Separation of Trp-Arg and Arg-Trp using G-quartet-forming DNA oligonucleotides in open-tubular capillary electrochromatography

DNA oligonucleotides that form intramolecular G‐quartet structures were investigated as stationary phase reagents for separation of mixtures of the isomeric dipeptides Trp‐Arg and Arg‐Trp in open‐tubular capillary electrochromatography (OTCEC). The oligonucleotides included a thrombin‐binding aptamer that forms a biplanar G‐quartet structure and an oligonucleotide that forms a 4‐plane G‐quartet structure. Fluorescence, circular dichroism and UV‐visible absorbance spectroscopies were used in batch solution studies to indicate interactions between the dipeptides and the biplanar G‐quartet structure. Results for OTCEC separations were compared with results obtained for capillary zone electrophoresis separations on a bare capillary. Temperature studies suggest that resolution is improved when the G‐quartet structure is partially destabilized, but control experiments in which potassium chloride was not included in the mobile phase indicate that the G‐quartet structure nevertheless plays a role in the separations.