pH-Responsive Interaction of Fluorogenic Antimalarial Drug Quinine with Macrocyclic Host Cucurbit7 uril: Modulations in Photophysical and Acid-Base Properties

摘要

abstract_textpIntriguing changes in photophysical and acid-base properties of fluorogenic antimalarial drug, quinine (QN), are presented on its interaction with macrocyclic cucurbit7 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 similar to 1 and similar to 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./p/abstract_text