The hydrolysis of chlorine nitrate ClONO 2 + H 2 O f HOCl + HNO 3 on a type-II polar stratospheric cloud ice aerosol is modeled via the ClONO 2 ‚(H 2 O) 3 reaction system at the HF/6-31+G** level of theory with microsolvation by three additional STO-3G waters, and with electron correlation accounted for at the MP2 level. The calculations suggest a fast reaction, consistent with experimental observations, and portray a transition state that involves a nucleophilic attack of a water molecule on chlorine concerted with proton transfer from the attacking water to the ice lattice. The results also give insight on the observed slow desorption of the produced HOCl and indicate a source of rate suppression on sulfate and nitrate containing type-I polar stratospheric cloud ice aerosols.

The direct ClONO2 + HCl → Cl2 + HNO3 reaction on ice, implicated in polar stratospheric ozone depletion, is studied quantum chemically on a model ice lattice comprising nine water molecules. The reaction path is calculated at the HF/(HW*,3-21G) level, using the Hay−Wadt effective core potential for Cl. At these geometries, energies are recalculated at the MP2/(SBK+*,6-31+G*) level, with the Stevens−Bash−Krauss effective core potential for Cl. HCl is found to be ionized in the reactant complex. The calculated reaction internal energy barrier, including zero-point energy correction, is 6.4 kcal/mol. The reaction mechanism involves proton transfer in the ice lattice, accompanied by nucleophilic attack of Cl- on the Clδ+ in ClONO2; the lattice is an active participant in the reaction. Implications for heterogeneous atmospheric chemistry are discussed.

The acid dissociation of a nitric acid HNO(3) molecule located at various depths in a water slab is investigated via Car-Parrinello molecular dynamics simulations. HNO(3) is found to remain molecular when it is adsorbed on top of the surface with two hydrogen-bonds, and to dissociate--although not always--by transferring a proton to a water molecule within a few picoseconds when embedded at various depths within the aqueous layer. The acid dissociation events are analyzed and discussed in terms of the proton donor-acceptor O-O hydrogen bonding distance and the configurations of the nearest-neighbor solvent waters of an HNO(3).H(2)O pair. Four key structural features for the HNO(3) acid dissociation are identified and employed to analyze the trajectory results. Key solvent motions for the dissociation include the decrease of the proton donor-acceptor O-O hydrogen bonding distance and a 4 to 3 coordination number change for the proton-accepting water. The Eigen cation (H(3)O(+)), rather than the Zundel cation (H(5)O(2)(+)), is found to be predominant next to the NO(3)(-) ion in contact ion pairs in all cases.

The first key step in the oxidation of water to O(2) by the oxidized species [(bpy)(2)(O)Ru(V)ORu(V)(O)(bpy)(2)](4+) of the Ru blue dimer is studied using density functional theory (DFT) and an explicit solvent treatment. In the model reaction system [L(2)(O)Ru(V)ORu(V)(O)L(2)](4+)·(H(2)O)(4)·W(76), the surrounding water solvent molecules W are described classically while the inner core reaction system is described quantum mechanically using smaller model ligands (L). The reaction path found for the O--O single bond formation involves a proton relay chain: direct participation of two water molecules in two proton transfers to yield the product [L(2)(HOO)Ru(IV)ORu(IV)(OH)L(2)](4+)·(H(2)O)(3)·W(76). The calculated ∼3 kcal/mol reaction free energy and ∼15 kcal/mol activation free energy barrier at 298 K are consistent with experiment. Structural changes and charge flow along the intrinsic reaction coordinate, the solvent's role in the reaction barrier, and their significance for water oxidation catalysis are examined in detail.

Acute fulminant myocarditis (AFM) may represent a life-threatening event, characterized by rapidly progressive cardiac compromise that ultimately leads to refractory cardiogenic shock or cardiac arrest. Venoarterial extracorporeal membrane oxygenation (VA-ECMO) provides effective cardiocirculatory support in this circumstance, but few clinical series are available about early and long-term results. Data from a multicenter study group are reported which analyzed subjects affected by AFM and treated with VA-ECMO during a 5-year period

The issue of acid dissociation of nitric acid at an aqueous surface is relevant in various portions of the atmosphere in connection with ozone depletion. This proton-transfer reaction is studied here via electronic structure calculations at the HF/SBK+(d) level of theory on the HNO(3) x (H(2)O)(3) model reaction system embedded in clusters comprising 33, 40, 45, and 50 classical, polarizable waters with an increasing degree of solvation of the nitrate group. Free energy estimates for all the cases examined favor undissociated, molecular nitric acid over the 0-300 K temperature range, including that relevant for the upper troposphere, where it is connected to the issue of the mechanism of nitric acid uptake by water ice aerosols. The presence of molecular HNO(3) at 300 K at the surface is further supported by vibrational band assignments in good agreement with a very recent surface-sensitive vibrational spectroscopy study of diluted HNO(3)/H(2)O solutions.

Gas-phase alkali-metal halide dissociation is inÑuenced by the crossing of the covalent and ionic potential-energy surfaces at a certain internuclear separation, leading to interesting dynamical e †ects. The dissociation fragments for e.g. NaI may be trapped in a well formed by the avoided crossing of the covalent and ionic surfaces, and then undergo a non-adiabatic curve crossing transition to form atomic products. On the other hand, ionic products are stabilized by a polar environment and might be energetically accessible in solution. More generally, the photodissociation dynamics could be inÑuenced by the solvent. A theoretical study of NaI photodissociation in a weakly polar solvent is presented here to explore the mechanism and timescale by which the ions are produced subsequent to photoexcitation. A solution-phase valence-bond resonance theory predicts that the diabatic ionic and covalent solution Gibbs free energy curves do not cross in the equilibrium solvation regime, such that atomic products would result. When considering non-equilibrium solvation and dynamical e †ects, the theory indicates the short-time dissociation products in solution to be atoms, but that on the ms timescale they could convert to ions by activated inverted regime electron transfer (ET). However, the radiative lifetime is estimated to be much shorter (Bns) than this timescale, so that in fact no excited state ET is expected. Instead, the formation of ions proceeds by radiative deactivation of the photoexcited NaI and is followed by ionic recombination on the ground-state surface. Nevertheless it is estimated that the photodissociation of NaI in small clusters may proceed via activated ET and lead to some ionic dissociation products.

Tissue-engineered heart valves are proposed as novel viable replacements granting longer durability and growth potential. However, they require extensive in vitro cell-conditioning in bioreactor before implantation. Here, the propensity of non-preconditioned decellularized heart valves to spontaneous in body self-regeneration was investigated in a large animal model. Decellularized porcine aortic valves were evaluated for right ventricular outflow tract (RVOT) reconstruction in Vietnamese Pigs (n = 11) with 6 (n = 5) and 15 (n = 6) follow-up months. Repositioned native valves (n = 2 for each time) were considered as control. Tissue and cell components from explanted valves were investigated by histology, immunohistochemistry, electron microscopy, and gene expression. Most substitutes constantly demonstrated in vivo adequate hemodynamic performances and ex vivo progressive repopulation during the 15 implantation months without signs of calcifications, fibrosis and/or thrombosis, as revealed by histological, immunohistochemical, ultrastructural, metabolic and transcriptomic profiles. Colonizing cells displayed native-like phenotypes and actively synthesized novel extracellular matrix elements, as collagen and elastin fibers. New mature blood vessels, i.e. capillaries and vasa vasorum, were identified in repopulated valves especially in the medial and adventitial tunicae of regenerated arterial walls. Such findings correlated to the up-regulated vascular gene transcription. Neoinnervation hallmarks were appreciated at histological and ultrastructural levels. Macrophage populations with reparative M2 phenotype were highly represented in repopulated valves. Indeed, no aspects of adverse/immune reaction were revealed in immunohistochemical and transcriptomic patterns. Among differentiated elements, several cells were identified expressing typical stem cell markers of embryonic, hematopoietic, neural and mesenchymal lineages in significantly higher number and specific topographic distribution in respect to control valves. Following the longest follow-up ever realized in preclinical models, non-preconditioned decellularized allogeneic valves offer suitable microenvironment for in vivo cell homing and tissue remodeling. Manufactured with simple, timesaving and cost-effective procedures, these promising valve replacements hold promise to become an effective alternative, especially for pediatric patients.