Abstract
An approach for hyperpolarized (129) Xe molecular sensors is explored using paramagnetic relaxation agents that can be deactivated upon chemical or enzymatic reaction with an analyte. Cryptophane encapsulated (129) Xe within the vicinity of the paramagnetic center experiences fast relaxation that, through chemical exchange of xenon atoms between cage and solvent pool, causes accelerated hyperpolarized (129) Xe signal decay in the dissolved phase. In this proof-of-concept work, the relaxivity of Gadolinium(III) -DOTA on (129) Xe in the solvent was increased eightfold through tethering of the paramagnetic molecule to a cryptophane cage. This potent relaxation agent can be 'turned off' specifically for (129) Xe through chemical reactions that spatially separate the Gd(III) centre from the attached cryptophane cage. Unlike (129) Xe chemical shift based sensors, the new concept does not require high spectral resolution and may lead to a new generation of responsive contrast agents for molecular MRI.
Highlights
A new approach for hyperpolarized 129Xe molecular sensors is explored using paramagnetic relaxation agents that can be deactivated upon chemical or enzymatic reaction with an analyte
The relaxation data generated in this study demonstrates a dramatic increase in relaxivity of a GdDOTA for 129Xe when the complex is tethered to a cryptophane cage
The dissolved phase 129Xe signal decays at a rate that is the average of the relaxation rate in the cage and the relaxation rate in the solvent, scaled by the duration that the xenon atoms remain in the two respective phases
Summary
A new approach for hyperpolarized 129Xe molecular sensors is explored using paramagnetic relaxation agents that can be deactivated upon chemical or enzymatic reaction with an analyte. For CrA-GdDOTA, where GdDOTA is tethered to the cryptophane cage, the GdIII relaxivity for 129Xe(sol) increased more than 8 times to R1/[Rx] = 0.416 s-1mM-1.
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