ABSTRACTS: April 2003
Journal Archive
ABSTRACTS: April 2003
of current literature on the platinum metals and their alloys
CHEMICAL COMPOUNDS
Theoretical Study of Methyl-Pd11 N-Heterocyclic Silylene and Germylene Complexes: Comparisons to N-Heterocyclic Carbene Reactivity
d. s. mcguinness, b. f. yates and k. j. cavell, Organometallics, 2002, 21, (24), 5408–5414
A density functional analysis of the tide complexes revealed a very low activation barrier for methyl migration to the silylene or germylene ligand. In the absence of solvent or counterion effects, reductive elimination of silicenium or germacenium cations is less likely. The activation barrier for coupling of the methyl group was in the order: Si < Ge < C.
Cyclooctadienemethylpalladium Complexes: Synthesis, Structures and Reactivity
a. klein, a. dogan, m. feth and h. bertagnolli, Inorg. Chim. Acta, 2003, 343, 189–201
[(COD)PdMe(L)]n+ (n = 0, L = Cl, OH, OMe, OEt, Oi Pr, OPh, OTol, OMes; n = 1, L = H2O, PPh3, pyridine, collidine; n = 2, L = N-methyl-pyrazinium) undergo fast ligand exchange reactions in solution to give new mono or binuclear Pd complexes. Neutral complexes with oxo-ligands OR are highly reactive towards oxo-nucleophiles, including H2O. [(COD)PdMe(OH)] and [(µ-OH) {(COD)PdMe} 2]+ seem to play an important role in hydrolysis reactions.
Crystal Structure and Gas Adsorption Property of Rhodium(II) Benzoate Pyrazine
s. takamizawa, t. hiroki, e. nakata, k. mochizuki and w. mori, Chem. Lett., 2002, 31, (12), 1208–1209
[Rh2(O2CPh)4(pyz)]∞ (1) has perfect linear geometry with the chain skeleton bridged by pyrazine in the axial direction of the lantern-like Rh benzoate. (1) indicated N2 adsorption on a microporous medium although it probably does not have a microporous structure. The structure of (1) may open the crystal packing for gas molecules.
Mass Spectrometry of Polystyrene and Polypropene Ruthenium Complexes. A New Tool for Polymer Characterization
k. royo and h. h. brintzinger,j. Organomet. Chem., 2002, 663, (1–2), 213–220
Reaction of [Ru(C5H5)(NCCH3)3][PF6] with polystyrene (PS) of numerical mass average (M n) 1430-135,000 in a ratio [Ru]/[PS] = 1:1 to 3:1 favours effective ionisation of the polymer by MALDI-MS techniques. An increase in signal intensity is achieved over that obtained with Ag+ salts. Polypropylene (PP) salts of M n 2700 and 6100 are ionised after reaction with (RuC5Me5)3H5. This is the first observation of MALDI-MS signals for PP.
ELECTROCHEMISTRY
Specificity of Electrochemical Reactivity of Small Aliphatic Oximes to Geometries of Pt(111) and (100) Surfaces
b. pierozynski and b. e. conway, j. Electroanal Chem., 2002, 538—539, 87–97
Electrochemical CV experiments on the reactivity of formamidoxime and acetaldehyde oxime on Pt(111) and (100) single crystal surfaces revealed remarkable specificity to surface geometry upon adsorption. The roles of Faradaic reduction coupled with electrosorption, including participation of diffusion control, were clearly distinguishable.
Microstructure, Electrochemical Surface and Electrocatalytic Properties of IrO2+Ta2O5 Oxide Electrodes
j.-m. hu, j. q. zhang, h. m. meng and c.-n. cao, j. Mater. Sci., 2003, 38, (4), 705–712
Surface electrochemical properties of Ti/IrO2Ta2O5 electrodes indicate a ‘double-layer’ electrochemical structure containing the ‘inner’ and ‘outer’ layers. The voltammetric charge declines with the decrease of grain size of the oxide coatings due to surface tension.
Electrochemical Behavior of Dopamine and Ascorbic Acid at Osmium(ll) Complex Cationic Monolayer Modified Gold Electrodes
j. zhang and i. c. jeon, Anal Sci., 2002, 18, (10), 1085–1088
At an [Os(bpy)2(bpy-(CH2)13SH)]2+/Au electrode, the oxidation peak of dopamine (DA) shifted to a much more positive potential as compared with that of a bare Au electrode, but the oxidation peak poten”tial of ascorbic add (AA) exhibited a slightly negative shift. When CH3(CH2)11SH was mixed into the cationic monolayer, the enhanced packing of the mixed monolayer blocked the access of DA or AA to the electrode, resulting in further positive shifts for both oxidation peak potentials.
Synthesis and Electrochemical Behavior of [SiW11O39RuIII(H2O)]5- and Its Oxo-Bridged Dimeric Complex [SiW11O39RuIVORuIIISiW11O39]11-
m. sadakane and m. higashijima, Dalton Trans., 2003, (4), 659–664
CV showed that [SiW11O39RuIII(H2O)]5- was reversibly reduced to the aquaRu(II) derivative, oxidised to the aquaRu(IV), hydroxyRu(IV) and oxoRu(IV) complexes depending on the pH, and could be further oxidised to the oxoRu(V) complex. (SiW11O39RuIVORuIIISiW11O39]11- was reversibly oxidised/ reduced to the RuIVORuIV/RuIIIORuIII complex.
PHOTOCONVERSION
Luminescence of the Nonclassical Homoleptic Metal Carbonyl Complex [Rh(CO4]+
t. w. bitner, j. i. zink, m. d. havighurst and s. h. strauss, Inorg. Chem., 2002, 41, (24), 6187–6189
[Rh(CO)4]+ (1) is luminescent at low temperature with a peak maximum at 19,640 cm-1 and a full-width at half-maximum of 2900 cm-1. The solution absorption and low temperature solid state luminescence spectra of [Rh(CO)4](l-Et-CB11F11) are reported. Rh—C bond length changes of ∼ 0.07 Á in the excited state are calculated. The calculated bond length changes in (1) are similar to those in classical metal carbonyls.
Synthesis of New iridium Complexes and Their Electrophosphorescent Properties in Polymer Light-Emitting Diodes
w. zhu, c. liu, l. su, w. yang, m. yuan and y. cao, J. Mater .Chem., 2003, 13, (1), 50–55
Ir complexes with p-substituted 2-phenylpyridine ligands were incorporated into PLEDs using poly[1,4-bis(6’-cyano-6’-methylheptyloxy)phenylene] (CNPPP) as the host and these materials were compared with fac -tris(2-phenylpyridinato)Ir-doped devices. Green electrophosphorescence was observed, with peak emissions at ∼ 495 and 515 nm. fac -Tris[2-(4-teri -butylphenyl)pyridinato]Ir-doped CNPPP gave an external quantum efficiency of 4.4% (photoluminescence/electroluminescence) and a luminous efficiency of 10 cd A- 1at 120 cd m-2. These values are 4.2% and 10 cd A-1, respectively, at 2500 cd m-2.
Flow Injection Chemiluminescent Method for the Successive Determination of L-Cysteine and L-Cystine Using Photogenerated Tris(2,2’-Bipyridyl) Ruthenium (III)
t. pÉrez-ruiz, c. martÍnez-lozano, v. tomÁs and j.martÍn, Talanta, 2002, 58, (5), 987–994
The title method is based on the reaction of L-cys-teine with Ru(bipy)32+ and peroxydisulfate under UV irradiation to produce chemiluminescence. Cystine is determined after reduction to cysteine in a Cu-coated Cd reductor mini-column in the flow system. The inclusion of a selection valve allows the successive determination of the two analytes.
Light-Induced Metastable Linkage Isomers of Ruthenium Sulfur Dioxide Complexes
a. yu. kovalevsky, k. a bagley,j. m. cole and p. coppens, Inorg. Chem., 2003, 42, (1), 140–147
The irradiation of trans -[RuII(NH3)4(SO2)X]Y (1) (X = C1-, H2O, CF3COO-; Y = C1-, C6H5SO3-, Tos-, CF3COO-) with laser light at low temperatures caused linkage isomerisation of SO2, starting with η1- planar S -bound to η2-side S,O-bound SO2. The stability of the MS2 metastable state correlates with increasing σ-donating ability of the trans ligand and the size of the counterion.
ELECTRODEPOSITION AND SURFACE COATINGS
Morphology and Luminescence of Porous GaN Generated via Pt-Assisted Electroless Etching
d. j. dÍaz, t. l. williamson, i. adesida, p. w. bohn and r.j. molnar, J. Vac. Sci. Technol B, 2002, 20, (6), 2375–2383
Ultrathin Pt films were sputtered onto the surface of GaN and then etched with a 1:2:1 or 1:2:2 solution of CH3OH:HF:H2O2. Etching proceeded by first forming a network of small pores, after which ridge structures formed, with the porous network in trenches between the ridges. As etching progressed further, the sidewalls of the ridges became steeper, and then the ridges started to disappear. The light emission properties of the etched porous GaN varied depending on the original, nonporous GaN.
Studies of Codeposited Hydrogen in Palladium Electrodeposition
c. -h. huang and i-y. wei, Plat. Surf. Finish,, 2002, 89, (12), 60–63
The tensile stress of Pd electrodeposits (1) on Ni cathodes is influenced by the amount and nature of codeposited H. The escape-state of codeposited H in (1) was identified. A softer escape-state was predict”ed when the Pd bath contained an optimum amount of wetter at lower current densities (CDs). This gave less codeposited H during plating and less deposit cracking. A wetter concentration of 2.0 g I-1 and a CD of 0.1 A dm-2 gave crack-free (1).
APPARATUS AND TECHNIQUE
Design and Performance of a Microcantilever- Based Hydrogen Sensor
d. r. baselt, b. fruhberger, e. klaassen, s. cemalovic, c. l. britton, s. v. patel, t. e. mlsna, d. mccorkle and b. warmack, Sens. Actuators B, Chem., 2003, 88, (2), 120–131
The title sensor (1) contains an array of 10 micromachined cantilever beams. Each cantilever is 500 μm wide × 267 μm long × 2 μm thick and has a capacitance readout capable of measuring cantilever deflection to within 1 nm. A 20 nm thick coating of 90% Pd-10% Ni bends some of the cantilevers in the presence of H2. The Pd-Ni coatings are deposited in UHV. (1) can detect H concentrations of 0.1–100% with ∼ linear response at 10–90% H. Humidity, temperature and O concentration affect its operation.
Gas Sensor Activity of ArgoGel Resin-Supported Pentaruthenium Clusters
c. m. g. judkins, k. a. knights, b. f. g. johnson and y. r de miguel, Polyhedron, 2003, 22, (1), 3–7
[Ru5C(CO)15] (1) clusters have been attached to phosphine ligands supported on ArgoGel amine resin. These cluster-containing beads exhibit a characteristic colour change and FTIR shift when treated with H2S, S02 or CO. The reactions probably involve the polyhedral rearrangement of (1) from its original square pyramid to a bridged-butterfly metal core.
HETEROGENEOUS CATALYSIS
Steady-State Multiplicity and Superadiabatic Extinction Waves in the Oxidation of CO/H2 Mixtures over a Pt/AI2O3-Coated Monolith
m. sun, e. b. croiset, r r. hudgins, p. l. silveston and m. menzinger, Ind Eng. Chem. Res., 2003, 42, (1), 37–45
Under experimental conditions, steady-state multiplicity phenomena exist in a certain range of CO and H2 concentrations for the catalytic oxidation of CO/H2 over a cordietite monolith washcoated with Pt/A12O3. CO inhibits the ignition of H2, whereas H2 assists the ignition of CO. Extinction of the reaction due to a step increase of CO or a step decrease of H2 occurred in the form of a downstream-moving wave accompanied by a sharply localised superadiabatic temperature excursion.
Hydrodechlorination of CCI4 over Pt/Al2O3: Effects of Platinum Particle Size on Product Distribution
j. w. bae, i. g. kim.j. s. lee, k. h. lee and e. j. jang, Appl. Catal. A: Gen., 2003, 240, (1–2), 129–142
Impregnated Pt/Al2O3 catalysts had different Pt particle sizes depending on the Pt precursor (Pt(NH3)2(NO2)2 or H2PtCl4) and on the pH of the Al2O3 suspension. The average Pt particle size increased with decrease in pH for the Pt(NH3)2(NO2)2-based Al2O3 suspension, but this trend was reversed for H2PtCl6. In the hydrodechlorination of CCl4, the larger the Pt particle size, the higher the selectivity to CHCl3. On small Pt particles, strong chemisorption of CCl4 occurs and formation of completely dechlotinated CH4 was favoured.
The Drastic Effect of Platinum on Carbon- Supported Ruthenium-Tin Catalysts Used for Hydrogenation Reactions of Carboxylic Acids
y. hara and k. endou, Appl. Catal. A: Gen., 2003, 239, (1–2), 181–195
When Pt was incorporated on Ru-Sn/active C, the reaction rate was almost tripled for the hydrogenation of 1,4-cyclohexanedicarboxylic acid. The Pt also prevented the Sn from dissolving into the reaction mixture, whereas for bimetallic Ru-Sn/active C dissolved Sn was detected during hydrogenation. The durability of the Pt-Ru-Sn/active C was verified by carrying out a catalyst recycling test up to 7 cycles. For Pt-Ru-Sn/active C, Sn(0) was the major Sn species.
Hydrogenation of Alkenes over Palladium and Platinum Metals Supported on a Variety of Metal(IV) Phosphates
r. a. w. johnstone, j.-y. liu, l. lu and d. whittaker J. Mol. Catal A: Chem., 2003, 191, (2), 289–294
A substantial variation in relative rates of hydrogenation of 1-octene and 4-methylcyclohexene over platinised and palladised metal(TV) phosphates has been found; some being more effective than a standard Pd/C. Steric effects due to substrate/support interactions affected selectivity to hydrogenation.
Catalytic Combustion of Methane over Palladium-Based Catalysts
d. ciuparu, m. r. lyubovsky, e. altman, l. d. pfefferle and a. datye, Catal Rev., 2002, 44, (4), 593–649
The literature on supported Pd catalysts for combustion of CH4 is reviewed. The oxidation/reduction mechanisms for supported Pd, the poisoning, restructuring, the form of oxygen on the surface, CH4 activation over Pd and PdO phases, and transient behaviour are all discussed. The relevance for practi”cal catalytic combustors is included. (131 Refs.)
Palladium-Containing Zeolite Beta Macrostructures Prepared by Resin Macrotemplating
v. naydenov, l.tosheva and j. sterte, Chem. Mater., 2002, 14, (12), 4881–4885
Self-bonded Pd-containing zeolite beta spheres (1) were prepared by a multistep procedure using a macroporous anion exchange resin as a macrotemplate. Pd is homogeneously distributed within the zeolite spheres as PdO. The Pd dispersions decreased with an increase in Pd content. The pore structure of (1) consisted of both micropores (from the zeolite) and meso/macropores (from the resin removal). (1) may be directly used as catalysts (in fixed bed reac”tors) thus excluding further processing to form macroparticles and avoiding deterioration effects due to the addition of binders in conventionally prepared zeolite-supported catalysts.
HOMOGENEOUS CATALYSIS
Total Synthesis of Deoxymannojirimycin and D-Mannolactam via Carbonylation of 5-Vinyloxazolidin-2-ones
j. g. knight and k. tchabanenko, Tetrabedron, 2003, 59, (3), 281–286
The Pd-catalysed decarboxylative carbonylation of a serine-derived 5-vinyloxazolidinone (1) has been successfully applied to the stereoselective total synthesis of the polyhydroxylated piperidine alkaloids; deoxymannojirimycin and D-mannolactam. Heating a solution of (1) in EtOH at 60°C under pressure of CO (65 atm) in the presence of PdCl2(PPh3)2 (10 mo1%) for 32 h gave a δ-lactam intermediate in 81% yield, which was subsequently converted.
Development of the Suzuki-Miyaura Cross-Coupling Reaction: Use of Air-Stable Potassium Alkynyltrifluoroborates in Aryl Alkynylations
g. a. molander b. w. katona and f. machrouhi, J. Org. Chem., 2002, 67, (24), 8416–8423
The Pd-catalysed cross-coupling reactions of K alkynyltrifluoroborates with aryl halides or triflates gave moderate to excellent yields. PdCl2(dppf)·CH2Cl2 with Cs2CO3 in THF-H2O or THF were the most effective systems. Air-stable, highly functionalised alkynyltrifluoroborates can be simply prepared and stored indefinitely. This provides an advantage in combinatorial chemistry applications.
A Novel and Efficient Method for the Pd-Catalysed Oxidative Carbonylation of Amines to Symmetrically and Unsymmetrically Substituted Ureas
b. gabriele, r. mancuso, g. salerno and m. costa, Chem. Commun., 2003, (4), 486–487
A new method for the Pdl2 with KI catalysed oxidative carbonylation of amines to symmetrically and unsymmetrically substituted ureas has been developed. Unprecedented catalytic efficiencies for this kind of reaction were obtained. The use of a coordinating aprotic solvent of low polarity, such as 1,2-dimefhoxyethane, was essential for the success of the reaction. Using an excess of CO2 (40 atm) had a beneficial effect on the carbonylation of primary aliphatic amines.
Development of a Manufacturing Route to 1-Hydroxy-4-(3-pyridyl)butan-2-one Using Heck Methodology
d. ainge and l-m. vaz, Org. Process Res. Dev., 2002, 6, (6), 811–813
The manufacturing route to a key synthetic intermediate, l-hydroxy4-(3-pyridyl)butan-2-one, was optimised and scaled-up. The Heck coupling of 3- bromopyridine with 3-butene-l,2-diol was utilised. The catalyst system Pd(OAc)2 with NBu3/P(o -toly)3 required a reaction time of 3 h. The reaction was car”ried out in toluene under reflux conditions. For a 3 kg scale reaction, HPLC showed 80% consumption of 3-bromopyridine.
The Suzuki Coupling of Aryl Chlorides in TBAB-Water Mixtures
r. b. bedford, m. e blake, c. p. butts and d. holder, Chem. Commun., 2003, (4), 466–467
Pd catalysts formed in situ from Pd(OAc)2 in the presence of tetrabutylammonium bromide (TBAB) and H2O and in the absence of added ligands are found to be effective in the Suzuki coupling of deactivated aryl chlorides. For these reactions, the true active catalysts are Pd colloids supported by the TBAB. Further studies are being carried out to optimise the use of such catalysts in a range of aryl chloride coupling reactions.
An Efficient Synthesis of 4-Alkenyl/Alkynyl-6- methyl-2-pyrones via Pd-Cataiysed Coupling on 4-Bromo-6-methyl-2-pyrone
l. r. marrison, j. m. dickinson, r. ahmed and i. j. s. fairlamb, Tetrahedron Lett., 2002, 43, (49), 8853–8857
The syntheses of biologically active 4-alkenyl- and 4-alkynyl-6-methyl-2-pyrones was achieved using Pd-catalysed coupling procedures. Pd/C with PPh, was the most effective catalyst combination for Sonogashira cross-coupling of terminal acetylenes with 4-bromo-6-methyl-2-pyrone in yields ≤ 95%. Only when the alkyne possessed strongly electron- withdrawing substituents were the Pd(0) catalysts, Pd(OAc)2/PPh3 and Pd(PPh3)4, more effective.
Extended Scope of Dirhodium(ll)-Catalysed Enantioselective Intramolecular 1,3-Dipolar Cycloadditions of Carbonyl Ylides with Alkene and Alkyne Dipolarophiles
d. m. hodgson, a h. labande and f. y. t. m. pierard, Synlett, 2003, (1), 59–62
The effect on ee of altering the dipolarophile in intramolecular carbonyl ylide cycloadditions was examined. Various substrates with Rh2[(S )-DOSP]4 and Rh2[(R)-DDBNP]4 catalysts in hexane were used. The stereospecificity of the process, the creation of up to 4 stereocentres, and enantioselective intramolecular cycloadditions with alkynes (≤ 86% ee) were all demonstrated for the first time.
Hydroformylation of Alkenes in Supercritical Carbon Dioxide Catalysed by Rhodium Trialkylphosphine Complexes
m. f. sellin, i. bach, j. m. webster, f. montilla, v. rosa, t. avilÉs, m. poliakoff and d. j. cole-hamilton, j. Chem. Soc., Dalton Trans., 2002, (24), 4569–4576
[Rh2(OAc)4] modified by simple trialkylphosphines gives catalysts which are soluble in sc-CO2, and allows hydroformylation of alkenes to take place. The Rh catalyst derived from PEt3 is more active and slighdy more selective for the linear products in sc-CO2 than in toluene. Under supercritical conditions of 200 bar total pressure, aldehydes are obtained with 97% selectivity.
FUEL CELLS
CO Tolerance of Pd-Rich Platinum Palladium Carbon-Supported Electrocatalysts
d. c. papageorgopoulos, m. keijzer, j. b. j. veldhuis and f. a. de bruijn, J. Electrochem. Soc., 2002, 149, (11), A1400-A1404
The use of PtPdy /C (y = 1–6) electrocatalysts as CO tolerant anodes for PEMFCs has been investigated. CV at 80°C revealed that upon CO saturation, a lower fraction of the PtPdy surface sites are poisoned compared to Pt, resulting in higher amounts of adsorbed H. PtPdy, improved performance compared to Pt and PtRu, especially at CO ≥ 100 ppm in the fuel stream. PtPd4 gave the best performance.
Array Membrane Electrode Assemblies for High Throughput Screening of Direct Methanol Fuel Cell Anode Electrocatalysts
r. liu and e. s. smotkin, J. Electroanal. Chem., 2002, 535, (1—2), 49–55
A fuel cell with an array MEA was developed for the high throughput screening of electrocatalysts. Standard MEA and electrode assembly methods were employed. The use of modified fuel cell hardware enabled catalyst testing with realistic reactant expo”sure histories (conditioning) and steady state reaction conditions. The device accommodates an array of 25 spots permitting repetitive testing of catalysts.
Correlation of Electrochemical and Physical Properties of PtRu Alloy Electrocatalysts for PEM Fuel Cells
g. a. camara, m. j. giz, v. a paganin and e. a. ticianelli, J. Electroanal. Chem., 2002, 537, (1–2), 21–29
PtRu/C (1) electrocatalysts were prepared by a sulfide-complex method and modified in oxidising and reducing environments. For non-treated (1), the Ru atoms are segregated from the Pt f.c.c. structure, probably forming an amorphous Ru oxide phase, while for (1) heat treated at 700°C under H2 a true alloy with a metal PtRu composition of ∼ 3:1 was formed. This alloy gave the best CO tolerance.
Influence of Preparation Process of MEA with Mesocarbon Microbeads Supported Pt-Ru Catalysts on Methanol Electrooxidation
y.-c. liu, x.-p. qiu, y.-q. huang, w.-t. zhu and g.-s. wu, J. Appl. Eletrochem., 2002, 32, (11), 1279–1285
The effects of a mesocarbon microbead support material for Pt-Ru catalysts on the anode perfor”mance of a DMFC were studied. Polarisation characteristics of the anode were low due to the fast rate of mass transport in the electrode. The anode with appropriate Nafion content (10 wt.%) and hot press pressure (7.5 MPa) for the MEA exhibited the best performance at MeOH concentrations > 1.0 M at high cell temperature.
Electrochemical Oxidation of NADH Catalyzed by Diaphorase Conjugated with Poly-1 -vinylimidazole Complexed with Os(2,2r-dipyridylamine)2CI
s. tsujimura, k. kano and t. ikeda, Chem. Lett., 2002, 31, (10), 1022–1023
A redox polymer containing poly-1-vinylimidazole (PVI) and Os (E°’ = -0.15 V vs. Ag|AgCl), PVI- Os(dpa)2Cl (1), was synthesised. (1) was an efficient mediator of the diaphorase-catalysed electrochemical oxidation of NADH and a support to immobilise enzyme(s) on electrode surfaces. NAD-enzyme/ diaphorase-coimmobilised Os polymer electrodes can be used as biofuel cell anodes.
ELECTRICAL AND ELECTRONIC ENGINEERING
Admittance Study of a Pt/C60/ln/AI Schottky-Barrier Cell
i. hiromitsu, r. shinto, m. kitano, t. kitauchi and t. ito, Jpn. J. Appl Phys., Part 1, 2002, 41, (11A), 6517–6524
The electrical properties of a Pt/C60/In/Al photovoltaic cell, in which the Schottky barrier is formed at the Pt/C60 interface, were studied by an admittance measurement, and also by a current density-voltage measurement. The latter shows that the rectification is caused by the asymmetry of the electron injection efficiencies from the electrodes. The conductance and capacitance are significantly affected by the localised charges produced by the injection or by illumination.
Low-Resistance and Thermally Stable Pd/Ru Ohmic Contacts to p-Type GaN
j.-s. jang, c.-w. lee, s.-j. park, t.-y. seong and i. t. ferguson, J. Electron. Mater., 2002, 31, (9), 903–906
The tide ohmic contacts to surface treated p -GaN (3 x 1017 cm-3) have been prepared. Annealing at 500°C for 2 min in N2 improved ohmic contact properties (specific contact resistance of 2.4(±0.2) x 10 -5 Ω cm2). AFM showed that the surface of the as-deposited and annealed Pd/Ru contacts were smooth with root mean square roughness of ∼ 0.6 nm. For the asdeposited contact, thermionic field emission is dominant, while for the annealed contact, field emission dominates the current flow.
MEDICAL USES
Monofunctionally trans -Diammine Platinum(ll)- Modified Peptide Nucleic Acid Oligomers: A New Generation of Potential Antisense Drugs
k. s. schmidt, m. boudvillain, a. schwartz, g. a. van der marel.j. h. van boom, j. reedijk and b. lippert, Chem. Eur. J., 2002, 8, (24), 5566–5570
A solid-phase approach allows access to monofunctionally trans -PdII-modified PNA oligomers of arbitrary sequence for potential use in both antigene and antisense strategies. The synthesis of a platinated building block and its subsequent incorporation into 3 different PNA oligomers by solid-phase synthesis was achieved. In a model cross-linking reaction, one of the latter recognised sequence-specifically a target oligonucleotide and cross-linked to it. This gave a tram- PtII cross-linked PNA/DNA duplex.
Preparation, Spectral Characterization, In Vitro Antitumour and Thermal Studies of New Platinum(IV) and Palladium(ll) Thiohydrazone Complexes
n. manav and n. k. kaushik, Transition Met. Chem., 2002, 27, (8), 849–855
Pt(L)2Cl2] and [Pd(HL)Cl2] (HL = thiohydrazone derivatives) were prepared by addition of the desired thiohydrazone dissolved in H2O/EtOH (1:1) to an aqueous solution of K2PtCl6 and PdCl2, respectively. The in vitro antitumour activity of some complexes was measured.
Thermally Inert Metal Ammines as Light-lnducible DNA-Targeted Agents. Synthesis, Photochemistry, and Photobiology of a Prototypical Rhodium(lll)-Intercalator Conjugate
c. g. barry, e. c. turney, c. s. day, g. saluta, g. l. kucera and u. bierbach, Inorg. Chem., 2002, 41, (26), 7159–7169
[Rh(NH3)5L]4+ (1) (L = l-[2-(acridin-9-ylamino)-ethyl]-l,3,3-trimethylthiourea; acridinium cation) was shown to be a true “light-only” cytotoxic agent in clonogenicity assays. In HL-60 leukemia, (1) showed a pronounced photocytotoxic effect with IC50 = 44 nM. The photoreactivity and DNA interactions of (1) and its individual components were studied.
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