Nuclear magnetic relaxation dispersion study of the dynamics in solid homopolypeptides.

The (1)H nuclear magnetic relaxation dispersion profiles were measured from 10 kHz to 30 MHz as a function of temperature for polyglycine, polyalanine, polyvaline, and polyphenylalanine to examine the contributions of different side chain motions to the polypeptide proton relaxation rate constants. The spin-fracton theory for (1)H relaxation is modified to account for high frequency motions of side chains that are dynamically connected to the linear polymer backbone. The (1)H relaxation is dominated by propagation of rare disturbances along the backbone of the polymer. The side-chain dynamics cause an off-set in the field dependence of the (1)H spin-lattice relaxation rate constants which obey a power law in the Larmor frequency in the limit of low and high magnetic field strength. Copyright 2007 Wiley Periodicals, Inc.