Department of Chemical and Biomolecular Engineering

The oxygen reduction reaction (ORR) plays a key role in renewable energy transformation processes. Unfortunately, it is inherently sluggish, which greatly limits its industrial application. Sub-nano-cluster-decorated electrode interfaces are promising candidate ORR electrocatalysts. However, understanding the nature of the active sites on these catalysts under electrocatalytic conditions presents a formidable challenge for both experiment and theory, due to their dynamic fluxional character. Here, we combine global optimization with the electronic Grand Canonical DFT to elucidate the structure and dynamics of subnano Ptnclusters deposited on electrified graphite. We show that, under electrochemical conditions, these clusters exist as statistical ensembles of multiple states, whose fluxionality is greatly affected by the applied potential, electrolyte, and adsorbate coverage. The results reveal the presence of potential-dependent active sites and, hence, reaction energetics.

Organophosphorus chemical warfare agents (CWAs) such as sarin are highly toxic and inhalation hazards for personnel at risk to exposure to such compounds are typically mitigated using metal-impregnated activated carbon in gas mask filters. In this work we considered anatase (a-) TiO₂ and a Pt cluster supported on a-TiO₂ as potential active filtration materials. Density functional theory (DFT) calculations combined with Fourier transform infrared (FTIR) spectroscopy were used to probe sarin adsorption and decomposition mechanisms. Using the grand canonical basin hopping (GCBH) technique, the structural stability and reactivity of Pt₆O_x clusters supported on a-TiO₂(101) were examined under ambient oxidative conditions, identifying the global minimum and thermodynamically accessible metastable configurations. The Pt₆ cluster is partially oxidized to Pt₆O₁₀ on a-TiO₂ in ambient conditions. The kinetic barriers associated with key bond cleavages decrease in the presence of the Pt cluster compared to the bare a-TiO₂ surface. a-TiO₂ effectively binds phosphonate groups, while the fragments from bond cleavage adsorb to the Pt cluster. The influence of water on sarin adsorption and decomposition was studied to better reflect realistic operating conditions. Sarin was found to displace surface water and chemisorb onto Ti centers. P-O cleavage becomes both thermodynamically and kinetically favorable followed by acetone formation. The presence of water further enhances the thermodynamic stability by facilitating hydrogen bonding with the dissociated fragments. Overall, this combined study reveals that Pt-decorated a-TiO₂ can actively decompose sarin under humid ambient conditions, with synergistic effects between the oxide surface, metal cluster, and water. These insights can guide the development of improved metal oxide-based filtration materials that can both capture and catalytically degrade CWAs in realistic environments.

BACKGROUND: A major hurdle in the use of exogenous stems cells for therapeutic regeneration of injured myocardium remains the poor survival of implanted cells. To date, the delivery of stem cells into myocardium has largely focused on implantation of cell suspensions. METHODOLOGY AND PRINCIPAL FINDINGS: We hypothesize that delivering progenitor cells in an aggregate form would serve to mimic the endogenous state with proper cell-cell contact, and may aid the survival of implanted cells. Microwell methodologies allow for the culture of homogenous 3D cell aggregates, thereby allowing cell-cell contact. In this study, we find that the culture of cardiac progenitor cells in a 3D cell aggregate augments cell survival and protects against cellular toxins and stressors, including hydrogen peroxide and anoxia/reoxygenation induced cell death. Moreover, using a murine model of cardiac ischemia-reperfusion injury, we find that delivery of cardiac progenitor cells in the form of 3D aggregates improved in vivo survival of implanted cells. CONCLUSION: Collectively, our data support the notion that growth in 3D cellular systems and maintenance of cell-cell contact improves exogenous cell survival following delivery into myocardium. These approaches may serve as a strategy to improve cardiovascular cell-based therapies.