Silica Immobilised Metal Ion Activated Molecular Receptors

Author: Jozef Andrew Zbigniew Hodyl

Hodyl, Jozef Andrew Zbigniew, 2008 Silica Immobilised Metal Ion Activated Molecular Receptors, Flinders University, School of Chemical and Physical Sciences

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Immobilisation of functional entities, such as, enzymes, onto solid supports, as a means of facilitating their removal from the surrounding environment and subsequent regeneration has been in practice for many decades. This work focuses on the immobilisation and analysis of three-walled (pendant armed), cyclen based receptor complexes immobilised onto a silica surface for the purpose of sequestering aromatic anions from aqueous solution: Si-GPS-[Cd(Trac)](ClO4)2, Si-GPS-[Cd(DiPTrac)](ClO4)2, and Si-GPS-[Cd(TriPTrac)](ClO4)2 were the immobilised receptors used. Initially, synthesis of a three-walled model receptor, [Cd(TracHP12)](ClO4)2, that is not bound to silica yet mimics the properties of the silica anchored receptor complexes with a hydroxypropyl pendant arm was effected. Aromatic anion binding constant measurements were made on the model receptor using 1H NMR monitored titrations in DMSO-d6 which showed that, in comparison to the first generation four-walled receptors, the removal of one of the pendant arms did not affect the binding capability of the receptor's cavity significantly. It was shown that the binding strength correlated well with the pKa of the particular anion with, for example, p-hydroxybenzoate > m-hydroxybenzoate > o-hydroxybenzoate. The precursor to this receptor was then immobilised onto a silica surface and subjected to metal ion uptake studies to gauge its coordination properties with a number of divalent metal(II) ions: Cd(II), Pb(II), Zn(II), Cu(II) and Ca(II). The three Cd(II) coordinated receptor complexes mentioned above were then subjected to inclusion studies with a number of aromatic anions in aqueous conditions whereupon a reversal of the previously mentioned trend, i.e. o-hydroxybenzoate > m-hydroxybenzoate > p-hydroxybenzoate was observed. This indicated that the presence of water in the system changes the hydrogen bonding mode of the host-guest complexes, and was a major discovery arising from this work.

Keywords: molecular receptors,silica immobilisation,aromatic anion inclusion,cyclen

Subject: Chemistry thesis

Thesis type: Doctor of Philosophy
Completed: 2008
School: School of Chemical and Physical Sciences
Supervisor: Prof.Kevin P. Wainwright