Sorption and reactivity in flexible amino acid-based nanoporous materials

Zeolites and carbons are rigid sorbents which form the basis of large industries. Metal-organic frameworks have properties complementary to these classical systems. The proposal team have demonstrated the new science that can arise from these properties, in particular through the flexible response of these systems to guests. This proposal exploits two recent advances from our group (the isolation of nanoporous materials based on amino acids and the demonstration that flexible open-framework materials can act as containers for the direct observation of chemical reactions by diffraction) to develop and understand functionalised porous materials for selective sorption and reactivity enhanced or permitted by flexibility.The two new families of materials create linked scientific opportunities. The porous amino acid-based materials have smaller pores than previous chiral open-framework materials but the high density of functional groups lining the pores results in superior enantioselective sorption for guests which have the correct disposition of sites for interaction - 1,3-diols are enantioselectively sorbed whereas 1,2-diols show little resolution. The reactive frameworks (reported in Science 2007) consist of distinct modules with structural and reactive roles, and pre-position two guest molecules involved in an intrapore chemical reaction at distinct sites, suggesting the development of such systems for the control of reactivity and catalysis within the pores.The project will develop these materials towards the long-term target of synthetic materials with properties resembling those of enzymes, by expanding the chemistry and developing an integrated combination of structural, dynamics, and computational approaches to identify the features controlling the behaviour of the new systems. Flexibility-enhanced (host distortion by the guest) and flexibility-permitted (guest not admitted by the rigid host) sorption will be developed. The three strands required to achieve these goals are- a synthesis programme to generate larger pores with enhanced capability to control molecular positioning and generate unusual reactive sites for catalysis (e.g.amino acid protonation to afford Bronsted acid sites). This programme involves complex phase fields and in some cases necessarily small-scale initial synthesis-search reactions, and is thus enabled by the high-throughput facilities in the Centre for Materials Discovery;- a computational methodology which enables understanding of how host flexibility controls the response to guests, and permits the identification of guests which exploit the properties of the new materials. A screening methodology to permit the identification of chiral guests best suited to enantioselective sorption and of hosts which can locate multiple guests and respond flexibly to them will be developed. Detailed understanding of specific sorption processes (distinguished by high ee sorption or unique flexibility) will involve DFT and forcefield-based MD (showing how host dynamics influence guest uptake) to ensure the influence of both charge-based (e.g. hydrogen bonding) and dispersive interactions are identified;- an experimental programme measuring sorption, structure (diffraction, focussing on intra-pore reactivity), dynamics (NMR) and catalysis to both test computational prediction and evaluate the behaviour against an existing set of guests for enantioselective sorption, non-chiral separations and candidate catalytic reactions;- a partner group of industrial research labs to carry out specific evaluations of the materials for separations (ThermoFisher) focussed on specific targets of pharmaceutical interest (Pfizer) and assist development of the modelling approach (Unilever), focussing on flexible guest response by host materials.