Development of assay,isotopic and trace actinide measurements on solid plutonium and uranium samples by high resolution gamma spectrometry

Journal of Radioanalytical and Nuclear Chemistry - The precise analysis of sub-gram quantities of actinide materials for regulatory and specification requirements currently relies on destructive,...     

Addition of a thallium vertex to empty and centered nine-atom deltahedral zintl ions of germanium and tin

Nickel atoms were inserted into nine-atom deltahedral Zintl ions of E(9)(4-) (E = Ge, Sn) via reactions with Ni(cod)(2) (cod = cyclooctadiene), and [Ni@Sn(9)](3-) was structurally characterized. Both the empty and the Ni-centered clusters react with TlCp (Cp = cyclopentadienyl anion) and add a thallium vertex to form the deltahedral ten-atom closo-species [E(9)Tl](3-) and [Ni@E(9)Tl](3-), respectively. The structures of [Ge(9)Tl](3-) and [Ni@Sn(9)Tl](3-) showed that, as expected, the geometry of the ten-atom clusters is that of a bicapped square antiprism where the Tl-atom occupies one of the two capping vertices. This illustrates that centering a nine-atom cluster with a nickel atom does not change its reactivity toward TlCp. All compounds were characterized by electrospray mass spectrometry.     

Halogen Bonding between Anions and Iodoperfluoroorganics: Solution‐Phase Thermodynamics and Multidentate‐Receptor Design

The interactions of iodoperfluoroarenes and ‐alkanes with anions in organic solvent were studied. The data indicates that favorable halogen‐bonding interactions exist between halide anions and the monodentate model compounds C₆F₅I and C₈F₁₇I. These data served as a basis for the development of preorganized multidentate receptors capable of high‐affinity anion recognition. Several new receptor architectures were prepared, and the multidentate‐iodoperfluorobenzoate‐ester design, as described in a preliminary communication, was evaluated in more detail. Computation was employed to better interpret the structure–activity relationships arising from these studies. Investigations of the thermodynamics of anion binding (by van't Hoff analysis) and solvent effects reveal details of these halogen bonding interactions.     

An Improved Procedure for the Conversion of Carbonyl Compounds to α,β-Unsaturated Carboxylic Acids

The two carbon homologation of aldehydes and ketones to give α,β-unsaturated carboxylic acids is often carried out via the corresponding ester using metallated phosphonate reagents² (1) (Equation I). When alkyl esters (la) are employed problems are sometimes encountered in the hydrolysis step due to acid or base sensitivity but these problems can be overcome using the silyl ester (lb)³.     

Preparation and characterisation of synthetic mixtures of lithium isotopes

Re-certification of the absolute isotopic composition of the natural lithium isotopic reference material (IRM), IRMM-016, requires measurements calibrated by means of synthetic mixtures of highly enriched lithium isotopes. Ten such mixtures were prepared by weighing and mixing of two well characterised, isotopically enriched, Li₂CO₃ compounds. The starting materials, 99.9981% enriched ⁶Li, and 99.9937% enriched ⁷Li, were purified by ion exchange, and the purified materials converted from LiOH to Li₂CO₃ by reaction with CO₂. Ten new mixtures were prepared by mixing different weighed amounts of these dissolved Li₂CO₃ carrier compounds. The compounds had an estimated level of impurities of 100 ± 100 μg · g^–1 (expanded uncertainty with a coverage factor of 2). In the ten mixtures, the n(⁶Li)/n(⁷Li) ratio varies from 0.025 to 14 and the achieved expanded relative uncertainty on the amount ratio prepared is typically 2 · 10^–4. These mixtures were then used to determine the correction factor, K, for mass discrimination of the measurement procedure and instrument concerned. Received: 6 November 1997 / Revised: 22 December 1997 / Accepted: 24 January 1998     

Studies on Bis(5′-Adenosyl)-P1, P4-Tetraphosphate,Appppa, and Some Synthetic Isosteric and Isopolar Phosphonate Analogues Using the Specific Appppaases from Artemia and Lupin

Abstract

We have recently reported the synthesis and separation of three diastereoisomers of diadenosine 5′, 5″-P¹,P⁴-(P¹, P⁴-dithiO-P², P³-methylene)-tetraphosphate, (Ap₅pCH₂pp₅A), and demonstrated their resistance to hydrolysis by and competitive inhibition of the asymmetrica1 NppppNase from Artemia (1), while Guranowski et al.(2) have studied the ability of four phosphonate analogues of AppppA to act as substrates and inhibitors of the lupin and E. coli NppppNases, lupin phosphodiesterase I, and the yeast AppppA phosphorylase.     

Transition metal mediated asymmetric synthesis X. Homochiral π-complexes with planar chirality: synthetic equivalents of chiral cyclohexadiene dications

Homochiral 6-methoxy-substituted dienyltricarbonyliron complexes have been obtained from 1-methylcyclohexa-1,3-diene-5,6-diol (available via microbial oxidation of toluene) by complexation and removal of an allylic substituent with acids or with triphenylcarbenium tetrafluoroborate. A variety of optically active tricarbonyliron complexes have been produced from these compounds. The optical purity of the product and the stereochemistry of the complexation reaction have been determined. The high efficiency of chirality transfer during complexation of 5,6-dimethoxy-substituted dienes makes this method suitable as a general route to resolved organoiron complexes.     

The Chemistry of Some Isopolar Analogues of Phosphoric and Pyrophosphoric Acids

Abstract

We have previously established that the α-fluorination of alkanephosphonates provides analogues of phosphate esters which have improved ‘isopolarity’ relative to simple alkanephosphonates.¹ This property is manifest, inter alia, in enhanced acidity and in the upfield shift for the ³¹P n.m.r. resonance. Indeed, for a range of halomethanephosphonic acids we have found the relationship “δ_P=9.61 (pK_a2 - 4.59) ppm” gives an excellent correlation between these parameters. In this context, the properties of CF₂CIPO(OR)₂ species, derived from the Michaelis-Becker reaction of dialkyl phosphonates with Freon 22, CF₂Cl₂, will be described.