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PubMed2005

Molecular and multidimensional polyoxotungstates functionalized by {Cu(bpy)}2+ groups.

Five new materials built from polyoxotungstates and Cu(ii) ions as linkers have been synthesized by hydrothermal reactions from a mixture of sodium tungstate, copper chloride and bipyridine. The value of the initial pH, the nature of the heteroelement (P or Si) and of the ligand (2,2'- and/or 4,4'-bipyridine) permit the control of the nature of the polyoxotungstate clusters and their connectivity via the copper ions, and hence the dimensionality of the framework. A single phase has been obtained with silicon as heteroelement at an initial pH of 5, namely the 2D material [SiW(12)O(40)][Cu(2,2'-bpy)(2)](2).10H(2)O (1) with saturated Keggin polyoxotungstates linked by {Cu(2,2'-bpy)(2)}(2+) groups. With phosphorous as heteroelement and at the same initial pH, three different structures have been isolated according to the nature of the ligand. Indeed, the two 1D materials [{Cu(5)(2,2'-bpy)(5)(H(2)O)(HPO(4))(PO(4))}PW(11)CuO(39)].6H(2)O (2) with 2,2'-bpy and [4,4'-Hbpy][{Cu(2)(2,2'-bpy)(2)(4,4'-bpy)(2.5)}PW(11)CuO(39)].16H(2)O (3) with a mixture of 2,2'- and 4,4'-bpy have been characterized, and a coordination polymer with polyoxometalate guests Na(3)[4,4'-Hbpy]{Cu(4)(4,4'-bpy)(8)(H(2)O)(8)}[PW(11)CuO(39)(H(2)O)][PW(10)Cu(2)O(38)(H(2)O)(2)].38H(2)O (4) with 4,4'-bpy has been obtained. Finally, in basic medium (pH = 10) the unprecedented molecular cluster Na(2)[{Cu(8)(2,2'-bpy)(8)}(PW(8)O(31))(2)].15H(2)O (5) has been evidenced. Magnetic studies of compound 2 revealed that the predominant interactions involve only 4 paramagnetic centers, which are interacting within pairs, among the 6 Cu(ii) centers. The chi(M)T=f(T) curve can be fitted using the dinuclear expression appropriate to the HDVV isotropic exchange Hamiltonian H=-JS(1)xS(2), with S(1)=S(2)=(1/2) and J=-105.4 cm(-1), showing strong antiferromagnetic interactions within the two Cu(ii) pairs.

2,2'-Dipyridyl↗
PubMedDate not supplied

Non-linear renal and biliary clearances of antiviral polyoxometalates in rats.

The polyoxometalates, JM 1591 (K12H2[P2W12O48].24 H2O), JM 1596 (K10[P2W18Zn4(H2O)2O68].20 H2O), and JM 2820 ([Me3NH]8[Si2W18Nb6O77]) have been shown to have potent activity against HIV-1 and HIV-2. The pharmacokinetics of JM 1591, JM 1596 and JM 2820 after intravenous administration of 50 mg/kg were investigated in rats. Renal and biliary clearances of the three compounds were found to be dependent on unbound plasma polyoxometalate concentration. Computer modeling was performed by fitting nonlinear pharmacokinetic models simultaneously to unbound plasma concentration, urinary excretion rate and biliary excretion rate versus time data. The renal clearances of JM 1591 and JM 2820 were described by glomerular filtration, saturated active tubular secretion at all plasma concentrations observed and saturable active tubular reabsorption. The urinary excretion of JM 1596 was characterized by glomerular filtration, saturable active tubular secretion and apparent linear reabsorption. Biliary clearances of all three polyoxometalates were described by a Michaelis-Menten function.

Animals↗
PubMed1994

Use of a flavivirus RNA-dependent RNA polymerase assay to investigate the antiviral activity of selected compounds.

We have developed an assay using flavivirus RNA-dependent RNA polymerase to test the inhibitory activity of potential antiviral agents. The effects of antiviral agents on RNA synthesis were examined in this assay using extracts of Vero cells infected with dengue virus type 2 or Kunjin virus. Several different classes of known polymerase inhibitors were tested. The synthesis of double-stranded replicative form RNA was inhibited in a dose-dependent fashion in the presence of the polyoxometalate HPA-23 [(NH4)18(NaW21Sb9O86)17].14 H2O and several structurally related compounds.

Animals↗
PubMed2006

Density functional theory and Hartree-Fock studies: geometry, vibrational frequencies and electronic properties of Anderson-type heteropolyanion, [XM6O24]n- (X=TeVI, IVII and M=Mo, W) and [SbVW6O24]7-.

The geometry, IR and Raman spectra and electronic properties of Anderson-type heteropolyanions with main-group high oxidation state heteroatom, [Te(VI)Mo(6)O(24)](6-), [I(VII)Mo(6)O(24)](5-), [Sb(V)W(6)O(24)](7-), [Te(VI)W(6)O(24)](6-) and [I(VII)W(6)O(24)](5-) have been investigated using Hartree-Fock (HF) and density functional theory (DFT) methods. HF method has good results in geometry parameters but poorer than DFT method in the results of vibrational frequencies. Also we have investigated the effect of LanL2DZ augmented in the vibrational frequencies. With attention to relative charge and size of the cavity occupied by XO(6) subunit in these anions, we suggest that the general formula [XO(6)(n-)@M(6)O(18)] to describe electronic properties of these anions.

Antimony↗
PubMed1998

Adherence of Candida albicans to denture-base materials with different surface finishes.

OBJECTIVES: To assess the in vitro adherence of Candida albicans to heat-cured hard and soft denture-base materials with varying surface roughness, and to observe the effect of a mixed salivary pellicle on candidal adhesion to these surfaces. METHODS: In vitro adhesion assays on heat-cured acrylic resin (Trevalon), Molloplast B and Novus using the type strain of C. albicans (NCPF 3153A). Surfaces for the assays were prepared using clinically appropriate rotary instruments. Unstimulated, pooled and clarified whole saliva was used to assess its effect on adhesion. RESULTS: Significantly greater adhesion of C. albicans to rough rather than smooth surfaces was found (P < 0.001), as well as increased adhesion to the machined soft lining materials compared with acrylic. Pre-coating denture-base materials with saliva reduced candidal adhesion on all materials. CONCLUSIONS: Rough surfaces on denture-base materials promote the adhesion of C. albicans in vitro. However, saliva reduces adhesion of C. albicans and thus diminishes the effect of surface roughness and free surface energy differences between materials.

Acrylic Resins↗
PubMed2000

Total synthesis of (+)-blastmycinone, (-)-litsenolide C1, and related natural trisubstituted lactones via alkynyltungsten compounds.

A general method for total synthesis of natural trisubstituted gamma-lactones is developed on the basis of the chemistry of alkynyltungsten compounds. The key step in this approach involves the cycloalkenation of tungsten-eta1-(3R,4S)-pent-1-yne-3,4-diol with aldehydes to give tungsten-oxacarbenium salts, further leading to 3-alkylidene-4-hydroxy-5-methyl-gamma-lactones upon demetalation. This synthetic sequence proceeds well for alkynylaldehydes and the MOM derivative of tungsten-eta1-(3R,4S)-pent-1-yne-3,4-diol. The resulting butyrolactone products are transformed into natural trisubstituted butyrolactones including (+)-blastmycinone, (+)-blastmycinolactol, (+)-antimycinone, NFX-2, and (+)-isodihydromahubanolide A. By using the same approach based on (R)-ethyl lactate, the natural (-)-litsenolide C1 can be prepared in a few steps.

4-Butyrolactone↗
PubMed1984

Energy imparted to fluorescent screens from primary and scattered radiation. Variations with atomic composition and screen thickness.

The effects of thickness and atomic composition of fluorescent screens on the impartation of primary and scattered radiation is analysed. Different fluorescent screens give rise to different quotients epsilon p/epsilon s of energy imparted from primary and scattered radiation respectively, due to their variation in atomic composition and thickness. The image contrast in a given radiation field therefore varies with the choice of screen. Energy imparted by primary and scattered radiation in different fluorescent screens has been calculated as a function of tube voltage using a simple analytical model. Comparison of the results for fluorescent screens of different thicknesses with hypothetical screens with both negligible and total absorption has been made. From the results it is evident that the image contrast increases with increased detector thickness if scattered radiation is present. The trends found in the calculations have been confirmed by measurements of the energy imparted from scattered and primary radiation for a number of fluorescent screens including both commercial and specially made screens. Differences in the ratio epsilon p/epsilon s of up to 50% have been measured, and differences reported by other authors are discussed. Their use of detectors with different response to scattered and primary radiation may explain the discrepancies found.

Calcium Compounds↗
PubMedDate not supplied

High-resolution digital x-ray detector utilizing a discrete array of CdWO4 scintillators and a self-scanned photodiode array.

A high-resolution x-ray detector array for x-ray imaging is described. It consists of a discrete array of CdWO4 scintillators and a Reticon 1024S photodiode array with a fiber-optic faceplate. The scintillator elements measure 0.099 X 3 X 4 mm and are bonded together with aluminum foil separators to minimize light crossover. Detective quantum efficiency (DQE) of individual detector channels was 0.38. Systematic variations between channels were substantial. With only a simple correction for between channel variations, DQE for the entire array was 0.04. Evaluation of the edge response function of the array showed that resolution is similar to a detector whose line spread function is Gaussian with a standard deviation of 0.172 mm.

Cadmium↗
PubMedDate not supplied

Finishing and polishing of a hybrid composite and a heat-pressed glass ceramic.

This study assessed the finishing and polishing of a hybrid composite and a glass-ceramic. Ninety Tetric specimens were divided into three groups of 30 specimens and finished with three different finishing procedures. The 30 specimens were subsequently subdivided into six groups of five and polished using the following polishing systems: Sof-Lex disks, the Ceramiste kit, a diamond polisher, Diafix-oral, the MPS gel and the Politip system. Seventy-five IPS-Empress specimens were divided into groups of 25 and finished with three different procedures. The 25 specimens were then subdivided into five groups of five and polished with the same systems, except for the Politip technique. The polished surfaces were evaluated quantitatively by laser stylus profilometry with respect to Ra and profile-length-ratio (LR). Qualitative assessment was carried out by SEM. Quantitative results were examined statistically by one- and two-way Anova and LSD test with significance level of 0.05. The lowest roughness on composite specimens was achieved by the MPS gel and Diafix after finishing according to FM 3 and FM 2. With respect to all methods used, there were no significant differences among the five methods with the lowest Ra-values. The ceramic specimens were able to be polished to lower roughness values (p<0.001 for LR). The best results on ceramic surfaces were achieved with the MPS system after finishing according to FM 3 and FM 2. There were no significant differences among the three methods with the lowest Ra-values and the glazed surface. SEM evaluation largely confirmed the quantitative results. Composite specimens exhibited signs of selective resin matrix removal when the Ceramiste system or the Politip system were used.

Aluminum Oxide↗
PubMed1990

[Combinations of borotungstic acid with nitrogenous compounds].

On combinations of borotungstic acid with nitrogenous compounds. Under definite conditions, these combinations are borotungstates of quinine, cinchonine, cinchonidine, brucine, strychnine, morphine, sparteine, pilocarpine, nicotine, stovaine, procaine, choline and acetylcholine. Their composition is probably variable according to the pH (ex.: procaïne).

Acid-Base Equilibrium↗
PubMed2006

Sensitization of photo-reduction of the polyoxometalate anions [S(2)M(18)O(62)](4-) (M = Mo, W) in the visible spectral region by the [Ru(bpy)(3)](2+) cation.

Voltammetric, photo-physical and photo-electrochemical properties of the Dawson polyoxometalate anions alpha-[S(2)M(18)O(62)](4-) (M = Mo, W) are presented, both in the presence and absence of a series of [Ru(II)L(n)](+/2+) cations [L(n) = (bpy)(3), (bpy)(2)(Im)(2), (bpy)(2)(dpq), (bpy)(2)(box) and (biq)(2)(box)]. Electrochemical processes for both the anion and Ru(II/III) couples were detected in solutions of the salts [Ru(II)L(n)](2)[S(2)M(18)O(62)] in dimethylformamide (0.1 M Bu(4)NPF(6)) by both cyclic and hydrodynamic voltammetries. Responses were also detected when the solid salts were adhered to the surface of a glassy carbon electrode in contact with an electrolyte in which they are insoluble (CH(3)CN; 0.1M Bu(4)NPF(6)). Photolysis experiments were performed on solutions of the salts [R(4)N](4)[S(2)M(18)O(62)] (R = n-butyl or n-hexyl) and [Ru(II)L(n)](2)[S(2)M(18)O(62)] at 355 and 420 nm in dimethylformamide and acetonitrile in the presence and absence of benzyl alcohol (10% v/v). When associated with [Ru(bpy)(3)](2+), the molybdate anion exhibited a large increase in the quantum yield for photo-reduction at 420 nm. The quantum yield for the tungstate analogue was lower but the experiments again provided clear evidence for sensitization of the photo-reduction reaction in the visible spectral region. The origin of this sensitization is ascribed to the new optical transition observed around 480 nm in static ion clusters {[Ru(bpy)(3)][S(2)M(18)O(62)]}(2-) and {[Ru(bpy)(3)](2)[S(2)M(18)O(62)]} present in solution. Measurable photocurrents resulted from irradiation of solutions of the anions with white light in the presence of the electron donor dimethylformamide. Evidence is also presented for possible quencher-fluorophore interactions in the presence of certain [Ru(II)L(n)](+) cations.

Anions↗
PubMed1995

Anti-(human immunodeficiency virus) activity of polyoxotungstates and their inhibition of human immunodeficiency virus reverse transcriptase.

Heteropolyoxotungstates of the Keggin class containing different heteroatoms were tested for inhibition of two strains of human immunodeficiency virus 1 (HIV-1); they exhibited varying antiviral activity. Compounds containing boron were inactive, only one of those containing phosphorus showed selective anti-viral activity, whereas all silicon-containing compounds exhibited significant anti-viral activity in C8166 cells infected with the IIIB strain. Their effectiveness was some 10-fold higher in JM cells with selectivity indices of about 2000. The silicotungstates were effective inhibitors of HIV reverse transcriptase, showing greater inhibition with RNA/DNA template primers than with DNA/DNA template.primer. Kinetic analysis demonstrated that they inhibit the enzyme by different mechanisms, as, of the four compounds examined, two competed with template.primer and two competed with deoxynucleoside triphosphate. Inhibition of DNA polymerase activity by these compounds was compared using polymerases from different sources, including human; although not necessarily most specific for HIV-1 reverse transcriptase, they did not inhibit all DNA polymerases to a similar degree.

Antiviral Agents↗