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Abstract
The supramolecular interactions of the ocular drug tropicamide (TR) with cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated in aqueous solutions by using 1H NMR, ESI-MS and UV–vis spectroscopic techniques. The results indicate a 1:1 binding stoichiometry of TR with CB7 and CB8. The binding constants of TR in its protonated form were higher (e.g. K = 4 × 106 M− 1 with CB8) than in its neutral form (e.g. K = 1.4 × 104 M− 1 with CB8), which led to a complexation-induced increase in its pK a value of ca. 0.5 and 2 units with CB7 and CB8, respectively. In the presence of about 1% (w/v) CB8, the ionisation degree of 0.1% (w/v) TR was increased from 2% to 62% at neutral pH. The increase in the pK a value and thus stabilisation of the protonated TR species at neutral pH is discussed in the context of supramolecular drug delivery of ophthalmologic drugs.
Acknowledgements
NS would like to acknowledge the Research Affairs at the United Arab Emirates University for their financial support of this project under grant number 1563-02-01-10, Dr Ribhi Hazin (MD in ophthalmology at Harvard Medical School, USA) for his encouragements to conduct this study, and Dr Fawaz Sarayreh (MD in ophthalmology at the Faculty of Medicine, Mu'tah University, Jordan) for his fruitful discussion. IG and WMN would like to thank the Deutsche Forschungsgemeinschaft (DFG, NA 686/6) for financial support.