Jozef Hodyl PhD Thesis - Theses - Flinders University

and D-histidinate. Guest inclusion with an additional two amino acid guests D- andL-phenylalanate was also attempted. It was of interest to observe whether the percentinclusion values obtained for this set of guest species would mirror their respectivebinding constants as determined in DMSO-d 6 with receptor 49. The results for guestinclusion studies with this series of guests and silica bound receptor 94 are tabulatedin Table 6.1.Table 6.1Percent guest inclusion of with Si-GPS-[Cd(Trac)] 2+ , 94, conducted in aqueous solutionwith a guest concentration of 5 x 10 -3 mol dm -3 at pH 7 in 0.01 mol dm -3 HEPES buffercompared with logK determined for [Cd(TracHP12)] 2+ , 49, by 1 H NMR monitoredtitration in DMSO-d 6 .Si-GPS-[Cd(Trac)] 2+ , 94 [Cd(TracHP12)] 2+ , 49Guest Species % Inclusion a logK b cpK ap-nitrophenolate 72 d 3.45 ± 0.05 7.15acetate 7 e 4.96p-nitrobenzoate 16 4.7 ± 0.3 3.44phenoxyacetate 27 4.5 ± 0.3 3.17L-phenylalanate 23 f 2.20 gD-phenylalanate 24 f 2.20 gL-histidinate 35 3.37 ± 0.04 1.82 gD-histidinate 35 3.54 ± 0.09 1.82 ga Error = ± 3%. b Determined by 1 H NMR monitored titration in DMSO-d 6 . c Data for the protonatedspecies in H 2 O acquired from NIST database. d Guest stock solution unbuffered 10% v/v DMSO inacetonitrile. e No change in chemical shift. f Not attempted. g COOH.With these guest species the only good correlation between receptor 94 andreceptor 49 is with p-nitrophenolate. In this case, according to Figure A.1 inAppendix A, the observation of 72 ±3% inclusion at a 50% excess of the guest overhost approximately correlates with a logK value of 3.45 ±0.05. However, as the p-96