Charge state effects in the decompositions of single-nucleobase oligonucleotide polyanions

Abstract

A series of anions derived from electrospray ionization of small oligonucleofides, each consisting of a single nucleobase (adenine, thymine, cytidine or guanine), have been subjected to ion trap tandem mass spectrometry. The data set allows for comparisons of dissociation behavior as functions of parent ion charge, oligomer length, and nucleobase identity. Parent ion charge is seen to play a major role in determining the most important dissociation channels. Dramatic changes in the relative contributions of the various possible dissociation channels are observed from one parent ion charge state to the next. Parent ion charge apparently can alter the relative order of the threshold energies required for the various competitive sequence channels. In addition, the ion trap collisional activation experiment is highly sensitive to differences in the energy requirements for the lowest energy dissociation pathways. Nucleobase identity also is an important factor, with each series of single-nucleobase oligomers showing unique dissociation behavior. For example, poly-T anions show an enhanced tendency for the loss of the 5′ thymine relative to the same charge states of oligomers comprised of the other nucleobases whereas the poly-G anions show a lower tendency for the loss of the 5′ guanine. Poly-A anions show consecutive nucleobase loss as a reaction channel that competes with those that provide direct sequence information. This tendency increases with increasing oligomer size and charge.