Gas-phase hydrogen-deuterium exchange in phosphorothioate d(GTCAG) and d(TCGAT)

The gas-phase hydrogen-deuterium exchange of phosphorothioate d(GTCAG) and d(TCGAT) has been examined using electrospray Fourier transform ion cyclotr on resonance (FTICR) mass spectrometry, The monitored for the [M-2H](2-), [ M-3H](3-), and [M-4H](4-) charge states. The mole fractions of each partial ly exchanged species have been calculated as a function of time. The rates of initial exchange could not be fit to simple exponential functions. The r esults suggest that each ion can adopt more than one gas-phase conformation , and that these conformers exchange at different rates. Observation of slo wly interconverting populations is consistent with a model where initial io n conformations contain internal hydrogen bonds between the bases and charg ed residues that are disrupted over time. Copyright (C) 1999 John Wiley & S ons, Ltd.