Jozef Hodyl PhD Thesis - Theses - Flinders University

6.1.6 Guest inclusion studies with guest species containing differentsubstituentsTo check whether variation of substituents in the para position would affect bindingvalues a series of different benzoate guests was also subjected to guest inclusionexperiments with Si-GPS-[Cd(Trac)](ClO 4 ) 2 , 94. The guest molecules used were p-methylbenzoate, p-fluorobenzoate, p-chlorobenzoate and p-formylbenzoate.Also a set of hydroxybenzoates with the phenolic hydroxy group deprotonated inaddition to the carboxy group were used in these experiments to see if endowing aguest molecule with more than one oxoanion would have an influence on bindingstrength. The guests for these experiments were p-carboxyphenolate and m-carboxyphenolate. Preparation of p-carboxyphenolate and m-carboxyphenolate wasby treatment of their conjugate acids with NaOH while maintaining the solutionabove pH 12. This series of experiments was conducted at pH 12 using 0.02 mol dm 3CAPS buffer.Furthermore to ascertain whether π-π interactions between guest and host specieswould also increase binding, two π enriched guest molecules: 1-naphthoate and 2-naphthoate were also used in guest inclusion experiments. The rationale was thateither guest π-π interactions (edge to face or face to face) directly with the host orπ ... H-O-H ... π H 2 O bridged hydrogen bonding would contribute to the overall bindingin the host-guest complexes formed. Table 6.7 shows the percent inclusion valuesfor these sets of experiments.It appears from the percent inclusion values attained for series 1 that the characterof the substituent in this case does not alter these values significantly as they tend toagree with the binding values expected with respect to the basicity of the guestspecies.109