Structure of Polydopamine: A Never-Ending Story?
Structure of Polydopamine: A Never-Ending Story?
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DOI：
10.1021/la4020288
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发表时间：
2013-08-20
期刊：
影响因子：
3.9
通讯作者：
Beck, Sebastian
中科院分区：
文献类型：
--
作者：
Liebscher, Juergen;Mrowczynski, Radoslaw;Beck, Sebastian
由多巴胺氧化形成的聚多巴胺（PDA）是一种重要的聚合物，特别是用于涂覆各种表面。它由二羟基吲哚、吲哚二酮和多巴胺单元组成，这些单元被认为是共价连接的。虽然PDA已经以多种方式应用，但其结构仍在讨论中。在作为衍生自L-DOPA的天然存在的深色聚合物颜料的黑色素/真黑色素中已经观察到相似性。最近，提出了PDA的替代结构，其中二羟基吲哚啉、吲哚啉二酮和最终多巴胺单元彼此不共价连接，而是通过氧原子之间的氢键或π堆叠保持在一起。在这项研究中，我们表明，考虑到通过不同分析方法获得的明确结果，这种结构建议不太可能发生，其中包括C-13 CPPI MAS NMR（交叉极化极化反转魔角自旋NMR），H-1 MAS NMR（魔角旋转NMR），和ES-HRMS（电喷雾电离高分辨率质谱），除了XPS（X射线光电子能谱）和FTIR光谱。结果得到一个验证的结构分配PDA，其中二羟基吲哚和吲哚二酮单元具有不同程度的（不）饱和度共价连接的C-C键之间的苯环。此外，在PDA中的开链（多巴胺）单体单元的证据。先进的DFT计算意味着安排的几个PDA链，最好是通过醌-氢醌型相互作用，在一个平行或反平行的方式。从所有这些结果中，一些假设发表之前可以实验支持或被发现是矛盾的，从而导致更好地了解PDA的结构。
Polydopamine (PDA) formed by the oxidation of dopamine is an important polymer, in particular, for coating various surfaces. It is composed of dihydroxyindole, indoledione, and dopamine units, which are assumed to be covalently linked. Although PDA has been applied in a manifold way, its structure is still under discussion. Similarities have been observed in melanins/eumelanins as naturally occurring, deeply colored polymer pigments derived from L-DOPA. Recently, an alternative structure was proposed for PDA wherein dihydroxyindoline, indolinedione, and eventually dopamine units are not covalently linked to each other but are held together by hydrogen bonding between oxygen atoms or pi stacking. In this study, we show that this structural proposal is very unlikely to occur taking into account unambiguous results obtained by different analytical methods, among them C-13 CPPI MAS NMR (cross-polarization polarization-inversion magic angle spinning NMR), H-1 MAS NMR (magic angle spinning NMR), and ES-HRMS (electrospray ionization high-resolution mass spectrometry) for the first time in addition to XPS (X-ray photoelectron spectroscopy) and FTIR spectroscopy. The results give rise to a verified structural assignment of PDA wherein dihydroxyindole and indoledione units with different degrees of (un)saturation are covalently linked by C-C bonds between their benzene rings. Furthermore, proof of open-chain (dopamine) monomer units in PDA is provided. Advanced DFT calculations imply the arrangements of several PDA chains preferably by quinone-hydroquinone-type interactions in a parallel or antiparallel manner. From all of these results, a number of hypotheses published before could be experimentally supported or were found to be contradictory, thus leading to a better understanding of the PDA structure.