Synthesis and application of cryptophanol hosts: 129Xe NMR spectroscopy of a deuterium-labeled (Xe)2@bis-cryptophane complex

Abstract

The new bis-cryptophanes 7–9 were prepared from cryptophanols 1–3 and illustrate the synthetic possibilities offered by the latter for the design of new host systems featuring the preparation of large supramolecular receptors and new polycryptophane bio-sensors for NMR imaging. Hosts 1–3 were obtained from the monoprotected cryptophanes 4–6 following a multi-step strategy. The complexation of xenon by the dissymmetrical bis-cryptophane 8 was studied by ¹²⁹Xe NMR spectroscopy. At low temperature, a strong discrimination (Δδ = 1.16 ppm) of the encapsulated xenon guests inside the two cryptophane cavities was observed. The kinetic parameters for the complexation process were determined from 1D-EXSY ¹²⁹Xe NMR experiments. The activation energy E_a = 39.0 ± 3 kJ mol⁻¹ and associated parameters ΔH^≠ = 37.0 ± 3 kJ mol⁻¹ and ΔS^≠ = −46.0 ± 10 kJ mol⁻¹ K⁻¹ are in agreement with the values determined for cryptophane-A and [D₂₇]-cryptophane-A.