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Modulation in the acidity constant of acridine dye with cucurbiturils: stimuli-responsive pKa tuning and dye relocation into live cells

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Abstract

The noncovalent host–guest interactions of the cationic (AcH+) and neutral (Ac) forms of an acridine dye with macrocyclic hosts such as cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) have been investigated to evaluate the effect of cavity size on the photophysical properties and the protolytic equilibrium of the acridine dye. The cationic form undergoes significant complexation with CB7 (Keq = 106 M−1), causing a sharp decrease in the fluorescence intensity, whereas the neutral Ac form of the dye undergoes weak complexation with CB7 (Keq = 103 M−1) and the binding constant is lowered by three orders of magnitude compared to that of the CB7–AcH+ system. The Job plot revealed that both forms form a 1 : 1 complex with CB7. On the other hand, the AcH+ form shows strong emission quenching on interaction with CB8 and the formation of the 1 : 2 CB8 : AcH+ complex has been confirmed from the Job plot. The strong affinity of CB7 and CB8 to the protonated form resulted in a large upward pKa shift (ΔpKa ∼ 3.4 units for CB7 and ∼1.3 units for CB8) in the dye. Taking advantage of the above modulations in the fluorescence and pKa values, adamantylamine-induced fluorescence regeneration, controlled pKa tuning and dye relocation from the CB7 cavity to cell lines have been established for the first time, which find potential applications in fluorescence offon sensing and drug delivery.

Graphical abstract: Modulation in the acidity constant of acridine dye with cucurbiturils: stimuli-responsive pKa tuning and dye relocation into live cells

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Publication details

The article was received on 26 Aug 2017, accepted on 06 Sep 2017 and first published on 06 Sep 2017


Article type: Paper
DOI: 10.1039/C7OB02135F
Citation: Org. Biomol. Chem., 2017, Advance Article
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    Modulation in the acidity constant of acridine dye with cucurbiturils: stimuli-responsive pKa tuning and dye relocation into live cells

    R. Khurana, N. Barooah, A. C. Bhasikuttan and J. Mohanty, Org. Biomol. Chem., 2017, Advance Article , DOI: 10.1039/C7OB02135F

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