Anion binding host systems based on calix[4]arenes and nanoparticles

Abstract

A range of novel host molecules with various degrees of pre-organisation for the supramolecular complexation of anionic guest species have been synthesized. Both organic core and nanoparticle-based derivatives of the ligands have been prepared and the properties of the new host ligands studied with particular reference to their anion binding behaviour. Two types of calix[4]arene derived cationic hosts for anions with, respectively, 1,3-altemate and cone conformations have been prepared. The affinity of the tetrasubstituted calix[4]arene hosts for a variety of anions has been probed with Ή NMR spectroscopic titration. The ԼՅ-alternate system binds dicarboxylate anions in a ditopic manner while the cone compounds have the highest affinity for bromide anion and are deprotonated by carboxylates. The potentially fluorescent 1,3-altemate calix[4]arene that contains a pyridinium functionality coupled via a methylene spacer to a pyrene group undergoes selective chloride-induced conformational change which results in strong increase in both monomer and excimer emission. Gold nanoparticles protected with 5-[l ,2]dithiolan-3yl-pentanoic acid pyridin-3-ylamide remain stable as colloidal solution in methanol and the UV aborption spectra demonstrate the nanoparticles' response to exposure of a variety of anions by red shift with concomitant decrease in intensity. Titration of the colloidal solution with silver tetrafluoroborate results in an increase in absorption indicating possible interaction of silver cations with the pyridyl nitrogen atoms