Protocols for the Sequential Solid‐State NMR Spectroscopic Assignment of a Uniformly Labeled 25 kDa Protein: HET‐s(1‐227)

The sequence‐specific resonance assignment of a protein forms the basis for studies of molecular structure and dynamics, as well as to functional assay studies by NMR spectroscopy. Here we present a protocol for the sequential ¹³C and ¹⁵N resonance assignment of uniformly [¹⁵N,¹³C]‐labeled proteins, based on a suite of complementary three‐dimensional solid‐state NMR spectroscopy experiments. It is directed towards the application to proteins with more than about 100 amino acid residues. The assignments rely on a walk along the backbone by using a combination of three experiments that correlate nitrogen and carbon spins, including the well‐dispersed C^β resonances. Supplementary spectra that correlate further side‐chain resonances can be important for identifying the amino acid type, and greatly assist the assignment process. We demonstrate the application of this assignment protocol for a crystalline preparation of the N‐terminal globular domain of the HET‐s prion, a 227‐residue protein.     

A facile method for the study of slow physical and chemical processes in polymeric systems

A method is described for continuously following a long-duration process in a complex polymeric system by isothermal calorimetry. Computerized models for slow physical or chemical processes have been applied to calorimetric runs under different conditions and these have given information in the form of thermodynamic and kinetic data. The method also gives a means of determining the relationship between molecular weight and functionality for one of the polymers used, the order of reaction, and the degree of conversion before the start of the measurements. An example is given of a kinetic study of the reaction of hydroxyl-terminated polybutadiene with two different diisocyanates. The temperature dependence of the formation of urethanes, the rate constants, and the degree of conversion before the start of the measurements were determined as well as the heat of reaction for the formation of urethanes using hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI) as curing agents. The results have been compared with other kinetic studies of these systems.     

Der Einfluß von Kerben auf das Zeitfestigkeitsverhalten von Stählen

Bei wiederholten mechanischen und/oder thermischen Belastungen von Bauteilen mit Kerben können im Kerbgrund durch inhomogene Spannungs- und Dehnungsverteilungen überelastische Verformungen auftreten, die bereits im Zeitfestigkeitsgebiet zu einem Versagen des Bauteils führen können. Zur Ermittlung des Kerbeinflusses wurden Zugschwellversuche ohne und mit Haltezeiten bei Raumtemperatur und 530°C durchgeführt. Die Ergebnisse wurden mit Zeitstand- und Dehnungswechselversuchen verglichen und Dehnungsund Spannungsformzahlen ermittelt.     

Modelling of simultaneous two-sided migration into water and olive oil from nylon food packaging

Nylon 6 and nylon 12 food packaging materials used as sausage casings are typically exposed to fatty food on one side and boiling water on the other during the cooking process. To simulate the migration behaviour under these conditions, a special migration cell was constructed and filled with olive oil on one side of the polymer and water on the other to find out what amounts of the migrants will transfer to either side and phase at 100 °C. Results show that when a nylon 6 film is exposed to the conditions as described above, total mass transfer of the monomer—caprolactam—into the water phase occurs after 2 h at 100 °C. Nylon 12 sausage casings release similar amounts of their monomer—laurolactam—into both the aqueous and oil phase. An existing computer migration model was adapted to simulate the situation of simultaneous two-sided migration applying previously determined diffusion and partitioning coefficients. The suitability of the model was confirmed by experimental data.     

Leitsysteme für Produktion und Labor „Stärken und Schwächen der heutigen Hardware und Software,Entwicklungstrends und Zukunftsaussichten

Control systems for production and laboratory. Strengths and weaknesses of contemporary hardware and software, developmental trends and future prospects . The state of the art of control systems in production and laboratory is considered with the aid of some representative examples. The strengths and weaknesses of available control systems are discussed. It is shown that further rationalization in production can only be achieved when the interchange of information between the control layers of production is improved. Also open to considerable improvement is the flow of information in the laboratory and the cross-flow between laboratory and production. The present development of microelectronics (microprocessors, personal computers, data busses, local area networks (LAN)) will greatly change process control technology.     

Investigation of solid oxide fuel cell sealing behavior under stack relevant conditions at Forschungszentrum Jülich

Hermetic sealing is a key requirement for the operation of solid oxide fuel cell (SOFC) stacks in a system environment. The sealant material has to withstand stresses due to mechanical loading, mismatch in thermal expansion coefficient and thermal gradients that arise during operation. Based on leakage tests performed at Forschungszentrum Jülich it was obvious that stacks, having been operated successfully in a furnace, are not necessarily usable in a system, e.g. because of deviating pressure differences and temperature gradients. Thorough investigations including stack and stack dummy tests, and finite element modeling (FEM) were performed to get a comprehensive understanding of the various parameters, influencing the leak tightness of the sealing material. It was found that even small temperature differences especially in the area of gas and air manifolds can create excessively high tensile stresses. Based on initial FEM analyses, a better understanding of the problem has been obtained and a tool was developed that can assist in the design of more robust stacks. These investigations and modeling activities will be continued with a main focus on thermal cycling, which is the next step in the list of requirements.     

Proton conductivity of ordered mesoporous materials containing aluminium

In order to check the influence of Brønsted acidic Al sites in the walls of mesoporous materials on their proton conductivity, we introduced aluminium into the mesoporous SiO₂ framework Si-MCM-41, which possesses hexagonally ordered channels, by using different Al sources, i.e. sodium aluminate, aluminium sulphate and aluminium isopropoxide. The successful synthesis of ordered mesoporous material with incorporated Al species was proven by X-ray diffraction, energy-dispersive X-ray spectroscopy, nitrogen adsorption, scanning electron microscopy and solid state ²⁷Al MAS NMR. By realizing Si/Al ratios of 8-40 it was found that the proton conductivity of the mesoporous aluminium silicates measured by impedance spectroscopy significantly increases with the Al content, reaching a conductivity of 3 × 10⁻³ S cm⁻¹ at 140 °C. The increase of the proton conductivities compared to Al-free Si-MCM-41 results from (i) an improved hydrophilicity enhancing the water storage capability, (ii) a decreased particle size from the micrometer to the nanometer scale (50-100 nm) and (iii) the existing Brønsted acidity in the mesoporous Al-MCM-41. The Al source NaAlO₂ gives clearly the best results because the entire Al incorporated within the framework is tetragonally coordinated, while for samples prepared with Al₂(SO₄)₃ or AIP also octahedral coordination of oxygen around the Al centers is observed by ²⁷Al MAS NMR.     

Standardization of egg collection from aquatic birds for biomonitoring--a critical review

Collecting bird eggs is an established method of biomonitoring for specific pollution hazards. One of the most critical problems with this method is the extreme biological variability in bird eggs, but standardizing the collection and preservation of eggs can reduce these problems. Furthermore, standard practices are required so that the results can be compared among studies because mistakes cannot be corrected by laboratory analysis. Therefore, a standard procedure for collecting and preserving bird eggs may be necessary. The objective of this review is to investigate the current standard of quality assurance in the field by analyzing 86 peer-reviewed papers describing egg collection and use for aquatic birds. We show that little attention has been paid to standardizing how eggs are collected and stored in the field. Important information is often absent, including crucial aspects of sample collection and preservation, such as the freshness of the eggs, the position of the eggs in the laying sequence, the selection criteria, random sampling, and the duration and temperature of transport. Potential standards are suggested and discussed as a foundation for the development of quality assurance standards in the field.