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Reaction of the lithium triamidostannate [MeSi[SiMe(2)N(p-Tol)](3)SnLi(OEt(2))] (1) with 0.5 molar equivalents of MCl(2) (M=Zn, Cd, Hg) in toluene afforded the corresponding heterodimetallic complexes [MeSi[SiMe(2)N(p-Tol)](3)Sn](2)M [M=Hg (2), Cd (3), and Zn (4)]. The molecular structures of the mercury and cadmium complexes were determined by X-ray diffraction and found to adopt a linear Sn-M-Sn metal-metal bonded array (d(Sn-Hg) 2.6495(2), d(Sn-Cd) 2.6758(1) A), these being the first Hg-Sn and Cd-Sn bonds to be characterized by X-ray diffraction. That the Hg-Sn bonds are shorter than the Cd-Sn bonds in the isomorphous complexes is attributed to relativistic effects in the mercury system. In contrast, the structure of the Zn analogue is unsymmetrical with one stannate unit being Sn-Zn bonded (d(Sn(1)-Zn) 2.5782(4) A), while the Zn(II) atom bridges two amido functions of the second stannate cage, thus representing a second isomeric form of these complexes. The different degree of metal-metal bond polarity is reflected in the (119)Sn NMR chemical shifts of the three complexes. Variable-temperature NMR studies and a series of (1)H ROESY experiments of the cadmium complex 3 in solution revealed a dynamic exchange between the two isomers.
One Cu(II)-containing ligand and two Cu(II)-Ag(I) mixed-metal coordination polymers have been synthesized. [Cu(2-methylpyrazine-5-carboxylate)2(H2O)].3H2O (1) was obtained as a molecular complex with two uncoordinated nitrogen donors by the reaction of 2-methylpyrazine-5-carboxylate sodium with CuCl(2).2H2O in water. Compound 1 crystallized in the triclinic space group P1, with a = 10.498(2) A, b = 11.000(2) A, c = 8.1424(16) A, alpha = 98.33(3) degrees, beta = 101.83(3) degrees, gamma = 66.68(3) degrees, and Z = 2. Reactions of 1 with silver(I) salts have been studied. Two Cu(II)-Ag(I) mixed-metal coordination polymers, namely, Ag[Cu(2-methylpyrazine-5-carboxylate)2.(H2O)2](BF4) (2) and Ag[Cu(2-methylpyrazine-5-carboxylate)2.(H2O)2](NO3) (3), have been generated by treating 1 with AgBF4 and AgNO3, respectively. Compound 2 crystallized in the monoclinic space group C2/c, with a = 25.827(5) A, b = 9.6430(19) A, c = 7.4525(15) A, beta = 94.74(3) degrees, and Z = 4. Compound 3 also crystallized in the monoclinic space group C2/c, with a = 25.855(5) A, b = 9.782(2) A, c = 7.1201(14) A, beta = 96.90(3) degrees, and Z = 4. The main structural feature in both 2 and 3 is a zigzag Cu(II)-Ag(I) mixed-metal chain, in which the alternating Cu(II) and Ag(I) centers are linked by 2-methylpyrazine-5-carboxylate spacers. The effect of the nitrate counterion was illustrated by compound 3, in which a novel [Ag+...NO3-] coordination chain has been found which acts as the connector to cross-link the one-dimensional zigzag chains into a three-dimensional network. In addition, an identical interchain O-H...O hydrogen bonding system has been found in both 2 and 3 and has been shown to play a significant role in directing the alignment of the one-dimensional mixed-metal polymer chains in the crystalline state. The magnetic susceptibilities of 2 and 3 were measured and found to follow the Curie law (mu eff = 1.85 for 2 and 1.83 for 3).
This case-control study was performed to investigate the hypothesis that metal-on-metal (M-M) bearings reduce the risk of aseptic component loosening when compared with metal-on-polyethylene (M-PE) bearings. Cases were identified from a computerized joint database as patients who had received a primary total hip arthroplasty using an M-M or M-PE bearing and had documented revision or radiographic loosening of the stem or cup. Multiple controls were matched to each case for gender, age, diagnosis, hospital, operation date, follow-up, stem type, and cup design. Odds ratios were determined to identify the risk of component loosening for either bearing surface. In all, 505 cases and 1,605 controls were identified. M-M bearings demonstrated a lower risk of aseptic stem and/or cup loosening than M-PE bearings; however, this was not statistically significant.
A prospective study was performed to investigate changes in metal levels and chromosome aberrations in patients within 2 years of receiving metal-on-metal hip arthroplasties. There was a statistically significant increase of cobalt and chromium concentrations, with a small increase in molybdenum, in whole blood at 6, 12, and 24 months after surgery. There was also a statistically significant increase of both chromosome translocations and aneuploidy in peripheral blood lymphocytes at 6, 12, and 24 months after surgery. The changes were generally progressive with time, but the change in aneuploidy was much greater than in chromosome translocations. No statistically significant correlations were found in secondary analyses between chromosome translocation indices and cobalt or chromium concentration in whole blood. Although the clinical consequences of these changes, if any, are unknown, future epidemiological studies could usefully include direct comparisons of patients with implants of different composition.
A lysimeter approach (under natural climatologic conditions) was used to evaluate the effect of four metal immobilizing soil treatments [compost (C), compost+cyclonic ashes (C+CA), compost+cyclonic ashes+steel shots (C+CA+SS)) and cyclonic ashes+steel shots (CA+SS)] on metal leaching through an industrially contaminated soil. All treatments decreased Zn and Cd leaching. Strongest reductions occurred after CA+SS and C+CA+SS treatments (Zn: -99.0% and -99.2% respectively; Cd: -97.2% and -98.3% respectively). Copper and Pb leaching increased after C (17 and >30 times for Cu and Pb respectively) and C+CA treatment (4.4 and >3.7 times for Cu and Pb respectively). C+CA+SS or CA+SS addition did not increase Cu leaching; the effect on Pb leaching was not completely clear. Our results demonstrate that attention should be paid to Cu and Pb leaching when organic matter additions are considered for phytostabilization of metal contaminated soils.
In a lysimeter set-up, compost addition to an industrial contaminated soil slightly reduced phytotoxicity to bean seedlings. The "Phytotoxicity Index" (on a scale from 1 to 4) decreased from 3.5 to 2.8. The same treatment also reduced metal accumulation in grasses: mean Zn, Cd and Pb concentrations decreased respectively from 623 to 135, from 6.2 to 1.3 and from 10.7 to <6 mg kg-1 dry weight. When combined with inorganic metal immobilizing amendments, compost had a beneficial effect on plant responses additional to the inorganic amendments alone. Best results were obtained when using compost (C)+cyclonic ashes (CA)+steel shots (SS). The "Phytotoxicity Index" decreased to 1.7, highest diversity of spontaneously colonizing plants occurred, and metal accumulation in grasses reduced to values for uncontaminated soils. Based on the first year evaluation, C+CA+SS showed to be an efficient treatment for amendment assisted phytostabilization of the contaminated Overpelt soil.
The hexahomotrioxacalix[3]arene macrocycles 1a,b are observed to bind Sc(3+), Lu(3+), Y(3+), and La(3+) more strongly than alkali or alkaline earth metal ions. Binding constants have been determined for the trivalent metal ions using an NMR titration method and are observed to increase with increasing charge-to-radius ratio for the metal ion (Na(+), Li(+), Ca(2+) < Mg(2+) < La(3+) << Y(3+) < Lu(3+) << Sc(3+)) and increasing macrocycle acidity [p-tert-butyloxacalix[3]arene (1a) < p-chlorooxacalix[3]arene (1b)]. Macrocycle 1b is observed to transport Sc(3+) across a liquid membrane without any detectable transport of Li(+) or Mg(2+).
Reactions of [CpMCl(&mgr;(2)-SH)(2)MCpCl] (1, M = Ir; 2, M = Rh; Cp = eta(5)-C(5)Me(5)) with excess FeCl(2).4H(2)O in THF gave the paramagnetic trinuclear clusters [(CpM)(2)(&mgr;(3)-S)(2)FeCl(2)] (3, M = Ir; 4, M = Rh), which were further converted into the dicationic 78e(-) pentanuclear bow-tie cluster [(CpIr)(2)(&mgr;(3)-S)(2)Fe(&mgr;(3)-S)(2)(IrCp)(2)](2+) (5) by treatment with NaBPh(4). When complex 1 was allowed to react with CoCl(2) and NiCl(2).6H(2)O or Ni(cod)(2) (cod = cyclooctadiene), the related pentanuclear 79e(-) and 80e(-) bow-tie clusters [(CpIr)(2)(&mgr;(3)-S)(2)M(&mgr;(3)-S)(2)(IrCp)(2)](2+) (6, M = Co; 7, M = Ni) were obtained directly, respectively. Cyclic voltammograms of 5[BPh(4)](2), 6[BPh(4)](2), and 7[BPh(4)](2) showed two reversible reduction waves at -0.25 to -0.43 V and -1.04 to -1.34 V. In both redox couples, the redox potential was in the order Fe < Co < Ni. One-electron reduction of clusters 5[BPh(4)](2), 6[BPh(4)](2), and 7[BPh(4)](2) with Co(eta(5)-C(5)H(5))(2) gave the corresponding monocationic pentanuclear 79-81e(-) bow-tie clusters [(CpIr)(2)(&mgr;(3)-S)(2)M(&mgr;(3)-S)(2)(IrCp)(2)](+) (8, M = Fe; 9, M = Co; 10, M = Ni). The molecular structures of 3, 4, 5[BPh(4)](2).CH(2)Cl(2), 6[CoCl(3)(NCMe)](2), 7[NiCl(4)].CH(2)Cl(2), 8[BPh(4)], 9[BPh(4)], and 10[BPh(4)] were unambiguously determined by X-ray diffraction study. The structures of the pentanuclear bow-tie cluster cores remarkably changed stepwise as the core electrons increased from 78 to 81. Two of the M-Ir (M = Fe, Co) bonds in the 79e(-) clusters 6 and 8 show significant elongation in comparison with the Fe-Ir bonds in the 78e(-) cluster 5. Two different types of the bow-tie structures were observed for the 80e(-) clusters 7 and 9. Cluster 7 has a Z-shaped metal core with only two Ni-Ir bonds, while in cluster 9, the six metal-metal bonds in the bow-tie structure are retained with slight elongation of the Co-Ir bonds in comparison with the corresponding dication 6. The 81e(-) cluster 10 has two normal Ni-Ir bonds and one long Ni-Ir bonding interaction with the fourth nonbonding Ni-Ir contact. This structural variation is interpreted in terms of the total electron counts and molecular orbital calculations of the clusters.
Metal activation of metallothionein gene transcription depends mainly on the presence of regulatory DNA sequences termed metal-regulatory elements (MREs) and involves MRE-binding transcription factor-1 (MTF-1) interacting with the MREs in a Zn(2+)-dependent manner. We previously identified and characterized a nuclear protein, termed metal element protein-1 (MEP-1), specifically binding with high affinity to MRE elements. The precise relationship between MTF-1 and MEP-1 was unclear, and to determine whether MEP-1 and MTF-1 were distinct protein species, we performed DNA binding analyses to characterize the binding properties of both proteins. Electrophoretic mobility-shift assays showed that MTF-1, produced in COS cells, produces a slower-migrating band compared with that obtained with purified MEP-1. Using an anti-MTF-1 antibody, we showed that both the MTF-1-MRE and the MEP-1-MRE complexes are supershifted by an anti-MTF-1 antibody, thus demonstrating that MEP-1 is antigenically related to MTF-1. RNase protection analyses carried out with RNA prepared from different tissues and cell lines failed to reveal the presence of MTF-1 splicing variants. This indicates that MEP-1 may be a proteolytic fragment of MTF-1. MTF-1 DNA-binding activity was rapidly activated in vivo by Zn(2+) ions but not by Cd(2+), UV irradiation or PMA, and occurred on ice as well as at 21 degrees C. In control and Zn(2+)-treated cell extracts, DNA-binding activity was not enhanced in vitro following the addition of exogenous Zn(2+) or a preincubation at 37 degrees C. However, recombinant MTF-1 produced in vitro required Zn(2+) activation for DNA binding. Interestingly, treatment of nuclear extracts with calf intestine phosphatase completely abrogated MTF-1 DNA-binding activity, thus suggesting that phosphorylation is involved in the regulation of MTF-1 activity.
We prepared a series of ligands possessing two binding sites for metal coordination: in each ligand molecule, two binding sites with the same functionality (2,2'-dipicolylamino group) were placed at the of various methyl arenes. Thus, the distances between the metal binding sites were different from ligand to ligand. We examined the rate of the hydrolysis of RNA dimer catalyzed by La3+ ion binuclear complexes of the ligands. The catalytic activity of the binuclear complexes increased as the distance between the metal binding sites was decreased.
An approach is described for stabilizing metal-metal epitaxial interfaces using a thin metallic interlayer. Rutherford backscattering and channeling techniques along with low-energy electron diffraction and keV He+ ion backscattering are used to demonstrate that an atomically thin layer of Ti deposited at the Fe-Al interface, a system well known for considerable intermixing at room temperature, forms a thin interface alloy that prevents interdiffusion and improves epitaxial growth of Fe on Al(100). The structure is stable up to about 200 degrees C.
New dental precious metal alloys for resin bonding without alloy surface modification were developed by adding base metals (In, Zn, or Sn). Before this, binary alloys of Au, Ag, Cu, or Pd containing In, Zn, or Sn were studied for water durability and bonding strength with 4-META resin. The adhesion ability of the binary alloys was improved by adding In equivalent to 15% of Au content, Zn equivalent to 20% of Ag content, and In, Zn, or Sn equivalent to 5% of Cu content. There was no addition effect of the base metals on Pd, however 15% of In addition improved adhesion with Pd-based alloys containing equi-atomic % of Cu and Pd. The alloy surfaces were analyzed by XPS and showed that oxides such as In2O3, ZnO, or SnO play an important role in improving the adhesive ability of the alloys.
The autometallographic procedure represents a new technique that can substitute for the normal methods of physical development (PD). The physical developer (a solution of reducing substance, silver salt and protection colloid) is replaced by a photographic emulsion and chemical developer. Accumulations of gold, silver, metal sulphides and metal selenides can be amplified by the present technique. Tissue sections placed on glass slides are covered by a silver bromide containing emulsion, dried and exposed to a chemical developer. After development the emulsion is either removed or cleared and the sections are counterstained and embedded. The autometallographic procedure can also be applied to ultrathin sections.
The new quaternary niobium thiophosphates ANb(2)P(2)S(12) (A=K, Rb, Cs) have been prepared and characterized. The title compounds were synthesized by reacting Nb metal, A(2)S, P(2)S(5), and S at 600-700 degrees C in evacuated silica tubes. They crystallize as "stuffed" variants of the tetragonal TaPS(6) structure type in the tetragonal space group I$\bar 4$2d with eight formula units per unit cell and lattice constants a=15.923(2) and c=13.238(3) A for CsNb(2)P(2)S(12), a=15.887(3) and c=13.132(3) A for RbNb(2)P(2)S(12), and a=15.850(2) and c=13.119(3) A for KNb(2)P(2)S(12). Their structures are based on double helices formed from interpenetrating, noninteracting spiral chains of binuclear [Nb(2)S(12)] cluster units and [PS(4)] thiophosphate groups. The cavities and tunnels, which are formed by the helical chains, are filled with A(+) ions. Temperature-dependent conductivity studies reveal thermally activated electrical transport behavior. This result is consistent with the observation of a temperature-dependent contribution to the (31)P MAS-NMR shift, suggesting that the delocalized s-electron spin density increases with increasing temperature. These findings are supported by the results of tight-binding band structure calculations which reveal that the unusual electrical transport behavior of ANb(2)P(2)S(12) is a consequence of the structure symmetry. Therefore, CsNb(2)P(2)S(12) may be considered a chalcogenide analogue of metal phosphate bronzes.
Structural, spectroscopic properties on the dinuclear [M(2)(dcpm)(2)(CN)(4)] (M = Pt, 1a; Ni, 2a, dcpm = bis(dicyclohexylphosphino)methane) and [M(2)(dmpm)(2)(CN)(4)] (M = Pt, 1b; Ni, 2b, dmpm = bis(dimethylphosphino)methane) and the mononuclear trans-[M(PCy(3))(2)(CN)(2)] (M = Pt, 3; Ni, 4, PCy(3) = tricyclohexylphosphine) and theoretical investigations on the corresponding model compounds are described. X-ray structural analyses reveal Pt.Pt and Ni.Ni distances of 3.0565(4)/3.189(1) A and 2.957(1)/3.209(8) A for 1a/1b and 2a/2b, respectively. The UV-vis absorption bands at 337 nm (epsilon 2.41 x 10(4) dm(3) mol(-)(1) cm(-)(1)) for 1a and 328 nm (epsilon 2.43 x 10(4) dm(3) mol(-)(1) cm(-)(1)) for 1b in CH(2)Cl(2) are assigned to (1)(5d(sigma) --> 6p(sigma)) electronic transitions originating from Pt(II)-Pt(II) interactions. Resonance Raman spectroscopy of 1a, in which all the Raman intensity appears in the Pt-Pt stretch fundamental (93 cm(-)(1)) and overtone bands, verifies this metal-metal interaction. Complexes 1a and 1b exhibit photoluminescence in the solid state and solution. For the dinuclear nickel(II) complexes 2a and 2b, neither spectroscopic data nor theoretical calculation suggests the presence of Ni(II)-Ni(II) interactions. The intense absorption bands at lambda > 320 nm in the UV-vis spectra of 2a and 2b are tentatively assigned to d --> d transitions.
Using conducting probe atomic force microscopy (CP-AFM), we have formed molecular tunnel junctions consisting of alkanethiols and alkane isonitrile self-assembled monolayers sandwiched between gold, platinum, silver, and palladium contacts. We have measured the resistance of these junctions at low bias (dV/dI |V=0) as a function of alkane chain length. Extrapolation to zero chain length gives the contact resistance, R0 . R0 is strongly dependent on the type of metal used for the contacts and decreases with increasing metal work function; that is, R0,Ag > R0,Au > R0,Pd > R0,Pt. R0 is approximately 10% smaller for Au junctions with isonitrile versus thiol surface linkers. We conclude that the Fermi level of the junction lies much closer to the HOMO than to the LUMO.