Adaptable Porous Materials

点击翻译按钮获取中文摘要

Porous materials find widespread application in storage, separation and catalytic technologies. The sorption of a guest molecule by a rigid porous material such as a zeolite or active carbon is controlled by the fixed size and shape of the pores.Nature catalyses chemical processes and manipulates molecules using proteins. Proteins are characterised by an adaptable response to their environment, produced by conformational selection of an appropriate functional structure (e.g. for enzyme catalysis, or pore opening of the mechanosensitive channel of small conductance in an ion channel) from a large ensemble of energetically low-lying and kinetically accessible states. This is enabled by the manifold torsions available to polypeptide chains, which allow folding into the required structures.The project team have recently (Rabone et al Science 2010) used a simple dipeptide linker to assemble a crystalline porous framework through metal-binding. The resulting material combines pre-formed pores with the degrees of freedom from a peptide linker required for conformational selection. This peptide-based open framework displays adaptable porosity that evolves continuously from an open to a partially disordered closed structure in response to the guest content. The functional porous behavior is unconventional, displaying cooperative feedback characteristic of cooperative interactions as the pore topography changes in response to the number of guests occupying the pore volume of the host. The peptide-based material displays adaptable porosity. It undergoes dynamical structural changes on guest loading because there are many accessible sorption states with low energy barriers between them. This energy landscape arises because of the low energies required for torsional changes to the structure of the peptide linker.This opens up the possibility of designed adaptable porous materials which respond to guests in a manner analogous to that of a biomolecule undergoing conformational selection, produced by the modular assembly of multiple amino acid residues around several metal centres to access large and functionally diverse unit cells. This vision cannot be presently realized due to the large numbers of potential chemical constituents of such materials and the absence of computational tools to understand and predict how they would respond to guests. Such materials would though be unprecedented and offer new and potentially useful sorption and catalysis functionality.The proposed research aims to develop the tools to allow the isolation of such materials by focussing on adaptable porous materials derived from chemically simple di- and tripeptide linkers containing two and three amino acid residues respectively. We will identify the characteristics of both individual peptide linkers and metal-based units which give adaptable porous behaviour. This will allow the development of second-generation systems in which multiple peptide and metal units are used, making the key advance of demonstrating modular amino acid residue assembly in a functional porous solid. Rigid linkers will be introduced together with the peptides to produce structures where rigid sub-units are repositioned by the flexible peptide-based units, in a manner analogous to the repositioning of rigid helix and sheet units in protein folding.Given the diversity of possible peptide components, descriptor-based computational methods including machine-learning will be developed as a complementary approach to the selection of synthetic targets in the second- and third-generation families.The response of adaptable porous materials to guests does not follow classical models, and will be evaluated from experimental sorption, dynamics and structural data coupled with computational models appropriate to the dynamical restructuring of the adaptable porous host around a guest, to move beyond the current static view of host-guest interactions in synthetic porous materials.