bluuebunny/crossref_metadata_2025 huggingface dataset:
Rate Constant for the Reaction of NH (X3Σ−) with O2 Determined by Pulsed Vacuum UV Photolysis of NH3 and Resonance Fluorescence Detection of NH
Authors: Zetzsch C. , Hansen I.
Published: September 2012

The kinetics of NH (X3σ−) was studied using resonance fluorescence of NH (A3 →II Σ X3Σ−). From the pulsed vacuum uv photolysis of mixtures containing NH3, O2, and He the rate constant for the reaction magnified image. was found to be (at 296 K): magnified image.
Designed Monolayer Assemblies
Authors: Möbius Dietmar
Published: September 2012

Various techniques have been used for organizing molecules at interfaces to form monolayers. With these components of designed monolayer assemblies complex systems of cooperating molecules have been constructed and it is shown that the planned functions of the artificial units depend strongly on the spatial and energetic coordination of the constituent molecules.
Light Induced Electron Transfer between Spatially Separated Donor and Acceptor
Authors: Möbius Dietmar
Published: September 2012

Quenching of fluorescence due to electron transfer is observed in monolayer assemblies when electron donor and electron acceptor, both immobile, are either in the same monolayer or in adjacent monolayers. When the donor and acceptor monolayers are separated by two fatty acid interlayers no fluorescence quenching is detected.

Two types of light induced electron transfer have been observed.

The donor is excited and the electron is transferred from the S1 state of the donor into the lowest unoccupied orbital of the acceptor. The donor fluorescence is quenched.

The acceptor is excited and the electron is transferred from the S0 state of the donor into the highest occupied orbital of the acceptor. The acceptor fluorescence is quenched.

In both processes the initial situation is recovered by back transfer of an electron from the reduced acceptor to the highest occupied orbital of the donor.

These electron transfer processes have been studied by varying the concentration of the acceptor. The fluorescence quenching depends on the average distance R̃ between acceptor molecules and values of R̃1/2 (average distance in the acceptor layer at which the fluorescence intensity is half of the intensity without electron transfer) have been determined.

The value of R̃1/2 depends on the energetic position of both the electron donating level and the electron accepting level as calculated from electrochemical and spectroscopic data.
Sensitized Photocurrent through a Semiconductor Electrode by Consecutive Energy and Electron Transfer in Dye Monolayers
Authors: Arden Wolfgang , Fromherz Peter
Published: September 2012

Electron injection from photoexcited cyanine dyes into the conduction band of a thin film semiconductor (indiumoxide) is investigated in an electrochemical cell. The sensitizing dyes are incorporated into tenside monolayers covering the electrode. Separation of the chromophores from the electrode by two tenside layers suppresses sensitized photocurrent. Insertion of an appropriate second dye at the semiconductor surface recovers the sensitizing yield of the distant dye. The distant dye absorbs light, transfers energy to the second dye at the semiconductor surface which transfers an electron into the electrode. The processes in this concerted energy‐electron‐transfer system are characterized by simultaneous measurement of photocurrent and fluorescence emission.
Adsorption of Polar Molecules on the Surface of Water
Authors: Baumer Doris , Mang H. , Findenegg G. H.
Published: September 2012

The adsorption of fluorobenzene, chlorobenzene, and benzonitrile on the surface of water has been determined by measurements of the surface tension as a function of the vapor pressure of the organic vapor. The standard thermodynamic quantities of adsorption, δGo, δHo, and δSo, were calculated at the zero‐coverage limit. δHo is less negative than the enthalpy of condensation of the respective pure vapor. Near the saturation vapor pressure chlorobenzene forms a single monolayer whereas fluorobenzene tends to multilayer formation. The stability of adsorbed films on water is predicted by the Lifshitz formula in the correct sequence fluorobenzene > benzene > chlorobenzene.
The Effect of Chain Length Compatibility on Molecular Area, Intermolecular Spacing, Dispersion Energies and Evaporation Resistance of Mixed Monolayers
Authors: Shah D. O. , Shiao S. Y.
Published: September 2012

Using mixed monolayers of alkyl alcohols, it was established that the unequal chain lengths cause an expansion in the area/molecule in mixed monolayers. Assuming the cross‐sectional area of molecules to be circles, it was shown that a difference of two methylene groups between the two components of the mixed monolayer causes an increase in the intermolecular spacing of about 0.05 A. The small increase in intermolecular spacing strikingly decreases the resistance of mixed monolayers to evaporation of water. The surface viscosity was found to be maximum when the chain‐lengths of the components were equal. The dispersion energy between alcohol molecules in the mixed monolayer was calculated using Salem's approach. It was found that a small increase in intermolecular spacing (0.05Å) can decrease the dispersion energy by 6.7 kJ/mol. The magnitude of this decrease is about 1/4 of the energy of a hydrogen bond. It was further shown that the small increase in intermolecular spacing, decreases the melting point of mixed crystals by about 9°C. The chainlength compatibility of mixed surfactants also influences the bubble size, bubble stability, emulsion stability, lubrication, contact angle and wettability. In summary, using the monolayer approach, it was experimentally shown that a small change of 0.05 Å in intermolecular spacing, brought about by a difference of 2 methylene groups between the two surfactant molecules, can strikingly influence the dispersion energy between the molecules. The small change in dispersion energy influences the characteristics of many engineering processes such as bubbles, foams, emulsions, lubrication and wettability.
Vergleich des Polymorphismus in Phospholipid‐Mono‐und geordneten Multischichten
Authors: Albrecht O. , Jürgens E.
Published: September 2012

1. Durch direkte Messung von Isobaren mit einer konventionellen Langmuir‐Filmwaage konnten in mehreren Lipiden (Lecithine, Phosphatidsäuren), neben dem bekannten Phasenübergang 1. Ordnung und dem Gas‐Fluüssigkeitsübergang bei sehr niederen Drücken, zwei weitere Phasenübergänge 2. Ordnung nachgewiesen werden.

Es wird auch eine Zuordnung zwischen der Hauptumwandlung von Multischichten und Monoschichten angeboten, die nicht die Phasenumwandlungstemperatur gleichsetzt, sondern die Umwandlungsenthalpie und die Flächenänderung beim Phasensprung.

2. Geordnete Multischichten wurden nach der Methode von L. Powers und N. A. Clark hergestellt. Der Polymorphismus wurde mit Hilfe der Spinlabel‐Technik und optischen Methoden untersucht.
The Association of Water on Molecular Layers
Authors: Steinbach H. , Sucker ChR.
Published: September 2012

Hydrocomplexes which form around the hydrophilic group of surface‐active compounds are one of the basic requirements for the colloid‐chemical behaviour of these compounds. According to our conception, the complex in which four water molecules are attached to the hydrophilic group is in equilibrium with the one‐water‐molecule‐complex while compressing a myristic acid monolayer by a Langmuir‐balance. The space requirements of these complexes can be calculated from the size of the hydrophilic group and from the space requirement of the water molecules, which amount to 7.3 Å2 for each one. Polymeric substances follow the same laws, as will be demonstrated by the example of polydimethyl‐siloxane.

Depending on the surface area available, a discrete number of water molecules per (CH3)2SiO unit attach themselves to polydimethylsiloxane spread upon water. When such films are compressed, four defined states of orientation will result.

This concept is transferred to surfaces of solids. It is shown that when silicone‐treated glass plates are sprayed with water, four defined states of wetting will form which are to be co‐ordinated with the states of orientation.

Glass plates with these different states of silicone coating are prepared; they are subjected to measurement of contact angles which they form with various fluids. Informative relationships of adhesion energy, surface tension on solids, wettability, etc. to the interfacial coating are shown when the surface tension of the fluid is plotted versus the adhesion energy.

Pronounced polarization of the molecules within the complexes is found while they are adsorbed on the interface of the solid.

The heat of association, which is the same whether the poly‐dimethylsiloxane films are adsorbed on water or glass, is calculated from the adhesion energy. Finally, the heat of association allows conclusions to be drawn as to the tensile strength of silicone rubber.
Studies of Lipase and Phospholipase A2 Acting on Lipid Monolayers
Authors: Verger R. , Pieroni G. , Rietsch J. , Pattus F. , Ferrato F. , De Haas G. H. , Desnuelle P.
Published: September 2012

The penetration process of various lipolytic enzymes into lipid monolayers was studied by the use of a surface barostat technique. The induction time, measured during pre‐steady state conditions, increased abruptly for a given value of the surface pressure. This appears to be due to a degree of lipid packing above which the enzyme no longer can penetrate the lipid film.

Pancreatic lipase and phospholipase A2 have been shown by the monomolecular film technique to be progressively inactivated when adsorbed at the interface of their respective substrates. This inactivation is faster for lipase than for phospholipase. It is also enhanced by low film pressure and film transfer.

The use of radioactive phospholipase and lipase samples offered the possibility to measure for the first time the amount of enzyme adsorbed at a monomolecular film. This adsorption was found to be relatively slow under the conditions of the assays.

The existence of an optimum in the velocity versus surface pressure profile is the result of at least two counterbalancing factors. As the surface pressure increases, the amount of enzyme present in the interface decreases, whereas the minimal specific activity of the enzyme increases.

Using radioactively labelled lipase, we have shown for the first time in a bile salt free system that the critical surface pressure above which lipase can no longer penetrate a negatively charged monolayer is around 23 dynes/cm. This critical surface pressure is shifted up to 30 dynes/cm in the presence of colipase. The 23 to 30 dynes/cm range may be the critical region where colipase displays assistance during the penetration process of lipase under physiological conditions.

From this study with monolayers, we can conclude that activity of lipolytic enzymes used as tools for probing biological membranes will be greatly influenced by the physicochemical nature of the membrane‐water interface.
Bilayer Lipid Membranes
Authors: Stark G.
Published: September 2012

Thin lipid membranes formed across an aperture in a teflon foil are frequently used as model systems to simulate the hydrophobic diffusion barrier of biological membranes. These membranes have a thickness of about twice the length of a lipid molecule (bilayer membranes) and are prepared either by a spontaneous transition of a thick lamella made from a solution of lipids in a hydrocarbon [1] or by a direct “addition” of two monomolecular lipid layers on the two water surfaces separated by the teflon foil [2]. The aqueous phases on both sides of these planar membranes are easily accessible by electrodes which may serve to study the electrical properties of the membranes. The whole system allows the application of steady state electrical methods as well as that of fast relaxation methods. The latter include the voltage jump‐current relaxation technique [3,6], the charge pulse method [4,5] as well as the temperature jump method [6]. These kinetic techniques have been used throughout recent years to investigate ion transport phenomena across bilayer lipid membranes.

Unmodified lipid membranes have been found to represent high energy barriers for the movement of inorganic cations and anions. A simple equivalent electrical circuit of the membrane consists of a parallel arrangement of the membrane resistance RM and the membrane capacitance CM (typical values: RM = 106‐108μcm2, CM = 0.3‐0.8μF/cm2). A refined version composed of three of such elements (one for the hydrocarbonlike membrane interior, the two others for the polar membrane‐water interfaces) has been suggested on the basis of a.c. measurements [7]. These measurements were, however, confined to the rather small band width of 0.1‐100 Hz. A different possibility of testing such a circuit is to make use of the voltage jump method. The induced current relaxation may be measured with a time resolution of at least 1 μs and very high sensitivity by using signal averaging techniques. For the three element circuit described above the relaxation should consist of two exponential terms. At least five different relaxation times were, however, necessary to obtain a sufficiently good fit to the experimental data [8.9]. This finding indicates that even the refined equivalent circuit is insufficient for a phenomenological description of the high frequency behaviour of bilayer lipid membranes. The complex current relaxation may be interpreted on the basis of cooperative dielectric relaxation phenomena associated with the dipoles of the polar head groups of the lipid molecules.
Ring Micelles in Membranes – the Concept of a Simple Pore Structure
Authors: Boheim G.
Published: September 2012

Ionic surfactants form spherical micelles in surfactant‐water systems. The kinetics of micelle formation is analyzed by means of conductivity measurements of surfactant monomers. Pressure‐jump experiments exhibit two relaxation processes. The slow process is assigned to a change in micelle concentration and the fast one to a change in micelle size distribution [1].

Pore formation of alamethicin‐type antibiotics in two dimensional lipid membranes shows striking similarities to micelle formation. Voltage‐jump experiments demonstrate the existence of two relaxation processes which are accordingly assigned to changes in pore concentration (slow process) and to changes in pore size distribution (fast process). Contrary to the situation with spherical surfactant micelles in the case of alamethicin ring micelles (pores) the conductance of an ensemble of pores is measured. Furthermore, it is possible to analyze single fluctuating pores and the interpretation of the two relaxation processes is confirmed by independent direct measurements [2, 3].

Since the molecular models of the two kinds of aggregates are based on the same mechanism: a small nucleus is formed which then grows by uptake of monomers until a steady‐state distribution of aggregates of statistically fluctuating size is reached, the theoretical description of both systems has to be equivalent.
Change of Lecithin Aggregation Due to Valinomycin‐Lipid Interaction
Authors: Walz D.
Published: September 2012

Valinomycin added to a suspension of lecithin vesicles with chlorophyll a or b incorporated into their membranes induces slight changes in the absorption spectrum of chlorophyll. The analysis of these changes revealed that this effect is not associated with the ionophoric properties of valinomycin but indicates a valinomycinlecithin interaction. As a consequence, the aggregational state of the lecithin molecules is altered in a domain which comprises about 40 lipids around one valinomycin molecule. The ability of the chlorophylls to detect different lipid aggregations arises from their solvatochromic behaviour. Using spectroscopic data for chlorophyll in different solvents, it could be inferred that a change in electrostatic interaction is the main reason for the difference of the spectrum of chlorophyll embedded in lecithin of different aggregational states. This interaction originates from a strong electric field associated with the polar moieties of the lipids which is much larger than the field imposed by transmembrane potentials. Hence the absorbance changes of chlorophyll due to such potentials are rather small compared to those induced by valinomycin.
Fluorescence Spectroscopic and Thermodynamic Studies of Monolayers Containing Pheophytin a and Lecithin
Authors: Heithier H. , Galla H.‐J. , Möhwald H.
Published: September 2012

Mixed monolayers of pheophytin a and L‐α‐dimyristoyllecithin (DML) are investigated on the water surface. The studies gain their special value from the simultaneous measurement of surface pressure and fluorescence intensity as a function of the covered area per molecule. A phase separation in the liquid state of the mono‐layer is established. Phase (1) exists almost exclusively of pheophytin molecules. Phase (2) exists essentially of DML domains solubilizing pheophytin in a concentration of 15 mol‐%. During the DML main transition the pheophytin solubility decreases to about 2 mol‐%, the excess pheophytin being precipitated within the surface layer. During the pheophytin main transition an ordered structure below the surface layer is formed. A stabilizing interaction between the pheophytin domains and their environment is observed and discussed. A sharp fluorescence change at a pressure below 0.5 dyn/cm indicates another phase transition. It very probably involves an unwrapping of pheophytin from water molecules.
Energy Transfer and Fluorescence Quenching in Chlorophyll Containing Vesicles
Authors: Luisetti J. , Galla H.‐J. , Möhwald H.
Published: September 2012

Fluorescence spectroscopic experiments are reported on dimyristoyllecithin (DML) vesicles containing pheophytin a, chlorophyll a or chlorophyll b. From the temperature as well as from the concentration dependence of the fluorescence intensity a phase separation at low temperatures is observed: The chlorophylls are solubilized by the DML phase only up to concentrations of the order of 1 mole‐%. the excess molecules being precipitated in domains containing almost exclusively the chlorophylls. – Whereas at high temperatures (30°C) for chlorophyll a containing vesicles a phase separation could not be established, this was possible in the pheophytin case. The pheophytin solubility in the liquid DML phase amounts to about 10 mole‐%, which is consistent with monolayer studies of the system. – The efficiency of energy transfer from chlorophyll b to chlorophyll a increases with decreasing temperature for small chlorophyll concentrations (< 1 mol‐%). This is due to the decrease in intermolecular distance on solidification of the lipid. The temperature dependence of the transfer efficiency is reversed at high chlorophyll concentrations (≤ 20 mole‐%). This is interpreted as a consequence of the decrease of the chlorophyll solubility in the DML phase that causes a decrease in the chlorophyll‐chlorophyll distance.
Structure and Dynamics of Phospholipid Multihilayers : An E.S.R. Study Using Biradicals as Spin Probes
Authors: Kothe G. , Ohmes E. , Meler P. , Blume A.
Published: September 2012

The Alexander‐Kaplan method is applied to develop a com‐ prehensive line shape model, which accounts for the E.S.R. spectra of biradicals in the fast‐rotational and slow‐motional region [1]. The spin hamiltonian employed considers Zeeman, exchange, dipole‐dipole and hyperfine interactions of the two unpaired electrons. Orientational order is described by an orientational distribution function with adjustable parameters.

Temperature and angular dependent E.S.R. spectra of biradicals in phospholipid multibilayers are studied [2]. Computer simulations provide the orientational distribution functions and rotational correlation times of the spin probes. They occupy two different sites in the bilayer membrane.

The orientation and motion of the spin probes is related to the structure and dynamics of the phospholipid phases. In the gel phase of dimiristoyllecith in the tilt angle is 6 = 30°. At the pre‐transition temperature 6 decreases. A small spread in 6 indicates a long periodic ripple on the bilayer surface. In the liquid crystalline phase 6 = 0°. The viscosity of the phospholipid bilayers changes abruptly at the phase transitions and varies between q = 0.2 P at 310 K and q = 3.0 P at 275 K. The fusion activation energy E, for all three phases is nearly constant and amounts to 28.9 kJ/mol I E, s 33.5 kJ/mol.

Many important motions' in membranes occur with rotational times τr> 10−7 s, but the E.S.R. Of the monly employed nitroxide spin probes have been found useful, Only measuring faster motions C3i. With biradical 'pin probes, however, slower motions can be detected. This particular sensitivity of biradicals results from the anisotropy of the electron dipolar interactions, not available in monoradicals.
Lipid‐Protein‐Interaction in Model Membranes: Binding of Melittin to Lecithin Bilayer Vesicles
Authors: Galla H.‐J. , Hartmann W. , Sackmann E.
Published: September 2012

We have studied the interaction of melittin with lecithin bilayer membranes. Fluorescence polarisation measurements were performed beside the use of excimer forming pyrene derivatives.

1. Diphenyl hexatriene, a fluorescence polarisation probe, was used to investigate the lipid phase transition. Addition of melittin leads to an increase of the transition temperature. Characteristic breaks were obtained plotting Tu as a function of the melittin concentration. The change in the width of the phase transition gives an indication of phase separation phenomenon.

2. Pure pyrene lecithin membranes were agitated by melittin. A dramatic decrease in the excimer to monomer ratio was observed showing the same characteristic breaks.

3. No change in the lipid phase transition temperature was obtained using pyrene decanoic acid and pyrene lecithin as probe molecules. Pyrene lecithin is involved in the lipid‐protein‐complex and therefore prevented from undergoing the lipid phase transition. Rigid patches surrounding the peptide molecule were formed. The pyrene decanoic acid is squeezed out from these regions leading to an increase of the excimer yield in the bulk lipid.

4. High melittin concentration (c > 10 mole‐%) leads to a membrane disruption followed by the formation of a stable melittin micell furnished with lipids.
Infrared Spectroscopic Study of the Interaction of Alamethicin with Oriented Bilayers of Lecithin
Authors: Fringeli U. P. , Fringeli M. , Günthard H.
Published: September 2012

Alamethicin is a linear peptide of 19 residues [1,2]. When added to lipid bilayer membranes a correctly applied electric field induces pores with fluctuating diameter [3,4]. Our investigation deals with peptide‐lipid interaction in the absence of an electric field.

Alamethicin and L‐α‐dipalmitoyl‐lecithin/alamethicin mixtures (molar ratios 25:1 to 250:1) were dissolved in chloroform. Oriented layers (thickness 100–500 Å) are obtained by evaporation of the solvent. Incorporation of alamethicin into the lecithin bilayers required exposure of the sample to liquid water for several hours.

The same samples are obtained, when alamethicin is dissolved in the aqueous surrounding of oriented lecithin bilayers. The most prominent feature of this system is a significant change of peptide structure in going from dry or hydrated (90% rel. humidity, 25°C) to aqueous environment. In both states alamethicin is incorporated into the lecithin bilayer. In the former one about 90% of the peptide assumes a helical structure with the helix axis parallel to the hydrocarbon chains. By H–D‐exchange measurements it turned out that the helix flexibility is greater near the C‐terminus, which is found to interact with the polar headgroups of lecithin. However, in aqueous environment most probably the helices are unfolded, spanning now the lipid bilayer. The shape of the amide I band is typical for associated, unfolded alamethicin molecules (parallel β‐structure). The number of associated molecules varies from dimers to multimers. Considerable reduction of helical content in going from unpolar to polar solvent has also been observed by CD and NMR [5]. Concerning the influence of alamethicin on lecithin structure it should be mentioned that significant interaction between PO2− and ‐N(CH3)3+ groups of lecithin and Glu18, Gln19 of the peptide C‐terminus is observed. Hydrocarbon chain ordering is not influenced in the dry and hydrated state, however, it is significantly reduced in aqueous environment.
Temperature Dependent Aggregation of Bacteriorhodopsin in Dipalmitoyl‐ and Dimyristoylphosphatidylcholine Vesicles
Authors: Heyn M. P. , Cherry R. J.
Published: September 2012

Bacteriorhodopsin has been incorporated into large unilamellar vesicles of dipalmitoyl‐ and dimyristoylphosphatidylcholine. The state of aggregation of bacteriorhodopsin in these vesicles was investigated using X‐ray diffraction, freeze fracture electron microscopy, circular dichroism and rotational diffusion measurements.

At temperatures below the lipid phase transition, the X‐ray diffraction results show that bacteriorhodopsin crystallizes into patches with the same hexagonal lattice as is observed in the purple membrane. This hexagonal lattice is clearly visible in the electron micrographs. Measurements of the rotational diffusion of the protein, using the decay of flash‐induced dichroism, show that the protein is completely immobilized. In agreement with these results the circular dichroism spectra exhibit the typical exciton coupling bands of the native lattice.

Above the phase transition, the lattice disaggregates and the protein molecules are monomeric provided the lipid to protein ratio is sufficiently high. In the X‐ray diffraction pictures both the protein and the lipid long‐range order are absent. The freeze fracture electron micrographs show that the bacteriorhodopsin particles are randomly distributed in the plane of the lipid bilayer. In harmony with these observations rotational diffusion measurements demonstrate that the bacteriorhodopsin molecules are free to rotate about an axis normal to the plane of the membrane. The rotational correlation time shows a marked dependence on the lipid to protein ratio. The absence of exciton coupling bands in the circular dichroism spectra indicates that specific bacteriorhodopsin aggregates are absent.

It seems probable that the mechanism of bacteriorhodopsin crystallisation involves the growth of crystalline lipid areas from which the protein is excluded.
Permeability of Cyclic Nucleotides Across Black Lipid Membranes
Authors: Micelli S. , Gallucci E. , Lippe C.
Published: September 2012

There are many evidences that cyclic AMP is the intracellular mediator or ADH effect in the urinary bladder, and that theophylline, an active inhibitor of cyclic AMP phosphodiesterase, increases cellular pool of cyclic AMP.

Recently, some Authors [1‐3] reported that the effect of cyclic AMP on urea permeability in toad and frog urinary bladders is evident after treatment with theophylline.

Mendoza and Nakamoto [4], studying the action of theophylline when the serosal medium contained high potassium concentration concluded that theophylline “stimulates osmotic water flow and short‐circuit current across the toad bladder by a mechanism other than by inhibition of cyclic nucleotide phosphodiesterase or alteration in permeability to cyclic AMP”. Furthermore, Urakabe et al. [5] have suggested that theophylline reduces the permeability of the toad bladder to cyclic nucleotide by decreasing its efflux from the epithelial cells.

In the present work we studied the permeability of the cyclic AMP (AMPc), monobutyryl cyclic AMP (mb‐AMPc), dibutyryl cyclic AMP (db‐AmPc), 5'‐AMP, adenine, adenosine, urea and acetamide across the black lipid membranes, and the effect of theophylline on their permeability.
Photochemically Induced Reactions in Vesicles
Authors: Morris D. , Thomas J. K.
Published: September 2012

Excited states of pyrene P, were produced in lecithin vesicles by excitation with a‐very short < 1 nsec pulse of Cerenkov light. Several different reactions of excited pyrene in the vesicles were subsequently studied:

The reaction of excited pyrene with ground state pyrene to produce excimers

The quenching of P with hydrophillic quenchers located mainly in the aqueous phase and

With hydrophobic quenchers located in the lipid phase.

The kinetics of the reaction depend uniquely on the spacial configuration of the reactants and, two dimensional as well as conventional three dimensional kinetics were observed. In particular data in type a) shows a tendency for pyrene to aggregate' in the lipid phase, as cited earlier by Sackmann et al.
Pulse Radiolysis Studies in Model Lipid Systems. The Influence of Aggregation on Kinetic Behavior of OH Induced Radicals in Aqueous Sodium Linoleate
Authors: Patterson L. K. , Hasegawa K.
Published: September 2012

The kinetic and spectral behavior of radicals formed by hydroxyl radical attack on linoleate anions has been studied by pulse radiolysis. Reactivity of ·OH toward this surfactant is an order of magnitude greater in monomeric form [k·OH+linoleate= 8.0 ± 109M−1sec−1] than in micellar form [k·OH+lin(micelle)= 1.0 ± 109M−1sec−1]. Abstraction of a hydrogen atom from the doubly allylic position gives rise to an intense absorption in the UV region (δmax= 282–286 nm, ε 3·104M−1cm−1) which may be used as a probe of radical activity at that site. This abstraction may occur, to a small extent, directly via ·OH attack. However, greater than 90% of initial attack occurs at other sites. Subsequent secondary abstraction of doubly allylic H atoms appears to occur predominantly by: (1) intramolecular processes in monomers, (2) intermolecular processes in micelles. Disappearance of radicals by secondary processes is slower in the micellar pseudo phase than in monomeric solution.
Behaviour of Mixtures of Different Surfactant Types in Solution and on Interfaces
Authors: KurzendC.‐W C.‐P. , Schwuger M.‐J. , Lange H.
Published: September 2012

The formation of mixed micelles and mixed adsorption layers in aqueous solutions of homologous and non‐homologous surfactants was investigated according to various complementary methods. – Mixed solutions of homologous surfactants show ideal mixing behaviour in the mixed micelles and mixed monolayers, in which the homologue with the longer chain prevails. – Mixed micelles and mixed monolayers of anionic and nonionic surfactants, however, show a strong deviation of the ideal behaviour within the meaning of an enhanced association and surface activity. The cause is the decrease of the electric repulsion of the ionic groups of the anionic surfactants by the ethylene oxide chains of the nonionic surfactants which are incorporated in the micelles and the monolayers. In the range of small concentrations mainly micelles of the nonionic component are formed at first. With increasing concentration there occurs an enhanced incorporation of the anionic surfactant in the micelle even below the critical micelle concentration of the pure anionic surfactant. Investigations on the equilibrium adsorption on hydrophobic interfaces clearly contribute to the problematic nature of non‐homologous surfactants.
Liquid Crystalline Structures in the Lecithin‐Cholate‐Water System Studied by NMR and X‐Ray Diffraction Methods
Authors: Arvidson G. , Fontell K. , Johansson L. B.‐Å , Lindblom G. , Ulmius J. , Wennerström H.
Published: September 2012

Although bile salts have several properties typical for a surfactant substance they show features that differ from those of ordinary amphiphiles. For instance, they do not aggregate in the cooperative manner and they never form lyotropic liquid crystalline phases. However, they have a large capacity to break lecithin bilayers by forming mixed micellar aggregates.

The phase diagram for egg yolk lecithin‐sodium cholate‐water has been determined by Small and coworkers [1]. The extension and appearance of the different phases are similar to those in the phase diagrams for ordinary soap‐alcohol‐water systems. Concerning the structures on the molecular level of the different phases, suggestions have been given by Small, but no unambiguous experimental evidence for most of these structures have been reported.

Here we present some different NMR studies in order to inquire into the molecular packing and order in the aggregates. Complementary x‐ray studies are also performed. 1H‐NMR shows that, in contrast to what is found for ordinary soap systems, spectra for lecithin‐cholate systems are essentially the same for the so called hexagonal (E) and lamellar phases at a given lecithin/cholate ratio. The order parameter calculated from 2H quadrupole splittings of the‐methyl groups of dilauroyl lecithin vary continuously between the E and lamellar phases, contrary to data obtained for soap systems. All these findings show that the molecular ordering is very similar in the two phases.

It is also found that the molecular order decreases strongly with increasing cholate concentration.

The x‐ray diffraction picture for the E‐phase shows reflexions that do not unambiguously fit the hexagonal structure.

2H water quadrupole splittings of a between glass plates macroscopically oriented E‐phase sample showed that it orients uniaxially with at least a three‐fold symmetry around the symmetry axis.

Lipid diffusion coefficients can be conveniently obtained with pulsed NMR for both cubic [2] and lamellar [3] phases. The diffusion coefficients obtained are of the same order of magnitude, leading to the conclusion that the molecular diffusion occur over macroscopical distances in the cubic phase [2,3]. Thus the cubic phase consists of continuous lipid aggregates. Preliminary diffusion data obtained for the E‐phase indicate that also this phase consists of continuous amphiphile aggregates. This is not compatible with the structure previously proposed, where micelles are stacked to form long rods.
Spectroscopic Investigations of Viscoelastic Solutions Containing the Cetyltrimethylammonium Ion
Authors: Johansson L. B. , Lindblom G. , Ulmius J. , Wennerström H.
Published: September 2012

It has previously been shown [1] that very dilute solutions of cetyltrimethylammonium salts can show strong viscoelastic behaviour. In order to elucidate the molecular organization specific for the viscoelastic behaviour we have, using several spectroscopic techniques, investigated aqueous solutions containing cetyltrimethylammonium salicylate.

Using proton magnetic resonance it is found by simulation of the bandshapes [2] that in these dilute (<1%( micellar solutions the viscoelastic behaviour correlates with the aggregate size, both with respect to changes in composition and in temperature. Thus a necessary condition for viscoelastic behaviour is aggregates larger than the minimal spherical micelle.

The viscoelastic solutions were oriented by Couette flow. The orientation was monitored through the linear dichroism (LD) of the solution and it is found that the LD increases with increasing concentration. The temperature for obtaining zero LD is in agreement with the disappearance of the viscoelastic properties of the solution.

An independent measure of aggregate sizes was obtained by studying the quasielastic light scattering (QLS) of the solutions which also indicates a transition from large to smaller aggregates at higher temperatures.

It is suggested that electrostatic and anisotropic interactions between the large aggregates cause a specific periodic colloidal structure that is responsible for the viscoelastic behaviour.
Quasielastic Light Scattering Studies on Micellar Solutions
Authors: Rohde A. , Sackmann E.
Published: September 2012

The scattered light intensity and the intensity‐correlation function of sodium dodecyl sulfate solutions with surfactant concentrations ranging from below the critical micellar concentration up to 50 mM were measured.

From plots of the scattered light intensity versus SDS‐concentration it followed that aggregates of long chain alcohols were absent. These were removed by a foaming procedure. Intensity‐correlation functions were measured with a digital autocorrelator (Malvern) operating in the clipping mode. Using a procedure introduced by Koppel (1972) the measured intensity correlation functions were fitted to a power series in time. In the case of a pure diffusive motion this procedure allowed the determination of the (number‐averaged) diffusion constant and to estimate the width of the size distribution of the diffusing particles.

The main results are:

There is an overall increase of the diffusion coefficient with increasing SDS‐concentration, possibly due to the interaction of micelles.

The calculation of the hydrodynamic radius of the micelles by using the Einstein relation gives a lower value than would be expected from the chain length of the SDS‐molecules. This could be attributed to the dependence of the diffusion coefficient on the charge of the micelles.

There is a dip in the diffusion constant versus SDS‐concentration plot between 20 and 25 mM. Because no abrupt change can be seen in the integrated intensity, we assume that the correlation function in that concentration region is not only affected by the diffusive motion of the micelles but also by some other dynamic processes of the system.
Spectroscopic Investigations of Viscoelastic Solutions Containing the Cetyltrimethylammonium Ion
Authors: Johansson L. B. , Lindblom G. , Ulmius J. , Wennerströ H.
Published: September 2012

It has previously been shown [1] that very dilute solutions of cetyltrimethylammonium salts can show strong viscoelastic behaviour. In order to elucidate the molecular organization specific for the viscoelastic behaviour we have, using several spectroscopic techniques, investigated aqueous solutions containing cetyltrimethylammonium salicylate.

Using proton magnetic resonance it is found by simulation of the bandshapes [2] that in these dilute (<1 %) micellar solutions the viscoelastic behaviour correlates with the aggregate size, both with respect to changes in composition and in temperature. Thus a necessary condition for viscoelastic behaviour is aggregates larger than the minimal spherical micelle.

The viscoelastic solutions were oriented by Couette flow. The orientation was monitored through the linear dichroism (LD) of the solution and it is found that the LD increases with increasing concentration. The temperature for obtaining zero LD is in agreement with the disappearance of the viscoelastic properties of the solution.

An independent measure of aggregate sizes was obtained by studying the quasielastic light scattering (QLS) of the solutions which also indicates a transition from large to smaller aggregates at higher temperatures.

It is suggested that electrostatic and anisotropic interactions between the large aggregates cause a specific periodic colloidal structure that is responsible for the viscoelastic behaviour.
Spreading of Biomembranes at the Air/Water Interface
Authors: Pattus F. , Verger R.
Published: September 2012

This poster presents an original technique for spreading membranes at the air/water interface.

We have characterized enzymatically lipoproteins films from intestinal brush border membranes. In an attempt to study the mechanism of formation and the structure of the films obtained we used the simplest model of membrane: the liposome. Two types of films structures are formed when liposomes are spread at the air/water interface. At zero surface pressure, there is a slow transformation of the closed bilayered structure into a lipid monolayer. The internal content of the liposomes is released into the aqueous subphase. In contrast when liposomes are spread against a surface pressure they retain their internal content at the air/water interface by forming multilayered structures.

We present the compression isotherms obtained by spreading intestinal brush border, erythrocyte and E. Coli cytoplasmic membranes at the air/water interface.

At zero surface pressure we obtained, with a good yield, unilamellar membrane films. At high surface pressure multilamellar structures are formed. Once formed, the films are particularly stable and could be manipulated without loss of the membranous material. From doubly labelled E. Coli cytoplasmic membrane, we could show that the phospholipids and proteins spread with the same yield; as a single unit. We studied the influence of hydrolytic enzymes, chemical agents and cations on the compression isotherm of biomembranes. The changes in architecture of membrane films can provide a very simple method to study the influence of the membrane packing on the catalytic activity and protein conformation of membrane bound proteins.
‘Catalysis’ of Metal Complex Formation on Micelle Surfaces. The Reaction between Divalent Metal Ions and PADA in the Presence of Sodium Dodecyl Sulphate
Authors: Holzwarth Joseph , Knoche Wilhelm , Robinson Brian H.
Published: September 2012

The rate of complex formation between PADA and Ni2+ or Mn2+ in aqueous solution is strongly enhanced by the presence of sodium dodecylsulphate in the region of the cmc. Above the cmc the mechanism of this enhancement can be explained quantitavely by the enrichment of the reacting species in the region of the micelle surface. Below the cmc the reaction rate is increased too, which is explained by the existence of pre‐micellar aggregates.
Ultrasonic Relaxation Measurements in Lyotropic Liquid Crystals
Authors: Walsh M. F. , Wyn‐Jones E.
Published: September 2012

Ultrasonic relaxation measurements covering the frequency range 5–100 MHz have been carried out in the isotropic as well as the hexagonal and lamellar liquid crystalline phases of aqueous solutions of the surfactants: caesium perfluorooctanoate, mono‐olein, mono‐caprylin, tetraethylene glycol dodecyl ether (CE04), pentaethylene glycol dodecyl ether (CEO) and di‐(2‐ethylhexyl) sodium sulfosuccinate (aerosol OT). The absorption data obtained in concentrated isotropic solution and also the hexagonal and lamellar phases can be fitted into an equation involving a single relaxation time in the frequency range 25–100 MHz. The concentration and temperature dependence of the relaxation times and amplitudes have been determined. A discussion of the likely mechanisms causing the relaxation will be given. These measurements also show that there is a pronounced increase in the quantity as the different phase boundaries are approached. This is very close to the behaviour of absorption data near the critical point in liquid mixtures.
Änderung des Austrittspotentials von Nickel‐Filmen bei der Bildung einer Monoschicht adsorbierten Wassers
Authors: Heras J. M. , Viscido L. , Amorebieta V.
Published: September 2012

Es wurde die änderung des Austrittspotentials bei der Adsorption einer Monoschicht von Wassermolekulen bei 77 K auf polykristallinen Ni‐Filmen bekannter Topographie untersucht Die Filmen waren unter UHV‐Bedingungen aufgedampft worden. – Die Resultate wurden mit Hilfe des von Macdonald und Barlow (1966) vorgeschlagenen Modells analysiert. Zur Anpassung der Theorie an die experimentellen Daten hat das Modell zwei Parameter: β, den Abstand zwischen adsorbierter Dipolschicht und Bildebene, und αa, die Polarisierbarkeit der adsorbierten Moleküle. Beide sind durch eine effektive Dielektrizitätskonstante ε1 verknüpft. – Zur Anpassung wurde ein Programm in Fortran IV entwickelt, das zu folgenden Werten führte: β = 0,125 nm; αa = 2,29·10−24 cm3, woraus sich das Dipolmoment für das adsorbierte Molekül zu μa = 1,875.10−30 Cm berechnet. In der Monoschicht ist ε1 = 1.2.
Involvement of Surface States in the Spectral Sensitization of Zinc Oxide Electrodes
Authors: Yamase T. , Gerischer H. , Lübke M. , Pettinger B.
Published: September 2012

The sensitization photocurrent at single crystalline ZnO electrodes in contact with an aqueous solution of crystal violet has been investigated during excitation by a 1 msec laser pulse. The photocurrent shows relaxation phenomena which can be explained by an involvement of “surface states. They capture electrons from the excited dye molecules followed by electron injection into the conduction band or recombination” with the oxidized dye molecules. – The quantum yield for the electron injection is in the order of 2%. This relatively low value a high efficiency of the recombination via surface states. – In the presence of hydroquinone, a slight increase of the quantum observed which is attributed to a photoreduction of the excited dye molecules. The reduced crystal violet molecule can inject an electron into the conduction band from its ground state.
Electrochemical Oxidation and Reduction of the RuO2/Ti Electrode Surface
Authors: Doblhofer K. , Metikoš M. , Ogumi Z. , Gerischer H.
Published: September 2012

Using a refined technique, thin, homogeneous RuO2 films were prepared reproducibly on highly polished Ti surfaces by thermal decomposition of ruthenium salts. The produced electrodes were investigated with electrochemical techniques. Chronocoulometry experiments were found to be particularly useful because they permitted a clear separation of surface and bulk processes. – The oxidation state of the surface Ru atoms was found to change in the potential range between hydrogen and oxygen evolution in 1 M H2SO4 from +2 to +6. Hydrogen adsorption is proposed at potentials more cathodic than +0.4 V (RHE). The associated bulk diffusion processes are discussed.
NMR‐Untersuchungen zur Austauschkinetik von Wasser in und zwischen den großen und kleinen Hohlräumen des Zeolithen NaY
Authors: Basler Wolf D.
Published: September 2012

Mittels H/D‐Isotopenmarkierung und gepulster H‐NMR wurden die Geschwindigkeit, mit der Wassermolekeln zwischen den großen und kleinen Hohlräumen des Zeolithen NaY austauschen, gemessen und der intermolekulare Protonenaustausch sowohl in den großen als auch in den kleinen Hohlräumen abgeschätzt. Es ergab sich eine Austauschrate von einer Molekel pro 4 Tagen bei 295 K. Aus der Unabhängigkeit von der Wasseraktivität wird geschlossen, daß der Austritt aus den kleinen Hohlräumen die Austauschrate bestimmt. In den kleinen Hohlräumen wird kein intermolekularer Protonenaustausch innerhalb einiger Wochen beobachtet, in den großen Hohlräumen findet er in weniger als Millisekunden statt.
The Association of Three Branched Alkyl Derivatives of 3‐Pentanol
Authors: Kunst M. , van Duijn D. , Bordewijk P.
Published: September 2012

Infrared absorptions in the hydroxyl stretching range and static dielectric constants have been determined for solutions of 2,2,4‐trimethyl‐3‐pentanol, 2,4‐dimethyl‐3‐enthyl‐3‐pentanol and 2,2,4,4‐tetramethyl‐3‐isopropyl‐3‐pentanol in carbon tetrachloride at several temperatures. – The results are interpreted with a monomer‐dimer‐tetramer equilibrium for the first two alcohols and with a monomer‐dimer equilibrium for the last one, and the relevant parameters are given.
Messungen dielektrischer Eigenschaften bei hohen Drücken und tiefen Temperaturen. I: Die statische DK von Cyclohexanon
Authors: Würflinger A.
Published: September 2012

Es wird eine Apparatur beschrieben zur Messung dielektrischer Eigenschaften von flüssigen und plastischen Phasen bei Drücken bis zu 3000 bar und Temperaturen von –180°C bis +50°C. Der Hochdruckautoklav ist aus einer Kupfer‐Berryllium‐Legierung gefertigt. Tiefe Temperaturen werden über einen Kühlmantel mit flüssigem Stickstoff erzeugt, dessen Menge mit einer Dampfblasenpumpe geregelt wird. Als druckübertragendes Medium dient Helium. Gemessen wird die Durchgriffskapazität verschiedener Zylinderkondensatoren in dreipoliger Meßanordnung bis zu Frequenzen von 10 MHz. Gleichzeitig wird die Leitfähigkeit bzw. der Verlustwinkel registriert – Mit dieser Apparatur wird das dielektrische Verhalten von Cyclohexanon untersucht. Diese Substanz besitzt eine plastische Phase unterhalb des Schmelzpunktes. In dieser Phase zeigt Cyclohexanon hohe Werte der Dielektrizitatskonstanten (DK), welche für die bei tieferer Temperatur liegenden Fest‐Fest‐Umwandlung um eine Größenordnung abnehmen. Dieser DK‐Sprung findet bei höheren Drücken in zwei Stufen statt, weil Cyclohexanon unter Druck eine zusätzliche Fest‐Fest‐Umwandlung zeigt. Unterhalb 10 MHz läßt sich keine dielektrische Absorption nachweisen.