Proton Migration on the Boron Sheets Surface

Borophene is a two-dimensional allotrope of boron and it is also known as boron sheet. First it has been predicted theoretically in the mid-1990s, experimentally borophene was confirmed in 2015 when the structure was successfully synthesized in 2015. One of the key features of borophene is its strong anisotropy – the dependence of mechanical and electrical properties on direction. This phenomenon is not typical for 2D materials and has never been observed in 2D metals before. Borophene has the highest tensile strength of all known two-dimensional materials. In early works, it was found that the adsorption of a hydrogen atom on the surface of borophene is possible and the analyses of electronic density showed that atom H became a proton. Therefore, in this work, the authors have studied the proton migration over the surface of boron sheets of two types and have found the most energetically favorable path of proton motion. The electron-energy characteristics of the process of migration of a single proton along the surface of boron layers of two types are determined and it is established that in all the considered cases the proton is able to move along the surface almost barrier-free. The type of conductivity of pure boron layers and layers modified by a single proton is determined. In the A-type boron layer, the proton increases the band gap by 0.04 eV, and in the B-type layer, the band gap changes by 0.05 eV. It is proved that two-dimensional boron nanostructures can be considered as a new class of boron topological structure with proton conductivity.

The influence of base pair tautomerism on single point mutations in aqueous DNA

The relationship between base pair hydrogen bond proton transfer and the rate of spontaneous single point mutations at ambient temperatures and pressures in aqueous DNA is investigated. By using an ensemble-based multiscale computational modelling method, statistically robust rates of proton transfer for the A:T and G:C base pairs within a solvated DNA dodecamer are calculated. Several different proton transfer pathways are observed within the same base pair. It is shown that, in G:C, the double proton transfer tautomer is preferred, while the single proton transfer process is favoured in A:T. The reported range of rate coefficients for double proton transfer is consistent with recent experimental data. Notwithstanding the approximately 1000 times more common presence of single proton transfer products from A:T, observationally there is bias towards G:C to A:T mutations in a wide range of living organisms. We infer that the double proton transfer reactions between G:C base pairs have a negligible contribution towards this bias for the following reasons: (i) the maximum half-life of the G*:C* tautomer is in the range of picoseconds, which is significantly smaller than the milliseconds it takes for DNA to unwind during replication, (ii) statistically, the majority of G*:C* tautomers revert back to their canonical forms through a barrierless process, and (iii) the thermodynamic instability of the tautomers with respect to the canonical base pairs. Through similar reasoning, we also deduce that proton transfer in the A:T base pair does not contribute to single point mutations in DNA.