纳米CeO2形貌与表面Ce化学状态的鉴定及其模拟酶活性之研究

Recently, nanoceria has been found as enzyme mimetics of phosphatase, superoxide dismutase and catalase. Some studies have attributed the enzyme mimetic properties of nanoceria to the concentration of surface Ce3+, while some other studies have demonstrated the presence of surface Ce4+ is the key active site. However, its enzyme mimetic activities were also shown to closely associate with their morphology (or exposed facet) rather than surface [Ce3+]/[Ce4+] ratio. Nowadays, the role of surface Ce of nanoceria in enzyme mimetic reactions is still not fully understood. In our opinion, the blocking stone to deeper the understanding on the chemical state of surface atom and its host facet in above enzymatic reactions is the lack of proper surface characterization technique/method that can provide information on both qualitative and quantitative manner. In this proposal, we will firstly prepare CeO2 morphologies with various exposed facets. With the assistance of probe-assisted nuclear magnetic resonance (NMR), we can investigate surface micro-environments using the chemical shifts of a given probe molecule and thus differentiate the chemical state of Ce hosted by various CeO2 facets. The quantitative nature of NMR would then allow us to re-investigate the role of surface Ce on nanoceria in enzymatic reactions. We believe the implementation of this proposal will not only elucidate the key active site and reaction mechanism of CeO2 as enzyme mimetics, it will also be beneficial for future design of CeO2-based materials with high catalytic activity.

纳米CeO2被报道可作为磷酸酶、超氧化物歧化酶和过氧化氢酶模拟物，但其模拟酶活性位点存在较大争议。一部分研究认为表面活性位点为Ce3+，另一部分则认为是Ce4+。此外，也有报道在表面[Ce3+]/[Ce4+]比相同的情况下，CeO2酶促活性与其形貌高度相关。这些争议可能主要来自于传统表征手段无法精确地定性/定量表面Ce原子的化学状态/浓度，进而无法判断表面Ce在反应中的角色。针对该问题，本项目拟采取合成不同形貌纳米CeO2的手段，实现不同晶面的暴露以及表面Ce化学状态的调控。通过探针-核磁共振技术，基于探针所产生的化学位移测定CeO2各晶面上Ce的化学状态与浓度。最后，研究纳米CeO2的酶促活性并与其形貌、表面Ce化学状态及浓度建立依赖关系，鉴定出关键活性位点。本项目的有效实施不仅有望解决活性位点的争端，还可能揭示纳米CeO2酶模拟活性的真实反应机理，为构筑高活性CeO2材料提供指导。

本项目首先合成不同形貌的纳米CeO2来实现对不同暴露晶面的调控。再借助探针-核磁共振技术，通过测量探针分子的化学位移区分催化剂表面的微环境，并研究和测定各CeO2晶面上Ce化学状态与浓度。最后，测定纳米CeO2的酶促活性并与其表面Ce化学状态及浓度建立构-效关系，揭示CeO2作为脱磷酸酶、过氧化氢酶和过氧化物酶的关键活性位点和控制因素。除CeO2外，课题组也拓展到TiO2、Fe3O4、HNb3O8等常见过渡金属材料于不同模拟酶反应构-效关系的研究。课题组接着通过一系列的实验揭露了这些过渡金属氧化物作为过氧化物(和过氧化氢)模拟酶的反应机理，我们发现表面金属阳离子与H2O2的氧化还原反应是决定过氧化物酶促活性的限速步骤。对于单原子纳米酶而言，由于活性中心被载体上高电负度的氮或是氧螯合而带正电，大大阻碍了H2O2的还原(及OH自由基的产生)。相比之下，我们发现在团簇纳米酶中金属金属键的生成大大提高了活性中心的电子密度因此促进了H2O2→OH自由基的转化。因此团簇纳米酶虽然没有单原子纳米酶的高位点利用率，在归一化活性位点数目之后仍能提供较高的活性。本项目对未来设计高活性过渡金属氧化物模拟酶特别是过氧化氢酶具有重要地指导性意义。

内容获取失败，请点击重试