The dynamics of dendrimers by NMR relaxation: interpretation pitfalls.

NMR is a powerful tool to study the dynamics of dendrimers. By analogy to linear polymers, shorter T(1) relaxation times have been traditionally associated to less mobile nuclei and hence, dendrimers described with reduced local motions at either the core or the periphery. Herein we report a NMR relaxation study [(1)H and (13)C T(1), T(2); (13)C{(1)H}NOE; various fields and temperatures] which reveals profound differences between the relaxation behavior of dendrimers and linear polymers. Dendrimers show slower dynamics at internal layers and on increasing generation and may display internal nuclei in the slow motional regime with larger T(1) values than the periphery. In contrast to the relaxation properties of linear polymers, these T(1) increments should not be interpreted as resulting from faster dynamics. Only the recording of T(1) data at various temperatures (alternatively, T(2) or NOE at one temperature) ensures the correct interpretation of dendrimer dynamics.