Structural comparisons of the species of recognition of Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Ag+ with 1,3-di-conjugates of calix[4]arene by DFT computations

Calixarenes are versatile macromolecular systems, which would exhibit better host-guest chemistry upon appropriate derivatization. Our group has been involved in the synthesis of a variety of calix[4]arene conjugates, which were found to selectively recognize metal ions. Though such recognitions have been demonstrated, based on different experimental studies, the qualitative and semi-quantitative understanding of the coordination aspects are still lacking owing to the non-availability of the crystal structures of the species of recognition. Hence, in order to understand the coordination chemistry of the interactions between the host calix[4]arene receptor and the guest metal ion species, computational modelling studies have been carried out. In this regard, five conjugates of calix[4]arene, which are 1,3-di-O-derivised at the lower-rim and appended over an amide as well as Schiff base linker have been studied. The computational modelling studies have been carried out at the level of density functional theory to yield coordination geometries, which are intune with the experimental observations and comparable to those reported in the literature in the case of similar receptor systems. The species of recognition obtained with the metal ions are found to have some structural resemblances with the metal sites present in metalloproteins. The modelling studies and the coordination geometries are discussed in this article