Dehydrogenation and Other Non-radiative Relaxation Processes in Gas-Phase Metal−DNA Base Complexes

Abstract

Photoinduced dehydrogenations of gas-phase Al−guanine, Mn−guanine, and the Al-base pair adduct Al−guanine−cytosine have been observed. Upper and lower limits on the minimum photon energy required to effect the dehydrogenation have been determined for these species. Species were generated using a laser ablation source and were detected with laser photoionization/time-of-flight mass spectrometry. Only metalated species were observed to dehydrogenate, and the effect of metal on the photochemistry of guanine and cytosine has been investigated using density functional theory (DFT). Avoided crossings between the ground and first electronically excited states are features specific to the metalated species and are likely responsible for the metal-specific dehydrogenation observed. The rapid nonradiative relaxation believed to manifest the dehydrogenation is consistent with the dominance of multiphoton contributions to the mass spectral signals observed which also stems from rapid nonradiative relaxation. In this context, the photophysics of the gas-phase complexes is similar to that of solution-phase bases where nonradiative relaxation processes also dominate.