An Insight into the Crystal Growth of 7-Aminodeacetoxycephalosporanic Acid from the Perspective of the Growth Unit

Crystal growth plays a key role in product attributes and downstream processing, whereas insight into the crystal growth mechanism, especially growth unit structures and behaviors, has been limited. In this work, the growth unit structures and behaviors of 7-aminodeacetoxycephalosporanic acid were explored by experiments and molecular simulations. First, its growth units were determined as the monomer MON I and dimers connected by N₅–H₇···O₄═C₂₀ (AGG I, 1.619 Å/166 °) and N₅–H₆···O₃–C₂₀ (AGG II, 1.779 Å/174 °), using spectroscopy and molecular simulation. On the (0 0 1), (1 −1 0), and (1 1 −1) faces, MON I was preferred to diffuse from the bulk solution and adsorb over others, while on the (0 1 1) face, AGG I was favored to diffuse and adsorb. Moreover, the differences in all the growth units that diffused and attached to the crystal faces led to a specific crystal morphology.