Molecular Interactions Chlorin Assemblies and NMR Separations

Photosynthesis is a chemical process in which the energy of the light quanta is transformed into chemical energy. Chlorophyll (Chl) molecules play a key role in photosynthesis; they function in the antennae systems and in the photosynthetic reaction center where the primary charge separation (CS) takes place. Bio-inspired mimicry of the CS is an essential unit in dye-sensitized solar cells. Aim of this study was to design and develop electron donor-acceptor (EDA) pairs from Chls and fullerenes (C60) or carbon nanotubes (CNT). The supramolecular approach was chosen, as long synthetic sequences required by the covalent approach lead to long reaction schemes and low yields. Here, a π-interaction between soluble CNTs and Chl was used in EDA construction. Also, a beta-face selective two-point bound Chl-C60 EDA was introduced. In addition, the photophysical properties of the supramolecular EDA dyads were analyzed. In organic chemistry, nuclear magnetic resonance (NMR) spectroscopy is the most vital analytical technique in use. Multi-dimensional NMR experiments have enabled a structural analysis of complex natural products and proteins. However, in mixture analysis NMR is still facing difficulties. In many cases overlapping signals can t be resolved even with the help of multi-dimensional experiments. In this work, an NMR tool based on simple host-guest chemistry between analytes and macromolecules was developed. Diffusion ordered NMR spectroscopy (DOSY) measures the mobilities of compounds in an NMR sample. In a liquid state NMR sample, each of the analytes has a characteristic diffusion coefficient, which is proportional to the size of the analyte. With normal DOSY experiment, provided that the diffusion coefficients of the analytes differ enough, individual spectra of analytes can be extracted. When similar sized analytes differ chemically, an additive can be introduced into the sample. Since macromolecules in a liquid state NMR sample can be considered practically stationary, even faint supramolecular interaction can change the diffusion coefficient of the analyte sufficiently for a successful resolution in DOSY. In this thesis, polyvinylpyrrolidone and polyethyleneglycol enhanced DOSY NMR techniques, which enable mixture analysis of similar in size but chemically differing natural products, are introduced.

Ion-regulatory proreins in neuronal development and communication

Brain function is critically dependent on the ionic homeostasis in both the extra- and intracellular compartment. The regulation of brain extracellular ionic composition mainly relies on active transport at blood brain and at blood cerebrospinal fluid interfaces whereas intracellular ion regulation is based on plasmalemmal transporters of neurons and glia. In addition, the latter mechanisms can generate physiologically as well as pathophysiologically significant extracellular ion transients. In this work I have studied molecular mechanisms and development of ion regulation and how these factors alter neuronal excitability and affect synaptic and non-synaptic transmission with a particular emphasis on intracellular pH and chloride (Cl-) regulation. Why is the regulation of acid-base equivalents (H+ and HCO3-) and Cl- of such interest and importance? First of all, GABAA-receptors are permeable to both HCO3- and Cl-. In the adult mammalian central nervous system (CNS) fast postsynaptic inhibition relies on GABAA-receptor mediated transmission. Today, excitatory effects of GABAA-receptors, both in mature neurons and during the early development, have been recognized and the significance of the dual actions of GABA on neuronal communication has become an interesting field of research. The transmembrane gradients of Cl- and HCO3- determine the reversal potential of GABAA-receptor mediated postsynaptic potentials and hence, the function of pH and Cl- regulatory proteins have profound consequences on GABAergic signaling and neuronal excitability. Secondly, perturbations in pH can cause a variety of changes in cellular function, many of them resulting from the interaction of protons with ionizable side chains of proteins. pH-mediated alterations of protein conformation in e.g. ion channels, transporters, and enzymes can powerfully modulate neurotransmission. In the context of pH homeostasis, the enzyme carbonic anhydrase (CA) needs to be taken into account in parallel with ion transporters: for CO2/HCO3- buffering to act in a fast manner, CO2 (de)hydration must be catalyzed by this enzyme. The acid-base equivalents that serve as substrates in the CO2 dehydration-hydration reaction are also engaged in many carrier and channel mediated ion movements. In such processes, CA activity is in key position to modulate transmembrane solute fluxes and their consequences. The bicarbonate transporters (BTs; SLC4) and the electroneutral cation-chloride cotransporters (CCCs; SLC12) belong the to large gene family of solute carriers (SLCs). In my work I have studied the physiological roles of the K+-Cl- cotransporter KCC2 (Slc12a5) and the Na+-driven Cl--HCO3- exchanger NCBE (Slc4a10) and the roles of these two ion transporters in the modualtion of neuronal communication and excitability in the rodent hippocampus. I have also examined the cellular localization and molecular basis of intracellular CA that has been shown to be essential for the generation of prolonged GABAergic excitation in the mature hippocampus. The results in my Thesis provide direct evidence for the view that the postnatal up-regulation of KCC2 accounts for the developmental shift from depolarizing to hyperpolarizing postsynaptic EGABA-A responses in rat hippocampal pyramidal neurons. The results also indicate that after KCC2 expression the developmental onset of excitatory GABAergic transmission upon intense GABAA-receptor stimulation depend on the expression of intrapyramidal CA, identified as the CA isoform VII. Studies on mice with targeted Slc4a10 gene disruption revealed an important role for NCBE in neuronal pH regulation and in pH-dependent modulation of neuronal excitability. Furthermore, this ion transporter is involved in the basolateral Na+ and HCO3- uptake in choroid plexus epithelial cells, and is thus likely to contribute to cerebrospinal fluid production.

Diffusion of Be, Co and Mn impurities in compound semiconductors and glassy carbon studied by the modified radiotracer technique

The main method of modifying properties of semiconductors is to introduce small amount of impurities inside the material. This is used to control magnetic and optical properties of materials and to realize p- and n-type semiconductors out of intrinsic material in order to manufacture fundamental components such as diodes. As diffusion can be described as random mixing of material due to thermal movement of atoms, it is essential to know the diffusion behavior of the impurities in order to manufacture working components. In modified radiotracer technique diffusion is studied using radioactive isotopes of elements as tracers. The technique is called modified as atoms are deployed inside the material by ion beam implantation. With ion implantation, a distinct distribution of impurities can be deployed inside the sample surface with good con- trol over the amount of implanted atoms. As electromagnetic radiation and other nuclear decay products emitted by radioactive materials can be easily detected, only very low amount of impurities can be used. This makes it possible to study diffusion in pure materials without essentially modifying the initial properties by doping. In this thesis a modified radiotracer technique is used to study the diffusion of beryllium in GaN, ZnO, SiGe and glassy carbon. GaN, ZnO and SiGe are of great interest to the semiconductor industry and beryllium as a small and possibly rapid dopant hasn t been studied previously using the technique. Glassy carbon has been added to demonstrate the feasibility of the technique. In addition, the diffusion of magnetic impurities, Mn and Co, has been studied in GaAs and ZnO (respectively) with spintronic applications in mind.