Ingested nanomaterials are exposed to many metabolites that are produced, modified, or regulated by members of the enteric microbiota. The adsorption of these metabolites potentially affects the... Show moreIngested nanomaterials are exposed to many metabolites that are produced, modified, or regulated by members of the enteric microbiota. The adsorption of these metabolites potentially affects the identity, fate, and biodistribution of nanomaterials passing the gastrointestinal tract. Here, we explore these interactions using in silico methods, focusing on a concise overview of 170 unique enteric microbial metabolites which we compiled from the literature. First, we construct quantitative structure–activity relationship (QSAR) models to predict their adsorption affinity to 13 metal nanomaterials, 5 carbon nanotubes, and 1 fullerene. The models could be applied to predict log k values for 60 metabolites and were particularly applicable to ‘phenolic, benzoyl and phenyl derivatives’, ‘tryptophan precursors and metabolites’, ‘short-chain fatty acids’, and ‘choline metabolites’. The correlations of these predictions to biological surface adsorption index descriptors indicated that hydrophobicity-driven interactions contribute most to the overall adsorption affinity, while hydrogen-bond interactions and polarity/polarizability-driven interactions differentiate the affinity to metal and carbon nanomaterials. Next, we use molecular dynamics (MD) simulations to obtain direct molecular information for a selection of vitamins that could not be assessed quantitatively using QSAR models. This showed how large and flexible metabolites can gain stability on the nanomaterial surface via conformational changes. Additionally, unconstrained MD simulations provided excellent support for the main interaction types identified by QSAR analysis. Combined, these results enable assessing the adsorption affinity for many enteric microbial metabolites quantitatively and support the qualitative assessment of an even larger set of complex and biologically relevant microbial metabolites to carbon and metal nanomaterials. Show less
This thesis focuses on the synthesis, characterization and performance towards CO2 electroreduction of mono and bi-metallic particles based on p-block metals. With an industrial perspective in mind... Show moreThis thesis focuses on the synthesis, characterization and performance towards CO2 electroreduction of mono and bi-metallic particles based on p-block metals. With an industrial perspective in mind, we try to synthesize particulate, high surface area materials with clean, scalable synthesis methods where possible and test their performance in H-Cell and gas diffusion electrode flow cell configurations. With a combination of characterization techniques, we find possible explanations for the catalytic behaviors. Show less
In surface science there is great effort to move from studying simple, flat model surfaces in vacuum to investigating more complex model catalysts in gas environments (in situ). This thesis gives... Show moreIn surface science there is great effort to move from studying simple, flat model surfaces in vacuum to investigating more complex model catalysts in gas environments (in situ). This thesis gives three examples of such studies using microscopy and spectroscopy.Exposure of ZnO(10-10) to moderate pressures of water in an in situ scanning tunneling microscope reveals that the surface roughens. The flat ZnO(10-10) is thus only conditionally suited as a model catalyst for reactions involving water.In the same microscope, surface gold oxide formation is observed on TiO2/Au(111) during CO oxidation at 1 bar pressure. Comparisons to the Au(111) surface suggest that the titania does not supply atomic oxygen to the Au(111) substrate as part of the reaction mechanism of the CO oxidation.Co(0001) is investigated as a model catalyst for Fischer-Tropsch synthesis, the reaction of CO and H2 to form hydrocarbons. In this thesis the oxidation behavior of the cobalt and the adsorption of carbon species during the reaction are investigated using near-ambient pressure X-ray photoelectron spectroscopy.Generally, this thesis exemplifies the significant influence that small concentrations of contaminants in gases and materials can have on the structure and behavior of surfaces in in situ studies. Show less
The biological application of photoactivatable ruthenium anticancer prodrugs is limited by the need to use poorly penetrating high-energy visible light for their activation. Upconverting... Show moreThe biological application of photoactivatable ruthenium anticancer prodrugs is limited by the need to use poorly penetrating high-energy visible light for their activation. Upconverting nanoparticles (UCNPs), which produce high-energy light under near-infrared (NIR) excitation, can solve this issue, provided that they form stable, water (H2O)-dispersible nano-conjugates with the prodrug and that there is efficient energy transfer from the UCNP to the ruthenium complex. Herein, we report on the synthesis and photochemistry of the ruthenium(II) polypyridyl complex [Ru(bpy)(2)(3(H))](PF6)(2) ([1](PF6)(2)), where bpy = 2,2-bipyridine and 3(H) is a photocleavable bis(thioether) ligand modified with two phosphonate moieties. This ligand was coordinated to the ruthenium center through its thioether groups and could be dissociated under blue-light irradiation. Complex [1](PF6)(2) was bound to the surface of NaYF4:Yb3+,Tm3+@ NaYF4:Nd3+@NaYF4 core-shell-shell (CSS-)UCNPs through its bis(phosphonate) group, thereby creating a H2O-dispersible, thermally stable nanoconjugate (CSS-UCNP@[1]). Conjugation to the nanoparticle surface was found to be most efficient in neutral to slightly basic conditions, resulting in up to 2.4 x 10(3) Ru-II ions per UCNP. The incorporation of a neodymium-doped shell layer allowed for the generation of blue light using low-energy, deep-penetrating light (796 nm). This wavelength prevents the undesired heating seen with conventional UCNPs activated at 980 nm. Irradiation of CSS-UCNP@[1] with NIR light led to activation of the ruthenium complex [1](PF6)(2). Although only one of the two thioether groups was dissociated under irradiation at 50 W.cm(-2), we provide the first demonstration of the photoactivation of a ruthenium thioether complex using 796 nm irradiation of a H2O-dispersible nanoconjugate. Show less
Cathodic corrosion is a relatively unknown phenomenon that can severely etch metallic electrodes at cathodic (negative) potentials. In spite of these remarkable changes that are caused by cathodic... Show moreCathodic corrosion is a relatively unknown phenomenon that can severely etch metallic electrodes at cathodic (negative) potentials. In spite of these remarkable changes that are caused by cathodic corrosion, the phenomenon is stil not fully understood. Cathodic corrosion is therefore the focus of this PhD thesis. The first three experimental chapters of the thesis focus on characterizing platinum, rhodium and gold electrodes before and after cathodic corrosion in a variety of working solutions. In doing so, these chapters establish surprisingly mild corrosion onset potentials and reveal an etching anistropy that depends on the cation in the working solution. Additional density functional theory calculations suggest a similarly significant role for adsorbed hydrogen. These result suggest the existence of ternary metal hydrides during cathodic corrosion. The role of hydrides is further studied in the fourth experimental chapter through X-ray absorption spectroscopy. These four fundamental chapters are followed by two more applied chapters. The first of these tailors the activity of a platinum single crystal towards oxygen reduction, by using cathodic corrosion. The second applied chapter uses cathodic corrosion to create and thoroughly characterize alloyed nanoparticles. Combined, these fundamental and applied chapters provide valuable new information towards understanding and applying cathodic corrosion. Show less
Nature__s own building block, peptide/protein derived materials have been of great interest for supramolecular chemists. The amino acids in peptides/proteins are linked via amide bonds, which makes... Show moreNature__s own building block, peptide/protein derived materials have been of great interest for supramolecular chemists. The amino acids in peptides/proteins are linked via amide bonds, which makes them more stable against degradation as compared to other natural materials such as oligonucleotides. Peptides adopt a secondary structure which is determined by their amino acid sequence resulting in a structure with a specific fold like a beta sheet, a helix or a random coil conformation.These secondary structures can govern the supra-molecular structure of the macromolecule to achieve specific function. Peptides can be short, such as dipeptides or as long as a small protein, which are able to selfassemble into a designed nanostructure and thus providing a wide choice of biomaterials for a chemical biologist. In last decade, peptides have been shown to have great versatility and inherent high affinity for their target to carry out various functions which is the scope of this thesis presented here. Show less
This project has dealt with the mechanistic study of the electrocatalytic nitrite reduction, the selectivity-determining step of nitrate reduction. Nitrate is a polluting ion targeted by wastewater... Show moreThis project has dealt with the mechanistic study of the electrocatalytic nitrite reduction, the selectivity-determining step of nitrate reduction. Nitrate is a polluting ion targeted by wastewater remediation; electrochemistry strives to achieve selectivity to harmless products (N2). A multi-pronged approach has been followed, aimed at establishing the influence of several variables (electrocatalyst material, surface structure, pH and electrode potential) on the catalytic activity and the product distribution, which has been determined with in situ analytical techniques (mass spectrometry and infrared spectroscopy). The molecular underpinnings of nitrite reduction have thereby been unravelled for transition metals, showing that an optimal catalytic performance is achieved when metals intermediate affinities to reaction intermediates (Sabatier Principle). The all-important concept of structure sensitivity also applies to nitrite reduction at Pt electrodes, although only in alkaline media: a Pt(100) single-crystal is the sole Pt surface able to achieve the desired direct conversion of nitrite into 100% N2. Such selectivity is unparalleled for a simple monometallic surface and is an outstanding finding. Additionally, the nitrite-reducing performance of bio-inspired catalysts, (electroactive metalloporphyrins) was investigated. A further side-project of this PhD thesis has also been the electrochemical characterization of preferentially-oriented cuboid Pt nanoparticles synthesized with the innovative __cathodic corrosion__. Show less
Clearly gold deposited as nanoparticles on a support is a very active catalyst in contrast to bulk gold which does not show any catalytic activity. The question arises if this particle size effect... Show moreClearly gold deposited as nanoparticles on a support is a very active catalyst in contrast to bulk gold which does not show any catalytic activity. The question arises if this particle size effect is exclusively valid for gold catalysis or can a similar effect be found in other metals? In the research described in this thesis we investigated copper and silver based catalysts for similar particle size effects as for gold based catalysts. In contrast to gold bulk silver and copper are known to be active in catalysis and both metals are used as catalysts. Silver is the metal of choice for the formation of ethylene oxide from ethylene but also for the formation of formaldehyde in the BASF process. A Cu/Zn-based catalyst is used for the synthesis of methanol from CO and \hydrogen, and copper-based catalysts are also active in oxidation reactions. As the interaction between the gold nanoparticles with the additives is very important for the catalytic activity, the effect of additions of lithiumoxide and ceria have also been investigated for the silver and copper based catalysts. These additives stabilize the nanoparticles and ceria which is known for its oxygen storage and oxidation capacities and is one of the best additives for gold based catalysts. Various oxidation and dehydrogenation reactions have been investigated over copper, silver and gold based catalysts, which are presented in this thesis. In chapter 2 the preferential oxidation of CO is discussed. Chapter 3 deals with the selective oxidation of \ammonia. Chapter 4 is devoted to the oxidation and dehydrogenation of methanol. Chapter 5 presents the results of formation of ethylene oxide in the oxidation and dehydrogenation of ethanol on silver and copper based catalysts. In chapter 6 more results of ethanol dehydrogenation and oxidation on gold based catalysts are presented. Chapter 7 gives insight into the activity of gold based catalysts in oxidation and dehydrogenation of 1-propanol and 2-propanol. Show less
