Fluorophore–quencher complexes (Cu2+/Al3+) of coumarin Schiff bases as chemosensors for the detection of l-glutamic acid and l-arginine: in vitro and in vivo studies

Abstract

This study reports the development of new probes RR1 ((1E)-1-(1-(6-bromo-2-oxo-2H-chromen-3-yl)ethylidene)ethyl thiosemicarbazone) and RR2 ((1E)-1-(1-(6-bromo-2-oxo-2H-chromen-3-yl)ethylidene)phenyl thiosemicarbazone), which selectively showed fluorescence turn ‘OFF’ response towards Cu²⁺ and Al³⁺. Further, complexes of RR1-Cu²⁺ and RR2-Al³⁺ acted as chemosensors for the detection of L-amino acids. RR1-Cu²⁺ selectively detected L-arginine (fluorescence turn ‘ON’), and RR2-Al³⁺ selectively detected L-glutamic acid (fluorescence turn ‘ON’). The existence of the fluorophore–quencher complexes RR1-Cu²⁺ and RR2-Al³⁺ was confirmed by theoretical studies. Further, the chemosensors RR1-Cu²⁺ and RR2-Al³⁺ have three possible structural isomers (RR1-Cu²⁺-L-arginine – A, B and C) and (R2-Al³⁺-L-glutamic acid – D, E and F), as confirmed by theoretical studies. In vitro bio-imaging of the probes (RR1 and RR2), complexes (RR1-Cu²⁺ and RR2-Al³⁺) and complexes associated with L-arginine (RR1-Cu²⁺-L-arginine) and L-glutamic acid (R2-Al³⁺-L-glutamic acid) was performed in the MDA-MB-231 cell line using their IC₅₀ concentrations. In addition, in vivo live cell imaging studies were conducted using C. elegans as the model organism.