Metal-organic frameworks have utility in adsorption and release of ethylene and 1-methylcyclopropene in fresh produce packaging

Metal organic frameworks (MOFs) are synthetic porous materials consisting of metal ions or ion clusters bound to organic molecules to create a crystalline structure with a very high internal surface area. MOF molecules have been found to have potential utility in the selective adsorptive binding and release of gaseous fuel and other chemicals. We explored the ability of selected MOFs to bind ethylene and the ethylene action inhibitor, 1-methylcyclopropene (1-MCP) with the intent of evaluating their usefulness in regulating ethylene responses for perishable produce. We screened several MOF compounds and selected two (Basolite C300 and Basolite A520) for in-depth characterization based on their superior capacity for binding ethylene. Basolite C300 is a copper-based MOF with a trimesic acid linker group and Basolite A520 is an aluminum-based MOF with a fumaric acid linker group. Binding efficacy was compared to zeolite Z13X, which was also found to bind ethylene. The copper-based Basolite C300 was more effective at binding and retaining ethylene than the other compounds tested. When ethylene-charged sorbents were moved to dry air, they released little ethylene. However, in the presence of free water, Basolite C300 desorbed a majority of its bound ethylene. Adsorption and desorption behavior differed for other alkenes. Basolite C300 had the highest affinity for 1-MCP, but did not release bound 1-MCP in the presence of humidified air. In contrast, the compound 1-butene, often used as a surrogate to quantify 1-MCP, was bound tightly by the MOF and quickly released in the presence of humidified air. We tested the potential for in-package release of bioactive compounds from a MOF. In a proof-of-concept experiment, we found that ethylene-loaded Basolite C300 released ethylene rapidly into packages of banana fruit and induced ripening; MOF without ethylene loading did not induce ripening. The data suggest that MOFs have the potential to sorb, store, and release gaseous compounds that impact plant physiology and may have some utility as a delivery system for volatile plant growth regulators.