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PubMed1999

Occupational asthma caused by palladium.

Occupational exposure to complex platinum salts is a well-known cause of occupational asthma. Although there is evidence that platinum refinery workers may also be sensitized to other precious metals, such as palladium or rhodium, no instances of occupational asthma due to an isolated sensitization to palladium have been reported. A case is reported of occupational rhinoconjunctivitis and asthma in a previously healthy worker exposed to the fumes of an electroplating bath containing palladium. There was no exposure to platinum. Sensitization to palladium was documented by skin-prick tests. The skin-prick test was positive with Pd(NH3)4Cl2, but not with (NH4)2PdCl4. Corresponding salts of platinum were all negative. A bronchial provocation test with Pd(NH3)4Cl2 (0.0001% for a total of 315 s, followed by 0.001% for a total of 210 s) led to an early decrease in forced expiratory volume in one second (-35%). A similar exposure (0.001% for a total of 16 min) in an unrelated asthmatic gave no reaction. This case shows that an isolated sensitization to palladium can occur and that respiratory exposure to palladium is a novel cause of metal-induced occupational asthma.

Adult↗
PubMed2001

Evaluation of high-temperature distortion of high-palladium metal-ceramic crowns.

STATEMENT OF PROBLEM: Crown fit is a prerequisite for long-term clinical success; however, crown distortion may occur during porcelain firing. The dimensional stability of some high-palladium alloys at high temperatures has been questioned. PURPOSE: The purpose of this study was to use a new method to measure the distortion of copings for metal-ceramic single units of selected high-palladium alloys with compositions representative of commercial alloys. MATERIAL AND METHODS: Four high-palladium alloys containing copper and 3 containing no copper were tested. A palladium-silver alloy was included for comparison, and a gold-palladium alloy served as the control. By using reference points scribed on the margin, the mesiodistal and buccolingual margin diameters of identical copings were measured with a traveling microscope at 4 stages: as-cast, oxidized, after 2 simulated opaque porcelain firings, and after 2 simulated dentin porcelain firings. The margin distortions for the various specimen groups representing combinations of alloys, stages, and measurement diameters were compared with the use of 1-way analysis of variance and a multiple range test. RESULTS: Most of the high-palladium alloys had high-temperature distortions that were not significantly different from those of the control alloy. The distortions occurred principally during the oxidation cycle. The effect of mesiodistal groove reinforcement on preventing distortion was not the same for all alloys. CONCLUSION: The results suggest that small observed distortions of these alloys will not produce clinical problems. Several laboratory techniques are available to counteract the distortions.

Analysis of Variance↗
PubMed2002

Palladium--a review of exposure and effects to human health.

Palladium is a metal the output and use of which has more than doubled in the past ten years. It is used in dental appliances, chemical catalysts, electrical appliances and jewelry, but the greatest increase in Pd demand has been in automotive emission control catalysts. Studies on Pd concentrations in ancient ice and recent snow samples reflect the increase in mining, smelting and use of palladium in the last decades. Increases of palladium in the environment have been shown in air and dust samples. There is no data as yet available to assess the effect of this exposure. A major source of health concern is the sensitization risk of Pd as very low doses are sufficient to cause allergic reactions in susceptible individuals. Persons with known nickel allergy may be especially susceptible. Workers occupationally exposed to Pd include miners, dental technicians and chemical workers. The latter are exposed mainly to Pd salts several of which may cause primary skin and eye irritations. It is advised that persons with known Pd allergy should not work with Pd compounds. The general population may come into contact with palladium mainly through mucosal contact with dental restorations and jewelry containing palladium and possibly via emissions from Pd catalysts. Protection of the public from related adverse effects may be achieved by the use of alloys with high corrosion stability and thus minimal release of palladium. In general, in dental patients who are sensitive to Pd, restorations using Pd-containing materials should not be used although Pd has been used without allergic effects in some of these individuals. Further, those patients who have an allergy to nickel should be informed that use of Pd-containing dental materials may cause Pd allergy, though this risk appears to be low.

Air Pollutants↗
PubMed2005

Cross-reactivity between nickel and palladium demonstrated by systemic administration of nickel.

Concomitant patch test reactions to nickel and palladium have frequently been reported in patients undergoing investigation because of suspected allergic contact dermatitis. Theoretically, these reactions can be explained by multiple, concomitant, simultaneous sensitization as well as cross-sensitization. We studied whether concomitant reactions to nickel and palladium could represent cross-sensitization in females hypersensitive to combinations of nickel, palladium and cobalt. Females were patch tested with serial dilutions of nickel sulfate, cobalt chloride and palladium chloride on the upper back. 1 month later, when the patch test reactions were gone, the patients were randomized into 2 groups that were challenged orally with either nickel or placebo. 1 day later, the areas of previous positive patch test reactions were read in a blind way looking for flare-up reactions. Nickel provocation but not placebo yielded flare-up reactions on sites previously tested with nickel (P = 0.012) and palladium (P = 0.006), but were also observed on sites previously tested with cobalt, even though this was not statistically significant. Flare-up reactions of previous patch test reactions to nickel and palladium after oral challenge with nickel speak in favour of a cross-reactivity mechanism.

Administration, Oral↗
PubMed1994

Metal release from high-copper amalgams containing palladium.

BACKGROUND: High-copper amalgam containing palladium has been successfully developed. However, the effect of palladium on the release of corrosion products remains unknown. We studied the effect of palladium addition on the electrochemical properties of amalgams by measuring the amount of the elements released from the experimental Pd-containing amalgams into Ringer's solution. METHODS: A series of specimens of high-copper amalgams containing different concentrations of palladium, from 0.42 w% to 3.33 w% in the final amalgam, fabricated from a blend of traditional amalgam alloy and copper-silver-palladium ternary alloy, were subjected to free corrosion in Ringer's solution at 37 degrees C for 3 months. Aliquots of 10 microL of electrolyte were removed serially with time, and the concentrations of Ag, Sn, Cu, Pd and Zn were evaluated by graphite furnace atomic absorption technique. In addition, dissolved Hg was evaluated by cold vapor atomic absorption technique in the same aliquotes. Various kinds of commercial amalgam including traditional (Spheraloy), high-copper blends (Dispersalloy and Valiant-Ph.D.) and high-copper spherical (Valiant) were employed as controls. RESULTS: Ag and Sn cations released from the amalgams containing palladium were similar in concentration to those released from the commercial amalgams. The concentrations of released Cu and Hg cations decreased as a function of increased Pd concentration in the experimental amalgams. Averaging an order of magnitude of released Cu and Hg cations less than commercial controls for amalgam containing 1.7 w% Pd. Detection of Pd was essentially below the resolution of the technique and Zn was only detected in case of Dispersalloy. CONCLUSIONS: Pd addition to high-copper amalgam alloy reduces the release of mercury and copper from the Pd-containing amalgam.

Copper↗
PubMed2003

Organometallic chemistry of azuliporphyrins: synthesis, spectroscopy, electrochemistry, and structural characterization of nickel(II), palladium(II), and platinum(II) complexes of azuliporphyrins.

Four azuliporphyrins, two meso-unsubstituted and two meso-tetraaryl substituted, were investigated in the synthesis of novel organometallic compounds. The meso-unsubstituted or "etio" series azuliporphyrins 8 reacted with nickel(II) acetate, palladium(II) acetate, and platinum(II) chloride in DMF to give the corresponding chelates 14-16, where the metal cation lies within the macrocyclic cavity and binds to all three nitrogens and the internal carbon atom. The newly available meso-tetraarylazuliporphyrins 13 similarly afforded the corresponding nickel(II), palladium(II), and platinum(II) complexes, 17-19, respectively. The new organometallic complexes are stable nonpolar compounds and were fully characterized spectroscopically and by mass spectrometry. The UV-vis data indicate that these complexes, in common with the parent azuliporphyrin system 8, do not possess porphyrin-type aromaticity. However, electron donation from the azulene unit can give rise to dipolar resonance contributors that provide a degree of carbaporphyrin-type aromatic character. The platinum(II) azuliporphyrins 16 gave noteworthy proton NMR spectra where the meso-protons showed satellite peaks due to transannular coupling to platinum-195. The pyrrolic protons of the platinum(II) meso-tetraarylazuliporphyrin 19b also showed similar satellite peaks due to coupling from the platinum-195 isotope. The electrochemistry of free base tetraphenylazuliporphyrin 13a and the related nickel(II) and palladium(II) complexes was investigated using cyclic voltammetry, and these data indicate that metal coordination improves the reversibility of the ligand-based oxidations. Nickel(II) azuliporphyrin 14a and palladium(II) tetrakis(4-chlorophenyl)azuliporphyrin 18b were also structurally characterized by X-ray crystallography. The macrocyclic core of the palladium(II) complex 18b was significantly more planar than the nickel(II) derivative 14b, and this difference was attributed to the better size match between the azuliporphyrin cavity and the larger palladium(II) ion. The straightforward synthesis of metalloazuliporphyrins under mild conditions, and their interesting spectroscopic, electrochemical, and structural features, demonstrates that the azuliporphyrin system holds great promise as a platform for organometallic chemistry.

Journal Article↗
PubMed2004

Palladium pincer complex-catalyzed trimethyltin substitution of functionalized propargylic substrates. An efficient route to propargyl- and allenyl-stannanes.

Palladium pincer complex-catalyzed reaction of functionalized propargyl chloride (and mesylate) derivatives with hexamethylditin gives allenyl- and propargyl-stannane products. This catalytic activity is in sharp contrast with the reactivity of commonly used palladium(0) catalysts inducing addition of hexamethylditin to the triple bond. The product distribution of the pincer complex-catalyzed reaction is controlled by the substituent effects of the propargylic substrate: electron-withdrawing functionalities give mainly allenyl stannane products, while with electron-donating groups the main product is propargyl stannane. The catalytic reaction proceeds under very mild conditions tolerating many functionalities such as OH, OAc, NR3, and NR2Ac groups. Our mechanistic studies indicate that the key intermediate of the reaction is a monotrimethylstannane palladium pincer complex. A remarkable feature of the studied catalytic process is that the palladium catalyst does not undergo redox reactions, but its oxidation state is restricted to palladium(II). Since palladium(0) intermediates does not occur in this process, the catalyst is very stable and highly chemoselective.

Journal Article↗
PubMed2001

Reaction of vinyl epoxides with palladium-switchable bisnucleophiles: synthesis of carbocycles.

The selective activation of substrates I, potential bisnucleophiles, was achieved by using different palladium catalysts. The synthetic potential of this strategy has been demonstrated in the regiodivergent synthesis of carbocycles from substrates of type I, bearing malonate-type pronucleophiles and an alkenyl stannane, with vinyl epoxides. A selective palladium-catalyzed reaction of I with the vinyl epoxide gives rise to an allylic alcohol, which, after activation as a carbonate, led to the cyclization product by a second palladium-catalyzed reaction. The transmetalation process is favored with palladium-catalysts without phosphines or arsines as the ligands. On the other hand, the use of palladium complexes with PPh3 as the ligand inhibits the transmetalation pathway and promotes the nucleophilic attack of the malonate-type anions on the intermediate (eta 3-allyl)-palladium complexes.

Journal Article↗
PubMed2005

The application of infrared spectroscopy to probe the surface morphology of alumina-supported palladium catalysts.

Five alumina-supported palladium catalysts have been prepared from a range of precursor compounds [palladium(II) nitrate, palladium(II) chloride, palladium(II) acetylacetonate, and tetraamminepalladium(II) tetraazidopalladate(II)] and at different metal loadings (1-7.3 wt %). Collectively, this series of catalysts provides a range of metal particle sizes (1.2-8.5 nm) that emphasize different morphological aspects of the palladium crystallites. The infrared spectra of chemisorbed CO applied under pulse-flow conditions reveal distinct groupings between metal crystallites dominated by low index planes and those that feature predominantly corner/edge atoms. Temperature-programmed infrared spectroscopy establishes that the linear CO band can be resolved into contributions from corner atoms and a combination of (111)(111) and (111)(100) particle edges. Propene hydrogenation has been used as a preliminary assessment of catalytic performance for the 1 wt % loaded catalysts, with the relative inactivity of the catalyst prepared from palladium(II) chloride attributed to a diminished hydrogen supply due to decoration of edge sites by chlorine originating from the preparative process. It is anticipated that refinements linking the vibrational spectrum of a probe molecule with surface structure and accessible adsorption sites for such a versatile catalytic substrate provide a platform against which structure/reactivity relationships can be usefully developed.

Journal Article↗
PubMed2005

Extraction mechanism for palladium(II) from hydrochloric acid solution with 2-dodecylthiomethylpyridine using a stirred transfer cell.

2-Dodecylthiomethylpyridine (DTP) was newly synthesized to study its extraction properties for precious metals. DTP was a selective extractant for palladium(II) and gold(III) over base metals. The loading test for palladium(II) showed that one palladium ion reacted with one molecule of DTP. The extraction rate of palladium with DTP was measured using a Lewis-type transfer cell at 303 K. The extraction reaction of palladium with DTP has been found to be a first order reaction with respect to palladium ion, DTP, and hydrogen ion concentrations. This reaction is inversely proportional to chloride ion concentration. The rate-determining step was the parallel reactions of DTP with PdCl3(-) and PdCl4(2-) in the aqueous phase.

Journal Article↗
PubMed1991

Palladium 103 ophthalmic plaque radiotherapy.

We compared the ocular radiation distribution of palladium 103 (103Pd) vs iodine 125 (125I) ophthalmic plaques sewn to 12 human donor eyes. We then performed preoperative comparative simulations on the first seven patients to be treated with palladium 103 plaque therapy for choroidal melanoma. The in vitro experiment involved palladium 103 seeds placed into a Silastic seed holder, which was affixed into standard 14-mm gold eye plaques. Then the plaques were sewn onto 12 human donor eyes so as to approximate either the nasal (six eyes) or temporal (six eyes) equator. Three sets of two thermoluminescent dosimeters were used to quantify the amount of radiation delivered by the episcleral plaques. Thermoluminescent dosimeters were sewn to the sclera in three locations: on the center of the cornea, on the sclera beneath the macula, and at the equator in a position opposite the plaque. This experiment was then repeated with iodine 125 seeds and thermoluminescent dosimeters. After the plaques were adjusted to equalize their activity (plaque strength), the palladium 103 plaques were found to deliver less radiation to the three target points. Comparative clinical dosimetry also reflected this difference. Preoperative simulations comparing equal doses to the tumors' apex revealed that the palladium 103 ophthalmic plaques delivered more radiation to the tumor and less radiation to most normal ocular structures.

Brachytherapy↗
PubMed2001

Mechanism of the Heck reaction using a phosphapalladacycle as the catalyst: classical versus palladium(IV) intermediates.

The mechanism of the (Mizoroki-)Heck vinylation of aryl bromides catalyzed by the phosphapalladacycle [[PdCH2C6H4P(o-Tol)2(OAc)]2] (1) was investigated in order to determine whether palladium(IV) intermediates play a significant role in the catalytic cycle. The phosphapalladacycle 1 was compared to the related palladium(0) catalyst [Pd[P(o-Tol)3]2] (2) and an intermediate of the classical catalytic cycle [[PdAr[P(o-Tol)3]Br]2] (3) obtained by oxidative addition of an aryl bromide to 2. Small, yet measurable deviations of the phosphapalladacycle 1 from the other catalysts 2 and 3 in the product distribution of styrene, in competition experiments of styrene and n-butyl acrylate, in the isotope effect on styrene, and the Hammett correlation on aryl bromides led to the conclusion that a different catalytic cycle is operative. Nevertheless, due to only small differences in these competition experiments a modified classical catalytic cycle with a novel, cyclometallated, anionic palladium(0) species 6 is proposed rather than palladium(IV) intermediates. Species 6 accounts for the observed high activity and stability of palladacycle catalysts in the Heck reaction. Palladium(IV) intermediates can be ruled out by taking into account the experiments performed here and recently published by others.

Alkenes↗
PubMedDate not supplied

Complexometric determination of palladium(II) using thioacetamide as a selective masking agent.

A simple, rapid and accurate complexometric method for the determination of palladium(II) is proposed, based on the selective masking property of thioacetamide towards palladium(II). In the presence of diverse metal ions, palladium(II) is complexed with excess of EDTA and the surplus EDTA is back titrated at pH 5-5.5 (acetic acid-sodium acetate buffer) with standard lead nitrate solution using xylenol orange as indicator. An excess of a 0.5% aqueous solution of thioacetamide is then added to displace EDTA from Pd(II)-EDTA complex. The released EDTA is titrated with the same standard lead nitrate solution as before. Reproducible and accurate results are obtained in the concentration range 0.5 mg - 17.80 mg of palladium with relative error of +/- 0.16% and coefficient of variation not exceeding 0.26%. The effect of diverse ions is studied. The method is used for the determination of palladium in its complexes, catalysts and synthetic alloy mixtures.

Alloys↗
PubMedDate not supplied

Simultaneous determination of palladium, platinum and rhodium by on-line column enrichment and HPLC with 5-(2,4-dihydroxyphenylazo)-rhodanine as pre-column derivatization reagent.

In this paper, a new method for the simultaneous determination of palladium, platinum and rhodium ions was developed using a rapid column high performance liquid chromatography equipped with on-line enrichment technique. The palladium, platinum and rhodium ions were pre-column derivatized with DHAR to form colored chelates. The Pb-DHAR, Pt-DHAR and Rh-DHAR chelates could be absorbed onto the front of the enrichment column when they were injected into the injector and sent to the enrichment column [ZORBAX Stable Bound, 4.6 x 10 mm, 1.8 microm] with a 0.05 mol L(-1) of phosphoric acid solution as mobile phase. After enrichment, and by switching the six ports switching valve, the retained chelates were back-flushed by mobile phase and traveling towards the analytical column. The separation of these chelates on the analytical column [ZORBAX Stable Bound, 4.6 x 50 mm, 1.8 microm] was satisfactory with 54% acetonitrile (containing 0.05 mol L(-1) of phosphoric acid and 0.1% of tritonX-100) as mobile phase. Palladium, platinum and rhodium were separated completely within 2 min. By on-line enrichment technique, the enrichment factor of 100 was achieved, and the detection limits (S/N = 3) of palladium, platinum and rhodium reaches 1.4 ng L(-1), 1.6 ng L(-1) and 2.0 ng L(-1), respectively. This method was applied to the determination of palladium, platinum and rhodium in water, urine and soil samples with good results.

Acetonitriles↗
PubMed1996

Cyto- and genotoxic effects of coordination complexes of platinum, palladium and rhodium in vitro.

The growing industrial use of platinum group elements as catalysts, especially in automobile exhaust detoxification (trimetal catalytic converters), is causing increasing occupational and environmental pollution. The cytotoxic and mutagenic properties of industrially used coordination complexes of platinum, palladium and rhodium were investigated using the neutral red cytotoxicity assay on two established cell lines and the Salmonella typhimurium/microsome test system (Ames test). Cytotoxic effects of the platinum complexes, measured as ED50, occurred at test concentrations of 0.2 mM. The analogous palladium salts tested were 3 times less toxic with ED50 being 0.6 mM, while the rhodium salts proved to be 30 times less toxic (ED50 = 6 mM). Levels of toxicity of the different complexes of a particular metal did not differ significantly from each other, which indicates that the metal itself is responsible for the toxic effects. In the Ames test, the spontaneous mutation rates increased by factors of 3 to 20 when the four tester strains were exposed to the platinum complexes. The analogous rhodium compounds proved to be considerably less mutagenic, and palladium demonstrated no mutagenic potential. As all of the four tester strains contain different mutations, the mutagenic potential of platinum and rhodium complexes appears to be based on a variety of mechanisms that damage DNA. From these in vitro experiments, it can be concluded that water-soluble complex salts of rhodium are less toxic and have a smaller mutagenic potential than the analogous platinum complexes. For palladium there is no evidence of any mutagenic property. From this point of view, the development of a catalytic converter containing predominantly palladium may be a possible means of minimizing potential health risks from this exhaust detoxification technique.

Animals↗
PubMed1992

Effects of palladium addition on properties of dental amalgams.

Palladium-containing amalgam alloys were developed utilizing the atomization method. Single-compositional type alloys were fabricated and palladium was substituted for silver in concentrations up to 5 w/o. Alloy powder with a particle size of less than 45 microns was collected and triturated with mercury. Creep, compressive strength and dimensional change tests were performed according to ADA Specification No. 1 along with controls of Tytin, Valiant and Valiant-Ph.D. Values for creep decreased and compressive strength increased markedly with additions of palladium. Current densities of the experimental amalgams containing palladium were determined to be an order of magnitude less than the original amalgams in the electrochemical test. A trend of positive relationships between properties and palladium additions was indicated.

Corrosion↗
PubMed2005

Simultaneous determination of palladium, platinum, rhodium and gold by on-line solid phase extraction and high performance liquid chromatography with 5-(2-hydroxy-5-nitrophenylazo)thiorhodanine as pre-column derivatization regents.

In this paper, 5-(2-hydroxy-5-nitrophenylazo)thiorhodanine (HNATR) was synthesized. A new method for the simultaneous determination of palladium, platinum, rhodium and gold ions as metal-HNATR chelates was developed using a rapid analysis column high performance liquid chromatography equipped with on-line solid phase extraction technique. The samples (Water, human urine, geological samples and soil) were digested by microwave acid-digestion. The palladium, platinum, rhodium and gold ions in the digested samples were pre-column derivatized with HNATR to form colored chelates. The Pd-HNATR, Pt-HNATR, Rh-HNATR and Au-HNATR chelates can be absorbed onto the front of the enrichment column when they were injected into the injector and sent to the enrichment column [Zorbax Stable Bound, 10 mm x 4.6 mm, 1.8 microm] with a buffer solution of 0.05 mol L(-1) phosphoric acid as mobile phase. After the enrichment had finished, by switching the six ports switching valve, the retained chelates were back-flushed by mobile phase and travelling towards the analytical column. These chelates separation on the analytical column [Zorbax Stable Bound, 10 mm x 4.6 mm, 1.8 microm] was satisfactory with 72% acetonitrile (containing 0.05 mol L(-1) of phosphoric acid and 0.1% of Triton X-100) as mobile phase. The palladium, platinum, rhodium and gold chelates were separated completely within 2.5 min. Compared to the routine chromatographic method, more then 80% of separation time was shortened. By on-line solid phase extraction system, a large volume of sample (10 mL) can be injected, and the sensitivity of the method was greatly improved. The detection limits (S/N=3, the sample injection volume is 10 mL) of palladium, platinum, rhodium and gold in the original samples reaches 1.4, 1.8, 2.0 and 1.2 ng L(-1), respectively. The relative standard deviations for five replicate samples were 2.4-3.6%. The standard recoveries were 88-95%. This method was applied to the determination of palladium, platinum, rhodium and gold in human urine, water and geological samples with good results.

Chromatography, High Pressure Liquid↗
PubMed2005

Gold and gold-palladium coated polypropylene grafts in a S. epidermidis wound infection model.

BACKGROUND: The use of non-absorbable mesh grafts in both abdominal wall defects and inguinal hernias are impossible in the presence of contamination. This study was conducted for evaluation of the efficiencies of polypropylene mesh grafts coated with gold and palladium-gold. MATERIALS AND METHODS: Ten piece of 1 x 2 cm of polypropylene mesh grafts were used in each group of naïve, gold-coated, and palladium-gold-coated. The grafts were incubated in physiological saline buffered and 0.5 McFarland slime positive Staphylococcus epidermidis for 24 h. At intervals of 6, 12, 24, 48, 72 h grafts were washed with saline and vortexed for 2 min in 2 ml of physiological saline. There were 100 microl of samples of vortexed material incubated in blood agar and 24 h later, colony numbers were assessed. In the second part of study, the grafts were implanted below the musculoaponeurotic layer at inguinal region of rats following the same procedure of incubation and washing. On the 8th day, the rats were examined for infection rate and their wound cultures were obtained. RESULTS: The least amount of bacterial growth was detected in the samples obtained from gold-palladium coated grafts; whereas the highest rate of growth was found in samples of naive grafts. The superficial surgical site infection rate was 0% in gold-palladium coated, 30% in gold-coated and 100% in naïve polypropylene group. The bacterial growth rate from wound cultures confirmed the superficial surgical site infection rates in all groups. CONCLUSION: Prosthetic graft infection with S. epidermidis can be prevented by coating the graft with gold-palladium or gold.

Abdominal Wall↗