Investigation of
the Complexation between 4‑Aminoazobenzene
and Cucurbit[7]uril through a Combined Spectroscopic, Nuclear Magnetic
Resonance, and Molecular Simulation Studies
Cucurbiturils are well known for their ability to form
supramolecular
systems with ultrahigh affinities binding. Inclusion complex between
4-aminoazobenzene and cucurbit[7]uril has been investigated in aqueous
solution by ultraviolet (UV)-spectroscopy, 1H NMR, and
molecular simulations. 4-aminoazobenzene shows high affinity in acidic
solutions while no association was detected in neutral solutions.
The thermodynamic properties of complex formation are investigated
using both UV spectroscopy and nuclear magnetic resonance (NMR) measurements.
Our results highlight that the high binding constant between CB7 and
4AA (log K = 4.9) is the result of a large negative
change in ΔrH° (−19
kJ/mol) and a small positive change in TΔrS° (9 kJ/mol). The analysis of the experimental
data lead to hypothesis on the structure of the complex. We have used
molecular dynamics simulation to interpret experiments. Interestingly,
the cis–trans isomerization
of aminoazobenzene is considered. All the results are discussed and
compared with those previously obtained with other host molecules.