Adsorption of fluorescein by protein crystals.

Adsorption characteristics of native and cross-linked lysozyme crystals were examined using fluorescein as model adsorbate. The adsorption isotherms exhibited Langmuir or linear behavior. The affinity constant (b1) and the adsorption capacity (Qsat) for fluorescein were found to depend on the type and concentration of co-solute present in the solution. The dynamics of adsorption isotherm transition from Langmuir to linear showed that affinity of lysozyme for solutes increases in the order 2-(cyclohexylamino)ethanesulphonic acid (CHES), 4-morpholinepropanesulphonic acid (MOPS), acetate, fluorescein. Furthermore, the crystal morphology, the degree of cross-linking of the crystals, and, in particular, solution pH were identified as factors determining fluorescein adsorption by the lysozyme crystals. These factors seem to affect crystal capacity for the solute more than affinity for the solute. Adsorption of fluorescein by cross-linked tetragonal lysozyme crystals was exponentially dependent on the lysozyme net charge calculated from the final solution pH. The 3-5-fold increase in the fluorescein adsorption as a result of cross-linking is presumably due to the increasing hydrophobicity of the lysozyme crystal.

Surfactant-aided size exclusion chromatography.

The flexibility and selectivity of size exclusion chromatography (SEC) for protein purification can be modified by adding non-ionic micelle-forming surfactants to the mobile phase. The micelles exclude proteins from a liquid phase similar to the exclusion effect of the polymer fibers of the size exclusion resin. This surfactant-aided size exclusion chromatography technology (SASEC) is demonstrated on the separation of two model proteins; bovine serum albumin (BSA) and myoglobin (Myo). The effect of the added surfactants on the distribution behavior of the proteins is predicted adequately by a size exclusion model presented in this paper.

Mental disturbances and perceived complexity of nursing care in medical inpatients: results from a European study.

AIMS AND OBJECTIVES: The relationship between mental disturbances - anxiety and depression, somatization and alcohol abuse - on admission to internal medicine units and perceived complexity of care as indicated by the nurse at discharge was studied. The goal was to study the utility of short screeners for mental disturbances to select patients for case-management on admission. DESIGN: The study had a cohort design: patients were included on admission and followed through their hospital stay until discharge. The study was conducted within the framework of the European Biomed 1 Risk Factor study. RESEARCH METHODS AND INSTRUMENTS: In the first 3 days of admission the patients were interviewed by a trained health care professional, who scored the SCL-8D, a somatization questionnaire based on the Whiteley-7 and the CAGE. At discharge, nurses rated the complexity of the patient's care. RESULTS: Patients with high scores on anxiety and depression (SCL-8D) and on somatization received higher ratings on perceived nursing complexity than those with low scores, with and without control for age, severity of illness and chronicity. The actual nursing intensity and medical care utilization, as measured daily by means of a checklist, could not explain these relations. No differences were found between patients with high or low scores on alcohol abuse. CONCLUSIONS: The study shows a potential use of screeners for mental disturbances to detect patients for whom nurses might need additional help. However, mental disturbance is not the sole criterion: functional status and other variables that predict medical and nursing care utilization should be included in a screening strategy for case-management programmes.

Course of pH during the formation of amoxicillin by a suspension-to-suspension reaction.

Amoxicillin can be produced in an enzymatic suspension-to-suspension reaction in which the substrate(s) and product(s) are mainly present as solid particles, while the reaction takes place in the liquid phase. During these suspension-to-suspension reactions different subprocesses take place, such as dissolution/crystallization of substrates and products, enzymatic synthesis of the product(s), and undesired enzymatic hydrolysis of substrates and/or products. All these subprocesses are influenced by pH and also influence the pH because the reactants are weak electrolytes. This paper describes a quantitative model for predicting pH and concentrations of reactants during suspension-to-suspension reactions. The model is based on mass and charge balances, pH-dependent solubilities of the reactants, and enzyme kinetics. For the validation of this model, the kinetically controlled synthesis of amoxicillin from 6-aminopenicillanic acid and D-(p)hydroxyphenylglycine methyl ester was studied. The pH and the dissolved concentrations took a very different course at different initial substrate amounts. This was described quite reasonably by the model. Therefore, the model can be used as a tool to optimize suspension-to-suspension reactions of weak electrolytes.

Countercurrent multistage fluidized bed reactor for immobilized biocatalysts: II. Operation of a laboratory-scale reactor.

In Part I of this series,(1) we derived a model and made simulations for a multistage fluidized bed reactor (MFBR). It was concluded that the MFBR can be an attractive alternative for a fixed bed reactor when operated with a deactivating biocatalyst. In Part II of this series, the design of a laboratory-scale MFBR and its evaluation to investigate the practical feasibility of this reactor type, will be described. Experiments with a duration as long as 10 days were carried out successfully using immobilized glucose isomerase as a model reaction system. The results predicted by the model are in good agreement with the measured glucose concentration and biocatalyst activity gradients, indicating perfect mixing of the particles in the reactor compartments.The diameters of the biocatalyst particles used in the experiments showed a large spread, with the largest being 1.7 times the smallest. Therefore, an additional check was carried out, to make sure that the particles were not segregating according to size. Particles withdrawn from the reactor compartments were investigated using an image analyzer. Histograms of particle size distribution do not indicate segregation and it is concluded that the particles used have been mixed completely within the compartments. As a result, transport of biocatalyst is nearly plug flow.

Countercurrent multistage fluidized bed reactor for immobilized biocatalysts: III. Hydrodynamic aspects.

In Parts I and II of this series we described the modelling, design, and operation of a multistage fluidized bed reactor (MFBR) for immobilized biocatalysts. This article deals with those aspects of the MFBR which are different from single-stage fluidized beds which are operated in batch mode with respect to the solids. The semicontinuous transport of the particles requires perfect mixing of the particles in the reactor compartments, because particles are mainly transported from the bottom of these compartments. A large spread in the physical properties of the biocatalyst particles, especially of both size and density, may cause the particles to segregate into layers with different diameter and/or density. This affects the efficient use of the biocatalyst. The properties of the particles are dependent on the immobilization method. The suitability of different methods for possible future application in the MFBR is therefore compared. Because of segregation, successful use of a biofilm catalyst with a nonuniform thickness of the biofilm is doubtful. Experiments in a small scale reactor (+/- 0.1 m diameter) demonstrated that perfect particle mixing is possible using commercially available biocatalyst particles of uniform density. Co-immobilization of the biocatalyst with glass powder in a gel is a simple and effective method of increasing gel density. High density particles allow high liquid flow rates, and thus an improved external mass transfer can be achieved.The distributor plates, which separate the reactor compartments, must allow unhindered transport of particles. Therefore, the holes in these plates must have a diameter of at least 4.5 times that of the largest particles which are present in the particle mixture used. Furthermore, the plates must be designed such that, when scaling-up the reactor, a uniform liquid distribution over the cross-sectional area of the reactor occurs. Large-scale experiments were not carried out, but published correlations, indicate that particle mixing and a uniform liquid distribution can be accomplished in a large-scale reactor under similar flow conditions.