Jozef Hodyl PhD Thesis - Theses - Flinders University

arm framework. The relative magnitude of the other pairs of logK values shown inTable 3.1 indicated a slight, but less significant, lowering of the guest bindingconstant upon loss of one aromatic moiety. Overall these measurements suggestedthat the loss of one aromatic ring through silica attachment, in the way proposed,would not be a serious impediment to anion binding.Table 3.1Binding constants (logK) for guest anion binding with Cd(II) coordinated receptorcomplexes, determined by 1 H NMR monitored titrations in DMSO-d 6 at 298 K.[Cd(TracHP12)] 2+ ,49[Cd((S)thphpc12] 2+ ,26 aGuest species logK logK pK abp-nitrophenolate 3.45 ± 0.05 4.2 ± 0.2 7.15phenoxyacetate 4.5 ± 0.3 >4.5 3.17p-nitrobenzoate 4.7 ± 0.3 4.5 ± 0.8 3.44acetate c 3.3 ± 0.2 4.76D-histidinate d 3.37 ± 0.04 4.2 ± 0.21.82, 6.02 e ,9.17 fL-histidinate d 3.54 ± 0.09 4.2 ± 0.41.82, 6.0c e ,9.17 fa Previous study conducted by Smith. 93, 94 b Data for the protonated species in H 2 O acquired from NISTdatabase. 200c No chemical shift change. d Guest stock solution: 10% (v/v) D 2 O in DMSO-d 6 conductedat 313 K e imidazole f NH 2 .3.2.61 H NMR monitored titrations of amino acid anions with receptor[Cd(TracHP12)](ClO 4 ) 2 , 49The host-guest binding constants for both D- and L- histidinate with 49 weremeasured to ascertain whether or not the host would exhibit any level ofenantioselectivity. The choice of D- and L-histidinate was derived from spectralstudies of histidine indicating that at least the H A proton (Figure 3.9) would bevisible throughout the full range of the titration. 186 Thus, the H A proton, which has itsresonance furthest downfield, was used to derive the desired binding constants.61