"By following the fractionation of 233U, 235U, 236U and 238U during the enzymatic reduction of hexavalent U to tetravalent U by the bacterium Shewanella oneidensis, we provide the first direct evidence of the nuclear field shift effect during biologically controlled kinetic isotope fractionation."
https://www.geochemicalperspectivesletters.org/article2333/ - "Contribution of the nuclear field shift to kinetic uranium isotope fractionation", Geochemical Perspectives Letters v27
"By following the fractionation of 233U, 235U, 236U and 238U during the enzymatic reduction of hexavalent U to tetravalent U by the bacterium Shewanella oneidensis, we provide the first direct evidence of the nuclear field shift effect during biologically controlled kinetic isotope fractionation."