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[Li.sup.+] and [Ca.sup.+] binding to the carbonyl oxygen sites of a model peptide system is studied by [sup.17.O] solid-state NMR spectroscopy and [sup.17.O] chemical shift (CS) and quadrupole coupling (QC) tensors are determined in four Gly-(Gly-[sup.17.O])-Gly polymorphs by a combination of stationary and fast magic-angle spinning (MAS) methods at high magnetic field, 19.6 T. The effects of the ion binding are found to be almost an order of magnitude greater than those induced by hydrogen bonding.

Single-crystal NMR is used to determine (super 15)N shielding tensors for the central peptide groups in GGV, AGG, and APG. The findings show that the angle between the downfield component [delta(sub 11)] and the N-H or the N-C(super delta)(pro) bonds is in the range of 20-23 degree.

Single-crystal NMR is used to determine (super 15)N shielding tensors for the central peptide groups in GGV, AGG, and APG. The findings show that the angle between the downfield component [delta(sub 11)] and the N-H or the N-C(super delta)(pro) bonds is in the range of 20-23 degree.

15N chemical shielding parameters are reported for central glycyl residues in crystallographically characterized tripeptides. It is a prediction scheme for the 2 degrees structure of glycyl residues in proteins based on shielding parameters is proposed.

Presented here is a centrally controlled, automated parahydrogen-based polarizer with in situ detection capability. A 20% polarization, corresponding to a 5 000 000-fold signal enhancement at 48 mT, is demonstrated on 2-hydroxyethyl-1-13C-propionate-d2,3,3 using a double-tuned antenna and pulsed polarization transfer. In situ detection is a refinement of first-generation devices enabling fast calibration of rf pulses and B0, quality assurance of hyperpolarized contrast agents, and stand-alone operation without the necessity of high-field MR spectrometers. These features are essential for biomedical applications of parahydrogen-based hyperpolarization and for clinical translation. We demonstrate the flexibility of the device by recording 13C signal decay due to longitudinal relaxation of a hyperpolarized contrast agent at 48 mT corresponding to 2 MHz proton frequency. This appears to be the longest recorded T1 (101 ± 7 s) for a 13C hyperpolarized contrast agent in water. [ABSTRACT FROM AUTHOR]

Li+ and Ca2+ binding to the carbonyl oxygen sites of a model peptide system has been studied by 170 solid-state NMR spectroscopy. 170 chemical shift (CS) and quadrupole coupling (QC) tensors are determined in four Gly-(Gly-17O)-Gly polymorphs by a combination of stationary and fast magic-angle spinning (MAS) methods at high magnetic field, 19.6 T. In the crystal lattice, the carbonyl oxygen of the central glycyl residue in two gly-gly-gly polymorphs form intermolecular hydrogen bonds with amides, whereas the corresponding carbonyl oxygens of the other two polymorphs form interactions with Li+ and Ca2+ ions. This permits a comparison of perturbations on 17O NMR properties by ion binding and intermolecular hydrogen bonding. High quality spectra are augmented by density functional theory (DFT) calculations on large molecular clusters to gain additional theoretical insights and to aid in the spectral simulations. Ion binding significantly decreases the two 170 chemical shift tensor components in the peptide plane, δ11 and δ22, and, thus, a substantial change in the isotropic chemical shift. In addition, quadrupole coupling constants are decreased by up to 1 MHz. The effects of ion binding are found to be almost an order of magnitude greater than those induced by hydrogen bonding. [ABSTRACT FROM AUTHOR]

15N shielding tensors were determined for the central peptide groups in GGV, AGG, and APG by single-crystal NMR. We find that the angle between the downfield component (δ11) and the N-H or the N-Cδ6 (pro) bonds is in the range of 20-23° and in accord with previous solid-state NMR measurements. However, AGG, unlike APG or GGV, has a distorted peptide plane, and δ11 lies approximately in the plane of N, Cα, and H rather than in the peptide plane defined by heavy atoms. Accurate orientations of δ22 and δ33 were determined, and the usual assumption that δ22 is along the peptide normal was found only in APG which has a highly nonaxial tensor. More generally, δ22 and δ33 are rotated about the δ11 axis (36° in GGV). These results are compared with DFT calculations to gain a structural understanding of the effects of intermolecular interactions on shielding tensor principal components and orientations. Trimeric clusters containing H-bonded neighbors predict the orientations of the principal components within 2-3°, but calculated principal components are less quantitative. Possible reasons for this disagreement are explored. [ABSTRACT FROM AUTHOR]

[SUP15]N chemical shielding parameters are reported for central glycyl residues in crystallographically characterized tripeptides with α-helix, β-strand, polyglycine II (3[SUB1]-helix), and extended structures. Accurate values of the shielding components (2-5 ppm) are determined from MAS and stationary spectra of peptides containing [2-[SUP13]C,[SUP15]N]Gly. Two dipolar couplings, [SUP1]H-[SUP15]N and [SUP13]C[SUPα-[SUP15]N, are used to examine [SUP15]N shielding tensor orientations in the molecular frame and the results indicate that the δ[SUB11], δ[SUB33] plane of the shielding tensor is not coincident with the peptide plane. The observed isotropic shifts, which vary over a range of 13 ppm, depend on hydrogen bonding (direct and indirect) and local conformation. Tensor spans, δ[SUBspan] = δ[SUB11] - δ[SUB33], and their deviations from axial symmetry, δ[SUBdev] = δ[SUB22] - δ[SUB33], vary over a larger range and are grouped according to 2° structure. Augmented by previously reported [SUP13]Q[SUPα] shielding parameters, a prediction scheme for the 2° structure of glycyl residues in proteins based on shielding parameters is proposed. [ABSTRACT FROM AUTHOR]