Real-time observation of a correlation-driven sub 3 fs charge migration in ionised adenine

Our group (CFEL-ATTO) with the key participation of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) has demonstrated that ultrashort laser pulses can be used to protect one of the DNA building blocks against destruction induced by vacuum ultraviolet (VUV) radiation. We unveiled that a second laser flash in the infrared, timed shortly (only a few millionths of billions of a second) after the first VUV flash, prevented the adenine molecule to disintegrate, therefore stabilising it. We presents our work in the journal Communications Chemistry published by Nature publishing group.

High energy radiation can cause irreparable damage to our own biological molecules – such as DNA – leading to mutations and potentially cell death. Damage is often occurring as a consequence of the molecular ionization, inducing the fragmentation of the DNA subunits. So far, protection against radiation damage has hardly been achieved, as the photo-induced dissociation process could not be stopped. Through ultra-short-time experiments, our research group and collaborators have discovered that, by taking advantage of mechanisms that take place on extremely fast time scales, it is indeed possible to protect the molecule. Our group works with extremely short light flashes in the attosecond range, with the idea of imaging and controlling electron movements in complex molecules. In doing so, we are particularly interested in investigating the role of electrons in photochemical processes, i.e. processes that are triggered by light. In our recent experiments, we exposed molecules of the DNA building block adenine to an intense VUV flash for a time of attoseconds (10-18 s), which regularly causes the molecule to be destroyed. When we shone an infrared light flash on the molecule only two femtoseconds (10-15 s) afterwards, we found that the molecule stabilised itself by emitting an electron and its dissociation was stopped. Instead, a doubly ionised but otherwise intact adenine molecule remained. Overall, we were thus able to save about one per cent of the molecules from destruction. The key mechanism behind this stabilization has been found to be “electron charge migration”: a purely electronic process involving an ultrafast charge inflation away from the molecule. In our experiments we have entered the attosecond range and were thus able to show - for the first time - that with our technology it is possible to take advantage of electron movements to change the fate of a molecular reaction. Until now, there have been only speculations about this possibility and the usual assumption was that controlling the movements of the atomic nuclei in the molecules was key for the molecular stabilisation. This study has been conducted over time scales in which the atoms in the molecule can be considered as frozen, therefore unveiling a purely electronic mechanism so far unexplored for the building blocks of DNA. These new findings are an important step towards understanding the fastest mechanisms activated by the interaction of biomolecules with light and their role in photoprotection. The demonstration of an ultrafast stabilisation protocol for a DNA subunit, by interrogating the system before the nuclear motion take place, can substantially improve our ability of controlling ionisation damage effects, with interesting perspectives for protecting molecules against light.

The full publication can be found at:

https://www.nature.com/articles/s42004-021-00510-5

 

This work has been done in collaboration with MPSD (Hamburg), Politecnico di Milano (Milano, Italy), CNR-IFN, (Milano, Italy), INRS-EMT, (Varennes, QC, Canada), CNR-ISM (Monterotondo Scalo, Italy), Università di Roma Tor Vergata (Roma, Italy), Queen’s University Belfast (Belfast, UK).