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1

1H, 13C and 17O NMR spectral study of chlorinated 3,4-dihydroxybenzaldehydes (protocatechualdehydes)  

NASA Astrophysics Data System (ADS)

Chlorinated 3,4-dihydroxybenzaldehydes have been studied by means of 1H, 13C and 17O NMR spectroscopy. The 1H and 13C NMR spectral assignments are based on 2-dimensional 13C- 1H chemical shift correlation spectroscopy (COSY). The 17O NMR measurements at natural isotope content in organic solvents are problematic owing to the poor solubility of the compounds and/or broadness of the resonance lines. In aqueous alkaline solutions, however, all protocatechualdehydes exhibit "easy-to-detect" 17O NMR spectral characteristics. The 17O NMR chemical shifts in the range of 140-480 p.p.m. are interpreted as arising from the different canonical structures of formyl substituted phenolate anions. The 13C NMR data reveal that the hydroxyl at the para-position to the formyl group is predominantly transformed to the corresponding phenolate anion in aqueous alkaline environment.

Kolehmainen, Erkki T.; Laihia, Katri P.; Hyötyläinen, Juha M. I.; Kauppinen, Reijo T.

1995-03-01

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

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

NASA Astrophysics Data System (ADS)

Two robust combinations of spectral editing techniques with 2D 13Csbnd 13C NMR have been developed for characterizing the aromatic components of 13C-enriched low-temperature carbon materials. One method (exchange with protonated and nonprotonated spectral editing, EXPANSE) selects cross peaks of protonated and nearby nonprotonated carbons, while the other technique, dipolar-dephased double-quantum/single-quantum (DQ/SQ) NMR, selects signals of bonded nonprotonated carbons. Both spectra are free of a diagonal ridge, which has many advantages: Cross peaks on the diagonal or of small intensity can be detected, and residual spinning sidebands or truncation artifacts associated with the diagonal ridge are avoided. In the DQ/SQ experiment, dipolar dephasing of the double-quantum coherence removes protonated-carbon signals; this approach also eliminates the need for high-power proton decoupling. The initial magnetization is generated with minimal fluctuation by combining direct polarization, cross polarization, and equilibration by 13C spin diffusion. The dipolar dephased DQ/SQ spectrum shows signals from all linkages between aromatic rings, including a distinctive peak from polycondensed aromatics. In EXPANSE NMR, signals of protonated carbons are selected in the first spectral dimension by short cross polarization combined with dipolar dephasing difference. This removes ambiguities of peak assignment to overlapping signals of nonprotonated and protonated aromatic carbons, e.g. near 125 ppm. Spin diffusion is enhanced by dipolar-assisted rotational resonance. Before detection, Csbnd 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 Cdbnd O carbons, which is particularly useful for identifying furan and arene rings. The Cdbnd 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.

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

2013-09-01

4

1H and 13C NMR spectral study of some 3,5-bis[(E)-thienylmethylene]piperidin-4-ones  

NASA Astrophysics Data System (ADS)

1H and 13C NMR spectra have been recorded for 3,5-bis[(E)-thienylmethylene]piperidin-4-one ( 1a), 3',3?-dimethyl-3,5-bis[(E)-thienylmethylene]piperidin-4-one ( 1b), 5',5?-dibromo-3,5-bis[(E)-thienylmethylene]piperidin-4-one ( 1c), their 1-methyl derivatives 2a- c and 3,5-bis[(E)-thienylmethylene]-2r,6c-diphenylpiperidin-4-one ( 3a). For selected compounds 2D spectra have been recorded. The spectral data are used to study the configuration and conformation of these molecules. The chemical shifts are discussed in light of steric, electronic and magnetic anisotropic effects. The magnetic anisotropic effects of thiophene ring and phenyl group are noteworthy. 1H- 1H COSY spectrum of 2b suggests that long-range 1H- 1H coupling, up to seven bonds, is possible in it. HMBC spectrum of 2b displays the magnetic nonequivalence of C-2 and C-6 and protons at these carbons.

Rajeswari, K.; Pandiarajan, K.

2011-03-01

5

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

PubMed Central

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

6

Complete 1H-NMR and 13C-NMR spectral analysis of the pairs of 20(S) and 20(R) ginsenosides  

PubMed Central

Background Ginsenosides, the major ingredients of Panax ginseng, have been studied for many decades in Asian countries as a result of their wide range of pharmacological properties. The less polar ginsenosides, with one or two sugar residues, are not present in nature and are produced during manufacturing processes by methods such as heating, steaming, acid hydrolysis, and enzyme reactions. 1H-NMR and 13C-NMR spectroscopic data for the identification of the less polar ginsenosides are often unavailable or incomplete. Methods We isolated 21 compounds, including 10 pairs of 20(S) and 20(R) less polar ginsenosides (1–20), and an oleanane-type triterpene (21) from a processed ginseng preparation and obtained complete 1H-NMR and 13C-NMR spectroscopic data for the following compounds, referred to as compounds 1–21 for rapid identification: 20(S)-ginsenosides Rh2 (1), 20(R)-Rh2 (2), 20(S)-Rg3 (3), 20(R)-Rg3 (4), 6?-O-acetyl-20(S)-Rh2 [20(S)-AcetylRh2] (5), 20(R)-AcetylRh2 (6), 25-hydroxy-20(S)-Rh2 (7), 25-hydroxy-20(S)-Rh2 (8), 20(S)-Rh1 (9), 20(R)-Rh1 (10), 20(S)-Rg2 (11), 20(R)-Rg2 (12), 25-hydroxy-20(S)-Rh1 (13), 25-hydroxy-20(R)-Rh1 (14), 20(S)-AcetylRg2 (15), 20(R)-AcetylRg2 (16), Rh4 (17), Rg5 (18), Rk1 (19), 25-hydroxy-Rh4 (20), and oleanolic acid 28-O-?-D-glucopyranoside (21). PMID:25378994

Yang, Heejung; Kim, Jeom Yong; Kim, Sun Ok; Yoo, Young Hyo; Sung, Sang Hyun

2014-01-01

7

Separation of floridoside and isofloridosides by HPLC and complete (1)H and (13)C NMR spectral assignments for D-isofloridoside.  

PubMed

Isofloridosides (1-O-alpha-D-galactopyranosylglycerol) and floridoside (2-O-alpha-D-galactopyranosylglycerol) were extracted from the red alga Porphyra umbilicalis (Linné) Kützing (Bangiales, Rhodophyta). Their separation was achieved by HPLC (NH(2) P50 column) after successive purification of the crude extract by ion-exchange chromatography and HPLC (Sugar-Pak TM1 column). 1D and 2D NMR spectroscopy experiments allowed to completely assign the (1)H and (13)C spectra of D-isofloridoside. PMID:17765883

Bondu, Stéphanie; Kervarec, Nelly; Deslandes, Eric; Pichon, Roger

2007-11-26

8

Quantitative (13)C NMR analysis of lignins with internal standards.  

PubMed

Novel protocols for acquiring quantitative (13)C NMR spectra of lignins have been developed using the internal reference compounds 1,3,5-trioxane and pentafluorobenzene. Trioxane offers a convenient internal standard for collecting inverse gated proton decoupled (13)C NMR spectra for lignins, whereas pentafluorobenzene can be used to provide information on the amount of methine carbon using the DEPT experiment. In each case, the internal reference compounds provide single, un-overlapped sharp signals in the middle of the spectral region, permitting facile integration. These integrals could be used to determine the amounts of different structural features of lignins, expressed in absolute units of millimoles per gram. The optimum parameters for these experiments were validated for a variety of spectrometer platforms, and standard errors were determined for different spectral areas using lignin model compounds and "standard" lignins. In addition, the data derived for the International Round Robin "standard" lignins showed good agreement with the data from quantitative (31)P NMR spectroscopy and published data, obtained by independent laboratories using independent methods of analysis. PMID:11513630

Xia, Z; Akim, L G; Argyropoulos, D S

2001-08-01

9

1H, 13C and 15N NMR spectral and theoretical studies of some methyl and alkylamino derivatives of 4-halopyridine N-oxides  

NASA Astrophysics Data System (ADS)

Nine new and three earlier known 4-halogen (Cl and Br) substituted pyridine N-oxides have been prepared and their 1H, 13C and 15N NMR chemical shifts assigned based on PFG 1H, X (X= 13C and 15N) HMQC and HMBC experiments as well as the comparison with our earlier results for substituted pyridine N-oxide derivatives. The 15N resonances of the pyridine nitrogen are 27-40 ppm more shielded in 4-halo-2-alkylamino-6-methyl-5-nitropyridine N-oxide than in parent 4-halopyridine N-oxide. According to quantum chemical ab initio HF/6-311G** calculations the amino tautomer of 4-chloro-2-methylamino-6-methyl-5-nitropyridine N-oxide is more stable than its imino form. Using B3LYP/6-311G** optimized structures both 13C and 15N shifts were calculated by density functional B3LYP/6-311G** CSGT methods for the amino and imino tautomers as well as for the dimeric structure for 4-chloro-2-methylamino-6-methyl-5-nitropyridine N-oxide. The 15N NMR and DFT calculations suggest the prevailing of the dimeric amino form for one congener, which is further supported by ESI-TOF MS data.

Laihia, K.; Puszko, A.; Linnanto, J.; Kolehmainen, E.

2006-02-01

10

Functional groups identified by solid state 13C NMR spectroscopy  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

11

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

12

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

13

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

14

Study of molecular interactions with 13C DNP-NMR  

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

15

A 13C-NMR study of azacryptand complexes.  

PubMed

An azacryptand has been solubilised in aqueous media containing 50% (v/v) dimethyl sulphoxide. (13)C-NMR has been used to determine how the azacryptand is affected by zinc binding at pH 10. Using (13)C-NMR and (13)C-enriched bicarbonate we have been able to observe the formation of 4 different carbamate derivatives of the azacryptand at pH 10. The azacryptand was shown to solubilise zinc or cadmium at alkaline pHs. Two moles of zinc are bound per mole of azacryptand and this complex binds 1 mole of carbonate. By replacing the zinc with cadmium-113 we have shown that the (13)C-NMR signal of the (13)C-enriched carbon of the bound carbonate is split into two triplets at 2.2 °C. This shows that two cadmium complexes are formed and in each of these complexes the carbonate group is bound by two magnetically equivalent metal ions. It also demonstrates that these cadmium complexes are not in fast exchange. From temperature studies we show that in the zinc complexes both complexes are in fast exchange with each other but are in slow exchange with free bicarbonate. HOESY is used to determine the position of the carbonate carbon in the complex. The solution and crystal structures of the zinc-carbonate-azacryptand complexes are compared. PMID:25091182

Wild, Aljoscha A C; Fennell, Kevin; Morgan, Grace G; Hewage, Chandralal M; Malthouse, J Paul G

2014-09-28

16

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

PubMed Central

Carbon-13 NMR spectroscopy in combination with 13C-labeled substrate infusion is a powerful technique to measure a large number of metabolic fluxes non-invasively in vivo. It has been used to quantify glycogen synthesis rates, establish quantitative relationships between energy metabolism and neurotransmission and evaluate the importance of different substrates. All measurements can, in principle, be performed through direct 13C NMR detection or via indirect 1H-[13C] NMR detection of the protons attached to 13C nuclei. The choice for detection scheme and pulse sequence depends on the magnetic field strength, whereas substrate selection depends on the metabolic pathways that are studied. 13C NMR spectroscopy remains a challenging technique that requires several non-standard hardware modifications, infusion of 13C-labeled substrates and sophisticated processing and metabolic modeling. Here the various aspects of direct 13C and indirect 1H-[13C] NMR are reviewed with the aim of providing a practical guide. PMID:21919099

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

2013-01-01

17

Spectroscopic separation of (13) C NMR spectra of complex isomeric mixtures by the CSSF-TOCSY-INEPT experiment.  

PubMed

Isomeric mixtures from synthetic or natural origins can pose fundamental challenges for their chromatographic separation and spectroscopic identification. A novel 1D selective NMR experiment, chemical shift selective filter (CSSF)-TOCSY-INEPT, is presented that allows the extraction of (13) C NMR subspectra of discrete isomers in complex mixtures without physical separation. This is achieved via CSS excitation of proton signals in the (1) H NMR mixture spectrum, propagation of the selectivity by polarization transfer within coupled (1) H spins, and subsequent relaying of the magnetization from (1) H to (13) C by direct INEPT transfer to generate (13) C NMR subspectra. Simple consolidation of the subspectra yields (13) C NMR spectra for individual isomers. Alternatively, CSSF-INEPT with heteronuclear long-range transfer can correlate the isolated networks of coupled spins and therefore facilitate the reconstruction of the (13) C NMR spectra for isomers containing multiple spin systems. A proof-of-principle validation of the CSSF-TOCSY-INEPT experiment is demonstrated on three mixtures with different spectral and structural complexities. The results show that CSSF-TOCSY-INEPT is a versatile, powerful tool for deconvoluting isomeric mixtures within the NMR tube with unprecedented resolution and offers unique, unambiguous spectral information for structure elucidation. Copyright © 2014 John Wiley & Sons, Ltd. PMID:25616134

Yang, Lu; Moreno, Aitor; Fieber, Wolfgang; Brauchli, Robert; Sommer, Horst

2015-04-01

18

Complete 1H and 13C spectral assignment of floridoside.  

PubMed

Floridoside (2-O-alpha-D-galactopyranosylglycerol) was extracted from the red marine alga Rhodymenia palmata, and purified by ion-exchange chromatography: 1D and 2D NMR spectroscopy experiments were used to unambiguously assign the complete 1H and 13C spectra. PMID:11844498

Simon-Colin, Christelle; Kervarec, Nelly; Pichon, Roger; Deslandes, Eric

2002-02-11

19

(13)C and (15)N solid-state NMR studies on albendazole and cyclodextrin albendazole complexes.  

PubMed

(13)C and (15)N solid-state nuclear magnetic resonance (NMR) spectra were recorded from albendazole (ABZ) and from ABZ:?-cyclodextrin, ABZ:methyl-?-cyclodextrin, ABZ:hydroxypropyl-?-cyclodextrin and ABZ:citrate-?-cyclodextrin, which were prepared by the spray-drying technique. ABZ signals were typical of a crystalline solid for the pure drug and of an amorphous compound obtained from ABZ:cyclodextrin samples. Relevant spectral differences were correlated with chemical interaction between ABZ and cyclodextrins. The number and type of complexes revealed a strong dependence on the cyclodextrin group substituent. Solid-state NMR data were consistent with the presence of stable inclusion complexes. PMID:25843843

Ferreira, M João G; García, A; Leonardi, D; Salomon, Claudio J; Lamas, M Celina; Nunes, Teresa G

2015-06-01

20

Asymmetric 13C-13C polarization transfer under dipolar-assisted rotational resonance in magic-angle spinning NMR  

NASA Astrophysics Data System (ADS)

A two-dimensional (2D) homonuclear exchange NMR spectrum in solids often shows an asymmetric cross-peak pattern, which disturbs a quantitative analysis of peak intensities. When magnetization is prepared using cross polarization (CP), the asymmetry can naively be ascribed to nonequilibrium initial magnetization. We show, however, that the CP effect cannot fully explain the observed mixing-time dependence of the peak intensities in 2D C13-C13 exchange spectra of [2,3-C13] l-alanine (2,3-Ala) under C13-H1 dipolar-assisted rotational resonance (DARR) recoupling, which has recently been proposed for a broadband recoupling method under magic-angle spinning. We develop a theory to describe polarization transfer in a two-spin system under DARR recoupling. By taking into account the effects of the partial spectral overlap among C13 signals, which is a unique feature of DARR recoupling, and H1-H1 flip-flop exchange, we can successfully explain the observed mixing-time dependence of the peak intensities of 2D C13-C13 DARR exchange spectra of 2,3-Ala. A simple initial-rate analysis is also examined.

Ohashi, Ryutaro; Takegoshi, K.

2006-12-01

21

(13)C-(1)H and (13)C-(13)C NMR J-couplings in (13)C-labeled N-acetyl-neuraminic acid: correlations with molecular structure.  

PubMed

N-acetyl-neuraminic acid (Neu5Ac, 2) was prepared enzymatically containing single sites of (13)C-enrichment at C1, C2, and C3. Aqueous solutions of the three (13)C isotopomers were studied by (1)H and (13)C NMR spectroscopy at p(2)H 2 and pH 8 to obtain J(CH) and J(CC) values involving the labeled carbons. Experimental studies were complemented by DFT calculations of the same set of J-couplings in protonated and ionized structural mimics of 2 to determine how well theoretical predictions match the experimental findings in saccharides bearing ionizable functionality. Results show that: (a) (2)J(C2,H3ax/eq) values in 2 depend on anomeric configuration, thus complementing (3)J(C1,H3ax/eq) behavior, (b) J(CH) and J(CC) values involving C2 depend on anomeric configuration, the C1-C2 bond torsion, and solution pH, and (c) long-range (4)J(C2,H7) is sensitive to glycerol side-chain conformation. Intraring J(HH) and most (2)J(CH), (3)J(CH), (2)J(CC), and (3)J(CC) involving C1-C3 of 2 appear largely unaffected by the ionization state of the carboxyl group. In vacuo and solvated DFT calculations of geminal and vicinal J(CH) and J(CC) values are similar and reproduce the experimental data well, but better agreement with experiment was observed for (1)J(C1,C2) in the solvated calculations. The present work provides new information for future treatments of trans-glycoside couplings involving Neu5Ac residues by (a) providing new standard values of intraring J(CC) for coupling pathways that mimic those for trans-glycoside J(CC), (b) identifying potential effects of solution pH on trans-glycoside couplings inferred through the behavior of related intraring couplings, and (c) providing specific guidelines for more reliable DFT predictions of J(CH) and J(CC) values in ionizable saccharides. PMID:18489160

Klepach, Thomas; Zhang, Wenhui; Carmichael, Ian; Serianni, Anthony S

2008-06-20

22

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

23

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

24

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

E-print Network

Solid-State 13C NMR of Liquid Crystalline Polyesters: Variations in Morphology, Alignment, the structures of these polyesters were examined by high-resolution solid-state 13C NMR. It was found that while

Frydman, Lucio

25

In vivo 13C NMR study of glucose and lactate catabolism by isolated hindgut  

E-print Network

In vivo 13C NMR study of glucose and lactate catabolism by isolated hindgut bacteria. J Stévani 1 saturated). At time To (1-!3C) glucose or (3-!3C) lactate, 99.9% labelled, were injected in the thick was quickly degraded and gave rise to a transient C3-labelled lactate accumulation. As soon as the glucose

Paris-Sud XI, Université de

26

Applications of 1 H and 13 C NMR spectroscopy in structural investigations of Vinca indole alkaloids  

Microsoft Academic Search

This review considers the laws connecting the parameters of the1H and13C NMR spectra with the structure of the substances and the use of these laws for solving structural and stereochemical problems of theVinca indole alkaloids and other compounds of closely related structure. For each type of alkaloids, characteristic features of the PMR and13C NMR spectra are given that permit the

M. R. Yagudaev

1986-01-01

27

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

Microsoft Academic Search

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

Soon Ng

1985-01-01

28

Differentiation of Fish Oils According to Species by 13 C-NMR Regiospecific Analyses of Triacyglycerols  

Microsoft Academic Search

The aim of this study was to use 13C-nuclear magnetic resonance (NMR) regiospecific analyses of triacylglycerols to distinguish fish oils from different fish\\u000a species for authentication purposes. 13C-NMR data of muscle lipids from Atlantic salmon (Salmo salar L.), mackerel (Scomber scombrus) and herring (Clupea harengus) were obtained, and the distribution of omega-3 polyunsaturated fatty acids between the sn-1,3 and sn-2

Inger B. Standal; David E. Axelson; Marit Aursand

2009-01-01

29

Di-n-butyltin(IV) Complexes Derived from Heterocyclic ?-diketones and N-Phthaloyl Amino Acids: Preparation, Biological Evaluation, Structural Elucidation Based upon Spectral [IR, NMR (1H, 13C, 19F and 119Sn)] Studies  

PubMed Central

Stable, six coordinated Bu2SnLA type complexes have been prepared [where LH = RCOC:C(OH)N(C6 H5)N:CCH3; R = -4-F-C6H4-(L1H), R = -4-Cl-C6H4-(L2H), R= -4-Br-C6H4-(L3H), R=-CF3(L4H) and AH = C(O)C6 H4 C(O)NCHR'COOH; R'= -H(A1H), -CH3(A2H), -CH(CH3)2(A3H)] by the interaction of 1:1:1 molar ratios of di-n-butyltin(IV) dichloride with corresponding organic moieties in refluxing benzene using two moles of Et3N as a base. In these complexes LH and AH behave as bidentate and coordination is taking place through oxygen, this is inferred from IR and 13C NMR studies. These complexes possess tin atoms in skew trapezoidal bipyramidal geometry with the C-Sn-C angles ranging from 149.88° to 156.84°. Some of these complexes with their corresponding organic moieties (LH, AH) were tested for their antimicrobial activities. PMID:18365100

Verma, Shashi; Gaurb, R. B.; Sharma, R. R.

2005-01-01

30

Variability of cork from Portuguese Quercus suber studied by solid-state (13)C-NMR and FTIR spectroscopies.  

PubMed

A new approach is presented for the study of the variability of Portuguese reproduction cork using solid-state (13)C-NMR spectroscopy and photoacoustic (PAS) FTIR (FTIR-PAS) spectroscopy combined with chemometrics. Cork samples were collected from 12 different geographical sites, and their (13)C-cross-polarization with magic angle spinning (CP/MAS) and FTIR spectra were registered. A large spectral variability among the cork samples was detected by principal component analysis and found to relate to the suberin and carbohydrate contents. This variability was independent of the sample geographical origin but significantly dependent on the cork quality, thus enabling the distinction of cork samples according to the latter property. The suberin content of the cork samples was predicted using multivariate regression models based on the (13)C-NMR and FTIR spectra of the samples as reported previously. Finally, the relationship between the variability of the (13)C-CP/MAS spectra with that of the FTIR-PAS spectra was studied by outer product analysis. This type of multivariate analysis enabled a clear correlation to be established between the peaks assigned to suberin and carbohydrate in the FTIR spectrum and those appearing in the (13)C-CP/MAS spectra. PMID:11745122

Lopes, M H; Barros, A S; Pascoal Neto, C; Rutledge, D; Delgadillo, I; Gil, A M

2001-01-01

31

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

32

Isotopically enriched 13C diffusion-ordered NMR spectroscopy: analysis of methyllithium.  

PubMed

We report the development of isotopic-labeled (13)C diffusion-ordered NMR spectroscopy (DOSY) NMR with diffusion coefficient-formula weight (D-FW) analysis and its application in characterizing the aggregation state of methyllithium aggregates and complexes with several widely used diamines. Commercially available (13)C-labeled benzene and several easily synthesized (13)C-labeled compounds using (13)C-labeled iodomethane as the isotopic source are developed as internal references for diffusion-formula weight analysis (D-FW). The technique greatly expands the applicability of DOSY D-FW analysis to a much wider variety of compounds because of isotopic labeling. These results reveal that methyllithium exists as a tetrasolvated tetramer in diethyl ether and exclusively as bis-solvated dimers with chelating diamines. PMID:24134615

Su, Chicheung; Hopson, Russell; Williard, Paul G

2013-12-01

33

NMR of Enzymatically Synthesized Uniformly 13C15N-Labeled DNA Oligonucleotides  

Microsoft Academic Search

A procedure for the enzymatic synthesis of uniformly 13C15N-labeled DNA oligonucleotides in milligram quantities for NMR studies is described. Deoxynucleotides obtained from microorganisms grown on 13C and 15N nutrient sources are enzymatically phosphorylated to dNTPs, and the dNTPs are incorporated into oligonucleotides using a 3'-5' exonuclease-deficient mutant of Klenow fragment of DNA polymerase I and an oligonucleotide template primer designed

Daniel P. Zimmer; Donald M. Crothers

1995-01-01

34

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

Microsoft Academic Search

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

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

1995-01-01

35

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

36

13C INEPT Diffusion-Ordered NMR Spectroscopy (DOSY) with Internal References  

PubMed Central

13C INEPT Diffusion-Ordered NMR Spectroscopy (DOSY) with an internal reference system was developed to study the aggregation state of THF solvated LDA dimeric complex. Six components are clearly identified in the diffusion dimension and their DOSY-generated 13C INEPT spectrum slices agree extremely well with their respective INEPT spectra. The correlation between log D and log FW of the linear least squares fit to reference points of all components is exceptionally high – (r = 0.9985). PMID:18251549

Li, Deyu; Hopson, Russell; Li, Weibin; Liu, Jia; Williard, Paul G.

2011-01-01

37

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

NASA Astrophysics Data System (ADS)

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

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

1993-01-01

38

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

SciTech Connect

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

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

1980-07-01

39

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

NASA Astrophysics Data System (ADS)

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

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

1998-02-01

40

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

PubMed Central

We explore the possibility of using dynamic nuclear polarization (DNP) to enhance signals in structural studies of biological solids by solid state NMR without sample spinning. Specifically, we use 2D 13C-13C exchange spectroscopy to probe the peptide backbone torsion angles (?,?) in a series of selectively 13C-labeled 40-residue ?-amyloid (A?1–40) samples, in both fibrillar and non-fibrillar states. Experiments are carried out at 9.39 T and 8 K, using a static double-resonance NMR probe and low-power microwave irradiation at 264 GHz. In frozen solutions of A?1–40 fibrils doped with DOTOPA-TEMPO, we observe DNP signal enhancement factors of 16–21. We show that the orientation- and frequency-dependent spin polarization exchange between sequential backbone carbonyl 13C labels can be simulated accurately using a simple expression for the exchange rate, after experimentally determined homogeneous 13C lineshapes are incorporated in the simulations. The experimental 2D 13C-13C exchange spectra place constraints on the ? and ? angles between the two carbonyl labels. Although the data are not sufficient to determine ? and ? uniquely, the data do provide non-trivial constraints that could be included in structure calculations. With DNP at low temperatures, 2D 13C-13C exchange spectra can be obtained from a 3.5 mg sample of A?1–40 fibrils in 4 hr or less, despite the broad 13C chemical shift anisotropy line shapes that are observed in static samples. PMID:23562665

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

2013-01-01

41

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

42

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

43

Measuring level alignment at the metal-molecule interface by in situ electrochemical (13) C NMR.  

PubMed

A new technique to measure energy-level alignment at a metal-molecule interface between the Fermi level of the metal and the frontier orbitals of the molecule is proposed and experimentally demonstrated. The method, which combines the electrochemistry of organo-ligand-stabilized Au nanoparticles with (13) C NMR spectroscopy (i.e. in situ electrochemical NMR), enables measuring both occupied and unoccupied states. PMID:25639536

Li, Ying; Zelakiewicz, Brian S; Allison, Thomas C; Tong, YuYe J

2015-03-16

44

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

SciTech Connect

Application of sets of {sup 13}C-{sup 13}C 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 {sup 13}C-{sup 13}C distances in uniformly {sup 13}C-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 ({sup 13}C?) and aliphatic ({sup 13}C{sub aliphatic}) 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 {sup 13}C,{sup 15}N-labeled-L-isoleucine. In a more challenging biological application, FOLD 2D experiments are used to determine a large number of {sup 13}C?-{sup 13}C{sub aliphatic} distances in amyloid fibrils formed by the SNNFGAILSS fibrillating core of the human islet amyloid polypeptide with uniform {sup 13}C,{sup 15}N-labeling on the FGAIL fragment.

Straasø, Lasse Arnt; Nielsen, Jakob Toudahl; Bjerring, Morten; Nielsen, Niels Chr., E-mail: ncn@inano.au.dk [Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, DK-8000 Aarhus C (Denmark); Khaneja, Navin [Division of Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)

2014-09-21

45

Structure and orientation of dynorphin bound to lipid bilayers by 13C solid-state NMR  

NASA Astrophysics Data System (ADS)

Secondary structure and orientation of dynorphin bound to dimyristoylphosphatidylcholine (DMPC) bilayer were investigated by solid-state 13C NMR spectroscopy. For this purpose, 13C NMR spectra of the site-specifically 13C-labeled dynorphin were measured in the membrane-bound state under static, magic angle spinning (MAS), and slow MAS conditions. In the static experiment, magnetically oriented vesicle system (MOVS) induced by dynorphin was successfully used to investigate the orientation of dynorphin bound to the lipid bilayers. It was found that dynorphin adopts an ?-helical structure in the N-terminus from Gly 2 to Leu 5 by analyses of the isotropic chemical shifts obtained from the MAS experiments. In contrast, it adopts disordered conformations from the center to the C-terminus and is located on the membrane surface. The static 13C NMR spectra indicated that MOVS-bound dynorphin was oriented to the magnetic field and rotated rapidly about the bilayer normal. Subsequently, we analyzed the 13C chemical shift tensors of carbonyl carbons in the peptide backbone by considering the rotational motion of the N-terminal ?-helix. It was revealed that the N-terminal ?-helix is inserted into the membrane with the tilt angle of 21° to the bilayer normal. This structure suggests a possibility that dynorphin interacts with the extracellular loop II of the ?-receptor through a helix-helix interaction.

Uezono, Takiko; Toraya, Shuichi; Obata, Maki; Nishimura, Katsuyuki; Tuzi, Satoru; Saitô, Hazime; Naito, Akira

2005-07-01

46

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

47

QUANTITATIVE 13C NMR CHARACTERIZATION OF MILLED WOOD LIGNINS ISOLATED BY DIFFERENT MILLING TECHNIQUES  

Technology Transfer Automated Retrieval System (TEKTRAN)

MWL preparations prepared from finely milled wood flour produced by different milling techniques were compared by quantitative 13C NMR. Wiley wood meal was milled for either six weeks in a porcelain rotary mill with porcelain balls, or by two variations of our standard technique. Specifically the Wi...

48

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

E-print Network

fibers with several remarkable material properties including strength, heat stabil- ity, and chemical director, in synchrony with the acquisition of a 2D chemical shift correlation spectrum. By monitoring liquid crystal systems. © 2001 Academic Press Key Words: mesophases; two-dimensional NMR; 13 C chemical

Frydman, Lucio

49

13C CP/MAS NMR study of a genistein/piperazine complex  

NASA Astrophysics Data System (ADS)

13C CP/MAS NMR indicates that piperazine forms a hydrogen bond with the C7?OH group of genistein. The hydroxyl proton is transferred to the piperazine nitrogen atom. It is shown that the I- I*- S model of the polarization transfer in isolated spin clusters is also valid for quaternary carbon atoms.

Kolodziejski, Waclaw; Mazurek, Aleksander P.; Kasprzycka-Guttman, Teresa

2000-09-01

50

1H and 13C Solid-state NMR of Gossypium barbadense (Pima) Cotton  

Technology Transfer Automated Retrieval System (TEKTRAN)

The interaction of water with cellulose and its influence on the nuclear spin dynamics in G. barbadense (Pima) cotton were investigated by 1H and 13C solid-state NMR techniques. 1H spin diffusion results from a Goldman-Shen experiment indicate that the water is multilayered. 1H MAS experiments pro...

51

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

52

Following Glycolysis Using 13C NMR: An Experiment Adaptable to Different Undergraduate Levels  

NASA Astrophysics Data System (ADS)

This paper describes a laboratory exercise where the glycolysis of [1-13C] glucose under anaerobic conditions was followed using 13C NMR spectroscopy. The exercise is described in terms of its suitability for a variety of different undergraduate levels, although the emphasis in this paper is on its use in a n advanced chemistry laboratory course. The kinetics of the loss of glucose and the production of ethanol were investigated and found not to fit simple first or second order kinetics. In addition, the relative reaction rates of the two anomeric forms of glucose were analyzed, and it was determined that the a anomeric form reacted faster than the ? anomeric form. Using proton-coupled 13C NMR, some of the metabolites were identified including ethanol (major) and glycerol (minor). Reaction and spectroscopic details are included.

Mega, T. L.; Carlson, C. B.; Cleary, D. A.

1997-12-01

53

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

54

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

55

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

NASA Astrophysics Data System (ADS)

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

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

2001-06-01

56

Restricted internal segmental rotational diffusion model with segment-segment interactions. Application to 13C NMR  

NASA Astrophysics Data System (ADS)

The restricted rotational-diffusion model developed by Wittebort and Szabo ( J. Chem. Phys., 69, 1722 (1978)) and London and Avitabile ( J. Am. Chem. Soc., 100, 7159 (1978)) is extended to include in a mean field sense, dynamic interactions between the diffusing motional unit, and an environment that may have Fourier components on the same time scale as the reorienting unit. Furthermore in contrast to previous work, an exact closed form, analytical expression for the spectral density is derived. Illustrative calculations are presented for the spin-lattice relaxation time, T1 spin-spin relaxation time, T2, and nuclear Overhauser enhancement factor for a 13C nucleus relaxing by a dipolar mechanism with the directly bonded proton; a comparison of T1, T2, and NOE of the weak and strong coupling limits of the segment-segment dynamic interaction model is also made. It is proposed that NMR relaxation experiments be performed over a range of external field strengths H0 to differentiate between a restricted rotational model with and without dynamic interactions.

Skolnick, Jeffrey; Perchak, Dennis; Yaris, Robert

57

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

58

Structural monitoring of oligosaccharides through 13C enrichment and NMR observation of acetyl groups.  

PubMed

Structural characterization of biomolecules by NMR methods frequently requires the enrichment of magnetically active isotopes at particular molecular sites. Introduction is usually achieved biosynthetically through the use of bacterial cultures grown on isotopically enriched media, but for certain types of molecules-cell-surface carbohydrates of mammalian origin, for example-this is not practical. Here we explore a means of introducing 13C-enriched sites, postisolation in natural carbohydrate products, and illustrate an ability to acquire sufficient information to select appropriate conformational models from among energetically allowed sets. The application presented involves replacement of native N-acetyl groups with 13C-labeled acetyl groups in a simple disaccharide derivative, (GlcNAc)2-OBu, or O-butyl-chitobiose. The assignment of the two acetyl groups introduced is based on a novel combination of NMR and mass spectrometry data. Structural information is obtained from chemical shift anisotropy offsets of 13C carbonyl resonances and 13C-13C dipolar couplings between the labeled methyl and carbonyl carbons of the acetyl groups. Although the application is to a relatively simple system, it lays the groundwork for application to biologically important complex carbohydrate systems. PMID:16782783

Yu, Fei; Prestegard, J H

2006-09-01

59

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

60

A new method for the determination of specific 13C enrichment in phosphorylated [1-13C]glucose metabolites. 13C-coupled, 1H-decoupled 31P-NMR spectroscopy of tissue perchloric acid extracts.  

PubMed

A 31P-NMR method for the determination of 13C enrichment in phosphorylated [1-(13)C]glucose metabolites was developed by taking advantage of the 13C satellites detectable for 31P-NMR signals of metabolites such as UDP-hexoses, UDP-N-acetylhexosamines and other phosphorylated compounds generated during glycolysis and subsequent anabolism. HT-29 cells were incubated in culture medium containing 4.5 g/l [1-(13)C]glucose for 24 h prior to cell extraction, and high-resolution 31P-NMR spectra were acquired from perchloric acid extracts. Since glucose and its phosphorylated products are key metabolites for many different metabolic processes, this method may be very helpful for studying specific metabolic pathways involving phosphorylated glucose metabolites. PMID:8681960

Lutz, N W; Yahi, N; Fantini, J; Cozzone, P J

1996-06-01

61

13C INEPT diffusion-ordered NMR spectroscopy (DOSY) with internal references.  

PubMed

13C INEPT Diffusion-ordered NMR spectroscopy (DOSY) with an internal reference system was developed to study the aggregation state of THF-solvated LDA dimeric complex. Six components are clearly identified in the diffusion dimension, and their DOSY-generated 13C INEPT spectrum slices agree extremely well with their respective INEPT spectra. The correlation between log D and log FW of the linear least-squares fit to reference points of all components is exceptionally high: (r = 0.9985). PMID:18251549

Li, Deyu; Hopson, Russell; Li, Weibin; Liu, Jia; Williard, Paul G

2008-03-01

62

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

SciTech Connect

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

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

1990-07-01

63

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

64

13C NMR Spectroscopy for the Quantitative Determination of Compound Ratios and Polymer End Groups  

PubMed Central

13C 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 1H NMR spectroscopic integration, gas chromatography, and high-performance liquid chromatography and were found to be within <3.4% of 1H 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 1H NMR spectroscopy and matrix-assisted laser desorption-ionization time-of-flight spectrometry. PMID:24601654

2015-01-01

65

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

NASA Astrophysics Data System (ADS)

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

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

1999-08-01

66

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

NASA Astrophysics Data System (ADS)

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

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

2002-08-01

67

Dielectric and 13 C NMR studies of sulfur dioxide-hydroquinone clathrates  

Microsoft Academic Search

Dielectric measurements of SO2 quinol clathrates show that the reorientation of encaged SO2 molecules is very rapid and depends greatly on the degree of cage occupancy. For aß-quinol sample of cage occupancy? = 0.57, the reorientation rate was ~ 1 MHz at 6 K, with a reorientational activation energy of 673 J\\/mol. For a sample identified by13C NMR asa-quinol, and

D. W. Davidson; J. E. D. Davies; S. R. Gough; D. Leaist; J. A. Ripmeester

1990-01-01

68

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

Microsoft Academic Search

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

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

2000-01-01

69

An efficient procedure for studying pectin structure which combines limited depolymerization and 13 C NMR  

Microsoft Academic Search

A protocol for partial thermally-induced depolymerization of differently methoxylated pectin samples is described. The resulting\\u000a macromolecules have been fully characterized with various complementary techniques, such as size exclusion chromatography\\u000a (SEC), potentiometry, viscometry and 13C NMR. Optimum conditions afford samples at 50–80% yield with weight-average molecular weights in the 4 to 20 kDa range. The\\u000a major fraction of these polysaccharides adopts

Laurent Catoire; Renée Goldberg; Monique Pierron; Claudine Morvan; C. Hervé du Penhoat

1998-01-01

70

13C NMR determination of substituent distribution in carboxymethylcellulose by use of its peresterified derivatives  

Microsoft Academic Search

The distribution of carboxymethyl groups in a series of sodium O-(carboxymethyl)cellulose (CMC) samples was determined by 13C NMR analysis of their peresterified derivatives. Thus sodium carboxymethyl groups were first converted into methyl ester groups by treatment with dimethyl sulfate in Me2SO at 40 °C, to produce methyl-esterified CMC (MCMC). Subsequent propanoation of unsubstituted hydroxyl groups by propanoic anhydride in N,N-dimethyl-acetamide-LiCl

Yasuyuki Tezuka; Yoshikazu Tsuchiya; Tomoo Shiomi

1996-01-01

71

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

NASA Astrophysics Data System (ADS)

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

Tossell, J. A.

1995-04-01

72

Metabolism of [3-13C]pyruvate and [3-13C]propionate in normal and ischaemic rat heart in vivo: 1H- and 13C-NMR studies.  

PubMed Central

The oxidation of [3-13C]pyruvate and [3-13C]propionate was studied in vivo in infused rats. The infused [3-13C]pyruvate was quickly converted to [3-13C]lactate in the blood, and the [3-13C]lactate formed was well metabolized in both normoxic and ischaemic hearts. Large differences (200-600%) in the 13C enrichment of alanine (C-3) and acetyl-CoA (C-2) compared with lactate (C-3) were found in both normoxic and ischaemic hearts, suggesting that the extracellular [3-13C]lactate preferentially entered a region of the cytoplasm which specifically transfers the labelled pyruvate (formed from [3-13C]lactate) to the mitochondria. The highly enriched mitochondrial pyruvate gave high enrichment in alanine and acetyl-CoA, which was detected by 1H- and 13C-NMR spectroscopy. Ischaemia increased 13C incorporation into the main cytoplasmic lactate pool and decreased 13C incorporation into citric acid cycle intermediates, mainly decreasing the pyruvate anaplerosis. Isoprenaline-induced ischaemia of the heart caused only a slight decrease in pyruvate oxidation. In contrast to the decreased anaplerosis of pyruvate, the anaplerosis of propionate (and propionyl-carnitine) increased significantly in ischaemic hearts, which may contribute to the protective effect of propionyl-carnitine seen in ischaemia. In addition, we found that [3-13C]propionate preferentially labelled aspartate C-3 in rat heart, suggesting incomplete randomization of label in the succinyl-CoA-malate span of the citric acid cycle. These data show that proton observed 13C edited spectroscopic methods, i.e. heteronuclear spin-echo and the one-dimensional heteronuclear multiple quantum coherence sequence, can be successfully used to study heart metabolism in vivo. PMID:7492338

Sumegi, B; Podanyi, B; Forgo, P; Kover, K E

1995-01-01

73

Giant residual dipolar 13C-1H couplings in high-spin organoiron complexes: elucidation of their structures in solution by 13C NMR spectroscopy.  

PubMed

High-spin Fe(II)-alkyl complexes with bis(pyridylimino)isoindolato ligands were synthesized and their paramagnetic (1)H and (13)C NMR spectra were analyzed comprehensively. The experimental (13)C-(1)H coupling values are temperature (T(-1))- as well as magnetic-field (B(2))-dependent and deviate considerably from typical scalar (1)J(CH) couplings constants. This deviation is attributed to residual dipolar couplings (RDCs), which arise from partial alignment of the complexes in the presence of a strong magnetic field. The analysis of the experimental RDCs allows an unambiguous assignment of all (13)C NMR resonances and, additionally, a structural refinement of the conformation of the complexes in solution. Moreover the RDCs can be used for the analysis of the alignment tensor and hence the tensor of the anisotropy of the magnetic susceptibility. PMID:23307582

Kruck, Matthias; Wadepohl, Hubert; Enders, Markus; Gade, Lutz H

2013-01-28

74

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

ERIC Educational Resources Information Center

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

Gasyna, Zbigniew L.; Jurkiewicz, Antoni

2004-01-01

75

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

SciTech Connect

The hormonal regulation of ketogenesis in the liver of living rat has been studied noninvasively with /sup 13/C nuclear magnetic resonance. The spatial selection for the liver was better than 90%, with extrahepatic adipose tissue contribution only a very small amount of signal. The metabolic activities of the liver were investigated by infusion of /sup 13/C-labeled butyrate in the jugular vein of the anesthetized rat. The rate of butyrate infusion was chosen to be close to the maximum oxidative capacity of the rat liver, and the /sup 13/C signal intensities were enhanced by using doubly labeled (1,3-/sup 13/C)butyrate as a substrate. Different /sup 13/C NMR spectra and hence different metabolites were observed depending on the hormonal state of the animal. The /sup 13/C NMR studies demonstrate that even when rate of acetyl-CoA production are high, the disposal of this compound is not identical in fasted and diabetic animals. This supports previous suggestions that the redox state of the mitochondrion represents the most important factor in regulation. For a given metabolic state of the animal, different signal intensities were obtained depending on whether butyrate was labeled at C-1, C-3, or C-1,3. From the ratios of incorporation of /sup 13/C label into the carbons of 3-hydroxybutyrate, it could be estimated that a large fraction of butyrate evaded ..beta..-oxidation to acetyl-CoA but was converted directly to acetoacetyl-CoA. /sup 13/C-labeled glucose could be detected in vivo in the liver of diabetic rats.

Pahl-Wostl, C.; Seelig, J.

1986-11-04

76

Solid state NMR study of [epsilon-13C]Lys-bacteriorhodopsin: Schiff base photoisomerization.  

PubMed Central

Previous solid state 13C-NMR studies of bacteriorhodopsin (bR) have inferred the C = N configuration of the retinal-lysine Schiff base linkage from the [14-13C]retinal chemical shift (1-3). Here we verify the interpretation of the [14-13C]-retinal data using the [epsilon-13C]lysine 216 resonance. The epsilon-Lys-216 chemical shifts in bR555 (48 ppm) and bR568 (53 ppm) are consistent with a C = N isomerization from syn in bR555 to anti in bR568. The M photointermediate was trapped at pH 10.0 and low temperatures by illumination of samples containing either 0.5 M guanidine-HCl or 0.1 M NaCl. In both preparations, the [epsilon-13C]Lys-216 resonance of M is 6 ppm downfield from that of bR568. This shift is attributed to deprotonation of the Schiff base nitrogen and is consistent with the idea that the M intermediate contains a C = N anti chromophore. M is the only intermediate trapped in the presence of 0.5 M guanidine-HCl, whereas a second species, X, is trapped in the presence of 0.1 M NaCl. The [epsilon-13C]Lys-216 resonance of X is coincident with the signal for bR568, indicating that X is either C = N anti and protonated or C = N syn and deprotonated. PMID:8369438

Farrar, M R; Lakshmi, K V; Smith, S O; Brown, R S; Raap, J; Lugtenburg, J; Griffin, R G; Herzfeld, J

1993-01-01

77

13C and 1H NMR study of cellulose metabolism by Fibrobacter succinogenes S85.  

PubMed

Fibrobacter succinogenes S85, a cellulolytic rumen bacterium, is very efficient in degrading lignocellulosic substrates and could be used to develop a biotechnological process for the treatment of wastes. In this work, the metabolism of cellulose by F. succinogenes S85 was investigated using in vivo 13C NMR and 13C-filtered spin-echo difference 1H NMR spectroscopy. The degradation of unlabelled cellulose synthesised by Acetobacter xylinum was studied indirectly, in the presence of [1-13C]glucose, by estimating the isotopic dilution of the final bacterial fermentation products (glycogen, succinate, acetate). During the pre-incubation period of F. succinogenes cells with cellulose fibres, some cells ('non-adherent') did not attach to the solid material. Results for 'adherent' cells showed that about one fourth of the glucose units entering F. succinogenes metabolism originated from cellulose degradation. A huge reversal of succinate metabolism pathway and production of large amounts of unlabelled acetate which was observed during incubation with glucose only, was found to be much decreased in the presence of solid substrate. The synthesis of glucose 6-phophate was slightly increased in the presence of cellulose. Results clearly showed that 'non-adherent' cells were able to metabolise glucose very efficiently; consequently the metabolic state of these cells was not responsible for their 'non-adherence' to cellulose fibre. PMID:10674213

Bibollet, X; Bosc, N; Matulova, M; Delort, A M; Gaudet, G; Forano, E

2000-01-28

78

Quantitation of aliphatic suberin in Quercus suber L. cork by FTIR spectroscopy and solid-state (13)C-NMR spectroscopy.  

PubMed

This work determined that the percentage of suberin in cork may be found by solid-state (13)C cross polarization/magic angle spinning (CP/MAS) NMR spectroscopy and by FTIR with photoacoustic detection (FTIR-PAS) spectroscopy. A linear relationship is found between the suberin content measured through CP/MAS spectral areas and that measured gravimetrically. Furthermore, application of a partial least squares (PLS1) regression model to the NMR and gravimetric data sets clearly correlates the two sets, enabling suberin quantification with 90% precision. Suberin quantitation by FTIR-PAS spectroscopy is also achieved by a PLS1 regression model, giving 90% accurate estimates of the percentage of suberin in cork. Therefore, (13)C-CP/MAS NMR and FTIR-PAS proved to be useful and accurate noninvasive techniques to quantify suberin in cork, thus avoiding the traditional time consuming and destructive chemical methods. PMID:11054654

Lopes, M H; Neto, C P; Barros, A S; Rutledge, D; Delgadillo, I; Gil, A M

2000-01-01

79

NMR-based structural modeling of graphite oxide using multidimensional 13C solid-state NMR and ab initio chemical shift calculations.  

PubMed

Chemically modified graphenes and other graphite-based materials have attracted growing interest for their unique potential as lightweight electronic and structural nanomaterials. It is an important challenge to construct structural models of noncrystalline graphite-based materials on the basis of NMR or other spectroscopic data. To address this challenge, a solid-state NMR (SSNMR)-based structural modeling approach is presented on graphite oxide (GO), which is a prominent precursor and interesting benchmark system of modified graphene. An experimental 2D (13)C double-quantum/single-quantum correlation SSNMR spectrum of (13)C-labeled GO was compared with spectra simulated for different structural models using ab initio geometry optimization and chemical shift calculations. The results show that the spectral features of the GO sample are best reproduced by a geometry-optimized structural model that is based on the Lerf-Klinowski model (Lerf, A. et al. Phys. Chem. B 1998, 102, 4477); this model is composed of interconnected sp(2), 1,2-epoxide, and COH carbons. This study also convincingly excludes the possibility of other previously proposed models, including the highly oxidized structures involving 1,3-epoxide carbons (Szabo, I. et al. Chem. Mater. 2006, 18, 2740). (13)C chemical shift anisotropy (CSA) patterns measured by a 2D (13)C CSA/isotropic shift correlation SSNMR were well reproduced by the chemical shift tensor obtained by the ab initio calculation for the former model. The approach presented here is likely to be applicable to other chemically modified graphenes and graphite-based systems. PMID:20359218

Casabianca, Leah B; Shaibat, Medhat A; Cai, Weiwei W; Park, Sungjin; Piner, Richard; Ruoff, Rodney S; Ishii, Yoshitaka

2010-04-28

80

1H and 13C NMR assignments of two new indolic enamide diastereomers from a mangrove endophytic fungus Aspergillus sp.  

PubMed

Terpeptin A (1) and B (2), two new members of the indolic enamides, along with three known compounds (3-5) were identified from a strain of Aspergillus sp. (w-6), an endophytic fungus associated with Acanthus ilicifolius. The complete (1)H and (13)C NMR assignments for these compounds were carried out using (1)H, (13)C, DEPT, COSY, HMQC, and HMBC NMR experiments. Terpeptin A and B exhibited modest cytotoxicity against A-549 cell line. PMID:18846581

Lin, Zhenjian; Zhu, Tianjiao; Fang, Yuchun; Gu, Qianqun

2008-12-01

81

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

SciTech Connect

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

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

1992-02-01

82

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

SciTech Connect

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

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

1989-06-01

83

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

84

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

SciTech Connect

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

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

1999-11-19

85

13C-detected 1H dipolar magic-angle-spinning nmr experiments with isotropic mixing  

NASA Astrophysics Data System (ADS)

Cross polarization using the WIM-24 (windowless isotropic mixing) pulse sequence and also 13C-detected 1H dipolar magic-angle-spinning nuclear magnetic resonance employing the WIM-24 pulse sequence during the mixing period on a sample of the urea tridecane inclusion compound was investigated. Numerical calculations of the theoretically expected spectra were performed, using equations derived by two methods: (l) from average Hamiltonian theory and (2) the time-evolution operator obtained by multiplying together the instantaneous time-evolution operators (the multistep method). In comparisons of the calculated 13C-detected 1H dipolar MAS NMR spectra from these two methods with the experimental spectra, quantitative agreement was found only with the results from the multistep method. The effects of errors in the pulse phases and amplitude of the WIM-24 pulse sequence were investigated by computer simulations based on equations derived from the multistep method. Although the WIM-24 cross-polarization curve was changed significantly by the presence of 2° errors of the pulse phases, or 10% errors in the pulse amplitudes, the 13C-detected 1H dipolar MAS NMR spectra obtained by using the WIM24 mixing were found to be rather insensitive to those pulse imperfections. Cross-polarization curves were also calculated for the WALTZ-4 pulse sequence applied synchronously to both the 13C and the 1H channels during the mixing period to study rotational resonance effects. The calculations were performed for dipolar and J mixing. The results show that the WALTZ-4 sequence couples with the sample rotation more intensely than does the WIM-24 sequence.

Kubo, Atsushi; McDowell, Charles A.

86

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

87

Detailed 1H and 13C NMR structural assignment and relative stereochemistry determination for three closely related sesquiterpene lactones.  

PubMed

A complete analysis of (1)H and (13)C NMR spectra of the trypanocidal sesquiterpene lactone eremantholide C and two of its analogues is described. These structurally similar sesquiterpene lactones were submitted to (1)H NMR, (13)C {(1)H} NMR, gCOSY, gHSQC, gHMBC, J-resolved and DPFGSE-NOE NMR techniques. The detailed analysis of those results, correlated to some computational calculations (molecular mechanics), led to the total and unequivocal assignment of all (1)H and (13)C NMR data. The determination of all (1)H/(1)H coupling constants and all signal multiplicities, together with the elimination of previous ambiguities were also achieved. PMID:18357570

Heleno, Vladimir Constantino Gomes; de Oliveira, Kleber Thiago; Lopes, João Luis Callegari; Lopes, Norberto Peporine; Ferreira, Antonio Gilberto

2008-06-01

88

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

Microsoft Academic Search

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

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

2010-01-01

89

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

90

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

SciTech Connect

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

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

1987-09-01

91

13C-NMR study of 4-azasteroids in solution and solid state.  

PubMed

A group of biologically active 4-azasteroids was studied by 13C-NMR spectroscopy in solution and in the solid phase. A full assignment of signals in the spectra of samples in chloroform was performed for thirteen 4-azasteroids using two-dimensional techniques. Substituent and steric effects of a nitrogen atom, and their influence on chemical shifts of the neighboring carbon atoms are discussed. CP MAS spectra were obtained for five 4-azasteroids including finasteride. The spectra confirmed polymorphism of the latter compound. In addition to the polymorphic forms that are already known, a new molecular complex of finasteride with dioxane is reported. PMID:11996935

Morzycki, Jacek W; Wawer, Iwona; Gryszkiewicz, Agnieszka; Maj, Jadwiga; Siergiejczyk, Leszek; Zaworska, Alicja

2002-06-01

92

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

93

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

PubMed

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

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

2012-10-10

94

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

95

/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

96

13C-13C NMR spin-spin coupling constants in saccharides: structural correlations involving all carbons in aldohexopyranosyl rings.  

PubMed

13C-13C Spin-spin coupling constants (JCC) have been measured in a group of aldohexopyranoses and methyl aldopyranosides singly labeled with 13C at different sites to confirm and extend prior correlations between JCC magnitude and sign and saccharide structure. Structural correlations for 2JC1,C3, 2JC2,C4, 2JC4,C6, and 2JC1,C5 have been confirmed using density functional theory calculations to test empirical predictions. These geminal couplings depend highly on the orientation of C-O bonds appended to the terminal coupled carbons, but new evidence suggests that 2JCCC values are also affected by intervening carbon structure and C-O bond rotation. 3JC1,C6 and 3JC3,C6 values show Karplus-like dependences but also are affected by in-plane terminal hydroxyl substituents. In both cases, rotation about the C5-C6 bond modulates the coupling due to the alternating in-plane and out-of-plane O6. 3JC3,C6 is also affected by C4 configuration. Both 3JC1,C6 and 3JC3,C6 are subject to remote effects involving the structure at C3 and C1, respectively. New structural correlations have been determined for 2JC3,C5, which, like 3JC3,C6, shows a remote dependence on anomeric configuration. Investigations of dual pathway 13C-13C couplings, 3+3JC1,C4 and 3+3JC2,C5, revealed an important additional internal electronegative substituent effect on 3JCC in saccharides, a structural factor undocumented previously and one of importance to the interpretation of trans-glycoside 3JCOCC in oligosaccharides. PMID:17824645

Bose-Basu, Bidisha; Klepach, Thomas; Bondo, Gail; Bondo, Paul B; Zhang, Wenhui; Carmichael, Ian; Serianni, Anthony S

2007-09-28

97

Cytoplasmic malate levels in maize root tips during K+ ion uptake determined by 13C-NMR spectroscopy.  

PubMed

13C-NMR spectroscopy was used to determine the level of cytoplasmic malate in maize root tips that exhibited different rates of malate synthesis. Intracellular malate was 13C-labeled at carbons 1 and 4 by perfusing root tips with 5 nM H13CO3-. This labeling reflects the activities of phosphoenolpyruvate carboxylase and malate dehydrogenase (production of [4-13C]malate), and fumarase (scrambling of 13C-label between C1 and C4 of malate). In vivo 13C-NMR spectra contained a clearly resolved resonance from cytoplasmic [4-13C]malate, while the resonance from cytoplasmic [1-13C]malate overlapped with others. After 90 min of H13CO3- treatment, 13C-labeling of organic acid pools had reached steady-state. Thereafter, the ratios [13C]malate/[12C + 13C]malate and [1-13C]malate/[4-13C]malate in tissue extracts remained constant; evidence is presented that these ratios were the same for both cytoplasmic and total cellular malate. Hence, the intensity of the cytoplasmic [4-13C]malate signal was proportional to the amount of cytoplasmic malate in root tips. Potassium sulfate stimulate malate synthesis in maize root tips, relative to root tips perfused with HCO3- alone; total cellular malate doubled after approx. 1 h of 5 mM K2SO4-treatment. Cytoplasmic malate increased from approx. 3.5 mM to approx. 7.5 mM within 45 min of the onset of K2SO4-treatment, declining slightly thereafter. The possible effects of these changing cytoplasmic malate concentration on the enzymes involved in malate metabolism are discussed. PMID:2009309

Chang, K; Roberts, J K

1991-03-19

98

Preparation of 13C and 15N labelled RNAs for heteronuclear multi-dimensional NMR studies.  

PubMed Central

A procedure is described for the efficient preparation of isotopically enriched RNAs of defined sequence. Uniformly labelled nucleotide 5'triphosphates (NTPs) were prepared from E.coli grown on 13C and/or 15N isotopically enriched media. These procedures routinely yield 180 mumoles of labelled NTPs per gram of 13C enriched glucose. The labelled NTPs were then used to synthesize RNA oligomers by in vitro transcription. Several 13C and/or 15N labelled RNAs have been synthesized for the sequence r(GGCGCUUGCGUC). Under conditions of high salt or low salt, this RNA forms either a symmetrical duplex with two U.U base pairs or a hairpin containing a CUUG loop respectively. These procedures were used to synthesize uniformly labelled RNAs and a RNA labelled only on the G and C residues. The ability to generate milligram quantities of isotopically labelled RNAs allows application of multi-dimensional heteronuclear magnetic resonance experiments that enormously simplify the resonance assignment and solution structure determination of RNAs. Examples of several such heteronuclear NMR experiments are shown. PMID:1383927

Nikonowicz, E P; Sirr, A; Legault, P; Jucker, F M; Baer, L M; Pardi, A

1992-01-01

99

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

PubMed Central

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

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

2013-01-01

100

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

NASA Astrophysics Data System (ADS)

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

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

2001-03-01

101

sup 113 Cd and sup 13 C NMR of cadmium(II) transferrins  

SciTech Connect

The cadmium(II) derivatives of ovotransferrin and human serum transferrin have been investigated through {sup 113}Cd and {sup 13}C NMR spectroscopy. A sharp {sup 113}Cd signal due to the bound Cd(II) ion is observed at 21.6 and 11.7 ppM for ovotransferrin and human serum transferrin, respectively. These chemical shift values are consistent with the involvement of only one histidine in each metal-binding set of the protein, as indicated by the recent x-ray structure of human lactoferrin. In the {sup 13}C NMR spectra the protein-bound carbonate signal is found in both cases at 168.2 ppM, and it clearly splits into a doublet (J {approximately} 20 Hz) when the protein contains {sup 113}Cd-enriched cadmium, thus giving further evidence of direct metal-carbonate binding. The addition of the nonsynergistic anion perchlorate to the ovotransferrin derivative resulted in the removal of the bound cadmium. 29 refs., 5 figs.

Sola, M. (Univ. of Modena (Italy))

1990-03-21

102

{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

103

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

PubMed

Esterification of fatty acids with the small polar molecule carnitine is a required step for the regulated flow of fatty acids into mitochondrial inner matrix. We have studied the interactions of acyl carnitines (ACs) with model membranes [egg yolk phosphatidylcholine (PC) vesicles] by (13)C-nuclear magnetic resonance (NMR) spectroscopy. Using AC with (13)C-enrichment of the carbonyl carbon of the acyl chain, we detected NMR signals from AC on the inside and outside leaflets of the bilayer of small unilamellar vesicles prepared by cosonication of PC and AC. However, when AC was added to the outside of pre-formed PC vesicles, only the signal for AC bound to the outer leaflet was observed, even after hours at equilibrium. The extremely slow transmembrane diffusion ("flip-flop") is consistent with the zwitterionic nature of the carnitine head group and the known requirement of transport proteins for movement of ACs through the mitochondrial membrane. The partitioning of ACs (8-18 carbons) between water and PC vesicles was studied by monitoring the [(13)C]carbonyl chemical shift of ACs as a function of pH and concentration of vesicles. Significant partitioning into the water phase was detected for ACs with chain lengths of 12 carbons or less. The effect of ACs on the integrity of the bilayer was examined in vesicles with up to 25 mol% myristoyl carnitine; no gross disruption of the bilayer was observed. We hypothesize that the effects of high levels of long-chain AC (as found in ischemia or in certain diseases) on cell membranes result from molecular effects on membrane functions rather than from gross disruption of the lipid bilayer. PMID:12235174

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

2002-09-01

104

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

PubMed

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

Henderson, Terry J; Cullinan, David B

2007-11-01

105

Estimation of glucose carbon recycling in children with glycogen storage disease: A sup 13 C NMR study using (U- sup 13 C)glucose  

SciTech Connect

A stable isotope procedure to estimate hepatic glucose carbon recycling and thereby elucidate the mechanism by which glucose is produced in patients lacking glucose 6-phosphatase is described. A total of 10 studies was performed in children with glycogen storage disease type I (GSD-I) and type III (GSD-III) and control subjects. A primed dose-constant nasogastric infusion of D-(U-{sup 13}C)glucose or an infusion diluted with nonlabeled glucose solution was administered following different periods of fasting. Hepatic glucose carbon recycling was estimated from {sup 13}C NMR spectra. The values obtained for GSD-I patients coincided with the standard (U-{sup 13}C)glucose dilution curve. These results indicate that the plasma glucose of GSD-I subjects comprises only a mixture of 99% {sup 13}C-enriched D-(U-{sup 13}C)glucose and unlabeled glucose but lacks any recycled glucose. Significantly different glucose carbon recycling values were obtained for two GSD-III patients in comparison to GSD-I patients. The results eliminate a mechanism for glucose production in GSD-I children involving gluconeogenesis. However, glucose release by amylo-1,6-glucosidase activity would result in endogenous glucose production of non-{sup 13}C-labeled and nonrecycled glucose carbon, as was found in this study. In GSD-III patients gluconeogenesis is suggested as the major route for endogenous glucose synthesis. The contribution of the triose-phosphate pathway in these patients has been determined.

Kalderon, B.; Korman, S.H.; Gutman, A.; Lapidot, A. (Weizmann Institute of Science, Rehovot (Israel))

1989-06-01

106

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 13C13C exchange spectrum of selectively 13C-labeled ?-amyloid fibrils. PMID:22743540

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

2012-01-01

107

The entry of [1- 13C]glucose into biochemical pathways reveals a complex compartmentation and metabolite trafficking between glia and neurons: a study by 13C-NMR spectroscopy  

Microsoft Academic Search

Glial–neuronal interactions were investigated in rats injected intraperitoneally with [1-13C]glucose and killed after 15, 30, 45, or 60 min. Brain extracts were analyzed by 13C-NMR spectroscopy and the fractional 13C-enrichment at individual carbon positions was measured for amino acids, lactate, and N-acetyl-aspartate. [1-13C]Glucose was shown to be metabolized by both neurons and glia, with the anaplerotic pathway through pyruvate carboxylase

Tommaso Aureli; Maria Enrica Di Cocco; Menotti Calvani; Filippo Conti

1997-01-01

108

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

USGS Publications Warehouse

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

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

1991-01-01

109

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

110

Acetate and Bicarbonate Assimilation and Metabolite Formation in Chlamydomonas reinhardtii: A 13C-NMR Study  

PubMed Central

Cellular metabolite analyses by 13C-NMR showed that C. reinhardtii cells assimilate acetate at a faster rate in heterotrophy than in mixotrophy. While heterotrophic cells produced bicarbonate and CO2aq, mixotrophy cells produced bicarbonate alone as predominant metabolite. Experiments with singly 13C-labelled acetate (13CH3-COOH or CH3-13COOH) supported that both the 13C nuclei give rise to bicarbonate and CO2aq. The observed metabolite(s) upon further incubation led to the production of starch and triacylglycerol (TAG) in mixotrophy, whereas in heterotrophy the TAG production was minimal with substantial accumulation of glycerol and starch. Prolonged incubation up to eight days, without the addition of fresh acetate, led to an increased TAG production at the expense of bicarbonate, akin to that of nitrogen-starvation. However, such TAG production was substantially high in mixotrophy as compared to that in heterotrophy. Addition of mitochondrial un-coupler blocked the formation of bicarbonate and CO2aq in heterotrophic cells, even though acetate uptake ensued. Addition of PSII-inhibitor to mixotrophic cells resulted in partial conversion of bicarbonate into CO2aq, which were found to be in equilibrium. In an independent experiment, we have monitored assimilation of bicarbonate via photoautotrophy and found that the cells indeed produce starch and TAG at a much faster rate as compared to that in mixotrophy and heterotrophy. Further, we noticed that the accumulation of starch is relatively more as compared to TAG. Based on these observations, we suggest that acetate assimilation in C. reinhardtii does not directly lead to TAG formation but via bicarbonate/CO2aq pathways. Photoautotrophic mode is found to be the best growth condition for the production of starch and TAG and starch in C. reinhardtii. PMID:25207648

Singh, Himanshu; Shukla, Manish R.; Chary, Kandala V. R.; Rao, Basuthkar J.

2014-01-01

111

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

PubMed Central

Heparin is a polydisperse sulphated copolymer consisting mostly of 1-->4 linked glucosamine and uronic acid residues, i.e. 2-deoxy-2-sulphamido-D-glucopyranose 6-sulphate and L-idopyranosyluronic acid 2-sulphate. 13C NMR has been used to study the interactions of heparinase-derived and purified heparin disaccharide with N- and C-terminally-blocked tripeptides GRG and GKG. Titration of the disaccharide with peptide indicates that GRG binds the disaccharide more strongly than does GKG, with interactions in either case being stronger at uronate ring positions. In the presence of GRG, a carboxylate pKa depression suggests electrostatic interactions between the arginine guanidinium group and the uronate carboxylate group. 13C relaxation data have been acquired for all disaccharide and peptide carbons in the presence and absence of GRG and GKG. 13C relaxation rates for the disaccharide are significantly faster in the presence of peptide, especially with GRG. Analysis of these relaxation data has been done in terms of molecular diffusion constants, D [symbol: see text] and D parallel, and an angle alpha between D parallel and a molecular frame defined by the moment of inertia tensor calculated for an internally rigid disaccharide. Disaccharide conformational space in these calculations has been sampled for both uronate half-chair forms (2H1 and 1H2) and over a range of glycosidic bond angles defined by motional order parameters and inter-residue nuclear Overhauser effects (+/- 30 degree from the average). In the absence of peptide, the ratio D [symbol: see text] /D parallel falls between 0.4 and 0.7; therefore molecular diffusion occurs preferentially about D parallel, which runs through both disaccharide rings. In the presence of peptide, D [symbol: see text] /D parallel is decreased, indicating that GRG is oriented along D parallel and proximal to the uronic acid ring. A model for this is shown. PMID:8615813

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

1996-01-01

112

Mapping cerebral glutamate 13C turnover and oxygen consumption by in vivo NMR.  

PubMed

Regional rates of 13C incorporation from glucose to glutamate were detected in anesthetized rat brain in vivo at 7T with high temporal and spatial resolution using NMR method ICED PEPSI (in vivo carbon edited detection with proton echo planar spectroscopic imaging). Time courses of regional glutamate 13C turnover were fitted by a metabolic model to obtain regional tri-carboxylic acid (TCA) cycle flux and cerebral metabolic rate of oxygen consumption (CMRO2) in each voxel (8 microL) of rat cortex. CMRO2 maps obtained for rats under either alpha-chloralose or morphine anesthesia revealed average cortical values of 1.5 +/- 0.2 (n = 3) and 3.2 +/- 0.3 (n = 4) mumol/g/min, respectively. These values of CMRO2 are in good agreement with previous cortical measurements with coarser spatial resolution. The heterogeneity within each map, which depicted predominantly gray and white matter differences, was significantly greater under morphine (higher cortical activity) than under-alpha-chloralose (lower cortical activity) anesthesia. The regional variations in the basal awake state, which are expected to be even greater, should be considered to avoid partial-volume artifacts in functional activation studies of awake subjects. PMID:14562702

Hyder, Fahmeed; Brown, Peter; Nixon, Terennce W; Behar, Kevin L

2003-01-01

113

Partial NMR assignments for uniformly (13C, 15N)-enriched BPTI in the solid state.  

PubMed

We demonstrate that high-resolution multidimensional solid state NMR methods can be used to correlate many backbone and side chain chemical shifts for hydrated micro-crystalline U-13C,15N Basic Pancreatic Trypsin Inhibitor (BPTI), using a field strength of 800 MHz for protons, magic angle sample spinning rates of 20 kHz and proton decoupling field strengths of 140 kHz. Results from two homonuclear transfer methods, radio frequency driven dipolar recoupling and spin diffusion, were compared. Typical 13C peak line widths are 0.5 ppm, resulting in Calpha-Cbeta and Calpha-CO regions that exhibit many resolved peaks. Two-dimensional carbon-carbon correlation spectra of BPTI have sufficient resolution to identify and correlate many of the spin systems associated with the amino acids. As a result, we have been able to assign a large number of the spin systems in this protein. The agreement between shifts measured in the solid state and those in solution is typically very good, although some shifts near the ion binding sites differ by at least 1.5 ppm. These studies were conducted with approximately 0.2 to 0.4 micromol of enriched material; the sensitivity of this method is apparently adequate for other biological systems as well. PMID:10805127

McDermott, A; Polenova, T; Bockmann, A; Zilm, K W; Paulson, E K; Martin, R W; Montelione, G T; Paulsen, E K

2000-03-01

114

Cigarette butt decomposition and associated chemical changes assessed by 13C CPMAS NMR.  

PubMed

Cigarette butts (CBs) are the most common type of litter on earth, with an estimated 4.5 trillion discarded annually. Apart from being unsightly, CBs pose a serious threat to living organisms and ecosystem health when discarded in the environment because they are toxic to microbes, insects, fish and mammals. In spite of the CB toxic hazard, no studies have addressed the effects of environmental conditions on CB decomposition rate. In this study we investigate the interactive effects of substrate fertility and N transfer dynamics on CB decomposition rate and carbon quality changes. We carried out an experiment using smoked CBs and wood sticks, used as a slow decomposing standard organic substrate, incubated in both laboratory and field conditions for two years. CB carbon quality changes during decomposition was assessed by 13C CPMAS NMR. Our experiment confirmed the low degradation rate of CBs which, on average, lost only 37.8% of their initial mass after two years of decomposition. Although a net N transfer occurred from soil to CBs, contrary to our hypothesis, mass loss in the medium-term (two years) was unaffected by N availability in the surrounding substrate. The opposite held for wood sticks, in agreement with the model that N-rich substrates promote the decomposition of other N-poor natural organic materials with a high C/N ratio. As regards CB chemical quality, after two years of decomposition 13C NMR spectroscopy highlighted very small changes in C quality that are likely to reflect a limited microbial attack. PMID:25625643

Bonanomi, Giuliano; Incerti, Guido; Cesarano, Gaspare; Gaglione, Salvatore A; Lanzotti, Virginia

2015-01-01

115

Cigarette Butt Decomposition and Associated Chemical Changes Assessed by 13C CPMAS NMR  

PubMed Central

Cigarette butts (CBs) are the most common type of litter on earth, with an estimated 4.5 trillion discarded annually. Apart from being unsightly, CBs pose a serious threat to living organisms and ecosystem health when discarded in the environment because they are toxic to microbes, insects, fish and mammals. In spite of the CB toxic hazard, no studies have addressed the effects of environmental conditions on CB decomposition rate. In this study we investigate the interactive effects of substrate fertility and N transfer dynamics on CB decomposition rate and carbon quality changes. We carried out an experiment using smoked CBs and wood sticks, used as a slow decomposing standard organic substrate, incubated in both laboratory and field conditions for two years. CB carbon quality changes during decomposition was assessed by 13C CPMAS NMR. Our experiment confirmed the low degradation rate of CBs which, on average, lost only 37.8% of their initial mass after two years of decomposition. Although a net N transfer occurred from soil to CBs, contrary to our hypothesis, mass loss in the medium-term (two years) was unaffected by N availability in the surrounding substrate. The opposite held for wood sticks, in agreement with the model that N-rich substrates promote the decomposition of other N-poor natural organic materials with a high C/N ratio. As regards CB chemical quality, after two years of decomposition 13C NMR spectroscopy highlighted very small changes in C quality that are likely to reflect a limited microbial attack. PMID:25625643

Bonanomi, Giuliano; Incerti, Guido; Cesarano, Gaspare; Gaglione, Salvatore A.; Lanzotti, Virginia

2015-01-01

116

Characterization of microbial poly (?- L-lysine) by FT-IR, Raman and solid state 13C NMR spectroscopies  

NASA Astrophysics Data System (ADS)

The molecular structure and conformation of microbial poly(?- L-lysine) (M-?-PL) produced by a variant of Streptomyces albulus were studied by means of FT-IR, FT-Raman and solid-state 13C NMR spectroscopies. Vibrational results indicate that M-?-PL assumes a ?-sheet conformation in the solid state. Solid state 13C NMR spectra of the crystalline and the amorphous components were observed separately and the degree of crystallinity was estimated to be 63%. A plausible conformation model was proposed.

Maeda, Shiro; Kunimoto, Ko-Ki; Sasaki, Chizuru; Kuwae, Akio; Hanai, Kazuhiko

2003-07-01

117

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

118

Hyperpolarized (13)C spectroscopy and an NMR-compatible bioreactor system for the investigation of real-time cellular metabolism.  

PubMed

The purpose of this study was to combine a three-dimensional NMR-compatible bioreactor with hyperpolarized (13)C NMR spectroscopy in order to probe cellular metabolism in real time. JM1 (immortalized rat hepatoma) cells were cultured in a three-dimensional NMR-compatible fluidized bioreactor. (31)P spectra were acquired before and after each injection of hyperpolarized [1-(13)C] pyruvate and subsequent (13)C spectroscopy at 11.7 T. (1)H and two-dimensional (1)H-(1)H-total correlation spectroscopy spectra were acquired from extracts of cells grown in uniformly labeled (13)C-glucose, on a 16.4 T, to determine (13)C fractional enrichment and distribution of (13)C label. JM1 cells were found to have a high rate of aerobic glycolysis in both two-dimensional culture and in the bioreactor, with 85% of the (13)C label from uniformly labeled (13)C-glucose being present as either lactate or alanine after 23 h. Flux measurements of pyruvate through lactate dehydrogenase and alanine aminotransferase in the bioreactor system were 12.18 +/- 0.49 nmols/sec/10(8) cells and 2.39 +/- 0.30 nmols/sec/10(8) cells, respectively, were reproducible in the same bioreactor, and were not significantly different over the course of 2 days. Although this preliminary study involved immortalized cells, this combination of technologies can be extended to the real-time metabolic exploration of primary benign and cancerous cells and tissues prior to and after therapy. PMID:20099325

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

2010-02-01

119

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

Microsoft Academic Search

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

Kristina Wickholm; Per Tomas Larsson; Tommy Iversen

1998-01-01

120

Simple method for identification of skeletons of aporphine alkaloids from 13C NMR data using artificial neural networks.  

PubMed

This paper describes the use of artificial neural networks as a theoretical tool in the structural determination of alkaloids from (13)C NMR chemical shift data, aiming to identify skeletal types of those compounds. For that, 162 aporphine alkaloids belonging to 12 different skeletons were codified with their respective (13)C NMR chemical shifts. Each skeleton pertaining to aporphine alkaloid type was used as output, and the (13)C NMR chemical shifts were used as input data of the net. Analyzing the obtained results, one can then affirm the skeleton to which each one of these compounds belongs with high degree of confidence (over 97%). The relation between the correlation coefficient and the number of epochs and the architecture of net (3-layer MLP or 4-layer MLP) were analyzed, too. The analysis showed that the results predicted by the 3-layer MLP networks trained with a number of the epochs higher than 900 epochs are the best ones. The artificial neural nets were shown to be a simple and efficient tool to solve structural elucidation problems making use of (13)C NMR chemical shift data, even when a similarity between the searched skeletons occurs, offering fast and accurate results to identification of skeletons of organic compounds. PMID:15921454

Rufino, Alessandra R; Brant, Antônio J C; Santos, João B O; Ferreira, Marcelo J P; Emerenciano, Vicente P

2005-01-01

121

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

Microsoft Academic Search

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

Moses O Adebajo; Ray L Frost

2004-01-01

122

Determination of octane numbers of gasoline compounds from their chemical structure by 13C NMR spectroscopy and neural networks  

Microsoft Academic Search

A new theoretical model has been developed which explains the association between the molecular structure and the knock resistance of individual gasoline compounds convincingly. The constitutions of more than 300 individual gasoline components were correlated with their knock rating (Blending Research Octane Number, BRON) simultaneously. 13C NMR spectra of all compounds were binned in 28 chemical shift regions of different

R. Meusinger; R. Moros

2001-01-01

123

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

124

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

125

A Novel Model-Free Analysis of 13C NMR Relaxation of Alanine-Methyl Side-Chain Motions in Peptides  

NASA Astrophysics Data System (ADS)

Alanine residues in two peptide sequences derived from the ?- sheet domain of platelet factor-4: IA*TLK(P5) and TAQL IA*TLKNGRKICLDLQA (P20), were synthesized with 13C enriched in C ?and C ?positions. 13C NMR relaxation measurements (proton coupled and decoupled) were performed at two NMR frequencies (150 and 62.5 MHz) and over a wide range of temperatures (5 to 75°C) to study motional dynamics of the alanine side-chain methyl group and alanine side-chain-backbone motional correlations. Cross-correlation spectral densities, JHCH(? C), for C ?H 3in both peptides are positive, indicating methyl-group rotational anisotropy. Various rotational models and model-free approaches have been used to analyze NMR relaxation data. The overall correlation times show a stronger temperature dependence in P20 than in P5, indicating the influence on alanine motions of folded conformational populations in P20. For analysis of alanine side-chain motions, an alternative model-free approach parameterized with a novel mixing parameter, A2, that depends on the "geometry" of C ?-C ?and C ?-H bond rotations is proposed. By plotting the standard order parameter S2versus A2, motional models may be visually differentiated. Molecular dynamics calculations were performed to compare C ?-C ?and C ?-H motions. Significant anti-correlated ?( t) and ?( t) backbone rotations can explain NMR relaxation data for P20.

Daragan, Vladimir A.; Mayo, Kevin H.

126

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

PubMed

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

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

2013-05-28

127

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

128

(13)C CP MAS NMR and crystal structure of methyl glycopyranosides.  

PubMed

The X-ray diffraction analysis, (13)C CP MAS NMR spectra and powder X-ray diffraction patterns were obtained for selected methyl glycosides: alpha- and beta-d-lyxopyranosides (1, 2), alpha- and beta-l-arabinopyranosides (3, 4), alpha- and beta-d-xylopyranosides (5, 6) and beta-d-ribopyranoside (7) and the results were confirmed by GIAO DFT calculations of shielding constants. In X-ray diffraction analysis of 1 and 2, a characteristic shortening and lengthening of selected bonds was observed in molecules of 1 due to anomeric effect and, in crystal lattice of 1 and 2, hydrogen bonds of different patterns were present. Also, an additional intramolecular hydrogen bond with the participation of ring oxygen atom was observed in 1. The observed differences in chemical shifts between solid state and solution come from conformational effects and formation of various intermolecular hydrogen bonds. The changes in chemical shifts originating from intermolecular hydrogen bonds were smaller in magnitude than conformational effects. Furthermore, the powder X-ray diffraction (PXRD) performed for 4, 5 and 7 revealed that 7 existed as a mixture of two polymorphs, and one of them probably consisted of two non-equivalent molecules. PMID:18547551

Paradowska, Katarzyna; Gubica, Tomasz; Temeriusz, Andrzej; Cyra?ski, Micha? K; Wawer, Iwona

2008-09-01

129

Metabolic Effects of Hypoxia in Colorectal Cancer by 13C NMR Isotopomer Analysis  

PubMed Central

13C NMR isotopomer analysis was used to characterize intermediary metabolism in three colorectal cancer cell lines (WiDr, LS1034, and C2BBe1) and determine the “metabolic remodeling” that occurs under hypoxia. Under normoxia, the three colorectal cancer cell lines present high rates of lactate production and can be seen as “Warburg” like cancer cells independently of substrate availability, since such profile was dominant at both high and low glucose media contents. The LS1034 was the less glycolytic of the three cell lines and was the most affected by the event of hypoxia, raising abruptly glucose consumption and lactate production. The other two colorectal cell lines, WiDr and C2BBe1, adapted better to hypoxia and were able to maintain their oxidative fluxes even at the very low levels of oxygen. These differential metabolic behaviors of the three colorectal cell lines show how important an adequate knowledge of the “metabolic remodeling” that follows a given cancer treatment is towards the correct (re)design of therapeutic strategies against cancer. PMID:25093181

Abrantes, Ana M.; Tavares, Ludgero C.; Casalta-Lopes, João; Mendes, Cândida; Grazina, Manuela M.; Carvalho, Rui A.; Botelho, Maria Filomena

2014-01-01

130

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

131

A 13C-NMR study of the inhibition of papain by a dipeptide-glyoxal inhibitor.  

PubMed Central

Z-Phe-Ala-glyoxal (where Z is benzyloxycarbonyl) has been synthesized and shown to be a competitive inhibitor of papain with a K(i)=3.30+/-0.25 nM. (13)C-NMR has been used to show that in aqueous media, Z-Phe-[2-(13)C]Ala-glyoxal gives signals at 207.7 p.p.m. and 96.3 p.p.m. showing that both the alpha-keto carbon and its hydrate are present. When this inhibitor is bound to papain a single signal at 209.7 p.p.m. is observed due to the (13)C-enriched carbon. This demonstrates that the glyoxal alpha-keto carbon is not hydrated when it is bound to papain and that it does not form a thiohemiketal with the thiol group of Cys-25. Z-Phe-[1-(13)C]Ala-glyoxal has also been synthesized and its aldehyde carbon is fully hydrated in aqueous solution giving signals at 88.7 p.p.m. and 90.2 p.p.m. when the alpha-keto carbon and its hydrate are present respectively. When this inhibitor is bound to papain a single signal at 71.04 p.p.m. was observed due to the (13)C-enriched carbon showing that the (13)C-enriched aldehyde carbon forms a thiohemiacetal with Cys-25. PMID:12061892

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

2002-01-01

132

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

SciTech Connect

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

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

1989-02-15

133

Relaxation-compensated difference spin diffusion NMR for detecting (13)C- (13)C long-range correlations in proteins and polysaccharides.  

PubMed

The measurement of long-range distances remains a challenge in solid-state NMR structure determination of biological macromolecules. In 2D and 3D correlation spectra of uniformly (13)C-labeled biomolecules, inter-residue, inter-segmental, and intermolecular (13)C-(13)C cross peaks that provide important long-range distance constraints for three-dimensional structures often overlap with short-range cross peaks that only reflect the covalent structure of the molecule. It is therefore desirable to develop new approaches to obtain spectra containing only long-range cross peaks. Here we show that a relaxation-compensated modification of the commonly used 2D (1)H-driven spin diffusion (PDSD) experiment allows the clean detection of such long-range cross peaks. By adding a z-filter to keep the total z-period of the experiment constant, we compensate for (13)C T1 relaxation. As a result, the difference spectrum between a long- and a scaled short-mixing time spectrum show only long-range correlation signals. We show that one- and two-bond cross peaks equalize within a few tens of milliseconds. Within ~200 ms, the intensity equilibrates within an amino acid residue and a monosaccharide to a value that reflects the number of spins in the local network. With T1 relaxation compensation, at longer mixing times, inter-residue and inter-segmental cross peaks increase in intensity whereas intra-segmental cross-peak intensities remain unchanged relative to each other and can all be subtracted out. Without relaxation compensation, the difference 2D spectra exhibit both negative and positive intensities due to heterogeneous T1 relaxation in most biomolecules, which can cause peak cancellation. We demonstrate this relaxation-compensated difference PDSD approach on amino acids, monosaccharides, a crystalline model peptide, a membrane-bound peptide and a plant cell wall sample. The resulting difference spectra yield clean multi-bond, inter-residue and intermolecular correlation peaks, which are often difficult to resolve in the parent 2D spectra. PMID:25510834

Wang, Tuo; Williams, Jonathan K; Schmidt-Rohr, Klaus; Hong, Mei

2015-02-01

134

Complete assignment of the 1H and 13C NMR spectra of garciniaphenone and keto-enol equilibrium statements for prenylated benzophenones.  

PubMed

This article reports the structural elucidation by IR, UV and MS spectroscopic data along with 1H and 13C NMR chemical shift assignments of two benzophenones isolated from the fruit pericarp of Garcinia brasiliensis Mart. (Clusiaceae): garciniaphenone, (1R,5S,7S)-3-benzoyl-4-hydroxy-6,6-dimethyl-5,7-di(3-methyl-2-butenyl)bicyclo[3.3.1]non-3-ene-2,9-dione, a novel triprenylated benzophenone; and 7-epi-clusianone, a tetraprenylated benzophenone that has already been extracted from another species of the same family. Furthermore, the keto-enol tautomeric equilibrium at solution-state was described for these compounds by 1D and 2D NMR spectral methods and one attempt to rationalize the different ratios between the noted tautomers was based on stereochemical features. PMID:18236418

Derogis, Priscilla B M C; Martins, Felipe T; de Souza, Thiago C; de C Moreira, Maria E; Souza Filho, José D; Doriguetto, Antonio C; de Souza, Kamila R D; Veloso, Marcia P; Dos Santos, Marcelo H

2008-03-01

135

Higher-Rank Correlation NMR Spectra with Spectral Moment Filtering  

PubMed Central

Higher-rank correlation spectroscopy is introduced as an alternative to 3D Fourier-transform (FT) NMR spectroscopy for resonance assignment and molecular structure determination. The method combines standard 2D FT spectra that share a common frequency dimension, such as a 2D 13C-1H HSQC and a 2D 1H-1H TOCSY spectrum, and constructs higher-rank correlation spectra with ultra-high spectral resolution. Spectral overlap along a common dimension, in particular the 1H dimension, is addressed by a spectral filtering method, which identifies mismatches between the 1st and 2nd moments of cross-peak profiles. The method, which provides a substantial speed-up over traditional 3D FT spectroscopy while effectively suppressing false peaks, is demonstrated for the triple-rank 13C-1H HSQC-TOCSY spectrum of a cyclic decapeptide with different mixing times. Higher-rank correlation spectroscopy is usefully applicable to the analysis of a wide range of NMR spectra of synthetic and natural products. PMID:20436937

Bingol, Kerem; Salinas, Roberto K.; Brüschweiler, Rafael

2010-01-01

136

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

137

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

PubMed

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

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

2003-07-22

138

High-field 13C NMR spectroscopy of tissue in Vivo. A double-resonance surface-coil probe  

NASA Astrophysics Data System (ADS)

A double-resonance surface-coil NMR probe is described for performance of high-field (8.5 T) proton decoupled carbon-13 experiments with tissue in vivo. The probe may be accommodated in standard, 89 mm i.d. clear bore, commercial spectrometers and is suitable for studies utilizing small laboratory animals such as mice, hamsters, and rats. A coaxial coil design is employed (10 mm diameter 13C coil, 20 mm diameter 1H coil) which provides ca. 40 dB attenuation between the 13C observe and 1H decouple channels. The inherent efficiency of the surface-coil configuration provides a sensitivity comparable to a commercial probe of the same nominal dimension (10 mm Helmholtz coil) and assures adequate decoupling in conductive samples with ca. 3-5 W power. In the absence of 13C isotopic enrichment, NMR spectra of rat leg, liver, and brain in vivo provide signalto-noise sufficient for 10 min time resolution. Administration of 100 mg of 90% 13C-labeled glucose into a peripheral vein of a ca. 300 g rat resulted in a liver glucose resonance which could be monitored with good signal-to-noise and 3 min time resolution.

Reo, Nicholas V.; Ewy, Coleen S.; Siegfried, Barry A.; Ackerman, Joseph J. H.

139

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

Microsoft Academic Search

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

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

140

1H and 13C NMR spectra and solution structures of novel derivatives of 5-substituted creatinines  

Microsoft Academic Search

Five creatinine derivatives were prepared by the treatment of creatinine with activated carbon and appropriate alcohol (1–4), or ammonia solution (5). Product structures were determined by 1H and 13C NMR spectroscopy in solution, including 2D HSQC and HMBC experiments. Then, the proton and carbon chemical shifts for these compounds were calculated using GIAO–DFT [B3LYP\\/6-311G(2d,p)] method and the Gaussian 03W program

Hanna Krawczyk; Agnieszka Pietras; Anna Kraska

2007-01-01

141

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

Microsoft Academic Search

13C NMR spectra of 1,3-dimethylbarbituric acid in aqueous solutions of various acidities and for various solute concentrations have been recorded and interpreted. The spectra recorded at pH=2 and below contain the signals of the neutral solute molecule exclusively, while the ones recorded at pH=7 and above only the signals of the appropriate anion, which has been confirmed by theoretical GIAO-DFT

A. Gryff-Keller; A. Kraska-Dziadecka

142

Dynamic mechanical analysis (DMA), 13 c solid state nmr and micro-thermomechanical studies of historical parchment  

Microsoft Academic Search

DMA and solid state 13C NMR techniques were used to measure historical parchment samples within the framework of the project (MAP) Micro Analysis\\u000a of Parchment (EC contract No. SMT4-96-2101) in collaboration with the School of Conservation in Copenhagen. DMA was used in\\u000a both thermal scan and creep modes. Thermal scans provided information on the transitions associated with the collagen polymer.

M. Odlyha; N. S. Cohen; G. M. Foster; A. Aliev; E. Verdonck; D. Grandy

2003-01-01

143

sup 13 C NMR investigation of the anomeric specificity of CMP-N-acetylneuraminic acid synthetase from Escherichia coli  

SciTech Connect

The anomeric specificity of Escherichia coli CMP-N-acetylneuraminic acid (CMP-NeuAc) synthetase was investigated by NMR using {sup 13}C-labeled N-acetylneuraminic acid (NeuAc). Consumption of the {beta}-anomer of (2-{sup 13}C)N-acetylneuraminic acid was observed upon addition of enzyme, with a concomitant appearance of an anomeric resonance for CMP-N-acetylneuraminic acid. Inhibition by substrate analogues confirms the importance of the anomeric center for interaction of substrate with the enzyme. The fate of the anomeric oxygen was determined in a similar manner using (2-{sup 13}C,(50 atom %){sup 18}O)N-acetylneuraminic acid. An upfield shift of 1.5 Hz in the anomeric resonance of both the ({sup 13}C)NeuAc substrate and CMP-({sup 13}C)NeuAc product was observed due to the {sup 18}O substitution. This result implies conservation of the NeuAc oxygen. Results of steady-state kinetic analysis suggest a sequential-type mechanism and therefore no covalent intermediate. Thus, CMP-{beta}-NeuAc is probably formed by a direct transfer of the anomeric oxygen of {beta}-NeuAc to the {alpha}-phosphate of CTP.

Ambrose, M.G.; Freese, S.J.; Reinhold, M.S.; Vann, W.F. (Food and Drug Administration, Bethesda, MD (United States)); Warner, T.G. (Genentech Inc., San Francisco, CA (United States))

1992-01-28

144

1H and 13C NMR of 3-O and 4-O conjugates of dopamine and other catecholamines.  

PubMed

Dopamine and its conjugates are widely distributed among biological species and are utilized for a variety of functions. Insects metabolize dopamine for cuticle melanization and sclerotization. Among the most abundant dopamines found in the larval and pupal development stages of Manduca sexta, the tobacco hornworm, are N-acetyldopamine and N-beta-alanyldopamine. In addition, glycosylated derivatives of these dopamines are found mainly in the hemolymph just prior to cuticulogenesis. The 1H and 13C NMR resonances of dopamine, its 3-O-methyl, 4-O-methyl, N-acetyl, and N-beta-alanyl derivatives, norepinephrine, 4-O-(beta-D-glucuronopyranosyl)dopamine, and the glycosylated products of N-beta-alanyldopamine and dopamine have largely been assigned. Assignments were based on one- and two-dimensional NMR analyses of the above compounds combined with that of specifically enriched [C7-13C]dopamine. 1H NMR showed that the major glycosylated natural product isolated from M. sexta pupal hemolymph was a 3-O-glycosyl derivative of N-beta-alanyldopamine. 13C NMR confirmed that the carbohydrate was D-glucose probably in a beta-linkage. 1H NMR of the aromatic ring protons provided the most definitive method to distinguish 3-O- from 4-O-derivatives of dopamine. In addition, the 3-O-glucosyl conjugate of N-beta-alanyldopamine had unique chemical shifts and coupling patterns compared to those of 4-O-(beta-D-glucuronosyl)- and 3-O-(beta-D-glucopyranosyl)dopamine. PMID:8431512

Mueller, D D; Morgan, T D; Wassenberg, J D; Hopkins, T L; Kramer, K J

1993-01-01

145

Combined experimental and theoretical studies on the X-ray crystal structure, FT-IR, 1H NMR, 13C NMR, UV-Vis spectra, NLO behavior and antimicrobial activity of 2-hydroxyacetophenone benzoylhydrazone.  

PubMed

A Schiff base ligand, 2-hydroxyacetophenone benzoylhydrazone (HL) was synthesized and fully characterized with FT-IR, elemental analyses, UV-Vis, (1)H NMR and (13)C NMR spectra. DFT calculations using B3LYP/6-31+G(d,p) and PW91/DZP are performed to optimize the molecular geometry. Optimized structures are used to calculate FT-IR, UV-Vis, (1)H NMR and (13)C NMR spectra of the compound. Also the energies of the frontier molecular orbitals (FMOs) have been determined. The results obtained from the optimization and spectral analyses are in good agreement with the experimental data. To investigate non-linear optical properties, the electric dipole moment (?), polarizability (?) and molecular first hyperpolarizability (?) were computed. The linear polarizabilities and first hyperpolarizabilities of the studied molecule indicate that the compound can be a good candidate of nonlinear optical materials. In addition, the minimal inhibitory concentration (MIC) of this compound against Staphylococcus aureus, and Candida albicans was determined. PMID:24508893

Sheikhshoaie, Iran; Ebrahimipour, S Yousef; Sheikhshoaie, Mahdeyeh; Rudbari, Hadi Amiri; Khaleghi, Moj; Bruno, Giuseppe

2014-04-24

146

Conformational equilibrium isotope effects in glucose by (13)C NMR spectroscopy and computational studies.  

PubMed

Anomeric equilibrium isotope effects for dissolved sugars are required preludes to understanding isotope effects for these molecules bound to enzymes. This paper presents a full molecule study of the alpha- and beta-anomeric forms of D-glucopyranose in water using deuterium conformational equilibrium isotope effects (CEIE). Using 1D (13)C NMR, we have found deuterium isotope effects of 1.043 +/- 0.004, 1.027 +/- 0.005, 1.027 +/- 0.004, 1.001 +/- 0.003, 1.036 +/- 0.004, and 0.998 +/- 0.004 on the equilibrium constant, (H/D)K(beta/alpha), in [1-(2)H]-, [2-(2)H]-, [3-(2)H]-, [4-(2)H]-, [5-(2)H]-, and [6,6'-(2)H(2)]-labeled sugars, respectively. A computational study of the anomeric equilibrium in glucose using semiempirical and ab initio methods yields values that correlate well with experiment. Natural bond orbital (NBO) analysis of glucose and dihedral rotational equilibrium isotope effects in 2-propanol strongly imply a hyperconjugative mechanism for the isotope effects at H1 and H2. We conclude that the isotope effect at H1 is due to n(p) --> sigma* hyperconjugative transfer from O5 to the axial C1--H1 bond in beta-glucose, while this transfer makes no contribution to the isotope effect at H5. The isotope effect at H2 is due to rotational restriction of OH2 at 160 degrees in the alpha form and 60 degrees in the beta-sugar, with concomitant differences in n --> sigma* hyperconjugative transfer from O2 to CH2. The isotope effects on H3 and H5 result primarily from syn-diaxial steric repulsion between these and the axial anomeric hydroxyl oxygen in alpha-glucose. Therefore, intramolecular effects play an important role in isotopic perturbation of the anomeric equilibrium. The possible role of intermolecular effects is discussed in the context of recent molecular dynamics studies on aqueous glucose. PMID:11456704

Lewis, B E; Schramm, V L

2001-02-21

147

Solid-state (13)C CP MAS NMR spectroscopy of mushrooms gives directly the ratio between proteins and polysaccharides.  

PubMed

The solid-state (13)C CP MAS NMR technique has the potential of monitoring the chemical composition in the solid state of an intact food sample. This property has been utilized to study mushrooms of different species (Pleurotus ostreatus, Pleurotus eryngii, Pleurotus pulmunarius, and Lentinula edodes), already characterized by chemical analyses for protein and dietary fiber components. Solid-state (13)C CP MAS NMR spectroscopy reveals a large difference in the ratio between the glucidic and the proteic resonances probably depending on the mushroom species. An accurate inspection by model compounds and suitable mixtures of proteins and saccharides gives a methodology to interpret these experimental data. A good correlation (R(2) = 0.93; R(2) = 0.81) has been obtained by comparing the NMR data with the results of the chemical analyses. The results suggest the possibility to perform a taxonomic study and/or a nutritional study on the basis of the ratio between protein and polysaccharide levels determined by NMR or chemical methodologies. PMID:11087506

Pizzoferrato, L; Manzi, P; Bertocchi, F; Fanelli, C; Rotilio, G; Paci, M

2000-11-01

148

Solid state NMR spectroscopy of specifically 13C-enriched lignin in wheat straw from coniferin  

Microsoft Academic Search

Three coniferins, specifically 13C-enriched at side chain ?, ? and ? carbons, and natural abundance (unenriched) coniferin were administered to internode cavities of lignifying culms of dwarf wheat. Difference 13C CP\\/MAS spectra were obtained between the spectra of the coniferin-fed and the unfed wheat straws, or between the spectra of straws fed with enriched coniferin and unenriched coniferin. The difference

Noritsugu Terashima; Rajai H. Atalla; David L. Vanderhart

1997-01-01

149

Local structure and molecular motions in imidazolium hydrogen malonate crystal as studied by 2H and 13C NMR  

NASA Astrophysics Data System (ADS)

The local structure and molecular motion of the imidazolium hydrogen malonate crystal were investigated using solid-state 2H and 13C NMR. The imidazolium ion undergoes isotropic rotation, which is correlated with a defect in the crystal, as observed by 2H NMR broadline spectra above 263 K. A 180? flip of the imidazolium ion in the regular site was observed from 2H NMR quadrupole Carr-Purcell-Meiboom-Gill (QCPMG) spectra. The Grotthuss mechanism was accompanied by a 180? flip of the imidazolium ion in regular sites. Moreover, the proton transfer associated with the imidazolium ion of the defective crystal is important for proton conductivity of the imidazolium hydrogen malonate crystal.

Mizuno, M.; Chizuwa, M.; Umiyama, T.; Kumagai, Y.; Miyatou, T.; Ohashi, R.; Ida, T.; Tansho, M.; Shimizu, T.

2014-10-01

150

1H and 13C NMR assignments of three nitrogen containing compounds from the mangrove endophytic fungus (ZZF08).  

PubMed

A new natural product, named phomopsin A, 1-(meta-hydroxyphenyl)-4-hydroxy-3-isoquinolone (1), together with two known compounds cytochalasin H (2) and glucosylceramide (3), was isolated from the mangrove endophytic fungus Phomopsis sp. (ZZF08) obtained from the South China Sea coast. The structures were elucidated by 1D and 2D NMR experiments including COSY, HMQC, and HMBC. According to NMR and single-crystal X-ray diffraction, it was found that some assignments about (1)H and (13)C NMR data for cytochalasin H (2) were probably uncorrected in the previous reports. In our cytotoxicity assays, compound 1 showed moderate cytotoxicity toward KB cells with IC(50) at 28.0 microg ml(-1) and KBv200 cells with IC(50) at 16.8 microg ml(-1), and compound 2 exhibited strong cytotoxicity toward KB cells and KBv200 cells with IC(50) less than 1.25 microg ml(-1). PMID:18297742

Tao, Yiwen; Zeng, Xianjian; Mou, Chengbo; Li, Jun; Cai, Xiaoling; She, Zhigang; Zhou, Shining; Lin, Yongcheng

2008-05-01

151

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

SciTech Connect

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

Shanks, J.V.

1989-01-01

152

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

PubMed Central

In vivo imaging/spectroscopic biomarkers for solid tumor aggressiveness are needed in the clinic to facilitate cancer diagnosis and treatment strategies. In mouse models of human melanoma and breast cancer we were able to detect the metabolic differences among tumors of different metastatic potential and between normal and cancer tissues by optical imaging of the mitochondrial redox state of snap-frozen tissue samples. Such metabolic differences indicate that tumors of different aggressiveness have different metabolic homeostasis, which supports that kinetic parameters such as rate constant(s) can also serve as bio-markers for cancer aggressiveness and treatment response. Here we present our preliminary study on the mouse xenografts of the aggressive and indolent human breast cancer cell lines using the hyperpolarized 13C-NMR (HP-NMR) technique. By recording the time courses of 13C-pyruvate tracer and its metabolite signals in vivo, particularly the 13C-lactate signal, the apparent rate constants of both the forward and reverse reactions catalyzed by lactate dehydrogenase (LDH) were extracted via the ratiometric modeling of the two-site exchange reaction that we developed. Data from four breast tumors (MCF-7, MDA-MB-468, and MDA-MB-231 medium and large) with different aggressiveness are included. We demonstrate the feasibility to quantify the apparent rate constants of LDH reactions in breast tumor xenografts. PMID:23852500

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

2014-01-01

153

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

SciTech Connect

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

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

2010-01-01

154

Uranyl nitrate inhibits lactate gluconeogenesis in isolated human and mouse renal proximal tubules: a 13C-NMR study.  

PubMed

As part of a study on uranium nephrotoxicity, we investigated the effect of uranyl nitrate in isolated human and mouse kidney cortex tubules metabolizing the physiological substrate lactate. In the millimolar range, uranyl nitrate reduced lactate removal and gluconeogenesis and the cellular ATP level in a dose-dependent fashion. After incubation in phosphate-free Krebs-Henseleit medium with 5 mM L-[1-13C]-, or L-[2-13C]-, or L-[3-13C]lactate, substrate utilization and product formation were measured by enzymatic and NMR spectroscopic methods. In the presence of 3 mM uranyl nitrate, glucose production and the intracellular ATP content were significantly reduced in both human and mouse tubules. Combination of enzymatic and NMR measurements with a mathematical model of lactate metabolism revealed an inhibition of fluxes through lactate dehydrogenase and the gluconeogenic enzymes in the presence of 3 mM uranyl nitrate; in human and mouse tubules, fluxes were lowered by 20% and 14% (lactate dehydrogenase), 27% and 32% (pyruvate carboxylase), 35% and 36% (phosphoenolpyruvate carboxykinase), and 39% and 45% (glucose-6-phosphatase), respectively. These results indicate that natural uranium is an inhibitor of renal lactate gluconeogenesis in both humans and mice. PMID:19747499

Renault, Sophie; Faiz, Hassan; Gadet, Rudy; Ferrier, Bernard; Martin, Guy; Baverel, Gabriel; Conjard-Duplany, Agnès

2010-01-01

155

Comment on the paper: "[ 1H] and [ 13C]NMR studies on the importance of aromatic structures in fulvic and humic acids" ( RUGGIEROet al., 1979)  

NASA Astrophysics Data System (ADS)

Some statements referring to our work on 13C NMR of humic and fulvic acids have been recently reported in this journal by Ruggiero and co-workers. They are discussed in order to avoid possible misinterpretations.

Wilson, M. A.; Goh, K. M.

1981-03-01

156

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

PubMed

Oxindole alkaloids, isolated from the bark of Uncaria tomentosa [Willd. ex Schult.] Rubiaceae, are considered to be responsible for the biological activity of this herb. Five pentacyclic and two tetracyclic alkaloids were studied by solid-state NMR and theoretical GIAO DFT methods. The (13)C and (15)N CPMAS NMR spectra were recorded for mitraphylline, isomitraphylline, pteropodine (uncarine C), isopteropodine (uncarine E), speciophylline (uncarine D), rhynchophylline and isorhynchophylline. Theoretical GIAO DFT calculations of shielding constants provide arguments for identification of asymmetric centers and proper assignment of NMR spectra. These alkaloids are 7R/7S and 20R/20S stereoisomeric pairs. Based on the (13)C CP MAS chemical shifts the 7S alkaloids (delta C3 70-71ppm) can be easily and conveniently distinguished from 7R (deltaC3 74.5-74.9ppm), also 20R (deltaC20 41.3-41.7ppm) from the 20S (deltaC20 36.3-38.3ppm). The epiallo-type isomer (3R, 20S) of speciophylline is characterized by a larger (15)N MAS chemical shift of N4 (64.6ppm) than the allo-type (3S, 20S) of isopteropodine (deltaN4 53.3ppm). (15)N MAS chemical shifts of N1-H in pentacyclic alkaloids are within 131.9-140.4ppm. PMID:19019638

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

2008-11-01

157

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

PubMed

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

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

2013-06-01

158

13C- and 31P-NMR studies of human colon cancer in-vitro and in-vivo.  

PubMed

We report comparative 31P-NMR studies in-vivo and in-vitro of the human adenocarcinoma cell line HCT-116 in a high-density, perfused microcarrier culture and as a tumour from the same cell line grown in three different immune-suppressed animal models (NIH triple deficient, Nude, SCID). The phosphate metabolite ratios, pHNMR and intracellular free magnesium, derived from the 31P-NMR spectra, were compared for the in-vivo and in-vitro systems. Results obtained with HCT-116 cells on microcarrier beads are quantitatively similar to that of small (122 mm3), tumours in-vivo derived from the same cell line in any of the immune-suppressed animal systems studied. This suggests that in-vitro microcarrier cell culture serves as a useful model system for deriving information about metabolism of small, tumours in-vivo. It offers the additional advantages of allowing for precise control of substrate milieu, perfusion and oxygenation. The microcarrier system was also used to measure flux through glycolysis and the pentose cycle. In particular, we measured glucose utilization and the production of lactate, alanine, glutamine and glycogen in proton-decoupled 13C-NMR experiments following administration of [1-13C]glucose. We found that (63% +/- 6%) of the glucose utilized was released as [3-13C] lactate in the presence of oxygen, indicating that the HCT-116 cells have a high level of aerobic glycolysis. Serial labelling experiments with [1-13C] glucose and [6-13C] glucose reveal that at least (11.6% +/- 1.3%) of the glucose utilized enters the pentose cycle. We determined that (6.9% +/- 1.2%) of the glucose utilized is recycled to glucose via the pentose cycle while (4.7% +/- 1.4%) of the glucose utilized enters the pentose cycle to form lactate. The high rate of recycling via the pentose cycle suggests that a significant fraction of cellular NADPH is generated by the pentose cycle as opposed to generation by the malate-pyruvate shuttle. PMID:8252195

Singer, S; Okunieff, P; Gostin, C; Thilly, W G; Chen, L B; Neuringer, L J

1993-01-01

159

(1)H NMR and (1)H-(13)C HSQC surface characterization of chitosan-chitin sheath-core nanowhiskers.  

PubMed

Surface deacetylation of chitin nanowhiskers (CtNWs) to chitosan-sheath/chitin-core nanowhiskers (CsNWs) was successfully monitored by liquid-state high-resolution NMR of colloidal suspensions of these never-dried nanowhiskers. CtNWs were derived from acid hydrolysis (3N HCl, 30mL/g, 90min, 104°C) of chitin at 65% yield and 86% CrI. Deacetylation (50% NaOH, 48h, 50°C) of CtNWs generated CsNWs with unchanged nanowhisker morphology and overall length and width dimensions, but a reduced CrI of 54%. Successful step-wise exchanging the aqueous media with acetone, then D2O prevented agglomeration of nanowhiskers and enabled NMR detection of individual nanowhiskers. The crystalline structure of CtNWs and CsNWs provided different chemical environments for the glucosamine hydrogen atom H2, splitting the NMR signals into 2 peaks (? 3.0 and ? 3.35ppm) which differed from that reported for soluble chitosan (? 3.2ppm). Besides, (1)H-(13)C HSQC was only possible for CsNWs indicating the NMR phenomenon observed to represent that of the surfaces where the outer layers were highly mobile and less crystalline. The degree of acetylation at the surfaces was determined from (1)H NMR data to be 56% and 9% for CtNWs and CsNWs, respectively. PMID:25843833

Pereira, Antonio G B; Muniz, Edvani C; Hsieh, You-Lo

2015-06-01

160

(13)C, (2)h NMR studies of structural and dynamical modifications of glucose-exposed porcine aortic elastin.  

PubMed

Elastin, the principal component of the elastic fiber of the extracellular matrix, imparts to vertebrate tissues remarkable resilience and longevity. This work focuses on elucidating dynamical and structural modifications of porcine aortic elastin exposed to glucose by solid-state NMR spectroscopic and relaxation methodologies. Results from macroscopic stress-strain tests are also presented and indicate that glucose-treated elastin is mechanically stiffer than the same tissue without glucose treatment. These measurements show a large hysteresis in the stress-strain behavior of glucose-treated elastin-a well-known signature of viscoelasticity. Two-dimensional relaxation NMR methods were used to investigate the correlation time, distribution, and population of water in these samples. Differences are observed between the relative populations of water, whereas the measured correlation times of tumbling motion of water across the samples were similar. (13)C magic-angle-spinning NMR methods were applied to investigate structural and dynamical modifications after glucose treatment. Although some overall structure is preserved, the process of glucose exposure results in more heterogeneous structures and slower mobility. The correlation times of tumbling motion of the (13)C-(1)H internuclear vectors in the glucose-treated sample are larger than in untreated samples, pointing to their more rigid structure. The (13)C cross-polarization spectra reveal a notably increased ?-helical character in the alanine motifs after glucose exposure. Results from molecular dynamics simulations are provided that add further insight into dynamical and structural changes of a short repeat, [VPGVG]5, an alanine pentamer, desmosine, and isodesmosine sites with and without glucose. The simulations point to changes in the entropic and energetic contributions in the retractive forces of VPGVG and AAAAA motifs. The most notable change is the increase of the energetic contribution in the retractive force due to peptide-glucose interactions of the VPGVG motif, which may play an important role in the observed stiffening in glucose-treated elastin. PMID:25863067

Silverstein, Moshe C; Bilici, Kübra; Morgan, Steven W; Wang, Yunjie; Zhang, Yanhang; Boutis, Gregory S

2015-04-01

161

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

PubMed

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

Duquesnoy, Emilie; Castola, Vincent; Casanova, Joseph

2008-04-01

162

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

163

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

164

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

NASA Technical Reports Server (NTRS)

Initial investigations have been made into the use of high resolution nuclear magnetic resonance (NMR) for the characterization of radiation effects in graphite and Kevlar fibers, polymers, and the fiber/matrix interface in graphite/polyetherimide composites. Sample preparation techniques were refined. Essential equipment has been procured. A new NMR probe was constructed to increase the proton signal-to-noise ratio. Problem areas have been identified and plans developed to resolve them.

Ferguson, Milton W.

1989-01-01

165

JOURNAL OF MAGNETIC RESONANCE 94,209-2 13 ( 199 1) Three-DimensionalTriple-ResonanceNMR of 13C/ 15N-Enriched  

E-print Network

JOURNAL OF MAGNETIC RESONANCE 94,209-2 13 ( 199 1) Three-DimensionalTriple-ResonanceNMR of 13C/ 15N that 3D triple-resonance NMR provides a practical alternative for obtaining sequential resonance in this approach correlate backbone Ha and Ca resonances with either the intraresidue carbonyl resonance (CO

Powers, Robert

166

PMR and 13 C NMR Spectra of Biologically Active Compounds. XII. Taraxasterol and Its Acetate from the Aerial Part of Onopordum acanthium  

Microsoft Academic Search

Crystalline taraxasterol and its acetate were isolated for the first time from Onopordum acanthium. Two-dimensional COSY, HSQC, and HMBC NMR experimentswere carried out forcomplete assignment of signals in the PMR and 13C NMR. Chemical shifts of stereochemically important methyl C atoms C-28 and C-29 were measured.

L. M. Khalilov; A. Z. Khalilova; E. R. Shakurova; I. F. Nuriev; V. V. Kachala; A. S. Shashkov; U. M. Dzhemilev

2003-01-01

167

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

SciTech Connect

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

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

1996-12-01

168

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

SciTech Connect

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

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

1995-12-31

169

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

170

Assessing the quantitative reliability of solid-state 13C NMR spectra of kerogens across a gradient of thermal maturity.  

PubMed

Five type II kerogens, shown by elemental analysis and Rock-Eval pyrolysis to represent a gradient of thermal maturity, were further characterized using a range of solid-state 13C NMR spectroscopic techniques. 13C cross polarization (CP) NMR spectra of the kerogens confirmed the well-established pattern of increasing aromaticity with increasing thermal maturity. Spin counting showed that CP observability was around 50% for the immature kerogens, and only 14-25% for the mature kerogens. Spin counting also showed that the direct polarization (DP) observabilities were >80% for all but one of the kerogens. Despite the large differences in observability between the two techniques, aromaticities derived from corresponding CP and DP spectra differed by only 1-15%. The RESTORE technique showed that the low CP observability of the immature kerogens was due mostly to rapid T(1rho)H relaxation, whereas both rapid T(1rho)H relaxation and slow polarization transfer contributed to the low CP observability of the mature kerogens. PMID:16310345

Smernik, Ronald J; Schwark, Lorenz; Schmidt, Michael W I

2006-06-01

171

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

172

Complete assignments of (1)H and (13)C NMR data for two 3beta,8beta-epoxymexicanolides from the fruit of a Chinese mangrove Xylocarpus granatum.  

PubMed

Three 3beta,8beta-epoxymexicanolides, including xyloccensin K, 6-acetoxycedrodorin and a new one named xyloccensin W, were isolated from the fruit of a Chinese mangrove Xylocarpus granatum. Their structures were determined by spectroscopic analyses. The first complete assignment of (1)H and (13)C NMR data for xyloccensin W was achieved by means of 2D NMR techniques, including (1)H-(1)H COSY, HSQC, HMBC and NOESY spectra. In addition, the confusion of (1)H and (13)C NMR data previously reported for xyloccensin K was clarified. PMID:16261504

Wu, Jun; Xiao, Zhihui; Song, Yang; Zhang, Si; Xiao, Qiang; Ma, Cha; Ding, Haixin; Li, Qingxin

2006-01-01

173

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

PubMed Central

A new inhibitor, Z-Ala-Pro-Phe-glyoxal (where Z is benzyloxycarbonyl),has been synthesized and shown to be a competitive inhibitor of delta-chymotrypsin, with a K(i) of 25+/-8 nM at pH 7.0 and 25 degrees C. Z-Ala-Pro-[1-(13)C]Phe-glyoxal and Z-Ala-Pro-[2-(13)C]Phe-glyoxal have been synthesized, and (13)C-NMR has been used to determine how they interact with delta-chymotrypsin. Using Z-Ala-Pro-[2-(13)C]Phe-glyoxal we have detected a signal at 100.7 p.p.m. which we assign to the tetrahedral adduct formed between the hydroxy group of Ser-195 and the (13)C-enriched keto-carbon of the inhibitor. This signal is in a pH-dependent slow exchange with a signal at 107.6 p.p.m. which depends on a pK(a) of approximately 4.5, which we assign to oxyanion formation. Thus we are the first to detect an oxyanion pK(a) in a reversible chymotrypsin-inhibitor complex. A smaller titration shift of 100.7 p.p.m. to 103.9 p.p.m. with a pK(a) of approximately 5.3 is also detected due to a rapid exchange process. This pK(a) is also detected with the Z-Ala-Pro-[1-(13)C]Phe-glyoxal inhibitor and gives a larger titration shift of 91.4 p.p.m. to 97.3 p.p.m., which we assign to the ionization of the hydrated aldehyde hydroxy groups of the enzyme-bound inhibitor. Protonation of the oxyanion in the oxyanion hole decreases the binding efficiency of the inhibitor. From this decrease in binding efficiency we estimate that oxyanion binding in the oxyanion hole reduces the oxyanion pK(a) by 1.3 pK(a) units. We calculate that the pK(a)s of the oxyanions of the hemiketal and hydrated aldehyde moieties of the glyoxal inhibitor are both lowered by 6.4-6.9 pK(a) units on binding to chymotrypsin. Therefore we conclude that oxyanion binding in the oxyanion hole has only a minor role in decreasing the oxyanion pK(a). We also investigate how the inhibitor breaks down at alkaline pH, and how it breaks down at neutral pH in the presence of chymotrypsin. PMID:11853541

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

2002-01-01

174

The solid state 13C-NMR and 19F-NMR spectra of some graphite fluorides  

Microsoft Academic Search

The solid state 13C nuclear magnetic resonance spectra of fluorinated graphites show two resonances, one of which is assigned to aromatic carbon and the other to aliphatic carbon. The resonances are very broad with the high-field resonance centered at about 35 ppm below tetramethylsilane (TMS) and a low-field resonance centered at about 160 ppm below tetramethylsilane. The high-field resonance is

Charles A. Wilkie; Gong-Yu Lin; Daniel T. Haworth

1979-01-01

175

Observation of (1)H-(13)C and (1)H-(1)H proximities in a paramagnetic solid by NMR at high magnetic field under ultra-fast MAS.  

PubMed

The assignment of NMR signals in paramagnetic solids is often challenging since: (i) the large paramagnetic shifts often mask the diamagnetic shifts specific to the local chemical environment, and (ii) the hyperfine interactions with unpaired electrons broaden the NMR spectra and decrease the coherence lifetime, thus reducing the efficiency of usual homo- and hetero-nuclear NMR correlation experiments. Here we show that the assignment of (1)H and (13)C signals in isotopically unmodified paramagnetic compounds with moderate hyperfine interactions can be facilitated by the use of two two-dimensional (2D) experiments: (i) (1)H-(13)C correlations with (1)H detection and (ii) (1)H-(1)H double-quantum?single-quantum correlations. These methods are experimentally demonstrated on isotopically unmodified copper (II) complex of l-alanine at high magnetic field (18.8T) and ultra-fast Magic Angle Spinning (MAS) frequency of 62.5kHz. Compared to (13)C detection, we show that (1)H detection leads to a 3-fold enhancement in sensitivity for (1)H-(13)C 2D correlation experiments. By combining (1)H-(13)C and (1)H-(1)H 2D correlation experiments with the analysis of (13)C longitudinal relaxation times, we have been able to assign the (1)H and (13)C signals of each l-alanine ligand. PMID:25557861

Li, Shenhui; Trébosc, Julien; Lafon, Olivier; Zhou, Lei; Shen, Ming; Pourpoint, Frédérique; Amoureux, Jean-Paul; Deng, Feng

2015-02-01

176

Restraints on backbone conformations in solid state NMR studies of uniformly labeled proteins from quantitative amide 15N–15N and carbonyl 13C13C dipolar recoupling data  

PubMed Central

Recent structural studies of uniformly 15N, 13C-labeled proteins by solid state nuclear magnetic resonance (NMR) rely principally on two sources of structural restraints: (i) restraints on backbone conformation from isotropic 15N and 13C chemical shifts, based on empirical correlations between chemical shifts and backbone torsion angles; (ii) restraints on inter-residue proximities from qualitative measurements of internuclear dipole–dipole couplings, detected as the presence or absence of inter-residue crosspeaks in multidimensional spectra. We show that site-specific dipole–dipole couplings among 15N-labeled backbone amide sites and among 13C-labeled backbone carbonyl sites can be measured quantitatively in uniformly-labeled proteins, using dipolar recoupling techniques that we call 15N-BARE and 13C-BARE (BAckbone REcoupling), and that the resulting data represent a new source of restraints on backbone conformation. 15N-BARE and 13C-BARE data can be incorporated into structural modeling calculations as potential energy surfaces, which are derived from comparisons between experimental 15N and 13C signal decay curves, extracted from crosspeak intensities in series of two-dimensional spectra, with numerical simulations of the 15N-BARE and 13C-BARE measurements. We demonstrate this approach through experiments on microcrystalline, uniformly 15N, 13C-labeled protein GB1. Results for GB1 show that 15N-BARE and 13C-BARE restraints are complementary to restraints from chemical shifts and inter-residue crosspeaks, improving both the precision and the accuracy of calculated structures. PMID:22449573

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

2013-01-01

177

13C NMR investigation of cholesterol esterification rate in human whole blood  

Microsoft Academic Search

We have previously used NMR spectroscopy to measure the acyl transfer from phospholipid to cholesterol in human plasma. In the present study we investigated the processes of transfer of cholesterol and exchange of cholesteryl ester between lipoproteins during incubation of human whole blood. The rate of cholesteryl ester increase was much greater during whole blood incubation (86–118, mean = 90

M. Hossein Nouri-Sorkhabi; David R. Sullivan; Philip W. Kuchel

1995-01-01

178

Molecular composition of recycled organic wastes, as determined by solid-state {sup 13}C NMR and elemental analyses  

SciTech Connect

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

Eldridge, S.M., E-mail: simon.eldridge@dpi.nsw.gov.au [Environmental Futures Centre, School of Environment, Griffith University, Nathan, QLD 4111 (Australia); NSW Department of Primary Industries, Bruxner Highway, Wollongbar, NSW 2477 (Australia); Chen, C.R. [Environmental Futures Centre, School of Environment, Griffith University, Nathan, QLD 4111 (Australia); Xu, Z.H. [Environmental Futures Centre, School of Biomolecular and Physical Sciences, Griffith University, Nathan, QLD 4111 (Australia); Nelson, P.N. [School of Earth and Environmental Sciences, James Cook University, Cairns, QLD 4870 (Australia); Boyd, S.E. [Environmental Futures Centre, School of Biomolecular and Physical Sciences, Griffith University, Nathan, QLD 4111 (Australia); Meszaros, I. [Formerly NSW Department of Primary Industries, Richmond, NSW 2753 (Australia); Chan, K.Y. [Graduate School of Environment, Macquarie University, North Ryde, NSW 2109 (Australia); Formerly NSW Department of Primary Industries, Richmond, NSW 2753 (Australia)

2013-11-15

179

On the problem of resonance assignments in solid state NMR of uniformly (15)N,(13)C-labeled proteins.  

PubMed

Determination of accurate resonance assignments from multidimensional chemical shift correlation spectra is one of the major problems in biomolecular solid state NMR, particularly for relative large proteins with less-than-ideal NMR linewidths. This article investigates the difficulty of resonance assignment, using a computational Monte Carlo/simulated annealing (MCSA) algorithm to search for assignments from artificial three-dimensional spectra that are constructed from the reported isotropic (15)N and (13)C chemical shifts of two proteins whose structures have been determined by solution NMR methods. The results demonstrate how assignment simulations can provide new insights into factors that affect the assignment process, which can then help guide the design of experimental strategies. Specifically, simulations are performed for the catalytic domain of SrtC (147 residues, primarily ?-sheet secondary structure) and the N-terminal domain of MLKL (166 residues, primarily ?-helical secondary structure). Assuming unambiguous residue-type assignments and four ideal three-dimensional data sets (NCACX, NCOCX, CONCA, and CANCA), uncertainties in chemical shifts must be less than 0.4ppm for assignments for SrtC to be unique, and less than 0.2ppm for MLKL. Eliminating CANCA data has no significant effect, but additionally eliminating CONCA data leads to more stringent requirements for chemical shift precision. Introducing moderate ambiguities in residue-type assignments does not have a significant effect. PMID:25797013

Tycko, Robert

2015-04-01

180

(13)C and (15)N NMR characterization of amine reactivity and solvent effects in CO2 capture.  

PubMed

Factors influencing the reactivity of selected amine absorbents for carbon dioxide (CO2) capture, in terms of the tendency to form amine carbamate, have been studied. Four linear primary alkanolamines at varying chain lengths (MEA, 3A1P, 4A1B , and 5A1P ), two primary amines with different substituents in the ?-position to the nitrogen (1A2P and ISOB), a secondary alkanolamine (DEA), and a sterically hindered primary amine (AMP) were investigated. The relationship between the (15)N NMR data of aqueous amines and their ability to form carbamate, as determined at equilibrium by quantitative (13)C NMR experiments, was analyzed, taking into account structural-chemical properties. For all the amines, the (15)N chemical shifts fairly reflected the observed reactivity for carbamate formation. In addition to being a useful tool for the investigation of amine reactivity, (15)N NMR data clearly provided evidence of the importance of solvent effects for the understanding of chemical dynamics in CO2 capture by aqueous amine absorbents. PMID:25093443

Perinu, Cristina; Arstad, Bjørnar; Bouzga, Aud M; Jens, Klaus-J

2014-08-28

181

Mathematical Modeling and Data Analysis of NMR Experiments using Hyperpolarized 13C Metabolites  

PubMed Central

Rapid-dissolution dynamic nuclear polarization (DNP) has made significant impact in the characterization and understanding of metabolism that occurs on the sub-minute timescale in several diseases. While significant efforts have been made in developing applications, and in designing rapid-imaging radiofrequency (RF) and magnetic field gradient pulse sequences, very few groups have worked on implementing realistic mathematical/kinetic/relaxation models to fit the emergent data. The critical aspects to consider when modeling DNP experiments depend on both nuclear magnetic resonance (NMR) and (bio)chemical kinetics. The former constraints are due to the relaxation of the NMR signal and the application of ‘read’ RF pulses, while the kinetic constraints include the total amount of each molecular species present. We describe the model-design strategy we have used to fit and interpret our DNP results. To our knowledge, this is the first report on a systematic analysis of DNP data. PMID:25114541

Pagès, Guilhem; Kuchel, Philip W.

2013-01-01

182

2 H and 13 C NMR study of guest molecule orientation in clathrate hydrates  

Microsoft Academic Search

At relatively high temperatures (200–270K), clathrate hydrate cages achieve their full crystallographic symmetry because of time averaging of different cage configurations which exist because of disorder in the water molecule orientations. The average orientation of guest molecules in the cages can be obtained from the NMR spectrum, in case of spin 1\\/2 nuclei from the nuclear shielding tensor, in case

D. W. Davidson; C. I. Ratcliffe; J. A. Ripmeester

1984-01-01

183

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

184

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

185

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

186

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

PubMed

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

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

2014-07-01

187

Increased tricarboxylic acid cycle flux in rat brain during forepaw stimulation detected with 1H[13C]NMR.  

PubMed Central

NMR spectroscopy was used to test recent proposals that the additional energy required for brain activation is provided through nonoxidative glycolysis. Using localized NMR spectroscopic methods, the rate of C4-glutamate isotopic turnover from infused [1-(13)C]glucose was measured in the somatosensory cortex of rat brain both at rest and during forepaw stimulation. Analysis of the glutamate turnover data using a mathematical model of cerebral glucose metabolism showed that the tricarboxylic acid cycle flux [(V(TCA)] increased from 0.49 +/- 0.03 at rest to 1.48 +/- 0.82 micromol/g/min during stimulation (P < 0.01). The minimum fraction of C4-glutamate derived from C1-glucose was approximately 75%, and this fraction was found in both the resting and stimulated rats. Hence, the percentage increase in oxidative cerebral metabolic rate of glucose use (CMRglc) equals the percentage increases in V(TCA) and cerebral metabolic rate of oxygen consumption (CMRO2). Comparison with previous work for the same rat model, which measured total CMRglc [Ueki, M., Linn, F. & Hossman, K. A. (1988) J. Cereb. Blood Flow Metab. 8, 486-4941, indicates that oxidative CMRglc supplies the majority of energy during sustained brain activation. Images Fig. 2 PMID:8755523

Hyder, F; Chase, J R; Behar, K L; Mason, G F; Siddeek, M; Rothman, D L; Shulman, R G

1996-01-01

188

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

189

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

NASA Astrophysics Data System (ADS)

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

Adebajo, Moses O.; Frost, Ray L.

2004-08-01

190

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

PubMed

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

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

2014-07-01

191

Synthesis and total 1H- and 13C-NMR assignment of cephem derivatives for use in ADEPT approaches.  

PubMed

We report the synthesis and total NMR characterization of 5-thia-1-azabicyclo-[4.2.0]oct-2-ene-2-carboxylic acid-3-[[[(4''-nitrophenoxy)carbonyl]oxy]-methyl]-8-oxo-7-[(2-thienyloxoacetyl)amino]-diphenylmethyl ester-5-dioxide (5), a new cephalosporin derivative. This compound can be used as the carrier of a wide range of drugs containing an amino group. The preparation of the intermediate product, 5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid-3-[methyl 4-(6-methoxyquinolin-8-ylamino)pentylcarbamate]-8-oxo-7-[(2-thienyloxoacetyl)amino]-diphenylmethyl ester-5-dioxide (6), as well as the synthesis of the antimalarial primaquine prodrug 5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid-3-[methyl 4-(6-methoxyquinolin-8-ylamino)pentylcarbamate]-8-oxo-7-[(2-thienyloxoacetyl)amino]- 5-dioxide (7) are also described, together with their total (1)H- and (13)C-NMR assignments. PMID:18463586

Blau, Lorena; Menegon, Renato Farina; Ferreira, Elizabeth Igne; Ferreira, Antonio Gilberto; Boffo, Elisangela Fabiana; Tavares, Leila Aley; Heleno, Vladimir Constantino Gomes; Chung, Man-Chin

2008-01-01

192

Conformational preferences of chondroitin sulfate oligomers using partially oriented NMR spectroscopy of 13C-labeled acetyl groups.  

PubMed

A new method is presented for the retrieval of information on the conformation of glycosaminoglycan oligomers in solution. The method relies on the replacement of acetyl groups in isolated native oligomers with 13C labeled acetyl groups and the extraction of orientational constraints from residual dipolar couplings (RDCs) and chemical shift anisotropy (CSA) offsets observed in NMR spectra of partially oriented samples. A novel method for assignment of resonances based on the correlation of resonance intensities with isotope ratios determined from mass spectrometric analysis is also presented. The combined methods are used in conjunction with more traditional NMR structural data to determine the solution structure of a pentasaccharide, GalNAc6S(beta1-4)GlcA(beta1-3)GalNAc4S(beta1-4)GlcA(beta1-3)GalNAc4S-ol, derived by enzymatic hydrolysis of chondroitin sulfate. The geometry derived is compared to that for similar molecules that have been reported in the literature, and prospects for use of the new types of data in the study of protein-bound oligosaccharides are discussed. PMID:17924631

Yu, Fei; Wolff, Jeremy J; Amster, I Jonathan; Prestegard, James H

2007-10-31

193

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

PubMed

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

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

2013-01-01

194

Orientational order of difluorinated liquid crystals: a comparative 13C-NMR, Optical, and dielectric study in nematic and smectic B phases.  

PubMed

Structural and orientational order properties of 3Cy2CyBF2 and of 5CyCy2BF2 have been investigated by means of (13)C-NMR, optical, and dielectric spectroscopy methods. In the case of NMR, order parameters have been independently obtained from the analysis of either (13)C-(19)F dipolar couplings or (13)C chemical shift anisotropies, both measured from (13)C-{(1)H} NMR static spectra. The assignment of the (13)C resonances has been carried out thanks to the comparison with solution state spectra and DFT calculations, and the relevant geometrical parameters and (13)C chemical shift tensors needed to derive orientational order parameters have been calculated by DFT methods. In the analysis of (13)C-(19)F dipolar couplings, empirical corrections for vibrations and anisotropic scalar couplings have been included. Dielectric measurements have been performed over a broad frequency range for two orientations of the nematic director with respect to the measuring field. At low frequencies (static case) a positive dielectric anisotropy has been determined, which has enabled the calculation of the order parameters according to a well-tested procedure. At high frequencies the dielectric anisotropy changes its sign, a property which can be useful in designing a dual addressing display. The nematic order parameter determined from optical, dielectric, and NMR methods have been compared: their trends with temperature are very similar, apart from some slight shifts, and were analyzed by Haller and Chirtoc models. The differences among the results obtained by the four methods have been discussed in detail, also with reference to the assumptions and approximations used in each case, and to the results recently reported for similar fluorinated nematogens. The presence of a non-negligible order biaxiality has been related to the presence of a CH2CH2 bridging group, linking one cyclohexylic unit with either the other cyclohexyl or the phenyl ring. PMID:18646816

Geppi, M; Marini, A; Veracini, C A; Urban, S; Czub, J; Kuczy?ski, W; Dabrowski, R

2008-08-14

195

Global fold of human cannabinoid type 2 receptor probed by solid-state 13C-, 15N-MAS NMR and molecular dynamics simulations.  

PubMed

The global fold of human cannabinoid type 2 (CB2 ) receptor in the agonist-bound active state in lipid bilayers was investigated by solid-state (13)C- and (15)N magic-angle spinning (MAS) NMR, in combination with chemical-shift prediction from a structural model of the receptor obtained by microsecond-long molecular dynamics (MD) simulations. Uniformly (13)C- and (15)N-labeled CB2 receptor was expressed in milligram quantities by bacterial fermentation, purified, and functionally reconstituted into liposomes. (13)C MAS NMR spectra were recorded without sensitivity enhancement for direct comparison of C?, C?, and C=O bands of superimposed resonances with predictions from protein structures generated by MD. The experimental NMR spectra matched the calculated spectra reasonably well indicating agreement of the global fold of the protein between experiment and simulations. In particular, the (13) C chemical shift distribution of C? resonances was shown to be very sensitive to both the primary amino acid sequence and the secondary structure of CB2. Thus the shape of the C? band can be used as an indicator of CB2 global fold. The prediction from MD simulations indicated that upon receptor activation a rather limited number of amino acid residues, mainly located in the extracellular Loop 2 and the second half of intracellular Loop 3, change their chemical shifts significantly (? 1.5 ppm for carbons and ? 5.0 ppm for nitrogens). Simulated two-dimensional (13) C?(i)-(13)C=O(i) and (13)C=O(i)-(15)NH(i + 1) dipolar-interaction correlation spectra provide guidance for selective amino acid labeling and signal assignment schemes to study the molecular mechanism of activation of CB2 by solid-state MAS NMR. PMID:23999926

Kimura, Tomohiro; Vukoti, Krishna; Lynch, Diane L; Hurst, Dow P; Grossfield, Alan; Pitman, Michael C; Reggio, Patricia H; Yeliseev, Alexei A; Gawrisch, Klaus

2014-03-01

196

Some applications of 13 C NMR spectroscopy in heterocyclic structure assignments  

Microsoft Academic Search

The usefulness of13CNMR spectral data in solving otherwise intractable structural problems in heterocyclic chemistry is illustrated with ring systems\\u000a such as imidazoles, pyrazoles, thiazoles, pyrimidines, benzodioxoles, benzodioxanes, benzoxazines, benzothiazines, quinoxalines,\\u000a imidazopyrazoles, imidazothiazoles, pyridobenzoxazines, thiazolobenzimidazoles, thiazinobenzimidazoles, pyrimidobenzimidazoles,\\u000a naphthodioxanes and perimidines. For example, using both chemical shifts and coupling constants, especially the one across\\u000a three bonds, it has been possible to assign

K. Nagarajan

1985-01-01

197

Effects of insulin on perfused liver from streptozotocin-diabetic and untreated rats: /sup 13/C NMR assay of pyruvate kinase flux  

SciTech Connect

The effects of insulin in vitro on perfused liver from streptozotocin-diabetic rats and their untreated littermates during gluconeogenesis from either (3-/sup 13/C)alanine + ethanol or (2-/sup 13/C)pyruvate + NH/sub 4/Cl + ethanol were studied by /sup 13/C NMR. A /sup 13/C NMR determination of the rate of pyruvate kinase flux under steady-state conditions of active gluconeogenesis was developed; this assay includes a check on the reuse of recycled pyruvate. The preparations studied provided gradations of pyruvate kinase flux within the confines of the assay's requirement of active gluconeogenesis. By this determination, the rate of pyruvate kinase flux was 0.74 +/- 0.04 of the gluconeogenic rate in liver from 24-h-fasted controls; in liver from 12-h fasted controls, relative pyruvate kinase flux increased to 1.0 +/- 0.2. In diabetic liver, this flux was undetectable by the authors NMR method. Insulin's hepatic influence in vitro was greatest in the streptozotocin model of type 1 diabetes: upon treatment of diabetic liver with 7 nM insulin in vitro, a partial reversal of many of the differences noted between diabetic and control liver was demonstrated by /sup 13/C NMR. A major effect of insulin in vitro upon diabetic liver was the induction of a large increase in the rate of pyruvate kinase flux, bringing relative and absolute fluxes up to the levels measured in 24-h-fasted controls. By way of comparison, the effects of ischemia on diabetic liver were studied by /sup 13/C NMR to test whether changes in allosteric effectors under these conditions could also increase pyruvate kinase flux. A large increase in this activity was demonstrated in ischemic diabetic liver.

Cohen, S.M.

1987-01-27

198

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

199

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

SciTech Connect

The plasticizing - antiplasticizing effect of water and glycerol contents on native corn starch samples is investigated by FT-Raman and {sup 13}C 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. [Academy of Romanian Scientists, Splaiul Independentei 54, 050094, Bucharest, Romania and National Institute of Research-Development for Machines and Installations Designed to Agriculture and Food Industry - INMA Bucure?ti - Cluj-Napoca Branch (Romania)] [Academy of Romanian Scientists, Splaiul Independentei 54, 050094, Bucharest, Romania and National Institute of Research-Development for Machines and Installations Designed to Agriculture and Food Industry - INMA Bucure?ti - Cluj-Napoca Branch (Romania); Filip, C.; Tripon, C. [National Institute for Research and Development of Isotopic and Molecular Technologies, 65-103 Donath, 400293 Cluj-Napoca (Romania)] [National Institute for Research and Development of Isotopic and Molecular Technologies, 65-103 Donath, 400293 Cluj-Napoca (Romania); Cioica, N.; Co?a, C.; Nagy, E. M. [National Institute of Research-Development for Machines and Installations Designed to Agriculture and Food Industry - INMA Bucure?ti - Cluj-Napoca Branch, RO-400458 Cluj-Napoca (Romania)] [National Institute of Research-Development for Machines and Installations Designed to Agriculture and Food Industry - INMA Bucure?ti - Cluj-Napoca Branch, RO-400458 Cluj-Napoca (Romania)

2013-11-13

200

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

201

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

202

PMR and 13 C NMR spectra of biologically active compounds. XIII.* Structure and stereochemistry of a new phenylpropanoid glycoside isolated from Onopordum acanthium seeds  

Microsoft Academic Search

The structure of a new compound was determined using PMR and 13C NMR spectroscopy (HHCOSY, HSBC, HMBC, ROESY) as 2-[3?-methoxy,4-O-?-D-galactopyranos-1-yl)benzyl]-3-(3?,4?-dimethoxybenzyl)-4hydroxybutyric acid, which was isolated for the first time from\\u000a seeds of Scotch thistle Onopordum acanthium L.

T. V. Tyumkina; I. F. Nuriev; L. M. Khalilov; V. R. Akhmetova; U. M. Dzhemilev

2009-01-01

203

Chemical structures of swine-manure chars produced under different carbonization conditions investigated by advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy  

Technology Transfer Automated Retrieval System (TEKTRAN)

Two types of swine manure chars, hydrothermally-produced hydrochar and slow-pyrolysis pyrochar, and their raw swine manure solid were characterized using advanced 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. Compared with the parent raw swine manure, both hydrochars and pyrochar di...

204

CHANGES IN PROTEIN AND STARCH CONFORMATION DURING VARIABLE TEMPERATURE PARBOILING OF RICE: FT-RAMAN AND 13C CP-MAS NMR SPECTROSCOPIC ASSESSMENT  

Technology Transfer Automated Retrieval System (TEKTRAN)

FT-Raman and solid-state 13C cross polarization magic-angle spinning (CP-MAS) NMR spectroscopies were employed to assess the conformational changes to protein and starch in paddy rice under variable conditions of parboiling. Rice variety, TOX 3108 from Ghana, was parboiled by the soaking-steaming-d...

205

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

ERIC Educational Resources Information Center

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

Pelter, Michael W.; Walker, Natalie M.

2012-01-01

206

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  

NASA Astrophysics Data System (ADS)

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.

Wang, Tao; Wang, Xueliang

2015-01-01

207

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

208

1H NMR, 13C NMR, and computational DFT studies of the structure of 2-acylcyclohexane-1,3-diones and their alkali metal salts in solution.  

PubMed

1H and 13C NMR spectra of 2-acyl-substituted cyclohexane-1,3-diones (acyl = formyl, 1; 2-nitrobenzoyl, 2; 2-nitro-4-trifluoromethylbenzoyl, 3) and lithium sodium and potassium salts of 1 have been measured. The compound 3, known as NTBC, is a life-saving medicine applied in tyrosinemia type I. The optimum molecular structures of the investigated objects in solutions have been found using the DFT method with B3LYP functional and 6-31G** and/or 6-311G(2d,p) basis set. The theoretical values of the NMR parameters of the investigated compounds have been calculated using GIAO DFT B3LYP/6-311G(2d,p) method. The theoretical data obtained for compounds 1-3 have been exploited to interpret their experimental NMR spectra in terms of the equilibrium between different tautomers. It has been found that for these triketones an endo-tautomer prevails. The differences in NMR spectra of the salts of 1 can be rationalized taking into account the size of the cation and the degree of salt dissociation. It seems that in DMSO solution the lithium salt exists mainly as an ion pair stabilized by the chelation of a lithium cation with two oxygen atoms. The activation free energy the of formyl group rotation for this salt has been estimated to be 51.5 kJ/mol. The obtained results suggest that in all the investigated objects, including the free enolate ions, all atoms directly bonded to the carbonyl carbons lie near the same plane. Some observations concerning the chemical shift changes could indicate strong solvation of the anion of 1 by water molecules. Implications of the results obtained in this work for the inhibition mechanism of (4-hydroxyphenyl) pyruvate dioxygenase by NTBC are commented upon. PMID:16749798

Szczeci?ski, Przemys?aw; Gryff-Keller, Adam; Molchanov, Sergey

2006-06-01

209

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

NASA Astrophysics Data System (ADS)

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

Conte, P.; van Lagen, B.

2009-04-01

210

1H and 13C NMR spectra and solution structures of novel derivatives of 5-substituted creatinines  

NASA Astrophysics Data System (ADS)

Five creatinine derivatives were prepared by the treatment of creatinine with activated carbon and appropriate alcohol ( 1-4), or ammonia solution ( 5). Product structures were determined by 1H and 13C NMR spectroscopy in solution, including 2D HSQC and HMBC experiments. Then, the proton and carbon chemical shifts for these compounds were calculated using GIAO-DFT [B3LYP/6-311G(2d,p)] method and the Gaussian 03W program and furthermore for 1 and 5 using polarizable continuum model (PCM). The conclusions coming from the comparison of the experimental and theoretical spectra supported the adopted signal assignments and solved the structural problems due to the potential annular tautomerism of the investigated compounds. One can predict that 5-substituted creatinines, just like creatinine, appear in solution in the form of 2-amino-1,5-dihydro-1-methyl-4-imidazolone. Correlations between experimental and calculated substituent-induced chemical shifts for two tautomeric forms of 5-substituted creatinines indicate that the mechanism of the substituent influence in both tautomers for the investigated compounds appears to be analogous. We can predict that in solution this accepting inductive effect of substituent groups does not significantly influence the structure of creatinine molecule in solution. The analysis of coupling constants for 5-substituted creatinines gives information about conformation of the investigated molecules in solution.

Krawczyk, Hanna; Pietras, Agnieszka; Kraska, Anna

2007-01-01

211

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

SciTech Connect

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

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

2009-03-15

212

13C NMR measurements of Zeeman limited superconductivity in ?-(BEDT-TTF)2Cu(NCS)2  

NASA Astrophysics Data System (ADS)

The class of superconductors formulated by the BEDT-TTF molecule offers a unique ability to study superconductivity which is Zeeman limited, utilizing their qausi-2D layered structure. The critical field Hc2, which usually limits superconductivity due to orbital screening currents, can be suppressed by aligning the applied magnetic field parallel to the conducting layers. In this orientation, the field penetrates in the form of Josephson vortices, and the dominant effect of the magnetic field is from the Zeeman interaction with quasiparticles. We present 13C NMR measurements of the spin lattice relaxation rate as a function of applied field on a single crystal of ?-(BEDT-TTF)2Cu(NCS)2 after aligning the field in this orientation. A quadratic dependence is observed: R(B) ˜ B^2, which gives clear evidence of k-space nodes in the superconducting gap. Extending these measurements to field strengths near and above the Pauli limit, we observe a phase transition within the superconducting state at B=21.5T, and we comment on the compatibility of these results with the sought after FFLO state.

Wright, Jeffrey; Brugger, James; Schlueter, John; Kato, Reizo; Brown, Stuart

2011-03-01

213

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

214

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

PubMed

Gaseous ozone chemically reacts with unsaturated triglyceride substrates leading to ozonated derivatives with a wide potential applications, ranging from the petrochemical to the pharmaceutical industry. To date, an ultimate understanding of the ozone reactivity during sesame oil ozonation process as well as detailed (1)H and (13)C NMR assignments are lacking. A practical advantage of NMR is that a single NMR sample measurement can explain many issues, while similar analysis by traditional methods may require several independent and time-consuming measurements. Moreover, significant relationships among NMR spectra and both conventional chemical analysis and viscosity measurements have been found. Eventually, NMR could play an important role for quality attributes of ozonated oil derivatives. PMID:19900426

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

2010-02-01

215

NMR 13C-isotopic enrichment experiments to study carbon-partitioning into organic solutes in the red alga Grateloupia doryphora.  

PubMed

The red alga Grateloupia doryphora Montagne (Howe) (Cryptonemiales, Halymeniaceae) was used as a model to investigate the effects of changes in seawater salinity on the intracellular low-molecular-weight organic compounds. Carbon-partitioning into major organic solutes was followed by 13C nuclear magnetic resonance (NMR) spectroscopy on living algae incubated in NaH13CO3-enriched seawater, and by high resolution 1H and 13C NMR experiments performed on 13C-enriched algal extracts. NMR and high performance liquid chromatography (HPLC) analyses both demonstrated that floridoside level was the most affected by changes in salinity: it rose under the hypersaline treatment and decreased under hyposaline one. Moreover, at low salinity, the high labeling of floridoside (45.3% 13C-enrichment for C1) together with its low concentrations both provided evidence of great increase in the de novo biosynthesis and turnover rate. Our experiments also demonstrated a high incorporation of photosynthetic carbon into amino acids, especially glutamate, under hypoosmotic conditions. On the other hand, isethionic acid and N-methyl-methionine sulfoxide were only partly labeled, which indicates they do not directly derive from carbon photoassimilation. In algae exposed to high salinity, elevated concentrations of floridoside coupled to a low labeling (9.4%) were observed. These results suggest that hyperosmotic conditions stimulated floridoside biosynthesis from endogen storage products rather than from carbon assimilation through photosynthesis. PMID:15061080

Simon-Colin, Christelle; Kervarec, Nelly; Pichon, Roger; Deslandes, Eric

2004-01-01

216

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

NASA Astrophysics Data System (ADS)

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

Albrecht, Remy; Sebag, David; Verrecchia, Eric

2013-04-01

217

The 'Nuts and Bolts' of 13C NMR Spectroscopy at Elevated-Pressures and -Temperatures for Monitoring In Situ CO2 Conversion to Metal Carbonates  

NASA Astrophysics Data System (ADS)

We will present details of newly-constructed specialized NMR designed to conduct in situ elevated-pressure, elevated-temperature 13C NMR studies on unmixed slurries of minerals in the presence of CO2 or other gases. This static probe is capable of achieving 300 bar, 300C conditions, and it is designed to spectroscopically examine 13C signals in mixtures of solids, liquids, gases, and supercritical fluids. Ultimately, our aim is to monitor CO2 uptake in both ultramafic rocks and in more porous geological materials to understand the mechanisms of chemisorption as a function of temperature, pressure and pH. We will give details of the hardware setup, and we will show a variety of static in situ NMR, as well as ex situ 'magic-angle spinning' NMR to show the analyses that are possible of minerals in pure form and in mixtures. In addition, specific NMR pulse sequences, techniques, and modeling will be described in detail. In this in situ NMR probe, we are able to simulate processes at geologically relevant fluid pressures and temperatures, monitoring the kinetics of CO2 conversion to carbonates. The in situ NMR experiments consist of heterogeneous mixtures of rock, salty brine solution, and moderate pressure CO2 gas at elevated temperatures. The purpose of studying these reactions is to determine conditions that affect the efficacy of carbonate formation in various targeted geological reservoirs (i.e., peroditite, or others). Via 13C NMR, we have spectroscopically characterized and quantified the conversion of CO2 to magnesium carbonate and calcium carbonate minerals, including metastable intermediates (such as hydromagnesite, or dypingite in the case of magnesium carbonate species, or vaterite in the case of calcium carbonate species). Such species are distinguishable from a combination of the 13C isotropic chemical shift, the static 13C lineshape, and changes in spin-lattice (T1) relaxation times. We will demonstrate that NMR can be used for quantitative characterization of multiple metastable mineral phases in pure forms and in mixtures. Notably, NMR spectroscopy is able to observe signals from amorphous materials, and mixtures of both crystalline and amorphous species can be analyzed. NMR results are verified through a combination of Raman spectroscopy and powder XRD (of crystalline species). Further, we have examined the effects on mineralization reactions of pH gradients in the sample--also monitored in situ by NMR--and these results will be presented. Reference: 'In Situ Measurement of Magnesium Carbonate Formation from CO2 Using Static High-Pressure and -Temperature 13C NMR' J. Andrew Surface, Philip Skemer, Sophia E. Hayes, and Mark S. Conradi, Environ. Sci. Technol. 2013, 47, 119-125. DOI: 10.1021/es301287n

Moore, J. K.; Surface, J. A.; Skemer, P. A.; Conradi, M. S.; Hayes, S. E.

2013-12-01

218

A new Schiff base compound N,N'-(2,2-dimetylpropane)-bis(dihydroxylacetophenone): synthesis, experimental and theoretical studies on its crystal structure, FTIR, UV-visible, 1H NMR and 13C NMR spectra.  

PubMed

The Schiff base compound, N,N'-(2,2-dimetylpropane)-bis(dihydroxylacetophenone) (NDHA) is synthesized through the condensation of 2-hydroxylacetophenone and 2,2-dimethyl 1,3-amino propane in methanol at ambient temperature. The yellow crystalline precipitate is used for X-ray single-crystal determination and measuring Fourier transform infrared (FTIR), UV-visible, (1)H NMR and (13)C NMR spectra. Electronic structure calculations at the B3LYP, PBEPBE and PW91PW91 levels of theory are performed to optimize the molecular geometry and to calculate the FTIR, (1)H NMR and (13)C NMR spectra of the compound. Time-dependent density functional theory (TDDFT) method is used to calculate the UV-visible spectrum of NDHA. Vibrational frequencies are determined experimentally and compared with those obtained theoretically. Vibrational assignments and analysis of the fundamental modes of the compound are also performed. All theoretical methods can well reproduce the structure of the compound. The (1)H NMR and (13)C NMR chemical shifts calculated by all DFT methods are consistent with the experimental data. However, the NMR shielding tensors computed at the B3LYP/6-31+G(d,p) level of theory are in better agreement with experimental (1)H NMR and (13)C NMR spectra. The electronic absorption spectrum calculated at the B3LYP/6-31+G(d,p) level by using TD-DFT method is in accordance with the observed UV-visible spectrum of NDHA. In addition, some quantum descriptors of the molecule are calculated and conformational analysis is performed and the results were compared with the crystallographic data. PMID:21763188

Saheb, Vahid; Sheikhshoaie, Iran

2011-10-15

219

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

220

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

221

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

USGS Publications Warehouse

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

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

2004-01-01

222

Density functional investigation of intermolecular effects on {sup 13}C NMR chemical-shielding tensors modeled with molecular clusters  

SciTech Connect

A quantum-chemical method for modeling solid-state nuclear magnetic resonance chemical-shift tensors by calculations on large symmetry-adapted clusters of molecules is demonstrated. Four hundred sixty five principal components of the {sup 13}C chemical-shielding tensors of 24 organic materials are analyzed. The comparison of calculations on isolated molecules with molecules in clusters demonstrates that intermolecular effects can be successfully modeled using a cluster that represents a local portion of the lattice structure, without the need to use periodic-boundary conditions (PBCs). The accuracy of calculations which model the solid state using a cluster rivals the accuracy of calculations which model the solid state using PBCs, provided the cluster preserves the symmetry properties of the crystalline space group. The size and symmetry conditions that the model cluster must satisfy to obtain significant agreement with experimental chemical-shift values are discussed. The symmetry constraints described in the paper provide a systematic approach for incorporating intermolecular effects into chemical-shielding calculations performed at a level of theory that is more advanced than the generalized gradient approximation. Specifically, NMR parameters are calculated using the hybrid exchange-correlation functional B3PW91, which is not available in periodic codes. Calculations on structures of four molecules refined with density plane waves yield chemical-shielding values that are essentially in agreement with calculations on clusters where only the hydrogen sites are optimized and are used to provide insight into the inherent sensitivity of chemical shielding to lattice structure, including the role of rovibrational effects.

Holmes, Sean T.; Dybowski, Cecil [Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716 (United States); Iuliucci, Robbie J. [Department of Chemistry, Washington and Jefferson College, Washington, Pennsylvania 15301 (United States); Mueller, Karl T. [Department of Chemistry, Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)

2014-10-28

223

Geometries and tautomerism of OHN hydrogen bonds in aprotic solution probed by H/D isotope effects on (13)C NMR chemical shifts.  

PubMed

The (1)H and (13)C NMR spectra of 17 OHN hydrogen-bonded complexes formed by CH(3)(13)COOH(D) with 14 substituted pyridines, 2 amines, and N-methylimidazole have been measured in the temperature region between 110 and 150 K using CDF(3)/CDF(2)Cl mixture as solvent. The slow proton and hydrogen bond exchange regime was reached, and the H/D isotope effects on the (13)C chemical shifts of the carboxyl group were measured. In combination with the analysis of the corresponding (1)H chemical shifts, it was possible to distinguish between OHN hydrogen bonds exhibiting a single proton position and those exhibiting a fast proton tautomerism between molecular and zwitterionic forms. Using H-bond correlations, we relate the H/D isotope effects on the (13)C chemical shifts of the carboxyl group with the OHN hydrogen bond geometries. PMID:20849091

Tolstoy, Peter M; Guo, Jing; Koeppe, Benjamin; Golubev, Nikolai S; Denisov, Gleb S; Smirnov, Sergei N; Limbach, Hans-Heinrich

2010-10-14

224

A straightforward method for stereospecific assignment of val and leu prochiral methyl groups by solid-state NMR: Scrambling in the [2-13C]Glucose labeling scheme  

NASA Astrophysics Data System (ADS)

The unambiguous stereospecific assignment of the prochiral methyl groups in Val and Leu plays an important role in the structural investigation of proteins by NMR. Here, we present a straightforward method for their stereospecific solid-state NMR assignment based on [2-13C]Glucose ([2-13C]Glc) as the sole carbon source during protein expression. The approach is fundamentally based on the stereo-selective biosynthetic pathway of Val and Leu, and the co-presence of [2-13C]pyruvate produced mainly by glycolysis and [3-13C]/[1,3-13C]pyruvate most probably formed through scrambling in the pentose phosphate pathway. As a consequence, the isotope spin pairs 13C?-13C?2 and 13C?-13C?1 in Val, and 13C?-13C?2 and 13C?-13C?1 in Leu are obtained. The approach is successfully demonstrated with the stereospecific assignment of the methyl groups of Val and Leu of type 3 secretion system PrgI needles and microcrystalline ubiquitin.

Lv, Guohua; Faßhuber, Hannes Klaus; Loquet, Antoine; Demers, Jean-Philippe; Vijayan, Vinesh; Giller, Karin; Becker, Stefan; Lange, Adam

2013-03-01

225

Mechanism of formation of humus coatings on mineral surfaces 3. Composition of adsorbed organic acids from compost leachate on alumina by solid-state 13C NMR  

USGS Publications Warehouse

The adsorption of compost leachate DOC on alumina is used as a model for elucidation of the mechanism of formation of natural organic coatings on hydrous metal oxide surfaces in soils and sediments. Compost leachate DOC is composed mainly of organic acid molecules. The solid-state 13C NMR spectra of these organic acids indicate that they are very similar in composition to aquatic humic substances. Changes in the solid-state 13C NMR spectra of compost leachate DOC fractions adsorbed on alumina indicate that the DOC molecules are most likely adsorbed on metal oxide surfaces through a combination of polar and hydrophobic interaction mechanisms. This combination of polar and hydrophobic mechanism leads to the formation of bilayer coatings of the leachate molecules on the oxide surfaces.

Wershaw, R.L.; Llaguno, E.C.; Leenheer, J.A.

1996-01-01

226

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

227

Direct quantification of M\\/G ratio from 13C CP-MAS NMR spectra of alginate powders by multivariate curve resolution  

Microsoft Academic Search

Multivariate curve resolution (MCR) was applied to 13C cross-polarisation (CP) magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of non-depolymerised alginate powders obtained from brown seaweed plus a pure mannuronate sample isolated from Pseudomonas fluorescens for estimation of the mannuronic acid\\/guluronic acid ratio (M\\/G ratio). An excellent MCR model with a correlation coefficient of r2=0.99 was established between the

Tina Salomonsen; Henrik Max Jensen; Flemming Hofmann Larsen; Stefan Steuernagel; Søren Balling Engelsen

2009-01-01

228

Solution 13C NMR spectroscopy of polyamide homopolymers (nylons 6, 11, 12, 66, 69, 610 and 612) and several commercial copolymers  

Microsoft Academic Search

Well-resolved 13C NMR spectra of nylons 6, 11, 12, 66, 69, 610, and 612 dissolved in 4:1 TFE\\/CDCl3 allowed complete assignment of all major backbone peaks. In addition, several low intensity peaks were identified representing cis amide groups, acid end-groups and amine end-groups. Several peaks associated with the trans amide units in the spectra of each polyamide homopolymer were identified

R. D. Davis; W. L. Jarrett; L. J. Mathias

2001-01-01

229

GlyNest and CASPER: two independent approaches to estimate 1H and 13C NMR shifts of glycans available through a common web-interface  

Microsoft Academic Search

GlyNest and CASPER (www.casper.organ.su.se\\/ casper\\/) are two independent services aiming to predict 1H- and 13C-NMR chemical shifts of glycans. GlyNest estimates chemical shifts of glycans based on a spherical environment encoding scheme for each atom. CASPER is an increment rule-based approach which uses chemical shifts of the free reducing monosaccharides which are altered according to attached residues of an oligo-

Alexander Loß; Roland Stenutz; Eberhard Schwarzer; Claus-wilhelm Von Der Lieth

2006-01-01

230

1H and 13C NMR assignments for 6-demethylvermistatin and two penicillide derivatives from the mangrove fungus Guignardia sp. (No. 4382) from the South China Sea.  

PubMed

One new compound 6-demethylvermistatin (1), together with two known compounds, the penicillide derivatives (2) and (3) were isolated from the mangrove fungus Guignardia sp. No. 4382 obtained from the South China Sea. Their structures were assigned using high-resolution electron ionization mass spectrometry(HREIMS), (1)H and (13)C NMR spectra, DEPT, and by 2D COSY, HMQC, and HMBC experiments. The absolute configuration of 1 was established by comparison of its CD with that of vermistatin. PMID:18338749

Xia, Xue-Kui; Liu, Fan; She, Zhi-Gang; Yang, Li-Guo; Li, Meng-Feng; Vrijmoed, L L P; Lin, Yong-Cheng

2008-07-01

231

1H, 13C and 15N NMR study of 2-alkylnitrosoamino-4-nitropyridines and N-oxides: An example on restricted inversion of sp 3 nitrogen  

NASA Astrophysics Data System (ADS)

The 1H, 13C and 15N NMR chemical shifts of seven 2-alkylnitrosoamino-4-nitropyridines and seven 2-alkylnitrosoamino-4-nitropyridine N-oxides have been assigned. The GIAO/DFT 13C chemical shifts of energetically optimized structures have been calculated. The results were compared to the chemical shifts of previously studied 2-alkylamino and 2-alkylnitramino derivatives of 4-nitropyridine and 4-nitropyridine N-oxide. In sterically crowded ortho-substituted congener (2-ethylnitrosoamino-3-methyl-4-nitropyridine N-oxide) restricted inversion of pyramidal amino nitrogen forms a chiral center in the molecule and makes the geminal protons of N-CH 2-moiety diastereotopic. In 5- and 6-CH 3-substituted derivatives this diastereotopism disappears, but the rotation around N-CH 2 sigma bond in all congeners is so slow in NMR time scale, that 1H, 13C and 15N NMR chemical shifts could be detected for two conformers. In 4-nitropyridine and 4-nitropyridine N-oxide derivatives the shielding of aromatic nitrogen is very sensitive to the ring substituents. 2-Alkylnitrosoamino group produces a significant shielding based on conjugation between the ring and the nitrosoamino group.

Laihia, K.; Puszko, A.; Kolehmainen, E.; Lorenc, J.

2007-04-01

232

Analysis of affinity supports by 13C CP/MAS NMR spectroscopy: application to carbonyldiimidazole- and novel tresyl chloride-synthesized agarose and silica gels.  

PubMed

A major problem in affinity technology is the analysis of the synthesized solid supports, since liquid phase methodology can generally not be applied. Recently we reported a novel reaction sequence for the 2,2,2-trifluoroethanesulfonyl chloride (tresyl chloride) coupling of nucleophiles [Demiroglou et al. (1994) Angew. Chem. Int. Ed. Engl. 33, 120-123] to agarose and concluded that previously proposed structures could not be correct. However it was not possible for us to conclusively define the new reaction products because the agarose derivatives could not be solubilized for customary liquid state 13C NMR analysis. Therefore in this paper solid state 13C CP/MAS NMR spectroscopy is applied for the first time to the polysacharide agarose. Using alkyl agarose derivatives prepared by the carbonyldiimidazol method as control we found that reliable spectra in agreement with the published reaction mechanism could be obtained. The method was then applied to the novel reaction products of the tresyl chloride reaction. From the solid state 13C NMR spectra and other quantitative data it is concluded that a beta-sulfonyl carboxylic acid is generated during alkaline hydrolysis of tresyl agarose and that alkyl amines are coupled by a beta-sulfonyl amide bond in an elimination-addition reaction in the absence of SO- and SC-scission of the tresyl group. In the case of alkane thiol coupling the absence of SC-scission cannot be demonstrated indicating either a different reaction mechanism or possibly a mixture of reaction products. PMID:9052977

Zumbrink, T; Demiroglou, A; Jennissen, H P

1995-01-01

233

Hydrogen bond geometries and proton tautomerism of homoconjugated anions of carboxylic acids studied via H/D isotope effects on 13C NMR chemical shifts.  

PubMed

Ten formally symmetric anionic OHO hydrogen bonded complexes, modeling Asp/Glu amino acid side chain interactions in nonaqueous environment (CDF(3)/CDF(2)Cl solution, 200-110 K) have been studied by (1)H, (2)H, and (13)C NMR spectroscopy, i.e. intermolecularly H-bonded homoconjugated anions of acetic, chloroacetic, dichloroacetic, trifluoroacetic, trimethylacetic, and isobutyric acids, and intramolecularly H-bonded hydrogen succinate, hydrogen rac-dimethylsuccinate, hydrogen maleate, and hydrogen phthalate. In particular, primary H/D isotope effects on the hydrogen bond proton signals as well as secondary H/D isotope effects on the (13)C signals of the carboxylic groups are reported and analyzed. We demonstrate that in most of the studied systems there is a degenerate proton tautomerism between O-H···O(-) and O(-)···H-O structures which is fast in the NMR time scale. The stronger is the proton donating ability of the acid, the shorter and more symmetric are the H-bonds in each tautomer of the homoconjugate. For the maleate and phthalate anions exhibiting intramolecular hydrogen bonds, evidence for symmetric single well potentials is obtained. We propose a correlation between H/D isotope effects on carboxylic carbon chemical shifts and the proton transfer coordinate, q(1) = ½(r(OH) - r(HO)), which allows us to estimate the desired OHO hydrogen bond geometries from the observed (13)C NMR parameters, taking into account the degenerate proton tautomerism. PMID:22738093

Guo, Jing; Tolstoy, Peter M; Koeppe, Benjamin; Golubev, Nikolai S; Denisov, Gleb S; Smirnov, Sergei N; Limbach, Hans-Heinrich

2012-11-26

234

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

PubMed Central

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

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

2014-01-01

235

Synthesis and NMR spectral studies of some 2,6-diarylpiperidin-4-one O-benzyloximes  

NASA Astrophysics Data System (ADS)

Variously substituted 2,6-diarylpiperidin-4-one O-benzyloximes were synthesized by the direct condensation of the corresponding 2,6-diarylpiperidin-4-ones with O-benzylhydroxylamine hydrochloride. All the synthesized compounds are characterized by IR, Mass and NMR spectral studies. NMR spectral assignments are made unambiguously by their one-dimensional ( 1H NMR and 13C NMR) and two-dimensional ( 1H- 1H COSY, NOESY, HSQC and HMBC) NMR spectra. All the synthesized compounds are resulted as single isomer, i.e., exclusively E isomer ( 9- 14). The conformational preference of 2,6-diarylpiperidin-4-one oxime ethers with and without alkyl substituents at C-3 and C-5 has also been discussed using the spectral studies. The observed chemical shifts and coupling constants suggest that compounds 8- 13 adopt normal chair conformation with equatorial orientation of all the substituents while compound 14 contributes significant boat conformation along with the predominant chair conformation in solution. The effect of oximination on ring carbons, their associated protons, alkyl substituents and ipso carbons are studied. Every proton in the piperidone ring of the oxime ether is observed as distinct signal due to oximination. The order of chemical shift magnitude in compound 8 is H-2a > H-6a > H-5e > H-3e > H-3a > H-5a. For 9- 12, the order is H-6a > H-5e > H-2a > H-3a > H-5a, for 13, H-6a > H-2a > H-5e > H-3a > H-5a and for 14, the order is H-2a > H-6a > H-5e > H-3a > H-5a while the 13C chemical shift magnitude for 8- 14 due to oximination is C-2 > C-6 > C-3 > C-5.

Parthiban, P.; Balasubramanian, S.; Aridoss, G.; Kabilan, S.

2008-06-01

236

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

USGS Publications Warehouse

We have used advanced and quantitative solid-state nuclear magnetic resonance (NMR) techniques to investigate structural changes in a series of type II kerogen samples from the New Albany Shale across a range of maturity (vitrinite reflectance R0 from 0.29% to 1.27%). Specific functional groups such as CH3, CH2, alkyl CH, aromatic CH, aromatic C-O, and other nonprotonated aromatics, as well as "oil prone" and "gas prone" carbons, have been quantified by 13C NMR; atomic H/C and O/C ratios calculated from the NMR data agree with elemental analysis. Relationships between NMR structural parameters and vitrinite reflectance, a proxy for thermal maturity, were evaluated. The aromatic cluster size is probed in terms of the fraction of aromatic carbons that are protonated (???30%) and the average distance of aromatic C from the nearest protons in long-range H-C dephasing, both of which do not increase much with maturation, in spite of a great increase in aromaticity. The aromatic clusters in the most mature sample consist of ???30 carbons, and of ???20 carbons in the least mature samples. Proof of many links between alkyl chains and aromatic rings is provided by short-range and long-range 1H-13C correlation NMR. The alkyl segments provide most H in the samples; even at a carbon aromaticity of 83%, the fraction of aromatic H is only 38%. While aromaticity increases with thermal maturity, most other NMR structural parameters, including the aromatic C-O fractions, decrease. Aromaticity is confirmed as an excellent NMR structural parameter for assessing thermal maturity. In this series of samples, thermal maturation mostly increases aromaticity by reducing the length of the alkyl chains attached to the aromatic cores, not by pronounced growth of the size of the fused aromatic ring clusters. ?? 2010 Elsevier Ltd. All rights reserved.

Mao, J.; Fang, X.; Lan, Y.; Schimmelmann, A.; Mastalerz, M.; Xu, L.; Schmidt-Rohr, K.

2010-01-01

237

A [sup 13]C NMR study of ethylene adsorbed on reduced and oxygen-covered Ag surfaces  

SciTech Connect

[sup 13]C-enriched ethylene was adsorbed on both clean and oxygen-covered Ag particles dispersed on [eta]-Al[sub 2]O[sub 3]. Irreversibly adsorbed C[sub 2]H[sub 4] on O-covered Ag exhibited an upfield shift of [minus]20 ppm relative to gas-phase C[sub 2]H[sub 4], whereas a narrower line and smaller shift of [minus]5 ppm occurred for C[sub 2]H[sub 4] reversibly adsorbed on reduced Ag. In addition to the resonance at 103 ppm for irreversibly adsorbed C[sub 2]H[sub 4], CP/MAS NMR spectra also gave resonances at 179, 170, 164, 159, and 19 ppm for the O-covered Ag sample. The CP/MAS spectrum for Ag acetate powder clearly identified the 179- and 19-ppm peaks as those associated with the carboxyl and methyl carbons of the acetate anion, and the peaks at 159, 164, and 170 ppm were assigned to oxalate, formate, and carbonate (or possibly acetic anhydride) species, respectively, based on previous studies. When heated to 473 K the adsorbed C[sub 2]H[sub 4] disappeared and only acetate and oxalate groups were observed, and continued heating to 573 K removed almost all resonances. No C[sub 2]H[sub 4]O was unambiguously detected, thus with this unpromoted Ag catalyst utilizing a high-surface-area alumina the observable surface species appeared to be those associated with complete combustion, with acetate and oxalate predominating during reaction. These results directly confirm the presence of an Ag acetate species which has been proposed previously to be an intermediate in complete combustion, and the presence of the other three species support earlier tentative assignments based on IR and TPR spectroscopy. Chemical shifts at 61, 28, and 13 ppm were indicative of alkoxy species formed on Bronsted-acid sites on the Al[sub 2]O[sub 3] surface. 58 refs., 8 figs., 4 tabs.

Plischke, J.K.; Benesi, A.J.; Vannice, M.A. (Pennsylvania State Univ., University Park, PA (United States))

1992-11-01

238

Extraction of multiple pure component 1H and 13C NMR spectra from two mixtures: novel solution obtained by sparse component analysis-based blind decomposition.  

PubMed

Sparse component analysis (SCA) is demonstrated for blind extraction of three pure component spectra from only two measured mixed spectra in (13)C and (1)H nuclear magnetic resonance (NMR) spectroscopy. This appears to be the first time to report such results and that is the first novelty of the paper. Presented concept is general and directly applicable to experimental scenarios that possibly would require use of more than two mixtures. However, it is important to emphasize that number of required mixtures is always less than number of components present in these mixtures. The second novelty is formulation of blind NMR spectra decomposition exploiting sparseness of the pure components in the wavelet basis defined by either Morlet or Mexican hat wavelet. This enabled accurate estimation of the concentration matrix and number of pure components by means of data clustering algorithm and pure components spectra by means of linear programming with constraints from both (1)H and (13)C NMR experimental data. The third novelty is capability of proposed method to estimate number of pure components in demanding underdetermined blind source separation (uBSS) scenario. This is in contrast to majority of the BSS algorithms that assume this information to be known in advance. Presented results are important for the NMR spectroscopy-associated data analysis in pharmaceutical industry, medicine diagnostics and natural products research. PMID:19808106

Kopriva, Ivica; Jeri?, Ivanka; Smrecki, Vilko

2009-10-27

239

Suppression of spectral anomalies in SSFP-NMR signal by the Krylov Basis Diagonalization Method.  

PubMed

Krylov Basis Diagonalization Method (KBDM) is a numerical procedure used to fit time domain signals as a sum of exponentially damped sinusoids. In this work KBDM is used as an alternative spectral analysis tool, complimentary to Fourier transform. We report results obtained from (13)C Nuclear Magnetic Resonance (NMR) by Steady State Free Precession (SSFP) measurements in brucine, C23H26N2O4. Results lead to the conclusion that the KBDM can be successfully applied, mainly because it is not influenced by truncation or phase anomalies, as observed in the Fourier transform spectra. PMID:24747788

Moraes, Tiago Bueno; Santos, Poliana Macedo; Magon, Claudio Jose; Colnago, Luiz Alberto

2014-06-01

240

Dynamic characterization of a DNA repair enzyme: NMR studies of [methyl-13C]methionine-labeled DNA polymerase beta.  

PubMed

Crystallographic characterization of DNA polymerase beta (pol beta) has suggested that multiple-domain and subdomain motions occur during substrate binding and catalysis. NMR studies of [methyl-(13)C]methionine-labeled pol beta were conducted to characterize the structural and dynamic response to ligand binding. The enzyme contains seven methionine residues, one of which is at the amino terminus and is partially removed by the expression system. Three of the methyl resonances were readily assigned using site-directed mutants. Assignment of the resonances of Met155, Met158, and Met191 was more difficult due to the spatial proximity of these residues, so that assignments were based on NOESY-HSQC data and on the response to paramagnetic Co(2+) addition, as well as shift perturbations observed for the site-directed mutants. The response of the methyl resonances to substrate binding was evaluated by the serial addition of a template oligonucleotide, a downstream 5'-phosphorylated oligonucleotide, and a primer oligonucleotide to create a two-nucleotide-gapped DNA substrate. Addition of the single-stranded template DNA resulted in selective broadening of the methyl resonance of Met18 in the 8 kDa lyase domain, and this resonance then shifted and sharpened upon addition of a 5'-phosphate-terminated downstream complementary oligonucleotide. Conversion of the two-nucleotide-gapped DNA substrate to a single-nucleotide-gapped substrate by incorporation of ddCMP produced a small perturbation of the Met236 resonance, which makes contact with the primer strand in the crystal structure. The addition of a second equivalent of ddCTP to form the pol beta-DNA-ddCTP ternary complex resulted in significant shifts for the resonances corresponding to Met155, Met191, Met236, and Met282. The Met155 methyl resonance is severely broadened, while the Met191 and Met282 resonances exhibit significant but less extreme broadening. Since only Met236 makes contact with the substrate, the effects on Met155, Met236, and Met282 result from indirect conformational and dynamic perturbations. Previous crystallographic characterization of this abortive complex indicated that a polymerase subdomain or segment (alpha-helix N) repositions itself to form one face of the binding pocket for the nascent base pair. Met282 serves as a probe for motion in this segment. Addition of Mg(2+)-dATP to pol beta in the absence of DNA produced qualitatively similar but much smaller effects on Met191 and Met155, but did not strongly perturb Met282, leading to the conclusion that Mg(2+)-dATP alone is insufficient to produce the large conformational changes that are observed in the abortive complex involving the gapped DNA with a blocked primer and ddNTP. Thus, the NMR data indicate that the nucleotide-DNA interaction appears to be essential for conformational activation. PMID:15248749

Bose-Basu, Bidisha; DeRose, Eugene F; Kirby, Thomas W; Mueller, Geoffrey A; Beard, William A; Wilson, Samuel H; London, Robert E

2004-07-20

241

Detailed analysis of coupling constants and isotope effects in NMR spectra of isotopomers of (12)C(68) (13)C(2).  

PubMed

A preliminary study of the long-range (i.e. two-bond or longer) (13)C--(13)C coupling constants in natural abundance C(70) shows, consistent with recent theoretical calculations by Peralta et al. that the largest long-range J(CC) values for the polar and equatorial sites are clearly smaller than the largest long-range J(CC) values for the other three sites. The unusually large size of the (2)J(CC) couplings between inequivalent carbons in a nonpolar pentagon in C(70) has no analog among (2)J(CC) data reported for planar aromatic compounds. No long-range J(CC) values appear to have been reported for any curved aromatic compounds. In addition, much more precise (1)J(CC) values were obtained for C(70) than was possible about 15 years ago. Comparing the chemical shifts for each of the five isotopomers of C(70) containing only one (13)C nucleus and the frequencies of the satellites for each of the four isotopomers containing two adjacent and inequivalent (13)C nuclei indicates that replacing (12)C with (13)C shields the adjacent (13)C nucleus by 15 to 23 ppb, consistent with the limited (1)Delta(13)C((13/12)C) isotope effect data available on a few small aromatic molecules. Such measurements become possible with natural abundance C(70) only by using a (13)C cryoprobe and a high-field spectrometer (700 MHz). The additional information that could be obtained from a spectrum obtained under ultrahigh resolution conditions is discussed. Secure identification of the singlets arising from the four (12)C(68) (13)C(2) isotopomers with equivalent adjacent (13)C nuclei is necessary to allow the largest long-range J(CC) values to be precisely determined. The presence of numerous isotopomers containing two or more (13)C nuclei would present a great challenge in interpreting the various signals in a spectrum obtained under ultrahigh resolution conditions. PMID:16477686

Anklin, Clemens; Alemany, Lawrence B

2006-03-01

242

Improvement of the inverse-gated-decoupling sequence for a faster quantitative analysis by 13C NMR  

Microsoft Academic Search

The inverse-gated-decoupling sequence enables quantitative 1H decoupled 13C spectra to be obtained. We modified this sequence so as to obtain the same result in less time. For that, we determined the optimal 13C longitudinal-magnetisation initial value for a faster relaxation while 1H decoupler is stopped. This value can be calculated via the longitudinal relaxation times and the nuclear Overhauser effects.

Patrick Giraudeau; Jian Long Wang; Évelyne Baguet

2006-01-01

243

1H- and 13C-nmr assignments of phyllanthin and hypophyllanthin: lignans that enhance cytotoxic responses with cultured multidrug-resistant cells.  

PubMed

Complete 1H-nmr data and unambiguous assignments of the 13C-nmr spectra of phyllanthin [1] and hypophyllanthin [2] were obtained through extensive nmr studies, including homonuclear COSY, homonuclear decoupling, APT, HETCOR, nOe difference, selective INEPT, and COLOC experiments. The absolute configuration of hypophyllanthin [2] was determined by cd. Neither of these lignans demonstrated significant cytotoxic activity when evaluated with a battery of cultured mammalian cells, but both were found to enhance the cytotoxic response mediated by vinblastine with multidrug-resistant KB cells. In addition, 1 was found to displace the binding of vinblastine with membrane vesicles derived from this cell line, suggesting an interaction with the P-glycoprotein. PMID:8385184

Somanabandhu, A; Nitayangkura, S; Mahidol, C; Ruchirawat, S; Likhitwitayawuid, K; Shieh, H L; Chai, H; Pezzuto, J M; Cordell, G A

1993-02-01

244

Differences between lignin in unprocessed wood, milled wood, mutant wood, and extracted lignin detected by 13C solid-state NMR.  

PubMed

Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy was applied to intact and isolated loblolly pine wood samples to identify potential structural changes induced by tree age, milling, lignin extraction, or naturally occurring mutations. Special attention was paid to ketone and aldehyde as well as nonpolar alkyl groups, which could be observed at low concentrations (<2 in 1000 C) using improved spinning-sideband suppression with gated decoupling. Carbonyl structures were present in intact wood, and there are more keto groups than aldehydes. Their concentrations increased from juvenile to mature wood and with milling time, whereas extraction did not alter the C=O fraction. Significant amounts of aldehyde and dihydroconiferyl alcohol residues were present in coniferyl aldehyde dehydrogenase-deficient wood, confirming solution-state NMR spectra of the corresponding lignin. These results demonstrate the utility of solid-state NMR as an assay for changes in the lignin structure of genetically modified plants. PMID:17177487

Mao, Jingdong; Holtman, Kevin M; Scott, Jay T; Kadla, John F; Schmidt-Rohr, Klaus

2006-12-27

245

NMR studies of the stability, protonation States, and tautomerism of (13)C- AND (15)N-labeled aldimines of the coenzyme pyridoxal 5'-phosphate in water.  

PubMed

We have measured the pH-dependent (1)H, (13)C, and (15)N NMR spectra of pyridoxal 5'-phosphate ((13)C(2)-PLP) mixed with equal amounts of either doubly (15)N-labeled diaminopropane, (15)N(?)-labeled l-lysine, or (15)N(?)-labeled l-lysine as model systems for various intermediates of the transimination reaction in PLP-dependent enzymes. At low pH, only the hydrate and aldehyde forms of PLP and the free protonated diamines are present. Above pH 4, the formation of single- and double-headed aldimines (Schiff bases) with the added diamines is observed, and their (13)C and (15)N NMR parameters have been characterized. For 1:1 mixtures the single-headed aldimines dominate. In a similar way, the NMR parameters of the geminal diamine formed with diaminopropane at high pH are measured. However, no geminal diamine is formed with l-lysine. In contrast to the aldimine formed with the ?-amino group of lysine, the aldimine formed with the ?-amino group is unstable at moderately high pH but dominates slightly below pH 10. By analyzing the NMR data, both the mole fractions of the different PLP species and up to 6 different protonation states including their pK(a) values were obtained. Furthermore, the data show that all Schiff bases are subject to a proton tautomerism along the intramolecular OHN hydrogen bond, where the zwitterionic form is favored before deprotonation occurs at high pH. This observation, as well as the observation that around pH 7 the different PLP species are present in comparable amounts, sheds new light on the mechanism of the transimination reaction. PMID:21067170

Chan-Huot, Monique; Sharif, Shasad; Tolstoy, Peter M; Toney, Michael D; Limbach, Hans-Heinrich

2010-12-28

246

The conformational stability, solvation and the assignments of the experimental infrared, Raman, (1)H and (13)C NMR spectra of the local anesthetic drug lidocaine.  

PubMed

The structure, vibrational and (1)H and (13)C NMR spectra of the local anesthetic drug lidocaine were investigated by the B3LYP/6-311G(??) calculations. The molecule was predicted to have the non-planar cis (NCCN?0°) structures being about 2-6kcal/mol lower in energy than the corresponding trans (NCCN?180°) forms. The calculated NCCN (9.6°) and CNCC (-132.2°) torsional angles were in a good qualitative agreement with the reported X-ray angles (3.1 and 13.0°, -102.67 and -77.9°, respectively, for H-bonded dimers). The Gibbs energy of solution of lidocaine in formamide, water, dimethylsulfoxide, acetonitrile, methanol, ethanol and chloroform solutions was estimated at the B3LYP level. The predicted affinity of lidocaine toward the alcohols, acetonitrile and chloroform solutions was in excellent agreement with the reported experimental solubility of the drug in organic solvents. The analysis of the observed vibrational spectra is consistent with the presence of lidocaine in only one conformation at room temperature. The (1)H and (13)C NMR spectra of lidocaine were interpreted by experimental and DFT calculated chemical shifts of the drug. The RMSD between experimental and theoretical (1)H and (13)C chemical shifts for lidocaine is 0.47 and 8.26ppm, respectively. PMID:25721654

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

2015-05-01

247

Rate determining step in phospholipase A/sub 2/ mechanism: /sup 18/O isotope exchange determined by /sup 13/C NMR  

SciTech Connect

Pancreatic and venom phospholipase A/sub 2/ display a marked preference for micellar substrates and act poorly on monomeric substrates. The authors have now examined the merit of the proposal that the product-release step is slow, but is accelerated when the enzyme acts on aggregated phospholipids. Measurements of H/sub 2/ /sup 18/O isotope exchange into specifically-labeled substrate was used to obtain information on the rate-limiting step in the enzyme action. A novel technique of distinguishing /sup 18/O incorporation by /sup 13/C-/sup 18/O vs /sup 13/C-/sup 16/O chemical shift differences at 126 MHz for /sup 13/C NMR was employed. The enzymatic hydrolysis of a micellar phosphatidylcholine analogue of platelet activating factor, 1-alkyl, 2 (1-/sup 13/C)-lauroyl-sn-glycero-3-phosphoryl-choline proceeds by O-acyl cleavage of the sn-2 ester bond. The reaction was examined for the possibility of simultaneous /sup 18/O incorporation into the substrate. No exchange was found suggesting that the catalytic step is not followed by a higher energy transition state and that it or a step before it appears to be rate-limiting.

Fanni, T.; Lombardo, D.; Plueckthun, A.; Dennis, E.A.

1986-05-01

248

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

NASA Astrophysics Data System (ADS)

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

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

2008-02-01

249

Discrimination of 13C NMR signals in solid material with liquid-like behavior presenting residual dipolar proton-proton homonuclear interactions: application on seeds  

NASA Astrophysics Data System (ADS)

In this communication, we propose, a modified spin echo fourier transform (SEFT) experiment run under magic angle spinning (MAS) to obtain structural informations of the liquid-like domains inside complex organic materials. It includes a proton-proton dipolar decoupling such as BLEW12 or Lee-Goldburg sequence just after the 180° 13C refocusing pulse and short echo delays are used in order to overcome T2 relaxation. This very easy implemented sequence allows a clear discrimination among fast relaxing 13C signals between those with a pure liquid-like behavior and those presenting residual proton-proton dipolar coupling. The interests of the sequence, combined with other classical NMR experiments, are illustrated on whole vegetable seeds that represent an example of a complex material.

Bardet, Michel; Foray, Marie F.

2003-02-01

250

Direct quantification of M/G ratio from (13)C CP-MAS NMR spectra of alginate powders by multivariate curve resolution.  

PubMed

Multivariate curve resolution (MCR) was applied to (13)C cross-polarisation (CP) magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of non-depolymerised alginate powders obtained from brown seaweed plus a pure mannuronate sample isolated from Pseudomonas fluorescens for estimation of the mannuronic acid/guluronic acid ratio (M/G ratio). An excellent MCR model with a correlation coefficient of r(2)=0.99 was established between the estimated M/G ratios and the M/G ratios obtained from the traditional (1)H solution state NMR method. The new method allows for successful determination of the M/G ratio independent of the calcium content (at least up to 2.4%, which was the upper limit in this study) with a root mean square error of prediction of 0.05. It is thus concluded that (13)C CP-MAS NMR in combination with multivariate curve resolution is a reliable, convenient (no sample preparation is required) and relatively rapid method for M/G ratio determinations of alginates and it may serve as a good alternative to the chemical techniques traditionally used. PMID:19619871

Salomonsen, Tina; Jensen, Henrik Max; Larsen, Flemming Hofmann; Steuernagel, Stefan; Engelsen, Søren Balling

2009-10-12

251

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

252

Solid-state sup 13 C and sup 15 N NMR study of the low pH forms of bacteriorhodopsin  

SciTech Connect

The visible absorption of bacteriorhodopsin (bR) is highly sensitive to pH, the maximum shifting from 568 nm (pH 7) to approximately 600 nm (pH 2) and back to 565 nm (pH 0) as the pH is decreased further with HCl. Blue membrane is also formed by deionization of neutral purple membrane suspensions. Low-temperature, magic angle spinning 13C and 15N NMR was used to investigate the transitions to the blue and acid purple states. The 15N NMR studies involved (epsilon-15N)lysine bR, allowing a detailed investigation of effects at the Schiff base nitrogen. The 15N resonance shifts approximately 16 ppm upfield in the neutral purple to blue transition and returns to its original value in the blue to acid purple transition. Thus, the 15N shift correlates directly with the color changes, suggesting an important contribution of the Schiff base counterion to the opsin shift. The results indicate weaker hydrogen bonding in the blue form than in the two purple forms and permit a determination of the contribution of the weak hydrogen bonding to the opsin shift at a neutral pH of approximately 2000 cm-1. An explanation of the mechanism of the purple to blue to purple transition is given in terms of the complex counterion model. The 13C NMR experiments were performed on samples specifically 13C labeled at the C-5, C-12, C-13, C-14, or C-15 positions in the retinylidene chromophore. The effects of the purple to blue to purple transitions on the isotropic chemical shifts for the various 13C resonances are relatively small. It appears that bR600 consists of at least four different species. The data confirm the presence of 13-cis- and all-trans-retinal in the blue form, as in neutral purple dark-adapted bR. All spectra of the blue and acid purple bR show substantial inhomogeneous broadening which indicates additional irregular distortions of the protein lattice.

de Groot, H.J.; Smith, S.O.; Courtin, J.; van den Berg, E.; Winkel, C.; Lugtenburg, J.; Griffin, R.G.; Herzfeld, J. (Massachusetts Institute of Technology, Cambridge (USA))

1990-07-24

253

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

254

Synthesis, mass spectral characterization, NMR analyses, and DFT calculations of 1-desoxymaquindox and 4-desoxymaquindox  

NASA Astrophysics Data System (ADS)

Maquindox, 3-methyl-2-acetylquinoxaline-1,4-dioxide, is a quinoxaline-N,N-dioxide used in veterinary medicine as a feed additive. 1-Desoxymaquindox and 4-desoxymaquindox, two novel deoxidized metabolites of maquindox are synthesized from their parent drug. This study deals with the structural and spectral properties of the maquindox metabolites by employing experimental and theoretical methods. The investigation, using ultra-performance liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry, shows independent proof of the structures. Gauge-including atomic orbital NMR chemical shifts are calculated for isomeric quinoxaline metabolite pairs and several different parameters (correlation coefficient, mean absolute error, and corrected mean absolute error) are investigated. Comparison of the experimental and calculated 1H and 13C NMR chemical shifts allows the reliable assignment of the isomeric quinoxaline compound pairs.

Zhang, Jiaheng; Peng, Qingrong; Zhang, Suxia; Li, Yubo; Li, Songqing; Gao, Haixiang; Zhou, Zhiqiang

2011-02-01

255

Relationship between gas chromatographic retention indices and chemical shifts in the 13C NMR spectra of structural isomers of compounds of tetracoordinated phosphorus  

NASA Astrophysics Data System (ADS)

A method for determining the gas chromatographic retention indices of structural isomers of compounds of tetracoordinated phosphorus, based on the correlation between chemical shifts in 13C nuclear magnetic resonance (NMR) spectra and the retention indices of the structural isomers, and on the theory of intermolecular interactions, is proposed. The capabilities of the method are demonstrated for structural isomers of O-alkylmethylfluorophosphonates, which are typical representatives of compounds from the class of tetracoordinated phosphonates. The results from using the correlation approach are compared to experimental data.

Zhokhov, A. K.; Fomenko, P. V.; Aparkin, A. M.; Belousov, E. B.

2015-01-01

256

Mn(II), Cu(II) and Cd(II) p-coumarates: FT-IR, FT-Raman, 1H and 13C NMR and thermogravimetric studies  

NASA Astrophysics Data System (ADS)

Manganese(II), copper(II) and cadmium(II) complexes of p-coumaric acid (p-hydroxycinnamic acid) were synthesized. Their composition was established by means of elementary and thermogravimetric analysis. To study the molecular structure of synthesized compounds many miscellaneous analytical methods, which complement one another, were used: infrared (FT-IR), Raman (FT-Raman) and nuclear magnetic resonance (1H, 13C NMR). The spectroscopic studies lead to conclusions concerning the distribution of the electronic charge in complexes in comparison with p-coumaric acid molecule and the type of metal ion coordination.

Kalinowska, M.; Laderiere, B.; Champagne, P.; Kowczyk-Sadowy, M.; Lewandowski, W.

2013-02-01

257

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

258

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

NASA Astrophysics Data System (ADS)

This study reports the characterization of disperse red 1 acrylate compound by spectral techniques and quantum chemical calculations. The spectroscopic properties were analyzed by FT-IR, UV-vis, 1H NMR and 13C NMR techniques. FT-IR spectrum in solid state was recorded in the region 4000-400 cm -1. The UV-vis absorption spectrum of the compound that dissolved in methanol was recorded in the range of 200-800 nm. The 1H and 13C NMR spectra were recorded in CDCl 3 solution. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational wavenumbers were calculated and scaled values were compared with experimental FT-IR spectrum. A satisfactory consistency between the experimental and theoretical spectra was obtained and it shows that the hybrid DFT method is very useful in predicting accurate vibrational structure, especially for high-frequency region. The complete assignments were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts were calculated using the gauge-invariant atomic orbital (GIAO) method. A study on the electronic properties were performed by timedependent DFT (TD-DFT) and CIS(D) approach. To investigate non linear optical properties, the electric dipole moment ?, polarizability ?, anisotropy of polarizability ? ? and molecular first hyperpolarizability ? were computed. The linear polarizabilities and first hyperpolarizabilities of the studied molecule indicate that the compound can be a good candidate of nonlinear optical materials.

Cinar, Mehmet; Coruh, Ali; Karabacak, Mehmet

2011-12-01

259

Solid state 15N and 13C NMR study of dioxomolybdenum (VI) complexes of Schiff bases derived from trans-1,2-cyclohexanediamine  

NASA Astrophysics Data System (ADS)

The 13C, 15N CP MAS NMR and FT-IR spectra of dioxomolybdenum (VI) complexes of trans- N, N'-bis-(R-salicylidene)-1,2-cyclohexanediamine (R=H, R=3,5-diCl, R=3,5-diBr, R=4,6-diOCH 3), trans- N, N'-bis-(2-OH-naphthylidene)-1,2-cyclohexanediamine and trans- N-(salicylidene)- N'-(2-OH-naphthylidene)-1,2-cyclohexanediamine have been measured. Comparative analysis of the NMR and IR spectra of the complexes with those of the corresponding ligands has shown that the complexation of the di-Schiff bases leads to changes in the conformation of the ligands and the charge redistribution. The asymmetric structure and non-planar structure of the complexes have been suggested.

Schilf, W.; Kamie?ski, B.; Rozwadowski, Z.; Ambroziak, K.; Bieg, B.; Dziembowska, T.

2004-08-01

260

Solution Structures of the Prototypical 18 kDa Translocator Protein Ligand, PK 11195, Elucidated with 1H/13C NMR Spectroscopy and Quantum Chemistry  

PubMed Central

Eighteen kilodalton translocator protein (TSPO) is an important target for drug discovery and for clinical molecular imaging of brain and peripheral inflammatory processes. PK 11195 [1a; 1-(2-chlorophenyl)-N-methyl-(1-methylpropyl)-3-isoquinoline carboxamide] is the major prototypical high-affinity ligand for TSPO. Elucidation of the solution structure of 1a is of interest for understanding small-molecule ligand interactions with the lipophilic binding site of TSPO. Dynamic 1H/13C NMR spectroscopy of 1a revealed four quite stable but interconverting rotamers, due to amide bond and 2-chlorophenyl group rotation. These rotamers have been neglected in previous descriptions of the structure of 1a and of the binding of 1a to TSPO. Here, we used quantum chemistry at the level of B3LYP/6-311+G(2d,p) to calculate 13C and 1H chemical shifts for the rotamers of 1a and for the very weak TSPO ligand, N-desmethyl-PK 11195 (1b). These data, plus experimental NMR data, were then used to characterize the structures of rotamers of 1a and 1b in organic solution. Energy barriers for both the amide bond and 2?-chlorophenyl group rotation of 1a were determined from dynamic 1H NMR to be similar (ca.17 to 18 kcal/mol), and they compared well with those calculated at the level of B3LYP/6-31G*. Furthermore, the computed barrier for Z to E rotation is considerably lower in 1a(18.7 kcal/mol) than in 1b (25.4 kcal/mol). NMR (NOE) unequivocally demonstrated that the E rotamer of 1a is the more stable in solution by about 0.4 kcal/mol. These detailed structural findings will aid future TSPO ligand design and support the notion that TSPO prefers to bind ligands as amide E-rotamers. PMID:22860199

2012-01-01

261

Complete (1) H and (13) C NMR spectral assignments for the glycoalkaloid dehydrocommersonine.  

PubMed

The normal levels and types of glycoalkaloids found in commercial varieties of potato (Solanum tuberosum) appear to present no hazard to human health. However when wild Solanum species are used in breeding endeavors, new and untested glycoalkaloids may be introduced. Recent studies of domestic crosses with a wild Solanum oplocense accession indicated that the levels of a non-indigenous glycoalkaloid appeared associated with reduced defoliation by the Colorado potato beetle. The non-indigenous glycoalkaloid was isolated from foliage of the wild S. oplocense accession and unambiguously characterized by high-resolution electrospray ionization mass spectrometry and NM analysis as the glycoalkaloid dehydrocommersonine. PMID:22847870

King, Russell R; Calhoun, Larry A

2012-09-01

262

Application of /sup 1/H and /sup 13/C NMR spectroscopy in structural investigations of Vinca indole alkaloids  

SciTech Connect

This paper considers the laws connecting the parameters of the H 1 and C 13 NMR spectra with the structure of the substances and the use of these laws for solving structural and stereochemical problems of the Vinca indole alkaloids and other compounds of closely related structure. For each type of alkaloid, characteristic features of the PMR and C 13 NMR spectra are given that permit the structures of similar bases to be established and their stereochemical identification to be performed.

Yagudaev, M.R.

1986-07-01

263

/sup 13/C NMR analysis of the effects of electron radiation on graphite/polyetherimide composites. Final report  

SciTech Connect

Initial investigations have been made into the use of high resolution nuclear magnetic resonance (NMR) for the characterization of radiation effects in graphite and Kevlar fibers, polymers, and the fiber/matrix interface in graphite/polyetherimide composites. Sample preparation techniques were refined. Essential equipment has been procured. A new NMR probe was constructed to increase the proton signal-to-noise ratio. Problem areas have been identified and plans developed to resolve them.

Ferguson, M.W.

1989-03-01

264

Two-Dimensional NMR Experiments for the Assignment of Aromatic Side Chains in 13C-labeled Proteins  

NASA Astrophysics Data System (ADS)

As aromatic residues very often are part of the hydrophobic core of proteins, the unambiguous assignment of the aromatic proton resonances is essential for an accurate and precise structure determination. Instead of transferring1H?coherence to the aromatic protons via13C?like in a number of published methods, in our new experiments the13C?resonances are first correlated with the1H?chemical shifts in one experiment and then with the aromatic proton resonances in four other experiments. Their short coherence transfer pathways make the experiments applicable to proteins with a molecular weight larger than 20 kDa, as is demonstrated forFusarium solani pisicutinase (214 residues). The dispersion of the C?chemical shifts between different aromatic residue types is obvious, but even the dispersion within one type is sufficient to combine the experiments using only the C?chemical shift and to assign nearly all aromatic proton resonances of cutinase.

Prompers, Jeanine J.; Groenewegen, Anneke; Hilbers, Cornelis W.; Pepermans, Henri A. M.

1998-01-01

265

(1)H- and (13)C-NMR spectroscopy of Thy-1-APPSL mice brain extracts indicates metabolic changes in Alzheimer's disease.  

PubMed

Biochemical alterations underlying the symptoms and pathomechanisms of Alzheimer's disease (AD) are not fully understood. However, alterations of glucose metabolism and mitochondrial dysfunction certainly play an important role. (1)H- and (13)C-NMR spectroscopy exhibits promising results in providing information about those alterations in vivo in patients and animals, especially regarding the mitochondrial tricarboxylic acid (TCA) cycle. Accordingly, transgenic mice expressing mutant human amyloid precursor protein (APPSL)-serving as a model of neuropathological changes in AD-were examined with in vitro 1D (1)H- and 2D (1)H-(13)C-HSQC-NMR spectroscopy after oral administration of 1-(13)C-glucose and acquisition of brain material after 30 min. Perchloric acid extracts were measured using a 500 MHz spectrometer, providing more detailed information compared to in vivo spectra achievable nowadays. Area under curve (AUC) data of metabolite peaks were obtained and normalized in relation to the creatine signal, serving as internal reference. Besides confirming well-known metabolic alterations in AD like decreased N-acetylaspartate (NAA)/Creatine (Cr) ratio, new findings such as a decrease in phosphorylcholine (PC) are presented. Glutamate (Glu) and glutamine (Gln) concentrations were decreased while ?-aminobutyric acid (GABA) was elevated in Thy1-APPSL mice. (13)C-NMR spectroscopy revealed a shift in the Glx-2/Glx-4-ratio-where Glx represents a combined Glu/Gln-signal-towards Glx-2 in AD. These findings correlated well with the NAA/Cr-ratio. The Gln-4/Glu-4-ratio is altered in favor of Glu. Our findings suggest that glutamine synthetase (GS), which is predominantly present in glial cells may be impaired in the brain of Thy1-APPSL transgenic mice. Since GS is an ATP-dependent enzyme, mitochondrial dysfunction might contribute to reduced activity, which might also account for the increased metabolism of glutamate via the GABA shunt, a metabolic pathway to bypass intra-mitochondrial ?-ketoglutarate-dehydrogenase, resulting in elevated GABA levels. PMID:25742870

Doert, A; Pilatus, U; Zanella, F; Müller, W E; Eckert, G P

2015-04-01

266

Prediction of the 1H and 13C NMR spectra of alpha-D-glucose in water by DFT methods and MD simulations.  

PubMed

We have applied computational protocols based on DFT and molecular dynamics simulations to the prediction of the alkyl 1H and 13C chemical shifts of alpha-d-glucose in water. Computed data have been compared with accurate experimental chemical shifts obtained in our laboratory. 13C chemical shifts do not show a marked solvent effect. In contrast, the results for 1H chemical shifts provided by structures optimized in the gas phase are only fair and point out that it is necessary to take into account both the flexibility of the glucose structure and the strong effect exerted by solvent water thereupon. Thus, molecular dynamics simulations were carried out to model both the internal geometry as well as the influence of solvent molecules on the conformational distribution of the solute. Snapshots from the simulation were used as input to DFT NMR calculations with varying degrees of sophistication. The most important factor that affects the accuracy of computed 1H chemical shifts is the solute geometry; the effect of the solvent on the shielding constants can be reasonably accounted for by self-consistent reaction field models without the need of explicitly including solvent molecules in the NMR property calculation. PMID:17718506

Bagno, Alessandro; Rastrelli, Federico; Saielli, Giacomo

2007-09-14

267

Mechanism of Au(III) reduction by chitosan: comprehensive study with 13C and 1H NMR analysis of chitosan degradation products.  

PubMed

The mechanism of Au(III) reduction by chitosan has been proposed on the basis of comprehensive study of kinetics of Au(III) reduction and chitosan chain degradation using UV-vis spectroscopy and viscosimetry, and identification of reaction products using colloid titration and (13)C, (1)H NMR spectroscopy. We have shown that formation of gold nanoparticles in H[AuCl4]/chitosan solutions starts with hydrolysis of chitosan catalyzed by Au(III). The products of chitosan hydrolysis rather than chitosan itself act as the main reducing species. According to (13)C and (1)H NMR spectroscopy data, chitosan/Au(0) composites contain chitosan with reduced molecular weight and acetylation degree, whereas water-soluble by-products consist of chitosan oligomers with higher acetylation degree, derivatives of glucosamine acids, and formate ion. Chitosan degradation has significantly contributed to the decrease of its efficiency as a gold nanoparticles stabilizer. The gold particle size increased from 6.9 nm to 16.2 nm, when Au(III)/chitosan molar ratio changed from 1:80 to 1:10. PMID:25498610

Pestov, Alexander; Nazirov, Alexander; Modin, Evgeny; Mironenko, Alexander; Bratskaya, Svetlana

2015-03-01

268

/sup 13/C and /sup 1/H NMR spectra and structure of the products from the condensation of 1,3-dicarbonyl compounds with aldehydes  

SciTech Connect

The structure of the diadducts formed in the reaction of 1,3-dicarbonyl compounds with aldehydes in a ratio of 2:1 under the conditions of the Knoevenagel condensation was studied by /sup 13/C and /sup 1/H NMR spectroscopy. It was shown that acyclic tetracarbonyl compounds are formed in the absence of a catalyst while substituted cyclohexanones are formed in the presence of piperidine. The acyclic tetracarbonyl compounds exist mainly in the tetraketo form in solution, and the presence of the monoenol form was established for dimethyl 2,4-diacetylpentanedioate in CD/sub 2/Cl/sub 2/. The most characteristic signals which distinguish between the cyclic diadducts and the acyclic products are the signals of the C/sup 5/ (delta 72 ppm) and C/sup 6/ (delta 52 ppm) atoms. The presence of a keto-enol equilibrium in 2,4-diacetyl-5-hydroxy-3-(p-methoxyphenyl)-5-methylcyclohexanone was demonstrated by /sup 13/C NMR.

Emelina, E.E.; Gindin, V.A.; Ershov, B.A.

1988-05-20

269

sup 13 C and sup 15 N NMR studies on the interaction between 6,7-dimethyl-8-ribityllumazine and lumazine protein  

SciTech Connect

The interaction between the prosthetic group 6,7-dimethyl-8-(1{prime}-D-ribityl)lumazine and the lumazine apoproteins from two marine bioluminescent bacteria, one from a relatively thermophilic species, Photobacterium leiognathi, and the other from a psychrophilic species, Photobacterium phosphoreum, was studied by {sup 13}C and {sup 15}N NMR using various selectively enriched derivatives. It is shown that the electron distribution in the protein-bound 6,7-dimethyl-8-ribityllumazine differs from that of free 6,7-dimethyl-8-ribityllumazine in buffer. The {sup 13}C and {sup 15}N chemical shifts indicate that the protein-bound 6,7-dimethyl-8-ribityllumazine is embedded in a polar environment and that the ring system is strongly polarized. It is concluded that the two carbonyl groups play an important role in the polarization of the molecule. The N(3)-H group is not accessible to bulk solvent. The N(8) atom is sp{sup 2} hybridized and has {delta}+ character. Nuclear Overhauser effect studies indicate that the 6,7-dimethyl-8-ribityllumazine ring is rigidly bound with no internal mobility. The NMR results indicate that the interaction between the ring system and the two apoproteins is almost the same.

Vervoort, J.; Mueller, F. (Agricultural Univ., Wageningen (Netherlands)); O'Kane, D.J.; Lee, J. (Univ. of Georgia, Athens (USA)); Bacher, A.; Strobl, G. (Technical Univ. of Munich (West Germany))

1990-02-20

270

Residue specific hydration of primary cell wall potato pectin identified by solid-state 13C single-pulse MAS and CP/MAS NMR spectroscopy.  

PubMed

Hydration of rhamnogalacturonan-I (RG-I) derived from potato cell wall was analyzed by (13)C single-pulse (SP) magic-angle-spinning (MAS) and (13)C cross-polarization (CP) MAS nuclear magnetic resonance (NMR) and supported by (2)H SP/MAS NMR experiments. The study shows that the arabinan side chains hydrate more readily than the galactan side chains and suggests that the overall hydration properties can be controlled by modifying the ratio of these side chains. Enzymatic modification of native (NA) RG-I provided samples with reduced content of arabinan (sample DA), galactan (sample DG), or both side chains (sample DB). Results of these samples suggested that hydration properties were determined by the length and character of the side chains. NA and DA exhibited similar hydration characteristics, whereas DG and DB were difficult to hydrate because of the less hydrophilic properties of the rhamnose-galacturonic acid (Rha-GalA) backbone in RG-I. Potential food ingredient uses of RG-I by tailoring of its structure are discussed. PMID:21462966

Larsen, Flemming H; Byg, Inge; Damager, Iben; Diaz, Jerome; Engelsen, Søren B; Ulvskov, Peter

2011-05-01

271

(1)H-(13)C HSQC NMR Spectroscopy for Estimating Procyanidin/Prodelphinidin and cis/trans-Flavan-3-ol Ratios of Condensed Tannin Samples: Correlation with Thiolysis.  

PubMed

Studies with a diverse array of 22 purified condensed tannin (CT) samples from nine plant species demonstrated that procyanidin/prodelphinidin (PC/PD) and cis/trans-flavan-3-ol ratios can be appraised by (1)H-(13)C HSQC NMR spectroscopy. The method was developed from samples containing 44-?100% CT, PC/PD ratios ranging from 0/100 to 99/1, and cis/trans ratios ranging from 58/42 to 95/5 as determined by thiolysis with benzyl mercaptan. Integration of cross-peak contours of H/C-6' signals from PC and of H/C-2',6' signals from PD yielded nuclei-adjusted estimates that were highly correlated with PC/PD ratios obtained by thiolysis (R(2) = 0.99). cis/trans-Flavan-3-ol ratios, obtained by integration of the respective H/C-4 cross-peak contours, were also related to determinations made by thiolysis (R(2) = 0.89). Overall, (1)H-(13)C HSQC NMR spectroscopy appears to be a viable alternative to thiolysis for estimating PC/PD and cis/trans ratios of CT if precautions are taken to avoid integration of cross-peak contours of contaminants. PMID:25629428

Zeller, Wayne E; Ramsay, Aina; Ropiak, Honorata M; Fryganas, Christos; Mueller-Harvey, Irene; Brown, Ronald H; Drake, Chris; Grabber, John H

2015-02-25

272

Structure in solid state of 3,3?-diindolylmethane derivatives, potent cytotoxic agents against human tumor cells, followed X-ray diffraction and 13C CP/MAS NMR analyses  

NASA Astrophysics Data System (ADS)

The 5,5'-disubstituted-3,3'-diindolylmethanes 1, 2 have been prepared and their structure was analyzed by X-ray and NMR techniques. The X-ray diffraction studies revealed interesting C-H⋯ ? intermolecular interactions which may play role in characterization of their biological features. In 1H and 13C NMR spectra in solution and in 13C CPMAS NMR spectra in solid state only a single pattern of signals was observed. Both compounds reduce the growth of MCF7 (breast), NCI-H460 (lung), and SF-268 (NCS) cells dramatically.

Maciejewska, Dorota; Wolska, Irena; Niemyjska, Maria; ?ero, Pawe?

2005-10-01

273

In situ variable-temperature MAS sup 13 C NMR study of the reactions of isobutylene in zeolites HY and HZSM-5  

SciTech Connect

The low-temperature chemistry of isobutylene in zeolites HY and HZSM-5 was probed by in situ variable-temperature {sup 13}C NMR spectroscopy with magic-angle spinning (MAS). Isobutylene interacts with Bronsted acid sites of the zeolites at a temperature of ca. 123 K to form a hydrogen-bonded species, as indicated by 2{sup 13}{Delta}{delta} value (relative to the 2-{sup 13}C resonance of isobutylene) of 12 ppm in HY and a {Delta}{delta} value of 16 ppm in HZSM-5. The greater {Delta}{delta} value observed for hydrogen-bonded isobutylene in HZSM-5 is consistent with the acid sites in HZSM-5 being more acidic than those in HY. The maximum number of hydrogen-bonded species detected did not exceed the number of Bronsted acid sites in the zeolites. As the temperature was raised from 123 K, hydrogen-bonded isobutylene was presumably converted to an unobserved symmetrical intermediate (a tert-butylcarbenium ion) that either underwent deprotonation to re-form isobutylene and the acid site or reacted with another isobutylene molecule to form a dimer. Evidence for this process included scrambling between the 1- and 3-{sup 13}C labels of isobutylene. In all of the spectra obtained by either cross polarization or single-pulse excitation, no peaks were observed that could be assigned to a surface-bound silyl ether species. However, in experiments performed on the 2-methyl-2-propanol-2-{sup 13}C/HZSM-5 system, the formation of a surface-bound tert-butyl silyl ether species was observed, as was reported earlier by another laboratory.

Lazo, N.D.; Richardson, B.R.; Schettler, P.D.; White, J.L.; Munson, E.J.; Haw, J.F. (Texas A and M Coll., College Station (United States))

1991-11-14

274

A [sup 13]C NMR study of ethylene adsorbed on reduced and oxygen-covered Ag surfaces  

Microsoft Academic Search

[sup 13]C-enriched ethylene was adsorbed on both clean and oxygen-covered Ag particles dispersed on [eta]-Al[sub 2]O[sub 3]. Irreversibly adsorbed C[sub 2]H[sub 4] on O-covered Ag exhibited an upfield shift of [minus]20 ppm relative to gas-phase C[sub 2]H[sub 4], whereas a narrower line and smaller shift of [minus]5 ppm occurred for C[sub 2]H[sub 4] reversibly adsorbed on reduced Ag. In addition

J. K. Plischke; A. J. Benesi; M. A. Vannice

1992-01-01

275

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

PubMed Central

The cytochromes P450 (CYPs) play a central role in a variety of important biological oxidations, such as steroid synthesis and the metabolism of xenobiotic compounds, including most drugs. Because CYPs are frequently assayed as drug targets or as anti-targets, tools that provide confirmation of active-site binding and information on binding orientation would be of great utility. Of greatest value are assays that are reasonably high throughput. Other heme proteins, too—such as the nitric oxide synthases (NOSs), with their importance in signaling, regulation of blood pressure, and involvement in the immune response—often display critical roles in the complex functions of many higher organisms, and also require improved assay methods. To this end, we have developed an analog of cyanide, with a 13CH3-reporter group attached to make methyl isocyanide. We describe the synthesis and use of 13C-methyl isocyanide as a probe of both bacterial (P450cam) and membrane-bound mammalian (CYP2B4) CYPs. The 13C-methyl isocyanide probe can be used in a relatively high-throughput 1-D experiment to identify binders, but it can also be used to detect structural changes in the active site based on chemical shift changes, and potentially nuclear Overhauser effects between probe and inhibitor. PMID:23475666

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

2014-01-01

276

Structure, dynamics and mapping of membrane-binding residues of micelle-bound antimicrobial peptides by natural abundance (13)C NMR spectroscopy.  

PubMed

Worldwide bacterial resistance to traditional antibiotics has drawn much research attention to naturally occurring antimicrobial peptides (AMPs) owing to their potential as alternative antimicrobials. Structural studies of AMPs are essential for an in-depth understanding of their activity, mechanism of action, and in guiding peptide design. Two-dimensional solution proton NMR spectroscopy has been the major tool. In this article, we describe the applications of natural abundance (13)C NMR spectroscopy that provides complementary information to 2D (1)H NMR. The correlation of (13)Calpha secondary shifts with both 3D structure and heteronuclear (15)N NOE values indicates that natural abundance carbon chemical shifts are useful probes for backbone structure and dynamics of membrane peptides. Using human LL-37-derived peptides (GF-17, KR-12, and RI-10), as well as amphibian antimicrobial and anticancer peptide aurein 1.2 and its analog LLAA, as models, we show that the cross peak intensity plots of 2D (1)H-(13)Calpha HSQC spectra versus residue number present a wave-like pattern (HSQC wave) where key hydrophobic residues of micelle-bound peptides are located in the troughs with weaker intensities, probably due to fast exchange between the free and bound forms. In all the cases, the identification of aromatic phenylalanines as a key membrane-binding residue is consistent with previous intermolecular Phe-lipid NOE observations. Furthermore, mutation of one of the key hydrophobic residues of KR-12 to Ala significantly reduced the antibacterial activity of the peptide mutants. These results illustrate that natural abundance heteronuclear-correlated NMR spectroscopy can be utilized to probe backbone structure and dynamics, and perhaps to map key membrane-binding residues of peptides in complex with micelles. (1)H-(13)Calpha HSQC wave, along with other NMR waves such as dipolar wave and chemical shift wave, offers novel insights into peptide-membrane interactions from different angles. PMID:19682427

Wang, Guangshun

2010-02-01

277

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

278

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

279

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

280

Automatic maximum entropy spectral reconstruction in NMR.  

PubMed

Developments in superconducting magnets, cryogenic probes, isotope labeling strategies, and sophisticated pulse sequences together have enabled the application, in principle, of high-resolution NMR spectroscopy to biomolecular systems approaching 1 megadalton. In practice, however, conventional approaches to NMR that utilize the fast Fourier transform, which require data collected at uniform time intervals, result in prohibitively lengthy data collection times in order to achieve the full resolution afforded by high field magnets. A variety of approaches that involve nonuniform sampling have been proposed, each utilizing a non-Fourier method of spectrum analysis. A very general non-Fourier method that is capable of utilizing data collected using any of the proposed nonuniform sampling strategies is maximum entropy reconstruction. A limiting factor in the adoption of maximum entropy reconstruction in NMR has been the need to specify non-intuitive parameters. Here we describe a fully automated system for maximum entropy reconstruction that requires no user-specified parameters. A web-accessible script generator provides the user interface to the system. PMID:17701276

Mobli, Mehdi; Maciejewski, Mark W; Gryk, Michael R; Hoch, Jeffrey C

2007-10-01

281

Solid-state 13C NMR studies of a large fossil gymnosperm from the Yallourn Open Cut, Latrobe Valley, Australia  

USGS Publications Warehouse

A series of samples taken from the cross section of a 3-m-diameter fossilized gymnospermous log (Araucariaceae) in the Yallourn Seam of the Australian brown coals was examined by solid state 13C nuclear magnetic resonance to delineate chemical changes related to the combined processes of peatification and coalification. The results show that cellulosic materials were degraded and lost on the periphery of the log, however, the degree of such degradation in the central core is substantially less. The lignin is uniformly altered by coalification reactions to a macromolecular substance displaying decreased aryl ether linkages but significantly greater amounts of carbon linkages compared to modern lignin. Changes in the methoxyl carbon contents of lignin in cross section reveal demethylation reactions, but these do not appear to be related to degree of carbon linking. Both the degredation of cellulosic materials and demethylation of lignin appear to be early diagenetic processes occurring during peatification independently of the coalification reactions. ?? 1989.

Bates, A.L.; Hatcher, P.G.

1989-01-01

282

(1)H, (13)C, (15)N HMBC, and (19)F NMR spectroscopic characterisation of seized flephedrone, cut with benzocaine.  

PubMed

Flephedrone (4-fluoromethcathinone, 4-FMC) was analysed using (1)H, (13)C, (15)N HMBC, and (19)F observe spectroscopy, gas chromatography-flame ionisation detection (GC-FID), and electrospray ionisation-mass spectrometry (ESI-MS). Analysis of four 4-FMC samples (from a Bristol nightclub in 2013) showed that they all contained benzocaine as the cutting agent present in different amounts from 5 to 12%. Using these methods, we successfully differentiated between flephedrone regioisomers and mephedrone in an analytical method validated for flephedrone as a substituted cathinone. The data show that these now illegal cathinone-derived stimulants (highs) are now being cut; users cannot be certain of the purity of the drug they are taking. Furthermore, there are risks from the pharmaceutically active cutting agents themselves. PMID:25638692

Alotaibi, Majdah R; Husbands, Stephen M; Blagbrough, Ian S

2015-03-25

283

Ultrafast MAS solid-state NMR permits extensive 13C and 1H detection in paramagnetic metalloproteins.  

PubMed

We show here that by combining tailored approaches based on ultrafast (60 kHz) MAS on the Co(II)-replaced catalytic domain of matrix metalloproteinase 12 (CoMMP-12) we can observe and assign, in a highly paramagnetic protein in the solid state, (13)C and even (1)H resonances from the residues coordinating the metal center. In addition, by exploiting the enhanced relaxation caused by the paramagnetic center, and the low power irradiation enabled by the fast MAS, this can be achieved in remarkably short times and at very high field (21.2 T), with only less than 1 mg of sample. Furthermore, using the known crystal structure of the compound, we are able to distinguish and measure pseudocontact (PCS) contributions to the shifts up to the coordinating ligands and to unveil structural information. PMID:20356036

Bertini, Ivano; Emsley, Lyndon; Lelli, Moreno; Luchinat, Claudio; Mao, Jiafei; Pintacuda, Guido

2010-04-28

284

Solid-state 13C-NMR spectroscopy shows that the xyloglucans in the primary cell walls of mung bean (Vigna radiata L.) occur in different domains: a new model for xyloglucan-cellulose interactions in the cell wall  

Microsoft Academic Search

Xyloglucans (XG) with different mobilities were identified in the primary cell walls of mung beans (Vigna radiata L.) by solid-state 13C-NMR spectro- scopy. To improve the signal:noise ratios compared with unlabelled controls, Glc labelled at either C-1 or C-4 with 13C-isotope was incorporated into the cell- wall polysaccharides of mung bean hypocotyls. Using cell walls from seedlings labelled with D-(1-

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

2004-01-01

285

Crystal structure of ionic and non-ionic surfactants based on polyoxyethylenated dodecanol: A 13 C-CP-MAS-NMR and x-ray investigation  

Microsoft Academic Search

Crystal structure of monodisperse non-ionic surfactants having the general formula C12H25O-(CH2-CH2-O)nH (C12En),n=7,9, 10, 15, 16 and ionic derivatives, C12H25-O-(CH2-CH2-O)n-CH2COONa (C12EnC),n=3,4,5,6,7,9, 12 has been investigated by13C-CP-MAS-NMR and x-ray diffraction. A structural model, in which aliphatic and polyether segments are segregated in bilayers stacking parallel to the elongation direction of the molecules, fits the experimental data for both series. The experimental values

C. Corno; S. Ghelli; G. Perego; E. Platone

1991-01-01

286

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

287

Use of 13C NMR and ftir for elucidation of degradation pathways during natural litter decomposition and composting I. early stage leaf degradation  

USGS Publications Warehouse

Oxidative degradation of plant tissue leads to the formation of natural dissolved organic carbon (DOC) and humus. Infrared (IR) and 13C nuclear magnetic resonance (NMR) spectrometry have been used to elucidate the chemical reactions of the early stages of degradation that give rise to DOC derived from litter and compost. The results of this study indicate that oxidation of the lignin components of plant tissue follows the sequence of O-demethylation, and hydroxylation followed by ring-fission, chain-shortening, and oxidative removal of substituents. Oxidative ring-fission leads to the formation of carboxylic acid groups on the cleaved ends of the rings and, in the process, transforms phenolic groups into aliphatic alcoholic groups. The carbohydrate components are broken down into aliphatic hydroxy acids and aliphatic alcohols.

Wershaw, R.L.; Leenheer, J.A.; Kennedy, K.R.; Noyes, T.I.

1996-01-01

288

NMR studies of nucleic acids. Deuterium isotope effects on sup 13 C chemical shifts in hydrogen-bonded complexes of pyrimidines and purines  

SciTech Connect

{sup 13}C NMR spectra were recorded for chloroform solutions of 2',3'-O-isopropylidene-5'-O-acetyladenosine (1), 2',3',5'-O-tribenzoyluridine (2), 2',3'-O-isopropylidene-5'-O-acetyluridine (2a), 2',3'-O-isopropylidene-5'-O-(tert-butyldimethylsilyl)guanosine (3), and 2',3'-O-isopropylidene-5'-O-(tert-butyldimethylsilyl)cytidine (4) in which the imino hydrogens were partially exchanged with deuterium. Upfield two-bond deuterium isotope effects (DIE) on {sup 13}C chemical shifts were detected under conditions of slow exchange as multiple peaks for the appropriate resonances and ranged in magnitude from 40 ppB for the amino interaction with C2 in guanosine to 217 ppB for the imino interaction with C4 in the uridine self-association dimer. {sup 13}C chemical shifts and DIEs for 2 were measured at 12 different concentrations from 219 to 231 K. The data were used in an iterative procedure to estimate chemical shifts at C2 and C4 for monomeric and dimeric forms of 2, equilibrium constants and enthalpies for self-association, and the distribution of isomeric self-association dimers. Enthalpies for formation of hydrogen bonds to C2 and C4 in 2 were similar, {Delta}H = {minus}1.8 kcal/mol. DIEs at C2 and C4 increased upon formation of a hydrogen bond to the carbonyl oxygens. The maximal increase for each center was estimated to be 90 ppB. Small increases were also observed in DIEs when nucleosides 1-4 were mixed with their complementary bases. 38 refs., 3 figs., 7 tabs.

Gmeiner, W.H.; Poulter, C.D.

1988-11-09

289

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

290

Quantitative comparison of structure and dynamics of elastin following three isolation schemes by (13)C solid state NMR and MALDI mass spectrometry.  

PubMed

Methods for isolating elastin from fat, collagen, and muscle, commonly used in the design of artificial elastin based biomaterials, rely on exposing tissue to harsh pH levels and temperatures that usually denature many proteins. At present, a quantitative measurement of the modifications to elastin following isolation from other extracellular matrix constituents has not been reported. Using magic angle spinning (13)C NMR spectroscopy and relaxation methodologies, we have measured the modification in structure and dynamics following three known purification protocols. Our experimental data reveal that the (13)C spectra of the hydrated samples appear remarkably similar across the various purification methods. Subtle differences in the half maximum widths were observed in the backbone carbonyl suggesting possible structural heterogeneity across the different methods of purification. Additionally, small differences in the relative signal intensities were observed between purified samples. Lyophilizing the samples results in a reduction of backbone motion and reveals additional differences across the purification methods studied. These differences were most notable in the alanine motifs indicating possible changes in cross-linking or structural rigidity. The measured correlation times of glycine and proline moieties are observed to also vary considerably across the different purification methods, which may be related to peptide bond cleavage. Lastly, the relative concentration of desmosine cross-links in the samples quantified by MALDI mass spectrometry is reported. PMID:25592991

Papaioannou, A; Louis, M; Dhital, B; Ho, H P; Chang, E J; Boutis, G S

2015-05-01

291

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

NASA Astrophysics Data System (ADS)

In this work, we use Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy ( 13C NMR) data to quantify the changes of major chemical compound classes (carboxylic acid, amide, ester, aliphatic, aromatic and carbohydrate) in high molecular weight (HMW, >1 kDa) dissolved organic matter (DOM) isolated along a transect through the Elizabeth River/Chesapeake Bay system to the coastal Atlantic Ocean off Virginia, USA. Results show that carboxylic acids and aromatic compounds are lost along the transect, while HMW DOC becomes enriched in carbohydrate moieties that could have a mid-transect source, perhaps the intensive red tide bloom ( Choclodinium polykrikoides) which occurred during our sampling period. Taking the second derivative of the FTIR spectra resolved three pools of de-protonated carboxylic acids at our Dismal Swamp site (used to represent terrestrial organic matter in this area): one carboxylic acid pool, complexed with iron, seems to be lost between the Dismal Swamp and river sites; the second appears biogeochemically active throughout the riverine transect, disappearing in the coastal ocean sample; the third seems refractory, with the potential to be transported to and to accumulate within the open ocean. Five-member ring esters (?-lactones) were the major ester form in the Dismal Swamp; aliphatic and acetate esters were the dominant esters in the estuary/marine DOM. No amide groups were detectable in Dismal Swamp DOM; secondary amides were present at the estuarine/marine sites. Coupling FTIR with 13C NMR provides new insights into the biogeochemical roles of carboxylic acid, amide and ester compounds in aquatic ecosystems.

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

2010-07-01

292

NMR studies of (U- sup 13 C)cyclosporin A bound to cyclophilin: Bound conformation and protions of cyclosporin involved in binding  

SciTech Connect

Cyclosporin A (CsA), a potent immunosuppressant, is known to bind with high specificity to cyclophilin (CyP), a 17.7 kDa protein with peptidyl-prolyl isomerase activity. In order to investigate the three-dimensional structure of the CsA/CyP complex, the authors have applied a variety of multidimensional NMR methods in the study of uniformly {sup 13}C-labeled CsA bound to cyclophilin. The {sup 1}H and {sup 13}C NMR signals of cyclosporin A in the bound state have been assigned, and, from a quantitative interpretation of the 3D NOE data, the bound conformation of CsA has been determined. Three-dimensional structures of CsA calculated from the NOE data by using a distance geometry/simulated annealing protocol were found to be very different form previously determined crystalline and solution conformations of uncomplexed CsA. In addition, from CsA/CyP NOEs, the portions of CsA that interact with cyclophilin were identified. For the most part, those CsA residues with NOEs to cyclophilin were the same residues important for cyclophilin binding and immunosuppressive activity as determined from sturcture/activity relationships. The structural information derived in this study together with the known structure/activity relationships for CsA analogues may prove useful in the design of improved immunosuppressants. Moreover, the approach that is described for obtaining the structural information is widely applicable to the study of small molecule/large molecule interactions.

Fesik, S.W.; Gampe, R.T. Jr.; Eaton, H.L.; Gemmecker, G.; Olejniczak, E.T.; Neri, P.; Holzman, T.F.; Egan, D.A.; Edalji, R.; Simmer, R.; Helfrich, R.; Hochlowski, J.; Jackson, M. (Abbott Labs., Abbott Park, IL (United States))

1991-07-02

293

Enzymatic hydrolysis of ionic liquid-pretreated celluloses: contribution of CP-MAS 13C NMR and SEM.  

PubMed

The supramolecular structure of four model celluloses was altered prior to their enzymatic saccharification using two ionic liquid pretreatments: one with the commonly used 1-ethyl-3-methylimidazolium acetate ([Emim](+)[CH(3)COO](-)) and the other with the newly developed 1-ethyl-3-methylimidazolium methylphosphonate ([Emim](+)[MeO(H)PO(2)](-)). The estimation of crystallinity index (CrI) by solid state (13)C nuclear magnetic resonance for each untreated/pretreated celluloses was compared with the performances of their enzymatic hydrolysis. For ?-cellulose, both pretreatments led to a significant decrease in CrI from 25% to 5% but had no effect on glucose yields. In contrast, The [Emim](+)[MeO(H)PO(2)](-) pretreatment on the long fibers of cellulose had no significant effect on the CrI although a conversion yield in glucose of 88% is obtained versus 32% without pretreatment. However, scanning electron microscopy analysis suggested a loss of fiber organization induced by both ionic liquid pretreatments leading to a larger accessibility by cellulases to the cellulose surface. PMID:21612918

Husson, Eric; Buchoux, Sébastien; Avondo, Carine; Cailleu, Dominique; Djellab, Karim; Gosselin, Isabelle; Wattraint, Olivier; Sarazin, Catherine

2011-08-01

294

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

295

Assessing the Comparative use of 13C {1H} CPMAS NMR Analyses Across Soil and Dissolved Organic Matter Samples from a Boreal Watershed  

NASA Astrophysics Data System (ADS)

In aquatic ecosystems, dissolved organic matter (DOM) plays a major role in carbon (C), energy and nutrient budgets, particularly in boreal watersheds. Understanding the sources of DOM and what regulates its cycling in the aquatic environment can be increased by a more thorough understanding of its chemical and structural components. 13C cross polarization magic angle spinning nuclear magnetic resonance (13C {1H} CPMAS NMR, hereafter referred to as CP) spectroscopy has been used extensively in the study of both DOM and soil organic matter. It allows assignment of functional groups of C in relative proportions, which informs our understanding of the chemical composition, source, and diagenetic state of DOM. It is well known that CP introduces a matrix effect caused by the dependence of signal strength of different C groups on the hydrogen environment surrounding it, resulting in functional groups of C being over- or under-represented in terms of relative proportion. To better understand the actual composition of the sample, 13C single pulse NMR (13C SPMAS NMR, hereafter referred to as SP) can be performed to determine the actual proportions of C functional groups. Two stream DOM samples were run using both CP and SP to see if an average correction factor could be applied by functional group across a wide range of DOM samples taken from a large boreal watershed in western Newfoundland. Five C functional groups (aliphatic, carbohydrate, aromatic, carboxylic, and carbonyl) were assessed across all samples and sample types. Amplification or under representation of C groups via CP was consistent in both DOM samples. The greatest effect observed was the underrepresentation of aromatic C (by a factor of greater than four), while both carbohydrate and aliphatic C were the most amplified (by a factor of approximately two). Applying this correction across the larger sample dataset for this watershed changed the overall interpretation of these stream DOM samples significantly, particularly in regards to aromaticity and diagenetic state. This same methodological comparison was applied to organic horizon soil and DOM derived from organic horizon soils (leachate) to determine if these corrections would be consistent across sample types. While aromatic C was again underrepresented and the aliphatic and carbohydrate groups amplified in the CP technique, the magnitude of these differences was less than that observed in stream DOM samples, and varied between soil and leachate samples, indicating that comparisons of CP results is not valid across different sample types. The large correction factors required for stream DOM samples may be due to the lower C abundance relative to other matrix components and are particularly important as we consider how the chemical composition of watershed DOM relates to the landscape. The large correction required for aromatic C is critical as it and the diagenetic indices that stem from these measures are greatly impacted. This work indicates that using CP across these sample types is not appropriate but application of a correction factor using SP measurements may be a useful approach enabling such comparisons.

Bonnell, J.; Schneider, C.; Ziegler, S. E.

2011-12-01

296

1H, 13C, 195Pt NMR study on platinum(II) interaction with sulphur containing Amadori compounds  

Microsoft Academic Search

The NMR study on the interaction of Pt(II) with Amadori compounds is performed. The Amadori compounds are derived from the reaction of ?-d-glucose with l-cystine leading to N,N?-di-(1-deoxy-?-fructos-1-yl)-l-cystine [FruCyscys], and with l-methionine leading to N-(1-deoxy-?-fructos-1-yl)-l-methionine [FruMet].The great instability of 2-(1,2,3,4,5-pentahydroxypentyl)-1,3-thiazolidine-4-carboxylic acid [GlcCys], formed by the condensation reaction of ?-d-glucose and l-cysteine, prevents the formation of its Pt(II) complexes. Differently, FruMet

Erika Ferrari; Romano Grandi; Sandra Lazzari; Gaetano Marverti; Maria Cecilia Rossi; Monica Saladini

2007-01-01

297

In Situ 13C and 23Na Magic Angle Spinning NMR Investigation of Supercritical CO2 Incorporation in Smectite-Natural Organic Matter Composites  

SciTech Connect

This paper presents an in situ NMR study of clay-natural organic polymer systems (a hectoritehumic acid [HA] composite) under CO2 storage reservoir conditions (90 bars CO2 pressure, 50°C). The 13C and 23Na NMR data show that supercritical CO2 interacts more strongly with the composite than with the base clay and does not react to form other C-containing species over several days at elevated CO2. With and without organic matter, the data suggest that CO2 enters the interlayer space of Na-hectorite equilibrated at 43% relative humidity. The presence of supercritical CO2 also leads to increased 23Na signal intensity, reduced line width at half height, increased basal width, more rapid 23Na T1 relaxation rates, and a shift to more positive resonance frequencies. Larger changes are observed for the hectorite-HA composite than for the base clay. In light of recently reported MD simulations of other polymer-Na-smectite composites, we interpret the observed changes as an increase in the rate of Na+ site hopping in the presence of supercritical CO2, the presence of potential new Na+ sorption sites when the humic acid is present, and perhaps an accompanying increase in the number of Na+ ions actively involved in site hopping. The results suggest that the presence of organic material either in clay interlayers or on external particle surfaces can significantly affect the behavior of supercritical CO2 and the mobility of metal ions in reservoir rocks.

Bowers, Geoffrey M.; Hoyt, David W.; Burton, Sarah D.; Ferguson, Brennan O.; Varga, Tamas; Kirkpatrick, Robert J.

2014-01-29

298

The effects of anticalcification treatments and hydration on the molecular dynamics of bovine pericardium collagen as revealed by 13C solid-state NMR.  

PubMed

This article describes a solid-state NMR (SSNMR) investigation of the influence of hydration and chemical cross-linking on the molecular dynamics of the constituents of the bovine pericardium (BP) tissues and its relation to the mechanical properties of the tissue. Samples of natural phenethylamine-diepoxide (DE)- and glutaraldehyde (GL)-fixed BP were investigated by (13)C cross-polarization SSNMR to probe the dynamics of the collagen, and the results were correlated to the mechanical properties of the tissues, probed by dynamical mechanical analysis. For samples of natural BP, the NMR results show that the higher the hydration level the more pronounced the molecular dynamics of the collagen backbone and sidechains, decreasing the tissue's elastic modulus. In contrast, in DE- and GL-treated samples, the collagen molecules are more rigid, and the hydration seems to be less effective in increasing the collagen molecular dynamics and reducing the mechanical strength of the samples. This is mostly attributed to the presence of cross-links between the collagen plates, which renders the collagen mobility less dependent on the water absorption in chemically treated samples. PMID:20641133

deAzevedo, E R; Ayrosa, A M I B; Faria, G C; Cervantes, H J; Huster, D; Bonagamba, T J; Pitombo, R N M; Rabbani, S R

2010-09-01

299

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

300

The dodecahedryl cation and 1,16-dodecahedryl dication. sup 1 H and sup 13 C NMR spectroscopic studies and theoretical investigations  

SciTech Connect

Ionization of dodecahedryl derivatives (4, X = Cl, OH) as well as of the parent hydrocarbon 1 itself under superacidic conditions (SbF{sub 5}/SO{sub 2}ClF) gave the dodecahedryl cation, 2, which was found to be a static ion with no tendency to undergo degenerate hydrogen scrambling (on the NMR time scale) up to 0{degree}C. The unique ion 2 was characterized by {sup 1}H and {sup 13}C NMR spectroscopy. Upon prolonged exposure to the superacidic medium, the dodecahedryl cation was irreversibly transformed into the 1,16-dodecahedryl dication, 3, which opens up the possibility for regioselective difunctionalization of the dodecahedrane sphere. According to semiempirical SCF-MO calculations, the dodecahedrane skeleton is incapable of accommodating a planar cation geometry. This situation is still more acute in dictation 3, which is considered to constitute the first true sp{sup 3}-hybridized carbocation. Likewise, the static nature of these cations is shown to be due to unfavorable bending in the transition state for intramolecular 1,2-hydride shifts on the convex surface of the cage. 36 refs., 8 figs., 2 tabs.

Olah, G.A.; Prakash, G.K.S.; Fessner, W. (Univ. of Southern California, Los Angeles (USA)); Tomoshige Kobayashi; Paquette, L.A. (Ohio State Univ., Columbus (USA))

1988-12-21

301

NMR ((1)H and (13)C) based signatures of abnormal choline metabolism in oral squamous cell carcinoma with no prominent Warburg effect.  

PubMed

At functional levels, besides genes and proteins, changes in metabolome profiles are instructive for a biological system in health and disease including malignancy. It is understood that metabolomic alterations in association with proteomic and transcriptomic aberrations are very fundamental to unravel malignant micro-ambient criticality and oral cancer is no exception. Hence deciphering intricate dimensions of oral cancer metabolism may be contributory both for integrated appreciation of its pathogenesis and to identify any critical but yet unexplored dimension of this malignancy with high mortality rate. Although several methods do exist, NMR provides higher analytical precision in identification of cancer metabolomic signature. Present study explored abnormal signatures in choline metabolism in oral squamous cell carcinoma (OSCC) using (1)H and (13)C NMR analysis of serum. It has demonstrated down-regulation of choline with concomitant up-regulation of its break-down product in the form of trimethylamine N-oxide in OSCC compared to normal counterpart. Further, no significant change in lactate profile in OSCC possibly indicated that well-known Warburg effect was not a prominent phenomenon in such malignancy. Amongst other important metabolites, malonate has shown up-regulation but d-glucose, saturated fatty acids, acetate and threonine did not show any significant change. Analyzing these metabolomic findings present study proposed trimethyl amine N-oxide and malonate as important metabolic signature for oral cancer with no prominent Warburg effect. PMID:25769954

Bag, Swarnendu; Banerjee, Deb Ranjan; Basak, Amit; Das, Amit Kumar; Pal, Mousumi; Banerjee, Rita; Paul, Ranjan Rashmi; Chatterjee, Jyotirmoy

2015-04-17

302

Conformational analysis, spectroscopic study (FT-IR, FT-Raman, UV, 1H and 13C NMR), molecular orbital energy and NLO properties of 5-iodosalicylic acid  

NASA Astrophysics Data System (ADS)

In this study, 5-iodosalicylic acid (5-ISA, C7H5IO3) is structurally characterized by FT-IR, FT-Raman, NMR and UV spectroscopies. There are eight conformers, Cn, n = 1-8 for this molecule therefore the molecular geometry for these eight conformers in the ground state are calculated by using the ab-initio density functional theory (DFT) B3LYP method approach with the aug-cc-pVDZ-PP basis set for iodine and the aug-cc-pVDZ basis set for the other elements. The computational results identified that the most stable conformer of 5-ISA is the C1 form. The vibrational spectra are calculated DFT method invoking the same basis sets and fundamental vibrations are assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method with PQS program. Total density of state (TDOS) and partial density of state (PDOS) and also overlap population density of state (COOP or OPDOS) diagrams analysis for C1 conformer were calculated using the same method. The energy and oscillator strength are calculated by time-dependent density functional theory (TD-DFT) results complement with the experimental findings. Besides, charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap, molecular electrostatic potential (MEP) are calculated and presented. The NMR chemical shifts (1H and 13C) spectra are recorded and calculated using the gauge independent atomic orbital (GIAO) method. Mulliken atomic charges of the title molecule are also calculated, interpreted and compared with salicylic acid. The optimized bond lengths, bond angles and calculated NMR and UV, vibrational wavenumbers showed the best agreement with the experimental results.

Karaca, Caglar; Atac, Ahmet; Karabacak, Mehmet

2015-02-01

303

Oligomeric complexes of some heteroaromatic ligands and aromatic diamines with rhodium and molybdenum tetracarboxylates: (13) C and (15) N CPMAS NMR and density functional theory studies.  

PubMed

Seven new oligomeric complexes of 4,4'-bipyridine; 3,3'-bipyridine; benzene-1,4-diamine; benzene-1,3-diamine; benzene-1,2-diamine; and benzidine with rhodium tetraacetate, as well as 4,4'-bipyridine with molybdenum tetraacetate, have been obtained and investigated by elemental analysis and solid-state nuclear magnetic resonance spectroscopy, (13) C and (15) N CPMAS NMR. The known complexes of pyrazine with rhodium tetrabenzoate, benzoquinone with rhodium tetrapivalate, 4,4'-bipyridine with molybdenum tetrakistrifluoroacetate and the 1?:?1 complex of 2,2'-bipyridine with rhodium tetraacetate exhibiting axial-equatorial ligation mode have been obtained as well for comparison purposes. Elemental analysis revealed 1?:?1 complex stoichiometry of all complexes. The (15) N CPMAS NMR spectra of all new complexes consist of one narrow signal, indicating regular uniform structures. Benzidine forms a heterogeneous material, probably containing linear oligomers and products of further reactions. The complexes were characterized by the parameter complexation shift ?? (???=??complex ?-??ligand ). This parameter ranged from around -40 to -90?ppm in the case of heteroaromatic ligands, from around -12 to -22?ppm for diamines and from -16 to -31?ppm for the complexes of molybdenum tetracarboxylates with 4,4'-bipyridine. The experimental results have been supported by a density functional theory computation of (15) N NMR chemical shifts and complexation shifts at the non-relativistic Becke, three-parameter, Perdew-Wang 91/[6-311++G(2d,p), Stuttgart] and GGA-PBE/QZ4P levels of theory and at the relativistic scalar and spin-orbit zeroth order regular approximation/GGA-PBE/QZ4P level of theory. Nucleus-independent chemical shifts have been calculated for the selected compounds. Copyright © 2015 John Wiley & Sons, Ltd. PMID:25614975

Leniak, Arkadiusz; Kamie?ski, Bohdan; Ja?wi?ski, Jaros?aw

2015-05-01

304

/sup 13/C NMR study of effects of fasting and diabetes on the metabolism of pyruvate in the tricarboxylic acid cycle and of the utilization of pyruvate and ethanol in lipogenesis in perfused rat liver  

SciTech Connect

/sup 13/C NMR has been used to study the competition of pyruvate dehydrogenase with pyruvate carboxylase for entry of pyruvate into the tricarboxylic acid (TCA) cycle in perfused liver from streptozotocin-diabetic and normal donor rats. The relative proportion of pyruvate entering the TCA cycle by these two routes was estimated from the /sup 13/C enrichments at the individual carbons of glutamate when (3-/sup 13/C)alanine was the only exogenous substrate present. In this way, the proportion of pyruvate entering by the pyruvate dehydrogenase route relative to the pyruvate carboxylase route was determined to be 1:1.2 +/- 0.1 in liver from fed controls, 1:7.7 +/- 2 in liver from 24-fasted controls, and 1:2.6 +/- 0.3 in diabetic liver. Pursuant to this observation that conversion of pyruvate to acetyl coenzyme A (acetyl-CoA) was greatest in perfused liver from fed controls, the incorporation of /sup 13/C label into fatty acids was monitored in this liver preparation. With the exception of the repeating methylene carbons, fatty acyl carbons labeled by (1-/sup 13/C)acetyl-CoA (from (2-/sup 13/C)pyruvate) gave rise to resonances distinguishable on the basis of chemical shift from those observed when label was introduced by (3-/sup 13/C)alanine plus (2-/sup 13/C)ethanol, which are converted to (2-/sup 13/C)acetyl-CoA. Thus, measurement of /sup 13/C enrichment at several specific sites in the fatty acyl chains in time-resolved spectra of perfused liver offers a novel way of monitoring the kinetics of the biosynthesis of fatty acids. In addition to obtaining the rate of lipogenesis, it was possible to distinguish the contributions of chain elongation from those of the de novo synthesis pathway and to estimate the average chain length of the /sup 13/C-labeled fatty acids produced.

Cohen, S.M.

1987-01-27

305

Application of ChemDraw NMR Tool: Correlation of Program-Generated (Super 13)C Chemical Shifts and pK[subscript a] Values of Para-Substituted Benzoic Acids  

ERIC Educational Resources Information Center

A study uses the ChemDraw nuclear magnetic resonance spectroscopy (NMR) tool to process 15 para-substituted benzoic acids and generate (super 13)C NMR chemical shifts of C1 through C5. The data were plotted against their pK[subscript a] value and a fairly good linear fit was found for pK[subscript a] versus delta[subscript c1].

Hongyi Wang

2005-01-01

306

Quantification of xylooligomers in hot water wood extract by 1H-13C heteronuclear single quantum coherence NMR.  

PubMed

A new method that employs 2D-HSQCNMRwasdeveloped to determine xylooligomer concentrations in the hot water extracts of Paulownia elongata, aspen, sugar maple, southern hardwood mixture, and willow woodchips. Equations for computing oligomer concentrations calculation were developed based on HSQC corresponding resonance integrals of xylooligomer C1H1 and monomeric sugar standard curves. The degree of polymerization (DP) of xylooligomers in the hot water extract was computed by equation obtained from a series of xylooligomer standard solutions with DPs that ranged from 2 to 6. Another group of hot water wood extract that is served as a control group was hydrolyzed by 4% sulfuric acid at 121 °C for 60 min in order to convert all xylooligomer into xylose. As 2D-HSQC resonance response is different for acetylated xylo-units, as compared with non-acetylated units, proton NMR was used to calibrate the acetylated xylooligomer concentration. Xylooligomer concentrations determined from HSQC compared fairly well with data after hydrolysis. PMID:25498715

Yan, Jipeng; Kiemle, David; Liu, Shijie

2015-03-01

307

Effect of organic matter application on CP-MAS-13C-NMR spectra of humic acids from a brown soil  

NASA Astrophysics Data System (ADS)

The humified SOM or humic substances (HS) composed of humic acid (HA), fulvic acid (FA) and humin (HM) represent the most microbially recalcitrant and stable reservoir of organic carbon in soil (Piccolo et al., 2004). OM applications can influence the amount and structural characteristics of HS(Dou et al., 2008). During the past few decades, there has been much research on HS, but their chemical structure is still not fully understood (Dong, 2006).CP-MAS-13C-NMR spectroscopy was considered as an effective method to study structures of HS without dissolving problem compared with liquid 13C-NMR (Conte et al., 1997; Dou et al., 2008). It can directly measure the carbon framework and reflect the nature of HS transformation after OM application (Spaccini et al., 2000). For that reason, this method was applied in this study. The objective of this paper was to clarify the effect of long term OM application on the changes of structural characteristics in HAs, which provided new information for improving soil fertility by OM application. The experiment was carried out on a brown soil (Paleudalf in USDA Soil Taxonomy) at Shenyang Agricultural University, Liaoning province, China (N41°48'-E123°25'). The experiment included 3 treatments: zero-treatment (CKbr), and two pig manure (PM) treatments (O1 and O2) at the rates of 0.9 t ha-1 and 1.8 t ha-1 of organic carbon, respectively. The samples of the HA fraction were extracted, separated and purified according to the method described by Dou et al. (1991). Elemental composition, Differential thermal analysis (DTA), -lgK value, FT-IR and CP-MAS- 13C-NMR of HAs were performed. Effects on the contents of orgaic carbon and its composition. The contents of TOC were from 8.77 g kg-1 to 12.25 g kg-1. The relative contents in TOC for WSS, HA, and FA were 6.87%, 14.2% and 19.8%. Comparing the CKbr, the contents of WSS, HA and FA for O1 and O2 increased, but relative contents of WSS and FA decreased. The content of the HA increased after OM application, which was consistent with other studies (Wang et al., 2001). The content of the WSS increased after the OM application indicating that the increase of labile organic carbon. The C/H mole ratio of the HS could reflect the degree of condensation (Dou et al., 1995). Effects on HA chemical and optical properties. The chemical and optical properties of HA were listed. The C/H ratios decreased after OM application, from 0.830 (CKbr) to 0.754 (O2). While ?lgK increased, from 0.623 (CKbr) to 0.658 (O2). The HA structure tended to become simpler. The C/H ratio of the HA decreased after OM application. This indicates that OM application decreased the degree of condensation. The ?lgK values can be used as the index of HA molecule complexity in the soil. If ?lgK increased, the molecular structure becomes simpler. After OM application, ?lgK increased indicating that the molecular structure became simpler. Effects on HA thermal properties. It could be seen that HA had exothermic peaks in moderate and high temperature regions. After OM application, heat (H2) of exothermic peak increased in moderate temperature region, while heat (H3) of exothermic peak decreased in high temperature region. The the heat ratio of exothermic peaks in high temperature region to moderate (H3/H2) decreased. From CKbr to O2, H3/H2 decreased from 4.31 to0.86. The HA had moderate and high temperature exothermic peaks. The heat of exothermic peaks in the moderate temperature region might show that aliphatic compounds decomposed and peripheral functional groups decarboxylated. The heat of the exothermic peaks in the high temperature region might show that the HA was oxidized completely and inter-aromatic structures in the molecule decomposed. The heat ratio of the high to moderate temperature exothermic regions (H3/H2) decreased significantly after PM application, indicating that the proportion of aromatic structure decreased and the HA molecular structure simplified. Effects on CP-MAS-13C-NMR spectrum of HA. The CP-MAS- 13C-NMR spectra of the HA were quite similar to each other

Dou, S.

2009-04-01

308

The NMR investigation of alkaloids. IX. /sup 13/C NMR spectra and stereochemistry of convolvine, convolamine, convoline, convolidine, subhirsine and 6-hydroxyhyoscyamine  

SciTech Connect

A correlation has been made on the basis of the results of a study of the C 13 NMR spectra, of the CSs of the C 13 carbon nuclei with the structure and stereochemistry of the tropane alkaloids convolvine, convolamine, convoline, convolidine, subhirsine, and 6-hydroxyhyoscyamine. It has been established that the N-CH/sub 3/ group in convolamine and the -OH group in convoline are oriented equatorially, and the N-CH/sub 3/ in hydroxyhyoscyamine axially.

Yagudaev, M.R.; Aripova, S.F.

1986-07-01

309

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

310

- 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

311

Optimization of {sup 1}H and {sup 13}C NMR methods for structural characterization of acetone and pyridine soluble/insoluble fractions of a coal tar pitch  

SciTech Connect

{sup 1}H and {sup 13}C high-resolution liquid-state NMR methods were used for the quantitative characterization of different molecular weight fractions of a coal tar pitch (CTP). Three fractions were studied: pitch acetone solubles (PAS), pitch pyridine soluble-acetone insolubles (PPS), and pitch pyridine insolubles (PPI). Standard liquid-state NMR methods were modified and calibrated for use with undeuterated quinoline or undeuterated 1-methyl-2-pyrrolidinone (NMP) as the solvent. This made it possible to calculate the average structural parameters for the higher molecular weight (MW) fractions of the coal tar pitch. Quantitative comparisons of structural differences between the solubility-separated fractions of the pitch are reported. The aromaticity and the average number of aromatic rings per polynuclear aromatic structure were both found to decrease with increasing solubility. Similarly, pericondensed and all other quaternary carbon species were found to decrease with increasing solubility. This suggests that 'continental' type structures become more dominant as the solvent solubility of these coal derived fractions diminishes. The estimated average number of aromatic rings ranged from 1 to 2 rings in the PAS fraction, 4 to 21 rings in the PPS fraction, and 11 to 210 rings in the PPI fraction. These ring-numbers were directly related to the number average molecular mass (M{sub n}) assigned to the particular fraction in the average structural parameter (ASP) calculations. The lower-limit of the M{sub n} values was derived from the ASP calculations as 200, 450, and 6200 u for the PAS, PPS, and PPI fractions, respectively. 66 refs., 7 figs., 15 tabs.

Trevor J. Morgan; Anthe George; David B. Davis; Alan A. Herod; Rafael Kandiyoti [Imperial College London, London (United Kingdom). Department of Chemical Engineering and Chemical Technology

2008-05-15

312

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

313

1H, 13C and 15N NMR Assignments of the C1A and C1B Subdomains of PKC-delta  

PubMed Central

The Protein Kinase C family of enzymes is a group of serine/threonine kinases that play central roles in cell-cycle regulation, development and cancer. A key step in the activation of PKC is translocation to membranes and binding of membrane-associated activators including diacylglycerol (DAG). Interaction of novel and conventional isotypes of PKC with DAG and phorbol esters occurs through the two C1 regulatory domains (C1A and C1B), which exhibit distinct ligand binding selectivity that likely controls enzyme activation by different co-activators. PKC has also been implicated in physiological responses to alcohol consumption and it has been proposed that PKC? [1, 2], PKC? [3] and PKC? [4, 5] contain specific alcohol-binding sites in their C1 domains. We are interested in understanding how ethanol affects signal transduction processes through its affects on the structure and function of the C1 domains of PKC. Here we present the 1H, 15N and 13C NMR chemical shift assignments for the Rattus norvegicus PKC? C1A and C1B proteins. PMID:21132404

Ziemba, Brian P.; Booth, Jamie C.; Jones, David N. M.

2015-01-01

314

13C-NMR Assessment of the Pattern of Organic Matter Transformation during Domestic Wastewater Treatment by Autothermal Aerobic Digestion (ATAD)  

PubMed Central

The pattern of biodegradation and the chemical changes occurring in the macromolecular fraction of domestic sludge during autothermal thermophilic aerobic digestion (ATAD) was monitored and characterised via solid-state 13C-NMR CP-MAS. Major indexes such as aromaticity, hydrophobicity and alkyl/O-alkyl ratios calculated for the ATAD processed biosolids were compared by means of these values to corresponding indexes reported for sludges of different origin such as manures, soil organic matter and certain types of compost. Given that this is the first time that these techniques have been applied to ATAD sludge, the data indicates that long-chain aliphatics are easily utilized by the microbial populations as substrates for metabolic activities at all stages of aerobic digestion and serve as a key substrate for the temperature increase, which in turn results in sludge sterilization. The ATAD biosolids following treatment had a prevalence of O-alkyl domains, a low aromaticity index (10.4%) and an alkyl/O-alkyl ratio of 0.48 while the hydrophobicity index of the sludge decreased from 1.12 to 0.62 during the treatment. These results have important implications for the evolution of new ATAD modalities particularly in relation to dewatering and the future use of ATAD processed biosolids as a fertilizer, particularly with respect to hydrological impacts on the soil behaviour. PMID:19742161

Piterina, Anna V.; Barlett, John; Pembroke, J. Tony

2009-01-01

315

Backbone and side-chain (1)H, (13)C, and (15)N NMR assignments of the N-terminal domain of Escherichia coli LpoA.  

PubMed

The peptidoglycan is a major component of the bacterial cell wall and is essential to maintain cellular integrity and cell shape. Penicillin-Binding Proteins (PBPs) catalyze the final biosynthetic steps of peptidoglycan synthesis from lipid II precursor and are the main targets of ?-lactam antibiotics. The molecular details of peptidoglycan growth and its regulation are poorly understood. Presumably, PBPs are active in peptidoglycan synthesizing multi-enzyme complexes that are controlled from inside the cell by cytoskeletal elements. Recently, two outer-membrane lipoproteins, LpoA and LpoB, were shown to be required in Escherichia coli for the function of the main peptidoglycan synthases, PBP1A and PBP1B, by stimulating their transpeptidase activity. However, the mechanism of PBP-activation by Lpo proteins is not known, and the Lpo proteins await structural characterization at atomic resolution. Here we present the backbone and side-chain (1)H, (13)C, (15)N NMR assignments of the N-terminal domain of LpoA from E. coli for structural and functional studies. PMID:24493340

Jean, Nicolas L; Bougault, Catherine; Derouaux, Adeline; Callens, Gilles; Vollmer, Waldemar; Simorre, Jean-Pierre

2015-04-01

316

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

317

Modification of crystallinity and crystalline structure of Acetobacter xylinum cellulose in the presence of water-soluble beta-1,4-linked polysaccharides: 13C-NMR evidence.  

PubMed

Cellulose produced by Acetobacter xylinum in medium containing 0.5% xyloglucan or glucomannan showed altered crystallinities and shifted I alpha/I beta ratios when analysed by solid-state 13C-NMR. By estimating the spectra of cellulose components in each composite, a decreased I alpha content was shown to be countered by increased I beta content in cellulose aggregated in the presence of xyloglucan, causing minimal loss of crystallinity. However, the I alpha decrease was linked primarily to increased disordered content in cellulose produced in medium containing glucomannan. These results are considered in the light of two models for the morphological disposition of the I alpha phase: (i) a series model, proposed on the basis of electron diffraction measurements for an algal cellulose, in which regions of I alpha and I beta alternate along the length of a microfibril, and (ii) a superlattice model, in which the I alpha and I beta domains co-exist throughout the cross-section of each microfibril and form as a result of hierarchical aggregation. The latter model offers clearer insight into the role of the polysaccharides in inhibiting the formation of I alpha crystalline regions. In this superlattice model, polysaccharides adsorbed on surfaces of the most elementary aggregates are displaced to varying degrees during subsequent aggregation, with the presence of these polysaccharides altering the extent of I alpha production at interfaces. PMID:7848969

Hackney, J M; Atalla, R H; VanderHart, D L

1994-08-01

318

Structural characterisation of macromolecular organic material in air particulate matter using Py-GC-MS and solid state 13C-NMR.  

PubMed

Organic air particulate matter was analysed by applying the techniques of Py-GC-MS (pyrolysis-gas chromatography-mass spectrometry) and solid state 13C-NMR (nuclear magnetic resonance). Particles dislodged from air particulate filters and humic acid extracted from these filters were studied for structural components. The structural components of the air particles and extracted humic acid consisted of compounds originating from biomacromolecules, namely, lignin, carbohydrates, protein and lipids. The main components identified for each class included: (1) methoxyphenols originating from lignin; (2) furans, aldehydes and ketones from carbohydrates; (3) pyrrole, indoles from protein; and (4) many hydrocarbons from lipid structures. Single ion monitoring (SIM) and tetramethyl ammonium hydroxide (TMAH) methylation were utilised for detection of aliphatic hydrocarbons and acidic components, respectively. Hydrocarbons ranging from C9 to C28 were detected by SIM analysis, while aliphatic acids ranged from C9 to C18. The majority of components analysed directly in the air particles were similar to those from the humic acid extracts. Many of the structural components of air particles were typical of humic substances of soil and aqueous systems and these were attributed to both biogenic and anthropogenic sources. PMID:11296741

Subbalakshmi, Y; Patti, A F; Lee, G S; Hooper, M A

2000-12-01

319

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

320

Formation of 1:1 and 2:1 host-guest inclusion complexes of ?-cyclodextrin with cycloalkanols: A 1H and 13C NMR spectroscopic study  

NASA Astrophysics Data System (ADS)

Binding constants (Ka's) for the formation of inclusion complexes of ?-cyclodextrin (?-CD) with cycloalkanols (c-CnOH; n = 4-8) were determined by means of 1H and 13C NMR titration, under two different conditions: (i) only 1:1 host-guest inclusion complexes are formed when the guest is in excess; (ii) the formation of 2:1 inclusion complexes occurs only after that of 1:1 inclusion complexes, when the host is in excess. The results of this work showed that ?-CD can include c-C4OH or c-C5OH only when the molar ratio is 1:1; larger ring-sized cycloalkanols such as c-C6OH, c-C7OH or c-C8OH can be included only when the molar ratio is 2:1. These findings, together with those obtained for the four derivatives of ?-CD, per-6-O-methyl-?-CD, per-2-O-methyl-?-CD, per-3-O-methyl-?-CD, and per-2,6-di-O-methyl-?-CD, suggested that ?-CD forms 2:1 inclusion complexes with c-C6OH, c-C7OH or c-C8OH in a tail-to-tail manner, in which the secondary hydroxy sides of the two CD molecules face each other. Two-dimensional ROESY measurements confirmed our results.

Akita, Tomoki; Yoshikiyo, Keisuke; Yamamoto, Tatsuyuki

2014-09-01

321

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

322

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

323

NMR spectral assignments of two sterols from a soft coral Sinularia brassica.  

PubMed

Two new steroids, named 4?,22-dimethyl-Cholest-22-en-3?-ol (1) and 4?-methyl-Cholest-7,22-dien-3?-ol (2), along with two known steroids, were isolated from the soft coral Sinularia brassica. The structures of the new compounds were determined on the basis of extensive spectroscopic data (MS, (1)H and (13)C NMR, (1)H-(1)H COSY, (13)C-(1)H COSY, HMBC and NOESY) analysis. PMID:21140427

Ou, Yun-Fu; Xu, Shi-Hai; Yin, Ping-He; Peng, Cai-Hua; Liao, Liu

2011-01-01

324

Analysis of essential oils of Artemisia absinthium L. from Lithuania by CC, GC(RI), GC-MS and 13C NMR.  

PubMed

Different techniques have been utilized to determine the composition of Artemisia absinthum (wormwood) essential oil. The oil was fractionated on a silica gel column and each fraction analyzed by GC(RI), GC-MS and 13C NMR. This allowed the identification, for the first time in A. absinthium, of two diterpenes, 9-geranyl-p-cymene and 9-geranyl-alpha-terpinene, and two homoditerpenes, 9-(15,16-dihydro-15-methylene)-geranyl-p-cymene and 9-(15,16-dihydro-15-methylene)-geranyl-alpha-terpinene. Chemical variability of A. absinthium essential oils from plants collected in the surroundings of Vilnius city over several years (1999-2007) was also shown. Chemical composition was determined by GC and GC-MS. Thujones (cis+trans, 10.2-36.3%) and trans-sabinyl acetate (9.8-39.2%) were the two predominant constituents of almost all the investigated oils (13 out of 15 samples). The third major compound was myrcene (5.1-9.2%, in four samples), beta-pinene (5.4-10.4%, in 5), linalool (4.7% in one), trans-sabinol (6.4%, in one) and 1,8-cineole (5.2-7.1%, in two). In one oil, the prevailing components were thujones (cis+trans, 11.2%), trans-sabinene hydrate (11.0%) and trans-sabinyl acetate (8.8%), while another sample was characterized by a large quantity of trans-sabinyl acetate (55.2%) and the absence of thujones. PMID:19768995

Judzentiene, Asta; Tomi, Félix; Casanova, Joseph

2009-08-01

325

Site-Specific Protonation Kinetics of Acidic Side Chains in Proteins Determined by pH-Dependent Carboxyl (13)C NMR Relaxation.  

PubMed

Proton-transfer dynamics plays a critical role in many biochemical processes, such as proton pumping across membranes and enzyme catalysis. The large majority of enzymes utilize acid-base catalysis and proton-transfer mechanisms, where the rates of proton transfer can be rate limiting for the overall reaction. However, measurement of proton-exchange kinetics for individual side-chain carboxyl groups in proteins has been achieved in only a handful of cases, which typically have involved comparative analysis of mutant proteins in the context of reaction network modeling. Here we describe an approach to determine site-specific protonation and deprotonation rate constants (kon and koff, respectively) of carboxyl side chains, based on (13)C NMR relaxation measurements as a function of pH. We validated the method using an extensively studied model system, the B1 domain of protein G, for which we measured rate constants koff in the range (0.1-3) × 10(6) s(-1) and kon in the range (0.6-300) × 10(9) M(-1) s(-1), which correspond to acid-base equilibrium dissociation constants (Ka) in excellent agreement with previous results determined by chemical shift titrations. Our results further reveal a linear free-energy relationship between log kon and pKa, which provides information on the free-energy landscape of the protonation reaction, showing that the variability among residues in these parameters arises primarily from the extent of charge stabilization of the deprotonated state by the protein environment. We find that side-chain carboxyls with extreme values of koff or kon are involved in hydrogen bonding, thus providing a mechanistic explanation for the observed stabilization of the protonated or deprotonated state. PMID:25665463

Wallerstein, Johan; Weininger, Ulrich; Khan, M Ashhar I; Linse, Sara; Akke, Mikael

2015-03-01

326

Orbital interactions and their effects on 13C NMR chemical shifts for 4,6-disubstituted-2,2-dimethyl-1,3-dioxanes. A theoretical study.  

PubMed

A theoretical study is employed to describe the orbital interactions involved in the conformers' stability, the energies for the stereoelectronic interactions, and the corresponding effects of these interactions on the molecular structure (bond lengths) for cis- and trans-4,6-disubstituted-2,2-dimethyl-1,3-dioxanes. For cis-4,6-disubstituted-2,2-dimethyl-1,3-dioxanes, two LPO --> sigma*C(2)-Me(8) interactions are extremely important and the energies involved in these interactions are in the range 6.81-7.58 kcal mol(-1) for the LP(O)(1) --> sigma*C(2)-Me(8) and 7.58-7.71 kcal mol(-1) for the LP(O)(3) --> sigma*C(2)-Me(8) interaction. These two LP(O) --> sigma*C(2)-Me(8) interactions cause an upfield shift, indicating an increased shielding (increased electron density) of the ketal carbon C(2) as well as the axial Me(8) group in the chair conformation. These LP(O) --> sigma*C(2)-Me(8) hyperconjugative anomeric type interactions can explain the 13C NMR chemical shifts at 19 ppm for the axial methyl group "Me(8)" and 98.5 ppm for the ketal carbon "C(2)". The observed results for the trans derivatives showed that for compounds 2a-c (R = -CN, -C[triple bond]CH, and -CHO, respectively) the chair conformation is predominant, whereas for 2d,f-h [-CH3, -Ph, -C6H4(p-NO2), -C6H4(p-OCH3), respectively] the twist-boat is the most stable compound and for 2e [-C(CH3)3] is the only form. PMID:16833944

Tormena, Claudio F; Dias, Luiz C; Rittner, Roberto

2005-07-14

327

13C and 15N—Chemical Shift Anisotropy of Ampicillin and Penicillin-V Studied by 2D-PASS and CP/MAS NMR  

NASA Astrophysics Data System (ADS)

The principal values of the chemical shift tensors of all13C and15N sites in two antibiotics, ampicillin and penicillin-V, were determined by 2-dimensionalphaseadjustedspinningsideband (2D-PASS) and conventional CP/MAS experiments. The13C and15N chemical shift anisotropies (CSA), and their confidence limits, were evaluated using a Mathematica program. The CSA values suggest a revised assignment of the 2-methyl13C sites in the case of ampicillin. We speculate on a relationship between the chemical shift principal values of many of the13C and15N sites and the ?-lactam ring conformation.

Antzutkin, Oleg N.; Lee, Young K.; Levitt, Malcolm H.

1998-11-01

328

C60 with complete pentagon orientational ordering: A dielectric and 13C NMR study of solid C60 charged with NO  

NASA Astrophysics Data System (ADS)

Solid C60 was stored in NO under high pressure and the gas molecules NO were found to diffuse into the octahedral interstitial sites in its fcc crystal lattice. Its 13C nuclear magnetic resonance magic angle spinning spectra composed of a primary resonance at 143.7 ppm, accompanied by two minor peaks shifted 0.4 and 0.8 ppm downfield, respectively. The dopant was found to depress its phase-transition temperature at 260 K in pure C60, and to reduce substantially the drop ??' at the phase-transition temperature. Furthermore, the spectral features associated with relaxation during glass transition at lower temperature, as observed in impedance spectra, were smeared. The fraction of P orientation below Tc has been calculated from the impedance data. These results show that a nearly completely P oriented phase had occurred in (NO)0.1C60, and this phase is favored by a negative pressure on C60 lattice exerted by NO, as well as the electrostatic interaction between the two.

Gu, Min; Tang, Tong B.; Feng, Duan

2002-08-01

329

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

SciTech Connect

Room temperature graphite fluorides consisting of raw material and samples post-treated in pure fluorine atmosphere in the temperature range 100-500 deg. C have been studied by solid-state NMR. Several NMR approaches have been used, both high and low-field {sup 19}F, {sup 19}F MAS and {sup 13}C MAS with {sup 19}F to {sup 13}C 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 deg. C. It is shown that covalency increases with temperature.

Giraudet, J. [Matiere Condensee et Resonance Magnetique, Universite Libre de Bruxelles, Faculte des Sciences, CP 232, Boulevard du Triomphe, B-1050 (Belgium); Dubois, M. [Laboratoire des Materiaux Inorganiques, UMR-CNRS 6002-Universite Blaise Pascal, 24 av. des Landais, 63177 Aubiere Cedex (France); Guerin, K. [Laboratoire des Materiaux Inorganiques, UMR-CNRS 6002-Universite Blaise Pascal, 24 av. des Landais, 63177 Aubiere Cedex (France); Pinheiro, J.P. [Laboratoire des Materiaux Inorganiques, UMR-CNRS 6002-Universite Blaise Pascal, 24 av. des Landais, 63177 Aubiere Cedex (France); Hamwi, A. [Laboratoire des Materiaux Inorganiques, UMR-CNRS 6002-Universite Blaise Pascal, 24 av. des Landais, 63177 Aubiere Cedex (France); Stone, W.E.E. [Matiere Condensee et Resonance Magnetique, Universite Libre de Bruxelles, Faculte des Sciences, CP 232, Boulevard du Triomphe, B-1050 (Belgium); Pirotte, P. [Matiere Condensee et Resonance Magnetique, Universite Libre de Bruxelles, Faculte des Sciences, CP 232, Boulevard du Triomphe, B-1050 (Belgium); Masin, F. [Matiere Condensee et Resonance Magnetique, Universite Libre de Bruxelles, Faculte des Sciences, CP 232, Boulevard du Triomphe, B-1050 (Belgium)]. E-mail: fmasin@ulb.ac.be

2005-04-15

330

Bacteriopheophytin a in the active branch of the reaction center of rhodobacter sphaeroides is not disturbed by the protein matrix as shown by 13C photo-CIDNP MAS NMR.  

PubMed

The electronic structure of bacteriopheophytin a (BPhe a), the primary electron acceptor (?A) in photosynthetic reaction centers (RCs) of the purple bacterium Rhodobacter sphaeroides, is investigated by photochemically induced dynamic nuclear polarization (photo-CIDNP) magic-angle spinning (MAS) NMR spectroscopy at atomic resolution. By using various isotope labeling systems, introduced by adding different (13)C selectively labeled ?-aminolevulinic acid precursors in the growing medium of R. sphaeroides wild type (WT), we were able to extract light-induced (13)C NMR signals originating from the primary electron acceptor. The assignments are backed by theoretical calculations. By comparison of these chemical shifts to those obtained from monomeric BPhe a in solution, it is demonstrated that ?A in the active branch appears to be electronically close to free bacteriopheophytin. Hence, there is little effect of the protein surrounding on the cofactor functionally which contributes with its standard redox potential to the electron transfer process that is asymmetric. PMID:23452037

Sai Sankar Gupta, Karthick Babu; Alia, A; Buda, Francesco; de Groot, Huub J M; Matysik, Jörg

2013-03-28

331

Secondary Structure, Backbone Dynamics, and Structural Topology of Phospholamban and Its Phosphorylated and Arg9Cys-Mutated Forms in Phospholipid Bilayers Utilizing 13C and 15N Solid-State NMR Spectroscopy  

PubMed Central

Phospholamban (PLB) is a membrane protein that regulates heart muscle relaxation rates via interactions with the sarcoplasmic reticulum Ca2+ ATPase (SERCA). When PLB is phosphorylated or Arg9Cys (R9C) is mutated, inhibition of SERCA is relieved. 13C and 15N solid-state NMR spectroscopy is utilized to investigate conformational changes of PLB upon phosphorylation and R9C mutation. 13C=O NMR spectra of the cytoplasmic domain reveal two ?-helical structural components with population changes upon phosphorylation and R9C mutation. The appearance of an unstructured component is observed on domain Ib. 15N NMR spectra indicate an increase in backbone dynamics of the cytoplasmic domain. Wild-type PLB (WT-PLB), Ser16-phosphorylated PLB (P-PLB), and R9C-mutated PLB (R9C-PLB) all have a very dynamic domain Ib, and the transmembrane domain has an immobile component. 15N NMR spectra indicate that the cytoplasmic domain of R9C-PLB adopts an orientation similar to P-PLB and shifts away from the membrane surface. Domain Ib (Leu28) of P-PLB and R9C-PLB loses the alignment. The R9C-PLB adopts a conformation similar to P-PLB with a population shift to a more extended and disordered state. The NMR data suggest the more extended and disordered forms of PLB may relate to inhibition relief. PMID:24511878

2015-01-01

332

Solid-State Dipolar INADEQUATE NMR Spectroscopy with a Large Double-Quantum Spectral Width  

E-print Network

Solid-State Dipolar INADEQUATE NMR Spectroscopy with a Large Double-Quantum Spectral Width Mei Hong Academic Press Key Words: solid-state NMR; INADEQUATE; double-quan- tum; C7; dipolar recoupling. Recently, solid-state homonuclear double-quantum NMR spec- troscopy has been increasingly employed to obtain

Hong, Mei

333

Regioselective Syntheses of [13C]4-Labelled Sodium 1-Carboxy-2-(2-ethylhexyloxycarbonyl)ethanesulfonate and Sodium 2-Carboxy-1-(2-ethylhexyloxycarbonyl)ethanesulfonate from [13C]4-Maleic Anhydride  

PubMed Central

The entitled monohydrolysis products, also known as ?- and ?-ethylhexyl sulfosuccinate ('EHSS'), of the surfactant diisooctyl sulfosuccinate ('DOSS') were synthesized in stable isotope labelled form from [13C]4-maleic anhydride. Sodium [13C]4-1-carboxy-2-(2-ethylhexyloxycarbonyl)ethanesulfonate (?-EHSS) was prepared by the method of Larpent by reaction of 2-ethylhexan-1-ol with [13C]4-maleic anhydride followed by regioselective conjugate addition of sodium bisulfite to the resulting monoester (38% overall yield). The regiochemical outcome of bisulfite addition was confirmed by a combination of 13C/13C (INADEQUATE) and 1H/13C (HMBC) NMR spectral correlation experiments. Sodium [13C]4-2-carboxy-1-(2-ethylhexyloxycarbonyl)ethanesulfonate (?-EHSS) was prepared in four steps by reaction of 4-methoxybenzyl alcohol (PMBOH) with [13C]4-maleic anhydride, regioselective sodium bisulfite addition, DCC mediated esterification with 2-ethylhexan-1-ol, and PMB ester deprotection with trifluoroacetic acid (13% overall yield). The regiochemical outcome of the second synthesis was confirmed by a combination of 1JCC scalar coupling constant analysis and 1H/13C (HMBC) NMR spectral correlation. The materials prepared are required as internal standards for the LC-MS/MS trace analysis of the degradation products of DOSS, the anionic surfactant found in Corexit, the oil dispersant used during emergency response efforts connected to the Deepwater Horizon oil spill of April 2010. PMID:24700711

Barsamian, Adam L.; Perkins, Matt J.; Field, Jennifer A.; Blakemore, Paul R.

2014-01-01

334

A spectral atlas of the nu(sub 12) fundamental of (13)C(12)CH6 in the 12 micron region  

NASA Technical Reports Server (NTRS)

The recent discovery of the minor isotopomer of ethane, (13)C(12)CH6, in the planetary atmospheres of Jupiter and Neptune, added ethane to the molecules which can be used to determine isotopic (12)C(12)C ratios for the jovian planets. The increased spectral resolution and coverage of the IR and far-IR instruments to be carried on the Cassini mission to Saturn and Titan may enable the detection of the minor isotopomer. Accurate frequency and cross-section measurements of the nu(sub 12) fundamental under controlled laboratory condition are important to interpret current and future planetary spectra. High resolution spectra of the minor isotopomer (13)C(12)CH6 have been recorded in the 12.2 micron region using the Kitt Peak Fourier Transform (FTS) and the Goddard Tunable Diode Laser spectrometer (TDL). In a global fit to 19 molecular constants in a symmetric top Hamiltonian, transition frequencies of the nu(sub 12) fundamental ranging up to J=35 and K=20 have been determined with a standard deviation of less than 0.0005 cm(exp -1). From selected line intensity measurements, a vibrational dipole moment for the nu(sub 12) fundamental has been derived. Observed and calculated spectra covering the region from 740 cm(exp -1) and to 910 cm(exp -1) are presented. A compilation of transition frequencies, line intensities, and lower state energies are included for general use in the astronomical community.

Weber, Mark; Reuter, Dennis C.; Sirota, J. Marcos; Blass, William E.; Hillman, John J.

1994-01-01

335

Models for cytochromes c': spin states of mono(imidazole)-ligated (meso-tetramesitylporphyrinato)iron(III) complexes as studied by UV-Vis, 13C NMR, 1H NMR, and EPR spectroscopy.  

PubMed

A number of mono(imidazole)-ligated complexes of perchloro(meso-tetramesitylporphyrinato)iron(III), [Fe(TMP)L]ClO(4), have been prepared, and their spin states have been examined by (1)H NMR, (13)C NMR, and EPR spectroscopy as well as solution magnetic moments. All the complexes examined have shown a quantum mechanical spin admixed state of high and intermediate-spin (S = 5/2 and 3/2) states though the contribution of the S = 3/2 state varies depending on the nature of axial ligands. While the complex with extremely bulky 2-tert-butylimidazole (2-(t)()BuIm) has exhibited an essentially pure S = 5/2 state, the complex with electron-deficient 4,5-dichloroimidazole (4,5-Cl(2)Im) adopts an S = 3/2 state with 30% of the S = 5/2 spin admixture. On the basis of the (1)H and (13)C NMR results, we have concluded that the S = 3/2 contribution at ambient temperature increases according to the following order: 2-(t)BuIm < 2-(1-EtPr)Im < 2-MeIm NMR and EPR data has revealed that the S = 3/2 contribution changes sensitively by the temperature; the S = 3/2 contribution decreases as the temperature is lowered for all the mono(imidazole) complexes examined in this study. The solvent polarity also affects the spin state; polar solvents such as methanol and acetonitrile increase the S = 3/2 contribution while nonpolar solvents such as benzene decrease it. These results are explained in terms of the structurally flexible nature of the mono(imidazole) complexes; structural parameters such as the Fe(III)-N(axial) bond length, displacement of the iron from the N4 core, tilting of the Fe(III)-N(axial) bond to the heme normal, orientation of the coordinated imidazole ligand, etc., could be altered by the nature of the axial ligands as well as by the solvent polarity and temperature. Some mysteries on the spin states of cytochromes c' isolated from various bacterial sources are possibly explained in terms of the flexible nature of the mono(imidazole)-ligated structure. PMID:12444764

Ikezaki, Akira; Nakamura, Mikio

2002-12-01

336

Improvement of the inverse-gated-decoupling sequence for a faster quantitative analysis of various samples by 13C NMR spectroscopy  

Microsoft Academic Search

The inverse-gated-decoupling sequence enables quantitative 1H decoupled 13C spectra to be obtained. We modified this sequence so as to obtain the same result in less time for molecules containing carbons with various relaxation properties. For that, we determined the optimal 13C longitudinal-magnetization initial value for a faster relaxation while 1H decoupler is stopped. This value can be calculated precisely via

Patrick Giraudeau; Evelyne Baguet

2006-01-01

337

C NMR Spectra C NMR Spectra  

E-print Network

S16 1 H and 13 C NMR Spectra (see p S3) Me N-i-Pr #12;S17 1 H and 13 C NMR Spectra (see p S3) Me NBn #12;S18 1 H and 13 C NMR Spectra (see p S4) NBn #12;S19 1 H and 13 C NMR Spectra (see p S4) NBn Me Me Me #12;S20 1 H and 13 C NMR Spectra (see p S4) N-n-Bu Me Me Me #12;S21 1 H and 13 C NMR Spectra

Collum, David B.

338

E-2-Benzylidenebenzocycloalkanones. IV. Studies on transmission of substituent effects on 13C NMR chemical shifts of E-2-(X-benzylidene)-1-tetralones, and -benzosuberones. Comparison with the 13C NMR data of chalcones and E-2-(X-benzylidene)-1-indanones  

NASA Astrophysics Data System (ADS)

Single substituent parameter (SSP) and dual substituent parameter (DSP) analyses were applied to study the transmission of substituent effects on selected 13C NMR chemical shifts of the cyclic chalcone analogues, E-2-(4'-X-benzylidene)-1-tetralones ( 2) and E-2-(4'-X-benzylidene)-1-benzosuberones ( 3). In order to study how the geometry of the cyclic chalcone analogues affects the transmission of substituent effects similar investigations with the respective chalcones ( 4) were also performed. The results obtained earlier with the five-membered analogue E-2-(4'-X-benzylidene)-1-indanones ( 1) were also involved in the comparisons. Geometry optimization of the unsubstituted 1a, 2a, 3a and 4a as well as the substituted 2 and 3 was performed by ab initio quantum chemical calculations. Both SSP and DSP analyses reflected that resonance effects contribute more to the chemical shift of C-? (C2), while inductive effects primarily affect that of C-? (C10) of the enone moiety of all the four series. This latter effect, however, is far not as pronounced as that of the former one. It was found that DSP analysis data ( ?F and ?R values) of transmission of substituent effects on the ?C2 data can serve as a measure of choice to study the conformation (planarity) of the investigated enones in the four series.

Perjési, Pál; Linnanto, Juha; Kolehmainen, Erkki; ?sz, Erzsébet; Virtanen, Elina

2005-04-01

339

Porcine cytosolic aspartate aminotransferase reconstituted with (4 prime - sup 13 C)pyridoxal phosphate. pH and ligand-induced changes of the coenzyme observed by sup 13 C NMR spectroscopy  

Microsoft Academic Search

Apoenzyme samples of aspartate aminotransferase (AspAT) purified from the cytosolic fraction of pig heart were reconstituted with (4â²-¹³C)pyridoxal 5â²-phosphate (pyridoxal-P). The ¹³C NMR spectra of AspAT samples thus generated established the chemical shift of 165.3 ppm for C4â² of the coenzyme bound as an internal aldimine with lysine 258 of the enzyme at pH 5. In the absence of ligands

Tsuyoshi Higaki; Sumio Tanase; Fujio Nagashima; Yoshimasa Morino; A. I. Scott; H. J. Williams; N. J. Stolowich

1991-01-01

340

(1)H-(13)C-(29)Si triple resonance and REDOR solid-state NMR-A tool to study interactions between biosilica and organic molecules in diatom cell walls.  

PubMed

Triple resonance solid-state NMR experiments using the spin combination (1)H-(13)C-(29)Si are still rarely found in the literature. This is due to the low natural abundance of the two heteronuclei. Such experiments are, however, increasingly important to study hybrid materials such as biosilica and others. A suitable model substance, ideally labeled with both (13)C and (29)Si, is thus very useful to optimize the experiments before applying them to studies of more complex samples such as biosilica. Tetraphenoxysilane could be synthesized in an easy, two-step synthesis including double isotope labelling. Using tetraphenoxysilane, we established a (1)H-(13)C-(29)Si double CP-based HETCOR experiment and applied it to diatom biosilica from the diatom species Thalassiosira pseudonana. Furthermore, we carried out (1)H-(13)C{(29)Si} CP-REDOR experiments in order to estimate the distance between the organic matrix and the biosilica. Our experiments on diatom biosilica strongly indicate a close contact between polyamine-containing parts of the organic matrix and the silica. This corroborates the assumption that the organic matrix is essential for the control of the cell wall formation. PMID:25638422

Wisser, Dorothea; Brückner, Stephan I; Wisser, Florian M; Althoff-Ospelt, Gerhard; Getzschmann, Jürgen; Kaskel, Stefan; Brunner, Eike

2015-01-01

341

Performic acid oxidation of exo-2-syn-7-bicyclo[2.2.1]hept-5-enediol. 1H and 13C NMR spectroscopic structure elucidation of the reaction products  

NASA Astrophysics Data System (ADS)

Performic acid oxidation of exo-2-syn-7-bicyclo[2.2.1]hept-5-enediol (norborn-5-enediol) gives exo-3-exo-5-syn-7-tricyclo[2.2.1.0 2,6]heptanetriol-(nortricyclenetriol), exo-2-endo-3-endo-5-syn-7-, exo-2-endo-3-endo5-anti-7- and exo-2-endo-3-exo-5-anti-7-bicyclo[2.2.1]heptanetetrols (norbornanetetrols) as reaction products, the relative amounts being 13.7%, 48.1%, 20.2% and 10.4% respectively. The structures of these polyols were elucidated using 1H and 13C NMR spectroscopy including 2D 1H? 1H NOESY, 1H? 1H COSY, 13C? 1H COSY and 13C? 13C INADEQUATE spectra. The reaction mechanism, which consists first of the formation of a norbornyl cation gives, after deprotonation, a triol as an end product. The mechanism leading to the three tetrols includes (1) a Wagner-Meerwein (W-M) rearrangement, (2) a 6,2-hydride shift, (3) another W-M rearrangement and (4) exo attack of the formate anion. The mechanism has been described using the known classical carbocation intermediates. The absence of three theoretically possible reaction products can be explained by intermediates, where the attack of the formate anion on a carbocation is hindered by the vicinal exo hydroxyl group.

Laihia, K.; Kolehmainen, E.; Mänttäri, P.; Ryynänen, R.; Messala-Rannanpiha, M.; Vepsäläinen, J.; Sundelin, J.-P.

1996-05-01

342

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

343

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

344

Plakilactones G and H from a marine sponge. Stereochemical determination of highly flexible systems by quantitative NMR-derived interproton distances combined with quantum mechanical calculations of 13C chemical shifts  

PubMed Central

Summary In this paper the stereostructural investigation of two new oxygenated polyketides, plakilactones G and H, isolated from the marine sponge Plakinastrella mamillaris collected at Fiji Islands, is reported. The stereostructural studies began on plakilactone H by applying an integrated approach of the NOE-based protocol and quantum mechanical calculations of 13C chemical shifts. In particular, plakilactone H was used as a template to extend the application of NMR-derived interproton distances to a highly flexible molecular system with simultaneous assignment of four non-contiguous stereocenters. Chemical derivatization and quantum mechanical calculations of 13C on plakilactone G along with a plausible biogenetic interconversion between plakilactone G and plakilactone H allowed us to determine the absolute configuration in this two new oxygenated polyketides. PMID:24454574

Di Micco, Simone; Zampella, Angela; D’Auria, Maria Valeria; Festa, Carmen; De Marino, Simona; Riccio, Raffaele

2013-01-01

345

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

346

Solid-state 13C-NMR spectroscopy shows that the xyloglucans in the primary cell walls of mung bean (Vigna radiata L.) occur in different domains: a new model for xyloglucan-cellulose interactions in the cell wall.  

PubMed

Xyloglucans (XG) with different mobilities were identified in the primary cell walls of mung beans (Vigna radiata L.) by solid-state 13C-NMR spectroscopy. To improve the signal:noise ratios compared with unlabelled controls, Glc labelled at either C-1 or C-4 with 13C-isotope was incorporated into the cell-wall polysaccharides of mung bean hypocotyls. Using cell walls from seedlings labelled with d-[1-13C]glucose and, by exploiting the differences in rotating-frame and spin-spin proton relaxation, a small signal was detected which was assigned to Xyl of XGs with rigid glucan backbones. After labelling seedlings with d-[4-13C]glucose and using a novel combination of spin-echo spectroscopy with proton spin relaxation-editing, signals were detected that had 13C-spin relaxations and chemical shifts which were assigned to partly-rigid XGs surrounded by mobile non-cellulosic polysaccharides. Although quantification of these two mobility types of XG was difficult, the results indicated that the partly-rigid XGs were predominant in the cell walls. The results lend support to the postulated new cell-wall models in which only a small proportion of the total surface area of the cellulose microfibrils has XG adsorbed on to it. In these new models, the partly-rigid XGs form cross-links between adjacent cellulose microfibrils and/or between cellulose microfibrils and other non-cellulosic polysaccharides, such as pectic polysaccharides. PMID:14966211

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

2004-03-01

347

(1)H, (13)C and (15)N NMR assignments of Mg (2+) bound form of UV inducible transcript protein (UVI31+) from Chlamydomonas reinhardtii.  

PubMed

Almost complete sequence specific (1)H, (13)C and (15)N resonance assignments of Mg(2+) bound form of UV inducible transcript protein (UVI31+) from Chlamydomonas reinhardtii are reported, as a prelude to its structural and functional characterization. PMID:24638198

Singh, Himanshu; Verma, Deepshikha; Rao, B J; Chary, Kandala V R

2015-04-01

348

Preparation and structural organisation of heteroleptic tetraphenylantimony(V) complexes comprising unidentately and bidentately coordinated O, O?-dialkyldithiophosphate groups: Multinuclear ( 13C, 31P) CP\\/MAS NMR and single-crystal X-ray diffraction studies  

Microsoft Academic Search

O,O?-dipropyldithiophosphate and O,O?-di-iso-butyldithiophosphate (Dtph) tetraphenylantimony(V) complexes of the general formula [Sb(C6H5)4{S2P(OR)2}] (R=C3H7, i-C4H9) were prepared and studied by means of 13C, 31P CP\\/MAS NMR spectroscopy and single-crystal X-ray diffraction. Distorted octahedral and trigonal bipyramidal molecular structures have been established for prepared complexes. These unexpected structural distinctions between chemically related compounds are defined by the principally different coordination modes of O,O?-dipropyldithiophosphate

Maxim A. Ivanov; Oleg N. Antzutkin; Vladimir V. Sharutin; Alexander V. Ivanov; Antonya P. Pakusina; Mikhail A. Pushilin; Willis Forsling

2007-01-01

349

NMR study of non-structural proteins-part I: (1)H, (13)C, (15)N backbone and side-chain resonance assignment of macro domain from Mayaro virus (MAYV).  

PubMed

Macro domains are ADP-ribose-binding modules present in all eukaryotic organisms, bacteria and archaea. They are also found in non-structural proteins of several positive strand RNA viruses such as alphaviruses. Here, we report the high yield expression and preliminary structural analysis through solution NMR spectroscopy of the macro domain from New World Mayaro Alphavirus. The recombinant protein was well-folded and in a monomeric state. An almost complete sequence-specific assignment of its (1)H, (15)N and (13)C resonances was obtained and its secondary structure determined by TALOS+. PMID:25217003

Melekis, Efstathios; Tsika, Aikaterini C; Lichière, Julie; Chasapis, Christos T; Margiolaki, Irene; Papageorgiou, Nicolas; Coutard, Bruno; Bentrop, Detlef; Spyroulias, Georgios A

2015-04-01

350

{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

351

1H and 13C NMR assignments of two new diaryl ethers phomopsides A and B from the mangrove endophytic fungus (ZZF08).  

PubMed

Two new diaryl ethers, named phomopside A (1) and B (2), together with known excelsione (3) were isolated from the mangrove endophytic fungus Phomopsis sp. (ZZF08) obtained from the South China Sea coast. The structure of 1 was elucidated by NMR spectroscopy and confirmed by X-ray crystallography. Compounds 2 and 3 were identified by NMR spectroscopy and comparing the spectroscopic data with literature values. In addition, the plausible biogenetic path of 1, 2 and 3 is discussed. PMID:18449854

Tao, Yiwen; Mou, Chengbo; Zeng, Xianjian; Xu, Fang; Cai, Jiwen; She, Zhigang; Zhou, Shining; Lin, Yongcheng

2008-08-01

352

CCSD(T) calculation of NMR chemical shifts: consistency of calculated and measured 13C chemical shifts in the 1-cyclopropylcyclopropylidenemethyl cation  

Microsoft Academic Search

The source of conspicuous disagreement between theory and experiment for the chemical shift of C? in the 1-cyclopropylcyclopropylidenemethyl cation is identified as an inadequate treatment of electron correlation effects in a previous theoretical study. When the sophisticated CCSD(T) method is used, all calculated 13C chemical shifts agree with the experimental values to within 2.2 ppm. These findings undermine the basis

John F. Stanton; Jürgen Gauss; Hans-Ullrich Siehl

1996-01-01

353

1-Cyclohepta-2,4,6-trienyl-selanes--a 77Se NMR study: indirect nuclear 77Se--13C spin-spin coupling constants and application of density functional theory (DFT) calculations.  

PubMed

1-Cyclohepta-2,4,6-trienyl-selanes Se(C(7)H(7))(2) (2c), R--Se--C(7)H(7) with R = Bu, (t)Bu, Ph, 4-F--C(6)H(4) (12a,b,c,d) were prepared by the reaction of the corresponding silanes, Si(SeMe(3))(2) and R--Se--SiMe(3), respectively, with tropylium bromide C(7)H(7)Br. In spite of the low stability of the selanes even in dilute solutions and at low temperature, they could be characterised by their (1)H, (13)C and (77)Se NMR parameters. Coupling constants (1)J((77)Se,(13)C) were measured and calculated by DFT methods at the B3LYP/6-311+G(d,p) level of theory. The comparison of experimental and calculated coupling constants (1)J((77)Se,(13)C) included numerous selenium carbon compounds with largely different Se--C bonds, revealing a satisfactory agreement. Both the spin-dipole (SD) and the paramagnetic spin-orbital (PSO) terms contributed significantly to the spin-spin coupling interaction, in addition to the Fermi contact (FC) term. PMID:17183533

Wrackmeyer, Bernd; Hernández, Zureima García; Herberhold, Max

2007-03-01

354

(15)N and (13)C group-selective techniques extend the scope of STD NMR detection of weak host-guest interactions and ligand screening.  

PubMed

Saturation transfer difference (STD) is a valuable tool for studying the binding of small molecules to large biomolecules and for obtaining detailed information on the binding epitopes. Here, we demonstrate that the proposed (15)N/(13)C variants of group-selective, "GS-STD" experiments provide a powerful approach to mapping the binding epitope of a ligand even in the absence of efficient spin diffusion within the target protein. Therefore, these experimental variants broaden the scope of STD studies to smaller and/or more-dynamic targets. The STD spectra obtained in four different experimental setups (selective (1)H STD, (15)N GS-STD, (13)C(Ar) and (13)C(aliphatic) GS-STD approaches) revealed that the signal-intensity pattern of the difference spectra is affected by both the type and the spatial distribution of the excited "transmitter" atoms, as well as by the efficiency of the spin-diffusion-mediated magnetization transfer. The performance of the experiments is demonstrated on a system by using the lectin, galectin-1 and its carbohydrate ligand, lactose. PMID:20878964

Kövér, Katalin E; Wéber, Edit; Martinek, Tamás A; Monostori, Eva; Batta, Gyula

2010-10-18

355

Vibrational (FT-IR and FT-Raman), electronic (UV-Vis), NMR (1H and 13C) spectra and reactivity analyses of 4,5-dimethyl-o-phenylenediamine.  

PubMed

The structure of 4,5-dimethyl-o-phenylenediamine (C8H12N2, DMPDA) was investigated on the basis of spectroscopic data and theoretical calculations. The sterochemical structure was determined by FT-IR, FT-Raman, UV, 1H and 13C NMR spectra. An experimental study and a theoretical analysis were associated by using the B3LYP method with Gaussian09 package program. FT-IR and FT-Raman spectra were recorded in the region of 4000-400 cm(-1) and 4000-10 cm(-1), respectively. The vibrational spectra were calculated by DFT method and the fundamental vibrations were assigned on the basis of the total energy distribution (TED), calculated with scaled quantum mechanics (SQM) method with Parallel Quantum Solutions (PQS) program. The UV absorption spectrum of the compound that dissolved in ethanol solution were recorded in the range of 190-400 nm. Total density of state (TDOS) and partial density of state (PDOS) of the DMPDA in terms of HOMOs and LUMOs were calculated and analyzed. Chemical shifts were reported in ppm relative to tetramethylsilane (TMS) for 1H and 13C NMR spectra. The compound was dissolved in dimethyl sulfoxide (DMSO). Also, 1H and 13C chemical shifts calculated using the gauge independent atomic orbital (GIAO) method. Mullikan atomic charges and other thermo-dynamical parameters were investigated with the help of B3LYP (DFT) method using 6-311++G** basis set. On the basis of the thermodynamic properties of the title compound at different temperatures have been carried out, revealing the correlations between heat capacity (C), entropy (S), enthalpy changes (H) and temperatures. The optimized bond lengths, bond angles, chemical shifts and vibrational wavenumbers showed the best agreement with the experimental results. PMID:24813280

Atac, Ahmet; Karaca, Caglar; Gunnaz, Salih; Karabacak, Mehmet

2014-09-15

356

Vibrational (FT-IR and FT-Raman), electronic (UV-Vis), NMR (1H and 13C) spectra and reactivity analyses of 4,5-dimethyl-o-phenylenediamine  

NASA Astrophysics Data System (ADS)

The structure of 4,5-dimethyl-o-phenylenediamine (C8H12N2, DMPDA) was investigated on the basis of spectroscopic data and theoretical calculations. The sterochemical structure was determined by FT-IR, FT-Raman, UV, 1H and 13C NMR spectra. An experimental study and a theoretical analysis were associated by using the B3LYP method with Gaussian09 package program. FT-IR and FT-Raman spectra were recorded in the region of 4000-400 cm-1 and 4000-10 cm-1, respectively. The vibrational spectra were calculated by DFT method and the fundamental vibrations were assigned on the basis of the total energy distribution (TED), calculated with scaled quantum mechanics (SQM) method with Parallel Quantum Solutions (PQS) program. The UV absorption spectrum of the compound that dissolved in ethanol solution were recorded in the range of 190-400 nm. Total density of state (TDOS) and partial density of state (PDOS) of the DMPDA in terms of HOMOs and LUMOs were calculated and analyzed. Chemical shifts were reported in ppm relative to tetramethylsilane (TMS) for 1H and 13C NMR spectra. The compound was dissolved in dimethyl sulfoxide (DMSO). Also, 1H and 13C chemical shifts calculated using the gauge independent atomic orbital (GIAO) method. Mullikan atomic charges and other thermo-dynamical parameters were investigated with the help of B3LYP (DFT) method using 6-311++G** basis set. On the basis of the thermodynamic properties of the title compound at different temperatures have been carried out, revealing the correlations between heat capacity (C), entropy (S), enthalpy changes (H) and temperatures. The optimized bond lengths, bond angles, chemical shifts and vibrational wavenumbers showed the best agreement with the experimental results.

Atac, Ahmet; Karaca, Caglar; Gunnaz, Salih; Karabacak, Mehmet

2014-09-01

357

Localized In Vivo 1H NMR Detection of Neurotransmitter Labeling in Rat Brain During Infusion of [1-13C] D-Glucose  

E-print Network

biochemical pathways in localized areas of resting rat brain as well as during focal activation usingLocalized In Vivo 1H NMR Detection of Neurotransmitter Labeling in Rat Brain During Infusion of [1 obtained from rat brain in vivo. Time-resolved label incorporation was measured with a new adiabatic carbon

Jegelka, Stefanie

358

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

359

Model-free estimation of the effective correlation time for C-H bond reorientation in amphiphilic bilayers: 1H-13C solid-state NMR and MD simulations  

NASA Astrophysics Data System (ADS)

Molecular dynamics (MD) simulations give atomically detailed information on structure and dynamics in amphiphilic bilayer systems on timescales up to about 1 ?s. The reorientational dynamics of the C-H bonds is conventionally verified by measurements of 13C or 2H nuclear magnetic resonance (NMR) longitudinal relaxation rates R1, which are more sensitive to motional processes with correlation times close to the inverse Larmor frequency, typically around 1-10 ns on standard NMR instrumentation, and are thus less sensitive to the 10-1000 ns timescale motion that can be observed in the MD simulations. We propose an experimental procedure for atomically resolved model-free estimation of the C-H bond effective reorientational correlation time ?e, which includes contributions from the entire range of all-atom MD timescales and that can be calculated directly from the MD trajectories. The approach is based on measurements of 13C R1 and R1? relaxation rates, as well as 1H-13C dipolar couplings, and is applicable to anisotropic liquid crystalline lipid or surfactant systems using a conventional solid-state NMR spectrometer and samples with natural isotopic composition. The procedure is demonstrated on a fully hydrated lamellar phase of 1-palmitoyl-2-oleoyl-phosphatidylcholine, yielding values of ?e from 0.1 ns for the methyl groups in the choline moiety and at the end of the acyl chains to 3 ns for the g1 methylene group of the glycerol backbone. MD simulations performed with a widely used united-atom force-field reproduce the ?e-profile of the major part of the acyl chains but underestimate the dynamics of the glycerol backbone and adjacent molecular segments. The measurement of experimental ?e-profiles can be used to study subtle effects on C-H bond reorientational motions in anisotropic liquid crystals, as well as to validate the C-H bond reorientation dynamics predicted in MD simulations of amphiphilic bilayers such as lipid membranes.

Ferreira, Tiago Mendes; Ollila, O. H. Samuli; Pigliapochi, Roberta; Dabkowska, Aleksandra P.; Topgaard, Daniel

2015-01-01

360

Design, synthesis, structural characterization by IR, (1) H, (13) C, (15) N, 2D-NMR, X-ray diffraction and evaluation of a new class of phenylaminoacetic acid benzylidene hydrazines as pfENR inhibitors.  

PubMed

Recent studies have revealed that plasmodial enoyl-ACP reductase (pfENR, FabI), one of the crucial enzymes in the plasmodial type II fatty acid synthesis II (FAS II) pathway, is a promising target for liver stage malaria infections. Hence, pfENR inhibitors have the potential to be used as causal malarial prophylactic agents. In this study, we report the design, synthesis, structural characterization and evaluation of a new class of pfENR inhibitors. The search for inhibitors began with a virtual screen of the iResearch database by molecular docking. Hits obtained from the virtual screen were ranked according to their Glide score. One hit was selected as a lead and modified to improve its binding to pfENR; from this, a series of phenylamino acetic acid benzylidene hydrazides were designed and synthesized. These molecules were thoroughly characterized by IR, (1) H, (13) C, (15) N, 2D-NMR (COSY, NOESY, (1) H-(13) C, (1) H-(15) N HSQC and HMBC), and X-ray diffraction. NMR studies revealed the existence of conformational/configurational isomers around the amide and imine functionalities. The major species in DMSO solution is the E, E form, which is in dynamic equilibrium with the Z, E isomer. In the solid state, the molecule has a completely extended conformation and forms helical structures that are stabilized by strong hydrogen bond interactions, forming a helical structure stabilized by N-H…O interactions, a feature unique to this class of compounds. Furthermore, detailed investigation of the NMR spectra indicated the presence of a minor impurity in most compounds. The structure of this impurity was deduced as an imidazoline-4-one derivative based on (1) H-(13) C and (1) H-(15) H HMBC spectra and was confirmed from the NOESY spectra. The molecules were screened for in vitro activity against recombinant pfENR enzyme by a spectrophotometric assay. Four molecules, viz. 17, 7, 10, and 12 were found to be active at 7, 8, 10, and 12 ?m concentration, respectively, showing promising pfENR inhibitory potential. A classification model was derived based on a binary QSAR approach termed recursive partitioning (RP) to highlight structural characteristics that could be tuned to improve activity. PMID:23398677

Samal, Ramanuj P; Khedkar, Vijay M; Pissurlenkar, Raghuvir R S; Bwalya, Angela Gono; Tasdemir, Deniz; Joshi, Ramesh A; Rajamohanan, P R; Puranik, Vedavati G; Coutinho, Evans C

2013-06-01

361

Model-free estimation of the effective correlation time for C-H bond reorientation in amphiphilic bilayers: (1)H-(13)C solid-state NMR and MD simulations.  

PubMed

Molecular dynamics (MD) simulations give atomically detailed information on structure and dynamics in amphiphilic bilayer systems on timescales up to about 1 ?s. The reorientational dynamics of the C-H bonds is conventionally verified by measurements of (13)C or (2)H nuclear magnetic resonance (NMR) longitudinal relaxation rates R1, which are more sensitive to motional processes with correlation times close to the inverse Larmor frequency, typically around 1-10 ns on standard NMR instrumentation, and are thus less sensitive to the 10-1000 ns timescale motion that can be observed in the MD simulations. We propose an experimental procedure for atomically resolved model-free estimation of the C-H bond effective reorientational correlation time ?e, which includes contributions from the entire range of all-atom MD timescales and that can be calculated directly from the MD trajectories. The approach is based on measurements of (13)C?R1 and R1? relaxation rates, as well as (1)H-(13)C dipolar couplings, and is applicable to anisotropic liquid crystalline lipid or surfactant systems using a conventional solid-state NMR spectrometer and samples with natural isotopic composition. The procedure is demonstrated on a fully hydrated lamellar phase of 1-palmitoyl-2-oleoyl-phosphatidylcholine, yielding values of ?e from 0.1 ns for the methyl groups in the choline moiety and at the end of the acyl chains to 3 ns for the g1 methylene group of the glycerol backbone. MD simulations performed with a widely used united-atom force-field reproduce the ?e-profile of the major part of the acyl chains but underestimate the dynamics of the glycerol backbone and adjacent molecular segments. The measurement of experimental ?e-profiles can be used to study subtle effects on C-H bond reorientational motions in anisotropic liquid crystals, as well as to validate the C-H bond reorientation dynamics predicted in MD simulations of amphiphilic bilayers such as lipid membranes. PMID:25638007

Ferreira, Tiago Mendes; Ollila, O H Samuli; Pigliapochi, Roberta; Dabkowska, Aleksandra P; Topgaard, Daniel

2015-01-28

362

Synthesis, spectral (IR, UV-Vis and variable temperature NMR) characterization and crystal structure of (N-benzyl-N-furfuryldithicarbamato-S,S')(thiocyanato-N)(triphenylphosphine)nickel(II).  

PubMed

Planar (N-benzyl-N-furfuryldithiocarbamato-S,S')(thiocyanato-N)(triphenylphospine)nickel(II), [Ni(bfdtc)(NCS)(PPh3)], (1) was prepared from bis(N-benzyl-N-furfuryldithiocarbamato-S,S')nickel(II), [Ni(bfdtc)2], (2) and characterized by elemental analysis, cyclic voltammetry, electronic, IR and variable temperature (1)H and (13)C NMR spectra. For complex 1, the thioureide vCN value is shifted to higher wavenumber compared to 2 and N(13)CS2 carbon signal observed for 1 is additionally shielded compared to the parent complex 2, suggesting increased strength of the thioureide bond due to the presence of the ?-accepting phosphine. In the room temperature (13)C NMR spectrum of 1, two pseudo doublets are observed in the aliphatic region. Variable temperature (13)C NMR spectral studies suggest that the fast thiocyanate exchange appears to be responsible for the appearance of pseudo doublets. Single crystal X-ray structural analysis of 1 and 2 confirm the presence of four coordinated nickel in a distorted square planar arrangement with the NiS2PN and NiS4 chromophores, respectively. The NiS bonds are symmetric in 2 (2.1914(14) and 2.2073(13)Å). But significant asymmetry in NiS bond distances was observed in 1 (2.2202(8)Å and 2.1841Å). This observation clearly supports the less effective trans effect of SCN(-) over PPh3. Cyclic voltammetric studies revealed easier reduction of nickel(II) to nickel(I) in complex 1 compared to 2. PMID:24747850

Valarmathi, P; Thirumaran, S; Sarmal, Lovely; Kant, Rajni

2014-08-14

363

Synthesis, spectral (IR, UV-Vis and variable temperature NMR) characterization and crystal structure of (N-benzyl-N-furfuryldithicarbamato-S,S?)(thiocyanato-N)(triphenylphosphine)nickel(II)  

NASA Astrophysics Data System (ADS)

Planar (N-benzyl-N-furfuryldithiocarbamato-S,S?)(thiocyanato-N)(triphenylphospine)nickel(II), [Ni(bfdtc)(NCS)(PPh3)], (1) was prepared from bis(N-benzyl-N-furfuryldithiocarbamato-S,S?)nickel(II), [Ni(bfdtc)2], (2) and characterized by elemental analysis, cyclic voltammetry, electronic, IR and variable temperature 1H and 13C NMR spectra. For complex 1, the thioureide vCsbnd N value is shifted to higher wavenumber compared to 2 and N13CS2 carbon signal observed for 1 is additionally shielded compared to the parent complex 2, suggesting increased strength of the thioureide bond due to the presence of the ?-accepting phosphine. In the room temperature 13C NMR spectrum of 1, two pseudo doublets are observed in the aliphatic region. Variable temperature 13C NMR spectral studies suggest that the fast thiocyanate exchange appears to be responsible for the appearance of pseudo doublets. Single crystal X-ray structural analysis of 1 and 2 confirm the presence of four coordinated nickel in a distorted square planar arrangement with the NiS2PN and NiS4 chromophores, respectively. The Nisbnd S bonds are symmetric in 2 (2.1914(14) and 2.2073(13) Å). But significant asymmetry in Nisbnd S bond distances was observed in 1 (2.2202(8) Å and 2.1841 Å). This observation clearly supports the less effective trans effect of SCN- over PPh3. Cyclic voltammetric studies revealed easier reduction of nickel(II) to nickel(I) in complex 1 compared to 2.

Valarmathi, P.; Thirumaran, S.; Sarmal, Lovely; Kant, Rajni

2014-08-01

364

Determination of the tautomeric equilibria of pyridoyl benzoyl ?-diketones in the liquid and solid state through the use of deuterium isotope effects on 1H and 13C NMR chemical shifts and spin coupling constants  

NASA Astrophysics Data System (ADS)

The tautomeric equilibria for 2-pyridoyl-, 3-pyridoyl-, and 4-pyridoyl-benzoyl methane have been investigated using deuterium isotope effects on 1H and 13C chemical shifts both in the liquid and the solid state. Equilibria are established both in the liquid and the solid state. In addition, in the solution state the 2-bond and 3-bond J(1H-13C) coupling constants have been used to confirm the equilibrium positions. The isotope effects due to deuteriation at the OH position are shown to be superior to chemical shift in determination of equilibrium positions of these almost symmetrical -pyridoyl-benzoyl methanes. The assignments of the NMR spectra are supported by calculations of the chemical shifts at the DFT level. The equilibrium positions are shown to be different in the liquid and the solid state. In the liquid state the 4-pyridoyl derivative is at the B-form (C-1 is OH), whereas the 2-and 3-pyridoyl derivatives are in the A-form. In the solid state all three compounds are on the B-form. The 4-pyridoyl derivative shows unusual deuterium isotope effects in the solid, which are ascribed to a change of the crystal structure of the deuteriated compound.

Hansen, Poul Erik; Borisov, Eugeny V.; Lindon, John C.

2015-02-01

365

Determination of the tautomeric equilibria of pyridoyl benzoyl ?-diketones in the liquid and solid state through the use of deuterium isotope effects on (1)H and (13)C NMR chemical shifts and spin coupling constants.  

PubMed

The tautomeric equilibria for 2-pyridoyl-, 3-pyridoyl-, and 4-pyridoyl-benzoyl methane have been investigated using deuterium isotope effects on (1)H and (13)C chemical shifts both in the liquid and the solid state. Equilibria are established both in the liquid and the solid state. In addition, in the solution state the 2-bond and 3-bond J((1)H-(13)C) coupling constants have been used to confirm the equilibrium positions. The isotope effects due to deuteriation at the OH position are shown to be superior to chemical shift in determination of equilibrium positions of these almost symmetrical -pyridoyl-benzoyl methanes. The assignments of the NMR spectra are supported by calculations of the chemical shifts at the DFT level. The equilibrium positions are shown to be different in the liquid and the solid state. In the liquid state the 4-pyridoyl derivative is at the B-form (C-1 is OH), whereas the 2-and 3-pyridoyl derivatives are in the A-form. In the solid state all three compounds are on the B-form. The 4-pyridoyl derivative shows unusual deuterium isotope effects in the solid, which are ascribed to a change of the crystal structure of the deuteriated compound. PMID:24070650

Hansen, Poul Erik; Borisov, Eugeny V; Lindon, John C

2015-02-01

366

An NMR microscopy study of water absorption in cork  

Microsoft Academic Search

NMR Microscopy is used to measure the imbibition of water into natural cork, extractives-free cork and desuberised cork. The results clearly indicate that suberin is the key constituent which determines the ability of cork to resist water uptake. Furthermore, a particular suberin with distinct spectral properties as viewed by 13C NMR is shown to be the component responsible for cork

A. M. Gil; M. H. Lopes; C. Pascoal Neto; P. T. Callaghan

2000-01-01

367

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

SciTech Connect

Human interferon-stimulated gene 15 protein (ISG15), also called ubiquitin cross-reactive protein (UCRP), is the first identified ubiquitin-like protein containing two ubiquitin-like domains fused in tandem. The active form of ISG15 is conjugated to target proteins via the C-terminal glycine residue through an isopeptide bond in a manner similar to ubiquitin. The biological role of ISG15 is strongly associated with the modulation of cell immune function, and there is mounting evidence suggesting that many viral pathogens evade the host innate immune response by interfering with ISG15 conjugation to both host and viral proteins in a variety of ways. Here we report nearly complete backbone 1HN, 15N, 13CO, and 13Ca, as well as side chain 13Cb, methyl (Ile-d1, Leu, Val), amide (Asn, Gln), and indole NH (Trp) NMR resonance assignments for the 157-residue human ISG15 protein. These resonance assignments provide the basis for future structural and functional solution NMR studies of the biologically important human ISG15 protein.

Yin, Cuifeng; Aramini, James M.; Ma, LiChung; Cort, John R.; Swapna, G.V.T.; Krug, R. M.; Montelione, Gaetano

2011-10-01

368

Degradation of mangrove tissues by arboreal termites (Nasutitermes acajutlae) and their role in the mangrove C cycle (Puerto Rico): Chemical characterization and organic matter provenance using bulk ?13C, C/N, alkaline CuO oxidation-GC/MS, and solid-state 13C NMR  

NASA Astrophysics Data System (ADS)

Arboreal termites are wood decaying organisms that play an important role in the first stages of C cycling in mangrove systems. The chemical composition of Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa leaf, stem, and pneumatophore tissues as well as associated sediments was compared to that of nests of the termite Nasutitermes acajutlae. Nests gave ?13C values of -26.1 to -27.2‰ (±0.1) and C/N of 43.3 (±2.0) to 98.6 (±16.2) which were similar to all stem and pneumatophores but distinct from mangrove leaves or sediments. Organic matter processed by termites yielded lignin phenol concentrations (?, lambda) that were 2-4 times higher than stem or pneumatophores and 10-20 times higher than that of leaves or sediments, suggesting that the nests were more resistant to biodegradation than the mangrove vegetation source. 13C NMR revealed that polysaccharide content of mangrove tissues (50-69% C) was higher than that of the nests (46-51% C). Conversely, lignin accounted for 16.2-19.6% C of nest material, a threefold increase relative to living mangrove tissues; a similar increase in aromatic methoxyl content was also observed in the nests. Lipids (aliphatic and paraffinic moieties) were also important but rather variable chemical components of all three mangrove species, representing between 13.5 and 28.3% of the C content. Termite nests contained 3.14 Mg C ha-1 which represents approximately 2% of above ground C storage in mangroves, a value that is likely to increase upon burial due to their refractory chemical composition.

Vane, Christopher H.; Kim, Alexander W.; Moss-Hayes, Vicky; Snape, Colin E.; Diaz, Miguel Castro; Khan, Nicole S.; Engelhart, Simon E.; Horton, Benjamin P.

2013-08-01

369

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

370

Synthesis of 3H and 13C labeled mRNA cap dinucleotides--useful tools for NMR, biochemical, and biological studies.  

PubMed

For deeper understanding the roles of the mRNA cap structure in cellular processes isotopically labeled dinucleotide cap analogues have been synthesized as tools for NMR and in vivo studies. Tritium or carbon C-13 labeled methyl iodide was used as a source of the isotope material. In order to minimize the number of steps during the radioisotopic synthesis the methylation with tritium labeled methyl iodide was performed with Gp(3)G as a substrate. The C-13 isotope was introduced into the cap dinucleotide by methylation of GDP with C-13 Methyl iodide, followed by coupling the product with guanosine 5'-phosphorimidazolide in DMF with zinc chloride as a catalyst. PMID:18066775

Jemielity, Jacek; Stolarski, Ryszard; Darzynkiewicz, Edward

2007-01-01

371

(1)H and (13)C NMR spectroscopic studies of hexane-extractable lipids from soils under shelterbelts of different age and composition of plants.  

PubMed

Comparative study of the composition of lipids extracted with n-hexane from soils under shelterbelts of different age and composition of plants and adjoining cultivated fields in agrolandscape has been carried out with the application of (1)? and (13)? NMR spectroscopy. The lipid content correlates with the organic carbon content in soils and is the highest in the soil under the 200-years old shelterbelt. The data received indicate that hexane-extractable lipids from the soil under the 200-years old shelterbelt have undergone the most significant biochemical and chemical transformations (oxidation, hydrolysis, polymerization) with the accumulation of resistant compounds and destruction of esters of o-phthalic acid as anthropogenic contaminants compared to the lipids from the soil under the 14-years old shelterbelt and soils of adjoining arable fields. PMID:25454205

Szajdak, Lech Wojciech; Maryganova, Victoria; Skakovskii, Eugene; Tychinskaya, Ludmila

2015-01-01

372

The electronic structure of the primary electron donor of reaction centers of purple bacteria at atomic resolution as observed by photo-CIDNP 13C NMR  

PubMed Central

Composed of the two bacteriochlorophyll cofactors, PL and PM, the special pair functions as the primary electron donor in bacterial reaction centers of purple bacteria of Rhodobacter sphaeroides. Under light absorption, an electron is transferred to a bacteriopheophytin and a radical pair is produced. The occurrence of the radical pair is linked to the production of enhanced nuclear polarization called photochemically induced dynamic nuclear polarization (photo-CIDNP). This effect can be used to study the electronic structure of the special pair at atomic resolution by detection of the strongly enhanced nuclear polarization with laser-flash photo-CIDNP magic-angle spinning NMR on the carotenoid-less mutant R26. In the electronic ground state, PL is strongly disturbed, carrying a slightly negative charge. In the radical cation state, the ratio of total electron spin densities between PL and PM is 2:1, although it is 2.5:1 for the pyrrole carbons, 2.2:1 for all porphyrinic carbons, and 4:1 for the pyrrole nitrogen. It is shown that the symmetry break between the electronic structures in the electronic ground state and in the radical cation state is an intrinsic property of the special pair supermolecule, which is particularly attributable to a modification of the structure of PL. The significant difference in electron density distribution between the ground and radical cation states is explained by an electric polarization effect of the nearby histidine. PMID:20018724

Daviso, Eugenio; Prakash, Shipra; Alia, A.; Gast, Peter; Neugebauer, Johannes; Jeschke, Gunnar; Matysik, Jörg

2009-01-01

373

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

374

Model of 2,3-bisphosphoglycerate metabolism in the human erythrocyte based on detailed enzyme kinetic equations: in vivo kinetic characterization of 2,3-bisphosphoglycerate synthase/phosphatase using 13C and 31P NMR.  

PubMed Central

This is the first in a series of three papers [see also Mulquiney and Kuchel (1999) Biochem. J. 342, 579-594; Mulquiney and Kuchel (1999) Biochem. J. 342, 595-602] that present a detailed mathematical model of erythrocyte metabolism which explains the regulation and control of 2,3-bisphosphoglycerate (2,3-BPG) metabolism. 2,3-BPG is a modulator of haemoglobin oxygen affinity and hence plays an important role in blood oxygen transport and delivery. This paper presents an in vivo kinetic characterization of 2,3-BPG synthase/phosphatase (BPGS/P), the enzyme that catalyses both the synthesis and degradation of 2,3-BPG. Much previous work had indicated that the behaviour of this enzyme in vitro is markedly different from that in vivo. (13)C and (31)P NMR were used to monitor the time courses of selected metabolites when erythrocytes were incubated with or without [U-(13)C]glucose. Simulations of the experimental time courses were then made. By iteratively changing the parameters of the BPGS/P part of the model until a good match between the NMR-derived data and simulations were achieved, it was possible to characterize BPGS/P kinetically in vivo. This work revealed that: (1) the pH-dependence of the synthase activity results largely from a strong co-operative inhibition of the synthase activity by protons; (2) 3-phosphoglycerate and 2-phosphoglycerate are much weaker inhibitors of 2,3-BPG phosphatase in vivo than in vitro; (3) the K(m) of BPGS/P for 2,3-BPG is significantly higher than that measured in vitro; (4) the maximal activity of the phosphatase in vivo is approximately twice that in vitro, when P(i) is the sole activator (second substrate); and (5) 2-phosphoglycollate appears to play no role in the activation of the phosphatase in vivo. Using the newly determined kinetic parameters, the percentage of glycolytic carbon flux that passes through the 2, 3-BPG shunt in the normal in vivo steady state was estimated to be 19%. PMID:10477268

Mulquiney, P J; Bubb, W A; Kuchel, P W

1999-01-01

375

Probing chemical disorder in glasses using silicon-29 NMR spectral editing.  

PubMed

Chemical disorder can be characterized in silicate glasses using spectral editing in (29)Si solid-state NMR. Resonances of the Q(n)(mX) (i.e. Si(OX)(m)(OSi)(n-m)) molecular motifs, which strongly overlap in the (29)Si solid-state NMR spectra of silicate glasses, can be separated and quantified using 2 to n-quantum filters in INADEQUATE-like experiments, without prior knowledge of assigned chemical shifts, offering a new probe for the microscopic origins of residual entropy in glassy materials. PMID:19652827

Hiet, Julien; Deschamps, Michaël; Pellerin, Nadia; Fayon, Franck; Massiot, Dominique

2009-08-28

376

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

377

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

NASA Astrophysics Data System (ADS)

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 1H and 13C NMR chemical shifts of the molecules have been analysed.

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

2015-01-01

378

Development and validation of a RP-HPLC method for stability-indicating assay of gemifloxacin mesylate including identification of related substances by LC-ESI-MS/MS, 1H and 13C NMR spectroscopy.  

PubMed

A validated stability indicating RP-HPLC assay of gemifloxacin mesylate was developed by separating its related substances on an Inertsil-ODS3V-C18 (4.6 × 250 mm; 5 ?m) column using 0.1% trifluoroaceticacid (pH 2.5) and methanol as a mobile phase in a gradient elution mode at a flow rate of 1.0 mL/min at 27°C. The column effluents were monitored by a photodiode array detector set at 287 nm. The method was validated in terms of accuracy, precision and linearity as per ICH guidelines. Forced degradation of gemifloxacin (GFX) was carried out under acidic, basic, thermal, photolysis and peroxide conditions and the degradation products were separated and characterized by ESI-MS/MS, (1) H and (13) C NMR spectroscopy. The method was successfully applied to the analysis of bulk drugs and the recoveries of gemifloxacin and impurities were in the range of 97.60-102.90 and 96.99-102.10%, respectively. No previous reports were found in the literature on identification of degradation products of gemifloxacin. PMID:21370250

Rao, R Nageswara; Naidu, Ch Gangu; Prasad, K Guru; Narasimha, R

2011-11-01

379

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

PubMed

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 (1)H and (13)C NMR chemical shifts of the molecule have been anlysed. PMID:24316546

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

2014-03-25

380

Onium ions. 34. The methoxydiazonium ion: preparation, /sup 1/H, /sup 13/C, and /sup 15/N NMR and IR structural studies, theoretical calculations, and reaction with aromatics. Attempted preparation and the intermediacy of the hydroxydiazonium ion  

SciTech Connect

Nitrous oxide is methylated with CH/sub 3/F ..-->.. SbF/sub 5/F/sub 2/ or with CH/sub 3/O/sup +/SOClF in SO/sub 2/ClF to give the stable methoxydiazonium ion CH/sub 3/ON/sub 2//sup +/ (1), which was characterized by NMR (/sup 15/N, /sup 13/C, /sup 1/H) and FT IR spectroscopic studies. It is stable below -30 /sup 0/C, above which it decomposes, regenerating N/sub 2/O. When reacted with aromatics, such as toluene, 1 gives only methylation products and no methoxy derivatives are formed. Spectroscopic and chemical data indicate that the mesomeric form CH/sub 3/O-N=N/sup +/ is a significant contributor to the overall structure of 1. Consideration of computed charge distribution (4-31 G with full geometry optimization and 4-31 G*) also supports this conclusion. Independent generation of 1 was also studied by solvolysis of methylazoxy triflate and diazotization of methoxylamine with NO/sup +/BF/sub 4//sup -/. Preparation of the elusive hydroxydiazonium ion HON/sub 2//sup +/(4) was attempted by protonation of nitrous oxide in super acids, but no long-lived ion could be observed. Diazotization of hydroxylamine with NO/sup +/BF/sub 4//sup -/ gives nitrous oxide indicative of the intermediacy of 4.

Olah, G.A.; Herges, R.; Laali, K.; Segal, G.A.

1986-04-16

381

A 13C and 1H NMR spectroscopic investigation of the structure of the iminium ion with a dipolar form in metal complexes of 2-N-substituted N-confused porphyrins.  

PubMed

The crystal structures of chloro(2-aza-2-ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N?N??) zinc(II) [Zn(2-NCH2COOC2H5NCTPP)Cl; 4], (2-aza-2-ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N?N??) palladium(II) [Pd(2-NCH2COOC2H5NCTPP); 5], bromo(2-aza-2-ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N?N??) manganese(III) [Mn(2-NCH2COOC2H5NCTPP)Br; 6], [2-aza-(3?-phenoxypropyl)-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N?N??] nickel(II) [Ni(2-NCH2CH2CH2OC6H5NCTPP); 7] and chloro(2-aza-2-methoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N?N??) zinc(II) [Zn(2-NCH2COOCH3NCTPP)Cl; 8] have been established. The g value of 9.54, which was measured from the parallel polarization of the X-band EPR spectra in CHCl3 at 4 K, is consistent with the high spin mononuclear manganese(III) centre (S = 2) in 6. The magnitude of the axial (D) zero-field splitting (ZFS) for the mononuclear Mn(III) centre in 6 was determined approximately to be 1.63 cm(?1) by paramagnetic susceptibility measurements. The NMR spectroscopic investigation of the iminium ion with a dipolar canonical contribution to the metal complexes 5–7, Pd(2-NCH2C6H5NCTPP) (10) and Ni(2-NCH2C6H5NCTPP) (11) in CDCl3 is reported. A resonance between the dipolar canonical form II and covalent canonical form I exists for complexes 5–7, 10 and 11 in CDCl3. To develop the correlations between ?13C [C(3)], ?1H [H(3)] and the canonical form II in 5–7, 10 and 11, this work thoroughly examines the 13C and 1H NMR of N+=CH(Ar) fragment on seven metal complexes of 2-N substituted N-confused porphyrin. According to these results, the 13C [C(3)] and 1H [H(3)] chemical shifts of the N+=CH(Ar) fragment at 20 °C in CDCl3 are separately located at 152.6 ± 0.5 and 8.30 ± 0.15 ppm respectively for the iminium ion. This exists as a dipolar canonical form II for complexes 5–7, 10 and 11, and the N–CH(Ar) group appears at 121.1 ± 0.1 ppm and 6.35 ± 0.01 ppm, which is in a covalent canonical form I contribution to complexes 4 and 8. X-Ray diffraction data indicate that N(2)–C(3) = 1.315 ± 0.011 Å for the dipolar contribution of 5–7, 10–13, while N(2)–C(3) = 1.331 ± 0.008 Å for the covalent contribution of 4 and 8. PMID:23010770

Chang, Wen-Pin; Lin, Wen-Chain; Chen, Jyh-Horung; Wang, Shin-Shin; Tung, Jo-Yu

2012-11-21

382

The program XEASY for computer-supported NMR spectral analysis of biological macromolecules.  

PubMed

A new program package, XEASY, was written for interactive computer support of the analysis of NMR spectra for three-dimensional structure determination of biological macromolecules. XEASY was developed for work with 2D, 3D and 4D NMR data sets. It includes all the functions performed by the precursor program EASY, which was designed for the analysis of 2D NMR spectra, i.e., peak picking and support of sequence-specific resonance assignments, cross-peak assignments, cross-peak integration and rate constant determination for dynamic processes. Since the program utilizes the X-window system and the Motif widget set, it is portable on a wide range of UNIX workstations. The design objective was to provide maximal computer support for the analysis of spectra, while providing the user with complete control over the final resonance assignments. Technically important features of XEASY are the use and flexible visual display of 'strips', i.e., two-dimensional spectral regions that contain the relevant parts of 3D or 4D NMR spectra, automated sorting routines to narrow down the selection of strips that need to be interactively considered in a particular assignment step, a protocol of resonance assignments that can be used for reliable bookkeeping, independent of the assignment strategy used, and capabilities for proper treatment of spectral folding and efficient transfer of resonance assignments between spectra of different types and different dimensionality, including projected, reduced-dimensionality triple-resonance experiments. PMID:22911575

Bartels, C; Xia, T H; Billeter, M; Güntert, P; Wüthrich, K

1995-07-01

383

A Study of spectral integration and normalization in NMR-based metabonomic analyses  

Microsoft Academic Search

Metabonomics involves the quantitation of the dynamic multivariate metabolic response of an organism to a pathological event or genetic modification [J.K. Nicholson, J.C. Lindon, E. Holmes, Xenobiotica 29 (1999) 1181–1189]. The analysis of these data involves the use of appropriate multivariate statistical methods; Principal Component Analysis (PCA) has been documented as a valuable pattern recognition technique for 1H NMR spectral

Bobbie-Jo M. Webb-Robertson; David F. Lowry; Kristin H. Jarman; Sam J. Harbo; Quanxin Meng; Alfred F. Fuciarelli; Joel G. Pounds; K. Monica Lee

2005-01-01

384