Jozef Hodyl PhD Thesis - Theses - Flinders University

of 100 mg of the host material, Si-GPS[Cd(Trac)](ClO 4 ) 2 , 94, Si-GPS-[Cd(DiPTrac)](ClO 4 ) 2 , 95, or Si-GPS-[Cd(TriPTrac)](ClO 4 ) 2 , 96, with 10 cm 3of an aqueoussolution containing a ca. 50% excess of the sodium salt of the appropriate guestspecies at a concentration of 5 x 10 -3 mol dm -3 at pH 7 in 0.01 mol dm -3 HEPESbuffer. HEPES buffer was brought to pH 7 from its native pH of ~5.3 by the additionof 1 M NaOH. All phenolate inclusion was conducted in an unbuffered 10%DMSO/acetonitrile mixture to avoid protonation of the oxoanion moiety. Thehost/guest suspension was stirred for one hour at 298 K after which the solid phasewas isolated by filtering the aqueous phase into a 250 ml volumetric flask andwashing it with ample amounts of de-ionised water. Percent guest inclusion was thenestablished by calculation of guest species remaining in the filtrate using the methoddescribed. An example of the general host-guest complexation reaction with silicaimmobilised receptors is shown in Scheme 6.1.GuestSi-GPS-[Cd(Trac)](ClO 4 ) 2 , 94GuestH 2 OOOOSiOONOHHH HO OOCd 2+ ONNNOClO 4-Silica SurfaceScheme 6.1 General procedure for guest inclusion with silica immobilised receptor complexes,depicted here with four hydrogen bonds to the host binding pocket.6.1.2 Guest molecule inclusion with Si-GPS-[Cd(Trac)] 2+ , 94To enable comparisons with binding studies conducted with model receptor 49 it wasdecided that the initial series of inclusion experiments with the silica immobilisedreceptors would involve the same set of guest species p-nitrophenolate (in 10%DMSO v/v in acetonitrile), acetate, p-nitrobenzoate, phenoxyacetate, L-histidinate95