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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Molecular Dynamics Simulations of Porphyrin-Dendrimer Systems:Toward Modeling Electron Transfer in Solution
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Molecular Dynamics Simulations of Porphyrin-Dendrimer Systems:Toward Modeling Electron Transfer in Solution

机译：卟啉-登德里默体系的分子动力学模拟：溶液中电子转移的建模

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摘要

We have performed computational simulations of porphyrin-dendrimer systems-a cationic porphyrin electrostatically associated to a negatively charged dendrimei-using the method of classical molecular dynamics(MD)with an atomistic force field.Previous experimental studies have shown a strong quenching effect of the porphyrin fluorescence that was assigned to electron transfer(ET)from the dendrimer's tertiary amines(Paulo,P.M.R.;Costa,S.M.B.J.Phys.Chem.B 2005,109,13928).In the present contribution,we evaluate computationally the role of the porphyrin-dendrimer conformation in the development of a statistical distribution of ET rates through its dependence on the donor-acceptor distance.We started from simulations without explicit solvent to obtain trajectories of the donor-acceptor distance and the respective time-averaged distributions for two dendrimer sizes and diffferent initial configurations of the porphyrin-dendrimer pair.By introducing explicit solvent(water)in our simulations,we were able to estimate the reorganization energy of the medium for the systems with the dendrimer of smaller size.The values obtained are in the range 0.6-1.5 eV and show a linear dependence with the inverse of the donor-acceptor distance,which can be explained by a two-phase dielectric continuum model taking into account the medium heterogeneity provided by the dendrimer organic core.Dielectric relaxation accompanying ET was evaluated from the simulations with explicit solvent showing fast decay times of some tens of femtoseconds and slow decay times in the range of hundreds of femtoseconds to a few picoseconds.The variations of the slow relaxation times reflect the heterogeneity of the dendrimer donor sites which add to the complexity of ET kinetics as inferred from the experimental fluorescence decays.
机译：我们使用具有原子力场的经典分子动力学方法对卟啉-树枝状大分子体系（与负电荷的树枝状聚合物静电缔合的阳离子卟啉）进行了计算模拟。先前的实验研究表明，卟啉具有很强的猝灭作用从树枝状大分子的叔胺转移到电子转移（ET）的荧光（Paulo，PMR; Costa，SMBJPhys.Chem.B 2005,109,13928）。在目前的贡献中，我们通过计算评估了卟啉-树枝状大分子的作用通过依赖于供体-受体距离的ET率统计分布的发展过程中的构象。我们从没有显式溶剂的模拟开始，获得了两种树枝状分子大小和不同树突的供体-受体距离的轨迹以及各自的时间平均分布卟啉-树状聚合物对的初始构型。通过在模拟中引入显式溶剂（水），我们能够估计具有较小尺寸的树枝状大分子的系统的介质重组能。获得的值在0.6-1.5 eV范围内，并且显示出与供体-受体距离成反比的线性关系，这可以解释考虑到树枝状聚合物有机核提供的介质异质性，通过两相介质连续介质模型进行了模拟。在显性溶剂的模拟下，评估了ET伴随的介电弛豫，显示出快速的衰变时间为数十飞秒，而缓慢的衰变时间为10毫秒。从几百飞秒到几皮秒。慢弛豫时间的变化反映了树状聚合物供体位点的异质性，这增加了从实验荧光衰减推断出的ET动力学的复杂性。

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