Materials and Process Simulation Center (M/C 139-74), California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA.
J Am Chem Soc. 2009 Mar 4;131(8):2798-9. doi: 10.1021/ja8100227.
Atomistic molecular dynamics (MD) simulations of a G4-NH(2) PAMAM dendrimer were carried out in aqueous solution using explicit water molecules and counterions (with the Dreiding III force field optimized using quantum mechanics). Our simulations predict that the radius of gyration (R(g)) of the dendrimer changes little with pH from 21.1 A at pH approximately 10 (uncharged PAMAM) to 22.1 A at pH approximately 5 (charged with 126 protons), which agrees quantitatively with recent small angle neutron scattering (SANS) experiments (from 21.4 A at pH 10 to 21.5 A at pH 5). Even so we predict a dramatic change in the conformation. The ion pairing in the low pH form leads to a locally compact dense shell with an internal surface area only 37% of the high pH form with a dense core. This transformation from "dense core" at high pH to "dense shell" at low pH could facilitate the encapsulation and release of guest molecules (e.g., drugs) using pH as the trigger, making dendrimers a unique drug delivery vehicle.
在水溶液中使用显式水分子和抗衡离子（使用量子力学优化的 Dreiding III 力场）对 G4-NH(2)PAMAM 树枝状大分子进行了原子分子动力学 (MD) 模拟。我们的模拟预测，树枝状大分子的回转半径 (R(g)) 在 pH 值从大约 10（不带电荷的 PAMAM）到大约 5（带 126 个质子）的范围内变化很小，这与最近的小角中子散射 (SANS) 实验定量一致（从 pH 10 时的 21.4A 到 pH 5 时的 21.5A）。即便如此，我们预测构象会发生剧烈变化。在低 pH 形式下的离子配对导致局部紧凑的密集外壳，其内部表面积仅为高 pH 形式的 37%，具有密集的核心。这种从高 pH 的“密集核心”到低 pH 的“密集外壳”的转变可以促进使用 pH 作为触发因素的客体分子（例如药物）的封装和释放，使树枝状大分子成为一种独特的药物输送载体。
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