Effect of Chirality on the Structural Behaviour of Hydrogen-Bonded n-Alkylammonium Pyroglutamates in the Crystalline and Smectic State

• Published in: Chemistry : a European journal 2003-11, Vol.9 (21), p.5250-5258
• Main Authors: Tsiourvas, Dimitris, Paleos, Constantinos M., Skoulios, Antoine
• Format: Article
• Language: English
• Subjects: amino acids; chirality; Crystallization; Crystallography, X-Ray; Dimerization; Drug Stability; Heating; Hydrogen Bonding; liquid crystals; Models, Molecular; Molecular Structure; Pyrrolidonecarboxylic Acid - analogs & derivatives; Pyrrolidonecarboxylic Acid - chemical synthesis; Pyrrolidonecarboxylic Acid - chemistry; Quaternary Ammonium Compounds - chemical synthesis; Quaternary Ammonium Compounds - chemistry; self-assembly; Stereoisomerism; Structure-Activity Relationship; supramolecular chemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200304985

A set of optically active and racemic n‐alkylammonium pyroglutamates from dodecyl to octadecyl were synthesized and characterised. Their thermotropic polymorphism was investigated by polarizing optical microscopy, differential scanning calorimetry and dilatometry. Their structure in the crystalline and smectic state was analysed by X‐ray diffraction. The hydrogen bonding of the molecules in the crystalline and smectic layers was examined by infrared spectroscopy. The chirality control over the supramolecular self‐assembly of the molecules along with the homochiral and heterochiral architecture of the self‐assembled dimers are briefly discussed. Thermally stable hydrogen‐bonded dimers exhibiting two different crystalline structures and smectic A phases with the same structural parameters are formed by optically active and racemic alkylammonium pyroglutamates (see picture). The racemic series of compounds consist of dl dimers in the crystalline phase while in the smectic phase the heterochiral dl dimers transform into a mixture of homochiral dd and ll dimers.