Gupta Shilpa, Biswas Parbati
Department of Chemistry, University of Delhi, Delhi 110007, India.
J Chem Phys. 2020 Nov 21;153(19):194902. doi: 10.1063/5.0030270.
This study investigates the conformational properties of complexes of poly(propylene imine) dendrimers with a linear polyelectrolyte (LPE) at neutral pH in an aqueous solution via molecular dynamics simulations. Various conformational properties, such as the atomic density profile, counterion density distribution, charge distribution, cavity volume, and the static structure factor are studied as a function of the charge and chain length of the LPE. The lower generation dendrimer complexes encapsulate the shorter linear PE chains, while the longer PE chains are adsorbed on the dendrimer surface that screen the surface charge and prevent the penetration of the counterions and water molecules. However, the overall charge of the higher generation dendrimers is not neutralized by the charge of the PE chains, which results in chloride counterion penetration within the dendrimers. The adsorption of the PE chains on the dendrimers is also verified from the charge distribution of the dendrimer-PE complexes. The charge on the lower generation dendrimer complexes is overcompensated by the longer PE chains resulting in an overall negative charge on the complexes, while the PE chains do not completely neutralize the charge of the higher generation dendrimers and produce positively charged complexes. The results of the structure factor indicate a conformational transition of the dendrimer-PE complexes from a dense compact structure to an open one with an increase in the PE chain length. This transition is characterized by an increase in the cavity volume in dendrimers with an increase in the PE chain length.
本研究通过分子动力学模拟，研究了在中性pH值的水溶液中，聚（丙烯亚胺）树枝状大分子与线性聚电解质（LPE）形成的复合物的构象性质。研究了各种构象性质，如原子密度分布、抗衡离子密度分布、电荷分布、空腔体积和静态结构因子，它们是LPE电荷和链长的函数。较低代数的树枝状大分子复合物包封较短的线性PE链，而较长 的PE链吸附在树枝状大分子表面，该表面屏蔽表面电荷并阻止抗衡离子和水分子的渗透。然而，较高代数树枝状大分子的总电荷并未被PE链的电荷中和，这导致氯离子抗衡离子渗透到树枝状大分子内部。从树枝状大分子 - PE复合物的电荷分布也证实了PE链在树枝状大分子上的吸附。较低代数树枝状大分子复合物上的电荷被较长的PE链过度补偿，导致复合物整体带负电荷，而PE链并未完全中和较高代数树枝状大分子的电荷，从而产生带正电荷的复合物。结构因子的结果表明，随着PE链长度的增加，树枝状大分子 - PE复合物的构象从致密紧凑结构转变为开放结构。这种转变的特征是随着PE链长度的增加，树枝状大分子中的空腔体积增大。
