Number Of Pt Atoms Research Articles

Diameter effect of electrospun carbon fiber support for the catalysis of Pt nanoparticles in glucose oxidation

Electrospun carbon fibers (CFs) with diameters of 39nm (CF39nm), 158nm (CF158nm), and 309nm (CF309nm) were used as Pt-catalyst supports for a glucose oxidation reaction. Based on experimentally balanced comparisons using electrochemical methods, CF39nm with higher curvature and smaller diameter had a greater number of Pt atoms on the surface. Compared with the CF158nm and CF309nm systems, CF39nm has a higher electrochemically real surface area and greater catalytic activity on glucose oxidation. The Tafel analyses demonstrated that the exchange current density from an early rest potential (−0.81V) for the CF39nm system was 9.08×10−3mAcm−2, greater than 8.41×10−3mAcm−2 for CF158nm-supported Pt nanoparticles and 7.39×10−3mAcm−2 for CF309nm-supported Pt nanoparticles. In addition, as data supporting the catalytic characterization for glucose oxidation, all of the CF-supported Pt nanoparticles showed remarkable tolerance to foreign substances in the application of a non-enzymatic glucose sensor, where CF39nm-supported Pt nanoparticles (Pt/CF39nm) showed a higher sensitivity (2.03μAmM−1cm−2), detection limit (33μM), and linear range (0.3–17mM). The high recovery by serum sample analyses further confirmed the potential of Pt/CF39nm as a glucose sensor. The promising results showed the feasibility of these electrospun CFs being applied for both glucose fuel cells and non-enzymatic glucose sensors.

Complex magnetic structure of clusters and chains of Ni and Fe on Pt(111)

We present an approach to control the magnetic structure of adatoms adsorbed on a substrate having a high magnetic susceptibility. Using finite Ni-Pt and Fe-Pt nanowires and nanostructures on Pt(111) surfaces, our ab initio results show that it is possible to tune the exchange interaction and magnetic configuration of magnetic adatoms (Fe or Ni) by introducing different numbers of Pt atoms to link them, or by including edge effects. The exchange interaction between Ni (or Fe) adatoms on Pt(111) can be considerably increased by introducing Pt chains to link them. The magnetic ordering can be regulated allowing for ferromagnetic or antiferromagnetic configurations. Noncollinear magnetic alignments can also be stabilized by changing the number of Pt-mediated atoms. An Fe-Pt triangularly-shaped nanostructure adsorbed on Pt(111) shows the most complex magnetic structure of the systems considered here: a spin-spiral type of magnetic order that changes its propagation direction at the triangle vertices.

Dendrimer Encapsulated Pt Nanoparticle-Immobilized Glassy Carbon Electrode with High Electrocatalytic Redox Activity to Hydrogen Peroxide and Its Application for Biosensing

Dendrimers, which are highly-branched monodisperse macromolecules with well-defined size, shape, and surface functionality, have been widely used in the modification of electrode surfaces due to their good biocompatibility and adequate functional groups. The intriguing properties of dendrimers allow the dendrimer-coated surfaces to be utilized in a variety of fundamental and applied researches. For example, the use of dendrimers has been proposed for the design of microarray chips because dendrimer-immobilized surfaces provide a unique three-dimensional architecture with flexible branched arms connected to numerous functional groups. This allows for the effective immobilization of biomolecules with a high density as well as minimization of biomolecule denature. In addition, dendrimer-immobilized surfaces have been proven to be useful in improving sensitivity as well as selectivity for biosensing applications. Recently, we also reported facile surface modification of carbon-based materials with amine-terminated dendrimers and its applications to construct catalytic bifunctional surfaces for electrochemical reactions of chemicals such as hydrazine and oxygen. Here, we report the electrochemical modification of glassy carbon electrodes (GCEs) via electrooxidative coupling of the dendrimers encapsulating electrocatalytic Pt nanoparticles and the promising potential of the resulting dendrimer encapsulated Pt nanoparticle-decorated GCEs as biosensing platforms. Since Pt nanoparticles were encapsulated inside the cores of dendrimers, the electrooxidative coupling of the dendrimers onto GCEs resulted in modification of GCEs with the catalytic Pt nanoparticles. As illustrated in Scheme 1, we synthesized dendrimer encapsulated Pt nanoparticles (Pt DENs, diameter 2.1 ± 0.3 nm) using amine-terminated sixth-generation polyamidoamine (G6-NH2 PAMAM) dendrimers and immobilized the Pt DENs on GCEs via electrooxidative coupling of the terminal amino groups of dendrimers. The resulting Pt DEN-immobilized GCEs showed much higher electrocatalytic activity toward redox reactions of H2O2 than that shown by bare GCEs. The enhanced electrocatalytic activity of Pt DEN-decorated GCEs was further applied to glucose sensing. Figure 1 shows a TEM image and a corresponding histogram of the particle size distribution of the as-synthesized Pt DENs denoted as G6-NH2(Pt250), where the numerical subscript of Pt represents the original PtCl4 :G6-NH2 ratio used for the synthesis and thus the average number of Pt atoms in each dendrimer. The Pt nanoparticles were found to be nearly monodispersed in size and rarely aggregated due to stabilization of the nanoparticles via their encapsulation inside the dendrimers (Figure 1). The measured average diameter (2.1 ± 0.3 nm) of the Pt DENs was slightly larger than the theoretical value (1.9 nm) for nanoparticles containing 250 Pt atoms (Figure 1, inset), which is presumably

Theoretical Studies of the Electronic Structures and Spectrum Properties of Pt n Ni m (n + m = 7, n, m ≠ 0) Clusters

We studied PtnNim (n + m = 7, n, m ≠ 0) clusters within the framework of the density functional theory (B3LYP) at the LANL2DZ level. The calculated results show that the Fermi levels are determined by the number of Pt atoms, which gain electrons from Ni atoms. Meanwhile, multifarious orbital hybridization is found in the frontier molecular orbital, and the more platinum or nickel atoms, the smaller energy gap it has. Moreover, the calculated IR and Raman spectrum indicates the aromatic character, which is vital for transitional metal clusters.

Supported Noble Metals on Hydrogen‐Treated TiO2 Nanotube Arrays as Highly Ordered Electrodes for Fuel Cells

Hydrogen-treated TiO2 nanotube (H-TNT) arrays serve as highly ordered nanostructured electrode supports, which are able to significantly improve the electrochemical performance and durability of fuel cells. The electrical conductivity of H-TNTs increases by approximately one order of magnitude in comparison to air-treated TNTs. The increase in the number of oxygen vacancies and hydroxyl groups on the H-TNTs help to anchor a greater number of Pt atoms during Pt electrodeposition. The H-TNTs are pretreated by using a successive ion adsorption and reaction (SIAR) method that enhances the loading and dispersion of Pt catalysts when electrodeposited. In the SIAR method a Pd activator can be used to provide uniform nucleation sites for Pt and leads to increased Pt loading on the H-TNTs. Furthermore, fabricated Pt nanoparticles with a diameter of 3.4 nm are located uniformly around the pretreated H-TNT support. The as-prepared and highly ordered electrodes exhibit excellent stability during accelerated durability tests, particularly for the H-TNT-loaded Pt catalysts that have been annealed in ultrahigh purity H2 for a second time. There is minimal decrease in the electrochemical surface area of the as-prepared electrode after 1000 cycles compared to a 68 % decrease for the commercial JM 20 % Pt/C electrode after 800 cycles. X-ray photoelectron spectroscopy shows that after the H-TNT-loaded Pt catalysts are annealed in H2 for the second time, the strong metal-support interaction between the H-TNTs and the Pt catalysts enhances the electrochemical stability of the electrodes. Fuel-cell testing shows that the power density reaches a maximum of 500 mWcm(-2) when this highly ordered electrode is used as the anode. When used as the cathode in a fuel cell with extra-low Pt loading, the new electrode generates a specific power density of 2.68 kWg(Pt) (-1) . It is indicated that H-TNT arrays, which have highly ordered nanostructures, could be used as ordered electrode supports.

Characterisation of platinum-based fuel cell catalyst materials using 195Pt wideline solid state NMR

This study demonstrates the utility of the novel Field Sweep Fourier Transform (FSFT) method for acquiring wideline (195)Pt NMR data from various sized Pt nanoparticles, Pt-Sn intermetallics/bimetallics used to catalyse oxidative processes in fuel cell applications, and various other related Pt3X alloys (X = Al, Sc, Nb, Ti, Hf and Zr) which can facilitate oxygen reduction catalysis. The (195)Pt and (119)Sn NMR lineshapes measured from the PtSn intermetallic and Pt3Sn bimetallic systems suggest that these are more ordered than other closely related bimetallic alloys; this observation is supported by other characterisation techniques such as XRD. From these reconstructed spectra the mean number of atoms in a Pt nanoparticle can be accurately determined, along with detailed information regarding the number of atoms present effectively in each layer from the surface. This can be compared with theoretical predictions of the number of Pt atoms in these various layers for cubo-octahedral nanoparticles, thereby providing an estimate of the particle size. A comparison of the common NMR techniques used to acquire wideline data from the I = 1/2 (195)Pt nucleus illustrates the advantages of the automated FSFT technique over the Spin Echo Height Spectroscopy (SEHS) (or Spin Echo Integration Spectroscopy (SEIS)) approach that dominates the literature in this area of study. This work also presents the first (195)Pt NMR characterisation of novel small Pt13 nanoclusters which are diamagnetic and thus devoid of metallic character. This unique system provides a direct measure of an isotropic chemical shift for these Pt nanoparticles and affords a better basis for determining the actual Knight shift when compared to referencing against the primary IUPAC shift standard (1.2 M Na2PtCl6(aq)) which has a very different local chemical environment.

Spin polarizedI-Vcharacteristics and shot noise of Pt atomic wires

We report a first-principles investigation of spin polarized transport properties of Pt atomic chains in contact with two semi-infinite Pt slabs along the (111) direction. Our approach is based on the nonequilibrium Green's function coupled with density functional theory so that the Coulomb interaction is included in the calculation of current and shot noise on the Hartree level. For Pt atomic chains with different numbers of Pt atoms, we calculate the spin polarized I-V curve and shot noise. Our results show that the current increases almost linearly with bias for all Pt atomic structures. The calculated Fano factors are comparable to the recent experimental data and show sub-Poissonian behavior.

Potential Energy Surfaces for Oxygen Adsorption, Dissociation, and Diffusion at the Pt(321) Surface

We report a first-principles, periodic supercell analysis of oxygen adsorption, diffusion, and dissociation at the kinked Pt(321) surface. Binding energies and binding site preferences of isolated oxygen atoms and molecules have been determined, and we show that both atomic and molecular oxygen prefer binding in bridge sites involving coordinatively unsaturated kink Pt atoms. Binding energies of atomic and molecular oxygen in different sites correlate well with the average metallic Pt coordination number of Pt atoms forming each site, although differences exist between adsorbates in symmetrically similar sites due to the inherent chirality of the surface. Atomic O in the strongest binding bridge sites experiences relatively small energy barriers for diffusion to neighboring sites compared to O on Pt(111). However, due to the structure of the surface, O diffusion is only rapid between different sites around the kink Pt atom, whereas the effective long-range tracer diffusion, as determined from a simple course-grain model, is shown to be anisotropic and slower than on the Pt(111) surface. Four dissociation pathways for O(2) at low coverage are also reported and found to be in agreement with experimental observations of facile dissociation, even at low temperature.

Adsorption and Migration of Pt Atoms on <em>γ</em>-Al<sub>2</sub>O<sub>3</sub>(001) Surface

We present a systematic study using density functional theory (DFT) with the generalized gradient approximation (GGA) method to understand the adsorption and migration of Pt atoms on the γ-Al2O3(001) surface. Energetically the most favorable adsorption sites were identified and all these adsorption configurations were found to show substantial structural relaxation. Our calculated adsorption and energy barrier of migration results indicate that the Pt clusters can be stably anchored onto the surface. A significantly higher adsorption energy at the O site is largely attributed to the fact that charge transfer from Pt to O atoms results in positively charged Pt atoms. The repulsion between Pt and Al atoms leads to much weaker bonds. The calculated average adsorption energies were found to be size and shape dependent and in general decrease as the number of Pt atoms increases. The highest energy barrier for Pt atom migration on the γ-Al2O3(001) surface is about 0.51 eV. The formation of a metal cluster would be strongly preferred upon high Pt atom loading. Consequently, the evolution of Pt atoms on the γ-Al2O3(001) surface is unlikely to be smooth and agglomeration can occur under certain conditions.

Dependence of low-potential CO electrooxidation on the number of Pt monolayers on gold

Abstract The Pt–CO system is the only one in which a mere change of the potential at which the electrode is held while the compound to be oxidized is introduced in the cell dramatically affects the activity of the electrode. So, if the Pt electrode is held at a potential in the hydrogen region while CO is bubbled in the electrolyte, electrooxidation of dissolved CO occurs at a potential of 0.6 V vs the relative hydrogen electrode, which is considerably lower than the usual one of 0.9 V at which CO is oxidized when bubbled at open circuit. We have studied the dependence of this unique phenomenon on the number of Pt monolayers (MLs) deposited on Au. The peak potential in CVs of CO-stripping decreased with increasing number of Pt MLs, showing an increasing activity of the Pt film for CO oxidation. This is in agreement with the d-band model of Norskov, which predicts that CO binds more strongly to a Pt ML on Au than to bulk Pt. Other contributing factor to the increasing activity of the Pt film with increasing number of Pt MLs is the increasing number of Pt atoms in step and kink positions, known to be active centres for the oxidation of both adsorbed and dissolved CO. This second factor is inferred from the monotonic increase of the hydrogen charge, which indicates that the second and successive MLs become increasingly rougher. As for the electrooxidation at low potentials of dissolved CO, it was completely absent with one Pt ML, and progressively emerged with increasing number of Pt MLs, a well-defined peak appearing with four MLs. The parallel evolution of the peak of dissolved CO oxidation and of the pre-peak in CO-stripping CVs confirms that dissolved CO oxidation takes place only on those Pt atoms that have become free of adsorbed CO by its oxidation in the pre-peak.

Quantitative analysis of Pt–PAMAM ligand exchange reactions: Time and concentration effects

The goal of this work is to quantitatively evaluate the extent of Pt–PAMAM complexation for conditions used in practice to prepare PAMAM-stabilized Pt nanoparticles for catalysis applications. UV–visible spectrophotometry (UV–vis), atomic absorption (AA) spectroscopy, and ion chromatography (IC) are used to monitor the progress of ligand exchange reactions between PtCl 4 2− and G4OH PAMAM dendrimers. A specific objective was to quantify the fraction of Pt that covalently binds with PAMAM as a function of time, nominal Pt:PAMAM ratio, and PAMAM concentration. UV–vis and IC results show that ligand exchange reactions between PtCl 4 2− and G4OH continue to produce new Pt–PAMAM bonds and release chloride ions over periods as long as 3 months. The overall kinetics of ligand exchange follows a log(time) dependence. Dialysis of G4OH–(Pt 2+) n solutions followed by AA analysis shows that fractional covalent binding is greater than 90% for n < 30. Fractional binding decreases significantly for n > 40, showing that the actual number of Pt atoms that are irreversibly, covalently bound by G4OH is less than the nominal Pt:G4OH ratio ( n). Incomplete binding leaves free, aquated Pt complexes in solution that may impact subsequent reduction and nanoparticle formation. We show that the 250 nm peak absorbance due to ligand-to-metal charge transfer (LMCT) increases non-linearly with the bound Pt:G4OH ratio. We speculate that the change in the extinction coefficient may be due to a graduate transition from multidentate to monodentate complexation as the bound Pt:G4OH ratio increases.

Structures of Pt clusters on graphene by first-principles calculations

The interactions between Pt n clusters ( n ⩽ 13 ) and a graphene sheet have been investigated by first-principles calculations based on density functional theory. For single Pt-atom and Pt 2 -dimer adsorptions, the stable adsorption sites are bridge sites between neighboring carbon atoms. When the number of Pt atoms in a cluster increases, the Pt–C interaction energy per contacting Pt atom becomes smaller. For smaller clusters ( 3 ⩽ n ⩽ 7 ) , the adsorption as a vertical planar cluster is more stable than that as parallel planar or three-dimensional (3D) clusters, due to the stability of a planar configuration itself and the stronger planar-edge/graphene interaction, while the adsorption as a parallel planer cluster becomes stable for larger cluster ( n ⩾ 7 ) via the deformation of the planar configuration so as to attain the planar-edge/graphene contact. For much larger clusters ( n ⩾ 10 ) , the adsorption as a 3D cluster becomes the most stable due to the stability of the 3D configuration itself as well as substantial Pt–C interactions of edge or corner Pt atoms. The interfacial interaction between a Pt cluster and graphene seriously depends on the shape and size of a cluster and the manner of contact on a graphene sheet.

Simulation of growth process of Pt-particles - first-principles calculations

First-principles calculations have been applied to investigate the interactions between Ptn (n = 1 ~ 4) clusters and a graphene sheet as models of Pt/C fuel-cell catalytic electrodes. A Pt atom is stably adsorbed on the bridge site between two carbon atoms with the adsorption energy of about 2eV. For the case of Pt2, both of the Pt atoms are adsorbed on the bridge site. For the case of Pt3, the triangular cluster is more stable than the linear cluster. For the case of Pt4, the tetrahedral cluster is more stable than the planar cluster. The adsorption energies on the surface without defects are 0.55 eV/adatom for Pt2 and 0.05 eV/adatom for Pt3. The interaction energy between the Pt cluster and the graphite surface per Pt atom becomes weaker as the number of Pt atoms increases. The adsorption energy for a Pt atom on the vacant site is 8.00 eV/adatom, which is stronger than the formation energy of a Pt-Pt bond (about 2 eV/bond) for small clusters.

2 Dimensional Dendrites and 3 Dimensional Growth of Electrodeposited Platinum Nanoparticles

Platinum (Pt) nanoparticles are of particular interest as catalysts or electrocatalysts in the electrochemical reduction of oxygen. The morphology of Pt nanoparticles is correlated to their catalytic activity. A mechanism for heteroepitaxial Pt particle dendrite formation (2D growth) and coalescence (3D growth) on highly ordered pyrolytic graphite (HOPG) was observed. The mechanism of 2D dendrite growth, which appeared to be the dominant mechanism at low ionic concentration, was similar to colloidal aggregation, while 3D growth occurred at a high ionic concentration. With increasing number of Pt atoms in a cluster, the simulated interaction energy between the Pt cluster and HOPG substrate decreases. The DLVO theory gives some insight into two different growth mechanisms. The energy barrier between coalescing particles decreases with increasing concentration of electrolytes. Various morphologies of Pt electrodeposition on HOPG were suggested based on the competition between 3D growth and 2D particle growth.

Cell-killing efficiency and number of platinum atoms binding to DNA, RNA, and protein molecules of HeLa cells treated with combinations of hyperthermia and cis-diamine(glycolato)platinum(II).

HeLa S-3 cells were treated with 195mPt-radiolabeled cis-diamine(glylato)platinum(II) (254-S) for 60 min at various temperatures, and the relationship between the lethal effect and the number of Pt atoms binding to DNA, RNA, and proteins was examined. The mean lethal concentration (D0) of 254-S for a 60-min treatment at 0 degree C, 25 degrees C, 37 degrees C, 40 degrees C, 42 degrees C, and 44 degrees C was 233, 132, 61.1, 42.7, 25.6, and 9.9 microM, respectively. By using identically treated cells, the numbers of Pt atoms combined with DNA, RNA, and protein molecules were determined in the subcellular fractions. Thus, the D0 values given as drug concentrations were replaced with the number of Pt atoms combined in each fraction. The, the cell-killing efficiency of the Pt atom was expressed as the reciprocal of the number of Pt atoms combined and was calculated for each molecule. The efficiency for the DNA molecule was 0.61 x 10(4), 1.09 x 10(4), 1.88 x 10(4), 1.90 x 10(4), 2.66 x 10(4), and 5.88 x 10(4) nucleotides, respectively, for the conditions described. From 0 degree C to 44 degrees C, the cell-killing efficiency of Pt atoms increased by a factor of 9.6.

Cell-killing efficiency and number of platinum atoms binding to DNA, RNA and protein molecules of HeLa cells treated with combinations of hyperthermia and carboplatin

The effect of hyperthermia on the cell killing efficiency of Pt atoms binding to DNA, RNA and protein molecules of HeLa cells treated withcis-diamine(1,1-cyclobutanedicarboxylato)platinum(II) (CBDCA) was examined. HeLa S-3 cells were treated with195mPt-radiolabeled CBDCA for 60 minutes at various temperatures, and the relationship between the lethal effect and the number of Pt atoms binding to DNA, RNA and proteins was examined. The mean lethal concentration (D0) of carboplatin for a 60 min-treatment at 0, 25, 37, 40, 42 and 44°C was 671.2, 201.5, 67.3, 33.4, 20.2 and 15.6 μM, respectively. By using identically treated cells, the number of Pt-atoms combined with DNA, RNA and protein molecules were determined in the subcellular fractions. Thus, the D0's given as the drug concentrations were replaced with the number of Pt-atoms combined in each fraction. Then, the cell-killing efficiency of the Pt atom was expressed as the reciprocal of the number of Pt-atoms combined and was calculated for each molecule. The efficiency for DNA molecules was 0.699, 1.42, 2.65, 4.84, 7.74 and 8.28·104 nucleotides, respectively, for the conditions described above. From 0 to 44°C, the cell-killing efficiency of Pt atoms increased by a factor of 11.9.

Cell-killing efficiency and number of platinum atoms binding to DNA, RNA and protein molecules of HeLa cells treated with combinations of trans-diaminedichloroplatinum(II) and hyperthermia.

The effect of hyperthermia on the cell‐killing efficiency of Pt atoms binding to DNA, RNA and protein molecules was examined. HeLa S‐3 cells were treated with 195mPt‐radiolabeled trans‐diaminedichloro‐platinum(II) (TDDP) for 60 min at various temperatures, and the relationship between the lethal effect and the number of Pt atoms binding to DNA, RNA and proteins was examined. The mean lethal concentration (D0) of TDDP for a 60‐min treatment at 0, 25, 37, 40, 42 and 44°C was 1714,1016, 302, 179,125 and 42.5 μM, respectively. (D0 is defined as the dose that would give an average of one lethal event per member of the population; for further details, see Fig. 1). By using identically treated cells, the numbers of Pt‐atoms combined with DNA, RNA and protein molecules were determined in the subcellular fractions. Thus, the D0's given as the drug concentrations were replaced with the number of Pt‐atoms combined in each fraction. Then, the cell‐killing efficiency of the Pt atom was expressed as the reciprocal of the number of Pt‐atoms combined and was calculated for each molecule. The efficiency for DNA was 0.206, 0.273, 0.779,1.28,1.77 and 5.14×103 nucleotides, respectively, for the conditions described above. It seemed that hyperthermia potentially interacted not only with bifunctional, but also with monofunctional bonds. Thus, it was concluded that TDDP was markedly less cytotoxic than cis‐diaminedichloroplatinum (CDDP) at 37°C, but was more cytotoxic than CDDP at 44°C.

Relationship between Cell‐killing Efficiency and Number of Platinum Atoms Binding to DNA, RNA, and Protein Molecules in HeLa Cells Treated with cis‐Diamine(glycolato)platinum(II)

HeLa S‐3 cells were treated with 195mPt‐radiolabeled cis‐diamine(glycolato)platinum(II) (254‐S) under various conditions, and the relationship between the lethal effect and the numbers of Pt atoms binding to DNA, RNA, and proteins was examined. The mean lethal concentrations for the cells treated with 254‐S at 37°C for 0.5, 1, 2, and 3 h were 67.1, 47.0, 26.8 and 8.1 μM1, respectively. Using identically treated cells, we determined the numbers of Pt atoms combined with DNA, RNA, and protein molecules after fractionation of the cells. In this way, the D0 values (D0, the dose that causes an average of one lethal event per member of the population), expressed as the drug concentration, could he related to the number of Pt atoms combined with each fraction. The efficiency of the Pt atom in killing the cells, expressed as the reciprocal of the D0 values, was then calculated for each fraction. The results suggested that DNA was the primary target for cell killing by 254‐S. The target volumes for DNA were 3.96, 4.97, and 11.77 × 104 nucleotides for 1‐, 2‐, and 3‐h treated cells, respectively. In terms of the target volume, the cell‐killing effects of 254‐S were comparable to those of cis‐diamine‐dichloroplatinum(II) (CDDP), for which the target volumes under identical conditions were determined to be 5.17, 5.71, and 10.3 × 104 nucleotides, respectively, while in terms of the mean lethal dose (D0), the cell‐killing effects of 254‐S were lower than those of CDDP by a factor of 5.1 (47.0/9.3), 4.0 (26.8/6.7), or 2.5 (8.1/3.2) for 1‐, 2‐, or 3‐h treatment, respectively.

Chemisorption of H2 on supported Pt clusters probed by129Xe NMR

The surface of Pt clusters with average size between 1 and 8 nm supported on SiO2, γ-Al2O3 or Y-zeolite was probed by129Xe NMR as the Pt surface coverage with hydrogen, θ, was increased. A distinct change in the structure of the hydrogen overlayer at θ≈ 0.3 was inferred from the NMR spectra. This change is believed to take place when the chemisorbed hydrogen fills all the next nearest neighbor metal sites and the nearest neighbors start to be occupied. These new observations clarify previously reported determinations of the average number of Pt atoms in supported clusters by means of Xe NMR and other techniques. It also appears that interfacial metal-support interactions may be probed by Xe NMR.

Determination of the target volume of HeLa cells treated with platinum-195m radiolabeled trans-diaminedichloroplatinum(II): a comparison with cis-diaminedichloroplatinum(II)

HeLa S-3 cells were treated with 195mPt-radiolabeled trans-diaminedichloroplatinum(II) (TDDP) under various conditions, and the relationship between lethal effect and the number of Pt atoms binding to DNA, RNA and proteins was examined. The mean lethal concentrations for the cells treated with TDDP at 37 °C for 1, 2 and 3 h were 163.7, 65.8 and 24.9μM, respectively. By using identically treated cells, the number of Pt atoms combined with DNA, RNA and protein molecules was determined after the cells were fractionated using the method of Schneider. In this way, the D 0 values given as the drug concentration were substituted for the number of Pt atoms combined with each fraction, then the target volumes, expressed as the reciprocals of the D 0 values, were calculated for each fraction. The results suggested that DNA and high molecular weight RNAs (except t-RNA), under some limited condition, could be the target molecules for cell killing by TDDP. The target volumes for DNA were 1.31 × 10 3, 3.01 × 10 3 and 6.26 × 10 3 nucleotides for 1, 2 and 3 h treated cells, respectively. Cell killing effects of TDDP were lower than CDDP by a factor of 39.5, 19.0 and 16.5 for 1, 2 and 3 h treatments at 37 °C, respectively, when viewed from the stand point of the target volume, while those from the mean lethal dose ( D 0) were 17.6, 9.8 and 6.7, respectively.