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Norbadione A: Kinetics and Thermodynamics of Cesium Uptake in Aqueous and Alcoholic Media

A. Korovitch, L. B. Mulon, V. Souchon, I. Leray, B. Valeur, A. Mallinger, B. Nada, T. Le Gall, C. Lion, N. T. Ha-Duong and J. Chahine J. Phys. Chem. B, 2010, 114 (39), 12655-12665

Norbadione A (NbA) is a mushroom pigment, which is assumed to be involved in Cs-137 accumulation all over Europe during the Chernobyl nuclear accident. NbA bears seven acid-base functional groups, among which are two enolic and two carboxylic acid moieties. This work deals with complex formation of Cs+ and NbA in ethanol, ethanol/water (9:1) (M1), and water with, when required, the support of two Cs+ ionophore probes, calix[4]arene-bis(crown-6-ether)dioxycoumarine (Al) and its tetrasuslfonated form (A2). In ethanol, two Cs+ complexes are formed, with the affinity constants K-1EtOH = (1.1 0.25) x 10(5) and K-2EtOH = (2.1 0.4) x 10(3). In MI, a single Cs + complex occurs when only the enols are deprotonated, whereas a bicomplex is formed when both enols and carboxylic acids are deprotonated: K-IM1 = (1.5 0.3) x 10(5) and K-2M1 = (4 2) x 10(3). These data are confirmed by stopped-flow and T-jump kinetics. In ethanol, a fast Cs+ exchange occurs between NbA and A 1: direct rate constant, lc, = (3.1 0.1) x 10(7) M-1 s(-1); reverse rate constant = (2.8 +/- 1) x 10(5) M-1 s+1; and Cs+ exchange constant, K, Exchange = (9 4) x 10-3. In Ml, the quenching of A2 fluorescence by NbA is used to determine the kinetics of complex formation with Cs+ k(2) = (1.8 +/- 0.4) x 10(9) M-1 s(-1); k(-2) = (1.80 +/- 0.15) x 10(4) s(-1); and K-IM1 = (1.5 0.5) x 10(5). The affinity of NbA for Cs+ is probably the result of the particular structure in which the two pulvinic acid arms adopt a conformation that forms two complexation sites composed of the two etiolates and/or the two carboxylates. This renders the efficiency in Cs+ uptake comparable to that of some calixarenes or crown ethers.

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Publication

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Paru le 1 octobre 2010

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doi 10.1021/jp1060232