Jozef Hodyl PhD Thesis - Theses - Flinders University

methoxy group, as portrayed by the generic example in Figure 6.4.Figure 6.4A generic example of a methoxy substituted benzoate guest molecule.The guest species chosen for this study were p-methoxybenzoate, m-methoxybenzoate, o-methoxybenzoate and 2,6-dimethoxybenzoate. The results fromthis study are tabulated in Table 6.3.Table 6.3Comparison of inclusion data for hydroxybenzoate and methoxybenzoate guest specieswith Si-GPS-[Cd(Trac)](ClO 4 ) 2 , 94, in aqueous solution with a guest concentration of 5x 10 -3 mol dm -3 at pH 7 in 0.01 mol dm -3 HEPES buffer at 298 K.Guest Species % pK aaGuest Species % pK aap-hydroxybenzoate 32 4.54 p-methoxybenzoate 60 4.47m-hydroxybenzoate 48 4.30 m-methoxybenzoate 55 4.09o-hydroxybenzoate 81 2.97 o-methoxybenzoate 29 3.902,6-dihydroxybenzoate 95 1.05 2,6-dimethoxybenzoate 23 3.44a Values obtained in H 2 O from PHYSPROP database for their respective conjugate acids. 202It would be expected that without the influence of non-classical hydrogenbonding that the more basic methoxybenzoate species would exhibit stronger bindingcapacities. This is the case with the methoxybenzoate guests, giving a data set that isa virtual mirror image of that observed for hydroxybenzoate inclusion in DMSO-d 6with receptor 49 and, a reversal of the trend observed with receptor 94 in aqueousconditions with the same set of hydroxybenzoate guest molecules. Comparing102