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Proton transfer in fluorescent secondary amines: synthesis, photophysics, theoretical calculation and preparation of photoactive phosphatidylcholine-based liposomes

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Abstract

In this article, new fluorescent lipophilic based benzazoles were synthesized from the reaction between photoactive formyl derivatives and aliphatic amines followed by NaBH4 reduction with good yields. The photophysics of the benzazoles was investigated experimentally and theoretically. These compounds present absorption maxima in the UV region (∼339 nm) and fluorescence emission maxima in the cyan to green region with a large Stokes shift (∼175 nm) due to a proton transfer process in the excited state. Two fluorophores were successfully used as a proof of concept to produce stable photoactive liposomes prepared from phosphatidylcholine (PC) and were characterized by zeta potential, small angle X-ray scattering (SAXS), FTIR and UV-Vis experiments (turbidity). The scattering data indicate that the presence of compounds 20 and 23 reduces the overall surface charge of the PC vesicles, possibly due to the partial neutralization of phosphatidic acid and/or phosphatidylinositol phosphate by the amine groups, and they also modify the structural features of the assemblies, leading, in particular, to a reduction in the thickness of the hydrophobic inner segment (tt) of the liposomes. DFT and TD-DFT calculations were performed with the ωB97XD functional. Geometric analyses show that the 2-(2′-hydroxyphenyl)benzazolic planar portion allows an effective ππ* electronic transition. Additionally, the calculations indicate a small energy barrier to proton transfer. The results of the absorption and emission maxima show a slight solvent influence on the wavelengths.

Graphical abstract: Proton transfer in fluorescent secondary amines: synthesis, photophysics, theoretical calculation and preparation of photoactive phosphatidylcholine-based liposomes

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Publication details

The article was received on 11 Jan 2019, accepted on 15 Feb 2019 and first published on 18 Feb 2019


Article type: Paper
DOI: 10.1039/C9PP00017H
Citation: Photochem. Photobiol. Sci., 2019, Advance Article

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    Proton transfer in fluorescent secondary amines: synthesis, photophysics, theoretical calculation and preparation of photoactive phosphatidylcholine-based liposomes

    T. Kroetz, M. C. dos Santos, R. Beal, G. M. Zanotto, F. S. Santos, F. C. Giacomelli, P. F. B. Gonçalves, V. R. de Lima, A. G. Dal-Bó and F. S. Rodembusch, Photochem. Photobiol. Sci., 2019, Advance Article , DOI: 10.1039/C9PP00017H

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