DNA Hairpin, Pseudoknot, and Cruciform Stability in a Solvent-Free Environment

The secondary structures of DNA hairpins, pseudoknots and cruciforms are of great interest because of their possible role in materials applications and biological functions such as regulating transcription. To determine the stability of these structures, DNA sequences capable of forming each were analyzed with mass spectrometry, ion mobility, and molecular dynamics calculations. Nano-ESI mass spectra indicated that stoichiometries compatible with hairpin, pseudoknot, and cruciform structures were present. Ion mobility spectrometry (IMS) was utilized to obtain experimental collision cross sections for all complexes. These cross sections were compared with structures from molecular dynamics, and in all cases, the lowest-charge states could be matched with a structure for an intact hairpin, pseudoknot, or cruciform. However, as the charge states of the single-stranded hairpins and pseudoknots increased, their structures elongated, and all Watson-Crick pairs were broken.