Wednesday, October 31, 2007

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*

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.

Thursday, October 25, 2007

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

Friday, October 19, 2007

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

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

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.

Friday, October 12, 2007

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*

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.

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*

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*

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.

Wednesday, October 10, 2007

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

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.

Tuesday, October 09, 2007

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)

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.

Saturday, October 06, 2007

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

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

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.

Friday, October 05, 2007

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.

Tuesday, October 02, 2007

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