On the effect of aqueous organic mobile phases on the enantioseparation of halogenated 4,4’-bipyridines using polysaccharide carbamate-based chiral columns

In the last decade, the contribution of halogen bond (HaB) in liquid phase enantioseparation of halogenated analytes was demonstrated by using polysaccharide-based chiral stationary phases (CSPs) and n-hexane-containing mixtures as mobile phases. On the other hand, it was also shown that polar organic solvents (POSs) like methanol and ethanol weaken or suppress the contribution of HaB to binding and recognition, whereas hydrophobic mechanisms become dominant by using alcohol-based mobile phases. Although some recent studies demonstrated that HaB-based systems exhibit an improved water resistance compared to the analogous hydrogen bond (HB)-based systems, currently no information is available in the literature about the effect of using aqueous organic mobile phases on the enantioseparations of halogenated compounds driven by HaB in normal phase mode. With the aim to gain information about this topic, we investigated the effect of adding water to the mobile phase on the enantioseparation of four hexahalogenated 4,4’-bipyridines by using amylose and cellulose tris(3,5- dimethylphenylcarbamate)-based chiral columns. As a result, chromatographic behaviours dependent on the distinctive halogen atom featuring the analytes were observed. The study confirmed that, when polar organic solvents and aqueous organic mixtures were used as mobile phase, both iodine-dependent and hydrophobic noncovalent interactions contributed to the enantioseparation of iodinated 4,4’-bipyridines.