DiffusionNMR Study of Generation-Five PAMAM DendrimerMaterials

摘要

Commercial generation-five poly(amidoamine) dendrimer material (G5c) was fractionated into its major structural components. Monomeric G5 (G5m; 21–30 kDa) was isolated to compare its functional properties to the G5c material. Diffusion-ordered nuclear magnetic resonance spectroscopy was employed to measure the self-diffusion coefficients and corresponding hydrodynamic radii of G5m and other G5c components as a function of dendrimer size (i.e., molecular weight) and tertiary structure (i.e., generational or oligomeric nature). It was found that the hydrodynamic radius (RH) scales with approximate numbers of atoms in the trailing generations, G5m, and oligomeric material at a rate of RH ∝ N^0.35, in good agreement with previous reports of RH scaling for PAMAM dendrimer with generation. G5c materials can be thought of as a heterogeneous mixture of dendrimers ranging in size from trailing generation two to tetramers of G5, approximately the same in size as a G7 dendrimer, with G5m comprising ∼65% of the material. The radius of hydration for G5m was measured to be 3.1 ± 0.1nm at pH 7.4. The 10% swelling in response to a drop in pH observedfor the G5c material was not observed for isolated G5m; however, theisolated G5–G5 dimers had an increase of 44% in RH, indicating that the G5c pH response results from theincrease in RH of the oligomeric fractionupon protonation. Finally, the data allow for an experimental testof the “slip” and “stick” boundary modelsof the Stokes–Einstein equation for PAMAM dendrimer in water.