ABSTRACT
Three novel lower rim hexamide derivatives 5(6), 7(6), and 9(6) of p-hydroxycalix[6]arene and four octamides 5(8), 7(8)-9(8) derived from the corresponding p-hydroxycalix[8]arene were synthesized, and their potential as extractants in radioactive waste treatment was evaluated, in comparison with upper rim analogues 12(6) and 12(8) and other existing selective neutral ionophores currently used in radioactive waste treatment. Extraction of alkali and alkaline earth metal picrates from water to dichloromethane, and of the corresponding nitrates from acidic water solution simulating radioactive waste, to 2-nitrophenyl hexyl ether (NPHE), showed that the lower rim amides extract divalent cations much better than monovalent ones. The upper rim hexa-12(6) and octamide 12(8) are very inefficient ligands, hardly extracting any cation. In all cases, p-alkoxy octamides are more efficient and selective extractants than the corresponding hexamides. In the case of simulated waste solutions, the distribution coefficients for strontium removal by octamides (6.5 < D(Sr) < 30) are much higher than the corresponding value (D(Sr)) found for dicyclohexyl-18-crown-6 (DC18C6), and the same applies for the strontium/sodium selectivity, which is 6500 < D(Sr)/D(Na) < 30 000 for octamides and 47 for DC18C6. ESI-MS, UV-vis, and X-ray crystal structure studies give consistent results and indicate the formation of 2:1 (cation/ligand) strontium complexes for all octamides tested. Stability constants were determined in homogeneous methanol solution for alkali metal (log beta(11) < or = 2), calcium (4.3 < or = log beta(11) < or = 6.0; 9.4 < or = log beta(21) < or = 12.0), and strontium (5.6 < or = log beta(11) < or = 12.3) ions using a UV-vis competition method with 1-(2-pyridylazo)-2-naphthol (PAN). They confirm the high efficiency and high divalent/monovalent selectivity found in metal ion extraction experiments for the new octamide ligands. Evidence for a positive cooperative effect between the two metal ion binding sites was obtained in the case of the Ca(2+) complex of octamide 1(8).
ABSTRACT
Complexation and protonation equilibria were studied in aqueous solution for a new range of aminocryptand ligands, N(CH2CH2NHCH2RCH2NHCH2CH2)3N, (R = m-xylyl, p-xylyl, 2,5-furan, 2,6-pyridine) and demonstrate that stability constants for first transition series ions Co2+ to Zn2+ are relatively high. X-ray crystallography shows that the cryptands are reasonably well preorganized for complexation. The furan-spaced cryptand L6.H2O crystallizes in the rhomobohedral space group R3 (no. 148) with a = 14.645(1), b = 14.645(1), and c = 25.530(4) A, whereas the m-xylyl-spaced cryptand L4 crystallizes in the triclinic space group P1 (no. 2) with a = 9.517(1), b = 15.584(2), and c = 23.617(4) A. The highest formation constant (log beta21 = 33.07) is observed for the dicopper cryptate of a pyridine-spaced cryptand, suggesting involvement in complexation of donors from the spacer link. This pyridine-spaced host also shows good selectivity for copper(II) over zinc(II), making it a possible candidate for treatment of copper-excess pathology.
ABSTRACT
A new PC compatible computer program SIRKO for the calculation of the equilibrium constants by means of the simultaneous processing of different experimental data from various techniques is given. This program is characterized by the application of a universal response function, which allows many different physicochemical methods to be used to study equilibria without any modification of the program. It is also possible to refine additional parameters (electrode parameters, initial analytic concentration, etc). We have used the least-squares method with the weightings calculated according to the error propagation rule taking into account all independent variables. To minimize the function, singular Jacobian decomposition is applied. This allows control of its range and forms a set of parameters, determined from the experimental data.
