Metal organic frameworks (MOFs) have been reported as drug delivery vehicles that control the release of the drug to specific sites based on the pH of the cellular environment. This targeted release is important in the treatment of cancerous cells, which have a lower pH than normal healthy cells. There are two approaches typically used to encapsulate drug molecules within the porous frameworks of a MOF: post-synthesis loading and co-synthesis. In the post-synthesis loading method, the MOF is completely synthesized and then introduced to a solution containing the target drug. Loading is diffusion driven and limited not only by the high concentration of the drug required in the solution, but by the small pore sizes of the MOF. In co-synthesis, the drug is introduced during the MOF synthesis, typically alongside the inorganic node or organic linker molecule. Co-synthesis allows for pore expansion as the framework forms around the drug, which is an advantage over post synthetic loading. A problem in the co-synthesis encapsulation process of drug materials inside the MOF is the percent loading is relatively low compared to the amount of drug used. The lower the percent loading of encapsulation, the greater the amount of waste will be left over in the solution, which is especially critical when dealing with high cost pharmaceuticals. We have systematically investigated different aspects of the co-synthesis procedure including using different concentrations of encapsulation materials (dyes to mimic drug molecules) and changing the drip rate of the solution addition. The dye chosen, Rhodamine B, has a similar structure and chemical properties (hydrophobicity, polarity) to drugs that can be administered utilizing the same MOFs. Finding the greatest percent loading can ensure that future encapsulations of drugs in MOFs can be done with minimal waste of material, drugs, and money.

Optimizing rhodamine B encapsulation in ZIF-8 metal organic frameworks (MOFs)

ACS Spring 2022

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