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PubMed2006

The role of electrochemistry in the development of pi-basic dearomatization agents.

Dihapto-coordination of aromatic molecules promotes numerous organic transformations that are not observed for the free aromatics. The development of osmium, rhenium, tungsten and molybdenum complexes that are capable of such binding is described in this perspective. The stability of these complexes strongly correlates to the metal d5/d6 reduction potential and electrochemical data has played a central role in their design.

Benzene↗
PubMed1994

A study on cellular reactions and fibrogenic effects of mineral dusts.

In vivo cytotoxicity including cellular metabolic activity, lysozyme content and total protein content in rat bronchoalveolar lavage, capacity of interleukin-1 released from rat pulmonary cells and fibrogenic effects evaluated from rat lung dry weight, collagen content of the whole lung and pathological grading induced by mineral dust were assayed. The results showed that: (1) The relationship among in vivo cytotoxicity, interleukin-1 release, fibrogenic effects on the lung induced by mineral dusts correlated well with the free SiO2 content in mineral dusts in most (but not all) cases; (2) The biological harmful effects of mixed dusts were not simply the additive effect of single dust. In the group of WO3-SiO2 mixture, the fibrogenicity was mainly due to SiO2, tungsten trioxide (WO3) showed neither fibrogenic effect, nor significant potentiality to enhance SiO2 fibrogenicity, while in the group of SnO2-SiO2, SnO2 was suppressive to the effect of SiO2, although the contents of SiO2 in the two mixed dusts were similar.

Animals↗
PubMedDate not supplied

Surface geometry of three packable and one hybrid composite after polishing.

This study evaluated the surface quality of four composite materials after polishing with six different polishing techniques. Eighty specimens were made using three packable composites (Definite/Degussa, SureFil/ Dentsply and Solitaire/Heraeus-Kulzer) and one hybrid composite (Herculite XRV/Kerr). Five specimens of each material were polished using flexible Sof-Lex discs. The remaining 75 specimens of each composite were prepared using three finishing protocols: a single 30 microm diamond (n = 25), two finishing diamonds (30/20 microm; n = 25) and a 30 microm diamond followed by a tungsten carbide finishing bur (n = 25). Final polishing of each of the three finishing groups was accomplished with SuperBuff, Diafix-oral, OneGloss, Astropol and HaWe Composite Polishers (n = 5, each). Surface roughness was evaluated quantitatively by laser-stylus profilometry. Average roughness (R(a)) was calculated; statistical analysis of the data was performed with two-way ANOVA and Scheffé post-hoc tests. The polished surfaces were examined qualitatively by SEM. The results showed significant effects on surface roughness from the different composites (p = 0.011) and polishing systems (p < 0.001). After polishing, the Solitaire surfaces (R(a) = 0.72 microm) were smoother than Definite (R(a) = 0.87 microm) and SureFil (R(a) = 0.89 microm) and significantly smoother than Herculite (R(a) = 0.92 microm; p = 0.011). Three of the polishing methods (SuperBuff, Diafix-oral and Astropol) achieved lower R(a)-values than Sof-Lex discs. The polishing quality of the one-step systems SuperBuff and Diafix-oral was strongly affected by the initial finishing protocol.

Aluminum Oxide↗
PubMed2006

Photocatalytic degradation of textile dye X-3B using polyoxometalate-TiO2 hybrid materials.

Titanium dioxide functionalized with Keggin type polyoxometalate (POMs) [X(n+)W(12)O(40)]((8-n)-) (XW(12); X(n+)=P(5+), Si(4+), Ge(4+)) were prepared by sol-gel method. The Keggin structure and dispersion state of POMs were monitored by FT-IR and XRD. The composites showed higher photocatalytic activity than pure TiO(2), pure POMs or mechanical mixture of TiO(2) and POMs for X-3B degradation. Among the three POMs-TiO(2) hybrid materials, the reactivity was: PW(12)>SiW(12)>GeW(12). With different loading weights for the same POMs, the reactivity followed the order: 30wt.%>15wt.%>45wt.%.

Azo Compounds↗
PubMed1998

Syntheses and Characterizations of a Series of Tetradecanuclear Molybdenum(Tungsten)/Copper/Sulfur Heterobimetallic Cluster Compounds.

Using sulfide ion to substitute the weakly copper(I)-philic ligands of MS(4)(-)(n)()(2)(-)O(n)()/Cu(+) compounds, (M = Mo, W; n = 0, 1), we have prepared and characterized four novel tetradecanuclear clusters having the general formula [(n-Bu)(4)N](4)[M(4)Cu(10)S(16)E(2)E']H(2)O, (M = Mo, E = E' = O for complex 1; M = W, E = (1)/(2)O + (1)/(2)S, E' = O, for complex 2; M = Mo, E = S, E' = (1)/(2)O + (1)/(2)S for complex 3; M = W, E = E' = S, for complex 4). Crystal structures of compounds 1-4 were determined; they are isomorphous and crystallized in the orthorhombic space group Pna2(1), with a = 26.6997(2) Å, b = 19.3133(4) Å, c = 21.4577(4) Å, V = 11064.9(3) Å(3), Z = 4 for [(n-Bu)(4)N](4)[Mo(4)Cu(10)S(18)O].H(2)O (3) and with a = 26.8141(8) Å, b = 19.4412(6) Å, c = 21.4039(5) Å, V = 11157.8(5) Å(3), Z = 4 for [(n-Bu)(4)N](4)[W(4)Cu(10)S(19)].H(2)O (4). The cluster cores have approximate sigma symmetry. The anions 1-4 may be viewed as consisting of one incomplete cubane-like Cu(3)MS(3)E fragment, one trigonal prism-type Cu(3)MS(4), and two butterfly-type Cu(2)MS(3)E' fragments, bridged by two &mgr;(3)-S and one &mgr;(4)-S atoms. There are two (&mgr;(3)-S)Cu(3) configurations in the compounds. Infrared, Raman, and UV/vis spectra of the above compounds are discussed, and the main absorption bands are assigned. (95)Mo NMR spectra and cylic voltammograms are investigated and compared with those of other compounds, (95)Mo NMR spectra show that in the solution there are three kinds of coordination environments of Mo in complexes 1 and 3, and cyclic voltammograms indicate that complexes 1-4 have irreversible electrochemical reductions.

Journal Article↗
PubMed2003

Different methods of finishing and polishing enamel.

STATEMENT OF PROBLEM: Highly polished enamel surfaces are recommended for axial tooth surfaces that will serve as guiding planes and be contacted by component parts of a removable partial denture. There is little evidence to support the assumption that this tooth modification will provide accurate adaptation of the framework and prevent build-up of plaque. PURPOSE: The aim of this investigation was to evaluate the surface roughness of the tooth enamel, prepared to serve as guiding planes, with different polishing systems. MATERIAL AND METHODS: Four different methods (designated A, B, C, and D) for finishing and polishing the prepared enamel surfaces of 20 freshly extracted third molar teeth were studied. Each method involved 3, 4, or 5 different steps. The roughness of each specimen was measured at the start of each method before recontouring, after recontouring, and after each step of the 4 finishing and polishing procedures. The 4 experimental finishing methods were applied after recontouring the axial surfaces (buccal, lingual, and proximal) of each tooth. Thus the 20 teeth (60 surfaces) were finished and polished by use of 1 of the experimental methods. Surface roughness was measured with a profilometer (microm); the readings of the unpolished enamel surfaces were recorded as control measurements. Results were statistically analyzed with one-way analysis of variance followed by Tukey's test at the 95% level of confidence. RESULTS: The highest roughness mean values (14.41 microm to 16.44 microm) were found when the diamond bur was used at a high speed for tooth preparation. A significant decrease in roughness values was observed with the diamond bur at a low speed (P<.05). Analysis of the roughness values revealed that all polishing methods produced surface roughness similar to that of the corresponding control teeth. CONCLUSION: Within the limitations of this study, all finishing procedures tested effectively promoted an enamel surface similar to the original unpolished enamel.

Analysis of Variance↗
PubMed2004

RETRACTED: A late-transition metal oxo complex: K7Na9[O=PtIV(H2O)L2], L = [PW9O34]9-.

Terminal mono-oxo complexes of the late transition metal elements have long been considered too unstable to synthesize because of repulsion between the oxygen electrons and the mostly filled metal d orbitals. A platinum(IV)-oxo compound flanked by two polytungstate ligands, K7Na9[O=Pt(H2O)L2], L = [PW9O34(9-)], has now been prepared and isolated at room temperature as air-stable brown crystals. X-ray and neutron diffraction at 30 kelvin revealed a very short [1.720(18) angstrom] Pt-O bond and no evidence of a hydrogen atom at the terminal oxygen, ruling out a better precedented Pt-OH complex. Density functional theory and spectroscopic data account for the stability of the Pt(IV)-oxo unit by electron withdrawal into delocalized orbitals of the polytungstates.

Chemical Phenomena↗
PubMed2000

Micro-morphometric assessment of titanium plasma-sprayed coating removal using burs for the treatment of peri-implant disease.

This study evaluated, in vitro, the effectiveness of diamond and carbide burs, and bur sequences to remove the plasma-sprayed titanium coating from IMZ fixture surfaces. Fifteen polishing procedures were tested. They included the use of 12, 16, 30 bladed carbide burs or bevered carbide burs and 30, 15, 8 microns mean-particles-size diamond burs. The treated surfaces were evaluated with profilometer and SEM. Worn burs and titanium debris produced by the grinding were observed with SEM. All procedures produce smoother surfaces than baseline plasma-sprayed surfaces for both Ra and Rz(DIN) parameters (P < 0.001). A roughening effect of the 8 microns mean-grit diamond bur and 30 bladed burs were noted. The single carbide burs produce polished surfaces affected by waviness. Waviness was minimized by sequence or diamond bur use. The carbide bur blades were variously damaged after their use. In contrast, the grit of diamond burs was observed to be clogged by titanium debris whose amount seemed to be inversely related to the diamond mean particle size. Debris produced by diamond burs was granular whereas that produced by carbide bladed burs showed needle or flake morphology. In conclusion, the most effective titanium plasma sprayed removal were obtained by 30 microns and 15 microns mean-particle-size diamond burs, i.e. 30 microns plus 15 microns diamond burs and carbide 12 plus 16 bladed burs used in sequence.

Analysis of Variance↗
PubMed2005

[The UV-Vis spectra and substituent effect of organoimido derivatives of polyoxometalates].

In the presence of a carbodiimine, i.e. DCC, a series of organoimido derivatives of polyoxometalates have been synthesized via the reaction of [alpha-Mo8O26]4- with aromatic amines and its hydrochloride salt. Elemental analysis, IR, 1H-NMR and UV-Vis spectra were used to characterize those hybrids, in particular their UV-Vis spectra have been studied. The results show that typical metal-ligand charge transfer (MLCT) transitions occur in the organic-inorganic hybrid molecules. There is a good linear relationship between the shift of UV-Vis absorptions (delta lamda max) and conjugation effect of the p-substituted group (sigmaR).

Carbodiimides↗
PubMed2004

Human 3'-phosphoadenosine 5'-phosphosulfate synthetase (isoform 1, brain): kinetic properties of the adenosine triphosphate sulfurylase and adenosine 5'-phosphosulfate kinase domains.

Recombinant human 3'-phosphoadenosine 5'-phosphosulfate (PAPS) synthetase, isoform 1 (brain), was purified to near-homogeneity from an Escherichia coli expression system and kinetically characterized. The native enzyme, a dimer with each 71 kDa subunit containing an adenosine triphosphate (ATP) sulfurylase and an adenosine 5'-phosphosulfate (APS) kinase domain, catalyzes the overall formation of PAPS from ATP and inorganic sulfate. The protein is active as isolated, but activity is enhanced by treatment with dithiothreitol. APS kinase activity displayed the characteristic substrate inhibition by APS (K(I) of 47.9 microM at saturating MgATP). The maximum attainable activity of 0.12 micromol min(-1) (mg of protein)(-1) was observed at an APS concentration ([APS](opt)) of 15 microM. The theoretical K(m) for APS (at saturating MgATP) and the K(m) for MgATP (at [APS](opt)) were 4.2 microM and 0.14 mM, respectively. At likely cellular levels of MgATP (2.5 mM) and sulfate (0.4 mM), the overall endogenous rate of PAPS formation under optimum assay conditions was 0.09 micromol min(-1) (mg of protein)(-1). Upon addition of pure Penicillium chrysogenum APS kinase in excess, the overall rate increased to 0.47 micromol min(-1) (mg of protein)(-1). The kinetic constants of the ATP sulfurylase domain were as follows: V(max,f) = 0.77 micromol min(-1) (mg of protein)(-1), K(mA(MgATP)) = 0.15 mM, K(ia(MgATP)) = 1 mM, K(mB(sulfate)) = 0.16 mM, V(max,r) = 18.7 micromol min(-1) (mg of protein)(-1), K(mQ(APS)) = 4.8 microM, K(iq(APS)) = 18 nM, and K(mP(PPi)) = 34.6 microM. The (a) imbalance between ATP sulfurylase and APS kinase activities, (b) accumulation of APS in solution during the overall reaction, (c) rate acceleration provided by exogenous APS kinase, and (d) availability of both active sites to exogenous APS all argue against APS channeling. Molybdate, selenate, chromate ("chromium VI"), arsenate, tungstate, chlorate, and perchlorate bind to the ATP sulfurylase domain, with the first five serving as alternative substrates that promote the decomposition of ATP to AMP and PP(i). Selenate, chromate, and arsenate produce transient APX intermediates that are sufficiently long-lived to be captured and 3'-phosphorylated by APS kinase. (The putative PAPX products decompose to adenosine 3',5'-diphosphate and the original oxyanion.) Chlorate and perchlorate form dead-end E.MgATP.oxyanion complexes. Phenylalanine, reported to be an inhibitor of brain ATP sulfurylase, was without effect on PAPS synthetase isoform 1.

Adenosine Phosphosulfate↗
PubMed2006

Analysis of weak interactions in the crystal packing of inorganic metalorganic hybrids based on Keggin polyoxometalates and dinuclear copper(II)-acetate complexes.

Reaction of in situ generated copper-monosubstituted Keggin polyoxometalate (POM) and copper-phenanthroline complexes in potassium or sodium acetate buffers led to the formation of the potassium salt of [[SiW(11)O(39)Cu(H(2)O)][Cu(2)(phen)(2)(H(2)O)(ac)(2)]](4-) (1) and [[Si(2)W(22)Cu(2)O(78)(H(2)O)][u(2)(phen)(2)(H(2)O)(ac)(2)](2)](8-) (2, where phen = phenanthroline and ac = acetate) hybrid polyanions, respectively. Both compounds are the first discrete mono- and bimolecular transition-metal-substituted Keggin POMs that support a binuclear copper-acetate complex. Despite the different nature of the POMs, the crystal packing of the two compounds is closely related, being formed of hybrid parallel layers that give rise to an alternate sequence of inorganic and metalorganic regions. This packing type seems to be determined by the extensive network of weak intermolecular interactions established by the dicopper complexes, as a Hirshfeld surface analysis shows. Electron paramagnetic resonance studies indicate that both the supported [Cu(2)(ac)(2)(phen)(2)(H(2)O)](2+) complexes and the copper(II)-monosubstituted POMs are magnetically isolated.

Acetates↗
PubMed1994

Synthesis, characterization, and biological activity of a new potent class of anti-HIV agents, the peroxoniobium-substituted heteropolytungstates.

The mono- and trisubstituted peroxyniobium polyoxotungstates of formulas [(CH3)3NH]7[Si-(NbO2)3W9O37], Cs7[Si(NbO2)3W9O37], alpha-K5[Si(NbO2)W11O39] and alpha-[(CH3)3NH]5[Si(NbO2)-W11O39], have been prepared, purified, and characterized spectroscopically by 29Si NMR, 183W NMR, and IR. The presence of peroxo groups was verified by the yellow color of the product and quantified by iodometric titration. The potency of both the complexes and the precursor complexes was evaluated in human peripheral blood mononuclear cells (PBMC) acutely infected with human immunodeficiency virus type 1 (HIV-1). Hexaniobate (K7H[Nb6O19]) was the least effective with a median effective concentration (EC50) of > 100 microM, while Cs7[Si(NbO2)3W9O37] was one of the most effective compounds with an EC50 of 1.0 microM. None of the compounds were toxic to uninfected PBMC with the exception of alpha-K8[SiW11O39], which had a median inhibitory concentration (IC50) of 79 microM. The potency and selectivity of the complexes against HIV-1 reverse transcriptase was also evaluated and shown to be quite high (IC50 values from 0.03 to 0.06 microM). The trimethylammonium salts of the complexes were tested for their ability to inhibit the interaction between gp120 and CD4 using a cell-free system. The complex [(CH3)3NH]7[Si(NbO2)3W9O37] inhibited this interaction by 70% at 25 microM.

Antiviral Agents↗