FIDDLE. Simultaneous Indexing and Structure Solution from Powder Diffraction Data using a Genetic Algorithm and Correlation Functions

A method for the determination of crystal structures from powder diffraction data is presented that circumvents the difficulties associated with separate indexing. For the simultaneous optimization of the parameters that describe a crystal structure a genetic algorithm is used together with a pattern matching technique based on auto and cross correlation functions.<br /

Effect of Solvent Composition on Solubility, Thermodynamics, Metastable Zone Width (MSZW) and Crystal Habit of L-Ascorbic Acid

This work investigates the effect of different solvent systems on solubility, thermodynamics, metastable zone width (MSZW), and crystal habit of ascorbic acid, in order to help optimize its crystallization process. The solubility curves and metastable zone (MSZ) limits were determined experimentally using the polythermal method in pure solvents: water and alcohols (methanol/ethanol/isopropanol), as well as water-alcohol binary solvent systems. The solubility decreases with increasing alcohol composition for all solvent systems. The solubility data were well correlated using the Jouyban–Acree model as a function of two variables: temperature and solvent composition. The dissolution enthalpy (ΔHdiss), dissolution entropy (ΔSdiss), and Gibbs free energy (ΔGdiss) were determined using Van’t Hoff and Jouyban–Acree models. The thermodynamic properties increase with increasing alcohol composition. The lowest and highest values of enthalpy were obtained for water (20.52 kJ mol −1) and isopropanol (35.33 kJ mol−1), respectively. Pure alcohols as solvents widen the metastable zone width, indicating high supersaturation required for the nucleation. Crystal images captured during cooling crystallization in water confirm the cubic crystal habit formation, whereas increasing alcohol composition in the solvent system promotes preferential growth along one crystallographic axis, leading to elongated prism-shaped crystals in methanol and ethanol and needle-shaped crystals in isopropanol