How Specific Interactions between Acetaminophen and Its Additive 4-Methylacetanilide Affect Growth Morphology: Elucidation Using Etching Patterns

Abstract

The growth of acetaminophen single crystals in the presence of the structurally similar or “tailor-made” additive, 4-methylacetanilide, showed elongation along the c axis and reduction along the a axis when the additive's concentration was increased from 1 to 6 mM. This may indicate preferred binding between the host and additive molecules along the a axis, but along the c axis there is little effect on the growth. In addition, at higher concentrations of 4-methylacetanilide (3 and 6 mM), new faces, {4̄01}, appeared while the {2̄01} were absent. The alignment of host molecules on the growth front is likely to be a coordinated result of the adsorption of additive molecules and the adsorption-induced relaxation of the host molecule conformation. Earlier etching studies provide support for this argument. The additive was chosen as a “surrogate” for a solvent with similar molecular structural properties as part of the ongoing effort to investigate the effect of solvent on crystal morphology.