Physical Chemistry Laboratory, Chemical Engineering Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece.
Phys Chem Chem Phys. 2009 Nov 21;11(43):10017-28. doi: 10.1039/b913986a. Epub 2009 Sep 11.
Models consisting of an amine-terminated poly(amidoamine) (PAMAM) dendrimer with and without the presence of a linear poly(ethylene oxide) (PEO) chain were studied in aqueous solutions by means of fully atomistic molecular dynamics simulations. Dendrimers of two generations, 3rd and 4th and at different pH conditions were examined, in order to address issues associated with characteristics pertinent to the shape of the dendrimers in the presence or absence of PEO as well as to the volume fraction of the penetrating solvent molecules and counterions as compared to recent experimental studies. In addition, hydrogen-bonding characteristics such as the intensity and the longevity of intra- and intermolecular hydrogen-bonded pairs are examined for the first time in these systems. It was found that the volume fraction of the penetrating solvent molecules increased upon decrease of pH, but no dependence on the size of the molecules was observed. The density of the solvent within the dendritic interior did not exceed that of the bulk, while the corresponding number of counterions entering the dendrimer boundaries exhibited a marked increase between the 3rd and the 4th generation of the dendrimers. Intramolecular hydrogen bonding was favored at high pH conditions, while intermolecular hydrogen bonding between PAMAM and the solvent or the PEO was significantly enhanced upon protonation of the dendrimer's amines. The presence of PEO imparted appreciable changes in the dendrimer's shape particularly in the physiological pH conditions. In addition, it incurred a decrease in intramolecular hydrogen bonding and acted antagonistically to the formation of water/dendrimer hydrogen bonds. The higher degree of hydrogen bonding between PAMAM and PEO was observed at low pH levels, indicating that under these conditions the formed complexes are expected to be more stable. The findings of the present study were found to be in good agreement with the relevant experimental findings where available, thus assessing the role of several structural and conformational details in the manifested behavior and providing further insight of the effects of non-covalent complexation of PAMAM dendrimers with linear poly(ethylene oxide).
本文采用全原子分子动力学模拟方法，研究了末端带有伯胺基的聚酰胺-胺（PAMAM）树状大分子及其带有或不带有线性聚（环氧乙烷）（PEO）链的模型在水溶液中的性质。研究了两代（第 3 代和第 4 代）、不同 pH 值条件下的树状大分子，以解决与树状大分子形状有关的特性问题，包括有无 PEO 存在以及与穿透溶剂分子和抗衡离子的体积分数有关的问题，这与最近的实验研究相关。此外，本文首次研究了这些体系中的氢键特征，如氢键的强度和持久性、分子内和分子间氢键对。研究发现，随着 pH 值的降低，穿透溶剂分子的体积分数增加，但没有观察到分子尺寸的依赖性。树突内部溶剂的密度不超过本体密度，而进入树突边界的抗衡离子数量在树突第 3 代和第 4 代之间显著增加。在高 pH 值条件下，分子内氢键占优势，而质子化后，PAMAM 与溶剂或 PEO 之间的分子间氢键显著增强。PEO 的存在对树状大分子的形状产生了明显的变化，特别是在生理 pH 值条件下。此外，它还降低了分子内氢键的形成，并与水/树突氢键的形成产生拮抗作用。在低 pH 值水平下，观察到 PAMAM 和 PEO 之间的氢键程度更高，这表明在这些条件下，形成的复合物预计会更稳定。本研究的结果与现有相关实验结果一致，从而评估了几种结构和构象细节在表现出的行为中的作用，并进一步深入了解了 PAMAM 树状大分子与线性聚（环氧乙烷）非共价络合的影响。
