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Free keywords:
cucurbituril; host-guest system; hyperpolarized xenon; kinetics; NMR spectroscopy
Abstract:
Cucurbit[6]uril and xenon form supramolecular complexes that are of great potential for biosensing by NMR. This host-guest system acts alike a signaler in sensors facilitating the ultrasensitive detection of biomarkers by saturation transfer of chemically exchanging, hyperpolarized Xe-129. Here, the exchange process is evaluated by NMR exchange spectroscopy utilizing the preparation of anti-parallel longitudinal magnetization with respect to free and host-bound xenon and the variation of xenon concentration. Evidence for dissociative as well as degenerate exchange mechanisms is revealed by a linear regression analysis of the determined exchange rates resulting in rate coefficients of 1131 +/- 11s(-1) (2390 +/- 70s(-1)) and 108500 +/- 4900M(-1)s(-1) (174200 +/- 13900M(-1)s(-1)), respectively, and an affinity constant of 289 +/- 8M(-1) (278 +/- 14M(-1)) in physiological saline at 298K (310K). The results elucidate the supramolecular exchange and underpin the high efficacy for biosensing of this host-guest system. The approach is generally applicable to enhanced host-xenon exchange dynamics, yet slow on the NMR timescale, for quantitative kinetics and biosensing analyses.
