J. Am. Chem. Soc., 2010, 132 (28), pp 9561–9563

Rapid Acquisition of Multidimensional Solid-State NMR Spectra of Proteins Facilitated by Covalently Bound Paramagnetic Tags
Philippe S. Nadaud, Jonathan J. Helmus, Ishita Sengupta and Christopher P. Jaroniec

We describe a condensed data collection approach that facilitates rapid acquisition of multidimensional magic-angle spinning solid-state nuclear magnetic resonance (SSNMR) spectra of proteins by combining rapid sample spinning, optimized low-power radio frequency pulse schemes and covalently attached paramagnetic tags to enhance protein 1H spin−lattice relaxation. Using EDTA-Cu2+-modified K28C and N8C mutants of the B1 immunoglobulin binding domain of protein G as models, we demonstrate that high resolution and sensitivity 2D and 3D SSNMR chemical shift correlation spectra can be recorded in as little as several minutes and several hours, respectively, for samples containing 0.1−0.2 μmol of 13C,15N- or 2H,13C,15N-labeled protein. This mode of data acquisition is naturally suited toward the structural SSNMR studies of paramagnetic proteins, for which the typical 1H longitudinal relaxation time constants are inherently a factor of at least 3−4 lower relative to their diamagnetic counterparts. To illustrate this, we demonstrate the rapid site-specific determination of backbone amide 15N longitudinal paramagnetic relaxation enhancements using a pseudo-3D SSNMR experiment based on 15N−13C correlation spectroscopy, and we show that such measurements yield valuable long-range 15N−Cu2+ distance restraints which report on the three-dimensional protein fold.



J. Am. Chem. Soc., 2010, 132 (29), pp 9952–9953
Validation of a Lanthanide Tag for the Analysis of Protein Dynamics by Paramagnetic NMR Spectroscopy
Mathias A. S. Hass, Peter H. J. Keizers, Anneloes Blok, Yoshitaka Hiruma and Marcellus Ubbink


Paramagnetic lanthanide tags potentially can enhance the effects of microsecond to millisecond dynamics in proteins on NMR signals and provide structural information on lowly populated states encoded in the pseudocontact shifts. We have investigated the microsecond to millisecond mobility of a two-point attached lanthanide tag, CLaNP-5, using paramagnetic 1H CPMG relaxation dispersion methods. CLaNP-5 loaded with Lu3+, Yb3+, or Tm3+ was attached to three sites on the surface of two proteins, pseudoazurin and cytochrome c. The paramagnetic center causes large relaxation dispersion effects for two attachment sites, suggesting that local dynamics of the protein at the attachment site causes mobility of the paramagnetic center. At one site the relaxation dispersions are small and limited to the immediate environment of the tag. It is concluded that paramagnetic relaxation dispersion could represent a sensitive method to probe protein dynamics. However, the selection of a rigid attachment site is of critical importance.


J. Am. Chem. Soc., 2010, 132 (29), pp 9956–9957
Solid-State 13C NMR Assignment of Carbon Resonances on Metallic and Semiconducting Single-Walled Carbon Nanotubes
Chaiwat Engtrakul*†, Mark F. Davis†, Kevin Mistry†, Brian A. Larsen†, Anne C. Dillon†, Michael J. Heben‡ and Jeffrey L. Blackburn*†


Solid-state 13C NMR spectroscopy was used to investigate the chemical shift of nanotube carbons on m- and s-SWNTs (metallic and semiconducting single-walled nanotubes) for samples with widely varying s-SWNT content, including samples highly enriched with nearly 100% m- and s-SWNTs. High-resolution 13C NMR was found to be a sensitive probe for m- and s-SWNTs in mixed SWNT samples with diameters of 1.3 nm. The two highly enriched m- and s-SWNT samples clearly exhibited features for m- and s-SNWT 13C nuclei (123 and 122 ppm, respectively) and were successfully fit with a single Gaussian, while five mixed samples required two Gaussians for a satisfactory fit.


J. Am. Chem. Soc., 2010, 132 (29), pp 9979–9981
Probing Slow Protein Dynamics by Adiabatic R1ρ and R2ρ NMR Experiments

Silvia Mangia, Nathaniel J. Traaseth, Gianluigi Veglia, Michael Garwood‡ and Shalom Michaeli

Slow μs/ms dynamics involved in protein folding, binding, catalysis, and allostery are currently detected using NMR dispersion experiments such as CPMG (Carr−Purcell−Meiboom−Gill) or spin-lock R1ρ. In these methods, protein dynamics are obtained by analyzing relaxation dispersion curves obtained from either changing the time spacing between 180° pulses or by changing the effective spin-locking field strength. In this Communication, we introduce a new method to induce a dispersion of relaxation rates. Our approach relies on altering the shape of the adiabatic full passage pulse and is conceptually different from existing approaches. By changing the nature of the adiabatic radiofrequency irradiation, we are able to obtain rotating frame R1ρ and R2ρ dispersion curves that are sensitive to slow μs/ms protein dynamics (demonstrated with ubiquitin). The strengths of this method are to (a) extend the dynamic range of the relaxation dispersion analysis, (b) avoid the need for multiple magnetic field strengths to extract dynamic parameters, (c) measure accurate relaxation rates that are independent of frequency offset, and (d) reduce the stress to NMR hardware (e.g., cryoprobes).

J Phys Chem A

Triple-Decker Sandwiches and Related Compounds of the First-Row Transition Metals Containing Cyclopentadienyl and Benzene Rings

Haibo Liu, Qian-shu Li, Yaoming Xie, R. Bruce King and Henry F. Schaefer

J. Phys. Chem. A, Article ASAP
DOI: 10.1021/jp104689r
Publication Date (Web): July 21, 2010

The triple-decker sandwich compound trans-Cp2V2(η6:η6-μ-C6H6) has been synthesized, as well as “slipped” sandwich compounds of the type trans-Cp2Co2(η4:η4-μ-arene) and the cis-Cp2Fe2(η4:η4-μ-C6R6) derivatives with an Fe−Fe bond (Cp = η5-cyclopentadienyl). Theoretical studies show that the symmetrical triple-decker sandwich structures trans-Cp2M2(η6:η6-μ-C6H6) are the global minima for M = Ti, V, and Mn but lie 10 kcal/mol above the global minimum for M = Cr. The nonbonding M···M distances and spin states in these triple decker sandwich compounds can be related to the occupancies of the frontier bonding molecular orbitals. The global minimum for the chromium derivative is a singlet spin state cis-Cp2Cr2(η4:η4-μ-C6H6) structure with a very short CrCr distance of 2.06 Å, suggesting a formal quadruple bond. A triplet state cis-Cp2Cr2(η4:η4-μ-C6H6) structure with a predicted Cr≡Cr distance of 2.26 Å lies only 3 kcal/mol above this global minimum. For the later transition metals the global minima are predicted to be cis-Cp2M2(η6:η6-μ-C6H6) structures with a metal−metal bond, rather than triple decker sandwiches. These include singlet cis-Cp2Fe2(η4:η4-μ-C6H6) with a predicted Fe═Fe double bond distance of 2.43 Å, singlet cis-Cp2Co2(η3:η3-μ-C6H6) with a predicted Co—Co single bond distance of 2.59 Å, and triplet cis-Cp2Ni2(η3:η3-μ-C6H6) with a predicted Ni—Ni distance of 2.71 Å.

J. Phys. Chem. C, vol.114, Issue 29

Molecular Modeling, Multinuclear NMR, and Diffraction Studies in the Templated Synthesis and Characterization of the Aluminophosphate Molecular Sieve STA-2

Maria Castro†, Valerie R. Seymour†, Diego Carnevale†, John M. Griffin†, Sharon E. Ashbrook*†, Paul A. Wright*†, David C. Apperley‡, Julia E. Parker§, Stephen P. Thompson§, Antoine Fecant and Nicolas Bats

J. Phys. Chem. C, 2010, 114 (29), pp 12698–12710
DOI: 10.1021/jp104120y
Copyright © 2010 American Chemical Society

Abstract: Molecular modeling has been used to assist in the design of a new structure directing agent (SDA) for the synthesis of the AlPO4 form of STA-2, bis-diazabicyclooctane-butane (BDAB). This is incorporated as a divalent cation within the large cages of STA-2, as determined via a combination of solid-state 13C and 15N MAS NMR, supported by 14N and 1H-15N HMQC solution NMR and density functional calculations. As-prepared AlPO4 STA-2 containing cationic SDA molecules achieves neutrality by the inclusion of hydroxide ions bridging between 5-fold coordinated framework Al atoms. Synchrotron X-ray powder diffraction data of the dehydrated as-prepared form indicates triclinic symmetry (Al12P12O48(OH)2·BDAB, P1, a = 12.3821(2) Å, b = 12.3795(2) Å, c = 12.3797(3) Å, α = 63.3585(8)°, β = 63.4830(7)°, γ = 63.4218(7)°) with the distortion from rhombohedral R symmetry resulting from the partial order of hydroxide ions in bridging Al−OH−Al sites within cancrinite cages. Upon calcination in oxygen, the organic SDA is removed, leaving AlPO4 STA-2 with a pore volume of 0.22 cm3 g−1 (R, Al36P36O144, a = 12.9270(2) Å, c = 30.7976(4) Å). Dehydrated calcined AlPO4 STA-2 has two crystallographically distinct P and Al sites: 31P MAS NMR resolves the two distinct P sites, and although 27Al MAS NMR only partially resolves the two Al sites, they are separated by MQMAS. Furthermore, 2D 27Al → 31P MQ-J-HETCOR correlation spectroscopy confirms that each framework Al is linked to the two different P sites via Al−O−P connections in a 3:1 ratio (and vice versa for P linked to different Al). The 27Al and 31P resonances are assigned to the crystallographic Al and P sites by calculation of the NMR parameters using the CASTEP DFT program for an energy-minimized AlPO4(SAT) framework.



Propane Aromatization on Zn-Modified Zeolite BEA Studied by Solid-State NMR in Situ

Anton A. Gabrienko†, Sergei S. Arzumanov†, Dieter Freude‡ and Alexander G. Stepanov*†
J. Phys. Chem. C, 2010, 114 (29), pp 12681–12688
DOI: 10.1021/jp103580f
Copyright © 2010 American Chemical Society

Abstract:The conversion of propane (propane-1-13C and propane-2-13C) on Zn/H-BEA zeolite at 520−620 K has been studied by 1H and 13C (CP) MAS NMR. Propene adsorption complex with zinc sites (π-complex) and σ-allylzinc species as intermediates have been identified in the course of propane conversion to aromatics. The mechanism leading to the formation of methane and ethane, which are constituents of an undesirable route in propane conversion, has been examined by kinetic modeling of the expected reaction network based on in situ 1H MAS NMR kinetic measurements of the reaction performance. The pathways for propane aromatization and hydrogenolysis have been proposed. Hydrogenolysis of propane has been concluded to occur with the involvement of both Brønsted acid sites and Zn sites.



13C Chemical Shift of Adsorbed Acetone for Measuring the Acid Strength of Solid Acids: A Theoretical Calculation Study

Hanjun Fang†‡, Anmin Zheng*†, Yueying Chu†‡ and Feng Deng*†
J. Phys. Chem. C, 2010, 114 (29), pp 12711–12718
DOI: 10.1021/jp1044749
Copyright © 2010 American Chemical Society

Abstract: Adsorption of basic probe molecules is one of the widely used methods to characterize the acid strength of solid acids. In this contribution, the adsorptions of acetone on various Brønsted and Lewis acid sites (from weak acid to superacid) are theoretically studied, in order to elucidate the quantitative relationships between 13C chemical shifts of acetone and intrinsic acid strength of solid acids. The Brønsted acid sites are represented by a series of 8T zeolite models with varying terminal Si−H bond lengths, and the different extents of acidic proton transfer from these acid sites to acetone are revealed explicitly. We found that three adsorption conformations (hydrogen-bonded, proton-shared, and ion-pair) exist for acetone, and concurrently, a correlation of three-broken lines is obtained for the 13C chemical shift of acetone versus the deprotonation energy (DPE). The correlation can be used as a scale for quantitatively measuring the Brønsted acid strength of solid acids. A threshold of 245 ppm is determined for superacidity, in good agreement with the experimental value (244 ppm). The Lewis acid sites are modeled by tricoordinate framework aluminum species and various extra-framework aluminum cations or neutral species such as Al3+, AlO+, AlOH2+, Al(OH)2+, Al(OH)3, and AlOOH. We found that acetone is coordinately adsorbed on the aluminum atoms of Lewis acid sites and that the 13C chemical shift of acetone is almost linear to the lowest unoccupied molecular orbital (LUMO) energy of the acid sites.

J. Phys. Chem C. v. 114, issue 28

45Sc Spectroscopy of Solids: Interpretation of Quadrupole Interaction Parameters and Chemical Shifts

Mara D. Alba*†, Pablo Chain†, Pierre Florian‡ and Dominique Massiot‡

J. Phys. Chem. C, 2010, 114 (28), pp 12125–12132
Publication Date (Web): June 28, 2010

Abstract: The aims of the present study is to describe for the first time the 45Sc MAS NMR spectra of X2-Sc2SiO5 and C-Sc2Si2O7, to combine the spectroscopic information with the structures published from diffraction data, and to propose a rational interpretation of the chemical shifts and quadrupolar parameters. For that purposed, we have correlated the experimental quadrupole coupling parameters of 45Sc determined for a number of scandium compounds to those found by a simple electrostatic calculation and we have found that the isotropic chemical shift of the 45Sc is linearly correlated to the shift parameter, calculated by bond-valence theory. We also show that a simple point charge calculation can approximate the electric field gradient to a sufficiently good approximation that it provides a valuable mean to assign the NMR spectra.


Nuclear Magnetic Resonance Study of Reorientational Motion in α-Mg(BH4)2
Alexander V. Skripov*†, Alexei V. Soloninin†, Olga A. Babanova†, Hans Hagemann‡ and Yaroslav Filinchuk§
J. Phys. Chem. C, 2010, 114 (28), pp 12370–12374
Copyright © 2010 American Chemical Society

Abstract: To study the reorientational motion of BH4 groups in the low-temperature (α) phase of Mg(BH4)2, we have performed nuclear magnetic resonance (NMR) measurements of the 1H and 11B spin−lattice relaxation rates in this compound over wide ranges of temperature (82−443 K) and resonance frequency (14−90 MHz for 1H and 14−28 MHz for 11B). It is found that the thermally activated reorientational motion in α-Mg(BH4)2 is characterized by a coexistence of at least three jump processes with strongly differing activation energies. Taking into account the anisotropy of the local environment of BH4 groups in α-Mg(BH4)2, these jump processes can be attributed to different types of reorientation. The nearly linear coordination of BH4 groups by two Mg atoms suggests that the fastest jump process corresponds to the rotation around the 2-fold axis connecting B and two Mg atoms, whereas the slowest process is associated with the rotation around two other 2-fold axes perpendicular to the Mg−B−Mg line.

Journal of Magnetic Resonance ASAP

A bit of shameless self-promotion:

Journal of Magnetic Resonance
Article in Press
doi:10.1016/j.jmr.2010.05.018

The application of frequency swept pulses for the acquisition of nuclear quadrupole resonance spectra
Aaron J. Rossinia, Hiyam Hamaeda and Robert W. Schurko, a,

Abstract:The acquisition of nuclear quadrupole resonance (NQR) spectra with wideband uniform rate and smooth truncation (WURST) pulses is investigated. 75As and 35Cl NQR spectra acquired with the WURST echo sequence are compared to those acquired with standard Hahn-echo sequences and echo sequences which employ composite refocusing pulses. The utility of WURST pulses for locating NQR resonances of unknown frequency is investigated by monitoring the integrated intensity and signal to noise of 35Cl and 75As NQR spectra acquired with transmitter offsets of several hundreds kilohertz from the resonance frequencies. The WURST echo sequence is demonstrated to possess superior excitation bandwidths in comparison to the pulse sequences which employ conventional monochromatic rectangular pulses. The superior excitation bandwidths of the WURST pulses allows for differences in the characteristic impedance of the receiving and excitation circuits of the spectrometer to be detected. Impedance mismatches have previously been reported by Marion and Desvaux [D.J.Y. Marion, H. Desvaux, J. Magn. Reson. (2008) 193(1) 153–157] and Muller et al. [M. Nausner, J. Schlagnitweit, V. Smrecki, X. Yang, A. Jerschow, N. Muller, J. Magn. Reson. (2009) 198(1) 73–79]. In this regard, WURST pulse sequences may afford an efficient new method for experimentally detecting impedance mismatches between receiving and excitation circuits, allowing for the optimization of solids and solution NMR and NQR spectrometer systems. The use of the Carr–Purcell Meiboom–Gill (CPMG) pulse sequence for signal enhancement of NQR spectra acquired with WURST pulses and conventional pulses is also investigated. Finally, the utility of WURST pulses for the acquisition of wideline NQR spectra is demonstrated by acquiring part of the 63/65Cu NQR spectrum of CuCN.

Magn. Reson. Chem. - July 2010

New perspectives in the PAW/GIPAW approach: JP-O-Si coupling constants, antisymmetric parts of shift tensors and NQR predictions

from Magnetic Resonance in Chemistry by Christian Bonhomme, Christel Gervais, Cristina Coelho, Frédérique Pourpoint, Thierry Azaïs, Laure Bonhomme-Coury, Florence Babonneau, Guy Jacob, Maude Ferrari, Daniel Canet, Jonathan R. Yates, Chris J. Pickard, Siân A. Joyce, Francesco Mauri, Dominique Massiot

In 2001, Pickard and Mauri implemented the gauge including projected augmented wave (GIPAW) protocol for first-principles calculations of NMR parameters using periodic boundary conditions (chemical shift anisotropy and electric field gradient tensors). In this paper, three potentially interesting perspectives in connection with PAW/GIPAW in solid-state NMR and pure nuclear quadrupole resonance (NQR) are presented: (i) the calculation of J coupling tensors in inorganic solids; (ii) the calculation of the antisymmetric part of chemical shift tensors and (iii) the prediction of 14N and 35Cl pure NQR resonances including dynamics. We believe that these topics should open new insights in the combination of GIPAW, NMR/NQR crystallography, temperature effects and dynamics. Points (i), (ii) and (iii) will be illustrated by selected examples: (i) chemical shift tensors and heteronuclear 2JP[bond]O[bond]Si coupling constants in the case of silicophosphates and calcium phosphates [Si5O(PO4)6, SiP2O7 polymorphs and [alpha]-Ca(PO3)2]; (ii) antisymmetric chemical shift tensors in cyclopropene derivatives, C3X4 (X = H, Cl, F) and (iii) 14N and 35Cl NQR predictions in the case of RDX (C3H6N6O6), [beta]-HMX (C4H8N8O8), [alpha]-NTO (C2H2N4O3) and AlOPCl6. RDX, [beta]-HMX and [alpha]-NTO are explosive compounds.

Received: 31 March 2010; Revised: 17 May 2010; Accepted: 20 May 2010
Digital Object Identifier (DOI)
10.1002/mrc.2635


Computation and NMR crystallography of terbutaline sulfate
from Magnetic Resonance in Chemistry by Robin K. Harris, Paul Hodgkinson, Vadim Zorin, Jean-Nicolas Dumez, Bénédicte Elena-Herrmann, Lyndon Emsley, Elodie Salager, Robin S. Stein

This article addresses, by means of computation and advanced experiments, one of the key challenges of NMR crystallography, namely the assignment of individual resonances to specific sites in a crystal structure. Moreover, it shows how NMR can be used for crystal structure validation. The case examined is form B of terbutaline sulfate. CPMAS 13C and fast MAS 1H spectra have been recorded and the peaks assigned as far as possible. Comparison of 13C chemical shifts computed using the CASTEP program (incorporating the Gauge Including Projector Augmented Wave principle) with those obtained experimentally enable the accuracy of the two distinct single-crystal evaluations of the structure to be compared and an error in one of these is located. The computations have substantially aided in the assignments of both 13C and 1H resonances, as has a series of two-dimensional (2D) spectra (HETCOR, DQ-CRAMPS and proton-proton spin diffusion). The 2D spectra have enabled many of the proton chemical shifts to be pinpointed. The relationships of the NMR shifts to the specific nuclear sites in the crystal structure have therefore been established for most 13C peaks and for some 1H signals. Emphasis is placed on the effects of hydrogen bonding on the proton chemical shifts.

Received: 26 March 2010; Revised: 20 May 2010; Accepted: 24 May 2010
Digital Object Identifier (DOI)
10.1002/mrc.2636


Prediction of NMR J-coupling in solids with the planewave pseudopotential approach
from Magnetic Resonance in Chemistry by Jonathan R. Yates
We review the calculation of NMR J-coupling in solid materials using the planewave pseudopotential formalism of Density Functional Theory. The methodology is briefly summarised and an account of recent applications is given. We discuss various aspects of the calculations which should be taken into account when comparing results with solid-state NMR experiments including anisotropy and orientation of the J tensors, the reduced coupling constant, and the relation between J and crystal structure. Copyright © 2010 John Wiley & Sons, Ltd.

Received: 20 April 2010; Revised: 2 June 2010; Accepted: 4 June 2010
Digital Object Identifier (DOI)
10.1002/mrc.2646


Comparing quantum-chemical calculation methods for structural investigation of zeolite crystal structures by solid-state NMR spectroscopy
from Magnetic Resonance in Chemistry by Darren H. Brouwer, Igor L. Moudrakovski, Richard J. Darton, Russell E. Morris

Combining quantum-chemical calculations and ultrahigh-field NMR measurements of 29Si chemical shielding (CS) tensors has provided a powerful approach for probing the fine details of zeolite crystal structures. In previous work, the quantum-chemical calculations have been performed on 'molecular fragments' extracted from the zeolite crystal structure using Hartree-Fock methods (as implemented in Gaussian). Using recently acquired ultrahigh-field 29Si NMR data for the pure silica zeolite ITQ-4, we report the results of calculations using recently developed quantum-chemical calculation methods for periodic crystalline solids (as implemented in CAmbridge Serial Total Energy Package (CASTEP) and compare these calculations to those calculated with Gaussian. Furthermore, in the context of NMR crystallography of zeolites, we report the completion of the NMR crystallography of the zeolite ITQ-4, which was previously solved from NMR data. We compare three options for the 'refinement' of zeolite crystal structures from 'NMR-solved' structures: (i) a simple target-distance based geometry optimization, (ii) refinement of atomic coordinates in which the differences between experimental and calculated 29Si CS tensors are minimized, and (iii) refinement of atomic coordinates to minimize the total energy of the lattice using CASTEP quantum-chemical calculations. All three refinement approaches give structures that are in remarkably good agreement with the single-crystal X-ray diffraction structure of ITQ-4.

Received: 31 March 2010; Revised: 27 May 2010; Accepted: 2 June 2010
Digital Object Identifier (DOI)
10.1002/mrc.2642

Prog. in NMR Spectrosc. - July 2010 - Floquet theory

Progress in Nuclear Magnetic Resonance Spectroscopy
doi:10.1016/j.pnmrs.2010.06.002
Floquet Theory in Solid-State Nuclear Magnetic Resonance
Michal Leskes, P.K. Madhu, Shimon Vega

Received 12 April 2010; accepted 11 June 2010. Available online 30 June 2010.

Keywords: Solid-state NMR; Floquet Theory; van Vleck transformation; Average Hamiltonian Theory

Journal Update

J. Am. Chem. Soc., 2010, 132 (16), pp 5538–5539

Breaking the T1 Constraint for Quantitative Measurement in Magic Angle Spinning Solid-State NMR Spectroscopy
Guangjin Hou, Shangwu Ding, Limin Zhang and Feng Deng

Quantitative solid-state NMR experimental schemes that break the conventional T1 constraint are described. The combination of broad-band homonuclear recoupling techniques and the conventional single pulse or cross-polarization (CP) schemes (referred as QUSP or QUCP) render the long T1 of low-? spins no longer a constraint for obtaining quantitative NMR spectra. During the mixing time when dipolar recoupling occurs, the nonuniformly CP enhanced or recovered spin magnetization is redistributed under the reintroduced homonuclear dipole-dipole interactions so that uniformly enhanced or recovered magnetization is achieved when the system reaches the quasi-equilibrium state. It is shown that quantitative NMR spectra can be obtained for the recycle delays substantially shorter than the conventionally required 5T1. In addition, the high efficiency gain can be achieved in QUSP and QUCP experiments with a relatively short recycle delay.


J. Am. Chem. Soc., 2010, 132 (16), pp 5546–5547

Detection of Transient Interchain Interactions in the Intrinsically Disordered Protein a-Synuclein by NMR Paramagnetic Relaxation Enhancement
Kuen-Phon Wu and Jean Baum


NMR paramagnetic relaxation enhancement experiments were applied to the intrinsically disordered protein a-synuclein, the primary protein in Parkinson's disease, to directly characterize transient intermolecular complexes at neutral and low pH. At neutral pH, we observed weak N- to C-terminal interchain contacts driven by electrostatic interactions, while at low pH, the C- to C-terminal interchain interactions are significantly stronger and driven by hydrophobic contacts. Characterization of these first interchain interactions will provide fundamental insight into the mechanism of amyloid formation.

J. Am. Chem. Soc., 2010, 132 (16), pp 5556–5557

Fibrillar vs Crystalline Full-Length ß-2-Microglobulin Studied by High-Resolution Solid-State NMR Spectroscopy
Emeline Barbet-Massin†, Stefano Ricagno‡§, Józef R. Lewandowski†, Sofia Giorgetti§, Vittorio Bellotti‡§, Martino Bolognesi, Lyndon Emsley† and Guido Pintacuda*†

Elucidating the fine structure of amyloid fibrils as well as understanding their processes of nucleation and growth remains a difficult yet essential challenge, directly linked to our current poor insight into protein misfolding and aggregation diseases. Here we consider ß-2-microglobulin (ß2m), the MHC-1 light chain component responsible for dialysis-related amyloidosis, which can give rise to amyloid fibrils in vitro under various experimental conditions, including low and neutral pH. We have used solid-state NMR to probe the structural features of fibrils formed by full-length ß2m (99 residues) at pH 2.5 and pH 7.4. A close comparison of 2D 13C-13C and 15N-13C correlation experiments performed on ß2m, in both the crystalline and fibrillar states, suggests that, in spite of structural changes affecting the protein loops linking the protein ß-strands, the protein chain retains a substantial share of its native secondary structure in the fibril assembly. Moreover, variations in the chemical shifts of the key Pro32 residue suggest the involvement of a cis-trans isomerization in the process of ß2m fibril formation. Lastly, the analogy of the spectra recorded on ß2m fibrils grown at different pH values hints at a conserved architecture of the amyloid species thus obtained.

J. Am. Chem. Soc., 2010, 132 (16), pp 5558–5559


Ultrafast MAS Solid-State NMR Permits Extensive 13C and 1H Detection in Paramagnetic Metalloproteins
Ivano Bertini, Lyndon Emsley§, Moreno Lelli, Claudio Luchinat, Jiafei Mao and Guido Pintacuda

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

J. Am. Chem. Soc., 2010, 132 (16), pp 5672–5676


NMR-Based Structural Modeling of Graphite Oxide Using Multidimensional 13C Solid-State NMR and ab Initio Chemical Shift Calculations
Leah B. Casabianca†, Medhat A. Shaibat†, Weiwei W. Cai‡, Sungjin Park‡, Richard Piner‡, Rodney S. Ruoff‡ and Yoshitaka Ishii†

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. B 1998, 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.


J. Am. Chem. Soc., 2010, 132 (16), pp 5779–5788


Proton-Evolved Local-Field Solid-State NMR Studies of Cytochrome b5 Embedded in Bicelles, Revealing both Structural and Dynamical Information
Ronald Soong†, Pieter E. S. Smith†, Jiadi Xu†, Kazutoshi Yamamoto†, Sang-Choul Im‡, Lucy Waskell‡ and Ayyalusamy Ramamoorthy*†

Structural biology of membrane proteins has rapidly evolved into a new frontier of science. Although solving the structure of a membrane protein with atomic-level resolution is still a major challenge, separated local field (SLF) NMR spectroscopy has become an invaluable tool in obtaining structural images of membrane proteins under physiological conditions. Recent studies have demonstrated the use of rotating-frame SLF techniques to accurately measure strong heteronuclear dipolar couplings between directly bonded nuclei. However, in these experiments, all weak dipolar couplings are suppressed. On the other hand, weak heteronuclear dipolar couplings can be measured using laboratory-frame SLF experiments, but only at the expense of spectral resolution for strongly dipolar coupled spins. In the present study, we implemented two-dimensional proton-evolved local-field (2D PELF) pulse sequences using either composite zero cross-polarization (COMPOZER-CP) or windowless isotropic mixing (WIM) for magnetization transfer. These PELF sequences can be used for the measurement of a broad range of heteronuclear dipolar couplings, allowing for a complete mapping of protein dynamics in a lipid bilayer environment. Experimental results from magnetically aligned bicelles containing uniformly 15N-labeled cytochrome b5 are presented and theoretical analyses of the new PELF sequences are reported. Our results suggest that the PELF-based experimental approaches will have a profound impact on solid-state NMR spectroscopy of membrane proteins and other membrane-associated molecules in magnetically aligned bicelles.

J. Am. Chem. Soc., 2010, 132 (16), pp 5803–5811

Changes in Transmembrane Helix Alignment by Arginine Residues Revealed by Solid-State NMR Experiments and Coarse-Grained MD Simulations
Vitaly V. Vostrikov‡†, Benjamin A. Hall§†, Denise V. Greathouse‡, Roger E. Koeppe, II*‡ and Mark S. P. Sansom*§

Independent experimental and computational approaches show agreement concerning arginine/membrane interactions when a single arginine is introduced at selected positions within the membrane-spanning region of acetyl-GGALW5LALALAL12AL14ALALW19LAGA-ethanolamide, designated GWALP23. Peptide sequence isomers having Arg in position 12 or position 14 display markedly different behaviors, as deduced by both solid-state NMR experiments and coarse-grained molecular dynamics (CG-MD) simulations. With respect to the membrane normal of DOPC or DPPC lipid bilayer membranes, GWALP23-R14 shows one major state whose apparent average tilt is 10° greater than that of GWALP23. The presence of R14 furthermore induces bilayer thinning and peptide displacement to "lift" the charged guanidinium toward the bilayer surface. By contrast, GWALP23-R12 exhibits multiple states that are in slow exchange on the NMR time scale, with CG-MD simulations indicating two distinct positions with different screw rotation angles in the membrane, along with an increased tendency to exit the lipid bilayer.

Hiyam's Journal Update

J. Am. Chem. Soc., 2010, 132 (21), pp 7321–7337

Molecular Silicate and Aluminate Species in Anhydrous and Hydrated Cements
Aditya Rawal, Benjamin J. Smith†, George L. Athens, Christopher L. Edwards, Lawrence Roberts, Vijay Gupta and Bradley F. Chmelka


The compositions and molecular structures of anhydrous and hydrated cements are established by using advanced solid-state nuclear magnetic resonance (NMR) spectroscopy methods to distinguish among different molecular species and changes that occur as a result of cement hydration and setting. One- and two-dimensional (2D) solid-state 29Si and 27Al magic-angle spinning NMR methodologies, including T1-relaxation-time- and chemical-shift-anisotropy-filtered measurements and the use of very high magnetic fields (19 T), allow resonances from different silicate and aluminate moieties to be resolved and assigned in complicated spectra. Single-pulse 29Si and 27Al NMR spectra are correlated with X-ray fluorescence results to quantify the different crystalline and disordered silicate and aluminate species in anhydrous and hydrated cements. 2D 29Si{1H} and 27Al{1H}heteronuclear correlation NMR spectra of hydrated cements establish interactions between water and hydroxyl moieties with distinct 27Al and 29Si species. The use of a 29Si T1-filter allows anhydrous and hydrated silicate species associated with iron-containing components in the cements to be distinguished, showing that they segregate from calcium silicate and aluminate components during hydration. The different compositions of white Portland and gray oilwell cements are shown to have distinct molecular characteristics that are correlated with their hydration behaviors.


A Resonance Assignment Method for Oriented-Sample Solid-State NMR of Proteins
Robert W. Knox†, George J. Lu‡, Stanley J. Opella‡ and Alexander A. Nevzorov

J. Am. Chem. Soc., 2010, 132 (24), pp 8255–8257

A general sequential assignment strategy for uniformly 15N-labeled uniaxially aligned membrane proteins is proposed. Mismatched Hartmann−Hahn magnetization transfer is employed to establish proton-mediated correlations among the neighboring 15N backbone spins. Magnetically aligned Pf1 phage coat protein was used to illustrate the method. Exchanged and nonexchanged separated local field spectra were acquired and overlaid to distinguish the cross-peaks from the main peaks. Most of the original assignments from the literature were confirmed without selectively labeled samples. This method is applicable to proteins with arbitrary topology and will find use in assigning solid-state NMR spectra of oriented membrane proteins for their subsequent structure determination.



The Polar Phase of NaNbO3: A Combined Study by Powder Diffraction, Solid-State NMR, and First-Principles Calculations
Karen E. Johnston†, Chiu C. Tang‡, Julia E. Parker‡, Kevin S. Knight§, Philip Lightfoot*† and Sharon E. Ashbrook*†

J. Am. Chem. Soc., 2010, 132 (25), pp 8732–8746

A polar phase of NaNbO3 has been successfully synthesized using sol-gel techniques. Detailed characterization of this phase has been undertaken using high-resolution powder diffraction (X-ray and neutron) and 23Na multiple-quantum (MQ) MAS NMR, supported by second harmonic generation measurements and density functional theory calculations. Samples of NaNbO3 were also synthesized using conventional solid-state methods and were observed to routinely comprise of a mixture of two different polymorphs of NaNbO3, namely, the well-known orthorhombic phase (space group Pbcm) and the current polar phase, the relative quantities of which vary considerably depending upon precise reaction conditions. Our studies show that each of these two polymorphs of NaNbO3 contains two crystallographically distinct Na sites. This is consistent with assignment of the polar phase to the orthorhombic space group P21ma, although peak broadenings in the diffraction data suggest a subtle monoclinic distortion. Using carefully monitored molten salt techniques, it was possible to eradicate the polar polymorph and synthesize the pure Pbcm phase.


NMR Methods for Characterizing the Pore Structures and Hydrogen Storage Properties of Microporous Carbons
Robert J. Anderson†, Thomas P. McNicholas‡, Alfred Kleinhammes*†, Anmiao Wang‡, Jie Liu‡ and Yue Wu†

J. Am. Chem. Soc., 2010, 132 (25), pp 8618–8626

1H NMR spectroscopy is used to investigate a series of microporous activated carbons derived from a poly(ether ether ketone) (PEEK) precursor with varying amounts of burnoff (BO). In particular, properties relevant to hydrogen storage are evaluated such as pore structure, average pore size, uptake, and binding energy. High-pressure NMR with in situ H2 loading is employed with H2 pressure ranging from 100 Pa to 10 MPa. An N2-cooled cryostat allows for NMR isotherm measurements at both room temperature (290 K) and 100 K. Two distinct 1H NMR peaks appear in the spectra which represent the gaseous H2 in intergranular pores and the H2 residing in micropores. The chemical shift of the micropore peak is observed to evolve with changing pressure, the magnitude of this effect being correlated to the amount of BO and therefore the structure. This is attributed to the different pressure dependence of the amount of adsorbed and non-adsorbed molecules within micropores, which experience significantly different chemical shifts due to the strong distance dependence of the ring current effect. In pores with a critical diameter of 1.2 nm or less, no pressure dependence is observed because they are not wide enough to host
non-adsorbed molecules; this is the case for samples with less than 35% BO. The largest estimated pore size that can contribute to the micropore peak is estimated to be around 2.4 nm. The total H2 uptake associated with pores of this size or smaller is evaluated via a calibration of the isotherms, with the highest amount being observed at 59% BO. Two binding energies are present in the micropores, with the lower, more dominant one being on the order of 5 kJ mol−1 and the higher one ranging from 7 to 9 kJ mol−1.


Characterization of RNA Invasion by 19F NMR Spectroscopy
Anu Kiviniemi and Pasi Virta*

J. Am. Chem. Soc., 2010, 132 (25), pp 8560–8562

19F NMR spectroscopy offers an efficient tool for monitoring RNA invasion. The invasion of 2′-O-methyl oligoribonucleotides into a 19F-labeled HIV-1 TAR RNA model and the temperature-dependent behavior of the complexes obtained have been examined.

J. Phys. Chem. A

Solid-State NMR Spectra and Long, Intra-Dimer Bonding in the π-[TTF]22+ (TTF = Tetrathiafulvalene) Dication

Merrill D. Halling, Joshua D. Bell, Ronald J. Pugmire, David M. Grant* and Joel S. Miller

J. Phys. Chem. A, 2010, 114 (24), pp 6622–6629
DOI: 10.1021/jp910509f
Publication Date (Web): June 2, 2010

The 13C chemical-shift tensor principal values for TTF and π-[TTF]22+ (TTF = tetrathiafulvalene) dimer dications have been measured in order to better understand the electronic structure and long intradimer bonding of these TTF-based dimer structures. The structure of π-[TTF]22+ is abnormal due to its two C−C and four S−S ca. 3.4 Å intradimer separations, which is less than the sum of the sulfur van der Waals radii, and has a singlet 1A1g electronic ground state. This study of TTF and [TTF]22+ was conducted to determine how the NMR chemical-shift tensor principal values change as a function of electronic structure. This study also establishes a better understanding of the interactions that lead to spin-pairing of the monomeric radical units. The density functional theory (DFT) calculated nuclear shielding tensors are correlated with the experimentally determined principal chemical-shift values. The embedded ion method (EIM) was used to investigate the electrostatic lattice potential in [TTF]22+. These theoretical methods provide information on the tensor magnitudes and orientations of their tensor principal values with respect to the molecular frame. The experimental chemical-shift principal values agree with the calculated quantum mechanical chemical-shielding principal values, within typical errors commonly seen for this class of molecular system. Relatively weak Wiberg bond orders between the two [TTF]+ components of the dimer dication correlate with the long bonds linking the two [TTF]+ monomers and substantiate the claim that there is weak multicenter bonding present.
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Interpretation of Indirect Nuclear Spin−Spin Couplings in Isomers of Adenine: Novel Approach to Analyze Coupling Electron Deformation Density Using Localized Molecular Orbitals

Radek Marek*, Aneka Kstkov, Kateina Malikov, Jaromr Touek, Jaromr Marek, Michal Hocek, Olga L. Malkina* and Vladimir G. Malkin

J. Phys. Chem. A, 2010, 114 (24), pp 6689–6700
DOI: 10.1021/jp102186r
Publication Date (Web): June 2, 2010

Adenine, an essential building block of nucleic acids present in all living systems, can occur in several tautomeric forms. The phenomenon of tautomerism can be investigated by several experimental methods, including nuclear magnetic resonance. In this study, long-range 1H−13C and 1H−15N coupling constants for N-alkyl derivatives related to four tautomers of adenine are investigated in DMSO and DMF solutions. To investigate the structural dependence of the coupling constants and to understand how polarization propagates in the system, Fermi contact (FC) terms were calculated for the individual isomers and analyzed by using density functional theory (DFT), and the coupling pathways were visualized using real-space functions. The coupling electron deformation densities (CDD) of several 1H−X (X = 13C, 15N) pairs are evaluated and compared. In order to analyze the CDD in more detail, a new approach to break down the CDD into contributions from Boys or Pipek−Mezey localized molecular orbitals (LMOs) has been developed. A similar approach has been applied to split the value of the FC contribution to the J coupling into the LMO contributions. On the basis of chemical concepts, the contributions of σ-bonds, π-electrons, and lone pairs of electrons are discussed. The lone pair of electrons at the nitrogen atom contributes significantly to the 1H−C═15N coupling, whereas the 1H−C═N−13C coupling is affected in a somewhat different way. Surprisingly, the contribution of the intervening C═N bond to the FC term for 1H−C═15N coupling originates exclusively in σ-electrons, with a vanishingly small contribution calculated for the π-electrons of this fragment. This behavior is rationalized by introducing the concept of “hard and soft J elements” derived from the polarizability of the individual components.
________________________________________

NMR Spectroscopic Parameters of Molecular Systems with Strong Hydrogen Bonds

Natalia Zarycz and Gustavo A. Aucar*

J. Phys. Chem. A, Article ASAP
DOI: 10.1021/jp1019334
Publication Date (Web): June 16, 2010

A series of closed H-bonded molecules that have (or not) delocalized bonds were studied. The dependence of both NMR spectroscopic parameters σ and J-couplings, and also the energy stability of such molecules with H-bond strength, were analyzed. The selected basic geometrical structure was that of malonaldehyde. From its full optimized geometry, the corresponding geometry of 3-OH propanal was obtained, fixing either the d(O−O) distance or a more extended local geometry and then optimizing the other part of the whole structure. Nitromalonaldehyde and nitromalonamide were also studied because they should have stronger H-bonds and their basic structure is also malonaldehyde. The last one also has electronic effects that may be varied by rotating the amino groups. By doing this it is possible to show that the effects on acidity of donors are more important than the equivalent effects on the basicity of acceptors. It is also shown that J-couplings that involve atoms close to the H-bond have important noncontact contributions that must be included in order to reproduce total J values. Noncontact contributions are more important than the Fermi contact (FC) one for J(O−O) in malonaldehyde. In nitromalonamide all three terms, FC, paramagnetic spin-orbital, and spin-dipolar are of the same order of magnitude when both amino groups are rotated. This does not happen for its planar configuration. Nuclear magnetic shielding of the hydrogen belonging to the H-bond is quite sensitive to it. The magnetic behavior of such hydrogen atom is modified when it is part of a closed H-bonded molecule. Then a relationship between the H-bond strength with the paramagnetic contributions of the shieldings of both atoms, C and O of the donor substructure, was obtained. We have found a cubic correlation between σp (C) of the C−O donor bond with σ (H) of the H-bonded hydrogen. It is observed that both the noncontact J-coupling contributions and shieldings on atoms belonging to the donor substructure, give a clear evidence about the presence of the resonance phenomenon in the model compounds that have been studied, malonaldehyde, nitromalonaldehyde, and nitromalonamide.
_________________________________

Spin-State-Corrected Gaussian-Type Orbital Basis Sets

Marcel Swart*, Mireia Gell, Josep M. Luis and Miquel Sola

J. Phys. Chem. A, Article ASAP
DOI: 10.1021/jp102712z
Publication Date (Web): June 16, 2010

Recently, we reported that the basis set has a profound influence on the computed values for spin-state splittings [ J. Phys. Chem. A 2008, 112, 6384]. In particular, small Gaussian-type orbital (GTO) basis sets were shown to be unreliable for the prediction of them. Here, we report simple modifications of the small Pople-type Gaussian-type orbital basis sets (3-21G, 3-21G*, 6-31G, 6-31G*), which correct their faulty behavior for the spin-state energies. We have investigated the basis sets for a set of 13 first-row transition-metal complexes for which reliable reference data have been obtained at the OPBE/TZ2P(STO) level. For several systems, we have used single and double spin-contamination corrections to avoid ambiguity of the results because of spin contamination, that is, the energies and geometries were obtained for the pure spin states. The spin ground states as predicted by the spin-state-corrected GTO basis sets (s6-31G, s6-31G*) are in complete agreement with the reference Slater-type orbital (STO) data, while those of the original basis sets and a recent modification by Baker and Pulay (m6-31G*) are not for all cases. The spin-state-corrected GTO basis sets also improve upon the original and modified basis sets for the accuracy of geometry optimization, while the accuracy of the vibrational frequencies is as good or better. At a limited additional cost, one therefore obtains very reliable results for these important spin-state energies.

Journal of Materials Chemistry

Probing the local structures and protonic conduction pathways in scandium substituted BaZrO₃ by multinuclear solid-state NMR spectroscopy

Lucienne Buannic ^a, Frédéric Blanc ^a, Ivan Hung ^b, Zhehong Gan ^b and Clare P. Grey *^ac

A comprehensive multinuclear solid-state NMR study of scandium-substituted BaZrO₃ is reported. Static low field and MQMAS very high field ⁴⁵Sc NMR data revealed the presence of both 5- and 6-coordinated scandium atoms, 5-coordinated scandium arising from Sc nearby an oxygen vacancy. ¹⁷O NMR spectra showed the presence of up to three different chemical oxygen environments assigned to Zr–O–Zr, Zr–O–Sc and Sc–O–Sc. From the ratios of these different oxygen sites, the distribution of the scandium cations was close to random but indicated that the maximum scandium incorporation was lower than expected, consistent with the observation of Sc₂O₃ impurities at substitution levels of 30% Sc for Zr. ¹H and ⁴⁵Sc NMR data on the hydrated materials revealed the presence of scandium next to protonic defects. Finally, variable temperature ¹H NMR showed the presence of at least two different proton environments in between which proton transfer occurs at ambient temperatures (300 K).

http://www.rsc.org/delivery/_ArticleLinking/ArticleLinking.cfm?JournalCode=JM&Year=2010&ManuscriptID=c0jm00155d&Iss=Advance_Article

DOI: 10.1039/c0jm00155d

Journal of Physical Chemistry B and C, v114, Issues 23

Crystalline Aluminum Hydroxide Fluorides AlFx(OH)3−x·H2O: Structural Insights from 1H and 2H Solid State NMR and Vibrational Spectroscopy

G. Scholz*, S. Brehme, R. Knig, D. Heidemann and E. Kemnitz*
J. Phys. Chem. C, 2010, 114 (23), pp 10535–10543
DOI: 10.1021/jp1023857

AbstractFor the first time, 1H/2H MAS NMR signals of crystalline hydroxide fluorides AlFx(OH)3−x·H2O, as well as of the dehydrated samples, both with pyrochlore structure, were resolved, identified, and assigned in direct correlation with vibrational bands of respective FT IR spectra. The use of magnetically diluted samples in combination with 1H spin−echo experiments, 2H MAS, and 19F−2H CP and 1H−2H CP MAS NMR experiments gave information on different 2H (1H) sites in relation to present structural motifs known from the crystal structure.

Angewandte Chemie International Edition

Angewandte Chemie International Edition
Early View (Articles online in advance of print)
Published Online: 8 Jun 2010

High-Resolution Studies of Uniformly 13C,15H-Labeled RNA by Solid-State NMR Spectroscopy

Alexey V. Cherepanov, Dr., Clemens Glaubitz, Prof. Dr., Harald Schwalbe, Prof. Dr.

Keywords: conformational analysis • freeze-quenching • NMR spectroscopy • RNA • solid-state structures

Abstract: Chilling out: Solid-state 13C NMR correlation spectroscopy was used to assign the signals of a uniformly labeled RNA hairpin infrozen aqueous solution. Conformational analysis shows that solutions of biologically relevant RNAs can freeze withoutsignificant changes in RNA structure and without critical loss of resolution and sensitivity in NMR experiments.

10.1002/anie.200906885


Angewandte Chemie International Edition
Early View (Articles online in advance of print)
Published Online: 8 Jun 2010

The Elusive Enamine Intermediate in Proline-Catalyzed Aldol Reactions: NMR Detection, Formation Pathway, and Stabilization Trends

Markus B. Schmid, Kirsten Zeitler, Dr., Ruth M. Gschwind, Prof. Dr.

Keywords: aldol reaction • enamines • NMR spectroscopy • organocatalysis • proline catalysis

Abstract: The missing link: The elusive enamine intermediate of nucleophilic proline catalysis was detected and stereochemicallycharacterized by NMR analysis of the aldehyde self-aldolization reaction in dipolar aprotic solvents. NMR exchange spectroscopy(EXSY) was used to observe direct enamine formation from oxazolidinones. Additionally, the stabilization of the intermediate bythe appropriate choice of solvent and substitution pattern on the aldehyde is presented.

10.1002/anie.200906629

Phys. Chem. Chem. Phys. 2010 Vol. 12 Issue 22

An entire issue dedicated to dynamic nuclear polarization NMR (cross polarization from an added paramagnetic agent to the nucleus of interest). Requires additional hardware but it is an interesting concept. The following is a good introductory journal:

Solid-state dynamic nuclear polarization at 263 GHz: spectrometer design and experimental results

Melanie Rosay, Leo Tometich, Shane Pawsey, Reto Bader, Robert Schauwecker, Monica Blank, Philipp M. Borchard, Stephen R. Cauffman, Kevin L. Felch, Ralph T. Weber, Richard J. Temkin, Robert G. Griffin and Werner E. Maas

________________________________________

Dynamic Nuclear Polarization (DNP) experiments transfer polarization from electron spins to nuclear spins with microwave irradiation of the electron spins for enhanced sensitivity in nuclear magnetic resonance (NMR) spectroscopy. Design and testing of a spectrometer for magic angle spinning (MAS) DNP experiments at 263 GHz microwave frequency, 400 MHz 1H frequency is described. Microwaves are generated by a novel continuous-wave gyrotron, transmitted to the NMR probe via a transmission line, and irradiated on a 3.2 mm rotor for MAS DNP experiments. DNP signal enhancements of up to 80 have been measured at 95 K on urea and proline in water–glycerol with the biradical polarizing agent TOTAPOL. We characterize the experimental parameters affecting the DNP efficiency: the magnetic field dependence, temperature dependence and polarization build-up times, microwave power dependence, sample heating effects, and spinning frequency dependence of the DNP signal enhancement. Stable system operation, including DNP performance, is also demonstrated over a 36 h period.

http://www.rsc.org/ej/CP/2010/c003685b.pdf

J. Phys. Chem B and C., vol. 114, Issues 22

Multireference Ab Initio Calculations of g tensors for Trinuclear Copper Clusters in Multicopper Oxidases

Steven Vancoillie‡, Jakub Chalupsk§, Ulf Ryde, Edward I. Solomon, Kristine Pierloot‡, Frank Neese¶* and Lubomr Rulek§*

J. Phys. Chem. B, 2010, 114 (22), pp 7692–7702
DOI: 10.1021/jp103098r

Abstract: EPR spectroscopy has proven to be an indispensable tool in elucidating the structure of metal sites in proteins. In recent years, experimental EPR data have been complemented by theoretical calculations, which have become a standard tool of many quantum chemical packages. However, there have only been a few attempts to calculate EPR g tensors for exchange-coupled systems with more than two spins. In this work, we present a quantum chemical study of structural, electronic, and magnetic properties of intermediates in the reaction cycle of multicopper oxidases and of their inorganic models. All these systems contain three copper(II) ions bridged by hydroxide or O2− anions and their ground states are antiferromagnetically coupled doublets. We demonstrate that only multireference methods, such as CASSCF/CASPT2 or MRCI can yield qualitatively correct results (compared to the experimental values) and consider the accuracy of the calculated EPR g tensors as the current benchmark of quantum chemical methods. By decomposing the calculated g tensors into terms arising from interactions of the ground state with the various excited states, the origin of the zero-field splitting is explained. The results of the study demonstrate that a truly quantitative prediction of the g tensors of exchange-coupled systems is a great challenge to contemporary theory. The predictions strongly depend on small energy differences that are difficult to predict with sufficient accuracy by any quantum chemical method that is applicable to systems of the size of our target systems.

Solid-state NMR of Radioactive Materials

A nice article in Chemical and Engineering News on solid-state NMR of radioactive materials.


http://pubs.acs.org/isubscribe/journals/cen/88/i21/html/8821sci1.html

J. Phys. Chem. C., vol. 114, Issue 20

1H, 29Si, and 27Al MAS NMR as a Tool to Characterize Volcanic Tuffs and Assess Their Suitability for Industrial Applications

Piero Ciccioli†, Paolo Plescia‡ and Donatella Capitani*§

J. Phys. Chem. C, 2010, 114 (20), pp 9328–9343
DOI: 10.1021/jp103082h
Publication Date (Web): April 29, 2010

Abstract: The type and quality of the information provided by the direct analysis of volcanic tuffs by 1H, 29Si, and 27Al NMR were investigated. At this aim, five tuffs, characterized by different origin, bonding mechanism, and clast composition, were used as test materials. Results consistent with the different nature of the tuff matrix and mineral composition were obtained. While the relative content of Al in the crystal and amorphous phase was determined by 27Al MAS and 3Q MAS NMR, the prevalent glassy or zeolitic nature of the matrix was assessed by 29Si and 1H MAS NMR. Zeolites present at levels as low as 15% w/w were detected by 29Si MAS NMR, and in some tuffs, identification of their framework type was performed together with the determination of the Si/Al ratio and, for the first time, of their configurational entropy. Data obtained were coherent with those provided by X-ray fluorescence (XRF), X-ray powder diffraction (XPRD), thermogravimetric analysis (TGA), differential thermal gravimetry (DTG), cation exchange capacity (CEC) determinations, and scanning electron microscopy, used in both backscattering imaging mode (SEM) and for elemental analysis (SEM-EDS). Results show that, under favorable conditions, solid state NMR techniques can provide a comprehensive view of the chemical and physicochemical behavior of a tuff. A combined use of these techniques is suitable for characterization of tuffs on a routine basis, and can be particularly useful to decide if a material is suitable for industrial applications.




The Comparison in Dehydrogenation Properties and Mechanism between MgCl2(NH3)/LiBH4 and MgCl2(NH3)/NaBH4 Systems

L. Gao†, Y. H. Guo†, Q. Li‡ and X. B. Yu*†

J. Phys. Chem. C, 2010, 114 (20), pp 9534–9540
DOI: 10.1021/jp103012t
Publication Date (Web): May 5, 2010

Abstract: The dehydrogenation properties and mechanism of MgCl2(NH3)/MBH4 (here, M is Li or Na) were investigated by thermogravimetric analysis and mass spectrometry, X-ray diffraction (XRD), solid-state 11B NMR, Fourier transform infrared, and differential scanning calorimetry (DSC). As for the MgCl2(NH3)/LiBH4 system, it was found that a new phase, namely, MgCl2(NH3)·LiBH4, to which the following dehydrogenation relates, is formed after ball milling. Judging from the reaction products, it is confirmed that MgCl2 is inclined to work as an ammonia carrier, and the ligand NH3, transferring from MgCl2, is able to combine with the LiBH4 to release H2 with a trace of ammonia at ca. 240 °C. With the increase of LiBH4 content in the mixture, the emission of ammonia was totally suppressed, and Mg(BH4)2 was produced by the decomposition reaction of MgCl2 with the excessive LiBH4 after the ligand NH3 was exhausted, resulting in an improved dehydrogenation in the whole system. As for the MgCl2(NH3)/NaBH4 system, no new phases are detected by XRD after ball milling. The MgCl2 works as a BH4− acceptor, and the ligand NH3 stays with Mg2+ to combine with the BH4−, which transfers from NaBH4 to Mg2+, resulting in a totally different decomposition route and thermal effects as compared with the MgCl2(NH3)/LiBH4 system. DSC results revealed that the decomposition of MgCl2(NH3)/LiBH4 presented an exothermic reaction with an enthalpy of −3.8 kJ mol−1 H2, while the MgCl2(NH3)/NaBH4 showed two apparent endothermic peaks associated with its two-step dehydrogenation with enthalpies of 8.6 and 2.2 kJ mol−1 H2, respectively. Moreover, the MS profiles of the MgCl2(NH3)/2NaBH4, with excessive BH4−, still released a trace of NH3, indicating that the NaBH4 is not so effective in suppressing the emission of NH3 as LiBH4 did.

Inorganic Chem

Novel Cis- and Trans-Configured Bis(oxime)platinum(II) Complexes: Synthesis, Characterization, and Cytotoxic Activity

Yulia Yu. Scaffidi-Domianello, Kristof Meelich, Michael A. Jakupec, Vladimir B. Arion, Vadim Yu. Kukushkin, Markus Galanski and Bernhard K. Keppler

Inorg. Chem., Article ASAP
DOI: 10.1021/ic100584b
Publication Date (Web): May 11, 2010

Abstract
Novel cis- and trans-configured bis(oxime)platinum(II) complexes have been synthesized and characterized by elemental analyses, IR, electrospray ionization mass spectrometry, multinuclear (1H, 13C, and 195Pt) NMR spectroscopy, and, in five cases, by X-ray diffraction. Their cytotoxicity was studied in the cisplatin-sensitive CH1 cell line as well as in inherently cisplatin-resistant SW480 cancer cells. Remarkably, every single dihalidobis(oxime)platinum(II) complex (with either a cis or trans configuration) shows a comparable cytotoxic potency in both cell lines, indicating a capacity of overcoming cisplatin resistance. Particularly strong cytotoxicities were observed in the case of trans-[PtCl2(R2C═NOH)2] (R = Me, n-Pr, i-Pr) with IC50 values in the high nanomolar concentration range in both CH1 and SW480 cancer cells. These complexes are as potent as cisplatin in CH1 cells and up to 20 times more potent than cisplatin in SW480 cells. In comparison to transplatin, the novel compounds are up to 90 (CH1) and 120 times (SW480) more cytotoxic. The previously reported observation that the trans geometry yields a more active complex in the case of [PtCl2(Me2C═NOH)2] could be confirmed for at least two structural analogues.
_______________________________________________________________________

Cesium Hydroperoxostannate: First Complete Structural Characterization of a Homoleptic Hydroperoxocomplex

Andrei V. Churakov, Sergey Sladkevich, Ovadia Lev, Tatiana A. Tripol’skaya and Petr V. Prikhodchenko

Inorg. Chem., Article ASAP
DOI: 10.1021/ic100554u
Publication Date (Web): May 11, 2010

Abstract

The crystal structure of cesium hexahydroperoxostannate Cs2Sn(OOH)6 is presented. The compound was characterized by single crystal and by powder X-ray diffraction, FTIR, 119Sn MAS NMR, and TG-DTA. Cs2Sn(OOH)6 crystallizes in the trigonal space group P, a = 7.5575(4), c = 5.1050(6) Å, V = 252.51(4) Å3, Z = 1, R1 = 0.0120 (I > 2σ(I)), wR2 = 0.0293 (all data), and comprises cesium cations and slightly distorted octahedral [Sn(OOH)6]2− anions lying on the threefold axis. The [Sn(OOH)6]2− unit forms 12 interanion hydrogen bonds resulting in anionic chains spread along the c-axis. All six hydroperoxo ligands are crystallographically equivalent; O−O distances are 1.482(2), only slightly longer than the O−O distance in hydrogen peroxide. FTIR and 119Sn MAS NMR reveal the similarity between all alkali hydroperoxostannates.
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J. Phys. Chem. C., v114, Issue 19

Solution State NMR Techniques Applied to Solid State Samples: Characterization of Benzoic Acid Confined in MCM-41

Thierry Azais*, Geoffrey Hartmeyer†, Sandrine Quignard, Guillaume Laurent and Florence Babonneau
J. Phys. Chem. C, 2010, 114 (19), pp 8884–8891
DOI: 10.1021/jp910622m

Abstract:In this paper we present an NMR methodology to characterize small organic molecules confined in mesoporous materials. In particular, we demonstrate that NMR techniques issued from solution state NMR are well suited to characterize benzoic acid encapsulated in hexagonally ordered mesoporous silica MCM-41 possessing two different averaged pore sizes (30 and 100 Å). As evidenced by differential scanning calorimetry, entrapped benzoic acid molecules are highly mobile at room temperature due to confinement effect and possess a glass phase transition temperature around −55 °C. Thus, the 13C NMR characterization of encapsulated molecules has to be adapted to that particular behavior. In particular, the cross-polarization technique traditionally used in solid state NMR to record 13C magic angle spinning (MAS) spectra is of poor efficiency due to weak 1H−13C dipolar interaction. Nevertheless, the presence of 1H−13C cross-relaxation phenomenon (nuclear Overhauser effect, NOE) allows us to record 13C spectra through power-gated techniques, routinely used in solution state NMR, in order to enhance the 13C signal through NOE. Furthermore, the long T2′(1H) values (up to 22 ms) are compatible with the setup of J-coupling-based experiments such as MAS refocused {1H}−13C INEPT experiments allowing us to characterize the sample through chemical bonds. These results combined with those of MAS 1H NOESY experiments lead us to distinguish unambiguously different benzoic acid populations within the large pore sample. Finally, we show that cooling down the samples at −35 °C diminishes the mobility and allows the reintroduction of the 1H−13C dipolar interaction. Thus, 2D MAS {1H}−13C HETCOR experiments can be performed at low temperature to explore spatial proximities.



Spin Canting of Maghemite Studied by 57Fe NMR and In-Field Mssbauer Spectrometry

T. Jean Daou†, Jean-Marc Greneche‡, Seong-Joo Lee§, Soonchil Lee§, Christophe Lefevre†, Sylvie Bgin-Colin† and Genevive Pourroy*†

J. Phys. Chem. C, 2010, 114 (19), pp 8794–8799
DOI: 10.1021/jp100726c

Abstract: Local probe techniques, 57Fe in-field Mssbauer, and 57Fe NMR spectrometries have been combined to describe the magnetic structure of maghemite nanoparticles of 39 (±5) nm in size and commercial maghemite. Maghemite nanoparticles were obtained from oxidation of magnetite nanoparticles. Commercial maghemite consists of nanostructured rods, and the size of crystalline domain fairly compares to that of nanoparticles. The structure of the two samples is a partially disordered spinel structure. Both local probe techniques agree that Fe magnetic moments of octahedral and tetrahedral sites are canted in both systems. It was concluded that the canting originates not only from surface effects but also from the bulk resulting from the disordered spinel structure and the frustrated cationic topology, giving rise to reversed Fe moments.

;o

Natural abundance high field 43Ca solid state NMR in cement science

Igor L. Moudrakovski, Rouhollah Alizadeh and James J. Beaudoin

Phys. Chem. Chem. Phys., 2010 DOI: 10.1039/c000353k

Abstract

This work is a systematic attempt to determine the possibilities and the limitations of the 43Ca high field solid state NMR in the study of cement-based materials. The low natural abundance (0.135%) and small gyromagnetic ratio of 43Ca present a serious challenge even in a high magnetic field. The NMR spectra of a number of cement compounds of known structure and composition are examined. The spectra of several phases important in cement science, e.g., anhydrous beta di-calcium silicate (-C2S) and tri-calcium (C3S) silicate were obtained for the first time and the relation of spectroscopic and structural parameters is discussed. The method was also applied to the hydrated C3S and synthetic calcium silicate hydrates (C–S–H) of different composition in order to understand the state of calcium and transformations in the structure during hydrolysis. The spectra of hydrated C3S reveals a calcium environment similar to that of the C–S–H samples and 11 Å Tobermorite. These observations support the validity of using layered crystalline C–S–H systems as structural models for the C–S–H that forms in the hydration of Portland cement.