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1

Probes for High Field Solid-state NMR of Lossy Biological Samples  

PubMed Central

In solid-state NMR exphydrated samples biopolymers are susceptible to radio-frequency heating and have a significant impact on probe tuning frequency and performance parameters such as sensitivity. These considerations are increasingly important as magnetic field strengths increase with improved magnet technology. Recent developments in the design, construction, and performance of probes for solid-state NMR experiments on stationary lossy biological samples at high magnetic fields are reviewed.

Grant, Christopher V.; Wu, Chin H.; Opella, Stanley J.

2010-01-01

2

Probing organic-mineral interface in intact bone using magic angle spinning solid state NMR  

Microsoft Academic Search

Organic-mineral interface plays an important role in defining the mechanical properties of bone. Ability to probe this poorly understood interface at the molecular level in intact bone is desirable, and solid state NMR is one of the few techniques available for this. An intact cortical bone was successfully machined and spun at 12.5kHz. The 13 C- 31 P REDOR pulse

O. Nikel; D. Laurencin; S. Besdos; D. Vashishth

2011-01-01

3

A LOW-E MAGIC ANGLE SPINNING PROBE FOR BIOLOGICAL SOLID STATE NMR AT 750 MHz  

PubMed Central

Crossed-coil NMR probes are a useful tool for reducing sample heating for biological solid state NMR. In a crossed-coil probe, the higher frequency 1H field, which is the primary source of sample heating in conventional probes, is produced by a separate low-inductance resonator. Because a smaller driving voltage is required, the electric field across the sample and the resultant heating is reduced. In this work we describe the development of a magic angle spinning (MAS) solid state NMR probe utilizing a dual resonator. This dual resonator approach, referred to as “Low-E,” was originally developed to reduce heating in samples of mechanically aligned membranes. The study of inherently dilute systems, such as proteins in lipid bilayers, via MAS techniques requires large sample volumes at high field to obtain spectra with adequate signal-to-noise ratio under physiologically relevant conditions. With the Low-E approach, we are able to obtain homogeneous and sufficiently strong radiofrequency fields for both 1H and 13C frequencies in a 4 mm probe with a 1H frequency of 750 MHz. The performance of the probe using windowless dipolar recoupling sequences is demonstrated on model compounds as well as membrane embedded peptides.

McNeill, Seth A.; Gor'kov, Peter L.; Shetty, Kiran; Brey, William W.; Long, Joanna R.

2009-01-01

4

Probing Quadrupolar Nuclei by Solid-State NMR Spectroscopy: Recent Advances  

SciTech Connect

Solid-state nuclear magnetic resonance (NMR) of quadrupolar nuclei has recently undergone remarkable development of capabilities for obtaining structural and dynamic information at the molecular level. This review summarizes the key achievements attained during the last couple of decades in solid-state NMR of both integer spin and half-integer spin quadrupolar nuclei. We provide a concise description of the first- and second-order quadrupolar interactions, and their effect on the static and magic angle spinning (MAS) spectra. Methods are explained for efficient excitation of single- and multiple-quantum coherences, and acquisition of spectra under low- and high-resolution conditions. Most of all, we present a coherent, comparative description of the high-resolution methods for half-integer quadrupolar nuclei, including double rotation (DOR), dynamic angle spinning (DAS), multiple-quantum magic angle spinning (MQMAS), and satellite transition magic angle spinning (STMAS). Also highlighted are methods for processing and analysis of the spectra. Finally, we review methods for probing the heteronuclear and homonuclear correlations between the quadrupolar nuclei and their quadrupolar or spin-1/2 neighbors.

Fernandez, Christian; Pruski, Marek

2011-06-08

5

(14)N solid-state NMR: a sensitive probe of the local order in zeolites.  

PubMed

Local order in as-synthesised zeolites templated by tetraalkylammonium cations is proven from solid-state (14)N NMR and related quadrupolar parameters, opening new perspectives in the study of porous materials. PMID:23877332

Dib, Eddy; Mineva, Tzonka; Gaveau, Philippe; Alonso, Bruno

2013-10-01

6

Solid-state NMR imaging system  

DOEpatents

An accessory for use with a solid-state NMR spectrometer includes a special imaging probe with linear, high-field strength gradient fields and high-power broadband RF coils using a back projection method for data acquisition and image reconstruction, and a real-time pulse programmer adaptable for use by a conventional computer for complex high speed pulse sequences.

Gopalsami, N.; Dieckman, S.L.; Ellingson, W.A.

1990-12-31

7

Solid-state NMR imaging system  

DOEpatents

An apparatus for use with a solid-state NMR spectrometer includes a special imaging probe with linear, high-field strength gradient fields and high-power broadband RF coils using a back projection method for data acquisition and image reconstruction, and a real-time pulse programmer adaptable for use by a conventional computer for complex high speed pulse sequences.

Gopalsami, Nachappa (Naperville, IL); Dieckman, Stephen L. (Elmhurst, IL); Ellingson, William A. (Naperville, IL)

1992-01-01

8

Probing the structure of metal-substituted molecular sieves by solid-state NMR  

SciTech Connect

Paramagnetic metal ions exert large influences on the NMR spectra of neighboring nuclei. The authors are using these effects to probe metal sites in zeolites and AlPO{sub 4} molecular sieves. In particular, they are studying [Co]-AlPO{sub 4}-5 because similar cobalt substituted AlPO{sub 4} sieves are reported in the literature. They have extended that work to probe the titanium zeolite TS-1 by comparing spectra of normal TS-1 to samples where the titanium has been reduced to the paramagnetic Ti{sup 3+}. This promises to be a useful technique for determining framework substitution in many zeolite systems.

Labouriau, A.; Crawford, S.N.; Ott, K.; Earl, W.L.

1998-08-01

9

Probing the interaction of polyphenols with lipid bilayers by solid-state NMR spectroscopy  

PubMed Central

Polyphenols are bioactive natural products that appear to act against a wide range of pathologies. Mechanisms of activity have not been established, but recent studies have suggested that some polyphenols bind to membranes. We examined the interaction between lipid bilayers and three structurally diverse polyphenols. We hypothesized that features of the polyphenols such as polarity, molecular size, molecular geometry, and number and arrangement of phenol hydroxyl groups would determine the tendency to interact with the bilayer. We examined a mixed polyphenol, (?) epigallocatechin gallate (EGCg); a proanthocyanidin trimer comprising catechin-(4?8)-catechin-(4?8)-catechin (cat3); and a hydrolysable tannin, 1,2,3,4,6-penta-O-galloyl-?-D-glucopyranose (PGG). These polyphenols were incorporated at different levels into 2H labeled 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) multi-lamellar vesicles (MLVs). 31P and 2H solid-state NMR experiments were performed to determine the dynamics of the headgroup region and the hydrophobic acyl chain region of the lipid bilayer upon addition of polyphenols. The chemical shift anisotropy (CSA) width of the 31P NMR spectra decreased upon addition of polyphenols. Addition of PGG induces a dramatic reduction on the CSA width compared with the control lipid bilayer sample, while addition of cat3 barely reduces the CSA width. The 2H quadupolar splitting of the lipids also decreased upon addition of polyphenols. At the same concentration, PGG substantially reduced the quadrupolar splitting while cat3 barely reduced it when compared with the control sample. By calculating the order parameters of the acyl chain region of the lipid bilayer, we concluded that the hydrophobic part of the lipid bilayer was perturbed by PGG while cat3 did not cause large perturbations. The data suggest that the polarity of the polyphenols affects the interaction between tannins and membranes. The interactions may relate to the biological activities of polyphenols.

Yu, Xueting; Chu, Shidong; Hagerman, Ann E.; Lorigan, Gary A.

2011-01-01

10

An efficient (1)H/(31)P double-resonance solid-state NMR probe that utilizes a scroll coil.  

PubMed

The construction and performance of a scroll coil double-resonance probe for solid-state NMR on stationary samples is described. The advantages of the scroll coil at the high resonance frequencies of (1)H and (31)P include: high efficiency, minimal perturbations of tuning by a wide range of samples, minimal RF sample heating of high dielectric samples of biopolymers in aqueous solution, and excellent RF homogeneity. The incorporation of a cable tie cinch for mechanical stability of the scroll coil is described. Experimental results obtained on a Hunter Killer Peptide 1 (HKP1) interacting with phospholipid bilayers of varying lipid composition demonstrate the capabilities of this probe on lossy aqueous samples. PMID:17719813

Grant, Christopher V; Sit, Siu-Ling; De Angelis, Anna A; Khuong, Kelli S; Wu, Chin H; Plesniak, Leigh A; Opella, Stanley J

2007-08-06

11

Probing the molecular-level control of aluminosilicate dissolution: A sensitive solid-state NMR proxy for reactive surface area  

NASA Astrophysics Data System (ADS)

For two suites of volcanic aluminosilicate glasses, the accessible and reactive sites for covalent attachment of the fluorine-containing (3,3,3-trifluoropropyl)dimethylchlorosilane (TFS) probe molecule were measured by quantitative 19F nuclear magnetic resonance (NMR) spectroscopy. The first set of samples consists of six rhyolitic and dacitic glasses originating from volcanic activity in Iceland and one rhyolitic glass from the Bishop Tuff, CA. Due to differences in the reactive species present on the surfaces of these glasses, variations in the rate of acid-mediated dissolution (pH 4) for samples in this suite cannot be explained by variations in geometric or BET-measured surface area. In contrast, the rates scale directly with the surface density of TFS-reactive sites as measured by solid-state NMR. These data are consistent with the inference that the TFS-reactive M-OH species on the glass surface, which are known to be non-hydrogen-bonded Q 3 groups, represent loci accessible to and affected by proton-mediated dissolution. The second suite of samples, originating from a chronosequence in Kozushima, Japan, is comprised of four rhyolites that have been weathered for 1.1, 1.8, 26, and 52 ka. The number of TFS-reactive sites per gram increases with duration of weathering in the laboratory for the "Icelandic" samples and with duration of field weathering for both "Icelandic" and Japanese samples. One hypothesis is consistent with these and published modeling, laboratory, and field observations: over short timescales, dissolution is controlled by fast-dissolving sites, but over long timescales, dissolution is controlled by slower-dissolving sites, the surface density of which is proportional to the number of TFS-reactive Q 3 sites. These latter sites are not part of a hydrogen-bonded network on the surface of the glasses, and measurement of their surface site density allows predictions of trends in reactive surface area. The TFS treatment method, which is easily monitored by quantitative 19F solid-state NMR, therefore provides a chemically specific and quantifiable proxy to understand the nature of how sites on dissolving silicates control dissolution. Furthermore, 27Al NMR techniques are shown here to be useful in identifying clays on the glass surfaces, and these methods are therefore effective for quantifying concentrations of weathering impurities. Our interpretations offer a testable hypothesis for the mechanism of proton-promoted dissolution for low-iron aluminosilicate minerals and glasses and suggest that future investigations of reactive surfaces with high-sensitivity NMR techniques are warranted.

Washton, Nancy M.; Brantley, Susan L.; Mueller, Karl T.

2008-12-01

12

Reduction of RF-induced sample heating with a scroll coil resonator structure for solid-state NMR probes.  

PubMed

Heating due to high power 1H decoupling limits the experimental lifetime of protein samples for solid-state NMR (SSNMR). Sample deterioration can be minimized by lowering the experimental salt concentration, temperature or decoupling fields; however, these approaches may compromise biological relevance and/or spectroscopic resolution and sensitivity. The desire to apply sophisticated multiple pulse experiments to proteins therefore motivates the development of probes that utilize the RF power more efficiently to generate a high ratio of magnetic to electric field in the sample. Here a novel scroll coil resonator structure is presented and compared to a traditional solenoid. The scroll coil is demonstrated to be more tolerant of high sample salt concentrations and cause less RF-induced sample heating. With it, the viable experimental lifetime of a microcrystalline ubiquitin sample has been extended by more than an order of magnitude. The higher B1 homogeneity and permissible decoupling fields enhance polarization transfer efficiency in 15N-13C correlation experiments employed for protein chemical shift assignments and structure determination. PMID:15705511

Stringer, John A; Bronnimann, Charles E; Mullen, Charles G; Zhou, Donghua H; Stellfox, Sara A; Li, Ying; Williams, Evan H; Rienstra, Chad M

2005-03-01

13

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

14

A Modified Alderman-Grant Coil makes possible an efficient cross-coil probe for high field solid-state NMR of lossy biological samples  

NASA Astrophysics Data System (ADS)

The design, construction, and performance of a cross-coil double-resonance probe for solid-state NMR experiments on lossy biological samples at high magnetic fields are described. The outer coil is a Modified Alderman-Grant Coil (MAGC) tuned to the 1H frequency. The inner coil consists of a multi-turn solenoid coil that produces a B1 field orthogonal to that of the outer coil. This results in a compact nested cross-coil pair with the inner solenoid coil tuned to the low frequency detection channel. This design has several advantages over multiple-tuned solenoid coil probes, since RF heating from the 1H channel is substantially reduced, it can be tuned for samples with a wide range of dielectric constants, and the simplified circuit design and high inductance inner coil provides excellent sensitivity. The utility of this probe is demonstrated on two electrically lossy samples of membrane proteins in phospholipid bilayers (bicelles) that are particularly difficult for conventional NMR probes. The 72-residue polypeptide embedding the transmembrane helices 3 and 4 of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) (residues 194-241) requires a high salt concentration in order to be successfully reconstituted in phospholipid bicelles. A second application is to paramagnetic relaxation enhancement applied to the membrane-bound form of Pf1 coat protein in phospholipid bicelles where the resistance to sample heating enables high duty cycle solid-state NMR experiments to be performed.

Grant, Christopher V.; Yang, Yuan; Glibowicka, Mira; Wu, Chin H.; Park, Sang Ho; Deber, Charles M.; Opella, Stanley J.

2009-11-01

15

Solid-State NMR Studies of Bone  

Microsoft Academic Search

Solid-state NMR studies on bone, bone mineral standards and collagen are reviewed. NMR spectroscopy was mostly applied to the bone mineral and confirmed that the structure resembles that of calcium carbonatoapatite of type B. Apatite in bone was found to be deficient in structural hydroxyl groups. Concentration and distribution of hydrogenphosphate and carbonate ions, and of water in apatite crystals

Waclaw Kolodziejski

16

Scalar operators in solid-state NMR  

SciTech Connect

Selectivity and resolution of solid-state NMR spectra are determined by dispersion of local magnetic fields originating from relaxation effects and orientation-dependent resonant frequencies of spin nuclei. Theoretically, the orientation-dependent resonant frequencies can be represented by a set of irreducible tensors. Among these tensors, only zero rank tensors (scalar operators) are capable of providing high resolution NMR spectra. This thesis presents a series of new developments in high resolution solid-state NMR concerning the reconstruction of various scalar operators motion in solid C{sub 60} is analyzed.

Sun, Boqin

1991-11-01

17

Probing physical and chemical changes in cortical bone due to osteoporosis and type 2 diabetes by solid-state NMR  

NASA Astrophysics Data System (ADS)

Approximately 1.5 million fractures occur each year in the U.S. due to osteoporosis, which is characterized by decreased bone mineral density and deterioration of bone micro-architecture. On the other hand, type 2 diabetes also significantly increases fracture risks, despite having a normal or even higher bone mineral density. Solid-state NMR has been applied to bone tissues from normal and disease-inflicted mouse models to study structural and chemical dynamics as the disease progresses. Proton relaxation experiments were performed to measure water populations in the bone matrix and pores. Collagen-bound water has strong influence on bone resilience, while water content in the pores reveals amount and size of pores from micro- to millimeter range. Other biochemical and atomic-scale structural alterations in the mineral and organic phases and their interface were investigated by proton, phosphorus, and carbon NMR spectroscopy. Experiments were designed to individually detect different types of phosphorus environments: near the mineral surface, similar to hydroxyapatite, and deficient of hydrogens due to substitution of the hydroxyl group by other ions. A new method was also developed for accurate quantification of each phosphorus species.

Zhou, Donghua; Taylor, Amanda; Rendina, Beth; Smith, Brenda

2013-03-01

18

A strip-shield improves the efficiency of a solenoid coil in probes for high field solid-state NMR of lossy biological samples  

PubMed Central

A strip-shield inserted between a high inductance double-tuned solenoid coil and the glass tube containing the sample improves the efficiency of probes used for high-field solid-state NMR experiments on lossy aqueous samples of proteins and other biopolymers. A strip-shield is a coil liner consisting of thin copper strips layered on a PTFE (polytetrafluoroethylene) insulator. With lossy samples, the shift in tuning frequency is smaller, the reduction in Q, and RF-induced heating are all significantly reduced when the strip-shield is present. The performance of 800 MHz 1H/15N and 1H/13C double-resonance probes is demonstrated on aqueous samples of membrane proteins in phospholipid bilayers.

Wu, Chin H.; Grant, Christopher V.; Cook, Gabriel A.; Park, Sang Ho; Opella, Stanley J.

2009-01-01

19

Probing structural and motional features of the C-terminal part of the Human Centrin 2/P17-XPC microcrystalline complex by solid-state NMR spectroscopy.  

PubMed

Insight into structural and motional features of the C-terminal part of the Human Centrin 2 in complex with the peptide P17-XPC was obtained by using complementary solid-state NMR methods. We demonstrate that the experimental conditions and procedures of sample crystallization determine the quality of solid-state NMR spectra and the internal mobility of the protein. Two-dimensional (2D) (13)C-(13)C and (15)N-(15)N correlation spectra reveal intra- and inter-residue dipolar connectivities and provide partial, site-specific assignments of (13)C and (15)N resonance signals. The secondary structure of the C-ter HsCen2/P17-XPC complex in a microcrystalline state appears similar to that found in solution. Conformational flexibility is probed through relaxation-compensated measurements of dipolar order parameters that exploit the dynamics of cross-polarization in multidimensional experiments. The extracted dipolar coupling constants and relevant order parameters reveal increased backbone flexibility of the loops except for residues involved in coordination with the Ca(2+) cation that stabilizes the hydrophobic pocket containing the peptide P17-XPC. PMID:23190348

Herbert-Pucheta, Jose-Enrique; Chan-Huot, Monique; Duma, Luminita; Abergel, Daniel; Bodenhausen, Geoffrey; Assairi, Liliane; Blouquit, Yves; Charbonnier, Jean-Baptiste; Tekely, Piotr

2012-12-11

20

Solid State NMR Investigations of Zeolite - Intercalate Structures  

SciTech Connect

We will describe two topics in which structural information on complexes of zeolites is obtained from solid state NMR. In the first, recent work on the determination of the complete three-dimensional structures of the complexes of zeolites with organic sorbates will be briefly reported. The method has been optimized and the presentation of the results systematized. In the second topic, we will describe how solid state NMR can be used in the reverse sense to probe for the existence and structures of “nanocrystals” whose dimensions are too small to give proper Bragg scattering and which have been proposed to be the synthesis route for the formation of zeolite ZSM-5. In this study, the spectral parameters of “probe” template molecules are used as being diagnostic of whether the local environment of the framework has been formed. These are independent of the “crystal” dimensions and this general approach may be applicable to other similar “nano” systems.

Fyfe, Colin A.; Diaz, Anix; Brouwer, Darren H.; Lee, Joseph; Schneider, Celine M.; Scheffler, Franziska A.; Darton, Richard J.

2006-07-24

21

[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

22

Local site symmetry and electronic structure of trialuminide and related intermetallic alloys probed by solid-state NMR  

NASA Astrophysics Data System (ADS)

Intermetallic aluminide alloys with the L12, DO22, DO23, and Al2Ti crystal structures have been examined by NMR using the 27Al resonance to investigate how changes in crystal structure affect the local environment as indicated by hyperfine interactions at the atomic nucleus. All nonequivalent Al sites have been clearly resolved. Further, the environment of the transition metal component in each intermetallic crystal structure has been investigated using the 45Sc resonance in the L12 structure of Al3Sc, the 49Ti resonance in the DO22 structure of Al3Ti, and in Al2Ti, the 51V resonance in the DO22 structure of Al3V and the 91Zr resonance in the DO23 structure of Al3Zr. Using a combination of static and magic-angle spinning Fourier transform NMR, and static field sweep spectroscopy, the isotropic Knight shifts (Kiso) and the nuclear quadrupole coupling constants (Cq) have been determined for all nuclei and all sites. In some cases the 27Al axial Knight shift (Kax) has been obtained. In the trialuminides each Al site located by NMR has been identified with the corresponding site in the unit cell of the crystal structure.

Bastow, T. J.; Forwood, C. T.; Gibson, M. A.; Smith, M. E.

1998-08-01

23

Probing water accessibility in HET-s(218-289) amyloid fibrils by solid-state NMR.  

PubMed

Despite the importance of protein fibrils in the context of conformational diseases, information on their structure is still sparse. Hydrogen/deuterium exchange measurements of backbone amide protons allow the identification hydrogen-bonding patterns and reveal pertinent information on the amyloid ?-sheet architecture. However, they provide only little information on the identity of residues exposed to solvent or buried inside the fibril core. NMR spectroscopy is a potent method for identifying solvent-accessible residues in proteins via observation of polarization transfer between chemically exchanging side-chain protons and water protons. We show here that the combined use of highly deuterated samples and fast magic-angle spinning greatly attenuates unwanted spin diffusion and allows identification of polarization exchange with the solvent in a site-specific manner. We apply this measurement protocol to HET-s(218-289) prion fibrils under different conditions (including physiological pH, where protofibrils assemble together into thicker fibrils) and demonstrate that each protofibril of HET-s(218-289), is surrounded by water, thus excluding the existence of extended dry interfibril contacts. We also show that exchangeable side-chain protons inside the hydrophobic core of HET-s(218-289) do not exchange over time intervals of weeks to months. The experiments proposed in this study can provide insight into the detailed structural features of amyloid fibrils in general. PMID:21094164

Van Melckebeke, Hélène; Schanda, Paul; Gath, Julia; Wasmer, Christian; Verel, René; Lange, Adam; Meier, Beat H; Böckmann, Anja

2010-11-19

24

Ligand-Induced Conformational Changes of the Multidrug Resistance Transporter EmrE Probed by Oriented Solid-State NMR Spectroscopy.  

PubMed

An EmrE-ging market: Oriented solid-state NMR spectroscopy and biochemical cross-linking experiments were used to show that the ligand-free membrane protein transporter EmrE forms anti-parallel dimers with different monomer tilt angles relative to the lipid bilayer. In addition, subtle conformational changes were detected upon drug binding that emphasize the need for an atomic-resolution structure. PMID:23939862

Gayen, Anindita; Banigan, James R; Traaseth, Nathaniel J

2013-08-12

25

Probing polymorphism and reactivity in the organic solid state using 13C NMR spectroscopy: Studies of p-Formyl-trans-cinnamic acid  

NASA Astrophysics Data System (ADS)

p-Formyl-trans-cinnamic acid (p-FCA) is known to exist in two different crystal phases (denoted ? and ?). When crystals of the ? phase of p-FCA are exposed to UV radiation, a solid state dimerization reaction occurs to produce 4,4'-diformyl-?-truxinic acid. In contrast, crystals of the ? phase of p-FCA are photostable. It is shown in this paper that high resolution solid state 13C NMR spectroscopy is a sensitive technique for distinguishing the ? and ? phases of p-FCA, and can be used to investigate, in detail, the chemical transformation that occurs upon UV irradiation of the ? phase. Specifically, the 13C NMR spectra presented here were recorded using the TOSS (total suppression of sidebands) pulse sequence; this is based upon the standard 13C CPMAS (cross polarization/magic angle sample spinning/high power 1H decoupling) method, but has the additional feature that all orders of spinning sidebands are eliminated from the spectrum. The photoproduct obtained from UV irradiation of ?-p-FCA contains a significant noncrystalline component (assessed via powder X-ray diffraction), and our NMR studies suggest that this noncrystalline component of the photoproduct contains some amount of the ? phase of the monomer p-FCA. A mechanism is proposed to explain the fact that UV irradiation of ?-p-FCA can generate, in addition to the expected photodimer, an impurity amount of the ? phase of p-FCA.

Harris, Kenneth D. M.; Thomas, John M.

1991-09-01

26

Probing the structural origins of vapochromism of a triarylboron-functionalized platinum(II) acetylide by optical and multinuclear solid-state NMR spectroscopy.  

PubMed

A vapoluminescent triarylboron-functionalized platinum(II) complex that displays a mechanism of vapochromism differing from all previously reported platinum(II) compounds has been synthesized. The luminescence color of 1 switches in response to many volatile organic compounds in the solid state, including hexanes, CH(2)Cl(2), benzene, and methanol. While vapochromism due to changes in Pt-Pt or ?-? stacking interactions has been commonly observed, absorption and luminescence studies and single-crystal and powder X-ray diffraction data as well as multinuclear solid-state NMR experiments ((195)Pt, (13)C, (11)B, (2)H, and (1)H) revealed that the vapochromic response of 1 is instead due to changes in the excited-state energy levels resulting from local interactions of solvent molecules with the complex. Furthermore, these interactions result in inversion of the lowest-energy excited states of the complex in some cases, the first observation of this phenomenon in the solid state. PMID:21425806

Hudson, Zachary M; Sun, Christina; Harris, Kristopher J; Lucier, Bryan E G; Schurko, Robert W; Wang, Suning

2011-03-22

27

Solid-State NMR Studies of Amyloid Fibril Structure  

NASA Astrophysics Data System (ADS)

Current interest in amyloid fibrils stems from their involvement in neurodegenerative and other diseases and from their role as an alternative structural state for many peptides and proteins. Solid-state nuclear magnetic resonance (NMR) methods have the unique capability of providing detailed structural constraints for amyloid fibrils, sufficient for the development of full molecular models. In this article, recent progress in the application of solid-state NMR to fibrils associated with Alzheimer's disease, prion fibrils, and related systems is reviewed, along with relevant developments in solid-state NMR techniques and technology.

Tycko, Robert

2011-05-01

28

Solid State NMR Studies of Amyloid Fibril Structure  

PubMed Central

Current interest in amyloid fibrils stems from their involvement in neurodegenerative and other diseases and from their role as an alternative structural state for many peptides and proteins. Solid state NMR methods have the unique capability of providing detailed structural constraints for amyloid fibrils, sufficient for the development of full molecular models. In this article, recent progress in the application of solid state NMR to fibrils associated with Alzheimer’s disease, prion fibrils, and related systems is reviewed, along with relevant developments in solid state NMR techniques and technology.

Tycko, Robert

2011-01-01

29

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...

30

Acid-base interactions and secondary structures of poly-L-lysine probed by 15N and 13C solid state NMR and Ab initio model calculations.  

PubMed

The interactions of the 15N-labeled amino groups of dry solid poly-L-lysine (PLL) with various halogen and oxygen acids HX and the relation to the secondary structure have been studied using solid-state 15N and 13C CPMAS NMR spectroscopy (CP = cross polarization and MAS = magic angle spinning). For comparison, 15N NMR spectra of an aqueous solution of PLL were measured as a function of pH. In order to understand the effects of protonation and hydration on the 15N chemical shifts of the amino groups, DFT and chemical shielding calculations were performed on isolated methylamine-acid complexes and on periodic halide clusters of the type (CH3NH3(+)X(-))n. The combined experimental and computational results reveal low-field shifts of the amino nitrogens upon interaction with the oxygen acids HX = HF, H2SO4, CH3COOH, (CH3)2POOH, H3PO4, HNO3, and internal carbamic acid formed by reaction of the amino groups with gaseous CO2. Evidence is obtained that only hydrogen-bonded species of the type (Lys-NH2***H-X)n are formed in the absence of water. 15N chemical shifts are maximum when H is located in the hydrogen bond center and then decrease again upon full protonation, as found for aqueous solution at low pH. By contrast, halogen acids interact in a different way. They form internal salts of the type (Lys-NH3(+)X(-))n via the interaction of many acid-base pairs. This salt formation is possible only in the beta-sheet conformation. By contrast, the formation of hydrogen-bonded complexes can occur both in beta-sheet domains as well as in alpha-helical domains. The 15N chemical shifts of the protonated ammonium groups increase when the size of the interacting halogen anions is increased from chloride to iodide and when the number of the interacting anions is increased. Thus, the observed high-field 15N shift of ammonium groups upon hydration is the consequence of replacing interacting halogen atoms by oxygen atoms. PMID:19367899

Dos, Alexandra; Schimming, Volkmar; Tosoni, Sergio; Limbach, Hans-Heinrich

2008-12-11

31

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

32

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

33

A Solid-State NMR Study of Phospholipid-Cholesterol Interactions: Sphingomyelin-Cholesterol Binary Systems  

Microsoft Academic Search

We used solid-state NMR techniques to probe the interactions of cholesterol (Chol) with bovine brain sphingomyelin (SM) and for comparison of the interactions of Chol with dipalmitoylphosphatidylcholine (DPPC), which has a similar gel-to-liquid crystalline transition temperature. 1H-, 31P-, and 13C-MASNMR yielded high-resolution spectra from multilamellar dispersions of unlabeled brain SM and Chol for analysis of chemical shifts and linewidths. In

Wen Guo; Volker Kurze; Thomas Huber; Nezam H. Afdhal; Klaus Beyer; James A. Hamilton

2002-01-01

34

Solid-State NMR Studies of Chemically Lithiated CFx  

PubMed Central

Three types of fluorinated carbon, all in their original form and upon sequential chemical lithiations via n-butyllithium, were investigated by 13C and 19F solid-state NMR methods. The three starting CFx materials [where x = 1 (nominally)] were fiber based, graphite based, and petroleum coke based. The aim of the current study was to identify, at the atomic/molecular structural level, factors that might account for differences in electrochemical performance among the different kinds of CFx. Differences were noted in the covalent F character among the starting compounds and in the details of LiF production among the lithiated samples.

Leifer, N. D.; Johnson, V. S.; Ben-Ari, R.; Gan, H.; Lehnes, J. M.; Guo, R.; Lu, W.; Muffoletto, B. C.; Reddy, T.; Stallworth, P. E.; Greenbaum, S. G.

2010-01-01

35

Solid-state NMR characterization of gas vesicle structure.  

PubMed

Gas vesicles are gas-filled buoyancy organelles with walls that consist almost exclusively of gas vesicle protein A (GvpA). Intact, collapsed gas vesicles from the cyanobacterium Anabaena flos-aquae were studied by solid-state NMR spectroscopy, and most of the GvpA sequence was assigned. Chemical shift analysis indicates a coil-?-?-?-?-coil peptide backbone, consistent with secondary-structure-prediction algorithms, and complementary information about mobility and solvent exposure yields a picture of the overall topology of the vesicle subunit that is consistent with its role in stabilizing an air-water interface. PMID:20858439

Sivertsen, Astrid C; Bayro, Marvin J; Belenky, Marina; Griffin, Robert G; Herzfeld, Judith

2010-09-22

36

Solid-state NMR characterization of Mowry Formation shales  

SciTech Connect

Solid-state [sup 13]C and [sup 29]Si NMR measurements were carried out on a series of petroleum source rocks from the Mowry Formation of the Powder River Basin in Wyoming. The objectives of this study wereto use CP/MAS [sup 13]C NMR measurements to monitor changes in the carbon structure of the kerogen that result from depth of burial, and to examine the feasibility of [sup 29]Si NMR for studying the thermal alteration of clay minerals during diagenesis. Carbon and silicon NMR measurements were made on a suite of samples covering a present-day depth interval of 3,000 to 11,500 ft.In general, the NMR results endorsed other geochemical analyses that were performed on the source rocks as part of another study to examine pressure compartmentalization in the Mowry Formation. The carbon aromaticity of the kerogen increased with depth of burial, and at depths greater that approximately 10,000 ft the kerogen showed little capacity to generate additional oil because of the small fraction of residual aliphatic carbon. By combining NMR and Rock-Eval measurements, an estimate of the hydrogen budget was obtained. The calculations indicated that approximately 20% of the kerogen was converted to hydrocarbons, and that sufficient hydrogen was liberated from aromatization and condensation reactions to stabilize the generated products. The [sup 29]Si NMR spectra were characterized by a relatively sharp quartz resonance and a broad resonance from the clay minerals. With increasing depth of burial, the clay resonance became broader and shifted slightly downfield. These changes qualitatively support X-ray analysis that shows progressive alteration of illite to smectite with depth of burial.

Miknis, F.P.

1992-04-01

37

Solid-state NMR characterization of Mowry Formation shales  

SciTech Connect

Solid-state {sup 13}C and {sup 29}Si NMR measurements were carried out on a series of petroleum source rocks from the Mowry Formation of the Powder River Basin in Wyoming. The objectives of this study wereto use CP/MAS {sup 13}C NMR measurements to monitor changes in the carbon structure of the kerogen that result from depth of burial, and to examine the feasibility of {sup 29}Si NMR for studying the thermal alteration of clay minerals during diagenesis. Carbon and silicon NMR measurements were made on a suite of samples covering a present-day depth interval of 3,000 to 11,500 ft.In general, the NMR results endorsed other geochemical analyses that were performed on the source rocks as part of another study to examine pressure compartmentalization in the Mowry Formation. The carbon aromaticity of the kerogen increased with depth of burial, and at depths greater that approximately 10,000 ft the kerogen showed little capacity to generate additional oil because of the small fraction of residual aliphatic carbon. By combining NMR and Rock-Eval measurements, an estimate of the hydrogen budget was obtained. The calculations indicated that approximately 20% of the kerogen was converted to hydrocarbons, and that sufficient hydrogen was liberated from aromatization and condensation reactions to stabilize the generated products. The {sup 29}Si NMR spectra were characterized by a relatively sharp quartz resonance and a broad resonance from the clay minerals. With increasing depth of burial, the clay resonance became broader and shifted slightly downfield. These changes qualitatively support X-ray analysis that shows progressive alteration of illite to smectite with depth of burial.

Miknis, F.P.

1992-04-01

38

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

39

Molecular Structure of Humin and Melanoidin via Solid State NMR  

PubMed Central

Sugar-derived humins and melanoidins figure significantly in food chemistry, agricultural chemistry, biochemistry and prebiotic chemistry. Despite wide interest and significant experimental attention, the amorphous and insoluble nature of the polymers has made them resistant to conventional structural characterization. Here we make use of solid-state NMR methods, including selective 13C substitution, 1H-dephasing, and double quantum filtration. The spectra, and their interpretation, are simplified by relying exclusively on hydronium for catalysis. The results for polymers derived from ribose, deoxyribose and fructose indicate diverse pathways to furans, suggest a simple route to pyrroles in the presence of amines, and reveal a heterogenous network-type polymer in which sugar molecules cross-link the heterocycles.

Herzfeld, Judith; Rand, Danielle; Matsuki, Yoh; Daviso, Eugenio; Mak-Jurkauskas, Melody; Mamajanov, Irena

2011-01-01

40

SIMPSON - An important driver for numerical simulations in solid-state NMR spectroscopy  

NASA Astrophysics Data System (ADS)

We present a historical recollection on the development of the software package SIMPSON (SIMulation Package for SOlid-state Nmr). This covers a brief description of the underlying ideas and events leading to creation of SIMPSON and numerous auxiliary programs as well as comments on its impact on the development and application of solid-state NMR in research laboratories world-wide.

Bak, Mads; Rasmussen, Jimmy Tønners; Nielsen, Niels Chr.

2011-12-01

41

Investigations of adsorption sites on oxide surfaces using solid-state NMR and TPD-IGC  

NASA Astrophysics Data System (ADS)

The number and chemical identity of reactive sites on surfaces of glass affects the processing, reliability, and lifetime of a number of important commercial products. Surface site densities, distributions, and structural identities are closely tied to the formation and processing of the glass surface, and exert a direct influence on strength and coating performance. The surface of a glass sample may vary markedly from the composition and chemistry of the bulk glass. We are taking a physicochemical approach to understanding adsorption sites on pristine multicomponent glass fibers surfaces, directly addressing the effect of processing on surface reactivity. This project aimed to understand the energy distributions of surface adsorption sites, the chemical/structural identity of those sites, and the relationship of these glasses to glass composition, thermal history, and in future work, surface coatings. We have studied the bulk and surface structure as well as the surface reactivity of the glass fibers with solid-state nuclear magnetic resonance (NMR) spectroscopy, inverse gas chromatography (IGC), and computational chemistry methods. These methods, solid-state NMR and IGC, typically require high surface area materials; however, by using probe molecules for NMR experiments or packing a column at high density for IGC measurements, lower surface area materials, such as glass fibers, can be investigated. The glasses used within this study were chosen as representative specimens of fibers with potentially different reactive sites on their surfaces. The two glass compositions were centered around a nominal E-glass, which contains very little alkali cations and mainly alkaline earth cations, and wool glass, which contains an abundance of alkali cations. The concentration of boron was varied from 0 to 8 mole % in both fiber compositions. Fibers were drawn from each composition at a variety of temperatures and draw speeds to provide a range of glass samples with varying diameters and thermal histories. The bulk structural features in both compositions of glass fibers were identified using high-resolution 29Si, 27Al, and 11B magic-angle spinning (MAS) NMR spectroscopic measurements. In multi-component glasses, the determination of silicon, aluminum, and boron distributions becomes difficult due to the competitive nature of the network-modifying oxides among the network-forming oxides. In pure silicates, 29Si MAS NMR can often resolve resonances arising from silicate tetrahedron having varying numbers of bridging oxygens. In aluminoborosilicate glasses, aluminum is present in four-, five-, and six- coordination with oxygen as neighbors. The speciation of the aluminum can be determined using 27Al MAS NMR. The fraction of tetrahedral boron species in the glass fibers were measured using 11B MAS NMR, which is typically used to study the short-range structure of borate containing glasses such as alkali borate, borosilicate, and aluminoborosilicate glasses. While solid-state NMR is a powerful tool for elucidating bonding environments and coordination changes in the glass structure, it cannot quantitatively probe low to moderate surface area samples due to insufficient spins. Chemical probes either physisorbed or chemisorbed to the fiber's surface can increase the surface selectivity of NMR for analysis of samples with low surface areas and provide information about the local molecular structure of the reactive surface site. Common chemical probe molecules contain NMR active nuclei such as 19F or may be enriched with 13C. A silyating agent, (3,3,3-trifluoropropyl)dimethylchlorosilane (TFS), reacts with reactive surface hydroxyls, which can be quantified by utilizing the NMR active nucleus (19F) contained in the probe molecule. The observed 19F MAS NMR peak area is integrated and compared against a standard of known fluorine spins (concentration), allowing the number of reactive hydroxyl sites to be quantified. IGC is a method used to study the surface properties of a material by examining the retention behavior of a probe molecule. The I

Golombeck, Rebecca A.

42

Biological solid-state NMR at ETH Zurich.  

PubMed

Solid-state Magnetic Resonance has been greatly developed over the past decade. Higher field spectrometers and other technical developments are expected to lead to further significant improvements. PMID:23146268

Zandomeneghi, Giorgia; Maas, Werner; Meier, Beat H

2012-01-01

43

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

44

Solid State FT-IR and (31)P NMR Spectral Features of Phosphate Compounds  

Technology Transfer Automated Retrieval System (TEKTRAN)

Solid-state spectroscopic techniques, including Fourier transform infrared (FT-IR) and solid-state 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies, are powerful tools for evaluating metal speciation and transformation mechanisms of P compounds in the environment. Studie...

45

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...

46

Solid-state NMR approaches to internal dynamics of proteins: from picoseconds to microseconds and seconds.  

PubMed

Solid-state nuclear magnetic resonance (NMR) spectroscopy has matured to the point that it is possible to determine the structure of proteins in immobilized states, such as within microcrystals or embedded in membranes. Currently, researchers continue to develop and apply NMR techniques that can deliver site-resolved dynamic information toward the goal of understanding protein function at the atomic scale. As a widely-used, natural approach, researchers have mostly measured longitudinal (T1) relaxation times, which, like in solution-state NMR, are sensitive to picosecond and nanosecond motions, and motionally averaged dipolar couplings, which provide an integral amplitude of all motions with a correlation time of up to a few microseconds. While overall Brownian tumbling in solution mostly precludes access to slower internal dynamics, dedicated solid-state NMR approaches are now emerging as powerful new options. In this Account, we give an overview of the classes of solid-state NMR experiments that have expanded the accessible range correlation times from microseconds to many milliseconds. The measurement of relaxation times in the rotating frame, T1?, now allows researchers to access the microsecond range. Using our recent theoretical work, researchers can now quantitatively analyze this data to distinguish relaxation due to chemical-shift anisotropy (CSA) from that due to dipole-dipole couplings. Off-resonance irradiation allows researchers to extend the frequency range of such experiments. We have built multidimensional analogues of T2-type or line shape experiments using variants of the dipolar-chemical shift correlation (DIPSHIFT) experiment that are particularly suited to extract intermediate time scale motions in the millisecond range. In addition, we have continuously improved variants of exchange experiments, mostly relying on the recoupling of anisotropic interactions to address ultraslow motions in the ms to s ranges. The NH dipolar coupling offers a useful probe of local dynamics, especially with proton-depleted samples that suppress the adverse effect of strong proton dipolar couplings. We demonstrate how these techniques have provided a concise picture of the internal dynamics in a popular model system, the SH3 domain of ?-spectrin. T1-based methods have shown that large-amplitude bond orientation fluctuations in the picosecond range and slower 10 ns low-amplitude motions coexist in these structures. When we include T1? data, we observe that many residues undergo low amplitude motions slower than 100 ns. On the millisecond to second scale, mostly localized but potentially cooperative motions occur. Comparing different exchange experiments, we found that terminal NH2 groups in side chains can even undergo a combination of ultraslow large-angle two-site jumps accompanied by small-angle fluctuations that occur 10 times more quickly. PMID:23875699

Krushelnitsky, Alexey; Reichert, Detlef; Saalwächter, Kay

2013-07-23

47

Characterization of azobenzene polymer networks using in situ solid state NMR and temperature dependent photostriction  

NASA Astrophysics Data System (ADS)

Azobenzene liquid crystal polymer networks (azo-LCNs) undergo a complex light-driven molecular conformation change of the azobenzene chromophore which imparts a macroscopic shape change within a glassy polymer network. To better understand molecular conformational changes which underlie macroscopic polymer deformation, we have collected solid-state nuclear magnetic resonance (NMR) data on 19F fluorinated side-chain azo-LCNs using an in situ visible light (450–458 nm) LED light source. We illustrate measurable changes in 19F NMR lineshapes under light irradiation, indicating that conformational changes can be probed by NMR. The measured effects of light on NMR spectra are also found to be reversible upon removal of the light source. We further show that sample heating does not affect azobenzene isomerization through analysis of temperature-dependent magic-angle-spinning NMR lineshapes. These results illustrate a narrowing of the lineshapes, but no change in the NMR peak positions, indicating that heating from 30 and 60?° C affects molecular dynamics but does not change the azobenzene conformation. In addition to NMR data, benchtop photomechanical uni-axial measurements are taken over a temperature range from 23 to 60?° C. Samples with the fluorinated side-chain azo-LCNs are compared to samples composed only of non-fluorinated main-chain azo-LCN composition. Similar stress relaxation was observed in both compositions under high pre-stretch. The amount of stress relaxation was found to depend on the pre-stretch, the ambient temperature, and the polarization of light.

Worden, Matthew; Wang, Hongbo; Paravastu, Anant; Oates, William

2013-09-01

48

A high?resolution solid?state NMR study on nano?structured HZSM?5 zeolite  

Microsoft Academic Search

Variations in the structure and acidity properties of HZSM?5 zeolites with reduction in crystal sizes down to nanoscale (less\\u000a than 100 nm) have been investigated by XRD, TEM and solid?state NMR with a system capable of in situ sample pretreatment.\\u000a As evidenced by a combination of 27Al MAS NMR, 29Si MAS, CP\\/MAS NMR and 1H MAS NMR techniques, the downsize

Weiping Zhang; Xinhe Bao; Xinwen Guo; Xiangsheng Wang

1999-01-01

49

Solid state NMR and LVSEM studies on the hardening of latex modified tile mortar systems  

SciTech Connect

Construction mortars contain a broad variety of both inorganic and organic additives beside the cement powder. Here we present a study of tile mortar systems based on portland cement, quartz, methyl cellulose and different latex additives. As known, the methyl cellulose stabilizes the freshly prepared cement paste, the latex additive enhances final hydrophobicity, flexibility and adhesion. Measurements were performed by solid state nuclear magnetic resonance (NMR) and low voltage scanning electron microscopy (LVSEM) to probe the influence of the latex additives on the hydration, hardening and the final tile mortar properties. While solid state NMR enables monitoring of the bulk composition, scanning electron microscopy affords visualization of particles and textures with respect to their shape and the distribution of the different phases. Within the alkaline cement paste, the poly(vinyl acetate) (VAc)-based latex dispersions stabilized by poly(vinyl alcohol) (PVA) were found to be relatively stable against hydrolysis. The influence of the combined organic additives methyl cellulose, poly(vinyl alcohol) and latexes stabilized by poly(vinyl alcohol) on the final silicate structure of the cement hydration products is small. But even small amounts of additives result in an increased ratio of ettringite to monosulfate within the final hydrated tile mortar as monitored by {sup 27}Al NMR. The latex was found to be adsorbed to the inorganic surfaces, acting as glue to the inorganic components. For similar latex water interfaces built up by poly(vinyl alcohol), a variation in the latex polymer composition results in modified organic textures. In addition to the networks of the inorganic cement and of the latex, there is a weak network build up by thin polymer fibers, most probably originating from poly(vinyl alcohol). Besides the weak network, polymer fibers form well-ordered textures covering inorganic crystals such as portlandite.

Rottstegge, J. [Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz (Germany); Arnold, M. [Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz (Germany); Herschke, L. [Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz (Germany); Glasser, G. [Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz (Germany); Wilhelm, M. [Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz (Germany); Spiess, H.W. [Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz (Germany)]. E-mail: spiess@mpip-mainz.mpg.de; Hergeth, W.D. [Wacker Polymer Systems GmbH and Co. KG, Johannes Hess Strasse 24, D-84483 Burghausen (Germany)

2005-12-15

50

Solid-State NMR Studies of Pharmaceutical Systems  

Microsoft Academic Search

High?and low?resolution solid?state nuclear magnetic resonance (SSNMR) applications to the study of pharmaceuticals are reviewed. Examples are shown involving the use of mono?and bidimensional SSNMR techniques based on different nuclear interactions and the measurement of several nuclear parameters, such as chemical shifts, line widths, and relaxation times (T1, T2, T1?). The systems investigated include pure active pharmaceutical ingredients (APIs), substances

Marco Geppi; Giulia Mollica; Silvia Borsacchi; Carlo Alberto Veracini

2008-01-01

51

A Solid-State NMR Experiment: Analysis of Local Structural Environments in Phosphate Glasses  

ERIC Educational Resources Information Center

|An experiment that can be used to directly study the local chemical environments of phosphorus in solid amorphous materials is demonstrated. The experiment aims at familiarizing the students of chemistry with the principles of solid-state NMR, by having them synthesize a simple phosphate glass, and making them observe the (super 31)P NMR…

Anderson, Stanley E.; Saiki, David; Eckert, Hellmut; Meise-Gresch, Karin

2004-01-01

52

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

SciTech Connect

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

Hosseini, S.

1992-01-01

53

Heat Management Strategies for Solid-state NMR of Functional Proteins  

PubMed Central

Modern solid-state NMR methods can acquire high-resolution protein spectra for structure determination. However, these methods use rapid sample spinning and intense decoupling fields that can heat and denature the protein being studied. Here we present a strategy to avoid destroying valuable samples. We advocate first creating a sacrificial sample, which contains unlabeled protein (or no protein) in buffer conditions similar to the intended sample. This sample is then doped with the chemical shift thermometer Sm2Sn2O7. We introduce a pulse scheme called TCUP (for Temperature Calibration Under Pulseload) that can characterize the heating of this sacrificial sample rapidly, under a variety of experimental conditions, and with high temporal resolution. Sample heating is discussed with respect to different instrumental variables such as spinning speed, decoupling strength and duration, and cooling gas flow rate. The effects of different sample preparation variables are also discussed, including ionic strength, the inclusion of cryoprotectants, and the physical state of the sample (i.e. liquid, solid, or slurry). Lastly, we discuss probe detuning as a measure of sample thawing that does not require retuning the probe or using chemical shift thermometer compounds. Use of detuning tests and chemical shift thermometers with representative sample conditions makes it possible to maximize the efficiency of the NMR experiment while retaining a functional sample.

Fowler, Daniel J.; Harris, Michael J.; Thompson, Lynmarie K.

2012-01-01

54

Heat management strategies for solid-state NMR of functional proteins  

NASA Astrophysics Data System (ADS)

Modern solid-state NMR methods can acquire high-resolution protein spectra for structure determination. However, these methods use rapid sample spinning and intense decoupling fields that can heat and denature the protein being studied. Here we present a strategy to avoid destroying valuable samples. We advocate first creating a sacrificial sample, which contains unlabeled protein (or no protein) in buffer conditions similar to the intended sample. This sample is then doped with the chemical shift thermometer Sm2Sn2O7. We introduce a pulse scheme called TCUP (for Temperature Calibration Under Pulseload) that can characterize the heating of this sacrificial sample rapidly, under a variety of experimental conditions, and with high temporal resolution. Sample heating is discussed with respect to different instrumental variables such as spinning speed, decoupling strength and duration, and cooling gas flow rate. The effects of different sample preparation variables are also discussed, including ionic strength, the inclusion of cryoprotectants, and the physical state of the sample (i.e. liquid, solid, or slurry). Lastly, we discuss probe detuning as a measure of sample thawing that does not require retuning the probe or using chemical shift thermometer compounds. Use of detuning tests and chemical shift thermometers with representative sample conditions makes it possible to maximize the efficiency of the NMR experiment while retaining a functional sample.

Fowler, Daniel J.; Harris, Michael J.; Thompson, Lynmarie K.

2012-09-01

55

Suppressing background signals in solid state NMR via the Electronic Mixing-Mediated Annihilation (EMMA) method  

NASA Astrophysics Data System (ADS)

A simple procedure to effectively suppress background signals arising from various probe head components (e.g. stator, rotors, inserts) in solid state NMR is presented. Similarly to the ERETIC™ method, which uses an electronic signal as an internal standard for quantification, the proposed scheme is based on an electronically generated time-dependent signal that is injected into the receiver coil of the NMR probe head during signal acquisition. More specifically, the line shape, width and frequency of this electronic signal are determined by deconvoluting the background signal in the frequency domain. This deconvoluted signal is then converted into a time-dependent function through inverse Fourier Transform, which is used to generate the shaped pulse that is fed into the receiver coil during the acquisition of the Free Induction Decay. The power of the shaped pulse is adjusted to match the intensity of the background signal, and its phase is shifted by 180° with respect to the receiver reference phase. This so-called Electronic Mixing-Mediated Annihilation (EMMA) methodology is demonstrated here with a 13C Single Pulse Magic Angle Spinning spectrum of an isotopically enriched 13C histidine solid sample recorded under quantitative conditions.

Mollica, Giulia; Ziarelli, Fabio; Tintaru, Aura; Thureau, Pierre; Viel, Stéphane

2012-05-01

56

Investigation of zeolites by solid state quadrapole NMR.  

National Technical Information Service (NTIS)

The subject of this thesis is the NMR investigation of zeolites. The nature and properties of zeolites are discussed. Some of the basic priniples of NMR techniques on quadrupole nuclei are presented. A special technique, namely a two-dimensional nutation ...

R. Janssen

1990-01-01

57

Detecting Substrates Bound to the Secondary Multidrug Efflux Pump EmrE by DNP-Enhanced Solid-State NMR.  

PubMed

Escherichia coli EmrE, a homodimeric multidrug antiporter, has been suggested to offer a convenient paradigm for secondary transporters due to its small size. It contains four transmembrane helices and forms a functional dimer. We have probed the specific binding of substrates TPP(+) and MTP(+) to EmrE reconstituted into 1,2-dimyristoyl-sn-glycero-3-phosphocholine liposomes by (31)P MAS NMR. Our NMR data show that both substrates occupy the same binding pocket but also indicate some degree of heterogeneity of the bound ligand population, reflecting the promiscuous nature of ligand binding by multidrug efflux pumps. Direct interaction between (13)C-labeled TPP(+) and key residues within the EmrE dimer has been probed by through-space (13)C-(13)C correlation spectroscopy. This was made possible by the use of solid-state NMR enhanced by dynamic nuclear polarization (DNP) through which a 19-fold signal enhancement was achieved. Our data provide clear evidence for the long assumed direct interaction between substrates such as TPP(+) and the essential residue E14 in transmembrane helix 1. Our work also demonstrates the power of DNP-enhanced solid-state NMR at low temperatures for the study for secondary transporters, which are highly challenging for conventional NMR detection. PMID:24047229

Ong, Yean Sin; Lakatos, Andrea; Becker-Baldus, Johanna; Pos, Klaas M; Glaubitz, Clemens

2013-10-11

58

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

59

Solid-state NMR studies of form I of atorvastatin calcium.  

PubMed

Solid-state (13)C, (19)F, and (15)N magic angle spinning NMR studies of Form I of atorvastatin calcium are reported, including chemical shift tensors of all resolvable carbon sites and fluorine sites. The complete (13)C and (19)F chemical shift assignments are given based on an extensive analysis of (13)C-(1)H HETCOR and (13)C-(19)F HETCOR results. The solid-state NMR data indicate that the asymmetric unit of this material contains two atorvastatin molecules. A possible structure of Form I of atorvastatin calcium (ATC-I), derived from solid-state NMR data and density functional theory calculations of various structures, is proposed for this important active pharmaceutical ingredient (API). PMID:22360640

Wang, Wei David; Gao, Xudong; Strohmeier, Mark; Wang, Wei; Bai, Shi; Dybowski, Cecil

2012-03-09

60

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

61

On the acidity of saponite materials: a combined HRTEM, FTIR, and solid-state NMR study.  

PubMed

Acid clays were prepared by exchanging a synthetic saponite in HCl solutions of different concentration (0.01 and 1M, respectively). A combined experimental approach (XRD, HRTEM, N2 physisorption, solid-state MAS NMR, and TGA) was used to investigate on the structural, morphological, and textural features of the samples treated under mild and strong acid conditions. FTIR spectroscopy of adsorbed probe molecules with different basicity (e.g., CO and NH3) was used to monitor the surface acid properties and acid site distribution. XRD and SS-MAS NMR indicated that the activation under mild acid conditions does not alter the clay structure, while a deep modification of the saponite framework occurred after ion exchange in 1 M HCl solution. The presence of porous amorphous silica phase after treatment under strong acid conditions was confirmed by TEM inspection augmented by SS-MAS NMR and FTIR spectroscopy. N2 and Ar physisorption measurements suggested that cavitation phenomena occurred in saponite structure. N2 physisorption confirmed that the porosity and surface area of the samples are strongly modified upon strong acid treatment. FTIR spectroscopy of adsorbed NH3 pointed out that the H-exchange in mild conditions increased the number of surface Brønsted acid sites. Conversely, these sites are significantly depleted after treatment under strong acid conditions. The use of CO as a FTIR probe molecule, which is applied for the first time to study synthetic acid clays, allowed to monitor distribution and strength of Brønsted acid sites, whose acidity is similar to that of strong acid zeolites. The Al-OH sites with medium acidity are also found in acid-activated saponites. The distribution of strong and medium acid sites is strictly dependent on the acid conditions adopted. PMID:18251562

Bisio, C; Gatti, G; Boccaleri, E; Marchese, L; Bertinetti, L; Coluccia, S

2008-02-06

62

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

SciTech Connect

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

Hosseini, S.

1992-07-21

63

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

SciTech Connect

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

Hosseini, S.

1992-07-21

64

Interactions of lipopolysaccharide with lipid membranes, raft models - a solid state NMR study.  

PubMed

Lipopolysaccharide (LPS) is a major component of the external leaflet of bacterial outer membranes, key pro-inflammatory factor and an important mediator of host-pathogen interactions. In host cells it activates the complement along with a pro-inflammatory response via a TLR4-mediated signalling cascade and shows preference for cholesterol-containing membranes. Here, we use solid state (13)C and (31)P MAS NMR to investigate the interactions of LPS from three bacterial species, Brucella melitensis, Klebsiella pneumoniae and Escherichia coli, with mixed lipid membranes, raft models. All endotoxin types are found to be pyrophosphorylated and Klebsiellar LPS is phosphonylated, as well. Carbon-13 MAS NMR indicates an increase in lipid order in the presence of LPS. Longitudinal (31)P relaxation, providing a direct probe of LPS molecular and segmental mobility, reveals a significant reduction in (31)P T1 times and lower molecular mobility in the presence of ternary lipid mixtures. Along with the ordering effect on membrane lipid, this suggests a preferential partitioning of LPS into ordered bilayer sphingomyelin/cholesterol-rich domains. We hypothesise that this is an important evolutionary drive for the selection of GPI-anchored raft-associated LPS-binding proteins as a first line of response to membrane-associated LPS. PMID:23567915

Ciesielski, Filip; Griffin, David C; Rittig, Michael; Moriyón, Ignacio; Bonev, Boyan B

2013-04-06

65

Proteorhodopsin: characterisation of 2D crystals by electron microscopy and solid state NMR.  

PubMed

Proteorhodopsin (PR) a recent addition to retinal type 1 protein family, is a bacterial homologue of archaeal bacteriorhodopsin. It was found to high abundance in gamma-proteobacteria in the photic zone of the oceans and has been shown to act as a photoactive proton pump. It is therefore involved in the utilisation of light energy for energy production within the cell. Based on data from biodiversity screens, hundreds of variants were discovered worldwide, which are spectrally tuned to the available light at different locations in the sea. Here, we present a characterisation of 2D crystals of the green variant of proteorhodopsin by electron microscopy and solid state NMR. 2D crystal formation with hexagonal protein packing was observed under a very wide range of conditions indicating that PR might be also closely packed under native conditions. A low-resolution 2D projection map reveals a ring-shaped oligomeric assembly of PR. The protein state was analysed by 15N MAS NMR on lysine, tryptophan and methionine labelled samples. The chemical shift of the protonated Schiff base was almost identical to non-crystalline preparations. All residues could be cross-polarised in non-frozen samples. Lee-Goldberg cross-polarisation has been used to probe protein backbone mobility. PMID:17964280

Shastri, Sarika; Vonck, Janet; Pfleger, Nicole; Haase, Winfried; Kuehlbrandt, Werner; Glaubitz, Clemens

2007-10-09

66

CARBON-13 NMR OR SOLID STATE HYDROCARBONS AND RELATED SUBSTANCES-FINAL REPORT  

SciTech Connect

CARBON-13 NMR OR SOLID STATE HYDROCARBONS AND RELATED SUBSTANCES-FINAL REPORT Abstract: During recent years we have been engaged in SSNMR (Solid State NMR) structural studies of unusual tetracyanoethylene compounds with unusually long bonds between four carbons centered on two electrons. The chemical shift tensors reflect these unusual atomic arrangements. Quantum chemistry predicts the strange tensor shifts. The three dimensional molecular structure may be determined in this manner. Despite significant advances in structural determination from powder diffraction data, NMR shift tensors argument the structural accuracy and also suggest initial trial structures. Mixtures of polymorphs are difficult to analyze with diffraction methods whereas the SSNMR methods are able to characterize such mixtures in one another’s presence. Spectroscopic developments in our laboratory include SSNMR INADEQUATE and FIREMAT methods. We have used these methods to study the 13C and 15N NMR explosive CL-20.

Grant, David M.

2007-08-16

67

Solid-state NMR triple-resonance backbone assignments in a protein  

Microsoft Academic Search

Triple-resonance solid-state NMR spectroscopy is demonstrated to sequentially assign the 13C' and 15N amide backbone resonances of adjacent residues in an oriented protein sample. The observed 13C' chemical shift frequency provides an orientational constraint complementary to those measured from the 1H and 15N amide resonances in double-resonance experiments.

Wee Meng Tan; Zhengtian Gu; Ana Carolina Zeri

1999-01-01

68

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

National Technical Information Service (NTIS)

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

S. Hosseini

1992-01-01

69

Investigation of Moisture Interaction with Cellulose Using Solid-State NMR  

Technology Transfer Automated Retrieval System (TEKTRAN)

The interaction of water with cellulose and its influence on the nuclear spin dynamics in Gossypium barbadense (Pima) cotton were investigated by 1H and 13C solid-state NMR techniques. 1H spin diffusion results indicate that water is present in multiple layers within the cotton fiber, each layer bei...

70

Magnetic field gradients in solid state magic angle spinning NMR.  

PubMed

Magnetic field gradients have proven useful in NMR for coherence pathway selection, diffusion studies, and imaging. Recently they have been combined with magic angle spinning to permit high-resolution measurements of semi-solids, where magic angle spinning averages any residual dipolar couplings and local variations in the bulk magnetic susceptibility. Here we show the first examples of coherence pathway selection by gradients in dipolar coupled solids. When the gradient evolution competes with dipolar evolution the experiment design must take into account both the strength of the dipolar couplings and the means to refocus it. Examples of both homonuclear and heteronuclear experiments are shown in which gradients have been used to eliminate the need for phase cycling. PMID:10527740

Maas, W E; Bielecki, A; Ziliox, M; Laukien, F H; Cory, D G

1999-11-01

71

Structure of a protein determined by solid-state magic-angle-spinning NMR spectroscopy  

NASA Astrophysics Data System (ADS)

The determination of a representative set of protein structures is a chief aim in structural genomics. Solid-state NMR may have a crucial role in structural investigations of those proteins that do not easily form crystals or are not accessible to solution NMR, such as amyloid systems or membrane proteins. Here we present a protein structure determined by solid-state magic-angle-spinning (MAS) NMR. Almost complete 13C and 15N resonance assignments for a micro-crystalline preparation of the ?-spectrin Src-homology 3 (SH3) domain formed the basis for the extraction of a set of distance restraints. These restraints were derived from proton-driven spin diffusion (PDSD) spectra of biosynthetically site-directed, labelled samples obtained from bacteria grown using [1,3-13C]glycerol or [2-13C]glycerol as carbon sources. This allowed the observation of long-range distance correlations up to ~7Å. The calculated global fold of the ?-spectrin SH3 domain is based on 286 inter-residue 13C-13C and six 15N-15N restraints, all self-consistently obtained by solid-state MAS NMR. This MAS NMR procedure should be widely applicable to small membrane proteins that can be expressed in bacteria.

Castellani, Federica; van Rossum, Barth; Diehl, Annette; Schubert, Mario; Rehbein, Kristina; Oschkinat, Hartmut

2002-11-01

72

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

73

Nutrient-dependent Structural Changes in S. aureus Peptidoglycan Revealed by Solid-State NMR Spectroscopy  

PubMed Central

The bacterial cell wall is essential to cell survival and is a major target of antibiotics. The main component of the bacterial cell wall is peptidoglycan, a cage-like macromolecule that preserves cellular integrity and maintains cell shape. The insolubility and heterogeneity of peptidoglycan pose a challenge to conventional structural analyses. Here we use solid-state NMR combined with specific isotopic labeling to probe a key structural feature of the Staphylococcus aureus peptidoglycan quantitatively and nondestructively. We observed that both the cell-wall morphology and the peptidoglycan structure are functions of growth stage in S. aureus synthetic medium (SASM). Specifically, S. aureus cells at stationary phase have thicker cell walls with non-uniformly thickened septa compared to cells in exponential phase and, remarkably, 12% (±2%) of the stems in their peptidoglycan do not have pentaglycine bridges attached. Mechanistically, we determined that these observations are triggered by the depletion of glycine in the nutrient medium, which is coincident with the start of the stationary phase, and that the production of the structurally altered peptidoglycan can be prevented by the addition of excess glycine. We also demonstrated that the structural changes primarily arise within newly synthesized peptidoglycan rather than through the modification of previously synthesized peptidoglycan. Collectively, our observations emphasize the plasticity in bacterial cell-wall assembly and the possibility to manipulate peptidoglycan structure with external stimuli.

Zhou, Xiaoxue; Cegelski, Lynette

2012-01-01

74

Cryogenic solid state NMR studies of fibrils of the Alzheimer's disease amyloid-? peptide: perspectives for DNP.  

PubMed

Dynamic Nuclear Polarization solid-state NMR holds the potential to enable a dramatic increase in sensitivity by exploiting the large magnetic moment of the electron. However, applications to biological solids are hampered in uniformly isotopically enriched biomacromolecules due to line broadening which yields a limited spectral resolution at cryogenic temperatures. We show here that high magnetic fields allow to overcome the broadening of resonance lines often experienced at liquid nitrogen temperatures. For a fibril sample of the Alzheimer's disease ?-amyloid peptide, we find similar line widths at low temperature and at room temperature. The presented results open new perspectives for structural investigations in the solid-state. PMID:23793606

Lopez del Amo, Juan-Miguel; Schneider, Dennis; Loquet, Antoine; Lange, Adam; Reif, Bernd

2013-06-22

75

Solid-state 19F-NMR analysis of 19F-labeled tryptophan in gramicidin A in oriented membranes.  

PubMed Central

The response of membrane-associated peptides toward the lipid environment or other binding partners can be monitored by solid-state NMR of suitably labeled side chains. Tryptophan is a prominent amino acid in transmembrane helices, and its (19)F-labeled analogues are generally biocompatible and cause little structural perturbation. Hence, we use 5F-Trp as a highly sensitive NMR probe to monitor the conformation and dynamics of the indole ring. To establish this (19)F-NMR strategy, gramicidin A was labeled with 5F-Trp in position 13 or 15, whose chi(1)/chi(2) torsion angles are known from previous (2)H-NMR studies. First, the alignment of the (19)F chemical shift anisotropy tensor within the membrane was deduced by lineshape analysis of oriented samples. Next, the three principal axes of the (19)F chemical shift anisotropy tensor were assigned within the molecular frame of the indole ring. Finally, determination of chi(1)/chi(2) for 5F-Trp in the lipid gel phase showed that the side chain alignment differs by up to 20 degrees from its known conformation in the liquid crystalline state. The sensitivity gain of (19)F-NMR and the reduction in the amount of material was at least 10-fold compared with previous (2)H-NMR studies on the same system and 100-fold compared with (15)N-NMR.

Grage, Stephan L; Wang, Junfeng; Cross, Timothy A; Ulrich, Anne S

2002-01-01

76

Probing Surface Charge Fluctuations with Solid-State Nanopores  

NASA Astrophysics Data System (ADS)

We identify a contribution to the ionic current noise spectrum in solid-state nanopores that exceeds all other noise sources in the frequency band 0.1-10 kHz. Experimental studies of the dependence of this excess noise on pH and electrolyte concentration indicate that the noise arises from surface charge fluctuations. A quantitative model based on surface functional group protonization predicts the observed behaviors and allows us to locally measure protonization reaction rates. This noise can be minimized by operating the nanopore at a deliberately chosen pH.

Hoogerheide, David P.; Garaj, Slaven; Golovchenko, Jene A.

2009-06-01

77

Protein Folding and Amyloid Formation: Good Questions for Solid State NMR  

NASA Astrophysics Data System (ADS)

Recent results from two ongoing projects will be described. These projects illustrate the expanding capability of solid state NMR spectroscopy to provide unique information about the molecular structure of complex biochemical systems that are of current interest in the biophysical and biomedical research communities. Methodological advances that facilitate progress on these projects will be discussed briefly. In the area of protein folding, we are using solid state NMR spectroscopy to characterize the distributions of molecular structures in unfolded and partially folded states of relatively simple model proteins. The measurements are carried out on frozen glassy solutions at low temperatures. Initial results for the chemical denaturation of the 35-residue helical protein HP35 show that unfolding does not occur by a simple two-state process and that local conformational distributions in the unfolded state are remarkably non-uniform. In the area of amyloid fibrils, we are using solid state NMR to develop experimentally-based models for the molecular structure of peptide fibrils associated with Alzheimer's disease and other amyloid diseases, and to develop an understanding of the interactions that stabilize amyloid fibril structures in general. The NMR data also reveal molecular-level polymorphism in amyloid fibrils, with implications for biomedical issues such as the etiological role of fibrils in amyloid diseases and the structural basis for strains in prion diseases.

Tycko, Robert

2005-03-01

78

Application of Solid-State Nuclear Magnetic Resonance (NMR) to the Study of Skin Hydration  

Microsoft Academic Search

The solid-state nuclear magnetic resonance (NMR) technique of carbon-13 cross-polarization\\/magic angle spinning (CP\\/MAS) has been successfully used to obtain high-resolution spectra of whole-thickness, hairy rat skin and to characterize the influence of hydration on the efficiency of cross-polarization and the proton spin-lattice relaxation time in the rotating frame (T1?H). Spectra obtained with hydrated samples, which were obtained with 50% more

Timothy Wiedmann

1988-01-01

79

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

Microsoft Academic Search

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

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

2001-01-01

80

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

PubMed

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

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

2013-08-30

81

Combined solid state and solution NMR studies of ?,?- 15 N labeled bovine rhodopsin  

Microsoft Academic Search

Rhodopsin is the visual pigment of the vertebrate rod photoreceptor cell and is the only member of the G protein coupled receptor\\u000a family for which a crystal structure is available. Towards the study of dynamics in rhodopsin, we report NMR-spectroscopic\\u000a investigations of ?,?-15N-tryptophan labeled rhodopsin in detergent micelles and reconstituted in phospholipids. Using a combination of solid state\\u000a 13C,15N-REDOR and

Karla Werner; Ines Lehner; Harpreet Kaur Dhiman; Christian Richter; Clemens Glaubitz; Harald Schwalbe; Judith Klein-Seetharaman; H. Gobind Khorana

2007-01-01

82

Protein dynamics by solid-state NMR: aromatic rings of the coat protein in fd bacteriophage.  

PubMed Central

The motions of the aromatic amino acids of the fd bacteriophage coat protein are described by solid-state 2H, 13C, and 15N NMR. Tryptophan-26 is immobile on time scales as slow as 10(3) HZ. The phenylalanine and tyrosine rings undergo 180 degree flips about the C beta--C gamma bond axis more often than 10(6) HZ as well as small-amplitude rapid motions in other directions.

Gall, C M; Cross, T A; DiVerdi, J A; Opella, S J

1982-01-01

83

Structures of Amyloid Fibrils and Protein Folding Intermediates: New Insights from Solid State NMR  

NASA Astrophysics Data System (ADS)

I will present recent results from two projects: (1) We are using a combination of solid state NMR techniques and electron microscopy techniques to develop full molecular models for amyloid fibrils formed by the beta-amyloid peptide of Alzheimer's disease and by other peptides and proteins. Amyloid fibrils are often polymorphic, so that the detailed molecular structure depends on growth conditions or other factors. I will describe two structural models for beta-amyloid fibrils with two distinct morphologies. I will also describe efforts to determine which fibril structure develops in the brains of Alzheimer's disease patients, and solid state NMR methods that contribute to our amyloid studies; (2) Structural properties of unfolded or partially folded states of proteins are not well understood. In principle, solid state NMR measurements on freeze-trapped samples can reveal site-specific, quantitative aspects of protein structures in unfolded states. I will describe experiments on thermodynamically unfolded states (i.e., denatured states) and on transient states that are trapped by freezing on the microsecond time scale. Both types of experiments reveal structural properties that are unanticipated and could not be detected by more conventional protein folding measurements.

Tycko, Robert

2009-03-01

84

LARGE SCALE PRODUCTION, PURIFICATION, AND 65CU SOLID STATE NMR OF AZURIN  

SciTech Connect

This paper details a way to produce azurin with an effi ciency over 10 times greater than previously described and demonstrates the fi rst solid state nuclear magnetic resonance spectrum of 65Cu(I) in a metalloprotein. A synthetic gene for azurin based upon the DNA sequence from Pseudomonas aeruginosa including the periplasmic targeting sequence was subcloned into a T7 overexpression vector to create the plasmid pGS-azurin, which was transformed into BL21 (DE3) competent cells. The leader sequence on the expressed protein causes it to be exported to the periplasmic space of Escherichia coli. Bacteria grown in a fermentation unit were induced to overexpress the azurin, which was subsequently purifi ed through an endosmotic shock procedure followed by high performance liquid chromatography (HPLC). 1,500 mg of azurin were purifi ed per liter of culture. 65Cu(II) was added to apo-azurin and then reduced. The 65Cu metal cofactor in azurin was observed with solid state nuclear magnetic resonance (NMR) to determine any structural variations that accompanied copper reduction. This is the fi rst solid state NMR spectra of a copper(I) metalloprotein. Analysis of the NMR spectra is being used to complement hypotheses set forth by x-ray diffraction and computational calculations of electron transfer mechanisms in azurin.

Gao, A.; Heck, R.W.

2008-01-01

85

Solid state NMR and pair distribution function studies of silicon electrodes for lithium-ion batteries  

NASA Astrophysics Data System (ADS)

The universally used negative electrode material in a LIB is carbon, because of its moderate capacity (372 mAhg-1 for graphite), cyclability and high rate capability. However, new, low cost, safe electrode materials with higher capacities are still urgently required for both portable and transportation applications. Silicon anodes are particularly attractive alternatives to carbon with extremely high gravimetric energy densities (3572 mAhg-1). Compared to graphite, silicon has a massive volumetric capacity of 8322 mAhcm-3 (calculated based on the original volume of silicon) which is approximately ten times that graphite. At room temperature, upon electrochemical lithiation, silicon undergoes a crystalline to amorphous phase transition forming a lithiated amorphous silicide phase. Unfortunately, due to the amorphous nature of the lithiated silicides, it is not possible to monitor all the structural changes that occur during lithium insertion/removal with conventional methods such as diffraction. The short range order of the amorphous materials remains unknown, preventing attempts to optimize performance based on electrochemical-structure correlations. In this work, a combination of local structure probes, ex-situ 7Li nuclear magnetic resonance (NMR) studies and pair distribution function (PDF) analysis of X-ray data was applied to investigate the changes in short range order that occur during the initial charge and discharge cycles. The distinct electrochemical profiles observed subsequent to the 1 st discharge have been shown to be associated with the formation of distinct amorphous lithiated silicide structures. A (de)lithiation model consisting of four different mechanisms, each being valid for regions of the charge or discharge process is proposed to explain the hysteresis and the steps in the electrochemical profile observed during lithiation and delithiation of Si. A spontaneous reaction of the fully lithiated lithium silicide with the electrolyte is directly observed in the in situ NMR experiments; this mechanism results in self-discharge, and potentially capacity loss. The rate of this self-discharge process is much slower when CMC (carboxymethylcellulose) is used as the binder. Previous work has shown that the electrochemical performance of nanoparticulate crystalline silicon is different from the bulk. The lithiation and delithiation mechanisms of nano-Si for lithium ion batteries are studied by using ex-situ solid state MAS NMR and PDF analysis. The main differences vs. bulk lithiation and delithiation are identified by characterizing the amorphous phases formed.

Key, Baris

86

Solid-state NMR and calorimetry of structural waters in helical peptides.  

PubMed

The peptide hydrates Gly-Gly-Val x 2H(2)O (GGV) and Gly-Ala-Leu x 3H(2)O (GAL) are known to adopt alpha-helical configurations containing waters of hydration in which each water is H-bonded to three or four peptide groups. Herein we report a thermodynamic and solid-state NMR ((2)H and (17)O) study of these peptides. From TGA and DSC, the average enthalpy per H-bond is 15 kJ/mol. The dynamics and average orientation of the hydrate are studied by powder and single-crystal (2)H NMR. Whereas waters that are shown by the X-ray structure to be coordinated by four hydrogen bonds do not yield observable (2)H NMR signals at room temperature, two of the three triply coordinated waters yield residual (2)H quadrupole coupling tensors characteristic of rapid 180 degrees flip motions and the orientation of the residual tensor is that expected from the X-ray structure-derived H-bonding pattern. At -65 degrees C, the flip motions of triply coordinated water in GGV slow into the (2)H NMR intermediate exchange regime whereas the tetrahedrally coordinated water approaches the slow-exchange limit and yields an observable NMR signal. Extensive isotope exchange between water vapor and crystalline GGV establishes the presence of additional hydrate dynamics and solid-state proton transfer along a chain of water-bridged protonated alpha-amino groups. PMID:11878990

Pometun, Maxim S; Gundusharma, Usha M; Richardson, John F; Wittebort, Richard J

2002-03-13

87

Characterization of Non-Innocent Metal Complexes Using Solid-State NMR Spectroscopy: o-Dioxolene Vanadium Complexes  

PubMed Central

51V solid-state NMR (SSNMR) studies of a series of non-innocent vanadium(V) catechol complexes have been conducted to evaluate the possibility that 51V 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 51V NMR chemical shifts cover a wide range from ?200 ppm to 400 ppm in solution and from ?219 to 530 ppm in the solid state. A linear correlation of 51V NMR isotropic solution and solid-state chemical shifts of complexes containing non-innocent ligands is observed. These experimental results provide the information needed for the application of 51V SSNMR spectroscopy in characterizing the electronic properties of a wide variety of vanadium-containing systems, and in particular those containing non-innocent ligands and that have chemical shifts outside the populated range of ?300 ppm 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 51V SSNMR experiments are a highly sensitive probe of subtle differences in electronic distribution and orbital occupancy in these compounds. Quantum chemical (DFT) calculations of NMR parameters for [VO(hshed)(Cat)] yield 51V CSA 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 the 51V 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 similar coordination chemistry as the vanadium catechol complexes.

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

2012-01-01

88

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

89

Combining insights from solid-state NMR and first principles calculation: applications to the 19F NMR of octafluoronaphthalene.  

PubMed

Advances in solid-state NMR methodology and computational chemistry are applied to the (19)F NMR of solid octafluoronaphthalene. It is demonstrated experimentally, and confirmed by density functional theory (DFT) calculations, that the spectral resolution in the magic-angle spinning spectrum is limited by the anisotropy of the bulk magnetic susceptibility (ABMS). This leads to the unusual observation that the resolution improves as the sample is diluted. DFT calculations provide assignments of each of the peaks in the (19)F spectrum, but the predictions are close to the limits of accuracy and correlation information from 2-D NMR is invaluable in confirming the assignments. The effects of non-Gaussian lineshapes on the use of 2-D NMR for mapping correlations of spectral frequencies (e.g. due to the ABMS) are also discussed. PMID:17492102

Robbins, Andrew J; Ng, William T K; Jochym, Dominik; Keal, Thomas W; Clark, Stewart J; Tozer, David J; Hodgkinson, Paul

2007-03-27

90

An Active Photoreceptor Intermediate Revealed by In Situ Photoirradiated Solid-State NMR Spectroscopy  

PubMed Central

A novel, to our knowledge, in situ photoirradiation system for solid-state NMR measurements is improved and demonstrated to successfully identify the M-photointermediate of pharaonis phoborhodopsin (ppR or sensory rhodopsin II), that of the complex with transducer (ppR/pHtrII), and T204A mutant embedded in a model membrane. The 13C NMR signals from [20-13C]retinal-ppR and ppR/pHtrII revealed that multiple M-intermediates with 13-cis, 15-anti retinal configuration coexisted under the continuously photoirradiated condition. NMR signals observed from the photoactivated retinal provide insights into the process of photocycle in the ppR/pHtrII complex.

Tomonaga, Yuya; Hidaka, Tetsurou; Kawamura, Izuru; Nishio, Takudo; Ohsawa, Kazuhiro; Okitsu, Takashi; Wada, Akimori; Sudo, Yuki; Kamo, Naoki; Ramamoorthy, Ayyalusamy; Naito, Akira

2011-01-01

91

Spatially Resolved Solid-State (1)H NMR for Evaluation of Gradient-Composition Polymeric Libraries.  

PubMed

Polyurethane libraries consisting of films with composition gradients of aliphatic polyisocyanate and hydroxy-terminated polyacrylate resin were characterized using methods of (1)H NMR microimaging (i.e., magnetic resonance imaging, (MRI)) and solid-state NMR. Molecular mobilities and underlying structural information were extracted as a function of the relative content of each of the two components. Routine NMR microimaging using the spin-echo sequence only allows investigations of transverse relaxation of magnetization at echo times >2 ms. A single-exponential decay was found, which is likely due to free, noncross-linked polymer chains. The mobility of these chains decreases with increasing content of the aliphatic polyisocyanate. The concept of a 1D NMR profiler is introduced as a novel modality for library screening, which allows the convenient measurement of static solid-state NMR spectra as a function of spatial location along a library sample that is repositioned in the rf coil between experiments. With this setup the complete transverse relaxation function was measured using Bloch decays and spin echoes. For all positions within the gradient-composition film, relaxation data consisted of at least three components that were attributed to a rigid highly cross-linked resin, an intermediate cross-linked but mobile constituent, and the highly mobile free polymer chains (the latter is also detectable by MRI). Analysis of this overall relaxation function measured via Bloch decays and spin echoes revealed only minor changes in the mobilities of the individual fractions. Findings with respect to the most mobile components are consistent with the results obtained by NMR microimaging. The major effect is the significant increase in the rigid-component fraction with the addition of the hydroxy-terminated polyacrylate resin. PMID:22676634

Leisen, Johannes; Gomez, Ismael J; Roper, John A; Meredith, J Carson; Beckham, Haskell W

2012-06-20

92

Freezing point depression of water in phospholipid membranes: a solid-state NMR study.  

PubMed

Lipid-water interaction plays an important role in the properties of lipid bilayers, cryoprotectants, and membrane-associated peptides and proteins. The temperature at which water bound to lipid bilayers freezes is lower than that of free water. Here, we report a solid-state NMR investigation on the freezing point depression of water in phospholipid bilayers in the presence and absence of cholesterol. Deuterium NMR spectra at different temperatures ranging from -75 to + 10 degrees C were obtained from fully (2)H2O-hydrated POPC (1-palmitoyl-2-oleoylphosphatidylcholine) multilamellar vesicles (MLVs), prepared with and without cholesterol, to determine the freezing temperature of water and the effect of cholesterol on the freezing temperature of water in POPC bilayers. Our 2H NMR experiments reveal the motional behavior of unfrozen water molecules in POPC bilayers even at temperatures significantly below 0 degrees C and show that the presence of cholesterol further lowered the freezing temperature of water in POPC bilayers. These results suggest that in the presence of cholesterol the fluidity and dynamics of lipid bilayers can be retained even at very low temperatures as exist in the liquid crystalline phase of the lipid. Therefore, bilayer samples prepared with a cryoprotectant like cholesterol should enable the performance of multidimensional solid-state NMR experiments to investigate the structure, dynamics, and topology of membrane proteins at a very low temperature with enhanced sample stability and possibly a better sensitivity. Phosphorus-31 NMR data suggest that lipid bilayers can be aligned at low temperatures, while 15N NMR experiments demonstrate that such aligned samples can be used to enhance the signal-to-noise ratio of is 15N chemical shift spectra of a 37-residue human antimicrobial peptide, LL-37. PMID:18991419

Lee, Dong-Kuk; Kwon, Byung Soo; Ramamoorthy, Ayyalusamy

2008-12-01

93

Solid-State NMR Studies of HIV-1 Capsid Protein Assemblies  

PubMed Central

In mature HIV-1 virions, a 26.6 kDa CA protein is assembled into a characteristic cone shaped core (capsid) that encloses the RNA viral genome. The assembled capsid structure is best described by a fullerene cone model that is made up from a hexameric lattice containing a variable number of CA pentamers, thus allowing for closure of tubular or conical structures. In this report, we present a solid-state NMR analysis of the wild type HIV-1 CA protein, prepared as conical and spherical assemblies that are stable and are not affected by magic angle spinning of the samples at frequencies between 10 and 25 kHz. Multidimensional homo- and heteronuclear correlation spectra of CA assemblies of uniformly 13C,15N-labelled CA exhibit narrow lines, indicative of conformational homogeneity of the protein in these assemblies. For the conical assemblies, partial residue-specific resonance assignments were obtained. Analysis of the NMR spectra recorded for the conical and spherical assemblies indicates that the CA protein structure is not significantly different in the different morphologies. The present results demonstrate that the assemblies of CA protein are amenable to detailed structural analysis by solid-state NMR spectroscopy.

Han, Yun; Ahn, Jinwoo; Concel, Jason; Byeon, In-Ja L.; Gronenborn, Angela M.; Yang, Jun; Polenova, Tatyana

2010-01-01

94

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

95

Motion-adapted pulse sequences for oriented sample (OS) solid-state NMR of biopolymers.  

PubMed

One of the main applications of solid-state NMR is to study the structure and dynamics of biopolymers, such as membrane proteins, under physiological conditions where the polypeptides undergo global motions as they do in biological membranes. The effects of NMR radiofrequency irradiations on nuclear spins are strongly influenced by these motions. For example, we previously showed that the MSHOT-Pi4 pulse sequence yields spectra with resonance line widths about half of those observed using the conventional pulse sequence when applied to membrane proteins undergoing rapid uniaxial rotational diffusion in phospholipid bilayers. In contrast, the line widths were not changed in microcrystalline samples where the molecules did not undergo global motions. Here, we demonstrate experimentally and describe analytically how some Hamiltonian terms are susceptible to sample motions, and it is their removal through the critical ??2 Z-rotational symmetry that confers the "motion adapted" property to the MSHOT-Pi4 pulse sequence. This leads to the design of separated local field pulse sequence "Motion-adapted SAMPI4" and is generalized to an approach for the design of decoupling sequences whose performance is superior in the presence of molecular motions. It works by cancelling the spin interaction by explicitly averaging the reduced Wigner matrix to zero, rather than utilizing the 2? nutation to average spin interactions. This approach is applicable to both stationary and magic angle spinning solid-state NMR experiments. PMID:24006989

Lu, George J; Opella, Stanley J

2013-08-28

96

Toxin-induced conformational changes in a potassium channel revealed by solid-state NMR  

NASA Astrophysics Data System (ADS)

The active site of potassium (K+) channels catalyses the transport of K+ ions across the plasma membrane-similar to the catalytic function of the active site of an enzyme-and is inhibited by toxins from scorpion venom. On the basis of the conserved structures of K+ pore regions and scorpion toxins, detailed structures for the K+ channel-scorpion toxin binding interface have been proposed. In these models and in previous solution-state nuclear magnetic resonance (NMR) studies using detergent-solubilized membrane proteins, scorpion toxins were docked to the extracellular entrance of the K+ channel pore assuming rigid, preformed binding sites. Using high-resolution solid-state NMR spectroscopy, here we show that high-affinity binding of the scorpion toxin kaliotoxin to a chimaeric K+ channel (KcsA-Kv1.3) is associated with significant structural rearrangements in both molecules. Our approach involves a combined analysis of chemical shifts and proton-proton distances and demonstrates that solid-state NMR is a sensitive method for analysing the structure of a membrane protein-inhibitor complex. We propose that structural flexibility of the K+ channel and the toxin represents an important determinant for the high specificity of toxin-K+ channel interactions.

Lange, Adam; Giller, Karin; Hornig, Sönke; Martin-Eauclaire, Marie-France; Pongs, Olaf; Becker, Stefan; Baldus, Marc

2006-04-01

97

Triple oscillating field technique for accurate distance measurements by solid-state NMR.  

PubMed

We present a new concept for homonuclear dipolar recoupling in magic-angle-spinning (MAS) solid-state NMR experiments which avoids the problem of dipolar truncation. This is accomplished through the introduction of a new NMR pulse sequence design principle: the triple oscillating field technique. We demonstrate this technique as an efficient means to accomplish broadband dipolar recoupling of homonuclear spins, while decoupling heteronuclear dipolar couplings and anisotropic chemicals shifts and retaining influence from isotropic chemical shifts. In this manner, it is possible to synthesize Ising interaction (2IzSz) Hamiltonians in homonuclear spin networks and thereby avoid dipolar truncation--a serious problem essentially all previous homonuclear dipolar recoupling experiments suffer from. Combination of this recoupling concept with rotor assisted dipolar refocusing enables easy readout of internuclear distances through comparison with analytical Fresnel curves. This forms the basis for a new class of solid-state NMR experiments with potential for structure analysis of uniformly 13C labeled proteins through accurate measurement of 13C-13C internuclear distances. The concept is demonstrated experimentally by measurement of C alpha-C', C beta-C', and C gamma-C' internuclear distances in powder samples of the amino acids L-alanine and L-threonine. PMID:18190225

Khaneja, Navin; Nielsen, Niels Chr

2008-01-01

98

Experiments optimized for magic angle spinning and oriented sample solid-state NMR of proteins.  

PubMed

Structure determination by solid-state NMR of proteins is rapidly advancing as a result of recent developments of samples, experimental methods, and calculations. There are a number of different solid-state NMR approaches that utilize stationary samples, aligned samples, or magic angle spinning of unoriented "powder" samples, and depending on the sample and the experimental method they can emphasize the measurement of distances or angles, ideally both, as sources of structural constraints. Multidimensional correlation spectroscopy of low-gamma nuclei such as (15)N and (13)C is an important step for making resonance assignments and measurements of angular restraints in membrane proteins. However, the efficiency of coherence transfer predominantly depends upon the strength of the dipole-dipole interaction, and this can vary from site to site and between sample alignments, for example, during the mixing of (13)C and (15)N magnetization in stationary aligned and in magic angle spinning samples. Here, we demonstrate that the efficiency of polarization transfer can be improved by using adiabatic demagnetization and remagnetization techniques on stationary aligned samples, and proton assisted insensitive nuclei cross-polarization in magic angle sample spinning samples. The adiabatic cross-polarization technique provides an alternative mechanism for spin-diffusion experiments correlating (15)N/(15)N and (15)N/(13)C chemical shifts over large distances. Improved efficiency in cross-polarization with 40-100% sensitivity enhancements is observed in proteins and single crystals, respectively. We describe solid-state NMR experimental techniques that are optimal for membrane proteins in liquid crystalline phospholipid bilayers under physiological conditions. The techniques are illustrated with data from single crystals both of peptides and of membrane proteins in phospholipid bilayers. PMID:24044695

Das, Bibhuti B; Lin, Eugene C; Opella, Stanley J

2013-10-07

99

Sensitivity and resolution enhancement of oriented solid-state NMR: Application to membrane proteins.  

PubMed

Oriented solid-state NMR (O-ssNMR) spectroscopy is a major technique for the high-resolution analysis of the structure and topology of transmembrane proteins in native-like environments. Unlike magic angle spinning (MAS) techniques, O-ssNMR spectroscopy requires membrane protein preparations that are uniformly oriented (mechanically or magnetically) so that anisotropic NMR parameters, such as dipolar and chemical shift interactions, can be measured to determine structure and orientation of membrane proteins in lipid bilayers. Traditional sample preparations involving mechanically aligned lipids often result in short relaxation times which broaden the (15)N resonances and encumber the manipulation of nuclear spin coherences. The introduction of lipid bicelles as membrane mimicking systems has changed this scenario, and the more favorable relaxation properties of membrane protein (15)N and (13)C resonances make it possible to develop new, more elaborate pulse sequences for higher spectral resolution and sensitivity. Here, we describe our recent progress in the optimization of O-ssNMR pulse sequences. We explain the theory behind these experiments, demonstrate their application to small and medium size proteins, and describe the technical details for setting up these new experiments on the new generation of NMR spectrometers. PMID:24160761

Gopinath, T; Mote, Kaustubh R; Veglia, Gianluigi

2013-08-12

100

Probing Access Resistance of Solid-state Nanopores with a Scanning Probe Microscope Tip  

PubMed Central

An apparatus that integrates solid-state nanopore ionic current measurement with a Scanning Probe Microscope has been developed. When a micrometer-scale scanning probe tip is near a voltage biased nanometer-scale pore (10–100 nm), the tip partially blocks the flow of ions to the pore and increases the pore access resistance. The apparatus records the current blockage caused by the probe tip and the location of the tip simultaneously. By measuring the current blockage map near a nanopore as a function of the tip position in 3D space in salt solution, we estimate the relative pore resistance increase due to the tip, ?R/R0, as a function of the tip location, nanopore geometry, and salt concentration. The amplitude of ?R/R0 also depends on the ratio of the pore length to its radius as Ohm’s law predicts. When the tip is very close to the pore surface, ~10 nm, our experiments show that ?R/R0 depends on salt concentration as predicted by the Poisson and Nernst-Planck equations. Furthermore, our measurements show that ?R/R0 goes to zero when the tip is about five times the pore diameter away from the center of the pore entrance. The results in this work not only demonstrate a way to probe the access resistance of nanopores experimentally, they also provide a way to locate the nanopore in salt solution, and open the door to future nanopore experiments for detecting single biomolecules attached to a probe tip.

Hyun, Changbae; Rollings, Ryan

2012-01-01

101

Dipolar recoupling in solid state NMR by phase alternating pulse sequences  

PubMed Central

We describe some new developments in the methodology of making heteronuclear and homonuclear recoupling experiments in solid state NMR insensitive to rf-inhomogeneity by phase alternating the irradiation on the spin system every rotor period. By incorporating delays of half rotor periods in the pulse sequences, these phase alternating experiments can be made ? encoded. The proposed methodology is conceptually different from the standard methods of making recoupling experiments robust by the use of ramps and adiabatic pulses in the recoupling periods. We show how the concept of phase alternation can be incorporated in the design of homonuclear recoupling experiments that are both insensitive to chemical-shift dispersion and rf-inhomogeneity.

Lin, J.; Bayro, M.; Griffin, R. G.; Khaneja, N.

2009-01-01

102

High precision measurement of the polarization in solid state polarized targets using NMR  

NASA Astrophysics Data System (ADS)

The factors are reviewed that can affect the systematic uncertainties in CW-NMR measurements of the polarization in solid state polarized targets. The main problem with large signals, typically obtained with protons, is non-linearity arising from failure of the constant RF drive current assumption. The non-linearity can be reduced by operation at lower than normal signal levels. With the much smaller size deuteron signals, a limiting factor may be the instability of the background signal generated by the resonant length cable, used in the standard system. A new system is demonstrated, using non-resonant length cables, which is expected to reduce these uncertainties to a low level.

Court, G. R.; Houlden, M. A.; Bültmann, S.; Crabb, D. G.; Day, D. B.; Prok, Y. A.; Penttila, S. I.; Keith, C. D.

2004-07-01

103

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

Microsoft Academic Search

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

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

2002-01-01

104

Solid-state NMR study of geopolymer prepared by sol-gel chemistry  

NASA Astrophysics Data System (ADS)

Geopolymers are a new class of materials formed by the condensation of aluminosilicates and silicates obtained from natural minerals or industrial wastes. In this work, the sol-gel method is used to synthesize precursor materials for the preparation of geopolymers. The geopolymer samples prepared by our synthetic route have been characterized by a series of physical techniques, including Fourier-transform infrared, X-ray diffraction, and multinuclear solid-state NMR. The results are very similar to those obtained for the geopolymers prepared from natural kaolinite. We believe that our synthetic approach can offer a good opportunity for the medical applications of geopolymer.

Tsai, Yi-Ling; Hanna, John V.; Lee, Yuan-Ling; Smith, Mark E.; Chan, Jerry C. C.

2010-12-01

105

Using chemical shift anisotropy to resolve isotropic signals in solid-state NMR  

NASA Astrophysics Data System (ADS)

A key problem in solid-state NMR is resolving overlapping isotropic signals. We present here a two-dimensional method which can enable sites with the same isotropic chemical shift to be distinguished according to their chemical shift anisotropy and asymmetry. The method involves correlating sideband spectra at different effective spinning rates using CSA-amplification pulse sequences. The resulting two-dimensional correlation pattern allows very accurate determination of the chemical shift principal values in addition to the recovery of parameters for two overlapping patterns which allows the resolution of overlapping signals.

Ironside, Matthew S.; Stein, Robin S.; Duer, Melinda J.

2007-09-01

106

Two-dimensional correlation of solid state and liquid state NMR using a laser temperature jump  

NASA Astrophysics Data System (ADS)

Solid state nuclear magnetic resonance (NMR) spectra and the corresponding liquid state spectra have been interrelated through two-dimensional experiments with a fast temperature jump during the mixing time. This jump must, as a minimum requirement, be shorter than the relevant spin lattice relaxation times, and was implemented using a CO2 laser heater. As the first demonstration of this experiment we report a 2D H-1 solid-liquid spectrum of camphor. Suggested applications of future 2D temperature jump experiments include studies of reversible chemical reactions, reorientational dynamics, phase behavior, and magnetic and electrical properties.

Ferguson, David B.; Krawietz, Thomas R.; Haw, James F.

1994-10-01

107

Application of Solid-State NMR Restraint Potentials in Membrane Protein Modeling  

PubMed Central

We have developed a set of orientational restraint potentials for solid-state NMR observables including 15N chemical shift and 15N-1H dipolar coupling. Torsion angle molecular dynamics simulations with available experimental 15N chemical shift and 15N-1H dipolar coupling as target values have been performed to determine orientational information of four membrane proteins and to model the structures of some of these systems in oligomer states. The results suggest that incorporation of the orientational restraint potentials into molecular dynamics provides an efficient means to the determination of structures that optimally satisfy the experimental observables without an extensive geometrical search.

Lee, Jinhyuk; Chen, Jianhan; Brooks, Charles L.; Im, Wonpil

2008-01-01

108

Mechanisms of Peptide-Induced Pore Formation in Lipid Bilayers Investigated by Oriented 31P Solid-State NMR Spectroscopy  

PubMed Central

There is a considerable interest in understanding the function of antimicrobial peptides (AMPs), but the details of their mode of action is not fully understood. This motivates extensive efforts in determining structural and mechanistic parameters for AMP’s interaction with lipid membranes. In this study we show that oriented-sample 31P solid-state NMR spectroscopy can be used to probe the membrane perturbations and -disruption by AMPs. For two AMPs, alamethicin and novicidin, we observe that the majority of the lipids remain in a planar bilayer conformation but that a number of lipids are involved in the peptide anchoring. These lipids display reduced dynamics. Our study supports previous studies showing that alamethicin adopts a transmembrane arrangement without significant disturbance of the surrounding lipids, while novicidin forms toroidal pores at high concentrations leading to more extensive membrane disturbance.

Bertelsen, Kresten; Dorosz, Jerzy; Hansen, Sara Krogh; Nielsen, Niels Chr.; Vosegaard, Thomas

2012-01-01

109

Homogeneous nanoparticles to enhance the efficiency of a hydrophobic drug, anti-hyperlipidemic Probucol, characterized by solid-state NMR  

PubMed Central

A low absorption in the gastrointestinal tract of hydrophobic pharmaceutical compounds in use today considerably limits their bioavailability and therefore they are taken in large doses in order to reach the therapeutic plasma concentration, which inevitably results in undesired side effects. In this study, we demonstrate a new nanoparticle approach to overcome this problem and our experimental results show that this approach has a high efficiency of drug loading and is easily adaptable to industrial scale. Characterization of nanoparticles containing a cholesterol-lowering hydrophobic drug, probucol, using a variety of biophysical techniques revealed higher homogeneity of these particles compared to those prepared using other approaches. Intermolecular interactions of these nanoparticles are probed at a high-resolution by magic angle spinning solid-state NMR experiments.

Io, Takeshi; Fukami, Toshiro; Yamamoto, Kazutoshi; Suzuki, Toyofumi; Xu, Jiadi; Tomono, Kazuo; Ramamoorthy, Ayyalusamy

2009-01-01

110

Structure determination in "shiftless" solid state NMR of oriented protein samples.  

PubMed

An efficient formalism for calculating protein structures from oriented-sample NMR data in the torsion-angle space is presented. Angular anisotropies of the NMR observables are treated by utilizing an irreducible spherical basis of rotations. An intermediate rotational transformation is introduced that greatly speeds up structural fitting by rendering the dependence on the torsion angles ? and ? in a purely diagonal form. Back-calculation of the simulated solid-state NMR spectra of protein G involving 15N chemical shift anisotropy (CSA), and 1H-15N and 1H?-13C? dipolar couplings was performed by taking into account non-planarity of the peptide linkages and experimental uncertainty. Even a relatively small (to within 1 ppm) random variation in the CSA values arising from uncertainties in the tensor parameters yields the RMSD's of the back-calculated structures of more than 10 Å. Therefore, the 15N CSA has been substituted with heteronuclear dipolar couplings which are derived from the highly conserved bond lengths and bond angles associated with the amino-acid covalent geometry. Using the additional 13C?-15N and 13C'-15N dipolar couplings makes it possible to calculate protein structures entirely from "shiftless" solid-state NMR data. With the simulated "experimental" uncertainty of 15 Hz for protein G and 120 Hz for a helical hairpin derived from bacteriorhodopsin, back-calculation of the synthetic dipolar NMR spectra yielded a converged set of solutions. The use of distance restraints dramatically improves structural convergence even if larger experimental uncertainties are assumed. PMID:21741286

Yin, Yuanyuan; Nevzorov, Alexander A

2011-07-07

111

Regenerated silk fibers: Structural studies and solid state NMR techniques for efficient multiple distance determinations in proteins  

NASA Astrophysics Data System (ADS)

Material Science is the science of understanding the relationship between the molecular level structure of a material and its macroscopic properties. Such research requires both the ability to determine molecular structure and the ability to control and modify the molecular structure. The present research into silks, especially the dragline silk from the spider Nephila clavipes , is occurring at a time when these two criteria are beginning to be met for proteins like spider silk. Genetic engineering has evolved to the point where material scientists have full control over the primary sequence of amino acids that comprise proteins. In addition, solid state nuclear magnetic resonance (NMR) techniques exist which allow us to probe molecular structure. This work applies solid state NMR to the study of the structure of silk fibers. In particular, we focus on techniques of fiber regeneration from solution. The purpose is not only to develop the techniques by which genetically engineered fibers could be spun into fibers for mass production but also as a tool into fundamental silk research. Results on these regenerated fibers show a correlation between the fraction of the silk's alanine residues which are in the ?-sheet conformation and the ultimate tensile strength of the fibers. In addition, in a clever mating of the fiber regeneration technique and the solid state NMR distance measurement experiment, rotational echo double resonance (REDOR), we investigate the supramolecular topology of the alanine ?-sheet crystals. Even though the REDOR technique has failings for the complicated ISn spin systems found in the silk samples, a qualitative analysis does indicate that the ?-sheet crystals are intermolecular. Finally, we investigate a new class of REDOR-like experiments which are designed to overcome the failings of REDOR in ISn spin systems. Experimental data is shown to validate these ideas. An alternate pulse sequence is also introduced and verified with experimental data. This pulse sequence highlights the similarities between multiple quantum NMR and REDOR. From this connection, we name this new class of experiments Multiple Quantum-REDOR. These experiments should allow for efficient simultaneous multiple distance determinations in proteins.

Liivak, Oskar

2000-09-01

112

Solid-State NMR-Based Approaches for Supramolecular Structure Elucidation.  

PubMed

Supramolecular chemistry provides structural and conformational information about complexes formed from multiple molecules. While the molecule is held together by strong intramolecular contacts like covalent bonds, supramolecular structures can be further stabilized by weaker or transient intermolecular interactions. These interactions can confer a great diversity and sensitivity to exogenous factors like temperature, pressure, or ionic strength to multimolecular arrangements. Solid-state nuclear magnetic resonance (ssNMR) can provide atomic-scale structural and dynamical information in highly disordered or heterogeneous biological systems, even in complex environments such as cellular membranes or whole cells. In these systems, the molecule of interest no longer exists as a separate unit, but it entangles with its surroundings in a dynamic interplay. Researchers have long accounted for the complexity of these intermolecular arrangements through a rather phenomenological description. But now the focus is shifting toward a detailed understanding of supramolecular structure at atomic resolution, constantly expanding our understanding of the stunning influence of the environment. In this Account, we discuss how ssNMR can help to dissect the remarkable interplay between intra- and intermolecular interactions. We describe biochemical and spectroscopic strategies that tailor ssNMR spectroscopic methods to the challenge of supramolecular structure investigation. In particular, we consider protein-protein interactions or the protein-membrane topology, and we review recent applications of these techniques. Furthermore, we summarize methods for integrating ssNMR information with other experimental techniques or computational methods, and we offer perspectives on how this overall information allows us to target increasingly large and intricate supramolecular structures of biomolecules. Advancements in ssNMR methodology and instrumentation, including the incorporation of signal enhancement methods such as dynamic nuclear polarization will further increase the potential of ssNMR spectroscopy, and together with additional developments in the field of NMR-hybrid strategies, ssNMR may become an ideal tool to study the heterogeneous, dynamic, and often transient nature of molecular interactions in complex biological systems. PMID:23586937

Weingarth, Markus; Baldus, Marc

2013-04-15

113

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

114

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

115

A solid-state NMR investigation of the structure of mesoporous silica nanoparticle supported rhodium catalysts  

SciTech Connect

A detailed study of the chemical structure of mesoporous silica catalysts containing rhodium ligands and nanoparticles (RhP-MSN) was carried out by multi-dimensional solid-state NMR techniques. The degree of functionalization of the rhodium-phosphinosilyl complex to the surface of the RhP-MSN channels was determined by {sup 29}Si NMR experiments. The structural assignments of the rhodium-phosphinosilyl complex were unambiguously determined by employing the novel, indirectly detected heteronuclear correlation ({sup 13}C-{sup 1}H and {sup 31}P-{sup 1}H idHETCOR) techniques, which indicated that oxidation of the attached phosphinosilyl groups and detachment of Rh was enhanced upon syngas conversion.

Rapp, Jennifer; Huang, Yulin; Natella, Michael; Cai, Yang; Lin, Victor S.-Y.; Pruski, Marek

2009-01-04

116

Quantitative structural characterization of POSS and octavinyl-POSS nanocomposites by solid state NMR.  

PubMed

The ratio between two different (29)Si atoms in chloromethylphenyl isobutyl Polyhedral Oligomeric Silsesquioxane (POSS) was determined based on the quantitative cross polarization (QCP) (Shu et al., Chem. Phys. Lett. 462 (2008) 125) in solid-state NMR. For a (29)Si/(1)H spin system, cross polarization and depolarization together with the reciprocity relation were performed with optimized experimental conditions. It saves considerable experimental time compared to the (29)Si direct polarization experiment. The same method was further applied to octavinyl-POSS nanocomposites containing perfluoropolyether (PFPE) for deriving directly and accurately the average numbers of reacted vinyl groups, which may not be obtained by combining FTIR and solution (1)H NMR. In principle, the aforementioned method proves to be valuable in quantitative characterization of silicon related structures in bulk materials. PMID:22503875

Zhao, Huipeng; Shu, Jie; Chen, Qun; Zhang, Shanmin

2012-02-21

117

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

PubMed

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

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

2009-09-02

118

The rehydration of metakaolinite to kaolinite: Evidence from solid-state NMR and cognate techniques  

SciTech Connect

The authors have studied the process of rehydroxylation of metakaolinite to kaolinite by {sup 27}Al and {sup 29}Si MAS NMR in tandem with Fourier transform infrared spectroscopy, powder X-ray diffraction, thermogravimetric analysis, specific surface area measurement, atomic absorption spectrophotometry, and electron microscopy. The efficiency of the process strongly depends on temperature. The reaction is initiated at the edges of metakaolinite particles and is followed by diffusion of the water into their bulk. Regions of the metakaolinite structure, which locally retain the symmetry of kaolinite, act as nuclei for the reconstitution of kaolinite particles. The latter grown perpendicular to the c{sup *} axis and their edges are parallel to those of metakaolinite, showing that rehydroxylation is a topotactic solid-state process. {sup 27}Al and {sup 29}Si MAS NMR reveal that metakaolinite is an ill-defined mixture of amorphous silica nd alumina, and can be transformed into kaolinite by a correct choice of experimental conditions.

Rocha, J.; Klinowski, J. (Univ. of Cambridge (England)); Adams, J.M. (ECC International Limited, Cornwall (England))

1990-12-01

119

[sup 29]Si solid state NMR study of tricalcium silicate and cement hydration at high temperature  

SciTech Connect

Oilwell cementing involves the placement of a cement slurry in the annulus between the metal casing and the geological formation. Its principal functions are to isolate the different zones within the wellbore and to support the casing at each stage of drilling. [sup 29]Si high resolution solid state NMR has been used to follow the hydration kinetics of class G Portland cement and of its major component: tricalcium silicate Ca[sub 3]SiO[sub 5] (C[sub 3]S). Samples were hydrothermally synthesized at temperatures between 60 and 120C; hydration was stopped at selected reaction times, from 30 minutes to 14 days, by the acetone-ether method of water-removing. [sup 29]Si NMR spectra of hydrates clearly show that, in silicate chains, the ratio between the silicon atoms of end groups and those of middle groups depends not only on the time of hydration, but also on the synthesis temperature.

Masse, S.; Zanni, H. (URA CNRS, Paris (France). Lab. de Physique et Mecanique des Milieux Heterogenes Univ. Pierre et Marie Curie, Paris (France)); Lecourtier, J.; Roussel, J.C.; Rivereau, A. (Inst. Francais du Petrole, Rueil Malmaison (France))

1993-09-01

120

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

121

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

SciTech Connect

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

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

1990-06-12

122

Peptide Conformation and Supramolecular Organization in Amylin Fibrils: Constraints from Solid State NMR  

PubMed Central

The 37-residue amylin peptide, also known as islet amyloid polypeptide, forms fibrils that are the main peptide or protein component of amyloid that develops in the pancreas of type 2 diabetes patients. Amylin also readily forms amyloid fibrils in vitro that are highly polymorphic under typical experimental conditions. We describe a protocol for the preparation of synthetic amylin fibrils that exhibit a single predominant morphology, which we call a striated ribbon, in electron microscope and atomic force microscope images. Solid state nuclear magnetic resonance (NMR) measurements on a series of isotopically labeled samples indicate a single molecular structure within the striated ribbons. We use scanning transmission electron microscopy and several types of one-dimensional and two-dimensional solid state NMR techniques to obtain constraints on the peptide conformation and supramolecular structure in these amylin fibrils, and derive molecular structural models that are consistent with the experimental data. The basic structural unit in amylin striated ribbons, which we call the protofilament, contains four-layers of parallel ?-sheets, formed by two symmetric layers of amylin molecules. The molecular structure of amylin protofilaments in striated ribbons closely resembles the protofilament in amyloid fibrils with similar morphology formed by the 40-residue ?-amyloid peptide that is associated with Alzheimer's disease.

Luca, Sorin; Yau, Wai-Ming; Leapman, Richard; Tycko, Robert

2008-01-01

123

Experimental aspects in acquisition of wide bandwidth solid-state MAS NMR spectra of low-? nuclei with different opportunities on two commercial NMR spectrometers  

NASA Astrophysics Data System (ADS)

The acquisition and different appearances observed for wide bandwidth solid-state MAS NMR spectra of low-? nuclei, using 14N as an illustrative nucleus and employing two different commercial spectrometers (Varian, 14.1 T and Bruker, 19.6 T), have been compared/evaluated and optimized from an experimental NMR and an electronic engineering point of view, to account for the huge differences in these spectra. The large differences in their spectral appearances, employing the recommended/standard experimental set-up for the two different spectrometers, are shown to be associated with quite large differences in the electronic design of the two types of preamplifiers, which are connected to their respective probes through a 50 ? cable, and are here completely accounted for. This has led to different opportunities for optimum performances in the acquisition of nearly ideal wide bandwidth spectra for low-? nuclei on the two spectrometers by careful evaluation of the length for the 50 ? probe-to-preamp cable for the Varian system and appropriate changes to the bandwidth (Q) of the NMR probe used on the Bruker spectrometer. Earlier, we reported quite distorted spectra obtained with Varian Unity INOVA spectrometers (at 11.4 and 14.1 T) in several exploratory wide bandwidth 14N MAS NMR studies of inorganic nitrates and amino acids. These spectra have now been compared/evaluated with fully analyzed 14N MAS spectra correspondingly acquired at 19.6 T on a Bruker spectrometer. It is shown that our upgraded version of the STARS simulation/iterative-fitting software is capable of providing identical sets for the molecular spectral parameters and corresponding fits to the experimental spectra, which fully agree with the electronic measurements, despite the highly different appearances for the MAS NMR spectra acquired on the Varian and Bruker spectrometers.

Jakobsen, Hans J.; Bildsøe, Henrik; Gan, Zhehong; Brey, William W.

2011-08-01

124

Comprehensive Solid-State NMR Characterization of Electronic Structure in Ditechnetium Heptoxide  

SciTech Connect

A relativistic density functional description of the electronic structure of Tc2O7 has been evaluated by comparison with solid state 99Tc and 17O NMR spectroscopic data (the former isotope a weak beta-emitter). Every site in the molecule can be populated by a nucleus with favorable NMR characteristics, providing the rare opportunity to obtain a comprehensive set of chemical shift and electric field gradient tensors for a small molecular transition metal oxide. NMR parameters were computed for the central molecule of a (Tc2O7)17 cluster, using standard ZORA optimized all-electron QZ4P basis sets for the central molecule and DZ basis sets for surrounding atoms. The magnitudes of the predicted tensor principal values appear to be uniformly larger than observed experimentally, but discrepancies were within the accuracy of the approximation methods used. The convergence of calculated and measured NMR data suggests that the theoretical analysis has validity for the quantitative understanding of structural, magnetic, and chemical properties of Tc(VII) oxides. The William R. Wiley Environmental Molecular Sciences Laboratory is a U.S. Department of Energy (DOE) national scientific user facility located at Pacific Northwest National Laboratory (PNNL) in Richland, Washington. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

Cho, Herman M.; De Jong, Wibe A.; Sattelberger, Alfred P.; Poineau, Frederic; Czerwinski, Ken

2010-09-29

125

Solid-state NMR characterization of Wilkinson's catalyst immobilized in mesoporous SBA-3 silica.  

PubMed

The Wilkinson's catalyst [RhCl(PPh(3))(3)] has been immobilized inside the pores of amine functionalized mesoporous silica material SBA-3 and The structure of the modified silica surface and the immobilized rhodium complex was determined by a combination of different solid-state NMR methods. The successful modification of the silica surface was confirmed by (29)Si CP-MAS NMR experiments. The presence of the T(n) peaks confirms the successful functionalization of the support and shows the way of binding the organic groups to the surface of the mesopores. (31)P-(31)P J-resolved 2D MAS NMR experiments were conducted in order to characterize the binding of the immobilized catalyst to the amine groups of the linkers attached to the silica surface. The pure catalyst exhibits a considerable (31)P-(31)P J-coupling, well resolvable in 2D MAS NMR experiments. This J-coupling was utilized to determine the binding mode of the catalyst to the linkers on the silica surface and the number of triphenylphosphine ligands that are replaced by coordination bonds to the amine groups. From the absence of any resolvable (31)P-(31)P J-coupling in off-magic-angle-spinning experiments, as well as slow-spinning MAS experiments, it is concluded, that two triphenylphosphine ligands are replaced and that the catalyst is bonded to the silica surface through two linker molecules. PMID:20446319

Grünberg, Anna; Yeping, Xu; Breitzke, Hergen; Buntkowsky, Gerd

2010-06-18

126

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

127

Solid-state NMR analysis of membrane proteins and protein aggregates by proton detected spectroscopy  

PubMed Central

Solid-state NMR has emerged as an important tool for structural biology and chemistry, capable of solving atomic-resolution structures for proteins in membrane-bound and aggregated states. Proton detection methods have been recently realized under fast magic-angle spinning conditions, providing large sensitivity enhancements for efficient examination of uniformly labeled proteins. The first and often most challenging step of protein structure determination by NMR is the site-specific resonance assignment. Here we demonstrate resonance assignments based on high-sensitivity proton-detected three-dimensional experiments for samples of different physical states, including a fully-protonated small protein (GB1, 6 kDa), a deuterated microcrystalline protein (DsbA, 21 kDa), a membrane protein (DsbB, 20 kDa) prepared in a lipid environment, and the extended core of a fibrillar protein (?-synuclein, 14 kDa). In our implementation of these experiments, including CONH, CO(CA)NH, CANH, CA(CO)NH, CBCANH, and CBCA(CO)NH, dipolar-based polarization transfer methods have been chosen for optimal efficiency for relatively high protonation levels (full protonation or 100 % amide proton), fast magic-angle spinning conditions (40 kHz) and moderate proton decoupling power levels. Each H–N pair correlates exclusively to either intra- or inter-residue carbons, but not both, to maximize spectral resolution. Experiment time can be reduced by at least a factor of 10 by using proton detection in comparison to carbon detection. These high-sensitivity experiments are especially important for membrane proteins, which often have rather low expression yield. Proton-detection based experiments are expected to play an important role in accelerating protein structure elucidation by solid-state NMR with the improved sensitivity and resolution.

Nieuwkoop, Andrew J.; Berthold, Deborah A.; Comellas, Gemma; Sperling, Lindsay J.; Tang, Ming; Shah, Gautam J.; Brea, Elliott J.; Lemkau, Luisel R.

2012-01-01

128

Applications of Solid State NMR to the Study of Molecular Structure  

NASA Astrophysics Data System (ADS)

This thesis illustrates several applications of dilute spin I = 1over2 solid state nmr spectroscopy to the study of molecular structure in systems of chemical interest. Specifically, the compounds studied include benzylideneaniline and several related imines, the first stable iminophosphenium cation containing a N,P triple bond and several tetracyclines. The first two applications describe the use of dipolar-chemical shift nmr of "isolated" spin-pairs to fully characterize chemical shift tensors. For example, the carbon and nitrogen shift tensors of the C=N linkage of the Schiff base benzylideneaniline have been completely specified. The most shielded principal component of both carbon and nitrogen shift tensors is approximately perpendicular to the imine fragment. For the imine carbon, the intermediate component of the shift tensor is directed approximately along the C=N bond whereas the corresponding component of the nitrogen shift tensor is oriented along the direction of the nitrogen lone pair. Examination of the nitrogen chemical shift parameters for several related imines suggests that variations in the least shielded principal component are mainly responsible for changes in the nitrogen shieldings in the imine system. For the N,P moiety of the iminophosphenium cation, the most shielded principal component of both nitrogen and phosphorus tensors is oriented along the N,P bond axis. Comparison of both shift tensors with those of related compounds suggests that the electronic environment surrounding the N,P moiety is similar to other systems containing a formal triple bond. The final application section demonstrates the utility of high-resolution ^{13} C and ^{15}N cp/mas nmr for studying the molecular structure of solid tetracycline antibiotics. Comparison of ^{15} C chemical shifts in the solid state to those determined in (CD_3)_2SO solutions indicates for the first time that the structural integrity of the A ring of the tetracyclines is maintained in solution.

Curtis, Ronald Dean

129

Topological, geometric, and chemical order in materials: insights from solid-state NMR.  

PubMed

Unlike the long-range order of ideal crystalline structures, local order is an intrinsic characteristic of real materials and often serves as the key to the tuning of their properties and their final applications. Although researchers can easily assess local ordering using two-dimensional imaging techniques with resolution that approaches the atomic level, the diagnosis, description, and qualification of local order in three dimensions is much more challenging. Solid-state nuclear magnetic resonance (NMR) and its panel of continually developing instruments and methods enable the local, atom-selective characterization of structures and assemblies ranging from the atomic to the nanometer length scales. By making use of the indirect J-coupling that distinguishes chemical bonds, researchers can use solid-state NMR to characterize a variety of materials, ranging from crystalline compounds to amorphous or glassy materials. In crystalline compounds showing some disorder, we describe and distinguish the contributions of topology, geometry, and local chemistry in ways that are consistent with X-ray diffraction and computational approaches. We give examples of materials featuring either chemical disorder in a topological order or topological disorder with local chemical order. For glasses, we show that we can separate geometric and chemical contributions to the local order by identifying structural motifs with a viewpoint that extends from the atomic scale up to the nanoscale. As identified by solid state NMR, the local structure of amorphous materials or glasses consists of well-identified structural entities up to at least the nanometer scale. Instead of speaking of disorder, we propose a new description for these structures as a continuous assembly of locally defined structures, an idea that draws on the concept of locally favored structures (LFS) introduced by Tanaka and coworkers. This idea provides a comprehensive picture of amorphous structures based on fluctuations of chemical composition and structure over different length scales. We hope that these local or molecular insights will allow researchers to consider key questions related to nucleation and crystallization, as well as chemically (spinodal decomposition) or density-driven (polyamorphism) phase separation, which could lead to future applications in a variety of materials. PMID:23883113

Massiot, Dominique; Messinger, Robert J; Cadars, Sylvian; Deschamps, Michaël; Montouillout, Valerie; Pellerin, Nadia; Veron, Emmanuel; Allix, Mathieu; Florian, Pierre; Fayon, Franck

2013-07-24

130

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

131

Solid state NMR study of SEI formation in lithium ion batteries  

NASA Astrophysics Data System (ADS)

Recently, rechargeable lithium ion batteries, which offer high energy density and long cycle life, are in great demand as power sources for our mobile electronic society. The formation of a solid electrolyte interphase (SEI) on the surface of electrodes in lithium ion batteries plays an essential role in their performance. This thesis presents solid state NMR and MAS NMR results on the SEI, which contribute to our understanding of SEI formation on both cathodes and anodes. This thesis is organized as following: Chapter 1 surveys the history of batteries and the challenges to further development of the lithium ion battery. Fundamental aspects and SEI formation mechanisms are also included in Chapter l. Chapter 2 deals with the principles and experimental techniques of solid state NMR. Chapter 3 presents studies of SEI formation on anode and cathode in lithium ion batteries using electrochemical impedance spectroscopy (EIS) and NMR. The results provide EIS and NMR evidence that cells containing electrolytes with high EC content display less irreversible capacity after high temperature storage. The irreversible capacity is attributed to SEI growth on electrode surfaces. NMR results on cathodes, on the other hand, imply that the presence of Ni in the cathode may reduce cell performance due to the oxidation of Ni 3+ to Ni4+. Our simulations show that a lower EC/DMC ratio is associated with a smaller SEI intensity for the cathode and higher intensity for the anode. Chapter 4 discusses the effect of temperature on SEI formation on anodes and cathodes. NMR measurements show that MCMB graphite based anodes exhibit high stability no chemical shift is evident over a wide temperature range. On cathodes, however, NMR does reveal changes in SEI intensity as a function of temperature. These changes are believed to be the result of decomposition of the SEI. Evidently, then, changes in the performance of the cell as a factor of temperature are, at least in part, due to changes in the SEI with temperature. In Chapter 5 we report on the use of NMR to study the effect of electrolyte/solvent and electrode structure on SEI formation. The intensity of the SEI in a cell containing LiBOB electrolyte with EC and DEC is greater than that in a cell with LiPF6 electrolyte with EC and DMC. This implies that the cell containing LiBOB electrolyte with EC and DEC is more stable. From the analysis of NMR of the cathode, it was found that it is easier to form SEI in layered structure cathode than in a spinel structure, suggesting that spinel structure materials may be better choices as cathode in lithium ion batteries. Evidently, then, the choice of electrolyte/solvent materials and electrode materials are key factors in determining the performance of lithium ion batteries.

Zhao, Dachun

132

Solid State CARBON-13 NMR Studies of the Morphology and Orientational Order of Polymer Fibers  

NASA Astrophysics Data System (ADS)

A fundamental understanding of the mechanism of fiber formation requires a detailed knowledge of fiber morphology. However due to the limitation of current techniques, the crystallization behavior is still not fully understood. Modern solid state NMR techniques enable one to approach this subject from different aspects. In this work we conducted detailed studies of the morphology of as-spun PET (poly (ethylene terephthalate)) and gel-spun PE (poly (ethylene)) fibers by ^{13}C CP/MAS (Cross Polarization/Magic Angle Spinning) NMR technique. The presence of multiple-component resonance lineshapes allows one to calculate the true population of various morphological components, after correcting for pin relaxation effects. From these NMR measurements, two different models for PET and PE polymer systems have been proposed. We have also employed and further developed the advanced two-dimensional rotor synchronized MAS (2D ROSMAS) technique to study the orientational order of various morphological components. A wide range of orientational order is clearly displayed on 2D spectra for samples under different fabrication conditions. A regression simulation program has been used to deduce the order parameter used in computing the orientational distribution function (ODF) for each component. Our results for the first time provide unique information about orientational order and morphology at the molecular level, thereby providing a much more complete basis for theoretical modeling of polymer system.

Tzou, Der-Lii Mike

133

Solid-state NMR and EPR study of fluorinated carbon nanofibers  

NASA Astrophysics Data System (ADS)

Carbon nanofibers were fluorinated in two manners, in pure fluorine gas (direct fluorination) and with a fluorinating agent (TbF4 during the so-called controlled fluorination). The resulting fluorinated nanofibers have been investigated by solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). This underlines that the fluorination mechanisms differ since a (CF)n structural type is obtained, whatever the temperature, with the controlled reaction, whereas, during the direct process, a (C2F)n type is formed over a wide temperature range. Through a careful characterization of the products, i.e. density of dangling bonds (as internal paramagnetic centers), structural type (acting on molecular motion) and specific surface area (related to the amount of physisorbed O2), the effect of atmospheric oxygen molecules on the spin-lattice nuclear relaxation has been underlined.

Zhang, Wei; Dubois, Marc; Guérin, Katia; Hamwi, André; Giraudet, Jérôme; Masin, Francis

2008-08-01

134

A Comparison of NCO and NCA Transfer Methods for Biological Solid-State NMR Spectroscopy  

PubMed Central

Three different techniques (adiabatic passage Hartman-Hahn cross-polarization, optimal control designed pulses, and EXPORT) are compared for transferring 15N magnetization to 13C in solid-state NMR experiments under magic-angle-spinning conditions. We demonstrate that, in comparison to adiabatic passage Hartman-Hahn cross-polarization, optimal control transfer pulses achieve similar or better transfer efficiencies for uniformly-13C,15N labelled samples and are generally superior for samples with non-uniform labeling schemes (such as 1,3- and 2-13C glycerol labeling). In addition, the optimal control pulses typically use substantially lower average RF field strengths and are more robust with respect to experimental variation and RF inhomogeneity. Consequently, they are better suited for demanding samples.

Loening, Nikolaus M.; Bjerring, Morten; Nielsen, Niels Chr.; Oschkinat, Hartmut

2011-01-01

135

Solid-state NMR evidence for inequivalent GvpA subunits in gas vesicles.  

PubMed

Gas vesicles are organelles that provide buoyancy to the aquatic microorganisms that harbor them. The gas vesicle shell consists almost exclusively of the hydrophobic 70-residue gas vesicle protein A, arranged in an ordered array. Solid-state NMR spectra of intact collapsed gas vesicles from the cyanobacterium Anabaena flos-aquae show duplication of certain gas vesicle protein A resonances, indicating that specific sites experience at least two different local environments. Interpretation of these results in terms of an asymmetric dimer repeat unit can reconcile otherwise conflicting features of the primary, secondary, tertiary, and quaternary structures of the gas vesicle protein. In particular, the asymmetric dimer can explain how the hydrogen bonds in the beta-sheet portion of the molecule can be oriented optimally for strength while promoting stabilizing aromatic and electrostatic side-chain interactions among highly conserved residues and creating a large hydrophobic surface suitable for preventing water condensation inside the vesicle. PMID:19232353

Sivertsen, Astrid C; Bayro, Marvin J; Belenky, Marina; Griffin, Robert G; Herzfeld, Judith

2009-02-14

136

An amyloid organelle, solid-state NMR evidence for cross-? assembly of gas vesicles.  

PubMed

Functional amyloids have been identified in a wide range of organisms, taking on a variety of biological roles and being controlled by remarkable mechanisms of directed assembly. Here, we report that amyloid fibrils constitute the ribs of the buoyancy organelles of Anabaena flos-aquae. The walls of these gas-filled vesicles are known to comprise a single protein, GvpA, arranged in a low pitch helix. However, the tertiary and quaternary structures have been elusive. Using solid-state NMR correlation spectroscopy we find detailed evidence for an extended cross-? structure. This amyloid assembly helps to account for the strength and amphiphilic properties of the vesicle wall. Buoyancy organelles thus dramatically extend the scope of known functional amyloids. PMID:22147705

Bayro, Marvin J; Daviso, Eugenio; Belenky, Marina; Griffin, Robert G; Herzfeld, Judith

2011-12-06

137

Solid-State NMR Characterization of Autofluorescent Fibrils Formed by the Elastin-Derived Peptide GVGVAGVG  

PubMed Central

The characterization of the molecular structure and physical properties of self-assembling peptides is an important aspect of optimizing their utility as scaffolds for biomaterials and other applications. Here we report the formation of autofluorescent fibrils by an octapeptide (GVGVAGVG) derived via a single amino acid substitution in one of the hydrophobic repeat elements of human elastin. This is the shortest and most well-defined peptide so far reported to exhibit intrinsic fluorescence in the absence of a discrete fluorophore. Structural characterization by FTIR and solid-state NMR reveals a predominantly ?-sheet conformation for the peptide in the fibrils, which are likely assembled in an amyloid-like cross-? structure. Investigation of dynamics and the effects of hydration on the peptide are consistent with a rigid, water excluded structure, which has implications for the likely mechanism of intrinsic fibril fluorescence.

2011-01-01

138

Solid-state NMR study of geopolymer prepared by sol-gel chemistry  

SciTech Connect

Geopolymers are a new class of materials formed by the condensation of aluminosilicates and silicates obtained from natural minerals or industrial wastes. In this work, the sol-gel method is used to synthesize precursor materials for the preparation of geopolymers. The geopolymer samples prepared by our synthetic route have been characterized by a series of physical techniques, including Fourier-transform infrared, X-ray diffraction, and multinuclear solid-state NMR. The results are very similar to those obtained for the geopolymers prepared from natural kaolinite. We believe that our synthetic approach can offer a good opportunity for the medical applications of geopolymer. -- Graphical abstract: Geopolymer prepared by the sol-gel route has the same spectroscopic properties as the sample prepared from the natural kaolinite. Display Omitted

Tsai, Yi-Ling [Department of Chemistry, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan ROC (China); Hanna, John V. [Department of Physics, The University of Warwick, Coventry CV4 7AL (United Kingdom); Lee, Yuan-Ling, E-mail: yuanlinglee@ntu.edu.t [Graduate Institute of Clinical Dentistry, National Taiwan University and Hospital, No. 1, Changde Street, Taipei 10048, Taiwan ROC (China); Smith, Mark E., E-mail: M.E.Smith.1@warwick.ac.u [Department of Physics, The University of Warwick, Coventry CV4 7AL (United Kingdom); Chan, Jerry C.C., E-mail: chanjcc@ntu.edu.t [Department of Chemistry, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan ROC (China)

2010-12-15

139

Multiple quantum solid-state NMR indicates a parallel, not antiparallel, organization of ?-sheets in Alzheimer's ?-amyloid fibrils  

PubMed Central

Senile plaques associated with Alzheimer's disease contain deposits of fibrils formed by 39- to 43-residue ?-amyloid peptides with possible neurotoxic effects. X-ray diffraction measurements on oriented fibril bundles have indicated an extended ?-sheet structure for Alzheimer's ?-amyloid fibrils and other amyloid fibrils, but the supramolecular organization of the ?-sheets and other structural details are not well established because of the intrinsically noncrystalline, insoluble nature of amyloid fibrils. Here we report solid-state NMR measurements, using a multiple quantum (MQ) 13C NMR technique, that probe the ?-sheet organization in fibrils formed by the full-length, 40-residue ?-amyloid peptide (A?1–40). Although an antiparallel ?-sheet organization often is assumed and is invoked in recent structural models for full-length ?-amyloid fibrils, the MQNMR data indicate an in-register, parallel organization. This work provides site-specific, atomic-level structural constraints on full-length ?-amyloid fibrils and applies MQNMR to a significant problem in structural biology.

Antzutkin, Oleg N.; Balbach, John J.; Leapman, Richard D.; Rizzo, Nancy W.; Reed, Jennifer; Tycko, Robert

2000-01-01

140

Preparation of uniformly isotope labeled KcsA for solid state NMR: expression, purification, reconstitution into liposomes and functional assay.  

PubMed

We report the expression, purification, liposome reconstitution and functional validation of uniformly (13)C and (15)N isotope labeled KcsA, a bacterial potassium channel that has high homology with mammalian channels, for solid-state NMR studies. The expression and purification is optimized for an average yield of ?35-40mg/L of M9 media in a time-efficient way. The protein purity is confirmed by gel electrophoresis and the protein concentration is quantified by UV-vis absorption spectroscopy. Protocols to efficiently reconstitute KcsA into liposomes are also presented. The presence of liposomes is confirmed by cryo-electron microscopy images and the effect of magic angle spinning on liposome packing is shown. High-resolution solid-state NMR spectra of uniformly isotope labeled KcsA in these liposomes reveal that our protocol yields to a very homogenous KcsA sample with high signal to noise and several well-resolved residues in NMR spectra. Electrophysiology of our samples before and after solid-state NMR show that channel function and selectivity remain intact after the solid-state NMR. PMID:23916531

Bhate, Manasi P; Wylie, Benjamin J; Thompson, Ameer; Tian, Lin; Nimigean, Crina; McDermott, Ann E

2013-08-01

141

Solid state NMR method development and studies of biological and biomimetic nanocomposites  

SciTech Connect

This thesis describes application and development of advanced solid-state nuclear magnetic resonance techniques for complex materials, in particular organic-inorganic nanocomposites and thermoelectric tellurides. The apatite-collagen interface, essential for understanding the biomineralization process in bone and engineering the interface for controlled bio-mimetic synthesis and optimized mechanical properties, is buried within the nanocomposite of bone. We used multinuclear solid-state NMR to study the composition and structure of the interface. Citrate has been identified as the main organic molecule strongly bound to the apatite surface with a density of 1/(2 nm){sup 2}, covering 1/6 of the total surface area in bovine bone. Citrate provides more carboxylate groups, one of the key functional groups found to affect apatite nucleation and growth, than all the non-collagenous proteins all together in bone; thus we propose that citrate stabilizes apatite crystals at a very small thickness of {approx}3 nm (4 unit cells) to increase bone fracture tolerance. The hypothesis has been confirmed in vitro by adding citrate in the bio-mimetic synthesis of polymerhydroxyapatite nanocomposites. The results have shown that the size of hydroxyapatite nanocrystals decreases as increasing citrate concentration. With citrate concentrations comparable to that in body fluids, similar-sized nanocrystals as in bone have been produced. Besides the dimensions of the apatite crystals, the composition of bone also affects its biofunctional and macroscopic mechanical properties; therefore, our team also extended its effort to enhance the inorganic portion in our bio-mimetic synthesis from originally 15 wt% to current 50 wt% compared to 65 wt% in bovine bone, by using Lysine-Leucine hydroxyapatite nucleating diblock co-polypeptide, which forms a gel at very low concentration. In this thesis, various advanced solid state NMR techniques have been employed to characterize nanocomposites. Meanwhile, we have developed new methods to achieve broadband high resolution NMR and improve the accuracy of inter-nuclear distance measurements involving quadrupolar spins. Broadband high resolution NMR of spin-1/2 nuclei has been accomplished by the adaptation of the magic angle turning (MAT) method to fast magic angle spinning, termed fast MAT, by solving technical problems such as off resonance effects. Fast MAT separates chemical shift anisotropy and isotropic chemical shifts over a spectral range of {approx}1.8 {gamma}B{sub 1} without significant distortions. Fast MAT {sup 125}Te NMR has been applied to study technologically important telluride materials with spectra spreading up to 190 kHz. The signal-to-noise ratio of the spectra is significantly improved by using echo-matched Gaussian filtering in offline data processing. The accuracy of the measured distances between spin-1/2 and quadrupolar nuclei with methods such as SPIDER and REAPDOR has been improved by compensating for the fast longitudinal quadrupolar relaxation on the sub-millisecond with a modified S{sub 0} pulse sequence. Also, the T1Q effect on the spin coherence and its spinning speed dependency has been explored and documented with analytical and numerical simulations as well as experimental measurements.

Hu, Yanyan

2011-02-07

142

Characterization of sinking particles from the northwest Mediterranean Sea using advanced solid-state NMR  

NASA Astrophysics Data System (ADS)

Sinking particles are the major transporter of organic carbon from surface to the deep ocean, and their chemical composition changes dramatically with depth. However, the exact mechanism controlling the chemical transformation as particles sink is not well understood, and little detail is known about the structural changes. This is mainly due to the paucity of techniques available to analyze the major macromolecular components of sinking particles. Here we applied advanced solid-state NMR techniques, including cross polarization/magic angle spinning (CPMAS), direct polarization/magic angle spinning (DPMAS), two-dimensional 1H- 13C heteronuclear correlation (2D HETCOR) and 1H T 1 inversion recovery, on sinking particles collected in the northwest Mediterranean Sea. The CPMAS 13C NMR spectrum of the 200-m particles is significantly different from that of the DPMAS 13C NMR spectrum: CPMAS overestimates the NCH and CHO groups, but underestimates the aliphatic components, which is attributed to the high mobility of polymethylene units. Thus DPMAS is more suitable for quantifying organic composition of sinking particles. Using 2D HETCOR with 1H spin diffusion, we estimated that the size of domains (similar structural entities either physically or chemically grouped together) in the 200-m sinking particles can be as large as tens of nanometers. The results of CPMAS 13C NMR and 1H inversion recovery on sinking particles from 200, 520 and 920 m indicate that the macromolecular heterogeneity observed in surface particles virtually disappears as particles sink into the deep ocean. This suggests that the macromolecular components at depth are different in structural composition than those in surface waters, and may be compositionally homogenized as particles sink.

Liu, Zhanfei; Mao, Jingdong; Peterson, Michael L.; Lee, Cindy; Wakeham, Stuart G.; Hatcher, Patrick G.

2009-02-01

143

Conformational Disorder of Membrane Peptides Investigated from Solid-State NMR Linewidths and Lineshapes  

PubMed Central

A challenge in the application of solid-state NMR spectroscopy to membrane peptides and proteins is the relatively broad linewidths compared to solution NMR spectra. To understand the linewidth contributions to membrane protein NMR spectra, we have measured the inhomogeneous and homogeneous linewidths of several well-studied membrane peptides under immobilized conditions. 13C T2 relaxation times of uniformly 13C-labeled residues show that the homogeneous linewidths of the peptides are comparable to those of crystalline model compounds under identical 1H decoupling and magic-angle-spinning conditions, indicating that the homogeneous linewidths are determined by conformation-independent factors, including residual dipolar coupling, J coupling and intrinsic T2 relaxation. However, the membrane peptides exhibit larger apparent linewidths than the crystalline compounds, indicating conformational disorder. A cationic cell-penetrating peptide, the human immunodeficiency virus TAT, exhibits the largest apparent linewidths, which are about 5-fold larger than the homogeneous linewidths, while the transmembrane helix of the influenza M2 peptide and the ?-hairpin antimicrobial peptide PG-1 show moderately larger apparent linewidths than the crystalline compounds. These results are consistent with the random coil nature of the TAT peptide, which contrasts with the intramolecularly hydrogen-bonded M2 and PG-1. Cross peak lineshapes of 2D double-quantum correlation spectra show that the conformational disorder can occur at the residue level and can result from three origins: lipid-peptide interaction, intrinsic conformational disorder encoded in the amino acid sequence, and sidechain rotameric averaging. A particularly important lipid-peptide interaction for cationic membrane peptides is guanidinium-phosphate ion pair interaction. Thus, NMR linewidths and lineshapes are useful for understanding the conformational disorder of membrane peptides and proteins.

Su, Yongchao; Hong, Mei

2011-01-01

144

SIMPSON: a general simulation program for solid-state NMR spectroscopy.  

PubMed

A computer program for fast and accurate numerical simulation of solid-state NMR experiments is described. The program is designed to emulate a NMR spectrometer by letting the user specify high-level NMR concepts such as spin systems, nuclear spin interactions, RF irradiation, free precession, phase cycling, coherence-order filtering, and implicit/explicit acquisition. These elements are implemented using the Tcl scripting language to ensure a minimum of programming overhead and direct interpretation without the need for compilation, while maintaining the flexibility of a full-featured programming language. Basically, there are no intrinsic limitations to the number of spins, types of interactions, sample conditions (static or spinning, powders, uniaxially oriented molecules, single crystals, or solutions), and the complexity or number of spectral dimensions for the pulse sequence. The applicability ranges from simple 1D experiments to advanced multiple-pulse and multiple-dimensional experiments, series of simulations, parameter scans, complex data manipulation/visualization, and iterative fitting of simulated to experimental spectra. A major effort has been devoted to optimizing the computation speed using state-of-the-art algorithms for the time-consuming parts of the calculations implemented in the core of the program using the C programming language. Modification and maintenance of the program are facilitated by releasing the program as open source software (General Public License) currently at http://nmr.imsb.au.dk. The general features of the program are demonstrated by numerical simulations of various aspects for REDOR, rotational resonance, DRAMA, DRAWS, HORROR, C7, TEDOR, POST-C7, CW decoupling, TPPM, F-SLG, SLF, SEMA-CP, PISEMA, RFDR, QCPMG-MAS, and MQ-MAS experiments. PMID:11097821

Bak, M; Rasmussen, J T; Nielsen, N C

2000-12-01

145

SIMPSON: A general simulation program for solid-state NMR spectroscopy  

NASA Astrophysics Data System (ADS)

A computer program for fast and accurate numerical simulation of solid-state NMR experiments is described. The program is designed to emulate a NMR spectrometer by letting the user specify high-level NMR concepts such as spin systems, nuclear spin interactions, RF irradiation, free precession, phase cycling, coherence-order filtering, and implicit/explicit acquisition. These elements are implemented using the Tel scripting language to ensure a minimum of programming overhead and direct interpretation without the need for compilation, while maintaining the flexibility of a full-featured programming language. Basicly, there are no intrinsic limitations to the number of spins, types of interactions, sample conditions (static or spinning, powders, uniaxially oriented molecules, single crystals, or solutions), and the complexity or number of spectral dimensions for the pulse sequence. The applicability ranges from simple ID experiments to advanced multiple-pulse and multiple-dimensional experiments, series of simulations, parameter scans, complex data manipulation/visualization, and iterative fitting of simulated to experimental spectra. A major effort has been devoted to optimizing the computation speed using state-of-the-art algorithms for the time-consuming parts of the calculations implemented in the core of the program using the C programming language. Modification and maintenance of the program are facilitated by releasing the program as open source software (General Public License) currently at http://nmr.imsb.au.dk. The general features of the program are demonstrated by numerical simulations of various aspects for REDOR, rotational resonance, DRAMA, DRAWS, HORROR, C7, TEDOR, POST-C7, CW decoupling, TPPM, F-SLG, SLF, SEMA-CP, PISEMA, RFDR, QCPMG-MAS, and MQ-MAS experiments.

Bak, Mads; Rasmussen, Jimmy T.; Nielsen, Niels Chr.

2011-12-01

146

Structural Analysis of Nanoscale Self-Assembled Discoidal Lipid Bilayers by Solid-State NMR Spectroscopy  

PubMed Central

Nanodiscs are an example of discoidal nanoscale self-assembled lipid/protein particles similar to nascent high-density lipoproteins, which reduce the risk of coronary artery disease. The major protein component of high-density lipoproteins is human apolipoprotein A-I, and the corresponding protein component of Nanodiscs is membrane scaffold protein 1 (MSP1), a 200-residue lipid-binding domain of human apolipoprotein A-I. Here we present magic-angle spinning (MAS) solid-state NMR studies of uniformly 13C,15N-labeled MSP1 in polyethylene glycol precipitated Nanodiscs. Two-dimensional MAS 13C-13C correlation spectra show excellent microscopic order of MSP1 in precipitated Nanodiscs. Secondary isotropic chemical shifts throughout the protein are consistent with a predominantly helical structure. Moreover, the backbone conformations of prolines derived from their 13C chemical shifts are consistent with the molecular belt model but not the picket fence model of lipid-bound MSP1. Overall comparison of experimental spectra and 13C chemical shifts predicted from several structural models also favors the belt model. Our study thus supports the belt model of Nanodisc structure and demonstrates the utility of MAS NMR to study the structure of high molecular weight lipid-protein complexes.

Li, Ying; Kijac, Aleksandra Z.; Sligar, Stephen G.; Rienstra, Chad M.

2006-01-01

147

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

148

Solid-state NMR investigation of n-heptane cracking over zeolite beta  

SciTech Connect

n-Heptane cracking over zeolite H-Beta has been studied by solid-state NMR spectroscopy. It is shown that isomerisation and cracking are two related processes at the early stages of the reaction. Isomerisation is proposed to proceed faster than cracking via the intermediacy of protonated cyclopropane wheras cracking is suggested to progress through the classical {beta}-scission route. Catalyst loading in the NMR experiments seems to be a very important factor for both initiation of the reaction and final product distribution. The initial source of i-butane, which is observed as primary product, is the isomer 2,2-dimethylpentane, which cracks to i-butane and propene. Propene, which has never been observed, is suggested to be involved in polymerisation reactions producing long hydrocarbon chains which can rearrange and finally crack to a number of C{sub 5}-C{sub 7} isomers. At later stages, the reaction becomes very complex. More of the heptane isomers crack by {beta}-scission to a number of C{sub 4} and C{sub 3} fractions. The carbenium ions desorb as paraffins by H-transfer while the olefinic fraction is involved in polymerisation reactions. At the final stages of the reaction, protolytic cracking starts contributing to this process, producing methane, ethane, and propane. Of great interest is the catalyst loading effect on this monomolecular reaction process which defines the final product distribution. 30 refs., 6 figs., 1 tab.

Philippou, A.; Anderson, M.W. [UMIST, Manchester (United Kingdom)

1996-02-01

149

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

150

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

151

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

Microsoft Academic Search

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

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

2000-01-01

152

Solid-State NMR Studies of Ionic Surfactants Adsorbed on Cyanopropyl Bonded Phases: Implications for Micellar Liquid Chromatography  

Microsoft Academic Search

Solid-state13C NMR spectroscopy techniques, including cross polarization (CP), magic angle spinning (MAS), and high-power proton decoupling, have been used to study the interactions of two ionic surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), with the cyanopropyl bonded phase. Variable contact time CP\\/MAS13C NMR data suggest that the unusual behavior of cyanopropyl bonded phase columns in SDS and CTAB

Barry K. Lavine; Sumar Hendayana; Yifang He; William T. Cooper

1996-01-01

153

Structure and Transformation of Amorphous Calcium Carbonate: A Solid-State 43Ca NMR and Computational Molecular Dynamics Investigation  

SciTech Connect

Amorphous calcium carbonate (ACC) is a metastable precursor to crystalline CaCO{sub 3} phases that precipitates by aggregation of ion pairs and prenucleation clusters. We use {sup 43}Ca solid-state NMR spectroscopy to probe the local structure and transformation of ACC synthesized from seawater-like solutions with and without Mg{sup 2+} and computational molecular dynamics (MD) simulations to provide more detailed molecular-scale understanding of the ACC structure. The {sup 43}Ca NMR spectra of ACC collected immediately after synthesis consist of broad, featureless resonances with Gaussian line shapes (FWHH = 27.6 {+-} 1 ppm) that do not depend on Mg{sup 2+} or H{sub 2}O content. A correlation between {sup 43}Ca isotropic chemical shifts and mean Ca-O bond distances for crystalline hydrous and anhydrous calcium carbonate phases indicates indistinguishable maximum mean Ca-O bond lengths of {approx}2.45 {angstrom} for all our samples. This value is near the upper end of the published Ca-O bond distance range for biogenic and synthetic ACCs obtained by Ca-X-ray absorption spectroscopy. It is slightly smaller than the values from the structural model of Mgfree ACC by Goodwin et al. obtained from reverse Monte Carlo (RMC) modeling of X-ray scattering data and our own computational molecular dynamics (MD) simulation based on this model. An MD simulation starting with the atomic positions of the Goodwin et al. RMC model using the force field of Raiteri and Gale shows significant structural reorganization during the simulation and that the interconnected carbonate/water-rich channels in the Goodwin et al. model shrink in size over the 2 ns simulation time. The distribution of polyhedrally averaged Ca-O bond distances from the MD simulation is in good agreement with the {sup 43}Ca NMR peak shape, suggesting that local structural disorder dominates the experimental line width of ACC.

Singer, Jared W.; Yazaydin, A. O.; Kirkpatrick, Robert J.; Bowers, Geoffrey M.

2012-05-22

154

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

Microsoft Academic Search

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

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

2001-01-01

155

Solid-state NMR evidence for elastin-like beta-turn structure in spider dragline silk.  

PubMed

Two-dimensional homo- and heteronuclear solid-state MAS NMR experiments on (13)C/(15)N-proline labeled Argiope aurantia dragline silk provide evidence for an elastin-like beta-turn structure for the repetitive Gly-Pro-Gly-X-X motif prevalent in major ampullate spidroin 2 (MaSp2). PMID:20733981

Jenkins, Janelle E; Creager, Melinda S; Butler, Emily B; Lewis, Randolph V; Yarger, Jeffery L; Holland, Gregory P

2010-08-23

156

Effect of pressure on structure of oxide glasses at high pressure: Insights from solid-state NMR of quadrupolar nuclides  

Microsoft Academic Search

Revealing the structure of oxide glasses at high pressure remains a fundamental yet difficult problem in modern physical and chemical sciences. The recent advances in solid-state NMR techniques used for quadrupolar nuclides offer a considerably improved resolution of atomic sites, unveiling previously unknown structural details of oxides glasses at high pressure. Here, we present an overview of the recent progress

Sung Keun Lee

2010-01-01

157

Solid state (sup 31)P NMR study of phosphonate binding sites in guanidine-functionalized, molecular imprinted silica xerogels.  

National Technical Information Service (NTIS)

Phosphonate binding sites in guanidine and ammonium surface-functionalized silica xerogels were prepared via the molecular imprinting technique and characterized using solid state (sup 31)P MAS NMR. One-point, two-point, and non-specific host-guest intera...

D. Y. Sasaki T. D. Alam

2000-01-01

158

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

159

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

160

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

SciTech Connect

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

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

1996-12-01

161

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

PubMed Central

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

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

2013-01-01

162

Evidence from Solid-State NMR for Nonhelical Conformations in the Transmembrane Domain of the Amyloid Precursor Protein  

PubMed Central

The amyloid precursor protein (APP) is subject to proteolytic processing by ?-secretase within neuronal membranes, leading to Alzheimer's disease-associated ?-amyloid peptide production by cleavage near the midpoint of the single transmembrane (TM) segment of APP. Conformational properties of the TM segment may affect its susceptibility to ?-secretase cleavage, but these properties have not been established definitively, especially in bilayer membranes with physiologically relevant lipid compositions. In this article, we report an investigation of the APP-TM conformation, using 13C chemical shifts obtained with two-dimensional solid-state NMR spectroscopy as site-specific conformational probes. We find that the APP-TM conformation is not a simple ?-helix, particularly at 37°C in multilamellar vesicles with compositions that mimic the composition of neuronal cell membranes. Instead, we observe a mixture of helical and nonhelical conformations at the N- and C-termini and in the vicinity of the ?-cleavage site. Conformational plasticity of the TM segment of APP may be an important factor in the ?-secretase cleavage mechanism.

Lu, Jun-Xia; Yau, Wai-Ming; Tycko, Robert

2011-01-01

163

Elucidating metabolic pathways for amino acid incorporation into dragline spider silk using 13C enrichment and solid state NMR.  

PubMed

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

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

2011-02-17

164

Solid-state NMR and IRMS characterization of smouldered peat from ombrotrophic cores  

NASA Astrophysics Data System (ADS)

Smouldering fires are slow, low temperature, flameless and the most persistent form of combustion of organic matter (OM) in porous form. Although smouldering fires of peatlands represent a large perturbation of the atmospheric chemistry, to date, most studies on smouldering focused on ignition, carbon (C) losses or emissions, whereas the literature still lacks understanding of the OM evolution following these events. The potential to track OM changes able to serve as new proxies for the identification of past fire events along peat cores is extremely important, especially considering that bogs are often used as natural archives of paleoenvironmental changes. In the present work we show preliminary results about solid-state Nuclear Magnetic Resonance (NMR) and Isotope-Ratio Mass Spectroscopy (IRMS) characterization of peat OM along three Sphagnum peat columns (26 cm deep) having different initial moisture contents (MC): 50% MC, 100% MC, and 200% MC. The 15N spectrum of fresh peat (FP) used as control shows, as expected, only an amide signal, which is in agreement with the 13C NMR spectrum where mainly signals of carbohydrates and alkyl C can be observed. Further signals can be observed in the aromatic region, most probably due to lignin derivatives. Following the smouldering event, selected peat samples from both the 50% and 100% MC series show, as expected, signals supporting the occurrence of fire. In detail, the 15N-signals between -200 and -250 ppm are typical for pyrrole or indole type N. This is in accordance with the 13C NMR spectra showing considerable intensity in the aromatic region, most likely from char residues. Isotopic signatures (i.e., ?13C and ?15N) show a very interesting behaviour. In detail, ?13C seems to be slightly affected by smouldering, although the information about vegetational changes are preserved, whereas the ?15N shows a trend positively correlated with the relative N enrichment observed in smouldered peat samples, as also supported by 15N NMR. While further research is in progress to find reliable proxies allowing reconstruction of ancient smouldering events along peat profiles, our data provide an additional important insight towards assessing palaeoenvironmental conditions and highlighting that smouldering fires may have been overlooked as the cause of molecular and chemical variations observed in peat cores. The present research was financed by the Italian PRIN program 2009 (2009NBHPWR - Project title: "Chemical and biomolecular indicators for reconstructing environmental changes in natural archives")

Zaccone, Claudio; Rein, Guillermo; Gioacchini, Paola; Knicker, Heike; Ciavatta, Claudio; Miano, Teodoro M.

2013-04-01

165

Solid state NMR analysis of peptides in membranes: Influence of dynamics and labeling scheme.  

PubMed

The functional state of a membrane-active peptide is often defined by its conformation, molecular orientation, and its oligomeric state in the lipid bilayer. These "static" structural properties can be routinely studied by solid state NMR using isotope-labeled peptides. In the highly dynamic environment of a liquid crystalline biomembrane, however, the whole-body fluctuations of a peptide are also of paramount importance, although difficult to address and most often ignored. Yet it turns out that disregarding such motional averaging in calculating the molecular alignment from orientational NMR-constraints may give a misleading, if not false picture of the system. Here, we demonstrate that the reliability of a simplified static or an advanced dynamic data analysis depends critically on the choice of isotope labeling scheme used. Two distinctly different scenarios have to be considered. When the labels are placed on the side chains of a helical peptide (such as a CD(3)- or CF(3)-group attached to the C(alpha)C(beta) bond), their nuclear spin interaction tensors are very sensitive to motional averaging. If this effect is not properly accounted for, the helix tilt angle tends to be severely underestimated. At the same time, the analysis of labels in the side chains allows to extract valuable dynamical information about whole-body fluctuations of the peptide helix in the membrane. On the other hand, the alternative labeling scheme where (15)N-labels are accommodated within the peptide backbone, will yield nearly correct helix tilt angles, irrespective as to whether dynamics are taken into account or not. PMID:19715662

Esteban-Martín, Santi; Strandberg, Erik; Salgado, Jesús; Ulrich, Anne S

2009-08-26

166

High-Resolution NMR of Quadrupolar Nuclei in the Solid State  

SciTech Connect

This dissertation describes recent developments in solid state nuclear magnetic resonance (NMR), for the most part involving the use of dynamic-angle spinning (DAS) NMR to study quadrupolar nuclei. Chapter 1 introduces some of the basic concepts and theory that will be referred to in later chapters, such as the density operator, product operators, rotations, coherence transfer pathways, phase cycling, and the various nuclear spin interactions, including the quadrupolar interaction. Chapter 2 describes the theory behind motional averaging experiments, including DAS, which is a technique where a sample is spun sequentially about two axis oriented at different angles with respect to the external magnetic field such that the chemical shift and quadrupolar anisotropy are averaged to zero. Work done on various rubidium-87 salts is presented as a demonstration of DAS. Chapter 3 explains how to remove sidebands from DAS and magic-angle spinning (MAS) experiments, which result from the time-dependence of the Hamiltonian under sample spinning conditions, using rotor-synchronized {pi}-pulses. Data from these experiments, known as DAH-180 and MAH-180, respectively, are presented for both rubidium and lead salts. In addition, the applicability of this technique to double rotation (DOR) experiments is discussed. Chapter 4 concerns the addition of cross-polarization to DAS (CPDAS). The theory behind spin locking and cross polarizing quadrupolar nuclei is explained and a method of avoiding the resulting problems by performing cross polarization at 0{sup o} (parallel) with respect to the magnetic field is presented. Experimental results are shown for a sodium-23 compound, sodium pyruvate, and for oxygen-17 labeled L-akmine. In Chapter 5, a method for broadening the Hartmann-Hahn matching condition under MAS, called variable effective field cross-polarization (VEFCI?), is presented, along with experimental work on adamantane and polycarbonate.

Gann, Sheryl Lee

1995-11-30

167

Dispersion of Silicate in Tricalcium Phosphate Elucidated by Solid-State NMR  

SciTech Connect

The dispersion of silicate in tricalcium phosphate, a resorbable bioceramics for bone replacement, has been investigated by various solid-state nuclear magnetic resonance (NMR) methods. In samples prepared with 5 and 10 mol% of both {sup 29}SiO{sub 2} and ZnO, three types of silicate have been detected: (i) SiO{sub 4}{sup 4-} (Q{sub 0} sites) with long longitudinal (T{sub 1,Si}) relaxation times ({approx} 10,000 s), which substitute for {approx}1% of PO{sub 4}{sup 3-}; (ii) silicate nanoinclusions containing Q{sub 2}, Q{sub 1}, and Q{sub 0} sites with T{sub 1,Si} 100 s, which account for most of the silicon; and (iii) crystalline Q{sub 4} (SiO{sub 2}) with long T{sub 1,Si}. Sensitivity was enhanced >100-fold by {sup 29}Si enrichment and refocused detection. The inclusions in both samples have a diameter of {approx}8 nm, as proved by {sup 29}Si{l_brace}{sup 31}P{r_brace} REDOR dephasing on a 30-ms time scale, which was simulated using a multispin approach specifically suited for nanoparticles. {sup 29}Si CODEX NMR with 30-s {sup 29}Si spin diffusion confirms that an inclusion contains >10 Si (consistent with the REDOR result of >100 Si per inclusion). Overlapping signals of silicate Q{sub 2}, Q{sub 1}, and Q{sub 0} sites were spectrally edited based on their J-couplings, using double-quantum filtering. The large inhomogeneous broadening of the Q{sub 2}, Q{sub 1}, and Q{sub 0} {sup 29}Si subspectra indicates that the nanoinclusions are amorphous.

Rewal, A.; Wei, X.; Akinc, M.; Schmidt-Rohr, K.

2008-03-12

168

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

NASA Astrophysics Data System (ADS)

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

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

2001-06-01

169

Lipid-Protein Correlations in Nanoscale Phospholipid Bilayers by Solid-State NMR  

PubMed Central

Nanodiscs are an example of discoidal nanoscale lipid/protein particles that have been extremely useful for the biochemical and biophysical characterization of membrane proteins. They are discoidal lipid bilayer fragments encircled and stabilized by two amphipathic helical proteins named membrane scaffolding protein (MSP), ~10 nm in size. Nanodiscs are homogeneous, easily prepared with reproducible success, amenable to preparations with a variety of lipids, and stable under a range of temperatures. Here we present solid-state NMR (SSNMR) studies on lyophilized, rehydrated POPC Nanodiscs prepared with uniformly 13C, 15N-labeled MSP1D1 (?1-11 truncated MSP). Under these conditions, by SSNMR we directly determine the gel-to-liquid crystal lipid phase transition to be at 3 ± 2 °C. Above this phase transition, the lipid 1H signals have slow transverse relaxation, enabling filtering experiments as previously demonstrated for lipid vesicles. We incorporate this approach into two- and three-dimensional heteronuclear SSNMR experiments to examine the MSP1D1 residues interfacing with the lipid bilayer. These 1H-13C and 1H-13C-13C correlation spectra are used to identify and quantify the number of lipid-correlated and solvent-exposed residues by amino acid type, which furthermore is compared with molecular dynamics studies of MSP1D1 in Nanodiscs. This study demonstrates the utility of SSNMR experiments with Nanodiscs for examining lipid-protein interfaces and has important applications for future structural studies of membrane proteins in physiologically relevant formulations.

Kijac, Aleksandra; Shih, Amy Y.; Nieuwkoop, Andrew J.; Schulten, Klaus; Sligar, Stephen G.; Rienstra, Chad M.

2011-01-01

170

29Si NMR in solid state with CPMG acquisition under MAS  

SciTech Connect

A remarkable enhancement of sensitivity can be often achieved in {sup 29}Si solid-state NMR by applying the well-known Carr-Purcell-Meiboom-Gill (CPMG) train of rotor-synchronized {pi} pulses during the detection of silicon magnetization. Here, several one- and two-dimensional (1D and 2D) techniques are used to demonstrate the capabilities of this approach. Examples include 1D {sup 29}Si{l_brace}X{r_brace} CPMAS spectra and 2D {sup 29}Si{l_brace}X{r_brace} HETCOR spectra of mesoporous silicas, zeolites and minerals, where X = {sup 1}H or {sup 27}Al. Data processing methods, experimental strategies and sensitivity limits are discussed and illustrated by experiments. The mechanisms of transverse dephasing of {sup 29}Si nuclei in solids are analyzed. Fast magic angle spinning, at rates between 25 and 40 kHz, is instrumental in achieving the highest sensitivity gain in some of these experiments. In the case of {sup 29}Si-{sup 29}Si double-quantum techniques, CPMG detection can be exploited to measure homonuclear J-couplings.

Wiench, J.W.; Lin, V.S.-Y.; Pruski, M.

2008-05-20

171

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

PubMed Central

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

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

2011-01-01

172

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

173

Solid-state NMR structure determination of whole anchoring threads from the blue mussel Mytilus edulis.  

PubMed

The molecular structure of the blue mussel Mytilus edulis whole anchoring threads was studied by two-dimensional (13)C solid-state NMR on fully labeled fibers. This unique material proves to be well ordered at a molecular level despite its heterogeneous composition as evidenced by the narrow measured linewidths below 1.5 ppm. The spectra are dominated by residues in collagen environments, as determined from chemical shift analysis, and a complete two-dimensional assignment (including minor amino acids) was possible. The best agreement between predicted and experimental backbone chemical shifts was obtained for collagen helices with torsion angles (-75°, +150°). The abundant glycine and alanine residues can be resolved in up to five different structural environments. Alanine peaks could be assigned to collagen triple-helices, ?-sheets (parallel and antiparallel), ?-turns, and unordered structures. The use of ATR-FTIR microscopy confirmed the presence of these structural environments and enabled their location in the core of the thread (collagen helices and antiparallel ?-sheets) or its cuticle (unordered structures). The approach should enable characterization at the molecular level of a wide range of byssus macroscopic properties. PMID:23163352

Arnold, Alexandre A; Byette, Frédéric; Séguin-Heine, Marc-Olivier; Leblanc, André; Sleno, Lekha; Tremblay, Réjean; Pellerin, Christian; Marcotte, Isabelle

2012-12-06

174

Homogeneous broadenings in 2D solid-state NMR of half-integer quadrupolar nuclei  

NASA Astrophysics Data System (ADS)

The question of the homogeneous broadening that occurs in 2D solid-state NMR experiments is examined. This homogeneous broadening is mathematically introduced in a simple way, versus the irreversible decay rates related to the coherences that are involved during t1 and t2. We give the pulse sequences and coherence transfer pathways that are used to measure these decay rates. On AlPO4 berlinite, we have measured the 27Al echo-type relaxation times of the central and satellite transitions on 1Q levels, so that of coherences that are situated on 2Q, 3Q, and 5Q levels. We compare the broadenings that can be deduced from these relaxation times to those directly observed on the isotropic projection of berlinite with multiple-quantum magic-angle spinning (MAS), or satellite-transition MAS. We show that the choice of the high-resolution method, should be done according to the spin value and the corresponding homogeneous broadening.

Amoureux, J. P.; Trébosc, J.

2006-04-01

175

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

176

Biomolecular solid state NMR with magic-angle spinning at 25 K  

PubMed Central

A magic-angle spinning (MAS) probe has been constructed which allows the sample to be cooled with helium, while the MAS bearing and drive gases are nitrogen. The sample can be cooled to 25 K using roughly 3 liters/hour of liquid helium, while the 4 mm diameter rotor spins at 6.7 kHz with good stability (±5 Hz) for many hours. Proton decoupling fields up to at least 130 kHz can be applied. This helium-cooled MAS probe enables a variety of one-dimensional and two-dimensional NMR experiments on biomolecular solids and other materials at low temperatures, with signal-to-noise proportional to 1/T. We show examples of low-temperature 13C NMR data for two biomolecular samples, namely the peptide A?14–23 in the form of amyloid fibrils and the protein HP35 in frozen glycerol/water solution. Issues related to temperature calibration, spin-lattice relaxation at low temperatures, paramagnetic doping of frozen solutions, and 13C MAS NMR linewidths are discussed.

Thurber, Kent R.; Tycko, Robert

2009-01-01

177

AssignFit: A program for simultaneous assignment and structure refinement from solid-state NMR spectra  

NASA Astrophysics Data System (ADS)

AssignFit is a computer program developed within the XPLOR-NIH package for the assignment of dipolar coupling (DC) and chemical shift anisotropy (CSA) restraints derived from the solid-state NMR spectra of protein samples with uniaxial order. The method is based on minimizing the difference between experimentally observed solid-state NMR spectra and the frequencies back calculated from a structural model. Starting with a structural model and a set of DC and CSA restraints grouped only by amino acid type, as would be obtained by selective isotopic labeling, AssignFit generates all of the possible assignment permutations and calculates the corresponding atomic coordinates oriented in the alignment frame, together with the associated set of NMR frequencies, which are then compared with the experimental data for best fit. Incorporation of AssignFit in a simulated annealing refinement cycle provides an approach for simultaneous assignment and structure refinement (SASR) of proteins from solid-state NMR orientation restraints. The methods are demonstrated with data from two integral membrane proteins, one ?-helical and one ?-barrel, embedded in phospholipid bilayer membranes.

Tian, Ye; Schwieters, Charles D.; Opella, Stanley J.; Marassi, Francesca M.

2012-01-01

178

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

179

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

180

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

181

Synthesis and Solid State Structure of Fluorous Probe Molecules for Fluorous Separation Applications.  

PubMed

A series of colored hydrocarbon and fluorocarbon tagged 1-fluoro-4-alkylamino-anthraquinones and 1,4-bis-alkylamino-anthraquinone probe molecules were synthesized from a (fluorinated) alkyl amine and 1,4-difluoroanthraquinone to aid in the development of fluorous separation applications. The anthraquinones displayed stacking of the anthraquinone tricycle and interdigitation of the (fluorinated) alkyl chains in the solid state. Furthermore, intramolecular N-H···O hydrogen bonds forced the hydrocarbon and fluorocarbon tags into a conformation pointing away from the anthraquinone tricycle, with the angle of the tricycle plane normal and the main (fluorinated) alkyl vector ranging from 1 to 39°. Separation of the probe molecules on fluorous silica gel showed that the degree of fluorination of the probe molecules plays only a minor role with most eluents (e.g., hexane-ethyl acetate and methyl nonafluorobutyl ethers-ethyl acetate). However, toluene as eluent caused a pronounced separation by degree of fluorination for fluorocarbon, but not hydrocarbon tagged probe molecules on both silica gel and fluorous silica gel. These studies suggest that hydrocarbon and fluorocarbon tagged anthraquinones are useful probe molecules for the development of laboratory scale fluorous separation applications. PMID:20305832

Lehmler, H-J; Telu, S; Vyas, S M; Shaikh, N S; Rankin, S E; Knutson, B L; Parkin, S

2010-04-01

182

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

NASA Astrophysics Data System (ADS)

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

Kameda, Tsunenori

2005-12-01

183

Susceptibility corrections in solid-state NMR experiments with oriented membrane samples. Part I: applications.  

PubMed

Chemical shift referencing of solid-state NMR experiments on oriented membranes has to compensate for bulk magnetic susceptibility effects that are associated with the non-spherical sample shape, as described in the accompanying paper [J. Magn. Reson. 164 (2003) 115-127]. The resulting frequency deviations can be on the order of 10 ppm, which is serious for nuclei with a narrow chemical shift anisotropy such as 1H or 13C, and in some cases even 19F. Two referencing schemes are proposed here to compensate for these effects: A flat (0.4 mm) glass container with an isotropic reference molecule dissolved in a thin film of liquid is stacked on top of the oriented membrane sample. Alternatively, the intrinsic proton signal of the hydrated lipid can be used for chemical shift referencing. Further aspects related to magnetic susceptibility are discussed, such as air gaps in susceptibility-matched probeheads, the benefits of shimming, and limitations in the accuracy of orientational constraints. A biological application is illustrated by a series of experiments on the antimicrobial peptide PGLa, aimed at understanding its concentration-dependent membranolytic effect. To address a wide range of molar peptide/lipid ratios between 1:3000 and 1:8, multilayers of hydrated DMPC containing a 19F-labeled peptide were oriented between stacked glass plates. Maintaining an approximately constant amount of peptide gives rise to thick samples (18 plates) at low, and thin samples (3 plates) at high peptide/lipid ratio. Accurate referencing was critical to reveal a small but significant change over 5 ppm in the anisotropic chemical shift of the 19F label on the peptide, indicative of a change in the orientation and/or dynamics of PGLa in the membrane. PMID:12932462

Glaser, Ralf W; Ulrich, Anne S

2003-09-01

184

Cellulose crystallinity and ordering of hemicelluloses in pine and birch pulps as revealed by solid-state NMR spectroscopic methods  

Microsoft Academic Search

Solid-state 13C NMR spectroscopy was used to determine the degree of cellulose crystallinity (CrI) in kraft, flow-through kraft and polysulphide–anthraquinone (PS–AQ) pulps of pine and birch containing various amounts of hemicelluloses. The applicability of acid hydrolysis and the purely spectroscopic proton spin-relaxation based spectral edition (PSRE) method to remove the interfering hemicellulose signals prior to the determination of CrI were

Tiina Liitiä; Sirkka Liisa Maunu; Bo Hortling; Tarja Tamminen; Osmo Pekkala; Antero Varhimo

2003-01-01

185

The thermal reactions of muscovite studied by high-resolution solid-state 29Si and 27AI NMR  

Microsoft Academic Search

Studies of two muscovites of different iron contents, using solid-state NMR with magic-angle-spinning (MAS) combined with X-ray powder diffraction, thermal analysis and57Fe Mössbauer spectroscopy, suggest that dehydroxylation occurs by a homogeneous rather than an inhomogeneous mechanism, forming a dehydroxylate in which the aluminium is predominantly 5-coordinate. On further decomposition at about 1100° C, the tetrahedral layer and interlayer K+ form

K. J. D. Mackenzie; I. W. M. Brown; C. M. Cardile; R. H. Meinhold

1987-01-01

186

Structural and motional features of benzene-solvated C 60 as revealed by high-resolution solid state NMR  

Microsoft Academic Search

Structural and motional features of C60 · 4C6H6 solvate has been investigated by high-resolution 13C solid-state NMR spectroscopy. 13C line shape analysis of the cross-polarization spectrum for the static sample at 293 K shows an unusual motional restriction of benzene molecules in this solvate. The existence of highly anisotropic motion of benzene fraction is visualized also by the detection of

P. Tekely; P Palmas; P Mutzenhardt; F Masin; A.-S Grell; I Messari; M Gelbcke

1998-01-01

187

Local environment and distribution of alkali ions in polyelectrolyte complexes studied by solid-state NMR.  

PubMed

Polyelectrolyte complexes (PECs) formed by the addition of substoichiometric amounts of (poly(diallyldimethyl ammonium chloride)) (PDADMAC) solutions to sodium or lithium poly(styrene sulfonate) (Na- or Li-PSS) solution contain adjustable amounts of charge balancing Li(+) or Na(+) cations, which possess ionic mobility of interest for solid electrolyte applications. Very little is known regarding the local environments and the spatial distributions of these cations and their interactions with the polyelectrolyte chains in these amorphous materials. To address such issues, the present work develops a comprehensive solid state NMR strategy based on complementary high-resolution magic-angle spinning (MAS) NMR and various dipolar spectroscopic techniques. (6,7)Li and (23)Na chemical shifts measured on a series of PECs with general composition described by B((2x-1))PSS(x)PDADMA((1-x)) (B = Li or Na and 0.53 ?x? 1) reveal composition-independent local cation environments. In contrast, (7)Li{(6)Li} spin echo double resonance (SEDOR) experiments measured on (6)Li enriched materials and (7)Li{(1)H} rotational echo double resonance (REDOR) experiments are consistent with an approximately random ion distribution. The same conclusion is suggested by (23)Na{(1)H} REDOR measurements on the analogous sodium containing system indicating a non-segregated PEC structure. In apparent contrast to this conclusion, (23)Na spin echo decay spectroscopy yields nearly constant dipolar second moments over a wide composition range. This can be explained by considering that the (23)Na spin echo decays are affected by both (23)Na-(23)Na homonuclear dipolar couplings and (23)Na-(1)H heteronuclear dipolar interactions in the presence of strong homonuclear (1)H-(1)H spin exchange. In protonated Na-PSS both contributions are of comparable magnitude. In the PECs the contribution from (23)Na-(23)Na interactions decreases, while that from (23)Na-(1)H dipolar couplings with the protons from the PDADMA chains increases with decreasing Na content, resulting in superimposed opposite dependences on the ion concentration. All results for Li and Na containing PECs point at a non-phase separated polymer network with uniform ionic sites of very similar environment. The cations can be viewed as randomly distributed and located close to the polyion sulfate groups. PMID:21465039

Causemann, Susanne; Schönhoff, Monika; Eckert, Hellmut

2011-04-04

188

High-resolution solid-state NMR of phosphate glasses using one- and two-dimensional heteronuclear correlation spectroscopy  

NASA Astrophysics Data System (ADS)

The structural characterization of solid materials can be hampered by compositional inhomogeneity, amorphous character, or the presence of impurities. In many cases, structural studies of these materials via diffraction methods yield results averaged over an entire sample which may lack long-range ordering or a homogeneous composition. An atomistic (or molecular-level) structural interpretation is then impossible, and little understanding is obtained relating the microstructural environments of the atoms to the observed physical properties of a complex material. Solid-state nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for the determination of local structure in complex inorganic materials, even those that lack long-range order or compositional homogeneity. As such, solid-state NMR is now widely used for characterization of structure and chemistry in complex systems. The work presented in this thesis outlines strategies and displays application of solid-state heteronuclear correlation NMR in studies of phosphate and aluminophosphate glass systems. One-dimensional CPMAS NMR experiments involving quadrupolar nuclei are particularly sensitive to local order in inorganic systems, revealing resonances only between nuclei that are close enough in space to have a substantial dipolar coupling. The dynamics of the heteronuclear cross-polarization processes is another important measure of the local microstructure near to backbone phosphorus atoms. Further, the use of two-dimensional CP heteronuclear correlation experiments provides an opportunity for spectral editing, enhancing our studies of local structures. Finally, we describe a two-dimensional method employing dynamic-angle spinning (DAS) NMR for quadrupolar nuclei coupled with CP to spin-1/2 nuclei, achieving for the first time true high resolution for both the quadrupolar and non-quadrupolar spins. With this arsenal of NMR connectivity experiments, the role of cation modification to phosphate glass networks is examined through direct investigation of atomic arrangement concerning both phosphorus network forming tetrahedra and modifying cation environments.

Wenslow, Robert Michael, Jr.

189

Monitoring tat peptide binding to TAR RNA by solid-state 31P-19F REDOR NMR  

PubMed Central

Complexes of the HIV transactivation response element (TAR) RNA with the viral regulatory protein tat are of special interest due in particular to the plasticity of the RNA at this binding site and to the potential for therapeutic targeting of the interaction. We performed REDOR solid-state NMR experiments on lyophilized samples of a 29 nt HIV-1 TAR construct to measure conformational changes in the tat-binding site concomitant with binding of a short peptide comprising the residues of the tat basic binding domain. Peptide binding was observed to produce a nearly 4 ? decrease in the separation between phosphorothioate and 2?F labels incorporated at A27 in the upper helix and U23 in the bulge, respectively, consistent with distance changes observed in previous solution NMR studies, and with models showing significant rearrangement in position of bulge residue U23 in the bound-form RNA. In addition to providing long-range constraints on free TAR and the TAR–tat complex, these results suggest that in RNAs known to undergo large deformations upon ligand binding, 31P–19F REDOR measurements can also serve as an assay for complex formation in solid-state samples. To our knowledge, these experiments provide the first example of a solid-state NMR distance measurement in an RNA–peptide complex.

Olsen, Greg L.; Edwards, Thomas E.; Deka, Pritilekha; Varani, Gabriele; Sigurdsson, Snorri Th.; Drobny, Gary P.

2005-01-01

190

Solid-State NMR on Bacterial Cells: Selective Cell Wall Signal Enhancement and Resolution Improvement using Dynamic Nuclear Polarization.  

PubMed

Dynamic nuclear polarization (DNP) enhanced solid-state nuclear magnetic resonance (NMR) has recently emerged as a powerful technique for the study of material surfaces. In this study, we demonstrate its potential to investigate cell surface in intact cells. Using Bacillus subtilis bacterial cells as an example, it is shown that the polarizing agent 1-(TEMPO-4-oxy)-3-(TEMPO-4-amino)propan-2-ol (TOTAPOL) has a strong binding affinity to cell wall polymers (peptidoglycan). This particular interaction is thoroughly investigated with a systematic study on extracted cell wall materials, disrupted cells, and entire cells, which proved that TOTAPOL is mainly accumulating in the cell wall. This property is used on one hand to selectively enhance or suppress cell wall signals by controlling radical concentrations and on the other hand to improve spectral resolution by means of a difference spectrum. Comparing DNP-enhanced and conventional solid-state NMR, an absolute sensitivity ratio of 24 was obtained on the entire cell sample. This important increase in sensitivity together with the possibility of enhancing specifically cell wall signals and improving resolution really opens new avenues for the use of DNP-enhanced solid-state NMR as an on-cell investigation tool. PMID:23362837

Takahashi, Hiroki; Ayala, Isabel; Bardet, Michel; De Paëpe, Gaël; Simorre, Jean-Pierre; Hediger, Sabine

2013-02-12

191

Magic Angle Spinning and Oriented Sample Solid State NMR Structural Restraints Combine for Influenza A M2 Protein Functional Insights  

PubMed Central

As a small tetrameric helical membrane protein, the M2 proton channel structure is highly sensitive to its environment. As a result, structural data from a lipid bilayer environment has proven to be essential for describing the conductance mechanism. While oriented sample solid state NMR has provided a high resolution backbone structure in lipid bilayers, quaternary packing of the helices and many of the sidechain conformations have been poorly restrained. Furthermore, an understanding of the quaternary structural stability has remained a mystery. Here, the isotropic chemical shift data and interhelical cross peaks from magic angle spinning solid state NMR of a liposomal preparation strongly support the quaternary structure of the transmembrane helical bundle as a dimer of dimers structure. The data also explains how the tetrameric stability is enhanced once two charges are absorbed by the His37 tetrad prior to activation of this proton channel. The combination of these two solid state NMR techniques appear to be a powerful approach for characterizing helical membrane protein structure.

Can, Thach V.; Sharma, Mukesh; Hung, Ivan; Gor'kov, Peter L.; Brey, William W.; Cross, Timothy A.

2012-01-01

192

Dynamics of benzimidazole ethylphosphonate: a solid-state NMR study of anhydrous composite proton-conducting electrolytes.  

PubMed

Imidazole phosphate and phosphonate solid acids model the hydrogen-bonding networks and dynamics of the anhydrous electrolyte candidate for proton exchange membrane fuel cells. Solid-state NMR reveals that phosphate and phosphonate anion dynamics dominate the rate of long-range proton transport, and that the presence of a membrane host facilitates proton mobility, as evidenced by a decreased correlation time of the composites (80 ± 15 ms) relative to the pristine salt (101 ± 5 ms). Benzimidazole ethylphosphonate (Bi-ePA) is chosen as a model salt to investigate the membrane system. The hydrogen-bonding structure of Bi-ePA is established using X-ray diffraction coupled with solid-state (1)H-(1)H DQC NMR. The anion dynamics has been determined using solid-state (31)P CODEX NMR. By comparing the dynamics of ethylphosphonate groups in pristine salt and membrane-salt composites, it is clear that the rotation process involves three-site exchange. Through data interpretation, a stretched exponential function is introduced with the stretching exponent, ?, ranging 0 < ? ? 1. The (31)P CODEX data for pristine salt are fitted with single exponential decay where ? = 1; however, the data for the membrane-salt composites are fitted with stretched exponential functions, where ? has a constant value of 0.5. This ? value suggests a non-Gaussian distribution of the dynamic systems in the composite sample, which is introduced by the membrane host. PMID:24056920

Yan, Z Blossom; De Almeida, Nicole E; Traer, Jason W; Goward, Gillian R

2013-10-01

193

Synthesis and solid-state NMR structural characterization of polysiloxane-immobilized amine ligands and their metal complexes  

Microsoft Academic Search

Polysiloxane-immobilized amine and diamine ligand systems have been made by hydrolytic condensation of Si(OEt)4 with (EtO)3Si(CH2)3NH2 or (MeO)3Si(CH2)3NH(CH2)2NH2. The corresponding triamine ligand was made from the reaction of 3-chloropropylpolysiloxane with diethylenetriamine (H2NCH2CH2NHCH2CH2NH2); solid-state 13C and 15N nuclear magnetic resonance (NMR) spectra can identify the structure of the product of this reaction. 29Si, 15N, 13C and 1H NMR spectra are in

Jane Jie Yang; Issa M El-Nahhal; I-Ssuer Chuang; Gary E Maciel

1997-01-01

194

Lipid bilayer preparations of membrane proteins for oriented and magic-angle spinning solid-state NMR samples.  

PubMed

Solid-state NMR spectroscopy has been used successfully for characterizing the structure and dynamics of membrane proteins as well as their interactions with other proteins in lipid bilayers. Such an environment is often necessary for achieving native-like structures. Sample preparation is the key to this success. Here we present a detailed description of a robust protocol that results in high-quality membrane protein samples for both magic-angle spinning and oriented-sample solid-state NMR. The procedure is demonstrated using two proteins: CrgA (two transmembrane helices) and Rv1861 (three transmembrane helices), both from Mycobacterium tuberculosis. The success of this procedure relies on two points. First, for samples for both types of NMR experiment, the reconstitution of the protein from a detergent environment to an environment in which it is incorporated into liposomes results in 'complete' removal of detergent. Second, for the oriented samples, proper dehydration followed by rehydration of the proteoliposomes is essential. By using this protocol, proteoliposome samples for magic-angle spinning NMR and uniformly aligned samples (orientational mosaicity of <1°) for oriented-sample NMR can be obtained within 10 d. PMID:24157546

Das, Nabanita; Murray, Dylan T; Cross, Timothy A

2013-10-24

195

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

196

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

197

Cs4P2Se10: A new compound discovered with the application of solid-state and high temperature NMR  

NASA Astrophysics Data System (ADS)

The new compound Cs4P2Se10 was serendipitously produced in high purity during a high-temperature synthesis done in a nuclear magnetic resonance (NMR) spectrometer. 31P magic angle spinning (MAS) NMR of the products of the synthesis revealed that the dominant phosphorus-containing product had a chemical shift of -52.8 ppm that could not be assigned to any known compound. Deep reddish brown well-formed plate-like crystals were isolated from the NMR reaction ampoule and the structure was solved with X-ray diffraction. Cs4P2Se10 has the triclinic space group P-1 with a=7.3587(11) Å, b=7.4546(11) Å, c=10.1420(15) Å, ?=85.938(2)°, ?=88.055(2)°, and ?=85.609(2)° and contains the [P2Se10]4- anion. To our knowledge, this is the first compound containing this anion that is composed of two tetrahedral (PSe4) units connected by a diselenide linkage. It was also possible to form a glass by quenching the melt in ice water, and Cs4P2Se10 was recovered upon annealing. The static 31P NMR spectrum at 350 °C contained a single peak with a -35 ppm chemical shift and a ˜7 ppm peak width. This study highlights the potential of solid-state and high-temperature NMR for aiding discovery of new compounds and for probing the species that exist at high temperature.

Gave, Matthew A.; Canlas, Christian G.; Chung, In; Iyer, Ratnasabapathy G.; Kanatzidis, Mercouri G.; Weliky, David P.

2007-10-01

198

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

PubMed Central

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

Mao, Yougang; Ba, Yong

2006-01-01

199

The structural and dynamic properties of 1-bromodecane in urea inclusion compounds investigated by solid-state (1) H, (13) C and (2) H NMR spectroscopy.  

PubMed

For asymmetric guest molecules in urea, the end-groups of two adjacent guest molecules may arrange in three different ways: head-head, head-tail and tail-tail. Solid-state (1) H and (13) C NMR spectroscopy is used to study the structural properties of 1-bromodecane in urea. It is found that the end groups of the guest molecules are randomly arranged. The dynamic characteristics of 1-bromodecane in urea inclusion compounds are probed by variable-temperature solid-state (2) H NMR spectroscopy (line shapes, spin-spin relaxation: T(2) , spin-lattice relaxation: T(1Z) and T(1Q) ) between 120 K and room temperature. The comparison between the simulation and experimental data shows that the dynamic properties of the guest molecules can be described in a quantitative way using a non-degenerate three-site jump process in the low-temperature phase and a degenerate three-site jump in the high-temperature phase, in combination with the small-angle wobbling motion. The kinetic parameters can be derived from the simulation. Copyright © 2011 John Wiley & Sons, Ltd. PMID:21751248

Yang, Xiaorong; Müller, Klaus

2011-07-12

200

A Suite of Solid-State NMR Experiments for RNA Intranucleotide Resonance Assignment in a 21?kDa Protein-RNA Complex.  

PubMed

Intranucleotide resonance of the 26mer box C/D RNA in complex with the L7Ae protein were assigned by solid-state NMR (ssNMR; see picture) spectroscopy. This investigation opens the way for studying RNA in large protein-RNA complexes by ssNMR spectroscopy. PMID:23893717

Marchanka, Alexander; Simon, Bernd; Carlomagno, Teresa

2013-07-26

201

High-resolution membrane protein structure by joint calculations with solid-state NMR and X-ray experimental data  

PubMed Central

X-ray diffraction and Nuclear Magnetic Resonance spectroscopy (NMR) are the staple methods for revealing atomic structures of proteins. Since crystals of biomolecular assemblies and membrane proteins often diffract weakly and such large systems encroach upon the molecular tumbling limit of solution NMR, new methods are essential to extend structures of such systems to high resolution. Here we present a method that incorporates solid-state NMR restraints alongside of X-ray reflections into the conventional model building and refinement steps of structure calculations. Using the 3.7 Å crystal structure of the integral membrane protein complex DsbB-DsbA as a test case yielded a significantly improved backbone precision of 0.92 Å in the transmembrane region, a 58% enhancement from using X-ray reflections alone. Furthermore, addition of solid-state NMR restraints greatly improved the overall quality of the structure by promoting 22% of DsbB transmembrane residues into the most favored regions of Ramachandran space in comparison to the crystal structure. This method is widely applicable to any protein system where X-ray data are available, and is particularly useful for the study of weakly diffracting crystals.

Tang, Ming; Sperling, Lindsay J.; Berthold, Deborah A.; Schwieters, Charles D.; Nesbitt, Anna E.; Nieuwkoop, Andrew J.; Gennis, Robert B.; Rienstra, Chad M.

2011-01-01

202

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

203

Solid-State NMR Study of Metastable Immiscibility in Alkali Borosilicate Glasses  

NASA Astrophysics Data System (ADS)

Liquid-liquid phase separation is a critical issue in controlling and designing the physical properties of borosilicate glasses such as chemical durability, crystal nucleation, and high temperature strength and can provide insight into unmixing in natural magmatic systems as well. It is important to clarify this phenomenon, especially the immiscibility boundaries, which can be difficult to determine by conventional methods. High resolution NMR can provide a sensitive probe for the observation of phase separation in glass systems. In the M2O-B2O3-SiO2 system (M= Li, Na, K), we have used oxygen-17 MQMAS (Multiple Quantum Magic Angle Spinning) technique to explore changes in connectivities between SiO4, BO3 and BO4 units, based on changes in populations of bridging oxygens, such as B-O-B, B-O-Si and Si-O-Si, and of non-bridging oxygens. We have also used boron-11 MAS and MQMAS to quantify populations of borate units with varying first shell coordination and connectivity to other network units, e.g., "ring" vs. "non-ring" BO3 groups. In a series of alkali borosilicates of the same stoichiometry, the population of Si-O-B oxygen for the Li glass is significantly lower than that for Na and K borosilicates. This implies that the Li glass has a greater degree of phase separation at a submicroscopic scale as expected from phase diagrams. O-17 MQMAS NMR is also useful in determining the effect of quenching rate and annealing temperature on the degree of phase separation. In the Na borosilicates, a reduced concentration of Si-O-B in compositions within the immiscibility region suggests that even optically homogeneous glasses have small-scale heterogeneity. In the B-11 MAS and MQMAS studies, the ratio of BO3 to BO4 does not change with annealing. The non-ring BO3, however, converts to ring BO3 with annealing, which increases the degree of phase separation. In the study of Na2O-B2O3-SiO2 glasses with different Na contents, Si-O-B(III) and Si-O-B(IV) as well as B-O-B(III) and B-O-B(IV) can be distinguished by O-17 MQMAS NMR for the first time. At least two BO4 species were found in the B-11 NMR study. These semi-quantitative results can provide a further understanding of the glass structure.

Du, L.; Stebbins, J. F.

2001-12-01

204

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR.  

PubMed

In this paper, we describe a 250 GHz gyrotron oscillator, a critical component of an integrated system for magic angle spinning (MAS) dynamic nuclear polarization (DNP) experiments at 9T, corresponding to 380 MHz (1)H frequency. The 250 GHz gyrotron is the first gyro-device designed with the goal of seamless integration with an NMR spectrometer for routine DNP enhanced NMR spectroscopy and has operated under computer control for periods of up to 21 days with a 100% duty cycle. Following a brief historical review of the field, we present studies of the membrane protein bacteriorhodopsin (bR) using DNP enhanced multidimensional NMR. These results include assignment of active site resonances in [U-(13)C, (15)N]-bR and demonstrate the utility of DNP for studies of membrane proteins. Next, we review the theory of gyro-devices from quantum mechanical and classical viewpoints and discuss the unique considerations that apply to gyrotron oscillators designed for DNP experiments. We then characterize the operation of the 250 GHz gyrotron in detail, including its long-term stability and controllability. We have measured the spectral purity of the gyrotron emission using both homodyne and heterodyne techniques. Radiation intensity patterns from the corrugated waveguide that delivers power to the NMR probe were measured using two new techniques to confirm pure mode content: a thermometric approach based on the temperature-dependent color of liquid crystalline media applied to a substrate and imaging with a pyroelectric camera. We next present a detailed study of the mode excitation characteristics of the gyrotron. Exploration of the operating characteristics of several fundamental modes reveals broadband continuous frequency tuning of up to 1.8 GHz as a function of the magnetic field alone, a feature that may be exploited in future tunable gyrotron designs. Oscillation of the 250 GHz gyrotron at the second harmonic of cyclotron resonance begins at extremely low beam currents (as low 12 mA) at frequencies between 320 and 365 GHz, suggesting an efficient route for the generation of even higher frequency radiation. The low starting currents were attributed to an elevated cavity Q, which is confirmed by cavity thermal load measurements. We conclude with an appendix containing a detailed description of the control system that safely automates all aspects of the gyrotron operation. PMID:17942352

Bajaj, Vikram S; Hornstein, Melissa K; Kreischer, Kenneth E; Sirigiri, Jagadishwar R; Woskov, Paul P; Mak-Jurkauskas, Melody L; Herzfeld, Judith; Temkin, Richard J; Griffin, Robert G

2007-09-20

205

Solid-state 23Na and 7Li NMR investigations of sodium- and lithium-reduced mesoporous titanium oxides.  

PubMed

Mesoporous titanium oxide synthesized using a dodecylamine template was treated with 0.2, 0.6, and 1.0 equiv of Li- or Na-naphthalene. The composite materials were characterized by nitrogen adsorption, powder X-ray diffraction, X-ray photoelectron spectroscopy, elemental analysis, thermogravimetric analysis, and solid-state 23Na and 7Li NMR spectroscopy. In all cases the wormhole mesoporosity was retained as evidenced by BET surface areas from 400 to 700 m(2)/g, Horvath-Kawazoe pore sizes in the 20 Angstroms range, and a lack of hysteresis in the nitrogen adsorption isotherms. Variable-temperature conductivity studies show that the Li-reduced materials are semiconductors, with conductivity values 3 orders of magnitude higher than those of the Na-reduced materials. Electrochemical measurements demonstrate reversible intercalation/deintercalation of Li+ ions into pristine mesoporous Ti oxides with good cycling capacity. Solid-state 23Na NMR reveals two distinct Na environments: one corresponding to sodium ions in the mesoporous channels and the other corresponding to sodium ions intercalated into the metal framework. 23Na NMR spectra also indicate that the relative population of the framework site increases with increased reduction levels. Solid-state 7Li NMR spectra display a single broad resonance, which increases in breadth with increased reduction levels, though individual resonances inferring the presence of channel and framework Li species are not resolved. Comparisons of the lithium chemical shifts with published values suggests an "anatase-like structure" with no long-range order in the least-reduced samples but a "lithium titanate-like structure" with no long-range order in the higher reduced materials. PMID:16472000

Lo, Andy Y H; Schurko, Robert W; Vettraino, Melissa; Skadtchenko, Boris O; Trudeau, Michel; Antonelli, David M

2006-02-20

206

Effect of melamine polyphosphate on thermal degradation of polyamides: a combined X-ray diffraction and solid-state NMR study  

Microsoft Academic Search

The effect of melamine polyphosphate (MpolyP) on the thermal degradation of both polyamide 66 (PA66) and polyamide 6 (PA6) was studied using a combination of solid-state techniques. The mixtures of MpolyP with polyamides were heated for different times at 350 and 450°C. The residues were then analyzed by X-ray diffraction and both solid-state 13C NMR and 31P NMR. The chemical

Shahab Jahromi; Wouter Gabriëlse; Ad Braam

2003-01-01

207

Separation of 47Ti and 49Ti Solid-State NMR Lineshapes by Static QCPMG Experiments at Multiple Fields  

SciTech Connect

Experimental procedures are proposed and demonstrated that separate the spectroscopic contribution from both 47Ti and 49Ti in solid-state nuclear magnetic resonance spectra. These take advantage of the different nuclear spin quantum numbers of these nuclei that lead to different ‘effective’ radiofrequency fields for the central transition nutation frequencies when these nuclei occur in sites with a significant electric field gradient. Numerical simulations and solid-state NMR experiments were performed on the TiO2 polymorphs anatase and rutile. For anatase the separation of the two isotopes at high field (21.1 T) facilitated accurate determination of both EFG- and CSA-interactions using the different scaling of the EFG-tensor for the two isotopes. Rutile, having a larger quadrupolar coupling constant (CQ) was examined by 49Ti selective experiments at different magnetic fields to obtain spectra with different scalings of the two anisotropic tensors. A small chemical shielding anisotropy (CSA) of -30 ppm was determined.

Larsen, Flemming H.; Farnan, Ian E.; Lipton, Andrew S.

2006-02-01

208

Monitoring of bentonite pore water with a probe based on solid-state microsensors.  

PubMed

Repositories for the disposal of radioactive waste generally rely on a multi-barrier system to isolate the waste from the biosphere. This multi-barrier system typically comprises the natural geological barrier provided by the repository host rock and its surroundings and an engineered barrier system (EBS). Bentonite is being studied as an appropriated porous material for an EBS to prevent or delay the release and transport of radionuclides towards biosphere. The study of pore water chemistry within bentonite barriers will permit to understand the transport phenomena of radionuclides and obtain a database of the bentonite-water interaction processes. In this work, the measurement of some chemical parameters in bentonite pore water using solid-state microsensors is proposed. Those sensors are well suited for this application since in situ measurements are feasible and they are robust enough for the long periods of time that monitoring is needed in an EBS. A probe containing an ISFET (ion sensitive field effect transistor) for measuring pH, and platinum microelectrodes for measuring conductivity and redox potential was developed, together with the required instrumentation, to study the chemical changes in a test cell with compacted bentonite. Response features of the sensors' probe and instrumentation performance in synthetic samples with compositions similar to those present in bentonite barriers are reported. Measurements of sensors stability in a test cell are also presented. PMID:17723733

Orozco, Jahir; Baldi, Antoni; Martín, Pedro L; Bratov, Andrei; Jiménez, Cecilia

2006-07-21

209

Solution and Solid-State NMR Structural Studies of Antimicrobial Peptides LPcin-I and LPcin-II  

PubMed Central

Lactophoricin (LPcin-I) is an antimicrobial, amphiphatic, cationic peptide with 23-amino acid residues isolated from bovine milk. Its analogous peptide, LPcin-II, lacks six N-terminal amino acids compared to LPcin-I. Interestingly, LPcin-II does not display any antimicrobial activity, whereas LPcin-I inhibits the growth of both Gram-negative and Gram-positive bacteria without exhibiting any hemolytic activity. Uniformly 15N-labeled LPcin peptides were prepared by the recombinant expression of fusion proteins in Escherichia coli, and their properties were characterized by electrospray ionization mass spectrometry, circular dichroism spectroscopy, and antimicrobial activity tests. To understand the structure-activity relationship of these two peptides, they were studied in model membrane environments by a combination of solution and solid-state NMR spectroscopy. We determined the tertiary structure of LPcin-I and LPcin-II in the presence of dodecylphosphorylcholine micelles by solution NMR spectroscopy. Magnetically aligned unflipped bicelle samples were used to investigate the structure and topology of LPcin-I and LPcin-II by solid-state NMR spectroscopy.

Park, Tae-Joon; Kim, Ji-Sun; Ahn, Hee-Chul; Kim, Yongae

2011-01-01

210

The structural topology of wild-type phospholamban in oriented lipid bilayers using 15N solid-state NMR spectroscopy.  

PubMed

For the first time, 15N solid-state NMR experiments were conducted on wild-type phospholamban (WT-PLB) embedded inside mechanically oriented phospholipid bilayers to investigate the topology of its cytoplasmic and transmembrane domains. 15N solid-state NMR spectra of site-specific 15N-labeled WT-PLB indicate that the transmembrane domain has a tilt angle of 13 degrees+/-6 degrees with respect to the POPC (1-palmitoyl-2-oleoyl-sn-glycero-phosphocholine) bilayer normal and that the cytoplasmic domain of WT-PLB lies on the surface of the phospholipid bilayers. Comparable results were obtained from site-specific 15N-labeled WT-PLB embedded inside DOPC/DOPE (1,2-dioleoyl-sn-glycero-3-phosphocholine/1,2-dioleoyl-sn-glycero-3-phosphoethanolamine) mechanically oriented phospholipids' bilayers. The new NMR data support a pinwheel geometry of WT-PLB, but disagree with a bellflower structure in micelles, and indicate that the orientation of the cytoplasmic domain of the WT-PLB is similar to that reported for the monomeric AFA-PLB mutant. PMID:17905829

Abu-Baker, Shadi; Lu, Jun-Xia; Chu, Shidong; Shetty, Kiran K; Gor'kov, Peter L; Lorigan, Gary A

2007-09-28

211

3D DUMAS: Simultaneous acquisition of three-dimensional magic angle spinning solid-state NMR experiments of proteins  

NASA Astrophysics Data System (ADS)

Using the DUMAS (Dual acquisition Magic Angle Spinning) solid-state NMR approach, we created new pulse schemes that enable the simultaneous acquisition of three dimensional (3D) experiments on uniformly 13C, 15N labeled proteins. These new experiments exploit the simultaneous cross-polarization (SIM-CP) from 1H to 13C and 15N to acquire two 3D experiments simultaneously. This is made possible by bidirectional polarization transfer between 13C and 15N and the long living 15N z-polarization in solid state NMR. To demonstrate the power of this approach, four 3D pulse sequences (NCACX, CANCO, NCOCX, CON(CA)CX) are combined into two pulse sequences (3D DUMAS-NCACX-CANCO, 3D DUMAS-NCOCX-CON(CA)CX) that allow simultaneous acquisition of these experiments, reducing the experimental time by approximately half. Importantly, the 3D DUMAS-NCACX-CANCO experiment alone makes it possible to obtain the majority of the backbone sequential resonance assignments for microcrystalline U-13C,15N ubiquitin. The DUMAS approach is general and applicable to many 3D experiments, nearly doubling the performance of NMR spectrometers.

Gopinath, T.; Veglia, Gianluigi

2012-07-01

212

Detection of fulleroid sites in fullerene-60 by high-resolution solid-state [sup 1]H NMR  

SciTech Connect

[sup 1]H solid-state NMR with magic-angle spinning (MAS NMR) detects dilute H-containing species in chromatographically purified C[sub 60]. Because of the weakness of the [sup 1]H-[sup 1]H dipolar couplings, the spectral peaks are very sharp and the T[sub 1] values are not averaged by spin diffusion. On the basis of chemical shifts and peak connectivities as revealed by COSY, we have identified various fulleroids, as well as toluene and dioctyl phthalate (DOP) impurities. The fulleroids contain HC=CHCH[sub 2]CH[sub 3], HC=CHCH[sub 3], and HC=CH groups. DOP is probably complexed to C[sub 60] via the aromatic moiety. Laboratory and rotating-frame spin-diffusion experiments show that the H-containing species are so diluted by bulk C[sub 60] that they cannot communicate by intermolecular spin diffusion. The intramolecular spin-diffusion paths suggest that the alkyl chains of DOP are folded back toward the aromatic ring. We have found that two-dimensional [sup 1]H NMR techniques work well in the solid state without a multiple-pulse homonuclear decoupling, provided that the species under study are sufficiently dilute by a nondipolar medium. 46 refs., 8 figs., 2 tabs.

Kolodziejski, W.; Corma, A. (Universidad Politecnica de Valencia (Spain)); Barras, J.; Klinowski, J. (Univ. of Cambridge (United Kingdom))

1995-03-09

213

Solid state {sup 31}P NMR study of phosphonate binding sites in guanidine-functionalized, molecular imprinted silica xerogels  

SciTech Connect

Phosphonate binding sites in guanidine and ammonium surface-functionalized silica xerogels were prepared via the molecular imprinting technique and characterized using solid state {sup 31}P MAS NMR. One-point, two-point, and non-specific host-guest interactions between phenylphosphonic acid (PPA) and the functionalized gels were distinguished by characteristic chemical shifts of the observed absorption peaks. Using solid state as well as solution phase NMR analyses, absorptions observed at 15.5 ppm and 6.5 ppm were identified as resulting from the 1:1 (one-point) and 2:1 (two-point) guanidine to phosphonate interactions, respectively. Similar absorptions were observed with the ammonium functionalized gels. By examining the host-guest interactions within the gels, the efficiency of the molecular imprinting procedure with regard to the functional monomer-to-template interaction could be readily assessed. Template removal followed by substrate adsorption studies conducted on the guanidine functionalized gels provided a method to evaluate the binding characteristics of the receptor sites to a phosphonate substrate. During these experiments, {sup 29}Si and {sup 31}P MAS NMR acted as diagnostic monitors to identify structural changes occurring in the gel matrix and at the receptor site from solvent mediated processes.

Sasaki, D.Y.; Alam, T.D.

2000-01-03

214

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

215

Solid-State Deuterium NMR Studies Reveal ?s-ns Motions in the HIV-1 TAR RNA Recognition Site  

PubMed Central

Solution and solid-state NMR measurements were used together to examine motion in three sites in the HIV-1 TAR RNA. We wished to investigate the dynamics facilitating the conformational rearrangements the TAR RNA must undergo for tat binding, and in particular to characterize the full range of motional timescales accessible to this RNA. Our results demonstrate that the dynamics in TAR involving residues essential to tat binding include not only the faster motions detected by solution relaxation measurements, but also a significant component in the ?s-ns timescale.

Olsen, Greg L.; Echodu, Dorothy C.; Shajani, Zahra; Bardaro, Michael F.; Varani, Gabriele; Drobny, Gary P.

2009-01-01

216

Local structure of hydroxy peroxy apatite: A combined XRD, FT-IR, Raman, SEM, and solid-state NMR study  

NASA Astrophysics Data System (ADS)

The synthesized hydroxyapatite (HAp) and hydroxy peroxy apatite are studied using various techniques, such as X-ray powder diffraction, FT-IR and Raman spectroscopy, scanning electron microscopy, and solid-state NMR spectroscopy. The experimental data suggest that hydroxy peroxy apatite contains a small amount of hydration of partially dehydroxylated hydroxyapatite phase and calcium hydroxide. The incorporation of peroxide ions into the lattice of HAp causes perturbations of the hydrogen environments and slight changes in its crystal morphology. The distance between H in some structural OH- and adjacent O along the c-axis becomes longer instead of forming a hydrogen bond after the incorporation of peroxide ions.

Yu, Huaguang; Zhang, Hailu; Wang, Xiaomin; Gu, Zhongwei; Li, Xudong; Deng, Feng

2007-10-01

217

Theoretical and experimental insights into applicability of solid-state 93Nb NMR in catalysis.  

PubMed

Ab initio DFT calculations of (93)Nb NMR parameters using the NMR-CASTEP code were performed for a series of over fifty individual niobates, and a good agreement has been found with experimental NMR parameters. New experimental and calculated (93)Nb NMR data were obtained for several compounds, AlNbO4, VNb9O25, K8Nb6O19 and Cs3NbO8, which are of particular interest for catalysis. Several interesting trends have been identified between (93)Nb NMR parameters and the specifics of niobium site environments in niobates. These trends may serve as useful guidelines in interpreting (93)Nb NMR spectra of complex niobium oxide systems, including amorphous samples and niobium-based multicomponent heterogeneous catalysts. Potential applications of (93)Nb NMR to study solid polyoxoniobates are discussed. PMID:23450163

Papulovskiy, Evgeniy; Shubin, Alexandre A; Terskikh, Victor V; Pickard, Chris J; Lapina, Olga B

2013-04-14

218

Evaluation of Bone Mineral Density Using Three-Dimensional Solid State Phosphorus31 NMR Projection Imaging  

Microsoft Academic Search

.   A solid state magnetic resonance imaging technique is used to measure true three-dimensional mineral density of synthetic\\u000a hydroxyapatite phantoms and specimens of bone ex vivo. The phosphorus-31 free induction decay at 2.0 T magnetic field strength is sampled following application of a short, hard\\u000a radiofrequency excitation pulse in the presence of a fixed amplitude magnetic field gradient. Multiple gradient

Y. Wu; J. L. Ackerman; D. A. Chesler; J. Li; R. M. Neer; J. Wang; M. J. Glimcher

1998-01-01

219

High-Resolution Conformation of Gramicidin A in a Lipid Bilayer by Solid State NMR  

Microsoft Academic Search

Solid-state nuclear magnetic resonance spectroscopy of uniformly aligned preparations of gramicidin A in lipid bilayers has been used to elucidate a high-resolution dimeric structure of the cation channel conformation solely on the basis of the amino acid sequence and 144 orientational constraints. This initial structure defines the helical pitch as single-stranded, fixes the number of residues per turn at six

R. R. Ketchem; W. Hu; T. A. Cross

1993-01-01

220

Toward a structure determination method for biomineral-associated protein using combined solid-state NMR and computational structure prediction  

PubMed Central

Summary Protein-biomineral interactions are paramount to materials production in biology, including the mineral phase of hard tissue. Unfortunately, the structure of biomineral-associated proteins cannot be determined by X-ray crystallography or solution NMR. Here we report a method for determining the structure of biomineral-associated proteins. The method combines solid-state NMR (ssNMR) and ssNMR-biased computational structure prediction. In addition, the algorithm is able to identify lattice geometries most compatible with ssNMR constraints, representing a quantitative, novel method for investigating crystal-face binding specificity. We use this new method to determine most of the structure of human salivary statherin interacting with the mineral phase of tooth enamel. Computation and experiment converge on an ensemble of related structures and identify preferential binding at three crystal surfaces. The work represents a significant advance toward determining structure of biomineral-adsorbed protein using experimentally biased structure prediction. This method is generally applicable to proteins that can be chemically synthesized.

Masica, David L.; Ash, Jason T.; Ndao, Moise; Drobny, Gary P.; Gray, Jeffrey J

2010-01-01

221

Crystallinity and compositional changes in carbonated apatites: Evidence from 31P solid-state NMR, Raman, and AFM analysis  

NASA Astrophysics Data System (ADS)

Solid-state (magic-angle spinning) NMR spectroscopy is a useful tool for obtaining structural information on bone organic and mineral components and synthetic model minerals at the atomic-level. Raman and 31P NMR spectral parameters were investigated in a series of synthetic B-type carbonated apatites (CAps). Inverse 31P NMR linewidth and inverse Raman PO43-?1 bandwidth were both correlated with powder XRD c-axis crystallinity over the 0.3-10.3 wt% CO32- range investigated. Comparison with bone powder crystallinities showed agreement with values predicted by NMR and Raman calibration curves. Carbonate content was divided into two domains by the 31P NMR chemical shift frequency and the Raman phosphate ?1 band position. These parameters remain stable except for an abrupt transition at 6.5 wt% carbonate, a composition which corresponds to an average of one carbonate per unit cell. This near-binary distribution of spectroscopic properties was also found in AFM-measured particle sizes and Ca/P molar ratios by elemental analysis. We propose that this transition differentiates between two charge-balancing ion-loss mechanisms as measured by Ca/P ratios. These results define a criterion for spectroscopic characterization of B-type carbonate substitution in apatitic minerals.

McElderry, John-David P.; Zhu, Peizhi; Mroue, Kamal H.; Xu, Jiadi; Pavan, Barbara; Fang, Ming; Zhao, Guisheng; McNerny, Erin; Kohn, David H.; Franceschi, Renny T.; Holl, Mark M. Banaszak; Tecklenburg, Mary M. J.; Ramamoorthy, Ayyalusamy; Morris, Michael D.

2013-10-01

222

Characterization by solid-state NMR and selective dissolution techniques of anhydrous and hydrated CEM V cement pastes  

SciTech Connect

The long term behaviour of cement based materials is strongly dependent on the paste microstructure and also on the internal chemistry. A CEM V blended cement containing pulverised fly ash (PFA) and blastfurnace slag (BFS) has been studied in order to understand hydration processes which influence the paste microstructure. Solid-state NMR spectroscopy with complementary X-ray diffraction analysis and selective dissolution techniques have been used for the characterization of the various phases (C{sub 3}S, C{sub 2}S, C{sub 3}A and C{sub 4}AF) of the clinker and additives and then for estimation of the degree of hydration of these same phases. Their quantification after simulation of experimental {sup 29}Si and {sup 27}Al MAS NMR spectra has allowed us to follow the hydration of recent (28 days) and old (10 years) samples that constitutes a basis of experimental data for the prediction of hydration model.

Brunet, F., E-mail: francine.brunet@cea.f [CEA, IRAMIS, Service Interdisciplinaire sur les Systemes Moleculaires et Materiaux, LSDRM, F-91191 Gif sur Yvette Cedex (France); Charpentier, T. [CEA, IRAMIS, Service Interdisciplinaire sur les Systemes Moleculaires et Materiaux, LSDRM, F-91191 Gif sur Yvette Cedex (France); Chao, C.N.; Peycelon, H. [CEA, DPC, Service de la Corrosion et du Comportement des Materiaux dans leur Environnement, F-91191 Gif sur Yvette Cedex (France); Nonat, A. [Institut Carnot de Bourgogne, UMR 5209 CNRS-Universite de Bourgogne, 9 Av. A. Savary, BP 47 870, F-21078 DIJON Cedex (France)

2010-02-15

223

Grid-free powder averages: On the applications of the Fokker–Planck equation to solid state NMR  

NASA Astrophysics Data System (ADS)

We demonstrate that Fokker–Planck equations in which spatial coordinates are treated on the same conceptual level as spin coordinates yield a convenient formalism for treating magic angle spinning NMR experiments. In particular, time dependence disappears from the background Hamiltonian (sample spinning is treated as an interaction), spherical quadrature grids are avoided completely (coordinate distributions are a part of the formalism) and relaxation theory with any linear diffusion operator is easily adopted from the Stochastic Liouville Equation theory. The proposed formalism contains Floquet theory as a special case. The elimination of the spherical averaging grid comes at the cost of increased matrix dimensions, but we show that this can be mitigated by the use of state space restriction and tensor train techniques. It is also demonstrated that low correlation order basis sets apparently give accurate answers in powder-averaged MAS simulations, meaning that polynomially scaling simulation algorithms do exist for a large class of solid state NMR experiments.

Edwards, Luke J.; Savostyanov, D. V.; Nevzorov, A. A.; Concistrè, M.; Pileio, G.; Kuprov, Ilya

2013-10-01

224

Residual methyl protonation in perdeuterated proteins for multi-dimensional correlation experiments in MAS solid-state NMR spectroscopy  

NASA Astrophysics Data System (ADS)

NMR studies involving perdeuterated proteins focus in general on exchangeable amide protons. However, non-exchangeable sites contain as well a small amount of protons as the employed precursors for protein biosynthesis are not completely proton depleted. The degree of methyl group protonation is in the order of 9% for CD2H using >97% deuterium enriched glucose. We show in this manuscript that this small amount of residual protonation is sufficient to perform 2D and 3D MAS solid-state NMR experiments. In particular, we suggest a HCCH-TOBSY type experiment which we successfully employ to assign the methyl resonances in aliphatic side chains in a perdeuterated sample of the SH3 domain of chicken ?-spectrin.

Agarwal, Vipin; Reif, Bernd

2008-09-01

225

?B-Crystallin: A Hybrid Solid-State/Solution-State NMR Investigation Reveals Structural Aspects of the Heterogeneous Oligomer  

SciTech Connect

Atomic-level structural information on ?B-Crystallin (?B), a prominent member of the small heat-shock protein family, has been a challenge to obtain due its polydisperse oligomeric nature. We show that magic-angle spinning solid-state NMR can be used to obtain high-resolution information on an ?580-kDa human ?B assembled from 175-residue 20-kDa subunits. An ?100-residue ?-crystallin domain is common to all small heat-shock proteins, and solution-state NMR was performed on two different ?- crystallin domain constructs isolated from ?B. In vitro, the chaperone-like activities of full-length ?B and the isolated ?-crystallin domain are identical. Chemical shifts of the backbone and C? resonances have been obtained for residues 64–162 (?-crystallin domain plus part of the C-terminus) in ?B and the isolated ?-crystallin domain by solid-state and solution-state NMR, respectively. Both sets of data strongly predict six ?-strands in the ?-crystallin domain. A majority of residues in the ?-crystallin domain have similar chemical shifts in both solid-state and solution-state, indicating similar structures for the domain in its isolated and oligomeric forms. Sites of intersubunit interaction are identified from chemical shift differences that cluster to specific regions of the ?-crystallin domain. Multiple signals are observed for the resonances of M68 in the oligomer, identifying the region containing this residue as existing in heterogeneous environments within ?B. Evidence for a novel dimerization motif in the human ?-crystallin domain is obtained by a comparison of (i) solid-state and solution-state chemical shift data and (ii) 1H–15N heteronuclear single quantum coherence spectra as a function of pH. The isolated ?-crystallin domain undergoes a dimer–monomer transition over the pH range 7.5–6.8. This steep pHdependent switch may be important for ?B to function optimally (e.g., to preserve the filament integrity of cardiac muscle proteins such as actin and desmin during cardiac ischemia, which is accompanied by acidosis).

Jehle, Stefan; van Rossum, Barth; Stout, Joseph R.; Noguchi, Satoshi M.; Falber, Katja; Rehbein, Kristina; Oschkinat, Hartmut; Klevit, Rachel E.; Rajagopal, Ponni

2009-02-06

226

Dipolar and Scalar Couplings in Solid State NMR of Quadrupolar Nuclei  

Microsoft Academic Search

Summary.  ?Most NMR-active nuclei found in the periodic table have a quadrupole moment. In combination with a nonsymmetric electron\\u000a distribution a strong NMR-active interaction results, which very often overshadows the dipolar and scalar couplings. This\\u000a article aims at reviewing how these interactions manifest themselves in quadrupolar NMR and how they can be exploited for\\u000a resonance assignment and structure elucidation, in spite

Alexej Jerschow

2002-01-01

227

Interaction of Cd and Zn with biologically important ligands characterized using solid-state NMR and ab initio calculations.  

PubMed

For the first time, coordination geometry and structure of metal binding sites in biologically relevant systems are studied using chemical shift parameters obtained from solid-state NMR experiments and quantum chemical calculations. It is also the first extensive report looking at metal-imidazole interaction in the solid state. The principal values of the (113)Cd chemical shift anisotropy (CSA) tensor in crystalline cadmium histidinate and two different cadmium formates (hydrate and anhydrate) were experimentally measured to understand the effect of coordination number and geometry on (113)Cd CSA. Further, (13)C and (15)N chemical shifts have also been experimentally determined to examine the influence of cadmium on the chemical shifts of (15)N and (13)C nuclei present near the metal site in the cadmium-histidine complex. These values were then compared with the chemical shift values obtained from the isostructural bis(histidinato)zinc(II) complex as well as from the unbound histidine. The results show that the isotropic chemical shift values of the carboxyl carbons shift downfield and those of amino and imidazolic nitrogens shift upfield in the metal (Zn,Cd)-histidine complexes relative to the values of the unbound histidine sample. These shifts are in correspondence with the anticipated values based on the crystal structure. Ab initio calculations on the cadmium histidinate molecule show good agreement with the (113)Cd CSA tensors determined from solid-state NMR experiments on powder samples. (15)N chemical shifts for other model complexes, namely, zinc glycinate and zinc hexaimidazole chloride, are also considered to comprehend the effect of zinc binding on (15)N chemical shifts. PMID:12716214

Kidambi, Srikanth S; Lee, Dong-Kuk; Ramamoorthy, A

2003-05-01

228

(31)P Solid-State NMR study of the chemical setting process of a dual-paste injectable brushite cements.  

PubMed

The composition and evolution of a brushite-type calcium phosphate cement was investigated by Solid-State NMR and X-ray during the setting process. The cement is obtained by mixing beta-tricalcium phosphate [Ca(3)(PO(4))(2), beta-TCP] and monocalcium phosphate monohydrate [Ca(H(2)PO(4))(2).H(2)O, MCPM] in presence of water, with formation of dicalcium phosphate dihydrate or brushite [CaHPO(2).2H(2)O, DCPD]. Analysis of the initial beta-TCP paste has shown the presence of beta-calcium pyrophosphate [Ca(2)P(2)O(7), beta-CPy] and that of the initial MCPM a mixture of MCPM and dicalcium phosphate [CaHPO(4), DCP]. Follow-up of the chemical composition by (31)P Solid-State NMR enables to show that the chemical setting process appeared to reach an end after 20 min. The constant composition observed at the end of the process was similarly determined. PMID:19365821

Legrand, A P; Sfihi, H; Lequeux, N; Lemaître, J

2009-10-01

229

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

230

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

231

High-resolution conformation of gramicidin A in a lipid bilayer by solid-state NMR.  

PubMed

Solid-state nuclear magnetic resonance spectroscopy of uniformly aligned preparations of gramicidin A in lipid bilayers has been used to elucidate a high-resolution dimeric structure of the cation channel conformation solely on the basis of the amino acid sequence and 144 orientational constraints. This initial structure defines the helical pitch as single-stranded, fixes the number of residues per turn at six to seven, specifies the helix sense as right-handed, and identifies the hydrogen bonds. Refinement of this initial structure yields reasonable hydrogen-bonding distances with only minimal changes in the torsion angles. PMID:7690158

Ketchem, R R; Hu, W; Cross, T A

1993-09-10

232

Structure solution of network materials by solid-state NMR without knowledge of the crystallographic space group.  

PubMed

An algorithm is presented for solving the structures of silicate network materials such as zeolites or layered silicates from solid-state (29)Si double-quantum NMR data for situations in which the crystallographic space group is not known. The algorithm is explained and illustrated in detail using a hypothetical two-dimensional network structure as a working example. The algorithm involves an atom-by-atom structure building process in which candidate partial structures are evaluated according to their agreement with Si-O-Si connectivity information, symmetry restraints, and fits to (29)Si double quantum NMR curves followed by minimization of a cost function that incorporates connectivity, symmetry, and quality of fit to the double quantum curves. The two-dimensional network material is successfully reconstructed from hypothetical NMR data that can be reasonably expected to be obtained for real samples. This advance in "NMR crystallography" is expected to be important for structure determination of partially ordered silicate materials for which diffraction provides very limited structural information. PMID:23415450

Brouwer, Darren H

2013-01-30

233

A comparative spectroscopic investigation of three pseudopolymorphs of testosterone using solid-state i.r. and high-resolution solid-state NMR  

NASA Astrophysics Data System (ADS)

Three pseudopolymorphic forms of testosterone have been examined by i.r. and CP/MAS NMR spectroscopies. The transmittance i.r. data clearly distinguish the forms. The NMR work also provides clear distinctions and shows crystallographic splittings for the ? form only, in accordance with the X-ray data. The NMR spectra are fully assigned. The effect of crystallisation procedure on the NMR spectra was explored. NMR can be used to quantitatively assess mixtures of the ? and ? forms.

Fletton, Richard A.; Harris, Robin K.; Kenwright, Alan M.; Lancaster, Robert W.; Packer, Kenneth J.; Sheppard, Norman

234

A solid-state NMR study of condensation/retrograde reactions during coal liquefaction  

SciTech Connect

The objective of this work is to perform an NMR study of the aromaticity in coal, coal derived products and/or model compounds generated by pyrolysis and thermal solubilization of coal in the presence of a hydrogen donor solvent. Cross Polarization with Magic-Angle Spinning (CP/MAS) will be used to measure the carbon aromaticity, and Combined Rotation and Multiple Pulse Spectroscopy (CRAMPS) NMR techniques will be used to measure the hydrogen aromaticity. From these NMR measurements the aromatic hydrogen-to-carbon ratio will be obtained and used to study condensation/retrograde reactions during coal liquefaction. 2 refs., 1 fig.

Miknis, F.P.

1989-11-01

235

Observation of a Low-Temperature, Dynamically Driven, Structural Transition in a Polypeptide by Solid State NMR Spectroscopy  

PubMed Central

At reduced temperatures, proteins and other biomolecules are generally found to exhibit dynamic as well as structural transitions. This includes a so-called protein glass transition that is universally observed in systems cooled between 200–230K, and which is generally attributed to interactions between hydrating solvent molecules and protein side chains. However, there is also experimental and theoretical evidence for a low-temperature transition in the intrinsic dynamics of the protein itself, absent any solvent. Here, we use low-temperature solid state NMR to examine site specific fluctuations in atomic structure and dynamics in the absence of solvents. In particular, we employ magic angle spinning NMR to examine a structural phase transition associated with dynamic processes in a solvent-free polypeptide, N-f-MLF-OH, lattice at temperatures as low as 90K. This transition is characterized by the appearance of an extra set of lines in 1D 15N spectra as well as additional cross peaks in 2D 13C-13C and 13C-15N spectra. Interestingly, the gradual, temperature-dependent appearance of the new spectral component is not accompanied by the line broadening typical of dynamic transitions. A direct comparison between the spectra of N-f-MLF-OH and the analog N-f-MLF-OMe, which does not display this transition, indicates a correlation of the structural transition to the temperature dependent motion of the aromatic phenylalanine side chain. Several quantitative solid state NMR experiments were employed to provide site-specific measurements of structural and motional features of the observed transition.

Bajaj, Vikram S.; van der Wel, Patrick C.A.; Griffin, Robert G.

2009-01-01

236

Does Solid-state 15 N NMR Spectroscopy Detect all Soil Organic Nitrogen?  

Microsoft Academic Search

Virtually all of the N detected by 15N cross polarization (CP) NMR spectra of four HF-treated soil clay fractions is amide N. However, the intensity of this 15N CP NMR signal (per unit N) is 27–57% lower than detected for a wheat protein, gliadin. There are two possible explanations – either the amide N in the soil clay fractions produces

Ronald J. Smernik; Jeffrey A. Baldock

2005-01-01

237

A solid-state NMR study of condensation/retrograde reactions during coal liquefaction  

SciTech Connect

The objective of this work is to perform an NMR study of the aromaticity in coals, coal derived products and/or compounds generated by pyrolysis and thermal solubilization of coal in the presence of a hydrogen donor solvent. Cross Polarization with Magic-Angle Spinning (CP/MAS) will be used to measure the carbon aromaticity, and Combined Rotation and Multiple Pulse Spectroscopy (CRAMPS) NMR techniques will be used to measure the hydrogen aromaticity. From these NMR measurements the aromatic hydrogen-to- carbon ratio will be obtained and used to study condensation/retrograde reactions during coal liquefaction. The study consists of four tasks: (1)develop NMR methods to determine aromatic carbon by CP/MAS and aromatic hydrogen by CRAMPS for low hydrogen containing organic solids such as coals, and coal residues; (2) characterize the feasibility of applying the NMR method for quantitative measures in coals; (3) analyze selected samples of coals and coal-derived products to demonstrate applicability of the NMR methods to study coal liquefaction, and (4) report the results to the Department of Energy. 4 refs., 5 figs., 2 tabs.

Miknis, F.P.

1990-01-01

238

A solid-state NMR study of condensation/retrograde reactions during coal liquefaction  

SciTech Connect

The objective of this work is to perform an NMR study of the aromaticity in coals, coal derived products and/or model compounds generated by pyrolysis and thermal solubilization of coal in the presence of a hydrogen donor solvent. Cross Polarization with Magic-Angle Spinning (CP/MAS) will be used to measure the carbon aromaticity, and Combined Rotation and Multiple Pulse Spectroscopy (CRAMPS) NMR techniques will be used to measure the hydrogen aromaticity. From these NMR measurements the aromatic hydrogen-to- carbon ratio will be obtained and used to study condensation/retrograde reactions during coal liquefaction. The study consists of the following tasks: develop NMR methods to determine aromatic carbon by CP/MAS and aromatic hydrogen by CRAMPS for low hydrogen containing organic solids such as coals, and coal residues; characterize the feasibility of applying the NMR methods for quantitative measurements in coals; and analyze selected samples of coals and coal-derived products to demonstrate applicability of the NMR methods to study-coal liquefaction. 5 refs., 7 figs., 1 tab.

Miknis, F.P.

1989-01-01

239

Designing dipolar recoupling and decoupling experiments for biological solid-state NMR using interleaved continuous wave and RF pulse irradiation.  

PubMed

Rapid developments in solid-state NMR methodologyhave boosted this technique into a highly versatile tool for structural biology. The invention of increasingly advanced rf pulse sequences that take advantage of better hardware and sample preparation have played an important part in these advances. In the development of these new pulse sequences, researchers have taken advantage of analytical tools, such as average Hamiltonian theory or lately numerical methods based on optimal control theory. In this Account, we focus on the interplay between these strategies in the systematic development of simple pulse sequences that combines continuous wave (CW) irradiation with short pulses to obtain improved rf pulse, recoupling, sampling, and decoupling performance. Our initial work on this problem focused on the challenges associated with the increasing use of fully or partly deuterated proteins to obtain high-resolution, liquid-state-like solid-state NMR spectra. Here we exploit the overwhelming presence of (2)H in such samples as a source of polarization and to gain structural information. The (2)H nuclei possess dominant quadrupolar couplings which complicate even the simplest operations, such as rf pulses and polarization transfer to surrounding nuclei. Using optimal control and easy analytical adaptations, we demonstrate that a series of rotor synchronized short pulses may form the basis for essentially ideal rf pulse performance. Using similar approaches, we design (2)H to (13)C polarization transfer experiments that increase the efficiency by one order of magnitude over standard cross polarization experiments. We demonstrate how we can translate advanced optimal control waveforms into simple interleaved CW and rf pulse methods that form a new cross polarization experiment. This experiment significantly improves (1)H-(15)N and (15)N-(13)C transfers, which are key elements in the vast majority of biological solid-state NMR experiments. In addition, we demonstrate how interleaved sampling of spectra exploiting polarization from (1)H and (2)H nuclei can substantially enhance the sensitivity of such experiments. Finally, we present systematic development of (1)H decoupling methods where CW irradiation of moderate amplitude is interleaved with strong rotor-synchronized refocusing pulses. We show that these sequences remove residual cross terms between dipolar coupling and chemical shielding anisotropy more effectively and improve the spectral resolution over that observed in current state-of-the-art methods. PMID:23557787

Bjerring, Morten; Jain, Sheetal; Paaske, Berit; Vinther, Joachim M; Nielsen, Niels Chr

2013-04-04

240

Chemical structure and heterogeneity differences of two lignins from loblolly pine as investigated by advanced solid-state NMR spectroscopy.  

PubMed

Advanced solid-state NMR was employed to investigate differences in chemical structure and heterogeneity between milled wood lignin (MWL) and residual enzyme lignin (REL). Wiley and conventional milled woods were also studied. The advanced NMR techniques included 13C quantitative direct polarization, various spectral-editing techniques, and two-dimensional 1H-13C heteronuclear correlation NMR with 1H spin diffusion. The 13C chemical shift regions between 110 and 160 ppm of two lignins were quite similar to those of two milled woods. REL contained much more residual carbohydrates than MWL, showing that MWL extraction more successfully separated lignin from cellulose and hemicelluloses than REL extraction; REL was also of higher COO, aromatic C-C, and condensed aromatics but of lower aromatic C-H. At a spin diffusion time of 0.55 ms, the magnetization was equilibrated through the whole structure of MWL lignin, but not through that of REL, indicating that REL is more heterogeneous than MWL. PMID:20726583

Holtman, Kevin M; Chen, Na; Chappell, Mark A; Kadla, John F; Xu, Ling; Mao, Jingdong

2010-09-22

241

Solid-State NMR, Crystallographic, and Computational Investigation of Bisphosphonates and Farnesyl Diphosphate Synthase-Bisphosphonate Complexes  

SciTech Connect

Bisphosphonates are a class of molecules in widespread use in treating bone resorption diseases and are also of interest as immunomodulators and anti-infectives. They function by inhibiting the enzyme farnesyl diphosphate synthase (FPPS), but the details of how these molecules bind are not fully understood. Here, we report the results of a solid-state {sup 13}C, {sup 15}N, and {sup 31}P magic-angle sample spinning (MAS) NMR and quantum chemical investigation of several bisphosphonates, both as pure compounds and when bound to FPPS, to provide information about side-chain and phosphonate backbone protonation states when bound to the enzyme. We then used computational docking methods (with the charges assigned by NMR) to predict how several bisphosphonates bind to FPPS. Finally, we used X-ray crystallography to determine the structures of two potent bisphosphonate inhibitors, finding good agreement with the computational results, opening up the possibility of using the combination of NMR, quantum chemistry and molecular docking to facilitate the design of other, novel prenytransferase inhibitors.

Mao,J.; Mukherjee, S.; Zhang, Y.; Cao, R.; Sanders, J.; Song, Y.; Zhang, Y.; Meints, G.; Gao, Y.; et al.

2006-01-01

242

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

PubMed

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

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

2013-01-18

243

An Investigation of Lanthanum Coordination Compounds by Using Solid- State 139La NMR Spectroscopy and Relativistic Density Functional Theory  

SciTech Connect

Lanthanum-139 NMR spectra of stationary samples of several solid LaIII coordination compounds have been obtained at applied magnetic fields of 11.75 and 17.60 T. The breadth and shape of the 139La NMR spectra of the central transition are dominated by the interaction between the 139La nuclear quadrupole moment and the electric field gradient (EFG) at that nucleus; however, the influence of chemical-shift anisotropy on the NMR spectra is non-negligible for the majority of the compounds investigated. Analysis of the experimental NMR spectra reveals that the 139La quadrupolar coupling constants (CQ) range from 10.0 to 35.6 MHz, the spans of the chemical-shift tensor (W) range from 50 to 260 ppm, and the isotropic chemical shifts (diso) range from -80 to 178 ppm. In general, there is a correlation between the magnitudes of CQ and W, and diso is shown to depend on the La coordination number. Magnetic shielding tensors, calculated by using relativistic zeroth-order regular approximation density functional theory (ZORA-DFT) and incorporating scalar only or scalar plus spin-orbit relativistic effects, qualitatively reproduce the experimental chemical-shift tensors. In general, the inclusion of spin-orbit coupling yields results that are in better agreement with those from the experiment. The magnetic-shielding calculations and experimentally determined Euler angles can be used to predict the orientation of the chemical-shift and EFG tensors in the molecular frame. This study demonstrates that solid state 139La NMR spectroscopy is a useful characterization method and can provide insight into the molecular structure of lanthanum coordination compounds.

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

2005-12-16

244

The structure, dynamics and orientation of antimicrobial peptides in membranes by multidimensional solid-state NMR spectroscopy.  

PubMed

Linear peptide antibiotics have been isolated from amphibians, insects and humans and used as templates to design cheaper and more potent analogues for medical applications. Peptides such as cecropins or magainins are < or = 40 amino acids in length. Many of them have been prepared by solid-phase peptide synthesis with isotopic labels incorporated at selected sites. Structural analysis by solid-state NMR spectroscopy and other biophysical techniques indicates that these peptide antibiotics strongly interact with lipid membranes. In bilayer environments they exhibit amphipathic alpha-helical conformations and alignments of the helix axis parallel to the membrane surface. This contrasts the transmembrane orientations observed for alamethicin or gramicidin A. Models that have been proposed to explain the antibiotic and pore-forming activities of membrane-associated peptides, as well as other experimental results, include transmembrane helical bundles, wormholes, carpets, detergent-like effects or the in-plane diffusion of peptide-induced bilayer instabilities. PMID:10590307

Bechinger, B

1999-12-15

245

Cationic membrane peptides: atomic-level insight of structure-activity relationships from solid-state NMR.  

PubMed

Many membrane-active peptides, such as cationic cell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs), conduct their biological functions by interacting with the cell membrane. The interactions of charged residues with lipids and water facilitate membrane insertion, translocation or disruption of these highly hydrophobic species. In this review, we will summarize high-resolution structural and dynamic findings towards the understanding of the structure-activity relationship of lipid membrane-bound CPPs and AMPs, as examples of the current development of solid-state NMR (SSNMR) techniques for studying membrane peptides. We will present the most recent atomic-resolution structure of the guanidinium-phosphate complex, as constrained from experimentally measured site-specific distances. These SSNMR results will be valuable specifically for understanding the intracellular translocation pathway of CPPs and antimicrobial mechanism of AMPs, and more generally broaden our insight into how cationic macromolecules interact with and cross the lipid membrane. PMID:23108593

Su, Yongchao; Li, Shenhui; Hong, Mei

2012-10-30

246

Solid-State NMR Studies of Fossil Fuels using One- and Two-Dimensional Methods at High Magnetic Field  

SciTech Connect

We examine the opportunities offered by advancements in solid-state NMR (SSNMR) methods, which increasingly rely on the use of high magnetic fields and fast magic angle spinning (MAS), in the studies of coals and other carbonaceous materials. The sensitivity of one- and two-dimensional experiments tested on several Argonne Premium coal samples is only slightly lower than that of traditional experiments performed at low magnetic fields in large MAS rotors, since higher receptivity per spin and the use of 1H detection of low-gamma nuclei can make up for most of the signal loss due to the small rotor size. The advantages of modern SSNMR methodology in these studies include improved resolution, simplicity of pulse sequences, and the possibility of using J-coupling during mixing.

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

2012-06-24

247

{sup 45}Sc Solid State NMR studies of the silicides ScTSi (T=Co, Ni, Cu, Ru, Rh, Pd, Ir, Pt)  

SciTech Connect

The silicides ScTSi (T=Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir, Pt) were synthesized by arc-melting and characterized by X-ray powder diffraction. The structures of ScCoSi, ScRuSi, ScPdSi, and ScIrSi were refined from single crystal diffractometer data. These silicides crystallize with the TiNiSi type, space group Pnma. No systematic influences of the {sup 45}Sc isotropic magnetic shift and nuclear electric quadrupolar coupling parameters on various structural distortion parameters calculated from the crystal structure data can be detected. {sup 45}Sc MAS-NMR data suggest systematic trends in the local electronic structure probed by the scandium atoms: both the electric field gradients and the isotropic magnetic shifts relative to a 0.2 M aqueous Sc(NO{sub 3}){sub 3} solution decrease with increasing valence electron concentration and within each T group the isotropic magnetic shift decreases monotonically with increasing atomic number. The {sup 45}Sc nuclear electric quadrupolar coupling constants are generally well reproduced by quantum mechanical electric field gradient calculations using the WIEN2k code. Highlights: Black-Right-Pointing-Pointer Arc-melting synthesis of silicides ScTSi. Black-Right-Pointing-Pointer Single crystal X-ray data of ScCoSi, ScRuSi, ScPdSi, and ScIrSi. Black-Right-Pointing-Pointer {sup 45}Sc solid state NMR of silicides ScTSi.

Harmening, Thomas [Institut fuer Anorganische und Analytische Chemie and NRW Graduate School of Chemistry, Universitaet Muenster, Corrensstrasse 30, D-48149 Muenster (Germany); Eckert, Hellmut, E-mail: eckerth@uni-muenster.de [Institut fuer Physikalische Chemie, Universitaet Muenster, Corrensstrasse 30, D-48149 Muenster (Germany); Fehse, Constanze M. [Institut fuer Physikalische Chemie, Universitaet Muenster, Corrensstrasse 30, D-48149 Muenster (Germany); Sebastian, C. Peter, E-mail: sebastiancp@jncasr.ac.in [New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064 (India); Poettgen, Rainer, E-mail: pottgen@uni-muenster.de [Institut fuer Anorganische und Analytische Chemie and NRW Graduate School of Chemistry, Universitaet Muenster, Corrensstrasse 30, D-48149 Muenster (Germany)

2011-12-15

248

Helium-cooling and -spinning dynamic nuclear polarization for sensitivity-enhanced solid-state NMR at 14 T and 30 K.  

PubMed

We describe a (1)H polarization enhancement via dynamic nuclear polarization (DNP) at very low sample temperature T?30 K under magic-angle spinning (MAS) conditions for sensitivity-enhanced solid-state NMR measurement. Experiments were conducted at a high external field strength of 14.1 T. For MAS DNP experiments at T<90 K, a new probe system using cold helium gas for both sample-cooling and -spinning was developed. The novel system can sustain a low sample temperature between 30 and 90K for a period of time >10 h under MAS at ?(R)?3 kHz with liquid He consumption of ?6 L/h. As a microwave source, we employed a high-power, continuously frequency-tunable gyrotron. At T?34 K, (1)H DNP enhancement factors of 47 and 23 were observed with and without MAS, respectively. On the basis of these observations, a discussion on the total NMR sensitivity that takes into account the effect of sample temperature and external field strength used in DNP experiments is presented. It was determined that the use of low sample temperature and high external field is generally rewarding for the total sensitivity, in spite of the slower polarization buildup at lower temperature and lower DNP efficiency at higher field. These findings highlight the potential of the current continuous-wave DNP technique also at very high field conditions suitable to analyze large and complex systems, such as biological macromolecules. PMID:23079589

Matsuki, Yoh; Ueda, Keisuke; Idehara, Toshitaka; Ikeda, Ryosuke; Ogawa, Isamu; Nakamura, Shinji; Toda, Mitsuru; Anai, Takahiro; Fujiwara, Toshimichi

2012-09-27

249

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

NASA Astrophysics Data System (ADS)

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

Chan, Jerry C. C.; Tycko, Robert

2003-05-01

250

Characterizing the Secondary Protein Structure of Black Widow Dragline Silk Using Solid-State NMR and X-ray Diffraction.  

PubMed

This study provides a detailed secondary structural characterization of major ampullate dragline silk from Latrodectus hesperus (black widow) spiders. X-ray diffraction results show that the structure of black widow major ampullate silk fibers is comprised of stacked ?-sheet nanocrystallites oriented parallel to the fiber axis and an amorphous region with oriented (anisotropic) and isotropic components. The combination of two-dimensional (2D) (13)C-(13)C through-space and through-bond solid-state NMR experiments provide chemical shifts that are used to determine detailed information about the amino acid motif secondary structure in black widow spider dragline silk. Individual amino acids are incorporated into different repetitive motifs that make up the majority of this protein-based biopolymer. From the solid-state NMR measurements, we assign distinct secondary conformations to each repetitive amino acid motif and, hence, to the amino acids that make up the motifs. Specifically, alanine is incorporated in ?-sheet (poly(Alan) and poly(Gly-Ala)), 31-helix (poly(Gly-Gly-Xaa), and ?-helix (poly(Gln-Gln-Ala-Tyr)) components. Glycine is determined to be in ?-sheet (poly(Gly-Ala)) and 31-helical (poly(Gly-Gly-Xaa)) regions, while serine is present in ?-sheet (poly(Gly-Ala-Ser)), 31-helix (poly(Gly-Gly-Ser)), and ?-turn (poly(Gly-Pro-Ser)) structures. These various motif-specific secondary structural elements are quantitatively correlated to the primary amino acid sequence of major ampullate spidroin 1 and 2 (MaSp1 and MaSp2) and are shown to form a self-consistent model for black widow dragline silk. PMID:24024617

Jenkins, Janelle E; Sampath, Sujatha; Butler, Emily; Kim, Jihyun; Henning, Robert W; Holland, Gregory P; Yarger, Jeffery L

2013-09-26

251

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

252

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

PubMed

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

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

2003-07-22

253

Quantitative solid state NMR analysis of residues from acid hydrolysis of loblolly pine wood.  

PubMed

The composition of solid residues from hydrolysis reactions of loblolly pine wood with dilute mineral acids is analyzed by (13)C Cross Polarization Magic Angle Spinning (CP MAS) NMR spectroscopy. Using this method, the carbohydrate and lignin fractions are quantified in less than 3h as compared to over a day using wet chemical methods. In addition to the quantitative information, (13)C CP MAS NMR spectroscopy provides information on the formation of additional extractives and pseudo lignin from the carbohydrates. Being a non-destructive technique, NMR spectroscopy provides unambiguous evidence of the presence of side reactions and products, which is a clear advantage over the wet chemical analytical methods. Quantitative results from NMR spectroscopy and proximate analysis are compared for the residues from hydrolysis of loblolly pine wood under 13 different conditions; samples were treated either at 150 degrees C or 200 degrees C in the presence of various acids (HCl, H(2)SO(4), H(3)PO(4), HNO(3) and TFA) or water. The lignin content determined by both methods differed on averaged by 2.9 wt% resulting in a standard deviation of 3.5 wt%. It is shown that solid degradation products are formed from saccharide precursors under harsh reaction conditions. These degradation reactions limit the total possible yield of monosaccharides from any subsequent reaction. PMID:19477123

Sievers, Carsten; Marzialetti, Teresita; Hoskins, Travis J C; Valenzuela Olarte, Mariefel B; Agrawal, Pradeep K; Jones, Christopher W

2009-05-23

254

Solid State 2H NMR Analysis of Furanose Ring Dynamics in DNA Containing Uracil  

PubMed Central

DNA damage has been implicated in numerous human diseases, particularly cancer, and the aging process. Single-base lesions, such as uracil, in DNA can be cytotoxic or mutagenic and are recognized by a DNA glycosylase during the process of base excision repair. Increased dynamic properties in lesion-containing DNAs have been suggested to assist recognition and specificity. Deuterium solid-state nuclear magnetic resonance (SSNMR) has been used to directly observe local dynamics of the furanose ring within a uracil: adenine (U:A) base pair and compared to a normal thymine:adenine (T:A) base pair. Quadrupole echo lineshapes, ?T1Z?, and ?T2e? relaxation data were collected, and computer modeling was performed. The results indicate that the relaxation times are identical within the experimental error, the solid lineshapes are essentially indistinguishable above the noise level, and our lineshapes are best fit with a model that does not have significant local motions. Therefore, U:A base pair furanose rings appear to have essentially identical dynamic properties as a normal T:A base pair, and the local dynamics of the furanose ring are unlikely to be the sole arbiter for uracil recognition and specificity in U:A base pairs.

Kinde-Carson, Monica N.; Ferguson, Crystal; Oyler, Nathan A.; Harbison, Gerard S.; Meints, Gary A.

2010-01-01

255

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

256

Characterisation of platinum-based fuel cell catalyst materials using (195)Pt wideline solid state NMR.  

PubMed

This study demonstrates the utility of the novel Field Sweep Fourier Transform (FSFT) method for acquiring wideline (195)Pt NMR data from various sized Pt nanoparticles, Pt-Sn intermetallics/bimetallics used to catalyse oxidative processes in fuel cell applications, and various other related Pt3X alloys (X = Al, Sc, Nb, Ti, Hf and Zr) which can facilitate oxygen reduction catalysis. The (195)Pt and (119)Sn NMR lineshapes measured from the PtSn intermetallic and Pt3Sn bimetallic systems suggest that these are more ordered than other closely related bimetallic alloys; this observation is supported by other characterisation techniques such as XRD. From these reconstructed spectra the mean number of atoms in a Pt nanoparticle can be accurately determined, along with detailed information regarding the number of atoms present effectively in each layer from the surface. This can be compared with theoretical predictions of the number of Pt atoms in these various layers for cubo-octahedral nanoparticles, thereby providing an estimate of the particle size. A comparison of the common NMR techniques used to acquire wideline data from the I = 1/2 (195)Pt nucleus illustrates the advantages of the automated FSFT technique over the Spin Echo Height Spectroscopy (SEHS) (or Spin Echo Integration Spectroscopy (SEIS)) approach that dominates the literature in this area of study. This work also presents the first (195)Pt NMR characterisation of novel small Pt13 nanoclusters which are diamagnetic and thus devoid of metallic character. This unique system provides a direct measure of an isotropic chemical shift for these Pt nanoparticles and affords a better basis for determining the actual Knight shift when compared to referencing against the primary IUPAC shift standard (1.2 M Na2PtCl6(aq)) which has a very different local chemical environment. PMID:24013445

Rees, Gregory J; Orr, Simon T; Barrett, Laurence O; Fisher, Janet M; Houghton, Jennifer; Spikes, Geoffrey H; Theobald, Brian R C; Thompsett, David; Smith, Mark E; Hanna, John V

2013-09-25

257

Spectral editing in solid-state MAS NMR of quadrupolar nuclei using selective satellite inversion  

Microsoft Academic Search

A sensitivity enhancement method based on selective adiabatic inversion of a satellite transition has been employed in a (?\\/2)CT–(?)ST1–(?\\/2)CT spectral editing sequence to both enhance and resolve multisite NMR spectra of quadrupolar nuclei. In addition to a total enhancement of 2.5 times for spin 3\\/2 nuclei, enhancements up to 2.0 times is reported for the edited sites in a mixture

Krishna K. Dey; S. Prasad; Jason T. Ash; Michael Deschamps; Philip J. Grandinetti

2007-01-01

258

Investigation of Polymorphism in Aspartame and Neotame Using Solid-State NMR Spectroscopy  

Microsoft Academic Search

We have been studying the artificial sweeteners aspartame (l-aspartyl-l-phenylalanine methyl ester) and neotame (N-(3,3-dimethylbutyl)-l-aspartyl-l-phenylalanine methyl ester) as compounds which exhibit polymorphism. 13C CP\\/MAS NMR shows that aspartame exists in three distinct forms at room temperature, depending on preparation conditions. For two of the forms, there exists three resonances for each carbon, indicating three crystallographically inequivalent sites and therefore three distinct

Mark T Zell; Brian E Padden; David J. W Grant; Stephen A Schroeder; Kurt L Wachholder; Indra Prakash; Eric J Munson

2000-01-01

259

Characterisation of indomethacin and nifedipine using variable-temperature solid-state NMR.  

PubMed

We have characterised the stable polymorphic forms of two drug molecules, indomethacin (1) and nifedipine (2) by 13C CPMAS NMR and the resonances have been assigned. The signal for the C-Cl carbon of indomethacin has been studied as a function of applied magnetic field, and the observed bandshapes have been simulated. Variable-temperature 1H relaxation measurements of static samples have revealed a T1rho minimum for indomethacin at 17.8 degrees C. The associated activation energy is 38 kJ mol(-1). The relevant motion is probably an internal rotation and it is suggested that this involves the C-OCH3 group. Since the two drug compounds are potential candidates for formulation in the amorphous state, we have examined quench-cooled melts in detail by variable-temperature 13C and 1H NMR. There is a change in slope for T1H and T1rhoH at the glass transition temperature (Tg) for indomethacin, but this occurs a few degrees below Tg for nifedipine, which is perhaps relevant to the lower real-time stability of the amorphous form for the latter compound. Comparison of relaxation time data for the crystalline and amorphous forms of each compound reveals a greater difference for nifedipine than for indomethacin, which again probably relates to real-time stabilities. Recrystallisation of the two drugs has been followed by proton bandshape measurements at higher temperatures. It is shown that, under the conditions of the experiments, recrystallisation of nifedipine can be detected already at 70 degrees C, whereas this does not occur until 110 degrees C for indomethacin. The effect of crushing the amorphous samples has been studied by 13C NMR; nifedipine recrystallises but indomethacin does not. The results were supported by DSC, powder XRD, FTIR and solution-state NMR measurements. PMID:16059964

Apperley, David C; Forster, Angus H; Fournier, Romain; Harris, Robin K; Hodgkinson, Paul; Lancaster, Robert W; Rades, Thomas

2005-11-01

260

Probing spin density and local structure in the Prussian blue analogues CsCd[Fe/Co(CN)6]·0.5H2O and Cd3[Fe/Co(CN)6]2·15H2O with solid-state MAS NMR spectroscopy.  

PubMed

Magic-angle spinning (MAS) NMR spectroscopy is used to study the local structure and spin delocalisation in Prussian blue analogues (PBAs). We selected two common archetypes of PBAs (A(I)M(II)[M(III)(CN)(6)]·xH(2)O and M(II)(3)[M(III)(CN)(6)](2)·xH(2)O, in which A(I) is an alkali ion, and M(II) and M(III) are transition-metal ions) that exhibit similar cubic frameworks but different microscopic structures. Whereas the first type of PBA contains interstitial alkali ions and does not exhibit any [M(III)(CN)(6)](3-) vacancies, the second type of PBA exhibits [M(III)(CN)(6)](3-) vacancies, but does not contain inserted alkali ions. In this study, we selected Cd(II) as a divalent metal in order to use the (113)Cd nuclei (I=1/2) as a probe of the local structure. Here, we present a complete MAS NMR study on two series of PBAs of the formulas Cd(II)(3)[Fe(III)(x)Co(III)(1-x)(CN)(6)](2)·15H(2)O with x=0 (1), 0.25 (2), 0.5 (3), 0.75 (4) and 1 (5), and CsCd(II)[Fe(III)(x)Co(III)(1-x)(CN)(6)]·0.5H(2)O with x=0 (6), 0.25 (7), 0.5 (8), 0.75 (9) and 1 (10). Interestingly, the presence of Fe(III) magnetic centres in the vicinity of the cadmium sites has a magnifying-glass effect on the NMR spectrum: it induces a striking signal spread such that the resolution is notably improved compared to that achieved for the diamagnetic PBAs. By doping the sample with varying amounts of diamagnetic Co(III) and comparing the NMR spectra of both types of PBAs, we have been able to give a view of the structure which is complementary to that usually obtained from X-ray diffraction studies. In particular, this study has shown that the vacancies are not randomly distributed in the mesoporous PBAs. Moreover the cadmium chemical shift, which is a measure of the hyperfine coupling, allows the estimation of the spin density on the cadmium nucleus, and consequently, the elucidation of the spin delocalisation mechanism in these compounds along with its dependency on structural parameters. PMID:21882267

Flambard, Alexandrine; Köhler, Frank H; Lescouëzec, Rodrigue; Revel, Bertrand

2011-08-31

261

New insights into frustrated Lewis pairs: structural investigations of intramolecular phosphane-borane adducts by using modern solid-state NMR techniques and DFT calculations.  

PubMed

Covalent bonding interactions between the Lewis acid and Lewis base functionalities have been probed in a series of "frustrated Lewis pairs" (FLPs) (mainly substituted vinylene linked intramolecular phosphane-borane adducts), using solid-state nuclear magnetic resonance techniques and accompanying DFT calculations. Both the (11)B NMR isotropic chemical shifts and nuclear electric quadrupolar coupling parameters turn out to be extremely sensitive experimental probes for such interactions, revealing linear correlations with boron-phosphorus internuclear distances. The principal component V(zz) of the (11)B electric field gradient tensor is tilted slightly away (~20°) from the boron-phosphorus internuclear vector, leading to an improved understanding of the remarkable reactivity of the FLPs. Complementary (31)P{(1)H}-CPMAS experiments reveal significant (31)P-(11)B scalar spin-spin interactions ((1)J ? 50 Hz), evidencing covalent bonding interactions between the reaction centers. Finally, (11)B{(31)P} rotational echo double resonance (REDOR) experiments show systematic deviations from calculated curves based on the internuclear distances from X-ray crystallography. These deviations suggest non-zero contributions from anisotropic indirect spin-spin (J anisotropy) interactions, thereby offering additional evidence for covalent bonding. PMID:22280301

Wiegand, Thomas; Eckert, Hellmut; Ekkert, Olga; Fröhlich, Roland; Kehr, Gerald; Erker, Gerhard; Grimme, Stefan

2012-02-21

262

Mechanistic insight into formation and changes of nanoparticles in MgF2 sols evidenced by liquid and solid state NMR.  

PubMed

The fluorolytic sol-gel reaction of magnesium methoxide with HF in methanol was studied by (19)F, (1)H and (13)C liquid and solid state NMR. In (19)F NMR five different species were identified, three of which belong to magnesium fluoride nanoparticles, i.e. NMR gave access to local structures of solid particles in suspensions. The long-term evolution of (19)F signals was followed and along with (19)F MAS NMR experiments of sols rotating at 13 kHz mechanistic insights into the ageing processes were obtained. PMID:22214975

Karg, M; Scholz, G; König, R; Kemnitz, E

2012-01-03

263

Using Solid-state NMR to Monitor the Molecular Consequences of Cryptococcus neoformans Melanization with Different Catecholamine Precursors  

PubMed Central

Melanins are a class of natural pigments associated with a wide range of biological functions, including microbial virulence, energy transduction, and protection against solar radiation. Because of their insolubility and structural heterogeneity, solid-state nuclear magnetic resonance (NMR) spectroscopy provides an unprecedented means to define the molecular architecture of these enigmatic pigments. The requirement of obligatory catecholamines for melanization of the pathogenic fungus Cryptococcus neoformans also offers unique opportunities for investigating melanin development. In the current study, pigments produced with L-dopa, methyl-L-dopa, epinephrine, and norepinephrine precursors are compared structurally using 13C and 1H magic-angle spinning (MAS) NMR. Striking structural differences were observed for both aromatic and aliphatic molecular constituents of the mature fungal pigment assemblies, thus making it possible to redefine the molecular prerequisites for formation of the aromatic domains of insoluble indole-based biopolymers, to rationalize their distinctive physical characteristics, and to delineate the role of cellular constituents in assembly of the melanized macromolecules with polysaccharides and fatty acyl chain-containing moieties. By achieving an augmented understanding of the mechanisms of C. neoformans melanin biosynthesis and cellular assembly, such studies can guide future drug discovery efforts related to melanin-associated virulence, resistance to tumor therapy, and production of melanin mimetics under cell-free conditions.

Chatterjee, Subhasish; Prados-Rosales, Rafael; Frases, Susana; Itin, Boris; Casadevall, Arturo; Stark, Ruth E.

2012-01-01

264

Multinuclear (27Al, 29Si, 47,49Ti) solid-state NMR of titanium substituted zeolite USY.  

PubMed

Multinuclear solid-state NMR spectroscopy, employing 29Si MAS,27Al MAS/3Q-MAS and (47,49)Ti wide-line experiments, has been used for the structural characterization of titanium substituted ultra-stable zeolite Y (Ti-USY). 27Al MAS experiments show the presence of aluminum in four (Al(IV)), five (Al(V)), and six (Al(VI)) coordination, whereas the multiplicity within Al(IV) and Al(VI) is revealed by 27Al 3Q-MAS experiments. Two different tetrahedral and octahedral Al environments are resolved and their isotropic chemical shifts (delta(CS)) and second-order quadrupole interaction parameters (P(Q)) have been determined by a graphical analysis of the 3Q-MAS spectra. The emergence of signal with higher intensity at -101 ppm in the 29Si MAS spectrum of Ti-USY samples indicates the possible occurrence of Q4(3Si,1Ti) type silicon environments due to titanium substitution in the faujasite framework. High-field (11.74T) operation, using a probehead specially designed to handle a large sample volume, has enabled the acquisition of 47,49Ti static spectra and identification of the titanium environment in the zeolite. The chemical shielding and electric field gradient tensors for the titanium environment in the zeolite have been determined by a computer simulation of the quadrupolar broadened static 47,49Ti NMR spectra. PMID:12943913

Ganapathy, S; Gore, K U; Kumar, Rajiv; Amoureux, Jean-Paul

265

Vanadium(V) environments in bismuth vanadates: A structural investigation using Raman spectroscopy and solid state 51V NMR  

NASA Astrophysics Data System (ADS)

The Bi2O3-V2O5 system was examined using Raman spectroscopy and solid state 51V wideline, magic-angle spinning (MAS), and nutation NMR spectroscopy. The methods are shown to be complementary in the identification of the various phases and in the characterization of their vanadium site symmetries. Most of the compositions examined (1:1 <= Bi:V <= 60:1) are multiphasic. Depending on the Bi:V ratio, the following phases have been identified: BiVO4, Bi4V2O11, a triclinic type-II phase, a cubic type-I phase, ?-Bi2O3 doped with V(V) (sillenite), and ?-Bi2O3. Detailed spectroscopic characterization reveals that vanadium is tetrahedrally coordinated in all these compounds, and that the degree of symmetry increases with increasing Bi:V ratio. At the highest Bi:V ratios, the combined interpretation of the Raman and NMR data provides strong evidence for the presence of Bi5+O4 tetrahedra.

Hardcastle, Franklin D.; Wachs, Israel E.; Eckert, Hellmut; Jefferson, David A.

1991-02-01

266

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

PubMed

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

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

2013-07-27

267

Solid state NMR study and density functional theory (DFT) calculations of structure and dynamics of poly(p-xylylenes).  

PubMed

High resolution solid state (13)C nuclear magnetic resonance (SS NMR) measurements were carried out on poly(p-xylylene) (PPX). The samples comprised vapor-deposited specimens as well as pure alpha and beta polymorphs of this polymer. The measurements were performed using cross-polarization and magic angle spinning (CP/MAS) techniques. Density functional theory gauge-including-atomic-orbital (DFT GIAO) calculations of NMR shielding parameters (13)C sigma(ii) were performed for the optimized geometry and structure of a xylylene trimer, acquired from the X-ray data, including intermolecular interactions. Two-dimensional phase adjusted spinning sideband (2D PASS) correlation was employed for the assignment of the values of the principal elements (13)C delta(ii) of the chemical shift tensor (CST). A comparative analysis of shielding (sigma(ii)) versus chemical shift (delta(ii)) parameters showed substantial differences between the molecular dynamics of alpha and beta polymorphs. This observation was further supported by the measurements of (13)C T(1) relaxation times and the analysis of cross-polarization kinetics. Frequency switched Lee-Goldburg heteronuclear correlation (FSLG HETCOR) for the (1)H-(13)C system was used in order to analyze molecular packing in both polymorphs. As a result of all of the above measurements, new insight into the mechanism of thermal phase transition from the alpha to the beta polymorph of poly(p-xylylene) is presented. PMID:19331396

Sroka-Bartnicka, A; Olejniczak, S; Ciesielski, W; Nosal, A; Szymanowski, H; Gazicki-Lipman, M; Potrzebowski, M J

2009-04-23

268

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

PubMed Central

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

Quist, P O

1998-01-01

269

Correlating fast and slow chemical shift spinning sideband patterns in solid-state NMR  

NASA Astrophysics Data System (ADS)

An experiment is presented that enables the measurement of small chemical shift anisotropy tensors under fast magic-angle spinning (MAS). The two-dimensional spectra obtained give a fast MAS sideband pattern in the directly observed dimension with the spinning sideband intensities equivalent to the chemical shift anisotropy scaled by a factor of N, or equivalently the sample spinning frequency scaled by 1/N, in the indirectly observed dimension. The scaling factor may be arbitrarily varied by changing the number and timings of the rotor synchronized ?-pulses used. Desirable features of the experiment include a fixed length pulse sequence and efficient sampling of the indirectly observed dimension. In addition, neither quadrature detection in the indirect dimension nor storage periods are required, consequently no signal intensity is discarded by the pulse sequence. The experiment is demonstrated using 31P NMR of sodium phosphate and 13C NMR of fumaric acid monoethyl ester for which a scaling factor of N = 10.2 was employed.

Orr, Robin M.; Duer, Melinda J.; Ashbrook, Sharon E.

2005-06-01

270

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

Microsoft Academic Search

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

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

2001-01-01

271

Insights into the Molecular Architecture of a Peptide Nanotube Using FTIR and Solid-State NMR Spectroscopic Measurements on an Aligned Sample.  

PubMed

Queuing up: Molecular orientation within macroscopically aligned nanotubes of the peptide AAAAAAK can be studied by solid-state NMR and IR spectroscopy. Line shape analysis of the NMR spectra indicates that the peptide N?H bonds are tilted 65-70° relative to the nanotube long axis. Re-evaluation of earlier X-ray fiber diffraction data suggests that the peptide molecules are hydrogen-bonded in a helical arrangement along the nanotube axis. PMID:23955926

Middleton, David A; Madine, Jillian; Castelletto, Valeria; Hamley, Ian W

2013-08-16

272

sup 13 C NMR and x-ray structure determination of 1-(arylazo)-2-naphthols. Intramolecular proton transfer between nitrogen and oxygen atoms in the solid state  

Microsoft Academic Search

The tautomeric reaction involving a single proton transfer in 1-(phenylazo)-2-naphthol and its 4â²-methoxy, ethoxy, and N,N-dimethylamino derivatives has been investigated with variable-temperature solution and high-resolution solid-state ¹³C NMR spectroscopy. Crystal structures of the parent unsubstituted compound and the 4â²-N,N-dimethylamino derivative have been determined. All of these compounds undergo a fast proton exchange on the NMR time scale between the tautomeric

Alejandro C. Olivieri; Roxy B. Wilson; Iain C. Paul; David Y. Curtin

1989-01-01

273

Solid-state C NMR Study of Scleroglucan Polysaccharide. Effect of the Drying Process and Hydration on Scleroglucan Structure and Dynamics  

Microsoft Academic Search

High-resolution solid-state C CP\\/MAS NMR was used to study the evolution of a polysaccharide (scleroglucan) conformation from the anhydrous to the hydrated form. The influence of a thermo-mechanical treatment applied during the drying process of scleroglucan is analyzed both on the dried and rehydrated product. C NMR spectra, C relaxation times (T1C) and H relaxation times in the rotating frame

M. Jeannin; S. A. Rezzoug; Z. Maache-rezzoug; S. Cohendoz; K. Allaf

2001-01-01

274

Characterization of membrane proteins in isolated native cellular membranes by dynamic nuclear polarization solid-state NMR spectroscopy without purification and reconstitution.  

PubMed

Membrane proteins in their native cellular membranes are accessible by dynamic nuclear polarization magic angle spinning solid-state NMR spectroscopy without the need of purification and reconstitution (see picture). Dynamic nuclear polarization is essential to achieve the required gain in sensitivity to observe the membrane protein of interest. PMID:22113890

Jacso, Tomas; Franks, W Trent; Rose, Honor; Fink, Uwe; Broecker, Jana; Keller, Sandro; Oschkinat, Hartmut; Reif, Bernd

2011-11-23

275

Quantifying the fraction of glycine and alanine in beta-sheet and helical conformations in spider dragline silk using solid-state NMR.  

PubMed

Solid-state two-dimensional refocused INADEQUATE MAS NMR experiments resolve distinct helical and beta-sheet conformational environments for both alanine and glycine in Nephila clavipes dragline silk fibers; the fraction of alanine and glycine in beta-sheet structures is determined to be 82% +/- 4% and 28% +/- 5%, respectively. PMID:18997954

Holland, Gregory P; Jenkins, Janelle E; Creager, Melinda S; Lewis, Randolph V; Yarger, Jeffery L

2008-09-29

276

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

SciTech Connect

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

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

1994-09-01

277

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

Microsoft Academic Search

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

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

2004-01-01

278

Solid-state [sup 113]Cd NMR of three structural isomers of [S[sub 4]Cd[sup 10](SPh)[sup 16  

SciTech Connect

Solid-state [sup 113]Cd NMR chemical shift ([delta][sup iso]) and chemical shift anisotropy ([delta][sub ii]) data are reported for crystalline samples of three different compounds containing the [S[sub 4]Cd[sup 10](SPh)[sub 16

Lee, G.S.H.; Fisher, K.J.; Dance, I.G. (Univ. of New South Wales, Kensington (Australia)); Vassallo, A.M.; Hanna, J.V. (CSIRO Division of Coal and Energy Technology, North Ryde (Australia))

1993-01-06

279

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

PubMed

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

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

2013-10-21

280

Quadrupolar Metal Nuclides in Bioinorganic Chemistry: Solid-State NMR Studies  

SciTech Connect

Metal ions play an important role in bioinorganic chemistry, however, following their respective chemistries is often complicated because several relevant metal ions (such as V5+, Cu1+, Zn2+, and Mg2+) are not always amenable to conventional UV/Vis or EPR spectroscopy. Rather, what we know of these metal sites has come from the characterization of the various compounds and proteins via x-ray crystallographic methods or from using surrogate metal probes for conventional spectroscopy

Lipton, Andrew S.; Ellis, Paul D.; Polenova, Tatyana E.

2009-09-16

281

Determination of structural topology of a membrane protein in lipid bilayers using polarization optimized experiments (POE) for static and MAS solid state NMR spectroscopy.  

PubMed

The low sensitivity inherent to both the static and magic angle spinning techniques of solid-state NMR (ssNMR) spectroscopy has thus far limited the routine application of multidimensional experiments to determine the structure of membrane proteins in lipid bilayers. Here, we demonstrate the advantage of using a recently developed class of experiments, polarization optimized experiments, for both static and MAS spectroscopy to achieve higher sensitivity and substantial time-savings for 2D and 3D experiments. We used sarcolipin, a single pass membrane protein, reconstituted in oriented bicelles (for oriented ssNMR) and multilamellar vesicles (for MAS ssNMR) as a benchmark. The restraints derived by these experiments are then combined into a hybrid energy function to allow simultaneous determination of structure and topology. The resulting structural ensemble converged to a helical conformation with a backbone RMSD ~0.44 Å, a tilt angle of 24° ± 1°, and an azimuthal angle of 55° ± 6°. This work represents a crucial first step toward obtaining high-resolution structures of large membrane proteins using combined multidimensional oriented solid-state NMR and magic angle spinning solid-state NMR. PMID:23963722

Mote, Kaustubh R; Gopinath, T; Veglia, Gianluigi

2013-08-21

282

Solid-state NMR study of intercalated species in poly(epsilon-caprolactone)/clay nanocomposites.  

PubMed

The structure and dynamics of surfactant and polymer chains in intercalated poly(epsilon-caprolactone)/clay nanocomposites are characterized by (31)P magic-angle spinning (MAS) and (13)C cross-polarization MAS NMR techniques. To obtain hybrid materials with the low polymer content required for this study, in situ intercalative polymerization was performed by adapting a published procedure. After nanocomposite formation, the chain motion of the surfactant is enhanced in the saponite-based materials but reduced in the Laponite ones. Compared to the starting clay, the trans conformer population of the surfactant hydrocarbon chain in the nanocomposite decreases for the saponite systems. Mobility of the polymer chain is higher in the nanocomposites than in the bulk phase. The charge of the modified saponite does not significantly influence chain mobility in the nanocomposites. PMID:15491221

Hrobarikova, J; Robert, J-L; Calberg, C; Jérôme, R; Grandjean, J

2004-10-26

283

Effects of molecular mobility on high resolution solid state NMR spectra: model systems  

SciTech Connect

It is the intention of this paper to point to some of the problems due to molecular motion and to suggest a few solutions to those problems. A few examples will be presented of model systems which demonstrate the effects of motion on the NMR spectroscopy and a very qualitative example of severe spectral distortion in fulvic acids will be shown. In the following discussions we will use concepts derived from the oft repeated thermodynamic picture shown in figure 1. When dealing with a homogeneous, pure compound this picture is sufficient but in a heterogeneous mixture, it is likely that there will be different compounds and different domains all with slightly different versions of figure 1 with poor thermodynamic contact between them. Thus optimal conditions for cross polarization in one domain may be totally inappropriate for another. 59 refs., 10 figs.

Earl, W.L.

1986-01-01

284

Dipole tensor-based atomic-resolution structure determination of a nanocrystalline protein by solid-state NMR  

PubMed Central

Magic-angle spinning (MAS) solid-state NMR (SSNMR) techniques have emerged in recent years for solving complete structures of uniformly labeled proteins lacking macroscopic order. Strategies used thus far have relied primarily on semiquantitative distance restraints, analogous to the nuclear Overhauser effect (NOE) routinely used in solution NMR. Here, we present a complementary approach for using relative orientations of molecular fragments, determined from dipolar line shapes. Whereas SSNMR distance restraints typically have an uncertainty of ?1 ?, the tensor-based experiments report on relative vector (pseudobond) angles with precision of a few degrees. By using 3D techniques of this type, vector angle (VEAN) restraints were determined for the majority of the 56-residue B1 immunoglobulin binding domain of protein G [protein GB1 (a total of 47 HN-HN, 49 HN-HC, and 12 HA-HB restraints)]. By using distance restraints alone in the structure calculations, the overall backbone root-mean-square deviation (bbRMSD) was 1.01 ± 0.13 ? (1.52 ± 0.12 ? for all heavy atoms), which improved to 0.49 ± 0.05 ? (1.19 ± 0.07 ?) on the addition of empirical chemical shift [torsion angle likelihood obtained from shift and sequence similarity (TALOS)] restraints. VEAN restraints further improved the ensemble to 0.31 ± 0.06 ? bbRMSD (1.06 ± 0.07 ?); relative to the structure with distances alone, most of the improvement remained (bbRMSD 0.64 ± 0.09 ?; 1.29 ± 0.07 ?) when TALOS restraints were removed before refinement. These results represent significant progress toward atomic-resolution protein structure determination by SSNMR, capabilities that can be applied to a large range of membrane proteins and fibrils, which are often not amenable to solution NMR or x-ray crystallography.

Franks, W. Trent; Wylie, Benjamin J.; Schmidt, Heather L. Frericks; Nieuwkoop, Andrew J.; Mayrhofer, Rebecca-Maria; Shah, Gautam J.; Graesser, Daniel T.; Rienstra, Chad M.

2008-01-01

285

Protein-ice interaction of an antifreeze protein observed with solid-state NMR  

PubMed Central

NMR on frozen solutions is an ideal method to study fundamental questions of macromolecular hydration, because the hydration shell of many biomolecules does not freeze together with bulk solvent. In the present study, we present previously undescribed NMR methods to study the interactions of proteins with their hydration shell and the ice lattice in frozen solution. We applied these methods to compare solvent interaction of an ice-binding type III antifreeze protein (AFP III) and ubiquitin a non-ice-binding protein in frozen solution. We measured 1H-1H cross-saturation and cross-relaxation to provide evidence for a molecular contact surface between ice and AFP III at moderate freezing temperatures of -35 °C. This phenomenon is potentially unique for AFPs because ubiquitin shows no such cross relaxation or cross saturation with ice. On the other hand, we detected liquid hydration water and strong water–AFP III and water–ubiquitin cross peaks in frozen solution using relaxation filtered 2H and HETCOR spectra with additional 1H-1H mixing. These results are consistent with the idea that ubiquitin is surrounded by a hydration shell, which separates it from the bulk ice. For AFP III, the water cross peaks indicate that only a portion of its hydration shell (i.e., at the ice-binding surface) is in contact with the ice lattice. The rest of AFP III’s hydration shell behaves similarly to the hydration shell of non-ice-interacting proteins such as ubiquitin and does not freeze together with the bulk water.

Siemer, Ansgar B.; Huang, Kuo-Ying; McDermott, Ann E.

2010-01-01

286

Exploration of structure and function in biomolecules through solid-state NMR and computational methods  

NASA Astrophysics Data System (ADS)

Solid-State Nuclear Magnetic Resonance (SSNMR) spectroscopy and quantum mechanical calculations are powerful analysis tools. Leveraged independently, each method yields important nuclear and molecular information. Used in concert, SSNMR and computational techniques provide complementary data about the structure of solids. These methods are particularly useful in characterizing the structures of microcrystalline organic compounds and revealing mechanisms of biological activity. Such applications may possess special relevance in analysis of pharmaceutical products; 90% of all pharmaceuticals are marketed as solids and bioactivity is strongly linked with molecular conformation. Accordingly, this dissertation employs both SSNMR and quantum mechanical computation to study three bioactive molecules: citrinin, two forms of Atrasentan (Abt-627), and paclitaxel (Taxol RTM). First, a computational study is utilized to determine the mechanism for unusual antioxidant activity in citrinin. Here, molecular geometries and bond dissociation enthalpies (BDE) of the citrinin O--H groups are calculated from first principles (ab initio). The total molecular Hamiltonian is determined by approximating the individual contributors to energy including electronic energy and contributions from modes of molecular vibration. This study of citrinin clearly identifies specific reaction sites in the active form, establishing the central role of intramolecular hydrogen bonding in this activity. Notably, it is discovered that citrinin itself is not the active species. Instead, a pair of hydrated Michael addition products of citrinin act as radical scavengers via O--H bond dissociation. Next, two separate compounds of the anticancer drug Abt-627 (form I and form II) are examined via SSNMR. The three principal values of the 13C diagonalized chemical shift tensor are acquired through the high resolution 2D experiment, FIREMAT. Isotropic chemical shift assignments are made utilizing both dipolar dephasing experiments and 1H-- 13C heteronuclear correlation (HETCOR) experiments. A comparison of spectral data confirms the presence of two molecules in the asymmetric unit for form II (Z'=2) and regions of conformational variation between the two forms are posited. Structural rigidity is found throughout both forms and extends into the alkyl groups at the amine with similarties between form I and form II in this moiety. Likely regions of motion are found around the bond axes formed by C1--C5 in form I. This motion is also observed in one of the two molecules of form II. Tensor differences between the two forms at the tetrahydro-pyrrole center indicate that conformational variation between form I and form II exists in the dihedral angles formed by the atoms C14--C13--C3--C2, O--C12--C2--C1, C10--C5--C1--N1 and C21--C20--N1--C4. Finally, SSNMR is applied in conjunction with quantum mechanical calculations in the analysis of a novel polymorph of the anticancer drug paclitaxel. The three dimensional structure of paclitaxel is established through a combination of SSNMR tensor (13C & 15N) and 1H--13C HETCOR data. With two molecules in the asymmetric unit (Z'=2), this represents the first conformational characterization with Z'>1 established solely by SSNMR. Semi-empirical models are constructed and fitted to experimental data by adjusting the conformation of the paclitaxel models and selecting those conformers which minimize the difference between predicted and measured tensors. This computational grid search exhausively samples the conformation of paclitaxel, utilizing more than 600 independent models. HETCOR data at thirteen key positions provide shift assignment to the asymmetric unit for each comparison. The two distinct molecules of the asymmetric unit possess nearly identical baccatin III moieties with matching conformations of the C10 acetyl moiety. Additionally, both are found to exhibit an extended conformation of the phenylisoserine sidechain at the C13 position. Notable differences between the two forms are centered around the rotation axes of O--C13,

Heider, Elizabeth M.

287

Energy transformations early in the bacteriorhodopsin photocycle revealed by DNP-enhanced solid-state NMR  

PubMed Central

By exploiting dynamic nuclear polarization (DNP) at 90 K, we observe the first NMR spectrum of the K intermediate in the ion-motive photocycle of bacteriorhodopsin. The intermediate is identified by its reversion to the resting state of the protein in red light and by its thermal decay to the L intermediate. The 15N chemical shift of the Schiff base in K indicates that contact has been lost with its counterion. Under these circumstances, the visible absorption of K is expected to be more red-shifted than is observed and this suggests torsion around single bonds of the retinylidene chromophore. This is in contrast to the development of a strong counterion interaction and double bond torsion in L. Thus, photon energy is stored in electrostatic modes in K and is transferred to torsional modes in L. This transfer is facilitated by the reduction in bond alternation that occurs with the initial loss of the counterion interaction, and is driven by the attraction of the Schiff base to a new counterion. Nevertheless, the process appears to be difficult, as judged by the multiple L substates, with weaker counterion interactions, that are trapped at lower temperatures. The double-bond torsion ultimately developed in the first half of the photocycle is probably responsible for enforcing vectoriality in the pump by causing a decisive switch in the connectivity of the active site once the Schiff base and its counterion are neutralized by proton transfer.

Mak-Jurkauskas, Melody L.; Bajaj, Vikram S.; Hornstein, Melissa K.; Belenky, Marina; Griffin, Robert G.; Herzfeld, Judith

2008-01-01

288

Solid state NMR methods for coal science. Progress report, October 1-December 31, 1985. [Cholesteryl acetate  

SciTech Connect

This report covers the progress made on the title project during the last quarter. During the last three months we have concentrated on further developing a new 2-D NMR method that should be useful for coals. As outlined in a previous report this new technique separates the contribution of methines, methylenes and methyl or quaternary carbons to the carbon-13 CPMAS spectra of coals. In contrast to the heteronuclear shift correlation method, which observes only protonated carbons, this method observes all carbon centers seen in a standard CPMAS spectrum. The method has been successfully applied to a rather complex molecule, cholesteryl acetate. Even though there is severe spectral overlap in this model compound's CPMAS spectrum, the dipolar-shift correlation method allows us to assign each resonance. The distribution of functional types of carbon determined in this experiment appears to be close to quantitative. In addition we have begun to test our ultra high field CPMAS equipment on chemically modified coals. 4 figs.

Zilm, K.W.

1986-04-01

289

Solid-State NMR Analysis of the PGLa Peptide Orientation in DMPC Bilayers: Structural Fidelity of 2H-Labels versus High Sensitivity of 19F-NMR  

PubMed Central

The structure and alignment of the amphipathic ?-helical antimicrobial peptide PGLa in a lipid membrane is determined with high accuracy by solid-state 2H-NMR. Orientational constraints are derived from a series of eight alanine-3,3,3-d3-labeled peptides, in which either a native alanine is nonperturbingly labeled (4×), or a glycine (2×) or isoleucine (2×) is selectively replaced. The concentration dependent realignment of the ?-helix from the surface-bound “S-state” to a tilted “T-state” by 30° is precisely calculated using the quadrupole splittings of the four nonperturbing labels as constraints. The remaining, potentially perturbing alanine-3,3,3-d3 labels show only minor deviations from the unperturbed peptide structure and help to single out the unique solution. Comparison with previous 19F-NMR constraints from 4-CF3-phenylglycine labels shows that the structure and orientation of the PGLa peptide is not much disturbed even by these bulky nonnatural side chains, which contain CF3 groups that offer a 20-fold better NMR sensitivity than CD3 groups.

Strandberg, Erik; Wadhwani, Parvesh; Tremouilhac, Pierre; Durr, Ulrich H. N.; Ulrich, Anne S.

2006-01-01

290

Atomic-resolution three-dimensional structure of HET-s(218-289) amyloid fibrils by solid-state NMR spectroscopy.  

PubMed

We present a strategy to solve the high-resolution structure of amyloid fibrils by solid-state NMR and use it to determine the atomic-resolution structure of the prion domain of the fungal prion HET-s in its amyloid form. On the basis of 134 unambiguous distance restraints, we recently showed that HET-s(218-289) in its fibrillar state forms a left-handed ?-solenoid, and an atomic-resolution NMR structure of the triangular core was determined from unambiguous restraints only. In this paper, we go considerably further and present a comprehensive protocol using six differently labeled samples, a collection of optimized solid-state NMR experiments, and adapted structure calculation protocols. The high-resolution structure obtained includes the less ordered but biologically important C-terminal part and improves the overall accuracy by including a large number of ambiguous distance restraints. PMID:20828131

Van Melckebeke, Hélène; Wasmer, Christian; Lange, Adam; Ab, Eiso; Loquet, Antoine; Böckmann, Anja; Meier, Beat H

2010-10-01

291

Ionization behavior of polyphosphoinositides determined via the preparation of pH titration curves using solid-state 31P NMR.  

PubMed

Detailed knowledge of the degree of ionization of lipid titratable groups is important for the evaluation of protein-lipid and lipid-lipid interactions. The degree of ionization is commonly evaluated by acid-base titration, but for lipids localized in a multicomponent membrane interface this is not a suitable technique. For phosphomonoester-containing lipids such as the polyphosphoinositides, phosphatidic acid, and ceramide-1-phosphate, this is more conveniently accomplished by (31)P NMR. Here, we describe a solid-state (31)P NMR procedure to construct pH titration curves to determine the degree of ionization of phosphomonoester groups in polyphosphoinositides. This procedure can also be used, with suitable sample preparation conditions, for other important signaling lipids. Access to a solid-state, i.e., magic angle spinning, capable NMR spectrometer is assumed. The procedures described here are valid for a Bruker instrument, but can be adapted for other spectrometers as needed. PMID:23681530

Graber, Zachary T; Kooijman, Edgar E

2013-01-01

292

Remote Tuning of NMR Probe Circuits  

NASA Astrophysics Data System (ADS)

There are many circumstances in which the probe tuning adjustments cannot be located near the rf NMR coil. These may occur in high-temperature NMR, low-temperature NMR, and in the use of magnets with small diameter access bores. We address here circuitry for connecting a fixed-tuned probe circuit by a transmission line to a remotely located tuning network. In particular, the bandwidth over which the probe may be remotely tuned while keeping the losses in the transmission line acceptably low is considered. The results show that for all resonant circuit geometries (series, parallel, series-parallel), overcoupling of the line to the tuned circuit is key to obtaining a large tuning bandwidth. At equivalent extents of overcoupling, all resonant circuit geometries have nearly equal remote tuning bandwidths. Particularly for the case of low-loss transmission line, the tuning bandwidth can be many times the tuned circuit's bandwidth, fo/Q.

Kodibagkar, Vikram D.; Conradi, Mark S.

2000-05-01

293

Remote tuning of NMR probe circuits.  

PubMed

There are many circumstances in which the probe tuning adjustments cannot be located near the rf NMR coil. These may occur in high-temperature NMR, low-temperature NMR, and in the use of magnets with small diameter access bores. We address here circuitry for connecting a fixed-tuned probe circuit by a transmission line to a remotely located tuning network. In particular, the bandwidth over which the probe may be remotely tuned while keeping the losses in the transmission line acceptably low is considered. The results show that for all resonant circuit geometries (series, parallel, series-parallel), overcoupling of the line to the tuned circuit is key to obtaining a large tuning bandwidth. At equivalent extents of overcoupling, all resonant circuit geometries have nearly equal remote tuning bandwidths. Particularly for the case of low-loss transmission line, the tuning bandwidth can be many times the tuned circuit's bandwidth, f(o)/Q. PMID:10783273

Kodibagkar, V D; Conradi, M S

2000-05-01

294

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

SciTech Connect

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

Sumner, S.C.J.

1986-01-01

295

Simultaneous processing of solid-state NMR relaxation and 1D-MAS exchange data: the backbone dynamics of free vs. binase-bound barstar.  

PubMed

Two types of dynamic solid-state NMR experiments-relaxation and 1D-MAS exchange-were combined for the investigation of the backbone dynamics of a 15% randomly 15N-enriched protein barstar in both free and binase-bound states. The main novelty of this work is a simultaneous quantitative processing of the results of these two types of experiments that we call Simultaneous Relaxation and Exchange Data Analysis (SREDA) approach. It extends the well-known model-free approach such that it permits to discriminate between various motional models (jumps between different sites, wobbling in a cone, etc.). This objective cannot be achieved by analyzing the relaxation or exchange data separately. The SREDA approach was applied to probe a modification of the average backbone dynamics of barstar upon forming a complex with another protein binase. T(1) and off-resonance T(1rho) relaxation times of 15N backbone nuclei were measured at three temperatures between 0 and 45 degrees C, 1D-MAS exchange (CODEX) data were obtained at room temperature within the mixing time range from 0.3 to 200 ms. It has been found that the barstar backbone participates in two molecular processes with correlation times in the 10(-9)-10(-7) and 10(-3)-10(-2) s ranges. Forming the complex with binase results in a significant decrease of the amplitudes of both motions, suggesting that the complex is a more rigid and stable structure than free barstar. PMID:12922175

Krushelnitsky, Alexey G; Hempel, Günter; Reichert, Detlef

2003-08-21

296

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

PubMed

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

Atalla, R H; Vanderhart, D L

1999-10-01

297

Characterization of covalent linkages in organically functionalized MCM-41 mesoporous materials by solid-state NMR and theoretical calculations.  

PubMed

The covalent linkages formed during functionalization of MCM-41 mesoporous molecular sieves with five chloroalkylsilanes ((EtO)3Si(CH2Cl), (MeO)3Si(CH2CH2CH2Cl), Cl3Si(CH2CH2CH3), Cl2Si(CH3)(CH2Cl) and Cl2Si(CH3)2) have been investigated using high-resolution solid-state NMR spectroscopy and DFT calculations. Structural information was obtained from 1H-13C and 1H-29Si heteronuclear (HETCOR) NMR spectra, in which high resolution in the 1H dimension was obtained by using fast MAS. The 1H-13C HETCOR results provided the assignments of 1H and 13C resonances associated with the surface functional groups. Sensitivity-enhanced 1H-29Si HETCOR spectra, acquired using Carr-Purcell-Meiboom-Gill refocusing during data acquisition, revealed the identity of 29Si sites (Qn, Tn, and Dn) and the location of functional groups relative to these sites. Optimal geometries of local environments representing the Qn, Tn and Dn resonances were calculated using molecular mechanics and ab initio methods. Subsequently, DFT calculations of 29Si, 13C, and 1H chemical shifts were performed using Gaussian 03 at the B3LYP/6-311++G(2d,2p) level. The theoretical calculations are in excellent accord with the experimental chemical shifts. This work illustrates that state-of-the-art spectroscopic and theoretical tools can be used jointly to refine the complex structures of inorganic-organic hybrid materials. PMID:17388623

Wiench, Jerzy W; Avadhut, Yamini S; Maity, Niladri; Bhaduri, Sumit; Lahiri, Goutam Kumar; Pruski, Marek; Ganapathy, Subramanian

2007-03-28

298

Crystal Polymorphism of Protein GB1 Examined by Solid-State NMR Spectroscopy and X-ray Diffraction  

SciTech Connect

The study of micro- or nanocrystalline proteins by magic-angle spinning (MAS) solid-state NMR (SSNMR) gives atomic-resolution insight into structure in cases when single crystals cannot be obtained for diffraction studies. Subtle differences in the local chemical environment around the protein, including the characteristics of the cosolvent and the buffer, determine whether a protein will form single crystals. The impact of these small changes in formulation is also evident in the SSNMR spectra; however, the changes lead only to correspondingly subtle changes in the spectra. Here, we demonstrate that several formulations of GB1 microcrystals yield very high quality SSNMR spectra, although only a subset of conditions enable growth of single crystals. We have characterized these polymorphs by X-ray powder diffraction and assigned the SSNMR spectra. Assignments of the 13C and 15N SSNMR chemical shifts confirm that the backbone structure is conserved, indicative of a common protein fold, but side chain chemical shifts are changed on the surface of the protein, in a manner dependent upon crystal packing and electrostatic interactions with salt in the mother liquor. Our results demonstrate the ability of SSNMR to reveal minor structural differences among crystal polymorphs. This ability has potential practical utility for studying the formulation chemistry of industrial and therapeutic proteins, as well as for deriving fundamental insights into the phenomenon of single-crystal growth.

Schmidt,H.; Sperling, L.; Gao, Y.; Wylie, B.; Boettcher, J.; Wilson, S.; Rienstra, C.

2007-01-01

299

New methods for the acquisition of ultra-wideline solid-state NMR spectra of spin-1/2 nuclides  

NASA Astrophysics Data System (ADS)

The Wideband Uniform Rate Smooth Truncation - Carr-Purcell Meiboom-Gill (WURST-CPMG) pulse sequence was recently introduced as a new method of acquiring ultra-wideline solid-state NMR (SSNMR) patterns of quadrupolar nuclei (Chem. Phys. Lett. 464 (2008) 97). Herein, we describe the application of the WURST-CPMG pulse sequence to stationary samples (i.e., non-spinning or "static" samples) of various spin-1/2 nuclides (119Sn, 207Pb, 199Hg and 195Pt) in order to examine its effectiveness for acquiring ultra-wideline SSNMR patterns. WURST-CPMG is compared to the CPMG and Cross Polarization (CP)-CPMG pulse sequences in select cases (119Sn and 207Pb, respectively), and its usefulness in obtaining ultra-wideline SSNMR spectra in a piecewise fashion is explored. In addition, a preliminary investigation of pulses generated using optimal control theory (OCT) for the purpose of wideline excitation is presented; spectra acquired using these pulses are compared with standard, rectangular pulses of similar pulse powers. Both methods show much promise for acquiring high quality wideline patterns dominated by chemical shift anisotropy, with minimal distortions and significantly reduced experimental times.

MacGregor, Alan W.; O'Dell, Luke A.; Schurko, Robert W.

2011-01-01

300

Structural topology of phospholamban pentamer in lipid bilayers by a hybrid solution and solid-state NMR method  

PubMed Central

Phospholamban (PLN) is a type II membrane protein that inhibits the sarcoplasmic reticulum Ca2+-ATPase (SERCA), thereby regulating calcium homeostasis in cardiac muscle. In membranes, PLN forms pentamers that have been proposed to function either as a storage for active monomers or as ion channels. Here, we report the T-state structure of pentameric PLN solved by a hybrid solution and solid-state NMR method. In lipid bilayers, PLN adopts a pinwheel topology with a narrow hydrophobic pore, which excludes ion transport. In the T state, the cytoplasmic amphipathic helices (domains Ia) are absorbed into the lipid bilayer with the transmembrane domains arranged in a left-handed coiled-coil configuration, crossing the bilayer with a tilt angle of approximately 11° with respect to the membrane normal. The tilt angle difference between the monomer and pentamer is approximately 13°, showing that intramembrane helix–helix association forces dominate over the hydrophobic mismatch, driving the overall topology of the transmembrane assembly. Our data reveal that both topology and function of PLN are shaped by the interactions with lipids, which fine-tune the regulation of SERCA.

Verardi, Raffaello; Shi, Lei; Traaseth, Nathaniel J.; Walsh, Naomi; Veglia, Gianluigi

2011-01-01

301

Structural topology of phospholamban pentamer in lipid bilayers by a hybrid solution and solid-state NMR method.  

PubMed

Phospholamban (PLN) is a type II membrane protein that inhibits the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA), thereby regulating calcium homeostasis in cardiac muscle. In membranes, PLN forms pentamers that have been proposed to function either as a storage for active monomers or as ion channels. Here, we report the T-state structure of pentameric PLN solved by a hybrid solution and solid-state NMR method. In lipid bilayers, PLN adopts a pinwheel topology with a narrow hydrophobic pore, which excludes ion transport. In the T state, the cytoplasmic amphipathic helices (domains Ia) are absorbed into the lipid bilayer with the transmembrane domains arranged in a left-handed coiled-coil configuration, crossing the bilayer with a tilt angle of approximately 11° with respect to the membrane normal. The tilt angle difference between the monomer and pentamer is approximately 13°, showing that intramembrane helix-helix association forces dominate over the hydrophobic mismatch, driving the overall topology of the transmembrane assembly. Our data reveal that both topology and function of PLN are shaped by the interactions with lipids, which fine-tune the regulation of SERCA. PMID:21576492

Verardi, Raffaello; Shi, Lei; Traaseth, Nathaniel J; Walsh, Naomi; Veglia, Gianluigi

2011-05-16

302

Signal enhancement for the sensitivity-limited solid state NMR experiments using a continuous, non-uniform acquisition scheme.  

PubMed

We describe a sampling scheme for the two-dimensional (2D) solid state NMR experiments, which can be readily applied to the sensitivity-limited samples. The sampling scheme utilizes continuous, non-uniform sampling profile for the indirect dimension, i.e. the acquisition number decreases as a function of the evolution time (t1) in the indirect dimension. For a beta amyloid (A?) fibril sample, we observed overall 40-50% signal enhancement by measuring the cross peak volume, while the cross peak linewidths remained comparable to the linewidths obtained by regular sampling and processing strategies. Both the linear and Gaussian decay functions for the acquisition numbers result in similar percentage of increment in signal. In addition, we demonstrated that this sampling approach can be applied with different dipolar recoupling approaches such as radiofrequency assisted diffusion (RAD) and finite-pulse radio-frequency-driven recoupling (fpRFDR). This sampling scheme is especially suitable for the sensitivity-limited samples which require long signal averaging for each t1 point, for instance the biological membrane proteins where only a small fraction of the sample is isotopically labeled. PMID:21930405

Qiang, Wei

2011-08-30

303

Crystal Polymorphism of Protein GB1 Examined by Solid-State NMR Spectroscopy and X-ray Diffraction  

PubMed Central

The study of micro- or nanocrystalline proteins by magic-angle spinning (MAS) solid-state NMR (SSNMR) gives atomic-resolution insight into structure in cases when single crystals cannot be obtained for diffraction studies. Subtle differences in the local chemical environment around the protein, including the characteristics of the co-solvent and the buffer, determine whether a protein will form single crystals. The impact of these small changes in formulation is also evident in the SSNMR spectra, but leads only to correspondingly subtle changes in the spectra. Here we demonstrate that several formulations of GB1 microcrystals yield very high-quality SSNMR spectra, although only a subset of conditions enable growth of single crystals. We have characterized these polymorphs by X-ray powder diffraction and assigned the SSNMR spectra. Assignments of the 13C and 15N SSNMR chemical shifts confirm that the backbone structure is conserved, indicative of a common protein fold, but sidechain chemical shifts are changed on the surface of the protein, in a manner dependent upon crystal packing and electrostatic interactions with salt in the mother liquor. Our results demonstrate the ability of SSNMR to reveal minor structural differences among crystal polymorphs. This ability has potential practical utility for studying formulation chemistry of industrial and therapeutic proteins, as well as for deriving fundamental insights into the phenomenon of single crystal growth.

Frericks Schmidt, Heather L.; Sperling, Lindsay J.; Gao, Yi Gui; Wylie, Benjamin J.; Boettcher, John M.; Wilson, Scott R.; Rienstra, Chad M.

2009-01-01

304

Fast acquisition of multi-dimensional spectra in solid-state NMR enabled by ultra-fast MAS  

NASA Astrophysics Data System (ADS)

The advantages offered by ultra-fast (>60 kHz) magic angle spinning (MAS) rotation for the study of biological samples, notably containing paramagnetic centers are explored. It is shown that optimal conditions for performing solid-state 13C NMR under 60 kHz MAS are obtained with low-power CW 1H decoupling, as well as after a low-power 1H,13C cross-polarization step at a double-quantum matching condition. Acquisition with low-power decoupling highlights the existence of rotational decoupling sidebands. The sideband intensities and the existence of first and second rotary conditions are explained in the framework of the Floquet-van Vleck theory. As a result, optimal 13C spectra of the oxidized, paramagnetic form of human copper zinc superoxide dismutase (SOD) can be obtained employing rf-fields which do not exceed 40 kHz during the whole experiment. This enables the removal of unwanted heating which can lead to deterioration of the sample. Furthermore, combined with the short 1H T1s, this allows the repetition rate of the experiments to be shortened from 3 s to 500 ms, thus compensating for the sensitivity loss due to the smaller sample volume in a 1.3 mm rotor. The result is that 2D 13C-13C correlation could be acquired in about 24 h on less than 1 mg of SOD sample.

Laage, Ségolène; Sachleben, Joseph R.; Steuernagel, Stefan; Pierattelli, Roberta; Pintacuda, Guido; Emsley, Lyndon

2009-02-01

305

Solid-state NMR calculations for metal oxides and gallates: Shielding and quadrupolar parameters for perovskites and related phases  

NASA Astrophysics Data System (ADS)

The NMR parameters obtained from solid-state DFT calculations within the GIPAW approach for 17O- and 69/71Ga-sites in a range of predominantly oxide-based (group II monoxides, SrTiO3, BaZrO3, BaSnO3, BaTiO3, LaAlO3, LaGaO3, SrZrO3, MgSiO3 and Ba2In2O5), and gallate (?- and ?-Ga2O3, LiGaO2, NaGaO2, GaPO4 and LaGaO3) materials are compared with experimental values, with a view to the future application of a similar approach to doped phases of interest as candidate intermediate temperature solid oxide fuel cell (ITSOFC) electrolytes. Isotropic and anisotropic chemical shift parameters, quadrupolar coupling constants, and associated asymmetries are presented and analyzed. The unusual GaO5 site occurring in LaGaGe2O7 is also fully characterised. In general, it is found that the theoretical results closely track the experimental trends, though some deviations are identified and discussed, particularly in regard to quadrupolar ?Q-values. The high quality of the computed results suggests that this approach can be extended to study more complex and disordered phases.

Middlemiss, Derek S.; Blanc, Frédéric; Pickard, Chris J.; Grey, Clare P.

2010-05-01

306

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

SciTech Connect

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

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

2012-02-15

307

Solid-state NMR calculations for metal oxides and gallates: shielding and quadrupolar parameters for perovskites and related phases.  

PubMed

The NMR parameters obtained from solid-state DFT calculations within the GIPAW approach for (17)O- and (69/71)Ga-sites in a range of predominantly oxide-based (group II monoxides, SrTiO(3), BaZrO(3), BaSnO(3), BaTiO(3), LaAlO(3), LaGaO(3), SrZrO(3), MgSiO(3) and Ba(2)In(2)O(5)), and gallate (alpha- and beta-Ga(2)O(3), LiGaO(2), NaGaO(2), GaPO(4) and LaGaO(3)) materials are compared with experimental values, with a view to the future application of a similar approach to doped phases of interest as candidate intermediate temperature solid oxide fuel cell (ITSOFC) electrolytes. Isotropic and anisotropic chemical shift parameters, quadrupolar coupling constants, and associated asymmetries are presented and analyzed. The unusual GaO(5) site occurring in LaGaGe(2)O(7) is also fully characterised. In general, it is found that the theoretical results closely track the experimental trends, though some deviations are identified and discussed, particularly in regard to quadrupolar eta(Q)-values. The high quality of the computed results suggests that this approach can be extended to study more complex and disordered phases. PMID:20335059

Middlemiss, Derek S; Blanc, Frédéric; Pickard, Chris J; Grey, Clare P

2010-01-13

308

Identification of sublattice damages in swift heavy ion irradiated N-doped 6H-SiC polytype studied by solid state NMR.  

PubMed

We have studied N-doped 6H-SiC in its pristine and Swift Heavy Ion (SHI) irradiated (150 MeV Ag(12+) ions) forms by solid state Nuclear Magnetic Resonance (NMR) at 7.01 T using (13)C and (29)Si as probe nuclei under magic angle spinning. We show that increased levels of nitrogen doping, than used before, lead to the observation of Knight shifts emanating from an increase in electron density in the conduction band, which in (13)C far exceed those in (29)Si MAS spectra. We have rationalized the differential effects in the MAS spectra and site-dependent paramagnetic shifts in terms of the nitrogen doping at the A, B, and C lattice sites. N-doping has a profound effect on (29)Si spin-lattice relaxation, and the site-dependent relaxation behavior is attributed to a difference in conduction electron properties at the different lattice sites. (29)Si T(1) measurements serve to identify the sublattice damages in SHI irradiated 6H-SiC. By determining the spin-lattice relaxation rates as a function of the SHI irradiation ion fluences, the change in relaxation behavior is correlated to the damage production mechanism. The sublattice damage leads to discernable changes in the interaction between the mobile unpaired electrons in the conduction band and the nuclear site, which profoundly influence the NMR relaxation properties. Our relaxation studies also provide evidence for site-dependent localized effects and a decrease in carrier spin density in the conduction band for the SHI irradiated 6H-SiC. PMID:21568313

Viswanathan, E; Kanjilal, D; Sivaji, K; Ganapathy, S

2011-05-26

309

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

PubMed

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

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

2007-10-04

310

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

PubMed

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

Komatsu, Takanori; Kikuchi, Jun

2013-09-06

311

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

USGS Publications Warehouse

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

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

1996-01-01

312

Solid-state NMR study of a 41 kDa membrane protein complex DsbA/DsbB.  

PubMed

The disulfide bond generation system in E. coli is led by a periplasmic protein, DsbA, and an integral membrane protein, DsbB. Here we present a solid-state NMR (SSNMR) study of a 41 kDa membrane protein complex DsbA/DsbB precipitated in the presence of native lipids to investigate conformational changes and dynamics that occur upon transient complex formation within the electron transfer pathway. Chemical shift changes in the periplasmic enzyme DsbA in three states (wild type, C33S mutant, and in complex with DsbB) reveal structural and/or dynamic information. We report a 4.9 ppm (15)N chemical shift change observed for Pro31 in the active site between the wild type and C33S mutant of DsbA. Additionally, the Pro31 residue remains elusive in the DsbA/DsbB complex, indicating that the dynamics change drastically in the active site between the three states of DsbA. Using three-dimensional SSNMR spectra, partial (13)C and (15)N de novo chemical shift assignments throughout DsbA in the DsbA/DsbB complex were compared with the shifts from DsbA alone to map site-specific chemical shift perturbations. These results demonstrate that there are further structural and dynamic changes of DsbA in the native membrane observed by SSNMR, beyond the differences between the crystal structures of DsbA and the DsbA/DsbB complex. PMID:23527473

Sperling, Lindsay J; Tang, Ming; Berthold, Deborah A; Nesbitt, Anna E; Gennis, Robert B; Rienstra, Chad M

2013-05-09

313

High-yield expression and purification of isotopically labeled cytochrome P450 monooxygenases for solid-state NMR spectroscopy  

PubMed Central

Cytochrome P450 monooxygenases (P450s), which represent the major group of drug metabolizing enzymes in humans, also catalyze important synthetic and detoxicative reactions in insects, plants and many microbes. Flexibilities in their catalytic sites and membrane associations are thought to play central roles in substrate binding and catalytic specificity. To date, E. coli expression strategies for structural analysis of eukaryotic membrane-bound P450s by X-ray crystallography have necessitated full or partial removal of their N-terminal signal anchor domain (SAD) and, often, replacement of residues more peripherally associated with the membrane (such as the F-G loop region). Even with these modifications, investigations of P450 structural flexibility remain challenging with multiple single crystal conditions needed to identify spatial variations between substrate-free and different substrate-bound forms. To overcome these limitations, we have developed methods for the efficient expression of 13C- and 15N-labeled P450s and analysis of their structures by magic-angle spinning solid-state NMR (SSNMR) spectroscopy. In the presence of co-expressed GroEL and GroES chaperones, full-length (53 kDa) Arabidopsis 13C,15N-labeled CYP98A3 is expressed at yields of 2–4 mg per liter of minimal media without the necessity of generating side chain modifications or N-terminal deletions. Precipitated CYP98A3 generates high quality SSNMR spectra consistent with a homogeneous, folded protein. These data highlight the potential of these methodologies to contribute to the structural analysis of membrane-bound proteins.

Rupasinghe, Sanjeewa G.; Duan, Hui; Frericks Schmidt, Heather L.; Berthold, Deborah A.; Rienstra, Chad M.; Schuler, Mary A.

2008-01-01

314

YPdSn and YPd2Sn: Structure, 89Y solid state NMR and 119Sn Mössbauer spectroscopy  

NASA Astrophysics Data System (ADS)

The stannides YPdSn and YPd2Sn were synthesized by high-frequency melting of the elements in sealed tantalum tubes. Both structures were refined on the basis of single crystal X-ray diffractometer data: TiNiSi type, Pnma, a=715.4(1), b=458.8(1), c=789.1(1) pm, wR2=0.0461, 510 F2 values, 20 variables for YPdSn and MnCu2Al type, Fm3¯m, a=671.44(8), wR2=0.0740, 55 F2 values, 5 parameters for YPd2Sn. The yttrium atoms in the new stannide YPdSn are coordinated by two tilted Pd3Sn3 hexagons (ordered AlB2 superstructure). In the Heusler phase YPd2Sn each yttrium atom has octahedral tin coordination and additionally eight palladium neighbors. The cubic site symmetry of yttrium is reflected in the 119Sn Mössbauer spectrum which shows no quadrupole splitting. In contrast, YPdSn shows a single signal at ?=1.82(1) mm/s subjected to quadrupole splitting of ?EQ=0.93(1) mm/s. Both compounds have been characterized by high-resolution 89Y solid state NMR spectroscopy, which indicates the presence of strong Knight shifts. The spectrum of YPd2Sn is characterized by an unusually large linewidth, suggesting the presence of a Knight shift distribution reflecting local disordering effects. The range of 89Y Knight shifts of several binary and ternary intermetallic yttrium compounds is briefly discussed.

Höting, Christoph; Eckert, Hellmut; Langer, Thorsten; Schellenberg, Inga; Pöttgen, Rainer

2012-06-01

315

Magic-Angle Spinning Solid-State NMR Spectroscopy of Nanodisc- Embedded Human CYP3A4†  

PubMed Central

Cytochrome P450 (CYP) 3A4 contributes to the metabolism of approximately 50% of commercial drugs by oxidizing a large number of structurally diverse substrates. Like other endoplasmic reticulum-localized P450s, CYP3A4 contains a membrane-anchoring N-terminal helix and a significant number of hydrophobic domains, important for the interaction between CYP3A4 and the membrane. Although the membrane affects specificity of CYP3A4 ligand binding, the structural details of the interaction have not been revealed so far because x-ray crystallography studies are available only for the soluble domain of CYP3A4. Here we report sample preparation and initial magic-angle spinning (MAS) solid-state NMR (SSNMR) of CYP3A4 (?3?12) embedded in a nanoscale membrane bilayer, or Nanodisc. The growth protocol yields ?2.5 mg of the enzymatically active, uniformly 13C, 15N-enriched CYP3A4 from a liter of growth medium. Polyethylene glycol 3350-precipitated CYP3A4 in Nanodiscs yields spectra of high resolution and sensitivity, consistent with a folded, homogeneous protein. CYP3A4 in Nanodiscs remains enzymatically active throughout the precipitation protocol as monitored by bromocriptine binding. The 13C line widths measured from 13C-13C 2D chemical shift correlation spectra are ?0.5 ppm. The secondary structure distribution within several amino acid types determined from 13C chemical shifts is consistent with the ligand-free x-ray structures. These results demonstrate that MAS SSNMR can be performed on Nanodisc-embedded membrane proteins in a folded, active state. The combination of SSNMR and Nanodisc methodologies opens up new possibilities for obtaining structural information on CYP3A4 and other integral membrane proteins with full retention of functionality.

Kijac, Aleksandra; Li, Ying; Sligar, Stephen G.; Rienstra, Chad M.

2008-01-01

316

Synthesis, characterization, and solid-state NMR investigation of organically modified bentonites and their composites with LDPE.  

PubMed

Polymer/clay nanocomposites show remarkably improved properties (mechanical properties, as well as decreased gas permeability and flammability, etc.) with respect to their microscale counterparts and pristine polymers. Due to the substantially apolar character of most of the organic polymers, natural occurring hydrophilic clays are modified into organophilic clays with consequent increase of the polymer/clay compatibility. Different strategies have been developed for the preparation of nanocomposites with improved properties, especially aimed at achieving the best dispersion of clay platelets in the polymer matrix. In this paper we present the preparation and characterization of polymer/clay nanocomposites composed of low-density polyethylene (LDPE) and natural clay, montmorillonite-containing bentonite. Two different forms of the clay have been considered: the first, a commercial organophilic bentonite (Nanofil 15), obtained by exchanging the natural cations with dimethyldioctadecylammonium (2C18) cations, and the second, obtained by performing a grafting reaction of an alkoxysilane containing a polymerizable group, 3-(trimethoxysilyl)propyl methacrylate (TSPM), onto Nanofil 15. Both the clays and LDPE/clay nanocomposites were characterized by thermal, FT-IR, and X-ray diffraction techniques. The samples were also investigated by means of (29)Si, (13)C, and (1)H solid-state NMR, obtaining information on the structural properties of the modified clays. Moreover, by exploiting the effect of bentonite paramagnetic (Fe(3+)) ions on proton spin-lattice relaxation times (T1's), useful information about the extent of the polymer-clay dispersion and their interfacial interactions could be obtained. PMID:23786424

Borsacchi, Silvia; Sudhakaran, Umayal; Geppi, Marco; Ricci, Lucia; Liuzzo, Vincenzo; Ruggeri, Giacomo

2013-07-09

317

Structure and topology of monomeric phospholamban in lipid membranes determined by a hybrid solution and solid-state NMR approach  

PubMed Central

Phospholamban (PLN) is an essential regulator of cardiac muscle contractility. The homopentameric assembly of PLN is the reservoir for active monomers that, upon deoligomerization form 1:1 complexes with the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA), thus modulating the rate of calcium uptake. In lipid bilayers and micelles, monomeric PLN exists in equilibrium between a bent (or resting) T state and a more dynamic (or active) R state. Here, we report the high-resolution structure and topology of the T state of a monomeric PLN mutant in lipid bilayers, using a hybrid of solution and solid-state NMR restraints together with molecular dynamics simulations in explicit lipid environments. Unlike the previous structural ensemble determined in micelles, this approach gives a complete picture of the PLN monomer structure in a lipid bilayer. This hybrid ensemble exemplifies the tilt, rotation, and depth of membrane insertion, revealing the interaction with the lipids for all protein domains. The N-terminal amphipathic helical domain Ia (residues 1–16) rests on the surface of the lipid membrane with the hydrophobic face of domain Ia embedded in the membrane bilayer interior. The helix comprised of domain Ib (residues 23–30) and transmembrane domain II (residues 31–52) traverses the bilayer with a tilt angle of ?24°. The specific interactions between PLN and lipid membranes may represent an additional regulatory element of its inhibitory function. We propose this hybrid method for the simultaneous determination of structure and topology for membrane proteins with compact folds or proteins whose spatial arrangement is dictated by their specific interactions with lipid bilayers.

Traaseth, Nathaniel J.; Shi, Lei; Verardi, Raffaello; Mullen, Daniel G.; Barany, George; Veglia, Gianluigi

2009-01-01

318

Membrane structure and conformational changes of the antibiotic heterodimeric peptide distinctin by solid-state NMR spectroscopy  

PubMed Central

The heterodimeric antimicrobial peptide distinctin is composed of 2 linear peptide chains of 22- and 25-aa residues that are connected by a single intermolecular S-S bond. This heterodimer has been considered to be a unique example of a previously unrecorded class of bioactive peptides. Here the 2 distinctin chains were prepared by chemical peptide synthesis in quantitative amounts and labeled with 15N, as well as 15N and 2H, at selected residues, respectively, and the heterodimer was formed by oxidation. CD spectroscopy indicates a high content of helical secondary structures when associated with POPC/POPG 3:1 vesicles or in membrane-mimetic environments. The propensity for helix formation follows the order heterodimer >chain 2 >chain 1, suggesting that peptide-peptide and peptide-lipid interactions both help in stabilizing this secondary structure. In a subsequent step the peptides were reconstituted into oriented phospholipid bilayers and investigated by 2H and proton-decoupled 15N solid-state NMR spectroscopy. Whereas chain 2 stably inserts into the membrane at orientations close to perfectly parallel to the membrane surface in the presence or absence of chain 1, the latter adopts a more tilted alignment, which further increases in the heterodimer. The data suggest that membrane interactions result in considerable conformational rearrangements of the heterodimer. Therefore, chain 2 stably anchors the heterodimer in the membrane, whereas chain 1 interacts more loosely with the bilayer. These structural observations are consistent with the antimicrobial activities when the individual chains are compared to the dimer.

Resende, Jarbas M.; Moraes, Cleria Mendonca; Munhoz, Victor H. O.; Aisenbrey, Christopher; Verly, Rodrigo M.; Bertani, Philippe; Cesar, Amary; Pilo-Veloso, Dorila; Bechinger, Burkhard

2009-01-01

319

Direct Speciation of Phosphorus in Alum-Amended Poultry Litter: Solid-State 31P NMR Investigation  

SciTech Connect

Amending poultry litter (PL) with aluminum sulfate (alum) has proven to be effective in reducing water-soluble phosphorus (P) in the litter and in runoff from fields that have received PL applications; it has therefore been suggested as a best management practice. Although its effectiveness has been demonstrated on a macroscopic scale in the field, little is known about P speciation in either alumamended or unamended litter. This knowledge is important for the evaluation of the long-term stability and bioavailability of P, which is a necessary prerequisite for the assessment of the sustainability of intensive poultry operations. Both solid state MAS and CP-MAS {sup 31}P NMR as well as {sup 31}P({sup 27}Al) TRAPDOR were used to investigate P speciation in alumamended and unamended PL. The results indicate the presence of a complex mixture of organic and inorganic orthophosphate phases. A calcium phosphate phase, probably a surface precipitate on calcium carbonate, could be identified in both unamended and alum-amended PL, as well as physically bound HPO{sub 4}{sup 2-}. Phosphate associated with Al was found in the alum-amended PL, most probably a mixture of a poorly ordered wavellite and phosphate surface complexes on aluminum hydroxide that had been formed by the hydrolysis of alum. However, a complex mixture of organic and inorganic phosphate species could not be resolved. Phosphate associated with Al comprised on average 40{+-}14% of the total P in alum-amended PL, whereas calcium phosphate phases comprised on average 7{+-}4% in the alum-amended PL and 14{+-}5% in the unamended PL.

Hunger, Stefan; Cho, Herman M.; Sims, James T.; Sparks, Donald L.

2004-02-01

320

Conformational analysis of the full-length M2 protein of the influenza A virus using solid-state NMR.  

PubMed

The influenza A M2 protein forms a proton channel for virus infection and mediates virus assembly and budding. While extensive structural information is known about the transmembrane helix and an adjacent amphipathic helix, the conformation of the N-terminal ectodomain and the C-terminal cytoplasmic tail remains largely unknown. Using two-dimensional (2D) magic-angle-spinning solid-state NMR, we have investigated the secondary structure and dynamics of full-length M2 (M2FL) and found them to depend on the membrane composition. In 2D (13) C DARR correlation spectra, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)-bound M2FL exhibits several peaks at ?-sheet chemical shifts, which result from water-exposed extramembrane residues. In contrast, M2FL bound to cholesterol-containing membranes gives predominantly ?-helical chemical shifts. Two-dimensional J-INADEQUATE spectra and variable-temperature (13) C spectra indicate that DMPC-bound M2FL is highly dynamic while the cholesterol-containing membranes significantly immobilize the protein at physiological temperature. Chemical-shift prediction for various secondary-structure models suggests that the ?-strand is located at the N-terminus of the DMPC-bound protein, while the cytoplasmic domain is unstructured. This prediction is confirmed by the 2D DARR spectrum of the ectodomain-truncated M2(21-97), which no longer exhibits ?-sheet chemical shifts in the DMPC-bound state. We propose that the M2 conformational change results from the influence of cholesterol, and the increased helicity of M2FL in cholesterol-rich membranes may be relevant for M2 interaction with the matrix protein M1 during virus assembly and budding. The successful determination of the ?-strand location suggests that chemical-shift prediction is a promising approach for obtaining structural information of disordered proteins before resonance assignment. PMID:24023039

Liao, Shu Yu; Fritzsching, Keith J; Hong, Mei

2013-10-07

321

Solid-state NMR investigations of the pyrolysis and thermo-oxidative decomposition products of a polystyrene\\/red phosphorus\\/magnesium hydroxide system  

Microsoft Academic Search

Thermal, thermo-oxidative and fire residues of high impact polystyrene\\/magnesium hydroxide\\/red phosphorus (HIPS\\/Mg(OH)2\\/Pr) are investigated by solid-state NMR and compared with the results for the binary subsystem Mg(OH)2\\/Pr. The influences of oxygen, nitrogen and temperature are discussed. For a thermal decomposition and pyrolysis during combustion, the main pyrolysis of HIPS takes place while the remaining residue is a rather intact polymer,

M. A. Fichera; U. Braun; B. Schartel; H. Sturm; U. Knoll; C. Jäger

2007-01-01

322

A high-resolution solid-state NMR study on starch–clay nanocomposites and the effect of aging on clay dispersion  

Microsoft Academic Search

High-resolution solid-state nuclear magnetic resonance (NMR) was applied as a bulk analysis method to provide an indication of clay dispersion in starch–clay nanocomposites. The starch composite containing 2.5 wt% nano-clay appeared as an exfoliated system with an average distance between clay platelets () of around 40 nm. Increasing the amount of nano-clay to 5.0 wt% reduced the value to around

Xiaoqing Zhang; Katherine Dean; Iko M Burgar; X Zhang

2010-01-01

323

Detailed investigation of the lattice structure of zeolite ZSM-11 by a combination of solid-state NMR and synchrotron X-ray diffraction techniques  

Microsoft Academic Search

The lattice structure of a pure and completely siliceous sample of zeolite ZSM-11 has been investigated by a combination of high-resolution solid-state ²⁹Si MAS NMR and synchrotron-based X-ray powder diffraction techniques. The structure is temperature dependent in the range 263-363 K and a good fit to the diffraction data at 363 K is obtained with space group I{anti 4}m2 and

Colin A. Fyfe; Hermann Gies; George T. Kokotailo; Connie Pasztor; Harald Strobl; David E. Cox

1989-01-01

324

Solid-state NMR characterization of cross-linking in EPDM\\/PP blends from 1H– 13C polarization transfer dynamics  

Microsoft Academic Search

A novel approach for solid-state NMR characterization of cross-linking in polymer blends from the analysis of 1H–13C polarization transfer dynamics is introduced. It extends the model of residual dipolar couplings under permanent cross-linking, typically used to describe 1H transverse relaxation techniques, by considering a more realistic distribution of the order parameter along a polymer chain in rubbers. Based on a

Mihaela Aluas; Claudiu Filip

2005-01-01

325

Molecular ordering of cellulose after extraction of polysaccharides from primary cell walls of Arabidopsis thaliana: a solid-state CP\\/MAS 13C NMR study  

Microsoft Academic Search

Solid-state CP\\/MAS 13C NMR spectroscopy was used to determine the effects of three different sequential extraction procedures, used to remove non-cellulosic polysaccharides, on the molecular ordering of cellulose in a cell-wall preparation containing mostly primary cell walls obtained from the leaves of the model dicotyledon, Arabidopsis thaliana. The extractions were 50 mM trans-1,2-diaminocyclohexane N,N,N?,N?-tetraacetic acid (CDTA) and 50 mM sodium

Lynette M. Davies; Philip J. Harris; Roger H. Newman

2002-01-01

326

Molecular motions of d-?-galacturonic acid (GA) and methyl- d-?-galacturonic acid methyl ester (MGAM) in the solid state-A proton NMR study  

Microsoft Academic Search

The molecular motions of d-?-galacturonic acid monohydrate (GA) and its derivative methyl-?-d-galacturonic acid methyl ester monohydrate (MGAM) in the solid state have been studied using 1H NMR. Both protonated and deuterium exchanged samples have been used. Spin-lattice relaxation times in the laboratory and rotating frames as well as second moments have been measured over the temperature range 90–370 K. Analysis

H. R Tang; P. S Belton

1998-01-01

327

Overexpression, purification, and characterization of recombinant Ca-ATPase regulators for high-resolution solution and solid-state NMR studies  

Microsoft Academic Search

Phospholamban (PLB) and Sarcolipin (SLN) are integral membrane proteins that regulate muscle contractility via direct interaction with the Ca-ATPase in cardiac and skeletal muscle, respectively. The molecular details of these protein–protein interactions are as yet undetermined. Solution and solid-state NMR spectroscopies have proven to be effective tools for deciphering such regulatory mechanisms to a high degree of resolution; however, large

Bethany Buck; Jamillah Zamoon; Tara L Kirby; Tara M DeSilva; Christine Karim; David Thomas; Gianluigi Veglia

2003-01-01

328

Nanoscale spatial resolution probes for scanning thermal microscopy of solid state materials  

NASA Astrophysics Data System (ADS)

Scanning thermal microscopy (SThM) uses micromachined thermal sensors integrated in a force sensing cantilever with a nanoscale tip that can be highly useful for exploration of thermal management of nanoscale semiconductor devices as well as mapping of surface and subsurface properties of related materials. Whereas SThM is capable to image externally generated heat with nanoscale resolution, its ability to map and measure thermal conductivity of materials has been mainly limited to polymers or similar materials possessing low thermal conductivity in the range from 0.1 to 1 W m-1 K-1, with lateral resolution on the order of 1 ?m. In this paper, we use linked experimental and theoretical approaches to analyse thermal performance and sensitivity of the micromachined SThM probes in order to expand their applicability to a broader range of nanostructures from polymers to semiconductors and metals. We develop physical models of interlinked thermal and electrical phenomena in these probes and their interaction with the sample on the mesoscopic length scale of few tens of nm and then validate these models using experimental measurements of the real probes, which provided the basis for analysing SThM performance in exploration of nanostructures. Our study then highlights critical features of these probes, namely, the geometrical location of the thermal sensor with respect to the probe apex, thermal conductance of the probe to the support base, heat conduction to the surrounding gas, and the thermal conductivity of tip material adjacent to the apex. It furthermore allows us to propose a novel design of the SThM probe that incorporates a multiwall carbon nanotube or similar high thermal conductivity graphene sheet material with longitudinal dimensions on micrometre length scale positioned near the probe apex that can provide contact areas with the sample on the order of few tens of nm. The new sensor is predicted to provide greatly improved spatial resolution to thermal properties of nanostructures as well as to expand the sensitivity of the SThM probe to materials with heat conductivity values up to 100-1000 W m-1 K-1.

Tovee, P.; Pumarol, M.; Zeze, D.; Kjoller, Kevin; Kolosov, O.

2012-12-01

329

Correlations between (51)V solid-state NMR parameters and chemical structure of vanadium (V) complexes as models for related metalloproteins and catalysts.  

PubMed

The parameters describing the quadrupolar and CSA interactions of 51V solid-state MAS NMR investigations of model complexes mimicking vanadoenzymes as well as vanadium containing catalysts and enzyme complexes are interpreted with respect to the chemical structure. The interpretation is based on the data of 15 vanadium complexes including two new complexes with previously unpublished data and 13 complexes with data previously published by us. Correlations between the chemical structure and the 51V solid-state NMR data of this class of compounds have been established. Especially for the isotropic chemical shift delta(iso) and the chemical shift anisotropy delta(sigma), correlations with specific structural features like the coordination number of the vanadium atom, the number of coordinating nitrogens, the number of oxygen atoms and the chemical surrounding of the complex could be established for these compounds. Moreover, quantitative correlations between the solid-state NMR parameters and specific bond angles and bond lengths have been obtained. Our results can be of particular interest for future investigations concerning the structure and the mode of action of related vanadoenzymes and vanadate protein assemblies, including the use of vanadate adducts as transition state analogs for phosphate metabolizing systems. PMID:20045295

Fenn, Annika; Wächtler, Maria; Gutmann, Torsten; Breitzke, Hergen; Buchholz, Axel; Lippold, Ines; Plass, Winfried; Buntkowsky, Gerd

2009-12-04

330

Orphan spin operators enable the acquisition of multiple 2D and 3D magic angle spinning solid-state NMR spectra  

NASA Astrophysics Data System (ADS)

We propose a general method that enables the acquisition of multiple 2D and 3D solid-state NMR spectra for U-13C, 15N-labeled proteins. This method, called MEIOSIS (Multiple ExperIments via Orphan SpIn operatorS), makes it possible to detect four coherence transfer pathways simultaneously, utilizing orphan (i.e., neglected) spin operators of nuclear spin polarization generated during 15N-13C cross polarization (CP). In the MEIOSIS experiments, two phase-encoded free-induction decays are decoded into independent nuclear polarization pathways using Hadamard transformations. As a proof of principle, we show the acquisition of multiple 2D and 3D spectra of U-13C, 15N-labeled microcrystalline ubiquitin. Hadamard decoding of CP coherences into multiple independent spin operators is a new concept in solid-state NMR and is extendable to many other multidimensional experiments. The MEIOSIS method will increase the throughput of solid-state NMR techniques for microcrystalline proteins, membrane proteins, and protein fibrils.

Gopinath, T.; Veglia, Gianluigi

2013-05-01

331

Orphan spin operators enable the acquisition of multiple 2D and 3D magic angle spinning solid-state NMR spectra.  

PubMed

We propose a general method that enables the acquisition of multiple 2D and 3D solid-state NMR spectra for U-(13)C, (15)N-labeled proteins. This method, called MEIOSIS (Multiple ExperIments via Orphan SpIn operatorS), makes it possible to detect four coherence transfer pathways simultaneously, utilizing orphan (i.e., neglected) spin operators of nuclear spin polarization generated during (15)N-(13)C cross polarization (CP). In the MEIOSIS experiments, two phase-encoded free-induction decays are decoded into independent nuclear polarization pathways using Hadamard transformations. As a proof of principle, we show the acquisition of multiple 2D and 3D spectra of U-(13)C, (15)N-labeled microcrystalline ubiquitin. Hadamard decoding of CP coherences into multiple independent spin operators is a new concept in solid-state NMR and is extendable to many other multidimensional experiments. The MEIOSIS method will increase the throughput of solid-state NMR techniques for microcrystalline proteins, membrane proteins, and protein fibrils. PMID:23676036

Gopinath, T; Veglia, Gianluigi

2013-05-14

332

The Nature of Polymerization in Silicate Glasses and Melts: Solid State NMR, Modeling and Qauntum Chemicial Calculations.  

NASA Astrophysics Data System (ADS)

Silicate melts are among the dominant constituents of the upper mantle and crust. The full understanding of atomic scale disorder is essential to the macroscopic properties of the melts such as viscosity and configurational thermodynamic properties. Recently, we quantified the various aspects of the extent of disorder in ›r­’charge-balanced silicate glasses (non bridging (NBO)/T=0)›r­_ using solid state NMR and theoretical analysis, which allowed the degree of randomness of these systems to be determined in terms of the degree of Al-avoidance and degree of phase separations (Lee and Stebbins, Geochim. Cosmochim. Acta. 66, 303). Quantitative estimation of the framework connectivity and the atomic structures of depolymerized silicate melts (NBO/T>0), however, are still poorly known and framework cations and anions have often been assumed to be randomly distributed. Here, we explore the extent of disorder and the nature of polymerization in several binary and ternary silicate glasses with varying NBO/T using O-17 NMR at varying magnetic fields of 7.1, 9.4 and 14.1 T in conjunction with quantum chemical calculations. We also quantify the extent of intermixing among non-framework cations in mixed cation glasses, and calculate corresponding configurational thermodynamic properties. Non-random distribution among cations is clearly demonstrated from the relative populations of oxygen sites and the variation of distribution of structurally relevant NMR parameters with NBO/T from O-17 3QMAS NMR. The proportion of NBO (Na-O-Si) in Na2O-SiO2 glasses increases with NBO/T. Its chemical shift distribution decreases about 18 % from NBO/T of 0.7 to 2, suggesting a reduced configurational disorder around NBO with Na contents. Preferential interactions among framework cations are further manifested in peralkaline Ca- and Na- aluminosilicate glasses where depolymerization of networks selectively occurs at Si rather than Al tetrahedra, forming Na-O-Si or Ca-O-Si. The result is consistent with our quantum chemical calculations based on density functional theory where the silicate chain with Al-NBO has energy penalty of about 108 kJ/mol compared with the cluster with Ca-O-Si. The degree of Al avoidance (Q) among framework units in Na- aluminosilicate is larger than that in Ca-aluminosilicates, as recently observed for fully polymerized glasses. On the other hand, Q varies with NBO/T. The above results support the significant chemical order in silicate glasses that leads to considerable mixing among framework units. The degree of intermixing among non-framework cations in mixed-cation glasses has remained controversial. The population of each Na-NBO in Ca-Na and Ba-Na mixed cation silicate glasses is smaller than the prediction given from random distribution of these cations, and thus supports the preference for dissimilar pairs of cations, which could explain a decrease in diffusivity in these melts. In this study, we provide new insights into the structure of silicate glasses with varying NBO/T, highlighting more complete, atomic-level understanding on the dynamic processes in silicate magmas.

Lee, S.; Stebbins, J. F.; Mysen, B.; Cody, G. D.

2002-12-01

333

Solid-state 207pb nmr studies of lead-group 16 and mixedtransition-metal-lead-group 16 element-containing materials  

SciTech Connect

207Pb solid-state NMR studies have been conducted on binarylead-group 16 and mixed transition-metal/lead group 16 materials,correlating the NMR chemical shifts of the materials with theirstructures. The experimental results show that the 207Pb chemical shiftsare strongly influenced by the local electronic structure. Data arereported for lead selenide, lead selenate, calcium plumbate, strontiumplumbite, barium plumbite, lead borate, lead zirconate, lead tungstate,lead meta-tantalate, lead niobate, lead molybdate, lead meta-vanadate,lead sulfite, and lead sulfate.

Van Bramer, S.E.; Glatfelter, A.; Bai, S.; Dybowksi, C.; GNeue,G.; Perry, D.L.

2005-08-26

334

Theoretical predictions of the two-dimensional solid-state NMR spectra: A case study of the 13C–1H correlations in metergoline  

NASA Astrophysics Data System (ADS)

A new method for the treatment of data from multidimensional solid-state NMR investigations is described. It approximates the theoretical NMR chemical shifts from the chemical shielding values obtained by first-principles calculations and subsequently treats these results to quantify the similarity between predicted and experimental chemical shift correlations. The test case of this approach is performed for the measured and several sets of computed 13C–1H heteronuclear correlations in the polymorphic form I of metergoline, which is relatively large, pharmaceutically active system. The proposed protocol is general, however, and it can be immediately applied to study other compounds and nuclei.

Czernek, Ji?í; Brus, J.

2013-10-01

335

A micromachined Kelvin probe for surface potential measurements in microfluidic channels and solid-state applications  

Microsoft Academic Search

This paper reports on a micromachined Kelvin probe structure with integrated scanning tip and dither actuation mechanism. It is fabricated by a modified micro electro-discharge machining process which allows electrical isolation within the micromachined structure using epoxy plugs. The device is used to measure changes in the external surface potential of a parylene microfluidic channel as a function of varying

L. L. Chu; K. Takahata; P. Selvaganapathy; J. L. Shohet; Y. B. Gianchandani

2003-01-01

336

A Micromachined Kelvin Probe With Integrated Actuator for Microfluidic and Solid-State Applications  

Microsoft Academic Search

This paper reports on a micromachined Kelvin probe structure with an integrated scanning tip and an integrated electrothermal actuator that provides axial dithering motion. The device is fabricated from metal foil by a modified microelectrodischarge machining process that allows electrical isolation within the device. In particular, it permits the incorporation of a wide epoxy plug that creates an insulating gap

Larry L. Chu; Kenichi Takahata; Ponnambalam Ravi Selvaganapathy; Yogesh B. Gianchandani; J. Leon Shohet

2005-01-01

337

Solid State  

NSDL National Science Digital Library

This is a webpage filled with Solid State learning objects with over 40 lessons in: Semiconductor Diodes, Rectifier Flitering and Regulation, D/A and A/D Converters, Opto Electronic Devices, Operational Amplifiers, Transistors, Thyristors, and Timers.

2012-12-28

338

Modeling hydrodesulfurization catalysis (HDS) by solid-state synthesis, homogeneous desulfurization and heterogeneous probe reactions  

Microsoft Academic Search

Three approaches towards modeling the HDS catalyst are discussed: structural investigations and catalytic measurements of intercalation compounds of MoSsb2, reactivity studies of soluble bimetallic clusters, and HDS of probe molecules over heterogeneous catalysts. In order to test the viability of the pseudo-intercalation model for the structure of the HDS active site, intercalation compounds of MoSsb2 were synthesized. Different Co species

Keenan Edward Dungey

1998-01-01

339

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

PubMed Central

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

2010-01-01

340

Synthesis and structural characterisation of Sr3Al10SiO20 by XRD and solid-state NMR  

NASA Astrophysics Data System (ADS)

The strontium aluminosilicate Sr3Al10SiO20 has been synthesised by a spray-drying process and characterised by powder X-ray diffraction. It crystallises in the monoclinic /I2/m space group with the cell parameters a=14.394(2)Å,b=11.189(2)Å,c=4.904(1)Å,?=90.793(1)°,Z=2. Its structure is built of double AlO6 octahedra chains interconnected by AlO4 and SiO4 tetrahedra forming a three-dimensional channel-like network where the strontium cations are located. The distribution of aluminium and silicon cations in the different tetrahedral and octahedral sites of the structure was probed using 29Si, 27Al MAS and 3Q-MAS NMR.

Capron, M.; Fayon, F.; Coutures, J.; Massiot, D.; Douy, A.

2002-11-01

341

NMR crystallography of enzyme active sites: probing chemically detailed, three-dimensional structure in tryptophan synthase.  

PubMed

NMR crystallography-the synergistic combination of X-raydiffraction, solid-state NMR spectroscopy, and computational chemistry-offers unprecedented insight into three-dimensional, chemically detailed structure. Initially, researchers used NMR crystallography to refine diffraction data from organic and inorganic solids. Now we are applying this technique to explore active sites in biomolecules, where it reveals chemically rich detail concerning the interactions between enzyme site residues and the reacting substrate. Researchers cannot achieve this level of detail from X-ray, NMR,or computational methodologies in isolation. For example, typical X-ray crystal structures (1.5-2.5 Å resolution) of enzyme-bound intermediates identify possible hydrogen-bonding interactions between site residues and substrate but do not directly identify the protonation states. Solid-state NMR can provide chemical shifts for selected atoms of enzyme-substrate complexes, but without a larger structural framework in which to interpret them only empirical correlations with local chemical structure are possible. Ab initio calculations and molecular mechanics can build models for enzymatic processes, but they rely on researcher-specified chemical details. Together, however, X-ray diffraction, solid-state NMR spectroscopy, and computational chemistry can provide consistent and testable models for structure and function of enzyme active sites: X-ray crystallography provides a coarse framework upon which scientists can develop models of the active site using computational chemistry; they can then distinguish these models by comparing calculated NMR chemical shifts with the results of solid-state NMR spectroscopy experiments. Conceptually, each technique is a puzzle piece offering a generous view of the big picture. Only when correctly pieced together, however, can they reveal the big picture at the highest possible resolution. In this Account, we detail our first steps in the development of NMR crystallography applied to enzyme catalysis. We begin with a brief introduction to NMR crystallography and then define the process that we have employed to probe the active site in the ?-subunit of tryptophan synthase with unprecedented atomic-level resolution. This approach has resulted in a novel structural hypothesis for the protonation state of the quinonoid intermediate in tryptophan synthase and its surprising role in directing the next step in the catalysis of l-Trp formation. PMID:23537227

Mueller, Leonard J; Dunn, Michael F

2013-03-28

342

A refinement protocol to determine structure, topology, and depth of insertion of membrane proteins using hybrid solution and solid-state NMR restraints  

PubMed Central

To fully describe the fold space and ultimately the biological function of membrane proteins, it is necessary to determine the specific interactions of the protein with the membrane. This property of membrane proteins that we refer to as structural topology cannot be resolved using X-ray crystallography or solution NMR alone. In this article, we incorporate into XPLOR-NIH a hybrid objective function for membrane protein structure determination that utilizes solution and solid-state NMR restraints, simultaneously defining structure, topology, and depth of insertion. Distance and angular restraints obtained from solution NMR of membrane proteins solubilized in detergent micelles are combined with backbone orientational restraints (chemical shift anisotropy and dipolar couplings) derived from solid-state NMR in aligned lipid bilayers. In addition, a supplementary knowledge-based potential, Ez (insertion depth potential), is used to ensure the correct positioning of secondary structural elements with respect to a virtual membrane. The hybrid objective function is minimized using a simulated annealing protocol implemented into XPLOR-NIH software for general use.

Shi, Lei; Traaseth, Nathaniel J.; Verardi, Raffaello; Cembran, Alessandro; Gao, Jiali

2010-01-01

343

Study of the Mechanism of Thermal Chemical Processes in the Crystals of YAF Tripeptides by Means of Mass Spectrometry and Solid State NMR.  

PubMed

Thermal reactions in two Tyr-Ala-Phe (YAF) tripeptide crystals with different molecular packing (monoclinic and hexagonal), distinct stereochemistry of central amino acid (D or L alanine) and specific arrangement of molecules in the crystal lattice (head-to-tail) were investigated. Samples were heated up to 180 °C, while the melting point for YAF crystals is above the 220 °C. Below the melting temperature, in both cases the chemical reactions leading to formation of cyclic dipeptides (YA diketopiperazine) and leaving of phenylalanine were observed. Two possible mechanisms of chemical reaction in the crystal lattice assuming intra- and/or intermolecular pathways were considered. (13)C and (15)N enriched YAF samples were employed to study of mechanism of solid state reactivity using mass spectrometry and advanced solid state NMR techniques (2D DARR (Dipolar Assisted Rotational Resonance) and 2D Double CP (Cross-Polarization) correlations). PMID:24070178

Drabik, Ewelina; Jeziorna, Agata; Bienias, Urszula; Trzeciak-Karlikowska, Katarzyna; Pawlak, Tomasz; Paluch, Piotr; Potrzebowski, Marek J

2013-10-10

344

THE RGI-20 RADIAC SYSTEMA WIDE RANGE BETA-GAMMA INSTRUMENT. II. THE SOLID STATE PULSED GM TUBE LOW RANGE ACCESSORY PROBE  

Microsoft Academic Search

A plug-on low-range accessory, consisting of a main unit and a cable-; connected probe, was developed for the RGI-20 radiac system. The solid-state ; circuit for pulsed GM tube operation is contained in the main unit whose ; dimensions are approximately 2 x 2 1\\/2 x 8 in. The GM tube is mounted in a cable-; connected probe with side

1963-01-01

345

Modeling hydrodesulfurization catalysis (HDS) by solid-state synthesis, homogeneous desulfurization and heterogeneous probe reactions  

NASA Astrophysics Data System (ADS)

Three approaches towards modeling the HDS catalyst are discussed: structural investigations and catalytic measurements of intercalation compounds of MoSsb2, reactivity studies of soluble bimetallic clusters, and HDS of probe molecules over heterogeneous catalysts. In order to test the viability of the pseudo-intercalation model for the structure of the HDS active site, intercalation compounds of MoSsb2 were synthesized. Different Co species and Co loadings were introduced into the MoSsb2 host by flocculation of aqueous suspensions of single-layer MoSsb2. The structures of the intercalation compounds were determined by EXAFS, electron diffraction, and powder X-ray diffraction. The MoSsb2 layers in these materials are distorted 1T-type structures consisting of linked trimolybdenum clusters. After using these materials as catalysts for the HDS of thiophene, the initial structures of the intercalates were found to be unstable: the sulfide phases 2H-MoSsb2 and Cosb9Ssb8 were the only phases detected by EXAFS. These results strongly suggest that the pseudo-intercalation model would not be thermodynamically nor kinetically stable under the conditions of HDS catalysis. The reactivity of the butterfly cluster Cpsb2MOsb2COsb2Ssb3(CO)sb4 (7b, Cp = etasp5-Csb5Hsb5) for the desulfurization of thiols was investigated as a homogeneous model for the HDS mechanism. Both cyclopropylmethyl thiol (CPMT) and 5-hexenethiol (HET) were stoichiometrically desulfurized at 110sp° C by cluster 7b to form the cubane cluster, CPsb2MOsb2Cosb2Ssb4(CO)sb2, and rearranged organic products expected of "radical clocks" (1-butene and methylcyclopentane, respectively). In neat HET, the reaction with cluster 7a resulted in a mixture of rearranged and unrearranged (1-hexene) desulfurization products which allowed the calculation of the rate of hydrogen abstraction (ksb{abs} = 3.7× 10sp6\\ Msp{-1}ssp{-1}). Thus the reagent thiol was identified as the hydrogen atom donor. The free radical mechanistic model was tested by reacting these same thiols over a conventionally prepared heterogeneous HDS catalyst. The initial product from the HDS of CPMT was 1-butene, while the HDS of HET formed a mixture of hexenes. In this case, the rearranged product (methylcyclopentane) was not formed. A free radical mechanism is proposed with the rate of hydrogen abstraction faster in the heterogeneous system than in the homogeneous one.

Dungey, Keenan Edward

346

A Slow Exchange Model of Non-rigid Rotational Motion in RNA for combined Solid-state and Solution NMR studies  

PubMed Central

Functional RNA molecules are conformationally dynamic and sample a multitude of dynamic modes over a wide range of frequencies. Thus, a comprehensive description of RNA dynamics requires the inclusion of a broad range of motions across multiple dynamic rates which must be derived from multiple spectroscopies. Here we describe a slow conformational exchange theoretical approach to combining the description of local motions in RNA that occur in the ns-?s window and are detected by solid-state NMR with non-rigid rotational motion of the HIV-1 TAR RNA in solution as observed by solution NMR. This theoretical model unifies the experimental results generated by solution and solid-state NMR and provides a comprehensive view of the dynamics of HIV-1 TAR RNA, a well-known paradigm of an RNA where function requires extensive conformational rearrangements. This methodology provides a quantitative atomic level view of the amplitudes and rates of the local and collective displacements of the TAR RNA molecule, and provides directly motional parameters for the conformational capture hypothesis of this classical RNA-ligand interaction.

Emani, Prashant S.; Olsen, Gregory L.; Echodu, Dorothy C.; Varani, Gabriele; Drobny, Gary P.

2011-01-01

347

Solid-state NMR studies of the membrane-bound closed state of the colicin E1 channel domain in lipid bilayers.  

PubMed Central

The colicin E1 channel polypeptide was shown to be organized anisotropically in membranes by solid-state NMR analysis of samples of uniformly 15N-labeled protein in oriented planar phospholipid bilayers. The 190 residue C-terminal colicin E1 channel domain is the largest polypeptide to have been characterized by 15N solid-state NMR spectroscopy in oriented membrane bilayers. The 15N-NMR spectra of the colicin E1 show that: (1) the structure and dynamics are independent of anionic lipid content in both oriented and unoriented samples; (2) assuming the secondary structure of the polypeptide is helical, there are both trans-membrane and in-plane helical segments; (3) trans-membrane helices account for approximately 20-25% of the channel polypeptide, which is equivalent to 38-48 residues of the 190-residue polypeptide. The results of the two-dimensional PISEMA spectrum are interpreted in terms of a single trans-membrane helical hairpin inserted into the bilayer from each channel molecule. These data are also consistent with this helical hairpin being derived from the 38-residue hydrophobic segment near the C-terminus of the colicin E1 channel polypeptide.

Kim, Y.; Valentine, K.; Opella, S. J.; Schendel, S. L.; Cramer, W. A.

1998-01-01

348

Structure and Membrane Interactions of the Antibiotic Peptide Dermadistinctin K by Multidimensional Solution and Oriented 15N and 31P Solid-State NMR Spectroscopy  

PubMed Central

DD K, a peptide first isolated from the skin secretion of the Phyllomedusa distincta frog, has been prepared by solid-phase chemical peptide synthesis and its conformation was studied in trifluoroethanol/water as well as in the presence of sodium dodecyl sulfate and dodecylphosphocholine micelles or small unilamellar vesicles. Multidimensional solution NMR spectroscopy indicates an ?-helical conformation in membrane environments starting at residue 7 and extending to the C-terminal carboxyamide. Furthermore, DD K has been labeled with 15N at a single alanine position that is located within the helical core region of the sequence. When reconstituted into oriented phosphatidylcholine membranes the resulting 15N solid-state NMR spectrum shows a well-defined helix alignment parallel to the membrane surface in excellent agreement with the amphipathic character of DD K. Proton-decoupled 31P solid-state NMR spectroscopy indicates that the peptide creates a high level of disorder at the level of the phospholipid headgroup suggesting that DD K partitions into the bilayer where it severely disrupts membrane packing.

Verly, Rodrigo M.; Moraes, Cleria Mendonca de; Resende, Jarbas M.; Aisenbrey, Christopher; Bemquerer, Marcelo Porto; Pilo-Veloso, Dorila; Valente, Ana Paula; Almeida, Fabio C.L.; Bechinger, Burkhard

2009-01-01

349

Study of host-guest interactions in benzodiazacoronands by means of solid state NMR spectroscopy, X-ray diffraction and quantum mechanical computations.  

PubMed

In this work we present solid state data for five host-guest complexes formed by N-(4,19-dioxo-2,8,15,21-tetraoxa-5,18-diazatricyclohexacosa-1(25),9(14),10,12,22(26),23-hexaen-26-yl)-benzamide (1) belonging to the group of benzodiazacoronands, achiral compounds for which chiral crystals were found (J. Kalisiak and J. Jurczak, Cryst. Growth Des., 2006, 6, 20). The X-ray structure was resolved for four of them. It was found that 1 crystallizes in P2(1)/c, P1 and P2(1)/n achiral space groups. Differentiation of molecular packing and the presence of guest molecules within the crystal lattice were analyzed with solid state NMR. An attempt was made to correlate changes in (13)C ?(ii) and (15)N ?(ii) chemical shift tensor values, obtained from analysis of spinning sidebands of 1D and 2D (2D PASS) NMR spectra, with changes in the strength of hydrogen bonding. Quantum mechanical DFT GIAO calculations of NMR shielding parameters carried out on structures with coordinates taken from XRD were employed for signals assignment and verification of structural constraints. PMID:21384038

Nowicka, Katarzyna; Bujacz, Anna; Paluch, Piotr; Sobczuk, Adam; Jeziorna, Agata; Ciesielski, W?odzimierz; Bujacz, Grzegorz D; Jurczak, Janusz; Potrzebowski, Marek J

2011-03-08

350

Tilt and Azimuthal Angles of a Transmembrane Peptide: A Comparison between Molecular Dynamics Calculations and Solid-State NMR Data of Sarcolipin in Lipid Membranes  

PubMed Central

We report molecular dynamics simulations in the explicit membrane environment of a small membrane-embedded protein, sarcolipin, which regulates the sarcoplasmic reticulum Ca-ATPase activity in both cardiac and skeletal muscle. In its monomeric form, we found that sarcolipin adopts a helical conformation, with a computed average tilt angle of 28 ± 6° and azymuthal angles of 66 ± 22°, in reasonable accord with angles determined experimentally (23 ± 2° and 50 ± 4°, respectively) using solid-state NMR with separated-local-field experiments. The effects of time and spatial averaging on both 15N chemical shift anisotropy and 1H/15N dipolar couplings have been analyzed using short-time averages of fast amide out-of-plane motions and following principal component dynamic trajectories. We found that it is possible to reproduce the regular oscillatory patterns observed for the anisotropic NMR parameters (i.e., PISA wheels) employing average amide vectors. This work highlights the role of molecular dynamics simulations as a tool for the analysis and interpretation of solid-state NMR data.

Shi, Lei; Cembran, Alessandro; Gao, Jiali; Veglia, Gianluigi

2009-01-01

351

Characterization of zeolite structure and fluorocarbon reactivity using solid state NMR and x-ray powder diffraction  

Microsoft Academic Search

The research presented in this thesis involves a combination of techniques used to study the structure and interactions zeolites adsorbed with fluorocarbons. This research is specifically aimed at understanding the processes of adsorption, binding, and reactivity of fluorocarbons on cation exchanged faujasite type zeolites. The solid state ion exchange process has also been studied since it is one way to

Michael Frank Ciraolo

2000-01-01

352

Solid state NMR spectroscopy as a precise tool for assigning the tautomeric form and proton position in the intramolecular bridges of o-hydroxy Schiff bases.  

PubMed

Two analogous Schiff bases, (S,E)-2-((1-hydroxy-3-methyl-1,1-diphenylbutan-2-ylimino)methyl)phenol (1) and (S,Z)-2-hydroxy-6-((1-hydroxy-3-methyl-1,1-diphenylbutan-2-ylamino)methylene)cyclohexa-2,4-dienone (2), exist in the solid state as phenol-imine and keto-amine tautomers, respectively. Their crystal structures were solved using the X-ray diffraction method. Sample 1 forms orthorhombic crystals of space group P2(1)2(1)2(1), while 2 forms monoclinic crystals of space group P2(1). In each sample, one molecule is in the asymmetric unit of the crystal structure. One-dimensional and two-dimensional solid state NMR techniques were used for structure assignment and for inspection of the (13)C and (15)N ?(ii) of the chemical shift tensor (CST) values. NMR study indicates that the span (? = ?(11)-?(33)) and the skew (? = 3(?(22)-?(iso)/?) are extremely sensitive to change in the tautomeric form of the Schiff bases. Theoretical calculations of NMR shielding parameters for 1 and 2 and a model compound with reduced aliphatic residue were performed using the GIAO method with B3LYP functional and 6-311++g(d,p) basis sets. From comparative analysis of the experimental and theoretical parameters, it was concluded that the position of hydrogen in the intramolecular bridge has tremendous influence on (13)C and (15)N CST parameters. Inspection of ? and ? parameters allowed for the establishment of the nature of the hydrogen bonding and the assignment of the equilibrium proton position in the intramolecular bridges in the solid state. PMID:21049987

Jaworska, Magdalena; Hrynczyszyn, Pawe? B; We?niak, Miros?aw; Wojtczak, Andrzej; Nowicka, Katarzyna; Krasi?ski, Grzegorz; Kassassir, Hassan; Ciesielski, W?odzimierz; Potrzebowski, Marek J

2010-11-04

353

Non-Equilibrium DNA Dynamics Probed by Delayed Capture and Recapture by a Solid-State Nanopore  

NASA Astrophysics Data System (ADS)

We studied the relaxation of ?-DNA following its translocation through a voltage-biased solid-state nanopore. The translocation process drives DNA into a non-equilibrium state because the ˜2 ms translocation time is roughly fifty times shorter that the polymer's characteristic (Zimm) relaxation time. By reversing the applied voltage at controlled delay times after a translocation event, the nanopore probed the configurations of recaptured molecules at various stages of relaxation. We monitored the disruptions of the ionic current through the nanopore and computed the integrated charge deficits (ECDs) resulting from DNA translocations. As the delay time between voltage reversals was decreased from 50 ms to 5 ms, the distribution of ECDs shifted to lower values. Furthermore, an increasing fraction of recapture events occurred in a shorter interval from the voltage reversal than the delay time. These observations are explained by the expansion of the DNA coil as it approaches equilibrium. Finally, we show that recapturing a molecule multiple times and averaging the ECDs reduces the measurement error, which is useful for molecular diagnostic applications. The variance decreases approximately as the inverse number of passes through the pore.

Mihovilovic, Mirna; Teich, Erin; Hagerty, Nicholas; Stein, Derek

2012-02-01

354

Crystal Structures and Vibrational and Solid-State (CPMAS) NMR Spectroscopy of Some Bis(triphenylphosphine)silver(I) Sulfate, Selenate and Phosphate Systems.  

SciTech Connect

The complexes [Ag2(PPh3)4EO4].2H2O(E=S, Se) (1,2), [Ag(PPh3)2HEO4].H2O (E=S, Se)(3,4) and [Ag9PPh3)2H2PO4].2EtOH (5) have been prepared and studied by X-ray crystallography and by infrared and solid-state 13C and 31 P cross-polarization, magic-angle-spinning (CPMAS) NMR spectroscopy.

Bowmaker, Graham A.; Hanna, John V.; Rickard, Clifton E.; Lipton, Andrew S.

2001-01-01

355

Solid-state Zn-67 NMR Spectroscopic Studies and ab initio Molecular Orbital Calculations on a Synthetic Analogue of Carbonic Anhydrase.  

SciTech Connect

The tris(pyrazolyl)hydroborato zinc complexes [TpBut,Me]ZnX (where X = Br, Cl, and OH) have been examined by low temperature solid-state 67Zn NMR spectroscopy. The value of the quadrupole coupling constant, Cq, for the zinc increased monotonically with the electronegativity of the bound substituent X, e.g. Br < Cl << OH. Calculations on the methylimidazole complex [(MeImH)3Zn(OH)]+ as a model for the active site of carbonic anhydrase indicate that the computed electric field gradient tensor is in good agreement with the experimental and calculated values for [TpBut,Me]ZnOH.

Lipton, Andrew S.; Bergquist, Catherine; Parkin, Gerard; Ellis, Paul D.

2003-04-02

356

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

SciTech Connect

Solid-state [sup 13]C NMR spectroscopy techniques, including cross polarization (CP), magic angle spinning (MAS), and high-power proton decoupling, have been used to study the interactions of two ionic surfactants with octadecylsilica (C-18) and octylsilica (C-8) HPLC stationary phases. The two surfactants, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), are commonly used in micellar reversed-phase liquid chromatography (RPLC). Variable contact time CP/MAS [sup 13] C NMR data suggest that differences in selectivity between SDS and CTAB micellar RPLC are due to the differing nature of the SDS and CTAB-bonded phase association. For CTAB the association leads to a more hydrophobic bulk stationary phase, whereas SDS adsorption results in the formation of an anionic, hydrophilic surface layer. These results suggest that proper matching of surfactant monomer and bonded stationary phase is critical to ensure selective separations in micellar RPLC.

Lavine, B.K.; Hendayana, S.; Han, J.H.; Tetreault, J. (Clarkson Univ., Potsdam, NY (United States). Dept. of Chemistry); Cooper, W.T. III; He, Y. (Florida State Univ., Tallahassee, FL (United States). Dept. of Chemistry)

1994-07-01

357

A general assignment method for oriented sample (OS) solid-state NMR of proteins based on the correlation of resonances through heteronuclear dipolar couplings in samples aligned parallel and perpendicular to the magnetic field  

NASA Astrophysics Data System (ADS)

A general method for assigning oriented sample (OS) solid-state NMR spectra of proteins is demonstrated. In principle, this method requires only a single sample of a uniformly 15N-labeled membrane protein in magnetically aligned bilayers, and a previously assigned isotropic chemical shift spectrum obtained either from solution NMR on micelle or isotropic bicelle samples or from magic angle spinning (MAS) solid-state NMR on unoriented proteoliposomes. The sequential isotropic resonance assignments are transferred to the OS solid-state NMR spectra of aligned samples by correlating signals from the same residue observed in protein-containing bilayers aligned with their normals parallel and perpendicular to the magnetic field. The underlying principle is that the resonances from the same residue have heteronuclear dipolar couplings that differ by exactly a factor of two between parallel and perpendicular alignments. The method is demonstrated on the membrane-bound form of Pf1 coat protein in phospholipid bilayers, whose assignments have been previously made using an earlier generation of methods that relied on the preparation of many selectively labeled (by residue type) samples. The new method provides the correct resonance assignments using only a single uniformly 15N-labeled sample, two solid-state NMR spectra, and a previously assigned isotropic spectrum. Significantly, this approach is equally applicable to residues in alpha helices, beta sheets, loops, and any other elements of tertiary structure. Moreover, the strategy bridges between OS solid-state NMR of aligned samples and solution NMR or MAS solid-state NMR of unoriented samples. In combination with the development of complementary experimental methods, it provides a step towards unifying these apparently different NMR approaches.

Lu, George J.; Son, Woo Sung; Opella, Stanley J.

2011-04-01

358

A General Assignment Method for Oriented Sample (OS) Solid-state NMR of Proteins Based on The Correlation of Resonances through Heteronuclear Dipolar Couplings in Samples Aligned Parallel and Perpendicular to the Magnetic Field  

PubMed Central

A general method for assigning oriented sample (OS) solid-state NMR spectra of proteins is demonstrated. In principle, this method requires only a single sample of a uniformly 15N-labeled membrane protein in magnetically aligned bilayers, and a previously assigned isotropic chemical shift spectrum obtained either from solution NMR on micelle or isotropic bicelle samples or from magic angle spinning (MAS) solid-state NMR on unoriented proteoliposomes. The sequential isotropic resonance assignments are transferred to the OS solid-state NMR spectra of aligned samples by correlating signals from the same residue observed in protein-containing bilayers aligned with their normals parallel and perpendicular to the magnetic field. The underlying principle is that the resonances from the same residue have heteronuclear dipolar couplings that differ by exactly a factor of two between parallel and perpendicular alignments. The method is demonstrated on the membrane-bound form of Pf1 coat protein in phospholipid bilayers, whose assignments have been previously made using an earlier generation of methods that relied on the preparation of many selectively labeled (by residue type) samples. The new method provides the correct resonance assignments using only a single uniformly 15N-labeled sample, two solid-state NMR spectra, and a previously assigned isotropic spectrum. Significantly, this approach is equally applicable to residues in alpha helices, beta sheets, loops, and any other elements of tertiary structure. Moreover, the strategy bridges between OS solid-state NMR of aligned samples and solution NMR or MAS solid-state NMR of unoriented samples. In combination with the development of complementary experimental methods, it provides a step towards unifying these apparently different NMR approaches.

Lu, George J.; Son, Woo Sung; Opella, Stanley J.

2011-01-01

359

Dynamic Structure of Bombolitin II Bound to Lipid Bilayers as Revealed by Solid-state NMR and Molecular-Dynamics Simulation  

PubMed Central

Bombolitin II (BLT2) is one of the hemolytic heptadecapeptides originally isolated from the venom of a bumblebee. Structure and orientation of BLT2 bound to 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membranes were determined by solid-state 31P and 13C NMR spectroscopy. 31P NMR spectra showed that BLT2-DPPC membranes were disrupted into small particles below the gel-to-liquid crystalline phase transition temperature (Tc) and fused to form a magnetically oriented vesicle system where the membrane surface is parallel to the magnetic fields above the Tc. 13C NMR spectra of site-specifically 13C-labeled BLT2 at the carbonyl carbons were observed and the chemical shift anisotropies were analyzed to determine the dynamic structure of BLT2 bound to the magnetically oriented vesicle system. It was revealed that the membrane-bound BLT2 adopted an ?-helical structure, rotating around the membrane normal with the tilt angle of the helical axis at 33°. Interatomic distances obtained from rotational-echo double-resonance experiments further showed that BLT2 adopted a straight ?-helical structure. Molecular dynamics simulation performed in the BLT2-DPPC membrane system showed that the BLT2 formed a straight ?-helix and that the C-terminus was inserted into the membrane. The ?-helical axis is tilted 30° to the membrane normal, which is almost the same as the value obtained from solid-state NMR. These results suggest that the membrane disruption induced by BLT2 is attributed to insertion of BLT2 into the lipid bilayers.

Toraya, Shuichi; Javkhlantugs, Namsrai; Mishima, Daisuke; Nishimura, Katsuyuki; Ueda, Kazuyoshi; Naito, Akira

2010-01-01

360

51V solid-state NMR and density functional theory studies of vanadium environments in V(V)O2 dipicolinic acid complexes.  

PubMed

(51)V solid-state NMR and density functional theory (DFT) investigations are reported for a series of pentacoordinate dioxovanadium(V)-dipicolinate [V(V)O(2)-dipicolinate] and heptacoordinate aquahydroxylamidooxovanadium(V)-dipicolinate [V(V)O-dipicolinate] complexes. These compounds are of interest because of their potency as phosphatase inhibitors as well as their insulin enhancing properties and potential for the treatment of diabetes. Experimental solid-state NMR results show that the electric field gradient tensors in the V(V)O(2)-dipicolinate derivatives are affected significantly by substitution on the dipicolinate ring and range from 5.8 to 8.3 MHz. The chemical shift anisotropies show less dramatic variations with respect to the ligand changes and range between -550 and -600 ppm. To gain insights on the origins of the NMR parameters, DFT calculations were conducted for an extensive series of the V(V)O(2)- and V(V)O-dipicolinate complexes. To assess the level of theory required for the accurate calculation of the (51)V NMR parameters, different functionals, basis sets, and structural models were explored in the DFT study. It is shown that the original x-ray crystallographic geometries, including all counterions and solvation water molecules within 5 A of the vanadium, lead to the most accurate results. The choice of the functional and the basis set at a high level of theory has a relatively minor impact on the outcome of the chemical shift anisotropy calculations; however, the use of large basis sets is necessary for accurate calculations of the quadrupole coupling constants for several compounds of the V(V)O(2) series. These studies demonstrate that even though the vanadium compounds under investigations exhibit distorted trigonal bipyramidal coordination geometry, they have a "perfect" trigonal bipyramidal electronic environment. This observation could potentially explain why vanadate and vanadium(V) adducts are often recognized as potent transition state analogs. PMID:18266434

Bolte, Stephanie E; Ooms, Kristopher J; Polenova, Tatyana; Baruah, Bharat; Crans, Debbie C; Smee, Jason J

2008-02-01

361

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

362

Solid-state acid-base interactions in complexes of heterocyclic bases with dicarboxylic acids: crystallography, hydrogen bond analysis, and 15N NMR spectroscopy.  

PubMed

A cancer candidate, compound 1, is a weak base with two heterocyclic basic nitrogens and five hydrogen-bonding functional groups, and is sparingly soluble in water rendering it unsuitable for pharmaceutical development. The crystalline acid-base pairs of 1, collectively termed solid acid-base complexes, provide significant increases in the solubility and bioavailability compared to the free base, 1. Three dicarboxylic acid-base complexes, sesquisuccinate 2, dimalonate 3, and dimaleate 4, show the most favorable physicochemical profiles and are studied in greater detail. The structural analyses of the three complexes using crystal structure and solid-state NMR reveal that the proton-transfer behavior in these organic acid-base complexes vary successively correlating with Delta pKa. As a result, 2 is a neutral complex, 3 is a mixed ionic and zwitterionic complex and 4 is an ionic salt. The addition of the acidic components leads to maximized hydrogen bond interactions forming extended three-dimensional networks. Although structurally similar, the packing arrangements of the three complexes are considerably different due to the presence of multiple functional groups and the flexible backbone of 1. The findings in this study provide insight into the structural characteristics of complexes involving heterocyclic bases and carboxylic acids, and demonstrate that X-ray crystallography and 15N solid-state NMR are truly complementary in elucidating hydrogen bonding interactions and the degree of proton transfer of these complexes. PMID:16787084

Li, Z Jane; Abramov, Yuriy; Bordner, Jon; Leonard, Jason; Medek, Ales; Trask, Andrew V

2006-06-28

363

Utilizing Afterglow Magnetization from Cross-Polarization Magic-Angle-Spinning Solid-State NMR Spectroscopy to Obtain Simultaneous Heteronuclear Multidimensional Spectra  

PubMed Central

The time required for data acquisition and subsequent spectral assignment are limiting factors for determining biomolecular structure and dynamics using solid state NMR spectroscopy. While strong magnetic dipolar couplings give rise to relatively broad spectra lines, the couplings also mediate the coherent magnetization transfer via the Hartmann Hahn cross polarization (HH-CP) experiment. This mechanism is used in nearly all backbone assignment experiments for carrying out polarization transfer between 1H, 15N, and 13C. In this Article, we describe a general spectroscopic approach to use the residual or afterglow magnetization from the 15N to 13C selective HH-CP experiment to collect a second multidimensional heteronuclear dataset. This approach allowed for the collection of two multidimensional (2D NCA and NCO or 3D NCACX and NCOCX) datasets at the same time. These experiments were performed using instrumentation available on all standard solid state NMR spectrometers configured for magic angle spinning and were demonstrated on uniformly [13C,15N] and [1,3-13C] glycerol labeled ubiquitin. This method is compatible with several other sensitivity enhancement experiments and can be used as an isotopic filtering tool to reduce the spectral complexity and decrease the time needed for assigning spectra.

Banigan, James R.; Traaseth, Nathaniel J.

2012-01-01

364

A sup 95 Mo solid-state NMR study of hydrodesulfurization catalysts. 1. Formation of fresh HDS catalyst precursors by adsorption of polyoxomolybdates onto. gamma. -alumina  

SciTech Connect

The solid-state {sup 95}Mo NMR of oxomolybdates and polyoxomolybdates adsorbed to {gamma}-alumina was utilized to characterize the molybdenum species present at circa monolayer coverages of molybdenum. This represents the first attempt at using solid-state NMR to look directly at the molybdenum species on the surface of 'fresh' hydrodesulfurization catalyst precursors. The selectively excited central {plus minus}1/2 transition line shapes were obtained, by the solid-echo technique, for several polyoxomolybdates, which are considered model compounds of the surface molybdena species, as well as for the uncalcined and calcined catalysts at various loadings. The spectra were obtained for static and magic angle spinning samples. Static sample spectra of the catalysts reveal inhomogeneously broadened lines owing to a range of surface species being present. Magic and angle spinning spectra show the presence of four possible species on the surface of the uncalcined catalysts and two possible species present on the surface of calcined catalysts. Spikelet echo spectra identified static adsorbed species (speculated to be predominantly adsorbed tetrahedral/octahedral molybdena, and perhaps Al{sub 2}(MoO{sub 4}){sub 3}), and a dynamic species (speculated to be disordered, surface-interactive tetrahedral and octahedral molybdates), in the uncalcined catalyst samples. Upon calcination the line widths of the static and MAS spectra are increased, indicating a polymerization of the surface species to form a MoO{sub 3}-like phase. 67 refs.

Edwards, J.C.; Adams, R.D.; Ellis, P.D. (Univ. of South Carolina, Columbia (United States))

1990-11-07

365

Structure determination of a bio-inspired self-assembled light-harvesting antenna by solid-state NMR and molecular modeling.  

PubMed

The molecular stacking of an artificial light-harvesting antenna self-assembled from 3(1)-aminofunctionalized zinc-chlorins was determined by solid-state NMR in combination with quantum-chemical and molecular-mechanics modeling. A library of trial molecular stacking arrangements was generated based on available structural data for natural and semisynthetic homologues of the Zn-chlorins. NMR assignments obtained for the monomer in solution were validated for self-assembled aggregates and refined with (1)H-(13)C heteronuclear correlation spectroscopy data collected from samples with (13)C at natural abundance. Solid-state ring-current shifts for the (1)H provided spatial constraints to determine the molecular overlap. This procedure allows for a discrimination between different self-assembled structures and a classification of the stacking mode in terms of electric dipole alignment and ?-? interactions, parameters that determine the functional properties of light-harvesting assemblies and conducting nanowires. The combination with quantum-mechanical modeling then allowed building a low-resolution packing model in silico from molecular stacks. The method allows for moderate disorder and residual polymorphism at the stack or molecular level and is generally applicable to determine molecular packing structures of aromatic molecules with structural asymmetry, such as is commonly provided by functionalized side chains that serve to tune the self-assembly process. PMID:23566216

Pandit, Anjali; Ocakoglu, Kasim; Buda, Francesco; van Marle, Thomas; Holzwarth, Alfred R; de Groot, Huub J M

2013-05-03

366

Induced Secondary Structure and Polymorphism in an Intrinsically Disordered Structural Linker of the CNS: Solid-State NMR and FTIR Spectroscopy of Myelin Basic Protein Bound to Actin  

PubMed Central

Abstract The 18.5 kDa isoform of myelin basic protein (MBP) is a peripheral membrane protein that maintains the structural integrity of the myelin sheath of the central nervous system by conjoining the cytoplasmic leaflets of oligodendrocytes and by linking the myelin membrane to the underlying cytoskeleton whose assembly it strongly promotes. It is a multifunctional, intrinsically disordered protein that behaves primarily as a structural stabilizer, but with elements of a transient or induced secondary structure that represent binding sites for calmodulin or SH3-domain-containing proteins, inter alia. In this study we used solid-state NMR (SSNMR) and Fourier transform infrared (FTIR) spectroscopy to study the conformation of 18.5 kDa MBP in association with actin microfilaments and bundles. FTIR spectroscopy of fully 13C,15N-labeled MBP complexed with unlabeled F-actin showed induced folding of both protein partners, viz., some increase in ?-sheet content in actin, and increases in both ?-helix and ?-sheet content in MBP, albeit with considerable extended structure remaining. Solid-state NMR spectroscopy revealed that MBP in MBP-actin assemblies is structurally heterogeneous but gains ordered secondary structure elements (both ?-helical and ?-sheet), particularly in the terminal fragments and in a central immunodominant epitope. The overall conformational polymorphism of MBP is consistent with its in vivo roles as both a linker (membranes and cytoskeleton) and a putative signaling hub.

Ahmed, Mumdooh A.M.; Bamm, Vladimir V.; Shi, Lichi; Steiner-Mosonyi, Marta; Dawson, John F.; Brown, Leonid; Harauz, George; Ladizhansky, Vladimir

2009-01-01

367

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

368

Satellite transitions in natural abundance solid-state 33S MAS NMR of alums—Sign change with zero-crossing of CQ in a variable temperature study  

NASA Astrophysics Data System (ADS)

Experiences obtained from recent improvements in the performance of solid-state 14N MAS NMR spectroscopy have been used in a natural abundance 33S MAS NMR investigation of the satellite transitions for this interesting spin I = 3/2 isotope. This study reports the first observation of manifolds of spinning sidebands for these transitions in 33S MAS NMR as observed for the two alums XAl(SO4)2·12H2O with X = NH4 and K. For the NH4-alum a variable temperature 33S MAS NMR study, employing the satellite transitions, shows that the 33S quadrupole coupling constant (CQ) exhibits a linear temperature dependence (in the range -35 °C to 70 °C) with a temperature gradient of 3.1 kHz/°C and undergoes a sign change with zero-crossing for CQ at 4 °C (277 K). For the isostructural K-alum a quite similar increase in the magnitude of CQ with increasing temperature is observed, and with a temperature gradient of 2.3 kHz/°C. Finally, for optimization purposes, a study on the effect of the applied pulse widths at constant rf field strength on the intensity and variation in second-order quadrupolar lineshape for the central (1/2 ? -1/2) transition of the K-alum has been performed.

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

2006-06-01

369

Effects of pH and cholesterol on DMPA membranes: a solid state 2H- and 31P-NMR study.  

PubMed Central

The effect of pH and cholesterol on the dimyristoylphosphatidic acid (DMPA) model membrane system has been investigated by solid state 2H- and 31P-NMR. It has been shown that each of the three protonation states of the DMPA molecule corresponds to a 31P-NMR powder pattern with characteristic delta sigma values; this implies additionally that the proton exchange on the membrane surface is slow on the NMR time scale (millisecond range). Under these conditions, the 2H-labeled lipid chains sense only one magnetic environment, indicating that the three spectra detected by 31P-NMR are related to charge-dependent local dynamics or orientations of the phosphate headgroup or both. Chain ordering in the fluid phase is also found to depend weakly on the charge at the interface. In addition, it has also been found that the first pK of the DMPA membrane is modified by changes in the lipid lateral packing (gel or fluid phases or in the presence of cholesterol) in contrast to the second pK. The incorporation of 30 mol% cholesterol affects the phosphatidic acid bilayer in a way similar to what has been reported for phosphatidylcholine/cholesterol membranes, but to an extent comparable to 10-20 mol % sterol in phosphatidylcholines. However, the orientation and molecular order parameter of cholesterol in DMPA are similar to those found in dimyristoylphosphatidylcholine.

Pott, T; Maillet, J C; Dufourc, E J

1995-01-01

370

Study and characterization of crystalline hydrate\\/polymorph forms of 5,11-dihydro-11-ethyl-5-methyl-8-(2-(1-oxido-4-quinolinyl)ethyl-6H-dipyrido(3,2B:2?,3?-E)(1,4)diazepin-6-one by solid-state NMR and solution NMR  

Microsoft Academic Search

A novel inhibitor of reverse transcriptase was studied by solid-state NMR. Three phases of the compound were examined which included the dihydrate and two anhydrous polymorphs (Form I and Form III). By correlating 1H and 13C solution NMR with the solid-state 13C NMR CP\\/MAS and CPPI spectral editing experiments, comparative 13C assignments were made for each phase. Polymorphs of Form

N. C. Gonnella; John A. Smoliga; Scot Campbell; Carl A. Busacca; Michael Cerreta; Richard Varsolona; Daniel L. Norwood

2010-01-01

371

Protein oligomers studied by solid-state NMR--the case of the full-length nucleoid-associated protein histone-like nucleoid structuring protein.  

PubMed

Members of the histone-like nucleoid structuring protein (H-NS) family play roles both as architectural proteins and as modulators of gene expression in Gram-negative bacteria. The H-NS protein participates in modulatory processes that respond to environmental changes in osmolarity, pH, or temperature. H-NS oligomerization is essential for its activity. Structural models of different truncated forms are available. However, high-resolution structural details of full-length H-NS and its DNA-bound state have largely remained elusive. We report on progress in characterizing the biologically active H-NS oligomers with solid-state NMR. We compared uniformly ((13)C,(15)N)-labeled ssNMR preparations of the isolated N-terminal region (H-NS 1-47) and full-length H-NS (H-NS 1-137). In both cases, we obtained ssNMR spectra of good quality and characteristic of well-folded proteins. Analysis of the results of 2D and 3D (13)C-(13)C and (15)N-(13)C correlation experiments conducted at high magnetic field led to assignments of residues located in different topological regions of the free full-length H-NS. These findings confirm that the structure of the N-terminal dimerization domain is conserved in the oligomeric full-length protein. Small changes in the dimerization interface suggested by localized chemical shift variations between solution and solid-state spectra may be relevant for DNA recoginition. PMID:23601147

Renault, Marie; García, Jesús; Cordeiro, Tiago N; Baldus, Marc; Pons, Miquel

2013-05-13

372

Understanding the high photocatalytic activity of (B, Ag)-codoped TiO2 under solar-light irradiation with XPS, solid-state NMR, and DFT calculations.  

PubMed

The origin of the exceptionally high activity of (B, Ag)-codoped TiO(2) catalysts under solar-light irradiation has been investigated by XPS and (11)B solid-state NMR spectroscopy in conjunction with density functional theory (DFT) calculations. XPS experimental results demonstrated that a portion of the dopant Ag (Ag(3+)) ions were implanted into the crystalline lattice of (B, Ag)-codoped TiO(2) and were in close proximity to the interstitial B (B(int.)) sites, forming [B(int.)-O-Ag] structural units. In situ XPS experiments were employed to follow the evolution of the chemical states of the B and Ag dopants during UV-vis irradiation. It was found that the [B(int.)-O-Ag] units could trap the photoinduced electron to form a unique intermediate structure in the (B, Ag)-codoped TiO(2) during the irradiation, which is responsible for the photoinduced shifts of the B 1s and Ag 3d peaks observed in the in situ XPS spectra. Solid-state NMR experiments including (11)B triple-quantum and double-quantum magic angle spinning (MAS) NMR revealed that up to six different boron species were present in the catalysts and only the tricoordinated interstitial boron (T*) species was in close proximity to the substitutional Ag species, leading to formation of [T*-O-Ag] structural units. Furthermore, as demonstrated by DFT calculations, the [T*-O-Ag] structural units were responsible for trapping the photoinduced electrons, which prolongs the life of the photoinduced charge carriers and eventually leads to a remarkable enhancement in the photocatalytic activity. All these unprecedented findings are expected to be crucial for understanding the roles of B and Ag dopants and their synergistic effect in numerous titania-mediated photocatalytic reactions. PMID:23316875

Feng, Ningdong; Wang, Qiang; Zheng, Anmin; Zhang, Zhengfeng; Fan, Jie; Liu, Shang-Bin; Amoureux, Jean-Paul; Deng, Feng

2013-01-22

373

High-level expression and purification of the second transmembrane domain of wild-type and mutant human melanocortin-4 receptor for solid-state NMR structural studies.  

PubMed

It has been demonstrated that human melanocortin-4 receptor (hMC4R) plays an important role in the control of energy homeostasis, and heterozygous mutations in the hMC4R gene are the most frequent genetic cause of severe human obesity. In order to obtain additional insight into the structure and function, we cloned, expressed, and purified the second transmembrane domain of the wild-type hMC4R (wt-TM2) and D90N mutant hMC4R (m-TM2). To facilitate structural studies of these hMC4R by solid-state NMR, efficient methods for the production of milligram quantities of isotopically labeled protein are necessary. However, large-scale production of most transmembrane proteins has been limited by experimental adversities due to insufficient yields and low solubility of protein. Nevertheless, through the optimization of the expression and purification approach, we could obtain uniformly or selectively labeled fusion proteins in yields as high as 200-250 mg per liter M9 minimal medium. These proteins were overexpressed in inclusion bodies as a fusion protein with ketosteroid isomerase (KSI) in Escherichia coli, and the fusion protein was purified using immobilized metal affinity chromatography under denaturing conditions. wt-/m-TM2 peptides were released from the fusion by cyanogen bromide cleavage at the Met residue and separated from the carrier KSI by size exclusion chromatography. Initial structural data obtained by solution NMR measurements of wt-/m-TM2 is also presented. The successful application to the production of the second transmembrane domain of human MC4R indicates that the method can be applied to other transmembrane proteins as well and also enable its structural and functional studies using solid-state NMR spectroscopy. PMID:18809499

Park, Tae-Joon; Choi, Sung-Sub; Gang, Ga-Ae; Kim, Yongae

2008-09-03

374

87Sr solid-state NMR as a structurally sensitive tool for the investigation of materials: antiosteoporotic pharmaceuticals and bioactive glasses.  

PubMed

Strontium is an element of fundamental importance in biomedical science. Indeed, it has been demonstrated that Sr(2+) ions can promote bone growth and inhibit bone resorption. Thus, the oral administration of Sr-containing medications has been used clinically to prevent osteoporosis, and Sr-containing biomaterials have been developed for implant and tissue engineering applications. The bioavailability of strontium metal cations in the body and their kinetics of release from materials will depend on their local environment. It is thus crucial to be able to characterize, in detail, strontium environments in disordered phases such as bioactive glasses, to understand their structure and rationalize their properties. In this paper, we demonstrate that (87)Sr NMR spectroscopy can serve as a valuable tool of investigation. First, the implementation of high-sensitivity (87)Sr solid-state NMR experiments is presented using (87)Sr-labeled strontium malonate (with DFS (double field sweep), QCPMG (quadrupolar Carr-Purcell-Meiboom-Gill), and WURST (wideband, uniform rate, and smooth truncation) excitation). Then, it is shown that GIPAW DFT (gauge including projector augmented wave density functional theory) calculations can accurately compute (87)Sr NMR parameters. Last and most importantly, (87)Sr NMR is used for the study of a (Ca,Sr)-silicate bioactive glass of limited Sr content (only ~9 wt %). The spectrum is interpreted using structural models of the glass, which are generated through molecular dynamics (MD) simulations and relaxed by DFT, before performing GIPAW calculations of (87)Sr NMR parameters. Finally, changes in the (87)Sr NMR spectrum after immersion of the glass in simulated body fluid (SBF) are reported and discussed. PMID:22738329

Bonhomme, Christian; Gervais, Christel; Folliet, Nicolas; Pourpoint, Frédérique; Diogo, Cristina Coelho; Lao, Jonathan; Jallot, Edouard; Lacroix, Joséphine; Nedelec, Jean-Marie; Iuga, Dinu; Hanna, John V; Smith, Mark E; Xiang, Ye; Du, Jincheng; Laurencin, Danielle

2012-07-19

375

YPdSn and YPd{sub 2}Sn: Structure, {sup 89}Y solid state NMR and {sup 119}Sn Moessbauer spectroscopy  

SciTech Connect

The stannides YPdSn and YPd{sub 2}Sn were synthesized by high-frequency melting of the elements in sealed tantalum tubes. Both structures were refined on the basis of single crystal X-ray diffractometer data: TiNiSi type, Pnma, a=715.4(1), b=458.8(1), c=789.1(1) pm, wR2=0.0461, 510 F{sup 2} values, 20 variables for YPdSn and MnCu{sub 2}Al type, Fm3 Macron m, a=671.44(8), wR2=0.0740, 55 F{sup 2} values, 5 parameters for YPd{sub 2}Sn. The yttrium atoms in the new stannide YPdSn are coordinated by two tilted Pd{sub 3}Sn{sub 3} hexagons (ordered AlB{sub 2} superstructure). In the Heusler phase YPd{sub 2}Sn each yttrium atom has octahedral tin coordination and additionally eight palladium neighbors. The cubic site symmetry of yttrium is reflected in the {sup 119}Sn Moessbauer spectrum which shows no quadrupole splitting. In contrast, YPdSn shows a single signal at {delta}=1.82(1) mm/s subjected to quadrupole splitting of {Delta}E{sub Q}=0.93(1) mm/s. Both compounds have been characterized by high-resolution {sup 89}Y solid state NMR spectroscopy, which indicates the presence of strong Knight shifts. The spectrum of YPd{sub 2}Sn is characterized by an unusually large linewidth, suggesting the presence of a Knight shift distribution reflecting local disordering effects. The range of {sup 89}Y Knight shifts of several binary and ternary intermetallic yttrium compounds is briefly discussed. - Graphical abstract: YPdSn and YPd{sub 2}Sn: Structure, {sup 89}Y solid state NMR and {sup 119}Sn Moessbauer spectroscopy. Highlights: Black-Right-Pointing-Pointer Synthesis and structure of ternary stannides YPdSn and YPd{sub 2}Sn. Black-Right-Pointing-Pointer {sup 119}Sn Moessbauer spectroscopic investigation of YPdSn and YPd{sub 2}Sn. Black-Right-Pointing-Pointer {sup 89}Y solid state NMR of intermetallics.

Hoeting, Christoph [Institut fuer Anorganische und Analytische Chemie, Universitaet Muenster, Corrensstrasse 30, D-48149 Muenster (Germany); Eckert, Hellmut [Institut fuer Physikalische Chemie, Universitaet Muenster, Corrensstrasse 30, D-48149 Muenster (Germany); Langer, Thorsten; Schellenberg, Inga [Institut fuer Anorganische und Analytische Chemie, Universitaet Muenster, Corrensstrasse 30, D-48149 Muenster (Germany); Poettgen, Rainer, E-mail: pottgen@uni-muenster.de [Institut fuer Anorganische und Analytische Chemie, Universitaet Muenster, Corrensstrasse 30, D-48149 Muenster (Germany)