Ligand effect on uranium isotope fractionations caused by nuclear volume effects: An ab initio relativistic molecular orbital study

Abstract

We have calculated the nuclear volume term ͑ln K nv ͒ of the isotope fractionation coefficient ͑͒ between 235 U-238 U isotope pairs by considering the effect of ligand coordination in a U͑IV͒-U͑VI͒ reaction system. The reactants were modeled as ͓UO 2 Cl 3 ͔ − and ͓UO 2 Cl 4 ͔ 2− for U͑VI͒, and UCl 4 for U͑IV͒. We adopted the Dirac-Coulomb Hartree-Fock method with the Gaussian-type finite nucleus model. The result obtained was ln K nv = 0.001 90 at 308 K, while the experimentally estimated value of ln K nv is 0.002 24. We also discuss how the ligand affects the value of ln K nv , especially for the various structures of different compounds, and different ligands within the halogen ion series ͑F, Cl, and Br͒.

Evidence of isotopic fractionation of natural uranium in cultured human cells

“…It has been demonstrated that, under hypoxic conditions, intracellular Cu was isotopically heavier than under normoxic conditions. This result is in agreement with the enrichment in 65 Cu in the tumor tissue of hepatocellular carcinoma with regard to the healthy surrounding tissue (9), thus suggesting that the tumor hypoxia was at the origin of the difference in Cu isotopic signature.…”

A modern framework for the interpretation of 238U/235U in studies of ancient ocean redox

“…The recently documented permil-level 238 U/ 235 U variability on Earth (e.g. Stirling et al, 2007;Weyer et al, 2008) is likely a consequence of the nuclear field shift process, whereby variations in nuclear volume interact with changing electron densities during redox transitions (Abe et al, 2010;Bigeleisen, 1996;Fujii et al, 2006;Schauble, 2007). 238 U/ 235 U has been measured in the two most important U outputs from the ocean, reducing sediments and carbonates (e.g.…”

Mass Dependence of Iron Isotope Fractionation in Fe(II)–Fe(III) Electron Exchange Equilibration

“…The observed uranium isotope fractionation among 232 U, 233 U, 234 U, 235 U, 236 U, and 238 U showed so called 'odd-even staggering' in parallel with the optical isotope shifts in the atomic emission spectral lines of the uranium isotopes; the mass-independent anomaly was observed on the odd mass number isotopes of 233 U and 235 U. These experimentally observed phenomena have been theoretically explained by Bigeleisen as the nuclear size-and-shape effect in the chemical isotope fractionations [2], and the isotopic fractionation factors α were reproduced by the computation of the energy states of all electrons in the isotopes [3].…”

“…Iron was then eluted with pure water and recharged to a small cation-exchange column. The adsorbed iron in the cation-exchange resin was eluted with 4 M HNO 3 . The eluted samples were heated to dryness to decompose organic impurities and re-dissolved with HNO 3 .…”