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At least 469 records · Page 26Linked to original sources
PubMed2000

Dosimetric and volumetric criteria for selecting a source activity and a source type ((125)I or (103)Pd) in the presence of irregular seed placement in permanent prostate implants.

PURPOSE: The dosimetric merit of a permanent prostate implant relies on two factors: the quality of the plan itself, and the fidelity of its implementation. The former factor depends on source type and on source strength, while the latter is a combination of skill and experience. The purpose of this study is to offer criteria by which to select a source type ((125)I or (103)Pd) and activity. METHODS AND MATERIALS: Given a prescription dose and potential seed positions along needles, treatment plans were designed for a number of seed types and activities, specifically for (125)I with activities ranging from 0.3 to 0.7 mCi, and for (103)Pd with activities in the range of 0.8 to 1.6 mCi. To avoid human planner bias, an automated computerized planning system based on integer programming was used to obtain optimal seed configurations for each seed type and activity. To simulate the effect of seed-placement inaccuracies, random seed-displacement "errors" were generated for all plans. The displacement errors were assumed to be uniformly distributed within a cube with side equal to 2sigma. The resulting treatment plans were assessed using two volumetric and two dosimetric indices. RESULTS: For (125)I implants a coverage index (CI) of 98.5% or higher can be achieved for all activities (CI is the fraction of the target volume receiving the prescribed or larger dose). The external volume index (EI) (i.e., the amount of healthy tissue, as percentage of the target volume, receiving the prescribed or larger dose) increases from 13.9% to 20% as the activity increases from 0.3 to 0.7 mCi. For implants using (103)Pd, the external volume index increases from 10. 2% to 13.9% whenever CI exceeds 98.5%. Volumetric and dosimetric indices (coverage index, external volume index, D90, and D80) are all sensitive to seed displacement, although the activity dependence of these indices is more pronounced for (125)I than for (103)Pd implants. CONCLUSIONS: For both isotopes, the lower activities studied systematically result in lower EIs. If seeds can be placed within approximately 0.5 cm of their intended position (103)Pd should be preferred because its EI is lower than that of (125)I. For all activities the coverage indices and D90 are within the required range. If seed placement uncertainties are larger than 0.5 cm, (125)I provides slightly better target coverage; however, in terms of external volume (healthy tissue) covered, (103)Pd is superior to (125)I.

Brachytherapy↗
PubMed2004

Single-drop microextraction combined with low-temperature electrothermal vaporization ICPMS for the determination of trace Be, Co, Pd, and Cd in biological samples.

A new method of single-drop microextraction combined with low-temperature electrothermal vaporization (LTETV)-ICPMS was proposed for the determination of trace Be, Co, Pd, and Cd with benzoylacetone (BZA) as both extractant and chemical modifier. Several factors that influence the microextraction efficiency, such as sample flow rate, microdrop volume, and extraction time, were investigated and the optimized microextraction conditions were established. Be, Co, Pd, and Cd in the postextraction organic phase were directly determined by LTETV-ICPMS with the use of BZA as chemical modifier. The chemical modification of BZA in LTETV-ICPMS was studied, and the factors affecting the formation of chelates and vaporization/transportation of chelates were investigated. Under the optimized conditions, the detection limits of the method were 0.12, 0.99, 1.5, and 0.27 pg/mL for Be, Co, Pd, and Cd, and the relative standard deviations for 0.1 ng/mL Be, Co, Pd, and Cd were 16, 14, 14, and 11%, respectively. After 10 min of extraction, the enrichment factors were 160 (Be), 125 (Co), 40 (Pd), and 180 (Cd). The proposed method was applied to the determination of trace Be, Co, Pd, and Cd in biological reference materials, and the determined values were in good agreement with the certified values.

Beryllium↗
PubMed2004

Concentration and distribution of platinum group elements (Pt, Pd, Rh) in airborne particulate matter in Frankfurt am Main, Germany.

The concentrations and distribution of platinum group elements (Pt, Pd, Rh) in airborne particulate matter were studied in a period of one year from August 2001 to July 2002 in urban and in nonurban areas. Airborne dust samples were collected as a total amount (particles with an aerodynamic diameter <22 microm) and classified using an eight-stage Andersen impactor (<10 microm) at three locations with different traffic density roads in the Frankfurt am Main and nonurban areas. Sampling at the three locations was performed simultaneously for total airborne dust and fractionated airborne dust. Pd was determined by total reflection X-ray fluorescence after Hg coprecipitation. Pt and Rh were analyzed by adsorptive striping voltammetry after HPA digestion. The results show that the PGE concentrations in airborne samples depend on the traffic density. The highest PGE concentrations in air were found in the vicinity of major roads with heavy traffic, and the lowest ones were found in the nonurban area. The presence of PGE at the sampling station relatively free of traffic in a nonurban area hints to a transport of some of the emitted PGE from the city to this station by wind. At all three sampling locations, a heterogeneous distribution of the Pd, Pt, and Rh concentrations during the sampling year can be observed. The sum of PGE concentrations in total airborne dust is comparable with the sum of impactor samples. However, the concentration of Pt and Rh in total airborne dust (<22 microm) is on average higher than in impactor samples (<10 microm). On the contrary, Pd concentration is higher in impactor samples in most cases. The airborne PGE distribution is dominated by Pt, followed by Pd and Rh. The impactor samples are dominated by Pd, followed by Pt and Rh. This fact indicates that palladium occurs mainly in relatively fine airborne particles. The main fraction of PGE is found on average in particle sizes between 1.1 and 4.7 microm. Knowledge of the size distribution of particles containing PGE is important with respect to risk assessment of human inhalation.

Air Movements↗
PubMed2004

Stable, chloride-induced monohapto-bonding mode for an allyl ligand in a Pd(II) complex bearing a new bidentate phosphonite-oxazoline ligand.

Bidentate ligands can lead to stable eta(1)-allyl complexes of Pd(II). A novel chelating phosphonite-oxazoline P,N ligand, abbreviated NOPO(Me2), has been prepared by reaction of 6-chloro-6H-dibenz[c,e][1,2]oxaphosphorin with the lithium alcoholate derived from 4,4-dimethyl-2-(1-hydroxy-1-methylethyl)-4,5-dihydrooxazole. Its reaction with [Pd(eta(3)-C(3)H(5))(micro-Cl)](2) afforded the new eta(1)-allyl Pd complex [PdCl(eta(1)-C(3)H(5))(NOPO(Me2))] 2 in 91% yield. This constitutes a still rare example of structurally characterized eta(1)-allyl Pd(II) complex. Chloride abstraction led to the corresponding cationic eta(3)-allyl complex [Pd(eta(3)-C(3)H(5))(NOPO(Me2))]PF(6) 3, which has also been characterized by X-ray diffraction. CO insertion into the Pd-C sigma-bond of the eta(1)-allyl ligand of 2 afforded the corresponding 3-butenoyl palladium complex [PdCl[C(O)C(3)H(5)](NOPO(Me2))] 4 under mild conditions, which supports the view that CO insertion into eta(3)-allyl palladium cationic complexes occurs via first coordination of the counterion to form a more reactive eta(1)-allyl intermediate.

Journal Article↗
PubMed2004

Metal-metal bonded homo- and heterobimetallic compounds of Pt(I) and Pd(I) supported by a bridging-N,P:N',P' moiety of a potentially hexadentate ligand.

Reactions of metal-metal bonded homobimetallic (Pd(2)) and heterobimetallic (PtPd) complexes, supported by a P,P'-bridging-bis(P,N-chelating) coordination mode of the potentially hexadentate ligand 1,1-bis[di(o-N,N-dimethylanilinyl)phosphino]methane (dmapm), with CO, diethylacetylenedicarboxylate (DEAD), and thiols (RSH) in CH(2)Cl(2) are described. At room temperature, rac-Pd(2)Cl(2)(mu-N,P:P',N'-dmapm) gives the stable complexes Pd(2)Cl(2)(mu-CO)(2)(mu-P:P'-dmapm) and PdCl(eta2-DEAD)(mu-P:P',N-dmapm)PdCl (which is fluxional in solution), while rac-PtPdCl(2)(mu-N,P:P',N'-dmapm) disproportionates to PtCl(2)(P,P'-dmapm) and Pd metal, although at low temperature intermediate carbonyl species are detected in the CO reaction. The reactions with thiols in the presence of triflic acid (HOTf) generate rac-[MPdCl(2)(mu-SR)(mu-N,P:P',N'-dmapm)][OTf] and H(2) for both M = Pt and Pd. In CH(2)Cl(2), PdX(2)(dmapm) species (X = halide or CN) exist as equilibrium mixtures of P,P'- and P,N-ligated forms. For X = Cl, the P,P'-P,N equilibrium is governed by DeltaH degrees = -5.5 +/- 0.5 kJ mol(-1) and DeltaS degrees = 10 +/- 1 J mol(-1) K(-1), and the ring-strain energy within the P,P'-isomer is approximately 32 kJ mol(-1); the equilibrium increasingly favors the P,N-form with X = CN >> I > Br > Cl. The solid-state structures of rac-[PtPdCl(2)(mu-SEt)(mu-N,P:P',N'-dmapm)][OTf] and PdCl(2)(P,N-dmapm) are presented; the latter contains both bound and free N- and P-atoms of identical types in the same molecule and permits an assessment of sigma- and pi-bonding between these atoms and Pd.

Journal Article↗
PubMed2000

Synthesis and dehydrative condensation of square-planar mono- and dinuclear hydroxopalladium complexes with the hydrotris(3,5-diisopropylpyrazolyl)borato ligand (TpiPr2), TpiPr2(Py)Pd-OH, and (mu-OH)2[PdTpiPr2(H2O)]2.

Mono- and dinuclear hydroxopalladium complexes (kappa 2-TpiPr2,X)(py)Pd-OH (1; X = H, Br) and (mu-OH)2[Pd(kappa 2-TpiPr2)(H2O)]2 (2) are prepared by base hydrolysis of the corresponding chloride complexes (kappa 2-TpiPr2,X)(py)Pd-Cl (3) and (mu-Cl)2[Pd(kappa 3-TpiPr2)]2 (4), respectively. Functionalization of the OH part in 1 is effected via dehydrative condensation with protic substrates (H-A) to give a series of substituted products, (kappa 2-TpiPr)(py)Pd-A (5), and treatment of the dinuclear complex 2 with excess acetic acid affords the mononuclear diacetato complex 6, (kappa 2-TpiPr2-H)Pd(OAc)2(HOAc). Complexes 1-4 and 6 have been characterized crystallographically, and it is revealed that complexes 2 and 6 involve cyclic hydrogen-bonding interaction among the nitrogen atom of the pendent noncoordinated pyrazolyl group, the hydrogen atom in the protic part of the ligand (OH, AcOH), and, in the case of 2, an external water molecule.

Journal Article↗
PubMed2002

Mechanistic insights into the Pd(BINAP)-catalyzed amination of aryl bromides: kinetic studies under synthetically relevant conditions.

Kinetic studies using reaction calorimetry were carried out under synthetically relevant conditions to study the mechanism of the amination of bromobenzene with primary and secondary amines using Pd(2)(dba)(3)/BINAP mixtures as well as preformed (dba)Pd(BINAP), (p-tolyl)(Br)Pd(BINAP), and Pd(BINAP)(2) complexes. The presence of a significant induction period in the reaction was attributed to the slow activation of the catalytic precursor, resulting in an increase in the concentration of active species within the catalytic cycle. The induction period can mask the true kinetics of the reaction, which exhibits positive order dependences on aryl bromide and amine and zero-order dependence on base. It is also determined that the bis-ligand complex Pd(BINAP)(2) does not play a role directly on the catalytic cycle. In addition to the conventionally accepted pathway involving oxidative addition of the aryl halide to (BINAP)Pd as the first step, a pathway initiated by addition of the amine to the catalyst is proposed and supported by kinetic modeling of sequential reaction experiments. A subtle dependence of the reaction mechanism on the relative concentrations of substrates is revealed in these studies. The dependence of the catalyst resting state on reaction conditions is also discussed. This work suggests that conclusions from kinetic studies may be meaningful only for the conditions under which they are carried out, calling into question the use of conventional kinetic methods in this system.

Amination↗
PubMed2004

"Polysiloxane-Pd" nanocomposites as recyclable chemoselective hydrogenation catalysts.

Polysiloxane-encapsulated "Pd"-nanoclusters were generated by reduction of Pd(OAc)(2) with polymethylhydrosiloxane, which functions as a reducing agent as well as a capping material for production and stabilization of catalytically active "Pd"-nanoparticles. Chemoselective hydrogenation of functional conjugated alkenes was achieved by in-situ- or ex-situ-generated polysiloxane-stabilized "Pd"-nanoclusters under mild reaction conditions in high yields. Electron microscopy, UV-vis, and NMR studies of the reaction mixture during the catalytic transformation were performed and, in conjunction with catalyst poisoning experiments, demonstrated unequivocally the role of polysiloxane-encapsulated "Pd"-nanoclusters as the real catalytic species. The recyclability of the "Pd"-nanoclusters was established by reusing the solid left after the reaction.

Journal Article↗
PubMed2006

Influence of the hydroxylation of gamma-Al2O3 surfaces on the stability and diffusion of single Pd atoms: a DFT study.

Using recent well-defined models of gamma-Al2O3 surfaces, we study the interaction of single Pd atoms with gamma-Al2O3 surfaces corresponding to realistic pretreatment conditions by means of density functional theory periodic calculations. For relevant hydroxylation states of the surface, we determine potential energy surfaces (PES) that depict the relationship between structure and interaction at the metal-oxide interface. This approach enables the determination of the low-energy diffusion paths of the adsorbed Pd species. We applied classical transition-state theory to derive the temperature-dependent hopping rate of Pd on gamma-Al2O3 surfaces. Our work provides new insight into the chemisorption and diffusion process of single Pd atoms on alumina and show that the binding energy and hopping rate of Pd atoms decrease as the surface OH coverage increases. These results offer new highlights on Pd cluster formation at the initial nucleation steps on gamma-Al2O3 surfaces.

Journal Article↗
PubMed2006

Nanoscopic Pd line arrays using nanocontact printed dendrimers.

High-density Pd line arrays with 55 nm line-width were obtained using nanocontact-printed dendrimer monolayers. Elastomeric PDMS stamps for nanocontact printing were replicated from silicon master molds which were fabricated by UV nanoimprinting in combination with reactive ion etching. The fabrication method effectively controlled the aspect ratios of high-density lines for resolving the problems encountered in both replicating silicon masters to PDMS stamps and printing with the replicated PDMS stamps. Using the PDMS nanostamp with an optimized aspect ratio, a self-assembled monolayer of dendrimer was patterned on a Pd film via nanocontact printing, which was facilitated by the strong interaction between Pd and amine groups of the dendrimer. The patterned self-assembled monolayer was used as an etch-resist mask against the wet etchant of Pd, leaving behind a high-density Pd line array over large areas. The resulting functional Pd nanopattern is of practical significance in microelectronics and bio- or gas-sensing devices.

Journal Article↗
PubMed2006

Characterization of Pd-Cu alloy nanoparticles on gamma-Al2O3-supported catalysts.

Cu-Pd/Al2O3 bimetallic catalysts have been characterized by XRD, TEM, and EDX techniques. The surface structure has been investigated by FT-IR spectroscopy of low-temperature adsorbed CO in the reduced and in the oxidized state. Evidence has been provided of the formation of Cu-Pd alloy nanoparticles, both of the alpha-phase (disordered fcc) and of the beta-phase (ordered CsCl-type). IR spectra suggest that Cu likely decorates the edges while Pd mostly stays at the main faces. Part of copper disperses as Cu+ on the support even after reduction. The presence of copper seems to modify strongly the sate of oxidized Pd centers in oxidized high-Pd content materials. The redox chemistry of the system, where Pd is reduced more easily than Cu, appears to be very complex.

Journal Article↗
PubMed2005

Enhanced gas sensing by individual SnO2 nanowires and nanobelts functionalized with Pd catalyst particles.

The sensing ability of individual SnO(2) nanowires and nanobelts configured as gas sensors was measured before and after functionalization with Pd catalyst particles. In situ deposition of Pd in the same reaction chamber in which the sensing measurements were carried out ensured that the observed modification in behavior was due to the Pd functionalization rather than the variation in properties from one nanowire to another. Changes in the conductance in the early stages of metal deposition (i.e., before metal percolation) indicated that the Pd nanoparticles on the nanowire surface created Schottky barrier-type junctions resulting in the formation of electron depletion regions within the nanowire, constricting the effective conduction channel and reducing the conductance. Pd-functionalized nanostructures exhibited a dramatic improvement in sensitivity toward oxygen and hydrogen due to the enhanced catalytic dissociation of the molecular adsorbate on the Pd nanoparticle surfaces and the subsequent diffusion of the resultant atomic species to the oxide surface.

Journal Article↗
PubMed2002

Asymmetric activation of the Pd catalyst bearing the tropos biphenylphosphine (BIPHEP) ligand with the chiral diaminobinaphthyl (DABN) activator.

[reaction: see text] The enantio- and diastereomerically pure Pd complex of the tropos biphenylphosphine (BIPHEP) ligand is obtained through complexation of the enantiopure (R)-diaminobinaphthyl (DABN) with either enantiomer of the BIPHEP-Pd catalyst, followed by tropo-inversion of the less favorable (S)-BIPHEP-Pd/(R)-DABN diastereomer to the more favorable (R)-BIPHEP-Pd/(R)-DABN diastereomer. The enantiopure BIPHEP-Pd catalyst with DABN affords higher enantioselectivity and catalytic efficiency as an activated Lewis acid catalyst than the enantiopure BIPHEP-Pd catalyst without DABN.

Journal Article↗
PubMed2001

Which is a less invasive pancreatic head resection: PD, PPPD, or DPPHR?

Less invasive pancreatic head resection, such as pylorus preserving pancreatoduodenectomy (PPPD) and duodenum preserving pancreatic head resection (DPPHR) has been introduced for the treatment of pancreatoduodenal lesions, especially for benign conditions, in consideration of postoperative quality of life. Surgical stress and exocrine and endocrine function of the residual pancreas were examined in 44 patients with PPPD, 10 with conventional pancreatoduodenectomy (PD) and six with DPPHR. Clinical findings including serum levels of C reactive protein (CRP), fasting blood sugar, a 120-min value of the 75-g oral glucose tolerance test (OGTT), N-benzol-L-tyrosyl-p-aminobenzoic acid (BT-PABA) excretion value (a pancreatic exocrine function test), and volume of postoperative pancreatic juice drainage were compared among the three different variants of pancreatectomy. Operation time and operative blood loss in PD were largest of the three, followed by PPPD and DPPHR. Postoperative elevation of serum CRP on postoperative day (POD) 2 or 3 was similar among the three different types of operation. Fasting blood sugar concentrations were not different among the three groups at short- and long-term after the operation, while the 120-min value of the GTT showed a marked elevation at long-term only after PPPD. The volume of pancreatic juice drainage increased up to POD 4 and became constant thereafter. The total amount of pancreatic juice drainage from POD 4 to 13 was smallest in PD (637 ml) followed by PPPD (1,255 ml) and DPPHR (1,431 ml). The BT-PABA value declined after PD (-20.3%, P = 0.0437) and PPPD (-20.2%, P = 0.0239) at short term, but not after DPPHR (8.2%). These findings suggest that the early impairment of the pancreatic exocrine function after PD and PPPD but not after DPPHR may indicate that the invasiveness of pancreatic head resection to the pancreatic functions is greater in PD and PPPD than in DPPHR.

4-Aminobenzoic Acid↗
PubMed2005

Pyridine-2-thionate as a versatile ligand in Pd(II) and Pt(II) chemistry: the presence of three different co-ordination modes in [Pd2(micro2-S,N-C5H4SN)(micro2-kappa2S-C5H4SN)(micro2-dppm)(S-C5H4SN)2].

Reactions of [MCl2(L-L)], M = Pt, Pd; L-L = bis(diphenylphosphino)methane (dppm) or bis(diphenylphosphino)ethane (dppe), with NaC5H4SN in a 1 : 2 molar ratio lead to mononuclear species [M(S-C5H4SN)2(P-P)], M = Pt; L-L = dppm (1) or dppe (2) and M = Pd; L-L = dppe (3), as well as to the dinuclear [Pd2(micro2-S,N-C5H4SN)(micro2-kappa2S-C5H4SN)(micro2-dppm)(S-C5H4SN)2] (4). In contrast, reaction of [MCl2(dppm)] with NaC5H4SN in a 1 : 1 molar ratio leads to [Pd2(micro2-S,N-C5H4SN)3(micro2-dppm)]Cl (5) and trans-[Pt(S-C5H4SN)2(PPh2Me)2] (6) respectively. The latter is formed in low yield by cleavage of the dppm ligand. The dinuclear derivatives 4 and 5 present an A-frame and lantern structure, respectively. The former showing three different co-ordination modes in the same molecule with a short Pd-Pd distance of 2.9583 (9) A and the latter with three bridging S,N thionate ligands showing a shorter Pd-Pd distance of 2.7291 (13) A. Both distances could be imposed by the bridging ligands or point to some sort of metal-metal interaction.

Journal Article↗
PubMed2006

In-situ UV-visible study of Pd nanocluster formation in solution.

The formation of Pd nanoclusters in solution is studied. This system has two types of light-absorbing species: Pd ions which absorb light via electronic transitions and Pd clusters and aggregates which absorb light via valence-conduction transitions and also scatter light due to their nanometric dimensions. Here we monitor these dynamic changes using UV-visible spectroscopy. The reduction and clustering concentration profiles are extracted from the raw data using a combination of net analyte signal (NAS) and principal component analysis (PCA) methods. PdCl2, Pd(OAc)2 and Pd(NO3)2 are used as Pd2+ precursors and various tetra-n-octylammonium carboxylates are applied as reducing and stabilising agents. This in situ approach enables the quantification of both the reduction of the Pd2+ ions and the growth of the Pd clusters. Kinetic models that account for ion reduction, cluster growth and aggregation are presented and the influence of the counteranions and the reducing agents on these processes is discussed.

Acetates↗
PubMed1985

[Retinal findings in the hereditary persistence of fetal hemoglobin and glucose-6-phosphate dehydrogenase deficiency (G-6-PD deficiency)].

Peripheral arteriolar occlusions of the retinal vessels and the 'black sunburst sign' as the first stage of sickle-cell retinopathy (Goldberg 1976) were found in a 34-year-old black patient from West Africa with hereditary persistence of fetal hemoglobin (HPFH) and glucose-6-phosphate dehydrogenase deficiency (G-6-PD-D). The patient's son was found to have HPFH without G-6-PD-D, his daughter HPFH as well as G-6-PD-D. Ophthalmoscopic findings in the two children were normal. In the mother - a white German without clinical symptoms - neither HPFH nor G-6-PD-D were found. This is the first description of the typical picture of 'sickle-cell retinopathy' in a patient with HPFH combined with G-6-PD-D. HPFH is not associated with any retinal symptoms or hematological abnormalities. Hemolytic crises induced by fava beans or drugs in G-6-PD-D alone lead to different ocular complications from those found in this patient.

Adult↗
PubMed2005

Rotationally inelastic scattering of HD from Cu(100) and Pd(111).

Rotational excitation of HD scattered from Cu(100), Pd(111), and Pd(111):H(D) was measured using molecular beam and quantum-state-specific laser spectroscopy techniques. Greater than 91% of the incident HD population was in the v = 0, J = 0 state. The final rotational distributions from Cu(100), Pd(111), and Pd(111):H(D) were compared for a HD beam at an incident energy of 74 meV. For all the three surfaces studied, rotationally inelastic scattering probabilities were large. We find that the final HD rotational distributions are remarkably similar for the three surfaces even though Pd(111) is very reactive to dissociative adsorption of HD whereas Cu(100) and Pd(111):H(D) are chemically inert.

Journal Article↗