Lehrstuhl für Theoretische Chemie/Computer Chemie Centrum Friedrich-Alexander Universität Erlangen-Nürnberg Nägelsbachstraße 25 , 91052 Erlangen , Germany.
Lehrstuhl für Physikalische Chemie 1 Friedrich-Alexander Universität Erlangen-Nürnberg Egerlandstraße 3 , 91058 Erlangen , Germany.
J Phys Chem A. 2019 Oct 31;123(43):9403-9412. doi: 10.1021/acs.jpca.9b08722. Epub 2019 Oct 18.
We present atomic scale models of differently sized eumelanin nanoaggregates from molecular dynamics simulations combined with a simulated annealing procedure. The analysis reveals the formation of secondary structures due to π-stacking on one hand, but on the other hand a broad distribution of stack geometries in terms of stack size, horizontal displacement angles, and relative torsion angles. The displacement angle distribution, which is a measure of the occurrence of zigzag and linear stacking motives, respectively, strongly depends on the aggregate size-and is hence controlled by the interplay of surface and bulk energy terms. Semiempirical spectra calculations of small stacks (up to five protomolecules) reveal a strong dependence on the precise stack structure and allow for a direct structure-property correlation. The observed spectral shifts result in an overall spectral broadening and, hence, further support the geometric disorder model, which complements the chemical disorder model in the interpretation of eumelanin's monotonically increasing broad-band absorption.
我们提出了不同大小的真黑素纳米聚集体的原子尺度模型，这些模型是通过分子动力学模拟与模拟退火程序相结合得到的。分析揭示了由于π堆积一方面形成二级结构，但另一方面在堆积大小、水平位移角度和相对扭转角度方面堆积几何形状的广泛分布。位移角度分布是衡量锯齿形和线性堆积动机出现的一种度量，它强烈依赖于聚集体的大小，因此受到表面和体能项相互作用的控制。对小聚集体（最多五个原分子）的半经验光谱计算表明，它们强烈依赖于精确的堆积结构，并允许进行直接的结构-性质相关。观察到的光谱位移导致整体光谱展宽，因此进一步支持了几何无序模型，该模型在解释真黑素单调递增的宽带吸收时补充了化学无序模型。
