The role of charge compensation on the nucleation of α and γ polymorphs of glycine from aqueous solution

The formation of α and γ nucleation in the aqueous solution of glycine is discussed in the context of self-charge compensation among the molecular clusters. Self-charge compensation is the main process responsible for the creation of dimers needed for the initiation of α nucleation in the solution which is more probable at most environmental conditions, whereas, the creation of γ nucleation is due to the assembly of monomers which requires sufficient/more number of monomers in the solution and has less probability to occur at normal circumstances. In the present work, a new induced charge compensation mechanism was adopted by adding selected externally Induced Charge Compensator (ICC) species by which the dimer formation was completely arrested into the solution and this paved a way for the nucleation of γ. The effect of concentration of the added species on the induction time, nucleation, growth and morphology of the nucleated polymorphs was studied. Structural affirmation of the nucleated polymorphs was confirmed by X-ray diffraction and their functional groups by FTIR analysis. Results reveal that, the changeover of the charge compensation mechanism from the self-charge compensation to the induced one occurs only at a critical concentration of the charged species. This approach is fruitful in the control of either only α or only γ nucleation in the system.

► For the first time, nucleation control of α and γ polymorphs of glycine from aqueous solution is explained based on the charge compensation mechanism.
► As a novel approach, the mechanistic changeover from self-charge compensation to induced charge compensation is defined at the critical concentration of ICC.
► Selected ICC successfully distinguishes α and γ nucleation without entering into the crystal lattices.
► Unique unidirectional growth behavior of polar γ crystal and growth inhibition on different growth faces of both α and γ crystals by ICC are revealed.