS or COOP) diagrams have been presented. Besides, frontier molecular orbitals (FMOs), molecular electrostatic potential surface (MEPs) and thermodynamic properties are performed. At the end of this work, the results are ensured beneficial for the literature contribution.

Karabacak, M.; Kose, E.; Atac, A.; Sas, E. B.; Asiri, A. M.; Kurt, M.

2014-11-01

195

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

Microsoft Academic Search

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 1.5MDa membrane-bound protein complexes comprise reaction centres as well as the antenna systems called light harvesting complexes I and II. Due to

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

2003-01-01

196

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

197

Ionization state of the catalytic dyad Asp25/25' in the HIV-1 protease: NMR studies of site-specifically 13C labelled HIV-1 protease prepared by total chemical synthesis.  

PubMed

Total chemical synthesis was used to site-specifically (13)C-label active site Asp25 and Asp25' residues in HIV-1 protease and in several chemically synthesized analogues of the enzyme molecule. (13)C NMR measurements were consistent with a monoprotonated state for the catalytic dyad formed by the interacting Asp25, Asp25' side chain carboxyls. PMID:22659831

Torbeev, Vladimir Yu; Kent, Stephen B H

2012-08-14

198

Fast Volumetric Spatial-Spectral MR Imaging of Hyperpolarized 13C-Labeled Compounds using Multiple Echo 3D bSSFP  

PubMed Central

PURPOSE The goal of this work was to develop a fast 3D chemical shift imaging technique for the non-invasive measurement of hyperpolarized 13C-labeled substrates and metabolic products at low concentration. MATERIALS AND METHODS Multiple echo 3D balanced steady state MR imaging (ME-3DbSSFP) was performed in vitro on a syringe containing hyperpolarized [1,3,3-2H3; 1-13C]2-hydroxyethylpropionate (HEP) adjacent to a 13C-enriched acetate phantom, and in vivo on a rat before and after IV injection of hyperpolarized HEP at 1.5 T. Chemical shift images of the hyperpolarized HEP were derived from the multiple echo data by Fourier transformation along the echoes on a voxel by voxel basis for each slice of the 3D data set. RESULTS ME-3DbSSFP imaging was able to provide chemical shift images of hyperpolarized HEP in vivo, and in a rat with isotropic 7 mm spatial resolution, 93 Hz spectral resolution and 16 second temporal resolution for a period greater than 45 seconds. CONCLUSION Multiple echo 3D bSSFP imaging can provide chemical shift images of hyperpolarized 13C-labeled compounds in vivo with relatively high spatial resolution and moderate spectral resolution. The increased signal-to-noise ratio (SNR) of this 3D technique will enable the detection of hyperpolarized 13C-labeled metabolites at lower concentrations as compared to a 2D technique. PMID:20171034

Perman, William H.; Bhattacharya, Pratip; Leupold, Jochen; Lin, Alexander P.; Harris, Kent C.; Norton, Valerie A.; Hovener, Jan B.; Ross, Brian D.

2010-01-01

199

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

200

Auto-induction medium for the production of [U-15N]- and [U-13C, U-15N]-labeled proteins for NMR screening and structure determination.  

PubMed

Protocols have been developed and applied for the high-throughput production of [U-15N]- or [U-13C-, U-15N]-labeled proteins using the conditional methionine auxotroph Escherichia coli B834. The large-scale growth and expression uses a chemically defined auto-induction medium containing salts and trace metals, vitamins including vitamin B12, and glucose, glycerol, and lactose. The results from nine expression trials in 2-L of the auto-induction medium (500 mL in each of four polyethylene terephthalate beverage bottles) gave an average final optical density at 600 nm of approximately 5, an average wet cell mass yield of approximately 9.5 g L(-1), and an average yield of approximately 20 mg of labeled protein in the six instances in which proteolysis of the fusion protein was observed. Correlations between the cell mass recovered, the level of protein expression, and the relative amounts of glucose, glycerol, and lactose in the auto-induction medium were noted. Mass spectral analysis showed that the purified proteins contained both 15N and 13C at levels greater than 95%. 1H-15N heteronuclear single quantum correlation spectroscopy as well as 13C; 15N-edited spectroscopy showed that the purified [U-15N]- and [U-13C, U-15N]-labeled proteins were suitable for structure analysis. PMID:15766868

Tyler, Robert C; Sreenath, Hassan K; Singh, Shanteri; Aceti, David J; Bingman, Craig A; Markley, John L; Fox, Brian G

2005-04-01

201

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/. PMID:23622232

2013-01-01

202

The 1H, 13C and 15N NMR study on 5-carboxymethyl-1,2,4-triazole and 5-oxo-1,2,4-triazine derivatives  

NASA Astrophysics Data System (ADS)

The 5-carboxymethyl-1,2,4-triazole ( 1, 2, 3) and 5-oxo-1,2,4-triazine ( 4, 5, 6) derivatives were examined in solution by the 1H, 13C and 15N NMR including g-HSQC, g-HMBC 2D techniques and in the solid phase by 13C CPMAS NMR. Molecular modelling shows that there is not enough space for free rotation of neighbouring substituents at C 3 and N 4 and the two rings, especially in 4- 6, should be twisted with respect to the central heterocyclic system. The X-ray diffraction analysis of 2 and 5 evidenced that in the crystal of 2 the twist angles of 2-pyridyl and phenyl rings are 20.4 and 74.0° whereas in 5 they are 51.6 and 80.5°, respectively. Intramolecular hydrogen bonds N 1H⋯O?C are formed in triazines 4- 6 in solution and in the solid state; the H⋯O distance in 5 is 2.079 Å.

Bednarek, E.; Modzelewska-Banachiewicz, B.; Cyra?ski, M. K.; Sitkowski, J.; Wawer, I.

2001-05-01

203

Electron correlations in the quasi-two-dimensional organic conductor ?-(BEDT-TTF)2I3 investigated by 13C NMR  

NASA Astrophysics Data System (ADS)

We report a 13C-NMR study on the ambient-pressure metallic phase of the layered organic conductor ?-(BEDT-TTF)2I3 (BEDT-TTF: bisethylenedithio-tetrathiafulvalene), which is expected to connect the physics of correlated electrons and Dirac electrons under pressure. The orientation dependence of the NMR spectra shows that all BEDT-TTF molecules in the unit cell are to be seen equivalent from a microscopic point of view. This feature is consistent with the orthorhombic symmetry of the BEDT-TTF sublattice and also indicates that the monoclinic I3 sublattice, which should make three molecules in the unit cell nonequivalent, is not practically influential on the electronic state in the conducting BEDT-TTF layers at ambient pressure. There is no signature of charge disproportionation in opposition to most of the ?-type BEDT-TTF salts. The analyses of NMR Knight shift K and the nuclear-spin-lattice relaxation rate 1/T1 revealed that the degree of electron correlation, evaluated by the Korringa ratio [?1/(T1TK2)], is in an intermediate regime. However, NMR relaxation rate 1/T1 is enhanced above ˜ 200 K, which possibly indicates that the system enters into a quantum critical regime of charge-order fluctuations as suggested theoretically.

Hirata, Michihiro; Miyagawa, Kazuya; Kanoda, Kazushi; Tamura, Masafumi

2012-05-01

204

Cold Denaturation of Barstar: 1H, 15N and 13C NMR Assignment and Characterisation of Residual Structure  

Microsoft Academic Search

Detection of residual structure in denatured proteins is of interest because fleetingly structured regions may be initiation points of the folding pathway. Residual structure in this context is not the definition of one stable conformation but a population phenomenon. Acid, thermal and solvent-denatured states have recently been examined by NMR spectroscopy, but cold-denatured states have not been characterised to date.

Kam-Bo Wong; Stefan M. V. Freund; Alan R. Fersht

1996-01-01

205

HCN, A Triple-Resonance NMR Technique for Selective Observation of Histidine and Tryptophan Side Chains in 13C/ 15N-Labeled Proteins  

NASA Astrophysics Data System (ADS)

HCN, a new 3D NMR technique for stepwise coherence transfer from 1H to 13C to 15N and reverse through direct spin couplings 1JCHand 1JCN, is presented as a method for detection and assignment of histidine and tryptophan side-chain 1H, 13C, and 15N resonances in uniformly 13C/ 15N-labeled proteins. Product-operator calculations of cross-peak volumes vs adjustable delay ? 3were employed for determination of optimal ? 3. For the phosphatidylinositol 3-kinase (PI3K SH3 domain, MW = 9.6 kD) at pH 6, H(C)N, the 1H/ 15N projection, produced observable cross peaks within 20 min. and was completely selective for the single tryptophan and single histidine. The 3D HCN experiment yielded well-defined cross peaks in 20 h for the 13C/ 15N-labeled origin-specific DNA binding domain from simian virus 40 T-antigen (T-ag-OBD 131-259, MW = 15.4 kD) at pH 5.5. Resonances from all six histidines in T-ag-OBD were observed, and 11 of the 12 1H and 13C chemical shifts and 10 of the 12 15N chemical shifts were determined. The 13C dimension proved essential in assignment of the multiply overlapping 1H and 15N resonances. From the spectra recorded at a single pH, three of the imidazoles were essentially neutral and the other three were partially protonated (22-37%). HCN yielded strong cross peaks after 18 h on a 2.0 m Msample of phenylmethanesulfonyl fluoride (PMSF)-inhibited ?-lytic protease (MW = 19.8 kD) at pH 4.4. No spectra have been obtained, however, of native or boronic acid-inhibited ?-lytic protease after 18 h at various temperatures ranging from 5 to 55°C, probably due to efficient relaxation of active-site imidazole 1H and/or 15N nuclei.

Sudmeier, James L.; Ash, Elissa L.; Günther, Ulrich L.; Luo, Xuelian; Bullock, Peter A.; Bachovchin, William W.

206

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

207

UV\\/vis, 1H, and 13C NMR spectroscopic studies to determine mangiferin p K a values  

Microsoft Academic Search

The acid constants of mangiferin (a natural xanthonoid) in aqueous solution were determined through an UV\\/vis spectroscopic study employing the SQUAD program as a computational tool. A NMR study complements the pKa values assignment and evidences a H-bridge presence on 1-C. The chemical model used was consistent with the experimental data obtained. The pKa values determined with this procedure were

Berenice Gómez-Zaleta; María Teresa Ramírez-Silva; Atilano Gutiérrez; Enrique González-Vergara; Marisol Güizado-Rodríguez; Alberto Rojas-Hernández

2006-01-01

208

Solid state 13C NMR analysis of shales and coals from Laramide Basins. Final report, March 1, 1995--March 31, 1996  

SciTech Connect

This Western Research Institute (WRI) jointly sponsored research (JSR) project augmented and complemented research conducted by the University of Wyoming Institute For Energy Research for the Gas Research Institute. The project, {open_quotes}A New Innovative Exploitation Strategy for Gas Accumulations Within Pressure Compartments,{close_quotes} was a continuation of a project funded by the GRI Pressure Compartmentalization Program that began in 1990. That project, {open_quotes}Analysis of Pressure Chambers and Seals in the Powder River Basin, Wyoming and Montana,{close_quotes} characterized a new class of hydrocarbon traps, the discovery of which can provide an impetus to revitalize the domestic petroleum industry. In support of the UW Institute For Energy Research`s program on pressure compartmentalization, solid-state {sup 13}C NMR measurements were made on sets of shales and coals from different Laramide basins in North America. NMR measurements were made on samples taken from different formations and depths of burial in the Alberta, Bighorn, Denver, San Juan, Washakie, and Wind River basins. The carbon aromaticity determined by NMR was shown to increase with depth of burial and increased maturation. In general, the NMR data were in agreement with other maturational indicators, such as vitrinite reflectance, illite/smectite ratio, and production indices. NMR measurements were also obtained on residues from hydrous pyrolysis experiments on Almond and Lance Formation coals from the Washakie Basin. These data were used in conjunction with mass and elemental balance data to obtain information about the extent of carbon aromatization that occurs during artificial maturation. The data indicated that 41 and 50% of the original aliphatic carbon in the Almond and Lance coals, respectively, aromatized during hydrous pyrolysis.

Miknis, F.P.; Jiao, Z.S.; Zhao, Hanqing; Surdam, R.C.

1998-12-31

209

Expression and purification of 15N- and 13C-isotope labeled 40-residue human Alzheimer’s ?-amyloid peptide for NMR-based structural analysis  

PubMed Central

Amyloid fibrils of Alzheimer’s ?-amyloid peptide (A?) are a primary component of amyloid plaques, a hallmark of Alzheimer’s disease (AD). Enormous attention has been given to the structural features and functions of A? in amyloid fibrils and other type of aggregates in associated with development of AD. This report describes an efficient protocol to express and purify high-quality 40-residue A?(1–40), the most abundant A? in brains, for structural studies by NMR spectroscopy. Over-expression of A?(1–40) with glutathione S-transferase (GST) tag connected by a Factor Xa recognition site (IEGR?) in E. Coli resulted in the formation of insoluble inclusion bodies even with the soluble GST tag. This problem was resolved by efficient recovery of the GST-A? fusion protein from the inclusion bodies using 0.5% (w/v) sodium lauroyl sarcosinate as solubilizing agent and subsequent purification by affinity chromatography using a glutathione agarose column. The removal of the GST tag by Factor Xa enzymatic cleavage and purification by HPLC yielded as much as ~7 mg and ~1.5 mg of unlabeled A?(1–40) and uniformly 15N- and/or 13C-protein A?(1–40) from 1 L of the cell culture, respectively. Mass spectroscopy of unlabeled and labeled A? and 1H/15N HSQC solution NMR spectrum of the obtained 15N-labeled A? in the monomeric form confirmed the expression of native A?(1–40). It was also confirmed by electron micrography and solid-state NMR analysis that the purified A?(1–40) self-assembles into ?-sheet rich amyloid fibrils. To the best of our knowledge, our protocol offers the highest yields among published protocols for production of recombinant A?(1–40) samples that are amendable for an NMR-based structural analysis. The protocol may be applied to efficient preparation of other amyloid-forming proteins and peptides that are 13C- and 15N-labeled for NMR experiments. PMID:21640828

Long, Fei; Cho, Wonhwa; Ishii, Yoshitaka

2011-01-01

210

Solid-state and solution /sup 13/C NMR in the conformational analysis of methadone-hydrochloride and related narcotic analgesics  

SciTech Connect

Solid state and solution /sup 13/C NMR have been used to study the conformations of the racemic mixtures and single enantiomers of methadone hydrochloride, alpha and beta methadol hydrochloride, and alpha and beta acetylmethadol hydrochloride. The NMR spectra acquired for the compounds as solids, and in polar and nonpolar solvents are compared, in order to determine the conformation of the molecules in solution. To determine the reliability of assigning solution conformations by comparing solution and solid state chemical shift data, three bond coupling constants measured in solution are compared with those calculated from X-ray data. The conformations of the racemic mixture and plus enantiomer of methadone hydrochloride have been shown to be very similar in the solid state, where minor differences in conformation can be seen by comparing NMR spectra obtained for the solids. Also shown is that the molecules of methadone hydrochloride have conformations in polar and in nonpolar solvents which are very similar to the conformation of the molecules in the solid state.

Sumner, S.C.J.

1986-01-01

211

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

212

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

213

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

214

Antioxidant Study and Assignments of NMR Spectral Data for 3?,4?,7-Trihydroxyflavanone 3?,7-Di-O-?-D-glucopyranoside (Butrin) and Its Hydrolyzed Product  

Microsoft Academic Search

The NMR spectral data including high resolution 1H, 13C and 2D NMR for butrin, 3',4',7-trihydroxyflavanone 3',7-di-O-ß-D-glucopyranoside, isolated from flowers of Butea monosperma, are reported here for the first time. Butrin was hydrolyzed using b-glucosidase to butin in high yield. They were subjected to free radical scavenging test using 2,2-diphenyl-1-picrylhydrazyl (DPPH) spectrophotometric assay. At a dose of 4 × 10-8 mol

Amir Reza Jassbi; Pahup Singh; Vivek Krishna; Pradeep K. Gupta; Satoshi Tahara

2004-01-01

215

Detecting a New Source for Photochemically Induced Dynamic Nuclear Polarization in the LOV2 Domain of Phototropin by Magnetic-Field Dependent (13)C NMR Spectroscopy.  

PubMed

Phototropin is a flavin mononucleotide (FMN) containing blue-light receptor, which regulates, governed by its two LOV domains, the phototropic response of higher plants. Upon photoexcitation, the FMN cofactor triplet state, (3)F, reacts with a nearby cysteine to form a covalent adduct. Cysteine-to-alanine mutants of LOV domains instead generate a flavin radical upon illumination. Here, we explore the formation of photochemically induced dynamic nuclear polarization (CIDNP) in LOV2-C450A of Avena sativa phototropin and demonstrate that photo-CIDNP observed in solution (13)C NMR spectra can reliably be interpreted in terms of solid-state mechanisms including a novel triplet mechanism. To minimize cross-polarization, which transfers light-induced magnetization to adjacent (13)C nuclei, our experiments were performed on proteins reconstituted with specifically (13)C-labeled flavins. Two potential sources for photo-CIDNP can be identified: The photogenerated triplet state, (3)F, and the triplet radical pair (3)(F(-•)W(+•)), formed by electron abstraction of (3)F from tryptophan W491. To separate the two contributions, photo-CIDNP studies were performed at four different magnetic fields ranging from 4.7 to 11.8 T. Analysis revealed that, at fields <9 T, both (3)(F(-•)W(+•)) and (3)F contribute to photo-CIDNP, whereas at high magnetic fields, the calculated enhancement factors of (3)F agree favorably with their experimental counterparts. Thus, we have for the first time detected that a triplet state is the major source for photo-CIDNP in a photoactive protein. Since triplet states are frequently encountered upon photoexcitation of flavoproteins, the novel triplet mechanism opens up new means of studying electronic structures of the active cofactors in these proteins at atomic resolution. PMID:25207844

Kothe, Gerd; Lukaschek, Michail; Link, Gerhard; Kacprzak, Sylwia; Illarionov, Boris; Fischer, Markus; Eisenreich, Wolfgang; Bacher, Adelbert; Weber, Stefan

2014-10-01

216

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

217

Mesoporous Silica Nanoparticles Loaded with Surfactant: Low Temperature Magic Angle Spinning 13C and 29Si NMR Enhanced by Dynamic Nuclear Polarization  

SciTech Connect

We show that dynamic nuclear polarization (DNP) can be used to enhance NMR signals of 13C and 29Si nuclei located in mesoporous organic/inorganic hybrid materials, at several hundreds of nanometers from stable radicals (TOTAPOL) trapped in the surrounding frozen disordered water. The approach is demonstrated using mesoporous silica nanoparticles (MSN), functionalized with 3-(N-phenylureido)propyl (PUP) groups, filled with the surfactant cetyltrimethylammonium bromide (CTAB). The DNP-enhanced proton magnetization is transported into the mesopores via 1H–1H spin diffusion and transferred to rare spins by cross-polarization, yielding signal enhancements ?on/off of around 8. When the CTAB molecules are extracted, so that the radicals can enter the mesopores, the enhancements increase to ?on/off ? 30 for both nuclei. A quantitative analysis of the signal enhancements in MSN with and without surfactant is based on a one-dimensional proton spin diffusion model. The effect of solvent deuteration is also investigated.

Lafon, Olivier [Universite de Lille Nord de France; Thankamony, Aany S. Lilly [Universite de Lille Nord de France; Kokayashi, Takeshi [Ames Laboratory; Carnevale, Diego [Ecole Polytechnique Federale de Lausanne; Vitzthum, Veronika [Ecole Polytechnique Federale de Lausanne; Slowing, Igor I. [Ames Laboratory; Kandel, Kapil [Ames Laboratory; Vezin, Herve [Universite de Lille Nord de France; Amoureux, Jean-Paul [Universite de Lille Nord de France; Bodenhausen, Geoffrey [Ecole Polytechnique Federale de Lausanne; Pruski, Marek [Ames Laboratory

2012-12-21

218

Ab initio/GIAO-CCSD(T) study of structures, energies, and 13C NMR chemical shifts of C4H7(+) and C5H9(+) ions: relative stability and dynamic aspects of the cyclopropylcarbinyl vs bicyclobutonium ions.  

PubMed

The structures and energies of the carbocations C 4H 7 (+) and C 5H 9 (+) were calculated using the ab initio method. The (13)C NMR chemical shifts of the carbocations were calculated using the GIAO-CCSD(T) method. The pisigma-delocalized bisected cyclopropylcarbinyl cation, 1 and nonclassical bicyclobutonium ion, 2 were found to be the minima for C 4H 7 (+) at the MP2/cc-pVTZ level. At the MP4(SDTQ)/cc-pVTZ//MP2/cc-pVTZ + ZPE level the structure 2 is 0.4 kcal/mol more stable than the structure 1. The (13)C NMR chemical shifts of 1 and 2 were calculated by the GIAO-CCSD(T) method. Based on relative energies and (13)C NMR chemical shift calculations, an equilibrium involving the 1 and 2 in superacid solutions is most likely responsible for the experimentally observed (13)C NMR chemical shifts, with the latter as the predominant equilibrating species. The alpha-methylcyclopropylcarbinyl cation, 4, and nonclassical bicyclobutonium ion, 5, were found to be the minima for C 5H 9 (+) at the MP2/cc-pVTZ level. At the MP4(SDTQ)/cc-pVTZ//MP2/cc-pVTZ + ZPE level ion 5 is 5.9 kcal/mol more stable than the structure 4. The calculated (13)C NMR chemical shifts of 5 agree rather well with the experimental values of C 5H 9 (+). PMID:18570420

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

2008-07-16

219

Precise side-chain conformation analysis of L-phenylalanine in ?-helical polypeptide by quantum-chemical calculation and 13C CP-MAS NMR measurement  

NASA Astrophysics Data System (ADS)

To clarify the positive role of side-chain conformation in the stability of protein secondary structure (main-chain conformation), we successfully calculated the optimization structure of a well-defined ?-helical octadecapeptide composed of L-alanine (Ala) and L-phenylalanine (Phe) residues, H-(Ala) 8-Phe-(Ala) 9-OH, based on the molecular orbital calculation with density functional theory (DFT/B3LYP/6-31G(d)). From the total energy and the precise secondary structural parameters such as main-chain dihedral angles and hydrogen-bond parameters of the optimized structure, we confirmed that the conformational stability of an ?-helix is affected dominantly by the side-chain conformation ( ?1) of the Phe residue in this system: model A ( T form: around 180° of ?1) is most stable in ?-helix and model B ( G + form: around -60° of ?1) is next stable, but model C ( G - form: around 60° of ?1) is less stable. In addition, we demonstrate that the stable conformation of poly( L-phenylalanine) is an ?-helix with the side-chain T form, by comparison of the carbonyl 13C chemical shift measured by 13C CP-MAS NMR and the calculated one.

Niimura, Subaru; Suzuki, Junya; Kurosu, Hiromichi; Yamanobe, Takeshi; Shoji, Akira

2010-04-01

220

Elucidating Metabolic Pathways for Amino Acid Incorporation Into Dragline Spider Silk using 13C Enrichment and Solid State NMR  

PubMed Central

Spider silk has been evolutionarily optimized for contextual mechanical performance over the last 400 million years. Despite precisely balanced mechanical properties, which have yet to be reproduced, the underlying molecular architecture of major ampullate spider silk can be simplified being viewed as a versatile block copolymer. Four primary amino acid motifs: polyalanine, (GA)n, GPGXX, and GGX (X = G,A,S,Q,L,Y) will be considered in this study. Although synthetic mimetics of many of these amino acid motifs have been produced in several biological systems, the source of spider silk’s mechanical integrity remains elusive. Mechanical robustness may be a product not only of the amino acid structure but also of the tertiary structure of the silk. Historically, solid state Nuclear Magnetic Resonance (ssNMR) has been used to reveal the crystalline structure of the polyalanine motif; however, limitations in amino acid labeling techniques have obscured the structures of the GGX and GPGXX motifs thought to be responsible for the structural mobility of spider silk. We describe the use of metabolic pathways to label tyrosine for the first time as well as to improve the labeling efficiency of proline. These improved labeling techniques will allow the previously unknown tertiary structures of major ampullate silk to be probed. PMID:21334448

Creager, Melinda S.; Izdebski, Thomas; Brooks, Amanda E.; Lewis, Randolph V.

2013-01-01

221

Slow Dynamics at the Glass Transition in Semicrystalline Polymers Studied by Pure-Exchange ^13C NMR  

NASA Astrophysics Data System (ADS)

The dynamics in the amorphous regions of semicrystalline polymers exert important influences on mechanical properties but have been difficult to characterize. New solid-state nuclear magnetic resonance (NMR) techniques, PUREX (pure-exchange) and CODEX (centerband-only detection of exchange), enable studies of the molecular motions near the glass transition (T_g) in the amorphous regions of semicrystalline polymers. This is achieved by selectively suppressing the dominant signals of the static segments in the crystallites. We have applied both techniques to analyze the geometry and time scale of the slow motions around Tg in isotactic poly(1-butene) (iPB1), in polypropylenes (iPP, sPP, aPP), and in fully amorphous polyisobutylene (PIB) for reference. The apparent activation energies for iPB1, sPP, and PIB were found to be 90, 125, and 115 kJ/mol, respectively. In iPB1, indications of slow motions in two distinct regions were observed.

Bonagamba, Tito J.; Deazevedo, Eduardo R.; Becker-Guedes, Fabio; Schmidt-Rohr, Klaus

2001-03-01

222

Significance of low-frequency local fluctuation motions in the transmembrane B and C a-helices of bacteriorhodopsin, to facilitate efficient proton uptake from the cytoplasmic surface, as revealed by site-directed solid-state 13 C NMR  

Microsoft Academic Search

13C NMR spectra of [1- 13C]Val- or -Pro-labeled bacteriorhodopsin (bR) and its single or double mutants, including D85N, were recorded at various pH values to reveal conformation and dynamics changes in the transmembrane ?-helices, in relation to proton release and uptake between bR and the M-like state caused by modified charged states at Asp85 and the Schiff base (SB). It

Atsushi Kira; Michikazu Tanio; Satoru Tuzi; Hazime Saitô

2004-01-01

223

Crystal structure and theoretical study of IR and 1H and 13C NMR spectra of cordatin, a natural product with antiulcerogenic activity  

NASA Astrophysics Data System (ADS)

Cordatin is a furan diterpenoid with a clerodane skeleton isolated from Croton palanostigma Klotzsch (Euphorbiaceae). This natural product shows significant antiulcerogenic activity, similar to cimetidine (Tagamet®), a compound used for the treatment of peptic ulcers. The crystal structure of cordatin was obtained by X-ray diffraction and its geometrical parameters were compared with theoretical calculations at the B3LYP theory level. The IR and NMR (1H and 13C chemical shifts and coupling constants) spectra were obtained and compared with the theoretical calculations. The B3LYP theory level, with the 6-31G(d,p) and 6-311G(d,p) basis set, provided IR absorption values close to the experimental data. Moreover, theoretical NMR parameters obtained in both gas phase and chloroform solvent at the B3PW91/DGDZVP, B3LYP/6-311+G(2d,p), and B3PW91/6-311+G(2d,p) levels showed good correlations with the experimental results.

Brasil, Davi S. B.; Alves, Cláudio N.; Guilhon, Giselle M. S. P.; Muller, Adolfo H.; Secco, Ricardo De S.; Peris, Gabriel; Llusar, Rosa

224

13C, 15N NMR and CP-MAS as well as FT-IR and PM5 studies of Schiff base of gossypol with L-phenylalanine methyl ester in solution and solid  

NASA Astrophysics Data System (ADS)

The Schiff bases of racemic gossypol with L-phenylalanine amino acid methyl ester (GSBA) was studied by FT-IR, 13C and 15N NMR spectroscopy as well as by the PM5 semiempirical method. The spectroscopic methods have provided clear evidence that GSBA exists in the solid state and in solution as enamine-enamine tautomer. The existence of diastereoisomers is very well evidenced in the 13C NMR spectra in the solution by the double character of all carbon atoms' signals of the naphthalene rings. The structure of GSBA and the hydrogen bonds within this structure are discussed.

Przybylski, Piotr; Schilf, Wojciech; Brzezinski, Bogumi?

2005-01-01

225

Solid-state 13C NMR investigation of the oxidative degradation of selectively labeled polypropylene by thermal aging and y-irradiation.  

SciTech Connect

Unstabilized polypropylene (PP) films having selective {sup 13}C isotopic labeling were subjected to thermal aging at 50, 80, and 109 C and to {gamma}-irradiation at 24 and 80 C. The oxidized films were examined using solid-state {sup 13}C nuclear magnetic resonance (NMR) spectroscopy. Dramatic differences were found in the type and distribution of oxidation products originating from the three carbon atom sites within the PP macromolecule (tertiary carbon, secondary carbon, and methyl side group). Most of the oxidation products that formed on the polymer chain originated through chemical reactions at the PP tertiary carbons. Under all of the aging conditions examined, tertiary peroxides (from the PP tertiary site) were the most abundant functional group produced. Also originating from the PP tertiary carbon were significant amounts of tertiary alcohols, together with several more minor products that included 'chain-end' methyl ketones. No significant amount of peroxides or alcohols associated with the PP secondary carbon sites was detected. A substantial yield of carboxylate groups was identified (acids, esters, etc.). The majority of these originated from the PP secondary carbon site, from which other minor products also formed, including in-chain ketones. We found no measurable yield of oxidation products originating from reaction at the PP methyl group. Remarkably similar distributions of the major oxidation products were obtained for thermal aging at different temperatures, whereas the product distributions obtained for irradiation at the different temperatures exhibited significant differences. Time-dependent concentration plots have been obtained, which show the amounts of the various oxidation products originating at the different PP sites, as a function of the extent of material oxidation.

Mowery, Daniel Michael; Assink, Roger Alan; Klamo, Sara B. (California Institute of Technology, Pasadena, CA); Clough, Roger Lee; Bernstein, Robert; Derzon, Dora Kay

2004-12-01

226

Astrocytic energy metabolism and glutamate formation--relevance for 13C-NMR spectroscopy and importance of cytosolic/mitochondrial trafficking.  

PubMed

Glutamate plays a double role in (13)C-nuclear magnetic resonance (NMR) spectroscopic determination of glucose metabolism in the brain. Bidirectional exchange between initially unlabeled glutamate and labeled ?-ketoglutarate, formed from pyruvate via pyruvate dehydrogenase (PDH), indicates the rate of energy metabolism in the tricarboxylic acid (V(TCA)) cycle in neurons (V(PDH, n)) and, with additional computation, also in astrocytes (V(PDH, g)), as confirmed using the astrocyte-specific substrate [(13)C]acetate. Formation of new molecules of glutamate during increased glutamatergic activity occurs only in astrocytes by combined pyruvate carboxylase (V(PC)) and astrocytic PDH activity. V(PDH, g) accounts for ~15% of total pyruvate metabolism in the brain cortex, and V(PC) accounts for another ~10%. Since both PDH-generated and PC-generated pyruvates are needed for glutamate synthesis, ~20/25 (80%) of astrocytic pyruvate metabolism proceed via glutamate formation. Net transmitter glutamate [?-aminobutyric acid (GABA)] formation requires transfer of newly synthesized ?-ketoglutarate to the astrocytic cytosol, ?-ketoglutarate transamination to glutamate, amidation to glutamine, glutamine transfer to neurons, its hydrolysis to glutamate and glutamate release (or GABA formation). Glutamate-glutamine cycling, measured as glutamine synthesis rate (V(cycle)), also transfers previously released glutamate/GABA to neurons after an initial astrocytic accumulation and measures predominantly glutamate signaling. An empirically established ~1/1 ratio between glucose metabolism and V(cycle) may reflect glucose utilization associated with oxidation/reduction processes during glutamate production, which together with associated transamination processes are balanced by subsequent glutamate oxidation after cessation of increased signaling activity. Astrocytic glutamate formation and subsequent oxidative metabolism provide large amounts of adenosine triphosphate used for accumulation from extracellular clefts of neuronally released K(+) and glutamate and for cytosolic Ca(2+) homeostasis. PMID:21820830

Hertz, Leif

2011-12-01

227

- and Cross-Polarization 13C NMR Evidence of Alterations in Molecular Composition of Humic Substances Following Afforestation with Eucalypt in Distinct Brazilian Biomes  

NASA Astrophysics Data System (ADS)

The effect of planting fast growing tree species on SOM quality in tropical regions has been overlooked. In the present study 13C-NMR approaches were used to evaluate the impact of eucalypt cultivation on humic and fulvic acids molecular composition. The results indicate that the replacement of native vegetation by eucalypt plantations increased the relative contribution of aliphatic groups in HA from soils previously under Atlantic Forest, Grassland, and the Cerrado (Curvelo site only). The same trend was observed for FA, except in the Curvelo site. A trend for degradation and smaller contribution of O-alkyl C (carbohydrates) in HA was observed in soils under eucalyptus in Atlantic Forest and Cerrado. For FA such decreases were seen in Cerrado and Grassland biomes after eucalypt planting. In the area cultivated with pasture in the Atlantic Forest biome and in the Grassland soil, the largest contributions of lignin-derived compounds were detected in HA. The HA from the Cerrado at the Curvelo site, where the woody vegetation is virtually devoid of grassy species, showed the lowest intensity of lignin signal then those from the Cerrado sensu stricto in Itacambira, where grass species are more abundant. At our study sites, charred material are most likely derived from burning of the native vegetation, as naturally occurs in the Cerrado region, or anthropogenic fires in the Grassland biome. Burning of harvest residues in eucalypt fields was also a common practice in the early rotations. The replacement of native vegetation by eucalypt plantations increases the relative contribution of nonpolar alkyl groups in HA from soils previously under Atlantic Forest, Grassland, and the Cerrado (Curvelo site only) biomes. There is evidence of substantial contribution of lignin-derived C to HA and FA, especially in sites planted with Brachiaria sp pastures. Eucalypt introduction decreases the relative contribution of carbohydrates in HA and FA. 13C DP/MAS NMR functional groups in the humic and fulvic acid samples from the Eucalypt and native vegetation soils in the Atlantic Forest, Cerrado and Grassland biomes

Silva, I. R.; Soares, E. M.; Schmidt-Rohr, K.; Novais, R.; Barros, N.; Fernandes, S.

2010-12-01

228

Using [sup 13]C CPMAS NMR to assess effects of cultivation on the organic matter of particle size fractions in a grassland soil  

SciTech Connect

We examined particle size fractions from the surface horizons of a native untilled grassland site and an adjacent field cultivated for 65 years in the Peace River region of British Columbia, Canada. While cultivation resulted in the loss of approximately 50% of the C and N in the soil, there was little change in the distribution of particle sizes, in their C/N ratios, and in the fraction of C found as carbohydrate. Changes in the nature of the organic C were generally small, but obvious differences were seen in the [sup 13] CPMAS NMR spectra of two of the size fractions. Compared with the native grassland, the sand fraction from the cultivated field had a lower proportion of O-alkyl C and a loss of resolution. The clay fraction from the cultivated field had lower O-alkyl and higher alkyl C than its grassland counterpart. Subtraction of linear combinations of spectra of the whole soils from the two sites showed a 10% increase with cultivation in the proportion of humified to decomposable organic C. All of these trends are consistent with a greater degree of decomposition in the cultivated site. The changes are small and do not suggest a serious degradation in the quality of the soil organic matter, compared with the large change in quantity. We also examined factors that might affect the quality and quantitative reliability of the [sup 13]C CPMAS NMR spectra. Dithionite treatment was not very effective in improving resolution or fraction of observable C for these samples. The latter was in the range of 10-30%, largely a result of the association of organic matter with paramagnetic iron. For this reason, comparison of relative areas must be interpreted with caution and confined to samples with reasonably similar contents of C and iron.

Preston, C.M. (Pacific Forestry Centre, British Columbia (Canada)); Newman, R.H. (Industrial Research Ltd., Lower Hutt (New Zealand)); Rother, P. (Univ. of British Columbia, Vancouver (Canada))

1994-01-01

229

Heteronuclear NMR studies of cobalamins. 9. Temperature-dependent NMR of organocobalt corrins enriched in /sup 13/C in the organic ligand and the thermodynamics of the base-on/base-off reaction  

SciTech Connect

The synthesis of alkylcobinamides (RCbi) enriched in /sup 13/C in the organic axial ligand by standard reductive alkylation procedures from /sup 13/C-enriched alkyl halides has been shown to lead essentially exclusively to ..beta..-alkylcobamides (i.e., the organic ligand in the upper axial ligand position) by uv-visible and NMR spectroscopy and HPLC coupled with direct synthesis of /sup 13/CH/sub 3/Cbi of known stereochemistry from /sup 13/C-enriched methylcobalamin (/sup 13/CH/sub 3/Cbl). The ionic strength dependence of the on/off pK/sub a/ of CH/sub 3/Cbl, CH/sub 3/CH/sub 2/Cbl, and ..cap alpha..-ribazole has also been investigated. Measurements of the relative /sup 13/C resonance frequency of /sup 13/CH/sub 3/Cbl and /sup 13/CH/sub 3/Cbi as a function of temperature at several ionic strengths have been used to investigate the thermodynamics of the base-on/base-off reaction of cobalamins. Additional evidence has thus been obtained for a previously detected species of base-off, but benzimidazole-deprotonated, cobalamin in which the benzimidazole B3 nitrogen atom is hydrogen-bonded to an e side chain N-H, and the thermodynamics of formation of this species have been evaluated. These results have been confirmed by similar measurements on mixtures of /sup -/OOC/sup 13/CH/sub 2/Cbl and /sup -/OOC/sup 13/CH/sub 2/Cbi. Although the new species is the predominant form (80-90%) of the base-off but benzimidazole-deprotonated cobalamins in solution at all ionic strengths, its presence has only a minor effect on the primary on/off equilibrium constants previously calculated for RCbl's. 45 references, 4 figures, 8 tables.

Brown, K.L.; Peck-Siler, S.

1988-10-05

230

Mechanism of cellulose dissolution in the ionic liquid 1-n-butyl-3-methylimidazolium chloride: a 13C and 35/37Cl NMR relaxation study on model systems.  

PubMed

13C and 35/37Cl NMR relaxation measurements on several model systems demonstrate that the solvation of cellulose by the ionic liquid (IL) 1-n-butyl-3-methylimidazolium chloride ([C4mim]Cl) involves hydrogen-bonding between the carbohydrate hydroxyl protons and the IL chloride ions in a 1 ratio 1 stoichiometry. PMID:16538244

Remsing, Richard C; Swatloski, Richard P; Rogers, Robin D; Moyna, Guillermo

2006-03-28

231

Spectral editing through laser-flash excitation in two-dimensional photo-CIDNP MAS NMR experiments.  

PubMed

In solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) MAS NMR experiments, strong signal enhancement is observed from molecules forming a spin-correlated radical pair in a rigid matrix. Two-dimensional (13)C-(13)C dipolar-assisted rotational resonance (DARR) photo-CIDNP MAS NMR experiments have been applied to obtain exact chemical shift assignments from those cofactors. Under continuous illumination, the signals are enhanced via three-spin mixing (TSM) and differential decay (DD) and their intensity corresponds to the electron spin density in pz orbitals. In multiple-(13)C labelled samples, spin diffusion leads to propagation of signal enhancement to all (13)C spins. Under steady-state conditions, direct signal assignment is possible due to the uniform signal intensity. The original intensities, however, are inaccessible and the information of the local electron spin density is lost. Upon laser-flash illumination, the signal is enhanced via the classical radical pair mechanism (RPM). The obtained intensities are related to isotropic hyperfine interactions aiso and both enhanced absorptive and emissive lines can be observed due to differences in the sign of the local isotropic hyperfine interaction. Exploiting the mechanism of the polarization, selectivity can be increased by the novel time-resolved two-dimensional dipolar-assisted rotational resonance (DARR) MAS NMR experiment which simplifies the signal assignment compared to complex spectra of the same RCs obtained by continuous illumination. Here we present two-dimensional time-resolved photo-CIDNP MAS NMR experiments providing both directly: signal assignment and spectral editing by sign and strength of aiso. Hence, this experiment provides a direct key to the electronic structure of the correlated radical pair. PMID:25063951

Sai Sankar Gupta, Karthick Babu; Daviso, Eugenio; Jeschke, Gunnar; Alia, A; Ernst, Matthias; Matysik, Jörg

2014-09-01

232

Spectral editing of two-dimensional magic-angle-spinning solid-state NMR spectra for protein resonance assignment and structure determination  

PubMed Central

Several techniques for spectral editing of 2D 13C–13C correlation NMR of proteins are introduced. They greatly reduce the spectral overlap for five common amino acid types, thus simplifying spectral assignment and conformational analysis. The carboxyl (COO) signals of glutamate and aspartate are selected by suppressing the overlapping amide N–CO peaks through 13C–15N dipolar dephasing. The sidechain methine (CH) signals of valine, lecuine, and isoleucine are separated from the overlapping methylene (CH2) signals of long-chain amino acids using a multiple-quantum dipolar transfer technique. Both the COO and CH selection methods take advantage of improved dipolar dephasing by asymmetric rotational-echo double resonance (REDOR), where every other ?-pulse is shifted from the center of a rotor period tr by about 0.15 tr. This asymmetry produces a deeper minimum in the REDOR dephasing curve and enables complete suppression of the undesired signals of immobile segments. Residual signals of mobile sidechains are positively identified by dynamics editing using recoupled 13C–1H dipolar dephasing. In all three experiments, the signals of carbons within a three bond distance from the selected carbons are detected in the second spectral dimension via 13C spin exchange. The efficiencies of these spectral editing techniques range from 60 % for the COO and dynamic selection experiments to 25 % for the CH selection experiment, and are demonstrated on well-characterized model proteins GB1 and ubiquitin. PMID:23053913

Schmidt-Rohr, K.; Fritzsching, K. J.; Liao, S. Y.

2013-01-01

233

Early estrogen-induced metabolic changes and their inhibition by actinomycin D and cycloheximide in human breast cancer cells: sup 31 P and sup 13 C NMR studies  

SciTech Connect

Metabolic changes following estrogen stimulation and the inhibition of these changes in the presence of actinomycin D and cycloheximide were monitored continuously in perfused human breast cancer T47D clone 11 cells with {sup 31}P and {sup 13}C NMR techniques. The experiments were performed by estrogen rescue of tamoxifen-treated cells. Immediately after perfusion with estrogen-containing medium, a continuous enhancement in the rates of glucose consumption, lactate production by glycolysis, and glutamate synthesis by the Krebs cycle occurred with a persistent 2-fold increase at 4 hr. Pretreatment with either actinomycin D or cycloheximide, at concentrations known to inhibit mRNA and protein synthesis, respectively, and simultaneous treatment with estrogen and each inhibitor prevented the estrogen-induced changes in glucose metabolism. This suggested that the observed estrogen stimulation required synthesis of mRNA and protein. These inhibitors also modulated several metabolic activities that were not related to estrogen stimulation. The observed changes in the in vivo kinetics of glucose metabolism may provide a means for the early detection of the response of human breast cancer cells to estrogen versus tamoxifen treatment.

Neeman, M.; Degani, H. (Weizmann Institute of Science, Rehovot (Israel))

1989-07-01

234

Development of a stability-indicating HPLC method of Etifoxine with characterization of degradation products by LC-MS/TOF, (1)H and (13)C NMR.  

PubMed

This paper describes a new LC-MS/TOF method for the degradation products determination when Etifoxine (ETI) is submitted to different stress conditions. Chromatography is performed by using Kromasil C18 column (250mm×4.6mm, 5?m particle size). The selected mobile phase consists of formate buffer 0.02M, pH 3 and methanol (70/30, v/v). ETI is submitted to oxidative, acidic, basic, hydrolytic, thermal and UV light degradations. Detection is made at 254nm by photodiode array detector and mass spectrometry. A number of degradation products (DPs) called DPA, DPB, DPC and DPD are found depending on the stress; DPA with heat, DPA and DPB in acidic media or under UV-light; DPA, DPB and DPC under basic stress; DPA, DPB, DPC and DPD with oxidation. LC-MS/TOF is used to characterize the four DPs of ETI resulting from different stress conditions. (1)H and (13)C NMR are used to confirm the DP structures. The ETI fragmentation pathway is proposed. The method is validated with reference to International Conference on Harmonization guidelines and ETI are selectively determined in presence of its DPs, demonstrating its stability-indicating nature. Finally, for the validation step, specificity, linearity, accuracy and precision are determined for ETI and its DPs. PMID:25117950

Djabrouhou, Nadia; Guermouche, Moulay-Hassane

2014-11-01

235

Application of /sup 13/C NMR, fluorescence, and light-scattering techniques for structural studies of oil-in-water microemulsions  

SciTech Connect

The nature of the microdroplets present in oil-in-water microemulsions was examined by using the 4-component model system water-hexadecane-sodium hexadecyl sulfate-pentanol. Three compositions were selected corresponding to regions in the pahse diagram where the content of water, cosurfactant, and oil, respectively, approached the tolerable limit to yield clear isotropic solutions. In the water-side microemulsion, the radius of the droplets is 127A as determined from quasi-elastic light-scattering measurements. Fluorescence experiments showed that the core of the microspheres has a microviscosity similar to hexadecane at room temperature. /sup 13/C NMR shift analysis was applied to test the partitioning of cosurfactant between the surface and the interior of the droplet. For all three compositions significant fractions of the cosurfactant are present in the interior. This is corroborated by results obtained from T/sub 1/ relaxation-time analysis at different field strengths. The influence of the field strength on T/sub 1/ is explained in terms of a model based on a distribution of correlation times. In particular, the importance of taking into account slower rotational modes such as the tumbling of the whole microsphere is illustrated.

Tricot, Y.; Kiwi, J.; Niederberger, W.; Graetzel, M.

1981-04-02

236

A comparative study of the conformational equilibria, vibrational, 1H and 13C NMR spectra of isobutyranilide and its derivative the anticancer drug flutamide  

NASA Astrophysics Data System (ADS)

The molecular structure of isobutyranilide and flutamide were investigated by DFT-B3LYP/6-311G** and MP2/6-311G** calculations. Isobutyranilide was predicted to exist predominantly in a planar cis conformation, while flutamide in non-planar structures with the CF3 and the NO2 groups adopting an out of the phenyl-plane configuration. The vibrational frequencies of the low energy structures of the two molecules were computed at the DFT-B3LYP level of theory. From the calculated Gibb's free energies, isobutyranilide is estimated to have an equilibrium mixture of 91% cis and 9% trans structures, while flutamide is calculated to have a mixture of 65% cis-cis and 28% trans-cis structures at 298.15 K. The analysis of the observed vibrational spectra supports the presence of isobutyranilide in only one conformation at room temperature. From a 1:1 acetonitrile solvent experiment flutamide is determined to exist in more than one conformation at ambient temperature. Complete vibrational assignments of the normal modes of isobutyranilide and flutamide were provided on the basis of combined normal coordinate calculations and experimental Infrared and Raman spectra. The 1H and 13C NMR spectra of isobutyranilide were measured and their chemical shifts were compared to the corresponding ones of flutamide.

Badawi, Hassan M.; Förner, Wolfgang; Ali, Shaikh A.

2014-10-01

237

Functional Groups Determine Biochar Properties (pH and EC) as Studied by Two-Dimensional 13C NMR Correlation Spectroscopy  

PubMed Central

While the properties of biochar are closely related to its functional groups, it is unclear under what conditions biochar develops its properties. In this study, two-dimensional (2D) 13C nuclear magnetic resonance (NMR) correlation spectroscopy was for the first time applied to investigate the development of functional groups and establish their relationship with biochar properties. The results showed that the agricultural biomass carbonized to biochars was a dehydroxylation/dehydrogenation and aromatization process, mainly involving the cleavage of O-alkylated carbons and anomeric O-C-O carbons in addition to the production of fused-ring aromatic structures and aromatic C-O groups. With increasing charring temperature, the mass cleavage of O-alkylated groups and anomeric O-C-O carbons occurred prior to the production of fused-ring aromatic structures. The regression analysis between functional groups and biochar properties (pH and electrical conductivity) further demonstrated that the pH and electrical conductivity of rice straw derived biochars were mainly determined by fused-ring aromatic structures and anomeric O-C-O carbons, but the pH of rice bran derived biochars was determined by both fused-ring aromatic structures and aliphatic O-alkylated (HCOH) carbons. In summary, this work suggests a novel tool for characterising the development of functional groups in biochars. PMID:23840381

Li, Xiaoming; Shen, Qirong; Zhang, Dongqing; Mei, Xinlan; Ran, Wei; Xu, Yangchun; Yu, Guanghui

2013-01-01

238

Early diagenesis of mangrove leaves in a tropical estuary: Bulk chemical characterization using solid-state 13C NMR and elemental analyses  

USGS Publications Warehouse

Changes in the chemical composition of mangrove (Rhizophora mangle) leaves during decomposition in tropical estuarine waters were characterized using solid-state 13C nuclear magnetic resonance (NMR) and elemental (CHNO) analysis. Carbohydrates were the most abundant components of the leaves accounting for about 50 wt% of senescent tissues. Tannins were estimated to account for about 20 wt% of leaf tissues, and lipid components, cutin, and possibly other aliphatic biopolymers in leaf cuticles accounted for about 15 wt%. Carbohydrates were generally less resistant to decomposition than the other constituents and decreased in relative concentration during decomposition. Tannins were of intermediate resistance to decomposition and remained in fairly constant proportion during decomposition. Paraffinic components were very resistant to decomposition and increased in relative concentration as decomposition progressed. Lignin was a minor component of all leaf tissues. Standard methods for the colorimetric determination of tannins (Folin-Dennis reagent) and the gravimetric determination of lignin (Klason lignin) were highly inaccurate when applied to mangrove leaves. The N content of the leaves was particularly dynamic with values ranging from 1.27 wt% in green leaves to 0.65 wt% in senescent yellow leaves attached to trees. During decomposition in the water the N content initially decreased to 0.51 wt% due to leaching, but values steadily increased thereafter to 1.07 wt% in the most degraded leaf samples. The absolute mass of N in the leaves increased during decomposition indicating that N immobilization was occurring as decomposition progressed. ?? 1990.

Benner, R.; Hatcher, P.G.; Hedges, J.I.

1990-01-01

239

Comprehensive quantum chemical and spectroscopic (FTIR, FT-Raman, 1H, 13C NMR) investigations of O-desmethyltramadol hydrochloride an active metabolite in tramadol - An analgesic drug  

NASA Astrophysics Data System (ADS)

O-desmethyltramadol is one of the main metabolites of tramadol widely used clinically and has analgesic activity. The FTIR and FT-Raman spectra of O-desmethyl tramadol hydrochloride are recorded in the solid phase in the regions 4000-400 cm-1 and 4000-100 cm-1, respectively. The observed fundamentals are assigned to different normal modes of vibration. Theoretical studies have been performed as its hydrochloride salt. The structure of the compound has been optimised with B3LYP method using 6-31G** and cc-pVDZ basis sets. The optimised bond length and bond angles are correlated with the X-ray data. The experimental wavenumbers were compared with the scaled vibrational frequencies determined by DFT methods. The IR and Raman intensities are determined with B3LYP method using cc-pVDZ and 6-31G(d,p) basic sets. The total electron density and molecular electrostatic potential surfaces of the molecule are constructed by using B3LYP/cc-pVDZ method to display electrostatic potential (electron + nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. Natural bond orbital analysis of O-desmethyltramadol hydrochloride has been performed to indicate the presence of intramolecular charge transfer. The 1H and 13C NMR chemical shifts of the molecule have been anlysed.

Arjunan, V.; Santhanam, R.; Marchewka, M. K.; Mohan, S.

2014-03-01

240

Early estrogen-induced metabolic changes and their inhibition by actinomycin D and cycloheximide in human breast cancer cells: 31P and 13C NMR studies.  

PubMed Central

Metabolic changes following estrogen stimulation and the inhibition of these changes in the presence of actinomycin D and cycloheximide were monitored continuously in perfused human breast cancer T47D clone 11 cells with 31P and 13C NMR techniques. The experiments were performed by estrogen rescue of tamoxifen-treated cells. Immediately after perfusion with estrogen-containing medium, a continuous enhancement in the rates of glucose consumption, lactate production by glycolysis, and glutamate synthesis by the Krebs cycle occurred with a persistent 2-fold increase at 4 hr. The content of phosphocholine had increased by 10% to 30% within the first hour of estrogen stimulation, but the content of the other observed phosphate metabolites as well as the pH remained unchanged. Pretreatment with either actinomycin D or cycloheximide, at concentrations known to inhibit mRNA and protein synthesis, respectively, and simultaneous treatment with estrogen and each inhibitor prevented the estrogen-induced changes in glucose metabolism. This suggested that the observed estrogen stimulation required synthesis of mRNA and protein. These inhibitors also modulated several metabolic activities that were not related to estrogen stimulation. The observed changes in the in vivo kinetics of glucose metabolism may provide a means for the early detection of the response of human breast cancer cells to estrogen versus tamoxifen treatment. PMID:2748604

Neeman, M; Degani, H

1989-01-01

241

I: Low Frequency NMR and NQR Using a dc SQUID. II: Variable-temperature 13C CP/MAS of Organometallics  

SciTech Connect

NMR and NQR at low frequencies are difficult prospects due to small nuclear spin polarization. Furthermore, the sensitivity'of the inductive pickup circuitry of standard spectrometers is reduced as the frequency is lowered. I have used a cw-SQUID (Superconducting QUantum Interference Device) spectrometer, which has no such frequency dependence, to study the local atomic environment of {sup 14}N via the quadrupolar interaction. Because {sup 14}N has spin I = 1 and a 0-6 MHz frequency range, it is not possible to obtain well-resolved spectra in high magnetic fields. I have used a technique to observe {sup 14}N NQR resonances via their effect on neighboring protons mediated by the heteronuclear dipolar interaction to study peptides and narcotics. The sensitivity of the SQUID is not enough to measure low-frequency surface (or other low spin density) systems. The application of spin-polarized xenon has been previously used to enhance polarization in conventional NMR experiments. Because xenon only polarizes spins with which it is in contact, it is surface selective. While differences in chemical shifts between surface and bulk spins are not large, it is expected that the differences in quadrupole coupling constant should be very large due to the drastic change of the electric field gradient surrounding spins at the surface. With this in mind, I have taken preliminary steps to measure SQUID detected polarization transfer from Xe to another spin species at 4.2 K and in small magnetic fields (<50 G). In this regime, the spin-lattice relaxation of xenon is dependent on the applied magnetic field. The results of our efforts to characterize the relaxation of xenon are presented. The final section describes the solid-state variable-temperature (VT) one- and two-dimensional {sup 13}C cross polarization (CP)/magic angle spinning (MAS) NMR of Hf({eta}{sup 5}-C{sub 5}H{sub 5}){sub 2}({eta}{sup 1}-C{sub 5}H{sub 5}){sub 2}, Zr({eta}{sup 5}-C{sub 5}H{sub 5}){sub 3}({eta}{sup 1}-C{sub 5}H{sub 5}) and Sn({eta}{sup 1}-C{sub 5}H{sub 5}){sub 4}. This work was undertaken in the hope of gaining insight into the intramolecuhrr dynamics, specifically which fluxional processes exist in the solid state, by what mechanism rearrangements are occurring, and the activation energies by which these processes are governed.

Ziegeweid, M.A.

1995-11-29

242

Study of stereospecificity of 1H, 13C, 15N and 77Se shielding constants in the configurational isomers of the selenophene-2-carbaldehyde azine by NMR spectroscopy and MP2-GIAO calculations.  

PubMed

In the (1)H and (13)C NMR spectra of selenophene-2-carbaldehyde azine, the (1)H-5, (13)C-3 and (13)C-5 signals of the selenophene ring are shifted to higher frequencies, whereas those of the (1)H-1, (13)C-1, (13)C-2 and (13)C-4 are shifted to lower frequencies on going from the EE to ZZ isomer or from the E moiety to the Z moiety of EZ isomer. The (15)N chemical shift is significantly larger in the EE isomer relative to the ZZ isomer and in the E moiety relative to the Z moiety of EZ isomer. A very pronounced difference (60-65 mg/g) between the (77)Se resonance positions is revealed in the studied azine isomers, the (77)Se peak being shifted to higher frequencies in the ZZ isomer and in the Z moiety of EZ isomer. The trends in the changes of the measured chemical shifts are reasonably reproduced by the GIAO calculations at the MP2 level of the (1)H, (13)C, (15)N and (77)Se shielding constants in the energy-favorable conformation with the syn orientation of both selenophene rings relative to the C = N groups. The NBO analysis suggests that such an arrangement of the selenophene rings may take place because of a higher energy of some intramolecular interactions. PMID:22002712

Afonin, Andrei V; Pavlov, Dmitry V; Albanov, Alexander I; Levanova, Ekaterina P; Levkovskaya, Galina G

2011-11-01

243

In vivo 13C NMR study of the bidirectional reactions of the Wood-Werkman cycle and around the pyruvate node in Propionibacterium freudenreichii subsp. shermanii and Propionibacterium acidipropionici.  

PubMed

This study used in vitro 13C NMR spectroscopy to directly examine bidirectional reactions of the Wood-Werkman cycle involved in central carbon metabolic pathways of dairy propionibacteria during pyruvate catabolism. The flow of [2-13C]pyruvate label was monitored on living cell suspensions of Propionibacterium freudenreichii subsp. shermanii and Propionibacterium acidipropionici under acidic conditions. P. shermanii and P. acidipropionici cells consumed pyruvate at apparent initial rates of 161 and 39 micromol min(-1) g(-1) (cell dry weight), respectively. The bidirectionality of reactions in the first part of the Wood-Werkman cycle was evident from the formation of intermediates such as [3-13C]pyruvate and [3-13C]malate and of products like [2-13C]acetate from [2-13C]pyruvate. For the first time alanine labeled on C2 and C3 and aspartate labeled on C2 and C3 were observed during [2-13C]pyruvate metabolism by propionibacteria. The kinetics of aspartate isotopic enrichment was evidence for its production from oxaloacetate via aspartate aminotransferase. Activities of a partial tricarboxylic acid pathway, acetate synthesis, succinate synthesis, gluconeogenesis, aspartate synthesis, and alanine synthesis pathways were evident from the experimental results. PMID:10937824

Deborde, C; Rolin, D B; Boyaval, P

1999-10-01

244

Spectroscopic (FTIR, FT-Raman, 13C and 1H NMR) investigation, molecular electrostatic potential, polarizability and first-order hyperpolarizability, FMO and NBO analysis of 1-methyl-2-imidazolethiol  

NASA Astrophysics Data System (ADS)

In this work, experimental and theoretical study on the molecular structure and vibrational spectra of 1-methyl-2-imidazolethiol (MIME) were presented. The vibrational frequencies of the title compound were obtained theoretically by ab initio HF and DFT (B3LYP/LSDA) employing 6-311G (d,p) and 6-311++G(d,p) basis sets and compared with experimental spectral bands (FTIR and FT-Raman). The thermodynamic properties of the studied compound have been computed at different temperatures. The atomic charges and charge delocalization of the molecule have been analyzed by natural bond orbital (NBO) analysis. The reactivity sites are identified by mapping the molecular electrostatic potential (MESP) surface. Electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. Besides, 13C and 1H nuclear magnetic resonance (NMR) chemical shifts of the molecule in chloroform solvent calculated using the Gauge-Independent Atomic Orbital (GIAO) method are found to be in good agreement with experimental values.

Xavier, R. John; Dinesh, P.

2014-01-01

245

A 13C NMR Study of pyridinium phenoxide series with increasing sterical hindrance reveals the dramatic influence of torsion on their structure  

Microsoft Academic Search

The 13C resonance signals of five twisted pyridinium phenoxides has been assigned in two different solvents (CD3OD and D6-DMSO), while the torsion angle was varied by changing the pyridinium substituents at ortho positions of the intercyclic bond. The experimental 13C chemical shifts of these compounds were adjusted using calculating shift parameters evaluated from reference compounds, revealing the changes of 13C

Hélène Chaumeil; Patrice Jacques; Vincent Diemer; Didier Le Nouën; Christiane Carré

2011-01-01

246

Multinuclear 183W and 13C NMR and indirect photometry study for the identification and the characterization of new complexes of sugar acids  

NASA Astrophysics Data System (ADS)

Colourless tungstate complexes of the sugar acids, L-manonnic, D-glucaric and galactaric acids have been studied in aqueous solutions. Multinuclear 13C and 183W NMR have been used to identify the structures of the complexes and the sites of chelation of each ligand. Indirect photometry has been used to determine the stoichiometry and the stability constants of the complexes. For mannonic acid, two complexes of the lactic type with a mono-nuclear and a di-nuclear tungsten core have been identified at acidic pH. In these complexes, a (OH) group at the carbon atom in ? position is necessary to the formation of the complex and only the hydroxyl groups (OH) of the carboxyl function and of the carbon atom in ? position belongs to the site of chelation. Upon increasing the pH, the lactic complexes disappear: first the mono-nuclear, then also the di-nuclear lactic complexes, however a new complex of mixed (lactic + erythro) type with a (5, 2) composition has been observed. Upon increasing the pH a single erythro complex appears and at pH 10 a small amount of threo (tetradentate) type complex has been observed. For glucaric and galactaric acids , a new tri-nuclear complex (3, 3, 6) is formed in acid medium, this complex is composed of three mono-nuclear bidentate sites of chelation related one to the other. Upon increasing the pH, these new tri-nuclear complexes disappear and only for the W-galactarate system there is formation of a di-nuclear tetradentate complex of type erythro analogous to the complex of the mannonic acid.

Hlaïbi, Miloudi; Hor, Mustapha; Riri, Mohamed; Benjjar, Abdelkhalek; Verchère, Jean-François

2009-02-01

247

Orientation and motion of tetrahydrofuran in graphite intercalation compounds. Proton NMR studies of Cs(THF){sub 1.3}C{sub 24} and K(THF){sub 2.5}C{sub 24}  

SciTech Connect

The orientation and motion of tetrahydrofuran (THF) in the ternary graphite intercalation compounds Cs(THF){sub 1.3}C{sub 24} and K(THF){sub 2.5}C{sub 24} have been studied by proton NMR. Simulations of the NMR spectra indicate that the THF molecules in Cs(THF){sub 1.3}C{sub 24} have their mean planes oriented parallel to the layers of the host lattice, while the THF molecules in K(THF){sub 2.5}C{sub 24} have their mean planes oriented at an angle between 50{degree} and 75{degree} from the graphite layers. The proton NMR spectra of both compounds show evidence that the THF molecules rotate about the normal to the graphite layers and confirm X-ray diffraction studies showing a degree of orientational disorder in the samples, corresponding to a mosaic spread in the graphite layer orientation. Simulations indicate that the conformation of intercalated THF is different than gas or liquid phase THF, which has been found to have a ring puckering amplitude of 0.38-0.44 A and to undergo nearly free pseudorotation through a series of conformations. Best agreement between simulated and experimental NMR spectra of Cs(THF){sub 1.3}C{sub 24} was obtained with THF interconverting between two conformations of C{sub s} symmetry and a puckering amplitude of 0.30 A. 31 refs., 15 figs.

Schmidt, C.; Rosen, M.E.; Caplan, D.F.; Pines, A. [Lawrence Berkeley Lab., CA (United States)]|[Univ. of California, Berkeley, CA (United States); Quinton, M.F. [Laboratoire de Physique Quantique, Paris (France)

1995-06-29

248

Whole-cell detection by 13C NMR of metabolic flux through the C1-tetrahydrofolate synthase/serine hydroxymethyltransferase enzyme system and effect of antifolate exposure in Saccharomyces cerevisiae.  

PubMed

Folate-mediated one-carbon metabolism is critical for the synthesis of numerous cellular constituents required for cell growth. A potential source of one-carbon units is formate. This one-carbon unit is activated to 10-formyltetrahydrofolate via the synthetase activity of the trifunctional enzyme C1-tetrahydrofolate (THF) synthase for use in purine synthesis or can be further reduced to 5,10-methylene-THF by the dehydrogenase activity of the same enzyme. 5,10-Methylene-THF is used by serine hydroxymethyltransferase (SHMT) in the synthesis of serine. Recently, 13C NMR has been used to establish that the C1-THF synthase/SHMT enzyme system is the only route from formate to serine in vivo in the yeast Saccharomyces cerevisiae [Pasternack et al. (1992) Biochemistry 31, 8713-8719]. In vitro studies have considered the kinetics of the C1-THF synthase/SHMT enzyme system in the catalytic conversion of formate to serine [Strong et al. (1987) J. Biol. Chem. 262, 12519-12525]. In the present work, we begin to study the kinetics of this two-enzyme system in its natural environment. Provision of [13C]formate and direct detection of an intracellular accumulating pool of [3-13C]serine by 13C NMR of whole cells allow us to monitor the rate of flux through this enzyme system in vivo. The rate of accumulation of soluble [3-13C]serine under [13C]formate-saturating conditions is 13.0 +/- 1.2 microM/min relative to an external standard of serine in D2O. The extracellular formate concentration at half-maximal flux was determined to be 900 microM.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8003483

Pasternack, L B; Laude, D A; Appling, D R

1994-06-14

249

Linear free energy relationships of 13C NMR chemical shifts in 4-substituted phenyl-4,5-dihydrobenzo[f][1,4]oxazepin-3(2H)-ones(thiones)  

NASA Astrophysics Data System (ADS)

Linear free energy relationships (LFER) were applied to the 13C NMR chemical shifts in 4-substituted phenyl-4,5-dihydrobenzo[f][1,4]oxazepin-3(2H)-ones(thiones). The correlation analysis for the substituent-induced chemical shifts (SCS) with inductive and resonance parameters (?, F and R) were carried out by using SSP (single substituent parameter) and DSP (dual substituent parameter). The presented calculation accounts satisfactorily for the polar and resonance substituent effects operating at benzoxazepine carbon atoms. Negative ? values were found for several correlations (reverse substituent effect). For a better understanding of the results, density functional theory (DFT) calculations were performed to determine the preferred geometry and to calculate the theoretical 13C NMR chemical shifts.

Agirbas, Hikmet; Kemal, Berat

2013-12-01

250

Sequential backbone assignment of uniformly 13C-labeled RNAs by a two-dimensional P(CC)H-TOCSY triple resonance NMR experiment.  

PubMed

A new 1H-13C-31P triple resonance experiment is described which allows unambiguous sequential backbone assignment in 13C-labeled oligonucleotides via through-bond coherence transfer from 31P via 13C to 1H. The approach employs INEPT to transfer coherence from 31P to 13C and homonuclear TOCSY to transfer the 13C coherence through the ribose ring, followed by 13C to 1H J-cross-polarisation. The efficiencies of the various possible transfer pathways are discussed. The most efficient route involves transfer of 31Pi coherence via C4'i and C4'i-1, because of the relatively large JPC4' couplings involved. Via the homonuclear and heteronuclear mixing periods, the C4'i and C4'i-1 coherences are subsequently transferred to, amongst others, H1'i and H1'i-1, respectively, leading to a 2D 1H-31P spectrum which allows a sequential assignment in the 31P-1H1' region of the spectrum, i.e. in the region where the proton resonances overlap least. The experiment is demonstrated on a 13C-labeled RNA hairpin with the sequence 5'(GGGC-CAAA-GCCU)3'. PMID:7533569

Wijmenga, S S; Heus, H A; Leeuw, H A; Hoppe, H; van der Graaf, M; Hilbers, C W

1995-01-01

251

1H, 13C and 15N NMR, FT-IR as well as PM5 studies of a new Schiff base of gossypol with 3,6-dioxadecylamine in solution  

NASA Astrophysics Data System (ADS)

The Schiff base of racemic gossypol with 3,6-dioxadecylamine (GSDN) has been synthesised and its structure has been studied by FT-IR, 1H, 13C and 15N NMR spectroscopy as well as by the PM5 semiempirical method. All spectroscopic methods have provided respective evidences that GSDN in solution exists exclusively in the enamine-enamine tautomeric form. The structure of the enamine-enamine tautomer is visualized and the hydrogen bonds stabilising this structure are discussed.

Przybylski, Piotr; Lewandowska, Weronika; Brzezinski, Bogumi?; Bartl, Franz

2006-09-01

252

13C- and 1H-NMR studies of oxyanion and tetrahedral intermediate stabilization by the serine proteinases: optimizing inhibitor warhead specificity and potency by studying the inhibition of the serine proteinases by peptide-derived chloromethane and glyoxal inhibitors.  

PubMed

Catalysis by the serine proteinases proceeds via a tetrahedral intermediate whose oxyanion is stabilized by hydrogen-bonding in the oxyanion hole. There have been extensive (13)C-NMR studies of oxyanion and tetrahedral intermediate stabilization in trypsin, subtilisin and chymotrypsin using substrate-derived chloromethane inhibitors. One of the limitations of these inhibitors is that they irreversibly alkylate the active-site histidine residue which results in the oxyanion not being in the optimal position in the oxyanion hole. Substrate-derived glyoxal inhibitors are reversible inhibitors which, if they form tetrahedral adducts in the same way as substrates form tetrahedral intermediates, will overcome this limitation. Therefore we have synthesized (13)C-enriched substrate-derived glyoxal inhibitors which have allowed us to use (13)C-NMR and (1)H-NMR to determine how they interact with proteinases. It is hoped that these studies will help in the design of specific and highly potent warheads for serine proteinase inhibitors. PMID:17511653

Malthouse, J P G

2007-06-01

253

2H-13C HETCOR MAS NMR for indirect detection of 2H quadrupole patterns and spin-lattice relaxation rates  

NASA Astrophysics Data System (ADS)

Two-dimensional (2D) cross-polarization magic angle spinning (CP-MAS) 2H-13C heteronuclear correlation (HETCOR) experiments were utilized to indirectly detect site-specific deuterium MAS powder patterns. The 2H-13C cross-polarization efficiency is orientation-dependent and non-uniform for all crystallites. This leads to difficulty in extracting the correct 2H MAS quadrupole powder patterns. In order to obtain accurate deuterium line shapes, 13C spin lock rf field, spin lock rf ramp and CP contact time were carefully calibrated with the assistance of theoretical simulations. The extracted quadrupole patterns for U-[2H/13C/15N]-alanine indicate that the methyl deuterium undergoes classic, three-site jumping in the fast motion regime (10-8-10-12 s) and the methine deuterium has a rigid deuterium powder pattern. For U-[2H/13C/15N]-phenylalanine, indirectly detected deuterium line shapes illustrate that the aromatic ring undergoes 180° flips in the fast motion regime while 2H? and 2H? are completely rigid. The experimental deuterium line shapes for U-[2H/13C/15N]-proline reflect that 2H?, 2H? and 2H? are subjected to fast, two-site reorientations at an angle of (15 ± 5)°, (30 ± 5)° and (25 ± 10)° respectively. In addition, an approach that combines a composite inversion pulse with 2H-13C CP-MAS is applied to measure 2H spin-lattice relaxation times in a site-specific, 13C-detected fashion.

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

2013-01-01

254

Prony-Burg method for NMR spectral analysis  

NASA Astrophysics Data System (ADS)

A new procedure, the Prony-Burg method (PBM), has been applied to process 31P NMR signals in the time domain (the free induction decays). As in the standard Prony method, it is assumed that the model for the signal is a sum of damped sinusoids. Our approach makes use of Burg's algorithm to calculate the autoregressive coefficients of the homogeneous equation associated with the model and the final prediction error criterion for the determination of the autoregression order. The spectral parameters, i.e., frequencies, damping factors, amplitudes, and phases, are then retrieved via polynomial rooting and singular value decomposition. The stability of the PBM is studied as a function of the signal-tonoise ratio of the free induction decay. The results indicate good spectral fidelity and stability so long as the signal-to-noise ratio is not very low.

Barone, P.; Guidoni, L.; Massaro, E.; Viti, V.

255

Hypermetabolic state in the 7-month-old triple transgenic mouse model of Alzheimer's disease and the effect of lipoic acid: a (13)C-NMR study.  

PubMed

Alzheimer's disease (AD) is characterized by age-dependent biochemical, metabolic, and physiologic changes. These age-dependent changes ultimately converge to impair cognitive functions. This study was carried out to examine the metabolic changes by probing glucose and tricarboxylic acid cycle metabolism in a 7-month-old triple transgenic mouse model of AD (3xTg-AD). The effect of lipoic acid, an insulin-mimetic agent, was also investigated to examine its ability in modulating age-dependent metabolic changes. Seven-month-old 3xTg-AD mice were given intravenous infusion of [1-(13)C]glucose followed by an ex vivo (13)C nuclear magnetic resonance to determine the concentrations of (13)C-labeled isotopomers of glutamate, glutamine, aspartate, gamma aminobutyric acid, and N-acetylaspartate. An intravenous infusion of [1-(13)C]glucose+[1,2-(13)C]acetate was given for different periods of time to distinguish neuronal and astrocytic metabolism. Enrichments of glutamate, glutamine, and aspartate were calculated after quantifying the total ((12)C+(13)C) concentrations by high-performance liquid chromatography. A hypermetabolic state was clearly evident in 7-month-old 3xTg-AD mice in contrast to the hypometabolic state reported earlier in 13-month-old mice. Hypermetabolism was evidenced by prominent increase of (13)C labeling and enrichment in the 3xTg-AD mice. Lipoic acid feeding to the hypermetabolic 3xTg-AD mice brought the metabolic parameters to the levels of nonTg mice. PMID:25099753

Sancheti, Harsh; Patil, Ishan; Kanamori, Keiko; Díaz Brinton, Roberta; Zhang, Wei; Lin, Ai-Ling; Cadenas, Enrique

2014-11-01

256

Evaluation of cerebral acetate transport and metabolic rates in the rat brain in vivo using 1H-[13C]-NMR  

PubMed Central

Acetate is a well-known astrocyte-specific substrate that has been used extensively to probe astrocytic function in vitro and in vivo. Analysis of amino acid turnover curves from 13C-acetate has been limited mainly for estimation of first-order rate constants from exponential fitting or calculation of relative rates from steady-state 13C enrichments. In this study, we used 1H-[13C]-Nuclear Magnetic Resonance spectroscopy with intravenous infusion of [2-13C]acetate-Na+ in vivo to measure the cerebral kinetics of acetate transport and utilization in anesthetized rats. Kinetics were assessed using a two-compartment (neuron/astrocyte) analysis of the 13C turnover curves of glutamate-C4 and glutamine-C4 from [2-13C]acetate-Na+, brain acetate levels, and the dependence of steady-state glutamine-C4 enrichment on blood acetate levels. The steady-state enrichment of glutamine-C4 increased with blood acetate concentration until 90% of plateau for plasma acetate of 4 to 5?mmol/L. Analysis assuming reversible, symmetric Michaelis–Menten kinetics for transport yielded 27±2mmol/L and 1.3±0.3??mol/g/min for Kt and Tmax, respectively, and for utilization, 0.17±0.24?mmol/L and 0.14±0.02??mol/g/min for KM_util and Vmax_util, respectively. The distribution space for acetate was only 0.32±0.12?mL/g, indicative of a large excluded volume. The astrocytic and neuronal tricarboxylic acid cycle fluxes were 0.37±0.03??mol/g/min and 1.41±0.11??mol/g/min, respectively; astrocytes thus comprised ?21%±3% of total oxidative metabolism. PMID:20125180

Patel, Anant B; de Graaf, Robin A; Rothman, Douglas L; Behar, Kevin L; Mason, Graeme F

2010-01-01

257

Evaluation of cerebral acetate transport and metabolic rates in the rat brain in vivo using 1H-[13C]-NMR.  

PubMed

Acetate is a well-known astrocyte-specific substrate that has been used extensively to probe astrocytic function in vitro and in vivo. Analysis of amino acid turnover curves from (13)C-acetate has been limited mainly for estimation of first-order rate constants from exponential fitting or calculation of relative rates from steady-state (13)C enrichments. In this study, we used (1)H-[(13)C]-Nuclear Magnetic Resonance spectroscopy with intravenous infusion of [2-(13)C]acetate-Na(+) in vivo to measure the cerebral kinetics of acetate transport and utilization in anesthetized rats. Kinetics were assessed using a two-compartment (neuron/astrocyte) analysis of the (13)C turnover curves of glutamate-C4 and glutamine-C4 from [2-(13)C]acetate-Na(+), brain acetate levels, and the dependence of steady-state glutamine-C4 enrichment on blood acetate levels. The steady-state enrichment of glutamine-C4 increased with blood acetate concentration until 90% of plateau for plasma acetate of 4 to 5 mmol/L. Analysis assuming reversible, symmetric Michaelis-Menten kinetics for transport yielded 27+/-2 mmol/L and 1.3+/-0.3 micromol/g/min for K(t) and T(max), respectively, and for utilization, 0.17+/-0.24 mmol/L and 0.14+/-0.02 micromol/g/min for K(M_util) and V(max_util), respectively. The distribution space for acetate was only 0.32+/-0.12 mL/g, indicative of a large excluded volume. The astrocytic and neuronal tricarboxylic acid cycle fluxes were 0.37+/-0.03 micromol/g/min and 1.41+/-0.11 micromol/g/min, respectively; astrocytes thus comprised approximately 21%+/-3% of total oxidative metabolism. PMID:20125180

Patel, Anant B; de Graaf, Robin A; Rothman, Douglas L; Behar, Kevin L; Mason, Graeme F

2010-06-01

258

Reproducibility and Absolute Quantification of Muscle Glycogen in Patients with Glycogen Storage Disease by 13C NMR Spectroscopy at 7 Tesla  

PubMed Central

Carbon-13 magnetic resonance spectroscopy (13C MRS) offers a noninvasive method to assess glycogen levels in skeletal muscle and to identify excess glycogen accumulation in patients with glycogen storage disease (GSD). Despite the clinical potential of the method, it is currently not widely used for diagnosis or for follow-up of treatment. While it is possible to perform acceptable 13C MRS at lower fields, the low natural abundance of 13C and the inherently low signal-to-noise ratio of 13C MRS makes it desirable to utilize the advantage of increased signal strength offered by ultra-high fields for more accurate measurements. Concomitant with this advantage, however, ultra-high fields present unique technical challenges that need to be addressed when studying glycogen. In particular, the question of measurement reproducibility needs to be answered so as to give investigators insight into meaningful inter-subject glycogen differences. We measured muscle glycogen levels in vivo in the calf muscle in three patients with McArdle disease (MD), one patient with phosphofructokinase deficiency (PFKD) and four healthy controls by performing 13C MRS at 7T. Absolute quantification of the MRS signal was achieved by using a reference phantom with known concentration of metabolites. Muscle glycogen concentration was increased in GSD patients (31.5±2.9 g/kg w. w.) compared with controls (12.4±2.2 g/kg w. w.). In three GSD patients glycogen was also determined biochemically in muscle homogenates from needle biopsies and showed a similar 2.5-fold increase in muscle glycogen concentration in GSD patients compared with controls. Repeated inter-subject glycogen measurements yield a coefficient of variability of 5.18%, while repeated phantom measurements yield a lower 3.2% system variability. We conclude that noninvasive ultra-high field 13C MRS provides a valuable, highly reproducible tool for quantitative assessment of glycogen levels in health and disease. PMID:25296331

Romain, Nadine; Cheshkov, Sergey; Ren, Jimin; Malloy, Craig R.; Haller, Ronald G.

2014-01-01

259

Effects of NMR spectral resolution on protein structure calculation.  

PubMed

Adequate digital resolution and signal sensitivity are two critical factors for protein structure determinations by solution NMR spectroscopy. The prime objective for obtaining high digital resolution is to resolve peak overlap, especially in NOESY spectra with thousands of signals where the signal analysis needs to be performed on a large scale. Achieving maximum digital resolution is usually limited by the practically available measurement time. We developed a method utilizing non-uniform sampling for balancing digital resolution and signal sensitivity, and performed a large-scale analysis of the effect of the digital resolution on the accuracy of the resulting protein structures. Structure calculations were performed as a function of digital resolution for about 400 proteins with molecular sizes ranging between 5 and 33 kDa. The structural accuracy was assessed by atomic coordinate RMSD values from the reference structures of the proteins. In addition, we monitored also the number of assigned NOESY cross peaks, the average signal sensitivity, and the chemical shift spectral overlap. We show that high resolution is equally important for proteins of every molecular size. The chemical shift spectral overlap depends strongly on the corresponding spectral digital resolution. Thus, knowing the extent of overlap can be a predictor of the resulting structural accuracy. Our results show that for every molecular size a minimal digital resolution, corresponding to the natural linewidth, needs to be achieved for obtaining the highest accuracy possible for the given protein size using state-of-the-art automated NOESY assignment and structure calculation methods. PMID:23874675

Tikole, Suhas; Jaravine, Victor; Orekhov, Vladislav Yu; Güntert, Peter

2013-01-01

260

1-13C amino acid selective labeling in a 2H15N background for NMR studies of large proteins.  

PubMed

Isotope labeling by residue type (LBRT) has long been an important tool for resonance assignments at the limit where other approaches, such as triple-resonance experiments or NOESY methods do not succeed in yielding complete assignments. While LBRT has become less important for small proteins it can be the method of last resort for completing assignments of the most challenging protein systems. Here we present an approach where LBRT is achieved by adding protonated (14)N amino acids that are (13)C labeled at the carbonyl position to a medium for uniform deuteration and (15)N labeling. This has three important benefits over conventional (15)N LBRT in a deuterated back ground: (1) selective TROSY-HNCO cross peaks can be observed with high sensitivity for amino-acid pairs connected by the labeling, and the amide proton of the residue following the (13)C labeled amino acid is very sharp since its alpha position is deuterated, (2) the (13)C label at the carbonyl position is less prone to scrambling than the (15)N at the alpha-amino position, and (3) the peaks for the 1-(13)C labeled amino acids can be identified easily from the large intensity reduction in the (1)H-(15)N TROSY-HSQC spectrum for some residues that do not significantly scramble nitrogens, such as alanine and tyrosine. This approach is cost effective and has been successfully applied to proteins larger than 40 kDa. PMID:17390105

Takeuchi, Koh; Ng, Elise; Malia, Thomas J; Wagner, Gerhard

2007-05-01

261

{sup 13}C and {sup 17}O NMR binding constant studies of uranyl carbonate complexes in near-neutral aqueous solution. Yucca Mountain Project Milestone Report 3351  

SciTech Connect

Valuable structural information, much of it unavailable by other methods, can be obtained about complexes in solution through NMR spectroscopy. From chemical shift and intensity measurements of complexed species, NMR can serve as a species-specific structural probe for molecules in solution and can be used to validate thermodynamic constants used in geochemical modeling. Fourier-transform nuclear magnetic resonance (FT-NMR) spectroscopy has been employed to study the speciation of uranium(VI) ions in aqueous carbonate solutions as a function of pH, ionic strength, carbonate concentration, uranium concentration, and temperature. Carbon-13 and oxygen-17 NMR spectroscopy were used to monitor the fractions, and hence thermodynamic binding constants of two different uranyl species U0{sub 2}(CO{sub 3}){sub 3}{sup 4{minus}} and (UO{sub 2}){sub 3}(CO{sub 3}){sub 6}{sup 6{minus}} in aqueous solution. Synthetic buffer solutions were prepared under the ionic strength conditions used in the NMR studies in order to obtain an accurate measure of the hydrogen ion concentration, and a discussion of pH = {minus}log(a{sub H}{sup +}) versus p[H] = {minus}log[H+] is provided. It is shown that for quantitative studies, the quantity p[H] needs to be used. Fourteen uranium(VI) binding constants recommended by the OECD NEA literature review were corrected to the ionic strengths employed in the NMR study using specific ion interaction theory (SIT), and the predicted species distributions were compared with the actual species observed by multinuclear NMR. Agreement between observed and predicted stability fields is excellent. This establishes the utility of multinuclear NMR as a species-specific tool for the study of the actinide carbonate complexation constants, and serves as a means for validating the recommendations provided by the OECD NEA.

Clark, D.L.; Newton, T.W.; Palmer, P.D.; Zwick, B.D.

1995-01-01

262

The origin of the splitting of 13C and 15N NMR signals of 3(5)-phenyl-5(3)-methylpyrazolium chloride and bromide in the solid state: Quantum Espresso calculations  

NASA Astrophysics Data System (ADS)

A combination of 13C and 15N CPMAS NMR spectroscopy and theoretical methods (DFT and DFT-D) was used to discuss the observation of large splittings affecting some atoms in 3(5)-phenyl-5(3)-methylpyrazolium chloride and bromide. Conventional calculations using fully optimized structures with C2 symmetry reproduce solution spectra, but the large splitting observed for the signals of several pyrazolium carbon and nitrogen atoms in the solid-state can only be explained by calculations employing the experimental P21/n geometry and periodic boundary calculations.

Alkorta, Ibon; Claramunt, Rosa M.; Elguero, José; Ferraro, Marta B.; Facelli, Julio C.; Provasi, Patricio F.; Reviriego, Felipe

2014-10-01

263

119Sn Mössbauer, NMR (1H, 13C and 119Sn) and infrared study of tetracoordinated tin(IV) complexes with 4-[(( E)-1-{2-hydroxy-5-[( E)-2-(aryl)-1-diazenyl]phenyl}methylidene)amino]benzoates  

NASA Astrophysics Data System (ADS)

A series of organotin(IV) complexes of composition R3Sn[O2CC6H4{ N= C(H)C6H3-2-OH( N= NC6H4R)}- p] (R = Ph or Bz; R = H, 2-CH3, 3-CH3, 4-CH3) have been investigated by 119Sn Mössbauer, 1H, 13C, 119Sn NMR and IR spectroscopic techniques. 119Sn Mössbauer data indicated a distorted tetrahedral geometry for the triphenyltin(IV) complexes while the tribenzyltin complexes exhibit a distorted trigonal bipyramidal coordination geometry with equatorial benzyl groups and the axial positions occupied by an O atom from the carboxylate ligand and the O atom from the water ligand. The 119Sn-NMR chemical shifts confirm that the Sn atom in triorganotin complexes is four-coordinate in CDCl3 solution.

Basu Baul, Tushar S.; Das, Pradip; Rivarola, Eleonora

2009-11-01

264

Orientational and structural properties of ferroelectric liquid crystal with a broad temperature range in the SmC(*) phase by (13)C NMR, x-ray scattering and dielectric spectroscopy.  

PubMed

Thermotropic liquid crystalline materials laterally substituted by a methyl group on the aromatic ring of the alkoxybenzoate unit far from the chiral centre exhibit a very broad temperature range in the ferroelectric smectic C* (SmC(*)) phase on cooling (including supercooling) with a very high spontaneous polarization (?210 nC cm(-2)) and tilt angle (?43°) at saturation. We are presenting a detailed study of the physical properties of a ferroelectric compound, representative of this category of liquid crystals, by means of solid state (13)C-NMR, small angle x-ray scattering, dielectric spectroscopy and optical methods of the tilted SmC(*). Values of the spontaneous tilt angle measured optically are compared to those determined from the x-ray data and discussed. In addition, the viscosity has been determined in the SmC(*) phase by different experimental methods. (13)C NMR data allowed us to get information about the degree of orientational order of the SmC(*) phase and revealed the complete unwinding of the helical axis at the magnetic field of 9.4 T. This result is discussed in the framework of recent publications on the effect of the magnetic field on the supra-molecular structure of the SmC(*) phase. PMID:21817261

Bubnov, Alexej; Domenici, Valentina; Hamplová, V?ra; Kašpar, Miroslav; Veracini, Carlo Alberto; Glogarová, Milada

2009-01-21

265

Determination of the (17)O Quadrupolar Coupling Constant and of the (13)C Chemical Shielding Tensor Anisotropy of the CO Groups of Pentane-2,4-dione and beta-Diketonate Complexes in Solution. NMR Relaxation Study.  

PubMed

13C NMR relaxation times T(1) of the carbonyl groups of pentane-2,4-dione and beta-diketonate complexes Al(acac)(3) and Zr(acac)(4) (acac: pentanedionate anion) were measured for various magnetic field strengths, allowing a determination of the contribution of the chemical shift anisotropy mechanism to the total relaxation. NOE and T(1) measurements for the (13)C nucleus of the central methine carbon furnished the correlation time tau(c) for the reorientation of theses species. The chemical shift tensor anisotropy Deltasigma could be deduced and compared to the values obtained in the solid state. The quadrupolar coupling constant (QCC) of the (17)O nucleus could also be determined by measuring the line width of the (17)O NMR signal and using the tau(c) value. QCC values for the complexes are in the same range as for the pentane-2,4-dione molecule, indicating similar electronic distribution and symmetry around the oxygen atom of these different species. Deltasigma for the complexes are close together, and the values obtained in solution are approximately those obtained in the solid state. They are close to the value reported in the literature for tetraacetylethane, which can be considered as a dimer of a beta-diketone, but slight differences are observed for the individual components of the chemical shielding tensor. PMID:11666182

Champmartin, D.; Rubini, P.

1996-01-01

266

Analysis of commercial proanthocyanidins. Part 4: solid state (13)C NMR as a tool for in situ analysis of proanthocyanidin tannins, in heartwood and bark of quebracho and acacia, and related species.  

PubMed

(13)C NMR is an effective method of characterizing proanthocyanidin (PAC) tannins in quebracho (Schinopsis lorentzii) heartwood and black wattle (Acacia mearnsii) bark, before and after commercial extraction. The B-rings of the constituent flavan-3-ols, catechols (quebracho) or pyrogallols (wattle), are recognized in unprocessed source materials by "marker" signals at ca. 118 or 105ppm, respectively. NMR allows the minimum extraction efficiency to be calculated; ca. 30%, and ca. 80%, for quebracho heartwood and black wattle bark, respectively. NMR can also identify PAC tannin (predominantly robinetinidin), and compare tannin content, in bark from other acacia species; tannin content decreases in the order A. mearnsii, Acacia pycnantha (87% of A. mearnsii), Acacia dealbata and Acacia decurrens (each 74%) and Acacia karroo (30%). Heartwood from an underexploited PAC tannin source, Searsia lancea, taxonomically close to quebracho, shows abundant profisetinidin and catechin PACs. NMR offers the advantage of being applicable to source materials in their native state, and has potential applications in optimizing extraction processes, identification of tannin sources, and characterization of tannin content in cultivar yield improvement programmes. PMID:23838626

Reid, David G; Bonnet, Susan L; Kemp, Gabre; van der Westhuizen, Jan H

2013-10-01

267

Isolation, NMR Spectral Analysis and Hydrolysis Studies of a Hepta Pyranosyl Diterpene Glycoside from Stevia rebaudiana Bertoni  

PubMed Central

From the commercial extract of the leaves of Stevia rebaudiana Bertoni, a minor steviol glycoside, 13-[(2-O-?-d-glucopyranosyl-3-O-?-d-glucopyranosyl-?-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-[(2-O-(3-O-?-d-glucopyranosyl-?-l-rhamnopyranosyl)-3-O-?-d-glucopyranosyl-?-d-glucopyranosyl) ester] (1); also known as rebaudioside O having seven sugar units has been isolated. Its structural characterization has been achieved by the extensive 1D (1H and 13C), and 2D NMR (COSY, HMQC, HMBC) as well as mass spectral data. Further, hydrolysis studies were performed on rebaudioside O using acid and enzymatic methods to identify aglycone and sugar residues in its structure as well as their configurations. PMID:24970189

Chaturvedula, Venkata Sai Prakash; Chen, Steven; Yu, Oliver; Mao, Guohong

2013-01-01

268

Isolation, NMR Spectral Analysis and Hydrolysis Studies of a Hepta Pyranosyl Diterpene Glycoside from Stevia rebaudiana Bertoni.  

PubMed

From the commercial extract of the leaves of Stevia rebaudiana Bertoni, a minor steviol glycoside, 13-[(2-O-?-D-glucopyranosyl-3-O-?-D-glucopyranosyl-?-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-[(2-O-(3-O-?-D-glucopyranosyl-?-L-rhamnopyranosyl)-3-O-?-D-glucopyranosyl-?-D-glucopyranosyl) ester] (1); also known as rebaudioside O having seven sugar units has been isolated. Its structural characterization has been achieved by the extensive 1D (1H and 13C), and 2D NMR (COSY, HMQC, HMBC) as well as mass spectral data. Further, hydrolysis studies were performed on rebaudioside O using acid and enzymatic methods to identify aglycone and sugar residues in its structure as well as their configurations. PMID:24970189

Chaturvedula, Venkata Sai Prakash; Chen, Steven; Yu, Oliver; Mao, Guohong

2013-01-01

269

Synthesis, NMR spectral and antimicrobial studies of some [N-methyl-3t-alkyl-2r,6c-diarylpiperidin-4-ylidine]-5?-methylthiazolidine-4-ones  

NASA Astrophysics Data System (ADS)

Four new [N-methyl-3t-alkyl-2r,6c-diaryl-4-ylidine]-5'-methylthiozolidin-4-ones 9-12 have been synthesized by the condensation of N-methyl-3t-alkyl-2r,6c-diarylpiperidin-4-one thiosemicarbazones with ethyl 2-bromopropionate. These compounds have been characterized using FT-IR, 1H NMR, 13C NMR spectral techniques. HOMOCOSY, HSQC and HMBC spectral study have been done for [N-methyl-3,3-dimethyl-2r,6c-bis(p-methoxyphenyl)piperidin-4-ylidine]-5'-methylthiazolidine-4-one (12). Two geometrical isomers are formed in this reaction. In all these compounds piperidin rings adopt chair conformation. The rotation of the aryl group at C-2 is rather slow in 10-12. Antimicrobial activities have also been studied for 9-12. These compounds are active against all the tested bacterial and fungal strains.

Prakash, S. M.; Pandiarajan, K.; Kumar, S.

2013-06-01

270

High-resolution characterization of intrinsic disorder in proteins: expanding the suite of (13)C-detected NMR spectroscopy experiments to determine key observables.  

PubMed

Order in disorder: The characterization of intrinsically disordered proteins by NMR spectroscopy is a necessity on the one hand and a continuous challenge on the other. We propose two experiments that provide diagnostic parameters to monitor the degree of unfolding of a polypeptide. The test was performed on the yeast Cox17 protein, known to gain its function through maturation from an intrinsically disordered state (see figure). PMID:23106082

Bertini, Ivano; Felli, Isabella C; Gonnelli, Leonardo; Vasantha Kumar, M V; Pierattelli, Roberta

2011-10-17

271

Accurate Measurement of Methyl 13 C Chemical Shifts by  

E-print Network

torsion angle results; moreover, the methyl 13 C chemical shifts are sensitive to 5° changes in the 1Accurate Measurement of Methyl 13 C Chemical Shifts by Solid-State NMR for the Determination Received February 27, 2009; E-mail: mhong@iastate.edu Abstract: The use of side chain methyl 13 C chemical

Hong, Mei

272

Solid-state distortions of nominally square-planar palladium and platinum (R sub 3 P) sub 2 MX sub 2 complexes as determined by a combination of sup 13 C( sup 1 H) and sup 31 P( sup 31 H) NMR spectroscopy  

SciTech Connect

Phosphorus-31 and carbon-13 NMR spectra have been obtained for a series of 20 (R{sub 3}P){sub 2}MX{sub 2} complexes (R{sub 3}P = MePh{sub 2}P and Me{sub 2}PhP; M = Pd, Pt; X = Cl, Br, I, CN, N{sub 3}) in the solid state by cross-polarization and magic-angle-spinning (CP/MAS) techniques. Comparison of these data with spectral data obtained at 300 K in CDCl{sub 3} solutions was made in order to investigate the influence of local symmetry on {sup 31}P and {sup 13}C chemical shifts in the solid state. It was found that most of these compounds, which have regular square-planar geometries in solution, are distorted in the solid state. The solid-state distortions are evidenced by additional {sup 31}P and {sup 13}C resonances in the CP/MAS spectra as compared to the solution spectra. The nature and degree of these distortions are discussed. 25 refs., 2 figs., 6 tabs.

Rahn, J.A.; Nelson, J.H. (Univ. of Nevada, Reno (USA)); O'Donnell, D.J.; Pamer, A.R. (Chemagnetics, Fort Collins, CO (USA))

1989-06-28

273

Solid-state 13C NMR investigations of 4,7-dihydro-1H-tricyclopenta[def,jkl,pqr]triphenylene (sumanene) and indeno[1,2,3-cd]fluoranthene: Buckminsterfullerene moieties.  

PubMed

4,7-Dihydro-1H-tricyclopenta[def,jkl,pqr]triphenylene (sumanene) and indeno[1,2,3-cd]fluoranthene (indenofluoranthene) are structural moieties related to Buckminsterfullerene (C(60)). As such, understanding their structural characteristics is of great interest because of the insight they shed upon C(60). Hence, solid-state NMR (ssNMR) and ab initio quantum mechanical calculations with Gaussian03 are used in order to understand and to better characterize the molecular conformation and properties of sumanene and indenofluoranthene. Sumanene has bowl shaped curvature in its natural conformation and indenofluoranthene is planar in its natural conformation, which led us to examine how altering the curvature affects the chemical shifts in relation to those of C(60). Using X-ray structures of both sumanene and indenofluoranthene as our starting model, we calculate the energy and chemical shielding tensors and compare these data with those collected utilizing the (13)C ssNMR FIREMAT experiment. We define curvature of sumanene and indenofluoranthene using the pi-orbital axis vector (POAV) pyramidalization angle (theta(p)). We calculate the energy of varying conformations of indenofluoranthene versus their theta(p) associated with each deformed conformation. PMID:20512180

Halling, Merrill D; Orendt, Anita M; Strohmeier, Mark; Solum, Mark S; Tsefrikas, Vikki M; Hirao, Toshikazu; Scott, Lawrence T; Pugmire, Ronald J; Grant, David M

2010-07-28

274

Quantum mechanical and spectroscopic (FT-IR, 13C, 1H NMR and UV) investigations of potent antiepileptic drug 1-(4-chloro-phenyl)-3-phenyl-succinimide  

NASA Astrophysics Data System (ADS)

This study represents an integrated approach towards understanding the vibrational, electronic, NMR, and structural aspects, and reactivity of 1-(4-chloro-phenyl)-3-phenyl-succinimide (CPPS). A detailed interpretation of the FT-IR, UV and NMR spectra were reported. The equilibrium geometry, bonding features, and harmonic vibrational frequencies have been investigated with the help of density functional theory (DFT) B3LYP method using 6-31G(d,p) and 6-311++G(d,p) basis set. The scaled theoretical wavenumber showed very good agreement with the experimental values. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge-Invariant Atomic Orbital (GIAO) method. Stability of the molecule, arising from hyperconjugative interactions and charge delocalization, has been analyzed using Natural Bond Orbital (NBO) analysis. The results show that ED in the ?* and ?* antibonding orbitals and second order delocalization energies E(2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. UV-Vis spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were calculated by Time-Dependent DFT (TD-DFT) approach. To estimate chemical reactivity of the molecule, the molecular electrostatic potential (MEP) surface map is calculated for the optimized geometry of the molecule.

Vitnik, Vesna D.; Vitnik, Željko J.; Banjac, Nebojša R.; Valenti?, Nataša V.; Uš?umli?, Gordana S.; Jurani?, Ivan O.

2014-01-01

275

Implementation of a Hybrid DFT Method for Calculating NMR Shieldings Using Slater-Type Orbitals with Spin-Orbital Coupling Included. Applications to 187Os, 195Pt, and 13C in Heavy-Metal Complexes  

NASA Astrophysics Data System (ADS)

We report on the implementation of an algorithm for the calculation of the NMR shielding tensor. Our scheme is based on the Hartree-Fock method and the zeroth-order regular approximation (ZORA) Hamiltonian with spin-orbital coupling included. Gauge-including atomic orbitals (GIAOs) are employed to ensure the origin invariance of the results. Unlike the previous implementation by Fukui and Baba [ J. Chem. Phys. 2002, 117, 7836 ], our computational scheme makes use of Slater-type orbitals. We have employed this method in B3LYP calculations of the 13C, 195Pt, and 187Os NMR chemical shifts in 5d metal carbonyls, Pt(II) square-planar complexes, and osmium phosphines, respectively. The calculated NMR chemical shifts are compared to the results obtained with the BP86 and BLYP functionals, as well as the Hartree-Fock method. Comparisons are also given to experimental values. For the 195Pt chemical shifts, we have found a small improvement with respect to experiment for the B3LYP results over the BP86 and BLYP values. For the other systems, use of the B3LYP method does not improve the agreement with experiment compared to results from pure functionals such as BP86 and BLYP.

Krykunov, Mykhaylo; Ziegler, Tom; Lenthe, Erik Van

2009-09-01

276

Monomeric and dimeric structures analysis and spectroscopic characterization of 3,5-difluorophenylboronic acid with experimental (FT-IR, FT-Raman, 1H and 13C NMR, UV) techniques and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

The spectroscopic properties of 3,5-difluorophenylboronic acid (3,5-DFPBA, C6H3F2B(OH)2) were investigated by FT-IR, FT-Raman UV-Vis, 1H and 13C NMR spectroscopic techniques. FT-IR (4000-400 cm-1) and FT-Raman spectra (3500-10 cm-1) in the solid phase and 1H and 13C NMR spectra in DMSO solution were recorded. The UV spectra that dissolved in ethanol and water were recorded in the range of 200-400 nm for each solution. The structural and spectroscopic data of the molecule have been obtained for possible three conformers from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibrations were assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. Hydrogen-bonded dimer of title molecule, optimized by counterpoise correction, was also studied B3LYP at the 6-311++G(d,p) level and the effects of molecular association through O-H⋯O hydrogen bonding have been discussed. 1H and 13C NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, oscillator strength, wavelengths, HOMO and LUMO energies, were performed by time-dependent density functional theory (TD-DFT) results complements with the experimental findings. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (OPDOS) diagrams analysis were presented. The effects due to the substitutions of boric acid group and halogen were investigated. The results of the calculations were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP), nonlinear optical properties (NLO) and thermodynamic features were performed.

Karabacak, Mehmet; Kose, Etem; Atac, Ahmet; Asiri, Abdullah M.; Kurt, Mustafa

2014-01-01

277

Optimized strategy of 1H and 13C solid-state NMR methods to investigate water dynamics in soil organic matter as well as the influence of crystallinity of poly(methylene) segments  

NASA Astrophysics Data System (ADS)

Water plays a crucial role in soil organic matter (SOM) having various different functions such as transport of material, elution of ,e. g., pollutants in soil, and also the sequestration of humic substances. Furthermore, the generation and quantification of hydrophilic and hydrophobic regions in soil has several effects on SOM which can also include the storage amount and time of certain material, especially chemical pollutants. The importance of water in soil is also documented by the multitude of scientific approaches to characterize soils including diffusion NMR to study the water channel structure in soil. Our focus is on the study of water dynamics and soil structure to elucidate mechanisms of physicochemical aging. The approach uses the application of various solid-state NMR techniques - including 1H and 13C NMR - to get a multitude of information on SOM. In non-rotating samples, 1H lines are usually very broad and unstructured. Nevertheless, this rather simple technique allows for a differentiation of 1H containing chemicals based on their dynamics in soil. This includes rather solid soil components and solid as well as mobile water molecules. Based on an optimized 1H solid-state NMR strategy to study soil material together with a straightforward lineshape analysis, a series of soils and peats are characterized. Although even 1H NMR with sample spinning (MAS) often gives only limited information on different structures, we present results on the application of 2D 1H-1H phase-modulated Lee-Goldburg sequences (PMLG), that show already at medium spinning speeds the separation of functional groups. Their quantification can be correlated with sample composition, type of sample conditioning, and other parameters such as cation type or concentration and heat treatment. We are especially interested to correlate NMR data with DSC measurements based on a certain heat treatment of the soils. Our proposed model describes the presence of water in soil as a matrix linking together organic matter via hydrogen bonding. The measurement profile includes a conditioning step under a certain humidity as a starting point. Then, the soil is heated up to 110°C for 30 minutes to destroy the present water matrix and then follow the regeneration of this matrix over time. Both in 1H static NMR and DSC this physical aging of the water structure in soil can be followed. While the bridges may be easily disrupted, re-formation is slow in the SOM matrix and can be on the order of weeks and even months depending on the soil. Apart from the water dynamics in soil, additional information can be obtained from 13C solid-state NMR which is the typical measurement technique for the study of soil due to the larger chemical shift range. In our approach, we propose a correlation of the analysis of soils based on functionality and quantification with results based on a special pyrolysis field ionization mass spectrometry optimized for soils to identify molecular mass distribution of soils. Furthermore, the presence of poly(methylene) groups that are present in both crystalline and amorphous morphologies, that can be clearly assigned by their chemical shifts, is interesting. Our heat treatment induces melting of the crystallites and depending on the cooling procedure (slow cooling in air or instant cooling in liquid nitrogen) changes the degree of crystallinity. The results on the NMR characterization show correlations with features observed from DSC measurements. Our studies were done on a series of different soils and peats with varying organic and water content. The overall goal is to identify certain features that are typical for soils which help to identify correlating results obtained from other characterization techniques and therefore improve the general understanding of soils.

Bertmer, Marko; Jaeger, Alexander; Schwarz, Jette; Schaumann, Gabriele

2010-05-01

278

Spectroscopic (FT-IR, FT-Raman, 1H, 13C NMR, UV/VIS), thermogravimetric and antimicrobial studies of Ca(II), Mn(II), Cu(II), Zn(II) and Cd(II) complexes of ferulic acid.  

PubMed

The molecular structure of Mn(II), Cu(II), Zn(II), Cd(II) and Ca(II) ferulates (4-hydroxy-3-methoxycinnamates) was studied. The selected metal ferulates were synthesized. Their composition was established by means of elementary and thermogravimetric analysis. The following spectroscopic methods were used: infrared (FT-IR), Raman (FT-Raman), nuclear magnetic resonance ((13)C, (1)H NMR) and ultraviolet-visible (UV/VIS). On the basis of obtained results the electronic charge distribution in studied metal complexes in comparison with ferulic acid molecule was discussed. The microbiological study of ferulic acid and ferulates toward Escherichia coli, Bacillus subtilis, Candida albicans, Pseudomonas aeruginosa, Staphylococcus aureus and Proteus vulgaris was done. PMID:24334064

Kalinowska, M; Piekut, J; Bruss, A; Follet, C; Sienkiewicz-Gromiuk, J; ?wis?ocka, R; Rz?czy?ska, Z; Lewandowski, W

2014-03-25

279

Organometallic derivatives of furan. LII. Synthesis of carbofunctional furylsilanes and their /sup 1/H, /sup 13/C, and /sup 29/Si NMR spectroscopic and quantum-chemical investigation  

SciTech Connect

Under the standard conditions for the synthesis of furan compounds it is possible to obtain the carbofunctional derivatives of silylated furfural with retention of the trimethylsilyl group in the ring. By NMR and CNDO/2 LCAO MO methods and also as a result of the investigation of the chemical characteristics of silylated furfural and its carbofunctional derivatives it was established that the introduction of a trimethylsilyl group at position 5 of the furan ring does not change the reactivity of the carbofunctional substituents at position 2. The electronic effects of the substituents are hardly transmitted through the furan ring at all. The effect of substituents in the carbofunctional furylsilanes on the electronic structure of the ring is additive.

Lukevits, E.; Erchak, N.P.; Castro, I.; Popelis, Yu.Yu.; Kozyrev, A.K.; Anoshkin, V.I.; Kovalev, I.F.

1986-03-10

280

Metabolic flux analysis of recombinant Pichia pastoris growing on different glycerol/methanol mixtures by iterative fitting of NMR-derived (13)C-labelling data from proteinogenic amino acids.  

PubMed

The yeast Pichia pastoris has emerged as one of the most promising yeast cell factories for the production of heterologous proteins. The readily available genetic tools and the ease of high-cell density cultivations using methanol or glycerol/methanol mixtures are among the key factors for this development. Previous studies have shown that the use of mixed feeds of glycerol and methanol seem to alleviate the metabolic burden derived from protein production, allowing for higher specific and volumetric process productivities. However, initial studies of glycerol/methanol co-metabolism in P. pastoris by classical metabolic flux analyses using (13)C-derived Metabolic Flux Ratio (METAFoR) constraints were hampered by the reduced labelling information obtained when using C3:C1 substrate mixtures in relation to the conventional C6 substrate, that is, glucose. In this study, carbon flux distributions through the central metabolic pathways in glycerol/methanol co-assimilation conditions have been further characterised using biosynthetically directed fractional (13)C labelling. In particular, metabolic flux distributions were obtained under 3 different glycerol/methanol ratios and growth rates by iterative fitting of NMR-derived (13)C-labelling data from proteinogenic amino acids using the software tool (13)CFlux2. Specifically, cells were grown aerobically in chemostat cultures fed with 80:20, 60:40 and 40:60 (w:w) glycerol/methanol mixtures at two dilutions rates (0.05 hour(-1) and 0.16 hour(-1)), allowing to obtain additional data (biomass composition and extracellular fluxes) to complement pre-existing datasets. The performed (13)C-MFA reveals a significant redistribution of carbon fluxes in the central carbon metabolism as a result of the shift in the dilution rate, while the ratio of carbon sources has a lower impact on carbon flux distribution in cells growing at the same dilution rate. At low growth rate, the percentage of methanol directly dissimilated to CO2 ranges between 50% and 70%. At high growth rate the methanol is completely dissimilated to CO2 by the direct pathway, in the two conditions of highest methanol content. PMID:23845285

Jordà, Joel; de Jesus, Sérgio S; Peltier, Solenne; Ferrer, Pau; Albiol, Joan

2014-01-25

281

Complete NMR spectral assignments of siloxanol based copolycarbonate including the configurational copolymer structure and the determination of each monomer conversion  

NASA Astrophysics Data System (ADS)

Siloxanol based copolycarbonate(SicoPC) of which the constitutional monomers are diphenyl carbonate, bisphenol A, and polydimethylsiloxanol(PDMS), was prepared by melt transesterification polymerization. The objective was to investigate the monomer conversion ratio for each monomer and the configurational structure of the SicoPC. A laboratory scale 5L reactor was used in the siloxanol preparation where the reactor jacket oil temperature was kept constant at 230 °C throughout the first and second polymerization phases. The reaction pressure was varied. For the first phase, the pressure was dropped from the atmospheric pressure 1000-200 mbar during the target reaction time of 30 min to remove the byproduct phenol. The second phase, the full vacuum pressure of was maintained for the second 30-min polymerization phase. An hour of reaction under such a condition gave a product of a highly viscous melt, of which the number average molecular weight read approximately 3000 g/mol. Complete NMR spectral assignments of the obtained melt (expected to be SicoPC) were made using both 1H and 13C, followed by 2D NMR spectroscopy. The measurements confirmed that the obtained melt was indeed the expected SicoPC; the conversion ratio of each monomer, BPA, DPC and PDMS were 100%, 99.5% and 86%, respectively. Furthermore, the HMBC (heteronuclear multiple quantum coherence) experiment confirmed the most important fact in determining the configurational structure of a SicoPC - all the PDMS monomers were located at the end chain of SicoPC.

Lim, Sung-Chul; Kim, Seong-Woo; Jung, Min-Hwan; Cho, Myo-kyung; Kim, Jong-Hoon; Cho, Hye-Sung; Ok, Jong-Hwa

2008-08-01

282

Spectroscopic (FT-IR, FT-Raman, UV absorption, 1H and 13C NMR) and theoretical (in B3LYP/6-311++G** level) studies on alkali metal salts of caffeic acid.  

PubMed

The effect of some metals on the electronic system of benzoic and nicotinic acids has recently been investigated by IR, Raman and UV spectroscopy [1-3]. Benzoic and nicotinic acids are regarded model systems representing a wide group of aromatic ligands which are incorporated into enzymes. In this work the FT-IR (in solid state and in solution), FT-Raman, UV absorption and (1)H and (13)C NMR spectra of caffeic acid (3,4-dihydroxycinnamic acid) and its salts with lithium, sodium, potassium, rubidium and caesium were registered, assigned and analyzed. The effect of alkali metals on the electronic system of ligands was discussed. Studies of differences in the number and position of bands from the IR, Raman, UV absorption spectra and chemical shifts from NMR spectra allowed to conclude on the distribution of electronic charge in the molecules, the delocalization energy of ? electrons and the reactivity of ligands in metal complexes. Optimized geometrical structures of studied compounds were calculated by B3LYP method using 6-311++G** basis set. Bond lengths, angles and dipole moments for the optimized structures of caffeic acid and lithium, sodium, potassium caffeinates were also calculated. The theoretical wavenumbers and intensities of IR spectra were obtained. The calculated parameters were compared to the experimental characteristics of investigated compounds. Microbial activity of studied compounds was tested against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Proteus vulgaris. PMID:22369898

?wis?ocka, Renata

2013-01-01

283

Tumbling motions of NH2(CH3)2 ions in [NH2(CH3)2]2ZnCl4 studied using 1H MAS NMR and 13C CP/MAS NMR  

NASA Astrophysics Data System (ADS)

The structure and the phase transition temperatures of [NH2(CH3)2]2ZnCl4 were determined using X-ray diffraction and DSC, respectively. The temperature dependence of chemical shifts and the spin-lattice relaxation time T1? in the rotating frame were measured for the 1H and 13C nuclei in [NH2(CH3)2]2ZnCl4. From these results, it was observed that the structural change by chemical shifts does not occur with temperature. However, T1? for 1H and 13C in [NH2(CH3)2]2ZnCl4 showed a minimum, and it is apparent that both T1? values are governed by the same tumbling motions. The activation energies of tumbling motions for 1H and 13C are nearly the same owing to the connection between CH3 and NH2 ions in the [NH2(CH3)2]+ group.

Kim, Nam Hee; Choi, Jae Hun; Lim, Ae Ran

2014-12-01

284

Complete analysis of the 1H and 13C NMR spectra of diastereomeric mixtures of (R,S- and S,S-)-3,6-dimethoxy-2,5-dihydropyrazine-substituted indoles and their conformational preference in solution.  

PubMed

Complete analysis of the (1)H and (13)C NMR spectra obtained with and without a chemical shift reagent (Eu(fod)(3)), of bis-lactim ether 1 (Schöllkopf auxiliary) and monosubstituted 3- or 2-{(2R,5S or 2S,5S)-5-isopropyl-3,6-dimethoxy-2,5-dihydropyrazin-2-yl]methyl}-1H-indoles is presented using gradient-selected one-dimensional (1D) and two-dimensional NMR techniques, such as 1D TOCSY, 1D NOESY (DPFGSE NOE), gCOSY, NOESY, ROESY gHETCOR, gHSQC and gHMBC. The contour plot of the gCOSY spectrum of 1-10 revealed cross peaks arising from the five-bond coupling between the H2 and H5 resonances of the dihydropyrazine ring for syn- ((5)J(H2, H5) = 4-5.7 Hz) and for anti-isomers ((5)J(H2, H5) = 3.4-3.8 Hz). The magnitude of the coupling constant was utilized to distinguish between the syn- and the anti-isomers (diastereomers). The precise values of (n)J(HH) (n = 3, 4, 5, 6) coupling constants for the indole and 2,5-dihydropyrazine moieties deduced from the calculated NMR spectra were supported by 1D TOCSY and gCOSY experiments and gauge invariant atomic orbital (GIAO) calculations. The magnitude of the coupling constants ((5)J(H2, H5)) indicates that the dihydropyrazine ring exists in a boat conformation. In both isomers, the indole group adopts a 'folded' conformation in which one diastereotopic face is effectively shielded by the aromatic benzene ring of the indole. This is supported by gradient-selected 1D NOESY and 2D NOESY experiments. Theoretical calculations of the conformation were performed to support the through-space shielding effect of the aromatic indole moiety based on the DFT/GIAO calculated (1)H NMR data (chemical shifts and coupling constants) for 2-syn- and 2-anti-diastereomers in CDCl(3). PMID:19998390

Akhmedov, Novruz G; Dacko, Christopher A; Güven, Alâattin; Söderberg, Björn C G

2010-02-01

285

Which prior knowledge? Quantification of in vivo brain 13C MR spectra following 13C glucose infusion using AMARES.  

PubMed

The recent developments in high magnetic field 13C magnetic resonance spectroscopy with improved localization and shimming techniques have led to important gains in sensitivity and spectral resolution of 13C in vivo spectra in the rodent brain, enabling the separation of several 13C isotopomers of glutamate and glutamine. In this context, the assumptions used in spectral quantification might have a significant impact on the determination of the 13C concentrations and the related metabolic fluxes. In this study, the time domain spectral quantification algorithm AMARES (advanced method for accurate, robust and efficient spectral fitting) was applied to 13 C magnetic resonance spectroscopy spectra acquired in the rat brain at 9.4 T, following infusion of [1,6-(13)C2 ] glucose. Using both Monte Carlo simulations and in vivo data, the goal of this work was: (1) to validate the quantification of in vivo 13C isotopomers using AMARES; (2) to assess the impact of the prior knowledge on the quantification of in vivo 13C isotopomers using AMARES; (3) to compare AMARES and LCModel (linear combination of model spectra) for the quantification of in vivo 13C spectra. AMARES led to accurate and reliable 13C spectral quantification similar to those obtained using LCModel, when the frequency shifts, J-coupling constants and phase patterns of the different 13C isotopomers were included as prior knowledge in the analysis. PMID:22886985

Lanz, Bernard; Duarte, João M N; Kunz, Nicolas; Mlynárik, Vladimir; Gruetter, Rolf; Cudalbu, Cristina

2013-06-01

286

1H, 13C NMR, FT-IR, ESI MS and PM5 studies of a new 3,6,9-trioxadecylamide of monensin A and its complexes with Li +, Na + and K + cations  

NASA Astrophysics Data System (ADS)

A new 3,6,9-trioxadecylamide of monensin A (M-AM4) has been synthesised and its ability to form complexes with Li +, Na + and K + cations has been studied by ESI mass spectrometry, 1H and 13C NMR, FT-IR spectroscopy and PM5 semiempirical method. The ESI MS data indicate that M-AM4 forms complexes with Li +, Na + and K + of exclusively 1:1 stoichiometry which are stable up to cv = 70 V. The formation of the M-AM4-Na + is strongly favoured. Above cv = 70 the fragmentation process is observed. The spectroscopic studies show that the structures of the M-AM4 and its complexes with the cations of 1:1 stoichiometry are stabilized by intramolecular hydrogen bonds in which the OH groups are always involved. The C dbnd O amide group is engaged in the complexation process of each cation. The M-AM4-K + complex can also assume a structure in which the C dbnd O amide group does not participate in the complexation but the complexes of such structure do not dominate.

?owicki, Daniel; Huczy?ski, Adam; Brzezinski, Bogumil; Bartl, Franz

2011-03-01

287

Comprehensive quantum chemical and spectroscopic (FTIR, FT-Raman, (1)H, (13)C NMR) investigations of (1,2-epoxyethyl)benzene and (1,2-epoxy-2-phenyl)propane.  

PubMed

Aromatic epoxides are causative factors for mutagenic and carcinogenic activity of polycyclic arenes. The 1,2- or 2,3-epoxy compounds are widely used to a considerable extent in the textile, plastics, pharmaceutical, cosmetics, detergent and photochemical industries. The FTIR and FT-Raman spectra of (1,2-epoxyethyl)benzene and (1,2-epoxy-2-phenyl)propane are recorded in the regions 4000-400 cm(-1) and 4000-100 cm(-1), respectively. The observed fundamentals are assigned to different normal modes of vibration. The structure of the compound has been optimised with B3LYP method using 6-311++G(**) and cc-pVTZ basis sets. The IR and Raman intensities are determined. The total electron density and molecular electrostatic potential surfaces of the molecule are constructed by using B3LYP/6-311++G(d,p) method to display electrostatic potential (electron+nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. Natural bond orbital analysis of the compounds has been performed to indicate the presence of intramolecular charge transfer. The (1)H and (13)C NMR chemical shifts of the molecules have been analysed. PMID:25062058

Arjunan, V; Anitha, R; Devi, L; Mohan, S; Yang, Haifeng

2015-01-25

288

Rotational spectral density functions for aqueous sucrose: experimental determination using ¹³C NMR  

Microsoft Academic Search

¹³C NMR spin-lattice relaxation times and nuclear Overhauser enhancements were measured as a function of concentration, temperature, and magnetic field strength for sucrose solutions in DâO. These data were used to determine the frequency dependence and amplitude of the rotational spectral density function, J(omega). The authors find that J(omega) has the same frequency dependence as the theoretical spectral density function

Douglas C. McCain; John L. Markley

1986-01-01

289

Three-Dimensional 13C- 13C-Correlated Experiments on Oligosaccharides  

NASA Astrophysics Data System (ADS)

The use of three-dimensional 1H-detected 13C- 13C-correlated experiments is demonstrated for the purpose of assigning all of the ring proton and carbon resonances from a digalactosyl diacylglyceride sample, uniformly 13C-enriched to 15% by microbiological methods. In addition to improving the previously published phase-cycled pulse sequences (Y. Q. Gosser, K. P. Howard, and J. H. Prestegard, J. Magn. Reson. Ser. B101, 126, 1993), we illustrate the efficacy of incorporating pulsed field gradients for coherence-pathway selection and solvent suppression. The gradient version of the experiment yields dramatic improvements in the overall resolution and suppression of artifacts, thus increasing the efficiency of the experiment to the point where applicability to NMR assignments of 13C-enriched oligosaccharides can become routine.

Chung, J.; Tolman, J. R.; Howard, K. P.; Prestegard, J. H.

290

1H, (13)C, and (15)N NMR stereochemical study of cis-fused 7a(8a)-methyl and 6-phenyl octa(hexa)hydrocyclopenta[d][1,3]oxazines and [3,1]benzoxazines.  

PubMed

Four 7a-methyl octa(or hexa)hydrocyclopenta[d][1,3]oxazines, five 8a-methyl octa(or hexa)hydro[3,1]benzoxazines, two 6-phenyl hexahydro[3,1]benzoxazinones, and 8a-methyl hexahydro[1,3]benzoxazinone, all cis-fused, were prepared and their stereostructures studied by various one- and two-dimensional (1)H, (13)C, and (15)N NMR spectroscopic methods. In solution, the cyclopentane-fused 2-oxo derivatives and the 1,3-benzoxazinone were found to attain exclusively the N-in/O-in conformation, whereas the 6-phenyl 2-oxo/thioxo derivatives were found to be present predominantly in the N-out conformation. The C-2 unsubstituted and the 2-oxo/thioxo 7a/8a-methyl derivatives were all present in solution as a rapidly interconverting equilibrium of the N-in and N-out conformations. The C-2 methyl derivatives were each found to be interconvertable mixtures of epimers (at C-2) with the N-in conformer predominating for one epimer and the N-out conformer predominating for the other, with both predominating conformers having the C-2 methyl group equatorially orientated. The substituent on the nitrogen (H or Me) was found to be always predominantly equatorial with respect to the heteroring, except for the epimeric 2-methyl derivatives with N-out conformations where steric constraints and the generalized anomeric effect resulted in the axial orientation of the C-2 methyl being favored. PMID:11835564

Tähtinen, Petri; Sinkkonen, Jari; Klika, Karel D; Nieminen, Ville; STájer, Géza; Szakonyi, Zsolt; FüLöp, Ferenc; Pihlaja, Kalevi

2002-01-01

291

Practical considerations over spectral quality in solid state NMR spectroscopy of soluble proteins.  

PubMed

Great theoretical and methodological advances are pushing the limits of resolution and sensitivity in solid state NMR (SSNMR). However, sample preparation remains a critical issue for the success of an experiment. The factors affecting spectral quality in SSNMR samples are discussed, examining cases encountered in the literature and presenting new experimental data. A discussion on resolution and sensitivity in sedimented solutes is framed in this context. PMID:23990200

Fragai, Marco; Luchinat, Claudio; Parigi, Giacomo; Ravera, Enrico

2013-10-01

292

Databases and Software for NMR-Based Metabolomics  

PubMed Central

New software and increasingly sophisticated NMR metabolite spectral databases are advancing the unique abilities of NMR spectroscopy to identify and quantify small molecules in solution for studies of metabolite biomarkers and metabolic flux. Public and commercial databases now contain experimental 1D 1H, 13C and 2D 1H-13C spectra and extracted spectral parameters for over a thousand compounds and theoretical data for thousands more. Public databases containing experimental NMR data from complex metabolic studies are emerging. These databases are providing information vital for the construction and testing of new computational algorithms for NMR-based chemometric and quantitative metabolomics studies. In this review we focus on database and software tools that support a quantitative NMR approach to the analysis of 1D and 2D NMR spectra of complex biological mixtures. PMID:24260723

Ellinger, James J.; Chylla, Roger A.; Ulrich, Eldon L.; Markley, John L.

2013-01-01

293

Distinguishing tautomerism in the crystal structure of (Z)-N-(5-ethyl-2,3-di-hydro-1,3,4-thia-diazol-2-yl-idene)-4-methyl-benzene-sulfonamide using DFT-D calculations and 13C solid-state NMR  

PubMed Central

The crystal structure of the title compound, C11H13N3O2S2, has been determined previously on the basis of refinement against laboratory powder X-ray diffraction (PXRD) data, supported by comparison of measured and calculated 13C solid-state NMR spectra [Hangan et al. (2010 ?). Acta Cryst. B66, 615–621]. The mol­ecule is tautomeric, and was reported as an amine tautomer [systematic name: N-(5-ethyl-1,3,4-thia­diazol-2-yl)-p-toluene­sulfonamide], rather than the correct imine tautomer. The protonation site on the mol­ecule’s 1,3,4-thia­diazole ring is indicated by the inter­molecular contacts in the crystal structure: N—H?O hydrogen bonds are established at the correct site, while the alternative protonation site does not establish any notable inter­molecular inter­actions. The two tautomers provide essentially identical Rietveld fits to laboratory PXRD data, and therefore they cannot be directly distinguished in this way. However, the correct tautomer can be distinguished from the incorrect one by previously reported qu­anti­tative criteria based on the extent of structural distortion on optimization of the crystal structure using dispersion-corrected density functional theory (DFT-D) calculations. Calculation of the 13C SS-NMR spectrum based on the correct imine tautomer also provides considerably better agreement with the measured 13C SS-NMR spectrum. PMID:25093360

Li, Xiaozhou; Bond, Andrew D.; Johansson, Kristoffer E.; Van de Streek, Jacco

2014-01-01

294

Following Suberization in Potato Wound Periderm by Histochemical and Solid-State 13C Nuclear Magnetic Resonance Methods.  

PubMed Central

The time course of suberization in wound periderm from potato (Solanum tuberosum L.) has been monitored by histochemical and high-resolution solid-state nuclear magnetic resonance (NMR) methods. Light microscopy conducted after selective staining of the lipid and double-bonded constituents shows that suberin is deposited at the outermost intact cell-wall surface during the first 7 d of wound healing; suberization forms a barrier to tissue infiltration at later times. Cross polarization-magic angle spinning 13C NMR spectra demonstrate the deposition of a polyester containing all major suberin functional groups after just 4 d of wound healing. Initially the suberin includes a large proportion of aromatic groups and fairly short aliphatic chains, but the spectral data demonstrate the growing dominance of long-chain species during the period 7 to 14 d after wounding. The results of preliminary 13C-labeling experiments with sodium [2-13C]acetate and DL-[1-13C]phenylalanine provide an excellent prospectus for future NMR-based studies of suberin biosynthesis. PMID:12232102

Stark, R. E.; Sohn, W.; Pacchiano Jr, R. A.; Al-Bashir, M.; Garbow, J. R.

1994-01-01

295

Getting Your Peaks in Line: A Review of Alignment Methods for NMR Spectral Data  

PubMed Central

One of the most significant challenges in the comparative analysis of Nuclear Magnetic Resonance (NMR) metabolome profiles is the occurrence of shifts between peaks across different spectra, for example caused by fluctuations in pH, temperature, instrument factors and ion content. Proper alignment of spectral peaks is therefore often a crucial preprocessing step prior to downstream quantitative analysis. Various alignment methods have been developed specifically for this purpose. Other methods were originally developed to align other data types (GC, LC, SELDI-MS, etc.), but can also be applied to NMR data. This review discusses the available methods, as well as related problems such as reference determination or the evaluation of alignment quality. We present a generic alignment framework that allows for comparison and classification of different alignment approaches according to their algorithmic principles, and we discuss their performance. PMID:24957991

Vu, Trung Nghia; Laukens, Kris

2013-01-01

296

13C NMR, 10428944 231 1H NMR, 10428944 231  

E-print Network

· 182 Access, 11892899 · 63 Acetylcholine, 10054774 · 229 acid-base homeostasis, 11961086 · 84 Acoustic neuroma, 10032929 · 48 10422603 · 174 Actin, 11434290 · 150 Actin Cytoskeleton Regulation, 10182580 · 68

297

Effect of 13C enrichment in the glassing matrix on dynamic nuclear polarization of [1-13C]pyruvate  

PubMed Central

Dimethyl sulfoxide (DMSO) can effectively form a glassy matrix necessary for dynamic nuclear polarization (DNP) experiments. We tested the effects of 13C enrichment in DMSO on DNP of [1-13C]pyruvate doped with trityl radical OX063Me. We found that the polarization build-up time ? of pyruvate in 13C-labelled DMSO glassing solution is twice as fast as the unenriched DMSO while the NMR enhancement was unchanged. This indicates that 13C-13C spin diffusion is a limiting factor in the kinetics of dynamic nuclear polarization in this system, but it has a minimal effect on the absolute value of polarization achievable for the target. PMID:21285486

Lumata, Lloyd; Kovacs, Zoltan; Malloy, Craig; Sherry, A. Dean; Merritt, Matthew

2011-01-01

298

Peak picking NMR spectral data using non-negative matrix factorization  

PubMed Central

Background Simple peak-picking algorithms, such as those based on lineshape fitting, perform well when peaks are completely resolved in multidimensional NMR spectra, but often produce wrong intensities and frequencies for overlapping peak clusters. For example, NOESY-type spectra have considerable overlaps leading to significant peak-picking intensity errors, which can result in erroneous structural restraints. Precise frequencies are critical for unambiguous resonance assignments. Results To alleviate this problem, a more sophisticated peaks decomposition algorithm, based on non-negative matrix factorization (NMF), was developed. We produce peak shapes from Fourier-transformed NMR spectra. Apart from its main goal of deriving components from spectra and producing peak lists automatically, the NMF approach can also be applied if the positions of some peaks are known a priori, e.g. from consistently referenced spectral dimensions of other experiments. Conclusions Application of the NMF algorithm to a three-dimensional peak list of the 23 kDa bi-domain section of the RcsD protein (RcsD-ABL-HPt, residues 688-890) as well as to synthetic HSQC data shows that peaks can be picked accurately also in spectral regions with strong overlap. PMID:24511909

2014-01-01

299

Studies of Hindered Rotation and Magnetic Anisotropy by 1H, 13C and 19F NMR. The Diels-Alder Adduct of N- Pentafluorophenylmaleimide and Phencyclone: A Model for Drugs  

Microsoft Academic Search

The potent Diels-Alder diene, phencyclone, 1, reacts with N-pentafluorophenylmaleimide, 2, to form an adduct, 3, characterized by H, C, and F NMR at 300, 75 and 282 MHz, respectively. The one-dimensional (1D) and two-dimensional (2D) H and C NMR spectra of 3 at ambient temperatures imply a slow exchange limit (SEL) regime with respect to rotation of the unsubstituted bridgehead

Mohsena F. Amin; Kevin Bynum; Ronald Callahan; Ron Prip; Robert Rothchild

1998-01-01

300

13C6-[Benzene Ring]-Indole-3-Acetic Acid  

PubMed Central

Indole-3-acetic acid (IAA) labeled with 13C in the six carbons of the benzene ring is described for use as an internal standard for quantitative mass spectral analysis of IAA by gas chromatography/selected ion monitoring. [13C6]IAA was compared to the available deuterium labeled compounds and shown to offer the advantages of nonexchangeability of the isotope label, high isotopic enrichment, and chromatographic properties identical to that of the unlabeled compound. The utility of [13C6]IAA for measurement of endogenous IAA levels was demonstrated by analysis of IAA in Lemna gibba G-3. PMID:16664570

Cohen, Jerry D.; Baldi, Bruce G.; Slovin, Janet Pernise

1986-01-01

301

Quantitative NMR-derived interproton distances combined with quantum mechanical calculations of 13C chemical shifts in the stereochemical determination of conicasterol F, a nuclear receptor ligand from Theonella swinhoei.  

PubMed

Here we report the first application of combined accurate ROE-distance analysis with DFT calculations of NMR chemical shifts to achieve the relative configuration assignment of a marine natural product, conicasterol F, a new polyhydroxylated steroid isolated from the marine sponge Theonella swinhoei. We demonstrate the substantial advantages of this combined approach as a tool for structural studies of natural products, providing a powerful alternative to, or information to underpin, total synthesis when more classical NMR data analysis fails to provide unequivocal results. In this paper, we also describe the isolation and structure elucidation of conicasterol F and its 24-ethyl derivative, theonellasterol I, and their pharmacological evaluation as human nuclear receptor modulators. PMID:22201476

Chini, Maria Giovanna; Jones, Catharine R; Zampella, Angela; D'Auria, Maria Valeria; Renga, Barbara; Fiorucci, Stefano; Butts, Craig P; Bifulco, Giuseppe

2012-02-01

302

Characterisation of 4- deoxy-?- l-threo- hex-4- enopyranosyluronic acid attached to xylan in pine kraft pulp and pulping liquor by 1H and 13C NMR spectroscopy  

Microsoft Academic Search

A new acidic sidegroup in xylans, from both kraft pulp and pulping liquor, was identified by NMR spectroscopy. Unmodified oligosaccharides from kraft pulp xylan were obtained by enzymatic hydrolysis with xylanase (Trichoderma reesei). The acidic oligosaccharides were separated from the neutral forms on an anion exchange resin. The new acidic sidegroup was identified as 4-deoxy-?-l-threo-hex-4-enopyranosyluronic acid (hexenuronic acid) by 1H

Anita Teleman; Vesa Harjunpää; Maija Tenkanen; Johanna Buchert; Tiina Hausalo; Torbjörn Drakenberg; Tapani Vuorinen

1995-01-01

303

Multiparametric optimization of (31)P NMR spectroscopic analysis of phospholipids in crude tissue extracts. 2. Line width and spectral resolution.  

PubMed

The quality of NMR spectra in general and of spectra to be used for analysis of compound mixtures in particular is essentially defined by two basic parameters: signal-to-noise ratio and spectral resolution. The latter is determined by signal dispersion (chemical shift differences) and line widths. The present study focuses on multiparametric optimization of spectral resolution in (31)P NMR spectra of phospholipids from brain tissue extracts. This report presents, for the first time, a systematic and comprehensive study of phospholipid (31)P NMR line widths as a function of four experimental parameters: (i) extract concentration, (ii) concentration of a chelating agent, (iii) pH of the aqueous component of the solvent system, and (iv) temperature of the NMR measurement. Theoretical underpinnings of observed line width variations (transversal relaxation effects) are briefly discussed. In conjunction with an analogous, concurrently published report on chemical shift effects in the same tissue extract system, this multiparametric line width study provides a complete set of methodological guidelines for (i) generating well-defined tissue extracts, and (ii) choosing matched and optimized measurement conditions for highly reproducible and well-resolved (31)P NMR spectra of brain phospholipids. This study also offers a comprehensive database and a strategy for rational and efficient optimization of phospholipid spectra from other tissue extracts. PMID:20443551

Lutz, Norbert W; Cozzone, Patrick J

2010-07-01

304

NMR crystallography: The effect of deuteration on high resolution 13 state NMR spectra of a 7-TM protein  

E-print Network

on the 13 C linewidths of U-13 C, 15 N 2D crystalline bacteriorhodopsin (bR) from Halobacterium salinariumNMR crystallography: The effect of deuteration on high resolution 13 C solid state NMR spectra, and indirect, 9­17 ppm, dimensions). The measured 13 C NMR line-widths observed for both protonated

Watts, Anthony

305

Study of the conformational equilibria of some 2-(2?-hydroxyphenyl)-4-aryl-3 H -1,5-benzodiazepines using 1 H, 13 C, and 15 N NMR spectroscopy  

Microsoft Academic Search

Variable temperature1H NMR experiments of 2-(2'-hydroxyphenyl)-4-phenyl-3H-1,5-benzodiazepine (5a) and its derivatives5d and5e were carried out in order to investigate the conformational behaviour of these compounds. The ?G* values for the ring inversion barriers of5a and5d areca. 52 kJ\\/mol,i.e. they do not differ significantly as compared to analogous compounds without phenolic OH group(s). This indicates that the hydrogen bond has not to

R. Ahmad; M. Zia-ul-Haq; H. Duddeck; L. Stefaniak; J. Sitkowski

1997-01-01

306

High-resolution NMR spectroscopy of tricyclic non-alternant systems containing seven-membered rings—II. 1H and 13C solvent and lanthanide-shift-reagent studies of 5-keto- and 5-hydroxy-substituted 5H-dibenzo[ a, d]cycloheptene  

NASA Astrophysics Data System (ADS)

220 MHz 1H NMR spectra of 5H-dibenzo[ a, d]cyclohepten-5-one (I) in carbon disulphide and in deuteriated chloroform solution and of 5H-dibenzo[ a, d]cyclohepten-5-ol (II) in deuteriated chloroform at temperatures 223-323 K have been analysed by the LAOCOON III program; at low concentrations, two peaks emerge for each of H(5) and O H in II. Concentration and temperature dependences of 1H shifts indicate intermolecular association in II and, together with changes in 13C shifts with addition of Eu(fod) 3, suggest a structural inversion in I. Shift-reagent 1H studies reveal contributions from two orientations of Eu to I in the Eu(fod) 3-I complex but of predominantly one in the corresponding complex with II. 1H? 1H ortho-coupling constants, spread more widely in I than II, are compared with values in related compounds.

Drake, J. A. G.; Jones, D. W.

307

NMR Spectral Quantitation by Principal-Component Analysis. II. Determination of Frequency and Phase Shifts  

NASA Astrophysics Data System (ADS)

This paper extends the use of principal-component analysis in spectral quantification to the estimation of frequency and phase shifts in a single resonant peak across a series of spectra. The estimated parameters can be used to correct the spectra accordingly, resulting in more accurate peak-area estimation. Further, the removal of the variations in phase and frequency caused by instrumental and experimental fluctuations makes it possible to determine more accurately the remaining variations, which bear biological significance. The procedure is demonstrated on simulated data, a 3D chemical-shift-imaging dataset acquired from a cylinder of inorganic phosphate (P i), and a set of 736 31P NMR in vivospectra taken from a kinetic study of rat muscle energetics. In all cases, the procedure rapidly and automatically identifies the frequency and phase shifts present in the individual spectra. In the kinetic study, the procedure is used twice, first to adjust the phase and frequency of a reference peak (phosphocreatine) and then to determine the individual frequencies of the P ipeak in each of the spectra which further can be used for estimation of pH changes during the experiment.

Brown, Truman R.; Stoyanova, Radka

308

Local Motions in Glassy Poly(alkyl methacrylate)s (PRMAs) and Motional Heterogeneities in Siloxane/Poly(ethylene glycol) Nanocomposites (Ormolytes) Studied by 13C Solid-State Exchange NMR  

NASA Astrophysics Data System (ADS)

Solid-state exchange NMR techniques, including the recently introduced Pure-Exchange (PUREX) and Centerband-Only Detection of Exchange (CODEX) methods, provide detailed information about both cooperative and local slow dynamics (0.1/s to 3000/s) in organic materials. Using these techniques backbone dynamics and the geometry of side-group motions responsible for the beta relaxation of PRMAs are analyzed in greater details than in our previous CODEX studies. In ormolytes, motional heterogeneities associated with siloxane/PEG interactions are directly observed. It is found that the hindrance to the slow motions of the polymer chains by the siloxane structures depends on the chain length and the nature of the interaction between the organic and inorganic phases.

Deazevedo, E. R.; Becker-Guedes, F.; Vidoto, E. L. G.; Reichert, D.; Dahmouche, K.; Judeinstein, P.; Schmidt-Rohr, K.; Bonagamba, T. J.

2002-03-01

309

Site-specific 13C content by quantitative isotopic 13C nuclear magnetic resonance spectrometry: a pilot inter-laboratory study.  

PubMed

Isotopic (13)C NMR spectrometry, which is able to measure intra-molecular (13)C composition, is of emerging demand because of the new information provided by the (13)C site-specific content of a given molecule. A systematic evaluation of instrumental behaviour is of importance to envisage isotopic (13)C NMR as a routine tool. This paper describes the first collaborative study of intra-molecular (13)C composition by NMR. The main goals of the ring test were to establish intra- and inter-variability of the spectrometer response. Eight instruments with different configuration were retained for the exercise on the basis of a qualification test. Reproducibility at the natural abundance of isotopic (13)C NMR was then assessed on vanillin from three different origins associated with specific ? (13)Ci profiles. The standard deviation was, on average, between 0.9 and 1.2‰ for intra-variability. The highest standard deviation for inter-variability was 2.1‰. This is significantly higher than the internal precision but could be considered good in respect of a first ring test on a new analytical method. The standard deviation of ? (13)Ci in vanillin was not homogeneous over the eight carbons, with no trend either for the carbon position or for the configuration of the spectrometer. However, since the repeatability for each instrument was satisfactory, correction factors for each carbon in vanillin could be calculated to harmonize the results. PMID:23845488

Chaintreau, Alain; Fieber, Wolfgang; Sommer, Horst; Gilbert, Alexis; Yamada, Keita; Yoshida, Naohiro; Pagelot, Alain; Moskau, Detlef; Moreno, Aitor; Schleucher, Jürgen; Reniero, Fabiano; Holland, Margaret; Guillou, Claude; Silvestre, Virginie; Akoka, Serge; Remaud, Gérald S

2013-07-25

310

Spectral analysis, vibrational assignments, NBO analysis, NMR, UV-Vis, hyperpolarizability analysis of 2-aminofluorene by density functional theory.  

PubMed

In this present investigation, the collective experimental and theoretical study on molecular structure, vibrational analysis and NBO analysis has been reported for 2-aminofluorene. FT-IR spectrum was recorded in the range 4000-400 cm(-1). FT-Raman spectrum was recorded in the range 4000-50 cm(-1). The molecular geometry, vibrational spectra, and natural bond orbital analysis (NBO) were calculated for 2-aminofluorene using Density Functional Theory (DFT) based on B3LYP/6-31G(d,p) model chemistry. (13)C and (1)H NMR chemical shifts of 2-aminofluorene were calculated using GIAO method. The computed vibrational and NMR spectra were compared with the experimental results. The total energy distribution (TED) was derived to deepen the understanding of different modes of vibrations contributed by respective wavenumber. The experimental UV-Vis spectra was recorded in the region of 400-200 nm and correlated with simulated spectra by suitably solvated B3LYP/6-31G(d,p) model. The HOMO-LUMO energies were measured with time dependent DFT approach. The nonlinearity of the title compound was confirmed by hyperpolarizabilty examination. Using theoretical calculation Molecular Electrostatic Potential (MEP) was investigated. PMID:24556129

Jone Pradeepa, S; Sundaraganesan, N

2014-05-01

311

Spectral analysis, vibrational assignments, NBO analysis, NMR, UV-Vis, hyperpolarizability analysis of 2-aminofluorene by Density Functional Theory  

NASA Astrophysics Data System (ADS)

In this present investigation, the collective experimental and theoretical study on molecular structure, vibrational analysis and NBO analysis has been reported for 2-aminofluorene. FT-IR spectrum was recorded in the range 4000-400 cm-1. FT-Raman spectrum was recorded in the range 4000-50 cm-1. The molecular geometry, vibrational spectra, and natural bond orbital analysis (NBO) were calculated for 2-aminofluorene using Density Functional Theory (DFT) based on B3LYP/6-31G(d,p) model chemistry. 13C and 1H NMR chemical shifts of 2-aminofluorene were calculated using GIAO method. The computed vibrational and NMR spectra were compared with the experimental results. The total energy distribution (TED) was derived to deepen the understanding of different modes of vibrations contributed by respective wavenumber. The experimental UV-Vis spectra was recorded in the region of 400-200 nm and correlated with simulated spectra by suitably solvated B3LYP/6-31G(d,p) model. The HOMO-LUMO energies were measured with time dependent DFT approach. The nonlinearity of the title compound was confirmed by hyperpolarizabilty examination. Using theoretical calculation Molecular Electrostatic Potential (MEP) was investigated.

Jone Pradeepa, S.; Sundaraganesan, N.

312

In vivo detection of intermediary metabolic products of [1-13C]ethanol in the brain using 13C magnetic resonance spectroscopy  

PubMed Central

In the present study, in vivo 13C magnetic resonance spectroscopy (MRS) was used to study the labeling of brain metabolites after intravenous administration of [1-13C]ethanol. After [1-13C]ethanol was systemically administrated to the rats, 13C labels were detected in glutamate, glutamine and aspartate in the carboxylic and amide carbon spectral region. 13C-labeled bicarbonate HCO3? (161.0 ppm) was also detected. Saturating acetaldehyde C1 at 207.0 ppm was found to have no effect on the ethanol C1 (57.7 ppm) signal intensity after extensive signal averaging, providing direct in vivo evidence that direct metabolism of alcohol by brain tissue is minimal. To compare the labeling of brain metabolites by ethanol with labeling by glucose, in vivo time course data were acquired during intravenous co-infusion of [1-13C]ethanol and [13C6]-D-glucose. In contrast to labeling by [13C6]-D-glucose which produced doublets of carboxylic/amide carbons with a J coupling constant of 51 Hz, the simultaneously detected glutamate and glutamine singlets are labeled by [1-13C]ethanol. Since 13C labels originated from ethanol enter brain after being converted into [1-13C]acetate in liver and the direct metabolism of ethanol by brain tissue is negligible, it is suggested that orally or intragastrically administered 13C-labeled ethanol may be used to study brain metabolism and glutamatergic neurotransmission in studies involving alcohol administration. In vivo 13C MRS of rat brain following intragastric administration of 13C-labeled ethanol is demonstrated. PMID:21312308

Xiang, Yun; Shen, Jun

2012-01-01

313

GIAO DFT 13C/15N chemical shifts in regioisomeric structure determination of fused pyrazoles.  

PubMed

The combined use of two-dimensional NMR correlation experiments and gauge including atomic orbital density functional theory in (13)C NMR chemical shift (CS) calculations allowed reliable and simple structural determination of regioisomeric heterocyclic systems that originate from the reactions of acylquinolinones with substituted hydrazines. Moreover, the results of differential analysis between the calculated (15)N NMR CSs for hypothetical structures and the experimental data of the title azaheterocyclic systems were even more advantageous with respect to (13)C because there was no need for correlational analysis: structures of the regioisomeric compounds could be determined just by direct comparison. PMID:20589725

Chimichi, Stefano; Boccalini, Marco; Matteucci, Alessandra; Kharlamov, Sergey V; Latypov, Shamil K; Sinyashin, Oleg G

2010-08-01

314

Rapid solid-state NMR of deuterated proteins by interleaved cross-polarization from ¹H and ²H nuclei.  

PubMed

We present a novel sampling strategy, interleaving acquisition of multiple NMR spectra by exploiting initial polarization subsequently from (1)H and (2)H spins, taking advantage of their different T(1) relaxation times. Different (1)H- and (2)H-polarization based spectra are in this way simultaneously recorded improving either information content or sensitivity by adding spectra. The so-called Relaxation-optimized Acquisition of Proton Interleaved with Deuterium (RAPID) (1)H?(13)C/(2)H?(13)C CP/MAS multiple-acquisition method is demonstrated by 1D and 2D experiments using a uniformly (2)H, (15)N,(13)C-labeled ?-spectrin SH3 domain sample with all or 30% back-exchanged labile (2)H to (1)H. It is demonstrated how 1D (13)C CP/MAS or 2D (13)C-(13)C correlation spectra initialized with polarization from either (1)H or (2)H may be recorded simultaneously with flexibility to be added or used individually for spectral editing. It is also shown how 2D (13)C-(13)C correlation spectra may be recorded interleaved with (2)H-(13)C correlation spectra to obtain (13)C-(13)C correlations along with information about dynamics from (2)H sideband patterns. PMID:22130517

Bjerring, Morten; Paaske, Berit; Oschkinat, Hartmut; Akbey, Umit; Nielsen, Niels Chr

2012-01-01

315

Conditions to obtain precise and true measurements of the intramolecular 13C distribution in organic molecules by isotopic 13C nuclear magnetic resonance spectrometry.  

PubMed

Intramolecular (13)C composition gives access to new information on the (bio) synthetic history of a given molecule. Isotopic (13)C NMR spectrometry provides a general tool for measuring the position-specific (13)C content. As an emerging technique, some aspects of its performance are not yet fully delineated. This paper reports on (i) the conditions required to obtain satisfactory trueness and precision for the determination of the internal (13)C distribution, and (ii) an approach to determining the "absolute" position-specific (13)C content. In relation to (i), a precision of <1% can be obtained whatever the molecule on any spectrometer, once quantitative conditions are met, in particular appropriate proton decoupling efficiency. This performance is a prerequisite to the measurement of isotope fractionation either on the transformed or residual compound when a chemical reaction or process is being studied. The study of the trueness has revealed that the response of the spectrometer depends on the (13)C frequency range of the studied molecule, i.e. the chemical shift range. The "absolute value" and, therefore, the trueness of the (13)C NMR measurements has been assessed on acetic acid and by comparison to the results obtained on the fragments from COOH and CH3 by isotopic mass spectrometry coupled to a pyrolysis device (GC-Py-irm-MS), this technique being the reference method for acetic acid. Of the two NMR spectrometers used in this work, one gave values that corresponded to those obtained by GC-Py-irm-MS (thus, the "true" value) while the other showed a bias, which was dependent to the range covered by the resonance frequencies of the molecule. Therefore, the former can be used directly for studying isotope affiliations, while the latter can only be used directly for comparative data, for example in authenticity studies, but can also be used to obtain the true values by applying appropriate correction factors. The present study assesses several key protocol steps required to enable the determination of position-specific (13)C content by isotopic (13)C NMR, irrespective of the NMR spectrometer: parameters to be adjusted, performance test using [1,2-(13)C2]acetic acid, generation of correction factors. PMID:25220137

Bayle, Kevin; Gilbert, Alexis; Julien, Maxime; Yamada, Keita; Silvestre, Virginie; Robins, Richard J; Akoka, Serge; Yoshida, Naohiro; Remaud, Gérald S

2014-10-10

316

13C-13C NOESY: an attractive alternative for studying large macromolecules.  

PubMed

13C direct detection provides a valuable alternative to 1H detection to overcome fast relaxation because of its smaller magnetic moment. 13C-13C NOESY spectra were acquired for a dimeric protein of molecular mass 32 000 and for a monomeric analogue. With increasing molecular mass, the quality of 13C-13C NOESY spectra improves while the scalar-based experiments become less sensitive, as predicted by the increase in the molecular mass. 13C-13C NOESY spectra of the dimer were acquired with different mixing times. The mixing time can be tuned to detect mainly one-bond correlations, or it can be increased to also detect correlations between nuclei at longer distances. It is proposed that 13C-13C dipolar-based experiments provide a promising tool for signal detection and assignment in large macromolecules, such as multimeric species and macromolecular complexes, for which scalar-based experiments become less effective. PMID:14719933

Bertini, Ivano; Felli, Isabella C; Kümmerle, Rainer; Moskau, Detlef; Pierattelli, Roberta

2004-01-21

317

Deuterium isotope shifts for backbone 1H, 15N and 13C nuclei in intrinsically disordered protein -synuclein  

PubMed Central

Intrinsically disordered proteins (IDPs) are abundant in nature and characterization of their potential structural propensities remains a widely pursued but challenging task. Analysis of NMR secondary chemical shifts plays an important role in such studies, but the output of such analyses depends on the accuracy of reference random coil chemical shifts. Although uniform perdeuteration of IDPs can dramatically increase spectral resolution, a feature particularly important for the poorly dispersed IDP spectra, the impact of deuterium isotope shifts on random coil values has not yet been fully characterized. Very precise 2H isotope shift measurements for 13C?, 13C?, 13C’, 15N, and 1HN have been obtained by using a mixed sample of protonated and uniformly perdeuterated -synuclein, a protein with chemical shifts exceptionally close to random coil values. Decomposition of these isotope shifts into one-bond, two-bond and three-bond effects as well as intra- and sequential residue contributions shows that such an analysis, which ignores conformational dependence, is meaningful but does not fully describe the total isotope shift to within the precision of the measurements. Random coil 2H isotope shifts provide an important starting point for analysis of such shifts in structural terms in folded proteins, where they are known to depend strongly on local geometry. PMID:22960996

Maltsev, Alexander S.; Ying, Jinfa; Bax, Ad

2012-01-01

318

LAMPF polarized sup 13 C targets  

SciTech Connect

Ethylene glycol, 1-butanol, and toluene highly enriched in {sup 13}C have been used at LAMPF to produce dynamically polarized {sup 13}C targets for scattering experiments with protons and pions. Preparation of the materials and characteristic properties of these targets are described. 17 refs., 1 fig.

Penttilae, S.; Jarmer, J.J.; Tanaka, N. (Los Alamos National Lab., NM (USA)); Bartlett, M.L.; Johnson, K.; Hoffmann, G.W.; Kielhorn, W.; Purcell, M. (Texas Univ., Austin, TX (USA)); Burleson, G.; Klein, A.; Kyle, G. (New Mexico State Univ., Las Cruces, NM (USA)); Brinkmoeller, B.; Dehnhard, D.; Yen, Yi-Fen (Minnesota Univ., Minneapolis, MN (USA)); Comfort, J.R.; Goergen, J.J. (Arizona State Univ., Tempe, AZ

1990-01-01

319

sup 13 C NMR investigation of crosslinking in organic aerogels  

SciTech Connect

Organic aerogels are a special type of low density foam produced from the supercritical drying of resorcinol-formaldehyde (RF) gels. These aerogels have continuous porosity, ultrafine cell/pore sizes (<1000 {angstrom}), and a microstructure composed of interconnected colloidal-like particles with diameters ranging from 30-175 {angstrom}. The particle size, surface area, density, and mechanical properties of the aerogels are largely determined by the catalysts concentration used in the sol-gel polymerization. In order to gain some insight into the crosslinks between RF particles, aerogels were labeled with C-13 formaldehyde at various times in the polymerization. CPMAS and IRCP techniques were used to correlate the relaxation behavior of the C-13 enriched aerogels with their different microstructures. 9 refs., 1 fig., 2 tabs.

Ward, R. L.; Pekala, R. W.

1989-09-15

320

New guidelines for ??13C measurements  

USGS Publications Warehouse

Consistency of ??13C measurements can be improved 39-47% by anchoring the ??13C scale with two isotopic reference materials differing substantially in 13C/12C. It is recommended that ??13C values of both organic and inorganic materials be measured and expressed relative to VPDB (Vienna Peedee belemnite) on a scale normalized by assigning consensus values of -46.6??? to L-SVEC lithium carbonate and +1.95??? to NBS 19 calcium carbonate. Uncertainties of other reference material values on this scale are improved by factors up to two or more, and the values of some have been notably shifted: the ?? 13C of NBS 22 oil is -30.03???. ?? 2006 American Chemical Society.

Coplen, T. B.; Brand, W. A.; Gehre, M.; Groning, M.; Meijer, H. A. J.; Toman, B.; Verkouteren, R. M.

2006-01-01

321

The 13C nuclear magnetic resonance in graphite intercalation compounds  

NASA Technical Reports Server (NTRS)

The (13)C NMR chemical shifts of graphite intercalation compounds were calculated. For acceptor types, the shifts come mainly from the paramagnetic (Ramsey) intra-atomic terms. They are related to the gross features of the two-dimensional band structures. The calculated anisotropy is about -140 ppm and is independent of the finer details such as charge transfer. For donor types, the carbon 2p pi orbitals are spin-polarized because of mixing with metal conduction electrons, thus there is an additional dipolar contribution which may be correlated with the electronic specific heat. The general agreement with experimental data is satisfactory.

Tsang, T.; Resing, H. A.

1985-01-01

322

Improving the quality of 2D solid-state NMR spectra of microcrystalline proteins by covariance analysisw  

E-print Network

Improving the quality of 2D solid-state NMR spectra of microcrystalline proteins by covariance transformation (2D FT). Since a high spectral resolution is mandatory in both dimensions of 13 C­13 C correlation is obtained from the prescription C = (FT ÁF)1/2 , where F is the matrix of the 2D FT spectrum, FT

323

Application of Metabolic 13C Labeling in Conjunction with High-Field Nuclear Magnetic Resonance Spectroscopy for Comparative Conformational Analysis of High Mannose-Type Oligosaccharides  

PubMed Central

High mannose-type oligosaccharides are enzymatically trimmed in the endoplasmic reticulum, resulting in various processing intermediates with exposed glycotopes that are recognized by a series of lectins involved in glycoprotein fate determination in cells. Although recent crystallographic data have provided the structural basis for the carbohydrate recognition of intracellular lectins, atomic information of dynamic oligosaccharide conformations is essential for a quantitative understanding of the energetics of carbohydrate–lectin interactions. Carbohydrate NMR spectroscopy is useful for characterizing such conformational dynamics, but often hampered by poor spectral resolution and lack of recombinant techniques required to produce homogeneous glycoforms. To overcome these difficulties, we have recently developed a methodology for the preparation of a homogeneous high mannose-type oligosaccharide with 13C labeling using a genetically engineered yeast strain. We herein successfully extended this method to result in the overexpression of 13C-labeled Man9GlcNAc2 (M9) with a newly engineered yeast strain with the deletion of four genes involved in N-glycan processing. This enabled high-field NMR analyses of 13C-labeled M9 in comparison with its processing product lacking the terminal mannose residue ManD2. Long-range NOE data indicated that the outer branches interact with the core in both glycoforms, and such foldback conformations are enhanced upon the removal of ManD2. The observed conformational variabilities might be significantly associated with lectins and glycan-trimming enzymes. PMID:24970159

Kamiya, Yukiko; Yanagi, Kotaro; Kitajima, Toshihiko; Yamaguchi, Takumi; Chiba, Yasunori; Kato, Koichi

2013-01-01

324

sup 1 H NMR studies of human lysozyme: Spectral assignment and comparison with hen lysozyme  

SciTech Connect

Complete main-chain (NH and {alpha}CH){sup 1}H NMR assignments are reported for the 130 residues of human lysozyme, along with extensive assignments for side-chain protons. Analysis of 2-D NOESY experiments shows that the regions of secondary structure for human lysozyme in solution are essentially identical with those found previously in a similar study of hen lysozyme and are in close accord with the structure of the protein reported previously from x-ray diffraction studies in the crystalline state. Comparison of the chemical shifts, spin-spin coupling constants, and hydrogen exchange behavior are also consistent with closely similar structures for the two proteins in solution. In a number of cases specific differences in the NMR parameters between hen and human lysozymes can be correlated with specific differences observed in the crystal structures.

Redfield, C.; Dobson, C.M. (Univ. of Oxford (England))

1990-08-07

325

A fixation mode of gold from solutions using heterogeneous reaction of cadmium dicyclohexyl dithiophosphate with H[AuCl4]. Structural and (13C, 31P) CP/MAS NMR studies and thermal behaviour of crystalline polymeric gold(I) dicyclohexyl dithiophosphate and bis(dicyclohexylthiophosphoryl) disulphide  

NASA Astrophysics Data System (ADS)

Two novel compounds: polynuclear catena-poly[bis(?3-O,O'-di-cyclo-hexyldithiophosphato-S,S,S')digold(I)] (Ausbnd Au) (1) and crystalline bis(O,O'-di-cyclo-hexylthiophosphoryl)disulphide, (cyclo-C6H11O)2P(S)Ssbnd S(S)P(O-cyclo-C6H11)2 (2) were prepared using heterogeneous reaction between freshly precipitated binuclear cadmium(II) dithiophosphate (Dtph), [Cd2{S2P(O-cyclo-C6H11}4] and H[AuCl4] in 2 M hydrochloric acid. The isolated compounds 1 and 2 (the fixation mode of gold from the solution and the oxidised form of Dtph groups, respectively) have been studied by means of single-crystal X-ray diffraction, 13C and 31P cross-polarisation/magic-angle-spinning (CP/MAS) NMR spectroscopy and simultaneous thermal analysis (STA). Centrosymmetric binuclear molecule of 1, [Au2{S2P(O-cyclo-C6H11)2}2] comprises a pair of ?-bridging di-cyclo-hexyl Dtph ligands, linking two neighbouring gold atoms, and displays additional intramolecular aurophilic bond Au⋯Au. At the supramolecular level of structural self-organisation of complex 1, infinite polymeric zigzag chains arise due to pairs of the secondary bonds Au···S between neighbouring binuclear molecules. Centrosymmetric molecule of 2 displays two O,O'-di-cyclo-hexythiophosphoryl fragments, which are connected by the chemical bond S(1)sbnd S(1)a, and a planar zigzag array [Sdbnd Psbnd Ssbnd Ssbnd Pdbnd S] passing through the central part of the molecule. To characterise additionally the Dtph groups in both compounds 1 and 2, chemical shift anisotropy (CSA) parameters (?aniso and ?) were calculated from spinning sideband manifolds in experimental 31P MAS NMR spectra. The thermal behaviour of complex 1 was studied using simultaneous thermal analysis (a combination of TG and DSC) under an argon atmosphere. The thermal behaviour displays stepwise mass loss, comprising thermal decompositions of the organic and inorganic parts of 1 with gold(I) dithio-meta-phosphate and reduced metallic gold as the intermediate and the final products, respectively.

Ivanov, Alexander V.; Korneeva, Eugenia V.; Lutsenko, Irina A.; Gerasimenko, Andrey V.; Antzutkin, Oleg N.; Larsson, Anna-Carin; Sergienko, Valentin I.

2013-02-01

326

Synthesis of single- and double-13C-labeled cholesterol oleate.  

PubMed

Cholesterol oleate with the 13C-label in oleic acid at the carbonyl and/or in the sterol ring at position 4 was synthesized by two methods: (1) cholesterol was condensed with oleic anhydride, prepared from [1-13C] oleic acid, in the presence of dimethylaminopyridine (DMAP) in anhydrous chloroform at room temperature for 4--5 h; (2) cholesterol or 13C-enriched cholesterol at position 4 were reacted with 90% [1-13C]-oleic acid in the presence of dicyclohexylcarbodiimide (DCC) and DMAP at room temperature in anhydrous chloroform for 1.25 h. The single-13C and double-13C-labeled cholesterol oleate were obtained in 90% yields after purification by silicic acid column chromatography. Their purity was assessed by thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC) and 13C-NMR spectroscopy. Tritium-labeled cholesterol oleate was also synthesized by method 1 using the fatty acid anhydride. PMID:3208413

Sripada, P K

1988-09-01

327

Synthesis Of [2h, 13c] And [2h3, 13c]Methyl Aryl Sulfides  

DOEpatents

The present invention is directed to labeled compounds, [.sup.2 H.sub.1, .sup.13 C], [.sup.2 H.sub.2, .sup.13 C] and [.sup.2 H.sub.3, .sup.13 C]methyl aryl sulfides wherein the .sup.13 C methyl group attached to the sulfur of the sulfide includes exactly one, two or three deuterium atoms and the aryl group is selected from the group consisting of 1-naphthyl, substituted 1-naphthyl, 2-naphthyl, substituted 2-naphthyl, and phenyl groups with the structure ##STR1## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, and R.sub.5 are each independently, hydrogen, a C.sub.1 -C.sub.4 lower alkyl, a halogen, an amino group from the group consisting of NH.sub.2, NHR and NRR' where R and R' are each a C.sub.1 -C.sub.4 lower alkyl, a phenyl, or an alkoxy group. The present invention is also directed to processes of preparing [.sup.2 H.sub.1, .sup.13 C], [.sup.2 H.sub.2,.sup.13 C] and [.sup.2 H.sub.3, .sup.13 C]methyl aryl sulfides wherein the .sup.13 C methyl group attached to the sulfur of the sulfide includes exactly one, two or three deuterium atoms. The present invention is also directed to the labeled compounds of [.sup.2 H.sub.1, .sup.13 C]methyl iodide and [.sup.2 H.sub.2, .sup.13 C]methyl iodide.

Martinez, Rodolfo A. (Santa Fe, NM); Alvarez, Marc A. (Santa Fe, NM); Silks, III, Louis A. (Los Alamos, NM); Unkefer, Clifford J. (Los Alamos, NM)

2004-03-30

328

Comparison of 13C?H and 15NH backbone dynamics in protein GB1  

PubMed Central

This study presents a site-resolved experimental view of backbone C?H and NH internal motions in the 56-residue immunoglobulin-binding domain of streptococcal protein G, GB1. Using 13C?H and 15NH NMR relaxation data [T1, T2, and NOE] acquired at three resonance frequencies (1H frequencies of 500, 600, and 800 MHz), spectral density functions were calculated as F(?) = 2?J(?) to provide a model-independent way to visualize and analyze internal motional correlation time distributions for backbone groups in GB1. Line broadening in F(?) curves indicates the presence of nanosecond time scale internal motions (0.8 to 5 nsec) for all C?H and NH groups. Deconvolution of F(?) curves effectively separates overall tumbling and internal motional correlation time distributions to yield more accurate order parameters than determined by using standard model free approaches. Compared to NH groups, C?H internal motions are more broadly distributed on the nanosecond time scale, and larger C?H order parameters are related to correlated bond rotations for C?H fluctuations. Motional parameters for NH groups are more structurally correlated, with NH order parameters, for example, being larger for residues in more structured regions of ?-sheet and helix and generally smaller for residues in the loop and turns. This is most likely related to the observation that NH order parameters are correlated to hydrogen bonding. This study contributes to the general understanding of protein dynamics and exemplifies an alternative and easier way to analyze NMR relaxation data. PMID:12717014

Idiyatullin, Djaudat; Nesmelova, Irina; Daragan, Vladimir A.; Mayo, Kevin H.

2003-01-01

329

SEAL by NMR: Glyco-Based Selenium-Labeled Affinity Ligands Detected by NMR Spectroscopy.  

PubMed

We report a method for the screening of interactions between proteins and selenium-labeled carbohydrate ligands. SEAL by NMR is demonstrated with selenoglycosides binding to lectins where the selenium nucleus serves as an NMR-active handle and reports on binding through (77) Se NMR spectroscopy. In terms of overall sensitivity, this nucleus is comparable to (13) C?NMR, while the NMR spectral width is ten times larger, yielding little overlap in (77) Se NMR spectroscopy, even for similar compounds. The studied ligands are singly selenated bioisosteres of methyl glycosides for which straightforward preparation methods are at hand and libraries can readily be generated. The strength of the approach lies in its simplicity, sensitivity to binding events, the tolerance to additives and the possibility of having several ligands in the assay. This study extends the increasing potential of selenium in structure biology and medicinal chemistry. We anticipate that SEAL by NMR will be a beneficial tool for the development of selenium-based bioactive compounds, such as glycomimetic drug candidates. PMID:25196366

Hamark, Christoffer; Landström, Jens; Widmalm, Göran

2014-10-20

330

Interaction of anisole with 3?-hydroxy-5?-cholan-24-oic acid macrolides. Part 1. Comparative 1H NMR spectral investigation  

NASA Astrophysics Data System (ADS)

1H NMR spectral investigation on the interaction of anisole (methoxybenzene) with five different (varying by ring size and substitution) cyclic 3?-hydroxy-5?-cholan-24-oic acid macrolides were performed. For 3?-hydroxy-5?-cholan-24-oic acid (lithocholic acid) macrolides (from triolide to pentolide) no effect was observed. In contrast, for 7?-trifluoroacetyloxy (7?-TFA) substituted lithocholate triolide obtained from chenodeoxycholic acid and for 12?-trifluoroacetyloxy (12?-TFA) substituted lithocholate triolide obtained from deoxycholic acid, clear site specific effects were observed. In the case of the 7?-TFA derivative, the aromatic guest causes the strongest up-field shift on the angular methyl 19 at the A/B ring junction of the steroid unit, and in 12?-TFA isomer the strongest effect is directed at the angular methyl 18 located at the C/D ring junction of the steroid skeleton. These findings are discussed in terms of steric factors and the size and flexibility of the cavity of the host molecule. Molecular mechanics is used in modeling the structures of three triolides.

Lappalainen, Kari V.; Kolehmainen, Erkki T.; Šaman, David

1995-08-01

331

NMR spectral mapping of Lipid A molecular patterns affected by interaction with the innate immune receptor CD14  

SciTech Connect

Soluble CD14 (sCD14) is a serum glycoprotein that binds to the Lipid A moiety of lipopolysaccharides (LPS) with high affinity as part of the innate immune response to bacterial endotoxins. In order to investigate structural interactions of Lipid A with sCD14, we have prepared an isotopically labeled form of a fully active and chemically defined endotoxin, Kdo{sub 2}-Lipid A, which allowed us to carry out detailed NMR spectral mapping of this agonist ligand bound to sCD14 and identify for the first time structural regions that are strongly affected during complex formation with sCD14. These map to two adjacent areas comprising the lower portions of the sugar headgroup and upper half of the acyl chains I, III, and V, which are spatially proximal to the 1- and 4'-phosphate ends. Additionally, we have detected for the first time, presence of differential dynamic behavior for the affected resonances, suggesting a likely role for dynamics in the mechanism of Lipid A pattern recognition by sCD14.

Albright, Seth; Agrawal, Prashansa [Biochemistry, Cellular and Molecular Biology Department, University of Tennessee, M407 Walters Life Sciences, Knoxville, TN 37996-0840 (United States); Jain, Nitin U. [Biochemistry, Cellular and Molecular Biology Department, University of Tennessee, M407 Walters Life Sciences, Knoxville, TN 37996-0840 (United States)], E-mail: njain@utk.edu

2009-01-23

332

Dereplication of depsides from the lichen Pseudevernia furfuracea by centrifugal partition chromatography combined to 13C nuclear magnetic resonance pattern recognition.  

PubMed

Lichens produce a diversity of secondary metabolites, among them depsides comprised of two or more hydroxybenzoic acid units linked by ester, ether, or CC-bonds. During classic solid support-based purification processes, depsides are often hydrolyzed and in many cases time, consuming procedures result only in the isolation of decomposition products. In an attempt to avoid extensive purification steps while maintaining metabolite structure integrity, we propose an alternative method to identify the major depsides of a lichen crude extract (Pseudevernia furfuracea var. ceratea (Ach.) D. Hawksw., Parmeliaceae) directly within mixtures. Exploiting the acidic character of depsides and differences in polarity, the extract was fractionated by centrifugal partition chromatography in the pH-zone refining mode resulting in twelve simplified mixtures of depsides. After (13)C nuclear magnetic resonance analysis of the produced fractions, the major molecular structures were directly identified within the fraction series by using a recently developed pattern recognition method, which combines spectral data alignment and hierarchical clustering analysis. The obtained clusters of (13)C chemical shifts were assigned to their corresponding molecular structures with the help of an in-house (13)C NMR chemical shift database, resulting in six unambiguously identified compounds, namely methyl ?-orcinolcarboxylate (1), atranorin (2), 5-chloroatranorin (3), olivetol carboxylic acid (4), olivetoric acid (5), and olivetonide (6). PMID:25220142

Oettl, Sarah K; Hubert, Jane; Nuzillard, Jean-Marc; Stuppner, Hermann; Renault, Jean-Hugues; Rollinger, Judith M

2014-10-10

333

Rapid proton-detected NMR assignment for proteins with fast magic angle spinning.  

PubMed

Using a set of six (1)H-detected triple-resonance NMR experiments, we establish a method for sequence-specific backbone resonance assignment of magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of 5-30 kDa proteins. The approach relies on perdeuteration, amide (2)H/(1)H exchange, high magnetic fields, and high-spinning frequencies (?r/2? ? 60 kHz) and yields high-quality NMR data, enabling the use of automated analysis. The method is validated with five examples of proteins in different condensed states, including two microcrystalline proteins, a sedimented virus capsid, and two membrane-embedded systems. In comparison to contemporary (13)C/(15)N-based methods, this approach facilitates and accelerates the MAS NMR assignment process, shortening the spectral acquisition times and enabling the use of unsupervised state-of-the-art computational data analysis protocols originally developed for solution NMR. PMID:25102442

Barbet-Massin, Emeline; Pell, Andrew J; Retel, Joren S; Andreas, Loren B; Jaudzems, Kristaps; Franks, W Trent; Nieuwkoop, Andrew J; Hiller, Matthias; Higman, Victoria; Guerry, Paul; Bertarello, Andrea; Knight, Michael J; Felletti, Michele; Le Marchand, Tanguy; Kotelovica, Svetlana; Akopjana, Inara; Tars, Kaspars; Stoppini, Monica; Bellotti, Vittorio; Bolognesi, Martino; Ricagno, Stefano; Chou, James J; Griffin, Robert G; Oschkinat, Hartmut; Lesage, Anne; Emsley, Lyndon; Herrmann, Torsten; Pintacuda, Guido

2014-09-01

334

Incorporation of [1- 13C]1-deoxy- d-xylulose into isoprenoids of the liverwort Conocephalum conicum  

Microsoft Academic Search

The incorporation of 13C labeled 1-deoxy-d-xylulose into the monoterpene bornyl acetate, the sesquiterpene cubebanol, and the diterpene phytol has been studied in axenic cultures of the liverwort Conocephalum conicum. Quantitative 13C NMR spectroscopic analysis of the labeling patterns of the sesquiterpene indicated a possible degradation of 1-deoxy-d-xylulose to acetate and subsequent incorporation via the mevalonic acid pathway. In bornyl acetate,

Rolf Thiel; Klaus Peter Adam

2002-01-01

335

NMR of a Phospholipid: Modules for Advanced Laboratory Courses  

NASA Astrophysics Data System (ADS)

A laboratory project is described that builds upon the NMR experience undergraduates receive in organic chemistry with a battery of NMR experiments that investigate egg phosphatidylcholine (egg PC). This material, often labeled in health food stores as lecithin, is a major constituent of mammalian cell membranes. The NMR experiments may be used to make resonance assignments, to study molecular organization in model membranes, to test the effects of instrumental parameters, and to investigate the physics of nuclear spin systems. A suite of modular NMR exercises is described, so that the instructor may tailor the laboratory sessions to biochemistry, instrumental analysis, or physical chemistry. The experiments include solution-state one-dimensional (1D) 1H, 13C, and 31P experiments; two-dimensional (2D) TOtal Correlated SpectroscopY (TOCSY); and the spectral editing technique of Distortionless Enhancement by Polarization Transfer (DEPT). To demonstrate the differences between solution and solid-state NMR spectroscopy and instrumentation, a second set of experiments generates 1H, 13C, and 31P spectra of egg PC dispersed in aqueous solution, under both static and magic-angle spinning conditions.

Gaede, Holly C.; Stark, Ruth E.

2001-09-01

336

Application of 13C Nuclear Magnetic Resonance To Elucidate the Unexpected Biosynthesis of Erythritol by Leuconostoc oenos  

PubMed Central

Natural-abundance 13C nuclear magnetic resonance (13C-NMR) revealed the production of erythritol and glycerol by nongrowing cells of Leuconostoc oenos metabolizing glucose. The ratio of erythritol to glycerol was strongly influenced by the aeration conditions of the medium. The elucidation of the metabolic pathway responsible for erythritol production was achieved by 13C-NMR and 1H-NMR spectroscopy using specifically 13C-labelled d-glucose. The 1H-NMR spectrum of the cell supernatant resulting from the metabolism of [2-13C]glucose showed that only 75% of the glucose supplied was metabolized heterofermentatively and that the remaining 25% was channelled to the production of erythritol. The synthesis of this polyol resulted from the reduction of the C-4 moiety of the intermediate fructose 6-phosphate. Oxygen has an inhibitory effect on the production of erythritol by L. oenos. Preaeration of a suspension of nongrowing cells of L. oenos resulted in 30% less erythritol and in 70% more glycerol formed during the anaerobic metabolism of glucose. The anaerobic production of erythritol from glucose was also found in growing cultures of L. oenos, although to a smaller extent. PMID:16348738

Veiga-Da-Cunha, Maria; Firme, Paula; Romao, M. Vitoria San; Santos, Helena

1992-01-01

337

Multi-Spectroscopic Analysis of Seed Quality and 13C-Stable-Iotopologue Monitoring in Initial Growth Metabolism of Jatropha curcas L.  

PubMed

In the present study, we applied nuclear magnetic resonance (NMR), as well as near-infrared (NIR) spectroscopy, to Jatropha curcas to fulfill two objectives: (1) to qualitatively examine the seeds stored at different conditions, and (2) to monitor the metabolism of J. curcas during its initial growth stage under stable-isotope-labeling condition (until 15 days after seeding). NIR spectra could non-invasively distinguish differences in storage conditions. NMR metabolic analysis of water-soluble metabolites identified sucrose and raffinose family oligosaccharides as positive markers and gluconic acid as a negative marker of seed germination. Isotopic labeling patteren of metabolites in germinated seedlings cultured in agar-plate containg 13C-glucose and 15N-nitrate was analyzed by zero-quantum-filtered-total correlation spectroscopy (ZQF-TOCSY) and 13C-detected 1H-13C heteronuclear correlation spectroscopy (HETCOR). 13C-detected HETOCR with 13C-optimized cryogenic probe provided high-resolution 13C-NMR spectra of each metabolite in molecular crowd. The 13C-13C/12C bondmer estimated from 1H-13C HETCOR spectra indicated that glutamine and arginine were the major organic compounds for nitrogen and carbon transfer from roots to leaves. PMID:25401292

Komatsu, Takanori; Ohishi, Risa; Shino, Amiu; Akashi, Kinya; Kikuchi, Jun

2014-01-01

338

1H, 13C and 15N resonance assignments of URNdesign, a computationally redesigned RRM protein  

SciTech Connect

Protein design represents one of the great challenges of computational structural biology. The ability to successfully design new proteins would allow us to generate new reagents and enzymes, while at the same time providing us with an understanding of the principles of protein stability. Here we report 1H, 15N and 13C resonance assignments of a redesigned U1A protein, URNdesign. U1A has been studied extensively by our group and hence was chosen as a design target. For the assignments we sued 2D and 3D heteronuclearNMR experiments with uniformly 13C, 15N-labeled URNdesign. The assignments for the backbone NH, CO,Ca and Cb nuclei are 94%complete. Sidechain 1Hand13C, aromatic andQ/NNH2 resonances are essentially complete with guanidinium and K NH3 residues unassigned. BMRB deposit with accession number 6493

Dobson, Neil; Dantas, Gautam; Varani, Gabriele

2005-10-01

339

Synthesis, spectral and single crystal X-ray diffraction studies of novel O-(Carboalkoxy)methyl oxime ethers of 3-alkyl and 3,5-dialkyl-1-methyl-2,6-diphenylpiperidin-4-ones  

NASA Astrophysics Data System (ADS)

A series of novel O-(Carboalkoxy)methyl oxime ether derivatives of 3-alkyl and 3,5-dialkyl-1-methyl-2,6-diphenylpiperidin-4-ones were synthesized and characterized through FT-IR, Mass, 1H NMR, 13C NMR, 1Hsbnd 1H COSY, 1Hsbnd 13C COSY and NOESY spectral techniques. The stereocontrolled formation of E-isomer exclusively in all the cases was confirmed by NMR spectral analysis. A1,3 strain induced epimerization of C5 carbon in the case of compounds 18 and 23 was also observed. The preferred conformation of compounds 16, 17, 20, 21, 22 and 25 was found to be chair and for compounds 19 &24 it was boat while compounds 18 and 23 adopt a twist boat conformation as observed by 1H NMR and NOESY spectra. The solid state geometry of compound 16 was established by single crystal X-ray diffraction analysis.

Velayutham Pillai, M.; Rajeswari, K.; Vidhyasagar, T.

2014-11-01

340

SDBS: Integrated Spectral Data Base System for Organic Compounds  

NSDL National Science Digital Library

Provided by Agency of Industrial Science and Technology of Japan, the Integrated Spectral Data Base System for Organic Compounds is a database of mass spectral, NMR (proton and carbon), and infrared spectra data. As of March 1999, the database contains 19,600 spectra of MS, 11,000 spectra of ^13 C NMR, 13,500 spectra of ^1 H NMR, 2,000 spectra of ESR, 47,500 spectra of IR, 3,500 spectra of Raman, and 30,000 compounds in the Compound Dictionary. A search engine (Frames) for the database allows the following fields to be specified: Compound Name, Molecular Formula, Number of Atoms (Carbon, Hydrogen, Oxygen, and Nitrogen), Molecular Weight, CAS Registry Number, and SDBS Number. Access is free; however, no more than 50 spectra and/or compound files may be downloaded in one day.

341

Synthesis of 2H- and 13C-substituted dithanes  

DOEpatents

The present invention is directed to labeled compounds, [2-.sup.13 C]dithiane wherein the .sup.13 C atom is directly bonded to one or two deuterium atoms. The present invention is also directed to processes of preparing [2-.sup.13 C]dithiane wherein the .sup.13 C atom is directly bonded to one or two deuterium atoms. The present invention is also directed to labeled compounds, e.g., [.sup.2 H.sub.1-2, .sup.13 C]methanol (arylthio)-, acetates wherein the .sup.13 C atom is directly bonded to exactly one or two deuterium atoms.

Martinez, Rodolfo A. (Santa Fe, NM); Alvarez, Marc A. (Santa Fe, NM); Silks, III, Louis A. (Los Alamos, NM); Unkefer, Clifford J. (Los Alamos, NM)

2003-01-01

342

Synthesis Of 2h- And 13c-Substituted Dithanes  

DOEpatents

The present invention is directed to labeled compounds, [2-.sup.13 C]dithane wherein the .sup.13 C atom is directly bonded to one or two deuterium atoms. The present invention is also directed to processes of preparing [2-.sup.13 C]dithane wherein the .sup.13 C atom is directly bonded to one or two deuterium atoms. The present invention is also directed to labeled compounds, e.g., [.sup.2 H.sub.1-2, .sup.13 C]methanol (arylthio)-, acetates wherein the .sup.13 C atom is directly bonded to exactly one or two deuterium atoms.

Martinez, Rodolfo A. (Santa Fe, NM); Alvarez, Marc A. (Santa Fe, NM); Silks, III, Louis A. (Los Alamos, NM); Unkefer, Clifford J. (Los Alamos, NM)

2004-05-04

343

Chemistry and biochemistry of 13C hyperpolarized magnetic resonance using dynamic nuclear polarization.  

PubMed

The study of transient chemical phenomena by conventional NMR has proved elusive, particularly for non-(1)H nuclei. For (13)C, hyperpolarization using the dynamic nuclear polarization (DNP) technique has emerged as a powerful means to improve SNR. The recent development of rapid dissolution DNP methods has facilitated previously impossible in vitro and in vivo study of small molecules. This review presents the basics of the DNP technique, identification of appropriate DNP substrates, and approaches to increase hyperpolarized signal lifetimes. Also addressed are the biochemical events to which DNP-NMR has been applied, with descriptions of several probes that have met with in vivo success. PMID:24363044

Keshari, Kayvan R; Wilson, David M

2014-03-01

344

Syntheses, spectral characterization, single crystal X-ray diffraction and DFT computational studies of novel thiazole derivatives  

NASA Astrophysics Data System (ADS)

A novel thiazole (E)-1-((E)-2-methyl-3-phenylallylidene)-2-(4-phenylthiazole-2-yl)hydrazine 2 and its derivatives 3-8 were synthesized by cyclo condensation of (1E)-1-((E)-2-methyl-3-phenylallylidene)thiosemicarbazide 1 with substituted 2-bromoacetophenones. The synthesized thiazole derivatives were characterized by FT-IR, 1H NMR and 13C NMR analyses. For compound 8 single crystals X-ray diffraction analysis and density functional theory (DFT) calculation were carried out. The compound 8 crystallizes in the monoclinic space group P21/c with a = 7.4601 (3) Å, b = 5.7259 (2) Å, c = 41.0823 (13) Å, ? = 90°, ? = 91.715 (2)° and ? = 90°. The molecular geometrical parameters, frontier molecular orbital energies (HOMO, LUMO), their energy gap (?E), molecular electrostatic potential (MEP) and natural bond orbital (NBO) analysis of the compounds 2 and8 have been calculated by using DFT/B3LYP with 6-311G (d, p) level. In addition, IR frequencies, 1H and 13C NMR chemical shifts of compound 8 were also calculated by using DFT calculations at the same level basis set. The calculated geometrical parameters, IR frequencies, 1H and 13C NMR chemical shifts of the compound 8 were in good agreement with the observed single crystal-XRD data, IR, 1H and 13C NMR spectral values.

Anbazhagan, R.; Sankaran, K. R.

2013-10-01

345

2D NMR Metabonomic Analysis: A Novel Method for Automated Peak Alignment  

E-print Network

Motivation: Comparative metabolic profiling by nuclear magnetic resonance (NMR) is showing increasing promise for identifying interindividual differences to drug response. Two dimensional (2D) 1 H- 13 C NMR can reduce spectral overlap, a common problem of 1D 1 H NMR. However, the peak alignment tools for 1D NMR spectra are not well suited for 2D NMR. An automated and statistically robust method for aligning 2D NMR peaks is required to enable comparative metabonomic analysis using 2D NMR. Results: A novel statistical method was developed to align NMR peaks that represent the same chemical groups across multiple 2D NMR spectra. The degree of local pattern match among peaks in different spectra is assessed using a similarity measure, and a heuristic algorithm maximizes the similarity measure for peaks across the whole spectrum. This peak alignment method was used to align peaks in 2D NMR spectra of endogenous metabolites in liver extracts obtained from four inbred mouse strains in the study of acetaminophen-induced liver toxicity. This automated alignment method was validated by manual examination of the top fifty peaks as ranked by signal intensity. Manual inspection of 1872 peaks in 39 different spectra demonstrated that the automated algorithm correctly aligned 1810 (96.7%) peaks. Availability: Algorithm is available upon request. Contact:

Ming Zheng; Peng Lu; Yanzhou Liu; Joseph Pease; Jonathan Usuka; Guochun Liao; Prof John Quackenbush

346

The 13C isotope and nuclear magnetic resonance: unique tools for the study of brain metabolism.  

PubMed

As studies of brain metabolism grow in complexity, investigators turn increasingly to nuclear magnetic resonance spectroscopy combined with 13C isotopic labeling. The unique ability to detect labeling non-destructively in specific carbon positions of individual compounds has opened the way to investigate brain metabolism in systems ranging from cellular preparations to the human brain in vivo. This review is written for investigators whose backgrounds do not include detailed knowledge of principles of nuclear magnetic resonance. Its purpose is to show the wide array of NMR techniques for 13C detection that are available for application in different systems to study aspects of brain metabolism, such as metabolic compartmentation and measurements of the tricarboxylic acid cycle rate in vivo. Basic NMR concepts are explained, and, because each detection method possesses specific advantages to address the requirements of different experimental goals, basic explanations and examples are given for each technique. The review should provide readers with a basic understanding of the methods of 13C detection by NMR and assess which of the methods are most applicable to the particular issues they may face in their own research. PMID:8979250

Mason, G F; Behar, K L; Lai, J C

1996-12-01

347

Simultaneous Measurement of Neuronal and Glial Metabolism in Rat Brain In Vivo Using Co-infusion of [1,6-13C2]glucose and [1,2-13C2]acetate  

PubMed Central

In this work the feasibility of measuring neuronal-glial metabolism in rat brain in vivo using co-infusion of [1,6-13C2]glucose and [1,2-13C2]acetate was investigated. Time courses of 13C spectra were measured in vivo while infusing both 13C-labeled substrates simultaneously. Individual 13C isotopomers (singlets and multiplets observed in 13C spectra) were quantified automatically using LCModel. The distinct 13C spectral pattern observed in glutamate and glutamine directly reflected the fact that glucose was metabolized primarily in the neuronal compartment and acetate in the glial compartment. Time courses of concentration of singly and multiply-labeled isotopomers of glutamate and glutamine were obtained with a temporal resolution of 11 min. Although dynamic metabolic modeling of these 13C isotopomer data will require further work and is not reported here, we expect that these new data will allow more precise determination of metabolic rates as is currently possible when using either glucose or acetate as the sole 13C-labeled substrate. PMID:19027334

Deelchand, Dinesh K.; Nelson, Christopher; Shestov, Alexander A.; Ugurbil, Kamil; Henry, Pierre-Gilles

2009-01-01

348

Towards hyperpolarized 13C-succinate imaging of brain cancer  

Microsoft Academic Search

We describe a novel 13C enriched precursor molecule, sodium 1-13C acetylenedicarboxylate, which after hydrogenation by PASADENA (Parahydrogen and Synthesis Allows Dramatically Enhanced Nuclear Alignment) under controlled experimental conditions, becomes hyperpolarized 13C sodium succinate. Fast in vivo 3D FIESTA MR imaging demonstrated that, following carotid arterial injection, the hyperpolarized 13C-succinate appeared in the head and cerebral circulation of normal and tumor-bearing

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

2007-01-01

349

Chemical structural studies of natural lignin by dipolar dephasing solid-state 13C nuclear magnetic resonance  

USGS Publications Warehouse

Two natural lignins, one from a gymnosperm wood the other from angiosperm wood, were examined by conventional solid-state and dipolar dephasing 13C nuclear magnetic resonance (NMR) techniques. The results obtained from both techniques show that the structure of natural lignins is consistent with models of softwood and hardwood lignin. The dipolar dephasing NMR data provide a measure of the degree of substitution on aromatic rings which is consistent with the models. ?? 1987.

Hatcher, P.G.

1987-01-01

350

Limitations & challenges for understanding of ?13C variation in soil  

NASA Astrophysics Data System (ADS)

Natural variation of ?13C (?13C natural abundance) in soil is frequently used for understanding of various processes, mainly: i) the equilibrium between the formation, stabilization and decomposition of soil organic matter (SOM) pools, ii) effects of environmental conditions on SOM, and iii) trends in the ?13C as a result of long-term effects. However, various factors affect simultaneously ?13C value of SOM pools and of CO2 and consequently limit application of the ?13C natural abundance approach. Frequently these factors affect ?13C in opposite directions, and may compensate each other. Additionally, unexplained spatial and/or temporal variation of ?13C within different scales makes the interpretation of data extremely difficult. Therefore, I aimed this overview on i) evaluation of the ranges of spatial and temporal variation of ?13C values in soil, ii) distinguishing between 13C fractionation and preferential substrate utilization, and iii) separation of variations from trends. Literature data and own results allowed to conclude that the spatial variation of ?13C of SOM within one agricultural field usually is more than 2‰. The CO2 in soil and CO2 flux from soil have spatial variation similar to that of SOM (~2‰), but temporal variation ?13C in CO2 is at least two times higher. This is connected with admixture of atmospheric CO2 depending on soil and air moisture and on contribution of CO2 from various soil depths. Within one meter soil depth the ?13C has an increasing trend of about 3‰ with variation up to ±2‰. Suess effect (1955) strongly depleted the ?13C of all SOM pools (especially in the upper soil horizons) up to -1.5‰ and this trend will be stronger and faster in the future. It is very difficult to separate two processes affecting ?13C of SOM pools: 13C fractionation and preferential substrate utilization. The ?13C fractionation means favored involvement in processes of the chemically identical substances but with light isotopes (here 12C). The preferential substrate utilization is caused by preferable utilization of chemically different substrates within a substrate mixture (e.g. plant residues components) having different ?13C values. To clarify this, typical ?13C differences between SOM, microbial biomass, dissolved organic C and CO2 were analyzed. Changes of ?13C values of CO2 during incubation studies were caused by sequential utilization of substrates with different ?13C values. Finally, an overview of various processes leading to the directed changes (trends) and to unexplained variations were compared.

Kuzyakov, Yakov

2013-04-01

351

Measurement of 13C-15N Distances in Uniformly 13C Labeled Biomolecules: J-Decoupled REDOR  

E-print Network

of the 13C spectrum that removes the coherent evolution of the spin system under homonuclear 13 C-13 C J distance), and the Euler angles and relate the principal axis system of the interaction to the rotor is refocused by rapid spinning (r/2 10 kHz) for integer multiples of the rotor period. For a coupled three

Griffin, Robert G.

352

Synthesis of aromatic (13)C/(2)H-?-ketoacid precursors to be used in selective phenylalanine and tyrosine protein labelling.  

PubMed

Recent progress in protein NMR spectroscopy revealed aromatic residues to be valuable information sources for performing structure and motion analysis of high molecular weight proteins. However, the applied NMR experiments require tailored isotope labelling patterns in order to regulate spin-relaxation pathways and optimize magnetization transfer. We introduced a methodology to use ?-ketoacids as metabolic amino acid precursors in cell-based overexpression of phenylalanine and/or tyrosine labelled proteins in a recent publication, which we have now developed further by providing synthetic routes to access the corresponding side-chain labelled precursors. The target compounds allow for selective introduction of (13)C-(1)H spin systems in a highly deuterated chemical environment and feature alternating (12)C-(13)C-(12)C ring-patterns. The resulting isotope distribution is especially suited to render straightforward (13)C spin relaxation experiments possible, which provide insight into the dynamic properties of the corresponding labelled proteins. PMID:25136818

Lichtenecker, R J

2014-10-14

353

Comparison of /sup 13/C nuclear magnetic resonance and /sup 14/C tracer studies of hepatic metabolism. [Rats and mice  

SciTech Connect

The gluconeogenic pathway from /sup 13/C-labeled substrates, each of which contained the /sup 14/C-labeled counterpart at a tracer level, has been followed in isolated rat liver cells and in isolated perfused mouse liver. The gluconeogenic flux from glycerol, the synthesis of glycogen, the synthesis of glycogen, the stimulation of glycogenolysis by glucagon, the recycling of triacylglycerol, and an increase in pentose cycle activity under the influence of phenazine methosulfate were all observed directly in the /sup 13/C NMR spectra of perfused liver or isolated hepatocytes. The relative concentrations of /sup 13/C label at specific carbons measured by the NMR spectra under these conditions agreed closely with /sup 14/C isotopic distributions measured in extracts of the same doubly labeled samples for specific activities of greater than or equal to 3%. The label distributions measured by both methods were the same to within the experimental errors, which ranged from +-2% to +-7% in these experiments.

Cohen, S.M. (Merck Inst. for Therapeutic Research, Rathway, NJ); Rognstad, R.; Shulman, R.G.; Katz, J.

1981-04-10

354

Novel methods based on (13)C detection to study intrinsically disordered proteins.  

PubMed

Intrinsically disordered proteins (IDPs) are characterized by highly flexible solvent exposed backbones and can sample many different conformations. These properties confer them functional advantages, complementary to those of folded proteins, which need to be characterized to expand our view of how protein structural and dynamic features affect function beyond the static picture of a single well defined 3D structure that has influenced so much our way of thinking. NMR spectroscopy provides a unique tool for the atomic resolution characterization of highly flexible macromolecules in general and of IDPs in particular. The peculiar properties of IDPs however have profound effects on spectroscopic parameters. It is thus worth thinking about these aspects to make the best use of the great potential of NMR spectroscopy to contribute to this fascinating field of research. In particular, after many years of dealing with exclusively heteronuclear NMR experiments based on (13)C direct detection, we would like here to address their relevance when studying IDPs. PMID:24656084

Felli, Isabella C; Pierattelli, Roberta

2014-04-01

355

Determination of the Concentrations of Metal Cations in Aqueous Solutions Using Proton NMR Spectral Area Integration of the EDTA Complexes  

Microsoft Academic Search

This paper introduces an alternative method to determine the concentrations of metal cations in aqueous solutions, using area integration of proton NMR spectra of EDTA (the disodium salt of ethylenediaminetetraacetic acid) metal complexes. Using this method, a certain volume of unknown metal cation solution is added to an excess amount of standard EDTA solution, and the ratio of the remaining

Steven Han; Yong Ba

2004-01-01

356

Two-dimensional filter-diagonalization: spectral inversion of 2D NMR time-correlation signals including degeneracies  

Microsoft Academic Search

Several years ago we introduced a new approach for signal extraction, Filter-Diagonalization, which is capable of handling signals containing millions of points or more. The method was recently extended to handle multidimensional signals, as appear in NMR, by us and separately by Mandelshtam and Taylor. We further extend the original formulation by showing that the method is capable of handling

Michael Robert Wall; Thorsten Dieckmann; Juli Feigon; Daniel Neuhauser

1998-01-01

357

Structural investigations on betacyanin pigments by LC NMR and 2D NMR spectroscopy  

Microsoft Academic Search

Four betacyanin pigments were analysed by LC NMR and subjected to extensive NMR characterisation after isolation. Previously, low pH values were applied for NMR investigations of betalains resulting in rapid degradation of the purified substances thus preventing extensive NMR studies. Consequently, up to now only one single 13C NMR spectrum of a betalain pigment, namely that of neobetanin (=14,15-dehydrobetanin), was

Florian C Stintzing; Jürgen Conrad; Iris Klaiber; Uwe Beifuss; Reinhold Carle

2004-01-01

358

Synthesis Of [2h, 13c]M [2h2m 13c], And [2h3,, 13c] Methyl Aryl Sulfones And Sulfoxides  

DOEpatents

The present invention is directed to labeled compounds, [.sup.2 H.sub.1, .sup.13 C], [.sup.2 H.sub.2, .sup.13 C] and [.sup.2 H.sub.3, .sup.13 C]methyl aryl sulfones and [.sup.2 H.sub.1, .sup.13 C], [.sup.2 H.sub.2, .sup.13 C] and [.sup.2 H.sub.3, .sup.13 C]methyl aryl sulfoxides, wherein the .sup.13 C methyl group attached to the sulfur of the sulfone or sulfoxide includes exactly one, two or three deuterium atoms and the aryl group is selected from the group consisting of 1-naphthyl, substituted 1-naphthyl, 2-naphthyl, substituted 2-naphthyl, and phenyl groups with the structure: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are each independently, hydrogen, a C.sub.1 -C.sub.4 lower alkyl, a halogen, an amino group from the group consisting of NH.sub.2, NHR and NRR' where R and R' are each a C.sub.1 -C.sub.4 lower alkyl, a phenyl, or an alkoxy group. The present invention is also directed to processes of preparing methyl aryl sulfones and methyl aryl sulfoxides.

Martinez, Rodolfo A. (Santa Fe, NM); Alvarez, Marc A. (Santa Fe, NM); Silks, III, Louis A. (Los Alamos, NM); Unkefer, Clifford J. (Los Alamos, NM); Schmidt, Jurgen G. (Los Alamos, NM)

2004-07-20

359

Spectral studies of 2-pyrazoline derivatives: structural elucidation through single crystal XRD and DFT calculations.  

PubMed

A series of biologically active N-thiocarbamoyl pyrazoline derivatives have been synthesized using anhydrous potassium carbonate as the catalyst. All the synthesized compounds were characterized by FT-IR, (1)H NMR, (13)C NMR spectral studies, LCMS, CHN Analysis and X-ray diffraction analysis (compound 7). In order to supplement the XRD parameters, molecular modelling was carried out by Gaussian 03W. From the optimized structure, the energy, dipolemoment and HOMO-LUMO energies of all the systems were calculated. PMID:24457935

Chinnaraja, D; Rajalakshmi, R; Srinivasan, T; Velmurugan, D; Jayabharathi, J

2014-04-24

360

Fast approximate Duplicate Detection for 2D-NMR Spectra  

E-print Network

Fast approximate Duplicate Detection for 2D-NMR Spectra Bj¨orn Egert1 , Steffen Neumann1. In contrast to 1D-NMR spectra, 2D-NMR spectra correlate the chemical shifts of 1 H and 13 C simultaneously a definition of duplicates with the desired robustness properties mandatory for 2D-NMR experiments. A major

Hinneburg, Alexander

361

Solid-state 13C nuclear magnetic resonance studies of coalified gymnosperm xylem tissue from Australian brown coals  

USGS Publications Warehouse

We report here on the use of solid-state 13C nuclear magnetic resonance (NMR) spectroscopy to contrast the average chemical composition of modern degraded gymnosperm woods with fossil gymnosperm woods from Australian brown coals (Miocene). We first established the quantitative nature of the NMR techniques for these samples so that the conventional solid-state 13C NMR spectra and the dipolar dephasing NMR spectra could be used with a high degree of reliability to depict average chemical compositions. The NMR results provide some valuable insights about the early coalification of xylem tissue from gymnosperms. Though the cellulosic components of wood are degraded to varying degrees during peatification and ensuing coalification, it is unlikely that they play a major role in the formation of aromatic structures in coalified woods. The NMR data show that gynmosperm lignin, the primary aromatic contribution to the coal, is altered in part by demethylation of guaiacyl-units to catechol-like structures. The dipolar dephasing NMR data indicate that the lignin also becomes more cross-linked or condensed. ?? 1989.

Hatcher, P.G.; Lerch, H. E., III; Bates, A.L.; Verheyen, T.V.

1989-01-01

362

Accelerated hepatic glycerol synthesis in rainbow smelt (Osmerus mordax) is fuelled directly by glucose and alanine: a 1H and 13C nuclear magnetic resonance study.  

PubMed

At seawater temperatures below 1 degrees C, rainbow smelt (Osmerus mordax) accumulate plasma levels of glycerol up to 400 mM. Aspects of the synthesis of glycerol in liver and its regulation were previously investigated, but the pathways leading to glycerol synthesis remained unconfirmed. Here, we report nuclear magnetic resonance (NMR) studies which elucidate, in more detail, the fuel sources for rapid glycerol synthesis in rainbow smelt. Initial NMR analysis of liver homogenates from fish held at cold (-1 degrees C) temperatures and from fish transferred from 8 degrees C to -1 degrees C showed elevated glycerol, whereas those from fish held at 8 degrees C had far lower glycerol levels. These results confirm a temperature-responsive glycerol synthesis and show that NMR is a suitable approach to investigate the phenomenon. Further studies with fish held at low temperature and injected with labelled L-[2,3-(13)C(2)] alanine or D-[U-(13)C(6)]glucose revealed conversion of both alanine and glucose to glycerol. (13)C spectra showed satellites ((1)J(CC)=41.1 Hz) about the glycerol resonances indicating intact incorporation of a (13)C-(13)C unit in liver glycerol of fish injected with L-[2,3-(13)C(2)]alanine and a (13)C-(13)C-(13)C unit in liver glycerol of fish injected with D[U-(13)C(6)]glucose. Thus, glycerol can be efficiently produced directly from amino acid precursors by glyceroneogenesis, which is an abbreviated gluconeogenesis process leading to glycerol through dihydroxyacetone phosphate (DHAP). Glucose can also be metabolised to glycerol via an abbreviated form of glycolysis that similarly leads to glycerol through DHAP. PMID:16506225

Walter, John A; Ewart, K Vanya; Short, Connie E; Burton, Ian W; Driedzic, William R

2006-06-01

363

MetaboMiner - semi-automated identification of metabolites from 2D NMR spectra of complex biofluids  

PubMed Central

Background One-dimensional (1D) 1H nuclear magnetic resonance (NMR) spectroscopy is widely used in metabolomic studies involving biofluids and tissue extracts. There are several software packages that support compound identification and quantification via 1D 1H NMR by spectral fitting techniques. Because 1D 1H NMR spectra are characterized by extensive peak overlap or spectral congestion, two-dimensional (2D) NMR, with its increased spectral resolution, could potentially improve and even automate compound identification or quantification. However, the lack of dedicated software for this purpose significantly restricts the application of 2D NMR methods to most metabolomic studies. Results We describe a standalone graphics software tool, called MetaboMiner, which can be used to automatically or semi-automatically identify metabolites in complex biofluids from 2D NMR spectra. MetaboMiner is able to handle both 1H-1H total correlation spectroscopy (TOCSY) and 1H-13C heteronuclear single quantum correlation (HSQC) data. It identifies compounds by comparing 2D spectral patterns in the NMR spectrum of the biofluid mixture with specially constructed libraries containing reference spectra of ~500 pure compounds. Tests using a variety of synthetic and real spectra of compound mixtures showed that MetaboMiner is able to identify >80% of detectable metabolites from good quality NMR spectra. Conclusion MetaboMiner is a freely available, easy-to-use, NMR-based metabolomics tool that facilitates automatic peak processing, rapid compound identification, and facile spectrum annotation from either 2D TOCSY or HSQC spectra. Using comprehensive reference libraries coupled with robust algorithms for peak matching and compound identification, the program greatly simplifies the process of metabolite identification in complex 2D NMR spectra. PMID:19040747

Xia, Jianguo; Bjorndahl, Trent C; Tang, Peter; Wishart, David S

2008-01-01

364

1H and 13C assignments of five cembrenes from guggul.  

PubMed

Chemical shift assignments of (1)H and (13)C of five cembrene compounds isolated from the hexane extract of guggul, the resin of Commiphora mukul, are reported. Using (1)H, (13)C, and 2D NMR methods their structures were determined as cembrene (1-isopropyl-4,8,12-trimethyl-cyclotetradeca-2,4,7,11-tetraene), cembrene A (1-isopropenyl-4,8,12-trimethyl-cyclotetradeca-4,8,12-triene), cembrenol (1-isopropyl-4,8,12-trimethyl-cyclotetradeca-3,7,11-trienol), mukulol (1-isopropyl-4,8,12-trimethyl- cyclotetradeca-3,7,11-trienol), and verticillol (4,8,12,15,15-pentamethyl-bicyclo[9.3.1]pentadeca-3,7-dien-12-ol). PMID:18470886

Bai, Shi; Jain, Mahendra

2008-08-01

365

Use of 13C nuclear magnetic resonance to assess fossil fuel biodegradation: fate of [1-13C]acenaphthene in creosote polycyclic aromatic compound mixtures degraded by bacteria.  

PubMed

[1-13C]acenaphthene, a tracer compound with a nuclear magnetic resonance (NMR)-active nucleus at the C-1 position, has been employed in conjunction with a standard broad-band-decoupled 13C-NMR spectroscopy technique to study the biodegradation of acenaphthene by various bacterial cultures degrading aromatic hydrocarbons of creosote. Site-specific labeling at the benzylic position of acenaphthene allows 13C-NMR detection of chemical changes due to initial oxidations catalyzed by bacterial enzymes of aromatic hydrocarbon catabolism. Biodegradation of [1-13C]acenaphthene in the presence of naphthalene or creosote polycyclic aromatic compounds (PACs) was examined with an undefined mixed bacterial culture (established by enrichment on creosote PACs) and with isolates of individual naphthalene- and phenanthrene-degrading strains from this culture. From 13C-NMR spectra of extractable materials obtained in time course biodegradation experiments under optimized conditions, a number of signals were assigned to accumulated products such as 1-acenaphthenol, 1-acenaphthenone, acenaphthene-1,2-diol and naphthalene 1,8-dicarboxylic acid, formed by benzylic oxidation of acenaphthene and subsequent reactions. Limited degradation of acenaphthene could be attributed to its oxidation by naphthalene 1,2-dioxygenase or related dioxygenases, indicative of certain limitations of the undefined mixed culture with respect to acenaphthene catabolism. Coinoculation of the mixed culture with cells of acenaphthene-grown strain Pseudomonas sp. strain A2279 mitigated the accumulation of partial transformation products and resulted in more complete degradation of acenaphthene. This study demonstrates the value of the stable isotope labeling approach and its ability to reveal incomplete mineralization even when as little as 2 to 3% of the substrate is incompletely oxidized, yielding products of partial transformation. The approach outlined may prove useful in assessing bioremediation performance. PMID:9546181

Selifonov, S A; Chapman, P J; Akkerman, S B; Gurst, J E; Bortiatynski, J M; Nanny, M A; Hatcher, P G

1998-04-01

366

Use of 13C Nuclear Magnetic Resonance To Assess Fossil Fuel Biodegradation: Fate of [1-13C]Acenaphthene in Creosote Polycyclic Aromatic Compound Mixtures Degraded by Bacteria†  

PubMed Central

[1-13C]acenaphthene, a tracer compound with a nuclear magnetic resonance (NMR)-active nucleus at the C-1 position, has been employed in conjunction with a standard broad-band-decoupled 13C-NMR spectroscopy technique to study the biodegradation of acenaphthene by various bacterial cultures degrading aromatic hydrocarbons of creosote. Site-specific labeling at the benzylic position of acenaphthene allows 13C-NMR detection of chemical changes due to initial oxidations catalyzed by bacterial enzymes of aromatic hydrocarbon catabolism. Biodegradation of [1-13C]acenaphthene in the presence of naphthalene or creosote polycyclic aromatic compounds (PACs) was examined with an undefined mixed bacterial culture (established by enrichment on creosote PACs) and with isolates of individual naphthalene- and phenanthrene-degrading strains from this culture. From 13C-NMR spectra of extractable materials obtained in time course biodegradation experiments under optimized conditions, a number of signals were assigned to accumulated products such as 1-acenaphthenol, 1-acenaphthenone, acenaphthene-1,2-diol and naphthalene 1,8-dicarboxylic acid, formed by benzylic oxidation of acenaphthene and subsequent reactions. Limited degradation of acenaphthene could be attributed to its oxidation by naphthalene 1,2-dioxygenase or related dioxygenases, indicative of certain limitations of the undefined mixed culture with respect to acenaphthene catabolism. Coinoculation of the mixed culture with cells of acenaphthene-grown strain Pseudomonas sp. strain A2279 mitigated the accumulation of partial transformation products and resulted in more complete degradation of acenaphthene. This study demonstrates the value of the stable isotope labeling approach and its ability to reveal incomplete mineralization even when as little as 2 to 3% of the substrate is incompletely oxidized, yielding products of partial transformation. The approach outlined may prove useful in assessing bioremediation performance. PMID:9546181

Selifonov, Sergey A.; Chapman, Peter J.; Akkerman, Simon B.; Gurst, Jerome E.; Bortiatynski, Jacqueline M.; Nanny, Mark A.; Hatcher, Patrick G.

1998-01-01

367

Reverse detection for spectral width improvements in spatially encoded dimensions of ultrafast two-dimensional NMR spectra.  

PubMed

Recently, the spatially encoded technique has been broadly used in the fast analyses of chemical systems and real-time detections of chemical reactions. In spatially encoded ultrafast 2D spectra, spectral widths and resolution in spatially encoded dimensions are contradictive, leading to the risk of insufficient spectral widths when providing satisfactory resolution values for all resonances. Here, a method named as reverse detection is proposed to improve the spectral width in the spatially encoded dimension. Experimental results show that spectral width improvements are at least twofold with reverse detection solely, and more improvements can be expected along with the gradient-controlled folding method. The proposed method can be applied to almost any spatially encoded scheme with echo planar spectroscopic imaging-like detection module and may promote wide applications of ultrafast 2D spectroscopy techniques in chemical analyses. Copyright © 2014 John Wiley & Sons, Ltd. PMID:25102814

Wei, Zhiliang; Yang, Jian; Lin, Liangjie; Liu, Guangcao; Lin, Yanqin; Chen, Zhong

2014-11-01

368

A high resolution ?13C record in a modern Porites lobata coral: Insights into controls on skeletal ?13C  

NASA Astrophysics Data System (ADS)

?13C was determined at a high spatial resolution by secondary ion mass spectrometry (SIMS) across a 1 year section of a modern Porites lobata coral skeleton from Hawaii. Skeletal ?13C is dominated by large oscillations of 5-7‰ that typically cover skeletal distances equivalent to periods of ˜14-40 days. These variations do not reflect seawater temperature and it is unlikely that they reflect variations in the ?13C of local seawater. We observe no correlation between skeletal ?13C and the pH of the calcification fluid (estimated from previous measurements of skeletal ?11B). We conclude that either the proportion of skeletal carbon derived from metabolic CO2 is not reflected by estimated ECF pH (as the [CO2] in the overlying coral tissue varies) and/or the ?13C composition of the metabolic CO2 is highly variable. We also observe no correlation between skeletal ?13C and previous ?18O SIMS measurements. Variations in skeletal ?13C and ?18O do not have a common timing, providing no evidence that skeletal ?13C and ?18O vary in response to a single factor. This suggests that skeletal ?13C is principally driven by variations in the ?13C composition of metabolic CO2 rather than by the abundance of metabolic CO2, which would also affect skeletal ?18O. The ?13C composition of metabolic CO2 reflects the processes of photosynthesis, heterotrophic feeding and respiration in the overlying coral tissue. Corals catabolise stored lipid reserves to meet energetic demands when photosynthesis conditions are sub-optimal. Variations in the amounts and types of reserves utilised could induce changes in the ?13C composition of metabolic CO2 and the resultant skeleton which are temporally offset from skeletal ?18O records.

Allison, Nicola; Finch, Adrian A.; EIMF

2012-05-01

369

FT-IR and NMR spectroscopic studies of salicylic acid derivatives. II. Comparison of 2-hydroxy- and 2,4- and 2,5-dihydroxy derivatives  

Microsoft Academic Search

The 2,4- and 2,5-dihydroxybenzamides (8, 9) were syn- thesized from their corresponding methyl esters. The struc- tures and the spectral properties of investigated salicylic acid (1), 2,4- and 2,5-dihydroxy benzoic acids (2, 3), their methyl esters (4-6) and amides (7-9) were analyzed by means of FT-IR and one- and two-dimensional homo- and heteronuclear 1H and 13C NMR spectroscopies. Com- parison

MILENA JADRIJEVI; MLADAR TAKA

370

Nuclear Magnetism and Electronic Order in 13 C Nanotubes  

E-print Network

Nuclear Magnetism and Electronic Order in 13 C Nanotubes Bernd Braunecker,1 Pascal Simon,1 on nuclear magnetism in one dimension. If the electrons are in the metallic, Luttinger liquid regime, we show that even a very weak hyperfine coupling to the 13C nuclear spins has a striking effect: The system

Braunecker, Bernd

371

Asymptotic Normalization Coefficients for 13C+p->14N  

E-print Network

The $^{13}C(^{14}N,^{13}C)^{14}N$ proton exchange reaction has been measured at an incident energy of 162 MeV. Angular distributions were obtained for proton transfer to the ground and low lying excited states in $^{14}N$. Elastic scattering of $^{14}N$ on $^{13}C$ also was measured out to the rainbow angle region in order to find reliable optical model potentials. Asymptotic normalization coefficients for the system $^{13}C+p\\to {}^{14}N$ have been found for the ground state and the excited states at 2.313, 3.948, 5.106 and 5.834 MeV in $^{14}N$. These asymptotic normalization coefficients will be used in a determination of the S-factor for $^{7}Be(p,\\gamma)^{8}B$ at solar energies from a measurement of the proton transfer reaction $^{14}N(^{7}Be,^{8}B)^{13}C$.

L. Trache; A. Azhari; H. L. Clark; C. A. Gagliardi; Y. -W. Lui; A. M. Mukhamedzhanov; R. E. Tribble; F. Carstoiu

1998-09-23

372

Detection of intracellular lactate with localized diffusion { 1H- 13C}-spectroscopy in rat glioma in vivo  

NASA Astrophysics Data System (ADS)

The aim of this study was to compare the diffusion characteristic of lactate and alanine in a brain tumor model to that of normal brain metabolites known to be mainly intracellular such as N-acetylaspartate or creatine. The diffusion of 13C-labeled metabolites was measured in vivo with localized NMR spectroscopy at 9.4 T (400 MHz) using a previously described localization and editing pulse sequence known as ACED-STEAM ('adiabatic carbon editing and decoupling'). 13C-labeled glucose was administered and the apparent diffusion coefficients of the glycolytic products, { 1H- 13C}-lactate and { 1H- 13C}-alanine, were determined in rat intracerebral 9L glioma. To obtain insights into { 1H- 13C}-lactate compartmentation (intra- versus extracellular), the pulse sequence used very large diffusion weighting (50 ms/?m 2). Multi-exponential diffusion attenuation of the lactate metabolite signals was observed. The persistence of a lactate signal at very large diffusion weighting provided direct experimental evidence of significant intracellular lactate concentration. To investigate the spatial distribution of lactate and other metabolites, 1H spectroscopic images were also acquired. Lactate and choline-containing compounds were consistently elevated in tumor tissue, but not in necrotic regions and surrounding normal-appearing brain. Overall, these findings suggest that lactate is mainly associated with tumor tissue and that within the time-frame of these experiments at least some of the glycolytic product ([ 13C] lactate) originates from an intracellular compartment.

Pfeuffer, Josef; Lin, Joseph C.; DelaBarre, Lance; Ugurbil, Kamil; Garwood, Michael

2005-11-01

373

Phenol-formaldehyde resins: A quantitative NMR study of molecular structure and molecular dynamics  

NASA Astrophysics Data System (ADS)

Phenol-formaldehyde (PF) resins have been the subject of this work. 13C liquid-state and solid-state NMR has been used to investigate the molecular structure of mainly novolak and partially of resole resins. 1H wideline in combination with 13C solid-state NMR relaxometry has been applied to study the curing and the molecular dynamics of phenolic resins. It was the intention to provide an insight in the relationship between resin composition, resin structure and subsequent resin properties (by means of the molecular dynamics). An improved 13C liquid-state NMR quantification technique of novolaks in THF-CDCl3 solutions is demonstrated. Full quantitative 13C liquid-state spectra of phenol-formaldehyde resins with high signal- to-noise ratio were obtained by using chromium acetylacetonate under optimized spectral conditions within a few hours spectrometer time. Attached proton test (APT) spectra enabled proper peak assignments in the region with significant overlap. For several novolaks, prepared under different catalytic conditions, the degree of polymerization, degree of branching, number average molecular weight, isomeric distribution, and the number of unreacted ortho and para phenol ring positions was determined with a reduced margin of error, by analyzing and integrating the 13C spectra. The power of 13C solid-state NMR in the analysis of cured PF resins is shown. Particular importance was ascribed to the question of the quantifiability of the experiments when it was desired to measure the degree of conversion by means of a 13C CP/MAS contact time study. The network structure present, and thus also the mechanical properties, is critically dependent upon the final degree of conversion obtained after curing. The degree of conversion, which depended on the cure conditions (cure temperature, cure pressure and cure time), was limited by vitrification as was demonstrated by DSC experiments. Changes in the spin-lattice relaxation time T 1H were observed, providing criteria to follow the curing evolution. FT-Raman spectroscopy showed to be complementary to 13C NMR for the determination of the degree of polymerization and of conversion in PF prepolymers or in cured PF resins. In the last part of this work it was shown that 1H wideline and 13C CP/MAS solid-state NMR relaxometry provides interesting information concerning the molecular dynamics of cured novolak resins and resole/novolak copolymers. The relaxation times investigated were the spin-lattice relaxation time (T 1H), the spin-lattice relaxation time in the rotating frame (T 1pH), and the spin-spin relaxation time (T 2H). It was noticed that these relaxation times of the PF resins, at temperatures below the glass transition temperature, were ascertained not only by dynamic phenomena, but also a contribution from the spin diffusion mechanism should be implemented. Measurements as a function of the temperature indicated for a reversible hydrogen bond deformation, confirmed by FT-IR measurements. 13C CP/MAS and 1H wideline NMR can be applied as complementary techniques in order to investigate phenol-formaldehyde resins in the solid state. The chemical structure and the molecular dynamics of these resins can be studied in an adequate manner. Correlations can be made between their relaxation times, their chemical structure and their macroscopic properties.

Ottenbourgs, Benjamin Tony

374

Compressed Sensing for Resolution Enhancement of Hyperpolarized 13C Flyback 3D-MRSI  

PubMed Central

High polarization of nuclear spins in liquid state through dynamic nuclear polarization has enabled the direct monitoring of 13C metabolites in vivo at very high signal to noise, allowing for rapid assessment of tissue metabolism. The abundant SNR afforded by this hyperpolarization technique makes high resolution 13C 3D-MRSI feasible. However, the number of phase encodes that can be fit into the short acquisition time for hyperpolarized imaging limits spatial coverage and resolution. To take advantage of the high SNR available from hyperpolarization, we have applied compressed sensing to achieve a factor of 2 enhancement in spatial resolution without increasing acquisition time or decreasing coverage. In this paper, the design and testing of compressed sensing suited for a flyback 13C 3D-MRSI sequence are presented. The key to this design was the undersampling of spectral k-space using a novel blipped scheme, thus taking advantage of the considerable sparsity in typical hyperpolarized 13C spectra. Phantom tests validated the accuracy of the compressed sensing approach and initial mouse experiments demonstrated in vivo feasibility. PMID:18367420

Hu, Simon; Lustig, Michael; Chen, Albert P.; Crane, Jason; Kerr, Adam; Kelley, Douglas A.C.; Hurd, Ralph; Kurhanewicz, John; Nelson, Sarah J.; Pauly, John M.; Vigneron, Daniel B.

2008-01-01

375

Study of Urban environmental quality through Isotopes ?13C  

NASA Astrophysics Data System (ADS)

Usually, trees with similar pH values on their bark develop epiphytes of similar species, the acidity to be a factor for growth. The aim of the study was evaluate the air quality through isotope ?13C in order to define the levels of environmental quality in the city of Queretaro, Mexico. In this work were collected at least 4 epiphytes positioned in trees of the species Prosopis Laevigata at 25 sites of Queretaro City. The samples were analyzed for trace elements with an inductively coupled plasma atomic emission spectroscopy (ICP). The collecting took place during dry period, in May and early rain June 2011 period, and on four sectors to identify the spatial distribution of pollution, using isotopic analysis of concentration of ? 13C. According with the results there are significant differences among the species in each of the sampled areas. The 5 February Avenue presented greater diversity and richness of ?13C, followed by those who were surveyed in the proximity of the UAQ and finally in the middle-east area. An average value of ?13C-17.92%, followed by those surveyed in the vicinity of the UAQ that correspond to sector I and II with an concentration of ?13C-17.55% and ?13C-17.22%, and finally the samples collected in trees scattered in the East-Sector II and IV with a value of ?13C-17.02% and ?13C-15.62%, respectively. Also were observed differences between the dry and wet period. It is likely that these results of ? 13C in moist period reflect the drag of the isotopes due to rain events that could mark a trend in the dilution of this element, however there is a trend in terms of abundance and composition of finding more impact in those species sampled in dry period, in May and early June 2011.

González-Sosa, E.; Mastachi-Loza, C.; Becerril-Piña, R.; Ramos-Salinas, N. M.

2012-04-01

376

Discrimination between 12 C and 13 C by marine plants  

Microsoft Academic Search

Summary  The natural abundance13C\\/12C ratios (as ?13C) of organic matter of marine macroalgae from Fife and Angus (East Scotland) were measured for comparison with the species'\\u000a ability to use CO2 and HCO\\u000a 3\\u000a -\\u000a for photosynthesis, as deduced from previously published pH-drift measurements. There was a clear difference in ?13C values for species able or unable to use HCO\\u000a 3\\u000a -

S. C. Maberly; J. A. Raven; A. M. Johnston

1992-01-01

377

Pursuing structure in microcrystalline solids with independent molecules in the unit cell using 1H-13C correlation data  

PubMed Central

The 1H–13C solid-state NMR heteronuclear correlation (HETCOR) experiment is demonstrated to provide shift assignments in certain powders that have two or more structurally independent molecules in the unit cell (i.e. multiple molecules per asymmetric unit). Although this class of solids is often difficult to characterize using other methods, HETCOR provides both the conventional assignment of shifts to molecular positions and associates many resonances with specific molecules in the asymmetric unit. Such assignments facilitate conformational characterization of the individual molecules of the asymmetric unit and the first such characterization solely from solid-state NMR data is described. HETCOR offers advantages in sensitivity over prior methods that assign resonances in the asymmetric unit by 13C–13C correlations and therefore allows shorter average analysis times in natural abundance materials. The 1H–13C analysis is demonstrated first on materials with known shift assignments from INADEQUATE data (santonin and Ca(OAc)2 phase I) to verify the technique and subsequently is extended to a pair of unknown solids: (+)-catechin and Ca(OAc)2 phase II. Sufficient sensitivity and resolution is achieved in the spectra to provide assignments to one of the specific molecules of the asymmetric unit at over 54% of the sites. PMID:17869558

Harper, James K.; Strohmeier, Mark; Grant, David M.

2007-01-01

378

The distribution of 13C in the Atlantic Ocean  

Microsoft Academic Search

Individual vertical profiles and north-south sections for the distribution of the delta13C of total dissolved inorganic carbon are presented for the Atlantic stations of the GEOSECS program. In most cases the delta13C data parallel the distribution of dissolved O2. Differences are attributed to in-situ oxidation of organic matter and dissolution of particles of CaCO3. Antarctic Bottom and Intermediate Waters have

P. Kroopnick

1980-01-01

379

NMR studies of some rifamycins  

NASA Astrophysics Data System (ADS)

The 13C and 1H NMR spectra of rifabutin 1 and five of its derivatives 2- 6, three of which are described for the first time, were assigned using 2D homo- and heteronuclear correlation NMR spectroscopy, proton exchange with deuterium, and selective proton decoupling methods to one bond and long distance. The study was also extended to the other well-known ansamycin antibiotics, rifamycin S 7 and rifampicin 8. Previous interpretations for the known compounds have been corrected.

Santos, L.; Medeiros, M. A.; Santos, S.; Costa, M. C.; Tavares, R.; Curto, M. J. M.

2001-05-01

380

Quantitative high resolution 13 C nuclear magnetic resonance of the olefinic and carbonyl carbons of edible vegetable oils  

Microsoft Academic Search

The acyl distribution and acyl positional distribution (1,3-acyl and 2-acyl) of triacylglycerols derived from edible vegetable\\u000a oils has been examined by13C nuclear magnetic resonance (NMR) spectroscopy. The acyl profile of three natural oils (corn, peanut, canola) and one specialty\\u000a oil (high oleic sunflower oil, Trisun 80) has been defined from the high resolution (medium field 75.4 MHz) spectrum of the

Kurt F. Wollenberg

1990-01-01

381

Utilizing Afterglow Magnetization from Cross-Polarization Magic-Angle-Spinning Solid-State NMR Spectroscopy to Obtain Simultaneous Heteronuclear Multidimensional Spectra  

PubMed Central

The time required for data acquisition and subsequent spectral assignment are limiting factors for determining biomolecular structure and dynamics using solid state NMR spectroscopy. While strong magnetic dipolar couplings give rise to relatively broad spectra lines, the couplings also mediate the coherent magnetization transfer via the Hartmann Hahn cross polarization (HH-CP) experiment. This mechanism is used in nearly all backbone assignment experiments for carrying out polarization transfer between 1H, 15N, and 13C. In this Article, we describe a general spectroscopic approach to use the residual or afterglow magnetization from the 15N to 13C selective HH-CP experiment to collect a second multidimensional heteronuclear dataset. This approach allowed for the collection of two multidimensional (2D NCA and NCO or 3D NCACX and NCOCX) datasets at the same time. These experiments were performed using instrumentation available on all standard solid state NMR spectrometers configured for magic angle spinning and were demonstrated on uniformly [13C,15N] and [1,3-13C] glycerol labeled ubiquitin. This method is compatible with several other sensitivity enhancement experiments and can be used as an isotopic filtering tool to reduce the spectral complexity and decrease the time needed for assigning spectra. PMID:22582831

Banigan, James R.; Traaseth, Nathaniel J.

2012-01-01

382

Cryopreservation Effects on Intermediary Metabolism in a Pancreatic Substitute: A 13C Nuclear Magnetic Resonance Study  

PubMed Central

Cryopreservation is important for clinical translation of tissue-engineered constructs. With respect to a pancreatic substitute, encapsulated islets or beta cells have been widely studied for the treatment of insulin-dependent diabetes mellitus. Besides cell viability loss, cryopreservation may affect the function of the remaining viable cells in a pancreatic substitute by altering fundamental processes in glucose-stimulated insulin secretion, such as pathways associated with intermediary metabolism, potentially leading to insulin-secretion defects. In this study, we used 13C nuclear magnetic resonance (NMR) spectroscopy and isotopomer analysis to determine the effects of conventional freezing and ice-free cryopreservation (vitrification) on carbon flow through tricarboxylic acid (TCA) cycle–associated pathways in encapsulated murine insulinoma ?TC-tet cells; the secretory function of the encapsulated cells postpreservation was also evaluated. Specifically, calcium alginate–encapsulated ?TC-tet cells were frozen or vitrified with a cryoprotectant cocktail. Beads were warmed and 13C labeling and extraction were performed. Insulin secretion rates were determined during basal and labeling periods and during small-scale glucose stimulation and K+-induced depolarization. Relative metabolic fluxes were determined from 13C NMR spectra using a modified single pyruvate pool model with the tcaCALC modeling program. Treatments were compared with nonpreserved controls. Results showed that relative carbon flow through TCA-cycle-associated pathways was not affected by conventional freezing or vitrification. However, vitrification, but not freezing, led to impaired insulin secretion on a per viable cell basis. The reduced secretion from the Vitrified group occurred irrespective of scale and was present whether secretion was stimulated by glucose or K+-induced depolarization, indicating that it might be due to a defect in late-stage secretion events. PMID:22697373

Ahmad, Hajira F.; Simpson, Nicholas E.; Lawson, Alison N.

2012-01-01

383

Analytical applications of flow FT-NMR. I. A recycled-flow experiment for the signal enhancement of NMR spectra. II. On-line analytical-scale HPLC/NMR  

SciTech Connect

The analytical utility of FT-NMR detection in flowing streams is explored through the development and implementation of recycled-flow NMR for signal enhancement and continuous flow analytical-scale HPLC/NMR. In addition, perturbation of the flow-NMR lineshape because of decreases in effective spin-lattice and spin-spin relaxation, previously well characterized only for CW-NMR, is examined both theoretically and empirically for the pulsed experiment. Flow /sup 13/C-NMR spectra of sample nuclei with inefficient spin-lattice relaxation (quaternary, carbonyl and deuterated sites) produce a factor of 4-10 signal enhancement when compared to static system spectra for equivalent acquisition times. The multinuclear capabilities of the flow technique extended to other spin-1/2 nuclei (/sup 15/N, /sup 31/P, /sup 113/Cd, and /sup 29/Si), demonstrate similar enhancement. Preliminary studies of immobilized free radical substrates, potential substitutes for large premagnetization volumes, provide a doubling of the spectral S/N when compared to static system results.

Laude, D.A. Jr.

1984-01-01

384

Influence of 13C-enriched foliage respired CO2 on ?13C of ecosystem-respired CO2  

Microsoft Academic Search

The ?13C of slash pine foliage dark-respired CO2 (?13CF) was measured at temperatures ranging from 6.6° to 30°C. The ?13CF was 13C-enriched initially after dark by as much as 9‰ and declined toward an asymptotic value after a few hours in the dark. Maximum enrichment in ?13CF occurred at the lowest temperatures and the decline in ?13CF toward the asymptotic

Behzad Mortazavi; Jeffrey P. Chanton; Matthew C. Smith

2006-01-01