Tesis sobre el tema "Platinum"

Background: Histone modifications play an important role in gene regulation. Their genomic locations are of great interest. Usually, the location is measured by ChIP-seq and analyzed with a peak-caller. Replicated ChIP-seq experiments become more and more available. However, their analysis is based on single-experiment peak-calling or on tools like PePr which allows peak-calling of replicates but whose underlying model might not be suitable for the conditions under which the experiments are performed. Results: We propose a new peak-caller called \"Sierra Platinum\" that allows peak-calling of replicated ChIP-seq experiments. Moreover, it provides a variety of quality measures together with integrated visualizations supporting the assessment of the replicates and the resulting peaks, as well as steering the peak-calling process. Conclusion: We show that Sierra Platinum outperforms currently available methods using a newly generated benchmark data set and using real data from the NIH Roadmap Epigenomics Project. It is robust against noisy replicates.

Dealloying is a corrosion process in which one or more elements are selectively removed from an alloy leading to a 3-dimensional porous structure of the more noble element(s). These porous structures have been known to cause stress corrosion cracking in noble metal alloy systems but more recent interest in using the corrosion process to produce porous metals has developed. Applications for these structures range from high surface area electrodes for biomedical sensors to use as skeletal structures for fundamental studies (e.g. low temperature heat exchangers or sensitivity of surface diffusivity to chemical environment). In this work we will review our current understanding of alloy corrosion including our most recent results demonstrating a more accurate method for calculating alloy critical potential based on potential hold experiments. The critical potentials calculated through the potential hold method were â 0.030VMSE, 0.110VMSE, and 0.175VMSE for Cu80Pt20, Cu75Pt25 Cu71Pt29 respectively. We will present the use of porous metals for making surface diffusivity measurements in the Pt systems as a function of chemical environment. A review of the use of small angle neutron scattering to make accurate measurements of pore size is presented and the sensitivity of pore size to electrolyte, electrolyte composition, applied potential and temperature will be explained. The production of porous Pt with pore sizes ranging from 2-200nm is demonstrated.
Ph. D.

Development of Non-Traditional Platinum Anticancer Agents: trans-Platinum Planar Amine Compounds and Polynuclear Platinum Compounds By Daniel E. Lee, Ph.D. A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Virginia Commonwealth University. Virginia Commonwealth University, 2015 Major Director: Nicholas P Farrell, Ph.D., Professor, Department of Chemistry Platinum anticancer compounds with cis geometry, similar to cisplatin, have been explored to circumvent the cisplatin resistance; however, they were not considered broadly active in cisplatin cells due to exhibiting similar or same cell death mechanism as cisplatin. Platinum compounds with trans geometry were less studied due to transplatin being clinically inactive; but with few structural modifications, they resulted in unaffected cytotoxic activities in cisplatin resistant cells with structural modification by exhibiting different modes of DNA binding. This research focused on further exploring and establishing structure-activity relationship of two promising non-classical series of platinum compounds with trans-geometry: trans-platinum planar amine (TPA) compounds and noncovalently binding polynuclear platinum compounds (PPC-NC). During this research, further optimizations of the reactivity of TPA compounds were accomplished by modifying the leaving carboxylate groups. The effects of modified reactivity were probed by a systematic combination of chemical and biophysical assays, followed by evaluating their biological effects in cells. To establish the structural-activity relationship of PPC-NCs, Mono-, Di-, Tri-, and Tetraplatin NC with charge of 4+, 6+, 8+, and 10+ were synthesized and evaluated by utilizing biophysical and biological assays. Lastly, a new class of polynuclear platinum compounds, Hybrid-PPCs, were synthesized and evaluated to overcome the pharmacokinetic problems of BBR3464, phase II clinical trial anticancer drug developed previously in our laboratory.

This study focused on the sequenced combinations of platinum drugs cisplatin and oxaliplatin and four phytochemicals celastrol, guggulsterone, garcinol and ellagic acid administered to human ovarian lines A2780, A2780cisR and A2780ZD0473R. Among the phytochemicals, celastrol is most active having comparable activity against all the three ovarian tumour models. As applied to binary combinations of platinum drugs and the phytochemicals, it was found that generally synergism was greater at higher concentrations (ED75 and ED90) of drugs than at lower concentrations (ED50) in all three cell lines. Often 0/0 h and 0/4 h sequences of administration were found to be more synergistic, giving support to the idea that pre-treatment or concurrent with the phytochemicals have served to activate the cancer cells towards assault by the platinum drugs. The reduced accumulation of platinum in the cisplatin resistant cell line A2780cisR as compared to the cisplatin sensitive cell line A2780, gives support to the concept that the reduced platinum accumulation is the principal mechanism by which the cisplatin resistant cell line A2780cisR cell line resist the platinum drugs action. The absence of any visible DNA band after interaction of A2780 cells with ellagic acid indicates total DNA damage so that the phytochemical is most damaging to DNA in A2780 cells. The results of the present study showed the levels of reduced form of glutathione (GSH) in the resistant cell line A2780cisR were higher than the parent cell line A2780, irrespective of whether the cells were treated with a single agent (cisplatin, oxaliplatin, or ellagic acid) or in combination, giving support to the idea that the higher levels of glutathione serve to be one of the central mechanisms of cisplatin resistance in ovarian cancer cells.

In this study a method was developed to identify and quantify platinum(II) complexes of the type [PtCl4-n(OH)n]2- and [PtCl4-n(H2O)n]2-n. Separation of the various species was achieved with the aid of a hyphenated reversed phase HPLC-ICP-MS technique coupled with an ion-pairing reagent, HMHDCl2. The adsorption of HMHD2+ onto a C-18 column was investigated by generating a series of breakthrough curves. It was found that the selectivity for high charge density anions originates from its low surface coverage relative to TBA+, which on the other hand could not separate Pt(II) complexes. The peaks in the chromatographic traces were assigned by following the stepwise ligand substitution of [PtCl4]2- in hydroxide medium with UV/Vis spectrophotometry and HPLC-ICP-MS simultaneously. A computer program was written by the author to analyse chromatographic data by deconvoluting the chromatogram into its individual components and calculating the mole fraction of each component. The validity of the consecutive pseudo-first order model was validated by constructing 3D Mauser diagrams with the raw spectrophotometric data (A1 vs A2 vs A3). Additional software was used to simulate the raw spectrophotometric data and processed chromatographic data. The pseudo-first order rate constants obtained in both cases were in agreement with each other. Hence, peaks were assigned to [PtCl4]2-, [PtCl3(OH)]2-, [PtCl2(OH)2]2-, [PtCl3(H2O)]-. The molar extinction coefficient spectra of [PtCl3(OH)]2- and [PtCl2(OH)2]2- were obtained by simulating the spectrophotometric data at wavelengths from 280 to 450 nm. The reaction of [PtCl4]2- with sodium hydroxide was investigated with UV/Vis spectrophotometry at 25 °C. A rate constant consisting of a first and second order term was obtained. The first order term agreed with what has been reported in the literature for aquation of [PtCl4]2- at 25 degrees C. The influence of temperature was established by conducting the experiment at different temperatures. It was found that the reaction proceeds essentially via aquation at elevated temperatures.

There has been an increased awareness of the inter-dependence between man and the environment since the 1960’s. Environmental awareness has evolved from representing fairly radical views opposing all development, to a current emphasis on sustainable development between development and the environment. Life Cycle Assessment (LCA) is defined as the identification and quantification of the environmental impacts of a product, process or service during the entire life cycle being studied. The life cycle starts at the extraction of raw materials and the production of energy used to create the product through the use and final disposal of the product. LCA therefore considers the production, use and disposal of a product, which constitutes the life cycle of the product. LCA can be combined with methodologies that study other parameters such as costs in order to optimise the benefits from LCA. It is suggested that cost implications of processes to reduce environmental impacts should be included in a methodology used for a Platinum LCA. A comment that is consistently raised in the case studies is that the minerals industry regards LCA as an effective tool to determine the impacts of the industry, however extraction & beneficiation of minerals are often grouped together, with accurate data not being available, and databases either not available or not updated. The case studies indicated several benefits from the various LCA’s conducted. A Platinum LCA should clearly define and group the environmental impacts being studied into categories such as greenhouse gas emissions, global warming, acidification, and resource consumption. A Platinum LCA will be resource- and time intensive due to the large scale of the processes involved. It is suggested that a Platinum LCA firstly focuses on the production phase, i.e. cradle-to-gate, with potential future work done on the use and end-of-life stages. It is suggested that individual facility-based LCA’s for AMPLATS and other platinum producers are conducted in order to get a true reflection of the environmental burden of each company, and then selectively share technological improvements to reduce the environmental burden without disclosing sensitive information. The benefit of LCA in the case of platinum will be optimised if it can be used to make business decisions, together with consideration of financial and production benefits in addition to anticipated environmental benefits of alterations to processes. It is essential that LCA is seen as a business tool that will assist the company to make informed business decisions about process improvements, as well as new projects and design of new facilities. LCA on its own will not determine which product or process is the most cost effective or works best. The information developed in a LCA study should be used as one component of a more comprehensive decision making process assessing the trade-offs with cost and performance. The results from a LCA could be used to make informed decisions about optimisation between costs and reduced environmental impacts.
Thesis (M. Environmental Management)--North-West University, Potchefstroom Campus, 2011.

[Formulae and special characters can only be approximated here. Please see the pdf version of the Abstract for an accurate reproduction.] Several inert platinum complexes were synthesised: [(en)Pt([special character]-dpzm)2Pt(en)]4+, [{Pt(dien)}2[special character]-dpzm]4+, [{Pt(dien)}2[special character]-H2N-(CH2)6-NH2]4+, cis-[(NH3)2Pt([special character]--dpzm)2Pt(NH3)2]4+, trans-[Pt(NH3)2([special character]-dpzm)2]2+. Three active complexes, all with chloro ligands, were also synthesised: trans-[{Pt(NH3)Cl2}2[special character]-dpzm)], trans-[{Pt(NH3)2Cl}2[special character]-dpzm]2+ (di-Pt) and trans-[trans-{Pt(NH3)2Cl}2{trans-[Pt(NH3)2([special character]-dpzm)2]}]4+ (tri-Pt). 1H NMR established that multi-nuclear platinum complexes will preferentially associate in the DNA minor groove with a preference for A/T sequences, and with a binding constant [special character]-105 M-1, regardless of the charge, linking ligand, length or shape. Using [(en)Pt([special character]-dpzm)2Pt(en)]4+ and the oligonucleotide d(GC)5 it was determined that the metal complex binds G/C rich sequences also in the minor groove, but with a much reduced binding constant, 103 M-1. CD studies showed [(en)Pt([special character]-dpzm)2Pt(en)]4+ was able to induce a DNA conformation change from B-type to what appeared to be a partial Z-type. Transcription assays showed that even though the metal complex does not bind DNA covalently, it is still able to inhibit DNA transcription at particular sites. The complexes di-Pt, tri-Pt, [{Pt(dien)}2[special character]-dpzm]4+ and trans-[Pt(NH3)2([special character]-dpzm)2]2+ were tested for anti-cancer activity in the L1210 murine leukaemia cell line, and gave values of 3.8, 2.5, [special character]200 and 64 [special character]M respectively. In the cisplatin resistant line (L1210/DDP), trans-[Pt(NH3)2([special character]-dpzm)2]2+ showed an increase in activity with a drop to 32 [special character]M, while both di-Pt and tri-Pt showed decreases in activity to values of 8.8 and 3.6 [special character]M. In the human ovarian carcinoma 2008 cell line and its cisplatin resistant derivative C13[special character]5, both complexes showed good activity with values of 2.5 and 20.9 [special character]M respectively, but again both showed decreases in activity in the resistant line with values of 17.8 and 37.7 [special character]M respectively. To help explain the difference between activity of these complexes and the complexes BBR3464 and BBR3005, cell uptake and DNA interstrand cross-linking experiments were performed. The cell uptake studies showed that both di-Pt and tri-Pt are taken up by cells at very high levels, when administered at 100 [special character]M, thus indicating that the difference is unlikely to be due to large differences in cell uptake. The DNA interstrand cross-linking studies showed both complexes readily form interstrand adducts (50% interstrand cross-linking at 12 nM and 22 nM respectively, c.f cisplatin 3 [special character]M). These results suggest that the rigid nature of the dpzm linker may be affecting the DNA adducts formed, with more interstrand links being formed than BBR3464. Possibly, it is this that causes the large differences in cytotoxicity. The DNA binding of di-Pt and tri-Pt was examined with the nucleosides adenosine and guanosine and the dinucleotide d(GpG). Both complexes bound at the N7 of guanosine, but 2-fold slower than cisplatin. In addition, di-Pt bound at the N7 and either the N1 or N3 of adenosine, 7-fold slower than guanosine. Di-Pt forms a large variety of cross-links between two d(GpG) molecules, however it could not be established whether the 1,2-intrastrand adduct could be formed. Di-Pt, however, forms a 1,2-GG interstrand adduct with the oligonucleotide d(ATGCAT)2 resulting in a conformation change away from B-type DNA. The sugar pucker of the G3 nucleoside changes from 2[special character]-endo towards 3[special character]-endo, and the position of the nucleotide relative to the sugar changes from anti to syn. The ability of multi-nuclear platinum complexes to form covalent adducts in the DNA minor groove remains unclear. It appears that di-Pt can form up to 33% minor groove adducts with the oligonucleotide d(AT)5, but when added to the oligonucleotide d(GCCAAATTTCCG)2 no definite minor groove adducts are seen and the major adduct appears to be a 1,2-interstrand cross-link between the two A6's or between the G1 and G11. Finally, a study of the encapsulation of platinum complexes within cucurbit[7]uril (Q7) as a means of reducing drug toxicity was made. For complex A and di-Pt, encapsulation of the linker ligand occurred. The effect of Q7 on the rate of hydrolysis of di-Pt was at least a 3-fold reduction as compared to free di-Pt with guanosine. Studies with [{Pt(dien)}2[special character]-dpzm]4+/Q7 and the oligonucleotide d(CGCGAATTCGCG)2 showed that the metal complex could dissociate from the Q7 and associate with the oligonucleotide, where an equilibrium is achieved with 15 % of the metal complex bound to the oligonucleotide and 75 % encapsulated in Q7. Tests in the L1210 and L1210/DDP cancer cell lines showed that di-Pt/Q7 has almost the same activity compared to free di-Pt.

Proton exchange membrane (PEM) fuel cells have the potential to provide a clean and convenient source of power for applications such as vehicle transport. At their heart lies a platinum catalyst which is used to reduce oxygen to water. Although platinum is expensive it is the best elemental catalyst for the reaction. In order to make better use of the platinum and reduce production costs, nanoparticulate platinum is dispersed onto a carbon support. This results in a greater surface area per gram of platinum used. Efforts to improve the performance of fuel cells and make them cost effective have so far revolved around increasing the surface area. However in doing this the inter-particle spacing and diffusional characteristics of the catalyst have been ignored. In order to address this oversight, this thesis takes a novel bottom up approach to better understanding the oxygen reduction reaction on nanoparticulate platinum, supported on carbon. By using a model system and simulating the diffusional environment, this work reveals new insights into the oxygen reduction reaction. In Chapter 1 the fundamental electrochemical principles which underpin the subsequent work shall are examined. Chapter 2 begins with a look at the history of fuel cell development, before assessing the modern PEM fuel cell and the challenges faced in the present day to make it ·a viable power source. In Chapter 3 carbon electrode materials are assessed with a view towards their use as a substrate for platinum ~atalysts. The results gained f:rom , ~~is prove useful in later chapters and are both novel and insightful for the selection of PEM fuel cell catalyst supports. In Chapters 4 and 5 voltammetry at nanomaterial modified electrodes are extensively analysed, using electrochemical simulation techniques. This reveals that diffusion can play a role in effects which are assumed to be purely kinetic. From this a major flaw is exposed in the currently accepted measures of oxygen reduction catalyst activity. Chapter 6 brings the information garnered from the previous chapters together. In this chapter nanoparticulate platinum dispersed onto a flat carbon substrate is used as a model system of a typical oxygen reduction catalyst. The resulting voltammetry from the model surfaces is then fitted effectively to results from electrochemical simulations, paying close attention to the diffusional environment around the nanoparticles. This approach leads to a key finding which had hitherto gone unrecognised.

The 2-picoline (2-methylpyridine) complex, cis-[PtCl₂(NH₃)(2-pic)] (AMD473), is promising new generation platinum antitumour agent currently in clinical trials and highly active cisplatin resistant cell-lines. The antitumour activity of trans platinum complexes has attracted renewed interest since it has been shown that some trans compounds, in particular those possessing planar amine ligands, are anticancer-active. Therefore, three trans isomers, trans-[PtCl₂(NH­₃)(2-pic)] (1), trans-[PtCl₂(NH₃)(3-pic)] (2) and trans-[PtCl₂(NH₃)(4-pic)] (3), were synthesised and characterised. The crystal structure of 1 shows steric hindrance induced by the 2-methyl group towards an axial approach to Pt, while its 3-pic (2) and 4-pic (3) analogues are less sterically hindered. Notable however, is that in the solid state complex 1 is less sterically-hindered than its cis isomer. ¹⁵N-labelling of complexes 1-3 allowed both the hydrolysis rates and pK_a values of the complexes to be determined using 2D[¹H, ¹⁵N] NMR spectroscopy. Adducts of cis- and trans-(PtCl₂(NH₃)(2-pic)] with neutral 9-ethylguanine (9-EtGH) and anionic (N1-deprotonated) 9-ethylguanine (9-EtG) were prepared and their structures determined by X-ray crystallography. Platinum is coordinated at the guanine N7 position with a head-to-tail arrangement of the bases in all cases. Two of the complexes exhibited intermolecular triple hydrogen bonding between neutral and deprotonated guanine ligands. In addition, adducts of cis- and trans-[PtCl­₂(NH₃)(2-pic)] with guanosine and 2’-deoxyguanosine were prepared and characterised in solution by NMR spectroscopy and ESI mass spectrometry. The complexes cis-[Pt(NH₃)(2-pic)(Guo)₂]²⁺, and cis- and trans-(Pt(NH₃)(2-pic)(2’-dGuo)₂]²⁺ were assigned as head-to-tail conformations, on the basis of their NOE cross-peaks. The reaction of cis-[Pt(¹⁵NH₃)(2-pic)(OH₂)₂]²⁺ and guanosine (Guo) was followed by 2D [¹H, ¹⁵N] NMR spectroscopy and was found to proceed through two mono(guanosine) intermediate species to yield the dominant product cis-[Pt(¹⁵NH₃)(2-pic)(Guo)₂]²⁺. Initial guanosine substitution trans to 2-picoline was faster than substitution cis to 2-picoline due to steric hindrance, but the rates of the second guanosine substitution were similar. The binding of ¹⁵N-labelled-1 to a self-complementary DNA duplex, d(TATGGTACCATA)₂, was investigated using 1D ¹H and 2D [¹H, ¹⁵H] NMR spectroscopy. The first aquation step appeared to be the rate-limiting step in the formation of the monofunctional adducts. Several DNA products were observed but could not be identified unambiguously. The rate constants for reactions between ¹⁵N-laabelled 1 and guanosine 5’-monophosphate (5’-GMP) were determined via 2D NMR studies, and compared to those previously reported for cis-[PtCl₂(NH₃)(2-pic)].

This thesis reports experimental work with two main aims: the first is the investigation of single nanoparticles with an emphasis on their porosity, and the second is to develop a more comprehensive understanding of their electrocatalytic behavior. The fundamental principles and techniques of electrochemistry are introduced in Chapter 1. Chapters 2 and 3 respectively summarize nanomaterials and their characterization methods. In particular, the technique of single particle electrochemical impacts, so-called "nanoimpacts", is used to study redox reactions at individual nanoparticles. Chapters 4 and 5 report the porosity of platinum nanoparticles (PtNPs) via tag-redox coulometry (TRC) and surface platinum oxidation, respectively. In the former, thioltagged PtNPs are employed and current transients upon impacts with a cathode are detected. This is due to the nitro group reduction on individual PtNPs. The charge per spike is measured and the number of tag molecules can be calculated. Therefore, the "electroactive surface area" of the PtNPs is revealed. In the latter, oxidative transients upon direct impacts are observed. The charge per current spike is measured and attributed to the formation of surface platinum oxides. XPS shows PtO and PtO₂ in different amounts and an average oxidation state is deduced as a function of potential. Thus the number of platinum atoms oxidized per PtNP can be estimated. Both experiments allow insight into extent to which the internal surface of the aggregate is "seen" by the solution and is electrochemically active, providing a fuller knowledge of the catalytic behavior of nanoparticles, as reflected from the reaction kinetics and the redox currents. Furthermore, results from Chapters 4 and 5 are in close agreement with each other, indicating the accuracy of the measurements in both studies. With this appreciation of the internal nanoscale structure, Chapter 6 investigates the kinetics of the hydrogen oxidation reaction (HOR) on mesoporous particles. The steadystate current for HOR is measured on both individual platinum particles and PtNPs drop-casted substrates. The kinetic parameters are determined and contrasted between these two approaches. Nanoimpacts are required in order to correctly understand the electrochemical reaction catalyzed by nanoparticles, as the aggregation or loss of ensemble drop-casted particles leads to errors. Chapter 7 further elaborates the role of nanomorphology of nanoparticles in catalyzing the HOR using individual mesoporous particles and low density random arrays of particles. At the single particle scale the activity of the platinum catalyst towards the hydrogen oxidation is potential dependent and exhibits two peaks, as reflected in the electrochemical current. This is due to the sensitivity of the reaction rate to the interfacial structure of PtNPs. The decrease in activity correlates directly with the potential at which the underpotential deposited hydrogen (H_upd) is removed from the catalytic interface. The contribution of the internal mesoporous nanoparticle structure towards the total particle catalytic activity is further corroborated through comparison of the current-time transients recorded for individual nanoparticles of differing morphology: solid vs mesoporous, and by evidencing the sensitivity of the single particle catalytic activity to the supporting electrolyte concentration. In Chapter 8, the underpotential deposition and removal of hydrogen from a mesoporous PtNP surface is shown to quantify the electrochemically active surface area (ECSA) of an individual nanoparticle. This surface area of the particle is concomitantly correlated with its individual catalytic activity (current density) towards the hydrogen evolution reaction (HER). In addition, conclusions in this chapter are compared with the results in Chapters 4 and 5, showing consistency in all structural measurements of the particles. Finally, Chapter 9 provides the main conclusions for the studies described in the thesis. The various discoveries in this thesis in respect of individual nanoparticles reflect generic methodological development, both fundamentally and applied, in studying electrochemistry at nanoscale. The overall major finding is that it is essential to recognize particle porosity to fully understand catalytic properties.

Includes abstract.
Includes bibliographical references.
The Pt[8]Zr ordering transformation in Pt 11 at. % Zr alloys has been studied. The study included determination of the formation of the Pt[8]Zr phase and its order/disorder transformation temperature (Tc). Electron diffraction patterns and dark field images were obtained from transmission electron microscopy to characterize the Pt[8]Zr phase. Microhardness measurements and light microscopy were used to investigate the Pt[8]Zr ordered phase and its effects on hardness and microstructure respectively. The Pt[8]Zr ordered phase was found to be present in the initial as-cast condition and in specimens heat treated up to a temperature of 1070 °C. This is consistent with the DSC measurements of Tc, determined to be 1068 °C. The nucleation of the ordered phase was found to be rapid at any temperature below Tc but the growth of this ordered phase was rather slow, probably due to inadequate vacancies present in the alloy. The domain size of the Pt[8]Zr phase was found to be approximately 10 nm for specimens heat treated at 1000 °C for up to 600 hours.

The platinum-based chemotherapy drugs cisplatin, carboplatin, and oxaliplatin remain, despite their long-term use, as integral components in the treatment of more than 25 different human cancers. As such, shortages in their supply can have serious health and societal impacts on both the outcome and welfare of patients and on the healthcare systems as a whole. As all three drugs are no longer under patent protection, they are supplied in Australia, the U.S. and the U.K. by between four and 17 different pharmaceutical companies, which reduces the risk of drug shortages. Determining the number and impact of platinum drug shortages in various regions of the world is difficult because legislation to monitor shortages has only been passed recently. All three drugs have suffered from shortages since 2017 with the most common shortage being due to discontinuation of the drug by the company. Other causes include production disruptions, changes in customer demand, problems in supply such as transport and storages, and other reasons. The median duration of drug shortage is 22 days (shortest and longest supply shortages are 3 and 79 days, respectively). Shortages appear to be rare in developed western countries and western European countries, but more common in eastern European countries where platinum drugs are never available or are available only half of the time. This project highlights the lack of information available on platinum drug shortages and the end to further examine platinum drug shortages in regions that are more likely to be impacted, such as Africa, south-east Asia, central and southern America, and the Middle East.

xix, 111 p. : ill. (some col.)
Since discovery of its biological effects in the late 1960's, cisplatin (cis-diamminedichloroplatinum( II)) has become one of the most broadly-prescribed cancer drugs in use today. A majority of efforts to understand the metallobiochemistry of this drug have focused on describing the interactions of cisplatin-derived Pt(II) complexes with DNA. Drug binding to this "high value" cellular target is believed to trigger the apoptotic pathways that underlie cisplatin's cytotoxic effects. Although RNA is chemically similar to DNA and responsible for accurately transferring, regulating, and transforming the same genetic information that is stored within the DNA genome, surprisingly little is known about platinum(II) drug binding to RNA. Accordingly, the first three chapters of this dissertation describe efforts to address questions regarding cisplatin coordination to RNA on the molecular scale. Chapter I reviews fundamental aspects of how metal complexes interact with nucleic acids, highlighting the bioinorganic chemistry of platinum(II) antitumor drugs. This chapter also introduces the idea that drug binding to RNA may form an important part of how these complexes work in the cell. Chapter II describes cisplatin crosslinking between RNA nucleobases located on opposite sides of the internal loop of an RNA subdomain derived from the catalytic core of the spliceosome. Chapter III describes how platinum adducts disrupt the activity of RNA processing enzymes similar to those that are necessary for maturation, maintenance and recycling of the transcriptome. Chapter III also describes the reversal of RNA platination using thiourea. The chemistry of platinum(II) is also characterized by preferential coordination to sulfur ligands, or thiophilicity. Incorporating this property into RNA chemistry, Chapters IV and V describe the reaction of platinum(II) complexes with phosphorothioate-substituted RNAs. Chapter IV describes engineering platinum(II) crosslinks in the Hammerhead ribozyme through the targeting of a platinum(II) complex to a specific phosphorothioate substitution installed in the active site of this catalytic RNA. Chapter V outlines efforts to characterize the cleavage and isomerization reactions promoted by platinum(II) coordination to phosphorothioate-substituted RNAs. Finally, Chapter VI summarizes the insights gained throughout the course of our studies and provides an outlook on the future of platinum-RNA chemistry. This dissertation includes co-authored material and previously published results.
Committee in charge: Michael M. Haley, Chair; Victoria J. DeRose, Advisor; David R. Tyler; Andrew J. Berglund; Eric A. Johnson

Neste trabalho foi investigada a eletrooxidação de etanol sobre eletrodos nanoparticulados binários Pt-M1 (M1 = Sn ou Re) e ternários Pt-M1-M2 (M1 e M2 = Sn e Re) suportados em carbono. Estes materiais foram preparados pelo método da redução por álcool e foram caracterizados por difração de raios-X e microscopia eletrônica de varredura associada a EDX. Os eletrodos foram montados utilizando-se a técnica de camada ultrafina. Os resultados eletroquímicos mostraram que a adição dos diferentes metais à platina aumentou a atividade catalítica tanto dos eletrodos binários quanto dos ternários. Os testes realizados na célula unitária mostraram que a presença de Sn nos catalisadores binário e de Sn e Re nos catalisadores ternários aumentou significativamente o desempenho da célula quando comparada ao ânodo de Pt pura suportada em carbono, preparado pela metodologia da redução do álcool ou ao comercial da E-TEK. O catalisador Pt70Sn10Re20/C foi o que apresentou a melhor densidade de corrente assim como a melhor densidade de potência com um valor máximo alcançado de aproximadamente 40 mW cm-2 durante a operação da célula a combustível a 90 oC.
In this work was investigated the electrooxidation of ethanol on nanostructured binary Pt-M1 (M1 = Sn or Re) and ternary Pt-M1-M2 (M1 and M2 = Re and Sn) electrodes supported on carbon. These materials were prepared by the alcohol reduction method and were characterized by X-ray diffraction and scanning electron microscopy associated to EDX. The ultra-thin layer technology was used to assemble the electrode. The electrochemical results showed that the addition of different metals to platinum increased the catalytic activity of the binary and ternary electrodes. Tests conducted in unitary fuel cell showed that the presence of Sn in the binary catalysts and Sn and Re in the ternary catalysts increased significantly the performance of the cell when compared to pure Pt anode supported on carbon, prepared by the alcohol methodology or the commercial E-TEK. The catalyst Pt70Sn10Re20/C presented the best current density as well the better power density with a maximum value of ca. 40 mW cm-2 reached during the operation of the fuel cell at 90 oC.

In this investigation, cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and rotating disc electrode (RDE) measurements of the oxygen reduction reaction (ORR) have been used to explore the complex three-phase Nafion-platinum-electrolyte interface. This interface is at the heart of the functioning membrane electrode assembly (MEA) of a fuel cell. CV was primarily used to analyse ultra-thin Nafion films, deposited (without contamination) onto various flat and stepped platinum and platinum bimetallic single crystal electrodes. For Pt{111}, XPS measurements were also used to determine Nafion surface layer thickness and to obtain surface chemical composition. CV results have shown that Nafion is a probe of adsorbed OH on platinum electrodes and for stepped surfaces, unusual structural sensitivity of Nafion-induced voltammetric peaks, ascribable to Nafion interactions with step sites, is observed as a function of average terrace width. Voltammetric results for palladium adlayers (up to two monolayers) adsorbed on Nafion coated Pt{111} and {100} in aqueous 0.1M HClO4, show the first layer palladium hydrogen underpotential deposition (HUPD) peak being much sharper and intense as compared to Nafion free surfaces. A similar phenomenon was found for platinum-palladium surface alloys in that Nafion adsorption would produce sharper, palladium HUPD peaks. This behaviour is ascribed to stronger specific adsorption of the Nafion sulphonate groups with palladium compared to platinum. It was interesting to note that for bismuth adlayers adsorbed onto Nafion coated Pt{111} and {100}, attenuation of HUPD features was identical whether or not Nafion was adsorbed but the Bi-OH redox features for Nafion coated surfaces exhibited marked differences, again ascribable to competitive adsorption of sulphonate and OH. Using RDE, it was found that the ORR for various Nafion coated Pt{hkl} electrodes was inhibited compared to Nafion free electrodes. The electrooxidation of formic acid on palladium modified, Nafion coated Pt{111}, in aqueous 0.1M HClO4, was found not to be affected by the presence of Nafion. However methanol electrooxidation was inhibited on palladium modified, Nafion coated Pt{111}. Finally a number of actual fuel cell electrocatalysts, provided by Johnson Matthey were characterised using CV. The {111} and {100} surface site densities were quantified using bismuth and germanium as surface probes. Comparisons between Nafion coated electrocatalysts and Nafion free electrocatalysts are also reported. It was found that only very marginal differences between the CV responses of both types of catalyst are recorded (in contrast to the single crystal data).

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 59).
The platinum market is a material market of increasing interest, as platinum demand has grown faster than supply in recent years. As a result, the price of platinum has increased, causing end-user firms to experience material scarcity through the presence of these high prices. A significant driver of this demand growth for the last several decades is demand automotive sector, which is responsible for almost 60% of total primary platinum demand, due to the use of platinum in three way catalysts. Platinum is one of the materials utilized to catalyze reactions that prevent vehicle emissions from entering the atmosphere, which can have a severe impact on air quality. Two factors will likely contribute to the future growth of automotive platinum demand: the trend in increased use of platinum per vehicle, and expected growth in the number of automobiles produced and sold around the world. While the automotive market is relatively saturated in developed economies, automotive sales growth potential is particularly high in developing areas, such as BRIC countries. It follows that future growth in automotive platinum demand is likely to be significant. As such, the study aims to characterize the drivers of automotive platinum demand and to establish how this demand sector impacts the platinum market as a whole. This characterization is achieved through regression analysis and by utilizing a platinum market simulation model.
(cont.) The regression results indicate that the automotive platinum demand has historically been an inelastic one. Global automotive sales have indeed been a driver of platinum demand behavior. Regression on automotive sales in India, a BRIC country has high correlation with wealth as measured by GDP per capita. In the US and Japan, automotive sales show high autocorrelation and additional correlative relationships were not confirmed. Model results show that the automotive industry drives platinum price increases when there is a combination of low elasticity of platinum demand and large growth rates in the global automotive industry. Recent news about new technologies suggests that demand elasticity may increase, and the model suggests that higher elasticity would reduce the impact of automotive industry growth on the total demand for platinum.
by Christopher George Whitfield.
S.B.

The hydrogen evolution reaction (HER) has been examined on a variety of Pt and Pt-group metal surfaces to investigate the rate of the reaction. Pt stepped single crystal surfaces were investigated in relation to the HER using cyclic voltammetry, linear sweep voltammetry and multi-frequency AC voltammetry. It was found that the hydrogen evolution reaction activity did not show a dependence on the structure of single crystal platinum electrode surfaces. Thick films of Au, Rh and Pd were deposited onto Pt {111} and successfully annealed to give pseudomorphic surfaces of the bulk metal. The aim of such measurements was to investigate whether strains within the crystal lattice of these films would result in enhanced HER activity. None of the surfaces investigated showed significant HER enhancement. Rather, results similar to those observed using the bulk metals were obtained. Rough Ir and Pt deposits on Pt{111} were also investigated. Enhanced HER activity was observed on these surfaces. This enhancement was interpreted in terms of the structural arrangement of the Ir and Pt deposits. For Pd films on Pt {111} (0 < fVPd < 2 monolayers) it was observed that Pt dominated the HER kinetics for Pd coverages up to one monolayer and was still influential on the HER at two monolayers of Pd. Similarly Pd-Pt surface alloys also showed that Pd had little or no influence on the HER kinetics even with 75 % Pd in the surface layer. Possible mechanisms for this behaviour have been proposed, in particular, the role of subsurface hydrogen in HER on Pt is discussed.

To date, the cost of high platinum loadings in polymer electrolyte fuel cells (PEFCs) remains one of the main deterrents preventing their broad commercialisation. The reaction of interest in this work is the oxygen reduction reaction (ORR) occurring at the cathode side of the PEFC. The ORR has been studied at great length owing to the sluggish kinetics of this reaction and thus the necessity of the higher platinum loadings required on the cathode side of the PEFC. Platinum particle size and surface morphology are thought to be directly related to the catalytic activity of platinum towards the ORR (Mayrhofer et al., 2005) A better understanding of the effects of platinum particle size and surface morphology on the mechanism and kinetics of the ORR is critical if platinum loadings are to be reduced whilst maintaining the US Department of Energy (DoE) target performance levels (Schwanitz et al., 2012). This study focuses on the effects of platinum surface morphology on ORR activity by the development of platinum supported carbon electrodes. The surface morphology was modified by varying the platinum loading, such that the surface was taken from isolated nanoparticles to an extended surface. The effects of the changes in surface morphology and particle size on the ORR were then investigated. First a model electrode system was developed by magnetron sputter deposition of platinum onto a carbon black (VulcanXC72) surface supported on a glassy carbon electrode. The model system was then translated into a practical system, whereby platinum supported on carbon catalysts were prepared by metal-organic chemical vapour deposition (MOCVD) with increasing weight percentages of platinum. Similar trends were observed for the MOCVD catalyst system and the model electrode system. The trends of particular interest were the effects of platinum loading on hydrogen peroxide formation during the ORR and the double voltammeric CO oxidation peak observed with increased platinum loading during CO stripping voltammetry experiments. Hydrogen peroxide formation was observed at potentials below 0.8 V vs. SHE/RHE and it was found that hydrogen peroxide formation was predominant on dispersed platinum nanoparticles compared with platinum agglomerates. This is most likely related to peroxide species, a partial reduction product from oxygen to water, being able to desorb from the active surface without being further reduced to water on an adjacent site as the inter-particle distance is greater for the low loading samples relative to the higher loading samples in both systems. A clear indication of differing surface morphology between the low and high loading samples was observed by the double voltammeric peak detected during CO stripping voltammetry experiments. The low potential peak attributed to platinum agglomerates was seen to increase in amplitude as platinum loading increased. The corresponding high potential peak attributed to isolated nanoparticles, decreased in amplitude with increasing platinum loading. This observation alludes to an increase in particle agglomeration with platinum loading, and physical characterisation methods such as TEM and XRD showed an increase in the average particle size with increasing platinum loading, which supports the CO stripping voltammetry findings. The findings indicate a profound dependence of the ORR on platinum particle size and surface morphology. A better insight into these properties could assist in improved catalyst design and the enhancement of platinum utilisation and ORR activity of platinum.

Methods to map small-molecule interactions with cellular RNAs are important for understanding endogenous activation, such as in riboswitches, as well as the potential for exogenous compounds to target RNA. Cisplatin is one of the most widely used of the platinum anticancer drugs that are prescribed in approximately 40-50% of all chemotherapy treatments (Dyson and Sava, 2006; Harper et al., 2010). Despite nearly 40 years of experience with this class of drugs, we still lack a comprehensive understanding of the targets of Pt compounds and their effects on cells. Pt(II) compounds are well-known DNA and RNA crosslinking agents, but the latter area is under-studied. In order to better understand the impacts of cisplatin and other platinum(II)-derived small molecules on cellular RNA, we have developed a technique we call “Platinum-seq,” which couples reverse transcription mapping of platinated RNAs to high-throughput sequencing. Chapter 1 is a study of cisplatin and a novel click-functionalized platinum compound (2-ADAP Pt) binding to the HDV ribozyme, a small catalytic RNA. Chapter 2 moves our platinum mapping approaches from low-throughput, sequencing gel based methods into next-generation sequencing for high-throughput analysis of all platinum sites in cellular RNA, a method we have named “Platinum-seq.” Chapter 3 is a study of differential gene expression of Saccharomyces cerevisiae treated with cisplatin and a second novel platinum(II) compound (azaplatin), using data acquired from the work in Chapter 2. Chapter 4 describes recent efforts to implement pre-enrichment of sequencing targets using click chemistry followed by DNA hybridization, in order to enrich for platinated fragments before sequencing library construction. Together, this work represents a significant step forward in advancing analysis of Pt(II) binding to cellular RNA, a potentially important target for this widely used class of anticancer compounds. Methods developed here are broadly applicable to genome-wide identification of platinum accumulation on DNA as well, which has not been pursued despite the extensive use of these compounds.

In this dissertation, the aim was to develop a platinum specific resin to be utilized for the early removal of platinum from the industrial feed solution. Efforts were therefore directed towards the syntheses of silica based resins, with active centra, designed for platinum. The large chlorometallate ions present in the feed stream, were characterized in terms of physical parameters relevant to phase distribution, namely distortability (RD), charge density, softness (σ) etc. Matching cations for each of the types were investigated. In order to attempt the design of platinum specific resins, different structural amines were used to aminate the silicone precursor and to subsequently fix these onto the silica framework. Two different solvents namely alcohol and dmf were used in this process, resulting in two sets of resins, with different properties. The design was based on previous experience with these ions, with reference to their behaviour towards different types of cations. The platinum species, PtCl6 2- and PtCl4 2-, as well as the most important contaminants in the feed stream, were typified, bearing in mind size, charge, charge density and distortability. Different types of cationic centra, having differences in charge density, stereochemical crowding and extent of hydrophobicity, were synthesized and tested-both as solvent extractants (where possible) and silica based resins. The results indicated that, partly screened secondary ammonium cationic resin species, which could be regarded as “intermediate”, proved to be satisfactory both in their high percentage extraction for PtCl4 2- and rejection of contaminants like chlororhodates, chloroiridates(III) and FeCl4 -. It was however necessary, to work at a redox potential, where iridium(IV) in the form of IrCl6 2-, was absent. Various 2-aminoalkane resins were prepared, with variation in the length of alkane group and synthesised by the two different solvents. The latter resulted in two sets of resins with not only differing compactness, but also having significantly different properties with reference to platinum specificity, HCl effect and stripping potential. The 2-aminobutane and 2-aminoheptane resins in particular, proved to be very satisfactory platinum specific resins, both with respect to selectivity, platinum capacity and stripping potential. The various physical parameters could be applied to identify the chemical behaviour of anions and assist in the development of anion specificity for the relevant species.

No presente trabalho foram preparados eletrodos recobertos com filmes contendo Pt, Ru e Sn pelo método de decomposição térmica de precursores poliméricos sobre um substrato de Ti. Este método permitiu a obtenção de filmes homogêneos e com estequiometria controlada. Foram avaliadas as variáveis relacionadas ao processo de preparação dos eletrodos tais como, temperatura de calcinação e proporções entre os óxidos. As caracterizações estrutural e morfológica dos eletrodos foram feitas pelas técnicas de Difração de Raios-X e Microscopia Eletrônica de Varredura. A atividade eletrocatalítica dos eletrodos foi avaliada pelas técnicas de Voltametria Cíclica, Cronoamperometria, Espectroscopia de Infra-Vermelho in situ e aplicação dos eletrocatalisadores em célula a combustível. Os resultados obtidos indicaram que o método utilizado proporcionou a preparação de eletrodos com alta área superficial devido a formação de uma morfologia contendo poros e trincas. Os eletrodos preparados com a adição de rutênio e estanho à platina apresentaram maior eficiência catalítica para a oxidação das moléculas em estudo em relação aos eletrodos contendo somente platina. Através dos espectros obtidos por FTIR in situ foi possível observar a formação espécies de CO adsorvido à superfície eletródica no potencial a partir de 100 mV (ERH) e CO2 foi produzido a partir de 400 mV (ERH). Estes valores de potencial observados são inferiores aos valores para os eletrodos de Pt pura e confirmam a contribuição do Ru para a oxidação das espécies adsorvidas que bloqueiam a superfície. Para a aplicação em células a combustível, foram preparados dois tipos de catalisadores (suportados e não suportados em pó de carbono), sendo que os catalisadores suportados apresentaram maior densidade de potência em relação aos não suportados. A composição contendo 60 % de Pt apresentou maior desempenho, confirmando os resultados obtidos em meia célula. O método de preparação do catalisador utilizado permitiu, portanto, a síntese de materiais possíveis de serem utilizados em células a combustível de metanol.
In this work we prepared electrodes containing Pt, Ru and Sn on the Ti substrate by thermal decomposition of polymeric precursors. This method yielded homogeneous films with controlled stoichiometry. The parameters of the preparation process like temperature and oxide composition were investigated. The structural and morphological material characterization were performed by X-ray Diffractometry and Scanning Electronic Microscopy. The electrocatalytic activity was investigated by Cyclic Voltammetry, Chronopotentiometry, in situ Infra-Red Spectroscopy and Fuel Cell tests. The obtained results showed that the preparation method lead to electrodes with a high surface area due to the formation of a cracked and porous morphology. The electrodes containing Ru, Sn and Pt presented the higher catalytic efficiency for the oxidation of small organic molecules than the electrodes of pure platinum. The FTIR spectra allow us to observe the formation of adsorbed CO species in potentials from 0.1 V vs RHE potential values and CO2 for potentials ranging from 0.4 V vs RHE. These values are lower than the expected for pure Pt and confirm the role of Ru in the oxidation of strongly adsorbed intermediates. In the Fuel Cell tests, it were prepared two types of catalysts (carbon supported and non supported catalysts). The carbon supported catalysts presented higher power density than the non-supported catalysts. The electrodes containing 60 % mol of Pt showed the high performance which confirms the results obtained in half cell experiments. The employed preparation method permitted the synthesis of materials that presented good possibilities for the application in Direct Methanol Fuel Cells.

The general objective of this investigation was to elucidate the effect that surface species such as OHads, Oads and the interfacial water layer have on the oxygen reduction reaction activity of active platinum and platinum alloy catalysts in perchloric acid electrolyte. To that end, these are the investigations that were carried out: [Pt n{111}x{100}] and [Pt n{100}x111}] series of surfaces. These surfaces exhibit OHads/Oads formation at terrace and step sites in the potential range relevant to loss in ORR activity. The increase in activity observed at low step density was assigned to the disruption by steps of a long range ordered OHads terrace over-layer. Hydrogen peroxide oxidation/reduction reaction activity of [Pt n{111}x{100}] and [Pt n{100}x{111}] series of surfaces. The results imply that if oxygen reduction proceeds via the series pathway the rate determining step lies in the later stages of the reaction, i.e after H2O2 formation. CV and ORR of kinked surfaces based upon Pt{332}. These results indicate that low-coordinate {100} kink sites do not have unique ORR activity, i.e. their activity is identical to {100} linear step sites. CV, XPS, STM and ORR of single crystal Pt{111}-M (where M=Ni, Co or Fe) alloy surfaces showed that the onset of electrochemical oxide formation shifts positive in the order Ni, Co, Fe. This shift correlated with increased activity towards the ORR which we ascribe to the greater availability of highly active metallic sites for oxygen reduction at ORR potentials. (1x1) and disordered (1x2) surface atomic arrangements of Pt{110} were created and compared. For the first time, the voltammetry of the Pt{110}-(1x1) surface has been reported in aqueous perchloric acid and sodium hydroxide. The activity of the Pt{110}-(1x1) surface for oxygen reduction was found to be approximately 30 - 40 mV less active than the disordered (1x2) surface.

La neuropatia perifèrica induïda per platins (NPIP) és un dels efectes adversos més freqüents del cisplatí, l’oxaliplatí i el carboplatí, agents quimioteràpics de tipus platins administrats pel tractament de càncers altament prevalents. Degut a la seva severitat, la NPIP pot causar reduccions en la dosis de quimioteràpia o inclús una aturada precoç del tractament, derivant en una disminució de les probabilitats de supervivència dels pacients oncològics. S’ha demostrat que la severitat de la NPIP es correlaciona amb la quantitat de platí acumulat en les neurones sensorials del gangli raquidi de l’arrel dorsal (GRD). Així mateix, s’han descrit varis mecanismes fisiopatològics involucrats en l’aparició de la NPIP, incloent el dany a l’ADN i les mitocòndries de les neurones sensorials, juntament amb alteracions en la funció dels canals iònics, entre altres. Malgrat el gran esforç dels clínics i els investigadors per trobar un tractament per la NPIP, els resultats obtinguts en models experimentals no s’han pogut traslladar a la clínica de forma exitosa. L’objectiu d’aquesta tesi doctoral era determinar els mecanismes moleculars més rellevants involucrats en el desenvolupament de la NPIP i així poder testar noves dianes terapèutiques. Mitjançant seqüenciació de l’ARN de cèl·lules aïllades, hem estudiat el perfil d’expressió gènica de les neurones sensorials del GRD en 2 models de ratolí de NPIP òptimament caracteritzats a nivell neurofisiològic. Un model es va desenvolupar mitjançant l’administració de cisplatí i l’altre, d’oxaliplatí. Hem demostrat que el tractament amb cisplatí causa una lesió permanent a l’ADN de les neurones sensorials, juntament amb un increment de l’expressió del gen Cdkn1a i el seu producte proteic p21. Mentre que les vies d’apoptosis no s’activen en resposta a aquest dany de l’ADN, les neurones sensorials sí expressen una sèrie de marcadors relacionats amb processos de senescència cel·lular, incloent l’enzim beta-galactosidasa, la fosforilació de la histona H2AX i la proteïna Nfkb-p65. El fenotip senescent de les neurones sensorials persisteix inclús 6 setmanes després de finalitzar el tractament amb cisplatí. Pel que fa a l’estudi amb oxaliplatí, els resultats de la seqüenciació mostren un increment en l’expressió dels gens Lxn i Klk5, juntament amb una disminució en l’expressió del gen Kyat3. Tots tres gens estan relacionats amb processos de inflamació, modulació del sistema immunitari i dolor. Tot i que no vam poder demostrar l’increment dels productes proteics dels gens Lxn i Klk5 en les neurones sensorials, els nivells de citocines pro-inflamatòries estaven augmentats en el GRD i el nervi ciàtic dels ratolins tractats amb oxaliplatí, juntament amb un increment del número de cèl·lules infiltrades. Basant-nos en aquests resultats, vam analitzar la possible activació de la resposta de mort cel·lular immunogènica, la qual s’activa en cèl·lules tumorals en resposta al tractament amb oxaliplatí. No obstant, no vam trobar evidències de l’activació d’aquesta via en el GRD. Per altra banda, i a diferència dels resultats obtinguts amb el cisplatí, el dany a l’ADN generat a les neurones sensorials per oxaliplatí és ràpidament reparat un cop finalitzat el tractament, fet que podria explicar la manca d’establiment d’un fenotip senescent. Tenint en compte les dades obtingudes en els models animals, les quals indiquen que la senescència pot jugar un paper important en el desenvolupament de la NPIP, finalment vam desenvolupar un model in vitro de senescència neuronal induïda per cisplatí, el qual serà de gran utilitat per testar noves dianes terapèutiques de forma ràpida i econòmica.
La neuropatía periférica inducida por platinos (NPIP) es uno de los efectos adversos mas frecuentes del cisplatino, el oxaliplatino i el carboplatino, fármacos de tipo platino administrados para el tratamiento de neoplasias malignas altamente prevalentes. Debido a su severidad, la NPIP puede causar reducciones en la dosis de quimioterapia e incluso el cese precoz del tratamiento, hecho que influye negativamente en la probabilidad de supervivencia de los pacientes oncológicos. Se ha demostrado que la severidad de la NPIP se correlaciona con la cantidad de platino acumulado en las neuronas sensoriales de los ganglios de la raíz dorsal (GRD). Así mismo, se han descrito varios mecanismos fisiopatológicos involucrados en la aparición de la NPIP, incluyendo la lesión del ADN y las mitocondrias de dichas neuronas, juntamente con una alteración en sus canales iónicos, entre otros. A pesar de los muchos esfuerzos de los clínicos e investigadores para encontrar un tratamiento frente la NPIP, los resultados obtenidos en modelos experimentales no se han podido trasladar a la clínica de forma exitosa. El objetivo de esta tesis doctoral era determinar los mecanismos moleculares mas relevantes involucrados en el desarrollo de la NPIP y así poder encontrar nuevas dianas terapéuticas. Mediante secuenciación del ARN de células aisladas, hemos estudiado el perfil de expresión génica de las neuronas sensoriales del GRD en 2 modelos de ratón de NPIP, óptimamente caracterizados a nivel neurofisiológico. Uno de los modelos se desarrolló a partir de la administración de cisplatino y el otro, de oxaliplatino. Hemos demostrado que el tratamiento con cisplatino causa una lesión permanente en el ADN de las neuronas sensoriales, juntamente con un incremento en la expresión del gen Cdkn1a y su producto proteico p21. Mientras que las vías de apoptosis no se activan en respuesta a la lesión del ADN, las neuronas sensoriales sí expresan marcadores de senescencia celular como la enzima -galactosidasa, la fosforilación de la histona H2AX y la proteína Nfkb-p65. Estos cambios perduran incluso 6 semanas después de finalizar el tratamiento con cisplatino. Referente al estudio con oxaliplatino, los resultados de la secuenciación muestran un incremento en la expresión de los genes Lxn y Klk5, juntamente con una disminución de la expresión del gen Kyat3, en los animales tratados con oxaliplatino. Los tres genes están relacionados con procesos de inflamación, modulación del sistema inmunitario y dolor. A pesar de que no pudimos demostrar un aumento de los productos proteicos de los genes Klk5 y Lxn en las neuronas sensoriales, los niveles de citoquinas pro-inflamatorias estaban elevados en el GRD y el nervio ciático de los ratones tratados con oxaliplatino, juntamente con un incremento en el numero de células infiltradas. En base a estos resultados, analizamos la posible activación de la respuesta de muerte celular immunogénica, la cual se activa en células tumorales en respuesta al tratamiento con oxaliplatino. No obstante, no encontramos evidencias de la activación de esta vía en el GDR. Por otro lado, y a diferencia de los resultados obtenidos con el cisplatino, la lesión del ADN producida por el oxaliplatino es rápidamente reparada al finalizar el tratamiento, hecho que pudiera explicar la falta de establecimiento del fenotipo senescente. Teniendo en cuenta que los resultados obtenidos con los modelos animales apuntan a que la senescencia podría jugar un papel importante en el desarrollo de la NPIP, finalmente desarrollamos un modelo in vitro de senescencia neuronal inducida por cisplatino, el cual nos servirá para testar nuevas dianas terapéuticas de una forma rápida y económica.
Platinum-Induced Peripheral Neuropathy (PIPN) is a frequent serious dose-limiting adverse event of the platinum-based cytostatic agent cisplatin, oxaliplatin and carboplatin, which are given as a first line treatment against high prevalent cancers. Due to its severity, PIPN often causes cancer treatment reduction or even cessation, thus decreasing the survival probabilities of oncologic patients. It has been extensively reported that PIPN severity correlates with the amount of platinum drugs cumulated in sensory neurons of the dorsal root ganglia (DRG). Several pathophysiological mechanisms have been described for PIPN development, including DNA damage, mytotoxicity and channels dysfunction in DRG sensory neurons, among others. Despite the efforts of clinicians and researchers during the last decades, no successful translation from pre-clinical settings to the clinics has been achieved. The aim of this study was to determine the exact molecular mechanisms involved in the development of PIPN following a non-hypothesis driven methodology to find new therapeutical targets. By single-cell RNA sequencing (scRNA-seq), we studied the transcriptomic profile of DRG sensory neurons from 2 well characterized neurophysiological mice models of PIPN: one induced by cisplatin administration, and the second by oxaliplatin. We demonstrated that cisplatin treatment induced persistent DNA damage and the up-regulation of the Cdkn1a gene and its protein product p21 in the DRG neuronal population. While apoptosis activation pathways were not observed in DRG sensory neurons of cisplatin-treated mice, these neurons did express several senescence hallmarks, including senescence-associated beta-galactosidase (SA-bGAL), phosphor(p)-H2AX and nuclear Nfkb-p65 proteins. The senescent phenotype seen in sensory neurons persisted up to 6 weeks after cisplatin treatment discontinuation. Regarding oxaliplatin study, results of scRNA-seq showed an up-regulation of Lxn and Klk5 genes, and a down-regulation of the Kyat3 gene in oxaliplatin treated animals, among others. All three genes have been involved in the modulation of inflammatory responses, the immune system and pain behaviors. Although the protein products of Klk5 and Lxn did not appear up-regulated in the DRG of oxaliplatin-treated mice, we did see an increase in the pro-inflammatory cytokine profile in both the DRG and the sciatic nerves of oxaliplatin-treated mice, altogether with increased number of infiltrated cells. Based on these results, we checked for factors involved of the so-called Immunogenic Cell Death (ICD) response, which is activated in tumor cells after oxaliplatin treatment. However, we did not find any evidence of ICD activation in DRG of oxaliplatin-treated mice at any time point evaluated. On the other hand, and in contrast to cisplatin, the rapid repair of DNA damage after oxaliplatin treatment cessation could explain the lack of establishment of a senescence phenotype in the DRG. In vivo data showed that senescence pathways could play a key role in platinum neurotoxicity. Thus, we finally set up an in vitro model of cisplatin-induced neuronal senescence in which to start the screening of potential neuroprotective targets in a cost- and time-effective way.
Universitat Autònoma de Barcelona. Programa de Doctorat en Neurociències

Since the chance discovery, in 1967, of the anti-tumour activity of cisplatin, cis-dichlorodiammineplatinum(II), research has focussed on studying the reactions of this and other related complexes in an effort to elucidate the nature of the biological activity. This thesis presents a study of the aqueous solution chemistry of some platinum(II) and platinum(IV) complexes in order to extend what is known about the simple chemistry of this biologically important class of compounds. The chloride ion anation of diaqua (cis-[Pt(OH₂)₂(N)₂]²⁺) complexes is investigated as is the bromide ion anation of the bromoaqua (cis-[PtBr(OH₂)(N)₂]⁺) and diaqua (cis-[Pt(OH₂)₂(N)₂]²⁺) species, all in 1.0 M HC1O₄. The kinetics are studied using UV/Vis spectroscopic methods - both conventional and stopped-flow. High-pressure stopped-flow is used for selected reactions to determine the effect of pressure on the anation process. The collective data are used to calculate activation parameters from which conclusions are drawn as to the mechanism of the reaction. The redox kinetics of the platinum(II)/platinum(IV) couple are investigated using a variety of redox agents. These data provide a basis on which to form mechanistic interpretations for both the oxidation and reduction processes. Extrapolations are made to the biological system for the reduction of anti-tumour active platinum(IV) drugs. Platinum(IV) complexes are known to be very inert. An investigation into the base hydrolysis of platinum(IV) complexes is presented and a mechanism proposed.

Fuel cells convert chemical energy from a fuel into electricity through chemical reaction with oxygen. This possesses some challenges like slow oxygen reduction reaction (ORR), overpotential, and methanol fuel cross over in a direct methanol fuel cell (DMFC). These challenges cause inefficiency and use of higher amounts of the expensive platinum catalyst. Several binary catalysts with better ORR activity have been reported. In this study we investigate the best catalyst with better ORR and MOR performances and lower over-potentials for PEMFC and DMFC applications by comparing the in-house catalysts (10%Pt/C, 20%Pt/C, 30%Pt15%Ru/C, 40%Pt20%Ru/C, 30%PtCo/C, 20%Pt20%Cu/C and 20%PtSn/C) with the commercial platinum based catalysts (10%Pt/C, 20%Pt/C, 20%Pt10%Ru/C, 20%PtCo/C, 20%PtCu/C and 20%PtSn/C) using the cyclic voltammetry and the rotating disk electrode to determine their oxygen reduction reaction and methanol tolerance. HRTEM and XRD techniques were used to determine their particle size, arrangement and the atomic composition. It was observed that the 20%Pt/C in-house catalyst gave the best ORR activity and higher methanol oxidation current peaks compared to others catalysts followed by 20%Pt10%Ru/C commercial catalyst. The 20%PtCo/C commercial, 30%PtCo/C in-house and 20%PtSn/C in-house catalysts were found to be the most methanol tolerant catalysts making them the best catalysts for ORR in DMFC. It was observed that the ORR activity of 20%PtCo/C commercial and 30%PtCo/C inhouse catalysts were enhanced when heat treated at 350 0C. From XRD and HRTEM studies, the particle sizes were between 2.72nm to 5.02nm with little agglomeration but after the heat treatment, the particles were nicely dispersed on the carbon support.
>Magister Scientiae - MSc

Photoactive platinum compounds have the potential to reduce some of the debilitating side-effects associated with conventional chemotherapeutics, such as cisplatin. Stable, inert platinum(IV) compounds which are reduced to active platinum(II) species only upon irradiation, could provide a site-specific treatment. The Pt^IV azide complexes, cis, trans, cis-[Pt(N₃)₂(OH)₂(NH₃)₂] and cis, trans-[Pt(en)(N₃)₂, have previously been shown to be stable in the dark but reduced to Pt^II upon irradiation. The synthesis and characterisation of new platinum azide compounds, designed to improve important properties such as solubility and wavelength of absorbance are described here. Complexes which have azide ligands in a trans position were synthesised, the general formula is trans, trans, trans-[Pt(N₃)₂(OH)₂(NH₃)R] where R is NH₃, pyridine, methylamine, ethylamine, thiazole, 2-picoline, 3-picoline, 4-picoline or cyclohexylamine. Several Pt^IV diazido compounds containing chelating aromatic ligands, such as 2,2’-bipyridine and 1,10-phenanthroline were also prepared. Many of the novel compounds synthesised were characterised by X-ray structure determination. The complexes with trans azides generally showed improved water solubility as well as a shift of the main absorbance band towards the visible region, compared to their cis analogues. A transcription mapping study of a fragment of pSP73KB plasmid DNA treated with cis, trans-[Pt(en)(N₃)₂(OH)₂] and visible light, has shown that platination mainly occurs at consecutive guanine bases. The major binding sites were similar to those of cisplatin. No platination was seen in an identical sample which was not irradiated.

In this work, trans-diazido Pt(IV) complexes with general formula [Pt(N3)2(OH)(OCOR)(pyr)2] (where OCOR is a carboxylate axial ligand) and [Pt(N3)2(OH)2(L1)(L2)] (where L1 and L2 are aromatic N-heterocyclic ligands) have been synthesised and characterised. The chemical and photochemical properties of these complexes, as well as their photobiological behaviour, have been studied in order to check their potential as photoactivatable anticancer drugs. Four trans-diazido Pt(IV) complexes with general formula trans, trans, trans- [Pt(N3)2(OH)(OCOR)(pyr)2] (OCOR= succinate, 4-oxo-4-propoxybutanoate, Nmethylisatoate and succinate-(RGD)f peptide ligands) have been obtained by axial derivatisation of one hydroxido ligand from trans, trans, trans- [Pt(N3)2(OH)2(pyr)2]. The crystal structures of three axially-derivatised complexes have been determined by X-ray diffraction. Photoirradiation studies have shown an improved photoactivity of the carboxylate versus the dihydroxido complexes at the longer wavelengths. Release of the axial ligands was observed in the studied complexes. This fact is especially relevant in the case of the Pt(IV)-(cRGD)f complex, where the RGD was incorporated as a tumour cell targeting moiety. DFT-TDDFT calculations performed on the complex trans, trans, trans- [Pt(N3)2(OH)(Succ)(pyr)2] showed dissociative transitions at longer wavelength, which could explain the photolability observed in these carboxylate derivatives. Studies of photoactivation of the diazido Pt(IV) complexes in the presence of 5’- GMP indicate the formation of a mono-GMP Pt(II) adduct as main photoproduct, therefore DNA could be considered a potential target site for these anticancer compounds. Additionally, EPR studies showed that azidyl radical release was observed when complexes bearing the succinate and 4-oxo-4-propoxybutanoate ligands were irradiated with green light. No such result was obtained for the dihydroxo precursor showing that these complexes could be phototoxic with longer wavelength light activation. Seven trans-diazido Pt(IV) complexes, trans, trans, trans- [Pt(N3)2(OH)2(L1)(L2)] (where L1 and L2 are pyridine, 2-picoline, 3-picoline, 4- picoline, thiazole or 1-methylimidazole ligands), have been obtained by oxidation of the corresponding trans-[Pt(N3)2(L1)(L2)] precursor. The X-ray crystal structures have been determined for four Pt(IV) diazido complexes from this family of compounds. Photoirradiation studies indicate that the incorporation of a sterically demanding ligand, e.g. trans, trans, trans-[Pt(N3)2(OH)2(2-pic)(pyr)], greatly enhances the photoactivity in these complexes. DFT-TDDFT calculations are in agreement with these results, since higher intensity transitions were observed for such complex at longer wavelength. Phototoxicity studies carried out on A2780, A2780cis and OE19 cell lines with the trans, trans, trans-[Pt(N3)2(OH)2(pyridine)(n-picoline)] family concluded that steric hindrance close to the platinum centre does not favour phototoxicity. Most of the complexes were equally potent in cisplatin resistance against the ovarian cancer cell line (A2780cis), except [Pt(N3)2(OH)2(3-pic)2] and [Pt(N3)2(OH)2(4-pic)2] which exhibited some cross resistance. All of the complexes tested in both OE19 and A2780 cell lines have shown less sensitivity to OE19 than to A2780. Studies in S. pombe yeast strains (WT and ΔRad3) with trans, trans, trans-[Pt(N3)2(OH)2(pyr)2] suggest that DNA is potentially an important target for this type of compounds, although other targets are not excluded. Furthermore, live-cell confocal microscopy was performed on A2780 cells treated with the complex trans, trans, trans-[Pt(N3)2(OH)2(pyr)2] and irradiated with a low dose of blue light. The cell death, monitored by propidium iodide uptake, was captured occurring 2 h 30 min post activation.

The hardening behaviour of three cold-worked platinum alloys, Pt 5 at% Mo, Pt 5 wt% Ru and Pt 5 wt% Cu, has been investigated through a systematic series of heat treatments. All three of the experimental alloys showed a hardness increase during annealing within a specific temperature range. The hardness of the Pt-Mo and Pt-Ru alloys was found to increase rapidly at annealing temperatures above the recrystallisation temperature, with the final hardness similar to the original coldworked hardness. The hardness of Pt-Cu showed an increase of up to 30% at low annealing temperatures of between 200°C and 500°C. In addition, the Pt-Cu alloy also showed the increased hardness found in Pt-Mo and Pt-Ru at high annealing temperatures, but the hardness increase was not to the same extent. Specimens subjected to the annealing treatments were studied by means of optical, scanning electron and transmission electron microscopy, in order to determine the effect of annealing on microstructure and structural order. Resistivity, XRD and OTA techniques were employed in order to study the mechanisms of ordering with temperature, but these techniques did not produce any significant results. It was concluded that the most likely cause for the hardness increase observed in all three experimental alloys was due to a change in structural order upon annealing. The Pt-Mo and Pt-Ru alloys hardened through an increase in short-range order at annealing temperatures above the recrystallisation temperature. The Pt-Cu alloy hardened through the development of long-range order on annealing between 200°C and 500°C. This increase in hardness was in· addition to the high dislocation density in the alloy specimen due to prior cold-work.

Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2009.
Title from electronic title page (viewed Jun. 26, 2009). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry. " Discipline: Chemistry; Department/School: Chemistry.

The interaction of oxygen with metal surfaces can lead to various structures; these include surface oxide films, oxygen penetration in the subsurface region and bulk oxides, at certain partial pressures and temperatures. This research focuses on the oxygen reduction reaction (ORR) within the proton exchange membrane fuel cell (PEMFC). PEMFC are believed to be kinetically limited for the ORR due to a loss of surface area at the cathode as a result of oxidation. One explanation for this phenomenon is the “so called place exchange mechanism” which leads to a thin surface oxide being formed. In an attempt to understand and verify this hypothesis, Pt and Pt/Ni alloys have been modelled in order to determine the relative propensity of surface oxide film formation. Density functional theory (DFT) has been used to model various facets of the catalyst particles, in particular the (111) and (100) surfaces. In addition, a range of oxygen coverages at high symmetry sites and oxide thin films have also been modelled as intermediates in the place exchange mechanism. The DFT data obtained from these calculations have been used in a statistical thermodynamics model. This allows one to bridge the temperature and pressure gap between the technological relevant conditions of the PEMFC and the electronic structure calculations.