Jozef Hodyl PhD Thesis - Theses - Flinders University

extent, meta-positioned hydroxy groups it was decided to revisit 1 H NMR monitoredtitration experiments with the receptor model [Cd(TracHP12)](ClO 4 ) 2 , 49, this timein 20% aqueous acetonitrile buffered at pH 7. The guest molecules used for thisseries of binding constant studies were benzoate, p-hydroxybenzoate, m-hydroxybenzoate, o-hydroxybenzoate and 2,6-dihydroxybenzoate. This was done inan attempt to mirror previous studies utilising 20% aqueous dioxane with receptor29. 129 The method used to obtain the binding constants was the same as for 1 H NMRmonitored titrations in DMSO-d 6 . A diversion from the previous study with 49 inDMSO-d 6 was that with 2,6-dihydroxybenzoate the H B protons were followed ratherthan the para proton as it was masked by the host resonances when in 20%D 2 O/CD 3 CN buffered at pH 7. The results of these experiments are shown in Table6.8.Table 6.8 Inclusion of hydroxybenzoate guest species with [Cd(TracHP12)](ClO 4 ) 2 , 49, in 20%D 2 O/CD 3 CN solution with a guest concentration of 10 -3 mol dm -3 at pH 7 in 0.01 moldm -3 HEPES buffer at 298 K, compared with inclusion for previously used systems.Solvent ConditionsDMSO CD 3 OD H 2 O a H 2 O/dioxane b D 2 O/CD 3 CN20% 20%Host SpeciesGuest Species 49 49 94 29 49 pK acbenzoate 4.11 ±0.06 3.96 ±0.09 30 2.3 ±0.1 3.10 ±0.08 4.19p-OH 4.09 ±0.07 d 32 4.5 ±0.3 3.18 ±0.28 4.54m-OH 4.16 ±0.09 d 48 5.3 ±0.5 3.49 ±0.17 4.30o-OH 3.08 ±0.08 3.23 ±0.03 81 7.1 ±0.5 3.70 ±0.15 2.972,6-diOH 2.05 ±0.03 d 95 7.5 ±0.9 4.64 ±0.36 1.05a Percent uptake. b Obtained by fluorescence studies. 129 c Values obtained from PHYSPROP databasefor their respective conjugate acids. 202 d Not attempted.118