The interaction between cucuribit[10]uril (Q[10]) and a series of 4-pyrrolidinopyridinium salts bearing aliphatic substituents at the pyridinium nitrogen, namely 4-(C4H8N)C5H5NRBr, where R = Et (g1), n-butyl (g2), n-pentyl (g3), n-hexyl (g4), n-octyl (g5), n-dodecyl (g6), has been studied in aqueous solution by 1H NMR spectroscopy, electronic absorption spectroscopy and mass spectrometry. The results revealed that the guests g1–g5 are located completely inside the cavity differing only in the orientation of g1, g4 and g5 which are aligned with the portal, whilst g2 and g3 are perpendicular to it. For g6, the tetrahydropyrrole moiety remains outside of the portal. DFT calculations confirm the stability of the guests in the Q[10] and the possibility of their curved structure inside the Q[10].
A new fluorescent probe composed of cucurbit[10]uril (Q[10]) and a water-soluble derivative of pyrene, aminopropyl-1-pyrenebutanamide (PBA), is designated. 1 H NMR spectroscopy reveals that PBA is encapsulated into Q[10] in an aqueous solution to form a stable 1:1 host-guest inclusion complex of PBA@Q[10]. This complex behaves as a highly selective fluorescence quenching probe for Fe 3+ in aqueous solutions that may be attributed to the efficient absorption of Fe 3+ , which hindering absorption of PBA@Q[10] probe at the excitation wavelength of 332 nm, and competitive experiments for the coexistence of Fe 3+ with one or all of the other metal ions (37 metal ions) reveals that the selectivity of PBA@Q[10] to Fe 3+ is not disturbed by the addition of 50.0 equiv. of the other metal ions. The limits of detection of Fe 3+ was determined to be 0.55 mM. Furthermore, the fluorescence enhancing effect of PBA@Q[10] for Ag + is detected at the above wavelength. According to the mechanistic studies, the fluorescence enhancing route involves interaction of Ag + ions with the probe, mainly under an internal charge transfer between Ag + and the probe. Outcomes of this study suggest that PBA@Q[10] probably functions as a potential and promising fluorescence sensor for monitoring of different polluting metal ions in waste waters.
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