Qing Zhe Ni, Evgeny Markhasin, Thach V. Can, Björn Corzilius, Kong Ooi Tan, Alexander B. Barnes, Eugenio Daviso, Yongchao Su, Judith Herzfeld, Robert G. Griffin

In DNP MAS NMR experiments at ~80-110 K, the structurally important -13CH3 and -15NH3+ signals in MAS spectra of biological samples disappear due to the interference of the molecular motions with the 1H decoupling. Here we investigate the effect of these dynamic processes on the NMR lineshapes and signal intensities in several typical systems: (1) microcrystalline APG, (2) membrane protein bR, (3) amyloid fibrils PI3-SH3, (4) monomeric alanine-CD3 and (5) the pro-tonated and deuterated dipeptide N-Ac-VL over 78-300 K. In APG, the 3-site hopping of the Ala-Cβ peak disappears com-pletely at 112 K, concomitant with the attenuation of CP signals from other 13C's and 15N's. Similarly, the 15N signal from Ala-NH3+ disappears ~173 K, concurrent with the attenuation in CP experiments of other 15N's as well as 13C's. In bR and PI3-SH3, the methyl groups are attenuated at ~95 K while all other 13C's remain unaffected. However, both systems exhibit substantial losses of intensity at ~243 K. Finally, with spectra of Ala and N-Ac-VL we show that it is possible to extract site specific dynamic data from the temperature dependence of the intensity losses. Furthermore, 2H labeling can assist with re-covering the spectral intensity. Thus, our study provides insight into the dynamic behavior of biological systems over a wide range of temperatures, and serves as a guide to optimizing the sensitivity and resolution of structural data in low temperature DNP MAS NMR spectra.