A Comparative Study on Chiral and Racemic 12-Hydroxyoctadecanoic Acids in the Solutions and Aggregation States: Does the Racemic Form Really Form a Gel?

作者：Sakurai Takara; Masuda Yuichi; Sato Hisako; Yamagishi Akihiko; Kawaji Hitoshi; Atake Tooru; Hori Kayako^*

来源：Bulletin of the Chemical Society of Japan, 2010, 83(2): 145-150.

DOI：10.1246/bcsj.20090242

Chiral and racemic forms of the title compound (12HOAs) were reinvestigated. Gels formed separately from D- and L-12HOAs became a solution containing crystallites on maintaining contact, confirming that DL-12HOA forms no gel, contrary to several reports published over more than ten years, which stated that DL-12HOA formed a gel (for example, P. Terech et al., Langmuir 1994, 10,3406). The powder X-ray diffraction pattern of D-12HOA was different from that of DL-12HOA and the simulated patterns of two crystal structures of DL-12HOA. C-13 NMR spectroscopy for solutions of C6D6 showed significant difference in the concentration dependence of the low-field shifts at the carboxyl C due to hydrogen-bond formation. Analysis based on multiple equilibria among monomer, dimer, and tetramer was successfully applied to the behavior of D-12HOA, but not to that of DL-12HOA. For DL-12HOA, a modified model including hexamer was applied. It is concluded that association of dimers to tetramers and higher aggregates is more favorable in the DL-12HOA solution than in the D-12HOA solution and that D- and L-12HOA molecules recognize each other even in a dilute solution (lower than 2 mmol L-1) of DL-12HOA. Different NMR spectra were also observed in the solid state.

• 出版日期2010-2-15