Artificial receptors for perrhenate and pertechnetate
Final Report Abstract
Perrhenate and pertechnetate are among the anions that are the most "difficult to bind" due to their relatively large size and low charge density. The development of artificial receptors for these anions may permit completely new approaches for the radiolabeling of organic compounds used in nuclear medicine, as well as they may solve remediation problems caused by pertechnetate. Using quantum chemical calculations new structures of receptors for target anions have been proposed and their binding properties towards anions have been assessed. The most promising structures have been successfully synthesized and include acyclic, foldamer-like and macrocyclic receptors. With receptors 1-3 it has been possible to elucidate the effect of the nature of binding site of the selectivity of receptors for target anions. Thus, receptors 1 and 2 have demonstrated the best selectivity for perrhenate. To the best of our knowledge, these hosts are the first neutral receptors that can bind selectively ReO4- and TcO4- and thus overcome the Hofmeiseter series. The receptors demonstrated excellent extraction ability of pertechnetate, which was even better than that for the charged extractant. In the next series of receptors (4-6) we have varied the linker between two parts and optimized the receptor structure for coordination of all four oxygen atoms of the anions by hydrogen bonding interactions. Alkyne linker in 6 has been proven to be the optimal for selective recognition of perrhenate in acetonitrile solution. Receptors 7 and 8 were selected for studies because the anthracene ring is placed directly to the binding centre and allows to follow binding events by means of spectroscopic titrations. The fluorescence titrations revealed that ReO4- and N3- and S2O3 to the 2- anions quench the fluorescence with the strongest efficiency. Thus, these studies have revealed that the effect of fluorescence quenching does not correlate with the degree of binding in aqueous solution, i.e. perrhenate was not bound as strong as oxalate, while perrhenate showed stronger fluorescence quenching. The quenching is mainly dependent on the redox properties of the anions. Receptor 9 was prepared for the future synthesis of bicyclic structure, which are currently underway.
Publications
- Selective recognition of oxalate in water: effect of pH on binding strength and sensing mechanisms. Chemical Communications, Vol. 53. 2017, Issue 82, pp. 11345-11348.
R. R. Mittapalli, S. S. R. Namashivaya, A. S. Oshchepkov, T. A. Shumilova, T. Rüffer, H. Lang, and E. A. Kataev
(See online at https://doi.org/10.1039/c7cc06955c) - Finding receptor design for selective recognition of perrhenate and pertechnetate: hydrogen vs. halogen bonding. Chemical Communications, Vol. 54. 2018, Issue 38, pp. 4826-4829.
A. Ravi, A. S. Oshchepkov, K. E. German, G. A. Kirakosyan, A. V. Safonov, V. N. Khrustalev, E. A. Kataev
(See online at https://doi.org/10.1039/c8cc02048e)
