Structural Persistence Masks Commit-Point Chemical Transformation in Copper-Imidazolate Nanosheet Metal-Organic...

Metal-organic frameworks (MOFs) are often assessed for stability using end-point structural metrics, yet their exposure-relevant chemical identity at the metal center may evolve on much shorter time scales in realistic aqueous environments. Here we examine nanoscale copper-imidazolate (CuIm) MOFs transformation across three benchmark matrices representing an abiotic-to-biorelevant gradient: a freshwater-like groundwater matrix (borehole water), a marine-like high-salinity matrix (artificial seawater), and a ligand-rich, protein-free cell-culture medium (serum-free DMEM) used here as a chemically complex challenge matrix. Using ex situ time-resolved separation of particle-associated and dissolved/complexed fractions coupled with copper-centered speciation analysis, we resolve a distinct kinetic hierarchy. CuIm remains largely conserved in borehole water, exhibits gradual reorganization in artificial seawater, and undergoes rapid transformation in serum-free DMEM, with the particle-associated fraction converging to an apparent end-state spectrum by ∼4 h. Medium-dependent copper mobilization to the dissolved/complexed pool accompanies these speciation trajectories. End-point characterization further indicates that framework-like structural signatures can persist while surface chemistry is substantially altered, demonstrating a decoupling between long-range order and node/surface identity. Collectively, these findings show that CuIm follows matrix-selected transformation trajectories with pronounced early-time trajectory shifts and that stability assessments must be grounded in time-resolved chemical identity rather than end-point crystallinity alone.