TY - THES A1 - Andersen, Audrée T1 - Surfactant dynamics at interfaces : a series of second harmonic generation experiments T1 - Surfactant Dynamik an Grenzflächen : eine Studie über SHG-Experimente N2 - Adsorption layers of soluble surfactants enable and govern a variety of phenomena in surface and colloidal sciences, such as foams. The ability of a surfactant solution to form wet foam lamellae is governed by the surface dilatational rheology. Only systems having a non-vanishing imaginary part in their surface dilatational modulus, E, are able to form wet foams. The aim of this thesis is to illuminate the dissipative processes that give rise to the imaginary part of the modulus. There are two controversial models discussed in the literature. The reorientation model assumes that the surfactants adsorb in two distinct states, differing in their orientation. This model is able to describe the frequency dependence of the modulus E. However, it assumes reorientation dynamics in the millisecond time regime. In order to assess this model, we designed a SHG pump-probe experiment that addresses the orientation dynamics. Results obtained reveal that the orientation dynamics occur in the picosecond time regime, being in strong contradiction with the two states model. The second model regards the interface as an interphase. The adsorption layer consists of a topmost monolayer and an adjacent sublayer. The dissipative process is due to the molecular exchange between both layers. The assessment of this model required the design of an experiment that discriminates between the surface compositional term and the sublayer contribution. Such an experiment has been successfully designed and results on elastic and viscoelastic surfactant provided evidence for the correctness of the model. Because of its inherent surface specificity, surface SHG is a powerful analytical tool that can be used to gain information on molecular dynamics and reorganization of soluble surfactants. They are central elements of both experiments. However, they impose several structural elements of the model system. During the course of this thesis, a proper model system has been identified and characterized. The combination of several linear and nonlinear optical techniques, allowed for a detailed picture of the interfacial architecture of these surfactants. N2 - Amphiphile vereinen zwei gegensätzliche Strukturelemente in einem Molekül, eine hydrophile Kopfgruppe und ein hydrophobe, meist aliphatische Kette. Aufgrund der molekularen Asymmetrie erfolgt eine spontane Adsorption an der Wasser-Luft Grenzfläche. Die Adsorptionsschicht verändert die makroskopischen Eigenschaften des Materials, z.B. die Grenzflächenspannung wird erniedrigt. Amphiphile sind zentrale Bauelemente der Kolloid- und Grenzflächenforschung, die Phänomene, wie Schäume ermöglichen. Eine Schaumlamelle besteht aus einem dünnen Wasserfilm, der durch zwei Adsorptionsschichten stabilisiert wird. Die Stabilität der Lamelle wird durch die Grenzflächenrheologie entscheidend geprägt. Die wesentliche makroskopische Größe in diesem Zusammenhang ist das so genannte Grenzflächendilatationsmodul E. Es beschreibt die Fähigkeit des Systems die Gleichgewichtsgrenzflächenspannung nach einer Expansion oder Dilatation der Adsorptionschicht wieder herzustellen. Das Modul E ist eine komplexe Größe, in dem der Imaginärteil direkt mit der Schaumstabilität korreliert. Diese Arbeit widmet sich der Grenzflächenrheologie. In der Literatur werden zwei kontroverse Modelle zur Interpretation dieser Größe diskutiert. Diese Modelle werden experimentell in dieser Arbeit überprüft. Dies erfordert die Entwicklung neuer experimenteller Aufbauten basierend auf nichtlinearen, optischen Techniken. Mit diesen Experimenten konnte eines der Modelle bestätigt werden. KW - Tensid KW - Grenzflächenchemie KW - Nichtlineare Spektroskopie KW - Oscillating Bubble KW - surfactants KW - nonlinear optics KW - surface rheology KW - air-water interface KW - oscillating bubble Y1 - 2005 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-6553 ER - TY - JOUR A1 - Andersen, S. O. A1 - Peter, Martin G. A1 - Roepstorff, Peter T1 - Cuticular sclerotization in insects Y1 - 1996 ER - TY - JOUR A1 - Andrews, N. L. P. A1 - Ferguson, T. A1 - Rangaswamy, A. M. M. A1 - Bernicky, A. R. A1 - Henning, N. A1 - Dudelzak, A. A1 - Reich, Oliver A1 - Barnes, Jack A. A1 - Loock, Hans-Peter T1 - Hadamard-Transform Fluorescence Excitation-Emission-Matrix Spectroscopy JF - Analytical chemistry N2 - We present a fluorescence excitation-emission-matrix spectrometer with superior data acquisition rates over previous instruments. Light from a white light emitting diode (LED) source is dispersed onto a digital micromirror array (DMA) and encoded using binary n-size Walsh functions ("barcodes"). The encoded excitation light is used to irradiate the liquid sample and its fluorescence is dispersed and detected using a conventional array spectrometer. After exposure to excitation light encoded in n different ways, the 2-dimensional excitation-emission-matrix (EEM) spectrum is obtained by inverse Hadamard transformation. Using this technique we examined the kinetics of the fluorescence of rhodamine B as a function of temperature and the acid-driven demetalation of chlorophyll into pheophytin-a. For these experiments, EEM spectra with 31 excitation channels and 2048 emission channels were recorded every 15 s. In total, data from over 3000 EEM spectra were included in this report. It is shown that the increase in data acquisition rate can be as high as [{n(n + 1)}/2]-fold over conventional EEM spectrometers. Spectral acquisition rates of more than two spectra per second were demonstrated. Y1 - 2017 U6 - https://doi.org/10.1021/acs.analchem.7b02400 SN - 0003-2700 SN - 1520-6882 VL - 89 SP - 8554 EP - 8564 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Andrews, Nicholas L. P. A1 - Ross, Rachel A1 - Munzke, Dorit A1 - van Hoorn, Camiel A1 - Brzezinski, Andrew A1 - Barnes, Jack A. A1 - Reich, Oliver A1 - Loock, Hans-Peter T1 - In-fiber Mach-Zehnder interferometer for gas refractive index measurements based on a hollow-core photonic crystal fiber JF - Optics express : the international electronic journal of optics N2 - We describe an in-fiber interferometer based on a gas-filled hollow-core photonic crystal fiber. Expressions for the sensitivity, figure of merit and refractive index resolution are derived, and values are experimentally measured and theoretically validated using mode field calculations. The refractive indices of nine monoatomic and molecular gases are measured with a resolution of delta(ns) < 10(-6). (C)2016 Optical Society of America Y1 - 2016 U6 - https://doi.org/10.1364/OE.24.014086 SN - 1094-4087 VL - 24 SP - 14086 EP - 14099 PB - Optical Society of America CY - Washington ER - TY - JOUR A1 - Andrianov, Ivan A1 - Saalfrank, Peter T1 - Free vibrational relaxation of H adsorbed on a Si(100) surface investigated with the multi-configurational time-dependent Hartree method JF - Chemical physics letters N2 - The results of a quantum-mechanical study of vibrational relaxation of hydrogen adsorbed on a Si(100) surface with the multi-configurational time-dependent Hartree (MCTDH) method are presented. A two-dimensional subsystem is coupled non-linearly to a bath of harmonic oscillators (phonons of the Si bulk), and the relaxation of subsystem vibrations proceeds primarily via a two-phonon process. Characteristic times of the system evolution agree well with our previous perturbation theory study. The vibrational population decay is non-exponential, exhibiting pronounced recurrences due to finite bath size. The dependence of the lifetimes of the vibrational levels on the bath size and on the coupling details is investigated. Y1 - 2006 U6 - https://doi.org/10.1016/j.cplett.2006.11.067 SN - 0009-2614 VL - 433 SP - 91 EP - 96 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Anklam, Elke A1 - Behler, Jörg A1 - Dingermann, Theodor A1 - Elsinghorst, Paul A1 - Fischer, Jochen A1 - Esselen, Melanie A1 - Foerster, Christian A1 - Fröhlich, Daniel A1 - Goedel, Werner Andreas A1 - Gregory, Peter A1 - Grimme, Stefan A1 - Hackenberger, Christian A1 - Hansmann, Max A1 - Heppekausen, Johannes A1 - Hasenstab-Riedel, Sebastian A1 - Kirchhoff, Erhard A1 - Kratz, Karl-Ludwig A1 - Krausz, Ferenc A1 - Linker, Torsten A1 - List, Benjamin A1 - Ray, Kallol A1 - Salzer, Reiner A1 - Schubert, Ulrich A1 - Schueth, Ferdi A1 - Schwarz, Helmut A1 - Schwietzke, Uta A1 - Strey, Reinhard A1 - Stumpf, Thorsten A1 - Vaagt, Franziska A1 - Volodkin, Dmitry A1 - Wilke, Guenther A1 - Zass, Engelbert A1 - Zemb, Thomas T1 - Awards JF - Nachrichten aus der Chemie : Zeitschrift der Gesellschaft Deutscher Chemiker Y1 - 2013 U6 - https://doi.org/10.1002/nadc.201390372 SN - 1439-9598 SN - 1868-0054 VL - 61 IS - 11 SP - 1145 EP - 1148 PB - Ges. Dt. Chemiker CY - Frankfurt, Main ER - TY - THES A1 - Antipov, Alexei T1 - Polyelectrolyte multilayer capsules as controlled permeability vehicles and catalyst carriers Y1 - 2003 ER - TY - JOUR A1 - Antoniou, Stella A1 - Pashalidis, I. A1 - Gessner, Andre A1 - Kumke, Michael Uwe T1 - The effect of humic acid on the formation and solubility of secondary solid phases (Nd(OH)CO3 and Sm(OH)CO3) JF - Radiochimica acta : international journal for chemical aspects of nuclear science and technology N2 - The formation of secondary Ln(III) solid phases (e.g. Nd(OH)CO3 and Sm(OH)CO3) has been studied as a function of the humic acid (HA) concentration in 0.1 M NaClO4 aqueous solution and their solubility has been investigated in the neutral pH range (6.5-8) under normal atmospheric conditions. Nd(III) and Sm(III) were selected as analogues for trivalent lanthanide and actinide ions. The solid phases under investigation have been prepared by alkaline precipitation and characterized by TGA, ATR-FTIR, XRD, TRLFS, DR-UV-Vis and Raman spectroscopy, and solubility measurements. The spectroscopic data obtained indicate that Nd(OH)CO3 and Sm(OH)CO3 are stable and remain the solubility limiting solid phases even in the presence of increased HA concentration (0.5 g/L) in solution. Upon base addition in the Ln(III)-HA system decomplexation of the previously formed Ln(III)-humate complexes and precipitation of two distinct phases occurs, the inorganic (Ln(OH)CO3) and the organic phase (HA), which is adsorbed on the particle surface of the former. Nevertheless, HA affects the particle size of the solid phases. Increasing HA concentration results in decreasing crystallite size of the Nd(OH)CO3 and increasing crystallite size of the Sm(OH)CO3 solid phase, and affects inversely the solubility of the solid phases. However, this impact on the solid phase properties is expected to be of minor relevance regarding the chemical behavior and migration of trivalent lanthanides and actinides in the geosphere. KW - Lanthanide ions KW - Humic acid KW - Solid phase KW - Solubility KW - Raman KW - TRLFS KW - DR-UV-Vis Y1 - 2011 U6 - https://doi.org/10.1524/ract.2011.1812 SN - 0033-8230 VL - 99 IS - 4 SP - 217 EP - 223 PB - De Gruyter CY - Berlin ER - TY - JOUR A1 - Antoniou, Stella A1 - Pashalidis, Ioannis A1 - Gessner, Andre A1 - Kumke, Michael Uwe T1 - Spectroscopic investigations on the effect of humic acid on the formation and solubility of secondary solid phases of Ln(2)(CO3)(3) JF - Journal of rare earths N2 - The formation of secondary Ln(III) solid phases (e.g., Nd-2(CO3)(3) and Sm-2(CO3)(3)) was studied as a function of the humic acid concentration in 0.1 mol/L NaClO4 aqueous solution in the neutral pH range (5-6.5). The solid phases under investigation were prepared by alkaline precipitation under 100% CO2 atmosphere and characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), time-resolved laser fluorescence spectroscopy (TRLFS), diffuse reflectance ultraviolet-visible (DR-UV-Vis), Raman spectroscopy, and solubility measurements. The spectroscopic data obtained indicated that Nd-2(CO3)(3) and Sm-2(CO3)(3) were stable and remained the solubility limiting solid phases even in the presence of increased humic acid concentration (0.5 g/L) in solution. Upon base addition in the Ln(III)-HA system, decomplexation of the previously formed Ln(III)-humate complexes and precipitation of two distinct phases occurred, the inorganic (Ln(2)(CO3)(3)) and the organic phase (HA), which was adsorbed on the particle surface of the former. Nevertheless, humic acid affected the particle size of the solid phases. Increasing humic acid concentration resulted in decreasing crystallite size of the Nd-2(CO3)(3) and increasing crystallite size of the Sm-2(CO3)(3) solid phase, and affected inversely the solubility of the solid phases. However, this impact on the solid phase properties was expected to be of minor relevance regarding the chemical behavior and migration of trivalent lanthanides and actinides in the geosphere. KW - lanthanide ions KW - humic acid KW - solid phase KW - solubility KW - Raman KW - TRLFS KW - DR-UV-Vis KW - rare earths Y1 - 2011 U6 - https://doi.org/10.1016/S1002-0721(10)60490-5 SN - 1002-0721 VL - 29 IS - 6 SP - 516 EP - 521 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Apitz, Sabine E. A1 - Bell, Elanor M. A1 - Damgaard, Lars A1 - Gilbert, Franck A1 - Glud, R A1 - Hall, P. O. J. A1 - Kershaw, P. J. A1 - Nickel, L A1 - Parker, R A1 - Rabouille, Christophe A1 - Shimmield, Grahamm A1 - Solan, Martin A1 - Soltwedel, Thomas A1 - Spagnoli, Federico A1 - Witte, Ursula T1 - Coastal Ocean Benthic Observatories (COBO) : integrated tools for the in situ observation and study of benthic ecosystem biogeochemical processes Y1 - 2005 ER - TY - THES A1 - Appajaiah, Anilkumar T1 - Climatic stability of polymer optical fibers (POF) N2 - Optische Polymerfasern stellen ein relativ neues Medium zur Hochgeschwindigkeitsdatenübertragung mittels moduliertem Licht dar. Sie gestatten die Verbreitung großer Datenmengen über Entfernungen bis zu ca. 100 m, ohne eine Beeinflussung durch externe elektromagnetischen Feldern. Jedoch reagieren die Fasern und somit auch ihre optischen Eigenschaften aufgrund des organischchemischen Faseraufbaus empfindlich auf das Klima ihrer Umgebung. Die Ursachen für die Abnahme der optischen Transmission aufgrund von klimatischen Einflüssen (Alterung, Degradation) werden mittels chemisch analytischer Verfahren wie Chemilumineszenz (CL) und Fourier Transform Infrarot (FTIR) Spektroskopie untersucht. Dabei kommen fünf, von verschiedenen Herstellern bezogene, Multimode- POFs aus PMMA in sieben verschiedenen Klimaten zum Einsatz. Drei dieser fünf POFs werden genauer untersucht, um den Einfluss einzelner Parameter festzustellen und optische Langzeitstabilität aufgrund von Kurzzeittests vorherzusagen. Als erstes erfolgt eine Kennzeichnung unbeanspruchter POF Komponenten (Kern, Mantel und nackte POF als Kombination von Kern und Mantel) über ihre physikalischen und chemischen Eigenschaften. Die Glas- und die Schmelztemperaturen liegen im Bereich von 120 °C bis 140 °C, das Molekulargewicht des Kerns bei größenordnungsmäßig 105 g mol-1 ;. FTIR-Messungen zeigen zwar Unterschiede in der chemischen Zusammensetzung der Mäntel aber keine Unterschiede bei den Kernen. Bei zwei der POF Proben , die als Kabel (Kern, Mantel und Schutzhülle) für 3300 Stunden einem Klima aus 92 °C und 95 % relativer Feuchte (r.F.) ausgesetzt waren, verringern sich daraufhin die optische Transmissionen in unterschiedlicher Weise. Die Untersuchung der zugehörigen nackten POFs mittels CL, FTIR, Thermogravimetrie (TG), UV/VIS und Gel Permeation Chromatographie (GPC) lässt eine stärkere Schädigung der Mäntel als der Kerne vermuten. Wahrscheinlich führt eine starke Manteldegradation zu einer erhöhten Absorption und Fehlstellen im Mantel und damit zu einer Transmissionsabnahme. Daher scheint die optische Stabilität der POF stärker durch die thermo-oxidative Stabilität des Mantels bestimmt zu sein als durch die des Kernes. Drei nackte POFs (Kern und Mantel) sind unterschiedlich lang (30 Stunden bis 3000 Stunden) folgenden Klimaten ausgesetzt: 92 °C / 95 % r.F., 92 °C / 50 % r.F., 50 °C / 95 % r.F., 90 °C / geringe Feuchte, 100 °C / geringe Feuchte, 110 °C / geringe Feuchte and 120 °C / geringe Feuchte. Auch in diesen Klimaten ergaben sich probenbedingte unterschiedliche Transmissionsänderungen. Die Ergebnisse deuten stark darauf hin, dass bei gleichzeitig hoher Temperatur und hoher Feuchte physikalische Änderungen wie die Volumenausdehnung die Hauptursachen für die Abnahme der optischen Transmission bilden. Ein weiterer Einflussfaktor ist die chemische Zusammensetzung der Mäntel. Bei Kombination von hoher Temperatur und geringer Feuchte erzeugen in den Anfangsstadien der Alterung physikalische Änderungen Transmissionsabnahmen, vermutlich entstehen Fehlstellen in der Kern-Mantel-Grenzschicht. Hinzukommen in den späteren Stadien wahrscheinlich zunehmende Lichtabsorption in Kern und Mantel. L. Jankowski (Doktorand in der BAM) bestätigt diese Annahme durch parallel ausgeführte optische Simulationsrechnungen. Auch für nackte POFs scheint also die thermo-oxidative Stabilität die optische Stabilität zu bestimmen. Kurzzeitalterungstests sollen Aufschluss über den Einfluss individueller Klimaparameter auf die POF Eigenschaften geben. Es zeigt sich bei dauerhaft hoher Temperatur und variabler Feuchte aufgrund des physikalisch absorbierten Wassers bis zu einem gewissen Grad ein reversibles Verhalten des Transmissionsverlustes. Dieses Verhalten tritt aber nur kaum merkbar auf, wenn bei konstanter hoher Feuchte die Temperatur variiert wird. Bei Raumtemperatur und variabler Feuchte stellt sich jedoch ein voll reversibles Verhalten des Transmissionsverlustes ein. Die hier beschriebenen Untersuchungen sind als Ausgangspunkt für weitergehende Forschungen zu verstehen. Die begrenzte Zurverfügungstellung von POF Basisdaten durch die Hersteller und der zeitaufwendige klimabedingte Alterungsprozess beschränken die Ergebnisse mehr oder weniger auf die untersuchten Proben. Signifikante allgemeine Aussagen erfordern aber beispielsweise zusätzliche statistische Daten der Produktionsschwankungen von POF Eigenschaften. Dennoch besitzen die hier beschriebenen Tests das Potential für eine Annäherung an die optische Langzeitstabilität und deren Vorhersage. N2 - Polymer optical fibers (POFs) are a rather new tool for high-speed data transfer by modulated light. They allow the transport of high amounts of data over distances up to about 100 m without be influenced by external electromagnetic fields. Due to organic chemical nature of POFs, they are sensitive to the climate of their environment and therefore the optical fiber properties are as well. Hence, the optical stability is a key issue for long-term applications of POFs. The causes for a loss of optical transmission due to climatic exposures (aging/degradation) are researched by means of chemical analytical tools such as chemiluminescence (CL) and Fourier transform infrared (FTIR) spectroscopy for five different (with respect to manufacturers) step-index multimode PMMA based POFs and for seven different climatic conditions. Three of the five POF samples are studied more in detail to realize the effects of individual parameters and for forecasting longterm optical stability by short-term exposure tests. At first, the unexposed POF components (core, cladding, and bare POF as combination of core and cladding) are characterized with respect to important physical and chemical properties. The glass transition temperature Tg, and the melting temperature Tm are in the region of 120 °C to 140 °C, the molecular weight (Mw) of cores is in the order of 105 g mol-1. POFs are found to have different chemical compositions of their claddings as could be detected by FTIR, but identical compositions of their cores. Two of the POFs are exposed as cables (core, cladding and jacket) for about 3300 hours to the climate 92 °C / 95 % relative humidity (RH) resulting in a different transmission decrease. Investigating the related unexposed and exposed bare POFs for degradation using CL, FTIR, thermogravimetry (TG), UV/visible transmittance and gel permeation chromatography (GPC) suggest that claddings of POFs are more affected than cores. Probably the observed loss of transmission is mainly due to increased light absorption and imperfections at the core-cladding boundary caused by a large degradation of claddings. Hence, it is highly possible that the optical transmission stability of POFs is governed mainly by the thermo-oxidative stability of the cladding and minor of the core. Three bare POFs (core and cladding only) are exposed for different duration of exposure time (30 hours to 4500 hours) to 92 °C / 95 %RH, 92 °C / 50 %RH, 50 °C / 95 %RH, 90 °C / low humidity, 100 °C / low humidity, 110 °C / low humidity and 120 °C / low humidity. In these climates their transmission variations are found to be different from each other, too. The outcomes strongly inform that under high temperature and high humid climates physical changes such as volume expansion, are the main sources for the loss of optical transmission. Also, the optical transmission stability of POFs is found to be dependent on chemical compositions of claddings. Under high temperature and low humid conditions, a loss of transmission at the early stages of the exposure is mainly caused by physical changes, presumable by corecladding interface imperfections. For the later stages of exposures it is proposed to an additional increase of light absorption by core and cladding owes to degradation. Optical simulation results obtained parallel by Mr. L. Jankowski (a PhD student of BAM) are found to confirm these results. For bare POFs, too, the optical stability of POFs seems to depend on their thermo-oxidative stability. Some short-term exposure tests are conducted to realize influences of individual climatic parameters on the transmission property of POFs. It is found that at stationary high temperature and variable humidity conditions POFs display to a certain amount a reversible transmission loss due to physically absorbed water. But in the case of varying temperature and constant high humidity such reversibility is hardly noticeable. However, at room temperature and varying humidity, POFs display fully reversible transmission loss. The whole research described above has to be regarded as a starting point for further investigations. The restricted distribution of fundamental POF data by the manufacturers and the time consuming aging by climatic exposures restrict the results more or less to the samples, investigated here. Significant general statements require for example additional information concerning the variation of POF properties due to production. Nevertheless the tests, described here, have the capability for approximating and forecasting the long-term optical transmission stability of POFs. -------------- Auch im Druck erschienen: Appajaiah, Anilkumar: Climatic stability of polymer optical fibers (POF) / Anilkumar Appajaiah. - Bremerhaven : Wirtschaftsverl. NW, Verl. für neue Wiss., 2005. - Getr. Zählung [ca. 175 S.]. : Ill., graph. Darst. - (BAM-Dissertationsreihe ; 9) ISBN 3-86509-302-7 T2 - Climatic stability of polymer optical fibers (POF) KW - POF; Reliabilität; Abbau; Chemilumineszenz KW - POF; reliability; degradation; chemiluminescence Y1 - 2004 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-0001661 ER - TY - JOUR A1 - Aravopoulou, Dionysia A1 - Kyriakos, Konstantinos A1 - Miasnikova, Anna A1 - Laschewsky, Andre A1 - Papadakis, Christine M. A1 - Kyritsis, Apostolos T1 - Comparative Investigation of the Thermoresponsive Behavior of Two Diblock Copolymers Comprising PNIPAM and PMDEGA Blocks JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - The thermoresponsive behavior of two diblock copolymers PS-b-PNIPAM and PS-b-PMDEGA, which both comprise a hydrophobic polystyrene (PS) block but different thermoresponsive blocks, also differing in length, poly(N-isopropylacrylamide) (PNIPAM) and poly(methoxy diethylene glycol acrylate) (PMDEGA), respectively, was comparatively investigated in a wide temperature range. Concentrated aqueous solutions containing 25 wt % polymer were studied by small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and broadband dielectric spectroscopy (BDS). DSC measurements show that, during the demixing phase transition, the hydration number per oligo(ethylene glycol) side chain in the PS-b-PMDEGA solution decreases rather gradually, even up to 20 °C above the onset of the transition, i.e., the cloud point (CP). In contrast, the PS-b-PNIPAM solution exhibits an abrupt, stepwise dehydration behavior at its CP, indicated by the sharp, narrow endothermic peak. BDS measurements suggest that the organization of the expelled water during the phase transition and the subsequent evolution of the micellar aggregates are different for the two copolymers. In the PS-b-PMDEGA solution, the long-range charge transport process changes significantly at its CP and strong interfacial polarization processes appear, probably due to charge accumulation at the interfaces between the micellar aggregates and the aqueous medium. On the contrary, in the PS-b-PNIPAM solution, the phase transition has only a marginal effect on the long-range conduction process and is accompanied by a reduction in the high-frequency (1 MHz) dielectric permittivity, ε′. The latter effect is attributed to the reduced polarization strength of local chain modes due to an enhancement of intra- and interchain hydrogen bonds (HBs) in the polymer-rich phase during the water detaching process. Surprisingly, our BDS measurements indicate that prior to both the demixing and remixing processes the local chain mobility increases temporally. Our dielectric studies suggest that for PS-b-PNIPAM the water detaching process initiates a few degrees below CP and that the local chain mobility and intra- and/or interchain HBs of the PNIPAM blocks may control its thermoresponsive behavior. Dielectric “jump” experiments show that the kinetics of micellar aggregation in the PS-b-PMDEGA solution is slower than that in the PS-b-PNIPAM solution and is independent of the target temperature within the two-phase region. From the experimental point of view, it is shown that the dielectric susceptibility, especially, the dielectric permittivity, ε′, is a well-suited probe for monitoring both the reversible changes in the molecular dipolar bond polarizability and the long-range interfacial polarization at the phase transition. Y1 - 2018 U6 - https://doi.org/10.1021/acs.jpcb.7b09647 SN - 1520-6106 VL - 122 IS - 9 SP - 2655 EP - 2668 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Arias, Hugo R. A1 - Feuerbach, Dominik A1 - Schmidt, Bernd A1 - Heydenreich, Matthias A1 - Paz, Cristian A1 - Ortells, Marcelo O. T1 - Drimane Sesquiterpenoids Noncompetitively Inhibit Human alpha 4 beta 2 Nicotinic Acetylcholine Receptors with Higher Potency Compared to Human alpha 3 beta 4 and alpha 7 Subtypes JF - Journal of natural products N2 - The drimane sesquiterpenoids drimenin, cinnamolide, dendocarbin A, and polygodial were purified from the Canelo tree (Drimys winteri) and chemically characterized by spectroscopic methods. The pharmacological activity of these natural compounds were determined on hα4β2, hα3β4, and hα7 nicotinic acetylcholine receptors (AChRs) by Ca2+ influx measurements. The results established that drimane sesquiterpenoids inhibit AChRs with the following selectivity: hα4β2 > hα3β4 > hα7. In the case of hα4β2 AChRs, the following potency rank order was determined (IC50’s in μM): drimenin (0.97 ± 0.35) > cinnamolide (1.57 ± 0.36) > polygodial (62.5 ± 19.9) ≫ dendocarbin A (no activity). To determine putative structural features underlying the differences in inhibitory potency at hα4β2 AChRs, additional structure–activity relationship and molecular docking experiments were performed. The Ca2+ influx and structural results supported a noncompetitive mechanism of inhibition, where drimenin interacted with luminal and nonluminal (TMD-β2 intrasubunit) sites. The structure–activity relationship results, i.e., the lower the ligand polarity, the higher the inhibitory potency, supported the nonluminal interaction. Ligand binding to both sites might inhibit the hα4β2 AChR by a cooperative mechanism, as shown experimentally (nH > 1). Drimenin could be used as a molecular scaffold for the development of more potent inhibitors with higher selectivity for the hα4β2 AChR. Y1 - 2018 U6 - https://doi.org/10.1021/acs.jnatprod.7b00893 SN - 0163-3864 SN - 1520-6025 VL - 81 IS - 4 SP - 811 EP - 817 PB - American Chemical Society CY - Washington ER - TY - CHAP A1 - Arlt, Olga A1 - Schwiebs, Anja A1 - Pfarr, Kathrin A1 - Ranglack, Annika A1 - Bouzas, Ferreiros Nerea A1 - Schreiber, Yannick A1 - Neuber, Corinna A1 - Kleuser, Burkhard A1 - Pfeilschifter, Josef M. A1 - Radeke, Heinfried H. T1 - Dynamic interaction between sphingolipid enzymes, S1P and inflammatory cytokine regulation in dendritic cells T2 - NAUNYN-SCHMIEDEBERGS ARCHIVES OF PHARMACOLOGY Y1 - 2014 SN - 0028-1298 SN - 1432-1912 VL - 387 SP - S91 EP - S91 PB - Springer CY - New York ER - TY - JOUR A1 - Armin, Ardalan A1 - Durrant, James R. A1 - Shoaee, Safa T1 - Interplay Between Triplet-, Singlet-Charge Transfer States and Free Charge Carriers Defining Bimolecular Recombination Rate Constant of Organic Solar Cells JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Despite the myriad of organic donor:acceptor materials, only few systems have emerged in the life of organic solar cells to, exhibit considerable reduced bimolecular recombination, with respect to the random encounter rate given by the Langevin equation. Monte Carlo simulations have revealed that the rate constant of the formation of electron-hole bound states depends on the random encounter of opposite charges and is nearly given by the Langevin equation for the domain sizes relevant to efficient bulk heterojunction systems. Recently, three studies :suggested that charge transfer states dissociating much faster than their decay rate to the ground state, can result in reduced bimolecular recombination by lowering the recombination rate to the ground state as a loss pathway. A separate study identified another loss pathway and suggested that forbidden back electron transfer from triplet charge transfer states to triplet excitons is a key to achieving reduced recombination. Herein we further explain the reduced bimolecular recombination by investigating the limitations of these two proposals. By solving kinetic rate equations for a BHJ system with realistic rates, we show that both of these previously presented conditions must only be held at the same time fora system to exhibit non-Langevin behavior. We demonstrate that suppression of both of the parallel loss channels of singlet and triplet states can be achieved through increasing the dissociation rate of the charge transfer states; a crucial requirement to achieve a high charge carrier extraction efficiency. Y1 - 2017 U6 - https://doi.org/10.1021/acs.jpcc.7b04825 SN - 1932-7447 VL - 121 SP - 13969 EP - 13976 PB - American Chemical Society CY - Washington ER - TY - BOOK A1 - Arndt, Barbara A1 - Arnold, Karin A1 - Belter, Heinz ED - Meyendorf, Gerhard T1 - Chemie : Stoffe, Reaktionen, Umwelt ; Ausgabe Sachsen-Anhalt, Sekundarschule, 7/8, Lehrbuch Y1 - 2000 PB - Volk und Wissen CY - Berlin ER - TY - BOOK A1 - Arndt, Barbara A1 - Arnold, Karin A1 - Belter, Heinz ED - Meyendorf, Gerhard T1 - Chemie : Stoffe, Reaktionen, Umwelt ; Ausgabe Mecklenburg-Vorpommern, Realschule, 10, Lehrbuch Y1 - 2000 PB - Volk und Wissen CY - Berlin ER - TY - JOUR A1 - Arotcarena, Michel A1 - Heise, Bettina A1 - Ishaya, Sultana A1 - Laschewsky, André T1 - Switching the inside and the outside of aggregates of water-soluble block copolymers with double thermoresponsivity N2 - Water-soluble block copolymers were prepared from the non-ionic monomer N-isopropylacrylamide (NIPA) and the zwitterionic monomer 3-[N-(3-methacrylamidopropyl)-N,N-dimethyl]-ammonio propane sulfonate (SPP) by sequential free radical polymerization via the RAFT process. Such block copolymers with two hydrophilic blocks exhibit double thermo- responsive behavior in water: the poly-NIPA block shows a lower critical solution temperature, whereas the poly-SPP block exhibits an upper critical solution temperature. Appropriate design of the block lengths leads to block copolymers which stay in solution in the full temperature range between 0°C and 100°C. Both blocks of these polymers dissolve in water at intermediate temperatures, whereas at high temperatures, the poly-NIPA block forms colloidal hydrophobic associates that are kept in solution by the poly-SPP block, and at low temperatures, the poly-SPP block forms colloidal polar aggregates that are kept in solution by the poly-NIPA block. In this way, colloidal aggregates can be prepared in water which switch reversibly, and without any additive, their "inside" to the "outside", and vice versa. The aggregates provide microdomains and surfaces of different character, which can be controlled by a simple thermal stimulus. Y1 - 2002 ER - TY - JOUR A1 - Arrieta, A. A1 - Beyer, L. A1 - Lehmann, J. A1 - Dargatz, M. A1 - Kleinpeter, Erich T1 - Synthese und 1H-NMR-spektroskopische Untersuchungen neuer Curcuminanaloga Y1 - 1992 ER - TY - JOUR A1 - Arys, Xavier A1 - Fischer, Peter A1 - Jonas, Alain M. A1 - Koetse, Marc M. A1 - Legras, Roger A1 - Laschewsky, André A1 - Wischerhoff, Erik T1 - Ordered polyelectrolyte multilayers : rules governing layering in organic binary multilayers Y1 - 2003 ER -