Iron(III) as Lewis acid catalyst in organosilicon and carbonyl chemistry

Iron is one of the most common elements in the earth’s crust and thus its availability and economic viability far exceed that of metals commonly used in catalysis. Also the toxicity of iron is miniscule, compared to the likes of platinum and nickel, making it very desirable as a catalyst. Despite this, prior to the 21st century, the applicability of iron in catalysis was not thoroughly investigated, as it was considered to be inefficient and unselective in desired transformations. In this doctoral thesis, the application of iron catalysis in combination with organosilicon reagents for transformations of carbonyl compounds has been investigated together with insights into iron catalyzed chlorination of silanes and silanols. In the first part of the thesis, the synthetic application of iron(III)-catalyzed chlorination of silanes (Si-H) and the monochlorination of silanes (SiH2) using acetyl chloride as the chlorine source is described. The reactions proceed under ambient conditions, although some compounds need to be protected from excess moisture. In addition, the mechanism and kinetics of the chlorination reaction are briefly adressed. In the second part of this thesis a versatile methodology for transformation of carbonyl compounds into three different compound classes by changing the conditions and amounts of reagents is discussed. One pot reductive benzylation, reductive halogenation and reductive etherification of ketones and aldehydes using silanes as the reducing agent, halide source or cocatalyst, were investigated. Also the reaction kinetics and mechanism of the reductive halogenation of acetophenone are briefly discussed.

Unsaturated σ-hydrocarbyl transition-metal complexes. Part 2. Synthesis and reactions of vinylplatinum complexes and a comparison with analogous fluorovinyl and alkynyl complexes

Alkenyl (CHCH2 or CFCF2) or alkynyl (CCPh) derivatives of trimethyltin are shown to be superior to lithium or magnesium reagents for the synthesis of corresponding mono-organoplatinum(II) species by metathesis (L = SnMe3R +cis-[PtCl2L2]→trans-[PtRClL2]+ SnMe3Cl tertiary phosphine). The reactivity order for SnMe3R is R = CCPh > CFCF2 > CHCH2. This order is also found for oxidative addition of SnMe3R to Pt0 to give cis-[PtRL2(SnMe3)]. When the latter complex (R = CHCH2) reacts with X2 or MeX further oxidative addition occurs exclusively at the platinum centre. Aromatic isonitriles (R′NC)co-ordinate to the platinum and give insertion products trans-[Pt{C(CHCH2)= NR′}ClL2] on heating or carbene complexes with NBunH2. The alkynyl trans-[Pt(CCPh)ClL2] also forms 1 :1 adducts with R′NC and carbene complexes therefrom, but no insertion products. Spectroscopic data for the new complexes are presented.

Bond-selective energy redistribution in the chemisorption of CH3D and CD3H on Pt{1 1 0}-(1 2): a first-principles molecular dynamics study

We have investigated the chemisorption of CH3D and CD3H on Pt{11 0}-(1 2) by performing first-principles molecular dynamics simulations of the recombinative desorption of CH3D (from adsorbed methyl and deuterium) and of CD3H (from adsorbed trideuteromethyl and hydrogen). Vibrational analysis of the symmetry adapted internal coordinates of the desorbing molecules shows that excitation of the single C– D (C–H) bond in the parent molecule is strongly correlated with energy excess in the reaction coordinate. The results of the molecular dynamics simulations are consistent with observed mode- and bond-specific reactivity measurements for chemisorption of methane and its isotopomers on platinum and nickel surfaces.

Electrocatalysis on noble metal and noble metal alloys dispersed on high surface area carbon

In this work, a simple route to prepare carbon supported Pt/C, Pt:Ru/C, Pt:Mo/C and Pt:Ru:Mo/C catalysts is reported. The electrochemical properties of the several carbon materials used as substrates in the absence and in the presence of supported platinum and platinum alloys catalysts were investigated using cyclic voltammetry and employing the thin porous coating electrode technique. The activity of the dispersed catalysts composed of Pt/C with respect to the oxygen reduction and of alloy/C with respect to methanol oxidation was investigated using steady state polarization measurements. The performance with respect to the oxygen reduction reaction of the Pt/C catalyst prepared on heat-treated Vulcan carbon substrate is equivalent to that reported in the literature for the state-of-the-art electrocatysts. Pt:Ru:Mo/C samples prepared in this work presented the higher catalytic effect for methanol electro-oxidation.

Preparation, microstructural and electrical characterization of SrTiO3 thin films prepared by chemical route

Polycrystalline SrTiO3 thin films having a cubic perovskite structure were prepared at different temperatures by the polymeric precursor method on platinum-coated silicon substrate. Crystalline films with uniform composition and thickness were prepared by spin-coating and the post-deposition heat treatment was carried out at different temperatures. The film showed good structural, dielectric, and insulating properties, Scanning electron microscopy (SEM) micrographs showed no occurrence of interdiffusion between the bottom electrode (platinum) and the film during post-annealing, indicating a stable interface between the SrTiO3 and the bottom electrode. The dielectric constant and dissipation factor at a frequency of 100 kHz were 250 and 0.01, respectively, for a 360 nm thick film annealed at 600 degreesC. The capacitance versus applied voltage characteristics showed that the capacitance was almost independent of the applied voltage. The I-V characteristics were ohmic in low fields and a Schottky emission and/or Poole-Frenkel emission were postulated in high fields. Room temperature leakage current density was found to be in the order of 10(-7) A/cm(2) for a 360 nm thick film in an applied electric field of about 100 kV/cm. The charge storage density of 36 fC/mum(2) was obtained in an applied electric field of about 100 kV/cm. (C) 2001 Published by Elsevier B.V. Ltd. All rights reserved.

Electrocatalytic Activity of Platinum-Niobium Nanoparticles for Ethanol Oxidation

Three nanostructured platinum-niobium supported on Vulcan XC-72R carbon black materials were prepared as catalysts for the ethanol electroxidation: (i) deposition of platinum and niobium on Vulcan XC-72R carbon black, (ii) platinum decorated on a mixture of commercial amorphous Nb2O5/carbon black, and (iii) the same than ii but using crystalline Nb2O5, by reduction of the precursors with sodium borohydride in ethanol. All the catalysts showed platinum crystal sizes in the range of 3-4 nm, with no or little modification of the lattice parameter. The analyses of the electronic structure from the XANES region of the XAS spectra displayed some interactions between platinum and niobium, despite the niobium was primarily in the form of pentoxide in all the catalysts. CO stripping exhibited a promising low onset potential and a large current density, especially in the case of the deposited catalyst. Ethanol electroxidation experiments revealed that the Pt-Nb(2)O(5)crystalline/C generated the largest current. However it was not effective to completely oxidize ethanol, leading to acetic acid as the main product. In this sense, the highest efficiency for the complete oxidation of ethanol was obtained for the deposited catalyst. These results were interpreted in terms of the physico-chemical characteristic displayed by the different catalysts. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.040210jes] All rights reserved.

Electrogeneration of platinum nanoparticles in a matrix of dendrimer-carbon nanotubes

Hybrid materials with enhanced properties can now be obtained by combining nanomaterials such as carbon nanotubes and metallic nanoparticles, where the main challenge is to control fabrication conditions. In this study, we demonstrate that platinum nanoparticles (PtNps) can be electrogenerated within layer-by-layer (LbL) films of polyamidoamine (PAMAM) dendrimers and single-walled carbon nanotubes (SWCNTs), which serve as stabilizing matrices. The advantages of the possible control through electrogeneration were demonstrated with a homogeneous distribution of PtNps over the entire surface of the PAMAM/SWCNT LbL films, whose electroactive sites could be mapped using magnetic force microscopy. The Pt-containing films were used as catalysts for hydrogen peroxide reduction, with a decrease in the reduction potential of 60 mV compared to a Pt film deposited onto bare ITO. By analyzing the mechanisms responsible for hydrogen peroxide reduction, we ascribed the enhanced catalytic activity to synergistic effects between platinum and carbon in the LbL films, which are promising for sensing and fuel cell applications.

Age Hardening of Silver-Platinum Alloys

The alloy system selected for study was the binary alloy of platinum and silver. An examination of the various silver alloy diagrams revealed that of several possible alloys, the silver platinum was the most suit­able with regard to solubility.

Estrogen-induced gene expression and patient survival in high-grade serous carcinoma of the ovary

Background. Assessment of estrogen receptor (ER) expression has inconsistent utility as a prognostic marker in epithelial ovarian carcinoma. In breast and endometrial cancers, the use of estrogen-induced gene panels, rather than ER expression alone, has shown improved prognostic capability. Specifically, over-expression of estrogen-induced genes in these tumors is associated with a better prognosis and signifies estrogen sensitivity that can be exploited with hormone antagonizing agents. It was therefore hypothesized that estrogen-induced gene expression in ovarian carcinoma would successfully predict outcomes and differentiate between tumors of varying estrogen sensitivities. Methods. Two hundred nineteen (219) patients with ovarian cancer who underwent surgery at M. D. Anderson between 2004 and 2007 were identified. Of these, eighty-three (83) patients were selected for inclusion because they had advanced stage, high-grade serous carcinoma of the ovary or peritoneum, had not received neoadjuvant chemotherapy, and had readily available frozen tissue for study. All patients had also received adjuvant treatment with platinum and taxane agents. The expression of seven genes known to be induced by estrogen in the female reproductive tract (EIG121, sFRP1, sFRP4, RALDH2, PR, IGF-1, and ER) was measured using qRT-PCR. Unsupervised cluster analyses of multiple gene permutations were used to categorize patients as high or low estrogen-induced gene expressors. QPCR gene expression results were then compared to ER and PR immunohistochemical (IHC) expression. Cox proportional hazards models were used to evaluate the effects of both individual genes and selected gene clusters on patient survival. Results. Median follow-up time was 38.7 months (range 1-68 months). In a multivariate model, overall survival was predicted by sFRP1 expression (HR 1.10 [1.02-1.19], p=0.01) and EIG121 expression (HR 1.28 [1.10-1.49], p<0.01). A cluster defined by EIG121 and ER was further examined because that combination appeared to reasonably segregate tumors into distinct groups of high and low estrogen-induced gene expressors. Shorter overall survival was associated with high estrogen-induced gene expressors (HR 2.84 [1.11-7.30], p=0.03), even after adjustment for race, age, body mass index, and residual disease at debulking. No difference in IHC ER or PR expression was noted between gene clusters. Conclusion. In sharp contrast to breast and endometrial cancers, high estrogen-induced gene expression predicts shorter overall survival in patients with high-grade serous ovarian carcinoma. An estrogen-induced gene biomarker panel may have utility as prognostic indicator and may be useful to guide management with estrogen antagonists in this population.^

Genetic variants in the mammalian target of rapamycin (mTOR) signaling pathway as predictors of survival and clinical response in women with ovarian cancer

Background. The mTOR pathway is commonly altered in human tumors and promotes cell survival and proliferation. Preliminary evidence suggests this pathway's involvement in chemoresistance to platinum and taxanes, first line therapy for epithelial ovarian cancer. A pathway-based approach was used to identify individual germline single nucleotide polymorphisms (SNPs) and cumulative effects of multiple genetic variants in mTOR pathway genes and their association with clinical outcome in women with ovarian cancer. ^ Methods. The case-series was restricted to 319 non-Hispanic white women with high grade ovarian cancer treated with surgery and platinum-based chemotherapy. 135 SNPs in 20 representative genes in the mTOR pathway were genotyped. Hazard ratios (HRs) for death and Odds ratios (ORs) for failure to respond to primary therapy were estimated for each SNP using the multivariate Cox proportional hazards model and multivariate logistic regression model, respectively, while adjusting for age, stage, histology and treatment sequence. A survival tree analysis of SNPs with a statistically significant association (p<0.05) was performed to identify higher order gene-gene interactions and their association with overall survival. ^ Results. There was no statistically significant difference in survival by tumor histology or treatment regimen. The median survival for the cohort was 48.3 months. Seven SNPs were significantly associated with decreased survival. Compared to those with no unfavorable genotypes, the HR for death increased significantly with the increasing number of unfavorable genotypes and women in the highest risk category had HR of 4.06 (95% CI 2.29–7.21). The survival tree analysis also identified patients with different survival patterns based on their genetic profiles. 13 SNPs on five different genes were found to be significantly associated with a treatment response, defined as no evidence of disease after completion of primary therapy. Rare homozygous genotype of SNP rs6973428 showed a 5.5-fold increased risk compared to the wild type carrying genotypes. In the cumulative effect analysis, the highest risk group (individuals with ≥8 unfavorable genotypes) was significantly less likely to respond to chemotherapy (OR=8.40, 95% CI 3.10–22.75) compared to the low risk group (≤4 unfavorable genotypes). ^ Conclusions. A pathway-based approach can demonstrate cumulative effects of multiple genetic variants on clinical response to chemotherapy and survival. Therapy targeting the mTOR pathway may modify outcome in select patients.^

(Table 3) Concentration of Au, Pd, and Pt in the interstitial waters of ODP Leg 125 samples

Palladium, platinum, and gold were analyzed for 20 interstitial water samples from Leg 125. No Pd or Pt was detected in fluids from serpentinite muds from Conical Seamount in the Mariana forearc, indicating that low-temperature seawater-peridotite interaction does not mobilize these elements into the serpentinizing fluids to levels above 0.10 parts per billion (ppb) in solution. However, Au may be mobilized in high pH solutions. In contrast, fluids from vitric-rich clays on the flanks of the Torishima Seamount in the Izu-Bonin forearc have Pd values of between 4.0 and 11.8 nmol/L, Pt values between 2.3 and 5.0 nmol/L and Au values between 126.9 and 1116.9 pmol/L. The precious metals are mobilized, and possibly adsorbed onto clay mineral surfaces, during diagenesis and burial of the volcanic-rich clays. Desorption during squeezing of the sediments may produce the enhanced precious metal concentrations in the analyzed fluids. The metals are mobilized in the fluids probably as neutral hydroxide, bisulfide, and ammonia complexes. Pt/Pd ratios are between 0.42 and 2.33, which is much lower than many of the potential sources for Pt and Pd but is consistent with the greater solubility of Pd compared with Pt in most natural low-temperature fluids.

Metal and precursor effect during 1-heptyne selective hydrogenation using an activated carbon as support

Palladium, platinum, and ruthenium supported on activated carbon were used as catalysts for the selective hydrogenation of 1-heptyne, a terminal alkyne. All catalysts were characterized by temperature programmed reduction, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. TPR and XPS suggest that the metal in all catalysts is reduced after the pretreatment with H2 at 673 K. The TPR trace of the PdNRX catalyst shows that the support surface groups are greatly modified as a consequence of the use of HNO3 during the catalyst preparation. During the hydrogenation of 1-heptyne, both palladium catalysts were more active and selective than the platinum and ruthenium catalysts. The activity order of the catalysts is as follows: PdClRX > PdNRX > PtClRX ≫ RuClRX. This superior performance of PdClRX was attributed in part to the total occupancy of the d electronic levels of the Pd metal that is supposed to promote the rupture of the H2 bond during the hydrogenation reaction. The activity differences between PdClRX and PdNRX catalysts could be attributed to a better accessibility of the substrate to the active sites, as a consequence of steric and electronic effects of the superficial support groups. The order for the selectivity to 1-heptene is as follows: PdClRX = PdNRX > RuClRX > PtClRX, and it can be mainly attributed to thermodynamic effects.

Optical fibre sensors with applications in gas and biological sensing

This thesis describes the study of various grating based optical fibre sensors for applications in refractive index sensing. The sensitivity of these sensors has been studied and in some cases enhanced using novel techniques. The major areas of development are as follows. The sensitivity of long period gratings (LPGs) to surrounding medium refractive index (SRI) for various periods was investigated. The most sensitive period of LPG was found to be around 160 µm and this was due to the core mode coupling to a single cladding mode but phase matching at two wavelength locations, creating two attenuation peaks, close to the waveguide dispersion turning point. Large angle tilted fibre gratings (TFGs) have similar behaviour to LPGs, in that they couple to the co-propagating cladding modes. The tilted structure of the index modulation within the core of the fibre gives rise to a polarisation dependency, differing the large angle TFG from a LPG. Since the large angle TFG couple to the cladding mode they are SRI sensitive, the sensitivity to SRI can be further increased through cladding etching using HF acid. The thinning of the cladding layer caused a reordering of the cladding modes and shifted to more SRI sensitive cladding modes as the investigation discovered. In a SRI range of 1.36 to 1.40 a sensitivity of 506.9 nm/URI was achieved for the etched large angle TFG, which is greater than the dual resonance LPG. UV inscribed LPGs were coated with sol-gel materials with high RIs. The high RI of the coating caused an increase in cladding mode effective index which in turn caused an increase in the LPG sensitivity to SRI. LPGs of various periods of LPG were coated with sol-gel TiO2 and the optimal thickness was found to vary for each period. By coating of the already highly SRI sensitive 160µm period LPG (which is a dual resonance) with a sol-gel TiO2, the SRI sensitivity was further increased with a peak value of 1458 nm/URI, which was an almost 3 fold increase compared to the uncoated LPG. LPGs were also inscribed using a femtosecond laser which produced a highly focused index change which was no uniform throughout the core of the optical fibre. The inscription technique gave rise to a large polarisation sensitivity and the ability to couple to multiple azimuthal cladding mode sets, not seen with uniform UV inscribed gratings. Through coupling of the core mode to multiple sets of cladding modes, attenuation peaks with opposite wavelength shifts for increasing SRI was observed. Through combining this opposite wavelength shifts, a SRI sensitivity was achieved greater than any single observed attenuations peak. The maximum SRI achieved was 1680 nm/URI for a femtosecond inscribed LPG of period 400 µm. Three different types of surface plasmon resonance (SPR) sensors with a multilayer metal top coating were investigated in D shape optical fibre. The sensors could be separated into two types, utilized a pre UV inscribed tilted Bragg grating and the other employed a post UV exposure to generate surface relief grating structure. This surface perturbation aided the out coupling of light from the core but also changed the sensing mechanism from SPR to localised surface plasmon resonance (LSPR). This greatly increased the SRI sensitivity, compared to the SPR sensors; with the gold coated top layer surface relief sensor producing the largest SRI sensitivity of 2111.5nm/URI was achieved. While, the platinum and silver coated top layer surface relief sensors also gave high SRI sensitivities but also the ability to produce resonances in air (not previously seen with the SPR sensors). These properties were employed in two applications. The silver and platinum surface relief devices were used as gas sensors and were shown to be capable of detecting the minute RI change of different gases. The calculated maximum sensitivities produced were 1882.1dB/URI and 1493.5nm/URI for silver and platinum, respectively. Using a DFB laser and power meter a cheap alternative approach was investigated which showed the ability of the sensors to distinguish between different gases and flow rates of those gases. The gold surface relief sensor was coated in a with a bio compound called an aptamer and it was able to detect various concentrations of a biological compound called Thrombin, ranging from 1mM to as low as 10fM. A solution of 2M NaCl was found to give the best stripping results for Thrombin from the aptamer and showed the reusability of the sensor. The association and disassociation constants were calculated to be 1.0638×106Ms-1 and 0.2482s-1, respectively, showing the high affinity of the Aptamer to thrombin. This supports existing working stating that aptamers could be alternative to enzymes for chemical detection and also helps to explain the low detection limit of the gold surface relief sensor.

Developing a high density platinum/alumina hermetic feedthrough

Typically, hermetic feedthroughs for implantable devices, such as pacemakers, use a alumina ceramic insulator brazed to a platinum wire pin. This combination of material has a long history in implantable devices and has been approved by the FDA for implantable hermetic feedthroughs. The growing demand for increased input/output (I/O) hermetic feedthroughs for implantable neural stimulator applications could be addressed by developing a new, cofired platinum/alumina multilayer ceramic technology in a configuration that supports 300 plus I/Os, which is not commercially available. Seven platinum powders with different particle sizes were used to develop different conductive cofire inks to control the densification mismatch between platinum and alumina. Firing profile (ramp rate, burn- out and holding times) and firing atmosphere and concentrations (hydrogen (wet/dry), air, neutral, vacuum) were also optimized. Platinum and alumina exhibit the alloy formation reaction in a reduced atmosphere. Formation of any compound can increase the bonding of the metal/ceramic interface, resulting in enhanced hermeticity. The feedthrough fabricated in a reduced atmosphere demonstrated significantly superior performance than that of other atmospheres. A composite structure of tungsten/platinum ratios graded thru the via structure (pure W, 50/50 W/Pt, 80/20 Pt/W and pure Pt) exhibited the best performance in comparison to the performance of other materials used for ink metallization. Studies on the high temperature reaction of platinum and alumina, previously unreported, showed that, at low temperatures in reduced atmosphere, Pt 3Al or Pt8Al21 with a tetragonal structure would be formed. Cubic Pt3Al is formed upon heating the sample to temperatures above 1350 °C. This cubic structure is the equilibrium state of Pt-Al alloy at high temperatures. The alumina dissolves into the platinum ink and is redeposited as a surface coating. This was observed on both cofired samples and pure platinum thin films coated on a 99.6 Wt% alumina and fired at 1550 °C. Different mechanisms are proposed to describe this behavior based on the size of the platinum particle

Biological and chemical strategies for the recovery of precious and rare metals as nanoparticles

Tese de Doutoramento, Ciências do Mar da Terra e do Ambiente, Ramo: Ciências e Tecnologias do Ambiente, Especialidade em Biotecnologia, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2016