Mono- and Di-Sc-Substituted Keggin Polyoxometalates: Effective Lewis Acid Catalysts for Nerve Agent Simulant Hydrolysis and Mechanistic Insights

Reducing Systematic Uncertainty in Computed Redox Potentials for Aqueous Transition-Metal-Substituted Polyoxotungstates

Polyoxometalates have attracted significant interest owing to their structural diversity, redox stability, and functionality at the nanoscale. In this work, density functional theory calculations have been employed to systematically study the accuracy of various exchange-correlation functionals in reproducing experimental redox potentials, U0Red in [PW11M(H2O)O39]q- M = Mn(III/II), Fe(III/II), Co(III/II), and Ru(III/II). U0Red calculations for [PW11M(H2O)O39]q- were calculated using a conductor-like screening model to neutralize the charge in the cluster. We explicitly located K+ counterions which induced positive shifting of potentials by > 500 mV. This approximation improved the reproduction of redox potentials for Kx[XW11M(H2O)O39]q-x M = Mn(III/II)/Co(III/II). However, uncertainties in U0Red for Kx[PW11M(H2O)O39]q-x M = Fe(III/II)/Ru(III/II) were observed because of the over-stabilization of the ion-pairs. Hybrid functionals exceeding 25% Hartree-Fock exchange are not recommended because of large uncertainties in ΔU0Red attributed to exaggerated proximity of the ion-pairs. Our results emphasize that understanding the nature of the electrode and electrolyte environment is essential to obtain a reasonable agreement between theoretical and experimental results.

Application of Cotton Swab-Ag Composite as Flexible Surface-Enhanced Raman Scattering Substrate for DMMP Detection

It is both important and required to quickly and accurately detect chemical warfare agents, such as the highly toxic nerve agent sarin. Surface-enhanced Raman scattering (SERS) has received considerable attention due to its rapid results, high sensitivity, non-destructive data acquisition, and unique spectroscopic fingerprint. In this work, we successfully prepared SERS cotton swabs (CSs) for the detection of the sarin simulant agent dimethyl methyl phosphonate (DMMP) by anchoring N1-(3-trimethoxysilylpropyl) diethylenetriamine (ATS)/silver nanoparticle (AgNP) nanocomposites on CSs using ATS as the stabilizer and coupling agent. Simultaneously, the binding mode and reaction mechanics between the AgNP, ATS, and CS were confirmed by XPS. The modified CSs exhibited good uniformity, stability, and adsorption capability for SERS measurements, enabling the adsorption and detection of DMMP residue from an irregular surface via a simple swabbing process, with a detection limit of 1 g/L. The relative standard deviations (RSDs) of RSD₇₁₀ = 5.6% had high reproducibility. In this research, the fabrication method could easily be extended to other cellulose compounds, such as natural fibers and paper. Furthermore, the versatile SERS CSs can be used for the on-site detection of DMMP, particularly in civil and defense applications, to guarantee food security and the health of the population.

Trisubstituted 4f- and 4d tungstoantimonates as artificial phosphoesterases for nerve agent degradation

Three new trisubstituted 4f- and 4d tungstoantimonates (TA) K₃Na₂₁[(M(CH₃COO))₃(HPO₃)(WO₄)(SbW₉O₃₃)₃]·nH₂O {M₃(HPO₃)Sb₃W₂₈} (M = Gd^III, Y^III, Yb^III, n = 35–36) were synthesized using a double-template synthetic approach. Following their characterization in the solid state employing single- and powder X-ray diffraction (XRD), IR-spectroscopy, and elemental – and thermogravimetric analyses (TGA), {M₃(HPO₃)Sb₃W₂₈} were subjected to a comprehensive set of solution characterization methods including UV/vis- and multinuclear ³¹P and ¹³C NMR spectroscopy. All representatives were shown to be highly active, recyclable, and stable Lewis-acid catalysts towards the nerve agent simulant O,O-dimethyl O-(4-nitrophenyl) phosphate (DMNP) at neutral pH (in Tris–HCl [125 mM] at pD 7.0 25 °C). Control experiments showing catalytic activity of the unsubstituted trilacunary TA [SbW₉O₃₃]⁹⁻ suggest the non-innocence of Tris in the DMNP hydrolysis for the first time.

With 3 Mio. people worldwide being yearly exposed to organophosphates (OPs), accounting for approximately 300 000 deaths, OPs are a current threat to mankind. This work reports on {M₃(HPO₃)Sb₃W₂₈} and {SbW₉} as recyclable OP degradation catalysts.

Solid-state degradation and visual detection of the nerve agent GB by SA@UiO-66-NH2@PAMAM hydrogel

A new sodium alginate (SA) composite hydrogel for rapid solid-state degradation of organophosphorus derivatives and can be used to monitor hydrolysis of nerve agent GB.

Hydrolysis of Organophosphorus Agents Catalyzed by Cobalt Nanoparticles Supported on Three-Dimensional Nitrogen-Doped Graphene

Catalytic chemical degradations and many other methodologies have been explored for the removal and/or degradation of organophosphorus agents (OPs) that are often used as pesticides, nerve agents, and plasticizers. To explore more efficient and recyclable catalysts for the removal and/or degradation of OPs, we fabricate the composites of cobalt nanoparticles and three-dimensional nitrogen-doped graphene (Co/3DNG). We demonstrate that OPs can be hydrolyzed efficiently at ambient temperature by the Co/3DNG. Because of the unique structural and chemical properties of the supporting matrix 3DNG and active species Co-N, the catalytic activities of Co/3DNG composites are much higher than those of bare 3DNG, Co nanoparticles, or the Co nanoparticles physically mixed with 3DNG. We conclude that in the Co/3DNG composites, the interaction between 3DNG and Co stabilizes and distributes well the Co nanoparticles and affords the active catalytic species Co-N.

Imidazole-Functionalized Polyoxometalate Catalysts for the Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran Using Atmospheric O2

Biomass as a sustainable and abundant carbon source has attracted considerable attention as a potential alternative to petroleum resources. The selective oxidation of 5-hydroxymethylfurfural (HMF), a versatile platform molecule, to value-added 2,5-diformylfuran (DFF) provides an efficient pathway for biomass valorization. Herein, three discrete imidazole-functionalized polyoxometalates (POMs), HPMo₈V^VI₄O₄₀(V^VO)₂[(V^IVO)(IM)₄]₂·nH₂O·(IM)_m (IM = 1-methylimidazole, n = 4, m = 8 for 1; IM = 1-ethylimidazole, n = 4, m = 9 for 2; IM = 1-propylimidazole, n = 0, m = 4 for 3), have been successfully synthesized by a facile solvothermal method and thoroughly characterized by routine techniques. Compounds 1-3 contain a bi-capped pseudo-Keggin {HPMo₈V₄O₄₀(VO)₂} and two imidazole-functionalized {(VO)(IM)₄} groups, which, to our knowledge, represent the first examples of organic-functionalized Mo-V clusters. Compounds 1-3 as heterogeneous catalysts can effectively promote the transformation of HMF to DFF using atmospheric O₂ as oxidant. Under minimally optimized conditions, 95% of HMF was converted by 1 with 95% selectivity for DFF and its catalytic activity was basically maintained after five cycles. Moreover, the important roles of the bi-capped pseudo-Keggin cluster and the functionalized V groups in the selective oxidation of HMF have been explored. According to experimental and spectroscopic results, a three-step oxidation mechanism of HMF to DFF has been proposed.

Design and synthesis of a new magnetic metal organic framework as a versatile platform for immobilization of acidic catalysts and CO2 fixation reaction

The first report of the use of an acidic magnetic metal organic framework for the chemical fixation of CO2 as an environmentally friendly reaction.

Synthesis, Characterization, and Phosphoesterase Activity of a Series of 4f- and 4d-Sandwich-Type Germanotungstates [(n-C4H9)4N]l/mH2[(M(H2O)3)(γ-GeW10O35)2] (M = CeIII, NdIII, GdIII, ErIII, l = 7; ZrIV, m = 6)

We report on a family of five new 4f- and 4d-doped sandwich-type germanotungstates with the general formula [(n-C₄H₉)₄N]_l/mH₂[(M(H₂O)₃)(γ-GeW₁₀O₃₅)₂]·3(CH₃)₂CO [M(H₂O)₃(GeW₁₀)₂] (M = Ce^III, Nd^III, Gd^III, Er^III, l = 7; Zr^IV, m = 6), which have been synthesized at room temperature in an acetone–water mixture. Among the compound series, [Zr(H₂O)₃(GeW₁₀)₂]^8–, which has been obtained in the presence of 30% H₂O₂, represents the first example of a 4d-substituted germanotungstate incorporating the intact dilacunary [γ-Ge^IVW₁₀O₃₆]^8– building block. All compounds were characterized thoroughly in the solid state by single-crystal and powder X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA), and elemental analysis and in solution by NMR and UV–vis spectroscopy. The phosphoesterase activity of [Ce(H₂O)₃(GeW₁₀)₂]^9– and [Zr(H₂O)₃(GeW₁₀)₂]^8– toward the model substrates 4-nitrophenyl phosphate (NPP) and O,O-dimethyl O-(4-nitrophenyl) phosphate (DMNP) was monitored with ¹H- and ³¹P-NMR spectroscopy revealing an acceleration of the hydrolytic reaction by an order of magnitude (k_corr = 3.44 (±0.30) × 10^–4 min^–1 for [Ce(H₂O)₃(GeW₁₀)₂]^9– and k_corr = 5.36 (±0.05) × 10^–4 min^–1 for [Zr(H₂O)₃(GeW₁₀)₂]^8–) as compared to the uncatalyzed reaction (k_uncat = 2.60 (±0.10) × 10^–5 min^–1). [Ce(H₂O)₃(GeW₁₀)₂]^9– demonstrated improved antibacterial activity toward Moraxella catarrhalis (MIC 32 μg/mL), compared to the unsubstituted [GeW₁₀O₃₆]^8– POM (MIC 64 μg/mL).

We report on the synthesis and characterization of five new monosubstituted 4f- and 4d-germanotungstates [(n-C₄H₉)₄N]_l/mH₂[(M(H₂O)₃)(γ-GeW₁₀O₃₅)₂]·3(CH₃)₂CO [M(H₂O)₃(GeW₁₀)₂] (M = Ce^III, Nd^III, Gd^III, Er^III, l = 7; Zr^IV; m = 6). The phosphoesterase properties of [Ce(H₂O)₃(GeW₁₀)₂]⁹⁻ and [Zr(H₂O)₃(GeW₁₀)₂]⁸⁻ were investigated by probing the hydrolytic activity toward 4-nitrophenyl phosphate (NPP) and O,O-dimethyl O-(4-nitrophenyl) phosphate (DMNP). Antibacterial tests revealed inhibiting activity of [Ce(H₂O)₃(GeW₁₀)₂]⁹⁻ against Moraxella catarrhalis.