bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimentelle Prüfung von approximativen Chiralitätsfunktionen [1, 2] am Beispiel der induziert cholesterischen Lösung chiraler Methan‐Derivate
Authors: Richter W. J. , Korte C. H. 
Published: September 2012

AbstractDie R‐Cotton‐Effekte von cholesterischen Lösungen, die durch chirale Methan‐Derivate in nematischen Phasen induziert werden, stellen Chiralitätsbeobachtungen dar, die durch approximative Chiralitätsfunktionen in guter Näherung beschrieben werden können. Die untersuchten Systeme sind Schiffsche Basen, gelöst in EBBA/MBBA sowie in Licristal®. Nur für die Lösung der Schiffschen Basen in EBBA/MBBA lassen sich bei Anwendung von Chiralitätsfunktionen ligandenspezifische Zahlen ermitteln.
Calculation of the Structure of Laminar Flat Flames III: Structure of Burner‐Stabilized Hydrogen‐Oxygen and Hydrogen‐Fluorine Flames
Authors: Warnatz J. 
Published: September 2012

AbstractThe development of proper boundary conditions permits the solution of the conservation equations for burner‐stabilized laminar flat flames. Hence, comparison is possible with corresponding experimental results. The examples considered are burner‐stabilized H2– O2and H2– F2– Ar flames. In both cases there is satisfactory agreement of calculation and experiment.
Photochemical and Thermal Reactions of Porphyrins and Organic Surfactants in Monolayer Assemblies. Modification of Reactivity in Condensed Hydrophobic Microenvironments [1]
Authors: Whitten David G. , Eaker David W. , Horsey Barbara E. , Schmehl Russell H. , Worsham Paul R. 
Published: September 2012

AbstractThis paper summarizes a number of investigations of reactions occurring in organized monolayer assemblies, monolayer films, and at monolayer assembly or film‐solution interfaces. In several cases, the reactions involve chromophores localized in relatively hydrophobic sites and pronounced differences in reactivity can be ascribed to the microenvironment. Metallation of free base porphyrins has been examined in assemblies and at film‐solution interfaces. Although several divalent metal ions can be incorporated, the order of reactivity varies from that observed in solution. Several porphyrins residing in highly hydrophobic sites are resistant to metallation while those lying near the hydrophilic interface react rapidly. Photooxidation of surfactant protoporphyrin esters residing in hydrophobic regions occurs in both micelles and monolayers but the product distribution is quite different from that obtained in solution. Iron and ruthenium porphyrins isolated in assemblies undergo ligand substitution reactions not readily observable in solution. The photoreactions of some surfactant styrenes has been examined; close packing of the styrene unit, which lies at the end of a hydrocarbon chain, leads to substantial ground state interaction and rapid and selective dimerization on irradiation. Different products are obtained from those formed on irradiation of the same compound in solution, micelles, and crystals. The photoreactivity of a surfactant phenyl ketone has been investigated in condensed monolayers. In solution the primary reaction of the ketone is the “type II” photoelimination which proceeds via α‐hydrogen abstraction. In condensed monolayers the required conformation for this reaction can evidently not be readily attained. Thus in the assemblies dramatic reduction in the efficiency of the type II process occurs concurrent with the onset of new reaction paths.
Three‐Phase Contact Line Motion in the Deposition of Spread Monolayers
Authors: Petrov J. G. , Kuhn H. , Möbius D. 
Published: September 2012

AbstractA monolayer of a water insoluble surfactant can be transferred with some maximum rate vmax from a water surface to the surface of a solid being taken out. This rate was measured by observing the motion of the three‐phase‐contact line (detecting fluorescence quenching or change of light reflection by water entrained). The rate vmax was found to be determined by the reactivity between the monolayer head groups and the solid surface. vmax is particularly large in the case of opposite sign of the charges of the immobile groups on the solid surface and in the monolayer. In the case of equal sign vmax is strongly increased by the presence of divalent counter‐ions in the solution. The hydration of the head groups decreases vmax and therefore optimal transfer is found when the charged head groups are separated from each other by uncharged head groups. Particularly large values of vmax are observed when the monolayer head groups and the solid surface interact by zipper like hydrogen bonding between undissociated carboxyl groups.
Alignment of Liquid Crystals by Amphiphilic Monolayers
Authors: Hiltrop K. , Stegemeyer H. 
Published: September 2012

AbstractThe action of solid surfaces coated with monomolecular films of amphiphilic compounds (especially lecithins) on adjacent liquid crystal phases resulting in an uniform homeotropic orientation has been investigated. The quality of orientation was found to be effected by molecular structure of the amphiphilics as well as the liquid crystals, the packing density of the film, and the temperature. The experimental results can be understood in terms of the following model: Lecithins form brush‐like films with the hydrophobic alkyl chains pointing off the glass surface. Under suitable conditions holes of molecular dimensions exist in the films into which nematogenic molecules can penetrate. By means of elastic interaction forces between these anchored molecules and the adjacent nematic bulk the homeotropization is induced.
Interactions between Lipid Monolayers and Band 3‐Protein from Human Erythrocyte Membranes
Authors: Klappauf E. , Schubert D. 
Published: September 2012

AbstractLipid monolayers at the air‐water interface were used as a model system to study the specificity of protein‐lipid interactions of band 3, the main integral protein (the anion transport protein) of human erythrocyte membranes.Band 3‐protein was isolated by zonal electrophoresis (in acetic acid/H2O/sucrose mixtures) of erythrocyte membranes preextracted in 10% acetic acid and solubilized in 92% acetic acid. Afterwards, the protein was transferred into aqueous solutions and injected into the aqueous subphase of monolayers of different lipid classes. The changes in monolayer surface pressure following protein addition were used as a measure of the strength of protein‐lipid interactions.
Calorimetric Investigations of Phosphatidic Acid Bilayers
Authors: Blume Alfred 
Published: September 2012

AbstractDifferential scanning calorimetry is a sensitive method for studying the phase transition of phospholipid bilayers. Up to now only few calorimetric investigations of the phase transition of charged phospholipids have been carried out [1–3]. We studied the phase behaviour of dihexadecyl‐phosphatidic acid (DHPA) as a function of the pH of the dispersion [4, 5]. Varying the pH induces different degrees of ionization of the phosphatidic acid head group. At high pH the head group has two negative charges leading to a decrease of the transition temperature to 49°C compared to 70°C at pH 9.0 and a decrease in transition enthalpy to 21.8 kJ/mol compared to 31.4 kJ/mol at pH 9.0. Lowering the pH below 9.0 leads to a gradual protonation of singly charged DHPA. With increasing protonation Tm rises to 74°C at pH 3.5 and then drops to 62°C at pH 1.5.The results obtained by calorimetry indicate, that probably two different phases can exist between pH 9.0 and 1.0. At half protonation at pH 3.5 a particular stable phase with high transition temperature and low transition enthalpy (11.3 kJ/mol) can be observed. Complete protonation leads to a phase, which has the same transition temperature as the melting point of dry crystalline protonated DHPA.The observed variation of the transition enthalpy with pH cannot be explained by assuming, that only the electrostatic potential of the bilayer surface is changed [6]. An influence of the degree of ionization of the head group on the hydrocarbon chain interactions has to be taken into account.From these experiments conclusions can be drawn upon the intermolecular interactions between the head groups of phosphatidic acids.
Raman Spectroscopic Investigations on Binary Lipid Mixtures
Authors: Knoll Wolfgang 
Published: September 2012

AbstractRaman spectra in the C‐H and C‐C stretching vibration region for dipalmitoyl‐phosphatidic acid and mixtures of dimyristoyl‐, dipalmitoyl‐ and distearoyl lecithin are reported. Suitable peak height ratios show characteristic changes with temperature. From the data of the pure lipids one can derive ordered‐fluid transition temperatures that are in good agreement with the values from other methods: 57°C for DPPA at pH 9, 23.5°C for DML, 42°C for DPL and 55°C for DSL. – For the DML/DPL mixture a somewhat broadened transition at intermediate temperature is found (33.5°C for DML: DPL = 1:1). – For a mixture of DPPA and polylysine‐bound DPPA two distinct transition temperatures can be seen, which reflect the immiscibility of the two components. – For mixtures of DML and DSL more complicated transition curves are found. The peak height ratios of C – H vibrations at 2880 and 2850 cm−1 nevertheless can be used to construct a phase diagram. The transition curve of C‐C stretching vibrations at 1130 and 1100 cm−1 seems to monitor a complex phase separation behaviour which cannot be explained for the moment in full detail without additional experimental results.
Formation and Some Properties of Micelles
Authors: Mukerjee Pasupati 
Published: September 2012

AbstractThe relationship of micelles to other types of organized structures formed by amphipathic monomers such as monolayers, bilayers, membranes, and adsorbed layers is pointed out. The patterns of self‐association followed by micelle‐forming surfactants is examined in terms of a general association model. The interactions responsible for micelle formation and the characteristic features of the local microenvironments of micelles are reviewed. The nature of solubilization by micelles is discussed in terms of the forces of interaction involved and problems of location, distribution and orientation.
Light Initiated Electron Transfer in Functional Surfactant Assemblies I: Micelles with Transition Metal Counterions
Authors: Moroi Yoshikiyo , Braun André , Grätzel Michael 
Published: September 2012

AbstractThe photo induced reduction of cupric ions by organic donors (D) was studied in functional surfactant assemblies in which the Cu2+ ions constitute the counterion atmosphere of the micelle. The donors employed were N‐methyl‐phenothiazine (MPTH) and N,N'‐Dimethyl‐5,11‐dihydroindolo‐[3,2‐b]carbazol (DI). Laser photolysis, steady state illumination and fluorescence techniques were used to investigate the photoredox processes. The transfer of an electron from the excited donor inside the micelle to the counterion occurs so rapidly that it cannot be resolved kinetically by nanosecond laser techniques. In the case of DI, the reactive excited state was found to be the first excited singlet state whose lifetime in the Cu2+ micelles is 1.2 · 10−9 s. The cuprous ion formed in the photoredox process escapes from the micelle into the bulk solution before back transfer of electrons to D+ can occur. There it may be used for a second redox reaction with a negative ion or a zwitter ion. In such a system, the back reaction between reduced acceptor ion and oxydized donor is prevented by the micellar surface potential allowing for storage of light energy. The dynamics of excited state interaction with micellar counterions was investigated also in aggregates with Co2+ and Ni2+ counterion atmospheres, respectively.
Free Tenside Radicals and Micellar Equilibria
Authors: Henglein A. , Proske H. 
Published: September 2012

AbstractThree tensides (1‐(6‐dodecylbenzene‐sulfonate)‐Na; myristyltriethyleneglycol‐ether‐sulfonate‐Na; cetyl‐21‐ethyleneglycol‐ether) were σ− and electron irradiated in aqueous solution. The OH radicals produced in the radiolysis of water attacked the tensides to form organic radicals either by hydrogen abstraction or addition to the aromatic ring. The decay of the organic radicals was followed optically and the rate constant for bimolecular deactivation measured at different tenside concentrations.In these case of the two anionic micelles, mutual deactivation of radicals in micelles is not possible because of the Coulombic repulsion between the micelles. Deactivation can occur after the exit of a radical from its micelle. The kinetics of radical‐radical deactivation is therefore strongly ruled by the dynamics of the micellar equilibrium Mn → Mn+1 K M. All rate constants of this equilibrium can be obtained from the analysis of the kinetic data.In the case of the neutral micelles, radicals in micelles do activate each other. In these micelles, more than one radical could be produced. Intramicellar radical‐radical deactivation was observed in the microsecond range, intermicellar deactivation in the millisecond range. σ‐irradiation led to crosslinking of the tenside molecules.
Nuclear Magnetic Resonance Studies of the Arrangement of Benzene Molecules in the Cavities of the Zeolite NaX
Authors: Lechert H. , Wittern K.‐P. 
Published: September 2012

AbstractThe second moments of the proton resonances of benzene in the cavities of a zeolite NaX with Si/Al = 1.32 have been measured for C6H6and C6H3D3, between 100 K and 200 K, and the intra‐ and intermolecular contribution extracted from the results. From the intramolecular contribution for coverages above four molecules in a large cavity below 150 K a rotation around the hexagonal axis of the benzene molecule can be concluded. For the explanation of the intermolecular contribution, model calculations have been carried out, showing that for four molecules in a large cavity the molecules are arranged flat on the walls above the S2‐sites with a distance of about 0.32 nm from the ions in these sites. The intermolecular second moment for a coverage above five molecules in a cavity can be explained only by arranging the fifth molecule in the window between two cavities parallel to the plane of the window. This arrangement explains the limiting coverage of about six molecule in a large cavity as well as the possibility of a motion of the molecules at higher temperatures.
Dependence of the Intensity of Fluorescence on the Quencher Concentration in Micellar Systems
Authors: Henglein A. , Scheerer R. 
Published: September 2012

AbstractThe quenching of the fluorescence of 2‐(4‐aminophenyl)‐3‐methylbenzothiazol solubilized in micelles of sodium dodecylsulfate by duroquinone was investigated. The decay constant k0, in the absence of quencher is 6.9·108 s−1. At constant concentrations of the fluorescing and the quenching compounds the fluorescence intensity decreases with decreasing surfactant concentration. This effect is explained by the changes in the distribution of the emitting and quenching molecules among the micelles. A relationship is given which takes into account the statistical distribution of solubilized molecules. The first order rate constant is km = m·k1, for quenching in a micelle carrying m molecules of the quencher. k1, the rate constant for quenching in a micelle containing 1 molecule of the quencher, was found to be 3.5·108 s−1. – The ion pair formation in micelles containing 2‐(4‐aminophenyl)‐3‐methylbenzothiazol and duroquinone, the biphotonic ionization of 2‐(4‐aminophenyl)‐3‐methylbenzo‐thiazol in anionic micelles and in methanol solution, and the formation of the triplet state of this compound in toluene and in acid aqueous solutions were studied by laser flash photolysis.
Fragmentierung von Halogenmethanen beim Stoß mit monochromatischen Elektronen niedriger Energie (0 – 10 eV)
Authors: Illenberger E. , Scheunemann H.‐U. , Baumgärtel H. 
Published: September 2012

AbstractMit Hilfe eines Trochoidal‐Elektronenmonochromators (δE ≈︁ 0.13 eV) und eines Quadrupol‐Massenfilters wird die energieselektive Fragmentierung von CF3Cl, CF2Cl2 und CFCl3 im Bereich niedriger Elektronenenergien (0 – 10 eV) untersucht. Innerhalb einer Anzahl verschiedener negativer Fragmente ist die überaus intensive Bildung von Cl− aus CFCl3 – das bereits bei 0.0 eV entsteht – besonders auffällig. Die hohen Bildungsquerschnitte machen deutlich, daß bereits niederenergetische Elektronen, ganz im Gegensatz zu Photonen. die chemisch sehr stabilen Gase zu dissoziieren vermögen. Es wird diskutiert, ob dieser Effekt die troposphärischen Lebensdauern der Halogenmethane beeinflußt.
Dynamics of Physisorbed Hydrogen on Charcoal and Microcrystalline Graphite
Authors: Stockmeyer R. , Stortnik H. , Wagner R. 
Published: September 2012

AbstractThe molecular motion in monolayers of hydrogen adsorbed on charcoal and on the basal planes of microcrystalline, partially oriented graphite have been studied by neutron spectroscopy at temperatures between 40 K and 140 K. At high temperature the H2 molecule is dominantly found in gas‐like states. At low temperature the adsorbed molecules populate mainly localized states, in which the molecules diffuse over the surface like in a surface lattice gas. The o‐H2 rotation is only slightly hindered. The localized states are separated from the non‐localized states by a band gap of about 12 meV.
Electrochemical Solar Cell Based on the d‐Band Semiconductor Tungsten‐Diselenide
Authors: Gobrecht J. , Gerischer H. , Tributsch H. 
Published: September 2012

AbstractIn a search for corrosion resistent electrode materials for electrochemical solar cells the covalent, layered semiconductor WSe2, has been investigated. Its photoactivity in the visible spectral region (band gap 1.57 eV) involves d‐d electron transitions which do not lead to an immediate photocorrosien. An energetically favourable energy band position makes it possible to operate p‐type material as photocathodes for energy conversion. Photocell outputs in the order of 15 mA/cm2 and 0.5 V were obtained in 100 mW/cm2 illumination (Xenon‐lamp). It is shown that the produced photovoltage is not systematically dependent on the redox potential of the redox agents but influenced by their chemical reactivity due to a specific interaction with the electrode surface.
Enhancement of the Proton Exchange Rate in Aqueous Solution by Small Amounts of Hydrophobic Substances, as Determined from Ultrasonic Relaxation
Authors: Nicola C. U. , Labhardt A. , Schwarz G. 
Published: September 2012

AbstractThe kinetics of the proton transfer reaction between dihydrogen phosphate and imidazole in water with some added methanol, ethanol, and dioxan, respectively, was investigated by means of ultrasonic absorption and velocity dispersion measurements in the frequency range from 0.5 to 36 MHz. The system exhibits a single chemical relaxation time. It reflects a diffusion controlled direct transfer mechanism. The two rate constants have been evaluated as a function of the volume percentage of the added solvent. Both show a sharp maximum at about 0.5%. This effect turned out to be the more pronounced the more hydrophobe the foreign molecules are. Comparatively few molecules of such material therefore seem to appreciably increase the hydrogen bonded water structure in the hydration shells through which proton transfer is mediated.
Neuere Untersuchungen zur Bindung von Ethidiumbromid an DNA 2. Mitteilung: Vergleich der Bindungskonstanten von Ethidiumbromid und verwandten Verbindungen. Diskussion der kompetitiven und nicht‐kompetitiven Bindung
Authors: Pauluhn Jürgen , Zimmermann Herbert W. 
Published: September 2012

AbstractDie Bindung einiger Derivate des Ethidiumbromids (2,7‐Diamino‐9‐phenyl‐phenanthridin DPP, DPPH⊕, 7‐Amino‐9‐phenyl‐10‐äthyl‐phenanthridinium‐bromid APEP, 9'‐Phenyl‐10‐äthyl‐phenanthridinium‐bromid PEP) an Kalbsthymus‐DNA wurde absorptionsspektroskopisch untersucht. Aus Scatchard‐Bindungsisothermen wurden die Bindungskonstanten für die kompetitive und die nicht‐kompetitive Bindung bestimmt und mit denen von Ethidiumbromid E verglichen. ‐ Die Bindung der Base DPP an DNA ist pH‐abhängig. In alkalischem Medium liegt die freie Base vor, die nicht an DNA gebunden wird. In saurem Medium wird die Base protoniert. DPPH⊕ kann ebenso wie E kompetitiv und nicht‐kompetitiv an DNA gebunden werden. Bei mittleren pH‐Werten existiert in Lösung ein Gleichgewicht zwischen freier Base und gebundener protonierter Base. Die freie Enthalpie der Bindung von DPPH⊕ an DNA erzwingt unter diesen Bedingungen die Protonierung der Base. — Die Monoaminoverbindung APEP wird kompetitiv und nicht‐kompetitiv gebunden. Der Wert der Bindungskonstante der kompetitiven Bindung KS2 ist im Vergleich zu E etwa halbiert. ‐ Das Kation PEP, das keine Aminogruppen enthält, wird nur noch sehr schwach kompetitiv gebunden. KS2 ist gegenüber E etwa um eine Zehnerpotenz erniedrigt. Die nicht‐kompetitive Bindung konnte nicht beobachtet werden. ‐ Aus dem Vergleich der Bindungskonstanten geht hervor, daß für ausgeprägte kompetitive und nicht‐kompetitive Bindungen eine positive Ladung und wenigstens eine Aminogruppe erforderlich sind. Intercalation und externe Bindung werden unter diesen Gesichtspunkten diskutiert.
Comparative Study of Adsorbate Systems and Corresponding Compounds Using X‐Ray and UV‐Photoemission I. Hexagonal (0001) Co/CO, O2 versus Oxides and Carbonyls
Authors: Freund Hans‐Joachim , Hohlneicher Georg 
Published: September 2012

AbstractPhotoemission studies using XPS and UPS (HeI, HeII) on clean and gas‐covered hexagonal (0001)‐Cobalt‐single‐crystal surfaces are reported (300 K). To interpret the results on the adsorbates namely Co/CO and Co/O2, compound systems, such as CoO, Co3O4 and Co2(CO)8 are studied parallel and comparison is made. It is shown that the emission from Co/O2 is similar to that from CoO and not to that from Co3O4 and that the Co/CO‐systems resembles the Co2(CO)8‐photoemission characteristics. Assignment of CO‐peaks as far as the sequence of the 4σ, 1π and 5σ is concerned is shown to be the same as in free CO. The C1s spectrum of the carbonyl is analysed using theoretical predictions of atomic populations, which show the bridging ligands to carry more electron density than terminal ones. From comparison with adsorbate systems it follows that the differences in the adsorbate system are not as pronounced as in the case of the carbonyls.
Nature of the Electron‐Hole Pair in the System Anthracene Crystal/Rhodamine B Adsorbed from Aqueous Solution. Dependence of Kinetics and Spin‐Dynamics on External Parameters. Part I: External Electric Field
Authors: Müller N. , Papier G. , Charlé K.‐P. , Willig F. 
Published: September 2012

AbstractWe have studied the influence of an applied electric field (up to 5 · 105 Vcm−1) and of a small applied magnetic field (up to 2 · 10−2 Tesla) on the irreversible separation of electron‐hole pairs (measured as sensitized hole current SHC) and on their geminate recombination (measured as sensitized delayed fluorescence SDF) at the interface between an organic crystal and an aqueous solution. The electron‐hole pairs have been generated via electron transfer from the surface of an anthracene crystal to the excited singlet state of adsorbed rhodamine B molecules. There is a steep decrease in the magnitude of the SDF and in the magnetic hyperfine modulation (HFM) of the SHC with rising applied electric field strength. The experimental results can be described with a theory taking into account the repeated dissociation and re‐formation of the bound electron‐hole pair. The magnetic field effect on the kinetics of the electron‐hole pair develops almost exclusively during the periods when the hole is released from the bound state and moves about at the crystal surface. The hitherto accepted model of Groff et al., in which only the bound state of the electron‐hole pair has been considered, cannot account for the behaviour of the system.