RESUMO
Selective extraction of highly radiotoxic actinides(III) is an important and challenging task in nuclear wastewater treatment. Many proposed ligands containing S or P atoms have drawbacks including high reagent consumption and possible secondary pollution after incineration. The present work reports five novel pillar[5]arene-based extractants that are anchored with picolinamide substituents of different electronic nature by varying spacer. These ligands reveal highly efficient separation of actinides(III) over lanthanides(III). Specifically, almost all of these ligands could extract Am(III) over Eu(III) selectively at around pH 3.0 (SFAm/Eu>11) with fast extraction kinetics. Variation of the pyridine nitrogen basicity via changing para-substitution leads to an increase in the distribution ratios by a factor of over 300 times for Am(III) with an electron-withdrawing group compared to those with an electron donating group. Investigation of complexation mechanism by slope analysis, NMR, IR, EXAFS, and DFT techniques indicates that each ligand binds two metal ions by pyridine nitrogen and amide oxygen. Finally, these ligands do not show obvious decrease in both extraction and separation ability after being exposed to 250â¯kGy absorbed gamma radiation. These results demonstrate the potential application of pillar[5]arene-picolinamides for actinide(III) separation.
RESUMO
A supramolecular approach to catalyzing the Ritter reaction by utilizing enhanced anion-binding affinity in the presence of alkali metal cations was developed with ditopic hydrogen-bonded amide macrocycles. With prebound cations in the macrocycle, particularly Li+ ion, their metal complexes exhibit greatly enhanced catalytic activities. The catalysis is switchable by removal or addition of the bound cation. The method described in this work may be generalized for use in other anion-triggered organic reactions involving heteroditopic receptors capable of ion pairing.
