Jozef Hodyl PhD Thesis - Theses - Flinders University

CHAPTER 5METAL ION UPTAKE STUDIES WITH SILICAIMMOBILISED MOLECULAR RECEPTORLIGANDS5.1 Metal(II) ion uptake studies with Si-GPS-Trac, 43Having successfully prepared the silica immobilised molecular receptor ligandsmetal ion uptake studies with Si-GPS-Trac, 43, were conducted to examine the leveland rate of metal ion uptake of this material for a select group of divalent metal ions,Cd(II), Zn(II), Cu(II), Pb(II), and Ca(II). This immobilised macrocyclic ligand wasexpected to possess similar if not identical metal uptake properties to the model 49and the first generation receptors, such as, 26, but this needed to be verified.A deviation from the attachment of four enantiomerically pure pendant arms isthat the GPTS linker precursor is racemic. So, the stereochemistry around thestereogenic carbon atom associated with the linker arm could be either R or S givingrise to two diastereomeric forms of the immobilised macrocycle: SSSS and SSSR. Itseemed remotely possible that the SSSR diastereomer could produce something otherthan the usual eight coordinate receptor complexes previously observed with Cd(II)and Pb(II) using homochiral ligands of this type. This is because of the possibility ofconformer C, shown in Figure 5.1, forming, whereby the uniform spirallingdirection of the (S)-pendant arms may be opposed by the (R)-pendant arm.silane linkageOphSOHONNHOCd 2+OHRNNHOSphOOphSsilane linkageOHONNsilane linkageSphphSSOOA B CRHOOHCd 2+NNOHSphOphOORNNHOOHCd 2+OHSNNOHOphphOSFigure 5.1Representation of some of the possible coordinative bonding arrangements with theSSSR enantiomeric form of the silica immobilised receptor material, 43.87