Deciphering the Supramolecular Organization of Multiple Guests Inside a Microporous MOF to Understand their Release Profile

Metal-organic frameworks (MOFs) give the opportunity of confining guest molecules into their pores even by a post-synthetic protocol. PUM168 is a Zn-based MOF characterized by microporous cavities that allows the encapsulation of a significant number of guest molecules. The pores engineered with different binding sites show a remarkable guest affinity towards a series of natural essential oils components, such as eugenol, thymol and carvacrol, relevant for environmental applications. Exploiting single crystal X-ray diffraction, it was possible to step-wisely monitor the rather complex three-components guest exchange process involving dimethylformamide (DMF, the pristine solvent) and binary mixtures of the flavoring agents. A picture of the structural evolution of the DMF-to-guest replacement occurring inside the MOF crystal was reached by a detailed single-crystal-to-single-crystal monitoring. The relation of the supramolecular arrangement in the pores with selective guests release was then investigated as a function of time and temperature by static headspace GC-MS analysis.

Automated summary

Metal-organic frameworks (MOFs) offer the opportunity to confine guest molecules within their pores, with PUM168 being a Zn-based MOF capable of encapsulating a significant number of guest molecules, especially natural essential oil components. By utilizing single crystal X-ray diffraction, researchers were able to monitor the complex guest exchange process and study the structural evolution of DMF-to-guest replacement inside the MOF crystal. The correlation between supramolecular arrangement in the pores and selective guest release was investigated over time and temperature using static headspace GC-MS analysis.