Computer-aided design of liquid crystal type macrocycles for sensors

Abstract

Macrocyclic compounds with liquid crystal properties show an interesting potential for sensor design as phase transitions can be seen on complexation with metal ions. In this work some novel macrocyclic compounds with side chains that could show liquid crystalline properties were investigated. Selectivity was investigated by solvent extraction of metal picrate salts. Chloroform was used as the solvent and the extraction method was validated with dibenzo-18-crown-6. Extraction values were calculated from analysis of the aqueous phase for the metals ions by ICP-AES, because high values were obtained with the spectrophotometric method due to the extraction of picric acid. No extraction was seen for the long chain liquid crystalline macrocycles and this was investigated further by molecular modelling. Minimized molecular models of the macrocycles showed that the side chains wrapped around the cavity (1.510 Å radius), suggesting that complexation might be sterically hindered. A short chain macrocycle was then modelled and in this case there appeared to be more favourable access to the cavity. Extraction experiments were then carried out with the short chain macrocycle for potassium, silver and sodium picrate resulting in statistically significant extraction values of 9, 5 and 3%, respectively. The selectivity in extraction could be related to the cavity size, with the best extraction being for the largest metal ion. Immobilization of the liquid crystal macrocycles in an elastomer is suggested as a way of overcoming the steric hindrance. Molecular modelling is shown to be a useful tool for designing novel compounds for sensor design.