Donato Fantauzzi

Atomic-scale insight into the interactions between hydroxyl radicals and DNA in solution using the ReaxFF reactive force field

Cold atmospheric pressure plasmas have proven to provide an alternative treatment of cancer by targeting tumorous cells while leaving their healthy counterparts unharmed. However, the underlying mechanisms of the plasma–cell interactions are not yet fully understood. Reactive oxygen species, and in particular hydroxyl radicals (OH), are known to play a crucial role in plasma driven apoptosis of malignant cells. In this paper we investigate the interaction of OH radicals, as well as H2O2 molecules and HO2 radicals, with DNA by means of reactive molecular dynamics simulations using the ReaxFF force field. Our results provide atomic-scale insight into the dynamics of oxidative stress on DNA caused by the OH radicals, while H2O2 molecules appear not reactive within the considered time-scale. Among the observed processes are the formation of 8-OH-adduct radicals, forming the first stages towards the formation of 8-oxoGua and 8-oxoAde, H-abstraction reactions of the amines, and the partial opening of loose DNA ends in aqueous solution.

Surface Buckling and Subsurface Oxygen: Atomistic Insights into the Surface Oxidation of Pt(111).

Platinum is a catalyst of choice in scientific investigations and technological applications, which are both often carried out in the presence of oxygen. Thus, a fundamental understanding of platinums (electro)catalytic behavior requires a detailed knowledge of the structure and degree of oxidation of platinum surfaces in operando. ReaxFF reactive force field calculations of the surface energies for structures with up to one monolayer of oxygen on Pt(111) reveal four stable surface phases characterized by pure adsorbate, high- and low-coverage buckled, and subsurface-oxygen structures, respectively. These structures and temperature programmed desorption (TPD) spectra simulated from them compare favorably with and complement published scanning tunneling microscopy (STM) and TPD experiments. The surface buckling and subsurface oxygen observed here influence the surface oxidation process, and are expected to impact the (electro)catalytic properties of partially oxidized Pt(111) surfaces.

Growth of Stable Surface Oxides on Pt(111) at Near‐Ambient Pressures

Detailed knowledge of the structure and degree of oxidation of platinum surfaces under operando conditions is essential for understanding catalytic performance. However, experimental investigations of platinum surface oxides have been hampered by technical limitations, preventing in situ investigations at relevant pressures. As a result, the time-dependent evolution of oxide formation has only received superficial treatment. In addition, the amorphous structures of many surface oxides have hindered realistic theoretical studies. Using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) we show that a time scale of hours (t≥4 h) is required for the formation of platinum surface oxides. These experimental observations are consistent with ReaxFF grand canonical Monte Carlo (ReaxFF-GCMC) calculations, predicting the structures and coverages of stable, amorphous surface oxides at temperatures between 430-680 K and an O2 partial pressure of 1 mbar.

Multiscale Modeling of Au-Island Ripening on Au(100)

We describe a multiscale modeling hierarchy for the particular case of Au-island ripening on Au(100). Starting at the microscopic scale, density functional theory was used to investigate a limited number of self-diffusion processes on perfect and imperfect Au(100) surfaces. The obtained structural and energetic information served as basis for optimizing a reactive forcefield (here ReaxFF), which afterwards was used to address the mesoscopic scale. Reactive force field simulations were performed to investigate more diffusion possibilities at a lower computational cost but with similar accuracy. Finally, we reached the macroscale by means of kinetic Monte Carlo (kMC) simulations. The reaction rates for the reaction process database used in the kMC simulations were generated using the reactive force field. Using this strategy, we simulated nucleation, aggregation, and fluctuation processes for monoatomic high islands on Au(100) and modeled their equilibrium shape structures. Finally, by calculating the step line tension at different temperatures, we were able to make a direct comparison with available experimental data.

Understanding homogeneous hydrogen evolution reactivity and deactivation pathways of molecular molybdenum sulfide catalysts

Molybdenum sulfides are highly active hydrogen evolution reaction (HER) catalysts based on earth abundant elements. Here, the molybdenum sulfide anion [Mo3S13]2− is used as a molecular model to rationalize HER reactivity of Mo–S-catalysts. For the first time, homogeneous, visible light-driven HER activity of [Mo3S13]2− is reported and high reactivity is observed (turnover number TON ∼23 000, maximum turnover frequency TOFmax ∼156 min−1). Experimental and theoretical studies shed light on the catalytic role of terminal disulfide ligands (S22−) and show that these ligands modulate catalyst redox-activity and electron transfer in solution. Partial substitution of the terminal disulfides with water ligands leads to the most active catalytic species, e.g. [Mo3S11(H2O)2]. In contrast, complete substitution of the terminal disulfides results in a significant loss of reactivity. These results could lay the foundations for the knowledge-based development of homogeneous and heterogeneous molybdenum sulfide catalysts.

Molybdenum Doping Augments Platinum-Copper Oxygen Reduction Electrocatalyst

Improving the efficiency of Pt-based oxygen reduction reaction (ORR) catalysts while also reducing costs remains an important challenge in energy research. To this end, we synthesized highly stable and active carbon-supported Mo-doped PtCu (Mo-PtCu/C) nanoparticles (NPs) from readily available precursors in a facile one-pot reaction. Mo-PtCu/C displays two-to-fourfold-higher ORR half-cell kinetics than reference PtCu/C and Pt/C materials, a trend that was confirmed in proof-of-concept experiments by using a H2 /O2 microlaminar fuel cell. This Mo-induced activity increase mirrors observations for Mo-PtNi/C NPs and possibly suggests an emerging trend. Electrochemical-accelerated stability tests revealed that dealloying was greatly reduced in Mo-PtCu/C in contrast to the binary alloys PtCu/C and PtMo/C. Supporting DFT studies suggested that the exceptional stability of Mo-PtCu could be attributed to oxidative resistance of the Mo-doped atoms. Furthermore, our calculations revealed that oxygen could induce segregation of Mo to the catalytic surface, at which it effected beneficial changes to the surface oxygen adsorption energetics in the context of the Sabatier principle.

Microkinetic modeling of the oxygen reduction reaction at the Pt(111)/gas interface

A microkinetic model of the oxygen reduction reaction (ORR) on Pt(111) under a gaseous

Reactive forcefield for simulating gold surfaces and nanoparticles

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