Biomedical subjects

S R Weijers

Publications and source records attributed to S R Weijers.

4 recordsLinked to original sources

PubMed2001

Developing a model based decision support tool for the identification of sustainable treatment options for domestic wastewater.

To enable decision makers to select sustainable wastewater treatment systems, insight into the sustainability of a wide variety of systems should be provided in a transparent way leaving room for adaptation and interpretation according to the local situation. To provide this insight a structured methodology comparing wastewater treatment systems with respect to sustainability is defined. Similar to life cycle assessment (LCA) three phases can be distinguished: (1) goal and scope definition, (2) inventory analysis, and (3) optimisation and results. In the goal and scope definition we set the system boundaries to include most of the water cycle and part of the food cycle. Furthermore, we defined a multi-disciplinary set of sustainability indicators including technical, economic, environmental, and socio-cultural aspects. In the inventory analysis these sustainability indicators are quantified using simple static models of wastewater unit operations. Selection of unit operations results in a model of a complete wastewater treatment system. In the optimisation phase the decision maker can weigh the different sustainability indicators and select sustainable options through integer programming.

Decision Support Techniques↗

PubMed1992

Enzyme stability in downstream processing. Part 1: enzyme inactivation, stability and stabilization.

In biotechnological recovery processes the instability of the product can lead to large losses in the sequence of recovery processes needed to purify the product. As the cost of the final active product is strongly dependent on the recovery yield, this will lead to an increase in product cost. Therefore knowledge of factors that influence stability is important. This Part 1 contains a review on the factors that influence stability. As stability is very important in enzyme purification this review deals about enzymes and their ability to retain catalytic activity. Inactivation mechanisms and agents are discussed. A short review is given of enzyme structure and stability. This is followed by stabilization strategies and methods.

Journal Article↗

PubMed1992

Enzyme stability in downstream processing. Part 2: quantification of inactivation.

In biotechnological recovery processes the instability of the product can lead to large losses in the sequence of recovery processes needed to purify the product. As the cost of the final active product is strongly dependent on the recovery yield, this will lead to an increase in product cost. Therefore knowledge of factors that influence stability is important. This Part 2 provides the basic principles for design and operation of processes in which inactivation takes place. Simple kinetics and reactor modelling are discussed. These are applied to a number of unit operations: cell disruption, membrane filtration, drying and reversed micellar extraction. It is thus shown that the basic tools for modeling of biochemical processes provide us with the data needed for optimal process design and operation.

Journal Article↗

PubMed1987

Time-resolved fluorescence and circular dichroism of porphyrin cytochrome c and Zn-porphyrin cytochrome c incorporated in reversed micelles.

Interactions between fluorescent horse heart cytochrome c derivatives (e. g. porphyrin cytochrome c and Zn-porphyrin cytochrome c) with surfactant interfaces in reversed micellar solutions have been studied, using different spectroscopic techniques. Anionic [sodium bis(2-ethylhexyl)sulfosuccinate, AOT] and cationic (cetyltrime-thylammonium bromide, CTAB) surfactant solutions have been used in order to investigate the effects of charge interactions between proteins and interfaces. Circular dichroism reveals that much of the protein secondary structure is lost in AOT-reversed micelles, especially when the molar water/surfactant ratio, wo, is high (wo = 40), whereas in CTAB-reversed micelles secondary structure seems to be preserved. Time-resolved fluorescence measurements of the porphyrin in the cytochrome c molecule yields information about the changes in structure and the dynamics of the protein upon interaction with surfactant assemblies both in aqueous and in hydrocarbon solutions. With AOT as surfactant a strong interaction between protein and interface can be observed. The effects found in aqueous AOT solution are of the same kind as in hydrocarbon solution. In the CTAB systems the interactions between protein and surfactant are much less pronounced. The measured effects on the fluorescence properties of the proteins are different in aqueous and hydrocarbon solutions. In general, the observations can be explained by an electrostatic attraction between the overall positively charged protein molecules and the anionic AOT interface. Electrostatic attraction can also occur between the cytochrome c derivatives and CTAB because there is a negatively charged zone on the surface of the proteins. From the fluorescence anisotropy decays it can be concluded that in the CTAB-reversed micellar system these interactions are not important, whereas in an aqueous CTAB solution the proteins interact with surfactant molecules.

Circular Dichroism↗