Temperature and pH driven association in uranyl aqueous solutions

Abstract

An association behavior of uranyl ions in aqueous solutions is explored. For this purpose a set of all-atom molecular dynamics simulations is performed. During the simulation, the fractions of uranyl ions involved in dimer and trimer formations were monitored. To accompany the fraction statistics one also collected distributions characterizing average times of the dimer and trimer associates. Two factors effecting the uranyl association were considered: temperature and pH. As one can expect, an increase of the temperature decreases an uranyl capability of forming the associates, thus lowering bound fractions/times and vice versa. The effect of pH was modeled by adding H + or OH − ions to a "neutral" solution. The addition of hydroxide ions OH − favors the formation of the associates, thus increasing bound times and fractions. The extra H + ions in a solution produce an opposite effect, thus lowering the uranyl association capability. We also made a structural analysis for all the observed associates to reveal the mutual orientation of the uranyl ions.

Structural changes in water exposed to electric fields: A molecular dynamics study

“…The hydration picture is more complicated for the uranyl 54 case. It is known [16,17] that the hydration shells of uranyl ions in aque-55 ous solutions consist of five or six water molecules or OH − ions [18][19][20]. 56 It is worthwhile to mention two recent studies of uranium/uranyl com-57 plexation [21,22] reporting that the uranium ions, U 3+ and U 4+ , are hy- to environmental chemistry [23][24][25][26].…”

“…The uranyl-water interaction coincides with the 145 one used in our earlier studies [18][19][20]. The potential parameters for the 146 uranyl ions were fitted by Guilbaud and Wipff [55,56].…”

Passage of TBP–uranyl complexes from aqueous–organic interface to the organic phase: insights from molecular dynamics simulation

“…Such ionic association of uranyl nitrate in aqueous solution is not surprising, and has been verified by many experimental and simulation studies. 41,42 The results from the coordination profile show that the number of coordinating water molecules in the solvation sphere of uranyl is decreased from five to two in the presence of NO 3 À .…”