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1

Protein structure determination with paramagnetic solid-state NMR spectroscopy.  

PubMed

Many structures of the proteins and protein assemblies that play central roles in fundamental biological processes and disease pathogenesis are not readily accessible via the conventional techniques of single-crystal X-ray diffraction and solution-state nuclear magnetic resonance (NMR). On the other hand, many of these challenging biological systems are suitable targets for atomic-level structural and dynamic analysis by magic-angle spinning (MAS) solid-state NMR spectroscopy, a technique that has far less stringent limitations on the molecular size and crystalline state. Over the past decade, major advances in instrumentation and methodology have prompted rapid growth in the field of biological solid-state NMR. However, despite this progress, one challenge for the elucidation of three-dimensional (3D) protein structures via conventional MAS NMR methods is the relative lack of long-distance data. Specifically, extracting unambiguous interatomic distance restraints larger than ?5 Å from through-space magnetic dipole-dipole couplings among the protein (1)H, (13)C, and (15)N nuclei has proven to be a considerable challenge for researchers. It is possible to circumvent this problem by extending the structural studies to include several analogs of the protein of interest, intentionally modified to contain covalently attached paramagnetic tags at selected sites. In these paramagnetic proteins, the hyperfine couplings between the nuclei and unpaired electrons can manifest themselves in NMR spectra in the form of relaxation enhancements of the nuclear spins that depend on the electron-nucleus distance. These effects can be significant for nuclei located up to ?20 Å away from the paramagnetic center. In this Account, we discuss MAS NMR structural studies of nitroxide and EDTA-Cu(2+) labeled variants of a model 56 amino acid globular protein, B1 immunoglobulin-binding domain of protein G (GB1), in the microcrystalline solid phase. We used a set of six EDTA-Cu(2+)-tagged GB1 mutants to rapidly determine the global protein fold in a de novo fashion. Remarkably, these studies required quantitative measurements of only approximately four or five backbone amide (15)N longitudinal paramagnetic relaxation enhancements per residue, in the complete absence of the usual internuclear distance restraints. Importantly, this paramagnetic solid-state NMR methodology is general and can be directly applied to larger proteins and protein complexes for which a significant fraction of the signals can be assigned in standard 2D and 3D MAS NMR chemical shift correlation spectra. PMID:23464364

Sengupta, Ishita; Nadaud, Philippe S; Jaroniec, Christopher P

2013-03-06

2

Quantitative {sup 29}Si MAS NMR spectroscopy of cement and silica fume containing paramagnetic impurities  

SciTech Connect

The low natural abundance and the long spin lattice relaxation time of {sup 29}Si lead to long measurement times and/or low signal-to-noise ratios using {sup 29}Si magic angle spinning NMR spectroscopy. By contrast, samples containing paramagnetic iron ions have much shorter relaxation times, making measurements up to seven times more efficient, but at the same time making quantitative analysis unreliable. To solve the problem, the spin-lattice relaxation times of ordinary Portland cement (opc) and silica fume with and without iron content has been determined with inversion recovery experiments. The effect of varying the spectrum repetition time on the quantitative analysis is demonstrated for mixtures of opc with silica fume. For opc and silica fume with iron impurities repetition times as short as 5 s has permitted accurate quantitative analysis of the silicates present in these materials.

Hilbig, H. [Center of Building Materials (CBM), Technische Universitaet Muenchen, Baumbachstr. 7, D-81245 Munich (Germany)]. E-mail: hilbig@cbm.bv.tum.de; Koehler, F.H. [Department Chemie, Technische Universitaet Muenchen, D-85747 Garching (Germany); Schiessl, P. [Center of Building Materials (CBM), Technische Universitaet Muenchen, Baumbachstr. 7, D-81245 Munich (Germany)

2006-02-15

3

Validation of a lanthanide tag for the analysis of protein dynamics by paramagnetic NMR spectroscopy.  

PubMed

Paramagnetic lanthanide tags potentially can enhance the effects of microsecond to millisecond dynamics in proteins on NMR signals and provide structural information on lowly populated states encoded in the pseudocontact shifts. We have investigated the microsecond to millisecond mobility of a two-point attached lanthanide tag, CLaNP-5, using paramagnetic (1)H CPMG relaxation dispersion methods. CLaNP-5 loaded with Lu(3+), Yb(3+), or Tm(3+) was attached to three sites on the surface of two proteins, pseudoazurin and cytochrome c. The paramagnetic center causes large relaxation dispersion effects for two attachment sites, suggesting that local dynamics of the protein at the attachment site causes mobility of the paramagnetic center. At one site the relaxation dispersions are small and limited to the immediate environment of the tag. It is concluded that paramagnetic relaxation dispersion could represent a sensitive method to probe protein dynamics. However, the selection of a rigid attachment site is of critical importance. PMID:20586489

Hass, Mathias A S; Keizers, Peter H J; Blok, Anneloes; Hiruma, Yoshitaka; Ubbink, Marcellus

2010-07-28

4

31P Magic Angle Spinning NMR Spectroscopy of Paramagnetic Rare Earth-Substituted Keggin and Wells-Dawson Solids  

PubMed Central

Paramagnetic rare-earth elements have been examined as NMR structural probes in polyoxoanionic solids, which have a variety of applications as luminescent materials that are usually disordered and therefore intractable by traditional structural methods. Thirteen Keggin and Wells-Dawson polyoxotungstates containing substitutions with lanthanides of different effective magnetic moments have been examined by 31P magic angle spinning NMR spectroscopy. The electron-nuclear dipolar interaction dominating the spinning sideband envelopes is determined by the lanthanide’s magnetic moment and was found to be a sensitive probe of the nature of the polyoxoanion, of the positional isomerism, and of the ion stoichiometry. Electron-nuclear dipolar anisotropies computed based on the point-dipole approximation are generally in good agreement with the experimental results. The choice of a specific lanthanide as a structural probe can be tailored to the desired distance range between the phosphorus atoms and the paramagnetic centers to be probed. This approach is expected to be particularly useful in the paramagnetic polyoxoanionic materials lacking long-range order.

Huang, Wenlin; Schopfer, Mark; Zhang, Cheng; Howell, Robertha C.; Todaro, Louis; Gee, Becky A.; Francesconi, Lynn C.; Polenova, Tatyana

2008-01-01

5

NMR Spectroscopy  

NSDL National Science Digital Library

Quiz questions from the organic chemistry question bank provide students with an excellent opportunity to review key concepts. These questions pertain to Nuclear magnetic resonance (NMR) spectroscopy and include topics such as: Chemical Shift, Proton NMR, and Carbon NMR.

Reich, Ieva

2008-03-25

6

The structure of the cytochrome p450cam-putidaredoxin complex determined by paramagnetic NMR spectroscopy and crystallography.  

PubMed

Cytochrome P450cam catalyzes the hydroxylation of camphor in a complex process involving two electron transfers (ETs) from the iron-sulfur protein putidaredoxin. The enzymatic control of the successive steps of catalysis is critical for a highly efficient reaction. The injection of the successive electrons is part of the control system. To understand the molecular interactions between putidaredoxin and cytochrome P450cam, we determined the structure of the complex both in solution and in the crystal state. Paramagnetic NMR spectroscopy using lanthanide tags yielded 446 structural restraints that were used to determine the solution structure. An ensemble of 10 structures with an RMSD of 1.3Å was obtained. The crystal structure of the complex was solved, showing a position of putidaredoxin that is identical with the one in the solution structure. The NMR data further demonstrate the presence of a minor state or set of states of the complex in solution, which is attributed to the presence of an encounter complex. The structure of the major state shows a small binding interface and a metal-to-metal distance of 16Å, with two pathways that provide strong electronic coupling of the redox centers. The interpretation of these results is discussed in the context of ET. The structure indicates that the ET rate can be much faster than the reported value, suggesting that the process may be gated. PMID:23856620

Hiruma, Yoshitaka; Hass, Mathias A S; Kikui, Yuki; Liu, Wei-Min; Olmez, Betül; Skinner, Simon P; Blok, Anneloes; Kloosterman, Alexander; Koteishi, Hiroyasu; Löhr, Frank; Schwalbe, Harald; Nojiri, Masaki; Ubbink, Marcellus

2013-07-13

7

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

8

1,3-Alternate calix[4]arene nitronyl nitroxide tetraradical and diradical: synthesis, X-ray crystallography, paramagnetic NMR spectroscopy, EPR spectroscopy, and magnetic studies  

PubMed Central

Calix[4]arenes constrained to 1,3-alternate conformation and functionalized at the upper rim with four and two nitronyl nitroxides have been synthesized, and characterized by X-ray crystallography, magnetic resonance (EPR and 1H NMR) spectroscopy, and magnetic studies. Such calix[4]arene tetraradicals and diradicals provide scaffolds for through-bond and through-space intramolecular exchange couplings.

Rajca, Andrzej; Pink, Maren; Mukherjee, Sumit; Rajca, Suchada; Das, Kausik

2009-01-01

9

NMR Spectroscopy  

NSDL National Science Digital Library

This site contains web-based programs that allow the user to predict chemical shifts, spin-spin coupling patterns and NMR line shapes affected by dynamic chemical exchange. This site will be most useful for students with a good background in the fundamentals of NMR theory.

Shattuck, Thomas W.

2011-07-01

10

NMR of paramagnetic complexes of radicals with organic ligands  

Microsoft Academic Search

Complex formation between stable amine oxide radicals and organic molecules generates paramagnetic shifts in the NMR spectra of the ligand nuclei and corresponding line broadening in these spectra. Analysis of the paramagnetic shifts yielded the magnitudes and signs of the isotopic hyperfine interaction constants for the protons in the radical complexes with hydroxyl-containing ligands. The equilibrium constants for the complex

N. A. Sysoeva; A. L. Buchachenko

1972-01-01

11

Exploring sparsely populated states of macromolecules by diamagnetic and paramagnetic NMR relaxation  

PubMed Central

Sparsely populated states of macromolecules, characterized by short lifetimes and high free-energies relative to the predominant ground state, often play a key role in many biological, chemical, and biophysical processes. In this review, we briefly summarize various new developments in NMR spectroscopy that permit these heretofore invisible, sparsely populated states to be detected, characterized, and in some instances visualized. Relaxation dispersion spectroscopy yields detailed kinetic information on processes involving species characterized by distinct chemical shifts with lifetimes in the ?50 ?s?10 ms range and populations as low as 0.5%. In the fast exchange regime (time scale less than ?250?500 ?s), the footprint of sparsely populated states can be observed on paramagnetic relaxation enhancement profiles measured on the resonances of the major species, thereby yielding structural information that is directly related to paramagnetic center-nuclei distances from which it is possible, under suitable circumstances, to compute a structure or ensemble of structures for the minor species. Finally, differential transverse relaxation measurements can be used to detect lifetime broadening effects that directly reflect the unidirectional rates for the conversion of NMR-visible into high-molecular weight NMR-invisible species. Examples of these various approaches are presented.

Clore, G Marius

2011-01-01

12

The impact of window functions on NMR-based paramagnetic relaxation enhancement measurements in membrane proteins.  

PubMed

Though challenging, solution NMR spectroscopy allows fundamental interrogation of the structure and dynamics of membrane proteins. One major technical hurdle in studies of helical membrane proteins by NMR is the difficulty of obtaining sufficient long range NOEs to determine tertiary structure. For this reason, long range distance information is sometimes sought through measurement of paramagnetic relaxation enhancements (PRE) of NMR nuclei as a function of distance from an introduced paramagnetic probe. Current PRE interpretation is based on the assumption of Lorentzian resonance lineshapes. However, in order to optimize spectral resolution, modern multidimensional NMR spectra are almost always subjected to resolution-enhancement, leading to distortions in the Lorentizian peak shape. Here it is shown that when PREs are derived using peak intensities (i.e., peak height) and linewidths from both real and simulated spectra that were produced using a wide range of apodization/window functions, that there is little variation in the distances determined (<1 A at the extremes). This indicates that the high degree of resolution enhancement required to obtain well-resolved spectra from helical membrane proteins is compatible with the use of PRE data as a source of distance restraints. While these conclusions are particularly important for helical membrane proteins, they are generally applicable to all PRE measurements made using resolution-enhanced data. PMID:19751702

Van Horn, Wade D; Beel, Andrew J; Kang, Congbao; Sanders, Charles R

2009-09-12

13

Keeping PASE with WEFT: SHWEFT-PASE pulse sequences for 1H NMR spectra of highly paramagnetic molecules.  

PubMed

Metalloproteins are a category of biomolecules in which the metal site is usually the locus of activity or function. In many cases, the metal ions are paramagnetic or have accessible paramagnetic states, many of which can be studied using NMR spectroscopy. Extracting useful information from (1)H NMR spectra of highly paramagnetic proteins can be difficult because the paramagnetism leads to large resonance shifts (~400 ppm), extremely broad lines, extreme baseline nonlinearity, and peak shape distortion. It is demonstrated that employing polychromatic and adiabatic shaped pulses in simple pulse sequences, then combining existing sequences, leads to significant spectral improvement for highly paramagnetic proteins. These sequences employ existing technology, with available hardware, and are of short duration to accommodate short nuclear T1 and T2. They are shown to display uniform excitation over large spectral widths (~75 kHz), accommodate high repetition rates, produce flat baselines over 75 kHz while maintaining peak shape fidelity, and can be used to reduce spectral dynamic range. High-spin (S = 5/2) metmyoglobin, a prototypical highly paramagnetic protein, was used as the test molecule. The resulting one-dimensional (1D) pulse sequences combine shaped pulses with super-water elimination Fourier transform, which can be further combined with paramagnetic spectroscopy to give shaped pulses with super-water elimination Fourier transform-paramagnetic spectroscopy. These sequences require, at most, direct current offset correction and minimal phasing. The performance of these sequences in simple (1)H 1D, 1D NOE, and two-dimensional NOESY experiments is demonstrated for metmyoglobin and Paracoccus denitrificans Co(2+)-amicyanin (S = 3/2), and employed to make new heme hyperfine resonance assignments for high-spin metBjFixLH(151-256), the heme sensing domain of Bradyrhizobium japonicum FixL. PMID:23401036

Helms, Gregory; Satterlee, James D

2013-02-10

14

NMR Spectroscopy - Theory  

NSDL National Science Digital Library

This web site begins with a simple quantum description of NMR and proceeds to introduce resonance absorption, relaxation, chemical shifts, and scalar couplings. This site will be useful for advanced undergraduate students needing a description of NMR that is more detailed than that given in most introductory Organic texts.

Lord, J. R.

2011-06-30

15

Paramagnetic tagging of diamagnetic proteins for solution NMR.  

PubMed

In this article, approaches towards the paramagnetic tagging of diamagnetic proteins are reviewed. Alignment can be achieved by adding paramagnetic fusion proteins or peptides to the C- or the N-terminus or by attaching paramagnetic tags to Cystein residues. Applications for the study of homodimer structures and protein/ligand interactions, as well as protein domain dynamics, are reviewed. PMID:16921533

Rodriguez-Castañeda, Fernando; Haberz, Peter; Leonov, Andrei; Griesinger, Christian

2006-07-01

16

Modern NMR Spectroscopy.  

ERIC Educational Resources Information Center

|Discusses direct chemical information that can be obtained from modern nuclear magnetic resonance (NMR) methods, concentrating on the types of problems that can be solved. Shows how selected methods provide information about polymers, bipolymers, biochemistry, small organic molecules, inorganic compounds, and compounds oriented in a magnetic…

Jelinski, Lynn W.

1984-01-01

17

"Solvent Effects" in 1H NMR Spectroscopy.  

ERIC Educational Resources Information Center

|Describes a simple undergraduate experiment in chemistry dealing with the "solvent effects" in nuclear magnetic resonance (NMR) spectroscopy. Stresses the importance of having students learn NMR spectroscopy as a tool in analytical chemistry. (TW)|

Cavaleiro, Jose A. S.

1987-01-01

18

Detection of Nitric Oxide by Electron Paramagnetic Resonance Spectroscopy  

PubMed Central

Electron paramagnetic resonance (EPR) spectroscopy has been used in a number of ways to study nitric oxide chemistry and biology. As an intrinsically stable and relatively unreactive diatomic free radical, the challenges for detecting this species by EPR are somewhat different than those for transient radical species. This review gives a basic introduction to EPR spectroscopy and discusses its uses to assess and quantify nitric oxide formation in biological systems.

Hogg, Neil

2010-01-01

19

Bulk magnetic susceptibility shifts in NMR studies of compartmentalized samples: use of paramagnetic reagents.  

PubMed

The bulk magnetic susceptibility (BMS) shift of a nuclear resonance frequency caused by a paramagnetic compound is of importance in vivo NMR, both magnetic resonance spectroscopy and magnetic resonance imaging. However, since it is a rather complicated phenomenon, it has been the source of many misinterpretations in the literature. We have reworked and organized the theory of the BMS shift. This includes accounting for the important effects of local susceptibility. We have conducted experiments on phantom samples in order to illustrate the principles involved. Our phantoms consist of capillaries and coaxial cylinders. They simulate the situations of blood vessels oriented parallel and perpendicular to the magnetic field and the interstitial spaces surrounding them. In most of our experiments, the paramagnetic compound was one of several different hyperfine shift reagents for cation resonances. These were chosen to cover a range of potencies, in both magnitude and sign, of the shifts they produce. However, we also used a reagent which was incapable of inducing a hyperfine shift and thus could cause only a BMS shift. Although we report only 23Na spectra in this paper, the latter samples simulate the cases where one observes the water 1H resonance in experiments employing hyperfine shift reagents for cations. There have been a number of such investigations recently reported in the literature. The principles considered in this paper allow us to offer new interpretations for the results of several experiments published in the last few years. PMID:2156125

Chu, S C; Xu, Y; Balschi, J A; Springer, C S

1990-02-01

20

Improvement of (31)P NMR spectral resolution by 8-hydroxyquinoline precipitation of paramagnetic Fe and Mn in environmental samples.  

PubMed

Solution (31)P nuclear magnetic resonance (NMR) spectroscopy is currently the main method for the characterization of phosphorus (P) forms in environment samples. However, identification and quantification of P compounds may be hampered by poor resolution of spectra caused by paramagnetic Fe and Mn. In this study, a novel technique was developed to improve spectral resolution by removing paramagnetic Fe and Mn from alkaline extracts via 8-hydroxyquinoline (8-HOQ) precipitation. Batch experiments showed that both Fe and Mn were effectively removed by the precipitation at pH 9.0, with the removal efficiencies of 83-91% for Fe and 67-78% for Mn from the extracts of five different environmental samples, while little effect was found on concentration of total P. The (31)P NMR analysis of a model P solution showed that addition of 8-HOQ and its precipitation with metal ions did not alter P forms. Further analyses of the five extracts with (31)P NMR spectroscopy demonstrated that the 8-HOQ precipitation was an ideal method compared with the present postextraction techniques, such as bicarbonate dithionate (BD), EDTA and Chelex-100 treatments, by improving spectral resolution to a large extent with no detrimental effects on P forms. PMID:20201571

Ding, Shiming; Xu, Di; Li, Bin; Fan, Chengxin; Zhang, Chaosheng

2010-04-01

21

Effects of added paramagnetic ions on the 13 C CP\\/MAS NMR spectrum of a de-ashed soil  

Microsoft Academic Search

A de-ashed soil was reacted with a series of paramagnetic (Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Pr3+, Eu3+) and non-paramagnetic (Na+, Ca2+, Zn2+) ions. Amendment with non-paramagnetic ions did not effect the NMR properties of the soil organic matter (SOM), whereas a number of NMR properties including signal intensity, broadness and relaxation rate constants (T1?H, T1H, T1C) were effected by the

Ronald J Smernik; J. Malcolm Oades

1999-01-01

22

Hyperpolarized 131Xe NMR spectroscopy  

PubMed Central

Hyperpolarized (hp) 131Xe with up to 2.2% spin polarization (i.e., 5000-fold signal enhancement at 9.4 T) was obtained after separation from the rubidium vapor of the spin-exchange optical pumping (SEOP) process. The SEOP was applied for several minutes in a stopped-flow mode, and the fast, quadrupolar-driven T1 relaxation of this spin I = 3/2 noble gas isotope required a rapid subsequent rubidium removal and swift transfer into the high magnetic field region for NMR detection. Because of the xenon density dependent 131Xe quadrupolar relaxation in the gas phase, the SEOP polarization build-up exhibits an even more pronounced dependence on xenon partial pressure than that observed in 129Xe SEOP. 131Xe is the only stable noble gas isotope with a positive gyromagnetic ratio and shows therefore a different relative phase between hp signal and thermal signal compared to all other noble gases. The gas phase 131Xe NMR spectrum displays a surface and magnetic field dependent quadrupolar splitting that was found to have additional gas pressure and gas composition dependence. The splitting was reduced by the presence of water vapor that presumably influences xenon-surface interactions. The hp 131Xe spectrum shows differential line broadening, suggesting the presence of strong adsorption sites. Beyond hp 131Xe NMR spectroscopy studies, a general equation for the high temperature, thermal spin polarization, P, for spin I?1/2 nuclei is presented.

Stupic, Karl F.; Cleveland, Zackary I.; Pavlovskaya, Galina E.; Meersmann, Thomas

2011-01-01

23

NMR Spectroscopy and Its Value: A Primer  

ERIC Educational Resources Information Center

Nuclear magnetic resonance (NMR) spectroscopy is widely used by chemists. Furthermore, the use of NMR spectroscopy to solve structures of macromolecules or to examine protein-ligand interactions is popular. Yet, few students entering graduate education in biological sciences have been introduced to this method or its utility. Over the last six…

Veeraraghavan, Sudha

2008-01-01

24

NMR Spectroscopy and Its Value: A Primer  

ERIC Educational Resources Information Center

|Nuclear magnetic resonance (NMR) spectroscopy is widely used by chemists. Furthermore, the use of NMR spectroscopy to solve structures of macromolecules or to examine protein-ligand interactions is popular. Yet, few students entering graduate education in biological sciences have been introduced to this method or its utility. Over the last six…

Veeraraghavan, Sudha

2008-01-01

25

Paramagnetic NMR investigation of dendrimer-based host-guest interactions.  

PubMed

In this study, the host-guest behavior of poly(amidoamine) (PAMAM) dendrimers bearing amine, hydroxyl, or carboxylate surface functionalities were investigated by paramagnetic NMR studies. 2,2,6,6-Tetramethylpiperidinyloxy (TEMPO) derivatives were used as paramagnetic guest molecules. The results showed that TEMPO-COOH significantly broaden the ¹H NMR peaks of amine- and hydroxyl-terminated PAMAM dendrimers. In comparison, no paramagnetic relaxation enhancement (PRE) was observed between TEMPO-NH?, TEMPO-OH and the three types of PAMAM dendrimers. The PRE phenomenon observed is correlated with the encapsulation of TEMPO-COOH within dendrimer pockets. Protonation of the tertiary amine groups within PAMAM dendrimers plays an important role during this process. Interestingly, the absence of TEMPO-COOH encapsulation within carboxylate-terminated PAMAM dendrimer is observed due to the repulsion of TEMPO-COO- anion and anionic dendrimer surface. The combination of paramagnetic probes and ¹H NMR linewidth analysis can be used as a powerful tool in the analysis of dendrimer-based host-guest systems. PMID:23762249

Wang, Fei; Shao, Naimin; Cheng, Yiyun

2013-06-10

26

Water exchange in plant tissue studied by proton NMR in the presence of paramagnetic centers.  

PubMed Central

The proton NMR relaxation of water in maize roots in the presence of paramagnetic centers, Mn2+, Mn- EDTA2 -, and dextran-magnetite was measured. It was shown that the NMR method of Conlon and Outhred (1972, Biochem. Biophys. Acta. 288:354-361) can be applied to a heterogenous multicellular system, and the water exchange time between cortical cells and the extracellular space can be calculated. The water exchange is presumably controlled by the intracellular unstirred layers. The Mn- EDTA2 - complex is a suitable paramagnetic compound for complex tissue, while the application of dextran-magnetite is probably restricted to studies of water exchange in cell suspensions. The water free space of the root and viscosity of the cells cytoplasm was estimated with the use of Mn- EDTA2 -. The convenience of proton NMR for studying the multiphase uptake of paramagnetic ions by plant root as well as their transport to leaves is demonstrated. A simple and rapid NMR technique (spin-echo recovery) for continuous measurement of the uptake process is presented.

Bacic, G; Ratkovic, S

1984-01-01

27

Introduction to spin label electron paramagnetic resonance spectroscopy of proteins.  

PubMed

An undergraduate laboratory exercise is described to demonstrate the biochemical applications of electron paramagnetic resonance (EPR) spectroscopy. The ?93 cysteine residue of hemoglobin is labeled by the covalent binding of 3-maleimido-proxyl (5-MSL) and 2,2,5,5-tetramethyl-1-oxyl-3-methyl methanethiosulfonate (MTSL), respectively. The excess spin label is removed by gel-exclusion chromatography. Changes in the mobility of the reporter groups attached to the protein are monitored by EPR spectroscopy. While the spectral parameters of the rigidly attached 5-MSL provide information on the rotation of the whole spin labeled protein, MTSL bound by a more flexible linkage describes the local environment of the cysteine residue in the interior of the protein structure. Students can study the known crystal structure of hemoglobin in comparison to the results they obtain by analyzing the EPR spectra. Overall, the exercise introduces them to laboratory techniques such as protein labeling, gel filtration, EPR spectroscopy, as well as familiarizes them with the online Protein Data Bank as a research resource and PyMOL software as a structure visualization tool. PMID:23281241

Melanson, Michelle; Sood, Abha; Török, Fanni; Török, Marianna

2012-12-27

28

Carbon CP-MASS NMR and X-ray crystal structure of paramagnetic lanthanide acetates  

Microsoft Academic Search

The X-ray crystal structures of praseodymium(III) acetate monohydrate and europium(III) acetate trihydrate have been solved and cross-polarization carbon-13 NMR spectra obtained in the polycrystalline solids. The static and magic angle spinning spectra are compared with diamagnetic acetate spectra. The shifts in the paramagnetic compounds are large, permitting sample heterogeniety to be readily detected. THE CP-MASS carbon spectra are assigned by

S. Ganapathy; V. P. Chacko; R. G. Bryant; M. C. Etter

1986-01-01

29

Accurate Structure and Dynamics of the Metal-Site of Paramagnetic Metalloproteins from NMR Parameters Using Natural Bond Orbitals  

PubMed Central

A natural bond orbital (NBO) analysis of unpaired electron spin density in metalloproteins is presented, which allows a fast and robust calculation of paramagnetic NMR parameters. Approximately 90% of the unpaired electron spin density occupies metal–ligand NBOs, allowing the majority of the density to be modeled by only a few NBOs that reflect the chemical bonding environment. We show that the paramagnetic relaxation rate of protons can be calculated accurately using only the metal–ligand NBOs and that these rates are in good agreement with corresponding rates measured experimentally. This holds, in particular, for protons of ligand residues where the point-dipole approximation breaks down. To describe the paramagnetic relaxation of heavy nuclei, also the electron spin density in the local orbitals must be taken into account. Geometric distance restraints for 15N can be derived from the paramagnetic relaxation enhancement and the Fermi contact shift when local NBOs are included in the analysis. Thus, the NBO approach allows us to include experimental paramagnetic NMR parameters of 15N nuclei as restraints in a structure optimization protocol. We performed a molecular dynamics simulation and structure determination of oxidized rubredoxin using the experimentally obtained paramagnetic NMR parameters of 15N. The corresponding structures obtained are in good agreement with the crystal structure of rubredoxin. Thus, the NBO approach allows an accurate description of the geometric structure and the dynamics of metalloproteins, when NMR parameters are available of nuclei in the immediate vicinity of the metal-site.

2012-01-01

30

QUANTITATIVE 15N NMR SPECTROSCOPY  

EPA Science Inventory

Line intensities in 15N NMR spectra are strongly influenced by spin-lattice and spin-spin relaxation times, relaxation mechanisms and experimental conditions. Special care has to be taken in using 15N spectra for quantitative purposes. Quantitative aspects are discussed for the 1...

31

?-NMR study of isolated 8Li+ in the enhanced paramagnet platinum  

NASA Astrophysics Data System (ADS)

We report ?-detected nuclear magnetic resonance (?-NMR) measurements of 8Li+ implanted into high purity Pt. The frequency of the 8Li ?-NMR resonance and the spin-lattice relaxation rates 1/T1 were measured at temperatures ranging from 3 to 300 K. Remarkably, both the spin-lattice relaxation rate and the Knight shift K depend linearly on temperature T although the bulk susceptibility does not. K is found to scale with the Curie-Weiss dependence of the Pt susceptibility extrapolated to low temperatures. This is attributed to a defect response of the enhanced paramagnetism of Pt, i.e., the presence of the interstitial Li+ locally relieves the tendency for the Curie-Weiss susceptibility to saturate at low T. We propose that the low temperature saturation in ? of Pt may be related to an interband coupling between the s and d bands that is disrupted locally by the presence of the Li+.

Ofer, Oren; Chow, K. H.; Fan, I.; Egilmez, M.; Parolin, T. J.; Hossain, M. D.; Jung, J.; Salman, Z.; Kiefl, R. F.; Levy, C. D. P.; Morris, G. D.; Pearson, M. R.; Saadaoui, H.; Song, Q.; Wang, D.; MacFarlane, W. A.

2012-08-01

32

Paramagnetic effects on the NMR spectra of "diamagnetic" ruthenium(bis-phosphine)(bis-semiquinone) complexes.  

PubMed

Ligand substitution on cis-Ru(PPh(3))(2)(1,2-O(2)C(6)H(4))(2) gives cis-RuL(1)L(2)(1,2-O(2)C(6)H(4))(2) (L(1) = PPh(3), L(2) = P(OPh)(3), PBu(3); L(1) = L(2) = PBu(3), P(OMe)(3)). Syntheses of cis-Ru(PPh(3))(2)(3,4-O(2)C(6)H(2)(5-OH)CO(2)Me)(2) and cis-Ru(PPh(3))(2)(AGSQ)(2) (AGSQ = the semiquinone derived from 1,2,3-trihydroxyanthracene-9,10-dione) are also reported. The upfield chemical shifts and line broadening of the semiquinone 4,5-proton resonances in the NMR spectra indicate that these complexes, while having no detectable magnetic moments, have a weak, temperature-, ligand- and solvent-variable residual paramagnetism, not previously recognized in this series. Density functional theory (DFT) calculations predict a low-lying triplet state, about 14 kJ/mol (0.15 eV) above the singlet ground state. The paramagnetic effects on the NMR spectra are attributed to singlet-triplet equilibria. Temperature dependence of the proton resonances of the semiquinone rings of cis-Ru(PPh(3))(2)(1,2-O(2)C(6)H(4))(2) was used to calculate the singlet-triplet free energy difference as 17.5-18.0 kJ/mol in toluene. PMID:19400557

Le Guennic, Boris; Floyd, Tavon; Galan, Brandon R; Autschbach, Jochen; Keister, Jerome B

2009-06-15

33

The effect of bulk magnetic susceptibility on solid state NMR spectra of paramagnetic compounds  

PubMed

The effect of bulk magnetic susceptibility (BMS) on solid state NMR spectra of paramagnetic compounds was investigated theoretically and experimentally. The BMS shift was calculated for cylindrical and spherocylinderical containers with some ratios of the length L and the diameter D. The results show the best resolution can be obtained by using a long cylindrical sample container with L/D > 10 and by exciting only the region near the center of the container. The effect of the random orientations and distributions of crystallites in a powder sample was also calculated according to a model proposed by Schwerk et al. [J. Magn. Reson. A 119, 157 (1996)] with removing the Fermi contact term from their model. Static and the magic-angle spinning 13C NMR spectra were recorded on two paramagnetic compounds of Ln(C2D5SO4)3 . 8H2O where Ln = Pr, Yb. The modified theory predicts the BMS broadening of the experimental spectra very well. Copyright 1998 Academic Press. PMID:9716476

Kubo; Spaniol; Terao

1998-08-01

34

Sensitivity enhancement using paramagnetic relaxation in MAS solid-state NMR of perdeuterated proteins  

NASA Astrophysics Data System (ADS)

Previously, Ishii et al., could show that chelated paramagnetic ions can be employed to significantly decrease the recycle delay of a MAS solid-state NMR experiment [N.P. Wickramasinghe, M. Kotecha, A. Samoson, J. Past, Y. Ishii, Sensitivity enhancement in C-13 solid-state NMR of protein microcrystals by use of paramagnetic metal ions for optimizing H-1 T-1 relaxation, J. Magn. Reson. 184 (2007) 350 356]. Application of the method is limited to very robust samples, for which sample stability is not compromised by RF induced heating. In addition, probe integrity might be perturbed in standard MAS PRE experiments due to the use of very short duty cycles. We show that these deleterious effects can be avoided if perdeuterated proteins are employed that have been re-crystallized from D2O:H2O = 9:1 containing buffer solutions. The experiments are demonstrated using the SH3 domain of chicken ?-spectrin as a model system. The labeling scheme allows to record proton detected 1H, 15N correlation spectra with very high resolution in the absence of heteronuclear dipolar decoupling. Cu edta as a doping reagent yields a reduction of the recycle delay by up to a factor of 15. In particular, we find that the 1H T1 for the bulk HN magnetization is reduced from 4.4 s to 0.3 s if the Cu edta concentration is increased from 0 mM to 250 mM. Possible perturbations like chemical shift changes or line broadening due to the paramagnetic chelate complex are minimal. No degradation of our samples was observed in the course of the experiments.

Linser, Rasmus; Chevelkov, Veniamin; Diehl, Anne; Reif, Bernd

2007-12-01

35

Molecular Structure and Dynamics by NMR Spectroscopy  

NSDL National Science Digital Library

This site provides PowerPoint slides for a lecture for a graduate-level course in NMR spectroscopy. The slides include useful animations which help to demonstrate the concepts described. While the casual student may find it hard to follow everything on the slides without an accompanying lecture, the files should be very useful for advanced students or educators putting together similar courses.

Edison, Arthur S.; Long, Joanna

2011-07-04

36

Tritiation methods and tritium NMR spectroscopy.  

National Technical Information Service (NTIS)

We have used a simple process for the production of highly tritiated water and characterized the product species by (sup 1)H and (sup 3)H NMR spectroscopy. The water is readily manipulated and used in subsequent reactions either as T(sub 2)O, CH(sub 3)COO...

D. K. Jaiswal H. Morimoto M. Salijoughian P. G. Williams

1991-01-01

37

Tritiation methods and tritium NMR spectroscopy  

SciTech Connect

We have used a simple process for the production of highly tritiated water and characterized the product species by {sup 1}H and {sup 3}H NMR spectroscopy. The water is readily manipulated and used in subsequent reactions either as T{sub 2}O, CH{sub 3}COOT or CF{sub 3}COOT. Development of tritiated diimide has progressed to the point where cis-hydrogenated products at 1-20 Ci/mmole S.A. are possible. Tri-n-butyl tin tritide has been produced at >95% tritium content and well characterized by multinuclear NMR techniques. 27 refs., 3 figs.

Jaiswal, D.K. [Defence Research and Development Establishment, Gwalior (India); Morimoto, H.; Salijoughian, M.; Williams, P.G. [Lawrence Berkeley Lab., CA (United States)

1991-09-01

38

Gamma-irradiated ExtraVit M nutritive supplement studied by electron paramagnetic resonance spectroscopy  

NASA Astrophysics Data System (ADS)

An unirradiated and ?-irradiated nutritive supplement named ExtraVit M was studied by electron paramagnetic resonance (EPR) spectroscopy in order to detect stable paramagnetic species following improvement of hygienic quality by ?-radiation. Free radicals were induced by ?-radiation in the studied samples from low absorbed doses, showing a certain sensibility of these samples to the radiation treatment. The EPR spectrum of irradiated ExtraVit M is typical for drugs or nutritive supplements containing high levels of sugars, vitamin C and cellulose.

Petri?or, Dina; Damian, Grigore; Simon, Simion

2008-04-01

39

A review of electron spin spectroscopy and its application to the study of paramagnetic defects in crystalline quartz  

Microsoft Academic Search

A comprehensive review (ca. 230 references) is presented of the present (1983) state of knowledge of paramagnetic defects in crystalline quartz, as derived from electron paramagnetic resonance spectroscopy and related techniques. An auxiliary description of relevant concepts in solid state electron paramagnetic resonance (EPR), suitable for the non-specialist, is included. The centres described include those arising from impurity ions (Al,

John A. Weil

1984-01-01

40

NMR study of hydrogen diffusion in metal hydrides containing paramagnetic impurities  

SciTech Connect

The pulsed NMR of hydrogen nuclei in LaH/sub x/ and YH/sub x/ with and without paramagnetic impurities (Ce, Nd, Gd, Dy, Er) was studied. Measurements of proton T/sub 1/ were carried out in the temperature range from 77K to 800K at a resonance frequency of 400MHz. The data for both pure LaH/sub x/ show unambiguously that the hydrogen diffusion rate increases with increasing hydrogen content. It is concluded that increased occupancy of the octahedral sublattice causes the potential wells at octahedral and tetrahedral sites to become shallower and lowers the energy barrier to motion between the two sublattices. For systems with controlled dilute paramagnetic impurities, an additional spin-lattice relaxation process was found and appears to be essentially due to the dipolar coupling between impurity and proton moments. The study showed that the impurity induced relaxation rate is very sensitive to the magnetic moment and relaxation rate of the impurity ion, as well as depending on the host hydride composition. Serious errors in deduced diffusion and electronic structure parameters may be made unless effects of impurities are recognized and allowed for.

Phua, T.T.

1982-01-01

41

Carbon-based standards for electron paramagnetic resonance spectroscopy  

Microsoft Academic Search

In order to meet the need for a good new EPR intensity andg-value standard whose paramagnetic species are carbon-based radicals, several materials were investigated, including coal,\\u000a fusinite (a coal maceral), and several carbohydrate chars. Of the prototypical standards prepared, a chemically-treated fusinite\\u000a is recommended as most suitable because of its chemical stability, spin density, EPR signal line shape and line

F. P. Auteri; R. L. Belford; S. Boyer; K. Motsegood; A. Smirnov; T. Smirnova; N. Vahidi; R. B. Clarkson

1994-01-01

42

Interdomain orientation of cardiac troponin C characterized by paramagnetic relaxation enhancement NMR reveals a compact state.  

PubMed

Cardiac troponin C (cTnC) is the calcium binding subunit of the troponin complex that triggers the thin filament response to calcium influx into the sarcomere. cTnC consists of two globular EF-hand domains (termed the N- and C-domains) connected by a flexible linker. While the conformation of each domain of cTnC has been thoroughly characterized through NMR studies involving either the isolated N-domain (N-cTnC) or C-domain (C-cTnC), little attention has been paid to the range of interdomain orientations possible in full-length cTnC that arises as a consequence of the flexibility of the domain linker. Flexibility in the domain linker of cTnC is essential for effective regulatory function of troponin. We have therefore utilized paramagnetic relaxation enhancement (PRE) NMR to assess the interdomain orientation of cTnC. Ensemble fitting of our interdomain PRE measurements reveals that isolated cTnC has considerable interdomain flexibility and preferentially adopts a bent conformation in solution, with a defined range of relative domain orientations. PMID:22811351

Cordina, Nicole M; Liew, Chu Kong; Gell, David A; Fajer, Piotr G; Mackay, Joel P; Brown, Louise J

2012-09-01

43

Dynamic nuclear polarization surface enhanced NMR spectroscopy.  

PubMed

Many of the functions and applications of advanced materials result from their interfacial structures and properties. However, the difficulty in characterizing the surface structure of these materials at an atomic level can often slow their further development. Solid-state NMR can probe surface structure and complement established surface science techniques, but its low sensitivity often limits its application. Many materials have low surface areas and/or low concentrations of active/surface sites. Dynamic nuclear polarization (DNP) is one intriguing method to enhance the sensitivity of solid-state NMR experiments by several orders of magnitude. In a DNP experiment, the large polarization of unpaired electrons is transferred to surrounding nuclei, which provides a maximum theoretical DNP enhancement of ?658 for (1)H NMR. In this Account, we discuss the application of DNP to enhance surface NMR signals, an approach known as DNP surface enhanced NMR spectroscopy (DNP SENS). Enabling DNP for these systems requires bringing an exogeneous radical solution into contact with surfaces without diluting the sample. We proposed the incipient wetness impregnation technique (IWI), a well-known method in materials science, to impregnate porous and particulate materials with just enough radical containing solution to fill the porous volume. IWI offers several advantages: it is extremely simple, provides a uniform wetting of the surface, and does not increase the sample volume or substantially reduce the concentration of the sample. This Account describes the basic principles behind DNP SENS through results obtained for mesoporous and nanoparticulate samples impregnated with radical solutions. We also discuss the quantification of the overall sensitivity enhancements obtained with DNP SENS and compare that with ordinary room temperature NMR spectroscopy. We then review the development of radicals and solvents that give the best possible enhancements today. With the best polarizing mixtures, DNP SENS enhances sensitivity by a factor of up to 100, which decreases acquisition time by five orders of magnitude. Such enhancement enables the detailed and expedient atomic level characterization of the surfaces of complex materials at natural isotopic abundance and opens new avenues for NMR. To illustrate these improvements, we describe the successful application of DNP SENS to characterize hybrid materials, organometallic surface species, and metal-organic frameworks. PMID:23517009

Rossini, Aaron J; Zagdoun, Alexandre; Lelli, Moreno; Lesage, Anne; Copéret, Christophe; Emsley, Lyndon

2013-03-21

44

Solution NMR spectroscopy for the determination of structures of membrane proteins in a lipid environment.  

PubMed

Several recent advancements have transformed solution NMR spectroscopy into a competitive, elegant, and eminently viable technique for determining the solution structures of membrane proteins at the level of atomic resolution. Once a good level of cell-based or cell-free expression and purification of a suitably sized membrane protein has been achieved, then NMR offers a combination of several versatile strategies, for example, choice of appropriate deuterated or non-deuterated detergents, temperature, and ionic strength; isotope labelling with (2)H, (13)C, (15)N, with or without protonation of Ile (?1), Leu, and Val methyl protons; combinatorial labelling of specific amino acids; transverse relaxation-optimized NMR spectroscopy-based, Nonuniform sampling-based, and other NMR experiments; measurement of residual dipolar couplings using stretched polyacrylamide gels or DNA nanotubes; and spin-labelling and paramagnetic relaxation enhancements. Strategic combinations of these advancements together with availability of highly sensitive cryogenically cooled probes equipped high-field NMR spectrometers (up to 1 GHz (1)H frequency) have allowed the perseverant investigator to successfully overcome several of the conventional pitfalls associated with the NMR technique and membrane proteins, viz., low sensitivity, poor sample stability, spectral crowding, and a limited number of NOEs and other constraints for structure calculations. This has resulted in an unprecedented growth in the number of successfully determined NMR structures of large and complex membrane proteins, and this technique now holds great promise for the structure determination of an ever larger body of membrane proteins. PMID:23404285

Arora, Ashish

2013-01-01

45

[Solid-state NMR spectroscopy and its pharmaceutical use].  

PubMed

Liquid-state NMR spectroscopy has become an essential analytical tool in almost all fields of chemical research. However, the scope of NMR spectroscopy is not confined to the analysis of fluids. The progress in the investigation of solid samples is remarkably fast and solid-state NMR has developed to a high performance method. The majority of drug substances and products manufactured in the pharmaceutical industry are formulated in solid state, their analysis gains the increasing potential of solid-state NMR spectroscopy. The aim of this work is to survey the basics of solid-state NMR and to highlight some pharmaceutical applications focusing on polymorphism. PMID:20443364

Marosi, Attila; Szalay, Zsófia; Demeter, Adám

2010-01-01

46

Paramagnetic ions as structural probes in solid-state NMR: Distance measurements in crystalline lanthanide acetates  

SciTech Connect

The rare earth acetates M(O[sub 2]CCH[sub 3])[sub 3][center dot]4H[sub 2]O (M = Nd, Sm, Eu, Y) and Pr(O[sub 2]CCH[sub 3])[sub 3][center dot]H[sub 2]O, and the analogous deuterated compounds, have been studied by [sup 13]C MAS-NMR. The paramagnetic materials show a large range of isotropic [sup 13]C chemical shifts which result largely from contact interactions with the rare earth electronic moments. They often show substantial linebroadening, which appears to result predominantly from anisotropic bulk magnetic susceptibility broadening for the deuterated compounds; the line widths for the protonated materials are increased further because of incomplete proton decoupling. Proton spectra acquired from a largely deuterated sample indicated that the spread in proton frequencies (40 kHz for Sm(O[sub 2]CCH[sub 3])[sub 3][center dot]4H[sub 2]O at 4.7 T, and calculated to be approximately 200 kHz for Eu(O[sub 2]CCH[sub 3])[sub 3][center dot]4H[sub 2]O) is too large for decoupling to be effective with attainable [sup 1]H power levels. The deuterated materials exhibit sufficiently good resolution to allow analysis of the large [sup 13]C spinning sideband manifolds; these result mainly from dipolar coupling to the paramagnetic centers. X-ray diffraction shows that the solid solutions Y[sub (1-x)]Ln[sub x](O[sub 2]CCH[sub 3])[sub 3][center dot]4H[sub 2]O (Ln = Pr, Nd, Sm, Eu; x [le] 0.1) crystallize with the Y(O[sub 2]CCH[sub 3])[sub 3][center dot]4H[sub 2]O crystal structure. MAS-NMR spectra of the [sup 13]C enriched deuterated analogues contain remarkably narrow resonances of only 100 Hz line width despite having spinning sideband envelopes spanning 1000 ppm. 53 refs., 6 figs., 3 tabs.

Brough, A.R.; Grey, C.P.; Dobson, C.M. (Univ. of Oxford (United Kingdom))

1993-08-11

47

Sensitivity Enhancement in 13C Solid-State NMR of Protein Microcrystals by Use of Paramagnetic Metal Ions for Optimizing 1H T1 Relaxation  

PubMed Central

We discuss a simple approach to enhance sensitivity for 13C high-resolution solid-state NMR for proteins in microcrystals by reducing 1H T1 relaxation times with paramagnetic relaxation reagents. It was shown that 1H T1 values can be reduced from 0.4-0.8 s to 60-70 ms for ubiquitin and lysozyme in D2O in the presence of 10 mM Cu(II)Na2EDTA without substantial degradation of the resolution in 13C CPMAS spectra. Faster signal accumulation using the shorter 1H T1 attained by paramagnetic doping provided sensitivity enhancements of 1.4-2.9 for these proteins, reducing the experimental time for a given signal-to-noise ratio by a factor of 2.0-8.4. This approach presented here is likely to be applicable to various other proteins in order to enhance sensitivity in 13C high-resolution solid-state NMR spectroscopy.

Wickramasinghe, Nalinda P.; Kotecha, Mrignayani; Samoson, Ago; Past, Jaan; Ishii, Yoshitaka

2007-01-01

48

NMR spectroscopy on domain dynamics in biomacromolecules.  

PubMed

Domain dynamics in biomacromolecules is currently an area of intense research because of its importance for understanding the huge quantity of available data relating the structure and function of proteins and nucleic acids. Control of structural flexibility is essential for the proper functioning of the biomacromolecules. Biophysical discoveries as well as computational algorithms and databases have reshaped our understanding of the often spectacular domain dynamics. At the residue level, such flexibility occurs due to local relaxation of peptide bond angles whose cumulative effect results in large changes in the secondary, tertiary or quaternary structures. The flexibility, or its absence, most often depends on the nature of interdomain linkages. Both the flexible and relatively rigid linkers are found in many multidomain biomacromolecules. Large-scale structural heterogeneity of multidomain biomacromolecules and their complexes is now seen as the norm rather than the exception. Absence of such motion, as in the so-called molecular rulers, also has desirable functional effects in architecture of biomacromolecules. The contemporary methods of NMR spectroscopy are capable to provide the detailed information on domain motions in biomacromolecules in the wide range of timescales related to the timescales of their functioning. We review here the current point of view on the nature of domain motions based on these last achievements in the field of NMR spectroscopy. Experimental and theoretical aspects of the collective intra- and interdomain motions are considered. PMID:23684958

Shapiro, Yury E

2013-05-15

49

Magnetism, optical absorbance, and 19F NMR spectra of nafion films with self-assembling paramagnetic networks  

SciTech Connect

Magnetization, optical absorbance, and {sup 19}F NMR spectra of Nafion transparent films as received and doped with Mn{sup 2+}, Co{sup 2+}, Fe{sup 2+}, and Fe{sup 3+} ions with and without treatment in 1H-1,2,4-triazole (trz) have been studied. Doping of Nafion with Fe{sup 2+} and Co{sup 2+} and their bridging to nitrogen of triazole yields a hybrid self-assembling paramagnetic system that exhibits interesting magnetic and optical properties. These include spin crossover phenomena between high-spin (HS) and low-spin (LS) states in Nafion-Fe{sup 2+}-trz and Nafion-Co{sup 2+}-trz accompanied by thermochromic effects in the visible range induced by temperature. A large shift of the magnetization curve induced by a magnetic field in the vicinity of the HS {leftrightarrow} LS, {approx}220 K, observed for Nafion-Fe{sup 2+}-trz has a rate of {approx}6 K/kOe, which is about three orders of magnitude larger than that in bulk spin crossover Fe{sup 2+} materials. Selective response of {sup 19}F NMR signals on doping with paramagnetic ions demonstrates that NMR can be used as spatially resolved method to study Nafion film with paramagnetic network. Both chemical shift and width of {sup 19}F NMR signals show that SO groups of Nafion, Fe or Co ions, and nitrogen of triazole are bonded whereas they form a spin crossover system. Based on a model of nanosize cylinders proposed for Nafion [K. Schmidt-Rohr and Q. Chen, Nat Mater (2008), 75], we suggest that paramagnetic ions are located inside these cylinders, forming self-assembling magnetically and optically active nanoscale networks.

Levin, E. M.; Chen, Q.; Bud'ko, S. L.

2012-01-15

50

Spin dynamics in the paramagnetic phase of YBa2Cu3O6.12 as seen by Cu NMR  

Microsoft Academic Search

We report a Cu nuclear magnetic resonance (NMR) study at both Cu sites in the paramagnetic phase of YBa2Cu3O6.12. By measuring the temperature dependence of the magnetic shift and the spin-lattice relaxation time, we have obtained the following major results. Above 500 K, the compound is in the renormalized classical regime of a two-dimensional quantum Heisenberg antiferromagnet (AF) with spin

R. Pozzi; M. Mali; D. Brinkmann; A. Erb

1999-01-01

51

Solid-state NMR of a paramagnetic DIAD-FeII catalyst: sensitivity, resolution enhancement, and structure-based assignments.  

PubMed

A general protocol for the structural characterization of paramagnetic molecular solids using solid-state NMR is provided and illustrated by the characterization of a high-spin Fe(II) catalyst precursor. We show how good NMR performance can be obtained on a molecular powder sample at natural abundance by using very fast (>30 kHz) magic angle spinning (MAS), even though the individual NMR resonances have highly anisotropic shifts and very short relaxation times. The results include the optimization of broadband heteronuclear (proton-carbon) recoupling sequences for polarization transfer; the observation of single or multiple quantum correlation spectra between coupled spins as a tool for removing the inhomogeneous bulk magnetic susceptibility (BMS) broadening; and the combination of NMR experiments and density functional theory calculations, to yield assignments. PMID:17031968

Kervern, Gwendal; Pintacuda, Guido; Zhang, Yong; Oldfield, Eric; Roukoss, Charbel; Kuntz, Emile; Herdtweck, Eberhardt; Basset, Jean-Marie; Cadars, Sylvian; Lesage, Anne; Copéret, Christophe; Emsley, Lyndon

2006-10-18

52

In vivo measurement of tissue oxygen using electron paramagnetic resonance spectroscopy with oxygen-sensitive paramagnetic particle, lithium phthalocyanine.  

PubMed

The partial pressure of oxygen (pO(2)) plays a determining role in the energy metabolism of aerobic cells. However, low pO(2) level induces pathophysiological conditions such as tumor hypoxia, ischemia or reperfusion injury, and delayed/altered wound healing. Especially, pO(2) level in the tumor is known to be related to tumor progression and effectiveness of radiotherapy. To monitor the pO(2) levels in vivo, continuous wave (CW) and time-domain (TD) electron paramagnetic resonance (EPR) spectroscopy method was used, in which surface coil resonator and Lithium phthalocyanine (LiPc) as oxygen sensor were crucial. Once LiPc particles are embedded in a desired location of organ/tissue, the pO(2) level can be monitored repeatedly and non-invasively. This method is based on the effect of oxygen concentration on the EPR spectra of LiPc which offers several advantages as follows: (1) high sensitivity, (2) minimum invasiveness, (3) repeated measurements, (4) absence of toxicity (non-toxic), and (5) measurement in a local region of the tissue with embedded LiPc. Therefore, in this chapter, we describe the method using CW and TD EPR spectroscopy with oxygen-sensitive particle, LiPc, for in vivo monitoring of oxygen. PMID:20013170

Hyodo, F; Matsumoto, S; Hyodo, E; Matsumoto, A; Matsumoto, K; Krishna, M C

2010-01-01

53

Web Spectra: Problems in NMR and IR spectroscopy  

NSDL National Science Digital Library

This site was established to provide chemistry students with a library of spectroscopy problems. Interpretation of spectra is a technique that requires practice - this site provides 1H NMR and 13 C NMR, DEPT, COSY and IR spectra of various compounds for students to interpret. Hopefully, these problems will provide a useful resource to better understand spectroscopy.

Merlic, Craig A.

2008-02-29

54

Access to NMR Spectroscopy for Two-Year College Students: The NMR Site at Trinity University  

ERIC Educational Resources Information Center

|Students at two-year colleges and small four-year colleges have often obtained their exposure to NMR spectroscopy through "canned" spectra because the cost of an NMR spectrometer, particularly a high-field spectrometer, is prohibitive in these environments. This article describes the design of a NMR site at Trinity University in which spectral…

Mills, Nancy S.; Shanklin, Michael

2011-01-01

55

Single Molecule Electron Paramagnetic Resonance Spectroscopy: Hyperfine Splitting Owing to a Single Nucleus  

Microsoft Academic Search

Individual pentacene-d14 molecules doped into a p-terphenyl-d14 host crystal have been studied by optically detected electron paramagnetic resonance spectroscopy. The magnetic resonance transitions between the triplet sublevels of the pentacene molecule and the splitting of the resonance lines for a molecule that contains a carbon-13 nucleus have been observed in an external magnetic field. This splitting is caused by the

J. Kohler; A. C. J. Brouwer; E. J. J. Groenen; J. Schmidt

1995-01-01

56

One and two-dimensional pulse electron paramagnetic resonance spectroscopy: concepts and applications  

Microsoft Academic Search

During the last two decades, the possibilities of pulse electron paramagnetic resonance (EPR) and pulse electron nuclear\\u000a double resonance (ENDOR) spectroscopy have increased tremendously. While at the beginning of the 1980s pulse-EPR and ENDOR\\u000a applications were still a rarity, the techniques are now very frequently applied in chemistry, physics, materials science,\\u000a biology and mineralogy. This is mainly due to the

S. Van Doorslaer; A. Schweiger

2000-01-01

57

sup 89 Y MAS NMR study of rare-earth pyrochlores: Paramagnetic shifts in the solid state  

SciTech Connect

{sup 89}Y MAS NMR spectra have been obtained from yttrium pyrochlores Y{sub 2-y}Ln{sub y}M{sub 2}O{sub 7} (Ln = Ce, Pr, Nd, Sm, Eu, Yb; M = Sn, Ti). Incorporation of the paramagnetic ions into the diamagnetic compounds was found to cause large reductions in the {sup 89}Y nuclear relaxation times enabling spectra to be accumulated in relatively short times in comparison to similar diamagnetic systems. In addition to the resonances of the diamagnetic end-member compounds, Y{sub 2}Sn{sub 2}O{sub 7} and Y{sub 2}Ti{sub 2}O{sub 7}, extra {sup 89}Y resonances were observed, due to the substitution of paramagnetic ions into the local coordination sphere surrounding an {sup 89}Y nucleus. The paramagnetic shifts were found to be proportional to the number of lanthanide ions substituted for yttrium in the first coordination sphere; the intensities of the resonances could be used to determine the concentration of paramagnetic rare-earth ions in the diamagnetic phase.

Grey, C.P.; Cheetham, A.K.; Dobson, C.M. (Univ. of Oxford (England)); Smith, M.; Dupree, R. (Univ. of Warwick, Coventry (England))

1990-06-06

58

WebSpectra: Problems in NMR and IR Spectroscopy  

NSDL National Science Digital Library

From the University of California at Los Angeles's Chemistry Department, WebSpectra provides chemistry students with a searchable library of Nuclear Magnetic Resonance (NMR) and Infrared (IR) spectroscopy problems. According to the makers of this innovative site, "Interpretation of spectra is a technique that requires practice - this site provides 1H NMR and 13C NMR, DEPT, COSY and IR spectra of various compounds for students to interpret." A set of instructional documents are entitled Solving Spectral Problems, Overview of NMR Spectroscopy, Notes on NMR Solvents, Types of NMR Spectra, Introduction to IR Spectra, and a Table of IR Absorptions. A wide variety of compounds and their spectra are available for interpretation and have been organized in categories from Beginning to Advanced. Spectrum for each compound may be magnified 16X by clicking on peaks. This is an outstanding learning tool for students coming to grips with interpreting NMR and IR spectra.

59

6Li MAS NMR spectroscopy and first-principles calculations as a combined tool for the investigation of Li2MnSiO4 polymorphs.  

PubMed

Polymorphism of Li(2)MnSiO(4) was inspected by (6)Li MAS NMR spectroscopy. The detected isotropic shifts and spinning-sideband patterns were successfully reproduced by first-principles calculations and offered an insight into structural differences among the polymorphs. The approach for predicting isotropic shifts was also tested on several other Li-containing paramagnetic structures. PMID:20372695

Mali, Gregor; Meden, Anton; Dominko, Robert

2010-04-06

60

Approaches to localized NMR spectroscopy in vivo  

SciTech Connect

Nuclear magnetic resonance (NMR) techniques are developed which allow spatially localized spectra to be obtained from living tissue. The localization methods are noninvasive and exploit the enhanced sensitivity afforded by surface coil probes. Techniques are investigated by computer simulation and experimentally verified by the use of phantom samples. The feasibility and utility of the techniques developed in this research are demonstrated by /sup 31/P spatial localization experiments involving various in vivo organs. In the first part of the thesis, two feasible approaches to localized spectroscopy, which were developed by other laboratories are theoretically analyzed by computer simulation. An alternative approach is provided by the rotating frame zeugmatography experiment which affords chemical-shift spectra displayed as a function of penetration distance into the sample. The further modification of the rotating frame experiment is developed, the Fourier series window (FSW) approach, which utilizes various types of window functions to afford localization in one or a few tissue regions of interest with high sensitivity. Theoretical comparisons with depth pulse methods are also included, along with methods to refine adverse off-resonance behavior.

Garwood, M.G.

1985-01-01

61

Applications of NMR spectroscopy to the Study of Zeolite Synthesis.  

National Technical Information Service (NTIS)

NMR spectroscopy is a powerful technique for identifying the structure and concentration of silicate and aluminosilicate anions in gels and solution used for zeolite synthesis. A review is presented of the types of species that have been observed and the ...

A. T. Bell

1989-01-01

62

Characterisation of ?-tricalcium phosphate-based bone substitute materials by electron paramagnetic resonance spectroscopy  

NASA Astrophysics Data System (ADS)

?-TCP based materials are frequently used as dental implants. Due to their resorption in the body and direct contact with tissues, in order to inactivate bacteria, fungal spores and viruses, they are usually sterilized by ?-irradiation. However, the current literature provides little information about effects of the ?-irradiation on the formation and stability of the free radicals in the bone graft materials during and after sterilization procedure. In this work five different bone graft substitution materials, composed of synthetic beta tricalcium phosphate (?-TCP) and hydroxyapatite (HAP) present in the market were characterized by electron paramagnetic resonance (EPR) spectroscopy, X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Paramagnetic species Mn2+, Fe3+, trapped H-atoms and CO2- radicals were detected in the biphasic material (60% HAP, 40% ?-TCP), while in ?-TCP materials only Mn2+ and\\or trapped hydrogen atoms were detected. EPR analysis revealed the details of the structure of these materials at the atomic level. The results have shown that EPR spectroscopy is a method which can be used to improve the quality control of bone graft materials after syntering, processing and sterilization procedure.

Matkovi?, Ivo; Maltar-Strme?ki, Nadica; Babi?-Ivan?i?, Vesna; Dutour Sikiri?, Maja; Noethig-Laslo, Vesna

2012-10-01

63

Detection of nitric oxide production in mice by spin-trapping electron paramagnetic resonance spectroscopy  

Microsoft Academic Search

We describe here a spin-trapping method combined with X-band electron paramagnetic resonance (EPR) spectroscopy for ex vivo measurement of nitric oxide (·NO) levels in the urine of both normal and lipopolysaccharide (LPS)-induced shock mice. Normal or LPS-treated mice were injected subcutaneously with a metal-chelator complex, N-methyl-d-glucamine dithiocarbamate-ferrous iron, [(MGD)2\\/Fe], which binds to ·NO and forms a water-soluble [(MGD)2\\/Fe-NO] complex. At

Andrei M. Komarov; Ching-San Lai

1995-01-01

64

Single molecule electron paramagnetic resonance spectroscopy: hyperfine splitting owing to a single nucleus.  

PubMed

Individual pentacene-d(14) molecules doped into a p-terphenyl-d(14) host crystal have been studied by optically detected electron paramagnetic resonance spectroscopy. The magnetic resonance transitions between the triplet sublevels of the pentacene molecule and the splitting of the resonance lines for a molecule that contains a carbon-13 nucleus have been observed in an external magnetic field. This splitting is caused by the hyperfine interaction of the triplet electron spin with the single carbon-13 nuclear spin. PMID:17843664

Köhler, J; Brouwer, A C; Groenen, E J; Schmidt, J

1995-06-01

65

Studies of organic paint binders by NMR spectroscopy  

NASA Astrophysics Data System (ADS)

Nuclear magnetic resonance spectroscopy is applied to the study of aged binding media used in paintings, namely linseed oil, egg tempera and an acrylic medium. High resolution 1D and 2D NMR experiments establish the state of hydrolysis and oxidation of the linseed and egg tempera binders after five years of aging, by determining several markers sensitive to the hydrolytic and oxidative processes of the binder lipid fraction. The composition of the acrylic binder co-polymer is determined by 2D NMR spectroscopy, while the identification of a surfactant, poly(ethylene glycol), found in greater amounts in aged acrylic medium, is reported. The non-destructive nature of the proposed analytical NMR methodology, and minimization of the amount of binder material needed through the use of sophisticated cryoprobes and hyphenated LC-NMR techniques, make NMR attractive for the arts analyst, in view of its rapid nature and experimental simplicity.

Spyros, A.; Anglos, D.

2006-06-01

66

An Integrated Laboratory Project in NMR Spectroscopy.  

ERIC Educational Resources Information Center

|Describes an advanced NMR project that can be done with a 60-MHz continuous-wave proton spectrometer. Points out the main purposes are to give students experience in second-order NMR analysis, the simplification of spectra by raising the frequency, and the effect of non-hydrogen nuclei on proton resonances. (MVL)|

Hudson, Reggie L.; Pendley, Bradford D.

1988-01-01

67

Localized in vivo13C NMR spectroscopy of the brain  

PubMed Central

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

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

2006-01-01

68

Proton Spin—Spin Coupling Constants from the NMR Spectra of Paramagnetic Molecules  

Microsoft Academic Search

``Chemical shifts'' for protons in the paramagnetic Ni II aminotroponeimineates are up to 250 times greater than for shifts of analogous protons in the diamagnetic chelates or ligands. These increased shifts are attributed to isotropic hyperfine contact interactions between protons and p? spin densities transferred from Ni II to aminotroponeimine ligand as the result of p?—d? bonding. Widths of the

D. R. Eaton; A. D. Josey; W. D. Phillips; R. E. Benson

1963-01-01

69

Cell signaling, post-translational protein modifications and NMR spectroscopy.  

PubMed

Post-translationally modified proteins make up the majority of the proteome and establish, to a large part, the impressive level of functional diversity in higher, multi-cellular organisms. Most eukaryotic post-translational protein modifications (PTMs) denote reversible, covalent additions of small chemical entities such as phosphate-, acyl-, alkyl- and glycosyl-groups onto selected subsets of modifiable amino acids. In turn, these modifications induce highly specific changes in the chemical environments of individual protein residues, which are readily detected by high-resolution NMR spectroscopy. In the following, we provide a concise compendium of NMR characteristics of the main types of eukaryotic PTMs: serine, threonine, tyrosine and histidine phosphorylation, lysine acetylation, lysine and arginine methylation, and serine, threonine O-glycosylation. We further delineate the previously uncharacterized NMR properties of lysine propionylation, butyrylation, succinylation, malonylation and crotonylation, which, altogether, define an initial reference frame for comprehensive PTM studies by high-resolution NMR spectroscopy. PMID:23011410

Theillet, Francois-Xavier; Smet-Nocca, Caroline; Liokatis, Stamatios; Thongwichian, Rossukon; Kosten, Jonas; Yoon, Mi-Kyung; Kriwacki, Richard W; Landrieu, Isabelle; Lippens, Guy; Selenko, Philipp

2012-09-26

70

Protein NMR spectroscopy: Hydrogen bonds under pressure  

NASA Astrophysics Data System (ADS)

Hydrogen bonds play a key role in defining the folding of proteins and the maintenance of their structure. A high-pressure NMR study of ubiquitin now provides unprecedented detail on the temperature and pressure dependence of its hydrogen-bond network.

Nielsen, Gerd; Schwalbe, Harald

2012-09-01

71

Observation of two N2-isobutyrylguanine tautomers by NMR spectroscopy.  

PubMed

N(2)-isobutyrylguanine was prepared by treatment of guanine with isobutyryl chloride. Two tautomers, 1,7-dihydro-2-(isobutyroyl)amino-6H-purin-6-one and 1,9-dihydro-2-(isobutyroyl)amino-6H-purin-6-one, were identified in almost 1:1 ratio in dichloromethane-dimethyl sulfoxide (1:1?v/v) by NMR spectroscopy. By using the selective-inversion experiments, enthalpy, entropy, and free energy for activation were determined. This work represents the first report of guanine tautomers observed directly by NMR spectroscopy. PMID:23166038

Yang, Lijing; Li, Jia; Simionescu, Razvan; Yan, Hongbin

2012-11-20

72

NMR Spectroscopy and Pediatric Brain Tumors  

Microsoft Academic Search

Proton nuclear magnetic resonance spectroscopy ( 1 H-NMRS) is a noninvasive in vivo technique that utilizes conventional MR imaging hardware to obtain biochemical information from a discrete volume of tissue after suppres- sion of the water signal. MR spectroscopy coupled with conventional MR imaging allows correlation of structural changes with biochemical processes in tissues by measur- ing specific metabolites present

KATHERINE E. WARREN

2004-01-01

73

Quantitative detection of plasma-generated radicals in liquids by electron paramagnetic resonance spectroscopy  

NASA Astrophysics Data System (ADS)

In this paper the qualitative and quantitative detection of oxygen radicals in liquids after plasma treatment with an atmospheric pressure argon plasma jet by electron paramagnetic resonance spectroscopy is investigated. Absolute values for ·OH and O_{2}^{\\cdot -} radical concentration and their net production rate in plasma-treated liquids are determined without the use of additional scavenging chemicals such as superoxide dismutase (SOD) or mannitol (D-MAN). The main oxygen-centred radical generation in PBS was found to originate from the superoxide radical. It is shown that hidden parameters such as the manufacturer of chemical components could have a big influence on the comparability and reproducibility of the results. Finally, the effect of a shielding gas device for the investigated plasma jet with a shielding gas composition of varying oxygen-to-nitrogen ratio on radical generation after plasma treatment of phosphate-buffered saline solution was investigated.

Tresp, H.; Hammer, M. U.; Winter, J.; Weltmann, K.-D.; Reuter, S.

2013-10-01

74

CHARACTERIZATION OF METABOLITES IN SMALL FISH BIOFLUIDS AND TISSUES BY NMR SPECTROSCOPY  

EPA Science Inventory

Nuclear magnetic resonance (NMR) spectroscopy has been utilized for assessing ecotoxicity in small fish models by means of metabolomics. Two fundamental challenges of NMR-based metabolomics are the detection limit and characterization of metabolites (or NMR resonance assignments...

75

Protein complexes studied by NMR spectroscopy  

Microsoft Academic Search

Recent advances in NMR methods now allow protein complexes to be studied in great detail in a wide range of solution conditions. Isotope-enrichment strategies, resonance-assignment approaches and structural-determination methods have evolved to the point where almost any type of complex involving proteins of reasonable size may be studied in a straigthforward way. A variety of isotope editing and filtering strategies

A Joshua Wand; S Walter Englander

1996-01-01

76

Binding of Iron to Neuromelanin of Human Substantia Nigra and Synthetic Melanin: An Electron Paramagnetic Resonance Spectroscopy Study  

Microsoft Academic Search

The binding of iron by melanin is a potentially important phenomenon as detailed knowledge of this binding is essential for understanding the role of melanin and iron in the pathogenesis of oxidative damage in the substantia nigra. Electron paramagnetic resonance spectroscopy is one of the most useful approaches in the investigation of melanins and their interaction with iron. This study

Toshihide Shima; Tadeusz Sarna; Harold M. Swartz; Antonella Stroppolo; Rosalba Gerbasi; Luigi Zecca

1997-01-01

77

Investigation of the generation of singlet oxygen in ensembles of photoexcited silicon nanocrystals by electron paramagnetic resonance spectroscopy  

Microsoft Academic Search

The generation of singlet oxygen is investigated and its concentration upon photoexcitation of silicon nanocrystals in porous silicon layers is determined using electron paramagnetic resonance spectroscopy. The relaxation times of spin centers, i.e., silicon dangling bonds, in vacuum and in an oxygen atmosphere in the dark and under illumination of the samples are measured for the first time. It is

E. A. Konstantinova; V. A. Demin; V. Yu. Timoshenko

2008-01-01

78

Protein folding on the ribosome studied using NMR spectroscopy.  

PubMed

NMR spectroscopy is a powerful tool for the investigation of protein folding and misfolding, providing a characterization of molecular structure, dynamics and exchange processes, across a very wide range of timescales and with near atomic resolution. In recent years NMR methods have also been developed to study protein folding as it might occur within the cell, in a de novo manner, by observing the folding of nascent polypeptides in the process of emerging from the ribosome during synthesis. Despite the 2.3MDa molecular weight of the bacterial 70S ribosome, many nascent polypeptides, and some ribosomal proteins, have sufficient local flexibility that sharp resonances may be observed in solution-state NMR spectra. In providing information on dynamic regions of the structure, NMR spectroscopy is therefore highly complementary to alternative methods such as X-ray crystallography and cryo-electron microscopy, which have successfully characterized the rigid core of the ribosome particle. However, the low working concentrations and limited sample stability associated with ribosome-nascent chain complexes means that such studies still present significant technical challenges to the NMR spectroscopist. This review will discuss the progress that has been made in this area, surveying all NMR studies that have been published to date, and with a particular focus on strategies for improving experimental sensitivity. PMID:24083462

Waudby, Christopher A; Launay, Hélène; Cabrita, Lisa D; Christodoulou, John

2013-07-27

79

Laser-enhanced NMR spectroscopy: Theoretical considerations  

SciTech Connect

W. S. Warren et al. report that the proton magnetic resonance spectra of chiral molecules are modified slightly by circularly polarized laser light. While it is not unexpected that circularly polarized radiation can influence chiral molecules, the large magnitude of the reported results is surprising. From conservation of parity, and under the conditions of the experiment, the relevant energy shifts per randomly oriented molecule show several simple relations. The chemical shielding of a chiral molecule in right circularly polarized light must be the same as its enantiomer in left circularly polarized light. However, the splitting of nuclear magnetic resonance (NMR) lines in left circular polarization will not necessarily equal that for right circular polarization because of the zero magnetic field term, b[sup 0]I[sub 0]. Direct calculation using the standard Hamiltonian descriptive of the interaction between radiation and matter in a magnetic field shows that for light intensities of 10 W cm[sup [minus]2] the nonchiral chemical shift in the NMR spectrum should yield a value of aI[sub 0] on the order of 10[sup [minus]15] [sigma][sub 0]. The chiral chemical shift, bI[sub 0], is on the order of 10[sup [minus]18] [sigma][sub 0]; for a magnetic field of 10[sup 4] gauss, this intensity-dependent shift corresponds to about 10[sup [minus]15] Hz. The zero magnetic field shift (b[sup 0]I[sub 0]) is about 10[sup [minus]10]Hz. In conclusion, the ordinary manifestation of chirality on light-perturbed chemical shifts is too small to be observed. Shining laser light on a racemic mixture and seeing a single NMR line split into two lines would provide a convincing experimental result. The authors' calculations predict that it will not occur. 3 refs., 1 tab.

Harris, R.A.; Tinoco, I. Jr. (Univ. of California, Berkeley (United States))

1993-02-05

80

First-principles calculation of parameters of electron paramagnetic resonance spectroscopy in solids.  

PubMed

The hyperfine A-tensor and Zeeman g-tensor parameterize the interaction of an 'effective' electron spin with the magnetic field due to the nuclear spin and the homogeneous external magnetic field, respectively. The A- and g-tensors are the quantities of primary interest in electron paramagnetic resonance (EPR) spectroscopy. In this paper, we review our work [E.S. Kadantsev, T. Ziegler, J. Phys. Chem. A 2008, 112, 4521; E. S. Kadantsev, T. Ziegler, J. Phys. Chem. A 2009, 113, 1327] on the calculation of these EPR parameters under periodic boundary conditions (PBC) from first-principles. Our methodology is based on the Kohn-Sham DFT (KS DFT), explicit usage of Bloch basis set made up of numerical and Slater-type atomic orbitals (NAOs/STOs), and is implemented in the 'full potential' program BAND. Our implementation does not rely on the frozen core approximation. The NAOs/STOs basis is well suited for the accurate representation of the electron density near the nuclei, a prerequisite for the calculation of highly accurate hyperfine parameters. In the case of g-tensor, our implementation is based on the method of Van Lenthe et al. [E. van Lenthe, P. E. S. Wormer, A. van der Avoird, J. Chem. Phys. 1997, 107, 2488] in which the spin-orbital coupling is taken into account variationally. We demonstrate the viability of our scheme by calculating EPR parameters of paramagnetic defects in solids. We consider the A-tensor of 'normal' and 'anomalous' muonium defect in IIIA-VA semiconductors as well as the S2 anion radical in KCl host crystal lattice. PMID:20821407

Kadantsev, Eugene S; Ziegler, Tom

2010-09-05

81

Measurement of a Pauli and Orbital Paramagnetic State in Bulk Gold Using X-Ray Magnetic Circular Dichroism Spectroscopy  

NASA Astrophysics Data System (ADS)

We show that bulk gold (Au) exhibits temperature-independent paramagnetism in an external magnetic field by x-ray magnetic circular dichroism spectroscopy at the Au L2 and L3 edges. Using the sum-rule analysis, we obtained a magnetic moment of 1.3×10-4?B/atom in an external magnetic field of 10 T and a paramagnetic susceptibility of 8.9×10-6 for the 5d orbit. The induced paramagnetism in bulk Au is characterized by a large (?30%) orbital contribution. This orbital component was retained even when Au atoms formed nanoparticles, playing an important role in stabilizing the spontaneous spin polarization in the Au nanoparticles.

Suzuki, Motohiro; Kawamura, Naomi; Miyagawa, Hayato; Garitaonandia, Jose S.; Yamamoto, Yoshiyuki; Hori, Hidenobu

2012-01-01

82

Silver-109 NMR spectroscopy of inorganic solids.  

PubMed

In this study the (109)Ag NMR spectra of the following solid inorganic silver-containing compounds were investigated: AgNO(3), AgNO(2), Ag(2)SO(4), Ag(2)SO(3), AgCO(3), Ag(3)PO(4), AgCl, AgBr, AgI, AgSO(3)CH(3), silver p-toluenesulfonate, NaAg(CN)(2), KAg(CN)(2), K(3)Ag(CN)(4), Me(4)NAgCl(2), silver diethylthiocarbamate, silver lactate, silver acetate, silver citrate, and bis[(N,N(1)-di-tert-butylformamidinato)silver(I)]. The magic angle spinning (MAS) spectra of all compounds were obtained. In some cases, when protons were available, the (1)H to (109)Ag cross-polarization (CP) technique was used to enhance the signal and shorten the experimental relaxation delay. It was possible to obtain slow MAS (or CP/MAS) or nonspinning spectra for 10 samples, allowing the determination of the principal components of the (109)Ag chemical shift (CS) tensors. The isotropic chemical shifts and the CS tensors are discussed in light of the available crystal structures. The need for an accepted standard for referencing (109)Ag chemical shifts and the use of AgSO(3)CH(3) as a CP setup sample are also discussed. PMID:15332810

Penner, Glenn H; Li, Wenli

2004-09-01

83

High-resolution characterization of organic phosphorus in soil extracts using 2D 1H-31P NMR correlation spectroscopy.  

PubMed

Organic phosphorus (P) compounds represent a major component of soil P in many soils and are key sources of P for microbes and plants. Solution NMR (nuclear magnetic resonance spectroscopy) is a powerful technique for characterizing organic P species. However, (31)P NMR spectra are often complicated by overlapping peaks, which hampers identification and quantification of the numerous P species present in soils. Overlap is often exacerbated by the presence of paramagnetic metal ions, even if they are in complexes with EDTA following NaOH/EDTA extraction. By removing paramagnetic impurities using a new precipitation protocol, we achieved a dramatic improvement in spectral resolution. Furthermore, the obtained reduction in line widths enabled the use of multidimensional NMR methods to resolve overlapping (31)P signals. Using the new protocol on samples from two boreal humus soils with different Fe contents, 2D (1)H-(31)P correlation spectra allowed unambiguous identification of a large number of P species based on their (31)P and (1)H chemical shifts and their characteristic coupling patterns, which would not have been possible using previous protocols. This approach can be used to identify organic P species in samples from both terrestrial and aquatic environments increasing our understanding of organic P biogeochemistry. PMID:22394413

Vestergren, Johan; Vincent, Andrea G; Jansson, Mats; Persson, Per; Ilstedt, Ulrik; Gröbner, Gerhard; Giesler, Reiner; Schleucher, Jürgen

2012-03-19

84

13 C NMR spectroscopy of amino acid mixtures  

Microsoft Academic Search

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

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

1982-01-01

85

Characterization of amorphous material in shocked quartz by NMR spectroscopy  

SciTech Connect

Nuclear magnetic resonance (NMR) analysis of the recovered products from a series of controlled explosive shock-loading experiments on quartz powders was performed to investigate shock-induced amorphization processes. Silicon-29 NMR spectroscopy is an excellent probe of the local bonding environment of silicon in minerals and is capable of detecting and characterizing amorphous and disordered components. NMR spectra obtained for the recovered material exhibit a narrow resonance associated with the shocked crystalline material, and a broad component consistent with an amorphous phase despite the absence of evidence for glass from optical microscopy. The NMR measurements were performed over a range of recycle times from 1 to 3 {times} 10{sup 5} S. Results demonstrate that the magnetization in both the crystalline and amorphous material following power-law behavior as a function of recycle time. The amorphous component dominates the spectra for short NMR recycle times due to its shorter relaxation time relative to the crystalline material. Fractal analysis of the power-law relations suggests a fractal dimension of 2 for the amorphous phase and 3 for the crystalline phase.

Assink, R.A.; Boslough, M.B.; Cygan, R.T.

1993-08-01

86

Introducing Hyperpolarized Xenon-131 Directly Detected by NMR Spectroscopy  

NASA Astrophysics Data System (ADS)

Previously, high-field NMR and MRI applications of hyperpolarized (hp) noble gasses focused on the isotopes helium-3 (spin I = 1/2), xenon-129 (spin I = 1/2) [1], and more recently krypton-83 (spin I = 9/2) [2]. In this contribution, hp xenon-131 (spin I = 3/2) was generated by spin-exchange optical pumping and separated from the rubidium vapor for high field NMR detection at 14.1 T field strength. Xenon-131 is of particular interest because of its quadrupolar nature that can be utilized for the study of surfaces [3] and for the investigation of high magnetic field effects on the electronic structure of the noble gas atom [4]. In addition, this isotope is a useful probe for quadrupolar processes during gas transfer and during NMR/MRI detection. Experiments with xenon-131, including multiple quantum filtered NMR spectroscopy [3], provides insights into similar processes present in krypton-83 and its more complicated spin system [5]. [1] D. Raftery Ann. Rep. NMR Spec., 57, 208 (2006). [2] G. Pavlovskaya, et al., Pro. Natl. Acad. Sci. U.S.A. 102, 18275 (2005). [3] T. Meersmann et al., Phys. Rev. Lett. 80, 1398 (1998). [4] T. Meersmann and M. Haake, Phys. Rev. Lett. 81, 1211 (1998). [5] Z. Cleveland, et al., J. Chem. Phys.124, 044312 (2006).

Stupic, Karl; Cleveland, Zackary; Pavlovskaya, Galina; Meersmann, Thomas

2007-03-01

87

NMR spectroscopy around filling factor three  

NASA Astrophysics Data System (ADS)

We probe the spin signatures of a two-dimensional electron system, confined to a GaAs quantum well, around filling factor three (?˜3) using resistively detected nuclear magnetic resonance (RDNMR) spectroscopy at milliKelvin temperatures. Whereas the existence of spin textures, known as skyrmions, around filling factor one is well established, an understanding of the spin degrees of freedom for odd-integer states in higher Landau levels remains elusive. It is believed that for skyrmions to exist at ?˜3, the Zeeman energy needs to be smaller than in the case of ?˜1 [1]. We measured the spin-lattice relaxation time, T1, which is sensitive to these spin textures as they trigger a rapid nuclear spin relaxation. Our T1 measurements around ?= 3 at 5 T find a small spin-lattice relaxation rate, suggesting the absence of skyrmions. In addition, our Knight shift measurements corroborate this interpretation. Furthermore, we report striking anomalies in the RDNMR spectral line shape and discuss their origin in conjunction with our findings. * [1]N. R. Cooper, Phys. Rev. B 55, R1934 (1997).

Rhone, Trevor David; Tiemann, Lars; Muraki, Koji

2013-03-01

88

Biophysical Characterisation of Globins and Multi-Heme Cytochromes Using Electron Paramagnetic Resonance and Optical Spectroscopy  

NASA Astrophysics Data System (ADS)

Heme proteins of different families were investigated in this work, using a combination of pulsed and continuous-wave electron paramagnetic resonance (EPR) spectroscopy, optical absorption spectroscopy, resonance Raman spectroscopy and laser flash photolysis. The first class of proteins that were investigated, were the globins. The globin-domain of the globin-coupled sensor of the bacterium Geobacter sulfurreducens was studied in detail using different pulsed EPR techniques (HYSCORE and Mims ENDOR). The results of this pulsed EPR study are compared with the results of the optical investigation and the crystal structure of the protein. The second globin, which was studied, is the Protoglobin of Methanosarcina acetivorans, various mutants of this protein were studied using laser flash photolysis and Raman spectroscopy to unravel the link between this protein's unusual structure and its ligand-binding kinetics. In addition to this, the CN -bound form of this protein was investigated using EPR and the influence of the strong deformation of the heme on the unusual low gz values is discussed. Finally, the neuroglobins of three species of fishes, Danio rerio, Dissostichus mawsoni and Chaenocephalus aceratus are studied. The influence of the presence or absence of two cysteine residues in the C-D and D-region of the protein on the EPR spectrum, and the possible formation of a disulfide bond is studied. The second group of proteins that were studied in this thesis belong to the family of the cytochromes. First the Mouse tumor suppressor cytochrome b561 was studied, the results of a Raman and EPR investigation are compared to the Human orthologue of the protein. Secondly, the tonoplast cytochrome b561 of Arabidopsis was investigated in its natural form and in two double-mutant forms, in which the heme at the extravesicular side was removed. The results of this investigation are then compared with two models in literature that predict the localisation of the hemes in this family of cytochromes. Finally the preliminary results of a detailed HYSCORE study of the four hemes in the cytochrome c3 of Desulfovibrio desulfuricans ATCC 27774 are presented.

Desmet, Filip

89

Non-invasive in vivo characterization of release processes in biodegradable polymers by low-frequency electron paramagnetic resonance spectroscopy  

Microsoft Academic Search

Using stable free radicals (nitroxides) whose spectra reflect microviscosity and pH, low-frequency electron paramagnetic resonance (EPR) spectroscopy was used to characterize the release pattern of subcutaneous implants of poly(d,l-lactide-co-glycolide) (PLGA) continuously and non-invasively in living mice. No significant changes occurred during the first days after implantation. After about 1 week, the recorded EPR spectra gave direct evidence for the formation

K. Mäder; B. Gallez; K. J. Liu; H. M. Swartz

1996-01-01

90

Investigation of the generation of singlet oxygen in ensembles of photoexcited silicon nanocrystals by electron paramagnetic resonance spectroscopy  

Microsoft Academic Search

The generation of singlet oxygen is investigated and its concentration upon photoexcitation of silicon nanocrystals in porous\\u000a silicon layers is determined using electron paramagnetic resonance spectroscopy. The relaxation times of spin centers, i.e.,\\u000a silicon dangling bonds, in vacuum and in an oxygen atmosphere in the dark and under illumination of the samples are measured\\u000a for the first time. It is

E. A. Konstantinova; V. A. Demin; V. Yu. Timoshenko

2008-01-01

91

Study of the Radiolysis of Tetracycline Hydrochloride in Powder Form, in Aqueous Solutions and in Benzyl Alcohol, at 77K, by Electron Paramagnetic Resonance Spectroscopy.  

National Technical Information Service (NTIS)

The radiolysis of tetracycline hydrochloride in powder form, dissolved in benzyl alcohol and in acid, neutral and alkaline aerated aqueous solutions at 77K is studied by electron paramagnetic resonance spectroscopy. Mechanisms of reactions that occur in t...

S. M. L. Guedes

1984-01-01

92

Proton NMR spectroscopy of human blood plasma and red blood cells  

SciTech Connect

The purpose of this article is to review some of the NMR techniques used to measure /sup 1/H NMR spectra of human plasma and red blood cells. The /sup 1/H NMR spectroscopy of plasma and red blood cells of interest because reported studies indicate that information relevant to biochemical and clinical applications can be obtained by /sup 1/H NMR.

Rabenstein, D.L.; Millis, K.K.; Strauss, E.J.

1988-12-15

93

Mitochondria-targeted antioxidant promotes recovery of skeletal muscle mitochondrial function after burn trauma assessed by in vivo 31P nuclear magnetic resonance and electron paramagnetic resonance spectroscopy.  

PubMed

Burn injury causes a major systemic catabolic response that is associated with mitochondrial dysfunction in skeletal muscle. We investigated the effects of the mitochondria-targeted peptide antioxidant Szeto-Schiller 31 (SS-31) on skeletal muscle in a mouse burn model using in vivo phosphorus-31 nuclear magnetic resonance ((31)P NMR) spectroscopy to noninvasively measure high-energy phosphate levels; mitochondrial aconitase activity measurements that directly correlate with TCA cycle flux, as measured by gas chromatography mass spectrometry (GC-MS); and electron paramagnetic resonance (EPR) to assess oxidative stress. At 6 h postburn, the oxidative ATP synthesis rate was increased 5-fold in burned mice given a single dose of SS-31 relative to untreated burned mice (P=0.002). Furthermore, SS-31 administration in burned animals decreased mitochondrial aconitase activity back to control levels. EPR revealed a recovery in redox status of the SS-31-treated burn group compared to the untreated burn group (P<0.05). Our multidisciplinary convergent results suggest that SS-31 promotes recovery of mitochondrial function after burn injury by increasing ATP synthesis rate, improving mitochondrial redox status, and restoring mitochondrial coupling. These findings suggest use of noninvasive in vivo NMR and complementary EPR offers an approach to monitor the effectiveness of mitochondrial protective agents in alleviating burn injury symptoms. PMID:23482635

Righi, Valeria; Constantinou, Caterina; Mintzopoulos, Dionyssios; Khan, Nadeem; Mupparaju, S P; Rahme, Laurence G; Swartz, Harold M; Szeto, Hazel H; Tompkins, Ronald G; Tzika, A Aria

2013-03-12

94

Structure and dynamics in B12 enzyme catalysis revealed by electron paramagnetic resonance spectroscopy  

NASA Astrophysics Data System (ADS)

Challenges to the understanding of how protein structure and dynamics contribute to catalysis in enzymes, and the use of time-resolved electron paramagnetic resonance (EPR) spectroscopic techniques to address the challenges, are examined in the context of the coenzyme B12-dependent enzyme, ethanolamine ammonia-lyase (EAL), from Salmonella typhimurium. EAL conducts the homolytic cleavage of the coenzyme cobalt-carbon bond, intraprotein radical migration (5-6 å), and hydrogen atom transfers, which enable the core radical-mediated rearrangement reaction. Thermodynamic and activation parameters are measured in two experimental systems, which were developed to isolate sub-sequences from the multi-step catalytic cycle, as follows: (1) A dimethylsulfoxide (DMSO)/water cryosolvent system is used to prepare the kinetically-arrested enzyme/coenzyme/substrate ternary complex in fluid solution at 230 K.[1] Temperature-step initiated cobalt-carbon bond cleavage and radical pair separation to form the Co(II)-substrate radical pair are monitored by using time-resolved, full-spectrum EPR spectroscopy (234<=T<=250 K).[1] (2) The Co(II)-substrate radical pair is cryotrapped in frozen aqueous solution at T<150 K, and then promoted to react by a temperature step. The reaction of the substrate radical along the native pathway to form the diamagnetic bound products is monitored by using time-resolved, full-spectrum EPR spectroscopy (187<=T<=217 K).[2] High temporal resolution is achieved, because the reactions are dramatically slowed at the low temperatures, relative to the initiation and spectrum acquistion times. The results are combined with high resolution structures of the reactant centers, obtained by pulsed-EPR spectroscopies,[3] and the protein, obtained by structural proteomics[4] and EPR and electron spin echo envelope modulation (ESEEM) in combination with site directed mutagenesis,[5] to approach a molecular level description of protein contributions to catalysis in EAL. [4pt] [1] Wang, M. & Warncke, K. J. Am. Chem. Soc. 2008, 130, 4846. [0pt] [2] Chen, Z. and Warncke, K. Biophys. J. 2008, 95 (December) [0pt] [3] Canfield, J. M. and Warncke, K. J. Phys. Chem. B 2002, 106, 8831. [0pt] [4] Sun, L. and Warncke, K. Proteins 2006, 64, 308. [0pt] [5] Sun, L., Groover, O., Canfield, J. M., and Warncke, K. Biochemistry 2008, 47, 5523.

Warncke, Kurt

2009-03-01

95

Maximum Entropy Reconstruction Methods in Electron Paramagnetic Resonance Imaging  

Microsoft Academic Search

Electron Paramagnetic Resonance (EPR) is a spectroscopic technique that detects and characterizes molecules with unpaired electrons (i.e., free radicals). Unlike the closely related nuclear magnetic resonance (NMR) spectroscopy, EPR is still under development as an imaging modality. Athough a number of physical factors have hindered its development, EPR's potential is quite promising in a number of important application areas, including

Calvin A. Johnson; Delia Mcgarry; John A. Cook; Nallathamby Devasahayam; James B. Mitchell; Sankaran Subramanian; Murali C. Krishna

2003-01-01

96

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

NASA Astrophysics Data System (ADS)

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

Yamaki, Daisuke; Hada, Masahiko

2012-12-01

97

Characterization of caged compounds binding to proteins by NMR spectroscopy.  

PubMed

Photolysable caged ligands are used to investigate protein function and activity. Here, we investigate the binding properties of caged nucleotides and their photo released products to well established but evolutionary and structurally unrelated nucleotide-binding proteins, rabbit muscle creatine kinase (RMCK) and human annexin A6 (hAnxA6), using saturation transfer difference NMR spectroscopy. We detect the binding of the caged nucleotides and discuss the general implications on interpreting data collected with photolysable caged ligands using different techniques. Strategies to avoid non-specific binding of caged compound to certain proteins are also suggested. PMID:20804737

Bandorowicz-Pikula, Joanna; Buchet, René; Cañada, F Javier; Clémancey, Martin; Groves, Patrick; Jiménez-Barbero, Jesus; Lancelin, Jean-Marc; Marcillat, Olivier; Pikula, Slawomir; Sekrecka-Belniak, Anna; Strzelecka-Kiliszek, Agnieszka

2010-09-04

98

RNA refolding studied by light-coupled NMR spectroscopy.  

PubMed

Conformational transitions (refolding) between long-lived conformational states constitute the time-limiting step during the folding process of large RNAs. As the dynamics of these reactions dominate the regulatory and other functional behavior of RNA molecules, it is of importance to characterize them with high spatial and temporal resolution. Here, we describe a method for the investigation of RNA refolding reactions based on the photolytic generation of preselected conformations in a non-equilibrium state, followed by the observation of the folding trajectory with real-time NMR spectroscopy. PMID:24136612

Schwalbe, Harald; Fürtig, Boris

2014-01-01

99

Studies of rare-earth stannates by sup 119 Sn MAS NMR. The use of paramagnetic shift probes in the solid state  

SciTech Connect

{sup 119}Sn MAS NMR spectra have been obtained from members of a series of rare-earth stannates Ln{sub 2}Sn{sub 2}O{sub 7} (Ln = La, Pr, Nd, Sm, Eu, Tm, Yb, Lu, and Y), all of which adopt the pyrochlore structure. Apart from La{sub 2}Sn{sub 2}O{sub 7}, Lu{sub 2}Sn{sub 2}O{sub 7}, and Y{sub 2}Sn{sub 2}O{sub 7}, these compounds are paramagnetic and exhibit a very large variation in {sup 119}Sn chemical shifts (from approximately +5,400 to {minus}4,200 ppm), which can be attributed principally to a Fermi contact shift mechanism. The spectra from the paramagnetic samples have large overall line widths associated with the substantial anisotropy of the shift, but the individual peaks within the spinning sideband manifolds remain sharp. Several tin pyrochlore solid solutions have also been studied (namely Y{sub 2-y}Ln{sub y}Sn{sub 2}O{sub 7} where Ln = Sm, Nd, Pr, and Eu and La{sub 2-y}Nd{sub y}Sn{sub 2}O{sub u}) by {sup 119}Sn MAS NMR. When the short relaxation times of nuclei close to paramagnetic centers were exploited, a series of peaks were observed, associated with the substitution of paramagnetic for diamagnetic lanthanide ions in the local coordination around a tin atom. For Y{sub 2-y}Sm{sub y}Sn{sub 2}O{sub 7} the composition of the solid solution could be determined from the intensities of these peaks. In the solid solutions the {sup 119}Sn nuclei were found to be sensitive not only to neighboring paramagnetic ions but also to paramagnetic ions in the second and third coordination spheres. The shifts induced in these cases arise primarily from a through-space dipolar pseudocontact mechanism and can be interpreted with a model for the site symmetry based on the crystal structure. 30 refs., 8 figs., 3 tabs.

Grey, C.P.; Dobson, C.M.; Cheetham, A.K.; Jakeman, R.J.B. (Univ. of Oxford (England))

1989-01-18

100

Linking local environments and hyperfine shifts: a combined experimental and theoretical (31)P and (7)Li solid-state NMR study of paramagnetic Fe(III) phosphates.  

PubMed

Iron phosphates (FePO(4)) are among the most promising candidate materials for advanced Li-ion battery cathodes. This work reports upon a combined nuclear magnetic resonance (NMR) experimental and periodic density functional theory (DFT) computational study of the environments and electronic structures occurring in a range of paramagnetic Fe(III) phosphates comprising FePO(4) (heterosite), monoclinic Li(3)Fe(2)(PO(4))(3) (anti-NASICON A type), rhombohedral Li(3)Fe(2)(PO(4))(3) (NASICON B type), LiFeP(2)O(7), orthorhombic FePO(4)·2H(2)O (strengite), monoclinic FePO(4)·2H(2)O (phosphosiderite), and the dehydrated forms of the latter two phases. Many of these materials serve as model compounds relevant to battery chemistry. The (31)P spin-echo mapping and (7)Li magic angle spinning NMR techniques yield the hyperfine shifts of the species of interest, complemented by periodic hybrid functional DFT calculations of the respective hyperfine and quadrupolar tensors. A Curie-Weiss-based magnetic model scaling the DFT-calculated hyperfine parameters from the ferromagnetic into the experimentally relevant paramagnetic state is derived and applied, providing quantitative finite temperature values for each phase. The sensitivity of the hyperfine parameters to the composition of the DFT exchange functional is characterized by the application of hybrid Hamiltonians containing admixtures 0%, 20%, and 35% of Fock exchange. Good agreement between experimental and calculated values is obtained, provided that the residual magnetic couplings persisting in the paramagnetic state are included. The potential applications of a similar combined experimental and theoretical NMR approach to a wider range of cathode materials are discussed. PMID:21053901

Kim, Jongsik; Middlemiss, Derek S; Chernova, Natasha A; Zhu, Ben Y X; Masquelier, Christian; Grey, Clare P

2010-11-05

101

27Al and 29Si NMR spectroscopy of MgSiO3 perovskite: mechanisms of Al and Fe incorporation  

NASA Astrophysics Data System (ADS)

The boundary between the Earth's upper and lower mantle is generally attributed to the decomposition of (Mg,Fe)2SiO4 ringwoodite into ferropericlase and perovskite-structured (Mg,Fe)SiO3, hereafter perovskite. Concomitant with this phase change is the more gradual disappearance of a separate Al-bearing phase (majoritic garnet) and dissolution of Al into perovskite. The mechanism of Al incorporation is strongly affected by the presence of Fe due to the co-substitution of Al3+ and Fe3+ for Si4+ and Mg2+, respectively. However, questions about specific substitution mechanisms, site occupancy, and long- and short-range ordering of Fe and Al are still not fully understood. These are questions that NMR is particularly suited to address. We are applying Mossbauer, and 27Al and 29Si MAS-NMR spectroscopy to a series of Al- and Fe-bearing MgSiO3 perovskites of nominal composition Mg1-xFexSi1-xAlxO3 (x = 0.01, 0.025, 0.05). These were synthesized in a multi-anvil cell press at 26 GPa and 1900°C from either glassy starting material or Fe-bearing, aluminous pyroxene synthesized at 8-10 GPa and 1200°C. 29Si spectra show the presence of only a narrow perovskite peak at -191.7 ppm and a broad peak at -81 ppm from an amorphous phase likely formed when crushing the multi-anvil run products. 27Al spectra contain one narrow peak at 6.4 ppm and one broad peak at -14.6 ppm, matching those seen in previous NMR studies of aluminous perovskite and corresponding to Al3+ substituting for Si4+ and Mg2+ respectively. The ratio of observable Al3+ in Si4+ vs. that in Mg2+ sites ranges from 5.5 to 6.3 when the signal to noise of the -14.6 ppm peak is sufficient for quantitation. NMR spectra of materials containing paramagnetic species (i.e. Fe2+ or Fe3+) are often complicated and difficult to interpret due to line broadening, signal loss, "contact" shifts, etc. However, with an understanding of paramagnetic interactions in NMR spectroscopy, valuable information can be gained about some Fe-bearing geological materials. For the pyroxene starting materials used here, NMR signal loss increases linearly with increasing Fe content, an expected result given the likely uncoupled substitution of Fe2+ and Al3+ in these materials. However, 27Al signal loss for the perovskite samples is non-linear with a nearly constant value going from Fe/(Fe + Mg) = 0.01 to 0.025 indicating strong ordering of Fe3+ and Al3+ onto adjacent crystallographic sites. Complete signal loss at Fe/(Fe + Mg) = 0.05 suggests the upper limit of Fe2+ and Fe3+ concentration at which useful NMR data can be obtained for this system. The results of this study are a start to a better understanding of the mechanism of solution of Fe and Al in perovskite and continued work on this problem could provide valuable information on this important lower mantle phase. In addition, this study has potential to give us more general insights into paramagnetic interactions in NMR spectroscopy of geological materials.

Palke, A.; Stebbins, J. F.; Frost, D. J.; McCammon, C. A.

2011-12-01

102

Report on neptunium speciation by NMR and optical spectroscopies  

SciTech Connect

Hydrolysis and carbonate complexation reactions were examined for NpO{sub 2}{sup 2+} and NpO{sub 2}{sup +} ions by a variety of techniques including potentiometric titration, UV-Vis-NIR and NMR spectroscopy. The equilibrium constant for the reaction 3NpO{sub 2}(CO{sub 3}){sub 3}{sup 4{minus}} + 3H{sup +} {rightleftharpoons} (NpO{sub 2}){sub 3}(CO{sub 3}){sub 6}{sup 6{minus}} + 3HCO{sub 3}{sup {minus}} was determined to be logK = 19.7 ({plus_minus} 0.8) (I = 2.5 m). {sup 17}O NMR spectroscopy of NpO{sub 2}{sup n+} ions (n = 1,2) reveals a readily observable {sup 17}O resonance for n = 2, but not for n = 1. The first hydrolysis constant for NpO{sub 2}{sup +} was studied as a function of temperature, and the functional form for the temperature-dependent equilibrium constant for the reaction written as NpO{sub 2}{sup +} + H{sub 2}O {rightleftharpoons} NpO{sub 2}OH + H{sup +} was found to be logK = 2.28 {minus} 3780/T, where T is in {degree}K. Finally, the temperature dependence of neptunium(V) carbonate complexation constants was studied. For the first carbonate complexation constant, the appropriate functional form was found to be log{beta}{sub 01} = 1.47 + 786/T.

Tait, C.D.; Palmer, P.D.; Ekberg, S.A.; Clark, D.L.

1995-11-01

103

NMR Measurements in the Paramagnetic State of Uranium-Phosphorus Compounds. I. Line Shifts of 31P in UP and in UP1-xSx  

Microsoft Academic Search

NMR line shifts DeltaH of 31P in the antiferromagnetic semimetal UP and in its solid solutions UP1-xSx (x~=0,14,12,34) in the paramagnetic state are proportional to the magnetization of the solid: K=DeltaHH=K0+alphachiM, where the parameters are nearly independent of composition x and fall within a narrow range K0=(-35+\\/-15)×10-4 alpha=5.2+\\/-0.5 (emu\\/mole)-1. This line shift is interpreted as superhyperfine (shf) polarization transferred through

F. Friedman; J. Grunzweig-Genossar

1971-01-01

104

NMR spectroscopy and MRI investigation of a potential bioartificial liver.  

PubMed

NMR feasibility was established for a coaxial hydrophobic-membrane bioreactor containing isolated rat hepatocytes with features designed to mimic the human liver. A novel triple-tuned NMR probe and a perfusion system controlling temperature, gas concentrations, flow-rate, and pH were used. We determined the optimum coaxial interfiber distance (i.e. diffusion distance) for maintaining hepatocyte viability in two bioreactor prototypes. Prototype no. 1 and no. 2 had diffusion distances of 500 microns and 200 microns, respectively. Cell viability was established by 31P NMR and trypan blue exclusion. Only prototype no. 2 maintained cell viability for more than 6 h, indicating the importance of diffusion distance. 31P spectra obtained over this 6 h time period were similar to in vivo spectra of rat liver. The 31P spectra were found to be more sensitive to subacute cell viability than trypan blue exclusion. In the 1H and 31P spectra, 1H2O and inorganic phosphate signals were split in two at all flow-rates, probably due to bulk magnetic susceptibility effects originating from the three bioreactor compartments. MRI was useful for quality control and determining flow dynamics, fiber integrity, and cell inoculate distribution. MRI revealed that the inner fibers were not centered in either prototype. Although an increased flow-rate did not influence spectral resolution or chemical shifts, significant degradation of MRI quality occurred above 50 mL/min. NMR spectroscopy and imaging provide valuable, real-time information on cell biochemistry and flow dynamics which can be used in development and monitoring of bioreactors designed as artificial livers. PMID:9608589

Macdonald, J M; Grillo, M; Schmidlin, O; Tajiri, D T; James, T L

1998-04-01

105

In vivo two-dimensional NMR correlation spectroscopy  

NASA Astrophysics Data System (ADS)

The poor resolution of in-vivo one- dimensional nuclear magnetic resonance spectroscopy (NMR) has limited its clinical potential. Currently, only the large singlet methyl resonances arising from N-acetyl aspartate (NAA), choline, and creatine are quantitated in a clinical setting. Other metabolites such as myo- inositol, glutamine, glutamate, lactate, and ?- amino butyric acid (GABA) are of clinical interest but quantitation is difficult due to the overlapping resonances and limited spectral resolution. To improve the spectral resolution and distinguish between overlapping resonances, a series of two- dimensional chemical shift correlation spectroscopy experiments were developed for a 1.5 Tesla clinical imaging magnet. Two-dimensional methods are attractive for in vivo spectroscopy due to their ability to unravel overlapping resonances with the second dimension, simplifying the interpretation and quantitation of low field NMR spectra. Two-dimensional experiments acquired with mix-mode line shape negate the advantages of the second dimension. For this reason, a new experiment, REVOLT, was developed to achieve absorptive mode line shape in both dimensions. Absorptive mode experiments were compared to mixed mode experiments with respect to sensitivity, resolution, and water suppression. Detailed theoretical and experimental calculations of the optimum spin lock and radio frequency power deposition were performed. Two-dimensional spectra were acquired from human bone marrow and human brain tissue. The human brain tissue spectra clearly reveal correlations among the coupled spins of NAA, glutamine, glutamate, lactate, GABA, aspartate and myo-inositol obtained from a single experiment of 23 minutes from a volume of 59 mL. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

Kraft, Robert A.

1999-10-01

106

NMR Spectroscopy and Protein Structure Determination: Applications to Drug Discovery and Development  

Microsoft Academic Search

Recent technological advances in NMR methods and instrumentation are having a significant impact in structural biology. These innovations are also impacting pharmaceutical biotechnology as it is now possible to use NMR spectroscopy to rapidly characterize a growing number of prospective protein drugs and protein drug targets. This review provides a general summary of how solution-state NMR can be used to

David Wishart

2005-01-01

107

Teaching the Fundamentals of Pulsed NMR Spectroscopy in an Undergraduate Physical Chemistry Laboratory  

Microsoft Academic Search

Pulsed nuclear magnetic resonance (NMR) spectroscopy has become the premiere technique for chemists and biochemists studying the conformational, structural, and dynamic properties of a wide variety of molecular and biological systems. The theories and physical concepts associated with pulsed NMR spectroscopy are difficult for undergraduate students to comprehend and often require a thorough understanding of spin physics. Additionally, undergraduates in

Gary A. Lorigan; Robert E. Minto; Wei Zhang

2001-01-01

108

Monitoring the enzymatic degradation of sinigrin from B. juncea meal using H NMR spectroscopy  

Microsoft Academic Search

A simple procedure for extracting and purifying sinigrin from Oriental mustard (Brassica juncea) meal using cold water was developed. Subsequently, the chemical degradation of sinigrin due to enzymatic activity was monitored using H NMR spectroscopy over the course of 30 h. The experimental findings show that sinigrin has been positively identified from B. juncea using H NMR spectroscopy and the

Kody A. Belliveau; Laura B. Romero-Zerón

2010-01-01

109

Paramagnetic electrodes and bulk magnetic susceptibility effects in the in situ NMR studies of batteries: Application to Li1.08Mn1.92O4 spinels  

NASA Astrophysics Data System (ADS)

To date, in situ nuclear magnetic resonance (NMR) studies of working batteries have been performed in static mode, i.e., in the absence of magic angle spinning (MAS). Thus, it is extremely challenging to apply the method to paramagnetic systems such as the cathodes spinels Li1+xMn2-xO4 primarily due to three factors: (1) the resonance lines are broadened severely; (2) spectral analysis is made more complicated by bulk magnetic susceptibility (BMS) effects, which depend on the orientation and shape of the object under investigation; (3) the difficulty in untangling the BMS effects induced by the paramagnetic and metallic components on other (often diamagnetic) components in the system, which result in additional shifts and line broadening. Here we evaluate the orientation-dependence of the BMS effect of Li1.08Mn1.92O4, analyzing the experimental results by using a simple long-distance Li-electron dipolar coupling model. In addition, we discuss the shape and packing density dependence of the BMS effect and its influence on the observed frequencies of other components, such as the Li metal and the electrolyte in the battery. Finally, we show that by taking these effects into account we are able to minimize the BMS induced shift by orienting the cell at a rotation angle, ?i = 54.7° which facilitates the interpretation of the in situ NMR spectra of a working battery with the paramagnetic Li1.08Mn1.92O4 cathode.

Zhou, Lina; Leskes, Michal; Ilott, Andrew J.; Trease, Nicole M.; Grey, Clare P.

2013-09-01

110

Electron paramagnetic resonance spectroscopy of Cr3+ in hexagonal Cs2NaGaF6 crystals  

NASA Astrophysics Data System (ADS)

Powder samples of hydrothermally grown Cr3+ -doped Cs-2 NaGaF6 crystals have been investigated with electron paramagnetic resonance spectroscopy at X - (9.5 GHz) and Q -band (34 GHz). Analysis of the spectra clearly demonstrates that there are two distinct Cr3+ centres in the Cs2NaGaF6 crystal, having nearly identical g factors, but differing largely from the viewpoint of their zero field splitting. By using the Cr-53 hyperfine spectra observed with electron nuclear double resonance spectroscopy, it is deduced that these centres have opposite signs for the zero field splitting. The spectroscopic properties of the Cr3+ centres in the isostructural Cs2NaGaF6 and Cs2NaAlF6 crystals are compared and discussed.

Vrielinck, H.; Khaidukov, N. M.; Callens, F.; Matthys, P.

111

Multiplicative or t1 Noise in NMR Spectroscopy  

SciTech Connect

The signal in an NMR experiment is highly sensitive to fluctuations of the environment of the sample. If, for example, the static magnetic field B{sub 0}, the amplitude and phase of radio frequency (rf) pulses, or the resonant frequency of the detection circuit are not perfectly stable and reproducible, the magnetic moment of the spins is altered and becomes a noisy quantity itself. This kind of noise not only depends on the presence of a signal, it is in fact proportional to it. Since all the spins at a particular location in a sample experience the same environment at any given time, this noise primarily affects the reproducibility of an experiment, which is mainly of importance in the indirect dimensions of a multidimensional experiment, when intense lines are suppressed with a phase cycle, or for difference spectroscopy techniques. Equivalently, experiments which are known to be problematic with regard to their reproducibility, like flow experiments or experiments with a mobile target, tend to be affected stronger by multiplicative noise. In this article it is demonstrated how multiplicative noise can be identified and characterized using very simple, repetitive experiments. An error estimation approach is developed to give an intuitive, yet quantitative understanding of its properties. The consequences for multidimensional NMR experiments are outlined, implications for data analysis are shown, and strategies for the optimization of experiments are summarized.

Granwehr, Josef

2005-01-25

112

Optical and electron paramagnetic resonance spectroscopies of diffusion-doped Co2+:ZnSe  

NASA Astrophysics Data System (ADS)

The efficacy of diffusing cobalt into window-grade polycrystalline ZnSe during high-temperature anneals has been studied. Absorption, photoluminescence (PL), time-resolved PL, and electron paramagnetic resonance (EPR) were used to characterize samples with cobalt concentrations ranging from 1017 to 1019 cm-3. Absorption and PL were used to monitor the optical properties of Co2+ impurities, as well as detect Ni2+ and Fe2+ ions due to unintentional contamination. The temperature dependence of the 3 ?m emission due to Co2+ ions was measured and lifetimes were determined. EPR was used to monitor the paramagnetic charge states (Co2+, Ni3+, and Fe3+) of the transition-metal ions in our samples. The effects of nickel and iron impurities on the Co2+ infrared emission intensity and lifetime are discussed.

Luo, Ming; Garces, N. Y.; Giles, N. C.; Roy, Utpal N.; Cui, Yunlong; Burger, Arnold

2006-04-01

113

Redox properties and electron paramagnetic resonance spectroscopy of the transition state complex of Azotobacter vinelandii nitrogenase  

Microsoft Academic Search

Nitrogenase is a two-component metalloenzyme that catalyzes a MgATP hydrolysis driven reduction of substrates. Aluminum fluoride plus MgADP inhibits nitrogenase by stabilizing an intermediate of the on-enzyme MgATP hydrolysis reaction. We report here the redox properties and electron paramagnetic resonance (EPR) signals of the aluminum fluoride-MgADP stabilized nitrogenase complex of Azotobacter vinelandii. Complex formation lowers the midpoint potential of the

J. H. Spee; A. F. Arendsen; H. Wassink; S. J. Marritt; W. R. Hagen; H. Haaker

1998-01-01

114

Interactions of lipopolysaccharide and polymyxin studied by NMR spectroscopy.  

PubMed

In the light of occurrence of bacterial strains with multiple resistances against most antibiotics, antimicrobial peptides that interact with the outer layer of Gram-negative bacteria, such as polymyxin (PMX), have recently received increased attention. Here we present a study of the interactions of PMX-B, -E, and -M with lipopolysaccharide (LPS) from a deep rough mutant strain of Escherichia coli. A method for efficient purification of biosynthetically produced LPS using reversed-phase high-performance liquid chromatography in combination with ternary solvent mixtures was developed. LPS was incorporated into a membrane model, dodecylphosphocholine micelles, and its interaction with polymyxins was studied by heteronuclear NMR spectroscopy. Data from chemical shift mapping using isotope-labeled LPS or labeled polymyxin, as well as from isotope-filtered nuclear Overhauser effect spectroscopy experiments, reveal the mode of interaction of LPS with polymyxins. Using molecular dynamics calculations the complex of LPS with PMX-B in the presence of dodecylphosphocholine micelles was modeled using restraints derived from chemical shift mapping data and intermolecular nuclear Overhauser effects. In the modeled complex the macrocycle of PMX is centered around the phosphate group at GlcN-B, and additional contacts from polar side chains are formed to GlcN-A and Kdo-C, whereas hydrophobic side chains penetrate the acyl-chain region. PMID:19244241

Mares, Jiri; Kumaran, Sowmini; Gobbo, Marina; Zerbe, Oliver

2009-02-25

115

Quantitative high-resolution on-line NMR spectroscopy in reaction and process monitoring.  

PubMed

On-line nuclear magnetic resonance spectroscopy (on-line NMR) is a powerful technique for reaction and process monitoring. Different set-ups for direct coupling of reaction and separation equipment with on-line NMR spectroscopy are described. NMR spectroscopy can be used to obtain both qualitative and quantitative information from complex reacting multicomponent mixtures for equilibrium or reaction kinetic studies. Commercial NMR probes can be used at pressures up to 35 MPa and temperatures up to 400 K. Applications are presented for studies of equilibria and kinetics of complex formaldehyde-containing mixtures as well as homogeneously and heterogeneously catalyzed esterification kinetics. Direct coupling of a thin-film evaporator is described as an example for the benefits of on-line NMR spectroscopy in process monitoring. PMID:14729025

Maiwald, Michael; Fischer, Holger H; Kim, Young-Kyu; Albert, Klaus; Hasse, Hans

2004-02-01

116

Electron paramagnetic resonance spectroscopy of Cu2+ in hen egg-white lysozyme.  

PubMed Central

We have obtained the electron paramagnetic resonance spectrum of Cu2+ bound in a tetragonal single crystal of hen egg-white lysozyme. A part of this spectrum has been shown to originate from Cu2+ ions bound at the site designated as B by Teichberg et al. [Teichberg, V.I., Sharon, N., Moult, J., Smilansky, A. & Yonath, A. (1974) J. Mol. Biol. 87, 357-368]. The values of the spin hamiltonian parameters that describe this part of the spectrum are reported. The implications of these values with respect to the chemical nature and configuration of ligands are discussed. The other features of the spectrum are also described.

Hutchison, C A; Singel, D J; Hadad, M N; Kemple, M D

1980-01-01

117

Characterization of paramagnetic species in N-doped TiO2 powders by EPR spectroscopy and DFT calculations.  

PubMed

Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations are combined for the first time in an effort to characterize the paramagnetic species present in N-doped anatase TiO2 powders obtained by sol-gel synthesis. The experimental hyperfine coupling constants are well reproduced by two structurally different nitrogen impurities: substitutional and interstitial N atoms in the TiO2 anatase matrix. DFT calculations show that the nitrogen impurities induce the formation of localized states in the band gap. Substitutional nitrogen states lie just above the valence band, while interstitial nitrogen states lie higher in the gap. Excitations from these localized states to the conduction band may account for the absorption edge shift toward lower energies (visible region) observed in the case of N-doped TiO2 with respect to pure TiO2 (UV region). Calculations also show that nitrogen doping leads to a substantial reduction of the energy cost to form oxygen vacancies in bulk TiO2. This suggests that nitrogen doping is likely to be accompanied by oxygen vacancy formation. Finally, we propose that the relative abundance of the two observed nitrogen-doping species depends on the preparation conditions, such as the oxygen concentration in the atmosphere and the annealing temperature during synthesis. PMID:16852395

Di Valentin, Cristiana; Pacchioni, Gianfranco; Selloni, Annabella; Livraghi, Stefano; Giamello, Elio

2005-06-16

118

NMR and NQR study of the tetrahedral frustrated quantum spin system Cu2Te2O5Br2 in its paramagnetic phase  

NASA Astrophysics Data System (ADS)

The quantum antiferromagnet Cu2Te2O5Br2 was investigated by NMR and nuclear quadrupole resonance (NQR). The T125e NMR investigation showed that there is a magnetic transition around 10.5 K at 9 T, in agreement with previous studies. From the divergence of the spin-lattice relaxation rate, we ruled out the possibility that the transition could be governed by a one-dimensional divergence of the spin-spin correlation function. The observed anisotropy of the T125e shift was shown to be due to a spin polarization of the 5s2 “E” doublet of the [TeO3E] tetrahedra, highlighting the importance of tellurium in the exchange paths. In the paramagnetic state, Br NQR and NMR measurements led to the determination of the Br hyperfine coupling and the electric field gradient tensor, and to the spin polarization of Brp orbitals. The results demonstrate the crucial role of bromine in the interaction paths between Cu spins.

Comment, Arnaud; Mayaffre, Hadrien; Mitrovi?, Vesna; Horvati?, Mladen; Berthier, Claude; Grenier, Béatrice; Millet, Patrice

2010-12-01

119

Mapping the landscape of RNA dynamics with NMR spectroscopy.  

PubMed

Among the three major classes of biomacromolecules (DNA, RNA, and proteins) RNA's pronounced dynamics are the most explicitly linked to its wide variety of functions, which include catalysis and the regulation of transcription, translation, and splicing. These functions are mediated by a range of RNA biomachinery, including such varied examples as macromolecular noncoding RNAs, microRNAs, small interfering RNAs, riboswitch RNAs, and RNA thermometers. In each case, the functional dynamics of an interconversion is characterized by an associated rate constant. In this Account, we provide an introduction to NMR spectroscopic characterization of the landscape of RNA dynamics. We introduce strategies for measuring NMR parameters at various time scales as well as the underlying models for describing the corresponding rate constants. RNA exhibits significant dynamic motion, which can be modulated by (i) intermolecular interactions, including specific and nonspecific binding of ions (such as Mg(2+) and tertiary amines), (ii) metabolites in riboswitches or RNA aptamers, and (iii) macromolecular interactions within ribonucleic protein particles, including the ribosome and the spliceosome. Our understanding of the nature of these dynamic changes in RNA targets is now being incorporated into RNA-specific approaches in the design of RNA inhibitors. Interactions of RNA with proteins, other RNAs, or small molecules often occur through binding mechanisms that follow an induced fit mechanism or a conformational selection mechanism, in which one of several populated RNA conformations is selected through ligand binding. The extent of functional dynamics, including the kinetic formation of a specific RNA tertiary fold, is dependent on the messenger RNA (mRNA) chain length. Thus, during de novo synthesis of mRNA, both in prokaryotes and eukaryotes, nascent mRNA of various lengths will adopt different secondary and tertiary structures. The speed of transcription has a critical influence on the functional dynamics of the RNA being synthesized. In addition to modulating the local dynamics of a conformational RNA ensemble, a given RNA sequence may adopt more than one global, three-dimensional structure. RNA modification is one way to select among these alternative structures, which are often characterized by nearly equal stability, but with high energy barriers for conformational interconversion. The refolding of different secondary and tertiary structures has been found to be a major regulatory mechanism for transcription and translation. These conformational transitions can be characterized with NMR spectroscopy, for any given RNA sequence, in response to external stimuli. PMID:21894962

Rinnenthal, Jörg; Buck, Janina; Ferner, Jan; Wacker, Anna; Fürtig, Boris; Schwalbe, Harald

2011-09-06

120

Monitoring the enzymatic degradation of sinigrin from B. juncea meal using (1)H NMR spectroscopy.  

PubMed

A simple procedure for extracting and purifying sinigrin from Oriental mustard (Brassica juncea) meal using cold water was developed. Subsequently, the chemical degradation of sinigrin due to enzymatic activity was monitored using (1)H NMR spectroscopy over the course of 30 h. The experimental findings show that sinigrin has been positively identified from B. juncea using (1)H NMR spectroscopy and the prescribed preparation procedure. The results that have been presented also offer unambiguous evidence that (1)H NMR spectroscopy can be used to detect changes in sinigrin concentration over time. PMID:20013469

Belliveau, Kody A; Romero-Zerón, Laura B

2010-01-01

121

Investigation of the generation of singlet oxygen in ensembles of photoexcited silicon nanocrystals by electron paramagnetic resonance spectroscopy  

SciTech Connect

The generation of singlet oxygen is investigated and its concentration upon photoexcitation of silicon nanocrystals in porous silicon layers is determined using electron paramagnetic resonance spectroscopy. The relaxation times of spin centers, i.e., silicon dangling bonds, in vacuum and in an oxygen atmosphere in the dark and under illumination of the samples are measured for the first time. It is revealed that the spin-lattice relaxation in porous silicon is retarded as compared to that in a single-crystal substrate. From analyzing experimental data, a microscopic model is proposed for interaction of oxygen molecules in the triplet state and spin centers at the surface of silicon nanocrystals. The results obtained have demonstrated that porous silicon holds promise for the use as a photosensitizer of molecular oxygen in biomedical applications.

Konstantinova, E. A., E-mail: liza35@mail.ru; Demin, V. A.; Timoshenko, V. Yu. [Moscow State University (Russian Federation)

2008-09-15

122

STUDYING RNA USING SITE-DIRECTED SPIN-LABELING AND CONTINUOUS-WAVE ELECTRON PARAMAGNETIC RESONANCE SPECTROSCOPY  

PubMed Central

In site-directed spin-labeling (SDSL), a stable nitroxide radical is attached to a specific location within a macromolecule and electron paramagnetic resonance (EPR) spectroscopy is used to interrogate the local environment surrounding the nitroxide. The SDSL strategy enables probing site-specific structural and dynamic features of RNA in solution without being limited by the size of the molecule, thus serving as a unique tool in biophysical studies of RNA. This chapter describes the use of continuous-wave (cw)-EPR to study dynamic features of RNAs as well as to monitor interactions between them. Various approaches for attaching nitroxide spin labels to nucleic acids are described, followed by detailed descriptions of cw-EPR spectral acquisition and processing procedures. Specific examples are subsequently used to illustrate analysis of EPR spectra, showing how information regarding the parent RNA can be extracted.

Zhang, Xiaojun; Cekan, Pavol; Sigurdsson, Snorri Th.; Qin, Peter Z.

2010-01-01

123

The (29)Si T(1) and T(2) NMR relaxation in porous paramagnetic material SiO(2)-MnO-Al(2)O(3).  

PubMed

The (29)Si spin-lattice relaxation in porous silica-based material 1, doped by ions Mn(2+) at a Si/Mn ratio of 3.5, is non-exponential, independent of magic-angle spinning (MAS) rates and governed by direct dipolar coupling between electron and nucleus where an electron relaxation time is estimated to be about 10(-8)s. In the absence of mutual energy-conserving spin flips (spin diffusion) in 1, the (29)Si T(2) time increases linearly with spinning rates. None was observed in diamagnetic porous system 2. The unexpected (29)Si T(2) dependence has been interpreted in terms of the large bulk magnetic susceptibility (BMS) effects. It has been shown that editing the (29)Si Hahn-echo MAS NMR spectra eliminates wide lines, belonging to (29)Si nuclei in the proximity of paramagnetic centers, and reduces the BMS broadenings in sideband patterns for nuclei remote from these centers. PMID:18995993

Bakhmutov, Vladimir I

2008-10-11

124

Solution 1H NMR characterization of substrate-free C. diphtheriae heme oxygenase; pertinence for determining magnetic axes in paramagnetic substrate complexes  

PubMed Central

Proton 2D NMR was used to confirm in solution a highly conserved portion of the molecular structure upon substrate loss for the heme oxygenase from the pathogenic bacterium Corynebacterium diphtheriae, HmuO. The chemical shifts for the conserved portion of the structure are assessed as references for the dipolar shifts needed to determine the orientation of the paramagnetic susceptibility tensor, ?, in paramagnetic substrate complexes of HmuO. It is shown that the chemical shifts for the structurally conserved portion of substrate-free HmuO serve as excellent references for residues with only small to moderate sized dipolar shifts in the cyanide-inhibited substrate complex of HmuO, yielding an orientation of ? that is essentially the same as conventionally obtained from large dipolar shifts based on empirical estimates of the diamagnetic reference. The implications of these diamagnetic chemical shifts for characterizing the hydrogen bonding in the physiologically relevant, resting-state, high-spin aquo complex are discussed. The pattern of labile proton exchange in the distal H-bond network of substrate-free HmuO allowed comparison of changes in dynamic stability of tertiary contacts in the substrate-free and substrate-bound HmuO and with the same complexes of human heme oxygenase.

Du, Zhenming; Unno, Masaki; Matsui, Toshitaka; Ikeda-Saito, Masao; La Mar, Gerd N.

2010-01-01

125

A new pulse width reduction technique for pulsed electron paramagnetic resonance spectroscopy.  

PubMed

We present a new technique for a microwave pulse modulator that generates a short microwave pulse of approximately 1ns for use in an electron paramagnetic resonance (EPR) spectrometer. A quadruple-frequency multiplier that generates a signal of 16-20GHz from an input of 4-5GHz was employed to reduce the rise and fall times of the pulse prepared by a PIN diode switch. We examined the transient response characteristics of a commercial frequency multiplier and found that the device can function as a multiplier for pulsed signal even though it was designed for continuous wave operation. We applied the technique to a Ku band pulsed EPR spectrometer and successfully observed a spin echo signal with a broad excitation bandwidth of approximately 1.6mT using 80 degrees pulses of 1.5ns. PMID:18248828

Ohba, Yasunori; Nakazawa, Shigeaki; Kazama, Shunji; Mizuta, Yukio

2007-12-15

126

Development of a Micro Flow-Through Cell for High Field NMR Spectroscopy.  

National Technical Information Service (NTIS)

A highly transportable micro flow-through detection cell for nuclear magnetic resonance (NMR) spectroscopy has been designed, fabricated and tested. This flow-through cell allows for the direct coupling between liquid chromatography (LC) and gel permeatio...

S. K. McIntyre T. M. Alam

2011-01-01

127

Measurement of Solution Viscosity via Diffusion-Ordered NMR Spectroscopy (DOSY)  

ERIC Educational Resources Information Center

|Increasingly, the undergraduate chemistry curriculum includes nuclear magnetic resonance (NMR) spectroscopy. Advanced NMR techniques are often taught including two-dimensional gradient-based experiments. An investigation of intermolecular forces including viscosity, by a variety of methods, is often integrated in the undergraduate physical and…

Li, Weibin; Kagan, Gerald; Hopson, Russell; Williard, Paul G.

2011-01-01

128

Functional group analysis in coal by sup 31 P NMR spectroscopy  

SciTech Connect

The purpose of this research is to determine the labile-hydrogen functional group composition of coal and coal-derived materials by the nmr spectroscopy of their derivatives made with reagents containing the nmr-active nuclei {sup 31}P, {sup 119}Sn, or {sup 205}Tl. 7 refs.

Verkade, J.G.

1989-05-01

129

Zinc Dialkyldithiophosphate Oxidation by Cumene Hydroperoxide: Kinetic Studies by Raman and P NMR Spectroscopy  

Microsoft Academic Search

The oxidation of zinc dialkyldithiophosphates (ZDDPs) by cumene hydroperoxide in cyclohexane is studied by Raman and P NMR spectroscopy. The reaction proceeds in two main stages: oxidation of ZDDP to basic ZDDP, and oxidation of basic ZDDP to other products. Observation of phosphorus-containing reaction products by the two techniques yields approximate rate coefficients for the two stages. P NMR spectra

J. L. Paddy; N. C. J. Lee; D. N. Waters; W. Trott

1990-01-01

130

Measurement of Solution Viscosity via Diffusion-Ordered NMR Spectroscopy (DOSY)  

ERIC Educational Resources Information Center

Increasingly, the undergraduate chemistry curriculum includes nuclear magnetic resonance (NMR) spectroscopy. Advanced NMR techniques are often taught including two-dimensional gradient-based experiments. An investigation of intermolecular forces including viscosity, by a variety of methods, is often integrated in the undergraduate physical and…

Li, Weibin; Kagan, Gerald; Hopson, Russell; Williard, Paul G.

2011-01-01

131

Development of a micro flow-through cell for high field NMR spectroscopy.  

SciTech Connect

A highly transportable micro flow-through detection cell for nuclear magnetic resonance (NMR) spectroscopy has been designed, fabricated and tested. This flow-through cell allows for the direct coupling between liquid chromatography (LC) and gel permeation chromatography (GPC) resulting in the possibility of hyphenated LC-NMR and GPC-NMR. The advantage of the present flow cell design is that it is independent and unconnected to the detection probe electronics, is compatible with existing commercial high resolution NMR probes, and as such can be easily implemented at any NMR facility. Two different volumes were fabricated corresponding to between {approx}3.8 and 10 {micro}L detection volume. Examples of the performance of the cell on different NMR instruments, and using different NMR detection probes were demonstrated.

Alam, Todd Michael; McIntyre, Sarah K.

2011-05-01

132

Can nuclear magnetic resonance (NMR) spectroscopy reveal different metabolic signatures for lung tumours?  

Microsoft Academic Search

This study aims to evaluate the potential of 1H NMR spectroscopy, combined with multivariate statistics, for discriminating between tumour and non-involved (control) pulmonary\\u000a parenchyma and for providing biochemical information on different histological types. Paired tissue samples from 24 primary\\u000a lung tumours were directly analysed by high-resolution magic angle spinning (HRMAS) 1H NMR spectroscopy (500 MHz), and their spectral profiles subjected to

Iola F. Duarte; Cláudia M. Rocha; António S. Barros; Ana M. Gil; Brian J. Goodfellow; Isabel M. Carreira; João Bernardo; Ana Gomes; Vitor Sousa; Lina Carvalho

2010-01-01

133

The magnetic properties of myoglobin as studied by NMR spectroscopy.  

PubMed

Deoxymyoglobin has been investigated by NMR spectroscopy to determine the magnetic anisotropy through pseudocontact shifts and the total magnetic susceptibility through Evans measurements. The magnetic anisotropy values were found to be Deltachi(ax)=-2.03+/-0.08 x 10(-32) m(3) and Deltachi(rh)=-1.02+/-0.09 x 10(-32) m(3). The negative value of the axial susceptibility anisotropy originates from the z tensor axis lying in the heme plane, unlike all other heme systems investigated so far. This magnetic axis is almost exactly orthogonal to the axial histidine plane. The other two axes lie essentially in the histidine plane, the closest to the heme normal being tilted by about 36 degrees from it, towards pyrrole A on the side of the proximal histidine. From the comparison with cytochrome c' it clearly appears that the position of the one axis lying in the heme plane is related to the axial histidine orientation. Irrespective of the directions, the magnetic anisotropy is smaller than that of the analogous reduced cytochrome c' and of the order of that of low-spin iron(III). The magnetic anisotropy of the system permits the measurement of residual dipolar couplings, which, together with pseudocontact shifts, prove that the solution structure is very similar to that in the crystalline state. Magnetic measurements, at variance with previous data, demonstrate that there is an orbital contribution to the magnetic moment, micro(eff)=5.5 micro(B). Finally, from the magnetic anisotropy data, the hyperfine shifts of iron ligands could be separated in pseudocontact and contact components, and hints are provided to understand the spin-delocalisation mechanism in S=2 systems by keeping in mind the delocalisation patterns in low-spin S=1/2 and high-spin S= 5/2 iron(III) systems. PMID:12772306

Bertini, Ivano; Luchinat, Claudio; Turano, Paola; Battaini, Giuseppe; Casella, Luigi

2003-05-23

134

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...

135

NMR spectroscopy of RNA duplexes containing pseudouridine in supercooled water  

Microsoft Academic Search

We have performed NMR experiments in supercooled water in order to decrease the temperature-dependent exchange of protons in RNA duplexes. NMR spectra of aqueous samples of RNA in bundles of narrow capillaries that were acquired at temperatures as low as ---188C reveal resonances of exchangeable protons not seen at higher temperatures. In particular, we detected the imino protons of terminal

KERSTEN T. SCHROEDER; JACK J. SKALICKY; NANCY L. GREENBAUM

2005-01-01

136

Diffusion-ordered NMR spectroscopy in the structural characterization of functionalized carbon nanotubes.  

PubMed

The emerging applications of functionalized carbon nanotubes (CNTs) in various research domains necessitate the use of many different analytical techniques to confirm their structural modifications in a fast and reliable manner. Thus far, NMR spectroscopy has not been among the main tools for characterization of organically modified carbon nanostructures. (1)H analysis is limited because the signals in these derivatives are typically weak and broad, resulting in uncertainties of a few parts per million, and because of the strong interference of residual solvent signals. To overcome these limitations, we investigated the applicability of proton NMR spectroscopy based on gradient-edited diffusion pulse sequences (1D diffusion-ordered spectroscopy, DOSY) in the characterization of CNT derivatives. In general, diffusion NMR experiments allow the separation of NMR signals of different species present in a mixture, according to their own diffusion coefficients, merging spectroscopy information with size analysis. In the present study, a selected set of CNT derivatives was synthesized and analyzed using 1D DOSY experiments by applying strong magnetic field gradients (up to 42.6 G cm(-1)). Colorimetric tests (i.e., Kaiser test) and TGA analysis support the NMR findings, which are related to isolated and/or bundled short SWNTs, on the basis of TEM and AFM characterization. The overall results show that the diffusion-based NMR spectroscopy is a fast and promising approach for the characterization of covalently modified CNT derivatives. PMID:19459637

Marega, Riccardo; Aroulmoji, Vincent; Dinon, Francesca; Vaccari, Lisa; Giordani, Silvia; Bianco, Alberto; Murano, Erminio; Prato, Maurizio

2009-07-01

137

Dielectric microwave resonators in TE(011) cavities for electron paramagnetic resonance spectroscopy.  

PubMed

The coupled system of the microwave cylindrical TE(011) cavity and the TE(01delta) dielectric modes has been analyzed in order to determine the maximum achievable resonator efficiency parameter of a dielectric inserted into a cavity, and whether this value can exceed that of a dedicated TE(01delta) mode dielectric resonator. The frequency, Q value, and resonator efficiency parameter Lambda for each mode of the coupled system were calculated as the size of the dielectric was varied. Other output parameters include the relative field magnitudes and phases. Two modes are found: one with fields in the dielectric parallel to the fields in the cavity center and the other with antiparallel fields. Results closely match those from a computer program that solves Maxwell's equations by finite element methods. Depending on the relative natural resonance frequencies of the cavity and dielectric, one mode has a higher Q value and correspondingly lower Lambda than the other. The mode with the higher Q value is preferentially excited by a coupling iris or loop in or near the cavity wall. However, depending on the frequency separation between modes, either can be excited in this way. A relatively narrow optimum is found for the size of the insert that produces maximum signal for both modes simultaneously. It occurs when the self-resonance frequencies of the two resonators are nearly equal. The maximum signal is almost the same as that of the dedicated TE(01delta) mode dielectric resonator alone, Lambda congruent with40 G/W(1/2) at X-band for a KTaO(3) crystal. The cavity is analogous to the second stage of a two-stage coupler. In general, there is no electron paramagnetic resonance (EPR) signal benefit by use of a second stage. However, there is a benefit of convenience. A properly designed sample-mounted resonator inserted into a cavity can give EPR signals as large as what one would expect from the dielectric resonator alone. PMID:19044441

Mett, Richard R; Sidabras, Jason W; Golovina, Iryna S; Hyde, James S

2008-09-01

138

Dielectric microwave resonators in TE011 cavities for electron paramagnetic resonance spectroscopy  

PubMed Central

The coupled system of the microwave cylindrical TE011 cavity and the TE01? dielectric modes has been analyzed in order to determine the maximum achievable resonator efficiency parameter of a dielectric inserted into a cavity, and whether this value can exceed that of a dedicated TE01? mode dielectric resonator. The frequency, Q value, and resonator efficiency parameter ? for each mode of the coupled system were calculated as the size of the dielectric was varied. Other output parameters include the relative field magnitudes and phases. Two modes are found: one with fields in the dielectric parallel to the fields in the cavity center and the other with antiparallel fields. Results closely match those from a computer program that solves Maxwell’s equations by finite element methods. Depending on the relative natural resonance frequencies of the cavity and dielectric, one mode has a higher Q value and correspondingly lower ? than the other. The mode with the higher Q value is preferentially excited by a coupling iris or loop in or near the cavity wall. However, depending on the frequency separation between modes, either can be excited in this way. A relatively narrow optimum is found for the size of the insert that produces maximum signal for both modes simultaneously. It occurs when the self-resonance frequencies of the two resonators are nearly equal. The maximum signal is almost the same as that of the dedicated TE01? mode dielectric resonator alone, ??40 G?W1?2 at X-band for a KTaO3 crystal. The cavity is analogous to the second stage of a two-stage coupler. In general, there is no electron paramagnetic resonance (EPR) signal benefit by use of a second stage. However, there is a benefit of convenience. A properly designed sample-mounted resonator inserted into a cavity can give EPR signals as large as what one would expect from the dielectric resonator alone.

Mett, Richard R.; Sidabras, Jason W.; Golovina, Iryna S.; Hyde, James S.

2008-01-01

139

Si-29 NMR Spectroscopy of Naturally-Shocked Quartz from Meteor Crater, Arizona: Correlation to Kieffer's Classification Scheme.  

National Technical Information Service (NTIS)

We have applied solid state Si-29 nuclear magnetic resonance (NMR) spectroscopy to five naturally-shocked Coconino Sandstone samples from Meteor Crater, Arizona, with the goal of examining possible correlations between NMR spectral characteristics and sho...

M. B. Boslough R. T. Cygan R. J. Kirkpatrick

1993-01-01

140

Phosphoesterase activity of polyoxomolybdates: diffusion ordered NMR spectroscopy as a tool for obtaining insights into the reactivity of polyoxometalate clusters.  

PubMed

Diffusion ordered NMR spectroscopy (DOSY NMR) is shown to be an excellent tool for observing reactive transients in the hydrolysis of the phosphatase model substrate (p-nitrophenyl)phosphate (NPP) promoted by polyoxomolybdate. PMID:18688306

Lokeren, Luk Van; Cartuyvels, Els; Absillis, Gregory; Willem, Rudolph; Parac-Vogt, Tatjana N

2008-04-04

141

High resolution phosphorus NMR spectroscopy of transfer ribonucleic acids  

Microsoft Academic Search

The temperature dependence of the 31P NMR spectra of yeast phenylalanine tRNA, E. coli tyrosine, glutamate (2), and formylmethione tRNA, and bovine liver aspartate (2b) tRNA is presented. The major difference between the 31P NMR spectra of the different acceptor tRNAs is in the main cluster region between -0.5 and -1.3 ppm. This confirms earlier assignment of the main cluster

D. G. Gorenstein; E. M. Goldfield

1982-01-01

142

NMR spectroscopy of rare earth–3d transition metal alloys  

Microsoft Academic Search

Recent nuclear magnetic resonance studies of magnetically ordered rare earth–3d transition metal alloys are reviewed. Selected experimental results for rare earth NMR of RETM2 Laves phases as well as RE2TM14B and interstitially modified RE2TM17Ax (A=N,C,H) materials for permanent magnet applications are surveyed. An analysis of the hyperfine parameters obtained from NMR experiments is presented and their relation to the physical

Czes?aw Kapusta

1998-01-01

143

Comparing the structural topology of integral and peripheral membrane proteins utilizing electron paramagnetic resonance spectroscopy.  

PubMed

The alignment of membrane proteins provides pertinent structural and dynamic information. Structural topology data gleaned from such studies can be used to determine the functional mechanisms associated with a wide variety of integral membrane proteins. In this communication, we successfully demonstrate, for the first time, the determination of the structural topology and helical tilt of an antimicrobial peptide magainin 2 using aligned X-band spin-label EPR spectroscopic techniques. This novel comparison unlocks many possibilities utilizing EPR spectroscopy to probe antimicrobial peptide topologies with increased sensitivity and may also give further clues to elucidate their corresponding mechanisms. PMID:18598031

Mayo, Daniel J; Inbaraj, Johnson J; Subbaraman, Nidhi; Grosser, Stuart M; Chan, Christopher A; Lorigan, Gary A

2008-07-04

144

Electron paramagnetic resonance spectroscopy of lactoperoxidase complexes: clarification of hyperfine splitting for the NO adduct of lactoperoxidase  

SciTech Connect

Electron paramagnetic resonance (EPR) studies of the nitrosyl adduct of ferrous lactoperoxidase (LPO) confirm that the fifth axial ligand in LPO is bound to the iron via a nitrogen atom. Complete reduction of the ferric LPO sample is required in order to observe the nine-line hyperfine splitting in the ferrous LPO/NO EPR spectrum. The ferrous LPO/NO complex does not exhibit a pH or buffer system dependence when examined by EPR. Interconversion of the ferrous LPO/NO complex and the ferric LPO/NO/sub 2//sup -/ complex is achieved by addition of the appropriate oxidizing or reducing agent. Characterization of the low-spin LPO/NO/sub 2//sup -/ complex by EPR and visible spectroscopy is reported. The pH dependence of the EPR spectra of ferric LPO and ferric LPO/CN/sup -/ suggests that a high-spin anisotrophic LPO complex is formed at high pH and an acid-alkaline transition of the protein conformation near the heme site does occur in LPO/CN/sup -/. The effect of tris(hydroxymethyl)aminomethane buffer on the LPO EPR spectrum is also examined.

Lukat, G.S.; Rodgers, K.R.; Goff, H.M.

1987-11-03

145

Metabolic profiling of potential probiotic or synbiotic cheeses by nuclear magnetic resonance (NMR) spectroscopy.  

PubMed

To assess ripening of potential probiotic cheeses (containing either Lactobacillus casei -01 or Bifidobacterium lactis B94) or synbiotic cheeses with fructooligosaccharides (FOS) or a 50:50 mix of FOS/inulin, metabolic profiles have been obtained via classical biochemical analyses and by NMR spectroscopy. The addition of prebiotics to the cheeses resulted in lower proteolysis indices, especially in those synbiotic cheeses inoculated with B. lactis B94. Among synbiotic cheeses the combination of FOS and inulin resulted in an increase in lipolytic activity. The metabolic profiles of the cheeses analyzed by NMR spectroscopy, combined with multivariate statistics, allowed profiles to be distinguished by maturation time, added probiotic bacteria, or, in the case of B. lactis B94 cheese, added prebiotic. The NMR results are in agreement with the biochemical analyses and demonstrate the potential of NMR for the study of metabolic processes in probiotic/synbiotic food matrices. PMID:21443163

Rodrigues, Dina; Santos, Claudio H; Rocha-Santos, Teresa A P; Gomes, Ana M; Goodfellow, Brian J; Freitas, Ana C

2011-04-05

146

GFT projection NMR spectroscopy for proteins in the solid state  

PubMed Central

Recording of four-dimensional (4D) spectra for proteins in the solid state has opened new avenues to obtain virtually complete resonance assignments and three-dimensional (3D) structures of proteins. As in solution state NMR, the sampling of three indirect dimensions leads per se to long minimal measurement time. Furthermore, artifact suppression in solid state NMR relies primarily on radio-frequency pulse phase cycling. For an n-step phase cycle, the minimal measurement times of both 3D and 4D spectra are increased n times. To tackle the associated ‘sampling problem’ and to avoid sampling limited data acquisition, solid state G-Matrix Fourier Transform (SS GFT) projection NMR is introduced to rapidly acquire 3D and 4D spectral information. Specifically, (4,3)D (HA)CANCOCX and (3,2)D (HACA)NCOCX were implemented and recorded for the 6 kDa protein GB1 within about 10% of the time required for acquiring the conventional congeners with the same maximal evolution times and spectral widths in the indirect dimensions. Spectral analysis was complemented by comparative analysis of expected spectral congestion in conventional and GFT NMR experiments, demonstrating that high spectral resolution of the GFT NMR experiments enables one to efficiently obtain nearly complete resonance assignments even for large proteins.

Franks, W. Trent; Atreya, Hanudatta S.; Szyperski, Thomas

2011-01-01

147

^1H NMR studies of the diamagnetic gallium (III) and paramagnetic iron (III) complexes of a chiral macrobicyclic ligand of bicapped tris (binaphtol) type  

NASA Astrophysics Data System (ADS)

^1H NMR studies of the diamagnetic gallium (III) and paramagnetic iron (III) complexes of a chiral macrobicyclic ligand of bicapped tris (binaphtol) type are described. The study of the gallium complex emphasizes: (i) that the inversion of the octahedral center is not observed and: (ii) the absence of exchange between free ligand and complex, at room temperature. In the case of the iron complex, assignments of the hyperfine shifted resolved resonances are achieved, based on temperature-behavior studies, which evidence the D3 symmetry of the complex. These assignments are in complete agreement with measured T1 values and proton-to-iron distances obtained from molecular modelling. Les complexes du gallium (III) et du fer (III) d'un ligand macrobicyclique chiral impliquant trois sous-unités de type binaphtol sont étudiés en RMN du proton en solution méthanolique. L'étude du complexe (diamagnétique) du gallium permet de montrer que le complexe : (i) ne subit pas d'inversion de la configuration (?/?) du site octaédrique et : (ii) qu'il n'y a pas d'échange entre ligand libre et complexe à la température ambiante. L'évolution du spectre du complexe paramagnétique du fer avec la température permet une attribution des protons du ligand et met en évidence la symétrie D3 du complexe. Une bonne corrélation est obtenue entre la distance fer-proton (donnée par la modélisation moléculaire) et le T1 du proton considéré.

Baret, P.; Beaujolais, V.; Bougault, C.; Gaude, D.; Pierre, J.-L.

1998-01-01

148

Detecting Intracellular Cysteine Redox States by in-Cell NMR Spectroscopy.  

PubMed

An in-cell perspective: Nowadays, in-cell NMR spectroscopy has proven to be a thrilling alternative for the investigation of biomacromolecules under physiological conditions at atomic resolution. A recent example demonstrating significant progress in in-cell NMR was published by the groups of Banci and Aricescu that investigated the post-translational maturation of human superoxide dismutase 1 (SOD1) in living human cells. PMID:23893841

Silvers, Robert; Schwalbe, Harald

2013-07-24

149

1H-NMR spectroscopy of body fluids: inborn errors of purine and pyrimidine metabolism  

Microsoft Academic Search

Background: The diagnosis of inborn errors of purine and pyrimidine metabolism is often difficult. We exam- ined the potential of 1H-NMR as a tool in evaluation of patients with these disorders. Methods: We performed 1H-NMR spectroscopy on 500 and 600 MHz instruments with a standardized sample volume of 500 mL. We studied body fluids from 25 patients with nine inborn

Ron A. Wevers; Udo F. H. Engelke; Sytske H. Moolenaar; Christa Brautigam; Jong de J. G. N; Ries Duran; Abreu de R. A; Gennip van A. H

1999-01-01

150

Synthesis and characterization of polyphosphazene copolymers using phosphorus-31 NMR spectroscopy  

SciTech Connect

It was observed that competitive nucleophilic addition processes may be observed by {sup 31}P NMR spectroscopy. Methoxyethoxyethanol (MEE) and p-methoxyphenol readily substitute for chlorineonto phosphorus and the relative rates are generally comparable to each other. Sterically, the phenol presents is slightly larger than MEE but this does not appear to effect substitution judging by the observed PN(OAr){sub 2} NMR signal. These processes are still being studied.

Stewart, F.F.; Peterson, E.S.; Stone, M.L. [Lockheed Martin Idaho Technologies Co., Idaho Falls, ID (United States); Singler, R.E. [Military Academy, West Point, NY (United States). Dept. of Chemistry

1997-01-01

151

Metabolomic analysis of methyl jasmonate treated Brassica rapa leaves by 2-dimensional NMR spectroscopy  

Microsoft Academic Search

The metabolomic analysis of Brassica rapa leaves treated with methyl jasmonate was performed using 2-dimensional J-resolved NMR spectroscopy combined with multivariate data analysis. The principal component analysis of the J-resolved NMR spectra showed discrimination between control and methyl jasmonate treated plants by principal components 1 and 2. While the level of glucose, sucrose and amino acids showed a decrease after

Yun-Sa Liang; Young Hae Choi; Hye Kyong Kim; Huub J. M. Linthorst; Robert Verpoorte

2006-01-01

152

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

Microsoft Academic Search

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

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

1997-01-01

153

Ligand screening by saturation-transfer difference (STD) NMR spectroscopy.  

SciTech Connect

NMR based methods to screen for high-affinity ligands have become an indispensable tool for designing rationalized drugs, as these offer a combination of good experimental design of the screening process and data interpretation methods, which together provide unprecedented information on the complex nature of protein-ligand interactions. These methods rely on measuring direct changes in the spectral parameters, that are often simpler than the complex experimental procedures used to study structure and dynamics of proteins. The goal of this review article is to provide the basic details of NMR based ligand-screening methods, with particular focus on the saturation transfer difference (STD) experiment. In addition, we provide an overview of other NMR experimental methods and a practical guide on how to go about designing and implementing them.

Krishnan, V V

2005-04-26

154

Toward contrast-enhanced, optically-detected NMR spectroscopy  

NASA Astrophysics Data System (ADS)

Optical detection of Nuclear Magnetic Resonance (NMR) takes place via a two-step process that relies on the interaction between optical photons and electrons on the one hand, and the hyperfine coupling between electrons and nuclear spins on the other. The latter depends on the material system under consideration while the former is dominated by the difference between the illumination and optical transition wavelengths. Here we use optical Faraday rotation to monitor nuclear spins in real time after resonant radio-frequency excitation at high-magnetic field. Comparison between inductively and optically detected NMR spectra in model sample fluids indicates that each of these mechanisms can lead to alternate forms of spectral contrast. Extension of these findings may find application in solvent suppression protocols, sensitivity-enhanced NMR of metalloproteins, or the characterization of molecular orbitals in diamagnetic systems.

Meriles, Carlos; Pagliero, Daniela

2011-03-01

155

NMR spectroscopy of RNA duplexes containing pseudouridine in supercooled water  

PubMed Central

We have performed NMR experiments in supercooled water in order to decrease the temperature-dependent exchange of protons in RNA duplexes. NMR spectra of aqueous samples of RNA in bundles of narrow capillaries that were acquired at temperatures as low as ?18°C reveal resonances of exchangeable protons not seen at higher temperatures. In particular, we detected the imino protons of terminal base pairs and the imino proton of a non-base-paired pseudouridine in a duplex representing the eukaryotic pre-mRNA branch site helix. Analysis of the temperature dependence of chemical shift changes (thermal coefficients) for imino protons corroborated hydrogen bonding patterns observed in the NMR-derived structural model of the branch site helix. The ability to observe non-base-paired imino protons of RNA is of significant value in structure determination of RNA motifs containing loop and bulge regions.

SCHROEDER, KERSTEN T.; SKALICKY, JACK J.; GREENBAUM, NANCY L.

2005-01-01

156

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

PubMed Central

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

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

2013-01-01

157

Structural determination of larger proteins using stable isotope labeling and NMR spectroscopy  

SciTech Connect

The project sought to employ stable isotope labeling and NMR spectroscopy to study protein structures and provide insight into important biochemical problems. A methylotrophic bacterial expression system has been developed for uniform deuterium and carbon-13 labeling of proteins for structural studies. These organisms grow using methanol as the sole source of carbon and energy. Because isotopically labeled methanol is relatively inexpensive, the methylotrophs are ideal for expressing proteins labeled uniformly with deuterium and/or carbon-13. This expression system has been employed to prepare deuterated troponin C. NMR spectroscopy measurements have been made on the inhibitory peptide from troponin I (residues 96--115), both as the free peptide and the peptide complexed with deuterated troponin C. Proton-NMR spectroscopy resonance-signal assignments have been made for the free peptide.

Unkefer, C.; Hernandez, G.; Springer, P.; Trewhella, J. [Los Alamos National Lab., NM (United States); Blumenthal, D. [Univ. of Utah, Salt Lake City, UT (United States); Lidstrom, M. [California Inst. of Tech., Pasadena, CA (United States)

1996-04-01

158

NMR spectroscopy and imaging of macerals in Argonne premium coals  

SciTech Connect

Macerals that have been separated from two high-volatile bituminous coals from the Argonne Premium Coal Sample Program are surveyed using chemical and NMR spectroscopic techniques. Quantitative aspects of the method are discussed. Alkylation using {sup 13}C enriched methyl iodide followed by solid {sup 13}C NMR analysis was used to determine the concentrations of acidic OH and CH sites in these macerals. Also, the first successful application of nuclear magnetic resonance imaging (MRI) for spatially mapping chemically distinct regions within a Utah coal has been demonstrated. 15 refs., 5 figs., 2 tabs.

Botto, R.E.; Choi, C.Y.; Dieckman, S.L.; Gopalsami, N.; Thompson, A.R.; Tsiao, C.J.

1990-01-01

159

Quantum Gates Based on Polarization Transfer NMR Spectroscopy  

NASA Astrophysics Data System (ADS)

We first introduce an alternative way to study the insensitive nuclei enhanced by polarization and distortionless enhancement by polarization transfer NMR experiments with the product operator descriptions for weakly coupled I (I=1/2, S=1/2) spin systems as a quantum controlled not gate and a not gate, respectively. In this framework we apply the density matrix operators obtained from the analytical descriptions of the mentioned pulse sequences by using product operator formalism step by step on the NMR spin product states represented in Dirac's notation.

Güleç, A.; Bahçeli, S.

2005-06-01

160

Aqueous flat cells perpendicular to the electric field for use in electron paramagnetic resonance spectroscopy.  

PubMed

An analytic solution of the Maxwell equations for aqueous flat cells in rectangular TE(102) cavities has led to the prediction of significant (3-6 times) X-band EPR signal improvement over the standard flat cell for a new sample configuration consisting of many flat cells oriented perpendicular to the electric field nodal plane. Analytic full wave solutions in the presence of sample and wall losses have been obtained and numerically evaluated. Observation of the predicted fields led to a classification of three distinct types of sample loss mechanisms, which, in turn inspired sample designs that minimize each loss type. The resulting EPR signal enhancement is due to the presence and centering of a tangential electric field node within each individual sample region. Samples that saturate with the available RF magnetic field and those that do not are considered. Signal enhancement appears in both types. These observations, done for the TE(102) mode, carry over to the uniform field (UF) modes, a relatively new class of microwave cavities for use in EPR spectroscopy developed in this laboratory. Rectangular UF modes have an RF magnetic field magnitude that is uniform in a plane. Based on this analysis, a practical multiple flat-cell design is proposed. PMID:14568524

Mett, Richard R; Hyde, James S

2003-11-01

161

Profiling formulated monoclonal antibodies by (1)h NMR spectroscopy.  

PubMed

Nuclear magnetic resonance (NMR) is arguably the most direct methodology for characterizing the higher-order structure of proteins in solution. Structural characterization of proteins by NMR typically utilizes heteronuclear experiments. However, for formulated monoclonal antibody (mAb) therapeutics, the use of these approaches is not currently tenable due to the requirements of isotope labeling, the large size of the proteins, and the restraints imposed by various formulations. Here, we present a new strategy to characterize formulated mAbs using (1)H NMR. This method, based on the pulsed field gradient stimulated echo (PGSTE) experiment, facilitates the use of (1)H NMR to generate highly resolved spectra of intact mAbs in their formulation buffers. This method of data acquisition, along with postacquisition signal processing, allows the generation of structural and hydrodynamic profiles of antibodies. We demonstrate how variation of the PGSTE pulse sequence parameters allows proton relaxation rates and relative diffusion coefficients to be obtained in a simple fashion. This new methodology can be used as a robust way to compare and characterize mAb therapeutics. PMID:24006877

Poppe, Leszek; Jordan, John B; Lawson, Ken; Jerums, Matthew; Apostol, Izydor; Schnier, Paul D

2013-09-24

162

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

PubMed

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

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

2011-10-07

163

Characterization of the essential oil of Agastache rugosa by NMR spectroscopy  

NASA Astrophysics Data System (ADS)

The composition of essential oil from Agastache rugosa (Fish. et Mey) O.Kuntze was studied by 1H and 13C NMR spectroscopy. Essential oil was isolated from the aerial part of plants growing in the Central Botanical Garden of the NAS of Belarus during flowering and fruiting. The oil chemical composition was found to depend little on the sampling time. It was shown that NMR spectroscopy could be successfully used to both monitor the content of the hepatotoxic substance (pulegone) and characterize the quality and authenticity of essential oils.

Skakovskii, E. D.; Kiselev, W. P.; Tychinskaya, L. Yu.; Schutova, A. G.; Gonsharova, L. W.; Spiridowish, E. W.; Bovdey, N. A.; Kiselev, P. A.; Gaidukevich, O. A.

2010-07-01

164

High Field/High Frequency Saturation Transfer Electron Paramagnetic Resonance Spectroscopy: Increased Sensitivity to Very Slow Rotational Motions  

PubMed Central

Saturation transfer electron paramagnetic resonance (ST-EPR) spectroscopy has been employed to characterize the very slow microsecond to millisecond rotational dynamics of a wide range of nitroxide spin-labeled proteins and other macromolecules in the past three decades. The vast majority of this previous work has been carried out on spectrometers that operate at X-band (?9 GHz) microwave frequency with a few investigations reported at Q-band (?34 GHz). EPR spectrometers that operate in the 94–250-GHz range and that are capable of making conventional linear EPR measurements on small aqueous samples have now been developed. This work addresses potential advantages of utilizing these same high frequencies for ST-EPR studies that seek to quantitatively analyze the very slow rotational dynamics of spin-labeled macromolecules. For example, the uniaxial rotational diffusion (URD) model has been shown to be particularly applicable to the study of the rotational dynamics of integral membrane proteins. Computational algorithms have been employed to define the sensitivity of ST-EPR signals at 94, 140, and 250 GHz to the correlation time for URD, to the amplitude of constrained URD, and to the orientation of the spin label relative to the URD axis. The calculations presented in this work demonstrate that these higher microwave frequencies provide substantial increases in sensitivity to the correlation time for URD, to small constraints in URD, and to the geometry of the spin label relative to the URD axis as compared with measurements made at X-band. Moreover, the calculations at these higher frequencies indicate sensitivity to rotational motions in the 1–100-ms time window, particularly at 250 GHz, thereby extending the slow motion limit for ST-EPR by two orders of magnitude relative to X- and Q-bands.

Hustedt, Eric J.; Beth, Albert H.

2004-01-01

165

On-line detection of nitric oxide formation in liquid aqueous phase by electron paramagnetic resonance spectroscopy.  

PubMed

A method for the detection of the nitric oxide radical (NO) in oxygen-containing aqueous solution by means of electron paramagnetic resonance spectroscopy (EPR) is described. NO evolving from the spontaneous decomposition of 3-morpholinosydnonimine (SIN-1) was trapped by Fe(2+)-diethyldithiocarbamate (DETC) complex dissolved in yeast cell membranes. The resulting mononitrosyl-Fe(2+)-(DETC)2 complex was stable and exhibited a characteristic EPR signal at g perpendicular = 2.04 and g parallel = 2.02 with an unresolved triplet hyperfine structure at g perpendicular in frozen solution and an isotropic triplet signal at gav = 2.03 at 37 degrees C. The amount of NO trapped was calculated from the amplitude of one of the triplet lines calibrated by means of a dinitrosyl-Fe(2+)-thiosulfate standard. The lower detection limit of NO was 0.5 nmol/(ml x h) due to a low background NO signal. The upper detection limit was about 10 nmol NO/40 mg traps (DETC-loaded yeast cells), because of saturation of traps. The trapping efficiency approached 60% under anaerobic conditions and with low concentrations of SIN-1, but decreased progressively with higher concentrations and in the presence of oxygen. Nitrite (up to 0.1 mM) did not increase the background NO level. The sensitivity was sufficient to follow the rate of NO release from SIN-1 on-line at 37 degrees C in a flat quartz cuvette. The time course of NO release detected by EPR spectrometry correlated with the time course of nitrite accumulation measured by diazotation. In conclusion, this method will permit the on-line detection of NO formation from endogenous and pharmacological sources in oxygen-containing aqueous media. PMID:1666941

Mordvintcev, P; Mülsch, A; Busse, R; Vanin, A

1991-11-15

166

Ratio Analysis NMR Spectroscopy (RANSY) for Selective Metabolite Identification in Complex Samples  

PubMed Central

Metabolite identification in the complex NMR spectra of biological samples is a challenging task due to significant spectral overlap and limited signal to noise. In this study we present a new approach, RANSY (Ratio Analysis NMR Spectroscopy), which identifies all the peaks of a specific metabolite based on the ratios of peak heights or integrals. We show that the spectrum for an individual metabolite can be generated by exploiting the fact that the peak ratios for any metabolite in the NMR spectrum are fixed and proportional to the relative numbers of magnetically distinct protons. When the peak ratios are divided by their coefficient of variations derived from a set of NMR spectra, the generation of an individual metabolite spectrum is enabled. We first tested the performance of this approach using one-dimensional (1D) and two-dimensional (2D) NMR data of mixtures of synthetic analogues of common body fluid metabolites. Subsequently, the method was applied to 1H NMR spectra of blood serum samples to demonstrate the selective identification of a number of metabolites. The RANSY approach, which does not need any additional NMR experiments for spectral simplification, is easy to perform and has the potential to aid in the identification of unknown metabolites using 1D or 2D NMR spectra in virtually any complex biological mixture.

Wei, Siwei; Zhang, Jian; Liu, Lingyan; Ye, Tao; Nagana Gowda, G. A.; Tayyari, Fariba; Raftery, Daniel

2011-01-01

167

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

168

From Molecular Structure to Global Processes : NMR Spectroscopy in Analytical/Environmental Chemistry  

NASA Astrophysics Data System (ADS)

NMR Spectroscopy is arguably the most powerful tool to elucidate structure and probe molecular interactions. A range of NMR approaches will be introduced with emphasis on addressing and understanding structure and reactivity of soil organic matter at the molecular level. The presentation will be split into three main sections. The first section will look at evidence from advanced NMR based approaches that when considered synergistically describes the major structural components in soil organic matter. Multidimensional NMR spectroscopy (1-3D NMR), automated pattern matching, spectral simulations, diffusion NMR and hybrid-diffusion NMR will be introduced in context of molecular structure. Finally the structural components in soil will be contrasted to those found in aquatic dissolved organic matter. Secondly molecular interactions of natural organic matter will be considered. Advanced structural studies have provided detailed spectral assignments which in turn permit the reactivity of various soil components to be elucidated. Aggregation and self-association of soil and dissolved organic matter will be discussed along with the structural components likely responsible for aggregation/colloid formation. Interactions of soil organic matter with anthropogenic chemicals will also be considered and NMR techniques based on "Saturation Transfer Difference" introduced. These techniques are extremely powerful and can be used to both; describe mechanistically how anthropogenic chemicals sorb to whole soils and identify the structural components (lignin, protein, cellulose, etc..) that are responsible for the binding/sorption in soil. In the last section, the "big questions" and challenges facing the field will be considered along with some novel experimental NMR based approaches that should, in future, assist in providing answers to these questions.

Simpson, A.

2009-04-01

169

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

Microsoft Academic Search

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

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

2006-01-01

170

Application of high-resolution magic-angle spinning NMR spectroscopy to define the cell uptake of MRI contrast agents.  

PubMed

A new method, based on proton high-resolution magic-angle spinning ((1)H HR-MAS) NMR spectroscopy, has been employed to study the cell uptake of magnetic resonance imaging contrast agents (MRI-CAs). The method was tested on human red blood cells (HRBC) and white blood cells (HWBC) by using three gadolinium complexes, widely used in diagnostics, Gd-BOPTA, Gd-DTPA, and Gd-DOTA, and the analogous complexes obtained by replacing Gd(III) with Dy(III), Nd(III), and Tb(III) (i.e., complexes isostructural to the ones of gadolinium but acting as shift agents). The method is based on the evaluation of the magnetic effects, line broadening, or induced lanthanide shift (LIS) caused by these complexes on NMR signals of intra- and extracellular water. Since magnetic effects are directly linked to permeability, this method is direct. In all the tests, these magnetic effects were detected for the extracellular water signal only, providing a direct proof that these complexes are not able to cross the cell membrane. Line broadening effects (i.e., the use of gadolinium complexes) only allow qualitative evaluations. On the contrary, LIS effects can be measured with high precision and they can be related to the concentration of the paramagnetic species in the cellular compartments. This is possible because the HR-MAS technique provides the complete elimination of bulk magnetic susceptibility (BMS) shift and the differentiation of extra- and intracellular water signals. Thus with this method, the rapid quantification of the MRI-CA amount inside and outside the cells is actually feasible. PMID:12165257

Calabi, Luisella; Alfieri, Goffredo; Biondi, Luca; De Miranda, Mario; Paleari, Lino; Ghelli, Stefano

2002-06-01

171

Solid-state NMR spectroscopy of membrane-associated myelin basic protein--conformation and dynamics of an immunodominant epitope.  

PubMed

Myelin basic protein (MBP) maintains the tight multilamellar compaction of the myelin sheath in the central nervous system through peripheral binding of adjacent lipid bilayers of oligodendrocytes. Myelin instability in multiple sclerosis (MS) is associated with the loss of positive charge in MBP as a result of posttranslational enzymatic deimination. A highly-conserved central membrane-binding fragment (murine N81-PVVHFFKNIVTPRTPPP-S99, identical to human N83-S101) represents a primary immunodominant epitope in MS. Previous low-resolution electron paramagnetic resonance measurements on the V83-T92 fragment, with Cys-mutations and spin-labeling that scanned the epitope, were consistent with it being a membrane-associated amphipathic alpha-helix. Pseudodeimination at several sites throughout the protein, all distal to the central segment, disrupted the alpha-helix at its amino-terminus and exposed it to proteases, representing a potential mechanism in the autoimmune pathogenesis of MS. Here, we have used magic-angle spinning solid-state NMR spectroscopy to characterize more precisely the molecular conformation and dynamics of this central immunodominant epitope of MBP in a lipid milieu, without Cys-substitution. Our solid-state NMR measurements have revealed that the alpha-helix present within the immunodominant epitope is shorter than originally modeled, and is independent of the pseudodeimination, highlighting the importance of the local hydrophobic effects in helix formation and stability. The main effect of pseudodeimination is to cause the cytoplasmic exposure of the fragment, potentially making it more accessible to proteolysis. These results are the first, to our knowledge, to provide atomic-level detail of a membrane-anchoring segment of MBP, and direct evidence of decreased MBP-membrane interaction after posttranslational modification. PMID:20713009

Ahmed, Mumdooh A M; Bamm, Vladimir V; Harauz, George; Ladizhansky, Vladimir

2010-08-01

172

PHOSPHINE SULPHIDES AND THEIR COMPLEXES WITH METALS: C NMR SPECTROSCOPY  

Microsoft Academic Search

C nuclear magnetic resonance data have been recorded for twenty-two tertiary phosphine sulphides. A discussion of the variation in chemical shifts and P?C coupling constants and a comparison of the data with some analogous phosphine oxides are included. The results are examined with respect to a description of the phosphoryl and thiophosphoryl bonds. The C and H nmr and infra-red

S. Roderick Postle

1977-01-01

173

Metabolomic investigations of American oysters using H-NMR spectroscopy.  

PubMed

The Eastern oyster (Crassostrea virginica) is a useful, robust model marine organism for tissue metabolism studies. Its relatively few organs are easily delineated and there is sufficient understanding of their functions based on classical assays to support interpretation of advanced spectroscopic approaches. Here we apply high-resolution proton nuclear magnetic resonance ((1)H NMR)-based metabolomic analysis to C. virginica to investigate the differences in the metabolic profile of different organ groups, and magnetic resonance imaging (MRI) to non-invasively identify the well separated organs. Metabolites were identified in perchloric acid extracts of three portions of the oyster containing: (1) adductor muscle, (2) stomach and digestive gland, and (3) mantle and gills. Osmolytes dominated the metabolome in all three organ blocks with decreasing concentration as follows: betaine > taurine > proline > glycine > ß-alanine > hypotaurine. Mitochondrial metabolism appeared most pronounced in the adductor muscle with elevated levels of carnitine facilitating ß-oxidation, and ATP, and phosphoarginine synthesis, while glycogen was elevated in the mantle/gills and stomach/digestive gland. A biochemical schematic is presented that relates metabolites to biochemical pathways correlated with physiological organ functions. This study identifies metabolites and corresponding (1)H NMR peak assignments for future NMR-based metabolomic studies in oysters. PMID:21116407

Tikunov, Andrey P; Johnson, Christopher B; Lee, Haakil; Stoskopf, Michael K; Macdonald, Jeffrey M

2010-10-08

174

Sensitivity enhancement of double quantum NMR spectroscopy by modified CPMG  

NASA Astrophysics Data System (ADS)

A modified Carr-Purcell-Meiboom-Gill (CPMG) sequence for sensitivity enhancement of dipolar coupled homonuclear spin pairs in static solid-state NMR is presented. The modified CPMG block uses the Hahn-solid-Hahn echo as basic element of the CPMG echo train to refocus the homonuclear dipolar coupling and chemical shift anisotropy. The new CPMG sequence is dubbed as Hahn-solid-Hahn Carr-Purcell-Meiboom-Gill (HSHCPMG). We demonstrate a gain in signal to noise ratio of approximately 4.2 using HSHCPMG sequence in double quantum filtered CP experiment for 5%-13C2-15N-glycine. The resulting gain in sensitivity in the spikelet spectrum does not compromise the anisotropic information that is available from static NMR lineshapes. As an example, relative orientation angles of chemical shift anisotropy tensors for the alpha and carbonyl carbons in glycine are determined from the 2D DOQSY experiment recorded with the HSHCPMG block in the acquisition dimension. The resultant relative orientation angles of the two CSA tensors are compared to those obtained from 2D DOQSY experiment acquired without sensitivity enhancement as well as to the data as available from single crystal NMR experiments.

Gowda, Chandrakala M.; Agarwal, Vipin; Kentgens, Arno P. M.

2012-10-01

175

Novel solution conformation of DNA observed in d(GAATTCGAATTC) by two-dimensional NMR spectroscopy  

Microsoft Academic Search

Resonance assignments of nonexchangeable base and sugar protons of the self-complementary dodecanucleotide d(GAATTCGAATTC) have been obtained by using the two-dimensional Fourier transform NMR methods correlated spectroscopy and nuclear Overhauser effect spectroscopy. Conformational details about the sugar pucker, the glycosidic dihedral angle, and the overall secondary structure of the molecule has been derived from the relative intensities of cross peaks in

K. V. R. Chary; R. V. Hosur; Girjesh Govil; T. Zu-kun; H. T. Miles

1987-01-01

176

Solid-State NMR Investigation of Paramagnetic Nylon-6 Clay Nanocomposites. 1. Crystallinity, Morphology, and the Direct Influence of Fe3+ on Nuclear Spins  

NSDL National Science Digital Library

Several exfoliated nylon-6/clay nanocomposites (NnCâs) were investigated and compared with pure nylon-6 using solid-state NMR, both proton and 13C. NnCâs had nominally 5 mass % clay and were generated both by blending and by in situ polymerization (IsP). Most of the studied NnCâs contained layered, naturally occurring montmorillonite clays having nonstoichiometric amounts of nonexchangeable Mg2+ and Fe3+ ions that substitute into octahedral Al3+ sites along the midplane of the 1-nm-thick clay layers. The Fe3+ ions impart a useful paramagnetism to the clay. Each Mg2+ ion leaves an embedded negative charge that must be neutralized with some cation at the surface of the clay. All clays were initially treated with a cationic so-called organic modifier (OM), often a substituted ammonium ion, which increases the clay layer spacing, attaching ionically to the surface of the clay layers. Clay is found to promote growth of the ç-crystalline phase of nylon-6 for both blended and IsP NnCâs; R-crystallites are characteristic of the pure nylon-6. Stability of the ç-phase to annealing at 214 °C was investigated. Conversion of ç- to R-crystallinity during annealing was minimal, except for an injection-molded IsP NnC, which had been exposed to a temperature of 295 °C during molding. This high processing temperature produced an irreversible change. An attempt was made to understand, at least qualitatively, the nature of the spectral density of magnetic fluctuations associated with the paramagnetic Fe3+ sites in the clay. For this purpose, we looked directly at the influence of Fe3+ on the 13C and proton observables in organically modified clays (OMC). We agree with other investigators that the spectral density of paramagnetic fluctuations at the surface of the clay is determined mainly by spin-exchange interactions between Fe3+ sites; thus, the spectral density can be altered by changing the Fe3+ concentration. Moreover, we find that the spectral density is very wide, having strong contributions all the way from mid-kHz fluctuations to MHz fluctuations near the proton Larmor frequencies. Significant variations in the R/ç ratio were also observed in the injection-molded disk, which reflect either a processing-induced heterogeneity in clay dispersion or a significant variation in cooling history from region to region. Proton spin diffusion and multiple-pulse methods were utilized to compare morphologies for a diamagnetic NnC and nylon-6 with the same thermal histories. Long spacing, crystallinity, and the mobility of the noncrystalline nylon-6 segments are very similar for NnCâs and nylon-6.

Vanderhart, D. L.; Asano, A.; Gilman, J. W.

2001-01-01

177

Probing oxidative degradation in polymers using {sup 17}O NMR spectroscopy  

SciTech Connect

Understanding the mechanism of oxidative degradation remains an important goal in being able to predict the aging process in polymer materials. Nuclear magnetic resonance (NMR) spectroscopy has previously been utilized to investigate polymer degradation, including both proton ({sup 1}H) and carbon ({sup 13}C) studies. These previous NMR studies, as well as other spectroscopic investigations, are complicated by the almost overwhelming signal arising from the native undegraded polymer. This makes the identification and quantification of degradation species at small concentrations difficult. In this note we discuss recent investigation into the use of oxygen ({sup 17}O) NMR spectroscopy to probe the oxidative degradation process in polymers at a molecular level. Due to the low natural abundance (0.037%) and a nuclear spin of I=5/2 possessing an appreciable quadrupolar moment, the use of {sup 17}O NMR in polymer investigations has been limited. By utilizing synthetically enriched oxygen gas during the accelerated aging process, both the difficulties of low natural abundance and background interference signals are eliminated. For enriched samples {sup 17}O NMR spectra now provide a unique probe since all of the observed NMR resonances are the direct result of oxidative degradation.

Alam, T.M.; Click, C.A.; Assink, R.A.

1997-09-01

178

Protein folding and unfolding studied at atomic resolution by fast two-dimensional NMR spectroscopy.  

PubMed

Atom-resolved real-time studies of kinetic processes in proteins have been hampered in the past by the lack of experimental techniques that yield sufficient temporal and atomic resolution. Here we present band-selective optimized flip-angle short transient (SOFAST) real-time 2D NMR spectroscopy, a method that allows simultaneous observation of reaction kinetics for a large number of nuclear sites along the polypeptide chain of a protein with an unprecedented time resolution of a few seconds. SOFAST real-time 2D NMR spectroscopy combines fast NMR data acquisition techniques with rapid sample mixing inside the NMR magnet to initiate the kinetic event. We demonstrate the use of SOFAST real-time 2D NMR to monitor the conformational transition of alpha-lactalbumin from a molten globular to the native state for a large number of amide sites along the polypeptide chain. The kinetic behavior observed for the disappearance of the molten globule and the appearance of the native state is monoexponential and uniform along the polypeptide chain. This observation confirms previous findings that a single transition state ensemble controls folding of alpha-lactalbumin from the molten globule to the native state. In a second application, the spontaneous unfolding of native ubiquitin under nondenaturing conditions is characterized by amide hydrogen exchange rate constants measured at high pH by using SOFAST real-time 2D NMR. Our data reveal that ubiquitin unfolds in a gradual manner with distinct unfolding regimes. PMID:17592113

Schanda, Paul; Forge, Vincent; Brutscher, Bernhard

2007-06-25

179

Protein folding and unfolding studied at atomic resolution by fast two-dimensional NMR spectroscopy  

PubMed Central

Atom-resolved real-time studies of kinetic processes in proteins have been hampered in the past by the lack of experimental techniques that yield sufficient temporal and atomic resolution. Here we present band-selective optimized flip-angle short transient (SOFAST) real-time 2D NMR spectroscopy, a method that allows simultaneous observation of reaction kinetics for a large number of nuclear sites along the polypeptide chain of a protein with an unprecedented time resolution of a few seconds. SOFAST real-time 2D NMR spectroscopy combines fast NMR data acquisition techniques with rapid sample mixing inside the NMR magnet to initiate the kinetic event. We demonstrate the use of SOFAST real-time 2D NMR to monitor the conformational transition of ?-lactalbumin from a molten globular to the native state for a large number of amide sites along the polypeptide chain. The kinetic behavior observed for the disappearance of the molten globule and the appearance of the native state is monoexponential and uniform along the polypeptide chain. This observation confirms previous findings that a single transition state ensemble controls folding of ?-lactalbumin from the molten globule to the native state. In a second application, the spontaneous unfolding of native ubiquitin under nondenaturing conditions is characterized by amide hydrogen exchange rate constants measured at high pH by using SOFAST real-time 2D NMR. Our data reveal that ubiquitin unfolds in a gradual manner with distinct unfolding regimes.

Schanda, Paul; Forge, Vincent; Brutscher, Bernhard

2007-01-01

180

Effect of pravastatin on LDL particle concentration as determined by NMR spectroscopy: a substudy of a randomized placebo controlled trial  

Microsoft Academic Search

Aim Recent data suggests that LDL particle concentration, as determined by Nuclear Magnetic Resonance (NMR) spectroscopy, may be associated with cardiovascular risk. We sought to determine the effect of randomization to pravastatin therapy on LDL particle concentration-NMR, among a primary prevention population. Methods and results LDL particle concentration-NMR, LDL size-NMR, and standard chemical lipid parameters were measured at baseline and

Gavin J. Blake; Michelle A. Albert; Nader Rifai; Paul M. Ridker

181

High-Resolution NMR Spectroscopy: An Alternative Fast Tool for Qualitative and Quantitative Analysis of Diacylglycerol (DAG) Oil  

Microsoft Academic Search

Multinuclear (1H, 13C, 31P) and multidimensional NMR spectroscopy was employed for the analysis of diacylglycerol (DAG) oil and the quantification\\u000a of its acylglycerols and acyl chains composition. A number of gradient selected two dimensional NMR techniques (TOCSY, HSQC-DEPT,\\u000a HSQC-TOCSY, and HMBC) facilitated the assignment of the complex one dimensional 1H- and 13C-NMR spectra. In several cases, the aforementioned 2D-NMR techniques

Emmanuel Hatzakis; Alexia Agiomyrgianaki; Sarantos Kostidis; Photis Dais

182

Nuclear resonance vibrational spectroscopy and electron paramagnetic resonance spectroscopy of 57Fe-enriched [FeFe] hydrogenase indicate stepwise assembly of the H-cluster.  

PubMed

The [FeFe] hydrogenase from Clostridium pasteurianum (CpI) harbors four Fe-S clusters that facilitate the transfer of an electron to the H-cluster, a ligand-coordinated six-iron prosthetic group that catalyzes the redox interconversion of protons and H(2). Here, we have used (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to study the iron centers in CpI, and we compare our data to that for a [4Fe-4S] ferredoxin as well as a model complex resembling the [2Fe](H) catalytic domain of the H-cluster. To enrich the hydrogenase with (57)Fe nuclei, we used cell-free methods to post-translationally mature the enzyme. Specifically, inactive CpI apoprotein with (56)Fe-labeled Fe-S clusters was activated in vitro using (57)Fe-enriched maturation proteins. This approach enabled us to selectively label the [2Fe](H) subcluster with (57)Fe, which NRVS confirms by detecting (57)Fe-CO and (57)Fe-CN normal modes from the H-cluster nonprotein ligands. The NRVS and iron quantification results also suggest that the hydrogenase contains a second (57)Fe-S cluster. Electron paramagnetic resonance (EPR) spectroscopy indicates that this (57)Fe-enriched metal center is not the [4Fe-4S](H) subcluster of the H-cluster. This finding demonstrates that the CpI hydrogenase retained an (56)Fe-enriched [4Fe-4S](H) cluster during in vitro maturation, providing unambiguous evidence of stepwise assembly of the H-cluster. In addition, this work represents the first NRVS characterization of [FeFe] hydrogenases. PMID:23249091

Kuchenreuther, Jon M; Guo, Yisong; Wang, Hongxin; Myers, William K; George, Simon J; Boyke, Christine A; Yoda, Yoshitaka; Alp, E Ercan; Zhao, Jiyong; Britt, R David; Swartz, James R; Cramer, Stephen P

2013-01-24

183

Relaxation filtered hyperfine (REFINE) spectroscopy: a novel tool for studying overlapping biological electron paramagnetic resonance signals applied to mitochondrial complex I.  

PubMed

A simple strategy to separate overlapping electron paramagnetic resonance (EPR) signals in biological systems is presented. Pulsed EPR methods (inversion- and saturation-recovery) allow the determination of the T(1) spin-lattice relaxation times of paramagnetic centers. T(1) may vary by several orders of magnitude depending on the species under investigation. These variations can be employed to study selectively individual species from a spectrum that results from an overlap of two species using an inversion-recovery filtered (IRf) pulsed EPR technique. The feasibility of such an IRf field-swept technique is demonstrated on model compounds (alpha,gamma-bisphenylene-beta-phenylallyl-benzolate, BDPA, and 2,2,6,6-tetramethyl-piperidine-1-oxyl, TEMPO) and a simple strategy for the successful analysis of such mixtures is presented. Complex I is a multisubunit membrane protein of the respiratory chain containing several iron-sulfur (FeS) centers, which are observable with EPR spectroscopy. It is not possible to investigate the functionally important FeS cluster N2 separately because this EPR signal always overlaps with the other FeS signals. This cluster can be studied selectively using the IRf field-swept technique and its EPR spectrum is in excellent agreement with previous cw-EPR data from the literature. In addition, the possibility to separate the hyperfine spectra of two spectrally overlapping paramagnetic species is demonstrated by applying this relaxation filter together with hyperfine spectroscopy (REFINE). For the first time, the application of this filter to a three-pulse electron spin-echo envelope modulation (ESEEM) pulse sequence is demonstrated to selectively observe hyperfine spectra on a system containing two paramagnetic species. Finally, REFINE is used to assign the observed nitrogen modulation in complex I to an individual iron-sulfur cluster. PMID:15049704

Maly, Thorsten; MacMillan, Fraser; Zwicker, Klaus; Kashani-Poor, Noushin; Brandt, Ulrich; Prisner, Thomas F

2004-04-01

184

The efficiency of DPPH as a polarising agent for DNP-NMR spectroscopy  

PubMed Central

The free radical 2,2-diphenyl-1-pycrylhydrazyl (DPPH) was tested as a polarising agent for fast dissolution dynamic nuclear polarisation (DNP) NMR spectroscopy. DPPH was found to be reasonably soluble in sulfolane and the optimum concentration for DNP is 20–40 mM depending upon whether short polarisation times or the maximum signal intensity is needed. W-band ESR measurements revealed that the ESR linewidth D of DPPH is intermediate between that of BDPA and 4-oxo-TEMPO. Several thousand-fold NMR signal enhancements in the liquid-state were achieved for 13C, 15N, 89Y, and 109Ag compounds, demonstrating that DPPH can be added to the list of polarising agents for DNP-NMR spectroscopy. Furthermore, the hydrophobic DPPH free radical can be easily filtered out from the dissolution liquid when water is used as the dissolution solvent.

Lumata, Lloyd; Merritt, Matthew; Khemtong, Chalermchai; Ratnakar, S. James; van Tol, Johan; Yu, Lu; Song, Likai

2012-01-01

185

In situ measurement of molecular diffusion during catalytic reaction by pulsed-field gradient NMR spectroscopy  

SciTech Connect

Pulsed-field gradient (PFG) NMR spectroscopy is applied to study the intracrystalline diffusivity of the reactant and product molecules during the conversion of cyclopropane to propene in Zeolite X. The diffusivities are found to be large enough that any influence of intracrystalline diffusion on the overall reaction in flow reactors may be excluded.

Hong, Y.; Kaerger, J.; Hunger, B. (Univ. Leipzig, Linnestrasse (Germany)); Feoktistova, N.N.; Zhdanov, S.P. (Grebenshchikov Inst., Saint Petersburg (Russian Federation))

1992-09-01

186

Solution structure of nucleic acids by nuclear magnetic resonance (NMR) spectroscopy  

Microsoft Academic Search

Evidence that dehydration effects and crystal packing effects can alter the global and local structure of nucleic acids in the crystalline state has led to attempts to determine their structure directly in solution. Parameterization of the non-bonded force fields for theoretical methods such as energy minimization and molecular dynamics calculations is incomplete and NMR spectroscopy appears to be the most

1992-01-01

187

Structure Determination of Unknown Organic Liquids Using NMR and IR Spectroscopy: A General Chemistry Laboratory  

ERIC Educational Resources Information Center

|This experiment introduced general chemistry students to the basic concepts of organic structures and to the power of spectroscopic methods for structure determination. Students employed a combination of IR and NMR spectroscopy to perform de novo structure determination of unknown alcohols, without being provided with a list of possible…

Pavel, John T.; Hyde, Erin C.; Bruch, Martha D.

2012-01-01

188

NMR imaging and spectroscopy of the mammalian central nervous system after heavy ion radiation  

SciTech Connect

NMR imaging, NMR spectroscopic, and histopathologic techniques were used to study the proton relaxation time and related biochemical changes in the central nervous system after helium beam in vivo irradiation of the rodent brain. The spectroscopic observations reported in this dissertation were made possible by development of methods for measuring the NMR parameters of the rodent brain in vivo and in vitro. The methods include (1) depth selective spectroscopy using an optimization of rf pulse energy based on a priori knowledge of N-acetyl aspartate and lipid spectra of the normal brain, (2) phase-encoded proton spectroscopy of the living rodent using a surface coil, and (3) dual aqueous and organic tissue extraction technique for spectroscopy. Radiation induced increases were observed in lipid and p-choline peaks of the proton spectrum, in vivo. Proton NMR spectroscopy measurements on brain extracts (aqueous and organic solvents) were made to observe chemical changes that could not be seen in vivo. Radiation-induced changes were observed in lactate, GABA, glutamate, and p-choline peak areas of the aqueous fraction spectra. In the organic fraction, decreases were observed in peak area ratios of the terminal-methyl peaks, the N-methyl groups of choline, and at a peak at 2.84 ppM (phosphatidyl ethanolamine and phosphatidyl serine resonances) relative to TMS. With histology and Evans blue injections, blood-brain barrier alternations were seen as early as 4 days after irradiation. 83 references, 53 figures.

Richards, T.

1984-09-01

189

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

Microsoft Academic Search

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

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

2006-01-01

190

Lanthanide and actinide speciation in molten fluorides: A structural approach by NMR and EXAFS spectroscopies  

Microsoft Academic Search

The objective of this paper is to describe the local structure in fluoride melts of nuclear interest. Our experimental approach combines NMR and EXAFS spectroscopies both sensitive to the microstructure of solid and liquid materials. These techniques allow identifying the complex formation in molten media. Thanks to the development of specific cells adapted to molten fluorides up to 1300°C, we

Catherine Bessada; Aydar Rakhmatullin; Anne-Laure Rollet; Didier Zanghi

2007-01-01

191

NATURAL ABUNDANCE 13C NMR SPECTROSCOPY OF DOUBLE-STRANDED DNA  

EPA Science Inventory

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

192

USING HIGH-RESOLUTION SOLUTION-STATE NMR SPECTROSCOPY TO INVESTIGATE PMDI REACTIONS WITH WOOD  

Technology Transfer Automated Retrieval System (TEKTRAN)

Solution-state NMR spectroscopy provides a powerful tool for understanding the formation of chemical bonds between wood components and adhesives. Finely ground cell wall (CW) material fully dissolves in a solvent system containing dimethylsulfoxide (DMSO-d6) and N-methyl¬imidazole (NMI-d6), keeping ...

193

Conceptual Design Study of a Novel Gyrotron for NMR\\/DNP Spectroscopy  

Microsoft Academic Search

In this paper we present some initial results from a conceptual design study focused on the development of a novel frequency tunable gyrotron for nuclear magnetic resonance (NMR) spectroscopy with signal enhancement based on the utilization of high field radiation and dynamic nuclear polarization (DNP) technique. The first variants of both the electron optical system and the resonant cavity which

S. Sabchevski; T. Idehara; S. Mitsudo; T. Fujiwara

2005-01-01

194

PCB/polymer based micro-fluidic system for NMR spectroscopy for nanoliters sample volume.  

PubMed

In this work, we report on the realization of an innovating micro system for NMR spectroscopy on small sample volume (30-100 nL). We propose a micro system based on Printed Circuit Board (PCB) technology for the NMR probe associated to a micro fluidic system made with polymer (COC). The comparison of several samples during the same NMR experiments could provide more precise information. In that context, we have realized a micro-fluidic system with two cavities, each cavity presenting a volume of 37 nl. The fabrication process is described, and first results are reported. The tight sealing of the micro-fluidic system has been demonstrated and preliminary NMR experiment results are presented. PMID:18002618

Pasquet, Guillaume; Chateaux, Jean-François; Deman, Anne-Laure; Fenet, Bernard; Morin, Pierre

2007-01-01

195

Virtual chromatographic resolution enhancement in cryoflow LC-NMR experiments via statistical total correlation spectroscopy.  

PubMed

A new approach to enhancing information recovery from cryogenic probe "on-flow" LC-NMR spectroscopic analyses of complex biological mixtures is demonstrated using a variation on the statistical total correlation spectroscopy (STOCSY) method. Cryoflow probe technology enables sensitive and efficient NMR detection of metabolites on-flow, and the rapid spectral scanning allows multiple spectra to be collected over chromatographic peaks containing several species with similar, but nonidentical, retention times. This enables 1H NMR signal connectivities between close-eluting metabolites to be identified resulting in a "virtual" chromatographic resolution enhancement visualized directly in the NMR spectral projection. We demonstrate the applicability of the approach for structure assignment of drug and endogenous metabolites in urine. This approach is of wide general applicability to any complex mixture analysis problem involving chromatographic peak overlap and with particular application in metabolomics and metabonomics. PMID:17394288

Cloarec, Olivier; Campbell, Alison; Tseng, Li-Hong; Braumann, Ulrich; Spraul, Manfred; Scarfe, Graeme; Weaver, Richard; Nicholson, Jeremy K

2007-03-30

196

Isolated cardiomyocytes in conjunction with NMR spectroscopy techniques to study metabolism and ion flux.  

PubMed

To distinguish cellular from vascular responses to physiological and pathophysiological stimuli, we developed methods to perform NMR spectroscopy on isolated ventricular cardiomyocytes. Isolated adult rat cardiomyocytes, placed in agarose beads and superfused with phosphate-free buffer (Media 199 (GIBCO 400-1100) gassed with 95% O2, 5% CO2), were used to evaluate a variety of cellular processes during different pharmacological and physiological interventions. Bioenergetic function was monitored with 31P NMR. Intermediary metabolism, gluconeogenesis, and glycolysis were monitored with 13C NMR. Sodium flux was monitored with 23Na NMR. Calcium flux was monitored with 19F NMR in conjunction with an intracellular calcium-chelating agent, 5F-1,2-bis(2-amino-phenoxy)ethane-N,N,N',N'-tetraacetic acid. Creatine kinase kinetics (forward rate constant (Kf) and flux of phosphocreatine to ATP) were estimated with 31P NMR saturation transfer data. Various combinations of NMR parameters were monitored simultaneously so that the interaction of metabolism and ion flux could be evaluated. We have demonstrated that it is possible to simultaneously monitor a variety of cellular processes in intact heart cells in real time, without the confounding influences of perfusion, contractile function, and extrinsic blood-borne neurohumoral agents. This model will be useful for longitudinal studies of myocyte metabolism and ion flux. PMID:1639780

Osbakken, M; Ivanics, T; Zhang, D; Mitra, R; Blum, H

1992-08-01

197

Use of NMR Saturation Transfer Difference Spectroscopy to Study Ligand Binding to Membrane Proteins  

PubMed Central

Detection of weak ligand binding to membrane-spanning proteins, such as receptor proteins at low physiological concentrations, poses serious experimental challenges. Saturation transfer difference nuclear magnetic resonance (STD-NMR) spectroscopy offers an excellent way to surmount these problems. As the name suggests, magnetization transferred from the receptor to its bound ligand is measured by directly observing NMR signals from the ligand itself. Low-power irradiation is applied to a 1H NMR spectral region containing protein signals but no ligand signals. This irradiation spreads quickly throughout the membrane protein by the process of spin diffusion and saturates all protein 1H NMR signals. 1H NMR signals from a ligand bound transiently to the membrane protein become saturated and, upon dissociation, serve to decrease the intensity of the 1H NMR signals measured from the pool of free ligand. The experiment is repeated with the irradiation pulse placed outside the spectral region of protein and ligand, a condition that does not lead to saturation transfer to the ligand. The two resulting spectra are subtracted to yield the difference spectrum. As an illustration of the methodology, we review here STD-NMR experiments designed to investigate binding of ligands to the human sweet taste receptor, a member of the large family of G-protein-coupled receptors. Sweetener molecules bind to the sweet receptor with low affinity but high specificity and lead to a variety of physiological responses.

Venkitakrishnan, Rani Parvathy; Benard, Outhiriaradjou; Max, Marianna; Markley, John L.

2013-01-01

198

Automated sample preparation station for studying self-diffusion in porous solids with NMR spectroscopy  

SciTech Connect

In studies of gas diffusion in porous solids with nuclear magnetic resonance (NMR) spectroscopy the sample preparation procedure becomes very important. An apparatus is presented here that pretreats the sample ex situ and accurately sets the desired pressure and temperature within the NMR tube prior to its introduction in the spectrometer. The gas manifold that supplies the NMR tube is also connected to a microbalance containing another portion of the same sample, which is kept at the same temperature as the sample in the NMR tube. This arrangement permits the simultaneous measurement of the adsorption loading on the sample, which is required for the interpretation of the NMR diffusion experiments. Furthermore, to ensure a good seal of the NMR tube, a hybrid valve design composed of titanium, a Teflon registered seat, and Kalrez registered O-rings is utilized. A computer controlled algorithm ensures the accuracy and reproducibility of all the procedures, enabling the NMR diffusion experiments to be performed at well controlled conditions of pressure, temperature, and amount of gas adsorbed on the porous sample.

Hedin, Niklas; DeMartin, Gregory J.; Reyes, Sebastian C. [Corporate Strategic Research, ExxonMobil Research and Engineering Company, 1545 Route 22 East, Annandale, New Jersey 08801 (United States)

2006-03-15

199

Positional isotope exchange studies on enzyme using NMR spectroscopy  

SciTech Connect

The isotopically enriched compounds, /sup 18/O-..beta..,..gamma..-ATP and /sup 18/O bridge-labeled pyrophosphate, synthesized previously in this laboratory, were used to investigate and measure the exchange vs. turnover of substrates and products from their central complexes in four selected enzyme systems. Using hi-field /sup 31/P NMR, we were able to differentiate between /sup 18/O labeled in the bridge vs. the non-bridge positions by virtue of the isotope shift upon the phosphorus nuclei. The bridge to non-bridge scrambling of the label was quantitated and the exchange vs. turnover ratios under a variety of conditions was determined. Using the substrate inhibitor carboxycreatinine, PIX experiments with /sup 18/O-..beta..,..gamma..-ATP and creatine kinase were conducted. It was shown that carboxycreatinine and creatine kinase promoted exchange of the /sup 18/O label as determined by NMR. We have concluded that carboxycreatinine is either a substrate that catalyzes very slow turnover or it catalyzes exchange by a dissociative (SN/sub 1//sub P/) type of mechanism

Matsunaga, T.O.

1987-01-01

200

Detection of nitric oxide and superoxide radical anion by electron paramagnetic resonance spectroscopy from cells using spin traps.  

PubMed

Reactive nitrogen/oxygen species (ROS/RNS) at low concentrations play an important role in regulating cell function, signaling, and immune response but in unregulated concentrations are detrimental to cell viability. While living systems have evolved with endogenous and dietary antioxidant defense mechanisms to regulate ROS generation, ROS are produced continuously as natural by-products of normal metabolism of oxygen and can cause oxidative damage to biomolecules resulting in loss of protein function, DNA cleavage, or lipid peroxidation, and ultimately to oxidative stress leading to cell injury or death. Superoxide radical anion (O2•-) is the major precursor of some of the most highly oxidizing species known to exist in biological systems such as peroxynitrite and hydroxyl radical. The generation of O2•- signals the first sign of oxidative burst, and therefore, its detection and/or sequestration in biological systems is important. In this demonstration, O2•- was generated from polymorphonuclear neutrophils (PMNs). Through chemotactic stimulation with phorbol-12-myristate-13-acetate (PMA), PMN generates O2•- via activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Nitric oxide (NO) synthase which comes in three isoforms, as inducible-, neuronal- and endothelial-NOS, or iNOS, nNOS or eNOS, respectively, catalyzes the conversion of L- arginine to L-citrulline, using NADPH to produce NO. Here, we generated NO from endothelial cells. Under oxidative stress conditions, eNOS for example can switch from producing NO to O2•- in a process called uncoupling, which is believed to be caused by oxidation of heme or the co-factor, tetrahydrobiopterin (BH4). There are only few reliable methods for the detection of free radicals in biological systems but are limited by specificity and sensitivity. Spin trapping is commonly used for the identification of free radicals and involves the addition reaction of a radical to a spin trap forming a persistent spin adduct which can be detected by electron paramagnetic resonance (EPR) spectroscopy. The various radical adducts exhibit distinctive spectrum which can be used to identify the radicals being generated and can provide a wealth of information about the nature and kinetics of radical production. The cyclic nitrones, 5,5-dimethyl-pyrroline-N-oxide, DMPO, the phosphoryl-substituted DEPMPO, and the ester-substituted, EMPO and BMPO, have been widely employed as spin traps--the latter spin traps exhibiting longer half-lives for O2•- adduct. Iron (II)-N-methyl-D-glucamine dithiocarbamate, Fe(MGD)2 is commonly used to trap NO due to high rate of adduct formation and the high stability of the spin adduct. PMID:22929836

Gopalakrishnan, Bhavani; Nash, Kevin M; Velayutham, Murugesan; Villamena, Frederick A

2012-08-18

201

Application of electron paramagnetic resonance spectroscopy to comparative examination of different groups of free radicals in thermal injuries treated with propolis and silver sulphadiazine.  

PubMed

Different groups of free radicals expressed in burn wounds treated with propolis and silver sulphadiazine were examined. The thermal effect forms major types of free radicals in a wound because of the breaking of chemical bonds. Free radicals, located in the heated skin, were tested after 21 days of treating by these two substances. The aim of this work was to find the method for determination of types and concentrations of different groups of free radicals in wound after high temperature impact during burning. The effects of the therapy by propolis and silver sulphadiazine on free radicals were studied. Since the chemical methods of free radicals studies are destructive, the usefulness of the electron paramagnetic resonance spectroscopy was tested in this work. The electron paramagnetic resonance spectra measured with the microwave power of 2.2?mW were numerically fitted by theoretical curves of Gaussian and Lorentzian shapes. The experimental electron paramagnetic resonance spectra of tissue samples are best fitted by the sum of one Gauss and two Lorentz lines. An innovatory numerical procedure of spectroscopic skin analysis was presented. It is very useful in the alternative medicine studies. PMID:23762162

Olczyk, Pawel; Ramos, Pawel; Bernas, Marcin; Komosinska-Vassev, Katarzyna; Stojko, Jerzy; Pilawa, Barbara

2013-05-23

202

Paramagnetism (GCMP)  

NSDL National Science Digital Library

Paramagnetism: this is a resource in the collection "General Chemistry Multimedia Problems". In this problem we will begin by observing the magnetism of three manganese compounds. These compounds have been placed in capsules, which will be pulled toward a magnet if the compound is paramagnetic. General Chemistry Multimedia Problems ask students questions about experiments they see presented using videos and images. The questions asked apply concepts from different parts of an introductory course, encouraging students to decompartmentalize the material.

203

Solvation and crystal effects in bilirubin studied by NMR spectroscopy and density functional theory.  

PubMed

The open-chain tetrapyrrole compound bilirubin was investigated in chloroform and dimethyl sulfoxide solutions by liquid-state NMR and as solid by (1)H, (13)C, and (15)N magic-angle spinning (MAS) solid-state NMR spectroscopy. Density functional theory (DFT) calculations were performed to interpret the data, using the B3LYP exchange-correlation functional to optimize geometries and to compute NMR chemical shieldings by the gauge-including atomic orbital method. The dependence of geometries and chemical shieldings on the size of the basis sets was investigated for the reference molecules tetramethylsilane, NH(3), and H(2)O, and for bilirubin as a monomer and in clusters consisting of up to six molecules. In order to assess the intrinsic errors of the B3LYP approximation in calculating NMR shieldings, complete basis set estimates were obtained for the nuclear shielding values of the reference molecules. The experimental liquid-state NMR data of bilirubin are well reproduced by a monomeric bilirubin molecule using the 6-311+G(2d,p) basis set for geometry optimization and for calculating chemical shieldings. To simulate the bilirubin crystal, a hexameric model was required. It was constructed from geometry-optimized monomers using information from the X-ray structure of bilirubin to fix the monomeric entities in space and refined by partial optimization. Combining experimental (1)H-(13)C and (1)H-(15)N NMR correlation spectroscopy and density functional theory, almost complete sets of (1)H, (13)C, and (15)N chemical shift assignments were obtained for both liquid and solid states. It is shown that monomeric bilirubin in chloroform solution is formed by 3-vinyl anti conformers, while bilirubin crystals are formed by 3-vinyl syn conformers. This conformational change leads to characteristic differences between the liquid- and solid-state NMR resonances. PMID:21846145

Rohmer, Thierry; Matysik, Jörg; Mark, Franz

2011-09-28

204

Solid-State NMR Investigation of Paramagnetic Nylon-6 Clay Nanocomposites. 2. Measurement of Clay Dispersion, Crystal Stratification, and Stability of Organic Modifiers  

NSDL National Science Digital Library

In this second paper of a two-part series dealing mainly with NMR characterization of nylon-6/clay nanocomposites (NnCâs) having nominally 5 mass % clay, measurements with application to processing are featured. The paramagnetism of the montmorillonite clays, discussed in the first paper, allowed us to use the corresponding spin-diffusion-moderated reduction in longitudinal proton relaxation time, T1 H, for two purposes, namely, to rank the quality of clay dispersion in NnC families with the same formulation and to investigate morphological stratification of the nylon-6 R- and ç-crystallites with respect to the clay surface. In a group of three NnCâs with the same formulation but different melt-blending conditions, variations in T1 H correlated well with previously published TEM assessments of the quality of the clay dispersion. Also, in a set of samples from an injection-molded, in situ polymerized NnC disk where strong variations in R/ç ratios were observed, it was found that these differences did not arise from processing-induced inhomogeneities in clay concentration; rather, variations in cooling histories throughout the disk was the more probable cause. In these latter samples, well-defined stratification of the ç-phase (versus the R-phase) crystallites nearer the clay surface did not occur until after annealing at 214 °C. We also examined the dependence of NnC T1 Hâs on the static field of the measurement. It is clear that the magnitude of the paramagnetic contribution to T1 H is a function of field and of Fe3+ concentration in the clay. Trends support the notion that spin-exchange interactions between the electrons on different Fe3+ ions largely define the spectral density of magnetic fluctuations near the clay surface. Some attention was, therefore, given to optimizing Fe3+ concentrations for the best NnC characterization. Finally, we investigated the chemical stability of a particular organic modifier (OM), which is used to pretreat the clay prior to melt blending. The OM, dimethyl, dehydrogenated-tallow ammonium ion, was followed in the process of blending this modified clay with nylon-6 at 240 °C. It was found that when such a clay surface was exposed to the nylon-6 during blending, most of the OM on that surface decomposed, releasing a free amine with one methyl and two tallow substituents. However, subsequent melting at 240 °C produced no further decomposition. The implication is that the combination of temperature and shear stress in blending causes decomposition, not just temperature alone. The susceptibility to chemical decomposition varied strongly with the OM. Ironically, extensive decomposition of the OM did not result in poor mixing; in fact, as judged by T1 H, the NnC with the best dispersion of clay also had the most extensively degraded OM. The implications of this degradation for the physical properties have not been explored in detail.

Vanderhart, D. L.; Asano, A.; Gilman, J. W.

2001-01-01

205

A solid-state 55Mn NMR spectroscopy and DFT investigation of manganese pentacarbonyl compounds  

SciTech Connect

Central transition 55Mn NMR spectra of several solid manganese pentacarbonyls acquired at magnetic field strengths of 11.75, 17.63, and 21.1 T are presented. The variety of distinct powder sample lineshapes obtained demonstrates the sensitivity of solid-state 55Mn NMR to the local bonding environment, including the presence of crystallographically unique Mn sites, and facilitates the extraction of the Mn chemical shift anisotropies, CSAs, and the nuclear quadrupolar parameters. The compounds investigated include molecules with approximate C4v symmetry, LMn(CO)5 (L ¼ Cl, Br, I, HgMn(CO)5, CH3) and several molecules of lower symmetry (L ¼ PhCH2, Ph3*nClnSn (n ¼ 1, 2, 3)). For these compounds, the Mn CSA values range from o100 ppm for Cl3SnMn(CO)5 to 1260 ppm for ClMn(CO)5. At 21.1 T the 55Mn NMR lineshapes are appreciably influenced by the Mn CSA despite the presence of significant 55Mn quadrupolar coupling constants that range from 8.0 MHz for Cl3SnMn(CO)5 to 35.0 MHz for CH3Mn(CO)5. The breadth of the solid-state 55Mn NMR spectra of the pentacarbonyl halides is dominated by the CSA at all three applied magnetic fields. DFT calculations of the Mn magnetic shielding tensors reproduce the experimental trends and the magnitude of the CSA is qualitatively rationalized using a molecular orbital, MO, interpretation based on Ramsey’s theory of magnetic shielding. In addition to the energy differences between symmetry-appropriate occupied and virtual MOs, the d-character of the Mn MOs is important for determining the paramagnetic shielding contribution to the principal components of the magnetic shielding tensor.

Feindel, Kirk W.; Ooms, Kristopher J.; Wasylishen, Roderick E.

2007-01-23

206

Broadband "Infinite-Speed" Magic-Angle Spinning NMR Spectroscopy  

SciTech Connect

High-resolution magic-angle spinning NMR of high-Z spin- 1/2 nuclei such as {sup 125}Te, {sup 207}Pb, {sup 119}Sn, {sup 113}Cd, and {sup 195}Pt is often hampered by large (>1000 ppm) chemical-shift anisotropies, which result in strong spinning sidebands that can obscure the centerbands of interest. In various tellurides with applications as thermoelectrics and as phase-change materials for data storage, even 22-kHz magic-angle spinning cannot resolve the center- and sidebands broadened by chemical-shift dispersion, which precludes peak identification or quantification. For sideband suppression over the necessary wide spectral range (up to 200 kHz), radio frequency pulse sequences with few, short pulses are required. We have identified Gan's two-dimensional magic-angle-turning (MAT) experiment with five 90{sup o} pulses as a promising broadband technique for obtaining spectra without sidebands. We have adapted it to broad spectra and fast magic-angle spinning by accounting for long pulses (comparable to the dwell time in t{sub 1}) and short rotation periods. Spectral distortions are small and residual sidebands negligible even for spectra with signals covering a range of 1.5 {gamma}B{sub 1}, due to a favorable disposition of the narrow ranges containing the signals of interest in the spectral plane. The method is demonstrated on various technologically interesting tellurides with spectra spanning up to 170 kHz, at 22 kHz MAS.

Hu, Yan-Yan; Levin, E.M; Schmidt-Rohr, Klaus

2009-06-02

207

Probing solvent accessibility of amyloid fibrils by solution NMR spectroscopy  

PubMed Central

Amyloid is the result of an anomalous protein and peptide aggregation, leading to the formation of insoluble fibril deposits. At present, 18 human diseases have been associated with amyloid deposits—e.g., Alzheimer's disease and Prion-transmissible Spongiform Encephalopathies. The molecular structure of amyloid is to a large extent unknown, because of lack of high-resolution structural information within the amyloid state. However, from other experimental data it has been established that amyloid fibrils predominantly consist of ?-strands arranged perpendicular to the fibril axis. Identification of residues involved in these secondary structural elements is therefore of vital importance to rationally designing appropriate inhibitors. We have designed a hydrogen/deuterium exchange NMR experiment that can be applied on mature amyloid to enable identification of the residues located inside the fibril core. Using a highly amyloidogenic peptide, corresponding to residues 25–35 within the Alzheimer A?(1–43) peptide, we could establish that residues 28–35 constitute the amyloid core, with residues 31 and 32 being the most protected. In addition, quantitative values for the solvent accessibility for each involved residue could be obtained. Based on our data, two models of peptide assembly are proposed. The method provides a general way to identify the core of amyloid structures and thereby pinpoint areas suitable for design of inhibitors.

Ippel, Johannes H.; Olofsson, Anders; Schleucher, Jurgen; Lundgren, Erik; Wijmenga, Sybren S.

2002-01-01

208

Probing solvent accessibility of amyloid fibrils by solution NMR spectroscopy.  

PubMed

Amyloid is the result of an anomalous protein and peptide aggregation, leading to the formation of insoluble fibril deposits. At present, 18 human diseases have been associated with amyloid deposits-e.g., Alzheimer's disease and Prion-transmissible Spongiform Encephalopathies. The molecular structure of amyloid is to a large extent unknown, because of lack of high-resolution structural information within the amyloid state. However, from other experimental data it has been established that amyloid fibrils predominantly consist of beta-strands arranged perpendicular to the fibril axis. Identification of residues involved in these secondary structural elements is therefore of vital importance to rationally designing appropriate inhibitors. We have designed a hydrogen/deuterium exchange NMR experiment that can be applied on mature amyloid to enable identification of the residues located inside the fibril core. Using a highly amyloidogenic peptide, corresponding to residues 25-35 within the Alzheimer Abeta(1-43) peptide, we could establish that residues 28-35 constitute the amyloid core, with residues 31 and 32 being the most protected. In addition, quantitative values for the solvent accessibility for each involved residue could be obtained. Based on our data, two models of peptide assembly are proposed. The method provides a general way to identify the core of amyloid structures and thereby pinpoint areas suitable for design of inhibitors. PMID:12072564

Ippel, Johannes H; Olofsson, Anders; Schleucher, Jürgen; Lundgren, Erik; Wijmenga, Sybren S

2002-06-18

209

Fundamental studies of supported bimetallic catalysts by NMR spectroscopy  

SciTech Connect

Various hydrogenation reactions on transition metals are important commercially whereas certain hydrogenolysis reactions are useful from fundamental point of view. Understanding the hydrogen mobility and kinetics of adsorption-desorption of hydrogen is important in understanding the mechanisms of such reactions involving hydrogen. The kinetics of hydrogen chemisorption was studied by means of selective excitation NMR on silica supported Pt, Rh and Pt-Rh catalysts. The activation energy of hydrogen desorption was found to be lower on silica supported Pt catalysts as compared to Rh and Pt-Rh catalysts. It was found that the rates of hydrogen adsorption and desorption on Pt-Rh catalyst were similar to those on Rh catalyst and much higher as compared to Pt catalyst. The Ru-Ag bimetallic system is much simpler to study than the Pt-Rh system and serves as a model system to characterize more complicated systems such as the K/Ru system. Ag was found to decrease the amounts of adsorbed hydrogen and the hydrogen-to-ruthenium stoichiometry. Ag reduced the populations of states with low and intermediate binding energies of hydrogen on silica supported Ru catalyst. The rates of hydrogen adsorption and desorption were also lower on silica supported Ru-Ag catalyst as compared to Ru catalyst. This report contains introductory information, the literature review, general conclusions, and four appendices. An additional four chapters and one appendix have been processed separately for inclusion on the data base.

Savargaonkar, N.

1996-10-17

210

Deuterium NMR spectroscopy of biosynthetically deuterated mammalian tissues  

SciTech Connect

The choline-containing phospholipids of mammalian membranes have been biosynthetically deuterated by raising rats on a diet supplemented with (HOCH2CH2N(CD3)3) Cl or (HOCD2CH2N(CH3)3) Cl . Deuterium NMR spectra have been obtained from excised deuterated brain, sciatic nerve, heart, and lung, from isolated brain myelin and brain microsomes, and from aqueous dispersions of lipid extracts. Measurements of residual quadrupole splittings for excised deuterated neural tissues demonstrate that the orientational order of the choline head group is similar to that observed in model membranes. The spin-lattice relaxation time of the choline head group in deuterated neural tissue is indistinguishable from that observed in model membranes. These results support the proposal that the conformation and motional dynamics of the choline head groups of the bulk choline-containing lipids of neural tissue are similar to those in model membranes. Spectra of biosynthetically deuterated brain myelin and brain microsomes exhibit similar quadrupole splittings. Since these membranes have significantly different protein contents, these results indicate that no strong polar interactions exist between membrane proteins and the choline head groups of choline-containing membrane lipids. Spectra of intact deuterated heart and lung exhibit broad lines and a range of quadrupole splittings.

Curatolo, W.; Jungalwala, F.B.; Sears, B.; Tuck, L.; Neuringer, L.J.

1985-07-30

211

Evaluation of the influence of intermolecular electron-nucleus couplings and intrinsic metal binding sites on the measurement of 15 N longitudinal paramagnetic relaxation enhancements in proteins by solid-state NMR  

Microsoft Academic Search

Magic-angle spinning solid-state NMR measurements of 15N longitudinal paramagnetic relaxation enhancements (PREs) in 13C,15N-labeled proteins modified with Cu2+-chelating tags can yield multiple long-range electron-nucleus distance restraints up to ~20 Å (Nadaud et al. in J Am Chem\\u000a Soc 131:8108–8120, 2009). Using the EDTA-Cu2+ K28C mutant of B1 immunoglobulin binding domain of protein G (GB1) as a model, we investigate the

Philippe S. Nadaud; Ishita Sengupta; Jonathan J. Helmus; Christopher P. Jaroniec

212

SPIN-1/2 AND BEYOND: A Perspective in Solid State NMR Spectroscopy  

NASA Astrophysics Data System (ADS)

Novel applications of solid state nuclear magnetic resonance (NMR) to the study of small molecules, synthetic polymers, biological systems, and inorganic materials continue at an accelerated rate. Instrumental to this uninterrupted expansion has been an improved understanding of the chemical physics underlying NMR. Such deeper understanding has led to novel forms of controlling the various components that make up the spin interactions, which have in turn redefined the analytical capabilities of solid state NMR measurements. This review presents a perspective on the basic phenomena and manipulations that have made this progress possible and describes the new opportunities and challenges that are being opened in the realms of spin-1/2 and quadrupole nuclei spectroscopies.

Frydman, Lucio

2001-10-01

213

Automatic Structure Determination of Regular Polysaccharides Based Solely on NMR Spectroscopy  

PubMed Central

The structural analysis of polysaccharides requires that the sugar components and their absolute configurations are determined. We here show that this can be performed based on NMR spectroscopy by utilizing butanolysis with (+)- and (?)-2-butanol that gives the corresponding 2-butyl glycosides with characteristic 1H and 13C NMR chemical shifts. The subsequent computer-assisted structural determination by CASPER can then be based solely on NMR data in a fully automatic way as shown and implemented herein. The method is additionally advantageous in that reference data only have to be prepared once and from a user’s point of view only the unknown sample has to be derivatized for use in CASPER.

2011-01-01

214

Automatic structure determination of regular polysaccharides based solely on NMR spectroscopy.  

PubMed

The structural analysis of polysaccharides requires that the sugar components and their absolute configurations are determined. We here show that this can be performed based on NMR spectroscopy by utilizing butanolysis with (+)- and (-)-2-butanol that gives the corresponding 2-butyl glycosides with characteristic (1)H and (13)C NMR chemical shifts. The subsequent computer-assisted structural determination by CASPER can then be based solely on NMR data in a fully automatic way as shown and implemented herein. The method is additionally advantageous in that reference data only have to be prepared once and from a user's point of view only the unknown sample has to be derivatized for use in CASPER. PMID:21955217

Lundborg, Magnus; Fontana, Carolina; Widmalm, Göran

2011-09-30

215

In vivo dephosphorylation of WR-2721 monitored by 31P NMR spectroscopy.  

PubMed

The in vivo dephosphorylation of the radioprotective agent S-2-[3-(aminopropylamino)]ethylphosphorothioic acid (WR-2721) in male CD2F1 mice was measured by 31P NMR spectroscopy after i.p. injection. The disappearance of the WR-2721 phosphate NMR signal with time was concurrent with an increase and splitting of the inorganic phosphate NMR signal. The more acidic inorganic phosphate resonance is shown to be attributed to phosphate (inorganic phosphate) in the urine. Using regression first-order kinetic analysis of data, after i.p. injection of 600 mg/kg, the half-life of WR-2721 was determined to be 40.9 +/- 5.9 (S.D.) min (n = 10). PMID:3001292

Knizner, S A; Jacobs, A J; Lyon, R C; Swenberg, C E

1986-01-01

216

Fast multidimensional localized parallel NMR spectroscopy for the analysis of samples.  

PubMed

A parallel localized spectroscopy (PALSY) method is presented to speed up the acquisition of multidimensional NMR (nD) spectra. The sample is virtually divided into a discrete number of nonoverlapping slices that relax independently during consecutive scans of the experiment, affording a substantial reduction in the interscan relaxation delay and the total experiment time. PALSY was tested for the acquisition of three experiments 2D COSY, 2D DQF-COSY and 2D TQF-COSY in parallel, affording a time-saving factor of 3-4. Some unique advantages are that the achievable resolution in any dimension is not compromised in any way: it uses conventional NMR data processing, it is not prone to generate spectral artifacts, and once calibrated, it can be used routinely with these and other combinations of NMR spectra. PMID:20661940

Vega-Vazquez, Marino; Cobas, Juan Carlos; Martin-Pastor, Manuel

2010-10-01

217

Nuclear charge-distribution effects on the NMR spectroscopy parameters  

NASA Astrophysics Data System (ADS)

We present here a systematic study about the influence of the size and type of nuclear charge-distribution models (Gaussian and point-like) on the NMR spectroscopic parameters, the nuclear magnetic shielding ? and the indirect nuclear spin J-coupling. We found that relativistic effects largely enhance the nuclear charge-distribution effects (NChDE) on those parameters being them quite sensitive to the nuclear model adopted for calculations. Results for two rare gas atoms (Kr, Rn) and few molecular systems like HX, (X = Br, I, At), CH4, SnH4, SnIH3, SnI2H2, and PbIH3 are presented. J-couplings are more sensitive than shieldings in both, relativistic and non-relativistic (NR) regimes. The highest effect (close to 11% of variation in relativistic calculations with that two different nuclear models) is observed for J(Pb-I) in PbIH3. A similar effect is found for J(Pb-H) in the same molecule, close to 9%. The NChDE for ?(Sn) in SnI4-nHn with n = 1, 2 is as large as few ppm (between 3 and 8.56 ppm). For J(Sn-H) in this set of molecules, it goes from 37 Hz for SnH4 to 54 Hz for SnI2H2. Furthermore, we found that the vicinal NChDE is very small though not zero. For 1J(Sn-H) in SnIH3, the NChDE of iodine is close to 2 Hz (0.1%). We also studied the NChDE on the ground state electronic energies of atoms and molecules. We found that these effects are only important within the relativistic regime but not within the NR one. They are in good agreement with previous works.

Maldonado, Alejandro F.; Giménez, Carlos A.; Aucar, Gustavo A.

2012-06-01

218

Nuclear charge-distribution effects on the NMR spectroscopy parameters.  

PubMed

We present here a systematic study about the influence of the size and type of nuclear charge-distribution models (Gaussian and point-like) on the NMR spectroscopic parameters, the nuclear magnetic shielding ? and the indirect nuclear spin J-coupling. We found that relativistic effects largely enhance the nuclear charge-distribution effects (NChDE) on those parameters being them quite sensitive to the nuclear model adopted for calculations. Results for two rare gas atoms (Kr, Rn) and few molecular systems like HX, (X = Br, I, At), CH(4), SnH(4), SnIH(3), SnI(2)H(2), and PbIH(3) are presented. J-couplings are more sensitive than shieldings in both, relativistic and non-relativistic (NR) regimes. The highest effect (close to 11% of variation in relativistic calculations with that two different nuclear models) is observed for J(Pb-I) in PbIH(3). A similar effect is found for J(Pb-H) in the same molecule, close to 9%. The NChDE for ?(Sn) in SnI(4-n)H(n) with n = 1, 2 is as large as few ppm (between 3 and 8.56 ppm). For J(Sn-H) in this set of molecules, it goes from 37 Hz for SnH(4) to 54 Hz for SnI(2)H(2). Furthermore, we found that the vicinal NChDE is very small though not zero. For (1)J(Sn-H) in SnIH(3), the NChDE of iodine is close to 2 Hz (0.1%). We also studied the NChDE on the ground state electronic energies of atoms and molecules. We found that these effects are only important within the relativistic regime but not within the NR one. They are in good agreement with previous works. PMID:22713039

Maldonado, Alejandro F; Giménez, Carlos A; Aucar, Gustavo A

2012-06-14

219

Structural properties of the range-II- and range-III order in amorphous-SiO2 probed by electron paramagnetic resonance and Raman spectroscopy  

NASA Astrophysics Data System (ADS)

In the present work we report an experimental investigation by electron paramagnetic resonance spectroscopy on the hyperfine structure of the E'_? point defect, probing the local arrangement of the network (range-II order), and by Raman spectroscopy on the D1 and D2 lines, probing mean features of the network (range-III order). Our studies, performed on a-SiO2 samples thermally treated at 1000 °C in air for different time durations, show that changes of the hyperfine structure and of the D1 and D2 lines occur in a correlated way. These results give strong evidence that the range-II and range-III order properties are intimately related to each other and that these properties are determined by the history of the material.

Vaccaro, G.; Buscarino, G.; Agnello, S.; Messina, G.; Carpanese, M.; Gelardi, F. M.

2010-07-01

220

In situ solid-state NMR spectroscopy of electrochemical cells: batteries, supercapacitors, and fuel cells.  

PubMed

Electrochemical cells, in the form of batteries (or supercapacitors) and fuel cells, are efficient devices for energy storage and conversion. These devices show considerable promise for use in portable and static devices to power electronics and various modes of transport and to produce and store electricity both locally and on the grid. For example, high power and energy density lithium-ion batteries are being developed for use in hybrid electric vehicles where they improve the efficiency of fuel use and help to reduce greenhouse gas emissions. To gain insight into the chemical reactions involving the multiple components (electrodes, electrolytes, interfaces) in the electrochemical cells and to determine how cells operate and how they fail, researchers ideally should employ techniques that allow real-time characterization of the behavior of the cells under operating conditions. This Account reviews the recent use of in situ solid-state NMR spectroscopy, a technique that probes local structure and dynamics, to study these devices. In situ NMR studies of lithium-ion batteries are performed on the entire battery, by using a coin cell design, a flat sealed plastic bag, or a cylindrical cell. The battery is placed inside the NMR coil, leads are connected to a potentiostat, and the NMR spectra are recorded as a function of state of charge. (7)Li is used for many of these experiments because of its high sensitivity, straightforward spectral interpretation, and relevance to these devices. For example, (7)Li spectroscopy was used to detect intermediates formed during electrochemical cycling such as LixC and LiySiz species in batteries with carbon and silicon anodes, respectively. It was also used to observe and quantify the formation and growth of metallic lithium microstructures, which can cause short circuits and battery failure. This approach can be utilized to identify conditions that promote dendrite formation and whether different electrolytes and additives can help prevent dendrite formation. The in situ method was also applied to monitor (by (11)B NMR) electrochemical double-layer formation in supercapacitors in real time. Though this method is useful, it comes with challenges. The separation of the contributions from the different cell components in the NMR spectra is not trivial because of overlapping resonances. In addition, orientation-dependent NMR interactions, including the spatial- and orientation-dependent bulk magnetic susceptibility (BMS) effects, can lead to resonance broadening. Efforts to understand and mitigate these BMS effects are discussed in this Account. The in situ NMR investigation of fuel cells initially focused on the surface electrochemistry at the electrodes and the electrochemical oxidation of methanol and CO to CO2 on the Pt cathode. On the basis of the (13)C and (195)Pt NMR spectra of the adsorbates and electrodes, CO adsorbed on Pt and other reaction intermediates and complete oxidation products were detected and their mode of binding to the electrodes investigated. Appropriate design and engineering of the NMR hardware has allowed researchers to integrate intact direct methanol fuel cells into NMR probes. Chemical transformations of the circulating methanol could be followed and reaction intermediates could be detected in real time by either (2)H or (13)C NMR spectroscopy. By use of the in situ NMR approach, factors that control fuel cell performance, such as methanol cross over and catalyst performance, were identified. PMID:24041242

Blanc, Frédéric; Leskes, Michal; Grey, Clare P

2013-06-21

221

Facile backbone structure determination of human membrane proteins by NMR spectroscopy  

PubMed Central

Although nearly half of today’s major pharmaceutical drugs target human integral membrane proteins (hIMPs), only 30 hIMP structures are currently available in the Protein Data Bank, largely owing to inefficiencies in protein production. Here we describe a strategy for the rapid structure determination of hIMPs, using solution NMR spectroscopy with systematically labeled proteins produced via cell-free expression. We report new backbone structures of six hIMPs, solved in only 18 months from 15 initial targets. Application of our protocols to an additional 135 hIMPs with molecular weight <30 kDa yielded 38 hIMPs suitable for structural characterization by solution NMR spectroscopy without additional optimization.

Klammt, Christian; Maslennikov, Innokentiy; Bayrhuber, Monika; Eichmann, Cedric; Vajpai, Navratna; Chiu, Ellis Jeremy Chua; Blain, Katherine Y; Esquivies, Luis; Kwon, June Hyun Jung; Balana, Bartosz; Pieper, Ursula; Sali, Andrej; Slesinger, Paul A; Kwiatkowski, Witek; Riek, Roland; Choe, Senyon

2013-01-01

222

Structural characterization of selenosubtilisin by sup 77 Se-NMR spectroscopy  

SciTech Connect

Selenosubtilisin is an artificial enzyme containing an active site selenocysteine residue. In this environment the selenium atom is a valuable probe of structure-function relationships and also confers novel redox and hydrolytic properties to the original protease template. The authors have used {sup 77}Se NMR spectroscopy to characterize different oxidation states of {sup 77}Se isotopically enriched selenosubtilisin. The oxidized form of the enzyme exhibits a {sup 77}Se resonance at 1,189 ppm. This is in good agreement with the {sup 77}Se chemical shifts for model seleninic acids, confirming that the prosthetic group is in the seleninic acid oxidation state. On treatment of the oxidized enzyme with three equivalents of 3-carboxy-4-nitrobenzenethiol at pH 5.0, they observe the enzyme bound selenenyl sulfide at 388.5 ppm. This work demonstrates the utility of {sup 77}Se NMR spectroscopy for examining structure-function relationships of selenium containing proteins.

House, K.L.; Dunlap, R.B.; Odom, J.D.; Wu, Z.P.; Hilvert. D. (Univ. of South Carolina, Columbia (United States) Research Inst. of Scripps Clinic, La Jolla, CA (United States))

1991-03-15

223

Determination of the solution-bound conformation of an amino acid binding protein by NMR paramagnetic relaxation enhancement: use of a single flexible paramagnetic probe with improved estimation of its sampling space.  

PubMed

We demonstrate the feasibility of elucidating the bound ("closed") conformation of a periplasmic binding protein, the glutamine-binding protein (GlnBP), in solution, using paramagnetic relaxation enhancements (PREs) arising from a single paramagnetic group. GlnBP consists of two globular domains connected by a hinge. Using the ligand-free ("open") conformation as a starting point, conjoined rigid-body/torsion-angle simulated annealing calculations were performed using backbone (1)H(N)-PREs as a major source of distance information. Paramagnetic probe flexibility was accounted for via a multiple-conformer representation. A conventional approach where the entire PRE data set is enforced at once during simulated annealing yielded poor results due to inappropriate conformational sampling of the probe. On the other hand, significant improvements in coordinate accuracy were obtained by estimating the probe sampling space prior to structure calculation. Such sampling is achieved by refining the ensemble of probe conformers with intradomain PREs only, keeping the protein backbone fixed in the open form. Subsequently, while constraining the probe to the previously found conformations, the domains are allowed to move relative to each other under the influence of the non-intradomain PREs, giving the hinge region torsional degrees of freedom. Thus, by partitioning the protocol into "probe sampling" and "backbone sampling" stages, structures significantly closer to the X-ray structure of ligand-bound GlnBP were obtained. PMID:19583434

Bermejo, Guillermo A; Strub, Marie-Paule; Ho, Chien; Tjandra, Nico

2009-07-15

224

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

225

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

Microsoft Academic Search

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

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

1989-01-01

226

A Stack of YBCO Annuli, Thin Plate and Bulk, for Micro-NMR Spectroscopy  

Microsoft Academic Search

A new annulus magnet, the latest in a series of compact magnets being developed for NMR spectroscopy applications at the MIT Francis Bitter Magnet Laboratory, was built and tested in a bath of liquid nitrogen at 77 K. The magnet, YP2800, a stack of 2800 thin YBCO plate annuli, each either 40- or 46-mm square and 0.08-mm thick with a

Seungyong Hahn; John Voccio; Dong Keun Park; Kwang-Min Kim; Masaru Tomita; Juan Bascunan; Yukikazu Iwasa

2012-01-01

227

Determination of degree of deacetylation of chitosan by 1 H NMR spectroscopy  

Microsoft Academic Search

This paper describes a novel method to determine the degree of deacetylation of chitosan by 1H NMR spectroscopy. Measurements were carried out at 70°C by using 2 wt% CD3COOD\\/D2O and 2 wt% DC1\\/D2O as solvents for chitosan. In the case of DC1\\/D2O system, effect on hydrolysis of chitosan should be taken into consideration, and the pulse repetition delay required for

Asako Hirai; Hisashi Odani; Akio Nakajima

1991-01-01

228

Elucidation of cross relaxation in liquids by two-dimensional N.M.R. spectroscopy  

Microsoft Academic Search

Two-dimensional N.M.R. spectroscopy is applied to the elucidation of cross relaxation pathways in liquids. The theory underlying two dimensional studies of cross relaxation and of transient nuclear Overhauser effects is developed. The influence of the correlation time of the molecular random process is investigated. It is found that in the limit of short correlation times (extreme narrowing limit) weak negative

S. Macura; R. R. Ernst

1980-01-01

229

High Temperature Superconducting Radio Frequency Coils for NMR Spectroscopy and Magnetic Resonance Imaging  

Microsoft Academic Search

High-temperature superconductivity has a significant opportunity to improve\\u000athe performance of nuclear magnetic resonance (NMR) spectroscopy and magnetic\\u000aresonance imaging (MRI) systems. The low rf losses and low operating\\u000atemperatures of superconducting coils allow them to improve the signal-to-noise\\u000aratio in applications where the system noise dominates that of the sample under\\u000astudy. These improvements translate into new capabilities and

Steven M. Anlage

2000-01-01

230

Identification of biochemical changes in lactovegetarian urine using 1 H NMR spectroscopy and pattern recognition  

Microsoft Academic Search

A vegetarian diet has been demonstrated to have a profound influence on human metabolism as well as to aid the prevention\\u000a of several chronic diseases relative to an omnivorous diet. However, there have been no systematic metabolomic studies on\\u000a all of the biochemical changes induced in human subjects by long-term vegetarianism. In this study, 1H NMR spectroscopy in combination with

Jingjing Xu; Shuyu Yang; Shuhui Cai; Jiyang Dong; Xuejun Li; Zhong Chen

2010-01-01

231

A Metabonomic Study on the Biochemical Effects of Doxorubicin in Rats Using H-NMR Spectroscopy  

Microsoft Academic Search

Metabonomic investigation of doxorubicin (adriamycin) was carried out in male Sprague-Dawley rats using high-resolution H nuclear magnetic resonance (NMR) spectroscopy coupled with multivariate statistics. Urine samples (d –1 to 7) from rats treated with doxorubicin at two dose levels (5 or 15 mg\\/kg body weight) were collected at each time point and doxorubicin-induced biomarkers were examined. Of metabolites, early elevated

Jong-Chul Park; Young-Shick Hong; Yeon Joo Kim; Ji-Young Yang; Eun-Young Kim; Seung Jun Kwack; Do Hyun Ryu; Geum-Sook Hwang; Byung Mu Lee

2009-01-01

232

Intramyocellular lipid concentrations are correlated with insulin sensitivity in humans: a 1H NMR spectroscopy study  

Microsoft Academic Search

Summary   Recent muscle biopsy studies have shown a relation between intramuscular lipid content and insulin resistance. The aim of\\u000a this study was to test this relation in humans by using a novel proton nuclear magnetic resonance (1H NMR) spectroscopy technique, which enables non-invasive and rapid ( ? 45 min) determination of intramyocellular lipid (IMCL)\\u000a content. Normal weight non-diabetic adults (n

M. Krssak; K. Falk Petersen; A. Dresner; L. DiPietro; S. M. Vogel; D. L. Rothman; G. I. Shulman; M. Roden

1999-01-01

233

Nanotechnology for biomaterials engineering: structural characterization of amphiphilic polymeric nanoparticles by 1H NMR spectroscopy  

Microsoft Academic Search

Nanoparticles composed of diblock poly(d,l-lactide-co-glycolide)-poly(ethylene glycol) (PLGA-PEG) or a branched, multiblock PLA-(PEG)3 were prepared by the single emulsion technique. Results of previous studies of these nanoparticles suggested that their structure is of the core-corona type with a polyester core and an outer PEG coating. In the present study, 1H NMR spectroscopy was utilized to provide direct evidence of the structure

Jeffrey S. Hrkach; Maria Teresa Peracchia; Avi Bomb; noah Lotan; Robert Langer

1997-01-01

234

Probing Electrostatic Interactions along the Reaction Pathway of a Glycoside Hydrolase:  Histidine Characterization by NMR Spectroscopy  

Microsoft Academic Search

We have characterized by NMR spectroscopy the three active site (His80, His85, and His205) and two non-active site (His107 and His114) histidines in the 34 kDa catalytic domain of Cellulomonas fimi xylanase Cex in its apo, noncovalently aza-sugar-inhibited, and trapped glycosyl-enzyme intermediate states. Due to protection from hydrogen exchange, the level of which increased upon inhibition, the labile 1H‰1 and

Mario Schubert; David K. Y. Poon; Jacqueline Wicki; Chris A. Tarling; Emily M. Kwan; Jens E. Nielsen; Stephen G. Withers; Lawrence P. McIntosh

2007-01-01

235

High Q factor RF planar microcoils for micro-scale NMR spectroscopy  

Microsoft Academic Search

We present the design, fabrication and test of high-Q factor radiofrequency planar microcoils for nuclear magnetic resonance (NMR) spectroscopy in small volume samples. The coils are fabricated on glass wafers using high-aspect ratio SU-8 photoepoxy and copper electroplating. On-wafer electrical characterization shows quality factors up to 40 at 800MHz. A 500?m diameter microcoil with a measured quality factor of 24

C. Massin; G. Boero; F. Vincent; J. Abenhaim; P.-A. Besse; R. S. Popovic

2002-01-01

236

In-Vivo NMR Spectroscopy of the Brain at High Fields  

Microsoft Academic Search

Increased magnetic fields in principle provide increased sensitivity and specificity. In vivo, however, the increase in magnetic\\u000a field alone does not automatically result in obvious improvements. Among the factors that are set to impede the improvements\\u000a in sensitivity for in-vivo NMR spectroscopy are the increased challenges in eliminating the macroscopic inhomogeneities caused\\u000a by mainly the air- tissue interface and increased

Rolf Gruetter; Pierre-Gilles Henry; Hongxia Lei; Silvia Mangia; Gülin Öz; Melissa Terpstra; Ivan Tkac

237

Analysis of Hydroperoxides in solid Polyethylene by NMR and EPR Spectroscopy  

SciTech Connect

The authors have shown that the hydroperoxide species in {gamma}-irradiated {sup 13}C-polyethylene can be directly observed by {sup 13}C MAS NMR spectroscopy. The experiment was performed without the need for special sample preparation such as chemical derivatization or dissolution. Annealing experiments were employed to study the thermal decomposition of the hydroperoxide species and to measure an activation energy of 98 kJ/mol. EPR spectroscopy suggests that residual polyenyl and alkylperoxy radicals are predominantly trapped in interracial or crystalline regions, while the peroxy radicals observed after UV-photolysis of hydroperoxides are in amorphous regions.

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

2000-06-12

238

Structural Studies of Biomaterials Using Double-Quantum Solid-State NMR Spectroscopy  

NASA Astrophysics Data System (ADS)

Proteins directly control the nucleation and growth of biominerals, but the details of molecular recognition at the protein-biomineral interface remain poorly understood. The elucidation of recognition mechanisms at this interface may provide design principles for advanced materials development in medical and ceramic composites technologies. Here, we describe both the theory and practice of double-quantum solid-state NMR (ssNMR) structure-determination techniques, as they are used to determine the secondary structures of surface-adsorbed peptides and proteins. In particular, we have used ssNMR dipolar techniques to provide the first high-resolution structural and dynamic characterization of a hydrated biomineralization protein, salivary statherin, adsorbed to its biologically relevant hydroxyapatite (HAP) surface. Here, we also review NMR data on peptides designed to adsorb from aqueous solutions onto highly porous hydrophobic surfaces with specific helical secondary structures. The adsorption or covalent attachment of biological macromolecules onto polymer materials to improve their biocompatibility has been pursued using a variety of approaches, but key to understanding their efficacy is the verification of the structure and dynamics of the immobilized biomolecules using double-quantum ssNMR spectroscopy.

Drobny, G. P.; Long, J. R.; Karlsson, T.; Shaw, W.; Popham, J.; Oyler, N.; Bower, P.; Stringer, J.; Gregory, D.; Mehta, M.; Stayton, P. S.

2003-10-01

239

Orientation of Amphipathic Helical Peptides in Membrane Bilayers Determined by Solid-State NMR Spectroscopy. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

Solid-state NMR spectroscopy was used to determine the orientations of two amphipathic helical peptides associated with lipid bilayers. A single spectral parameter provides sufficient orientational information for these peptides, which are known, from oth...

B. Bechinger Y. Kim L. E. Chirlian J. Gesell J. M. Neumann

1991-01-01

240

Evaluation of solvent effects on protonation using NMR spectroscopy: implication in salt formation.  

PubMed

Investigation of the use of solution NMR spectroscopy to determine the effect of organic solvents on chemical shift changes in bases on addition of acids is reported. This information can be useful in the evaluation of solvents and counterion selection for salt formation. (1)H and (15)N chemical shift changes in three bases (pyrazine, phthalazine, and pyridine) on the addition of acids (1:1 ratio) were determined in various solvents. The effect of acid strength on chemical shift changes was examined. (1)H and (15)N chemical shift changes indicated protonation (salt formation). The media used affected the observed chemical shift changes. In D(2)O the data followed the DeltapK(a) (base-acid) general rule, that the pK(a) value of the acids should be 2 units lower than the pK(a) of the base to ensure proton transfer. Protonation, as measured by chemical shift changes using solution NMR spectroscopy, provided novel insight on potential salt formation in different media. Solution NMR spectroscopy appears to be a useful tool to evaluate counter ion and solvent selection for salt formation reaction. PMID:19463928

Kim, Hyungchul; Gao, Jinhai; Burgess, Diane J

2009-05-20

241

Proton NMR spectroscopy shows lipids accumulate in skeletal muscle in response to burn trauma-induced apoptosis  

Microsoft Academic Search

Burn trauma triggers hypermetabolism and muscle wasting via increased cellular protein degra- dation and apoptosis. Proton nuclear magnetic resonance (1H NMR) spectroscopy can detect mobile lipids in vivo. To examine the local effects of burn in skeletal muscle, we performed in vivo 1H NMR on mice 3 days after burn trauma; and ex vivo, high-resolution, magic angle spinning 1 H

Loukas G. Astrakas; Igor Goljer; Shingo Yasuhara; Katie E. Padfield; Qunhao Zhang; Suresh Gopalan; Michael N. Mindrinos; George Dai; Yong-Ming Yu; J. A. Jeevendra Martyn; Ronald G. Tompkins; Laurence G. Rahme; A. Aria Tzika

2005-01-01

242

Functional group analysis in coal by (31)P NMR spectroscopy. Quarterly report, January 1, 1989-March 31, 1989.  

National Technical Information Service (NTIS)

The purpose of this research is to determine the labile-hydrogen functional group composition of coal and coal-derived materials by the nmr spectroscopy of their derivatives made with reagents containing the nmr-active nuclei (sup 31)P, (sup 119)Sn, or (s...

J. G. Verkade

1989-01-01

243

Determination of group composition of tar fractions from pyrolysis of worn-out tires by 1 H NMR spectroscopy  

Microsoft Academic Search

The advantage of IH NMR spectroscopy is the fact that the spectra of the products to be analyzed can be interpreted without first separating them. This makes it considerably simpler and faster to obtain information on the composition of the hydrocarbons under investigation. Both earlier [4, 5] and current [6, 7] integral structure analysis methods consider the entire NMR spectrum

S. S. Belyaeva; Yu. E. Shapiro; V. G. Lebedevskaya; A. B. Kufirin; N. A. Danilov

1991-01-01

244

High-sensitivity multinuclear NMR spectroscopy of a smectite clay and of clay-intercalated polymer.  

PubMed

The nuclear magnetic resonance (NMR) properties of a smectite clay low in paramagnetic ions, and NMR experiments to detect organic material near the silicate surfaces with high sensitivity, have been explored by 1H, 29Si, and 13C NMR. In oven-dried hectorite clay, 1H NMR reveals a sharp signal at 0.35 ppm that narrows significantly with spinning speed. It is assigned to the "inner" OH protons of the silicate layers. In fluorohectorite, where the OH groups are replaced by fluorines, no such 1H peak is observed. The assignment is further confirmed by the efficient cross-polarization observed in two-dimensional (2D) 1H-29Si HETCOR spectra, and by 29Si-detected REDOR experiments with 1H-dephasing in the 29Si dipolar field, which yield a 1H-29Si distance of 2.9 + 0.4 A. In these 1H-29Si experiments, the sensitivity of the 29Si signal is enhanced at least fivefold by refocusing the decay resulting from the inhomogeneous broadening of the single 29Si peak, stretching the 29Si signal out over 80 ms. The small 1H linewidth of this signal at spinning frequencies exceeding 4 kHz is attributed to the large proton-proton distances in the clay. The upfield isotropic chemical shift of the OH groups is explained by their inaccessibility to hydrogen-bonding partners, as a result of their location in hexagonal "cavities" of the clay structure. The well-resolved, easily selectable OH-proton signal and the high-sensitivity 29Si detection open excellent perspectives for NMR studies of composites of clays with organic molecules. Two-dimensional 1H-29Si and 1H-1H chemical-shift correlation experiments enable efficient detection of the 1H spectrum of organic segments near the clay surface. Combined with 1H spin diffusion, the organic segments at up to several nanometers from the clay surfaces can be probed. A 2D 1H-13C correlation experiment yields the 13C spectrum of the organic species near the clay surfaces. A mobility gradient of intercalated poly(ethylene oxide), PEO, segments is proven in 1H-3Si WISE experiments with spin diffusion. PMID:12469807

Hou, S S; Beyer, F L; Schmidt-Rohr, K

245

Probing structure and dynamics of protein assemblies by magic angle spinning NMR spectroscopy.  

PubMed

In living organisms, biological molecules often organize into multicomponent complexes. Such assemblies consist of various proteins and carry out essential functions, ranging from cell division, transport, and energy transduction to catalysis, signaling, and viral infectivity. To understand the biological functions of these assemblies, in both healthy and disease states, researchers need to study their three-dimensional architecture and molecular dynamics. To date, the large size, the lack of inherent long-range order, and insolubility have made atomic resolution studies of many protein assemblies challenging or impractical using traditional structural biology methods such as X-ray diffraction and solution NMR spectroscopy. In the past 10 years, we have focused our work on the development and application of magic angle spinning solid-state NMR (MAS NMR) methods to characterize large protein assemblies at atomic-level resolution. In this Account, we discuss the rapid progress in the field of MAS NMR spectroscopy, citing work from our laboratory and others on methodological developments that have facilitated the in-depth analysis of biologically important protein assemblies. We emphasize techniques that yield enhanced sensitivity and resolution, such as fast MAS (spinning frequencies of 40 kHz and above) and nonuniform sampling protocols for data acquisition and processing. We also discuss the experiments for gaining distance restraints and for recoupling anisotropic tensorial interactions under fast MAS conditions. We give an overview of sample preparation approaches when working with protein assemblies. Following the overview of contemporary MAS NMR methods, we present case studies into the structure and dynamics of two classes of biological systems under investigation in our laboratory. We will first turn our attention to cytoskeletal microtubule motor proteins including mammalian dynactin and dynein light chain 8. We will then discuss protein assemblies from the HIV-1 retrovirus. PMID:23402263

Yan, Si; Suiter, Christopher L; Hou, Guangjin; Zhang, Huilan; Polenova, Tatyana

2013-02-13

246

Sensitivity of 2H NMR spectroscopy to motional models: proteins and highly viscous liquids as examples.  

PubMed

In order to study to what extent mechanisms of molecular motion can be unambiguously revealed by (2)H NMR spectroscopy, (2)H spectra for proteins (chicken villin protein headpiece HP36, selectively methyl-deuterated at leucine-69, C(?) D(3)) and binary systems of high viscosity (benzene-d(6) in tricresyl phosphate) have been carefully analyzed as illustrative examples (the spectra are taken from the literature). In the first case, a model of restricted diffusion mediated by jumps between rotameric orientations has been tested against jump- and free diffusion models which describe rotational motion combined with jump dynamics. It has been found that the set of (2)H spectra of methyl-deuterated at leucine-69 chicken villin protein headpiece HP36 can be consistently explained by different motional models as well as by a gaussian distribution of correlation times assuming isotropic rotation (simple brownian diffusion model). The last finding shows that when the possible distribution of correlation times is not very broad one might not be able to distinguish between heterogeneous and homogenous (but more complex) dynamics by analyzing (2)H lineshapes. For benzene-d(6) in tricresyl phosphate, the dynamics is heterogeneous and it has been demonstrated that a gaussian distribution of correlation times reproduces well the experimental lineshapes, while for a Cole-Davidson distribution the agreement is somewhat worse. For inquires into the sensitivity of quadrupolar NMR spectral analysis (by "quadrupolar NMR spectroscopy we understand NMR spectroscopy of nuclei possessing quadrupole moment), the recently presented theoretical approach [Kruk et al., J. Chem. Phys. 135, 224511 (2011)] has been used as it allows simulating quadrupolar spectra for arbitrary motional conditions by employing the stochastic Liouville equation. PMID:22755589

Kruk, D; Mielczarek, A; Korpala, A; Kozlowski, A; Earle, K A; Moscicki, J

2012-06-28

247

Time-resolved NMR spectroscopy: ligand-induced refolding of riboswitches.  

PubMed

A detailed understanding of cellular mechanisms requires knowledge of structure and dynamics of the involved biomacromolecules at atomic resolution. NMR spectroscopy uniquely allows determination of static and dynamic processes at atomic level, including structured states often represented by a single state as well as by unstructured conformational ensembles. While a high-resolution description of structured states may also be obtained by other techniques, the characterization of structural transitions occurring during biomolecular folding is only feasible exploiting NMR spectroscopic methods. The NMR methodical strategy includes the fast initiation of a folding reaction in situ and the possibility to detect the induced process with sufficient time resolution on the respective NMR time scale. In the case of ligand-induced structural transitions of RNA, the initiation of the folding reaction can be achieved by laser-triggered deprotection of a photolabile caged ligand whose release induces folding of a riboswitch RNA. The strategy discussed here is general and can also be transferred to other biological processes, where at least one key reagent or substrate, e.g., ions, ligands, pH, or one specific conformational state, can be photochemically caged. The rates of reversible and irreversible reactions or structural transitions that can be covered by real-time NMR methods range from milliseconds up to hours.In this chapter, we discuss the application of a time-resolved NMR strategy to resolve the ligand-induced folding of the guanine-sensing riboswitch aptamer domain of the B. subtilis xpt-pbuX operon. PMID:19381559

Buck, Janina; Fürtig, Boris; Noeske, Jonas; Wöhnert, Jens; Schwalbe, Harald

2009-01-01

248

Coal liquefaction process streams characterization and evaluation: Estimation of total phenol concentrations in coal liquefaction resids by {sup 31}P NMR spectroscopy  

SciTech Connect

In this study, Iowa State University researchers used {sub 31}P-tagged reagents to derivatize the labile hydrogen functional groups in the THF-soluble portion of 850{degrees}F{sup +} distillation resid materials and the THF-soluble portion of process oils derived from direct coal liquefaction.{sup 31}P-NMR was used to analyze the derivatized samples. NMR peak assignments can be made by comparison to model compounds similarly derivatized. Species can be quantified by integration of the NMR signals. Different {sup 31}P-NMR tagged reagents can be used to produce different degrees of peak resolution in the NMR spectrum. This, in turn, partially dictates the degree of speciation and/or quantification of species, or classes of compounds, that can be accomplished. Iowa State chose a {sup 31}P-tagged reagent (ClPOCMe{sub 2}CMe{sub 2}O) which was shown previously to be particularly useful in the derivatization of phenols. The derivatized samples all exhibited a small group of peaks attributed to amines and a broad group of peaks in the phenol region. The presence of paramagnetic species in the samples caused the NMR signals to broaden. Electron paramagnetic resonance (EPR) spectra confirmed the presence of paramagnetic organic free radicals in selected samples. Various methods were employed to process the NMR data. The complexity and broadness of the phenol peak, however, made speciation of the phenols impractical.

Mohan, J.T.; Verkade, J.G. [Ames Lab., IA (United States)

1992-11-01

249

Coal liquefaction process streams characterization and evaluation: Estimation of total phenol concentrations in coal liquefaction resids by [sup 31]P NMR spectroscopy  

SciTech Connect

In this study, Iowa State University researchers used [sub 31]P-tagged reagents to derivatize the labile hydrogen functional groups in the THF-soluble portion of 850[degrees]F[sup +] distillation resid materials and the THF-soluble portion of process oils derived from direct coal liquefaction.[sup 31]P-NMR was used to analyze the derivatized samples. NMR peak assignments can be made by comparison to model compounds similarly derivatized. Species can be quantified by integration of the NMR signals. Different [sup 31]P-NMR tagged reagents can be used to produce different degrees of peak resolution in the NMR spectrum. This, in turn, partially dictates the degree of speciation and/or quantification of species, or classes of compounds, that can be accomplished. Iowa State chose a [sup 31]P-tagged reagent (ClPOCMe[sub 2]CMe[sub 2]O) which was shown previously to be particularly useful in the derivatization of phenols. The derivatized samples all exhibited a small group of peaks attributed to amines and a broad group of peaks in the phenol region. The presence of paramagnetic species in the samples caused the NMR signals to broaden. Electron paramagnetic resonance (EPR) spectra confirmed the presence of paramagnetic organic free radicals in selected samples. Various methods were employed to process the NMR data. The complexity and broadness of the phenol peak, however, made speciation of the phenols impractical.

Mohan, J.T.; Verkade, J.G. (Ames Lab., IA (United States))

1992-11-01

250

Novel monosaccharide fermentation products in Caldicellulosiruptor saccharolyticus identified using NMR spectroscopy  

PubMed Central

Background Caldicellulosiruptor saccharolyticus is a thermophilic, Gram-positive, non-spore forming, strictly anaerobic bacterium of interest in potential industrial applications, including the production of biofuels such as hydrogen or ethanol from lignocellulosic biomass through fermentation. High-resolution, solution-state nuclear magnetic resonance (NMR) spectroscopy is a useful method for the identification and quantification of metabolites that result from growth on different substrates. NMR allows facile resolution of isomeric (identical mass) constituents and does not destroy the sample. Results Profiles of metabolites produced by the thermophilic cellulose-degrading bacterium Caldicellulosiruptor saccharolyticus DSM 8903 strain following growth on different monosaccharides (D-glucose, D-mannose, L-arabinose, D-arabinose, D-xylose, L-fucose, and D-fucose) as carbon sources revealed several unexpected fermentation products, suggesting novel metabolic capacities and unexplored metabolic pathways in this organism. Both 1H and 13C nuclear magnetic resonance (NMR) spectroscopy were used to determine intracellular and extracellular metabolite profiles. One dimensional 1H NMR spectral analysis was performed by curve fitting against spectral libraries provided in the Chenomx software; 2-D homonuclear and heteronuclear NMR experiments were conducted to further reduce uncertainties due to unassigned, overlapping, or poorly-resolved peaks. In addition to expected metabolites such as acetate, lactate, glycerol, and ethanol, several novel fermentation products were identified: ethylene glycol (from growth on D-arabinose), acetoin and 2,3-butanediol (from growth on D-glucose, L-arabinose, and D-xylose), and hydroxyacetone (from growth on D-mannose, L-arabinose, and D-xylose). Production of ethylene glycol from D-arabinose was particularly notable, with around 10% of the substrate carbon converted into this uncommon fermentation product. Conclusions The present research shows that C. saccharolyticus, already of substantial interest due to its capability for biological ethanol and hydrogen production, has further metabolic potential for production of higher molecular weight compounds, such as acetoin and 2,3-butanediol, as well as hydroxyacetone and the uncommon fermentation product ethylene glycol. In addition, application of nuclear magnetic resonance (NMR) spectroscopy facilitates identification of novel metabolites, which is instrumental for production of desirable bioproducts from biomass through microbial fermentation.

2013-01-01

251

Ligand symmetry-equivalence on thiolate protected gold nanoclusters determined by NMR spectroscopy  

NASA Astrophysics Data System (ADS)

The Au144(SR)60 nanocluster has been a subject of structural conjecture since its initial description over a decade ago as a 29 kDa compound, yet a decisive empirical structure is elusive. Herein we show that 1H NMR spectroscopy can provide a detailed view of ligand-layer equivalence for thiolate protected gold nanoclusters. We show that Au25(SR)18, Au38(SR)24 and Au102(SR)44 nanoclusters have 1H NMR spectra where the number of distinct chemical environments for the R-groups is equivalent to the number of symmetry environments of the sulfur headgroups, which anchor each ligand. We also show that the Au144(SR)601H NMR spectrum is consistent with a previously published DFT-derived structural model for Au144(SR)60. We suggest that this analysis may be extended to other structurally obscure nanoclusters, such as a ~59 kDa compound for which we observe up to four symmetry environments.The Au144(SR)60 nanocluster has been a subject of structural conjecture since its initial description over a decade ago as a 29 kDa compound, yet a decisive empirical structure is elusive. Herein we show that 1H NMR spectroscopy can provide a detailed view of ligand-layer equivalence for thiolate protected gold nanoclusters. We show that Au25(SR)18, Au38(SR)24 and Au102(SR)44 nanoclusters have 1H NMR spectra where the number of distinct chemical environments for the R-groups is equivalent to the number of symmetry environments of the sulfur headgroups, which anchor each ligand. We also show that the Au144(SR)601H NMR spectrum is consistent with a previously published DFT-derived structural model for Au144(SR)60. We suggest that this analysis may be extended to other structurally obscure nanoclusters, such as a ~59 kDa compound for which we observe up to four symmetry environments. Electronic supplementary information (ESI) available: The syntheses and characterizations of Au102pMBA44 and Au144pMBA60, full 1H NMR spectra, along with the size determination of unknown AuNP with PAGE. See DOI: 10.1039/c2nr30259d

Wong, O. Andrea; Heinecke, Christine L.; Simone, Ashli R.; Whetten, Robert L.; Ackerson, Christopher J.

2012-06-01

252

Distinguishing Phosphate Structural Defects From Inclusions in Calcite and Aragonite by NMR Spectroscopy (Invited)  

NASA Astrophysics Data System (ADS)

Variations in the concentration of minor and trace elements are being studied extensively for potential use as proxies to infer environmental conditions at the time of mineral deposition. Such proxies rely fundamentally on a relationship between the activities in the solution and in the solid that would seem to be simple only in the case that the species substitutes into the mineral structure. Other incorporation mechanisms are possible, including inclusions (both mineral and fluid) and occlusion of surface adsorbate complexes, that might be sensitive to other factors, such as crystallization kinetics, and difficult to distinguish analytically. For example, it is known from mineral adsorption studies that surface precipitates can be nanoscopic, and might not be apparent at resolutions typical of microchemical analysis. Techniques by which a structural relationship between the substituting element and the host mineral structure are needed to provide a sound basis for geochemical proxies. NMR spectroscopy offers methods for probing such spatial relationship. We are using solid-state NMR spectroscopy to investigate phosphate incorporation in calcium carbonate minerals, including calcite speleothems and coral skeletal aragonite, at concentrations of the order 100 ?g P g -1. In 31P NMR spectra of most samples, narrow peaks arising from crystalline inclusions can be resolved, including apatite in coral aragonite and an unidentified phase in calcite. All samples studied yield also a broad 31P signal, centered near chemical shifts of +3 to +4 ppm, that could be assigned to phosphate defects in the host mineral and from which the fraction of P occurring in the carbonate mineral structure can be determined. To test this assignment we applied rotational-echo double-resonance (REDOR) NMR techniques that probe the molecular-scale proximity of carbonate groups to the phosphate responsible for the broad 31P peak. This method measures dipole-dipole coupling between 31P of phosphate and carbonate carbon, which varies with the inverse-cube of the internuclear distance. 31P{13C} REDOR NMR results for synthetic phosphate/(13C)-aragonite coprecipitates show that the broad peak is closely associated with carbonate, exhibiting a 31P-13C dipolar coupling qualitatively consistent with phosphate occupying an anion structural site (i.e., 6 C at 0.32 nm). 31P-detected 1H NMR spectra, which contain signal only from H located near P, show that structural water molecules help accommodate phosphate in the structure. Similar methods can be applied to other elements of potential paleo-proxy interest having NMR-active isotopes, including B, Mg, and Cd.

Phillips, B. L.; Mason, H. E.

2010-12-01

253

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

SciTech Connect

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

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

1989-11-28

254

Comparison of 1D and 2D NMR spectroscopy for metabolic profiling.  

PubMed

High-resolution, liquid state nuclear magnetic resonance (NMR) spectroscopy is a popular platform for metabolic profiling because the technique is nondestructive, quantitative, reproducible, and the spectra contain a wealth of biochemical information. Because of the large dynamic range of metabolite concentrations in biofluids, statistical analyses of one-dimensional (1D) proton NMR data tend to be biased toward selecting changes in more abundant metabolites. Although two-dimensional (2D) proton-proton experiments can alleviate spectral crowding, they have been mainly used for structural determination. In this study, 2D total correlation spectroscopy NMR was used to compare the global metabolic profiles of urine obtained from wild-type and Abcc6-knockout mice. The 2D data were compared to an improved 1D experiment in which signal contributions from macromolecules and the urea peak have been spectroscopically removed for more accurate quantitation of low-abundance metabolites. Although statistical models from both 1D and 2D data could differentiate samples acquired from the two groups of mice, only the 2D spectra allowed the characterization of statistically relevant changes in the low-abundance metabolites. While acquisition of the 2D data require more time, the data obtained resulted in a more meaningful and comprehensive metabolic profile, aided in metabolite identifications, and minimized ambiguities in peak assignments. PMID:18081246

Van, Que N; Issaq, Haleem J; Jiang, Qiujie; Li, Qiaoli; Muschik, Gary M; Waybright, Timothy J; Lou, Hong; Dean, Michael; Uitto, Jouni; Veenstra, Timothy D

2008-02-01

255

Stationary interphases with extended alkyl chains: a comparative study on chain order by solid-state NMR spectroscopy.  

PubMed

Stationary interphases with long n-alkyl chains (n = 18, 22, 30, 34) have been examined by solid-state NMR spectroscopy. The determination of the silane functionality and the degree of cross-linking of silane ligands on the silica surface was performed by 29Si CP/MAS NMR spectroscopy. High-speed 1H MAS and 13C CP/MAS NMR spectroscopy were utilized to assess alkyl chain order and mobility of the different bonded phases. For this purpose, 1H NMR line widths and 13C chemical shifts have been evaluated. It is shown that stationary phase order and rigidity increase with alkyl chain length. In addition, the temperature-dependent trans/gauche conformational change occurs at higher temperatures for a polymeric C34 phase compared with a C30 sorbent. This behaviour is discussed in the context of previously reported chromatographic (HPLC) shape selectivity differences. PMID:9477449

Pursch, M; Brindle, R; Ellwanger, A; Sander, L C; Bell, C M; Händel, H; Albert, K

1997-12-01

256

Connecting discrete stereoclusters by using DFT and NMR spectroscopy: the case of nivariol.  

PubMed

The structural determination of small organic molecules is mainly undertaken by using NMR techniques, although it is increasingly supplemented by using computational methods. NMR parameters, such as chemical shifts and coupling constants, are extremely sensitive indicators of local molecular conformation and are a source of structural evidence. However, their interpretation is fairly challenging in many circumstances, such as the case of the new polyether squalene derivative nivariol, the structure of which was elucidated by means of NMR spectroscopy and DFT calculations. The potential flexibility of this molecule and the high number of quaternary carbon atoms that it contains make its configurational assignment very difficult. Moreover, the relative configuration of four separated stereoclusters was established and subsequently connected by using NOE and J-based analysis, as well as by a comparison of its experimental (13)C?NMR chemical shifts with the corresponding population-weighted values, as calculated by using DFT methods. Limitations of these used approaches became apparent but were overcome by combining the two methods. PMID:23649973

Cen-Pacheco, Francisco; Rodríguez, Jaime; Norte, Manuel; Fernández, José J; Hernández Daranas, Antonio

2013-05-06

257

NASR: an effective approach for simultaneous noise and artifact suppression in NMR spectroscopy.  

PubMed

As a powerful tool for biological analysis, especially protein structure and dynamic studies, nuclear magnetic resonance (NMR) spectroscopy suffers from intrinsic low signal to nose ratio (SNR) and long acquisition time required for multidimensional (nD) experiments. Nonuniform sampling (NUS) can effectively speed up the experiment but often introduces artifacts into the spectrum. In addition to the development of highly sensitive hardware and NMR pulse sequences, data postprocessing is a relative simple and cost-effective method to improve the SNR and suppress the artifacts. In this work, we propose an effective approach for simultaneously suppressing noise and artifacts based on the resampling principle. The method is named NASR for short and tested using one-, two-, and three-dimensional (1D, 2D, and 3D) NMR spectra that were acquired using ether conventional or NUS (spiral and random, for 3D) approaches. The results reveal that the NASR is fast and applicable for improving the quality of 1D to nD NMR spectra with all kinds of sampling schemes. PMID:23339579

Jiang, Bin; Luo, Fan; Ding, Yiming; Sun, Peng; Zhang, Xu; Jiang, Ling; Li, Conggang; Mao, Xi-an; Yang, Daiwen; Tang, Chun; Liu, Maili

2013-02-01

258

Fast and accurate quantitation of glucans in complex mixtures by optimized heteronuclear NMR spectroscopy.  

PubMed

Nuclear magnetic resonance (NMR) spectroscopy is a widely used technique for mixture analysis, but it has shortcomings in resolving carbohydrate mixtures due to the narrow chemical shift range of glycans in general and fragments of homopolymers in particular. Here, we suggest a protocol toward fast spectroscopic glycan mixture analysis. We show that a plethora of oligosaccharides comprising only ?-glucopyranosyl residues can be resolved into distinct quantifiable signals with NMR experiments that are substantially faster than chromatographic runs. Conceptually, the approach fully exploits the narrow line widths of glycans (?1/2 < 3 Hz) in the (13)C spectral dimension while disregarding superfluous spectral information in compound identification and quantitation. The acetal (H1C1) groups suffice to spectroscopically resolve ?20 different starch fragments in optimized (1)H-(13)C NMR with a narrow (13)C spectral width (3 ppm) that allows sampling the indirect (13)C dimension at high resolution within 15 min. Rapid quantitations by high-resolution NMR data are achieved for glycans at concentrations as low as 10 ?g/mL. For validation, comparisons were made with quantitations obtained by more time-consuming chromatographic methods and yielded coefficients of determination (R(2)) above 0.99. PMID:23952648

Bøjstrup, Marie; Petersen, Bent O; Beeren, Sophie R; Hindsgaul, Ole; Meier, Sebastian

2013-08-23

259

NMR spectroscopy as a tool to close the gap on metabolite characterization under MIST.  

PubMed

Withdrawals from the market due to unforeseen adverse events have triggered changes in the way therapeutics are discovered and developed. This has resulted in an emphasis on truly understanding the efficacy and toxicity profile of new chemical entities (NCE) and the contributions of their metabolites to on-target pharmacology and off-target receptor-mediated toxicology. Members of the pharmaceutical industry, scientific community and regulatory agencies have held dialogues with respect to metabolites in safety testing (MIST); and both the US FDA and International Conference on Harmonisation have issued guidances with respect to when and how to characterize metabolites for human safety testing. This review provides a brief overview of NMR spectroscopy as applied to the structure elucidation and quantification of drug metabolites within the drug discovery and development process. It covers advances in this technique, including cryogenic cooling of detection circuitry for enhanced sensitivity, hyphenated LC-NMR techniques, improved dynamic range through new solvent-suppression pulse sequences and quantitation. These applications add to the already diverse NMR toolkit and further anchor NMR as a technique that is directly applicable to meeting the requirements of MIST guidelines. PMID:21083239

Caceres-Cortes, Janet; Reily, Michael D

2010-07-01

260

Probing a CMP-Kdn synthetase by 1H, 31P, and STD NMR spectroscopy.  

PubMed

CMP-Kdn synthetase catalyses the reaction of sialic acids (Sia) and cytidine-5'-triphosphate (CTP) to the corresponding activated sugar nucleotide CMP-Sia and pyrophosphate PP(i). STD NMR experiments of a recombinant nucleotide cytidine-5'-monophosphate-3-deoxy-d-glycero-d-galacto-nonulosonic acid synthetase (CMP-Kdn synthetase) were performed to map the binding epitope of the substrate CTP and the product CMP-Neu5Ac. The STD NMR analysis clearly shows that the anomeric proton of the ribose moiety of both investigated compounds is in close proximity to the protein surface and is likely to play a key role in the binding process. The relative rates of the enzyme reaction, derived from (1)H NMR signal integrals, show that Kdn is activated at a rate 2.5 and 3.1 faster than Neu5Ac and Neu5Gc, respectively. Furthermore, proton-decoupled (31)P NMR spectroscopy was successfully used to follow the enzyme reaction and clearly confirmed the appearance of CMP-Sia and the inorganic pyrophosphate by-product. PMID:15629150

Haselhorst, Thomas; Münster-Kühnel, Anja K; Stolz, Anita; Oschlies, Melanie; Tiralongo, Joe; Kitajima, Ken; Gerardy-Schahn, Rita; von Itzstein, Mark

2005-02-11

261

Determination of the biogenic secondary organic aerosol fraction in the boreal forest by NMR spectroscopy  

NASA Astrophysics Data System (ADS)

The study investigates the sources of fine organic aerosol (OA) in the boreal forest, based on measurements including both filter sampling (PM1) and online methods and carried out during a one-month campaign held in Hyytiälä, Finland, in spring 2007. Two aerosol mass spectrometers (Q-AMS, ToF-AMS) were employed to measure on-line concentrations of major non-refractory aerosol species, while the water extracts of the filter samples were analyzed by nuclear magnetic resonance (NMR) spectroscopy for organic functional group characterization of the polar organic fraction of the aerosol. AMS and NMR spectra were processed separately by non-negative factorization algorithms, in order to apportion the main components underlying the submicrometer organic aerosol composition and depict them in terms of both mass fragmentation patterns and functional group compositions. The NMR results supported the AMS speciation of oxidized organic aerosol (OOA) into two main fractions, which could be generally labelled as more and less oxidized organics. The more oxidized component was characterized by a mass spectrum dominated by the m/z 44 peak, and in parallel by a NMR spectrum showing aromatic and aliphatic backbones highly substituted with oxygenated functional groups (carbonyls/carboxyls and hydroxyls). Such component, contributing on average 50% of the OA mass throughout the observing period, was associated with pollution outbreaks from the Central Europe. The less oxidized component was enhanced in concomitance with air masses originating from the North-to-West sector, in agreement with previous investigations conducted at this site. NMR factor analysis was able to separate two distinct components under the less oxidized fraction of OA. One of these NMR-factors was associated with the formation of terrestrial biogenic secondary organic aerosol (BSOA), based on the comparison with spectral profiles obtained from laboratory experiments of terpenes photo-oxidation. The second NMR factor associated with western air masses was linked to biogenic marine sources, and was enriched in low-molecular weight aliphatic amines. Such findings provide evidence of at least two independent sources originating biogenic organic aerosols in Hyytiälä by oxidation and condensation mechanisms: reactive terpenes emitted by the boreal forest and compounds of marine origin, with the latter relatively more important when predominantly polar air masses reach the site. This study is an example of how spectroscopic techniques, such as proton NMR, can add functional group specificity for certain chemical features (like aromatics) of OA with respect to AMS. They can therefore be profitably exploited to complement aerosol mass spectrometric measurements in organic source apportionment studies.

Finessi, E.; Decesari, S.; Paglione, M.; Giulianelli, L.; Carbone, C.; Gilardoni, S.; Fuzzi, S.; Saarikoski, S.; Raatikainen, T.; Hillamo, R.; Allan, J.; Mentel, Th. F.; Tiitta, P.; Laaksonen, A.; Petäjä, T.; Kulmala, M.; Worsnop, D. R.; Facchini, M. C.

2012-01-01

262

Earle K. Plyler Prize for Molecular Spectroscopy Talk: Coherent Ultrafast Multidimensional Spectroscopy of Molecules; From NMR to X-rays  

NASA Astrophysics Data System (ADS)

Multidimensional spectroscopic techniques which originated with NMR in the 1970s have been extended over the past 15 years to the optical regime. NMR spectroscopists have developed methods for the design of pulse sequences that resolve otherwise congested spectra, enhance selected spectral features and reveal desired dynamical events. The major experimental and computational advances required for extending these ideas to study electronic and vibrational motions on the femtosecond timescale will be surveyed. The response of complex molecules and semiconductor nanostructures to sequences of optical pulses provides snapshots of their structure and dynamical processes. Two-dimensional correlation plots of the signals show characteristic cross-peak patterns which carry information about hydrogen bonding, secondary structure fluctuations of proteins and amyloid fibrils, and coherent and incoherent energy and charge transfer in photosynthetic complexes. Double quantum coherence signals that are induced by correlations among electrons or excitons allow the visualization of correlated wavefunctions. Future extensions to the attosecond regime using xray pulses will be discussed. Since core excitations are highly localized at selected atoms, such signals can monitor the motions of valence electron wavepackets in real space with atomic spatial resolution. Common principles underlying coherent spectroscopy techniques for spins, valence electrons, and core electronic excitations, spanning frequencies from radiowaves, infrared, ultraviolet all the way to hard X-rays will be discussed. [4pt] [1] "Coherent Multidimensional Optical Probes for Electronic Correlations and Exciton Dynamics; from NMR to X-rays", S. Mukamel, D. Abramavicius, L. Yang, W.Zhuang, I.V. Schweigert and D. Voronine. Acct.Chem.Res. Acct.Chem.Res. 42, 553-562 (2009). [0pt] [2] "Coherent Multidimensional Optical Spectroscopy Excitons in Molecular Aggregates; Quasiparticle vs. Supermolecule Perspectives", D. Abramavicius, B. Palmieri, D. Voronine, F. Sanda and S. Mukamel, Chem. Rev. 109, 2350-2408 (2009).

Mukamel, Shaul

2011-03-01

263

Organic carbon and sulphur compounds in wetland soils: insights on structure and transformation processes using Kedge XANES and NMR spectroscopy  

Microsoft Academic Search

X-ray absorption near-edge structure (XANES) and nuclear magnetic resonance (NMR) spectroscopy were used in combination to characterize organic carbon structures in a series of wetland soils in Saskatchewan, and XANES spectroscopy was also used to examine sulphur speciation in the soils. The organic C contents of most of the wetland soils are consistently higher by a factor of two to

Aleksander Jokic; Jeffrey N Cutler; Elena Ponomarenko; Garth van der Kamp; Darwin W Anderson

2003-01-01

264

Natural abundance high-resolution solid state 2 H NMR spectroscopy  

NASA Astrophysics Data System (ADS)

We report for the first time an approach for natural abundance solid state 2 H NMR spectroscopy involving magic angle sample spinning (MAS), high-power 1 H decoupling (HPPD) and 1 H- 2 H cross polarization (CP). Taking tetrakis(trimethylsilyl)silane (TTMSS), adamantane, 1-chloroadamantane, hexamethylbenzene (HMB), 2,2-dimethyl-1,3-propanediol (DMPD) and 2-hydroxymethyl-2-methyl-1,3-propanediol (HMPD) as examples, it has been shown that the combination of HPPD and MAS can be applied readily to study rotator phase solids, allowing isotropic peaks arising from chemically inequivalent 2 H nuclei to be resolved. For natural abundance samples of TTMSS and chloroadamantane, it has been shown that 2 H CP/HPPD/MAS NMR experiments, involving polarization transfer from 1 H to 2 H, may provide considerable sensitivity enhancement in comparison with single pulse experiments.

Aliev, Abil E.; Harris, Kenneth D. M.; Apperley, David C.

1994-08-01

265

Refolding of ribonuclease A monitored by real-time photo-CIDNP NMR spectroscopy.  

PubMed

Photo-CIDNP NMR spectroscopy is a powerful method for investigating the solvent accessibility of histidine, tyrosine and tryptophan residues in a protein. When coupled to real-time NMR, this technique allows changes in the environments of these residues to be used as a probe of protein folding. In this paper we describe experiments performed to monitor the refolding of ribonuclease A following dilution from a high concentration of chemical denaturant. These experiments provide a good example of the utility of this technique which provides information that is difficult to obtain by other biophysical methods. Real-time photo-CIDNP measurements yield residue-specific kinetic data pertaining to the folding reaction, interpreted in terms of current knowledge of the folding of bovine pancreatic ribonuclease A. PMID:19436956

Day, Iain J; Maeda, Kiminori; Paisley, Howard J; Mok, K Hun; Hore, P J

2009-05-13

266

Application of /sup 31/P-NMR spectroscopy to the study of striated muscle metabolism  

SciTech Connect

This review presents the principles and limitations of phosphorus nuclear magnetic resonance (/sup 31/P-NMR) spectroscopy as applied to the study of striated muscle metabolism. Application of the techniques discussed include noninvasive measurement of high-energy phosphate, intracellular pH, intracellular free Mg/sup 2 +/, and metabolite compartmentation. In perfused cat biceps (fast-twitch) muscles, but not in soleus (slow-twitch), NMR spectra indicate a substantially lower (1 mM) free inorganic phosphate level than when measured chemically (6 mM). In addition, saturation and inversion spin-transfer methods that enable direct measurement of the unidirectional fluxes through creatine kinase are described. In perfused cat biceps muscle, results suggest that this enzyme and its substrates are in simple chemical equilibrium.

Meyer, R.A.; Kushmerick, M.J.; Brown, T.R.

1982-01-01

267

Lipid profiling of cancerous and benign gallbladder tissues by 1H NMR spectroscopy.  

PubMed

Qualitative and quantitative (1) H NMR analysis of lipid extracts of gallbladder tissue in chronic cholecystitis (CC, benign) (n = 14), xanthogranulomatous cholecystitis (XGC, intermediate) (n = 9) and gallbladder cancer (GBC, malignant) (n = 8) was carried out to understand the mechanisms involved in the transformation of benign gallbladder tissue to intermediate and malignant tissue. The results revealed alterations in various tissue lipid components in gallbladder in CC, XGC and GBC. The difference in the nature of lipid components in benign and malignant disease may aid in the identification of the biological pathways involved in the etiopathogenesis of GBC. This is the first study on lipid profiling of gallbladder tissue by (1) H NMR spectroscopy, and has possible implications for the development of future diagnostic approaches. PMID:22945290

Jayalakshmi, Kamaiah; Sonkar, Kanchan; Behari, Anu; Kapoor, Vinay K; Sinha, Neeraj

2010-12-28

268

Strategy for the Stereochemical Assignment of Tris-Heteroleptic Ru(II) Complexes by NMR Spectroscopy  

PubMed Central

The relative stereochemistry of tris-heteroleptic ruthenium complexes [Ru(pp)(pp?)(pp?)](PF6)2, where pp = 1,10-phenanthroline-4-carboxamide, pp? = 5,6-dimethyl-1,10-phenanthroline, and pp? = 7,8-dimethyl dipyrido[3,2-a:2?,3?-c]phenazine, was studied using NMR spectroscopy. The 1H and 13C spectra were assigned by using (DQF)-COSY, HSQC, and HMBC experiments for the two diastereomers, each a pair of enantiomers. NOE contacts between the neighboring ligands differentiated the two halves of each symmetrical ligand, thus enabling a full assignment of the NMR signals and an accurate determination of the relative stereochemistry of the complexes. Introduction of an additional chiral center to ligand pp by coupling it with L-lysine caused removal of the enantiomerism. Thus four diastereomers were observed and their relative stereochemistry determined.

Xie, Xiulan; Mulcahy, Seann P.; Meggers, Eric

2009-01-01

269

NMR spectroscopy of hyperpolarized ^129Xe at high fields: Maintaining spin polarization after optical pumping.  

NASA Astrophysics Data System (ADS)

Spin-polarized ^129Xe has become an invaluable tool in nuclear magnetic resonance research, with applications ranging from medical imaging to high-resolution spectroscopy. High-field NMR studies using hyperpolarized xenon as a spectroscopic probe benefit from the high signal-to-noise ratios and large chemical shifts typical of optically-pumped noble gases. The experimental sensitivity is ultimately determined by the absolute polarization of the xenon in the sample, which can be substantially decreased during purification and transfer. NMR of xenon at high fields (9.4 Tesla) will be discussed, and potential mechanisms of spin relaxation during the distillation, storage(N. N. Kuzma, B. Patton, K. Raman, and W. Happer, Phys. Rev. Lett. 88), 147602 (2002)., and delivery of hyperpolarized xenon will be analyzed.

Patton, Brian; Kuzma, Nicholas N.; Lisitza, Natalia V.; Happer, William

2003-05-01

270

An instrument control and data analysis program for NMR imaging and spectroscopy  

SciTech Connect

We describe a software environment created to support real-time instrument control and signal acquisition as well as array-processor based signal and image processing in up to five dimensions. The environment is configured for NMR imaging and in vivo spectroscopy. It is designed to provide flexible tools for implementing novel NMR experiments in the research laboratory. Data acquisition and processing operations are programmed in macros which are loaded in assembled from to minimize instruction overhead. Data arrays are dynamically allocated for efficient use of memory and can be mapped directly into disk files. The command set includes primitives for real-time control of data acquisition, scalar arithmetic, string manipulation, branching, a file system and vector operations carried out by an array processor. 6 figs.

Roos, M.S.; Mushlin, R.A.; Veklerov, E.; Port, J.D.; Ladd, C.; Harrison, C.G.

1988-01-01

271

Structure of lysozyme dissolved in neat organic solvents as assessed by NMR and CD spectroscopies  

SciTech Connect

The structure of the model protein hen egg-white lysozyme dissolved in water and in five neat organic solvents (ethylene glycol, methanol, dimethylsufloxide (DMSO), formamide, and dimethylformamide (DMF)) has been examined by means of {sup 1}H NMR and circular dichroism (CD) spectroscopies. The NMR spectra of lysozyme reveal the lack of a defined tertiary structure in all five organic solvents, although the examination of line widths suggests the possibility of some ordered structure in ethylene glycol and in methanol. The near-UV CD spectra of the protein suggest no tertiary structure in lysozyme dissolved in DMSO, formamide, and DMF, while a distinctive tertiary structure is seen in ethylene glycol and a drastically changed one in methanol. A highly developed secondary structure was observed by far-UV CD in ethylene glycol and methanol; interestingly, the {alpha}-helix content of the protein in both was greater than in water, while the {beta}-structure content was lower.

Knubovets, T.; Klibanov, A.M. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Chemistry; Osterhout, J.J. [Rowland Inst. for Science, Cambridge, MA (United States)

1999-04-20

272

Tb3+ and Ca2+ binding to phosphatidylcholine. A study comparing data from optical, NMR, and infrared spectroscopies.  

PubMed Central

The paramagnetic and luminescent lanthanides are unique probes of cation-phospholipid interactions. Their spectroscopic properties provide the means to characterize and monitor complexes formed with lipids in ways not possible with biochemically more interesting cations, such as Ca2+. In this work, Tb3+-phosphatidylcholine complexes are described using the luminescence properties of Tb3+, the effect of its paramagnetism on the 31P NMR and 13C NMR spectra of the lipid, and changes in the infrared spectrum of the lipid induced by the cation. There are two Tb3+-phosphatidylcholine complexes with very different coordination environments, as evidenced by changes in the optical excitation spectrum of the lanthanide. The NMR experiments indicate that the two complexes differ in the number of phosphate groups directly coordinating Tb3+. Tb3+ binding induces changes in the phosphodiester infrared bands that are most consistent with bidentate chelation of Tb3+ by each phosphate, whereas Ca2+-induced changes are more consistent with monodentate coordination. The significance of this discrepancy is discussed.

Petersheim, M; Halladay, H N; Blodnieks, J

1989-01-01

273

Equilibrium forms of vitisin B pigments in an aqueous system studied by NMR and visible spectroscopy.  

PubMed

The main species in the acid-base equilibria of two pyranoanthocyanins (vitisins B), pyranomalvidin-3-glucoside I and pyranomalvidin-3-O-coumaroylglucoside II, and the respective pK(a) were determined using NMR, visible spectroscopy, and mass spectrometry techniques. The three equilibria involve protonation of the pyranoflavylium cation of vitisin B (pK(a1)) and two deprotonations (pK(a2) and pK(a3)). For pigment I, the values obtained through the titration curves of the chemical shift of some protons versus pH were (pK(a1) < 0.68; pK(a2) = 4.40 +/- 0.08; pK(a3) = 7.45 +/- 0.09) very close to the values obtained by visible spectroscopy (pK(a1) < 0.63; pK(a2) = 4.43 +/- 0.02; pK(a3) = 7.34 +/- 0.03). For pigment II, it was only possible to calculate the pK(a) by visible spectroscopy (pK(a1) < 0.75; pK(a2) = 4.66 +/- 0.10; pK(a3) = 6.76 +/- 0.10). NMR studies have shown that pigment I does not undergo hydration, and the hypothesis of the occurrence of hemiacetal forms in equilibrium was discarded. PMID:19719269

Oliveira, Joana; Mateus, Nuno; Silva, Artur M S; de Freitas, Victor

2009-08-13

274

Microfabricated Inserts for Magic Angle Coil Spinning (MACS) Wireless NMR Spectroscopy  

PubMed Central

This article describes the development and testing of the first automatically microfabricated probes to be used in conjunction with the magic angle coil spinning (MACS) NMR technique. NMR spectroscopy is a versatile technique for a large range of applications, but its intrinsically low sensitivity poses significant difficulties in analyzing mass- and volume-limited samples. The combination of microfabrication technology and MACS addresses several well-known NMR issues in a concerted manner for the first time: (i) reproducible wafer-scale fabrication of the first-in-kind on-chip LC microresonator for inductive coupling of the NMR signal and reliable exploitation of MACS capabilities; (ii) improving the sensitivity and the spectral resolution by simultaneous spinning the detection microcoil together with the sample at the “magic angle” of 54.74° with respect to the direction of the magnetic field (magic angle spinning – MAS), accompanied by the wireless signal transmission between the microcoil and the primary circuit of the NMR spectrometer; (iii) given the high spinning rates (tens of kHz) involved in the MAS methodology, the microfabricated inserts exhibit a clear kinematic advantage over their previously demonstrated counterparts due to the inherent capability to produce small radius cylindrical geometries, thus tremendously reducing the mechanical stress and tearing forces on the sample. In order to demonstrate the versatility of the microfabrication technology, we have designed MACS probes for various Larmor frequencies (194, 500 and 700 MHz) testing several samples such as water, Drosophila pupae, adamantane solid and LiCl at different magic angle spinning speeds.

Badilita, Vlad; Fassbender, Birgit; Kratt, Kai; Wong, Alan; Bonhomme, Christian; Sakellariou, Dimitris; Korvink, Jan G.; Wallrabe, Ulrike

2012-01-01

275

Effects of copper on Sambucus nigra L. seedlings studied by electron paramagnetic resonance and atomic absorption spectroscopies  

Microsoft Academic Search

We present in this work preliminary results on the translocation of copper, manganese and iron from soil to leaves of Sambucus nigra L. seedlings in the presence of increasing copper concentrations in the growth medium. The use of electron spin resonance spectroscopy and the comparison with atomic absorption spectroscopy is not presently common in the study of metal absorption in

Emilio Francesco Orsega; Francesca Agnoli; Giovanni Cacco; Eugenia Delaney; Emanuele Argese

2003-01-01

276

Chemistry of paramagnetic and diamagnetic contrast agents for Magnetic Resonance Imaging and Spectroscopy pH responsive contrast agents.  

PubMed

We provide a brief overview of the chemistry and most relevant properties of paramagnetic and diamagnetic contrast agents (CAs) for Magnetic Resonance Imaging and Magnetic Resonance Spectroscopic Imaging. Paramagnetic CAs for MRI consist mainly of Gd(III) complexes from linear or macrocyclic polyaminopolycarboxylates. These agents reduce, the relaxation times T(1) and T(2) of the water protons in a concentration dependent manner, increasing selectively MRI contrast in those regions in which they accumulate. In most instances they provide anatomical information on the localization of lesions and in some specific cases they may allow to estimate some physiological properties of tissues including mainly vascular performance. Because of its ability to discriminate easily between normal and diseased tissue, extracellular pH (pH(e)) has been added recently, to the battery of variables amenable to MRI investigation. A variety of Gd(III) containing macrocycles sensitive to pH, endogenous or exogenous polypeptides or even liposomes have been investigated for this purpose, using the pH dependence of their relaxivity or magnetization transfer rate constant (chemical exchange saturation transfer, CEST). Many environmental circumstances in addition to pH affect, however, relaxivity or magnetization transfer rate constants of these agents, making the results of pH measurements by MRI difficult to interpret. To overcome these limitations, our laboratory synthesized and developed a novel series of diamagnetic CAs for Magnetic Resonance Spectroscopic Imaging, a new family of monomeric and dimeric imidazolic derivatives able to provide unambiguous measurements of pH(e), independent of water relaxivity, diffusion or exchange. PMID:18455343

Pérez-Mayoral, Elena; Negri, Viviana; Soler-Padrós, Jordi; Cerdán, Sebastián; Ballesteros, Paloma

2008-05-01

277

Spectroscopy  

NSDL National Science Digital Library

This page is a set of concept test questions about organic chemistry spectroscopy. There are ten questions about topics including trans isomer and NMR spectra, C-X vibration, wavenumber absorption, and carbon signals.

2008-03-11

278

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

279

Functional group analysis in coal and on coal surfaces by NMR spectroscopy  

SciTech Connect

An accurate knowledge of the oxygen-bearing labile hydrogen functional groups (e.g., carboxylic acids, phenols and alcohols) in coal is required for today's increasingly sophisticated coal cleaning and beneficiation processes. Phospholanes (compounds having the general structure -POCH{sub 2}CH{sub 2}O (1)) are being investigated as reagents for the tagging of liable hydrogen functional groups in coal materials with the NMR-active {sup 31}P nucleus. Of twelve such reagents investigated so far, 2 (2-chloro-1,3-dioxaphospholane, ClPOCH{sub 2}CH{sub 2}O) and 8 (2-chloro-1,3-dithiaphospholane, ClPSCH{sub 2}CH{sub 2}S) have been found to be useful in identifying and quantitating, by {sup 31}P NMR spectroscopy, labile hydrogen functional groups in an Illinois No. 6 coal condensate. Reagent 2 has also been used to quantitate moisture in pyridine extracts of Argonne Premium Coal Samples. Preliminary {sup 119}Sn NMR spectroscopic results on model compounds with the new reagent CF{sub 3}C(O)NHSnMe{sub 3} (N-trimethylstannyltrifluoroacetamide, 14) suggest that labile hydrogen functional groups in coal materials may be more precisely identified with 14 than with phospholanes. 14 refs., 2 figs., 2 tabs.

Verkade, J.G.

1990-01-01

280

Quality assessment and authentication of virgin olive oil by NMR spectroscopy: a critical review.  

PubMed

Nuclear Magnetic Resonance (NMR) Spectroscopy has been extensively used for the analysis of olive oil and it has been established as a valuable tool for its quality assessment and authenticity. To date, a large number of research and review articles have been published with regards to the analysis of olive oil reflecting the potential of the NMR technique in these studies. In this critical review, we cover recent results in the field and discuss deficiencies and precautions of the three NMR techniques ((1)H, (13)C, (31)P) used for the analysis of olive oil. The two methodological approaches of metabonomics, metabolic profiling and metabolic fingerprinting, and the statistical methods applied for the classification of olive oils will be discussed in critical way. Some useful information about sample preparation, the required instrumentation for an effective analysis, the experimental conditions and data processing for obtaining high quality spectra will be presented as well. Finally, a constructive criticism will be exercised on the present methodologies used for the quality control and authentication of olive oil. PMID:23410622

Dais, Photis; Hatzakis, Emmanuel

2012-12-10

281

Investigation of Chiral Molecular Micelles by NMR Spectroscopy and Molecular Dynamics Simulation  

PubMed Central

NMR spectroscopy and molecular dynamics (MD) simulation analyses of the chiral molecular micelles poly-(sodium undecyl-(L,L)-leucine-valine) (poly-SULV) and poly-(sodium undecyl-(L,L)- valine-leucine) (poly-(SUVL)) are reported. Both molecular micelles are used as chiral selectors in electrokinetic chromatography and each consists of covalently linked surfactant chains with chiral dipeptide headgroups. To provide experimental support for the structures from MD simulations, NOESY spectra were used to identify protons in close spatial proximity. Results from the NOESY analyses were then compared to radial distribution functions from MD simulations. In addition, the hydrodynamic radii of both molecular micelles were calculated from NMR-derived diffusion coefficients. Corresponding radii from the MD simulations were found to be in agreement with these experimental results. NMR diffusion experiments were also used to measure association constants for polar and non-polar binaphthyl analytes binding to both molecular micelles. Poly(SUVL) was found to bind the non-polar analyte enantiomers more strongly, while the more polar analyte enantiomers interacted more strongly with poly(SULV). MD simulations in tum showed that poly(SUL V) had a more open structure that gave greater access for water molecules to the dipeptide headgroup region.

Morris, Kevin F.; Billiot, Eugene J.; Billiot, Fereshteh H.; Lipkowitz, Kenny B.; Southerland, William M.; Fang, Yayin

2013-01-01

282

Investigation of Oxidative Degradation in Polymers Using (17)O NMR Spectroscopy  

SciTech Connect

The thermal oxidation of pentacontane (C{sub 50}H{sub 102}), and of the homopolymer polyisoprene, has been investigated using {sup 17}O NMR spectroscopy. By performing the oxidation using {sup 17}O labeled O{sub 2} gas, it is possible to easily identify degradation products, even at relatively low concentrations. It is demonstrated that details of the degradation mechanism can be obtained from analysis of the {sup 17}O NMR spectra as a function of total oxidation. Pentacontane reveals the widest variety of reaction products, and exhibits changes in the relative product distributions with increasing O{sub 2} consumption. At low levels of oxygen incorporation, peroxides are the major oxidation product, while at later stages of degradation these species are replaced by increasing concentrations of ketones, alcohols, carboxylic acids and esters. Analyzing the product distribution can help in identification of the different free-radical decomposition pathways of hydroperoxides, including recombination, proton abstraction and chain scission, as well as secondary reactions. The {sup 17}O NMR spectra of thermally oxidized polyisoprene reveal fewer degradation functionalities, but exhibit an increased complexity in the type of observed degradation species due to structural features such as unsaturation and methyl branching. Alcohols and ethers formed from hydrogen abstraction and free radical termination.

Alam, Todd M.; Celina, Mathew; Assink, Roger A.; Clough, Roger L.; Gillen, Kenneth T.; Wheeler David R.

1999-07-20

283

Sensitivity and Resolution Enhancement in Solid-State NMR Spectroscopy of Bicelles  

PubMed Central

Magnetically aligned bicelles are becoming attractive model membranes to investigate the structure, dynamics, geometry, and interaction of membrane-associated peptides and proteins using solution- and solid-state NMR experiments. Recent studies have shown that bicelles are more suitable than mechanically aligned bilayers for multidimensional solid-state NMR experiments. In this work, we describe experimental aspects of the natural abundance 13C and 14N NMR spectroscopy of DMPC/DHPC bicelles. In particular, approaches to enhance the sensitivity and resolution and to quantify radio frequency heating effects are presented. Sensitivity of 13C detection using single pulse excitation, conventional cross-polarization (CP), ramp-CP, and NOE techniques are compared. Our results suggest that the proton decoupling efficiency of the FLOPSY pulse sequence is better than that of continuous wave decoupling, TPPM, SPINAL and WALTZ sequences. A simple method of monitoring the water proton chemical shift is demonstrated for the measurement of sample temperature and calibration of the radio-frequency-induced heating in the sample. The possibility of using 14N experiments on bicelles is also discussed.

Dvinskikh, Sergey V.; Yamamoto, Kazutoshi; Durr, Ulrich H. N.; Ramamoorthy, Ayyalusamy

2007-01-01

284

Enhanced Sensitivity by Nonuniform Sampling Enables Multidimensional MAS NMR Spectroscopy of Protein Assemblies  

PubMed Central

We report dramatic sensitivity enhancements in multidimensional MAS NMR spectra by the use of nonuniform sampling (NUS) and introduce Maximum Entropy Interpolation (MINT) processing that assures the linearity between the time- and frequency domains of the NUS acquired datasets. A systematic analysis of sensitivity and resolution in 2D and 3D NUS spectra reveals that with NUS at least one-and-a-half to two-fold sensitivity enhancement can be attained in each indirect dimension without compromising the spectral resolution. These enhancements are similar to or higher than those attained by the newest-generation commercial cryogenic probes. We explore the benefits of this NUS/MaxEnt approach in proteins and protein assemblies using 1-73-(U-13C,15N)/74-108-(U-15N) E. coli thioredoxin reassembly. We demonstrate that in thioredoxin reassembly, NUS permits acquisition of high-quality 3D-NCACX spectra, which are inaccessible with conventional sampling due to prohibitively long experiment times. Of critical importance, issues which hinder NUS-based SNR enhancement in 3D-NMR of liquids are mitigated in the study of solid samples where theoretical enhancements on the order of 3-4 fold are accessible by compounding the NUS-based SNR enhancement of each indirect dimension. NUS/MINT is anticipated to be widely applicable and advantageous for multidimensional heteronuclear MAS NMR spectroscopy of proteins, protein assemblies, and other biological systems.

Paramasivam, Sivakumar; Suiter, Christopher L.; Hou, Guangjin; Sun, Shangjin; Palmer, Melissa; Hoch, Jeffrey C.; Rovnyak, David; Polenova, Tatyana

2012-01-01

285

Rapid Etiological Classification of Meningitis by NMR Spectroscopy Based on Metabolite Profiles and Host Response  

PubMed Central

Bacterial meningitis is an acute disease with high mortality that is reduced by early treatment. Identification of the causative microorganism by culture is sensitive but slow. Large volumes of cerebrospinal fluid (CSF) are required to maximise sensitivity and establish a provisional diagnosis. We have utilised nuclear magnetic resonance (NMR) spectroscopy to rapidly characterise the biochemical profile of CSF from normal rats and animals with pneumococcal or cryptococcal meningitis. Use of a miniaturised capillary NMR system overcame limitations caused by small CSF volumes and low metabolite concentrations. The analysis of the complex NMR spectroscopic data by a supervised statistical classification strategy included major, minor and unidentified metabolites. Reproducible spectral profiles were generated within less than three minutes, and revealed differences in the relative amounts of glucose, lactate, citrate, amino acid residues, acetate and polyols in the three groups. Contributions from microbial metabolism and inflammatory cells were evident. The computerised statistical classification strategy is based on both major metabolites and minor, partially unidentified metabolites. This data analysis proved highly specific for diagnosis (100% specificity in the final validation set), provided those with visible blood contamination were excluded from analysis; 6–8% of samples were classified as indeterminate. This proof of principle study suggests that a rapid etiologic diagnosis of meningitis is possible without prior culture. The method can be fully automated and avoids delays due to processing and selective identification of specific pathogens that are inherent in DNA-based techniques.

Himmelreich, Uwe; Malik, Richard; Kuhn, Till; Daniel, Heide-Marie; Somorjai, Ray L.; Dolenko, Brion; Sorrell, Tania C.

2009-01-01

286

Biological effects and physical safety aspects of NMR imaging and in vivo spectroscopy  

SciTech Connect

An assessment is made of the biological effects and physical hazards of static and time-varying fields associated with the NMR devices that are being used for clinical imaging and in vivo spectroscopy. A summary is given of the current state of knowledge concerning the mechanisms of interaction and the bioeffects of these fields. Additional topics that are discussed include: (1) physical effects on pacemakers and metallic implants such as aneurysm clips, (2) human health studies related to the effects of exposure to nonionizing electromagnetic radiation, and (3) extant guidelines for limiting exposure of patients and medical personnel to the fields produced by NMR devices. On the basis of information available at the present time, it is concluded that the fields associated with the current generation of NMR devices do not pose a significant health risk in themselves. However, rigorous guidelines must be followed to avoid the physical interaction of these fields with metallic implants and medical electronic devices. 476 refs., 5 figs., 2 tabs.

Tenforde, T.S.; Budinger, T.F.

1985-08-01

287

Interaction of the replication terminator protein of Bacillus subtilis with DNA probed by NMR spectroscopy  

SciTech Connect

Termination of DNA replication in Bacillus subtilis involves the polar arrest of replication forks by a specific complex formed between the dimeric 29 kDa replication terminator protein (RTP) and DNA terminator sites. We have used NMR spectroscopy to probe the changes in {sup 1}H-{sup 15}N correlation spectra of a {sup 15}N-labelled RTP.C110S mutant upon the addition of a 21 base pair symmetrical DNA binding site. Assignment of the {sup 1}H-{sup 15}N correlations was achieved using a suite of triple resonance NMR experiments with {sup 15}N,{sup 13}C,70% {sup 2}H enriched protein recorded at 800 MHz and using TROSY pulse sequences. Perturbations to {sup 1}H-{sup 15}N spectra revealed that the N-termini, {alpha}3-helices and several loops are affected by the binding interaction. An analysis of this data in light of the crystallographically determined apo- and DNA-bound forms of RTP.C110S revealed that the NMR spectral perturbations correlate more closely to protein structural changes upon complex formation rather than to interactions at the protein-DNA interface.

Hastings, Adam F. [School of Molecular and Microbial Biosciences, University of Sydney, Sydney, NSW 2006 (Australia); Otting, Gottfried [Research School of Chemistry, Australian National University, Canberra, ACT (Australia); Folmer, Rutger H.A. [Structural Chemistry Laboratory, AstraZeneca R and D, S-431 83, Moelndal (Sweden); Duggin, Iain G. [School of Molecular and Microbial Biosciences, University of Sydney, Sydney, NSW 2006 (Australia); Wake, R. Gerry [School of Molecular and Microbial Biosciences, University of Sydney, Sydney, NSW 2006 (Australia); Wilce, Matthew C.J. [Biochemistry and Molecular Biology, Monash University, Melbourne, Vic. 3800 (Australia); Wilce, Jacqueline A. [Biochemistry and Molecular Biology, Monash University, Melbourne, Vic. 3800 (Australia)]. E-mail: Jackie.Wilce@med.monash.edu.au

2005-09-23

288

Actinide(IV) and actinide(VI) carbonate speciation studies by PAS and NMR spectroscopies; Yucca Mountain Project: Milestone report 3031-WBS 1.2.3.4.1.3.1  

SciTech Connect

Pulsed-laser photoacoustic spectroscopy (PAS) and Fourier-transform nuclear magnetic resonance (NMR) spectroscopy were used to study speciation of actinide(IV) and actinide(VI) ions (Np, Pu, Am) in aqueous carbonate solutions vs pH, carbonate content, actinide content, temperature. PAS focused on Pu(IV) speciation. Stability fields on a pH (8.4 to 12.0) versus total carbonate content (0.003 to 1.0 M) plot for dilute Pu(IV) carbonate species ([Pu]{sub tot} = 1 mM) were mapped. Four plutonium species, with absorption peaks at 486, 492, 500, and 512 nm were found. Loss of a single carbonate ligand does not account for the difference in speciation for the 486 and 492 nm absorption peaks, nor can any of the observed species be identified as colloidal Pu(IV). NMR data have been obtained for UO{sub 2}{sup 2+}, PuO{sub 2}{sup 2+} and AmO{sub 2}{sup 2+}. This report focuses on results for PuO{sub 2}{sup 2+}. The ligand exchange reaction between free and coordinated carbonate on the PuO{sub 2}(CO{sub 3}){sub 3}{sup 4{minus}} systems has been examined by variable temperature {sup 13}C NMR spectroscopy. In each of the six different PuO{sub 2}(CO{sub 3}){sub 3}{sup 4{minus}} samples, two NMR signals are present, one for the free carbonate ligand and one for the carbonate ligand coordinated to a paramagnetic plutonium metal center. The single{sup 13}C resonance line for coordinated carbonate is consistent with expectations of a monomeric PuO{sub 2}(CO{sub 3}){sub 3}{sup 4{minus}} species in solution. A modified Carr-Purcell-Meiboom-Gill NMR pulse sequence was used for determining ligand exchange parameters for paramagnetic actinide complexes. Eyring analysis at standard conditions provided activation parameters of {Delta}H = 38 KJ/M and {Delta}S = {minus}60 J/K for the plutonyl triscarbonate system, suggesting an associative transition state for the plutonyl(VI) carbonate complex self-exchange reaction.

Clark, D.L.; Ekberg, S.A.; Morris, D.E.; Palmer, P.D.; Tait, C.D.

1994-09-01

289

Confirming the 3D Solution Structure of a Short Double-Stranded DNA Sequence Using NMR Spectroscopy  

ERIC Educational Resources Information Center

|2D [superscript 1]H NOESY NMR spectroscopy is routinely used to give information on the closeness of hydrogen atoms through space. This work is based on a 2D [superscript 1]H NOESY NMR spectrum of a 12 base-pair DNA duplex. This 6-h laboratory workshop aims to provide advanced-level chemistry students with a basic, yet solid, understanding of how…

Ruhayel, Rasha A.; Berners-Price, Susan J.

2010-01-01

290

Mapping functional interaction sites of human prune C-terminal domain by NMR spectroscopy in human cell lysates.  

PubMed

Get well prune: The C-terminal third domain of h-prune is largely unfolded and involved in relevant protein-protein interactions, particularly with Nm23-H1, GSK-3? and gelsolin. This study shows that protein functions mediated by protein-protein interactions can be accurately followed in cell lysates by using fast NMR spectroscopy, which could be easily used for a very efficient NMR drug-discovery strategy. PMID:23939913

Diana, Donatella; Smaldone, Giovanni; De Antonellis, Pasquale; Pirone, Luciano; Carotenuto, Marianeve; Alonzi, Alessandro; Di Gaetano, Sonia; Zollo, Massimo; Pedone, Emilia M; Fattorusso, Roberto

2013-08-12

291

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

Microsoft Academic Search

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

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

1990-01-01

292

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

293

Multicomponent analysis of radiolytic products in human body fluids using high field proton nuclear magnetic resonance (NMR) spectroscopy  

Microsoft Academic Search

High field proton Hahn spin-echo nuclear magnetic resonance (NMR) spectroscopy has been employed to investigate radiolytic damage to biomolecules present in intact human body fluids. gamma-Radiolysis of healthy or rheumatoid human serum (5.00 kGy) in the presence of atmospheric O2 gave rise to reproducible elevations in the concentration of NMR-detectable acetate which are predominantly ascribable to the prior oxidation of

Martin C. Grootveld; Herman Herz; Rachel Haywood; Geoffrey E. Hawkes; Declan Naughton; Anusha Perera; Jacky Knappitt; David R. Blake; Andrew W. D. Claxson

1994-01-01

294

Electron paramagnetic resonance spectroscopy studies of oxidative degradation of an active pharmaceutical ingredient and quantitative analysis of the organic radical intermediates using partial least-squares regression.  

PubMed

Electron paramagnetic resonance (EPR) spectroscopy was used to study the radical species formed during the oxidation of an active pharmaceutical ingredient in the solid state. It was found that the extent of radical generation correlated to the formation of an oxidative degradation product. Multifrequency EPR and electron nuclear double resonance spectroscopy gave additional information on the identity of the organic radical species involved in the oxidation process, and a mechanism was proposed for the degradation, involving the formation of both carbon-centered and peroxy radicals. The multivariate analysis technique of partial least-squares (PLS) regression was then used to determine the extent of oxidation of the active pharmaceutical ingredient from the EPR spectra. The suitability of this approach was demonstrated from its application to a series of standards. The conventional approach for the quantitative analysis of EPR spectra is to measure the peak height or to perform double integration of the spectral region containing the signal of interest. Both of these methods have intrinsic errors associated with them, particularly for weak EPR signals with a poor signal-to-noise ratio or a sloping background response. The results obtained showed that greatly improved quantitation was obtained using the PLS regression approach. PMID:16408946

Williams, Helen Elizabeth; Loades, Victoria Catherine; Claybourn, Mike; Murphy, Damien Martin

2006-01-15

295

Single-Crystalline cooperite (PtS): Crystal-Chemical characterization, ESR spectroscopy, and {sup 195}Pt NMR spectroscopy  

SciTech Connect

Single-crystalline cooperite (PtS) with a nearly stoichiometric composition was characterized in detail by X-ray diffraction, electron-probe X-ray microanalysis, and high-resolution scanning electron microscopy. For the first time it was demonstrated that {sup 195}Pt static and MAS NMR spectroscopy can be used for studying natural platinum minerals. The {sup 195}Pt chemical-shift tensor of cooperite was found to be consistent with the axial symmetry and is characterized by the following principal values: {delta}{sub xx} = -5920 ppm, {delta}{sub yy} = -3734 ppm, {delta}{sub zz} = +4023 ppm, and {delta}{sub iso} = -1850 ppm. According to the ESR data, the samples of cooperite contain copper(II), which is adsorbed on the surface during the layer-by-layer crystal growth and is not involved in the crystal lattice.

Rozhdestvina, V. I., E-mail: veronika@ascnet.ru; Ivanov, A. V.; Zaremba, M. A. [Far East Division, Russian Academy of Sciences, Institute of Geology and Nature Management (Russian Federation); Antsutkin, O. N.; Forsling, W. [Lulea University of Technology (Sweden)

2008-05-15

296

Heterogeneous ordered-disordered structure of the mesodomain in frozen sucrose-water solutions revealed by multiple electron paramagnetic resonance spectroscopies.  

PubMed

The microscopic structure of frozen aqueous sucrose solutions, over concentrations of 0-75% (w/v), is characterized by using multiple continuous-wave and pulsed electron paramagnetic resonance (EPR) spectroscopic and relaxation techniques and the paramagnetic spin probe, TEMPOL. The temperature dependence of the TEMPOL EPR line-shape anisotropy reveals a mobility transition, specified at 205 K in pure water and 255 ± 5 K for >1% (w/v) added sucrose. The transition temperature is >Tg, where Tg is the homogeneous water glass transition temperature, which shows that TEMPOL resides in the mesoscopic domain (mesodomain) at water-ice crystallite boundaries and that the mesodomain sucrose concentrations are comparable at >1% (w/v) added sucrose. Electron spin-echo envelope modulation (ESEEM) spectroscopy of TEMPOL-(2)H2-sucrose hyperfine interactions also indicates comparable sucrose concentrations in mesodomains at >1% (w/v) added sucrose. Electron spin-echo (ESE) detected longitudinal and phase memory relaxation times (T1 and TM, respectively) at 6 K indicate a general trend of increased mesodomain volume with added sucrose, in three stages: 1-15, 20-50, and >50% (w/v). The calibrated TEMPOL concentrations indicate that the mesodomain volume is less than the predicted maximally freeze-concentrated value [80 (w/w); 120% (w/v)], with transitions at 15-20% and 50% (w/v) starting sucrose. An ordered sucrose hydrate phase, which excludes TEMPOL, and a disordered, amorphous sucrose-water glass phase, in which TEMPOL resides, are proposed to compose a heterogeneous mesodomain. The results show that the ratio of ordered and disordered volume fractions in the mesodomain is exquisitely sensitive to the starting sucrose concentration. PMID:23464733

Chen, Hanlin; Sun, Li; Warncke, Kurt

2013-03-19

297

Can nuclear magnetic resonance (NMR) spectroscopy reveal different metabolic signatures for lung tumours?  

PubMed

This study aims to evaluate the potential of (1)H NMR spectroscopy, combined with multivariate statistics, for discriminating between tumour and non-involved (control) pulmonary parenchyma and for providing biochemical information on different histological types. Paired tissue samples from 24 primary lung tumours were directly analysed by high-resolution magic angle spinning (HRMAS) (1)H NMR spectroscopy (500 MHz), and their spectral profiles subjected to principal component analysis (PCA) and partial least squares regression discriminant analysis (PLS-DA). Tumour and adjacent control parenchyma were clearly discriminated in the PLS-DA model with a high level of sensitivity (95% of tumour samples correctly classified) and 100% specificity (no false positives). The metabolites giving rise to this separation were mainly lactate, glycerophosphocholine, phosphocholine, taurine, reduced glutathione and uridine di-phosphate (elevated in tumours) and glucose, phosphoethanolamine, acetate, lysine, methionine, glycine, myo- and scyllo-inositol (reduced in tumours compared to control tissues). Furthermore, PLS-DA of a sub-set of tumour samples allowed adenocarcinomas to be discriminated from carcinoid tumours and epidermoid carcinomas, highlighting differences in metabolite levels between these histological types, and therefore revealing valuable knowledge on the biochemistry of different types of bronchial-pulmonary carcinomas. PMID:20941505

Duarte, Iola F; Rocha, Cláudia M; Barros, António S; Gil, Ana M; Goodfellow, Brian J; Carreira, Isabel M; Bernardo, João; Gomes, Ana; Sousa, Vitor; Carvalho, Lina

2010-10-13

298

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

PubMed

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

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

2011-03-01

299

High Resolution NMR Spectroscopy of Nanocrystalline Proteins at Ultra-High Magnetic Field  

PubMed Central

Magic-angle spinning (MAS) solid-state NMR (SSNMR) spectroscopy of uniformly-13C,15N labeled protein samples provides insight into atomic-resolution chemistry and structure. Data collection efficiency has advanced remarkably in the last decade; however, the study of larger proteins is still challenged by relatively low resolution in comparison to solution NMR. In this study, we present a systematic analysis of SSNMR protein spectra acquired at 11.7, 17.6 and 21.1 Tesla (1H frequencies of 500, 750, and 900 MHz). For two protein systems—GB1, a 6 kDa nanocrystalline protein and DsbA, a 21 kDa nanocrystalline protein—line narrowing is demonstrated in all spectral regions with increasing field. Resolution enhancement is greatest in the aliphatic region, including methine, methylene and methyl sites. The resolution for GB1 increases markedly as a function of field, and for DsbA, resolution in the C-C region increases by 42%, according to the number of peaks that can be uniquely picked and integrated in the 900 MHz spectra when compared to the 500 MHz spectra. Additionally, chemical exchange is uniquely observed in the highest field spectra for at least two isoleucine C?1 sites in DsbA. These results further illustrate the benefits of high-field MAS SSNMR spectroscopy for protein structural studies.

Sperling, Lindsay J.; Nieuwkoop, Andrew J.; Lipton, Andrew S.; Berthold, Deborah A.; Rienstra, Chad M.

2010-01-01

300

Phosphorus Speciation of Sequential Extracts of Organic Amendments using NMR Spectroscopy  

NASA Astrophysics Data System (ADS)

O.O. 1Akinremi Babasola Ajiboye and Donald N. Flaten 1Department of Soil Science, University of Manitoba, Winnipeg, R3T 2NT, Canada We carried out this study in order to determine the forms of phosphorus in various organic amendments using state-of-the art spectroscopic technique. Anaerobically digested biosolids (BIO), hog (HOG), dairy (DAIRY), beef (BEEF) and poultry (POULTRY) manures were subjected to sequential extraction. The extracts were analyzed by solution 31P nuclear magnetic resonance (NMR) spectroscopy. Most of the total P analysed by inductively coupled plasma-optical emission spectroscopy (ICP-OES) in the sequential extracts of organic amendments were orthophosphate, except POULTRY, which was dominated by organic P. The labile P fraction in all the organic amendments, excluding POULTRY, was mainly orthophosphate P from readily soluble calcium and some aluminum phosphates. In the poultry litter, however, Ca phytate was the main P species controlling P solubility. Such knowledge of the differences in the chemical forms of phosphorus in organic amendments are essential for proper management of these amendments for agro-environmental purposes Key words: organic amendments, solution NMR, sequential fractionation, labile phosphorus

Akinremi, O.

2009-04-01

301

Multiple conformations of SAM-II riboswitch detected with SAXS and NMR spectroscopy.  

PubMed

Riboswitches are a newly discovered large family of structured functional RNA elements that specifically bind small molecule targets out of a myriad of cellular metabolites to modulate gene expression. Structural studies of ligand-bound riboswitches by X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy have provided insights into detailed RNA-ligand recognition and interactions. However, the structures of ligand-free riboswitches remain poorly characterized. In this study, we have used a variety of biochemical, biophysical and computational techniques including small-angle X-ray scattering and NMR spectroscopy to characterize the ligand-free and ligand-bound forms of SAM-II riboswitch. Our data demonstrate that the RNA adopts multiple conformations along its folding pathway and suggest that the RNA undergoes marked conformational changes upon Mg(2+) compaction and S-adenosylmethionine (SAM) metabolite binding. Further studies indicated that Mg(2+) ion is not essential for the ligand binding but can stabilize the complex by facilitating loop/stem interactions. In the presence of millimolar concentration of Mg(2+) ion, the RNA samples a more compact conformation. This conformation is near to, but distinct from, the native fold and competent to bind the metabolite. We conclude that the formation of various secondary and tertiary structural elements, including a pseudoknot, occur to sequester the putative Shine-Dalgarno sequence of the RNA only after metabolite binding. PMID:22139931

Chen, Bin; Zuo, Xiaobing; Wang, Yun-Xing; Dayie, T Kwaku

2011-12-01

302

Proton-bound dimers of 1-methylcytosine and its derivatives: vibrational and NMR spectroscopy.  

PubMed

Vibrational spectroscopy and NMR demonstrate that the proton-bound dimer of 1-methylcytosine, , has an unsymmetrical structure at room temperature. In the gas phase, investigation of isolated homodimer reveals five fundamental NH vibrations by IR Multiple Photon Dissociation (IRMPD) action spectroscopy. The NHN stretching vibration between the two ring nitrogens exhibits a frequency of 1570 cm(-1), as confirmed by examination of the proton-bound homodimers of 5-fluoro-1-methycytosine, , and of 1,5-dimethylcytosine, , which display absorptions in the same region that disappear upon deuterium substitution. (13)C, and (15)N NMR of the solid iodide salt of confirm the nonequivalence of the two rings in the anhydrous proton-bound homodimer at room temperature. IRMPD spectra of the three possible heterodimers also show NHN stretches in the same domain, and at least one of the heterodimers, the proton-bound dimer of 1,5-dimethylcytosine with 1-methylcytosine, exhibits two bands suggestive of the presence of two tautomers close in energy. PMID:24096726

Ung, Hou U; Moehlig, Aaron R; Kudla, Ryan A; Mueller, Leonard J; Oomens, Jos; Berden, Giel; Morton, Thomas Hellman

2013-10-16

303

Multiple conformations of SAM-II riboswitch detected with SAXS and NMR spectroscopy  

PubMed Central

Riboswitches are a newly discovered large family of structured functional RNA elements that specifically bind small molecule targets out of a myriad of cellular metabolites to modulate gene expression. Structural studies of ligand-bound riboswitches by X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy have provided insights into detailed RNA–ligand recognition and interactions. However, the structures of ligand-free riboswitches remain poorly characterized. In this study, we have used a variety of biochemical, biophysical and computational techniques including small-angle X-ray scattering and NMR spectroscopy to characterize the ligand-free and ligand-bound forms of SAM-II riboswitch. Our data demonstrate that the RNA adopts multiple conformations along its folding pathway and suggest that the RNA undergoes marked conformational changes upon Mg2+ compaction and S-adenosylmethionine (SAM) metabolite binding. Further studies indicated that Mg2+ ion is not essential for the ligand binding but can stabilize the complex by facilitating loop/stem interactions. In the presence of millimolar concentration of Mg2+ ion, the RNA samples a more compact conformation. This conformation is near to, but distinct from, the native fold and competent to bind the metabolite. We conclude that the formation of various secondary and tertiary structural elements, including a pseudoknot, occur to sequester the putative Shine–Dalgarno sequence of the RNA only after metabolite binding.

Chen, Bin; Zuo, Xiaobing; Wang, Yun-Xing; Dayie, T. Kwaku

2012-01-01

304

Secondary structure determination of human. beta. -endorphin by /sup 1/H NMR spectroscopy  

SciTech Connect

The /sup 1/H NMR spectra of human ..beta..-endorphin indicate that the peptide exists in random-coil form in aqueous solution but becomes helical in mixed solvent. Thermal denaturation NMR experiments show that in water there is no transition between 24 and 75/sup 0/C, while a slow noncooperative thermal unfolding is observed in a 60% methanol-40% water mixed solvent in the same temperature range. These findings are consistent with circular dichroism studies by other workers concluding that ..beta..-endorphin is a random coil in water but that it forms 50% ..cap alpha..-helix or more in mixed solvents. The peptide in the mixed water-methanol solvent was further studied by correlated spectroscopy (COSY) and nuclear Overhauser effect spectroscopy (NOESY) experiments. These allow a complete set of assignments to be made and establish two distinct stretches over which the solvent induces formation of ..cap alpha..-helices: the first occurs between Tyr-1 and Thr-12 and the second between Leu-14 and extending to Lys-28. There is evidence that the latter is capped by a turn occurring between Lys-28 and Glu-31. These helices form at the enkephalin receptor binding site, which is at the amino terminus, and at the morphine receptor binding site, located at the carboxyl terminus. The findings suggest that these two receptors may specifically recognize ..cap alpha..-helices.

Lichtarge, O.; Jardetzky, O.; Li, C.H.

1987-09-08

305

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

PubMed

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

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

2005-12-01

306

NMR HRMAS spectroscopy of lung biopsy samples: Comparison study between human, pig, rat, and mouse metabolomics.  

PubMed

PURPOSE: Using the metabolomics by NMR high-resolution magic angle spinning spectroscopy, we assessed the lung metabolome of various animal species in order to identify the animal model that could be substituted to human lung in studies on fresh lung biopsies. METHODS: The experiments were conducted on intact lung biopsy samples of pig, rat, mouse, and human using a Bruker Advance III 500 spectrometer. Thirty-five to 39 metabolites were identified and 23 metabolites were quantified. Principal component analysis, partial least-squares discriminant analysis, and analysis of variance tests were performed in order to compare the metabolic profiles of each animal lung biopsies to those of the human lung. RESULTS: The metabolic composition between human and pig lung was similar. However, human lung was distinguishable from mouse and rat regarding: Trimethylamine N-oxide and betaïne which were present in rodents but not in human lung, carnitine, and glycerophosphocholine which were present in mouse but not in human lung. Conversely, succinic acid was undetected in rat lung. Furthermore, fatty acids concentration was significantly higher in rodent lungs compared to human lung. CONCLUSION: Using the metabolomics by NMR high-resolution magic angle spinning spectroscopy on lung biopsy, samples allowed to highlight that pig lung seems to be close to human lung as regarding its metabolite composition with more similarities than dissimilarities. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc. PMID:23412987

Benahmed, Malika A; Elbayed, Karim; Daubeuf, François; Santelmo, Nicola; Frossard, Nelly; Namer, Izzie J

2013-02-14

307

Spin Hamiltonian Parameters for Cu(II)-Prion Peptide Complexes from L-Band Electron Paramagnetic Resonance Spectroscopy  

PubMed Central

Cu(II) is an essential element for life but is also associated with numerous and serious medical conditions, particularly neurodegeneration. Structural modeling of crystallization-resistant biological Cu(II) species relies on detailed spectroscopic analysis. Electron paramagnetic resonance (EPR) can, in principle, provide spin Hamiltonian parameters that contain information on the geometry and ligand atom complement of Cu(II). Unfortunately, EPR spectra of Cu(II) recorded at the traditional X-band frequency are complicated by (i) strains in the region of the spectrum corresponding to the g|| orientation and (ii) potentially very many overlapping transitions in the g? region. The rapid progress of density functional theory computation as a means to correlate EPR and structure, and the increasing need to study Cu(II) associated with biomolecules in more biologically and biomedically relevant environments such as cells and tissue, have spurred the development of a technique for the extraction of a more complete set of spin Hamiltonian parameters that is relatively straightforward and widely applicable. EPR at L-band (1–2 GHz) provides much enhanced spectral resolution and straightforward analysis via computer simulation methods. Herein, the anisotropic spin Hamiltonian parameters and the nitrogen coordination numbers for two hitherto incompletely characterized Cu(II)-bound species of a prion peptide complex are determined by analysis of their L-band EPR spectra.

Kowalski, Jason M.; Bennett, Brian

2011-01-01

308

Comparison of I-123 IMP uptake and NMR spectroscopy in the brain following experimental carotid occlusion  

SciTech Connect

Both I-123 IMP scintigraphy and NMR have been suggested as sensitive detectors of changes shortly after acute cerebral infarction. The authors compared the uptake of N-isopropul I-123 p-iodoamphetamine (IMP) and NMR spectroscopy of the brain after internal carotid artery ligation. Thirteen gerbils were lightly anesthetized with ether. After neck dissection, an internal carotid artery was occluded. After 2.8 hours, 100 ..mu..Ci I-123 IMP was injected intravenously into the 13 experimental animals plus 3 controls. Seven gerbils remained asymptomatic while 6 developed hemiparesis. At 3 hours after ligation, the animals were killed. The brains were bisected and T/sub 1/ and T/sub 2/ relaxation times were determined for the right and left hemispheres by NMR spectroscopy immediately after dissection. I-123 IMP uptake was then determined in the samples. Interhemispheric differences in uptake for I-123 IMP uptake was 2.2% +- 0.5% in the control, 33.5% +- 9.6% in the asymptomatic and 54.6% +- 9.7% in the symptomatic animals. Significant differences were seen with I-123 IMP in 6/7 asymptomatic and 6/6 symptomatic animals. Significant differences in T/sub 1/ and T/sub 2/ were seen in 2/7 of the asymptomatic and 5/6 of the symptomatic animals. The authors conclude that I-123 is more sensitive than T/sub 1/ or T/sub 2/ for the detection of cerebral perfusion abnormalities while T/sub 1/ and T/sub 2/ more accurately separate symptomatic from asymptomatic animals.

Holman, B.L.; Jolesz, F.; Polak, J.F.; Kronauge, J.; Adams, D.F.

1984-01-01

309

Probing crystal structures and transformation reactions of ammonium molybdates by 14N MAS NMR spectroscopy.  

PubMed

The unique high-resolution feature offered by 14N magic-angle spinning (MAS) NMR spectroscopy of ammonium ions has been used to characterize the crystal structures of various ammonium molybdates by their 14N quadrupole coupling parameters, i.e., CQ, the quadrupole coupling constant, and etaQ, the asymmetry parameter. Two polymorphs of diammonium monomolybdate, (NH4)2MoO4, recently structurally characterized by single-crystal X-ray diffraction (XRD) and named mS60 and mP60, show distinct but different 14N MAS NMR spectra from each of which two sets of characteristic 14N CQ and etaQ values have been obtained. Similarly, the well-characterized ammonium polymolybdates (NH4)2Mo2O7, (NH4)6Mo7O24.4H2O, and (NH4)6Mo8O27.4H2O also give rise to distinct and characteristic 14N MAS NMR spectra. In particular, it is noted that simulation of the experimental (NH4)6Mo7O24.4H2O spectrum requires an iterative fit with six independent NH4+ sites. For the slow spinning frequencies employed (nu(r) = 1500-3000 Hz), all 14N MAS NMR spectra of the ammonium molybdates in this study are fingerprints of their identity. These different 14N MAS NMR fingerprints are shown to be an efficient tool in qualitative and quantitative assessment of the decomposition of (NH4)2MoO4 in humid air. Finally, by a combination of the 14N and 95Mo MAS NMR experiments performed here, it has become clear that a recent report of the 95Mo MAS spectra and data for the mS60 and mP60 polymorphs of (NH4)2MoO4 are erroneous because the sample examined had decomposed to (NH4)2Mo2O7. PMID:17173446

Hove, Anders R; Bildsøe, Henrik; Skibsted, Jørgen; Brorson, Michael; Jakobsen, Hans J

2006-12-25

310

Characterization of noninnocent metal complexes using solid-state NMR spectroscopy: o-dioxolene vanadium complexes.  

PubMed

(51)V solid-state NMR (SSNMR) studies of a series of noninnocent vanadium(V) catechol complexes have been conducted to evaluate the possibility that (51)V NMR observables, quadrupolar and chemical shift anisotropies, and electronic structures of such compounds can be used to characterize these compounds. The vanadium(V) catechol complexes described in these studies have relatively small quadrupolar coupling constants, which cover a surprisingly small range from 3.4 to 4.2 MHz. On the other hand, isotropic (51)V NMR chemical shifts cover a wide range from -200 to 400 ppm in solution and from -219 to 530 ppm in the solid state. A linear correlation of (51)V NMR isotropic solution and solid-state chemical shifts of complexes containing noninnocent ligands is observed. These experimental results provide the information needed for the application of (51)V SSNMR spectroscopy in characterizing the electronic properties of a wide variety of vanadium-containing systems and, in particular, those containing noninnocent ligands and that have chemical shifts outside the populated range of -300 to -700 ppm. The studies presented in this report demonstrate that the small quadrupolar couplings covering a narrow range of values reflect the symmetric electronic charge distribution, which is also similar across these complexes. These quadrupolar interaction parameters alone are not sufficient to capture the rich electronic structure of these complexes. In contrast, the chemical shift anisotropy tensor elements accessible from (51)V SSNMR experiments are a highly sensitive probe of subtle differences in electronic distribution and orbital occupancy in these compounds. Quantum chemical (density functional theory) calculations of NMR parameters for [VO(hshed)(Cat)] yield a (51)V chemical shift anisotropy tensor in reasonable agreement with the experimental results, but surprisingly the calculated quadrupolar coupling constant is significantly greater than the experimental value. The studies demonstrate that substitution of the catechol ligand with electron-donating groups results in an increase in the HOMO-LUMO gap and can be directly followed by an upfield shift for the vanadium catechol complex. In contrast, substitution of the catechol ligand with electron-withdrawing groups results in a decrease in the HOMO-LUMO gap and can directly be followed by a downfield shift for the complex. The vanadium catechol complexes were used in this work because (51)V is a half-integer quadrupolar nucleus whose NMR observables are highly sensitive to the local environment. However, the results are general and could be extended to other redox-active complexes that exhibit coordination chemistry similar to that of the vanadium catechol complexes. PMID:21842875

Chatterjee, Pabitra B; Goncharov-Zapata, Olga; Quinn, Laurence L; Hou, Guangjin; Hamaed, Hiyam; Schurko, Robert W; Polenova, Tatyana; Crans, Debbie C

2011-08-15

311

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

PubMed Central

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

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

2011-01-01

312

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

PubMed

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

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

2011-01-19

313

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

PubMed

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

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

2005-06-01

314

Measuring "Free" Iron Levels in Caenorhabditis Elegans Using Low-Temperature Fe(III) Electron Paramagnetic Resonance Spectroscopy  

PubMed Central

Oxidative stress, caused by free radicals within the body, has been associated with the process of aging and many human diseases. As free radicals, in particular superoxide, are difficult to measure, an alternative indirect method for measuring oxidative stress levels has been successfully used in E. coli and yeast. This method is based on a proposed connection between elevated superoxide levels and release of iron from solvent exposed [4Fe-4S] enzyme clusters, which eventually leads to an increase in hydroxyl radical production. In past studies using bacteria and yeast, a positive correlation was found between superoxide production or oxidative stress due to superoxide within the organism and EPR (electron paramagnetic resonance) detectable “free” iron levels. In the present study, we have developed a reliable and an efficient method for measuring “free” iron levels in C. elegans using low temperature Fe(III) EPR at g = 4.3. This method utilizes synchronized worm cultures grown on plates, which are homogenized and treated with desferrioxamine, an Fe(III) chelator, prior to packing the EPR tube. Homogenization was found not to alter “free” iron levels, while desferrioxamine treatment significantly raised these levels, indicating presence of both Fe(II) and Fe(III) in the “free” iron pool. The correlation between free radical levels and the observed “free” iron levels was examined by using heat stress and paraquat treatment. The intensity of the Fe(III) EPR signal and thus, the concentration of the “free” iron pool, varied with the treatments that altered radical levels without changing the total iron levels. This study provides the groundwork needed to uncover the correlation between oxidative stress, “free” iron levels, and longevity in C. elegans.

Pate, Kira T.; Rangel, Natalie A.; Fraser, Brian; Clement, Matthew H. S.; Srinivasan, Chandra

2007-01-01

315

Radical sites in Mycobacterium tuberculosis KatG identified using electron paramagnetic resonance spectroscopy, the three-dimensional crystal structure, and electron transfer couplings.  

PubMed

Catalase-peroxidase (KatG) from Mycobacterium tuberculosis, a Class I peroxidase, exhibits high catalase activity and peroxidase activity with various substrates and is responsible for activation of the commonly used antitubercular drug, isoniazid (INH). KatG readily forms amino acid-based radicals during turnover with alkyl peroxides, and this work focuses on extending the identification and characterization of radicals forming on the millisecond to second time scale. Rapid freeze-quench electron paramagnetic resonance spectroscopy (RFQ-EPR) reveals a change in the structure of the initially formed radical in the presence of INH. Heme pocket binding of the drug and knowledge that KatG[Y229F] lacks this signal provides evidence for radical formation on residue Tyr(229). High field RFQ-EPR spectroscopy confirmed a tryptophanyl radical signal, and new analyses of X-band RFQ-EPR spectra also established its presence. High field EPR spectroscopy also confirmed that the majority radical species is a tyrosyl radical. Site-directed mutagenesis, along with simulations of EPR spectra based on x-ray structural data for particular tyrosine and tryptophan residues, enabled assignments based on predicted hyperfine coupling parameters. KatG mutants W107F, Y229F, and the double mutant W107F/Y229F showed alteration in type and yield of radical species. Results are consistent with formation of a tyrosyl radical reasonably assigned to residue Tyr(229) within the first few milliseconds of turnover. This is followed by a mixture of tyrosyl and tryptophanyl radical species and finally to only a tyrosyl radical on residue Tyr(353), which lies more distant from the heme. The radical processing of enzyme lacking the Trp(107)-Tyr(229)-Met(255) adduct (found as a unique structural feature of catalase-peroxidases) is suggested to be a reasonable assignment of the phenomena. PMID:17204474

Ranguelova, Kalina; Girotto, Stefania; Gerfen, Gary J; Yu, Shengwei; Suarez, Javier; Metlitsky, Leonid; Magliozzo, Richard S

2007-01-04

316

Tannin fingerprinting in vegetable tanned leather by solid state NMR spectroscopy and comparison with leathers tanned by other processes.  

PubMed

Solid state ¹³C-NMR spectra of pure tannin powders from four different sources--mimosa, quebracho, chestnut and tara--are readily distinguishable from each other, both in pure commercial powder form, and in leather which they have been used to tan. Groups of signals indicative of the source, and type (condensed vs. hydrolyzable) of tannin used in the manufacture are well resolved in the spectra of the finished leathers. These fingerprints are compared with those arising from leathers tanned with other common tanning agents. Paramagnetic chromium (III) tanning causes widespread but selective disappearance of signals from the spectrum of leather collagen, including resonances from acidic aspartyl and glutamyl residues, likely bound to Cr (III) structures. Aluminium (III) and glutaraldehyde tanning both cause considerable leather collagen signal sharpening suggesting some increase in molecular structural ordering. The ²?Al-NMR signal from the former material is consistent with an octahedral coordination by oxygen ligands. Solid state NMR thus provides easily recognisable reagent specific spectral fingerprints of the products of vegetable and some other common tanning processes. Because spectra are related to molecular properties, NMR is potentially a powerful tool in leather process enhancement and quality or provenance assurance. PMID:21278677

Romer, Frederik H; Underwood, Andrew P; Senekal, Nadine D; Bonnet, Susan L; Duer, Melinda J; Reid, David G; van der Westhuizen, Jan H

2011-01-28

317

Characterization of Zn-containing metal-organic frameworks by solid-state 67Zn NMR spectroscopy and computational modeling.  

PubMed

Metal-organic frameworks (MOFs) are an extremely important class of porous materials with many applications. The metal centers in many important MOFs are zinc cations. However, their Zn environments have not been characterized directly by (67)Zn solid-state NMR (SSNMR) spectroscopy. This is because (67)Zn (I=5/2) is unreceptive with many unfavorable NMR characteristics, leading to very low sensitivity. In this work, we report, for the first time, a (67)Zn natural abundance SSNMR spectroscopic study of several representative zeolitic imidazolate frameworks (ZIFs) and MOFs at an ultrahigh magnetic field of 21.1 T. Our work demonstrates that (67)Zn magic-angle spinning (MAS) NMR spectra are highly sensitive to the local Zn environment and can differentiate non-equivalent Zn sites. The (67)Zn NMR parameters can be predicted by theoretical calculations. Through the study of MOF-5 desolvation, we show that with the aid of computational modeling, (67)Zn NMR spectroscopy can provide valuable structural information on the MOF systems with structures that are not well described. Using ZIF-8 as an example, we further demonstrate that (67)Zn NMR spectroscopy is highly sensitive to the guest molecules present inside the cavities. Our work also shows that a combination of (67)Zn NMR data and molecular dynamics simulation can reveal detailed information on the distribution and the dynamics of the guest species. The present work establishes (67)Zn SSNMR spectroscopy as a new tool complementary to X-ray diffraction for solving outstanding structural problems and for determining the structures of many new MOFs yet to come. PMID:22945610

Sutrisno, Andre; Terskikh, Victor V; Shi, Qi; Song, Zhengwei; Dong, Jinxiang; Ding, San Yuan; Wang, Wei; Provost, Bianca R; Daff, Thomas D; Woo, Tom K; Huang, Yining

2012-09-03

318

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

PubMed

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

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

2010-10-08

319

In vivo 31P-NMR spectroscopy of right ventricle in pigs.  

PubMed

The energy metabolism of the right ventricle (RV) in vivo has been largely unexplored. The goal of this study was to develop and implement techniques for in vivo 31P nuclear magnetic resonance (NMR) spectroscopy of the RV free wall. A two-turn, crossover-design elliptical surface coil was constructed to provide high sensitivity across the thin RV wall but minimal sensitivity in the blood-filled RV cavity. In 36 open-chest, anesthetized pigs, 31P spectroscopy of the RV free wall was performed with this coil at a field strength of 2 Tesla. Spectra were obtained from 800 acquisitions in 24 min with an average signal-to-noise ratio of 13.2 for phosphocreatine (PCr). The PCr-to-ATP (PCr/ATP) ratio of porcine RV was 1.42 +/- 0.05 (mean +/- SE), uncorrected for saturation at a repetition time of 1.8 s. With the use of literature values of the time constant of longitudinal relaxation (T1) to correct for partial saturation, the RV PCr/ATP was estimated to lie between 1.7 and 2.3. Decreased RV PCr/ATP was observed during RV ischemia and pressure overload. Thus in vivo 31P spectroscopy of the RV is readily accomplished with an appropriate surface coil and can provide new information about RV energy metabolism. PMID:1621852

Schwartz, G G; Steinman, S K; Weiner, M W; Matson, G B

1992-06-01

320

Metabolic characterization of Palatinate German white wines according to sensory attributes, varieties, and vintages using NMR spectroscopy and multivariate data analyses  

Microsoft Academic Search

1H NMR (nuclear magnetic resonance spectroscopy) has been used for metabolomic analysis of ‘Riesling’ and ‘Mueller-Thurgau’\\u000a white wines from the German Palatinate region. Diverse two-dimensional NMR techniques have been applied for the identification\\u000a of metabolites, including phenolics. It is shown that sensory analysis correlates with NMR-based metabolic profiles of wine.\\u000a 1H NMR data in combination with multivariate data analysis methods,

Kashif Ali; Federica Maltese; Reinhard Toepfer; Young Hae Choi; Robert Verpoorte

2011-01-01

321

On 29Si NMR relaxation as a structural criterion for studying paramagnetic supermicroporous silica-based materials: silica-based materials incorporating Mn2+ ions into the silica matrix of SiO2-Al2O3-MnO.  

PubMed

Supermicroporous paramagnetic materials SiO(2)-Al(2)O(3)-MnO and SiO(2)-MnO with different manganese concentrations have been probed by solid-state (29)Si NMR and magnetic susceptibility measurements. The (29)Si T(1) and T(2) experiments, performed in static and spinning samples, have resulted in determination of electron relaxation times, providing, in turn, quantitative interpretations of (29)Si T(1) times in terms of distances Mn-Si. The NMR relaxation data have revealed (29)Si T(1) time distributions, which are close to Gaussian and observed as different T(1) values obtained in MAS NMR experiments for isotropic (29)Si resonances and their sidebands. Such (29)Si T(1) distributions, being a common phenomenon in paramagnetic silica-based materials, can be however masked by the bulk magnetic susceptibility (BMS) effects increasing with concentrations of paramagnetic centers. The presence of T(1) distributions, in itself, is not a criterion for incorporation of paramagnetic ions into the silica matrix or its surface. However, a quantitative analysis of the experimentally-observed short (29)Si T(1) components, based on the well-determined electron relaxation times, can provide such a criterion. PMID:19765956

Bakhmutov, Vladimir I; Shpeizer, Boris G; Prosvirin, Andrey V; Dunbar, Kim R; Clearfield, Abraham

2009-08-27

322

Organic solute changes with acidification in Lake Skjervatjern as shown by 1H-NMR spectroscopy  

USGS Publications Warehouse

1H-NMR spectroscopy has been found to be a useful tool to establish possible real differences and trends between all natural organic solute fractions (fulvic acids, humic acids, and XAD-4 acids) after acid-rain additions to the Lake Skjervatjern watershed. The proton NMR technique used in this study determined the spectral distribution of nonexchangeable protons among four peaks (aliphatic protons; aliphatic protons on carbon ?? or attached to electronegative groups; protons on carbons attached to O or N heteroatoms; and aromatic protons). Differences of 10% or more in the respective peak areas were considered to represent a real difference. After one year of acidification, fulvic acids decreased 13% (relative) in Peak 3 protons on carbon attached to N and O heteratoms and exhibited a decrease in aromatic protons between 27% and 31%. Humic acids also exhibited an 11% relative decrease in aromatic protons as a result of acidification. After one year of acidification, real changes were shown in three of the four proton assignments in XAD-4 acids. Peak 1 aliphatic protons increased by 14% (relative), Peak 3 protons on carbons attached to O and N heteroatoms decreased by 13% (relative), and aromatic protons (Peak 4) decreased by 35% (relative). Upon acidification, there was a trend in all solutes for aromatic protons to decrease and aliphatic protons to increase. The natural variation in organic solutes as shown in the Control Side B of the lake from 1990 to 1991 is perhaps a small limitation to the same data interpretations of acid rain changes at the Lake Skjervatjern site, but the proton NMR technique shows great promise as an independent scientific tool to detect and support other chemical techniques in establishing organic solute changes with different treatments (i.e., additions of acid rain).

Malcolm, R. L.; Hayes, T.

1994-01-01

323

Optimization of designed armadillo repeat proteins by molecular dynamics simulations and NMR spectroscopy  

PubMed Central

A multidisciplinary approach based on molecular dynamics (MD) simulations using homology models, NMR spectroscopy, and a variety of biophysical techniques was used to efficiently improve the thermodynamic stability of armadillo repeat proteins (ArmRPs). ArmRPs can form the basis of modular peptide recognition and the ArmRP version on which synthetic libraries are based must be as stable as possible. The 42-residue internal Arm repeats had been designed previously using a sequence-consensus method. Heteronuclear NMR revealed unfavorable interactions present at neutral but absent at high pH. Two lysines per repeat were involved in repulsive interactions, and stability was increased by mutating both to glutamine. Five point mutations in the capping repeats were suggested by the analysis of positional fluctuations and configurational entropy along multiple MD simulations. The most stabilizing single C-cap mutation Q240L was inferred from explicit solvent MD simulations, in which water penetrated the ArmRP. All mutants were characterized by temperature- and denaturant-unfolding studies and the improved mutants were established as monomeric species with cooperative folding and increased stability against heat and denaturant. Importantly, the mutations tested resulted in a cumulative decrease of flexibility of the folded state in silico and a cumulative increase of thermodynamic stability in vitro. The final construct has a melting temperature of about 85°C, 14.5° higher than the starting sequence. This work indicates that in silico studies in combination with heteronuclear NMR and other biophysical tools may provide a basis for successfully selecting mutations that rapidly improve biophysical properties of the target proteins.

Alfarano, Pietro; Varadamsetty, Gautham; Ewald, Christina; Parmeggiani, Fabio; Pellarin, Riccardo; Zerbe, Oliver; Pluckthun, Andreas; Caflisch, Amedeo

2012-01-01

324

Summation solute hydrogen bonding acidity values for hydroxyl substituted flavones determined by NMR spectroscopy.  

PubMed

The flavonoids are a structurally diverse class of natural products that exhibit a broad spectrum of biochemical activities. The flavones are one of the most studied flavonoid subclasses due to their presence in dietary plants and their potential to protect human cells from reactive oxygen species (ROS). Several flavone compounds also mediate beneficial actions by direct binding to protein receptors and regulatory enzymes. There is current interest in using Quantitative Structure Activity Relationships (QSARs) to guide drug development based on flavone lead structures. This approach is most informative when it involves the use of accurate physical descriptors. The Abraham summation solute hydrogen bonding acidity (A) is a descriptor in the general solvation equation. It defines the tendency of a molecule to act as a hydrogen bond donor, or acid, when surrounded by solvent molecules that are hydrogen bonding acceptors, or bases. As a linear free energy relationship, it is useful for predicting the absorption and uptake of drug molecules. A previously published method, involving nuclear magnetic resonance (NMR) spectroscopy, was used to evaluate A for the monohydroxyflavones (MHFs). Values of A ranged from 0.02, for 5-hydroxyflavone, to 0.69 for 4'-hydroxyflavone. The ability to examine separate NMR signals for individual hydroxyl groups allowed the investigation of intramolecular interactions between functional groups. The value of A for the position 7 hydroxyl group of 7-hydroxyflavone was 0.67. The addition of a position 5 hydroxyl group (in 5,7-dihydroxyflavone) increased the value of A for the position 7 hydroxyl group to 0.76. Values of A for MHFs were also calculated by the program ACD-Absolve and these agreed well with values measured by NMR. These results should facilitate more accurate estimation of the values of A for structurally complex flavones with pharmacological activities. PMID:23472467

Whaley, William L; Okoso-amaa, Ekua M; Womack, Cody L; Vladimirova, Anna; Rogers, Laura B; Risher, Margaret J; Abraham, Michael H

2013-01-01

325

Dynorphin induced magnetic ordering in lipid bilayers as studied by (31)P NMR spectroscopy.  

PubMed

Lipid bilayers of dimyristoyl phosphatidylcholine (DMPC) containing opioid peptide dynorphin A(1-17) are found to be spontaneously aligned to the applied magnetic field near at the phase transition temperature between the gel and liquid crystalline states (T(m)=24 degrees C), as examined by 31P NMR spectroscopy. The specific interaction between the peptide and lipid bilayer leading to this property was also examined by optical microscopy, light scattering, and potassium ion-selective electrode, together with a comparative study on dynorphin A(1-13). A substantial change in the light scattering intensity was noted for DMPC containing dynorphin A(1-17) near at T(m) but not for the system containing A(1-13). Besides, reversible change in morphology of bilayer, from small lipid particles to large vesicles, was observed by optical microscope at T(m). These results indicate that lysis and fusion of the lipid bilayers are induced by the presence of dynorphin A(1-17). It turned out that the bilayers are spontaneously aligned to the magnetic field above T(m) in parallel with the bilayer surface, because a single 31P NMR signal appeared at the perpendicular position of the 31P chemical shift tensor. In contrast, no such magnetic ordering was noted for DMPC bilayers containing dynorphin A(1-13). It was proved that DMPC bilayer in the presence of dynorphin A(1-17) forms vesicles above T(m), because leakage of potassium ion from the lipid bilayers was observed by potassium ion-selective electrode after adding Triton X-100. It is concluded that DMPC bilayer consists of elongated vesicles with the long axis parallel to the magnetic field, together with the data of microscopic observation of cylindrical shape of the vesicles. Further, the long axis is found to be at least five times longer than the short axis of the elongated vesicles in view of simulated 31P NMR lineshape. PMID:11750262

Naito, Akira; Nagao, Takashi; Obata, Maki; Shindo, Yuriko; Okamoto, Manabu; Yokoyama, Shinya; Tuzi, Satoru; Saitô, Hazime

2002-01-01

326

Creatine transporter defect diagnosed by proton NMR spectroscopy in males with intellectual disability.  

PubMed

Creatine deficiency syndrome due to mutations in X-linked SLC6A8 gene results in nonspecific intellectual disability (ID). Diagnosis cannot be established on clinical grounds and is often based on the assessment of brain creatine levels by magnetic resonance spectroscopy (MRS). Considering high costs of MRS and necessity of sedation, this technique cannot be used as a first level-screening test. Likewise, gene test analysis is time consuming and not easily accessible to all laboratories. In this article feasibility of urine analysis (creatine/creatinine (Cr/Crn) ratio) performed by nuclear magnetic resonance (NMR) as a first level-screening test is explored. Before running a systematic selection of cases a preliminary study for further molecular analysis is shown. NMR urine spectra (n = 1,347) of male patients with an ID without a clinically recognizable syndrome were measured. On the basis of abnormal Cr/Crn ratio, three patients with the highest values were selected for molecular analysis. A confirmatory second urine test was positive in two patients and diagnosis was further confirmed by a decreased brain creatine level and by SLC6A8 gene analysis. A de novo mutation was identified in one. Another patient inherited a novel mutation from the mother who also has a mild ID. A repeat urine test was negative in the third patient and accordingly creatine level in the brain and SLC6A8 gene analysis both gave a normal result. We conclude that Cr/Crn ratio measured by NMR for male patients represents a rapid and useful first level screening test preceding molecular analysis. PMID:21910234

Mencarelli, Maria Antonietta; Tassini, Maria; Pollazzon, Marzia; Vivi, Antonio; Calderisi, Marco; Falco, Michele; Fichera, Marco; Monti, Lucia; Buoni, Sabrina; Mari, Francesca; Engelke, Udo; Wevers, Ron A; Hayek, Joussef; Renieri, Alessandra

2011-09-09

327

Creatine Transporter Defect Diagnosed by Proton NMR Spectroscopy in Males With Intellectual Disability  

PubMed Central

Creatine deficiency syndrome due to mutations in X-linked SLC6A8 gene results in nonspecific intellectual disability (ID). Diagnosis cannot be established on clinical grounds and is often based on the assessment of brain creatine levels by magnetic resonance spectroscopy (MRS). Considering high costs of MRS and necessity of sedation, this technique cannot be used as a first level-screening test. Likewise, gene test analysis is time consuming and not easily accessible to all laboratories. In this article feasibility of urine analysis (creatine/creatinine (Cr/Crn) ratio) performed by nuclear magnetic resonance (NMR) as a first level-screening test is explored. Before running a systematic selection of cases a preliminary study for further molecular analysis is shown. NMR urine spectra (n = 1,347) of male patients with an ID without a clinically recognizable syndrome were measured. On the basis of abnormal Cr/Crn ratio, three patients with the highest values were selected for molecular analysis. A confirmatory second urine test was positive in two patients and diagnosis was further confirmed by a decreased brain creatine level and by SLC6A8 gene analysis. A de novo mutation was identified in one. Another patient inherited a novel mutation from the mother who also has a mild ID. A repeat urine test was negative in the third patient and accordingly creatine level in the brain and SLC6A8 gene analysis both gave a normal result. We conclude that Cr/Crn ratio measured by NMR for male patients represents a rapid and useful first level screening test preceding molecular analysis. © 2011 Wiley-Liss, Inc.

Mencarelli, Maria Antonietta; Tassini, Maria; Pollazzon, Marzia; Vivi, Antonio; Calderisi, Marco; Falco, Michele; Fichera, Marco; Monti, Lucia; Buoni, Sabrina; Mari, Francesca; Engelke, Udo; Wevers, Ron A; Hayek, Joussef; Renieri, Alessandra

2011-01-01

328

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

SciTech Connect

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

Matwiyoff, N.A.

1981-01-01

329

Nondestructive size determination of thiol-stabilized gold nanoclusters in solution by diffusion ordered NMR spectroscopy.  

PubMed

Diffusion ordered NMR spectroscopy (DOSY) was used as an analytical tool to estimate the size of thiol-stabilized gold nanoclusters in solution, namely, phenylethanethiol (PET) stabilized Au25(PET)18, Au38(PET)24, and Au144(PET)60. This was achieved by determining the diffusion coefficient and hydrodynamic radius from solution samples that were confirmed to be monodispersed by electrospray ionization mass spectrometry. The average cluster diameters obtained by this technique were estimated to be 1.7, 2.2, and 3.1 nm for the Au25(PET)18, Au38(PET)24, and Au144(PET)60 nanoclusters, respectively, which were shown to agree well with the average diameters of the corresponding single crystal or theoretical structures reported in the literature. Consequently, the DOSY technique is demonstrated to be a potentially valuable nondestructive tool for characterization of nanoparticle mixtures and verifying the purity of product solutions. PMID:23506040

Salorinne, Kirsi; Lahtinen, Tanja; Koivisto, Jaakko; Kalenius, Elina; Nissinen, Maija; Pettersson, Mika; Häkkinen, Hannu

2013-03-21

330

Single-quantum coherence filter for strongly coupled spin systems for localized (1)H NMR spectroscopy.  

PubMed

A pulse sequence for localized in vivo (1)H NMR spectroscopy is presented, which selectively filters single-quantum coherence built up by strongly coupled spin systems. Uncoupled and weakly coupled spin systems do not contribute to the signal output. Analytical calculations using a product operator description of the strongly coupled AB spin system as well as in vitro tests demonstrate that the proposed filter produces a signal output for a strongly coupled AB spin system, whereas the resonances of a weakly coupled AX spin system and of uncoupled spins are widely suppressed. As a potential application, the detection of the strongly coupled AA'BB' spin system of taurine at 1.5 T is discussed. PMID:10910692

Trabesinger, A H; Mueller, D C; Boesiger, P

2000-08-01

331

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

NASA Astrophysics Data System (ADS)

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

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

1981-10-01

332

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

333

Probing the helical tilt and dynamic properties of membrane-bound phospholamban in magnetically aligned bicelles using electron paramagnetic resonance spectroscopy.  

PubMed

Wild-type phospholamban (WT-PLB), a Ca(2+)-ATPase (SERCA) regulator in the sarcoplasmic reticulum membrane, was studied using TOAC nitroxide spin labeling, magnetically aligned bicelles, and electron paramagnetic resonance (EPR) spectroscopy to ascertain structural and dynamic information. Different structural domains of PLB (transmembrane segment: positions 42 and 45, loop region: position 20, and cytoplasmic domain: position 10) were probed with rigid TOAC spin labels to extract the transmembrane helical tilt and structural dynamic information, which is crucial for understanding the regulatory function of PLB in modulating Ca(2+)-ATPase activity. Aligned experiments indicate that the transmembrane domain of wild-type PLB has a helical tilt of 13°±4° in DMPC/DHPC bicelles. TOAC spin labels placed on the WT-PLB transmembrane domain showed highly restricted motion with more than 100ns rotational correlation time (?(c)); whereas the loop, and the cytoplasmic regions each consists of two distinct motional dynamics: one fast component in the sub-nanosecond scale and the other component is slower dynamics in the nanosecond range. PMID:22172806

Ghimire, Harishchandra; Abu-Baker, Shadi; Sahu, Indra D; Zhou, Andy; Mayo, Daniel J; Lee, Ryan T; Lorigan, Gary A

2011-12-04

334

Probing the Helical Tilt and Dynamic Properties of Membrane-bound Phospholamban in Magnetically Aligned Bicelles Using Electron Paramagnetic Resonance Spectroscopy  

PubMed Central

Wild-type Phospholamban (WT-PLB), a Ca2+-ATPase (SERCA) regulator in the sarcoplasmic reticulum membrane, was studied using TOAC nitroxide spin labeling, magnetically aligned bicelles, and electron paramagnetic resonance (EPR) spectroscopy to ascertain structural and dynamic information. Different structural domains of PLB (transmembrane segment: positions 42 and 45, loop region: position 20, and cytoplasmic domain: position 10) were probed with rigid TOAC spin labels to extract the transmembrane helical tilt and structural dynamic information, which is crucial for understanding the regulatory function of PLB in modulating Ca2+-ATPase activity. Aligned experiments indicate that the transmembrane domain of wild-type PLB has a helical tilt of 13° ± 4° in DMPC/DHPC bicelles. TOAC spin labels placed on the WT-PLB transmembrane domain showed highly restricted motion with more than 100 ns rotational correlation time (?c); whereas the loop, and the cytoplasmic regions each consists of two distinct motional dynamics: one fast component in the sub-nanosecond scale and the other component is slower dynamics in the nanosecond range.

Ghimire, Harishchandra; Abu-Baker, Shadi; Sahu, Indra D.; Zhou, Andy; Mayo, Daniel J.; Lee, Ryan. T.; Lorigan, Gary. A.

2011-01-01

335

Electron paramagnetic resonance spectroscopy of site-directed spin labels reveals the structural heterogeneity in the N-terminal domain of apoA-I in solution.  

PubMed

Apolipoprotein A-I (apoA-I) is the major protein constituent of high density lipoprotein (HDL) and plays a central role in phospholipid and cholesterol metabolism. This 243-residue long protein is remarkably flexible and assumes numerous lipid-dependent conformations. Consequently, definitive structural determination of lipid-free apoA-I in solution has been difficult. Using electron paramagnetic spectroscopy of site-directed spin labels in the N-terminal domain of apoA-I (residues 1-98) we have mapped a mixture of secondary structural elements, the composition of which is consistent with findings from other in-solution methods. Based on side chain mobility and their accessibility to polar and non-polar spin relaxers, the precise location of secondary elements for amino acids 14-98 was determined for both lipid-free and lipid-bound apoA-I. Based on intermolecular dipolar coupling at positions 26, 44, and 64, these secondary structural elements were arranged into a tertiary fold to generate a structural model for lipid-free apoA-I in solution. PMID:17204472

Lagerstedt, Jens O; Budamagunta, Madhu S; Oda, Michael N; Voss, John C

2007-01-04

336

The "Beta-Clasp" model of apolipoprotein A-I - a lipid-free solution structure determined by electron paramagnetic resonance spectroscopy  

PubMed Central

Apolipoprotein A-I (apoA-I) is the major protein component of high density lipoproteins (HDL) and plays a central role in cholesterol metabolism. The lipid-free / lipid-poor form of apoA-I is the preferred substrate for the ATP-binding cassette transporter A1 (ABCA1). The interaction of apoA-I with ABCA1 leads to the formation of cholesterol laden high density lipoprotein (HDL) particles, a key step in reverse cholesterol transport and the maintenance of cholesterol homeostasis. Knowledge of the structure of lipid-free apoA-I is essential to understanding its critical interaction with ABCA1 and the molecular mechanisms underlying HDL biogenesis. We therefore examined the structure of lipid-free apoA-I by electron paramagnetic resonance spectroscopy (EPR). Through site directed spin label EPR, we mapped the secondary structure of apoA-I and identified sites of spin coupling as residues 26, 44, 64, 167, 217 and 226. We capitalize on the fact that lipid-free apoA-I self-associates in an anti-parallel manner in solution. We employed these sites of spin coupling to define the central plane in the dimeric apoA-I complex. Applying both the constraints of dipolar coupling with the EPR-derived pattern of solvent accessibility, we assembled the secondary structure into a tertiary context, providing a solution structure for lipid-free apoA-I.

Lagerstedt, Jens O.; Budamagunta, Madhu S.; Liu, Grace S.; DeValle, Nicole C.; Voss, John C.; Oda, Michael N.

2012-01-01

337

[Optimization of the methods for small peptide solution structure determination by NMR spectroscopy].  

PubMed

NMR spectroscopy was recognized as a method of protein structure determination in solution. However, determination of the conformation of small peptides, which undergo fast molecular motions, remains a challenge. This is mainly caused by impossibility to collect required quantity of the distance and dihedral angle restraints from NMR spectra. At the same time, short charged peptides play an important role in a number of biological processes, in particular in pathogenesis of neurodegenerative diseases including Alzheimer's disease. Therefore development of a method for structure calculation of small peptides in a water environment using the most realistic force fields seems to be of current importance. Such algorithm has been developed using the Amber-03 force field and software package Gromacs after updating its program code. The algorithm of calculation has been verified on a model peptide for which the solution structure is known, and on the metal binding fragment of rat beta-amyloid for which structure has been determined by alternative methods. The developed algorithm substantially increases quality of structures, in particular Ramachandran plot statistics, and decreases RMSD of coordinates of atoms inside calculated family. The described protocol of calculation can be used for determination of conformation of short peptides, and also for structure optimization of larger proteins containing poorly structured fragments. PMID:21290829

Istrate, A N; Mantsyzov, A B; Kozin, S A; Pol'shakov, V I

338

Microstructure determination of 2-hydroxy ethyl methacrylate and methyl acrylate copolymers by NMR spectroscopy  

NASA Astrophysics Data System (ADS)

Copolymers of 2-Hydroxy ethyl methacrylate and methyl acrylate (H/M) of different compositions were synthesized by free radical bulk polymerization using azobisisobutyronitrile (AIBN) as an initiator under nitrogen atmosphere. The copolymers compositions were calculated from 1H NMR spectra. The reactivity ratios for H/M copolymers obtained from a linear Kelen Tudos method (KT) and nonlinear error-in-variables method (EVM) are rH = 3.31 ± 0.08, rM = 0.23 ± 0.00 and rH = 3.32, rM = 0.23, respectively. The complete spectral assignment of methine, methylene, methyl and carbonyl carbon regions in terms of compositional and configurational sequences of H/M copolymers was done with the help of 13C{1H} NMR, distortionless enhancement by polarization transfer (DEPT), two-dimensional heteronuclear single quantum coherence (HSQC) along with total correlated spectroscopy (TOCSY). Further, the assignments of carbonyl region were made with the help of heteronuclear multiple bond coherence (HMBC) spectrum.

Brar, A. S.; Hooda, Sunita; Goyal, Ashok Kumar

2007-02-01

339

Detection of chiral defects in crystalline organic solids using solid-state NMR spectroscopy.  

PubMed

The marketing of enantiopure pharmaceuticals has become more common due to regulatory and safety concerns surrounding the potential differences in biological activity of opposite enantiomers. However, achieving the desired enantiopurity can be a challenge, and low levels of the undesired enantiomer (chiral impurity) may be present in the final product. The location and nature of this impurity can potentially alter pharmaceutically relevant properties. In this article, we show that it is possible to identify and quantitate the crystallographic locations of small amounts of one enantiomer (l) in the presence of predominantly the opposite D-enantiomer using solid-state nuclear magnetic resonance (NMR) spectroscopy. Proline was used as a model compound, and crystalline samples containing both D- and L-proline were prepared by solvent evaporation, lyophilization, spray drying, and cryogrinding. Isotopic labeling, (13)C cross polarization-magic angle spinning NMR spectral subtractions, and (1)H T(1) spin-lattice relaxation measurements allowed selective observation and characterization of the crystal environments into which the L-proline impurity was incorporated upon concurrent crystallization with D-proline. Results show that L-proline was incorporated in up to four different crystalline forms, including L-proline as a kinetically trapped substitutional chiral defect in the D-proline host crystal lattice. PMID:21280054

Berendt, Robert T; Munson, Eric J

2011-01-28

340

In vivo sup 31 P-NMR spectroscopy of chronically stimulated canine skeletal muscle  

SciTech Connect

Chronic stimulation converts skeletal muscle of mixed fiber type to a uniform muscle made up of type I, fatigue-resistant fibers. Here, the bioenergetic correlates of fatigue resistance in conditioned canine latissimus dorsi are assessed with in vivo phosphorus-31 nuclear magnetic resonance ({sup 31}P-NMR) spectroscopy. After chronic electrical stimulation, five dogs underwent {sup 31}P-NMR spectroscopic and isometric tension measurements on conditioned and contralateral control muscle during stimulation for 200, 300, 500, and 800 ms of an 1,100-ms duty cycle. With stimulation, phosphocreatine (PCr) fell proportional to the degree of stimulation in both conditioned and control muscle but fell significantly less in conditioned muscle at all the least intense stimulation period (200 ms). Isometric tension, expressed as a tension time index per gram muscle, was significantly greater in the conditioned muscle at the two longest stimulation periods. The overall small change in PCr and the lack of a plateau in tension observed in the conditioned muscle are similar to that seen in cardiac muscle during increased energy demand. This study indicates that the conditioned muscle's markedly enhanced resistance to fatigue is in part the result of its increased capacity for oxidative phosphorylation.

Clark, B.J. III; McCully, A.K.; Subramanian, H.V.; Hammond, R.L.; Salmons, S.; Chance, B.; Stephenson, L.W. (Children's Hospital of Philadelphia, Harrison (USA) Univ. of Pennsylvania School of Medicine, Philadelphia (USA) Univ. of Birmingham (England))

1988-02-01

341

1H NMR spectroscopy study of water adsorbed on the surface of layered ilerite  

NASA Astrophysics Data System (ADS)

The hydrated layered alkaline silicate ilerite synthesized by a hydrothermal methodology was characterized by various techniques that confirmed a good structural quality of the resulted material. In an attempting to investigate the characteristics of water boundary layers in this hydrated powder sorbent, 1H NMR spectroscopy method was performed to measure the temperature dependence of the observed proton signal intensities in water sorbed, from 200.15 to 298.15 K. Gibbs energy of water molecules at the sorbent water interface decreased due to the sorption interactions, causing the water dosed to the sorbent surface freezes at T < 273.15 K. Due to a disturbing action of the sorbent surface and confined space, water occurs in the quasi-liquid state. As a result, it is observed in the 1H NMR spectra narrow signal relatively, but increase in peak broadening with the decrease of temperature. The presence of two types of hydrogen bonding was observed with the presence of signals around 3.9 and 16 ppm. The water at the interface freezes when the Gibbs energies of the sorbed water ice are identical. The variation of energy of ice observed in this material was 4.37 kJ mol-1 at 200.15 K with a decrease to null value at 298.15 K.

Pires, Cléo T. G. V. M. T.; Airoldi, Claudio

2013-06-01

342

Identification and metabolite profiling of Sitophilus oryzae L. by 1D and 2D NMR spectroscopy.  

PubMed

The polyphagous insect Sitophilus oryzae L. (Coleoptera:Curculionidae) has a tremendous adaptability in feeding behaviour, making it a serious invasive pest of stored cereals. The present study identifies the metabolite composition of Sitophilus oryzae (S. oryzae) using Nuclear Magnetic Resonance (NMR) spectroscopy. Assignment of 1D-proton by NMR, 1H-1H COSY, 2D-TOCSY 1H-1H, had been done. Amongst the various biochemically important metabolites isoleucine, valine, leucine, beta-hydroxybutyrate, lysine, glutamate, glutamine, proline, lactate, alanine, di-methylamine, alpha-glucose, beta-glucose, choline, glycerophosphorylcholine and tyrosine are present in S. oryzae. In wheat-fed S. oryzae, the presence of threonine and the absence of lactate is observed. In rice-fed S. oryzae, however, the presence of lactate and the absence of threonine were observed. Barley-fed S. oryzae shows presence of both tyrosine and lactate. It is concluded that the pest S. oryzae has adaptability on different stored cereals and grains, depicting the presence of earlier reported metabolites. The present study aims to identify the key metabolic components and associated enzymes in Sitophilus oryzae fed on different cereals. PMID:19814847

Trivedi, A; Kaushik, P; Pandey, A

2009-10-09

343

Lanthanide and actinide speciation in molten fluorides: A structural approach by NMR and EXAFS spectroscopies  

NASA Astrophysics Data System (ADS)

The objective of this paper is to describe the local structure in fluoride melts of nuclear interest. Our experimental approach combines NMR and EXAFS spectroscopies both sensitive to the microstructure of solid and liquid materials. These techniques allow identifying the complex formation in molten media. Thanks to the development of specific cells adapted to molten fluorides up to 1300 °C, we give some structural description of LiF LnF3 systems (Ln = Y, Lu, Ce) and discuss the evolution of 19F spectra in terms of different fluorine configurations depending on the composition. This approach is further extended to the characterization of LiF ThF4 system by 19F NMR in melts from 0 to 100 mol% ThF4 at temperatures ranging from 600 to 1100 °C. We report also very first EXAFS spectra obtained in situ at high temperature, at the Thorium LIII edge, in LiF ThF4 molten mixtures.

Bessada, Catherine; Rakhmatullin, Aydar; Rollet, Anne-Laure; Zanghi, Didier

2007-01-01

344

?z/?: A transverse relaxation optimized spectroscopy NMR experiment measuring longitudinal relaxation interference  

NASA Astrophysics Data System (ADS)

NMR spin relaxation experiments provide a powerful tool for the measurement of global and local biomolecular rotational dynamics at subnanosecond time scales. Technical limitations restrict most spin relaxation studies to biomolecules weighing less than 10 kDa, considerably smaller than the average protein molecular weight of 30 kDa. In particular, experiments measuring ?z, the longitudinal 1HN-15N dipole-dipole (DD)/15N chemical shift anisotropy (CSA) cross-correlated relaxation rate, are among those least suitable for use with larger biosystems. This is unfortunate because these experiments yield valuable insight into the variability of the 15N CSA tensor over the polypeptide backbone, and this knowledge is critical to the correct interpretation of most 15N-NMR backbone relaxation experiments, including R2 and R1. In order to remedy this situation, we present a new 1HN-15N transverse relaxation optimized spectroscopy experiment measuring ?z suitable for applications with larger proteins (up to at least 30 kDa). The presented experiment also yields ?, the site-specific rate of longitudinal 1HN-1H' DD cross relaxation. We describe the ?z/? experiment's performance in protonated human ubiquitin at 30.0 °C and in protonated calcium-saturated calmodulin/peptide complex at 20.0 °C, and demonstrate preliminary experimental results for a deuterated E. coli DnaK ATPase domain construct at 34 °C.

Weaver, Daniel S.; Zuiderweg, Erik R. P.

2008-04-01

345

Quantitative determination of atractylon in Atractylodis Rhizoma and Atractylodis Lanceae Rhizoma by 1H-NMR spectroscopy.  

PubMed

(1)H-NMR spectroscopy was successfully applied to the quantitative determination of atractylon in Atractylodis Rhizoma (dried rhizomes of Atractylodes ovata and A. japonica) and Atractylodis Lanceae Rhizoma (dried rhizomes of Atractylodes lancea and A. chinensis). The analysis was carried out by comparing the integral of the H-12 singlet signal of atractylon, which was well separated in the range of delta 6.95-7.05 ppm in the NMR spectrum, with the integral of a hexamethyldisilane (HMD) signal at delta 0 ppm. The atractylon contents obtained by the (1)H-NMR spectroscopy were consistent with those obtained by the conventional HPLC analysis. The present method requires neither reference compounds for calibration curves nor sample pre-purification. It also allows simultaneous determination of multiple constituents in a crude extract. Thus, it is applicable to chemical evaluation of crude drugs as a powerful alternative to various chromatographic methods. PMID:20165926

Hasada, Keiko; Yoshida, Takamitsu; Yamazaki, Takeshi; Sugimoto, Naoki; Nishimura, Tetsuji; Nagatsu, Akito; Mizukami, Hajime

2010-02-19

346

Quantification of hydrophilic ethoxylates in polysorbate surfactants using diffusion H1 NMR spectroscopy.  

PubMed

Polysorbate surfactants (commercially available as Tween) are widely used in pharmaceutical, cosmetic and food products. They are generally considered as esters of ethoxylated sorbitan with fatty acids. Diffusion H1 NMR spectroscopy on a solution of polysorbate 20 in D2O revealed that only one diffusion coefficient was found for the fatty acyl part. Using the Stokes-Einstein equation, it became obvious that this diffusion behavior was caused by micelles. On the other hand, two significantly different diffusion coefficients were found for the methylene groups of ethylene oxide (EO). This indicates the presence of two distinct EO containing species in solution. Since the slowest diffusing EO species has the same diffusion coefficient as the fatty acyl part, it corresponds to the micellar (i.e. fatty acyl bound) ethoxylates. The diffusion coefficient of the fastest diffusing EO species was a factor of four larger than that of the slowly diffusing species and was attributed to water-soluble non-esterified ethoxylates. A solution of polysorbate 20 in the presence of NaOD was prepared to investigate if hydrolysis of the sorbitan ester could be the reason for the occurence of these hydrophilic ethoxylates. It was found that alkaline hydrolysis does lead to an increasing fraction of non-esterified ethoxylates, but is not the cause of its presence in untreated polysorbate samples since these species were also found in solutions of polyethylene glycol oleyl ether (commercially available as Brij), which are not susceptible to hydrolysis. Fractionation of the EO species present in polysorbate 20 into an amphiphilic and a hydrophilic fraction was only partly obtained by activated carbon adsorption. On the other hand, sequential extraction of aqueous polysorbate solutions by ethyl acetate and chloroform enabled a nearly complete fractionation. H1 NMR spectroscopy proved to be very useful since it allows in situ determination of the global composition of a surfactant sample, as well as quantification of both the amphiphilic and hydrophilic ethoxylate fractions via diffusion measurements. PMID:19846263

Verbrugghe, Maarten; Cocquyt, Ellen; Saveyn, Pieter; Sabatino, Paolo; Sinnaeve, Davy; Martins, José C; Van der Meeren, Paul

2009-09-27

347

Novel solution conformation of DNA observed in d(GAATTCGAATTC) by two-dimensional NMR spectroscopy  

SciTech Connect

Resonance assignments of nonexchangeable base and sugar protons of the self-complementary dodecanucleotide d(GAATTCGAATTC) have been obtained by using the two-dimensional Fourier transform NMR methods correlated spectroscopy and nuclear Overhauser effect spectroscopy. Conformational details about the sugar pucker, the glycosidic dihedral angle, and the overall secondary structure of the molecule has been derived from the relative intensities of cross peaks in the two-dimensional NMR spectra in aqueous solution. It is observed that d(GAATTCGAATTC) assumes a novel double-helical structure. The solution conformations of the two complementary strands are identical, unlike those observed in a related sequence in the solid state. Most of the five-membered sugar rings adopt an unusual O1'-endo geometry. All the glycosidic dihedral angles are in the anti domain. The AATT segments A2-T5 and A8-T11 show better stacking compared to the rest of the molecule. These features fit into a right-handed DNA model for the above two segments, with the sugar geometries different from the conventional ones. There are important structural variations in the central TCG portion, which is known to show preferences for DNase I activity, and between G1-A2 and G7-A8, which are cleavage points in the EcoRI recognition sequence. The sugar puckers for G1 and G7 are significantly different from the rest of the molecule. Further, in the three segments mentioned above, the sugar phosphate geometry is such that the distances between protons on adjacent nucleotides are much larger than those expected for a right-handed DNA. The authors suggest that such crevices in the DNA structure may act as hot points in initiation of protein recognition.

Chary, K.V.R.; Hosur, R.V.; Govil, G.; Zu-kun, T.; Miles, H.T.

1987-03-10

348

NMR spectroscopy with force-gradient detection on a GaAs epitaxial layer  

NASA Astrophysics Data System (ADS)

We demonstrate nuclear magnetic resonance spectroscopy on 35 ?m3 of 69Ga in a GaAs epitaxial layer in vacuum at 5 K, and 5 T yielding a linewidth on the order of 10 kHz. This was achieved by a force-gradient magnetic resonance detection scheme, using the interaction between the force-gradient of a Ni sphere-tipped single crystal Si cantilever and the nuclear spins to register changes in the spin state as a change in the driven cantilever's natural resonant frequency. The dichotomy between the background magnetic field (B0) homogeneity requirements imposed by NMR spectroscopy and the magnetic particle's large magnetic field gradient is resolved via sample shuttling during the NMR pulse encoding. A GaAs sample is polarized in a B0 of 5 T for 3 * T1. The sample is shuttled away from the magnetic particle to a region of negligible magnetic field inhomogeneity. A (?/2)x pulse rotates the polarization to the xy-plane, the magnetization is allowed to precess for 2–200 ?s before a (?/2)x or (?/2)y pulse stores the remaining spin along the z-axis that represents a single point of the free induction decay (FID). The sample is shuttled back to the established tip-sample distance. An adiabatic rapid passage (ARP) sweep inverts the spins in a volume of interest, causing the cantilever's natural resonance frequency to shift an amount proportional to the spin polarization in the volume. By varying the delay between the first and second (?/2) pulses the entire FID is measured.

Alexson, Dimitri A.; Smith, Doran D.

2013-10-01

349

QUANTIFICATION OF MYO-INOSITOL HEXAKISPHOSPHATE IN ALKALINE SOIL EXTRACTS BY SOLUTION PHOSPHORUS 31 NMR SPECTROSCOPY AND SPECTRAL DECONVULTION  

Technology Transfer Automated Retrieval System (TEKTRAN)

Inositol phosphates are the dominant class of organic phosphorus (P) compounds in most soils, but are poorly understood because they are not easily identified in soil extracts. This study reports a relatively simple technique using solution phosphorus 31 NMR spectroscopy and spectral deconvolution ...

350

NMR and IR Spectroscopy for the Structural Characterization of Edible Fats and Oils: An Instrumental Analysis Laboratory  

ERIC Educational Resources Information Center

|This article describes an upper-level instrumental laboratory for undergraduates that explores the complementary nature of IR and NMR spectroscopy for analysis of several edible fats and oils that are structurally similar but differ in physical properties and health implications. Five different fats and oils are analyzed for average chain length,…

Crowther, Molly W.

2008-01-01

351

Porosity of pillared clays studied by hyperpolarized 129Xe NMR spectroscopy and Xe adsorption isotherms.  

PubMed

The influence of the layer charge on the microstructure was studied for a series of three hybrid pillared interlayered clays based on the organic dication Me(2)DABCO(2+) and charge reduced synthetic fluorohectorites. To get a detailed picture of the local arrangements within the interlayer space, multinuclear solid-state NMR spectroscopy was performed in conjunction with high-resolution (129)Xe MAS NMR, temperature-dependent wide-line 1D and 2D (129)Xe NMR, and Ar/Ar(l) and Xe/Xe(l) physisorption measurements. The resulting layer charge (x) for the three samples are 0.48, 0.44, and 0.39 per formula unit (pfu). The samples exhibit BET equivalent surfaces between 150 and 220 m(2)/g and pore volumes which increase from 0.06 to 0.11 cm(3)/g while the layer charge reduces. 1D and 2D (1)H, (13)C, (19)F, and (29)Si MAS data reveal that the postsynthetic charge reduction induces regions with higher defect concentrations within the silicate layers. Although the pillars tend to avoid these defect-rich regions, a homogeneous and regular spacing of the Me(2)DABCO(2+) pillars is established. Both the Ar/Ar(l) physisorption and (129)Xe NMR measurements reveal comparable pore dimensions. The trend of the temperature-dependent wide-line (129)Xe spectra as well as the exchange in the EXSY spectra is typical for a narrow 2D pore system. (129)Xe high-resolution experiments allow for a detailed description of the microstructure. For x = 0.48 a bimodal distribution with pore diameters between 5.9 and 6.4 Å is observed. Reducing the layer charge leads to a more homogeneous pore structure with a mean diameter of 6.6 Å (x = 0.39). The adsorption enthalpies ?H(ads) determined from the temperature-dependent (129)Xe chemical shift data fit well to the ones derived from the Xe/Xe(l) physisorption measurements in the high-pressure limit while the magnitude of ?H(ads) in the low-pressure limit is significantly larger. Thus, the (129)Xe data are influenced by adsorbate-adsorbent as well as adsorbate-adsorbate interactions. PMID:23240993

Keenan, Caroline D; Herling, Markus M; Siegel, Renée; Petzold, Nikolaus; Bowers, Clifford R; Rössler, Ernst A; Breu, Josef; Senker, Jürgen

2013-01-03

352

/sup 31/P NMR studies of enzyme-bound substrate complexes of yeast 3-phosphoglycerate kinase. 2. Structure measurements using paramagnetic relaxation effects of Mn(II) and Co(II)  

SciTech Connect

Measurements of the paramagnetic effects of two dissimilar activating paramagnetic cations, Mn(II) and Co(II), on the spin relaxation rates of the /sup 31/P nuclei in the complexes of 3-phosphoglycerate kinase with ATP, ADP, and 3-P-glycerate have been used to study the structures of these enzyme-substrate complexes. All experiments were performed on enzyme-bound complexes, so that two exchanging complexes (with and without cation) contribute to the observed relaxation rate. Measurements were made at three /sup 31/P NMR frequencies, 81, 121.5, and 190.2 MHz, and as a function of temperature in the range 5-20/sup 0/C to determine the effect of exchange on the observed relaxation rates. Relaxation rates in E-MnADP and E-MnATP were shown to be exchange-limited, and therefore bereft of structural information, both by lack of frequency dependence and by temperature dependence with activation energies (deltaE) in the range 5-8 kcal/mol. These distances were all in the range 2.7-4.1 A, appropriate for direct coordination of Co(II) to the phosphate groups. In the quaternary complex E-MnADP-3-P-glycerate, although the /sup 31/P relaxation rates of ..cap alpha..-P and ..beta..-P (ADP) were exchange-limited, that for 3-P (3-P-glycerate) was not exchanged-limited, as evidenced by its frequency dependence and an activation energy of 1.8 kcal/mol. The frequency dependence of the relaxation times of 3-P-glycerate was used to determine a Mn(II)-/sup 31/P (3-P-glycerate) distance of 11.1 +/- 0.3 A, suggesting that in E-MnADP-3-P-glycerate the enzyme is in an open conformation.

Ray, B.D.; Nageswara Rao, B.D.

1988-07-26

353

LEGO-NMR Spectroscopy: A Method to Visualize Individual Subunits in Large Heteromeric Complexes.  

PubMed

Seeing the big picture: Asymmetric macromolecular complexes that are NMR active in only a subset of their subunits can be prepared, thus decreasing NMR spectral complexity. For the hetero heptameric LSm1-7 and LSm2-8 rings NMR spectra of the individual subunits of the complete complex are obtained, showing a conserved RNA binding site. This LEGO-NMR technique makes large asymmetric complexes accessible to detailed NMR spectroscopic studies. PMID:23946163

Mund, Markus; Overbeck, Jan H; Ullmann, Janina; Sprangers, Remco

2013-08-14

354

Characteristics of zero-quantum correlation spectroscopy in MAS NMR experiments  

NASA Astrophysics Data System (ADS)

Zero-quantum coherence generation and reconversion in magic-angle spinning solid-state NMR is analyzed. Two methods are discussed based on implementations using symmetry-based pulse sequences that utilize either isotropic J couplings or dipolar couplings. In either case, the decoupling of abundant proton spins plays a crucial role for the efficiency of the zero-quantum generation. We present optimized sequences for measuring zero-quantum single-quantum correlation spectra in solids, achieving an efficiency of 50% in ubiquitin. The advantages and disadvantages of zero-quantum single-quantum over single-quantum single-quantum correlation spectroscopy are explored, and similarities and differences with double-quantum single-quantum correlation spectroscopy are discussed. Finally, possible application of zero-quantum single-quantum experiments to polypeptides, where it can lead to better spectral resolution is investigated using ubiquitin, where we find high efficiency and high selectivity, but also increased line widths in the MQ dimension.

Köneke, Stephanie G.; van Beek, Jacco D.; Ernst, Matthias; Meier, Beat H.

2010-12-01

355

Molecular-level characterization of probucol nanocrystal in water by in situ solid-state NMR spectroscopy.  

PubMed

The molecular state of colloidal probucol nanoparticles with additives was evaluated by (13)C in situ solid-state NMR spectroscopy. The nanoparticles were obtained by dispersing a ternary co-ground mixture of probucol/polyvinylpyrrolidon (PVP)/sodium dodecyl sulfate (SDS) in water. Their mean particle size was found to be approximately 150 nm by dynamic light scattering and cryogenic-scanning electron microscopy measurements. The results of the (13)C in situ solid-state NMR spectroscopy showed that probucol existed in the crystalline state (form I) in water. (13)C liquid-state NMR results indicated that PVP and SDS interacted with probucol in water. Their broad signals suggested that the surface interaction of the probucol nanocrystal with PVP and SDS stabilized the suspension. In addition, a freeze-dried sample of the suspension was studied by (13)C solid-state NMR and powder X-ray diffraction experiments, which confirmed the presence of the probucol nanocrystals. The combination of the in situ solid-state, solid-state, and liquid-state NMR measurement results provided molecular-level insights about the role of intermolecular interactions in the design of nanoformulations. PMID:22138607

Zhang, Junying; Higashi, Kenjirou; Limwikrant, Waree; Moribe, Kunikazu; Yamamoto, Keiji

2011-11-26

356

Intermolecular zero-quantum coherence NMR spectroscopy in the presence of local dipole fields  

NASA Astrophysics Data System (ADS)

NMR experiments detecting intermolecular zero-quantum coherences (iZQCs) allow for observation of homogeneous line shapes under inhomogeneous magnetic fields. Local dipole fields impair the refocusing capacity of such experiments and render the available theoretical description of signal evolution invalid. In this article, the impact of local dipole fields on two-dimensional iZQC spectroscopy experiments was assessed by performing extensive numerical simulations, which solved the nonlinear Bloch equations for a binary solution in a magnetization array of 643 spatial points. Local dipole fields were simulated using spherical volumes with different magnetic susceptibility values corresponding to either a glass sphere or an air inclusion with a diameter of 100 ?m. The local field resulted in a broadened distribution of difference frequencies between locally interacting spins and led to the dominating effect of decreasing the amplitude of the solute peak, before line broadening was observed in the spectra. From simulations using a magnetic field strength of 17.6 T, the smallest ratio of sample to inclusion volume that still allowed for observation of the solute peak was determined to be ?limit=215 and ?limit=392 for glass and air inclusions, respectively. Experimental data acquired with a 100 ?m diameter glass sphere embedded in agar gel yielded a value of ?limit=252 and confirmed the order of magnitude obtained from the simulations. From these data, it was concluded that iZQC spectroscopy is possible as long as the relative volume occupied by air inclusions does not exceed the order of 0.1% of the sample volume. This limit, in contrast to the previous speculations, strongly excludes materials or tissues with high density of strong inhomogeneities from the investigation by iZQC spectroscopy.

Balla, David Z.; Faber, Cornelius

2008-04-01

357

Retinal Conformation and Dynamics in Activation of Rhodopsin Illuminated by Solid-state 2H NMR Spectroscopy  

PubMed Central

Solid-state NMR spectroscopy gives a powerful avenue for investigating G protein-coupled receptors and other integral membrane proteins in a native-like environment. This article reviews the use of solid-state 2H NMR to study the retinal cofactor of rhodopsin in the dark state as well as the meta I and meta II photointermediates. Site-specific 2H NMR labels have been introduced into three regions (methyl groups) of retinal that are crucially important for the photochemical function of rhodopsin. Despite its phenomenal stability 2H NMR spectroscopy indicates retinal undergoes rapid fluctuations within the protein binding cavity. The spectral lineshapes reveal the methyl groups spin rapidly about their three-fold (C3) axes with an order parameter for the off-axial motion of SC3 ? 0.9. For the dark state, the 2H NMR structure of 11-cis-retinal manifests torsional twisting of both the polyene chain and the ?-ionone ring due to steric interactions of the ligand and the protein. Retinal is accommodated within the rhodopsin binding pocket with a negative pretwist about the C11=C12 double bond. Conformational distortion explains its rapid photochemistry and reveals the trajectory of the 11-cis to trans isomerization. In addition, 2H NMR has been applied to study the retinylidene dynamics in the dark and light-activated states. Upon isomerization there are drastic changes in the mobility of all three methyl groups. The relaxation data support an activation mechanism whereby the ?-ionone ring of retinal stays in nearly the same environment, without a large displacement of the ligand. Interactions of the ?-ionone ring and the retinylidene Schiff base with the protein transmit the force of the retinal isomerization. Solid-state 2H NMR thus provides information about the flow of energy that triggers changes in hydrogen-bonding networks and helix movements in the activation mechanism of the photoreceptor.

Brown, Michael F.; Martinez-Mayorga, Karina; Nakanishi, Koji; Salgado, Gilmar F. J.; Struts, Andrey V.

2010-01-01

358

Exploring weak, transient protein-protein interactions in crowded in vivo environments by in-cell NMR spectroscopy  

PubMed Central

Biology relies on functional interplay of proteins in the crowded and heterogeneous environment inside cells, and functional protein interactions are often weak and transient. Thus, methods are needed that preserve these interactions and provide information about them. In-cell NMR spectroscopy is an attractive method to study a protein’s behavior in cells because it may provide residue-level structural and dynamic information. Yet several factors limit the feasibility of protein NMR spectroscopy in cells, and among them slow rotational diffusion has emerged as the most important. In this paper, we seek to elucidate the causes of the dramatically slow protein tumbling in cells and in so doing to gain insight into how the intracellular viscosity and weak, transient interactions modulate protein mobility. To address these questions, we characterized the rotational diffusion of three model globular proteins in E. coli cells using 2D heteronuclear NMR spectroscopy. These proteins have a similar molecular size and globular fold, but very different surface properties, and indeed, they show very different rotational diffusion in the E. coli intracellular environment. Our data are consistent with an intracellular viscosity approximately eight times that of water—too low to be a limiting factor to observing small globular proteins by in-cell NMR spectroscopy. Thus, we conclude that transient interactions with cytoplasmic components significantly and differentially affect the mobility of proteins and therefore their NMR detectability. Moreover, we suggest that an intricate interplay of total protein charge and hydrophobic interactions plays a key role in regulating these weak intermolecular interactions in cells.

Wang, Qinghua; Zhuravleva, Anastasia; Gierasch, Lila M.

2011-01-01

359

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

PubMed

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

Duquesnoy, Emilie; Castola, Vincent; Casanova, Joseph

360

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

Microsoft Academic Search

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

Michael Schilling; William T. Cooper

2004-01-01

361

Accurate measurement of alpha proton chemical shifts of excited protein states by relaxation dispersion NMR spectroscopy.  

PubMed

Carr-Purcell-Meiboom-Gill relaxation dispersion NMR spectroscopy can provide detailed information about low populated, invisible states of protein molecules, including backbone chemical shifts of the invisible conformer and bond vector orientations that can be used as structural constraints. Notably, the measurement of 1Halpha chemical shifts in excited protein states has not been possible to date because, in the absence of suitable labeling, the homonuclear proton scalar coupling network in side chains of proteins leads to a significant degradation in the performance of proton-based relaxation dispersion experiments. Here we have overcome this problem through a labeling scheme in which proteins are prepared with U-2H glucose and 50% D2O/50% H2O that results in deuteration levels of between 50-88% at the Cbeta carbon. Effects from residual 1Halpha-1Hbeta scalar couplings can be suppressed through a new NMR experiment that is presented here. The utility of the methodology is demonstrated on a ligand binding exchanging system and it is shown that 1Halpha chemical shifts extracted from dispersion profiles are, on average, accurate to 0.03 ppm, an order of magnitude better than they can be predicted from structure using a database approach. The ability to measure 1Halpha chemical shifts of invisible conformers is particularly important because such shifts are sensitive to both secondary and tertiary structure. Thus, the methodology presented is a valuable addition to a growing list of experiments for characterizing excited protein states that are difficult to study using the traditional techniques of structural biology. PMID:19152327

Lundström, Patrik; Hansen, D Flemming; Vallurupalli, Pramodh; Kay, Lewis E

2009-02-11

362

Cholesterol in oriented bilayers: Determination of order parameters by proton detected local field NMR spectroscopy  

NASA Astrophysics Data System (ADS)

Cholesterol order parameters are usually determined by deuterium NMR using specifically deuterated cholesterol. We demonstrate herein that the same information may be obtained from the C-H dipolar couplings using 2D experiments correlating 13C chemical shifts and H-C dipolar couplings (PDLF spectroscopy) which we have performed for the first time on oriented lipid bilayers. The order parameters of C4-Ha and C4-He vectors calculated from this experiment are in agreement with those previously determined on the same sample from deuterium NMR. This experiment opens the way to the simultaneous determination of order parameters of all C-H vectors without the need of specific labeling. La détermination des paramètres d'ordre du cholestérol dans une bicouche lipidique est possible par RMN du deutérium après synthèse de cholestérol spécifiquement marqué. Nous montrons dans cet article que la même information peut être extraite à partir des constantes de couplage dipolaire C-H à l'aide d'expériences 2D de corrélation déplacement chimique 13C - couplage dipolaire 13C-H, appelées PDLF, qui ont été réalisées pour la première fois sur des bicouches lipidiques orientées. Les paramètres d'ordre des vecteurs C4-Ha et C4-He issus de cette expérience sont en accord avec ceux déterminés précédemment, sur le même échantillon, par RMN du deutérium. Cette approche permet d'envisager la détermination en une seule expérience des couplages dipolaires de tous les vecteurs C-H sans avoir recours au marquage spécifique.

Massou, S.; Tropis, M.; Milon, A.

1999-10-01

363

Structural models of activated ?-alumina surfaces revisited: Thermodynamics, NMR and IR spectroscopies from ab initio calculations  

NASA Astrophysics Data System (ADS)

The activation of highly catalytic ?-alumina surfaces by thermal treatment and the description of the related chemical processes at atomic scale is a topical issue. According to a recent study [J. Am. Chem. Soc. 134 (2012) 14430], the enhanced reactivity of ?-alumina has been associated to tri-coordinated aluminum sites which supposedly are exposed exclusively on the (1 1 0) surfaces of this oxide. In this work, we explore this possibility by modeling the (1 0 0) and (1 1 0) terminations using Krokidis et al. [J. Phys. Chem. B 105 (2001) 5121] bulk structure and performing an extensive search of the most stable hydrated surface models at conditions consistent with experiment. Among the 156 structures analyzed, we identify several "metastable" models for the (1 1 0) surface with a considerable probability of containing the AlIII centers at OH coverages of 9.0 and 6.0 OH/nm2. We then test the reactivity of these sites through their Lewis acidity by simulating the CO adsorbtion on the surface and our results confirm the high reactivity of AlIII centers. Based on the Gibbs free energy of the explored structures, we carry on a thermodynamical analysis at varying hydroxylation degrees and pretreatment temperatures and simulate the experimental volcano-type behavior reported in [J. Am. Chem. Soc. 134 (2012) 14430] and predict the optimum pretreatment temperature as 700 °C, in very good agreement with experimental findings. We further use infrared and solid state MAS NMR spectroscopies and reproduce the 1H MAS NMR spectra under high vacuum conditions (10-5 Torr). The strong resemblance of spectra to the experimental ones in the literature [J. Phys. Chem. C 116 (2012) 834] validate further the structural models we have generated in this study.

Ferreira, Ary R.; Küçükbenli, Emine; de Gironcoli, Stefano; Souza, Wladmir F.; Chiaro, Sandra Shirley X.; Konstantinova, Elena; Leitão, Alexandre A.

2013-09-01

364

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

365

An electron paramagnetic resonance spectroscopy investigation of the retention mechanisms of Mn and Cu in the nanopore channels of three zeolite minerals  

SciTech Connect

The adsorption mechanisms of divalent cations in zeolite nanopore channels can vary as a function of their pore dimensions. The nanopore inner-sphere enhancement (NISE) theory predicts that ions may dehydrate inside small nanopore channels in order to adsorb more closely to the mineral surface if the nanopore channel is sufficiently small. The results of an electron paramagnetic resonance (EPR) spectroscopy study of Mn and Cu adsorption on the zeolite minerals zeolite Y (large nanopores), ZSM-5 (intermediate nanopores), and mordenite (small nanopores) are presented. The Cu and Mn cations both adsorbed via an outer-sphere mechanism on zeolite Y based on the similarity between the adsorbed spectra and the aqueous spectra. Conversely, Mn and Cu adsorbed via an inner-sphere mechanism on mordenite based on spectrum asymmetry and peak broadening of the adsorbed spectra. However, Mn adsorbed via an outer-sphere mechanism on ZSM-5, whereas Cu adsorbed on ZSM-5 shows a high degree of surface interaction that indicates that it is adsorbed closer to the mineral surface. Evidence of dehydration and immobility was more readily evident in the spectrum of mordenite than ZSM-5, indicating that Cu was not as close to the surface on ZSM-5 as it was when adsorbed on mordenite. Divalent Mn cations are strongly hydrated and are held strongly only in zeolites with small nanopore channels. Divalent Cu cations are also strongly hydrated, but can dehydrate more easily, presumably due to the Jahn-Teller effect, and are held strongly in zeolites with medium sized nanopore channels or smaller.

Ferreira, Daniel R.; Schulthess, Cristian P.; Amonette, James E.; Walter, Eric D.

2012-12-01

366

Raftlike Mixtures of Sphingomyelin and Cholesterol Investigated by Solid-State 2H NMR Spectroscopy  

PubMed Central

Sphingomyelin is a lipid that is abundant in the nervous systems of mammals, where it is associated with putative microdomains in cellular membranes and undergoes alterations due to aging or neurodegeneration. We investigated the effect of varying the concentration of cholesterol in binary and ternary mixtures with N-palmitoylsphingomyelin (PSM) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) using deuterium nuclear magnetic resonance (2H NMR) spectroscopy in both macroscopically aligned and unoriented multilamellar dispersions. In our experiments, we used PSM and POPC perdeuterated on the N-acyl and sn-1 acyl chains, respectively. By measuring solid-state 2H NMR spectra of the two lipids separately in mixtures with the same compositions as a function of cholesterol mole fraction and temperature, we obtained clear evidence for the coexistence of two liquid-crystalline domains in distinct regions of the phase diagram. According to our analysis of the first moments M1 and the observed 2H NMR spectra, one of the domains appears to be a liquid-ordered phase. We applied a mean-torque potential model as an additional tool to calculate the average hydrocarbon thickness, the area per lipid, and structural parameters such as chain extension and thermal expansion coefficient in order to further define the two coexisting phases. Our data imply that phase separation takes place in raftlike ternary PSM/POPC/cholesterol mixtures over a broad temperature range but vanishes at cholesterol concentrations equal to or greater than a mole fraction of 0.33. Cholesterol interacts preferentially with sphingomyelin only at smaller mole fractions, above which a homogeneous liquid-ordered phase is present. The reasons for these phase separation phenomena seem to be differences in the effects of cholesterol on the configurational order of the palmitoyl chains in PSM-d31 and POPC-d31 and a difference in the affinity of cholesterol for sphingomyelin observed at low temperatures. Hydrophobic matching explains the occurrence of raftlike domains in cellular membranes at intermediate cholesterol concentrations but not saturating amounts of cholesterol.

Bartels, Tim; Lankalapalli, Ravi S.; Bittman, Robert; Beyer, Klaus; Brown, Michael F.

2009-01-01

367

Raftlike mixtures of sphingomyelin and cholesterol investigated by solid-state 2H NMR spectroscopy.  

PubMed

Sphingomyelin is a lipid that is abundant in the nervous systems of mammals, where it is associated with putative microdomains in cellular membranes and undergoes alterations due to aging or neurodegeneration. We investigated the effect of varying the concentration of cholesterol in binary and ternary mixtures with N-palmitoylsphingomyelin (PSM) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) using deuterium nuclear magnetic resonance ((2)H NMR) spectroscopy in both macroscopically aligned and unoriented multilamellar dispersions. In our experiments, we used PSM and POPC perdeuterated on the N-acyl and sn-1 acyl chains, respectively. By measuring solid-state (2)H NMR spectra of the two lipids separately in mixtures with the same compositions as a function of cholesterol mole fraction and temperature, we obtained clear evidence for the coexistence of two liquid-crystalline domains in distinct regions of the phase diagram. According to our analysis of the first moments M1 and the observed (2)H NMR spectra, one of the domains appears to be a liquid-ordered phase. We applied a mean-torque potential model as an additional tool to calculate the average hydrocarbon thickness, the area per lipid, and structural parameters such as chain extension and thermal expansion coefficient in order to further define the two coexisting phases. Our data imply that phase separation takes place in raftlike ternary PSM/POPC/cholesterol mixtures over a broad temperature range but vanishes at cholesterol concentrations equal to or greater than a mole fraction of 0.33. Cholesterol interacts preferentially with sphingomyelin only at smaller mole fractions, above which a homogeneous liquid-ordered phase is present. The reasons for these phase separation phenomena seem to be differences in the effects of cholesterol on the configurational order of the palmitoyl chains in PSM-d31 and POPC-d31 and a difference in the affinity of cholesterol for sphingomyelin observed at low temperatures. Hydrophobic matching explains the occurrence of raftlike domains in cellular membranes at intermediate cholesterol concentrations but not saturating amounts of cholesterol. PMID:18839945

Bartels, Tim; Lankalapalli, Ravi S; Bittman, Robert; Beyer, Klaus; Brown, Michael F

2008-10-08

368

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

369

Non Destructive Testing of Thermoplastic Composites by NMR Imaging and Localised Spectroscopy  

Microsoft Academic Search

The application of NMR methods to the non-destructive testing of thermoplastic composites is discussed. NMR imaging of the polymer matrix is restricted to the detection of defects in excess of 5 mm using standard instrumentation. Higher resolution can be achieved by imaging the matrix at high temperatures or by more sophisticated NMR procedures with the practical limit of 0.1 mm

Nigel J. Clayden; Peter Jackson

1994-01-01

370

Application of 1H-NMR spectroscopy to validation of berberine alkaloid reagents and to chemical evaluation of Coptidis Rhizoma.  

PubMed

Berberine, palmatine, and coptisine are major pharmacologically active protoberberine alkaloids in Coptidis Rhizoma, and have been used as indices for chemical evaluation of the crude drug. (1)H-NMR spectroscopy was applied to determination of purities of commercial reagents of protoberberine alkaloids. The purities of the alkaloids were calculated from the ratios of the intensities of the H-13 singlet signal at about ? 8.7 ppm of target protoberberine alkaloids to integration of a hexamethyldisilane (HMD) signal at 0 ppm. The concentration of HMD was corrected with SI traceability using potassium hydrogen phthalate of certified reference material (CRM) grade. The purity of the reagent estimated by the (1)H-NMR was, in general, lower than that claimed by the manufacturer, leading to over-estimation of the alkaloid contents of Coptidis Rhizoma when determined by HPLC. The present quantitative (1)H-NMR method was also applicable to direct determination of protoberberine alkaloid contents in Coptidis Rhizoma. PMID:21188644

Hasada, Keiko; Yoshida, Takamitsu; Yamazaki, Takeshi; Sugimoto, Naoki; Nishimura, Tetsuji; Nagatsu, Akito; Mizukami, Hajime

2010-12-25

371

Direct detection of ligand binding to Sepharose-immobilised protein using saturation transfer double difference (STDD) NMR spectroscopy  

SciTech Connect

We report an easy and direct application of 'Saturation Transfer Double Difference' (STDD) NMR spectroscopy to identify ligands that bind to a Sepharose-immobilised target protein. The model protein, cytidine 5'-monophosphate sialic acid (CMP-Sia) synthetase, was expressed as a Strep-Tag II fusion protein and immobilised on Strep-Tactin Sepharose. STD NMR experiments of the protein-enriched Sepharose matrix in the presence of a binding ligand (cytidine 5'-triphosphate, CTP) and a non-binding ligand ({alpha}/{beta}-glucose) clearly show that CTP binds to the immobilised enzyme, whereas glucose has no affinity. This approach has three major advantages: (a) only low quantities of protein are required, (b) no specialised NMR technology or the application of additional data analysis by non-routine methods is required, and (c) easy multiple use of the immobilised protein is available.

Haselhorst, Thomas [Institute for Glycomics, Griffith University (Gold Coast Campus), PMB 50 Gold Coast Mail Centre, Qld 9726 (Australia); Muenster-Kuehnel, Anja K. [Abteilung Zellulaere Chemie, Medizinische Hochschule Hannover (MHH), Carl-Neuberg-Strasse 1, D-30625 Hannover (Germany); Oschlies, Melanie [Institute for Glycomics, Griffith University (Gold Coast Campus), PMB 50 Gold Coast Mail Centre, Qld 9726 (Australia); Abteilung Zellulaere Chemie, Medizinische Hochschule Hannover (MHH), Carl-Neuberg-Strasse 1, D-30625 Hannover (Germany); Tiralongo, Joe [Institute for Glycomics, Griffith University (Gold Coast Campus), PMB 50 Gold Coast Mail Centre, Qld 9726 (Australia); Gerardy-Schahn, Rita [Abteilung Zellulaere Chemie, Medizinische Hochschule Hannover (MHH), Carl-Neuberg-Strasse 1, D-30625 Hannover (Germany); Itzstein, Mark von [Institute for Glycomics, Griffith University (Gold Coast Campus), PMB 50 Gold Coast Mail Centre, Qld 9726 (Australia)]. E-mail: m.vonitzstein@griffith.edu.au

2007-08-10

372

Complex mixture analysis of organic compounds in green coffee bean extract by two-dimensional NMR spectroscopy.  

PubMed

A complex mixture analysis by one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy was carried out for the first time for the identification and quantification of organic compounds in green coffee bean extract (GCBE). A combination of (1)H-(1)H DQF-COSY, (1)H-(13)C HSQC, and (1)H-(13)C CT-HMBC two-dimensional sequences was used, and 16 compounds were identified. In particular, three isomers of caffeoylquinic acid were identified in the complex mixture without any separation. In addition, GCBE components were quantified by the integration of carbon signals by use of a relaxation reagent and an inverse-gated decoupling method without a nuclear Overhauser effect. This NMR methodology provides detailed information about the kinds and amounts of GCBE components, and in our study, the chemical makeup of GCBE was clarified by the NMR results. PMID:20818806

Wei, Feifei; Furihata, Kazuo; Hu, Fangyu; Miyakawa, Takuya; Tanokura, Masaru

2010-11-01

373

The Basics of NMR  

NSDL National Science Digital Library

This resource is an online textbook containing information about Nuclear Magnetic Resonance (NMR). Information inlcudes mathhematics of NMR, spin physics, Spectroscopy, pulse sequences, and NMR hardware. The "Practical Considerations" chapter emphasizes spectroscopic techniques.

Hornak, Joseph

2003-10-10

374

Indirectly detected chemical shift correlation NMR spectroscopy in solids under fast magic angle spinning  

SciTech Connect

The development of fast magic angle spinning (MAS) opened up an opportunity for the indirect detection of insensitive low-{gamma} nuclei (e.g., {sup 13}C and {sup 15}N) via the sensitive high-{gamma} nuclei (e.g., {sup 1}H and {sup 19}F) in solid-state NMR, with advanced sensitivity and resolution. In this thesis, new methodology utilizing fast MAS is presented, including through-bond indirectly detected heteronuclear correlation (HETCOR) spectroscopy, which is assisted by multiple RF pulse sequences for {sup 1}H-{sup 1}H homonuclear decoupling. Also presented is a simple new strategy for optimization of {sup 1}H-{sup 1}H homonuclear decoupling. As applications, various classes of materials, such as catalytic nanoscale materials, biomolecules, and organic complexes, are studied by combining indirect detection and other one-dimensional (1D) and two-dimensional (2D) NMR techniques. Indirectly detected through-bond HETCOR spectroscopy utilizing refocused INEPT (INEPTR) mixing was developed under fast MAS (Chapter 2). The time performance of this approach in {sup 1}H detected 2D {sup 1}H{l_brace}{sup 13}C{r_brace} spectra was significantly improved, by a factor of almost 10, compared to the traditional {sup 13}C detected experiments, as demonstrated by measuring naturally abundant organic-inorganic mesoporous hybrid materials. The through-bond scheme was demonstrated as a new analytical tool, which provides complementary structural information in solid-state systems in addition to through-space correlation. To further benefit the sensitivity of the INEPT transfer in rigid solids, the combined rotation and multiple-pulse spectroscopy (CRAMPS) was implemented for homonuclear {sup 1}H decoupling under fast MAS (Chapter 3). Several decoupling schemes (PMLG5{sub m}{sup {bar x}}, PMLG5{sub mm}{sup {bar x}x} and SAM3) were analyzed to maximize the performance of through-bond transfer based on decoupling efficiency as well as scaling factors. Indirect detection with assistance of PMLG{sub m}{sup {bar x}} during INEPTR transfer proved to offer the highest sensitivity gains of 3-10. In addition, the CRAMPS sequence was applied under fast MAS to increase the {sup 1}H resolution during t{sub 1} evolution in the traditional, {sup 13}C detected HETCOR scheme. Two naturally abundant solids, tripeptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (f-MLF-OH) and brown coal, with well ordered and highly disordered structures, respectively, are studied to confirm the capabilities of these techniques. Concomitantly, a simple optimization of {sup 1}H homonuclear dipolar decoupling at MAS rates exceeding 10 kHz was developed (Chapter 4). The fine-tuned decoupling efficiency can be obtained by minimizing the signal loss due to transverse relaxation in a simple spin-echo experiment, using directly the sample of interest. The excellent agreement between observed decoupling pattern and earlier theoretical predictions confirmed the utility of this strategy. The properties of naturally abundant surface-bound fluorocarbon groups in mesoporous silica nanoparticles (MSNs) were investigated by the above-mentioned multidimensional solid-state NMR experiments and theoretical modeling (Chapter 5). Two conformations of (pentafluorophenyl)propyl groups (abbreviated as PFP) were determined as PFP-prone and PFP-upright, whose aromatic rings are located above the siloxane bridges and in roughly upright position, respectively. Several 1D and 2D NMR techniques were implemented in the characterizations, including indirectly detected {sup 1}H{l_brace}{sup 13}C{r_brace} and {sup 19}F{l_brace}{sup 13}C{r_brace} 2D HETCOR, Carr-Purcell-Meiboom-Gill (CPMG) assisted {sup 29}Si direct polarization and {sup 29}Si{sup 19}F 2D experiments, 2D double-quantum (DQ) {sup 19}F MAS NMR spectra and spin-echo measurements. Furthermore, conformational details of two types of PFP were confirmed by theoretical calculation, operated by Dr. Takeshi Kobayashi. Finally, the arrangement of two surfactants, cetyltrimetylammoium bromide (CTAB) and cetylpyridinium bromide (CPB), mixed inside th

Mao, Kanmi

2011-08-15

375

Investigation of Local Structures in Layered Niobates by Solid-state NMR Spectroscopy  

NASA Astrophysics Data System (ADS)

Research on ion-exchangeable layered niobates has attracted great attention due to their unique structures and corresponding variations in properties and applications, such as ion conductors, solid acids, and water splitting catalysts. Families of layered niobates include double-layered or triple-layered Dion-Jacobson type perovskites (ALaNb2O7, A = Cs, Rb, K, H; AM2Nb3O10, A = Rb, K, H; M = Sr, Ca), layered niobates with both edge and corner sharing of NbO6 octahedra (KNb3O8, HNb3O6, Nb 6O17 and H4Nb6O17) and many others. Lately, more developments in the layered niobates through a variety of topochemical manipulations have been achieved. The topochemical reactions include ion exchange, exfoliation, substitution, and etc. As a result, many new materials have been successfully prepared, for example, solid solutions (ALa2NbTi2O10, ACaLaNb2TiO 10 and ACa2Nb3-xTaxO10, etc.), nanosheets (HNb3O8, H4Nb6O17, HLaNb2O7, HCa2Nb3O10, etc., to intercalate with organic molecules such as tetrabutylammonium hydroxide or n-butylamines), and nanoscrolls (from H2K2Nb 6O17). While these structural modifications often induce improvements in properties, the fundamental mechanisms of improvements in properties upon the modifications, especially local structural arrangements are poorly understood, which is often limited by structural characterizations. Particularly, the characterizations of the exfoliated nanosheets can be difficult by conventional X-ray diffraction (XRD) method due to disordered structures. Alternatively, solid-state nuclear magnetic resonance (NMR) spectroscopy is a useful tool to study local structures in solids. The structural information can be extracted by examining intrinsic interactions, such as quadrupolar, chemical shielding, and dipolar interactions, which are all associated with local environments surrounding a specific nucleus, 1H or 93Nb in layered niobates. The ultimate goal of this dissertation is to understand the relationships between local structures of layered niobates and their chemical or physical properties, and provide insights into further modifications and improvements. The primary objectives of this work are summarized below: I. Synthesis of series of layered niobates (ALaNb2O7 , A = Cs, Rb, K; KNb3O8; K4Nb 6O17; RbLa2NbTi2O10 and RbCaLaNb2TiO10) by microwave heating or cation exchange methods, their protonated forms by acid exchange (HLaNb2O 7, H3ONb3O8 and HNb3O 8, H4Nb8O17, HLa2NbTi 2O10 and HCaLaNb2TiO10), and three nanosheet niobates by exfoliation (HNb3O8, H4Nb 6O17 and HLaNb2O7 nanosheets). II. Structural characterizations of all niobates by powder XRD and solid-state NMR spectroscopy. Powder XRD is used to determine lattice constants and long-range structural ordering. Solid-state NMR is used to determine the electric field gradient parameters, chemical shift anisotropy parameters and dipolar coupling constants. Solid-state NMR techniques include 93Nb MQMAS, wide-line VOCS echo and WURST-echo; 1H{93Nb} CP, TRAPDOR, S-RESPDOR and iS-RESPDOR experiments. III. Understanding the trends of changes in NMR parameters with respect to cation exchange, exfoliation and compositional alteration, and correlation of the NMR parameters with local environments and possible structural rearrangements. IV. Identification of proton locations in the acid-exchanged niobates and surface acidity for the exfoliated nanosheets, based on 1H chemical shifts and dipolar coupling information from CP, S-RESPDOR and iS-RESPDOR experiments.

Liu, Ting

376

Conformational Analysis of (+)-Germacrene A by Variable Temperature NMR and NOE Spectroscopy  

PubMed Central

(+)-Germacrene A, an important intermediate in sesquiterpene biosynthesis, was isolated in pure form from a genetically engineered yeast and was characterized by chromatographic properties (TLC, GC), MS, optical rotation, UV, IR, 1H NMR and 13C NMR data. Variable-temperature 500 MHz 1H NMR spectra in CDCl3 showed that this flexible cyclodecadiene ring exists as three NMR-distinguishable conformational isomers in a ratio of about 5:3:2 at or below ordinary probe temperature (25° C). The conformer structures were assigned by 1H NMR data comparisons, NOE experiments, and vicinal couplings as follows: 1a (52%, UU), 1b (29% UD), and 1c (19%, DU).

Faraldos, Juan A.; Wu, Shuiqin; Chappell, Joe

2009-01-01

377

(19) F?NMR Spectroscopy as a Probe of Cytoplasmic Viscosity and Weak Protein Interactions in Living Cells.  

PubMed

Protein mobility in living cells is vital for cell function. Both cytosolic viscosity and weak protein-protein interactions affect mobility, but examining viscosity and weak interaction effects is challenging. Herein, we demonstrate the use of (19) F?NMR spectroscopy to measure cytoplasmic viscosity and to characterize nonspecific protein-protein interactions in living Escherichia?coli cells. The origins of resonance broadening in Escherichia?coli cells were also investigated. We found that sample inhomogeneity has a negligible effect on resonance broadening, the cytoplasmic viscosity is only about 2-3 times that of water, and ubiquitous transient weak protein-protein interactions in the cytosol play a significant role in governing the detection of proteins by using in-cell NMR spectroscopy. PMID:23922149

Ye, Yansheng; Liu, Xiaoli; Zhang, Zeting; Wu, Qiong; Jiang, Bin; Jiang, Ling; Zhang, Xu; Liu, Maili; Pielak, Gary J; Li, Conggang

2013-08-06

378

The degradation of zinc dialkyldithiophosphate additives in fully formulated engine oil as studied by P-31 NMR spectroscopy  

SciTech Connect

Two fully-formulated engine oils containing zinc dialkyldithiophosphate (ZDDP) were tested at different oil temperature regimes during long distance, high speed field tests (15000 km and 145 {plus_minus} 10 km/hr). P-31 NMR spectroscopy was used to characterize the ZDDPs and the degradation products formed during the field tests. It was found that basic ZDDP degradation products were thiophosphates and phosphates, and the thiophosphates could be further oxidized to form phosphates when the oil temperature was high. The dependence of the ZDDP degradation pathway with oil temperature is discussed. The amount of ZDDP in the used oil was related to the viscosity increase of that oil, which increased dramatically when the ZDDP was exhausted. In the fresh oil, ZDDP formed some sort of complex, but the complexed ZDDP was released during the field test as observed by P-31 NMR spectroscopy. 20 refs., 11 figs., 4 tabs.

Pu Peng; Shan-Zhen Hong; Wan-Zhen Lu [SINOPEC, Beijing (China)

1994-03-01

379

Proton-proton Overhauser NMR spectroscopy with polypeptide chains in large structures  

PubMed Central

The use of 1H–1H nuclear Overhauser effects (NOE) for structural studies of uniformly deuterated polypeptide chains in large structures is investigated by model calculations and NMR experiments. Detailed analysis of the evolution of the magnetization during 1H–1H NOE experiments under slow-motion conditions shows that the maximal 1H–1H NOE transfer is independent of the overall rotational correlation time, even in the presence of chemical exchange with the bulk water, provided that the mixing time is adjusted for the size of the structure studied. 1H–1H NOE buildup measurements were performed for the 472-kDa complex of the 72-kDa cochaperonin GroES with a 400-kDa single-ring variant of the chaperonin GroEL (SR1). These experiments demonstrate that multidimensional NOESY experiments with cross-correlated relaxation-enhanced polarization transfer and transverse relaxation-optimized spectroscopy elements can be applied to structures of molecular masses up to several hundred kilodaltabs, which opens new possibilities for studying functional interactions in large maromolecular assemblies in solution.

Horst, Reto; Wider, Gerhard; Fiaux, Jocelyne; Bertelsen, Eric B.; Horwich, Arthur L.; Wuthrich, Kurt

2006-01-01

380

Structure and dynamics of the deoxyguanosine-sensing riboswitch studied by NMR-spectroscopy  

PubMed Central

The mfl-riboswitch regulates expression of ribonucleotide reductase subunit in Mesoplasma florum by binding to 2?-deoxyguanosine and thereby promoting transcription termination. We characterized the structure of the ligand-bound aptamer domain by NMR spectroscopy and compared the mfl-aptamer to the aptamer domain of the closely related purine-sensing riboswitches. We show that the mfl-aptamer accommodates the extra 2?-deoxyribose unit of the ligand by forming a more relaxed binding pocket than these found in the purine-sensing riboswitches. Tertiary structures of the xpt-aptamer bound to guanine and of the mfl-aptamer bound to 2?-deoxyguanosine exhibit very similar features, although the sequence of the mfl-aptamer contains several alterations compared to the purine-aptamer consensus sequence. These alterations include the truncation of a hairpin loop which is crucial for complex formation in all purine-sensing riboswitches characterized to date. We further defined structural features and ligand binding requirements of the free mfl-aptamer and found that the presence of Mg2+ is not essential for complex formation, but facilitates ligand binding by promoting pre-organization of key structural motifs in the free aptamer.

Wacker, Anna; Buck, Janina; Mathieu, Daniel; Richter, Christian; Wohnert, Jens; Schwalbe, Harald

2011-01-01

381

Hetergeneous tumour response to photodynamic therapy assessed by in vivo localised 31P NMR spectroscopy.  

PubMed Central

Photodynamic therapy (PDT) is efficacious in the treatment of small malignant lesions when all cells in the tumour receive sufficient drug, oxygen and light to induce a photodynamic effect capable of complete cytotoxicity. In large tumours, only partial effectiveness is observed presumably because of insufficient light penetration into the tissue. The heterogeneity of the metabolic response in mammary tumours following PDT has been followed in vivo using localised phosphorus NMR spectroscopy. Alterations in nucleoside triphosphates (NTP), inorganic phosphate (Pi) and pH within localised regions of the tumour were monitored over 24-48 h following PDT irradiation of the tumour. Reduction of NTP and increases in Pi were observed at 4-6 h after PDT irradiation in all regions of treated tumours. The uppermost regions of the tumours (those nearest the skin surface and exposed to the greatest light fluence) displayed the greatest and most prolonged reduction of NTP and concomitant increase in Pi resulting in necrosis. The metabolite concentrations in tumour regions located towards the base of the tumour returned a near pre-treatment levels by 24-48 h after irradiation. The ability to follow heterogeneous metabolic responses in situ provides one means to assess the degree of metabolic inhibition which subsequently leads to tumour necrosis. Images Figure 4

Ceckler, T. L.; Gibson, S. L.; Kennedy, S. D.; Hill, R.; Bryant, R. G.

1991-01-01

382

Revealing the metabonomic variation of rosemary extracts using 1H NMR spectroscopy and multivariate data analysis.  

PubMed

The molecular compositions of rosemary ( Rosmarinus officinalis L.) extracts and their dependence on extraction solvents, seasons, and drying processes were systematically characterized using NMR spectroscopy and multivariate data analysis. The results showed that the rosemary metabonome was dominated by 33 metabolites including sugars, amino acids, organic acids, polyphenolic acids, and diterpenes, among which quinate, cis-4-glucosyloxycinnamic acid, and 3,4,5-trimethoxyphenylmethanol were found in rosemary for the first time. Compared with water extracts, the 50% aqueous methanol extracts contained higher levels of sucrose, succinate, fumarate, malonate, shikimate, and phenolic acids, but lower levels of fructose, glucose, citrate, and quinate. Chloroform/methanol was an excellent solvent for selective extraction of diterpenes. From February to August, the levels of rosmarinate and quinate increased, whereas the sucrose level decreased. The sun-dried samples contained higher concentrations of rosmarinate, sucrose, and some amino acids but lower concentrations of glucose, fructose, malate, succinate, lactate, and quinate than freeze-dried ones. These findings will fill the gap in the understanding of rosemary composition and its variations. PMID:18800806

Xiao, Chaoni; Dai, Hui; Liu, Hongbing; Wang, Yulan; Tang, Huiru

2008-09-19

383

Synthesis of prototypical fullerene cyclopropanes and annulenes. Isomer differentiation via NMR and UV spectroscopy  

SciTech Connect

Parent cyclopropanes, annulenes, and related derivatives of C{sub 60} and C{sub 70} have been prepared and subjected to extensive spectroscopic scrutiny. Photolysis of the diazomethane adduct of C{sub 60} afforded the C{sub 61}H{sub 2} cyclopropane 2, accompanied by the isomeric annulene 4. Reaction of dimethyldiazomethane with C{sub 60} led to C{sub 63}H{sub 6} annulene 11, which upon heating was smoothly converted to the cyclopropane isomer 10 with an activation energy of 25 {+-} 1 kcal-mol{sup -1}. Addition of diazomethane to a toluene solution of C{sub 70} generated a 12:1:2 mixture of pyrazolines. Photolysis of the mixture gave the C{sub 11}H{sub 2} cyclopropanes 6 and 7, whereas thermolysis furnished the isomeric annulenes 8 and 9. Criteria have been developed for distinguishing fullerene cyclopropane derivatives from the corresponding annulenes via NMR and UV spectroscopy. 57 refs., 12 figs., 1 tab.

Smith, A.B. III; Strongin, R.M.; Brard, L.; Furst, G.T.; Romanow, W.J. [Univ. of Pennsylvania, Philadelphia, PA (United States); Owens, K.G.; Goldschmidt, R.J.; King, R.C. [Drexel Univ., Philadelphia, PA (United States)

1995-05-24

384

Tetramethyltin study by NMR spectroscopy in the gas and liquid phase  

NASA Astrophysics Data System (ADS)

Tetramethyltin was studied by high-resolution NMR spectroscopy in liquid and gaseous states at 300 K. A small amount of this compound was introduced to the buffer gases: CO2 and N2O. Extrapolation of the gas-phase chemical shifts to the zero-density limit permitted the determination of 1H, 13C and 117/119Sn absolute nuclear magnetic shieldings in an isolated tetramethytin molecule. These new experimental results are useful for a reliable verification of the quantum chemical calculations of proton, carbon and tin nuclear magnetic shieldings in the molecule under study. The indirect spin-spin coupling constants were extracted from experimental spectra and compared with the values previously reported in the relevant literature. Intermolecular effects in the gaseous state, as well as in passing from gas to liquid are also found to be of essential significance here. The gas-to-liquid shifts measured are negative (deshielding) for proton and carbon but positive (shielding) for the tin nuclei.

Makulski, W?odzimierz

2012-06-01

385

1H Photo-CIDNP Enhancements in Heteronuclear Correlation NMR Spectroscopy  

PubMed Central

Photochemically induced dynamic nuclear polarization (photo-CIDNP) is usually employed as a probe of solvent exposure, in biomolecular NMR. The potential of the photo-CIDNP effect for sensitivity enhancement, however, remains poorly explored. Here, we introduce 1H-photo-CIDNP in heteronuclear correlation spectroscopy at low laser irradiation power (1 W), and compare the sensitivity of various 1H-Photo-CIDNP-enhanced- (HPE) 1H?15N heteronuclear correlation pulse sequences, including HSQC, HMQC, and SOFAST-HMQC, in terms of their ability to detect the Trp indole H?1 resonance. Both Trp and the Trp-containing protein apoHmpH were analyzed using flavin mononucleotide as photosensitizer in aqueous solutions either containing or lacking urea. We find that 1H?15N photo-CIDNP-SOFAST-HMQC, denoted here as HPE-SOFAST-HMQC, yields a two-fold higher signal-to-noise per unit time than the parent SOFAST-HMQC for the solvent-exposed Trp of urea-unfolded apoHmpH. Thus, HPE-SOFAST-HMQC is the most sensitive heteronuclear correlation pulse sequence for the detection of solvent-exposed Trp.

Sekhar, Ashok; Cavagnero, Silvia

2009-01-01

386

Quantitative analysis of protein backbone dynamics in microcrystalline ubiquitin by solid-state NMR spectroscopy.  

PubMed

Characterization of protein dynamics by solid-state NMR spectroscopy requires robust and accurate measurement protocols, which are not yet fully developed. In this study, we investigate the backbone dynamics of microcrystalline ubiquitin using different approaches. A rotational-echo double-resonance type (REDOR-type) methodology allows one to accurately measure (1)H-(15)N order parameters in highly deuterated samples. We show that the systematic errors in the REDOR experiment are as low as 1% or even less, giving access to accurate data for the amplitudes of backbone mobility. Combining such dipolar-coupling-derived order parameters with autocorrelated and cross-correlated (15)N relaxation rates, we are able to quantitate amplitudes and correlation times of backbone dynamics on picosecond and nanosecond time scales in a residue-resolved manner. While the mobility on picosecond time scales appears to have rather uniform amplitude throughout the protein, we unambiguously identify and quantitate nanosecond mobility with order parameters S(2) as low as 0.8 in some regions of the protein, where nanosecond dynamics has also been revealed in solution state. The methodology used here, a combination of accurate dipolar-coupling measurements and different relaxation parameters, yields details about dynamics on different time scales and can be applied to solid protein samples such as amyloid fibrils or membrane proteins. PMID:20977205

Schanda, Paul; Meier, Beat H; Ernst, Matthias

2010-10-26

387

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

PubMed Central

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

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

1992-01-01

388

Toroid cavity detectors for high-resolution NMR spectroscopy and rotating frame imaging: capabilities and limitations.  

PubMed

The capabilities of toroid cavity detectors for simultaneous rotating frame imaging and NMR spectroscopy have been investigated by means of experiments and computer simulations. The following problems are described: (a) magnetic field inhomogeneity and subsequent loss of chemical shift resolution resulting from bulk magnetic susceptibility effects, (b) image distortions resulting from off-resonance excitation and saturation effects, and (c) distortion of lineshapes and images resulting from radiation damping. Also, special features of signal analysis including truncation effects and the propagation of noise are discussed. B(0) inhomogeneity resulting from susceptibility mismatch is a serious problem for applications requiring high spectral resolution. Image distortions resulting from off-resonance excitation are not serious within the rather narrow spectral range permitted by the RF pulse lengths required to read out the image. Incomplete relaxation effects are easily recognized and can be avoided. Also, radiation damping produces unexpectedly small effects because of self-cancellation of magnetization and short free induction decay times. The results are encouraging, but with present designs only modest spectral resolution can be achieved. PMID:10648153

Momot, K I; Binesh, N; Kohlmann, O; Johnson, C S

2000-02-01

389

Structure and dynamics of the deoxyguanosine-sensing riboswitch studied by NMR-spectroscopy.  

PubMed

The mfl-riboswitch regulates expression of ribonucleotide reductase subunit in Mesoplasma florum by binding to 2'-deoxyguanosine and thereby promoting transcription termination. We characterized the structure of the ligand-bound aptamer domain by NMR spectroscopy and compared the mfl-aptamer to the aptamer domain of the closely related purine-sensing riboswitches. We show that the mfl-aptamer accommodates the extra 2'-deoxyribose unit of the ligand by forming a more relaxed binding pocket than these found in the purine-sensing riboswitches. Tertiary structures of the xpt-aptamer bound to guanine and of the mfl-aptamer bound to 2'-deoxyguanosine exhibit very similar features, although the sequence of the mfl-aptamer contains several alterations compared to the purine-aptamer consensus sequence. These alterations include the truncation of a hairpin loop which is crucial for complex formation in all purine-sensing riboswitches characterized to date. We further defined structural features and ligand binding requirements of the free mfl-aptamer and found that the presence of Mg(2+) is not essential for complex formation, but facilitates ligand binding by promoting pre-organization of key structural motifs in the free aptamer. PMID:21576236

Wacker, Anna; Buck, Janina; Mathieu, Daniel; Richter, Christian; Wöhnert, Jens; Schwalbe, Harald

2011-05-16

390

NMR Spectroscopy of Macrophages Loaded with Native, Oxidized or Enzymatically Degraded Lipoproteins  

PubMed Central

Oxidized and enzymatically modified low-density lipoproteins (oxLDL and eLDL) play a key role in early stages of atherogenesis. Their uptake by recruited macrophages leads to endolysosomal phospholipidosis or foam cell formation, respectively, each of which is preceded by highly differential lipid restructuring processes. We applied 1H-NMR spectroscopy (NMRS) to elucidate these structural rearrangements both in consequence of lipoprotein modifications and following phagocytosis. Being specifically sensitive to the mobile lipid subset, NMRS of oxLDL and eLDL revealed a partial and total immobilization of lipids, respectively. NMRS of intact macrophages showed a sixfold increase in mobile lipids in case of loading with eLDL but no significant changes for oxLDL or native LDL. This finding reflected the disparate lipid storage in lipid droplets and in multilamellar endolysosomal clusters when loaded with either eLDL or oxLDL, respectively. Moreover, a significant shift of the degree of saturation towards mainly polyunsaturated fatty acid chains was found for the mobile lipid pool in eLDL-loaded macrophages. Additional analyses of lipid extracts by NMRS and mass spectrometry (MS) reflected these changes in lipid content and in fatty acid composition only partially. In summary, in-cell NMRS represents a unique lipidomics tool to investigate structural changes within the mobile lipid pool following atherogenic triggers that can be not detected by the analysis of lipid extracts by MS or NMRS.

Ramm Sander, Paul; Peer, Markus; Grandl, Margot; Bogdahn, Ulrich; Schmitz, Gerd; Kalbitzer, Hans Robert

2013-01-01

391

NMR spectroscopy of macrophages loaded with native, oxidized or enzymatically degraded lipoproteins.  

PubMed

Oxidized and enzymatically modified low-density lipoproteins (oxLDL and eLDL) play a key role in early stages of atherogenesis. Their uptake by recruited macrophages leads to endolysosomal phospholipidosis or foam cell formation, respectively, each of which is preceded by highly differential lipid restructuring processes. We applied (1)H-NMR spectroscopy (NMRS) to elucidate these structural rearrangements both in consequence of lipoprotein modifications and following phagocytosis. Being specifically sensitive to the mobile lipid subset, NMRS of oxLDL and eLDL revealed a partial and total immobilization of lipids, respectively. NMRS of intact macrophages showed a sixfold increase in mobile lipids in case of loading with eLDL but no significant changes for oxLDL or native LDL. This finding reflected the disparate lipid storage in lipid droplets and in multilamellar endolysosomal clusters when loaded with either eLDL or oxLDL, respectively. Moreover, a significant shift of the degree of saturation towards mainly polyunsaturated fatty acid chains was found for the mobile lipid pool in eLDL-loaded macrophages. Additional analyses of lipid extracts by NMRS and mass spectrometry (MS) reflected these changes in lipid content and in fatty acid composition only partially. In summary, in-cell NMRS represents a unique lipidomics tool to investigate structural changes within the mobile lipid pool following atherogenic triggers that can be not detected by the analysis of lipid extracts by MS or NMRS. PMID:23457556

Ramm Sander, Paul; Peer, Markus; Grandl, Margot; Bogdahn, Ulrich; Schmitz, Gerd; Kalbitzer, Hans Robert

2013-02-15

392

Enhanced solid-state NMR correlation spectroscopy of quadrupolar nuclei using dynamic nuclear polarization.  

PubMed

By means of a true sensitivity enhancement for a solid-state NMR spectroscopy (SSNMR) experiment performed under dynamic nuclear polarization (DNP) conditions, corresponding to 4-5 orders of magnitude of time savings compared with a conventional SSNMR experiment, it is shown that it is possible to record interface-selective (27)Al-(27)Al two-dimensional dipolar correlation spectra on mesoporous alumina, an advanced material with potential industrial applications. The low efficiency of cross-polarization and dipolar recoupling for quadrupolar nuclei is completely negated using this technique. The important presence of pentacoordinated Al has not only been observed, but its role in bridging interfacial tetra- and hexacoordinated Al has been determined. Such structural information, collected at low temperature (?103 K) and 9.4 T with the use of DNP, would have been impossible to obtain under standard conditions, even using a higher magnetic field. However, here it is demonstrated that this information can be obtained in only 4 h. This work clearly opens a new avenue for the application of SSNMR to quadrupolar nuclei and notably the atomic-scale structure determination of catalysis materials such as mesoporous alumina. PMID:23095121

Lee, Daniel; Takahashi, Hiroki; Thankamony, Aany S L; Dacquin, Jean-Philippe; Bardet, Michel; Lafon, Olivier; Paëpe, Gaël De

2012-11-02

393

Evaluation of characteristic deuterium distributions of ephedrines and methamphetamines by NMR spectroscopy for drug profiling.  

PubMed

We have established a method for quantitative analysis of the deuterium contents (D/H) at the phenyl, methine, benzyl, N-methyl and methyl groups of l-ephedrine/HCl, d-pseudoephedrine/HCl and methamphetamine/HCl by 2H NMR spectroscopy. Comparison of the 5 position-specific D/H values of l-ephedrine/HCl and d-pseudoephedrine/HCl prepared by three methods (chemical synthesis, semichemical synthesis, and biosynthesis) showed that chemically synthesized ephedrines and semisynthetic ephedrines have highly specific distributions of deuterium at the methine position and at the benzyl position, compared with the other positions. The classification of several methamphetamine samples seized in Japan in terms of the D/H values at these two positions clearly showed that the methamphetamine samples had been synthesized from ephedrines extracted from Ephedra plants or semisynthetic ephedrines but not from synthetic ephedrine. This isotope ratio analysis method should be useful to trace the origins of seized methamphetamine in Southeast Asia. PMID:18271510

Matsumoto, Teruki; Urano, Yasuteru; Makino, Yukiko; Kikura-Hanajiri, Ruri; Kawahara, Nobuo; Goda, Yukihiro; Nagano, Tetsuo

2008-02-15

394

Analysis of the hydrolysis of inulin using real time 1H NMR spectroscopy  

PubMed Central

The hydrolysis of various carbohydrates was investigated under acidic conditions in real time by 1H NMR spectroscopy, with a focus on the polysaccharide inulin. Sucrose was used as a model compound to illustrate the applicability of this technique. The hydrolysis of sucrose was shown to follow pseudo first order kinetics and have an activation energy of 107.0 kJ.mol?1 (s.d. 1.7 kJ.mol?1). Inulin, pullulan and glycogen also all followed pseudo first order kinetics, but had an initiation phase at least partially generated by the protonation of the glycosidic bonds. It was also demonstrated that polysaccharide chain length has an effect on the hydrolysis of inulin. For short chain inulin (DPn 18, s.d. 0.70) the activation energy calculated for the hydrolytic cleavage of glucose was similar to sucrose at 108.5 kJ.mol?1 (std. dev. 0.60). For long chain inulin (DPn 30, s.d. 1.3) the activation energy for the hydrolytic cleavage of glucose was reduced to 80.5 kJ.mol?1 (s.d. 2.3 kJ.mol?1). This anomaly has been attributed to varied conformations for the two different lengths of inulin chain in solution.

Barclay, Thomas; Ginic-Markovic, Milena; Johnston, Martin R.; Cooper, Peter D.; Petrovsky, Nikolai

2012-01-01

395

Metabolic profiling for studying chemotype variations in Withania somnifera (L.) Dunal fruits using GC-MS and NMR spectroscopy.  

PubMed

Withania somnifera (L.) Dunal (Solanaceae), commonly known as Ashwagandha, is one of the most valued Indian medicinal plant with several pharmaceutical and nutraceutical applications. Metabolic profiling was performed by GC-MS and NMR spectroscopy on the fruits obtained from four chemotypes of W. somnifera. A combination of (1)H NMR spectroscopy and GC-MS identified 82 chemically diverse metabolites consisting of organic acids, fatty acids, aliphatic and aromatic amino acids, polyols, sugars, sterols, tocopherols, phenolic acids and withanamides in the fruits of W. somnifera. The range of metabolites identified by GC-MS and NMR of W. somnifera fruits showed various known and unknown metabolites. The primary and secondary metabolites observed in this study represent MVA, DOXP, shikimic acid and phenylpropanoid biosynthetic metabolic pathways. Squalene and tocopherol have been rated as the most potent naturally occurring compounds with antioxidant properties. These compounds have been identified by us for the first time in the fruits of W. somnifera. Multivariate principal component analysis (PCA) on GC-MS and NMR data revealed clear distinctions in the primary and secondary metabolites among the chemotypes. The variation in the metabolite concentration among different chemotypes of the fruits of W. somnifera suggest that specific chemovars can be used to obtain substantial amounts of bioactive ingredients for use as potential pharmacological and nutraceuticals agents. PMID:23578960

Bhatia, Anil; Bharti, Santosh K; Tewari, Shri K; Sidhu, Om P; Roy, Raja

2013-04-09

396

Chromophore/DNA interactions: femto- to nanosecond spectroscopy, NMR structure, and electron transfer theory.  

PubMed

The mechanism of photoinduced hole injection into DNA has been studied using an integrated approach that combines NMR structural analysis, time-resolved spectroscopy, and quantum-chemical calculations. A covalently linked acridinium derivative, the protonated 9-amino-6-chloro-2-methoxyacridine (X+), is replacing a thymine and separated from either guanine (G) or the easier to oxidize 7-deazaguanine (Z) by one adenine.thymine (A.T) base pair. The key features of this donor/acceptor system are the following: (i) In more than 95% of the duplexes, X+ is located in a central, coplanar position between the neighboring A.T base pairs with its long axis in parallel showing minimal twist and tilt angles (<15 degrees). The complementary adenine base is turned out into the extrahelical space. In a minority of less than 5%, X+ is found to be still attached to the duplex. X+ is most probably associated with one of the phosphates, since it is neither intercalated between more remote base pairs nor bound to sugars or grooves. This minority characterized by an excited state lifetime >10 ns gives rise to a small background signal in time-resolved measurements and contributes predominantly to steady-state fluorescence spectra. (ii) Although the intercalation mode of X+ is well defined, the NMR structure reveals that there are two conformations of X+ with respect to the arrangement of its methoxy substituent. In one conformation, the methoxy group is in the plane of the chromophore, while, in the other extraplanar conformation, the methoxy group forms an angle of 70 degrees with the acridinium ring. The fluorescence decay of 5'-ZAX and 5'-GAX tracts can be fitted to a biexponential function with similar amplitudes, reflecting the oxidation dynamics of G and Z, with the slower rate being determined by larger thermal activation energy. The attribution of biexponential electron transfer (ET) dynamics to the bimodal orientation of the methoxy group at the acridinium is supported by quantum-chemical calculations. These predict a larger free energy change for hole transfer in the nonplanar conformation as compared to the planar one, whereas the difference in the electronic couplings is negligible. (iii) Kinetic studies of the directionality of the 1(X+)* induced hole injection reveal similarly fast decay components in both directions of the duplex, that is, in 5'-ZAX and 5'-XAZ, with the amplitude of the fast component being significantly reduced in 5'-XAZ. The NMR structure shows that local structural deviations from B-DNA are much more pronounced in the 3'-5' direction than in the 5'-3' direction. According to quantum-chemical calculations, the directionality of charge injection is not a universal feature of the DNA duplex but depends critically on the rotation angle of the aromatic plane of the acridinium within the pi stack. The arrangement of X+ in 5'-ZAX and 5'-XAZ corresponds to a conformation with weak directionality of the electronic couplings. The increased disorder in the 3'-5'direction favors slow hole transfer components at the expense of the fast ones. (iv) A comparison of the hole transfer in 5'-GAX and 5'-ZAG shows that classical Marcus theory can explain the ratio of the charge shift rates of more than 2 orders of magnitude on the basis of a free energy difference between G and Z of 0.3 eV. Both NMR structures and quantum-chemical calculations justify the appreciable neglect of differences of electronic couplings as well as in the reorganization energy in 5'-GAX and 5'-ZAG. Despite the attractive concept for the behavior of floppy DNA oligonucleotides, in this acridinium/DNA system, there is no evidence for conformational gating, that is, for fluctuations in the electronic couplings that permit the ET to occur. PMID:18163608

von Feilitzsch, Till; Tuma, Jennifer; Neubauer, Heike; Verdier, Laurent; Haselsberger, Reinhard; Feick, Reiner; Gurzadyan, Gagik; Voityuk, Alexander A; Griesinger, Christian; Michel-Beyerle, Maria E

2007-12-29

397

Proton-detected scalar coupling based assignment strategies in MAS solid-state NMR spectroscopy applied to perdeuterated proteins  

NASA Astrophysics Data System (ADS)

Assignment of proteins in MAS (magic angle spinning) solid-state NMR relies so far on correlations among heteronuclei. This strategy is based on well dispersed resonances in the 15N dimension. In many complex cases like membrane proteins or amyloid fibrils, an additional frequency dimension is desirable in order to spread the amide resonances. We show here that proton detected HNCO, HNCA, and HNCACB type experiments can successfully be implemented in the solid-state. Coherences are sufficiently long lived to allow pulse schemes of a duration greater than 70 ms before incrementation of the first indirect dimension. The achieved resolution is comparable to the resolution obtained in solution-state NMR experiments. We demonstrate the experiments using a triply labeled sample of the SH3 domain of chicken ?-spectrin, which was re-crystallized in H2O/D2O using a ratio of 1/9. We employ paramagnetic relaxation enhancement (PRE) using EDTA chelated CuII to enable rapid data acquisition.

Linser, Rasmus; Fink, Uwe; Reif, Bernd

2008-07-01

398

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

Microsoft Academic Search

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

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

1997-01-01

399

Monitoring of cell volume and water exchange time in perfused cells by diffusion-weighted1H NMR spectroscopy  

Microsoft Academic Search

Diffusion of intracellular water was measured in perfused cells embedded in basement membrane gel threads. F98 glioma cells, primary astrocytes, and epithelial KB cells were used and were exposed to osmotic stress, immunosuppressiva, the water channel blocker p-chloromercuriobenzenesulfonate (pCMBS), and apoptotic conditions. With diffusion-weighted 1H NMR spectroscopy changes in the intracellular signal could be monitored and quantified with single signal

Josef Pfeuffer; Ulrich Flögel; Dieter Leibfritz

1998-01-01

400

The degradation of zinc dialkyldithiophosphate additives in fully formulated engine oil as studied by P-31 NMR spectroscopy  

Microsoft Academic Search

Two fully-formulated engine oils containing zinc dialkyldithiophosphate (ZDDP) were tested at different oil temperature regimes during long distance, high speed field tests (15000 km and 145 ± 10 km\\/hr). P-31 NMR spectroscopy was used to characterize the ZDDPs and the degradation products formed during the field tests. It was found that basic ZDDP degradation products were thiophosphates and phosphates, and

Pu Peng; Shan-Zhen Hong; Wan-Zhen Lu

1994-01-01