Gas-phase activation and dissociation studies of biomolecules, proteins and their non-covalent complexes using X-rays hold great promise for revealing new insights into the structure and function of biological samples.

A study on photodissociation dynamics of 2-bromo-5-iodo-nitroimidazole – a model radiosensitizer – using coincidence spectroscopy and computational methods.

The effectiveness of radiation therapy can be enhanced by understanding the fragmentation mechanisms of iodine-doped DNA oligonucleotide under tender X-rays, as explored experimentally and computationally in our study. By primarily targeting iodine atoms above their L-edge ionization energies, we observed a significant increase in the production of fragments critical to DNA backbone breakage, particularly within mass ranges associated with phosphate and sugar groups. The mass spectroscopy experiments demonstrated that iodine-doped DNA oligonucleotides undergo intense fragmentation at long distances from the initial photoactivation site. Born–Oppenheimer based molecular dynamics simulations confirmed the generation of numerous small fragments, including reactive oxygen species, which are pivotal in enhancing the radiation damage. These findings highlight the effectiveness of iodine doping in amplifying DNA damage in radiotherapy via iodine photoactivation, thereby improving the potential for targeted cancer treatment.

The present study investigates the photofragmentation behavior of iodine-enhanced nitroimidazole-based radiosensitizer model compounds in their protonated form using near-edge X-ray absorption mass spectrometry and quantum mechanical calculations. These molecules possess dual functionality: improved photoabsorption capabilities and the ability to generate species that are relevant to cancer sensitization upon photofragmentation. Four samples were investigated by scanning the generated fragments in the energy regions around C 1s, N 1s, O 1s, and I 3d-edges with a particular focus on NO₂ ⁺ production. The experimental summed ion yield spectra are explained using the theoretical near-edge X-ray absorption fine structure spectrum based on density functional theory. Born–Oppenheimer-based molecular dynamics simulations were performed to investigate the fragmentation processes.

Gas-phase activation and dissociation studies of biomolecules, proteins and their non-covalent complexes using X-rays hold great promise for revealing new insights into the structure and function of biological samples. This is due to the unique properties of X-ray molecular interactions, such as site-specific and rapid ionization. In this perspective, we report and discuss the promise of first proof-of-principle studies of X-ray-induced dissociation of native biological samples ranging from small 17 kDa monomeric proteins up to large 808 kDa non-covalent protein assemblies conducted at a synchrotron (PETRA III) and a free-electron laser (FLASH2). A commercially available quadrupole time-of-flight mass spectrometer (Q-ToF2, Micromass/Waters), modified for high-mass analysis by MS Vision, was further adapted for integration with the open ports at the corresponding beamlines. The protein complexes were transferred natively into the gas phase via nano-electrospray ionization and subsequently probed by extreme ultraviolet (FLASH2) or soft X-ray (PETRA III) radiation, in either their folded state or following collision-induced activation in the gas phase. Depending on the size of the biomolecule and the activation method, protein fragmentation, dissociation, or enhanced ionization were observed. Additionally, an extension of the setup by ion mobility is described, which can serve as a powerful tool for structural separation of biomolecules prior to X-ray probing. The first experimental results are discussed in the broader context of current and upcoming X-ray sources, highlighting their potential for advancing structural biology in the future.

Objective. Incorporating iodine into DNA bases offers a strategy to enhance radiotherapy. The iodine increases the photoabsorption cross‑section and can promote DNA disruption and cell death in cancerous tissue. In this study, we investigate the local fragmentation mechanisms of iodinated DNA and the spatial extent of damage propagation following photoactivation. Approach. Single‑stranded DNA oligonucleotides consisting of 2-5 bases, in which the methyl group of thymine is substituted with an iodine atom, were irradiated with synchrotron X‑rays above the iodine L-shell ionisation threshold (4900 eV). Fragmentation patterns were extracted by subtracting background spectra obtained below the threshold (4500 eV), and the results were complemented by Born–Oppenheimer molecular dynamics simulations to resolve bond breaking at the atomic level. Main results. We find that longer oligonucleotide chains predominantly generate larger, high‑m/z fragments, while shorter sequences produce a wider variety of small fragments. Backbone cleavage is observed in all sequences, with phosphate‑ and sugar‑based ions dominating the spectra. Bond scission extends up to five bases from the iodination site, with the heaviest stable fragment containing two bases. Significance. Suppose this effect is extrapolated to genomic DNA, which includes about 29.5\% thymine. In that case, the amount of thymine replaced by iodinated uracil can help estimate the extent of DNA damage that might occur during radiation therapy using iodine as a radiosensitiser.