bluuebunny/crossref_metadata_2025 huggingface dataset:
Current Noise Generated in Lipid Bilayer Membranes by Carrier‐Mediated Ion Transport
Authors: Kolb H.‐A. , Läuger P.
Published: September 2012

Valinomycin‐mediated ion transport generates in lipid bilayer membranes a characteristic type of current noise spectrum completely different from noise spectra in the presence of pore‐forming substances like gramicidin, alamethicin or monazomycin.

At equilibrium the current noise of the carrier system yields to a spectral intensity “white” (frequency independent) both at the low and high frequency end of the spectrum. Between the low and high frequency range of the spectrum the spectral intensity increases with frequency. The frequency range of transition is correlated to the characteristic relaxation time constants of this transport system. The experimental behaviour of the spectral intensity can be theoretically described on the basis of the Nyquist theorem applied for the carrier transport model.
Spannungsabhängige Beiträge zur Kapazität einer Lipidmembran
Authors: Carius W.
Published: September 2012

Die Spannungs‐ und Frequenzabhängigkeit der Kapazitäts‐änderung δC wurde unter verschiedenen experimentellen Bedingungen an ebenen Lipidmembranen gemessen. Dabei zeigten sich vielfach signifikante Abweichungen von der üblichen quadratischen Spannungsabhängigkeit δC = αU2. Der Beitrag von lateralen Schwingungen an der Grenzlinie Bilayer/Lipidlösung (z. B. am Torus) kann durch seine Frequenzabhängigkeit f−0.5 charakterisiert werden. Zur Erklärung der experimentellen. Befunde werden theoretische Modelle zur Diskussion gestellt.
On Domain Structure and Local Curvature in Lipid Bilayers
Authors: Krbecek R. , Gebhardt C. , Gruler H.
Published: September 2012

The lateral lipid organization and phase transition behaviour in giant bilayer vesicles of pure lipid systems and lipid mixtures were investigated. Both systems exhibit domain‐like structures at the surface of the vesicles. Since the domain structure often is accompanied by a local variation in curvature, freeze fracture electron microscopy was considered to be a suitable investigation technique.

Pure lipid systems show periodically rippled or spiral domain patterns, respectively. The rippled structure is obtained between the pre‐ and maintransition. It is explained by the concept of spinodal decomposition of metal alloys and the orientational elastic model of membranes. The periodicity of the ripples is determined by the spontaneous curvature of the decoupled mono‐ layers of a bilayer. Analysing the defect structure of the ripples one gets additional information on the molecular orientation. ‐ The spiral pattern is obtained in the case of coupled biaxial mono‐ layers below the pretransition. Binary and ternary lipid mixtures of smectic phases of different symmetry undergo lateral phase separation leading to rippled and spherically shaped domain organizations. The thermotropic phase separation behaviour of the various mixtures of phosphatidyl cholin, phosphatidic acid and cholesterol is discussed.

The oblique platinum shadowing leads to a different platinum layer thickness at different membrane locations. Densitometric analysis of the electron micrographs yields refined information upon the finestructure of the surface profile of the membranes.
The Stability of Phospholipid Dispersions
Authors: Rydhag Lisbeth , Rosenquist Kenneth
Published: September 2012

Lipid vesicles were made by sonication of well defined phospholipids above the chain‐melting temperature. Fractionation was obtained by ultracentrifugation. The vesicle size was determined with different methods, for example by different light scattering methods and by determination of the sedimentation coefficients in an analytical ultracentrifuge. The influence of size and charge were studied with respect to the stability of the lipid vesicles.
Thermotropic Phase Transition and Ultrasonic Absorption in Lecithin Bilayer Vesicle Preparations
Authors: Funck Th. , Eggers F.
Published: September 2012

Temperature dependent ultrasonic absorption spectra (frequency range 0.3‐150 MHz) of homogeneous lecithin bilayer vesicle preparations in the range of their liquid/liquid‐crystalline phase transition provide information on equilibrium shifts for various states of the lipid system. Furthermore the frequency dependence of the absorption reveals time constants of elementary processes which cause the ultrasonic absorption. From our measurement data the following conclusions can be drawn:

The thermotropic phase transition in our lipid system is not a one‐step reaction but incorporates various processes.

Predominant changes of the ultrasonic absorption with temperature, correlated with cooperative processes at the lipid/water interface, occur well below the temperature of the “calcrimetric” main effect.

Relaxation times of these processes are between 10 and 200 ns.

The observed ultrasonic absorption appears to be larger than expected values from equilibrium (“static”) data (e. g. dilatometry and calorimetry); consequently in this case the ultrasonic absorption indicates processes with compensating effects, which can only be resolved by “dynamic” methods on the time scale.

These kinetic observations are compared with results from calorimetry, density‐ and viscosity‐measurements on the same lipid preparations. A model mechanism for the thermotropic phase transition in lecithin bilayer vesicles is suggested.
Steric Interaction of Fluid Membranes
Authors: Helfrich W.
Published: September 2012

Optical observation of giant lecithin vesicles does not show any indication of cohesion between thin lecithin membranes consisting of a small number of bilayers (W. Harbich, H. J. Deuling, and W. Helfrich, J. Phys. (Paris) 38, 727 (1977). It may be concluded that cohesion, if it exists at all, must be weaker by orders ofmagnitude than the calculated strength of van der Waals interaction (B. W. Ninham and V. A. Parsegian, J. Chem. Phys. 53, 3398 (1970).

However, there should also be a repulsive force acting between fluid membranes, caused by the mutual steric hindrance of out‐of‐plane fluctuations. We show that the two interactions have the same range and may compete in strength. The experimental situation concerning multilayer systems and red blood cells is discussed from this point of view.
Procedure to Form Bilayer‐Gel Membranes
Authors: Lüschow Ullrich , Schulz‐Harder Jürgen
Published: September 2012

We developed a new procedure that induces multifunctional reagents to crosslink at an interface between a black bilayer and the adjacent water phase. This procedure yields “bilayer‐gel” membranes, i. e. membranes consisting of a bilayer and a polymer layer. The bilayer‐gel membrane may partially be considered to be a new membrane system, because the formation of the polymer layer changes some bilayer properties.

We studied bilayer‐gel membranes composed of a bilayer of oxidized cholesterol and of a polymer layer of poly‐1‐lysine crosslinked by glutardialdehyde. Compared to unmodified bilayers, this membrane system has an electrical conductance of the same magnitude, the same electrical capacity, and similar shapes of current‐voltage dependences. Yet, this system is asymmetrical and differs in the increased stability from an unmodified bilayer. The ion selectivity of bilayer‐gel membranes depends upon the chain length of the polylysine the polymer layer is formed with. Trilysine and tetralysine yield a membrane selectivity for cations. Polylysine with MW > 6000 D yields an anionic selectivity. Some properties of bilayer‐gel membranes, mainly their resistance, are sensitive to a change of the pH and to the ionic strength of the adjacent solutions.

The special kinetics of the formation of the polymer layer and the instability of the bilayer require some general conditions which must be observed for forming bilayer‐gel membranes.
Measurement of Micelle Diameters Using Dipole‐Dipole Energy Transfer
Authors: Roessler N. , Von Bünau G.
Published: September 2012

The anionic dyes fluoresceine and eosine are attracted to cationic micelles (e.g. cetyl trimethyl ammonium bromide, “CTAB”), as can be seen from the red shift in the absorption and emission spectra compared to solutions below the critical micelle concentration. Since these dyes are not incorporated into the core of a micelle, they should have no influence on its size, shape, etc. and are thus ideal probe molecules.

The spectral properties of these dyes are ideal for dipole‐dipole energy transfer (Förster mechanism): the maximum of the emission band of fluoresceine coincides almost exactly with the maximum of the absorption band of eosine. Thus, energy transfer from fluoresceine (donor) to eosine (acceptor) competes effectively with spontaneous emission at separation distances comparable with micellar dimensions.

We observed the quenching of the fluoresceine emission in CTAB solution as a function of the eosine concentration and obtained a linear Stern‐Volmer plot. Using Förster's equation for isolated donor acceptor pairs an effective separation distance of r = 5.5 nm was obtained. Since x‐ray measurements have indicated a micelle diameter of 4.8 nm, we conclude that the dye molecules are located at opposite sides of the micelle and that r is a measure of the micelle diameter.
Microviscosity Measurements in Micelles and Phospholipids
Authors: Zachariasse K. A.
Published: September 2012

Intramolecular excimer formation with diarylalkanes A‐(CH2)3‐A, with A = pyrenyl, naphthyl or phenyl, depends on the viscosity of the surrounding medium. The study of this phenomenon has been used to probe the microviscosity of micelles [1] and phospholipids. As the process magnified image. is quasi‐monomolecular, a small probe concentration (< 10−1 M) can be employed in the experiments.

The microviscosity of a number of anionic, cationic and nonionic micelles has been studied with the intramolecular excimer probes. The values so obtained for e.g. SDS (19 cP, 20°C) are similar to the values found via fluorescence depolarisation measurements [2].

Also phase transitions in phospholipids (e.g. dipalmitoyllecithin, DPL) can be studied using this method. With 1,3‐di(1‐naphthyl)‐propane as the fluorescence probe in DPL the phase transition is found to occur within 1°C. The experiments show that movement of the two aromatic moieties is still possible below the phase transition temperature, in contrast to what is observed with 1,3‐di‐(1‐pyrenyl)propane.

Excimer formation in monolayer assemblies will be briefly indicated [3].
Solvent and Micellar Effect on Electron‐Transfer Reactions. The System Phenothiazine‐Iron(III)
Authors: Pelizzetti Ezio , Pramauro Edmondo , Mentasti Edoardo
Published: September 2012

The effect of the solvent composition and of micelle‐forming surfactants on the electron‐transfer rate between phenothiazine and iron (III), according to the reaction magnified image.

Solvent composition affects the specific rate constant k1 in the order: methanol/water > ethanol/water > n‐propanol/water > acetone/water (all 50/50 v.v.).

Strong effect is exhibited by micelles in going from a large increase observed for anionic surfactant to a decrease for non‐ionic or cationic ones, in respect to the previous cited solvent compositions. The difference in reaction rate observed between an anionic surfactant and a cationic one is about 104 – 105. The effect of acidity, ionic strength and temperature has been also investigated.
Hydrate von Polyglykoläthern und ihre Strukturen
Authors: Heusch R. , Fontell K. , Johansson L. B.‐Å , Lindblom G. , Ulmius J. , Wennerström H.
Published: September 2012

Am Modell n‐Dodecylalkoholheptaglykolather/Wasser wird durch polarisationsoptische Untersuchungen, Viskositatsmessungen, Messung der Trübungspunkte, Aufnahme von automatischen Abkühlungskurven und durch Differentialthermoanalysen ein Phasendiagramm zusammengesetzt. Es wird gezeigt, daß die auftretenden Phasen durch verschiedene Hydrate bedingt sind, bei denen eine definierte Anzahl von Wassermolekeln an jede Polyglykolathermolekel angelagert ist.‐ Bei den niederen Hydraten wird durch die Anlagerung der Wassermolekeln, die Helixstruktur der wasserfreien Polyglykolather kaum verändert, während bei den höheren Polyglykolatherpolyhydraten für die einzelnen Hydratstufen typische flüssigkristalline Strukturen auftreten. ‐ Anhand von polarisationsoptischen Mikroaufnahmen werden die Strukturen der verschiedenen Hydrate vorgestellt. Ihr molekularer Aufbau und Bildungsmechanismus werden zur Diskussion gestellt.
Electron transfer reactions between transition metal complexes in micellar solutions
Authors: Bruhn H. , Holzwarth J.
Published: September 2012

We report a systematic investigation of the influence of anionic micelles (SDS) on the kinetics of diffusion controlled outer sphere electron transfer reactions between transition metal complexes. — The micelles interact with the reactants through electrostatic repulsion (e. g. IrCl62) or attraction which can cause ion association (e. g. Os(dipy)) as well as through hydrophobic forces (e. g. Fe(phen)2(CN)20). The rate constantskETof these reactions range in the order of 1010M−1s−1in aqueous solution and are decreased by more than four orders of magnitude if these forces superimpose. — By variation of the SDS concentrations and the ionic strengths electrostatic influences were largely eliminated. It was thus possible to establish a hydrophobic barrier in electron transfer reactions between complexes which are solubilized in the hydrophobic core of the micelles and substitution inert complexes in the bulk solution.
Ion Reactivity in Micro‐Emulsion Systems
Authors: Robinson Brian H. , Steytler David
Published: September 2012

We have studied various elementary reaction processes from a kinetic viewpoint in reversed micellar (W/O micro‐emulsion) systems (e.g. Aerosol‐OT, water, heptane). The dispersions formed have been characterised by a variety of physical methods including viscosity, ultracentrifugation, and light scattering, and water droplet diameters have been varied in the region 10‐50·10−10m.

Extensive measurements (using the stopped‐flow method) have been made on the metal‐ligand complexation reaction involving divalent metal ions (e.g. Ni2+) and the chromophoric ligand murexide, with both reactants initially contained in separate pools prior to mixing. (These reagents are particularly suitable for study since no partitioning of reactants out of the water pools takes place.

Useful information can then be obtained on the following processes.

The collision process between the micro‐emulsion droplets and the communication/exchange of reagents between pools.

The energetics of the reaction in the water‐pool environment compared with bulk water. The reaction can therefore be used to probe the nature of the heterogeneous water in which the complexation reaction occurs.

Our conclusions so far are as follows.

Reactions in micro‐emulsion droplet systems exhibit simple kinetic behaviour, and the rate dependence on droplet size and concentration can be explained quantitatively.

When Aerosol‐OT is used as a dispersant, there is virtually no energy barrier to communication of reagents between water pools, at least 1 in 104 of the collisions resulting in transfer. Activation energies of <20 kJ mol−1 can be predicted for this process.

As far as ligand substitution on divalent metal ions in heterogeneous water is concerned, the rates for loss of water and ligand are very similar to those measured in bulk water. This is in agreement with previous results obtained for the loss of water from Ni2+ when the metal ion is located close to the surface of an anionic micelle.
Magnetic Structures and Stresses in Thin Films II. Thermodynamical Treatment and Discussion
Authors: Göpel W.
Published: September 2012

Using a thermodynamic treatment of thin film magnetism, UHV‐experiments on the ferromagnetic resonance of Fe‐, NiFe‐, and Ni‐thin films in the 2– 50 monolayer range can be evaluated. – The discussion of the results about clean surfaces leads to the following conclusions: (a) Magnetic “dead layers” of Ni can be excluded with an accuracy of 0.2 monolayers. b) Results from the spin wave theory are applicable to explain the temperature and thickness dependence of the saturation magnetization of Ni although the films are not ideal on a microscopical scale, c) Magnetic surface anisotropies can be explained by Néel's phenomenological approach, d) Due to the high magnetostriction of Ni the data are affected by mechanical stresses. Therefore mechanical stresses of thin films can be estimated from experimentally determined magnetic anisotropic fields. Tentatively we describe these effects by simple models including stresses from interfacial energies. thermal expansions and grain boundaries. – Chemisorption of H2 and CO on Ni at T±500 K leads to changes in the surface magnetism: a)“Dead layers” are induced by chemisorption. One hydrogen atom diminishes the contribution of one nickel atom to the thin film ferromagnetism. Twice the effect is found for CO adsorption. b) Magnetic surface anisotropies are reduced. c) Mechanical stresses are reduced too. This effect depends on the coverage of chemisorbed particles, the film thickness and the concentration of crystallite boundaries. Only its lower limit can be estimated using a thermodynamic treatment of reduced surface free energies.
Die Temperatur‐ und Lösungsmittelabhängigkeit der Fluoreszenzquantenausbeuten von N‐substituierten Acridonen
Authors: Siegmund M. , Bendig J.
Published: September 2012

Die absoluten Fluoreszenzquantenausbeuten von N‐substituierten Acridonen wurden in Abhängigkeit von der Temperatur und der Polarität des Lösungsmittels bestimmt. – Die Temperaturabhängigkeit der Fluoreszenzquantenausbeute, die auf eine strahlungslose Desaktivierung des ersten angeregten Singulett‐Zustandes durch Interkombination zurückgeführt werden kann, läßt sich über die Arrhenius‐Gleichung quantitativ beschreiben. Aus dem linearen Zusammenhang zwischen den Größen In(1/πf – 1) und 1/T für N‐Methylacridon in 34 Lösungsmitteln wird geschlossen, daß die temperaturunabhängige Interkombination im Temperaturbereich von 287–350 K vernachlässigbar ist. – Mit steigender Polarität des Lösungsmittels nimmt die Aktivierungsenergie für die temperaturabhängige Interkombination zu. während der präexponentielle Faktor der Geschwindigkeitskonstante für diesen Übergang nicht signifikant von der Stärke der “solvens‐solute” Wechselwirkung abhängt. Die Fluoreszenzquantenausbeuten der untersuchten Acridone betragen bei 298 K in Cyclohexan 0,017±0,002(Ea, = 10,6kJmol1) und in äthanol 0,98 ± 0,01 (Ea ≈︁ 32,5kJ·mol−1). Der Mittelwert von kisc ist 4.55·1011s−1 bei N‐Methylacridon. – Es konnte weiterhin ein linearer Zusammenhang zwischen den berechneten Aktivierungsenergien und den Akzeptorzahlen der Lösungsmittel nachgewiesen werden. Dieser Befund weist auf die unterschiedliche Solvatation der an der Desaktivierung beteiligten Anregungszustände hin. Die halogensubstituierten Lösungsmittel führen aufgrund ihres äußeren Schweratomeffcktes zu relativ kleinen Fluoreszenzquantenausbeuten und zu kisc‐Werten, die um den Faktor fünf bis zehn größer sind. – Bei 77 K. erfolgt die Desaktivierung des S1Zustandes nahezu ausschließlich strahlend, wobei die beobachtete Phosphoreszenz der temperaturunabhängigen Interkombination zum T1‐Zustand zugeschrieben werden kann. – Zusätzliche spektroskopische und molekulare Daten (Solvatochroraie‐Effekte. Stokessche Verschiebungen, EPR‐Nullfeldparameter und Dipolmomente im Grundzustand) belegen eindeutig den π,π‐Charakter der S1‐ und T1‐Zustände der Acridone. – Diese Ergebnisse und vergleichende Termschemata‐Betrachtungen stehen im Einklang mit der Annahme, daß der temperaturabhängigen Interkombination ein Übergang vom S1(π,π)‐Zustand in den T2(π,π)‐Zustand zugrunde liegt.
Fluoreszenz und Fluoreszenzlöschung von meso‐substituierten Anthracenderivaten in Lösung
Authors: Schoof S. , Güsten H. , Von Sonntag C.
Published: September 2012

Die Elektronenabsorptionsspektren, absoluten Fluoreszenzspektren und Fluoreszenzquantenausbeuten, sowie die Fluoreszenzabkling‐zeiten von 25 mono‐ und disubstituierten meso‐Anthracenderivaten wurden in n‐Heptan mit und ohne Sauerstoff bei Raumtemperatur gemessen. Aus den gemessenen Daten werden die Geschwindigkeitskonstanten der Fluoreszenz, der strahlungslosen Desaktivierung und der Fluoreszenzlöschung des ersten angeregten Singulettzustands bestimmt. Während die Fluoreszenzabklingzeiten eine starke Substituentenabhängigkeit zeigen, wird die natürliche Lebensdauer der Fluoreszenz durch die Substitution kaum beeinflußt. wodurch gezeigt ist, daß die Substituenten in der meso‐Stellung des Anthracens nur die Geschwindigkeit der strahlungslosen Desaktivierung beeinflussen. Aus der durch Sauerstoff bestimmten Fluoreszenzlöschung wird über die Stern‐Volmer‐Gleichung für cyan‐substituierte meso‐Anthracen‐derivate eine Fluoreszenzlöschkonstante von 0,6·1010 1·mol−1sec−1 erhalten. Dagegen erfolgt die Fluoreszenzloschung bei den meso‐substituierten Anthracenen ohne Cyangruppe mit einer mittleren Löschkonstanten von 2,2·1010 1·mol−1sec−1 diffusionskontrolliert.
Analysis of Light‐Scattering and Specific Heat Data of Binary Liquid Mixtures in Terms of the Two‐Scale‐Factor Universality
Authors: Klein H. , Woermann D.
Published: September 2012

The two‐scale‐factor universality hypothesis of critical phenomena offers the possibility to calculate the critical part of specific heat and of the coefficient of thermal expansion of binary liquid mixtures of critical composition from light‐scattering data. The usefulness of this method is analyzed using experimental data.
Rasche Löschprozesse für NH(b1Σ+) und ND(b1Σ+): Die Löschung durch Xe, NO, Benzol, Propen, 1‐Buten, 1,3‐Butadien, Hydrazin, Methylamin und Methanol
Authors: Zetzsch C.
Published: September 2012

Durch gepulste Vakuum‐UV‐Photolyse von Ammoniak (NH3 bzw. ND3) in Gegenwart verschiedener Zusatzgase werden metastabile NH(b1 Σ+)‐und ND(b1 Σ+)‐Radikale erzeugt. Aus dem Abklingen der Emission der Iminoradikale im Interkombinationsöbergang (b1 Σ+ Σ X3Σ−) in Gegenwart der Zusatzgase Xe, NO, Benzol, Propen, 1‐Buten, 1,3‐Butadien, Hydrazin, Methylamin und Methanol werden die jeweiligen Löschgeschwindigkeitskonstanten bestimmt. Die erhaltenen Werte reichen von 1,3·10−15 cm3 s−1 (für die Löschung von ND(b1 Σ+) durch Xe) bis 2·10−10 cm3 s−1 (für die Löschung von NH(b1 Σ+) durch 1,3‐Butadien). Das Löschverhalten wird mit dem von O2(b1 Σg+) verglichen.
Tripletspectra of 4‐Nitrostilbenes in Polar and Non‐Polar Solvents at Different Temperatures and the Configuration of the Triplet State
Authors: Görner H. , Schulte‐Frohlinde D.
Published: September 2012

The absorption spectra of triplet states of various substituted nitrostilbenes (e.g. 4‐nitro‐, 4,4′‐dinitro‐,4‐nitro‐4′‐methoxy‐, and 4‐nitro‐4′‐dimethylaminostilbene) were measured in solvents of different polarity at room temperature and in glycerol triacetate at temperatures ranging from +25 to ‐80°C, corresponding to a viscosity range of 10−2 to 1011 poise. The spectra derived from 4‐nitro‐and 4,4′‐dinitrostilbene do not vary with the polarity of the solvent while those of 4‐nitro‐4′‐methoxy‐, and 4‐nitro‐4′‐dimethylaminostilbene are shifted to longer wavelengths on increasing solvent polarity. The triplet spectra of all nitrostilbenes investigated are very similar in the liquid and the glassy state of the solvent. For trans‐4‐nitrostilbenes the yield of triplet intermediate is temperature and viscosity independent. From these effects and the observed strong decrease of the direct trans → cis quantum yield in rigid media it is concluded that the triplet state of the nitrostilbenes has predominantly the planar trans configuration.
Die Vertikalverteilung von H2, CH4, CO, N2O, CFCl3 und CF2Cl2 in der Stratosphäre
Authors: Schmidt U. , Volz A. , Ehhalt D. H. , Khedim A. , Johnen F. J. , Röth E. P. , Fabian P. , Borchers R. , Seiler W. , Müller F.
Published: September 2012

Mit einer kryogenen Sammelapparatur wurden im Juni und September 1977 während vier Ballonaufstiegen über Südfrankreich Luftproben in der Stratosphäre zwischen 13 km und 35 km Höhe gewonnen. Zur Ergänzung wurden in der Troposphäre und unteren Stratosphäre Luftproben während mehreren Flugzeugaufstiegen gesammelt. In allen Proben wurde gaschromatographisch die Konzentration von H2, CH4, CO, N2O, CFCl3 und CF2Cl2 bestimmt. Die gemessene Vertikalverteilung der genannten Spurenstoffe wird diskutiert und mit theoretischen Profilen verglichen, die sich aus numerischen Berechnungen mit einem eindimensionalen Modell ergeben.
Bestimmung der mittleren Konzentration von OH‐Radikalen in der Troposphäre mittels des natürlichen 14CO‐Pegels
Authors: Volz A. , Ehhalt D. H. , Khedim A.
Published: September 2012

Kohlenmonoxid wurde aus jeweils 200 m3 großen Luftproben abgetrennt und auf seinen Gehalt an Radiokohlenstoff untersucht. Aufgrund der bekannten Produktionsrate für 14CO durch kosmische Strahlung läßt sich aus Messungen seiner absoluten Konzentration die Lebensdauer von CO in der Atmosphäre abschätzen. Diese wird bestimmt durch die Reaktion mit OH‐Radikalen. Die Methode ermöglicht also einen indirekten Weg zur Bestimmung der mittleren Konzentration von OH‐Radikalen in der Troposphäre.

Es wurde die jahreszeitliche Variation von 14CO in der BRD (52±N) untersucht. Dabei zeigt sich ein Minimum im Sommer – entsprechend einem Maximum der OH‐Konzentration.
Photomineralisierung von Fluorchlorkohlenwasserstoffen unter simulierten troposphärischen Bedingungen
Authors: Gäb S. , Korte F.
Published: September 2012

Der Abbau von Fluorchlorkohlenwasserstoffen durch heterogene Photolyse wurde untersucht. Dabei zeigte sich, daß die an Kieselgel adsorbierten Verbindungen CCl2F2 und CCl3F mit natürlichem Sonnenlicht in Bodennähe zu Kohlendioxid und Chlorwasserstoff mineralisiert werden. Für eine erste orientierende Bewertung wurden zum Vergleich die Abbauraten einiger Chlorkohlenwasserstoffe herangezogen.
Reaktionsgeschwindigkeitskonstanten der Reaktion von Sauerstoffatomen mit potentiellen Photosmog‐Inhibitoren
Authors: Filby W. G. , Güsten H.
Published: September 2012

Vor zwei Jahren wurde von J. Heicklen et al. vorgeschlagen, die Bildung des photochemischen Smogs über Städte und Ballungsgebiete durch Versprühen von Photosmog‐Inhibitoren, bevorzugt aliphatische Amine, zu verhindern bzw. zu mildern. Die Photosmog‐Inhibitoren sollen in die durch die NO2‐Photolyse ausgelösten Radikalkettenreaktionen eingreifen und dabei auch die schnelle Rückbildung des NO2 verhindern. Der in Smogkammerversuchen ermittelte Inhibitoreffekt hat eine beachtliche Diskussion über seine praktische Anwendbarkeit ausgelöst [1, 2].

Es wurden deshalb die Reaktionsgeschwindigkeitskonstanten der Reaktion von O(3P)‐Atomen mit potentiellen Photosmog‐Inhibitoren (äthylamin, Triäthylamin, N.N'‐Diäthylhydroxylamin, Anilin und Benzaldehyd) in einem Elektronenspinresonanz‐Strömungssystem bei Raumtemperatur und 4,7 Torr gemessen. Die Sauerstoffatome im Grundzustand wurden durch kalte Mikrowellenentladung des molekularen Sauerstoffs in Helium als Trägergas dargestellt. Die gemessenen Reaktionsgeschwindigkeitskonstanten liegen zwischen 10,9 und 0.24 · 10−12 (cm3 · Moleküle−1). Die Daten werden zusammen mit der Reaktionsgeschwindigkeitskonstanten der Reaktion des OH‐Radikals mit N,N‐Diäthylhydroxylamin im Zusammenhang mit der vorgeschlagenen Anwendung als Photosmog‐Inhibitor diskutiert, wobei besonders der Vergleich des Produktes k(Inhibitor) gegenüber k(Kohlenwasserstoff) als Maß für die Wirksamkeit der Photosmog‐Inhibierung in verschmutzter Luft betrachtet wird.
Chemische Komponenten des Reinluftaerosols in Abhängigkeit von Luftmassencharakter und meteorologischen Bedingungen
Authors: Reiter R. , Sládkovič R. , Pötzl K.
Published: September 2012

An einem Bergobservatorium (Wank‐Gipfel, 1780 m ü. M.) werden seit 1972 kontinuierliche Untersuchungen des atmosphärischen Aerosols auf die anorganischen Komponenten Na+, K+, NH4+, Ca++, Cl−, SO4− –, NO3− (wasserlösliche Ionen), CaO, SiO2, Al2O3, Fe2O3 (Mineralkomponenten) und Pb, Zn, Cd, Cu (toxische Schwermetalle) durchgeführt. Die Aerosole werden aus definierten Luftmengen auf Schwebstoffiltern gesammelt. – Der Probenahmeort liegt in weithin ungestörter Umgebung und zu 30–40% der Zeit über der Austauschschicht in Reinluft. In Verbindung mit einer innerhalb des höhengestaffelten Stationsnetzes des Instituts (Garmisch‐Partenkirchen 740 m/Wankgipfel 1780 m/Zugspitzgipfel 2963 m) durchgeführten dreidimensionalen Analyse aller meteorologischen Parameter und mit weiteren Reinluftkriterien (Zahl der Aitkenkerne, RaB‐Konzentration, Vertikalaustausch) lassen sich unterschiedliche Reinluftbedingungen genau definieren und die Aerosolzusammensetzung (Matrix) dem Typ der jeweiligen Luftmasse zuordnen. – Die chemischen Analysen werden nach naßchemischen Verfahren durchgeführt. Nur so können mit physikalischen Verfahren schlecht oder nicht bestimmbare, aber wichtige Komponenten, wie SiO2‐ und N‐Verbindungen, miterfaßt werden. – Tabellen der wichtigsten Analysen‐Ergebnisse geben für alle Komponenten der Aerosolmatrix an: Gesamtmittelwerte im Vergleich zu Werten in extremer Reinluft, ferner die Abhängigkeit der Aerosolmatrix von steigender Gesamt‐Aerosolmasse, von der Luftfeuchtigkeit und vom Luftmassen‐Typ. Zugehörige Reinluftkriterien (s. o.) und einige typische Elementverhältnisse im Aerosol im Vergleich zu denen in der Erdkruste bzw. im Meerwasser sind jeweils mit aufgeführt. – Es ergibt sich u.a.: SO4− – und NH4+ stellen den Hauptanteil des Aerosols. Sie sind verringert in Reinluft, wobei ein Anstieg von Na+ und CI auf einen höheren Anteil maritimer Quellen hinweist. Wenig veränderlich ist der relative Anteil typischer Krustenelemente (Si02, A1203. Fe,O,), was auf ihre weitgehend homogenisierte, zumindest hemispharische Verbreitung und ihre Herkunft aus größerer Entfernung (aride Zonen) schließen laßt. Auch Pb und Zn sind ‐selbst in Reinluft ‐signifikant mit höher relativer Konzentration vertreten. ‐ Hinsichtlich der Luftmassenabhängigkeit zeigt sich, daß der kontinentale bzw. maritime Charakter vor allem die Gesamt‐Aerosolmasse bestimmt, während die Element‐Matrix stärker von der polaren oder tropischen Herkunft gesteuert wird. ‐ Als Sonderfälle sind noch zwei “Durchgänge” von Wüstenstaub dargestellt, ‐nämlich aus Colorado/USA und der Sahara. Sie zeigen deutlich den erwarteten drastischen Anstieg von Krustenmaterial und sein Abklingen in der Nachperiode. ‐ Ein Werte‐Vergleich der Reinluftaerosolanalysen an unserer Station mit solchen in anderen Regionen der Erde schließt die Arbeit ab.
Über die Dynamik atmosphärischer Aitkenteilchen
Authors: Jaenicke Ruprecht
Published: September 2012

Mit der Annahme eines Gleichgewichtes zwischen der Produktion von atmosphärischen Aerosolteilchen aus der Gasphase und der Vernichtung dieser Teilchen durch Koagulation und Verschmelzen mit anderen Aerosolteilchen läßt sich berechnen, welche Teilchengrößen produziert werden müßten, um die beobachtete Größenverteilung des atmosphärischen Aerosols im Bereich der Aitkenteilchen (<0.1 μm) aufrechtzuerhalten. Diese Berechnungen gestatten auch Aussagen über die Aufenthaltszeit der Teilchen im atmosphärischen Aerosol. In diesem Zusammenhang werden alle Daten über die Aufenthaltszeit atmosphärischer Aerosolteilchen zusammengestellt, diskutiert und eine Gleichung entwickelt, die die Aufenthaltszeit als Funktion der Teilchengröße beschreibt.
On the Analysis of the Amplitudes in the Relaxation Processes in Micellar Solutions
Authors: Teubner M. , Diekmann S. , Kahlweit M.
Published: September 2012

If the relaxation processes in aqueous solutions of Na‐Decylsulfate and Na‐Dodecylsulfate are investigated by means of a pressure‐jump apparatus and followed by conductivity measurements, the amplitude of the slow relaxation process, if plotted versus the surfactant concentration, intersects twice with the abscissa, being negative in between. – Ananalysis of this result permits a decision between two alternative approximations used in the theory of micellation in favour of that made by Aniansson and Wall, at least for these systems. – The first zero is caused by the fact, that although the slow relaxation process takes place, its amplitude becomes indetectable because the changes of the contributions to the conductivity by monomers and micelles, respectively, compensate each other at this particular concentration. At the second zero the slow process itself vanishes, as there the change of the total number of micelles during the relaxation process changes its sign. Thus, at this particular concentration only the fast process takes place. – The results permit an independent determination of the width of the size distribution and the reaction volumes.
Solubility of Hydrogen in CuTi, CuTi2, PdTi2, and Cu0.5Pd0.5Ti2. Reactions of Titanium Alloys with Gaseous Hydrogen)
Authors: Kadel Rainer , Weiss Alarich
Published: September 2012

CuTi2, PdTi2, and Cu0.5Pd0.5Ti2are isotypic (MoSi2‐structure type). The solubility of hydrogen in these alloys and in CuTi was measured by means of a volumetric method in the range 0.01 bar ≤ PH2≤ bar and 250°C ≤T≤ 850°C. The thermodynamic data were derived from the absorption isotherms found. The relative partial molar enthalpies of solution at infinite dilution ΔHH0increase in the following order: α‐Ti (‐45.5kJ/mol H); Cu0.5Pd0.5Ti2(‐40.5kJ/mol H); CuTi (‐37.5kJ/mol H); PdTi2(‐37kJ/mol H and ‐33.5 kJ/mol H at 600850°C and 400700°C respectively); CuTi2(‐33kJ/mol H). ‐ From the excess entropies and enthalpies it is concluded that the number of available interstitial sites for the H‐atoms is reduced in the alloys compared with α‐Ti, thus indicating a preferred occupation of interstices which are tetrahedrally surrounded by Ti‐atoms only. ‐ CuTi, CuTi2and Cu0.5Pd0.5Ti2show decomposition reactions by which titanium hydrides and other intermetallic compounds are formed. For the systems CuTi‐H and CuTi2‐H the decomposition steps could be analysed thermodynamically and roentgenographically up to the end products (copper and γ‐titanium hydride). ‐ The experimentally determined enthalpies of formation of CuTi and CuTi2, are compared with calculated ones. ‐ PdTi2dissolves hydrogen gas up to the composition PdTi2H2which can be explained by a complete occupation of the interstices formed by Ti‐tetrahedrons.
Temperature Dependence of the Intrinsic Pitch in Induced Cholesteric Systems
Authors: Finkelmann H. , Stegemeyer H.
Published: September 2012

Based on the molecular‐statistical theory of Goossens a model has been developed to explain the temperature dependence of the intrinsic pitch in cholesteric systems induced in nematic host phases by chiral guest molecules. In the case of a rotational symmetric distribution function around the long axis of the chiral molecule the helix inducing dipole‐quadrupole interaction forces level out. Consequently, only a hindered long‐axis rotation causes the helical structure whose pitch increases with increasing temperature. The theoretically predicted value of the relative temperature gradient of reciprocal pitch 1/p−1(dp−1/dT) are in good agreement with the presented experimental data. The influence of structure of the chiral guest molecules on the helical twisting power as well as that of the nematic host phases also can be understood in terms of the proposed model.
Optical Properties of the Isotropic Mesophase Formed by Cholesteryl Esters
Authors: Bergmann K. , Stegemeyer H.
Published: September 2012

Optical rotatory dispersion (ORD) and selective reflection spectra (SR) of the isotropic so‐called “blue‐phase” (BP) of cholesteryl myristate and nonanoate have been studied. The anomalous ORD effect as well as the SR band is sharply separated from the corresponding effect of the cholesteric phase and positioned at longer wavelength. The sign of the ORD curve and the reflection of left circularly polarized light indicate any left‐handed helical arrangement in the BP. The refractive index of the isotropicBPis found to be related to that of the birefringent cholesteric phase by the Vuks formula. Requirements of structural models for theBPare discussed in terms of the experimental results.
ESR and PMR Studies of Alcohols Hydrogen Bonded with Nitroxide Radical
Authors: Kolodziejski Waclaw , Kecki Zbigniew
Published: September 2012

The ESR and PMR spectra of the solutions of 2,2,6,6‐tetramethylpiperidine nitroxide radical in the series of alcohols from methanol through ethanol, normal and branched propanols, butanols to pentanols were used to determine the 14N and the OH proton hyperfine coupling constants and to discuss trends of their changes. The dependence of the OH coupling constant on temperature was determined for four alcohols and explained in terms of oscillator anharmonicity of the radical‐alcohol hydrogen bond.
The Oxidative Dehydrogenation of 1‐Butene over Unsupported Vanadium Pentoxide Catalyst
Authors: Hauffe K. , Abd El‐Salaam K. M.
Published: September 2012

The gas phase oxidation of 1‐butene over unsupported V2O5 catalyst has been investigated with reference to the consumption of oxygen from the catalyst surface causing a deviation from the stoichiometry. Therefore, measurements of the weight change by an electromicrobalance in a flow system have been carried out. Simultaneously, electrical conductivity, the infrared absorption and catalytic oxidation in a microflow reactor in the range of 200500 °C were studied. In the overall reaction both the chemical reaction at the surface and the diffusion of oxygen through the lattice of the solid play a role in the rate of reaction. A kinetic model comprising these two steps is applied. The steady‐state composition of the catalyst at 350 °C which has the highest selectivity is V2O4.8. It is proposed that 1‐butene chemisorbed interacts with oxygen ions by donation of electrons to the catalyst surface as detected by the increase of the conductivity and the deviation from stoichiometry.
Reactivity of Silver Atoms in Aqueous Solution II. A Pulse Radiolysis Study
Authors: Tausch‐Treml R. , Henglein A. , Lilie J.
Published: September 2012

Free silver atoms were produced by reducing Ag+ with hydrated electrons or hydrogen atoms. AgH+ with a lifetime shorter than 10−8 s is postulated as an intermediate of the H atom reaction. Organic free radicals cannot reduce Ag+ in a single electron transfer process. CO2− reduces Ag+ in a complex manner. The rate constants of reactions of both Ag0 and Ag2+ with a number of inorganic and organic compounds were measured. Both particles were found to be electron donating agents with approximate standard redox potentials of ‐1.8 V (Ag0) and ‐1.2 V (Ag2+). Ag2+ reacts faster in the presence than absence of ammonia.  Ag2+ radical cations react with 2k = 3.0 ·108 M−1 s−1 (or 5.0 · 109 M−1 s−1 in the presence of ammonia) to form dimeric silver. Ag2+ whose standard reduction potential is approximately −0.5 V is reduced by 1‐hydroxyalkyl radicals; the reaction with CH2OH proceeds through the complex Ag2CH2OH+ (life time: 3.3 · 10−4s). 2‐hydroxyalkyl radicals oxidise Ag2+ ‐ Dimeric silver whose standard redox potential for two‐electron transfer is about − 0.9 V is strongly complexed by Ag+ ions to yield Ag42+. Ag0, Ag2+, and Ag42+ absorb in the near UV, the maximum of the band shifting towards shorter wavelengths in this order. Ag42+ disappears by reaction with another Ag42+ (2k = 1.1 · 107 M−1 s−1 or reaction with colloidal silver particles (produced by preirradiation). In the presence of small sulfate concentrations, the reaction between two Ag42+ particles is accelerated. Sulfate also catalyses subsequent agglomeration processes. Colloidal particles with an agglomeration number of about 200 are present after a few milliseconds. They strongly absorb at 390 nm. Larger particles which still absorb close to 390 nm but cause much stronger scattering of red light are present after a few seconds. Free radical reactions can be influenced by the presence of colloidal silver particles; several examples are discussed. – The hydrogen yield from γ‐irradiated silver solutions (25 to 130°C) is equal to the yield of 0.6 molecules/100 eV known as direct molecular yield. It is concluded that the smaller silver aggregates formed in the reduction of Ag+ do not react with water in spite of their negative redox potentials.
Translational Energies of CH3+, CHO+, CH2OH+, and CH3CO+ Ions from Oxygen‐Containing Molecules
Authors: Kumakura Minoru , Sugiura Toshio
Published: September 2012

The translational energies of CH3+, CHO+, CH2OH+, and CH3CO+ ions from oxygen‐containing molecules have been measured by a new method in a time‐of‐flight mass spectrometer. The method is developed by which the energy can be readily determined from the analysis of the decay curve of ion. A relation between the translational energy of ions and the structure of source molecules was discussed.
Viscosity of Aluminium Chloride and Acidic Sodium Chloroaluminate Melts
Authors: Brockner W. , Tørklep K. , Øye H. A.
Published: September 2012

The viscosity of NaCl‐AlCl3 melt mixtures has been determined in the range 0.50 ≤ X ≤ 0.80, 160°C to 300°C. The viscosity of pure AlCl3 was measured over the temperature span 196°C to 286°C. A recently designed oscillating vessel viscometer was used. The method, which utilizes closed cylindrical cups subjected to vapour pressures exceeding 11 atm, is absolute and requires no calibration against reference liquids. Results are corrected for surface effects and for evaporation within the crucible. Applying Arrhenius temperature dependencies and the Arrhenius mixing rule, the viscosity is expressed as a function of temperature and composition with an overall standard deviation of 0.4% when the presence of AlCl−4, Al2Cl−7, Al3Cl−10, and Al2Cl6 is assumed.
The Viscosity of CaCl2 Solutions in the Range 20–50°C
Authors: Gonçalves F. A. , Kestin J.
Published: September 2012

As a continuation of an earlier paper concerned with the viscosity of aqueous solutions of NaCl and KCl, the present paper communicates the results of precise, relative measurements of the viscosity of aqueous solutions of CaCl2. The measurements covered the entire range of composition up to saturation, all at atmospheric pressure and at 20.00, 25.00, 30.00, 40.00, and 50.00°C ± 0.01°C. The reproducibility was of the order of several parts per ten thousand, and the accuracy is estimated to be one of 0.3% at worst. ‐ As a byproduct, we obtained an accurate correlation between molality, c, and density, p, for these solutions measuring at 20.00 and 25.00°C (± 0.01°C).
The Radial Pair‐Distribution Function of Liquid CHCl3
Authors: Hoheisel Claus , Zeidler M. D.
Published: September 2012

The spherically symmetric part of the static pair‐distribution function of liquid CHCl3 determined by neutron and x‐ray scattering experiments is compared with results of molecular dynamics calculations based on an (18‐6) Lennard Jones type potential. The agreement is sufficient with respect to the simplicity of the model involved.
Anomalie im Diffusionsverhalten von n‐Alkanen in NaMgA‐Zeolithen bei höheren Temperaturen
Authors: Roethe Klaus‐Peter , Roethe Annemarie , Fiedler Klaus , Gelbin David
Published: September 2012

Bei Diffusionsmessungen mit n‐Alkanen in NaMgA‐Zeolithen wurde zwischen 523 und 750 K ein Übergang von einem Niedertemperaturzu einem Hochtemperaturzustand beobachtet. Wir deuten diesen Vorgang als eine Änderung der Kationenkonfiguration im Hohlraum unter Beteiligung des Adsorptivmoleküls. In einem thermischen Gleichgewichtsprozeß sollten derartige Kationenpositionswechsel zur Blockierung der Eingänge zum großen Hohlraum und dadurch zur Änderung des Sorptionscharakters von 5 A‐ zu 4A‐ähnlich führen. Auffallende Abweichungen vom Arrheniusgesetz und der Abfall der Mikroporen‐Diffusionskoeffizienten Dz bie hohen Mg‐Gehalten und 673 K sind durch die Zustandsänderung erklärbar. Der schwankende Verlauf der Dz mit der C‐Zahl der n‐Alkane bei 673 K läßt sich mit unseren Modellgleichungen nachrechnen.
Vibronic Coupling via the Non‐Totally Symmetric C‐H Bending Mode in Pyrazine
Authors: Brickmann Jürgen
Published: September 2012

The absorption and emission data for the forbidden S0 → S1 transition of pyrazine in the vapor phase and in a benzene host are analyzed with the aid of an intensity‐borrowing mechanism which involves vibronic coupling of the 1B3u(n, π) and 1B2u(π, π) states via the non‐totally symmetric 10a mode. The vibronic coupling is discussed in terms of a non‐adiabatic model (NA) which takes static and dynamic interactions into account, as well as in terms of static Herzberg‐Teller coupling (HT). By variation of different model parameters all observed quantities can be reproduced within experimental error with the NA model, while this is not generally possible with the HT scheme. It is observed that the adiabatic frequency of the 10a mode in the S1 state is much lower than the ground state frequency; the NA model predicts that the frequency of this mode in the S2 state is approximately equal to the ground state value.
On the Coupling of Vibronic States in NO2
Authors: Gerloff M. , Russegger P. , Brickmann J.
Published: September 2012

A model of indirect near resonance coupling of two vibronic states belonging to different excited Born‐Oppenheimer electronic states of a molecular system is presented. In the absence of direct coupling terms the two states can interfer via a third “messenger” state or via a manifold of such states. If the coupling is not too strong the messenger states act only in a seeming catalytic capacity, i. e. the two originally not coupled vibronic states seem to be coupled directly. The 5935Å laser‐excited fluorescence of NO2 is interpreted in terms of indirectly coupled 2B1‐ and 2B2‐vibronic states via highly excited 2A1 vibrational states. The Franck‐Condon factors are calculated within the rigid bender model of Hougen, Bunker, Johns, and Stone. Best agreement with experiment is obtained if one assumes that the fluorescent state is a linear combination of 2B1 (ν = 4) and 2B2 (ν = 7) vibronic states. The spectra calculated with a pure 2B1 or 2B2 initial vibronic state disagree with experimental material.
Vibrational Relaxation in Liquids. I: 1D‐Molecular‐Dynamics Studies of Mixtures of Bromine and Argon
Authors: Nehrkorn Christoph , Brickmann Jürgen
Published: September 2012

Vibrational energy relaxation in liquids is investigated using the molecular‐dynamics method. A one‐dimensional ensemble of liquid bromine and of mixtures of bromine and argon is simulated with different compositions and temperatures. The vibrational motion of the bromine molecules is described by a harmonic oscillator, and the intermolecular interactions are given by Lennard‐Jones (12, 6) potentials with the parameters being derived from different experiments. The observed energy relaxation times of initially excited bromine molecules decrease at higher temperature, and are longer in mixtures of bromine and argon than in the pure liquid. The effective collision strength is also calculated, the results disagree with the strong collision assumption used in reaction rate theories. It is demonstrated that the main aspects of vibrational energy relaxation in liquids can be adequately studied with the aid of one‐dimensional models.
The Shape of the Absorption Edge in Compressed Fluid Mercury Vapour
Authors: Popielawski J. , Uchtmann H. , Hensel F.
Published: September 2012

New optical absorption measurements near the absorption edge of dense supercritical mercury vapour are presented. An attempt is made to explain the shape of the edge on the basis of the model of the band‐state densities in disordered semiconductors suggested by Mott and others. It is shown that the shape of the edge can be explained with the assumption that it arises from electronic transitions between localized states in the band edge tails, the density of which is assumed to be a Gaussian function of the energy.