Marie-José Schwing-Weill

Calixarenes, new selective molecular receptors

Calixarenes are easily amenable to chemical modifications, e.g. derivatization of the phenolic hydrogen atoms or substitution at the para-positions, which can be operated separately or combined. They thus assume the role of platforms supporting arrays of functional groups able to act as ligating sites and resulting in a great variety of receptors displaying specific complexing abilities. A selection of examples are presented with the aim of illustrating the different factors of their ionic recognition properties and their already existing applications in the field of chemical sensors.

CALIXARENES FOR NUCLEAR WASTE TREATMENT

The fission of uranium or more generally of transuranium elements in reactors is an important energy source, arguably not very polluting for the environment. In use, the nuclear fuel undergoes increasingly important modifications until its replacement is considered to be necessary for the correct operation of the reactor, which occurs well before its total exhaustion in fissile matter. The spent fuels contain both fissile and fertile residues of significant energy value and radioactive products, alpha, beta, gamma and neutron emitters, which make them very irradiant and which release an important amount of heat (mainly due to and after five years of cooling). The radiotoxicity of these fuels can last for millions of years. Reprocessing is of great interest to recover uranium and plutonium, which can be recycled in the form of new nuclear fuels, and to optimize the conditioning of waste. The fuel is stored in pools for at least three years before its reprocessing. From the pool, fuel assemblies are routed to a shearing and dissolution unit before extraction of uranium and plutonium by tri-n-butylphosphate (TBP) (PUREX process). During the back extraction operations, uranium and plutonium are separated and then are purified by one or two supplementary solvent extraction cycles in order to obtain very pure products that can be used again. Acidic solutions arising from PUREX process contain minor actinides (neptunium, americium, curium) and 99 % of the non-gaseous fission products. Some of these radionuclides have long half-lives : The present strategy is to vitrify these high level activity wastes for disposal or long term storage. An alternative strategy, studied in France, Japan and Russia, is to separate the minor actinides and the long lived fission products from these wastes and destroy them by transmutation. This would also involve the recovery of other fission products, (27.7 y) and (30 y), which would remove about 90 % of the heat released by high activity wastes, allowing their volume to be reduced and facilitating their disposal or their intermediate storage. Reprocessing operations and particularly dismantling facilities generate medium level activity liquid wastes. A great part of these high salinity solutions has to be disposed of in stable geological formations or in long term storage after embedding due to

New Calix[4]arene-monobenzo- and -dibenzo-crown-6 as Cesium Selective Ionophores in the Radioactive Waste Treatment: Synthesis, Complexation and Extraction Properties

Cesium possesses two long lived isotopes 135Cs and 137Cs and the first one has a very long (2.3 × 106 y) half life and is one of the most mobile nuclides in a repository.Calix[4]arene-crowns-6 in the 1,3-alternate conformation areemerging as a new class of ionophores exhibiting a very high efficiency and selectivity in the complexation of cesium ion and itsremoval from highly acidic ([HNO3] = 3–4 M) radioactive waste having also high sodium nitrate concentration ([NaNO3] = 2–4 M). In order to improve both efficiency and cesium selectivity we have synthesised the novel calix[4]arene dibenzo-crowns-6 1 and 2 and thecalix[4]arene-monobenzocrown-6 3 in 1,3-alternate conformationand evaluated their complexation properties towards alkali metal cations in homogeneous solution and in two phase systems, togetherwith their performance in radioactive waste treatment. All data confirm the higher Cs/Na selectivity of the 1,3-alternate calix[4]crown-6 1–3 containing aromatic rings in the polyether loop, in comparison to previously synthesised compounds of the same series.

Metal-Ion Complexation by Narrow Rim Carbonyl Derivatives

Although calixarenes are now well established members of the family of macrocycles, ftheir full exploitation in supramolecular chemistry requires a better understanding of the many structural and environmental factors which influence the binding of metal cations by organic functional groups in solution. The new advances highlighted in this chapter confirm that the carbonyl group in its many manifestations continues to play an important role in the development of calixarene receptors. Not only do these studies help clarify the details of the complexed state, but they provide important pointers for future improvements in the design of selective metal ion receptors with predetermined properties and applications.

A supramolecular assembly of a multifunctional calix[4]arene with alkali and alkaline earth cations in solution and in the solid state

Abstract p-tert-Butylcalix[4]arene derivatives 2 and 4 bearing one carboxy-lic acid, one ester and two phenolic groups on the lower rim form pH-dependent mononuclear or binuclear assemblies with alkali (excluding lithium) and alkaline earth cations. The structures of binuclear K+ complexes 5 and 6 of 2 and 4, respectively, have been determined by X-ray diffraction.

Thermodynamics of the protonation of some cryptands in water and methanol

Abstract We report the results of thermochemical studies in water and anhydrous methanol of some cryptands, L = [2.2.2], [2.2.1], of general formula represented below: Protonation constants K 1 and K 2 , relative to the following equilibria: have been determined by pH-metry at 25°C, with I = 0.1 or 5 × 10 10−2 M(Et 4 NClO 4 ). The values of ΔH 1 and ΔH 2 have been determined from calorimetric measurements in both solvents. Corresponding ΔG and ΔS values have been calculated. Results are discussed in terms of conformational changes of the mon- and biprotonated cryptands in the different solvent water and methanol.