Selenium‐77 and carbon‐13 high‐resolution solid‐state NMR studies of selenomethionine

Abstract

77Se cross-polarization magic angle spinning (CP/MAS) and 13C CP/MAS experiments were employed to study the structure and dynamics of DL-selenomethionine (1) and L -selenomethionine (2) in the solid state. The 77Se principal elements of chemical shift tensors δ ii and shielding parameters for both compounds were calculated by means of the graphical method of Herzfeld and Berger. An attempt to assign the 77Se δii to the molecular structure of selenomethionine is presented. From 77Se and 13C NMR it is concluded that the unit cell of 2 contains A and B molecules and 2 is isomorphous with L -methionine. The significant distinction in side-chain dynamics for A and B molecules is apparent from 77Se T1 measurement (23 and 3.5 s). For 1 77Se T1 is established to be 16.5 s. It is found that 2 undergoes a phase transition at 305 K. 77Se CP/MAS revealed that both A and B molecules undergo isomerization and such a process causes changes in the selenium shielding parameters. Similar isomerization is observed at room temperature when the sample is rotated with a spinning rate of 14.5 kHz. Copyright © 1999 John Wiley & Sons, Ltd.