Unsaturated cryptophanes: toward dual PHIP/hyperpolarised xenon sensors

Abstract : Cryptophanes, cage-molecules constituted of aromatic bowls, are now well recognized as powerful xenon hosts in $^{129}$Xe NMR-based biosensing. In the quest of a dual probe that can be addressed only by NMR we have studied three cryptophanes bearing a tether with an unsaturated bond. The idea behind this is to build probes that can be detected both via hyperpolarised $^{129}$Xe NMR and Para-Hydrogen Induced Polarisation (PHIP) $^1$H NMR. Only two of the three cryptophanes experience a sufficiently fast hydrogenation enabling the PHIP effect. While the in-out xenon exchange properties are maintained after hydrogenation, the chemical shift of xenon encaged in these two cryptophanes is not strikingly modified, which impedes safe discrimination of the native and hydrogenated states via $^{129}$Xe NMR. However, a thorough examination of the hyperpolarised $^1$H spectra reveals some interesting features for the catalytic process and gives us clues for the design of doubly smart $^1$H/$^{129}$Xe NMR-based biosensors.