Determination of host–guest association on M–Salphen complexes (M = Ni, Cu and Zn) and multiwalled carbon nanotubes grafted nanomaterials using supramolecular UV–vis titration and fluorescence studies

This work displays the synthesis, characterisation and host–guest studies of novel M–Salphen complexes (M = Ni(II), Cu(II) and Zn(II)) bearing carboxylic acid moieties, and their use as a binding unit upon grafting of hydroxylated multiwalled carbon nanotubes (MWCNT-OH) to produce new MWCNT-g-[M–Salphen] hybrid counterparts. The supramolecular studies describe the influence of the hybrid nanomaterial on the performance of the M–Salphen complexes against different carboxylated guests to open the door to potential applications as sensors and stimuli-responsive systems. Spectrophotometric titrations in solution of the M–Salphen complexes and the hybrid nanomaterials carried out against suitable mono- and dicarboxylic acid guests (acetate, oxalate, malonate and succinate), exhibited the concurrence of 1:1 and 1:2 stoichiometries. Trends in association constants K11 and K12, global stabilities and selectivities showed differences triggered by the changes in the supramolecular environment at the binding site upon grafting, as well as the nature of the guests used.