[en] The radiation damage of adenine base was studied by B3LYP and MP2 methods in the presence of hydroxyl radicals to probe the reactivities of five possible sites of an isolated adenine molecule. Both methods predict that the C8 site is the more vulnerable than the other sites. For its bonding covalently with the hydroxyl radicals, B3LYP predicts a barrierless pathway, while MP2 finds a transition state with an energy of 106.1 kJ/mol. For the hydroxylation at the C2 site, the barrier was calculated to be 165.3 kJ/mol using MP2 method. For the dehydrogenation reactions at five sites of adenine, B3LYP method predicts that the free energy barrier decreases in the order of H8 > H2 > HN62 > HN61 > HN9. (special topic — soft matter and biological physics)

[en] The properties of graphene can be chemically altered by changing its local binding configurations. In the present work, we investigate fundamentals of chemisorption of atomic hydrogen on graphene and its influence on mechanical properties of as-hydrogenated graphene by means of molecular dynamics simulations. Our simulation results indicate that there are diversiform hydrogen-graphene configurations formed in the chemisorption process. Especially, energetically favorable hydrogen pairs result in less even no atomic distortion of graphene than sp³ hybridization. The hydrogenation-induced deterioration of mechanical properties of graphene shows a strong dependence on its chirality. The evolution of bond structures in uniaxial tension along armchair direction is more sensitive to local failure of graphene than zigzag direction, leading to a more pronounced decrease in both fracture stress and fracture strain. It is indicated that the chemisorption of hydrogen on graphene can be strongly affected by operating temperature primarily due to the temperature dependent graphene morphology. These findings advance our understanding of chemical vapor deposition of graphene synthesis and hydrogenation of graphene. (paper)