Spin-lattice relaxation of 15N nuclei

Design of a 15N Molecular Unit to Achieve Long Retention of Hyperpolarized Spin State

“…However, unexpectedly, it was found that TMPA 2 was still affected by 15 N– 1 H DD relaxation. The role of 15 N– 1 H DD relaxation in total relaxation, termed 15 N– 1 H DD relaxation%, can be discussed by measurement of nuclear Overhauser enhancement (NOE, 1 + η) as previously reported (equation 2)19202122. Such 15 N– 1 H DD relaxation% indicates whether it is possible to elongate T 1 value by reducing the DD relaxation.…”

“…To achieve a long T 1 for the extended hyperpolarization lifetime, we considered a relaxation mechanism (equation 1)1519202122. Generally, T 1 is affected by dipole–dipole (DD) relaxation, spin–rotation (SR) relaxation, chemical shift anisotropy (SA) relaxation, scalar coupling (SC) relaxation, and the other relaxation terms including dipolar relaxation from dissolved oxygen.…”

Nitrogen nuclear magnetic resonance spectroscopy in inorganic, organometallic, and bioinorganic chemistry

“…Nitrogen shielding can now be referred to an absolute scale50®'61 based on the NH3 sr constants obtained by Kukolich by very high resolution beam maser measurements, which give crav(N) = 264.5 ppm for the isolated molecule.506 The absolute shielding o' for nitrogen in other molecules can be derived from its chemical shift (5) relative to liquid NH3 at 25 °C by o' = 246.2 -8, or relative to liquid MeN02 at [25][26][27][28][29][30] °C by o' = -135.8 -8 (etc. ).50® It is important to specify the state of the molecule, for temperature corrections may be significant, and medium or gas-to-liquid shifts for nitrogen (in contrast to fluorine, for example) may be large and of either sign, dependent on the manner of the hydrogen bonding:46 thus 5(liq) -8(gas) ^20 ppm for NH3 and -12 for HCN.50® Such medium effects account for the discrepancies noted59 between sr values of nuclear shielding and chemical shifts measured in the liquid phase for NH3 and HCN.…”

Nitrogen-15 magnetic resonance spectroscopy of trioxodinitrate: N-protonation of an oxoanion

“…Spin-lattice relaxation of N(l) is therefore dominated by other mechanisms, presumably by spin-rotation as found for other small nitrogen-containing molecules in solution. 24 The observed NOE of-2.1 at pH 8.0 indicates a very substantial contribution from 'H-15N dipolar relaxation to N(l) relaxation in the anion HN203( about half of the total relaxation rate). In principle, this contribution could arise from either of the forms 0, 0"…”