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Abstract:
To demonstrate the influence of motions with medium-to-slow correlation times (milliseconds to nanoseconds), a systematic study of the spin-lattice relaxation in the rotating frame was conducted for several nuclei (1H, 13C, and 15N) in small membrane polypeptides, either in oriented or magic angle spinning samples. This study not only assesses the validity of some motional models, but also characterizes the magnetization relaxation rates crucial for the design of polarization transfer experiments. It was found that relaxation time constant (T1ρ) values on the order of 10−3–10−2s for backbone nuclei and their dependence on sample orientation are consistent with the model of transmembrane polypeptides undergoing axial diffusion (τc appr. 10−8–10−7s) and small amplitude off-axis reorientation (τc appr. 10−6–10−5s).
