Supramolecular Host‐Inhibited Excited‐State Proton Transfer and Fluorescence Switching of the Anti‐Cancer Drug, Topotecan

• DOI: 10.1002/cphc.201300461
• Publication Date: 2013-07-22T12:41:06Z
• Authors: Krishna Gavvala; Abhigyan Sengupta; Raj Kumar Koninti; Partha Hazra
• Keywords: Cationic polymerization

Abstract The effect of cucurbit[7]uril (CB[7]) nano‐caging on the photophysical properties, particularly excited‐state proton transfer (ESPT) reaction, an eminent anti‐cancer drug, topotecan (TPT), is demonstrated through steady‐state and time‐resolved fluorescence measurements. TPT in water (pH 6) exists exclusively as cationic form (C) ground state. However, drug emission mainly comes from zwitterionic (Z*) TPT, attributed to water‐assisted ESPT between 10‐hydroxyl group water, which leads transformation C* Z* TPT. In presence CB[7], it found that selective encapsulation C results formation a 1:1 inclusion complex (CB[7]:TPT), process inhibited by this process. As result, becomes dominant emitting species CB[7] rather than Z*, switching takes place green blue. Time‐resolved studies also support existence CB[7]‐encapsulated major macrocyclic host. Semi‐empirical quantum chemical calculations are employed gain insight into molecular picture orientation complex. It clearly seen optimised structure CB[7]:TPT both 9‐dimethylaminomethylene groups lie partly inside cavity, thereby inhibit Finally, controlled release achieved means introducing NaCl, rich cells, external stimulus.