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 T1 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 [1H and 13C T1, T2; 13C{1H}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 T1 values than the periphery. In contrast to the relaxation properties of linear polymers, these T1 increments should not be interpreted as resulting from faster dynamics. Only the recording of T1 data at various temperatures (alternatively, T2 or NOE at one temperature) ensures the correct interpretation of dendrimer dynamicsThis work was financially supported by the Spanish Government (CTQ2009-10963 and CTQ2009-14146-C02-02) and the Xunta de Galicia (10CSA209021PR and CN2011/037). L.F.P. thanks the Portuguese Foundation for Science and Technology (FCT MCTES) for a Ph.D. grant (SFRH/BD/37341/2007)S