Host–guest complexation studies of p-tertbutylcalix[4]arene against ions of interest for radiological decontamination

Abstract

Cesium, strontium, cobalt, thallium and iodine are the most common radionuclides in Nuclear and Radiological emergencies. Calix[n]arenes are supramolecular compounds capable of forming complexes with most of the metal ions. In the current study, host–guest complex properties of p-tertbutylcalix[4]arene against the five ions have been studied using a combination of experiments and density function theory (DFT) calculations. Characterization of the formed complexes has been done by 1H NMR, Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), circular dichroism (CD), UV–Vis. and fluorescence spectroscopy. Further, ex-vivo metal complexation studies have been performed using high-resolution sector field inductively coupled plasma mass spectroscopy (HR-SF-ICPMS). 1H NMR host–guest complex studies provide spatial information about the location of the guest molecules in the host cavities. A detailed interpretation of the ATR-FTIR has been done in order to derive important information about the interaction mechanism of host–guest complexes. CD spectra of the complexes provide information about the conformational changes in the ligand structure. UV–Visible and fluorescence spectroscopy further validate the complexation of the metal ions with p-tertbutylcalix[4]arene. Detailed electronic structures of the complexes have been elucidated using computational methods involving DFT calculations and further verified using X-ray crystallography. More than 96% complexation of p-tertbutylcalix[4]arene with the selected ions has been observed in ICP-MS. These studies confirm the utility of this supramolecular compound for topical radiological decontamination formulations.