Exploring the MOF-peptide interface: from phage display to materials synthesis, thin films and composites

具有复杂结构和明确性质的材料的合成是具有目标性质的扩展结构的定向组装的核心挑战，因为它们对经济增长和应对关键的社会挑战具有重要作用。在自然生物矿化过程中，多肽的自组装和识别特性被用来沉积具有精细结构和高度专业功能的无机材料(例如牙齿、骨骼、盔甲)，这些原理可以被合成化学家、纳米技术专家和表面科学家用来控制材料的结构和性能。由于其高比表面积，由金属离子和有机连接物组装的微孔金属有机骨架(MOF)具有明显的应用前景(如能源、可持续发展和医疗保健)，但为了促进其实际应用，往往需要一定程度的加工。这是MOF化学的一个迅速发展的领域，尽管已经取得了重大进展，但在制备薄膜和MOF基复合材料方面仍然存在挑战。如果能够很容易地识别出能够识别这些重要骨架材料的多肽序列，那么就可以更好地控制MOF的结构、性质和沉积。在这项工作中，我们将使用称为噬菌体的病毒组合文库来鉴定这些多肽。每个噬菌体的表面都显示一个独特的多肽，文库包含数百万种不同的病毒，因此具有潜在的结合序列。这个过程被称为噬菌体展示。通过在几个循环中将MOF晶体表面暴露于噬菌体，可以确定最强的结合序列作为框架组成、连接性和颗粒大小/形状的函数。一旦鉴定，这些多肽可以被合成并用于生物矿物启发的MOF合成。将研究已鉴定的多肽指导MOF生长的能力，从而允许控制MOF晶体的物理方面，如大小和形状，并有可能进一步影响骨架本身的网络结构和孔隙率。这些都是气体储存、催化和药物输送的重要性质。了解MOF与多肽的相互作用将有利于后者，我们对结合界面的研究将提供有价值的数据。生物矿化过程的特点是有机分子，包括多肽，在温和的条件下沉积无机材料的能力。一些MOF，如基于钛的MOF的制备仍然具有挑战性，但由于其光活性以及在光催化、光捕获和能源产生方面的明确应用，是非常理想的合成目标。为了克服其中一些合成障碍，我们将使用专门识别矿物二氧化钛的多肽来发现可持续应用的新型钛基MOF光催化剂。来自噬菌体展示的多肽也将能够根据组成、功能和晶面专门识别框架。这种识别能力将被用于增强MOF与其他功能成分的接口，如金属纳米颗粒和生物分子，以产生优化的催化和吸附的新复合材料。通过将不同的MOF表面图案化，将不同的MOF局部化到预定的位置，将允许制备多功能MOF薄膜，这是实现基于MOF的电子、光学、传感和能源应用的重要一步。概述的项目必然具有强烈的跨学科性质，涵盖组合生物学、材料科学、表面科学和纳米技术，并得到计算化学的进一步支持，以促进MOF的科学和技术。

The synthesis of materials with complex structures and well-defined properties is a central focus of the 'Directed assembly of extended structures with targeted properties' grand challenge, given their importance to economic growth and role in addressing key societal challenges. In natural biomineralisation processes the self-assembly and recognition properties of peptides are exploited to deposit inorganic materials with exquisite structures and highly specialist functions (e.g. teeth, bones, armour), and these principles can be used by synthetic chemists, nanotechnologists and surface scientists for control over materials structure and properties.Due to their high surface areas, tuneable compositions and functionality microporous metal-organic frameworks (MOFs) assembled from metal ions and organic linkers have demonstrable applications across numerous sectors (e.g. energy, sustainability and healthcare), but a degree of processing is often required in order to facilitate their practical use. This is a rapidly growing area of MOF chemistry and while significant progress has been made, challenges in the preparation of thin films and MOF-based composites still remain. If peptide sequences that can specifically recognise these important framework materials could be readily identified, then greater control over MOF structure, properties and deposition could be afforded.In this work we will use combinatorial libraries of viruses called bacteriophages to identify such peptides. Each phage displays a unique peptide on its surface, and the library contains millions of different viruses and hence potential binding sequences. This process is known as phage display. By exposure of MOF crystal surfaces to the phages over several cycles the strongest binding sequences can be determined as a function of framework composition, connectivity and particle size/shape. Once identified, the peptides can be synthesised and exploited for biomineral-inspired MOF synthesis.The ability of the identified peptides to direct MOF growth will be investigated permitting control over physical aspects of the MOF crystals such as size and shape, with potential to further influence the network structure and porosity of the framework itself. These are important properties for gas storage, catalysis and drug delivery. An understanding of MOF-peptide interactions will be beneficial to the latter, and our studies of the binding interface will provide valuable data. Biomineralisation processes are characterised by the ability of organic molecules, including peptides, to deposit inorganic materials under mild conditions. Some MOFs such as those based on titanium remain challenging to make, but are a highly desirable synthetic target for their photoactive properties and clear applications in photocatalysis, light harvesting and energy generation. To overcome some of these synthetic barriers we will use peptides that specifically recognise the mineral titania as a strategy to discover new titanium-based MOF photocatalysts for sustainable applications.The peptides derived from phage display will also be able to specifically recognise frameworks based on composition, functionality and crystal face. This recognition capability will be exploited for enhanced MOF interfacing with other functional components such as metal nanoparticles and biomolecules to yield new composites optimised for catalysis and adsorption. By patterning surfaces with multiple peptides, the ability to localise different MOFs into pre-defined positions will allow the preparation of multifunctional MOF thin films, a major step toward realising MOF-based devices for electronic, optical, sensing and energy applications.The project outlined is necessarily and strongly interdisciplinary in nature, spanning combinatorial biology, materials science, surface science and nanotechnology, further supported by computational chemistry, to advance the science and technology of MOFs.