ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Science and Technology Facilities Council, Didcot, OX11 0QX, UK.
Soft Matter. 2021 Sep 14;17(34):7940-7952. doi: 10.1039/d1sm00777g. Epub 2021 Aug 11.
The importance of electrically functional biomaterials is increasing as researchers explore ways to utilise them in novel sensing capacities. It has been recognised that for many of these materials the state of hydration is a key parameter that can heavily affect the conductivity, particularly those that rely upon ionic or proton transport as a key mechanism. However, thus far little attention has been paid to the nature of the water morphology in the hydrated state and the concomitant ionic conductivity. Presented here is an inelastic neutron scattering (INS) experiment on hydrated eumelanin, a model bioelectronic material, in order to investigate its 'water morphology'. We develop a rigorous new methodology for performing hydration dependent INS experiments. We also model the eumelanin dry spectra with a minimalist approach whereas for higher hydration levels we are able to obtain difference spectra to extract out the water scattering signal. A key result is that the physi-sorbed water structure within eumelanin is dominated by interfacial water with the number of water layers between 3-5, and no bulk water. We also detect for the first time, the potential signatures for proton cations, most likely the Zundel ion, within a biopolymer/water system. These new signatures may be general for soft proton ionomer systems, if the systems are comprised of only interfacial water within their structure. The nature of the water morphology opens up new questions about the potential ionic charge transport mechanisms within hydrated bioelectronics materials.
随着研究人员探索利用电功能生物材料在新型传感能力中的应用方法，电功能生物材料的重要性日益增加。人们已经认识到，对于许多这类材料而言，水合状态是一个关键参数，它会极大地影响导电性，特别是那些依赖离子或质子传输作为关键机制的材料。然而，到目前为止，人们对水合状态下水的形态以及伴随的离子电导率的性质关注甚少。本文介绍了一项针对水合真黑素（一种模型生物电子材料）的非弹性中子散射（INS）实验，以研究其“水形态”。我们开发了一种严格的新方法，用于进行依赖水合作用的 INS 实验。我们还采用极简主义方法对真黑素的干燥光谱进行建模，而对于更高的水合水平，我们能够获得差分光谱以提取出水散射信号。一个关键的结果是，真黑素内物理吸附水的结构主要由界面水主导，水层数在 3-5 层之间，没有体相水。我们还首次在生物聚合物/水体系中检测到质子阳离子（很可能是 Zundel 离子）的潜在特征。如果系统的结构仅由界面水组成，那么这些新特征可能适用于软质子离聚物系统。水形态的性质为水合生物电子材料中的潜在离子电荷输运机制提出了新的问题。
