Search

A study determined complete [super 17]O chemical shielding (CS) and quadrupole coupling (QC) tensors and their molecular orientations for the central residues in two tripeptides Gly-Gly-Val (GGV) and Ala-Gly-Gly (AGG) by single-crystal NMR methods. Results lead to the anticipation that [super17]O NMR should be generally useful for probing H-bonding and local electrostatic interactions in proteins and polypeptides.

[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.

Studies the jet-cooled spectrum of silylidene, a simple form of unsaturated silylene. Characteristics of band consisting the electronic transition; Excited state decay dynamics; Rotational levels specific intensity anomalies; Beat patterns due to coupling with high vibrational levels of the ground state.

Several supported metal catalysts were synthesized, characterized, and tested in heterogeneous hydrogenation of propene with parahydrogen to maximize nuclear spin hyperpolarization of propane gas using parahydrogen induced polarization (PHIP). The Rh/TiO2 catalyst with a metal particle size of 1.6 nm was found to be the most active and effective in the pairwise hydrogen addition and robust, demonstrating reproducible results with multiple hydrogenation experiments and stability for ≥1.5 years. 3D 1H magnetic resonance imaging (MRI) of 1 % hyperpolarized flowing gas with microscale spatial resolution (625×625×625 μm3) and large imaging matrix (128×128×32) was demonstrated by using a preclinical 4.7 T scanner and 17.4 s imaging scan time. [ABSTRACT FROM AUTHOR]

Indirect proton detection of 13C hyperpolarized contrast agents potentially enables greater sensitivity. Presented here is a study of sub-second projection imaging of hyperpolarized 13C contrast agent addressing the obstacle posed by water suppression for indirect detection in vivo. Sodium acetate phantoms were used to develop and test water suppression and sub-second imaging with frequency-selective RF pulses using spectroscopic and imaging indirect proton detection. A 9.8 m m aqueous solution of 13C PHIP hyperpolarized 2-hydroxyethyl-13C-propionate- d2,3,3 (HEP), ~25% was used for demonstration of indirect proton sub-second imaging detection. Balanced 2D FSSFP (fast steady-state free precession) allowed the recording of proton images with a field of view of 64 × 64 mm2 and spatial resolution 2 × 2 mm2 with total acquisition time of less than 0.2 s. In thermally polarized sodium 1-13C-acetate, 13C to 1H polarization transfer efficiency of 45.1% of the theoretically predicted values was observed in imaging detection corresponding to an 11-fold overall sensitivity improvement compared with direct 13C FSSFP imaging. 13C to 1H polarization transfer efficiency of 27% was observed in imaging detection, corresponding to a 3.25-fold sensitivity improvement compared with direct 13C FSSFP imaging with hyperpolarized HEP. The range of potential applications and limitations of this sub-second and ultra-sensitive imaging approach are discussed. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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]

Abstract: Gamma-aminobutyric acid (GABA) and glutamate (Glu) levels, normalized to total creatine (tCr), were measured in the anterior cingulate and cerebellar vermis in healthy adults (n=19, age=24.6±6.4 years) using 1H MRS at 3 T, and metabolite correlations across regions and subjects were determined. Mean anterior cingulate and cerebellar GABA/tCr ratios were 0.31 (0.08) and 0.23 (0.06), respectively, while corresponding Glu levels were 1.16 (0.10) and 0.70 (0.07), respectively. Anterior cingulate and cerebellar glutamate levels were correlated (r=0.6103, P=.0140), although it is noted that when adjusted for multiple comparisons, all correlations reported here cluster to a P value of .0583. It is unlikely that this correlation is driven by correlations in tCr, since interregional correlations were not observed for other metabolites referenced to tCr. Correlations were also observed among metabolites in both the anterior cingulate and cerebellar vermis. In the former, N-acetylasparate was linearly dependent on glutamate (r=0.6577, P=.0063) and, at or below this significance threshold, four metabolites were correlated in the cerebellar vermis (Ins/tCh: r=0.6261, P=.0109. NAA/tCh: r=0.6426, P=.0082. NAA/Glu: r=0.6412, P=.0085. tCh/Glu: r=0.6193, P=0.0122). [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]