Shinichi Yamashita

DNA damage arises not only from the direct action of ionizing radiation but also from indirect action mediated by highly reactive hydroxyl radicals (^•OH). This study aimed to determine whether the protective or sensitizing effects of amino acids against X-ray-induced DNA damage are associated with the side-chain characteristics of these amino acids. Seven amino acids with distinct side-chain properties were investigated. The rate constants for their reactions with ^•OH were determined by electron pulse radiolysis. Highly purified, scavenger-free plasmid DNA (pUC18) was irradiated with X-rays in the presence of each amino acid, whose concentrations were adjusted to scavenge ∼14% of ^•OH. DNA strand breaks (SSBs and DSBs) were quantified by agarose gel electrophoresis. At the same time, oxidative base lesions and apurinic/apyrimidinic (AP) sites were detected as enzyme-sensitive sites (ESSs) using formamidopyrimidine-DNA glycosylase (Fpg), endonuclease III (Nth), endonuclease IV (Nfo). Despite equivalent ^•OH scavenging capacities, the extent and spectrum of DNA damage varied markedly among the amino acids. Aspartic acid (Asp) and phenylalanine (Phe) exhibited the strongest overall protection, while glycine (Gly) showed the weakest protection, even with partial sensitization. Amino acids with highly hydrophilic or hydrophobic side chains tended to exhibit more substantial protective effects, although a clear correlation was not always observed for molecular weight or isoelectric point. Side-chain properties and potential chemical repair mechanisms are likely to contribute to the modulation of DNA damage. This work provides new mechanistic insights into amino acid-mediated DNA radioprotection, suggesting promising directions for molecular-level studies of amino acid-DNA interactions.

Nano-theranostics using biodegradable polymers are effective for the diagnosis and treatment of intractable cancers; however, there is a need for technology that controls bioavailability and biodegradability without compromising biocompatibility. In this study, peptide nanoparticles (NPs) with controlled particle size and biodegradability were prepared by ionizing radiation and loaded with imaging agents and anticancer drugs to develop novel nano-theranostics for pancreatic cancer diagnosis and treatment. Peptides composed of histidine, glycine, glutamic acid, and an arginine-glycine-aspartic acid motif were synthesized by the solid-phase synthesis method. Their aqueous solutions were irradiated with γ-rays to produce NPs with a particle size of less than 50 nm, enabling penetration of the pancreatic cancer stroma. The radiation crosslinking of peptides, with or without the arginine-glycine-aspartic acid motif, in water was investigated by pulse radiolysis. Peptide NPs loaded with fluorescent labeling or magnetic resonance imaging agents were efficiently taken up by pancreatic cancer cells. Cisplatin-loaded peptide NPs produced by higher-dose irradiation suppress drug-release rates owing to their lower biodegradability. In conclusion, peptide NPs with controllable particle size and biodegradability were produced by ionizing radiation and loaded with fluorescent labeling agents, magnetic resonance imaging agents, and anticancer drugs to develop a new nano-theranostics drug for pancreatic cancer diagnosis and treatment.

Ammonia (NH₃) is a vital component for sustaining global food supplies and fuel production, but its industrial production via the Haber-Bosch process remains energetically demanding and carbon-intensive. Here, we report an electron-beam-activated NH₃ synthesis strategy that utilizes only atmospheric N₂ and water as feedstocks under ambient conditions. This approach achieves an industrially relevant rate of 83.6 μmol g^-1 s^-1 with a substantially improved energy efficiency of 0.53 MJ/mol, which surpasses most laboratory-scale technologies and is comparable to that of the Haber-Bosch process. Time-resolved operando spectroscopic experiments, combined with theoretical calculations, reveal that this distinct activation mode enables rapid N₂→NH₃ conversion through a proton-coupled transfer of an in situ generated energetic hydrated electron. Furthermore, techno-economic analysis and life-cycle assessment demonstrate that the operational simplicity and exceptional throughput of the present N₂ fixation approach could promote nitrogen circularity in the sustainable chemical industry.

Pulse radiolysis was employed to investigate fundamental radiation chemical reactions, which are essential in the radiation protection of DNA. Two positively charged peptides (PCPs), histidine-tyrosine-histidine (His-Tyr-His) and lysine-tyrosine-lysine (Lys-Tyr-Lys), as well as the amino acids that constitute them, were involved. The reaction rate constants for tyrosine (Tyr), histidine (His), lysine (Lys), His-Tyr-His, and Lys-Tyr-Lys with OH radicals (^•OH) were (1.6 ± 0.3) × 10¹⁰, (9.0 ± 0.9) × 10⁹, (1.4 ± 0.3) × 10⁹, (1.8 ± 0.1) × 10¹⁰, and (1.0 ± 0.1) × 10¹⁰ M^-1s^-1, respectively, indicating that formation of peptide bond can affect the reaction of amino acids with ^•OH. Observed transient absorption spectra indicated a shielding effect of the His or Lys residues at both ends of the PCPs on the centrally located Tyr. The measurement of chemical repair capabilities using deoxyguanosine monophosphate (dGMP) as a model for DNA demonstrated that the reaction rate constants of Tyr, His-Tyr-His, and Lys-Tyr-Lys with dGMP radicals were (2.2 ± 0.5) × 10⁸, (2.3 ± 0.1) × 10⁸, and (3.3 ± 0.4) × 10⁸ M^-1s^-1, respectively, implying that the presence of a positive charge may enhance the chemical repair process.

Atomic oxygen (AO) is one of the dominant components of the residual atmosphere in low Earth orbit. AO collides with spacecraft with a translational energy of 5 eV, forming nanoscale protrusions on polymeric materials. To clarify the influences of a polymer's chemical structure on the formation of AO-induced microstructures, this study investigated the size of free-volume holes and the layer thickness that interacted with AO for polyethylene (PE), polypropylene (PP), and polystyrene (PS) by positron annihilation lifetime spectroscopy. The injection energies of positrons varied from 1.3 to 10 keV to adjust the injection depth (range) into the polymers (40 nm-1.6 μm). For the pristine films, the lifetime of ortho-positronium (o-Ps, τ₃) was longer in the order of PS, PP, and PE regardless of the injection energy of positrons, showing the different sizes of free-volume holes with radii of 0.29, 0.31, and 0.32 nm, respectively. The fraction of the decay component corresponding to o-Ps in all decay components (relative intensity of o-Ps, I₃) was used to investigate the chemical change induced by AO exposure. The I₃ values for the three polymers were decreased by AO exposure of (2-5) × 10¹⁸ atoms/cm² or more at a depth of 40-48 nm, obtained by 1.3 keV positrons. This indicates that AO formed polar groups (i.e., an oxidized layer) on the polymer surfaces. The maximum depths of such chemical change for PE and PP were deeper than that for PS. The different sizes of free-volume holes would affect the diffusion or ballistic penetration of AO, resulting in the difference in the oxidized layers' thicknesses and surface morphologies.

Reduced graphene oxide (rGO) composite aerogels were synthesized by the radiation reduction of graphene oxide (GO) with the assistance of Eu³⁺, which demonstrated excellent adsorption performance for diverse organic pollutants.

Nanoparticle-based drug delivery systems (DDS) have been developed as effective diagnostic and low-dose imaging agents. Nano-imaging agents with particles greater than 100 nm are difficult to accumulate in pancreatic cancer cells, making high-intensity imaging of pancreatic cancer challenging. Peptides composed of histidine and glycine were designed and synthesized. Additionally, aqueous peptide solutions were irradiated with γ-rays to produce peptide nanogels with an average size of 25–53 nm. The mechanisms underlying radiation-mediated peptide crosslinking were investigated by simulating peptide particle formation based on rate constants. The rate constants for reactions between peptides and reactive species produced by water radiolysis were measured using pulse radiolysis. HGGGHGGGH (H9, H—histidine; G—glycine) particles exhibited a smaller size, as well as high formation yield, stability, and biodegradability. These particles were labeled with fluorescent dye to change their negative surface potential and enhance their accumulation in pancreatic cancer cells. Fluorescent-labeled H9 particles accumulated in PANC1 human pancreatic cancer cells, demonstrating that these particles are effective nano-imaging agents for intractable cancers.

In this study, an improved method using scavenger-free plasmid DNA was established to accurately determine yields of DNA damage induced by direct and indirect actions of ionizing radiation. The scavenger-free plasmid DNA was obtained by dialysis over 5–7 days, and the DNA solvent was replaced with phosphate buffer to completely remove impurities, which could be scavengers of radicals produced as a result of water radiolysis. DNA samples of films and dilute aqueous solutions were used to separately evaluate contributions of the direct and indirect actions of X rays (150–160 kVp). The irradiated DNA was analyzed by agarose gel electrophoresis to quantify strand-break yields. The yields of single-strand breaks (SSBs), n(SSB), were determined to be (6.5 ± 2.0) × 10–10 and (3.1 ± 0.9) × 10–7 SSBs/Gy/Da for the film and solution samples, respectively, showing a significant contribution of hydroxyl radicals (•OH) compared with direct energy depositions from ionizing radiation to DNA. As observed in SSBs, the yields of double-strand breaks (DSBs), n(DSB), were (5.6 ± 1.1) × 10–11 and (1.3 ± 0.2) × 10–8 DSBs/Gy/Da for the film and solution samples, respectively. The yield ratio of DSBs to SSBs, that is, n(DSB)/n(SSB), was 0.091 ± 0.026 for the film samples, while it was much lower for the solution samples (0.045 ± 0.010), indicating that direct actions result in more localized strand breaks relative to indirect actions. Base excision repair enzymes, namely, endonuclease III (Nth) and formamidopyrimidine-DNA glycosylase (Fpg), were utilized after irradiations to convert base lesions and apurinic/apyrimidinic (AP) sites into strand breaks. The amounts of Nth and Fpg for the conversion were optimized to a few units per µg of DNA, although the optimal concentrations can differ among conditions.

Atomic oxygen (AO) is the main component of the residual atmosphere in a low Earth orbit. AO with a translational energy of 5 eV colliding with artificial satellites forms nano- and microscale protrusions on polymeric materials. This study investigated the influences of AO (fluence and velocity distribution) and a polymer’s chemical structure on such surface morphologies. The correlations between samples’ mass losses and positions in the irradiation field of an AO beam were analyzed with polyimide (Kapton) films, a standard reference material for AO fluence measurements. The characterizations of polyethylene (PE), polypropylene (PP), and polystyrene (PS) films were studied using gel permeation chromatography and X-ray diffraction. The sample surfaces were observed using a field emission scanning electron microscope. Nanoscale protrusions were formed on all the samples and were larger but fewer with increasing AO fluence. The numerical density of protrusions formed on PE and PP was lower than that on PS. However, the erosion yields and functional groups of PE, PP, and PS were similar per FT-IR spectra.