JRP 07-23

Partners

CEA

UCY

Contact

Thomas Zemb
Institut de Chimie séparative de Marcoule, UMR 5257, Marcoule, 30207 Bagnols sur Cèze, France
E-mail e-mail

Assessing complex anions containing uranium on the hofmeister scale : information from non-specific adsorption on model bilayers

Status

 
Terminated - Planned from October 2007 till October 2008

Goals

Neutral phospholipid bilayers, with a pH set by a buffer between the two pKs of the lipids, swell in the presence of salts. This experimental result, known since nearly thirty years, is incompatible with the standard theory of ionic behaviour at interfaces.
The first "explanation" of this phenomenon was suggested by Tatulian and co-workers, who noticed this anomalous swelling depended on the cosmotropic/chaotropic character of the anion. This observation was not enough to explain quantitatively the effect. The effect can be understood when the screening of the van der Waals force is taken into account, as well as nonspecific ion adsorption in an active surface layer. This investigation has been extended to a series of monovalent anions and was recently published by the two partners. A partitioning parameter in the lipid interface can be deduced and serves as a chaotropic indicator for each ion.

Since the mechanism is now much better understood, we can do the reverse: measure the anomalous swelling and deduce from this simple experiment the chaotropic/cosmotropic property on complex anions based on uranyl for the first time. uranyl is itself a divalent cation, hence cannot be directly accommodated by the new method we propose. However, several anionic uranyl complexes, such as carbonates, chlorides and fluorides are accessible.

Expected results

Expected impact on applied issues in the field of nuclear fission energy

Short term: The first quantitative assessment of Uranium-based anions on the Hofmeister scale.
Medium: To allow testing of the predictive power of theories of ion-interface interactions
Long term: Some cases may be found in which selectivity between anions by a neutral interface can be predicted. This effect is always additive to the site specific "complexation" and is probably of the same order of magnitude.
The project could allow the explicit prediction of selectivity by combining these two terms. This fundamental research will give general mechanisms and does not lead to patents directly.

Expected impact on long term integration

This work is an extension to actinides of the most modern approaches used to study interactions in colloidal systems and self-assembled complex fluids, a knowledge until now only shared by the best laboratories in the world working on colloids, nanoscience and complex fluid formulation.
In the long-term, applications to new methods of separation of lanthanides may be derived from this approach.

Reports