Optimierung der Beladekinetik bzw. der Phasenstabilität von Hydridspeichermaterialien bei elektrochemischer Wasserstoffbeladung

Wasserstoff besitzt als Energieträger viele Vorteile, nach wie vor bestehen aber beträchtliche Probleme bezüglich Speicherung und Transport. Wasserstoff kann gasförmig oder flüssig gespeichert werden, alternativ auch Form von Metallhydriden. Eine optimale Speicherung, die allen Anforderungen genügt, ist aber bisher noch nicht gefunden worden. Ziel dieser Dissertation ist eine systematische Untersuchung verschiedener Parameter, die bei elektrochemischer Wasserstoffbeladung die Beladekinetik nanokristalliner Mg-Elektroden bzw. die Phasenstabilität teilquasikristalliner Zr-Basis Legierungen beeinflussen. In nanokristallinen Mg-Elektroden kommt es auf Grund der durch die katalytischen Eigenschaften von Nb2O5 verringerten Wasserstoffüberspannung und erhöhten Austauschstromdichte zu verbesserten Absorption- und Desorptionsprozessen. Ähnliche elektrochemische Effekte wurden für nanokristalline Mg-Elektroden ohne Nb2O5, aber mit deutlich reduzierter Partikelgröße beobachtet. Da durch den Zusatz von PTFE und Graphit zu den Mg/Nb205-Elektroden keine signifikante Änderung der Wasserstoffüberspannung beobachtet werden konnte, wird angenommen, dass die wesentlichen Faktoren für die bessere Wasserstoffspeicherung die veränderte Oxidationsneigung sowie der höhere Lückengrad und der damit erleichterte Wasserstofftransport zu den Mg-Partikeln sind. Polymorphe Quasikristallbildung in Zr-Cu-Ni-Al-Gläser erfordert mehr als 68 At.-% Zr und ist auf einen sehr engen Al-Konzentrationsbereich beschränkt. Die "Quasigitter"-Konstante steigt mit dem Zr-Gehalt. Die beobachtete Abhängigkeit der Keimbildung von der Temperatur der Schmelze vor dem Schmelzspinnen deutet darauf hin, dass mit abnehmender Temperatur sich eine Nahordnung verstärkt, die beim Schmelzspinnen eingeschreckt wird und dann die spätere Quasikristallbildung begünstigt. Ein Zusatz von 2 At.-% Ag erhöht die Wachstumsgeschwindigkeit, so dass teilquasikristalline Gefüge mit erheblich größeren Quasikristallen als in der Ausgangslegierung Zr69,5Cu12Ni11Al7,5 eingestellt werden können. Es war bekannt, dass die Zunahme der Quasikristall-Durchmesser von 30-70 nm (30 Vol.-%) auf 40-90 nm (50 Vol.-%) in Zr69,5Cu12Ni11Al7,5 eine Erhöhung der Phasenstabilität bei elektrochemischer Wasserstoffbeladung bewirkt. Die erheblich größeren Quasikristalle in Zr71Cu11,5Ni10Al7,5 und Zr68,5Cu11Ni11Al7,5Ag2 zeigen dagegen eine signifikant geringere Stabilität. Diese Destabilisierung beruht vermutlich auf einer Schwächung der Bindung (größere Gitterkonstante) bzw. der leichteren Bildung von Phasonen

Detoxification capacity in different plant species with view to their use in phytoremediation of heavy metals

Die Auswirkungen von Schwermetallen auf Typha latifolia wurden quantifiziert, um Hinweise für die Verwendung von T. latifolia in der Phytoremediation zu liefern und insbesondere die Situation der Pflanze unter multipler Belastung mit Schwermetallen und organischen Schadstoffen zu beleuchten. Die Befunde wurden durch Untersuchungen in Mutanten von Helianthus annuus und Nicotiana tabacum, die als Metallakkumulatoren bekannt sind, erhärtet. Wichtiger Schwerpunkt waren die Enzyme des Halliwell-Asada Zyklus, die für das Überleben der Pflanzen unter Stress wichtig sind. Die Pflanzen sind fähig, Metallbelastung über längere Zeit zu überstehen und passen ihren Stoffwechsel an. Die Entgiftung organischer Fremdstoffe bleibt allerdings bei multipler Belastung begrenzt, da die Glutathion S-Transferasen zum Teil durch die HM gehemmt werden.The effects of heavy metals on Typha latifolia were quantified to find indicators for its utilization in phytoremediation and to understand its detoxification capacity under situations of multiple pollution with metals and organic xenobiotics. The results were corroborated by investigations of sunflower and tobacco mutants. Important focus of the investigation was the Halliwell-Asada-cycle that is of high importance for plants under stress. All investigated plants were able to survive heavy metal stress for longer periods of time due to adaptations of their metabolism. However the detoxification of organic xenobiotics was critical under multiple pollution scenarios, as glutathione S-transferases were shown to be inhibited by heavy metals

Root exudation pattern of Typha latifolia L. plants after copper exposure

Aims: Typha latifolia L. is an aquatic plant that has been widely exploited for the aims of phytoremediation. The main reason why we have chosen this plant species for the current study is its capacity to accumulate and detoxify heavy metals. The main topic of the investigation focused on the root uptake of copper (II) nitrate and copper (II) sulfate and the impact of different chemical copper species on the excreted organic acids. Methods: Oxalic, malic, acetic and lactic acids were determined using capillary electrophoresis; a comparison between the concentration and the time course during 7 days of treatment was performed. Results: There is a correlation between the total copper (II) sulfate concentration in the roots and the total amount of the excreted organic acids. In addition to that organic acids are involved in the detoxification mechanisms of Typha latifolia for copper (II) nitrate and copper (II) sulfate. Conclusions: Different from so far investigated plant species the highest amounts of organic acids are excreted from T. latifolia roots not in the first hours after treatment, but up to 7 days later

Nitro-oxidative stress contributes to selenite toxicity in pea (Pisum sativum L)

Background and aims: Selenium (Se) phytotoxicity at the cellular level disturbs the synthesis and functions of proteins, together with the generation of an oxidative stress condition. This study reveals the nitro-oxidative stress events, supplemented by a broad spectrumed characterisation of the Se-induced symptoms. Methods: Applying several, carefully selected methods, we investigated the selenite treatment-induced changes in the Se and sulphur contents, pigment composition, hydrogen peroxide level, activity of the most important antioxidative enzymes, glutathione, nitric oxide and peroxynitrite, lipid peroxidation and protein tyrosine nitration. Results: The Se content increased intensively and concentration-dependently in the organs of the treated plants, which led to altered vegetative and reproductive development. The level of the investigated reactive oxygen species and antioxidants supported the presence of the Se-induced oxidative stress, but also pointed out nitrosative changes, in parallel. Conclusions: The presented results aim to map the altered vegetative and reproductive development of Se-treated pea plants. Mild dose of Se has supportive effect, while high concentrations inhibit growth. Behind Se toxicity, we discovered both oxidative and nitrosative stress-induced modifications. Moreover, the presented data first reveals selenite-induced concentration- and organ-dependent tyrosine nitration in pea

Chronic exposure of soybean plants to nanomolar cadmium reveals specific additional high-affinity targets of cadmium toxicity

Solving the global environmental and agricultural problem of chronic low-level cadmium (Cd) exposure requires better mechanistic understanding. Here, soybean (Glycine max) plants were exposed to Cd concentrations ranging from 0.5 nM (background concentration, control) to 3 µM. Plants were cultivated hydroponically under non-nodulating conditions for 10 weeks. Toxicity symptoms, net photosynthetic oxygen production and photosynthesis biophysics (chlorophyll fluorescence: Kautsky and OJIP) were measured in young mature leaves. Cd binding to proteins [metalloproteomics by HPLC-inductively coupled plasma (ICP)-MS] and Cd ligands in light-harvesting complex II (LHCII) [X-ray absorption near edge structure (XANES)], and accumulation of elements, chloropyll, and metabolites were determined in leaves after harvest. A distinct threshold concentration of toxicity onset (140 nM) was apparent in strongly decreased growth, the switch-like pattern for nutrient uptake and metal accumulation, and photosynthetic fluorescence parameters such as Φ RE10 (OJIP) and saturation of the net photosynthetic oxygen release rate. XANES analyses of isolated LHCII revealed that Cd was bound to nitrogen or oxygen (and not sulfur) atoms. Nutrient deficiencies caused by inhibited uptake could be due to transporter blockage by Cd ions. The changes in specific fluorescence kinetic parameters indicate electrons not being transferred from PSII to PSI. Inhibition of photosynthesis combined with inhibition of root function could explain why amino acid and carbohydrate metabolism decreased in favour of molecules involved in Cd stress tolerance (e.g. antioxidative system and detoxifying ligands)

Sexual Dimorphism in the Response of Mercurialis annua to Stress

The research presented stemmed from the observations that female plants of the annual dioecious Mercurialis annua outlive male plants. This led to the hypothesis that female plants of M. annua would be more tolerant to stress than male plants. This hypothesis was addressed in a comprehensive way, by comparing morphological, biochemical and metabolomics changes in female and male plants during their development and under salinity. There were practically no differences between the genders in vegetative development and physiological parameters. However, under salinity conditions, female plants produced significantly more new reproductive nodes. Gender-linked differences in peroxidase (POD) and glutathione transferases (GSTs) were involved in anti-oxidation, detoxification and developmental processes in M. annua. 1H NMR metabolite profiling of female and male M. annua plants showed that under salinity the activity of the TCA cycle increased. There was also an increase in betaine in both genders, which may be explainable by its osmo-compatible function under salinity. The concentration of ten metabolites changed in both genders, while ‘Female-only-response’ to salinity was detected for five metabolites. In conclusion, dimorphic responses of M. annua plant genders to stress may be attributed to female plants’ capacity to survive and complete the reproductive life cycle

Minor cereals exhibit superior antioxidant effects on human epithelial cells compared to common wheat cultivars

In the present study, various minor cereals including rye, oat, spelt, primitive and wild wheat species (20 genotypes each) were tested for their antioxidative effects in cell biological studies, and the effects were compared with the effects of 12 common wheat genotypes. Ethanol soluble extracts of grains were used and studied in human cancer-derived cell lines including HeLa (cervical) and HCT116 (colorectal) cell lines by analyzing cellular levels of reactive oxygen species (ROS), mitochondrial health, DNA damage and cell survival. The cereal genotypes were also examined for the total phenolic concentration (TPC) and for the relationship between oxidative cell damage and TPC values. Most genotypes of the minor cereal species showed superior antioxidant effects in human cell cultures compared to the common wheat genotypes. Many of the minor cereal genotypes with high antioxidant capacities protected DNA and mitochondrial damage and prevented cell death in HeLa cells and colon-derived HCT116 human epithelial cells. There was no significant relationship between TPC values and oxidative cell damage. However, common wheat genotypes had, on average, lower TPC values. The results show that minor cereals contain potentially high levels of certain antioxidant substances which might be useful in preventing oxidative damage in cellular systems