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

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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.