Closer to the polydopamine structure: new insights from a combined 13C/1H/2H solid-state NMR study on deuterated samples†,Polymer Chemistry

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Closer to the polydopamine structure: new insights from a combined 13C/1H/2H solid-state NMR study on deuterated samples†
Polymer Chemistry ( IF 4.1 ) Pub Date : 2018-05-23 00:00:00 , DOI: 10.1039/c8py00633d
Monica Cîrcu _{1,

2,

3} , Claudiu Filip _{1,

2,

3}

Affiliation

Despite the large number of reported applications for polydopamine (PDA), a fundamental challenge still exists in this field: no complete structural elucidation of PDA is available to date. Herein, considering that this is due to the limitations of standard analytical techniques when applied to complex and heterogeneous systems, a solid-state NMR approach is introduced, which brings important novelties with respect to both sample engineering and the employed experimental techniques. ²H solid-echo, ¹H fast-MAS and ¹H double-quantum filtered ss-NMR experiments on PDA samples prepared under three different deuteration schemes are reported for the first time in the present work. The obtained results together with the results from ¹³C CP-MAS/CPPI ss-NMR experiments at 25 kHz MAS provide key structural and dynamic information, which can eliminate some of the uncertain structural characteristics present in the literature on PDA. It is found that at least half of the phenyl ring positions remain protonated in PDA and the majority of phenyl/indole rings are rigid, which is most probably due to π–π stacking. Considering the numerous models proposed to date, these results offer strong experimental evidence in favor of one particular monomer coupling and oligomer aggregation scheme in PDA. It is also evidenced from the ²H and ¹H ss-NMR data that water molecules undergo slow diffusion inside the sample as well as in and out the sample. All these findings combined with recent theoretical predictions represent important advances in understanding the complex structure of PDA.

中文翻译：

更接近聚多巴胺的结构：氘代样品的¹³ C / ¹ H / ² H固态NMR联合研究获得的新见解†

尽管已报告了聚多巴胺（PDA）的大量应用，但该领域仍存在一个基本挑战：迄今为止，尚无关于PDA的完整结构说明。在此，考虑到这是由于标准分析技术在应用于复杂和异构系统时的局限性，因此引入了固态NMR方法，这为样品工程和所采用的实验技术带来了重要的新颖性。在本工作中首次报道了在三种不同的氘化方案下制备的PDA样品的² H固体回波，¹ H快速MAS和¹ H双量子滤波ss-NMR实验。获得的结果以及来自¹³的结果25 kHz MAS的C CP-MAS / CPPI ss-NMR实验提供了关键的结构和动态信息，可以消除PDA文献中存在的某些不确定的结构特征。发现在PDA中至少有一半苯环位置保持质子化，而大多数苯/吲哚环是刚性的，这很可能是由于π-π堆积造成的。考虑到迄今为止提出的众多模型，这些结果提供了有力的实验证据，有利于PDA中一种特殊的单体偶联和低聚物聚集方案。² H和¹也证明了这一点H ss-NMR数据表明，水分子在样品内以及样品内外缓慢扩散。所有这些发现与最新的理论预测相结合，代表了在理解PDA复杂结构方面的重要进展。

更新日期：2018-05-23

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