Four-Dimensional Solid-State NMR Experiment That Correlates the Chemical-Shift and Dipolar-Coupling Frequencies of Two Heteronuclei with the Exchange of Dilute-Spin Magnetization

Some key aspects of the secondary structure of solid orexin-B, a 28 amino-acid peptide, have been investigated by solid-state NMR spectroscopy. The 13C15N dipolar coupling between the carbonyl carbon of Leu11 and the nitrogen of Leu15, as determined by rotational echo double resonance (REDOR) experiments, is 35 Hz, indicating that these nuclei are separated by approximately 4.5 Å. This distance is consistent with the α-helical structure determined for this segment of orexin-B by solution NMR measurements. REDOR measurements of the dipolar coupling between the carbonyl carbon of Ala17 and the nitrogen of Ala22 support the contention in an earlier solution NMR study that a bend exists between the two α helices of orexin-B. However, in the solid state the internuclear distance (6.4 Å) is significantly greater than that observed for orexin-B in aqueous solution. In addition to the distance measurements, the principal components of the amide carbonyl carbon chemical shift (CS) tensors for Leu11 and Ala17 and of the amide nitrogen CS tensors for Leu15 and Ala22 are reported. There are only minor differences between the amide carbonyl carbon CS tensors for Leu11 and Ala17 and between the nitrogen CS tensors for Leu15 and Ala22.Key words: orexin-B, solid-state NMR, REDOR, chemical shift tensors.

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Temperature-Dependent Solid-State NMR Proton Chemical-Shift Values and Hydrogen Bonding

10.26434/chemrxiv.14230043.v1 ◽

2021 ◽

Author(s):

Alexander A. Malär ◽

Laura A. Völker ◽

Riccardo Cadalbert ◽

Lauriane Lecoq ◽

Matthias Ernst ◽

...

Keyword(s):

Magnetic Field ◽

Hydrogen Bonding ◽

Solid State ◽

Chemical Shift ◽

Hydrogen Bonds ◽

Solid State Nmr ◽

Magic Angle Spinning ◽

Magic Angle ◽

Proton Chemical Shift ◽

Temperature Dependent

Temperature-dependent NMR experiments are often complicated by rather long magnetic-field equilibration times, for example occurring upon a change of sample temperature. We demonstrate that the fast temporal stabilization of the magnetic field can be achieved by actively stabilizing the temperature which allows to quantify the weak temperature dependence of the proton chemical shift which can be diagnostic for the presence of hydrogen bonds. Hydrogen bonding plays a central role in molecular recognition events from both fields, chemistry and biology. Their direct detection by standard structure determination techniques, such as X-ray crystallography or cryo-electron microscopy, remains challenging due to the difficulties of approaching the required resolution, on the order of 1 Å. We herein explore a spectroscopic approach using solid-state NMR to identify protons engaged in hydrogen bonds and explore the measurement of proton chemical-shift temperature coefficients. Using the examples of a phosphorylated amino acid and the protein ubiquitin, we show that fast Magic-Angle Spinning (MAS) experiments at 100 kHz yield sufficient resolution in proton-detected spectra to quantify the rather small chemical-shift changes upon temperature variations.<br>

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Probing solid iminobis(diorganophosphine chalcogenide) systems with multinuclear magnetic resonance

Canadian Journal of Chemistry ◽

10.1139/v08-150 ◽

2009 ◽

Vol 87 (1) ◽

pp. 348-360 ◽

Cited By ~ 1

Author(s):

Bryan A Demko ◽

Roderick E Wasylishen

Keyword(s):

Solid State ◽

Chemical Shift ◽

Solid State Nmr ◽

Magnetic Shielding ◽

Chemical Shift Tensors ◽

X Ray ◽

X Ray Crystallography ◽

Shielding Tensor ◽

Nuclear Magnetic Shielding Tensors ◽

Nuclear Magnetic

A 31P and 77Se solid-state NMR investigation of the iminobis(diorganophosphine chalcogenide) HN(R2PE)2 (R = Ph,iPr; E = O, S, Se) systems is presented. The NMR results are discussed in terms of the known HN(R2PE)2 structures available from X-ray crystallography. The phosphorus chemical shift tensors are found to be sensitive to the nature of the alkyl and chalcogen substituents. The nature of the R group also influences the selenium chemical shift tensors of HN(R2PSe)2 (R = Ph, iPr), which are shown to be sensitive to hydrogen bonding in the dimer structure of HN(Ph2PSe)2 and to the presence of disorder in the case of HN(iPr2PSe)2. Scalar relativistic ZORA DFT nuclear magnetic shielding tensor calculations were performed yielding the orientations of the corresponding chemical shift tensors. A theoretical investigation into the effect of the E-P···P-E “torsion” angle on the phosphorus and selenium chemical shift tensors of a truncated HN(Me2PSe)2 system indicates that the electronic effect of the alkyl group on the respective nuclear magnetic shielding tensors are more important than the steric effect of the E-P···P-E torsion angle.Key words: iminobis(diorganophosphine chalcogenide), solid-state NMR, 31P NMR, 77Se NMR, ZORA DFT.

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