van Dongen Mallory A, Orr Bradford G, Banaszak Holl Mark M
Departments of Chemistry, ‡Department of Physics, and §Program in Macromolecular Science and Engineering, University of Michigan , 930 North University Avenue, Ann Arbor, Michigan 48109, United States.
J Phys Chem B. 2014 Jun 26;118(25):7195-202. doi: 10.1021/jp504059p. Epub 2014 Jun 13.
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 (R(H)) scales with approximate numbers of atoms in the trailing generations, G5m, and oligomeric material at a rate of R(H)∝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 ± 0.1 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 44% in R(H), indicating that the G5c pH response results from the increase in R(H) 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.
商用第五代聚（酰胺胺）树枝状大分子材料（G5c）被分离成其主要结构成分。分离出单体G5（G5m；21 - 30 kDa）以比较其与G5c材料的功能特性。采用扩散有序核磁共振光谱法测量G5m和其他G5c成分的自扩散系数以及相应的流体动力学半径，作为树枝状大分子尺寸（即分子量）和三级结构（即代数或寡聚性质）的函数。研究发现，流体动力学半径（R(H)）与后几代、G5m和寡聚材料中的原子近似数量成比例，比例为R(H)∝N(0.35)，这与先前关于聚酰胺胺树枝状大分子R(H)随代数缩放的报道高度一致。G5c材料可被视为树枝状大分子的异质混合物，其尺寸范围从后两代到G5的四聚体，大小与G7树枝状大分子大致相同，其中G5m占材料的约65%。在pH 7.4时，G5m的水化半径测量值为3.1±0.1 nm。对于分离出的G5m未观察到G5c材料在pH下降时出现的10%膨胀；然而，分离出的G5 - G5二聚体的R(H)增加了44%，这表明G5c的pH响应是由于质子化后寡聚部分的R(H)增加所致。最后，这些数据允许对水中聚酰胺胺树枝状大分子的斯托克斯 - 爱因斯坦方程的“滑移”和“黏附”边界模型进行实验测试。
