Bryan's Journal Update, Part I

I know you've all been on the edge of your seats!

***

This may be useful for the purposes of CASTEP calculations. I think.

Chemical Physics Letters
Volume 484, Issues 4-6, 7 January 2010, Pages 374-379
doi:10.1016/j.cplett.2009.11.041

Influence of plane wave cut-off on structural and electronic properties in Sn-BEA and Ti-BEA zeolite water molecule interaction

Bhakti S. Kulkarni^a, Sailaja Krishnamurty^b and Sourav Pal^a,

^a Physical Chemistry Division, National Chemical Laboratory, Pune 411 008, India

^b Electrochemical Research Institute (CECRI), Karaikudi 630 006, India

Received 12 October 2009;

accepted 21 November 2009.

Available online 26 November 2009.

Abstract

Periodic systems are best described by the pseudo-potential methods. However, the accuracy of its description depends on the cut-off of plane wave basis. This is much more critical in the case of weak interactions, where a clear understanding on the influence of plane wave cut-off on the structural and electronic properties is not readily available in the literature. In the present work, we have taken a metal substituted beta zeolite–H₂O complex for understanding this objective. Our studies show that while a lower cut-off of 500 eV is sufficient for the convergence of the structural parameters, description of energy-dependent properties necessitates a high cut-off value.

***

Chemical Physics Letters
Volume 485, Issues 1-3, 18 January 2010, Pages 217-220
doi:10.1016/j.cplett.2009.11.066

NMR spectroscopy in the milli-Tesla regime: Measurement of ¹H chemical-shift differences below the line width

Stephan Appelt^a, , Stefan Glöggler^b, Friedrich W. Häsing^a, Ulrich Sieling^a, Ali Gordji Nejad^a and Bernhard Blümich^b

^a Zentralinstitut für Elektronik, Forschungszentrum Jülich, D-52425 Jülich, Germany

^b Institut für Technische Chemie und Makromolekulare Chemie, RWTH Aachen University, D-52056 Aachen, Germany

Received 16 October 2009;

accepted 29 November 2009.

Available online 1 December 2009.

Abstract

NMR spectroscopy for chemical analysis at high field employs precision measurements of resonance frequencies governed by chemical shift and nuclear spin interactions. At low field and in the absence of hetero-nuclear J-couplings the natural line width limits the chemical shift measurements. We have performed chemical-shift resolved proton NMR spectra in the milli-Tesla regime, and found that in the presence of hetero-nuclear J-coupling, proton chemical-shift differences smaller than the line width can be measured down to nuclear Larmor frequencies of 41 kHz. The measurement of J-couplings and chemical shifts with simple NMR devices operating in the milli-Tesla regime may develop as an attractive tool for chemical analysis.

***

Chemical Physics Letters
Volume 485, Issues 4-6, 26 January 2010, Pages 275-280
doi:10.1016/j.cplett.2009.12.054

Proton micro-magic-angle-spinning NMR spectroscopy of nanoliter samples

Andreas Brinkmann^{a, b,} , Suresh Kumar Vasa^a, Hans Janssen^a and Arno P.M. Kentgens^{a, ,}

^a Physical Chemistry/Solid State NMR, Institute for Molecules and Materials, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands

^b Steacie Institute for Molecular Sciences, National Research Council, 1200 Montreal Road, M-40 Ottawa, Ontario, Canada K1A 0R6

Received 22 October 2009;

accepted 16 December 2009.

Available online 23 December 2009.

Abstract

We present our recent progress in the development of micro-magic-angle-spinning solenoid-based probeheads for the application in high-resolution ¹H solid-state NMR of nanoliter sample volumes. The use of fused-silica capillaries as sample holders results in spectra without any ¹H background signal. It is possible to obtain ¹H spectra of 40–80 nl samples in a few scans. We obtained high-resolution ¹H spectra employing different homonuclear decoupling sequences on powdered samples of l-alanine, the tripeptide AGG, and a single crystal of l-tyrosine·HCl. In addition, we recorded high-resolution two-dimensional proton-detected ¹H–¹³C heteronuclear correlation spectra of [U-¹³C₃, ¹⁵N]-l-alanine and AGG with natural abundant isotope distribution.

***

Chemical Physics Letters
Volume 485, Issues 4-6, 26 January 2010, Pages 335-342
doi:10.1016/j.cplett.2009.12.044

NMR polarization transfer by second-order resonant recoupling: RESORT

Ingo Scholz^a, Beat H. Meier^a and Matthias Ernst^{, a,}

^a ETH Zurich, Physical Chemistry, 8093 Zurich, Switzerland

Received 13 November 2009;

accepted 15 December 2009.

Available online 22 December 2009.

Abstract

We describe a resonant second-order dipolar recoupling condition for magic-angle spinning (MAS) solid-state NMR where the active spins are irradiated by continuous-wave irradiation and the passive spins by a phase-alternating sequence. The phase-modulation frequency is matched to an integer multiple of the MAS frequency to produce a second-order homonuclear dipolar coupling Hamiltonian that promotes broadband homonuclear zero-quantum polarization transfer on the spin-locked active spins. The recoupling sequence is based on second-order cross terms between two heteronuclear dipolar couplings. Similarities and differences to the proton-assisted recoupling sequence are discussed.

***
Everyone loves ³H NMR!

Chemical Physics Letters
Volume 486, Issues 1-3, 5 February 2010, Pages 21-26
doi:10.1016/j.cplett.2009.12.087

³H NMR of the tritiated isotopologues of methane in nematic liquid-crystal solvents

Dedicated to the memory of Annalaura Segre (deceased 25 April 2008) and Jaap G. Snijders (deceased 13 August 2004).

E. Elliott Burnell^a, Cornelis A. de Lange^b, , Donatella Capitani^c, Giancarlo Angelini^c and Ornella Ursini^c

^a Chemistry Department, University of British Columbia, 2036 Main Mall, Vancouver (BC), Canada V6T 1Z1

^b Atomic, Molecular and Laser Physics, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands

^c Chemical Methodologies Institute, Consiglio Nazionale delle Ricerche, Area della Ricerca di Roma, C.P. 10 00016 Monterotondo Staz. (RM), Italy

Received 18 November 2009;

accepted 29 December 2009.

Available online 4 January 2010.

Abstract

The NMR spectra of the tritiated isotopologues of methane dissolved in several nematic liquid-crystalline solvents are measured. The spectral parameters obtained agree extremely well with those predicted from earlier NMR studies of the deuterated isotopologues, providing excellent confirmation of the theory for vibration–reorientation interaction developed earlier.

***

Chemical Physics Letters
Volume 487, Issues 4-6, 5 March 2010, Pages 232-236
doi:10.1016/j.cplett.2010.01.040

Solid-state ⁹⁵Mo NMR of mixed-valence polyoxomolybdates (V, VI) with localized or delocalized d¹ electrons

Takahiro Iijima^a, Toshihiro Yamase^b, Masataka Tansho^c, Tadashi Shimizu^c and Katsuyuki Nishimura^{a, ,}

^a Institute for Molecular Science, Okazaki 444-8585, Japan

^b Tokyo Institute of Technology, Nagatsuta, Yokohama 226-8503, Japan

^c National Institute for Materials Science, Tsukuba 305-0003, Japan

Received 23 October 2009;

accepted 19 January 2010.

Available online 25 January 2010.

Abstract

We report solid-state ⁹⁵Mo NMR of Mo^V, Mo^V,VI and Mo^VI species in mixed-valence polyoxomolybdates (V, VI) with localized or delocalized d¹ electrons. Parameters about chemical shift and quadrupole interactions of ⁹⁵Mo in diamagnetic crystals of with localized electrons and with delocalized ones were obtained by simulation of magic-angle-spinning (MAS) ⁹⁵Mo NMR spectra. The isotropic and anisotropic chemical shifts of sites of Mo^V in 1 and Mo^{V, VI} in 2, respectively, exhibited absolute values quite larger than those of other Mo^VI sites, which is examined by quantum chemical calculations.

***

Chemical Physics Letters
Volume 487, Issues 4-6, 5 March 2010, Pages 285-290
doi:10.1016/j.cplett.2010.01.048

Oxygen coordination of aluminum cations in dehydrated AlPW₁₂O₄₀ investigated by solid-state NMR spectroscopy

Arne Bressel^a, Jörg Frey^a, Urszula Filek^b, Bogdan Sulikowski^b, Dieter Freude^c and Michael Hunger^a

^a Institute of Chemical Technology, University of Stuttgart, Stuttgart, Germany

^b Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Kraków, Poland

^c Institute of Experimental Physics, University of Leipzig, Leipzig, Germany

Received 4 December 2009;

accepted 20 January 2010.

Available online 25 January 2010.

Abstract

Dehydrated aluminumdodecatungstophosphate (AlPW₁₂O₄₀) was investigated by ²⁷Al MAS NMR spectroscopy in magnetic fields of 9.4 and 17.6 T. Two kinds of octahedrally coordinated (δ_27Al = 1–2 ppm, C_Q = 2.4–2.5 MHz, and δ_27Al = 4–6 ppm, C_Q = 6.0–6.5 MHz), two kinds of penta-coordinated (δ_27Al = 24–30 ppm, C_Q = 7.0–7.3 MHz, and δ_27Al = 44 ppm, C_Q = 7.5–8.7 MHz), and a small amount of tetrahedrally coordinated aluminum cations (δ_27Al = 65 ppm, C_Q = 8.2–8.5 MHz) were found. Comparison with ¹H MAS NMR spectroscopic studies indicates that the dehydroxylation of aluminum OH groups (δ_1H = 4.2 ppm and 5.6 ppm) at temperatures of 473 and 573 K is accompanied by a partially irreversible change of the oxygen coordination of aluminum cations.

***

Chemical Physics Letters
Volume 488, Issues 1-3, 12 March 2010, Pages 10-16
doi:10.1016/j.cplett.2010.01.072

Broadband magnetization transfer using moderate radio-frequency fields for NMR with very high static fields and spinning speeds

Markus Weingarth^a, Geoffrey Bodenhausen^{a, b} and Piotr Tekely^a

^a Département de chimie, associé au CNRS, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris, France

^b Institut des Sciences et Ingénierie Chimiques, BCH, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland

Received 4 January 2010;

accepted 29 January 2010.

Available online 4 February 2010.

Abstract

We introduce a new dipolar recoupling scheme, dubbed PARIS-xy (phase-alternated recoupling irradiation scheme using orthogonal radio-frequency phases), to promote efficient broadband magnetization exchange between ¹³C nuclei using moderate radio-frequency amplitudes at very high magnetic field strengths and spinning speeds. Experimental observations for a wide range of spinning frequencies 30 ν_rot 60 kHz and magnetic field strengths (B₀ = 9.4, 17.6 and 21.2 T) are backed up by numerical simulations.

A solid-state NMR scheme dubbed PARIS-xy affords efficient low-power recoupling of dipolar interactions between nuclei such as carbon-13 over a wide range of isotropic chemical shifts. The scheme is suitable for very high magnetic fields up to 21.2 T (900 MHz) and spinning speeds up to 60 kHz.

***

Chemical Physics Letters
Volume 488, Issues 4-6, 22 March 2010, Pages 168-172
doi:10.1016/j.cplett.2010.02.015

DFT study of possible lattice defects in methane-hydrate and their appearance in ¹³C NMR spectra

Péter Terleczky^a and László Nyulászi

^a Budapest University of Technology and Economics, Department of Inorganic and Analytical Chemistry, H-1521 Szt Gellért tér 4, Budapest, Hungary

Received 14 December 2009;

accepted 9 February 2010.

Available online 12 February 2010.

Abstract

The effect of the possible cell defects in the methane-hydrate crystal on the chemical shift of the carbon core has been investigated by DFT calculations. The clathrate structure was modeled as a water monolayer, in mono and bicavital clusters. The results show that the radius of the clathrate cell correlates with the chemical shielding of the carbon core. The calculated chemical shifts for the most stable clusters are in good agreement with the observed NMR signals supporting the previous spectral assignment. The occupancy of a neighbouring cell in a bicavital cluster has a small effect on the calculated NMR shift.

***

Chemical Physics Letters
Volume 489, Issues 1-3, 1 April 2010, Pages 35-38
doi:10.1016/j.cplett.2010.02.051

A theoretical study of the stationary structures of the methane surface with special emphasis on NMR properties

Ibon Alkorta and José Elguero^a

^a Instituto de Química Médica (CSIC), Juan de la Cierva, 3, E-28006 Madrid, Spain

Received 22 January 2010;

accepted 18 February 2010.

Available online 21 February 2010.

Abstract

The seven stationary points of the methane hypersurface were first explored concerning geometries and energies to check previous data. On these geometries, absolute ¹H and ¹³C NMR shieldings as well as ¹J(CH) and ²J(HH) coupling constants were calculated. The results show important variations in the NMR parameters depending on the stationary point considered. Relationships have been found between the ¹H and ¹³C shieldings and between these NMR parameters and the relative energy of the different species.

***

Chemical Physics Letters
Volume 489, Issues 1-3, 1 April 2010, Pages 107-112
doi:10.1016/j.cplett.2010.02.026

¹H NMR noise measurements in hyperpolarized liquid samples

Patrick Giraudeau^{a, 1}, Norbert Müller^b, Alexej Jerschow^c and Lucio Frydman^a

^a Department of Chemical Physics, Weizmann Institute of Science, 76100 Rehovot, Israel

^b Institute of Organic Chemistry, Johannes Kepler University, Altenbergerstraße 69, A-4040 Linz, Austria

^c Chemistry Department, New York University, New York, NY 10003, United States

Received 31 August 2009;

accepted 9 February 2010.

Available online 12 February 2010.

Abstract

Noise measurements of nuclear spin systems using a tuned circuit can reveal the signatures of two different phenomena: Thermal circuit noise absorbed by the spin system, and nuclear spin-noise leading to tiny fluctuating magnetization components. Polarization enhancement can increase the observed noise amplitudes due to an enlarged coupling with the reception circuit. In this work we explore the detection of noise in ¹H NMR of liquid water samples whose spin alignment is enhanced via ex situ dynamic nuclear polarization. A number of ancillary phenomena related to this kind of experiments are also documented.

***

Chemical Physics Letters
Volume 489, Issues 4-6, 9 April 2010, Pages 248-253
doi:10.1016/j.cplett.2010.02.078

Characterization of the ¹⁹F chemical shielding tensor using cross-correlated spin relaxation measurements and quantum chemical calculations

S. Begam Elavarasi^a and Kavita Dorai^b

^a Department of Physics, Indian Institute of Technology-Madras, Chennai 600 036, India

^b Department of Physics, Indian Institute of Science Education and Research (IISER) Mohali, Chandigarh 160 019, India

Received 14 January 2010;

accepted 28 February 2010.

Available online 3 March 2010.

Abstract

The ¹⁹F chemical shift anisotropy (CSA) tensor is an indispensable structure estimation tool in the NMR investigations of flourinated biomolecules. This work focuses on the characterization of the ¹⁹F CSA tensor in small molecules, through the combined use of quantum chemical methods and liquid-state NMR cross-correlated spin relaxation experiments. The effect of different basis sets and quantum computational methods on the magnitude and orientation of the ¹⁹F CSA tensor are discussed. The results from ab initio methods and the liquid-state relaxation experiments match well and are comparable to values of the CSA tensor obtained from previous solid-state studies and from theoretical investigations of similar molecules.

***

Journal of Solid State Chemistry
Volume 183, Issue 1, January 2010, Pages 120-127
doi:10.1016/j.jssc.2009.10.006

MAS-NMR studies of lithium aluminum silicate (LAS) glasses and glass–ceramics having different Li2O/Al2O3 ratio

A. Ananthanarayanana, G.P. Kothiyala, L. Montagneb and B. Revelb

Keywords: Glass; Glass–ceramics; Silicates; Crystallization; MAS-NMR; XRD

Emergence of phases in lithium aluminum silicate (LAS) glasses of composition (wt%) xLi2O–71.7SiO2–(17.7−x)Al2O3–4.9K2O–3.2B2O3–2.5P2O5 (5.1≤x≤12.6) upon heat treatment were studied. 29Si, 27Al, 31P and 11B MAS-NMR were employed for structural characterization of both LAS glasses and glass–ceramics. In glass samples, Al is found in tetrahedral coordination, while P exists mainly in the form of orthophosphate units. B exists as BO3 and BO4 units. 27Al NMR spectra show no change with crystallization, ruling out the presence of any Al containing phase. Contrary to X-ray diffraction studies carried out, 11B (high field 18.8 T) and 29Si NMR spectra clearly indicate the unexpected crystallization of a borosilicate phase (Li,K)BSi2O6, whose structure is similar to the aluminosilicate virgilite. Also, lithium disilicate (Li2Si2O5), lithium metasilicate (Li2SiO3) and quartz (SiO2) were identified in the 29Si NMR spectra of the glass–ceramics. 31P NMR spectra of the glass–ceramics revealed the presence of Li3PO4 and a mixed phase (Li,K)3PO4 at low alkali concentrations.
______________________________________________________________________________

J. Phys. Chem. A, 2010, 114 (18), pp 5743–5751
DOI: 10.1021/jp100889t

A System for NMR Stark Spectroscopy of Quadrupolar Nuclei

Matthew R. Tarasek and James G. Kempf

Electrostatic influences on NMR parameters are well accepted. Experimental and computational routes have been long pursued to understand and utilize such Stark effects. However, existing approaches are largely indirect informants on electric fields, and/or are complicated by multiple causal factors in spectroscopic change. We present a system to directly measure quadrupolar Stark effects from an applied electric (E) field. Our apparatus and applications are relevant in two contexts. Each uses a radiofrequency (rf) E field at twice the nuclear Larmor frequency (2ω0). The mechanism is a distortion of the E-field gradient tensor that is linear in the amplitude (E0) of the rf E field. The first uses 2ω0 excitation of double-quantum transitions for times similar to T1 (the longitudinal spin relaxation time). This perturbs the steady state distribution of spin population. Nonlinear analysis versus E0 can be used to determine the Stark response rate. The second context uses POWER (perturbations observed with enhanced resolution) NMR. Here, coherent, short-time (T2, the transverse relaxation rate) excitation at 2ω0 is synchronized with an NMR multiple-pulse line-narrowing sequence. Linear analysis of the Stark response is then possible: a quadrupolar multiplet with splitting proportional to E0. The POWER sequence converts the 2ω0 interaction from off-diagonal/nonsecular to the familiar diagonal form (Iz2) of static quadrupole interactions. Meanwhile, background contributions to line width are averaged to zero, providing orders-of-magnitude resolution enhancement for correspondingly high sensitivity to the Stark effect. Using GaAs as a test case with well-defined Stark response, we provide the first demonstration of the 2ω0 effect at high-field (14.1 T) and room temperature. This, along with the simplicity of our apparatus and spectral approach, may facilitate extensions to a wider array of material and molecular systems. The POWER context, which has not previously been tested, is detailed here with new design insights. Several key aspects are demonstrated here, while complete implementation is to be presented at a later time. At present, we (1) account for finite pulse times in pulse sequence design, (2) demonstrate two-channel phase coherence for magnetic (ω0) and electric (2ω0) excitation, and (3) provide line narrowing by a factor of 103. In addition, we find that certain anomalous contributions to the line shape, observed in previous low-field (250 mT) applications, are absent here.

Synlett

Immobilization of TEMPO Derivatives in Saponite and Use of These Novel Hybrid Materials as Reusable Catalysts

Roben C , Studer A, Hemme WL, Eckert H
SYNLETT Issue: 7 Pages: 1110-1114 Published: APR 2010

Abstract: The letter describes a novel approach for immobilization of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) derivatives by cation-exchange reaction of TEMPO ammonium salts in a commercially available saponite. The organic-inorganic hybrid material is readily prepared and characterized by solid-state H-1 NMR spectroscopy. The hybrid material can be used as recyclable catalyst for oxidation of various alcohols. High catalytic activity for up to 10 runs is obtained. Leaching of the nitroxide salt out of the saponite occurs to a small extent. However, original high activity of the hybrid material can be restored by simply reloading the hybrid material with nitroxide salt by cation exchange.

Journal of Physical Chemistry C, vol. 114, Issue 18

The Role of the Cluster on the Relaxation of Endohedral Fullerene Cage Carbons: A NMR Spin−Lattice Relaxation Study of an Internal Relaxation Reagent

Sabrina Klod, Lin Zhang and Lothar Dunsch*

J. Phys. Chem. C, 2010, 114 (18), pp 8264–8267
DOI: 10.1021/jp101218p

Abstract: The endohedral cluster fullerenes Ih-Sc3N@C80, Ih-Y3N@C80, and Ih-Lu3N@C80 were investigated with respect to the strategy of an internal relaxation reagent by following the cluster size effects and the influence of f-electrons on the carbon relaxation. For endohedral nitride cluster fullerenes of Ih-C80 cage symmetry increased relaxation rates are observed. In general, the enlarged cage size increases the relaxation of the carbons. The encapsulated metal atoms give an additional dipole−dipole interaction to the relaxation rate of the carbon atoms depending on their magnetic character. For different metals the increased nitride cluster size is one reason for the observed stronger dipole−dipole interaction. In contrast, a higher shielding of a metal nucleus by its electron shell leads to a reduced magnetic effect. The negative charge on the cage increases the electron density, thus decreasing T1. In temperature-dependent studies, the diffusion is fast compared to the rotation of the molecule at higher temperatures which is typical for the spherical shape of the fullerene cage. Thus, only a minor deformation of the cage by the endohedral voluminous cluster is found. The shape of the cage is preserved and less influenced by the type and size of the cluster.



Fabrication of Hierarchical Channel Wall in Al-MCM-41 Mesoporous Materials to Enhance Their Adsorptive Capability: Why and How?

Fang Na Gu†‡, Feng Wei†, Jia Yuan Yang†, Ying Wang*‡ and Jian Hua Zhu*†
Key Laboratory of Mesoscopic Chemistry of MOE, College of Chemistry and Chemical Engineering, and Ecomaterials and Renewable Energy Research Center (ERERC), Nanjing University, Nanjing 210093, China
J. Phys. Chem. C, 2010, 114 (18), pp 8431–8439
DOI: 10.1021/jp1009143

Abstract:To overcome the inefficiency of mesoporous materials in the adsorption of small molecules, this article reports the effort how to create hierarchical channel wall in Al-MCM-41 and more important, how to distinguish the contribution of the newly formed micropores in adsorption by the mesoporous materials. Fabrication of hierarchical channel wall is realized through extracting framework aluminum of sample by acid leach to create micropores and defects, providing the fine geometric confinement toward tiny targets. The influence of original Al content of Al-MCM-41 on the controlled dealumination was studied, and X-ray diffraction, N2 adsorption−desorption, 27Al and 29Si MAS NMR, Fourier transform IR techniques were employed to characterize the resulting samples. Besides, volatile nitrosamine N-nitrosopyrrolidine (NPYR) was chosen as a probe to assess the adsorption of the resulting samples. Hierarchical channel wall in Al-MCM-41 significantly increased its ability to trap NPYR, and for the first time the adsorptive contribution of newly formed micropores and defects in the mesoporous silica was distinguished by the instantaneous adsorption under the carrier gas with different flow rate, which is beneficial for developing new functional materials to protect environment.



Structure, Connectivity, and Configurational Entropy of GexSe100−x Glasses: Results from 77Se MAS NMR Spectroscopy

E. L. Gjersing and S. Sen*, B. G. Aitken
J. Phys. Chem. C, 2010, 114 (18), pp 8601–8608
DOI: 10.1021/jp1014143

Abstract:High-resolution 77Se MAS NMR spectroscopy has been conducted at 11.7 T to investigate the short-and intermediate- range structure and chemical order in binary GexSe100−x glasses with 5 ≤ x ≤ 33.33. Four distinct Se environments are observed for the first time, corresponding to Se−Se−Se and Ge−Se−Se linkages as well as Ge−Se−Ge sites where the Se atom is shared by two GeSe4 tetrahedra in either corner-sharing or edge-sharing configuration. Assignments of corner and edge-shared tetrahedra were made based on the 77Se MAS NMR spectrum of crystalline β-GeSe2. Analysis of the compositional variation of the relative concentrations of these Se sites indicates that the structure of GexSe100−x glasses in this composition range can be described as a randomly interconnected network of GeSe4 tetrahedra and chains of Se atoms. The implications of this structural model are discussed in relation to the composition dependence of the glass-forming ability and kinetic fragility of the corresponding parent liquids.

Journal of Physical Chemistry B, vol. 114, Issues 18

Molecular Level Characterization of the Inorganic−Bioorganic Interface by Solid State NMR: Alanine on a Silica Surface, a Case Study

Ira Ben Shir†, Shifi Kababya†, Tal Amitay-Rosen‡, Yael S. Balazs† and Asher Schmidt*†

J. Phys. Chem. B, 2010, 114 (18), pp 5989–5996
DOI: 10.1021/jp100114v
Publication Date (Web): April 16, 2010

Abstract: The molecular interface between bioorganics and inorganics plays a key role in diverse scientific and technological research areas including nanoelectronics, biomimetics, biomineralization, and medical applications such as drug delivery systems and implant coatings. However, the physical/chemical basis of recognition of inorganic surfaces by biomolecules remains unclear. The molecular level elucidation of specific interfacial interactions and the structural and dynamical state of the surface bound molecules is of prime scientific importance. In this study, we demonstrate the ability of solid state NMR methods to accomplish these goals. l-[1-13C,15N]Alanine loaded onto SBA-15 mesoporous silica with a high surface area served as a model system. The interacting alanine moiety was identified as the −NH3+ functional group by 15N{1H}SLF NMR. 29Si{15N} and 15N{29Si}REDOR NMR revealed intermolecular interactions between the alanine −NH3+ and three to four surface Si species, predominantly Q3, with similar internuclear N···Si distances of 4.0−4.2 Å. Distinct dynamic states of the adsorbed biomolecules were identified by 15N{13C}REDOR NMR, indicating both bound and free alanine populations, depending on hydration level and temperature. In the bound populations, the −NH3+ group is surface anchored while the free carboxylate end undergoes librations, implying the carboxylate has small or no contributions to surface binding. When surface water clusters grow bigger with increased hydration, the libration amplitude of the carboxyl end amplifies, until onset of dissolution occurs. Our measurements provide the first direct, comprehensive, molecular-level identification of the bioorganic−inorganic interface, showing binding functional groups, geometric constraints, stoichiometry, and dynamics, both for the adsorbed amino acid and the silica surface.



Selective Chemical Shift Assignment of Bacteriochlorophyll a in Uniformly [13C−15N]-Labeled Light-Harvesting 1 Complexes by Solid-State NMR in Ultrahigh Magnetic Field

Anjali Pandit*, Francesco Buda, Adriaan J. van Gammeren†, Swapna Ganapathy and Huub J. M. de Groot
Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
J. Phys. Chem. B, 2010, 114 (18), pp 6207–6215
DOI: 10.1021/jp100688u

Abstract: Magic-angle spinning (MAS) 13C−13C correlation NMR spectroscopy was used to resolve the electronic ground state characteristics of the bacteriochlorophyll a (BChl a) cofactors in light-harvesting 1 (LH1) complexes of Rhodopseudomonas acidophila (strain 10050). The BChl a 13C isotropic chemical shifts of the LH1 complexes are compared to the 13C chemical shifts for BChl a dissolved in acetone-d6 and to 13C NMR data that has been obtained for the B800 and B850 BChl molecules in Rps. acidophila peripheral light-harvesting complexes (LH2). Since both complexes contain BChl a cofactors, we can address the chemical shift variability for specific carbon responses between the two types of antennae. The global shift pattern of the LH1 BChl's resembles the shift patterns of the LH2 α- and β-B850 BChl's, while some carbon responses, in particular the C3 and C31, show significant deviations. A comparison with density functional theory (DFT) shift calculations provides insight into the BChl concomitant structural and electronic interactions in the ground state. The differences in the LH1 BChl observed chemical shifts relative to the 13C responses of BChl a in solution cannot be explained by local side chain interactions, such as hydrogen bonding or nonplanarity of the C3 acetyl, but appear to be dominated by protein-induced macrocycle distortion. Such shaping of the macrocycle will contribute significantly to the red shift of the BChl Qy absorbance band in purple bacterial light-harvesting complexes.




Solid-State 137Ba NMR Spectroscopy: An Experimental and Theoretical Investigation of

Hiyam Hamaed†, Eric Ye‡, Konstantin Udachin§ and Robert W. Schurko*†

J. Phys. Chem. B, 2010, 114 (18), pp 6014–6022
DOI: 10.1021/jp102026m

Abstract: Ultrawideline 137Ba SSNMR spectra of several barium-containing systems (barium nitrate, barium carbonate, barium chlorate monohydrate, barium chloride dihydrate, anhydrous barium chloride, and barium hydrogen phosphate) were acquired at two different magnetic field strengths (9.4 and 21.1 T) using frequency-stepped techniques. The recently reported WURST−QCPMG pulse sequence (O’Dell et al. Chem. Phys. Lett. 2008, 464, 97−102) is shown to be very useful for rapidly acquiring high signal-to-noise 137Ba SSNMR spectra. The breadths of the second-order quadrupolar-dominated spectra and experimental times are notably reduced for experiments conducted at 21.1 T. Analytical simulations of the 137Ba SSNMR spectra at both fields yield the quadrupolar parameters, and in select cases the barium chemical shift anisotropies (CSAs). Quadrupolar interactions dominate the 137Ba powder patterns, with quadrupolar coupling constants, CQ(137Ba), ranging from 7.0 to 28.8 MHz. The 137Ba electric field gradient (EFG) parameters extracted from these spectra are correlated to the local environments at the barium sites, via consideration of molecular symmetry and structure, and first principles calculations of 137Ba EFG tensors performed using CASTEP software. The rapidity with which 137Ba SSNMR spectra can be acquired using the WURST pulse sequence and/or at ultrahigh magnetic fields and the sensitivity of the 137Ba EFG tensor parameters to the changes in the barium environment suggest that 137Ba SSNMR has great potential for structural characterization of a variety of barium-containing materials.

Phys. Chem. Chem. Phys., 2010, vol. 12, Issue 18 and 19

Phys. Chem. Chem. Phys., 2010, 12, 4813 - 4820, DOI: 10.1039/b927449a

Full quadrupolar tensor determination by NMR using a micro-crystal spinning at the magic angle

Suresh Kumar Vasa, Ernst R. H. van Eck, J. W. G. Janssen and Arno P. M. Kentgens

An implementation of rotor-synchronised Magic Angle Spinning (MAS) NMR is presented to determine the quadrupolar coupling tensor values from a single crystal study for half-integer quadrupolar nuclei. Using a microcoil based probehead for studying micro crystals with superior sensitivity, we successfully determine the full quadrupolar tensor of 23Na using a micro crystal of dimensions 210 × 210 × 700 m of NaNO3 as a model system. A two step simulation procedure is used to obtain the orientation of the quadrupolar tensor information from the experimental spectra and is verified by XRD analysis.



Phys. Chem. Chem. Phys., 2010, 12, 5126 - 5139, DOI: 10.1039/b921383j

Understanding the NMR chemical shifts for 6-halopurines: role of structure, solvent and relativistic effects

Stanislav Standara, Kateina Maliáková, Radek Marek, Jaromír Marek, Michal Hocek, Juha Vaara and Michal Straka

A prototypical study of NMR chemical shifts in biologically relevant heteroaromatic compounds containing a heavy halogen atom is presented for two isomers of halogen-substituted purines. Complete sets of 1H-, 13C- and 15N-NMR chemical shifts are determined experimentally in solution. Experimental results are complemented by quantum-chemical calculations that provide understanding of the trends in the chemical shifts for the studied compounds and which show how different physical effects influence the NMR parameters. Chemical shifts for isolated molecules are calculated using density-functional theory methods, the role of solvent effects is studied using polarised continuum models, and relativistic corrections are calculated using the leading-order Breit–Pauli perturbation theory. Calculated values are compared with the experimental data and the effects of structure, solvent and relativity are discussed. Overall, we observe a good agreement of theory and experiment. We find out that relativistic effects cannot be neglected even in the chlorine species when aiming at high precision and a good agreement with the experimental data. Relativity plays a crucial role in the bromine and iodine species. Solvent effects are of smaller importance for 13C shifts but are shown to be substantial for particular 15N shifts. The test of method performance shows that the BLYP and B3LYP functionals provide the most reliable computational results after inclusion of the solvent and relativistic effects while BHandHLYP may—depending on atom in question—slightly improve but mostly deteriorate the data. Ab initio Hartree–Fock suffers from triplet instability in the Breit–Pauli relativistic part while MP2 provides no clear improvement over DFT in the nonrelativistic region. This work represents the first full application of the Breit–Pauli perturbation theory to an organic chemistry problem.

J. Phys. Chem. C., vol. 114, Issue 17

Solid-State 65Cu and 31P NMR Spectroscopy of Bis(triphenylphosphine) Copper Species

Bryan E. G. Lucier†, Joel A. Tang†, Robert W. Schurko*†, Graham A. Bowmaker‡, Peter C. Healy§ and John V. Hanna*

J. Phys. Chem. C, 2010, 114 (17), pp 7949–7962
DOI: 10.1021/jp907477m

Abstract: Frequency-stepped ultrawideline (UW) 65Cu solid-state NMR (SSNMR) experiments have been performed on a series of nine bis(triphenylphosphine) copper(I) species, with eight of these having an oxyanion-based ligand and one a borohydride ligand. These copper atoms reside in spherically asymmetric environments featuring two covalent Cu−P bonds and coordination from single bidentate ligands. The QCPMG pulse sequence was utilized in NMR experiments on all of the samples, along with the WURST-QCPMG sequence on select samples, to acquire UWNMR spectra of high quality. In all cases, large 65Cu quadrupolar coupling constants (CQ) between 40.8 and 51.7 MHz are observed, and are confirmed by NQR measurements. The immense quadrupolar interactions and their correspondingly large contributions to the central-transition powder patterns make accurate quantification of copper chemical shift anisotropy (CSA) difficult, though CSA effects are observed. 1H−31P CP/MAS NMR spectra reveal one-bond J-couplings, 1J(65/63Cu, 31P), for all complexes, as well as the presence of residual dipolar coupling, which enables determinations of both the sign of CQ and the orientation of the EFG tensor with respect to the Cu−P dipolar vector (both of which are unavailable from standard 65Cu SSNMR experiments). The 65Cu EFG parameters and 1J(65/63Cu, 31P) coupling constants are sensitive to the local geometry and bond lengths about the Cu center. Ab initio calculations are used to confirm experimentally predicted orientations of the Cu EFG tensors, to predict experimental CQ, ηQ, and CS tensor values, and to aid in identifying relationships between the copper NMR parameters and molecular structures. This combination of experimental and theoretical NMR data enables the correlation of symmetry and local structure with copper NMR parameters, further extending the applicability of copper SSNMR spectroscopy to a wide variety of copper-containing systems.

Organometallics, vol. 29, Issue 9

There is no solid-state NMR in this article, but, it is a very handy set of reference data.

NMR Chemical Shifts of Trace Impurities: Common Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist

Gregory R. Fulmer*†, Alexander J. M. Miller‡, Nathaniel H. Sherden‡, Hugo E. Gottlieb§, Abraham Nudelman§, Brian M. Stoltz‡, John E. Bercaw‡ and Karen I. Goldberg†

Organometallics, 2010, 29 (9), pp 2176–2179
DOI: 10.1021/om100106e

Abstract: Tables of 1H and 13C NMR chemical shifts have been compiled for common organic compounds often used as reagents or found as products or contaminants in deuterated organic solvents. Building upon the work of Gottlieb, Kotlyar, and Nudelman in the Journal of Organic Chemistry, signals for common impurities are now reported in additional NMR solvents (tetrahydrofuran-d8, toluene-d8, dichloromethane-d2, chlorobenzene-d5, and 2,2,2-trifluoroethanol-d3) which are frequently used in organometallic laboratories. Chemical shifts for other organics which are often used as reagents or internal standards or are found as products in organometallic chemistry are also reported for all the listed solvents.

Energy Fuels, 2010, 24 (4), pp 2536–2544

Structural Features of a Bituminous Coal and Their Changes during Low-Temperature Oxidation and Loss of Volatiles Investigated by Advanced Solid-State NMR Spectroscopy
J.-D. Mao, A. Schimmelmann, M. Mastalerz, P. G. Hatcher and Y. Li

Abstract
Quantitative and advanced 13C solid-state NMR techniques were employed to investigate (i) the chemical structure of a high volatile bituminous coal, as well as (ii) chemical structural changes of this coal after evacuation of adsorbed gases, (iii) during oxidative air exposure at room temperature, and (iv) after oxidative heating in air at 75 °C. The solid-state NMR techniques employed in this study included quantitative direct polarization/magic angle spinning (DP/MAS) at a high spinning speed of 14 kHz, cross polarization/total sideband suppression (CP/TOSS), dipolar dephasing, CH, CH2, and CHn selection, 13C chemical shift anisotropy (CSA) filtering, two-dimensional (2D) 1H−13C heteronuclear correlation NMR (HETCOR), and 2D HETCOR with 1H spin diffusion. With spectral editing techniques, we identified methyl CCH3, rigid and mobile methylene CCH2C, methine CCH, quaternary Cq, aromatic CH, aromatic carbons bonded to alkyls, small-sized condensed aromatic moieties, and aromatic C−O groups. With direct polarization combined with spectral-editing techniques, we quantified 11 different types of functional groups. 1H−13C 2D HETCOR NMR experiments indicated spatial proximity of aromatic and alkyl moieties in cross-linked structures. The proton spin diffusion experiments indicated that the magnetization was not equilibrated at a 1H spin diffusion time of 5 ms. Therefore, the heterogeneity in spatial distribution of different functional groups should be above 2 nm. Recoupled C−H long-range dipolar dephasing showed that the fraction of large charcoal-like clusters of polycondensed aromatic rings was relatively small. The exposure of this coal to atmospheric oxygen at room temperature for 6 months did not result in obvious chemical structural changes of the coal, whereas heating at 75 °C in air for 10 days led to oxidation of coal and generated some COO groups. Evacuation removed most volatiles and caused a significant reduction in aliphatic signals in its DP/MAS spectrum. DP/MAS, but not CP/MAS, allowed us to detect the changes during low-temperature oxidation and loss of volatiles. These results demonstrate the applicability of advanced solid-state NMR techniques in chemical characterization of coal.

Angewandte Chemie International Edition Dec 30-Apr 13

Angewandte Chemie International Edition
Volume 49 Issue 20, Pages 3481 - 3484
Published Online: 13 Apr 2010
Nuclear Magnetic Resonance Using a Spatial Frequency Encoding: Application to J-Edited Spectroscopy along the Sample
Nicolas Giraud, Dr., Laetitia Béguin, Jacques Courtieu, Prof., Denis Merlet, Prof.
Keywords: homonuclear coupling • NMR spectroscopy • pulsed-field gradients • spatial encoding
Abstract: Finger on the pulse: Selective experiments can be simultaneously run on different parts of the sample when NMR sequences based on a spatial encoding are used. This approach was applied to a gradient-encoded selective refocusing sequence. The resultingdata provide a collection of all the couplings that involve a given proton spin, which can be conveniently assigned and measuredfrom only one spectrum.
10.1002/anie.200907103

Angewandte Chemie International Edition
Volume 49 Issue 6, Pages 1071 - 1074
Published Online: 7 Jan 2010
2D TR-NOESY Experiments Interrogate and Rank Ligand-Receptor Interactions in Living Human Cancer Cells
Silvia Mari, Chiara Invernizzi, Andrea Spitaleri, Luca Alberici, Michela Ghitti, Claudio Bordignon, Catia Traversari,Gian-Paolo Rizzardi, Giovanna Musco
Keywords: drug design • integrins • NMR spectroscopy • protein-ligand interactions
Abstract: Cell mates: Various ligand-receptor interactions in different human cancer cell lines were probed directly by two-dimensionaltransferred-NOE spectroscopy (see picture) to prove recognition specificity and determine an affinity ranking of severalligands.
10.1002/anie.200905941

Angewandte Chemie International Edition
Volume 49 Issue 6, Pages 1083 - 1086
Published Online: 30 Dec 2009
NMR Spectra of Terminal Oxo Gold and Platinum Complexes: Relativistic DFT Predictions
Alessandro Bagno, Riccardo Bini
Keywords: density functional calculations • platinum • polyoxometalates • terminal oxo complexes • tungsten
Abstract: Missing in action: Relativistic density-functional methods provide a reliable framework to predict the features of 195Pt,183W, and 17O NMR spectra of terminal oxo Pt and Au complexes (see picture for [P2W20O70Au(O)(OH2)3]9-; Au yellow, W blue,P orange, O red, H white). The complexes have an extremely small HOMO-LUMO gap, and both orbitals are localized on an MOfragment.
10.1002/anie.200905507

MRC - up to May 2010

Magnetic Resonance in Chemistry, ASAP

A comparison of experimental and DFT calculations of 195Pt NMR shielding trends for [PtXnY6-n]2- (X, Y = Cl, Br, F and I) anions
from Magnetic Resonance in Chemistry by Marga R. Burger, J. Kramer, H. Chermette, Klaus R. Koch

A comparison between experimental and calculated gas-phase as well as the conductor-like screening model DFT 195Pt chemical shifts of a series of octahedral [PtX6-nYn]2- complexes for X = Cl, Br, F, I was carried out to assess the accuracy of computed NMR shielding and to gain insight into the dominant [sigma]dia, [sigma]para and [sigma]SO shielding contributions. The discrepancies between the experimental and the DFT-calculated 195Pt chemical shifts vary for these complexes as a function of the coordinated halide ions, the largest being obtained for the fluorido-chlorido and fluorido-bromido complexes, while negligible discrepancies are found for the [PtCl6-nBrn]2- series; the discrepancies are somewhat larger where a significant deviation from the ideal octahedral symmetry such as for the geometric cis/trans or fac/mer isomers of [PtF6-nCln]2- and [PtF6-nBrn]2- may be expected. The discrepancies generally increase in the order [PtCl6-nBrn]2- < [PtBr6-nIn]2- < [PtCl6-nIn]2- < [PtF6-nBrn]2-[ap] [PtF6-nCln]2-, and show a striking correlation with the increase in electronegativity difference [Delta][chi] between the two halide ligands (X- and Y-) bound to Pt(IV) for these anions: 0.09

Digital Object Identifier (DOI)
10.1002/mrc.2607 About DOI

--

Magnetic Resonance in Chemistry
Volume 48 Issue 4, Pages 270 - 275
Published Online: 22 Feb 2010

Structural characterization of silver dialkylphosphite salts using solid-state 109Ag and 31P NMR spectroscopy, IR spectroscopy and DFT calculations
from Magnetic Resonance in Chemistry by Fu Chen, Roderick E. Wasylishen

High-resolution solid-state 109Ag and 31P NMR spectroscopy was used to investigate a series of silver dialkylphosphite salts, Ag(O)P(OR)2 (R = CH3, C2H5, C4H9 and C8H17), and determine whether they adopt keto, enol or dimer structures in the solid state. The silver chemical shift, CS, tensors and |J(109Ag, 31P)| values for these salts were determined using 109Ag ([Xi] = 4.652%) NMR spectroscopy. The magnitudes of J(109Ag, 31P) range from 1250 ± 10 to 1318 ± 10 Hz and are the largest reported so far. These values indicate that phosphorus is directly bonded to silver for all these salts and thus exclude the enol structure. All 31P NMR spectra exhibit splittings due to indirect spin-spin coupling to 107Ag (I = 1/2, NA = 51.8%) and 109Ag (I = 1/2, NA = 48.2%). The 1J(109Ag, 31P) values measured by both 109Ag and 31P NMR spectroscopy agree within experimental error. Analysis of 31P NMR spectra of stationary samples for these salts allowed the determination of the phosphorus CS tensors. The absence of characteristic P[double bond]O stretching absorption bands near 1250 cm-1 in the IR spectra for these salts exclude the simple keto tautomer. Thus, the combination of solid-state NMR and IR results indicate that these silver dialkylphosphite salts probably have a dimer structure. Values of silver and phosphorus CS tensors as well as 1J(109Ag, 31P) values for a dimer model calculated using the density functional theory (DFT) method are in agreement with the experimental observations.

Digital Object Identifier (DOI)
10.1002/mrc.2572

--
Magnetic Resonance in Chemistry
Volume 48 Issue 4, Pages 297 - 303
Published Online: 2 Mar 2010

Distribution and mobility of phosphates and sodium ions in cheese by solid-state 31P and double-quantum filtered 23Na NMR spectroscopy
from Magnetic Resonance in Chemistry by Mallory Gobet, Corinne Rondeau-Mouro, Solange Buchin, Jean-Luc Le Quéré, Elisabeth Guichard, Loïc Foucat, Céline Moreau

The feasibility of solid-state magic angle spinning (MAS) 31P nuclear magnetic resonance (NMR) spectroscopy and 23Na NMR spectroscopy to investigate both phosphates and Na+ ions distribution in semi-hard cheeses in a non-destructive way was studied. Two semi-hard cheeses of known composition were made with two different salt contents. 31P Single-pulse excitation and cross-polarization MAS experiments allowed, for the first time, the identification and quantification of soluble and insoluble phosphates in the cheeses. The presence of a relatively 'mobile' fraction of colloidal phosphates was evidenced. The detection by 23Na single-quantum NMR experiments of all the sodium ions in the cheeses was validated. The presence of a fraction of 'bound' sodium ions was evidenced by 23Na double-quantum filtered NMR experiments. We demonstrated that NMR is a suitable tool to investigate both phosphates and Na+ ions distributions in cheeses. The impact of the sodium content on the various phosphorus forms distribution was discussed and results demonstrated that NMR would be an important tool for the cheese industry for the processes controls. Copyright © 2010 John Wiley & Sons, Ltd.

Keywords
NMR • 23Na • 31P • double-quantum filter • magic angle spinning • solid state • bound sodium ions • phosphate distribution • semi-hard cheese

Digital Object Identifier (DOI)
10.1002/mrc.2576 About DOI

Chem. Soc. Rev. - up to May 2010 - Diagnosis of Cancer and NMR

Review
Magnetic Resonance Spectroscopy in Metabolic and Molecular Imaging and Diagnosis of Cancer
Kristine Glunde*†‡, Dmitri Artemov†‡, Marie-France Penet†, Michael A. Jacobs†‡ and Zaver M. Bhujwalla*†‡
Chem. Rev., Article ASAP
DOI: 10.1021/cr9004007
Publication Date (Web): April 12, 2010

Art and NMR: Acc. Chem. Res. update, May 2010

Noninvasive Testing of Art and Cultural Heritage by Mobile NMR
Bernhard Blmich*‡, Federico Casanova‡, Juan Perlo‡, Federica Presciutti§, Chiara Anselmi§ and Brenda Doherty§
Acc. Chem. Res., Article ASAP
DOI: 10.1021/ar900277h

Nuclear magnetic resonance (NMR) has many applications in science, medicine, and technology. Conventional instrumentation is large and expensive, however, because superconducting magnets offer maximum sensitivity. Yet NMR devices can also be small and inexpensive if permanent magnets are used, and samples need not be placed within the magnet but can be examined externally in the stray magnetic field. Mobile stray-field NMR is a method of growing interest for nondestructive testing of a diverse range of materials and processes. A well-known stray-field sensor is the commercially available NMR-MOUSE, which is small and can readily be carried to an object to be studied.

In this Account, we describe mobile stray-field NMR, with particular attention to its use in analyzing objects of cultural heritage. The most common data recorded are relaxation measurements of 1H because the proton is the most sensitive NMR nucleus, and relaxation can be measured despite the inhomogeneous magnetic field that typically accompanies a simple magnet design. Through NMR relaxation, the state of matter can be analyzed locally, and the signal amplitude gives the proton density. A variety of stray-field sensors have been designed. Small devices weighing less than a kilogram have a shallow penetration depth of just a few millimeters and a resolution of a few micrometers. Access to greater depths requires larger sensors that may weigh 30 kg or more.

The use of these sensors is illustrated by selected examples, including examinations of (i) the stratigraphy of master paintings, (ii) binder aging, (iii) the deterioration of paper, (iv) wood density in master violins, (v) the moisture content and moisture profiles in walls covered with paintings and mosaics, and (vi) the evolution of stone conservation treatments. The NMR data provide unique information to the conservator on the state of the object—including past conservation measures.

The use of mobile NMR remains relatively new, expanding from field testing of materials such as roads, bridge decks, soil, and the contents of drilled wells to these more recent studies of objects of cultural heritage. As a young field, noninvasive testing of artworks with stray-field NMR thus offers many opportunities for research innovation and further development.

Concepts in Magnetic Resonance - up to May 10, 2010

Concepts in Magnetic Resonance Part A
Volume 36A Issue 2, Pages 84 - 126
Published Online: 21 Apr 2010

Analysis of electric field gradient tensors at quadrupolar nuclei in common structural motifs
Jochen Autschbach, Shaohui Zheng, Robert W. Schurko

Keywords
electric field gradients • quadrupolar coupling • quantum chemistry • localized orbitals

Abstract
This article is concerned with the analysis of electric field gradients (EFGs) using first-principles theory along with model calculations. Simple atomic orbital (AO )models for the EFG are developed in the spirit of the Townes-Dailey (TD) analysis and applied to various sets of spn hybrid orbitals and to atomic d orbital shells. These AO models are then combined with modern analysis methods rooted in first principles theory which provide accurate localized molecular orbital contributions to the EFG. It is shown by density functional computations how such analyses of the EFG for a variety of typical structural motifs can provide an intuitive way of understanding the chemical origin of the magnitude and the sign of EFG tensors at atomic nuclei, as well as of their orientation with respect to the molecular coordinate frame. The utility of graphical visualizations of EFG tensors is also emphasized. The systems that are investigated span the range from very small molecules (carbon and sulfur EFGs in CO, CS, OCS) to small- and medium-sized molecules (nitrogen and aluminum EFGs in ammonia, methyl-cyanide and -isocyanide, aluminum AlX3 model systems and various alumino-organic systems), to the metal atom field gradient in transition metal complexes with Ru and Nb and a variety of ligands. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part A 36A: 84-126, 2010.
Received: 9 December 2009; Revised: 15 February 2010; Accepted: 2 March 2010

Digital Object Identifier (DOI)
10.1002/cmr.a.20155

--

Concepts in Magnetic Resonance Part A
Volume 36A Issue 2, Pages 49 - 83
Published Online: 21 Apr 2010

The product operator formalism: A physical and graphical interpretation
David P. Goldenberg *

Keywords
product operators • scalar coupling • quantum correlations • vector diagrams

Abstract
The product-operator formalism is the most commonly used tool for describing and designing multidimensional NMR experiments. Despite its relative simplicity and sound theoretical underpinnings, however, students and practitioners often find it difficult to relate the mathematical manipulations to a physical picture. In an effort to address this pedagogical challenge, the present article begins with a quantum-mechanical treatment of pure populations of scalar-coupled spin pairs, rather than the equilibrium population of spin pairs in different quantum states, which is the usual starting point for treatments based on the density matrix and product operators. In the context of pure populations, the product operators are shown to represent quantum correlations between the nuclei in individual molecules, and a new variation on the classical vector diagram is introduced to represent these correlations. The treatment is extended to mixed populations that begin at thermal equilibrium, and the density matrix is introduced as an efficient means of carrying out quantum calculations for a mixed population. Finally, it is shown that the operators for observable magnetization and correlations can be used as a basis set for the density matrix, providing the formal justification for the widely used rules of the product-operator treatment. Throughout the discussion, the vector diagrams are used to help maintain a connection between the mathematics and the sometimes subtle physical principles. An electronic supplement created with the Mathematica computer program is used to provide additional mathematical details and the means to carry out further calculations. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part A 36A: 49-83, 2010.
Received: 19 June 2009; Revised: 5 March 2010; Accepted: 5 March 2010

Digital Object Identifier (DOI)
10.1002/cmr.a.20156

J. Am. Chem. Soc., 2010, 132 (16), pp 5556–5557
Fibrillar vs Crystalline Full-Length β-2-Microglobulin Studied by High-Resolution Solid-State NMR Spectroscopy
Emeline Barbet-Massin, Stefano Ricagno, Józef R. Lewandowski, Sofia Giorgetti, Vittorio Bellotti, Martino Bolognes, Lyndon Emsley and Guido Pintacuda


Abstract
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 β-2-microglobulin (β2m), 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 β2m (99 residues) at pH 2.5 and pH 7.4. A close comparison of 2D 13C−13C and 15N−13C correlation experiments performed on β2m, in both the crystalline and fibrillar states, suggests that, in spite of structural changes affecting the protein loops linking the protein β-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 β2m fibril formation. Lastly, the analogy of the spectra recorded on β2m 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 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†

Abstract
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 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§

Abstract
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 5607–5609
Toward Flexibility−Activity Relationships by NMR Spectroscopy: Dynamics of Pin1 Ligands
Andrew T. Namanja†, Xiaodong J. Wang‡, Bailing Xu‡, Ana Y. Mercedes-Camacho‡, Brian D. Wilson†, Kimberly A. Wilson†, Felicia A. Etzkorn‡ and Jeffrey W. Peng*†


Abstract
Drug design involves iterative ligand modifications. For flexible ligands, these modifications often entail restricting conformational flexibility. However, defining optimal restriction strategies can be challenging if the relationship between ligand flexibility and biological activity is unclear. Here, we describe an approach for ligand flexibility−activity studies using Nuclear Magnetic Resonance (NMR) spin relaxation. Specifically, we use 13C relaxation dispersion measurements to compare site-specific changes in ligand flexibility for a series of related ligands that bind a common macromolecular receptor. The flexibility changes reflect conformational reorganization resulting from formation of the receptor−ligand complex. We demonstrate this approach on three structurally similar but flexibly differentiated ligands of human Pin1, a peptidyl-prolyl isomerase. The approach is able to map the ligand dynamics relevant for activity and expose changes in those dynamics caused by conformational locking. Thus, NMR flexibility−activity studies can provide information to guide strategic ligand rigidification. As such, they help establish an experimental basis for developing flexibility−activity relationships (FAR) to complement traditional structure−activity relationships (SAR) in molecular design.


J. Phys. Chem. A, 2010, 114 (16), pp 5365–5371
NMR and Quantum Chemistry Study of Mesoscopic Effects in Ionic Liquids
Vytautas Balevicius*†, Zofia Gdaniec‡, Kestutis Aidas§ and Jelena Tamuliene


Abstract
1H, 13C, and 81Br NMR spectra of the neat room-temperature ionic liquid (RTIL), namely, 1-decyl-3-methyl-imidazolium bromide ([C10mim][Br]) as well as its solutions in acetonitrile, dichloromethane, methanol, and water have been investigated. The most important observation of the present work is the significant broadening of 81Br NMR signal in the solutions of [C10mim][Br] in organic solvents, which molecules tend to associate into hydrogen bond networks and the appearance of the complex contour of 81Br NMR signal in the neat RTIL as well as in the liquid crystalline (LC) ionogel formed in RTIL/water solution. The complex structure of 81Br signal changes upon heating and dilution in water. It disappears at ca. 353 K and in the aqueous solution below ca. 0.1 mol fraction of RTIL. Several new 1H NMR signals appear at the [C10mim][Br]/water compositions just before the solidification of the sample (0.3 mol fraction of [C10mim][Br]). These additional peaks can be attributed to the H2O protons placed in inhomogeneous regions of the sample or due to the appearance of nonequivalent water sites in LC ionogel, the exchange between which is highly restricted or even frozen. The complex shape of 81Br NMR signal can originate from the presence of supra-molecular structures (mesoscopic domains) that live over the period of the NMR time-scale due to a very high viscosity of [C10mim][Br]. These domains exhibit some features of partially disordered solids (liquid- or plastic crystals). To evaluate the static and dynamic contributions into the relaxation rate of 81Br nuclei, the quantum chemistry calculations of the electronic structure, magnetic shielding, and electric field gradient (EFG) tensors of [C10mim][Br] and related model systems (Br−·6H2O cluster, with addition of the dipoles (hydrogen fluoride) and charged particles − cations: H+ or C1mim+) were performed.


J. Phys. Chem. A, 2010, 114 (16), pp 5279–5286
DFT Calculations of Indirect 29Si−1H Spin−Spin Coupling Constants in Organoalkoxysilanes
Jyothirmai Ambati and Stephen E. Rankin


Abstract
The performance of four basis sets (6-311+G(2d,p), IGLO-III, cc-PVTZ, and 6-31G) is evaluated in order to find a quantum mechanical technique that can be used to accurately estimate 29Si−1H spin−spin coupling constants in organoalkoxysilanes. The 6-31G basis set with the B3LYP functional is found to be an accurate, efficient, and cost-effective density functional theory method for predicting spin−spin coupling constants of organoalkoxysilanes. Knowledge of these scalar coupling constants and their dependence on structural variations is important to be able to fine-tune NMR experiments that rely on polarization transfer among nuclei, such as 29Si distortionless enhancement by polarization transfer (DEPT). The effects of size and the number of unhydrolyzable alkyl groups attached to silicon and the effects of substitution of alkoxy groups with hydroxyl groups on 29Si−1H spin−spin coupling constants are investigated using this DFT method. The results show that the predicted scalar coupling between silicon and organic groups depends weakly on the degree of hydrolysis of the alkoxysilanes. The effectiveness of this method is also illustrated for the determination of spin−spin coupling constants in a species containing a siloxane bond.

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

Abstract
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-γ 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 (15), pp 5479–5493

Solid-State 115In and 31P NMR Studies of Triarylphosphine Indium Trihalide Adducts
Fu Chen, Guibin Ma, Guy M. Bernard, Ronald G. Cavell, Robert McDonald, Michael J. Ferguson and Roderick E. Wasylishen

Abstract
Solid-state 115In and 31P NMR spectroscopy, relativistic density functional theory (DFT) calculations, and single-crystal X-ray diffraction were used to investigate a series of triarylphosphine indium(III) trihalide adducts, X3In(PR3) and X3In(PR3)2 (X = Cl, Br or I; PR3 = triarylphosphine ligand). The electric field gradient tensors at indium as well as the indium and phosphorus magnetic shielding tensors and the direct and indirect 115In−31P spin−spin coupling were characterized; for complexes possessing a C3 symmetry axis, the anisotropy in the indirect spin−spin coupling, ΔJ(115In,31P), was also determined. The 115In quadrupolar coupling constants, CQ(115In), range from ±1.25 ± 0.10 to −166.0 ± 2.0 MHz. For any given phosphine ligand, the indium nuclei are most shielded for X = I and least shielded for X = Cl, a trend also observed for other group-13 nuclei in M(III) complexes. This experimental trend, attributed to spin−orbit effects of the halogen ligands, is reproduced by the DFT calculations. The spans of the indium magnetic shielding tensors for these complexes, δ11 − δ33, range from 40 ± 7 to 710 ± 60 ppm; those determined for phosphorus range from 28 ± 1.5 to 50 ± 3 ppm. Values of 1J(115In,31P) range from 550 ± 20 to 2500 ± 20 Hz. For any given halide, the 1J(115In,31P) values generally increase with increasing basicity of the PR3 ligand. Calculated values of 1J(115In,31P) and ΔJ(115In,31P) duplicate experimental trends and indicate that both the Fermi-contact and spin−dipolar Fermi-contact mechanisms make important contributions to the 1J(115In,31P) tensors.

J. Am. Chem. Soc., 2010, 132 (15), pp 5443–5455

Si═X Multiple Bonding with Four-Coordinate Silicon? Insights into the Nature of the Si═O and Si═S Double Bonds in Stable Silanoic Esters and Related Thioesters: A Combined NMR Spectroscopic and Computational Study
Jan. D. Epping, Shenglai Yao, Miriam Karni, Yitzhak Apeloig and Matthias Driess

Abstract
The electronic structures and nature of silicon−chalcogen double bonds Si═X (X = O, S) with four-coordinate silicon in the unique silanoic silylester 2 and silanoic thioester 3 have been investigated for the first time, by 29Si solid state NMR measurements and detailed DFT and ab initio calculations. 29Si solid state NMR spectroscopy of the precursor silylene 1 was also carried out. The experimental and computational study of 2 and 3, which was also supported by a detailed computational study of smaller model systems with Si═O and Si═S bonds, provides a deeper understanding of the isotropic and tensor components of their NMR chemical shifts. The general agreement between the experimental NMR spectra and the calculations strongly support our previous NMR assignment deduced from experiment. The calculations revealed that in 2 δ(29Si(═O))iso is shifted upfield relative to H2Si═O by as much as 175 ppm; the substituents are responsible for ca. 100 ppm of this shift, while the remaining upfield shift is caused by change in the coordination number from three to four at the Si═O moiety. The change in coordination number leads to a nearly cylindrical symmetry in the plane which is perpendicular to the Si═O molecular axis (δ11 ≈ δ22), in contrast to the significant anisotropy found in this plane in typical doubly bonded compounds. The change in r(Si═O) or in the degree of pyramidality at the Si═O center which accompanies the change in coordination number has practically no effect on the chemical shift. δ(29Si(═S))iso in 3 is shifted downfield significantly relative to that in 2, and a similar trend is found in smaller models with Si═S vs those with Si═O subunits. This downfield shift can be explained by the smaller σ−π* energy difference in the Si═S bond, relative to that of the Si═O bond. The NMR measurements of 2 and 3 having a four-coordinate silicon−chalcogen moiety, and the calculations of their tensor components, their bond polarities, and their Wiberg bond indices revealed that the Si═X moieties in both 2 and 3 have a significant π(Si═X) character; yet, in both molecules there is a substantial contribution from a zwitterionic Si+—X− resonance structure, which is more pronounced in 2.

J. Am. Chem. Soc., 2010, 132 (15), pp 5387–5393

Molecular Wheels as Nanoporous Materials: Differing Modes of Gas Diffusion through Ga10 and Ga18 Wheels Probed by Hyperpolarized 129Xe NMR Spectroscopy
Chi-Yuan Cheng, Theocharis C. Stamatatos, George Christou and Clifford R. Bowers

Abstract
The study of crystals of molecular wheels as nanoporous materials is reported. Hyperpolarized 129Xe NMR spectroscopy has been used to characterize the mode of molecular diffusion and Xe interactions within the supramolecular nanochannels formed upon crystallization of the molecular wheels [Ga10(OMe)20(O2CMe)10] and [Ga18(pd)12(pdH)12(O2CMe)6(NO3)6](NO3)6. In agreement with expectations based on the collision diameter of the Xe atom relative to the differing internal diameters of the two types of gallium wheels, single-file diffusion occurs in the Ga10 channels, whereas in the Ga18 system the data are consistent with normal, Fickian diffusion. Information about the electronic environment inside the channels was probed by the Xe chemical shift. The interaction of the gas with the channel walls is found to be substantially stronger than the interaction in organic nanotubes and zeolites. The results establish the ability of crystals of molecular wheel compounds to function as a new class of porous nanotubular materials, and ones of a known and variable diameter, for studying the channel diameter dependence of molecular exchange and unidirectional diffusion on the micrometer length scale.