Typescript. / Digitized by Kansas Correctional Industries

by Ho Kai Wing Kevin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves 94-98). / ABSTRACT --- p.iv / ACKNOWLEDGEMENTS --- p.vi / Chapter CHAPTER ONE: --- INTRODUCTION --- p.1 / Chapter 1.1 --- Basic Co-NMR Theory --- p.1 / Chapter 1.2 --- Method Employed --- p.5 / Chapter 1.2.1 --- Solvent Dependent Studies on Cobalt(III) complexes using 59Co NMR Spectroscopy --- p.5 / Chapter 1.2.2 --- Relationship between δiso and NQCC of Cobalt(III) Complexes in Solid --- p.7 / Chapter 1.3 --- Donor Acceptor Interactions --- p.8 / Chapter 1.4 --- Objectives of this Thesis --- p.10 / Chapter CHAPTER TWO: --- EXPERIMENTAL --- p.11 / Chapter 2.1 --- Synthesis --- p.11 / Chapter 2.2 --- NMR Measurements --- p.13 / Chapter 2.2.1 --- 59Co NMR Measurements --- p.13 / Chapter 2.2.2 --- 13c NMR Measurements (T1 Measurements) --- p.14 / Chapter 2.3 --- Viscosity Measurements --- p.15 / Chapter 2.4 --- UV-Vis Spectral Measurements --- p.15 / Chapter CHAPTER THREE --- 59Co NMR STUDY OF MAGNETIC COBALT(III) COMPLEXES --- p.16 / Chapter 3.1 --- Solvent-Dependent Studies of Cobalt(III) Complexes --- p.16 / Chapter 3.1.1 --- "Study of [Co(en)3]Cl3 and cis, trans-[Co(en)2(N3)2]NO3" --- p.17 / Chapter 3.1.2 --- Study of trans- [Co(en)2(NH3)2]Cl3 and trans- [Co(en)2(N02)2]NO3 --- p.29 / Chapter 3.1.3 --- "Study of trans- Na[Co(acac)2 (N02)2],trans- [Co(acac)2(N02)(NH3)] and trans-[Co(acac)2(NH3)2]I" --- p.36 / Chapter 3.1.4 --- Summary --- p.48 / Chapter 3.2 --- "Simultaneous Determination of CSA, ic, and NQCC of Cobalt(III) complexes in Different Solvents" --- p.49 / Chapter 3.2.1 --- Method --- p.49 / Chapter 3.2.2 --- "Study of trans- Na[Co(acac)2(N02)2],trans- [Co(acac)2(N02)(NH3)] and trans-[Co(acac)2(NH3)2]I and trans-[Co(acac)2(MeNH2)2]I" --- p.52 / Chapter 3.2.3 --- Study of trans- [Co(en)2(N〇2)2]N03 and trans- [Co(en)2(NCS)2]NCS --- p.58 / Chapter 3.2.4 --- Study of trans- [Co(en)2(NH3)2]Cl3 and trans- [Co(en)2(N3)2]NO3 --- p.63 / Chapter 3.2.5 --- Summary --- p.68 / Chapter 3.3 --- Resolution of the d-d Electronic Transition Energies in Cobalt Complexes and its Application to the Donor-Acceptor Interactionsin Cobalt Complexes - Application of Equation 3.3.1 --- p.70 / Chapter 3.3.1 --- Method --- p.70 / Chapter 3.3.2 --- "Study of trans- [Co(en)2(N02)2]N03,trans- [Co(en)2(NCS)2]NCS, trans- [Co(en)2(N3)2]N03 and trans- [Co(en)2(NH3)2]Cl3" --- p.72 / Chapter 3.3.3 --- "Study of trans- Na[Co(acac)2(NO2)2],trans- [Co(acac)2(N02)(NH3)] and trans-[Co(acac)2(NH3)2]I" --- p.86 / Chapter CHAPTER FOUR --- CONCLUSION AND FUTURE WORKS --- p.92 / REFERENCES --- p.94

by Chung Sai Cheong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 94-99). / DESCRIPTIVE NOTE / ABSTRACT --- p.iii / ACKNOWLEDGEMENTS --- p.v / Chapter CHAPTER ONE: --- INTRODUCTION --- p.1 / Chapter CHAPTER TWO: --- EXPERIMENTAL --- p.6 / Chapter 2.1 --- Synthesis --- p.6 / Chapter 2.2 --- NMR Measurement --- p.6 / Chapter 2.2.1 --- Solid State 59Co NMR --- p.6 / Chapter 2.2.2 --- Solution NMR --- p.7 / Chapter 2.2.2.1 --- 59Co NMR Measurements --- p.7 / Chapter 2.2.2.2 --- 13C NMR Measurements --- p.8 / Chapter 2.3 --- UV-Vis Spectral Measurements --- p.9 / Chapter 2.4 --- Computer Simulation --- p.10 / Chapter CHAPTER THREE: --- QUANTITATIVE CORRELATION OF SHIELDING ANISOTROPY AND NQCC - APPLICATION TO SOLVATION STUDIES OF OCTAHEDRAL COBALT (III)COMPLEXES / Chapter 3.1 --- Introduction --- p.11 / Chapter 3.2 --- Theory --- p.15 / Chapter 3.3 --- Results and Discussion --- p.20 / Chapter 3.3.1 --- The 59Co NMR Powder Spectrum of Diamagnetic Cobalt Complexes --- p.20 / Chapter 3.3.2 --- The Correlation of NQCC with Chemical Shift Anisotropy in the Solid State --- p.34 / Chapter 3.3.3 --- Application of Equation 3.16in Solution Studies --- p.39 / Chapter 3.3.3.1 --- The Chemical Shift --- p.39 / Chapter 3.3.3.2 --- The Effective Correlation Time --- p.48 / Chapter 3.3.3.3 --- The Nuclear Quadrupole Coupling Constant --- p.49 / Chapter 3.4 --- Summary --- p.51 / Chapter CHAPTER FOUR: --- 59Co AND 13C RELAXATION OF Co(acac)3 IN HYDROGEN BONDING (KALOMETHANE) SOLVENTS / Chapter 4.1 --- Introduction --- p.53 / Chapter 4.2 --- Results and Discussion --- p.57 / Chapter 4.2.1 --- The Static NMR Powder Spectrum Co(acac)3 --- p.57 / Chapter 4.2.2 --- Chemical shift --- p.60 / Chapter 4.2.3 --- Relaxation --- p.67 / Chapter 4.2.3.1 --- The 13C Relaxation --- p.67 / Chapter 4.2.3.2 --- The 59Co Relaxation --- p.71 / The Spin Rotation Interaction --- p.71 / The Temperature Behaviour of Relaxa- tion Rate --- p.72 / The Nuclear Quadru- pole Coupling Constant --- p.76 / The Correlation Time --- p.82 / Chapter 4.3 --- Summary --- p.90 / Chapter CHAPTER FIVE: --- CONCLUSION --- p.91 / REFERENCES --- p.94

Thesis (M.Phil.)--Chinese University of Hong Kong. / Includes bibliographies.

α-synuclein (αS) is an intrinsically disordered protein that is strongly connected with Parkinson’s disease (PD) and a number of other neurodegenerative disorders, including Parkinson’s disease with dementia, dementia with Lewy bodies and multiple system amyotrophy. Fibrillar aggregates of αS have been identified as the major constituents of proteinaceous inclusions known as Lewy bodies that form inside the neurons of patients suffering from these conditions. A number of missense mutations, as well as duplications and triplications of the gene encoding αS have also been associated with familial forms of early onset PD. Despite the association between αS aggregation and neurodegeneration is now established, the specific function of αS is still currently unclear, however, a general consensus is forming on its key role in regulating the process of neurotransmitter release, which is associated with the ability of αS to bind a variety of biological membranes. Indeed, in dopaminergic neurons, αS exists in a tightly regulated equilibrium between water-soluble disordered state and membrane-associated forms that are rich in α-helix. Characterising the nature of this binding as well as the structural and functional properties of αS at the surface of biological membranes is currently a top challenge. In particular the intrinsic limitation of current analytical techniques in studying highly heterogeneous protein states in rapid equilibrium between different physical phases demands for novel approaches to be formulated. This PhD thesis describes major achievements in developing and applying a multidisciplinary approach based on solution and solid-state NMR and extending to a number of other biophysical techniques, including cryo electron microscopy, super resolution microscopy, FRET and cellular biophysics, which enabled us to elucidate in detail the balance between structural order and disorder associated with the membrane interaction of αS in view of its physiological and pathological roles. Using this approach, we identified the key elements that govern the binding of αS to synaptic vesicles (Chapter III). In particular, three regions of αS were shown to possess distinct structural and dynamical properties at the surface of synaptic vesicles, including an N-terminal helical segment having a role of membrane anchor, an unstructured C-terminal region that is weakly associated with the membrane and a central region acting as a sensor of the lipid properties and determining the affinity of αS membrane binding. We refined the structural ensemble of the N-terminal membrane anchor at the surface of synaptic membranes, showing that the partial insertion of this region in the membrane core promotes strong but reversible binding with biological membranes in such a way to enable a fast equilibrium between membrane-bound and cytosolic forms of the protein (Chapter III). Further studies of two mutational variants of αS that are associated to early onset PD, namely A30P and E46K, revealed that two key regions of the protein, namely the N-terminal membrane-anchor (residues 1 to 25) and the central segment of the sequence (residues 65–97, having significant overlap with the non-amyloid β component - NAC - region), have independent membrane-binding properties and therefore are not only able to interact with a single SV, but can also simultaneously bind to two different vesicles thereby promoting their clustering (Chapter IV). The resulting “double-anchor” mechanism explains the biological property of αS to promote clusters of synaptic vesicles within the processes of formation of distal pools to the active zone. The double-anchor mechanism reconciles literature data showing that the deletion of the segment 71–82 in the NAC region of αS or the impairment of the membrane affinity of the N-terminal anchor region of the protein severely affect vesicle clustering in vivo. Thus our data revealed that the NAC region is not only involved in the aggregation of αS, as extensive literature evidence has previously indicated, but also has a specific role in a key molecular mechanism associated with the normal function of αS. The structural characterisation also showed that the active conformations of αS to initiate the double-anchor mechanism are particularly vulnerable to self-association leading to αS aggregation at membrane surfaces, thereby providing a new mechanistic link between functional and pathological roles of αS. In addition to studying the physiological membrane interactions by αS, we characterised the fundamental mechanism of membrane disruption by αS oligomers resulting in the generation of neuronal toxicity in PD (Chapter V). Indeed, while fibrillar aggregates of αS represent the major histopathological hallmarks of PD, small oligomeric assemblies of this protein are believed to play a crucial role in neuronal impairment. We obtained a detailed structural characterisation of toxic αS oligomers and compared these results to the study of non-toxic oligomeric species. The results reveal the fundamental structural characteristics driving the toxicity of αS oligomers, including a highly lipophilic element that promotes strong interactions with biological membranes and a structured region that inserts into lipid bilayers and disrupts their integrity. We obtained additional support for these conclusions by showing that mutations targeting the region of αS promoting such interactions with the membrane dramatically suppress the toxicity of αS aggregates in neuroblastoma cells and primary cortical neurons. Taken together our studies enabled the characterisation of a series of structural properties of the membrane-bound states of αS in both its monomeric and oligomeric forms. The results revealed the nature of the fine balance between functional and pathological membrane interactions of αS and delineated how subtle perturbations of this equilibrium can lead to the rapid evolution of processes that trigger pathological mechanisms. Understanding this balance is a top challenge for advancing the research in PD and requires innovation across different disciplines to overcome current limitations in probing the conformational transitions of this disordered and metamorphic neuronal protein.

Supercapacitors (or electric double-layer capacitors) are high power energy storage devices that store charge by the non-faradaic adsorption of ions at the interface between porous carbon electrodes and an electrolyte solution. The development of new electrode materials and electrolytes with improved performances is an active area of research today, yet there are relatively few studies of the molecular mechanisms of the charge storage process. In this work, nuclear magnetic resonance (NMR) spectroscopy is developed for the study of the charge storage mechanisms of supercapacitors. Importantly, NMR experiments show that electrolyte ions adsorbed inside the pores of the carbon electrodes can be resolved from those in bulk electrolyte for a range of supercapacitor electrode materials. Chemical shift calculations show that the adsorbed species are subject to ring current effects, whereby the delocalised electrons in the carbon shield the nearby nuclei. The calculated effects depend on the local carbon structure, helping to rationalise the variations observed when different porous carbons are studied experimentally, and allowing structural information to be extracted from the spectra. NMR experiments performed on electrodes extracted from ionic liquid-based supercapacitors with different applied voltages allow the numbers of adsorbed ions to be measured upon charging. It is shown that supercapacitor charging involves the migration of both anions and cations in and out of the carbon pores in each electrode, with the anions dominating the charge storage process. When combined with lineshape measurements, which offer information about the diffusion of adsorbed ions, the power performances of supercapacitor devices with different electrolytes are rationalised. In situ NMR methods are then developed to allow mechanistic studies of working supercapacitors as they are charged and discharged inside the NMR magnet. The experiments reveal that the charge storage mechanism depends on both the electrolyte and the electrode material studied. During charging, reversible chemical shift changes are also observed, arising from the introduction of paratropic ring currents. Finally, cross polarisation experiments allow the selective observation of the adsorbed electrolyte species, and show that their motion slows down during supercapacitor charging. Overall, the NMR approach offers unique insights into the molecular mechanisms of the supercapacitance phenomenon.

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