Department of Chemistry , University of Delhi , Delhi 110007 , India.
J Phys Chem B. 2018 Oct 4;122(39):9250-9263. doi: 10.1021/acs.jpcb.8b04653. Epub 2018 Sep 25.
The behavior of poly(propylene imine) dendrimers at three different solution pH is investigated through molecular dynamics (MD) simulations in explicit solvent. MD simulations provide an insight into the conformational properties of dendrimers via the evaluation of their size, shape, radial density distribution, static structure factor, and scattering intensity. The size of the dendrimer increases from high solution pH to low pH. The internal structure of the dendrimer is quantified in terms of the radial atomic density profile and the terminal amine group density distribution. While the radial atomic density distribution shifts away from the core of the dendrimer with decreasing pH, a significant degree of back-folding of the outer generations is observed at high pH for higher generations of growth. Results from the structure factor and scattering intensity indicate two types of conformational transitions: (i) as a function of the solution pH, where the dendrimer evolves from an expanded structure at low pH to a highly compact one at high pH (except for higher generations), and (ii) with increasing generations, where the open structure of the dendrimer at lower generations transforms to a compact structure at higher generations at both high and low pH, characterized by a change in the fractal dimension.
通过在显式溶剂中进行分子动力学 (MD) 模拟，研究了聚（丙烯亚胺）树枝状大分子在三种不同溶液 pH 值下的行为。MD 模拟通过评估树枝状大分子的大小、形状、径向密度分布、静态结构因子和散射强度，深入了解了树枝状大分子的构象特性。树枝状大分子的大小从高溶液 pH 值增加到低 pH 值。通过径向原子密度分布和末端胺基密度分布来量化树枝状大分子的内部结构。随着 pH 值的降低，径向原子密度分布从树枝状大分子的核心移开，而在高 pH 值下，对于更高代的生长，外层会发生显著程度的反向折叠。结构因子和散射强度的结果表明存在两种构象转变：（i）作为溶液 pH 值的函数，树枝状大分子从低 pH 值下的扩展结构演变为高 pH 值下的高度紧凑结构（除了更高代），以及（ii）随着代的增加，在较低代的树枝状大分子的开放结构在高 pH 值下转变为更高代的紧凑结构，其特征在于分形维数的变化。
