bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aqueous Two‐Phase Polymer Systems for Liquid/Liquid Partition‐Chromatography of Biopolymers
Authors: Müller Werner 
Published: July 2012

AbstractThe paper presents a short review on the application of aqueous two‐phase systems, based on incompatible polymer pairs, for the fractionation of biopolymers by a liquid/liquid partition chromatography technique. In the development of this technique the problem of immobilizing one of the two phases on a support was solved by either using support materials incompatible with one of the two phase‐forming polymers, or by grafting water‐soluble linear polymers with such incompatibility properties on hydrophilic support particles. In both cases, the support particles repel that phase of the phase pair which is rich in the incompatible polymer and are wetted selectively by the second one which consequently forms the stationary phase in the column packing. — Among the aqueous two‐phase polymer system known, the polyethylene glycol (PEG)/dextran (Dx) system is the most common one. Since PEG is incompatible with cellulose and polyacrylamide, the Dx‐rich phase forms the stationary phase in columns prepared from these materials. The same holds for support particles on which linear polyacrylamide chains are fixed by a graft polymerisation. The capabilities of such columns for separating proteins and nucleic acids is documented by some examples.
Affinity Partitioning of Proteins
Authors: Kula M.‐R. , Walsdorf A. , Cordes A. 
Published: July 2012

AbstractIn affinity partitioning the effectivity of purification is a function of the number of binding sites of the protein and the dissociation constant of the ligand/protein complex. To design an optimal purification process a mathematical model has been developed. Taking formate dehydrogenase from Candida boidinii as an example these data were evaluated in single stage experiments and could be confirmed by affinity partition chromatography.
Reactive (Affinity) Extraction of Enzymes from Biomass
Authors: Schustolla D. , Ledoux C. , Papamichael N. , Hustedt H. 
Published: July 2012

AbstractThe separation of intracellular enzymes from disintegrated microbial cells is one of the most crucial steps in enzyme production. One way to overcome this problem is the application of physical extraction in polymer/salt based aqueous phase systems. An alternative, more recent approach being still under investigation is reactive extraction — called affinity partitioning/extraction in biotechnology — carried out in aqueous two‐polymer phase systems.In the intended contribution affinity extraction will be discussed with regard to the— physico‐chemical basis and general potential• parameters influencing affinity partitioning• modeling• selectivity• product yield• ways to improve performances• “product elution”/product separation from the ligand• limitations• comparison with physical extraction and— technical aspects• scale‐up• ligand recycling• continuous processing• economicsThe presentation will be based on recent literature data and several process examples being presently studied in the author's laboratories.
Chances of Reactive Extraction of Primary and Secondary Metabolites
Authors: Abbasian K. , Degener W. , Schügerl K. 
Published: July 2012

AbstractReactive extraction of special metabolites is of interest, since the technique can provide higher distribution coefficients than pure physical extraction. In addition, very polar carboxylic acids can only be extracted by using extractants such as organophosphorus compounds or high molecular weigth amines. In this paper, the extraction of typical metabolites such as penicillin G and α amino acids is discussed in regard to the nature of the extractant and modifier used.
Reactive Extraction of Citric Acid from an Aqueous Fermentation Broth
Authors: Bauer U. , Marr R. , Rückl W. , Siebenhofer M. 
Published: July 2012

AbstractThe common precipitation process for the isolation of citric acid produces 2,5 tons of waste per ton citric acid. This paper presents a way to separate citric acid from a fermentation broth by avoiding the waste production of CaSO4. A combination of an extraction/reextraction process using a tertiary‐amine‐containing solvent was developed.
Downstream Processing — Solvent Extraction and Liquid Membrane Permeation
Authors: Bart H. J. , Marr R. , Bauer U. 
Published: July 2012

AbstractUnit operations with intrinsic chemical reactions, like solvent extraction (SX) and liquid membrane permeation (LMP), offer the possibility to design selective separation processes. Ion exchanger types used for downstream processing are discussed. The influence of chemical parameters on the separation of an amino acid (1‐phenylanaline) is shown as an example. A comparison of LMP and SX technique is given with emphasis on the difference of mass transfer mechanism and devices needed.
Two‐Phase Kinetics of the Solubilization in Reverse Micelles — Extraction of Lysozyme
Authors: Plucinski P. , Nitsch W. 
Published: July 2012

AbstractThe rate of the solubilization of lysozyme in reverse AOT micelles was measured in a liquid‐liquid system using a two‐phase stirred cell. — Varying convectional motion on both sides of the horizontal interface in the used cell and applying the general concept of mass transfer resistances, it was possible to show that lysozyme transport was generally controlled by the convective process in the aqueous phase. The striking effect concerns the obtained flow dependencies of the transport coefficients, which can be attributed to the change of the fluid dynamic state of the interface. This leads to a comparison with known gradients of the interfacial tension in the used stirred cell, and thereby the appearance of negative tensions connected with interfacial encapsulation is derived.
Selection of Organic Solvents for in situ Extraction of Ethanol from Fermentations with Clostridium Thermohydrosulfuricum
Authors: Job Christopher , Blass Eckhart , Schertler Cosima , Staudenbauer Walter L. 
Published: July 2012

AbstractFifteen organic solvents were examined to determine their biocompatibility for in situ extraction of fermentation products from cultures of the thermophilic anaerobe Clostridium thermohydrosulfuricum. Five solvents (hexadecane, isooctane, kerosene, oleyl alcohol, Shellsol TD) were found to be non‐toxic to Clostridium thermohydrosulfuricum. Interfacial tensions, phase separation and partition coefficients for ethanol of the biocompatible solvents were compared. With the exception of kerosene, these solvents showed good separation from the aqueous phase. Oleyl alcohol was found to have the highest partition coefficient for ethanol (KD = 0.34 at 65°T). A continuous fermentation for 1200 hours showed no inhibition effects due to oleyl alcohol as extraction solvent.
Investigation of Retention Behaviour in Packed Column SFC
Authors: Upnmoor D. , Brunner G. 
Published: July 2012

AbstractRetention behaviour in supercritical fluid chromatography (SFC) with packed columns was investigated using two model mixtures. Xanthine bases (caffeine, theophylline, theobromine) were chosen as a relatively polar group while fat‐soluble vitamins (vitamin A, vitamin D2, vitamin E) were taken as a mixture of lower polarity. — Carbon dioxide based supercritical fluid chromatography of the model analytes was performed on columns with different stationary phases, e.g. alkyl‐, aminopropyl‐ and cyanopropyl‐bonded silica. Retention and selectivity were measured as a function of polar modifier content in carbon dioxide with methanol and 2‐propanol as organic modifiers. The results indicate that retention is not only determined by the molar content of alcohol modifier in the mobile phase but also by its polarity expressed by the Snyder parameter. For the polar solutes the adsorption of modifier molecules on residual silanol groups plays an important role.
Reduction of Membrane Fouling by Means of an Electric Field During Ultrafiltration of Protein Solutions
Authors: Brunner G. , Okoro E. 
Published: July 2012

AbstractPermeate flow during ultrafiltration of protein solutions drops to a fraction of the initial permeate flow due to membrane fouling. Direct current field, applied vertically to the membrane surface offers one possibility to enhance permeate flow in such a situation. — Using aqueous albumim solutions as a model system an investigation of the influence of pH, membrane material, electrical conductivity of the solution and field intensity was carried out. — Substantial enhancement of permeate flow could be observed for fluoro polymer membranes. At high pH‐values permeate flows exceed that of pure water. With increasing conductivity and increasing field intensity permeate flow also increases.
A Combination of Selective Mass Transport and Enzymatic Reaction: Enzyme Immobilization in Liquid Surfactant Membranes
Authors: Scheper T. , Barenschee E. R. , Barenschee T. , Hasler A. , Makryaleas K. , Schügerl K. 
Published: July 2012

AbstractThe liquid surfactant membrane technique for immobilization of enzymes in enzyme emulsions is described in this paper. This offers the combination of selective mass transport and specific enzymatic reaction. Several applications are presented to show the potential of this technique for integration of enzymatic reaction, purification, and product accumulation to one single process step. A strategy for membrane optimization is given and discussed. In addition information on the selective mass transport through liquid surfactant membranes (enzyme emulsions and solid supported liquid membranes) and on the reaction modeling are presented.
Free Flow Electrophoresis as a Purification Step of High Versatility for Bioproducts
Authors: Rutte Ralph 
Published: July 2012

AbstractElectrophoresis in general separates particles or molecules according to their specific mobility in an electric field. The mobility is a function of the net charge of the particle or the molecule, as well as of its size and the viscosity of the carrier. Unlike conventional gel electrophoresis (e.g. PAGE) free flow electrophoresis (FFE) continuously separates the components of a sample in ordinary buffer liquids. Thus in the case of FFE the net charge becomes the most important parameter. FFE devices are designed in a way that the influences of disturbing phenomena (e.g. electroosmosis, free convection, or adsorption), which lower the quality of the separation, are minimized. — Two FFE devices (ELPHOR VaP 22; BIOSTREAM) have been tested using a monoclonal antibody (IgG) and bovine serum albumin (BSA) as model substances. The aim of the tests was to determine the applicability of FFE to medium and large scale protein purification. — Compared to other purification methods (i.e. ion exchange) the costs of a FFE step in downstream processing are high. Thus the use of FFE in fields other than research may be limited to products of high value, where chromatography fails. There free flow electrophoresis may exhibit its specific advantages in the purification of fluids containing particles such as cell debris or organelles, or even in the separation of viable cells.
Continuous Separation of Proteins by Free‐Flow Zone Electrophoresis
Authors: Nath Sunil , Schütte Horst , Hustedt Helmut , Deckwer Wolf‐Dieter 
Published: July 2012

AbstractFree‐Flow Electrophoresis is a continuous technique for the separation of biological molecules and particles on a preparative scale. In the technique of Free‐Flow Zone Electrophoresis, an electrolyte with a certain pH and conductivity is continuously admitted in a laminar flow at the top of a rectangular electrophoresis chamber (50 cm x 10 cm x 0.05 cm on the Bender and Hobein VAP‐22 machine). A stream of sample is also injected continuously into the electrolyte flow. An electric field transverse to the electrolyte flow separates the sample according to differences in electrophoretic mobility. The separated products are collected by 90 output tubes at the lower end of the chamber. Free‐Flow Zone Electrophoresis has been used for throughput studies on a mixture of model proteins and for the separation of enzymes in Candida boidinii crude extract. Simultaneous separation of proteins, cell particles and debris was obtained. We have looked at the influence of electric field strength (100 – 150 V/cm), buffer residence time in the chamber (2 – 5 min), sample flow rate (1.5 – 6 ml/h) and sample concentration (2.5 – 40 mg/ml) on separation resolution, peak sharpness and skewness and throughput. Qualitative explanations for observed phenomena have been given. For throughput studies, multiple injections of the sample into the chamber were used. A throughput of 500 mg protein per hour was obtained. Other Free‐Flow techniques i.e. Free‐Flow Isoelectric focusing, Isotachophoresis and Field‐Step Electrophoresis can also be implemented on this electrophoresis apparatus.
Thermodynamics of Aqueous Electrolyte Solutions with Liquid‐Liquid Phase Separation
Authors: Weingärtner Hermann 
Published: July 2012

AbstractInitiated by the recent observation of liquid‐liquid phase separation in aqueous solutions of tetra‐n‐butylammonium thiocyanate, a treatment of the thermodynamic properties of aqueous electrolyte solutions in relation to liquid‐liquid phase equilibria is given. For analyzing the thermodynamic data, the ion interaction approach of Pitzer is used in which the osmotic coefficient is described by a long‐range term for Coulombic interaction plus a virial coefficient series to account for short‐range specific interactions. It is shown that the ion‐interaction approach is flexible enough to incorporate liquid‐liquid phase equilibria in a natural and simple way. For 1:1 electrolytes liquid‐liquid coexistence curves are predicted if the second virial coefficients entering into Pitzer's theory are large and negative and the third (or higher) virial coefficients are positive. Experimental data show that largely negative second virial coefficients are generally present if large cations are combined with large anions, so that coexistence curves are predicted for aqueous solutions of tetraalkylammonium salts with large anions. Many of these salts are practically insoluble at room temperature, but at higher temperatures, where crystallization does not interfere, these predictions are experimentally confirmed for tetrabutylammonium iodide, tetrapropylammonium perchlorate and tetrapropylammonium picrate. For 2:2 electrolytes phase separation can result from the behaviour of the long‐range contribution to the osmotic coefficient alone, even if the virial coefficients are positive. Thermodynamic data for aqueous MgSO4 solutions at elevated temperatures indicate a coexistence curve with a lower consolute point at about 239°C, submerged by the crystallization curve. The same approach predicts a coexistence curve for aqueous UO2SO4 solutions, in qualitative agreement with the observation of a lower critical point at 286°C. In earlier interpretations this coexistence curve has been attributed to the peculiar properties of the uranyl ion, but it would appear that to a first approximation the miscibility gap in aqueous UO2SO4 at elevated temperatures represents a general property of 2:2 electrolytes, which for UO2SO4 becomes visible due to the high solubility of this salt.
Coherence in Disordered Condensed Matter. IV: Conductivities of Molten Alkali Chlorides — A Novel Relation
Authors: Chatzidimitriou‐Dreismann C. A. , Brändas E. J. 
Published: July 2012

AbstractThe mechanism of the high electric conductivity of molten alkali chlorides is analysed in the light of the Complex Scaling Method (CSM) and its extension to quantum statistics of condensed phases. It is argued that the considered conductivities are due to quantum delocalization of the ions in the melt. Within the CSM‐treatment, a novel relation concerning the considered molar conductivities is derived. Its connection with experimental results on LiCl, NaCl, KCl and RbCl in the temperature range T = 800°C‐900°C reveals that the charge fluctuations in all these melts exhibit the same relaxation time. CsCl shows deviations from the above relation. A possible connection of this finding with the crystalline structures of the corresponding compounds is suggested. The “practical” importance of the relation derived is indicated.
Photochemistry and Radiation Chemistry of Colloidal Semiconductors 34. Properties of Q‐PbS
Authors: Gallardo S. , Gutiérrez M. , Henglein A. , Janata E. 
Published: July 2012

AbstractPrecipitation of lead ions by hydrogen sulfide in the presence of poly(vinyl alcohol) in aqueous or methanolic solution yields Q‐PbS particles (quantized particles) which have a structured absorption spectrum. The particles have a rod‐like or spherical shape (size quantization mainly in two or three dimensions, respectively). PbS with a structured absorption can also be made in acetonitrile using poly(ethylene oxide) as stabilizer. PbS stabilized by sodium polyphosphate has a structureless absorption spectrum. — Depending on the method of preparation and surface modification after preparation PbS samples fluorescing in the red or/and infrared are obtained. Methyl viologen generally quenches but can in certain cases promote the fluorescence when it is present in low concentration. Oxygen quenches when the colloid is stabilized by polyphosphate. — The rate of the photoanodic dissolution in the presence of air is increased by methyl viologen. Half reduced methyl viologen does not transfer an electron to Q‐PbS but can do so in the case of larger particles. — Illumination under argon leads to increased Ostwald ripening of the particles. However, when sulfite is present in the deaerated solution, photoanodic dissolution takes place. — Attack by hydroxyl radicals generated radiolytically leads to Pb2+ + SO2−4. The fluorescence of a Q‐PbS particle is efficiently decreased after the attack by a single OH radical (i.e. after injection of one positive hole). — Single electron transfer from 1‐hydroxy methyl ethyl radicals, (CH3)2COH, to Q‐PbS also leads to a decrease in fluorescence. These effects are attributed to interactions of the charge carriers deposited by the radicals on the colloidal particles with the exitonic state produced by light absorption. — Accumulated electron transfer to PbS‐particles from organic radicals yields lead metal and organic sulfur compounds. In the beginning of this process, the fluorescence strongly increases (10% quantum yield) which is explained by destruction of surface defect states.
Study of the Electrical Admittance due to Electron‐Hole Recombination in N‐GaAs and N‐GaP Electrodes
Authors: Vanmaekelbergh D. , Heide R. P. Ter , Kruijt W. 
Published: July 2012

AbstractThe additional impedance observed at n‐GaAs and N‐GaP electrodes under conditions of hole injection or illumination was measured as a function of the frequency, the generation rate of holes and the electrode potential. The additional capacitance in the potential region where the minority carriers (holes) recombine with electrons is analysed on the basis of two models, one accounting for recombination at the surface, the other dealing with recombination in the depletion layer. It could be concluded that in n‐GaAs electrodes surface recombination prevails, while in n‐GaP electrodes recombination in the depletion layer must also be taken into account. These results are compared with those obtained from independent measurement techniques.
Ionic Interactions in Aqueous Solutions of Organic Electrolytes: The System NaCl + NaHSucc + H2O at 25°C
Authors: Esteso Miguel A. , Fernandez‐Merida Luis , Gonzalez‐Diaz Oscar M. , Hernandez‐Luis Felipe F. 
Published: July 2012

AbstractActivity coefficients for the mixed system NaCl + NaHSucc + H2O (where Succ stands for the succinate anion) are determined from emf measurements. In all cases, the stoichiometric ionic strength was kept constant at 0.1, 0.5, 1, 2 and 3 mol kg−1, and the temperature at 25°C. At each ionic strength, different ionic strength fractions, yB = mB/(mA + mB), are studied. The results obtained were analyzed by means of various theoretical or empiric‐theoretical models (Harned, Scatchard‐Rush‐Johnson and Pitzer). From these, it can be deduced that some ionic association must have taken place in this system in which the presence of the HSucc anions play an important role. So, not only the (HSucc):‐ dimers, but also the triple interactions between like‐charged ions (CI‐HSucc‐HSucc) and the less important interactions between unlike‐charged ions (Na‐CI‐ HSucc) must be taken into account in this system, if the experimental results within the experimental error are to fit properly. Because the original Pitzer model does not consider these triple interactions, it cannot adequately describe the behaviour of this mixed electrolyte and, therefore, the Chan and Khoo extension of this equation must be used.
NMR Relaxation of Tetrahydrofuran in Clathrate Hydrate
Authors: Albayrak C. , Zeidler M. D. , Küchler R. , Kanert O. 
Published: July 2012

AbstractThe reorientational motion of the tetrahydrofuran guest molecule in the clathrate hydrate C4H8O · 17D2O was studied by proton NMR spin‐lattice relaxation measurements in the temperature range 4 — 278 K. The results are interpreted by a Davidson‐Cole distribution of correlation times with a distribution parameter ß = 0.12. The maximum or cutoff time τ0 in this distribution obeys an activation law with prefactor 3.75 · 10−13 s and activation energy 4140 J mol−1. At temperatures below 20 K the motion of the guest molecules can be described by a coupled ensemble of quantummechanical hindered rotators where the reorientation rate is again described by a Davidson‐Cole distribution.
Optical Rotation of Liquid Crystals with Absorbing Dopants
Authors: Rachkevich V. S. 
Published: July 2012

AbstractThe optical rotatory dispersion spectra of cholesteric liquid crystals with dopants absorbing within and beyond of the matrix selective reflection region are studied. The influence of temperature, dopant molecule concentration and size upon the shape and position of the above spectra is considered. The temperature shift of the induced gyrotropy band which correlates with a similar shift in the absorption spectra of the dopant dissolved in the liquid crystalline matrix is found. The shift value increases with increasing the dopant order parameter. A method for estimation of the cholesteric liquid crystal order parameter based on the induced gyrotropy spectra has been discussed.
Liquid Junction Potential at the Salt Bridge in Heterogeneous Systems
Authors: Tschapek M. , Wasowski C. , Sanchez R. M. Torres 
Published: July 2012

AbstractKnowledge of the limiting equivalent conductivity of the potential determining ions (i.e. the charges) permits to calculate the liquid junction potential at the salt bridge heterogeneous systems. — Calculations show that the salt bridge adequately suppresses the liquid junction potential also in heterogeneous systems. No abnormal junction potential occurs; not even under extremely severe conditions when the counterion transference number = l and the surface charges concentration > 1 mol l−1.