Experimental and Theoretical Study of Deprotonation of DNA Adenine Cation Radical

Among all the DNA components, extremely redox-active guanine （G） and adenine （A） bases are subject to facile loss of an electron and form cation radicals （G＋＂ and A＋＇） when exposed to irradiation or radical oxidants. The subsequent deprotonation of G＋＇ and A＋＇ can invoke DNA damage or interrupt hole transfer in DNA. However, compared with intensive reports for G＋, studies on the deprotonation of A＋ are still limited at present. Herein, we investigate the deprotonation behavior of A＋. by time-resolved laser flash photolysis. The deprotonation product of A（N6-H）＇ is observed and the deprotonation rate constant, （2.0±0.1）×10 7 s-1, is obtained at room temperature. Further, the deprotonation rate con- stants of A＋. are measured at temperatures varying from 280 K to 300 K, from which the activation energy for the N6-H deprotonation is determined to be （17.1±1.0） kJ/mol by Arrhenius equation. In addition, by incorporating the aqueous solvent effect, we perform density functional theory calculations for A＋ deprotonation in free base and in duplex DNA. Together with experimental results, the deprotonation mechanisms of A＋ in free base and in duplex DNA are revealed, which are of fundamental importance for understanding the oxidative DNA damage and designing DNA-based electrochemical devices.

Hydrogen Diffusion in Aluminum Melts: An ab initio Molecular Dynamics Study

The diffusion process of hydrogen in aluminum melts was investigated by molecular dynamics simulation. The pair correlation function, first peak position, and coordination number was calculated and differences in the structural properties among Al-H, Cl-H, and Al-Cl pair were examined. The mechanism of chlorine on improving hydrogen diffusion was discussed. From an ab initio molecular dynamics calculations, the diffusivity of hydrogen in liquid aluminum as D（T）=（0.118×10-4 m2/s）exp（-0.316 eV/kT） is obtained, which is in good agreement with the experimental data. Correspondingly the diffusivity with presence of chlorine is promoted as D（T）=（0.09×10-4 m2/s）exp（-0.251 eV/kT）. It can be concluded that the diffusion of hydrogen in aluminum melts can be enhanced in the presence of chlorine.

Low-Energy Driven Ring-Opening Behavior of Benzocyclobutene Derivatives

It's urgent to develop benzocyclobutene(BCB)-based polymers with low curing temperature for temperature-sensitive applications such as liquid crystal displays(LCDs)and flexible electronics.Herein,the effect of substituents on the ring-opening behavior of BCB derivatives was investigated.The ring-opening activation energy barriers(ΔGA)of BCB derivatives with one or two substituents on the four-membered alkyl ring were systematically calculated using the B3LYP function.Both mono-and di-substituted BCBs adopted the conrotatory ring-opening process,obeying the Woodward-Hoffmann's Rules upon heating.The mono-/di-substituted BCBs exhibited 8.2%—69%lowerΔGA compared with BCB,attributed to the electronic effects of the substituents.Disubstituted BCBs with both electron-donating and electron-withdrawing groups,e.g.,1-NH_(2)-8-NO_(2)-BCB,demonstrated the lowestΔGA.In addition,BCB derivatives with amide/ester/acyloxy group modified on C1 position were synthesized as model molecules,and their ring-opening temperature can be decreased by 20℃ compared to the unsubstituted one,also consistent with our calculation results.This work combined theoretical calculation methods with experimental results to provide valuable insights into the design and synthesis of BCB derivatives and next-generation BCB functional packaging materials with low ring-opening temperature.