The role of sodium chloride (NaCl) particles and ammonium sulfate ((NH4)2SO4) particles on the initial atmospheric corrosion of copper and zinc was investigated under in situ and ex situ conditions using microgravimetry, FTIR spectroscopy, ion chromatography, scanning electron microscopy with x-ray microanalysis and the scanning Kelvin probe. For the first time, in situ infrared spectra were collected on a micron level during particle induced atmospheric corrosion using a recently developed experimental set-up for in situ FTIR microspectroscopy. Lateral distribution of corrosion and reaction products on copper and zinc surfaces was determined and could be connected with the mechanisms of the initial particle induced corrosion. The recently discovered secondary spreading effect from NaCl electrolyte droplets on metal surfaces was studied under in situ conditions and the effect of CO2 on the spreading process was elaborated. The ambient level of CO2 (350 ppm, 1 ppm = 10-6 volume parts) results in a relatively low secondary spreading effect, whereas the lower level of CO2 (<5 ppm) causes a much faster secondary spreading effect over a large area. At low CO2 concentration alkaline conditions will prevail in the cathodic area, leading to large changes in the surface tension at the oxide/electrolyte interface in the peripherical parts of the droplet. This induces a surface tension driven convective flow of electrolyte from the NaCl droplet. The continuous growth of the secondary spreading area at low CO2 concentration is possible due to the galvanic coupling with the droplet leading to transport of sodium ions to this region and maintenance of the alkaline conditions. At 350 ppm CO2, carbonate formation in the secondary spreading area results in lowering of the pH, increasing the surface tension of the oxide/electrolyte interface and inhibiting the secondary spreading. CO2 strongly affects the NaCl-induced atmospheric corrosion rate of copper. The overall influence of CO2 and NaCl depends on at least three identified mechanisms. At low NaCl particle density, CO2 affects the secondary spreading effect from the electrolyte droplet. This leads to a larger effective cathodic area at low CO2 concentration and a higher corrosion rate. The more alkaline surface electrolyte present at low CO2 concentration also affects the formation of corrosion products and the amount of soluble copper chloride. Whereas the presence of larger amounts of soluble chloride tends to increase the corrosion rate, the formation of CuO results in a more protective surface film which decreases the corrosion rate. This effect was observed at higher NaCl particle densities, where the secondary spreading areas overlapped with adjacent NaCl particle clusters. The formation of CuO leads to lower corrosion rates compared to ambient CO2 concentration in which this phase was not formed. For zinc, the formation of a more protective corrosion product layer was not observed and the corrosion rate is generally higher for low than for ambient CO2 concentration. The presence of NaCl particles on the metal surfaces strongly affects the SO2 interaction with the metal surfaces. The oxidation of S(IV) turned out to be fast at the area of the NaCl-containing electrolyte droplet, both for copper and zinc. On copper surfaces, both sulphate (SO4 2-) and dithionate (S2O6 2-) ions formed which is consistent with a copper catalysed reaction route for sulfite oxidation including the formation of a Cu(II)–sulfito complex as an important step. For zinc, a surface mediated sulfite oxidation process leads to rapid formation of sulphate in the electrolyte droplet area. The presence of SO2 strongly inhibits the secondary spreading due to the decrease in pH induced by absorption of SO2 in the cathodic areas. The presence of gaseous oxidants, such as NO2 and O3, has previously been considered as an important prerequisite for the oxidation of sulfite on copper. The results obtained here suggest that the formation of local electrochemical cells induced by deposited NaCl particles could be another important route for S(IV)- oxidation to sulfate formation. On copper, SO2 was also found to promote the formation of less soluble copper chlorides, such as paratacamite (Cu2(OH)3Cl) and nantokite (CuCl). The electrolyte droplet was dried after 24 hours of exposure due to the formation of less soluble paratacamite (Cu2(OH)3Cl) and nantokite (CuCl) and led to a decrease in the corrosion rate. Thus, SO2 alone promotes the corrosion rate of copper, whereas in the presence of NaCl particles the corrosion rate of copper may slow down due to the formation of insoluble copper chloride compounds. The lateral distribution of corrosion products after exposure of NaCl contaminated copper and zinc surfaces to humid air with gaseous pollutants is a result of the formation of local electrochemical cells at the particles and concomitant differences in chemical composition and pH. For (NH4)2SO4 deposited copper and zinc surfaces the corrosion effects increase with the amount of pre-deposited particles and with the exposure time. On copper, the size of the particles affects the corrosion rate, smaller particles resulting in a higher corrosion rate than larger particles at equal amount of deposition. The formation of Cu2O was the dominant corrosion product after exposure longer than 10 days. (NH4)2SO4 particles result in enhanced Cu2O formation on copper due to a reaction sequence involving catalysis by NH3. The corrosion of copper by (NH4)2SO4 particles was much larger than that induced by NaCl particles. However, for zinc, the (NH4)2SO4 particles lead to smaller corrosion effects than those of NaCl particles. For both particles, significant corrosion attack was observed at relative humidity (RH) lower than the deliquescence point of the salts. / QC 20101001

Interaktion der FO Statoruntereinheiten a und b der ATP-Synthase aus Escherichia coli Die ATP-Synthase nimmt im Energiestoffwechsel vieler Organismen eine zentrale Stellung ein und ist ubiquitär in strukturell und funktionell homologer Form bei eukaryotischen Zellen in der inneren Mitochondrienmembran, der Thylakoidmembran von Chloroplasten und in der Cytoplasmamembran von Prokaryoten zu finden. Besonders zwischen F-, V- und A-Typ ATPasen bestehen strukturelle Ähnlichkeiten im Aufbaus des Gesamtenzyms aus zwei großen Subkomplexen. Darüber hinaus weisen die F-Typ ATPasen aller Organismen hohe Sequenzhomologien auf, welche sich auch in strukturellen Gemeinsamkeiten widerspiegeln. Als "Modellenzym" dient die FOF1 ATPase aus dem Enterobakterium Escherichia coli. Es setzt sich aus acht funktionell verschiedenen Untereinheiten zusammen, die unter Hydrolysebedingungen relativ zueinander rotieren. Die Unterteilung der Enzymstruktur in Rotor (g e -c-Oligomer) und Stator (a 3b 3d ab2) erfordert das Vorhandensein einer stabilisierenden Struktur, dem sog. "second stalk". Im Hinblick auf den Mechanismus der rotierenden ATP-Synthase und dem Modell der elastischen Kopplung erscheint die Untereinheit b geeignet, um die durch das g e -c-Oligomer aufgebaute Rotationsspannung zu speichern. Wie die beiden b Untereinheiten mit den anderen FO Untereinheiten a bzw. c interagieren ist weitgehend unbekannt. In der vorliegenden Dissertation wurden die Untereinheiten a und b auf mögliche Interaktionsstellen mit anderen Enzymuntereinheiten mittels genetisch eingefügte Cysteine und anschließender chemischer Quervernetzung untersucht. In der hier vorgestellten Arbeit konnte gezeigt werden, dass es mit dem Nulllängen Cross-linker Cu(1,10-Phenanthrolin)2SO4 [CuP] in der Region bP28C-bE39C möglich ist, Quervernetzungen zur Untereinheit a zu erzeugen. Mit den heterobifunktionellen Cross-linkern Benzophenon-4-maleimid [BPM] und N-[4-(p-Azidosalicylamido)butyl]-3´-(2´-pyridydithio)propionamid [APDP] vergrößert sich diese Region. Dabei sind die a-b Interaktionen in einer gewissen Periodizität (bP28C, bL29C, bM30C, bA31C, bK38C und bE39C) zu beobachten, was für eine Beteiligung beider b Untereinheiten spricht. Neben dem immunologischen Nachweis durch Antikörper, konnte auch über ein N-terminales Polyhistidinmotiv (His12) gezeigt werden, dass eine Interaktion zwischen den Untereinheiten a und b ausbildet wird. Der aN-His12-b Cross-link kann mittels Ni-NTA Affinitätschromatographie aufgereinigt werden. b-Dimerisierungen konnten für die Reste bS60C, bL65C und die Region bY24C-bA45C nachgewiesen werden. Der relative Abstand der b Untereinheiten zueinander nimmt dabei in ihrem Verlauf vom Cytoplasma in Richtung Membran zu, wie mit den Cross-link Reagenzien CuP, BPM und APDP gezeigt werden konnte. Ausgehend von der Untereinheit a konnten für die Reste aS27C, aN33C, aA130C, aG173C, aP182C, aN184C, aS202C und aG227C ebenfalls CuP vermittelte Quervernetzungen mit der Untereinheit b nachgewiesen werden. Die Reaktion an der Position aS27C weist auf eine cytoplasmatische Lokalisation des N-Terminus hin, die in einem 6 Transmembran-Sekundärstrukturmodell vorgeschlagen wird. Mit BPM konnte die Nähe der Aminosäuren aN33C und aP182C zum c-Oligomer gezeigt werden.

The temperature and/or entropy of electrically polarisable materials can be altered by changing electric field E. Research into this electrocaloric (EC) effect has focussed on increasing the size of the EC effects, with the long-term aim of building a cooler with an EC material at its heart. Materials and experimental methods are briefly reviewed. A ‘resetting’ indirect route to isothermal entropy change ∆S for hysteretic first-order transitions is described. An indirect route to adiabatic temperature change ∆T, without the need for field-resolved heat capacity data, is also described. Three temperature controllers were built: a cryogenic probe for 77-420 K with ∼5 mK resolution, a high-temperature stage with vacuum enclosure for 295-700 K with ∼15 mK resolution, and a low-temperature stage for 120-400 K with electrical access via micropositioners. Automation enables dense datasets to be compiled. Single crystals of inorganic salts (NH4)2SO4 , KNO3 and NaNO2 were obtained. Applying 380 kV cm−1 across (NH4)2SO4 , it was found that |∆S| ∼ 20 J K−1 kg−1 and |∆T | ∼ 4 K, using the indirect method near the Curie temperature TC = 223 K. Without the ‘resetting’ indirect method, |∆S| ∼ 45 J K−1 kg−1 would have been spuriously found. Preliminary indirect measurements on KNO3 and NaNO2 give |∆S| ∼ 75 J K−1 kg−1 for ∆E ∼ 31 kV cm−1 near TC = 400 K and |∆S| ∼ 14 J K−1 kg−1 for ∆E ∼ 15 kV cm−1 near TC = 435 K, respectively. A cation-ordered PbSc0.5Ta0.5O3 ceramic showing a nominally first-order transition at 295 K was obtained. The Clausius-Clapeyron phase diagram is revealed via indirect measurements where |∆S| ∼ 3.25 J K−1 kg−1 and |∆T | ∼ 2 K, and direct measurements where |∆T | ∼ 2 K. Clamped samples show broadening of the field-induced transition. Epitaxial, ∼64 nm-thick SrTiO3 films were grown by pulsed laser deposition on NdGaO3 (001) substrates with a La0.67Sr0.33MnO3 bottom electrode. The indirect method gives |∆S| ∼ 8 J K−1 kg−1 and |∆T | ∼ 3.5 K near 180 K with |∆E| = 780 kV cm−1. Finite element modelling (FEM) was used to optimise the geometry of multilayered capacitors (MLCs) for EC cooling. Intrinsic cooling powers of 25.9 kW kg−1 are predicted for an optimised MLC based on PVDF-TrFE with Ag electrodes.