Bryan's Blog Update, Part II

Hope you're ready for more SSNMR literature!

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Chem. Commun., 2010, 46, 4514-4516
DOI: 10.1039/B924936B , Communication

On-line monitoring of a microwave-assisted chemical reaction by nanolitre NMR-spectroscopy

M. Victoria Gomez, Hein H. J. Verputten, Angel Díaz-Ortíz, Andres Moreno, Antonio de la Hoz and Aldrik H. Velders

Abstract

We report the use of a nanolitre nuclear magnetic resonance (NMR) spectroscopy microfluidic chip hyphenated to a continuous-flow microlitre-microwave irradiation set-up, for on-line monitoring and rapid optimization of reaction conditions.

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Chem. Commun., 2010, 46, 4532-4534

DOI: 10.1039/C0CC00113A , Communication

Rational synthesis, enrichment, and ¹³C NMR spectra of endohedral C₆₀ and C₇₀ encapsulating a helium atom

Yuta Morinaka, Fumiyuki Tanabe, Michihisa Murata, Yasujiro Murata and Koichi Komatsu

Abstract

Endohedral fullerenes encapsulating a helium atom, i.e., He@C₆₀ and He@C₇₀, at occupation levels of 30% were prepared by rational chemical synthesis. The existence of weak interactions between the inner helium and the outer fullerene cages was demonstrated by experimental and computational investigations.

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Chem. Commun., 2010, 46, 4982-4984
DOI: 10.1039/C0CC01007C

Direct observation of a transient polymorph during crystallization

Colan E. Hughes and Kenneth D. M. Harris

Abstract

Application of a technique developed for in situ solid-state ¹³C NMR studies of crystallization processes reveals direct evidence that crystallization of glycine from a methanol/water solution involves the initial transient formation of the β polymorph, which then undergoes a solution-mediated polymorphic transformation to yield the more stable α polymorph.

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Chem. Commun., 2010, 46, 5879-5881
DOI: 10.1039/C0CC01271H

Probing heterocycle conformation with residual dipolar couplings

Chakicherla Gayathri, M. Carmen de la Fuente, Burkhard Luy, Roberto R. Gil and Armando Navarro-Vázquez

Abstract

Residual dipolar couplings (RDCs) obtained in a stretched polydimethylsiloxanegel are applied to determine the 7-membered ring conformation in a 2-phenyl-3-benzazepine derivative, and to simultaneously assign all methyleneproton pairs using only ¹D_CH RDCs and DFT molecular modelling data.

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Chem. Commun., 2010, 46, 6714-6716
DOI: 10.1039/C0CC00829J

Solid-state NMR evidence for elastin-like β-turn structure in spider dragline silk

Janelle E. Jenkins, Melinda S. Creager, Emily B. Butler, Randolph V. Lewis, Jeffery L. Yarger and Gregory P. Holland

Abstract

Two-dimensional homo- and heteronuclear solid-state MAS NMR experiments on ¹³C/¹⁵N-proline labeled Argiope aurantia dragline silk provide evidence for an elastin-like β-turn structure for the repetitive Gly-Pro-Gly-X-X motif prevalent in major ampullate spidroin 2 (MaSp2).

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Chem. Commun., 2010, 46, 6774-6776
DOI: 10.1039/C0CC01902J

Ultra-wideline ¹⁴N NMR spectroscopy as a probe of molecular dynamics

Luke A. O'Dell and Christopher I. Ratcliffe

Abstract

We show that ultra-wideline solid-state ¹⁴N NMR can be used as a quantitative probe of molecular dynamics. Jump rates for the molecular flipping mechanism in crystalline urea are determined at various temperatures and are shown to be in good agreement with other NMR techniques.

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Chem. Commun., 2010, 46, 7533-7535
DOI: 10.1039/C0CC01846E

Two-dimensional heteronuclear saturation transfer difference NMR reveals detailed integrin αvβ6 protein–peptide interactions

Jane L. Wagstaff, Sabari Vallath, John F. Marshall, Richard A. Williamson and Mark J. Howard

Abstract

We report the first example of peptide–protein heteronuclear two-dimensional (2D) saturation transfer difference nuclear magnetic resonance (STD NMR). This method, resulting in dramatically reduced overlap, was applied to the interaction of the integrin αvβ6 with a known peptide ligand and highlights novel contact points between the substrate and target protein.

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Chem. Commun., 2010, 46, 8192-8194
DOI: 10.1039/C0CC01953D

Proton hyperpolarisation preserved in long-lived states

Puneet Ahuja, Riddhiman Sarkar, Sami Jannin, Paul R. Vasos and Geoffrey Bodenhausen

Abstract

The polarisation of abundant protons, rather than dilute nuclei with low gyromagnetic ratios, can be enhanced in less than 10 min using dissolution DNP and converted into a long-lived state delocalised over an ensemble of three coupled protons. The process is more straightforward than the hyperpolarisation of heteronuclei followed by magnetisation transfer to protons.

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Chem. Commun., 2010, 46, 8273-8275
DOI: 10.1039/C0CC02730H

Artifact-free measurement of residual dipolar couplings in DMSO by the use of cross-linked perdeuterated poly(acrylonitrile) as alignment medium

Grit Kummerlöwe, Marc Behl, Andreas Lendlein and Burkhard Luy

Abstract

Perdeuterated poly(acrylonitrile) is introduced as a practically proton-free alignment medium for the measurement of anisotropic NMR parameters; its use in conventional glass tubes and in a Kalrez® 8002 UP-based stretching device with resulting spectra of astonishing quality are demonstrated.

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Bryan's Blog Update, Part I

Time for another update! Let's see what's happening in the world of SSNMR!

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Chemical Physics Letters
Volume 491, Issues 1-3, 7 May 2010, Pages 11-16

F–H···N hydrogen bonds: Influence of substituent and hybridization of nitrogen on H-bond properties and two-bond ¹⁹F–¹⁵N spin–spin coupling constants (^2hJ_F–N)
Pages 11-16
Ali Ebrahimi, Mostafa Habibi-Khorassani, Masoome Doosti
doi:10.1016/j.cplett.2010.03.051

Abstract

The effects of substituent and hybridization of nitrogen atom on hydrogen bonding in the F–H···NCX, F–H···N(H)CX, and F–H···N(H)₂–CX complexes have theoretically been studied by MP2 and DFT methods with aug-cc-pVDZ and 6-311++G** basis sets. With respect to the hybridization of nitrogen, sp³-hybridized nitrogen forms the strongest bond, followed by sp² and then sp. In equilibrium structures, the trend in the two-bond ¹⁹F–¹⁵N spin–spin coupling constants (^2hJ_F–N) is sp <>3 <>2. The results of atoms in molecules (AIM) and natural bond orbital (NBO) analyses are in meaningful relationships with other characteristics of hydrogen bonds, especially with the ^2hJ_F–N values.

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Chemical Physics Letters
Volume 491, Issues 1-3, 7 May 2010, Pages 72-74

Intactness and spatial proximity of acid–base groups in bifunctional SBA-15 as revealed by solid-state NMR
Pages 72-74
Wanling Shen, Wujun Xu, Qiang Gao, Jun Xu, Hailu Zhang, Anmin Zheng, Yao Xu, Feng Deng

doi:10.1016/j.cplett.2010.03.067

Abstract

The intactness and spatial proximity of acid and base groups in bifunctional mesoporous SBA-15 has been studied by various NMR techniques. The NMR results show that Brønsted acid and Lewis base groups coexist peacefully on the surface of the same support and maintain their acidity and basicity, respectively. Meanwhile, the acid groups and the base groups are in close proximity with suitable distance.

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Chemical Physics Letters
Volume 491, Issues 4-6, 17 May 2010, Pages 224-229

Contributions from orbital–orbital interactions to nucleus-independent chemical shifts and their relation with aromaticity or antiaromaticity of conjugated molecules
Pages 224-229
Ignacio Pérez-Juste, Marcos Mandado, Luis Carballeira

doi:10.1016/j.cplett.2010.03.077

Abstract

The out-of-plane components of the nucleus-independent chemical shifts (NICS) for a group of aromatic and antiaromatic [n]-annulenes have been separated into several contributions on the basis of the gauge-including atomic orbital (GIAO) method. The analysis of the orbital interactions responsible of the NICS(π)_zz values shows that the large and positive values found for antiaromatic compounds are due to the predominance of π → π * rotational transitions that overcome the diamagnetic and gauge contributions. However, NICS(π)_zz for aromatic compounds are dominated by contributions arising from the gauge transformation and no significant contributions are found from occupied–unoccupied orbital mixing. This analysis has been compared with previous work about ring currents in the same compounds.

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Chemical Physics Letters
Volume 492, Issues 1-3, 26 May 2010, Pages 174-178

Homonuclear decoupled proton NMR spectra in modest to severe inhomogeneous fields via distant dipolar interactions
Pages 174-178
Yuqing Huang, Wen Zhang, Shuhui Cai, Jianhui Zhong, Zhong Chen

doi:10.1016/j.cplett.2010.04.030

Abstract

On the basis of distant dipolar interactions, two new pulse sequences were proposed to obtain homonuclear broadband-decoupled proton NMR spectra in modest to severe inhomogeneous fields with time efficient acquisitions. Theoretical expressions for signals were derived according to the distant dipolar field (DDF) treatment combined with the product operator formalism. The measurements under either moderate (0.4 ppm) or severe (7 ppm) field inhomogeneity in a 500 MHz spectrometer show that the new sequences are complementary to each other and provide an attractive way to eliminate the influences of field inhomogeneities on homonuclear decoupled proton spectra.

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Chemical Physics Letters
Volume 492, Issues 4-6, 7 June 2010, Pages 302-308

Importance of the hybrid orbital operator derivative term for the energy gradient in the fragment molecular orbital method
Pages 302-308
Takeshi Nagata, Dmitri G. Fedorov, Kazuo Kitaura

doi:10.1016/j.cplett.2010.04.043

Abstract

The hybrid orbital operator is crucial in the fragment molecular orbital (FMO) method for the fragmentation across covalent bonds, however, its gradients have not been properly derived. We show that these very substantial contributions are the cause of the major part of the gradient error in FMO, impeding geometry optimizations and molecular dynamics. Capped alanine decamer (ALA)₁₀ and chignolin (PDB: 1UAO) solvated by 157 water molecules are used to assess the accuracy of the energy gradients, and the errors are reduced by approximately one order of magnitude.

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Chemical Physics Letters
Volume 493, Issues 1-3, 17 June 2010, Pages 27-32

The role of cation–π interactions in ethylenic complexes: A theoretical NMR study
Pages 27-32
Ali Ebrahimi, Mostafa Habibi Khorassani, Hamid Reza Masoodi

doi:10.1016/j.cplett.2010.04.064

Abstract

The effect of cation–π interactions on some NMR data of ethylenic complexes has been investigated by B97-1, PBE1KCIS and MPWKCIS1K methods using 6-311++G(3df,3pd) basis set. Unlike 3JH–H(cis), the chemical shift of ethylenic hydrogen (δ^H) and increases by cation–π interaction. The changes of NMR data have been considered with regard to geometry and direct electronic effects. Also, the distance dependence of NMR parameters has been studied in these complexes.
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Chemical Physics Letters
Volume 494, Issues 1-3, 9 July 2010, Pages 104-110
Improved resolution in dipolar NMR spectra using constant time evolution PISEMA experiment
Pages 104-110
T. Gopinath, Gianluigi Veglia
doi:10.1016/j.cplett.2010.05.078

Abstract

The atomic structure of small molecules and polypeptides can be attained from anisotropic NMR parameters such as dipolar couplings (DC) and chemical shifts (CS). Separated local field experiments resolve DC and CS correlations into two dimensions. However, crowded NMR spectra represent a significant obstacle for the complete resolution of these anisotropic parameters. Using the polarization inversion spin exchange at the magic angle (PISEMA) experiment as a foundation, we designed new pulse schemes that use a constant time evolution in the dipolar (indirect) dimension to measure DC and CS correlations at high resolution. We demonstrated this approach on a 4-pentyl-4′-cyanobiphenyl (5CB) liquid crystal sample, achieving a resolution enhancement ranging from 30% to 60% for the resonances in the dipolar dimension. These new experiments open the possibility of obtaining significant resolution enhancement for multidimensional NMR experiments carried out on oriented liquid crystalline samples as well as oriented membrane proteins.

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Chemical Physics Letters
Volume 494, Issues 4-6, 19 July 2010, Pages 326-330

Broadband heteronuclear dipolar recoupling without ¹H decoupling in solid-state NMR using simple cross-polarization methods
Pages 326-330
Morten Bjerring, Anders Bodholt Nielsen, Zdenek Tosner, Niels Chr. Nielsen

doi:10.1016/j.cplett.2010.06.018

Abstract

Heteronuclear dipolar recoupling experiments without ¹H decoupling based on simple cross polarization are introduced for applications in biological solid-state NMR. It is shown that standard or adiabatic variants of the cross-polarization experiment with irradiation on the low-γ (e.g., ¹³C,¹⁵N) spins even at modest spinning frequencies enable efficient band-selective or broadband dipolar recoupling without the need for intense ¹H decoupling. This facilitates experiments on expensive isotope-labelled protein samples for which sample heating by intense ¹H decoupling may lead to sample detoriation. The principle is demonstrated numerically and experimentally on uniformly ¹³C,¹⁵N-labelled samples of GB1 and fibrils of hIAPP [20], [21], [22], [23], [24], [25], [26], [27], [28] and [29] from the human islet amyloid labelled on the FGAIL part.

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Chemical Physics Letters
Volume 494, Issues 4-6, 19 July 2010, Pages 331-336

doi:10.1016/j.cplett.2010.06.019

Optimal control NMR differentiation between fast and slow sodium
Pages 331-336
Jae-Seung Lee, Ravinder R. Regatte, Alexej Jerschow

Abstract

Sodium ions in tissues and organs may experience motion on a variety of timescales, leading to NMR relaxation effects with quadrupolar coupling as the primary mechanism. The various effects that this fluctuating interaction has on spin dynamics can be exploited for distinguishing slow sodium ions from fast ones. Techniques such as triple-quantum filtering have been used for this purpose in the past. In this work we present optimal pulses which significantly improve the selectivity towards slow-tumbling sodium. These pulses can also be modified for robustness against magnetic field inhomogeneities, and could hence also become useful as MRI contrast methods.

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Chemical Physics Letters
Volume 495, Issues 4-6, 10 August 2010, Pages 287-291

doi:10.1016/j.cplett.2010.06.064

NMR relaxometry: Spin lattice relaxation times in the laboratory frame versus spin lattice relaxation times in the rotating frame
Pages 287-291
Emilie Steiner, Mehdi Yemloul, Laouès Guendouz, Sébastien Leclerc, Anthony Robert, Daniel Canet

Abstract

Relaxometry dispersion curves display the spin lattice relaxation rate as a function of the measurement frequency. However, as far as proton NMR is considered, dispersion curves usually start around 5 kHz and thus miss the very low frequency region. This gap can be filled by the measurement of the spin–lattice relaxation rate in the rotating frame. The issue of connecting both relaxation rates is considered for two relaxation mechanisms: (i) randomly varying magnetic fields, (ii) dipolar interaction within a system of two equivalent spins. Appropriate data processing is presented and the random field mechanism turns out to be adequate.

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Chemical Physics Letters
Volume 496, Issues 1-3, 20 August 2010, Pages 148-151

doi:10.1016/j.cplett.2010.07.063

Metal-alkyl species are formed on interaction of small alkanes with gallium oxide: Evidence from solid-state NMR
Pages 148-151
Anton A. Gabrienko, Sergei S. Arzumanov, Alexander V. Toktarev, Alexander G. Stepanov

Abstract

¹³C CP MAS NMR analysis of the products of the interaction of methane, ethane and propane with α-Ga₂O₃ or Ga-modified zeolite BEA at 523–623 K shows that dissociative adsorption of C₁–C₃ alkanes on the surface of gallium oxide or Ga-modified zeolite BEA results to the formation of Ga-methyl, Ga-ethyl and Ga-propyl species. This observation allows one to conclude that Ga-alkyls, rather than earlier suggested alkoxy species, could be the intermediates in small alkane dehydrogenation and aromatization on these catalysts.
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Chemical Physics Letters
Volume 496, Issues 1-3, 20 August 2010, Pages 162-166
doi:10.1016/j.cplett.2010.07.016
A magic-angle turning NMR experiment for separating spinning sidebands of half-integer quadrupolar nuclei
Pages 162-166
Ivan Hung, Zhehong Gan

Abstract

A two-dimensional magic-angle turning NMR experiment is described for separating spinning sidebands of half-integer quadrupolar nuclei. The experiment is an alternative to quadrupolar phase-adjusted sideband separation (QPASS) [Chem. Phys. Lett. 272 (1997) 295] that yields infinite speed spectra in one dimension and spinning sideband manifolds in the other dimension. A shear transformation is introduced for processing of quadrupolar magic-angle turning (QMAT) data with time evolution of only one rotor period. The QMAT experiment has the advantages of averaging the first-order modulation of the pulse sequence efficiencies giving smaller residual spinning sidebands, linearly incrementing pulse timings for convenient practical implementation, and easily adjustable pulse spacings suitable for higher spinning frequencies.

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Chemical Physics Letters
Volume 496, Issues 1-3, 20 August 2010, Pages 175-182

doi:10.1016/j.cplett.2010.07.027

Enantiodiscrimination and extraction of short and long range homo- and hetero-nuclear residual dipolar couplings by a spin selective correlation experiment
Pages 175-182
Nilamoni Nath, N. Suryaprakash

Abstract

A two dimensional correlation experiment for the measurement of short and long range homo- and hetero- nuclear residual dipolar couplings (RDCs) from the broad and featureless proton NMR spectra including ¹³C satellites is proposed. The method employs a single natural abundant ¹³C spin as a spy nucleus to probe all the coupled protons and permits the determination of RDCs of negligible strengths. The technique has been demonstrated for the study of organic chiral molecules aligned in chiral liquid crystal, where additional challenge is to unravel the overlapped spectrum of enantiomers. The significant advantage of the method is demonstrated in better chiral discrimination using homonuclear RDCs as additional parameters.
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Chemical Physics Letters
Volume 496, Issues 1-3, 20 August 2010, Pages 201-207
doi:10.1016/j.cplett.2010.07.037
Indirect high-resolution detection for quadrupolar spin-3/2 nuclei in dipolar HMQC solid-state NMR experiments
Pages 201-207
Julien Trébosc, Olivier Lafon, Bingwen Hu, Jean-Paul Amoureux

Abstract

We present a new kind of NMR pulse sequences to observe heteronuclear correlation (HETCOR) specifically between spin-1/2 and spin-3/2 nuclei with isotropic resolution on the quadrupolar channel. These methods, called HMQC-ST, feature a STMAS filter during the evolution period of the HMQC scheme. Compared to existing HETCOR techniques involving quadrupolar nuclei, the HMQC-ST combines high-resolution and high efficiency and allows indirect detection of spin-3/2 nuclei via sensitive nuclei. We study analytically and using simulations how through-bond and through-space HMQC-ST perform compared to regular HMQC sequence. HMQC-ST potential is demonstrated experimentally by recording through-space HETCOR 2D spectra of Na₂HPO₄ and NaH₂PO₄.

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Chemical Physics Letters
Volume 496, Issues 1-3, 20 August 2010, Pages 223-226

doi:10.1016/j.cplett.2010.07.05

Detection of magnetic environments in porous media by low-field 2D NMR relaxometry
Pages 223-226
Cinzia Casieri, Francesco De Luca, Luca Nodari, Umberto Russo, Camilla Terenzi

Abstract

The 2D ¹H NMR correlation maps of longitudinal (T₁) and transverse (T₂) relaxation times prove sensitive in monitoring the distribution of magnetic pore environments in porous systems. The comparison with Mössbauer data establishes a direct correspondence between the susceptibility-induced effects observed in the T₁–T₂ maps for pore–filling water and the Fe(III)-bearing magnetic compounds.

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Chemical Physics Letters
Volume 498, Issues 1-3, 30 September 2010, Pages 10-13

doi:10.1016/j.cplett.2010.08.040

The quadrupole moment of the As nucleus from molecular microwave data and calculated relativistic electric field gradients
Pages 10-13
Lukáš Demovič, Vladimir Kellö, Andrzej J. Sadlej

Abstract

The ‘molecular’ value of the nuclear quadrupole moment of the ⁷⁵As nucleus is determined combining the experimental data for quadrupole coupling constant and the calculated electric field gradient in the AsP molecule. The accurate calculations have been carried out at the CCSD(T) level. The relativistic effects were accounted for using the infinite-order two-component method in the scalar approximation. The new recommended value of the nuclear quadrupole moment of ⁷⁵As obtained in this work is 311(2) mb and is more precise than the previous ‘muonic’ value.
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Chemical Physics Letters
Volume 498, Issues 1-3, 30 September 2010, Pages 42-44
doi:10.1016/j.cplett.2010.08.054
Determination of chemical shift of gas-phase hydrogen molecules by ¹H nuclear magnetic resonance
Pages 42-44
Hirotada Fujiwara, Junichiro Yamabe, Shin Nishimura

Abstract

The precise and detailed chemical shift of gas-phase hydrogen molecules was successfully determined by ¹H nuclear magnetic resonance (NMR), avoiding the intervention of neighboring molecules such as in hydrogen occluding materials (free hydrogen). The measurement was conducted with double walled NMR sample tube taking into consideration the change of hydrogen pressure. The inner tube was filled with standard substance (DHO in D₂O at 4.8 ppm). The chemical shift of free hydrogen molecules was determined to be 7.40 ± 0.01 ppm at 0.18 MPa, 25 °C, which is different from previously reported chemical shifts of hydrogen gas with intervention of neighboring molecules.

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Chemical Physics Letters
Volume 498, Issues 1-3, 30 September 2010, Pages 214-220

doi:10.1016/j.cplett.2010.08.038

Homonuclear dipolar decoupling with very large scaling factors for high-resolution ultrafast magic angle spinning ¹H solid-state NMR spectroscopy
Pages 214-220
Elodie Salager, Jean-Nicolas Dumez, Robin S. Stein, Stefan Steuernagel, Anne Lesage, Bénédicte Elena-Herrmann, Lyndon Emsley

Abstract

We present a new phase modulated radio-frequency pulse sequence for homonuclear dipolar decoupling in proton solid-state NMR spectroscopy, eDUMBO-PLUS-1, with a chemical shift scaling factor of 0.73. This sequence was determined by screening random sequences, and experimentally optimizing the best candidates directly on ¹H NMR spectra with 60 kHz magic angle spinning. It yields efficient decoupling with linewidths as little as 150 Hz for 1.3 mm MAS probes on different spectrometers. Experiments and calculations support the hypothesis of a radio-frequency and MAS joint averaging regime, in which the large scaling factor contributes significantly to the overall performance of the decoupling sequence.

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Chemical Physics Letters
Volume 498, Issues 4-6, 8 October 2010, Pages 270-276

doi:10.1016/j.cplett.2010.08.077

Distinguishing hydrogen bonding networks in α-d-galactose using NMR experiments and first principles calculations
Pages 270-276
Mikhail Kibalchenko, Daniel Lee, Limin Shao, Mike C. Payne, Jeremy J. Titman, Jonathan R. Yates

Abstract

First principles calculations and solid-state NMR experiments are used to distinguish between possible hydrogen bonding networks in α-d-galactose. In contrast to ¹³C, the ¹H chemical shift parameters show differences which are sufficient to allow the correct network to be identified by comparison with experiments which make use of modern homonuclear decoupling schemes. In addition, clear linear correlations are established between both ¹H chemical shift and chemical shift anisotropy, and hydrogen bond length.

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Chemical Physics Letters
Volume 500, Issues 1-3, 10 November 2010, Pages 54-58

doi:10.1016/j.cplett.2010.09.061

Assignment of the He@C₈₄ isomers in experimental NMR spectra using density functional calculations
Pages 54-58
Petr Štěpánek, Petr Bouř, Michal Straka

Abstract

The ³He chemical shifts were calculated for He_n@C₈₄ (n = 1, 2) fullerenes to obtain characteristic NMR patterns for distinguishing their isomers in a mixture. The density functional methods were calibrated on experimental data. Accuracy within 1 ppm could be reached without further fitting of individual shifts. Such precision allows for a semi-quantitative assignment of ³He NMR spectra. Additional criteria in the identification are discussed, such as the relative energies of the isomers, positions of the satellite di-helium peaks, and the differential ³He shifts in the fullerenes reduced to anions. Endohedral ³He shifts are predicted for so far experimentally unknown He@C₈₄ and isomers.

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