Time- and concentration dependent reactivity of Cys, Hcy and GSH on the Diels Alder grafted conjugate of 1,3,5-tri-calix[6]arene to bring selectivity for Cys: Spectroscopy and microscopy, and its reactivity in cells

Abstract

Herein we report the synthesis and characterization of 7-oxanorbornadiene (OND)-appended 1,3,5-tris conjugate of calix[6]arene (L₂). L₂ has been shown to exhibit selective reactivity toward cysteine (Cys) over homocysteine (Hcy) and glutathione (GSH) under stoichiometric conditions. The selectivity of L₂ is attributed to the steric crowding of three Diels–Alder centers possessing OND units present on the calix[6]arene platform, while a control molecular system possessing only one such unit without the calix[6]arene platform (L₁) does not show any selectivity toward Cys. While L₂ exhibited spherical particles, its reactivity with Cys resulted in flowerlike morphological features, as revealed by scanning electron microscopy. However, the reaction with GSH did not result in any such morphological features, a result that is in agreement with that observed from fluorescence studies in solution. L₂ has been shown to react with Cys present in HeLa and Jurkat E6 cells by fluorescence microscopy.