2. Biotin: Biotin was purchased as a powder from Sigma. A saturated solution was prepared in water heated to 100 °C. The solution was allowed to slowly return to ambient temperature, during which colorless needle-shaped crystals formed. The crystal suspension was diluted tenfold in ethanol and saved for subsequent TEM sample preparation. Grids were prepared by pipetting 2 μL directly from this suspension, allowing the sample to settle on the grid for approximately 30 seconds, and then wicking off excess solvent with filter paper, leaving sub-micron thin needle-shaped crystals on the grid for microED analysis. The anticipated biotin crystal polymorph was in space group P2 1 2 1 2 1 , CCDC ID: .