G-quaruplex formation of thrombin binding aptamer under electrospray ionization mass spectrometry

The formation of G-quadruplex structure of thrombin binding aptamer under electrospray ionization mass spectrometry was investigated. The negative-ion electrospray mass spectrum of the aptamer, taken using an ion trap mass spectrometer, contains a series of multiply charged ions that are M ^-n(n=3-9). It was observed that the extent of adduct formation is qualitatively similar for both Ba and Sr ions, and in competition with K ion, adduct formation is more favorable for Sr and Ba ions. The results show that the binding of various metal ion adducts with the thrombin binding aptamer under ESI conditions is specific.