Dipartimento di Chimica "Giacomo Ciamician", University of Bologna, Via Selmi 2, 40126Bologna, Italy.
J Phys Chem Lett. 2022 Oct 27;13(42):9829-9833. doi: 10.1021/acs.jpclett.2c02239. Epub 2022 Oct 17.
The role of noncovalent supramolecular self-assembly in the formation of melanin-like NP, as well as the nature of the electronic transition at the basis of their unique optical properties, is strongly debated. Here we demonstrate that, during the first stage of formation of synthetic melanin, polydopamine (PDA), a small fraction of the molecular precursor dopamine (DA) is oxidized to quinone (Q) and a simple supramolecular charge-transfer (CT) adduct is formed thanks to the electron donor and electron acceptor properties of DA and Q, respectively. This adduct, also detectable by HPLC-MS, presents the broad absorption band in the red-NIR region typical of melanin-like materials. Importantly, its disaggregation upon dilution can be easily detected since it leads to the disappearance of the CT band, indicating the reversibility of the process. Moreover, the stability constant of the CT adduct could be obtained using a simple association model.
非共价超分子自组装在黑色素样纳米颗粒形成中的作用，以及它们独特光学性质的电子跃迁本质，存在很大争议。在这里，我们证明了在合成黑色素形成的第一阶段，聚多巴胺（PDA），一小部分分子前体多巴胺（DA）被氧化为醌（Q），并且由于 DA 和 Q 的电子给体和电子受体性质，形成了简单的超分子电荷转移（CT）加合物。该加合物也可以通过 HPLC-MS 检测到，具有黑色素样材料的典型的宽吸收带在红-近红外区域。重要的是，其在稀释时的解聚很容易被检测到，因为它导致 CT 带的消失，表明该过程是可逆的。此外，通过简单的缔合模型可以获得 CT 加合物的稳定常数。
