A Sulfonated Tweezer-Shaped Receptor Selectively Recognizes Caffeine in Water

Abstract

The selective recognition of caffeine in water among structurally related xanthines and purine or pyrimidine bases was achieved by a simple tweezer-shaped receptor featuring sulfonate hydrosolubilizing groups. The remarkable affinity for caffeine, among the highest reported thus far in the literature and larger than that shown by adenosine receptors of all subtypes, stems from a synergistic combination of hydrogen bonding, CH−π, and π-stacking interactions.

A Macrocyclic Tweezers‐Shaped Receptor for the Biomimetic Recognition of the Gal(α1‐3)Gal Disaccharide of the α‐Gal Antigen

“…The observation that the H−C and CH 2 protons shift upfield, both when concentration increases and when pH decreases, suggests that the strong perturbation affecting the two signals is related to an increase in the mole fraction of the trimeric species, whereby these protons most likely are affected by an intermolecular shielding effect caused by the aromatic rings. In addition, dilution experiment on receptor 3 at pH 11 does not show any self‐association phenomena (no variation in chemical shifts was observed, see Figure S13); this evidence indicates that self‐association, which in these systems is usually caused by π‐stacking interactions, [31] is here most probably driven by hydrogen bond formation between partially protonated phosphonate groups. NOESY spectra were thus carried out on receptor 3 at both, pH 7.4 (Figure 2b) and pH 11 (Figure S24–25).…”