Exploring Biliverdin’s\nMolecular Interactions\nwith Cu- and Fe-Based MOFs: A Unified In Vitro Study with Photoacoustic\nAnalysis

Metal–organic frameworks (MOFs) have shown promise\nin enhancing\nthe stability of biomolecules. Herein, biliverdin (BVD), a photoacoustic\n(PA) and fluorescent agent, was immobilized within the pores of NH<sub>2</sub>-MIL-101 (Fe) (FeMOFs) and on the surface of CuBTC crystallites\n(CuMOFs). MOFs were found to enhance the fluorescence emission and\nquench the PA intensity of biliverdin. Fluorescence and PA studies,\nin tandem with DFT simulations, demonstrated that the spectral interactions\nbetween MOFs and BVD resulted from interactions between biliverdin\nand the MOF pores and surfaces in addition to alterations in the HOMO–LUMO\nenergy gap. The MOF internal structure of the MOF played a role in\nBVD loading, with the FeMOFs enabling greater BVD encapsulation, while\nCuMOF interactions with BVD primarily took place on the MOF surface.\nThe role of these surface <i>vs</i> pore interactions in\nthe release of biliverdin was explored. This study demonstrates that\nthe effects of the MOF internal structure, surface interactions, and\nenergy interactions should be taken into consideration for biomolecule\nloading in MOFs.