Effect of metal oxidation state on FRET: a Cu(i) silent but selectively Cu(ii) responsive fluorescent reporter and its bioimaging applications

Abstract

Copper(II) and copper(I) complexes of a newly designed and crystallographically characterized Schiff base (HL) derived from rhodamine hydrazide and cinnamaldehyde were isolated in pure form formulated as [Cu(L)(NO3)] (L-Cu) (1) and [Cu(HL)(CH3CN)(H2O)]ClO4 (HL-Cu) (2), and characterized by physicochemical and spectroscopic tools. Interestingly, complex 1 but not 2 offers red fluorescence in solution state, and eventually HL behaves as a Cu(II) ions selective FRET based fluorosensor in HEPES buffer (1 mM, acetonitrile-water: 1/5, v/v) at 25 °C at biological pH with almost no interference of other competitive ions. The dependency of the FRET process on the +2 oxidation state of copper has been nicely supported by exhaustive experimental studies comprising electronic, fluorimetric, NMR titration, and theoretical calculations. The sensing ability of HL has been evaluated by the LOD value towards Cu(II) ions (83.7 nM) and short responsive time (5-10 s). Even the discrimination of copper(I) and copper(II) has also been done using only UV-Vis spectroscopic study. The efficacy of this bio-friendly probe has been determined by employing HL to detect the intercellular distribution of Cu(II) ions in HeLa cells by developing image under fluorescence microscope.

Two Ho(III) and Co(II) complexes constructed from bis(triazol‐1‐yl)benzoic acid with structurally similar carboxyl ligands: Syntheses, structures and biological activities

“…Cell nuclei were counterstained with Annexin‐V FITC and PI (FITC: 20 μg ml −1 ; PI: 50 μg ml −1 ) for 5 min. The cells were observed and imaged with a fluorescence microscope (fluorescent inverted microscope, XD30A‐RFL) with excitation at 496 nm and emission at 518 nm …”

FRET-based rhodamine–coumarin conjugate as a Fe3+ selective ratiometric fluorescent sensor in aqueous media

“…S9). 37,38 1=ðF x À F 0 Þ ¼ 1=ðF max À F 0 Þ þ ð1=K½CÞð1=ðF max À F 0 ÞÞ where F 0 , F x , and F max are the emission intensities (at 550 nm) of the organic moiety considered in the absence of metal ion, at an intermediate metal ion concentration, and at a concentration of complete interaction, respectively, and where K is the binding constant concentration. …”

A novel ratiometric fluorescent probe for detection of Fe3+ by rhodamine–quinoline conjugate

“…The binding constant value was determined from the emission intensity data following the modified Benesi-Hildebrand equation [35][36] (A): where F 0 , F x , and F max were the emission intensities (at 550 nm) of the organic moiety considered in the absence of metal ion, at an intermediate metal ion concentration, and at a concentration of complete interaction, respectively, and where K was the binding constant concentration.…”