Intriguing changes in photophysical and acid-base properties of fluorogenic antimalarial drug, quinine (QN), are presented on its interaction with macrocyclic cucurbit[7]uril (CB7)host. While dicationic QNH 2 2 + form shows large enhancement in both steady state and time-resolved fluorescence, monocationic QNH + and neutral QN forms show significant reductions. The pK a (1) and pK a (2) values of the drug undergo~1 and~1.7 units of upward shifts, respectively, on its binding to CB7 host, substantiating the differential binding strengths of various prototropic forms. Whereas the QNH 2 2 + and QNH + forms undergo 1:2 (dye to CB7) inclusion complex formation, the neutral QN is suggested to form 1:1 inclusion complex with CB7.Interestingly, the observed results in the present study are substantially different and in some cases quite contrasting to the results reported in a recently published paper (Phys. Chem. Chem. Phys., 2016, 18, 30520). In the present study we could unequivocally establish that there were many serious inconsistencies in the above paper, which we could now convincingly rectify, designing appropriate experimental and sample conditions. With the intriguing modulations observed in the photophysical and acid-base properties, the quinine-CB7 system is suggested to act as an improved fluorimetric standard than the free quinine system. Additionally, the modulations have implications in drug stabilization, drug delivery, sensors and other applications.

Herein we report a facile transformation of hydroxylated cucurbit[n]uril (CB[n], n = 6 and 7) to other functionality-conjugated CB[n]s by nucleophilic substitution of the hydroxyl group with a wide range of nitriles and alcohols. The reaction proceeds efficiently via generation of a superelectrophilic carbocation on the CB framework from hydroxylated CB[n]s under superacidic conditions. One of the resulting CB[n] derivatives with reactive functionality, monocarboxylated CB[7], is efficiently conjugated to an enzyme (horseradish peroxidase, HRP) by amide coupling. This provides a CB[7]conjugated functional biomaterial (CB[7]-HRP) that selectively detects proteins labeled with a guest, adamantylammonium (AdA), based on bioorthogonal high-affinity host−guest interactions between CB[7] and AdA. We demonstrated the potential of overcoming the limitations in preparing reactive functional CB[n] derivatives, enabling the exploration of novel bioapplications of CB[n]-based host−guest chemistry with new CB[n]-conjugated functional materials.

In this feature article, the two types (molecular amphiphile and supramolecular amphiphile) of CB-based amphiphiles, their self-assemblies and their applications for useful nanotherapeutics and theranostics are presented with future perspectives.

No abstract

No abstract