In-situ ESR spectroskopy on transition metal ions in ceramic oxides

Die Arbeit präsentiert ESR(Elektronenspinresonanz-Spektroskopie)-Messungen an den Oxidkeramiken BaTiO3, CeO2, ZrO2 und MgO. Als ESR-Sonden werden die Übergangsmetallionen Mn(II), Mn(IV), Fe(III), Cr(III), Cr(V), Gd(III) und Ti(III) eingesetzt. So weit möglich wurden die Untersuchungen in-situ, d.h. in der Regel bei Temperaturen von einigen hundert Grad Celsius und in definierten Sauerstoffaktivitäten durchgeführt. Im Mittelpunkt der Untersuchungen steht in vielen Fällen die Valenz der Sondenionen in Abhängigkeit vom Gleichgewicht der Oxide mit dem Sauerstoff der Umgebung. Die Existenz von Mn(II) in Mn-dotiertem BaTiO3 bei 800 Grad Celsius und niedrigen Sauerstoffpartialdrücken konnte direkt nachgewiesen werden. Beim Phasenübergang ferro- nach paraelektrisch zeigen die Messungen höchstwahrscheinlich die Reduktion von Mn(III) zu Mn(II) und von Fe(IV) zu Fe(III) in n-dotiertem BaTiO3. Darüberhinaus konnte für CeO2 ein seit längerem in der Literatur widersprüchlich diskutiertes ESR-Signal Cr(V) zugeordnet werden. Das Cr-Signal zeigt selbst bei niedrigen Temperaturen schnelle Intensitätsänderungen in Abhängigkeit vom Sauerstoffpartialdruck. Für Ti(III) in ZrO2 wurden durch temperaturabhängige ESR-Messungen 2 verschiedene Gitterplätze identifiziert. Bei MgO konnte die Diffusion der paramagnetischen Sonde Cr(III) in die nicht-ESR-sensitive Matrix beobachtet werden. Der hieraus bestimmte Diffusionskoeffizient stimmt sehr gut mit aus Tracerdiffusionsdaten ermittelten Literaturangaben überein.This work presents ESR(Electron-Spin-Resonance spectroscopy) measurements on the oxides BaTiO3, CeO2, ZrO2, and MgO. ESR probes doped into the ceramic samples are the transition ions Mn(II), Mn(IV), Fe(III), Cr(III), Cr(V), Gd(III), and Ti(III). During the measurements the samples were held as far as possible in in-situ conditions. This means for the solid state reactions temperatures of several hundred degrees Centigrade and an exact defined oxygen activity. In most cases the dependency of the probe ions valence on the equilibrium between sample and surrounding gas atmosphere is in the focus of the investigations. For BaTiO3 doped with manganese direct evidence could be found for the existence of Mn(II) at high temperatures and low oxygen partial pressures. For a variety of n-doped BaTiO3 samples additionally the changes in electronic configuration at the phase transition ferro- paraelectric are investigated. Iron and manganese acceptors show most probable the reduction of Fe(IV) to Fe(III) respective Mn(III) to Mn(II). In CeO2 a special ESR signal could be attributed to Cr(V). This signal has been controverselly discussed in literature before. The Cr signal shows fast changes in intensity even at low temperatures in dependence on oxygen partial pressures. For Ti(III) in ZrO2 two lattice sites could be identified by temperature dependent ESR measurements. For MgO the diffusion of Cr(III) into the dielectric matrix is observed in-situ at 800 degrees Centigrade. The herefrom derived coefficient of diffusion fits well into literature data won by tracer diffusion

Analysis of the link between the redox state and enzymatic activity of the HtrA (DegP) protein from Escherichia coli

Bacterial HtrAs are proteases engaged in extracytoplasmic activities during stressful conditions and pathogenesis. A model prokaryotic HtrA (HtrA/DegP from Escherichia coli) requires activation to cleave its substrates efficiently. In the inactive state of the enzyme, one of the regulatory loops, termed LA, forms inhibitory contacts in the area of the active center. Reduction of the disulfide bond located in the middle of LA stimulates HtrA activity in vivo suggesting that this S-S bond may play a regulatory role, although the mechanism of this stimulation is not known. Here, we show that HtrA lacking an S-S bridge cleaved a model peptide substrate more efficiently and exhibited a higher affinity for a protein substrate. An LA loop lacking the disulfide was more exposed to the solvent; hence, at least some of the interactions involving this loop must have been disturbed. The protein without S-S bonds demonstrated lower thermal stability and was more easily converted to a dodecameric active oligomeric form. Thus, the lack of the disulfide within LA affected the stability and the overall structure of the HtrA molecule. In this study, we have also demonstrated that in vitro human thioredoxin 1 is able to reduce HtrA; thus, reduction of HtrA can be performed enzymatically

Properties of the HtrA Protease From Bacterium Helicobacter pylori Whose Activity Is Indispensable for Growth Under Stress Conditions

The protease high temperature requirement A from the gastric pathogen Helicobacter pylori (HtrAHp) belongs to the well conserved family of serine proteases. HtrAHp is an important secreted virulence factor involved in the disruption of tight and adherens junctions during infection. Very little is known about the function of HtrAHp in the H. pylori cell physiology due to the lack of htrA knockout strains. Here, using a newly constructed ΔhtrA mutant strain, we found that bacteria deprived of HtrAHp showed increased sensitivity to certain types of stress, including elevated temperature, pH and osmotic shock, as well as treatment with puromycin. These data indicate that HtrAHp plays a protective role in the H. pylori cell, presumably associated with maintenance of important periplasmic and outer membrane proteins. Purified HtrAHp was shown to be very tolerant to a wide range of temperature and pH values. Remarkably, the protein exhibited a very high thermal stability with the melting point (Tm) values of above 85°C. Moreover, HtrAHp showed the capability to regain its active structure following treatment under denaturing conditions. Taken together, our work demonstrates that HtrAHp is well adapted to operate under harsh conditions as an exported virulence factor, but also inside the bacterial cell as an important component of the protein quality control system in the stressed cellular envelope

SurA-like and Skp-like Proteins as Important Virulence Determinants of the Gram Negative Bacterial Pathogens

In the Gram-negative bacteria, many important virulence factors reach their destination via two-step export systems, and they must traverse the periplasmic space before reaching the outer membrane. Since these proteins must be maintained in a structure competent for transport into or across the membrane, they frequently require the assistance of chaperones. Based on the results obtained for the model bacterium Escherichia coli and related species, it is assumed that in the biogenesis of the outer membrane proteins and the periplasmic transit of secretory proteins, the SurA peptidyl–prolyl isomerase/chaperone plays a leading role, while the Skp chaperone is rather of secondary importance. However, detailed studies carried out on several other Gram-negative pathogens indicate that the importance of individual chaperones in the folding and transport processes depends on the properties of client proteins and is species-specific. Taking into account the importance of SurA functions in bacterial virulence and severity of phenotypes due to surA mutations, this folding factor is considered as a putative therapeutic target to combat microbial infections. In this review, we present recent findings regarding SurA and Skp proteins: their mechanisms of action, involvement in processes related to virulence, and perspectives to use them as therapeutic targets

Local communication via the Internet in an aging society and the concept of active aging – the analysis of the content and functionality of the official websites of voivodeship's capitals.

Niniejsza praca odpowiada na pytanie, czy oficjalne strony internetowe miast wojewódzkich jako nowe media lokalne, uwzględniają kwestię współczesnej starości, dostosowując zarówno treść, jak i formę przekazu do potrzeb współczesnych osób starszych. Treść przekazywanych informacji jest istotna, gdyż może kształtować styl życia osób starszych. Z kolei forma przekazów może ułatwiać, bądź utrudniać ich odbiór. Zatem, główne wątki w pracy dotyczą aktualnych danych na temat starzejącego się społeczeństwa polskiego, sposobu postrzegania populacji seniorów na przestrzeni lat oraz realizowania idei współczesnej polityki senioralnej dotyczącej koncepcji aktywnej starości w środowisku lokalnym. Wyjaśniona jest również rola informująco-aktywizującą mediów lokalnych w dobie rozwoju komunikacji internetowej z osobami starszymi oraz zasady, jakimi powinni się kierować twórcy stron internetowych, uznając osoby starsze za potencjalnych użytkowników.The fast ageing of the population and the consequent both demographic and social problems are not only a problem but also a challenge. There is a growing number of elderly people and this trend, in line with forecasts, will be increasing. Hence, in the era of political promoting the idea of active aging , it becomes essential to take into account the issue of communication ( as an incentive element ) with seniors about opportunities to take their various activities. This master’s thesis shows a characteristic of the period of old age, current data and forecasts concerning the aging of the Polish society and society approach to this stage of life, including the position of old age in the media