Polyoxometalates as Potential Artificial Enzymes toward Biological Applications

Artificial enzymes, as alternatives to natural enzymes, have attracted enormous attention in the fields of catalysis, biosensing, diagnostics, and therapeutics because of their high stability and low cost. Polyoxometalates (POMs), a class of inorganic metal oxides, have recently shown great potential in mimicking enzyme activity due to their well-defined structure, tunable composition, high catalytic efficiency, and easy storage properties. This review focuses on the recent advances in POM-based artificial enzymes. Different types of POMs and their derivatives-based mimetic enzyme functions are covered, as well as the corresponding catalytic mechanisms (where available). An overview of the broad applications of representative POM-based artificial enzymes from biosensing to theragnostic is provided. Insight into the current challenges and the future directions for POMs-based artificial enzymes is discussed.

The crystal structure of catena-poly[bis[3-azoniapentane-1,5-diammonium][bis(μ4-oxo)-tetrakis(μ3-oxo)-heptakis(μ2-oxo)-tetradecaoxo-octa-molybdenum] dihydrate], (C8H36N6O29Mo8) n

(C8H36N6O29Mo8) n , monoclinic, P21/n (no. 14), a = 10.5883(4) Å, b = 9.4385(3) Å, c = 16.5154(7) Å, β = 94.616(4)°, V = 1645.15(11) Å3, Z = 2, R gt(F) = 0.0359, wR ref(F 2) = 0.0887, T = 293(2) K.

Enhancing the colorimetric detection of H2O2 and ascorbic acid on polypyrrole coated fluconazole-functionalized POMOFs

A new fluconazole-functionalized polyoxometalate-based metal-organic framework (POMOF) [Ag₃(FKZ)₂(H₂O)₂][H₃SiW₁₂O₄₀] (AgFKZSiW₁₂) was successfully constructed, and its polypyrrole (PPy) coated composite AgFKZSiW₁₂@PPy was also obtained via a facile 'in situ' oxidation polymerization process. The peroxidase-like activity evaluation indicates that the maximized synergistic effect from the integration of PPy, SiW₁₂ clusters, HFKZ drug molecules, and Ag ions deeply enhanced the overall performance. More importantly, AgFKZSiW₁₂@PPy exhibits the fastest response time (30 s) among all the reported peroxidase mimics to date, including the pristine AgFKZSiW₁₂ (2 min). Moreover, the AgFKZSiW₁₂@PPy-based colorimetric biosensing platform towards H₂O₂ and ascorbic acid (AA) exhibits limits of detection (LOD) as low as 0.12 μM and 2.7 μM, respectively. This work reveals a promising prospect in medical diagnosis and biotechnology for colorimetric biosensor fabrication with high performance through the introduction of PPy.

Luminescent, stabilized and environmentally friendly [EuW10O36]9--Chitosan films for sensitive detection of hydrogen peroxide

Fabrications and applications of luminescent films have been an interesting and important challenge within the realm of academia and industry. Herein, a novel fluorescence-based strategy for the H₂O₂ detection has been developed by fabrication of stabilized, thin, transparent, and luminescent films composed of europium-containing polyoxometalates (Eu-POM) and environmentally friendly chitosan (CS) via a facile solution casting approach. In comparison with pure Eu-POM, enhanced fluorescent properties are obtained from the as-prepared Eu-POM/CS films in terms of prolonged fluorescence lifetime and a remarkable fluorescent quenching effect in the presence of hydrogen peroxide (H₂O₂). The fluorescence intensity of Eu-POM/CS films exhibits a linear correlation in response to the H₂O₂ concentration over a wide range of 1.1-66 μM, with a detection limit of 0.11 μM. Furthermore, the fluorescent films display a high detection selectivity which are capable of differentiating hydrogen peroxide (H₂O₂) from the interfering species, such as sugars, l-amino acids, and other metabolites. All these advances towards the development of Eu-POM/CS films open up new applications for luminescent films, but most importantly, they can help in the far-reaching technological implementations of a simple, cost-effective method for the detection of H₂O₂ in many fields.

First Orange Fluorescence Composite Film Based on Sm-Substituted Tungstophosphate and Its Electrofluorochromic Performance

We chose a Sm-containing sandwich-type tungstophosphate K3Cs8[Sm(PW11O39)2]·10H2O (SmPW11) as a molecular dyad, which contains photoluminescence and electrochromism components in a skeletal structure, and investigated its electrofluorochromic performance both in solution and in composite films. First, the electrochemical activity and luminescence property of SmPW11 were studied in different pH solutions to determine the optimal pH solution medium; and then, the electrofluorochromic performance of SmPW11 was investigated under the optimized pH solution medium. Subsequently, the composite films containing SmPW11 were prepared on quartz substrates and conductive ITO substrates through a layer-by-layer (LbL) assembly method, using PDDA and PEI as molecular linkers. Characterization methods of the composite films include UV-vis spectra, fluorescence spectroscopy, cyclic voltammetry (CV), bulk electrolysis with coulometry, chronoamperometry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Finally, in situ UV-vis and fluorescence spectroelectrochemical systems were used to research electrofluorochromic properties for the composite films under electrochemical modulation. The results indicate that the composite films display not only orange luminescence emission but also reversible orange luminescence switching behaviors manipulated by the redox process of tungstophosphate species PW11 via the energy transfer between the orange luminescence component Sm and electroreduced species of tungstophosphate PW11.

A new organo-ruthenium substituted tungstotellurate: synthesis, structural characterization and catalytic properties

A novel organo-Ru supported tungstotellurate(iv) has been synthesized and its catalytic activity was assessed towards the oxidation of n-tetradecane using air without any additives or solvents.

Enhanced sensitivity of color/emission switching of fluorescein film by incorporation of polyoxometalate using HCl and NH3 gases as in situ stimuli

Highly transparent tricomponent hybrid film agarose–[P₅W₃₀O₁₁₀]¹⁵⁻–fluorescein displays enhanced sensitivity of color/emission switching for HCl and NH₃ gases.

An effective combination of electrodeposition and layer-by-layer assembly to construct composite films with luminescence switching behavior

A novel fabrication strategy for a functional composite film was explored, and the fluorescence performance was studied.

A high fatigue resistant, photoswitchable fluorescent spiropyran–polyoxometalate–BODIPY single-molecule

In the reported spiropyran/polyoxometalate/BODIPY triad, the fluorescence of the BODIPY can be highly reversibly quenched by the activation of the photochromic spiropyran.

Reversible electroswitchable luminescence in thin films of organic-inorganic hybrid assemblies

In this study, reversible electroswitched luminescence is realized in a novel hybrid composite of organic-inorganic polymers and Pyronin Y-doped silica nanoparticles (PYDS) in aqueous solutions for the first time. The electrochromic material, poly (3,4-ethylenedioxythiophene) (PEDOT), is electrodeposited on the electrode in the presence of phosphododecamolybdic acid (PMo(12)). The luminescence of PYDS can be effectively switched between "on" and "off" states by applying oxidation and reduction potentials of PEDOT via the corresponding luminescence quenching effect. The electrochromic devices (ECDs) we report here exhibit lots of advantages, such as easy fabrication, high contrast of fluorescence response, good reversibility, and long-time stability. The creative application of PEDOT in ECDs in aqueous solutions is anticipated to offer important hints and a basis for other organic materials in the field of photoelectric devices.