Selectivity of quadruplex DNA stationary phases toward amino acids in homodipeptides and alanyl dipeptides

Series of dipeptides, including homodipeptides and alanyl dipeptides, were separated using quadruplex (G-quartet) DNA stationary phases in open-tubular capillary electro-chromatography (OTCEC). The stationary phases were constructed by covalently attaching the DNA oligonucleotides to the inner capillary surface. Three different G-quartet forming oligonucleotides were investigated: the two-plane G-quartet forming thrombin-binding aptamer, the four-plane analogue of the thrombin-binding aptamer, and a two-plane oligonucleotide identical to the thrombin-binding aptamer except for the replacement of the guanine by thymine in the central bridging loop of the G-quartet structure. Results were compared with results obtained using capillary electrophoresis on a bare capillary and OTCEC using an oligonucleotide with the same base composition as the thrombin-binding aptamer but in a different sequence that does not allow G-quartet formation as the stationary phase.