UV-visible and (1)H-(15)N NMR spectroscopic studies of colorimetric thiosemicarbazide anion sensors

Spectroscopic and Colorimetric Studies for Anions with a New Urea-Based Molecular Cleft

A new simple urea-based dipodal molecular cleft (L) has been synthesized and studied for its binding affinity for a variety of anions by 1H-NMR, UV-Vis and colorimetric techniques in DMSO-d6 and DMSO, respectively. The results from titration studies suggest that the receptor forms a 1:2 complex with each of the anions used via hydrogen bonding interactions and exhibits strong selectivity for fluoride among halides, showing the binding affinity in the order of fluoride > chloride > bromide > iodide; meanwhile, it displays moderate selectivity for acetate among oxoanions, showing the binding affinity in the order of acetate > dihydrogen phosphate > bicarbonate > hydrogen sulfate > nitrate. Colorimetric studies of L for anions in DMSO reveal that the receptor is capable of detecting fluoride, acetate, bicarbonate and dihydrogen phosphate, displaying a visible color change in the presence of the respective anions.

The Mechanism of Adsorption of Rh(III) Bromide Complex Ions on Activated Carbon

In the paper, the mechanism of the process of the Rh(III) ions adsorption on activated carbon ORGANOSORB 10—AA was investigated. It was shown, that the process is reversible, i.e., stripping of Rh(III) ions from activated carbon to the solution is also possible. This opens the possibility of industrial recovery of Rh (III) ions from highly dilute aqueous solutions. The activation energies for the forward and backward reaction were determined These are equal to c.a. 7 and 0 kJ/mol. respectively. Unfortunately, the efficiency of this process was low. Obtained maximum load of Rh(III) was equal to 1.13 mg per 1 g of activated carbon.

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 pK_a 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^-.

Thieno[3,2-c]pyran: an ESIPT based fluorescence “turn-on” molecular chemosensor with AIE properties for the selective recognition of Zn2+ ion

Thieno[3,2-c]pyran was synthesized as a fluorescent turn-on chemosensor for the selective recognition of Zn²⁺ ions with a low detection limit (0.67 μM), and it also exhibited AIE properties.

Spectroscopic characterization of a new Re(i) tricarbonyl complex with a thiosemicarbazone derivative: towards sensing and electrocatalytic applications

A novel Re(i) complex with a thiosemicarbazone derivative is described and fully characterized. Its was further explored as CO₂ reduction electrocatalyst, being the first complex with a thiosemicarbazone derivative applied to this goal.

Anion-induced isomerization of fluorescent semi(thio)carbazones

An anion-controlled flapping motion has been observed in a series of novel semi(thio)carbazone molecules.

Water-Soluble Colorimetric Amino[bis(ethanesulfonate)] Azobenzene pH Indicators: A UV-Vis Absorption, DFT, and 1H-15N NMR Spectroscopy Study

Water-soluble azobenzene derivatives containing amino[bis(ethanesulfonate)] groups are demonstrated as colorful pH indicators in water and on filter paper. Vibrant color changes were observed from yellow/orange to pink between pH 1 and 4, which are attributed to an intramolecular charge-transfer mechanism. The pK _as of the indicators range from 2.1 to 2.6. ¹H/¹H-¹⁵N NMR studies in deuterium oxide reveal that the protonation of the azobenzene pH indicators occurs predominantly at the β-azo nitrogen atom, in agreement with the density functional theory calculations. Excellent selectivity for protons was confirmed in water over common biologically relevant metal ions. Studies in methanol, however, indicate that the pH indicator with a methoxy group ortho to the amino[bis(ethanesulfonate)] group facilitates the selective coordination of Cu²⁺ with a binding constant pβ_Cu2+ of 4.6 ± 0.1. The indicators complement the existing library of azobenzene indicator dyes and may be useful for measuring the environmental pH at higher proton concentrations.

Pyrrole-pyridine and pyrrole-naphthyridine hosts for anion recognition

The association constants of the complexes formed by two hosts containing pyrrole, amide and azine (pyridine and 1,8-naphthyridine) groups and six guests, all monoanions (Cl⁻, CH₃CO₂⁻, NO₃⁻, H₂PO₄⁻, BF₄⁻, PF₆⁻), have been determined using NMR titrations. The X-ray crystal structure of the host N²,N⁵-bis(6-methylpyridin-2-yl)-3,4-diphenyl-1H-pyrrole-2,5-dicarboxamide (1) has been solved (P2₁/c monoclinic space group). B3LYP/6-31G(d,p) and calculations were carried out in an attempt to rationalize the trends observed in the experimental association constants.

Pyridoxal-thiosemicarbazide: its anion sensing ability and application in living cells imaging

A new anion selective chemosensor L was derived through a direct condensation reaction between pyridoxal and thiosemicarbazide.