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Development of New Chiral Adsorbents for Enantioselective Separations

Final Report Summary - CHIRAL-MOF (Development of New Chiral Adsorbents for Enantioselective Separations)

Chirality is ubiquitous in biology, and production of chiral compounds is essential to the pharmaceutical, food, agricultural, and biotechnology industries. Particularly for pharmaceuticals, there is now great emphasis on the development of new techniques for asymmetric synthesis and enantiomeric separations, as both enantiomers (“hands”) of a drug can have different pharmacologic and toxicologic impacts. One of the most exciting developments in the field of nanoporous materials in recent years has been the explosion of new open-framework materials based on supramolecular coordination chemistry. Under solvothermal conditions, inorganic vertices can be interconnected by organic linker molecules to form extended frameworks known as metal-organic frameworks (MOFs) or porous coordination polymers. The building-block approach allows MOFs to be tailored to achieve particular properties, leading to exciting possibilities for gas storage, catalysis, sensing, separations and other applications. One obvious target for MOFs is to introduce chirality. From this perspective the overall objective of this multidisciplinary project is to use molecular modelling to predict enantioselective separation performance of MOFs and the in silico design of new MOFs for chiral separation.

The specific objectives were to
• Develop and test the necessary tools for molecular simulation of adsorption of chiral molecules in MOFs
• Use molecular modelling to guide the synthesis of new MOFs for targeted separation of some important racemic mixtures
• Collaborate with synthetic chemists to demonstrate experimentally that MOFs can perform enantioselective separations and test the results from simulations against experiments
• Gain a better understanding of chiral recognition and the factors that affect selectivity in chiral MOFs.

First we focussed on developing the necessary tools to simulate the adsorption of chiral molecules in MOFs and to design new MOFs computationally. We first tested our tools for the adsorption of small molecules such as CO2, SO2, NO, NO2, CH4 and N2 in MOFs successfully and this resulted in publications. However, in order to efficiently sample the chiral molecules which are complex and sometimes difficult to represent by classical force fields, more advanced methods were required. For this purpose we integrated sophisticated methods to our in-house written simulation code, such as the Continuous Fraction Monte Carlo (CFMC) approach. CFMC was originally developed for simulating very dense systems such as ionic liquids by Ed Maginn and his group at Notre Dame University. The adsorptive separation of chiral molecules mainly takes place in the liquid phase so CFMC was expected to aid in the sampling of chiral molecules which are confined in the pores of MOFs. This work was begun but not completed before Dr Yazaydin departed for UCL and the project was therefore terminated early.

One other significant achievement was the in silico design of new MOFs. Although not for a chiral MOF, we designed and guided experimental chemists in the synthesis of new MOFs which led to a publication. This approach included building the crystal structure of two hypothetical MOFs and predicting their adsorptive properties prior to their actual synthesis. Once synthesized, the experimental and predicted structural and adsorptive properties matched nicely.

The researcher/fellow, Dr Yazaydin, accepted a position at University College London (UCL), so the project terminated earlier than expected. Due to this some of the objectives were not achieved. On the other hand, the fellow completed his transition to Europe form US, and secured a permanent position first at the University of Surrey and then a UCL, one of the world’s leading research universities.