Mid-frequency Raman difference spectra (MFRDS) analysis can be used to reveal the selective crystallization from solutions through determining the degree of similarity of the short-range orders between the assemblies of small organic molecules in solutions and their solid phases. Four solid phases of inosine (IR) (α-anhydrous IR (α-IR), β-anhydrous IR (β-IR), IR dihydrate (IRD), and amorphous IR (AmIR)) and two IR solutions (aqueous and 70 vol% DMSO aqueous solution) were prepared and characterized using MFRDS here. The MFRDS analysis results indicate that the selective formation of IRD and AmIR from IR aqueous solution and β-IR from IR 70 vol% DMSO solution are originated from the high similarity of their short-range structures. Moreover, we propose that the formation of α-IR from IR aqueous solution benefits from the appearance of AmIR as an intermediate phase. MFRDS is a robust tool to explain and predict the possible precipitation products from various solutions of small organic molecules.
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