Proton spin relaxation induced by localized spin-dynamical coupling in proteins

The magnetic field dependence of H-1 spin-lattice relaxation rates in noncr ystalline macromolecular solids is described by a power law, 1/T-1 = A omeg a (-b)(0), where omega (0) is the Larmor frequency, A and b are constants. We show that the magnetic field dependence of the proton 1/T-1 may be quant itatively related to structural fluctuations along the backbone that modula te proton-proton dipolar couplings. A and b are related to the dipolar coup ling strength, the energy for the highest vibrational frequency in the poly mer backbone, the fractal dimensionality of the proton spatial distribution , and the spectral dimensionality that characterizes the random walk on a f ractal network. (C) 2001 Elsevier Science B.V. All rights reserved.