Environmental plutonium: Reference states and alpha coefficients

The results of plutonium oxidation state distribution calculations do not depend on special attention to any oxidation state as has been incorrectly supposed in some literature sources. Experimentally determined alpha coefficients for natural water could make the distribution of environmental plutonium easy to estimate with a programmable pocket calculator.Mound is operated for the U.S. Department of Energy by EG&G Mound Applied Technologies, Inc., under Contract No. DE-AC04-88DP43495.     

Continuous removal of radioactive cobalt from water

More than 99% of radioactive cobalt can be removed from water by precipitation as cobalt/III/ hydroxide. The process is continuous and uses either sodium hypochlorite or oxygen and calcium sulfite to oxidize the cobalt. Carbonate and phosphate interfere with cobalt removal, but the process has potential for other applications such as thallium removal and sewage treatment.Mound is operated by Monsanto Research Corporation for the U.S. Department of Energy under Contract No. DE-AC04-76-DP00053.     

Environmental plutonium: What is the redox potential of seawater?

The potential of seawater has recently been reported as 0.8 V. This number conflicts with many literature sources on oceanography.Mount is operated for the U.S. Department of Energy by EG&G Mound Applied Technologies Incorporated under contract No. DE-AC04-88DP43495.     

Charge balance vs. charge conservation for plutonium

A recent paper about plutonium disproportionation confuses charge balance with charge conservation. To explain disproportionation, impossible solutions in which the charges do not balance were proposed.Mound is operated for the U. S. Department of Energy by EG & G Mound Applied Technologies Incorporated under Contract NO. DE-AC04-88DP43495.     

Work integrals for plutonium

Free energy changes in Pu disproportionation reactions can be measured by integrating the reaction isotherm with respect to one of the reaction products. Separate integrations can be made for the isotherms of the component reactions contributing to the equilibrium.Mound is operated for the U.S. Department of Energy by EG&G Mound Applied Technologies Incorporated under contract No. DE-AC04-88DP43495.     

Charge balance equations for plutonium

Charge balance equations can be used to obtain relationships among oxidation states in plutonium solutions. These equations are prepared from the initial conditions in the solution; they can be checked using equations of mass and charge conservation.Mound is operated for the U. S. Department of Energy by EG&G Mound Applied Technologies, Inc., under Contract No. DE-AC04-88DP43495.     

The ratio Pu(V)/Pu(IV) in natural water

The behavior of the ratio Pu(V)/Pu(IV) depends on whether the symbols represent absolute concentrations of soluble species, or fractions of the total soluble plutonium, or insoluble, colloidal substances.Mound is operated by EG&G Mound Applied Technologies for the U.S. Department of Energy under Contract No. DE-AC04-88DP43495.     

Potentiometric titration of plutonium

In the potentiometric titration of plutonium(III), it has been customary to take the equivalence point as the inflection point on a plot of potential vs. volume of titrant.¹ That the stoichiometric end point corresponds to the inflection point does not seem to have been theoretically demonstrated, however. The purpose of this letter is to suggest that these points may not correspond in the potentiometric titration of plutonium(III). Mound Laboratory is operated by Monsanto Research Corporation for USERDA under contract No. EY-76-C-04-0053.     

Molecular dynamics simulation of liquid water and ice nanoclusters using a new effective HFD‐like model

We have determined a new two‐body interaction potential of water by the inversion of viscosity collision integrals of water vapor and fitted to achieve the Hartree–fock dispersion‐like (HFD‐like) potential function. The calculated two‐body potential generates the thermal conductivity, viscosity, and self‐diffusion coefficient of water vapor in an excellent accordance with experimental data at wide temperature ranges. We have also used a new many‐body potential as a function of temperature and density with the HFD‐like pair‐potential of water to improve the two‐body properties better than the SPC, SPC/E, TIP3P, and TIP4P models. We have also used the new corrected potential to simulate the configurational energy and the melting temperatures of the (H₂O)₅₀₀, (H₂O)₈₆₄, (H₂O)₂₀₄₈, and (H₂O)₆₉₁₂ ice nanoclusters in good agreement with the previous simulation data using the TIP4P model. The extrapolated melting point at the bulk limit is also in better agreement with the experimental bulk data. The self‐diffusion coefficients for the ice nanoclusters also simulated at different temperatures. © 2017 Wiley Periodicals, Inc.     

Extension of CAVS coarse‐grained model to phospholipid membranes: The importance of electrostatics

It is evident from experiment that electrostatic potential (or dipole potential) is positive inside PC or PE lipid bilayers in the absence of ions. MARTINI coarse‐grained (CG) model, which has been widely used in simulating physical properties of lipid bilayers, fails to reproduce the positive value for the dipole potential in the membrane interior. Although the total dipole potential can be correctly described by the BMW/MARTINI model, the contribution from the ester dipoles, playing a nontrivial role in the electrostatic potential across lipid membranes, is neglected by this hybrid approach. In the ELBA CG model, the role of the ester dipoles is considered, but it is overweighed because various atomistic models have consistently shown that water is actually the leading contributor of dipole potential. Here, we present a CG approach by combining the BMW‐like water model (namely CAVS model) with the ELBA‐like lipid model proposed in this work. Our CG model was designed not only to correctly reproduce the positive values for the dipole potential inside PC and PE lipid bilayers but also to properly balance the individual contributions from the ester dipoles and water, surmounting the limitations of current CG models in the calculations of dipole potential. © 2017 Wiley Periodicals, Inc.     

Electron and positron elastic scattering in gaseous and liquid water: A comparative study

In the present work, we present both theoretical differential and total cross sections for the elastic scattering process of positrons and electrons in liquid and vapour water for energies ranging from 10 eV to 10 keV. The calculations are performed in the partial-wave formalism by means of a complex interaction potential taking into account static potential as well as fine effects like exchange and polarization contributions. The theoretical results obtained in this free-parameter quantum-mechanical treatment are compared to available experimental data and good agreement is generally observed. Moreover, quantitative differences are reported between the positron and electron scattering, in vapour as well as in liquid water.     

Formation of plutonium/IV/ colloid from plutonyl cations

Solutions of plutonyl cations in dilute acids gradually form Pu/IV/ polymer under the influence of alpha radiations. These systems have properties that can be illuminated by assuming conditions to be near equilibrium and constrained by mass conservation.Mound is operated by Monsanto Research Corporation for the U.S. Department of Energy under Contract DE-AC04-76-DP00053.     

Photodynamic Inactivation of Bacteria in Ionic Environments Using the Photosensitizer SAPYR and the Chelator Citrate†

Many studies show that photodynamic inactivation (PDI) is a powerful tool for the fight against pathogenic, multiresistant bacteria and the closing of hygiene gaps. However, PDI studies have been frequently performed under standardized in vitro conditions comprising artificial laboratory settings. Under real-life conditions, however, PDI encounters substances like ions, proteins, amino acids and fatty acids, potentially hampering the efficacy of PDI to an unpredictable extent. Thus, we investigated PDI with the phenalene-1-one-based photosensitizer SAPYR against Escherichia coli and Staphylococcus aureus in the presence of calcium or magnesium ions, which are ubiquitous in potential fields of PDI applications like in tap water or on tissue surfaces. The addition of citrate should elucidate the potential as a chelator. The results indicate that PDI is clearly affected by such ubiquitous ions depending on its concentration and the type of bacteria. The application of citrate enhanced PDI, especially for Gram-negative bacteria at certain ionic concentrations (e.g. CaCl₂ or MgCl₂: 7.5 to 75 mmol L⁻¹). Citrate also improved PDI efficacy in tap water (especially for Gram-negative bacteria) and synthetic sweat solution (especially for Gram-positive bacteria). In conclusion, the use of chelating agents like citrate may facilitate the application of PDI under real-life conditions.     

Activation of uranium metal

Treatment of uranium with hydrochloric or hydrobromic acid produces an adherent layer of hydride on the metal surface. When this hydride is decomposed by heat in a vacuum, the resulting metal surface reacts immediately with hydrogen at ambient temperature.Mound is operated by Monsanto Researh Corporation for the U.S. Department of Energy under Contract No. DE-AC04-76-DP00053.     

Plutonium valence state distributions

A method for ascertaining equilibrium valence state distributions of plutonium in acid solutions as a function of the plutonium oxidation number and the solution acidity is illustrated with an example. The method may be more practical for manual use than methods based upon polynomial equations. Mound Laboratory is operated by Monsanto Research Corporation for the U.S. Atomic Energy Commission under Contract No. AT-33-1-GEN-53.     

The study of the electrochemical oxidation mechanism of diphenylamine derivatives in dipolar aprotic solvents: III. Effect of acids and bases of different strengths

The effect of addition of different acids and bases in a wide range of concentration on the voltammetric oxidation of both Variamine blue (VB) and 4-aminodiphenylamine (4-ADPA) was examined in acetonitrile (AcN). The oxidation potential values of either wave of both depolarizers were found to depend on the acid or base strength of the additive—relative to the depolarizer and solvent—and on their concentration in solution. Addition of strong acid as CH₃SO₃H resulted in a single oxidation wave at potentials either equal to or more positive than that of the original second wave. Relatively weak acids as picric and pyridinium ion only shifted the oxidation potential of the first wave to more positive values without affecting the general oxidation pattern.On the other hand, strong bases like ethanolamine, resulted in the formation of a preoxidation wave at more negative potential when present in low concentration and a single wave at identical negative potential at high enough concentrations. Bases of comparable strengths, as that of the depolarizer, like pyridine do not form prewaves but only shifted the final single oxidation wave to more negative potential values. Weaker bases like water and ethanol mainly shifted the oxidation potential of the second wave to less positive values.     

Health risk assessment of heavy metals and their source apportionment in drinking water of Kohistan region, northern Pakistan

The present study was conducted to investigate heavy metal (Cu, Co, Cr, Mn, Ni, Pb, Zn and Cd) concentrations of drinking water (surface water and groundwater) samples in Kohistan region, northern Pakistan. Furthermore, the study aimed to ascertain potential health risk of heavy metal (HM) concentrations to local population. HM concentrations were analyzed by using graphite furnace atomic absorption spectrometer (Perkin Elmer, AAS-PEA-700) and were compared with permissible limits set by Pakistan Environmental Protection Agency (Pak EPA) and World Health Organization (WHO). Based on HM concentrations the health risk assessment like chronic daily intake (CDI) and hazard quotient (HQ) was calculated. The values for CDI were found in the order of Zn > Cu > Mn > Pb > Cr > Ni > Cd > Co and the values of HQ were < 1 for all HM in drinking water samples indicating no health risk. Furthermore, multivariate statistical analysis like one-way ANOVA, inter-metal correlation, cluster analysis (CA) and principal component analysis (PCA) results revealed that geogenic and anthropogenic activities were major sources of water contamination in Kohistan region.     

An octanol hinge opens the door to water transport

Despite their prevalent use as a surrogate for partitioning of pharmacologically active solutes across lipid membranes, the mechanism of transport across water/octanol phase boundaries has remained unexplored. Using molecular dynamics, graph theoretical, cluster analysis, and Langevin dynamics, we reveal an elegant mechanism for the simplest solute, water. Self-assembled octanol at the interface reversibly binds water and swings like the hinge of a door to bring water into a semi-organized second interfacial layer (a “bilayer island”). This mechanism is distinct from well-known lipid flipping and water transport processes in protein-free membranes, highlighting important limitations in the water/octanol proxy. Interestingly, the collective and reversible behavior is well-described by a double well potential energy function, with the two stable states being the water bound to the hinge on either side of the interface. The function of the hinge for transport, coupled with the underlying double well energy landscape, is akin to a molecular switch or shuttle that functions under equilibrium and is driven by the differential free energies of solvation of H₂O across the interface. This example successfully operates within the dynamic motion of instantaneous surface fluctuations, a feature that expands upon traditional approaches toward controlled solute transport that act to avoid or circumvent the dynamic nature of the interface.

Despite their pharmacological relevance, the mechanism of transport across water/octanol phase boundaries has remained unexplored. Octanol molecular assemblies are demonstrated to reversibly bind water and swing like the hinge of a door.     

A reoptimization of the five-site water potential (TIP5P) for use with Ewald sums

The five-site transferable interaction potential (TIP5P) for water is most accurate at reproducing experimental data when used with a simple spherical cutoff for the long-ranged electrostatic interactions. When used with other methods for treating long-ranged interactions, the model is considerably less accurate. With small modifications, a new TIP5P-like potential can be made which is very accurate for liquid water when used with Ewald sums, a more physical and increasingly more commonly used method for treating long-ranged electrostatic interactions. The new model demonstrates a density maximum near 4 degrees C, like the TIP5P model, and otherwise is similar to the TIP5P model for thermodynamic, dielectric, and dynamical properties of liquid water over a range of temperatures and densities. An analysis of this and other commonly used water models reveals how the quadrupole moment of a model can influence the dielectric response of liquid water.