Abstract
In this paper, we report an extensive electrospray ionization mass spectrometry (ESIโMS) study of the noncovalent interactions between different intermolecular and intramolecular Gโquadruplex structures and several perylene and coronene ligands. The selectivity of these compounds toward quadruplex structures with respect to duplex DNA, a fundamental topic for the biological evaluation and the pharmacological application of these ligands as potential chemotherapeutic agents, has also been investigated. After exploring this topic according to the classical approach based on the very simple duplex model of an autocomplementary dodecamer, we extended our analysis reporting for the first time a competition ESIโMS experiment in the presence of genomic DNA fragments. Whereas those ligands showing a high level of selectivity between quadruplex and duplex oligonucleotides, in terms of binding constants and percentage of bound DNA, confirmed their selectivity in the competition experiment, the contrary was not always true: some ligands showing poor selectivity with the autocomplementary dodecamer resulted selective in the presence of genomic DNA fragments. This result suggests that physiologically nonrelevant interactions are possible with a short duplex oligonucleotide. This means that the dodecamer can fail in representing a biologically significant structural model, or, better, that it can be used to quickly screen potentially selective molecules, but bearing in mind the high probability of false negative results. Copyright ยฉ 2008 John Wiley & Sons, Ltd.