Recognition in water of bioactive substrates by a sulphonato p-tert-butylcalix[5]arene

Abstract

The molecular recognition in water of neurotransmitter monoamine and trace amine hydrochlorides by p-tert-butylcalix[5]-arene 1 – bearing 4-sulphonatobutoxy groups at the lower rim – has been investigated. According to ¹H NMR measurements, the hydrophobic cavity of receptor 1 best binds tyramine hydrochloride, K _a = 5370 ± 870 M^− 1.

Keywords::

• water-soluble calixarene
• neurotransmitters
• trace amines
• molecular recognition

Acknowledgements

We thank Dr Valentina Villari and Dr Norberto Micali (CNR-IPCF, Messina, Italy) for dynamic light scattering measurements.

Notes

^1. Besides our earlier assessment ( 6 ), the proclivity of 1 to self-assemble has now been confirmed by dynamic light scattering measurements indicating the presence of aggregates with a hydrodynamic radius of about 100 nm, even in a 0.1 mM aqueous solution. Species of this size fall outside the detection range of ¹H NMR spectroscopy.

^2. D₂O solutions of 1 (0.4 mM) were left to equilibrate at room temperature for 1 h and then filtered through a 0.1 μm membrane filter prior to determination of their effective concentration (see the Supplementary Material).

^3. Characterisation of these species is currently in progress and pertinent details will be reported in due course.

Additional information

Funding

Funding

MIUR (PRIN-2009A5Y3N9 project) is gratefully thanked for financial support.