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Cyclopentaphenylalanine as a fluorescent anion sensor in solution

In the last few years artificial ion transporters, which imitate natural systems in selective anion binding and are capable of passing the hydrophobic lipid barriers, have been intensively investigated.1, 2 As such, cyclopeptides could be used for selective binding and membrane transport of predominant anions in vivo (Cl–, HCO3–, and H2PO4–/HPO42–). These compounds generally exhibit improved metabolic stability and bioavailability as well as enhanced binding affinity and selectivity toward substrates compared to their more flexible linear analogs.2, 3 Cyclopeptides derived from fluorescent amino acids, like phenylalanine, could potentially be very sensitive fluorimetric ion sensors due to the high sensitivity of fluorescence spectroscopy. In the scope of this work, we conducted spectrophotometric and fluorimetric titrations to obtain stability constant of complexes of cyclopentaphenylalanine (Figure 1) with various anionic species in methanol and acetonitrile. Furthermore, we carried out classical molecular dynamics simulations in order to investigate conformational changes of the receptor upon anion complexation in solution. Figure 1. Structure of cyclopentaphenylalanine and its complex with chloride anion obtained by MD simulations. ACKNOWLEDGEMENTS This work was supported by the Croatian Science Foundation under project IP-2019- 04-9560 (MacroSol). 1. S. Kubik, Acc. Chem. Res. 2017, 50, 2870. 2. G. Horvat, S. Tarana, N. Vidović, N. Cindro, G. Speranza, V. Tomišić, J. Mol. Liq. 2021, 350, 116848. 3. N. Vidović, G. Horvat, D. Riva, T. Rinkovec, N. Cindro, V. Tomišić, G. Speranza, Org. Lett. 2020, 22, 2129.

anion-binding ; cyclohomopeptides ; MD simulations ; NMR ; flurimetry

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