Correlation between hydrophobic and molecular shape descriptors and retention data of polycyclic aromatic hydrocarbons in reversed-phase chromatography on non-liquid-crystalline, nematic, and smetic stationary phases

Abstract

The local anisotropic ordering of side-chain liquid-crystalline polymer (SCLCP) stationary phases has been revealed statistically. For this purpose the RP HPLC separation of polycyclic aromatic hydrocarbons (PAH) on silica coated with three classes (non-liquid-crystalline, nematic, and smectic) of side-chain polymer (SCP) has been compared. The logarithm of the capacity factor (logk) was correlated with three PAH descriptors-the connectivity index (χ) or the hydrophobic fragmental constant (logP), the length-to-breadth ratio (L/B), and a non-planarity term (Np). Statistical results revealed good correlation between the model and experimental data, enabling the different stationary phases to be compared. Recognition of solute size seems similar for each class of polymer but solute non-planarity recognition grows continuously as ordering of the liquid-crystal polymer increases. Recognition of solute lengthening is non-existent for non-liquid-crystalline polymers and suddenly, appears with liquid crystalline polymers. Shape recognition is better for smectic than for nematic SCP. The predictive, ability of this model was tested on highly condensed aromatic compounds. The connectivity index, χ, did not seem appropriate for such systems. its replacement by Rekker's hydrophobic, fragmental constant, logP, was necessary for fitting the retention of these solutes on liquid-crystalline stationary phases.