(R)-10-Hydroxystearic Acid: Crystals vs. Organogel

Abstract

The chiral (R)-10-hydroxystearic acid ((R)-10-HSA) is a positional homologue of both (R)-12-HSA and (R)-9-HSA with the OH group in an intermediate position. While (R)-12-HSA is one of the best-known low-molecular-weight organogelators, (R)-9-HSA is not, but it forms crystals in several solvents. With the aim to gain information on the structural role of hydrogen-bonding interactions of the carbinol OH groups, we investigated the behavior of (R)-10-HSA in various solvents. This isomer displays an intermediate behavior between (R)-9 and (R)-12-HSA, producing a stable gel exclusively in paraffin oil, while it crystallizes in other organic solvents. Here, we report the X-ray structure of a single crystal of (R)-10-HSA as well as some structural information on its polymorphism, obtained through X-ray Powder Diffraction (XRPD) and Infrared Spectroscopy (IR). This case study provides new elements to elucidate the structural determinants of the microscopic architectures that lead to the formation of organogels of stearic acid derivatives.