Detailed Analysis of Packing Efficiency Allows Rationalization of Solvate Formation Propensity for Selected Structurally Similar Organic Molecules

In structural study of seven bile acids it was identified that their propensity for solvate formation is directly related to the packing efficiency of the unsolvated phases: low packing index, voids, and unsatisfied hydrogen bonding lead to extensive solvate formation, whereas efficient packing leads to the opposite. This was determined to be caused by the presence of OH group attached to carbon C12. Solvate formation was determined to provide a noticeable improvement in the packing efficiency for compounds having ansolvates with inefficient packing

On the Formation and Desolvation Mechanism of Organic Molecule Solvates: A Structural Study of Methyl Cholate Solvates

Solvate formation and the desolvation mechanism of 25 obtained methyl cholate solvates were rationalized using crystal structure analysis and study of the phase transformations. The facile solvate formation was determined to be associated with the possibility for more efficient packing in structures containing solvent molecules. Most of the obtained solvates crystallized in one of the six isostructural solvate groups, with solvent selection based on the solvent capability to provide particular intermolecular interactions along with appropriate size and shape. In crystal structures several different methyl cholate conformers were observed, as apparently more efficient packing could be achieved by diversifying the molecule conformation and even adopting energetically quite unfavorable conformations. Nevertheless, the packing was generally controlled by the steroid ring system, particularly employing hydrogen bonding of the attached hydroxyl groups. Study of the desolvation mechanism showed that the primary desolvation product is determined by the structure similarity with the solvate, with thermodynamic stability of the desolvate having no directly identifiable effect. In the case of the absence of an acceptable structurally similar desolvate, desolvation produced an amorphous phase