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  • Resultat 1-10 av 586
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1.
  • REN, Yansong (författare)
  • Dynamic Chemistry for Asymmetric Synthesis, Molecular Motion and Constitutional Exchange
  • 2018
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Living matter is built on complex dynamic systems consisting of numerus biotransformations. By exploiting the adaptive and evolutive behaviors ofmolecular matter, dynamic chemistry has developed as an important tool tounderstand the organization of nonliving matter into complex living systems.This thesis concerns three aspects of dynamic chemistry with a general focus onthe influence of different stimuli on the structures and functions of dynamicsystems.The first section focuses on dynamic kinetic resolution, where enzymes areutilized for asymmetric synthesis of an enantiopure (2R,5R)-1,3-oxathiolane. Byemploying surfactant-treated subtilisin Carlsberg and Candida antarcticalipase B, the absolute configuration of the resulting 1,3-oxathiolane ring couldbe efficiently controlled.The second section addresses the motional dynamics of configurational enamineswitch systems controlled by multiple stimuli. Complete forward and backwardrotation around the enamine C=C bond could be precisely regulated uponaddition of acid/base or metal ions. The enamine switches exhibited specificsensing ability for CuII ions in solution. Moreover, the enamines exhibitedswitchable aggregation-induced emission in the solid state, which could beapplied in the development of sensors as well as fluorescent organogel.Lastly, the enamine switches could readily undergo constitutional exchange withprimary amines under catalytic acidic conditions, resulting in dynamic enaminesystems. However, under basic conditions or in the presence of excessive acid,this process exhibited extremely slow kinetics, leading to an efficient regulationof the exchange process by controlling the switch status with regulation of pHin the system.
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2.
  • Wang, Lei, 1985- (författare)
  • Artificial Photosynthesis: Molecular Catalysts for Water Oxidation
  • 2015
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Artificial photosynthesis provides a promising solution to the future sustainable energy system. Water is the only suitably sufficient protons and electrons supplier by the reaction of water oxidation. However, this reaction is both kinetically and thermodynamically demanding, leading to a sluggish kinetics unless the introduction of a catalyst.The theme of this thesis is to design, synthesize and evaluate molecular catalysts for water oxidation. This thesis consists of seven parts:The first chapter presents a general introduction to the field of homogenous catalysis of water oxidation, including catalysts design, examination and mechanistic investigation.The second chapter investigates the electronic and noncovalent-interaction effects of the ligands on the activities of the catalysts.In the third chapter, halogen substitutes are introduced into the axial ligands of the ruthenium catalysts. It is proved that the hydrophobic effect of the halogen atom dramatically enhanced the reactivity of the catalysts.Chapter four explores a novel group of ruthenium catalysts with imidazole-DMSO pair of axial ligands, in which the DMSO is proved to be crucial for the high efficiency of the catalysts.Chapter five describes the light-driven water oxidation including the three-component system and the sensitizer-catalyst assembled system. It is found that the common Ru(bpy)32+ dye can act as an electron relay and further benefit the electron transfer as well as the photo-stability of the system.In chapter six, aiming to the future application, selected ruthenium catalysts have been successfully immobilized on electrodes surfaces, and the electrochemical water oxidation is achieved with high efficiency.Finally, in the last chapter, a novel molecular catalyst based on the earth abundant metal ―nickel has been designed and synthesized. The activities as well as the mechanism have been explored.
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3.
  • Gao, Weiming, et al. (författare)
  • Attachment of a Hydrogen-Bonding Carboxylate Side Chain to an FeFe -Hydrogenase Model Complex : Influence on the Catalytic Mechanism
  • 2010
  • Ingår i: Chemistry - A European Journal. - Weinheim : Wiley. - 0947-6539 .- 1521-3765. ; 16:8, s. 2537-2546
  • Tidskriftsartikel (refereegranskat)abstract
    • Azapropanedithiolate (adt)-bridged model complexes of [FeFe]-hydrogenase bearing a carboxylic acid functionality have been designed with the aim of decreasing the potential for reduction of protons to hydrogen. Protonation of the bisphosphine complexes 4-6 has been studied by in situ IR and NMR spectroscopy, which revealed that protonation with triflic acid most likely takes place first at the N-bridge for complex 4 but at the Fe Fe bond for complexes 5 and 6. Using an excess of acid, the diprotonated species could also be observed, but none of the protonated species was sufficiently stable to be isolated in a pure state. Electrochemical studies have provided an insight into the catalytic mechanisms under strongly acidic conditions, and have also shown that complexes 3 and 6 are electro-active in aqueous solution even in the absence of acid, presumably due to hydrogen bonding. Hydrogen evolution, driven by visible light, has been observed for three-component systems consisting of [Ru(bpy)(3)](2+), complex 1, 2, or 3, and ascorbic acid in CH3CN/D2O solution by on-line mass spectrometry.
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4.
  • Karlsson, Karl Martin, 1981- (författare)
  • Design, Synthesis and Properties of Organic Sensitizers for Dye Sensitized Solar Cells
  • 2011
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • This thesis gives a detailed description of the design and synthesis of new organic sensitizers for Dye sensitized Solar Cells (DSCs). It is divided in 7 chapters, where the first gives an introduction to the field of DSCs and the synthesis of organic sensitizers. Chapters 2 to 6 deal with the work of the author, starting with the first publication and the other following in chronological order. The thesis is completed with some concluding remarks (chapter 7). The DSC is a fairly new solar cell concept, also known as the Grätzel cell, after its inventor Michael Grätzel. It uses a dye (sensitizer) to capture the incident light. The dye is chemically connected to a porous layer of a wide band-gap semiconductor. The separation of light absorption and charge separation is different from the conventional Si-based solar cells. Therefore, it does not require the very high purity materials necessary for the Si-solar cells. This opens up the possibility of easier manufacturing for future large scale production. Since the groundbreaking work reported in 1991, the interest within the field has grown rapidly. Large companies have taken up their own research and new companies have started with their focus on the DSC. So far the highest solar energy to electricity conversion efficiencies have reached ~12%. The sensitizers in this thesis are based on triphenylamine or phenoxazine as the electron donating part in the molecule. A conjugated linker allows the electrons to flow from the donor to the acceptor, which will enable the electrons to inject into the semiconductor once they are excited. Changing the structure by introducing substituents, extending the conjugation and exchanging parts of the molecule, will influence the performance of the solar cell. By analyzing the performance, one can evaluate the importance of each component in the structure and thereby gain more insight into the complex nature of the dye sensitized solar cell.
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5.
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6.
  • Privalov, Timofei, et al. (författare)
  • The O-O Bonding in Water Oxidation : the Electronic Structure Portrayal of a Concerted Oxygen Atom-Proton Transfer Pathway
  • 2011
  • Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 17:30, s. 8313-8317
  • Tidskriftsartikel (refereegranskat)abstract
    • The two-phased reaction: Calculations on the monomeric ruthenium catalyst with 1,10-phenanthroline-2,9-dicarboxylic acid reveals an interaction of the RuV=O complex with water that proceeds through two main phases and involves partial charge separation in an early encounter complex. Further along the reaction path, that effect leads to an electronic reorganization in the Ru complex; this directs the donor-acceptor interaction between the attacking water and the COO-group in concert with the O-atom transfer to form an O-O bond via a relatively low-energy barrier (see graphic).
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9.
  • Yang, Hao, 1995- (författare)
  • (Photo)electrochemical Water Oxidation: From Catalysis to Functional Device
  • 2023
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The key challenge within artificial photosynthesis is achieving efficient electro- or photo-driven water oxidation catalysis, a necessary process to supply the protons for the reduction reactions, thereby enabling solar fuel production. To facilitate efficient water (photo)electrolysis for solar fuel production, this thesis focuses on two aspects: 1) elucidating the O-O bond formation mechanism and developing efficient, stable, and economical water oxidation catalysts (WOCs); 2) exploring stable, low-cost, light-absorbing photoanode materials that have suitable band structures and excellent charge diffusion properties.Chapter 1 provides an overview of the development of homogeneous and heterogeneous WOCs, with a particular emphasis on the catalytic mechanisms. Subsequently, it introduces the advancements in light-harvesting materials for photoelectrochemical cells and highlights the progress in the burgeoning field of lead halide perovskite-based photoanodes.Chapter 2 clarifies the physical and electrochemical characterization methodologies, along with the protocols employed for mechanistic investigations in this thesis.Chapter 3 introduces a host-guest complex, self-assembled through Co2+ and cucurbit[5]uril (CB[5]), as a supramolecular WOC. This catalyst, Co@CB[5], was immobilized on indium tin oxide substrate and BiVO4 photoanode for electrochemical and photoelectrochemical water oxidation. The role of Co@CB[5] in interfacial charge transfer is investigated by spectroscopic and electrochemical studies.Chapter 4 reports a molecularly well-defined heterogeneous WOC with aza-fused, π-conjugated microporous polymer coordinated single cobalt sites (Aza-CMP-Co). Integrating experimental and theoretical results, this work highlights the significance of electrolyte pH and the role of regulating the intramolecular hydroxyl nucleophilic attack pathway in enhancing water oxidation activity.Chapter 5 presents a stable formamidinium lead bromide (FAPbBr3) photoanode for water oxidation to achieve an exceptionally low onset potential. Theoretical calculations and spectroscopic characterizations reveal the origin of low onset potential, which offers pivotal insights in guiding the development of photovoltaic material-based photoelectrodes for solar fuel applications.
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10.
  • Wang, Lei, et al. (författare)
  • A nickel (II) PY5 complex as an electrocatalyst for water oxidation
  • 2016
  • Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 335, s. 72-78
  • Tidskriftsartikel (refereegranskat)abstract
    • A Ni-PY5 [PY5 = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine)] complex has been found to act as an electrocatalyst for oxidizing water to dioxygen in aqueous phosphate buffer solutions. The rate of water oxidation catalyzed by the Ni-PY5 is remarkably enhanced by the proton acceptor base HPO42-, with rate constant of 1820 M-1 s(-1). Controlled potential bulk electrolysis with Ni-PY5 at pH 10.8 under an applied potential of 1.5 V vs. normal hydrogen electrode (NHE) resulted in dioxygen formation with a high faradaic efficiency over 90%. A detailed mechanistic study identifies the water nucleophilic attack pathway for water oxidation catalysis.
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