RESUMEN

The physico- and electrochemical behaviors of a series of [WZn3(H2O)2(ZnW9O34)2]12- (Zn-WZn3) and its first-row transition-metal-substituted analogues [WZn(TM)2(H2O)2(ZnW9O34)2]12- (Zn-WZn(TM)2; TM = MnII, CoII, FeIII, NiII and CuII) are reported. Various spectroscopic studies, including Fourier transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, electrospray ionization (ESI)-mass spectrometry, and Raman spectroscopy, show similar spectral patterns in all sandwich polyoxometalates (POMs) because of their isostructural geometry and constancy of the overall negative charge (-12). However, the electronic properties highly depend on the transition metals at the "sandwich core" and correlate well with the density functional theory (DFT) study. Further, depending on the substituted TM atoms, there is a decrease in the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) band-gap energy in these transition-metal-substituted POM (TMSP) complexes wrt Zn-WZn3, as confirmed by diffuse reflectance spectroscopy and DFT study. Cyclic voltammetry reveals that the electrochemistry of these sandwich POMs (Zn-WZn3 and TMSPs) is highly dependent on the pH of the solution. Moreover, the dioxygen binding/activation studies of these polyoxometalates show that Zn-WZn3 and Zn-WZnFe2 have better efficiency toward dioxygen binding, as confirmed by FTIR spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA), which is also reflected in their catalytic activity toward imine synthesis.

RESUMEN

To address the issues allied with cardiovascular diseases and the increased prevalence of hypertension, a novel electrochemical sensor was developed based on poly(ionic liquid) [PVIM]-cobalt polyoxometalate (Co5POM) supported on carbonaceous materials (MNCs) for the highly selective and ultrasensitive non-enzymatic detection of cholesterol. The novel composite exhibits excellent selectivity and sensitivity towards the non-enzymatic electrochemical detection of cholesterol with a low detection limit of 1 fM (1 × 10-15 M), a response time of ∼5 s, and a wide detection range of 1 fM-5 mM with two linear ranges of 1 fM-200 nM and 0.5 µM-5 mM with sensitivities of 210 and 64 µA µM-1 cm-2, respectively, even in the presence of ascorbic acid, glucose and uric acid. The proposed sensor was tested with a human blood serum sample at physiological pH in a physiologically relevant concentration range. A novel flexible sensor was developed with PVIM-Co5POM/MNC coated over Whatman filter paper and this shows a high sensitivity with a wide detection range of 1 fM-5 mM.

Asunto(s)

RESUMEN

A novel sandwich polyoxometalate (POM) Na12[WCo3(H2O)2(CoW9O34)2] and poly(vinylimidazolium) cation [PVIM+] in combination with nitrogen-doped carbon nanotubes (NCNTs) was developed for a highly selective and ultrasensitive detection of dopamine. Conductively efficient heterogenization of Co5POM catalyst by PVIM over NCNTs provides the synergy between PVIM-POM catalyst and NCNTs as a conductive support which enhances the electron transport at the electrode/electrolyte interface and eliminates the interference of ascorbic acid (AA) at physiological pH (7.4). The novel PVIM-Co5POM/NCNT composite demonstrates a superior selectivity and sensitivity with a lowest detection limit of 500 pM (0.0005 µM) and a wide linear detection range of 0.0005-600 µM even in the presence of higher concentration of AA (500 µM).