Temperature dependent 15N NMR study of nitric oxide (original) (raw)
Related papers
Journal of the American …, 1993
The three principal components of the nitrogen chemical shift (CS) tensor have been measured for the nitrosobenzene-15Nz dimer (1) and @-[lSN]nitroso)-N,N-dimethylaniline (2) using solid-state I5N N M R spectroscopy. Nitrosobenzene exists as a colorless dimer in the solid state, while 2 is a green monomeric nitroso species. This structural difference leads to very different 15N shielding tensors for these two compounds. For example, the I5N chemical shift anisotropy (CSA) for compound 1 is 285 ppm, whereas for 2 the corresponding value is 1479 ppm. This latter value is the largest nitrogen CSA reported to date. Analysis of the dipolar chemical shift N M R spectrum of 1 yields two possible orientations of the nitrogen CS tensor in the molecular frame; results from ab initio localized orbital/local origin chemical shielding calculations on a simple model compound indicate that the actual orientation has the most shielded component of the CS tensor 633 perpendicular to the molecular plane, while the intermediate component 622 makes an angle of 23O with respect to the N-N bond and is approximately perpendicular to the N-C,,,, bond. On the basis of shielding calculations and dipolar N M R studies on related molecules, the most shielded component of the nitrogen CS tensor of 2 is perpendicular to the C N O plane, while the intermediate component lies in the molecular plane and approximately along the bisector of the C N O bond angle. The experimental results obtained in this study are compared to those of earlier studies where nitrogen is part of a planar T system.
Journal of Magnetic Resonance, 2011
Optimization of nitroxides as probes for EPR imaging requires detailed understanding of spectral properties. Spin lattice relaxation times, spin packet line widths, nuclear hyperfine splitting, and overall lineshapes were characterized for six low molecular weight nitroxides in dilute deoxygenated aqueous solution at X-band. The nitroxides included 6-member, unsaturated 5-member, or saturated 5-member rings, most of which were isotopically labeled. The spectra are near the fast tumbling limit with T 1 $T 2 in the range of 0.50-1.1 ls at ambient temperature. Both spin-lattice relaxation T 1 and spin-spin relaxation T 2 are longer for 15 N-than for 14 N-nitroxides. The dominant contributions to T 1 are modulation of nitrogen hyperfine anisotropy and spin rotation. Dependence of T 1 on nitrogen nuclear spin state m I was observed for both 14 N and 15 N. Unresolved hydrogen/deuterium hyperfine couplings dominate overall line widths. Lineshapes were simulated by including all nuclear hyperfine couplings and spin packet line widths that agreed with values obtained by electron spin echo. Line widths and relaxation times are predicted to be about the same at 250 MHz as at X-band.
Nitrogen-15 spin relaxation in oximes
Journal of Magnetic Resonance (1969), 1979
"N NMR spectral parameters are reported for several aldoximes and ketoximes. Syn and anti isomers are resolved and observed for acetaldoxime and propanaldoxime. "N spin-lattice relaxation times (T,'s) for the non-protonated nitrogens in these small molecules are not excessively long (-25 to 50 set). Dipolar relaxation is significant; however, contributions from other mechanisms contribute 50-65% to "N relaxation. Oxime nitrogens are found to be stereoselectiuely sensitive to the presence of paramagnetic metals.
Solubility of nitric oxide (NO) in lipid aggregates as monitored by nuclear magnetic resonance
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1998
Nitric oxide (NO) is known as a multifaceted bioregulatory agent and an environmental pollutant. We investigated the role of nitric oxide in phospholipid solutions by NMR techniques. A mixture of lipids dissolved in a ternary solvent was used. 31p NMR spectra of this mixture before and after exposure to nitric oxide were recorded. Nitric oxide is a strongly paramagnetic molecule which is able to increase the spin lattice relaxation rates, and, after its addition, we observed a strong signal broadening at certain solvent concentrations. Many pure phospholipids, dispersed in organic solvents, can form reversed micelles by spontaneous self-association. These results suggest that the lipids form a colloidal dispersion in a homogeneous organic ternary mixture, where the NO solubility increases strongly and produces a broadening of the 31p NMR signal. ¢,
Current Developments in Solid State NMR Spectroscopy
Monatshefte f�r Chemie / Chemical Monthly, 2002
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A 13 C NMR method for determining secondary nitroxide-substrate associations
Magnetic Resonance in Chemistry, 2017
The major effects of nitroxides on substrates in proton spectra is well studied, while the effect on carbon spectra has received less attention. Present knowledge relies on chemical shift differences between diamagnetic and paramagnetic solutions of the substrates to propose interactions. Changes in scalar coupling constants (JCH) would, however, provide better insight. Herein, we present a method of utilizing coupled 13 C NMR spectra where differences in 1 JCH coupling show alternate modes of association between nitroxides and test substrates.