Evaluation of the Effect of Citronellol Group on Functionalized Mesogenic Materials by Capillary GC

In this paper, the effects of functionalization with terpenes on two new liquid-crystalline stationary phases for gas chromatography (GC) are described. Citronellol was used as the terminal group in the first material, and tetrahydrogeraniol was used with a second material. Inverse GC showed that the new materials have wide liquid-crystalline ranges (mesophases), 371–500 and 395–501 K, respectively. Moreover, they show good thermal stability up to 523 K and good potential as stationary phases for capillary GC. To clarify the effects of the liquid crystal structures and functional groups on retention and separation, the chromatographic behaviors of the two stationary phases were compared by eluting alkylbenzenes, polycyclic aromatic hydrocarbons, aromatic compounds, and terpenoids. The selectivities for a wide range of analytes achieved using the citronellol column were significantly better than those obtained using the tetrahydrogeraniol column. The columns showed different retention behaviors and fine resolutions for some of the main constituents of essential oils. Introduction of the double bond of citronellol greatly improved the polarization interactions involved in the shape recognition of the liquid-crystalline state for isomers. The new citronellol liquid-crystalline stationary phase, therefore, has a high affinity for natural compounds.

     

Synthesis,characterization and liquid chromatographic behaviours of a new chemically bonded liquid crystal

A new bonded liquid crystal stationary phase (2OC12) for high-performance liquid chromatography was studied. It resulted from coupling of LiChrospher Si 100 NH2 and a mesogenic carboxylic acid, 4-(4-(4-(3,4-didoceyloxystyrenyl)phenyl-diazenyl)phenyloxy-methylene) benzoic acid (ILC). ILC was characterized with proton NMR and differential scanning calorimetry, while 2OC12 was characterized by solid state 13C NMR and elemental analysis. 2OC12 surface area was determined by the BET method. The chromatographic behaviour of 2OC12 was investigated under both normal- and reversed-phase conditions. The plots of ln k against 1/T showed transition temperatures at 325 and 337 K. Polyaromatic hydrocarbons (PAHs) were separated using hexane, isooctane or hexane-chloroform. Above the transition temperatures, the bonded material exhibited a liquid crystal-like behaviour: (i) the plate number N was always highest possible, and (ii) the more retained the solute the more elongated it was (anthracene is eluted after phenanthrene, chrysene before tetracene, pentacene after dibenzo-a,h-anthracene). Using acetonitrile/water (60/40), reversed-phase data of aromatic hydrocarbons are similar (highest values of N, better resolution below than during the transitions).     

Three Nematogen Azobenzene-Based Stationary Phases for Capillary GC: Synthesis and Comparative Study

In this paper, three laterally substituted liquid crystals termed LCC₁, LCC₃ and LCC₄ were synthesized. Characterization of these substances was carried out by ¹H NMR and ¹³C NMR; they possess similar core and differ in their lateral substituents. Their thermal stability was conducted by thermogravimetric analysis and showed decomposition beginning at 212, 233 and 264 °C related to LCC₁, LCC₃ and LCC₄, respectively. Thermal properties were determined by differential scanning calorimetry, thermomicroscopy and inverse gas chromatography. The three novel compounds exhibited a nematic mesophase at a defined range of temperatures, which varied from 81 to 55 °C. Lengthening of the lateral substituent seemed to affect the nematic range by decreasing it. Fused-silica capillary columns (30 m × 0.32 mm) were employed for the analytical study. Numerous mixtures of components of various properties were injected. Particular attention was given to the selectivity towards the close-boiling isomers. These investigations indicated that lateral attached groups had considerable effect on the thermal and chromatographic properties of the liquid crystal compounds. These interesting results may guide in improving the development of new type of liquid crystals with desired properties for a widespread application.