Table 1. Summary of binding constants and ΔG° values for formation of complexes of neutral and charged forms of the guests with the host cage H (water, 298 K).
| Guest | pK a | Neutral form |
Charged form |
||
| K/M–1 | –ΔG°/kJ mol–1 | K/M–1 | –ΔG°/kJ mol–1 | ||
| 1-Amino-adamantane | 10.9 | 1.0(3) × 104 | 22.8(7) | 13(7) | 6(1) |
| 1-Adamantane-carboxylic acid | 5.1 | 8.0(2) × 104 | 28.0(1) | 9.0(5) × 102 | 17.0(3) |
| 1,3-Adamantane-dicarboxylic acid | 4.8, 5.9 | 2.3(4) × 105 | 30.6(4) | <300 a , b | <14 a , b |
| Isoquinoline | 5.5 | 1.2(5) × 104 | 23.3(8) | 10(2) | 5.7(5) |
| Detomidine | 7.2 | 70(30) | 10.5(8) | <3 a | <3 a |
| (–)-Nicotine | 8.1 | 81(20) | 10.9(5) | <4 a | <3 a |
| Aspirin | 3.5 | 1.2(3) × 102 | 11.9(6) | <3 a | <3 a |
aIn these cases, no evidence for guest binding was seen by 1H NMR spectroscopy at the concentrations used; upper limits for K (and hence ΔG) are estimated on the assumption that 5% of bound host is the minimum that could be detected.
bSee footnote.‡