Effect of pH and Counterions on the Encapsulation Properties of Xenon in Water-Soluble Cryptophanes

• Published in: Chemistry : a European journal Vol. 16; no. 43; pp. 12941 - 12946
• Main Authors: Berthault, Patrick, Desvaux, Hervé, Wendlinger, Thierry, Gyejacquot, Marina, Stopin, Antoine, Brotin, Thierry, Dutasta, Jean-Pierre, Boulard, Yves
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 15.11.2010; WILEY‐VCH Verlag; Wiley Subscription Services, Inc; Wiley-VCH Verlag
• Subjects: Algorithms; Biosensors; Chemical Sciences; Chemistry; Constants; cryptophanes; Derivatives; Holes; Hydrogen-Ion Concentration; hyperpolarization; Ion exchangers; Magnetic Resonance Spectroscopy; Molecular Structure; NMR spectroscopy; or physical chemistry; Polycyclic Compounds; sensors; Solubility; Theoretical and; Triazoles - chemistry; Tuning; Water - chemistry; Xenon; Xenon - chemistry; Xenon Isotopes - chemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201001170

In the 129Xe NMR‐based biosensing approach in which the hyperpolarized noble gas is transported to biological receptors for a sensitive molecular imaging, cryptophanes are excellent xenon host systems. However to avoid formation of self‐organized systems, these hydrophobic cage molecules can be rendered water soluble by introduction of ionic groups. We show that the sensitivity of xenon to its local environment and the presence of these ionic functions can lead to interesting properties. For a first water‐soluble cryptophane derivative, we show that a precise monitoring of the local pH can be performed. For a second cryptophane, the presence of ionic groups close to the cryptophane cavity modifies the xenon binding constant and in–out exchange rate. The latter allows the tuning of physical properties of xenon–cryptophane interactions without resorting to a change of the cavity size. These results open new perspectives on the influence of chemical modifications of cryptophanes for optimizing the biosensor properties. (Xe)eing is believing! The interaction of hyperpolarized xenon with two water‐soluble cryptophanes reveals interesting sensing properties. The presence of ionic substituents on the aromatic rings of the cage molecules renders the chemical shift of encapsulated xenon dependent on pH (see figure). When the ionic groups are, however, closer to the cavity portals, the nature of the counterion influences both the thermodynamics and the kinetics of the xenon binding.