CrIII-Substituted Heteropoly-16-Tungstates [CrIII2(B-β-XIVW8O31)2]14- (X = Si, Ge): Magnetic, Biological, and Electrochemical Studies

Arsenic(III)-Capped 12-Tungsto-2-Arsenates(III) [M2(AsIIIW6O25)2(AsIIIOH)x]n- (M = CrIII, FeIII, ScIII, InIII, TiIV, MnII) and Their Magnetic Properties

Six arsenic(III)-capped 12-tungsto-2-arsenates(III) of the type [M₂(As^IIIW₆O₂₅)₂(As^IIIOH)_x]^n- (M = Cr^III, 1; Fe^III, 2; Sc^III, 3; In^III, 4; Ti^IV, 5; Mn^II, 6) have been synthesized in aqueous medium by direct reaction of the elements using a one-pot strategy and structurally characterized by FT-IR spectroscopy, single-crystal XRD, and elemental analysis. Polyanions 1-6 are comprised of two octahedrally coordinated guest metal ions M sandwiched between two {AsW₆} units, resulting in a structure with C_2h point-group symmetry. Polyanions 1-5 contain tri- and tetravalent metal ion guests M (M = Cr^III, Fe^III, Sc^III, In^III, and Ti^IV, respectively), and they have one {As^IIIOH} group grafted on each {AsW₆} unit, whereas the divalent Mn^II-containing derivative 6 has two such {As^IIIOH} groups grafted on each {AsW₆} unit. Magnetic studies on polyanions 3-5 over the temperature range 1.8-295 K and magnetic fields of 0-7 T confirmed that they are diamagnetic. On the other hand, polyanions 1, 2, and 6 are strongly magnetic and follow the Curie-Weiss law above 30 K. The susceptibility plots of 1 and 6 exhibit broad peaks suggesting short-range antiferromagnetic ordering, while the very weak antiferromagnetic ordering of 2 is overshadowed by traces of a paramagnetic impurity. The magnetization data of 1, 2, and 6 at 1.8 K over 0-7 T were analyzed by using the Heisenberg exchange procedure. Small (negative) values of the obtained J values help in understanding the absence of long-range antiferromagnetic ordering.

Synthesis, structure, electrochemistry and magnetism of cobalt-, nickel- and zinc-containing [M4(OH)3(H2O)2(α-SiW10O36.5)2]13- (M = Co2+, Ni2+, and Zn2+)

Interaction of the trilacunary 9-tungstosilicate [A-α-SiW₉O₃₄]^10- with cobalt(ii), nickel(ii) and zinc(ii) ions in pH 9 aqueous medium at room temperature led to the formation of the respective M₄-containing heteropolytungstates [M₄(OH)₃(H₂O)₂(α-SiW₁₀O_36.5)₂]^13- (M = Co²⁺ (1), Ni²⁺ (2), and Zn²⁺ (3)). Polyanions 1-3 were characterized in the solid state by single-crystal XRD, FT-IR spectroscopy, and thermogravimetric and elemental analyses. Electrochemical studies showed that the Co²⁺ ions in 1 can be oxidized to Co³⁺ and the CVs of the W^VI centers of the polyanions feature well-defined and chemically reversible reduction waves. Magnetic measurements on 1 and 2 showed paramagnetism with complex ferromagnetic and antiferromagnetic interactions. A model was presented for extracting the exchange constants for the magnetic exchange interaction.

Synthesis, Anti-Tumor Activity and Apoptosis-Inducing Effect of Novel Dimeric Keggin-Type Phosphotungstate

A dimeric Keggin-type phosphotungstate (ODA)₁₀[(PW₁₁FeO₃₉)₂O]·9H₂O (abbreviated as ODA₁₀[(PW₁₁Fe)₂], ODA = octadecyltrimethylammonium bromide) was synthesized and investigated comprehensively its antitumor activity on MCF-7 and A549 cells. The dimeric structure and amorphous morphology were characterized by FT-IR, UV-vis-DRS, SEM and XRD. The in vitro MTT assay of ODA₁₀[(PW₁₁Fe)₂] showed anticancer activity on MCF-7 and A549 cells in a dose- and time-dependent manner, and the IC₅₀ values for MCF-7 and A549 cells at 48 h were 5.83 μg/ml and 3.23 μg/ml, respectively. The images of the ODA₁₀[(PW₁₁Fe)₂]-treated cells observed by inverted biological microscope exhibited the characteristic morphology of apoptosis. Flow cytometric analysis showed cell apoptosis and cycle arrested at S phase induced by ODA₁₀[(PW₁₁Fe)₂]. The above results illuminated the main mechanism of the antitumor action of ODA₁₀[(PW₁₁Fe)₂] on MCF-7 and A549 cells, indicating that this dimeric phosphotungstate is a promising anticancer drug.

Biological evaluation of Keggin-type polyoxometalates on tyrosinase: Kinetics and molecular modeling

Abnormal overexpression of tyrosinase activity can lead to the production of hyperpigmentation in human skin and enzymatic browning in fruits and vegetables. Herein, the inhibition and mechanism of the H₃ PMo₁₂ O₄₀ and two transition metal-substituted Keggin-type polyoxometalates (Na₇ PMo₁₁ CoO₄₀ and Na₇ PMo₁₁ ZnO₄₀ ) on tyrosinase were studied by kinetics and molecular modeling. Kinetic studies indicated that all compounds had more potent inhibitory activities than standard arbutin, and H₃ PMo₁₂ O₄₀ (IC₅₀  = 0.443 ± 0.006 mm) is ~15-fold stronger inhibition than arbutin. Additionally, all compounds inhibited tyrosinase in a reversible competitive manner. Intriguingly, molecular modeling elucidated that three compounds competitively bind to tyrosinase mainly through more interactions with Cu²⁺ ions and the amino acid residue capable of forming cation-π and hydrogen bonding, forming a reversible non-covalent complex. Molecular simulation study correlated well with the biological activity of three compounds in vitro. This work provided new insights into design and synthesis of polyoxometalates as tyrosinase inhibitors in the field of medicine, cosmetic, and food.

Incorporation of CrIII into a Keggin Polyoxometalate as a Chemical Strategy to Stabilize a Labile {CrIIIO4} Tetrahedral Conformation and Promote Unattended Single-Ion Magnet Properties

Polyoxometalates (POMs) provide rigid and highly symmetric coordination sites and can be used as a strategy for the stabilization of magnetic ions. Herein, we report a new member of the Keggin archetype, the Cr-centered Keggin anion [α-CrW12O40]5- (CrW12), with the unusual tetrahedral coordination of CrIII reported for the first time in POMs conferring unattended magnetic properties. POM chemistry has recently presented excellent examples of single-molecule and single-ion magnets (SMMs and SIMs) as well as molecular spin qubits; however, the majority of POM-based SIMs reported to date contain lanthanoid ions. CrW12, as the first example of a chromium(III) SIM, exhibits slow relaxation of magnetization and quantum tunneling with a single-ion magnetic behavior even above 10 K with an energy barrier for the reversal of the magnetization of 3.0 K. The first 3d-metal SIM based on a nonlacunary Keggin anion is the foundation for a new research area in POM chemistry.

Polyoxomolybdates as α-glucosidase inhibitors: Kinetic and molecular modeling studies

Noninsulin dependent diabetes mellitus is a serious global disease that is treated by inhibiting α-glucosidase to reduce the glucose content in the blood. Several incompletely satisfactory therapeutic drugs are already on the market. In this report, we showed that polyoxomolybdates based on Keggin-type architecture are promising candidates. Kinetic studies indicate that H₃PMo₁₂O₄₀, Na₄PMo₁₁VO₄₀, Na₆PMo₁₁FeO₄₀ and Na₇PMo₁₁CoO₄₀ strongly inhibit α-glucosidase with IC₅₀ values of 6.14 ± 0.38 μM, 52.33 ± 1.41 μM, 161.90 ± 7.68 μM and 103.10 ± 2.88 μM, respectively. Moreover, H₃PMo₁₂O₄₀, Na₄PMo₁₁VO₄₀, and Na₇PMo₁₁CoO₄₀ are reversible, competitive inhibitors with K_I values of 0.018 mM, 0.146 mM and 0.121 mM, respectively. Na₆PMo₁₁FeO₄₀ inhibited α-glucosidase in a reversible noncompetitive manner with K_I and K_IS of 0.312 mM and 0.412 mM, respectively. Molecular docking simulation suggested that H₃PMo₁₂O₄₀ binds into the substrate binding site in accordance with competitive inhibition behavior and offered, in addition, an initial insight into the polypeptide-inhibitor interactions. This work presents a promising new perspective for designing effective α-glucosidase inhibitors and further demonstrates the enormous potential of polyoxomolybdates as enzyme inhibitors.

Dimethyltin-functionalized cyclic selenotungstates based on {Se2W12} units

Two dimethyltin-functionalized cyclic selenotungstates based on {Se₂W₁₂} units were obtained, where (CH₃)₂Sn²⁺ moieties were first introduced into “pure” POMs wheels.