Neptunium(IV)-Hydroxamate Complexes:Their Speciation, and Kinetics and Mechanism of Hydrolysis

Simple hydroxamic acids such as acteohydroxamic acid (AHA) have been identified as suitable reagents for the control of Pu and Np in advanced separation processes for nuclear fuel reprocessing such as the Advanced PUREX or UREX based recycle processes, due to their ability to strip the tetravalent form of Pu and Np from tri-butyl phosphate into nitric acid. However, both free and metal bound hydroxamates are known to undergo acid catalysed hydrolysis at low pH, the kinetics of which must be characterised before implementation of PUREX/UREX based reprocessing flowsheets. In support of this implementation, a comprehensive thermodynamic and kinetic model that describes both the complex speciation and hydrolysis of AHA in the presence of Np(IV) has been developed. The model has two unique features: (i) in the case of the hydrolysis reaction kinetics, the model includes the hydrolysis of not only free AHA but also both the mono- and bishydroxamato-Np(IV) complexes; (ii) for the associated speciation calculations, the model explicitly includes the ionic strength dependence of not only the mono- and bishydroxamato-Np(IV) complexes but also the mono- and bisnitrato neptunium(IV) and monohydroxoneptunium(IV) complexes. For the latter three species, respective SIT coefficients of Δε1,NO3 = −0.13 ± 0.03 kg mol−1, Image ID:c8dt02194e-t1.gif, Δε2,NO3 = −0.37 ± 0.13 kg mol−1, Image ID:c8dt02194e-t2.gif Δε1,OH = −0.36 kg mol−1 and log10 K01,OH = −1.23 were also determined. Using experimental data from a series of kinetic studies on the Np(IV)–AHA system, this model has been used to determine the rate constants for hydrolysis of mono– and bis–acetohydroxamatoneptunium(IV) at 25 °C for the first time. These were found to be 3.5 × 10−5 ± 2.5 × 10−5 dm3 mol−1 s−1 and 1.9 × 10−3 ± 1.3 × 10−3 dm3 mol−1 s−1, respectively. Comparison of these values with the rate constants for hydrolysis of free AHA indicates that complexation of AHA with Np(IV) increases the rate of hydroxamate hydrolysis – an observation that we attribute to the electron withdrawing effect of the metal centre within the Np(IV)–AHA complex increasing the susceptibility of the AHA carbonyl carbon to nucleophilic attack, the accepted first step in its mechanism of hydrolysis

An Association of Multiple Well Differentiated Liposarcomas, Lipomatous Tissue and Hereditary Retinoblastoma

Well differentiated liposarcoma (atypical lipomatous tumour) is a low grade tumour, with no metastatic potential unless dedifferentiation supervenes. When superficial, it recurs locally only occasionally after marginal excision. We present a patient in whom bilateral childhood retinoblastoma was followed by later development of massive confluent areas of low grade liposarcoma and lipomatous tissue affecting the upper extremities and trunk. We discuss the role of mutations in the retinoblastoma gene (RB1) in linking these conditions and demonstrate the surgical management of an extremely unusual and challenging case

The Separation of 241

Electrical power sources used in outer planet missions are a key enabling technology for data acquisition and communications. State–of-the-art power sources generate electricity from alpha decay of 238Pu via thermoelectric conversion. However, production of 238Pu requires specialist facilities including a nuclear reactor, a source of 237Np for target irradiation and hotcells to chemically separate neptunium and plutonium within the irradiated targets. These specialist facilities are expensive to build and operate, so naturally, a more economical alternative is attractive to the industry. Within Europe 241Am is considered a promising alternative heat source for radioisotope thermoelectric generators (RTGs) and radioisotope heating units (RHUs). As a daughter product of 241Pu decay, 241Am exists in 1000 kgs quantities within the UK civil plutonium stockpile. A chemical separation process is required to extract the 241Am in a pure form and this paper describes the AMPPEX process (Americium and Plutonium Purification by Extraction), successfully developed over the past five years to isolate 241Am in high yield (> 99%) and to a high purity (> 99%). The process starts by dissolving plutonium dioxide in nitric acid with the aid of a silver(II) catalyst, which is generated electrochemically. The solution is then conditioned and fed to a PUREX type solvent extraction process, where the plutonium is separated from the americium and silver. The plutonium is converted back to plutonium dioxide and the americium is fed forward to a second solvent extraction step. Here the americium is selectively extracted leaving the silver in the aqueous phase. The americium is stripped from the solvent and recovered from solution as americium oxalate, which is calcined to give americium dioxide as the final product. This paper will describe the development of the separation process over a series of six solvent extraction separation trials using centrifugal contactors. The material produced (~ 4g 241Am) was used to make ceramic pellets to establish the behaviour of americium oxide material under high temperature (1450°C) sintering conditions. The chemical separation process is now demonstrated at concentrations expected on the full scale facility taking this process to TRL 4-5

Control of Oxo-Group Functionalization and Reduction of the Uranyl Ion

yesUranyl complexes of a large, compartmental N8-macrocycle adopt a rigid, “Pacman” geometry that stabilizes the UV oxidation state and promotes chemistry at a single uranyl oxo-group. We present here new and straightforward routes to singly reduced and oxo-silylated uranyl Pacman complexes and propose mechanisms that account for the product formation, and the byproduct distributions that are formed using alternative reagents. Uranyl(VI) Pacman complexes in which one oxo-group is functionalized by a single metal cation are activated toward single-electron reduction. As such, the addition of a second equivalent of a Lewis acidic metal complex such as MgN″2 (N″ = N(SiMe3)2) forms a uranyl(V) complex in which both oxo-groups are Mg functionalized as a result of Mg−N bond homolysis. In contrast, reactions with the less Lewis acidic complex [Zn(N″)Cl] favor the formation of weaker U−O−Zn dative interactions, leading to reductive silylation of the uranyl oxo-group in preference to metalation. Spectroscopic, crystallographic, and computational analysis of these reactions and of oxo-metalated products isolated by other routes have allowed us to propose mechanisms that account for pathways to metalation or silylation of the exo-oxogroup

What can we learn from learning analytics? A case study based on an analysis of student use of video recordings

Over recent years the use of lecture capture technology has become widespread in higher education. However, clear evidence of the learning benefits of this technology is limited, with contradictory findings reported in the literature. The reasons for this lack of consistent evidence may include methodological issues and differences in the context of previous studies. This paper describes a study using server log data to explore student use of video recordings quantitatively in the context of science courses at Imperial College London. The study had two aims: to understand more about the general principles that underpin a learning analytics study and to seek answers to the following specific research questions: (1) How much use is made of video recordings? (2) How does the use of recordings in a module vary over time? (3) Is the use of recordings different for different modules/subjects? (4) Is the use of recordings different for subgroups of students, e.g. students with specific learning differences or English as a second language, students attaining different grades? (5) Is the use of recordings different for different types of content? Using learning analytics enabled the discovery of context-specific actionable insights: recommendations for both staff and students and ideas for further research. General conclusions were also drawn on how best to undertake learning analytics studies in order to deliver evidence and insights to improve learning and teaching