Diss. (sammanfattning) Linköping : Univ., 2003. / Härtill 6 uppsatser.

<p>Molecular mimics of PS II, which consist of a photosensitizer linked to electron acceptors/donors, are attractive candidates for the conversion of solar energy into chemical energy. Several different classes of sensitizers have been studied and among these, ruthenium(II) polypyridyl complexes continue to attract major attention. </p><p>The first part of this thesis presents the photophysical properties, stereochemistry, and general synthesis of ruthenium(II) polypyridyl complexes based on 2,2´-bipyridyl and 2,2´:6´,2´´-terpyridyl ligands. The second part deals with ruthenium(II) polypyridyl complexes linked to electron acceptors (benzoquinone, naphthalene diimide) and electron donors (phenothiazine, tyrosine, manganese complexes). Functionalized 2,2´-bipyridines and 2,2´:6´,2´´-terpyridines were synthesized and used in the stepwise assembly of the chromophore-quencher complexes. These were fully characterized and the redox properties were studied by cyclic and differential pulse voltammetry. The intramolecular charge-separated states formed after light excitation of the ruthenium(II) unit were observed by time-resolved absorption and EPR spectroscopy. </p><p>In the third part of this thesis, the synthesis and photophysical properties of a novel class of bistridentate ruthenium(II) polypyridyl complexes based on bipyridyl-pyridyl methane ligamds are discussed. The solution structures of the homoleptic and heteroleptic complexes were studied by 2D NMR techniques. The X-ray structure of one of the homoleptic complexes has been solved. The effect on the excited state lifetime for these ruthenium(II) complexes compared to the parent [Ru(tpy)₂]²⁺ is discussed. Finally, in one of the heteroleptic complexes an interesting reversible linkage iomerization was observed that could be induced either electrochemically or chemically.</p>

<p>This work consists of mainly two parts. The first part deals with the sintering behaviour and the microstructural stability of SrFe_1-xCr_xO_3-δ, and the second with transport properties of membranes of the same compositions. The most important experimental tools have been dilatometry and oxygen permeability measurements. Supplementary tools were x-ray diffraction analysis (XRD), scanning electron microscope (SEM) and particle size distribution analysis. </p>

<p>Solid oxide fuel cells and oxygen permeable membranes have received considerable attention during the last decade due to the increasing demand for electrical energy and easily transportable fuels combined with the requirement of low emission of CO₂. This work concentrates on the stability of ceramic interfaces in general, and more specifically to heterophase solid state interfaces related to solid oxide fuel cells and oxygen permeable membranes. Reaction mechanisms are discussed and requirements and properties of suitable materials are determined. This thesis consists of three parts: 1) Structure of Ca-substituted lanthanum manganite (Paper I), 2) Reactions between cathode and electrolyte for SOFC applications (Papers II-IV) and 3) Chemical and mechanical aspects of sealing dense oxygen permeable membranes (Papers V and VI).</p>

<p>In this thesis the entropy production rate of diabatic distillation columns and a SO₂ converter were minimised. This is the same as maximising the second law energy efficiency of the systems. The development of chemical industry can be made more sustainable by knowing this minimum. We found that the entropy production rate of distillation could be reduced up to 50%. In order to achieve this reduction, heat exchangers were added on each tray. The characteristics of an optimum distillation column were presented. Furthermore, the entropy production rate of a SO₂ converter was reduced with 16.7% by altering the heights of catalytic beds, transfer areas of heat exchangers, and temperature differences over heat exchangers. These reductions show that there is still a large improvement potential in chemical industry. By applying the improved operations the world oil production can be reduced in the order of magnitude of 1%. A similar reduction in the emission of the greenhouse gas CO₂ can be expected. </p><p>For deriving the entropy production rate in a systematic manner the theory of irreversible thermodynamics was useful. A simpler and a more complicated equation for the entropy production rate of distillation were derived. The simpler equation used only one force-flux product. It was suitable for minimisation of the entropy production rate of columns with the assumption of equilibrium between the outlets on each tray. The more complicated equation was able to describe satisfactorily the entropy production rate of an experimental column that separated the non-ideal mixture water-ethanol. It was next used to derive an extended set of transport equations for distillation, that includes the interface and the Soret effect (or thermal diffusion). Finally, irreversible thermodynamics was used to describe the contributions to the entropy production rate of heat transfer in heat exchangers. This contribution had a significant impact on the results of the minimisations.</p><p>A method that can provide the chemical industry the thermodynamically optimum operation of distillation columns and reactors was constructed and exemplified. Once the system and its boundaries are determined, the objective function with its constraints and variables are set up. Several suitable minimisation procedures exist. Finally, the design of the thermodynamically optimum system is obtained from the state of minimum entropy production rate. </p>

<p>Enantiomerically pure amines and alcohols are particularly important synthons for the preparation of pharmaceuticals and agrochemicals. Notwithstanding the advances that have been achieved in asymmetric synthesis, resolution of racemates is probably the most current approach for the preparation of pure enantiomers. On the other hand, resolution processes suffer from disadvantages of low yields caused by the loss of at least 50% of the undesired isomer. Among the attractive methods for avoiding the drawbacks of resolution processes is inversion of configuration of the unwanted isomer. Although there are several existing methodologies for inversion and stereoselective transformations of chiral alcohols, corresponding methods for inversion of chiral amines has received less attention. The main objective of the project “Stereoselective transformations of chiral amines” was therefore to develop effective methods for inversion and stereoselective transformations of chiral amines.</p><p>This thesis discuss the utility of three nucleophilic substitution methods in stereoselective transformations of chiral amines.</p><p>The first investigation towards this goal was carried out using cyclic aryldisulfonylimide leaving group. Substitution of a chiral amine via N,Nnaphthalene- 1,2-disulfonylimide intermediate gave azide and alcohol products with 60-73% inversion of configuration, which was 20-25% lower compared to the previously studied relative disulfonylimides. Displacement of this group using aroxide anions afforded chiral aryl ethers with 70-87% inversion of stereochemistry. Chiral analysis of the ether products required synthesis of authentic reference compounds. This was achieved via benzyne route and by nucleophilic substitution on the derivatives of chiral alcohols. The benzyne route gave chiral phenyl ether from enantiopure alcohols with complete retention of configuration while the trifluoroacetate derivatives of chiral alcohols produced chiral aryl ethers with complete inversion of stereochemistry.</p><p>The 2,4,6-triphenylpyridinium cations were the next intermediates investigated in this study. These derivatives were synthesized from 2,4,6-triphenylpyrylium tetrafluoroborate in 84-90% yields using procedures described by Katritzky. Nucleophilic substitution on pyridinium salts of aliphatic chiral amines using azide and hydroxide anions gave products with 96 to 100% inversion of configuration.</p><p>The utility of diazonium salts for inversion of chiral amines was also investigated in the present study. This method was only focused on stereoselective transformations of α-amino acids as diazotization-dediazoniation of other aliphatic amines is of little interest for organic synthesis. Diazotization of L-alanine and L-phenylalanine ethyl esters hydrochlorides using alkyl nitrites in aprotic solvents, in the presence of azide anion, yielded optically active chloro substituents as the only products, instead of the intended azide compounds. Attempts to avoid counterion substitution by using ammonium tosylate to replace the ammonium chlorides was not useful and a tosyl product was isolated instead. Proposals to rectify this problem have been suggested. These include the use of much more inert counterions such as tetrafluoroborate or replacing the hydrochlorides with hydroazides. An alternative which could deliver the nucleophile in an intramolecular fashion has also been postulated. Investigations of these hypotheses are currently conducted.</p><p>Parallel to diazotization reactions was an investigation on inversion of α-amino acids via N,N-disulfonylimides and 2,4,6-triphenylpyridinium cation leaving groups. Studies with N,N-disulfonylimide derivatives showed that this leaving group is not useful for inversion of α-amino acids. Nucleophilic substitution on the 2,4,6-triphenylpyridinium salts of amino acids afforded partial racemized substitution products. The drawback in the utility of the pyridinium salts has been identified and efforts are underway to remove this impediment.</p>

<p>Palladium-promoted reactions have been employed for the synthesis of compounds labelled with ¹¹C (t_½ = 20.3 min). The precursor [¹¹C]methyl iodide was used in palladium-promoted cross-coupling reactions with organostannanes. With this method, large molecules with several functional groups, that is prostacyclin analogues, have been synthesised in up to 54 % decay-corrected radiochemical yield, calculated from [¹¹C]methyl iodide. However, since this method did not afford reproducible yields, a second method where copper(I) was used as a co-catalyst with palladium, was developed. In the second method, a lower reaction temperature could be used and more reproducible yields were obtained. Employing this method, a prostaglandin analogue was synthesised in 34 % decay-corrected radiochemical yield calculated from [¹¹C]methyl iodide. The total synthesis time was 30 min and the radiochemical purity was higher than 95 %. The specific radioactivity of the compounds obtained with these two methods was approximately 100 GBq/μmol.</p><p>¹¹C-Labelled aliphatic and aromatic alkenes were synthesised from [¹¹C]methyl iodide in a Wittig olefination reaction using a published method. The ¹¹C-labelled alkenes were reacted with five aromatic halidein Heck coupling reactions, producing five [¹¹C]stilbene analogues in 34-40 % decay-corrected radiochemical yield. The radiochemical purity was higher than 95 % and the total synthesis timwas 40 min. </p><p>¹¹C-Labelled alkenes were also synthesised from ¹¹C-labelled aldehydes. The ¹¹C-labelled aldehydes were obtained from [¹¹C]carbon monoxide in a palladium-mediated formylation of aryl iodides in 51-87 % radiochemical yield, determined by analytical LC and corrected for trappinefficiency. A range of palladium catalysts and hydride reagents were investigated. The labelled aldehydes were used in a subsequent Wittig olefination reaction where various Wittig salts were employed tsynthesise a variety of alkenes. The radiochemical yields were 30-76 %, determined by analytical LC.</p>

<p>In this thesis the isolation, synthesis and biological evaluation of natural defense compounds against herbivores or oxidative stress is discussed.</p><p>The first part concerns the metabolites of platyphylloside ((<i>5S</i>)-5-hydroxy-1,7-bis-(4-hydroxyphenyl)-3-heptanone-5-O-β-D-glucopyranoside), a phenolic glucoside found in birch (<i>Betula pendula</i>) that possess digestibility inhibiting activity in herbivores. The structure-activity relationship of platyphylloside analogues were investigated regarding to stereochemistry and substitution pattern on the aromatic rings. The metabolites formed <i>in vitro</i> in rumen fluid were synthesized and the active metabolite determined as (<i>R</i>)-centrolobol (1,7-bis-(4-hydroxyphenyl)-3-heptanol). Treatment of mice and rats with <i>rac</i>-centrolobol did not effect either food intake or body weight. Effect of platyphylloside in moose was also investigated, and the results indicate that there was an <i>in vivo</i> digestibility reducing activity.</p><p>The second part concerns naturally occurring antioxidants. Avenanthramides is a class of phenolic antioxidants found in oat (<i>Avena sativa</i>). Avenanthramides derived from either anthranilic acid or 5-hydroxyanthranilic acid were evaluated for their antioxidative capacity and quantified in oat extracts. Avenanthramides derived from 5-hydroxyanthranilic acid possessed higher activity than those from anthranilic acid. The order of reactivity depending on substitution pattern on the phenolic moiety was found to be 4-hydroxy < 4-hydroxy-3-methoxy < 3,5-dimethoxy-4-hydroxy and 3,4-dihydroxy. A synthesis towards antioxidative compounds such as 4-deoxycarbazomycin was developed.</p><p>The third part concerns the isolation of compounds from Lodgepole pine (<i>Pinus contorta</i>) with antifeedant activity against pine weevil (<i>Hylobius abietis</i>). Two compounds possessing high activity were isolated and identified.</p>

<p>Methods for liquid chromatography-mass spectrometry (LC/MS) with electrospray ionization (ESI) have been developed for the determination of specific radioactivity and for metabolic studies of radiolabelled compounds used in positron emission tomography (PET). These compounds often provide an analytical challenge mainly due to their low concentrations in complex sample matrices.</p><p>The effect on sensitivity using different mobile phase additives, such as trifluoroacetic acid and formic acid, was investigated. The ESI-MS response shows higher stability and sensitivity when volatile additives are used. For reversed phase ion-pair chromatography separations, however, non-volatile counter-ions are used that destabilize the detector response and reduce the sensitivity. A method was therefore developed for on-line removal of the ion-pairing reagents prior to detection. </p><p>Packed capillary columns and on-column focusing were used to improve mass sensitivity when analysing limited sample amounts. A commercial interface was modified to assist electrospray ionization at the low flow-rates (1 μl/min) required by columns with an inner diameter of 200 µm. </p><p>LC-MS methods were developed for determination of specific radioactivity of compounds labelled with short-lived radionuclides (<i>i.e.</i> ¹¹C with T_½=20.3 min and ⁷⁶Br T_½=16.2 h). In comparison with UV absorption detection, ESI-MS showed equal or improved sensitivity for all compounds investigated. The sensitivity of the developed methods allowed for detection of the radiolabelled isotope directly by mass spectrometry.</p><p>A packed capillary LC/MS method was developed for determination of raclopride in plasma samples taken from patients during PET studies after intravenous injection of nanomolar doses. The validated assay exhibited satisfactory accuracy and precision over the concentration range 0.2-15 nM.</p>

<p> In the first part, the preparation and properties of chalcogen-containing vitamin E analogues are described. The sulfur compound 3,3,4,6,7-pentamethyl-2,3-dihydrobenzo[<i>b</i>]thiophene-5-ol was prepared by two different routes using ionic and radical chemistry. Interesting rearrangements were observed in the two synthetic pathways. </p><p> A new methodology for the synthesis of dihydroselenophene and dihydrotellurophene derivatives is described. In the preparation of the vitamin E analogues 2,3-dihydrobenzo[<i>b</i>]selenophene-5-ol and 2,3-dihydrobenzo[<i>b</i>]tellurophene-5-ol a tellurium-mediated tandem S_RN1/S_Hi sequence was suggested to be operative. 2,3-Dihydrobenzo[<i>b</i>]thiophene-5-ol and the vitamin E-like selenide 2-methyl-2-(4,8,12-trimethyl-tridecyl)-selenochroman-6-ol were prepared via intramolecular homolytic substitution at sulfur and selenium, respectively. The first rate constant for intramolecular homolytic substitution at tellurium is also reported (5x10⁸s^-1 at 25 °C).</p><p> The antioxidant profile for 2,3-dihydrobenzo[<i>b</i>]furan-5-ol and its 1-thio, 1-seleno, and 1-telluro analogues is described. By means of pulse radiolysis, it was shown that the one-electron reduction potentials (ArO·/ArO^-) were independent of the chalcogen (0.49-0.52 V vs NHE). The O-H bond dissociation enthalpies for the compounds were also estimated to be similar (336-340 kJ mol^-1). The p<i>K</i>_a values and the oxidation potentials were also determined for these compounds. For some compounds the rate of hydrogen atom donation to <i>tert</i>-butoxyl radicals was determined by means of laser flash photolysis. Using a two-phase lipid peroxidation model, it was demonstrated that the selenium and tellurium analogues could be regenerated in the presence of a stoichiometric amount of a reducing agent. The organotellurium analogue also acted as a good glutathione-peroxidase mimic and as a potent inhibitor of lipid peroxidation in liver microsomes. </p><p> In the second part of the thesis the stabilizing capacity of bis[4-(dimethylamino)phenyl]telluride was investigated in the thermoplastic elastomer PACREL^®. It was demonstrated that the addition of 0.17-0.50 % of the telluride significantly improved the tensile strength and elongation at break of the polymer. Chemiluminescence measurements showed that the organotellurium compound prolonged the induction period of thermo-oxidation and reduced the total luminescence intensity of the material.</p>