Jozef Hodyl PhD Thesis - Theses - Flinders University

nitrophenolate inclusion experiment was conducted in a DMSO/acetonitrile mixtureto maintain the anionic character of this guest species, the observed result, is notaltogether surprising and is not comparable with those found for the other anions inTable 6.1 where uptake was performed in aqueous conditions.The other guest species, which all have a carboxylate hydrogen bond acceptorgroup, display a trend where the less basic species are more highly included. This isa reversal of the binding constant trend obtained with model receptor 49 in DMSO-d 6where the binding strength increased with increasing basicity, in conformity with theexpected strength of hydrogen bonding interactions between the guest species andthe base of the host binding pocket. The low uptake of acetate, which lacks anaromatic group, suggests that an aromatic moiety in the structure of the guestcontributes to molecular recognition of guest molecules.6.1.3 Inclusion of hydroxybenzoate guest species with silica immobilisedreceptorsA series of hydroxy substituted guest molecules was also subjected to guest inclusionwith receptor 94 in an aqueous environment in conditions identical with those for theprevious set of guest species. The data are tabulated in Table 6.2. It can be seen thatpercent inclusion for hydroxybenzoate guest species in aqueous conditionsdemonstrates a reversal of the trend o-hydroxybenzoate < m-hydroxybenzoate < p-hydroxybenzoate observed for this series of guest molecules with receptor 49 inDMSO-d 6 (Chapter 3). However, the percent inclusion values obtained in aqueousconditions with receptor 94 mirror the logK values acquired with receptor 29 fromfluorescence monitored titration experiments in 20% aqueous dioxane. Thus itappears that by switching from DMSO to aqueous conditions one can reverse thetrend in binding constants.97