bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrational Spectroscopic and Dielectric Studies of Nitromethane in Liquid Mixtures
Authors: Knözinger Erich , Kollhoff Helmut , Wittenbeck Rüdiger
Published: July 2012

IR spectroscopic data obtained for binary and ternary liquid mixtures show that nitromethane may act as proton donor for weak hydrogen bonds with appropriate acceptor groups. At low concentrations of nitromethane in CCl4 an equilibrium between monomer molecules and predominantly antiparallel (⇌) dimers may be inferred from IR spectroscopic and static dielectric studies. The IR and Raman spectroscopic data provide conclusive evidence for the preservation of a predominantly antiparallel correlation at high nitromethane concentrations and even in pure liquid nitromethane.
Theoretische und experimentelle Untersuchungen über die Stromverteilung in elektrochemischen Zellen mit Gasverzehrelektroden
Authors: Führer Oliver
Published: July 2012

This paper deals with charge dislocation problems occuring during overcharge in sealed nickel‐cadmium‐accumulators. In the case of catalyst particle forming gas consumption electrodes, the model “point electrode over flat electrode” was used for the determination of the current distribution. It was solved for linear polarized electrodes. The solution integral is analyzed numerically. A test apparatus for experimental testing was designed and built. This enlarged model enables a measurement of the current distribution. The theoretically predicted results are confirmed experimentally. Additionally the current distribution in the model “point electrode between two ideal unpolarized electrodes” is calculated.
aci‐nitromethane —generated and characterized by neutralization reionization mass spectrometry
Authors: Egsgaard Helge , Carlsen Lars , Florêncio Helena , Drewello Thomas , Schwarz Helmut
Published: July 2012

Neutral gaseous aci‐nitromethane has been generated and characterized by neutralization/reionization mass spectrometry (NRMS). Decomposition and isomerization patterns have been established based on studies of the corresponding nitromethane and methyl nitrite isomers in combination with appropriate deuterium labelling experiments. A comparison of the isomeric CH2NO(OH), CH3NO2 and CH3ONO neutrals as well as radical cations is presented.
Amplification of intrinsic fluctuations along the center manifold
Authors: Fernández Ariel
Published: July 2012

We consider a dissipative system sustaining a center manifold beyond a hard‐mode instability. The evolution towards the far‐from‐equilibrium organization is shown to be caused by the correlation of subsystems with a common coarse‐grained phase space. Critical induction periods are calculated for the onset of macroscopic organization.
Enthalpies of mixing of KCl‐AlCl3 melts
Authors: Hatem G. , Østvold T.
Published: July 2012

Partial enthalpies of mixing of solid KCl in the liquid mixture KCl‐AlCl3 were determined calorimetrically at 543 K in the concentration region 0.48 < XAlCl3 < 0.75. ΔH̄KCl(1) is negative and shows as expected a pronounced variation at XKCl = 0.5. Calculated integral enthalpies for the subsystems KCl‐KAlCl4, AlCl3‐KAlCl4 show regular enthalpies of mixing with the values — 3.1 kJ mol−1 and — 7.3 kJ mol−1, respectively, for XKAlCl4 = 0.5.
A structural phase transition in RNA
Authors: Fernández Ariel
Published: July 2012

We analyze a soliton‐induced structural phase transition in double‐stranded RNA. A novel feature emerges which is absent in the extensively studied DNA situation: A tautomeric rearrangement induced by the kink on the ribose residue is coupled directly to the cleavage of the hydrogen bond in the base pair. This feature appears to be a consequence of a potential catalytic rǒle of RNA in proton transfer events. Thus, a topological soliton is effective in energy transfer.
Photoionization Mass Spectrometry and Valence Photoelectron‐Photoion Coincidence Spectroscopy of Isolated Clusters in a Molecular Beam
Authors: Rademann Klaus
Published: July 2012

A new and versatile photoelectron‐photoion coincidence spectrometer has been developed and advanced to facilitate for the first time the investigation of the valence electronic structure of isolated metal atom clusters up to a mass range of approximately 40000 amu. The neutral cluster distribution, which is synthesized in a doubly skimmed seeded supersonic molecular beam, is probed 130 mm down‐stream by the pulsed and monochromatized output of a newly developed sub‐nanosecond vacuum‐UV/UV‐flashlamp in the photon energy range between 3 and 11.8 eV. Single photoelectrons are energy analyzed and time‐correlated detected either in a field‐free or in a magnetic type time‐of‐flight spectrometer. The corresponding cluster cations are mass analyzed and counted in coincidence in a modified Wiley‐McLaren time‐of‐flight mass spectrometer. The data acquisition electronics is capable of recording and storing simultaneously photoion‐photoelectron coincidence spectra of all those neutral clusters that have sufficient intensity in the molecular beam. First photoelectron spectroscopic results for mass selected mercury clusters up to Hg78 are used to discuss the performance of this new technique. — A photoionization mass spectrometry study of sodium cluster beams has revealed shell closings at the sizes being predicted by the cluster shell model. For the case of large mercury clusters a gradual transition from van der Waals type bonding to metallic cohesion occurs in the size range between 20 and 70 atoms. The occurrence of this transition, which has been observed by energy resolved mass spectrometry, is strongly confirmed by photoelectron‐photoion coincidence spectroscopy. Moreover, the photoelectron spectra clearly indicate that the evolution of the valence band structure toward the metallic state is almost fully accomplished for clusters larger than Hg70. The gradually size dependent transition is found to be induced by the rapid increase of the averaged number of nearest neighbours. Hence, the transition can be explained semi‐quantitatively in the framework of the tight‐binding approximation.
Dielectric Relaxation Rate and Static Dielectric Permittivity of Water and Aqueous Solutions at High Pressures
Authors: Pottel R. , Asselborn E. , Eck R. , Tresp V.
Published: July 2012

Measurements of the complex dielectric permittivity of water and various concentrated aqueous electrolyte and non‐electrolyte solutions were performed at several frequencies between 5.3 and 18 GHz in dependence of hydrostatic pressure up to 200 MPa at temperatures 5 and 25°C. The dielectric relaxation rate and static permittivity as derived from the experimental spectra show characteristic variations with rising pressure. These are discussed with respect to pressure‐induced changes in molecular motion and spatial arrangement.
Spectroscopic and Electrochemical Behavior of Polypyrrole Films Incorporating Methylene Blue, and Their Enhancement in Electrochromism
Authors: Amemiya T. , Itoh K. , Fujishima A.
Published: July 2012

A cationic dye methylene blue (M. B.) was incorporated into polypyrrole (P. P.) films in the course of electrochemical polymerization of pyrrole from aqueous solution containing pyrrole, methylene blue and KCl. The films obtained were blue in color. Absorption bands of M. B. incorporated into P. P. films were broadened compared with those of M. B. in water or in a solution of pyrrole monomer. Methylene Blue incorporated into P. P. films is probably aggregated and is nearly in solid state. Molar absorption coefficient (ϵ) for M. B. incorporated into P.P. films was about half the value of ϵ for M.B. in aqueous solution. The concentration of M.B. incorporated into P.P. films was ca. 0.42—0.49 mol dm−3, while the original concentration of M.B. was ca. 1 mmol dm−3. Methylene Blue was concentrated by a factor of 420–490. The colors of the film changed reversibly to blue by oxidation and to transparent yellow by reduction. The color change was more remarkable than that of P.P. film itself. This is because M.B. was reduced to form leuco M.B. (colorless material) and was reoxidized to form M.B. The response time of color changes between blue and transparent yellow was ca. 2 s.
A Comparative Study of the Solubility and Thermodynamics of Hydrogen in Pd1‐xREx (RE = Dy, Gd, Sm, and Y; x = 0.05 and 0.08) Solid Solution Alloys
Authors: Ramaprabhu Sundara , Rajalakshmi Natarajan , Weiss Alarich
Published: July 2012

Pressure‐composition‐temperature absorption isotherms have been determined for the Pd1‐xREx (RE = Dy, Gd, Sm, and Y; x = 0.05 and 0.08) solid solution face centered cubic alloys in the pressure and temperature ranges 2 ≦ P(H2)/mbar ≦ 1000 and 473 ≦ T/K ≦ 873 using the manometric method. The partial molar enthalpy of solution of hydrogen at infinite dilution (ΔH̄0H) becomes more exothermic with increasing content of RE. The partial molar excess entropy of hydrogen solution at infinite dilution (ΔS̄E.0H) decreases with xRE. A correlation of the atomic diameter (dRE) of the substituting rare‐earth metals when in solution in palladium with ΔH̄0H and with the metal‐hydrogen interaction shows that the increase in the exothermicity of the Pd1‐xREx solid solution alloys is due to the lattice expansion and an attractive metal‐hydrogen interaction. From the correlation of ΔH̄0H with dRE of Pd1‐xREx (x = 0.05 and 0.075), ΔH̄0H of Pd1‐xREx (RE = Yb, Ho, and Eu; x = 0.05 and 0.075) solid solution alloys have been predicted. The dependence of ΔH̄0H of the “expanded” and “contracted” Pd1‐xMx alloys on the size of the octahedral interstitial hole sites (rh) occupied by hydrogen atoms is discussed.
A SANS Study of High Pressure Phase Transitions in Model Biomembranes
Authors: Winter R. , Pilgrim W.‐C.
Published: July 2012

The phase behaviour and thermotropic and barotropic phase transitions of different model biomembranes (DPPC, DMPC, DEPC and POPC*)), which consist of different hydrocarbon chain length and degree of unsaturation, have been investigated by small‐angle neutron scattering (SANS) as a function of temperature and pressure up to about 65°C and 3 kbar, respectively. A pressure induced structural phase transition from a liquid‐crystalline to a gel state is observed for the whole temperature range studied. The pressure of this transition increases with increasing temperature with a slope dTm/dP of about 21°C/kbar, which is common for all the different lipids investigated. The SANS experiments indicate that the effect of the two trans double bonds in DEPC and the cis double bond in the sn‐2 hydrocarbon chain of POPC enhances the conformational disorder in the hydrocarbon chains not only in the liquid‐crystalline, but also in the gel state. For DEPC and POPC the prefered structural conformation in the gel state is probably not tilted as it is in the gel state of the saturated phospholipids DMPC and DPPC. Only for DPPC multilamellar vesicles, an additional gel phase at higher pressures has been observed, which can be ascribed to an interdigitation of the hydrocarbon chains of opposing chains in the lipid bilayer system.
Incision‐Excision DNA Repair Model: A Theoretical Analysis of the Effect of Enzyme Concentrations on DNA Repair
Authors: Bhat Ramachandra , Rao Saligrama C. Subba
Published: July 2012

Relationships between the concentration of exonuclease, DNA polymerase, and DNA ligase participating in the DNA incision‐excision repair pathway have been derived by applying steady state conditions to concentration of the species of interest. The analysis utilizes concentrations of damage excised, gapped DNA (DNAm—n) and gap filled unligated DNA (DNAm) at the steady state as the parameters to measure the extent of DNA repair. The concentrations of DNAm—n and DNAm have been expressed in terms of experimentally determinable constants such as Km, catalytic constants for the enzymes, enzyme, and substrate DNA concentrations, making it possible to verify the theoretical predictions. The analysis predicts a low ratio of exonuclease to polymerase to observe any significant repair activity, a conclusion consistent with in vitro observation of Hamilton et al. (1974) that significant DNA repair is observed when exonuclease: polymerase ratio is 0.5. The analyis predicts fairly large concentrations of DNA ligase to minimize DNAm concentration at the steady state. Under specific conditions, reversal of ligation has been predicted and has been suggested as a possible mechanism of initiation of multi‐centered DNA replication in eukaryotes. This suggestion has been substantiated by experimental demonstration that DNA nicked in the presence of DNA ligase and AMP is substrate for M. Luteus DNA polymerase but not for T4 DNA polymerase, suggesting that adenylated DNA intermediate is formed and only cleaved by 5′—3′ exonuclease which is present in vivo, and has been isolated and characterized. The relationships have been numerically evaluated for different enzyme concentrations using derived and literature values for the constants. The potential application of these results for in vitro introduction of “errors” into DNA has been indicated.
A Study of Ternary Geometrical Models
Authors: Chou Kuo‐Chih , Austin Chang Y.
Published: July 2012

The ternary geometrical model has been summarized, and a general formula has been presented for calculating the ternary Gibbs free energy of mixing in terms of three binary systems. This formula is applicable to any ternary model, including previous models and the many new models presented in this paper. A new nomenclature system is suggested for distinguishing all kinds of models which is very simple and convenient both for use and memory. Finally, the limiting activity coefficient of the third component in a binary solution is discussed in terms of various models.
Acid‐Base Properties of N,N‐bis‐(2‐hydroxyethyl) Glycine (Bicine) Buffers in Sea Water at Different Temperatures
Authors: El‐Harakany A. A. , Sadek H. , Taha A. A. , Khadr A. M.
Published: July 2012

The dissociation constant of bicinium ion in seven synthetic sea water samples at five temperatures from 25 to 45°C have been determined by emf measurements of cell:

Pt, H2 (g, 1 atm)/bicine HCl (m1)bicine(m2) in SW/AgCl, Ag.

The standard potentials in sea water media were determined in similar cells containing HCl. It is noticed that the pK values show small variation with temperature at a fixed salinity, and increase with incrasing the salinity of the medium up to 35%0 S. The associated the thermodynamic functions ΔG0, ΔS0 and ΔC0p for the dissociation process have been evaluated from the variation of the dissociation constant with temperature. The results are attributable to solute‐solvent interactions.
Streaming Potential Across Nafion Membranes
Authors: Scibona Giancarlo , Botrê Francesco , Botrê Claudio , Fabiani Claudio , Croce Fausto
Published: July 2012

Membranes / Nonequilibrium Phenomena / Streaming Potential / Thermodynamics / Transport Properties

The streaming potential Δϕ which arises between the uni‐univalent electrolyte solutions of the same concentration separated by nafion 125 membrane in the presence of a pressure difference ΔPapplied across the membrane has been studied. Different electrolytes have been studied, namely NaCl, LiOH, NaOH, KOH and CsOH. — The quantity Δϕ/ΔPincreases in the order Li > Na > K > Cs. According to the non‐equilibrium thermodynamic theories the ratio (Δϕ/ΔP)/Jv/I), withJv (volume flow)/I(electrical current flow) the electroosmotic quantity, approaches unit.
Electrolyte and Water Osmotic Flow Coefficients in Nafion Membranes
Authors: Scibona Giancarlo , Radatti Nunzia , Botrê Claudio , Botrê Francesco , Gavelli Giorgio
Published: July 2012

The isothermal transport coefficients describing the NaCl, volume and water osmotic flows across Nafion membranes are studied. These transport coefficients and others already reported are used to obtain the Lij phenomenological coefficients related to the flows of ions and water in the membrane.
Ionic Mobilities at Infinite Dilution: Structural Aspects
Authors: Kessler Y. M. , Kumeev R. S. , Vaisman I. I. , Lyalina R. B. , Bratishko R. H.
Published: July 2012

Empirical correlations between ionic mobilities and parameters characteristic of the solvent molecules motions for a variety of single ions and 1‐1 electrolytes at infinite dilution in 19 one‐component solvents and 8 aqueous‐nonaqueous mixed solvents are found, presented and discussed. The parameters are the self‐diffusion coefficient, the dipole relaxation time, the rotational correlation time of various NMR vectors, and the residence time of solvent molecules in the first ion solvation shell. The residual friction coefficients are considered in a more theoretical vein.
Side Reactions in Electroless Copper Solutions with Formaldehyde as Reducing Agent
Authors: van Meerakker J. E. A. M. , Scholtens E.
Published: July 2012

In alkaline electroless copper solutions with formaldehyde as reducing agent, side reactions between formaldehyde and hydroxide occur. In solutions of formaldehyde and sodium hydroxide below 70°C the only reaction found is the Cannizzaro reaction. The rate constant of this reaction was determined at different temperatures, yielding an activation energy of 87 kJ·mol−1. An increase of Na+ concentration leads to an increase of the rate of this reaction. The nature of the anion had no effect. Above 70°C a second reaction proceeds: aldol condensation. Oxygen suppletion inhibits the aldol condensation. Analyses of continuously operating electroless copper solutions showed that the kinetics found in alkaline HCHO solutions could be applied directly to real plating solutions.
Efficient Singlet Energy Migration in Amorphous Copolymer Film Having No Excimer Forming Site: Poly[2‐(9‐carbazolyl)ethyl methacrylate‐co‐methyl methacrylate]
Authors: Ohmori Satoru , Ito Shinzaburo , Yamamoto Masahide
Published: July 2012

Energy Transfer / Fluorescence / Polymers

Singlet energy migration in the solid state for the homopolymer of 2‐(9‐carbazolyl)ethyl methacrylate and the copolymers with methyl methacrylate was investigated using perylene as an acceptor molecule. In this system, the carbazole (Cz) chromophore is dispersed uniformly even in the homopolymer and a deep trap is not formed. The fluorescence spectra and their decays were measured for these samples and the energy migration was analyzed on the basis of three models, i.e., random hopping model, Smoluchowski diffusion model, and Yokota‐Tanimoto (Y‐T) Padé model. Among these models, the Y‐T Padé model gave the most reliable diffusion coefficient. The diffusion coefficient was obtained in a wide range of carbazole concentrations from 0.14 to 4.4 mol/l and we obtained the following conclusions.

1. The energy diffusion coefficient D is proportional to [Cz]4/3 as predicted from the Förster mechanism even for the samples of Cz concentration higher than 1 mol/l.

2. At a low temperature, the energy migration rate becomes slow owing to shallow traps. The activation energy in a low temperature region is about 4 kJ/mol.

3. Fast energy migration (D = 2.0·10−4 cm2/s) was found for the polymers whose concentration of Cz‐chromophore is high, but do not form excimer.
Collision‐Induced Intersystem Crossing in CH2 (ã 1A1): A Quantitative Analysis Using the Mixed‐State Model
Authors: Bley U. , Koch M. , Temps F. , Wagner H. Gg.
Published: July 2012

The mechanism of collision‐induced intersystem crossing (ISC) in CH2 from the ã 1A1 first excited singlet to the X̃ 3B1, triplet ground electronic state, CH2 (ã) + M → CH2 (X̃) + M, is investigated. Collisional ISC rate constants are calculated for four selected collider gases, M = He, Ar, N2, and CH4, using the “mixed‐state” model of Freed and Gelbart. The most important triplet‐perturbed rotational levels in the ã‐state are identified from the spectroscopic data reported in the literature. The rates of rotational relaxation processes, which according to the model effectively govern the collision‐induced ISC, are determined by studying the collision broadening of CH2 (X̃) Far Infrared Laser Magnetic Resonance (FIR‐LMR) transitions. The collisional ISC rate constants for CH2 in the ortho nuclear spin modification are calculated to be kISC = 1.4 · 1012, 4.0 · 1012, 7.8 · 1012, and 6.6 · 1012 cm3/mol · s for M = He, Ar, N2, and CH4, respectively. The results are in good agreement with published experimental rate constants.
An Investigation of the Reaction Between CH3 Radicals and Acetaldehyde‐d4 at High Temperatures
Authors: Klatt M. , Wagner H. Gg.
Published: July 2012

The reaction between CH3 radicals and acetaldehyde‐d4 was investigated behind incident shock waves at temperatures between 1050 and 1190 K and total densities about 2 · 1−6 mol cm−3. — The consumption of CH3 was followed by time‐resolved UV‐absorption measurements at λ = 216.5 nm. The measurements were carried out with perdeuterated acetaldehyde. — A rate constant of 1.1 · 1011 cm3 mole−1 s−1 for the reaction

CH3 + CD3 → CH3 + CD3CO (1)

at temperatures around 1100 K was determined.
Radiationless Deactivation of the Fluorescent State of 9‐Methoxyanthracene and of Related meso‐Substituted Anthracenes
Authors: Schoof Sabine , Güsten Hans
Published: July 2012

The temperature dependence of the fluorescence quantum yield, the fluorescence decay time, and the triplet‐triplet absorption spectrum of 9‐methoxyanthracene have been measured in n‐heptane. The sum of the fluorescence quantum yield and the quantum yield for intersystem crossing of 9‐methoxyanthracene and two partially deuterated 9‐methoxyanthracenes at room temperature is only ∼0.60. While the fluorescence quantum yield in methyl methacrylate has nearly the same value as in n‐heptane, the fluorescence quantum yield is twice as high in the rigid matrix of PMMA. When passing from fluid solutions to the PMMA matrix, a dramatic increase in the fluorescence quantum yield can be demonstrated for the following meso‐substituted anthracenes: 9.‐tert.butyl‐, 9‐cyano, 10‐tert.butyl‐ and 9‐cyano,10‐methoxyanthracene. Anthracene, 9‐chloro‐ and 9‐phenylanthracene do not show neither this matrix effect nor an anomalous temperature dependence on the fluorescence quantum yield in solution. — The anomalous temperature dependence of the fluorescence quantum yield and fluorescence decay time and the increase in fluorescence quantum yield in the rigid PMMA matrix of 9‐methoxy‐and some meso‐substituted anthracenes indicate that at moderate temperatures a very fast S1→ S0internal conversion is operative which competes with intersystem crossing.
Transient SANS Studies on p‐Tetrafluorethylen (p‐TFE)
Authors: Baumann J. , Kalus J. , Neubauer G. , Hoffmann H. , Ibel K.
Published: July 2012

Time dependent anisotropic small‐angle neutron scattering (SANS) patterns of p‐TFE fibrilles are presented. In the experiment the fibrilles were exposed to a parallel AC‐electric field in which the on and off cycle time had been adjusted to the orientation time of the fibrilles. The time resolution of the experiment was 40 ms. By an analysis of the time evolution of the SANS pattern relaxation times for alignment τ1 and randomisation τ2 were deduced. Both times, being equal within the error bars, are around 150 ns. The scattering curve for the fibrilles could only be fitted with the assumption of considerable polydispersity of their diameter.
Effect of Primary Structure Disorder on Coil‐Globule Phase Transitions in Heteropolymers
Authors: Fernández Ariel
Published: July 2012

We consider a phase transition induced by adsorption of self‐avoiding coils near the theta point in a macroscopic sample of random heteropolymers. The effect of primary structure disorder is shown to be enhanced on large scales within a neighborhood of the phase transition.
Absolute Measurements of the Thermal Conductivity of Some Aqueous Chloride Salt Solutions
Authors: Assael M. J. , Charitidou E. , Stassis J. Ch. , Wakeham W. A.
Published: July 2012

New absolute measurements of the thermal conductivity of aqueous NaCl, KCl and CaCl2 solutions are presented. The concentrations studied were 10% and 20% by weight of NaCl and KCl, and 10, 20 and 30% by weight of CaCl2. The measurements were performed in a transient hot‐wire apparatus employing two thin tantalum wires coated with an anodic tantalum pentoxide insulation layer. The temperature range examined was 290 to 345 K and the pressure was atmospheric. The uncertainty of the measurements is estimated to be ±0.5%, an estimate confirmed by the measurement of the thermal conductivity of water. — Existing correlations for the thermal conductivity of aqueous inorganic salt solutions are also examined. The measurements have been used to develop a simple consistent correlative and predictive scheme that allows the correlation of the thermal conductivity of these solutions with an uncertainty of ±0.7% and the prediction of the thermal conductivity to high pressures with an uncertainty of ±2.5%.
Acid‐Base‐Titration of a System Subdivided by a Semipermeable Membrane
Authors: Schlögl Reinhard W.
Published: July 2012

The theory of acid‐base‐titration is extended to systems subdivided into two compartments by a semipermeable membrane. Equal temperature of the outer phases, as well as ideal solutions are assumed. The membrane shall be impermeable to the ions constituting the “precipitation membrane”. It is shown that a neutral salt can adequately titrate the system.
Morphology of Paraphenylenediamine‐Aniline Conducting Copolymers
Authors: Mailhé‐Randolph C , McEvoy A. J.
Published: July 2012

Electrooxidation of aniline on conductive substrates, in an aqueous chloride electrolyte at low pH, produces adherent polyaniline (PANI) films. In the initial stage of polymerization the films exhibit a uniform globular microstructure which evolves to a fibrous deposit for thicker films. Although paraphenylenediamine (PPDA) itself does not electropolymerise to give a well defined electroactive film, in small admixtures it can modify dramatically the morphology of the copolymer with aniline. PPDA evidently promoted nucleation and cross‐linking during the electropolymerisation. Electrochemical characteristics and SEM micrographs of the doped PANI films are presented.
A Study on the 79Br Nuclear Quadrupole Spin‐Lattice Relaxation Times Affected by the Soft Acoustic Mode in Anilinium Bromide Crystals
Authors: Horiuchi Keizo , Nakamura Daiyu
Published: July 2012

The nuclear quadrupole spin‐lattice relaxation time T1Q, spin‐spin relaxation time T2Q, and NQR linewidth of 79Br in anilinium bromide were determined at various temperatures between 100 and 445 K. An unusual temperature variation of T1Q was observed over a wide range of temperature far below and also above the phase transition already reported, in addition to the normal temperature dependence (T−11Q α T2) due to lattice vibrations activated in crystals. The mechanism of the occurrence of the T1Q anomaly observed is explained in terms of the soft acoustic mode already reported to exist.
A New HeNe‐Laser Excitable Fluorescent Surfactant Probe
Authors: Kessler Manfred A. , Wolfbeis Otto S.
Published: July 2012

The fluorescence properties of four carbocyanine‐type probes which can be excited by the HeNe‐laser are investigated. Their fluorescence emission is red shifted and drastically enhanced in solutions of non‐ionic and cationic detergents at above the critical micellar concentration (CMC) as a result of the adsorption of the dye at the surface of the micelles. Since, at the same time, the absorption band is also shifted towards the 633 nm line, a drastic enhancement of the absorbance is also observed upon micellization. The most proper dye (2a) provides a fivefold increase of the 633 nm absorption in micellar solution of Triton X100 as compared to detergent solutions of below the CMC. It is shown that the CMC can be determined from the emission data of detergent solutions. The experimental data obtained with probe 2a are in agreement with the published values for a cationic, a neutral, and an anionic model detergent. The dyes (in particular 2a) are therefore considered as new useful probes for a sensitive determination of the CMC by laser fluorescence spectroscopy.
Structural Properties of Proteins as a Basis for Separation
Authors: Belfort Georges
Published: July 2012

As more and purer complex pharmacological proteins such as factor VIII, erythropoietin, colony stimulating factors, human growth factors, interferons, interleukins, monoclonal antibodies, and plasminogen activators need to be produced, increasing attention will be devoted to their recovery. In this brief review we focus on the molecular properties of proteins that are commonly exploited for their bioseparation. A formalism is then presented illustrating how structure (primary through quartenary) defines the properties of a protein and hence establishes the dominant interactions that determine the most appropriate group of separation processes that need to be considered for the recovery of the desired protein. A detailed example is used to illustrate this for electrostatic interactions during the adsorption of ribonuclease A onto mica. The paper concludes with the assertion that recombinant DNA techniques will play an increasingly important role in protein separations. These methods are already being used to increase the concentration and purity of a desired heterologous protein. Excretion of foreign proteins from the cytoplasmic space of E. coli into the medium is now a reality. Polypeptide marker fusion systems have also been used to facilitate excretion, purification, and identification of a desired protein. Clearly, combining rDNA techniques with biospecific affinity interactions augurs well for the future of efficient and highly selective separation processes.
Bioseparations, Especially by Hollow Fibers
Authors: Cussler E. L.
Published: July 2012

Downstream processing in biotechnology is best idealized as a four step process: removal of insolubles, isolation, purification, and polishing. The first and last steps are relatively easily achieved; the isolation and purification steps include most of the potential problems. While purification has often been presumed the most difficult, isolation may involve the greatest cost, presumably because it involves getting a small volume of concentrate from a large volume of feed. Both purification and isolation can sometimes use hollow fibers for extraction and chromatography.
Aqueous Two‐Phase Polymer Systems for Liquid/Liquid Partition‐Chromatography of Biopolymers
Authors: Müller Werner
Published: July 2012

The 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

In 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

The 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

• economics

The 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

Reactive 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

The 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

Unit 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

The 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

Fifteen 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

Retention 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

Permeate 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

The 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

Electrophoresis 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

Free‐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

Initiated 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

The 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.