Optimisation of isolation and purification of the jack bean enzyme urease by extraction and subsequent crystallization

A detailed investigation into the isolation by extraction and the purification by crystallization of the enzyme urease from jack bean meal is presented with a view to developing a large-scale process. The effect of different extraction solvents and additives upon the resulting crystals is characterised in terms of crystal size, protein yield and protein purity. The enzymatic activity of urease is exploited in order to quantify the amount and purity of the protein obtained. The extraction procedure was optimised and all stages of the process were monitored in order to provide as detailed a picture as possible of the impact of different process stages upon the intermediate products. Almost all protein is extracted in a single extraction step. Further extraction steps using the same meal but fresh solvent yield only small additional protein yields. Less than 10% of total protein is extracted in a second step, less than 3% in a third extraction. Different solvents lead to clear differences in product quality, with no single solvent optimising all quality criteria. In addition, the point at which the acetone precipitant is introduced into the process has a clear influence on the product. Judicious choice of extraction conditions can significantly increase the size of the urease crystals at the cost of product purity, quantified by specific activity. High product purity (a maximum 138-fold increase in purity was observed with a maximum yield of 8.4%), in contrast, leads to smaller crystals. Comparison to the purest commercially available urease revealed a similar urease content.     

Investigations on the self‐ignition of deposits containing combustibles

Self‐ignition of deposited combustibles is a possible reason for excessive fires occurring on deposits for recycling materials or on waste dumps. Two series of experiments were performed to assess the hazard of self‐ignition: hot storage tests with different homogeneous mixtures of combustible material and inert material and tests with pockets of combustible material embedded in inert matter. In the first test series considerable exothermicity (ΔT>60K) was observed for mass fractions of combustible material as low as 2.5%. In the second series it could be shown that the heat transfer from a pocket of burning material through the inert matter can ignite a second pocket of combustible matter. Based on the experimental data, numerical simulations were performed to predict self‐ignition on real‐scale waste deposits. For a deposit of specific size and shape, the influence of the ambient temperature on the occurrence of self‐ignition has been investigated. Copyright © 2008 John Wiley & Sons, Ltd.     

Current oscillations during chronoamperometric and cyclic voltammetric measurements in alkaline Cu(II)-citrate solutions

It is demonstrated that current oscillations can be observed during chronoamperometric and cyclic voltammetric experiments in solutions containing 0.4 M CuSO₄ and 1.2 M citrate at pH 11 and 50 °C. The oscillations, which are shown to originate from local variations in the pH, result in the deposition of nanostructured Cu and Cu₂O materials. It is concluded that the current oscillations are analogous to the previously described potential oscillations obtained under controlled current conditions in alkaline Cu(II)-lactate, -tartrate and -citrate solutions. Rotating disk electrode results clearly show that the reduction of the Cu(II)-complexes is kinetically controlled and that the rate of the reduction increases with increasing pH and temperature. It is also shown that the presence of a cathodic peak on the anodic scan in the cyclic voltammograms can be used to identify the experimental conditions leading to the spontaneous current (or potential) oscillations. Electrochemical quartz crystal microbalance results indicate that the cathodic peak stems from an increased rate of the reduction of the Cu(II)-citrate complexes due to a rapid increase in the local pH. This causes Cu₂O rather than Cu to be deposited which, however, results in a decrease in the local pH and a decreasing current. In situ ellipsometry data confirm that Cu₂O deposition replaces that of Cu in the potential region of the cathodic peak. The present findings should facilitate syntheses of nanolayered materials based on spontaneous potential or current oscillations.     

Elastic strain evolution and ε-martensite formation in individual austenite grains during in situ loading of a metastable stainless steel

The (hcp) ε-martensite formation and the elastic strain evolution of individual (fcc) austenite grains in metastable austenitic stainless steel AISI 301 has been investigated during in situ tensile loading up to 5% applied strain. The experiment was conducted using high-energy X-rays and the 3DXRD technique, enabling studies of individual grains embedded in the bulk of the steel. Out of the 47 probed austenite grains, one could be coupled with the formation of ε-martensite, using the reported orientation relationship between the two phases. The formation of ε-martensite occurred in the austenite grain with the highest Schmid factor for the active {111}<12¯1> slip system.     

Changes in free and protein-bound amino acids in elderberry fruit (Sambucus nigra) during maturation

Elderberry fruit was analysed for free and protein-bound amino acids during ripening and senescence. Maturation was characterised by an appreciable decrease in the total amino acid content, free and bound, and an increase of the total free amino acid concentration. The latter was mainly due to the massive rise of leucine, tyrosine, and phenylalanine which occurred during the late stages in the ripening process. These three amino acids accounted for 68 % of the total free amino acid content in ripe fruit vs 9% in the green fruit. The transition from optimal ripeness to senescence was associated with a slight increase of the total protein-bound and free amino acid contents. Assessment of the nutritional value of elderberry protein by comparison to whole egg revealed a chemical score of 0.94 for the total essential amino acids, indicating elderberry to be a good source of high biological value protein and thus a suitable source of raw material for a variety of food and dietary products.     

Measurements with multi-point microprobes: Effect of suspended solids on the hydrodynamics of bubble columns for application in chemical and biotechnological processes

Many experimental studies reveal that suspended solids considerably alter the coalescence behaviour and hydrodynamic functions of wo-phase flow. But no systematic efforts have yet been undertaken to separate the effects of different particle properties on local gas hold-up, bubble size and interfacial area gas/liquid. The aim of this paper is to present the local values of these parameters in three-phase fluidized beds of different solids, using miniaturized optical fiber and conductivity needle probes. It is shown that particle concentration, size and, in particular, density are decisive for the change in coalescence behaviour. Ranges of normal (?_S > ?_L) and inverse fluidization (?_S < ?_L) must be distinguished and the flow regime also exerts a strong influence on the interactions between the dispersed phases, the transition point itself being a function of particle properties can be observed, This effect is evaluated for different column diameters, between 0.1 and 0.3 m.     

PREDICTION OF MICROPORE GROWTH DURING GASIFICATION REACTIONS

The concept of changing pore geometry during the course of a reaction allows the microscopic solid-gas reaction models to have the potential to describe the porosity change during the reaction. However, only the bulk porous properties can be predicted due to the pore size range chosen for most of these models. The two population systems, micropore and macropore, chosen by the model of Zygourakls et al. [1] provides a method for predicting micropore property changes. However, this model over-predicts micropore property changes because it assumes that the average micropore radius is enlarged. By examining several sets of published carbon gasification data, it is shown that the average micropore radii are not enlarged by gasification. The commonly-used concept that reaction will enlarge all the pore radii is the major reason for the prediction error. A new concept is proposed in which the reaction will not enlarge the size of the micropores and will maintain a constant micropore length by reacting at both ends of micropores at equal rates. Based upon this concept, the model of Zygourakls et al. [1] has been modified. Both the original and the modified models can predict the gasification rate well by utilizing data from the carbon activation study of Yanai [2]. The model of Zygourakls et al. [1] gives a micropore surface area change close to the measured value, but the reaction enlarged micropores result in predicting high of values of micropore volume changes and average micropore sizes. The steady-state micropore concept used in the improved model predicts more realistic micropore property changes.