Superior Plasticity and Tabletability of Theophylline Monohydrate.

A theophylline monohydrate (THm) powder, with particle size and shape substantially similar to a theophylline anhydrate powder, was prepared by vapor-mediated phase conversion. The elimination of possible contributions by particle size and shape to tableting properties made it possible to unambiguously identify the role of bonding area and bonding strength on powder tableting performance. It was also shown that accurate true density is essential for correct analysis and understanding of tableting behavior of THm. Experimental evidence revealed surprisingly high plasticity of THm. This is explained by its unique ladder-like structure, where rigid molecular dimers (rungs) weakly connect to more rigid water chains (rails). The low energy barrier for moving rigid dimers down the rigid water chains enables facile propagation of dislocations in THm crystals when subjected to an external stress.