Climate change is one of the largest challenges faced by humanity. To combat this research into alternatives to fossil fuels is ongoing. Dihydrogen is considered a good alternative fuel, since its... Show moreClimate change is one of the largest challenges faced by humanity. To combat this research into alternatives to fossil fuels is ongoing. Dihydrogen is considered a good alternative fuel, since its burning only forms water. A promising means of acquiring dihydrogen is photocatalysis, which can be driven by sunlight. This involves water oxidation and proton reduction, both half-reactions require a catalyst and photosensitizer, generally metal complexes. The limited aqueous solubility and stability of these complexes poses a challenge in their application. In this thesis we investigated the use artificial metalloenzymes (ArMs) for the catalysis and photosensitization of both half-reactions. ArMs can improve the aqueous solubility of these catalysts and provide a second coordination sphere that can be used to improve the stability and activity. The ArMs in this thesis were prepared using the axial coordination of a catalyst or photosensitizer to a protein via histidine. We set up an effective screening method for this coordination using semi-native PAGE. We then prepared and characterized one of the first ArMs with photocatalytic water oxidation activity. We prepared eight photosensitizing ArMs, of which two also able to catalyse hydrogen evolution. Two of these ArM systems were entirely earth-abundant metal-based and showed good activity. Show less
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
Artificial photosynthesis has recognised potential to produce green and sustainable fuels from earth-abundant resources such as water, carbon dioxide (CO2), and sunlight. In an artificial... Show moreArtificial photosynthesis has recognised potential to produce green and sustainable fuels from earth-abundant resources such as water, carbon dioxide (CO2), and sunlight. In an artificial photosynthetic system, two half-reactions, such as water oxidation and proton reduction or CO2 reduction, have to be combined. To achieve such a system, it is crucial to have: a) efficient light-harvesting by the photosensitiser, b) stable catalysts for the oxidation and the reduction reaction, c) unidirectional proton and electron transport between the oxidation and the reduction site, ideally by a recyclable electron relay, d) efficient charge separation, and e) a strong, photostable membrane that does not leak molecular components. In natural photosynthesis, these requirements are achieved altogether using compartmentalisation, which consists in embedding the key components of the system, i.e. for green plants the oxygen evolving complex, photosystem I and II, and the natural electron relays, around the lipid bilayer of the thylakoid membrane. The use of spherical lipid membranes (such as liposomes) as biological mimics of the thylakoid membrane is a promising approach to confine half-reactions, facilitate charge separation, and avoid charge recombination and other undesired side-reactions. In the research described in this thesis, it was attempted to realise a full artificial photosynthetic system based on liposomes and several of the key intermediate steps were achieved: 1) unidirectional electron transfer across a liposomal membrane from an electron donor encapsulated in the interior of the liposome to an electron acceptor located outside (Chapter 2), and 2) photocatalytic reduction of CO2 (Chapter 3) and of protons (Chapter 4) at the surface of liposomes. Special attention was paid in Chapter 2 and Chapter 5 to the question of the (photo)stability of the membrane and light-induced leakage. Show less
Artificial photosynthesis (AP) is one of the scientific challenges that could help us achieving a global “carbon neutral” society. Photocatalytic water splitting is considered as the first... Show moreArtificial photosynthesis (AP) is one of the scientific challenges that could help us achieving a global “carbon neutral” society. Photocatalytic water splitting is considered as the first challenge of AP, which contains two half reactions: water oxidation and hydrogen evolution. It is widely accepted that a photocatalytic system needs a minimum of three components: a photosensitizer (PS), a catalyst (Cat) and a sacrificial electron donor or acceptor (SE). In such a photocatalytic system, at least three electron-transfer steps can be identified: one between the SE and the excited PS (PS*), one between the photo-reduced or photo-oxidized PS and the Cat, and one between the Cat and its substrate. This thesis on the one hand focused on developing improved molecular components for the two half reactions of water splitting in purely homogeneous systems. On the other hand optimized photocatalytic systems with balances between the driving force of electron transfer from the SE to the PS*, and that of electron transfer between the catalyst and the oxidized or reduced photosensitizer (PS+ or PS–). Show less
This thesis is concerned with the transfer of energy from light to matter. Over a century ago it was established that light consists of packets of energy [1], now known as photons. Not much later... Show moreThis thesis is concerned with the transfer of energy from light to matter. Over a century ago it was established that light consists of packets of energy [1], now known as photons. Not much later the energy levels of matter at the atomic scale were found to be discrete [2]. These phenomena required a new physical description that has become the theory of quantum mechanics [3]. Now, this theory of light and matter could contribute to tackling a fundamental socioeconomic and technological challenge: To find a sustainable supply of useful energy that is cheap, abundant and generated on-the-spot Show less
