Cucurbit[7]uril Complexation Drives Thermal trans–cis‐Azobenzene Isomerization and Enables Colorimetric Amine Detection
Tóm tắt
Từ khóa
Tài liệu tham khảo
The formation of the purple colored CB[7]⋅cis‐1⋅2 H+and CB[7]⋅cis‐3⋅2 H+complexes occurs immediately upon addition of CB[7] to a solution of1or3. It is well known (ref. [2]) that protonation of azobenzene derivatives substantially lowers the barrier to isomerization.
Kavalues of CB[7] with4–10:4 Ka=(4.08±0.10)×105 M−1;5 Ka=(3.61±0.10)×105 M−1;6 Ka=(1.12±0.03)×104 M−1;7 Ka=(3.18±0.06)×104 M−1;8 Ka=(2.02±0.12)×104 M−1;9 Ka<100 M−1;10 Ka=(1.14±0.02)×105 M−1.
The ratio of binding constants for ammonium versus amine is equal to 10ΔpKa. The pKashift of ≈3 units reported for1⋅2 H+corresponds to a ≈1000‐fold difference in binding constants.