Tuesday, June 19, 2007

Chemical Physics Letters (CPL) update

Simultaneous acquisition and effective separation of intermolecular multiple-quantum signals of different orders
Zhu, Xiaoqin; Chen, Song; Chen, Zhong; Cai, Shuhui; Zhong, Jianhui vol 438, iss 4-6, pp. 308-314.
Abstract: A three-pulse sequence was designed to simultaneously acquire intermolecular multiple-quantum coherence (iMQC) signals of coherence order n=2,1,0,−1,−2. Analytical expressions were derived from modified Bloch equations. Signal of a specific order was obtained by optimal combinations of data from different acquisition steps. This allows a time saving of 5/7 compared to the phase cycling designs targeted for individual coherence orders. The method also results in pure iMQC signal of all the above five orders which are insensitive to radio-frequency flip angle errors, in contrast to some previous methods. Theoretical predictions are supported by the experimental observations and numerically simulated results.

13C and 1H nuclear magnetic shielding and spin–spin coupling constants of 13C-enriched bromomethane in the gas phase 13C and 1H nuclear magnetic shielding and spin–spin coupling constants of 13C-enriched bromomethane in the gas phase
Jackowski, Karol; Kubiszewski, Marek; Wilczek, Marcin vol 440, iss 4-6, pp. 176-179.
Abstract: 13C and 1H NMR spectral parameters are investigated for 13CH3Br in gaseous matrices. It is found that both the 13C and 1H chemical shifts of 13CH3Br are linearly dependent on solvent density. Similar dependence is also detected for one-bond spin–spin coupling, 1J(CH). For the first time the 13C and 1H magnetic shielding constants and 1J(CH) spin–spin coupling are obtained for an isolated 13CH3Br molecule together with the coefficients responsible for solute–solvent molecular interactions in gaseous matrices. The present experimental results confirm the accuracy of some recent ab initio calculations of nuclear magnetic shielding performed for bromomethane.

Analysis of molecular structures by homo- and hetero-nuclear J-coupled NMR in ultra-low field J-coupled NMR in ultra-low field
Appelt, Stephan; Häsing, F. Wolfgang; Kühn, Holger; Sieling, Ulrich; Blümich, Bernhard vol 440, iss 4-6, pp. 308-312.
Abstract: The drawback of nuclear magnetic resonance (NMR) spectroscopy at ultra-low magnetic fields appears to be the lack of access to chemical information in terms of chemical shifts and homo-nuclear J-couplings. Here we report that a chemical group can be identified by the multiplet structure of the NMR spectrum in ultra-low fields if the condition of the strong hetero-nuclear J-coupling is fulfilled. Moreover we found that high-resolution ultra-low field proton-NMR spectra of liquids indeed reveal all hetero- and homo-nuclear J-couplings in terms of pairs of multiplets. This opens the door for the study of molecular structures at ultra-low magnetic fields.

Contribution of 43Ca MAS NMR for probing the structural configuration of calcium in glass 43Ca MAS NMR for probing the structural configuration of calcium in glass
Angeli, Frédéric; Gaillard, Marina; Jollivet, Patrick; Charpentier, Thibault vol 440, iss 4-6, pp. 324-328.
Abstract: The 43Ca MAS NMR spectra obtained for three calcium silicate glasses containing aluminum and/or sodium are analyzed. The 43Ca NMR parameters are shown to be highly sensitive to variations in its chemical environment. The transition from a charge-compensating role of [AlO4]− groups to a network-modifying role near nonbridging oxygen atoms results in an increase of both the isotropic chemical shift and the quadrupolar coupling constant of 43Ca. This effect can be related to the first coordination shell of calcium (through the Ca–O bond distance) which is affected by the chemical environment beyond the first neighbors of calcium.

Evaluation of nanometer-scale droplets in a ternary o/w microemulsion using SAXS and 129Xe NMR 129Xe NMR
Kataoka, Hiroshi; Ueda, Takahiro; Ichimei, Daisuke; Miyakubo, Keisuke; Eguchi, Taro; Takeichi, Nobuhiko; et. al. vol 441, iss 1-3, pp. 109-114.
Abstract: This study revealed a linear correlation between the nanometer-scale oil droplet sizes estimated using small angle X-ray scatterings (SAXS) and the 129Xe NMR chemical shift in an oil-in-water ternary microemulsion system comprising pentaethylene glycol mono-n-dodecyl ether, n-decane, and deuterium oxide. The absolute values of the droplet size estimated using 129Xe NMR show good agreement with those using SAXS. We also found that the results are consistent with a reported relation derived using small angle neutron scattering. The results suggest the validity of 129Xe NMR chemical shifts for investigation of colloidal systems to evaluate their internal structures’ characteristic sizes.

Monday, June 18, 2007

Chemistry - A European Journal (CEJ) updates

Sandwich-like Compounds Based on the All-Metal Aromatic Unit Al42− and the Main-Group Metals M (M=Li, Na, K, Be, Mg, Ca)
Yang, Li-Ming; Ding, Yi-Hong; Sun, Chia-Chung, vol 13, iss 9, pp. 2546 - 2555.

Molecular Tectonics of Metal–Organic Frameworks (MOFs): A Rational Design Strategy for Unusual Mixed-Connected Network Topologies
Du, Miao; Zhang, Zhi-Hui; Tang, Liang-Fu; Wang, Xiu-Guang; Zhao, Xiao-Jun; Batten, Stuart R. vol 13, iss 9, pp. 2578 - 2586.

Porous Liquids
O'Reilly, Niamh; Giri, Nicola; James, Stuart L. vol 13, iss 11, pp. 3020 - 3025.

First-Principles Molecular Dynamics Evaluation of Thermal Effects on the NMR 1JLi,C Spin–Spin Coupling 1JLi,C Spin–Spin Coupling
de la Lande, Aurélien; Fressigné, Catherine; Gérard, Hélène; et. al. vol 13, iss 12, pp. 3459 - 3469.

High-Density Storage of H2 in Microporous Crystalline Silica at Ambient Conditions 2 in Microporous Crystalline Silica at Ambient Conditions
van den Berg, Annemieke W. C.; Pescarmona, Paolo P.; Schoonman, Joop; Jansen, Jacobus C. vol 13, iss 13, pp. 3590 - 3595.

Reversible Transformation of ZnII Coordination Geometry in a Single Crystal of Porous Metal-Organic Framework [Zn3(ntb)2(EtOH)2]s4 EtOH II Coordination Geometry in a Single Crystal of Porous Metal-Organic Framework [Zn3(ntb)2(EtOH)2]s4 EtOH
Suh, Myunghyun Paik; Cheon, Young Eun; Lee, Eun Young vol 13, iss 15, pp. 4208 - 4215.

51V NMR Chemical Shifts Calculated from QM/MM Models of Vanadium Chloroperoxidase 51V NMR Chemical Shifts Calculated from QM/MM Models of Vanadium Chloroperoxidase
Waller, Mark P.; Bühl, Michael; Geethalakshmi, K. R.; Wang, Dongqi; Thiel, Walter vol 13, iss 17, pp. 4723 - 4732.

Unmasking Melon by a Complementary Approach Employing Electron Diffraction, Solid-State NMR Spectroscopy, and Theoretical Calculations—Structural Characterization of a Carbon Nitride Polymer
Lotsch, Bettina V.; Döblinger, Markus; Sehnert, Jan; Seyfarth, Lena; Senker, Jürgen; et. al. vol 13, iss 17, pp. 4969 - 4980.

Semiconductor Behavior of a Metal-Organic Framework (MOF)
Alvaro, Mercedes; Carbonell, Esther; Ferrer, Belén; Llabrés i Xamena, Francesc X.; et. al. vol 13, iss 18, pp. 5106 - 5112.

Journal of Solid State Chemistry (JSSC) updates

Structural modulation in K2V3O8 2V3O8
Chakoumakos, B.C.; Custelcean, R.; Kamiyama, T.; Oikawa, K.; Sales, B.C.; Lumsden, M.D. vol 180, pp. 812-817.

Preparation of mesoporous cadmium sulfide nanoparticles with moderate pore size
Han, Zhaohui; Zhu, Huaiyong; Shi, Jeffrey; Parkinson, Gordon; Lu, G.Q. vol 180, pp. 902-906.

Porous properties of silylated mesoporous silica and its hydrogen adsorption
Takei, Takahiro; Houshito, Ohki; Yonesaki, Yoshinori; Kumada, Nobuhiro; Kinomura, Nobukazu vol 180, pp. 1180-1187.

Monday, June 11, 2007

Chem. Soc. Rev. articles to check out

Chem. Soc. Rev. articles to check out

Five-membered metallacycles of titanium and zirconium – attractive compounds for organometallic chemistry and catalysis

Uwe Rosenthal, Vladimir V. Burlakov, Marc A. Bach and Torsten Beweries, Chem. Soc. Rev., 2007, 36, 719
DOI: 10.1039/b605734a

Main-chain organometallic polymers: synthetic strategies, applications, and perspectives
Kyle A. Williams, Andrew J. Boydston and Christopher W. Bielawski, Chem. Soc. Rev., 2007, 36, 729
DOI: 10.1039/b601574n

Metalloid group 14 cluster compounds: An introduction and perspectives to this novel group of cluster compounds
Andreas Schnepf, Chem. Soc. Rev., 2007, 36, 745
DOI: 10.1039/b516379j

CdSe nanocrystal based chem-/bio- sensors
Rebecca C. Somers, Moungi G. Bawendi and Daniel G. Nocera, Chem. Soc. Rev., 2007, 36, 579
DOI: 10.1039/b517613c

The chemistry of functionalised N-heterocyclic carbenes
Olaf Kühl, Chem. Soc. Rev., 2007, 36, 592
DOI: 10.1039/b603765h

195Pt NMR—theory and application
Brett M. Still, P. G. Anil Kumar, Janice R. Aldrich-Wright and William S. Price, Chem. Soc. Rev., 2007, 36, 665
DOI: 10.1039/b606190g

Harbison`s STREAQI for large quadrupolar interactions

Journal of Magnetic Resonance
Volume 186, Issue 2, June 2007, Pages 347-351

Slow turning reveals enormous quadrupolar interactions (STREAQI)

John Persons and Gerard S. Harbison
Department of Chemistry, University of Nebraska at Lincoln, Lincoln, NE 68588-0304, USA
Received 18 December 2006; revised 1 March 2007. Available online 12 March 2007.


We introduce a new solid-state NMR method, which uses very slow sample rotation to visualize NMR spectra whose width exceeds feasible spectrometer bandwidths. It is based on the idea that if we reorient a tensor by a known angle about a known axis, the shifts in the NMR frequencies observed across the spectral width allow us to reconstruct the entire tensor. Called STREAQI (Slow Turning Reveals Enormous Anisotropic Quadrupolar Interactions), this method allows us to probe NMR nuclei that are intractable to current methods. To prove the concept and demonstrate its promise we have implemented the method for several 79Br containing samples with quadrupolar coupling constants in the range of 10–50 MHz.

Keywords: Quadrupolar interactions; Sample rotation; NMR; Bromine-79

Journal of Magnetic Resonance, up to May 2007

Journal of Magnetic Resonance
Vol: 186, Issue: 1, May, 2007
pp. 26-33

Title: The role of 15N CSA and CSA/dipole cross-correlation in 15N relaxation in solid proteins
Authors: Sein, Juliena; Giraud, Nicolasa; Blackledge, Martinb; Emsley, Lyndona
Affiliations: a. Laboratoire de Chimie (UMR 5182 CNRS/ENS Lyon), Ecole Normale Supérieure de Lyon, 69364 Lyon, France
b. Institut de Biologie Structurale Jean Pierre Ebel (UMR 5075 CNRS/CEA/UJF), 38027 Grenoble, France
Keywords: Nitrogen-15 longitudinal relaxation; Solid-state NMR; Protein dynamics; Cross-correlation; Magic angle spinning

The influence of the 15N CSA on 15N longitudinal relaxation is investigated for an amide group in solid proteins in powder form under MAS. This contribution is determined to be typically 20–33% of the overall longitudinal relaxation rate, at 11.74 and 16.45T, respectively. The improved treatment is used to analyze the internal dynamics in the protein Crh, in the frame of a motional model of diffusion in a cone, using the explicit average sum approach. Significant variations with respect to the determined dynamics parameters are observed when properly accounting for the contribution of 15N CSA fluctuations. In general, the fit of experimental data including CSA led to the determination of diffusion times (tw) which are longer than when considering only an 15N–1H dipolar relaxation mechanism. CSA-Dipole cross-correlation is shown to play little or no role in protonated solids, in direct contrast to the liquid state case.
# 10.1016/j.jmr.2007.01.010

Journal of Magnetic Resonance
Vol: 186, Issue: 1, May, 2007
pp. 94-99

Title: Resolution enhancement using a new multiple-pulse decoupling sequence for quadrupolar nuclei
Authors: Delevoye, L.a; Trébosc, J.a; Gan, Z.b; Montagne, L.a; Amoureux, J-P.a
Affiliations: a. UCCS, CNRS-8181, ENSCL-USTL, 59652 Villeneuve d’Ascq, France
b. NHMFL, 32310 Tallahassee, FL, USA
Keywords: Solid-state NMR; Quadrupolar nuclei; Decoupling; Scalar coupling

A new decoupling composite pulse sequence is proposed to remove the broadening on spin S=1/2 magic-angle spinning (MAS) spectra arising from the scalar coupling with a quadrupolar nucleus I. It is illustrated on the 31P spectrum of an aluminophosphate, AlPO4-14, which is broadened by the presence of 27Al/31P scalar couplings. The multiple-pulse (MP) sequence has the advantage over the continuous wave (CW) irradiation to efficiently annul the scalar dephasing without reintroducing the dipolar interaction. The MP decoupling sequence is first described in a rotor-synchronised version (RS-MP) where one parameter only needs to be adjusted. It clearly avoids the dipolar recoupling in order to achieve a better resolution than using the CW sequence. In a second improved version, the MP sequence is experimentally studied in the vicinity of the perfect rotor-synchronised conditions. The linewidth at half maximum (FWHM) of 65Hz using 27Al CW decoupling decreases to 48Hz with RS-MP decoupling and to 30Hz with rotor-asynchronised MP (RA-MP) decoupling. The main phenomena are explained using both experimental results and numerical simulations.
# 10.1016/j.jmr.2007.01.018

Journal of Magnetic Resonance
Vol: 186, Issue: 1, May, 2007
pp. 156-159

Title: Multiple Ca2+ environments in silicate glasses by high-resolution 43Ca MQMAS NMR technique at high and ultra-high (21.8T) magnetic fields
Authors: Shimoda, Keijia; Tobu, Yasuhiroa; Shimoikeda, Yuichib; Nemoto, Takahirob; Saito, Kojia
Affiliations: a. Advanced Technology Research Laboratories, Nippon Steel Corporation, 20-1 Shintomi, Futtsu 293-8511, Japan
b. JEOL Ltd., 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan
Keywords: 7QMAS; Ca-43; Silicate glass; Ultra-high magnetic field; Solid-state NMR

We here show the 43Ca 5QMAS NMR spectra at high field (16.4T) and the first 7QMAS spectrum at ultra-high field (21.8T) for geologically important Ca-containing glasses. The high-resolution MQMAS spectra present a clear evidence of multiple Ca sites in the amorphous structures that have never been identified by other analytical methods. The present study suggests that the Ca2+ ions are mainly in 7- and 8-fold coordination sites. This will offer valuable insights for dynamic properties of magmatic liquids. The MQMAS NMR technique at high magnetic field is a unique tool to understand the detailed structural information on a specific element in solids including organic and inorganic compounds.
# 10.1016/j.jmr.2007.01.019

Journal of Magnetic Resonance
Vol: 185, Issue: 2, April, 2007
pp. 326-330

Title: Spectral editing in solid-state MAS NMR of quadrupolar nuclei using selective satellite inversion
Authors: Dey, Krishna K.a; Prasad, S.a; Ash, Jason T.a; Deschamps, Michaelb; Grandinetti, Philip J.a
Affiliations: a. Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210-1173, USA
b. CRMHT-CNRS, UPR4212, 45071 Orleans cedex2, France
Keywords: Quadrupolar nuclei; Sensitivity enhancement; Inversion; Spectral editing; Satellite inversion

A sensitivity enhancement method based on selective adiabatic inversion of a satellite transition has been employed in a (p/2)CT– Formula Not Shown –(p/2)CT spectral editing sequence to both enhance and resolve multisite NMR spectra of quadrupolar nuclei. In addition to a total enhancement of 2.5 times for spin 3/2 nuclei, enhancements up to 2.0 times is reported for the edited sites in a mixture of rubidium salts.
# 10.1016/j.jmr.2006.12.013

Journal of Magnetic Resonance
Vol: 185, Issue: 2, April, 2007
pp. 318-325

Title: Spin-locking and recoupling of homonuclear dipolar interaction between spin-3/2 nuclei under magic-angle sample spinning
Author: Mali, Gregora
Affiliations: a. National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia
Keywords: Quadrupolar nuclei; MAS; Spin-lock; Homonuclear dipolar recoupling

Numerical simulations and experiments were used to examine the possibility of employing strong spin-lock fields for recoupling of homonuclear dipolar interactions between spin-3/2 quadrupolar nuclei and to compare it to the rotary-resonance recoupling at weak spin-lock fields. It was shown that strong spin-lock pulses under MAS conditions can lead to recoupling, provided that the electric-field gradient principal axes systems of the coupled nuclei are aligned and that their quadrupolar coupling constants are approximately the same. The phenomenon is based on the fact that strong spin-lock pulses induce adiabatic transfer of magnetization between the central-transition coherence and the triple-quantum coherence with equal periodicity as is the periodicity of the time-dependent dipolar coupling. Because of the synchronous variation of the state of the spin system and of the dipolar interaction, the effect of the latter on the central-transition coherence and on the triple-quantum coherence is not averaged out by sample rotation. The approach is, however, very sensitive to the relative orientation of the electric-field gradient principal axes systems and therefore less robust than the approach based on weak spin-lock pulses that satisfy rotary-resonance condition.
# 10.1016/j.jmr.2007.01.008

Journal of Magnetic Resonance
Vol: 185, Issue: 1, March, 2007
pp. 159-163

Title: Long-term stability of rotor-controlled MAS frequencies to 0.1Hz proved by 14N MAS NMR experiments and simulations
Authors: Jakobsen, Hans J.a; Hove, Anders R.a; Bildsøe, Henrika; Skibsted, Jørgena; Brorson, Michaelb
Affiliations: a. Instrument Centre for Solid-State NMR Spectroscopy, Department of Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark
b. Haldor Topsøe A/S, Nymøllevej 55, DK-2800 Lyngby, Denmark
Keywords: 0.1Hz MAS stability; Air pressure stabilization; 14N MAS NMR; Ammonium monomolybdate polymorphs; STARS simulations

Experimental and simulated 14N MAS NMR spectra of the Formula Not Shown ions in the two polymorphs, mS60 and mP60, of (NH4)2MoO4 are used to illustrate that a long-term stability of rotor-controlled MAS frequencies to 0.1Hz can be achieved using commercial instrumentation (MAS speed controller and 7.5mm MAS probe with a single marked rotor) attached to a highly pressure-stabilized air supply. A new modification of the STARS simulation software employs a Gaussian distribution for the experimental spinning frequency around the frequency set for the MAS speed controller. A simulated spectrum is then obtained by summation of several calculated spectra for evenly spaced spinning frequencies around the set frequency with relative weight factors corresponding to the Gaussian distribution.
# 10.1016/j.jmr.2006.12.008

Journal of Magnetic Resonance
Vol: 185, Issue: 1, March, 2007
pp. 173-178

Title: Symmetry-based recoupling of proton chemical shift anisotropies in ultrahigh-field solid-state NMR
Authors: Brouwer, Darren H.a; Ripmeester, John A.a
Affiliations: a. Steacie Institute for Molecular Sciences, National Research Council, 100 Sussex Drive, Ottawa, Ont., Canada K1A 0R6
Keywords: Proton MAS NMR; Chemical shift anisotropy; Recoupling; CRAMPS; Hydrogen bonding

A two-dimensional NMR experiment for estimating proton chemical shift anisotropies (CSAs) in solid powders under magic-angle spinning conditions is demonstrated in which 1H CSAs are reintroduced with a symmetry-based recoupling sequence while the individual proton sites are resolved according to their isotropic chemical shifts by magic-angle spinning (MAS) or combined rotation and multiple pulse (CRAMPS) homonuclear decoupling. The experiments where carried out on an ultrahigh-field solid-state NMR instrument (900MHz 1H frequency) which leads to increased resolution and reliability of the measured 1H CSAs. The experiment is expected to be important for investigating hydrogen bonding in solids.
# 10.1016/j.jmr.2006.12.003

Magnetic Resonance in Chemistry, up to July 2007

Magnetic Resonance in Chemistry
Vol: 45, Issue: 7, July 2007
pp. 532 - 543

Title: NMR spectra, GIAO and charge density calculations of five-membered aromatic heterocycles
Authors: Katritzky, Alan R.a; Akhmedov, Novruz G.a; Doskocz, Jacek; Mohapatra, Prabhu P.a; Hall, C. Dennisa; Güven, Alâattinb
Affiliations: a. Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, FL 32611‐7200, USA
b. Department of Chemistry, Faculty of Sciences, Anadolu University, 26470 Eskisehir, Turkey
Keywords: NMR; coupling constants; GIAO; pyrrole; five-membered heterocycles
Abstract (English):

The B3LYP/6-31 + G(d) molecular geometry optimized structures of 17 five-membered heterocycles were employed together with the gauge including atomic orbitals (GIAO) density functional theory (DFT) method at the B3LYP/6-31 + G(d,p), B3LYP/6-311 + + G(d,p) and B3LYP/6-311 + G(2d,p) levels of theory for the calculation of proton and carbon chemicals shifts and coupling constants. The method of geometry optimization for pyrrole (1), N-methylpyrrole (2) and thiophene (7) using the larger 6-311 + + G(d,p) basis sets at the B3LYP/6-31 + G(d,p), B3LYP/6-311 + + G(d,p), B3LYP/6-31 + G(2d,p) and B3LYP/cc-pVTZ levels of theory gave little difference between calculated and experimental values of coupling constants. In general, the 1H and 13C chemical shifts for all compounds are in good agreement with theoretical calculations using the smaller 6-31 basis set. The values of nJHH(n = 3, 4, 5) and rmnJCH(n = 1, 2, 3, 4) were predicted well using the larger 6-31 + G(d,p) and 6-311 + + G(d,p) basis sets and at the B3LYP/6-31 + G(d,p), B3LYP/6-311 + + G(d,p), B3LYP/6-31 + G(2d,2p) levels of theory. The computed atomic charges [Mülliken; Natural Bond Orbital Analysis (NBO); Merz-Kollman (MK); CHELP and CHELPG] for the B3LYP/6-311 + + G(d,p) geometry optimized structures of 1–17 were used to explore correlations with the experimental proton and carbon chemical shifts. Copyright © 2007 John Wiley & Sons, Ltd.
Publisher: John Wiley & Sons, Ltd.
Language of Publication: English
# 1097-458X(200707)45:7<532::aid-mrc1967>3.0.CO;2-C
# http://www.interscience.wiley.com/jpages/0749-1581/suppmat/

Magnetic Resonance in Chemistry
Vol: 45, Issue: 7, July 2007
pp. 547 - 556

Title: Solid-state 17O NMR study of the electric-field-gradient and chemical shielding tensors in polycrystalline amino acids
Authors: Yamada, Kazuhikoa; Shimizu, Tadashib; Tansho, Masatakab; Nemoto, Takahiroc; Asanuma, Miwakoa; Yoshida, Mitsurud; Yamazaki, Toshioa; Hirota, Hiroshia
Affiliations: a. RIKEN Genomic Sciences Center, 1‐7‐22 Suehiro, Tsurumi, Yokohama, 230‐0045 Japan
b. Tsukuba Magnet Laboratory, National Institute for Materials Science, 3‐13 Sakura, Tsukuba, 305‐003 Japan
c. Analytical R&D team NM&sol;ER Group, Analytical Instrument Division, JEOL Ltd, 3‐1‐2 Musashino Akishima, Tokyo, 189‐8558 Japan
d. Analytical Science Division, National Food Research Institute, 2‐1‐12 Kannondai, Tsukuba, 305‐8642 Japan
Keywords: NMR; 17O; electric-field-gradient tensor; chemical shielding tensor; amino acids; hydrogen bond; MQMAS
Abstract (English):

We have presented a systematic experimental investigation of carboxyl oxygen electric-field-gradient (EFG) and chemical shielding (CS) tensors in crystalline amino acids. Three 17O-enriched amino acids were prepared: L-aspartic acid, L-threonine, and L-tyrosine. Analysis of two-dimensional 17O multiple-quantum magic-angle spinning (MQMAS), MAS, and stationary NMR spectra yields the 17O CS, EFG tensors and the relative orientations between the two tensors for the amino acids. The values of quadrupolar coupling constants (CQ) are found to be in the range of 6.70–7.60 MHz. The values of diso lie in the range of 268–292 ppm, while those of the d11 and d22 components vary from 428 to 502 ppm, and from 303 to 338 ppm, respectively. There is a significant correlation between the magnitudes of d22 components and C—O bond lengths. Since C—O bond length may be related to hydrogen-bonding environments, solid-state 17O NMR has significant potential to provide insights into important aspects of hydrogen bonds in biological systems. Copyright © 2007 John Wiley & Sons, Ltd.
# 10.1002/mrc.2002

Magnetic Resonance in Chemistry
Vol: 45, Issue: 7, July 2007
pp. 595 - 600

Title: Janocchio—a Java applet for viewing 3D structures and calculating NMR couplings and NOEs
Authors: Evans, David A.a; Bodkin, Michael J.a; Baker, S. Richarda; Sharman, Gary J.a
Affiliations: a. Eli Lilly and Company Ltd, Lilly Research Centre, Windlesham, Surrey, GU20 6PH, UK
Keywords: J-coupling; NOE; Java; applet
Abstract (English):

We present a Java applet, based on the open source Jmol program, which allows the calculation of coupling constants and NOEs from a three-dimensional structure. The program has all the viewing features of Jmol, but adds the capability to calculate both H–H and H–C 3-bond couplings constants. In the case of H—H couplings, the Altona equation is used to perform this. The program also calculates NOEs using the full relaxation matrix approach. All these calculations are driven from a simple point and click interface. The program can calculate values for multi-structure files, and can produce input files for the conformational fitting program NAMFIS. Copyright © 2007 John Wiley & Sons, Ltd.
# 10.1002/mrc.2016

Magnetic Resonance in Chemistry
Vol: 45, Issue: 6, June 2007
pp. 488 - 495

Title: Dynamics and conformations of PEO chains chemically bonded on silica: comparison between 1H and 2H NMR
Authors: Tajouri, T.a; Hommel, H.b
Affiliations: a. Université de Tunis ‐ IPEIT ‐ UR 0113/04, 2, rue Jawhar Let Nahrou ‐ Montfleury, 1008 Tunis, Tunisia
b. Laboratoire de Physico‐Chimie des Polymères et des Milieux Dispersés, E.S.P.C.I., U.M.R. 7615 C.N.R.S., 10 rue Vauquelin, 75231 Paris Cedex 05, France
Keywords: NMR; 1H; 2H; poly(ethylene oxide); grafted polymer; interfaces

1H NMR was used to study the motion of monomer units in a layer of poly(ethylene oxide) chains grafted on silica. First, the dependence of the relaxation times on the grafting ratios is discussed qualitatively from a phenomenological point of view. Next, the NMR line narrowing effect by high-speed rotation is observed in the same samples with different grafting ratios. The magic angle spinning technique permits determination of two correlation times for each grafting ratio: tc characteristic of an environment with a fast motion and tl characteristic of an environment with a slow motion. In addition, the dynamics of these grafted chains are investigated by deuterium NMR (2H NMR), which is sensitive to the anisotropy of molecular motion. The evolution has been studied for two extreme grafting ratios and each time as a function of temperature. The anisotropy is more marked at low temperatures and for a low grafting ratio. The results are consistent with the 1H NMR relaxation times measured as a function of temperature. Copyright © 2007 John Wiley & Sons, Ltd.
# 10.1002/mrc.1997

Magnetic Resonance in Chemistry
Vol: 45, Issue: 6, June 2007
pp. 488 - 495

Title: Dynamics and conformations of PEO chains chemically bonded on silica: comparison between 1H and 2H NMR
Authors: Tajouri, T.a; Hommel, H.b
Affiliations: a. Université de Tunis ‐ IPEIT ‐ UR 0113/04, 2, rue Jawhar Let Nahrou ‐ Montfleury, 1008 Tunis, Tunisia
b. Laboratoire de Physico‐Chimie des Polymères et des Milieux Dispersés, E.S.P.C.I., U.M.R. 7615 C.N.R.S., 10 rue Vauquelin, 75231 Paris Cedex 05, France
Keywords: NMR; 1H; 2H; poly(ethylene oxide); grafted polymer; interfaces

1H NMR was used to study the motion of monomer units in a layer of poly(ethylene oxide) chains grafted on silica. First, the dependence of the relaxation times on the grafting ratios is discussed qualitatively from a phenomenological point of view. Next, the NMR line narrowing effect by high-speed rotation is observed in the same samples with different grafting ratios. The magic angle spinning technique permits determination of two correlation times for each grafting ratio: tc characteristic of an environment with a fast motion and tl characteristic of an environment with a slow motion. In addition, the dynamics of these grafted chains are investigated by deuterium NMR (2H NMR), which is sensitive to the anisotropy of molecular motion. The evolution has been studied for two extreme grafting ratios and each time as a function of temperature. The anisotropy is more marked at low temperatures and for a low grafting ratio. The results are consistent with the 1H NMR relaxation times measured as a function of temperature. Copyright © 2007 John Wiley & Sons, Ltd.
# 10.1002/mrc.1997

Magnetic Resonance in Chemistry
Vol: 45, Issue: 5, May 2007
pp. 401 - 409

Title: Solid-state 19F MAS NMR study on the conformation and molecular mobility of poly(chlorotrifluoroethylene)
Authors: Tatsuno, Hirotoa; Aimi, Keitaroa; Ando, Shinjia
Affiliations: a. Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama, Meguro‐ku, Tokyo 152‐8552, Japan
Keywords: NMR; 19F; magic angle spinning; dipolar–filter; T1r–filter; 19F shieldings; poly(chlorotrifluoroethylene); conformation; molecular mobility
Abstract (English):

The temperature dependence of molecular mobility and conformational changes of poly(chlorotrifluoro- ethylene) (PCTFE) have been investigated by solid-state 19F magic angle spinning (MAS) NMR spectroscopy. The pulse techniques of dipolar–filter and T1r–filter allow selective observation of the amorphous and crystalline domains, respectively. The temperature dependence of T1rF revealed that the segmental motion in the amorphous domain becomes vigorous above ca 80 °C, which is well above the glass transition (Tg) temperature (52 °C) and more close to the b-relaxation temperature (95 °C). On the other hand, vigorous molecular motions in the crystalline domain occur above 120 °C, which is much below the melting temperature (212 °C). This indicates that the polymer chains in the PCTFE crystallites are more mobile than those of typical semicrystalline fluoropolymers like poly(vinylidene fluoride) (PVDF), which can be associated with structural imperfections in the crystallites. In addition, the density functional theory (DFT) calculations of 19F magnetic shielding suggest that the high-frequency shifts observed for the crystalline signals above 80 °C can be ascribed to the conformational change around meso diads toward more twisted and/or helical conformations in the main chain. Copyright © 2007 John Wiley & Sons, Ltd.
# 10.1002/mrc.1982

Progress in NMR, up to August 2007

Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 51, Issue: 1, August 30, 2007
pp. 1-35
Title: Proton multiple-quantum NMR for the study of chain dynamics and structural constraints in polymeric soft materials
Author: Saalwächter, Kaya
Affiliations: a. Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Friedemann-Bach-Platz 6, D-06108 Halle, Germany
Keywords: Residual dipolar couplings; Transverse relaxation; Double-quantum NMR; Polymer dynamics; Elastomers; Networks; Rubber; Swelling; Poly(isoprene); Poly(butadiene); Poly(dimethylsiloxane)
# 10.1016/j.pnmrs.2007.01.001

Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 50, Issue: 4, July 30, 2007
pp. 179-198
Forty years of Progress in Nuclear Magnetic Resonance Spectroscopy
Emsley, J.W.a; Feeney, J.b
a. Chemistry Department, University of Southampton, Southampton SO17 1BJ, UK
b. Molecular Structure Division, MRC National Institute for Medical Research, The Ridgeway, Mill
Keywords: NMR history; Progress in NMR Spectroscopy; NMR Milestones
# 10.1016/j.pnmrs.2007.01.002

Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 50, Issue: 4, July 30, 2007
pp. 199-251
Title: Probing proton–proton proximities in the solid state
Author: Brown, Steven P.a
Affiliations: a. Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
Keywords: Solid-state NMR; MAS; 1H; Double quantum; Dipolar couplings
# 10.1016/j.pnmrs.2006.10.002

Solid-state NMR update to April 2007

Solid State Nuclear Magnetic Resonance
Volume 31, Issue 2, April 2007, Pages 100-114

Simulations of molecular dynamics in solid-state NMR spectra of spin-1 nuclei including effects of CSA- and EFG-terms up to second order

Flemming H. Larsen
Department of Food Science, Quality and Technology, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg, Denmark
Received 15 October 2006; revised 28 January 2007. Available online 1 March 2007.


By numerical simulations MAS and QCPMG methods for acquiring spectra of spin-1 nuclei were compared in order to determine the most sensitive experiment for analysis of molecular dynamics. To comply with the large quadrupolar constants for 14N and the CSA reported for 6Li both of these interactions are included up to second order. For 2H and 6Li both QCPMG and single-pulse MAS experiments were suitable for dynamics studies whereas the single-pulse MAS experiment were the method of choice for investigation of 14N dynamics for CQ's larger than 750 kHz at 14.1 T. This property prohibits excitation of the 14N lineshape using either single hard or softer composite rf-pulses. Focusing on 14N it was demonstrated that the centerband lineshape is sensitive toward both off-MAS and CSA effects. In addition, excitation by real-time pulses showed that proper lineshapes corresponding to a site with a CQ of 3 MHz may be excited by a very short pulse.

Keywords: QCPMG; MAS; 2H; 6Li; 14N; Solid-state; Multiple-site jump; Molecular dynamics

Solid State Nuclear Magnetic Resonance
Volume 31, Issue 2, April 2007, Pages 63-71 Result list | previous <> next

Effect of magnetic particles on NMR spectra of Murchison meteorite organic matter and a polymer-based model system

E.M. Levin, S.L. Bud’ko, J.D. Mao Y. Huang and K. Schmidt-Rohr
aAmes Laboratory DOE, Iowa State University, Ames, IA 50011-3020, USA
bDepartment of Physics and Astronomy, Iowa State University, Ames, IA 50011-3020, USA
cDepartment of Chemistry, Iowa State University, Ames, IA 50011-3020, USA
dDepartment of Chemistry and Biochemistry, Old Dominion University, 4541 Hampton Boulevard, Norfolk, VA 23529-0126, USA
eDepartment of Geological Sciences, Brown University, Providence, RI 02912, USA
Received 26 September 2006; revised 29 November 2006. Available online 26 January 2007.


Organic matter from the Murchison meteorite shows pronounced spinning sidebands of the 1H MAS NMR spectrum and exhibits a large bulk magnetization of 0.75 emu/g extrapolated to 94 kOe at 300 K. By comparison with data of diamagnetic polystyrene and laponite clay mixed with ferrimagnetic γ-Fe2O3 nano-particles, we show that the spinning sidebands arise from a combination of dipolar couplings of a given 1H to magnetic particles, seen in a backscattered-electron image, and to other protons. Signal loss and significant broadening of protonated-carbon peaks in 13C MAS NMR spectra of polystyrene with Fe2O3 nano-particles is demonstrated, and implications for 13C NMR spectroscopy of Murchison meteorite are discussed.

Keywords: Solid-state nuclear magnetic resonance; Paramagnetic effect; Meteorite organic matter; Magnetic particles; 1H sidebands

Thursday, June 07, 2007

Aaron's Journal Update (J Phys Chem B and C, Macromolecules, Organometallics)

Not too much SSNMR to be found in J Phys Chem B or C this time around.

-Marek Pruski and Ganapathy. Nice work on HETCOR and CP/CPMG of MCM-41 systems

J. Phys. Chem. B, 111 (15), 3877 -3885, 2007. 10.1021/jp067417x S1520-6106(06)07417-7 Web Release Date: March 28, 2007
Characterization of Covalent Linkages in Organically Functionalized MCM-41 Mesoporous Materials by Solid-State NMR and Theoretical Calculations
Jerzy W. Wiench, Yamini S. Avadhut, Niladri Maity, Sumit Bhaduri,* Goutam Kumar Lahiri, Marek Pruski,* and Subramanian Ganapathy*
Abstract: The covalent linkages formed during functionalization of MCM-41 mesoporous molecular sieves with five chloroalkylsilanes ((EtO)3Si(CH2Cl), (MeO)3Si(CH2CH2CH2Cl), Cl3Si(CH2CH2CH3), Cl2Si(CH3)(CH2Cl) and Cl2Si(CH3)2) have been investigated using high-resolution solid-state NMR spectroscopy and DFT calculations. Structural information was obtained from 1H-13C and 1H-29Si heteronuclear (HETCOR) NMR spectra, in which high resolution in the 1H dimension was obtained by using fast MAS. The 1H-13C HETCOR results provided the assignments of 1H and 13C resonances associated with the surface functional groups. Sensitivity-enhanced 1H-29Si HETCOR spectra, acquired using Carr-Purcell-Meiboom-Gill refocusing during data acquisition, revealed the identity of 29Si sites (Qn, Tn, and Dn) and the location of functional groups relative to these sites. Optimal geometries of local environments representing the Qn, Tn and Dn resonances were calculated using molecular mechanics and ab initio methods. Subsequently, DFT calculations of 29Si, 13C, and 1H chemical shifts were performed using Gaussian 03 at the B3LYP/6-311++G(2d,2p) level. The theoretical calculations are in excellent accord with the experimental chemical shifts. This work illustrates that state-of-the-art spectroscopic and theoretical tools can be used jointly to refine the complex structures of inorganic-organic hybrid materials.

- Gillian Goward. Studies of the structure and dynamics of benzimidazole salts

J. Phys. Chem. B, 111 (20), 5602 -5609, 2007. 10.1021/jp071471b S1520-6106(07)01471-X Web Release Date: May 2, 2007
A Solid-State NMR Study of Hydrogen-Bonding Networks and Ion Dynamics in Benzimidazole Salts
Jason W. Traer, James F. Britten, and Gillian R. Goward*
Abstract: On the basis of our solid-state NMR characterization of dynamics in two model salts, we draw the analogy to the fuel cell membrane candidate, phosphoric acid-doped poly(benzimidazole), and conclude that phosphate anion dynamics contribute to long-range proton transport, whereas the mobility of the polymer itself is not a contributing factor. This is contrasted with emerging membrane candidates, which rely on fully covalently bonded acid donors and acceptors, and target high-temperature PEM fuel cell operation in the absence of liquid electrolyte. The hydrogen-bonding structures of benzimidazolium phosphate and benzimidazolium methane phosphonate are established using X-ray diffraction paired with solid-state 1H DQF NMR. By comparing the dynamics of the phosphate and methane phosphonate anions with the dynamics of imidazolium and benzimidazolium cations, the relative importance of these processes in proton transport is determined. The imidazolium cation is known to undergo two-site ring reorientation on the millisecond time scale. In contrast, it is shown here that the benzimidazolium rings are immobile in analogous salts, on a time scale extending into the tens of seconds. Therefore, we look to the phosphate anions and demonstrate that the time scale of tetrahedral reorientation is comparably fast (50 ms). Moreover, the 31P CODEX NMR data clearly indicate a four-site jump process. In contrast, the methane phosphonate undergoes a three-site jump on a slower time scale (75 ms). A mechanism for a zigzag pathway of proton transport through the phosphonate salt crystallites is developed based on the 31P CODEX and 1H variable-temperature MAS NMR data.

-129Xe NMR of mesoporous materials

J. Phys. Chem. C, 111 (15), 5694 -5700, 2007. 10.1021/jp066163c S1932-7447(06)06163-2
Probing Xe Exchange in Delaminated Zeolites by Hyperpolarized 129Xe NMR
M.-A. Springuel-Huet,* F. Guenneau, A. Gédéon, and A. Corma
Abstract: MCM-22 and ferrierite zeolites and the corresponding delaminated materials, ITQ-2 and ITQ-6, respectively, have been studied by 129Xe NMR of adsorbed xenon and by nitrogen adsorption at 77 K. One-dimensional 129Xe NMR spectra of delaminated materials show additional lines compared with those of the parent zeolites. For ITQ-2, these new lines are attributed to Xe exchanging between the adsorbed phase and the intercrystallite gaseous phase, with the extent of exchange depending on the particle size, the distribution of which is discrete. For ITQ-6, the additional lines are attributed to the presence of mesopores in the particles. Two-dimensional NMR spectra of ITQ-6 samples under magic angle spinning conditions and continuous flow of hyperpolarized Xe allowed us to investigate the exchange between different sites and to obtain information on the delamination process.

-C13 diffusion spectroscopy of CO molecules on a Pt surface. Eric Oldfield

J. Phys. Chem. C, 111 (19), 7078 -7083, 2007. 10.1021/jp066803b S1932-7447(06)06803-8 Coverage Dependence of CO Surface Diffusion on Pt Nanoparticles: An EC-NMR Study
Takeshi Kobayashi, Panakkattu K. Babu, Jong Ho Chung, Eric Oldfield,
* and Andrzej Wieckowski
Abstract:We have studied the effects of CO surface coverage on the diffusion rates of CO adsorbed on commercial Pt-black in sulfuric acid media by using 13C electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy in the temperature range 253-293 K. The temperature range chosen for these measurements was such that the electrolyte is in a liquid-like and liquid environment. For CO coverage between = 1.0 and 0.36, the CO diffusion coefficients (DCO) follow a typical Arrhenius behavior and both the activation energies (Ed) as well as the pre-exponential factors ( ) show CO coverage dependence. For partially CO covered samples, Ed decreases linearly with increasing CO coverage, indicating that the repulsive CO-CO interactions exert a stronger influence on the coverage dependence of the activation energy than does the nature of the CO adlayer structure. On the other hand, shows an exponential decrease with increasing CO coverage, consistent with the free site hopping model [Gomer, R. Rep. Prog. Phys. 1990, 53, 917] as the major mechanism for surface diffusion of CO at partial coverages, unlike the situation found with a fully CO covered surface [Kobayashi et al., J. Am. Chem. Soc., 2005, 127, 14164]. Overall, these results are of interest since they improve our understanding of the surface dynamics of molecules at electrochemical interfaces, and may help facilitate better control of fuel cell reactions in which the presence of surface CO plays a crucial role in controlling electrocatalytic reaction rates.

-Melt state 13C NMR of polymers.

Macromolecules, 40 (9), 3505 -3509, 2007. 10.1021/ma070377q S0024-9297(07)00377-4
Microstructural Analysis of Insoluble Polyolefins by Melt-State 13C NMR at Very High Temperatures
Wei Hu,
Hideaki Hagihara, and Toshikazu Miyoshi*
Introduction: For polyolefins, their macroscopic properties, namely, crystallinity, crystallization temperature, lamellar thickness, and mechanical properties, are closely related to their microstructural parameters such as molecular weight, molecular weight distribution, stereoregularity, regiodefect concentration, branch length, and concentration.1-5 Therefore, the control of such microstructural parameters is industrially and scientifically important for producing various types of polyolefins with different macroscopic properties.1,3,4 The analysis of the microstructural parameters is also an important topic for newly synthesized polymers, and 13C solution-state NMR analysis has been successfully applied to characterizing locally heterogeneous structures such as end groups, regiodefects, stereodefects,6-11 and branch structures.12,13 On the other hand, solution-state 13C NMR analysis always suffers from the sensitivity of small signals corresponding to minor defect structures. Furthermore, by this technique, it is impossible to apply insoluble polymers such as cross-linked polyolefins and C3 branch poly( -olefins) such as isotactic poly(3-methyl-1-butene) (iP3M1B)14-17 and isotactic poly(3-methyl-1-penentene) (iP3M1P).18 For such polymers, microstructural analysis cannot be realized by solution-state NMR. In these cases, fractionation by solvent extraction has been utilized as a simple and practical means of performing a rough microstructural analysis. Also, solution-state NMR was applied to the analysis of the soluble fractions and the decomposition of insoluble parts by heat treatment,18 or of model compounds of oligomers,15,16 or a sample with a low tacticity.17
To overcome sensitivity and solubility problems, melt-state NMR has also been developed for the microstructural analysis of polymers.
19-22 In the melt state, rapid dynamics in the molten state considerably averages out 13C line widths broadened because of anisotropic interactions such as heteronuclear 1H-13C dipolar interactions and chemical shift anisotropy and because of conformations and disorders of chain packing. Furthermore, the combined use of typical solid-state NMR techniques, magic-angle sample spinning (MAS), and 1H dipolar decoupling (DD) in the detection period further decreases the line widths. Consequently, high-resolution NMR is feasible with the solid-state NMR apparatus at high temperatures above Tm. Melt-state NMR analysis requires no solvent, and therefore, a high polymer density (a high filling factor) within the NMR coil induces a large enhancement in signal intensities. Recently, Pollard et al. have optimized experimental times using a high filling factor and a transient nuclear Overhauser enhancement (NOE) effect and concluded that the sensitivity enhancement for melt-state 13C NMR is 30 times higher than that for solution-state NMR.21 Very recently, Klimke et al. have further investigated spectral resolution and sensitivity of melt-state NMR using different NMR rotor sizes (4 and 7 mm) and those by various 1H DD methods at various magnetic fields from 300 to 700 MHz.22 They concluded that the application of a high magnetic field of 500 MHz and a 7 mm probe head provides the best sensitivity and that decoupling effectively increases spectral resolution and allows a full observation of free induction decay (FID). Consequently, they successfully evaluated branch content with a concentration of 0.01% and copolymer contents by melt-state NMR analysis.22

-More ­13C NMR of Polymers

Macromolecules, 40 (10), 3615 -3623, 2007. 10.1021/ma062689j S0024-9297(06)02689-1
Identification of Oxidation Products in Selectively Labeled Polypropylene with Solid-State 13C NMR Techniques
Daniel M. Mowery,* Roger L. Clough, and Roger A. Assink
Abstract: Oxidatively degraded polypropylene (PP) samples, with selective 13C labeling of the three carbon sites on the PP chain (tertiary, secondary, and methyl carbons), have been analyzed with a suite of one- and two-dimensional solid-state 13C nuclear magnetic resonance (NMR) experiments that have been used to assign several 13C resonances attributed to oxidation-induced functional groups. These NMR techniques, several of which were recently developed, included dipolar dephasing for MAS speeds 10 kHz, chemical shift anisotropy (CSA) filtering, SUPER NMR to separate quasi-static CSA patterns, and 1H-13C heteronuclear correlation (HETCOR). In the course of the study, it has been demonstrated that NMR experiments which utilize the 13C CSA for resonance identification can be sensitive to sample temperature as a result of molecular motion-induced averaging of the CSA. These experiments have allowed hemiketal groups to be identified for the first time to our knowledge in oxidized PP. Possible mechanisms for the formation of hemiketals and other functional groups have been discussed.

-Microwave spectroscopy used to determine the structure of a metallocene.

Organometallics, 26 (8), 2070 -2076, 2007. 10.1021/om061027f S0276-7333(06)01027-2
Microwave Spectra and Gas-Phase Structural Parameters of Bis( 5-cyclopentadienyl)tungsten Dihydride
Brandon S. Tackett, Chandana Karunatilaka, Adam M. Daly, and Stephen G. Kukolich* Abstract: Microwave spectra for 11 isotopomers of bis( 5-cyclopentadienyl)tungsten dihydride ((C5H5)2WH2) were recorded in the 5-14 GHz region using a Flygare-Balle-type pulsed beam spectrometer. Spectra arising from four tungsten isotopomers of both the (C5H5)2WH2 and (C5H5)2WHD species and three W isotopomers for the (C5H5)2WD2 complex have been measured. The ~250 b-type transition frequencies assigned for these near-prolate asymmetric top molecules were accurately described ( fit = 2-4 kHz) using the rotational parameters A, B, and C and one centrifugal distortion constant, J. The small value obtained for J indicates a fairly rigid structure. From a least-squares fit using the resulting 33 rotational constants to obtain the molecular structure, we were able to determine the W-H bond length, r(W-H) = 1.703(2) Å, the H-W-H bond angle, (H-W-H) = 78.0(12) , the W-Cp centroid distance, r(W-Cp) = 1.940(8) Å, the angle made by the Cp centroids with tungsten, (Cp-W-Cp) = 155(2) , and the average C-C bond length, r(C-C) = 1.429(8) Å. The hydrogen atom separation is r(H-H) = 2.14(2) Å, indicating that this is clearly a "classical dihydride" rather than an " 2-dihydrogen" complex. The WH2 moiety parameters determined from Kraitchman's equations (r(W-H) = 1.682(2) Å, (H-W-H) = 78.6(2), r(H-H) = 2.130(2) Å) agree well with the least-squares results. Furthermore, the re parameters obtained from DFT calculations agree well with the experimental r0 structural parameters. To our knowledge, this work marks the first microwave study of a bent-metallocene complex. The present measurements were made with a pulsed-beam Fourier transform spectrometer employing a homodyne-type detection system, and this configuration is described. This homodyne system greatly simplifies the microwave circuit, with no apparent loss in sensitivity.

Wednesday, June 06, 2007

Joel's Journal Update (March '07 - Present)

A Solid-State 17O NMR Study of Local Order and Crystallinity in Amine-Templated Mesoporous Nb Oxide
Boris O. Skadtchenko, Yuxiang Rao, Tom F. Kemp, Prodipta Bhattacharya, Pamela A. Thomas, Michel Trudeau, Mark E. Smith, Dave M. Antonelli
Angewandte (2007)46, 2635
Order locally: 17O magic-angle-spinning NMR spectroscopy of bulk sol-gel-prepared Nb2O5 and mesoporous, template-free Nb2O5 (see picture) shows very high local order in the mesoporous sample. The oxygen atoms are coordinated only as ONb2 in contrast with bulk phases in which the oxygen atoms are always present in a mixture of ONb2 and ONb3 coordination environments.

First-principles calcualtions of solid-state 17O and 29Si NMR spectra of Mg2SiO4 polymorphs
S.E. Ashbrook, L. Le Polles, C.J. Pickard, A.J. Berry, S. Wimperis, I Farnan.
The nuclear magnetic resonance (NMR) shielding and electric field gradient (EFG) tensors of three polymorphs of Mg2SiO4, forsterite (-Mg2SiO4), wadsleyite (-Mg2SiO4) and ringwoodite (-Mg2SiO4), have been calculated using a density functional theory (DFT) approach with a planewave basis set and pseudopotential approximation. These Mg2SiO4 polymorphs are the principal components of the Earth down to depths of 660 km and have been proposed as the hosts of water in the Earths upper mantle and transition zone. A comparison of our calculations with single-crystal spectroscopic data in the literature for the -polymorph, forsterite, shows that both the magnitude and orientation of the shielding and EFG tensors for O and Si can be obtained with sufficient accuracy to distinguish subtle differences in atomic positions between published structures. We compare calculated 17O MAS NMR quadrupolar powder lineshapes directly with experimental lineshapes and show that we are able to reproduce them within the precision with which the NMR parameters may be determined from multi-parameter fitting. The relatively small amounts of sample available for the - and -polymorphs, arising from the high pressures required for synthesis, has hindered the extraction of NMR parameters in previous work. The application of DFT calculations to these high-pressure polymorphs confirms previous spectral assignments, and provides deeper insight into the empirical correlations and observations reported in the literature. These first-principles methods are highly promising for the determination of local bonding in more complex materials, such as the hydrated forms of Mg2SiO4, by aiding analysis of their multinuclear NMR spectra.

2H-solid state NMR and DSC study of isobutyric acid in mesoporous silica materials
A. Vyalikh, Th. Emmler, I. Shenderovich, Y. Zeng, G. H. Findenegg and G. Buntkowsky
Solid state deuterium NMR has been used to study the molecular motion of d6-isobutyric acid (d6-iBA) in the pure (unconfined) state and confined in the cylindrical pores of two periodic mesoporous silica materials (MCM-41, pore size 3.3 nm and SBA-15, pore size 8 nm), and in a controlled pore glass (CPG-10-75, pore size ca. 10 nm). The line shape analysis of the spectra at different temperatures revealed three rotational states of the iBA molecules: liquid (fast anisotropic reorientation of the molecule), solid I (rotation of the methyl group) and solid II (no rotational motion on the time scale of the experiment). Transition temperatures between these states were determined from the temperature dependence of the fraction of molecules in these states. Whereas the solid I–solid II transition temperature is not affected by confinement, a significant lowering of the liquid–solid I transition temperature in the pores relative to the bulk acid was found for the three matrix materials, exhibiting an unusual dependence on pore size and pore morphology. Complementary DSC measurements on the same systems show that the rotational melting (solid I–liquid) of d6-iBA in the pores occurs at a temperature 20–45 K below the thermodynamic melting point. This finding indicated that the decoupling of rotational and translational degrees of freedom in phase transitions in confined systems previously found for benzene is not restricted to molecules with non-specific interactions, but represents a more general phenomenon.

19F Magic angle spinning NMR reporter molecules: empirical measures of surface shielding, polarisability and H-bonding
Vitaliy L. Budarin, James H. Clark, Fabien E. I. Deswarte, Karl T. Mueller and Stewart J. Tavener
Magic Angle Spinning (MAS) 19F NMR spectra have been obtained and chemical shifts measured for 37 molecules in the gas phase and adsorbed on the surfaces of six common materials: octadecyl- and octyl-functionalised chromatography silicas, Kieselgel 100 silica, Brockmann neutral alumina, Norit activated charcoal and 3-(1-piperidino)propyl functionalised silica. From these six surfaces, octadecyl-silica is selected as a non-polar reference to which the others are compared. The change in chemical shift of a fluorine nucleus within a molecule on adsorption to a surface from the gas phase, surfacegas, is described by the empirical relationship: , where s and r are constants that describe the chemical shift induced by the electromagnetic field of the surface under investigation and reference surface, s and r are the relative surface polarisability for the surface and reference, s is an additional contribution to the surface polarisabilities due to its ability to interact with aromatic molecules, and HBA and HBD are measurements of the hydrogen acceptor and donor properties of the surface. These empirical parameters are measured for the surfaces under study. Silica and alumina are found to undergo specific interactions with aromatic reporter molecules and both accept and donate H-bonds. Activated charcoal was found to have an extreme effect on shielding but no specific interactions with the adsorbed molecules. 3-(1-Piperidino)propyl functionalised silica exhibits H-bond acceptor ability, but does not donate H-bonds.

Combining insights from solid-state NMR and first principles calculation: applications to the 19F NMR of octafluoronaphthalene
Andrew J. Robbins, William T. K. Ng, Dominik Jochym, Thomas W. Keal, Stewart J. Clark, David J. Tozer and Paul Hodgkinson
Advances in solid-state NMR methodology and computational chemistry are applied to the 19F NMR of solid octafluoronaphthalene. It is demonstrated experimentally, and confirmed by density functional theory (DFT) calculations, that the spectral resolution in the magic-angle spinning spectrum is limited by the anisotropy of the bulk magnetic susceptibility (ABMS). This leads to the unusual observation that the resolution improves as the sample is diluted. DFT calculations provide assignments of each of the peaks in the 19F spectrum, but the predictions are close to the limits of accuracy and correlation information from 2-D NMR is invaluable in confirming the assignments. The effects of non-Gaussian lineshapes on the use of 2-D NMR for mapping correlations of spectral frequencies (e.g. due to the ABMS) are also discussed.

Double Quantum 1H MAS NMR Studies of Hydrogen-Bonded Protons and Water Dynamics in Materials
Todd M. Alam,* May Nyman, and Sarah K. McIntyre
Two-dimensional double quantum (DQ) 1H MAS NMR was used to investigate different proton environments in a series of alkali (Na, K, Rb, Cs) [Nb6O19]8- Lindqvist salts, with the water and hydrogen-bound intercluster protons being clearly resolved. Through the analysis of the DQ 1H NMR spinning sideband pattern, it is possible to extract both the mean and distribution of the motionally averaged intramolecular homonuclear 1H-1H dipolar coupling for the different water environments and the intercluster protons. Motional order parameters for the water environments were then calculated from the averaged dipolar couplings. The influence of additional intermolecular dipolar couplings due to multispin interactions were simulated and discussed.

Ring Current Effects in Crystals. Evidence from 13C Chemical Shift Tensors for Intermolecular Shielding in 4,7-Di-t-butylacenaphthene versus 4,7-Di-t-butylacenaphthylene
Zhiru Ma, Merrill D. Halling, Mark S. Solum, James K. Harper, Anita M. Orendt, Julio C. Facelli, Ronald J. Pugmire, David M. Grant,* Aaron W. Amick, and Lawrence T. Scott
13C chemical shift tensor data from 2D FIREMAT spectra are reported for 4,7-di-t-butylacenaphthene and 4,7-di-t-butylacenaphthylene. In addition, calculations of the chemical shielding tensors were completed at the B3LYP/6-311G** level of theory. While the experimental tensor data on 4,7-di-t-butylacenaphthylene are in agreement with theory and with previous data on polycyclic aromatic hydrocarbons, the experimental and theoretical data on 4,7-di-t-butylacenaphthene lack agreement. Instead, larger than usual differences are observed between the experimental chemical shift components and the chemical shielding tensor components calculated on a single molecule of 4,7-di-t-butylacenaphthene, with a root mean square (rms) error of ±7.0 ppm. The greatest deviation is concentrated in the component perpendicular to the aromatic plane, with the largest value being a 23 ppm difference between experiment and theory for the 13CH2 carbon 11 component. These differences are attributed to an intermolecular chemical shift that arises from the graphitelike, stacked arrangement of molecules found in the crystal structure of 4,7-di-t-butylacenaphthene. This conclusion is supported by a calculation on a trimer of molecules, which improves the agreement between experiment and theory for this component by 14 ppm and reduces the overall rms error between experiment and theory to 4.0 ppm. This intermolecular effect may be modeled with the use of nuclei independent chemical shieldings (NICS) calculations and is also observed in the isotropic 1H chemical shift of the CH2 protons as a 4.2 ppm difference between the solution value and the solid-state chemical shift measured via a 13C-1H heteronuclear correlation experiment.