科研之友
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摘要
Commercial generation-five poly(amidoamine) dendrimer material (G5c) was fractionated into its major structural components. Monomeric GS (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 (R-H) scales with approximate numbers of atoms in the trailing generations, G5m, and oligomeric material at a rate of R-H proportional to N-0.35, in good agreement with previous reports of R-H 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 GS, approximately the same in size as a G7 dendrimer, with G5m comprising similar to 65% of the material. The radius of hydration for G5m was measured to be 3.1 +/- 0.1 nm at pH 7.4. The 10% swelling in response to a drop in pH observed for the G5c material was not observed for isolated G5m; however, the isolated G5-G5 dimers had an increase of 4496 in R-H, indicating that the G5c pH response results from the increase in RI, of the oligomeric fraction upon protonation. Finally, the data allow for an experimental test of the "slip" and "stick" boundary models of the Stokes-Einstein equation for PAMAM dendrimer in water.
- 出版日期2014-6-26
