A Giant Heterometallic Polyoxometalate Nanocluster for Enhanced Brain-Targeted Glioma Therapy.

Giant heterometallic polyoxometalate (POM) clusters with precise atom structures, flexibly adjustable and abundant active sites are promising for constructing functional nanodrugs. However, current POM drugs are almost vacant in orthotopic brain tumor therapy due to the inability to effectively penetrate the blood-brain barrier (BBB) and low drug activity. Here, we designed the largest (3.0 nm × 6.0 nm) transition-metal-lanthanide co-encapsulated POM cluster {[Ce10 Ag6 (DMEA)(H2 O)27 W22 O70 ][B-α-TeW9 O33 ]9 }2 88- featuring 238 metal centers via synergistic coordination between two geometry-unrestricted Ce3+ and Ag+ linkers with tungsten-oxo cluster fragments. This POM was combined with brain-targeted peptide to prepare a brain-targeted nanodrug that could efficiently traverse BBB and target glioma cells. The Ag+ active centers in the nanodrug specifically activate reactive oxygen species to regulate the apoptosis pathway of glioma cells with a low half-maximal inhibitory concentration (5.66 µM). As the first brain-targeted POM drug, it efficiently prolongs the survival of orthotopic glioma-bearing mice.

An Unusual Bismuth-Antimony-Europium Cluster-Imbedded Polyoxotungstate and Its Bidirectional Luminescence Detection.

An unprecedented aggregate formed by two bismuth-antimony-europium cluster-imbedded tungsten-oxo clusters and one Krebs-type polyoxotungstate linker [H2N(CH3)2]14Na30H6[W4O10][B-ß-BiW9O33]2{[Bi5.35Sb0.65Eu3O9(H2O)9][B-α-SbW9O33]3}2·124H2O (1) was prepared. The polyoxoanion skeleton of 1 contains a Krebs-type polyoxotungstate [W4O10][B-ß-BiW9O33]2}14- ({Bi2W22}) (1a) as a linker that offers six active coordinate O atoms (two µ3-O and four µ2-O atoms) to grasp two Bi-Sb-Eu cluster-imbedded tungsten-oxo clusters {[Bi5.35Sb0.65Eu3O9(H2O)9][B-α-SbW9O33]3}18- (1b) through Bi-O-W and Sb-O-W bonds. 1b comprises an unprecedented nona-nuclearity Bi-Sb-Eu [Bi5.35Sb0.65Eu3O9(H2O)9]9+ cluster encircled by three trivacant [B-α-SbW9O33]9-segments in a triangular motif through Eu-O-W, Sb-O-W, and Bi-O-W linkages into a trilobal trimer. Moreover, a bidirectional detection method by using 1 as an effective luminescence probe was proposed to recognize both Mn2+ and CO32- through an "on-off-on" mode. 1 can be used as an "on-off" luminescent sensor to detect Mn2+ ions in aqueous solution. The limit of detection was 0.05 µM (9 × 10-6 mg L-1), which is much lower than the World Health Organization (WHO) guideline for Mn2+ concentration in drinking water (0.05 mg L-1). Then the Mn2+-quenching system can be used as an "off-on" sensor to detect CO32- in water system. This work provides a new research idea for the application of rare-earth-imbedded polyoxotungstate-based materials in the field of optical smart detection.

Lanthanide-Incorporated Polyoxometalates Assembled from Mixed-Heteroatom-Oriented Three-Layered Cage Clusters.

Discovering innovative metal-oxo cluster materials with uncommon building blocks and exploiting their application potentiality are fairly challengeable. Here, we provide a novel type of lanthanide-incorporated polyoxometalates [H2N(CH3)2]10Na8H6{[Ln0.5/Na0.5(HGCA)(H2O)1.5]2[(BiO3)(SeO3)2W21O66]2}·36H2O [Ln = Eu3+ (1), Er3+ (2), H2GCA = α-glycolic acid] synthesized by a dual-heteroatom-directed synergetic strategy, which are established from two unique BiIII-SeIV heteroatom-oriented cylindrical three-layered [(BiO3)(SeO3)2W21O66]13- cage clusters integrated by lanthanide-organic groups. Compound 1 works as a fluorescence probe for high-sensitivity detection toward a neurotransmitter dopamine. This finding not only shows the enormous possibility and feasibility to create novel polyoxometalate building units by means of the self-categorization of different heteroatoms, which are subsequently employed for further assembly chemistry, but also provides a platform to exploit latent utilizations of polyoxometalate-based materials in the realm of detecting biological molecules.

Multicomponent Self-Assembly of a Giant Heterometallic Polyoxotungstate Supercluster with Antitumor Activity.

The hierarchical aggregation of molecular nanostructures from multiple components is a grand synthetic challenge, which requires highly selective linkage control. We demonstrate how two orthogonal linkage groups, that is, organotin and lanthanide cations, can be used to drive the aggregation of a giant molecular metal oxide superstructure. The title compound {[(Sn(CH3 )2 )2 O]4 {[CeW5 O18 ] [TeW4 O16 ][CeSn(CH3 )2 ]4 [TeW8 O31 ]4 }2 }46- (1 a) features dimensions of ca. 2.2×2.3×3.4 nm3 and a molecular weight of ca. 25 kDa. Structural analysis shows the hierarchical aggregation from several independent subunits. Initial biomedical tests show that 1 features an inhibitory effect on the proliferation of HeLa cells based on an apoptosis pathway. In vivo experiments in mice reveal the antiproliferative activity of 1 and open new paths for further development of this new compound class.

Engineering polyoxometalate-intercalated layered double hydroxides for catalytic applications.

Polyoxometalate-intercalated layered double hydroxide (POM-LDH) nanocomposites have received considerable attention in recent years because such nanocomposites not only inherit the intrinsic properties of POMs and LDHs but also exert significant synergistic effects during the catalytic process. In this frontier article, we present the latest advances on the POM-LDH nanocomposites ranging from new synthetic methods to catalytic applications. By making use of the host layer modification method and exfoliation assembly method, the as-prepared POM-LDH nanocomposites show a wide range of catalytic applications. The challenges and future opportunities are also discussed by highlighting some creative work on related POM- or LDH-based materials.

1-D Chain Tungstotellurate Hybrids Constructed from Organic-Ligand-Connecting Iron-Lanthanide Heterometal Encapsulated Tetrameric Polyoxotungstate Units.

A family of inorganic-organic hybrid one-dimensional (1-D) chain iron-lanthanide (Ln) heterometal encapsulated tungstotellurates [H2N(CH3)2]8K2Na4[Ln2(Ac)2(H2O)4Fe2(Hpdca)2(B-ß-TeW9O33)2][Ln2(H2O)8Fe2(Hpdca)2(B-ß-TeW9O33)2]·50H2O [Ln = Eu3+ (1), Tb3+ (2), Dy3+ (3), Er3+ (4), HAc = acetate acid, H2pdca = 2,5-pyridinedicarboxylic acid] were prepared using a facile "one-pot" reaction. The molecular structures of 1-4 consist of an intriguing organic-ligand-connecting Fe-Ln heterometal inserted tetrameric unit [Ln2(Ac)2(H2O)4Fe2(Hpdca)2(B-ß-TeW9O33)2][Ln2(H2O)8Fe2(Hpdca)2(B-ß-TeW9O33)2]14-. Appealingly, the tetrameric unit is composed of two sandwich-type subunits [Ln2(Ac)2(H2O)4Fe2(Hpdca)2(B-ß-TeW9O33)2]8- and [Ln2(H2O)8Fe2(Hpdca)2(B-ß-TeW9O33)2]6-, in which each sandwich-type subunit can be regarded as a derivative of two Ln-organic complexes substituting two external FeIII ions in the classic Krebs-type [Fe4(H2O)10(ß-TeW9O33)2]4- fragment. Furthermore, adjacent tetrameric units are interconnected into a 1-D chain arrangement by Hpdca- bridges. 1-4 represent the first examples of Fe-Ln heterometal encapsulated tungstotellurates. Comprehensive magnetic measurements of 3 imply the possible single-molecule magnet properties in 3 with an estimated relaxation time τ0 ≈ 6.06 × 10-6 s at Hdc = 0 Oe and τ0 ≈ 6.97 × 10-5 s at Hdc = 1500 Oe. In addition, the solid-state photoluminescence spectra of 1 and 2 at room temperature exhibit the typical f-f transitions of Ln cations. The Commission International d'Eclairage (CIE) color coordinates of (0.540 24, 0.442 44) for 1 and (0.428 71, 0.428 30) for 2 along with the correlated color temperatures of 1995 and 3278 K, dominant wavelengths of 586 and 578 nm, and color purities of 95.09% and 57.27% for 1 and 2 are obtained.

Aggregation of Giant Cerium-Bismuth Tungstate Clusters into a 3D Porous Framework with High Proton Conductivity.

The exploration of high nuclearity molecular metal oxide clusters and their reactivity is a challenge for chemistry and materials science. Herein, we report an unprecedented giant molecular cerium-bismuth tungstate superstructure formed by self-assembly from simple metal oxide precursors in aqueous solution. The compound, {[W14 CeIV6 O61 ]([W3 Bi6 CeIII3 (H2 O)3 O14 ][B-α-BiW9 O33 ]3 )2 }34- was identified by single-crystal X-ray diffraction and features 104 metal centers, a relative molar mass of ca. 24 000 and is ca. 3.0×2.0×1.7 nm3 in size. The cluster anion is assembled around a central {Ce6 } octahedron which is stabilized by several molecular metal oxide shells. Six trilacunary Keggin anions ([B-α-BiW9 O33 ]9- ) cap the superstructure and limit its growth. In the crystal lattice, water-filled channels with diameters of ca. 0.5 nm are observed, and electrochemical impedance spectroscopy shows pronounced proton conductivity even at low temperature.

Rare-Earth-Incorporated Tellurotungstate Hybrids Functionalized by 2-Picolinic Acid Ligands: Syntheses, Structures, and Properties.

A series of organic-inorganic rare-earth-incorporated tellurotungstate hybrids, Na4[RE2(H2O)4(pica)2W2O5][(RE(H2O)W2(Hpica)2O4)(B-ß-TeW8O30H2)2]2·38H2O (RE = LaIII (1), CeIII (2), NdIII (3), SmIII (4), EuIII (5); Hpica = 2-picolinic acid), were prepared via a one-step assembly reaction of Na2WO4·2H2O, RE(NO3)3·6H2O, K2TeO3, Hpica, and triethylamine (tea). Notably, the solubilization of tea toward Hpica and the solubilization of Hpica toward RE cations in the reaction system play an important role in the formation of 1-5. The most significant feature of 1-5 consists of an intriguing tetrameric [RE2(H2O)4(pica)2W2O5][(RE(H2O)W2(Hpica)2O4)(B-ß-TeW8O30H2)2]24- polyoxoanion constructed from two tetravacant Keggin sandwich-type [(RE(H2O)W2(Hpica)2O4)(B-ß-TeW8O30H2)2]5- entities linked by a RE-W-Hpica {RE2(H2O)4(pica)2W2O5}6+ cluster, in which Hpica ligands not only play a key bridging role in linking RE and W centers by carboxylic groups in an irregular N-O-RE-O-W-O six-membered-ring motif but also can directly chelate with W centers via N and O atoms in a stable N-O-C-O-W five-membered-ring fashion. 1-5 represent rare organic-inorganic hybrid RE-substituted tellurotungstates. Moreover, the solid-state photoluminescence properties of 3-5 have been deeply investigated, and these compounds exhibit the characteristic emission stemming from intra-4f transitions of RE ions. The energy transfer of the O → W transitions sensitizing the emission of SmIII centers in 4 is convincingly proved by time-resolved emission spectra (TRES); the increase in the strongest typical emission of SmIII ions at a decay time of 17 µs is accompanied by the decline of O → W emission, and the CIE 1931 diagram was obtained from the corresponding TRES. Furthermore, a comparison of the luminescence behaviors of 5 in the solid state and in solution reveals the structural skeletal integrity of 5 in solution and a shorter decay lifetime in the solution caused by the high-frequency O-H oscillators.

Tellurotungstate-Based Organotin-Rare-Earth Heterometallic Hybrids with Four Organic Components.

A family of unprecedented tellurotungstate-based organotin-rare-earth (RE) heterometallic hybrids [H2N(CH3)2]6H12Na2 {[Sn(CH3)W2O4(IN)][(B-α-TeW8O31)RE(H2O) (Ac)]2}2·25H2O [RE = CeIII (1), PrIII (2), NdIII (3), SmIII (4), EuIII (5), GdIII (6), TbIII (7); HIN = isonicotinic acid, HAc = acetic acid] were synthesized and characterized by elemental analyses, IR spectra, UV spectra, thermogravimetric analyses, powder X-ray diffraction, and single-crystal X-ray diffraction. The polyoxoanionic skeletons {[Sn(CH3)W2O4(IN)][(B-α-TeW8O31)RE(H2O) (Ac)]2}220- of 1-7 are constructed from two symmetrical units {[Sn(CH3)W2O4(IN)][(B-α-TeW8O31)RE(H2O) (Ac)]2}10- linked by two acetate connectors, which not only represent the first inorganic-organic hybrid RE-substituted tellurotungstates involving three different organic ligands, but also stand for the first samples of organotin-RE heterometallic polyoxometalate derivatives. The solid-state luminescent emission properties of 2-5 mainly display the characteristic emission bands of REIII cations, whereas during the emission procedure of 7, [B-α-TeW8O31]10- segments make a nonignorable contribution to the PL behavior of 7 accompanying by the occurrence of the intramolecular energy transfer from O→W LMCT energy to Tb3+ centers. Furthermore, 4@CTAB composites with peanutlike and honeycombed morphologies were prepared by a surfactant cetyltrimethylammonium bromide (CTAB). The time-resolved emission spectra of the 4@CTAB composite with CTAB/4 = 0.033/0.05 consolidate the energy transfer from CTAB to REIII centers. Variable-temperature magnetic susceptibility measurements for 2, 3, and 4 were performed.

First quadruple-glycine bridging mono-lanthanide-substituted borotungstate hybrids.

A class of novel organic-inorganic hybrid lanthanide (Ln)-substituted Keggin-type borotungstates K4Na4H4[Ln2(gly)4(α-BW11O39)2]·23H2O [Ln = Ce3+ (1), Pr3+ (2), Nd3+ (3), Sm3+ (4), Eu3+ (5), Tm3+ (6); gly = glycine] have been synthesized from the reaction of K8[BW11O39H]·13H2O, NaAc·6H2O and Ln(NO3)3·6H2O by employing gly ligands as structure-stabilizing agents in the conventional aqueous solution system and structurally characterized by elemental analyses, IR spectroscopy, thermogravimetric (TG) analyses, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. The common prominent structural feature of isomorphic 1-6 is that all of them consist of two mono-Ln-substituted Keggin [Ln(α-BW11O39)]6- fragments linked by four gly ligands, furnishing an intriguing dimeric assembly of the quadruple-gly-connective mono-Ln-substituted borotungstate, in which each carboxylic oxygen atom from gly ligands is bound to Ln3+ cations in the µ2-O or µ3-O mode. To the best of our knowledge, 1-6 represent the first examples of inorganic-organic hybrid Ln-substituted borotungstates functionalized by quadruple amino acid bridges. The solid-state photoluminescence properties of 3-5 have been determined at ambient temperature and the photoluminescence emission spectra exhibit the characteristic emission bands derived from Ln3+ centers. The thermostability of 1-6 has been studied and the thermal decomposition procedure of 3 has been comprehensively investigated with the assistance of variable-temperature PXRD patterns and variable-temperature IR spectra. Furthermore, magnetic susceptibility measurements of 1, 2 and 4 have been conducted.

Effect of quercetin on chronic enhancement of spatial learning and memory of mice.

In this study we evaluated the effect of quercetin on D-galactose-induced aged mice using the Morris water maze (MWM) test. Based on the free radical theory of aging, experiments were performed to study the possible biochemical mechanisms of glutathione (GSH) level and hydroxyl radical (OH-) in the hippocampus and cerebral cortex and the brain tissue enzyme activity of the mice. The results indicated that quercetin can enhance the exploratory behavior, spatial learning and memory of the mice. The effects relate with enhancing the brain functions and inhibiting oxidative stress by quercetin, and relate with increasing the GSH level and decreasing the OH- content. These findings suggest that quercetin can work as a possible natural anti-aging pharmaceutical product.