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PubMed2006

In-vitro evaluation of the material characteristics of stainless steel and beta-titanium orthodontic wires.

INTRODUCTION: The exact composition and material properties of the metal alloys used in orthodontics are usually not identified by or even available from manufacturers. This makes meaningful comparisons between wires impossible and is unacceptable with regard to biocompatibility issues. The aim of this study was to investigate the material characteristics of contemporary stainless steel (SS) and beta-titanium (beta-Ti) wires, also known as titanium-molybdenum alloy (TMA), for comparison. METHODS: Twenty-two different SS and beta-Ti wires, preferably straight wires sized 0.43 x 0.64 mm, (0.017 x 0.025 in) were tested blindly for wire dimensions, chemical compositions, bending and tensile properties, and surface characteristics. RESULTS: Four chemical compositions were found for the beta-Ti wires: titanium-11.5, molybdenum-6, zirconium-4.5 tin; titanium-3, aluminum-8, vanadium-6, chromium-4, molybdenum-4, zirconium; titanium-6, aluminum-4, vanadium, and titanium-45 niobium. The SS wires were of AISI type 304 or the nickel-free variant BioDur 108. All beta-Ti wires showed high surface roughness values. TMA 02 significantly had the highest E-modulus, TMA 02 and TMA 11 had the highest 0.2% yield strength, TMA 02 had the highest hardness, and TMA 12 was the most ductile wire of the beta-Ti wires. All SS wires showed high 0.2% yield strength, SS 10 significantly had the lowest E-modulus and was the most ductile wire, and SS 08 significantly showed the lowest hardness values of all SS wires. CONCLUSIONS: Significant differences were found between SS and beta-Ti wires, but there was little or no difference between the mechanical and physical characteristics tested in each subgroup. However, the morphological analysis clearly demonstrated that the finishing phase (annealing, polishing) of the wires' production process lacks the quality one would expect with regard to good mechanical properties and biocompatibility issues. Accurate specifications are urgently needed concerning the quality of orthodontic wires on the market.

Analysis of Variance↗
PubMed2005

Material-specific thrombin generation following contact between metal surfaces and whole blood.

Little is known about the blood compatibility of metals used in various medical devices. We have previously shown that titanium and derivatives thereof are among the most thrombogenic materials which may explain its outstanding osteointegrating properties. The aim of the present study was to characterize the thrombogenic and complement-activating properties of various metals used today in medical applications. Polyester chips were coated with 50- to 100-nm thick layers of aluminium, iridium, indium, nickel, tantalum, tin, titanium, or zirconium using magnetron sputtering. The metal-coated chips were then incubated in direct contact with whole blood in an in vitro chamber model, and the blood was then analyzed for platelet counts, thrombin-antithrombin (AT), fXIIa-AT, fXIa-AT and fXIIa-C1INH complexes and the complement parameters C3a and sC5b-9. Titanium, tantalum and indium were found to exhibit pronounced thrombogenic properties, whereas aluminium, nickel and, in particular, iridium were essentially non-thrombogenic. Tin and zirconium were intermediate activators. All metals activated complement to a similar degree, with the exception of aluminium, which had more pronounced activating properties. This study clearly indicates that metals indeed have varying thrombogenic and complement activating properties. These studies have implications for the selection of metals intended for medical applications.

Biocompatible Materials↗
PubMed2003

Sorption of uranium (VI) species on zircon: structural investigation of the solid/solution interface.

This work is an investigation of the mechanisms of interaction between uranium (VI) ions and zirconium silicate. The speciation of uranium (VI) sorbed on zircon was studied using four complementary techniques as probes of the local structure around the uranium atom: laser spectrofluorimetry, X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier-transformed (DRIFT) spectroscopy, and EXAFS spectroscopy. The sorption of uranyl on zirconium oxide was also studied to allow structural comparisons. Spectrofluorimetry and XPS results allowed an identification of the silicate sorption sites on the solid. These methods associated with spectrofluorimetry and DRIFT led to a characterization of the sorbed surface complexes, taking into account the influence of the nature of the background salt and of the pH on the structure of the U(VI) surface species. EXAFS measurements, either on air-dried samples or in situ, were then carried out on well-characterized samples and allowed identification of the sorption mechanism on zircon as the formation of an inner-sphere polydentate surface complex.

Journal Article↗
PubMed1997

Potent inhibition of respiratory syncytial virus by polyoxometalates of several structural classes.

A series of polyoxometalates (POM) were synthesized and evaluated for anti-respiratory syncytial virus (RSV) activity. POM containing zirconium, tungsten, silicon, platinum, niobium or germanium of a variety of structural types have been evaluated. Sixteen of the compounds had very striking anti-RSV activity against a clinical isolate, Utah 89, with median effective concentration (EC50) values < or = 3 microM and selective indices > 80 as determined by viral cytopathic inhibition effect, neutral red uptake and virus yield reduction assays. The EC50 values for all three assays correlated very well (Pearson correlation coefficients > 0.90). POM containing sodium cations were totally inactive. Germanium-, niobium-, tin- and zirconium-containing compounds were found to be highly potent and selective. The antiviral activity was not cell line-dependent. The median cytotoxic concentration (IC50) values were generally greater than 100 microM. The compounds were also comparably active against a known laboratory RSV strain, A2, as well as other RSV strains. To detect any virus strain-specific inhibitory activity, seven POM were tested against other RSV strains; all were nearly equally inhibitory to the human virus strains, suggesting no strain specificity. Timing studies suggested that these compounds were most inhibitory during virus adsorption and penetration, although RSV was still significantly inhibited when the compound was added 3 h post-infection; which is considered well into the eclipse period. These data suggest that these potent, non-toxic compounds should be further studied as potential chemotherapeutic agents for treating RSV infections.

Animals↗
PubMed2002

Trace elements distribution in renal cell carcinoma depending on stage of disease.

OBJECTIVES: The aim of this study was to identify those trace elements which can be used to distinguish between normal and malignant tissue in renal cell cancer (RCC) kidney and to assess changes in trace elements concentration in tissue with progressing malignant disease. METHODS: In case control study, 36 cases of RCC were analyzed by Synchrotron Radiation Induced X-ray Emission (SRIXE) in order to establish the concentration of 19 elements. Patients with RCC were examined to obtain staging of disease after radical nephrectomy, which was performed in each case. Results were compared with 15 control kidney cortex tissue obtained during autopsy in which cause of death was trauma. RESULTS: The most relevant decrease was detected in Cd content: from 81 +/- 39.2 ppm in normal control samples to 16.6 +/- 22.2 ppm concentration in RCC. We found that the concentrations of Ti, Pb and Rb were also lower in RCC tissue. On the other hand, the RCC tissue was rich in iron and zirconium. With the progress of malignant disease, assessed by TNM (UICC 1997) scale, lower concentration of S and higher concentration of Ca in both RCC and neoplastic kidney cortex can be seen. The same tendency is observed in Zn and Se concentrations. Cadmium shows raising concentration with progress of RCC only in cortex of neoplastic kidney. In all cases it was shown that the relatively high tissue concentration of iron in both investigated tissues is decreasing with the progress of disease. The zirconium has shown raising tissue concentration in advanced disease. CONCLUSION: Trace elements concentration is different in malignant tissue and surrounding macroscopically unchanged kidney cortex. Progress of the disease is connected with changes in trace elements concentration. This may reflect different biology of compared tissue with potential practical implication.

Aged↗
PubMed2001

Study of the local atomic strain field in a Zr-doped TiAl intermetallic alloy by EXAFS and ab initio FLAPW calculations.

The mechanical properties of gamma-TiAl-based intermetallic alloys are strongly influenced by Ti d-Ti d and Al p-Ti d hybridizations. These directional bonds supply good mechanical properties at high temperature but they are also associated with a low ductility at room temperature. Small amounts (about 3%) of additional elements can improve this behaviour noticeably and modify the mechanical properties. In the present case, the addition of zirconium in the gamma-TiAl-based alloys has been reported to increase their ductility at low temperature. Beyond the modifications of the directional bonds which come directly from the band structure, the different atomic volumes of the solute atoms induce local deformation fields which interact with the dislocations. We present ab initio calculations (FLAPW method) compared with an EXAFS study which the aim is to determine the site preference of zirconium in the TiAl lattice and the deformation fields around the solute atoms.

Journal Article↗
PubMed2003

Capabilities of laser ablation mass spectrometry in the differentiation of natural and artificial opal gemstones.

The potentialities of laser ablation coupled to ion cyclotron resonance Fourier transform mass spectrometry are evaluated to distinguish natural and artificial opals. The detection of specific species in both ion detection modes leads us to obtain relevant criteria of differentiation. In positive ions, species including hafnium and large amounts of zirconium atoms are found to be specific for artificial opal. In contrast, aluminum, titanium, iron, and rubidium are systematically detected in the study of natural opals. Moreover, some ions allow us to distinguish between natural opal from Australia and from Mexico. Australian gemstone includes specifically strontium, cesium, and barium. Moreover, it is also found that the yield of (H2O)0-1(SiO2)nX- (X- = O-, OH-, KO-, NaO-, SiO2-, AlO1-2-, FeO2-, ZrO2-, and ZrO3-) and (Al2O3)(SiO2)nAlO2- ions depends on the composition of the sample when opals are laser ablated. Ions, which include zirconium oxide species, are characteristics of artificial gem. In contrast, natural opals lead us, after laser ablation, to the production of ions including H2O, Al2O3 motifs and AlO-, KO-, NaO-, and FeO2- species.

Journal Article↗
PubMed2005

Use of sol-gels as solid matrixes for trace analysis by UV laser ablation and laser-enhanced ionization detection.

Zirconium and silicon sol-gels were investigated as solid materials for trace elemental analysis of pelletized solid samples by laser ablation and laser-enhanced ionization. The highly homogeneous dispersion of an internal standard spiked in the solid material obtained with the sol-gel formation process leads to a significant improvement in signal repeatability and to an increase in the precision of measurements through better correction of variations in the laser ablation rate. Signal repeatability values of 5-8% RSD were obtained for Pb in NIST 1632c Bituminous Coal sample pellets prepared using both sol-gels, as compared to 9-21% for graphite-based sample pellets. Furthermore, the zirconium sol-gel was shown to offer better resilience to signal bias due to preferential ablation and a more accurate correction of ablation rate using the internal standardization method.

Journal Article↗
PubMedDate not supplied

Structure-property relationships of copolymers obtained by ring-opening polymerization of glycolide and epsilon-caprolactone. Part 1. Synthesis and characterization.

A series of copolymers with various compositions were synthesized by bulk ring-opening polymerization of glycolide and epsilon-caprolactone, using stannous (II) octoate or zirconium (IV) acetylacetonate as initiator. Reaction time and temperature were varied so as to induce different chain microstructures. The resulting copolymers were characterized by (1)H NMR, SEC, DSC, and X-ray diffraction. The average lengths of glycolyl (L(G)) and caproyl sequences (L(C)) and the degree of randomness (R) were calculated and compared to the values of completely random chains. The concentration of CGC sequences was also obtained which resulted from transesterification reactions. Data showed that stannous (II) octoate leads to less transesterification than zirconium (IV) acetylacetonate, and lower temperatures lead to less transesterification than higher ones. The copolymers exhibited a more or less blocky chain structure because of the reactivity difference between glycolide and epsilon-caprolactone. The crystalline structure and thermal properties depend on both the composition and the chain microstructure. PGA- and PCL-type crystallites were obtained for copolymers with intermediate compositions.

Caproates↗
PubMed2004

Synthesis and group 4 complexes of tris(pyrrolyl-alpha-methyl)amine.

The tetradentate, trianionic ligand tris(pyrrolyl-alpha-methyl)amine (H(3)tpa) is available in 84% yield in a single step by a triple Mannich reaction involving 3 equiv of pyrrole, 3 equiv of formaldehyde, and ammonium chloride. The new ligand is readily placed on titanium by transamination on Ti(NMe(2))(4), which generates Ti(NMe(2))(tpa) (1) in 73% yield. Treating 1 with 1 equiv of 1,3-dimethyl-2-iminoimidazolidine (H-imd) in toluene provided a rare example of a titanium 2-iminoimidazolidinide, which displays some interesting structural features. Of note is the Ti-N(imd) distance of 1.768(2) A, a typical Ti-N double to triple bond distance. Reaction of Zr(NMe(2))(4) with H(3)tpa gave a complex of variable composition, probably varying in the amount of labile dimethylamine retained. However, stable discreet compounds were available by addition of THF, pyridine, or 4,4'-di-tert-butyl-2,2'-bipyridine (Bu(t)bpy) to in situ generated Zr(NMe(2))(NHMe(2))(x)(tpa). Three chloro zirconium complexes were generated using three different strategies. Treating Zr(tpa)(NMe(2))(Bu(t)bpy) (5) with ClSiMe(3) afforded Zr(tpa)(Cl)(Bu(t)bpy) (6) in 92% yield. Reaction of Li(3)tpa with ZrCl(4)(THF)(2) in THF gave a 72% yield of ZrCl(tpa)(THF)(2) (7). In addition, treatment of ZrCl(NMe(2))(3) with H(3)tpa cleanly generated ZrCl(NHMe(2))(2)(tpa) (8) in 95% yield. An organometallic zirconium complex was generated on treatment of 6 with LiCtbd1;CPh; alkynyl Zr(Ctbd1;CPh)(tpa)(Bu(t)bpy) (9) was isolated in 62% yield. 1, Ti(imd)(tpa) (2), 6, and 9 were characterized by X-ray diffraction.

Journal Article↗
PubMed2005

Deuterium-induced copper pairing in Zr2CuD(approximately 5).

Deuteration of Zr2Cu leads to a reconstruction of its MoSi2-type metal atom arrangement. While the tetragonal alloy contains isolated copper atoms (Cu-Cu = 3.22 angstroms) in a cubic zirconium atom environment, the monoclinic deuteride Zr2CuD4.71 contains Cu2 dumbbells (Cu-Cu = 2.39 angstroms), of which each copper atom has a trigonal-prismatic zirconium atom environment. Deuterium occupies five sites, of which four have tetrahedral metal configurations (two Zr4-type and two Zr3Cu-type) and are fully occupied while one has a trigonal-bipyramidal metal configuration (Zr3Cu2-type) and is partially occupied (71%). Copper is bonded to four deuterium atoms in a saddle-like configuration (Cu-D = 1.73-1.87 angstroms). Two of the ligands connect copper in a nearly linear Cu-D-Cu arrangement to partially interrupted dimeric [Cu2D6](n)() ribbons running perpendicular to the Cu2 dumbbell direction. At the upper phase limit, the ribbons are presumably no longer interrupted and the deuteride can be described by the limiting ionic formula 2Zr2+[Cu(+)D3](2-)2D-.

Journal Article↗
PubMed1999

Synthesis, Structure, and Properties of Group 4 and 5 Metal Pyrazolato Chloride Complexes.

Treatment of titanium tetrachloride with 3,5-di-tert-butylpyrazole (2 equiv) and triethylamine (2 equiv) in toluene afforded dichlorobis(3,5-di-tert-butylpyrazolato)titanium(IV) (93%). A similar reaction with 3 equiv of 3,5-di-tert-butylpyrazole and triethylamine gave chlorotris(3,5-di-tert-butylpyrazolato)titanium(IV) (91%). Trichloro(3,5-di-tert-butylpyrazolato)titanium(IV) was prepared in 93% yield through reaction of titanium tetrachloride with 1-trimethylsilyl-3,5-di-tert-butylpyrazole (1 equiv) in toluene. Treatment of zirconium and hafnium tetrachlorides with 3,5-di-tert-butylpyrazolatopotassium (4 equiv) in toluene afforded the homoleptic pyrazolato complexes tetrakis(3,5-di-tert-butylpyrazolato)zirconium(IV) (90%) and tetrakis(3,5-di-tert-butylpyrazolato)hafnium(IV) (68%). Analogous reaction of 3,5-di-tert-butylpyrazolatopotassium (>/=3 equiv) with niobium and tantalum pentachlorides gave dichlorotris(3,5-di-tert-butylpyrazolato)niobium(V) (98%) and dichlorotris(3,5-di-tert-butylpyrazolato)tantalum(V) (83%). Reaction of the complexes tetrakis(3,5-di-tert-butylpyrazolato)metal(IV) (metal = Zr, Hf) and dichlorotris(3,5-di-tert-butylpyrazolato)metal(V) (metal = Nb, Ta) with the metal tetrachlorides and metal pentachlorides, respectively, in dichloromethane afforded the complexes chlorotris(3,5-di-tert-butylpyrazolato)metal(IV) (metal = Zr, 89%; Hf, 97%) and trichlorobis(3,5-di-tert-butylpyrazolato)metal(V) (metal = Nb, 90%; Ta, 84%). Crystal structures of trichloro(3,5-di-tert-butylpyrazolato)titanium(IV), chlorotris(3,5-di-tert-butylpyrazolato)hafnium(IV), and dichlorotris(3,5-di-tert-butylpyrazolato)niobium(V) were determined. Trichloro(3,5-di-tert-butylpyrazolato)titanium(IV) crystallizes in the space group C2/c with a = 22.6542(8) Å, b = 9.5147(3) Å, c = 16.5329(6) Å, beta = 113.5780(10) degrees, and Z = 8. Chlorotris(3,5-di-tert-butylpyrazolato)hafnium(IV) crystallizes in the space group P2(1)/c with a = 10.4529(7) Å, b = 10.1437(6) Å, c = 36.986(3) Å, beta = 93.3080(10) degrees, and Z = 4. Dichlorotris(3,5-di-tert-butylpyrazolato)niobium(V) crystallizes in the space group P2(1)/c with a = 10.2051(3) Å, b = 38.3650(12) Å, c = 9.7585(3) Å, beta = 93.3280(10) degrees, and Z = 4. Kinetic analysis of a dynamic process observed for dichlorotris(3,5-di-tert-butylpyrazolato)niobium(V) is described. The results of this study suggest that eta(2)-pyrazolato donors may be useful ancillary ligands in the development of new reactive early transition metal complexes.

Journal Article↗
PubMed2000

Formation of charge-transfer complexes from neutral bis(porphyrin) sandwiches.

Lanthanide(III) bis(porphyrin) sandwich complexes of octaethyltetraazaporphyrin (OETAP) were synthesized and characterized by UV-vis, IR, and NMR spectroscopies. Cyclic voltammetry results indicate that these neutral sandwich complexes are very easily reduced. Charge-transfer reactions were performed in solution with Ln-(OETAP)2 sandwiches and zirconium(IV) bis(porphyrin) sandwiches. The lanthanide sandwiches partially oxidize the zirconium sandwiches in solution, and a solvent dependence of the charge-transfer reaction was observed. The solid-state properties of these charge-transfer materials were also studied. Magnetic susceptibility results suggest weak intermolecular interactions between the sandwiches. The conductivities of the charge-transfer species are greatly improved relative to those of the insulating undoped sandwiches, but the conductivities are in the lower semiconducting region. The low conductivity values are thought to be due to poor intermolecular overlap.

Journal Article↗
PubMed2002

Photocurrent generation in multilayer organic-inorganic thin films with cascade energy architectures.

Zirconium organobisphosphonate multilayer thin films of viologen derivatives were grown on copper dithiolate multilayers of 5,15-di(p-thiolphenyl)-10,20-di(p-tolyl)porphyrin (POR) and 5,15-di(p-thiolphenyl)-10,20-di(p-tolyl)porphyrinzinc (ZOR) on a variety of substrates (e.g. Au, SiO(2)), using solution depositions methods. The multilayer structures were studied by atomic force microscopy, UV-vis spectroscopy, and ellipsometry. In the case of copper dithiolate thin films, layer-by-layer lamellar growth with low surface roughness resulted, while higher surface roughness was observed in the growth of Zr viologen bisphosphonate films. Gold electrodes modified with zirconium bisphosphonate multilayers of viologen on top of copper dithiolate multilayers of porphyrin derivatives (ZOR or POR) were photoelectroactive and produced efficient and stable photocurrents using visible light. By arranging the zinc-porphyrin (ZOR) and the free base porphyrin (POR) donors in an energetically favorable fashion, according to their redox potentials and optical energy gaps, the photoinduced charge separation was improved, and higher photocurrent quantum yields ( approximately 4%) and fill factor ( approximately 50%) of the photoelectrode were achieved.

Journal Article↗
PubMed2003

Degenerative transfer living Ziegler-Natta polymerization: application to the synthesis of monomodal stereoblock polyolefins of narrow polydispersity and tunable block length.

The neutral dimethyl pentamethylcyclopentadienylzirconium acetamidinate, (eta(5)-C(5)Me(5))ZrMe(2)[N(t-Bu)C(Me)N(Et)], can serve as a highly active initiator for the living Ziegler-Natta polymerization of alpha-olefins to produce polyolefins of narrow polydispersity (D < or = 1.05) when "activated" through mono demethylation by a substoichiometric amount of the borate, [PhNMe(2)H][B(C(6)F(5))(4)]. The mechanism by which this living polymerization proceeds is through a process of degenerative transfer involving rapid and reversible methyl group exchange between cationic (active) zirconium propagating centers and neutral (dormant) methyl, polymeryl zirconium end groups. Facile metal-centered epimerization of the dormant species is responsible for a loss of stereocontrol during propagation that produces iso-rich material in contrast to the pure isotactic polymer microstructure obtained when degenerative transfer is not present. By turning degenerative transfer "on" and "off" between successive monomer polymerizations, a successful strategy for the production of monomodal stereoblock polyolefins of narrow polydispersity and tunable block length has been demonstrated.

Journal Article↗
PubMed2004

On the origin of dinitrogen hydrogenation promoted by [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2).

The origin of the hydrogenation of the dinitrogen ligand in [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2) has been investigated by a combined computational and experimental study. Density functional theory calculations on the zirconocene dinitrogen complex demonstrate significant imido character in the zirconium nitrogen bonds, arising from effective pi-back-bonding from the low-valent zirconium and the side-on bound N2 ligand. The twisted ground-state structure of the N2 complex is a key requirement for nitrogen hydrogenation, as calculations on the model complex [(eta5-C5H5)2Zr]2(mu2,eta2,eta2-N2) reveal reduced overlap as the dihedral angle between the zirconocene wedges approaches 0 degrees . Experimentally, isotopic labeling studies on the microscopic reverse are consistent with a 1,2-addition mechanism for nitrogen hydrogenation.

Journal Article↗
PubMed2007

High-yield activation of scaffold polymer surfaces to attach cell adhesion molecules.

Zirconium tetra(tert-butoxide) reacts with surface amide groups of polyamide nylon 6/6 to give (eta(2)-amidate)zirconium complexes in high yield. These surface complexes react to bond the cell-adhesive peptide arginine-glycine-aspartic acid (RGD) to the polymer surface. A surface loading of 0.18 nmol/cm(2) of RGD is achieved, which is 20-1000 times higher than previously reported attainable on natural or synthetic polymers by other strategies. Approximately 40% of the nylon surface is covered by the RGD, which gives a surface that is both stable to hydrolysis and highly active for cell adhesion and spreading in vitro.

Animals↗
PubMed1996

Reduction of Secondary Carboxamides to Imines.

This article reports in detail on the discovery that zirconium(IV) salts of secondary amides and lactams are transformed by Cp(2)ZrHCl to N-substituted imines in one step. The method represents the first controlled reduction of amides and lactams to the corresponding imines, a transformation that is otherwise very difficult to achieve because imines are reduced more rapidly than carboxamides by most metal hydride reagents. No products of reductive cleavage of the carboxamides are observed. Efforts to replace 2 mol equiv of Cp(2)ZrHCl with simpler, less costly alternatives led to the finding that a diisobutylaluminum enolate can be substituted for the initial zirconium enolate. Such aluminum amides are smoothly reduced to the corresponding imine using Cp(2)ZrHCl in good yield. Moreover, aluminum amides are also reduced to imines using either low-valent titanium species or triethylsilane. In these alternative procedures, use of Cp(2)ZrHCl is eliminated altogether in the title transformation.

Journal Article↗