Reactivity-Based Detection of Copper(II) Ion in Water: Oxidative Cyclization of Azoaromatics as Fluorescence Turn-On Signaling Mechanism

Abstract

An oxidative cyclization reaction transforms nonemissive azoanilines into highly fluorescent benzotriazoles. We have found that introduction of multiple electron-donating amino groups onto a simple o-(phenylazo)aniline platform dramatically accelerates its conversion to the emissive polycyclic product. Notably, this chemistry can be effected by μM-level concentrations of copper(II) ion in water (pH = 6-8) at room temperature to elicit >80-fold enhancement in the green emission at λ(em) = 530 nm. Comparative kinetic and electrochemical studies on a series of structural analogues have established that the accelerated reaction rates correlate directly with a systematic cathodic shift in the oxidation onset potential of the azo precursors. In addition, single-crystal X-ray crystallographic analysis on the most reactive derivative revealed the presence of a five-membered ring intramolecular hydrogen-bonding network. An enhanced contribution of the quinoid-type resonance in such conformation apparently facilitates the mechanistically required proton transfer step, which, in conjunction with electron transfer at lower oxidation potential, contributes to a rapid cyclization reaction triggered by copper(II) ion in water.

Selective Capture of CWAs and Containment of Their Neutralization Byproducts by Porous Frameworks Presenting Self-Amplifying and Self-Regulating Reactivities

“…15 N NMR spectra obtained from a sample of thermally treated UiO-66-C showed a decrease in the intensity of the hemiaminal product peak at 93 ppm and an increased intensity of the aziridine peak at 71 ppm. The isotopically enriched 13 C NMR spectrum showed an analogous relationship between the hemiaminal and aziridine resonances, further confirming the 15 N assignments. Again, to quantify the transformation, direct excitation of the 15 N NMR spectrum showed a ratio of 3:1:5 (1:0.28:1.68) for the protonated amine/ hemiaminal/aziridine.…”

“…The MAS 13 C NMR spectrum of UiO-66-B synthesized from isotopically labeled 13 CH3 13 CHO supports the assignment, displaying resonance peaks at 85 and 49 ppm due to the secondary and primary carbon atoms of the hemiaminal, respectively. The additional peak at 71 ppm in the 15 N NMR spectrum is consistent with the presence of an aziridine ring, which is also supported by the isotopically enriched 13 C MAS NMR spectrum in the resonance at 20 ppm. Integration of a direct-excitation NMR spectrum gavie approximate yields of each reaction with 3:5:2 (1:1.74:0.72) of the protonated amine, hemiaminal, and aziridine, respectively.…”

“…Contact angle measurements confirmed increased hydrophobicity of the modified surface (13). Copper-catalyzed Huisgen [3 + 2] dipolar cycloaddition of 3 onto 13 proceeded cleanly under ambient conditions to furnish covalently-modified glass surface (14) presenting "masked" reagent modules derived from 3.…”

Target induced interfacial self-assembly of nanoparticles: A new platform for reproducible quantification of copper ions

“…5b). With such well-prepared SERS substrate, TINSAI protocol shows better sensitivity (< 0.5 nM) than many previously reported methods, such as inductively coupled plasma optical emission spectrometry (ICP/OES) [44], flame atomic absorption spectrometry (FAAS) [45], and some user-friendly optical platforms [46][47][48]. Meanwhile, TINSAI protocol also possesses sensitivity comparable with the novel electrochemical systems [49,50] and some highly sensitive fluorescent sensors [51,52].…”

Coumarine–imino–C2-glucosyl conjugate as receptor for Cu2+ in blood serum milieu, on silica gel sheet and in Hep G2 cells and the characterization of the species of recognition

“…When the concentration of the copper ions is unregulated, it can catalyze the production of reactive oxygen species which will damage biomolecules and thus can exhibit its role in oxidative stress and neurodegenerative disorders [3][4][5][6][7][8][9]. Therefore the researchers put considerable efforts in the design and development of fluorescent chemosensors, some of which are usable even in cellular imaging besides providing sensitive and selective detection toward Cu 2+ [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. A number of molecular receptors reported in the literature suffer from poor water solubility, high detection limit and cytotoxicity toward normal cells [24][25][26][27].…”