Live cell imaging by 3-imino-(2-phenol)-1,8-naphthalimides: The effect of ex vivo hydrolysis

Abstract

A series of 3-amino-N-substituted-1,8-naphthalimides and their salicylic Schiff base derivatives were synthesized. The structure of the obtained compounds was confirmed using ¹H and ¹³C NMR, FT-IR spectroscopy and elemental analysis and COSY and HMQC for the representative molecules. The photophysical (UV-Vis, PL) and biological properties of all of the prepared compounds were studied. It was found that the amine with the n-hexyl group in EtOH had the highest PL quantum yield (Ф = 85%) compared to the others. Moreover, the chelating properties of the azomethines with the n-hexyl group (1a, 1b, 1c) were tested against various cations (Al³⁺, Ba²⁺, Co²⁺, Cu²⁺, Cr³⁺, Fe²⁺, Fe³⁺, Mn²⁺, Ni²⁺, Pb²⁺, Sr²⁺ and Zn²⁺) in an acetonitrile, acetone and PBS/AC mixture. Compounds that contained the electron withdrawing groups (-Br, -I) had the ability to chelate most of the studied cations, while the unsubstituted derivative chelated only the trivalent cations such as Al³⁺, Cr³⁺ and Fe³⁺ in acetonitrile. The effect of the environment on the keto-enol tautomeric equilibrium was also demonstrated, especially in the case of the derivative with a bromine atom. The biological studies showed that the tested molecules had no cytotoxicity. Additionally, the ability to image intracellular organelles such as the mitochondria and endoplasmic reticulum was revealed. The crucial role of the hydrolysis of imines for cellular imaging was presented.

Keywords: 1,8-Naphthalimides; Hydrolysis of imines; Live cell imaging.