Hiyam's Journal Update

Phys. Rev. B 76, 165122 (2007)
Spin and orbital magnetic response in metals: Susceptibility and NMR shifts
Mayeul d'Avezac, Nicola Marzari, and Francesco Mauri
(Received 12 July 2007; published 23 October 2007)
A DFT-based method is presented which allows the computation of all-electron NMR shifts of metallic compounds with periodic boundary conditions. NMR shifts in metals measure two competing physical phenomena. Electrons interact with the applied magnetic field (i) as magnetic dipoles (or spins), resulting in the Knight shift, and (ii) as moving electric charges, resulting in the chemical (or orbital) shift. The latter is treated through an extension to metals of the gauge-invariant projector augmented wave developed for insulators. The former is modeled as the hyperfine interaction between the electronic spin polarization and the nuclear dipoles. NMR shifts are obtained with respect to the computed shieldings of reference compounds, yielding fully ab initio quantities which are directly comparable to experiment. The method is validated by comparing the magnetic susceptibility of interacting and noninteracting homogeneous gas with known analytical results, and by comparing the computed NMR shifts of simple metals with experiment.

Phys. Rev. B 76, 155201 (2007)

Long-lived spin echoes in a magnetically dilute system: An NMR study of Ge single crystals
A. M. Panich, N. A. Sergeev, and I. Shlimak
(Received 22 March 2007; revised 1 August 2007; published 1 October 2007)

Owing to the well-developed technology, isotopic engineering of Si and Ge semiconductors permits one to control the density of nuclear spins and vary the spin coherence time, a crucial parameter in spintronics and quantum computing where nuclear spin is used as a qubit. In the present paper, we report on the NMR study of 73Ge nuclear spin decoherence in germanium single crystals with different abundances of the 73Ge isotope. Our measurements of Hahn- and solid-echo decays show that they are well fit by a superposition of two exponentials; at that, the deviation from the single exponential is more pronounced in the more spin-diluted sample, causing long-lived echoes. We show that the decay of these echoes becomes slower with the reduction of 73Ge abundance and is therefore caused by dipole-dipole interaction, reflecting the fundamental decoherence process in the spin system. The fast decay at the beginning of the relaxation process is shown to be mainly caused by the quadrupole interaction. Our experimental findings are supported by the calculations of Hahn- and solid-echo decays in the germanium crystals under study. Quite good agreement between the theory and experiment is demonstrated.

Hiyam's Journal Update

Phys. Rev. B 76, 132510 (2007)
77Se NMR measurements of the -d exchange field in the organic conductor -(BETS)2FeCl4
Guoqing Wu, W. G. Clark, S. E. Brown, J. S. Brooks, A. Kobayashi, and H. Kobayashi
(Received 6 June 2007; published 26 October 2007)

77Se-NMR spectrum and frequency shift measurements in the paramagnetic metal and antiferromagnetic insulating phases are reported for a small single crystal of the organic conductor -(BETS)2FeCl4 as a function of temperature (T) and field alignment for an applied magnetic field B0=9 T. The results show that in the low T limit, where the localized Fe3+ spins (Sd=5/2) are almost fully polarized, the conduction electrons (Se electrons, spin s=1/2) in the BETS molecules experience an exchange field (Bd) from the Fe3+ spins with a value of −32.7±1.5 T at 5 K and 9 T aligned opposite to B0. This large negative value of Bd is consistent with that predicted by the resistivity measurements and supports the Jaccarino-Peter internal field-compensation mechanism being responsible for the origin of field-induced superconductivity.


Phys. Rev. B 76, 144511 (2007)
11B NMR in the layered diborides OsB2 and RuB2
B. J. Suh, X. Zong, Y. Singh, A. Niazi, and D. C. Johnston
(Received 4 June 2007; published 23 October 2007)

11B nuclear magnetic resonance (NMR) measurements have been performed on 11B enriched OsB2 and RuB2 polycrystalline powder samples in an external field of 4.7 T and in the temperature range, 4.2 K
Phys. Rev. B 76, 144405 (2007)
Multiple quantum NMR dynamics in dipolar ordered spin systems
S. I. Doronin, E. B. Fel'dman, and E. I. Kuznetsova G. B. Furman and S. D. Goren
(Received 6 December 2006; revised 28 August 2007; published 2 October 2007)

We investigate analytically and numerically the multiple-quantum (MQ) NMR dynamics in systems of nuclear spins 1/2 coupled by the dipole-dipole interactions in the case of the dipolar ordered initial state. We suggest two different methods of MQ NMR. One of them is based on the measurement of the dipolar temperature in the quasiequilibrium state which is established after the time of order (loc is the dipolar local field) after the MQ NMR experiment. The other method uses an additional resonance (/4)y pulse after the preparation period of the standard MQ NMR experiment in solids. Many-spin clusters and correlations are created faster in such experiments than in the usual MQ NMR experiments and can be used for the investigation of many-spin dynamics of nuclear spins in solids.

Phys. Rev. B 76, 144433 (2007)
NMR study of ordered states in NpFeGa5: Orbitally related ordering below 78 K
S. Kambe,H. Sakai, Y. Tokunaga, R. E. Walstedt, D. Aoki, Y. Homma, and Y. Shiokawa
(Received 18 July 2007; published 29 October 2007)

We report NMR studies on a single crystal of NpFeGa5, which has the tetragonal HoCoGa5(115) structure and exhibits two antiferromagnetically ordered states. In the antiferromagnetic I phase below 118 K, the observed internal field at the Ga(2) (4i) site is consistent with the ordered structure revealed by neutron diffraction measurements. Below 78 K in the antiferromagnetic II phase, two different Ga(2) sites with different electric field gradient tensors appear, which indicates an orbitally related ordering. A possible quadrupolar ordering in the antiferromagnetic II phase is discussed.

Hiyam's Journal Update

J. Am. Chem. Soc., 129 (44), 13396 -13397, 2007. 10.1021/ja0761636 S0002-7863(07)06163-X

Characterization of Chemical Exchange Using Residual Dipolar Coupling
Tatyana I. Igumenova, Ulrika Brath, Mikael Akke, and Arthur G. Palmer, III*

Abstract:
NMR line shape analysis and relaxation dispersion measurements for N,N-dimethyltrichloroacetamide (DMTCA) weakly aligned using poly--benzyl-L-glutamate, which forms a lyotropic nematic phase when dissolved in chloroform, were used to characterize chemical exchange kinetics for the rotation around the C-N amide bond. At low temperatures (<312>312 K), a single population-averaged 13C methyl quartet is observed; in this regime, the differences in RDCs contribute to differential line broadening of the quartet components. Self-consistent measurements of the difference in RDCs are obtained from both line shape and relaxation dispersion techniques. The results show that NMR spectroscopy of weakly aligned molecules allows complete characterization of chemical exchange processes using RDCs, even if exchange broadening is absent in isotropic samples.

New neuron-rich elements

C&EN Latest News, Oct 24, 2007
Nuclear Chemistry
by Jyllian Kemsley

Neutron-Rich Isotopes Discovered
Magnesium-40 and aluminum-42 push the limits of nuclear stability

Hiyam's Journal Update

Chem. Mater., ASAP Article 10.1021/cm0715388 S0897-4756(07)01538-4 Web Release Date: October 19, 2007 Copyright © 2007 American Chemical Society
Vacancy and Cation Distribution in Yttria-Doped Ceria: An 89Y and 17O MAS NMR Study
Namjun Kim* and Jonathan F. Stebbins

Abstract:
The local structure and dynamics of oxide ions in yttria-doped ceria (YDC, 5 to 30% Y2O3) were studied using high-resolution 89Y and 17O MAS NMR spectroscopy at ambient temperature and high temperatures to 500 C. Eight-, seven-, and six-coordinated yttrium cations are clearly resolved in 89Y MAS NMR spectra, and their relative populations were measured. The derived average coordination number of yttrium is smaller than that for a random distribution of oxygen vacancies, suggesting that there is strong association between yttrium cations and vacancies and there is the possibility of pairing of two yttrium cations with one vacancy. In the 17O MAS NMR spectra, resonances for oxygens with different coordination environments are resolved and are assigned to oxygens with different numbers of yttrium cations in the first coordination sphere. The relative intensities of the 17O resonances also deviate from those expected from a random distribution, again indicating possible pairing of yttrium cations. High-temperature 17O MAS NMR shows coalescence among various peaks. The exchange between oxygen sites with yttrium neighbors appears to occur at a lower temperature (about 100 C) than the exchange that involves the sites without yttrium neighbors; rapid exchange of all oxide anions throughout the structure occurs above 400 C.

Hiyam's Journal Update

Chem. Mater., ASAP Article 10.1021/cm070496k S0897-4756(07)00496-6 Web Release Date: October 18, 2007 Copyright © 2007 American Chemical Society
NMR Structural Study on the As-P-S Glassy System
S. H. Santagneli, I. Skripatchev, S. J. L. Ribeiro, and Y. Messaddeq,J. Schneider

Abstract:
Glasses having the composition As2S3(1-x)-P2S5(x) with x ranging from 0 to 0.7 have been investigated to determine the compositional effect on properties and local structure. Glass transition temperature (Tg) decreases and molar volume (Vm) increases with an increase in P content. Using 31P NMR, we measured the strength of the 31P-31P magnetic dipolar interaction in the glass samples and the AsPS4 crystallized phase. Based on these data, we observed the formation of the As2P2S8 network, which reflects an increase in the average coordination number and a decrease in the degree of rigidity.

Hiyam's Journal Update

J. Am. Chem. Soc., ASAP Article 10.1021/ja073170l S0002-7863(07)03170-8 Web Release Date: October 6, 2007 Copyright © 2007 American Chemical Society

Internuclear 31P-51V Distance Measurements in Polyoxoanionic Solids Using Rotational Echo Adiabatic Passage Double Resonance NMR Spectroscopy
Wenlin Huang, Alexander J. Vega,* Terry Gullion, and Tatyana Polenova*

Abstract:
We report the first results establishing rotational echo adiabatic passage double resonance (REAPDOR) experiments for distance measurements between a spin-1/2 (31P) and spin-7/2 (51V) pair in a series of vanadium-substituted polyoxoanionic solids from the Keggin and Wells-Dawson families. We have quantitatively measured 31P-51V distances in monovanadium substituted K4PVW11O40, 1-K7P2VW17O62, and 4-K7P2VW17O62. Numerical simulations of the experimental data yield very good agreement with the averaged P-W/P-V distances determined from the X-ray diffraction measurements in the same or related compounds. REAPDOR is therefore a very sensitive P-V distance probe anticipated to be especially useful in the absence of long-range order. Our results suggest that REAPDOR spectroscopy could be broadly applicable for interatomic distance measurements in other spin-7/2-spin-1/2 nuclear pairs.

J. Am. Chem. Soc., ASAP Article 10.1021/ja074428a S0002-7863(07)04428-9 Web Release Date: October 9, 2007 Copyright © 2007 American Chemical Society
17O and 29Si NMR Parameters of MgSiO3 Phases from High-Resolution Solid-State NMR Spectroscopy and First-Principles Calculations
Sharon E. Ashbrook,* Andrew J. Berry, Daniel J. Frost, Alan Gregorovic, Chris J. Pickard, Jennifer E.

Abstract:
The 29Si and 17O NMR parameters of six polymorphs of MgSiO3 were determined through a combination of high-resolution solid-state NMR and first-principles gauge including projector augmented wave (GIPAW) formalism calculations using periodic boundary conditions. MgSiO3 is an important component of the Earth's mantle that undergoes structural changes as a function of pressure and temperature. For the lower pressure polymorphs (ortho-, clino-, and protoenstatite), all oxygen species in the 17O high-resolution triple-quantum magic angle spinning (MAS) NMR spectra were resolved and assigned. These assignments differ from those tentatively suggested in previous work on the basis of empirical experimental correlations. The higher pressure polymorphs of MgSiO3 (majorite, akimotoite, and perovskite) are stabilized at pressures corresponding to the Earth's transition zone and lower mantle, with perovskite being the major constituent at depths >660 km. We present the first 17O NMR data for these materials and confirm previous 29Si work in the literature. The use of high-resolution multiple-quantum MAS (MQMAS) and satellite-transition MAS (STMAS) experiments allows us to resolve distinct oxygen species, and full assignments are suggested. The six polymorphs exhibit a wide variety of structure types, providing an ideal opportunity to consider the variation of NMR parameters (both shielding and quadrupolar) with local structure, including changes in coordination number, local geometry (bond distances and angles), and bonding. For example, we find that, although there is a general correlation of increasing 17O chemical shift with increasing Si-O bond length, the shift observed also depends upon the exact coordination environment.

J. Am. Chem. Soc., ASAP Article 10.1021/ja075272h S0002-7863(07)05272-9 Web Release Date: October 9, 2007 Copyright © 2007 American Chemical Society
Conformational Preferences of Chondroitin Sulfate Oligomers Using Partially Oriented NMR Spectroscopy of 13C-Labeled Acetyl Groups
Fei Yu, Jeremy J. Wolff, I. Jonathan Amster, and James H. Prestegard*

Abstract:
A new method is presented for the retrieval of information on the conformation of glycosaminoglycan oligomers in solution. The method relies on the replacement of acetyl groups in isolated native oligomers with 13C labeled acetyl groups and the extraction of orientational constraints from residual dipolar couplings (RDCs) and chemical shift anisotropy (CSA) offsets observed in NMR spectra of partially oriented samples. A novel method for assignment of resonances based on the correlation of resonance intensities with isotope ratios determined from mass spectrometric analysis is also presented. The combined methods are used in conjunction with more traditional NMR structural data to determine the solution structure of a pentasaccharide, GalNAc6S(1-4)GlcA(1-3)GalNAc4S(1-4)GlcA(1-3)GalNAc4S-ol, derived by enzymatic hydrolysis of chondroitin sulfate. The geometry derived is compared to that for similar molecules that have been reported in the literature, and prospects for use of the new types of data in the study of protein-bound oligosaccharides are discussed.

J. Am. Chem. Soc., ASAP Article 10.1021/ja075768z S0002-7863(07)05768-X Web Release Date: October 10, 2007 Copyright © 2007 American Chemical Society
Hyperpolarized 89Y Offers the Potential of Direct Imaging of Metal Ions in Biological Systems by Magnetic Resonance
Matthew E. Merritt, Crystal Harrison, Zoltan Kovacs, Preeti Kshirsagar, Craig R. Malloy, and A. Dean Sherry*

Abstract:
Hyperpolarization of 89YCl3 and three 89Y-complexes was achieved by dynamic nuclear polarization of aqueous samples. The long T1s of 89Y make its application as an NMR imaging probe extremely promising. In addition, the wide chemical shift range for various chelates of 89Y means that agents sensitive to their biological/chemical milieu could serve as exquisite sensors of important biological events.

Hiyam's Journal Update

J. Am. Chem. Soc., 129 (41), 12406 -12407, 2007.
2H Solid-State NMR of Mobile Protons: It Is Not Always the Simple Way
Young Joo Lee, Tatiana Murakhtina, Daniel Sebastiani, and Hans Wolfgang Spiess

Abstract:
A combined study of 2H line-shape analysis and ab initio molecular dynamics simulations was carried out on poly[vinyl phosphonic acid] (a water-free proton conducting material). We can elucidate the geometry and even time scale of the complex motional process, where dynamical proton motion occurs via the rearrangement of H-bonding networks, involving both intra- and interchain transfers.

Hiyam's Journal Update

Chem. Mater., 19 (21), 5067 -5073, 2007.
Synthesis, Crystal Structure, and Characterization (Vibrational and Solid-State 31P MAS NMR Spectroscopy) of the High-Temperature Modification of Calcium catena-Polyphosphate(V)

Abstract:
The metastable high-temperature modification of calcium catena-polyphosphate, -Ca(PO3)2, was obtained by quenching the recrystallized sample from a temperature shortly below the melting point. The novel crystal structure [Cc, Z = 16, a = 13.6835(14) Å, b = 19.981(2) Å, c = 6.7535(7) Å, = 94.514(2), V = 1840.7(3) Å3, 4929 structure factors, 326 parameters, R[F2 > 2(F2)] = 0.0561] was determined from a combined X-ray diffraction and solid-state 31P NMR study. The unit cell features a pseudoinversion center. The structure contains 4 Ca, 8 P, and 24 O atoms in the asymmetric unit and is composed of two different kinds of polyphosphate chains, with one helical chain running with a periodicity P of 12 parallel to [101], whereas the second chain is corrugated and directed parallel to [001] with a periodicity P of 4. 31P chemical shift parameters were determined for all eight phosphorus positions, and peaks were assigned to the two different polyphosphate chains. -(CaPO3)2 was further characterized by IR and Raman spectroscopy.

Hiyam's Journal Update

J. Am. Chem. Soc., ASAP Article 10.1021/ja073234s S0002-7863(07)03234-9
Combined Analysis of 15N Relaxation Data from Solid- and Solution-State NMR Spectroscopy
Veniamin Chevelkov, Anastasia V. Zhuravleva, Yi Xue, Bernd Reif, and Nikolai R. Skrynnikov

Abstract:
It is well-known that structures of globular proteins in liquid and in crystalline solid are essentially identical. Many lines of evidence suggest that internal dynamics are also similar (assuming that the solid sample is well-hydrated and the measurements are conducted at the same temperature). On the basis of this premise, we undertake a combined analysis of solid- and liquid-state 15N relaxation data from a small globular protein, -spectrin SH3 domain. The interpretation using the extended Lipari-Szabo model demonstrates that liquid R1, R2, NOE, and solid R1 data measured at multiple fields are mutually consistent. To validate these results, we prepared a series of samples where the protein is dissolved in a water-glycerol solvent. The presence of glycerol ensures that the overall protein tumbling is slowed, thus increasing the visibility of nanosecond time-scale internal motions. When additional data are included in the fitting procedure, a credible picture of protein dynamics is obtained. In particular, the analysis suggests that ns time-scale motions with very low amplitude, S2 0.95, are present throughout the protein. It is envisaged that combined analyses of liquid- and solid-state data can provide an efficient method for detailed characterization of internal dynamics in proteins at multiple time scales.

J. Am. Chem. Soc., ASAP Article 10.1021/ja075846i S0002-7863(07)05846-5
Probing Supramolecular Structure from Measurement of Methyl 1H-13C Residual Dipolar Couplings
Remco Sprangers and Lewis E. Kay

Abstract:
A simple NMR experiment is presented for the measurement of methyl 1H-13C residual dipolar couplings in fractionally aligned supramolecular protein complexes. The approach makes use of methyl-TROSY spectroscopy that significantly increases the lifetime of the NMR signal, along with highly deuterated, methyl-protonated samples that minimize relaxation contributions from protons external to the methyl group probes. An application to a 360 kDa half-proteasome complex is presented, establishing the methodology.

A new renewable energy source

C&EN, latest news (Oct 4, 2007)
Title: Turing Water Into Fuel
by Mitch Jacoby

A new silicide semiconductor was discovered. It can be used with sunlight and oxygen to generate H2 from H2O.

interesting article

Clarifying HIV Entry Process
New details of virus's embrace with cell surface
By Stu Borman

C&EN, October 1, 2007
Volume 85, Number 40
p. 7

Sept 28, 2007 - Journal Updates

Aluminum Siting in Silicon-Rich Zeolite Frameworks: A Combined High-Resolution 27Al NMR Spectroscopy and Quantum Mechanics / Molecular Mechanics Study of ZSM-5
Stepan Sklenak, Jií Ddeek, Chengbin Li, Blanka Wichterlová, Vendula Gábová, Marek Sierka, Joachim Sauer
Angewandte (2007)46, 7286.
Summary:
Finding Al: The distribution of catalytically active sites over crystallographic positions in zeolites is not random but controlled by synthesis. For differently synthesized ZSM-5 samples, distinct 27Al resonances have been identified by NMR spectroscopy. Shift calculations by DFT show that the observed resonances belong to Al in different crystallographic sites.

Structural and dynamical properties of guest molecules confined in mesoporous silica materials revealed by NMR
Gerd Buntkowsky, Hergen Breitzke, Anna Adamczyk, Frank Roelofs, Thomas Emmler, Egbert Gedat, Bob Grünberg, Yeping Xu, Hans-Heinrich Limbach, Ilja Shenderovich, Anastasia Vyalikh and Gerhard Findenegg
PCCP(2007)9,4843.
Abstract:
In the last fifteen years several novel porous silica materials, which are periodically structured on the mesoscopic length scale, have been synthesized. They are of broad interest for fundamental studies of surface–substrate interactions, for studies of the dynamics of guest molecules in confinement and for studies of the effect of confinement on the structural and thermophysical properties of fluids. Examples of such confinement effects include the change of the freezing and melting points or glass transitions of the confined liquids. These effects are studied by combinations of several NMR techniques, such as 15N- and 2H-solid-state NMR line shape analysis, MAS NMR and NMR diffusometry with physico-chemical characterization techniques such as nitrogen adsorption and small angle diffraction of neutrons or X-rays. This combination does not require crystalline samples or special clean and well defined surfaces such as conventional surface science techniques, but can work with typical ill-defined real world systems. The review discusses, after a short introduction, the salient features of these materials and the applied NMR experiments to give the reader a basic knowledge of the systems and the experiments. The rest of the review then focuses on the structural and dynamical properties of guest molecules confined in the mesoporous silica. It is shown that the confinement into the pores leads to fascinating new features of the guests, which are often not known for their bulk phases. These features depend strongly on the interplay of the their interactions with the silica surface and their mutual interactions.


Solid-state NMR opf endoheral hydrogen-fullerene complexes
M. Carravetta, A. Danquigny, S. Mamone, F. Cuda, O. G. Johannessen, I. Heinmaa, K. Panesar, R. Stern, M. C. Grossel, A. J. Horsewill, A. Samoson, M. Murata, Y. Murata, K. Komatsu and M. H. Levitt
PCCP(2007)9,4879.
Abstract:
We present an overview of solid-state NMR studies of endohedral H2-fullerene complexes, including 1H and 13C NMR spectra, 1H and 13C spin relaxation studies, and the results of 1H dipole–dipole recoupling experiments. The available data involves three different endohedral H2-fullerene complexes, studied over a wide range of temperatures and applied magnetic fields. The symmetry of the cage influences strongly the motionally-averaged nuclear spin interactions of the endohedral H2 species, as well as its spin relaxation behaviour. In addition, the non-bonding interactions between fullerene cages are influenced by the presence of endohedral hydrogen molecules. The review also presents several pieces of experimental data which are not yet understood, one example being the structured 1H NMR lineshapes of endohedral H2 molecules trapped in highly symmetric cages at cryogenic temperatures. This review demonstrates the richness of NMR phenomena displayed by H2-fullerene complexes, especially in the cryogenic regime.

Hiyam's Journal Update

J. Am. Chem. Soc., ASAP Article 10.1021

Chemical Shift Correlation NMR Spectroscopy with Indirect Detection in Fast Rotating Solids: Studies of Organically Functionalized Mesoporous Silicas
Jerzy W. Wiench, Charles E. Bronnimann, Victor S.-Y Lin, and Marek Pruski*

Abstract:
The first indirectly detected 13C-1H solid-state NMR correlation spectra of species bound to a surface are reported. The experiments were performed at 14.1 T under fast (40 kHz) MAS. The sensitivity gain was demonstrated on a mesoporous silica sample containing approximately 300 g of covalently bound allyl groups, in the absence of templating molecules and without isotope enrichment. A well-resolved two-dimensional spectrum was acquired in 15 min, which is more than 10 times faster than using direct detection of 13C nuclei.

Hiyam's Journal Update

Proton-Detected Solid-State NMR Spectroscopy of Fully Protonated Proteins at 40 kHz Magic-Angle Spinning
Donghua H. Zhou, Gautam Shah, Mircea Cormos, Charles Mullen, Dennis Sandoz, and Chad M. Rienstra

Abstract:
Remarkable progress in solid-state NMR has enabled complete structure determination of uniformly labeled proteins in the size range of 5-10 kDa. Expanding these applications to larger or mass-limited systems requires further improvements in spectral sensitivity, for which inverse detection of 13C and 15N signals with 1H is one promising approach. Proton detection has previously been demonstrated to offer sensitivity benefits in the limit of sparse protonation or with ~30 kHz magic-angle spinning (MAS). Here we focus on experimental schemes for proteins with ~100% protonation. Full protonation simplifies sample preparation and permits more complete chemical shift information to be obtained from a single sample. We demonstrate experimental schemes using the fully protonated, uniformly 13C,15N-labeled protein GB1 at 40 kHz MAS rate with 1.6-mm rotors. At 500 MHz proton frequency, 1-ppm proton line widths were observed (500 ± 150 Hz), and the sensitivity was enhanced by 3 and 4 times, respectively, versus direct 13C and 15N detection. The enhanced sensitivity enabled a family of 3D experiments for spectral assignment to be performed in a time-efficient manner with less than a micromole of protein. CANH, CONH, and NCAH 3D spectra provided sufficient resolution and sensitivity to make full backbone and partial side-chain proton assignments. At 750 MHz proton frequency and 40 kHz MAS rate, proton line widths improve further in an absolute sense (360 ± 115 Hz). Sensitivity and resolution increase in a better than linear manner with increasing magnetic field, resulting in 14 times greater sensitivity for 1H detection relative to that of 15N detection.

interesting article

C&EN
September 17, 2007
Volume 85, Number 38 , p. 10
Nuclear Chemistry

Exotic Molecule

Dipositronium molecule contains only electrons and positrons

Hiyam's Journal Update

Solid-State NMR Structural Measurements on the Membrane-Associated Influenza Fusion Protein Ectodomain
Jaime Curtis-Fisk, Casey Preston, Zhaoxiong Zheng, R. Mark Worden, and David P. Weliky*

Abstract:
The 185 residue "FHA2" domain of the influenza virus hemagglutinin protein lies outside the virus and plays a significant role in catalyzing fusion between viral and host cell membranes. FHA2 was expressed in Escherichia coli with a yield of 3 mg/L of fermentation and after purification was shown to be folded in detergent and to rapidly catalyze vesicle fusion. More than half of the FHA2 residues are the first residue in a unique sequential pair, and for a particular pair, 13CO and 15N amino acid type labeling was, respectively, done for the first and second residues in the pair. For membrane-associated FHA2, NMR filtering allowed selective observation of the 13CO signal of the first residue, and the 13CO chemical shift was correlated with local secondary structure. Such shift/conformational measurements were made at critical glycine residues in the functionally important "fusion peptide" region of FHA2 and at a more C-terminal leucine. This should be a general approach to mapping the conformation of membrane-associated FHA2 and for testing FHA2 structure-function models. The approach will also be applicable to other viral fusion proteins and other large membrane proteins.

J. Am. Chem. Soc., 129 (37), 11438 -11446, 2007.

Phosphate-Mediated Arginine Insertion into Lipid Membranes and Pore Formation by a Cationic Membrane Peptide from Solid-State NMR
Ming Tang, Alan J. Waring, and Mei Hong*

Abstract:
The insertion of charged amino acid residues into the hydrophobic part of lipid bilayers is energetically unfavorable yet found in many cationic membrane peptides and protein domains. To understand the mechanism of this translocation, we measured the 13C-31P distances for an Arg-rich -hairpin antimicrobial peptide, PG-1, in the lipid membrane using solid-state NMR. Four residues, including two Arg's, scattered through the peptide were chosen for the distance measurements. Surprisingly, all residues show short distances to the lipid 31P: 4.0-6.5 Å in anionic POPE/POPG membranes and 6.5-8.0 Å in zwitterionic POPC membranes. The shortest distance of 4.0 Å, found for a guanidinium C at the -turn, suggests N-H···O-P hydrogen bond formation. Torsion angle measurements of the two Arg's quantitatively confirm that the peptide adopts a -hairpin conformation in the lipid bilayer, and gel-phase 1H spin diffusion from water to the peptide indicates that PG-1 remains transmembrane in the gel phase of the membrane. For this transmembrane -hairpin peptide to have short 13C-31P distances for multiple residues in the molecule, some phosphate groups must be embedded in the hydrophobic part of the membrane, with the local 31P plane parallel to the -strand. This provides direct evidence for toroidal pores, where some lipid molecules change their orientation to merge the two monolayers. We propose that the driving force for this toroidal pore formation is guanidinium-phosphate complexation, where the cationic Arg residues drag the anionic phosphate groups along as they insert into the hydrophobic part of the membrane. This phosphate-mediated translocation of guanidinium ions may underlie the activity of other Arg-rich antimocrobial peptides and may be common among cationic membrane proteins.

Hiyam's Journal Update

J. Am. Chem. Soc., 129 (36), 11161 -11171, 2007.
Brnsted/Lewis Acid Synergy in Dealuminated HY Zeolite: A Combined Solid-State NMR and Theoretical Calculation Study
Shenhui Li, Anmin Zheng, Yongchao Su, Hailu Zhang, Lei Chen, Jun Yang, Chaohui Ye, and Feng Deng*

Abstract:
The Brnsted/Lewis acid synergy in dealuminated HY zeolite has been studied using solid-state NMR and density function theory (DFT) calculation. The 1H double quantum magic-angle spinning (DQ-MAS) NMR results have revealed, for the first time, the detailed spatial proximities of Lewis and Brnsted acid sites. The results from 13C NMR of adsorbed acetone as well as DFT calculation demonstrated that the Brnsted/Lewis acid synergy considerably enhanced the Brnsted acid strength of dealuminated HY zeolite. Two types of Brnsted acid sites (with enhanced acidity) in close proximity to extra-framework aluminum (EFAL) species were identified in the dealuminated HY zeolite. The NMR and DFT calculation results further revealed the detailed structures of EFAL species and the mechanism of Brnsted/Lewis acid synergy. Extra-framework Al(OH)3 and Al(OH)2+ species in the supercage cage and Al(OH)2+ species in the sodalite cage are the preferred Lewis acid sites. Moreover, it is the coordination of the EFAL species to the oxygen atom nearest the framework aluminum that leads to the enhanced acidity of dealuminated HY zeolite though there is no direct interaction (such as the hydrogen-bonding) between the EFAL species and the Brnsted acid sites. All these findings are expected to be important in understanding the roles of Lewis acid and its synergy with the Brnsted acid in numerous zeolite-mediated hydrocarbon reactions.

J. Am. Chem. Soc.,
An Exchange-Free Measure of 15N Transverse Relaxation: An NMR Spectroscopy Application to the Study of a Folding Intermediate with Pervasive Chemical Exchange
D. Flemming Hansen, Daiwen Yang, Haniqiao Feng, Zheng Zhou, Silke Wiesner, Yawen Bai, and Lewis E. Kay

Abstract:
A series of experiments are presented that provide an exchange-free measure of dipole-dipole 15N transverse relaxation, Rdd, that can then be substituted for 15N R1 or R2 rates in the study of internal protein dynamics. The method is predicated on the measurement of a series of relaxation rates involving 1H-15N longitudinal order, anti-phase 1H and 15N single-quantum coherences, and 1H-15N multiple quantum coherences; the relaxation rates of all coherences are measured under conditions of spin-locking. Results from detailed simulations and experiments on a number of protein systems establish that Rdd values are independent of exchange and systematic errors from dipolar interactions with proximal protons are calculated to be less than 1-2%, on average, for applications to perdeuterated proteins. Simulations further indicate that the methodology is rather insensitive to the exact level of deuteration so long as proteins are reasonably highly deuterated (>50%). The utility of the methodology is demonstrated with applications involving protein L, ubiquitin, and a stabilized folding intermediate of apocytochrome b562 that shows large contributions to 15N R1 relaxation from chemical exchange.

J. Am. Chem. Soc.,
Proton-Detected Solid-State NMR Spectroscopy of Fully Protonated Proteins at 40 kHz Magic-Angle Spinning

Donghua H. Zhou, Gautam Shah, Mircea Cormos, Charles Mullen, Dennis Sandoz, and Chad M. Rienstra*

Abstract:
Remarkable progress in solid-state NMR has enabled complete structure determination of uniformly labeled proteins in the size range of 5-10 kDa. Expanding these applications to larger or mass-limited systems requires further improvements in spectral sensitivity, for which inverse detection of 13C and 15N signals with 1H is one promising approach. Proton detection has previously been demonstrated to offer sensitivity benefits in the limit of sparse protonation or with ~30 kHz magic-angle spinning (MAS). Here we focus on experimental schemes for proteins with ~100% protonation. Full protonation simplifies sample preparation and permits more complete chemical shift information to be obtained from a single sample. We demonstrate experimental schemes using the fully protonated, uniformly 13C,15N-labeled protein GB1 at 40 kHz MAS rate with 1.6-mm rotors. At 500 MHz proton frequency, 1-ppm proton line widths were observed (500 ± 150 Hz), and the sensitivity was enhanced by 3 and 4 times, respectively, versus direct 13C and 15N detection. The enhanced sensitivity enabled a family of 3D experiments for spectral assignment to be performed in a time-efficient manner with less than a micromole of protein. CANH, CONH, and NCAH 3D spectra provided sufficient resolution and sensitivity to make full backbone and partial side-chain proton assignments. At 750 MHz proton frequency and 40 kHz MAS rate, proton line widths improve further in an absolute sense (360 ± 115 Hz). Sensitivity and resolution increase in a better than linear manner with increasing magnetic field, resulting in 14 times greater sensitivity for 1H detection relative to that of 15N detection.

Hiyam's Journal Update

J. Am. Chem. Soc.,

Molecular Dynamics Computational Study of the 199Hg-199Hg NMR Spin-Spin Coupling Constants of [Hg-Hg-Hg]2+ in SO2 Solution
Jochen Autschbach* and Mariusz Sterzel

Abstract:
The isotropic one-bond and two-bond 199Hg-199Hg nuclear magnetic spin-spin coupling constants (J-couplings) of [Hg-Hg-Hg]2+ were calculated using density functional theory, the zeroth-order regular approximation (ZORA) to treat relativistic effects, and Born-Oppenheimer molecular dynamics (BOMD) including SO2 molecules explicitly for the description of solvent effects. The final BOMD average of 150 kHz for 1J (199Hg-199Hg) agrees well with the experimental spin-spin coupling of 140 kHz measured in liquid SO2, while computations not considering explicit solvation at the quantum-mechanical level yielded one-bond coupling constants between 230 and 260 kHz. The two-bond coupling is similarly strongly affected by solvent effects. An analysis of the BOMD data shows that the effect is mainly due to close contacts between the terminal Hg atoms of [Hg-Hg-Hg]2+ and the solvent's oxygen atoms. The results highlight the importance of solvent effects for the NMR parameter of heavy metals and demonstrate the usefulness of treating such solvent effects with the help of molecular dynamics-based averaging.