The gadolinium complexes with polyoxometalates as potential MRI contrast agents

Polyoxometalate-based nanocomposites for antitumor and antibacterial applications

Polyoxometalates (POMs), as emerging inorganic metal oxides, have been shown to have significant biological activity and great medicinal value. Nowadays, biologically active POM-based organic-inorganic hybrid materials have become the next generation of antibacterial and anticancer drugs because of their customizable molecular structures related to their highly enhanced antitumor activity and reduced toxicity to healthy cells. In this review, the current developed strategies with POM-based materials for the purpose of antibacterial and anticancer activities from different action principles inducing cell death and hyperpolarization, cell plasma membrane destruction, interference with bacterial respiratory chain and inhibiting bacterial growth are overviewed. Moreover, specific interactions between POM-based materials and biomolecules are highlighted for a better understanding of their antibacterial and anticancer mechanisms. POMs have great promise as next-generation antibacterial and anticancer drugs, and this review will provide a valuable systematic reference for the further development of POM-based nanomaterials.

Multinuclear Lanthanide-Implanted Tetrameric Dawson-Type Phosphotungstates with Switchable Luminescence Behaviors Induced by Fast Photochromism

A series of benzoate-decorated lanthanide (Ln)-containing tetrameric Dawson-type phosphotungstates [N(CH₃)₄]₆H₂₀[{(P₂W₁₇O₆₁)Ln(H₂O)₃Ln(C₆H₅COO)(H₂O)₆]}{[(P₂W₁₇O₆₁)Ln(H₂O)₃}]₂Cl₂·98H₂O [Ln = Sm (1), Eu (2), and Gd (3)] were made using a facile one-step assembly strategy and characterized by several techniques. Notably, the Ln-containing tetrameric Dawson-type polyoxoanions [{(P₂W₁₇O₆₁)Ln(H₂O)₃Ln(C₆H₅COO)(H₂O)₆]}{[(P₂W₁₇O₆₁)Ln(H₂O)₃}]₂^24- are all established by four monolacunary Dawson-type [P₂W₁₇O₆₁]^10- segments, encapsulating a Ln³⁺ ion with two benzoates coordinating to the Ln³⁺ ions. 1-3 exhibit reversible photochromism, which can change from intrinsic white to blue for 6 min upon UV irradiation, and their colors gradually recover for 30 h in the dark. The solid-state photoluminescence spectra of 1 and 2 display characteristic emissions of Ln components based on 4f-4f transitions. Time-resolved emission spectra of 1 and 2 were also measured to authenticate the energy transfer from the phosphotungstate and organic chromophores to Eu³⁺. In particular, 1 shows an effectively switchable luminescence behavior induced by its fast photochromism.

Polyoxometalate-Based Nanomaterials Toward Efficient Cancer Diagnosis and Therapy

As an emerging class of inorganic metal oxides, organically functionalized polyoxometalates (POMs) or POM-based nanohybrids have been demonstrated promising potential for the inhibition of various cancer types by the virtue of their diversity in structures and significantly reduced toxicity. This contribution summarizes the latest achievement of POM-based nanomaterials in cancer diagnosis and various therapeutics to put forward our fundamental viewpoints on the design principles of modified POMs based on their application. In addition, major challenges and perspectives in this field are also discussed. We expect that this review will provide a valuable and systematic reference for the further development of POM-based nanomaterials.

Fe/Mn multilayer nanowires as dual mode T1 -T2 magnetic resonance imaging contrast agents

To overcome the negative contrast limitations, and to improve the sensitivity of the magnetic resonance signals, the mesoporous silica coated Fe/Mn multilayered nanowires (NWs) were used as a T₁ -T₂ dual-mode contrast agents (CAs). The single component Fe and Mn NWs, and Fe/Mn multilayer NWs were synthesized by electrodeposition in the homemade anodic aluminum oxide (AAO) templates with the aperture of about 30 nm. The structural characterization and morphology of single component and multisegmented NWs was done by X-ray diffraction and transmission electron microscopy. The elemental composition of Fe/Mn multilayerd NWs was confirmed by energy-dispersive X-ray and energy-dispersive spectrometer. Vibrating sample magnetometer was used to test the magnetic properties, and 1.5 T magnetic resonance imaging (MRI) scanner was used to measure the relaxation efficiency. Importantly, the MRI study indicated that the Fe/Mn multilayer NWs showed a significant T₁ -T₂ imaging effect, and have longitudinal relaxivity (r₁ ) value, that is, 1.25 ± 0.0329 × 10^-4 μM^-1 s^-1 and transverse relaxivity (r₂ ), that is, 5.13 ± 0.123 × 10^-4 μM^-1 s^-1 , which was two times of r₁ value (0.654 ± 0.00899 × 10^-4 μM^-1 s^-1 ) of Mn NWs, and r₂ value (2.96 ± 0.0415 × 10^-4 μM^-1 s^-1 ) of Fe NWs. Hence, Fe/Mn multilayer NWs have potential to be used as T₁ -T₂ dual-mode CAs.

Polyoxometalate-based high-spin cluster systems: a NMR relaxivity study up to 1.4 GHz/33 T

Paramagnetic polyoxometalates are of special interest with regard to their application as alternative contrast agents in nonhuman magnetic resonance imaging which is increasingly used in materials science and process engineering.

Synthesis and characterization of self-assembled inorganic-organic hybrid arsenotungstates

A series of 12 inorganic-organic hybrid 4f-substituted arsenotungstates decorated with 3d-based complexes along with acetate bridging, viz. {[Cu₂(H₂O)(1,10-phen)₂(μ-CH₃COO)₂]₄[Ln₂(H₂O)₂(μ-CH₃COO)₂(α-AsW₁₁O₃₉)₂]}^2- (Ln^III = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), have been synthesized. These compounds were isolated using a one-pot synthetic strategy with copper, lanthanoid, trilacunary arsenotungstate and 1,10-phenanthroline as precursors. They were characterized using various analytical techniques, such as single-crystal X-ray diffraction (SC-XRD), powder XRD (PXRD), Fourier transform IR (FT-IR) spectroscopy, UV-Vis spectroscopy and thermogravimetric analysis (TGA). In all these compounds, a dinuclear Ln₂(ac)₂ moiety is sandwiched between two monolacunary [AsW₁₁O₃₉]^7- polyoxometalates (POMs), where the Ln₂(ac)₂ moiety is comprised of two acetate ligands in a μ-κO,O':κO fashion. Moreover, the anion is decorated by a copper-phenanthroline-acetate complex through a terminal O atom of the polyanion.

Synthesis and characterization of carbonate-encapsulated ytterbium- and yttrium-containing polyoxotungstates

A sandwiched-type carbonate-encapsulated yttrium-containing arsenotungstate(III) has been synthesized under mild reaction conditions. The polyanion [NaCH₃COO{Y₂(H₂O)₃(B-α-AsW₉O₃₃)₂(W₂O₅)(CO₃)}]^12- (1) was isolated as a solid crystalline material by the reaction of a Y^III salt with the sodium salt of trilacunary [AsW₉O₃₃]^9- in sodium acetate solution. The sodium salt of the polyanion, i.e. Na₁₂[Na(CH₃COO){Y₂(AsW₉O₃₃)₂(W₂O₅)(CO₃)(H₃O)₃}]·22H₂O (1a), was characterized by various analytical techniques, such as FT-IR, single-crystal X-ray diffraction (SC-XRD), TGA (thermogravimetric analysis), ¹³C NMR and ESI-MS (electrospray ionization mass spectrometry). SC-XRD studies revealed that the polyanion crystallizes in the triclinic space group P-1. The structure showed that the polyanion is a carbonate-encapsulated sandwich-type species, consisting of two trilacunary B-α-[AsW₉O₃₃]^9-, with a lone-pair-containing As^III heteroatom, together with two extra tungsten centres and two yttrium cations at the sandwich position, where CH₃COO^- and Na⁺ ions act as linkers between the two polyanion units. In addition, we have also synthesized two carbonate-encapsulated germanotungstates(IV), without lone-pair-containing heteroatoms, with the formula [Ln₃(A-β-GeW₉O₃₄)₂(CO₃)(H₂O)₃]^13- [Ln = Y^III (2) and Yb^III (3)], i.e. Y₂K₃Na₄[Y₃(A-β-GeW₉O₃₄)₂(CO₃)(H₂O)₃]·19H₂O (2a) and YbK₈Na₂[Yb(A-β-GeW₉O₃₄)₂(CO₃)(H₂O)₃]·16H₂O (3a), and characterized them by FT-IR, SC-XRD, TGA and ESI-MS. Here, the lanthanide ions act as linkers, extending the structures into higher dimensions. Sodium and potassium ions also play a key role as linkers, further extending the structure. The packing shows the presence of certain hydrophilic pores within the structure.

Nano-assemblies of cationic mPEG brush block copolymers with gadolinium polyoxotungstate [Gd(W5O18)2]9- form stable, high relaxivity MRI contrast agents

Polyoxometalates (POMs) incorporating paramagnetic ions, such as gadolinium, show promise as contrast agents for application in magnetic resonance imaging (MRI). Specifically, [Gd(W5O18)2]9- (denoted as GdWO) has been reported to have a higher relaxivity than commercially available contrast agents, but it's clinical utility has been limited by the intrinsic instability of POMs at physiological pH (7.4). In the current report we present a stability study on neat GdWO and nano-assemblies of block copolymers with GdWO in the pH range 5.0-7.4 to assess their suitability as MRI contrast agents. Neat GdWO only maintained structural stability between pH 5.4 and 6.4, and demonstrated poor MRI contrast at pH 7.4. To address this pH instability, GdWO was self-assembled with cationic mPEG brush block copolymers containing 20 or 40 units derived from the cationic monomer, 2-dimethylaminoethyl methacrylate (DMAEMA). Nano-assemblies with different charge ratios were synthesised and characterised according to their size, stability, contrasting properties and toxicity. The longitudinal relaxivity (r1) of the nano-assemblies was found to be dependent on the charge ratio, but not on the length of the cationic polymer block. Further investigation of PDMAEMA20 nano-assemblies demonstrated that they were stable over the pH range 5.0-7.4, exhibiting a higher r1 than either neat GdWO (2.77 s-1 mM-1) or clinical MRI contrast agent Gd-DTPA (4.1 s-1 mM-1) at pH 7.4. Importantly, the nano-assembly with the lowest charge ratio (0.2), showed the highest r1 (12.1 s-1 mM-1) whilst, stabilising GdWO over the pH range studied, eliciting low toxicity with MDA-MB231 cells.

Biocompatible supramolecular dendrimers bearing a gadolinium-substituted polyanionic core for MRI contrast agents

Two hybrid supramolecular complexes comprising magnetic core and dendritic periphery were prepared, which exhibited uniform size, definite molecular weight and chemical composition, and were applicable as enhanced contrast agents.

Phase transfer preparation of ultrasmall MnS nanocrystals with a high performance MRI contrast agent

In this paper, a phase transfer method is reported which was used to prepare ultrasmall manganese(ii) sulfide nanocrystals in which prefabricated MnS aggregations are transferred from cyclohexane into an aqueous solution of sodium citrate.

Synthesis, crystal structure and catalytic activity of the guanidinium cation directed nickel(ii)-containing open Wells–Dawson 19-tungstodiarsenate(iii) [{Ni(H2O)4}2{Na(H2O)}As2W19O67(H2O)]9−

Guanidinium directed open Wells–Dawson type [{Ni(H₂O)₄}₂{Na(H₂O)}As₂W₁₉O₆₇(H₂O)]⁹⁻ polyanion 1 has been synthesized on reacting nickel chloride and trilacunary Na₉[B-α-AsW₉O₃₃] in aqueous solution (pH ∼ 5.8), in presence of pyridine-2,6-dicarboxylic acid.

Syntheses, crystal structure, electrochemistry and luminescence properties of lanthano–germanotungstates

[Ln(α-GeW₁₁O₃₉)₂]¹³⁻ (Ln = La^III and Ce^III) and [{Ln(μ-CH₃COO)GeW₁₁O₃₉(H₂O)}₂]¹²⁻ (Ln = Pr^III, Nd^III and Sm^III) complexes were synthesized using a one-pot reaction. Similar complexes were isolated and their electrochemical and photochromic properties were studied.

Lanthano-phosphotungstate: A water soluble and reusable catalyst for oxidation of alcohols using H2O2 as an oxidant

Oxidation of alcohols using H₂O₂ to corresponding carbonyl compounds in good yields for lanthano-phosphotungstates catalysts and its recyclability up to five cycles was envisaged in water.

Dimeric complexes of rare-earth substituted Keggin-type silicotungstates: syntheses, crystal structure and solid state properties

A series of rare-earth substituted dimeric complexes of Keggin-type silicotungstates were synthesized and characterized using various analytical techniques like SCXD, photoluminescence, ¹H and ¹³C NMR spectroscopy.

Lanthanoid containing phosphotungstates: the syntheses, crystal structure, electrochemistry, photoluminescence and magnetic properties

A series of Peacock and Weakley type dimers was synthesized in a one pot reaction with high yield using ligand [P₂W₁₉O₆₉(H₂O)]¹⁴⁻. All nano clusters were structurally characterized by various analytical techniques.

HIV-1 protease inhibition potential of functionalized polyoxometalates

Polyoxometalates (POMs) are interesting biomedical agents due to their versatile anticancer and antiviral properties, such as remarkable anti-HIV activity. Although POMs are tunable and easily accessible inorganic drug prototypes in principle, their full potential can only be tapped by enhancing their biocompatibility, for example, through organic functionalization. We have therefore investigated the HIV-1 protease inhibition potential of functionalized Keggin- and Dawson-type POMs with organic side chains. Their inhibitory performance was furthermore compared to other POM types, and the buffer dependence of the results is discussed. In addition, chemical shift mapping NMR experiments were performed to exclude POM–substrate interactions. Whereas the introduction of organic side chains into POMs is a promising approach in principle, the influence of secondary effects on the reaction system also merits detailed investigation.

The photophysics of europium and terbium polyoxometalates and their interaction with serum albumin: a time-resolved luminescence study

Polyoxometalates (POMs) are emerging as useful materials for a variety of applications. Many show potential for use in the biological and medical fields. Those incorporating lanthanides, with their narrow emission bands, large Stokes' shift and tuneable emission are of particular interest for the labelling and imaging of biological molecules. Their longer emission timescale (micros to ms) also allows autofluorescence from the biological samples to be removed by time gating the emission decay. This means that the characterisation of their photophysical properties is required to enable their application. In this work we present a time-resolved emission study of two types of POM structure, a simple europium containing decatungstate and a more complex high nuclear polyoxotungstate, containing either europium or terbium. A concentration study, made monitoring the lanthanide emission helped elucidate POM-POM interactions. The use of global analysis hints at the presence of defined POM aggregates. Interaction with serum albumin was ascertained, both by monitoring the lanthanide emission of the POM and the tryptophan emission from the serum albumin. This showed that the more complex structure had a significantly higher affinity for the protein than the simple structure.

MRI in ocular drug delivery

Conventional pharmacokinetic methods for studying ocular drug delivery are invasive and cannot be conveniently applied to humans. The advancement of MRI technology has provided new opportunities in ocular drug-delivery research. MRI provides a means to non-invasively and continuously monitor ocular drug-delivery systems with a contrast agent or compound labeled with a contrast agent. It is a useful technique in pharmacokinetic studies, evaluation of drug-delivery methods, and drug-delivery device testing. Although the current status of the technology presents some major challenges to pharmaceutical research using MRI, it has a lot of potential. In the past decade, MRI has been used to examine ocular drug delivery via the subconjunctival route, intravitreal injection, intrascleral injection to the suprachoroidal space, episcleral and intravitreal implants, periocular injections, and ocular iontophoresis. In this review, the advantages and limitations of MRI in the study of ocular drug delivery are discussed. Different MR contrast agents and MRI techniques for ocular drug-delivery research are compared. Ocular drug-delivery studies using MRI are reviewed.