New synergistic antibacterial mechanism of bulky mixed Ti/w hetero-polyoxometalates composed of multi lacunary Keggin structure with oxacillin against vancomycin intermediate-resistant Staphylococcus aureus

Considering the lack of detailed research on the antibacterial mechanism of polyoxometalates, we examined the synergistic effect of novel bulky mixed Ti/W hetero-polyoxometalates (K9.5H2.5 ［α-Ge2Ti4W20O78］・ 29H2O; αTi4, K9H5 ［α-Ge2Ti6W18O77］・16H2O; αTi6, K23H5［α-Ge4Ti12W36O154］・39H2O; αTi12, K9H5 ［β-Ge2Ti6W18O77］・ 45H2O; βTi6) with the antibiotic oxacillin against vancomycin intermediate-resistant Staphylococcus aureus (VISA) using fractional inhibitory concentration (FIC) index and growth curve in this study. All polyoxometalates used in this study showed remarkable synergistic effects with oxacillin. Its synergistic antibacterial mechanism was examined using reverse transcription PCR (RT-PCR) and penicillin binding protein-2' (PBP2') latex agglutination test. The results suggested that these polyoxometalates did not inhibit mecA gene transcription but resulted in PBP2' protein malfunction. From these results, we concluded that the substances producing resistance in VISA were affected by polyoxometalates depending on their molecular size, facilitating a synergistic antibacterial effect with oxacillin.

"Mixed-Valence Decatungstates" Revisited: Crystal Structure and Aqueous Solution Chemistry of [W10O32]6- and an ESR Study on Electron Delocalization

A [ⁱPrNH₃]⁺/Na⁺-mixed salt of unprotonated two-electron-reduced decatungstate, [ⁱPrNH₃]₈[W₁₀O₃₂]·(NaCl₂)₂H₂O (1), is isolated from the photolyte obtained by the UV photolysis of the Na₂WO₄·2H₂O/[ⁱPrNH₃]Cl aqueous solution at pH 6.5 and characterized in the solid state (X-ray diffraction and elemental analysis) and solution (UV-vis absorption and electrochemistry). [W₁₀O₃₂]^5-, as a paramagnetic contaminant in the crystallite of diamagnetic 1, shows only a broadened singlet-like electron spin resonance (ESR) line around g = 1.82 with an unresolved ¹⁸³W-hyperfine interaction (A_W) at low temperatures. To determine the effective electronic delocalization in the reduced decatungstates consisting of two polar WO₆ (W_pO₆) and eight equatorial WO₆ (W_eqO₆) octahedra with an approximate D_4h symmetry, we calculated isotropic ESR spectral patterns of the protonated reduced decatungstate, [HW₁₀O₃₂]^4-, for a variety of |A_W| on the basis of interactions of the 5d¹-electronic spin with eight magnetically equivalent nuclear spins of W_eq and the proton ¹H (I_H = 1/2) and took |A_W| = 2|A_H| (A_H = ¹H-superhyperfine interaction) as the best choice for direct comparison with the experimental single-crystal ESR spectral pattern of [HW₁₀O₃₂]^4- at 77 K. Electronically fully delocalized over eight W_eqO₆ octahedron mixed-valence sites of class-III-type clusters, [W₁₀O₃₂]^5- ≡ [W_p⁶⁺₂(W_eq^5.875+)₈O₃₂]^5- and [W₁₀O₃₂]^6- ≡ W_p⁶⁺₂(W_eq^5.75+)₈O₃₂]^6-, are demonstrated with the help of ESR spectroscopy of [HW₁₀O₃₂]^4- ≡ [W_p⁶⁺₂(H_0.125W_eq^5.875+)₈O₃₂]^4- which revealed that both the 5d¹-electron and proton are situated at each equatorial WO₆ octahedron site with a 1/8 occupancy at low temperatures (≤77 K). The nucleation process to [W₁₀O₃₂]^6- through the UV photolysis of [W₇O₂₄]^6- at pH 6.5 is also discussed based on the electrospray ionization mass spectrometry of the photolyte.

In-vitro anti Myxovirus Activity and Mechanism of Antiinfluenzavirus Activity of Polyoxometalates PM-504 and PM-523

Sixty polyoxometalates were examined for anti-influenza A virus (FluV-A) activity in vitro. Two of the most potent and least cytotoxic compounds, PM-504 K9H5(Ge2Ti6W18O77)16H2O] and PM-523 (iPrNH3)6H [PTi2W10O38(O2)9H2O2] were selected for further studies. Examination of the antiviral effects of PM-504 and PM-523 against other human ortho- and paramyxoviruses revealed that both compounds had broad spectrum antimyxovirus activities. From a time of addition study and FACS analysis for influenza A virus infected cells, the compounds were found not to inhibit binding of virus to MDCK cells. However, these compounds inhibited haemolysis of chicken erythrocytes by virus and also inhibited fluorescence dequenching of octadecylrhodamine B-labelled virus after binding to cells. This indicates that these polyoxometalates inhibited fusion of the virus envelope to the cellular membrane.

Antiviral Activity of a Keggin Polyoxotungstate PM-19 against Herpes Simplex Virus in Mice

The in vivo activity of the Keggin polyoxotungstate PM-19 [K7(PTi2W10O40)·6H2O] was investigated against herpes simplex virus type 2 (HSV-2) in ddY mice. A single dose of PM-19 at 100mg kg−1administered intraperitoneally (i.p.) immediately after i.p. infection of ddY mice with HSV-2 offered 92% protection against an otherwise lethal HSV-2 infection. PM-19 was less or not effective if given by any route other than the i.p. route. When repeated doses of PM-19 were administered i.p. on day 0 (immediately after infection) and day 1 and 2 after infection, it proved protective over a dosage range of 0.1-50 mg kg−1day−1, its ED50 (50% effective dose, based on the number of survivors) being 0.25 mg kg−1day−1. Under these conditions, ACV was not effective even at doses up to 100 mg kg−1day−1.

Molecular and electron-spin structures of a ring-shaped mixed-valence polyoxovanadate (IV, V) studied by (11)B and (23)Na solid-state NMR spectroscopy and DFT calculations

(11)B and (23)Na solid-state nuclear magnetic resonance (NMR) spectra of ring-shaped paramagnetic crystals of H15[V7(IV)V5(V)B32O84Na4]·13H2O containing seven d(1) electrons from V(IV) were studied. Magic-angle-spinning (MAS) and multiple-quantum MAS NMR experiments were performed at moderate (9.4T) and ultrahigh magnetic fields (21.6T). The NMR parameters for quadrupole and isotropic chemical shift interactions were estimated by simulation of the NMR spectra and from relativistic density functional theory (DFT) calculations. Four Na ions incorporated into the framework were found to occupy four distinct sites with different populations. The DFT calculation showed that d(1) electrons with effectively one up-spin caused by strong antiferromagnetic interactions were delocalized over the 12V ions.

Dual-emissive photoluminescent Langmuir-Blodgett films of decatungstoeuropate and an amphiphilic iridium complex

Langmuir monolayers and Langmuir-Blodgett (LB) films of the decatungstoeuropate [Eu(W(5)O(18))(2)](9-) (EuW(10)) and the amphiphilic Ir complex 1 have been successfully fabricated by using the adsorption properties of the EuW(10) polyanion dissolved in the aqueous subphase onto a positively charged 1 monolayer at the air-water interface. The compression isotherms and Brewster angle microscopy (BAM) of monolayers of 1 on pure water (1 monolayer) and on a subphase containing 10(-6) M EuW(10) and 10(-3) M NaCl (1/EuW(10) monolayer) have been studied. Infrared and UV-vis spectroscopy of the transferred LB films indicate that EuW(10) and 1 molecules are incorporated within these LB films. X-ray reflectivity (SXR) and atomic force microscopy (AFM) experiments indicate that LB films of 1 present a heterogeneous morphology while 1/EuW(10) films show a flatter and more homogeneous surface as well as a layered structure with a periodicity of 4.1 nm. Mixed monolayers of 1 and DODA (dimethyldioctadecylammonium bromide) have been prepared with EuW(10) polyanions in the subphase to control the concentration of 1 and EuW(10) polyanions within the LB films. AFM and SXR experiments with the transferred LB films show that the dilution of 1 with DODA improves the layered structure. The luminescence of 1 is partially quenched by EuW(10) in the 1/EuW(10) LB films, while emission from EuW(10) is not detected. On the other hand, emission from both entities is preserved in the LB films prepared from mixed DODA/1 monolayers, in which the red and yellow emissions arise independently from EuW(10) and 1, respectively. The different DODA:1 ratios lead to changes in the emission color. Therefore, they constitute a promising color-tunable luminescent material.

Controllable Layered Structures in Polyoxomolybdate-Surfactant Hybrid Crystals

Inorganic-organic hybrid crystals containing α-octamolybdate (Mo₈) or hexamolybdate (Mo₆) were isolated by using hexadecyltrimethylammonium (C₁₆) surfactant. The packing mode of the inorganic layers depended on a difference in the polyoxomolybdate molecular structure. The structure for both crystals consisted of alternate stacking of C₁₆ organic bilayers and polyoxomolybdate inorganic layers with a periodicity of 24.4–24.6 Å. However, the C₁₆-Mo₈ crystals contained Mo₈ monolayers, while the C₁₆-Mo₆ crystals contained Mo₆ bilayers. These lattice structures for the polyoxometalate/organic hybrid will be designed by the molecular structures of polyoxometalate.

Coordination of {Mo142} Ring to La3+ Provides Elliptical {Mo134La10} Ring with a Variety of Coordination Modes

A 28-electron reduced C_2h-Mo-blue 34Ǻ outer ring diameter circular ring, [Mo₁₄₂O₄₂₉H₁₀(H₂O)₄₉(CH₃CO₂)₅(C₂H₅CO₂)]^30- (≡{Mo₁₄₂(CH₃CO₂)₅(C₂H₅CO₂)}) comprising eight carboxylate-coordinated (with disorder) {Mo₂} linkers and six defect pockets in two inner rings (four and three for each, respectively), reacts with La³⁺ in aqueous solutions at pH 3.5 to yield a 28-electron reduced elliptical C_i-Mo-blue ring of formula [Mo₁₃₄O₄₁₆H₂₀(H₂O)₄₆{La(H₂O)₅}₄{La(H₂O)₇}₄{LaCl₂(H₂O)₅}₂]^10- (≡{Mo₁₃₄La₁₀}), isolated as the Na₁₀[Mo₁₃₄O₄₁₆H₂₀(H₂O)₄₆{La(H₂O)₅}₄{La(H₂O)₇}₄{LaCl₂(H₂O)₅}₂]·144 H₂O Na⁺ salt. The elliptical structure of {Mo₁₃₄La₁₀} showing 36 and 31 Å long and short axes for the outer ring diameters is attributed to four (A-D) modes of LaO₉/LaO₇Cl₂ tricapped-trigonal-prismatic coordination (TTP) geometries. Two different LaO₂(H₂O)₇ and one LaO₂(H₂O)₂Cl₂ TTP geometries (as A-C modes) for each of two inner rings result from the coordination of all three defect pockets of the inner ring for {Mo₁₄₂(CH₃CO₂)₅(C₂H₅CO₂)}, and two LaO₄(H₂O)₅ TTP geometries (as D mode) result from the displacement of two (acetate/propionate-coordinated) binuclear {Mo₂} linkers with La³⁺ in each inner ring. The isothermal titration calorimetry (ITC) of the ring modification from circle to ellipsoid, showing the endothermic reaction of [La³⁺]/[{Mo₁₄₂(CH₃CO₂)₅(C₂H₅CO₂)}] = 6/1 with ΔH = 22 kJ⋅mol^-1, ΔS = 172 J⋅K^-1⋅mol^-1, ΔG = −28 kJ⋅mol^-1, and K = 9.9 × 10⁴ M^-1 at 293 K, leads to the conclusion that the coordination of the defect pockets to La³⁺ precedes the replacement of the {Mo₂} linkers with La³⁺. ¹³⁹La- NMR spectrometry of the coordination of {Mo₁₄₂(CH₃CO₂)₅(C₂H₅CO₂)} ring to La³⁺ is also discussed.

Langmuir-Blodgett films of a Mo-blue nanoring [Mo(142)O(429)H(10)(H(2)O)(49)(CH(3)CO(2))(5)(CH(3)CH(2)CO(2))](30)(-) (Mo(142)) by the semiamphiphilic method

Langmuir monolayers and LB films of the ring-shaped mixed-valence polyoxomolybdate [Mo142O429H10(H2O)49(CH3CO2)5(CH3CH2CO2)](30-) (Mo142) dissolved in the aqueous subphase have been successfully fabricated by using the adsorption properties of a DODA monolayer. Infrared and ultraviolet-visible spectroscopy of the LB films indicates that Mo142 and DODA molecules are incorporated within these LB films. X-ray reflectivity experiments indicate that the LB films exhibit a well-defined lamellar structure formed by bilayers of DODA molecules alternating with monolayers of Mo142. Using behenic acid-modified hydrophobic quartz substrate is critical for the formation of the well-defined lamellar structure. From the values of the periodicity obtained by these experiments it is clear that the Mo142 clusters lie flat along the charged organic layers. AFM images also showed the flat and homogeneous films on the quartz substrates treated with behenic acid. Cyclic voltammograms of Mo142-LB films deposited on ITO substrates showed quasi-reversible oxidation/reduction waves with positive shift of the potential compared to the case of solution.

Enhancement Effect of Polyoxometalates on NGF-Induced Neurite-Outgrowth of PC12 Cells

Nerve growth factor (NGF)-induced neurite-outgrowth of PC12 cells was enhanced by polyoxometalates such as Na9[SbW(9)O(33)].19.5H(2)O (SbW(9)) and (NH(3)Pr(i))6[Mo(7)O(24)].3H(2)O (Mo(7)). Western blotting analysis of polyoxometalate/NGF-treated PC12 cells showed a strong expression of growth-associated protein 43 (GAP-43), which is associated with the neurite outgrowth. Similar effects were observed for other polyoxometalates, K(11)H[(VO)3(SbW(9)O(33))2].27H(2)O ((VO)3(SbW(9))2), K6[P(2)W(18)O(62)].14H(2)O (P(2)W(18)), and K7[PTi(2)W(10)O(40)].6H2O (PTi(2)W(10)), in contrast with little effect for monomeric tungstate and molybdate. Of the polyoxometalates tested in this study, SbW(9) and Mo(7) were the most potent.

Ferromagnetic Exchange Interactions for Cu612+ and Mn612+ Hexagons Sandwiched by Two B-α-[XW9O33]9- (X = AsIII and SbIII) Ligands in D3d-Symmetric Polyoxotungstates

Two novel Cu6 and Mn6 hexagon sandwiched polyoxometalates, [(CuCl)6(AsW9O33)2]12- (1a) and [(MnCl)6(SbW9O33)2]12- (2a), have been synthesized and characterized by X-ray single-crystal analysis and magnetic measurements. These complexes are D3d symmetric and were isolated as [n-BuNH3]+ salts from aqueous solutions: (n-BuNH3)12[(CuCl)6(AsW9O33)2].6H2O (1), rhombohedral, R, a = 20.33(1) A, c = 26.35(2) A, Z = 3 and (n-BuNH3)12[(MnCl)6(SbW9O33)2].6H2O (2). Six Cu (or Mn) atoms, each of which shows 5-fold coordination, make an approximately equatorial hexagon with a first-neighboring Cu...Cu (Mn...Mn) distance of 2.913(2) A (3.248(1) A) and a Cu-O-Cu (Mn-O-Mn) bond angle of 94.5(2) degrees (100.4(2) degrees ). The magnetic behavior investigated by magnetic susceptibility measurements shows the ferromagnetic exchange interactions with J/k = +12.7 K (J/hc = +8.82 cm(-1)) and a S = 3 ground state for 1 and J/k = +0.20 K (J/hc = +0.14 cm(-1)) and a S = 15 ground state for 2, when only J refers to the isotropic magnetic-exchange interactions for first-neighbor atoms of the approximately equilateral Cu6(12+) and Mn6(12+) hexagons. The single-crystal ESR spectroscopy of 1 under the orientation of the magnetic field along a Cu6 hexagon's nearly 6-fold axis equal to the c axis on the variation of temperature supports the S = 3 ground state and allows an estimate of the zero-field (fine-structure) energy separation between Sz = 0 and Sz = +/-1 of D = -0.182 K to be obtained.

Antitumor activity of polyoxomolybdate, [NH3Pri]6[Mo7O24].3H2O, against, human gastric cancer model

Polyoxometalates are negatively charged inorganic compounds which contain metal ions such as tungsten, molybdenum, vanadium etc. and which make clusters with the surrounding oxygen atoms. [NH3Pri]6[Mo7O24].3H2O (PM-8) was found to be a significant antitumor polyoxomolybdates. It had already been reported that the PM-8 suppressed the growth of Co-4 human colon cancer, MX-1 human breast cancer and OAT human lung cancer xenografted in nude mice. However, the mechanism of the antitumor activity has not been clarified. In this study, the antitumor activity of one of the metal oxide clusters (polyoxometalates), hexabis(isopropylammonium) heptamolybdate trihydrate, [NH3Pri]6[Mo7O24].3H2O (PM-8) were shown in an MTS assay. DNA ladder formation and detection of apoptotic bodies in nuclei were revealed that antitumor activity of PM-8 in MKN45 cells was due to apoptosis. It is concluded that the observation of significant tumor growth suppression of PM-8 in MKN45-bearing mice results from the induction of apoptosis. PM-8 shows promise as a novel anti-cancer agent.

Anticancer activity of polyoxomolybdate

Anticancer polyoxomolybdates have been investigated for medical application of polyoxometalates as discrete cluster anions of metal oxides. [NH3Pri]6[Mo7O24].3H2O (PM-8) has been recognized as one of significant antitumoral polyoxomolybdates. PM-8 had shown the growth suppression against several tumors, for examples, Co-4, human colon cancer, MX-1, human breast cancer, and OAT, human lung cancer. PM-8 showed the tumor growth suppression for MKN-45 human gastric cancer in tumor bearing mice. PM-8 inhibited the cell growth of AsPC-1 which depended on the dose with showing DNA ladder formation and DNA fragmentation, and positive Hoechst staining indicating apoptosis. The ratio of apoptotic cells on flow cytometry analysis were 35%, and 57% with treatment of PM-8 after 48, and 72 h, respectively. One of the anti-tumor activity of PM-8 result from the activation of apoptotic pathway. It is thought that polyoxomolybdates will be applied as a novel anti-tumor agent especially against cancers which are difficult to be treated clinically.

Synergistic effect of polyoxometalates in combination with oxacillin against methicillin-resistant and vancomycin-resistant Staphylococcus aureus: a high initial inoculum of 1 x 108 cfu/ml for in vivo test

Synergistic effect of polyoxometalates, K(6)[P(2)W(18)O(62)].14H(2)O (P(2)W(18)), K(4)[SiMo(12)O(40)].3H(2)O (SiMo(12)), K(7)[PTi(2)W(10)O(40)].6H(2)O (PTi(2)W(10)), and K(9)H(5)[alpha-Ge(2)Ti(6)W(18)O(77)].16H(2)O (Ge(2)Ti(6)W(18)), in combination with a beta-lactam oxacillin against methicillin-resistant and vancomycin-resistant Staphylococcus aureus (characterized by possessing the penicillin-binding protein 2' (PBP2') as a cell-wall synthesis enzyme) with a high initial inoculum of 1 x 10(8) cfu/ml (for in vivo test) was investigated with a help of the growth curve and the reverse transcription polymerase chain reaction (RT-PCR) analyses. The growth curves showing the suppression of cell proliferation of the strains based on the synergistic effect of the polyoxometalates in combination with oxacillin indicated a recovery of the cell proliferation during continuous cultivation. The duration of the suppression of the cell proliferation increased with increasing the concentration of the polyoxometalates, depending on the amounts of the initial inoculum of the strain. The RT-PCR results for P(2)W(18), SiMo(12), and PTi(2)W(10) indicated the suppression of expression of the PBP2'-encoding mecA gene in contrast to the ones for Ge(2)Ti(6)W(18). The difference in the RT-PCR results among the polyoxometalates suggests that there remain other factors for the inhibition of PBP2' production such as post-transcription process.

Anti-RNA virus activity of polyoxometalates

The anti-RNA virus activity of polyoxometalates (POM) is reviewed, with a special emphasis on the anti-respiratory virus activities. There are many causative agents of acute viral respiratory infections; and it is rather difficult to identify the relevant agent in a given case by rapid clinical means. During acute progress of infection before the definitive diagnosis is obtained physicians need to prescribe certain broad spectrum anti-viral drugs. A titanium containing polyoxotungstate, PM-523 exhibited potent anti-influenza virus (FluV) A and anti-respiratory syncytial virus (RSV) activities in vitro. Therapeutic effect of FluV A infected mice with aerosol inhalation of PM-523 was proven. A vanadium substituted polyoxotungstate, PM-1001 has antiviral activity against FluV A, RSV, parainfluenza virus (PfluV) type 2, Dengue fiver virus, HIV-1 and SARS coronavirus in vitro. Thus, POMs have been proven to be broad spectrum and non-toxic anti-RNA virus agents in both in vitro and in vivo experiments and are promising candidates for first-line therapeutics in acute respiratory diseases.

Prevention of the interaction between HVEM, herpes virus entry mediator, and gD, HSV envelope protein, by a Keggin polyoxotungstate, PM-19

One of the Keggin-type heteropolyoxotungstates (K7[PTi2W10O40]6H2O:PM-19) is a potent inhibitor of the replication of herpes simplex virus (HSV) both standard strain 169 and the thymidine kinase-defective strain YS-4C-1 in vitro and in vivo. HSV envelope protein, gD, is necessary for virus entry into the cells. Some cellular molecules, such as HVEM, were reported to act as cofactors during the viral entry step. We determined whether PM-19 prevents these interactions between HSV-gD and HVEM. These activities were investigated using the Ciphergen and BIACORE system. Using a protein chip, many kinds of gD-specific binding proteins were captured, but these proteins could not be identified. Several proteins in these gD-binding proteins were inhibited its interaction with gD due to the presence of PM-19. Using the BIACORE system, the affinity of PM-19 to gD was low, because PM-19 has no direct inactivation activity against the virion. The specific binding of HVEM to the gD was shown as KD of 1.1e-9. The affinity of PM-19 for HVEM was high (KD:2e-9). To determine the competitive binding, the PM-19 (10 microg/ml) and several concentrations of HVEM solution mixtures were injected over the gD-fixed sensor surface. Each binding signal was stable in the range of approximately 270-300 RU. In the case of the addition of PM-19 to HVEM solution, the binding signals were elevated by PM-19 dose dependently. These results suggest that the bindings of PM-19 to gD are not disturbed by the presence of HVEM. PM-19 prevents the interaction between HVEM and gD.

Enhancement of antibacterial activity of beta-lactam antibiotics by [P2W18O62]6-, [SiMo12O40]4-, and [PTi2W10O40]7- against methicillin-resistant and vancomycin-resistant Staphylococcus aureus

The enhancement of antibacterial activity of beta-lactam antibiotics by polyoxometalates against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant S. aureus (VRSA) was investigated by using K6[P2W18O62] . 14H2O (P2W18), K4[SiMo12O40] . 3H2O (SiMo12), and K7[PTi2W10O40] . 6H2O (PTi2W10). Susceptibility test by a beta-lactam-disk method showed the synergistic effect of the polyoxometalates in combination with oxacillin against both MRSA and VRSA. Energy dispersive X-ray analysis of the strain treated with P2W18 revealed localization of the polyoxometalate-tungsten atoms at the periphery of the cell, and the biological reduction of P2W18 and SiMo12 proceeded within both cells of MRSA and VRSA as far as they keep alive. These results indicate that the polyoxometalates can penetrate through the cell wall consisting of peptidoglycan layers and reach cytoplasmic membrane. The inhibitory effect of the polyoxometalates on both mecA- and pbp-induced mRNA expression of both MRSA and VRSA cells, verified by the RT-PCR-electrophoresis analysis, is observed, and the mechanism of the synergistic effect by the polyoxometalates is discussed in terms of the depression of penicillin-binding protein 2' (PBP2') coded by mecA gene.

Regular two-dimensional molecular array of photoluminescent Anderson-type polyoxometalate constructed by Langmuir-Blodgett technique

A regular two-dimensional photoluminescent array of Anderson-type polyoxometalates (POMs) was constructed as built-up Langmuir-Blodgett (LB) films. LB films of hexatungstoantimonate (SbW(6)) and -manganate (MnW(6)) were successfully fabricated by using dimethyldioctadecylammonium (DODA) as cationic partner, while hexamolybdochromate (CrMo(6)) was unsuccessful. Specular X-ray reflectivity (SXR) and grazing incidence X-ray diffraction (GIXD) measurements revealed that both SbW(6)/DODA and MnW(6)/DODA LB films exhibited well-ordered layers consisting of periodic arrangement of the planar-structured Anderson-type molecules. Surprising periodicity was observed in SbW(6)/DODA LB film, in which the distance between SbW(6) and DODA layers was 4.40 nm, and SbW(6) anions would form a two-dimensional square lattice with a length of 1.4 nm. SbW(6)/DODA LB films exhibited photoluminescence at 77 K, while emission spectra were observed at room temperature for SbW(6) solid.

31P NMR and isothermal titration calorimetry studies on polyoxomolybdates-catalyzed hydrolysis of ATP

ATP hydrolysis in the presence of polyoxomolybdates at pH levels of 6, 4, and 2 has been investigated with a help of high pressure liquid chromatography (HPLC) analyses, 31P- and 1H NMR measurements, and isothermal titration calorimetry (ITC). The polyoxomolybdates-induced ATP-hydrolysis proceeded satisfactorily in pH < 6 media at 20 degrees C with an optimum pH level of 4, while it was significantly depressed at low temperature of < or = 5 degrees C. At pH levels of 6 and 4, ADP was a main product, and the involvement of [(PO4)2Mo5O15](6-)-like ATP-molybdate complex as an intermediate was implied. At pH 2 ATP was decomposed to AMP with small generation of ADP through the formation of the ATP-molybdate complex isostructural with [(O3POPO3)Mo6O18(H2O)4]4- as an intermediate. The ITC result at pH 4 showed an occurrence of two types of the exothermic binding reactions between molybdate and ATP with binding constants (K) of 6.61x10(4) and 9.40x10(3) M(-1) and molar enthalpy values (deltaH) of -6.32x10(4) and -4.73x10(3) J mol(-1), respectively. Together with the results of 1H NMR measurements, it is deduced that the molybdates interact with not only phosphate sites in the ATP side-chain, but also adenine-ring with an accompanying aggregation of molybdates at pH 4.

A novel anti-tumor agent, polyoxomolybdate induces apoptotic cell death in AsPC-1 human pancreatic cancer cells

Anti-tumoral polyoxomolybdates have been investigated in the course of study of the medical application of polyoxometalates as discrete cluster anions of metal oxides. [NH(3)Pr(i)](6)[Mo(7)O(24)].3H(2)O (PM-8) has been recognized as one of significantly anti-tumoral polyoxomolybdates. PM-8 inhibited the cell growth of human pancreatic cells (AsPC-1) depending on the dose. DNA ladder formation and DNA fragmentation were observed by Hoechst and TUNEL staining and flowcytometry analysis. The ratio of apoptotic cells were 29%, 35%, and 57% with treatment of PM-8 after 24, 48, and 72 h, respectively, which suggested that the anti-tumor activity of PM-8 results from the activation of the apoptotic pathway. Polyoxomolybdates provide promising, novel anti-tumor agent, especially for the treatment of cancers that are difficult to treat.

Antibacterial activity of highly negative charged polyoxotungstates, K27[KAs4W40O140] and K18[KSb9W21O86], and Keggin-structural polyoxotungstates against Helicobacter pylori

The antibacterial activity of polyoxometalates (PMs) against Helicobacter pylori was investigated based on determinations of minimum inhibitory concentration (MIC) and fractional inhibitory concentration (FIC), time-killing of the bacteria, bacterial morphology and PM-uptake into the bacteria cell. The result of MIC values revealed that, of 13 PMs used in this study, highly negative-charged polyoxotungstates, such as K27[KAs4W40O140] and K18[KSb9W21O86], and Keggin-structural polyoxotungstates exhibited a potent antibacterial activity with the MIC values of less than 256 microg/ml. The former was the most active, and superior to metronidazole (MTZ) against MTZ-susceptible and resistant strains and also to clarithromycin (CLR) against CLR-resistant strains. In contrast, most of polyoxomolybdates showed little antibacterial activity with the MIC values of more than 256 microg/ml. The result of FIC index values indicated that the antibacterial polyoxotungstates had partially synergistic effect in combination with MTZ and CLR but indifferent effect in combination with amoxicillin (AMX). From the results of the time-killing and scanning electron microscope images, K27[KAs4W40O140] and K18[KSb9W21O86] proved the concentration-dependent bactericidal activity with the morphological change from bacillary form to coccoid form, while Keggin-structural K5[SiV(V)W11O40] showed the bacteriostatic activity with small change of morphology to coccoid form. The fluorescent X-ray analysis demonstrated that these polyoxotungstates were taken into the bacteria cell. It is pointed out that the Keggin-structure and/or high negativity polyoxotungstates are an important factor for the antibacterial activity against H. pylori.

Photoreductive self-assembly from [Mo7O24]6- to carboxylates-coordinated {Mo142} Mo-blue nanoring in the presence of carboxylic acids

The primary steps of the photoredox reaction between [Mo7O24]6- and carboxylic acid electron (and proton) donors in aqueous solutions are investigated by the chemically induced dynamic electron spin polarization (CIDEP) spectroscopy. The excitation of the O-->Mo ligand-to-metal charge-transfer (LMCT) bands of [Mo7O24]6- in the presence of CH3CO2H induces the emissive electron spin polarization (ESP) of *CH2CO2 and *CH3 radicals with an accompanying formation of the one-electron reduced species [Mo7O23(OH)]6-, which is demonstrated by the triplet mechanism involving the O --> Mo LMCT triplet states. The prolonged photolysis of the solution containing [Mo7O24]6- and CH3CO2H at pH = 3.4 leads to the formation of the acetate/propionate-coordinated {Mo142} Mo-blue nanoring, [MoV28MoV(I)114O429H10(H2O)(49)(CH3)CO2 triple bond Ac5(C2H5CO2 triple bond Pr)]30- (1a) through the formation of the cis-configured dimeric dehydrative condensation to two-electron reduced Mo-blue [(Mo7O23)2]10- ({Mo14}). 1a is isolated as a [NH4]+/[Me3NH]+-mixed salt which is formulated as [NH4]27[Me3NH]3[Mo(V)28Mo(VI)114O429H10(H2O)49(CH3CO2)5(C2H5CO2)].150 +/- 10H2O (1) by results of elementary analysis, single-crystal X-ray analysis, 1H NMR, IR, and UV/Vis measurements, and manganometric redox titration. Based on the building-block sequence of for 1a, the bottom-up processes from [Mo7O24]6- to the {Mo142} ring in the coexistence of beta-[Mo8O26]4- are discussed by (i) the stabilization of the molecular curvature of {Mo14} through both the intramolecular transfer of monomolybdates and the intermolecular transfer of monomolybdates as degradation fragments of beta-[Mo8O26]4-, to yield {Mo21} and {Mo20} building blocks, (ii) the outer-ring formation resulting from seven successive two-electron-photoreductive condensations among {Mo21} and {Mo20}, and (iii) inner-ring formation resulting from eight successive dehydrative condensations between monomolybdate linkers attached to the neighboring head Mo sites.

Current status of anti-SARS agents

Severe acute respiratory syndrome (SARS) is a disease that has newly emerged in the 21st century, and is both severe and highly contagious. SARS first surfaced in late 2002 and spread within a few months from its origin in Guandong province, China, to more than 30 countries (World Health Organization, 2003). In this review, several antiviral substances shown to be active in vitro will be introduced and summarized in the order of the virus' replication steps; that is, binding to cellular receptor, fusion and entry to the cells, viral RNA replication and transcription, protein processing and so on. The possible clinical use of several synthetic peptides, including those that mimic the S-binding domain, the HR2 fusion protein and SARS proteinase substrates, will be discussed. Monoclonal antibodies (Mabs) and established drugs, such as interferons and HIV proteinase inhibitors, are also discussed in relation to anti-SARS clinical use.

Spin-frustrated (VO)36+-triangle-sandwiching octadecatungstates as a new class of molecular magnets

Spin-frustrated polyoxometalates, K(11)H[(VO)(3)(SbW(9)O(33))(2)].27H(2)O (1) and K(12)[(VO)(3)(BiW(9)O(33))(2)].29H(2)O (2), containing approximately equilateral and isosceles (VO)(3)(6+)-triangles (V(IV)...V(IV) separation of 5.4-5.5 A) sandwiched by two diamagnetic alpha-B nonatungstate ligands ([SbW(9)O(33)](9)(-) and [BiW(9)O(33)](9)(-)) with approximate D(3)(h) symmetry, are found to show magnetization jumps with distinct hysteresis for the S = (1)/(2) <--> S = (3)/(2) level crossing under fast sweeping pulsed magnetic fields (approximately 10(3) T/s) at T < or = 0.5 K. This unusual phenomenon is attributed to the theoretical prediction of half step magnetization, which is expected for an antiferromagnetic spin triangle with antisymmetrical Dzyaloshinky-Moriya interaction. The degeneracy of the S = (1)/(2) states for 1 is removed by slightly lower symmetry effects of triangular structure for 2. The calorimetry of 1 and 2 shows the heat capacity anomaly at 2 < or = T < or = 20 K which is associated with a thermal excitation from the S = (1)/(2) ground states to the S = (3)/(2) state at zero field. Zero-field splitting energies (5-7 K) between S = (1)/(2) and S = (3)/(2) states for 1 and 2, readily estimated by the level-crossing field for the magnetization, allow us to measure the hyperfine-structural 22 lines due to three equivalent I = (7)/(2) (51)V nuclei, the fine-structural triplet line of the S = (3)/(2) excited state, and the g anisotropy on the high-frequency ESR spectra. The spin-frustrated (VO)(3)(6+)-triangle for 1 and 2 is a good model of the magnetization between pure quantum states S = (1)/(2) and (3)/(2) and provides a new class of single-molecule magnets.