Values For Pd Research Articles

Modeling fractional crystallization of group IVB iron meteorites

A 187Re– 187Os isochron including data for all twelve IVB irons gives an age of 4579 ± 34 Ma with an initial 187Os/ 188Os of 0.09531 ± 0.00022, consistent with early solar system crystallization. This result, along with the chemical systematics of the highly siderophile elements (HSE) are indicative of closed-system behavior for all of the HSE in the IVB system since crystallization. Abundances of HSE measured in different chunks of individual bulk samples, and in spot analyses of different portions of individual chunks, are homogeneous at the ±10% level or better. Modeling of HSE in the IVB system, therefore, is not impacted by sample heterogeneities. Concentrations of some other elements determined by spot analysis, such as P, Cr and Mn, however, vary by as much as two orders of magnitude and reflect the presence of trace phases. Assuming initial S in the range of 0 to 2 wt.%, the abundances of the HSE Re, Os, Ir, Ru, Pt, Rh, Pd and Au in bulk IVB irons are successfully accounted for via a fractional crystallization model. For these elements, all IVB irons can be interpreted as being representative of equilibrium solids, liquids, or mixtures of equilibrium solids and liquids. Our model includes changes in bulk D values (ratio of concentration in the solid to liquid) for each element in response to expected increases in S and P in the evolving liquid. For this system, the relative D values are as follow: Os > Re > Ir > Ru > Pt > Rh > Pd > Au. Osmium, Re, Ir and Ru were compatible elements (favor the solid) throughout the IVB crystallization sequence; Rh, Pd and Au were incompatible (favor the liquid). Extremely limited variation in Pt concentrations throughout the IVB crystallization sequence requires that D(Pt) remained at unity. In general, D values derived from the slopes of logarithmic plots, compared with those calculated from recent parameterizations of D values for metal systems are similar, but not identical. Application of D values obtained by the parameterization method is problematic for comparisons of the compatible elements with similar partitioning characteristics. The slope-based approach works well for these elements. In contrast, the slope-based approach does not provide viable D values for the incompatible elements Pd and Au, whereas the parameterization method appears to work well. Modeling results suggest that initial S for this system may have been closer to 2% than 0, but the elements modeled do not tightly constrain initial S. Consistent with previous studies, our calculated initial concentrations of HSE in the IVB parent body indicate assembly from materials that were fractionated via high temperature condensation processes. As with some previous studies, depletions in redox sensitive elements and corresponding high concentrations of Re, Os and Ir present in all IVB irons are interpreted as meaning that the IVB core formed in an oxidized parent body. The projected initial composition of the IVB system was characterized by sub-chondritic Re/Os and Pt/Os ratios. The cause of this fractionation remains a mystery. Because of the refractory nature of these elements, it is difficult to envision fractionation of these elements (especially Re–Os) resulting from the volatility effects that evidently affected other elements.

Transport properties and growth parameters of PdC and WC nanowires prepared in adual-beam microscope

In this work we investigate the electrical transport properties and growth conditions oftungsten carbon (WC) and palladium carbon (PdC) nanostructures on Si substrates usinga focused ion beam and scanning electron microscope. In situ energy dispersive x-ray(EDX) characterizations reveal that electron-beam-induced WC and PdC nanostructuredepositions (EBID) show a lower metal concentration (below 3% atomic percentage)than in ion-beam-induced deposition (IBID) (above 20%). In the case of PdC thegrowth pattern and the Pd/C content were optimized by adjusting the depositiontemperature of the precursor material. In situ measurements of the resistivity ofthe nanostructures as a function of thickness reveal a minimum at a thickness∼200 nm. The lowest resistivity obtained for the PdC and WC structures is two orders ofmagnitude higher than the corresponding bulk values for pure Pd and W. The EBIDsamples show a non-metallic behaviour due to the low metal content. The temperature andmagnetic field dependence of the IBID structures reveal a behaviour similar to disorderedor granular conductors. The upper critical field and critical current density of theWC structures were measured below the superconducting critical temperatureof ∼5 K.

A Novel Thrombopoiesis-Stimulating Agent, AMG 531: Pharmacokinetics and Pharmacodynamics in FcRn Knock-Out and Wild Type Mice.

AMG 531 is a novel platelet-stimulating peptibody that targets the thrombopoietin (TPO) receptor, resulting in an increased production of platelets. This molecule consists of an Mpl receptor binding domain of peptide and a carrier Fc domain. The purpose of this study was to evaluate pharmacokinetics (PK) and platelet response profiles (pharmacodynamics; PD) of AMG 531 in FcRn knock-out (KO) vs. wild type (WT) mice. Male C5BL/6J-B2m FcRn KO mice (n = 177) and male C57BL/6J WT (n = 162) received a single dose of 100 or 1000 μg/kg of AMG 531 intravenously (IV). One additional group of KO mice (n = 87) received a single IV dose of 300 μg/kg of AMG 531. At defined times, approximately 0.3 mL of blood per animal was collected by cardiac puncture from 3 mice for the measurement of serum AMG 531 concentration (PK) and platelet counts (PD). Serum AMG 531 concentrations were determined by a sandwich enzyme-linked immunosorbent assay (ELISA) with a lower limit of quantification (LLOQ) of 1.774 ng/mL. The composite mean values for PK and PD at each time point were analyzed by the non-compartmental method. Serum AMG 531 concentration-time profiles showed that AMG 531 was eliminated faster in KO mice compared to WT. After a single IV (100 – 1000 μg/kg) administration, AMG 531 exhibited non-linear pharmacokinetics in both KO and WT mice. A 24- and 16-fold increase in systemic clearance (CL) was observed in KO mice (128 and 318 mL/h/kg) relative to the WT (8.23 and 13.1 mL/h/kg) at the 100 and 1000 μg/kg dose levels, respectively. The estimated apparent half-life of AMG 531 was shorter in KO mice (1.3–2.2 hours) than in WT (6.5–12.5 hours). The estimated steady-state volumes of distribution were greater in KO mice (193–464 mL/kg) than in WT (104–158 mL/kg), suggesting that the absence of the binding of AMG 531 to the FcRn receptor in KO mice may enhance the extent of peripheral distribution. Pharmacodynamic response (increase of platelet counts after AMG 531 administration) was more pronounced in WT than in KO mice. The mean baseline platelet count at predose ranged from 1250 to 1390 x103/mm3 in KO mice and from 805 to 1280 x103/mm3 in WT. After single IV administration of AMG 531, a dose-dependent increase in the maximum platelet count (Pmax): initial minimum platelet count ratios of 1.8 to 2.1-fold for KO mice and 4.7 to 8.4-fold for WT were observed. When the dose increased from 100 to 1000 μg/kg, the Pmax values increased from approximately 2240 to 2550 x103/mm3 in KO mice and 4900 to 6722 x103/mm3 in WT. The Pmax values occurred at 96 to 120 hours (4–5 days) in KO mice and 92 to 264 hours (8–11 days) in WT. These results suggest that the FcRn receptor may act as a salvage receptor for AMG 531, maintaining serum concentrations in mice. The higher AMG 531 exposure in WT mice resulted in elevated platelet response relative to KO mice in a dose-dependent manner. This novel construct with a carrier Fc domain may sustain the exposure of the molecule and therefore provide added efficacy and increase the clinical benefit of AMG 531.

In situ monitoring of oxide-supported platinum-group metal catalysts by energy dispersive EXAFS

Energy dispersive EXAFS (EDE), using a Laue monochromator on ID24 of the ESRF, and multiple ion monitoring mass spectrometry have been used to monitor the structure and function of alumina-supported rhodium and palladium catalysts within a microreactor. Metallic 5%-Rh/Al2O3 was preformed in situ by hydrogen reduction, and shown to react rapidly with NO at room temperature yielding an oxidised phase. In order for this material to catalyse the reduction of NO by H2 (to N2), it was shown that the metallic phase must be reformed. The “light-off” temperature at which the metallic phase was formed and catalysis commenced varied with NO : H2 stoichiometry, this temperature lowering in more reducing conditions. N2O formation was concomitant with the conversion from the oxidised to the metallic phase.The EDE configuration allowed the simultaneous monitoring of structure at both the rhodium and palladium K-edges. Incorporation of a 20% palladium mole fraction into 5%-Rh-Pd/Al2O3 protected rhodium from oxidation and also reduced the light-off temperature, and this is reflected in low coordination number values for the composite Pd to Rh/Pd shell. This favours palladium being preferentially on the surface of the nanoparticles. At higher temperatures there are changes in coordination numbers than imply a redistribution of metal sites under catalytic conditions. Future plans to include infrared spectroscopy as a third simultaneous technique will be outlined.

Static displacements of Pd in the solid solution PdBy (0 <y < 0.2) as determined by neutron diffraction

The mean square atomic displacement parameter of Pd in the fcc interstitial solid solution PdB y , (u 2 Pd (y)), was determined for atomic ratios of y = 0.050, 0.100, and 0.184 using neutron powder diffraction data obtained at 15 K and 300 K. The values determined are significantly larger than those determined for pure Pd, (u 2 Pd (0)), at the same temperatures. Assuming that the dynamic (thermal) contribution to (u 2 Pd (y)) equals (u 2 Pd (0)), the static mean square atomic displacement parameter (u 2 Pd (y))) st = (u 2 Pd (y)) - (u 2 Pd (0)) was obtained as 0.0020(1) A 2 to 0.0027(1) A 2 . (u 2 Pd (y)) st showed no systematic variation with y or the sample temperature. This contrasts with an expected y(1 - y) concentration dependence for (u 2 Pd (y)) st . Comparison of (u 2 Pd (y)) st with values for the static mean square displacements of the metal atoms in different defect-NaCl type transition metal nitrides and carbides indicates that the current values for Pd in PdB y are exceptionally small.

The development of a high accuracy method for the analysis of Pd, Pt and Rh in auto catalysts using a multi-collector ICP-MS

Catalysts containing the platinum group elements (PGEs) are employed for a variety of industrial and chemical uses. Palladium (Pd), platinum (Pt) and rhodium (Rh) are the active components in automobile catalytic converters as well as catalysts used in pharmaceutical/biological applications and petroleum refining. In all cases the high economic value of these catalysts means that it is important to be able to measure the precious metal loading very accurately. The aim of this work was to develop a robust and reliable high accuracy/precision method for the analysis of Pd, Pt and Rh metals in autocatalysts with a target expanded uncertainty (i.e., k = 2, 95% confidence) of approximately 1% relative. A microwave digestion procedure was developed that provided a relatively quick total dissolution of the precious metals in a 0.2 g sample. An ultrasonic nebuliser with desolvation enabled the effects of the key interferences to be negated. Thus it was possible to make the comparison between a multi-collector ICP-MS and a more conventional quadrupole instrument. For Pd and Pt, high accuracy analysis was underpinned by an approximate matching isotope dilution calibration procedure. In the case of monoisotopic Rh an approximate matching bracketing calibration procedure was used (which had originally been developed for high accuracy ICP-OES) with Ru as the internal standard. Using the procedures reported here, the multi-collector ICP-MS provided data for the NIST autocatalyst reference material (SRM 2556) which showed excellent agreement with the reference values for Pd, Pt and Rh, with expanded uncertainties (i.e., k = 2, 95% confidence) of 0.9%, 1.1% and 0.9%, respectively. The equivalent data from the conventional quadrupole ICP-MS shows an approximately two-fold increase in these uncertainty estimates. Such a difference is likely to be very significant when dealing with these very precious materials which have a very high intrinsic economic value.

Experimental constraints on the partitioning of rhenium and some platinum-group elements between olivine and silicate melt

We have performed partitioning experiments to assess the role of olivine in controlling the behavior of rhenium and the platinum group elements (PGEs) during basalt petrogenesis. Olivines were crystallized from an iron-bearing basalt at 1 bar (105 Pa) and log fO2 of −2.6, −4.9 and −7.4 (FMQ +4.3, +2 and −0.5, respectively). In situ analyses of olivine and glass by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) reveal a homogeneous distribution of Ru, Rh, Pd, Re, and Pt, but significant Os heterogeneity at the μm scale. This latter behavior arises from the presence of undissolved Os micronuggets suspended in the melt, and included in olivine crystals. Olivine–melt partition coefficients (Ds) for Re and the PGEs follow the order: DRh>DRu≫DPd∼DRe∼DPt. With decreasing fO2, Rh and Ru become more compatible, with maximum partition coefficients of ∼2.6 and ∼2, respectively, at log fO2 of −4.9. In contrast, D values for Pd become smaller with decreasing fO2, to a value of ∼0.006 at log fO2 of −7.4. Olivine–melt partitioning of Rh, Ru, Pd, Re and Pt derived from our experiments is confirmed by the behavior of these elements in lavas that have evolved by olivine fractionation. An elastic strain model predicts the olivine–melt partitioning of these elements, excepting our measured value of DPt, which is much lower. The fO2 dependence on partitioning implies that at higher fO2 some portion of PGEs exist in higher valence states than predicted from their solubility.

Palladium and platinum concentration in soils from the Napoli metropolitan area, Italy: possible effects of catalytic exhausts

Soils from the Napoli metropolitan area (Italy) were evaluated for Pt and Pd concentrations. One hundred and ninety-five (195) samples were collected from residual soils and non-residual soils from flower-beds in a 120 km 2 area on a 0.5 km grid in the downtown-urbanized area and on 1 km grid in suburban zones. The soils <100 mesh size fraction (150 μm) was analyzed for Pt, Pd and 37 other elements by ICP-ES and ICP-MS after aqua regia digestion. Pt and Pd contents range between <2 and 52 μg/kg and between <10 and 110 μg/kg, respectively. A large number of samples from the metropolitan area were characterized by anomalous values for Pt (>6 μg/kg) and Pd (>17 μg/kg). Non-residual soils from flower-beds are located mainly in the urbanized downtown areas subject to heavy traffic and have higher Pt and Pd contents than residual soils from suburban areas. Geochemical maps show a strong correlation between roads with major traffic flow and high Pt and Pd concentrations. In addition, data from most of the downtown flower-beds fall within the three-way catalytic converters (TWC) field identified by [Ely JC, et al. Environ Sci Technol; 35:3816–3822]. This suggests that emissions of abraded fragments from vehicle exhausts may be the source of the high values and geographic distributions of Pd and especially Pt in urban soils of Napoli. Catalytic converters (Pt/Pd/Rh) have been mandatory for gasoline-powered vehicles in Europe since 1993. Italy permitted the use of non-catalytic motor until January, 2002. This is responsible for the high values for both Pt and Pd in the non-residual soils of the urban areas of Napoli.

Hydrogen-sensitive GaN Schottky diodes

Pt/n-GaN and Pd/n-GaN Schottky diodes were characterized for their response to hydrogen as a function of measurement temperature. Even at modest temperatures (80–140 °C), an 80 μm diameter diode shows a large increase (⩾0.5 mA) in forward current upon introduction of ∼10% H 2 into a N 2 ambient. The change in current increases with measurement temperature and begins essentially immediately upon introduction of the hydrogen. Cycling the ambient from N 2 to 10% H 2 in N 2 and back to N 2 produces reproducible cycling of the forward current at fixed forward bias. The decrease in barrier height of Pt on GaN was 50 mV at 25 °C and 70 mV at 150 °C upon introduction of H 2 into the ambient, with lower values for Pd. At high temperature, the time response of the sensors appears to be controlled by hydrogen diffusion to the metal/GaN interface, while at low temperatures (<100 °C), dissociation of the gas appears to be the rate-determining step.

The potentials of zero charge of Pd(1 1 1) and thin Pd overlayers on Au(1 1 1)

The potential of zero charge (pzc) of Pd(1 1 1) has been determined in dilute NaF solutions by measuring the Gouy–Chapman minimum of the double-layer capacity. For a massive Pd(1 1 1) single crystal electrode a pzc of −0.12 V vs. SCE has been found. The corresponding values for thin Pd(1 1 1) overlayers on Au(1 1 1) have also been determined. While the pzc of the first, pseudomorphic Pd layer on Au(1 1 1) is −0.09 V vs. SCE, the pzc of a five monolayers thick Pd film on Au(1 1 1) is practically identical to the pzc of the massive Pd(1 1 1) electrode. By comparing pzc's and work functions for Au(1 1 1) and Pd(1 1 1), the dipole contribution to the potential drop across the Pd(1 1 1)/water interface is estimated.

PD 142893, SB 209670, and BQ 788 selectively antagonize vascular endothelial versus vascular smooth muscle ET(B)-receptor activity in the rat.

The purpose of this study was to determine whether vascular endothelial and vascular smooth-muscle endothelin ET(B) receptors could be quantitatively differentiated by PD 142893 (PD), SB 209670 (SB), and BQ 788 (BQ) in the same species by using closely matched experimental conditions. The isolated perfused rat kidney (vascular smooth muscle) and isolated perfused rat mesentery (vascular endothelium) were challenged with increasing bolus doses of sarafotoxin S6c in the absence and presence of antagonist. PD, SB, and BQ produced parallel concentration-dependent rightward shifts in the S6c dose-response curve in the kidney. PD and SB also produced parallel concentration-dependent rightward shifts in the S6c dose-response curve in the mesentery. In contrast, BQ produced an insurmountable antagonism. Schild-derived pA2 values for PD and SB were significantly greater for inhibiting endothelial versus smooth-muscle ET(B) receptors. Furthermore, PD and SB differed in their relative potency between the two assays. Because BQ produced an insurmountable antagonism in the mesentery, it was not possible quantitatively to compare the antagonist activity in the two assays. These results indicate that PD, SB, and BQ selectively antagonize endothelial ET(B)-receptor activity over smooth-muscle ET(B)-receptor activity.

Nuclear Spin-lattice Relaxation Rates of Ni and Ru in Fe

We have determined the nuclear spin-lattice relaxation (SLR) rates of Ni and Ru as dilute impurities in iron using the method of thermal cycling on oriented nuclei. The samples were prepared by recoil implantation from the heavy ion reactions used to produce the radioactive Ni and Ru isotopes employed in the measurements. In the 3d impurity series, only Sc, Ti, and Cu remain to complete the systematics of the SLR in iron host; in the 4d series, values for Zr and Pd are still missing and the datum for Rh has a large experimental uncertainty. We discuss the comparison with theory and with other experimental results.

Transport Characteristics of the Colonic Epithelium of the Japanese Quail ( Coturnix coturnix)

The colon of the domestic fowl sustains a reabsorptive Na + current on both high- and low-sodium diets. However, there is a marked shift in the apical transport step under these two extreme conditions, from amino acid/hexose cotransport on high-salt diets to amiloride-sensitive Na + channels on low-salt diets. The present experiments were performed to study colonic Na + transport in another galliform species, the Japanese quail ( Coturnix coturnix). Birds were maintained on a commercial game feed containing 0.18% Na + (78 μmoles/g), an intermediate level of salt intake. Experiments were performed on unstripped colons in standard Ussing chambers with bicarbonate/CO 2 buffer solution on both sides. Baseline values ( n = 11) for PD (3.13 ± 0.68 mV) and short circuit current (SCC, 30.87 ± 7.79 μA/cm 2) were lower than those reported for chickens on a similar diet, whereas tissue resistance (76.06 ± 4.19 Ω·cm 2) was similar. Addition of amino acids (4 mM leucine + lysine) increased SCC by 10.85 ± 1.97 μA/cm 2. Both phloridzin (1 mM) and amiloride (10 −5M) decreased SCC, by 7.05 ± 1.26 and 9.64 ± 2.68 μA/cm 2, respectively. Thus, on this diet the quail colonic epithelium maintains both amino acid/hexose cotransporter activity and amiloride sensitive channel activity. Arginine vasotocin (10 −6 M) caused a small, but consistent decrease in SCC, while acetazolamide increased SCC. Aldosterone (128 μg/kg), given 4 hr prior to the experiment ( n = 4) significantly reduced the amino acid stimulated SCC. These results confirm, for the Japanese quail, the presence of multiple apical Na + entry mechanisms in colonic epithelium. Amino acid cotransporter activity, in particular, appears to be highly sensitive to aldosterone suppression.

Implications of composition for experimental partitioning of platinum-group elements and gold between sulfide liquid and basalt melt: The significance of nickel content

Experimental partitioning of platinum-group elements (PGE) Os, Ir, Ru, Pt, and Pd, and Au between (Fe, Ni)-sulfide liquid and basaltic melt have been carried out at high Ni content with 67 ± 1 mol% NiS and 50 to 400 ppm PGE in the sulfide fraction. The study was designed to evaluate the significance of major element composition, in particular high Ni content, on partitioning of these noble metals. Charges were held at 1250°C for 48 h. Mean partition coefficients D (wt fraction PGE in sulfide/ wt fraction PGE in silicate) obtained were: D( Os) = (10±2.6 x 10 3); D( Ir) = (51±20 x 10 3); D( Ru) = (7.0±5.4 x 10 3);D( Pt) = (16.5±6.3 x 10 3); D( Pd) = (28±12.5 x 10 3); D( Au) = (1.21±0.95 x 10 3) and pertain to 7 samples for Os, Ir, and Ru, 6 samples for Pt and Pd, and 5 for Au. The average values for Ir, Ru, Pt, and Pd are comparable with D values reported by Fleet et al. (1996) for a series of 5 samples equilibrated under virtually identical experimental conditions but on charges with lower Ni content. A significant correlation of individual D values with PGE in quenched sulfide was observed for Ru, Pt, and Pd, suggesting that variable concentrations of these metals in initial charges contribute to the inter-experiment variation in D. A marked increase in D(Au) to 13.6 × 101 3 was found when the Au content of initial charges was increased from a ppb to a ppm range, a trend comparable to that of Ru, Pt, and Pd. D(PGE) values for ⋍50 ppm PGE in the sulfide liquid are D(Ru) = 1.45 × 10 3, D(Pt) = 10.5 × 10 3, and D(Pd) = 17.8 × 10 3. The significance of NiS for PGE-Au partitioning was investigated by comparing D values for controlled atmosphere experiments ranging from ∼4 to 67 mol% NiS in quenched sulfide. Sulfide liquids with less than ∼38 mol% NiS are associated with more variable D values for all PGE-Au than those of higher NiS content, which yield more consistent D values. Ruthenium is an exception and behaves in a reverse manner. There is no strong correlation of the magnitude of D with composition of the sulfide liquid but rather a correlation of the variance in D. It is suggested that the Ni/Fe proportions of the silicate melt strongly affect the behaviour of PGE-Au in silicate melts, probably through a control on speciation and solubility of noble metals.

SCN − effect on the palladium(II) transfer in two and three phases systems using triphenylphosphine sulfide as a carrier

The extraction of Pd(II) by triphenylphosphine sulfide (TPPS) in toluene from hydrochloric acid solutions containing small amounts of SCN − has been investigated. The role of thiocyanate on the Pd(II) extraction is explained as a trans-effect with the formation of mixed complexes PdC l4− n (SCN) n 2−, less inert to ligand substitution than the chloride complexes. The analysis of metal distribution data by numerical calculations suggested the formation of the species Pd(SCN) 2·TPPS and Pd(SCN) 2·2TPPS in the organic phase with formation constants log K 021 = 13.00 and log K 022 = 14.24, respectively. A comparison of the results with those obtained using triisobutylphosphine sulfide (TIBPS) under similar conditions reveals a lower influence of SCN − concentration and also lower values for Pd(II) extraction, which can be attributed to the electron withdrawing characteristics of the aromatic ring with a decrease of the solvating power of the S atom for TPPS. The results obtained on Pd(II) distribution have been exploited in a three phases system by implementing a solid supported liquid membrane, being thiocyanate concentration the driving force of the mass transfer process. The behavior of the system is similar to that observed in the two phases.

Palladium, platinum and ruthenium in iron meteorites and their taxonomic significance

Pd, Pt and Ru have been quantified in 117 iron meteorites by procedures involving a combination of extraction into organic solvents and analysis of the extracts by graphite furnace atomic absorption spectrometry. Our data for these three metals, particularly for Pd, have enabled us to assemble a sufficient largee pool of information from which to draw conclusions clusions concerning their taxonomic potential based on their distribution pattern in iron meteorites. Unlike Ru and Pt, the Pd concentrations give a positive slope when plotted against Ni contents and their mass abundance ratios are very close to the cosmic ratio. Pd and Ni are probably enriched in the later solid during fractionation. Distribution coefficients (solid/liquid concentration ratios) for Ir, Pt, Ru and Pd as determined from the Rayleigh equation are 4.0, 1.4, 1.1 and 0.8, respectively. This sequence is some measure of the usefulness of the elements for taxonomic classification of iron meteorites and is the same sequence as obtained elsewhere by statistical interpretation of abundance data. The positive correlation between the Pt and Ru abundances is extremely close and there is also a good negative correlation between concentrations of Pd and each of Pt and Ru. It is proposed that low-Ni IIICD meteorites belong more appropriately to group IAB since we have been unable to find intermediate values for Ru, Pd, or Pt linking the low-Ni and high-Ni subgroups of IIICD.

Partitioning of the platinum group elements and gold between silicate and sulphide magmas in the Munni Munni Complex, Western Australia

The Munni Munni Complex in the Archaean Pilbara Block contains PGE mineralization in the form of disseminated sulphides within pyroxenite. The uppermost sulphide-bearing layer shows a characteristic vertical distribution of PGE and Au. Peak values for Pd, Pt, and the other PGEs are systematically offset by up to 5 metres below the horizon of maximum S, Ni, and Cu abundance. The Main Sulphide Zone of the Great Dyke of Zimbabwe, which occurs in an identical stratigraphic setting, shows very similar features. This distribution of PGEs with respect to the sulphide peak cannot be explained in terms of postcumulus mobilisation from an initially homogenous sulphide layer, for a number of reasons: the offset profiles are remarkably consistent along several km of strike; remobilization would be expected to affect Pd and Au more than the other PGEs; and underlying sulphide concentrations show coincident trends for all the PGE, Au, Cu, Ni, and S. The offset between PGE and Ni-Cu-S peaks has been interpreted by workers on the Great Dyke as the result of fractional sulphide segregation, combined with different values for sulphide liquid-silicate melt partition coefficient (SSD) for the various PGEs, Au, Ni, and Cu. A series of model calculations has been performed in an attempt to apply this interpretation to the Munni Munni case, with the object of making quantitative estimates of SSD values for the PGEs and Au. Results in general support the conclusions of Great Dyke studies that apparent SSDs decrease in the order Ir = Ru = Rh = Os ≥ Pd > Pt > Au > Cu = Ni. However, it proves impossible to duplicate some highly regular and persistent features of the Munni Munni offset sulphide layer with any model that assumes constant values for these SSDs. The inadequacy of the fractional sulphide segregation model implies that sulphide liquid is not the sole collector of the PGEs. The observed behaviour of the PGEs requires a sudden increase in the apparent affinity of the PGEs for the sulphide fraction at the base of the main sulphide peak, unattributable to any significant change in parent magma composition or crystallization conditions. Natural profiles can be modelled successfully by describing this apparent affinity of PGE for the sulphide fraction in terms of widely variable “virtual” partition coefficients. This behaviour can be explained if the silicate melt, and consequently the co-existing sulphide melt, is saturated with respect to solid PGE phases. The association of PGE with sulphides is necessary because of the extremely low concentrations of PGE in the silicate melt, which makes it kinetically impossible to nucleate solid phases even at substantial degrees of supersaturation. Pre-concentration by several orders of magnitude due to partitioning into sulphide liquid allows solid PGE phases to nucleate within sulphide droplets, giving rise to an apparently very strongly PGE-enriched sulphide fraction.

Increased density of α-adrenoceptors in vas deferens of spontaneously hypertensive rats (SHR), indicated by functional and receptor binding studies

Pharmacological parameters were determined from conractile responses mediated by α-adrenoceptors in vas deferens from spontaneously hypertensive rats (SHR) and corresponding normotensive controls, Wistar Kyoto rats (WKY), and compared with data obtained from radioligard binding assays. Contractile responses induced in longitudinal and circular muscle layers by the α-adrenoceptor agonist noradrenaline (NA) and by barium chloride were recorded as described previously. In both muscle layers the maximal effects induced by NA, but not by BaCl 2, were significantly greater in SHR. As a consequence, the relative responsiveness ratio (ϱ) for the α-adrenoceptor was also larger for SHR than for WKY. NA-induced contractions of both muscle layers were competitively antagonized by indoramine. The pA 2 values for indoramine and pD 2 values for NA were the same in SHR and WKY, indicating that α-adrenoceptor affinity was not changed in SHR. Additionally, binding studies with the α-adrenoceptor ligand [ 3H]WB4101 revealed that B max values were greater in the vas deferens of SHR, whereas K d values were not significantly different from those of WKY controls. In summary, although differences could not be detected for affinity-related parameters, a greater density of α-adrenoceptors was shown for SHR in receptor binding studies and this was corroborated by functional studies.

Permeability of liposomal membranes to water: results from the magnetic field dependence of T1 of solvent protons in suspensions of vesicles with entrapped paramagnetic ions.

The diffusive permeability to water molecules, Pd, of lipid vesicles with entrapped paramagnetic solute ions can be determined rapidly from analysis of the magnetic field dependence (nuclear magnetic relaxation dispersion, or NMRD profile) of T1 of exterior solvent water protons. Such data yield tau, the mean lifetime of solvent molecules inside the vesicles, from tau = (fT1Para) - T1Ves, where f is the volume fraction of entrapped water, T1Para is the observed T1 corrected for buffer background, and T1Ves is the relaxation time of water protons in the entrapped solution. For small spherical unilamellar vesicles of inner radius R, Pd = R/3 tau, f can be obtained accurately from knowledge of both the concentration of Gd(DTPA)2- in the solution in which the vesicles were formed and the average concentration of ions in the final sample. At low temperatures, in the limit of slow exchange, T1Para becomes independent of field and tau = fT1Para; the observation of a field-independent profile is a control that confirms that no paramagnetic material is external to the vesicles. We have measured T1Para, using a field-cycling relaxometer, for suspensions of POPC (1-palmitoyl-2-oleoyl-lecithin) vesicles with 100-500 mM entrapped Gd(DTPA)2- and membrane concentrations of cholesterol ranging from 0 to 40 mol %. These profiles, which span the field range 0.01-50 MHz proton Larmor frequency, were taken at 5, 15, 25, and 35 degrees C. Concentrations of Gd(DTPA)2- were determined independently by both ICP analyses and NMRD methods. Values for Pd for vesicles with 100 mM Gd(DTPA)2- and outer diameters 100 nm +/- 20%, as determined by quasielastic light scattering, are 63, 47, 24, 16, and 8.7 x 10(-4) cm s-1, at 25 degrees C, for cholesterol concentrations of 0, 10, 20, 30, and 40%, respectively. The corresponding activation enthalpies are 14, 14, 14, 17, and 17 kcal/M. Comparison with 2H NMR studies of deuterated POPC vesicles with no cholesterol at 20 degrees C, and with 10% at 40 degrees C, which yielded the same order parameter for the palmitoyl acyl chains, gives no indication of a correlation between order parameter and permeability.

Determination of trace metals in platinum by electrothermal atomic absorption spectrometry following a closed-vessel microwave dissolution procedure

A closed-vessel microwave dissolution procedure has been shown to reduce the time and amount of aqua regia(3 parts HCl + part HNO3) required to dissolve platinum in comparison with conventional open-vessel hot-plate dissolution. Analytical results for the determination of Au, Pd and Pt indicated that both the microwave and hot-plate procedures gave low acid blank concentration values for Pb and Pd. Experiments with gold indicate that the closed-vessel microwave dissolution procedure should be used in areas where the risk of environmental contamination is high.