Structure of PAMAM dendrimers:: Generations 1 through 11
Structure of PAMAM dendrimers:: Generations 1 through 11
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DOI：
10.1021/ma035629b
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发表时间：
2004-08-10
期刊：
影响因子：
5.5
通讯作者：
Goddard, WA
中科院分区：
文献类型：
--
作者：
Maiti, PK;Çagin, T;Goddard, WA
聚酰胺-酰胺（PAMAM）树枝状大分子的结构和动力学研究一直是科学和工业界关注的热点，但其分子内部的原子、通道和应变等重要特征至今仍未得到解决。本文报道了乙二胺（EDA）为核心的PAMAM树枝状大分子的原子结构的系统调查的结果，通过第11代（294 852个原子），在这一点上的应变能已经上升到一个点，限制了额外的层的均匀生长。在这里，我们报告，作为一个功能的生成，结构特性，如回转半径，形状张量，非球面性，分形维数，单体密度分布，溶剂可及表面积，分子体积和端基分布函数，所有评估从广泛的分子动力学（MD）在300 K。我们发现，在整个世代范围内的回转半径为R，N 113，这表明所有世代的空间填充相当均匀。与常见的预期相反，我们发现，即使对于G11，外部子代也基本上渗透到树枝状聚合物的内部。因此，末端胺基团分布在整个内部，而不仅仅是在树枝状聚合物的外围。然而，对于G6到G11，有一个大的均匀密度区域，支持经常用于解释SANS（小角中子散射）和SAXS（小角X射线散射）数据的均匀散射模型，这导致尺寸与计算非常一致。计算出的单粒子形状因子随着代数的增加而接近球形。对于较大的世代，我们发现，使用连续配置偏置蒙特卡罗（CCBB MC）是必不可少的，以构建初始配置，导致较低的最终应变能。
The structure and dynamics of poly(amido amide) (PAMAM) dendrimers have been of great interest both scientifically and industrially, but such important features as the distributions of atoms, channels, and strain inside these molecules remain unresolved. This paper reports results from systematic investigations of the atomistic structure of ethylenediamine (EDA) cored PAMAM dendrimer up through the 11th generation (294 852 atoms), at which point the strain energy has risen to a point that limits uniform growth of additional layers. Here we report, as a function of generation, structural properties such as radius of gyration, shape tensor, asphericity, fractal dimension, monomer density distribution, solvent accessible surface area, molecular volume, and end group distribution functions, all evaluated from extensive molecular dynamics (MD) at 300 K. We find that the radius of gyration scales as R, N 113 over the entire range of generations, suggesting rather uniform space filling for all generations. Contrary to common expectation, we find that the outer subgenerations penetrate substantially into the interior of the dendrimer, even for G11. Consequently, the terminal amine groups are distributed throughout the interior, not just on the periphery of the dendrimer. However for G6 through G11 there is a large region of uniform density, supporting the uniform scattering model often used in interpreting the SANS (small-angle neutron scattering) and SAXS (small-angle X-ray scattering) data, which lead to sizes in excellent agreement with the calculations. The calculated single particle form factor approaches that of a sphere as the generation number increases. For the larger generations, we found that the use of continuous configuration biased Monte Carlo (CCBB MC) was essential to construct initial configurations that lead to lower final strain energies.