Phosphinimines as potential technetium environmental sensors

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file (viewed on September 4, 2007)Vita.Includes bibliographical references.Thesis (Ph. D.) University of Missouri-Columbia 2007.Dissertations, Academic -- University of Missouri--Columbia -- Chemistry.Phosphinimines, R₃P=NSiMe₃, undergo hydrolysis to form the phosphiniminiumcation, R₃P=NH₂+, which forms the ion pair [R₃P=NH₂+][X-] in the presence of an anion.Preliminary studies show that in the presence of TcO₄-, Ph₃P=NSiMe₃ forms [Ph₃P=NH₂+][TcO₄-] and [Ph₃P=NH₂+] is selective for TcO₄- over other anions.Technetium-99 is present as environmental contamination in the form of ⁹⁹TcO₄-, which is extremely mobile. Currently available methods to measure this contamination are time consuming and tedious. A method to preconcentrate and measure ⁹⁹Tc environmental contamination in a quick and efficient manner is needed. The selectivity of the phosphiniminium cation for TcO₄- may make phosphinimines suitable for such preconcentration and possibly for measurement. Several phosphinimines were synthesized and characterized for their stability and selectivity with ⁹⁹TcO₄-, including Ph₃P=NSiMe₃, (9-anthracenyl)Ph₂P=NSiMe₃, (1-napthyl)Ph₂P=NSiMe₃, and (p-COOMe)C₆H₄Ph₂P=NSiMe₃. (9-anthracenyl)Ph₂P=NSiMe₃ and (1-napthyl)Ph₂P=NSiMe₃ include possible reporter groups and (p-COOMe)C₆H₄Ph₂P=NSiMe₃ contains a linking moiety for incorporating reporter groups or attaching the phosphinimine to a polymer support. The use of internal and external reporter groups to generate a signal in the presence of TcO₄- is also investigated

Uranium: The problem, or the solution?

Abstract only availableUranium is of great importance as a nuclear fuel and is used to generate electrical power, produce isotopes, and to make weapons. The possibility of developing a realistic flow scheme for nuclear fuel reprocessing or separation for segregation is one that the Chemistry Department at MU consistently looks into. One way to better optimize waste extraction is to possibly bind two separate functional groups to uranyl(VI) [UO22+] so that the reactions will occur selectively. The product of interest is a mixed uranyl iodide/amide and is a novel uranium compound generated for further study. This is accomplished with the following reactions. UO3 --TfOTf--- UO2(OTf)2 UO2I2(THF)3 + 2KOTfUO2(OTf)2 + 2KI ---THF---- UO2I[N(SiMe3)] + KIUO2I2(THF)3 + K[N(SiMe3)3] ----THF- After completing the reactions under an inert atmosphere, an orange product formed. The next step in this research requires NMR analysis and X-Ray crystallography to determine if this product is the target molecule desired.NSF-REU Radiochemistr

Physical controls on the macrofaunal benthic biomass in Barrow Canyon, Chukchi Sea

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(5), (2021): e2020JC017091, https://doi.org/10.1029/2020JC017091.A region of exceptionally high macrofaunal benthic biomass exists in Barrow Canyon, implying a carbon export process that is locally concentrated. Here we offer an explanation for this benthic “hotspot” using shipboard data together with a set of dynamical equations. Repeat occupations of the Distributed Biological Observatory transect in Barrow Canyon reveal that when the northward flow is strong and the density front in the canyon is sharp, plumes of fluorescence and oxygen extend from the pycnocline to the seafloor in the vicinity of the hotspot. By solving the quasi-geostrophic omega equation with an analytical flow field fashioned after the observations, we diagnose the vertical velocity in the canyon. This reveals that, as the along stream flow converges into the canyon, it drives a secondary circulation cell with strong downwelling on the cyclonic side of the northward flow. The downwelling quickly advects material from the pycnocline to the seafloor in a vertical plume analogous to those seen in the observations. The plume occurs only when the phytoplankton reside in the pycnocline, since the near-surface vertical velocity is weak, also consistent with the observations. Using a wind-based proxy to represent the strength of the northward flow and hence the pumping, in conjunction with a satellite-derived phytoplankton source function, we construct a time series of carbon supply to the bottom of Barrow Canyon.This work was funded by National Science Foundation grants PLR-1504333 and OPP-1733564 (Robert S. Pickart, Frank Bahr), OPP-1822334 (Michael A. Spall), PLR-1304563 (Kevin R. Arrigo), OPP-1204082 and OPP-1702456 (Jacqueline M. Grebmeier); National Oceanic and Atmospheric Administration grants NA14OAR4320158 and NA19OAR4320074 (Robert S. Pickart, Peigen Lin, Leah T. McRaven), CINAR-22309.02 (Jacqueline M. Grebmeier)

Viral adaptation to immune selection pressure by HLA class I–restricted CTL responses targeting epitopes in HIV frameshift sequences

CD8+ cytotoxic T lymphocyte (CTL)–mediated immune responses to HIV contribute to viral control in vivo. Epitopes encoded by alternative reading frame (ARF) peptides may be targeted by CTLs as well, but their frequency and in vivo relevance are unknown. Using host genetic (human leukocyte antigen [HLA]) and plasma viral sequence information from 765 HIV-infected subjects, we identified 64 statistically significant (q < 0.2) associations between specific HLA alleles and sequence polymorphisms in alternate reading frames of gag, pol, and nef that did not affect the regular frame protein sequence. Peptides spanning the top 20 HLA-associated imprints were used to test for ex vivo immune responses in 85 HIV-infected subjects and showed responses to 10 of these ARF peptides. The most frequent response recognized an HLA-A*03–restricted +2 frame–encoded epitope containing a unique A*03-associated polymorphism at position 6. Epitope-specific CTLs efficiently inhibited viral replication in vitro when viruses containing the wild-type sequence but not the observed polymorphism were tested. Mutating alternative internal start codons abrogated the CTL-mediated inhibition of viral replication. These data indicate that responses to ARF-encoded HIV epitopes are induced during natural infection, can contribute to viral control in vivo, and drive viral evolution on a population level

PRex: an experiment to investigate detection of near-field particulate deposition from a simulated underground nuclear weapons test vent

A radioactive particulate release experiment to produce a near-field ground deposition representative of small-scale venting from an underground nuclear test was conducted to gather data in support of treaty capability development activities. For this experiment, aCO₂‐driven “air cannon” was used to inject ¹⁴⁰La, a radioisotope of lanthanum with 1.7‐d half-life and strong gamma-ray emissions, into the lowest levels of the atmosphere at ambient temperatures.Witness plates and air samplers were laid out in an irregular grid covering the area where the plume was anticipated to deposit based on climatological wind records. This experiment was performed at the Nevada National Security Site, where existing infrastructure, radiological procedures, and support personnel facilitated planning and execution of the work. A vehicle-mounted NaI(Tl) spectrometer and a polyvinyl toluene-based backpack instrument were used to survey the deposited plume. Hand-held instruments, including NaI(Tl) and lanthanum bromide scintillators and high purity germanium spectrometers, were used to take in situ measurements. Additionally, three soil sampling techniques were investigated and compared. The relative sensitivity and utility of sampling and survey methods are discussed in the context of on-site inspection.Keywords: environmental transport, airborne, radioactivity, atomic bomb, accidents, transpor

Fiscal Year 2012

Accurate and timely analysis of plutonium in spent nuclear fuel is critical in nuclear safeguards for detection of both protracted and rapid plutonium diversions. Gamma spectroscopy is a viable method for accurate and timely measurements of plutonium provided that the plutonium is well separated from the interfering fission and activation products present in spent nuclear fuel. Electrochemically modulated separation (EMS) is a method that has been used successfully to isolate picogram amounts of Pu from nitric acid matrices. With EMS, Pu adsorption may be turned “on” and “off” depending on the applied voltage, allowing for collection and stripping of Pu without the addition of chemical reagents. In this work, we have scaled up the EMS process to isolate microgram quantities of Pu from matrices encountered in spent nuclear fuel during reprocessing. Several challenges have been addressed including surface area limitations, radiolysis effects, electrochemical cell performance stability, and chemical interferences. After these challenges were resolved, 6 µg Pu was deposited in the electrochemical cell with approximately an 800-fold reduction of fission and activation product levels from a spent nuclear fuel sample. Modeling showed that these levels of Pu collection and interference reduction may not be sufficient for Pu detection by gamma spectroscopy. The main remaining challenges are to achieve a more complete Pu isolation and to deposit larger quantities of Pu for successful gamma analysis of Pu. If gamma analyses of Pu are successful, EMS will allow for accurate and timely on-site analysis for enhanced Pu safeguards

Structure and Bonding Investigation of Plutonium Peroxocarbonate Complexes Using Cerium Surrogates and Electronic Structure Modeling

Herein, we report the synthesis and structural characterization of K₈[(CO₃)₃Pu]₂(μ-η²-η²-O₂)₂·12H₂O. This is the second Pu-containing addition to the previously studied alkali-metal peroxocarbonate series M₈[(CO₃)₃A]₂(μ-η²-η²-O₂)₂·<i>x</i>H₂O (M = alkali metal; A = Ce or Pu; <i>x</i> = 8, 10, 12, or 18), for which only the M = Na analogue has been previously reported when A = Pu. The previously reported crystal structure for Na₈[(CO₃)₃Pu]₂(μ-η²-η²-O₂)₂·12H₂O is not isomorphous with its known Ce analogue. However, a new synthetic route to these M₈[(CO₃)₃A]₂(μ-η²-η²-O₂)₂·12H₂O complexes, described below, has produced crystals of Na₈[(CO₃)₃Ce]₂(μ-η²-η²-O₂)₂·12H₂O that <i>are</i> isomorphous with the previously reported Pu analogue. Via this synthetic method, the M = Na, K, Rb, and Cs salts of M₈[(CO₃)₃Ce]₂(μ-η²-η²-O₂)₂·<i>x</i>H₂O have also been synthesized for a systematic structural comparison with each other and the available Pu analogues using single-crystal X-ray diffraction, Raman spectroscopy, and density functional theory calculations. The Ce salts, in particular, demonstrate subtle differences in the peroxide bond lengths, which correlate with Raman shifts for the peroxide O_p–O_p stretch (O_p = O atoms of the peroxide bridges) with each of the cations studied: Na⁺ [1.492(3) Å/847 cm^–1], Rb⁺ [1.471(1) Å/854 cm^–1], Cs⁺ [1.474(1) Å/859 cm^–1], and K⁺ [1.468(6) Å/870 cm^–1]. The trends observed in the O_p–O_p bond distances appear to relate to supermolecular interactions between the neighboring cations

FY 2009 Progress: Process Monitoring Technology Demonstration at PNNL

Pacific Northwest National Laboratory (PNNL) is developing and demonstrating three technologies designed to assist in the monitoring of reprocessing facilities in near-real time. These technologies include 1) a multi-isotope process monitor (MIP), 2) a spectroscopy-based monitor that uses UV-Vis-NIR (ultraviolet-visible-near infrared) and Raman spectrometers, and 3) an electrochemically modulated separations approach (EMS). The MIP monitor uses gamma spectroscopy and pattern recognition software to identify off-normal conditions in process streams. The UV-Vis-NIR and Raman spectroscopic monitoring continuously measures chemical compositions of the process streams including actinide metal ions (uranium, plutonium, neptunium), selected fission products, and major cold flow sheet chemicals. The EMS approach provides an on-line means for separating and concentrating elements of interest out of complex matrices prior to detection via nondestructive assay by gamma spectroscopy or destructive analysis with mass spectrometry. A general overview of the technologies and ongoing demonstration results are described in this report