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The molecular mechanism of structural change caused by the beta-decay of substituted tritium on DNA or polymeric materials is still being unsolved and it is hard to study the decay effect of tritium solely by experiment. In order to study the structural changes of damaged polyethylene caused by the decay effect of tritium, we randomly removed hydrogen atoms from the polyethylene chain and performed molecular dynamics (MD) simulations using the reactive force field (ReaxFF). We adopted two parameter sets of ReaxFF and evaluated their reliability by comparing the atomic forces with density functional theory calculations. The results of MD simulations at a low temperature of 100 K show that the structure of polyethylene will be less ordered when losing more hydrogen atoms. It is observed that a double bond or a cyclic structure will be formed when two carbon atoms, which are the nearest or next-nearest neighbors, lose hydrogen atoms.

Using molecular dynamics (MD) simulation, we simulate the structural change of a telomeric DNA by β-decay of substituted tritium to helium-3. The configuration of the telomeric DNA is obtained by removing TRF2 protein from the TRF2-Dbd-DNA complex (Protein Data Bank ID is 3SJM). We assume that hydrogens (H) of guanines in the telomeric DNA are replaced to helium-3. Since this replacement of the H atoms to the 3He atoms changes the charge distribution significantly, the charge distribution used in the MD simulation for the modified guanine is obtained by the density functional theory calculations. We adopt, as the MD simulation, nanoscale molecular dynamics code with CHARMM36 force field using Langevin thermostat and Nosé–Hoover Langevin piston to control the temperature and pressure of the system, respectively. Moreover, changing both the number of replaced guanine N and the temperature of the system T, we calculate the root mean square deviation RMSD to quantify the dependence of the durability of the telomeric DNA on the β-decays. From the MD simulation, it is found that as N or T becomes larger, the RMSD of the DNA becomes also larger. Namely, it denotes that as the intensity of the β-decays becomes larger or as the temperature is increased, the DNA structure becomes more fragile.

Vinylidene fluoride/trifluoroethylene copolymer thin films cast from dilute cyclohexanone solution on vacuum-evaporated Pt, Al, Cu, and Au were annealed at 420 K for 1 h. Transmission electron microscopic observation revealed that the high-temperature phase (HP) of the copolymers was frozen even at room temperature with molecular chains normal to the substrate after the annealing. The maximum lattice mismatch was 3.3% between the (001) plane of the HP of the copolymers and the {111} or {110} plane of the Pt crystals. Coulomb's interaction between the copolymer molecules and metallic atoms is suggested to have an important role in causing such phenomena.