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Issue 4, 2013
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pH Induced dual “OFF–ON–OFF” switch: influence of a suitably placed carboxylic acid

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Abstract

The design and synthesis of molecular probes competent for pH signaling within or beyond a certain range is a complicated matter. Herein a new mechanism for ‘‘OFF–ON–OFF’’ absorbance and fluorescence intensities vs. pH behaviour is described. The probe design is based on the connection of carboxylic acid derivatized benzoxazole and 7-hydroxycoumarin/iminocoumarin parts. The protonation/deprotonation of the carboxylic acid (–COOH), N atom of benzoxazole ring and hydroxy part of the coumarin ring have been used for this mechanistic study. We have designed the molecule in such a fashion that deprotonation of the hydroxy part takes place at a lower pKa compared to deprotonation of the –COOH. The dual ‘‘OFF–ON–OFF’’ properties of our probes depend on the C–C bond between the two different heterocyclic parts. Quantum mechanical calculations showed that the particular ‘C–C’ bond has an additional π-character. The twisting around this bond in different forms is responsible for such an ‘‘OFF–ON–OFF’’ property. This mechanism is new in fluorescence alteration processes. The delocalization of charge from one heterocyclic part to the other heterocyclic part in the mono- and dianionic forms controls the ‘‘OFF–ON–OFF’’ properties. The role of the carboxylic acid group was examined using an acetyl substituted derivative. One of our probes was successfully applied in live cell imaging studies in media at different pH.

Graphical abstract: pH Induced dual “OFF–ON–OFF” switch: influence of a suitably placed carboxylic acid

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Publication details

The article was received on 07 Jun 2012, accepted on 21 Sep 2012 and first published on 11 Oct 2012


Article type: Paper
DOI: 10.1039/C2OB26630J
Org. Biomol. Chem., 2013,11, 563-568

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    pH Induced dual “OFF–ON–OFF” switch: influence of a suitably placed carboxylic acid

    K. K. Sadhu, S. Mizukami, A. Yoshimura and K. Kikuchi, Org. Biomol. Chem., 2013, 11, 563
    DOI: 10.1039/C2OB26630J

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