Peptide ¹⁷O Chemical Shielding and Electric Field Gradient Tensors

Abstract

Complete 17O chemical shielding (CS) and quadrupole coupling (QC) tensors and their molecular orientations were determined for the central residues in two tripeptides Gly-Gly-Val (GGV) and Ala-Gly-Gly (AGG) by single-crystal NMR methods. Tensor orientations in the two peptides are very similar, however, principal components are different. The most shielded CS and smallest magnitude QC components are normal to the peptide plane, while the most deshielded CS and largest QC components are in the peptide plane either at an angle of 17°(CS) or perpendicular (QC) to the CdO bond. Comparisons of principal components from experiment and DFT calculations indicate that the smaller shielding tensor span in GGV (549 ppm) compared to AGG (606 ppm) is likely due to two factors: a shorter "direct" H-bond distance to the peptide carbonyl oxygen and an "indirect" H bond of the peptide NH to a carboxylate rather than a carbonyl. We anticipate that 17 O NMR should be generally useful for probing H-bonding and local electrostatic interactions in proteins and polypeptides. Using the single-crystal data as an accurate reference, we show that a useful subset of the NMR parameters, QC and CS principal components and their relative orientation, can be obtained with reasonable accuracy from a very high-field (21.2 T), stationary sample powder spectrum.

The determination of17O NMR parameters of hydroxyl oxygen: A combined deuteration and DOR approach

“…As reported in Table 1, the 17 O CSA span for carboxyl and hydroxyl oxygens is found to be quite different, 540 and 210 ppm respectively. Similar large 17 O values for the carboxyl oxygens have also been reported for amides 26 and peptides 11,27 using either static or single-crystal NMR experiments, where 17 O values of 500-650 ppm are found. The different 17 O values arise from the fact that these oxygens are in different functional groups with different electronic environments: -bonds versus -bonds.…”

Chemical shift tensor – The heart of NMR: Insights into biological aspects of proteins

“…Nevertheless, several attempts to record solid-state 17 O NMR have been made with an emphasis on attempts to elucidate the hydrogen-bonded structure of peptides and polypeptides [206–218]. 17 O enrichment [206–211,216,217] together with higher-frequency solid-state NMR techniques are necessary to overcome the detection problems [219].…”

“…The eight parameters were obtained by applying a curve-fitting procedure to the experimental spectra, and the results are summarized in Table 8. Static 17 O NMR spectra of the central Gly residues in two single crystalline 17 O labeled Gly*GlyVal (GGV) and Ala*GlyGly (AGG) were measured, where *Gly indicates 17 O labeled Gly [218]; the determined tensor orientations in the two peptides are very similar but the principal components are different. The most shielded CSA and smallest magnitude quadrupolar coupling (QC) components are normal to the peptide plane, while the most deshielded CSA and largest QC components are in the peptide plane either at an angle of 17° (CS) or perpendicular (QC) to the C=O bond (see Fig.…”

High field 17O solid-state NMR study of alanine tripeptides

“…The combination of 17 O-labeled samples with higher magnetic fields has minimized these problems, and applications of 17 O solid-state NMR of amino acids, peptides and polypeptides with magic angle spinning (MAS) have progressed steadily over the past decade [4][5][6][7]. In recent years detailed studies of chemical shifts and quadrupolar tensors have been investigated to understand the NMR parameters of hydrogen bonded structures and how they can be applied to determine hydrogen bond lengths and bond angles [8][9][10][11]. In addition, dipolar recoupling experiments have been performed to determine the carbon-oxygen distance of hydrogen bonded systems [12][13][14].…”