Showing papers by "Braunschweig University of Technology published in 1983"

Pore size and properties of spherical Ca-alginate biocatalysts

Abstract: A method for the production of spherical alginate gels from few μm up to several mm diameter is described. Alginate beads with diameters from 0.5 to 3 mm are used to immobilize microorganisms as biocatalysts. Micro size alginate gels are used as column packing material for inverse steric exclusion chromatography to determine their pore sizes from dextran standards of known molecular weight. The results indicate that alginate gels have pores which are large enough to release catalytic acting enzymes out of the matrix.

Formation of novel anionic trehalosetetraesters from Rhodococcus erythropolis under growth limiting conditions

Abstract: The paraffin oxidizing bacterium Rhodococcus erythropolis was cultivated in shake flasks on a mixture of C14 - C15 n-alkanes or kerosene under growth limiting conditions. For example, nitrogen deficiency caused the formation of new glycolipids in fermentation broth. These lipids proved to be so far unknown substances were identified as α,α-trehalose-2,3,4,2′-tetraesters. The main component is esterified with two decanoyl, one octanoyl and one succinoyl residue.

Improvement of productivity and efficiency in ethanol production with ca-alginate immobilized zymomonas mobilis

Abstract: A three-stage reactor system was used to obtain high ethanol concentration (74 g/1) with immobilized Zymomonas mobilis DSM 424. The catalyst efficiency was improved by formation of small diameter beads and arrangement of the biocatalyst in a reactor configuration adapted to the kinetics of ethanol production. A higher productivity than reported before was obtained with 56,5 g/lh based on total working volume at a sugar conversion rate of 98%. The bioreactor was run continuously for 65d.

Methods for the Immobilization of Microbial Cells

Abstract: Publisher Summary This chapter discusses methods for the immobilization of microbial cells. Immobilized cells are those cells that are physically confined or localized in a certain defined region of space with retention of their catalytic activity and—if possible or even necessary—their viability and that can be used repeatedly and continuously. The methods of immobilization can be put into a scheme in which the type of bonding of the cells in the catalyst particle is the dominating parameter. This scheme, however, is oriented toward the state of the immobilized cell catalyst and not so much toward the route along which the catalyst has been prepared. Thereafter, the overall macroscopic parameter to quantify the operational stability of a biocatalyst is its half-life. The operational stability is influenced by a great number of parameters; and it is helpful to distinguish between two types of processes with immobilized cells: single-enzyme systems and multistep enzyme systems. Subsequently, the industrial application of the immobilization of cells has three aspects—the first aspect is the shape and size of the catalyst and the problems involved in the scale-up of the immobilization procedure; the second aspect to be considered is the characterization of the mechanical properties of the biocatalyst; and finally, the third engineering aspect is the kinetic performance of the biocatalyst.

Production L-tryptophan by Escherichia coli cells

Abstract: Whole cells of Escherichia coli B 10 having high tryptophan synthetase activity were used directly as an enzyme source to produce L-tryptophan from indole and L- or D,L-serine. This strain is tryptophan auxotrophic, which is tryptophanase negative and, in addition, L- and D-serine deaminase negative under production conditions. To avoid inhibition of tryptophan synthetase by a high concentration of indole, nonaqueous organic solvents, Amberlite XAD-2 adsorbent, and nonionic detergents were used as reservoirs of indole in the reaction mixture for the production of L-tryptophan. As a result, different effects were observed on the production of L-tryptophan. Particularly, among the nonionic detergents, Triton X-100 was very efficient. Using Triton X-100 for production of L-tryptophan from indole and L- or D,L-serine by whole cells of Escherichia coli B 10, 14.14 g/100 mL and 14.2 g/100 mL of L-tryptophan were produced at 37 degrees C for 60 h.

Biosynthesis of Cyanogenic Glycosides in Butterflies and Moths: Incorporation of Valine and Isoleucine into Linamarin and Lotaustralin by Zygaena and Heliconius Species (Lepidoptera)

Abstract: Abstract C -13 NMR data for linamarin and lotaustralin, obtained after feeding of either Zygaena Jilipendulae or Heliconius melpomone (Lepidoptera) with C-13 enriched valine and isoleucine respectively, indicate that intact units of amino acid with loss of the carboxyl group are incorporated during the biosynthesis of these cyanogenic glycosides.

Study on the molecular weight dependence of dilute solution properties of narrowly distributed polystyrene in toluene and in the unperturbed state

Abstract: Intrinsic viscosities [η], second and third virial coefficients A2 and A3, respectively, and mean square radius of gyration 〈RG2〉 of a polymer homologous series of narrow-molecular-weight-distribution polystyrene samples in a molecular weight range of 2000 up to 24 · 106 were determined in toluene at 25°C by light scattering and viscometry measurements. The results are (3 · 104 < Mw < 24 · 106, Mw/Mn ≤ 1,3): These results were obtained by consideration of the limit of the dilute solution regime, the determination of zero-shear rate intrinsic viscosities, and the molecular weight dependence of the refractive index increment dn/dc. It was found that dn/dc increases slightly up to Mw = 1,8 · 106. A comparison of the [η]−Mw-relationship with literature data is given. In addition the unperturbed (theta) dimension parameters K0, 〈h2〉0/M, the characteristic ratio C∞, the steric factor σ, and the thermodynamic interaction parameter B were calculated from the modified Burchard-Stockmayer-Fixman procedure using polymolecularity correction and the results compared with experimental data from the literature.

A model for magnetic abnormalies of FeNi Invar alloys

Abstract: A model based on the idea of localized magnetic moments is presented which allows to calculate the local magnetic moment expectation values of FeNi alloys. The only parameters of the model are the exchange integralsJ FeFe,J FeNi,J NiNi. By assuming a “mixed” exchange interaction the concentration dependence of the exchange integralsJ FeFe andJ FeNi is calculated. The model allows the iron magnetic moments to orient parallel or antiparallel to the magnetization axis, depending on the local environment. It explains the magnetic abnormalies of FeNi Invar alloys as for example the concentration dependence of the mean magnetic moment and the Curie temperatures as well as the characteristic “flat” courves of the spontaneous magnetization.

Sudividing multivariate splines

Abstract: Four subdivision algorithms for multivariate splines are discussed in a geometrical manner. The proofs given are mostly geometrical also and thus easy to follow. An illustrative example demonstrates the effect of the algorithms to a sample surface.

A Digital Pulsewidth Modulator Employing Advanced Modulation Techniques

Abstract: Advanced pulsewidth modulation (PWM) techniques for inverters allow the use of high-efficiency ac drives with low torque and speed pulsations and with reduced losses. A digital control scheme for a thyristor inverter is presented, where firing patterns satisfying given requirements like harmonic elimination or loss minimization have been calculated and stored in programmable read-only memory (PROM). Moreover, such a tontrol permits a continuous variation of output voltage over the modulation range for full inverter utilization. Evaluation using a 22-kW induction motor drive verified that the control provides a clean frequency spectrum over the operating range of the drive (0?100 Hz).

Lead isotope data from selected galena occurrences in the North Eifel and North Sauerland, Germany

Abstract: The isotopic ratios of Pb have been determined from 33 galena samples collected from a variety of occurrences in the north Eifel and north Sauerland. On the basis of the data presented, it is not possible to distinguish between the isotopic characteristics of galena-Pb from veins, carbonate cavity-filling and sandstone-hosted disseminated mineralisation in the north Eifel. In the north Sauerland, Saxonian (late Mesozoic-Tertiary) disseminated Pb mineralisation in Cretaceous-Tertiary sediments is generally more radiogenic than Saxonian vein mineralisation in Paleozoic country rocks. Variscan vein-type mineralisation (Ramsbeck, Ebbe Mountains) proved to have the least radiogenic Pb. The results are discussed in terms of potential sources of the Pb, and are compared to other data reported from European deposits.

Relaxation of metallic glass structure measured by elastic modulus and internal friction

Abstract: Young's modulus and internal friction of metallic glass ribbons (METGLAS 2826A) was measured by the vibrating reed technique to monitor structural relaxation far below and near to the glass transition temperature Tg. The activation energies of relaxation processes, determined from steplike isothermal heating treatments, are distributed in a broad spectrum which according to the thermal history commences approximately steplike around 1 eV and continues beyond 1.6 eV in the amorphous state. With the beginning of crystallization the spectrum rises steeply around 2 eV. In the range of higher temperatures (still

Continuous production of L‐tryptophan from indole and L‐serine by immobilized Escherichia coli cells

Abstract: Escherichia coli B 10, which has high activity of tryptophan synthetase, was grown in a 50-L batch culture in order to determine in which growth phase the cells have the highest specific tryptophan productivity. Accordingly, whole cells of the stationary phase were used for immobilization in polyacrylamide beads. After immobilization, these immobilized cells had 56% activity of tryptophan synthetase compared with that of free cells. First, the properties of immobilized cells were investigated. Next, discontinuous productions of L-tryptophan were carried out by using immobilized cells. In discontinuous production of L-tryptophan by the batch, the activity remaining of immobilized cells was 76-79% after 30 times batchwise use. In continuous production of L-tryptophan with a continuous stirred tank reactor (CSTR), the activity remaining of the immobilized cells was 80% after continuous use for 50 days. The maximum productivity of L-tryptophan in this CSTR system was 0.12 g tryptophan L(-1) h(-1).

Studies of Relaxation of Metallic Glasses by Dilatometry and Density Measurements

Abstract: High-precision density measurements on cold-rolled Pd77.5Cu6Si16.5 glass rods before and after relaxation anneals showed that 30–40% rolling leads to a density reduction of ∼0.14%, recoverable on subsequent annealing below Tg. This change is about half of the density increase attainable by recovery-annealing the as-quenched glass. Density changes in Fe40Ni40B20 glass ribbon, resulting from recovery-annealing, were studied indirectly by measuring isothermal length changes through dilatometry of foil sandwiches. The experimental conditions for reliable isothermal dilatometry, using a commercial instrument, are outlined. It was found that the kinetics of length change in the longitudinal and transverse directions were quite different, being faster in the former. Prolonged recovery-annealing prior to dilatometry removed this difference. The intermediate stage of each isotherm followed logt kinetics. Experiments were performed with Fe40Ni40B20, Ni64Zr36 and Cu66Ti34 to search for a reversible component of length change during cyclic isothermal holds at two temperatures. Such a component probably exists but is extremely small, less than 1% of the limiting irreversible length change. The implications of the various findings are discussed in the light of recent literature.

Borchelate von Salicylaldoxim und Derivaten

Abstract: Formation and structure of boron chelates of salicylaldoxime are studied with O-alkyloximes and O-acyloximes of salicylaldehyde. The six-membered ring chelates thus obtained are synthesized also by alkylation resp. acylation of the preformed salicylaldoxime boron chelates. Thermolysis of the difluoroboron or diphenylboron chelates gives fluoroboronic resp. phenylboronic acid derivatives of salicylaldoxime that are isolated as dimeric compounds.

On-line measurement of ethanol with a gas-sensor-dip-electrode

Abstract: A simple gas-sensor-dip-electrode (GSDE) for the direct measurement of ethanol in the culture broth is described. The GSDE was used for the online ethanol determination for a period of 2 month during a continuous fermentation with immobilized cells.