Addition Of AcO Research Articles

Selective acetate recognition and sensing using SWCNTs functionalized with croconamides

Croconamides are a new class of dual-hydrogen bond donors that have attracted interest in anion recognition and sensing applications due to their strong H-bond donation capability. In this work, we report chemiresistive sensors for the detection of anions based on poly(4-vinylpyridine) (P4VP)-wrapped single-walled carbon nanotubes (SWCNTs) functionalized with croconamide-based selectors. Model structures of asymmetric N,N-substituted croconamide selectors with N,N-substitutional groups of alkyl cationic pyridinium and electron-withdrawing moieties such as aniline (6) and 3,5-bis(trifluoromethyl)phenyl (7) groups were synthesized and their binding affinities for various anions were characterized using UV–vis and 1H NMR titrations. Switchable binding of oxoanions was observed with selector 7, wherein HSO4– formed hydrogen bonding interactions and acetate (AcO–) induced deprotonation of the NH protons of the croconamide. Large sensitivity transitions were obtained toward AcO– for both P4VP-6-SWCNT (S = 95.68 ± 2.11 %) and P4VP-7-SWCNT (S = 140.91 ± 3.68 %) at 83.33 mM, which was attributed to deprotonation of the croconamide selectors upon addition of AcO–. Three serial sensors were assembled in a sensor array that rapid and selective screening of AcO– was demonstrated against other oxoanions such as HSO4– and H2PO4– in real-time.

Functional Single-Walled Carbon Nanotubes for Anion Sensing.

We report an anion-sensing platform wherein conductance changes are triggered by chemical interactions between selectors and anions. The selector design incorporates both a cationic moiety (i.e., pyridinium) and a thiourea-based dual-hydrogen-bond donor. Anion binding by a model selector (2) was studied using 1H NMR and UV-vis titrations, which reveal a binding strength toward acetate ions (AcO-) followed by Cl- > Br- > NO3-. These studies reveal that selector 2 is deprotonated upon addition of AcO-, whereas it undergoes hydrogen bonding associated with Cl-, Br-, and NO3-. The cationic pyridinium moiety improves anion binding affinity by lowering the pKa value of selector 2 and enhancing the hydrogen-bond donor capability as confirmed by spectroscopic titrations and DFT calculations. The selector is covalently attached to poly(4-vinylpyridine) (P4VP), which wraps single-walled carbon nanotubes (SWCNTs) (i.e., P4VP-2-SWCNT) to transduce an electrical signal. As a result, continuous anion sensing was achieved with high sensitivity represented by a normalized resistance change of 101.9 ± 10.3% toward 16.7 mM AcO-, whereas negligible sensitivity was observed toward Cl-, Br-, and NO3-. The sensitivity transition was attributed to the internal charge transfer of 2 by deprotonation of the thiourea proton upon addition of AcO-.

Electroanalytical and spectral investigation of organic receptors as colorimetric and absorption ratiometric anion chemosensor

Colorimetric receptors R1 and R2 have been designed and synthesized by Schiff base condensation and characterised by standard spectroscopic techniques. Anion binding ability of the receptors have been investigated quantitatively through optical, electrochemical and 1HNMR titration studies. UV-vis spectra of receptor R1 and R2 exhibited a significant red shift for F− and AcO− ions with a visual color response. Receptor R1 exhibited selective response towards AcO− ion in the presence of HEPES buffer media. Incremental color change of receptor R2 with the higher equivalence of AcO− ions clearly represent the ratiometric response. Cyclic voltammetric studies of R1 and R2 exhibits shift in oxidation and reduction peak with successive addition of AcO− ions indicating the anion induced oxidation of -NH and reduction of the keto group and nitro species. Electrooptical and 1H NMR titration studies of R2 collectively reflects the anion induced change of chromophore from C=N to N=N indicative of azo-hydrazone tautomeric signaling in the presence of AcO− ions. Lower detection limit of 2.1 and 0.41 ppm achieved with sodium salt of AcO− ion with R1 and R2 reflects their utility as colorimetric chemosensor.

Electrooptical characteristics and anion binding behaviour of organic receptors: Effect of substitution on colorimetric response

A series of four organic receptors, R1, R2, R3 and R4 possessing NH unit as binding site with varied positional substitution of OH and NO2 functionalities have been synthesized and studied for their anion binding ability. Significant changes were observed in the UV–vis spectra of receptors with the addition of AcO− ion justifying the observed color changes visible to naked eye. Receptors R1, R2 and R3 showed mild color changes in the presence of F− and H2PO4− ions whereas R4 exhibited selective response towards AcO− ion. UV–vis titration and cyclic voltammetric studies performed with the incremental addition of AcO− ion to the receptors confirmed the anion binding process. The band gap value derived from the experimental results of UV–vis spectroscopic and cyclic voltammetric studies support the formation of AcO− ion-receptor complex. 1H NMR titration studies performed with the addition of AcO− ion to receptor R3 confirms the deprotonation of the NH proton involved in the binding mechanism.

A pyrenyl-appended organogel for fluorescence sensing of anions

A 1,2,3-trioctyloxyphenyl-based organogel (G1) containing a pyrene fluorophore and urea-sulfonamide anion binding sites was designed and synthesized. Gelator G1 can form stable organogels with dramatic aggregation-induced emission (AIE) in some organic solvents. The self-assemble mechanism of G1 was investigated by concentration depended 1H NMR, XRD, FT-IR and SEM techniques. In addition, G1 shows good fluorescence sensing ability to some selected anions such as F− and AcO−. In DMF solution, the addition of F− into the organogel G1 shows a gel-gel phase change with the AIE quenched. However, the addition of AcO− leads to a gel-sol transition with little fluorescence change.

Naphthalene based colorimetric sensor for bioactive anions: Experimental and DFT study

A simple anion selective colorimetric sensor L has been designed by combining 2-hydroxy-1-naphthaldehyde with 2-aminothiophenol. Sensor L portrayed a necked-eye detectable color change from light green to red upon addition of AcO−, F− and H2PO4- anions in CH3CN, where as no significant color change was observed upon addition of other anions such as Cl−, Br−, I− and HSO4-. Sensor L showed selectivity towards AcO− under competitive environment, with a detection limit (3σ/S) down to 1.1×10−7M. In addition, the anion sensing ability of L was explored in mixed H2O/CH3CN (v/v) medium. Further, the nature of interactions between the sensor L and AcO− was investigated by 1H NMR and the probable structure of the L-AcO− complex was predicted by B3LYP/6-31G(d,p) method.

Synthesis of a Phenylhydrazone‐based Colorimetric Anion Sensor with Complementary IMP/INH Logic Functions

AbstractA dinitrophenyl hydrazone colorimetric anion sensor (receptor 1) was synthesized and its recognition properties towards various anions were investigated by naked eye observation and spectroscopic methods, namely UV‐vis and 1H NMR titrations in DMSO. The addition of AcO−, F− and H2PO4− to receptor 1 resulted in marked red shift of the charge‐transfer absorbance band (Δλ=91 nm, 407 nm to 498 nm) concomitant with a 'naked‐eye' detectable colour change from yellow to pink. However, both the colour and spectral changes were reversible by the addition of cations (MII) of 3d5‐10 as well as CdII, HgII, MgII and CaII. Subsequently, complementary IMP/INH logic functions based on colour and spectral switching (ON/OFF) were affirmed. The sensor can, thus be utilized as a colorimetric molecular switch modulated by F−/MII.

Use of a new thiacalix[4]arene derivative bearing two 4-chloro-7-nitrobenzofurazan groups as a colorimetric and fluorescent chemosensor for Ag+ and AcO−

The synthesis and spectroscopic studies of a thiacalix[4]arene-based sensor of 1,3-alternate-25,27-bis(2-aminoethoxy)-26,28-bis(2-methoxyethyl)-thiacalix[4]arene linked 4-chloro-7-nitrobenzofurazan (NBD-Cl) are described. The properties of the compound were evaluated and show that it is a colorimetric and fluorescence sensor for Ag+ and AcO−. The addition of Ag+ results in a red shift of the absorption spectrum of the sensor, which is clearly visible to the naked eye, accompanied by a strong quenching of the fluorescence. With the addition of AcO−, the fluorescence was severely quenched, and the absorbance increased significantly, with a new absorption band appearing at shorter wavelength. This demonstrated that the multifunctional sensing compound prepared from a novel thiacalix[4]arene was highly selective for AcO−.

Mercapto thiadiazole-based sensor with colorimetric specific selectivity for AcO − in aqueous solution

A novel acetate selective anion sensor 3 based on azophenol and mercapto thiadiazole had been designed and synthesized. Sensor 3 behaves a single selectivity and sensitivity in the recognition for AcO − anion over other anions such as F −, Cl −, Br −, I −, H 2PO 4 −, HSO 4 − and ClO 4 − by naked-eyes and UV–vis spectra changes in aqueous solution (H 2O/DMSO, 5:5, v/v). The color of the solution containing sensor 3 had an obvious change from colorless to orange only after the addition of AcO − in aqueous solution while other anions did not cause obvious color change. 1H NMR titration results revealed that the binding process includes two steps: (i) hydrogen bonding interactions (for small quantities of acetate) and (ii) proton transfer between the sensor 3 and the coordinated anion (for high quantities of acetate). The association constant K a was 7.35 × 10 3 M −1. The detection limitation of AcO − with the sensor 3 was 1.0 × 10 −6 mol L −1.

Synthesis of Schiff Base Bearing Phenolic Hydroxy Group and Its Anion Recognition

A new anion receptor bearing phenolic hydroxy group based on 3,5-ditertbutylsalicylaldehyde-p-nitrophenylhydrazone (1) was designed and synthesized. Upon addition of AcO− and F−, the receptor exhibited visible color changes from deep yellow to purple. However, no obvious color changes were observed on addition of the other anions tested (H2PO4−, Cl−, Br−, I−). The binding properties of the receptor with anions such as AcO− and F− were investigated by UV-Vis and fluorescent titrations. The result indicated that the receptor 1 had a higher affinity to AcO− and F− and a 1:1 host-guest complex was formed through H-bond interactions between 1 and anions.

Fluorescence Spectroscopic Evidence for Hydrogen Bonding and Deprotonation Equilibrium between Fluoride and a Thiourea Derivative

Interaction of anions with thiourea-linked acridinedione fluorophore was studied by absorption, (1)H NMR, steady-state and time-resolved fluorescence techniques. Addition of AcO(-) and H(2)PO(4)(-) shows a genuine H-bonded complex with thiourea receptor; whereas, F(-) shows stepwise H-bonding and deprotonation of thiourea NH as confirmed by (1)H NMR titration. Free receptor 1 shows emission maximum at 418 nm; whereas, H-bonded complex of 1·F(-) shows a new redshifted emission maximum at 473 nm and the deprotonated 1 exhibits an emission peak at 502 nm. Presence of these three different emitting species was probed by 3D emission spectroscopic studies. Equilibrium between the free receptor 1, 1·F(-) H-bonded complex and deprotonated 1 was confirmed by time-resolved fluorescence studies. Time-resolved area normalised emission spectra (TRANES) of 1 in the presence of F(-) shows two isoemissive points at 456 and 479 nm between time delays of 0-0.5 ns and 1-20 ns, respectively, due to the existence of three emitting species in equilibrium. Observation of such an equilibrium based on fluorescence spectroscopic studies further proves the earlier reported absorption and (1)H NMR spectroscopic studies of H-bonding and deprotonation processes and also illustrates the dynamics of anion-receptor interactions.

Colorimetric ‘naked-eye’ sensor for anions based on conformational flexible tripodal receptor

A new tripodal receptor for anion sensing based on amide-pyridinium as recognition site and nitro-benzene as signaling unit was designed and successfully synthesized. This receptor showed high selectivity and strong binding affinity toward AcO− over the investigated anions, especially over H2PO4−. Addition of AcO− induced clear color change of solution from colorless to yellow, realizing the “naked-eye” detection. UV–Vis and 1H NMR experiments indicated the selectivity might origin from the synergistic effects arising from hydrogen bonding, electrostatic interactions and conformational change.

Anion Recognition Using Novel and Colorimetric Tweezer Receptors: 1,3‐Phenylenedi(carbonylhydrazone) in Aqueous‐organic Binary Solvents

AbstractTwo novel artificial tweezer receptors 1,3‐phenylenedi(carbonylhydrazone) derivatives with a symmetrical structure have been synthesized. Receptor 3a [1,3‐di(salicylidenehydrazinocarbonyl)benzene] for anions (F−, Cl−, Br−, I−, AcO−, HSO4−, H2PO4−, ClO4−) was investigated by UV‐Vis spectroscopy in DMSO and even 85% DMSO‐15% H2O binary solutions, respectively. Remarkable color changes from colorless to yellow were observed by the naked‐eye upon addition of AcO−, F− and H2PO4− to the solution of receptor 3a. The 1H NMR signals indicated that the receptor 3a underwent deprotonation after the addition of an excess of fluoride anion. In particular, the anion recognition was successfully applied to CH3COONa in 15% H2O‐85% DMSO. These findings were expected to be of significance for designing and developing novel color‐based anion sensors operated in aqueous media.

Anion-induced ring-opening of fluorescein spirolactam: fluorescent OFF–ON

N-(2,7-Dichlorofluorescein)lactam- N′-phenylthiourea ( L) was developed as a colorimetric and fluorescent chemosensor for anions such as AcO −, F − and H 2 PO 4 - . The addition of AcO − anion to the solution of L in CH 3CN results in a distinct fluorescence “ ON” observation as well as color change (from colorless to pink). The H-bonding interaction between AcO − anion and thiourea moiety of L induced the ring-opening of the spirolactam of fluorescein moiety, which gave rise to the dual chromo- and fluorogenic changes.

Anionic Fluororeceptors based on Thiourea and Hydrazide: Synthesis and Recognition Properties

Two new neutral receptors (1 and 2) containing thiourea and hydrazide groups were synthesized by simple steps in high yields. The binding properties of 1 and 2 for various anions were characterized by UV–Vis and fluorescence spectra. Receptor 1 had a good selectivity for AcO- in comparison with other anions. The association constants of 1·AcO- and 2·p-NO2PhO- were greater than those of other anions ( Cl-, Br- and I-). In particular, an obvious color change from light yellow to orange–red was observed upon addition of AcO- to the solution of 1 in DMSO. The results of nonlinear curve fitting by fluorescence spectral data indicate that a complex of 1:1 stoichiometry is formed between compound 1 or 2 and the anions through hydrogen-bonding interaction.

The synthesis of two novel neutral receptors and their anion binding properties

Two new neutral receptors (1 and 2) containing thiourea and amide groups were synthesized by simple steps in good yields. The binding properties of 1 and 2 with anions were examined by UV–vis, fluorescence, and 1H NMR spectroscopy. Receptor 1 had a better AcO–: H2PO4– selectivity in comparison with that for receptor 2. The association constants of 1·AcO–, 2·AcO–, and 2·H2PO4– were higher in comparison with those of other anions (Cl–, Br–, I–, p-NO2PhO–, and p-NO2PhOPO32–). In particular, a clear color change was observed, from pale yellow to red-brown, upon addition of AcO– to the solution of 1 in DMSO. The UV–vis and fluorescence data indicate that a 1:1 stoichiometry complex is formed between compound 1 or 2 and anions through hydrogen-bonding interactions.Key words: neutral receptors, anion recognition, synthesis, hydrogen bonds.

Synthesis of Novel Anionic Receptors with (Thio) urea and Amide Binding Sites and the Recognition Properties for Anions

AbstractTwo new neutral receptors (1 and 2) containing (thio) urea and amide groups were synthesized by simple steps in good yields. The binding properties for anions of 1 and 2 were characterized by UV‐vis and fluorescence spectra. Receptor 1 had an excellent selectivity for AcO− in comparison with other anions. The association constants of 1 · AcO− and 2 · p‐NO2PhOPO23− were higher than those of other anions (Cl−, Br−, I−, H2PO−4 and p‐NO2PhO−). In particular, an obvious color change was observed from light yellow to golden yellow upon addition of AcO− to the solution of 1 in DMSO. The results of non‐linear curve fitting by UV‐vis and fluorescence spectral data indicate that a 1:1 stoichiometry complex is formed between compound 1 or 2 and anions through a hydrogen bonding interaction.