✍ Scribed by Christian Pattaroni; Jürgen Lauterwein
No coin nor oath required. For personal study only.
The 13C spin-lattice relaxation times and nuclear Overhauser enhancement factors of all-trans-retinal were measured in acetone-d, at two different magnetic field strengths. The extent to which the chemical shift anisotropy mechanism was found to contribute to the relaxation rate of the quaternary olefinic carbons was between 23 and 37% at 4.70 T and between 48 and 66% at 8.45T. Assuming anisotropic molecular motion and an asymmetric chemical shift tensor, the shielding anisotropies of carbons C-5, C-6, C-9 and C-13 were calculated to be 185, 172, 188 and 228 ppm, respectively. These are qualitatively similar to those obtained in a recent I3C NMR study of all-trans-retinal in the solid state. In contrast, the quaternary aliphatic carbon C-1 was much less relaxed by the chemical shift anisotropy mechanism (contribution < 110/0). The relaxation of the proton-bearing carbons was independent of the magnetic field and determined only by the dipole-dipole interaction mechanism.
📜 SIMILAR VOLUMES
We present a simple method for extracting interference effects between chemical shift anisotropy (CSA) and dipolar coupling from spin relaxation measurements in macromolecules, and we apply this method to extracting cross-correlation rates involving interference of amide 15N CSA and 15N-1H dipolar c