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      Squaramide—Naphthalimide Conjugates as “Turn-On” Fluorescent Sensors for Bromide Through an Aggregation-Disaggregation Approach

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          Abstract

          The syntheses of two new squaramide-naphthalimide conjugates ( SQ1 and SQ2) are reported where both compounds have been shown to act as selective fluorescence “turn on” probes for bromide in aqueous DMSO solution through a disaggregation induced response. SQ1 and SQ2 displayed a large degree of self-aggregation in aqueous solution that is disrupted at increased temperature as studied by 1H NMR and Scanning Electron Microscopy (SEM). Moreover, the fluorescence behavior of both receptors was shown to be highly dependent upon the aggregation state and increasing temperature gave rise to a significant increase in fluorescence intensity. Moreover, this disaggregation induced emission (DIE) response was exploited for the selective recognition of certain halides, where the receptors gave rise to distinct responses related to the interaction of the various halide anions with the receptors. Addition of F rendered both compounds non-emissive; thought to be due to a deprotonation event while, surprisingly, Br resulted in a dramatic 500–600% fluorescence enhancement thought to be due to a disruption of compound aggregation and allowing the monomeric receptors to dominate in solution. Furthermore, optical sensing parameters such as limits of detection and binding constant of probes were also measured toward the various halides (F , Cl , Br , and I ) where both SQ1 and SQ2 were found to sense halides with adequate sensitivity to measure μM levels of halide contamination. Finally, initial studies in a human cell line were also conducted where it was observed that both compounds are capable of being taken up by HeLa cells, exhibiting intracellular fluorescence as measured by both confocal microscopy and flow cytometry. Finally, using flow cytometry we were also able to show that cells treated with NaBr exhibited a demonstrable spectroscopic response when treated with either SQ1 or SQ2.

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          Most cited references55

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          Anion Recognition and Sensing: The State of the Art and Future Perspectives

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            Determining association constants from titration experiments in supramolecular chemistry.

            The most common approach for quantifying interactions in supramolecular chemistry is a titration of the guest to solution of the host, noting the changes in some physical property through NMR, UV-Vis, fluorescence or other techniques. Despite the apparent simplicity of this approach, there are several issues that need to be carefully addressed to ensure that the final results are reliable. This includes the use of non-linear rather than linear regression methods, careful choice of stoichiometric binding model, the choice of method (e.g., NMR vs. UV-Vis) and concentration of host, the application of advanced data analysis methods such as global analysis and finally the estimation of uncertainties and confidence intervals for the results obtained. This tutorial review will give a systematic overview of all these issues-highlighting some of the key messages herein with simulated data analysis examples.
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              Thermodynamics of solvation of ions. Part 5.—Gibbs free energy of hydration at 298.15 K

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                Author and article information

                Contributors
                Journal
                Front Chem
                Front Chem
                Front. Chem.
                Frontiers in Chemistry
                Frontiers Media S.A.
                2296-2646
                22 May 2019
                2019
                : 7
                : 354
                Affiliations
                [1] 1Department of Chemistry, Maynooth University, National University of Ireland , Maynooth, Ireland
                [2] 2Department of Biology, Maynooth University, National University of Ireland , Maynooth, Ireland
                [3] 3Maynooth University Human Health Research Institute, Maynooth University, National University of Ireland , Maynooth, Ireland
                Author notes

                Edited by: Tony D. James, University of Bath, United Kingdom

                Reviewed by: Valeria Amendola, University of Pavia, Italy; Philip A. Gale, University of Sydney, Australia

                *Correspondence: Robert B. P. Elmes robert.elmes@ 123456mu.ie

                This article was submitted to Supramolecular Chemistry, a section of the journal Frontiers in Chemistry

                Article
                10.3389/fchem.2019.00354
                6540876
                ca22b458-7e98-4bd8-a197-dc7de46cb716
                Copyright © 2019 Kumawat, Abogunrin, Kickham, Pardeshi, Fenelon, Schroeder and Elmes.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                History
                : 15 February 2019
                : 29 April 2019
                Page count
                Figures: 10, Tables: 2, Equations: 0, References: 63, Pages: 14, Words: 9197
                Funding
                Funded by: Science Foundation Ireland 10.13039/501100001602
                Funded by: Irish Research Council 10.13039/501100002081
                Funded by: National University of Ireland, Maynooth 10.13039/501100001633
                Categories
                Chemistry
                Original Research

                supramolecular chemistry,squaramide,1,8-naphthalimide,fluorescent sensor,anion recognition

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