Solvatochromic behavior of a pyrene-pyrimidine-based Schiff base and detection of heavy metal ions in aqueous media

A highly selective silver ion optical chemosensor based on isoxazolyl-azo pyrimidine: synthesis, spectroscopy, DFT calculations and applications

In this work, an isoxazolyl-azo pyrimidine optical chemosensor (PICS) was efficiently synthesized and applied for naked-eye detection of Ag⁺ ions in solution. The chemical formula of the PICS was recognized by UV-vis, FTIR and NMR analyses. The detection ability of PICS toward various ions was assessed. The results revealed the excellent selectivity and sensitivity of the chemosensor PICS to Ag⁺ ions in aqueous DMSO solutions. The PICS displayed an obvious color change from yellow to dark red in the presence of silver ions. The PICS could efficiently detect Ag⁺ ions over a wide pH range of 6-11, which makes it suitable for detection of Ag⁺ under physiological conditions. PICS also binds Ag⁺ ions to form a 1 : 1 stoichiometry complex (PICS-Ag⁺), resulting in a bathochromic shift in the absorption maximum from 372 to 410 nm. The detection limit of the probe PICS towards Ag⁺ was calculated to be 1.78 μM. Furthermore, the probe PICS shows excellent detection performance in the solid state, and PICS-based test strips were fabricated and applied as efficient Ag⁺ test kits for detection of silver ions in water samples. In addition, the sensing mechanism of PICS-Ag⁺ was completely evaluated using the density functional theory (DFT) calculations. Results indicated that the calculated energy gap between the HOMO and LUMO (3.41 eV) of PICS-Ag is lower than that of the free PICS (3.57 eV). This suggests that a red shift occurred upon addition of the Ag⁺ ion to PICS.

A new and efficient diaminopyrimidine-based colorimetric and fluorescence chemosensor for the highly selective and sensitive detection of Cu2+ in aqueous media and living cells

In this paper, a new and effective diaminopyrimidine-based chemosensor (DAPCS) was developed for the highly selective and ultra-sensitive detection of Cu²⁺ ion in aqueous media and living cell. Characterization and structure determining of DAPCS was determined by UV-Vis, FTIR and NMR analyses. It is observed that DAPCS and Cu (II) forms a ligand to metal charge transfer (LMCT) complex which produces distinguishable red color. The results also indicate that the DAPCS easily interacts with Cu²⁺ ion to form a 1:1 stoichiometry complex (DAPCS -Cu²⁺), resulting in a bathochromic shift in absorption maximum (429 nm to 449 nm) and remarkable quenching fluorescence intensity at the wavelength of 501 nm in DMSO-H₂O solution. Furthermore, the detection limit of DAPCS towards Cu²⁺ was calculated to be 3.19 µM. Meanwhile, DAPCS was applied as fluorescent probe for detection of Cu²⁺ ions with the detection limit of 0.014 µM. The optimal pH range of probe DAPCS for quantitative analysis of Cu²⁺ ions was 9-11, which renders it suitable for detection of Cu²⁺ under physiological conditions. Additionally, the DAPCS could be applied to detect Cu²⁺ in real water samples and in HeLa cells, indicating the practical uses of DAPCS in real analyses.

On the Electroanalytical Detection of Zn Ions by a Novel Schiff Base Ligand-SPCE Sensor

A novel bidentate Schiff base (L) is here proposed for the detection of Zn ions in water. The structure of the synthesized Schiff base L was characterized by FT-IR, ¹H NMR and ¹³C NMR. Optical characteristics were addressed by UV-Visible spectroscopy and Photoluminescence (PL) measurements. PL demonstrated that L displays a "turn-off" type fluorescence quenching in the presence of Zn²⁺ ion in aqueous solution, indicating its ability to preferentially coordinate this ion. Based on these findings, an L-M (where M is a suitable membrane) modified screen-printed carbon electrode (SPCE) was developed to evaluate the electrochemical behavior of the Schiff base (L) with the final objective of undertaking the electroanalytical determination of Zn ions in water. Using various electrochemical techniques, the modified L-M/SPCE sensor demonstrates high sensitivity and selectivity to Zn ions over some common interferents ions, such as Ca²⁺, Mg²⁺, K⁺, Ni⁺⁺ and Cd⁺⁺. The potentiometric response of the L-M/SPCE sensor to Zn ions was found to be linear over a relatively wide concentration range from 1 μM to 100 mM.