Chiral selectivity of guanosine media in capillary electrophoresis.

Gels formed by self-association of monomeric guanosine compounds join numerous other agents such as cyclodextrins, crown ethers, chiral surfactants, antibiotics, proteins, and polysaccharides for chiral separations. Guanosine gels (G-gels) are self-assembled networks of hydrogen-bonded tetrads formed by guanosine nucleotides and their derivatives. The tetrads stack upon themselves to form columnar, helical aggregates that are stabilized by π-π interactions and centrally located cations. Previous work showed the effectiveness of G-gels formed by guanosine-5'-monophophate for separation of the enantiomers of the cationic drug propranolol using capillary electrophoresis. Subsequently, it was found that not all chiral compounds could be resolved into their enantiomers, leading us to investigate in this work the structural features that appear to be correlated to enantiomerically selective interactions of chiral compounds with G-gels. For those compounds (anionic 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate and zwitterionic tryptophan) for which enantiomeric resolution was achieved, the effects of experimental conditions and G-gel composition were examined. For other compounds with no net charge (hydrobenzoin and zwitterionic amino acids and derivatives), the migration times were used as an indicator of the extent of interaction with the G-gel run buffer. It was found that the extent of interaction alone does not determine the chiral selectivity of the G-gel, indicating that the mechanism of chiral separation involves particular structural characteristics of the chiral compounds.