Journal of Physical Chemistry B, Vol. 113, Issues 25 to 30

Glassy Dynamics in Nanoconfinement as Revealed by 31P NMR
S. Gradmann, P. Medick and E. A. Rssler*
Experimentalphysik II, Universitt Bayreuth, 95440 Bayreuth, Germany
J. Phys. Chem. B, 2009, 113 (25), pp 8443–8445

Abstract: We investigated the glass former m-tricresyl-phosphate confined in different nanoporous silica matrices with defined pore radii from 2−150 nm. While applying different 31P NMR techniques, we were able to detect the extremely stretched correlation functions extending over 7−8 decades in time and reflecting strong dynamic heterogeneities. The experimental results were explained by a topological model for which the broad distribution of correlation times G(ln τ) becomes inhomogeneous in space; that is, the “local” dynamics given by a correlation time τ(r) depend on the distance from the pore center. As τ(r) changes with temperature, we were able to reintroduce the idea of a dynamic correlation length.



Hierarchical Dynamics of As2P2S8 Quasi-Molecular Units in a Supercooled Liquid in the As−P−S System: A 31P NMR Spectroscopic Study

E. L. Gjersing and S. Sen*
J. Phys. Chem. B, 2009, 113 (25), pp 8514–8519
DOI: 10.1021/jp901388j
Abstract: The dynamics of As2P2S8 quasi-molecular units caged in an As−S network in the supercooled chalcogenide liquid of composition (As2S3)90(P2S5)10 have been studied near the glass transition region (Tg = 468 ≤ T ≤ 628 K) using 31P NMR line shape analysis and spin−lattice relaxation techniques. 31P NMR line shape analysis indicates the presence of isotropic rotational reorientation of As2P2S8 quasi-molecular units at frequencies on the order of tens of kilohertz at T <>


Proton Assisted Recoupling at High Spinning Frequencies†
Jzef R. Lewandowski‡§, Gal De Pape‡, Matthew T. Eddy‡, Jochem Struppe, Werner Maas and Robert G. Griffin*‡
J. Phys. Chem. B, 2009, 113 (27), pp 9062–9069
DOI: 10.1021/jp810280t

2008 marked the Centennial of the American Chemical Society’s Division of Physical Chemistry. To celebrate and to highlight the field of physical chemistry from both historical and future perspectives, The Journal of Physical Chemistry is publishing a special series of Centennial Feature Articles. These articles are invited contributions from current and former officers and members of the Physical Chemistry Division Executive Committee and from J. Phys. Chem. Senior Editors.,

Abstract: We demonstrate the successful application of 13C−13C proton assisted recoupling (PAR) on [U−13C,15N] N-f-MLF-OH and [U−13C,15N] protein GB1 at high magic angle spinning (MAS) frequencies (ωr/2π = 65 kHz). Specifically, by combining PAR mixing with low power heteronuclear decoupling (ω1H/2π 16 kHz) and high spinning frequencies, we obtain high resolution 2D spectra displaying long-range 13C−13C contacts from which distance estimates can be extracted. These experiments therefore demonstrate the possibility of performing high resolution structural studies in the limit of high spinning frequency and low power 1H decoupling, a regime which optimizes the resolution of protein samples and preserves their integrity.



Self-Diffusion and Mutual Diffusion of Small Molecules in High-Set Curdlan Hydrogels Studied by 31P NMR
Marc-Andr Gagnon and Michel Lafleur*
J. Phys. Chem. B, 2009, 113 (27), pp 9084–9091
DOI: 10.1021/jp811105p

Abstract: Self-diffusion and mutual diffusion are two different transport mechanisms experimentally characterized on different length and time scales. NMR spectroscopy is a highly suitable technique to characterize these two phenomena as both mechanisms can be studied on the same system and in the same experimental conditions. Pulsed field gradient (PFG) NMR was used to measure the self-diffusion whereas 31P NMR profiling provided an approach to determine the mutual diffusion coefficients. We have characterized the diffusion of phosphate, trimetaphosphate, alendronate, and d-glucose-6-phosphate in hydrogels prepared with 10% (w/v) curdlan, a bacterial polysaccharide built of linear (1→3)-β-d-glucose repeating units. These solutes are small compared to the average pore size of the hydrogel, as inferred from environmental scanning electron microscopy (eSEM). Our results show that the self- and mutual-diffusion coefficients of small molecules in curdlan hydrogels are similar and are reduced by 30% compared to those measured in aqueous solutions. These observations are validated for the complete series of investigated analytes. It is therefore concluded that, for this system, the analyte diffusion in the gel is essentially reduced because of interactions at the molecular level and that the open structure of this gel has a very limited influence at the mesoscopic length scale. A literature survey indicates that these conditions prevail for the large majority of the systems that have been investigated up to now.


Validating a Strategy for Molecular Dynamics Simulations of Cyclodextrin Inclusion Complexes through Single-Crystal X-ray and NMR Experimental Data: A Case Study
Giuseppina Raffaini*†, Fabio Ganazzoli†, Luciana Malpezzi†, Claudio Fuganti†, Giovanni Fronza‡, Walter Panzeri‡ and Andrea Mele*†
J. Phys. Chem. B, 2009, 113 (27), pp 9110–9122
DOI: 10.1021/jp901581e

Abstract: A theoretical and experimental study about the formation and structure of the inclusion complex (−)-menthyl-O-β-D-glucopyranoside 1 with β-cyclodextrin (β-CD) 2 is presented as paradigmatic case study to test the results of molecular dynamics (MD) simulations. The customary methodological approach—the use of experimental geometrical parameters as restraints for MD runs—is logically reversed and the calculated structures are a posteriori compared with those obtained from NMR spectroscopy in D2O solution and single crystal X-ray diffraction so as to validate the simulation procedure. The guest molecule 1 allows for a broad repertoire of intermolecular interactions (dipolar, hydrophobic, hydrogen bonds) concurring to stabilize the host−guest complex, thus providing the general applicability of the simulation procedure to cyclodextrin physical chemistry. Many starting geometries of the host−guest association were chosen, not assuming any a priori inclusion. The simulation protocol, involving energy minimization and MD runs in explicit water, yielded four possible inclusion geometries, ruling out higher-energy outer adducts. By analysis of the average energy at room temperature, the most stable geometry in solution was eventually obtained, while the kinetics of formation showed that it is also kinetically favored. The reliability of such geometry was thoroughly checked against the NOE distances via the pair distribution functions, that is, the statistical distribution of intermolecular distances among selected diagnostic atoms calculated from the MD trajectories at room temperature. An analogous procedure was adopted both with implicit solvent and in vacuo. The most stable geometry matched that found with explicit solvent but major differences were observed in the relative stability of the metastable complexes as a consequence of the lack of hydration on the polar moiety of the guest. Finally, a control set of geometrical parameters of the thermodynamically favored complex matched the corresponding one obtained from the X-ray structure, while local conformational differences were indicative of packing effects.


1H Solid-State NMR Investigation of Structure and Dynamics of Anhydrous Proton Conducting Triazole-Functionalized Siloxane Polymers
mit Akbey†, Sergio Granados-Focil‡, E. Bryan Coughlin§, Robert Graf† and Hans Wolfgang Spiess*†
J. Phys. Chem. B, 2009, 113 (27), pp 9151–9160
DOI: 10.1021/jp9030909

Abstract:1H MAS solid-state NMR methods are applied to elucidate the conduction mechanism of an anhydrous proton conducting triazole-functionalized polysiloxane. At temperatures below T = 260 K, hydrogen bonding between neighboring heterocycles is observed and a dimer formation can be excluded. From the temperature dependence of 1H MAS NMR spectra, different dynamic processes of the triazole ring contributing to the proton conduction process are qualitatively and quantitatively analyzed and detailed insight into the conduction mechanism and temperature-dependent structural changes is obtained. Although the dynamics processes on the molecular level are qualitatively in good agreement with the findings from macroscopic conductivity measurements, temperature-dependent factors on mesoscopic scales beyond the local molecular mobility influence the macroscopic conductivity and hamper quantitative interpretation.


Intra- and Intermolecular Effects on 1H Chemical Shifts in a Silk Model Peptide Determined by High-Field Solid State 1H NMR and Empirical Calculations
Yu Suzuki†, Rui Takahashi†, Tadashi Shimizu‡, Masataka Tansho‡, Kazuo Yamauchi†, Mike P. Williamson§ and Tetsuo Asakura*†
J. Phys. Chem. B, 2009, 113 (29), pp 9756–9761
DOI: 10.1021/jp903020p

Abstract: A combination of solid state 1H NMR chemical shift measurements and empirical chemical shift calculations has been used to interpret 1H solid state chemical shifts of a model peptide (Ala-Gly)15 for the crystalline domain of Bombyx mori silk fibroin in silk I and silk II structures, including a treatment of both intra- and intermolecular arrangements. Silk I and silk II are the structures of silk fibroin before and after spinning, respectively. Two peaks with equal intensity were observed for the amide protons of (AG)15 in silk I, whereas only one broad peak was observed for silk II, reflecting a difference of 1.1 ppm in Ala HN shift between silk I and silk II, but a difference of only 0.2 ppm in Gly HN shift. Chemical shift calculations predicted chemical shifts that are in good agreement with the experimental observations and showed that the origin of these chemical shift differences was predominantly the magnetic anisotropy effect from the C═O bond that hydrogen bonds with HN, which has a more favorable geometry for Ala HN in silk II than for the other HN. This result shows that we could distinguish between proton chemical shift effects arising from intermolecular interactions and those from intramolecular interactions by combining observation of the solid state 1H NMR chemical shift and empirical chemical shift calculation.


1H Photo-CIDNP Enhancements in Heteronuclear Correlation NMR Spectroscopy
Ashok Sekhar and Silvia Cavagnero*
J. Phys. Chem. B, 2009, 113 (30), p 10548
DOI: 10.1021/jp905605u
Publication Date (Web): July 9, 2009
Copyright © 2009 American Chemical Society

J. Am. Chem. Soc., 2009, 131 (29), pp 9884–9885

15N−1H Scalar Coupling Perturbation: An Additional Probe for Measuring Structural Changes Due to Ligand Binding
Junhe Ma, James M. Gruschus and Nico Tjandra*

Abstract
Chemical shift perturbation mapping of backbone amides is one of the most widely employed techniques in biomolecular NMR, providing residue-by-residue information on interaction interfaces, ligand binding, and chemical modification sites, even for samples where poor solubility, short lifetime, or large size precludes more sophisticated experimental approaches. Significant changes can also occur in the amide one-bond 15N−1H scalar coupling constants for glutamine binding protein (GlnBP) due to ligand binding. Like chemical shift perturbations, large changes (>1 Hz) are seen near the site of glutamine binding, though perturbations also occur distant to the site. The coupling constant perturbations correlate with significant structural changes, especially changes in backbone hydrogen bonding. Thus, amide scalar coupling perturbation can serve as an adjunct to chemical shift perturbation, providing additional information on both short-range and longer-range, allosteric structural changes.

Progress in NMR, up to Volume 55, Issue 2, August 2009

Progress in NMR, up to Volume 55, Issue 2, August 2009
- HRMAS NMR for biomedical studies
- natural abundance 2H NMR
- second-order cross terms interactions in MAS NMR spectra of quadrupoles

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Progress in Nuclear Magnetic Resonance Spectroscopy
Volume 55, Issue 2, August 2009, Pages 79-100

doi:10.1016/j.pnmrs.2008.11.004

High-resolution magic angle spinning NMR spectroscopy: Application to biomedical studies

John C. Lindon, Olaf P. Beckonert, Elaine Holmes and Jeremy K. Nicholson

Department of Biomolecular Medicine, Faculty of Medicine, Imperial College London, Sir Alexander Fleming Building, South Kensington, London SW7 2AZ, UK

Keywords: Magic angle spinning; Tissue; Cells; Cancer; Pharmaceuticals; Toxins

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Progress in Nuclear Magnetic Resonance Spectroscopy
Volume 55, Issue 2, August 2009, Pages 128-159

doi:10.1016/j.pnmrs.2009.01.001

Natural abundance deuterium NMR spectroscopy: Developments and analytical applications in liquids, liquid crystals and solid phases

Philippe Lesot and Jacques Courtieu

Université de Paris Sud 11, ICMMO, UMR CNRS 8182, Laboratoire de RMN en Milieu Orienté, Bât. 410, F-91405 Orsay Cedex, France

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Progress in Nuclear Magnetic Resonance Spectroscopy
Volume 55, Issue 2, August 2009, Pages 128-159

doi:10.1016/j.pnmrs.2009.04.002

Second-order cross-term interactions in high-resolution MAS NMR of quadrupolar nuclei

Sharon E. Ashbrook, Jamie McManus, Michael J. Thrippleton and Stephen Wimperis

School of Chemistry and EaStCHEM, University of St Andrews, North Haugh, St Andrews KY16 9ST, UK; Winchester College, Winchester SO23 9NA, UK; Department of Chemistry and WestCHEM, University of Glasgow, Glasgow G12 8QQ, UK

Chem. Soc. Rev. How molecules stick together in organic crystals: weak intermolecular interactions

Tutorial Review

Article citation: Jack D. Dunitz, Chem. Soc. Rev., 2009, DOI: 10.1039/b822963p

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How molecules stick together in organic crystals: weak intermolecular interactions

Jack D. Dunitz and Angelo Gavezzotti

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This tutorial review introduces the fundamentals of intermolecular interactions in terms of the underlying physics and goes on to illustrate the most popular methods for the computer simulation of intermolecular interactions, from atom–atom potentials to ab initio methods, including intermediate, hybrid methods, with an appreciation of their relative merits and costs. Typical results are critically presented, culminating in the most difficult exercise of all, the computer prediction of crystal structures. Perspectives on our present and future ability to understand and exploit intermolecular interactions are given.

Chem. Mater., Article ASAP

Investigation of the Conversion Reaction Mechanisms for Binary Copper(II) Compounds by Solid-State NMR Spectroscopy and X-ray Diffraction

Naoko Yamakawa†‡, Meng Jiang† and Clare P. Grey*†

Abstract
The conversion reaction mechanisms of CuS, CuF2, and CuO during the electrochemical reaction with Li are studied by solid-state 63Cu, 19F, and 7Li nuclear magnetic resonance (NMR) and X-ray diffraction (XRD). For CuS, a two-step reaction is observed that is associated with an insertion reaction involving first limited incorporation of Li into CuS and then a two-phase reaction to form a material with the approximate composition LiCuS. This is followed by a conversion reaction to form Li2S and Cu, Cu1.96S being formed as a side product of the decomposition of LiCuS. Evidence for the insertion phases is found from both NMR and XRD. A direct conversion reaction to form LiF and Cu is seen for CuF2, whereas the 7Li NMR results indicate that CuO can tolerate a small amount of Li substitution before reacting to form Li2O and Cu. Both the diffraction and NMR results indicate that the size of the Cu particles formed on discharge are much larger in the CuS system, which is thought to result from the higher Cu1+ mobilities in the intermediate intercalation compounds LixCuS. The factors that control the possible mechanisms for these conversion reactions are discussed.

J. Am. Chem. Soc., Article ASAP

Solid-State and Solution NMR Studies of the CAP-Gly Domain of Mammalian Dynactin and Its Interaction with Microtubules

Shangjin Sun†, Amanda Siglin‡, John C. Williams*‡ and Tatyana Polenova*†

Abstract
Microtubules (MTs) and microtubule binding proteins (MTBPs) play fundamental physiological roles including vesicle and organelle transport, cell motility, and cell division. Despite the importance of the MT/MTBP assemblies, there remains virtually no structural or dynamic information about their interaction at the atomic level due to the inherent insolubility and lack of long-range order of MTs. In this study, we present a combined magic angle spinning solid-state and solution NMR study of the MTBP CAP-Gly domain of mammalian dynactin and its interaction with paclitaxel-stabilized microtubules. We report resonance assignments and secondary structure analysis of the free CAP-Gly in solution and in the solid state by a combination of two- and three-dimensional homo- and heteronuclear correlation spectra. In solution, binding of CAP-Gly to microtubules is accompanied by the broadening of the majority of the peaks in HSQC spectra except for the residues at the termini, precluding further structural analysis of the CAP-Gly/microtubule complexes. In the solid state, DARR spectra of free CAP-Gly and its complex with microtubules display well-resolved lines, permitting residue-specific resonance assignments. Interestingly, a number of chemical shifts in the solid-state DARR spectra of the CAP-Gly/microtubule complex are perturbed compared to those of the free CAP-Gly, suggesting that conformational changes occur in the protein upon binding to the microtubules. These results indicate that CAP-Gly/microtubule assemblies are amenable to detailed structural characterization by magic angle spinning NMR spectroscopy and that solid-state NMR is a viable technique to study MT/protein interactions in general.

J. Am. Chem. Soc., Article ASAP

Identifying the Local Structures Formed during Lithiation of the Conversion Material, Iron Fluoride, in a Li Ion Battery: A Solid-State NMR, X-ray Diffraction, and Pair Distribution Function Analysis Study

Naoko Yamakawa†‡, Meng Jiang†, Baris Key† and Clare P. Grey*†

Abstract
The structural transformations that occur when FeF3 is cycled at room temperature in a Li cell were investigated using a combination of X-ray diffraction (XRD), pair distribution function (PDF) analysis, and magic-angle-spinning NMR spectroscopy. Two regions are seen on discharge. The first occurs between Li = 0 and 1.0 and involves an insertion reaction. This first region actually comprises two steps: First, a two-phase reaction between Li = 0 and 0.5 occurs, and the Li0.5FeF3 phase that is formed gives rise to a Li NMR resonance due to Li+ ions near both Fe3+ and Fe2+ ions. On the basis of the PDF data, the local structure of this phase is closer to the rutile structure than the original ReO3 structure. Second, a single-phase intercalation reaction occurs between Li = 0.5 and 1.0, for which the Li NMR data indicate a progressive increase in the concentration of Fe2+ ions. In the second region, the conversion reaction, superparamagnetic, nanosized (3 nm) Fe metal is formed, as indicated by the XRD and NMR data, along with some LiF and a third phase that is rich in Li and F. The charge process involves the formation of a series of intercalation phases with increasing Fe oxidation state, which, on the basis of the Li NMR and PDF data, have local structures that are similar to the intercalation phases seen during the first stage of the discharge process. The solid-state NMR and XRD results for the rutile phase FeF2 are presented for comparison, and the data indicate that an insertion reaction also occurs, which is accompanied by the formation of LiF. This is followed by the formation of Fe nanoparticles and LiF via a conversion reaction.

J. Am. Chem. Soc., 2009, 131 (26), pp 9239–9249

Real-Time NMR Investigations of Structural Changes in Silicon Electrodes for Lithium-Ion Batteries
Baris Key†, Rangeet Bhattacharyya†, Mathieu Morcrette‡, Vincent Seznc‡, Jean-Marie Tarascon‡ and Clare P. Grey*

Abstract
Lithium-ion batteries (LIBs) containing silicon negative electrodes have been the subject of much recent investigation because of the extremely large gravimetric and volumetric capacity of silicon. The crystalline-to-amorphous phase transition that occurs on electrochemical Li insertion into crystalline Si, during the first discharge, hinders attempts to link structure in these systems with electrochemical performance. We apply a combination of static, in situ and magic angle sample spinning, ex situ 7Li nuclear magnetic resonance (NMR) studies to investigate the changes in local structure that occur in an actual working LIB. The first discharge occurs via the formation of isolated Si atoms and smaller Si−Si clusters embedded in a Li matrix; the latter are broken apart at the end of the discharge, forming isolated Si atoms. A spontaneous reaction of the lithium silicide with the electrolyte is directly observed in the in situ NMR experiments; this mechanism results in self-discharge and potential capacity loss. The rate of this self-discharge process is much slower when CMC (carboxymethylcellulose) is used as the binder.

Science vol. 324: High-Resolution NMR in Magnetic Fields with Unknown Spatiotemporal Variations

Science 26 June 2009:Vol. 324. no. 5935, pp. 1693 - 1697DOI: 10.1126/science.1175102

High-Resolution NMR in Magnetic Fields with Unknown Spatiotemporal Variations
Philippe Pelupessy,1,* Enrico Rennella,2 Geoffrey Bodenhausen1,3

Nuclear magnetic resonance (NMR) experiments are usually carried out in homogeneous magnetic fields. In many cases, however, high-resolution spectra are virtually impossible to obtain because of the inherent heterogeneity of the samples or living organisms under investigation, as well as the poor homogeneity of the magnets (particularly when bulky samples must be placed outside their bores). Unstable power supplies and vibrations arising from cooling can lead to field fluctuations in time as well as space. We show how high-resolution NMR spectra can be obtained in inhomogeneous fields with unknown spatiotemporal variations. Our method, based on coherence transfer between spins, can accommodate spatial inhomogeneities of at least 11 gauss per centimeter and temporal fluctuations slower than 2 hertz.

J. Am. Chem. Soc., 2009, 131 (25), pp 9086–9093

Diffusion-Ordered NMR Spectroscopy in the Structural Characterization of Functionalized Carbon Nanotubes
Riccardo Marega†‡, Vincent Aroulmoji‡¶, Francesca Dinon‡, Lisa Vaccari§, Silvia Giordani, Alberto Bianco, Erminio Murano‡ and Maurizio Prato†

Abstract
The emerging applications of functionalized carbon nanotubes (CNTs) in various research domains necessitate the use of many different analytical techniques to confirm their structural modifications in a fast and reliable manner. Thus far, NMR spectroscopy has not been among the main tools for characterization of organically modified carbon nanostructures. 1H analysis is limited because the signals in these derivatives are typically weak and broad, resulting in uncertainties of a few parts per million, and because of the strong interference of residual solvent signals. To overcome these limitations, we investigated the applicability of proton NMR spectroscopy based on gradient-edited diffusion pulse sequences (1D diffusion-ordered spectroscopy, DOSY) in the characterization of CNT derivatives. In general, diffusion NMR experiments allow the separation of NMR signals of different species present in a mixture, according to their own diffusion coefficients, merging spectroscopy information with size analysis. In the present study, a selected set of CNT derivatives was synthesized and analyzed using 1D DOSY experiments by applying strong magnetic field gradients (up to 42.6 G cm−1). Colorimetric tests (i.e., Kaiser test) and TGA analysis support the NMR findings, which are related to isolated and/or bundled short SWNTs, on the basis of TEM and AFM characterization. The overall results show that the diffusion-based NMR spectroscopy is a fast and promising approach for the characterization of covalently modified CNT derivatives.

Cryst. Growth Des., 2009, 9 (7), pp 3124–3128

Engineering Crystal Packing and Internal Dynamics in Molecular Gyroscopes by Refining their Components. Fast Exchange of a Phenylene Rotator by 2H NMR
Miguel A. Garcia-Garibay* and Carlos E. Godinez

Abstract
Using quadrupolar echo 2H NMR, we have determined that a relatively simple change on the periphery of the triptycene stators of molecular gyroscopes may have a profound effect on the packing arrangements, packing coefficients, and rotary dynamics of the central phenylene rotators. The previously reported crystal structure of 1,4-bis-[2-(9-triptycyl)-ethynyl]benzene (1) is characterized by the inclusion of meta-xylene and a very tightly interdigitated packing arrangement that effectively prevents the rotary motion of the phenylene rotator. Structural modifications to prevent this interdigitation led to the design and synthesis of 1,4-bis[2-(2,3,6,7,12,13-hexamethyl-10-propyl-9-triptycyl)ethynyl]benzene (2), which had been shown to crystallize in the desired manner but with the inclusion of bromobenzene. Using crystals of 2 with a 2H-labeled phenylene rotator, we determined by quadrupolar echo 2H NMR line shape analysis that rotation occurs by a 180° site exchange (2-fold flip) with frequencies in the MHz regime at low temperatures (150−183 K). From the temperature dependence of the rotational exchange frequency, we determined a barrier of 4.4 kcal/mol, which is only 1.4 kcal/mol higher than the internal barrier for ethane in the gas phase. Additional spectral narrowing observed at higher temperature was analyzed in terms of a model that considers larger amplitude excursions between the 180° jumps.

Cryst. Growth Des., 2009, 9 (7), pp 3111–3118

Rheo-NMR Measurements of Cocoa Butter Crystallized Under Shear Flow
Elizabeth M. Mudge and Gianfranco Mazzanti*

Abstract
Modifications of a benchtop NMR instrument were made to apply temperature control to a shearing NMR cell. This has enabled the determination in situ of the solid fat content (SFC) of cocoa butter under shearing conditions. The cocoa butter was cooled at 3 °C/min to three final temperatures of 17.5, 20.0, and 22.5 °C with applied shear rates between 45 and 720 s−1. Polymorphic transitions of the cocoa butter were determined using synchrotron X-ray diffraction with an identical shearing system constructed of Lexan. Sheared samples were shown to have accelerated phase transitions compared to static experiments. In experiments where form V was confirmed to be the dominant polymorph, the final SFC averaged around 50%. However, when other polymorphic forms were formed, a lower SFC was measured because the final temperature was within the melting range of that polymorph and only partial crystallization happened. A shear rate of 720 s−1 delayed phase transitions, likely due to viscous heating of the sample. Pulsed NMR is an invaluable tool for determining the crystalline fraction in hydrogen containing materials, yet its use for fundamental and industrial research on fat or alkanes crystallization under shear has only recently been developed.

Cryst. Growth Des., 2009, 9 (7), pp 2999–3002

Guest Molecules Confined in Amphipathic Crystals as Revealed by X-ray Diffraction and MAS NMR†
Angiolina Comotti*‡, Silvia Bracco‡, Piero Sozzani‡, Samuel M. Hawxwell#, Chunhua Hu# and Michael D. Ward*#

Abstract
Multinuclear 1H−13C heterocorrelated (HETCOR) NMR spectroscopy combined with X-ray diffraction revealed the unusual dual properties of identical guest molecules confined in two crystallographically distinct host cavities within single crystals based on hexagonal frameworks comprising guanidinium ions and organomonosulfonates. The environments of the two cavities differ substantially, as one is lined by the highly polar quasihexagonal guanidinium-sulfonate network, while the other is defined by walls consisting of nonpolar aromatic groups. The effect of these different environments on the NMR properties of the guest molecules is evident from chemical shift data and two-dimensional HETCOR spectra. The large magnetic susceptibility effect due to ring currents of the aromatic hosts enables determination of the host−guest distances and suggests intermolecular CH···π interactions. The 13C relaxation times reveal the molecular dynamics of the guests in two nanoscale environments that differ with respect to shape and dimensionality.

J. Am. Chem. Soc., Article ASAP

Chemical Shift Anisotropy of Imino 15N Nuclei in Watson−Crick Base Pairs from Magic Angle Spinning Liquid Crystal NMR and Nuclear Spin Relaxation
Alexander Grishaev†, Lishan Yao†, Jinfa Ying†, Arthur Pardi‡ and Ad Bax*†

Abstract
Knowledge of 15N chemical shift anisotropy is prerequisite both for quantitative interpretation of nuclear spin relaxation rates in terms of local dynamics and for the use of residual chemical shift anisotropy (RCSA) as a constraint in structure determination. Accurate measurement of the very small RCSA from the difference in 15N chemical shift under isotropic and weakly aligning liquid crystalline conditions is very sensitive to minute differences in sample conditions, such as pH or ionic strength. For this reason, chemical shifts were measured for the same solution, under static liquid crystalline alignment, and under magic angle spinning conditions where alignment relative to the magnetic field is removed. Measurements were made for 14 well-resolved G−N1 and 6 U−N3 15N nuclei in a sample of tRNAVal. Fitting these RCSA data together with 15N−1H dipole-CSA cross-correlated relaxation measurements to the recently refined structural model of tRNAVal yields the magnitude, asymmetry, and orientation of the 15N CSA tensors.

J. Am. Chem. Soc., Article ASAP

Solvation and Hydrogen Bonding in Alanine- and Glycine-Containing Dipeptides Probed Using Solution- and Solid-State NMR Spectroscopy
Manasi P. Bhate, Jaie C. Woodard and Manish A. Mehta*

Abstract
The NMR chemical shift is a sensitive reporter of peptide secondary structure and its solvation environment, and it is potentially rich with information about both backbone dihedral angles and hydrogen bonding. We report results from solution- and solid-state 13C and 15N NMR studies of four zwitterionic model dipeptides, l-alanyl-l-alanine, l-alanyl-glycine, glycyl-l-alanine, and glycyl-glycine, in which we attempt to isolate structural and environmental contributions to the chemical shift. We have mapped hydrogen-bonding patterns in the crystalline states of these dipeptides using the published crystal structures and correlated them with 13C and 15N magic angle spinning chemical shift data. To aid in the interpretation of the solvated chemical shifts, we performed ab initio quantum chemical calculations to determine the low-energy conformers and their chemical shifts. Assuming low energy barriers to interconversion between thermally accessible conformers, we compare the Boltzmann-averaged chemical shifts with the experimentally determined solvated-state shifts. The results allow us to correlate the observed differences in chemical shifts between the crystalline and solvated states to changes in conformation and hydrogen bonding that occur upon solvation.

J. Am. Chem. Soc., Article ASAP

Characterization of Dispersed Heteropoly Acid on Mesoporous Zeolite Using Solid-State 31P NMR Spin−Lattice Relaxation
Kake Zhu, Jianzhi Hu, Xiaoyan She, Jun Liu*, Zimin Nie, Yong Wang, Charles H. F. Peden and Ja Hun Kwak

Abstract
Dispersion and quantitative characterization of supported catalysts is a grand challenge in catalytic science. In this paper, heteropoly acid H3PW12O40 (HPA) is dispersed on mesoporous zeolite silicalite-1 derived from hydrothermal synthesis using carbon black nanoparticle templates, and the catalytic activity is studied for 1-butene isomerization. The HPAs supported on conventional zeolite and on mesoporous zeolite exhibit very different activities and thus provide good model systems to investigate the structure dependence of the catalytic properties. The HPA on mesoporous silicalite-1 shows enhanced catalytic activity for 1-butene isomerization, while HPA on conventional silicalite-1 exhibits low activity. To elucidate the structural difference, supported HPA catalysts are characterized using a variety of techniques, including 31P magic angle spinning nuclear magnetic resonance, and are shown to contain a range of species on both mesoporous and conventional zeolites. However, contrary to studies reported in the literature, conventional NMR techniques and chemical shifts alone do not provide sufficient information to distinguish the dispersed and aggregated surface species. The dispersed phase and the nondispersed phase can only be unambiguously and quantitatively characterized using spin−lattice relaxation NMR techniques. The HPA supported on mesoporous zeolite contains a fast relaxation component related to the dispersed catalyst, giving a much higher activity, while the HPA supported on conventional zeolite has essentially only the slow relaxation component with very low activity. The results obtained from this work demonstrate that the combination of spinning sideband fitting and spin−lattice relaxation techniques can provide detailed structural information on not only the Keggin structure for HPA but also the degree of dispersion on the support.

Chem. Mater., 2009, 21 (12), pp 2518–2524

A One-Step Mechanochemical Route to Core−Shell Ca2SnO4 Nanoparticles Followed by 119Sn MAS NMR and 119Sn Mssbauer Spectroscopy

Vladimir epelk*† and Klaus Dieter BeckerChem

Abstract
Calcium stannate (Ca2SnO4) nanoparticles with an average size of about 15 nm were synthesized via single-step mechanochemical processing of binary oxide precursors at room temperature. High-resolution TEM studies revealed a nonuniform structure of mechanosynthesized Ca2SnO4 nanoparticles consisting of an ordered core surrounded by a disordered surface shell region. The inner core of a Ca2SnO4 nanoparticle possesses a fully ordered orthorhombic structure, and the surface shell exhibits the thickness of about 1.5 nm. The volume fraction of surface shell regions in the nanostructured mechanosynthesized stannate is estimated to be about 50%. Because of the ability of both solid-state 119Sn MAS NMR and 119Sn Mssbauer spectroscopies to probe the local environment of Sn nuclei, valuable complementary insight into the local structural disorder in mechanosynthesized Ca2SnO4 was obtained. It was concluded that the near-surface layers of stannate nanoparticles are disordered because of broadly distorted geometry of SnO6 octahedra. The octahedra are deformed in such a way that they become more regular.

J. Am. Chem. Soc., 2009, 131 (24), pp 8587–8594

NMR Detected Hydrogen−Deuterium Exchange Reveals Differential Dynamics of Antibiotic-and Nucleotide-Bound Aminoglycoside Phosphotransferase 3′-IIIa
Adrianne L. Norris† and Engin H. Serpersu*†‡§

Abstract
In this work, hydrogen−deuterium exchange detected by NMR spectroscopy is used to determine the dynamic properties of the aminoglycoside phosphotransferase 3′-IIIa (APH), a protein of intense interest due to its involvement in conferring antibiotic resistance to both Gram negative and Gram positive microorganisms. This represents the first characterization of dynamic properties of an aminoglycoside-modifying enzyme. Herein we describe in vitro dynamics of apo, binary, and ternary complexes of APH with kanamycin A, neomycin B, and metal−nucleotide. Regions of APH in different complexes that are superimposable in crystal structures show remarkably different dynamic behavior. A complete exchange of backbone amides is observed within the first 15 h of exposure to D2O in the apo form of this 31 kDa protein. Binding of aminoglycosides to the enzyme induces significant protection against exchange, and 30% of the amides remain unexchanged up to 95 h after exposure to D2O. Our data also indicate that neomycin creates greater solvent protection and overall enhanced structural stability to APH than kanamycin. Surprisingly, nucleotide binding to the enzyme−aminoglycoside complex increases solvent accessibility of a number of amides and is responsible for destabilization of a nearby β-sheet, thus providing a rational explanation for previously observed global thermodynamic parameters. Our data also provide a molecular basis for broad substrate selectivity of APH.

Macromolecules, v42, issue 10-12

Chain Folding and Diffusion in Monodisperse Long n-Alkanes by Solid-State NMR

Giuseppe Grasso*† and Jeremy J. Titman
Macromolecules, 2009, 42 (12), pp 4175–4180
DOI: 10.1021/ma801049j

Abstract: The size of the folded segment of the alkane chain in the integer-folded F2 form of C246H494 has been measured directly by NMR and shown to contain an average of 8 ± 2 carbon atoms at 293 K. This tight fold is in contrast to the looser fold obtained indirectly for similar samples in earlier NMR work but in good agreement with the picture provided by SAXS and LAM Raman spectroscopy studies. The recovery after saturation of the carbon-13 magnetization associated with the all-trans carbon-13 peak has also been measured for recovery times as long as 4000 s. The behavior as a function of recovery time has been compared with simple simulations which model the combined effects of chain diffusion and spin−lattice relaxation. These results suggest that at short times the mechanism for the magnetization recovery involves the alkane chain diffusing around the fold with the methyl groups constrained from entering the crystal through the opposite surface of the lamella. Hence, only small fluctuations in the length of the fold segment occur, and the two linked stems move in a loosely co-operative fashion. Despite the tight fold, the rate of magnetization recovery is compatible with a frequency for the underlying chain jump process similar to that responsible for the α-relaxation in polyethylene.

J. Phys Chem B and C, vol. v113, i24

1H Photo-CIDNP Enhancements in Heteronuclear Correlation NMR Spectroscopy

Ashok Sekhar and Silvia Cavagnero*
J. Phys. Chem. B, 2009, 113 (24), pp 8310–8318

Abstract:Photochemically induced dynamic nuclear polarization (photo-CIDNP) is usually employed as a probe of solvent exposure in biomolecular NMR. The potential of the photo-CIDNP effect for sensitivity enhancement, however, remains poorly explored. Here, we introduce 1H-photo-CIDNP in heteronuclear correlation spectroscopy at low laser irradiation power (1 W), and compare the sensitivity of various 1H-photo-CIDNP-enhanced- (HPE) 1H−15N heteronuclear correlation pulse sequences, including HSQC, HMQC, and SOFAST-HMQC, in terms of their ability to detect the Trp indole Hε1 resonance. Both Trp and the Trp-containing protein apoHmpH were analyzed using flavin mononucleotide as photosensitizer in aqueous solutions either containing or lacking urea. We find that 1H−15N photo-CIDNP-SOFAST-HMQC, denoted here as HPE-SOFAST-HMQC, yields a 2-fold higher signal-to-noise per unit time than the parent SOFAST-HMQC, for the solvent-exposed Trp of urea-unfolded apoHmpH. Thus, HPE-SOFAST-HMQC is the most sensitive heteronuclear correlation pulse sequence for the detection of solvent-exposed Trp.



Solid-State NMR Study of Nanodiamonds Produced by the Detonation Technique
Marc Dubois*†, Katia Gurin†, Elodie Petit†, Nicolas Batisse†, Andr Hamwi†, Naoki Komatsu‡, Jrme Giraudet§, Pascal Pirotte§ and Francis Masin*§
J. Phys. Chem. C, 2009, 113 (24), pp 10371–10378

Abstract:Nanodiamonds obtained by the detonation method have been investigated by means of solid-state magnetic nuclear resonance (NMR) and electron paramagnetic resonance. 13C and 1H magic angle spinning (MAS) NMR and 13C MAS NMR with 1H to 13C cross-polarization allow the determination of surface-hydrogenated groups (CH, CH2, and COH) and the quasi-absence of an sp2 carbon fullerene-like shell on the diamond surface to be underlined. The 1H and 13C spin−lattice relaxation time (T1) and second moment measurements are presented as a function of the temperature. Relaxation is shown to be mainly caused by paramagnetic centers in the case of 13C nuclei, whereas the presence of a molecular motion with an activation energy of 11.15 kJ·mol−1 is involved for 1H nuclei.



Identification of Mixed Valence Vanadium in ETS-10 Using Electron Paramagnetic Resonance, 51V Solid-State Nuclear Magnetic Resonance, and Density Functional Theory Studies

Kristopher Ooms† and Tatyana Polenova
Michael J. Nash‡ and Raul F. Lobo*
J. Phys. Chem. C, 2009, 113 (24), pp 10477–10484

Abstract: Microporous vanadium-substituted titanosilicate ETS-10 solids are promising photocatalysts for decomposition of organic molecules. The dopant vanadium metal modulates the electronic environment of the titanosilicate matrix and plays a major role in the enhancement of the photocatalytic activity. However, the local electronic and geometric structure of the vanadium sites in these materials is a subject of controversy. Using vanadium electron paramagnetic resonance (EPR) and 51V nuclear magnetic resonance (NMR) spectroscopy, we have characterized the local environments of the vanadium sites in vanadium-substituted ETS-10 samples with different vanadium loadings. The measurements reveal clearly the presence of V(IV) and V(V) oxidation states. The EPR results suggest that V(IV) is in octahedral sites and, therefore, must substitute for Ti in the framework. 51V NMR studies indicate that the V(V) species are adjacent to the V(IV) species in most cases on the basis of significant electron−nuclear dipolar interaction between the V(V) nuclei and the unpaired electron on V(IV). The NMR chemical shift and electric field gradient parameters estimated from the NMR spectra are used in conjunction with density functional theory calculations to propose a model where the V(V) species preferentially occupy sites at the ends of the octahedral chains.



Long-Time Scale Ionic Dynamics in Dense Clay Sediments Measured by the Frequency Variation of the 7Li Multiple-Quantum NMR Relaxation Rates in Relation with a Multiscale Modeling
Patrice Porion*, Anne Marie Faugre and Alfred Delville*
J. Phys. Chem. C, 2009, 113 (24), pp 10580–10597

Abstract: 7Li NMR relaxation measurements under spin-locking conditions are used to probe the dynamical properties of the lithium counterions within dense dispersions of charged anisotropic nanoplatelets. By simultaneously measuring the T1ρ and T2ρ relaxation times in addition to triple-quantum filtered relaxation times under the same spin-locking conditions, it is possible to separately quantify the contributions from the quadrupolar and the heterogeneous dipolar relaxation mechanisms. Thanks to the contribution from the residual quadrupolar coupling felt by the condensed lithium counterions, that procedure allows a broad dynamical range to be probed by performing spin-locking relaxation measurements using a limited number of irradiation powers. As illustrated by a multiscale modeling of the lithium diffusion and relaxation within such heterogeneous system, the frequency variation of the spectral densities characterizing the decorrelation of the quadrupolar coupling is a sensitive probe of the ionic mobility and the structure of the colloidal dispersion.



Proton Dynamics in Layered Double Hydroxides: A 1H T1 Relaxation and Line Width Investigation

Marc X. Reinholdt*†, Panakkattu K. Babu†‡§ and R. James Kirkpatrick†
J. Phys. Chem. C, 2009, 113 (24), pp 10623–10631

Abstract:The investigation of the dynamics of water and organic species confined in minerals or adsorbed at their surface is of significant geochemical, environmental, catalytic, biomedicine, and life’s growth interests but is poorly understood on the molecular scale. This work explores the behavior of water molecules and glutamate species adsorbed on and between the double hydroxide layers of hydrotalcite [HT; (Mg2Al)(OH)6A−·nH2O, where A− is a counteranion which may bear different charges] and compares the results to those for HT containing small inorganic anions. The relative humidity (RH) dependence of the 1H T1 relaxation rates for all samples reveals the existence of two separate spin systems with 1/T1 relaxation rates differing by a factor of approximately 2 × 103. The static 1H spectral line widths allow assigning the fast relaxing protons to the fixed “static” interlayer and adsorbed species—i.e. bound water, bound organic species, and most of the structural hydroxyl groups (-OH)—and the slow ones to the “mobile” species—i.e. free water and solvated organic molecules and some of the structural -OH groups.




Transformation of AlPO-53 to JDF-2: Reversible Dehydration of a Templated Aluminophosphate Studied by MAS NMR and Diffraction

Sharon E. Ashbrook*†, Marica Cutajar‡, John M. Griffin†, Zoe A. D. Lethbridge§, Richard I. Walton*§ and Stephen Wimperis*‡
J. Phys. Chem. C, 2009, 113 (24), pp 10780–10789

Abstract:We describe a detailed study of the aluminum phosphate AlPO-53 in both its as-made and calcined forms. In its as-made state, AlPO-53(A), the material is templated by methylammonium cations and contains occluded water molecules and also hydroxide ions that bridge pairs of aluminum atoms, increasing their coordination number to 5. Solid-state NMR experiments confirm the local environment of the aluminum and phosphorus atoms proposed in a previous structural model from powder X-ray diffraction. 31P NMR shows the presence of four distinct resonances with an intensity ratio of 1:1:2:2, consistent with the expected six crystallographic P sites. 27Al triple-quantum MAS NMR resolves five aluminum peaks, two with NMR parameters characteristic of four-coordinate Al and three of five-coordinate Al. One of these latter signals has a greater intensity than that of the others, consistent with the presence of two overlapping signals from two distinct crystallographic Al sites. First-principles calculations of NMR parameters provide a complete spectral assignment and confirm our interpretation of unresolved spectra. AlPO-53(A) is found to convert easily into a second crystalline phase on moderate heating (upon spinning in the NMR rotor for an extended period, for example), and variable-temperature powder X-ray experiments, together with TGA, suggest that this is a dehydration process yielding a second aluminophosphate, JDF-2. This is confirmed using both 31P and 27Al NMR, with the spectral assignment of JDF-2 supported by first-principles calculations. Calcination of AlPO-53(A) or of the dehydrated material, JDF-2, at 300 °C yields the microporous open-framework material AlPO-53(B), a tetrahedral network with three Al and three P sites, as confirmed by NMR and first-principles calculations. In addition to demonstrating the power of the combined use of NMR, first-principles calculations, and diffraction for detailed structural investigations, we show that the possibility of a reversible dehydration in as-made AlPO-53 and similar systems is an important consideration in structural studies and provides evidence that the published structural model for AlPO-53(A) may be incomplete.