Reactivity toward low-energy electrons (LEE) has been hypothesized as a cause of radio-modifying properties for various molecules. LEE's transient nature, however, prevents the establishment of clear links between initial processes at the sub-ps time scale and the final products of radiolysis. Here, such links are explored for the radio-modifying compound RRx-001 (1-bromoacetyl-3,3-dinitroazetidine). Picosecond pulse radiolysis demonstrates the high scavenging capacity of the molecule for secondary quasi-free and solvated electrons forming stable parent anions confirmed by studies of microsolvated RRx-001 in clusters. The anions decay either via auto-detachment of an electron or dissociate involving hydrogen transfer from solvent, resulting in NO2 and 1-(bromoacetyl)-3-nitroazetidine. Surprisingly, no Br dissociation is observed despite its high electron affinity. We assign this behavior to the "inaccessibility" of sigma virtual states for electrons in the solvent, which can be of a general nature.

• Keywords
• catalytic electron, electron attachment, low‐energy electrons, radiosensitizer, state selective,
• Publication type
• Journal Article MeSH

Cysteine-water cluster cations Cys(H2O)3,6+ and Cys(H2O)3,6H+ are assembled in He droplets and probed by tandem mass spectrometry with collision-induced activation. Benchmark experimental data for this biologically important system are complemented with theory to elucidate the details of the collision-induced activation process. Experimental energy thresholds for successive release of water are compared to water dissociation energies from DFT calculations showing that clusters do not only fragment exclusively by sequential emission of single water molecules but also by the release of small water clusters. Release of clustered water is observed also in the ADMP (atom centered density matrix propagation) molecular dynamics model of small Cys(H2O)3+ and Cys(H2O)3H+ clusters. For large clusters Cys(H2O)6+ and Cys(H2O)6H+ the less computationally demanding statistical Microcanonical Metropolis Monte-Carlo method (M3C) is used to model the experimental fragmentation patterns. We are able to detail the energy redistribution in clusters upon collision activation. In the present case, about two thirds of the collision energy redistribute via an ergodic process, while the remaining one third is transferred into a non-ergodic channel leading to ejection of a single water molecule from the cluster. In contrast to molecular fragmentation, which can be well described by statistical models, modelling of collision-induced activation of weakly bound clusters requires inclusion of non-ergodic processes.

• Publication type
• Journal Article MeSH