超顺磁/稳定单畴磁铁矿颗粒的仿生矿化及岩石磁学研究

Viscous superparamagnetic (VSP) magnetite nanoparticle at the superparamagnetic (SP) to stable single domain(SSD) threshold is a key researching field of environmental magnetism. However, the rock magnetic properties of such magnetic particles are limited for understanding, because ideal magnetic nanoparticles are hardly acquired. This project is inspired by biomineralization of magnetotactic bacterium, which can synthesize magnetosomes in the cell from small superparamgnetic to big stable single domain magnetite nanoparticles. A key protein of MmsF regulating the size and shape of magnetosomes of Magnetospirillum magneticum AMB-1 will be genetically engineered and prokaryotically expressed in Escherichia coli. We will use MmsF protein as a biotemplate to synthesize ideal SP, VSP and SSD magnetite nanoparticles with high monodispersity, no crystal defect, controlled magnetotactic interactions, uniform shape and controlled sized distribution. Through strictly controlled the size distribution, the growth of magnetite crystal will stepwisely passing the SP/SSD threshold. To reveal the biomimetic mineralization mechanisms of MmsF and determine threshold diameter of SP/SSD magnetite nanoparticles, combined techniques of electron microscopy and magnetic mesurement will be used to study the crystal and magnetic properties of these non-interacting or interacting magnetite nanoparticles. Finally, we will experimentally mixture SP, VSP and SSD magnetite nanoparticles with different concentration, size distribution and magnetostatic interaction to mimick the environment and quantitatively determine the relationship of size distribution and concentration with each rock magnetic parameter, especially the frequency-dependent susceptibility. This project will enable better understanding of the rock magnetic properties of magnetite and further help to explain magnetic parameters measured from the environmental samples.

从超顺磁（SP）转变为稳定单畴（SSD）临界区间的粘滞超顺磁（VSP）磁铁矿颗粒是环境磁学的重要研究对象，但是由于难以获得理想样品，这些颗粒的岩石磁学实验研究极其薄弱。项目受到趋磁细菌磁小体合成经历从小到大，SP转变为SSD磁铁矿过程的启示，拟以趋磁螺菌AMB-1的矿化蛋白MmsF为研究对象，建立新型的仿生矿化技术，合成单分散、无晶格缺陷、磁相互作用可控、粒径均一、形状为立方八面体的理想SP、VSP和SSD磁铁矿颗粒，控制粒径逐渐跨越SP/SSD临界区间。综合运用电子显微学和岩石磁学方法对这些颗粒进行系统的晶体学和岩石磁学研究，揭示MmsF控制磁铁矿的晶体生长机制，确定SP/SSD磁铁矿的临界粒径。最后，通过不同含量、粒径和磁相互作用的SP、VSP和SSD磁铁矿颗粒的混合，定量各种岩石磁学参数（尤其是频率磁化率）与磁铁矿的粒径和含量的关系，为解释自然样品的环境磁学参数提供实验依据。

本项目通过生物矿化和生物地磁学科交叉，以嗜热菌铁蛋白、聚合物以及融合表达的MmsF蛋白，仿生矿化合成超顺磁磁铁矿纳米颗粒与趋磁细菌产生的单畴磁铁矿颗粒为研究对象，开展了系统的应用基础科学研究，取得多项创新性成果：1）发现嗜热菌铁蛋白相比人H亚基铁蛋白更加耐热，能耐受110 oC的高温，并且在90 oC能够合成粒径和形状均一的磁性铁蛋白，这种磁性铁蛋白是一种优良的磁性纳米颗粒，比传统磁性铁蛋白具有更高饱和磁化强度和磁热效应； 2）这种具有强磁热效应的磁性铁蛋白可以通过多巴胺与海绵实现高效结合，进一步通过疏水修饰可以制备具有电磁加热、光加热和快速吸油的多功能材料，能够实现高粘度稠油漏油污染的快速升温降粘和连续回收；3）发现磺化聚苯乙烯和丙二酸的共聚物（PSS-co-MA）能够自组装成类似于铁蛋白的笼型结构，仿生合成粒径可控的超顺磁磁铁矿纳米颗粒，这种聚合物磁性纳米颗粒可以耐受高温和高盐的储层条件，结合金属离子制备纳米乳液，并且在极低浓度下能够稳定大乳液；4）发现趋磁细菌的MmsF蛋白可以与耐热拟杆菌的胶囊蛋白融合形成约40纳米的笼型结构；5）系统研究趋磁细菌MSR-1的磁小体的岩石磁学性质和磁热效应，发现趋磁细菌磁小体链的磁热效应高于常规同粒径的磁铁矿纳米颗粒，其磁热效应的机制是由于磁滞效应。以磁性铁蛋白为代表的超顺磁纳米磁铁矿颗粒和以趋磁细菌磁小体为代表的单畴磁铁矿颗粒的混合为环境自然样品提供了很好的模拟材料。