Producing green energy has become the main goal in our society in the search of reducing or eliminating the carbon emission from fossil fuels. In this project, proteins were used as a tool to... Show moreProducing green energy has become the main goal in our society in the search of reducing or eliminating the carbon emission from fossil fuels. In this project, proteins were used as a tool to develop an artificial system capable of promoting the most demanding reaction in photosynthesis, water oxidation, as a new concept of producing energy from a green source. For this purpose, a screening study of the interaction between selected proteins and a library photocatalytic ruthenium and cobalt complexes was carried out. The results from such study allowed the production of two types of artificial metalloenzymes (ArM) which were proven to be able to perform water oxidation reaction via blue light irradiation. As well, an unusual interaction between proteins which promote the photocatalytic O2 evolution from water. These findings lead to develop ruthenium and cobalt metalloenzymes as promising candidates for artificial photosynthesis in bio-inspired systems Show less
The redox-conversion reaction of metal-disulfide and metal-thiolate complexes are important, as they may shed light on electron-transfer reactions that often occur in Nature. Despite their... Show moreThe redox-conversion reaction of metal-disulfide and metal-thiolate complexes are important, as they may shed light on electron-transfer reactions that often occur in Nature. Despite their importance, very few examples have been reported. In addition to that, there is a limited understanding of how the coordination environment of the metal ion affects this reaction. In this thesis, our investigation was set based on the ligand-field theory to determine its correlation with the redox-conversion reactions in cobalt-based systems. Our experiments revealed that using an exogenous ligand with a strong ligand-field character may induce the redox conversion from cobalt(II)-disulfide complexes to cobalt(III)-thiolate complexes. Using this knowledge, the possibility of the redox-conversion reaction was also extended from cobalt(II)-diselenide to cobalt(III)-selenolate complexes.Finally, we have come up with several conclusions about the redox-conversion reactions of the cobalt(II)-dichalcogenide complexes. It was revealed that the conversion is affected by the ligand-field strength of the dichalcogenide ligand. The smaller ligand-field strength can be counterbalanced with the introduction of the strong auxiliary ligand. Lastly, the cleanliness of the conversion depends on the magnitude of the overall ligand-field splitting energy of the complex. Show less
The hydroaminomethylation (HAM) reaction converts alkenes into N-alkylated amines and has been well studied for rhodium- and ruthenium-based catalytic systems. Cobalt-based catalytic systems are... Show moreThe hydroaminomethylation (HAM) reaction converts alkenes into N-alkylated amines and has been well studied for rhodium- and ruthenium-based catalytic systems. Cobalt-based catalytic systems are able to perform the essential hydroformylation reaction, but are also known to form very active hydrogenation catalysts, therefore we examined such a system for its potential use in the HAM reaction. Thus, we have quantum-chemically explored the hydrogenation activity of [HCo(CO)(3)] in model reactions with ethene, methyleneamine, formaldehyde, and vinylamine using dispersion-corrected relativistic density functional theory at ZORA-BLYP-D3(BJ)/TZ2P. Our computations reveal essentially identical overall barriers for the catalytic hydrogenation of ethene, formaldehyde, and vinylamine. This strongly suggests that a cobalt-based catalytic system will lack hydrogenation selectivity in experimental HAM reactions. Our HAM experiments with a cobalt-based catalytic system (consisting of Co-2(CO)(8) as cobalt source and P(n-Bu)(3) as ligand) resulted in the formation of the desired N-alkylated amine. However, significant amounts of hydrogenated starting material as well as alcohol (hydrogenated aldehyde) were always formed. The use of cobalt-based catalysts in the HAM reaction to selectively form N-alkylated amines seems therefore not feasible. This confirms our computational prediction and highlights the usefulness of state-of-the-art DFT computations for guiding future experiments. Show less
Three pyridyl‐amide substituted (benz)imidazolium salts H2L1Cl, H2L2Cl and H2L3Cl were synthesized and successfully employed as ligand precursors for the syntheses of novel nickel(II) and cobalt... Show moreThree pyridyl‐amide substituted (benz)imidazolium salts H2L1Cl, H2L2Cl and H2L3Cl were synthesized and successfully employed as ligand precursors for the syntheses of novel nickel(II) and cobalt(III) complexes. The compounds H2L1Cl and H2L2Cl are precursors to tetradentate ligands and differ in the nature of the N‐heterocyclic carbene (NHC) functionality, being imidazole‐based and benzimidazole‐based, respectively. The ligand precursor H2L3Cl resembles H2L1Cl, but with one of the pyridyl groups replaced with a benzyl group, thus yielding a potential tridentate ligand. The nickel(II) compounds [Ni(L1)]Cl and [Ni(L2)]PF6 were obtained, bearing tetradentate ligands comprising an amidate and two pyridine nitrogen donor atoms and an (NHC) carbon donor. Single crystal X‐ray crystallography revealed that the nickel ions in both compounds are in slightly distorted square‐planar geometries. Reactions of cobalt salts with the ligands H2L1Cl and H2L3Cl resulted in the cobalt(III) compounds [Co(L1)2]Cl and [Co(L3)2]PF6; the cobalt ions in both complexes are in octahedral geometries, bound by two tridentate ligands in a meridional binding mode, with two dangling pyridine and benzyl groups, respectively. The four compounds show electrocatalytic activity in proton reduction in dimethylformamide solutions in presence of acetic acid; their activity is compared using cyclic voltammetry and quantified with gas chromatography. Show less
Graphene nanoribbons (GNRs) are used as a current carrying substrate in investigation of current-induced forces in a low-temperature STM (chapter 2). We demonstrate induced migration of Co adatoms... Show moreGraphene nanoribbons (GNRs) are used as a current carrying substrate in investigation of current-induced forces in a low-temperature STM (chapter 2). We demonstrate induced migration of Co adatoms on GNRs and on Au(111) using voltage pulses from the STM tip and we argue that motion is due to thermal excitations rather than the wind force. In chapter 3 we show that voltage signal is induced in a graphene strip when a droplet of ionic liquid is moved across its surface. Here we show that even deionized water can induce voltage over charged graphene surface due to the polarizability of water molecules. In chapter 4 we present a method for fabrication of graphene nanoelectrodes which we further test electrically in a modified STM. For the first time we demonstrate that the gap between two graphene nanoelectrodes can be tuned with subnanometric precision Show less
In the last decade, the redox interconversion between metal thiolate and disulfide compounds has been extensively investigated for copper, but not for other transition metal ions. In this... Show moreIn the last decade, the redox interconversion between metal thiolate and disulfide compounds has been extensively investigated for copper, but not for other transition metal ions. In this thesis, our investigations are described of the possibility to extend the metal thiolate/disulfide redox interconversion reactions to cobalt or iron compounds. A number of cobalt(II) disulfide and cobalt(III) thiolate compounds of different ligands and different anions are reported in this thesis. It was revealed that the anion of cobalt(II) salts, the structure of disulfide ligands, and the type of solvent influence the formation of either cobalt(II) disulfide or cobalt(III) thiolate compounds. However, a consistent trend cannot be provided to predict which of the species is generated. An important conclusion of this work is that the cobalt(II) disulfide to cobalt(III) thiolate interconversion reaction might be related to the ligand field strength of the ligand, and the binding strength and ligand field strength of the anions and solvent used. Apart from the cobalt compounds, two iron(II) disulfide compounds were reported in this thesis as well. However, so far we were not able to trigger the conversion of these compounds to their respective iron(III) thiolate compounds. Show less
This thesis evaluates two total hip implant designs used in the younger aged patient population; (1) a cementless THR with a conventional cobalt on polyethylene (CoP) bearing and (2) a THR with a... Show moreThis thesis evaluates two total hip implant designs used in the younger aged patient population; (1) a cementless THR with a conventional cobalt on polyethylene (CoP) bearing and (2) a THR with a MoM bearing. An analysis into outcome and failure mechanisms on both designs was performed with focus on: The clinical outcome and survival of a conventional MoP THA cohort with the 24-year follow-up and an analysis into factors associated with clinical and radiographic outcome. The clinical evaluation of a large head MoM THA cohort. Analysis of failure of the MoM THA in relation to anatomical reconstruction of the hip. The failure mechanisms of the MoM THA as visualised at MRI images. The reproducibility of the histological scoring system of peri-articulair tissue reactions of failed MoM THA. Show less
The dissertation describes TEM experiments on heterogeneous catalysts. Starting with characterization of (Ni/Co)MoS2 on Alumina and the effect of oxidation, and sequential resulfidation. After that... Show moreThe dissertation describes TEM experiments on heterogeneous catalysts. Starting with characterization of (Ni/Co)MoS2 on Alumina and the effect of oxidation, and sequential resulfidation. After that, Co-based catalysts are used for high-resolution (S)TEM/EDX caracterization studies, and in situ catalysis experiments. Show less
Smeekes, C.; Ongkiehong, B.; Wal, B. van der; Wolterbeek, R.; Henseler, J.F.; Nelissen, R. 2015
