Triarylamine Rhodanine Derivatives as Red Emissive Sensor for Discriminative Detection of Ag⁺ and Hg²⁺ ions in Buffer-Free Aqueous Solutions

Abstract

A completely water-soluble, red emitting, multibranched sensor based on the electron-rich triphenylamine and electron-deficient rhodanine-3-acetic acid has been developed. The sensors mRA, dRA, and tRA, respectively, have one, two, and three rhodanine-3-acetic acid groups, responsible for the interaction with the metal ions as well as the solubility of the probe in water. mRA, dRA, and tRA senses Ag+ and Hg2+ ions in a buffer-free aqueous solution with the lowest detection level of 0.06 and 0.02 ppm, respectively. The yellow color of free sensor turns into purple and colorless in the presence of Ag+ and Hg2+ ions, respectively, which can be witnessed even by the naked eye. The metal ion preferentially binds with electron-deficient rhodanine-3-acetic acid owing to the presence of an ideal coordination environment. The distinctly different signals for Ag+ and Hg2+ ions occur because of the dissimilar binding modes, wherein the former extends and the latter breaks the π-electron conjugation that results in a different signaling mechanism. Nevertheless, the additional binding sites of dRA and tRA influences the binding constant and sensitivity; however, additional metal ion binding does not occur because of the changes in the electronic properties after initial binding. The applicability of these sensors in the biological medium was also tested using HaCaT cells using Ag+ and Hg2+ ions, which demonstrated the quenching of intense red fluorescence of the probe, and thus, these probes can be also be used as a potential biosensor.

A Chiral Molecular Cage Comprising Diethynylallenes and N‐Heterotriangulenes for Enantioselective Recognition

“…[13][14][15] On this firm basis, we advocate the use of bridged triarylamines, known as N-heterotriangulenes (N-HTAs), in the role of chromophoric aromatic lids, in order to achieve redox-active nanosized cavities [16][17][18][19][20] for larger chiral guests, aiming at setting foot on the realm of enantioselective discrimination. [21][22][23] Precedents of sensing examples involving triarylamines range from the detection of metallic cations, [24] to toxic anions [25] or anions present in chemical weapons, [26] nitroaromatic explosives, [27] biological metabolites, [28] toxic gases, [29,30] and pH determination. [31] Regarding the implementation of triarylamines in both macrocyclic and cage structures, few examples can be tracked down in literature, [32][33][34][35][36][37][38][39] and even scarcer examples are found for their bridged analogues, N-HTAs, whose presence in complexing and sensing processes is limited.…”

“…Precedents of sensing examples involving triarylamines range from the detection of metallic cations, [24] to toxic anions [25] or anions present in chemical weapons, [26] nitroaromatic explosives, [27] biological metabolites, [28] toxic gases,[ 29 , 30 ] and pH determination. [31] Regarding the implementation of triarylamines in both macrocyclic and cage structures, few examples can be tracked down in literature,[ 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ] and even scarcer examples are found for their bridged analogues, N ‐HTAs, whose presence in complexing and sensing processes is limited.…”

Triphenylamine-based small-molecule fluorescent probes

“…Easwaramoorthi et al designed and synthesized three probes 58–60 based on triphenylamine and rhodanine-3-acetic acid for the dual detection of Ag + and Hg 2+ in buffer-free aqueous solutions. 92 All the three chemosensors showed distinct colour changes for Ag + and Hg 2+ by the naked eye. Probe 58 in solution showed a change in color from yellow to purple or colorless in the presence of Ag + and Hg 2+ , respectively.…”

Bioinspired Luminescent Europium-Based Probe Capable of Discrimination between Ag+ and Cu+

“…Indeed, only a few probes are soluble in purely aqueous solutions. [16][17][18][19][20][21][22][23] Another issue when developing a Ag + -responsive probe for biological application is the selectivity with respect to Cu + . The similarity in coordination properties of these two cations may cause a similar response for both.…”