Abstract
A series of fluorescent pH probes based on the spiro-cyclic rhodamine core, aminomethylrhodamines (AMR), was synthesized and the effect of cycloalkane ring size on the acid/base properties of the AMR system was explored. The study involved a series of rhodamine 6G (cAMR6G) and rhodamine B (cAMR) pH probes with cycloalkane ring sizes from C-3 to C-6 on the spiro-cyclic amino group. It is known that the pKa value of cycloalkylamines can be tuned by different ring sizes in accordance with the Baeyer ring strain theory. Smaller ring amines have lower pKa value, i.e., they are less basic, such that the relative order in cycloalkylamine basicity is: cyclohexyl > cyclopentyl > cyclobutyl > cyclopropyl. Herein, it was found that the pKa values of the cAMR and cAMR6G systems can also be predicted by Baeyer ring strain theory. The pKa values for the cAMR6G series were shown to be higher than the cAMR series by a value of approximately 1.
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Acknowledgments
The authors gratefully acknowledge support fully or in part from the National Institutes of Health (NIH-1R15GM080721-01A1), the National Science Foundation (NSF-CHEM-0719185). The authors also thank the Department of Chemistry and Biochemistry, Southern Illinois University for partial support of this research.
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Liu, C., Best, Q.A., Suarez, B. et al. Cycloalkyl-AminoMethylRhodamines: pH Dependent Photophysical Properties Tuned by Cycloalkane Ring Size. J Fluoresc 25, 231–237 (2015). https://doi.org/10.1007/s10895-015-1519-z
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DOI: https://doi.org/10.1007/s10895-015-1519-z