Solid Phases in the System L-Valine L-Isoleucine

Two model compounds-valine C5H11NO2- (L-Val) and isoleucine C6H13NO2 (L-Ile)-were chosen to study isomorphism of the compounds formed by enantiomeric molecules having similar Shapes, but differing in the number of chiral centers. The X-ray powder diffraction method was applied to investigate samples with various ratios of valine and isoleucine crystallized from aqueous solutions by cooling and isothermal methods. Limited solid state miscibility between valine and isoleucine was established. A non-equimolar discrete compound with the molecular ratio Val:Ile = 2:1 (V2I) has been discovered, and its crystal structure was determined. Accordingly, the corresponding regions of solid solutions and two-phase areas in-between were distinguished. Solubility data in water support the phase behavior in the system.