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Water in the Earth’s Interior: Thermodynamics and kinetics of hydrogen incorporation in olivine and wadsleyite (2004)

Sylvie Demouchy

(1) Hydrogen diffusion in olivine The kinetics of hydration of dry single crystals of San Carlos olivine was determined by performing experiments under water-saturated conditions. The experiments were performed at 1.5 GPa, 1000°C for 5 hours in a piston cylinder apparatus, or at 0.2 GPa, 900°C, for 1 and 20 hours in TZM cold-seal vessels. Polarized Fourier-transform infrared spectrometry (FTIR) was employed to quantify the hydroxyl distributions in the samples after the experiments. The new data obtained show a strong anisotropy of diffusion, with the diffusion coefficient D[100]>D[010]> D[001] at 900°C for short duration experiments. This initial mechanism of diffusion possibly involved a redox-exchange between proton and polaron. After longer duration experiment, the anisotropy of diffusion is different with D[001]>D[010]» D[100]. For this second stage of diffusion a model of hydrogen-metal vacancy associated defects is proposed, where the vacancies are the slower diffusing species with the diffusion laws: [100], [010] = 10-(5.6±3.2) exp [-(175 ± 76)/RT] [001] = 10-(1.4±0.5) exp [-(258 ± 31)/RT] (2) Hydrogen diffusion in forsterite The kinetics of hydration linked to magnesium-vacancy diffusion within dry synthetic forsterite single crystals was determined by performing similar experiments and analyses as in the previous section. The experiments were performed at 1.5 GPa, 1000°C for 3 hours in piston cylinder apparatus, or at 0.2 GPa, 900-1110°C, for 3-20 hours in TZM cold-seal vessels. The chemical diffusion coefficients are marginally slower than in iron-bearing olivine for the same diffusion process, but the anisotropy of diffusion is the same, with the [001] axis the fastest direction of diffusion and [100] the slowest. Fits of the diffusion data to an Arrhenius law yield similar activation energies for each of the crystallographic axes; a global fit to all the diffusion data gave an activation energy around 211 ± 18 kJmol-1. Thus hydration likely occurs by coupled diffusion of protons and octahedrally coordinated metal vacancies. The diffusion rates are fast enough to modify water contents within xenoliths ascending from the mantle but they are probably too slow to permit a total equilibration in a new dry or wet environment. (3)Dehydration profiles in natural mantle-derived olivine within basalt First evidence for water diffusion in a natural mantle-derived olivine are presented from peridotite samples. The samples are olivine crystals within lherzolite xenoliths from the Quaternary alkali basalts of the Pali-Aike volcanic field in Patagonia. Water content and distribution was studied using unpolarized and polarized FTIR and analyses shows that olivine, Cr-diopside and orthopyroxene contain a significant amount of water, with up to 13 wt ppm H2O for olivine and up to 250 wt ppm H2O in the pyroxenes. In contrast, analysis of optically clear-parts of small garnet crystals indicates that they are dry. Oriented Infrared profiles show that olivine grains larger than 0.5 mm have hydroxyl-depleted rims. These water concentration profiles suggest that partial dehydration occurred during the ascent of the xenolith-bearing magma to the Earth’s surface, confirming that dehydration is occurring in the nature. From a combination of analyses of natural xenoliths with experimental diffusion works, ascent duration of the host magma is estimated to several hours, suggesting a fast rise up to the surface. (4)Temperature and pressure dependence of water solubility in iron-free wadsleyite Previous experimental studies indicate that the maximum solubility of water in wadsleyite may vary as a function of pressure and temperature. Therefore wadsleyite samples were synthesized using a multi-anvil press. One series of experiments were performed at a fixed pressure of 15 GPa and at various temperatures and in a second series the temperature was fixed at 1200°C and pressure was varied from 13 to 18 GPa. The starting material corresponds to a composition of Mg2SiO4 + 5wt% H2O. The water content was quantified by ion probe (SIMS). Results show that at 15 GPa, the water concentration decreases significantly with increasing temperature from 2.5 wt% H2O at 900oC down to 0.93 wt% H2O at 1400oC; the corresponding wadsleyite Mg/Si ratios increase from 1.79 to 1.93 over this temperature range. Up to 17 GPa, no significant effect of pressure on the water content was observed. Moreover, together with previous results on ringwoodite, these data imply a strong decrease of the water partition coefficient between wadsleyite and ringwoodite with temperature. (5) Computer simulation on hydrous point defect in iron-free wadsleyite The general utility lattice program (GULP), a semi-empirical method, was used to simulate the formation of point defects (Mott-Littleton method) in wadsleyite and especially hydrogen incorporation and their corresponding infrared frequencies.

Measuring juvenile hormone and ecdysteroid titers in insect haemolymph simultaneously by LC-MS: The basis for determining the effectiveness of plant-derived alkaloids as insect growth regulators (2004)

Stephanie Westerlund

Aim of this thesis was to develop a liquid chromatography-mass spectrometry (LC-MS) method to monitor hormones and their metabolites in the haemolymph of insects simultaneously. Furthermore, some plant-derived alkaloids were structurally elucidated, which may be used as insect growth regulators thus affecting haemolymph hormone titers in putative pest species. Juvenile hormones (JHs), JH diols and ecdysteroids were easily separated by high performance-liquid chromatography (HPLC) in less than 20 min using a reversed-phase C18 column and a methanol-water gradient. Subjecting the JH-JHBP (juvenile hormone binding protein) complex to HPLC was sufficient in releasing JH from the JHBP. In order to prevent JH from binding to glass surfaces, it was necessary to include a carrier in the solvent. JHs have a high affinity to polypropylene vials and should therefore be avoided, if no carrier is being used, such as triton X-100. The darkening of the haemolymph due to eumelanin production by phenol oxidases served as a visual indicator of general enzyme activity in the haemolymph. Isooctane:MeOH (1:1, v/v) inactivated the phenol oxidase system when used at a solvent-haemolymph ratio of 10. An isooctane:MeOH extract of haemolymph was most efficient in keeping JH distributed evenly in solution and prevented JH from adhering to the glass vessel. JH concentration in standard solutions was reduced with increasing sonication time. Highest ionization of JH was achieved in MeOH for MS compared to ACN or by using formic acid as an additive. In the positive ESI (electrospray ionization) mode the most abundant ions formed in haemolymph extract of Gryllus bimaculatus was the sodium adduct for JHs, JH diols and JH acids. At higher JH concentrations, the potassium adduct was also observed. The sodium and the potassium adducts were present in ecdysteroid analysis. The same ionization pattern was observed in Spodoptera frugiperda, Myrmicaria eumenoides and Acyrthosiphon pisum haemolymph. Method validation of the LC-MS method confirmed reproducibility and repeatability. The LODs for JHs and JH diols were between 6 to 12 pg, and 93 pg for ecdysteroids. 72 haemolymph samples can be processed per day by the LC-ESI-MS method using an autosampler. JH and ecdysteroid titer measurements showed good agreement between haemolymph titers and developmental events in Spodoptera frugiperda and Gryllus bimaculatus larvae and Gryllus bimaculatus adults. In Gryllus bimaculatus female and male last instar larvae, the JH titers were low and steady until day 6. The ecdysone peak maximum shifted from day 3 to a 20-hydroxyecdysone maximum peak on day 5, coinciding with the onset of adult ecdysis. JH III titers increased on day 3 in paired Gryllus bimaculatus males, occurring simultaneously with spermatophore maturation and deposition. A similar response was seen with ecdysone titers. Mated female crickets experienced a JH III titer increase on day 4 which coincides with egg deposit on day 4. Ecdysone titers reach a maximum on day 3 and ovary weights on day 4. Besides JH III, JH I was found in 5 to 8-day old female adult crickets, and in 6 and 7-day old male adult crickets. 20-Hydroxyecdysone was found neither in female nor in male Gryllus bimaculatus mated adults. The “classical” interplay between JHs and ecdysteroids was observed in 5th instar Spodoptera frugiperda larvae. JH titers decreased towards the end of the larval stadium and 20-hydroxyecdysone gave a sharp peak on the last day of the 5th instar. Extremely low levels of JH were measured in 6th instar larvae. 20-Hydroxyecdysone and ecdysone titers increased simultaneously in prepupae. The already known alkaloids arborinine and arborine, and the for the first time isolated 4-methoxy-1-methyl-2(1H)-quinolinone from Glycosmis pentaphylla, were extracted from Glycosmis pentaphylla leaves and are discussed as possible insect growth regulators affecting hormone titers in the haemolymph of insect pest species.

Importance of floral scent compounds for the interaction between Silene latifolia (Caryophyllaceae) and the nursery pollinator Hadena bicruris (Lepidoptera: Noctuidae) (2004)

Stefan Dötterl

In the present study, the role of floral volatiles for the interaction between the nocturnal Caryophyllaceae Silene latifolia, and the noctuid moth Hadena bicruris was determined. This insect-plant relationship is one of the known nursery pollination systems, where pollinators reproduce within the flowers they pollinate. Silene latifolia is a dioecious weed, native to Europe and formerly introduced to North America. It is the main larval host plant of H. bicruris, which is distributed in Europe and North Africa. Especially night-active moths, among them H. bicruris, which are attracted by the flower scent, pollinate S. latifolia. However, until now, nothing was known about the role of single flower scent compounds for the attraction of the moths. This thesis describes the chemical composition and the geographical variability in the flower scent of S. latifolia. Furthermore, electrophysiological and behavioural tests with floral scent extracts and single authentic standard compounds were carried out in H. bicruris to identify the attractive compounds of the complex floral scent. To get an insight into the role of floral scent in guiding potential pollinators on flowers, the spatial fragrance pattern within the flowers of S. latifolia was determined, additionally. The variability in floral scent was very high, especially between different populations, and different chemotypes were characterised.Typical compounds in floral scent of S. latifolia were lilac aldehyde isomers, trans-beta-ocimene, benzaldehyde, phenyl acetaldehyde, or veratrole. Some of these compounds are known to attract nocturnal Lepidoptera species. To characterise antennal and behavioural responses of H. bicruris to various floral scent chemotypes of S. latifolia, and to S. vulgaris (which is rarely also used as host plant), different S. latifolia extracts, and a S. vulgaris extract were analysed using GC-MS methods. These extracts were further used in GC-FID/EAG and GC-MS/EAG detections, respectively. Main compounds in the tested extracts often elicited main signals in the antennae (e.g. lilac aldehydes, phenyl acetaldehyde). Some compounds elicited main signals in the antennae, though they were only minor components in the extracts (e.g. 3-methyl-butyl-aldoxime, benzaldehyde). Other compounds elicited only weak signals in the antennae, though they were abundant in the extracts (e.g. myrcene, methyl benzoate). The compounds of the most common chemotypes of S. latifolia were very sensitively detected by Hadena bicruris, whereas compounds of less abundant chemotypes were less sensitively detected. Floral scent blends that were dominated by lilac aldehydes or phenyl acetaldehyde effectively attracted moths. Hadena bicruris can electrophysiologically and behaviourally distinguish between its main host plant, S. latifolia, and the similarly scented S. vulgaris, another rarely used larval host plant, only by their floral scent. To identify floral scent compounds of S. latifolia that are important for the attraction of H. bicruris, the GC-FID/EAD or the GC-MS/EAD method was used in a first step to identify compounds that elicit signals in the antennae of the moth. Electrophysiologically very active compounds were tested in wind tunnel bioassays, and the attractivity of these compounds was compared to the attractivity of the natural scent of whole flowers of S. latifolia. The antennae of H. bicruris detected substances of several compound classes such as monoterpenoids, benzenoids, fatty acid derivatives, and nitrogen-bearing compounds. Lilac aldehydes were the most attractive compounds in wind tunnel bioassays, and attracted 90% of the tested moths, as did the scent of single flowers. Some compounds did not attract any moth, though they elicited significant signals in the antennae. To determine the parts of the female and male flowers responsible for scent emission, volatiles from attached intact flowers were sampled and then single flower parts were progressively removed. After each preparation step, volatiles were collected from the remaining “flower”. Especially the petals and the anthophore emitted the typical flower volatiles of S. latifolia; and compounds emitted from the petals differed from the compounds emitted by the anthophore. The anthophore emitted only lilac aldehydes and alcohols. Lilac aldehydes are known to be behaviourally very attractive for noctuid Lepidoptera such as Autographa gamma and Hadena bicruris, and they may serve as nectar guides in S. latifolia.

Facultative butterfly-ant interactions - the role of variation in composition of nectar secretions (2004)

Holger Daniels

The significance of variation in nectar secretions of facultatively ant-associated lycaenid butterfly larvae was investigated. The strongly myrmecophilous European Polyommatus coridon, and two moderately myrmecophilous species, the Palaearctic P. icarus and the subtropical Zizeeria knysna were used. Both Polyommatus species are closely related, Z. knysna is a far more distant relative. To obtain high numbers of caterpillars a new method for breaking the egg diapause of the univoltine P. coridon was established, resulting in 65% subitaneously hatching larvae. Based on observations of ants tending caterpillars a new “artificial ant” was assembled, allowing further studies on the ants’ stimulatory antennation pattern. Nectar-harvesting with micro-capillaries from caterpillars attended by ants was optimised and allowed determination of individual secretion droplet size based on large samples. Mean droplet size was 3.7nl in P. coridon, 2nl in P. icarus and 1.4nl in Z. knysna, in the latter two species 65-79% smaller than previously reported. Comparative chemical analyses (HPLC) revealed sucrose as main sugar component in nectar of all three species. In P. coridon it was accompanied by glucose and rarely by further sugars, but never by melezitose. In P. icarus and Z. knysna melezitose was the second most-important component, followed by fructose and glucose. Total sugar contents were 43.6±14.8g/l for P. coridon, 74.2g/l for P. icarus and 68.3±22.6g/l for Z. knysna. P. coridon nectar contained up to 14 amino acids. Major component was always leucine (50% of total), further important were tyrosine, proline, arginine, and phenylalanine. P. icarus nectar comprised up to six amino acids, dominated by tyrosine and phenylalanine. Z. knysna nectar contained only alanine and proline. Total amino acid contents were 9.7±3.4g/l for P. coridon, 1.2g/l for P. icarus and 0.3±0.2g/l for Z. knysna. Nectar composition was considerably different from hemolymph composition. Larval food had minor influence on P. coridon nectar composition. Caterpillars fed with semi-synthetic diet secreted more sucrose, with a trend towards higher total sugar content, and produced nectar with a more homogeneous amino acid pattern than larvae reared on natural host plants. Bioassays with ants from three different subfamilies (Lasius niger (Formicinae), Myrmica rubra (Myrmicinae), Tapinoma melanocephalum (Dolichoderinae)) demonstrated a preference for sucrose (standard concentration 0.1mol/l, as in P. coridon nectar) over monosaccharides. Melezitose in nectar concentration (P. icarus) was not preferred to sucrose. Some single amino acids in sucrose solutions were preferred over pure sucrose, e.g. leucine by L. niger, or phenylalanine and tyrosine by M. rubra. In general, raising amino acid concentration did not enhance preferences and even reduced them in some cases. Mixtures of four or eleven amino acids in sucrose and complete nectar analoga were preferred to sucrose. L. niger preferred a balanced mixture over an energetically similar, less balanced mixture. Due to the tremendous variability in gustatory preferences exhibited by the broad range of largely unpredictable ant visitors, lycaenid caterpillars should either decide on a balanced mixture, containing possible amino acid ‘key compounds’ in moderate concentrations, or if this investment does not pay, should secrete sugar-rich nectars. Using the data from the HPLC analyses and the droplet size measurements combined with published studies on secretion rates allowed estimations of the lifetime energetic value of secretions. One P. coridon caterpillar would deliver 5.5-24.4J, one P. icarus 1.9-14.2J and one Z. knysna 0.7-2.8J. Dissection and gravimetric analysis allowed estimation of the caloric equivalent of larval biomass. One early P. coridon third instar (onset of nectar secretion) would yield 17.6J, and prepupae 656J. Z. knysna second instars would yield 0.95J, third instars 3.2J, and prepupae 83.1J. Thus preying on the caterpillars rather than harvesting their secretions would be of greater energetic benefit. Comparisons of this model with further reports show the rather low benefit accruing to ants from tending facultatively myrmecophilous lycaenids, underpinning that manipulation of ants (by means of still unknown chemicals) must also be involved. The model data also suggest that the mutualistic nature of facultative caterpillar-ant associations will not always be granted, and be strongly conditional. Nectar composition data support the view that in myrmecophilous lycaenids secretions rich in amino acids are related to intimate, often obligate ant-associations, whereas facultative and unspecific myrmecophiles rely more on sugars. Degree of myrmecophily seems to be a better predictor of secretion content than taxonomic relatedness. The low investment costs of the caterpillars into nectar secretions well explain the enormous taxonomic and geographical distribution of facultative myrmecophily.

Optically induced orientational transitions in nematic liquid crystals (2004)

Dmitry Krimer

I have presented in this thesis a theoretical study of some dynamical phenomena and orientational transitions induced by intense light in homeotropically oriented nematic layers. A large number of experiments has been performed in such systems and various interesting dynamical regimes have been identified. However, systematical theories capable of describing the observed phenomena have been derived for some cases only. In other cases oversimplified models exist with limited applicability. In Chapter 2 I considered the case of a circularly polarized plane light wave incident perpendicularly on the layer. I have constructed a theory that is capable of describing the observed regimes of director motion and the transitions between them in detail. The first instability is the Freedericksz transition from the homeotropic state to a small-amplitude reoriented state with uniform director precession around the layer normal. With increasing light intensity, this state destabilizes via a supercritical Hopf bifurcation and a new frequency in the time Fourier spectra of the dynamical variables appears. This regime is quasiperiodic and corresponds to a precession and nutation of the director. As the intensity increases further, this state disappears at a certain critical value where the period of nutation becomes infinite. There a strongly hysteretic transition to a state with large reorientation occurs via a homoclinic bifurcation. The homoclinic orbit involved is of the simplest type where a limit cycle collides with a saddle point having one unstable direction. The new state corresponds to a uniform precession of the director, however, with very large period and with large reorientation. I have also investigated the influence of an additional static electric field on the dynamical scenario described above. In Chapter 3 the treatment is generalized to the case of elliptically polarized light. The complete bifurcation diagram with the light intensity and the ellipticity as control parameters has been calculated in the region where rotating states exist. I have shown that for a fairly narrow region of ellipticities close to circular polarization the first periodic rotating state loses its stability in a supercritical Hopf bifurcation. I have found that with increasing light intensity at different ellipticities different sequences of transitions all finally lead to a state with large director distortion as the intensity is increased. The nature of this largely distorted state, as well as intermediate regimes vary with ellipticity. Some of the regimes that appear at lower intensities were studied previously, both experimentally and theoretically, but a complete picture up to the largely distorted regime was missing. In the theoretical treatments developed in the Chapters above, as in all other treatments, the velocity field induced by the director motion (backflow) has been neglected. In Chapter 4 I have investigated the influence of backflow on the dynamical scenario described in Chapter 2 and have shown that the backflow leads to substantial quantitative changes. It turns out that the regime of nonuniform precession shifts to higher light intensities and exists in a larger interval. I have also found unanticipated spatial oscillations of the backflow across the layer for the state with large director distortion. This is a signature of the interference pattern of the light within the layer. Actually, in the theory presented, for the first time, a light-induced dynamical phenomenon has been derived from the full nematodynamic equations. Thus, for the first time, full quantitative comparison with experiments using a transversally extended laser light could be done. Also, in all previous theoretical treatments involving plane wave incident light, it was assumed that the director distortion does not depend on the coordinates in the plane of the layer, i.e. one dealt with a one dimensional situation. In Chapter 5 I have studied the instabilities induced by a linearly polarized ordinary light wave incident at a small oblique angle allowing for spatial variations of the director in the plane of the layer and including the case of a dye-doped nematic. It was previously known that for sufficiently small angles of incidence the homeotropic state looses stability in a stationary, homogeneous pitchfork bifurcation. I have shown that the resulting stationary distorted state looses stability via a secondary Hopf bifurcation to spatially inhomogeneous state (nonzero critical wavenumber) that leads to the formation of travelling waves in the plane of the layer. The wavelength of these waves depend on the angle of incidence and the ratios of the elastic constants. It is typically several times larger than the thickness of the layer.

Synthesis, Molecular Structure and Reactivity of Di(1-cyclohepta-2,4,6-trienyl) thioether, S(C7H7)2 and Tri(1-cyclohepta-2,4,6-trienyl) amine, N(C7H7)3 (2004)

Jinnan Liu

This thesis describes the synthesis, characterization and coordination chemistry of di(1-cyclohepta-2,4,6-trienyl) thioether, S(C7H7)2 (1), tri(1-cyclohepta-2,4,6-trienyl) amine, N(C7H7)3 (24), and di(1-cyclohepta-2,4,6-trienyl) amine, NH(C7H7)2 (25). The reaction of tropylium bromide, C7H7Br, with the gas hydrogen sulfide (H2S) leads to the di(1-cyclohepta-2,4,6-trienyl) thioether, S(C7H7)2 (1), which can undergo Diels-Alder reactions with maleic anhydride, maleimide and N-phenyl maleimide to give the adducts S(C7H7)(C7H7C4H2O3) (4a), S(C7H7)(C7H7C4H3NO2) (4b) and S(C7H7)(C7H7C10H7NO2) (4c), respectively. In these three compounds, one cyclohepta-2,4,6-trienyl ring has remained intact, whereas the other seven-membered ring was involved in the Diels-Alder reaction. The advantage of the potential ligand S(C7H7)2 (1) in comparison to other simple sulfanes is that it can act as a chelate ligand, using one of the non-planar seven-membered rings. In general, the central double bond of one of the seven-membered rings becomes coordinated to the metal. The disadvantage of the sulfane 1 is its sensitivity towards oxidation and its low thermal stability. The reactions of either Cr(CO)5(thf) or Cr(CO)4(eta4-C7H8) with one equivalent of 1 lead to the monosubstituted derivative Cr(CO)5[PhCH2S(C7H7)] (7), in which one seven-membered ring has remained unchanged and the other seven-membered ring has been transformed into a benzyl substituent. From the reaction of 1 with a mixture of chromium(carbonyl)(acetonitrile) complexes, Cr(CO)6-x(CH3CN)x (x = 1, 2, 3), the pentacarbonyl Cr(CO)5[S(C7H7)2] (6) could be obtained, in which both cycloheptatrienyl ring substituents are freely pending. Using the same method as for the chromium complexes, tetracarbonyl molybdenum Mo(CO)4[(eta2-C7H7)S(C7H7)] (10) was obtained from the reactions of either Mo(CO)5(thf) or Mo(CO)4(eta4-C7H8) with the sulfane 1. In complex 10 the ligand S(C7H7)2 is coordinated to the metal both through a lone pair of electrons at the sulfur atom and the central C=C double bond of a cyclohepta-2,4,6-trienyl substituent. Mo(CO)5[S(C7H7)2] (9) could be obtained from Mo(CO)6-x(CH3CN)x (x = 1, 2, 3); in analogy to 6, the sulfane ligand in 9 is coordinated to molybdenum exclusively through a lone pair of electrons at the sulfur atom. From the intermediate W(CO)5(thf), the pentacarbonyltungsten complex W(CO)5[S(C7H7)2] (13) was obtained, which could be converted thermally to the benzyl complex W(CO)5[PhCH2S(C7H7)] (14). In the reaction with the mixture of tungsten(carbonyl)(acetonitrile) complexes, W(CO)6-x(CH3CN)x (x = 1, 2, 3), the compounds W(CO)4[(eta2-C7H7)S(C7H7)] (15) and W(CO)5[S(C7H7)2] (13) were obtained; complex 15 was the main product. The reactions of either Mn2(CO)10 (under irradiation) or Mn(CO)5X (X = Cl, Br) with di(1-cyclohepta-2,4,6-trienyl) thioether (1) led to the organothiolato-bridged dimer Mn2(CO)8[S(C7H7)]2 (17) in addition to ditropyl, (C7H7)2. Subsequent substitution of two carbonyl ligands in 17 by stronger sigma-donor-pi-acceptor ligands such as tert-butyl isocyanide and trimethyl phosphite (tBuNC and P(OMe)3) gave the complexes Mn2(CO)6[tBuNC]2[S(C7H7)]2 (18) and Mn2(CO)6[P(OMe)3]2[S(C7H7)]2 (19). Both 17 and 18 contain a planar Mn2S2 core with the 1-cyclohepta-2,4,6-trienyl substituents in anti-position. In addition, some investigations with tri(1-cyclohepta-2,4,6-trienyl) amine, N(C7H7)3 (24), and di(1-cyclohepta-2,4,6-trienyl) amine, NH(C7H7)2 (25) were carried out. In analogy to the sulfane S(C7H7)2 (1), 24 and 25 can undergo Diels-Alder reactions with maleimide and N-phenyl maleimide to give the educts (C7H7)2N(C7H7C4H3O2N) (26b), (C7H7)N(C7H7C10H7NO2)2 (26c), (C7H7)NH(C7H7C4H3O2N) (27b) and (C7H7)NH(C7H7C10H7NO2) (27c), respectively. Similar to the synthesis of 24 and 25, the mixed tertiary amines di(1-cyclohepta-2,4,6-trienyl)phenylamine, N(Ph)(C7H7)2 (28), and (1-cyclohepta-2,4,6-trienyl)diphenylamine, N(Ph)2(C7H7) (29) were prepared using aniline or diphenylamine. The reaction of N(C7H7)3 (24) with [C7H7]BF4 (1:1) leads to the N-tropylidene-N-(1-cyclohepta-2,4,6-trienyl)immonium tetrafluoroborate salt, [(C7H6)N(H)(C7H7)]BF4 (30). Compound 30 has also been obtained using NH(C7H7)2 (25) as the educt. As expected, the tertiary amine N(Ph)(C7H7)2 (28) reacted with [C7H7]BF4 to give the dark-red salt [(C7H6)N(Ph)(C7H7)]BF4 (31). Attempts to use the amine N(C7H7)3 (24) as a ligand in transition metal complexes were unsuccessful. However, NH(C7H7)2 (25) reacts with the mixture of tungsten(carbonyl)(acetonitrile) derivatives to give the chelate tetracarbonyl complex W(CO)4[(C7H7)NH(eta2-C7H7)] (32), which is similar to the sulfane complexes 10 and 15. Compared with the versatile phosphane ligand tri(1-cyclohepta-2,4,6-trienyl) phosphane, P(C7H7)3, the analogous amine N(C7H7)3 (24) is unable to act as a coordination ligand, probably as a result of the steric shielding of the lone pair of electrons at the nitrogen atom.

Template-Controlled Synthesis of Magnetic/Semiconducting Nanoparticles within Amphiphilic Core-Shell Cylindrical Polymer Brushes (2004)

Mingfu Zhang

Core-shell cylindrical polymer brushes with poly(t-butyl acrylate)-b-poly(n-butyl acrylate) (PtBA-b-PnBA) diblock copolymer side chains were synthesized via the “grafting from” technique using a combination of anionic polymerization (for the synthesis of the backbone) and atom transfer radical polymerization (ATRP, for the synthesis of the side chains). The formation of well-defined brushes was confirmed by 1H-NMR and GPC. The selective hydrolysis of the PtBA block of the side chains resulted in novel amphiphilic core-shell cylindrical polymer brushes with poly(acrylic acid)-b-poly(n-butyl acrylate) (PAA-b-PnBA) side chains. The characteristic core-shell cylindrical structure of the brushes was directly visualized on mica by scanning force microscopy (SFM). Amphiphilic brushes with 1500 block copolymer side chains and a length distribution of lw/ln = 1.04 at a total length ln = 179 nm were obtained. These amphiphilic polymer brushes can be regarded as unimolecular cylindrical micelles, because of the core-shell structure and the amphiphilicity of side chains. The amphiphilic brushes can be used as single molecular templates for the synthesis of inorganic nanoparticles, because the carboxylic acid groups (or carboxylate groups, after neutralization) in the polymer core can coordinate with various metal ions. The hydrophilic core of polymer brushes, poly(acrylic acid), was neutralized by NaOH and afterward iron cations (Fe3+ and Fe2+) were loaded into the polymer core via ion exchange. The formation of the polychelates of polymer brushes and iron cations was confirmed and characterized by various techniques such as Fourier transform infrared spectroscopy (FTIR), UV/vis spectroscopy, transmission electron microscopy (TEM) and SFM. A peculiar “pearl necklace” morphology was observed for the polychelates, which is caused by the physical cross-linking of the side chains via multivalent iron cations. Formation of crystalline alpha-Fe2O3 (hematite) was observed during the He-Ne laser irradiation in the confocal Raman microscopy measurement of the polychelate containing Fe3+ ions. Magnetic nanoparticles were successfully produced from the coordinated iron cations within polymer brushes via single molecule templating technique, as confirmed by various techniques such as SFM, TEM, and UV/visible spectroscopy. Superconducting quantum interference device (SQUID) magnetization measurements show that the hybrid nanocylinders are superparamagnetic at room temperature. The polymer shell provides not only the stability of the nanoparticles but also the solubility of the hybrid nanocylinders. After the formation of the magnetic nanoparticles, the carboxylate coordination sites within the polymer brushes are liberated and ready for further coordination with more iron ions, thus it is possible to increase the amount and/or particle size of the nanoparticles by multi-cycles of iron ion loading and particle formation. The as-prepared hybrid nanocylinders combine the promising properties of polymers and superparamagnetic nanoparticles, and may find potential applications such as in ferrofluids. Similarly, using the amphiphilic core-shell cylindrical polymer brush with PAA core and PnBA shell as template, wire-like assemblies of CdS nanoparticles were successfully synthesized under mild solution conditions, as confirmed by various characterization techniques. Quantum confinement of the CdS nanoparticles was observed, indicated by the blue shift of the absorbance edge in UV/visible spectrum. The technique using a single cylindrical molecule as template for inorganic nanoparticle fabrication presented in this thesis is not restricted to magnetic/semiconductor nanoparticles, but can also be used for the preparation of a number of metal, metal oxide, and metal chalcogenide nanoparticles.

Biomass and Nutrient Studies of Selected Tree Species of Natural and Plantation Forests: Implications for a Sustainable Management of the Munessa-Shashemene Forest, Ethiopia (2004)

Asferachew Abate

Plantation forests with exotic tree species have been introduced to alleviate the problems of deforestation in Ethiopia. In the future, more plantation forests with fast growing species should be grown for coping with the ever-increasing demands for fuelwood and other forest products. However, it is not known whether plantation forests are sustainable or not. For the sustainability of plantation forests with exotic tree species, it is of paramount importance to thoroughly understand their ecological and social attributes through a holistic approach. For this reason, a multidisciplinary project was initiated in the Munessa-Shashemene Forest. Such an approach gives valuable information about the sustainability of plantation forests when the basic ecological features of the natural forests are compared with plantation forests. As an integral part of the multidisciplinary project, the objectives of this study are to: 1) quantify the fine roots and aboveground biomass of selected tree species in both natural and plantation forests; 2) quantify the macronutrient stocks of the fine roots and aboveground components of selected trees species in both natural and plantation forests; and 3) evaluate the implication of the changes in the biomass and macronutrient stocks for a sustainable management of forests. The study focused on four tree species, Podocarpus falcatus (Thunb.) Mirb., Podocarpaceae and Croton macrostachys Hochst. ex Del. Euphorbiaceae, were selected from a natural forest. Cupressus lusitanica Miller, Cupressaceae and Eucalyptus globulus Labill. Myrtaceae were selected from plantation forests. Root architectures of the study trees were studied by excavation. The live fine root biomass (<2 mm in diameter) of the dry and wet seasons was determined from samples collected at the distances of 1, 2 and 3 meters from the bole of the study trees. At each of the distances, root cores were taken at the depth intervals 0-10, 10-35, 35-60, 60-85 and 85-100 cm using a hand auger. Linear regression equations were used to estimate the aboveground biomass on the basis of the relation between DBH and dry weights of the aboveground plant components. Macronutrient concentrations were determined following a standard laboratory procedure. Studies on the root architecture revealed that C. lusitanica has a shallow root and is more susceptible to windthrow compared to E. globulus. With the exception of E. globulus, the dry season live fine root (LFR) biomass was higher for all trees studied. The seasonal variation in the fine root biomass was attributed to the changes in soil moisture of the study area. For all trees investigated, the mean annual LFR biomass was highest at the depth interval 0-10 cm at all distances. The favorable soil texture, pH and organic matter content at the depth interval 0-10 cm might be responsible for higher LFR biomass. The significantly higher LFR biomass of P. falcatus (1.34 kg m-2) coupled with its higher macronutrient stocks compared to C. macrostachys (0.32 kg m-2) suggest the importance of P. falcatus in the sustainability of the natural forest by transferring more macronutrients to the soil through its fine roots. Similarly, the significantly higher total LFR biomass of C. lusitanica (0.88 kg m-2) coupled with its higher macronutrient stock compared to E. globulus (0.27 kg m-2) indicated less depletion of soil nutrients by the former. The stand structure of the natural and plantation forests differed largely. In the natural forest, the density of C. macrostachys was much higher (143 ± 72 trees ha-1) than the density of P. falcatus (73 ± 39 trees ha-1). Generally, the structural change of the natural forest due to selective cutting of P. falcatus was found to have negative implications on the sustainability of the natural forest. The differences in the structure of C. lusitanica and E. globulus, despite their similar densities, resulted in a significantly lower understory ground cover by herbaceous and shrub species in the former. The effect of a poor understory growth on the floor litter thickness and thereby on nutrient capital of the soil may negatively affect the sustainability of C. lusitanica plantation. The harvesting of the stemwood of C. lusitanica and E. globulus removes a substantial amount of nutrients from the plantation sites. Furthermore, the current practice of collecting foliage, twigs and branches for firewood by the local people results in a higher depletion of nutrients. In order to make the plantation forests sustainable, the silvicultural practice in the future should consider on site conservation of foliage and bark. It is recommended that more studies on aboveground and belowground biomass, fine root turnover, and nutrient concentrations of the plantation forests should be carried out in a chronosequence in order to gain more insight on their sustainability.

Pigment-Pigment Interactions and Protein Dynamics in Light-Harvesting Complexes: a Single-Molecule Study (2004)

Clemens Hofmann

Light harvesting complexes that are involved in the first steps of photosynthesis in purple bacteria were studied with low-temperature optical single molecule spectroscopy. In one series of experiments the spectral properties of the bacteriochlorophyll a molecules within the complexes were studied in the view of model systems of molecular aggregates. It was found that the excitations in the B800 band of the light harvesting 2 complex are mainly localised on individual chromophores although evidence was found for an electronic coupling in the weak to intermediate range between individual bacteriochlorophyll a molecules. In contrast, for the B850 band of the light harvesting complex 2 as well as for the B870 band of the light harvesting complex 1 it was found that the assembly of bacteriochlorophyll molecules represents a strongly coupled system and that the excitation is coherently delocalised over a substantial part of the chromophores. By performing Monte-Carlo simulation an estimate on the amount of random and correlated energetic disorder in the site energies of the chromophores as well as on structural properties of the complexes could be given. In experiments on individual LH2-LH1-RC complexes, the energy transfer within a single photosynthetic unit was observed. In further experiments the chromophores were used as local probes to monitor conformational fluctuations of the protein residues in their binding pocket. Looking at the spectral diffusion of individual chromophores allowed to elucidate the organisation of the protein-energy landscape in tiers. In addition a clear correlation for the transition rates between those states and the energy separation of the levels involved could be uncovered. To simplify and automatise the analysis of a large number of consecutively recorded spectra a pattern recognition approach using multivariate statistical analysis proved to be a very useful tool. Apart from elucidating spectral diffusion processes detailed information about the line shape of individual chromophore absorptions could be gained from which it was inferred that the electron-phonon coupling in the B800 pigment pool is very weak. In summary, this thesis demonstrates that low-temperature single-molecule spectroscopy provides a unique method to reveal details of pigment-pigment interactions in the weak to intermediate as well as strong coupling limit that are inaccessible by other experimental methods.

Convection and Magnetic Field Generation in Rotating Spherical Fluid Shells (2004)

Radostin D. Simitev

The dissertation reports results from numerical and analytical studies of convection and dynamo action in rotating fluid spheres and spherical shells. This research is motivated by the geophysical problem of the origin and properties of the Earth's magnetism. Extensive numerical simulations are performed in order to advance the understanding of the basic physical components and mechanisms believed to be responsible for the generation and the variations in time of the main geomagnetic field. Questions such as linear onset and nonlinear finite-amplitude properties of rotating convection, generation and equilibration of magnetic fields in electrically conducting fluids, nonlinear feedback effects of the generated magnetic fields on convection, spatio-temporal structures of magnetic and velocity fields, oscillations and coherent processes in turbulent regimes and other questions are studied in dependence on all basic parameters of the problem, as well as for various choices of the magnetic, thermal and velocity boundary conditions and for some secondary assumptions such as a finitely-conducting inner core and various basic temperature profiles. Because of the lack of knowledge of the properties of the Earth's core and the uncertain details of the processes that take place there, this research is necessary in order to provide the tools for extrapolation to realistic models of the geodynamo. Of particular interest are various types of oscillations of dipolar fields. In contrast to quadrupolar and hemispherical dynamos dipolar dynamos have been originally considered to be non-oscillatory. But the six different types of dipolar oscillations, among which is the ``invisible'' one, reported in this dissertation alter this view. Generation of magnetic fields by convection shows a strong dependence on the Prandtl number P of the fluid. But this fact has received little attention in the past. Convection-driven dynamo action at Prandtl numbers larger than unity is studied with the goal to test the validity of the magnetostrophic approximation. The latter is found to be poorly satisfied for P < 300. Dynamos in this regime require magnetic Prandtl numbers Pm which increase with P. The same trend continues to hold for values of P less then unity and this regime thus seems to be best suited to reach the goal of minimal values of Pm. For Pm=P=0.1 a hemispherical dynamo is obtained in the case of a rotation parameter tau=10**5. A further reduction of Pm leads to a decay of magnetic field irrespective of the Rayleigh numbers used. Apart from numerical simulations and parameter studies of basic physical mechanisms, the dissertation includes an analytical study of inertial convection in rotating spheres in the limit of small Prandtl numbers and large rotation rates. Explicit expressions for the dependence of the Rayleigh number on the azimuthal wavenumber and on the product of P tau are derived and new results for the case of a nearly thermally insulating boundary are obtained. Limited comparisons with actually observed features of the geomagnetic field are also presented. An example are the torsional Alfven waves found in the numerical simulations of this dissertation. They are geophysically relevant as a possible cause for the observed secular variation impulses of the Earth's magnetic field. Reversals of the magnetic field polarity have also been observed in our simulations. Dynamo intermittency and interaction between dipolar and quadrupolar components are preconditions for aperiodic dipolar reversals similar to those of the Earth's main field. However, the opportunities for quantitative comparisons with geophysical observations are rather limited by the complexity of the self-consistent dynamo problem and by the computational restrictions of our numerical simulations.

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