Quinoxalinol based ligand for molecular recognition and selective extraction

Abstract

As the current age of nuclear reactors gets older, more waste and a greater possibility of leaks can occur. There is a need for an on-site real time ability to be able to detect actinides in the environment to prevent a greater problem, or to help remedy clean up. Due to competing metals such as copper or iron, designing a ligand to selectively detect actinides is often very difficult. 2-quinoxolinol backbone was synthesized and two 3,5-di-t-butylsalicylaldehydes were attached as imines to provide a 2N-2O donor system as a binding pocket. This ligand by itself gave a signal in the UV-Vis at ~389 nm. When bound to uranyl, the peak shifted to higher energies to ~367 nm with a shoulder at 450 nm. When bound to copper, the peak was lower energy shifted to 450 nm. The detection limits were ~25 ppm for uranyl and ~1 ppm for copper. This became the starting point for designing a better sensor using computational chemistry. What was found was that changing from a salicylaldehyde to a 2-aminobenzaldehyde should give greater selectivity in the UV-Vis spectrum. Much needs to be investigated to increase the signal to noise and lower the detection limit. Finally, extractions were performed to determine the ligands ability to separate actinides from lanthanides. Typical of mixed N,O-donor ligands, the Salqu ligand decomposed at >1 M HNO3 and would only have efficient extractions between 1x10-1 – 1x10-3 M HNO3 with distribution for uranyl ~3 and separation factors ~5.