文摘
Molecular dynamics of metabolites are important for their interactions and functions. To understand the structural dependence of molecular dynamics for N-methylated glycines, we comprehensively measured the 13C and 1H spin鈥搇attice relaxation times for sarcosine, N,N-dimethylglycine, betaine, and betaine hydrochloride over a temperature range of 178鈥?60 K. We found that the reorientations of methyl groups were observed for all these molecules, whereas reorientations of whole trimethylamine groups were detected in betaines. While similar rotational properties were observed for methyl groups in N,N-dimethylglycine and those in betaine, three methyl groups in betaine hydrochloride had different motional properties (Ea 鈮?20.5 kJ/mol, 蟿0 鈮?1.85 脳 10鈥?3 s; Ea 鈮?13.9 kJ/mol, 蟿0 鈮?2.1 脳 10鈥?2 s; Ea 鈮?15.8 kJ/mol, 蟿0 鈮?1.1 脳 10鈥?2 s). N,N-Dimethylglycine showed a phase transition at 348.5 K with changed relaxation behavior for methyl groups showing distinct Ea and 蟿0 values. The DIPSHIFT experiments showed that CH3 and CH2 moieties in these molecules had dipolar-dephasing curves similar to these moieties in alanine and glycine. The activation energies for CH3 rotations positively correlated with the number of substituted methyl groups. These findings provided useful information for the structural dependence of molecular dynamics for N-methylated glycines and demonstrated solid-state NMR as a useful tool for probing the structure鈥揹ynamics relationships.