*2.1. Materials*

Solid standards of curcumin, demethoxycurcumin (both >98%, TCI Chemicals) and bis(demethoxy)curcumin (>99%, ChemFaces China) were used as standards for HPLC and X-ray powder diffraction (XRPD) analysis. The solid standard of curcumin was also used to determine the solubility and nucleation behaviors. During the study, four crude solid mixtures of CURDs were purchased from Sigma Aldrich and Acros. The content of CUR, DMC and BDMC in the solids, determined by means of HPLC, is summarized in Table 2.

**Table 2.** Comparison of the crude solids purchased from Sigma Aldrich (crude solids No. 1–3) and Acros (crude solid no. 4), each representing a ternary mixture of the three CURDs.


The highest CUR content of 80.7% was found in the crude solid obtained from Acros. The CUR content in the crude solids from Sigma Aldrich varies between 67.2% and 75.0% depending on the purchased charge, but is most similar to that of plant extract [28]. Accordingly, the solids from Sigma Aldrich were used as crude mixture for crystallization experiments. It should be emphasized that the analyzed significant differences of the CUR content in the three solid charges made the implementation of the designed crystallization process more challenging.

Acetone, acetonitrile, ethanol, methanol and 2-propanol (>99.8%, HiPerSolv CHROMANORM, VWR Chemicals, Germany) were used for solubility studies and for the crystallization experiments.
