“…Moreover, the properties of these cage molecules can be modified by acting on the size of the complexing macrocycle and on the functionalization of lateral groups. During the last decades, their applications in various domains led to numerous experimental studies in the fields of chemical sensing, – ionic transport, or separation and host−guest chemistry. – One of these applications concerns the extraction of actinide elements from various media such as tap or seawater, , nuclear wastes, – or even urine to monitor the health of nuclear workers. – To select an efficient calixarene-based uranophile extractant, three criteria must be taken into account: the size of the cage, the macrocycle structure imposed by the chelating groups, and finally the nature of the functionalized groups on the lower rim. The size of the cage can vary from 4 to 6 basic phenolic units in most cases up to 12 units encompassing two uranyl cations, as evidenced by recent studies. – From X-ray crystallographic studies, Shinkai et al showed that a single uranyl cation may adopt either a pseudoplanar penta- or hexacoordinated structure. , Hence, they proved that these coordination numbers are favored with calix[5]arenes or calix[6]arenes-based complexes.…”
Section: Introductionmentioning
confidence: 99%
“…Chem nuclear wastes, or even urine to monitor the health of nuclear workers. [30][31][32][33] To select an efficient calixarene-based uranophile extractant, three criteria must be taken into account: the size of the cage, the macrocycle structure imposed by the chelating groups, and finally the nature of the functionalized groups on the lower rim. The size of the cage can vary from 4 to 6 basic phenolic units in most cases up to 12 units encompassing two uranyl cations, as evidenced by recent studies.…”
A theoretical study on the complexation of uranyl cation (UO2(2+)) by three different functional groups of a calix[6]arene cage, that is, two hydroxamic and a carboxylic acid function, has been carried out using density functional theory calculations. In particular, interaction energies between the uranyl and the functional groups have been used to determine their affinity toward uranyl, whereas pKa calculations give some information on the availability of the functional groups in the extraction conditions. On the one hand, calculations of the interaction energies have pointed out clearly a better affinity with the hydroxamic groups. The stabilization of this complex was rationalized in terms of a stronger electrostatic interaction between the uranyl cation and the hydroxamic groups. The presence of a water molecule in the first coordination sphere of uranyl does not destabilize the complex, and the most stable complex is obtained with two functional groups and two water molecules, leading to a coordination number of 8 for the central uranium atom. On the other hand, pKa theoretical evaluation shows that both hydroxamic (deprotonated on the oxygen site) and carboxylic groups are potential extractants in aqueous medium with a preference for carboxylic functions at low pH. Moreover, these data allowed to unambiguously identify the oxygen of the alcohol function as the favored deprotonation site on the hydroxamic function.
“…Moreover, the properties of these cage molecules can be modified by acting on the size of the complexing macrocycle and on the functionalization of lateral groups. During the last decades, their applications in various domains led to numerous experimental studies in the fields of chemical sensing, – ionic transport, or separation and host−guest chemistry. – One of these applications concerns the extraction of actinide elements from various media such as tap or seawater, , nuclear wastes, – or even urine to monitor the health of nuclear workers. – To select an efficient calixarene-based uranophile extractant, three criteria must be taken into account: the size of the cage, the macrocycle structure imposed by the chelating groups, and finally the nature of the functionalized groups on the lower rim. The size of the cage can vary from 4 to 6 basic phenolic units in most cases up to 12 units encompassing two uranyl cations, as evidenced by recent studies. – From X-ray crystallographic studies, Shinkai et al showed that a single uranyl cation may adopt either a pseudoplanar penta- or hexacoordinated structure. , Hence, they proved that these coordination numbers are favored with calix[5]arenes or calix[6]arenes-based complexes.…”
Section: Introductionmentioning
confidence: 99%
“…Chem nuclear wastes, or even urine to monitor the health of nuclear workers. [30][31][32][33] To select an efficient calixarene-based uranophile extractant, three criteria must be taken into account: the size of the cage, the macrocycle structure imposed by the chelating groups, and finally the nature of the functionalized groups on the lower rim. The size of the cage can vary from 4 to 6 basic phenolic units in most cases up to 12 units encompassing two uranyl cations, as evidenced by recent studies.…”
A theoretical study on the complexation of uranyl cation (UO2(2+)) by three different functional groups of a calix[6]arene cage, that is, two hydroxamic and a carboxylic acid function, has been carried out using density functional theory calculations. In particular, interaction energies between the uranyl and the functional groups have been used to determine their affinity toward uranyl, whereas pKa calculations give some information on the availability of the functional groups in the extraction conditions. On the one hand, calculations of the interaction energies have pointed out clearly a better affinity with the hydroxamic groups. The stabilization of this complex was rationalized in terms of a stronger electrostatic interaction between the uranyl cation and the hydroxamic groups. The presence of a water molecule in the first coordination sphere of uranyl does not destabilize the complex, and the most stable complex is obtained with two functional groups and two water molecules, leading to a coordination number of 8 for the central uranium atom. On the other hand, pKa theoretical evaluation shows that both hydroxamic (deprotonated on the oxygen site) and carboxylic groups are potential extractants in aqueous medium with a preference for carboxylic functions at low pH. Moreover, these data allowed to unambiguously identify the oxygen of the alcohol function as the favored deprotonation site on the hydroxamic function.
“…[3][4][5][6][7][8] Thus, calix [6]arenes bearing carboxylic, phosphonic, or hydroxamic acid groups have been widely studied as specific ligands for the uranyl ion (UO 2 2+ ). [9][10][11][12][13][14][15][16][17] More recently, it has been shown that calix [6]arenes bearing hydroxamic functions, such as the 1,3,5-OMe-2,4,6OCH 2 CONHOH-p-tert-butylcalix [6]arene (Figure 1) are particularly suitable to complex selectively the uranyl ion. [11][12][13]18 In an experimental context, the understanding of the conformation behavior of calixarenes is a necessary prerequisite to rationalize their properties and to drive future syntheses.…”
Section: Introductionmentioning
confidence: 99%
“…Within these applications, these macrocyclic molecules are particularly interesting for their properties related to the actinide extraction. , In fact, they can selectively extract neutral or charged molecules, and such properties can be easily modified and tuned, since they depend on the size of the molecular cavity, the geometry of coordination, and the functionalization of lateral groups . A large number of experimental studies on the complexation mechanism have been carried out in the past years. − Thus, calix[6]arenes bearing carboxylic, phosphonic, or hydroxamic acid groups have been widely studied as specific ligands for the uranyl ion (UO 2 2+ ). − More recently, it has been shown that calix[6]arenes bearing hydroxamic functions, such as the 1,3,5-OMe-2,4,6OCH 2 CONHOH- p-tert -butylcalix[6]arene (Figure ) are particularly suitable to complex selectively the uranyl ion. − , 1 Structure of most stable conformer of 1,3,5-OMe-2,4,6-OCH 2 CONHOH- p- tert -butylcalix[6]arene (cone conformation). Hydrogen atoms are omitted for clarity.…”
An experimental and theoretical study on the conformational behavior of the 1,3,5-OMe-2,4,6-OCH(2)CONHOH-p-tert-butylcalix[6]arene has been carried out. In particular, semiempirical (AM1) and density functional theory (DFT) calculations have been performed in order to identify the possible conformers. The obtained results show that the cone structure is the most stable conformer at any level of theory, even if significant differences have been obtained for the other species. The inclusion of solvent effect, through a continuum model, also points out the relevant role played by the solvent in the stabilization of the cone structure in solution. These latter results have been confirmed by NMR experiments, which clearly show the presence of only the cone conformer in a polar solvent, such as DMSO. Finally, (1)H and (13)C NMR spectra on model systems, i.e., two successive phenol rings (Ar(1)-CH(2)-Ar(2)), have been computed at the DFT level and compared with the experimental spectra of the complete molecule. The results show an overall good agreement with the experimental data, thus leading to an unambiguous assignment of the experimental spectra.
“…At a calixarene:uranium molar ratio of 16 (i.e., uranium concentration of the contaminated solution of 25 mg l −1 ), the calixarene nanoemulsion efficiency is divided by two and becomes nil for smaller calixarene:uranium molar ratios. To obtain a quantitative uranium extraction rate in liquid-liquid extraction experiments under similar conditions, the molar ratio was shown to be much higher than 10,000 (Baglan et al, 1997;Boulet et al, 2006), which shows the interest of our emulsified system.…”
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