Gas Phase Hydrolysis and Oxo-Exchange of Actinide Dioxide Cations: Elucidating Intrinsic Chemistry from Protactinium to Einsteinium

Gas-phase bimolecular reactions of metal cations with water provide insights into intrinsic characteristics of hydrolysis. For the actinide dioxide cations, actinyl(V) AnO₂⁺, melding of experiment and computation provides insights into trends for hydrolysis, as well as for oxo-exchange between actinyls and water that proceeds by a hydrolysis pathway. Here this line of inquiry is further extended into the actinide series with CCSD(T) computations of potential energy surfaces, for the reaction pathway for oxo-exchange through hydrolysis of nine actinyl(V) ions, from PaO₂⁺ to EsO₂⁺. The computed surfaces are in accord with previous experimental results for oxo-exchange, and furthermore predict spontaneous exchange for CmO₂⁺, BkO₂⁺, CfO₂⁺ and EsO₂⁺, but not for AmO₂⁺. Natural Bond Order analysis of the species involved in both hydrolysis and oxo-exchange reveals an inverse correlation between the barrier to hydrolysis and the charge on the actinide centre, q(An). Based on this correlation, it can be concluded that hydrolysis, and related phenomena such as oxo-exchange, become less favourable as the charge on the metal centre decreases. The new results provide a straightforward rationalization of trends across a wide swathe of the actinide series.     

Universal Trends between Acid Dissociation Constants in Protic and Aprotic Solvents

pKa values in non-aqueous solvents are of critical importance in many areas of chemistry. Our knowledge is, despite their relevance, still limited to the most fundamental properties and few pKa values in the most common solvents. Taking advantage of a recently introduced computationally efficient procedure we computed the pKa values of 182 compounds in 21 solvents. This data set is used to establish for the first time universal trends between all solvents. Our computations indicate, that the total charge of the molecule and the charge of the acidic group combined with the Kamlet-Taft solvatochromic parameters are sufficient to predict pKa values with at least semi- quantitative accuracy. We find, that neutral acids such as alcohols are strongly affected by the solvent properties. This is contrasted by cationic acids like ammonium ions whose pKa is often almost completely independent from the choice of solvent.     

Diamond Ice

The bounded version of the ice model of statistical mechanics is studied. We consider it in a diamond domain on the Z ²-lattice. The configurations sharing a boundary configuration are shown to be connected under simple loop perturbations. This enables an efficient generation of the configurations with a probabilistic cellular automaton. The fill-in from the boundary is critically dependent on the values of the height function along the boundary. We characterize the phenomena at the extrema of this function as well as in some highly nontrivial cases where results analogous to and more complex than the Arctic Circle Theorem for dominoes hold.     

Lactose oxidation over palladium catalysts supported on active carbons and on carbon nanofibres

Liquid-phase lactose oxidation was investigated over supported Pd/C and Pd-carbon nanofibre catalysts, which were characterized by several methods. A complex relationship between catalyst activity and catalyst acidity was established, i.e. optimum catalyst acidity resulted in the highest activity in lactose oxidation. In-situ catalyst potential measurements during lactose oxidation gave information about the extent of accumulation of oxygen on the metal surface. These results could be correlated with catalyst deactivation, which was extensive over the most acidic catalysts at low reaction temperatures. Selectivity for the desired product, lactobionic acid, was a maximum of approximately 83% at 93% conversion. The main side-product was lactulose formed via isomerisation of lactose. Lower selectivity toward lactobionic acid was obtained when the rate of oxidation of lactose was low.     

Rapid generation of an anthrax immunotherapeutic from goats using a novel non-toxic muramyl dipeptide adjuvant

Background  

There is a clear need for vaccines and therapeutics for potential biological weapons of mass destruction and emerging diseases. Anthrax, caused by the bacterium Bacillus anthracis, has been used as both a biological warfare agent and bioterrorist weapon previously. Although antibiotic therapy is effective in the early stages of anthrax infection, it does not have any effect once exposed individuals become symptomatic due to B. anthracis exotoxin accumulation. The bipartite exotoxins are the major contributing factors to the morbidity and mortality observed in acute anthrax infections.     

Thrust distribution and decays of the ϒ bound states

We have studied the topologies of hadronic events in e⁺e^- annihilation data taken in the region of the upsilon resonances with the non-magnetic CUSB detectors at CESR. Using a thrust-like variable we compare the decay of ?, ?′ and ?Prime; find for ?″ a significant excess of high thrust events, which we interpret as evidence for electric dipole transitions.     

Point defects and diffusion in NiO

A defect model for NiO is developed and is fit to the electrical-conductivity data [26], the deviation-from-stoichiometry data [7], and the cation-self-diffusion data [14, 17]. This model involves neutral, singly charged, and doubly charged nickel vacancies and charge-compensating electron holes. Both singly and doubly charged cation vacancies are required to explain the data; neutral cation vacancies (if present) are not required by the present data. However, the jump frequencies of the two types of charged cation vacancies are generally not equal; the doubly charged cation vacancy moves with the smaller activation enthalpy. The defect data are quantitatively consistent with the chemical-diffusion data [26] and with a correlation factor?v = 0.75.