Polar Dissolution and Regrowth of (±)-Modafinil Twins Grown in Gels

Abstract

Although (±)-modafinil form I crystallizes in the centrosymmetric space group P21/a, a significant proportion of twins crystallized in polymerized TMOS gel exhibit a polar dissolution. In a slightly undersaturated solution, one body of the twin dissolves smoothly. leading to a progressive disappearance of every face; the second body dissolves heterogeneously, leading to lamellar fragments. This phenomenon could be explained by the insertion of (001) layers of form IIIa metastable noncentrosymmetric modification (SG Pna21)inside a single body of the twinned form I. Because the slice (001) is common to polymorphs I and III, the interlacing of the two forms is compatible with the formation of well-shaped crystals. Regrowth experiments on partially dissolved twins in slightly supersaturated solutions confirms the sustainability of the heterogeneous character for a single body only of the twins.

Dissolution Behavior of Lysozyme Crystals

“…Inside the protein crystals is buffer (the “free water”), and it has clearly a diffusion exchange with the solution in which the crystals are dispersed. In the literature, − the “falling apart” mechanism is only described in similar way in the case of a binary system at conditions when only one of the components will dissolve or will partially be molten. We do not face this situation here.…”

Limits of the Co-crystal Concept and Beyond

“…Some chiral racemic compounds crystallize in the 73 non-chiral and noncentrosymmetric space groups such as Pc, Pna2 1 (form III of rac_modafi-nil 18,19 ), Pca2 1 Fdd2 (form IV rac-modafinil 20 ), and so on. Very rare examples of racemic compounds crystallizing in one if the 65 chiral space groups have been spotted so far (obviously Z' is greater or equal to 2).…”