Molecular Dynamics of Polymer Chains and Alkyl Groups in Solution

Abstract

For carbons possessing a directly bonded proton, the carbon-13 spin lattice relaxation time, T1, spin-spin relaxation time, T2, and the nuclear Overhauser enhancement, NOE, comprise a set of parameters which characterize molecular motions. In the case of simple isotropic motion, the dependence is in terms of a single correlation time characterizing the exponential decay of the auto-correlation function. However, in many instances, the assumption of isotropic motion is not valid. For rigid systems, the relaxation behavior can then often be predicted by assuming simple anisotropic motion (1). Often, superposition of two or more independent motions must be used to satisfactorily interpret observed relaxation behavior (1,2) . Recently, however, the widespread availability of 13C nmr instruments, has led to a number of examples where these models have proved unsatisfactory. Deviations from predicted relaxation behavior have been observed for large proteins (3-7) , polymers (8,9) and highly associated small molecules (10). Particularly