Investigation of the effects on proton relaxation times upon encapsulation in a water-soluble synthetic receptor

Sequestration of small molecule guests in the cavity of a water-soluble deep cavitand host has a variety of effects on their NMR properties. The effects of encapsulation on the longitudinal ( T 1 ) and transverse ( T 2 ) relaxation times of the protons in variably sized guest molecules are analyzed here, using inversion recovery and spin-echo experiments. Sequestration of neutral organic species from the bulk solvent reduces the overall proton relaxation times, but the magnitude of this effect on different protons in the same molecule has a variety of contributors, from the motion of the guest when bound, to the position of the protons in the cavity and the magnetic anisotropy induced by the aromatic walls of the host. These subtle effects can have large consequences on the environment experienced by the bound guest, and this sheds light on the nature of small molecules in enclosed environments. The T 1 and T 2 relaxation rates of different protons in small cyclic and polycyclic guests can be controlled by encapsulation in a water-soluble synthetic receptor.